text:
\section{Introduction}
Colloidal systems have long been used as a model for investigating
fundamental questions in condensed matter physics. Two dimensional
(2D) systems are of particular interest, both for the rich physical phenomena they display
\cite{MurrayPRB1990,ZahnPRL1999} and for the ease with which
they can be imaged, via video or confocal microscopy
\cite{CrockerGrier1996}. To create such a system, colloidal
particles must somehow be confined to a surface. This can be done by
using colloids sedimented onto a solid or fluid substrate
\cite{ZahnPRL1999,BubeckPRL1999,SkinnerPRL2010}, by physically
confining colloids between the parallel walls of a thin sample chamber
\cite{MurrayPRB1990,ZhengPRL2011}, or by using charged particles that
bind electrostatically to a fluid interface \cite{Leunissen2007,
IrvinePNAS2013}. The latter system has the advantage that the surface
to which the particles bind does not have to be flat, and so is
particularly useful in exploring the role of background curvature in
determining the structure and dynamics of topological defects in 2D
materials \cite{IrvineNature2010, IrvineNatMat2012}. However, the
phase behavior of colloids in this kind of system, which is necessary
for a full understanding of experiments undertaken at finite
temperature, has not been investigated.

In this work, we study systems of 10$^{3}$ - 10$^{4}$ charged
colloidal particles that are electrostatically bound to an almost-flat
fluid interface, shown schematically in Fig.~\ref{fig:conf_diag}. We
demonstrate that the interaction between particles is consistent with
a dipolar pair potential. We measure the dipole moment of the
particles, which allows us to directly compare the phase behavior of
our system to previous experiments and simulations using dipolar
particles~\cite{LinPRE2006,ZahnPRL1999, DeutschlanderPRL2014}.

Using density as the control parameter, we show that the phase behavior of our
system is consistent with the theory of defect-mediated melting due to
Kosterlitz, Thouless, Halperin, Nelson and Young (KTHNY), whereby the
transition from isotropic fluid to crystalline solid happens via an
intermediate hexatic phase \cite{KosterlitzThoulessJPhys1973,
YoungPRB1979, HalperinNelsonPRL1979}. We identify the solid, isotropic
fluid, and hexatic phases by measuring the bond-orientational order
parameter $\psi_{6}$ and associated space and time correlation
functions $g_{6}(r)$ and $g_{6}(\tau)$. Finally, we show that the
classification of our samples into solid, isotropic fluid and hexatic phases is
consistent both with the topological defect structure predicted by
KTHNY theory, and with the dynamical behavior that has been described
previously \cite{ZahnPRL2000}.

\begin{figure}[t!]
\begin{centering}
\includegraphics[scale=0.23]{fig1.pdf}
\caption{(Color online.) Schematic of the experimental geometry. In
the ``side view'' panel, the height $h$ of the droplet is exaggerated
compared to the base diameter $D$. In experimental samples, $h\lesssim
5 \,\mu$m. Particles sitting on the interface (shown in full color)
are mobile, while the remaining particles (shown as faded) bind
randomly and irreversibly to the bare glass surface. The boundary of
the droplet is delineated by a row of particles stuck to the
glass. The inset shows the origin of the dipolar repulsion between
interfacial particles.
\label{fig:conf_diag}}
\end{centering}
\end{figure}

\begin{figure*}[t!]
\center
\includegraphics[scale=0.36]{fig2.pdf}
\caption{(Color online.) Three samples of hydrophobic PMMA particles
electrostatically bound to almost-flat droplets, at areal densities
$\rho$ of (a) $0.036$, (b) $0.043$, and (c) $0.049 \,\mu$m$^{-2}$.
The top row shows a confocal micrograph of each sample. For samples
(b) and (c), the entire, roughly circular droplet is shown (see
Fig.~\ref{fig:conf_diag}). In each sample, the inset square has a side
length of 100$\,\mu$m. The middle row shows Delaunay triangulations of
the particle positions in a selected region, in the first frame of
each movie. Particles with five or seven nearest neighbors are respectively
indicated by red triangles and green disks. The bottom row shows
the particle trajectories over 25 minutes.
\label{fig:confocal_plus_trajectoires}}
\end{figure*}

\section{\label{sec:Materials}Materials \& methods}
Our experimental system is composed of diameter $d=1.1 \, \mu$m
poly(methyl methacrylate) (PMMA) particles that bind electrostatically
to the interface between an oil and an aqueous phase.  The particles
are initially dispersed in a 1:1 volumetric mixture of cyclohexyl
bromide (CHB) and dodecane, while the aqueous phase consists of a 10mM
solution of NaCl in a 90 wt\% glycerol-water mixture.  The dielectric
constant $\epsilon$ of the oil is $4.3\, \epsilon_{0}$, where
$\epsilon_{0}$ is the permittivity of the vacuum
\cite{YoolengaPhysica1965}. The CHB is purified and stored according
to the protocols given in references \cite{Leunissen2007} and \cite{
EvansPRE2016}. The PMMA particles are sterically stabilized with
covalently bound poly(12-hydroxystearic acid) (PHS)
\cite{ElsesserHollingsworth2010}. Previous work has shown that, when
dispersed in similar oils, micron-sized PHS-coated PMMA particles
acquire a charge $q$ of around +500$\,$e, where e is the elementary
charge \cite{KelleherPRE2015, Leunissen2007}. While the charging
mechanism is still incompletely understood \cite{MirjamLeunissenPhD,
vanderLindenLangmuir2014, EvansPRE2016}, particle
charging in our system is robust and reproducible \cite{KelleherPRE2015}. To
facilitate measurement of particle dynamics with confocal microscopy,
we fluorescently dye the particles with absorbed rhodamine 6G
\cite{ElsesserEtAl2011}.

To prepare the particle-laden interfaces we use in our experiments, we
use an atomizer to deposit droplets of the aqueous phase onto a cover
slip. We then incorporate the cover slip into the construction of a
glass capillary channel, which is filled with the particle dispersion
at the desired concentration. As the particle dispersion flows into
the chamber, some of the particles bind irreversibly to the surface of
the droplets, while others bind to the bare glass surface. The
experimental geometry is shown schematically in
Fig.~\ref{fig:conf_diag}. Particles that are bound to the interface
are mobile, and can reach thermodynamic equilibrium. To control the
flatness of the fluid interfaces, prior to the droplet deposition
step, the cover slip is immersed in a bath of KOH-saturated
isopropanol (IPA), and rinsed sequentially with DI water, acetone and
IPA. The cover slip is blown dry with an N$_{2}$ sprayer and dried in
an oven at 70$^{\circ}$C for at least 15 mins prior to use. By varying
the immersion time of the cover slips in the KOH solution, we control
the advancing contact angle of the deposited droplets of the aqueous
phase \cite{Note1}. We find that
immersing the cover slips for 30 mins.~gives contact angles of
approximately 1$^{\circ}$, which are appropriate for this
experiment. Apart from the KOH immersion step, we follow the same
protocol to clean all glass surfaces that come into contact with the
particle dispersion. Once the capillary channel has been filled, we
seal it: first with a buffer layer of glycerol and then with optical
adhesive (Norland Products Inc. NOA \#68).

Following the above procedures, we obtain a sample chamber that
contains several particle-laden interfaces, ranging in base diameter,
$D$, from around 200 to 500$\,\mu$m. Each interface has a slightly
different areal density, $\rho$, of PMMA particles, thus allowing us
to approximately uniformly sample areal densities in the range
0.01-0.15$\,\mu$m$^{-2}$. We estimate the
curvature of the droplets as follows: using a 10$\times$ magnification
NA 0.3 air objective mounted on a Leica TCS SP5 II confocal
microscope, we image the particles in a single confocal slice.  If all
the particles appear in the field of view, the maximum thickness of
the drop must then be less than the the optical section thickness,
around $5\,\mu$m. Since the dimensions of our droplet are far smaller
than the capillary length, we ignore the effect of gravity
\cite{Note2}, and assume that the droplets take the shape of a spherical cap. Since
$D >200\,\mu $m, and the thickness is $<5\,\mu$m, the radius of
curvature must be at least $1\,$mm: far greater than the length scales
probed in our experiments.  Thus, when analyzing our experimental
data, we treat the droplet surface as flat.

After waiting at least a day for the samples to equilibriate, we use
confocal microscopy to record the motion of the particles for up to
several hours, at a rate of 0.25-1.0 frames/s.  Using standard
routines \cite{CrockerWeeksTracking}, we locate the
particles in the field of view. Delaunay triangulations of the
instantaneous particle positions identify sites with more or fewer
than six nearest neighbors, called disclinations.  Trajectories
obtained by by linking particle positions in adjacent frames reveal
the mobility of individual particles.

Snapshots and movies of particle layers of different densities
captured and analyzed in this way display the qualitative features of
the three phases predicted by KTHNY.  The low-density, isotropic fluid
phase shown in Fig.~\ref{fig:confocal_plus_trajectoires} (a) is
characterized by homogeneously distributed disclination defects and
uniformly mobile particles. By contrast, the high-density, equilibrium
crystal phase, shown in Fig.~\ref{fig:confocal_plus_trajectoires} (c),
is only capable of supporting sparse clusters of tighly-bound defects
that do not affect the long-range order of the lattice. In this phase, the
particles that compose the crystal are uniformly confined to the
vicinity of their lattice sites.  As we show in Section~\ref{sec:model},
the resulting caged diffusion can be used to measure in-situ the strength of
the inter-particle interactions.

