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1.
Effects of pressure on structural,electronic, and mechanical properties of α,β,and γ uranium
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The first-principles methods have been employed to calculate the structural, electronic, and mechanical properties of the α, β, and γ phases of uranium under pressure up to 100 GPa. The electronic structure has been viewed in forms of density of states and band structure. The mechanical stability of metal U in the α, β, and γ phases have been examined.The independent elastic constants, polycrystalline elastic moduli, as well as Poisson's ratio have been obtained. Upon compression, the elastic constants, elastic moduli, elastic wave velocities, and Debye temperature of α phase are enhanced pronouncedly. The value of B/G illustrates that α and γ phases are brittle in ground state. 相似文献
2.
Zadjia Atik 《Journal of Molecular Liquids》2011,163(2):89-92
The volumetric properties were evaluated from density data for the binary mixtures of (fluorobenzene + tert-butylmethyl ether), (α,α,α-trifluorotoluene + tert-butylmethyl ether), (tert-butylmethyl ether + ethanol), and the ternary mixtures of (fluorobenzene + tert-butylmethyl ether + ethanol) and (α,α,α-trifluorotoluene + tert-butylmethyl ether + ethanol). The observed densities were obtained by means of a vibrating-tube densimeter at the temperature 298.15 K and the pressure 101 kPa.The excess molar volumes of the ternary mixtures were estimated from binary solution data using several empirical equations with mean standard deviation less than 0.03 cm3·mol-1. Stable chemical cross-associations among the molecules forming the mixtures were revealed. 相似文献
3.
K.S. Bond N.D. Collett E.P. Fuller J.L. Hardwick E.E. Hinds T.W. Keiber I.S.G. Kelly-Morgan C.M. Matthys M.J. Pilkenton K.W. Sinclair A.A. Taylor 《Applied physics. B, Lasers and optics》2008,90(2):255-262
Pressure broadening and shift coefficients for the ν1+ν3 band of 12C2H2 have been measured for He, Ne, and Ar at a temperature of 195 K using high resolution diode laser spectroscopy. The pressure
broadening and shifts follow patterns with rotational assignment that are similar to those at room temperature but are generally
larger in magnitude. The change in magnitude is qualitatively described by assuming, for each transition, a constant cross
section for pressure broadening or shifting. Better agreement may be obtained for pressure broadening coefficients by using
empirically determined temperature exponents; better agreement still is obtained from close coupling calculations of the pressure
broadening cross sections.
PACS 33.70.Jg 相似文献
4.
《Ultrasonics sonochemistry》2014,21(3):930-936
The effect of ultrasound on the activity of α-amylase, papain and pepsin was investigated and the mechanism of the effect was explored by determining their conformational changes. With the irradiation of power ultrasound, the activity of α-amylase and papain was inhibited, while the activity of pepsin was activated. According to the analysis of circular dichroism, Fourier transform infrared and fluorescence spectroscopy, the πo → π1 amide transitions and secondary structural components, especially β-sheet, of these three enzymes were significantly influenced by ultrasound. The tryptophan fluorescence intensity of the three enzymes was also observed to be affected by sonication. Furthermore, it was found that the pepsin molecule might gradually be resistant to prolonged ultrasonic treatment and recover from the ultrasound-induced damage to its original structure. The results suggested that the activity of α-amylase, papain and pepsin could be modified by ultrasonic treatment mainly due to the variation of their secondary and tertiary structures. 相似文献
5.
Highly correlated ab initio methods were used in order to calculate potential energy curves (PECs) of the bound electronic states of CH? and NH? anions and the long-range parts of their excited states. The spin–orbit interaction between electronic states has been calculated for the cases in which the couplings were assumed to be responsible for perturbations. The spectroscopic constants of bound states were calculated from the PECs and compared with previous theoretical and/or available experimental values. Also, from the ground states of CH/CH? and NH/NH?, the adiabatic electron affinities were given and discussed. 相似文献
6.
