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Dost's Journey into the Heart of UP - 2021
A Monitoring and Assessment Perspective
By Rashmi Sharma and Aman Arora
We at Dost have always believed in one simple mission - to turn every home into a nurturing place for a child to learn, develop and thrive. Our program prides itself on reaching parents across the vast technological divide present in the country. We make responsive caregiving accessible to parents across broad socio-economic backgrounds. Since 2017, with our simple phone-cast products, we have reached these caregivers without accessibility barriers like the internet, smartphones, or even digital literacy.
It is known that the last couple of years have been years of unprecedented adversities. In India, too, the pandemic struck fatal blows to countless families- thousands of people lost their loved ones, unemployment skyrocketed, and the economy shattered. The year also saw multiple nationwide lockdowns where everyone was restricted within their homes and schools, and Anganwadi Centers across the country were shut down. As a result, there came a vast learning gap for most children, the worst affected being families from marginalized and vulnerable communities.
At this critical juncture, we partnered with UNICEF to expand our program under the title 'Dular' in the biggest state of India, Uttar Pradesh. The program went live in two districts of UP- Chitrakoot and Banda- enabling thousands of new caregivers across these two districts to hear our phone call-based ECD program.
Here, we expand on the monitoring and assessment studies we undertook to understand the users and our program outcomes.
A. What do we know about these caregivers? (Demography)
We conducted various studies to gather demographic information about our users.
We conducted an in-person demographic survey on 100 users to understand their occupations, educational levels, family structures, phone access, etc. Through the survey, we noticed that most of our target households rely on farming (60%) and manual labor (20%) to earn their livelihoods. And owing to poor infrastructure, 60% of the primary caregivers surveyed had not studied beyond Class X, and 12% were illiterate. To understand the family structure of our beneficiaries, we also collected data on no. of children below the ages of 6- 50% of the respondents have 2 or more children (with an average of 2 children per household) below 6 years. Furthermore, 65% of primary caregivers reported using the internet on phones, However, our on-field observations suggest that they are not active internet users and do not consistently access the internet on their phones.
Dular's predominant target caregivers have always been the primary caregivers - those primarily responsible for caring for the child. We noticed that 80% of our respondents were mothers, the child's primary caregivers. All of them were homemakers. We also found that around 20% of these mothers did not have access to personal phones. Phones are usually present with the fathers, who often go out to work. Thus, mothers keen on listening to our content do not get to listen to our calls.
B. Methods of intervention
Throughout the year, we implemented different methods of intervention. Starting with simple field visits where we talked to a few caregivers to design specific quantitative and qualitative surveys over time. These studies helped us to connect with the caregivers and understand their progress in knowledge, mindset and behavior level changes. The variety in our methods ensured that we gained a comprehensive understanding of user journeys and their everyday experiences.
Touch Tone Response Survey (TTR survey): Short tools administered at different points in the caregiver's journey into the program- baseline, midline and endline- over phone calls to measure attitude and behavior. The users received pre-recorded questions and had to choose appropriate responses from the options.
Prompts: Single and straightforward questions (quiz-like) accompany the core content messages to measure caregivers' outcomes and feedback. 25,746 users have received one or more prompts, with an encouraging participation rate.
Phone survey: A pre-post mixed-method study was conducted with caregivers who registered for the pilot launched in Feb 2021. This allowed us to map overtime changes in caregivers' awareness and adoption levels. The post-quant survey was administered with 36 caregivers, given a dropout rate of 60% since the pre-survey.
In-person survey: This was a separate tool administered in person with a stratified random sample of 100 caregivers across the two districts of Banda and Chitrakoot in December 2021. The survey focused on understanding parental knowledge, attitude, and behavior.
Observational study: We collected 40 videos of the parent interacting with their child using a picture book. The Anganwadi workers facilitated this.
C. Initial Awareness Levels (Baseline)
We analyzed the caregivers' initial awareness, mindsets, and behaviors through pre-post methods. The initial focus of the study was to collect product feedback, which was later expanded to collect caregiver knowledge, mindset and behavioral level information also.
As most of the users were from remote and rural settings, we found out that there was already some evidence of free play - 70% agreed that children learned through play and reported that their children play with household items. However, when asked about 'structured play', around 40% of the caregivers (45% in Birth-3 yrs & 34% in 3-6 yrs) reported not playing with children regularly; 56% reported having no specific playtime or no playtime at all. One possible inference can be that these caregivers engage their children through household chores but no other recreations.
We also found evidence of caregivers in the Birth-3 yrs program who practiced but did not understand the importance of talk-touch-play - 20% reported not talking to their infant at all. Similarly, 33% were unsure if singing or talking to a very young child helps their development.
Additionally, we observed weak KAB (knowledge, attitude, and behavioral) evidence of caregivers in using Art for the child's learning and social-emotional development. 61% of caregivers (3-6 yrs) agreed that 'creative activities are only good as a hobby', and 46% of users agreed that 'too much time spent on activities like drawing, singing, and dancing makes the child develop slowly.'
This conventional mentality was also seen around the socio-emotional aspects- 77% of caregivers agreed that children do not understand or get affected by parents fighting or using abuse. However, many caregivers (70% ) reported knowing of 'such stress, which can affect the child's whole life'. While measuring Parental Impact, we realized that it is crucial to address parental stress. We saw an alarming 67% of caregivers reporting that most of their stress comes from being parents.
D. Our Findings across Methods
We employed subsequent phases of assessment once the caregivers had listened to most of our content to investigate if there were any significant and sustainable improvements in their knowledge, awareness, and adoption levels.
Through our methods, we found out that after listening to the calls, parents recognized the importance of the home environment in a child's life - 65% of caregivers (vs. 14% in pre-study) agreed that the home environment is not just limited to caregiving, but is also conducive to learning. Furthermore, around 86% of caregivers reported that home environment could help the child to learn something new (see chart below for program-wise responses).
Birth to Three Years Three to Six Years
% Caregivers who report that the household is adequate for the child to learn something new
*based on responses to in-built product quizzes - endline prompts
81% of the caregivers in the post-study (vs. 40% in pre) agreed that young children (birth-3 yrs) need parents to actively engage them through 'talk, touch, and play'. In the qualitative survey, most caregivers reported becoming aware of the 'home environment as the first place of learning' and the 'primary caregiver as their first teacher'.
We also observed positive behavioral shifts in parental management of tantrums post-intervention. Only 6% of caregivers by midline (vs. 47% in the baseline) reported to 'always scolding/threatening the child when child gets stubborn.'
Further, we noticed a shift in perspective for art as a learning medium. In Qual Post-study, most caregivers reported that they saw value in their child practicing non-academic activities such as drawing, singing, and playing. Caregivers also linked art-based activities with brain development- one caregiver reported, "Trying out new things leads to mental development."
Overall, around 70% of caregivers, through multiple surveys, reported that they learned something new and helpful from the program. Parents (75%) also reported adopting these new learnings. A breakdown of themes mentioned by parents can be found in the chart below:
67% Caregivers reported knowledge that 0-6 yrs is when most of the development happens*
*Open-ended question asked in Endline via Phone interviews - 36 (as part of pre-post)
E. Parent Testimonials
A father of a 5 yr old from Chitrakoot UP says:
"I used to be busy with my work and hardly used to spend time with my child, but after listening to the 'Dulaar Program' I got to know the importance of spending time with my child. Now I ensure that I take some time out from my schedule daily to talk and play with my child. It has become a routine now"
2. A mother of a 2.5 years old child from Chitrakoot UP says:
"Parents can teach whatever they want to the child with the help of Dulaar activities like teaching through play, identifying relations, how to speak to people, and color identification. Additionally, how parents behave with their child is how the child turns out as an adult".
F. The Way Forward
This year, we at Dost have started moving ahead of the parent-reported data. Through a well-established research method, we collected videos that are now going through observational analysis. We are also developing child-level indicators to understand the program's impact on the caregiver's children. After creating a special place in the hearts of Banda and Chitrakoot's parents, Dulaar is all set to launch in 9 aspirational districts, enabling us to reach thousands of new caregivers. As you can see, while we have come a long way, we have only just begun.
How I met friends whom I work with …
A deep dive into caregiver behavior through a gender lens


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Q: How to set which browser to use in a QTextBrowser link? I am using PyQt4's QTextBroswer to display a html link.
Whenever users click on the link, a browser will be used to open the internet page.
My question is, is there a way to set so that our own prefered browser is used to open the url page instead of the preset one?
Thanks in advance.

A: QTextBrowser provides an actual browser. If you want to open a document in the user's desktop environment-specified browser, then you'd use QDesktopServices::openUrl.
You can use QProcess to start random programs:
QObject *parent;
...
QString program = "/path/to/browser";
QStringList arguments;
arguments << "--your-browser-url-option-if-any" << "http://www.example.com";

QProcess *myProcess = new QProcess(parent);
myProcess->start(program, arguments);

A: I am not sure if this will help you or this is what you were looking for. I found that by setting the openExternalLinks flag to True I was able to get the link to open in Firefox.
I just called the setOpenExternalLinks method with True as argument.
This method is only for using the default browser and won't let you to actually set the browser.

redpajama_set_name: RedPajamaStackExchange


text:
\section{Introduction}
\label{sec:Introduction}

Liquid crystals (LCs) are phases of matter in which the anisotropy of the particles determines under specific conditions a partial spontaneous breaking of the spatial symmetries of the system, thus manifesting features in between the crystalline solid and the isotropic liquid phase. The notion that entropic effects alone are sufficient to drive the self-assembly of ordered liquid crystal phases is well established in colloid science \cite{onsager, israelachvili, forsyth, flory, frenkel2}. Model systems of hard particles constitute the natural choice to describe the phase and aggregation behavior of most colloidal systems, as the main interactions established between their particles have a repulsive, steric origin. As a consequence, a hard-particle fluid does not have internal energy and minimizing its free energy is equivalent to maximizing its entropy.

