text:
\section{Introduction}

Electronic transport through nano-scale systems coupled to
ferromagnetic leads reveals new phenomena which arise due to the
interplay of charge and spin degrees of freedom. In the case of
metallic grains or large quantum dots, this leads to
magnetic-dependent Coulomb blockade and Coulomb oscillations
phenomena \cite{barnas98,weymann03,ernult04}, spin accumulation,
negative differential conductance, and inverse tunnel
magnetoresistance (TMR) effect
\cite{shimada02,yakushiji05,weymannDSET06}. Transport through a
quantum dot with a few electrons reveals further features
resulting from discreteness of the dot energy spectrum and from
electron correlations
\cite{kouwenhoven97,kouwenhoven98,deshmukh02,hanson03,zambuhl04}.
When the dot is weakly coupled to the leads, one can distinguish
two different regimes of electronic transport: sequential and
cotunneling ones \cite{averin90,geerligs90,golovach04}. Sequential
transport through a single-level quantum dot coupled to
ferromagnetic leads was studied quite recently for collinear
\cite{bulka00,rudzinski01} and non-collinear
\cite{koenig03,braun04,braun06} configurations of the magnetic
moments of electrodes. Spin polarized transport in the cotunneling
regime has also been addressed
\cite{weymannPRB05BR,pedersen05,weymannEPJB05}. It has been shown
\cite{weymannPRB05BR} that the interplay of various spin dependent
cotunneling processes gives rise to anomalous behavior of the
differential conductance when the leads' magnetic moments are
antiparallel. This, in turn, leads to the corresponding zero-bias
anomaly in the tunnel magnetoresistance. Moreover, the even-odd
electron number parity effect in tunnel magnetoresistance has also
been found \cite{weymannPRB05a}. In both cases intrinsic spin
relaxation in the dot was neglected, and spin in the dot could
relax only due to cotunneling events.

In this paper we consider transport through single-level quantum
dots coupled to ferromagnetic leads in the cotunneling regime. In
particular, we show how the intrinsic spin relaxation in the dot
affects the dot occupation probabilities, spin accumulation,
conductance and the TMR effect. We analyze the cases of quantum
dots with degenerate and non-degenerate energy levels, which are
symmetrically (equal spin polarizations of the leads) and
asymmetrically (unequal spin polarizations of the leads) coupled
to the leads. The latter case is of particular interest as the
corresponding transport characteristics are highly asymmetric with
respect to the bias reversal. We show that this diode-like
behavior may be enhanced by intrinsic spin-flip relaxation
processes in the dot. Moreover, we show that the zero-bias
anomaly, found previously \cite{weymannPRB05BR} in the
antiparallel configuration, can occur in any magnetically
asymmetric system, in particular when one electrode is nonmagnetic
while the other one is ferromagnetic.

The systems considered in this paper may be realized
experimentally in various ways, including self-assembled dots in
ferromagnetic semiconductors \cite{chye02}, ultrasmall metallic
particles \cite{ralph02}, granular structures \cite{zhang05},
carbon nanotubes \cite{tsukagoshi99,zhao02,sahoo05}, and other
molecules \cite{pasupathy04}. In the case of quantum dots coupled
to nonmagnetic leads, differential conductance in the cotunneling
regime has also been measured experimentally \cite{koganPRL04}.

In section 2 we present the model and theoretical formulation of
the problem. Numerical results for symmetric and asymmetric
systems are shown and discussed in sections 3 and 4, respectively.
Final conclusions are given in section 5.

\section{Model and method}

We consider a single-level quantum dot coupled to ferromagnetic
leads and for simplicity restrict our considerations to the case
when magnetic moments of the leads are either parallel or
antiparallel. The system is described by the Hamiltonian $H=H_{\rm
L}+H_{\rm R}+H_{\rm D}+H_{\rm T}$. The first two terms represent
the left and right reservoirs in the noninteracting particle
approximation, $H_{\nu}=\sum_{k\sigma} \varepsilon_{\nu
k\sigma}c^{\dagger}_{\nu k\sigma} c_{\nu k\sigma}$, where
$\varepsilon_{\nu k\sigma}$ denotes energy of an electron with the
wave number $k$ and spin $\sigma$ in the lead $\nu={\rm L,R}$. The
dot Hamiltonian $H_{\rm D}$ involves two terms, $H_{\rm
D}=\sum_{\sigma=\uparrow,\downarrow}
\varepsilon_{\sigma}d^{\dagger}_{\sigma} d_{\sigma}+U
d^{\dagger}_{\uparrow} d_{\uparrow}
d^{\dagger}_{\downarrow}d_{\downarrow}$, where the first term
describes noninteracting electrons in the dot, whereas the second
one takes into account Coulomb interaction with $U$ denoting the
correlation parameter. The tunneling Hamiltonian reads, $H_{\rm
T}=\sum_{\nu=\rm L,R}\sum_{k\sigma}\left( T_{\nu}c^{\dagger}_{\nu
k\sigma} d_{\sigma}+T^{*}_{\nu}d_{\sigma}^{\dagger}c_{\nu
k\sigma}\right)$, where $T_{\nu}$ denotes the corresponding tunnel
matrix elements. Coupling of the dot to external leads can be
described by the parameters $\Gamma_{\nu}^{\sigma}= 2\pi
|T_{\nu}|^2 \rho_{\nu\sigma}$, with $\rho_{\nu\sigma}$ being the
spin-dependent density of states in the lead $\nu$. When defining
the spin polarization of lead $\nu$ as $p_{\nu}=(\Gamma_{\nu}^{+}-
\Gamma_{\nu}^{-})/ (\Gamma_{\nu}^{+}+ \Gamma_{\nu}^{-})$, the
coupling parameters can be written as
$\Gamma_{\nu}^{+(-)}=\Gamma_{\nu}(1\pm p_{\nu})$, with
$\Gamma_{\nu}= (\Gamma_{\nu}^{+} +\Gamma_{\nu}^{-})/2$. Here,
$\Gamma_{\nu}^{+}$ and $\Gamma_{\nu}^{-}$ correspond to
spin-majority and spin-minority electrons, respectively. In the
following we assume $\Gamma_{\rm L}=\Gamma_{\rm R}\equiv\Gamma/2$.
In the weak coupling regime, typical values of the dot-lead
coupling strength $\Gamma$ are of the order of tens of $\mu$eV,
whereas the measurements are usually carried out at temperatures
of the order of tens of mK \cite{koganPRL04}.

In order to analyze electronic transport in the cotunneling regime
we employ the second-order perturbation theory
\cite{averin90,kang97}. The cotunneling rate for electron
transition from the left to right leads is then given by
\begin{equation}\label{Eq:cotunnelingrate}
\gamma_{\rm LR}=\frac{2\pi}{\hbar}
\left|\sum_{v}\frac{\bra{\Phi_L}H_{T}\ket{\Phi_v}\bra{\Phi_v} H_T
\ket{\Phi_R}} {\varepsilon_i-\varepsilon_{v}}\right|^2\delta
(\varepsilon_i-\varepsilon_f),
\end{equation}
where $\varepsilon_i$ and $\varepsilon_f$ denote the energies of
initial and final states, $\ket{\Phi_\nu}$ is the state with an
electron in the lead $\nu$, whereas $\ket{\Phi_v}$ is a virtual
state with $\varepsilon_{v}$ denoting the corresponding energy.
Generally, one can distinguish between single-barrier and
double-barrier cotunneling as well as between cotunneling
processes that leave unchanged magnetic state of the dot and those
which reverse spin of the dot. The non-spin-flip cotunneling
processes are elastic and coherent, whereas the spin-flip ones are
incoherent (and inelastic when the dot level is spin split).
Unlike the double-barrier processes, the single-barrier ones do
not contribute directly to electric current. However, they can
change the occupation probabilities, and this way also the current
flowing through the system.

In numerical calculations we have included all possible
cotunneling events. Furthermore, we have allowed for intrinsic
spin relaxation processes in the dot \cite{rudzinski01}. Such
processes can result, for instance, from spin-orbit interaction in
the dot or coupling of the electron spin to nuclear spins. We will
not consider a particular microscopic mechanism of the intrinsic
spin-flip processes, but simply assume their presence and describe
them by the relevant spin-flip relaxation time $\tau_{\rm sf}$.
The relaxation processes have been then taken into account {\it
via} a relaxation term in the appropriate master equation for the
occupation probabilities,
\begin{equation}
  0=\sum_{\nu,\nu^\prime = {\rm L,R}}\left(-\gamma_{\nu\nu^\prime}
  ^{\sigma\rightarrow\bar{\sigma}} P_{\sigma} +
  \gamma_{\nu\nu^\prime} ^{\bar{\sigma}\rightarrow\sigma}
  P_{\bar{\sigma}}\right)
  -\frac{2}{\tau_{\rm sf}}\frac{P_\sigma e^{\beta\varepsilon_\sigma} -
   P_{\bar{\sigma}} e^{\beta\varepsilon_{\bar{\sigma}}} }
   {e^{\beta\varepsilon_\sigma}+e^{\beta\varepsilon_{\bar{\sigma}}}},
\end{equation}
where $\beta=1/(k_{\rm B}T)$, $P_\sigma$ denotes the probability
that the dot is occupied by a spin-$\sigma$ electron, and
$\gamma_{\nu\nu^\prime} ^{\sigma\rightarrow\bar{\sigma}}$ is the
cotunneling rate from lead $\nu$ to lead $\nu^\prime$ with a
change of the dot spin from $\sigma$ to $\bar{\sigma}$
($\bar{\sigma}=-\sigma$). The last term describes the spin
relaxation processes. In the case of spin-degenerate dot level
this term is reduced to $-(P_\sigma - P_{\bar{\sigma}})/\tau_{\rm
sf}$.

We consider the case when the dot is singly occupied at
equilibrium ($\varepsilon_\sigma<0$, $\varepsilon_\sigma+U>0$) and
the system is in a deep Coulomb blockade regime; $\Gamma,k_{\rm
B}T \ll |\varepsilon_\sigma|,\varepsilon_\sigma+U$. In such a case
the sequential tunneling is exponentially suppressed, and
cotunneling gives the dominant contribution to electric current
\cite{weymannPRB05BR}. Both non-spin-flip and spin-flip
cotunneling processes are then allowed and have to be taken into
account.

