Yair Shokef - Research Interests

Yair Shokef

(formerly Srebro)

Postdoctoral Fellow


Research	Publications	CV	Contact	Home


Geometric Frustration in Buckled Colloidal Monolayers (with Tom Lubensky)
	Densely-packed hard-spheres between walls separated slightly more than one sphere diameter are reminiscent of anti-ferromagnetic Ising spins on a triangular lattice. Maximization of free volume induces effective repulsion between spheres, which thus select two states close to either wall. As in the Ising model, each triplet of neighbors is frustrated since they cannot simultaneously have all pairs close to opposite walls. Diameter-tunable microgel spheres have recently been used in Arjun Yodh`s lab at Penn to investigate the single-particle dynamics of this system. We participated in analyzing these experiments, and we furthermore constructed a simple model to estimate the total free volume of the system and used it in conjunction with three-dimensional Monte-Carlo simulations to explore the anti-ferromagnetic analogy. We showed how and why mapping to the Ising model fails. We explained the zigzagged stripe patterns found in experiments and simulations by mapping the sphere packing problem to tiling of the plane with isosceles triangles. The hard-sphere system has lower ground-state degeneracy than the Ising model and zero-energy modes are absent, which explains the slow dynamics observed in experiments and simulations.
		Geometric Frustration in Buckled Colloidal Monolayers Y. Han(), Y. Shokef(), A.M. Alsayed, P. Yunker, T.C. Lubensky, and A.G. Yodh () These authors contributed equally to this work. Submitted to Nature, preprint arXiv:0807.3905 Stripes, Zigzags, and Slow Dynamics in Buckled Hard Spheres Y. Shokef* and T.C. Lubensky Submitted to Physical Review Letters, preprint arXiv:0807.4884

Non-Equilibrium Statistical Mechanics of Dividing Cell Populations (with Naama Brenner)
	We suggested a model describing the dynamics of protein distributions in a proliferating cell population, motivated by chemostasis experiments on yeast in steady state growth performed in Erez Braun`s lab at the Technion. Protein variation in our model is affected by a stochastic source internal to the cells and variation in division and inheritance at the population level, enabling us to assess the contribution and character of each of these components separately. We drew an analogy between the dynamics of protein distributions along cell generations and that of stress in layers of granular material. In both cases a model with deterministic production and uniform division can be solved exactly. However, in contrast to the granular model, where a universal tail has been found, here we found sensitivity to the division function due to the inheritance structure of the biological population.
		Non-equilibrium statistical mechanics of dividing cell populations N. Brenner and Y. Shokef Physical Review Letters 99, 138102 (2007)

Contact between non-equilibrium systems (with Gal Shulkind and Dov Levine)
	In order to understand what happens when systems in steady states far from thermodynamic equilibrium are connected, we suggested dynamics that dissipate energy locally but conserve it globally. We demonstrated that entropy does not necessarily increase due to contact between systems, and that it may in fact decrease when the macroscopic constraint separating the systems is removed. We found that several commonly used definitions of effective temperatures do not describe the dynamics, since none of them tends to equalize across different systems in contact. We identified the operational temperature of these systems, which controls energy flow until equalizing in the mutual steady state the systems reach, and does not depend on the contact details but only on each system�s properties. During the investigation of such isolated non-equilibrium systems we also showed how the irreversibility of the dynamics brings about net probability currents and detailed balance violation, as well as ergodicity breaking in the form of dynamically inaccessible states.
		Isolated non-equilibrium systems in contact Y. Shokef, G. Shulkind, and D. Levine Physical Review E 76, 030101(R) (2007)

Minimal Modeling of Driven Dissipative Systems (with Dov Levine and Guy Bunin)
	During my PhD, we began by constructing molecular dynamics simulations to investigate energy distributions and spatial clustering in granular gases. Scaling arguments and mean-field calculations performed for the granular temperature in these systems helped us gain insight on the nature of energy flow in more general driven dissipative systems. We then introduced a solvable stochastic model for dissipative interactions in generic systems, including granular materials, foams, colloidal suspensions and bacterial baths. We solved the non-Boltzmann energy distribution and demonstrated the variance between different effective temperatures and the violation of time-dependent fluctuation-dissipation relations. By considering distributions in possible phase spaces we showed that an allegedly non-equilibrium model presented by Bertin, Dauchot & Droz is in fact in equilibrium. In the Maxwell model for driven granular gases, where all grains are equally likely to collide with each other, we showed that time dependent fluctuation-dissipation relations exactly hold in any spatial dimension. For actual dilute gases, where the collision rate is proportional to the relative velocity of each pair of particles, we connected a previously established result concerning the long time limit with analysis we performed for the short time limit in order to show that the ratio of correlation to response depends weakly on the measurement time-scale.
		Exactly solvable model for driven dissipative systems Y. Srebro and D. Levine Physical Review Letters 93, 240601 (2004) Comment on "Temperature in nonequilibrium systems with conserved energy" Y. Srebro and D. Levine Physical Review Letters 94, 208901 (2005) Fluctuation-dissipation relations in driven dissipative systems Y. Shokef, G. Bunin and D. Levine Physical Review E 73, 046132 (2006) Energy distribution and effective temperatures in a driven dissipative model Y. Shokef and D. Levine Physical Review E 74, 051111 (2006) Frequency-dependent fluctuation-dissipation relations in granular gases G. Bunin, Y. Shokef, and D. Levine Physical Review E 77, 051301 (2008)

