7 research outputs found
Brownian yet non-Gaussian thermal machines
We investigate the performance of a Brownian thermal machine working in a
heterogeneous heat bath. The mobility of the heat bath fluctuates and it is
modelled as an Ornstein Uhlenbeck process. We trap the Brownian particle with
time-dependent harmonic potential and by changing the stiffness coefficient and
bath temperatures, we perform a Stirling cycle. We numerically calculate the
average absorbed work, the average ejected heat and the performance of the heat
pump. For shorter cycle times, we find that the performance of a Brownian yet
non-Gaussian heat pump is significantly higher than the normal (Gaussian) heat
pump. We numerically find the coefficient of performance at maximum heating
power.Comment: Comments and suggestions are most welcom
Microscopic origin of frictional rheology in dense suspensions: correlations in force space
We develop a statistical framework for the rheology of dense, non-Brownian
suspensions, based on correlations in a space representing forces, which is
dual to position space. Working with the ensemble of steady state
configurations obtained from simulations of suspensions in two dimensions, we
find that the anisotropy of the pair correlation function in force space
changes with confining shear stress () and packing fraction
(). Using these microscopic correlations, we build a statistical theory
for the macroscopic friction coefficient: the anisotropy of the stress tensor,
. We find that decreases (i) as is increased
and (ii) as is increased. Using a new constitutive relation
between and viscosity for dense suspensions that generalizes the
rate-independent one, we show that our theory predicts a Discontinuous Shear
Thickening (DST) flow diagram that is in good agreement with numerical
simulations, and the qualitative features of that lead to the generic
flow diagram of a DST fluid observed in experiments.Comment: 6 pages, 4 figures, +Supplemental Materia
Rejection-free cluster Wang-Landau algorithm for hard-core lattice gases
We introduce a rejection-free, flat histogram, cluster algorithm to determine the density of states of hard-core lattice gases. We show that the algorithm is able to efficiently sample low entropy states that are usually difficult to access, even when the excluded volume per particle is large. The algorithm is based on simultaneously evaporating all the particles in a strip and reoccupying these sites with a new appropriately chosen configuration. We implement the algorithm for the particular case of the hard-core lattice gas in which the first k next-nearest neighbors of a particle are excluded from being occupied. It is shown that the algorithm is able to reproduce the known results for k=1,2,3 both on the square and cubic lattices. We also show that, in comparison, the corresponding flat histogram algorithms with either local moves or unbiased cluster moves are less accurate and do not converge as the system size increases
The freezing phase transition in hard core lattice gases on triangular lattice with exclusion up to seventh next-nearest neighbor
Hard core lattice gas models are minimal models to study entropy driven phase
transitions. In the -NN lattice gas, a particle excludes all sites upto the
-th next-nearest neighbors from being occupied by another particle. As
increases from one, it extrapolates from nearest neighbor exclusion to the hard
sphere gas. In this paper, we study the model on the triangular lattice for
using a flat histogram algorithm that includes cluster moves. Earlier
studies had focused on . We show that for , the system
undergoes a single phase transition from a low-density fluid phase to a
high-density sublattice-ordered phase. Using partition function zeros and
non-convexity properties of the entropy, we show that the transitions are
discontinuous. The critical chemical potential, coexistence densities, and
critical pressure are determined accurately.Comment: 14 pages and 20 figures in main paper. 5 pages and 4 figures in
supplemental materia
Freezing phase transition in hard-core lattice gases on the triangular lattice with exclusion up to seventh next-nearest neighbor
Hard-core lattice-gas models are minimal models to study entropy-driven phase transitions. In the k-nearest-neighbor lattice gas, a particle excludes all sites up to the kth next-nearest neighbors from being occupied by another particle. As k increases from one, it extrapolates from nearest-neighbor exclusion to the hard-sphere gas. In this paper we study the model on the triangular lattice for k≤7 using a flat histogram algorithm that includes cluster moves. Earlier studies focused on k≤3
. We show that for 4≤k≤7, the system undergoes a single phase transition from a low-density fluid phase to a high-density sublattice-ordered phase. Using partition function zeros and nonconvexity properties of the entropy, we show that the transitions are discontinuous. The critical chemical potential, coexistence densities, and critical pressure are determined accurately