2,832 research outputs found
4D-XY quantum criticality in a doped Mott insulator
A new phenomenology is proposed for the superfluid density of strongly
underdoped cuprate superconductors based on recent data for ultra-clean single
crystals of YBCO. The data feature a puzzling departure from Uemura scaling and
a decline of the slope as the T_c = 0 quantum critical point is approached. We
show that this behavior can be understood in terms of the renormalization of
quasiparticle effective charge by quantum fluctuations of the superconducting
phase as described by a (3+1)-dimensional XY model. We calculate the
renormalization of the superfluid density and its slope, explain the new
phenomenology, and predict its eventual demise close to the QCP.Comment: Version published in PRL. For additional info and related work visit
http://www.physics.ubc.ca/~fran
Emergence of the stochastic resonance in glow discharge plasma
stochastic resonance, glow discharge plasma, excitable medium, absolute mean
differenceComment: St
Accurate implementation of leaping in space: The spatial partitioned-leaping algorithm
There is a great need for accurate and efficient computational approaches
that can account for both the discrete and stochastic nature of chemical
interactions as well as spatial inhomogeneities and diffusion. This is
particularly true in biology and nanoscale materials science, where the common
assumptions of deterministic dynamics and well-mixed reaction volumes often
break down. In this article, we present a spatial version of the
partitioned-leaping algorithm (PLA), a multiscale accelerated-stochastic
simulation approach built upon the tau-leaping framework of Gillespie. We pay
special attention to the details of the implementation, particularly as it
pertains to the time step calculation procedure. We point out conceptual errors
that have been made in this regard in prior implementations of spatial
tau-leaping and illustrate the manifestation of these errors through practical
examples. Finally, we discuss the fundamental difficulties associated with
incorporating efficient exact-stochastic techniques, such as the next-subvolume
method, into a spatial-leaping framework and suggest possible solutions.Comment: 15 pages, 9 figures, 2 table
Coherence resonance in an unijunction transistor relaxation oscillator
The phenomenon of coherence resonance (CR) is investigated in an unijunction
transistor relaxation oscillator (UJT-RO) and quantified by estimating the
normal variance (NV). Depending upon the measuring points two types of NV
curves have been obtained. We have observed that the degradations in coherency
at higher noise amplitudes in our system is probably the result of direct
interference of coherent oscillations and the stochastic perturbation.
Degradation of coherency may be minimal if this direct interference of noise
and coherent oscillations is eliminated.Comment: 4 pages, Coherence resonace, Uni junction relaxation oscillato
Evolutionary history and identification of conservation units in the giant otter, Pteronura brasiliensis.
The giant otter, Pteronura brasiliensis, occupies a range including the major drainage basins of South America, yet the degree of structure that exists within and among populations inhabiting these drainages is unknown. We sequenced portions of the mitochondrial DNA (mtDNA) cytochrome b (612 bp) and control region (383 bp) genes in order to determine patterns of genetic variation within the species. We found high levels of mtDNA haplotype diversity (h = 0.93 overall) and support for subdivision into four distinct groups of populations, representing important centers of genetic diversity and useful units for prioritizing conservation within the giant otter. We tested these results against the predictions of three hypotheses of Amazonian diversification (Pleistocene Refugia, Paleogeography, and Hydrogeology). While the phylogeographic pattern conformed to the predictions of the Refugia Hypothesis, molecular dating using a relaxed clock revealed the phylogroups diverged from one another between 1.69 and 0.84 Ma, ruling out the influence of Late Pleistocene glacial refugia. However, the role of Plio-Pleistocene climate change could not be rejected. While the molecular dating also makes the influence of geological arches according to the Paleogeography Hypothesis extremely unlikely, the recent Pliocene formation of the Fitzcarrald Arch and its effect of subsequently altering drainage pattern could not be rejected. The data presented here support the interactions of both climatic and hydrological changes resulting from geological activity in the Plio-Pleistocene, in shaping the phylogeographic structure of the giant otter
Noise invoked resonances near a homoclinic bifurcation in the glow discharge plasma
Stochastic Resonance (SR) and Coherence Resonance (CR) have been studied
experimentally in the discharge plasma close to a homoclinic bifurcation. For
the SR phenomena, it is observed that a superimposed subthreshold periodic
signal can be recovered via stochastic modulations of the discharge voltage.
Furthermore, it is realized that even in the absence of a subthreshold
deterministic signal, the system dynamics can be recovered and optimized using
noise. This effect is defined as CR in the literature. In the present
experiments, induction of SR and CR are quantified using the Absolute Mean
Difference (AMD) and Normalized Variance (NV) techniques respectively. AMD is a
new statistical tool to quantify regularity in the stochastic resonance and is
independent of lag.Comment: 6 pag
An Enhanced Entropy Approach to Detect and Prevent DDoS in Cloud Environment
Distributed Denial of Service (DDoS) attack launched in Cloud computing environment resulted in loss of sensitive information, Data corruption and even rarely lead to service shutdown. Entropy based DDoS mitigation approach analyzes the heuristic data and acts dynamically according to the traffic behavior to effectively segregate the characteristics of incoming traffic. Heuristic data helps in detecting the traffic condition to mitigate the flooding attack. Then, the traffic data is analyzed to distinguish legitimate and attack characteristics. An additional Trust mechanism has been deployed to differentiate legitimate and aggressive legitimate users. Hence, Goodput of Datacenter has been improved by detecting and mitigating the incoming traffic threats at each stage. Simulation results proved that the Enhanced Entropy approach behaves better at DDoS attack prone zones. Profit analysis also proved that the proposed mechanism is deployable at Datacenter for attack mitigation and resource protection which eventually results in beneficial service at slenderized revenu
Chaotic to ordered state transition of cathode-sheath instabilities in DC glow discharge plasmas
Transition from chaotic to ordered state has been observed during the initial
stage of a discharge in a cylindrical dc glow discharge plasma. Initially it
shows a chaotic behavior but increasing the discharge voltage changes the
characteristics of the discharge glow and shows a period substraction of order
7 period 5 period 3 period 1 period i.e. the system goes to
single mode through odd cycle subtraction. On further increasing the discharge
voltage, the system goes through period doubling, like 1 period 2 period
4 period. On further increasing the voltage, the system goes to stable
state without having any oscillations.Comment: chathode-sheath, instabilities, chaos, period-subtraction,
bifurcation, dc-discharg
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