共查询到20条相似文献,搜索用时 93 毫秒
1.
Karen B. Paul 《Central European Journal of Physics》2005,3(1):115-126
A monocrystal ofFe
3
O
4 is characterized by resistance, magnetoresistance and magnetic measurements in a temperature range from 4.2 K to 350 K and
magnetic field-cycling from −9 T to 9 T. The resistance measurements revealed a metal-insulator Verwey transition (VT) atT
v
=123.76 K with activation energy E=92.5 meV at T >T
v
and temperature-substitute for the activation energy below the VT,T
0=E/k
B
≈3800 K within 70 K–110K. The magnetotransport results independently verified the VT at 123.70 K, with discontinuous change
in the magnetic moment ΔM≈0.21 ΔM≈0.21μ
B
and resistance hysteresis, dependent on the magnetic field in a narrow temperature range of 0.4° around theT
v
. The magnetic characterization established self consistentlyT
v
as ≈123.67 K, the jump in the magnetization at the VT≈0.25μ
B
and confirmed, that the magnetocrystalline anisotropy is the main microscopic mechanism responsible for the magnetization
of the monocrystal (88%) with additional natural and imposed defects contributing as 12%. 相似文献
2.
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
3.
Nathalie Besson Maarten Boonekamp Esben Klinkby Sascha Mehlhase Troels Petersen 《The European Physical Journal C - Particles and Fields》2008,57(3):627-651
We present a study of the LHC sensitivity to the W boson mass based on simulation studies. We find that both experimental and phenomenological sources of systematic uncertainties
can be strongly constrained with Z measurements: the lineshape, dσ
Z
/dm, is robustly predicted, and its analysis provides an accurate measurement of the detector resolution and absolute scale,
while the differential cross-section analysis, d2
σ
Z
/dydp
T
, absorbs the strong interaction uncertainties. A sensitivity δ
m
W
∼7 MeV for each decay channel (W→e
ν, W→μ
ν), and for an integrated luminosity of 10 fb−1, appears as a reasonable goal. 相似文献
4.
We study the ground state phase diagram of the two dimensional t — t′ — U Hubbard model concentrating on the competition between antiferro-, ferro-, and paramagnetism. It is known that unrestricted
Hartree–Fock- and quantum Monte Carlo calculations for this model predict inhomogeneous states in large regions of the parameter
space. Standard mean field theory, i.e., Hartree–Fock theory restricted to homogeneous states, fails to produce such inhomogeneous
phases. We show that a generalization of the mean field method to the grand canonical ensemble circumvents this problem and
predicts inhomogeneous states, represented by mixtures of homogeneous states, in large regions of the parameter space. We
present phase diagrams which differ considerably from previous mean field results but are consistent with, and extend, results
obtained with more sophisticated methods.
PACS: 71.10.Fd, 05.70.Fh, 75.50.Ee 相似文献
5.
L.?Pálfalvi B.?C.?Tóth G.?Almási J.?A.?Fül?p J.?Hebling 《Applied physics. B, Lasers and optics》2009,97(3):679-685
A novel Z-scan theory based on the solution of the nonlinear paraxial wave equation, completed by the Huygens–Fresnel principle is
introduced. This theory is valid for the general case, i.e. for thick samples and large nonlinearities including both nonlinear
refraction and absorption. In both limiting cases of thin sample and weak nonlinearity, predictions of this model are in good
agreement with theories not using parabolic approximation for the beam profile. It is shown that the widely used parabolic
approximation leads to inadequate results when evaluating Z-scan measurements. 相似文献
6.
7.
A switching of the S-type in the 20–200 μm thick polycrystalline n-CdTe:In layers with resistance of 103–106 Ω·cm is studied. The electric instability in the layers is found to be due to the electron-thermal breakdown mechanism. The
dependence of the switching threshold parameters on the intensity of exposure can be used for fabrication of infrared-radiation
controlled electric switches on the basis of n-CdTe:In layers.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 28–30, June, 2005. 相似文献
8.
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
9.
A two-photon impurity absorption coefficient of the “quantum dot — D(−)-center” complexes synthesized in a transparent dielectric matrix is calculated within the model of zero-radius potential.
The evolution of spectral dependence of the absorption coefficient of the nanoheterostructure based on semiconductor CdS
x
Se
1−x
glasses is studied versus the average quantum-dot radius. It is shown that the contribution of the two-photon impurity absorption
to the exited two-photon luminescence is fairly significant at a reasonable quantum-dot concentration.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 46–50, July, 2005. 相似文献
10.
