11,421 research outputs found
Quasi-ballistic transport in HgTe quantum-well nanostructures
The transport properties of micrometer scale structures fabricated from
high-mobility HgTe quantum-wells have been investigated. A special photoresist
and Ti masks were used, which allow for the fabrication of devices with
characteristic dimensions down to 0.45 m. Evidence that the transport
properties are dominated by ballistic effects in these structures is presented.
Monte Carlo simulations of semi-classical electron trajectories show good
agreement with the experiment.Comment: 3 pages, 3 figures; minor revisions: replaced "inelastic mean free
path" with "transport mean free path"; corrected typing errors; restructered
most paragraphs for easier reading; accepted for publication in AP
Two-State Migration of DNA in a structured Microchannel
DNA migration in topologically structured microchannels with periodic
cavities is investigated experimentally and with Brownian dynamics simulations
of a simple bead-spring model. The results are in very good agreement with one
another. In particular, the experimentally observed migration order of Lambda-
and T2-DNA molecules is reproduced by the simulations. The simulation data
indicate that the mobility may depend on the chain length in a nonmonotonic way
at high electric fields. This is found to be the signature of a nonequilibrium
phase transition between two different migration states, a slow one and a fast
one, which can also be observed experimentally under appropriate conditions.Comment: Revised edition corresponding to the comments by the referees,
submitted to Physical Review
More Than Routing: Joint GPS and Route Modeling for Refine Trajectory Representation Learning
Trajectory representation learning plays a pivotal role in supporting various
downstream tasks. Traditional methods in order to filter the noise in GPS
trajectories tend to focus on routing-based methods used to simplify the
trajectories. However, this approach ignores the motion details contained in
the GPS data, limiting the representation capability of trajectory
representation learning. To fill this gap, we propose a novel representation
learning framework that Joint GPS and Route Modelling based on self-supervised
technology, namely JGRM. We consider GPS trajectory and route as the two modes
of a single movement observation and fuse information through inter-modal
information interaction. Specifically, we develop two encoders, each tailored
to capture representations of route and GPS trajectories respectively. The
representations from the two modalities are fed into a shared transformer for
inter-modal information interaction. Eventually, we design three
self-supervised tasks to train the model. We validate the effectiveness of the
proposed method on two real datasets based on extensive experiments. The
experimental results demonstrate that JGRM outperforms existing methods in both
road segment representation and trajectory representation tasks. Our source
code is available at Anonymous Github
Integrability and Disorder in Mesoscopic Systems: Application to Orbital Magnetism
We present a semiclassical theory of weak disorder effects in small
structures and apply it to the magnetic response of non-interacting electrons
confined in integrable geometries. We discuss the various averaging procedures
describing different experimental situations in terms of one- and two-particle
Green functions. We demonstrate that the anomalously large zero-field
susceptibility characteristic of clean integrable structures is only weakly
suppressed by disorder. This damping depends on the ratio of the typical size
of the structure with the two characteristic length scales describing the
disorder (elastic mean-free-path and correlation length of the potential) in a
power-law form for the experimentally relevant parameter region. We establish
the comparison with the available experimental data and we extend the study of
the interplay between disorder and integrability to finite magnetic fields.Comment: 38 pages, Latex, 7 Postscript figures, 1 table, to appear in Jour.
Math. Physics 199
A Laterally Modulated 2D Electron System in the Extreme Quantum Limit
We report on magnetotransport of a two-dimensional electron system (2DES),
located 32 nm below the surface, with a surface superlattice gate structure of
periodicity 39 nm imposing a periodic modulation of its potential. For low
Landau level fillings , the diagonal resistivity displays a rich pattern
of fluctuations, even though the disorder dominates over the periodic
modulation. Theoretical arguments based on the combined effects of the
long-wavelength, strong disorder and the short-wavelength, weak periodic
modulation present in the 2DES qualitatively explain the data.Comment: 4 pages, 5 figures. to appear in Phys. Rev. Let
Statistical and agent-based modelling of the transmissibility of different SARS-CoV-2 variants in England and impact of different interventions
The English SARS-CoV-2 epidemic has been affected by the emergence of new viral variants such as B.1.177, Alpha and Delta, and changing restrictions. We used statistical models and the agent-based model Covasim, in June 2021, to estimate B.1.177 to be 20% more transmissible than the wild type, Alpha to be 50-80% more transmissible than B.1.177 and Delta to be 65-90% more transmissible than Alpha. Using these estimates in Covasim (calibrated 1 September 2020 to 20 June 2021), in June 2021, we found that due to the high transmissibility of Delta, resurgence in infections driven by the Delta variant would not be prevented, but would be strongly reduced by delaying the relaxation of restrictions by one month and with continued vaccination. This article is part of the theme issue 'Technical challenges of modelling real-life epidemics and examples of overcoming these'
Frequency-dependent magnetotransport and particle dynamics in magnetic modulation systems
We analyze the dynamics of a charged particle moving in the presence of
spatially-modulated magnetic fields. From Poincare surfaces of section and
Liapunov exponents for characteristic trajectories we find that the fraction of
pinned and runaway quasiperiodic orbits {\em vs}. chaotic orbits depends
strongly on the ratio of cyclotron radius to the structure parameters, as well
as on the amplitude of the modulated field. We present a complete
characterization of the dynamical behavior of such structures, and investigate
the contribution to the magnetoconductivity from all different orbits using a
classical Kubo formula. Although the DC conductivity of the system depends
strongly on the pinned and runaway trajectories, the frequency response
reflects the topology of all different orbits, and even their unusual temporal
behavior.Comment: Submitted to PRB - 14 figure files - REVTEX tex
Finite Cluster Typical Medium Theory for Disordered Electronic Systems
We use the recently developed typical medium dynamical cluster (TMDCA)
approach~[Ekuma \etal,~\textit{Phys. Rev. B \textbf{89}, 081107 (2014)}] to
perform a detailed study of the Anderson localization transition in three
dimensions for the Box, Gaussian, Lorentzian, and Binary disorder
distributions, and benchmark them with exact numerical results. Utilizing the
nonlocal hybridization function and the momentum resolved typical spectra to
characterize the localization transition in three dimensions, we demonstrate
the importance of both spatial correlations and a typical environment for the
proper characterization of the localization transition in all the disorder
distributions studied. As a function of increasing cluster size, the TMDCA
systematically recovers the re-entrance behavior of the mobility edge for
disorder distributions with finite variance, obtaining the correct critical
disorder strengths, and shows that the order parameter critical exponent for
the Anderson localization transition is universal. The TMDCA is computationally
efficient, requiring only a small cluster to obtain qualitative and
quantitative data in good agreement with numerical exact results at a fraction
of the computational cost. Our results demonstrate that the TMDCA provides a
consistent and systematic description of the Anderson localization transition.Comment: 20 Pages, 19 Figures, 3 Table
Mobility and Aging: Older Drivers’ Visual Searching, Lane Keeping and Coordination
This thesis examined older drivers’ mobility and behaviour through comprehensive measurements of driver-vehicle-environment interaction and investigated the associations between driving behaviour and cognitive functions. Data were collected and analysed for 50 older drivers using eye tracking, GNSS tracking, and GIS. Results showed that poor selective attention, spatial ability and executive function in older drivers adversely affect lane keeping, visual search and coordination. Visual-motor coordination measure is sensitive and effective for driving assessment in older drivers
- …