In his seminal work, Onsager showed that mere hard-core repulsions between infinitely thin rigid cylinders are able to determine an entropy-driven phase transition from the isotropic to the nematic phase, and hence the existence of a spontaneous orientational order \cite{onsager}. The evolution of simulation techniques in the past decades allowed to investigate the more realistic case of rods with finite size, showing that by varying the length-to-diameter ratio one- (smectic), two- (columnar) and three- (crystal) dimensional translational ordered phases can be encountered \cite{stroobants1,stroobants2}. Further more accurate studies showed that for a monodisperse system of both aligned \cite{veerman} and freely rotating \cite{bolhuis} hard spherocylinders the columnar phase happens to be metastable with respect to the smectic phase for each value of the length-to-diameter ratio. The complexity of the phase behavior of linear particles becomes even more pronounced by proceeding from monodisperse systems to mixtures \cite{stroobants,cui,bates,martinez,varga}. In particular, size polydispersity introduces a sensible change in the phase behavior of rod-like particles as their packing is not as effective as that of monodisperse rods. In fact, it was observed that in a system of hard spherocylinders the formation of smectic layers can be inhibited by introducing a length bidispersity, in such a way that the columnar phase can become thermodynamically stable \cite{stroobants,cui}. Entropy-driven columnar phase transitions have been observed in monodisperse systems of disc-like particles, such as cut spheres or oblate spherocylinders \cite{frenkel3,veerman2,cuetos,filion}. As far as rod-like particles are concerned, theoretical studies indicated that the columnar order can be observed not only in bidisperse mixtures, but also in more realistic polydisperse systems of parallel cylinders \cite{bohle}. Polydispersity is not the only element which favors the stabilization of the columnar phase in a system of rods, as was shown in Ref. \cite{wensink} where a monodisperse system of soft-core rods was considered. On the other hand, the effect of rod flexibility in stabilizing the columnar phase is still under debate \cite{hentschke,sear,cinacchi,grelet2}.

With the improvement in understanding and describing static and thermodynamic properties of LCs, the interest towards the dynamics correspondingly increased. In particular, most of the studies in this direction were devoted to analyze the anisotropy of the diffusion by the measurement of the self-diffusion coefficients in different mesophases \cite{hess,lowen,bates2,cifelli}. For lyotropic LCs these results found good overall agreement with experiments based on techniques such as fluorescence recovery after photobleaching (FRAP) \cite{bu,vbruggen1,vbruggen2,cush}. On the other hand, only few studies focused on the analysis of the dynamical phenomena at the single-particle level, where fluorescence microscopy was applied to investigate the LC phases in colloidal suspensions of \textit{fd} virus \cite{lettinga2,lettinga}. This approach allowed to observe for the first time the mechanism of interlayer diffusion, or permeation, which characterizes the dynamics of the system in the smectic phase \cite{lettinga}. In fact, the layered structure of smectic LCs, which determines an effective periodic mean-field potential, influences the motion in the direction perpendicular to the smectic layers with the appearance of jumps of the order of the rod length. As a result of this quasi-quantized diffusion, at intermediate time intervals one can distinguish between ``slow'' particles, which rattle around the center of a column, and ``fast'' particles, which jump to another column. This heterogeneous dynamics accounts for deviations from Gaussianity in the diffusion, a phenomenon which is also well known in homogeneous complex fluids such as supercooled liquids \cite{kob,gray} and gels \cite{puertas,gao}. In the light of these results, a theoretical approach based on dynamic density functional theory using the second virial approximation focused on the role played by the local fluid structure of the system, which competes with the permanent barriers due to the smectic structure, thus increasing even more the analogies with fluids close to a dynamical arrest transition \cite{bier,grelet}. Simulations on aligned \cite{matena} and freely rotating \cite{patti,patti2} hard spherocylinders confirmed qualitatively both these studies and pointed out the effect of dynamical heterogeneities on the structural relaxation of the system, which deviates from the exponential decay expected for simple fluids. Furthermore, in Refs. \cite{patti,patti2} it was shown that the heterogeneous dynamics in the smectic phase of hard spherocylinders is tightly related to cooperative motion of particles through the smectic layers.

Following this line of research and motivated by a recent experiment on \textit{fd} virus \cite{pouget}, we investigate in this paper the dynamics of a binary mixture of rod-like particles which exhibits a stable columnar liquid crystal phase. Using Monte Carlo (MC) simulations we are able to study for the first time the dynamical heterogeneities which arise from the columnar structure and their effect on the diffusion and on the long-time structural relaxation of the system. Furthermore, we measure the height of the inter-column energetic barriers and compare our results with the simulation data available for the smectic phase \cite{matena,patti,patti2}. Conventional MC dynamics has been extensively applied to study the origin of non-exponential relaxation of glass-forming liquids \cite{doliwa,doliwa2,berthier,brambilla,berthier2}. MC and Molecular Dynamics (MD) simulations of Lennard-Jones fluids \cite{huitema} showed that the particle dynamics at large time scales are the same, but are different at small time scales, as the stochastic motion of particles cannot be detected by the deterministic approach of MD simulations.

The paper is organized as follows. In section II we introduce the model, the simulation details and the physical properties which were measured in order to describe the dynamics of the system. The results of these measurements, which confirm the presence of dynamical heterogeneities also in the columnar phase and are in general agreement with the observations in the smectic phase, are discussed in section III, whereas in section IV we illustrate our conclusions.

\section{Model and Simulations}
\label{sec:Model and Simulations}

We study a system containing $N=1600$ perfectly aligned hard spherocylinders with aspect ratio $L^{*}=L/D$, where $L$ and $D$ are, respectively, the length and diameter of a cylindrical body capped by two hemispheres with diameter $D$. The phase diagram of a monodisperse system containing such rod-like particles shows stable nematic, smectic, and crystal phases, but lacks a stable columnar phase in the range $0\leq L^{*}< \infty$ \cite{veerman}. Stroobants studied the phase behavior of bidisperse systems of hard rods and found that the bidispersity can favor and stabilize columnar order over smectic order \cite{stroobants}. Therefore, to prevent the formation of smectic layers, we investigate a binary mixture of hard spherocylinders with the same diameter $D$ (used as our unit of length), but different lengths $L^{*}_{1}$ and $L^{*}_{2}$, with $L^{*}_{1}>L^{*}_{2}$. In this model, the rotational degrees of freedom are frozen out and hence the particles are forced to be aligned along a common nematic director, oriented along the \textit{z} axis. The relative concentration of the two species is set in such a way that the binary mixture is kept at its equivalence point, where the volume fractions of each component are the same. The phase diagram at fixed $L^{*}_{2}=1.0$ displays a region of stability of the columnar phase which increases with $L^{*}_{1}$ and disappears at $L^{*}_{1} \leq 1.6$, where a nematic-smectic transition is observed \cite{stroobants}. Here we study a columnar ordered binary mixture of rods with $L^{*}_{1}=2.1$ and $L^{*}_{2}=1.0$, and relative concentrations $x_{1}=N_{1}/N=0.375$ and $x_{2}=N_{2}/N=0.625$, respectively. For lower pressures, this columnar phase transforms into a nematic phase, while for higher pressures it freezes into a crystal phase.

We performed standard MC simulations in a rectangular box of volume $V$ with periodic boundary conditions. To equilibrate the columnar phase, we performed runs in the isobaric-isothermal (\textit{NPT}) ensemble, where the particle moves were accepted according to the Metropolis algorithm \cite{frenkel}, that is if no particle overlap was detected. Each MC cycle consisted of \textit{N} attempts to displace a randomly selected particle, plus an attempt to modify the box volume with independent changes of the three box sides. The system was considered to be in equilibrium when the volume reached a stationary value within the statistical fluctuations. We run simulations at several reduced pressures $P^{*}=\beta PD^{3}$, where $\beta = 1/k_{B}T$, $k_{B}$ is the Boltzmann's constant and \textit{T} the absolute temperature. In particular, we equilibrated a nematic phase at $P^{*}=2.5$ (packing fraction $\eta= N(x_1 v_1+x_2 v_2)/V=0.470$ with $v_i$ ($i=1,2$) the single particle volume) which is very close to the nematic-columnar transition, and three different columnar phases at $P^{*}=3.0$ ($\eta=0.535$), $3.5$ ($\eta=0.563$) and $4.0$ ($\eta=0.580$). In all these cases, our starting configuration consisted of a highly packed columnar structure with the rods randomly located along the \textit{z} direction, and hexagonally ordered in the \textit{xy} plane. The minimum number of MC cycles needed for an equilibration run was $5\times10^{5}$, and was followed by a production run of $2\times10^{6}$ MC cycles in the canonical (\textit{NVT}) ensemble to simulate the relaxation dynamics and evaluate all the physical properties of interest. In this case, the box volume was kept fixed to prevent unphysical collective moves which do not mimic the Brownian dynamics of the particles properly. It was proved that in rod suspensions the contribution of hydrodynamics can at first approximation be neglected with respect to steric effects, which result in excluded volume interactions \cite{pryamitsyn}. Under these conditions, the MC approach offers an important tool to study the dynamics of colloids, since, in spite of its intrinsically non-dynamical nature, it is able to reproduce the Brownian diffusion typical of such kind of systems \cite{sanz}. To pursue this goal, one must set a small enough maximum MC displacement, typically of the order of one tenth of the shortest dimension of the particle. The optimal value of the mean particle displacement is strictly linked to the acceptance rate and hence to the CPU time per simulation run. If the displacement is chosen too small, the system would need longer runs to properly explore the configurational space. The same effect is expected with too big displacements, as most of the particle moves would cause overlaps and therefore would be rejected. However, any reasonable and  convenient choice of the average step size should not affect the dynamics at long time scales. We tested that, apart from an overall scaling, this was the case. The maximum displacement was fixed to give an acceptance rate of roughly 50\% per move. Furthermore, to take into account the non-spherical shape of the particles, the maximum MC displacement was set in such a way that at short times it reproduces the anisotropic diffusion of a single colloidal rod. More specifically, this means that the ratio between the maximum MC displacement in the $xy$ plane $\Delta x_{max}=\Delta y_{max}$ and in the $z$ direction $\Delta z_{max}$ must be set as

