4,820 research outputs found
Fractional Brownian motion with a reflecting wall
Fractional Brownian motion, a stochastic process with long-time correlations
between its increments, is a prototypical model for anomalous diffusion. We
analyze fractional Brownian motion in the presence of a reflecting wall by
means of Monte Carlo simulations. While the mean-square displacement of the
particle shows the expected anomalous diffusion behavior , the interplay between the geometric confinement and the
long-time memory leads to a highly non-Gaussian probability density function
with a power-law singularity at the barrier. In the superdiffusive case,
, the particles accumulate at the barrier leading to a divergence of
the probability density. For subdiffusion, , in contrast, the
probability density is depleted close to the barrier. We discuss implications
of these findings, in particular for applications that are dominated by rare
events.Comment: 6 pages, 6 figures. Final version as publishe
Investigation of the dc-excited xenon laser final report, 24 mar. 1964 - 24 mar. 1965
Electron energy spectra in gas laser discharges and investigation of new discharge configuration
Valley current characterization of high current density resonant tunnelling diodes for terahertz-wave applications
We report valley current characterisation of high current density InGaAs/AlAs/InP resonant tunnelling diodes (RTDs) grown by metal-organic vapour phase epitaxy (MOVPE) for THz emission, with a view to investigate the origin of the valley current and optimize device performance. By applying a dual-pass fabrication technique, we are able to measure the RTD I-V characteristic for different perimeter/area ratios, which uniquely allows us to investigate the contribution of leakage current to the valley current and its effect on the PVCR from a single device. Temperature dependent (20 – 300 K) characteristics for a device are critically analysed and the effect of temperature on the maximum extractable power (PMAX) and the negative differential conductance (NDC) of the device is investigated. By performing theoretical modelling, we are able to explore the effect of typical variations in structural composition during the growth process on the tunnelling properties of the device, and hence the device performance
Intrinsic localized modes in the charge-transfer solid PtCl
We report a theoretical analysis of intrinsic localized modes in a
quasi-one-dimensional charge-transfer-solid (PtCl). We discuss strongly nonlinear features of resonant Raman
overtone scattering measurements on PtCl, arising from quantum intrinsic
localized (multiphonon) modes (ILMs) and ILM-plus-phonon states. We show, that
Raman scattering data displays clear signs of a non-thermalization of lattice
degrees-of-freedom, manifested in a nonequilibrium density of intrinsic
localized modes.Comment: 4 pages, 4 figures, REVTE
Extinction Transitions in Correlated External Noise
We analyze the influence of long-range correlated (colored) external noise on extinction phase transitions in growth and spreading processes. Uncorrelated environmental noise (i.e., temporal disorder) was recently shown to give rise to an unusual infinite-noise critical point [Europhys. Lett. 112, 30002 (2015)EULEEJ0295-507510.1209/0295-5075/112/30002]. It is characterized by enormous density fluctuations that increase without limit at criticality. As a result, a typical population decays much faster than the ensemble average, which is dominated by rare events. Using the logistic evolution equation as an example, we show here that positively correlated (red) environmental noise further enhances these effects. This means, the correlations accelerate the decay of a typical population but slow down the decay of the ensemble average. Moreover, the mean time to extinction of a population in the active, surviving phase grows slower than a power law with population size. To determine the complete critical behavior of the extinction transition, we establish a relation to fractional random walks, and we perform extensive Monte Carlo simulations
Thermoelectric transport of perfectly conducting channels in two- and three-dimensional topological insulators
Topological insulators have gapless edge/surface states with novel transport
properties. Among these, there are two classes of perfectly conducting channels
which are free from backscattering: the edge states of two-dimensional
topological insulators and the one-dimensional states localized on dislocations
of certain three-dimensional topological insulators. We show how these novel
states affect thermoelectric properties of the systems and discuss
possibilities to improve the thermoelectric figure of merit using these
materials with perfectly conducting channels.Comment: 10 pages, 6 figures, proceedings for The 19th International
Conference on the Application of High Magnetic Fields in Semiconductor
Physics and Nanotechnology (HMF-19
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