2,716 research outputs found
A Language and Toolset for the Synthesis and Efficient Simulation of Clock-Cycle-True Signal-Processing Algorithms
Optimal simulation speed and synthesizability are contradictory requirements for a hardware description language. This paper presents a language and toolset that enables both synthesis and fast simulation of fixed-point signal processing algorithms at the register-transfer level using a single system description. This is achieved by separate code generators for different purposes. Code-generators have been developed for fast simulation (using ANSI-C) and for synthesis (using VHDL). The simulation performance of the proposed approach has been compared with other known methods and turns out to be comparable in speed to the fastest among them
Generalized Fokker-Planck equation, Brownian motion, and ergodicity
Microscopic theory of Brownian motion of a particle of mass in a bath of
molecules of mass is considered beyond lowest order in the mass ratio
. The corresponding Langevin equation contains nonlinear corrections to
the dissipative force, and the generalized Fokker-Planck equation involves
derivatives of order higher than two. These equations are derived from first
principles with coefficients expressed in terms of correlation functions of
microscopic force on the particle. The coefficients are evaluated explicitly
for a generalized Rayleigh model with a finite time of molecule-particle
collisions. In the limit of a low-density bath, we recover the results obtained
previously for a model with instantaneous binary collisions. In general case,
the equations contain additional corrections, quadratic in bath density,
originating from a finite collision time. These corrections survive to order
and are found to make the stationary distribution non-Maxwellian.
Some relevant numerical simulations are also presented
The Three Faces of the Second Law: II. Fokker-Planck Formulation
The total entropy production is the sum of two contributions, the so-called
adiabatic and nonadiabatic entropy production, each of which is non-negative.
We derive their explicit expressions for continuous Markov processes, discuss
their properties and illustrate their behavior on two exactly solvable models.Comment: 7 pages, 1 figur
Implementation of a Combined OFDM-Demodulation and WCDMA-Equalization Module
For a dual-mode baseband receiver for the OFDMWireless LAN andWCDMA standards, integration of the demodulation and equalization tasks on a dedicated hardware module has been investigated. For OFDM demodulation, an FFT algorithm based on cascaded twiddle factor decomposition has been selected. This type of algorithm combines high spatial and temporal regularity in the FFT data-flow graphs with a minimal number of computations. A frequency-domain algorithm based on a circulant channel approximation has been selected for WCDMA equalization. It has good performance, low hardware complexity and a low number of computations. Its main advantage is the reuse of the FFT kernel, which contributes to the integration of both tasks. The demodulation and equalization module has been described at the register transfer level with the in-house developed Arx language. The core of the module is a pipelined radix-23 butterfly combined with a complex multiplier and complex divider. The module has an area of 0.447 mm2 in 0.18 ¿m technology and a power consumption of 10.6 mW. The proposed module compares favorably with solutions reported in literature
Effect of Inhomogeneity in Translocation of Polymers through Nanopores
The motion of polymers with inhomogeneous structure through nanopores is
discussed theoretically. Specifically, we consider the translocation dynamics
of polymers consisting of double-stranded and single-stranded blocks. Since
only the single-stranded chain can go through the nanopore the double-stranded
segment has to unzip before the translocation. Utilizing a simple analytical
model, translocation times are calculated explicitly for different polymer
orientations, i.e., when the single-stranded block enters the pore first and
when the double-stranded segment is a leading one. The dependence of the
translocation dynamics on external fields, energy of interaction in the
double-stranded segment, size of the polymer and the fraction of
double-stranded monomers is analyzed. It is found that the order of entrance
into the pore has a significant effect on the translocation dynamics. The
theoretical results are discussed using free-energy landscape arguments.Comment: 12 pages, 5 figures, submitted to J. Chem. Phy
Slow transport by continuous time quantum walks
Continuous time quantum walks (CTQW) do not necessarily perform better than
their classical counterparts, the continuous time random walks (CTRW). For one
special graph, where a recent analysis showed that in a particular direction of
propagation the penetration of the graph is faster by CTQWs than by CTRWs, we
demonstrate that in another direction of propagation the opposite is true; In
this case a CTQW initially localized at one site displays a slow transport. We
furthermore show that when the CTQW's initial condition is a totally symmetric
superposition of states of equivalent sites, the transport gets to be much more
rapid.Comment: 5 pages, 7 figures, accepted for publication in Phys. Rev.