\begin{equation}
\frac{\Delta x_{max}}{\Delta z_{max}}=\frac{\Delta y_{max}}{\Delta z_{max}}=\sqrt{\frac{D_{\perp}}{D_{\parallel}}},
\label{eq0}
\end{equation}
where we denoted with $D_{\perp}$ and $D_{\parallel}$ the short-time self-diffusion coefficients of the rod in the direction parallel and perpendicular to its long axis, respectively. To give an estimate for the ratio $D_{\perp}/D_{\parallel}$, which solely depends on the geometry of the particle, we referred to the semi-empirical expression derived in Ref. \cite{tirado}. In that work, the authors used a numerical approach to evaluate the translational self-diffusion coefficients of a cylindrical particle for different values of the length-to-diameter ratio $p$, finding good overall agreement with experimental data in the range $2<p<30$ \cite{tirado1}. A least-square quadratic fitting in $p^{-1}$ of the data allowed the authors to give an expression for the transverse and longitudinal self-diffusion coefficients as functions of the parameter $p$. Since here we consider spherocylinders, we evaluated the ratio $D_{\perp}/D_{\parallel}$ by setting $p=(L+D)/D$, arguing that possible deviations given by the non-cylindrical shape of the particles were irrelevant. According to the above-mentioned expression, the ratio between the maximum MC displacement perpendicular and parallel to the $z$ axis was set to $0.92$ for particles of species $1$ and $0.94$ for those of species $2$. Moreover, since the transverse section of the particles is the same for the two species, we set the same maximum MC displacement along the $z$ axis for the two components. Once the short-time self-diffusion coefficients are known, it is possible to introduce a time scale defined by $\tau=D^{2}/D_{tr}$, where the total translational diffusion coefficient $D_{tr}=(\langle D_{\parallel} \rangle +2 \langle D_{\perp} \rangle)/3$ is evaluated in terms of the longitudinal and transverse short-time diffusion coefficients averaged over the two species \cite{matena}.

In order to analyze the heterogeneous diffusion and the structural relaxation of the system, the following physical properties were calculated: (i) the transverse mean-field potential, (ii) the self-part of the van Hove function (SVHF), (iii) the distinct-part of the van Hove function (DVHF), (iv) the mean square displacement (MSD), (v) the non-Gaussian parameter (NGP) and (vi) the self-part of the intermediate scattering function (SISF).

\textit{\mdseries{Transverse mean-field potential.}} In a liquid crystal phase characterized by columnar order the translational invariance is spontaneously broken in the plane perpendicular to the nematic director. This gives rise to a non homogeneous (relative) probability $\pi_{i}(x,y)$ of finding a particle of species $i=1,2$ at position $(x,y)$ in the plane perpendicular to the nematic director. The effective energetic barrier which tends to confine the particle inside a column is given by the mean-field potential $U_{i}(x,y)$, defined as \cite{lettinga}

\begin{equation}
\pi_{i}(x,y) \propto \exp \left[ -\frac{U_{i}(x,y)}{k_{B} T} \right],
\label{eq1}
\end{equation}
where the proportionality constant is chosen in such a way that the minima of the potential is set to zero.

\textit{\mdseries{Self-part of the van Hove function.}} The heterogeneous dynamics and hopping-type inter-column diffusion can be quantitatively described by the SVHF \cite{vanhove}

\begin{equation}
 G_{s}(\mathbf{r},t) = \frac{1}{N} \left\langle \sum_{j=1}^{N} \delta(\mathbf{r} - \mathbf{r}_{j}(t+t_{0}) + \mathbf{r}_{j}(t_{0})) \right\rangle,
\label{eq2/0}
\end{equation}
which measures the probability distribution for a particle displacement $\mathbf{r}$ in a time interval $t$. Since the present system is characterized by a translational symmetry along the nematic director, it is natural to separately study the diffusion along the \textit{z} axis and in the \textit{xy} plane. This can be done by partially integrating the SVHF on the $xy$ plane to get its longitudinal component

\begin{equation}
 G_{s}^{\parallel}(z,t) = \frac{1}{N} \left\langle \sum_{j=1}^{N} \delta(z - z_{j}(t+t_{0}) + z_{j}(t_{0})) \right\rangle,
\label{eq2}
\end{equation}

and along the $z$ axis to get its transverse component, which can be further averaged over the azimuthal angle of $\mathbf{r}$
\begin{equation}
 G_{s}^{\perp}(R,t) = \frac{1}{N} \left\langle \sum_{j=1}^{N} \delta(\mathbf{R} - \mathbf{R}_{j}(t+t_{0}) + \mathbf{R}_{j}(t_{0})) \right\rangle_{2 \pi}.
\label{eq3}
\end{equation}

In the above equations $(\mathbf{R}_j(t),z_j(t))$ is the position of particle $j$ at time $t$, $\delta$ is the Dirac delta, $\langle...\rangle$ stands for an ensemble average and the index $2 \pi$ indicates an additional average over the polar angle, which defines the bidimensional vector $\mathbf{R}=(x,y)$ with modulus $R=|\mathbf{R}|$. It should be noticed that for freely diffusive particles these functions are described by a Gaussian.

 \textit{\mdseries{Distinct-part of the van Hove function.}} A description of the influence of the surrounding particles background on the single particle diffusion is given by the DVHF, which is the probability distribution on the relative position $\mathbf{r}$ of two different particles at different times

\begin{equation}
 G_{d}(\mathbf{r},t) = \frac{1}{N} \left\langle \sum_{j\neq i=1}^{N} \delta(\mathbf{r} - \mathbf{r}_{j}(t+t_{0}) + \mathbf{r}_{i}(t_{0})) \right\rangle.
\label{eq4}
\end{equation}
In order to separately study the caging regime related to the local fluid structure in the direction longitudinal and transverse to the nematic director, we actually measured the DVHF partially integrated over the size occupied by the spherocylinder in the \textit{xy} plane and along the \textit{z} axis, defined, respectively, by

\begin{equation}
 G^{\parallel}_{d}(z,t) = \left(\frac {\pi D^{2}} {4}\right) ^{-1} \int_{0}^{D/2} R dR \int_{0}^{2 \pi} d\theta G_{d}(\mathbf{r},t),
\label{eq5}
\end{equation}
\begin{equation}
 G^{\perp}_{d}(R,t) = (2 \pi L)^{-1} \int_{-L/2}^{L/2} dz \int_{0}^{2 \pi} d\theta G_{d}(\mathbf{r},t),
\label{eq6}
\end{equation}
where we set $L=\min\{L_{1},L_{2}\}$ and $\theta$ is the azimuthal angle of $\mathbf{r}$ in the $xy$ plane.

 \textit{\mdseries{Non-Gaussian parameter.}} The deviations of the diffusion from Gaussian behavior can be estimated by the NGP, defined as \cite{rahman}

\begin{equation}
 \alpha_{2}(t) = \frac{\langle \Delta \mathbf{r}^{4}(t) \rangle}{(1+2/d) \langle \Delta \mathbf{r}^{2}(t) \rangle^{2}} - 1,
\label{eq7}
\end{equation}
where $\Delta \mathbf{r}(t)$ is the displacement of a particle during a time interval $t$. The parameter $d$ corresponds to the number of dimensions considered, so that $d=1$ for the linear diffusion longitudinal to the nematic director ($\alpha_{2,z}(t)$) and $d=2$ for the planar transverse diffusion ($\alpha_{2,xy}(t)$). As pointed out in Ref. \cite{doliwa}, when treating mixtures one should be careful in not taking into account trivial non-Gaussianity due to a size-dependent particle mobility. In order to describe the dynamical heterogeneities related exclusively to the permanent barriers of the LC phase, one has to calculate the NGP $\alpha_{2}^{(i)}$ as defined in Eq. (\ref{eq7}) for each species $i=1,2$ separately and then perform an average weighted over the concentrations $x_i$, i.e.

\begin{equation}
 \langle \alpha_{2}(t) \rangle = x_{1} \alpha_{2}^{(1)}(t) + x_{2} \alpha_{2}^{(2)}(t).
\label{eq7bis}
\end{equation}
With these definitions heterogeneous diffusion can be detected when the NGP deviates from zero value.

