1,682 research outputs found
Anchored burning bijections on finite and infinite graphs
Let be an infinite graph such that each tree in the wired uniform
spanning forest on has one end almost surely. On such graphs , we give a
family of continuous, measure preserving, almost one-to-one mappings from the
wired spanning forest on to recurrent sandpiles on , that we call
anchored burning bijections. In the special case of , ,
we show how the anchored bijection, combined with Wilson's stacks of arrows
construction, as well as other known results on spanning trees, yields a power
law upper bound on the rate of convergence to the sandpile measure along any
exhaustion of . We discuss some open problems related to these
findings.Comment: 26 pages; 1 EPS figure. Minor alterations made after comments from
refere
Logarithmic current fluctuations in non-equilibrium quantum spin chains
We study zero-temperature quantum spin chains which are characterized by a
non-vanishing current. For the XX model starting from the initial state |... +
+ + - - - ...> we derive an exact expression for the variance of the total spin
current. We show that asymptotically the variance exhibits an anomalously slow
logarithmic growth; we also extract the sub-leading constant term. We then
argue that the logarithmic growth remains valid for the XXZ model in the
critical region.Comment: 9 pages, 4 figures, minor alteration
TCP over High Speed Variable Capacity Links: A Simulation Study for Bandwidth Allocation
New optical network technologies provide opportunities for fast, controllable bandwidth management. These technologies can now explicitly provide resources to data paths, creating demand driven bandwidth reservation across networks where an applications bandwidth needs can be meet almost exactly. Dynamic synchronous Transfer Mode (DTM) is a gigabit network technology that provides channels with dynamically adjustable capacity. TCP is a reliable end-to-end transport protocol that adapts its rate to the available capacity. Both TCP and the DTM bandwidth can react to changes in the network load, creating a complex system with inter-dependent feedback mechanisms. The contribution of this work is an assessment of a bandwidth allocation scheme for TCP flows on variable capacity technologies. We have created a simulation environment using ns-2 and our results indicate that the allocation of bandwidth maximises TCP throughput for most flows, thus saving valuable capacity when compared to a scheme such as link over-provisioning. We highlight one situation where the allocation scheme might have some deficiencies against the static reservation of resources, and describe its causes. This type of situation warrants further investigation to understand how the algorithm can be modified to achieve performance similar to that of the fixed bandwidth case
Testing the Elliott-Yafet spin-relaxation mechanism in KC8; a model system of biased graphene
Temperature dependent electron spin resonance (ESR) measurements are reported
on stage 1 potassium doped graphite, a model system of biased graphene. The ESR
linewidth is nearly isotropic and although the g-factor has a sizeable
anisotropy, its majority is shown to arise due to macroscopic magnetization.
Albeit the homogeneous ESR linewidth shows an unusual, non-linear temperature
dependence, it appears to be proportional to the resistivity which is a
quadratic function of the temperature. These observations suggests the validity
of the Elliott-Yafet relaxation mechanism in KC8 and allows to place KC8 on the
empirical Beuneu-Monod plot among ordinary elemental metals.Comment: 6 pages, 4 figures, submitted to Phys. Rev.
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