In the following we will distinguish between the fast and slow
spin relaxation limits. The former (latter) limit corresponds to
the situation when the time between successive cotunneling events,
$\tau_{\rm cot}$, is significantly  longer (shorter) than the
intrinsic spin relaxation time $\tau_{\rm sf}$. A typical spin
relaxation time for quantum dots can be relatively long, up to
$\mu$s \cite{fujisawa02,elzerman04}. On the other hand, the time
between successive cotunneling events can be estimated taking into
account the fact that the rate of spin-flip cotunneling is
generally larger than that of non-spin-flip cotunneling (for a
finite parameter $U$). Assuming
$\varepsilon_\uparrow=\varepsilon_\downarrow=\varepsilon$, one
then finds
\begin{equation}\label{Eq:tcot}
  \tau_{\rm cot}\approx
  \frac{h\varepsilon^2(\varepsilon+U)^2}{AU^2\Gamma^2}\,,
\end{equation}
with $A={\rm max}\{|eV|,k_{\rm B}T \}$ and $h=2\pi\hbar$. Assuming
typical parameters \cite{koganPRL04}, one can roughly estimate
$\tau_{\rm cot}$ to range from $10^{-3}$ ns to $1$ ns. Thus,
having spin relaxation time in the dot and the system parameters
entering Eq.~(\ref{Eq:tcot}), one can estimate whether the
system's behavior corresponds to the fast or slow spin relaxation
regimes. Both the time between successive cotunneling events and
the spin relaxation time depend on the system parameters and can
be tuned, for example by applying a weak magnetic field, varying
coupling to nuclear spins, etc. Thus, the regimes of fast and slow
spin relaxation are achievable experimentally.

Electric current flowing through the system from the left to right
leads is given by
\begin{equation}
  I = e \sum_{\sigma\sigma'} P_\sigma \left[
  \gamma^{\sigma \rightarrow \sigma'}_{\rm LR} -
  \gamma^{\sigma \rightarrow \sigma'}_{\rm RL} \right].
\end{equation}
In the following we discuss the influence of intrinsic spin
relaxation on differential conductance and tunnel
magnetoresistance of the quantum dot in the cotunneling regime
both in the presence and absence of external magnetic field $B$.
The TMR effect is defined as
\begin{equation}\label{Eq:TMR}
{\rm TMR} = \frac{I_{\rm P}-I_{\rm AP}}{I_{\rm AP}} \,,
\end{equation}
with $I_{\rm P}$ ($I_{\rm AP}$) denoting the current flowing
through the system in the parallel (antiparallel) magnetic
configuration at a constant bias voltage $V$ applied to the
system.

\section{Quantum dots symmetrically coupled to the leads}

First, let us proceed with the case of quantum dots coupled to
ferromagnetic leads with equal spin polarizations $(p_L=p_R\equiv
p)$. Our considerations will also include the cases of quantum
dots with non-degenerate and degenerate energy levels. The former
situation is discussed in the following subsection.

\subsection{The case of spin-degenerate dot level}

In the case of $B=0$ the dot level is spin degenerate,
$\varepsilon_{\uparrow}= \varepsilon_{\downarrow} =\varepsilon$.
The differential conductance $G=dI/dV$ for parallel and
antiparallel magnetic configurations is shown in Fig.
\ref{Fig1}(a) for the case of no intrinsic spin relaxation in the
dot ($1/\tau_{\rm sf}\rightarrow 0$). In the parallel
configuration one finds typical parabolic behavior of the
conductance with increasing transport voltage. However, this is
not the case for antiparallel configuration, where a maximum in
the differential conductance appears in the small bias voltage
regime. This anomalous behavior of the differential conductance,
in turn, leads to respective minimum in the tunnel
magnetoresistance, as shown by the solid curve in Fig.
\ref{Fig1}(c).

\begin{figure}[t]
  \includegraphics[width=0.7\columnwidth]{Fig1.eps}
  \caption{\label{Fig1} The differential conductance in the parallel
  and antiparallel configurations (a,b) and tunnel magnetoresistance
  (c) as a function of the bias voltage for different spin
  relaxation $r=h/(\tau_{\rm sf}\Gamma)$. The parameters are:
  $k_{\rm B}T=0.2\Gamma$,
  $\varepsilon =-15\Gamma$, $U=30\Gamma$,
  and $p_{\rm L}=p_{\rm R}=0.5$.}
\end{figure}

Physical mechanism of the zero-bias anomaly was considered in
Ref.~[\onlinecite{weymannPRB05BR}] for the case of no intrinsic
spin relaxation. It was pointed out that the anomaly results from
the relative difference between the fastest cotunneling events
(which involve only the majority electrons of the leads)
contributing directly to the charge current in the parallel and
antiparallel configurations. In the parallel configuration, the
main contribution to electric current comes from the non-spin-flip
cotunneling processes, whereas spin-flip cotunneling is dominant
for antiparallel alignment. In addition, the spin asymmetry in
tunneling processes leads to a nonequilibrium spin accumulation in
the dot in the antiparallel configuration, which increases with
increasing bias voltage. The spin accumulation, defined as
$(P_\uparrow - P_\downarrow)/2$, is shown in
Fig.~\ref{accumulation} as a function of the bias voltage for
different spin relaxation times. For the parameters assumed here
and for negative bias ($eV <0$, current flows from right to left,
while electrons flow from left to right), there is a larger
probability to find in the dot a spin-up electron than a spin-down
one. This, in turn, diminishes the contribution coming from the
fastest spin-flip cotunneling processes. However, there are also
single-barrier spin-flip cotunneling events which reverse spin of
the dot and open the system for the fastest transport processes.
The rate of single-barrier processes is proportional to
temperature (but independent of the applied voltage), whereas that
of double-barrier processes increases with the transport voltage,
being roughly independent of temperature. Thus, when $|eV|\lesssim
k_{\rm B}T$, the single-barrier processes play a significant role
-- they decrease the spin accumulation in the dot and open the
system for the fastest cotunneling events. Consequently, the main
contribution to current comes then from the most probable
spin-flip cotunneling processes. When $|eV|\gg k_{\rm B}T$, the
relative role of single-barrier processes is diminished due to an
increased role of double-barrier cotunneling, and the differential
conductance decreases. The zero-bias maximum in differential
conductance appears then as a result of the competition between
single- and double-barrier cotunneling processes.

\begin{figure}[t]
  \includegraphics[width=0.7\columnwidth]{Fig2.eps}
  \caption{\label{accumulation} The spin accumulation
  in the antiparallel configuration
  as a function of the bias voltage for different spin
  relaxation $r=h/(\tau_{\rm sf}\Gamma)$. The parameters are the
  same as in Fig.~\ref{Fig1}.}
\end{figure}

The anomalous behavior of differential conductance in the
antiparallel configuration results from spin asymmetry of
tunneling processes. This asymmetry leads to nonequivalent
occupation of the dot by spin-up and spin-down electrons (spin
accumulation), as illustrated in Fig.~\ref{accumulation}. From the
above discussion follows that the spin accumulation is crucial for
the occurrence of the zero-bias anomaly. Thus, one may expect that
intrinsic spin-flip processes in the dot should suppress the
anomaly. Indeed, intrinsic spin relaxation in the dot
significantly modifies the conductance maximum at zero bias, and
totally suppresses this anomalous behavior in the limit of fast
spin relaxation. This behavior is displayed in Fig.~\ref{Fig1}(b),
where different curves correspond to different values of the
parameter $r$ defined as $r=h/(\tau_{\rm sf}\Gamma)$. Thus, $r=0$
describes the case with no intrinsic spin relaxation, whereas the
curves corresponding to nonzero $r$ describe the influence of
intrinsic relaxation processes. First of all, one can note that
small amount of intrinsic spin-flip processes enhances the
zero-bias anomaly [see the curve for $r=10^{-2}$ in
Fig.~\ref{Fig1}(b)]. This is because such processes play then a
role similar to that of single-barrier spin-flip cotunneling. In
the case of fast spin relaxation, on the other hand, the spin
accumulation is suppressed and the anomaly disappears, as can be
seen in Fig.~\ref{Fig1}(b) and Fig.~\ref{accumulation} for $r=1$.
It is also worth noting that spin-flip processes in the dot
enhance the overall conductance in the antiparallel configuration.
In the parallel configuration, however, the differential
conductance does not depend on intrinsic relaxation. This is
because there is no spin accumulation in the parallel
configuration, and consequently the intrinsic spin-flip processes
in the dot do not play any role.

In the case of a deep Coulomb blockade one can take only the
lowest order corrections in $x/y$, with $x=k_{\rm B}T,|eV|$ and
$y=\vert\varepsilon\vert,\varepsilon +U$, and derive some
approximate formulas for the differential conductance. For the
parallel configuration, the differential conductance can be then
expressed as
\begin{equation}\label{Eq:GP}
  G^{\rm P} = \frac{e^2}{h}\frac{\Gamma^2}{2} \left[
    \frac{1}{\varepsilon^2} + \frac{1}{(\varepsilon +U)^2}
    + \frac{1-p^2}{|\varepsilon| (\varepsilon +U)} \right].
\end{equation}
In the antiparallel configuration and for $|eV| \ll k_{\rm B}T$,
the conductance is given by the expression
\begin{eqnarray}\label{Eq:GAPmax}
  G^{\rm AP}_{\rm max} &=& \frac{e^2}{h}
  \frac{\Gamma^2}{2} \bigg\{(1-p^2) \left[
    \frac{1}{\varepsilon^2} + \frac{1}{(\varepsilon +U)^2}
    + \frac{1}{|\varepsilon| (\varepsilon +U)} \right]\nonumber\\
  &&+\frac{p^2U^2h/\tau_{\rm sf}}{\varepsilon^2(\varepsilon+U)^2h
  /\tau_{\rm sf}+ k_{\rm B}TU^2\Gamma^2}
  \bigg\},
\end{eqnarray}
which describes the maximum of the differential conductance at
zero bias for arbitrary value of $r$. On the other hand, when
$|eV| \gg k_{\rm B}T$ and $r\ll 1$ one finds the formula
\begin{eqnarray}\label{Eq:GAPmin}
  \lefteqn{  G^{\rm AP}_{\rm min} = \frac{e^2}{h}
  \frac{\Gamma^2}{2}\bigg\{ \frac{1-p^2}{1+p^2} \left[
    \frac{1}{\varepsilon^2} + \frac{1}{(\varepsilon +U)^2}
    + \frac{1-p^2}{|\varepsilon| (\varepsilon +U)}
    \right] }\nonumber \\
  && + \frac{4p^2}{1+p^2}  \frac{U^2h/\tau_{\rm sf}}{2\varepsilon^2
  (\varepsilon+U)^2 h/\tau_{\rm sf}+ (1+p^2)k_{\rm B}TU^2\Gamma^2}
  \bigg\},
\end{eqnarray}
which in turn approximates the local minimum value of the
differential conductance. The expression for $G^{\rm AP}_{\rm
min}$ for arbitrary spin relaxation time is too complex to be
presented here. It is clearly evident from the above expressions
that the conductance depends on intrinsic spin relaxation only in
the antiparallel configuration, in agreement with numerical
results. The variation of the linear conductance in the
antiparallel configuration with the parameter $r$ is displayed in
Fig.~\ref{Fig3}(a) for several values of temperature. As one can
see, there is a clear crossover between the limits of fast and
slow spin relaxation in the dot. The crossover depends on
temperature and is shifted towards shorter relaxation times as the
temperature increases.