 \textit{\mdseries{Self-part of the intermediate scattering function.}} The structural relaxation of the system is conveniently described by measuring the self-part of the intermediate scattering function

\begin{equation}
F_{s}(\mathbf{k},t) = \frac{1}{N} \left\langle \sum_{j=1}^{N} \exp[i \mathbf{k} \cdot ( \mathbf{r}_{j}(t+t_{0}) - \mathbf{r}_{j}(t_{0})) ] \right\rangle,
\label{eq8}
\end{equation}
which describes the density auto-correlations decay in the reciprocal space. Since most of the relevant structural information is contained at the first peak $\mathbf{k}^{*}$ of the structure factor, we can focus on the transverse and longitudinal relaxations by evaluating this function at $(k_{x}^{*},k_{y}^{*},0)$ and $(0,0,k_{z}^{*})$ respectively, so that $F_{s,xy}(t)=F_s((k_{x}^{*},k_{y}^{*},0),t)$ and $F_{s,z}(t)=F_s((0,0,k_{z}^{*}),t)$.

\section{Results}
\label{sec:Results}

\begin{figure}
\center
\includegraphics[scale=1.0]{fig1.eps}
\caption{\label{fig1} (Color online) Side and top views of two typical configurations in the nematic ($P^{*}=2.5$, left figure) and in the columnar phase ($P^{*}=4.0$, right figure) of a binary mixture of perfectly aligned hard spherocylinders with length-to-diameter ratios $L_1^*=2.1$ and $L_2^*=1.0$ and relative concentrations $x_1=0.375$ and $x_2=0.625$.}
\end{figure}

When the difference in length between the two components of a binary system of aligned hard spherocylinders is sufficiently high, the system undergoes a transition from a nematic to a columnar phase by increasing the pressure. The structure of the columnar phase is characterized by the development of an hexagonal order in the plane perpendicular to the nematic director \cite{stroobants}. This is the case for our parameter choice $L^{*}_1=2.1$ and $L^*_2=1.0$ as illustrated in Fig. \ref{fig1}, where two typical configurations in the nematic ($P^{*}=2.5$) and in the columnar phase ($P^{*}=4.0$) are compared.

\begin{figure}
\center
\includegraphics[scale=1.0]{fig2.eps}
\caption{\label{fig2} (Color online) Mean-field effective potential $U(x,y)$ in units of $k_{B}T$ in the bulk columnar phase of a binary mixture of perfectly aligned hard spherocylinders at $P^{*}=3.0$, $P^{*}=3.5$ and $P^{*}=4.0$ (from top to bottom). The images on the left correspond to the long rods (species $1$), whereas those on the right to the short ones (species $2$). In order to ease the visualization, the black lines at the top of each graph identify the isopotential points in the $xy$ plane with increments of $3 k_BT$.}
\end{figure}

\begin{figure}
\center
\includegraphics[scale=1.0]{fig2bis.eps}
\caption{\label{fig2bis} Transverse section of the mean-field effective potential in Fig. \ref{fig2} for a binary mixture of long (a) and short (b) hard spherocylinders at $P^*=3.0$ ($\circ$), $P^*=3.5$ ($\blacktriangle$) and $P^*=4.0$ ($\vartriangle$). The solid lines are fits (see text).}
\end{figure}

The development of a long-range translational order allows to interpret the diffusion as the motion of a single particle subject to a periodic mean-field potential $U(x,y)$ as defined in Eq. (\ref{eq1}). This approach was applied in experiments \cite{lettinga} and simulations \cite{matena,patti,patti2} to characterize the hopping-type diffusion in smectic liquid crystals along the nematic director. These authors found that the free-energy cost for the layer-to-layer diffusion is in the order of few $k_{B}T$ per particle, depending mostly on the packing of the system, but also on the anisotropy and rotational degrees of freedom of the rods. Since the system studied here is composed of two species, the mean-field potential was evaluated separately for each component and is shown in Fig. \ref{fig2} for several pressures. The minima of the potential correspond to the lattice position, and the height of the energetic barriers gives a quantitative description of the energetic demand associated to a column-to-column jump. In order to estimate the height of the energetic barriers for each species as a function of pressure, we report in Fig. \ref{fig2bis} a transverse section of the energy landscapes in Fig. \ref{fig2}. Following the procedure in Ref. \cite{matena}, the experimental points in Fig. \ref{fig2bis} were fitted with a function
\begin{equation}
 U(R) = \sum_{k=1}^{n} U_k \left[ \sin \left( \frac {\pi R}{h} \right) \right]^{2k},
\label{pot_fit}
\end{equation}
with $U_k$ and $h$ fit parameters and $n=5$. As expected, the height of the potential barrier increases with the packing fraction and with the particle anisotropy, as already observed in Ref. \cite{patti}. At significant packing fractions, we detect that the energetic barriers appear higher for long rods. In particular, at $P^{*}=3.5$ and $4.0$ the column-to-column jumps become so rare that the associated statistics is too poor to furnish a precise estimate of the barrier height. In other words, the long rods are constrained to rattle in their cage, the jump to a neighboring column being too demanding. This is due to the fact that at high packing fraction no MC configuration showed a long rod in the region between the columns, with the result that the mean-field potential was characterized by an unphysical divergence. Furthermore, one should notice that the typical height of the barriers, close to and even higher than $10 k_{B}T$, is significantly higher than in the smectic phase \cite{matena,patti,patti2}. This can be seen by comparing our data at $P^{*}=3.5$ ($\eta=0.563$)
with those in Ref. \cite{matena} for the smectic phase of a system of aligned hard spherocylinders with $L^{*}=5.0$ at pressure $P^{*}=5.0$ ($\eta=0.563$). In the latter the height of the energy barrier reaches a value close to $8 k_{B}T$, which is expected to be even lower for shorter rods, as noticed in Ref. \cite{patti}.

\begin{figure}
\center
\includegraphics[scale=1.0]{fig3.eps}
\caption{\label{fig3} (Color online) A typical trajectory projected on the $xy$ plane of a long (red line) and short (green line) rod in the columnar phase at $P^{*}=3.0$ after an interval of time $\Delta t=380\tau$.}
\end{figure}

The effect of the periodic mean-field potential can be further appreciated in Fig. \ref{fig3}, where we show a typical trajectory projected on the $xy$ plane of a long and a short particle at $P^{*}=3.0$. The difference with the Gaussian diffusion typical of a simple liquid, where the particle trajectories resemble the behavior of a random walker, is evident. In this case, the dynamics of the system is characterized by a hopping-type diffusion, in which each particle tends to rattle around the center of a column until it finds suitable conditions to overcome the energetic barrier and jump to another column in quasi-quantized steps. The spread in the total displacement between the two species is due to the higher barriers felt by the long rods, which significantly inhibit the inter-column diffusion. This behavior is observed in the whole range of pressures considered here, and its effects on the long-time relaxation dynamics of the system are crucial. More specifically, the long rods are expected to sample the configurational space on a time scale which might be significantly longer than that needed for the small ones. As a consequence, the decay of the correlation functions is strongly affected by the slow diffusion of the long particles, as we show later on.

\begin{figure}
\center
\includegraphics[scale=1.0]{fig4.eps}
\caption{\label{fig4} Transverse component of the self-part of the van Hove function $G_s^{\perp}(R,t)$ as a function of $R/D$ for a binary mixture of perfectly aligned hard spherocylinders with length-to-diameter ratio $L_1^*=2.1$ and $L_2^*=1.0$ and relative concentrations $x_1=0.375$ and $x_2=0.625$ at $t/\tau=1$ (solid lines), $t/\tau=10$ (dashed lines) and $t/\tau=100$ (dotted lines) for the system at pressure $P^{*}=2.5$ (a),  $P^{*}=3.0$ (b), $P^{*}=3.5$ (c) and $P^{*}=4.0$ (d).}
\end{figure}

In order to quantitatively study the distribution of displacements of the particles at different pressures and after different time intervals, we report in Fig. \ref{fig4} and \ref{fig5} the self-part of the van Hove function (SVHF) in its transverse and longitudinal components respectively. The comparison between the behavior of the transverse SVHF in the nematic (Fig. \ref{fig4}a) and in the columnar (Fig. \ref{fig4}b, \ref{fig4}c, and \ref{fig4}d) phase reveals a drastic change in the dynamics. The SVHF in the nematic phase is a monotonic function which broadens with time. By entering the columnar phase one observes the appearance of peaks which correspond to the positions of the hexagonal lattice in the $xy$ plane. As expected, after a fixed time interval the number and height of the peaks depend on the packing fraction of the system, so that by increasing the pressure the number of peaks decreases due to higher energetic barriers. These results confirm what was already observed for the smectic phase in experiments \cite{lettinga}, simulation \cite{patti} and theory \cite{bier}, i.e. the partial translational symmetry breaking in a liquid crystal gives rise to a non-Gaussian quasi-quantized diffusion related to a hopping-type dynamics.

\begin{figure}
\center
\includegraphics[scale=1.0]{fig5.eps}
\caption{\label{fig5} Longitudinal component of the self-part of the van Hove function $G_s^{\parallel}(z,t)$ as a function of $z/D$ for $t/\tau=20$ and pressure $P^{*}=2.5$ (a),  $P^{*}=3.0$ (b), $P^{*}=3.5$ (c) and $P^{*}=4.0$ (d). The curves refer to Gaussian fits over points near the origin (solid lines) and the tails (dashed lines).}
\end{figure}

