text:
\section{Introduction}

The photon plays the fundamental role as the gauge
boson of mediating electromagnetic interactions through the coupling to charged particles.
The photon appears to be in this respect as a point-like particle (Figure \ref{fig1} (a)).
However, a photon is subject to quantum fluctuations, as denoted in Figure \ref{fig1}.
It can fluctuate into a lepton/anti-lepton pair, $\lep\mathrm{\bar{l}}$, or a
quark/anti-quark pair, ${\mathrm q}\mathrm{\bar{q}}$ (Figure \ref{fig1} (b) and (c)).
If, e.g in $\gamma {\mathrm p}$ interactions, the fluctuation time is large compared to the
interaction time, $\gamma {\mathrm p}$ interactions can proceed through the interaction of
a ${\mathrm q}\mathrm{\bar{q}}$ pair and the proton, which gives rise to a hadronic type reaction \cite{ref1_ioffe}.
This behavior has been incorporated in the vector dominance model (VDM) \cite{ref2_sakurai} which
describes $\gamma {\mathrm p}$ interactions as the interaction of the proton and a vector meson
resulting from a quantum fluctuation of the photon with the vector meson state
having the same quantum numbers as the photon, i.e. $J^{PC}=1^{--}$.
\begin{wrapfigure}{r}{8.2cm}
\vspace*{-0.8cm}
\setlength{\unitlength}{1.0cm}
\begin{picture} (15.0,2.5)
\put (0.25,1.25){{\small (a)}}
\put (3.0,1.25){{\small (b)}}
\put (5.75,1.25){{\small (c)}}
\put (0.25,0.0){{\small point-like}}
\put (5.0,0.0){{\small VM ($J^{PC}=1^{--}$)}}
\put (-0.25,0.5){\mbox{\epsfig{figure=fluc_gamma_red.eps,width=8.5cm,clip=}}}
\end{picture}
\caption{\it{Dual nature of the photon.}}
\label{fig1}
\end{wrapfigure}
This dual nature of the photon, i.e. point-like and hadron-like,
leads to a variety of phenomena which have been investigated
in $\gamma {\mathrm p}$ and $\gamma \gamma$/${\mathrm e}\gamma$\footnote{Positrons are referred to as electrons
in this review unless otherwise stated.} scattering at several experiments at HERA and
LEP, respectively \cite{ref3_erdmann}. The underlying
kinematics at the ${\mathrm e^{+}}{\mathrm e^{-}}$ collider LEP is shown in Figure \ref{fig2}.
The initial state consists
of the incoming electron and positron, each of which - to lowest order
in $\alpha_{\rm em}$ - emits a virtual photon.
The square of the four momentum transfer or the virtuality of the mediated virtual photons
is denoted by $Q^{2}=-q^{2}=(k_{1}-k_{1}^{'})^{2}$, which will be later referred to as the probe
virtuality, and $P^{2}=-p^{2}=(k_{2}-k_{2}^{'})^{2}$ which will be later referred to as the
target virtuality. $Q^{2}$ ($P^{2}$)
can be reconstructed from the energy and angle of the respective detected (tagged) electron
as follows:
$Q^{2}=2E_{\rm beam}E_{\rm tag,1}(1-\cos\theta_{\rm tag,1})$
($P^{2}=2E_{\rm beam}E_{\rm tag,2}(1-\cos\theta_{\rm tag,2})$).
The invariant mass of the final state ${\mathrm X}$ is denoted
by $W=(q+p)^{2}$. The Bjorken scaling variable $x$ is defined as $x=Q^{2}/(Q^{2}+P^{2}+W^{2})$ and
the `inelasticity' as $y=(p \cdot q)/(p \cdot k)$. The inelasticity can be reconstructed
from the energy and angle of the tagged electron as follows:
$y=1-E_{\rm tag,1}/E_{\rm beam}(\cos^{2}\theta_{\rm tag,1}/2)$.

Three event classes can be distinguished depending on whether the electron in the final
state is tagged or not. If both final state electrons are not tagged, both
virtualities $Q^{2}$ and $P^{2}$ - depending on the detector acceptance - are small,
and the photons can be considered as quasi-real, i.e. $Q^{2} \simeq 0 $ and $P^{2} \simeq 0$.
This is the case of anti-tagged events which allows
to investigate $\gamma\gamma$ scattering and thus photon interactions.
If one of the scattered electrons,
is detected (tagged), the process shown in Figure~\ref{fig2}
can be considered as the scattering of an electron
off a quasi-real photon. In this case of $e\gamma$ scattering (single-tagged events)
one is able to study
the photon structure similarly to the case of lepton-nucleon scattering
($Q^{2} \gg P^{2}$). The case in which both
final state electrons are tagged is referred to as double-tagged events.
\begin{wrapfigure}{r}{8.2cm}
\hspace*{1.0cm}
\epsfig{figure=kin_no_charge.eps,width=5.0cm,clip=}
\caption{\it{Kinematics of two-photon induced processes in ${\mathrm e^{+}}{\mathrm e^{-}}$ collisions:
$k_{1}$ ($k_{1}^{'}$) and $k_{2}$ ($k_{2}^{'}$) are the four-momenta of the incoming (outgoing)
electrons. $q$ and $p$ are the four-momenta of the mediated virtual photons.
$W$ is the invariant mass of the final state system~${\mathrm X}$.}}
\label{fig2}
\end{wrapfigure}

Unlike to ${\mathrm e}{\mathrm p}$ and $\gamma {\mathrm p}$ scattering e.g. at HERA, the invariant mass $W$
and therefore $x$ in ${\mathrm e}\gamma$ and $\gamma \gamma$ scattering at LEP
can only be reconstructed from the final state ${\mathrm X}$.
In case of ${\mathrm X}$ being a hadronic final state, contrary to the case of lepton pairs such as
${\mathrm \mu^{+}}{\mathrm \mu^{-}}$ pairs,
the reconstruction of $W$ suffers from particle losses due to a limited detector acceptance.
This gives
rise to the fact that the measured invariant mass $W_{\rm vis}$ is different from the
invariant mass $W$.
One therefore needs to unfold the true result from the visible measurement. This requires a good
Monte Carlo (MC) simulation of the underlying event structure. This will be
discussed in more detail in section 2.2.
Only double-tagged events permit a reconstruction of $W$ independent of the hadronic final state
through the reconstruction of both photon virtualities $Q^{2}$ and $P^{2}$ from the tagged
final state electrons.

The OPAL experiment at LEP has performed a variety of measurements of single-tagged
and anti-tagged events to gain a deeper insight into the structure of the photon and its
interactions. The following review will provide a summary of various measurements of those two
event classes. This includes in the case of single-tagged events the investigation of the
photon structure through the extraction of the
photon structure function for the case of hadronic final states and a final state which
consists of a ${\mathrm \mu^{+}}{\mathrm \mu^{-}}$ pair as well as the study of azimuthal correlations of
${\mathrm \mu^{+}}{\mathrm \mu^{-}}$ pairs. Anti-tagged
events have been used to study the production of jets and hadrons in $\gamma\gamma$ scattering as
well as for a measurement of the total hadronic $\gamma\gamma$ cross-section.
Results from these measurements will be presented in detail in section 2 for single-tagged events
and section 3 for anti-tagged events. Section 4 provides a short summary and an outlook of
further results on the structure of the photon and its interactions to be expected from the OPAL
experiment at LEP.

\section{Electron-Photon scattering}

\subsection{General considerations}

The starting point to study ${\mathrm e}\gamma$ scattering and thus the structure of the photon
in a similar way as ${\mathrm e}{\mathrm p}$ scattering at LEP, is the process
${\mathrm e} {\mathrm e} \rightarrow {\mathrm e} {\mathrm e} {\mathrm X}$.
It can be viewed as deep-inelastic scattering of an electron on a quasi-real photon.
This requires to transform the cross-section $d\sigma_{{\mathrm e} {\mathrm e} \rightarrow {\mathrm e} {\mathrm e} {\mathrm X}}$
into an ${\mathrm e}\gamma$ cross-section,
$d\sigma_{{\mathrm e} \gamma \rightarrow {\mathrm e} {\mathrm X}}$:
\begin{equation}
d\sigma_{{\mathrm e}\e \rightarrow {\mathrm e}\e {\mathrm X}} = d\sigma_{{\mathrm e}\gamma\rightarrow {\mathrm e} {\mathrm X}} \cdot f_{\gamma/{\mathrm e}}
\end{equation}
The flux factor $f_{\gamma/{\mathrm e}}$, which denotes the flux of the target photon off the
incoming electron, takes
into account the momentum spread of the target photon. This is in contrast to ${\mathrm e} {\mathrm p}$
scattering where the energy of both incoming particles is known.
The calculation of the flux factor $f_{\gamma/{\mathrm e}}$ is carried out using the
equivalent photon approximation (EPA) \cite{ref4_weiz,ref5_budnev}.
Provided that the target photon is almost real, i.e.
$P^{2}\simeq 0$,
and thus almost solely transversally polarized, the ${\mathrm e} \gamma$ cross-section can be
reduced to two components only,
$\sigma_{TT}$ and $\sigma_{LT}$. The first index denotes the polarization of the
probing
photon whereas the second index refers to the polarization of the target photon.
The following relations are defined:
\begin{eqnarray}
F_{1}^{\gamma}(x,Q^{2}) & = & \frac{Q^{2}}{4\pi^{2}\alpha}\frac{1}{2x} \cdot \sigma_{TT} \nonumber \\
F_{2}^{\gamma}(x,Q^{2}) & = & \frac{Q^{2}}{4\pi^{2}\alpha} \cdot (\sigma_{TT}+\sigma_{LT})
\end{eqnarray}
$F_{1,2}^{\gamma}$ are denoted as the photon structure functions.
$F_{L}^{\gamma}=F_{2}^{\gamma}-2xF_{1}^{\gamma}$ is the longitudinal structure function.
Using these relations, the
following expression for the cross-section of deep-inelastic ${\mathrm e}\gamma$ scattering is obtained:
\begin{equation}
\frac{d^{2}\sigma({\mathrm e}\gamma\rightarrow {\mathrm e} {\mathrm X})}{dxdQ^{2}}=\frac{2\pi\alpha^{2}}{xQ^{4}}\left[(1+(1-y)^{2})F_{2}^{\gamma}(x,Q^{2})-y^{2}F_{L}^{\gamma}(x,Q^{2})\right]
\end{equation}
with $\alpha$ being the fine structure constant.
For energies of the tagged electron larger than half the beam energy, which is used to reject
beam-associated background events, $y$ is much less than $1$ and thus the contribution of
$y^{2}F_{L}^{\gamma}$
to $d^{2}\sigma({\mathrm e}\gamma\rightarrow e {\mathrm X})/dxdQ^{2}$ is small and can therefore be neglected.
In this case, $d^{2}\sigma({\mathrm e}\gamma\rightarrow e {\mathrm X})/dxdQ^{2}$ is directly proportional to
$F_{2}^{\gamma}$.

The above expression for $d^{2}\sigma({\mathrm e}\gamma\rightarrow {\mathrm e} {\mathrm X})/dxdQ^{2}$
is deduced for the case of transversally polarized target photons, i.e.
only the two components $\sigma_{TT}$ and $\sigma_{LT}$ are taken into account. In case of virtual
target photons ($P^{2}\neq 0$),
i.e. in the case of double-tagged events, this simplification no longer holds and additional
cross-section terms have to be taken into account. This will change in particular the contribution
of $F_{2}^{\gamma}$ to $d^{2}\sigma({\mathrm e}\gamma\rightarrow {\mathrm e} {\mathrm X})/dxdQ^{2}$
\cite{ref5_budnev,ref9_pluto}.

For a final state ${\mathrm X}$ which consists of lepton pairs (described by QED) the
photon structure functions
are referred to as $F_{1,2, {\rm QED}}^{\gamma}$ (leptonic structure functions),
whereas for a hadronic final state ${\mathrm X}$ created by a ${\mathrm q}\mathrm{\bar{q}}$ pair (described by QCD),
the photon structure functions are denoted as $F_{1,2}^{\gamma}$ (hadronic structure functions).
$F_{2, {\rm QED}}^{\gamma}$ is predicted by QED and a measurement of
$F_{2, {\rm QED}}^{\gamma}$ serves as a test of QED. $F_{2}^{\gamma}$ however
cannot be calculated in a similar way from first principles for all $x$ and $Q^{2}$.
Several models have been developed
based on perturbative QCD (pQCD) and a particular non-perturbative QCD ansatz.
A measurement of $F_{2}^{\gamma}$ thus allows to investigate QCD.