In order to describe the zero-bias anomaly in the differential
conductance in the antiparallel configuration, it is useful to
introduce the relative height of the maximum at $V=0$, defined as
$x_{\rm G} = (G^{\rm AP}_{\rm max}- G^{\rm AP}_{\rm min})/G^{\rm
AP}_{\rm min}$. The variation of $x_{\rm G}$ with the spin
relaxation time is shown in Fig.~\ref{Fig3}(b) for different
temperatures. First of all, one can see that the relative height
depends on $r$ in a nonmonotonic way. In the limit of slow spin
relaxation and low temperature one finds $x_{\rm G}=4p^2/(3-p^2)$,
whereas in the limit of fast spin relaxation $x_{\rm G}$ tends to
zero, independently of temperature. Indeed, in the limit of fast
spin relaxation $G^{\rm AP}_{\rm max}$ and $G^{\rm AP}_{\rm min}$
are equal and given by
\begin{equation}
  G^{\rm AP} = \frac{e^2}{h}\frac{\Gamma^2}{2} \left[
    \frac{1}{\varepsilon^2} + \frac{1}{(\varepsilon +U)^2}
    + \frac{1+p^2}{|\varepsilon| (\varepsilon +U)} \right].
\end{equation}
On the other hand, the relative height exhibits a maximum for a
certain value of spin relaxation. This maximum, in turn, is
decreased and shifts towards shorter relaxation times with
increasing temperature, see Fig.~\ref{Fig3}(b). One can show that
the maximum occurs when the relaxation time is approximately given
by
\begin{equation}\label{Eq:tmax}
  \tau_{\rm sf}^{\rm max}\approx
  \frac{h\varepsilon^2\left(\varepsilon+U\right)^2}
  {k_{\rm B}T U^2 \Gamma^2} \,.
\end{equation}
When comparing Eqs (\ref{Eq:tcot}) and (\ref{Eq:tmax}) one can
conclude that the maximum in the relative height of the
conductance anomaly occurs when the spin relaxation time
$\tau_{\rm sf}$ is roughly equal to the time between successive
cotunneling events, $\tau_{\rm cot}$, in the zero bias limit. This
also means that the maximum separates the fast and slow spin
relaxation regimes, in agreement with Fig.~\ref{Fig3}. The
enhancement of $x_{\rm G}$ can range from a few percent for small
spin polarization of the leads, $p\lesssim 0.2$, to several
hundred percent for $p\gtrsim 0.9$. For the parameters assumed in
Fig.~\ref{Fig3}(b), the relative height of the zero-bias maximum
in differential conductance for $\tau_{\rm sf}=\tau_{\rm sf}^{\rm
max}$ is enhanced by about $65\%$ as compared to the case of
$\tau_{\rm sf}\rightarrow\infty$. Assuming typical parameters for
the quantum dot \cite{koganPRL04}, one can estimate $\tau_{\rm
sf}^{\rm max}$ to be $\tau_{\rm sf}^{\rm max}\approx 50$ns, which
is accessible experimentally. \cite{fujisawa02,elzerman04}

\begin{figure}[t]
  \includegraphics[width=0.74\columnwidth]{Fig3.eps}
  \caption{\label{Fig3} The spin relaxation time dependence of the
  linear conductance in the antiparallel configuration (a)
  and the relative height of the zero-bias anomaly
  in differential conductance (b),
  as well as the linear-response TMR (c).
  The parameters are the same as in Fig.~\ref{Fig1}.}
\end{figure}

Intrinsic spin-flip scattering in the dot modifies conductance in
the antiparallel configuration, and thus also the tunnel
magnetoresistance, as shown in Fig.~\ref{Fig1}(c). Since the
zero-bias maximum in conductance is suppressed in the fast spin
relaxation limit, the corresponding dip in TMR at small voltages
is also suppressed by the intrinsic relaxation processes. More
specifically, the dip in TMR broadens with increasing $r$ and
disappears in the limit of fast relaxation (see the curve for
$r=1$).

An interesting and new feature of TMR in the presence of spin-flip
scattering in the dot is the crossover from positive to negative
values when $r$ increases, as illustrated in Fig.~\ref{Fig1}(c).
Thus, the difference between conductances in the parallel and
antiparallel magnetic configurations persists even for fast spin
relaxation in the dot, contrary to the sequential tunneling
regime, where such a difference disappears \cite{rudzinski01}.
This seemingly counterintuitive behavior can be understood by
taking into account the following two facts: (i) absence of spin
accumulation in the dot for fast spin relaxation ($P_\uparrow
=P_\downarrow $), and (ii) difference in the fastest cotunneling
processes contributing to the current in the two magnetic
configurations. As the point (i) is rather obvious in view of the
results presented in Fig.~\ref{accumulation}, the point (ii)
requires additional clarification. The fastest double-barrier
cotunneling processes involve only the majority-spin electrons of
the two leads --  thus, in the parallel configuration the fastest
cotunneling processes are the non-spin-flip ones. They take place
either {\it via} the empty-dot virtual state (for one orientation
of the dot spin) or {\it via} the doubly occupied dot virtual
state (for the second orientation of the dot spin). The dominant
contribution to the current is then proportional to
$1/\varepsilon^2 + 1/(\varepsilon +U)^2$. On the other hand, in
the antiparallel magnetic configuration the fastest cotunneling
processes are the spin-flip ones, which can occur only for one
particular orientation of the dot spin. However, for this spin
orientation cotunneling can take place {\it via} both empty and
doubly occupied dot virtual states. The corresponding dominant
contribution to electric current is then proportional to
$[1/\varepsilon- 1/(\varepsilon +U)]^2=1/\varepsilon^2 +
1/(\varepsilon +U)^2 -2/[\varepsilon (\varepsilon +U)]$. It is
thus clear that the difference in currents flowing through the
system in the antiparallel and parallel configurations is equal to
$-2/[\varepsilon (\varepsilon +U)]$, which results from the
interference term. Since $\varepsilon <0$ and $\varepsilon +U>0$,
this interference contribution is positive. As a result, the
current in the antiparallel configuration is larger than the
current in the parallel configuration.

An analysis similar to that done above for differential
conductance [see Eqs~(\ref{Eq:GP})-(\ref{Eq:GAPmin})] can be
performed for tunnel magnetoresistance. The minimum in TMR at zero
bias in the case of a symmetric Anderson model can be then
expressed as
\begin{equation}
  {\rm TMR_{min} } = \frac{2p^2 \left(4k_{\rm B}T\Gamma^2 -\varepsilon^2
  h/\tau_{\rm sf} \right)}{12(1-p^2)k_{\rm B}T\Gamma^2+(3+p^2)\varepsilon^2
  h/\tau_{\rm sf}},
\end{equation}
whereas for $|eV|\gg k_{\rm B}T$ and $r\ll 1$ one finds
\begin{equation}
  {\rm TMR_{max} } = \frac{2p^2 \left[ 2(3-p^2)k_{\rm B}T\Gamma^2
  -\varepsilon^2 h/\tau_{\rm sf} \right]}
  {2(1-p^2)(3-p^2)k_{\rm B}T\Gamma^2+(3+p^2)\varepsilon^2
  h/\tau_{\rm sf}}.
\end{equation}
The latter formula approximates the value of TMR corresponding to
the bias voltage at which the differential conductance has a local
minimum. In the slow spin relaxation limit one finds ${\rm
TMR_{min} }=2p^2/(3-3p^2)$, and ${\rm TMR_{max} }=2p^2/(1-p^2)$.
However, in the limit of fast spin relaxation TMR becomes negative
and is given by
\begin{equation}
{\rm TMR_{min} }={\rm TMR_{max} }=-2p^2/(3+p^2),
\end{equation}
which is consistent with numerical results displayed in
Fig.~\ref{Fig1}(c).

The explicit variation of the minimum in TMR at zero bias with
spin relaxation time is shown in Fig.~\ref{Fig3}(c). The
transition between slow and fast spin relaxation in the dot is
clearly evident. This transition is associated with a change of
the TMR sign from positive to negative.

\subsection{The case of spin-split dot level}

The discussion up to now was limited to the case of degenerate dot
level. The situation changes when
$\varepsilon_\uparrow\ne\varepsilon_\downarrow$, e.g., due to an
external magnetic field. The magnetic field splits the dot level,
consequently the occupation probabilities for the spin-up and
spin-down electrons are not equal at equilibrium ($V=0$). The
level splitting is described by the parameter
$\Delta=\varepsilon_\downarrow- \varepsilon_\uparrow$, where the
magnetic field is assumed to be along the magnetic moment of the
left electrode. In Fig.~\ref{Fig4} we show the bias voltage
dependence of the differential conductance in the parallel and
antiparallel configurations for different values of parameter $r$.
\begin{figure}[t]
  \includegraphics[width=0.7\columnwidth,height=9.5cm]{Fig4.eps}
  \caption{\label{Fig4} The differential conductance in the
  nonlinear response regime for different spin relaxation in the
  parallel (a) and antiparallel (b) configurations. The parameters
  are: $k_{\rm B}T=0.2\Gamma$, $\varepsilon_{\uparrow}=-16\Gamma$,
  $\varepsilon_{\downarrow}=-14\Gamma$, $U=30\Gamma$ and $p=0.5$.}
\end{figure}
In the limit of no intrinsic spin relaxation in the dot (solid
line in Fig.~\ref{Fig4}) and at low bias voltage, the dot is
occupied by a spin-up electron and the current flows mainly due to
non-spin-flip cotunneling. The spin-flip cotunneling processes are
suppressed for $\vert \Delta\vert \gtrsim \vert eV\vert, k_{\rm
B}T$, which results in the steps in differential conductance at
$\vert\Delta\vert \simeq \vert eV\vert$. The suppression of
spin-flip inelastic cotunneling was recently used as a tool to
determine the spectroscopic $g$-factor \cite{koganPRL04}. When
$\vert eV\vert$ becomes larger than $\vert\Delta\vert$, spin-flip
cotunneling is allowed, consequently the conductance increases.
However, there is a large asymmetry of differential conductance in
the antiparallel configuration with respect to the bias reversal.
To understand this asymmetry, it is crucial to realize that when
the splitting $\Delta =\varepsilon_\downarrow -
\varepsilon_\uparrow$ is larger than $k_{\rm B}T$, the
single-barrier spin-flip cotunneling processes can occur only when
the dot is occupied by a spin-down electron. This follows simply
from the energy conservation rule. (The situation may be changed
for negative $\Delta$.) Thus, the single-barrier processes can
assist the fastest double-barrier cotunneling processes, but only
for positive bias. This is because the fastest processes can occur
when the dot is occupied by a spin-down electron for negative bias
and by a spin-up electron for positive bias, leading to larger
conductance for positive than for negative bias voltage. This is
indeed the case in the numerically calculated characteristics
shown in Fig.~\ref{Fig4}(b). No such asymmetry occurs in the
parallel configuration [see Fig.~\ref{Fig4}(a)], as now the system
is fully symmetric with respect to bias reversal.