In Ref. \cite{bier} it was shown that, in order to accurately describe the dynamics of a liquid crystal system, it is not sufficient to take into account the permanent barriers due to the long-range structure, but also the transient caging effect given by the surrounding particles. In this sense, the local fluid structure can affect the diffusion by determining dynamical heterogeneities which make the system deviate from Gaussianity. A careful analysis on the longitudinal component of the SVHF in Fig. \ref{fig5} shows that this is indeed the case for the present columnar system. In fact, if along the $z$ axis the diffusion was Gaussian, it would be possible to fit the points in Fig. \ref{fig5} with a single Gaussian function. On the contrary, by performing this fit on different intervals on the $z$ axis, i.e. in the region near the origin (solid curve in figure) and the tails (dashed curve), one can observe that two different curves are obtained. Although in the present system the deviations between the two curves are small, this behavior manifests interesting resemblances with the heterogeneous dynamics of some amorphous systems, such as supercooled liquids and gels, where the two-Gaussian fitting is used to distinguish between ``slow'' and ``fast'' particles \cite{kegel,weeks}. In this sense, one can affirm that in the longitudinal direction the diffusion can be regarded as that of a dilute supercooled liquid, more than a normal liquid. The effect described so far should not be considered as strictly due to the columnar structure of the system, since analogous deviations are also observed in Fig. \ref{fig5}a for the nematic phase. Instead, the high packing fraction causes these small discrepancies from Gaussian diffusion.

\begin{figure}
\center
\includegraphics[scale=1.0]{fig6.eps}
\caption{\label{fig6} (Color online) Transverse $G_d^{\perp}(R,t)$ (a-d) and longitudinal $G_d^{\parallel}(z,t)$ (e-h) component of the distinct-part of the van Hove function evaluated for the same system and statepoints as in Fig. \ref{fig4} and \ref{fig5} and at $t/\tau=0.02$ (blue dotted line), $t/\tau=2$ (green dashed line), $t/\tau=20$ (red solid line) at $P^*=2.5$, $3.0$, $3.5$ and $4.0$ (from top to bottom).}
\end{figure}

A description of the transient caging regime due to the nearest-neighbor (solvation) shell around each particle can be given in terms of the distinct-part of the van Hove function (DVHF) defined in Eq. (\ref{eq5}) and (\ref{eq6}) and reported in Fig. \ref{fig6} for $t/\tau=0.02$, $2$ and $20$. According to the definition given in Eq. (\ref{eq4}), at time $t=0$ the DVHF coincides with the pair distribution function, and it is thus characterized by a region around the origin where its value is equal to zero due to the excluded volume interaction. On the other hand, in the limit $t \rightarrow \infty$ the DVHF is expected to be a constant in a translationally homogeneous system due to the decay of the positional correlations; this is not the case in presence of translational order, since the mutual position of two particles at different times is influenced by the permanent long-range structure of the whole system. At $t/\tau=0.02$ a region around the origin where the DVHF is close to zero suggests that each particle is still rattling around its initial position. Beyond this region a series of peaks indicate the preferential positions of the particles with respect to the one placed at the origin at the initial time. In the nematic phase at $t/\tau=0.02$ one can recognize in both the transverse (Fig. \ref{fig6}a) and longitudinal (Fig. \ref{fig6}e) components the liquid-like structure of the system, where the lack of long-range order is testified by the rapid decay of the peaks by moving away from the origin. One should also notice the speed at which the gap region around the origin is filled, giving rise to a DVHF almost constant already at $t/\tau=2$. Therefore, during this time interval a given particle $i$ can escape the trapping cage formed by its nearest neighbors $j$, and the space originally occupied by $i$ will be filled by one of the $j$ particles. The situation changes appreciably when we pass to the columnar phase, where the long-range modulations in the transverse component of the DVHF (Fig. \ref{fig6}b-d) indicate the presence of a permanent structure. On the other hand, the longitudinal component (Fig. \ref{fig6}f-h) does not display any dramatic change in shape, but from its time evolution one can observe that the time a particle needs to leave its initial position increases considerably. In fact, whereas the relaxation times of the longitudinal DVHF in the three systems manifesting columnar order are comparable (Fig. \ref{fig6}f-h), one can notice a faster relaxation in the nematic phase (Fig. \ref{fig6}e), which cannot be due to the difference in packing fraction exclusively. This seems to suggest that the inhomogeneous structure and the resulting dynamics in the transverse plane appreciably affect the dynamics in the longitudinal direction. We argue that the higher in-plane mobility of the nematic phase with respect to the columnar affects the mobility along the nematic director albeit only slightly. This is coherent with the results of Ref. \cite{bier}, where a coupling between transverse and longitudinal diffusion in the smectic phase was pointed out.

\begin{figure}
\includegraphics[scale=1.0]{fig7.eps}
\caption{\label{fig7} Mean square displacement in the direction perpendicular $\langle \Delta R^2 \rangle$ (a) and parallel $\langle \Delta z^2 \rangle$ (b) to the nematic director in units of $D^2$ as a function of $t/\tau$ for the same system and statepoints as in Fig. \ref{fig4}-\ref{fig6}.}
\end{figure}

\begin{figure}
\includegraphics[scale=1.0]{fig8.eps}
\caption{\label{fig7bis} Non-Gaussian parameter $\langle \alpha_{2,xy} \rangle (t)$ of the diffusion in the plane perpendicular to the nematic director as a function of $t/\tau$ for the same system and statepoints as in Fig. \ref{fig4}-\ref{fig7}. In the inset we compare at $P^{*}=3.0$ the non-Gaussian parameter averaged over the concentrations (open circles) with those relative to species $1$ (dashed line), to species $2$ (dotted line) and of the whole system (solid line).}
\end{figure}

An alternative way to analyze dynamical heterogeneities is to look for deviations from linearity of the mean square displacement. The effect of local cage trapping in systems close to dynamical arrest and the presence of permanent long-range inhomogeneities as in liquid crystals manifest themselves in a region at intermediate times where the dynamics is strongly sub-diffusive. In Fig. \ref{fig7} we show the MSD both in the $xy$ plane and in the $z$ direction. In the plane perpendicular to the nematic director (Fig. \ref{fig7}a) one can appreciate the almost linear trend of the MSD in the nematic phase, whereas by increasing the pressure and going to the columnar phase a plateau region appears, manifesting the development of a heterogeneous dynamics. These deviations from linearity are tightly related to the non-Gaussian behavior of the self-part of the van Hove function, and can be quantitatively estimated by the non-Gaussian parameter defined in Eq. (\ref{eq7}). In Fig. \ref{fig7bis} we report the NGP in the $xy$ plane averaged over the species concentrations as described in Eq. (\ref{eq7bis}). This parameter remains close to zero in the nematic phase, while it displays a peak at intermediate times in the columnar phase indicating deviations from Gaussianity. On the other hand, along the $z$ direction (not shown here) the NGP does not deviate significantly from zero. The choice of calculating the NGP for the whole system by averaging over the value it assumes for the two species separately allows to take into account just the effects related to the long-range structure of the system. For the sake of completeness we show in the inset of Fig. \ref{fig7bis} a comparison between the NGP at $P^*=3.0$ for each species, their weighted average and that corresponding to the whole system. As expected, the operation of average does not affect significantly the position of the peak, but decreases only the peak height, suggesting that in this way the non-Gaussianity due to particle size difference is subtracted. One should notice that this particular treatment is not necessary for the rest of the physical properties measured in this paper, since with the exception of the NGP they result to be linear in the particle species, i.e. their value for the system as a whole corresponds to a weighted average over the species.

The dynamic inhomogeneities as captured by both the MSD and the NGP allow to identify three different time intervals. At short times the MSD follows the usual linear trend and the NGP maintains a value close to zero, which means that particles diffuse freely since they do not feel yet the trapping cage due to the surrounding particles. At intermediate times the MSD becomes strongly sub-diffusive and the NGP is characterized by a monotonic growth, thus meaning that the free diffusion is inhibited by the columnar structure of the fluid. At this stage one can distinguish between particles which still rattle around the position of their column and others which succeeded in overcoming the energetic barrier and jumped to another column. The end of the subdiffusive plateau and the return to the linear trend of the MSD roughly correspond to the peak of the NGP, which starts decreasing monotonically to zero indicating the end of the caging regime, i.e. most of the particles succeeded in leaving their initial column. A deeper inspection on the pressure dependence of the NGP shows that the degree of non-Gaussianity, i.e. the height of the peak, and the duration of the caging regime, i.e. the position of the peak, increase with packing fraction. This fact can be explained by considering that the cage escape is related to a rearrangement of the surrounding particles, which becomes slower at higher packing fraction as it involves more of them. Furthermore, the small deviations from linearity in the MSD in the direction parallel to the nematic director confirm the presence of a weakly heterogeneous dynamics, as already pointed out by analyzing the self-part of the van Hove function in this direction.

\begin{figure}
\center
\includegraphics[scale=1.0] {fig9.eps}
\caption{\label{fig8} Self-part of the intermediate scattering function $F_{s,xy}(t)$ and $F_{s,z}(t)$ evaluated at wave vectors corresponding to the first peak of the structure factor in the plane perpendicular to the nematic director (a) and along it (b). The data correspond to the same system and statepoints as in Fig. \ref{fig4}-\ref{fig7bis}. The solid lines are fits (see text).}
\end{figure}

