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1.
We report here high-pressure x-ray diffraction (XRD) studies on tellurium (Te) at room temperature up to 40 GPa in the diamond
anvil cell (DAC). The XRD measurements clearly indicate a sequence of pressure-induced phase transitions with increasing pressure.
The data obtained in the pressure range 1 bar to 40 GPa fit five different crystalline phases out of Te: hexagonal Te (I)
→ monoclinic Te(II) → orthorhombic Te (III) → Β-Po-type Te(IV) → body-centered-cubic Te(V) at 4, 6.2, 11 and 27 GPa, respectively. The volume changes across these transitions
are 10%, 1.5%, 0.3% and 0.5%, respectively.
Self consistent electronic band structure calculations both for ambient and high pressure phases have been carried out using
the tight binding linear muffin tin orbital (TB-LMTO) method within the atomic-sphere approximation (ASA). Reported here apart
from the energy band calculations are the density of states (DOS), Fermi energy (E
f) at various high-pressure phases. Our calculations show that the ambient pressure hexagonal phase has a band gap of 0.42
eV whereas high-pressure phases are found to be metallic. We also found that the pressure induced semiconducting to metallic
transition occurs at about 4 GPa which corresponds to the hexagonal phase to monoclinic phase transition. Equation of state
and bulk modulus of different high-pressure phases have also been discussed. 相似文献
2.
A differential thermal analysis in vacuum and studies of the coefficients of electrical conductivity and thermal conductivity,
and of the thermal emf are made in Ag2Te in the neighborhood of the structural phase transition. It is shown that these data can be used to calculate the switching
factor L(T), determine the region in which the phases coexist within the transition, and calculate the thermodynamic parameters. Prior
to and after the main phase transition, additional displacement transitions are observed. It is found that the phase transition
takes place roughly according to the scheme α
385 K→α′405 K→β′420 K→β
440 K. The specific heat C
p, changes in entropy ΔS and transition enthalpy ΔH, as well as the minimum phase fluctuation volume V, and the heat Q of the phase transition are determined. It is shown that excesses of Te and Ag have almost no effect on the transition temperatures
T
0, but have a substantial effect on the thermodynamic parameters.
Fiz. Tverd. Tela (St. Petersburg) 40, 1693–1697 (September 1998) 相似文献
3.
A differential thermal analysis ΔT
y
(T) in vacuum has been performed, and the temperature gradient ΔT
x
(T) along the Ag2Se sample during the transition α → β has been studied. It has been shown that the transitions α → α′ and β′ → β are displacive
transitions and that the transition α′ → β′ is a reconstructive transition. It has been found that the temperature gradient
along the sample during the transition α′ → β′ passes through a deep minimum due to a strong increase in the specific heat
capacity. 相似文献
4.
Gui-Jun Ding Rong-Gang Ping Mu-Lin Yan 《The European Physical Journal A - Hadrons and Nuclei》2006,28(3):351-360
X(1835) has been treated as a baryonium with sizable gluon content, and to be almost flavor singlet. This picture allows us
to rationally understand X(1835) production in J/ψ radiative decays, and its large couplings with pˉ, η′ππ. The processes ϒ(1S) → γX(1835) and J/ψ → ωX(1835) have been examined. It has been found that Br(ϒ(1S) → γX(1835))Br(X(1835) → pˉ) < 6.45×10-7, which is compatible with CLEO's recent experimental result (Phys. Rev. D 73, 032001 (2006) hep-ex/0510015). The branching fractions Br(J/ψ → ωX(1835)), Br(J/ψ → ρX(1835)) with X(1835) → pˉ and X(1835) → η′π+π- have been estimated by the quark-pair creation model. We show that they are heavily suppressed, so the signal of X(1835) is very difficult, if not impossible, to be observed in these processes. The experimental checks for these estimations
are expected. The existence of the baryonium nonet is conjectured, and a model-independent derivation of their production
branching fractions is presented. 相似文献
5.
A. V. Luchinsky 《Physics of Atomic Nuclei》2007,70(1):53-55
The leading twist contribution to χ
c0,2 → ωω decays in the color-singlet approximation is considered. It is shown that the prediction for Br(χ
c0 → ωω) is in good agreement with the experimental data, while Br(χ
c2 → ωω) differs from the experiment significantly.
The text was submitted by the author in English. 相似文献
6.
