366 research outputs found
Manipulation of electronic and magnetic properties of MC (M=Hf, Nb, Sc, Ta, Ti, V, Zr) monolayer by applying mechanical strains
Tuning the electronic and magnetic properties of a material through strain
engineering is an effective strategy to enhance the performance of electronic
and spintronic devices. Recently synthesized two-dimensional transition metal
carbides MC (M=Hf, Nb, Sc, Ta, Ti, V, Zr), known as MXenes, has aroused
increasingly attentions in nanoelectronic technology due to their unusual
properties. In this paper, first-principles calculations based on density
functional theory are carried out to investigate the electronic and magnetic
properties of MC subjected to biaxial symmetric mechanical strains. At the
strain-free state, all these MXenes exhibit no spontaneous magnetism except for
TiC and ZrC which show a magnetic moment of 1.92 and 1.25 /unit,
respectively. As the tensile strain increases, the magnetic moments of MXenes
are greatly enhanced and a transition from nonmagnetism to ferromagnetism is
observed for those nonmagnetic MXenes at zero strains. The most distinct
transition is found in HfC, in which the magnetic moment is elevated to 1.5
/unit at a strain of 15%. We further show that the magnetic properties
of HfC are attributed to the band shift mainly composed of Hf(5) states.
This strain-tunable magnetism can be utilized to design future spintronics
based on MXenes
Effect of Silica Fume in Concrete on Mechanical Properties and Dynamic Behaviors under Impact Loading
The effect of silica fume (SF) in concrete on mechanical properties and dynamic behaviors was experimentally studied by split Hopkinson pressure bar (SHPB) device with pulse shaping technique. Three series of concrete with 0, 12%, and 16% SF as a cement replacement by weight were produced firstly. Then the experimental procedure for dynamic tests of concrete specimens with SF under a high loading rate was presented. Considering the mechanical performance and behaviors of the concrete mixtures, those tests were conducted under five different impact velocities. The experimental results clearly show concrete with different levels of SF is a strain-rate sensitive material. The tensile strength under impact loading of the tested specimens was generally improved with the increasing content of SF levels in concrete. Additionally, the tensile strength under impact loading of the concrete enhances with the increase of the strain rates. Finally, failure modes, dynamic tensile strength, dynamic increase factor (DIF), and critical strain are discussed and analyzed. These investigations are useful to improve the understanding of the effect of SF in concrete and guide the design of concrete structures
Effect of Silica Fume in Concrete on Mechanical Properties and Dynamic Behaviors under Impact Loading
The effect of silica fume (SF) in concrete on mechanical properties and dynamic behaviors was experimentally studied by split Hopkinson pressure bar (SHPB) device with pulse shaping technique. Three series of concrete with 0, 12%, and 16% SF as a cement replacement by weight were produced firstly. Then the experimental procedure for dynamic tests of concrete specimens with SF under a high loading rate was presented. Considering the mechanical performance and behaviors of the concrete mixtures, those tests were conducted under five different impact velocities. The experimental results clearly show concrete with different levels of SF is a strain-rate sensitive material. The tensile strength under impact loading of the tested specimens was generally improved with the increasing content of SF levels in concrete. Additionally, the tensile strength under impact loading of the concrete enhances with the increase of the strain rates. Finally, failure modes, dynamic tensile strength, dynamic increase factor (DIF), and critical strain are discussed and analyzed. These investigations are useful to improve the understanding of the effect of SF in concrete and guide the design of concrete structures
Link between K-absorption edges and thermodynamic properties of warm-dense plasmas established by improved first-principles method
A precise calculation that translates shifts of X-ray K-absorption edges to
variations of thermodynamic properties allows quantitative characterization of
interior thermodynamic properties of warm dense plasmas by X-ray absorption
techniques, which provides essential information for inertial confinement
fusion and other astrophysical applications. We show that this interpretation
can be achieved through an improved first-principles method. Our calculation
shows that the shift of K-edges exhibits selective sensitivity to thermal
parameters and thus would be a suitable temperature index to warm dense
plasmas. We also show with a simple model that the shift of K-edges can be used
to detect inhomogeneity inside warm dense plasmas when combined with other
experimental tools
On Enhancing Expressive Power via Compositions of Single Fixed-Size ReLU Network
This paper explores the expressive power of deep neural networks through the
framework of function compositions. We demonstrate that the repeated
compositions of a single fixed-size ReLU network exhibit surprising expressive
power, despite the limited expressive capabilities of the individual network
itself. Specifically, we prove by construction that can approximate
-Lipschitz continuous functions on with an error
, where is realized by a fixed-size
ReLU network, and are two affine
linear maps matching the dimensions, and denotes the
-times composition of . Furthermore, we extend such a result
to generic continuous functions on with the approximation error
characterized by the modulus of continuity. Our results reveal that a
continuous-depth network generated via a dynamical system has immense
approximation power even if its dynamics function is time-independent and
realized by a fixed-size ReLU network
Whole Sky Infrared Remote Sensing of Cloud
AbstractClouds are important factors in weather and climate change. Cloud amount, type and height are measured by means of both visual observation on ground and satellites ever before. In recent years, instruments of measuring clouds on ground have been developed. This paper introduces our progress on ground based whole sky infrared remote sensing of cloud. Some results are given. A method for determining clear sky radiance threshold was suggested, and cloud identification combined threshold method with texture method was discussed. An algorithm retrieving cloud base height from downwelling infrared radiance was suggested. Cloud classification of ground based whole sky cloud images was discussed. Structural features are better than texture features in classifying clouds
First-Principles Calculation of Principal Hugoniot and K-Shell X-ray Absorption Spectra for Warm Dense KCl
Principal Hugoniot and K-shell X-ray absorption spectra of warm dense KCl are
calculated using the first-principles molecular dynamics method. Evolution of
electronic structures as well as the influence of the approximate description
of ionization on pressure (caused by the underestimation of the energy gap
between conduction bands and valence bands) in the first-principles method are
illustrated by the calculation. Pressure ionization and thermal smearing are
shown as the major factors to prevent the deviation of pressure from global
accumulation along the Hugoniot. In addition, cancellation between electronic
kinetic pressure and virial pressure further reduces the deviation. The
calculation of X-ray absorption spectra shows that the band gap of KCl persists
after the pressure ionization of the electrons of Cl and K taking place at
lower energy, which provides a detailed understanding to the evolution of
electronic structures of warm dense matter
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