At intermediate particle densities, such as that shown in
Fig.~\ref{fig:confocal_plus_trajectoires} (b), isolated disclinations
condense into the defect clusters that characterize the hexatic phase.
These clusters facilitate particle mobility, disrupt translational
order, and induce long-lived spatial inhomogeneities in the structure
and dynamics of the particles.

\begin{figure}[t!]
\center
\includegraphics[scale=0.45]{fig3.pdf}
\caption{(a) Nearest-neighbor relative mean square displacement curves for
three crystalline samples, at different densities $\rho$. (b)
Log-log plot of the limiting value of the n.n.-MSD, as a function of
areal density. The dashed line is the best-fit line with
slope -5/2, as predicted by Eqn.~\eqref{eq:drVsRho}. This fit
gives an electric dipole moment $p = (455 \pm 20)\,$e$\cdot \mu$m.
\label{fig:dr2VsRho}}
\end{figure}

\section{\label{sec:model}Model for interparticle interactions \& measurement of
  dipole moment of particles}
To compare the phase behavior of our system with that observed in
other systems~\cite{LinPRE2006, ZahnPRL1999, HanPRE2008,
DeutschlanderPRL2014}, it is important to know both the form and
magnitude of the interparticle repulsion~\cite{KapferKrauthPRL2015}.
In previous work, we studied the behavior of PHS-coated PMMA particles
at an interface between two fluids which are similar in composition to
those described here~\cite{KelleherPRE2015}. In our system, the PMMA
particles appear to be wet very little (or possibly not at all) by the
aqueous phase, and can be described as spheres with charge $q$ sitting
on top of a conducting medium, as shown in the inset to
Fig.~\ref{fig:conf_diag}. In the same work, we showed that the force
binding individual particles to the interface is electrostatic in
origin, and that the interaction between pairs of particles is
dipolar.  These results are consistent with previous experimental and
theoretical work \cite{GouldingHansenMP1998, AveyardPRL2002,
OettelPRE2007} on systems of charged particles in the vicinity of a
fluid interface. In our system and similar ones, the interaction of
two charged particles is the sum of the Coulomb repulsion between the
particles and the Coulomb attraction between each particle and the
image charge of the other. Thus, in the limit where the interparticle
distance $r$ is large compared to the diameter $d$ of the particles,
the net interaction between two interfacially bound particles can be
approximated by a pair potential of the form:
\begin{equation*}
U(r) \simeq \frac{A}{r^{3}},
\end{equation*}
where $ A =p^{2} /8 \pi \epsilon$, and $p = qd$ is the magnitude of
the electric dipole moment of the particles \cite{Note3}.  As shown in
Fig.~\ref{fig:confocal_plus_trajectoires} (c-iii), when the
interfacial density of the particles is high enough, they form a
crystalline solid phase. In a hexagonal lattice composed of repulsive
dipolar particles, the average value of $p$ can be estimated by
observing the fluctuations of the particles relative to the cage
formed by their nearest neighbors. To quantify the interactions
between our interfacial PMMA particles, we use a method due to
Parolini et al.~\cite{ParoliniJCPM2015}, which we now outline briefly.

We begin by identifying a region of the interface where several
hundred particles are arranged in a defect-free crystal lattice which
is at least 20$\,\mu$m from the droplet boundary. We consider only
samples where the density gradient across the subregion of interest is
less than 0.3\% per interparticle spacing, and avoid the grain
boundaries or isolated dislocations that are occasionally present in
our samples. These non-equilibrium features may be identified
quantitatively, for instance by anomalous behavior of the dynamic
Lindemann parameter, $\gamma_{L}(\tau)$, or the non-Gaussian parameter,
$\alpha_{2}(\tau)$, which we define in Section~\ref{sec:dynamics}. To
further check that we are measuring equilibrium properties, we verify
that our results do not depend strongly on the particular choice of
subregion.

At each instant $t$ in time, the Delaunay triangulation defines
$\mathcal{N}_{i}$, the set of nearest neighbors of particle $i$. The
position of particle $i$ relative to its neighbors is given by
\begin{equation*}
\mathbf{r}_{i, \text{n.n.}}(t) =\mathbf{r}_{i}(t) - \frac{1}{n_{b}}
\sum_{j  \, \in \, \mathcal{N}_{i}}\mathbf{r}_{j}(t),
\end{equation*}
where the sum is taken over the $n_{b}$ neighbors of particle $i$.
The nearest-neighbor relative mean square displacement (n.n.-MSD) as a
function of time interval $\tau$ is defined as
\begin{equation}
\langle \delta \mathbf{r}_{\text{n.n.}}(\tau)^{2} \rangle =
\langle (\mathbf{r}_{i, \text{n.n.}}(t+\tau) - \mathbf{r}_{i,
  \text{n.n.}}(t))^{2}\rangle,
\label{eq:nnMSd}
\end{equation}
where the average is taken over particles $i$ and starting times
$t$. When calculating the quantity $\mathbf{r}_{i,
\text{n.n.}}(t+\tau)$, we use the set of neighbors defined at time
$t$, even if those particles no longer share a Delaunay bond with
particle $i$ at time $t+\tau$. The upper panel of
Fig.~\ref{fig:dr2VsRho} shows $\langle \delta
\mathbf{r}_{\text{n.n.}}(\tau)^{2} \rangle$ curves three crystalline
samples, at different densities $\rho$. In all these samples, $\langle
\delta \mathbf{r}_{\text{n.n.}}(\tau)^{2} \rangle$ reaches a plateau
value $\langle \delta \mathbf{r}_{\text{n.n.}}^{2}\rangle$. According
to~\cite{ParoliniJCPM2015}, this value is related to the force
constant $A$, and hence to the dipole moment $p$, by the equation
\begin{equation}
\langle \delta \mathbf{r}_{\text{n.n.}}^{2} \rangle = \frac{2^{9/2}
\alpha \, k_{B}T}{3^{5/4}A}\rho^{-5/2},
\label{eq:drVsRho}
\end{equation}
where we have used the relation between $\rho$ and interparticle
spacing $a$ in a hexagonal lattice, $\rho = 2/a^{2}\sqrt{3}$. The
constant $\alpha$ is calculated in reference \cite{ParoliniJCPM2015},
and is approximately equal to 0.0531.  The lower panel of
Fig.~\ref{fig:dr2VsRho} shows the results of applying this method to
10 crystalline samples at different areal densities. The error bars
show the discrepancy between the results of calculating the limiting
value of $\langle\delta \mathbf{r}_{\text{n.n.}}^{2}\rangle$ in two
different ways: first by using the plateau in the n.n.-MSD curve as a
function of time; and second by computing the variance of the
histogram of frame-to-frame displacements in the $x-$ and $y-$
directions separately. For a particle diffusing in an isotropic
harmonic potential, sampled over sufficiently long times, these two
methods should give the same result. Fitting the data to
Eq.~\ref{eq:drVsRho}, we find that $p = (455 \pm 20)\,$e$\cdot \mu$m.

When discussing phase behavior in this system, it is convenient to
introduce the dimensionless interaction parameter $\Gamma$,
\begin{equation*}
\Gamma = \frac{A(\pi \rho)^{3/2}}{\, k_{B}T},
\end{equation*}
where $T = 293\,$K is the temperature at which the experiments take
place. Using $\Gamma$ to describe the effective temperature of the
system allows us to directly compare our results with previous
experiments \cite{KusnerPRL1994, ZahnPRL1999} and simulations
\cite{LinPRE2006} using dipolar repulsive particles.

\begin{figure}[t!]
\center
\includegraphics[scale=0.37]{fig7.pdf}
\caption{(Color online.) Delaunay triangulations of typical particle
configurations, taken from the samples shown in
Fig.~\ref{fig:confocal_plus_trajectoires}. Five- and seven-coordinated
disclinations are marked by red triangles and green disks
respectively.  Sample (a) shows three unpaired disclinations, while
(b) shows two unpaired dislocations (5-7 pairs). Sample (c) shows a
pair of dislocations with opposite Burgers' vector. This configuration
is not a topological defect.
\label{topdefects}}
\end{figure}

\section{KTHNY theory: topological defects and orientational correlations}
Over the past several decades, KTHNY theory has been shown to describe
the phase behavior of a broad class of 2D materials, including dipolar
repulsive particles \cite{NelsonDefectsBook, GasserChemPhysChem2010,
KapferKrauthPRL2015}. According to this theory, melting of a 2D
crystalline solid takes place via two continuous transitions, which
can be understood in terms of the topological defects present in the
material. Two types of topological defects are important:
disclinations, points which have a number of nearest neighbors other
than six; and dislocations, bound pairs of one five-coordinated and
one seven-coordinated disclination. A dislocation is characterized by
a Burgers' vector, which represents the magnitude and direction of the
lattice distortion induced by the dislocation
\cite{HirthAndLothe}. Some examples of these kinds of defects are
shown in Fig.~\ref{topdefects} (a) and (b).

\begin{figure*}[t!]
\center
\includegraphics[scale=0.5]{fig5.pdf}
\caption{(Color online.) Log-log plots of orientational correlation functions
$g_{6}(r)$ and $g_{6}(\tau)$, for nine samples at different values of
$\Gamma$. The sloped dashed lines in each plot indicate algebraic
decay with the exponents expected at the fluid-hexatic transition,
while the horizontal dashed line in the $g_{6}(r)$ plot separates the
curves which decay ($\Gamma \leq 74$) from those that reach a constant
value ($\Gamma \geq 79$). Using these curves, we identify the
fluid-hexatic and solid hexatic transitions at $\Gamma_{\textsc{FH}}
= 68 \pm 2$ and $\Gamma_{\textsc{HS}} = 76 \pm 3 $.
\label{fig:g6s}}
\end{figure*}

According to KTHNY theory, in the solid phase at equilibrium, no free
topological defects are present. However, there may be thermally
activated pairs of dislocations of opposite Burgers' vector which are
bound by an attractive potential. These kinds of structures, an
example of which is shown in Fig.~\ref{topdefects} (c), are not
topological, since they can occur via local rearrangements of the
lattice. At sufficiently low $\Gamma$, this attraction can be overcome
by thermal fluctuations, and the dislocation pairs
dissociate. Although the resulting free dislocations destroy the
finite shear modulus of the crystal lattice, the resulting material is
not an isotropic fluid, but rather a liquid crystalline hexatic
phase. The transition to the isotropic fluid is completed when the
dislocations themselves unbind into their constituent disclinations.

\begin {table}[b!]
\begin{center}
\begin{tabular}{ | c || c | c | c  | } \hline
\makecell{\phantom{m}\\\phantom{m} }   & \makecell{isotropic  \\ fluid}   & \makecell{\\ hexatic  \\ \phantom{.}} & solid  \\
\hline \hline
\makecell{ \\\phantom{i} topological \phantom{i}\\ defects \\ \phantom{.}} &\makecell{ free \\ \phantom{i} disclinations\phantom{i}  } & \makecell{free \\ \phantom{i} dislocations \phantom{i} }  &  \makecell{none}    \\

\hline

\makecell{$g_{6}(r) \propto $ \\\tiny{$r \rightarrow \infty $}} & $\exp{(-r/\xi_{6})}$ &$r^{-\eta_{6}}$& \makecell{\\\phantom{M} const. \phantom{M}\\ \phantom{.}} \\

\hline

\makecell{$g_{6}(\tau) \propto $ \\\tiny{$\tau \rightarrow \infty $}} & $\exp{(-\tau/\tau_{6})}$&$\tau^{-\eta_{6}/2}$&   \makecell{\\const. \\ \phantom{.}} \\
\hline

\end{tabular}
\caption {Topological defect structure and properties of correlation
functions $g_{6}(r)$ and $g_{6}(\tau)$ in the solid, hexatic and fluid
phases, according to KTHNY theory. \label{tab:PhaseProperties}}
\end{center}
\end {table}

Using data from experiments and simulations, different groups have
explored various ways of quantitatively testing the predictions of
KTHNY theory \cite{DillmannJPCM2012, HanPRE2008}. Of particular
interest is the bond-orientational order parameter $\psi_{6}$, since
it can be easily calculated from real-space data, and because the
functional form of the associated correlation functions, $g_{6}(r)$ and
$g_{6}(\tau)$, clearly discriminate between the phases of the material.

