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BEGIN:VEVENT
UID:calendar:4498:field_when:0:0
SUMMARY:Strength of Multicomponent Materials
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190515T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190515T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4498
LOCATION:Colloquium Rm. 301
DESCRIPTION:Speaker: Kulveer Singh\n
\n
Abstract:\n
TBA
END:VEVENT
BEGIN:VEVENT
UID:calendar:4481:field_when:0:1
SUMMARY:The microbiome and host altruism
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190410T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190410T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4481
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Lilach Hadany\n
\n
Abstract:\n
TBA
END:VEVENT
BEGIN:VEVENT
UID:calendar:4506:field_when:0:2
SUMMARY:New statistical perspectives on chaotic attractors
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190522T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190522T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4506
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Michael Wilkinson\n
\n
Abstract:\n
It is well known that strange attractors are characterised \n
by their fractal dimensions\, which quantify the mass \n
clustered into a small ball. Recent work\, using statistical \n
approaches\, has revealed other generic properties of \n
chaotic systems.\n
The fractal dimensions characterise the dense regions \n
of the attractor using a power-law\, but the distribution of \n
density in the sparse regions is also characterised by a \n
power-law\, which we term the 'lacunarity exponent'. \n
The fractal dimension describes the mass of the attractor\n
contained in small regions\, but it is also possible to study the\n
shape of clusters of points which sample the attractor. The \n
statistics of the shape of these clusters is characterised by \n
power laws. The exponents of these lower-laws are found to \n
exhibit phase transitions. \n
Physical applications of these phenomena will also \n
be discussed\, including particles advected in fluid flows\n
and ray trajectories in random media.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4445:field_when:0:3
SUMMARY:Absorbing phase transitions and temporal intermittency in collisional \n
aggregation-fragmentation models.
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190313T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190313T113000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4445
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Bijoy Daga\n
\n
Abstract:\n
In aggregation\, masses coalesce irreversibly to form a cluster\, and in frag-\n
\n
mentation\, clusters break up into smaller ones. These processes occur in a\n
\n
wide range of phenomena varying from tissue development in cell biology\n
\n
to the formation of planetary rings. Our work is motivated by astro-\n
\n
physical applications\, in particular Saturn rings. A model describing such\n
\n
systems considers binary collision reactions between masses\, and upon\n
\n
collision\, the two clusters can either aggregate or fragment completely\n
\n
(shatter) into the smallest constituent masses. At the mean-field level\,\n
\n
the time evolution of the cluster sizes is described by the deterministic\n
\n
Smoluchowski equation.\n
\n
\n
\n
We have studied the effects of stochasticity and finite total mass in these\n
\n
models. In such a setting\, the Smoluchowski equation does not give the\n
\n
correct answer for the mass distribution. We therefore use Monte Carlo\n
\n
simulation to study the system. The key question that we address is\n
\n
whether such a system shows a phase transition\, and if so\, what is the\n
\n
nature of the phases? There is indeed an active-absorbing phase transition\n
\n
in the system\; in the absorbed phase\, all masses aggregate into a single\n
\n
cluster. The active phase\, depending upon the locality of the reaction\n
\n
Kernel shows temporal intermittency. Details of these aspects will be\n
\n
given during the talk.\n
\n
END:VEVENT
BEGIN:VEVENT
UID:calendar:4446:field_when:0:4
SUMMARY:How spatial structure determines the dynamical regimes of ecosystems
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190227T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190227T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4446
LOCATION:Colloquium Rm. 301
DESCRIPTION:Speaker: Yuval Zelnick\n
\n
Abstract:\n
Identifying the drivers of ecosystem and population dynamical behavior is a \n
fundamental aspect of ecology. In a spatially explicit context\, the basic \n
ingredients to consider are the spatial structure of the landscape\, the local \n
dynamics at play\, and the dispersal and diffusion which mediates between the \n
former two. Numerous studies has looked at each of these components \n
separately\, but little is known on the interplay between them. Missing has \n
been a more integrative approach\, able to map and identify the possible \n
dynamical regimes in the system\, and in particular its response to \n
perturbations.\n
I will focus my talk on a simple\, yet relatively general\, scenario: the \n
recovery of a homogeneous metapopulation from a single\, spatially localized \n