Despite the similarity of the differential cross-sections for ${\mathrm e} \gamma$ scattering
and ${\mathrm e} {\mathrm p}$ scattering, there are subtle differences in the behavior of the structure functions
which will be briefly summarized in the following.

As pointed out in the previous section, the photon shows in its interaction contributions
from a point-like as well as a hadron-like behavior. The lowest-order point-like
contribution, i.e. the purely electromagnetic process $\gamma^{*}\gamma \rightarrow {\mathrm q} \mathrm{\bar{q}}$,
can already be predicted in the Quark-Parton model (QPM) and allows therefore a prediction of the photon
structure function.
The hadronic contribution cannot
be calculated from first principles similarly to the case of the proton. One relies on a
non-perturbative QCD input such as an estimate within the framework of the
vector dominance model (VDM).
$F_{2}^{\gamma}$ is large for high values of $x$, whereas the proton structure function $F_{2}^{p}$
decreases at large $x$. Furthermore, $F_{2}^{\gamma}$ increases with $Q^{2}$ at all values
of $x$, which is expected already from the QPM, i.e. from the point-like
contribution and thus without the presence of gluon radiation. This is in striking contrast
to the $Q^{2}$ dependence of $F_{2}^{p}$.

\begin{wrapfigure}{r}{8.2cm}
\hspace*{0.5cm}
\epsfig{figure=pr185_02_new.eps,width=7.0cm,clip=}
\caption{\it Hadronic energy flow per event $(1/N) \cdot dE/d\eta$ as a
function of pseudorapidity $\eta$ obtained from the HERWIG MC generator.}
\label{fig4}
\end{wrapfigure}

The description of the photon structure functions in terms of parton distributions
and their $Q^{2}$ evolution based on the DGLAP equations can be developed in a similar
way as for the proton. The point-like contribution due to the splitting
process $\gamma^{*}\gamma \rightarrow {\mathrm q}\mathrm{\bar{q}}$
can be incorporated as an additional
splitting function besides the usual QCD splitting functions. This additional term
results in the fact that the DGLAP equations are no longer homogeneous. The solution
of the inhomogeneous part is determined by the photon splitting function due
to the splitting process $\gamma^{*}\gamma \rightarrow {\mathrm q}\mathrm{\bar{q}}$ whereas
the homogeneous solution obeys the hadron-like evolution of the DGLAP equations.

In summary, the hadronic photon structure function $F_{2}^{\gamma}$ is given as the sum
of a point-like, $F_{2}^{\gamma,{\rm pl}}$, and a hadron-like, $F_{2}^{\gamma,{\rm hadr.}}$,
contribution:
\begin{equation}
F_{2}^{\gamma}=F_{2}^{\gamma,{\rm pl}}+F_{2}^{\gamma,{\rm hadr.}}
\end{equation}
At large $x$ and asymptotically large $Q^{2}$, the value of $F_{2}^{\gamma, {\rm hadr.}}$ can be
calculated
from pQCD. The NLO result obtained by Bardeen and Buras \cite{ref11_bardeen} is given as
follows:
\begin{equation}
\frac{F^{\gamma}_{2}}{\alpha}=\frac{a(x)}{\alpha_{s}(Q^{2})}+b(x)
\end{equation}
$a(x)$ and $b(x)$ are calculable functions which diverge for $x\rightarrow 1$. $\alpha_{s}(Q^{2})$
is the strong coupling constant. The first term reflects the LO result by Witten
\cite{ref12_witten}. The $Q^{2}$ evolution of $F_{2}^{\gamma, {\rm hadr.}}$ will eventually
allow to extract the QCD scale $\Lambda_{{\rm QCD}}$ provided that the
presence of non-perturbative contributions are under control.

Various models have been developed in the past on the description of the photon structure function
such as the model by Gl\"{u}ck, Reya and Vogt (GRV) \cite{ref_grv} and the model by Schuler and
Sj\"{o}strand (SaS) \cite{ref_sas}.
Common to these descriptions is a non-perturbative ansatz for the hadronic contribution at a
starting scale $Q^{2}_{0}$ and a subsequent DGLAP evolution, including a
particular treatment of the charm contribution. They differ in the way this procedure is
carried out. Section 2.3 will discuss in more detail these models by comparing them to
experimental results on $F_{2}^{\gamma}$.

\subsection{Hadronic energy flows}

The measurement of the hadronic structure function $F_{2}^{\gamma}$
requires the determination of the invariant mass $W$ from the hadronic final state as
pointed out in section~1.
The need to unfold the invariant mass, $W$, from the measured result, $W_{\rm vis}$,
requires a modeling of the hadronic final state incorporated in a particular Monte Carlo (MC)
generator. The
measurement of $F_{2}^{\gamma}$ and the simulation of the hadronic final state are
thus closely connected.

\begin{wrapfigure}{r}{8.2cm}
\hspace*{0.5cm}
\vspace*{-0.5cm}
\epsfig{figure=pr185_03.eps,width=7.0cm,clip=}
\caption{\it Correlation between the observed
hadronic invariant mass $W_{\rm vis}$ and the generated hadronic invariant mass $W$.}
\label{fig5}
\end{wrapfigure}

Several investigations have been carried out by OPAL \cite{ref14_opal},
comparing various observables such as the hadronic
energy flow between data and MC to gain a deeper insight into the simulation of the hadronic final state.
The two general purpose QCD based MC generators HERWIG \cite{ref15_herwig} and PYTHIA \cite{ref16_pythia}
have been used for these studies. In addition, the F2GEN generator \cite{ref17_twogen} has been
applied to study
various aspects of the simulation of a ${\mathrm q}\mathrm{\bar{q}}$ final state in the $\gamma^{*}\gamma$ centre-of-mass
system. The F2GEN `point-like' mode represents the unphysically extreme case of a two-quark state
in the $\gamma^{*}\gamma$ centre-of-mass system with an angular distribution as in lepton pair production
from two real photons. The F2GEN `permiss' mode reflects a physics motivated mixture of point-like
and peripheral interactions, where peripheral means that the transverse momentum of outgoing quarks
is given by an exponential distribution as if the photons interacted as pre-existing hadrons and direct
photon-quark couplings never occurred.

The hadronic system ${\mathrm X}$ is strongly boosted along the beam direction, accentuating the loss of
particles within the well-measured region. Figure \ref{fig4} shows the prediction of the HERWIG
MC generator for the hadronic energy flow per event, $(1/N) \cdot dE/d\eta$, as a function of
the pseudorapidity $\eta=-\ln\,\tan(\theta/2)$. The tagged electron is not included in the energy flow.
By definition, it lies in the
negative rapidity region $-3.5 < \eta < -2.8$. The generated energy flow is shown as the light
shaded region. The dark shaded region shows the energy flow after reconstruction by the OPAL
detector including a simulation of the detector response. A significant fraction of the energy flow
goes into the forward direction. Approximately $50\%$ is deposited in the central region whereas
$33\%$ are deposited in the forward region. Only $8\%$ of the total hadronic energy flow lies outside
the detector acceptance.
Figure \ref{fig5} shows the
correlation between the generated hadronic invariant mass $W$ and the observed
hadronic invariant mass $W_{\rm vis}$ with and without sampling the hadronic energy using the
OPAL forward detectors (FD). Including a measurement of the hadronic energy in the forward
direction by sampling the hadronic energy using the OPAL forward detectors substantially
improves the correlation between $W$ and $W_{\rm vis}$. The degree of correlation
depends on the MC model.

The comparison between data and MC distributions of the hadronic energy flow is shown in Figure
\ref{fig7} as a function of the pseudorapidity $\eta$ for two values of $Q^{2}$ of
$13.0\,$GeV$^{2}$ and $135\,$GeV$^{2}$. The data distribution has been corrected for detector
effects. Large differences are seen between data and all MC models both within the central
region ($|\eta|<2.3$), where the energy is well measured and the forward region where the
energy is only sampled. The discrepancy increases towards small value of $Q^{2}$ and thus towards
small values of $x$.

\begin{figure}[t]
\setlength{\unitlength}{1.0cm}
\begin{picture} (15.0,6.0
)
\put (1.25,0.0){\mbox{\psfig{figure=pr185_10.eps,width=6.0cm,clip=}}}
\put (8.75,0.0){\mbox{\psfig{figure=pr185_11.eps,width=6.0cm,clip=}}}
\end{picture}
\caption{\it Hadronic energy flow per event as a function of pseudorapidity $\eta$ for
low $Q^{2}$ ($Q^{2}=13.0\,$GeV$^{2}$) and high $Q^{2}$ ($Q^{2}=135\,$GeV$^{2}$) events.
The data distributions have been corrected for detector effects.}
\label{fig7}
\end{figure}

\begin{wrapfigure}{r}{8.2cm}
\epsfig{figure=f2_low_x.eps,width=8.5cm,clip=}
\caption{\it OPAL results on
$F_{2}^{\gamma}/\alpha$ as a function of $x$ for $Q^{2}=1.86\,{\rm GeV}^{2}$
and $Q^{2}=3.76\,{\rm GeV}^{2}$ together with results from other experiments.}
\label{fig8}
\end{wrapfigure}

It is apparent from this section that unfolding the distribution
$W$ from the observed
distribution $W_{{\rm vis}}$ will result in large systematic errors on the extracted photon
structure function
$F_{2}^{\gamma}$ as long as the hadronic energy flow between the different MC
models and
the hadronic energy flow in data remains in clear disagreement. This is expected to affect in
particular
the low $Q^{2}$ and low $x$ region.

Better general purpose MC generators are required to provide a better description of the hadronic
energy flow in data
and thus to reduce the large systematic uncertainties of the extracted photon structure function
$F_{2}^{\gamma}$ (Section 2.3) \cite{ref18_leif}.
These questions are being addressed
in a LEP-wide working group with the aim of a common and consistent presentation of the hadronic energy flow
in data. An improvement
of general purpose MC generators based on such investigations is eagerly awaited. It
is only then that an improvement in the systematic uncertainties due to the description of the hadronic
final state in the extraction of $F_{2}^{\gamma}$ can be expected.

\begin{wrapfigure}{r}{8.2cm}
\epsfig{figure=f2_all_x.eps,width=8.5cm,clip=}
\caption{\it OPAL results on
$F_{2}^{\gamma}/\alpha$ as a function of $x$ for several $Q^{2}$ values
together with results from other experiments.}
\label{fig9}
\end{wrapfigure}

\subsection{Hadronic structure function \boldmath{$F_{2}^{\gamma}$}}

The measurement of the hadronic structure function $F_{2}^{\gamma}$ has been
carried at OPAL as a function of $x$ and $Q^{2}$ over a wide kinematic range of
$0.0025<x \mathrel{\rlap{\lower4pt\hbox{\hskip1pt$\sim$}~1$
and $1.1\,{\rm GeV}^{2}<Q^{2}<400\,{\rm GeV}^{2}$. Details on the
analysis to extract $F_{2}^{\gamma}$ can be found in \cite{ref14_opal,ref19_opal}.
The $Q^{2}$ dependence is expected to be logarithmic within the framework of pQCD.
The $x$ dependence of the proton structure function $F_{2}^{p}$
has been studied in detail at HERA
which shows a steep rise towards small values of $x$ at not too low $Q^{2}$
values \cite{ref37_zeus,ref20_hera}.
If the photon were purely hadron-like, a similar rise of $F_{2}^{\gamma}$ is
expected.
A measurement of $F_{2}^{\gamma}$ as a function of $x$ and $Q^{2}$ therefore
allows to shed light on the structure and the underlying dynamics of the photon as pointed
out in section 2.1.