V. I. Ritus 《Journal of Experimental and Theoretical Physics》1998,87(1):25-34
This paper discusses the symmetry of the wave field that lies to the right and left of a two-sided accelerated mirror in 1+1
space and satisfies a single condition on it. The symmetry is embodied in the Bogolyubov matrix coefficients α and β that connect the two complete sets of solutions of the wave equations. The amplitudes of the quantum processes in the right
and left half-spaces are expressed in terms of α and β and are related to each other by the transformation (12). The coefficient β
ω′ω
*
plays the role of the source amplitude of a pair of oppositely directed particles with frequencies ω and ω′ of which one is in the left half-space and the other is in the right half-space because one of them has undergone reflection.
Such an interpretation makes β
ω′ω
*
observable and explains why, as shown by Eq. (1) and found earlier by Nikishov and Ritus [Zh. éksp. Teor. Fiz. 108, 1121 (1995); transl. JETP 81, 615 (1995)] and by Ritus [Zh. éksp. Teor. Fiz. 110, 526 (1996); transl. JETP 83, 282 (1996)], the emission spectra of a mirror in 1+1 space coincide with those of charges in 3+1 space. The reason is that
the angular momentum of the pair emitted by the mirror coincides with the angular momentum of the single particle emitted
by the charge.
Zh. éksp. Teor. Fiz. 114, 46–62 (July 1998) 相似文献
7.
A. I. Alekseev 《Journal of Experimental and Theoretical Physics》1997,84(1):35-50
The properties of the density matrix and the multipole moments arising in oriented and aligned atoms with zero nuclear spin
through the interaction with strong resonant ultrashort pulses with wave vector k
0 and circular or linear polarization have been found. Calculations have been made for the time-dependent light-induced magnetization
μ(t′) of a gas of pre-oriented and prealigned atoms following the passage of a weak resonant elliptically polarized pulse with
frequency ω and wave vector k collinear with k
0. It is shown that for oriented atoms, μ(t′) is an even function of the detuning from resonance, ω-ω
ba, and can be split into two terms whose directions are a consequence of symmetry and are determined by the vectors k
0 and k as well as by the direction of rotation of the electric fields corresponding to the pulses. For aligned atoms the vector
μ(t′) is collinear with k, and the first term is an even function of ω-ω
ba. However, the second term is an odd function of ω-ω
ba and reverses direction when the sign of ω-ω
ba changes, as well as when the orientation of the axes of the polarization ellipse is changed. It is shown that if a series
of weak linearly polarized pulses pass through the gas, the light-induced magnetization of the oriented and aligned gas atoms
can be decomposed into three factors: the first determines the direction and is a consequence of the symmetry; the second
(with the dimensions of magnetic moment) depends on the characteristics of the resonant transitions; and the third is a universal
function of t′ and ω-ω
ba that does not depend on the underlying characteristics of the resonant transition. These vector factors and the universal
functions are in principle different for oriented and aligned atoms.
Zh. éksp. Teor. Fiz. 111, 63–92 (January 1997) 相似文献
8.
G.I. Lykasov W. Cassing A. Sibirtsev M.V. Rzjanin 《The European Physical Journal A - Hadrons and Nuclei》1999,6(1):71-81
We calculate the elastic and inelastic ωN→ωN, →πN, →ρN, →ρπN, →ππN, →σN reactions within a boson exchange approximation where the ωρπ coupling constant and form factor are fixed by the reaction
πN→ωN in comparison to the experimental data. We find rather large ωN cross sections at low relative momenta of the ω-meson which
leads to a substantial broadening of the ω-meson width in nuclear matter. The implications of the ωN final state interactions are studied for ω production in 12C +12C, 40Ca +40Ca and 58Ni +58Ni reactions at about 2 · A GeV within the HSD transport approach; the drastic changes of the transverse mass spectra relative
to a general m
T-scaling (for π0 and η mesons) might be controlled experimentally by the TAPS Collaboration.
Received: 28 April 1999 / Revised version: 7 June 1999 相似文献
9.
Ronggang Tian Jiuxun Sun Wei Yang Xinying Xue Fei Yu 《Central European Journal of Physics》2008,6(3):704-710
The analytic mean-field approach (AMFP) was applied to study the thermodynamic properties of Zirconium (Zr). The analytic
expressions for the Helmholtz free energy, internal energy and equation of state have been derived. The formalism for the
case of the Morse potential is used in this work. The four potential parameters are determined by fitting the molar volume
of the three phases of Zr. The calculated molar volume of α, β and ω Zr are in fairly good agreement with the available experimental data. The results presented in this paper verify that the
AMFP is a useful approach to study the thermodynamic properties of Zr. Furthermore, we predict the variation of the relationship
of free energy and internal energy versus the molar volume at various temperatures and the dependence of the bulk modulus,
the thermal expansion coefficient and the heat capacity on temperature at zero pressure of α, β and ω Zr.
