共查询到20条相似文献,搜索用时 31 毫秒
1.
C-field cosmological models based on Hoyle-Narlikar theory with variable gravitational constant G in the frame work of FRW (Friedmann-Robertson-Walker) space–time for positive and negative curvatures are investigated. To
get the deterministic solutions in terms of cosmic time t, we have assumed G=R
n
and discussed for n=−1, −2, R being scalar factor. In both the cases, creation field C increases with time, the gravitational constant G and matter density (ρ) decrease with time in the model (21). In the model (41) G decreases with time and matter density (ρ) is constant. The other physical aspects of the models are also discussed. 相似文献
2.
A. Gasparyan J. Haidenbauer C. Hanhart K. Miyagawa 《The European Physical Journal A - Hadrons and Nuclei》2007,32(1):61-67
The prospects of utilizing the strangeness production reaction γd→K
+
Λn for the determination of the Λn low-energy scattering parameters are investigated. The spin observables that need to be measured in order to isolate the
Λn singlet (1
S
0) and triplet (3
S
1) states are identified. Possible kinematical regions where the extraction of the Λn scattering lengths might be feasible are discussed. 相似文献
3.
Dubna Cascade Code (version-2004) has been used for the Monte Carlo simulation of the 1500 MWt accelerator driven sub-critical system (ADS) with 233U + 232Th fuel using the IAEA benchmark. Neutron spectrum, cross-section of (n, xn) reactions, isotopic yield, heat spectra etc. are simulated. Many of these results that help in understanding the IAEA benchmark
are presented. It is revealed that the code predicts the proton beam current required for the 1500 MWt ADS for K
eff = 0.98 to be 11.6 mA. Radial distribution of heat is fairly in agreement with other codes like the EA-MC and it needs nearly
1% less enrichment than given by other codes. This may be because the code takes care of the role of larger order of the (n, xn) reactions. It is emphasized that there is a strong need to study (n, xn) reactions both theoretically and experimentally for better design.
This talk is dedicated to the fond memory of late Professor V S Barashenkov, JINR, Dubna 相似文献
4.
In this study, production rates of 125,123Xe and 133,131,129,128Ba medical isotopes produced by 127I(p, 3n)125Xe, 127I(p, 5n)123Xe, 133Cs(p, n)133mg
Ba, 133Cs(p, 3n)131mg
Ba, 133Cs(p, 5n)129Ba, and 133Cs(p, 6n)128Ba reactions have been investigated up to 100 MeV incident proton energy. The preequilibrium calculations involve the hybrid
model, the geometry-dependent hybrid model and the cascade exciton model. The calculated results are compared with the experimental
data taken from the literature. 相似文献
5.
The properties of polycrystalline CdTe with a grain size of 5–30 μm have been investigated using the microphotoluminescence
methods of spectral analysis and topography. This material has been prepared by direct synthesis in a vapor flow of components
at a low temperature. The dominance of the Y and Z bands in the spectra reflects a nonequilibrium character of the crystallization processes. The superlinear dependences of
the luminescence intensity on the level of the band-to-band excitation indicate the exciton nature of the corresponding transitions.
The activation energies for temperature quenching of luminescence in the temperature range T = 100–150 K are found to be 120 meV for the Y luminescence and 180 meV for the Z luminescence, which correspond to the dissociation of excitons bound to defects with the transition of charge carriers to
the conduction and valence bands. The monochromatic topography data indicate that Y and Z defects have different material bases. 相似文献
6.
A γ-rigid version (with γ = 0) of the X(5) critical point symmetry is constructed. The model, to be called X(3) since it is proved to contain three degrees of freedom, utilizes an infinite well potential, is based on exact separation
of variables, and leads to parameter-free (up to overall scale factors) predictions for spectra and B(E2) transition rates which are in good agreement with existing experimental data for 172Os and 186Pt. An unexpected similarity of the β
1 bands of the X(5) nuclei 150Nd, 152Sm, 154Gd, and 156Dy to the X(3) predictions is observed.