Figure \ref{fig8} shows OPAL results on $F_{2}^{\gamma}$ as a function
$x$ at low values of $Q^{2}$. OPAL results on
$F_{2}^{\gamma}$ together with other experimental results are shown in Figure \ref{fig9}.
The full error bars show the statistical and systematic errors added in quadrature.
In Figure \ref{fig8}, the statistical errors are displayed by horizontal lines across the
respective errors bars. The precision of the measurement is dominated by systematic
uncertainties due to
the modeling of the hadronic final state as pointed out in detail in the previous section.
As can be seen from Figure \ref{fig8}, the OPAL results at the two lowest $Q^{2}$ values
agree within errors with
the published results from PLUTO. However, the results both from PLUTO and OPAL are higher and
different in shape than the previous measurement from TPC in a similar kinematic
region.
Taking into account the large uncertainties, $F_{2}^{\gamma}$ is found
to be rather flat (Figure \ref{fig8}) although a small rise towards low $x$
cannot be excluded.
It can be seen from Figures \ref{fig8} and \ref{fig9} that
$F_{2}^{\gamma}$ rises smoothly towards large $x$. This behavior is reasonably
well described by the GRV and SaS models. It can be seen from Figure \ref{fig8}
that the higher-order GRV prediction (GRV-HO) follows the data more closely compared
to the leading-order GRV prediction (GRV-LO).

The $Q^{2}$ dependence of $F_{2}^{\gamma}$ is shown in Figure \ref{fig10}
for the currently available data for four active flavors. It should be noted that
the quoted $x$ ranges by different experiments are not the same which makes a comparison
rather difficult since several predictions for different ranges in $x$
show a large difference for $Q^{2}>100\,$GeV$^{2}$.
All results on $F_{2}^{\gamma}$ as shown in Figure \ref{fig10}
agree reasonably well, taking into account the large uncertainties. A logarithmic rise
of $F_{2}^{\gamma}$ is seen in the data as predicted by pQCD.
However, the systematic uncertainties on $F_{2}^{\gamma}$ are too large
to perform a precision test of pQCD.
Both, the GRV and SaS model allow to describe the data equally well. The observed
logarithmic rise of $F_{2}^{\gamma}$ in $Q^{2}$ can be reasonably
well represented by the pQCD leading order asymptotic solution.
It is found that the hadronic contribution to
$F_{2}^{\gamma}$ decreases towards larger $x$ and $Q^{2}$ values, and
amounts to only about $15\%$ at $Q^{2}=59\,$GeV$^{2}$ and $x=0.5$.

\begin{wrapfigure}{r}{8.2cm}
\hspace*{0.25cm}
\epsfig{figure=f2_q2.eps,width=7.5cm,clip=}
\caption{\it OPAL results on
$F_{2}^{\gamma}/\alpha$ as a function of $Q^{2}$ for different ranges in $x$
together with results from  other experiments \cite{nisius}.}
\label{fig10}
\end{wrapfigure}

All OPAL results on $F_{2}^{\gamma}$ have not been corrected for the fact
that in the single-tagged mode, $P^{2}$ is only
approximately zero. Several theoretical predictions exit on how $F_{2}^{\gamma}$
varies as a function of $P^{2}$ \cite{ref_p2}.
It has been estimated based on the SaS model
that $F_{2}^{\gamma}$ with $P^{2}\neq 0$ would be approximately
$10\%$ lower compared to the case of $P^{2}=0$. The $P^{2}$ distribution in the data
and the correct theoretical prescription are not known. This is reason why
no correction has been applied to the data on $F_{2}^{\gamma}$.
The larger centre-of-mass energy at
LEP compared to former experiments at PETRA makes this effect to become more important.
The investigation of the virtual structure of the photon through double-tag events
and the measurement of $F_{2, {\rm QED}}^{\gamma}$ (Section 2.4)
will allow to gain some experimental knowledge in that respect.

Improvements in the precision of $F_{2}^{\gamma}$ require considerable
improvements of general purpose MC models to
better describe the hadronic final state. It is only
then that the study of the low $x$ behavior of $F_{2}^{\gamma}$ as well as
as the $Q^{2}$ evolution could be carried out with higher precision.

\begin{wrapfigure}{r}{8.2cm}
\vspace*{-0.25cm}
\hspace*{0.25cm}
\epsfig{figure=f2qed.eps,width=7.0cm,clip=}
\caption{\it $F_{2, {\rm QED}}^{\gamma}/\alpha$ as a function of $x$ \cite{nisius}.}
\label{fig11}
\end{wrapfigure}

\subsection{Leptonic structure function \boldmath{$F_{2, {\rm QED}}^{\gamma}$}}

The differential cross-section (3) with
$\gamma^{*}\gamma \rightarrow {\mathrm l^{+}} {\mathrm l^{-}}$
allows to measure the leptonic structure function of the photon,
$F_{2, {\rm QED}}^{\gamma}$.
A measurement of $F_{2, {\rm QED}}^{\gamma}$ has been carried out at OPAL
by reconstructing ${\mathrm \mu^{+}}{\mathrm \mu^{-}}$ pairs
in the final state \cite{ref23_opal}.
Such a clean environment allows to unfold the invariant mass
$W$ from the observed invariant mass $W_{\rm vis}$ with higher precision compared
to the case of a hadronic final state which yields a much more precise determination of
the leptonic photon structure function compared to the hadronic case.

Figure \ref{fig11} shows OPAL results on
$F_{2, {\rm QED}}^{\gamma}$ as a function of $x$ together with other experiments.
The full error bars show the statistical and systematic errors added in quadrature, whereas
the statistical errors are displayed by horizontal lines across the
respective errors bars. The precision of the data allow for a test of QED. The solid
lines in Figure~\ref{fig11} show the results of a QED calculation. All measurements
are consistent with QED expectations. The data are so precise that subtle effects
such as the $P^{2}$ dependence can be investigated in more
detail.

\begin{wrapfigure}{r}{8.2cm}
\hspace*{0.5cm}
\epsfig{figure=f2_qed_all.eps,width=6.0cm,clip=}
\caption{\it OPAL results on the ratios $f_{A}^{\gamma}/F_{2}^{\gamma}$ and
$(1/2)F_{B}^{\gamma}/F_{2}^{\gamma}$
as a function of $x$.}
\label{fig13}
\end{wrapfigure}

\subsection{Azimuthal correlations of lepton pairs}

It has been pointed out that azimuthal correlations in the final-state particles of
two photon collisions, i.e. $\gamma^{*}\gamma \rightarrow {\mathrm X}$, are sensitive to additional
structure functions \cite{ref13_lep2}.
Azimuthal correlations can therefore supplement the direct measurement of the photon
structure functions.

OPAL has performed a measurement of azimuthal correlations in single-tagged
events of $\gamma^{*}\gamma \rightarrow {\mathrm \mu^{+}} {\mathrm \mu^{-}}$ \cite{ref26_opala}. Two angles are defined
which allow azimuthal correlations and thus more subtle structure functions to be
studied.
The azimuthal angle $\chi$ is the angle between the planes defined by
the $\gamma^{*}\gamma$ axis and the two-body final state and the
$\gamma^{*}\gamma$ axis and the tagged electron. The second angle
$\eta=\cos\theta^{*}$ is defined by the angle $\theta^{*}$ as the angle between the
${\mathrm \mu^{-}}$ and the $\gamma^{*}\gamma$ axis.

With the assumption that the target photon is only transversely polarized, the
cross-section for ${\mathrm e}\gamma \rightarrow {\mathrm e} {\mathrm \mu^{+}} {\mathrm \mu^{-}}$ differential in $x$, $y$
and the two angles $\chi$ and $\eta$ is given as follows:
\begin{equation}
\frac{d\sigma({\mathrm e}\gamma\rightarrow e{\mathrm \mu^{+}}{\mathrm \mu^{-}})}{dxdyd\eta d\chi/2\pi} \approx \frac{2\pi\alpha^{2}}{Q^{2}}\left(\frac{1+(1-y)^{2}}{xy}\right) \left[2x\tilde{F}^{\gamma}_{T}+\tilde{F}_{L}^{\gamma}-\tilde{F}_{A}^{\gamma}\cos\chi+\frac{\tilde{F}_{B}^{\gamma}}{2}\cos 2\chi\right]
\end{equation}
The conventional structure functions can be recovered by integrating over
$\chi$ and $\eta$:
\begin{equation}
F_{T,L,A,B}^{\gamma} = \frac{1}{2\pi}\int_{-1}^{+1}d\eta\int_{0}^{2\pi}d\chi \tilde{F}_{T,L,A,B}^{\gamma}
\end{equation}
In leading order and for massless muons,
the following identity holds, $F_{B}^{\gamma}=F_{L}^{\gamma}$ although $F_{B}^{\gamma}$
and $F_{L}^{\gamma}$ are due to different helicity states of the photon. The
structure function $F_{A}^{\gamma}$ results from interference terms between
longitudinal and transverse photons whereas the structure function $F_{B}^{\gamma}$
refers to interference terms between solely transverse polarized photons.
Figure \ref{fig13} shows published and preliminary results on the $x$ dependence of the ratios
$f_{A}^{\gamma}/F_{2}^{\gamma}$ and $(1/2)F_{B}^{\gamma}/F_{2}^{\gamma}$ where
$f_{A}^{\gamma}=(1/2)(f_{A}^{+}-f_{A}^{-})$ with
$f_{A}^{+}=(1/2\pi)\int_{0}^{+1}d\eta\int_{0}^{2\pi}d\chi \tilde{F}_{A}^{\gamma}$
and $f_{A}^{-}=(1/2\pi)\int_{-1}^{0}d\eta\int_{0}^{2\pi}d\chi \tilde{F}_{A}^{\gamma}$.
The solid
line is the result of a QED prediction. The observed variation in $x$ of the
data is consistent with QED. Both ratios are significantly different from zero.
These results not only serve as an interesting approach to supplement
the conventional structure function measurements in itself, they also mark the first step
to perform such a measurement in the much more complex environment
of a hadronic final state.

\section{Photon-Photon scattering}

\subsection{Introduction}

Anti-tagged events in ${\mathrm e^{+}}{\mathrm e^{-}}$ scattering at LEP allow to study collisions of two quasi-real photons,
i.e. $\gamma\gamma \rightarrow {\mathrm X}$ with $Q^{2} \simeq 0 $ and $P^{2} \simeq 0$ as introduced
in section 1. The median $Q^{2}$ ($P^{2}$) amounts to approximately $10^{-4}\,$GeV$^{2}$ for
$Q^{2}<4\,$GeV$^{2}$.
The ${\mathrm e^{+}}{\mathrm e^{-}}$ collider LEP is in this respect a $\gamma\gamma$ collider with a centre-of-mass
energy of the $\gamma\gamma$ system of $10<W_{\gamma\gamma}<110\,$GeV.

The interaction of two photons can be classified
to be either a direct process where two bare photons interact, a single-resolved process
where a bare photon interacts with a parton of the other photon
or a double-resolved process where partons of
both photons interact together. The last two processes are due to the possibility
of a photon to interact as a hadronic fluctuation. This classification is only uniquely
defined in LO QCD, but not in NLO QCD.

In LO QCD, the experimental signature, neglecting multiple parton interactions,
consists of two hard parton jets with large transverse energy $E_{T}^{\rm jet}$ (direct events).
In single- or double-resolved interactions, the
two hard parton jets are expected to be accompanied by one or two remnant jets.