The situation changes when intrinsic spin-flip relaxation
processes occur in the dot. For the parameters assumed in
Fig.~\ref{Fig4}, the spin relaxation in the dot affects the
conductance only for $|eV|\gtrsim|\Delta|$, while for
$|eV|\lesssim|\Delta|$ the conductance is basically independent of
$r$ (see Fig.~\ref{Fig4}). This is because for
$|eV|\lesssim|\Delta|$ and $|\Delta|\gg k_{\rm B}T$, the dot is
predominantly occupied by a spin-up electron and the transitions
to the spin-down state due to relaxation processes are
energetically forbidden. As a consequence, the current flows
mainly due to non-spin-flip cotunneling, irrespective of spin
relaxation time. This scenario holds for both magnetic
configurations of the system.

When $|eV|\gtrsim|\Delta|$, the spin-flip cotunneling processes
can take place and the dot can be either in the spin-up or
spin-down state. In the parallel configuration,
Fig.~\ref{Fig4}(a), the conductance is slightly reduced by the
spin-flip relaxation processes. This can be understood by
realizing the fact that the fastest non-spin-flip cotunneling
processes in the parallel configuration are more probable when the
dot is occupied by a spin-down electron than by a spin-up one [due
to smaller energy denominator, see
Eq.~(\ref{Eq:cotunnelingrate})]. Since the spin-down state (as
that of larger energy) relaxes relatively fast to the spin-up
state (which has definitely smaller energy), this leads to a
reduction in the conductance. On the other hand, the differential
conductance in the antiparallel configuration is enhanced by the
relaxation processes for positive bias and diminished for negative
bias voltages. Consider first the situation for positive bias. As
already discussed above for $r=0$, an important role in that
transport regime is played by the single-barrier spin-flip
cotunneling processes, which open the system for the fast
double-barrier cotunneling by reversing spin of the dot from the
spin-down to the spin-up state. The relaxation processes play a
role similar to that of the single-barrier cotunneling, and lead
to a certain increase in the conductance. For negative bias
voltage, in turn, the fast double-barrier cotunneling processes
occur when the dot is occupied by a spin-down electron. The
probability of such events is decreased by spin relaxation,
leading to a reduced conductance. An interesting consequence of
the enhancement (reduction) of the differential conductance for
positive (negative) bias voltage is an increase of the asymmetry
with respect to the bias reversal -- see the curve for $r=1$ in
Fig.~\ref{Fig4}(b).

\section{Quantum dots asymmetrically coupled to the leads}

An interesting situation occurs when the quantum dot is coupled
asymmetrically to the left and right leads $(p_{\rm L}\neq p_{\rm
R})$. For this situation we first present the results in the case
of degenerate dot level and then proceed with the discussion of
the case when the degeneracy is lifted, e.g. by an external
magnetic field.

\subsection{The case of spin-degenerate dot level}

The differential conductance for a system with one electrode
nonmagnetic and the other one made of a ferromagnet with large
spin polarization (in the following referred to as strong
ferromagnet) is shown in Fig.~\ref{Fig5}. The parts (a) and (c)
correspond to the cases when the dot is described by an asymmetric
Anderson model ($\vert\varepsilon\vert\ne\varepsilon +U$). The
difference between (a) and (c) is due to different position of the
dot level $\varepsilon$, and consequently also $\varepsilon +U$,
with respect to the Fermi level at equilibrium. More precisely,
(a) and (c) are symmetric in the sense that
$\vert\varepsilon\vert$ in (a) is equal to $\varepsilon +U$ in
(c), and vice-versa, $\vert \varepsilon\vert$ in (c) is equal to
$\varepsilon +U$ in (a). Part (b), in turn, corresponds to the dot
described by a symmetric Anderson model, with $\vert
\varepsilon\vert$ equal to $\varepsilon +U$.

Consider first the situation in the absence of intrinsic spin
relaxation in the dot (solid curves in Fig.~\ref{Fig5}). There is
then a significant asymmetry of electric current with respect to
the bias reversal in the situations displayed in
Fig.~\ref{Fig5}(a) and (c), whereas no such an asymmetry occurs
for the symmetric Anderson model [part (b)]. Another feature of
the curves shown in Fig.~\ref{Fig5} is the presence of zero-bias
anomaly in the case described by the symmetric Anderson model
[part (b)]. This anomaly is similar to that shown in
Fig.~\ref{Fig1}(a) for antiparallel configuration. The anomaly
still exists, although it is less pronounced when the dot is
described by the asymmetric Anderson model, as clearly visible in
Fig.~\ref{Fig5}(a) and (c).

\begin{figure}[t]
  \includegraphics[width=0.7\columnwidth]{Fig5.eps}
  \caption{\label{Fig5} The differential conductance in the
  nonlinear response regime for the asymmetric (a,c) and symmetric
  (b) Anderson model for different spin relaxation. The parameters
  are: $k_{\rm B}T=0.2\Gamma$, $U=60\Gamma$, $p_{\rm L}=0.95$ and
  $p_{\rm R}=0$.}
\end{figure}

Let us discuss now the physical mechanism of the asymmetry with
respect to the bias reversal displayed in Fig.~\ref{Fig5}(a) and
(c). When $\vert eV\vert \gg k_{\rm B}T$, one can neglect the
influence of single-barrier cotunneling \cite{weymannPRB05BR}. The
cotunneling processes which transfer charge from one lead to
another take place {\it via} two possible virtual states -- empty
dot (an electron residing in the dot tunnels to one of the leads
and another electron from the second lead enters the dot) and
doubly occupied dot (an electron of spin opposite to that in the
dot enters the dot and then one of the two electrons leaves the
dot). Consider first the situation shown in Fig.~\ref{Fig5}(a) for
positive bias ($eV>0$, electrons flow from right to left, i.e.,
from normal metal to strong ferromagnet), and assume for clarity
of discussion that the strong ferromagnet is a half-metallic one
with full spin polarization (only spin-up electrons can then
tunnel to the left lead). When a spin-down electron enters the
dot, it has no possibility to leave the dot for a long time. The
allowed cotunneling processes occur then  {\it via } doubly
occupied dot  virtual states. In the absence of intrinsic spin
relaxation in the dot, the only processes which can reverse the
dot spin are the single-barrier cotunneling ones, which however
play a minor role when $k_{\rm B}T\ll \vert eV\vert$. Thus, the
current flows due to non-spin-flip cotunneling {\it via}
doubly-occupied dot virtual states, whereas cotunneling through
empty-dot virtual states is suppressed. The situation is changed
for negative bias (electrons flow from strong ferromagnet to
normal metal). Now, the dot is mostly occupied by a spin-up
electron, which suppresses cotunneling {\it via} doubly-occupied
dot virtual state and the only contribution comes from cotunneling
{\it via} empty-dot virtual state. The ratio of cotunneling rates
through the empty dot and doubly occupied dot virtual states is
approximately equal to $\xi=[\varepsilon/ (\varepsilon+U) ]^{-2}$.
In the situation presented in Fig.~\ref{Fig5}(a) one finds $\xi\gg
1$. Accordingly, the conductance for negative bias is much larger
than for positive bias voltage. In turn, in the case displayed in
Fig.~\ref{Fig5}(c) the ratio of the respective cotunneling rates
is exactly equal to the inverse of this ratio corresponding to the
case shown in Fig.~\ref{Fig5}(a). Thus, now we have $\xi\ll 1$,
and the conductance is smaller for negative bias than for
positive. In turn, in the case presented in Fig.~\ref{Fig5}(b) the
ratio  $\xi$ is equal to 1, consequently both cotunneling rates
are equal and the conductance is symmetric with respect to the
bias reversal.

When $\vert eV \vert$ becomes of the order of $k_{\rm B}T$ or
smaller, the rate of single-barrier cotunneling is of the order of
the rate of double-barrier cotunneling. Therefore, the
single-barrier processes can play an important role in transport.
More precisely, single-barrier cotunneling processes can reverse
spin of an electron in the dot and thus can open the system for
the fast cotunneling processes. This behavior can be observed in
Fig.~\ref{Fig5}(a) and (c). In the symmetric case shown in
Fig.~\ref{Fig5}(b), the single-barrier processes lead to the
zero-bias anomaly similar to that shown in Fig.~\ref{Fig1}(a) for
antiparallel configuration in a system with two ferromagnetic
electrodes coupled symmetrically to the dot. The mechanism of the
anomaly is the same, i.e., the single-barrier cotunneling, which
occurs for $k_{\rm B}T \gg \vert eV\vert$, opens the system for
the fast cotunneling processes. This leads to an increase in
conductance in the small bias range. The zero-bias anomaly exists
also in asymmetric cases illustrated in Fig.~\ref{Fig5}(a) and
(c). However, the maximum in conductance is slightly shifted away
from $V=0$ and is much less pronounced.

Intrinsic spin-flip processes in the dot have similar influence on
electronic transport as in the symmetric case studied in the
previous section. As before, relaxation processes remove the
asymmetry with respect to the bias reversal and suppress the
zero-bias anomaly. Thus, the diode-like behavior can appear only
in the limit of slow spin relaxation, and is suppressed in the
limit of fast spin relaxation, as shown in Fig.~\ref{Fig5} by the
curves corresponding to $r=1$.

