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1.
G. Dietz K. Richter F. Stein H. C. Schäfer 《Zeitschrift für Physik B Condensed Matter》1990,81(2):223-228
Dependent on
is produced through electrodeposition in three modifications: microcrystalline if
, amorphous if
and in a mixed state containing both components if
. The interpretation of results of large and small angle X-ray scattering, of measurements of the coercivity and of the mechanical density shows that the three modifications consist of two phases. The structure of the grain boundary phase in the microcrystalline alloys differs considerably from that of the amorphous phase. This arises from the dependence of the atomic volume on the average phosphorus content
. The volume fraction of the crystalline component decreases with increasing
up to
. But even in alloys revealing X-ray patterns without any peaks coming from crystalline particles small angle X-ray scattering indicates the existence of metal-rich inclusions occupying some percent of the total volume. 相似文献
2.
We use the recursion method to calculate the vibrational density of states
of site percolation clusters slightly above the percolation threshold. It is found that
is proportional to at long wavelengths. At shorter length scales,
is proportional to
, with the fraction dimension
. The cross-over from phonon to fraction regime is characterized by a rapid rise in
in agreement with effective medium calculations. 相似文献
3.
We use the real-space renormalization group method to study the critical behavior of self-avoiding walks (SAWs) on both site percolation clusters at percolation threshold and site lattice animals in a square lattice. The correlation length exponents of SAWs are found to be
on the percolation clusters atp
c
and
SAW
LA
=0.804 on lattice animals. These results are compared with Kremer's suggestion of modified Flory formula
where
is the fractal dimension of the fractal object. 相似文献
4.
Models of random systems whose Hamiltonian reads
, where
and
i
,=1,...,n are independent, identically distributed random variables are discussed.J
ij
are assumed to be symmetric, with respect toJ
0, random variables and also symmetric functions of components of
. A question of dependence of a phase diagram on a probability distribution of
is addressed. A class of distributions and interactionsJ
ij
, which give rise to phase diagrams called typical is selected. Then a problem of obtaining typical phase diagrams, containing a certain region with an infinite number of pure phases, is studied. 相似文献
5.
Pin-Zhen Bi 《Zeitschrift fur Physik C Particles and Fields》1991,52(1):105-109
The ellipsoidal bag model is used to describe heavy quark systems such asQ
,Q
g andQ
2
. Instead of two step model, these states are described by an uniform picture. The potential derived from the ellipsoidal bag forQ
is almost equivalent to the Cornell potential. For aQ
2
system with large quark pair separation, an improvement of 70 MeV is obtained comparing with the spherical bag. 相似文献
6.
An explicit construction in a manifestly Lorentz-invariant and cyclically symmetric form is given for a three-hadron (H) coupling through their respective (q
) constituents interacting via a quark triangle loop under the most general conditions of unequal mass kinematics atboth the elementary quark and composite-hadron levels. The only ansatz employed is that theHq
vertex function H at each vertexi is a function of
i
, the relative momentumtransverse to the corresponding hadron momentumP
i, an assumption which can be justified from several independent angles. The resulting structure
, withD(
) being a model-independent function, has proved crucial for an explicit integration over the time-like component of the loop momentum, and thus provided an analytical, cyclically symmetric structure free of overlapping pole singularities. The applicational potential of this quantity is outlined. 相似文献
7.
A. Bartl W. Majerotto B. Mösslacher N. Oshimo 《Zeitschrift fur Physik C Particles and Fields》1991,52(4):677-684
We present a detailed study of
and
and the subsequent decays of
,
, and
at the LHC
. We explore the relevant supersymmetry parameter range. We calculate the cross sections as well as the rates for interesting signatures such as the production of one or two leptons on the lepton side. 相似文献
8.
T. Nattermann M. Feigelman I. Lyuksyutov 《Zeitschrift für Physik B Condensed Matter》1991,84(3):353-359
We analyze the influence of thermal and frozen-in disorder on the flux line (FL) density
close to the lower critical fieldH
c1. Arguments which consider the steric repulsion of fluctuating FLs give
with the roughness exponent of a single FL andd the space dimensionality. We show by a phenomenological scaling approach and a renormalization group treatment, that this is correct only fordd
c
=2/–1, i.e. for
. Ford>d
c
the steric FL repulsion at scales more than some critical one is irrelevant and
. For disordered superconductorsd
c
=2 and
ford=2, 3. We also found the melting line for a FL lattice in the presence of frozen-in impurities close toH
c1. 相似文献
9.
M. Guillot F. Tchéou A. Marchand P. Feldmann 《Zeitschrift für Physik B Condensed Matter》1984,56(1):29-39
Using neutron diffraction data, the thermal evolution of the magnetic structure of Ho3Fe5O12 has been studied. Below the compensation temperature (T
comp=137 K), the umbrella structure parameters which fit the spontaneous ferrite magnetizations have been determined. AboveT
comp, the compound behaves as a Néel type ferrimagnet. Particular attentions have been given to the magnetic form factors of both iron sublattice on one hand and on the other hand to a rhombohedral distorsion fromI a3d toR
below 30 K and in first approximation toR
c forT>30 K. 相似文献
10.
A. Kirk 《Czechoslovak Journal of Physics》1990,40(7):737-752
The non-Abelian nature of QCD suggests that particles that have a gluon constituent, such as glueballs or hybrids, should exist. In addition,q
q
states are also predicted. This paper describes a search for these non-q
q mesons performed by experiment WA 76 using the CERN Omega Spectrometer and discusses three candidates which have been observed.Invited talk at HEXAM 89, Bechyn Castle, Czechoslovakia, June 25–30, 1989. 相似文献
11.