The cone jet finding algorithm has been applied throughout the following studies
unless otherwise specified.

\begin{wrapfigure}{r}{8.2cm}
\hspace*{0.5cm}
\epsfig{figure=pr250_05.eps,width=7.5cm,clip=}
\caption{\it Jet shape $\psi(r=0.5)$ as a function of $\bar{E}_{T}^{\rm jet}$ (a) and
$|\eta^{\rm jet}|$ (b). $\psi(r)$ as a function of $r$ for $x_{\gamma}^{\pm}<0.8$ (c)
and $x_{\gamma}^{\pm}>0.8$ (d).}
\label{fig14}
\end{wrapfigure}

The above three event classes can be separated using the fraction of the photon's momentum which
participates in the hard interaction. It can be specified using the
following relations \cite{ref13_lep2}:
\begin{equation}
x_{\gamma}^{\pm}=\frac{\sum_{{\rm jets=1,2}}(E\pm p_{z})}{\sum_{{\rm hadrons}}(E\pm p_{z})}
\end{equation}
$p_{z}$ is the momentum component along the $z$ axis and $E$ is the energy
of the respective energy depositions of the jets or hadrons.
These variables provide some separation of direct and resolved two-jet events \cite{ref27_opal}

The underlying processes for $\gamma\gamma$ scattering have been calculated in LO \cite{ref28_lo} and
NLO perturbative QCD (pQCD) \cite{ref29_nlo}.
In the case of direct events, the only LO contributing matrix element is
$\gamma\gamma \rightarrow {\mathrm q} \mathrm{\bar{q}}$ whereas for double-resolved events, quark-gluon, gluon-quark
and gluon-gluon type matrix elements have to be taken into account. The observed jet events
are thus related to the underlying dynamics which allows to examine the structure the photon
and the dynamics of the $\gamma\gamma$ processes.
The measured inclusive two-jet cross-section as well as the angular distribution
of the parton scattering angle in the two-jet centre-of-mass frame have been
compared to NLO pQCD calculations.
These two items together with a study of jet shapes in two-jet events
and an investigation of the influence of an underlying event in two-jet events will be
presented in the next section. The production of charged hadrons and
$\chi_{c2}$ mesons will be discussed in section 3.3.
The measurement of the total hadronic
$\gamma\gamma$ cross-section will be focused on in detail in section 3.4.

\begin{wrapfigure}{r}{8.2cm}
\hspace*{0.5cm}
\epsfig{figure=pr250_03.eps,width=7.5cm,clip=}
\caption{\it Angular distribution $d\sigma/d|\cos\theta^{*}|$ as function
of $|\cos\theta^{*}|$ for $x_{\gamma}^{\pm}>0.8$ and $x_{\gamma}^{\pm}<0.8$
in comparison to NLO pQCD calculations.}
\label{fig15}
\end{wrapfigure}

\subsection{Jet production}

\subsubsection{Jet shapes}

The internal structure of jets produced in two-jet events has been studied based
on the following jet shape definition:
\begin{equation}
\psi(r)=\frac{1}{N_{{\rm jet}}}\sum_{{\rm jet}}\frac{E_{T}(r)}{E_{T}(r=R)}
\end{equation}
$\psi(r)$ denotes the fraction of the jet's energy that lies inside
an inner cone of radius $r$, thus $\psi(r=R)=1$.
$E_{T}(r)$ is the transverse energy within the inner
cone of radius $r$ and $N_{{\rm jet}}$ refers to the total number of jets in the sample.

Figure \ref{fig14} shows the fraction of the transverse energy of the jets
inside a cone of radius $r=0.5$ around the jet axis (a) as a function of
$\bar{E}_{T}=(1/2)(E_{T}^{\rm jet1}+E_{T}^{\rm jet2})$ and (b) as
a function of $|\eta^{\rm jet}|=|(1/2)(\eta^{\rm jet1}+\eta^{\rm jet2})|$
with $E_{T}^{{\rm jet}\, i}$ and $\eta^{{\rm jet}\, i}$ defined in the lab frame.
The jet shapes have been corrected to the hadron level.
The data points are
compared to PYTHIA with and without multiple interactions and to PYTHIA
with and without initial (ISR) and final state (FSR) QCD radiation along with
a prediction from PHOJET \cite{ref28_phojet}.
Jets without initial and final
state QCD radiation are significantly narrower. Multiple
interactions as simulated within PYTHIA have only a minor effect on
the jet shape.
As expected, the jets become narrower with increasing $\bar{E}_{T}$.
No significant dependence of $\psi(r=0.5)$
on $|\eta^{\rm jet}|$ has been found.

The gluon and quark
content in direct and double-resolved events is expected to be different
from the above discussion in section 3.1.
Samples of large fractions of direct and double-resolved events have
been selected by requiring $x_{\gamma}^{\pm}$ to be larger
or less than $0.8$, respectively. The jet shape $\psi(r)$ is shown in
Figure \ref{fig14} as a function of $r$ for $x_{\gamma}^{\pm}<0.8$ (c)
and $x_{\gamma}^{\pm}>0.8$ (d). The observed jet shapes are found to be
broader for the double-resolved event sample ($x_{\gamma}^{\pm}<0.8$)
than those for direct events ($x_{\gamma}^{\pm}>0.8$).
Gluon jets
are known to be broader than quark jets which is consistent with the
difference in the jet shapes of direct and double-resolved events
due to the expected difference in the gluon and quark composition.

The PYTHIA and PHOJET jet shape prediction are found to be in good agreement
with the data.

\subsubsection{Angular distributions in direct and resolved events}

The angular distribution for direct and double-resolved events in the two-jet
centre-of-mass frame is expected to be different due to the different
gluon and quark composition and thus the different contributing matrix elements.
The angle $\cos\theta^{*}$ between the jet axis and the axis of the incoming partons
or direct photons
in the two-jet centre-of-mass frame can be estimated as follows:
\begin{equation}
\cos\theta^{*}=\tanh\left(\frac{\eta^{\rm jet1}-\eta^{\rm jet2}}{2}\right)
\end{equation}
In LO, the direct process $\gamma\gamma \rightarrow {\mathrm q}\mathrm{\bar{q}}$ leads to an
angular dependence of the form $\propto 1/(1-\cos^{2}\theta^{*})$ whereas
for double-resolved events which involves gluon initiated matrix elements,
the angular dependence can be approximated as $\propto 1/(1-\cos^{2}\theta^{*})^{2}$.

\begin{wrapfigure}{r}{8.2cm}
\hspace*{0.75cm}
\vspace*{0.05cm}
\epsfig{figure=jet.eps,width=6.0cm,clip=}
\vspace*{-0.05cm}
\caption{\it The inclusive two-jet cross-section as a function of $E_{T}^{\rm jet}$
for $|\eta^{\rm jet}|<2$ in comparison to NLO pQCD calculations.}
\label{fig16}
\end{wrapfigure}

Figure \ref{fig15} shows the angular distribution $d\sigma/d|\cos\theta^{*}|$ as a function
of $|\cos\theta^{*}|$ for samples with a large fraction of direct ($x_{\gamma}^{\pm}>0.8$) and
double-resolved ($x_{\gamma}^{\pm}<~0.8$) events.
The data are compared to NLO pQCD calculations for
the cross-section $d\sigma/d|\cos\theta^{*}|$ and the contributing single cross-sections.
Events with $x_{\gamma}^{\pm}>~0.8$ show only a small rise with increasing
$|\cos\theta^{*}|$ whereas
events with $x_{\gamma}^{\pm}<0.8$ show a much larger rise as a function of $|\cos\theta^{*}|$. This
behavior follows the QCD expectation taking into account the expected difference in the
gluon and quark composition of direct and double-resolved events. The result of the NLO
pQCD calculations agrees well with the observed shape of the data.

\subsubsection{Inclusive two-jet cross-section and NLO calculations}

Figure \ref{fig16} shows the inclusive two-jet cross-section as a function of $E_{T}^{\rm jet}$
for $|\eta^{\rm jet}|<2$ at $\sqrt{s_{{\mathrm e^{+}}{\mathrm e^{-}}}}=161-172\,$GeV.
The measurements are compared to NLO pQCD calculations by Kleinwort and Kramer \cite{ref29_kramer}
which are using the GRV parton parameterizations of the photon. The predictions for the
direct, single- and double-resolved contributions as well as their sum are shown separately. The data
points are in good agreement with NLO pQCD calculations except for the first bin.
However, experimental as well
as theoretical uncertainties are large in this kinematic region. The direct component dominates
the cross-section at high $E_{T}^{\rm jet}$, whereas the resolved cross-section is the largest
component for $E_{T}^{\rm jet}<8\,$GeV.

\subsubsection{Influence of the underlying event}

The possibility for an underlying event in the $\gamma\gamma$ scattering process is
not taken
into account in the NLO pQCD calculations. However, an underlying event leads to an
increased
jet cross-section.
Resolved photons such as in double-resolved events
involve multiple partons which are subject to multiple interactions.
The effect of the simulation of the underlying event is therefore important. The
MC models PYTHIA and PHOJET use the concept of multiple interactions in the simulation of the underlying
event.
The contribution of multiple interactions has to be tuned using quantities which are not
directly correlated to the jets. Only then effects due to parton distributions and
due to the underlying event can be disentangled. The model dependence for the simulation of
the underlying event through multiple interactions can be tuned using the transverse cutoff parameter $p_{t}^{\rm mi}$
for multiple interactions.

\begin{wrapfigure}{r}{8.2cm}
\hspace*{0.05cm}
\vspace*{0.25cm}
\epsfig{figure=pr250_07.eps,width=8.5cm,clip=}
\caption{\it Transverse energy flow outside the jets in the central rapidity region
$|\eta^{*}|<1$ as a function of $x_{\gamma}$.}
\label{fig16}
\end{wrapfigure}

The investigation of an underlying event in the $\gamma\gamma$ scattering process
starts from the observation that the transverse energy flow outside the jets measured
as a function of $x_{\gamma}$ is correlated to the underlying event \cite{ref30_h1}.
At small $x_{\gamma}$, the transverse energy flow outside the jets increases which can
be used to tune the number of multiple interactions.
The transverse energy flow corrected to the hadron level outside the jets, excluding
the region of $R<1.3$ in the energy sum, is shown in Figure \ref{fig16} as a function of $x_{\gamma}$
in comparison to different MC model predictions using different values for $p_{t}^{\rm mi}$.
The impact of multiple interactions has been found to be large for PYTHIA and PHOJET using
the LAC1 parameterization.
Their impact is small when using either GRV or SaS-1D. The
optimal transverse cutoff parameter $p_{t}^{\rm mi}$ shows a strong dependence on the underlying
parton distributions in case of PYTHIA. Using GRV, $p_{t}^{\rm mi}$ has been set to $2.0\,$GeV,
SaS-~1D requires a value for $p_{t}^{\rm mi}$ of $1.4\,$GeV whereas for LAC1, $p_{t}^{\rm mi}$ has been
set to $2.5\,$GeV. In case of PHOJET the default cutoff parameter
$p_{t}^{\rm mi}$ of $2.5\,$GeV
provides for GRV as well as for SaS-1D a reasonable description of the transverse energy flow.

\begin{wrapfigure}{r}{8.2cm}
\hspace*{0.05cm}
\epsfig{figure=eta35bc_col.eps,width=8.5cm,clip=}
\caption{\it Inclusive two-jet cross-section as a function of $|\eta^{\rm jet}|$ for
(left) $x_{\gamma}^{\pm}<0.8$ and (right) $x_{\gamma}^{\pm}>0.8$.}
\label{fig17}
\end{wrapfigure}

\subsubsection{Inclusive two-jet cross-section as a function of \boldmath{$|\eta^{\rm jet}|$}}

Having tuned the simulation of the underlying event through multiple interactions using the
transverse cutoff parameter $p_{t}^{\rm mi}$, the sensitivity of the jet cross-section on the
underlying parton distribution can be investigated. The inclusive two-jet cross-section is
shown in Figure~\ref{fig17} as a function of $|\eta^{\rm jet}|$ for $E_{T}^{\rm jet1}>5\,$GeV
and $E_{T}^{\rm jet2}>3\,$GeV with (left) large samples of double-resolved events ($x_{\gamma}^{\pm}<0.8$)
and (right) large samples of direct events ($x_{\gamma}^{\pm}>0.8$).
A large dependence on the underlying
parton distribution is found for double-resolved events compared to direct events. The impact
of the gluon distribution is expected to be larger for double-resolved events compared to direct events.
LAC1 compared to GRV and SaS-1D, which increases the cross-section for gluon-initiated
processes, leads to a strong overestimation of the two-jet cross-section.

\begin{wrapfigure}{r}{8.2cm}
\hspace*{0.75cm}
\epsfig{figure=wa69_c.eps,width=7.0cm,clip=}
\caption{\it $p_{T}$ distribution of $\gamma\gamma$, $\gamma {\mathrm p}$, $\pi {\mathrm p}$ and ${\mathrm K} {\mathrm p}$ scattering.}
\label{fig18}
\end{wrapfigure}

\subsection{Hadron production}

\subsubsection{Production of charged hadrons}

The contribution of direct photon processes in photon induced interactions
is expected to lead to a harder transverse momentum distribution of charged hadrons
for $\gamma\gamma$ scattering
than for $\gamma {\mathrm p}$ or hadron-${\mathrm p}$ scattering. The $p_{T}$ distribution for $\gamma\gamma$ scattering
as obtained by OPAL \cite{ref31_opal} with $10<W<30\,$GeV is shown in Figure \ref{fig18} together with data
on $\gamma {\mathrm p}$, $\pi {\mathrm p}$ and ${\mathrm K} {\mathrm p}$ data from WA69 with a hadronic invariant mass of $16\,$GeV.
The WA69 data are normalized to the $\gamma\gamma$
data at $p_{T}\approx 200\,$MeV. ZEUS data on charged particle production in
$\gamma {\mathrm p}$ scattering with a diffractively dissociated photon, having an average invariant
mass of the `$\gamma$-Pomeron' system of $10\,$GeV,
are shown as well.