If particle $k$ has position $\mathbf{r}_{k}$ at time $t$, the
bond-orientational order parameter $\psi_{6}(\mathbf{r}_{k},t)$ is the
defined by
\begin{equation*}
\psi_{6}(\mathbf{r}_{k},t) = \frac{1}{n_{b}}\sum_{j  \, \in \, \mathcal{N}_{k}}e^{6i\theta_{kj}},
\end{equation*}
where the sum is taken over the $n_{b}$ nearest neighbors of particle
$k$. The angle between particle $k$ and its $j-$th neighbor,
$\theta_{kj}$, is taken with respect to an arbitrary but fixed
axis. The degree of local hexagonal order is given by $|\psi_{6}|$. In
the crystal phase, the orientation of the hexagonal
unit cell is given by $\frac{1}{6}\arg{\psi_{6}}$. The space and time correlation functions
$g_{6}(r)$ and $g_{6}(\tau)$ are defined
\begin{equation*}
\begin{aligned}
g_{6}(r) &= \text{Re} \big{\{} \big{\langle} \psi_{6}^{*}(\mathbf{r}_{k},t) \psi_{6}(\mathbf{r}_{l},t)
\big{\rangle}_{\abs{\mathbf{r}_{k}-\mathbf{r}_{l}}=r} \big{\}} \quad \text{and} \\
g_{6}(\tau) &=  \text{Re} \big{\{} \big{\langle} \psi_{6}^{*}(\mathbf{r}_{k},t) \psi_{6}(\mathbf{r}_{k},t+\tau)
\big{\rangle}\big{\}}.
\end{aligned}
\end{equation*}
When calculating $g_{6}(r)$, the averages are taken over time and
pairs of particles $\{k,l\}$ satisfying the condition
$\abs{\mathbf{r}_{k}-\mathbf{r}_{l}}=r$. For $g_{6}(\tau)$, the
averages are taken over all particles $k$ and starting times
$t$. Thus, $g_{6}(r)$ is a two-particle correlation function, while
$g_{6}(\tau)$ is a single-particle quantity. According to KTHNY
theory, these correlation functions have distinct behaviors in each of
the three phases: for large $r$ and $\tau$, both functions tend to a
constant value in the solid phase, decay algebraically in the hexatic
phase, and decay exponentially in the isotropic fluid, with a
characteristic decay length [time] $\xi_{6}$ [$\tau_{6}$]. KTHNY
theory predicts that, in the hexatic phase, the exponent $\eta_{6}$ of
the power-law decay of $g_{6}(r)$ is twice the exponent of the
power-law decay of $g_{6}(\tau)$, and further dictates that, at the
fluid-hexatic transition, $\eta_{6}$ reaches a critical value of -1/4
\cite{NelsonDefectsBook}. Some of these predictions are summarized in
Table~\ref{tab:PhaseProperties}.

Figure~\ref{fig:g6s} (a) and (b) respectively show $g_{6}(r)$ and
$g_{6}(\tau)$, plotted for nine samples at values of $\Gamma$ ranging
from 53 to 91. In our analysis of the temporal correlation function
$g_{6}(\tau)$, we rescale $\tau$ by the average time $\tau_{0}$
required for a freely diffusing particle to traverse the mean distance
between particles $a$. This step is necessary because the thickness of
the aqueous layer underneath the particles (see
Fig.~\ref{fig:conf_diag}) varies between samples. Thus, even in the
limit of very low particle density, different samples may have
diffusion coefficients $D_{0}$ that vary by as much as a factor of
four. We estimate $\tau_{0}$ from the small-time behavior of the
n.n.-MSD curves, such as those shown in Fig.~\ref{fig:dr2VsRho}. At
the smallest time intervals for which we have data, we assume that the
particle is freely diffusing inside its cage of nearest neighbors, and
fit the first two data points of the $\langle \delta
\mathbf{r}_{\text{n.n.}}(\tau)^{2} \rangle$ curve by a straight line,
containing the origin, with slope $4 D_{0}$ \cite{Note4}. This allows us to estimate the
time for a freely diffusing particle to traverse one interparticle
spacing, $\tau_{0} = a^{2}/4D_{0}$. For our samples, $\tau_{0}$ is
of order 30 mins.

For samples with $\Gamma \leq 67$, both $g_{6}(r)$ and $g_{6}(\tau)$ show the
exponential decay characteristic of the isotropic fluid phase, while
for $\Gamma \geq 79$, both functions tend to a constant
value at large $r$ and $\tau$.  For the sample at $\Gamma = 74$,
$g_{6}(r)$ shows behavior consistent with the power-law decay expected
in the hexatic phase. For $\Gamma = 68$, the slope of
$g_{6}(r)$ equals the critical value of -1/4 within experimental
error, and so we cannot unambiguously assign this sample to either phase.  As
can be seen from the right panel of Fig.~\ref{fig:g6s}, for the
samples at $\Gamma = 68$ and $\Gamma = 74$, our data for $g_{6}(\tau)$
do not allow us to distinguish between algebraic decay with a small
negative power, and a constant value.  Thus, we estimate that the
transition between the hexatic and the isotropic fluid phases occurs at
$\Gamma_{\textsc{FH}} = 68$, and the transition between the hexatic
and the ordered phase occurs at $\Gamma_{\textsc{HS}} = 76$.

We also note that the $g_{6}(r)$ and $g_{6}(\tau)$ curves for the
$\Gamma = 79$ sample lie above those for the sample at $\Gamma = 83$,
indicating that the former sample is more ordered. This apparent
non-monotonic behavior might reflect sample-to-sample variation in
electric dipole moment $p$, which would cause experimental uncertainty
in our calculated values of $\Gamma$, and may also account for some of
the spread of the data in Fig.~\ref{fig:dr2VsRho}. In fact, since the
limiting values of the correlation functions should be a monotonic
function of $\Gamma$, we can use the deviation from monotonicity to
estimate the uncertainty in our stated values of $\Gamma$. Doing this,
we find that the uncertainty in $\Gamma$ is approximately $3\%$.
This figure only accounts for sample-to-sample
variation: the uncertainty in the mean value of the electric dipole
moment $p$ calculated from the data in Fig.~\ref{fig:dr2VsRho} could
lead to all the stated values of $\Gamma$ being shifted systematically
from their true values by as much as 8\%. In spite of these
experimental uncertainties, the values of $\Gamma_{\textsc{FH}}$ and
$\Gamma_{\textsc{HS}}$ that we find are in quantitative agreement
with those found in previous experiments \cite{ZahnPRL2000,
DeutschlanderPRL2014}.

\begin{figure}[t!]
\center
\includegraphics[scale=0.55]{fig4.pdf}
\caption{(Color online.) (a) Absolute value of the
average bond-orientational order parameter,
plotted as a function of interaction parameter $\Gamma$. The dashed
lines indicate the values of $\Gamma$ at the fluid-hexatic and
hexatic-solid transitions, as defined by the behavior of the
correlation functions $g_{6}(r)$ and $g_{6}(\tau)$ (see
Fig.~\ref{fig:g6s}). (b) Fraction of particles which do not
have six nearest neighbors. (c) Fraction of particles which
form unpaired disclinations or dislocations. To enable these
quantities to be displayed on the same plot, the fraction of unpaired
disclinations is multiplied by a factor of 5.
\label{fig:psirow}}
\end{figure}

The final orientational quantity we define is the average
orientational order parameter $\Psi_6 = \langle
\psi_{6}(\mathbf{r}_{k},t) \rangle$, where the average is taken over all
points $k$ and times $t$. We expect that, in the isotropic fluid
phase, $|\Psi_6| = 0$, while in the crystalline solid phase,
$|\Psi_6|$ takes a finite positive value, which tends to unity as
$\Gamma$ increases. In the top panel of Fig.~\ref{fig:psirow}, we plot
$|\Psi_{6}|$ as a function of interaction parameter $\Gamma$. The middle
panel of the same figure shows the total defect fraction, defined as
the fraction of particles which have a number of nearest neighbors
other than six. Between $\Gamma_{\textsc{FH}}$ and
$\Gamma_{\textsc{HS}}$, the defect fraction drops dramatically, and we
see a corresponding growth in the orientational order $|\Psi_{6}|$ in
the system.

The bottom panel of Fig.~\ref{fig:psirow} shows a plot of the fraction
of unpaired dislocations and disclinations, $n_{\text{disloc.}}$ and
$n_{\text{disc.}}$. A topological defect is defined as unpaired if it
is does not share a Delaunay bond with any other defect. Thus, the
5-coordinated disclination in the center of Fig.~\ref{topdefects} (a)
is unpaired, as are the two dislocation defects in
Fig.~\ref{topdefects} (b). On the other hand, both the cluster of
defects in the top right of Fig.~\ref{topdefects} (a) and the two
adjacent dislocations of opposite Burgers' vector in
Fig.~\ref{topdefects} (c) are paired, and neither contributes to
$n_{\text{disloc.}}$ or $n_{\text{disc.}}$.  While computationally
straightforward, our definition of \textit{unpaired} defects does not
provide a direct measurement of the concentration of \textit{free}
defects in the sense of KTHNY theory. This is true for at least two
reasons: first, our definitions of $n_{\text{disloc.}}$ and
$n_{\text{disc.}}$ treat energetically bound but non-adjacent defects
as unpaired. This leads us to overestimate the number of free defects,
especially in the solid and hexatic phases. Second, our definitions
completely neglect defect clusters, such as the structure in the top
right of Fig.~\ref{topdefects} (a), which may contain one or several
net topological defects. This will cause us to underestimate the
number of free defects, especially in the fluid phase, where such
clusters proliferate. Despite these shortcomings, we find that
$n_{\text{disloc.}}$ and $n_{\text{disc.}}$ display the expected
behavior in the vicinity of the transitions: near $\Gamma =
\Gamma_{\textsc{FH}} $, $n_{\text{disc.}}$ drops dramatically, while
near $\Gamma = \Gamma_{\textsc{HS}} $, $n_{\text{disloc.}}$ does the
same.

