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1.
2.
Z. A. Kazei N. P. Kolmakova A. A. Sidorenko L. V. Takunov 《Physics of the Solid State》1998,40(9):1513-1515
The thermal expansion anomalies in TbVO4 due to the cooperative Jahn-Teller effect were studied experimentally and theoretically. Characteristic magnetoelastic anomalies
were observed in the curves of Δa/a and Δc/c of the cell parameters at T<T
c. Calculations of the magnetoelastic contribution to Δa/a and Δc/c from fully symmetric
and
and low-symmetry ɛδ modes were performed using the general crystal-field formalism, and the values of the magnetoelastic coefficient B
δ were obtained from spectroscopic and spontaneous-deformation data. It is shown that the thermal expansion of TbVO4 in both the tetragonal and orthorhombic phases can be described well on the basis of a general model based on a single set
of interaction parameters.
Fiz. Tverd. Tela (St. Petersburg) 40, 1663–1666 (September 1998) 相似文献
3.
Ellipsometric spectroscopy has been performed on nonpolar ZnO
surfaces in the spectral range 1.5 eV<ħω<4.0 eV. Absolute measurements with two different crystal orientations in air allow
the determination of the optical constantsn
∥,k
∥ andn
⊥,k
⊥ for light polarized parallel and perpendicular to thec-axis. The ellipsometric angles Δ and ψ are changed remarkably on ultrahigh vacuum cleaved surfaces near the band gap energy
of ∼3.4eV when oxygen or atomic hydrogen is adsorbed or when the crystal is annealed. This observation is interpreted in terms
of a field effect on the optical constants in the space charge layer. 相似文献
4.
A Fe+5.07 at.%Si single crystal has been studied by ultrasonic-pulse technique. Its density and elastic constants were determined
for p=0 and T=293 K. The dependence of the elastic properties of silicious iron on Si concentration was constructed. The compression, the
effective elastic constants, and the Grüneisen parameters were measured at hydrostatic pressures of up to 9 GPa. It was found
that for p=0,
and
. The elastic constants c
44 and c′ increase linearly with pressure by 19.3 and 18.2% by p=9 GPa. The elastic anisotropy does not vary with pressure. For p>4 GPa, c
11, c
12, and K
S were observed to increase nonlinearly with decreasing pressure derivative. The Grüneisen parameter γ
LA decreases with pressure down to 0.70 at 9 GPa to become negative when extrapolated to the region of the α−ɛ phase transformation. The anomalies in c
11 and the negative values of γ
LA for p>11 GPa indicate that the phase transformation in silicious iron at 13.5 GPa can take place by the crystallographic mechanism
of the α−ɛ transformation in pure iron, i.e. by lattice compression in the [001] direction and shearing of the (110) planes along
or
. An assumption is put forward that pressure gives rise in silicious iron to sp-d hybridization, which results in increased screening of the ion-ion interaction and in anomalies in elastic properties. Similar
phenomena are expected to occur in pure bcc Fe as well.
Fiz. Tverd. Tela (St. Petersburg) 41, 516–522 (March 1999) 相似文献
5.
A theoretical study of the magnetic susceptibility of multilayered carbon nanotubes in fields both parallel, H
∥, and perpendicular, H
⊥, to the tube axis has been carried out disregarding electron-electron interaction. The temperature dependences of the magnetic
susceptibility obtained exhibit a nontrivial form for H
∥, which is related to the quasi-one-dimensionality of such a system as the nanotube. The dependences of the magnetic susceptibility
on chemical potential χ(μ) have also been derived. At low temperatures, χ(μ) has sharp peaks in fields H
∥, which is connected with the presence of
singularities in the density of states of nanotubes. The effect of interlayer coupling on magnetic susceptibility of small-radius
tubes has been investigated numerically.
Fiz. Tverd. Tela (St. Petersburg) 40, 1950–1954 (October 1998) 相似文献
6.
The effect of microwave radiation on magnetotransport in single GaAs quantum wells with anisotropic mobility, whose maximum
corresponds to the
direction and minimum to the [110] direction, is investigated using the Van der Pauw method. In samples shaped as squares
with sides oriented along the
and [110] directions, giant oscillations of magnetoresistance arise under the effect of a microwave field for the both
and [110] orientations of the measuring current I
ac. In the anisotropic two-dimensional system under study, the relative amplitude of microwave photoresistance oscillations
in a magnetic field weakly depends on the orientation of I
ac. At a temperature of 4.2 K and a microwave frequency of 130 GHz, magnetic field intervals characterized by close-to-zero
resistance manifest themselves only for the case of the [110] orientation of I
ac. The aforementioned experimental results are qualitatively explained by a quasi-one-dimensional potential modulation of the
two-dimensional electron gas in the [110] direction.
