3,225 research outputs found
A potential superhard material m-BCN
We here propose a new superhard material m-BCN with comparable Vickers hardness to cBN by the use of first-principles calculations. The calculations show that the mentioned m-BCN is a thermodynamically and kinetically stable semiconductor. Hydrostatic calculation shows that it is anisotropic and its incompressibility is very close to c-BN. Structural analysis shows that its excellent mechanical property and thermodynamically stability are inherited from diamond and cBN. These results provide a new clue to find new superhard phase.Запропоновано новий надтвердий матеріал m-BCN, твердість за Віккерсом якого за розрахунками за першими принципами порівняна з твердістю cBN. Розрахунки показали, що згаданий m-BCN за термодинамічними і кінетичними показниками є стабільним напівпровідником. Гідростатичний розрахунок показав, що він є анізотропним і його нестисливість дуже близька до нестисливості cBN. Структурний аналіз показав, що його відмінні механічні властивості і термодинамічна стабільність успадковані від алмаза і cBN. Дані результати забезпечують нову схему пошуку нових надтвердих фаз.Предложен новый сверхтвердый материал m-BCN, твердость по Виккерсу которого по расчетам по первым принципам сравнима с твердостью cBN. Расчеты показывают, что упомянутый m-BCN по термодинамическим и кинетическим показателям является стабильным полупроводником. Гидростатический расчет показал, что он анизотропный и его несжимаемость очень близка к несжимаемости cBN. Структурный анализ показал, что его отличные механические свойства и термодинамическая стабильность унаследованы от алмаза и cBN. Данные результаты обеспечивают новую схему поиска новых сверхтвердых фаз
First-principles calculations of the structural, electronic, vibrational and magnetic properties of C_{60} and C_{48}N_{12}: a comparative study
In this work, we perform first-principles calculations of the structural,
electronic, vibrational and magnetic properties of a novel azafullerene. Full geometrical optimization shows that is characterized by several distinguishing features: only
one nitrogen atom per pentagon, two nitrogen atoms preferentially sitting in
one hexagon, symmetry, 6 unique nitrogen-carbon and 9 unique
carbon-carbon bond lengths. The highest occupied molecular orbital of is a doubly degenerate level of symmetry and its
lowest unoccupied molecular orbital is a nondegenerate level of
symmetry. Vibrational frequency analysis predicts that has in total 116 vibrational modes: 58 infrared-active and 58
Raman-active modes. is also characterized by 8
and 2 NMR spectral signals. Compared to , shows an enhanced third-order optical
nonlinearities which implies potential applications in optical limiting and
photonics.Comment: a long version of our manuscript submitted to J.Chem.Phy
Relation between millimeter wavelengths emission and high-energy emission for active galactic nuclei
After comparing the flux densities of a sample of active galactic nuclei
detected by energetic gamma-ray experiment telescope at 90 and 230 GHz with the
-ray emissions detected by Compton Gamma Ray Observatory and x-ray
emission, a strong correlation between the emissions at the millimeter
wavelength and the -ray emission is found. The average flux density of
x-ray is almost proportional to the average flux density at the millimeter
wavelength for quasars detected by energetic gamma-ray experiment telescope,
which strongly supports the previous idea that the x-ray emissions of this kind
sources are mainly produced by Synchrotron Self-Compton process.Comment: 6 pages, Chinese Physics Letters in pres
Spatiotemporal Changes of China's Carbon Emissions
Spatiotemporal changes in China's carbon emissions during the 11th and 12th Five‐Year Plan periods are quantified for the first time through a reconstructed nationwide high‐resolution gridded data set. The hot spots of carbon emissions in China have expanded by 28.5% (toward the west) in the north and shrunk by 18.7% in the south; meanwhile, the emission densities in North and South China have increased by 15.7% and 49.9%, respectively. This suggests a clear transition to a more intensive economic growth model in South China as a result of the energy conservation and emission reduction policies, while the expanded carbon hot spots in North China are mainly dominated by the Grand Western Development Program. The results also show that China's carbon emissions exhibit a typical spatially intensive, high‐emission pattern, which has undergone a slight relaxation (up to 3%) from 2007 to 2012 due to a typical urbanization process
Designing Optimal Perovskite Structure for High Ionic Conduction.