A. E. Dorokhov N. I. Kochelev Yu. A. Zubov 《Zeitschrift fur Physik C Particles and Fields》1995,65(4):667-679
The spectrum of
, Jp=0+, 2+ mesons is discussed. We have shown that due to instanton-induced forces the physical states are strong mixtures of theSU
f
(3) group basis states. The cross-sections for annihilation of the
system into
mesons are obtained. Thea
0(980) meson is considered as
meson consisting of 9
f
and 36
f
plets. The branchings are also predicted for the cross-sections for production of thea
0(980) and tensor
mesons in
annihilation. 相似文献
12.
In magnetic systems the radio frequency fieldH
1 seen by the nuclei is often enhanced by a factor . If the atomic spins are distributed in multi directions, as in Bloch walls or spin glasses, one has to consider a spatial distribution (r) of enhancement factors. The usual way to define a mean enhancement factor
is shown to lead to inconsistent results giving rise to errors up to more than 100%. One has to distinguish between two mean factors,
and
, depending on measuring conditions. Their deviations from the true value
are discussed. 相似文献
13.
A. Möbius 《Zeitschrift für Physik B Condensed Matter》1990,80(2):213-223
A detailed phenomenological re-analysis of previously published conductivity data, (T, x), is presented. It was shown in [1] that the cusp-like low-temperature contribution can be described by
wherep=0.19±0.03. Starting from this result, two furtherT dependent contributions are separated: The high-temperature region is dominated by a positive contribution ht (T, x), which is approximately independent ofx, nearly linear inT above 100 K and nearly quadratic inT below 30 K. ForT 4 K, there is a small deviation, increasing withT, from the superposition of the above mechanisms. The relation between
, being negative, and theT independent part,
, exhibits a singularity,
where
and=0.68±0.05 –(p–0.19). This singularity should be related to the metal-semiconductor transition, taking place atT
c
0.14. The quantity
should be interpreted as minimum metallic conductivity. The limitingT dependences asxx
c
+0 agrees quantitatively with that one obtained previously for the activated region,xx
c
–0. Extrapolation of the phenomenological model obtained leads to the hypothesis that the interplay of
and ht could be the main origin of the temperature coefficient changing its sign in the Mooijregion, at
tc=0. The model enables several trend predictions concerning the value of
tc=0. 相似文献
14.
15.
We show that the Ashtekar-Isham extension
of the configuration space of Yang-Mills theories
is (topologically and measure-theoretically) the projective limit of a family of finite dimensional spaces associated with arbitrary finite lattices.These results are then used to prove that
is contained in a zero measure subset of
with respect to the diffeomorphism invariant Ashtekar-Lewandowski measure on
. Much as in scalar field theory, this implies that states in the quantum theory associated with this measure can be realized as functions on the extended configuration space
. 相似文献
16.
The field dependence of the hyperfine interaction of161Dy impurities in Cu has been studied in external magnetic fields up to 3.21 T by means of Mössbauer spectroscopy.
161Dy was introduced into a single crystal of Cu by means of low temperature ion implantation. From the measurements we determine the parameters of the cubic crystalline electric field acting on the Dy nuclei:A
4<r4>=–28±58 K and
. The ground state is a
doublet, separated well from a
excited quartet by
. 相似文献
17.
Domingos H. U. Marchetti 《Journal of statistical physics》1990,61(3-4):909-911
A simple argument is presented by which one can show that the critical inverse temperature
c
of a two-dimensional Coulomb gas (standard or hard-core) with activityz satisfies
, where
in the low-activity limit. Previous results yield
. 相似文献
18.
The theorem that each derivation of aC*-algebra
extends to an inner derivation of the weak-operator closure (
)– of
in each faithful representation of
is proved in sketch and used to study the automorphism group of
in its norm topology. It is proved that the connected component of the identity in this group contains the open ball of radius 2 with centerl and that each automorphism in extends to an inner automorphism of (
)–.Research conducted with the partial support of the NSF and ONR. 相似文献
19.
We study analogues of the Yangian of the Lie algebra
for the other classical Lie algebras
and
. We call them twisted Yangians. They are coideal subalgebras in the Yangian of
and admit homomorphisms onto the universal enveloping algebras U(
) and U(
) respectively. In every twisted Yangian we construct a family of maximal commutative subalgebras parametrized by the regular semisimple elements of the corresponding classical Lie algebra. The images in U(
) and U(
) of these subalgebras are also maximal commutative. 相似文献
20.
José M. Figueroa-O'Farrill 《Communications in Mathematical Physics》1996,177(1):129-156
Let
be a finite-dimensional Lie algebra (not necessarily semisimple). It is known that if
is self-dual (that is, if it possesses an invariant metric) then it admits anN=1 (affine) Sugawara construction. Under certain additional hypotheses, thisN=1 structure admits anN=2 extension. If this is the case,
is said to possess anN=2 structure. It is also known that anN=2 structure on a self-dual Lie algebra
is equivalent to a vector space decomposition
, where
are isotropic Lie subalgebras. In other words,N=2 structures on
in one-to-one correspondence with Manin triples
. In this paper we exploit this correspondence to obtain a classification of thec=9N=2 structures on solvable Lie algebras. In the process we also give some simple proofs for a variety of Lie algebras. In the process we also give some simple proofs for a variety of Lie algebraic results concerning self-dual Lie algebras admitting symplectic or Kähler structures. 相似文献