\section{Dynamical measures of phase behavior \label{sec:dynamics}}
As well as displaying distinctive spatial structure, different phases
of a material are typically characterized by their dynamics.  To
investigate this aspect of the phase behavior of our samples, we plot,
in Fig.~\ref{fig:dynamicQuants}, the dynamic Lindemann parameter
$\gamma_{L}(\tau)$ and the non-Gaussian parameter $\alpha_{2}(\tau)$
\cite{ZahnPRL2000}. The dynamic Lindemann parameter $\gamma_{L}(\tau)$
is defined
\begin{equation}
\gamma_{L}(\tau) = \frac{\langle \delta
  \mathbf{r}_{\text{n.n.}}(\tau)^{2} \rangle }{2 a^{2}},
\label{LindemannParam}
\end{equation}
where the n.n.-MSD $\langle \delta \mathbf{r}_{\text{n.n.}}(\tau)^{2} \rangle$ is
defined in Eqn.~\eqref{eq:nnMSd}. The non-Gaussian parameter
$\alpha_{2}(\tau)$ is defined as
\begin{equation*}
\alpha_{2}(\tau) = \frac{\langle \delta
  \mathbf{r}_{\text{n.n.}}(\tau)^{4}\rangle}{2 \langle \delta
  \mathbf{r}_{\text{n.n.}}(\tau)^{2}\rangle^{2}}-1.
\end{equation*}
This quantity measures the extent to which the histogram of particle
displacements deviates from the normal distribution. Using the phase
classification based on the behavior of the correlation functions
$g_{6}(r)$ and $g_{6}(\tau)$, our measurements of $\gamma_{L}(\tau)$
and $\alpha_{2}(\tau)$ are consistent with previous measurements of
the dynamics of systems in the solid, fluid and hexatic
phases~\cite{ZahnPRL2000}.

In the solid phase, the dynamic Lindemann parameter reaches a plateau
value at long time. The observed critical value of the dynamic
Lindemann parameter is $\gamma_{L}^{c} = 0.012 \pm 0.001$. This is
close to the value predicted by evaluating Eqns.~\eqref{eq:drVsRho}
and~\eqref{LindemannParam} at the density $\rho_{\textsc{HS}}$
corresponding to the hexatic-solid transition, $\gamma_{L}^{c} =
0.0097\pm 0.005$. This comparison serves as a consistency check on
Eqn.~\eqref{eq:drVsRho}, and the measured value of
$\Gamma_{\textsc{HS}}$. In the solid phase, the non-Gaussian parameter
$\alpha_{2}(\tau)$ has a small positive value independent of time.
This may be because the quantities $\mathbf{r}_{i,
\text{n.n.}}$ are not statistically independent, as they take into
account the positions of the nearest neighbors.

\begin{figure}[t!]
\center
\includegraphics[scale=0.5]{fig6.pdf}
\caption{(Color online.) Log-log plots of: (a) dynamic Lindemann parameter
$\gamma_{\textsc{L}}(\tau)$; and (b) non-Gaussian parameter
$\alpha_{2}(\tau)$. Panel (a) shows that, for samples identified as belonging
to the ordered phase by our analysis of the correlation functions,
$\gamma_{\textsc{L}}(\tau)$ reaches a constant value, while the
samples with $\Gamma < \Gamma_{\textsc{HS}}$ behave diffusively or
subdiffusively. The horizontal dashed line indicates the critical
value $\gamma_{L}^{c} = 0.0097$ predicted by Eqns.~\eqref{eq:drVsRho}
and \eqref{LindemannParam}, evaluated at the density
$\rho_{\textsc{HS}}$ corresponding to $\Gamma_{\textsc{HS}}$.  Panel
(b) shows that, in the isotropic fluid, $\alpha_{2}$ peaks at
some intermediate timescale, while in the candidate hexatic samples
($\Gamma =$ 68 and 74), non-Gaussian behavior grows over the
timescales we observe. The inset in the lower plot highlights the
dramatic growth in the maximum value of $\alpha_{2}$ in the hexatic
phase. The vertical dashed lines indicate $\Gamma_{\textsc{FH}}$, and
$\Gamma_{\textsc{HS}}$, as defined by the behavior of the correlation
functions $g_{6}(r)$ and $g_{6}(\tau)$.
  \label{fig:dynamicQuants}}
\end{figure}

In the fluid phase, we observe diffusive behavior, $\gamma_{L}(\tau)
\propto \tau$, at long times, while the non-Gaussian parameter
$\alpha_{2}(\tau)$ displays a local maximum at time intervals
$\tau/\tau_{0} \sim 0.1$. These timescales also correspond to the
presence of a shoulder in the $\gamma_{L}(\tau)$ curves, and are also
similar to the characteristic times $\tau_{6}$ of the exponential
decay of the $g_{6}(\tau)$ curves shown in Fig.~\ref{fig:g6s}. All
these timescales may originate in collective rearrangements of defect
clusters, such as that shown in Fig.~\ref{topdefects} (a).

In the sample we identify as belonging unambiguously to the hexatic
phase ($\Gamma = 74$), $\gamma_{L}(\tau)$ behaves subdiffusively over
observed times.  For the sample at $\Gamma = 68$, the correlation
functions $g_{6}(r)$ and $g_{6}(\tau)$ are consistent with critical
behavior, and we are unable to assign it to either the fluid or the
hexatic phase. For this sample, the slope of $\gamma_{L}(\tau)$
appears to be approaching 1 at the longest times we measure, perhaps
indicating that it is indeed a fluid. Previously, Zahn and Maret
showed that $\alpha_{2}(\tau)$ tends to a constant value of order
unity for systems in the hexatic phase~\cite{ZahnPRL2000}. Our data
are consistent with this finding, but we do not record our candidate
hexatic samples for sufficiently long times to verify the limiting
behavior. We do, however, observe the sharp growth in the maximum
value of $\alpha_{2}(\tau)$ in the hexatic phase that was reported in
the same study.

\section{Conclusions}
In this work, we study a system of charged colloidal particles that
are electrostatically bound to a fluid interface, and interact via electric
dipole-dipole repulsion. We show that the phase behavior of this
system is well-described by KTHNY theory, with density
as the control parameter. Using the orientational correlation
functions $g_{6}(r)$ and $g_{6}(\tau)$, we assign each sample to the
solid, isotropic fluid, or hexatic phase. We demonstrate that the concentration
of unpaired dislocations and disclinations are consistent with the
KTHNY picture of defect-mediated melting. Finally, we find that each
phase displays distinctive dynamical behavior, as measured by the the
dynamic Lindemann parameter $\gamma_{L}(\tau)$ and the non-Gaussian
parameter $\alpha_{2}(\tau)$.

\begin{figure}[b!]
\center
\includegraphics[scale=0.28]{fig8.pdf}
\caption{(Color online.) Plot of the Delaunay triangulation of
interfacially bound particles in a single quadrant of a roughly
circular droplet. This sample has $\Gamma = 120$, and approximately
2000 particles in total. The color map shows the local orientation of
the lattice, given by $\frac{1}{6}\arg{\psi_{6}}$, while 5- and
7-coordinated disclinations are indicated by triangles and disks
respectively. The thick black curve identifies the droplet
edge. (Disclinations are not plotted for the particles on the
boundary.) Away from the edge, the system forms a monocrystal that
spans the interior of the droplet. Immediately adjacent to the droplet
edge, the lattice is aligned with the edge. Where the orientation of
the interior region does not match that of the edge, grain boundaries
form, a few lattice spacings from the boundary. These grain boundaries
are delineated by a chain of polarized dislocations (5-7 pairs).
  \label{fig:edgeGrain}}
\end{figure}

Given the small number of particles in our system, the extent to which
our data are well-modeled by KTHNY theory is quite surprising. This
agreement is only possible because the orientation of the droplet
edge, which is delineated by a line of pinned particles (see
Fig.~\ref{fig:confocal_plus_trajectoires}), does not propagate into
the interior of the droplet. In the fluid phase, this is expected,
since orientational correlations decay exponentially over lengths of a
few interparticle spacings -- this decay is evident in the $\Gamma
\leq 67$ curves in Fig.~\ref{fig:g6s} (a). In the crystal phase, as
shown in Fig.~\ref{fig:edgeGrain}, the orientation inherited from the
droplet edge is destroyed by a series of grain boundaries that run
around the inner perimeter of the droplet. These grain boundaries
separate an interior monocrystalline region from an outside layer, a
few interparticle spacings wide, which is aligned with the edge of the
droplet. Evidently, the strain fields associated with these grain
boundaries are not large enough to significantly disrupt the phase
behavior of the material in the interior region. In the hexatic, it is
not immediately clear how the system accommodates the presence of the
droplet edge, since grain boundaries are difficult to identify
unambiguously in this phase.

The concurrence between our findings and previous work on larger
systems of dipolar repulsive particles extends to quantitative
agreement on the transition values of the interaction parameter
$\Gamma$ \cite{ZahnPRL1999, DeutschlanderPRL2014}, although the
sparsity our data, as well as the error bars for $\Gamma$ shown for
example in Fig.~\ref{fig:psirow}, limit our ability to determine the
width of the hexatic window.

This work was supported primarily by the National Science Foundation
under Award No. DMR-1105417, and partially by the Materials Research
Science and Engineering Center (MRSEC) program of the National Science
Foundation under Award No. DMR-1420073. Additional financial support
was provided by NASA (NNX13AR67G).