Finally, the structural relaxation of the system is analyzed in terms of the self-part of the intermediate scattering function (SISF) defined in Eq. (\ref{eq8}). Whereas along the $z$ direction the relaxation is characterized by a single step decay at each pressure (Fig. \ref{fig8}b), a plateau region, which characterizes the relaxation in the $xy$ plane at intermediate times, develops in the columnar phase. This plateau, whose value increases with pressure, indicates the time extension of the cage regime and is expected to divide a short-time decay ($\beta$-relaxation) from a long-time one ($\alpha$-relaxation). As previously observed in recent work on smectic liquid crystals \cite{matena,patti,patti2} and in out-of-equilibrium supercooled liquids \cite{berthier}, the SISF decays likely to zero at long times, indicating the loss of density auto-correlations. This kind of behavior was described for the smectic phase in Refs. \cite{matena,patti,patti2}, where the $\alpha$-relaxation decay was fitted by a stretched exponential function of the form $\exp[(t/t_{r})^{\beta}]$ with $\beta\simeq0.6$ and $t_r$ the characteristic relaxation time. In the present simulations we did not observe any $\alpha$-relaxation as the relaxation time of the systems exceeds probably our simulation time. On the other hand, from the data available a close accordance with the features of the structural relaxation of the smectic phase can be observed. In particular, the $\beta$-relaxation in the $xy$ plane is reasonably described by an exponential decay, as expected for simple liquids, due to the lack of interactions of the particles with the nearest neighbors at small times. Also the relaxation along the $z$ axis resembles accurately the relaxation of the smectic phase inside the smectic layers. In fact, in both these cases the SISF depends weakly on the pressure and it is characterized by an exponential decay at small times, which eventually becomes a stretched exponential with $\beta\simeq0.6$. In this sense we can confirm what the authors observed in Ref. \cite{matena}, i.e. the relaxation of a liquid crystal in the direction(s) in which the system is homogeneous is closer to that of a low-density supercooled liquid, than a simple liquid, where instead an exponential relaxation is to be expected.

\section{Conclusions}
\label{sec:Conclusions}

In summary, we used Monte Carlo simulations to analyze for the first time the presence of dynamical heterogeneities in a columnar liquid crystal of perfectly aligned hard spherocylinders. The long-range hexagonal order in the plane perpendicular to the nematic director determines an effective mean-field potential, whose effect is to maintain particles inside a column preventing them to occupy a position in between the columns. In analogy with previous analyses on the smectic phase, the height of the energetic barriers of this effective potential increases with the packing fraction and the particle anisotropy. As a consequence, in the $xy$ plane the dynamics of a rod is characterized by a quasi-quantized behavior in which particles rattle around the position of the column and jump to another column only when the configuration of the surrounding particles allows it.

The rattling-and-jumping dynamics in the in-plane evolution of the system gives rise to three different time regimes. At very short times, the particles diffuse almost freely because they do not feel yet the presence of the trapping cage formed by their surrounding nearest neighbors. At this stage the behavior of the system is that typical of a simple fluid, characterized by a Gaussian distribution of displacements, a linear mean square displacement and a fast exponential structural relaxation. A second stage starts when particles begin experiencing the cage due to the long-range structure of the system, in such a way that the diffusion results to be inhibited and only occasionally a column-to-column jump takes place and is made possible by the instantaneous configuration of the system. As a result, the mean square displacement as well as the self-intermediate scattering function develop a plateau, which testifies the slowing down of the dynamics and whose time extension increases with packing fraction. On the other hand, the distribution of displacements show marked deviations from Gaussianity due to the appearance of peaks which correspond to the lattice positions in the plane. Nonetheless, after longer time intervals the number of ``fast'' particles, which succeeded in overcoming the energetic barrier, increases with respect to the ``slow'' ones. Consequently, when most of the particles succeeded in leaving their initial column, a second diffusive regime starts, indicating the end of the cage regime.

We observed interesting analogies with the dynamics in smectic phases by considering the in-column dynamics. In fact, along the direction defined by the nematic director, the system does not develop any long-range order, and it is thus expected to behave like a liquid. On the other hand, we noticed interesting, although slight, deviations from Gaussian diffusion both in the distribution of displacements and in the mean square displacement. As far as the structural relaxation is concerned, this fact is testified by a self-intermediate scattering function well approximated by a stretched-exponential, as it happens in dense liquids. In this sense we confirm previous studies on the smectic phase, that along the direction in which a liquid crystal does not develop any long-range order the dynamics is similar to a dense liquid. These results are to be compared with recent experiments on the columnar phase of a suspension of \textit{fd} virus particles \cite{pouget}, where huge discrepancies from Gaussianity were observed along the nematic director. We argue that the higher length-to-diameter ratio, the flexibility or the charge of the rods could account for a more pronounced non-Gaussian diffusive behavior than what was observed in the present study.

\section{Acknowledgements}
\label{sec:Acknowledgements}

It is a pleasure to thank M. P. Lettinga, E. Grelet and E. Pouget for sharing preliminary experimental results that motivated this work and D. El Masri and P. van der Schoot for stimulating discussions.

This work is financed by a NWO-VICI grant and is part of the research program of the ``Stichting door Fundamenteel Onderzoek der Materie (FOM)'', which is financially supported by the ``Nederlandse organisatie voor Wetenschappelijk Onderzoek (NWO)''.

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2015 Firecracker Award Winner
2015 Bookseller's Best Finalist
They'll risk everything until there's nothing left to burn
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From Patty's Blog
Posted Jan 6 2020 in Anthology, Filles Vertes, Love on Main Street, young adult romance
Welcome to this leg of the Filles Vertes Publishing LOVE ON MAIN blog hop!
If you somehow landed on this page and haven't heard about the blog hop, click here:
I'm Patty Blount and my short story, SILVER FOR GOLD, takes place in The Hamptons on Long Island and follows Ethan Lewis and Alli Santanta, servers who work at upscale restaurant. Ethan is shy and hates to talk but when Alli is harassed by a customer, he must find just the right words.
If you haven't already, add LOVE ON MAIN to your Goodreads TBR here: http://bit.ly/LoveOnMain
Also, pre-orders are available at FVPub.com, Amazon, Barnes & Noble, Book Depository, or your fave bookseller. Convenient links are listed below:
FVP: www.fillesvertespublishing.com/product/love-on-main-a-romance-anthology/
Amazon: www.amazon.com/Love-Annual-Short-Story-Anthology/dp/1946802549
Barnes & Noble: www.barnesandnoble.com/w/love-on-main-patty-blount/1135129372?ean=9781946802545
Book Depository: www.bookdepository.com/Love-on-Main-Patty-Blount/9781946802545
Enjoy this entertaining character interview and get a glimpse of the intriguing stories awaiting you in LOVE ON MAIN. Remember to look for the keyword/phrase and take a note of it!
Author Patty Blount sits in her office, staring at a boy, a young man. He's tall, with messy hair and a bit of scruff on his strong jaw. His eyes are bright but cautious and every once in a while, if she doesn't blink, Patty sees a dimple flirt on his cheek. He holds a phone in his hand, open to an eReader app.
Patty: "Ethan, you've been working at Saluti for a while now. Do you like it?"
Ethan: "Sure."
Patty waits a beat. Waits some more. Clears her throat. "What do you like about it?"
Ethan grins briefly and that dimple winks. "The tips."
Patty indicates the app on his phone. "What are you reading there?"
Ethan: "I am Malala."
Patty: "Do you like it?"
Ethan: "Yes."
Sighing, Patty grins: "You're a man of few words. What's up with that?"
Ethan shrugs. "Talking causes…" he circles his hand, tries to <FIND> the right word. "Drama." He shakes his head. "I hate drama."
Patty: "Yes. I know. Can you tell us why?"
He breathes out a laugh. "That would mean talking."
Patty: "Good point. Okay, my friend. Tell me about Alli."
Ethan's head snaps up. "Is she here?"
Patty: "Possibly. Tell me about her."
Ethan: "She's cool."
Patty sighs. "What's cool about her, Ethan?"
Ethan frowns. "Everything, okay?"
Patty's eyebrows climb. "Now we're getting somewhere. You like her, don't you?"
He nods. "Sure."
"You know why."
Patty nods. "I do. Of course I do. I want to hear it from you. Words matter, Ethan."
Ethan stares at his author. "I know that better than anybody. That's why I don't talk much."
Patty changes tactics. "Do you know why I call this story SILVER FOR GOLD?"
Ethan shrugs. "Silver tongue?"
Patty grins. "Close. It's from an old saying, 'Speech is silver but silence is golden.' Do you know what it means?"
Ethan waits patiently for Patty to explain.
"It means that patience and listening are often more important, more valuable, than eloquence. Do you agree?"
"I do," Ethan replies immediately.
Patty: "Would you also agree that there are times when speaking up is valuable — maybe even crucial?"
Ethan looks away. Shrugs. Shakes his head.
"I can't think of any."
Patty smiles. "You can. You will. When the time is right, you will."
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Tweets by PattyBlount