It can be clearly inferred from Figure \ref{fig18} that $\gamma\gamma$ interactions show a significantly
harder $p_{T}$ distribution than $\gamma {\mathrm p}$ and hadron-${\mathrm p}$ interactions. The measured
$p_{T}$ distribution has been compared to NLO pQCD calculations which have been found to be in good
agreement with the data. The direct interactions yield the largest contribution at high $p_{T}$
compared to single- and double-resolved interactions.

\begin{wrapfigure}{r}{8.2cm}
\hspace*{0.75cm}
\epsfig{figure=chic2_mass.eps,width=6.5cm,clip=}
\caption{\it Mass difference between the $\lep\lep\gamma$ and $\lep\lep$ invariant masses,
$M_{\lep\lep\gamma}-M_{\lep\lep}$.}
\label{fig19}
\end{wrapfigure}

\subsubsection{Production of \boldmath{$\chi_{c2}$} mesons}

OPAL has carried out an analysis reconstructing $\chi_{c2}$ mesons in the decay channel
$\chi_{c2}\rightarrow J/\psi\;\gamma \rightarrow {\mathrm l^{+}}{\mathrm l^{-}}\gamma \;\;\;(\lep={\mathrm e},\mu)$
which resulted in a measurement of the two-photon width $\Gamma(\chi_{c2}\rightarrow \gamma\gamma)$
\cite{ref32_opal}.
The data sample consists of all data taken at ${\mathrm e^{+}}{\mathrm e^{-}}$ centre-of-mass energies of $91\,$GeV
and $183\,$GeV corresponding to integrated luminosities of $167\,$pb$^{-1}$ and $55\,$pb$^{-1}$, respectively.
Figure \ref{fig19} shows the mass difference between the $\lep\lep\gamma$ and $\lep\lep$ invariant masses,
$M_{\lep\lep\gamma}-M_{\lep\lep}$.
$34$ events have been selected in the $\chi_{c2}$ signal region of $330<M_{\lep\lep\gamma}-M_{\lep\lep}<550\,$MeV
including a background of $12.4\pm 3.3$ events.
The contribution from $\chi_{c0}$ and $\chi_{c1}$ is estimated not to exceed a few percent.
The two-photon width has been determined to be
$\Gamma(\chi_{c2}\rightarrow \gamma\gamma)=1.76 \pm 0.47 \pm 0.37 \pm 0.15\,$keV. The first error
denotes the statistical and the second the systematic error. The third error reflects the uncertainty of the
branching
ratios in the decay $\chi_{c2}\rightarrow J/\psi\;\gamma \rightarrow {\mathrm l^{+}}{\mathrm l^{-}}\gamma$. This result
agrees with results from CLEO, TPC/2$\gamma$ and R704, but is about two standard deviations larger
than the E760 result and the current world average \cite{ref33_barnett}.
Furthermore the determined two-photon width is found to be two standard deviations larger than the
prediction by Schuler \cite{ref34_schuler}.

\begin{figure}[ht]
\setlength{\unitlength}{1.0cm}
\begin{picture} (15.0,6.0
)
\put (1.25,0.0){\mbox{\psfig{figure=tot_bw2.eps,width=6.0cm,clip=}}}
\put (8.75,0.0){\mbox{\psfig{figure=tot_bw3.eps,width=6.0cm,clip=}}}
\end{picture}
\caption{\it Total cross-section for $\gamma\gamma\rightarrow {\rm hadrons}$,
$\sigma_{\gamma\gamma}$, as
a function of $W=\sqrt{s_{\gamma\gamma}}$ from OPAL in comparison to L3 results and
theoretical predictions (left). Comparison of preliminary OPAL results on $\sigma_{\gamma\gamma}$
with L3 results obtained with PYTHIA and PHOJET (right) \cite{ref3_soldner}.}
\label{fig20}
\end{figure}

\subsection{Total cross-sections}

The total cross-section for $\gamma\gamma \rightarrow \; {\rm hadrons}$, $\sigma_{\gamma\gamma}$,
at large centre-of-mass energies $W=\sqrt{s_{\gamma\gamma}}$
is expected to be dominated by interactions of hadronic fluctuations of
the colliding photons. A measurement of $\sigma_{\gamma\gamma}$ should therefore
improve our understanding of the hadronic nature of the photon and in particular
clarify the question whether the $W$ dependence of $\sigma_{\gamma\gamma}$ exhibits the same behavior
as total hadronic cross-sections. This could lead to an answer of the question
if there is an universal behavior of total cross-sections in $\gamma\gamma$, $\gamma {\mathrm p}$ and
${\mathrm p}\p$/${\mathrm p}\bar{{\mathrm p}}$
scattering.

Pre-Lep data are restricted to rather
low energies in $W$, which is too low to observe
the expected rise of total hadronic cross-sections due to Pomeron exchange in
the language of Regge phenomenology.
A measurement at LEP taking into account the large centre-of-mass energy compared
to previous experiments at PETRA allow to study the behavior of $\sigma_{\gamma\gamma}$
at higher energies.

The extraction of the total cross-section, $\sigma_{\gamma\gamma}$,
relies heavily on a particular Monte Carlo (MC) program to be used for the unfolding.
It is therefore
expected that systematic uncertainties on the extracted total cross-sections are
dominated by the simulation of the hadronic final state.

Figure \ref{fig20} (left) shows the preliminary OPAL results \cite{ref35_opal}
on the total cross-section, $\sigma_{\gamma\gamma}$, as
a function of $W=\sqrt{s_{\gamma\gamma}}$ in the range of $10 \leq W \leq 110\,$GeV
in comparison to L3 results \cite{ref36_l3} for $5 \leq W \leq 145\,$GeV.
Various curves from theoretical predictions are overlaid.
The preliminary OPAL cross-section results are quoted
by taking the average of the cross-section results obtained with the MC models
PHOJET and PYTHIA. The difference between theses results has been
included in the systematic error evaluation.
However, L3 has used PHOJET to determine the central values. No
model dependence is reflected in their quoted systematic errors. The unfolded L3
results using PHOJET and PYTHIA together with their average values are shown in Figure
\ref{fig20} (right). Comparing theses cross-section values with the preliminary results obtained
by OPAL and thus providing a consistent bases for a detailed comparison, no significant
discrepancy between both results is found.

Relating the total cross-section, $\sigma_{\gamma\gamma}$, to the total cross-sections
for $\gamma {\mathrm p}$, ${\mathrm p}\p$ and $\bar{{\mathrm p}}{\mathrm p}$ scattering,
results in the prediction shown as the solid line
in Figure \ref{fig20} (left).
It describes the general trend of $\sigma_{\gamma\gamma}$ as a function of $W$.
It has been argued by many authors to expect a faster rise of the total cross-section
for $\gamma\gamma$ scattering compared to $\gamma {\mathrm p}$ scattering and hadron-hadron scattering
due to the possibility of two photons interacting directly. In a Regge-type fit to the data,
L3 determined a Pomeron intercept of
$\alpha_{I\!\!P}=1.158 \pm 0.006 \, ({\rm stat}) \pm 0.028 \, ({\rm sys})$
which is
larger than the Pomeron intercept of
$\alpha_{I\!\!P}=1.100 \pm 0.002 \, ({\rm stat}) \pm 0.012 \, ({\rm sys})$
obtained from a recent ZEUS analysis of total
$\gamma {\mathrm p}$ cross-section results based on an extrapolation of total
$\gamma^{*} {\mathrm p}$ cross-section data \cite{ref37_zeus}. The soft Pomeron intercept by
Donnachie and Landshoff
\cite{ref_dl} of $\alpha_{I\!\!P}=1.0808$ is smaller than those obtained from total-cross section
results involving at least one photon in the scattering process.

\section{Summary and Outlook}

OPAL has performed a wide range of measurements of ${\mathrm e}\gamma$ and $\gamma\gamma$
scattering in ${\mathrm e^{+}}{\mathrm e^{-}}$ collisions at LEP.

The hadronic photon structure function
$F_{2}^{\gamma}$ has been measured for
$0.0025<x \mathrel{\rlap{\lower4pt\hbox{\hskip1pt$\sim$} 1$ and
$1.1<Q^{2}<400\,{\rm GeV}^{2}$. The current systematic
uncertainties on $F_{2}^{\gamma}$ are dominated by the model dependence
in the simulation of the hadronic final state. Only considerable
improvements of general purpose Monte Carlo (MC) models to
better describe the hadronic final state will allow
to study the low $x$ behavior of $F_{2}^{\gamma}$ as well as
the $Q^{2}$ evolution with higher precision. Data on the leptonic structure function
$F_{2, {\rm QED}}^{\gamma}$ are precise enough to test QED and to be sensitive
to more subtle effects such as the $P^{2}$ dependence.

It has been shown that the measured inclusive two-jet cross-sections in $\gamma\gamma$ scattering
can be well understood within the framework of NLO perturbative QCD (pQCD).
Two-jet cross-section
measurements provide
a useful means to constrain the gluon density in the photon. The
total cross-section results of the process $\gamma\gamma \rightarrow {\rm hadrons}$ from OPAL
and L3 were shown to be consistent. It has been found that the total $\gamma\gamma$
cross-section rises faster with $W$ than in $\gamma {\mathrm p}$ scattering and
even faster than in ${\mathrm p}\p$ or ${\mathrm p}\bar{{\mathrm p}}$ scattering.

The main concern for future measurements of $F_{2}^{\gamma}$ and
$\sigma_{\gamma\gamma}$ is to reduce the large systematic uncertainties
due to the simulation of the hadronic final state. Improvements of general purpose
MC models are eagerly awaited \cite{ref18_leif}.
With the larger centre-of-mass energy $\sqrt{s_{{\mathrm e^{+}}{\mathrm e^{-}}}}$ at LEP2 and the higher
statistics it will be possible to extend the kinematic range towards larger values in
$Q^{2}$ and $W^{2}$.
Finally, the study of double-tagged events to investigate the virtual structure of the
photon will be one of the main analysis topics for the future.

An exciting time is ahead of us until 2000 investigating the structure of the
photon and its interactions at LEP2\footnote{At the time of writing this report, the
OPAL experiment at LEP has recorded more than $175\,$pb$^{-1}$ of data during the '98 run
at a centre-of-mass energy of $189\,$GeV.}.

