1,036 research outputs found
General Routing Algorithms for Star Graphs
In designing algorithms for a specific parallel architecture, a programmer has to cope with topological and cardinality variations. Both these problems always increase the programmer\u27s effort. However, an ideal shared memory abstract parallel model called the parallel random access machine (PRAM) [KRUS86, KRUS88] that avoids these problems and also simple-to-program has been proposed. Unfortunately, the PRAM does not seem to be realizable in the present or even foreseeable technologies. On the other hand, a packet routing technique can be employed to simulate the PRAM on a feasible parallel architecture without significant loss of efficiency. The problem of routing is also important due to its intrinsic significance in distributed processing and its important role in the simulations among parallel models.
The routing problem is defined as follows: Given a specific network and a set of packets of information in which a packet is an (origin, destination) pair. To start with, the packets are placed on their origins, one per node. These packets must be routed in parallel to their own destinations such that at most one packet passes through any link of the network at any time and all packets arrive at their destinations as quickly as possible. We are interested in a special case of the general routing problem called permutation routing in which the destinations form some permutation of the origins. A routing algorithm is said to be oblivious if the path taken by each packet is only dependent on its source and destination. An oblivious routing strategy is preferable since it will lead to a simple control structure for the individual processing elements. Also oblivious routing algorithms can be used in a distributed environment. In this paper we are concerned with only oblivious routing strategies
A New Transport Regime in the Quantum Hall Effect
This paper describes an experimental identification and characterization of a
new low temperature transport regime near the quantum Hall-to-insulator
transition. In this regime, a wide range of transport data are compactly
described by a simple phenomenological form which, on the one hand, is
inconsistent with either quantum Hall or insulating behavior and, on the other
hand, is also clearly at odds with a quantum-critical, or scaling, description.
We are unable to determine whether this new regime represents a clearly defined
state or is a consequence of finite temperature and sample-size measurements.Comment: Revtex, 3 pages, 2 figure
Emulating long-term synaptic dynamics with memristive devices
The potential of memristive devices is often seeing in implementing neuromorphic architectures for achieving brain-like computation. However, the designing procedures do not allow for extended manipulation of the material, unlike CMOS technology, the properties of the memristive material should be harnessed in the context of such computation, under the view that biological synapses are memristors. Here we demonstrate that single solid-state TiO2 memristors can exhibit associative plasticity phenomena observed in biological cortical synapses, and are captured by a phenomenological plasticity model called triplet rule. This rule comprises of a spike-timing dependent plasticity regime and a classical hebbian associative regime, and is compatible with a large amount of electrophysiology data. Via a set of experiments with our artificial, memristive, synapses we show that, contrary to conventional uses of solid-state memory, the co-existence of field- and thermally-driven switching mechanisms that could render bipolar and/or unipolar programming modes is a salient feature for capturing long-term potentiation and depression synaptic dynamics. We further demonstrate that the non-linear accumulating nature of memristors promotes long-term potentiating or depressing memory transitions
Impacts of environmental factors and human disturbance on composition of roadside vegetation in Xishuangbanna National Nature Reserve of Southwest China
AbstractVegetation-disturbance-environment relationships in Xishuangbanna Nature Reserve (XNR) was examined using multivariate analysis to understand the impacts of environmental factors and human disturbance on vegetation along the highway corridor. The results show that native forests were the best habitat for protected/endangered species and native species. The exotic plants Eupatorium odoratum and Eupatorium adenophora were found primarily in secondary forests and their presence was positively associated with altitude and soil potassium concentrations. The distribution of two protected plants, Phoebe nanmu and Pometia tomentosa, was negatively associated with road disturbance. Understanding the complex effects of environmental factors and human disturbance is key for developing conservation and restoration strategies for roadside plant ecosystems
Skyrmion Excitation in Two-Dimensional Spinor Bose-Einstein Condensate
We study the properties of coreless vortices(skyrmion) in spinor
Bose-Einstein condensate. We find that this excitation is always energetically
unstable, it always decays to an uniform spin texture. We obtain the skyrmion
energy as a function of its size and position, a key quantity in understanding
the decay process. We also point out that the decay rate of a skyrmion with
high winding number will be slower. The interaction between skyrmions and other
excitation modes are also discussed.Comment: 5 pages, 4 figures, final version published in Phys. Rev.