Original Russian Text ? A.A. Bykov, D.R. Islamov, A.V. Goran, A.K. Bakarov, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ
i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 12, pp. 891–895. 相似文献
7.
Summary The crystal size in accretions grown in an icing wind tunnel at ambient temperatures −18≥T
a
≥−27°C and different substrate temperatureT
s
<0°C is studied. For constantT
s
the mean area
of crystal sections shows an approximately exponential dependence onT
a
which may be written as
, where ΔT≃−T
a
represents the droplet supercooling. On the other hand, for fixedT
a
, the crystal size is observed to decrease markedly withT
s
. By considering previous results on the orientation of crystals forming the accretions, it is shown that the value of the
mean angle
formed by the crystalc-axis with the growth direction depends as well both onT
a
andT
s
. The exponential dependence of
andT
a
and the observed correspondence between the behaviour of
and
are correlated with a nucleation mechanism, accompanied by a process of orientation selection, which would be responsible
of both the crystal size and the orientation. The application of the crystal structure analysis to the determination of the
growth conditions of hailstones is discussed.
To speed up publication, the authors of this paper has agreed to not receive the proofs for correction.
Comisión Nacional de Energía Atómica and Consejo Nacional de Investigaciones Científicas y Técnicas. 相似文献
Riassunto Si studia la dimensione di un cristallo in accrezioni cresciute in una galleria a vento congelante a temperature ambienti −18≥T a ≥−27 °C e diversa temperatura di substratoT s <0 °C. PerT s costante, l’area media delle sezioni di cristallo mostra una dipendenza daT a approssimativamente esponenziale che potrebbe essere scritta così: , dove ΔT≃−T a rappresenta il superraffreddamento della gocciolina. D’altra parte, perT a fisso, si osserva che la dimensione del cristallo decresce marcatamente conT s . Considerando precedenti risultati sull’orientamento dei cristalli che formano le accrezioni, si mostra che anche il valore dell’angolo medio formato dall’assec del cristallo con la direzione di accrescimento dipende sia daT a che daT s . La dipendenza esponenziale di daT a e la corrispondenza osservata tra il comportamento di e di sono collegate con il meccanismo di nucleazione, accompagnato da un processo di selezione dell’orientamento, che dovrebbe essere responsabile sia della dimensione che dell’orientamento del cristallo. Si discute l’applicazione dell’analisi della struttura del cristallo alla determinzione delle condizioni di accrescimento dei chicchi di grandine.
To speed up publication, the authors of this paper has agreed to not receive the proofs for correction.
Comisión Nacional de Energía Atómica and Consejo Nacional de Investigaciones Científicas y Técnicas. 相似文献
8.
Ersan Demiralp 《Czechoslovak Journal of Physics》2005,55(9):1081-1084
We have investigated bound state solutions of the Schrodinger equation for one-dimensional harmonic oscillator potential together
with even number of Dirac delta functions. These point interactions are located at symmetric points x = x
i
and x = −x
i
(i = 1, 2,..., N) and they have complex conjugate strengths
and
, respectively. We present explicit forms of eigenfunctions and an algebraic eigenvalue equation and numerical solutions for
this
-symmetric Hamiltonian.
Presented at the 3rd International Workshop “Pseudo-Hermitian Hamiltonians in Quantum Physics”, Istanbul, Turkey, June 20–22,
2005. 相似文献
9.
10.
We examine the absorption and amplification bands of a weak probe signal in the presence of Bose-Einstein condensation of
excitons that emerges in nonequilibrium conditions in the field of coherent laser radiation with a wave vector k
0. We assume that the detuning
from resonance between the energy ħω
ex
(k
0)+L
0 of the exciton level, which is shifted because of exciton-exciton interaction, and the laser photon energy ħω
L
, is generally nonzero. The elementary excitation spectrum consisting of the quasiexcitonic and quasienergy branches determines
the optical properties of the system. When there is real induced Bose-Einstein condensation, at
the two branches touch, as they do in spontaneous Bose-Einstein condensation. In virtual induced Bose-Einstein condensation,
when
, instabilities emerge in the spectrum in certain regions of the k-space. These instabilities are caused by a real transformation of two laser photons into two extracondensate particles. Nonequilibrium
extracondensate excitons strongly affect the absorption and amplification of the probe light signal. We show that light absorption
is due to the quantum transition from the ground state of the crystal to the quasiexcitonic branch of the spectrum. On the
other hand, amplification of the signal is caused by the transition from the quasienergy branch to the ground state of the
crystal. The same transition can be explained by a real transformation of two laser photons into a vacuum photon of frequency
ħcq and a crystal exciton with a wave vector 2k
0−q. Finally, we show that the excitonic absorption and light-amplification bands are essentially anisotropic at
and depend on the orientation of the vectors q and k
0.
