6,813 research outputs found
Magnetoresistance from Fermi Surface Topology
Extremely large non-saturating magnetoresistance has recently been reported
for a large number of both topologically trivial and non-trivial materials.
Different mechanisms have been proposed to explain the observed
magnetotransport properties, yet without arriving to definitive conclusions or
portraying a global picture. In this work, we investigate the transverse
magnetoresistance of materials by combining the Fermi surfaces calculated from
first principles with the Boltzmann transport theory approach relying on the
semiclassical model and the relaxation time approximation. We first consider a
series of simple model Fermi surfaces to provide a didactic introduction into
the charge-carrier compensation and open-orbit mechanisms leading to
non-saturating magnetoresistance. We then address in detail magnetotransport in
three representative materials: (i) copper, a prototypical nearly free-electron
metal characterized by the open Fermi surface that results in an intricate
angular magnetoresistance, (ii) bismuth, a topologically trivial semimetal in
which very large magnetoresistance is known to result from charge-carrier
compensation, and (iii) tungsten diphosphide WP2, a recently discovered type-II
Weyl semimetal that holds the record of magnetoresistance in compounds. In all
three cases our calculations show excellent agreement with both the field
dependence of magnetoresistance and its anisotropy measured at low
temperatures. Furthermore, the calculations allow for a full interpretation of
the observed features in terms of the Fermi surface topology. These results
will help addressing a number of outstanding questions, such as the role of the
topological phase in the pronounced large non-saturating magnetoresistance
observed in topological materials.Comment: 13 pages, 9 figure
User's manual for tooth contact analysis of face-milled spiral bevel gears with given machine-tool settings
Research was performed to develop a computer program that will: (1) simulate the meshing and bearing contact for face milled spiral beval gears with given machine tool settings; and (2) to obtain the output, some of the data is required for hydrodynamic analysis. It is assumed that the machine tool settings and the blank data will be taken from the Gleason summaries. The theoretical aspects of the program are based on 'Local Synthesis and Tooth Contact Analysis of Face Mill Milled Spiral Bevel Gears'. The difference between the computer programs developed herein and the other one is as follows: (1) the mean contact point of tooth surfaces for gears with given machine tool settings must be determined iteratively, while parameters (H and V) are changed (H represents displacement along the pinion axis, V represents the gear displacement that is perpendicular to the plane drawn through the axes of the pinion and the gear of their initial positions), this means that when V differs from zero, the axis of the pionion and the gear are crossed but not intersected; (2) in addition to the regular output data (transmission errors and bearing contact), the new computer program provides information about the contacting force for each contact point and the sliding and the so-called rolling velocity. The following topics are covered: (1) instructions for the users as to how to insert the input data; (2) explanations regarding the output data; (3) numerical example; and (4) listing of the program
Birkhoff Center and Statistical Behavior of Competitive Dynamical Systems
We investigate the location and structure of the Birkhoff center for
competitive dynamical systems, and give a comprehensive description of
recurrence and statistical behavior of orbits. An order-structure dichotomy is
established for any connected component of the Birkhoff center, that is, either
it is unordered, or it consists of strongly ordered equilibria. Moreover, there
is a canonically defined countable disjoint family of invariant
-cells such that each unordered connected component of the Birkhoff
center lies on one of these cells. We further show that any connected component
of the supports of invariant measures either consists of strongly ordered
equilibria, or lies on one element of . In particular, any
-dimensional competitive flow has topological entropy
Unraveling the Complexity of Metal Ion Dissolution: Insights from Hybrid First-Principles/Continuum Calculations
The study of ion dissolution from metal surfaces has a long-standing history,
wherein the gradual dissolution of solute atoms with increasing electrode
potential, leading to their existence as ions in the electrolyte with integer
charges, is well-known. However, our present work reveals a more intricate and
nuanced physical perspective based on comprehensive first-principles/continuum
calculations. We investigate the dissolution and deposition processes of 22
metal elements across a range of applied electrode potentials, unveiling
diverse dissolution models. By analyzing the energy profiles and valence states
of solute atoms as a function of the distance between the solute atom and metal
surface, we identify three distinct dissolution models for different metals.
Firstly, solute atoms exhibit an integer valence state following an
integer-valence jump, aligning with classical understandings. Secondly, solute
atoms attain an eventual integer valence, yet their valence state increases in
a non-integer manner during dissolution. Lastly, we observe solute atoms
exhibiting a non-integer valence state, challenging classical understandings.
Furthermore, we propose a theoretical criterion for determining the selection
of ion valence during electrode dissolution under applied potential. These
findings not only contribute to a deeper understanding of the dissolution
process but also offer valuable insights into the complex dynamics governing
metal ion dissolution at the atomic level. Such knowledge has the potential to
advance the design of more efficient electrochemical systems and open new
avenues for controlling dissolution processes in various applications.Comment: still dont hav
Variational Monte Carlo study of chiral spin liquid in the extended Heisenberg model on the Kagome lattice
We investigate the extended Heisenberg model on the Kagome lattice by using
Gutzwiller projected fermionic states and the variational Monte Carlo
technique. In particular, when both second- and third-neighbor super-exchanges
are considered, we find that a gapped spin liquid described by non-trivial
magnetic fluxes and long-range chiral-chiral correlations is energetically
favored compared to the gapless U(1) Dirac state. Furthermore, the topological
Chern number, obtained by integrating the Berry curvature, and the degeneracy
of the ground state, by constructing linearly independent states, lead us to
identify this flux state as the chiral spin liquid with fractionalized
Chern number.Comment: 9 pages, 7 figure
Aircraft Landing Time Prediction with Deep Learning on Trajectory Images
Aircraft landing time (ALT) prediction is crucial for air traffic management,
especially for arrival aircraft sequencing on the runway. In this study, a
trajectory image-based deep learning method is proposed to predict ALTs for the
aircraft entering the research airspace that covers the Terminal Maneuvering
Area (TMA). Specifically, the trajectories of all airborne arrival aircraft
within the temporal capture window are used to generate an image with the
target aircraft trajectory labeled as red and all background aircraft
trajectory labeled as blue. The trajectory images contain various information,
including the aircraft position, speed, heading, relative distances, and
arrival traffic flows. It enables us to use state-of-the-art deep convolution
neural networks for ALT modeling. We also use real-time runway usage obtained
from the trajectory data and the external information such as aircraft types
and weather conditions as additional inputs. Moreover, a convolution neural
network (CNN) based module is designed for automatic holding-related
featurizing, which takes the trajectory images, the leading aircraft holding
status, and their time and speed gap at the research airspace boundary as its
inputs. Its output is further fed into the final end-to-end ALT prediction. The
proposed ALT prediction approach is applied to Singapore Changi Airport (ICAO
Code: WSSS) using one-month Automatic Dependent Surveillance-Broadcast (ADS-B)
data from November 1 to November 30, 2022. Experimental results show that by
integrating the holding featurization, we can reduce the mean absolute error
(MAE) from 82.23 seconds to 43.96 seconds, and achieve an average accuracy of
96.1\%, with 79.4\% of the predictions errors being less than 60 seconds.Comment: In 2023 13th SESAR Innovation Days (SIDS2023
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