text:
Mindy McCready's Heartbreak Over Death Of Her Soul Mate: 'The Point Of Me Living Is Waiting To Die' - Hear Her Tragic Call To A Friend
Feb. 21 2013, Published 7:30 a.m. ET
Just days before she killed herself, country singer Mindy McCready called a friend and told him she couldn't bear to live without her boyfriend David Wilson - who had died just weeks earlier after shooting himself in the head - and RadarOnline.com has exclusive audio of their heartbreaking conversation.
The grieving mother-of-two reached out to her longtime friend Danno Hanks shortly before she committed suicide herself on Sunday -- and the level of pain and suffering she was attempting to deal with following her tragic loss is all too apparent.
Choking on tears the tortured country star said the 34-year-old singer-songwriter was her "soul mate."
"The point of me living is waiting to die so I can be with him," Mindy admitted, in a chilling admission.
"Danno, this is a real love story. It is… I have been with people before. I have loved. I have done all kinds of things where I could say that I was in 'something' with that person.
"But David was my soul mate. He was."
Offering up touching insight into their most intimate moments, Mindy told her friend, "We held hands while we slept together every single night.
"No matter what we argued about during the day – if it was some dumb thing – we still kissed and hugged and loved each other and held hands all night long.
"He was my soul mate and I'll never have another. He was it."
In the call, Mindy also insisted that the relationship was "the real thing" and not "like some tabloid story, not like some bulls***."
"This was the real thing. It only comes around maybe once in a lifetime and…I will never, ever experience it again. I could wait for a million years," she said.
Ever since David took his own life there has been speculation that Mindy may have had something to do with his death. But during the conversation the 37-year-old revealed that she desperately tried to save the life of the man she loved – who reportedly suffered from bipolar disorder along with substance abuse issues.
And she clearly felt guilty that she couldn't do more to stop his self-destructive behavior.
"He was so sick Danno…" she said of the father of her 10-month-old son Zayne. "I did everything I could...but I couldn't be a mom to two children and him at the same time. I was failing miserably."
When her friend chided her for feeling guilty Mindy asked: "How could I not…?
"If I had been just a little bit stronger I could have saved him. But I wasn't. I wasn't adequate enough.
"You have no idea how many things I've thought of. What if I had broken up his pills and put it in his food?" She added.
"What if I had broken up his pills and put it in his drink? What if I had begged and pleaded and said 'I'll eventually do…whatever?'
"It's on me. It's all on me."
Throughout the conversation Danno desperately tries to comfort his friend, to reassure her that she did all she could and that she had no reason to feel guilty.
But the Ten Thousand Angels singer wouldn't listen or be comforted.
"In my mind, in my heart, with everything inside me…how in the world can I ever, ever move on?" She asked.
"There has to be something that I could have done."
Hear the audio on RadarOnline.com
As RadarOnline.com previously reported, Mindy and Danno had just finished working on a music video together publicizing suicide-prevention before she took her own life.
If you, or anyone you know is struggling with thoughts of suicide, please immediately seek help - you can speak with a skilled, trained counselor at a national Suicide Prevention Lifeline crisis center in your area, anytime 24/7 - call 1-800-273-TALK (8255)


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Made by a small studio in Jingdezhen, this teapot has an unglazed, rough clay interior and high-fired, white glaze with blush-red highlights.
This teapot features a 21 hole ball filter, holds approximately 120ml of liquid and pours empty in approximately 7 seconds.
Please note that as this teapot is made from rough clay, the lid may or may not seal perfectly, especially compared to tighter fitting purple clay pots. If you find the seal to leak, we advise using a smooth, steady pour to avoid drips without sacrificing pouring speed.
Learn more about the artist of this teapot here.


text:
Q: NetLogo - unilaterally exchange values of nearby turtles With regard to this question (NetLogo - calculate the difference of a variable of neighbouring agents), I am trying to change (for another scenario) the code so that another breed can change unilaterally the values of nearby members of the other breed (if their values are above a certain threshold) and by means of randomness can even change the value of one of (any) distant member of the other breed.
My code is (pseudo code in brackets):
breed [ greens green ]
greens-own [ variable ]

breed [ reds red ]

to setup
    create-greens 100 [
        set variable random 10
    ]
    create-reds 1
end

to start
   ask reds [
   exchange
   ]
end

to exchange
  rt random 360
  fd 0.5
  ask reds-on neighbors [
      let both-turtles (turtle-set self myself)
      "greens with variable > 6.9" [ set variable variable + 0.5]
 ]
 "one-of greens [ set variable variable + 1]"
end

How can I convert the pseudo-code to NetLogo code?

A: any turtle can instruct any turtle to change values with ask. you can simply state something like ask one-of greens [ set variable variable + 1] or ask greens with [variable > 6.9][...]. You need to take some care here, though, because you will be asking every red on a neighbour to ask ALL greens to change variable value as currently pseudo-coded.


Today's Photo Of The Day is "Dancing Diamonds" by Leah J Smith. Location: Arkansas.
See more of Leah J Smith's photography at www.leahjsmithphotography.com.
The post Photo Of The Day By Leah J Smith appeared first on Outdoor Photographer.


Bouna Medoune Seye has photographed slidewalks with people of misfits, marginalized, mad men of the city, in Dakar, Senegal.
Bouna Medoune Seye was born in Dakar in 1956. He studied in France, Marseilles, and then went back to Dakar where, with Djibril Sy, Moussa Mbaye and Boubacar Touré, he tries to design an artistic African photography.
In the 80's, his first exhibitions showed the strong personality of his work. He did numerous reportages trying to show the urban reality of his country : a certain idea of modernity. In 1993, he realised an exhibition/installation of photographs on Canadian-Indians, at the Chambre Blanche Gallery in Quebec. He directed in 1994 his first short film, "Bandits Cinéma", and moves to film activities as "Saï Saï By" produced by Revue Noire.


text:
Yanlei Diao
Email: {first-name}@cs.umass.edu
Address: Department of Computer Science Room 232
140 Governors Drive
Assistant: Rachel Lavery {last-name}@cs.umass.edu
[Home] [Funding] [Teaching] [Publications] [Talks] [Service] [Misc] [Curriculum Vitae] [DB Group]
My research interests lie in big data analytics and scalable intelligent information systems, with a focus on optimization in big data analytics, interactive data exploration, explainable anomaly detection, data streams, and uncertain data management.
Data systems Research for Exploration, Analytics, and Modeling (DREAM) Lab, co-directed with Prof. Miklau, Meliou and Haas
Some of our recent project websites:
Cloud data analytics and data stream analytics
Interactive data exploration
GESALL: Genomic scalable analysis with low latency
SCALLA: Scalable low-latency analytics
CLARO: Uncertain data stream processing
SASE: Complex event processing over streams
STONES: Flash-based data management system
SPIRE: RFID data stream processing
GESALL, our project on genomic data processing, obtained new NSF funding, joint with the New York Genome Center; a new publication at CIDR 2015; and a new research video, joint with the Harvard Medical School and Boston Children's Hospital.
Doctoral student, Yunmeng Ban, received the 2014 Microsoft Research Graduate Women's Scholarship, one of ten scholars chosen from 101 applicants!
Yanlei Diao received the 2013 CRA-W Borg Early Career Award for significant contributions to research and outreach!
Complete list of honors and awards: here
Curriculum vitae: here
GESALL: GEnomic Scalable Analysis with Low Latency. Next-generation sequencing has transformed genomics into a new paradigm of data-intensive computing, raising several salient challenges. First, the deluge of genomic data needs to undergo deep analysis to mine biological information, which requires a full pipeline that integrates many data processing and analysis tools. Second, deep analysis pipelines often take long to run, which entails a long cycle for algorithm and method development. This project aims to bring the latest big data technology and database technology to the genomics domain to revolutionize its data crunching power. The proposed research includes: development of a deep pipeline for genomic data analysis by assembling state-of-the-art methods; automatic parallelization of the workflow using the big data technology; a principled approach to optimizing the genomic pipeline; and integration of streaming technology to reduce latency of important results. The prototype system will be deployed in both private and public cloud environments, and fully evaluated using existing long-running pipelines and in a variety of real use cases.
SCALLA: Scalable Low-Latency Analytics. An integral part of many data-intensive applications is the need to collect and analyze enormous data sets, such as social network data, server log data, scientific data, and big bio data. Concurrently, new programming models and architectures have been developed for large-scale cluster computing, exemplified by recent MapReduce systems. In these big data systems, however, data needs to be loaded to the cluster before any queries can be run, resulting in a high delay to start query processing. Morever, answers to a long-running query are returned only when the entire job completes, causing a long delay in returning query answers. In this project, we design, develop, and evaluate a scalable, low-latency analytics platform, called Scalla, that fundamentally transforms the existing cluster computing paradigm into an incremental parallel processing paradigm, and further extends to near real-time analytics. We further develop a few applications in the domains of social network data analysis and big bio data analysis on the Scalla platform.
CLARO: Uncertain Data Management. The goal of this project is to design and develop a data management system that captures data uncertainty from data collection to query processing to final result generation. Such uncertain data stream processing is crucial to many real-world applications such as hazardous weather monitoring and traffic monitoring. To achieve this goal, our project takes a principled approach grounded in probability and statistical theory to support uncertainty as a first-class citizen, and efficiently integrate this approach into high-volume stream processing. In particular, we aim to capture uncertainty of raw data streams as they are produced as well as changes of uncertainty as data propagates through various query processing operators.
SASE: Complex Event Processing over Streams. We study stream processing in the context of large-scale event-based systems that are gaining adoption in applications such as supply chain management, financial services, and network and application monitoring. These systems create high volumes of events. End applications require these events to be filtered and correlated for complex pattern detection, aggregated on different temporal and geographic scales, and transformed to new events that reach a semantic level appropriate for the applications. We address issues involved in stream-based event processing ranging from the query language to computation complexity to fast implementation. We further consider complex pattern evaluation with imprecise timestamps of events, which commonly arise in event processing in distributed systems.
STONES: Flash-based Data Management Systems. Recent advances in flash technology have enabled embedded devices, personal computers, and high-end servers to be equipped with high-capacity flash memory and its packaged devices such as solid state drives (SSDs). Flash memory and SSDs provide faster random access and more energy-efficient operations over traditional hard disks. In this project, we are designing new storage systems and query processing algorithms for large-scale data analysis and high-performance databases that employ hybrid storage of flash memory and hard disks.
SPIRE: RFID Data Stream Processing. Radio Frequency Identification (RFID) technology is gaining acceptance in an increasing number of applications for tracking and monitoring purposes. Despite its promise to provide unprecedented visibility in various domains, RFID technology presents numerous challenges, including incomplete and noisy data, lack of information about inter-object relationships, and high volumes. In this project, we develop an RFID stream processing system that employs probabilistic inference to derive locations of unobserved objects and inter-object relationships such as containments and further supports probabilistic query processing to derive high-level information.
Fast and Memory-Efficient Packet Content Scanning. Packet content scanning compares the packet payload against a set of patterns specified as regular expressions. Memory requirements using traditional methods for fast packet scanning are prohibitively high. We develop regular expression rewrite techniques to reduce memory usage, and grouping schemes to increase the regular expression matching speed without increasing memory usage. Our implementation can achieve orders-of-magnitude performance improvements over the implementations used in the Linux L7-filter and Snort system. Such efficient packet content scanning enables new technologies such as real-time worm detection, content lookup in overlay networks, fine-grained load balancing, etc.
ONYX: Internet-Scale XML Data Dissemination. We study Internet-scale data dissemination that delivers XML-encoded documents from multiple publishing sites to millions of subscribers based on the subscribers' data interests. We explore the idea of content-based routing of documents in distributed dissemination systems. We seek to enhance such data dissemination with advanced services such as stateful publish/subscribe and QoS. We investigate implementations that are able to meet demanding efficiency and scalability requirements.
YFilter: High-Volume XML Message Brokering. We design a message brokering system that provides fast, on-the-fly filtering of incoming XML messages for large numbers of simultaneous queries, and transforms the matching messages according to recipient-specific requirements. We explore the key issues including shared processing of queries for efficient and scalable filtering and leveraging the filtering solutions for customized result generation. We released YFilter 1.0, a freely available software system containing the filtering engine and the query workload generator of YFilter.
Stream-based XQuery Processing. We develop a memoization-based approach to shared processing for the full XQuery language in a stream-based environment. We implement the approach by extending the streaming XQuery processor that BEA Systems incorporates as part of their BEA WebLogic Integration 8.1 product. We demonstrate the effectiveness of the approach in typical use cases of XQuery.
Boduo Li
Liping Peng
Haopeng Zhang
Yunmeng Ban
Wenzhao Liu
MS Students
Thanh Tran (Twitter)
Edward Mazur (Google, New York)
Richard Cocci (Harvard Law School)
Ravishankar Guruswamy Rajamony (Goldman Sachs)
Daniel Gyllstrom (UMass)
Zhao Cao (IBM Research China)
Yanming Nie