Zh. éksp. Teor. Fiz. 112, 167–179 (July 1997) 相似文献
11.
H. G. Schuster 《Zeitschrift für Physik B Condensed Matter》1977,27(3):251-259
The critical behaviour of random uniaxial ferromagnetic (ferroelectric) systems with both short range and long range dipolar interactions is investigated, using the field theoretic renormalization method of Brézin et al. for the free energy above and below the transition pointT
c. The randomness is due to externally introduced fluctuations in the short range interactions (quenched case) or (and) magneto-elastic coupling to the lattice (annealed case). Strong deviations in the critical behaviour with respect to the pure systems are found. In the quenched case e.g. the specific heatC and the coefficientf
2 (ofM
3 in the equation of state, whereM is the magnetization) change fromC |ln|t1/3,f
2 |ln|t–1 in the pure system toC
is the reduced temperature andA
±,C
± are constants) in the random situation. This change should e.g. be experimentally observable by deuterization of the ferroelectric tri-glycine sulfate where the logarithmic behaviour off
2 has already been detected in the pure case. For nonvanishing magnetoelastic coupling a complex critical behaviour is obtained and discussed. We find the interesting result that if both quenched randomness and a weak magnetoelastic coupling are present the quenched random critical behaviour dominates in the close vicinity ofT
c. Finally the influence of the magnetoelastic coupling on the longitudinal phonons in investigated and it is found that the relative changes in the corresponding elastic constant and structure factor are proportional to the specific heat and the wavevector dependent energy-energy correlation function respectively, suggesting new experiments. 相似文献
12.
M. Canepa P. Cantini S. Lo Vetere L. Mattera M. Salvietti S. Terreni 《Il Nuovo Cimento D》1993,15(2-3):501-510
Summary The OH(1×1)−Ag(110) phase obtained after H2O dissociation on the O(2×1)−Ag(110) surface is investigated. Structural and electronic properties are studied by He diffractive
scattering and angularly resolved ultraviolet photoemission spectroscopy (ARUPS). Diffractive data are interpreted in terms
of the hard corrugated wall (HCW) potential leading to the determination of the corrugation function ζ(R). The shape of ζ(R) indicates that the phase under study is formed of OH rows along
where hydroxil groups interact strongly. The interaction between rows instead is weak and essentially republsive.
In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching. 相似文献
13.
G. Czajkowski 《Il Nuovo Cimento D》1987,9(12):1541-1544
Summary Certain statistical ensembles,e.g. open chemical systems with randomly varying number of particles, are characterized by partition functions of the type
,n being a natural number anda
j
’s generalized temperatures. The state of the system is well defined if one knows the dependence ofa
j
’s on ensemble averages 〈n
j
〉. For making the equations 〈n
j
〉=〈n
j
〉 (a
1, ...,a
s) at least more accessible for numerical calculations a transformation of the partition function to a series of Fourier integrals
is proposed. In the special case of
the integrals can be calculated analytically transforming the statistical sum into a series of error functions. 相似文献
14.
15.
N. M. Panyunin 《Russian Journal of Mathematical Physics》2007,14(4):501-504
In the note, a Smolyanov-Shavgulidze model of infinite-dimensional superspace H
Λ = Λ0
H
0 ⊕ Λ1
H
1 corresponding to a Hilbert space H = H
0 ⊕ H
1 over a Hilbert superalgebra Λ = Λ0 ⊕ Λ1 is considered. Its relation to the Khrennikov superspace is discussed. Moreover, H
Λ is equipped with the structure of Hilbert superspace with an inner superproduct (·, ·)Λ. The supermeasures are defined as Λℂ
(∧H
1)-valued measures on H
0 (Λℂ stands for the complexification of Λ). The definition of the Fourier supertransform is similar to the ordinary one,
(y) =
μ(dz). It turns out that the values of the Fourier supertransform of a supermeasure on the subspace
= H
0 ⊕ Λ1
H
1 can be obtained by applying a certain operator to the values of the classical Fourier transform. The main result is the theorem
claiming that the Fourier supertransform of supermeasures is isometric on superspaces with zero even part (H
0 = {0}). As a corollary, we note that the operator of Fourier supertransform is injective. We also give necessary and sufficient
conditions for the countable additivity of cylindrical supermeasures in terms of continuity of their Fourier supertransforms
(an analog of the Minlos-Sazonov theorem). 相似文献
16.
