5,363 research outputs found
Topological Crystalline Insulator Nanomembrane with Strain-Tunable Band Gap
The ability to fine-tune band gap and band inversion in topological materials
is highly desirable for the development of novel functional devices. Here we
propose that the electronic properties of a free-standing nanomembrane of
topological crystalline insulator (TCI) SnTe and PbSn(Se,Te) are
highly tunable by engineering elastic strain and controlling membrane
thickness, resulting in tunable band gap and giant piezoconductivity. Membrane
thickness governs the hybridization of topological electronic states on
opposite surfaces, while elastic strain can further modulate the hybridization
strength by controlling the penetration length of surface states. We propose a
frequency-resolved infrared photodetector using force-concentration induced
inhomogeneous elastic strain in TCI nanomembrane with spatially varying width.
The predicted tunable band gap accompanied by strong spin-textured electronic
states will open up new avenues for fabricating piezoresistive devices,
thermoelectrics, infrared detectors and energy-efficient electronic and
optoelectronic devices based on TCI nanomembrane.Comment: 10 pages, 9 figure
Anisotropic Electron-Hole Excitation and Large Linear Dichroism in Two-Dimensional Ferromagnet CrSBr with In-Plane Magnetization
The observation of magnetic ordering in atomically thin CrI and
CrGeTe monolayers has aroused intense interest in condensed matter
physics and material science. Studies of van de Waals two-dimensional (2D)
magnetic materials are of both fundamental importance and application interest.
In particular, exciton-enhanced magneto-optical properties revealed in CrI
and CrBr monolayers have expanded the understanding of exciton physics in
2D materials. Unlike CrI and CrBr with out-of-plane magnetization,
CrSBr has an in-plane magnetic moment, therefore, providing a good opportunity
to study the magnetic linear dichroism and high-order magneto-optical effects.
Here, based on the many-body perturbation method within density-functional
theory, we have studied quasiparticle electronic structure, exciton, and
optical properties in CrSBr monolayer. Strongly bounded exciton has been
identified with the first bright exciton located at 1.35 eV, in good agreement
with an experiment of photoluminescence (Nat. Mater. \textbf{20}, 1657 (2021)).
Strong contrast in the optical absorption is found between the electric fields
lying along the in-plane two orthogonal directions. In accordance with a
typical and realistic experimental setup, we show that the rotation angle of
linear polarized light, either reflected or transmitted, could be comparable
with those revealed in black phosphorene. Such large linear dichroism arises
mainly from anisotropic in-plane crystal structure. The magnetic contribution
from the off-diagonal component of dielectric function to the linear dichroism
in CrSBr is negligible. Our findings not only have revealed excitonic effect on
the optical and magneto-optical properties in 2D ferromagnet CrSBr, but also
have shown its potential applications in 2D optics and optoelectronics.Comment: 47 pages, 24 figure
Transport Regulation of Two-Dimensional Receptor-Ligand Association
AbstractThe impact of flow disturbances on platelet adhesion is complex and incompletely understood. At the molecular scale, platelet glycoprotein Ibα (GPIbα) must associate with the von Willebrand factor A1 domain (VWF-A1) with a rapid on-rate under high hemodynamic forces, as occurs in arterial thrombosis, where various transport mechanisms are at work. Here, we theoretically modeled the coupled transport-reaction process of the two-dimensional (2D) receptor-ligand association kinetics in a biomembrane force probe to explicitly account for the effects of molecular length, confinement stiffness, medium viscosity, surface curvature, and separation distance. We experimentally verified the theoretical approach by visualizing association and dissociation of individual VWF-A1-GPIbα bonds in a real-time thermal fluctuation assay. The apparent on-rate, reciprocal of the average time intervals between sequential bonds, decreased with the increasing gap distance between A1- and GPIbα-bearing surfaces with an 80-nm threshold (beyond which bond formation became prohibitive) identified as the combined contour length of the receptor and ligand molecules. The biomembrane force probe spring constant and diffusivity of the protein-bearing beads also significantly influenced the apparent on-rate, in accordance with the proposed transport mechanisms. The global agreement between the experimental data and the model predictions supports the hypothesis that receptor-ligand association behaves distinctly in the transport- and reaction-limited scenarios. To our knowledge, our results represent the first detailed quantification of physical regulation of the 2D on-rate that allows platelets to sense and respond to local changes in their hemodynamic environment. In addition, they provide an approach for determining the intrinsic kinetic parameters that employs simultaneous experimental measurements and theoretical modeling of bond association in a single assay. The 2D intrinsic forward rate for VWF-A1-GPIbα association was determined from the measurements to be (3.5 ± 0.67) × 10−4 μm2 s−1
