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1.
We have performed self-consistent full potential LAPW calculations of Cu2O. Since the new results agree well with a previous muffin-tin calculation, it can be concluded that non-muffin-tin effects
are relatively small in Cu2O. By using the present self-consistent charge density, we, obtain the electric field gradient (EFG) at the Cu site without
further approximations. Our theory yields a value of −0.85 e/au3, in good agreement with experiment but in contrast to a previous cluster calculation in which a positive sign of the EFG
was obtained. The origin of the EFG and the discrepancies between our band structure and the cluster calculation is analyzed. 相似文献
2.
Nanocrystalline indium (nano-In) was prepared with different particle sizes by electrochemical deposition. The temperature
dependence of the local electric field gradient (EFG) of nano-In was investigated in a temperature range of 20–300 K using
the probe 111In for perturbed γγ angular correlation (PAC) experiments. The temperature dependence of the EFG of nano-In can be described
by a (1−BT
3/2) dependence as in bulk-In. It is shown that the low temperature value of the EFG and the proportionality constant B vary
systematically with particle size. 相似文献
3.
Recent theoretical calculations show for defect complexes in semiconductors, characterized by electric field gradients (EFG),
that their chemical compositions, electronic charge states and the induced lattice relaxations can be obtained by comparing
the experimental and calculated EFG. The experimental data are obtained by perturbed γγ angular correlation experiments and
the calculations are performed using ab initio full potential methods in the framework of density functional theory.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
4.
E.Ya. Paryev 《The European Physical Journal A - Hadrons and Nuclei》2000,7(1):127-137
The inclusive K+ meson production in photon–induced reactions in the near threshold and subthreshold energy regimes is analyzed with respect
to the one–step (γN→K
+
Y, Y=Λ,Σ) incoherent production processes on the basis of an appropriate new folding model, which takes properly into account
the struck target nucleon removal energy and internal momentum distribution (nucleon spectral function), extracted from recent
quasielastic electron scattering experiments and from many–body calculations with realistic models of the NN interaction.
Simple parametrizations for the total and differential cross sections of the K+ production in photon–nucleon collisions are presented. Comparison of the model calculations of the K+ differential cross sections for the reaction γ+C12 in the threshold region with the existing experimental data is given, that displays the contributions to the K+ production at considered incident energies coming from the use of the single–particle part as well as high momentum and high
removal energy part of the nucleon spectral function. Detailed predictions for the K+ total and differential cross sections from γH2, γC12 and γPb208 reactions at subthreshold and near threshold energies are provided. The influence of the uncertainties in the elementary
K+ production cross sections on the K+ yield is explored.
Received: 12 April 1999 / Revised version: 11 September 1999 相似文献
5.
A computational study of the 51V electric field gradient (EFG) tensors in pyrovanadates, α-Zn2V2O7, Cd2V2O7, β-Mg2V2O7 and BaCaV2O7, and the metavanadates, LiVO3, α-NaVO3, KVO3, ZnV2O6 and MgV2O6, is presented. Restricted Hartree–Fock and hybrid density functional theory calculations have been used to investigate the
effects of the size of vanadium-oxygen clusters, basis set size, proton-termination and embedded cluster techniques on the
accuracy of the calculated EFG tensors. Good agreement between theory and experiment is obtained for most of the vanadates.
A sound methodology is suggested for calculating the EFG tensor in pyrovanadates which contain isolated V2O7
4− clusters. For metavanadates, the charges of the bridging oxygen atoms can be differentiated from those of terminal oxygen
atoms by terminating the former with hydrogen atoms, and embedded cluster molecular orbital calculations are useful in accounting
for the long-range electrostatic interactions which influence the EFG tensor components. EFG tensor orientations vary for
different pyrovanadate structural types, and individual components are confined by symmetry elements in the metavanadates.
A preliminary comparison is made between 51V EFG tensors calculated with ab initio and plane wave methods. Theoretical EFG tensor components and orientations, in combination
with experimental 51V solid-state nuclear magnetic resonance data, are demonstrated to be useful tools for prediction of molecular structure.
Authors' address: Robert W. Schurko, Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B
3P4, Canada 相似文献
6.