Light Cone Condition for a Thermalized QED Vacuum
Within the QED effective action approach, we study the propagation of
low-frequency light at finite temperature. Starting from a general effective
Lagrangian for slowly varying fields whose structure is solely dictated by
Lorentz covariance and gauge invariance, we derive the light cone condition for
light propagating in a thermalized QED vacuum. As an application, we calculate
the velocity shifts, i.e., refractive indices of the vacuum, induced by
thermalized fermions to one loop. We investigate various temperature domains
and also include a background magnetic field. While low-temperature effects to
one loop are exponentially damped by the electron mass, there exists a maximum
velocity shift of in the
intermediate-temperature domain .Comment: 9 pages, 3 figures, REVTeX, typos corrected, final version to appear
in Phys. Rev.
Generalized measurements by linear elements
I give a first characterization of the class of generalized measurements that
can be exactly realized on a pair of qudits encoded in indistinguishable
particles, by using only linear elements and particle detectors. Two immediate
results follow from this characterization. (i) The Schmidt number of each POVM
element cannot exceed the number of initial particles. This rules out any
possibility of performing perfect Bell-measurements for qudits. (ii) The
maximum probability of performing a generalized incomplete Bell-measurement is
1/2.Comment: 4 pages. Submitted to Phys. Rev.
Short-Range Interactions and Scaling Near Integer Quantum Hall Transitions
We study the influence of short-range electron-electron interactions on
scaling behavior near the integer quantum Hall plateau transitions. Short-range
interactions are known to be irrelevant at the renormalization group fixed
point which represents the transition in the non-interacting system. We find,
nevertheless, that transport properties change discontinuously when
interactions are introduced. Most importantly, in the thermodynamic limit the
conductivity at finite temperature is zero without interactions, but non-zero
in the presence of arbitrarily weak interactions. In addition, scaling as a
function of frequency, , and temperature, , is determined by the
scaling variable (where is the exponent for the temperature
dependence of the inelastic scattering rate) and not by , as it would
be at a conventional quantum phase transition described by an interacting fixed
point. We express the inelastic exponent, , and the thermal exponent, ,
in terms of the scaling dimension, , of the interaction strength
and the dynamical exponent (which has the value ), obtaining
and .Comment: 9 pages, 4 figures, submitted to Physical Review
Bi-Large Neutrino Mixing See-Saw Mass Matrix with Texture Zeros and Leptogenesis
We study constraints on neutrino properties from texture zeros in bi-large
mixing See-Saw mass matrix and also from leptogenesis. Texture zeros may occur
in the light (class a)) or in the heavy (class b)) neutrino mass matrices. Each
of these two classes has 5 different forms which can produce non-trivial three
generation mixing with at least one texture zero. We find that two types of
texture zero mass matrices in both class a) and class b) can be consistent with
present data on neutrino masses, mixing and produce the observed baryon
asymmetry of the universe. None of the neutrinos can have zero masses with the
lightest of the light neutrinos having a mass larger than about 0.039 eV for
class a) and 0.002 eV for class b). In these models although CKM CP violating
phase vanishes, non-zero Majorana phases, however, can exist and play an
important role in producing the observed baryon asymmetry in our universe
through leptogenesis mechanism. The requirement of producing the observed
baryon asymmetry can further distinguish different models and also restrict the
See-Saw scale to be in the range GeV.Comment: 21 pages, 7 figures revised version, some references added, to be
submitted to PR
The elusive source of quantum effectiveness
We discuss two qualities of quantum systems: various correlations existing
between their subsystems and the distingushability of different quantum states.
This is then applied to analysing quantum information processing. While quantum
correlations, or entanglement, are clearly of paramount importance for
efficient pure state manipulations, mixed states present a much richer arena
and reveal a more subtle interplay between correlations and distinguishability.
The current work explores a number of issues related with identifying the
important ingredients needed for quantum information processing. We discuss the
Deutsch-Jozsa algorithm, the Shor algorithm, the Grover algorithm and the power
of a single qubit class of algorithms. One section is dedicated to cluster
states where entanglement is crucial, but its precise role is highly
counter-intuitive. Here we see that distinguishability becomes a more useful
concept.Comment: 8 pages, no figure
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