\pagebreak

\begin{flushleft}
{\Large\bf Acknowledgement}
\end{flushleft}

I want to thank Richard Nisius, Gerhard Schuler and Stefan S\"{o}ldner-Rembold
for carefully reading the manuscript. I am very grateful to Goran Jarlskog
for giving me the opportunity to go to this excellent workshop.

redpajama_set_name: RedPajamaArXiv


text:
package eu.bcvsolutions.idm.core.bulk.action.impl.contract;

import java.util.*;

import org.junit.After;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
import org.springframework.beans.factory.annotation.Autowired;

import com.google.common.collect.Sets;

import eu.bcvsolutions.idm.core.api.bulk.action.dto.IdmBulkActionDto;
import eu.bcvsolutions.idm.core.api.config.domain.EventConfiguration;
import eu.bcvsolutions.idm.core.api.domain.AutomaticRoleAttributeRuleComparison;
import eu.bcvsolutions.idm.core.api.domain.AutomaticRoleAttributeRuleType;
import eu.bcvsolutions.idm.core.api.dto.IdmAutomaticRoleAttributeDto;
import eu.bcvsolutions.idm.core.api.dto.IdmIdentityContractDto;
import eu.bcvsolutions.idm.core.api.dto.IdmIdentityDto;
import eu.bcvsolutions.idm.core.api.dto.IdmRoleDto;
import eu.bcvsolutions.idm.core.api.dto.IdmTreeNodeDto;
import eu.bcvsolutions.idm.core.api.dto.filter.IdmIdentityContractFilter;
import eu.bcvsolutions.idm.core.api.service.IdmIdentityContractService;
import eu.bcvsolutions.idm.core.api.service.IdmIdentityRoleService;
import eu.bcvsolutions.idm.core.api.service.IdmIdentityService;
import eu.bcvsolutions.idm.core.model.entity.IdmIdentityContract;
import eu.bcvsolutions.idm.core.model.entity.IdmIdentity_;
import eu.bcvsolutions.idm.core.security.api.domain.GuardedString;
import eu.bcvsolutions.idm.test.api.AbstractBulkActionTest;

/**
 * Delete contracts integration test.
 *
 * @author Radek Tomiška
 *
 */
public class IdentityContractDeleteBulkActionIntegrationTest extends AbstractBulkActionTest {

	@Autowired private IdmIdentityContractService contractService;
	@Autowired private IdmIdentityService identityService;
	@Autowired private IdmIdentityRoleService identityRoleService;

	@Before
	public void login() {
		loginAsAdmin();
	}

	@After
	public void logout() {
		super.logout();
	}

	@Test
	public void processBulkActionByIds() {
		List<IdmIdentityContractDto> dtos = createBulk(5);

		IdmBulkActionDto bulkAction = findBulkAction(IdmIdentityContract.class, IdentityContractDeleteBulkAction.NAME);

		Set<UUID> ids = this.getIdFromList(dtos);
		bulkAction.setIdentifiers(ids);
		IdmBulkActionDto processAction = bulkActionManager.processAction(bulkAction);

		checkResultLrt(processAction, 5l, null, null);

		for (UUID id : ids) {
			Assert.assertNull(contractService.get(id));
		}
	}

	@Test
	public void processBulkActionByFilter() {
		List<IdmIdentityContractDto> dtos = createBulk(5);
		List<IdmIdentityContractDto> otherDtos = createBulk(2);

		IdmIdentityContractFilter filter = new IdmIdentityContractFilter();
		filter.setIdentity(dtos.get(0).getIdentity());

		List<IdmIdentityContractDto> checkDtos = contractService.find(filter, null).getContent();
		Assert.assertEquals(6, checkDtos.size()); // with primary

		IdmBulkActionDto bulkAction = findBulkAction(IdmIdentityContract.class, IdentityContractDeleteBulkAction.NAME);
		bulkAction.setTransformedFilter(filter);
		bulkAction.setFilter(toMap(filter));
		IdmBulkActionDto processAction = bulkActionManager.processAction(bulkAction);
		checkResultLrt(processAction, 6l, null, null);

		for (IdmIdentityContractDto dto : dtos) {
			Assert.assertNull(contractService.get(dto));
		}

		Assert.assertNotNull(contractService.get(otherDtos.get(0)));
		Assert.assertNotNull(contractService.get(otherDtos.get(1)));
	}

	@Test
	public void testForceDeleteAsync() {
		// create identity
		String description = getHelper().createName();
		IdmIdentityDto identity = getHelper().createIdentity((GuardedString) null);
		identity.setDescription(description);
		IdmIdentityDto identityOne = identityService.save(identity);
		// create role
		IdmRoleDto role = getHelper().createRole();
		// create automatic roles - by tree and by attribute too
		IdmAutomaticRoleAttributeDto automaticRoleOne = getHelper().createAutomaticRole(role.getId());
		getHelper().createAutomaticRoleRule(automaticRoleOne.getId(), AutomaticRoleAttributeRuleComparison.EQUALS,
				AutomaticRoleAttributeRuleType.IDENTITY, IdmIdentity_.description.getName(), null, description);
		IdmTreeNodeDto treeNode = getHelper().createTreeNode();
		IdmIdentityContractDto contract = getHelper().getPrimeContract(identityOne);
		contract.setWorkPosition(treeNode.getId());
		contractService.save(contract);
		getHelper().createRoleTreeNode(role, treeNode, false);
		// create manuallyAssigned roles
		getHelper().createIdentityRole(identityOne, role);
		//
		Assert.assertEquals(3, identityRoleService.findAllByIdentity(identityOne.getId()).size());
		// remove role async
		try {
			getHelper().setConfigurationValue(EventConfiguration.PROPERTY_EVENT_ASYNCHRONOUS_ENABLED, true);
			//
			// delete by bulk action
			IdmBulkActionDto bulkAction = this.findBulkAction(IdmIdentityContract.class, IdentityContractDeleteBulkAction.NAME);
			bulkAction.setIdentifiers(Sets.newHashSet(contract.getId()));
			IdmBulkActionDto processAction = bulkActionManager.processAction(bulkAction);
			checkResultLrt(processAction, 1l, 0l, 0l);
			//
			getHelper().waitForResult(res -> {
				return contractService.get(contract) != null;
			});
			//
			Assert.assertTrue(identityRoleService.findAllByIdentity(identityOne.getId()).isEmpty());
			Assert.assertNull(contractService.get(contract));
		} finally {
			getHelper().setConfigurationValue(EventConfiguration.PROPERTY_EVENT_ASYNCHRONOUS_ENABLED, false);
		}
	}

	private List<IdmIdentityContractDto> createBulk(int count) {
		List<IdmIdentityContractDto> results = new ArrayList<>();
		//
		IdmIdentityDto owner = getHelper().createIdentity((GuardedString) null);
		for (int i = 0; i < count; i++) {
			results.add(getHelper().createContract(owner));
		}
		//
		return results;
	}
}

redpajama_set_name: RedPajamaGithub


text:
Jutsu Type
Revision as of 15:20, 17 October 2019 by Seelentau (talk | contribs) (Reverted edits by Lehur (talk) to last version by Omnibender)
An example of genjutsu being used.
Genjutsu (幻術, literally meaning: Illusionary Techniques) is one of the main jutsu categories which uses chakra. Unlike ninjutsu, the effects of genjutsu are not real, being only sensory illusions experienced by those who fall victim to it. According to the Second Mizukage, genjutsu falls under the broad category of Yin Release.[1]
2 Countering
A genjutsu is created when a ninja controls the chakra flow of a target's cerebral nervous system, thereby affecting their five senses; this is frequently used to create false images and/or trick the body into believing its has experienced physical pain. It is further explained in the anime that, because genjutsu affects activity throughout the prosencephalon structure of the brain, humans, dogs and other species of mammal are therefore all affected by genjutsu; however, the kikaichū, like all insects, lack such a structure to their brains, and so do not even notice it: as Shino Aburame put it, insects are ruled almost solely by their senses alone, which makes them immune to genjutsu and gives the Aburame clan an ability to detect it, even when heightened senses become succeptible.[2]
Genjutsu can also be used to manipulate others - similar to brainwashing - by feeding the victim illusive suggestions. Methods include integration with nature transformation, as shown with Water and Lightning Release, and in the anime, ingesting special pills that activate when the target sleeps.[3] Audible genjutsu is deemed the most dangerous because the user can trap victims from long distances.[4]
Despite its usefulness, genjutsu is rarely employed, most shinobi preferring the real, tangible effects of ninjutsu and taijutsu over the imagined effects of genjutsu. The difficulty of performing genjutsu in the first place presents an additional barrier to its use: genjutsu require precise chakra control in order to manipulate the target's senses and advanced intelligence to make the illusion convincing,[5] prerequisites that even someone as skilled as Jiraiya lacks.[6] Some, however, are able to specialise in genjutsu, with Kurenai Yūhi being regarded as one of Konoha's experts in the field and members of the Uchiha clan being particularly feared because of their Sharingan's generic genjutsu. According to Hagoromo, the Byakugan can also be used to extend the range of genjutsu.
Those under the influence of genjutsu will either appear to be unconscious or continue to move around under the pretence of the genjutsu. The latter is very effective in battle as a genjutsu user can make themselves appear to be somewhere else and attack the victim from behind or change the environment to make the victim see a flat plain where there is a steep cliff.
Countering
There are several options to combat genjutsu:
A victim's chakra flow, if disrupted enough, can break the caster's influence. This "Genjutsu Dissipation" (幻術解, Genjutsu Kai, literally meaning: Illusion Technique Dissipation) or "Genjutsu Reversal" (幻術返し, Genjutsu Gaeshi, literally meaning: Illusion Technique Reversal)[7] can be done by the victim themselves, (assuming they realise they're under a genjutsu's influence) or an ally who emits chakra into them;[8] jinchūriki who have formed a good relationship with their tailed beast prefer the latter method whenever they need it.[9]
Pain that is not caused by the genjutsu can bring victims back to their senses.[10]
If a caster's vision is obstructed, such as by the Hiding in Mist Technique, that at least prevents the use of ocular genjutsu.[11]
Possessing a Sharingan renders one largely invulnerable to genjutsu as their acute vision allows them to recognise its flaws and influence. They can also free others from genjutsu by inserting themselves into the opponent's illusion and release it.[12]
Deidara is somehow able to condition his left eye to break genjutsu.[13]
In the anime, kikaichū are impervious to genjutsu because their brain structures aren't sophisticated enough, allowing members of the Aburame clan a method to identify and counter genjutsu.[14]
In the anime, strong smells, such as those from Chilli Pepper Bombs, can counteract genjutsu.[15]
In the anime, Kabuto Yakushi attempted to use his own genjutsu on himself in order to override the one Itachi Uchiha placed on him, though due to the complex nature, it failed.[16]
List of genjutsu
Izanagi has the opposite effects to normal genjutsu, changing reality to illusion and vice versa.
Obito Uchiha had been able to completely control Yagura Karatachi with a genjutsu, despite the latter being a perfect jinchūriki.[17]
In the anime, genjutsu even works on Mecha-Naruto, corrupting its internal system.[18]
Because genjutsu are not real, they are not supposed to be able to kill victims. However, Izumi Uchiha is killed with Tsukuyomi in Itachi Shinden: Book of Dark Night.
In the anime, due to the Kurama Clan's kekkei genkai, certain members can use their exceptional talent for genjutsu to make the brain to believe the illusions are physically real, which can cause the victim to be potentially killed.
Itachi claimed that his Tsukuyomi can only be broken by a Sharingan user who shares the same blood with him.[19]
↑ Naruto episode 206
↑ Naruto: Shippūden episode 318
↑ Second Databook, page 163
↑ Naruto Shippūden episode 484
↑ Naruto chapter 345, pages 8-9
↑ Naruto chapter 26, page 13
Retrieved from "https://naruto.fandom.com/wiki/Genjutsu?oldid=1340772"