The text was submitted by the authors in English. 相似文献
7.
A. Yu. Loginov 《Physics of Atomic Nuclei》2011,74(5):740-754
The (1 + 1)-dimensional nonlinear O(3) σ model involving an explicitly broken symmetry is considered. Sphalerons are known to exist in this model. These sphalerons
are of a topological origin and are embedded kinks of the sine-Gordon model. In the case of a compact spatial manifold S
1, sine-Gordon multikinks exist in the model. It is shown that the model admits a nonstatic generalization of the sine-Gordon
kink/multikink, Q kink/multikink. Explicit expressions are obtained for the dependence of the Q kink energy and charge on the phase frequency of rotation. The Q kink is studied for stability, and expressions are obtained for the eigenfunctions and eigenfrequencies of the operator of
quadratic fluctuations. It is shown that the Q kink is unstable over the entire admissible frequency range ω ∈ [−1, 1]. The one-loop quantum correction to the static-kink mass is calculated, and the Q-kink zero mode is quantized. It is shown that, in a general static case, the field equations of the model are integrable
in quadratures. 相似文献
8.
A. Kaplan H. Büyükuslu E. Tel A. Aydin M. H. B?lükdemir 《Indian Journal of Physics》2011,85(11):1615-1629
In this study, neutron-emission spectra produced by (n,xn) reactions up to 26 MeV for some deformed target nuclei as 165Ho, 181Ta, 184W, 232Th and 238U have been investigated. Also, the mean free path parameter’s effect for (n,xn) neutron-emission spectra has been examined.
In the calculations, pre-equilibrium neutron-emission spectra have been calculated by using new evaluated hybrid model and
geometry dependent hybrid model, full exciton model and cascade exciton model. The reaction equilibrium component has been
calculated by Weisskopf-Ewing model. The obtained results have been discussed and compared with the available experimental
data and found agreement with each other. 相似文献
9.
B. V. Zhuravlev A. A. Lychagin N. N. Titarenko V. G. Demenkov V. I. Trykova 《Physics of Atomic Nuclei》2010,73(7):1111-1115
The spectra of neutrons from the (p, n) reactions on the 208Pb and 209Bi nuclei were measured in the proton-energy range 8–11 MeV. These measurements were performed by using a time-of-flight spectrometer
of fast neutrons on the basis of the pulsed tandem accelerator EGP-15 of the Institute of Physics and Power Engineering (Obninsk,
Russian Federation). A high resolution and stability of the time-of-flight spectrometermade it possible to identify reliably
low-lying discrete levels alongwith the continuum section of the neutron spectra. The measured data were analyzed on the basis
of the statistical equilibrium and preequilibrium models of nuclear reactions. The respective calculations were performed
by using the precise formalism of Hauser-Feshbach statistical theory together with the generalizedmodel of a superfluid nucleus
and the back-shifted Fermi gas model for the nuclear-level density. The nuclear-level densities in 208Bi and 209Po were determined along with their energy dependences and model parameters. Our results are discussed together with available
experimental data and recommendations of model systematics. 相似文献
10.
V. Ya. Aleshkin L. V. Gavrilenko D. M. Gaponova Z. F. Krasil’nik D. I. Kryzhkov D. I. Kuritsyn S. M. Sergeev V. G. Lyssenko C. B. Sørensen 《JETP Letters》2011,93(7):394-398
Processes occurring when a static transverse electric field is applied to a GaAs/AlGaAs n-i-n heterostructure with single quantum wells and asymmetric tunnel-coupled double quantum wells have been investigated by optical
methods. The difference between the energies of exciton transitions for quantum wells of different widths makes it possible
to attribute the observed photoluminescence peaks to particular pairs of wells or particular single quantum wells. The local
electric field for each quantum well has been determined in terms of the Stark shift and splitting of exciton lines in a wide
range of external voltage. A qualitative model has been proposed to explain the nonmonotonic distribution of the electric
field over the depth of the heterostructure. 相似文献
11.