pulse disturbance. We find that the response can take one of three forms\, \n
each representing one of three dynamical regimes: Isolated\, Interplay and \n
Mixing. Using dimensional analysis we can predict the transition points \n
between these regimes\, and how these change with basic system properties such \n
as its total area and the nonlinearities of local dynamics. This enables us \n
to address pertinent issues in ecology\, such as habitat fragmentation\, \n
synchrony-induced extinctions\, and mechanisms of biomass productivity in \n
metacommunities.\n
I will finish the talk by briefly presenting a few extensions of this work. \n
In particular\, a possible indicator of bistability based on the spatial \n
extent of disturbances\, the spatial aggregation of disturbances when their \n
frequency is high\, and the spatial patterns of ecosystem engineers along an \n
environmental gradient.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4439:field_when:0:5
SUMMARY:Exact solution for a 1 + 1 etching model
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190320T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190320T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4439
LOCATION:TBA
DESCRIPTION:Speaker: Fernando Oliveira\n
\n
Abstract:\n
We present a method to derive analytically the growths exponents of a \n
surface of 1 + 1 dimensions whose dynamics is ruled by cellular automata. \n
Starting from the automata\, we write down the time evolution for the \n
height's average and height's variance (roughness). We discuss the existence \n
of a Probability distribution for the congurations. We apply the method to \n
the etching model[1\,2] than we obtain the dynamical exponents\, which \n
perfectly match the numerical results obtained from simulations. Those \n
exponents are exact and they are the same as those exhibited by the KPZ \n
model[3] for this dimension. Therefore\, it shows that the etching model and \n
KPZ belong to the same universality class[4]. Moreover\, we proof that in the \n
continuous limit the majors terms leads to KPZ [5].
END:VEVENT
BEGIN:VEVENT
UID:calendar:4416:field_when:0:6
SUMMARY:Theory of microbial genome evolution
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190123T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20190123T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4416
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Itamar Sela\n
\n
Abstract:\n
The rapid accumulation of genome sequences from diverse organisms presents an \n
opportunity and a challenge for theoretical research: is it possible to \n
derive quantitative laws of genome evolution and an underlying theory? \n
Microbes have small genomes with tightly packed protein-coding genes\, and the \n
different functional classes of genes (such as information processing\, \n
metabolism\, or regulation) show distinct scaling exponents with the genome \n
size. The compactness of microbial genomes is traditionally explained by \n
genome streamlining under selection for high replication rate but so far\, \n
there has been no general theoretical model to account for the observed \n
universal laws of genome content scaling. We developed a model for microbial \n
genome evolution within the framework of population genetics and tested it \n
against extensive data from multiple genome comparisons. The analyses \n
indicate that the evolution of genome size is not governed by streamlining \n
but rather\, reflects the balance between the benefit of additional genes and \n
the intrinsic preference for DNA deletion over acquisition. These results \n
explain the observation that\, contrary to the common belief\, microbes with \n
large genomes are subject to stronger selection than small genomes. Employing \n
this model to recover the differential scaling of functional gene classes in \n
bacterial genomes allowed us to identify the underlying factors that govern \n
the evolution of the genome content. A key factor that we termed genome \n
plasticity shapes genome evolution and provides a simple mathematical \n
representation of evolvability\, a central but elusive concept in evolutionary \n
biology. These findings demonstrate that key aspects of genome evolution can \n
be captured by general population genetics models\, and pave the way for \n
further theoretical analyses of fundamental evolutionary mechanisms.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4343:field_when:0:7
SUMMARY:Title: Learning force fields from stochastic trajectories
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20181205T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20181205T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4343
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Anna Frishman\n
\n
Abstract:\n
Particles in biological and soft matter systems undergo Brownian dynamics: \n
their deterministic motion\, induced by forces\, competes with random diffusion \n
due to thermal noise. More broadly\, Brownian dynamics is a generic and simple \n
model for dynamical systems with noise. Provided only with the time-series of \n
positions of such a system\, i.e a trajectory in phase space\, it is \n
challenging to infer what force field had produced it. At the same time\, this \n