redpajama_set_name: RedPajamaCommonCrawl


text:
Category: carly mann
art, art studio, carly mann, Uncategorized
Redwood ➸ Harwood ↞The Lost Woods
July 30, 2016 August 6, 2016 carlymannart
Leaving behind friends and a memorable experience at Willow Creek Farm I was greatly anticipating getting stuck into an art project. A lovely roast lamb cooked by farm co-worker/new friend Annie made for a great evening's grub and company before heading to Motueka to meet Barbara. Myself and Barbara had exchanged many emails regarding an exhibition she had ideas for one gallery or maybe more…
Barbara was a kind soul, deeply interested in philosophy and art- particularly important shifts in art movements pre 20th century. I arrived after a scenic bridge drive over to the other side of Motueka where I was welcomed into Redwood Cottage. This was to be my home for the next week, and how perfect this turned out to be. I felt instantly comfortable and in a great mind-set to discuss the artworks Barbara wanted me to create. We had interesting discussions about our ideas and where to begin, I was very much in a position of planning, curating, and offering my advice and experience. Barbara had many intriguing books particularly focussed around Paleolithic and Neolithic art- right up my street. The Lascaux cave paintings situated in France seemed like a fitting starting point given the chronological date and my deep interest in caves and sacred stone structures. The very next day I began work armed with all the materials I could possibly need, listening to The Pentangle, Neil Young and Leonard Cohen to set the tone.
Work flowed organically. I played with texture, different scales, a limited colour palette, as well as metallics to produce a coherent set that I believe evoke the feel of the caves and invite the viewer to experience a unique insight. I was on a creative buzz all week, enjoying down time chatting to friendly Japanese and German wwoofers staying in Barbara's house, and friends back home over a gin or 3 in the cottage that felt so like home.
Renee was staying in nearby Nelson and joined me for my last night, drinking gin (a theme?) and playing board games- we had previously enjoyed the Light Nelson event, which was a free event creatively lighting up the city. It was pretty impressive (what I can remember of it!) But I wanted one last trek up Abel Tasman way, and managed to twist Renee's arm into joining me. This place was called Harwoods Hole, at 176 metres deep it is the known as the 'biggest vertical shaft' in New Zealand (tee hee) The walk to it was also used for filming scenes of 'Chetwood Forest' in Lord of the Rings.
We walked, Renee with her melodica in hand (we found it at the cottage) and decided to play Zelda tunes as we walked around (we're too cool) when approaching the semi circle of immensely high rock formations we could feel this was a special place, egging each other on to get nearer the edge and peer down, I've never seen anything quite like it. Awesome, enigmatic, and bloody scary all at the same time. A look out point on the way down proved to be a justified detour, that is until I fell onto very sharp angular rocks, giving myself a good few good cuts and bruises. It's moments like this that it's important to have a mate around- I was glad to have Ren there as I concerned my knee had given up the ghost.
Time to depart through the famously scenic Queen Charlotte Track, gradually heading south towards Kaikoura, situated on the east coast. Kaikoura is predominantly known for its whale and seal watching and was a beautiful first glimpse of those famous snow capped mountains. I stopped off at the Ohau Stream Walk to watch baby seals swimming playfully, it's also where I happened to bump into Danny- the super cool bus driver from Hobbiton , well met with a hug and quick catchup, this lifted my spirits even more. After a night in Kaikoura it was time to swing on down to Christchurch. Christchurch was a place I certainly wanted to at least pass through whilst in New Zealand. It is another large city, but this one experienced a devastating earthquake, a 6.3 on the richter scale in fact, killing many and destroying the surroundings and leaving the city unrecognisable. When I arrived it was a grey day and I was moved by the mess of it all. People I'd met on my journey so far had spoken about the optimisim and creative regeneration emerging through shipping containers, and impressive 'cardboard cathedral' and the like- sadly, it certainly had a long way to go in my opinion. As a diversion from isolating feelings of walking around a now soul-less city, it was to be a sociable few days ahead.
I sat myself in a nearby Mexican restaurant sipping a tasty margarita, anticipating the arrival of Californian Steve. Steve purchased one of my first ever glass works I created, inspired by the band Dead Can Dance. We had been in contact since then, and the dates worked so that we could meet up on his last night in New Zealand. We greeted with a hug and it felt instantly comfortable with flowing conversation including his incredible life stories managing bands, running radio stations, hanging out with famous faces, his INCREDIBLE music collection oh, and he's an award-winning racquetball extraordinaire. We spoke for hours over a tasty Asian meal, I left feeling glad we had the chance to meet.
The next day was time to meet a friend from back home, Matt, who has just recently secured permanent residency in New Zealand. We have been friends for many years, usually frequenting at the Beautiful Days festival or numerous Levellers gigs. Although he wasn't feeling 100% when we met (more like 40% in fact) he was sweet conversation and it felt like all was well.
The following day was The Cure day! I flew myself (I've grown wings) up to Auckland to meet free-spirited Linda (Hobbiton bus driver) as we had previously bonded over a love of great music and stayed in regular contact since my departure. To say I was excited to see The Cure would be an understatement. I have loved them and been inspired by Robert Smith since I was about 12. The fun, quirky, gothy, playful goodness of the band is so unique, and 40 years later they haven't 'sold out', they are still attracting fans of all ages, and quite frankly write bloody good songs and perform them exceptionally well. Altogether an emotionally exilerating 3.5hr gig that confirmed my love for the band- the first time I'd seen them myself and my partner at the time cried afterwards- it was overwhelming 🙂 Linda and I sunk a few, rocked out with fellow fans, and just had a bloody good time.
A hungover Carly, a cancelled flight, and 2 days of waiting at the airport failed to take off the shine…
Soundtrack: The Cure – How Beautiful You Are, The Doors – The Crystal Ship
Tagged art, artist, carly mann, cave art, caves, exhibition, gallery, lascaux, motueka, nelson, new zealand, paleolithic, south island, studio, tramping, travel, working visa, wwoofingLeave a comment


And here's the deal: You can't buy those seats.
The fans in Turner's Block don't pay for their seats … well, not with cash.
They have to try out to get in.
And people do actually try out. Like, a lot of people. This year's tryouts went down a few days ago. It's one of the best days I have each year, and ultimately it reinforced something I've known for awhile: Indiana Pacers fans have absolutely, positively no chill.
And that's what makes them the best.
I know you've heard that one before. Of course every player says his fans are the best. But like, I don't think you get it. These people, man, they're crazy.
In short, these Hoosiers be wildin'.
But then you get people in Indiana around a basketball court, throw some blue and gold on them? A switch flips. They're freaks, man. Like, in the best possible way. Basketball maniacs. Trust me, I got the receipts.
Here's how the tryouts work: People show up and get 20 seconds on stage to do something that will impress me, something that will prove their fandom. And man, people choose to use that time in … all kinds of ways.
One fan, I swear to God, showed up in a full-on wedding dress. She actually came up on stage, got down on one knee, presented me with a cherry ring pop and proposed to be in my fan section.
Welcome to The Block, Wedding Dress Lady.
One guy came up on stage and did a cover of "Black & Yellow," the Wiz Khalifa song, except he replaced the chorus with "Blue & Yellow" — and he wrote all new lyrics to make it about the Pacers, both current and historical. I think he dropped a Rik Smits line. It was very detailed. He absolutely killed it. Welcome to The Block, bro.
I'm pretty sure that the same guy created a homemade music video for the song. It doesn't have nearly enough views IMO. Can we change that?
I should be clear, though: Not everyone made the cut.
It's a cutthroat tryout, you know what I mean? And some fans, if I'm being real, made some strategic miscalculations. Like the guy who responded "Victor Oladipo" when we asked who the most talented player on the Pacers was.
Look, Vic is my favorite Pacer, too … but come on. Know your audience. It's the Myles Turner fan section. Like, just lie or something. That was intended to be an easy question.
We had one guy who prepared a whole act but got some serious stage fright and wasn't able to do it. Shout out to that dude, I'll be on the lookout for you next year. You got this.
People get creative. Another guy came out with 20 T-shirts on and managed to take all of them off within 20 seconds while running around in circles screaming. Like I'm saying, receipts. Tell me that man's not an athlete. You can't. You won't. Respect that hustle. NO CHILL. You know he made the squad. Welcome, T-Shirt Man.
We had men, women, children — really every type of person you can imagine. Even got an Elvis impersonator, which really makes me feel like Turner's Block has arrived.
I guess the point I'm making is that all of these people — each and every one down to their very core — had absolutely no chill. And that's the thing: When it comes to basketball, the state of Indiana has no chill. They're absolutely crazy about this sport. They're crazy about this team. And I genuinely love them for that.
Because I feel the exact same way.
The first guy I met with after joining the Pacers in 2015 was our trainer Josh Corbiel.
Josh's personality reminds me of that guy on Two and Half Men. What's the guy's name? The one who's not Charlie Sheen. Or the kid. The guy who plays the other man. That guy. That's what Josh is like.
Right after I was drafted, I was definitely kind of nervous about moving to a new place. The draft process had come with a ton of scrutiny that I wasn't expecting. Like teams at the combine literally asked me to walk in a straight line to prove … something?
And it was the Pacers who ended up drafting me … so I guess I passed?
Anyhow, what I remember most about that first interaction with Josh was that he was super direct. No real pleasantries. He said, "I heard you have some tendonitis in your left knee, so we're going to get to work on that." Then minutes after meeting him, he was digging his hands into my quad. It hurt so bad I just about jumped off the table. I know other places might just hand you a stim machine and an ice pack. Not Indiana. Josh worked on me and he worked on me until it no longer hurt.
When I signed my extension with the Pacers a couple of days ago, I thought about how thankful I am to the people in this organization, like Josh, who have done so many things behind the scenes to help me. I'm really excited to be staying in Indy for a lot reasons, but one of the biggest is that this place is a community. It's a place where relationships matter, and where I know I can grow.
There's a lot of time to kill in the trainer's room so me, Josh and Carl Eaton — who also works with the team — talk about plenty of stuff. One of the things we all feel pretty passionately about is Star Wars.
For the most part, we're in agreement on the franchise. The only really big Star Wars disagreement we've ever gotten in was over Solo. Carl and I liked it. Josh thought it was corny and that it wasn't faithful to the tone of the other movies in the franchise. He's wrong, but that's O.K. We're past that.
Anyway, when you're a big enough fan of Star Wars, you start seeing parallels between the characters in the movies and the people you interact with in real life.
An example: My first two years in Indy, Big Al Jefferson was my Yoda.
You know, reverse the phrasing a bit and that's basically Yoda.
Strong with Big Al, the force is.
And Nate, our coach? He's like Mace Windu, no nonsense, always about taking care of business. Just a baaaad man.
Myself? I'd like to think I'm like Obi Wan in his prime years. Like Episodes I to III Obi Wan, when he was super legit.
And as far as Vic goes, well, that's more challenging. Vic isn't … like anyone else. He really takes on different personas at different times. Because Vic away from the floor is always either joking or singing. Those are basically his two modes. He's a pretty good singer too. He comes to the locker room with a ton of range in terms of what he'll sing on any given day. Sometimes it's gospel, sometimes R&B, and when you aren't paying attention he might hit you with some country.
But on the floor, whole different ball game. As soon as the ball tips he has that Pacer mentality. Absolutely no chill. He's a freak of nature out there with his intensity and aggression. If we aren't bringing it on a particular night, he'll be in our faces shouting "What are we gonna do? What the f*** are we gonna do? Who the f*** are we going to be?" Just thinking about that kind of gets me hyped. But there are so many other ways he distinguishes himself as a leader behind the scenes.
Like I remember early last year, I played one game where just about nothing went right. It was my first game back after my concussion and my coordination was off. I had no feel for the game. I was pretty down, but I didn't make a big display of it. Nothing anyone would notice.
After the game, Vic did something I didn't expect. Something really cool. He came to my house to try to lift me up. He told me not to let one bad game get to me. He said the team needed me. That really meant a lot to me. He's just a really good guy who I feel really honored to compete with. I'll roll with him into any battle.
So maybe he's like Han? Let's go with Han.
I'm really happy that I get to spend at least four more years here. I say "at least" because, with what we're building, I hope to be here much longer than that.
Throughout the offseason, I tried to keep contract stuff out of my head. I'm lucky to have a team of people who take care of that stuff for me. I trusted them to find a way for me to stay here.
It actually wasn't until the other day, after I signed my extension, that all of this really hit. When my parents and I got back to my apartment after the signing, we all sat together and broke down in tears of joy. They worked so hard to put me in a position to realize my dreams. Growing up we weren't broke, but we were damn near broke. My dad took on night shifts and my mom worked her way up the corporate ladder at a hotel chain so that I would be able to attend the right tournaments and be on the right teams to get the exposure I needed to play in college. But ultimately, it wasn't just how they supported me financially, but also the way they showed me how to work. The example they set for me and my sister is something that can't be measured in dollars and cents.
I'm also thankful to Frank Vogel, my first coach. My rookie year got off to a rough start. There was a lot of skepticism surrounding the decision to draft me, and then when I broke my thumb early on, I think people around the league were already prepared to write me off as a bust. But for some reason Coach saw something in me. I'll never forget when got back from a road game and I was positive I was gonna get sent down to the G League. I actually had my bags packed, ready to go to Fort Wayne. Coach Vogel came up to me and said, "Hey kid, you ready?" Apparently we'd had a couple of injuries — Coach didn't only want me to stay on the roster, he wanted to give me more playing time. I said something to the extent of "F*** yeah, I'm ready!" And on that road trip, I killed it. I hit my career highs in every category and never looked back.
I wouldn't be in this position today if it wasn't for him. There are also all the assistant coaches who never get the credit they deserve. There's Bill Bayno who has spent so many hours in the gym with me working in the post. He makes me do all the little things right, over and over and over until it's habit. I get to learn from Popeye Jones, who had a long career in the league and dispenses knowledge to me every day that makes me better. All I want is to become as good at basketball as his son is at hockey.
There's Dan Burke, our defensive specialist. Dan is as passionate about basketball as anyone I've ever met. And he's mean as hell while he's coaching you. Like he will give s*** to every player he works with, no matter what their level is. And we all happily (well not always happily, that's not true) take it because he makes us better. When we're locking teams up at the end of games, that's Dan.
And then obviously there's Coach McMillan. Coach always takes the extra time to watch a lot of film with me. Even during the draft process, I vibed with him really well. He was one of the coaches I wanted to play for, and I'm really grateful that I get to.
But more than anything else, the reason I'm writing this is because I want to give a shout out to the fans. In my three years here, this place already feels like home. And I'm so damn excited to able to keep the core of this team intact. Yeah, what we did last year during that series with Cleveland was crazy. During those home games it felt like y'all were on the floor with us. I was so proud to represent each and every one of you. But that was only a taste of what we can do. We have much bigger ambitions. I don't need to tell you that we need you. You know the drill at this point.
But for everyone who isn't repping the Pacers right now? People who are going to come around later on, once we take this thing to another level?
I'm sorry, but you're going to have to wait in line.
Maybe try again next season.


