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Stringer M.J.,Stanford University | Stringer M.J.,Kavli Institute of Theoretical Physics | Brooks A.M.,California Institute of Technology | Brooks A.M.,Kavli Institute of Theoretical Physics | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

Recent focus on the importance of cold, unshocked gas accretion in galaxy formation - not explicitly included in semi-analytic studies - motivates the following detailed comparison between two inherently different modelling techniques: direct hydrodynamical simulation and semi-analytic modelling. By analysing the physical assumptions built into the gasoline simulation, formulae for the emergent behaviour are derived which allow immediate and accurate translation of these assumptions to the galform semi-analytic model. The simulated halo merger history is then extracted and evolved using these equivalent equations, predicting a strikingly similar galactic system. This exercise demonstrates that it is the initial conditions and physical assumptions which are responsible for the predicted evolution, not the choice of modelling technique. On this level playing field, a previously published galform model is applied (including additional physics such as chemical enrichment and feedback from active galactic nuclei) which leads to starkly different predictions. © 2010 The Authors. Journal compilation © 2010 RAS.

Moetakef P.,University of California at Santa Barbara | Jackson C.A.,University of California at Santa Barbara | Hwang J.,University of California at Santa Barbara | Balents L.,Kavli Institute of Theoretical Physics | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We investigate correlation physics in high-density, two-dimensional electron liquids that reside in narrow SrTiO 3 quantum wells. The quantum wells are remotely doped via an interfacial polar discontinuity and the three-dimensional (3D) carrier density is modulated by changing the width of the quantum well. It is shown that even at 3D densities well below one electron per site, short-range Coulomb interactions become apparent in transport, and an insulating state emerges at a critical density. We also discuss the role of disorder in the insulating state. © 2012 American Physical Society.

Truong Quang B.-A.,Aix - Marseille University | Mani M.,Kavli Institute of Theoretical Physics | Mani M.,University of California at Santa Barbara | Markova O.,Aix - Marseille University | And 2 more authors.
Current Biology | Year: 2013

Background E-cadherin plays a pivotal role in tissue morphogenesis by forming clusters that support intercellular adhesion and transmit tension. What controls E-cadherin mesoscopic organization in clusters is unclear. Results We use 3D superresolution quantitative microscopy in Drosophila embryos to characterize the size distribution of E-cadherin nanometric clusters. The cluster size follows power-law distributions over three orders of magnitude with exponential decay at large cluster sizes. By exploring the predictions of a general theoretical framework including cluster fusion and fission events and recycling of E-cadherin, we identify two distinct active mechanisms setting the cluster-size distribution. Dynamin-dependent endocytosis targets large clusters only, thereby imposing a cutoff size. Moreover, interactions between E-cadherin clusters and actin filaments control the fission in a size-dependent manner. Conclusions E-cadherin clustering depends on key cortical regulators, which provide tunable and local control over E-cadherin organization. Our data provide the foundation for a quantitative understanding of how E-cadherin distribution affects adhesion and might regulate force transmission in vivo. © 2013 Elsevier Ltd.

Ambegaonkar A.A.,Rutgers University | Pan G.,Rutgers University | Mani M.,Kavli Institute of Theoretical Physics | Feng Y.,Rutgers University | Irvine K.D.,Rutgers University
Current Biology | Year: 2012

The Fat pathway controls both planar cell polarity (PCP) and organ growth [1, 2]. Fat signaling is regulated by the graded expression of the Fat ligand Dachsous (Ds) and the cadherin-domain kinase Four-jointed (Fj). The vectors of these gradients influence PCP [1], whereas their slope can influence growth [3, 4]. The Fj and Ds gradients direct the polarized membrane localization of the myosin Dachs, which is a crucial downstream component of Fat signaling [5-7]. Here we show that repolarization of Dachs by differential expression of Fj or Ds can propagate through the wing disc, which indicates that Fj and Ds gradients can be measured over long range. Through characterization of tagged genomic constructs, we show that Ds and Fat are themselves partially polarized along the endogenous Fj and Ds gradients, providing a mechanism for propagation of PCP within the Fat pathway. We also identify a biochemical mechanism that might contribute to this polarization by showing that Ds is subject to endoproteolytic cleavage and that the relative levels of Ds isoforms are modulated by Fat. © 2012 Elsevier Ltd.

Mittal S.,University of Maryland University College | Orre V.V.,University of Maryland University College | Hafezi M.,University of Maryland University College | Hafezi M.,Kavli Institute of Theoretical Physics
Optics Express | Year: 2016

We theoretically study the transport of time-bin entangled photon pairs in a two-dimensional topological photonic system of coupled ring resonators. This system implements the integer quantum Hall model using a synthetic gauge field and exhibits topologically robust edge states. We show that the transport through edge states preserves temporal correlations of entangled photons whereas bulk transport does not preserve these correlations and can lead to significant unwanted temporal bunching or anti-bunching of photons. We study the effect of disorder on the quantum transport properties; while the edge transport remains robust, bulk transport is very susceptible, and in the limit of strong disorder, bulk states become localized. We show that this localization is manifested as an enhanced bunching/anti-bunching of photons. This topologically robust transport of correlations through edge states could enable robust on-chip quantum communication channels and delay lines for information encoded in temporal correlations of photons. © 2016 Optical Society of America.

De Back W.,TU Dresden | Zhou J.X.,Institute for Systems Biology | Zhou J.X.,Kavli Institute of Theoretical Physics | Brusch L.,TU Dresden
Journal of the Royal Society Interface | Year: 2013

The cell fate decision of multi-potent pancreatic progenitor cells between the exocrine and endocrine lineages is regulated by Notch signalling, mediated by cell-cell interactions. However, canonical models of Notch-mediated lateral inhibition cannot explain the scattered spatial distribution of endocrine cells and the cell-type ratio in the developing pancreas. Based on evidence from acinar-to-islet cell transdifferentiation in vitro, we propose that lateral stabilization, i.e. positive feedback between adjacent progenitor cells, acts in parallel with lateral inhibition to regulate pattern formation in the pancreas. A simple mathematical model of transcriptional regulation and cell-cell interaction reveals the existence of multi-stability of spatial patterns whose simultaneous occurrence causes scattering of endocrine cells in the presence of noise. The scattering pattern allows for control of the endocrine-to-exocrine cell-type ratio by modulation of lateral stabilization strength. These theoretical results suggest a previously unrecognized role for lateral stabilization in lineage specification, spatial patterning and cell-type ratio control in organ development. © 2012 The Author(s) Published by the Royal Society. All rights reserved.

Chervanyov A.I.,Leibniz Institute of Polymer Research | Chervanyov A.I.,Kavli Institute of Theoretical Physics | Heinrich G.,Leibniz Institute of Polymer Research
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

By applying the Edwards self-consistent field theory, we calculate the polymer density and free energy excesses caused by the presence of nanocolloids in the excluded volume polymer system. Using the obtained results, we have calculated the depletion potential U as a function of the separation between colloids, colloid radius, polymer volume fraction, and polymer gyration radius. Upon analyzing the obtained results against the known exact asymptotic small-separation limit and scaling relations, we propose an approximate expression for U that builds upon our exact result. This expression is shown to give excellent agreement with Monte Carlo simulations. Reliability of the derived analytical expression for the depletion potential and its relation to the previous theoretical and simulation work are thoroughly discussed. © 2012 American Physical Society.

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