is the key information about the dynamical system\, which would allow to \n
characterize it completely. I will show that there is an \n
information-theoretic bound on the rate at which information about the force \n
field can be extracted from a trajectory\, quantified by a channel capacity. I \n
will discuss the relation between this capacity and the entropy production \n
rate\, as defined in stochastic thermodynamics. I will then present a \n
practical method\, Stochastic Force Inference\, that uses the information \n
contained in a trajectory to approximate force fields. This technique also \n
permits the evaluation of out-of-equilibrium currents and entropy production. \n
It thus makes it possible to quantify subtle time-irreversibility in \n
biological systems at the mesoscale\, and opens the door to an understanding \n
of the importance of time- irreversibility.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4349:field_when:0:8
SUMMARY:Non-linear dependence measures and non-Gaussian diffusion
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20181031T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20181031T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4349
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Jakub Slezak\n
\n
Abstract:\n
We show that a non-linear measure of dependence called the codifference is a \n
useful tool in studying ergodicity breaking and non-Gaussianity. Codifference \n
was previously studied mainly in the context of stable and infinitely \n
divisible processes. We extend its range of applicability to random parameter \n
and diffusing diffusivity models which are important in contemporary physics\, \n
biology and financial engineering. We prove that the codifference detects \n
forms of dependence and ergodicity breaking which are not visible analysing \n
covariance and correlation. At the same time the differences between the \n
covariance and codifference can be used to analyse non-Gaussianity.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4363:field_when:0:9
SUMMARY:From biology to engineering: how lessons from territorial animals inspire \n
spatial coverage algorithms in robot swarms
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20181024T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20181024T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4363
LOCATION:Colloquium room 301
DESCRIPTION:Speaker: Luca Giuggioli\n
\n
Abstract:\n
Various animals\, mammals in particular\, display some form of territorial \n
behaviour for which they make their presence conspicuous to others claiming \n
exclusive ownership of regions of space. The signals employed to perform this \n
form of spatial exclusion may be visual\, auditory or olfactory depending on \n
the species and the environment. When the mechanism of territorial exclusion \n
occurs via marks deposited on the terrain (olfactory cues)\, one talks about \n
stigmergy\, a form of environment-mediated interaction often encountered in \n
social insect societies.\n
\n
To study the emergence of spatial segregation in stigmergic systems I have \n
introduced a new type of collective animal movement model where alignment of \n
the agents does not play any role. It is called the territorial random walker \n
model as agents move freely as random walkers on a lattice\, scent-marking the \n
terrain wherever they go. As deposited marks remain active for a finite \n
amount of time\, each walker retreats upon encountering an active foreign \n
scent. The emerging spatio-temporal dynamics of the system can be quite rich \n
and can be studied at the meso-scale (the territories) as well as at the \n
micro-scale (the agents).\n
\n
At the meso-scale short-lived marks produce rapidly morphing and highly \n
mobile territories\, while long-lived marks yield slow territories with a \n
narrowly defined shape distribution. More importantly the full dependence in \n
territory mobility as a function of the time for which individual marks \n
remain active is accompanied by a liquid-hexatic-solid transition akin to the \n
Kosterlitz-Thouless melting scenario\, apparently the first ecological model \n
to predict such a transition.\n
\n
The dynamics at the micro-scale is in general non-Markovian\, but when \n
population density is sufficiently large some mean-field analytic approaches \n
have proved useful. By considering localized walls to mimic the sharp \n
(retreat) interaction when an animal encounters a foreign scent\, it is \n
possible to represent via a Fokker-Planck formalism an animal roaming within \n
neighbouring territorial boundaries. Application of this analytic model to \n
movement data from a red fox population in Bristol\, UK\, is also shown.\n
\n
Inspired by the findings on territorial dynamics\, it is natural to ask \n
whether it is possible to devise a swarm of independent and decentralised \n
territorial robots. Given that building robots with actual marker reading and \n
writing mechanisms is quite difficult in practice\, inspiration comes from the \n
behaviour of territorial birds which detect each other presence at a given \n
location by chirping a challenge which is then countered. Rather than \n
broadcasting a scent signal detectable by any individual passing by\, the \n
signalling occurs only between two individuals nearby. While the exclusion \n
