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1.
The phonon dispersion curves, phonon frequency distribution function as well as the lattice specific heat of body-centred
tetragonal indium have been deduced using a lattice dynamical model which includes central, angular and volume forces. Six
elastic constants, four zone boundary frequencies and an equilibrium condition were used in the evaluation of the force constants.
It is shown that this model is elastically consistent and satisfies the symmetry requirements of the lattice, the phonon frequencies
of indium deduced from it are in very good agreement with the experimental values of Reichardt and Smith and the theoretical
values of Garrett and Swihart, and theθ
D values compare well with the experimental values over a wide temperature range. The apparent discrepancies in the phonon
dispersion curves and theθ
D-T curves obtained from deficient models, importance of umklapp processes and the significance of angular forces in the lattice
dynamical models are discussed. 相似文献
2.
P P Divakaran 《Pramana》1979,13(3):237-260
A gauge model for the weak interactions of the leptons (v
e, e, μ, νμ) and the quarks (q
p, qn,qλ,q
p′) is presented in which deviations from universality, such as the Cabibbo suppression, are explicitly and spontaneously generated.
The gauge group is, to begin with SU(4). There are three quartets of Higgs scalars with suitable vacuum expectation values,
sufficient and necessary to give masses to all gauge bosons. It turns out that this gauge group is too ‘large’ and fails to
account for many observed symmetries of weak interactions, especially electron-muon symmetry. This symmetry corresponds to
a discrete transformationR which is an element of SU(4). To accommodate it, the gauge group is restricted to the subgroup of SU(4) which commutes withR. There are now 7 gauge bosons, 4 charged and 3 neutral. One pair of charged bosons is necessarily heavier than the other
pair (denotedW
±) and two neutrals are necessarily heavier than the third (W
0). The electron and the muon become massive while the neutrinos and the quark fields remain massless.
The dominant charged weak currents coupling toW
± havee-μ universality and Cabibbo universality for both of whichR-symmetry is essential—the Cabibbo angle is a simple function of the vacuum expectation values. The same symmetry ensurese-μ symmetry and the absence of flavour-changing components in the neutral currents. The currents coupling to the heavier gauge
bosons break all these symmetries but these bosons can be made arbitrarily heavy and so are relevant only in the domain of
‘ultraweak’ interactions.
The Cabibbo angleϑ
c itself is determined by minimising a very general class of Higgs potentials, leading to a numerical valueϑ
c = ±π/8, | tanϑ
c | = √2 − 1 (an alternative solution | tanϑ
c | = (√2+1) is rejected), independent of the parameters and of the precise form of the potential. This is the ‘bare’ϑ
c; in low energy/momentum transfer processes, this value is renormalised by the structure of the hadrons. A model is given
for this renormalisation which reduces the renormalised value of | tanϑ
c | to about 0.2–0.3 from the bare value 0.41. Recent data on highly inelastic neutrino interactions are shown to be not inconsistent
with | tanϑ
c | = 0.4. 相似文献
3.
S. Ağduk G. Gökoğlu 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,79(4):509-514
We present the results of ab initio calculations of lattice dynamics and the second order
elastic stiffness constants of nickel-based magnetic shape memory alloy Ni2MnIn in
stoichiometric composition. The plane wave basis sets and pseudopotential
method within spin-polarized generalized gradient approximation (σ-GGA) scheme of the density functional theory (DFT) is applied. Elastic
constants are calculated by tetragonal and monoclinic isochoric strains
on cubic L21 structure. The calculated elastic constants
agree very well with the recent ultrasonic experimental data. Phonon dispersion spectra are investigated within linear response
technique
of the density functional perturbation theory (DFPT). A vibrational anomaly is observed in phonon spectra at the transverse
acoustic mode (TA2) in [ζ
ζ0]
direction at wavevector ζ = 0.3 as an indication of the structural instability of the system to shear deformation. This anomaly is also verified by
the
low shear modulus and large elastic anisotropy ratio. Phonon dispersion curves are in excellent agreement with the results
of recent neutron diffraction experiments. 相似文献
4.