redpajama_set_name: RedPajamaArXiv


text:
jim.r.gillespie
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Commented on Service update
The effect on UK politics interests me too: if Scottish independence would ensure Tory control of the rest of the UK (which is also my understanding, at least for the next election), why are the Tories against it? It seems...
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I don't know if things are different in the US (or just with Motorola) but on my Samsung Galaxy S2 running 4.1.2, in the Application Manager I can uninstall all updates for built-in apps (even the Samsung ones) and then...
Commented on The Snowden leaks; a meta-narrative
Let us not forget that QDOS originally stood for "Quick & Dirty Operating System" - not something that fills me with confidence....
Commented on "Write me something fresh and new, but make it just like the last one"
On architectural fiction, how about Heinlein's And He Built A Crooked House :-)...
Commented on Circumstantial connections
If all of these thousands-to-one shots came off, I would expect at least a few survivors in liferafts, which I assume would at least have radar corners installed. Secondary thought: with no power for radio, transponders and so on, would...
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[In the US] a 16 year old can undress in front of her boyfriend, but is a child pornographer if she texts him a picture of herself in the shower. I'm not sure about the age limits here in...
Commented on Sitrep
Unfortunately a lot of people do want to build houses in and around London. So what we first have to do is to make other parts of the country more attractive. According to this map the highlands and islands appear...
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"I think we need a more decisive move to open document standards like ODF" Unfortunately for the the world, officially Office Open XML is an open standard: http://en.wikipedia.org/wiki/Office_Open_XML. To cut a long story short, after governments started to demand that...
Commented on Another deceptively simple question
Re: Books with musical accompaniment built in? I'll second @paws4thot's NOOOOOO!!!!!!, and raise it to a HELL NOOOOOO!!!!!! for laugh tracks in comedy books ;-)...
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rich! commented on Service update
I thought it was the media reaction to his policy in interviews. We Brits are very traditional about our feudal overlords, and the "Westminister media" tends to respect that. The bellicose Labour chap had such a long term relationship with the media pool that he was "call me Tony" Blair - "please, treat me as your friend rather than the head of state". The Rt Hon D. Cameron, Bullingdon Club, attempted to pick up some of this credibility, by playing down his formal rank, hence, "call-me-dave"....
Antonia T Tiger commented on Service update
"Feudal overlords" doesn't fit. Fealty goes both ways. If they don't protect us, if they don't put their lives and honour on the line for us, we cannot be their vassals. The media sucking up to those in power is a whole different ugliness....
Martin commented on Service update
:) You're not suggesting that there's a reason that the many children of the hereditary nobility get packed off to Sandhurst or Dartmouth*, and a few years of getting cold or hot, miserable, and shot at, are you? :) It's rather in contrast to the children of politicians getting packed off to an internship with a US Senator, then a quiet parachuting in for a constituency selection... You'll notice I didn't say Cranwell, one must have some standards :)...
El commented on Service update
I'm sure there's a reason. Not convinced an outdated sense of feudal duty is the one though. Some of them, like having a family doctor, lawyer and the like make sense when viewed from the outside. Family army officer or naval officer, not so immediately obvious. But it seems to work for them....
Well, those who were convinced there was a master plan how are you feeling in light of the appearance of a mad scrabble to firm up plans for both the time-table and the details of exactly what devo-max will entail after a no vote to try and persuade (or bribe depending on your POV) the Scots back to voting no? Even the BBC, which the Scots feel has been quite biased in it's coverage (pro-No) had an element of glee in their interview with Alistair Darling on Today this morning asking just how badly the wheels had come off and...
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text:
Q: Replace 1 value in a subsection of dataframe with value of another column I have a one hot encoded dataframe such as:
|  qtd|   a |   b |  c |   d |  e | ...z|
|-----+-----+-----|----|----+-----+-----|
|  90 |   1 |   0 |  0 |   0 |  0 |   0 |
|  10 |   0 |   0 |  0 |   0 |  0 |   1 |
|  40 |   0 |   1 |  0 |   0 |  0 |   0 |
|  80 |   0 |   0 |  1 |   0 |  0 |   0 |
|  90 |   0 |   1 |  0 |   0 |  0 |   0 |

I want to replace the values of the columns a to infinite with the value in qtd where the column has 1 as value, there is only one 1 value in the a to infinite dataframe subframe.
Such as:
|  qtd|   a |   b |  c |   d |  e | ...z|
|-----+-----+-----|----|----+-----+-----|
|  90 |  90 |   0 |  0 |   0 |  0 |   0 |
|  10 |   0 |   0 |  0 |   0 |  0 |  10 |
|  40 |   0 |  40 |  0 |   0 |  0 |   0 |
|  80 |   0 |   0 | 80 |   0 |  0 |   0 |
|  90 |   0 |  90 |  0 |   0 |  0 |   0 |

A: You can select all columns without first by DataFrame.iloc and multiple by column with DataFrame.mul:
df.iloc[:, 1:] = df.iloc[:, 1:].mul(df['qtd'], axis=0)
print (df)
   qtd   a   b   c  d  e   z
0   90  90   0   0  0  0   0
1   10   0   0   0  0  0  10
2   40   0  40   0  0  0   0
3   80   0   0  80  0  0   0
4   90   0  90   0  0  0   0

If column is not always first is possible get columns names by Index.difference and select by subset:
cols = df.columns.difference(['qtd'])
df[cols] = df[cols].mul(df['qtd'], axis=0)

If first column is index:
df = df.mul(df.index, axis=0)
print (df)
      a   b   c  d  e   z
qtd
90   90   0   0  0  0   0
10    0   0   0  0  0  10
40    0  40   0  0  0   0
80    0   0  80  0  0   0
90    0  90   0  0  0   0

A: Here is numpy broadcast way
df.values[:,1:]*=df.qtd[:,None]
df
Out[461]:
   qtd   a   b   c  d  e   z
0   90  90   0   0  0  0   0
1   10   0   0   0  0  0  10
2   40   0  40   0  0  0   0
3   80   0   0  80  0  0   0
4   90   0  90   0  0  0   0

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Greetings! What is the name of an organic compound, that is essential in small quantities for healthy human growth and development? A vitamin! Where can they be found? This calls for earnest study.
The vitamins are present in all seeds-the grains, legumes, and nuts. They are in the fruits, leaves, and roots. They are in all vegetation. They are one of the essential factors of growth. As in all plants, so in animals. The life and growth of all animals depend upon the vitamins found in seeds, fruits, leaves, and roots. The vitamins function in some way as an activating principle which sets going the processes that develop energy, power, and activity. All animals are dependent upon this life principle to sustain their lives. A monkey fed a food ration but with vitamins removed, died in ninety days.
As in plants and animals, so in man. His life and growth depend upon the vitamins found in all vegetation. They are as necessary to the daily food as any other element. When vitamins were discovered they were designated by the letters of the alphabet-A, B, C, and so on. The number of vitamin factors discovered has grown until names as well as letters are used to designate them. Knowledge of them is developing rapidly. The chemical nature of several vitamins is now known; others are being studied, and no one knows how many more will be found in the years to come. Fifteen are now known and others are postulated. Advance in knowledge concerning them is developing so rapidly that any book written today about them is out of date tomorrow.
The number of them known, and the variety of their functions and their sources, constitute a field so broad that a library of books is required to cover it. To try to cover this field in this class would only confuse the student, and we shall not attempt to do so.
However the ready may rest assured that he will lose nothing that is necessary to protect the health because of the brevity of this class. It is all as simple as this: No vitamin has been discovered or ever will be found that has not been in natural foods since the dawn of time; no scientist can discover anything which God did not set in operation thousands of years ago. When He made man and commanded his rations to grow out of the earth, He provided all of man's necessities. Our confidence in our Creator is complete, and we are free to say that scientist will never find a nutritional need of the human body that is not met by natural foods-whole grains, vegetables, fruits, legumes, and nuts.
It appears that vitamins assist in the maintenance of every life process and the normal conditions of every cell in the body. This, then, includes every organ, gland, tissue, nerve, bone, and tooth; the eyes, skin, hair, blood, digestive juices and all other fluids-everything that can be named in the body.
Certain ones promote growth; some contribute to the health of the skin and mucous membrane and glands throughout the body; others maintain nerve vitality; some sustain the health of the capillaries; still others assist in building bones, or aid digestion, or reproduction, or coagulation, and so on at length. This is marvelous indeed. The chemical composition of several vitamins is now known, but how they work to accomplish the marvels of oxygen, twenty of carbon, and thirty of hydrogen. It seems wonderful that the composition of a vitamin can be caught by the camera, but even that does not help to solve the mysteries of their functions. How can oxygen, carbon, and hydrogen do the things that are attributed to vitamin A? The mystery is as deep as ever! We are no nearer the solution of the mystery of life than we were before the vitamins were known.
"This attitude is illustrated by an interview with Dr. Willis R. Whitney, vice-president of the General Electric Company and director of its research department. This interview appeared in the New York Times Magazine, November 2, 1930, cited by George McCready Price.
Join us next week, as we dig a little deeper into the mysteries of vitamins!


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Thai famous papaya salad, a combination of green papaya, green beans, garlic, chili, tomatoes, peanuts, carrots, dried and fresh shrimp.
Chef's specialty sald, shrimp, squids, scallops, mussels, mints, onions, cucumbers tossed in house chili dressing.
Soft and tender beef salad with mints, onions, cucumber in lime chili dressing.
Grilled beef mixed with roasted rice powder, red onions, mints leaves, fresh lime juice and chili powder.
Mango, tomato, onions, cashew nuts in lime chili dressing.
Seasoned chicken on a bed of mixed greens in lime dressing.
Grilled shrimps with seasonal greens and lime dressing.
Choice of ground beef or chicken, tossed with red pepper, onions and parched rice served with lettuce.
House mixed greens on crispy rice sheet, topped with dried raisin and cranberry, mango, crispy noodle with Beyond's peanuts dressing.
Choice of ground beef or chicken, mixed with a perfect blend of spices, onion, lemongrass, Thai chili powder and fresh lime juice.


text:
Gluten Triggers 1 in 4 Cases of Sporadic Ataxia
Jefferson Adams
Jefferson Adams is a freelance writer living in San Francisco. His poems, essays and photographs have appeared in Antioch Review, Blue Mesa Review, CALIBAN, Hayden's Ferry Review, Huffington Post, the Mississippi Review, and Slate among others.
He is a member of both the National Writers Union, the International Federation of Journalists, and covers San Francisco Health News for Examiner.com.
View all articles by Jefferson Adams
Image: CC– Dierk Schaefer
Celiac.com 01/16/2017 – Cerebellar ataxias can be caused by a wide range of disease processes, either genetic or acquired. Establishing a clear diagnosis requires a methodical approach with expert clinical evaluation and investigation.
A team of researchers recently published a description of the causes of ataxia in 1500 patients with cerebellar ataxia. The research team included M Hadjivassiliou, J Martindale, P Shanmugarajah, R A Grünewald, P G Sarrigiannis, N Beauchamp, K Garrard, R Warburton, D S Sanders, D Friend, S Duty, J Taylor, and N Hoggard.
They are variously affiliated with the Academic Department of Neurosciences, Royal Hallamshire Hospital, Sheffield Teaching Hospitals NHS Trust, Sheffield, UK; Sheffield Diagnostic Genetics Service, Sheffield Children's NHS Foundation Trust, Sheffield, UK; the Department of Gastroenterology, Royal Hallamshire Hospital, Sheffield Teaching Hospitals NHS Trust, Sheffield, UK; and the Department of Neuroradiology, Royal Hallamshire Hospital, Sheffield Teaching Hospitals NHS Trust, Sheffield, UK.
All patients in the study were referred to the Sheffield Ataxia Centre, UK, and underwent extensive examination, including, where appropriate genetic testing using next-generation sequencing (NGS).
The team followed-up patients on a 6-month basis for reassessment and further investigations, as needed.
The team assessed a total of 1500 patients over 20 years. Twenty per cent of those patients had a family history of ataxia, with the remaining having sporadic ataxia.
The most common cause of sporadic ataxia was gluten ataxia at 25%. They found a genetic cause in 156, or 13% of sporadic cases, with alcohol excess causing 12% and a cerebellar variant of multiple system atrophy causing 11% of sporadic cases.
Using NGS, they obtained positive results in 32% of 146 patients tested. The most common ataxia they found was EA2. A total of 57% of all familial ataxias were supported by genetic diagnosis. The most common genetic ataxias were Friedreich's ataxia (22%), SCA6 (14%), EA2 (13%), SPG7 (10%) and mitochondrial disease (10%).
The diagnostic yield following attendance at the Sheffield Ataxia Centre was 63%. Immune-mediated ataxias are common. Advances in genetic testing have significantly improved the diagnostic yield of patients suspected of having a genetic ataxia.
Making a diagnosis of the cause of ataxia is essential due to potential therapeutic interventions for immune and some genetic ataxias.
Gluten is a culprit is 25% of sporadic ataxia cases, and clinicians should keep this in mind when diagnosing patients, as many of these cases can be reversed with a gluten-free diet.


