658 research outputs found
Multiple Fermi pockets revealed by Shubnikov-de Haas oscillations in WTe2
We use magneto-transport measurements to investigate the electronic structure
of WTe2 single crystals. A non-saturating and parabolic magnetoresistance is
observed in the temperature range between 2.5 to 200 K and magnetic fields up
to 8 T. Shubnikov - de Haas oscillations with beating patterns are observed.
The fast Fourier transform of the SdH oscillations reveals three oscillation
frequencies, corresponding to three pairs of Fermi pockets with comparable
effective masses , m* ~ 0.31 me. By fitting the Hall resistivity, we infer the
presence of one pair of electron pockets and two pairs of hole pockets,
together with nearly perfect compensation of the electron-hole carrier
concentration. These magnetotransport measurements reveal the complex
electronic structure in WTe2, explaining the nonsaturating magnetoresistance.Comment: Submitted to journal on 1 April, 2015, 4 Figure
Observation of topological transition of Fermi surface from a spindle-torus to a torus in large bulk Rashba spin-split BiTeCl
The recently observed large Rashba-type spin splitting in the BiTeX (X = I,
Br, Cl) bulk states due to the absence of inversion asymmetry and large charge
polarity enables observation of the transition in Fermi surface topology from
spindle-torus to torus with varying the carrier density. These BiTeX systems
with high spin-orbit energy scales offer an ideal platform for achieving
practical spintronic applications and realizing non-trivial phenomena such as
topological superconductivity and Majorana fermions. Here we use Shubnikov-de
Haas oscillations to investigate the electronic structure of the bulk
conduction band of BiTeCl single crystals with different carrier densities. We
observe the topological transition of the Fermi surface (FS) from a
spindle-torus to a torus. The Landau level fan diagram reveals the expected
non-trivial {\pi} Berry phase for both the inner and outer FSs. Angle-dependent
oscillation measurements reveal three-dimensional FS topology when the Fermi
level lies in the vicinity of the Dirac point. All the observations are
consistent with large Rashba spin-orbit splitting in the bulk conduction band.Comment: 28 pages, supplementary informatio
A train dispatching model based on fuzzy passenger demand forecasting during holidays
Purpose: The train dispatching is a crucial issue in the train operation adjustment when passenger flow outbursts. During holidays, the train dispatching is to meet passenger demand to the greatest extent, and ensure safety, speediness and punctuality of the train operation. In this paper, a fuzzy passenger demand forecasting model is put up, then a train dispatching optimization model is established based on passenger demand so as to evacuate stranded passengers effectively during holidays.
Design/methodology/approach: First, the complex features and regularity of passenger flow during holidays are analyzed, and then a fuzzy passenger demand forecasting model is put forward based on the fuzzy set theory and time series theory. Next, the bi-objective of the train dispatching optimization model is to minimize the total operation cost of the train dispatching and unserved passenger volume during holidays. Finally, the validity of this model is illustrated with a case concerned with the Beijing-Shanghai high-speed railway in China.
Findings: The case study shows that the fuzzy passenger demand forecasting model can predict outcomes more precisely than ARIMA model. Thus train dispatching optimization plan proves that a small number of trains are able to serve unserved passengers reasonably and effectively.
Originality/value: On the basis of the passenger demand predictive values, the train dispatching optimization model is established, which enables train dispatching to meet passenger demand in condition that passenger flow outbursts, so as to maximize passenger demand by offering the optimal operation plan.Peer Reviewe
Mobilizing Personalized Federated Learning in Infrastructure-Less and Heterogeneous Environments via Random Walk Stochastic ADMM
This paper explores the challenges of implementing Federated Learning (FL) in
practical scenarios featuring isolated nodes with data heterogeneity, which can
only be connected to the server through wireless links in an
infrastructure-less environment. To overcome these challenges, we propose a
novel mobilizing personalized FL approach, which aims to facilitate mobility
and resilience. Specifically, we develop a novel optimization algorithm called
Random Walk Stochastic Alternating Direction Method of Multipliers (RWSADMM).
RWSADMM capitalizes on the server's random movement toward clients and
formulates local proximity among their adjacent clients based on hard
inequality constraints rather than requiring consensus updates or introducing
bias via regularization methods. To mitigate the computational burden on the
clients, an efficient stochastic solver of the approximated optimization
problem is designed in RWSADMM, which provably converges to the stationary
point almost surely in expectation. Our theoretical and empirical results
demonstrate the provable fast convergence and substantial accuracy improvements
achieved by RWSADMM compared to baseline methods, along with its benefits of
reduced communication costs and enhanced scalability.Comment: 28 pages, 7 figures, 3 tables, 1 algorithm. Proof details are
provided in the main body of the pape
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