相似文献
10.
X.-J. Wang J.-H. Jiang M.-L. Yan 《The European Physical Journal A - Hadrons and Nuclei》2002,14(2):219-224
In terms of effective field theory and mixed-propagator approach, we show that there is a larger hidden effect of isospin
breaking in ρ→πγ decay due to a ω exchange, ρ→ω→πγ. The branching ratio is predicted as B(ρ→πγ) = (11.67±2.0)×10-4, which is much larger than Particle Data Group's datum (6.8±1.7)×10-4 and one of charged mode, B(ρ±→π±γ) = (4.5±0.5)×10-4.
Received: 7 January 2002 / Accepted: 2 April 2002 相似文献
11.
The branching ratios and photon spectra of the rare processes ρ(ω) → π
0
π
0
γ, ρ(ω) → ηπ
0
γ are calculated in the framework of the standard local quark Nambu-Jona-Lasinio model. Three types of diagrams are considered:
the quark box and the pole diagrams with scalar (σ, α
0(980)) and vector (ρ, ω) mesons. The obtained estimates for the widths of the processes ρ(ω) → π
0
π
0
γ are in satisfactory agreement with existing experimental data. Predictions are made for the widths of the processes ρ(ω) → ηπ
0
γ.
The text was submitted by the authors in English. 相似文献
12.
S. L. Qiu P. M. Marcus 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,81(4):411-418
First principles calculations of the total energy of Imma states have found instabilities in states near the β-Sn phase and in states near the simple hexagonal (sh) phase of Si crystal. In agreement with experiment the two instability
ranges narrow the stable range between them and also in
agreement with experiment the instabilities force first-order transitions to both the β–Sn and sh phases when the pressure is held constant, the experimental condition. The transition pressures to the β-Sn and sh phases for a non-vibrating crystal model are found to be 96 and 110 kbar respectively. These pressure values are
considerably lower than the experimental values, but we show that lattice vibrations will increase the equilibrium-state pressures.
We find widespread occurrence of instability in the equilibrium states of the three phases and show the presence of three
kinds of instability. Near and up to the sh phase structure we find the unusual case of stability at constant volume, but,
as observed, instability at constant pressure p. Two special computational procedures are discussed, which locate the unstable ranges of structure. One is based on finding
phases from minima of total energy E at constant V and the other finds phases from minima of the Gibbs free energy G at constant p. When the minima cease to exist the Imma phase is unstable. 相似文献
13.
The two-neutrino double beta decay of96Zr isotope for 0+ → 2+ transition has been studied in the PHFB model. In our earlier work, the reliability of the intrinsic wave functions of96Zr and96Mo isotopes has been established by obtaining an overall agreement between a number of theoretically calculated spectroscopic
properties as well as half-lives of 2vββ decay for 0+ → 0+ transition and the available experimental data. In the present work, the half-life of 2vββ decay for 0+ ar 2+ transition T
1
2/2v
(0+ →2+) has been calculated using the same set of intrinsic wave functions. 相似文献
14.
A. A. Ovchinnikov M. Ya. Ovchinnikova 《Journal of Experimental and Theoretical Physics》1999,89(3):564-576
The properties of spin excitations superposed on a uniform ground state with antiferromagnetic (or spiral) spin structure
are studied in a 2D Hubbard model. Expressions are derived for the spin susceptibility in the random phase approximation (RPA) using split Hubbard
bands as a zeroth approximation. The calculated collective modes with dispersion ω(Q)=c|Q−(π, π)| near Q∼(π, π) reproduce well the characteristics of the spin excitations observed in undoped cuprates. For doped systems with an
antiferromagnetic structure of the ground state, calculating X″(Q,ω→0) gives the same mode with a peak at Q∼(π, π), regardless of the type of Fermi surface. It is shown that in doped systems with a spiral ground state spin structure,
X″(Q,ω→0) peaks occur with incommensurate quasimomenta Q that are coupled to the spirality vector.
Zh. éksp. Teor. Fiz. 116, 1058–1080 (September 1999) 相似文献
15.