The electric-field-gradient (EFG) tensor at both cation sites of the bixbyite structure in 181Hf-implanted Lu- and Sm-sesquioxides was determined by the PAC technique. The cumulated EFG data at Ta-impurity sites in binary
oxides enable us to discuss the “universal” character of the empirical correlation between local and ionic contributions to
the EFG in these systems. An EFG factorization in terms of the electronic characteristics of the probe and the geometry of
the cation coordination is proposed, which explains the experimental EFG results at Ta/Cd impurity sites in bixbyites and
agrees with a simplified decomposition of the EFG valence contribution coming from ab-initio calculations.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
Nuclear γ-transitions via an electronic-bridge (EB) mechanism are considered theoretically. The relative probabilities for
the elastic and inelastic EB deexcitation effect are calculated in the framework of Dirac-Hartree-Slater (DHS) model of atom.
The probability of O+−O+ γ-transitions due to EB mechanism are discussed. The results of calculations are compared with experimental data. 相似文献
8.
The crystallographic structure and electronic properties of HfNi were studied as a function of pressure by combining X-ray
diffraction results with the full potential linearized augmented plane wave (LAPW) calculations. No phase transition was observed
up to a pressure of 35.3 GPa, with a total volume contraction of V/V
0 = 0.85, a bulk modulus value of B
0 = 52 ± 3 GPa and B
0
′ = 1.29 ± 0.26. The calculated linear increase in the V
zz
value as a function of the pressure induced volume reduction at the hafnium site was attributed mainly to the p–p contribution,
while in the nickel site, a non negligible d–d contribution to V
zz
is also observed, and attributed to the high 3d-partial DOS near the nickel nucleus. Based on the total electronic DOS at
E
Fermi calculated for 0 K (N(E
0
Fermi)), a value of 6.85 and 5.03 (mJ/mol/k2) was calculated for the band contribution (γ
band) to the electronic specific heat coefficient (γ) at a pressure of 0 and 35.3 GPa, respectively. 相似文献
9.
Double-tagged interactions of photons with virtualities Q2 between 10 GeV2 and 200 GeV2 are studied with the data collected by DELPHI at LEPII from 1998 to 2000, corresponding to an integrated luminosity of 550 pb-1. The γ*γ*→μ+μ- data agree with QED predictions. The cross-section of the reaction γ*γ*→hadrons is measured and compared to the LO and NLO BFKL calculations. 相似文献
10.
In the “naive” but fairly successful model by Bodenstedt and Perscheid, the electric field gradient (EFG) in a hcp s-p metal
is first evaluated by the lattice sum method, postulating a conduction electron charge shift and approximating the new conduction
electron distribution by point charges. Adding to this EFG, a contribution due to the anisotropy of lattice vibrations, i.e.
(<z
2>−<x
2>), was presumed to give the total temperature-dependent EFG. We find, however, from the EFG results of the present calculation
for111CdCd and the original result for67ZnZn, that the experimental data are better represented without the addition of the anisotropic vibration term. This finding,
as well as the outline of the present evaluation of <z
2> and <x
2> and hence the EFG for Cd, are discussed. 相似文献
11.
T. Shizuma T. Ishii H. Makii T. Hayakawa S. Shigematsu M. Matsuda E. Ideguchi Y. Zheng M. Liu T. Morikawa P. M. Walker M. Oi 《The European Physical Journal A - Hadrons and Nuclei》2006,30(2):391-396
Excited states in neutron-rich 188W have been populated using a 186W(18O,16O) reaction. In-beam γ-rays were measured in coincidence with scattered particles detected by a high-resolution ΔE-E Si telescope. In this experiment, the ground-state band has been identified up to I
π = 8+. The γ band, the K
π = 2- octupole band, and a 2-quasiparticle state were also observed. The results are compared with predictions of self-consistent
HFB cranking calculations and blocked-BCS multi-quasiparticle calculations. 相似文献
12.