Granular Packing (with Dov Levine)
	We investigated the role of friction in compaction and segregation of dense granular packings. We incorporated friction into the thermodynamic hypothesis of Edwards, and analyzed grain segregation in this context. This provided a testable consequence of the Edwards approach.
		Role of friction in compaction and segregation of granular materials Y. Srebro and D. Levine Physical Review E 68, 061301 (2003)

Hydrodynamic Instabilities and Inertial Confinement Fusion (with Dov Shvarts et al.)
	During my MSc, we used numerical simulations supported by simple physical arguments to study the equivalence between nonuniformities in the laser intensity and effective mass perturbations in the target during direct drive inertial confinement fusion implosions. This work involved planning and analyzing experiments conducted at the OMEGA laser at the University of Rochester. To study the effect of turbulent mixing on inertial confinement fusion, we integrated various models for turbulent mixing with detailed hydrodynamic simulations, related to implosion experiments at the OMEGA laser. We developed simple models combined with numerical simulations to investigate the non-linear evolution of instabilities at accelerated fluid interfaces, generalizing the Rayleigh-Taylor and Richtmyer-Meshkov instabilities. During our collaboration with experiments done in Gabi Ben-Dor`s lab at Ben-Gurion University, we considered the evolution of turbulent mixing from the multi-mode perturbations at an initially flat interface, the growth of pre-imposed single- and bi- modal distributions, and the response of intruder bubbles to shock waves.
		Nonlinear evolution of broad-bandwidth, laser-imprinted nonuniformities in planar targets accelerated by 351-nm laser light V. A. Smalyuk, T. R. Boehly, D. K. Bradley, V. N. Gonocharov, J. A. Delettrez, J. P. Knauer, D. D. Meyerhofer, D. Oron, D. Shvarts , Y. Srebro and R. P. J. Town Physics of Plasmas 6, 4022-4036 (1999) Studies in the nonlinear evolution of the Rayleigh-Taylor and Richtmyer-Meshkov instabilities and their role in inertial confinement fusion D. Oron, O. Sadot, Y. Srebro, A. Rikanati, Y. Yedvab, U. Alon, L. Erez, G. Erez, G. Ben-Dor, L. A. Levin, D. Ofer and D. Shvarts Laser and Particle Beams 17, 465-475 (1999) Scaling laws of nonlinear Rayleigh-Taylor and Richtmyer-Meshkov instabilities in two and three dimensions D. Shvarts, D. Oron, D. Kartoon, A. Rikanati, O. Sadot, Y. Srebro, Y. Yedvab, D. Ofer, A. Levin, E. Sarid, G. Ben-Dor, L. Erez, G. Erez, A. Yosef-Hai, U. Alon and L. Arazi Comptes Rendus de l'Acad�mie des Sciences - Series IV - Physics 1, 719-726 (2000) Optical and plasma smoothing of laser imprinting in targets driven by lasers with SSD bandwidths up to 1 THz T. R. Boehly, V. N. Goncharov, O. Gotchev, J. P. Knauer, D. D. Meyerhofer, D. Oron, S. P. Regan, Y. Srebro, W. Seka, D. Shvarts, S. Skupsky and V. A. Smalyuk Physics of Plasmas 8, 2331-2337 (2001) Modeling turbulent mixing in inertial confinement fusion implosions Y. Srebro, D. Kushnir, Y. Elbaz and D. Shvarts Laser and Particle Beams 21, 355-361 (2003) A general buoyancy-drag model for the evolution of the Rayleigh-Taylor and Richtmyer-Meshkov instabilities Y. Srebro, Y. Elbaz, O. Sadot, L. Arazi and D. Shvarts Laser and Particle Beams 21, 347-353 (2003) Scaling in the shock-bubble interaction K. Levy, O. Sadot, A. Rikanati, D. Kartoon, Y. Srebro, A. Yosef-Hai, G. Ben-Dor and D. Shvarts Laser and Particle Beams 21, 335-339 (2003) Two-dimensional simulations of plastic-shell, direct-drive implosions on OMEGA P. B. Radha, V. N. Goncharov, T. J. B. Collins, J. A. Delettrez, Y. Elbaz, V. Yu. Glebov, R. L. Keck, D. E. Keller, J. P. Knauer, J. A. Marozas, F. J. Marshall, P. W. McKenty, D. D. Meyerhofer, S. P. Regan, T. C. Sangster, D. Shvarts, S. Skupsky, Y. Srebro, R. P. J. Town and C. Stoeckl Physics of Plasmas 12, 032702 (2005) Multidimensional analysis of direct-drive, plastic-shell implosions on OMEGA P. B. Radha, T. J. B. Collins, J. A. Delettrez, Y. Elbaz, R. Epstein, V. Yu. Glebov, V. N. Goncharov, R. L. Keck, J. P. Knauer, J. A. Marozas, F. J. Marshall, R. L. McCrory, P. W. McKenty, D. D. Meyerhofer, S. P. Regan, T. C. Sangster, W. Seka, D. Shvarts, S. Skupsky, Y. Srebro and C. Stoeckl Physics of Plasmas 12, 056307 (2005) Studying hydrodynamic instabilities using shock-tube experiments O. Sadot, K. Levy, A. Yosef-Hai, D. Cartoon, Y. Elbaz, Y. Srebro, G. Ben-Dor and D. Shvarts Astrophysics and Space Science 298, 305 (2005)