The Inn above Tide is perfectly located for city exploration one day and wine country the next. Noted herein are a just a few spots for day touring to the Napa and Sonoma wine regions. With close to 400 wineries open to the public or by appointment in the greater region, the choices abound. Please allow the concierge staff to help create your personalized experience.


Remove the PCIe riser from slots 3 and 4.
Remove the internal host bus adapter card from the riser.
Hold the riser in one hand and use your other hand to carefully remove the card from slot 4 of the riser.
Disconnect the SAS cables and the super capacitor cable from the internal HBA card and place the card on an antistatic mat.
If you are replacing the internal HBA card, use a No. 2 Philips screwdriver to remove the special fitted bracket from the HBA card.
You will need to install the special fitted bracket on the replacement HBA card. Set aside the bracket and screws until you are ready to install the replacement HBA card.
Lift the super capacitor up to release the reclosable fasteners that secure it to the server's chassis [1, 2].
Note - If you are removing and replacing only the internal HBA card, you do not need to remove the HBA super capacitor. You can disconnect the HBA super capacitor cable from the internal HBA card and then remove the internal HBA card from the system.
Note - (Optional) Disconnect the data cable from the disk backplane to allow easy access to the super capacitor.
Disconnect the super capacitor cable from the super capacitor and place the super capacitor on an antistatic mat .
Carefully remove the SAS cables and super capacitor cable from the server by lifting them from the left-side cable trough.
See Remove the Internal HBA Cables.


text:
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	$stm = $conexao->prepare($sql);
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	$conexao = conexao::getInstance();
	$sql = 'SELECT 	idCurso, nomeCurso, nomeArtista, razaoParceiro, inicio, fim, total, status, foto FROM tab_cursos WHERE nomeCurso LIKE :nomeCurso OR nomeArtista LIKE :nomeArtista';
	$stm = $conexao->prepare($sql);
	$stm->bindValue(':nomeCurso', $termo.'%');
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redpajama_set_name: RedPajamaGithub


In 1543, a book that would forever change the world was published. That book was De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres). This would be outline a new model for our world. This new model would project that the sun was at the center of the known universe, not the earth. This theory was proposed by Nicolaus Copernicus.
Then around 1600 the first telescope (or looker as some called it) was invented. Lenses had been grinded and shaped for many years prior so that others could wear glasses. Galileo would continue his work to discover the true nature of the universe, further supporting Copernicus' original theory. For this work to continue the telescope had to be improved. It would be nearly a hundred years later for telescope to evolve to use reflection rather than refraction.
That was quite a different world four hundred years ago, than the one we live in now. Hours, days, and years would be spent discovering facts. Sometimes, it would take hundreds of years to discover the facts.
I wonder, when Copernicus first had a hunch that the sun might be at the center of our solar system, did he have ever ask "What does this mean for me? What does it mean for us?" Would he have taken the time to consider how the tides, seasons, weather changes, and even migration patterns are connected to the way in which our solar system works?
Yet, today we take those facts for granted. And hundreds of years after first proposing that the sun is the center of the known universe, we are able to reflect what it means for us.
We no longer spend years, days, or hours developing or discovering the facts. Thanks to the internet, we can usually discover them in a matter of minutes. Facts, information, and content of any kind are readily available.
Some of the youth I work with often have their cell phones out or they are easily within reach at any given moment. They have the facts of the world at their fingertips. A few in my group will even look up stories, dates, and people as we go through our lessons.
In ministry, this provides us with an opportunity unlike any other before it. We have the privilege to spend more time helping young people to discover what scripture means for them.
What does it mean for me? What does it mean for you? What does it mean for us?
Answering these questions has the potential for life changing transformation for young people in the church today.


text:
Private Equity Firms Seeing Increasing Scrutiny Under the False Claims Act–Emerging Trends
By Ethan Wright |
| January 05, 2022
Private equity firms are facing increasing scrutiny under the False Claims Act (FCA). Recently, the Massachusetts Attorney General announced the largest reported healthcare fraud settlement against a private equity firm, amounting to $25 million. The case was brought under the qui tam provisions of Massachusetts's FCA.
Earlier this year, the DOJ reported a $15.3 million settlement with medical testing company Alliance Family of Companies LLC, resolving claims brought under the FCA. Importantly, the DOJ also reported a $1.8 million settlement with Alliance Family's minority owner, the private equity firm Ancor Holdings LP. According to the DOJ, Ancor discovered Alliance Family's alleged fraud but took no actions to stop it.
In the past, private equity firms have agreed to settle FCA claims involving allegations of kickbacks and promoting drug-device systems for unapproved uses. The recent push towards holding private equity firms accountable through the FCA makes it worthwhile to review the ways in which private equity firms can face FCA liability.
Reaching Private Equity Firms Through the FCA
In order to hold private equity firms liable under the FCA, the government (or private relators suing under the FCA's qui tam provisions) must show that the firm was both aware of the illegal conduct and caused the false claims to be presented to the government.
For instance, in the Alliance Family case, the DOJ alleged that Ancor "learned of the kickbacks based on due diligence it performed prior to investing in Alliance and then caused false claims by allowing that conduct to continue once it entered into an agreement to manage Alliance."
In another case, a private equity firm agreed to settle FCA allegations premised on its subsidiary's continued illegal activity after being acquired by the firm.
The Need for Whistleblowers
Like any other type of fraud, healthcare fraud involving private equity firms can be extremely difficult to discern from the outside. As a result, individuals with inside knowledge are crucial to preventing the continued abuse of our healthcare system.
By bringing allegations of fraud through the FCA's qui tam provisions, private whistleblowers can receive between 15%-30% of any recovered sum, which includes triple damages. In addition, whistleblowers are protected by the FCA's anti-retaliation provisions.
At Price Armstrong, we have extensive experience litigating healthcare fraud cases under the False Claims Act. We work hard to protect whistleblowers every step of the way under the False Claims Act while maximizing their recovery. Contact us for a free initial consultation and review of your case.


text:
import { SuperheroUiPage } from './app.po';

describe('superhero-ui App', function() {
  let page: SuperheroUiPage;

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    page = new SuperheroUiPage();
  });

  it('should display message saying app works', () => {
    page.navigateTo();
    expect(page.getParagraphText()).toEqual('superhero-ui works!');
  });
});


text:
36 Million Americans Have Filed For Unemployment Benefits Since Coronavirus Lockdown Began
36 million Americans have filed for unemployment benefits since coronavirus lockdown began.
As America begins to reopen its economy, the government is re-examining its dependency on other nations with a focus on China, U.S. Labor Secretary Eugene Scalia stated Saturday.
Appearing on "Cavuto LIVE" with host Neil Cavuto, Scalia explained that a "reappraisal" could be key to understanding the United States' economic future.
"And earlier this week Neil, as you know, the president took action to prevent federal retiree funds from being invested in Chinese companies including Chinese munitions manufacturers," he remarked. "That was not in our national security interest. it wasn't in the interest of those retirees — some of whom are military — because of some risks that are presented by these Chinese companies."
"That's just one example of a reappraisal that I think will happen about our dependence on other countries –particularly China," Scalia noted.
President Donald Trump signs a trade agreement with Chinese Vice Premier Liu He, in the East Room of the White House, Wednesday, Jan. 15, 2020, in Washington.
In order to continue reversing course during an extraordinarily difficult time for the American people, Scalia said there needs to be an examination of additional measures to sustain American manufacturing — an aspect of the "America First" approach President Trump has touted during the course of his tenure in office.
"It was NAFTA more than anything else that prompted the president to run. USMCA has been one of his great achievements and that was about saving American manufacturing, saving American jobs, and I think [a] continued focus on that makes sense," Scalia added. "In terms of other measures, let's see what we need. Congress [and] the president acted so quickly in March. There's been a lot of stimulus in there, and the focus now from my perspective is on the reopening."
As of Thursday, the U.S. Bureau of Labor Statistics had reported 36.5 million Americans had filed for unemployment claims since the president declared a national emergency in mid-March.
As restaurants shutter for good and retail giants file for bankruptcy, the economic crisis has raised many questions about what the future holds. January's U.S.-China trade deal seems a distant memory now — another question that has hung in the air since the beginning of the pandemic.
Cavuto asked Scalia if the deal was "all but up in smoke right now" and if he had any concern about whether China's promises to America are now in doubt due to their dishonesty surrounding the virus's outbreak.
"Well, we'll need them to abide by their commitments, obviously," Scalia replied. "And, I think that assumes greater importance, not less, because of other misgivings that they've caused from how they handled the virus."
"But I think as we look forward, again, millions of Americans out of work — what we're focused on is making that temporary by safely reopening the economy right now, putting people back to work, and as we reopen across the country we're already seeing that," he concluded. "This has been so fluid, Neil, and we're finally seeing people getting back to work. It's a good sign."
Bollywood updates: Stunning Barfi actress is on fire, young sensation Kartik Aryan is ready for his new challenge to surpass Akshay. And let's have a sneak peak in life of Mira Rajput also.
Uddhav Thackeray has one month To Keep His Job
Doomsday is Very near Now
Deal of century aims to sell the Palestinian land, Jalali said on the occasion of World Quds Day
Pakistan's foreign minister Shah Mehmood Qureshi is blaming India for LAC confrontation
Bollywood superstar Amitabh Bachchan explained how he is doing Kaun Banega Crorepati 12 during The Lockdown
UN Covid-19 Human Rights Disaster Houston Food Bank Intel Corporation Israeli company Moovit Sherlyn Chopra sexy pics Iran.Pakistan Riddhima Kapoor Migrant Workers Problem Migrant workers Actress Debina Bonnerjee One Belt One Road(OBOR) Boris Johnson Hera Pheri 3 Movie
Beirut Explosion - Curse or Inco...
Kangana Ranaut : The Queen of Co...
What does India expect from Budg...
Biography of Israeli extremist N...
Akshara is going bounce back in ...
India Vs New Zealand World Test ...


12 December 2017: a friend recently discovered an image of Syrian American U.S. Army translator George Abraham Matook, a figure who plays a major role in chapter 3 of my forthcoming book, Between the Ottomans and the Entente.
Born in Boston, Massachusetts to Syrian parents, George Matook enlisted in 1918 and was sent to France to serve as an interpreter between a contingent of Arabic-speaking troops and the larger 101st Engineer Corps. I have written about Matook in a couple places: I introduced one of his letters home from the Western Front, preserved in a digital sourcebook, Cultural Exchange in a Time of Global Conflict (link) and in the collections of the Arab American National Museum in Dearborn, MI. Matook (and that letter) also appears in my 2016 article in the Journal of Global History (full text).
It is nice to put a face with the name and to include this photograph in the book, out next year with Oxford University Press.