mechanism is not stigmergic anymore\, it can still be exploited to segregate \n
partially the robot population and limit spatial oversampling in search \n
tasks. \n
\n
\n
\n
References\n
\n
[1] A. Heiblum-Robles and L. Giuggioli\, Phase transitions in stigmergic \n
territorial systems\, accepted.\n
\n
[2] L. Giuggioli\, I. Ayre\, A. Heiblum Robles and G.A. Kaminka\, From ants to \n
birds: a novel bio-inspired approach to on-line area coverage\, in Groß R et \n
al. (eds) Distributed Autonomous Robotic Systems\, Springer Proceedings in \n
Advanced Robotics\, vol 6\, pp. 31-43 (2018).\n
\n
[3] L. Giuggioli and V.M. Kenkre\, Consequences of animal interactions on \n
their dynamics: emergence of home ranges and territoriality\, Move. Ecol. \n
2(1)\, 20 (2014).\n
\n
[4] L. Giuggioli\, J.R. Potts\, D.I. Rubenstein and S.A. Levin\, Stigmergy\, \n
collective actions and animal social spacing\, Proc. Natl. Acad. Sci. USA \n
110(42):16904-9 (2013).\n
\n
[5] J.R. Potts\, S. Harris and L. Giuggioli\, Quantifying behavioral changes in \n
territorial animals caused by sudden population declines\, Am. Nat. \n
182:e73-e82 (2013).\n
\n
[6] L. Giuggioli\, J.R. Potts and S. Harris\, Predicting oscillatory dynamics \n
in the movement of territorial animals\, J. Roy. Soc. Interface 9(72):1529-43 \n
(2012).\n
\n
[7] J.R. Potts\, S. Harris and L. Giuggioli\, Territorial dynamics and stable \n
home range formation for central place foragers\, PLoS ONE 7(3):e34033 (2012).\n
\n
[8] L. Giuggioli\, J.R. Potts and S. Harris\, Brownian walkers within \n
subdiffusing territorial boundaries\, Phys. Rev. E 83:061138/1-11 [1] (2011).\n
\n
[9] L. Giuggioli\, J.R. Potts and S. Harris\, Animal interactions and the \n
emergence of territoriality\, PLoS Comp. Biol. 7(3):e1002008/1-9 (2011).\n
\n
\n
[1] tel:061138/1-11
END:VEVENT
BEGIN:VEVENT
UID:calendar:4290:field_when:0:10
SUMMARY:Growth and division of chemically active droplets: A model for protocells
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180717T110000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180717T110000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4290
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Dr. Rabea Seyboldt\n
\n
Abstract:\n
Macromolecular phase separation and droplet formation have long been proposed \n
as key elements in the formation of protocells during the origin of life. A \n
simple model of a protocell consists of a droplet\, where droplet material is \n
produced outside the droplet\, and chemical reactions inside the droplet play \n
the role of a simple metabolism. Our theoretical study shows that such \n
chemically active droplets can have a flux-driven shape instability that \n
leads to a symmetric droplet division. We analyze the dependence of the \n
instability on the droplet viscosity and parameters that characterize the \n
metabolism and material production. Our work provides a physical mechanism \n
for the division of early protocells before the appearance of membranes.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4278:field_when:0:11
SUMMARY:From kB to kB: Entropy evaluation made easy
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180620T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180620T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4278
LOCATION:Resnick (#209) - room 210
DESCRIPTION:Speaker: Prof. Roy Beck-Barkai\, School of Physics and Astronomy\, Tel-Aviv \n
University\n
\n
Abstract:\n
Entropy and free-energy estimation are key in thermodynamic characterization \n
of simulated systems ranging from spin models through polymers\, colloids\, \n
protein structure\, and drug-design. Current techniques suffer from being \n
model specific\, requiring abundant computation resources and simulation at \n
conditions far from the studied realization. In this talk\, I will present a \n
novel universal scheme to calculate entropy using lossless compression \n
algorithms and validate it on simulated systems of increasing \n
complexity. Our results show accurate entropy values compared to benchmark \n
calculations while being computationally effective. In molecular-dynamics \n
simulations of protein folding\, we exhibit unmatched detection capability \n
of the folded states by measuring previously undetectable entropy \n
fluctuations along the simulation timeline. Such entropy evaluation opens a \n
new window onto the dynamics of complex systems and allows efficient \n
free-energy calculations.\n
\n
END:VEVENT
BEGIN:VEVENT
UID:calendar:4277:field_when:0:12
SUMMARY:A biophysical model of higher-order chromatin architecture
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180627T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180627T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4277
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Ankit Agrawal\n
\n
Abstract:\n
Energy consuming processes are important in determining the large-scale \n
organization of chromatin. Experiments indicate that chromosomes are \n
organized in a non-random manner and occupy specific regions of a nucleus\, \n
called chromosome territories (CTs)\, with gene rich regions (euchromatin) \n
more centrally positioned than gene-poor (heterochromatin) regions. Further\, \n
