20,895 research outputs found
Raman spectroscopic determination of the length, strength, compressibility, Debye temperature, elasticity, and force constant of the C-C bond in graphene
From the perspective of bond relaxation and vibration, we have reconciled the
Raman shifts of graphene under the stimuli of the number-of-layer,
uni-axial-strain, pressure, and temperature in terms of the response of the
length and strength of the representative bond of the entire specimen to the
applied stimuli. Theoretical unification of the measurements clarifies that:
(i) the opposite trends of Raman shifts due to number-of-layer reduction
indicate that the G-peak shift is dominated by the vibration of a pair of atoms
while the D- and the 2D-peak shifts involves z-neighbor of a specific atom;
(ii) the tensile strain-induced phonon softening and phonon-band splitting
arise from the asymmetric response of the C3v bond geometry to the C2v
uni-axial bond elongation; (iii) the thermal-softening of the phonons
originates from bond expansion and weakening; and (iv) the pressure- stiffening
of the phonons results from bond compression and work hardening. Reproduction
of the measurements has led to quantitative information about the referential
frequencies from which the Raman frequencies shift, the length, energy, force
constant, Debye temperature, compressibility, elastic modulus of the C-C bond
in graphene, which is of instrumental importance to the understanding of the
unusual behavior of graphene
Anisotropic superconducting properties of aligned SmLaFeAsOF microcrystalline powder
The SmLaFeAsOF compound is a quasi-2D
layered superconductor with a superconducting transition temperature T = 52
K. Due to the Fe spin-orbital related anisotropic exchange coupling
(antiferromagnetic or ferromagnetic fluctuation), the tetragonal
microcrystalline powder can be aligned at room temperature using the
field-rotation method where the tetragonal -plane is parallel to the
aligned magnetic field B and -axis along the rotation axis.
Anisotropic superconducting properties with anisotropic diamagnetic ratio
2.4 + 0.6 was observed from low field susceptibility
(T) and magnetization M(B). The anisotropic low-field phase diagram
with the variation of lower critical field gives a zero-temperature penetration
depth (0) = 280 nm and (0) = 120 nm. The magnetic
fluctuation used for powder alignment at 300 K may be related with the pairing
mechanism of superconductivity at lower temperature.Comment: 4 pages, 6 figure
A coupled remote sensing and the Surface Energy Balance with Topography Algorithm (SEBTA) to estimate actual evapotranspiration over heterogeneous terrain
Evapotranspiration (ET) may be used as an ecological indicator to address the ecosystem complexity. The accurate measurement of ET is of great significance for studying environmental sustainability, global climate changes, and biodiversity. Remote sensing technologies are capable of monitoring both energy and water fluxes on the surface of the Earth. With this advancement, existing models, such as SEBAL, S_SEBI and SEBS, enable us to estimate the regional ET with limited temporal and spatial coverage in the study areas. This paper extends the existing modeling efforts with the inclusion of new components for ET estimation at different temporal and spatial scales under heterogeneous terrain with varying elevations, slopes and aspects. Following a coupled remote sensing and surface energy balance approach, this study emphasizes the structure and function of the Surface Energy Balance with Topography Algorithm (SEBTA). With the aid of the elevation and landscape information, such as slope and aspect parameters derived from the digital elevation model (DEM), and the vegetation cover derived from satellite images, the SEBTA can account for the dynamic impacts of heterogeneous terrain and changing land cover with some varying kinetic parameters (i.e., roughness and zero-plane displacement). Besides, the dry and wet pixels can be recognized automatically and dynamically in image processing thereby making the SEBTA more sensitive to derive the sensible heat flux for ET estimation. To prove the application potential, the SEBTA was carried out to present the robust estimates of 24 h solar radiation over time, which leads to the smooth simulation of the ET over seasons in northern China where the regional climate and vegetation cover in different seasons compound the ET calculations. The SEBTA was validated by the measured data at the ground level. During validation, it shows that the consistency index reached 0.92 and the correlation coefficient was 0.87
Influence of Fermion Velocity Renormalization on Dynamical Mass Generation in QED
We study dynamical fermion mass generation in (2+1)-dimensional quantum
electrodynamics with a gauge field coupling to massless Dirac fermions and
non-relativistic scalar bosons. We calculate the fermion velocity
renormalization and then examine its influence on dynamical mass generation by
using the Dyson-Schwinger equation. It is found that dynamical mass generation
takes place even after including the scalar bosons as long as the bosonic
compressibility parameter is sufficiently small. In addition, the fermion
velocity renormalization enhances the dynamically generated mass.Comment: 6 pages, 3 figures, Chinese Physics Letter, Vol 29, page 057401(2012
Incommensurate magnetic order in the alpha-Fe(Te,Se) superconductor systems
Magnetic spin fluctuations is one candidate to produce the bosonic modes that
mediate the superconductivity in the ferrous superconductors. Up until now, all
of the LaOFeAs and BaFe2As2 structure types have simple commensurate magnetic
ground states, as result of nesting Fermi surfaces. This type of
spin-density-wave (SDW) magnetic order is known to be vulnerable to shifts in
the Fermi surface when electronic densities are altered at the superconducting
compositions. Superconductivity has more recently been discovered in
alpha-Fe(Te,Se), whose electronically active antifluorite planes are
isostructural to the FeAs layers found in the previous ferrous superconductors
and share with them the same quasi-two-dimensional electronic structure. Here
we report neutron scattering studies that reveal a unique complex
incommensurate antiferromagnetic order in the parent compound alpha-FeTe. When
the long-range magnetic order is suppressed by the isovalent substitution of Te
with Se, short-range correlations survive in the superconducting phase.Comment: 27 pages, 7 figures, 1 tabl
Relaxed 2-D Principal Component Analysis by Norm for Face Recognition
A relaxed two dimensional principal component analysis (R2DPCA) approach is
proposed for face recognition. Different to the 2DPCA, 2DPCA- and G2DPCA,
the R2DPCA utilizes the label information (if known) of training samples to
calculate a relaxation vector and presents a weight to each subset of training
data. A new relaxed scatter matrix is defined and the computed projection axes
are able to increase the accuracy of face recognition. The optimal -norms
are selected in a reasonable range. Numerical experiments on practical face
databased indicate that the R2DPCA has high generalization ability and can
achieve a higher recognition rate than state-of-the-art methods.Comment: 19 pages, 11 figure
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