2,962 research outputs found
Driven inelastic Maxwell gases
We consider the inelastic Maxwell model, which consists of a collection of
particles that are characterized by only their velocities, and evolving through
binary collisions and external driving. At any instant, a particle is equally
likely to collide with any of the remaining particles. The system evolves in
continuous time with mutual collisions and driving taken to be point processes
with rates and respectively. The mutual collisions
conserve momentum and are inelastic, with a coefficient of restitution . The
velocity change of a particle with velocity , due to driving, is taken to be
, mimicking the collision with a vibrating wall,
where the coefficient of restitution of the particle with the "wall" and
is Gaussian white noise. The Ornstein-Uhlenbeck driving mechanism given
by is found to be a special case of the driving
modeled as a point process. Using both the continuum and discrete versions we
show that while the equations for the one-particle and the two-particle
velocity distribution functions do not close, the joint evolution equations of
the variance and the two-particle velocity correlation functions close. With
the exact formula for the variance we find that, for , the system
goes to a steady state. On the other hand, for , the system does not
have a steady state. Similarly, the system goes to a steady state for the
Ornstein-Uhlenbeck driving with , whereas for the purely
diffusive driving (), the system does not have a steady state.Comment: 9 pages, 4 figure
Fluctuation theorem in quantum heat conduction
We consider steady state heat conduction across a quantum harmonic chain
connected to reservoirs modelled by infinite collection of oscillators. The
heat, , flowing across the oscillator in a time interval is a
stochastic variable and we study the probability distribution function .
In the large limit we use the formalism of full counting statistics
(FCS) to compute the generating function of exactly. We show that
satisfies the steady state fluctuation theorem (SSFT) regardless of the
specifics of system, and it is nongaussian with clear exponential tails. The
effect of finite and nonlinearity is considered in the classical limit
through Langevin simulations. We also obtain predictions of universal heat
current fluctuations at low temperatures in clean wires.Comment: 4 pages, 2 figure
Eulerian Walkers as a model of Self-Organised Criticality
We propose a new model of self-organized criticality. A particle is dropped
at random on a lattice and moves along directions specified by arrows at each
site. As it moves, it changes the direction of the arrows according to fixed
rules. On closed graphs these walks generate Euler circuits. On open graphs,
the particle eventually leaves the system, and a new particle is then added.
The operators corresponding to particle addition generate an abelian group,
same as the group for the Abelian Sandpile model on the graph. We determine the
critical steady state and some critical exponents exactly, using this
equivalence.Comment: 4 pages, RevTex, 4 figure
Mean field analysis of quantum phase transitions in a periodic optical superlattice
In this paper we analyze the various phases exhibited by a system of
ultracold bosons in a periodic optical superlattice using the mean field
decoupling approximation. We investigate for a wide range of commensurate and
incommensurate densities. We find the gapless superfluid phase, the gapped Mott
insulator phase, and gapped insulator phases with distinct density wave orders.Comment: 6 pages, 7 figures, 4 table
Quantum Phases of Ultracold Bosonic Atoms in a One Dimensional Optical Superlattice
We analyze various quantum phases of ultracold bosonic atoms in a periodic
one dimensional optical superlattice. Our studies have been performed using the
finite size density matrix renormalization group (FS-DMRG) method in the
framework of the Bose-Hubbard model. Calculations have been carried out for a
wide range of densities and the energy shifts due to the superlattice
potential. At commensurate fillings, we find the Mott insulator and the
superfluid phases as well as Mott insulators induced by the superlattice. At a
particular incommensurate density, the system is found to be in the superfluid
phase coexisting with density oscillations for a certain range of parameters of
the system.Comment: 7 pages, 11 figure
Simultaneous Ejection of Six Electrons at a Constant Potential by Hexakis(4-ferrocenylphenyl)benzene
A simple synthesis of a dendritic hexaferrocenyl electron donor (5) is described in which six ferrocene moieties are connected at the vertices of the propeller of the hexaphenylbenzene core. The molecular structure of 5 is confirmed by X-ray crystallography. An electrochemical analysis along with redox titrations (which are tantamount to coulometry) confirmed that it ejects six electrons at a single potential
I Stood Up: Social Design in Practice
Through practice-based research, we explore how interdisciplinary design projects can function to address social issues concerning environmental and social problems. Using two case studies developed between London in the United Kingdom, and Delhi and Ahmedabad in India, we discuss the importance of engagement with the people who the design ultimately serves. Finally, we argue that design concerned with complex social problems require equally complex, multidimensional responses, informed by bodies of knowledge, practices and approaches that lie outside of traditional design approaches
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