68 research outputs found
Fluctuation-Induced Casimir Forces in Granular Fluids
We have numerically investigated the behavior of driven non-cohesive granular
media and found that two fixed large intruder particles, immersed in a sea of
small particles, experience, in addition to a short range depletion force, a
long range repulsive force. The observed long range interaction is
fluctuation-induced and we propose a mechanism similar to the Casimir effect
that generates it: the hydrodynamic fluctuations are geometrically confined
between the intruders, producing an unbalanced renormalized pressure. An
estimation based on computing the possible Fourier modes explains the repulsive
force and is in qualitative agreement with the simulations.Comment: 4 pages, 3 figures. Accepted in Phys. Rev. Letter
Analytic thermodynamics and thermometry of Gaudin-Yang Fermi gases
We study the thermodynamics of a one-dimensional attractive Fermi gas (the
Gaudin-Yang model) with spin imbalance. The exact solution has been known from
the thermodynamic Bethe ansatz for decades, but it involves an infinite number
of coupled nonlinear integral equations whose physics is difficult to extract.
Here the solution is analytically reduced to a simple, powerful set of four
algebraic equations. The simplified equations become universal and exact in the
experimental regime of strong interaction and relatively low temperature. Using
the new formulation, we discuss the qualitative features of finite-temperature
crossover and make quantitative predictions on the density profiles in traps.
We propose a practical two-stage scheme to achieve accurate thermometry for a
trapped spin-imbalanced Fermi gas.Comment: 4 pages, 2 figures; published version (v2
Reentrant Peak Effect in an anisotropic superconductor 2H-NbSe_2 : Role of disorder
The reentrant nature of Peak Effect is established in a single crystal of
2H-NbSe_2 via electrical transport and dc magnetisation studies. The role of
disorder on the reentrant branch of PE has been examined in three single
crystals with varying levels of quenched random disorder. Increasing disorder
presumably shrinks the (H,T) parameter space over which vortex array retains
spatial order. Although, the upper branch of the PE curve is somewhat robust,
the lower reentrant branch of the same curve is strongly affected by disorder.Comment: 5 Pages of text, 4 figure
Determination of Boundary Scattering, Intermagnon Scattering, and the Haldane Gap in Heisenberg Chains
Low-lying magnon dispersion in a S=1 Heisenberg antiferromagnetic (AF) chain
is analyzed using the non-Abelian DMRG method. The scattering length of the boundary coupling and the inter-magnon scattering length are
determined. The scattering length is found to exhibit a
characteristic diverging behavior at the crossover point. In contrast, the
Haldane gap , the magnon velocity , and remain constant at the
crossover. Our method allowed estimation of the gap of the S=2 AF chain to be
using a chain length longer than the correlation length
.Comment: 6 pages, 3 figures, 1 table, accepted in Phys. Rev.
Criticality and isostaticity in fiber networks
The rigidity of elastic networks depends sensitively on their internal
connectivity and the nature of the interactions between constituents. Particles
interacting via central forces undergo a zero-temperature rigidity-percolation
transition near the isostatic threshold, where the constraints and internal
degrees of freedom are equal in number. Fibrous networks, such as those that
form the cellular cytoskeleton, become rigid at a lower threshold due to
additional bending constraints. However, the degree to which bending governs
network mechanics remains a subject of considerable debate. We study disordered
fibrous networks with variable coordination number, both above and below the
central-force isostatic point. This point controls a broad crossover from
stretching- to bending-dominated elasticity. Strikingly, this crossover
exhibits an anomalous power-law dependence of the shear modulus on both
stretching and bending rigidities. At the central-force isostatic point---well
above the rigidity threshold---we find divergent strain fluctuations together
with a divergent correlation length , implying a breakdown of continuum
elasticity in this simple mechanical system on length scales less than .Comment: 6 pages, 5 figure
Slow Relaxation and Phase Space Properties of a Conservative System with Many Degrees of Freedom
We study the one-dimensional discrete model. We compare two
equilibrium properties by use of molecular dynamics simulations: the Lyapunov
spectrum and the time dependence of local correlation functions. Both
properties imply the existence of a dynamical crossover of the system at the
same temperature. This correlation holds for two rather different regimes of
the system - the displacive and intermediate coupling regimes. Our results
imply a deep connection between slowing down of relaxations and phase space
properties of complex systems.Comment: 14 pages, LaTeX, 10 Figures available upon request (SF), Phys. Rev.
E, accepted for publicatio
Active Tension Network model suggests an exotic mechanical state realized in epithelial tissues.
Mechanical interactions play a crucial role in epithelial morphogenesis, yet understanding the complex mechanisms through which stress and deformation affect cell behavior remains an open problem. Here we formulate and analyze the Active Tension Network (ATN) model, which assumes that the mechanical balance of cells within a tissue is dominated by cortical tension and introduces tension-dependent active remodeling of the cortex. We find that ATNs exhibit unusual mechanical properties. Specifically, an ATN behaves as a fluid at short times, but at long times supports external tension like a solid. Furthermore, an ATN has an extensively degenerate equilibrium mechanical state associated with a discrete conformal - "isogonal" - deformation of cells. The ATN model predicts a constraint on equilibrium cell geometries, which we demonstrate to approximately hold in certain epithelial tissues. We further show that isogonal modes are observed in the fruit y embryo, accounting for the striking variability of apical areas of ventral cells and helping understand the early phase of gastrulation. Living matter realizes new and exotic mechanical states, the study of which helps to understand biological phenomena
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