共查询到20条相似文献,搜索用时 31 毫秒
1.
Siegfried Bethke 《The European Physical Journal C - Particles and Fields》2009,64(4):689-703
Measurements of α
s, the coupling strength of the Strong Interaction between quarks and gluons, are summarised and an updated value of the world
average of as(MZ0)\alpha_{\mathrm{s}}(M_{\mathrm{Z}^{0}}) is derived. Special emphasis is laid on the most recent determinations of α
s. These are obtained from τ-decays, from global fits of electroweak precision data and from measurements of the proton structure function F2, which are based on perturbative QCD calculations up to O(as4)\mathcal{O}(\alpha_{\mathrm{s}}^{4}); from hadronic event shapes and jet production in e+e− annihilation, based on O(as3)\mathcal{O}(\alpha_{\mathrm{s}}^{3}) QCD; from jet production in deep inelastic scattering and from ϒ decays, based on O(as2)\mathcal{O}(\alpha_{\mathrm{s}}^{2}) QCD; and from heavy quarkonia based on unquenched QCD lattice calculations. A pragmatic method is chosen to obtain the world
average and an estimate of its overall uncertainty, resulting in
as(MZ0)=0.1184±0.0007.\alpha_\mathrm{s}(M_{\mathrm{Z}^0})=0.1184\pm 0.0007. 相似文献
2.
H.-F. Li Y. Su Y. G. Xiao J. Persson P. Meuffels Th. Brückel 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(2):149-157
A neutron powder diffraction (NPD) study on the crystal and magnetic structure of a crushed La1-xSrxMnO3 (x ≈ 1/8) single crystal has been performed. The sample belongs to orthorhombic (Pnma, O) above the Jahn-Teller (JT) transition temperature (TJT) and monoclinic (P121/c1, M′) in the JT regime. We have also refined the NPD data below the charge/orbital ordering (CO/OO) temperature (TCO/OO) with a monoclinic (P121/c1, M′′) model because the experimental resolution was insufficient to clearly identify a triclinic structure. The refined lattice parameters show an obvious breathing-mode distortion between TCO/OO and TJT, accompanied by a large deviation of the monoclinic angle β from 90°, signifying a very strong cooperative JT distortion.
A ferromagnetic (FM) moment of 3.43(5)μ
B/Mn besides an A-type antiferromagnetic (A-AFM) moment of 0.54(2) μ
B/Mn is directed mainly along the b axis in P121/c1 symmetry at 5 K. With increasing temperature, the A-AFM domains transform into FM ones above ~100 K and the FM spin orientation
turns from the b to the c axis in crystallographic b-c plane below Tc = 187(1) K. The magnetization measurements show typical anomalies around TCO/OO and TJT. The measured saturation moment of 3.9(1)μ
B/Mn at 70 kOe and 5 K is well consistent with the sum 3.97(5)μ
B/Mn of the refined FM and A-AFM moments at 5 K, implying the A-AFM spins are aligned in field direction at 70 kOe. The applied
magnetic field can affect the paramagnetic insulating (PMI) state in the range of magnetic polarons. Based on the size of
JT distortion and the bond-valence sums (BVS’s), the CO/OO phenomenon is being discussed. 相似文献
3.
B. Drossel M.A. Moore 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):589-594
We study the low-temperature phase of the three-dimensional ±
J Ising spin glass in Migdal-Kadanoff approximation. At zero temperature, T
= 0, the properties of the spin glass result from the ground-state degeneracy and can be elucidated using scaling arguments based
on entropy. The approach to the asymptotic scaling regime is very slow, and the correct exponents are only visible beyond
system sizes around 64. At T
> 0, a crossover from the zero-temperature behaviour to the behaviour expected from the droplet picture occurs at length scales
proportional to T
-2/ds
where ds is the fractal dimension of a domain wall. Canonical droplet behaviour is not visible at any temperature for systems whose
linear dimension is smaller than 16 lattice spacings, because the data are either affected by the zero-temperature behaviour
or the critical point behaviour.
Received 18 February 2001 相似文献
4.
5.
The hyperfine splittings in heavy quarkonia are studied in a model-independent way using experimental data on dielectron widths.