Low-lying equilibrium geometric structures of Phosphorus-doped aluminum cluster Al
n
P (n = 2–12) clusters obtained by an all-electron linear combination of atomic orbital approach, within spin-polarized density
functional theory, are reported. The binding energy, dissociation energy, and stability of these clusters are studied within
the local spin density approximation (LSDA) and the three-parameter hybrid generalized gradient approximation (GGA) due to
Becke-Lee-Yang-Parr (B3LYP). Ionization potentials, electron affinities, hardness, and static polarizabilities are calculated
for the ground-state structures within the GGA. It is observed that symmetric structures with the P atom occupying a peripheral
position are lowest-energy geometries of Al
n
P (n = 2, 4–11), while the P impurities of Al3P and Al12P prefer to occupy internal sites in the aluminum clusters. Generalized gradient approximation extends bond lengths as compared
to the LSDA lengths. The odd-even oscillations in the dissociation energy, the second differences in energy, the HOMO–LUMO
gaps, the ionization potential, the electron affinity, and the hardness are more pronounced within both GGA and LSDA. The
stability analysis based on the energies clearly shows the clusters with an even number of valence electrons are more stable
than clusters with odd number of valence electrons. 相似文献
12.
M. Davier S. Descotes-Genon A. Höcker B. Malaescu Z. Zhang 《The European Physical Journal C - Particles and Fields》2008,56(3):305-322
We revisit the determination of α
S
(m
τ
2) using a fit to inclusive τ hadronic spectral moments in light of (1) the recent calculation of the fourth-order perturbative coefficient K
4 in the expansion of the Adler function, (2) new precision measurements from BABAR of e+e− annihilation cross sections, which decrease the uncertainty in the separation of vector and axial-vector spectral functions,
and (3) improved results from BABAR and Belle on τ branching fractions involving kaons. We estimate that the fourth-order perturbative prediction reduces the theoretical uncertainty,
introduced by the truncation of the series, by 20% with respect to earlier determinations. We discuss to some detail the perturbative
prediction of two different methods: fixed-order perturbation theory (FOPT) and contour-improved perturbative theory (CIPT).
The corresponding theoretical uncertainties are studied at the τ and Z mass scales. The CIPT method is found to be more stable with respect to the missing higher order contributions and to renormalization
scale variations. It is also shown that FOPT suffers from convergence problems along the complex integration contour. Nonperturbative
contributions extracted from the most inclusive fit are small, in agreement with earlier determinations. Systematic effects
from quark-hadron duality violation are estimated with simple models and found to be within the quoted systematic errors.
The fit based on CIPT gives α
S
(m
τ
2)=0.344±0.005±0.007, where the first error is experimental and the second theoretical. After evolution to M
Z
we obtain α
S
(M
Z
2)=0.1212±0.0005±0.0008±0.0005, where the errors are respectively experimental, theoretical and due to the evolution. The result
is in agreement with the corresponding N3LO value derived from essentially the Z width in the global electroweak fit. The α
S
(M
Z
2) determination from τ decays is the most precise one to date. 相似文献
13.
A. G. Kochur T. M. Ivanova A. V. Shchukarev A. A. Sidorov M. A. Kiskin V. M. Novotortsev I. L. Eremenko 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(5):625-630
The Mn3s X-ray photoelectron spectra of manganese at oms in mono-, bi-, tri-, and hexanuclear trimethylacetate Mn complexes and MnIICl2, MnIIIOOH, MnIVO2. ionic compounds were measured. The 3s spectra of the manganese atoms in MnII, MnIII, and MnIV valent states were calculated within the isolatedion approximation. The relationship between the characteristics of the Mn3s spectra and the magnetic moments of the manganese ions in the complexes is discussed. 相似文献
14.