Peter Pesic 《Physics in Perspective (PIP)》2013,15(3):256-294
Emerging from music and the visual arts, questions about hearing and seeing deeply affected Hermann Helmholtz’s and Bernhard Riemann’s contributions to what became called the “problem of space [Raumproblem],” which in turn influenced Albert Einstein’s approach to general relativity. Helmholtz’s physiological investigations measured the time dependence of nerve conduction and mapped the three-dimensional manifold of color sensation. His concurrent studies on hearing illuminated musical evidence through experiments with mechanical sirens that connect audible with visible phenomena, especially how the concept of frequency unifies motion, velocity, and pitch. Riemann’s critique of Helmholtz’s work on hearing led Helmholtz to respond and study Riemann’s then-unpublished lecture on the foundations of geometry. During 1862–1870, Helmholtz applied his findings on the manifolds of hearing and seeing to the Raumproblem by supporting the quadratic distance relation Riemann had assumed as his fundamental hypothesis about geometrical space. Helmholtz also drew a “close analogy … in all essential relations between the musical scale and space.” These intersecting studies of hearing and seeing thus led to reconsideration and generalization of the very concept of “space,” which Einstein shaped into the general manifold of relativistic space-time. 相似文献
7.
Ramadevi V. Ravi G. Radha Velchuri Sameera Devi C. H. Prasad G. Vithal M. 《Ionics》2014,20(3):373-380
The pyrochlore oxide of composition YLnTiZrO7 (Ln?=?La, Nd, Sm, and Eu) was prepared by sol–gel method. All the samples were characterized by powder X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), diffused reflectance spectroscopy, and impedance spectroscopy. The powder XRD and Raman studies reveal that these samples were crystallized in cubic lattice with pyrochlore structure. The Rietveld analysis of the samples was carried out to obtain the unit cell parameters and reliability factors. The broad Raman bands observed for all the samples are due to cation/anion disorder in the lattice and nanosize. The XPS analysis of the samples shows the characteristic peaks belonging to Y3+, Ln3+ (Ln?=?La, Nd, Sm, and Eu), Ti4+, and Zr4+. Electrical conductivity of YLaTiZrO7 (YLTZ) and YEuTiZrO7 (YETZ) samples was calculated from the impedance as a function of frequency and temperature. These samples have shown conductivity of the order of 10?5 scm?1 at 500 °C. 相似文献
8.
John Crepeau 《Physics in Perspective (PIP)》2009,11(4):357-378
Josef Loschmidt (1821–1895) and Josef Stefan (1835–1893) were eminent scientists in the Institute of Physics at the University
of Vienna during the second half of the nineteenth century but are not well known today, as their legacies have been recognized
differently by the scientific community. Loschmidt first described the structure of the benzene molecule and determined the
size of air molecules, from which the number of molecules per unit volume can easily be determined, yet others received the
credit for these achievements. Stefan posited the fourth-power temperature radiation law, but neither he nor his student Ludwig
Boltzmann (1844–1906) calculated the proportionality constant now known as the Stefan-Boltzmann constant. These are instances
of Stigler’s Law of Eponymy. Besides these achievements, perhaps the greatest unheralded contribution of both Loschmidt and
Stefan was the experimental evidence they provided in support of the emerging kinetic theory of gases. 相似文献
9.
J. Arenas-Alatorre Y. Silva-Velazquez A. Alva?Medina M. Rivera 《Applied Physics A: Materials Science & Processing》2010,98(3):617-624
This paper presents results from the study of two fragments of pre-Hispanic pottery, decorated with red pigment, using Optical Microscopy (OM), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), Atomic Force Microscopy (AFM) and Magnetic Force Microscopy (MFM). Capabilities and limitations of these techniques in the analysis of archaeological material are highlighted with special emphasis on TEM, AFM and MFM due to their contribution in the study of the pigment layer at micro and nano scale. The analyzed samples come from the archaeological sites of El Tajin and Xochicalco, both in Mexico. Results of conventional TEM and HRTEM analysis of the red pigment showed nanometric Fe2O3 particles in both samples but different particle shape and size distributions: specimen from El Tajin presented irregular particles between 50–100 nm while that from Xochicalco exhibited semispherical shapes in the 3–25 nm range. AFM images showed the topography of the pigments, which are related to the texture of their surface and thus to the production process. Finally, MFM showed different contrast regions suggesting the presence of ferromagnetic elements forming clusters and domain orientations on the color layer. 相似文献
10.