Some analytical expressions for the conductance can be obtained in
the limit $\vert eV\vert \gg k_{\rm B}T$ and when assuming $p_{\rm
L}=p$, $p_{\rm R}=0$. The approximate formulas for the
differential conductance then read
\begin{eqnarray}
  G &=& \frac{e^2}{h}\frac{\Gamma^2}{2} \left[
    \frac{1}{(\varepsilon+U)^2} + \frac{(1-p^2)U}
    {\varepsilon^2(\varepsilon+U)} \right.\nonumber\\
    &&\left.+ \frac{p^2\varepsilon^2 U (\varepsilon+U)^3}
    {\left[\varepsilon^2 (\varepsilon+U)^2-
    eVU^2\Gamma^2 \tau_{\rm sf}/(4h)\right]^2}
    \right]
\end{eqnarray}
for positive bias, and
\begin{eqnarray}
  G &=& \frac{e^2}{h}\frac{\Gamma^2}{2} \left[
    \frac{1}{\varepsilon^2} + \frac{(1-p^2)U}
    {\vert\varepsilon\vert(\varepsilon+U)^2} \right.\nonumber\\
    &&\left.+\frac{p^2\vert\varepsilon\vert^3 U (\varepsilon+U)^2}
    {\left[\varepsilon^2 (\varepsilon+U)^2+
    eVU^2\Gamma^2 \tau_{\rm sf}/(4h)\right]^2}
    \right]
\end{eqnarray}
for negative bias. In order to describe the diode operation it is
useful to define the ratio  $\alpha$ of the conductances for
positive and negative bias voltages. In the limit of long spin
relaxation this ratio is given by
\begin{equation}
\alpha = \frac{\varepsilon^2+(1-p^2)(\varepsilon+U)U}
{(\varepsilon+U)^2+(1-p^2)\vert\varepsilon\vert U}.
\end{equation}
It is also worth noting that the operation of the diode can be
tuned by the gate voltage (which shifts energy of the dot level).

\begin{figure}[t]
  \includegraphics[width=0.7\columnwidth]{Fig6.eps}
  \caption{\label{Fig6} The differential conductance in the
  nonlinear response regime for different spin relaxation. The
  parameters are: $k_{\rm B}T=0.2\Gamma$, $\varepsilon_{\uparrow}=
  \varepsilon-\Delta/2$, $\varepsilon_{\downarrow}=
  \varepsilon+\Delta/2$, $\Delta=2\Gamma$, $U=60\Gamma$, $p_{\rm
  L}=0.95$ and $p_{\rm R}=0$.}
\end{figure}

\subsection{The case of spin-split dot level}

In Figure~\ref{Fig6} we illustrate the influence of spin splitting
of the dot level due to an applied magnetic field,
$\varepsilon_\uparrow\neq\varepsilon_\downarrow$. The bias voltage
dependence of the differential conductance is shown there for
different values of the parameter $r$, for symmetric (b) and
asymmetric (a,c) Anderson models. The parameters used in numerical
calculations are the same as in Fig.~\ref{Fig5}, except for the
dot level energy which was spin degenerate in Fig.~\ref{Fig5} and
now is spin split.

Let us first focus on Fig.~\ref{Fig6}(a), which corresponds to the
case of asymmetric Anderson model, $\varepsilon=-U/4$. Two new
features of the conductance in the limit of no intrinsic spin
relaxation appear in this figure. First, the conductance is now
suppressed above a certain finite positive value of the bias
voltage, and not for $eV>0$ as in the case shown in
Fig.~\ref{Fig5}(a). Strictly speaking, the conductance drops when
$eV$ is equal to the level splitting $\Delta$, $eV\approx \Delta$.
The shift of the main slope in the conductance from $eV=0$ to
$eV\approx \Delta$ is due to the fact that the dot is blocked for
cotunneling {\it via} the empty state by a spin-down electron only
when $eV$ exceeds the level splitting. This results from the
energy conservation. Thus, in the case shown in Fig.~\ref{Fig5}(a)
the main drop of the conductance was at $eV=0$, whereas in
Fig.~\ref{Fig6}(a) it is at $eV\approx\Delta$. When a spin-down
electron appears in the dot, then, for $eV<\Delta$, it can always
tunnel back to the source electrode and open the dot for fast
cotunneling through the empty state.

The second feature of the differential conductance in the $r=0$
case is the peak at $eV\approx\Delta$, and a shallow plateau for
$\vert eV\vert \lesssim\Delta$. The origin of the peak is similar
to the origin of the zero-bias anomaly in the case of
spin-degenerate dot level. On the other hand, the plateau in the
small bias range is due to suppression of the spin-flip
cotunneling for $|eV|\lesssim\Delta$, similarly as in
Fig.~\ref{Fig4}. However, the plateau is now very weak and
shallow. This is a consequence of the minor role of the spin-flip
cotunneling, which results from the strong spin polarization of
ferromagnetic electrode.

Qualitatively similar behavior may be also observed for
$\varepsilon=-3U/4$. This situation is shown in Fig.~\ref{Fig6}(c)
and is analogous to the one illustrated in Fig.~\ref{Fig5}(c). In
the case of $\varepsilon=-U/2$ shown in Fig.~\ref{Fig6}(b), the
influence of magnetic field is qualitatively similar to that found
in the case of a quantum dot coupled to two ferromagnetic leads in
the antiparallel configuration, see Fig.~\ref{Fig4}.

Transport characteristics are modified by the spin relaxation in
the dot. As before, the changes occur for $|eV| \gtrsim |\Delta|$.
For positive bias voltage, the spin relaxation processes modify
the conductance mainly for $\varepsilon=-U/4$ and
$\varepsilon=-U/2$ [Fig.~\ref{Fig6}(a,b)], while for
$\varepsilon=-3U/4$ [Fig.~\ref{Fig6}(c)] the changes are
significantly smaller. For negative bias, on the other hand, the
conductance is slightly suppressed by the spin relaxation. This is
because for negative bias the dot is mainly occupied by a spin-up
electron, and spin relaxation from the spin-up to spin-down dot
states is suppressed due to $\Delta \gg k_{\rm B}T$. Contrarily,
for positive bias, $|eV| \gtrsim |\Delta|$, and for $\tau_{\rm
sf}\rightarrow\infty$, the dot is mostly occupied by a spin-down
electron. Spin relaxation processes in the dot lead then to a
certain increase in the occupation probability of the spin-up dot
level ($P_\uparrow\approx 1$ in the long spin relaxation time
limit). This in turn may give rise to an increase in the
differential conductance.

\section{Concluding remarks}

We have considered numerically and analytically the influence of
intrinsic spin relaxation in the dot on the differential
conductance and the TMR effect in the cotunneling regime. It has
been  shown that the zero-bias anomaly in the antiparallel
configuration is enhanced in the weak spin-flip scattering regime
in the dot. The optimal conditions for a maximum enhancement have
also been derived. However, in the limit of fast spin relaxation
both the zero-bias anomaly and the dip in tunnel magnetoresistance
at zero bias become suppressed. Moreover, we have found the
inversion of sign of tunnel magnetoresistance in the presence of
fast intrinsic spin relaxation in the dot.

We have also demonstrated that the zero-bias anomaly exists in
systems with only one ferromagnetic electrode (the second one may
be nonmagnetic). Such devices display diode-like transport
characteristics. The diode-like behavior exists also when the
system is in an external magnetic field, but the operation range
is changed, i.e., the bias voltage at which the conductance drops
depends on the level splitting (magnetic field). Furthermore, we
have shown that this behavior may be enhanced by intrinsic spin
relaxation processes in the dot.

The work was supported by the Polish State Committee for
Scientific Research through the projects PBZ/KBN/044/P03/2001 and
2 P03B 116 25, and by EU through RTN 'Spintronics' (contract
HPRN-CT-2000-000302). We also acknowledge discussions with Jan
Martinek and J\"urgen K\"onig.