A. L. Kataev 《JETP Letters》2012,94(11):789-794
The generalized Crewther relations in the channels of the non-singlet and vector quark currents are considered. These relations
follow from the double application of the operator product expansion approach to the same axial vector-vector-vector triangle
amplitude in two regions, adjoining to the angle sides (x, y) (or p
2, q
2). We assume that the generalized Crewther relations in these two kinematic regimes result in the existence of the same perturbation
expression for two products of the coefficient functions of annihilation and deepinelastic scattering processes in the non-singlet
and vector channels. This feature explains the conformal symmetry motivated cancellations between the singlet α
s
3 corrections to the Gross-Llewellyn Smith sum rule S
GLS of νN deep inelastic scattering and the singlet α
s
3 correction to the e
+
e
−-annihilation Adler function D
A
V
in the product of the corresponding perturbative series. Taking into account the Baikov-Chetyrkin-Kuhn fourth order result
for S
GLS and the perturbative effects of the violation of the conformal symmetry in the generalized Crewther relation, we obtain the
analytical contribution to the singlet α
s
4 correction to the D
A
V
function. Its a-posteriori comparison with the recent result of direct diagram-by-diagram evaluation of the singlet fourth
order corrections to D
A
V
function demonstrates the coincidence of the predicted and obtained ζ32-contributions to the singlet term. They can be obtained in the conformal invariant limit from the original Crewther relation.
Therefore, on the contrary to previous belief, the appearance of ζ3-terms in the perturbative series in quantum field theory gauge models does not contradict to the property of the conformal
symmetry and can be considered as regular feature. The Banks-Zaks motivated relation between our predicted and the obtained
directly fourth order corrections is mentioned. It confirms the expectation, previously made by Baikov-Chetykin-Kuhn, that
at the 5-loop level the generalized Crewther relation in the channel of vector currents may receive additional singlet contribution,
which in this order of perturbation theory is proportional to the first coefficient of the QCD β function. 相似文献
5.
The rapid solidification of Sb60Ag20Cu20 ternary alloy was realized by high undercooling method, and the maximum undercooling is up to 142 K (0.18TL). Within the wide undercooling range of 40-142 K, the solidified microstructures are composed of (Sb), θand ε phases. High undercooling enlarges the solute solubility of (Sb) phase, which causes its crystal lattice to expand and its crystal lattice constants to increase. Primary (Sb) phase grows in two modes at small undercoolings non-faceted dendrite growth is the main growth form; whereas at large undercoolings faceted dendrite growth takes the dominant place. The remarkable difference of crystal structures between (Sb) and θphases leads to (θ Sb) pseudobinary eutectic hard to form, whereas strips of θform when the alloy melt reaches the (θ Sb) pseudobinary eutectic line. The cooperative growth of θand ε phases contributes to the formation of (ε θ) pseudobinary eutectic easily. In addition, the crystallization route has been determined via microstructural characteristic analysis and DSC experiment. 相似文献
6.
F. C. Hoh 《International Journal of Theoretical Physics》1997,36(2):509-531
The recently developed spinor strong interaction theory, which successfully accounts for linear confinement and classification
of mesons as well as unmixed meson spectra, is applied to semileptonic decays of the π,K, D, andB mesons. These mesons themselves generate massM
w
for the mediating gauge boson; no Higgs boson is needed. The theory is also applied to purely leptonic interactions. It is
shown that the results of the standard electroweak model can be taken over with the Higgs boson replaced by the above mesons.
The Cabbibo angle ϑC is given by tan ϑC=(pion mass)/(kaon mass), in agreement with data. The pion decay constantF is essentially a ratio between two large constants introduced to make certain infinite integrals finite.M
w is also related to a similar cutoff constant.
Dragarbrunnsg. 9B. 相似文献
7.
Considering a CP-violating QCD interaction, the electric dipole moment of neutron (EDMN) is estimated in a quark model of
light mesons with a dynamical breaking of chiral symmetry through a non-trivial vacuum structure. Pion and kaon, being treated
consistently within the model, yield to the constituent quark wave functions as well as the dynamical quark masses and thus
determine the constituent quark field operators with respect to light quark flavors. Using the translationally invariant hadronic
states and these constituent quark field operators, the EDMN estimated here remains well within the recent experimental bound
ofD
n<11 × 10−26 e-cm with the CP-violation parameter |ϑ|=10−8, which in fact accounts for a strong CP-violation. 相似文献
8.
R. Kamiński J. R. Peláez F. J. Ynduráin 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):479-484
We first review the results of an analysis of ππ interactions in S, P and D waves for the two-pion effective mass from threshold to about 1.4GeV. In particular, we show a recent improvement of this
analysis above the Kˉ threshold using more data for phase shifts and including the S0-wave inelasticity from ππ→Kˉ. In addition, we have improved the fit to the f
2(1270)-resonance and used a more flexible P-wave parametrization above the Kˉ threshold and included an estimation of the D2-wave inelasticity. The better accuracy thus achieved also required a refinement of the Regge analysis above 1.42GeV. Finally,
in this work we check that the ππ scattering amplitudes obtained in this approach satisfy remarkably well forward dispersion relations and Roy's equations. 相似文献
9.