Hamiltonian for coupled flux qubits
An effective Hamiltonian is derived for two coupled three-Josephson-junction
(3JJ) qubits. This is not quite trivial, for the customary "free" 3JJ
Hamiltonian is written in the limit of zero inductance L. Neglecting the
self-flux is already dubious for one qubit when it comes to readout, and
becomes untenable when discussing inductive coupling. First, inductance effects
are analyzed for a single qubit. For small L, the self-flux is a "fast
variable" which can be eliminated adiabatically. However, the commonly used
junction phases are_not_ appropriate "slow variables", and instead one
introduces degrees of freedom which are decoupled from the loop current to
leading order. In the quantum case, the zero-point fluctuations (LC
oscillations) in the loop current diverge as L->0. Fortunately, they merely
renormalize the Josephson couplings of the effective (two-phase) theory.
In the coupled case, the strong zero-point fluctuations render the full
(six-phase) wave function significantly entangled in leading order. However, in
going to the four-phase theory, this uncontrollable entanglement is integrated
out completely, leaving a computationally usable mutual-inductance term of the
expected form as the effective interaction.Comment: REVTeX4, 16pp., one figure. N.B.: "Alec" is my first, and "Maassen
van den Brink" my family name. Informal note. v2: completely rewritten;
correction of final result and major expansion. v3: added numerical
verification plus a discussion of Ref. [2
Nonlinear response theory for Markov processes: Simple models for glassy relaxation
The theory of nonlinear response for Markov processes obeying a master
equation is formulated in terms of time-dependent perturbation theory for the
Green's functions and general expressions for the response functions up to
third order in the external field are given. The nonlinear response is
calculated for a model of dipole reorientations in an asymmetric double well
potential, a standard model in the field of dielectric spectroscopy. The static
nonlinear response is finite with the exception of a certain temperature
determined by the value of the asymmetry. In a narrow temperature range around
, the modulus of the frequency-dependent cubic response shows a peak at a
frequency on the order of the relaxation rate and it vanishes for both, low
frequencies and high frequencies. At temperatures at which the static response
is finite (lower and higher than ), the modulus is found to decay
monotonously from the static limit to zero at high frequencies. In addition,
results of calculations for a trap model with a Gaussian density of states are
presented. In this case, the cubic response depends on the specific dynamical
variable considered and also on the way the external field is coupled to the
kinetics of the model. In particular, a set of different dynamical variables is
considered that gives rise to identical shapes of the linear susceptibility and
only to different temperature dependencies of the relaxation times. It is found
that the frequency dependence of the nonlinear response functions, however,
strongly depends on the particular choice of the variables. The results are
discussed in the context of recent theoretical and experimental findings
regarding the nonlinear response of supercooled liquids and glasses.Comment: 23 pages, 10 figure
A model for alignment between microscopic rods and vorticity
Numerical simulations show that microscopic rod-like bodies suspended in a
turbulent flow tend to align with the vorticity vector, rather than with the
dominant eignevector of the strain-rate tensor. This paper investigates an
analytically solvable limit of a model for alignment in a random velocity field
with isotropic statistics. The vorticity varies very slowly and the isotropic
random flow is equivalent to a pure strain with statistics which are
axisymmetric about the direction of the vorticity. We analyse the alignment in
a weakly fluctuating uniaxial strain field, as a function of the product of the
strain relaxation time and the angular velocity about
the vorticity axis. We find that when , the rods are
predominantly either perpendicular or parallel to the vorticity
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