redpajama_set_name: RedPajamaArXiv


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Teachers, administrators, community members, and students help create successful school gardens in some tough places through the power of community.
At Madera Elementary in El Cerrito, California, "lunchtime" has new meaning. When the noon bell rings, it's time to eat — but it's also time to work, play, and dream in the school's one-acre garden. Students cuddle with chickens, play house under the avocado tree, discover slugs in the lettuce, and "give compost gifts" to hungry soil. Anything goes, as long as it's done with care and respect.
On a fall day that feels like mid-summer, Madera garden coordinator Molly Wahl presides over this lush patch of earth humming with happy activity. "We're like a secret garden tucked away," she says, "and then there's the synergy of adding children to this landscape." Third- to sixth-grade classes hop through the gate, check out the "to do" list of options scrawled on the shed's whiteboard, and grab their gardening tools of choice. Some mix compost into raised beds, now emptied of summer crops; others hunker down to weed, water, and sweep. Many go on "chicken patrol" while peppering a patient Wahl with questions about their four feathered friends.
It's hard to imagine that seven years ago, "There was nothing here but rubble from the school expansion," Wahl recalls. A terraced hillside bursts with sunflowers, lavender, artichokes, plums, clementines, corn, gourds, and more. Natives, elderberries, and alpine strawberries flourish on a neighboring hillside, along with kitchen herbs, lemon trees, and a "wildlife habitat" buzzing with birds and bees. Quail, hummingbirds, newts, and deer are among many faithful visitors. It won't be long before kale, chard, and other fall-winter edibles take root in 12 raised beds and 20 wine half-barrels; once harvested, they will be sold in the school's popular Farmers Market, run by third-graders on Fridays from January to June.
Over the past five years, veteran teacher Wahl has transformed the Madera garden into a fertile outdoor classroom fully integrated into daily life. But it takes a village. "I have 100-percent buy-in here," she says. "I'm working with every class from kindergarten to sixth grade. Our principal is totally on board, and the teachers are really seeing the benefits. Everything taught in the classroom can be taught here." In addition to lunchtime, the garden hosts regular instructional time throughout the academic year, in after-school enrichment classes, and during a summer schedule made possible by staff, family, and community volunteers.
Wahl works constantly to keep things interesting, offering yoga in the garden, a mobile cooking cart, and a "Garden Girls" group for fourth- to sixth-graders who "need a little work on resilience, self-esteem, and communication." In creating curriculum for Garden Girls as well as all other classes, Wahl turned to the Center for Ecoliteracy's latest book, Ecoliterate: How Educators Are Cultivating Emotional, Social, and Ecological Intelligence. "I've tied the five Ecoliterate practices into everything we're doing this year," she says. The kindergarten unit, "Roots and Shoots: Using Our Senses to Study Plants," for example, is designed to help students develop empathy for all forms of life and make the invisible visible. Another unit addressing all five practices turns sixth-graders into apprentice landscapers. "They restore and plant natives and create habitats for bees and butterflies," Wahl explains. "They produce scaled site plans and present them to a panel of judges. The winning plan gets a budget, and then the students make it happen. It's a very real, practical learning experience. That's the direction STEM curriculum wants us to go."
Wahl stresses that gardens are the ideal place for children to develop emotional and social intelligence. "I say that day in and day out. Students will get into heated arguments at recess, but then they'll come to me and ask if they can go into the garden and talk. Parents will actually bring in kids who have ongoing problems with each other and have them work it out in the garden. You get rid of artifice and fear and speak from the heart here. To me, gardens are much more holistic in what they offer."
Thanks to a recent Center for Ecoliteracy grant, Wahl is one step closer to fulfilling her dream of two separate spaces — a "learning garden" dedicated to cross-curricular, hands-on activities and a "market garden" focused on crops for the Farmers Market. "We were able to hire a landscaper to design a really beautiful site plan for the market garden," she says. "It's something that we can take to the district to show our vision."
The grant is one of many given by the Center for Ecoliteracy to gardens throughout West Contra Costa Unified School District (WCCUSD), which serves more than 30,000 students pre-K to 12th grade. Eighty-six percent are students of color, with one in three receiving services for English-language learners; more than two-thirds of all students are eligible for free or reduced-price lunches. Gangs, drugs, and violence rock cities like Richmond, where poverty rates are double the national average. "Many neighborhoods in WCCUSD are urban food deserts," says Carolie Sly, the Center for Ecoliteracy's education program director. "And yet the school garden community and culture is thriving. Richmond in particular is a Transition Town, and the mayor is really behind improving community resilience, so we felt they were ripe for change."
This growing movement is nurtured by a grassroots collaborative of teachers, administrators, community members, and students. Recently renamed West County DIGS (Developing Instructional Gardens in the Schools), they came together in 2007 with one mission: to make their school garden programs more successful and sustainable through the power of community. Today, the district boasts over 30 working gardens — and counting. DIGS conducted a district-wide survey for the first time last year and identified major needs (e.g. paid staffing) and benefits (e.g. increased curiosity); the results enabled them to successfully lobby for the inclusion of school gardens in WCCUSD's five-year strategic plan.
In addition to funding release time for DIGS members to develop lessons, the Center for Ecoliteracy grants are helping their garden programs realize their potentials. Mira Vista Elementary in Richmond purchased apple trees to plant a small orchard; a donated apple press will further engage students. Making Waves Academy and El Cerrito High are revitalizing their gardens with needed improvements and supplies. Hercules High School is expanding its garden so that a biology teacher can use it to teach about life systems and the chef can incorporate fresh food in school meals. And Richmond High's Urban Agriculture Institute is upgrading its greenhouse and starting an aquaponics system.
The Institute at Richmond High is one of several bright spots in Richmond run by DIGS partner Urban Tilth. The local agriculture and food justice nonprofit also oversees the Verde Elementary School Partnership Garden, which serves as an outdoor laboratory for classroom learning and an affordable, healthy food source for the underserved community, many of whom are immigrants who personally tend their crops. Washington Elementary's Edible Education Garden Program includes cooking and nutrition education, teacher training, and resiliency small groups.
"DIGS isn't daunted by the challenges of working with kids from unstable households and dangerous neighborhoods," notes Sly. "They're just completely dedicated to bringing fresh food and healthy relationships to these schools." As part of the Center for Ecoliteracy's ongoing support of the collaborative, Sly meets with members every six weeks to facilitate resource sharing, community outreach, and making the connection to academic standards. "We see our role as helping them build their own capacity. They started this a long time ago without us. We're there to help them keep the momentum going." Adds Wahl, "The Center for Ecoliteracy is providing wisdom. All of us have our feet on the ground, but they're coming in from another place, and that helps us see from a new perspective."
The ambitions of DIGS are evolving. "We have these brilliant individuals doing really cool things," Wahl notes. "They're all over, but they're secrets! We're trying to reveal what's happening and create linkages. It's just not sustainable to do solo work. We succeed through sharing and community, not reinventing the wheel." While increased visibility and promotion are priorities, building strength from within is paramount. "Many of our goals have relied on the district," she says. "We want to have the table set so they can join us, but we have to use our own expertise in the here and now to bring us all up together. One of the things that I think is really special about DIGS is that it is so grassroots — everyday folks coming together in their off-work hours to do something they believe in. These gardens are happening around the edges and in the margins. They are happening in spite of and against all odds. Nature sets the bar high, and everyone rises to it."
Download our 51-page guide for creating school gardens as outdoor classrooms.
A downloadable booklet with advice for designing, creating, and maintaining five types of educational gardens.
A video showing how third-graders explore interactions among diverse plants and animals in their school garden.


Hiking to highest peak of Volcano Semeru could be done via several routes, general climbing routes is Route Ranu Pani ,a most popular climbing route for Mahameru, summit of volcano Semeru.The route is also most intensively in used by both domestic or international trekkers/hikers/climbers,used to be functioned as climbing basecamp by most climbers.This route is also most recommended ones.While the most popular touristic volcano of East Java : Bromo possessing it's basecamp at Cemoro Lawang, a closest caldera rim down to volcano Bromo crossing the sandsea of Tengger Caldera. Cemoro Lawang is touristic area, most accommodation from hotel to basic guesthouse are available here as well transport, mostly Jeep.View Volcano Semeru in the distance is well visible from view point Pananjakan area, a mountain that's still in one complex of Bromo Tengger Semeru.
Closest access to Climbing Basecamp Ranu Pani are Tumpang and Cemoro Lawang.Tumpang it self is accessible via from Malang or Surabaya, while Cemoro Lawang is also accessible either from Malang or Surabaya, but most international travelers accessed them from Surabya,East Java.
While Bromo area is accessible 3-4 hours drive from Surabaya, also accessible from Malang, even from Ranu Pani,the last village on the foot of Volcano Semeru.To access Bromo area from this last village, rent a car jeep is needed to drive cross "Sand Sea of Tengger" head for Bromo area locally popular as Cemoro Lawang. The hike to Bromo crater's rim from Cemoro Lawang takes approx two hours or one and half hours on horseback.While reach volcano Pananjakan from Cemoro Lawan can be done by car jeep in early morning to catch best panoramic views of Bromo-Tengger-Semeru from top of volcano Pananjakan. Common local trip is commenced at Cemoro Lawang head for Pananjakan, then down to sandsea for visiting Bromo, and return to Cemoro Lawang.
Volcano Semeru and Bromo are under management of national park format. Report,registration,permit and entrance ticket are required to do hiking climbing here.When alert level over normal active, and or extreme weather condition, hiking activity is normally only allowed till certain distance, even may not allowed due to other reason such to recover ecosystem, accident and there's rescue operation at the time.More detail about this, contact relevant resource.
Ranu pani is the trailhead of hiking, also name of lake located on foot of volcano Semeru and name of village usually used as trekking / hiking base both domestic or international climbers trekkers.This base accessible approx two hours by car Jeep from Tumpang, while Tumpang itself is accessible 30 minutes by bus from Malang with distance 18 km.En route Tumpang-Ranupane you experience views of caldera environment in the distance...also "Sand Sea" which is locally called Segara Wedi.At Ranu Pane, available: Information center, trekking basecamp, as well as guesthouse.
Ascent to summit of volcano Semeru is commenced from trekking basecamp at Ranu Pani head for Watu Rejeng distance 5 km pass through relatively flat trekking path.Then continue heading for Lake Ranu Kumbolo distance 4,5 km.At Ranu Kumbolo, there was already available camp site plus shelter which are normally used by domestic trekkers / hikers for overnight.
Next...to reach the summit of volcano Semeru, then proceed the trek heads for Kali Mati distance 4,9 km pass through steeper path locally called "Tanjangan Cinta. Kali Mati is name of dry river or river without water, while "Tanjangan Cinta" is name of trail / route part covers 200 m in length. This trail part is steeper and hikers normally strive to tackle this trail part without taking any break.Tanjangan mean steep forward trail, while cinta mean love.Upon finishing "Tanjankan Cinta", then enter to savana zone locally called Oro-Oro Ombo.Next...forest zone locally called Cemoro Kandang.Savana zone is ideal point for taking break for your refreshment since it relatively flat, and more important...you can take in views of Mahameru, peak of volcano Semeru from this point.
From Kalimati you need only to hike 1 km heading for Arcopodo.Arcopodo itself come from local words: arco and podo, arco mean statue, while podo mean same.So...Arcpodo mean the same statue. According to local resource, In the past time there were found two twin statues on this site, and there fore this site called as Arcpodo.To reach peak of volcano Semeru from Arcopodo, it's need to continue hiking head for Cemoro Tunggal.Cemoro Tunggal is a border between vegetation forest and steep sandy route part.Cemoro mean Cemara, a kind of tree, while tunggal mean single. From this point, it's need only approx two hour hiking to reach summit of volcano Semeru through sandy steeper route part, the crux ones.
Distance from Arcopodo head for summit of Semeru is about 1,5 km. To do summit push from Arcopodo or Kalimati, it is better to be done in early morning to get more possible better weather, and witness the volcanic explosion of Crater Jonggring Seloka every 15 - 30 minutes, more important...you get safer from risk of positioned gas of crater Jonggring Seloka.There is no need to stay long on summit zone, just few minutes then descent in the morning as photo capts or sight seeing already done, before fogy / cloudy.
Rest day prior to hike commencement could be done at closest district. Guest house / homestay available at Tumpang, also available at closest village Ranu Pani. Local guides and porters for hiking Semeru are also available at Ranu Pani.Cemoro Lawang is more touristic area, located on caldera rim of Tengger, overlooking sea sand below and surrounding volcanoes such Bromo. Hotel, guest house,local guide,Jeep and restaurant are widely available here.
Visit Bromo surrounding can be done whole years, but best time normally on April - November when you have a better chance of catching a blood red sunrise over volcanoes surrounding. However...this area is overrun by conventional mass tourists three times a year, normally on February when an annual festival ceremony takes place, over Christmas, and during July - August.If you don't like crowds, so...plan your visit for another time. Alert level of Bromo normally effects safety distance.
Volcano Semeru attracts many hikers / trekkers both domestic or international trekkers particularly International lovers volcano, high hiking season normally on July-August,too crowded on peak season 15-18 august by domestic hikers wishing to celebrates Indonesia Independent day on Mahameru, the summit of volcano Semeru.Visit volcano Semeru for hiking up it's summit could be done on dry season, normally June-Sept. Remember...weather could change from it's normal pattern anytime. Other important aspect should be paid attention before visiting this volcano is the Early Alert Level.Check out allowed safety distance for your safety before you go.While on rainy season...SCONDARY VOLCANIC HAZARD in form of Lava Flood normally could happen due to high intensity of rain, and objective danger normally appear in form of bad weather.
Deadline of staying on Mahameru peak zone is generally till 10:00 am (check out to officer for more updated condition). Descent in the morning before that deadline will be safer since by that time wind began to blow to north side. So...descending before wind blows to the north and sweeps gas head for trekking / hiking trail is very important aspect of trekking at Semeru for safer. Gathering updated relevant info of last condition of volcano alert,seismic trend and weather is important prio to departure.
In case of emergency at climbing route that could not be handled by self rescue, contact closest relevant authority office such National Park Bromo Tengger Semeru.Relevant team Sar is normally standby at basecamp.Closest medical center locally called "Puskesmas" is available at Tumpang. Health-check up possible to be done at medical center.Normal available transport and standard one is Jeep specially for accessing Tumpang - Ranupane.
Photo Contributors By: Olenk Ambo Upe,Peo & Indah "samagram"