The electronic, structural, and thermodynamic properties of the TiZr equiatomic alloy have been calculated in terms of the
electron density functional theory and Debye-Grüneisen model. The calculated lattice parameters a and c/a agree well with experimental data for the α, ω, and β phases. It has been shown that the ω phase is stable at atmospheric
pressure and low temperatures, and it remains energetically more favorable up to T = 600 K. In the temperature range 600 K < T < 900 K, the α phase becomes stable, and above 900 K, the β phase of the TiZr alloy is stable. The phase diagram constructed
in this study agrees qualitatively with the available experimental data. A tendency toward separation of the TiZr equiatomic
alloy in the ω phase has been analyzed. It has been demonstrated that, in the ground state, the TiZr equiatomic alloy in the
ω phase exhibits a tendency toward ordering rather than toward phase separation. 相似文献
16.
The nonadiabatic corrections to the self-energy part Σs(q, ω) of the phonon Green’s function are studied for various values of the phonon vectors q resulting from electron-phonon interactions. It is shown that the long-range electron-electron Coulomb interaction has no
direct influence on these effects, aside from a possible renormalization of the corresponding constants. The electronic response
functions and Σs(q, ω) are calculated for arbitrary vectors qand energy ω in the BCS approximation. The results obtained for q=0 agree with previously obtained results. It is shown that for large wave numbers q, vertex corrections are negligible and Σs(q, ω) possesses a logarithmic singularity at ω=2Δ, where Δ is the superconducting gap. It is also shown that in systems with nesting, Σs(Q, ω) (where Q is the nesting vector) possesses a square-root singularity at ω=2Δ, i.e., exactly of the same type as at q=0. The results are used to explain the recently published experimental data on phonon anomalies, observed in nickel borocarbides
in the superconducting state, at large q. It is shown, specifically, that in these systems nesting must be taken into account in order to account for the emergence
of a narrow additional line in the phonon spectral function S(q, ω)≈−π
−1 Im D
s
(q, ω), where D
s
(q, ω) is the phonon Green’s function, at temperatures T<T
c
.
Zh. éksp. Teor. Fiz. 115, 1799–1817 (May 1999) 相似文献
17.
M. Ya. Amus’ya A. I. Mikhailov I. A. Mikhailov 《Journal of Experimental and Theoretical Physics》1998,86(2):299-304
Inelastic photon scattering by helium atoms and helium-like ions with simultaneous excitation of the two-electron transition
1s
2→2s
2 is examined in the nonrelativistic energy range I≪ω≪m (I is the ionization potential, ω is the photon energy, m is the electron mass, and ℏ=c=1). The electrons are assumed to be moving in the Coulomb field of the nucleus, and the electron-electron interaction is
taken into account in the lowest perturbation order. The differential and total cross sections of the process and the autoionization
width of the 2s
2 energy level are calculated. The numerical value of the autoionization width is found to agree with the results of the more
rigorous calculations of other researchers.
Zh. éksp. Teor. Fiz. 113, 539–549 (February 1998) 相似文献
18.
Energy levels of three particles moving in two dimensions in the presence of an external magnetic field are computed by means
of the 1/N-expansion, where N is roughly the angular momentum. The interparticle interaction is taken as the Calogero potential, r
2/6 +β
2/r
2. The harmonicoscillator (β→ 0) and Wigner (β→∞) limits are reproduced exactly. Level ordering as a function of β and the magnetic field is studied. The results are in excellent qualitative agreement with numerical calculations for three
electrons in a parabolic GaAs quantum dot.
Received July 24, 1995; revised November 20, 1995; accepted for publication February 6, 1996 相似文献
19.
David Trnka 《Pramana》2006,66(5):915-920
Recent experimental results on the in-medium modification of the ω meson are discussed. The experiment described was performed
at the ELSA accelerator facility in Bonn using the combined detector system of Crystal Barrel and TAPS. Theω-meson was identified via the reaction γ+A → ω +X → π0 γ +X 相似文献
20.
We have investigated the absorption spectrum of thin films of the superionic conductor RbCu4Cl3I2 synthesized on NaCl crystalline substrates. It is shown that the electron and exciton excitations in the energy interval
3–6 eV are associated with optical transitions in the CuHal sublattice, and the edge of the fundamental band is controlled
by optical transitions in the Cu(II)Hal sublattice. It is found that the large band gap of this compound (E
g
=3.86 eV) in comparison with those of CuCl and CuI is a result of the small number of Cu ions in the second coordination sphere.
The temperature dependence of the spectral position and half-width of the low-temperature exciton band reveals features associated
with the phase transitions γ→β (T
c1=170 K) and β→α (T
c2=220 K) and with disordering of the cation sublattice attendant to the transition to the superionic state.
Fiz. Tverd. Tela (St. Petersburg) 40, 1022–1026 (June 1998) 相似文献