Envelope function method for electrons in slowly-varying inhomogeneously deformed crystals
We develop a new envelope-function formalism to describe electrons in
slowly-varying inhomogeneously strained semiconductor crystals. A coordinate
transformation is used to map a deformed crystal back to geometrically
undeformed structure with deformed crystal potential. The single-particle
Schr\"{o}dinger equation is solved in the undeformed coordinates using envelope
function expansion, wherein electronic wavefunctions are written in terms of
strain-parametrized Bloch functions modulated by slowly varying envelope
functions. Adopting local approximation of electronic structure, the unknown
crystal potential in Schr\"{o}dinger equation can be replaced by the
strain-parametrized Bloch functions and the associated strain-parametrized
energy eigenvalues, which can be constructed from unit-cell level ab initio or
semi-empirical calculations of homogeneously deformed crystals at a chosen
crystal momentum. The Schr\"{o}dinger equation is then transformed into a
coupled differential equation for the envelope functions and solved as a
generalized matrix eigenvector problem. As the envelope functions are slowly
varying, coarse spatial or Fourier grid can be used to represent the envelope
functions, enabling the method to treat relatively large systems. We
demonstrate the effectiveness of this method using a one-dimensional model,
where we show that the method can achieve high accuracy in the calculation of
energy eigenstates with relatively low cost compared to direct diagonalization
of Hamiltonian. We further derive envelope function equations that allow the
method to be used empirically, in which case certain parameters in the envelope
function equations will be fitted to experimental data.Comment: 15 pages, 8 figure
Calculating Phase-Coherent Quantum Transport in Nanoelectronics with \u3cem\u3eab initio\u3c/em\u3e Quasiatomic Orbital Basis Set
We present an efficient and accurate computational approach to study phase-coherent quantum transport in molecular and nanoscale electronics. We formulate a Green’s-function method in the recently developed ab initio nonorthogonal quasiatomic orbital basis set within the Landauer-Büttiker formalism. These quasiatomic orbitals are efficiently and robustly transformed from Kohn-Sham eigenwave functions subject to the maximal atomic-orbital similarity measure. With this minimal basis set, we can easily calculate electrical conductance using Green’s-function method while keeping accuracy at the level of plane-wave density-functional theory. Our approach is validated in three studies of two-terminal electronic devices, in which projected density of states and conductance eigenchannel are employed to help understand microscopic mechanism of quantum transport. We first apply our approach to a seven-carbon atomic chain sandwiched between two finite crosssectioned Al(001) surfaces. The emergence of gaps in the conductance curve originates from the selection rule with vanishing overlap between symmetry-incompatible conductance eigenchannels in leads and conductor. In the second application, a (4,4) single-wall carbon nanotube with a substitutional silicon impurity is investigated. The complete suppression of transmission at 0.6 eV in one of the two conductance eigenchannels is attributed to the Fano antiresonance when the localized silicon impurity state couples with the continuum states of carbon nanotube. Finally, a benzene-1,4-dithiolate molecule attached to two Au(111) surfaces is considered. Combining fragment molecular orbital analysis and conductance eigenchannel analysis, we demonstrate that conductance peaks near the Fermi level result from resonant tunneling through molecular orbitals of benzene- 1,4-dithiolate molecule. In general, our conductance curves agree very well with previous results obtained using localized basis sets while slight difference is observed near the Fermi level and conductance edges
Towards Prototyping Driverless Vehicle Behaviors, City Design, and Policies Simultaneously
Autonomous Vehicles (AVs) can potentially improve urban living by reducing
accidents, increasing transportation accessibility and equity, and decreasing
emissions. Realizing these promises requires the innovations of AV driving
behaviors, city plans and infrastructure, and traffic and transportation
policies to join forces. However, the complex interdependencies among AV, city,
and policy design issues can hinder their innovation. We argue the path towards
better AV cities is not a process of matching city designs and policies with
AVs' technological innovations, but a process of iterative prototyping of all