chromosomes are largely seen to be positioned radially by gene density\, \n
although positioning by chromosomes size is also seen. Our model for \n
large-scale nuclear architecture incorporates the effects of non-equilibrium \n
processes driven by the consumption of ATP\, associated to cell-type specific \n
transcriptional processes that are inhomogeneous within and across \n
chromosomes. It yields predictions which compare favorably to experimental \n
data including statistics of positional distributions\, shapes and overlaps of \n
each chromosome. Our simulation also reproduce common organizing principles \n
underlying large-scale nuclear architecture across interphase human cell \n
nucleus. These include the differential positioning of two X chromosomes in \n
female cells\, the territorial organisation of chromosomes including both \n
gene-density-based and size-based chromosome radial positioning schemes\, \n
statistics of the shape of chromosomes\, and contact probabilities of \n
individual chromosomes. We proposed that biophysical consequences of the \n
distribution of transcriptional activity across chromosomes should be central \n
to any chromosome positioning code.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4263:field_when:0:13
SUMMARY:"Adaptation and hitchhiking in spatially-structured populations"
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180522T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180522T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4263
LOCATION:Resnick (Bldg. 209) 2nd floor seminar room
DESCRIPTION:Speaker: Daniel Weismann\, Emory\n
\n
Abstract:\n
Most populations are spread over spatial ranges that are far larger than \n
individuals typically disperse. How does this affect how quickly they can \n
adapt\, and what kinds of patterns of neutral genetic diversity do we expect? \n
We find that spatial structure creates a large gap in adaptibility between \n
populations which are totally asexual and those that occasionally recombine. \n
We also find that adaptation creates a kind of effective long-range \n
dispersal\, increases relatedness between spatially distant individuals.\n
\n
END:VEVENT
BEGIN:VEVENT
UID:calendar:4159:field_when:0:14
SUMMARY:Condensate\, fluctuations and symmetries - a tale of 2D turbulence
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180425T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180425T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4159
LOCATION:Resnick (Bldg. 209) 2nd floor seminar room
DESCRIPTION:Speaker: Anna Frishman\n
\n
Abstract:\n
Earths jet streams\, Jupiters Great Red Spot and its zonal winds are all \n
examples of persistent\n
\n
large scale ows\, whose dynamics is to a good approximation two-dimensional. \n
These ows are\n
\n
also highly turbulent\, and the interaction between the turbulence and these \n
coherent structures\n
\n
remains poorly understood. Apart from its geophysical relevance\, 2D \n
turbulence is a rich and\n
\n
beautiful fundamental system|where turbulence takes a counter-intuitive role. \n
Indeed\, in 2D\,\n
\n
energy is transferred to progressively larger scales\, which can terminate in \n
the self organization of\n
\n
the turbulence into a large scale coherent structure\, a so called condensate\, \n
on top of small scale\n
\n
\n
\n
I will describe a recent theoretical framework in which the prole of this \n
coherent mean \n
\n
can be obtained\, along with the mean momentum ux of the uctuations. I will \n
explain how\n
\n
and when the relation between the two can be deduced from dimensional \n
analysis and symmetry\n
\n
considerations\, and how it can be derived. Finally\, I will show that\, to \n
leading order\, the velocity\n
\n
two-point correlation function solves a scale invariant advection equation. \n
The solution determines\n
\n
the average energy of the uctuations\, but does not contribute at this order \n
to the momentum \n
\n
due to parity + time reversal symmetry. Using analytic expressions for the \n
solutions\, matched to\n
\n
data from extensive numerical simulations\, it is then possible to determine \n
the main characteristics\n
\n
of the average energy. This is the rst-ever self-consistent theory of \n
turbulence-ow interaction.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4037:field_when:0:15
SUMMARY:Models of ecological communities: genericity and criticality
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180424T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180424T113000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4037
LOCATION:Resnick (Bldg. 209) 2nd floor seminar room
DESCRIPTION:Speaker: Guy Bunin\n
\n
Abstract:\n
Theoretical models are central to how we think of ecosystems\, and yet in many \n
aspects remain poorly understood. We identify a small number of parameters \n
that are sufficient to predict the large-scale properties of a wide variety \n
ecological-community models. These parameters thus play a role similar to \n
temperature and pressure in thermodynamics. We go on to study the generic \n
model that emerges\, and describe its phases\, including a critical phase where \n
all states are marginally stable.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4223:field_when:0:16
