1,125 research outputs found
The 3D printing of a polymeric electrochemical cell body and its characterisation
An undivided flow cell was designed and constructed using additive manufacturing technology and its mass transport characteristics were evaluated using the reduction of ferricyanide, hexacyanoferrate (III) ions at a nickel surface. The dimensionless mass transfer correlation Sh = aRebScdLee was obtained using the convective-diffusion limiting current observed in linear sweep voltammetry; this correlation compared closely with that reported in the literature from traditionally machined plane parallel rectangular flow channel reactors. The ability of 3D printer technology, aided by computational graphics, to rapidly and conveniently design, manufacture and re-design the geometrical characteristics of the flow cell ishighlighted
On the second reference state and complete eigenstates of the open XXZ chain
The second reference state of the open XXZ spin chain with non-diagonal
boundary terms is studied. The associated Bethe states exactly yield the second
set of eigenvalues proposed recently by functional Bethe Ansatz. In the
quasi-classical limit, two sets of Bethe states give the complete eigenstates
of the associated Gaudin model.Comment: Latex file, 12 pages; New version appears in JHE
Quantum renormalization group of XYZ model in a transverse magnetic field
We have studied the zero temperature phase diagram of XYZ model in the
presence of transverse magnetic field. We show that small anisotropy (0 =<
Delta <1) is not relevant to change the universality class. The phase diagram
consists of two antiferromagnetic ordering and a paramagnetic phases. We have
obtained the critical exponents, fixed points and running of coupling constants
by implementing the standard quantum renormalization group. The continuous
phase transition from antiferromagnetic (spin-flop) phase to a paramagnetic one
is in the universality class of Ising model in transverse field. Numerical
exact diagonalization has been done to justify our results. We have also
addressed on the application of our findings to the recent experiments on
Cs_2CoCl_4.Comment: 5 pages, 5 figures, new references added to the present versio
Establishing the relationship between galaxies and dark matter
We use two methods to establish the relationship between galaxies and dark matter halos. One is based the conditional luminosity function model, which links galaxies and dark matter halos by matching the number density and clustering properties of galaxies with those of dark matter halos in the current CDM model. The second is based on galaxy systems identified from large redshift surveys of galaxies. The galaxy - dark halo relationships established by these two methods match well, and can provide important constraints on how galaxies form and evolve in the univers
Entanglement in quantum computers described by the XXZ model with defects
We investigate how to generate maximally entangled states in systems
characterized by the Hamiltonian of the XXZ model with defects. Some proposed
quantum computers are described by such model. We show how the defects can be
used to obtain EPR states and W states when one or two excitations are
considered.Comment: 4 pages, 1 figur
Behaviour of the energy gap near a commensurate-incommensurate transition in double layer quantum Hall systems at nu=1
The charged excitations in the system of the title are vortex-antivortex
pairs in the spin-texture described in the theory by Yang et al which, in the
commensurate phase, are bound together by a ``string''. It is shown that their
excitation energy drops as the string lengthens as the parallel magnetic field
approaches the critical value, then goes up again in the incommensurate phase.
This produces a sharp downward cusp at the critical point. An alternative
description based on the role of disorder in the tunnelling and which appears
not to produce a minimum in the excitation energy is also discussed. It is
suggested that a similar transition could also occur in compressible
Fermi-liquid-like states.Comment: latex file, 17 page
Lorenz-like systems and classical dynamical equations with memory forcing: a new point of view for singling out the origin of chaos
A novel view for the emergence of chaos in Lorenz-like systems is presented.
For such purpose, the Lorenz problem is reformulated in a classical mechanical
form and it turns out to be equivalent to the problem of a damped and forced
one dimensional motion of a particle in a two-well potential, with a forcing
term depending on the ``memory'' of the particle past motion. The dynamics of
the original Lorenz system in the new particle phase space can then be
rewritten in terms of an one-dimensional first-exit-time problem. The emergence
of chaos turns out to be due to the discontinuous solutions of the
transcendental equation ruling the time for the particle to cross the
intermediate potential wall. The whole problem is tackled analytically deriving
a piecewise linearized Lorenz-like system which preserves all the essential
properties of the original model.Comment: 48 pages, 25 figure
Phase diagram of a coupled tetrahedral Heisenberg model
The phase diagram of a coupled tetrahedral Heisenberg model is obtained. The
quantum chain has a local gauge symmetry and its eigenspectrum is obtained by
the composition of the eigenspectra of spin-1/2 XXZ chains with arbitrary
distribution of spin-3/2 impurities. The phase diagram is quite rich with an
infinite number of phases with ferromagnetic, antiferromagnetic or
ferrimagnetic order. In some cases the ground state and the low lying
eigenlevels of the model can be exactly calculated since they coincide with the
eigenlevels of the exactly integrable XXZ chain. The thermodynamical properties
of the model at low temperatures is also studied through finite-size analysis.Comment: 23 pages, 15 figure
Effects of dimers on cooperation in the spatial prisoner's dilemma game
We investigate the evolutionary prisoner's dilemma game in structured
populations by introducing dimers, which are defined as that two players in
each dimer always hold a same strategy. We find that influences of dimers on
cooperation depend on the type of dimers and the population structure. For
those dimers in which players interact with each other, the cooperation level
increases with the number of dimers though the cooperation improvement level
depends on the type of network structures. On the other hand, the dimers, in
which there are not mutual interactions, will not do any good to the
cooperation level in a single community, but interestingly, will improve the
cooperation level in a population with two communities. We explore the
relationship between dimers and self-interactions and find that the effects of
dimers are similar to that of self-interactions. Also, we find that the dimers,
which are established over two communities in a multi-community network, act as
one type of interaction through which information between communities is
communicated by the requirement that two players in a dimer hold a same
strategy.Comment: 12 pages and 3 figure
Lifetime elongation for wireless sensor network using queue-based approaches
A wireless sensor network (WSN) is envisioned as a cluster of tiny power-constrained devices with functions of sensing and communications. Sensors closer to a sink node have a larger forwarding traffic burden and consume more energy than nodes further away from the sink. The whole lifetime of WSN is deteriorated because of such an uneven node power consumption patterns, leading to what is known as an energy hole problem (EHP). From open literatures, most research works have focused on how to optimally increase the probability of sleeping states using various wake-up strategies. In this article, we propose a novel power-saving scheme to alleviate the EHP based on the N-policy M/M/1 queuing theory. With little or no extra management cost, the proposed queue-based power-saving technique can be applied to prolong the lifetime of the WSN economically and effectively. A mathematical analysis on the optimal control parameter has been made in detail. Focusing on many-to-one WSN, numerical and network simulation results validate that the proposed approach indeed provides a feasibly cost-effective approach for lifetime elongation of WSN
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