A 6 year old girl's dream is instilling hope in those wearing a badge. Caityln has been a friend of the Massillon, Ohio Police Department for a couple of years now. With a dream to one day join the force, the little girl reminds the department each time she visits that they are making a positive impact.
Sgt. Brian Muntean joined another officer in fulfilling the little girl's birthday wish, which was to have real-life officers at her 6th birthday party. And this past weekend Officer Caityln got just that.
The little girl didn't sport a princess dress and a crown, but rather a police uniform complete with a badge. She also, was apparently on duty.
Muntean says it is inspiring to see someone so young with a dream to make a positive difference by way of becoming a police officer.


On Wednesday June 27 2018 I spoke to Lighter Footprints, a community group in eastern Melbourne, on home batteries. Here are the presentation slides. Here is a video recording of the presentation.
The presentation references a spreadsheet model for efficient homes with batteries. You can find it here.


text:
Comm Eye Health Vol. 28 No. 89 2015 pp 03 - 06. Published online 08 June 2015.
Diagnosing and managing microbial keratitis
Madan P Upadhyay
President: BP Eye Foundation, Kathmandu, Nepal. madanupadhyay@hotmail.com
Muthiah Srinivasan
Director and Chief of Cornea Services: Aravind Eye Hospital, Madurai, India.
John P Whitcher
Professor Emeritus: Francis I Proctor Foundation and Department of Ophthalmology, University of California, San Francisco, USA
Figure 1. Severe microbial keratitis due to a filamentary fungal infection. Extensive infiltrate, satellite lesions and a hypopyon are present. Credit: Matthew Burton
Infections of the cornea can lead to corneal opacity and blindness if not identified quickly and managed appropriately. The terms 'microbial keratitis', 'infective keratitis' and 'suppurative keratitis' are all used to describe suppurative infections of the cornea. In this issue we use the term microbial keratitis. These infections are characterised by the presence of white or yellowish infiltrates in the corneal stroma, with or without an overlaying corneal epithelial defect, and associated with signs of inflammation (Figure 1).
The common symptomatic complaints of patients with microbial keratitis are as follows (all with varying degrees of severity):
redness of the eye
blurring of vision
watering or discharge from the eye.
The aim of this article is to review both bacterial and fungal keratitis, with an emphasis on identification and management at the primary, secondary, and tertiary levels. Guidelines for referral will be suggested.
Figure 2. A bacterial ulcer. The eye is very red and inflamed; note the ring infiltrate in the cornea and a large hypopyon in the anterior chamber. Credit: Dr M Srinivasan/Aravind Eye Hospital
History taking
History taking is an important step in the management of corneal infection. If there has been an injury, ask when and where the injury was sustained, what the patient was doing at the time of injury, whether or not he or she sought help following the injury, and what treatment – including traditional eye medications – had been used. A past history of conjunctivitis may suggest that the infection is secondary to a conjunctival pathogen.
1 Visual acuity
Visual acuity should always be recorded in co-operative patients. If it is not possible to record the visual acuity of a child, for example, a note of this should be made. Vision should be recorded first in the unaffected eye, then in the affected eye; with or without glasses. This provides a useful guide to the prognosis and response to treatment. It is also important documentation in the event of medico-legal issues.
Figure 3. Fluorescein staining of the cornea. Epithelial defects appear bright green under blue light
2 Examination of the cornea
A torch with a good source of focused light and a loupe for magnification are essential. A slit lamp microscope, if available, is always helpful, but not absolutely essential. Another essential tool is fluorescein dye, either in a sterile strip or a sterile solution. Fluorescein stains any part of the cornea that has lost the epithelium, even due to a trivial injury, and appears brilliant green when viewed under blue light (Figure 3).
3 Clinical signs
When you examine the eye, look for the presence of the following signs and document them carefully in the clinical notes. This will be helpful when considering whether the eye is responding to treatment.
a. Eyelid abnormalities – such as trichiasis and lagophthalmos
b. Reduced corneal sensation
c. Conjunctival inflammation and discharge
d. Corneal epithelial defects (confirmed with fluorescein) – size and shape
e. Corneal inflammatory infiltrate – size and shape
f. Thinning or perforation of the cornea
g. Hypopyon.
Please refer to the article on clinical signs for clues about the likely cause of the infection.
For lesions >2mm in diameter, a corneal scrape sample should be collected for microbiological analysis whenever possible. Please refer to the article, "Taking a corneal scrape and making a diagnosis."
Management at primary level
Microbial keratitis is an ophthalmic emergency, which should be referred to the nearest secondary/district eye centre for proper management. The following are useful guidelines when referring the patient.
Do apply antibiotic drops or ointment.
Do instruct patients and/or their accompanying persons to apply drops frequently until patients arrive at the centre.
Do instruct patients and/or their accompanying persons to avoid traditional medicines.
Don't give systemic antibiotics; they are not helpful.
Don't use steroid drops and/or ointment; they can be dangerous.
Don't routinely patch the eye; it is not necessary.
Management at secondary level
More complete management of corneal infections begins at the secondary level of eye care where there is an ophthalmologist and/or an ophthalmic nurse/assistant, or a physician trained in managing common eye diseases. At the secondary level:
A corneal scraping should be taken, if diagnostic microbiology services are available (see page 8).
In some units, microbiology support may not be available. In these circumstances the choice of treatment is empirical, based on the clinical presentation (see page 6) and the known patterns of disease in the local area.
It should be remembered that, in tropical regions, bacterial and fungal infections occur with similar frequency.
The patient should be admitted to the hospital to ensure adequate treatment and frequent follow-up.
Ensure clear documentation of the clinical state, its progression and the specific treatments provided.
Specific initial treatment
1 No fungal elements seen on microscopy, or fungal keratitis is not suspected on clinical grounds (see page 6):
treat with either
Cefazolin 5% and gentamicin 1.4% eye drops, hourly, or
Ciprofloxacin or ofloxacin eye drops, hourly.
If it is not possible to administer hourly drops, a subconjunctival injection can be given.
2 Fungal elements seen on microscopy, or fungal keratitis is suspected on clinical grounds:
treat with natamycin 5% eye drops hourly, particularly if filamentary fungi are seen on microscopy. If yeasts (Candida) are suspected, use freshly reconstituted amphotericin-B 0.15% eye drops hourly.
Antibiotics may have a limited role to play in such cases and may occasionally be harmful. Clinical judgment correlated with laboratory tests are the best guide in such cases.
Adjunctive treatment
Atropine 1% or homatropine 2% could be used twice a day to dilate the pupil; this helps to prevent synechiae and relieve pain
Oral analgesics will help to minimise pain
Anti-glaucoma medication may be advisable if the intraocular pressure is high
Vitamin A supplements may be helpful, particularly in countries where vitamin A deficiency is prevalent.
Remember the five As: Antibiotic/antifungal, Atropine, Analgesics, Anti-glaucoma medications, and Vitamin A.
Subsequent management
Microbial keratitis patients should be admitted and examined daily (if possible with a slit lamp) so that their response to treatment can be evaluated and the frequency of antibiotics adjusted accordingly.
Reduce the frequency of antibiotic administration when the patient experiences symptomatic improvement (less tearing and photophobia, relief from pain and improvement in vision), and when the ulcer shows signs of improvement, including:
decrease in lid oedema
decrease in conjunctival chemosis and bulbar conjunctival injection
reduction in density of the infiltrate and area of epithelial ulceration
reduction of haziness of the perimeter of the ulcer and of the stromal infiltrate
decrease in inflammation, cells, fibrin, and level of hypopyon
dilatation of pupil.
If the patient is judged to be improving, the dose of antibiotics and/or antifungal drops should be reduced from hourly to 2-hourly, then 4-hourly over the next 2 weeks for bacterial ulcers. For fungal ulcers, treatment should be continued with three-hourly drops for at least three weeks, as late reactivation of infection can occur. Longer courses may be needed in more severe cases.
Note: In the case of bacterial infection, the inflammatory reaction may be enhanced by endotoxin release during the first 48 hours of treatment; however, definite progression at this stage is unusual and implies that either the organisms are resistant to therapy, or the patient is not instilling the drops as prescribed.1
Guidelines for referral to a tertiary centre
Immediate referral on presentation if:
the ulcer is in an only eye
the patient is a child
there is impending or actual perforation.
Following initial treatment, if cases of bacterial ulcer fail to show any improvement within 3 days, and fungal ulcers within a week, patients should be referred to a tertiary care centre.
Management of corneal ulcer at tertiary level
Many tertiary eye care centres have their own protocol for the management of corneal ulcer. The management suggested is based on a WHO recommendation with suitable modification according to local circumstances.2
Background, examination, and recording of findings
By the time patients have reached a tertiary centre, they will have travelled from one place to another (with attendant hassles) received several treatments, may have lost faith in eye care personnel, and may already have run out of money, (particularly in low-income countries). Considering this broader personal situation is important in the overall care of corneal ulcer patients.
A careful history of the development of the disease may point to the existence of an underlying predisposing condition such as diabetes mellitus, immunosuppression due to local or systemic steroids (or other immunosuppressants), dacryocystitis, or other ocular conditions. A full list of drugs used by the patient should be obtained to ensure that drugs which have not helped in the past are not repeated; this may also help to discover possible drug allergies. Findings should be carefully noted on a standard form.
A meticulous corneal scraping subjected to laboratory processing often provides a sound guideline to treatment (see page 8).
This provides patients with rest and adequate medication; they can also receive frequent follow-up, management of systemic problems, such as diabetes, and further surgical intervention, if warranted.
The initial treatment (see Tables 1 and 2) depends on the results of the corneal scrape and the local pattern of pathogens and antibiotic resistance.
If microscopy is negative, if it is not possible to perform a corneal scrape, if Gram-positive or Gram-negative bacteria are visualised, treat the patient with antibiotic eyedrops. Use either a combination of cefazolin 5% and gentamycin 1.4%, or fluoroquinolone monotherapy (e.g. ciprofloxacin 0.3% or ofloxacin 0.3%). To begin with, drops should be given hourly for 2 days and then tapered, based on response.
If microscopy reveals fungal hyphae, topical natamycin 5% or amphotericin-B 0.15% should be used hourly for a week and then tapered.
If the ulcer seems to respond well to treatment, continue therapy as before for 2 weeks for a bacterial ulcer and at least 3 weeks for a fungal ulcer.
If the response is poor and the culture shows growth of a bacterial organism, the choice of antibiotic is guided by the sensitivity reports.
Natamycin 5% suspension is recommended for treatment of most cases of filamentous fungal keratitis, particularly those caused by Fusarium sp. Natamycin 5% was found to be more effective than voriconazole in a recent clinical trial.
Most clinical and experimental evidence suggests that topical amphotericin-B (0.15 – 0.5%) is the most efficacious agent available to treat yeast keratitis. Amphotericin-B is also effective for fungal keratitis caused by Aspergillus sp.
Oral anti-fungal agents may be considered as an adjunctive therapy in more severe fungal keratitis with deep corneal or intraocular involvement. Oral fluconazole (200–400 mg/day) has been used successfully for severe keratitis caused by yeasts. Oral itraconazole (200 mg/day) has broad-spectrum activity against all Aspergillus sp. and Candida but has variable activity against Fusarium sp. More recently oral voriconazole has been used in cases of keratitis due to filamentary fungus.
Other agents such as polyhexamethylene biguanide (PHMB) 0.02%, chlorhexidine 0.02%, povidone iodine 1.5 – 5% and silver sulfadiazine 1% have been reported to possess variable antifungal activity and may be used if other drugs are not available.
Fungal infection of the deep corneal stroma may not respond to topical antifungal therapy because of poor penetration of these agents in the presence of an intact epithelium. It has been reported that a 5 mm epithelial debridement (as a diagnostic scraping or therapeutic procedure) greatly enhances the penetration of antifungal drugs. Animal experiments indicate that frequent topical application (every five minutes) for an hour can readily achieve therapeutic level.
Table 1. Preparation of fortified antibiotic eye drops
Antibiotic
Final concentration
Cefazolin/cefuroxime Add 10 ml sterile water to 500 mg cefazolin powder; mix and use as topical drops. Shelf life: 5 days 50 mg/ml (5%)
Gentamicin (tobramycin) Add 2 ml parenteral gentamicin (40 mg/ml) to a 5 ml bottle of commercial ophthalmic gentamicin (3 mg/ml) ) 14 mg/ml (1.4%
Penicillin G Add 10 ml of artificial tears to a 1 million unit vial of Penicillin G powder; mix and decant into empty artificial tear bottle or xylocaine vials (30 ml) 100,000 units/ml
Vancomycin Add 10 ml sterile water to a 500 mg vial of vancomycin powder; mix, add sterile cap and use immediately &50 mg/ml (5%)
Amikacin Add 2 ml of parenteral amikacin containing 200 mg of the antibiotic to 8 ml artificial tears or sterile water in a sterile empty vial. 20 mg/ml (2%)
Although a large number of antifungal drugs are available for systemic mycoses, only a few are effective for treatment of corneal ulcers. The commonly recommended drugs are listed in Table 2.
Table 2. Commonly recommended antifungal drugs
Amphotericin-B 0.15–0.5% drops IV infusion
Natamycin 5% drops Not available
Econazole 2% drops Not available
Voriconazole 1% drops Oral tablets 100–200 mg/day
Figure 4. Subtotal fungal ulcer. Credit: Dr Whitcher/UCSF
The range of surgical interventions available for management of corneal ulcers can include debridement, corneal biopsy, tissue adhesives, conjunctival flap, tarsorraphy, or therapeutic corneal graft. Evisceration of the eye is performed for severe pain, panophthalmitis, or lifethreatening complications.
Tarsorrhaphy
This is an old surgical technique that is still very useful today. Tarsorrhaphy often leads to rapid resolution of persistent epithelial defects, whatever the underlying cause. Tarsorrhapy is effective in promoting healing in microbial keratitis caused by fungal and bacterial infections, provided the ulcer has been sterilised by effective antibacterial and/or antifungal treatment. It can be difficult to instil drops and to see the cornea following central tarsorrhaphy, so it is vital to ensure that the infection is under control before closing the eyelids. See page 10 for a description of two useful tarsorrhaphy techniques.
Conjunctival flap
The principle of this technique is to promote healing of a corneal lesion by providing adequate nutrition via the conjunctival blood vessels. The flap could be of three types:
A total flap covering the entire cornea, called Gunderson's flap.
A pedicle (racquet) flap. This carries its own blood supply from the limbus and is useful for ulcers near the limbus.
A bucket handle flap. This carries its blood supply from both ends of the flap and may be less likely to retract. It is more useful for central corneal ulcers.
This procedure can be performed under local anaesthesia. Harvesting adequate bulbar conjunctiva in eyes which have had previous surgery may be difficult. The flap should be as thin as possible, with minimal adherent subconjunctival tissue. Following removal of any remaining corneal epithelium, the flap should be sutured to the cornea with 10-0 nylon sutures.
The conjunctival flap promotes healing by vascularisation. It is particularly useful in patients with impending perforation, when it may preserve the globe and allow subsequent corneal grafting. However, a flap may limit the penetration of topical antibiotics, so it should only be performed once the ulcer has been sterilised and the infection brought under control.
Management of microbial keratitis remains a major challenge worldwide, more so in low- and middle-income countries with inadequate health care resources. Although the outcome of treatment has improved significantly, many patients continue to deteriorate in spite of the best treatment that can be offered. The continued emergence of strains of microorganisms that are resistant to an ever-expanding range of antimicrobials poses an additional challenge. Further research related to prevention of microbial keratitis and enhancing host resistance are two worthwhile goals to pursue. Large-scale public education programmes to alert those at risk of microbial keratitis, and to encourage earlier presentation, should be undertaken. Coupled with this, education of practitioners, general physicians, and other health workers, as well as general ophthalmologists, will go a long way towards ensuring correct diagnosis, appropriate treatment and timely referral before extensive damage to the cornea occurs. Several studies have indicated that the best way to prevent corneal ulcers in low- and middle-income countries is to treat corneal abrasions in the primary care setting within 48 hours of the injury.3-6 This could be adopted in any population and is cost-effective for both health providers and the patient.
1 Allan BD, Dart JK. Strategies for the management of microbial keratitis. Br J Ophthalmol 1995;79 777–786.
2 Guidelines for the management of corneal ulcer at primary, secondary and tertiary health care facilities. World Health Organization, South East Asia Regional Office; 2004.
3 Upadhyay M, Karmacharya S, Koirala S, et al. The Bhaktapur Eye Study: ocular trauma and antibiotic prophylaxis for the prevention of corneal ulceration in Nepal. Br J Ophthalmol 2001;85 388–392.
4 Srinivasan S, Upadhyay MP, Priyadarsini B, Mahalakshmi, John P Whitcher. Corneal ulceration in south-east Asia III: prevention of fungal keratitis at the village level in South India using topical antibiotics. Br J Ophthalmol 2006;90 1472–1475.
5 Getshen K, Srinivasan M, Upadhyay MP, et al. Corneal ulceration in south-east Asia I: a model for the prevention of bacterial ulcers at the village level in rural Bhutan. Br J Ophthalmol 2006;90 276–278.
6 Maung N, Thant CC, Srinivasan M, et al. Corneal ulceration in south-east Asia II: a strategy for prevention of fungal keratitis at the village level in Myanmar. Br J Ophthalmol 2006;90 968–970.