text:
REVEALED: Top South Burnett schools for student suspensions
Data has revealed in the past five years, South Burnett schools have handed out more than 7000 suspensions, with just three of the region's 21 schools making up half of that number.
Dominic Elsome
MORE than 7000 suspensions have been dished out to students in the South Burnett region in a five-year period, new data has revealed.
Murgon State High School issued 1630 suspensions, which included 1533 short suspensions, 48 long suspensions and 13 exclusions.
The data comes as the South Burnett Times and Courier Mail reveal a staggering 374,506 suspensions have been given to students across five years – three times as that of the ACT and twice as many as NSW schools.
In the South Burnett region, 21 schools handed out 7050 suspensions between 2015 and 2019.
Kingaroy State High School recorded the second highest number of suspensions with 1453, while Nanango State High School issued 1327 suspensions.
Kingaroy State School, with 700, and Murgon State School, 541, round out the top five schools for the region.
QUT education expert Professor Linda Graham said the suspension rates were "way too high", as per 1000 students, the ACT had 58.05 suspensions, NSW had 87.62 and Queensland had 150.37 suspensions.
She said suspensions were not effective in resolving student behavioural problems.
"It either doesn't solve it, or makes the problem worse and reinforces the behaviour, we know that it doesn't work and there are better alternatives," she said.
Professor Graham said preventive strategies were required to teach students the skills to manage their own behaviour.
"We need to explicitly teach them about what behaviour expectations are and ways to avoid breaking those," she said.


The average price at the pump for a gallon of diesel fuel dropped 2.4 cents this week to its lowest price since January 20, according to the U.S. Dept. of Energy.
The department's Energy Information Administration said the average price fell to $1.484, which is 28.7 cents less that it was when it reached an all-time high eight weeks ago.
At $1.635, New England has the highest price at the pump, and is the only region above the $1.60 mark.
The Gulf Coast average dropped to $1.39, and the region is the only one below $1.40.


Q: How do I find Kiwanis Hilton Children's Centre in the Port Alberni phone book ? I can't find it listed there.
A: It is listed under "Kiwanis Hilton Centre". It is also listed in error under "Hilton Centre" which will give you the Preschool Speech office, not the main office. Please be sure to use the 723-7345 for any messages related to the administration of the centre. Although we have contacted the phone book company and Telus several times, the incorrect listing is still being published.
Q: I called the Main Office (723-7345) to get my son's speech appointment changed for that day and no one got back to me. Why is that?
A: The staff in the main office only work part time and may not be available to take your call. Also, the main office does not serve as a switchboard so it is best to call the program you need directly (see program directory for program contact info).
Q: I called the main office to make sure the daycare bus picked up Jane today because she needed to come to daycare, but no one got the message. What happened?
A: Since the staff in the main office only work part time, it is really important to direct your calls right to the program you need, especially if it is of an urgent nature. We can not guarantee that calls directed to the main office will be dealt with immediately. Please see the program directory for program contact info.
Have other questions? Please contact us at 250-723-7345, or email hiltoncentre@outreachtherapy.org.


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Story Island: an adventure in pictures
Come on a journey of imagination at your local public library to discover secret trapdoors, touch the skin of a dragon and hide away in a reading pod!
Peter Gouldthorpe, 'The boy felt water swirling about his feet', published in First light by Gary Crew (Lothian Books, 1993)
Julie Vivas, 'Possum magic animals in parade formation', merchandise illustration for Possum magic by Mem Fox (Omnibus Books, 1983), reproduced by permission of Scholastic Australia Pty Ltd
Elise Hurst, 'Hopping on a tourist bus', in The elephants' big day out (Lothian Books, 2003)
Lisa Stewart, 'Cuddle', in Can I cuddle the moon? by Kerry Brown (Scholastic Press, 2011), reproduced by permission of Scholastic Australia Pty Ltd
10 June 2016–20 January 2018
Various Victorian public libraries
(see locations and dates below)
Enjoy the magical world of children's book illustrations in Story Island! Between 2016 and 2018 this delightful exhibition of works from Australia's favourite children's book illustrators and authors will appear at 12 public libraries throughout Victoria.
Please see the list of locations and dates below. The exhibition is not appearing at State Library Victoria.
Encourage your child's sense of discovery, play and exploration with the suggested activities at the exhibition. Foster a lifelong love of books and reading by spending time looking at and talking about the pictures and stories. Be inspired to find other wonderful children's books at your local library to take home, and share the magic of storytelling together.
This free exhibition is a joint initiative of State Library Victoria and Public Libraries Victoria Network to promote the development of early years literacy skills. It features a selection of beautiful illustrations reproduced from the Scholastic Dromkeen Children's Literature Collection at State Library Victoria.
For children aged 0 to 8 years old, their parents and carers.
Exhibition locations and dates
Experience the Story Island exhibition at any one of these locations:
REALM (Ringwood Town Square, 179 Maroondah Highway), 10 June to 23 July 2016
Glenroy Library (737 Pascoe Vale Road, Glenroy), 29 July to 10 September 2016
Yarram Library (156 Grant Street, Yarram), 16 September to 29 October 2016
Wonthaggi Library (Murray Street, Wonthaggi), 5 November to 13 December 2016
Frankston Library (60 Playne Street, Frankston), 20 December 2016 to 4 February 2017
Braybrook Community Hub (107-109 Churchill Avenue, Braybrook), 10 February to 25 March 2017
Horsham Library (Mibus Centre, 28 McLachlan Street, Horsham), 31 March to 13 May 2017
Newcomb Library (corner Bellarine Highway and Wilsons Road), 19 May to 8 July 2017
Kerang Library (corner Shadforth Street and Murray Valley Highway), 14 July to 26 August 2017
Castlemaine Library (Barker Street, Castlemaine), 1 September to 14 October 2017
Craigieburn Library (Hume Global Learning Centre, 75-95 Central Park Avenue, Craigieburn), 20 October to 2 December 2017
Sunshine Library (301 Hampshire Road, Sunshine), 8 December 2017 to 20 January 2018
Recommended books for children (PDF) (pdf,205.63 KB)
Activities: Story Island (PDF) (pdf,4.29 MB)
Notes for teachers: Story Island (PDF) (pdf,5.11 MB)
Explore the 'Story Island' online image gallery
About the Dromkeen Collection
Explore our collection of children's books
Read our guide to children's literature
Find out about our collaboration with Victorian public libraries


Your opinion matters. Leave A Review Or Edit This Listing for Any Baby Can.
At Any Baby Can, we believe every child deserves a strong family. We focus on Family Strengthening, through parenting education and child abuse prevention, and Family Health by serving children with chronic illnesses and developmental delays.
We always need more information on our pantries. If you know of any details, volunteer information, website, hours or more description information about Any Baby Can please add a comment (below the map on this page), with information. We will then display this for all visitors on this page.


Has anyone done work on upgrading there AO-101 for automatic bed leveling?
Getting tired of my hex and mini wrench.
No, I added a micrometer height adjust, that's about it. It would be doable though, mirror what the taz 6 does, etc.
Do you have any photos of what you did? I am not following you.
I think you can see it here https://www.thingiverse.com/thing:547327 if not, it's in the linear rail mod.


A variety of foodstuffs which includes meat, Chicken, vegetables, fruits, rice, matooke, posho and others is provided to our learners and staff. Click here to download the school menu.
We have a resident school nurse who attends to the day to day health problems.
We have clean spacious dormitories suitable for pupil accommodation.
We cater for all categories of pupils regardless of their background, race, self religion or political affiliations.
All pupils must attend school in correct uniform. This can be purchased from the school including PE kit, caps in house colours, school sweaters and others.


text:
DirtFork
Home Featured The World's Smallest Wireless Record Player Provides Quality Sound Anywhere
The World's Smallest Wireless Record Player Provides Quality Sound Anywhere
Ed Miller
Photo Courtesy of RokBlok
Over the last several years, there's been an enormous resurgence in vinyl, with more and more people reverting back to the original, often more-preferred, sound. Hell, even major retail stores such as Best Buy and Target now feature a record section. The only knock with vinyl is that, for the most part, it is a completely stationary technology and cannot be used while on the go, however there's a brand new device that might just change the way we're able to listen to records.
The RokBlok by Pink Donut is the world's smallest turntable, allowing users to listen to a record anywhere there's a flat surface, producing the sound right in a little box. Essentially, the RokBlok is a mini wooden vehicle that drives around on your record, following the vinyl's grooves and, if it's not loud enough for your current environment, simply connect it to a wireless speaker to turn it up to 11. It's perfect for someone who wants to enjoy vinyl but doesn't want the hassle of setting up a full turntable and at $100, the price tag isn't outrageous.
At about the size of a cell phone, though much thicker, this gadget can go anywhere and be used with little effort, playing EP, LPs and singles – basically any type of record. The built-in Bluetooth allows for connection to any wireless speakers or headphones within a 30-foot radius and the rechargeable battery, which lasts for up to four hours, ensures never having to grab AAAs.
Originally launched via Kickstarter by creator Logan Riley – a former Creative Education Lead at Apple – who launched his startup Pink Donut in 2015, the product has continued to grow ever since. Among other gadgets and apps, RokBlok's campaign raised over $351,000 for RokBlok and it even led to Riley's product appearing on an episode of ABC's Shark Tank, where he eventually accepted an offer.
While some complained about the gadget's ability to produce sound without a speaker, the overall reviews of RokBlok are positive and have created several other competitors. It's currently available on RokBlok's website, just in time for Record Store Day.
Pink Donut
RokBlok
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Ed is the co-founder of Dirtfork, a native Philadelphian and an alum of Arizona State University's Walter Cronkite School of Journalism who has freelanced for a number of print and web-based outlets during his career, including seven years with CraveOnline. When he's not interviewing J.J. Watt and riding in an IndyCar with Mario Andretti, Ed enjoys spouting off obscure movie quotes, devouring a great plate of Mexican food and going on adventures with his wife and adopted dog.
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Thirsty Thursday: Almanac Beer Company's Sunshine & Opportunity
Ed Miller - July 9, 2019
On a cool, breezy night in Cleveland, a packed Progressive Field witnessed the 2019 Home Run Derby, an instant classic which produced...
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© DirtFork Magazine
Thirsty Thursday: Ballast Point Brewing Company's Aloha Sculpin
Ed Miller - August 2, 2018
Welcome to Thirsty Thursday, a weekly column where we pick a beer from our fridge and review it, because in a world where two...


At the next Girl Geek event in Ottawa, WebFueler Helen Faber will be discussing the State of Search in Canada and focusing on the technical side of #SEO2014. She will also share tales and stories about search related issues in Canada.
Helen Faber (@HelenFaber) was an early adopter of the Internet (mid 90's) and has been on the scene – even before Google.
Ten years ago, she founded WebFuel. In 2009, she launched the Ottawa Search & Digital Marketing Meetup. Helen also sits on the Algonquin Advertising & Marketing Communication Advisory Board.
While she doesn't really consider herself a geek, her friends & family do.