SUMMARY:Rayleigh-Taylor Instabilities by means of magnetic levitation of fluids
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180516T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180516T113000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4223
LOCATION:TBA
DESCRIPTION:Speaker: Charles Rosenblatt\, Case-Western\n
\n
Abstract:\n
The RT instability\, in which a dense fluid invades a less dense fluid under \n
acceleration such as gravity\, is pervasive throughout nature. General RT \n
instabilities lie at the heart of myriad applications and diverse \n
phenomena. For example\, RT instabilities occur during liquid impact and \n
atomization\, the explosion of supernovae\, inertial confinement fusion\, and \n
in granular media. More prosaically\, the RT instability affects resolution \n
control of ink-jet printers and appears when a bottle of vinegar-and-oil \n
salad dressing is turned upside down.\n
\n
Experimental work on the RT instability in fluids has\, until now\, been \n
plagued by jitter during acceleration of the tank that contains the fluids. \n
Here I will discuss our development of an alternate method that obviates this \n
problem\, viz.\, magnetic levitation of the dense fluid above the less dense \n
fluid. Using this approach\, we have been able to obtain a dispersion \n
relationship for the instability for not only a two fluid / one-interface \n
system\, but multiple layers as well. In the latter case\, the multiple \n
interfaces are found to couple and modify the dispersion relationship when \n
the intervening fluid layer is sufficiently thin. I will compare our \n
experimental results with long-standing\, but until now never tested\, \n
theoretical predictions.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4118:field_when:0:17
SUMMARY:Doppler Cooling of Lithium
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180117T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180117T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4118
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Yaakov Yudkin\n
\n
Abstract:\n
Different laser cooling mechanisms have been rising important questions from \n
thermodynamics and statistical physics point of view ever since the \n
beginning of this research field (over 40 years ago). Sisyphus cooling is \n
especially well known in this respect providing experimentally accessible \n
regime to study deviations from thermal equilibrium. Here we discuss the \n
Doppler cooling mechanism (the most basic laser cooling mechanism which \n
works even for a simple two-level atom) and show that it also supports \n
deviations from Gaussian statistics for a certain parameters range. We study \n
experimentally the Doppler cooling in Lithium and point out an interesting \n
deviation from the simple\, two-level theory\, namely cooling at resonance. We \n
develop a realistic theory which accounts for all energy levels of lithium \n
atoms and all laser fields and show its successes and failures.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4123:field_when:0:18
SUMMARY:Ferromagnetic Potts models with multi-site interaction
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180124T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20180124T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4123
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Nir Schreiber\n
\n
Abstract: The Potts model has been widely explored in the literature for the \n
last few decades. While many analytical and numerical results concern with \n
the traditional two site interaction model in various geometries and \n
dimensions\, little is yet known about models where more than two spins \n
simultaneously interact. We consider a ferromagnetic four site interaction \n
Potts model on the Square lattice\, where the four spins reside in the corners \n
of an elementary square. Each spin can take an integer value $1\,2\,...\,q$. We \n
write the partition function as a sum over clusters consisting of \n
monochromatic faces. When the number of faces becomes large\, tracing out spin \n
configurations is equivalent to enumerating large scale lattice animals. \n
This\, together with the observation that typically\, in large animals\, the \n
number of sites (to leading order) is equal to the number of faces\,implies \n
that systems with $q\leq 4$ and $q>4$ exhibit a second and first order phase \n
transitions\, respectively.However\, higher order terms can make the borderline \n
$q=4$ systems fall into the first order regime.We find ${1}/{\log q}$ to be \n
an upper bound on $T_c$\, the exact critical point.Using a low temperature \n
expansion\, we show that ${1}/{\theta\log q}$\, where $\theta>1$ is a $q$ \n
dependent geometrical term\, is an improved upper bound on $T_c$.Moreover\, \n
since large animals uniquely control long range order\, we expect that \n
$T_c=1/\theta\log q$.This expression is used to estimate the finite \n
correlation length in the first order transition case.These results can be \n
extended to other lattices.Our analytical predictions are confirmed \n
numerically by an extensive studyof the four site interaction model using the \n
Wang-Landau entropic sampling method for $q=3\,4\,5$.In particular\, the $q=4$ \n