The parish of St. Lucy is the most northern parish on the island of Barbados. Up on the north-eastern coast of this parish, exists a simple, yet charming part of the island, known as River Bay. It is an expansive cove-like area with river pools dotted over what can only be described as a very rocky part of the island. Stunning and scenic, to say the least, it may be considered by some to be a bit off the beaten track, however if one is a lover of wide open spaces and clean, fresh air, then it is well worth the journey. River Bay is a very popular stop with locals on weekends and public holidays. One may see as many as ten (10) Transport Board buses, plus mini-buses and private vehicles parked at this destination on some weekends and most public holidays. It is frequented during the week as well; however the numbers are likely to be much smaller unless it is during a vacation period when schools are out, such as Christmas, Easter or the long summer holiday.
Centuries ago, back in 1780, two (2) foreign explorers came upon something special, the likes of which have never been found on any other part of Barbados. The Animal Flower Cave is located at North Point, in the parish of St. Lucy and is located underground below the cliff face and is the only accessible sea cove on the island of Barbados. The coral floor of the Cave is estimated to be some five hundred thousand (500,000) years old and some level of credence can be given to this information as the dating of these elements was undertaken by a German Geographical Institute. In addition, this cave, which was previously below sea level, now stands at some six (6) ft above the high tide mark and therefore it is apparent that some geographical shifts and changes are taking place over time. Factually, the island of Barbados has been rising an inch every 1000 years.
As you approach the end of the ABC Highway on the island of Barbados, this church will quickly come into view. It is positioned on the northern side of the Sir Theodore Brancker (Barbadian Politian) Roundabout in Fairfield, in the parish of St. Lucy. St. Lucy Parish Church was one of the original six (6) parish churches constructed on the island when it was first developed under the administration of the governor at the time, Sir William Tufton. Incidentally, the parish of St. Lucy in Barbados is the only parish that is named after a female patron saint; the parish also claims the honour of being the birthplace of Barbados' first Prime Minister, the Rt. Hon. Errol Walton Barrow.
A look through our list of attractions throughout the parish of St. Lucy will give you a better idea of what this parish has to offer.


Susan Leal is passionate about drawing attention to the global looming water crises. She regularly speaks to audiences across the spectrum, from private industry to public forums to utilities, about real-world answers she and others in the field have implemented to address local and regional water and wastewater challenges.
Please contact us if you are interested in having Susan speak at an upcoming event.


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Why Don't They Just QUIT? (90-min)DVD Roundtable Discussion: What Families And Friends Need To Know About Addiction And Recovery.


Trade shows are very busy events, with thousands of visitors trying to gain the attention of the exhibitors. To achieve the most out of your visit you need to get organised. Read our top tips, and download our handy checklist, to help you prepare for a successful trade show visit.
Be specific about what you want to achieve from the trade show and what your end goal is. What information, products or services do you need to source?
For instance, if you are a designer visiting a sourcing show such as Make it British Live! make sure you've thought about your range plan in advance and you know what sort of manufacturers or products you are looking for.
If you can, take a look at the event website to see if they include a floor plan or list of exhibitors to help you plan your visit.
If you are attending Make it British Live! you'll find our exhibitor list here.
If there is an exhibitor list take the time to do your research on them to help you create a checklist of exhibitors that you want to target during your visit. If possible also email some of them in advance to make an appointment at the show.
From your goals and exhibitor research prepare your questions in advance so you don't forget what to ask when you meet them. And take a notebook along to write down the answers.
Trying to explain your ideas verbally can be difficult. If you can take samples, swatches or sketches with you then it can really help you communicate with the exhibitors.
If an exhibitor has a queue of people they are trying to attend to, don't make it difficult for them by taking up too much of their time. Get the essential information you need, making a note of who they are, their contact details, stand number and what they do. Then you can either follow-up after the show, or make a return visit to their stand towards the end of the day, when trade shows tend to be a lot less busy than when they first open.
Finally, don't forget to take these things with you!
Download your trade show preparation checklist here.