R. Loritz O. Iordanov E. Galindo A. Jungclaus D. Kast K.P. Lieb C. Teich F. Cristancho Ch. Ender T. Härtlein F. Köck D. Schwalm 《The European Physical Journal A - Hadrons and Nuclei》1999,6(3):257-268
Subpicosecond lifetimes of high spin states in the rotational nuclei 73Se, 74Se and 74Br have been measured using the 58Ni +19F compound reaction and the Doppler Shift Attenuation method. Six EUROBALL Cluster detectors arranged in cube geometry allowed
us to select the relevant transitions in γγ coincidence mode. The high counting statistics achieved in this setup also facilitated
the determination of average sidefeeding times, which were found to agree rather well with the results of Monte-Carlo calculations
of the particle and γ-ray evaporation process. The deduced quadrupole strengths and deformations are compared with the results
of previous measurements and the predictions of Cranked Shell Model calculations. In 74Br, a large and constant prolate deformation of β2= 0.37(1) was found for the presumed 4+ and 3− two-quasiparticle bands.
Received: 2 July 1999 相似文献
13.
C. Mazzocchi Z. Janas J. Döring M. Axiotis L. Batist R. Borcea D. Cano-Ott E. Caurier G. de Angelis E. Farnea A. Faßbender A. Gadea H. Grawe A. Jungclaus M. Kapica R. Kirchner J. Kurcewicz S.M. Lenzi T. Martínez I. Mukha E. Nácher D.R. Napoli E. Roeckl B. Rubio R. Schwengner J.L. Tain C.A. Ur 《The European Physical Journal A - Hadrons and Nuclei》2001,12(3):269-277
By using the fusion-evaporation reaction 28Si(36Ar,p3n) and spectroscopy of β-delayed γ-rays and charged particles on mass-separated sources, β-decay properties of the neutron-deficient
isotope 60Ga were studied for the first time. The half-life of 60Ga was determined to be 70(15) ms, and, based on βγγ coincidences, the isobaric-analogue state in 60Zn was identified at 4851.9(7) keV. A semiempirical proton separation energy value of 40(70) keV was deduced for 60Ga. The experimental results on half-life, mass excess, proton separation energy, and structure of the 60Zn daughter states are discussed in comparison with various model predictions, including large-scale shell model calculations.
Received: 4 September 2001 / Accepted: 12 November 2001 相似文献
14.
Lepton-pair production from deep inelastic scatteringin peripheral relativistic heavy ion collisions
U. Dreyer T. Baier K. Hencken D. Trautmann 《The European Physical Journal C - Particles and Fields》2006,45(3):783-795
We calculate the inelastic electron- and muon-pair production in peripheral relativistic heavy ion collisions in the region
of large Q2 of one of the photons. This offers a possibility to study the quark distribution functions in ions in "ultraperipheral heavy
ion collisions". The calculations are compared with those making use of the equivalent photon and the equivalent lepton approximation.
We compare the results for Pb-Pb and Pb-p collisions at RHIC (γ ≈ 100) and LHC (γ ≈ 3000) energies. Furthermore we include nuclear modifications to the parton distribution
functions in our calculations to study their effect on the cross sections. 相似文献
15.
V. V. Varlamov B. S. Ishkhanov V. N. Orlin V. A. Chetvertkova 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(6):833-841
A combined analysis of experimental data on total and partial photoneutron reaction cross sections, obtained using bremsstrahlung
γ-radiation and quasi-monoenergetic annihilation photon beams, was performed for nine Sn isotopes. The partial reactions σeval(γ, nX) and σeval(γ, 2nX) cross sections were evaluated using an approach free of the shortcomings of experimental neutron multiplicity sorting methods.
This approach involves calculations within the photonuclear reaction model, based on Fermi gas densities and considering the
effects of nucleus deformation, the isospin splitting of its giant dipole resonance (GDR), and experimental data on the total
photoneutron cross sections σexp(γ, xn) = σexp(γ, nX) + 2σexp(γ, 2nX) = σexp(γ, n) + σexp(γ, np) + … + 2σexp(γ, 2n) + 2σexp(γ, 2np) + …. The evaluated σeval(γ, nX) and σeval(γ, 2nX) reactions cross sections were obtained using the introduced transition multiplicity functions F
theor = σtheor(γ, 2nX)/σtheor(γ, xn) = σtheor(γ, 2nX)/[σtheor(γ, nX) + 2σtheor(γ, 2nX) + …]; and σeval.(γ, 2nX) = F
theor.σexp.(γ, xn) = σeval(γ, nX) = (1 − 2F
theor)σexp(γ, xn). The evaluated partial reaction cross sections were used to assess the total photoneutron reaction cross sections σeval(γ, sn) = σeval(γ, nX) + σeval(γ, 2nX) + … as functions of the mass number A. The GDR features of 112, 114, 116, 117, 118, 119, 120, 122, 124Sn isotopes were studied and are discussed here. 相似文献
16.