text:
The Chemistress
Chemistry captures everything.
Chemistry of People
Chemistry of Things
Chemistry of Food and Drink
Best Book Ever: East of Eden vs. Catch-22
March 28, 2020 / The Chemistress
You knew there were going to be a few heartbreaks with a random draw. Both of these are solid contenders to win it all, but unfortunately we'll have to say goodbye to one now.
East of Eden by John Steinbeck
For years, all I knew of Steinbeck was that The Grapes of Wrath seemed like a huge and boring -you have to read this- classic piece of literature, so I didn't read it. But then I asked for book recommendations, and with East of Eden being one of the few on the list I hadn't already read, it was the winner.
A wandering and winding story telling one of the oldest tales in time over and over again. East of Eden recreates the story of Cain and Able over and over through the lives of two sets of brothers -Charles and Adam as the older generation and Caleb and Aron as the younger. But as all humans do, they live the same stories of love, jealousy, and pride. The novel is a discussion of man's ability to choose his destiny -to choose to do good and follow an honest path even when your inborn proclivities drive you towards sin. With insanely quotable and poignant passages, it's a book I turn to constantly when I'm in need of advice. As Steinbeck himself stated, "It has everything in it I have been able to learn about my craft or profession in all these years."
Goodreads Score: 4.37
Length: 3 – East of Eden is a little big, but not disagreeably so. In retrospect, it's wholly amazing Steinbeck was able to fit the breadth of the story into just 600 pages.
Readability: 3.5 – Often broken up into short segments, the book is easily digestible even with all there is going on.
Language: 5 – We could sit here for hours and discuss how good the writing is -the dialogue, the descriptions, the imagery -but let's just leave and say it's very, very good.
Characters/Plot: 5 – You'll laugh, you'll cry, you'll be overwhelmed, you'll feel all too much called out. A+ for cast of characters and considerations.
Overall Score: 20.87
Built from his experiences in World War II and his criticism of the Korean War, Joseph Heller wrote Catch-22 as a critique of war and the military but even moreso of the governments who control them. Catch-22 is now a ubiquitous phrase for a situation in which there is no solution because the options are intrinsically tied. One highlight example in the novel being that Captain John Yossarian seeks to be discharged from the military by way of an insanity plea, however, by seeking to get out of the military, he only proves his sanity. The novel is riddled with such instances of circular logic drawing you into its absurdity to the point where you nearly forget the backdrop is World War II. Until it showcases the siege, and you're filled with horror. Yet the novel ends on a hopeful note for as with real war, people survive and move on, going on living anyway.
Length: 3 – Catch-22 comes in at a 400ish pages depending on the version which is very conquerable.
Readability: 4 –The book had me so entertained I finished it in a couple of days. Highly readable.
Language: 4 – Catch-22 is filled with examples of its namesake. Every character struggles with a back and forth of "Not this but that, But wait, it can't be this." Decidedly clever whether it's turn of phrase or character diatribe, Catch-22 has some great language.
Characters/Plot: 4.25 – Rare is the protagonist as relateable as Yossarian. Determined to stay alive even while he's obsessed with dying, his outrage at the futility of war is raw and assured.
"And don't tell me God works in mysterious ways", Yossarian continued, hurtling over her objections. "There's nothing so mysterious about it. He's not working at all. He's playing or else He's forgotten all about us. That's the kind of God you people talk about—a country bumpkin, a clumsy, bungling, brainless, conceited, uncouth hayseed. Good God, how much reverence can you have for a Supreme Being who finds it necessary to include such phenomena as phlegm and tooth decay in His divine system of creation?
Again, you hate to see one of these leave so early, but as good as Catch-22 is, it's hard to compete with the mastery of East of Eden. What story is more essential than that of good vs. evil and our ability to choose?
'We're a violent people, Cal. Does it seem strange to you that I include myself? Maybe it's true that we're all descended from the restless, the nervous, the criminals, the arguers and the brawlers, but also the brave and independent and generous. If our ancestors had not been that, they would have stayed in their home plots in the other worlds and starved over the squeezed out soil.'.
-East of Eden by John Steinbeck
best book ever, catch-22, east of eden, john steinbeck, joseph heller
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Best Book Ever: Midnight's Children vs. Faust →


UPSC CMS Exam 2016 notification has been published for recruitment of 1009 Assistant Divisional Medical Officer, Assistant Medical Officer, Junior Scale Posts, General Duty Medical Officer vacancies on temporary basis. Details for UPSC CMS Exam 2016 like age limit, educational qualification, exam pattern, application procedure is given below.
(a) A candidate for this examination must not have attained the age of 32 years as on 1st January, 2016, i.e. the candidate must have been born not earlier than 2nd January, 1984.
NOTE-1: A candidate who has appeared or has yet to appear at the final M.B.B.S. Examination may also apply. Such candidates will be admitted to the examination if otherwise eligible but the admission would be deemed to be provisional and subject to cancellation, if they do not produce proof of having passed the written and practical part of the final M.B.B.S. Examination.
Note-2: A candidate who has yet to complete the compulsory rotating internship is educationally eligible for admission to the examination but on selection he/she will be appointed.
Candidates are required to apply Online by using the website or by clicking on the given below link.
The candidates are required to pay a fee of Rs. 200/- (Rupees Two Hundred only) [excepting SC/ST/Female candidates who are exempted from payment of fee] either by depositing the money in any branch of SBI by cash, or by using net banking facility of State Bank of India/State Bank of Bikaner & Jaipur/State Bank of Hyderabad/State Bank of Mysore/ State Bank of Patiala/State Bank of Travancore or by using any Visa/Master Credit/Debit Card.
The Online Applications (Part I and II) can be filled from 05th March, 2016 to 01st April, 2016 till 11.59 p.m., after which link will be disabled.
Applicants should avoid submitting multiple applications. However, if due to any unavoidable circumstances, any applicant submits multiple applications then he/ she must ensure that the application with higher RID is complete in all respects.
Admit card for UPSC Combined Medical Services Examination 2016 is available on UPSC website three weeks before the exam date.
Part-II Personality Test: (100 Marks): Personality test carrying 100 marks of such of the candidates who qualify on the results of the Computer based examination.
For complete information refer UPSC CMS Exam 2016 information brochure.


From Tuesday, December 8 through Thursday, December 10, E-TEC will be participating in the 2009 Elektro Exhibition at the Event Hall, Hardenberg and we will be delighted to welcome you at our stand.
E-TEC is a Solutions Provider in the field of Electrical Power, Computer Rooms and Datacenters, but at the exhibition we will have have our focus mainly on Standby Generators and UPS Systems.
Your visit to the E-TEC stand will be well worthwhile!