Relativistic correlations are taken into account together with the smearing of spin-spin interaction. The radius of smearing
is fixed by known G/ψ−η
c(1S), ψ(2S)−η
c′(2S) splittings, which appears to be small, r
ss ≅ 0.06 fm. Nevertheless, even with such a small radius, substantial suppression of hyperfine splittings (∼50%) is observed
in bottomonium. For nS b
states (n = 1, 2, ..., 6), our predicted splittings (in MeV) are 28, 12, 10, 5, 6, 3. For the 3S and 4S charmonium states, the splittings 16(2) and 12(4) MeV are obtained.
The text was submitted by the authors in English. 相似文献
6.
In this paper, a new type of chaos synchronization in continuous-time is proposed by combining inverse matrix projective synchronization (IMPS) and generalized synchronization (GS). This new chaos synchronization type allows us to study synchronization between different dimensional continuous-time chaotic systems in different dimensions. Based on stability property of integer-order linear continuous-time dynamical systems and Lyapunov stability theory, effective control schemes are introduced and new synchronization criterions are derived. Numerical simulations are used to validate the theoretical results and to verify the effectiveness of the proposed schemes. 相似文献
7.
O. A. Savinskaya A. P. Nemudry A. N. Nadeev S. V. Tsybulya N. Z. Lyakhov 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(8):1053-1054
The structure of high-temperature SrFe1 − x
Mo
x
O3 − z
(0 ≤ x ≤ 0.5) phases was studied. Such studies are necessary to understand the mechanism of oxygen transport in membrane materials
used for high-temperature oxygen separation. 相似文献
8.
B. Song Y. Yong J. Hou P. He 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,59(3):399-406
Density-functional theory with generalized gradient approximation for the exchange-correlation potential has been used to
calculate the structural and electronic properties of
Si
n
C
n
(n = 10–15) clusters. We find that the Si
n
C
n
clusters prefer cagelike structures. An extensive isomer search shows that the lowest-energy arrangements are those in which
the silicon atoms and the carbon atoms form two distinct subunits. It is found that the carbon atoms favor to form fullerene-like
structure due to the
sp
2-like bond. The silicon atoms are trying to cope with an unfavorable
sp
2 environment, but distorted tetrahedra still show up somewhere of the cagelike structures. On the basis of the lowest-energy
geometries obtained, the binding energy, HOMO–LUMO gap, Mulliken charge, ionization potential and electron affinity of the
clusters have been computed and analyzed. An electronic charge transfer from the Si-populated to the C-populated regions is
observed. 相似文献
9.
S. P. Baranov A. V. Lipatov N. P. Zotov 《The European Physical Journal C - Particles and Fields》2011,71(4):1631
We investigate the inclusive photoproduction of J/ψ mesons at HERA within the framework of the k
T
-factorization QCD approach. Our study is based on the color singlet model supplemented with the relevant off-shell matrix
elements and the CCFM and KMR unintegrated gluon densities in a proton and in a photon. Both the direct and resolved photon
contributions are taken into account. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS
collaborations. Special attention is put on the J/ψ polarization parameters λ and ν, which are sensitive to the production dynamics. 相似文献
10.
11.
Garrett Johnson 《Letters in Mathematical Physics》2010,94(2):115-122
We give an interpretation of the Cremmer–Gervais r-matrices for
\mathfraksln{\mathfrak{sl}_n} in terms of actions of elements in the rational and trigonometric Cherednik algebras of type GL
2 on certain subspaces of their polynomial representations. This is used to compute the nilpotency index of the Jordanian r-matrices, thus answering a question of Gerstenhaber and Giaquinto. We also give an interpretation of the Cremmer–Gervais
quantization in terms of the corresponding double affine Hecke algebra. 相似文献
12.
The process γ*γ → σ is investigated in the framework of the SU(2)×SU(2) chiral NJL model. The form factor of the process is derived for arbitrary virtuality of γ* in the Euclidean kinematic domain. The asymptotic behavior of this form factor resembles the asymptotic behavior of the γ*γ → π form factor. 相似文献
13.
S. K.?Vogel N.?Pavin N.?Maghelli F.?Jülicher I. M.?Toli?-N?rrelykke 《The European physical journal. Special topics》2009,178(1):57-69
A key aspect of life is sexual reproduction, which requires concerted movement. For successful mixing of the genetic material,
molecular motors move the nucleus back and forth inside the cell. How motors work together to produce these large-scale movements,
however, remains a mystery. To answer this question, we studied nuclear movement in fission yeast, which is driven by motor
proteins pulling on microtubules. We show that motor proteins dynamically redistribute from one part of the cell to the other,
generating asymmetric patterns of motors and, consequently, of forces that generate movement. By combining quantitative live
cell imaging and laser ablation with a theoretical model, we find that this dynamic motor redistribution occurs purely as
a result of changes in the mechanical strain sensed by the motor proteins. Our work therefore demonstrates that spatio-temporal
pattern formation within a cell can occur as a result of mechanical cues (Vogel et al., 2009), which differs from conventional
molecular signaling, as well as from self-organization based on a combination of biochemical reactions and diffusion. 相似文献
14.