model shows an ambiguous finite size pseudo-critical behavior.\n
END:VEVENT
BEGIN:VEVENT
UID:calendar:4077:field_when:0:19
SUMMARY:Enhancing the stability of stochastic populations via non-demographic noise
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20171227T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20171227T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4077
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Michael Assaf\n
\n
Abstract:\n
In the usual setting non-demographic noise\, emanating\, e.g.\, from \n
environmental variability\, is manifested by time-varying reaction rates. In \n
this work we investigate a different type of non-demographic noise in the \n
form of uncertainty in the reaction step-size\, and demonstrate that this type \n
of noise can have a dramatic effect on the stability of self-regulating \n
populations. By employing the usual reaction scheme mA->kA\, but allowing\, \n
e.g.\, the product number k to be a-priori unknown and sampled from a given \n
distribution\, we show that such non-demographic noise can greatly increase \n
the population's stability compared to the case of fixed k. Our analysis is \n
tested against numerical simulations\, and by using empirical data of \n
different species\, we argue that certain distributions may be more \n
evolutionary beneficial than others.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4073:field_when:0:20
SUMMARY:The Ideas behind the Self Consistent Expansion
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20171122T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20171122T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4073
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Moshe Schwartz\n
\n
Abstract:\n
A number of complex physical systems will be presented in a unified way and \n
the main idea of the SCE of mimicking the complex system by a simple but \n
arbitrary simple system will be outlined. Two very simple problems will be \n
presented as models for the application of the SCE\, showing its obvious \n
superiority over conventional treatments. Results for some of the complex \n
systems including KPZ and noise driven Navier-Stokes will be discussed.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4063:field_when:0:21
SUMMARY:Universality of biochemical feedback and its application to immune cells
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20171025T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20171025T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4063
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Amir Erez ( Princeton University)\n
\n
Abstract:\n
Positive feedback in biochemical networks can lead to a bifurcation in state \n
space. Universality implies that if molecules are well mixed\, this \n
bifurcation should exhibit the critical scaling behavior of the Ising \n
universality class in the mean-field limit. Making this statement \n
quantitative requires the appropriate mapping between the biochemical \n
parameters and the Ising parameters. Here we derive this mapping rigorously \n
and uniquely for a broad class of stochastic birth-death models with \n
feedback\, and show that the expected static and dynamic critical exponents \n
emerge. The generality of the mapping allows us to extract the order \n
parameter\, effective temperature\, magnetic field\, and heat capacity from T \n
cell flow cytometry data without needing to know the underlying molecular \n
details. We find that T cells obey critical scaling relations and exhibit \n
critical slowing down\, and that the heat capacity determines molecule number \n
from fluorescence data. We demonstrate that critical scaling holds even as \n
our system is driven out of its steady state\, via the Kibble-Zurek mechanism \n
for driven critical systems. Our approach places a ubiquitous biological \n
mechanism into a known class of physical systems and is immediately \n
applicable to other biological data.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4049:field_when:0:22
SUMMARY:A diverging length scale in the structure of jammed systems
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20171108T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20171108T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4049
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Daniel Hexner\n
\n
Abstract:\n
As temperature is lowered\, motion becomes more sluggish. Below the glass \n
transition temperature\, the dynamics of super-cooled liquids becomes so slow \n
that the system falls out of equilibrium. One hypothesis for this dynamic \n
arrest is that it is due to a thermodynamic phase transition with a diverging \n
length scale. However\, there is scant evidence of such a length scale \n
appearing in the structure. Motivated by this\, we study another amorphous \n
system that undergoes a phase transition: jammed soft repulsive spheres at \n
zero temperature. We have discovered a subtle correlation length\, \n
associated with the local coordination of particles\, that is not seen in the \n
two-point correlation function\, g(r). We argue that this scale plays an \n
important role in determining the local rigidity of the system\, and diverges \n
with an exponent 2/(d+1) as the jamming transition is approached.