I don't know about you guys, but I'm pretty fond of the Earth and wishing her a Happy Earth Day seems even more poignant this year. With the rocky politics, and the complete disregard for the environment coming out of Washington, this years Earth Day is even more important.
I have always loved camping, and hiking, and just getting out in nature. But living in the RV, and staying mostly on public land has brought me a new closeness, and appreciation for the natural world. We need nature! Everyone needs the opportunity to get away from the soul sucking cities and breath fresh air, and listen to absolutely nothing.
John Muir wrote – Keep close to Nature's heart… and break clear away, once in awhile, and climb a mountain or spend a week in the woods. Wash your spirit clean.
And Ralph Waldo Emerson wrote as part of a poem, "The Earth laughs in Flowers." I completely agree with this. You can't look at a hillside covered with colors, and not see the joy.
The earth proves to us everyday how resilient, yet fragile she is.
My biggest wish for the Earth, and for all of us, is that people will treat her with the respect she deserves, so that future generations can enjoy all the beauty that is out there.
I feel honored that my birthday is tomorrow, followed by the day we celebrate our beautiful home. Spring, new beginnings, my beginnings and the hope that we can bring awareness is invigorating. But frustration always manages to play a role in the ongoing effort to find ways to be more responsible. You are so right; such a disregard coming from the top is infuriating. Lovely dedication today, Mary!
We have to care for the planet as we only have one and it is in need of some TLC.
Hello, great post for Earth Day. I agree whole-heartly about taking care of our Earth. Our government now is all about greed. So sad.
Your photos are all beautiful, I love the field of flowers. Great quotes too! Happy weekend to you!
Your photos are beautiful Mary.
Wonderful quotes and yes, respect is a must, as it should be for all life.
I love that you honor/celebrate the Earth EVERY DAY, not just on Earth Day!
Your photos show so eloquently why we need to take care of Earth. They are a lovely tribute to the day.
We share your wish. Your photos illustrate all that we need to preserve. I worry every day now about our earth's future not being respected. The outdoors, and the beautiful earth, are what feeds my soul. (I honestly can't comprehend how people live in cities).
Happy Earth Day, Mary. Beautiful thoughts and photos.
All gorgeous photos, but that last one really strikes me. It's incredible.
Beautifully put, both in words and in pictures.
Although I know nature shows her face everywhere, living in the less-protected environment of the boat helps me notice more. I never miss a sunrise or sunset. I notice the phases of the moon. And I'm always on the look out for nearby animals.
There's no reason I couldn't do the same thing living in a house. But for some reason, I just didn't.
There's something to be said for being close to nature and having it affect you more.
Amen sister. And not just the earth, for the creatures who share her with us as well.


On November 29, 2018, the SEC's Office of Investor Education and Advocacy issued an investor alert warning investors, including individuals who may receive lump sum payouts from insurance companies and others as a result of damage from the California wildfires, about fraudulent investment scams.
Sales of stock in small publicly-traded companies as part of "pump-and-dump" scams (promising high returns for investments in companies that supposedly will reap huge profits from recovery and cleanup efforts).
Some scams, according to the SEC, are circulated through unsolicited e-mail or social media, as well as by telephone. Fraudsters also may target individuals receiving money from insurance companies or other sources. The SEC warns that individuals, including those receiving lump sum insurance payouts, should be extremely wary of potential investment scams.
The SEC advises investors that one of the best ways to avoid investment fraud is to ask questions. Investors should be suspect, if approached by somebody touting an investment opportunity. It is important for an investor to ask that individual whether he or she is licensed and whether the investment is registered with the SEC or with a state. Investors should confirm their answers with an objective source, such as the SEC's Office of Investor Education and Advocacy or a state securities regulator. Importantly, promises of high or guaranteed profits with little or no risk are classic signs of fraud.
Investors should carefully review their entire financial situation, before making any investment decision, especially if a recipient of a lump-sum payment. The SEC reminds investors that a payment may have to help finance rebuilding and recovery as well as last one and his/her family for a long time.
The SEC's publication, Ask Questions, discusses many of the other questions to ask anyone who wants you to make an investment.
Saving and Investing: a Roadmap to Your Financial Security through Saving and Investing. This publication is also available in Spanish.
Ask Questions: Questions You Should Ask about Your Investments. This publication is also available in Spanish.


owner. "Will Drake can't die until after I marry him… and take every penny," she told her spunky side piece (who's lucky he's so slammin', because that's pretty much all he has going for him right now).
Of course, I can think of two people we probably shouldn't expect to see on the guest list: Donovan and his new bestie/kidnapper Ramona Royale, an actress-turned-vampire-turned-huntress who also happens to be a fellow ex-lover of the Countess. But, honestly, who isn't at this point?
' grand tradition of forcing Kathy Bates into miserable mother-son relationships, Wednesday's episode served us Iris and Donovan's twisted backstory in a neat little package. He apparently holds a pretty nasty grudge against her for all sorts of things, including kicking his father out of the house and getting him into weird eating habits. ("I had so much fiber in my diet that I s–t my pants at school!") When Iris tried to convince him to move in with her, he simply responded, "Kill yourself," which she — unfortunately — took a bit too closely to heart.
Okay this season is so good so far almost as good as Asylum.. Gaga is slaying so hard!!!
Been a pretty good season so far. I really like Matt Bomer's character and would like to know a little more about Evan Peters character. Hope it keeps up this pace.


text:
Zhangjiajie-Jishou-Huaihua High-speed Railway Opens Today
Mao Weiming, deputy secretary of the CPC Hunan Provincial Committee and Hunan governor, announces the launch of the railway at Jishou East Railway Station on December 6, 2021. (Photo/Liu Shangwen)
The Zhangjiajie-Jishou-Huaihua (Zhangjihuai) High-speed Railway opened to traffic at about 9 o'clock on December 6, 2021. Hence, the travel time between Zhangjiajie and Changsha is shortened to 2.5 hours.
Mao Weiming, deputy secretary of the CPC Hunan Provincial Committee and Hunan governor, attended the opening ceremony and announced the launch of the railway at Jishou East Railway Station.
The opening ceremony. (Photo/Liu Shangwen)
Li Dianxun, member of the Standing Committee of the CPC Hunan Provincial Committee and executive vice governor, attended and addressed the ceremony. Provincial leaders Ye Hongzhuan and Zhang Jian were present.
Deng Qunce, secretary general of the Hunan Provincial People's Government, presided over the ceremony.
Governor Mao learns about the construction and operation of Zhangjihuai High-speed Railway at Jishou East Railway Station before the opening ceremony. (Photo/Liu Shangwen)
Construction of Zhangjihuai High-speed Railway began in December 2016. It is a regional link in China's "eight vertical and eight horizontal" high-speed rail network. It starts from western Hunan, linking with Qianjiang-Zhangjiajie High-speed Railway in the north and Shanghai-Kunming High-speed and Huaihua-Shaoyang-Hengyang railways in the south.
Zhangjihuai High-speed Railway was funded by Hunan government and the China State Railway Group Co., Ltd. With a total investment of 37.65 billion yuan, the 245-kilometer line is designed for trains running at up to 350 kilometers per hour. There are seven passenger train stations along the line –Zhangjiajie West; Furong Town; Guzhang West; Jishou East; Fenghuang Ancient Town; Mayang West; and, Huaihua South stations. Sixteen pairs of trains will be operated on the line, with a speed of 300 km per hour in the initial stage.
As a part of Hunan's ten major infrastructure projects, Zhangjihuai High-speed Railway will facilitate trips for the residents along the line, and promote rural revitalization. It is of great significance for Hunan's participation in the national Belt and Road Initiative, developing the Yangtze River Economic Belt Development, and accelerating construction of a new modern socialist Hunan.
The railway connects several well-known scenic areas, such as Wulingyuan, Tianmen Mountain, Furong Town, Aizhai Grand Bridge, and Fenghuang Ancient Town, and is thus reputed as the "most beautiful high-speed railway in western Hunan". It will bring more travelers to western Hunan, and inject new vitality into the tourism of western Hunan and even the whole province.
Translator: Pang Yuehui

redpajama_set_name: RedPajamaCommonCrawl


text:
A Louis Delluc-díj (franciául: Prix Louis-Delluc) egy francia filmművészeti elismerés, amelyet neves filmkritikusokból és filmes szakemberekből álló zsűri ítél oda minden év végén a legjobb francia filmnek.

A díjat 1937-ben alapította Maurice Bessy író, filmtörténész és Marcel Idzkowski kritikus, színházi szakember a fiatalon elhunyt Louis Delluc (1890–1924) avantgárd filmrendező, forgatókönyvíró és filmkritikus, a francia filmklub hálózat alapítója emlékére. A neves irodalmi elismerés analógiájára a Louis Delluc-díjat gyakran nevezik "a filmművészet Goncourt-díjának".

1999 óta a legjobb első filmnek is odaítélnek egy külön Louis Delluc-díjat.

A díjazás
Minden év decemberének második csütörtökén, ünnepélyes keretek között díjazzák az abban az évben forgalomba került legjobb francia filmet. A mintegy húszfős zsűrit filmkritikusok és filmes szakemberek alkotják, munkájukat egy elnök irányítása alatt végzik. A zsűri végső döntése, annak nyilvánosságra hozatala, valamint az oklevél átadása a párizsi Fouquet's étteremben történik, a Champs-Élysées-n.

A díjátadás történetében előfordult, hogy a díjazott film mégsem került időben a mozikba; 1958-ban az Én, a néger című filmdrámát végül is csak 1960 márciusában mutatták be, az 1979-ben díjazott A király és a madár című rajzfilmet a következő év márciusában, az 1982-ben nyertes Dantont pedig csak egy hónappal később, januárban.

A díjazott alkotásnak egyszerre kell megfelelnie a magas művészi értékkel bíró szerzői filmekkel szemben támasztott követelményeknek, és a közönség elismerésének, függetlenül attól, hogy elsőfilmes alkotásról, vagy már egy, akár többszörösen elismert szerző filmjéről van szó. Ez utóbbi rendezők közül Alain Resnais három alkalommal vehette át a díjat (1966, 1993 és 1997), Louis Malle kétszer (1957 és 1987), akárcsak Michel Deville (1967, 1988), Claude Sautet (1969 és 1995), és Abdellatif Kechiche (2007, 2013).