The intensities of Si X-ray emission spectra of Si, β-SiC, stishovite, and β-cristobalite crystals are calculated. The wave
functions of the initial and final states are obtained in the framework of the density-functional theory with the use of the
norm-conserving and ultrasoft pseudopotentials. The all-electron crystal orbitals are reconstructed from the one-electron
pseudowave functions. The probabilities of X-ray emission transitions are calculated by reconstructing the all-electron orbitals
in two different gauges, namely, the length and velocity gauges. The calculated intensities are compared with the experimental
spectra and the partial densities of states. 相似文献
11.
Effects of shape and dopant on structural,optical absorption,Raman, and vibrational properties of silver and copper quantum clusters: A density functional theory study
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We investigate the effects of shape and single-atom doping on the structural, optical absorption, Raman, and vibra- tional properties of Ag13, Ag12CUl, CUl3, and Cul2Agl clusters by using the (time-dependent) density functional the- ory. The results show that the most stable structures are cuboctahedron (COh) for Ag13 and icosahedron (Ih) for CUl3, Agl2CUlcore, and Cul2Aglsur. In the visible-near infrared optical absorption, the transitions consist of the interband and the intraband transitions. Moreover, red shifts are observed as follows: 1) clusters change from Agl2CUlcore to Ag13 to Ag12Culsur with the same motifs, 2) the shapes of pure Agl3 and Agl2CUlcore clusters change from COh to Ih to decahe- dron (Dh), 3) the shape of Agl2CUlsur clusters changes from Ih to COh to Dh, and 4) the shapes of pure CU13 and Cu12Agl clusters change from Ih to Dh to COb. All of the Raman and vibrational spectra exhibit many significant vibrational modes related to the shapes and the compositions of the clusters. The ranges of vibrational spectra of Ag13, Agl2CUl or CU13, and Cu12Agl clusters become narrower and the vibrational intensities increase as the shape of the clusters changes from Ih to Dh to COh. 相似文献
12.
Synthesis, characterization of the pentacene and fabrication of pentacene field-effect transistors
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A comprehensive understanding of the organic semiconductor material pentacene is meaningful for organic fieldeffect transistors (OFETs). Thin films of pentacene are the most mobile molecular films known to date. This paper reported that the pentacene sample was successfully synthesized. The purity of pentacene is up to 95%. The results of a joint experimental investigation based on a combination of infrared absorption spectra, mass spectra (MS), element analysis, x-ray diffraction (XRD) and atom force microscopy (AFM). The authors fabricated OFET with the synthesized pentacene. Its field effect mobility is about 1.23 cm^2/(V·s) and on-off ratio is above 10^6. 相似文献
13.
在近代量子力学的图像中,环绕着原子与分子的电子云具有各种不同的形态结构,一般在某一测定时间内,其形状为球状或哑铃状.这类形状通常称为电子轨道,它们可在飞秒量级的时间内明显地观测到.这些电子轨道也可在简并态(具有相同能量的量子态)间相互跃迁;如在相同轴上由垂直哑铃转变为水平哑铃等. 相似文献
14.
First-principles calculation of the structural,electronic, elastic,and optical properties of sulfur-doping ε-GaSe crystal
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The structural,electronic,mechanical properties,and frequency-dependent refractive indexes of GaSe_(1-x)S_x(x=0,0.25,and 1) are studied by using the first-principles pseudopotential method within density functional theory.The calculated results demonstrate the relationships between intralayer structure and elastic modulus in GaSe_(1-x)S_x(x=0,0.25,and 1).Doping of ε-GaSe with S strengthens the Ga-X bonds and increases its elastic moduli of C_(11) and C_(66).Born effective charge analysis provides an explanation for the modification of cleavage properties about the doping of e-GaSe with S.The calculated results of band gaps suggest that the distance between intralayer atom and substitution of S_(Se),rather than interlayer force,is a key factor influencing the electronic exciton energy of the layer semiconductor.The calculated refractive indexes indicate that the doping of ε-GaSe with S reduces its refractive index and increases its birefringence. 相似文献
15.