17.
Yields of (γ, n) reactions on tin isotopes 124Sn, 118Sn, 114Sn, and 112Sn and yields of (γ, p) reactions on 117Sn, 116Sn, and 112Sn were measured in the present study. The obtained results are compared to those from earlier experiments and theoretical
calculations. The yields of reactions with the production of nuclei in isomeric states are presented. 相似文献
18.
Z. Liu X. Sun X. Zhou X. Lei Y. Guo Y. Zhang X. Chen H. Jin Y. Luo S.X. Wen C.X. Yang G.J. Yuan G.S. Li X.A. Liu W.D. Luo Y.S. Chen 《The European Physical Journal A - Hadrons and Nuclei》1998,1(2):125-135
High-spin states of 117Xe were investigated by means of in-beam γ-ray spectroscopic techniques via the reaction of 28Si bombarding a 92Mo target at beam energies of 100-120 MeV. A positive-parity rotational band decaying into the yrast negative-parity band
by a series of enhanced E1 transitions was observed for the first time, implying the existence of octupole correlations in
117Xe. The B(E1) values increase with spin. The νd5/2 band was firmly established up to 27/2+ and the B(M1)/B(E2) ratios were extracted from the relative intensities of γ-rays in this band. The previously known νh11/2 and νg7/2 [413]5/2+α=−1/2 bands were confirmed and extended up to high spins and two bandcrossings are observed in the latter at ħω=0.33 and
0.44 MeV, respectively. The bandcrossings and configurations of these bands are discussed by TRS and CSM calculations. In
a γ–γ–t measurement, the 11/2− and 7/2− levels were identified as two isomers with half-lives of 59.4±20 ns and 16.5±8.0 ns, respectively.
Received: 17 June 1997 / Revised version: 29 September 1997 相似文献
19.
Recently linearized versions of the augmented plane wave (APW) method have been introduced. The quadratic-APW (QAPW) method is presented which is a more general formulation of the linear-APW (LAPW) methods. Here the exact radial solution inside the muffin-tin (MT) sphere is replaced by its Taylor expansion with respect to the energy, truncated after the quadratic term, i.e. with higher accuracy when compared with the standard LAPW method which uses only the linear term. The standard LAPW method is obtained as a special case from our formulation. Similarly to the standard LAPW method, the energy independent APW's are formed from approximate radial wave functions which lead to the secular equations linear in energy. The analysis of the solution inside the MT-sphere shows that the eigenvalue error is proportional to (E-E
0)6 in the method suggested as compared with (E-E
0)4 for the standard LAPW method. As an application both non-self-consistent and self-consistent calculations are presented for the band structure of FCC copper metal. 相似文献
20.
Maria José González-álvarez José Vicente Carmen Ortiz Mellet José Maria García Fernández Francisco Mendicuti 《Journal of fluorescence》2009,19(6):975-988
The thermodynamics of the dimer formation of 2I,3I-O-(o-xylylene)-per-O-Me-γ-cyclodextrin (XmγCD) in aqueous solution was studied by fluorescence techniques, Molecular Mechanics and Molecular Dynamics. Lifetime averages
á t
ñ \left\langle \tau \right\rangle , obtained from fluorescence decay profiles upon excitation of the xylylene appended group, were used as the property sensitive
to the association process. The dimerization equilibrium constants (K
D) were obtained from non-linear regression analysis of the plots of
á t
ñ \left\langle \tau \right\rangle against [XmγCD] at several temperatures and they were compared with the values obtained for the counterparts Xmα- and XmβCDs. The van’t Hoff plot allows us to obtain the ΔH and ΔS showing that the dimerization process was also entropically disfavoured. Molecular Mechanics as well as Molecular Dynamics
calculations in the presence of water were also employed to study the conformational behaviour of isolated XmγCDs, the possible structure of the dimers formed and the driving forces involved in such association processes. Results indicate
that those conformations where Xy moiety does not block the cavity entrance are favoured. Dimers are preferably formed by
head-to-head CD approaching. However, the formation of stable head-to-tail is not dismissed. 相似文献