Díjazott alkotások

Louis Delluc-díj

1930-as évek

1940-es évek

1950-es évek

1960-as évek

1970-es évek

1980-as évek

1990-es évek

2000-es évek

2010-es évek

2020-as évek

Louis Delluc-díj első filmnek

1990-es évek

2000-es évek

2010-es évek

2020-as évek

Jegyzetek
Megjegyzések

Hivatkozások

Fordítás

Források

Kapcsolódó szócikkek
 Francia filmművészet
 César-díj
 Arany Csillag

További információk
 Prix Louis-Delluc az Internet Movie Database-n

Francia filmes díjak

redpajama_set_name: RedPajamaWikipedia


text:
Rescued from the Depths of Despair
HOPE and STRENGTH for Jessica
2020 was a tough year for all of us.
But for Jessica of Michigan, it was almost a deal breaker.
"I've really struggled," she said. "My life was a mess. My son was estranged from me got to a point where I no longer wanted to be alive. I just wanted to die."
The music and programs YOU make possible through Family Life Radio quite possibly saved Jessica's life!
"I'm not really sure I would be here today if I had not turned on the radio and started listening," said Jessica.
One day, Jessica was driving in her car, feeling especially depressed. As her mind played out various suicidal scenarios, God spoke to her . . .
"A song came on the radio that really touched my heart," said Jessica. "Then another and another, as if they were playing just for me."
The lifesaving message Jessica needed in that moment came through Family Life Radio—thanks to YOU and others who give so generously!
"I knew it was God talking to me through those songs," she said. "He was telling me not to give up on hope, that He was there for me, and that I truly was stronger than I believed."
Hope across the airwaves
Family Life Radio's spirit-filled music lifted Jessica out of the depths of despair.
"Your songs really touch my soul," says Jessica. "They give me a newfound hope. Hope and strength to keep going, to keep praying and to just keep listening. I just want to say how amazing your station is. Thank you!"
On behalf of Jessica and so many others who experience healing and hope through the Christ-centered messages you make possible through Family Life Radio, thank you!
Christmas Blessings Abound – Thanks to YOU!
The Power of Loving Your Neighbor
A Note From Evan
Help People Experience Hope
Be inspired and equipped with these free resources!
Experience Hope Daily Devotional
Family Life Radio Updates
Become A Monthly Partner
rescued-from-the-depths-of-despair-family-life-radio


Saint Joseph's Oratory is defending its modern, "hipster" take on the nativity scene, saying that Christmas tableaus of Jesus's birth have always kept with the times.
"It's not a tradition scene, but it's in the tradition of representing nativity scenes in the [current] culture and era," Chantal Turbide, the Saint Joseph's Oratory museum's curator said.
The nativity scene which stirred up controversy was created in California by two American brothers, Casey and Corey Wright.
It shows the proud parents, Mary and Joseph, snapping a selfie with their new bundle of joy and three wise men looking on from atop their Segways.
Mary also appears to be wearing leather pants and is refueling after her labour with a big take-out cup of coffee.
"It's like a mirror on our society, we see ourselves," Turbide said, explaining why some people may find the image so uncomfortable.
The tongue-in-cheek Millennial Nativity set sells for about $60 US.
"Each set is hand-crafted and hand-painted by a real-life hipster," manufacturer Gorilla Goodies states on its website.
The museum bought the contemporary nativity and has added it to its collection of more than 1,000 sets.
For the ongoing exhibition A World in a Crèche, the museum brought together 100 nativity scenes from 100 countries.
Turbide said nativities have throughout the centuries been updated and altered to show current styles and to place them geographically.
"In Africa we can see a nativity scene with a zebra instead of donkey," Turbide said.
The very North American, 21st Century nativity can be seen at the Oratory Museum, is located in the heart of the Basilica. Entry is $4 for adults and $2 for youth.


text:
Q: Measuring the energy of an alpha particle I would like to measure the energies of particles emitted from a variety of ionizing radiation sources (alpha and beta), and then convert these energies to velocities. However, I am not too sure about how I might go about measuring these energies. Would this even be feasible? If so, how could it be done? How are these energies measured by professionals?

A: I believe Germanium is commonly used for alpha particle spectroscopy. It is a semiconductor, measures the amount of electrons that result from the creation of electron-hole pairs as the alpha particle passes through the material. The electronics connected to the anode (+) plate measures the voltage change across the two plates sandwiching the sensitive area of the detector. The number of free electrons produced is proportional to the energy loss of the alpha particle, and (I think) that is also proportional to the energy of the alpha particle.

A: In Rutherford Backscattering Spectrometry (RBS), the detector of choice for MeV protons and alphas is a surface barrier detector. As @onelineproof mentions, some are made of germanium. For the last 30 years or so, silicon detectors have been much more common.  These are basically reverse-biased diodes with a very thick active area to collect charge generated by electronic stopping of the energetic ion. Protons and alphas lose almost all their energy through electronic stopping, so there is very little 'nuclear deficit', or energy lost to nuclear collisions.  Right now I've to a 2 millimeter-thick device sitting in front of a neutron source to accurately measure Si recoil energy distributions. As mentioned in my brief comment, Ortec is one supplier of such devices in a variety of areas and thicknesses.
So, an incident ion will (rapidly) generate a pulse of current coming out of the device.  This is sent to a pre-amplifier, and then to a spectroscopy amplifier, which outputs a signal with a voltage proportional to the collected current.  A multi-channel analyzer is then used to build up a spectrum of the number of particles detected with a given energy. Again, these instruments are quite common in nuclear physics labs, from Ortec, Canberra, ..., often found sitting in NIM bins. Ask around.
Now, if you really want to go old school - the original papers from Geiger, Marsden, and Rutherford (and others) differentiated alphas from different materials through their path length in air. A beam of natural alphas, collimated by apertures, was sent through air, and the number of flashes on a zinc selenide phosphor screen was plotted vs distance from the collimated source. Decay lengths for ~5MeV alphas are on the order of a meter or two. For sources kept in vacuum they used thin mica windows; nowadays mylar would be a good replacement.
There was also mention of magnetic separation. While certainly possible, this has really only been used for medium energy ion scattering (MEIS) where the ~4keV resolution of a surface barrier detector just doesn't cut it. However, you need a magnet and a good position sensitive detector if you want to accurately measure energies.  If you just want to separate a few different particle energies you can do just fine.

redpajama_set_name: RedPajamaStackExchange


text:
THQ halving core game slate
Publisher details quality-over-quantity approach, plans to produce just one or two titles for the hardcore market each year.
By Brendan Sinclair on November 13, 2008 at 11:37AM PST
THQ talked generally about placing its emphasis on quality instead of quantity after a wave of studio closures last week, but today at the BMO Capital Markets Interactive Entertainment Conference, the publisher talked specific numbers.
During his half-hour presentation, THQ CEO Brian Farrell told attendees that the company's new model called for "one or two" core gamer products each year. The publisher's previous development model called for three or four such games annually.
"When we focus--as we did with Saints Row 2 and Saints Row--we win," Farrell said.
Given the publisher's current pipeline of titles, it may be a year or two before the new model is fully implemented. The 2009 slate already has a handful of core gamer projects scheduled, including Red Faction: Guerilla, Warhammer 40,000: Dawn of War 2, Darksiders: Wrath of War, and the stand-alone PC expansion Company of Heroes: Tales of Valor.
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Is Chesapeake Energy Corporation About to Repeat its Biggest Mistake?
After years of focusing on liquids, Chesapeake Energy Corporation is looking to drill for more natural gas.
The Haynesville Shale was once one of the hottest new natural gas plays. Because of that, companies like Chesapeake Energy Corporation (NYSE:CHK) poured billions of dollars into the play, causing gas production to surge. The problem was that once the bubble burst on gas prices, so did the enthusiasm for the Haynesville Shale.
Things got so bad for Chesapeake Energy that the Haynesville Shale was one of the areas where it sold acreage in order to bridge its funding gap. Last year it unloaded 5,600 net acres in the Haynesville to EXCO Resources Inc (NYSE:XCO) for $320 million. The deal included interests in 170 wells that EXCO Resources already operated, as well as some drilling sections that Chesapeake Energy operated. While the deal made sense for both companies at the time, Chesapeake Energy was still viewed as a forced seller, suggesting that it didn't get as good a price as it could if it waited until natural gas recovered.
Now that we are seeing a recovery in natural gas prices, we're seeing a bit of Chesapeake Energy's enthusiasm for the Haynesville Shale return. Chesapeake Energy, which discovered the Haynesville Shale in 2008, is returning its attention to growing production from the play. The company noted earlier this month that it was planning to spend 10% of its capital budget to fund seven to nine rigs in the play. That's a 25% increase from last year. It's a plan that had analysts scratching their heads and investors wondering if the company is about to repeat its past mistake.
On the conference call with analysts, one noted that the company gets better returns in the Marcellus Shale, which made him wonder why the company would now turn its attention to the Haynesville. Chesapeake Energy CEO Doug Lawler, however, reminded everyone that the "Haynesville asset is just simply a world class." However, he also noted that it has not yet been optimized the way the industry has optimized other plays. Because of this he sees the opportunity to see significant cost improvements and therefore higher returns. For Chesapeake Energy that makes the Haynesville Shale a much more competitive investment for the company than investors realize.
Chesapeake Energy believes it can get its drilling costs down to $7.9 million per well this year. That's 23% less than the $10.3 million cost per well it spent just two years ago. The use of multi-well pad drilling will play a big factor in bringing these costs.
With a little more work the company likely could get those well costs down even further. EXCO Resources, for example, achieved record low average drilling costs of $7.5 million per well in the third quarter. Lower well costs, when combined with wells that are producing higher volumes, can indeed produce solid returns. For example, a natural gas price of $5.00/mcf could yield a return over 100% with well costs of $7.9 million for Chesapeake Energy.
While natural gas prices are high now thanks to the rough winter experienced by much of the U.S., one bad winter isn't exactly a long-term trend. What is a developing long-term trend is natural gas exports, with Cheniere Energy (NYSEMKT:LNG) expected to begin exporting natural gas from its Sabine Pass LNG terminal late next year. That terminal just happens to be located in Louisiana, the same state as the Haynesville Shale.
There are a number of LNG export facilities planned along the Gulf Coast, including a second facility by Cheniere Energy in Corpus Christi. These facilities will need to be supplied with natural gas, with the Haynesville Shale being strategically located to benefit from exports. This suggests that Chesapeake Energy and even EXCO Resources could benefit from investing in the Haynesville to ramp up production ahead of these facilities being built.
The Chesapeake Energy of today is a much different company than the one that went all in on natural gas a few years ago. Today the company is investing within its cash flow and keeping its costs down. That's why I don't see the company's move to invest to grow its gas production from the Haynesville Shale being a repeat of a previous mistake.


This lively Trio in C Major was published by Ricordi in 1832. It is in two movements, and Allegro Moderato and a Rondo alla Polonaise. There are extra parts so that an oboe or a violin can play the clarinet part. What fun!
/wp-content/uploads/2013/07/mp3-trio-concertant-in-c-major-by-laurence-w-key.mp3Performed by an automatic synthesizer.


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