Jinjing Shi Ronghua Shi Ying Guo Xiaoqi Peng Moon Ho Lee Dongsun Park 《International Journal of Theoretical Physics》2012,51(4):1038-1049
A novel (t,n)-threshold scheme for the multi-party quantum group signature is proposed based on the irregular quantum Fourier transform,
in which every t-qubit quantum message needs n participants to generate the quantum group signature. All the quantum operation gates in the quantum circuit can be distributed
and arranged randomly in the irregular QFT algorithm, which can increase the von Neumann entropy of the signed quantum message
and the randomicity of the quantum signature generation significantly. The generation and verification of the quantum group
signature can be both performed in quantum circuits with the parallel algorithm. Security analysis shows that an available
and legal quantum (t,n)-threshold group signature can be achieved. 相似文献
15.
Though the predictions of the standard model (SM) are in excellent agreement with experiments, there are still several theoretical
problems associated with the Higgs sector of the SM, where it is widely believed that some new physics will take over at the
TeV scale. One beyond the SM theory which resolves these problems is the Little Higgs (LH) model. In this work we have investigated
the effects of the LH model on γγ → γγ scattering [1].
相似文献
16.
A. Kanaev L. Museur F. Edery T. Laarmann T. Möller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):261-268
We have studied the fluorescence of electronically excited OH*, H* and H2O+* dissociation fragments after VUV excitation ( h
ν≥11.6
eV) of rare-gas clusters (Rg = Ne, Ar) doped with H2O molecules. In contrast to a free molecule, where Balmer H-series dominate the UV-visible spectra, only the OH
*
(
A
2
Σ
+
↦
X
2
Π) emission band is observed in neon clusters. No emission of excited water ions has been observed. We find that while higher
excitation energies (Ne vs. Ar) induce higher vibrational excitation of the OH*
(
A
) fragment, the rotational temperature is lower. This effect is attributed to the difference in the geometric position of the
H2O molecule on the surface or inside the Rg-cluster. The rotational relaxation in neon clusters is rapid while the vibrational
relaxation is slow because of the coupling with the low energy matrix phonons.
Received 7 March 2002 / Received in final form 27 May 2002 Published online 19 July 2002 相似文献
17.
Cosmological models with variable G in C-field cosmology for barotropic fluid distribution in FRW space-time are investigated. To get the deterministic model of the
universe, we have assumed that G=R
n
where R is the scale factor and n the constant. To obtain the results in terms of cosmic time t, we have assumed n=−1. We find that for n=−1, Creation field (C) and spatial volume increase with time, G and ρ (matter density) decreases with time, the model represent accelerating universe. Thus inflationary scenario exists in the
model. The model is also free from horizon. The results so obtained match with the astronomical observations. 相似文献
18.
We have calculated the potential energy surfaces forN = Z,20Ne-112Ba nuclei in an axially deformed relativistic mean field approach. A quadratic constraint scheme is applied to determine the
complete energy surface for a wide range of the quadrupole deformation. The NL3, NL-RA1 and TM1 parameter sets are used. The
phenomenon of (multiple) shape coextistence is studied and the calculated ground and excited state binding energies, quadrupole
deformation parameters and root mean square (rms) charge radii are compared with the available experimental data and other
theoretical predictions. 相似文献
19.
20.
Through phase transformation kinetic analysis and experimental observation, the δ/γ transformation occurring in the non-equilibrium peritectic Fe-4.33at.%Ni alloys was systematically investigated. According to JMA solid-state transformation kinetic theory, the Time-Temperature-Transformation (TTT) curves of the δ/γ transformation in peritectic Fe-Ni alloy were calculated. On this basis, the physical correlation between the δ/γ transformation and the initial undercooling of melt (△T) was elucidated. The results indicate that the change of △T can alter not only the overall δ/γ transformation pathways but also the transformation fraction with respect to each transformation mechanism. 相似文献