The strain behaviors as well as the structural and magnetic changes relative to the pretransition in the Ni50.5Mn24.5Ga25 single crystals have been characterized by various methods, such as pretransition strain, magnetostriction, magnetization measurements, and TEM observations. A large magnetostriction up to 505 ppm measured in the [001] direction of the sample is obtained at the pretransition temperature with only a low magnetic field of about 1 kOe applied along the [010] direction. We found that not only the pretransition strain pronounces a more large change, but also the magnetostriction at a certain temperature exhibits a more large magnitude for field applied along the [010] direction than with field along the [001] direction. It is concluded that the magnetoelastic interaction is responsible for the premartensitic transition, and the magnetoelastic interaction in the [010] direction is stronger than that in the [001] direction. 相似文献
17.
Nearly a 50% decrease of the resistivity ρ(T, x) is observed upon just 4% Cu doping at the Mn site of La2/3Ca1/3Mn1−x
CuxO3. When the observed phenomenon is attributed to a decrease of the spin-polaron energy E
σ(x) below T
C
(x), all of the data are found to be well fitted by the nonthermal coherent tunneling expression
, assuming that the magnetization in the ferromagnetic state is given by the expression
. The best fits through all the data points suggest
and E
σ(x)≃E
σ(0)(1−x)4 for the explicit x dependence of the Cu-induced modifications of the Mn-spin-dominated zero-temperature spontaneous magnetization, residual
paramagnetic contribution, and spin-polaron tunneling energy, respectively, with E
σ(0)=0.12 eV.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 812–815 (10 June 1999)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
18.
Itzhak Goldman 《International Journal of Theoretical Physics》1982,21(8-9):665-672
Dirac’s large number hypothesis (LNH), in the formG/G
0=HH
0
−1
, is applied to the matter-dominated cosmological era, using the framework of the scale covariant theory (Canuto et al., 1977).
We obtain explicit expressions forR andβ
a
as functions ofR
E
, whereR andR
E
are the scale factors of the cosmological Robertson-Walker metric, expressed in atomic and gravitational units, respectively,
andβ
a
is the ratio between the rates of gravitational and atomic clocks. The parameters in these expressions are
, the deceleration parameter in gravitational units, and
(t
0)H
0
−1
where
(t
0) is the present epoch value of the derivative ofβ
a
with respect to atomic time. We find that a necessary condition for the LNH to be compatible with a Robertson-Walker model
is that
(t
0)H
0
−1
≥
2
1
. The only experimental values for
(t
0) available at present are those based on the lengthening of the Moon’s period of revolution around the Earth, suggesting
0.86≥
(t
0)H
0
−1
≥0.21; the more promising technique of radar ranging to the inner planets has not yet produced a value for
(t
0). Using the lunar data, it follows that 0≤
≲0.42 corresponding to an open universe (k=−1). Closed models (k=1,
>1/2) are not compatible with the LNH since the required values of
(t
0)H
0
−1
are more than an order of magnitude above the observational upper limit.
Presented at the Dirac Symposium, Loyola University, New Orleans, 1981. 相似文献
19.
Defining the ratiosr
p
=σ(vp →vx)/σ(vp →μ
−
x) and
we obtain the bounds 0.28 ⩽r
p
⩽ 0.61 and
using only the parton model and the data of CDHS group with iron target. We also give the complete set of parton-model relations
which would allow the determination of all the neutral-current coupling constants from inclusive cross sections alone. 相似文献
20.
V. I. Al’shits N. N. Bekkauer A. E. Smirnov A. A. Urusovskaya 《Journal of Experimental and Theoretical Physics》1999,88(3):523-526
A constant magnetic field is found to have a substantial effect on the macroplasticity of NaCl crystals when they are being
actively strained at a constant rate
during magnetic treatment. We have measured the dependence of the yield point σ
y
on the magnetic induction B=0–0.48 T and the strain rate
. It is shown that this magnetic effect has a threshold character and is observed only for B>B
c
, where B
c
grows with increasing
as
. The lower the strain rate
, the larger the relative decrease in the yield point σ
y
(B)/σ
y
(0) at fixed field B>B
c
. At small enough strain rates
the threshold field B
c
ceases to depend on
and goes constant. A theoretical model is proposed which is in good agreement with the observed regularities. The model is
based on the competition between thermally activated and magnetically stimulated depinning of dislocations from paramagnetic
impurity centers.
Zh. éksp. Teor. Fiz. 115, 951–958 (March 1999) 相似文献