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
11.
Ctirad Klimčík 《International Journal of Theoretical Physics》2007,46(10):2443-2463
We show that D-branes in the Euclidean AdS
3 can be naturally associated to the maximally isotropic subgroups of the Lu–Weinstein double of SU(2). This picture makes very transparent the residual loop group symmetry of the D-brane configurations and gives also immediately the D-branes shapes and the σ-model boundary conditions in the de Sitter T-dual of the SL(2,C)/SU(2) WZW model. 相似文献
12.
S.-A. Ku C.-W. Luo H.-L. Lio K.-H. Wu J.-Y. Juang A. I. Potekaev O. P. Tolbanov S. Yu. Sarkisov Yu. М. Andreev G. V. Lanskii 《Russian Physics Journal》2008,51(10):1083-1089
Transmission spectra and phase matching conditions for second harmonic generation in GaSe1–x
S
x
(0 < x ≤ 0.4) solid solution crystals are experimentally investigated. An algorithm is suggested and dispersion equations are derived
that allow the phase matching angles describing best the available experimental data to be estimated as a function of the
mixing ratio x.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 80–85, October, 2008. 相似文献
13.
Films of Mn1−x
Fe
x
Se (x = 0–0.45) solid solutions were flash-sputtered. We measured the transmission spectra of the films in the wavelength
range 200–1000 nm at room temperature. From these spectra, we calculated the absorption coefficients and determined the fundamental
absorption edge, the position of which is shifted from 2.65 eV in MnSe to 2.30 eV in solid solutions of compositions x = 0.20–0.45.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 136–138, January–February, 2007. 相似文献
14.
The LEP2 data set on the Bhabha process is analyzed with the aim to detect the signals of the heavy virtual Z′ gauge boson. The state interacting with the left-handed Standard Model doublets and called the chiral Z′ is investigated. This particle was introduced already as the low-energy state allowed by the renormalizability. The contribution
of the chiral-Z′ state to the Bhabha process is described by two parameters: the coupling to electrons and the Z–Z′ mixing angle. The sign-definite one-parameter observable is proposed to measure the Z′ coupling to the electron current. The one-parameter fit of the data shows no signals of the particle. The alternative two-parameter
fit of the differential cross sections is also performed. It also shows no chiral-Z′ signals. The comparisons with other fits are discussed.
The text was submitted by the authors in English. 相似文献
15.
T.-J. Wang J.-C. Gao Yu. M. Andreev S. A. Bereznaya T. N. Kopylova Z. V. Korotchenko G. V. Lanskii T. D. Malinovskaya A. N. Morozov S. Yu. Sarkisov 《Russian Physics Journal》2007,50(6):560-565
The most probable parameters of the pure, doped, and mixed GaSe1−xSx (x ≤ 0.4) crystals (solid solutions) are presented together with the results of investigations of their crystal structure
and defects, optical and mechanical properties, and damage thresholds.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 35–40, June, 2007. 相似文献
16.
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
17.
R. Escribano 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):454-457
The scalar contributions to the radiative decay φ→K
0ˉ0
γ are studied within the framework of the Linear Sigma Model (LσM). Theoretical predictions for the associated subprocesses φ→f
0
γ and φ→a
0
γ as well as the ratio φ→f
0
γ/a
0
γ are also given. 相似文献
18.
N. M. Agababyan V. V. Ammosov M. Atayan N. Grigoryan H. Gulkanyan A.A. Ivanilov Zh. Karamyan V. A. Korotkov 《Physics of Atomic Nuclei》2007,70(11):1904-1912
The characteristics of the charged-current neutrino—nuclear interactions are investigated for the first time at E
ν
= 1–3 GeV using the data obtained with SKAT propane-freon bubble chamber irradiated in the neutrino beam at the Serpukhov
accelerator. The E
ν
dependence of the mean multiplicities of different types of secondary particles and their multiplicity, momentum, and angular
distributions are measured.
The text was submitted by the authors in English. 相似文献
19.
Employing the transfer matrix method, we study the electromagnetic field of one-dimensional photonic crystals with a defect
inserted by pairs of μ-negative (MNG) and ε-negative (ENG) material layers. The fields within the pairs of layers and the matrix defect are independent of each other,
and the whole field is their superposition. The whole defect field can be significantly enhanced by pairs of ε-negative and μ-negative layers. In contrast to the conventional defect modes, the intensity and volume of the defect field with pairs of
ε-negative and μ-negative layers can be precisely adjusted. 相似文献
20.
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