《Physics letters. [Part B]》1988,215(3):542-550
Poincaré, BRST and Parisi-Sourlas supersymmetries are usually viewed as unrelated. Here we argue that they are in fact closely related. We argue that fermions in Poincaré SUSY theories can be interpreted as negative-dimensional phase space coordinates, in the Parisi-Sourlas sense. The Bose-Fermi balance then implies that the effective phase space dimensionality vanishes. We show that interacting Poincaré SUSY theories are related to the corresponding free theories by superrotations similar to BRST transformations. For superstrings we find that spacetime can be viewed as a zero-dimensional manifold in the sense of Parisi-Sourlas. 相似文献
16.
The effects of γ radiation on glycylglycine, triglycine, and polyglycine have been studied using ESR spectroscopy. The radiation exposures have been performed under vacuum at room temperature. All those irradiated substances show a doublet absorption signal often ascribed to a radical formed on the α carbon of the peptide chain. The magnetic susceptibility has been found to depend on temperature according to the Curie-Weiss law. The radio-sensitivity parameter Gr , the hyperfine splitting constant Ah and the spectroscopic factor g nave been determinated as well as θ which is the temperature corresponding to the Curie temperature of the irradiated substance. The results on Cr , θ and Ah for all peptides studied here agree with the assumption of radiation induced free radicals located at the α carbon of the peptide chain, leading to conclude that the degree of delocalization of the unpaired electron increases for increasing number of glycine units in the peptide. Finally, from negative θ values obtained, a conclusion has been reached on the antiferromagnetic nature of the interaction between unpaired spins. 相似文献
17.
The method of orbits traditionally applied to geometric quantization problems is used to study homogeneous spaces. Based on the proposed classification of the orbits of co-adjoint representation (K-orbits), a classification of homogeneous spaces is constructed. This classification allows one, in particular, to point out the explicit form of identities – functional relations between the transform-group generators – which are of great importance in applied problems (e.g., in the theory of separation of variables). All four-dimensional homogeneous spaces with the group of Poincaré and de Sitter transforms are classified and all independent identities on these spaces are given in explicit form. 相似文献
18.
19.
《声学学报:英文版》1999,(3)
1IntroductionThermoacousticswithpotelltialsinrefrigerationandcryogenictechnology,ha-sprogressedvigorouslyinlasttwelltyyears,asanexampleofsynchronousdevelopmentofscienceandprac-ticeofmodernsciences.Botthermoacousticphenomenawerediscoveredearlyinhistory,andittookmorethantwohundredyearsoftheeffortofscieatiststoarriveatthisperiod.Thisalsoservesasanexampleoftheduncultandtortuouswayinthecognitionofnature.Aretrthspectionoftheprogressofthermoacousticsinthelastyearsnotonlyhelpstounderstandthephysicsoft… 相似文献
20.
Polymer–clay nanocomposites have been prepared by melt blending of commercial organoclay Cloisite 15A with blends of polyethylenes (PE) and maleic-anhydride-grafted PE (PE/PE-g-MA) with wide range of composition. Three types of PE/PE-g-MA blends with different molecular structure, namely blends of high-density PE (HD) with HD-g-MA (HDMA), blends of low-density PE (LD) with LD-g-MA (LDMA), and blends of linear low-density PE (LL) with LL-g-MA (LLMA) were used. The influence of the molecular structure of the PE matrixes and the compatibility between the blend components on the morphology of the nanocomposites was studied. The thermal properties, microhardness, and transparency of the nanocomposites were investigated. The influence of the degree of exfoliation/intercalation on the materials characteristics is discussed. 相似文献