B. Canals D.A. Garanin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):439-447
Thermodynamic quantities and correlation functions (CFs) of the classical antiferromagnet on the checkerboard lattice are
studied for the exactly solvable infinite-component spin-vector model, D↦∞. In contrast to conventional two-dimensional magnets with continuous symmetry showing extended short-range order at distances
smaller than the correlation length, r
ξ
c∝ exp(T
*/T), correlations in the checkerboard-lattice model decay already at the scale of the lattice spacing due to the strong degeneracy
of the ground state characterized by a macroscopic number of strongly fluctuating local degrees of freedom. At low temperatures,
spin CFs decay as <
>∝ 1/r
2 in the range a
0≪r≪ξ
c∝T
-1/2, where a0 is the lattice spacing. Analytical results for the principal thermodynamic quantities in our model are very similar with
MC simulations, exact and analytical results for the classical Heisenberg model (D = 3) on the pyrochlore lattice. This shows that the ground state of the infinite-component spin vector model on the checkerboard
lattice is a classical spin liquid.
Received 16 November 2001 and Received in final form 12 February 2002 相似文献
10.
U. Köbler A. Hoser 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(2):151-159
The basic issues of renormalization group (RG) theory, i.e. universality, crossover phenomena, relevant interactions etc.
are verified experimentally on magnetic materials. Universality is demonstrated on account of the saturation of the magnetic
order parameter for T ↦ 0. Universal means that the deviations with respect to saturation at T = 0 can perfectly be described
by a power function of absolute temperature with an exponent ε that is independent of spin structure and lattice symmetry.
Normally the Tε function holds up to ~0.85Tc where crossover to the critical power function occurs.
Universality for T ↦ 0 cannot be explained on the basis of the material specific magnon dispersions that are due to atomistic
symmetry. Instead, continuous dynamic symmetry has to be assumed. The quasi particles of the continuous symmetry can be described
by plane waves and have linear dispersion in all solids. This then explains universality. However, those quasi particles cannot
be observed using inelastic neutron scattering. The principle of relevance is demonstrated using the competition between crystal
field interaction and exchange interaction as an example. If the ratio of crystal field interaction to exchange interaction
is below some threshold value the local crystal field is not relevant under the continuous symmetry of the ordered state and
the saturation moment of the free ion is observed for T ↦ 0. Crossover phenomena either between different exponents or between
discrete changes of the pre-factor of the Tε function are demonstrated for the spontaneous magnetization and for the heat capacity. 相似文献
11.
The laser Raman spectrum of tere-phthalaldehyde powder has been recorded on a Jobin Yvonhg 2S spectrophotometer with a~100 mW Argon-Ion laser. The infrared spectrum of the solid substance has been recorded on a Perkin-Elmer
621 spectrophotometer in the region 300–4000 cm-1 using KBr and nujol mull techniques. The observed frequencies have been assigned in terms of the fundamentals, overtones
and combinations assumingD
2h point-group symmetry. 相似文献
12.
S N Vaidya 《Pramana》1979,12(1):23-32
A theory of melting based on vacancy model is formulated. The polymer solution theory is used for derivation of the melting
equation for a two-species model of melting solid. Under simplifying assumptions the analysis leads to a simple correlation
betweenT
m and 〈v〉, the average energy of interaction between the vibrating atoms. Pseudopotential method is used for calculating 〈v〉 for the alkali metals lithium, sodium, potassium and rubidium at temperatureT
m. The calculated values ofT
m〈v〉 are in accord with those expected from our model. Application to the high pressure melting curves of solids is also discussed. 相似文献
13.
The (4, 4*) ⊕ (4*, 4) model of broken chiral SU (4) × SU (4) symmetry has been used to calculate the third-order coupling
constants involving charmed and ordinary pseudoscalar mesons. These coupling constants are exploited to derive some interesting
new relations among the masses and decay constants of these charmed particles. Using the known masses and decay constants
as inputs, we exploit these relations to predict:F
D = −1·41F
π
,F
F = −1·13F
π
,F
D/FF = 1·25,m(D
s) = 1·43 GeV,m(F
s) = 1·39 GeV andm(K
s) = 1·02 GeV. 相似文献
14.
V. I. Tsidilkovski 《Ionics》1998,4(3-4):316-320
A method for calculation of hopping transport phenomena in lattices which allows for strong interparticle interactions by
means of cluster expansion constructions for transport coefficients is presented. The method developed is applied to the oxygen
transfer in YBa2Cu3O6+x taking into account interactions both between oxygen ions in lattice sites and between hopping oxygen in the saddle point
and surroundings. It is shown that the oxygen mobility μ decreases as the oxygen content increases in contrast to the chemical
diffusivityD which rises withx. The effective activation energiesU
eff forD and μ have peculiarities at the phase transition points. At fixedx valuesU
eff of μ falls by ≈ 0.1– 0.15 eV at the ortho-tetraphase transition whileU
eff ofD practically doesn't change.
Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998. 相似文献
15.
It has recently been shown that any physical quantity ℛ, in perturbation theory, can be obtained as a function of only the
renormalization scheme (rs) invariants,ρ
0,ρ
1,ρ
2, … Physical predictions, to any given order, are renormalization scheme independent in this approach. Quantum chromodynamics
(qcd) predictions to second order, within thisrs-invariant perturbation theory, are given here for several processes. These lead to some novel relations between experimentally
measurable quantities, which do not involve the unknownqcd scale parameter Λ. They can therefore be directly confronted with experiments and this has been done wherever possible. It
is suggested that these relations can be used to probe the neglected higher order corrections. 相似文献
16.
Investigations of the dependence of lattice vibrations of alkali metals on their interatomic distance,r reveal that they satisfy an empirical relation,Mv
2
r
=(q), a constant which depends on, with q=2·48 ± 0·19 at all wave vectors and hence are homologous. It is shown that the observed crossover of [00] branches of lithium is not an anomalous property, but only manifests itself in alkali metals with smaller interatomic distance due to small variations of . The role played by interatomic distance which is closely related to that of the electron gas constantC in producing a crossover and a possible reason for the observed homology are discussed.The authors are grateful to Professor B. Sharan and Mr. S. B. Rajendraprasad for many valuable and stimulating discussions. One of the authors (M. S.) is greatly indebted to Professor D. M. Sen, principal, and Professor L. V. Sud of Regional Engineering College, Kurukshetra, for granting him study leave. 相似文献
17.
G. Landi 《Russian Journal of Mathematical Physics》2009,16(3):429-445
We present two (classes of) examples of gauged Laplacian operators. The first one is a model of spin-Hall effect on a noncommutative
four-sphere S
ϑ
4 with isospin degrees of freedom, coming from a noncommutative instanton, and invariant under the quantum group SO
ϑ
(5). The second one, a Hall effect on a quantum 2-dimensional sphere S
q
2, describes ‘excitations moving on the quantum sphere’ in the field of a magnetic monopole with symmetry coming from the quantum
group SU
q
(2). For both models, ample symmetries provide a complete diagonalization. 相似文献
18.
The formulas of crystal field theory are derived for a particular case of the C
3v
symmetry group. Convenient and numerically simple methods are proposed to take into account the polarization of the local
environment of the Cr3+ impurity ion in LiNbO3. The parameters of intraion interactions for Cr3+ in lithium and niobium positions in the lithium niobate lattice and the distortion of the niobium octahedron in lithium niobate,
which is caused by the incorporation of trivalent chromium ion, are determined. 相似文献
19.
M. I. Abd-Elrahman 《Physics of Wave Phenomena》2011,19(1):13-17
Fundamental (lattice, rotational, and intermolecular) vibrations of the H2AsO4− anion in (C6H9N2)H2AsO4 crystal are calculated using the correlation theorem based on the group theory. The correlation between anionic site of symmetry
C
s and the factor group D
2h
of the crystal yields 12 modes for both lattice and rotational vibrations. The infrared and Raman spectra of these modes
do not coincide. Addition of two hydrogen atoms to AsO4− ion yields two As-OH bonds in the H2AsO4− anion. As a result, the molecular symmetry is reduced from T
d
to C
2υ
. The free H2AsO4− anion having C
2υ
symmetry gives in total 15 fundamental normal vibrations. Under the crystal field splitting effects, the number of intermolecular
vibrations for the anion in infrared and Raman spectra is calculated to be 56 active vibrations. The calculated fundamental
vibrationsmanifest themselves as the main features in an experimental infrared spectrum. 相似文献
20.
The damage spreading of the Ising model on the 3–12 lattice with competing Glauber and Kawasaki dynamics is studied. The difference
between the two kinds of nearest-neighboring spin interactions (interaction between two 12-gons, or interaction between a
12-gon and a triangle) are considered in the Hamiltonian. It is shown that the ratio of the interaction strengthF between the two kinds of interactions plays an important role in determining the critical temperature Td of phase transition from frozen to chaotic. Two methods are used to introduce the bond dilution on the Ising model on the
3–12 lattice: regular and random. The maximum of the average damage spreading 〈D〉max can approach values lower than 0.5 in both cases and the reason can be attributed to the ’survivors’ among the spins. We
have also, for the first time, presented the phase diagram of the mixed G-K dynamics in the 3–12 lattice which shows what
happens when going from pure Glauber to pure Kawasaki 相似文献