Solid-oxide fuel/electrolyzer cells are limited by a dearth of electrolyte materials with low ohmic loss and an incomplete understanding of the structure-property relationships that would enable the rational design of better materials. Here, using epitaxial thin-film growth, synchrotron radiation, impedance spectroscopy, and density-functional theory, the impact of structural parameters (i.e., unit-cell volume and octahedral rotations) on ionic conductivity is delineated in La0.9 Sr0.1 Ga0.95 Mg0.05 O3- δ . As compared to the zero-strain state, compressive strain reduces the unit-cell volume while maintaining large octahedral rotations, resulting in a strong reduction of ionic conductivity, while tensile strain increases the unit-cell volume while quenching octahedral rotations, resulting in a negligible effect on the ionic conductivity. Calculations reveal that larger unit-cell volumes and octahedral rotations decrease migration barriers and create low-energy migration pathways, respectively. The desired combination of large unit-cell volume and octahedral rotations is normally contraindicated, but through the creation of superlattice structures both expanded unit-cell volume and large octahedral rotations are experimentally realized, which result in an enhancement of the ionic conductivity. All told, the potential to tune ionic conductivity with structure alone by a factor of ≈2.5 at around 600 °C is observed, which sheds new light on the rational design of ion-conducting perovskite electrolytes
The QE numerical simulation of PEA semiconductor photocathode
Several kinds of models have already been proposed for explaining the
photoemission process. The exact photoemission theory of semiconductor
photocathode was not well established after decades of research. In this paper
an integral equation of quantum efficiency (QE) is constructed to describe the
photoemission of positive electron affinity (PEA) semiconductor photocathode
based on three-step photoemission model. The influences of forbidden gap,
electron affinity, photon energy, incident angle, degree of polarization,
refractive index, extinction coefficient, initial/final electron energy,
relaxation time and external electric field on the QE of PEA semiconductor
photocathode are taken into account. In addition, a computer code is also
programmed to calculate the QE of K2CsSb photocathode theoretically at 532nm
wavelength, the result is in line with the experimental value by and large.
What are the reasons caused to the distinction between the experimental
measuring and theoretical QE are discussed.Comment: 12 pages,3 figures,2 tables,submitted to Chinese Physics
Analysis of the Sound Field Characteristics of a Muffler at Different Flow Conditions
To reduce the noise in a pump piping system and increase the usage time of equipment, a new type of porous muffler is proposed in this paper. A water guide cone is incorporated into the muffler structure, which may help to redirect the fluid media in the piping system. The porous structure is adapted from a muffler shell, water cone wall and round bottom plate. According to this structure, the muffler sample is made, and a pump pipeline system test bench is set up. The outlet noise of the pump pipeline system is measured after installing the muffler. At the same time, the muffler is numerically simulated by combining computational fluid mechanics and Lighthill acoustic theory. The characteristics of the flow field and external sound field under three different flow conditions of 200 m3/h, 400 m3/h and 600 m3/h are assessed. The numerical simulation results show the same dominant frequency and trend as the experimental results. The rationality of the numerical simulation is verified. Research shows that: the level of sound pressure at the muffler's outlet is lower than at the inlet, causing muffling, and the characteristics of a quadrupole sound source appear at the outlet. The proposed muffler has a certain effect in reducing noise in the pump pipeline system
The Hippo/YAP pathway interacts with EGFR signaling and HPV oncoproteins to regulate cervical cancer progression
The Hippo signaling pathway controls organ size and tumorigenesis
through a kinase cascade that inactivates Yes-associated
protein (YAP). Here, we show that YAP plays a central role in
controlling the progression of cervical cancer. Our results suggest
that YAP expression is associated with a poor prognosis for cervical
cancer. TGF-α and amphiregulin (AREG), via EGFR, inhibit the Hippo
signaling pathway and activate YAP to induce cervical cancer cell
proliferation and migration. Activated YAP allows for up-regulation
of TGF-α, AREG, and EGFR, forming a positive signaling loop to
drive cervical cancer cell proliferation. HPV E6 protein, a major
etiological molecule of cervical cancer, maintains high YAP protein
levels in cervical cancer cells by preventing proteasome-dependent
YAP degradation to drive cervical cancer cell proliferation. Results
from human cervical cancer genomic databases and an accepted
transgenic mouse model strongly support the clinical relevance of
the discovered feed-forward signaling loop. Our study indicates
that combined targeting of the Hippo and the ERBB signaling pathways
represents a novel therapeutic strategy for prevention and
treatment of cervical cancer
Raman scattering in C_{60} and C_{48}N_{12} aza-fullerene: First-principles study
We carry out large scale {\sl ab initio} calculations of Raman scattering
activities and Raman-active frequencies (RAFs) in
aza-fullerene. The results are compared with those of .
Twenty-nine non-degenerate polarized and 29 doubly-degenerate unpolarized RAFs
are predicted for . The RAF of the strongest Raman
signal in the low- and high-frequency regions and the lowest and highest RAFs
for are almost the same as those of .
The study of reveals the importance of electron correlations and
the choice of basis sets in the {\sl ab initio} calculations. Our best
calculated results for with the B3LYP hybrid density functional
theory are in excellent agreement with experiment and demonstrate the desirable
efficiency and accuracy of this theory for obtaining quantitative information
on the vibrational properties of these molecules.Comment: submitted to Phys.Rev.
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