three simultaneously: Innovations can happen step-wise as the knot of AV, city,
and policy design loosens and tightens, unwinds and reties. In this paper, we
ask: How can innovators innovate AVs, city environments, and policies
simultaneously and productively toward better AV cities? The paper has two
parts. First, we map out the interconnections among the many AV, city, and
policy design decisions, based on a literature review spanning HCI/HRI,
transportation science, urban studies, law and policy, operations research,
economy, and philosophy. This map can help innovators identify design
constraints and opportunities across the traditional AV/city/policy design
disciplinary bounds. Second, we review the respective methods for AV, city, and
policy design, and identify key barriers in combining them: (1) Organizational
barriers to AV-city-policy design collaboration, (2) computational barriers to
multi-granularity AV-city-policy simulation, and (3) different assumptions and
goals in joint AV-city-policy optimization. We discuss two broad approaches
that can potentially address these challenges, namely, "low-fidelity
integrative City-AV-Policy Simulation (iCAPS)" and "participatory design
optimization".Comment: Published to the CHI '23 Workshop: Designing Technology and Policy
Simultaneousl
An Empirical Research of Concentration of China’s Civil Aviation Industry
With China’s sustained and rapid economic development, China’s civil aviation industry gradually market-oriented, and has undergone several major reforms, gradual deregulation. At the same time, industry concentration showed a gradual downward trend. The internationally accepted measure of industrial concentration of two indicators: Industry moderate and HHI index. We described and analyzed the industry concentration and development trends on China’s civil aviation industry, and we got the main factors of the change of industry concentration. Also put forward policy recommendations
The Role of Integrative Leadership in the Transformation Process of Public Services Delivery: From the Perspective of IS Strategy Triangle Theory
In the era of Government 2.0, the government should transform into a citizen-centric and service-oriented government. In the terms of public services delivery, more innovative IT-based methods are pursued. However, on the perspective of organizational management, leadership plays a major role in using IT to make public services delivery efficient. Therefore, this paper presents a conceptual framework for understanding how integrative leadership influence the transformation of IT-based public services delivery. From the perspective of IS strategy triangle theory, we define integrative leadership as bringing diverse leaderships—strategy leadership, organization leadership and IT leadership—in an organization together with a close-coupled association to accomplish the complex and public issue and archive the united strategic goal. The framework is illustrated with a case of a local government, Pingfang District of Harbin in China, a pilot unit of Smart City providing more convenient and effective public services under the guidance of the District Mayor, the Organization Department Minister and the Informatization Office Director that are responsible for the coordination of strategy formulation, organization restructuration and information construction respectively. The framework is, to our best knowledge, the first of their kind in the new research field of key component elements of intra-organizational integrative leadership and provides significant insights for future exploration
Physiological Integration of Photosynthates and Changes of Endogenous ABA and IAA in the Connected Ramets of \u3ci\u3eBuchloe dactyloides\u3c/i\u3e (Nutt.) Texoka after Supply of Water Heterogeneity
Predication Method for China’s Civil Aviation Fuel Consumption
With the China’s civil aviation industry gradual market-oriented and the rapid development of China’s economy, China’s civil aviation transportation fuel consumption has grown significantly in nearly past three decades. Therefore, it’s a very important strategic significance of the prediction of China’s civil aviation transportation fuel consumption. In this paper, gray system and neural network approach, combined with China’s civil aviation industry 1980-2010 total traffic volume of the data, we establish gray system GM (1,1) model and BP neural network model for civil aviation transport volume. Training and simulation of the back propagation neutral network model and the gray system GM(1,1) used MATLAB. BP neural network modeling takes into account in three factors: the number of aircraft aviation industry, flight hours and total turnover. The fitting precision of the gray system GM(1,1) model is 64.2% while the fitting precision of the back propagation neutral network model is 90.16%. Thus, the back propagation neutral network model is better for estimating Civil aviation fuel consumption
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