New Rb3PO4-based ceramic materials with high rubidium-cation conductivity in the Rb3–2x Pb x PO4 system have been synthesized and studied. Introduction of Pb2+ cations leads to a sharp increase in the conductivity of rubidium orthophosphate due to formation of cation vacancies and, at temperatures 350–550°C, also due to the stabilization of high-temperature cubic modification Rb3PO4. At high temperatures, the electrolytes prepared have very high ion conductivity higher than 10–1 S cm–1 at 700°C, which is higher than the values previously obtained in similar systems with additions of tin and cadmium ions. The factors influencing the transport properties of the materials under study are discussed. 相似文献
15.
The fundamental absorption edge of glassy alloys of an As–Sb–S system was studied in the temperature range 77–300 K. The spectral and thermal behavior of the fundamental absorption edge of As40–x SbxS60 glasses was shown to be described by an exponential function of phonon energy. The temperature and concentration behavior of the optical band gap in the studied glasses was established. The well-known Varshni relationship was used to describe the temperature dependence of the optical band gap. 相似文献
16.
The electronic structure and ground state parameters of B2 RuAl-based refractory alloys have been investigated in the framework of the density functional theory using the exact muffin-tin
orbital method in combination with the coherent potential approximation. It has been demonstrated that the number of states
at the Fermi level for the Ru1 − x
Me
x
Al alloys as a function of the alloying metal content has a minimum, which indicates a change in the Fermi surface topology
and the presence of specific features in the behavior of elastic constants. It has been concluded that the electronic structure
of the alloys can be described in terms of the rigid band model. The nonlinear variations of the lattice parameters of the
alloys has been explained. 相似文献
17.
S. S. Aplesnin V. V. Kretinin A. M. Panasevich K. I. Yanushkevich 《Physics of the Solid State》2017,59(4):667-673
The capacitance, inductance, and dissipation factor of the Gd x Bi1–x FeO3 films were measured in the temperature range of 100 K < T < 800 K in magnetic fields of up to 8 kOe at frequencies of 0.1–100 kHz. The magnetic susceptibility maxima in the low-temperature region and dependences of the relaxation time and inductance on prehistory of the films cooled in zero and nonzero magnetic fields are established. The giant increase in magnetic capacitance in the external bias electric field is found. The results obtained are explained by the domain structure transformation in external electric and magnetic fields. 相似文献
18.
L. T. Denisova L. G. Chumilina N. V. Belousova V. M. Denisov 《Physics of the Solid State》2016,58(9):1933-1937
Orthovanadates Ce1–xBixVO4 (1 ≥ x ≥ 0) have been produced by solid-phase synthesis from initial oxides CeO2, Bi2O3, and V2O5 upon step-by-step burning. The high-temperature heat capacity of Ce1–xBixVO4 has been measured by differential scanning calorimetry. The experimental data on Cp = f(T) were used to calculate the thermodynamic properties (the enthalpy changes, the entropy changes, and the Gibbs energy). 相似文献
19.
E. Sh. Alekperov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2017,11(5):960-962
The formation of the short-range order structure of amorphous nanometer-thick TlIn1–x Sn x Te2 films (х = 0.02–0.09) obtained via vacuum deposition onto substrates of fresh KCl and KJ chips and celluloid at a temperature below Т = 213 K is studied by high-energy electron diffraction. Both freshly deposited films and films held in vacuum (10–2 Pa) at room temperature in darkness for several months are studied. The effect of the tin concentration on the interatomic distances, the coordination numbers, and the time of amorphous phase stability of TlIn1–x Sn x Te2 films due to a great spread in bond lengths and bond angles is established. 相似文献
20.
Results of investigations into the temperature dependences (4.2–300 K) of the low-frequency ultrasound velocity in Cd
x
Hg1–x
Te single crystals are presented. The elastic moduli and the Debye temperatures are calculated for different solid solution
compositions. Based on the data obtained, possible stresses are estimated on the heteroboundary of the materials with a number
of substrates. 相似文献
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