END:VEVENT
BEGIN:VEVENT
UID:calendar:4001:field_when:0:23
SUMMARY:Emergent Many-body Interactions Suggest Inapplicability in Practice of Hard \n
Sphere Theory
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20171115T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20171115T120000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/4001
LOCATION:Colloquium Room 301
DESCRIPTION:Speaker: Yoav Pollack\n
\n
Abstract:\n
Inter-particle forces in amorphous solids such as glasses\, colloids and \n
granular material can be used to study phenomena such as jamming and \n
force-chains. So far\, no generally applicable methods exist for measuring \n
the forces between each and every particle in the system. Our recently \n
developed methods aim to x this unfortunate situation in both a-thermal and \n
thermal systems\, and produce some interesting insights as to the nature of \n
these forces. In the a-thermal case all that is required for nding the \n
force-law are the xed particle positions and the pressure. The method is \n
shown to accurately recover the force-law in simulation. In the thermal \n
case\, we are developing a method to extract an eective potential\, using the \n
mean positions. This will allow for analysis of thermal systems using tools \n
hitherto reserved for a-thermal ones\, and thereby prediction of \n
thermodynamic properties\, study of stability\, etc. Quite remarkably we \n
observe the emergence of eective many-body interactions\, even when the bare \n
interactions are purely 2-body. This resolves the puzzle posed by recent \n
studies that showed a quantitative match between 2D/3D measurements and the \n
innite dimension mean-eld prediction.\n
\n
END:VEVENT
BEGIN:VEVENT
UID:calendar:3976:field_when:0:24
SUMMARY:Anomalous dynamics of atoms in a 1D dissipative optical lattices
DTSTAMP;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20200529T225143
DTSTART;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20170607T103000
DTEND;TZID=Asia/Tel_Aviv;VALUE=DATE-TIME:20170607T103000
URL;VALUE=URI:https://physics.biu.ac.il/en/node/3976
LOCATION:Seminar Room\, 2nd Floor\, Resnick Bldg
DESCRIPTION:Speaker: Gadi Afek\n
\n
Abstract:\n
In this talk I will present an experimental study of the anomalous dynamics \n
of ultra-cold Rb atoms propagating in a 1D\, dissipative\, Sisyphus-type \n
optical lattice. We find that the width of the cloud exhibits a power-law \n
time dependence with an exponent that depends on the lattice depth. Moreover\, \n
the distribution exhibits fractional self-similarity with the same \n
characteristic exponent. The self-similar shape of the distribution is found \n
to be well fitted by a Lévy distribution. I will further present a \n
measurement of the phase-space density distribution (PSDD) of the cloud of \n
atoms. The PSDD is imaged using a direct tomographic method comprised of \n
velocity selection and spatial imaging. We show that the position-velocity \n
correlation function\, obtained from the PSDD\, decays asymptotically as a \n
function of time with a power-law that we relate to a simple scaling theory \n
involving the power-law asymptotic dynamics of the position and velocity. The \n
generality of this scaling theory is confirmed using Monte-Carlo simulations \n
of two distinct models of anomalous diffusion dynamics.\n
\n
END:VEVENT
END:VCALENDAR