共查询到20条相似文献,搜索用时 15 毫秒
1.
Nikolai N. Nikolaev Vladimir R. Zoller 《Zeitschrift fur Physik C Particles and Fields》1992,56(4):623-628
One expects a similarity of the energy dependence of the difference
tot(*p)–
tot(*n) for virtual (deep inelastic scatteringQ
2m
2) and real (Q
2=0) photons. Previous analysis of D structure functions with allowence for nuclear shadowing (NS) in the deuteron has led to conclusion that
tot(*p)–
tot(*n)<0>0>x<0.015. the=" early=" evidence=" from=" the=" real=" photoproduction=" data=">0.015.>
tot(p)–
tot(n)<0. we=" critically=" reexamine=" determinations=" of=" the=">0.>
tot(p)–
tot(n), using more accurate calculations of NS correction to
tot(D), and discuss a possibility of
tot(n)
tot(p) at moderately high energies. 相似文献
2.
M. C. Abreu C. Baglin A. Baldisseri A. Baldit C. Barrière M. Bedjidian P. Bordalo A. Bussière P. Busson R. Cases J. Castor T. Chambon C. Charlot B. Chaurand D. Contardo E. Descroix A. Devaux O. Drapier J. Fargeix X. Felgeyrolles R. Ferreira P. Force L. Fredj J. M. Gago C. Gerschel P. Gorodetzky B. Grosdidier J. Y. Grossiord A. Guichard J. P. Guillaud R. Haroutunian D. Jouan L. Kluberg R. Kossakowski G. Landaud P. Liaud C. Lourenço S. Papillon L. Peralta J. R. Pizzi C. Racca S. Ramos A. Romana R. A. Salmeron P. Sonderegger F. Staley S. Silva X. Tarrago J. Varela F. Vazeille 《Zeitschrift fur Physik C Particles and Fields》1992,55(3):365-371
Meson production in proton, oxygen and sulphur interactions with uranium targets at 200 GeV/nucleon is studied. We measure the inclusive meson cross-section d /dP
T
2
and its evolution fromp+U to S+U. The cross-section fitted with an exponential gives an inverse slopeP
T0 of the order of 210 MeV/c. As a function of the neutral transverse energy,P
T0 values show a slight rise followed by a plateau. The normalized difference (+––)/– between positive and negative meson cross-sections is found to increase withE
T
.also at ISEL 相似文献
3.
Ross Graham 《Journal of statistical physics》1982,29(2):177-183
We establish the following new correlation inequalities for the truncated twopoint function of an Ising ferromagnet in a positive external field:
j
;
l
T
j
;
k
T
k
;
l
T
, and
j
;
l
T
k K
j
;
k
T
k
l
, whereK is any set of sites which separatesj froml. The inequalities are also valid for the pure phases with zero magnetic field at all temperatures. Above the critical temperature they reduce to known inequalities of Griffiths and Simon, respectively.NSERC Postgraduate Fellow, 1978–1981. Research supported in part by NSF Grant No. PHY-78-25390-A02. 相似文献
4.
We find the asymptotic decrease of correlations <
A +y
,
B
>,yZ
v
+1, |y|, in the Ising model at high temperatures. For the case when monomials
A
and
B
both are odd, using the saddle-point method, we find the asymptotics of the correlations for any dimension . For even monomials
A
,
B
we formulate a general hypothesis about the form of the asymptotics and confirm it in two cases: (1) =1 and the vectory has an arbitrary direction, (2)y is directed along a fixed axis and arbitrary . Here we use besides the saddle-point method, some arguments from scattering theory. 相似文献
5.
We report the first measurement of the total charge-loss cross section tot=em+nuc and partial cross sections (for Z=1, 2, ..., 9) of 11.4 A GeV197Au nuclei in various targets. The large Coulomb barrier for Au reduces the electromagnetic contribution em in a Pb target to only 18% of nuc, compared with 70% for 14.5 A GeV28Si and 120% for 200 A GeV32S. With em taken to be Z
T
1.8
, nuc can be fitted with nuc=(A
P
1/3
+A
T
1/3
–b)2, with b=0.83 and =59 mb, essentially the same as found at energies of 1 to 2 A GeV. Electromagnetic partial cross sections for Z=1 exceed 40 mb in the Pb, Sn, Cu, and Fe targets and are substantial for larger values ofZ in the heavier targets.We are indebted to D. Beavis and the staff of the Alternating Gradient Synchrotron at Brookhaven National Laboratory for producing the beam of 11.4 A GeV Au ions, to D. Snowden-Ifft for his efforts in developing the automated scanning system, and to S. Hirzebruch for a useful discussion. This work was supported in part by the Office of Energy Research, Office of High Energy and Nuclear Physics, Division of High Energy Physics, of the Department of Energy under contract No. DEAC03-76SF00098. 相似文献
6.
We have studied the voltage distribution for a two-component random mixture of conductances a and b. A scaling theory is developed for the moments of the distribution, which predicts, for small values ofh=a/b, an infinite number of crossover exponents, one for each moment, for Euclidean dimensiond >2, and only one crossover exponent ford=2. Monte Carlo results on the square lattice confirm this prediction. 相似文献
7.
The effective conductivity
* of an infinitely interchangeable two-component random medium is considered. This class of media includes cell materials in the continuum and the bond lattice on
d
, where the cells or bonds are randomly assigned the conductivities
1 and
2 (
1,
2ne0) with probabilitiesp
1 andp
2=1–p
1. A rigorous basis for the very old and widely used low volume fraction expansion of
* is established, by proving that
* is an analytic function ofp
2 in a suitable domain containing [0, 1]. In the case of the bond lattice ind=2, rigorous fourth-order upper and lower bounds on
* valid for allp
2,
1, and
2 are derived. The four perturbation coefficients entering into the bounds are obtained from the first-order volume fraction coefficient using the method of infinite interchangeability. 相似文献
8.
An analytical expression for the two-frequency correlation function of reflected radiation
is derived in the framework of the Kirchhoff approximation, assuming that the mean square roughness heights 1,2 of the upper (1) and lower (2) boundaries are large compared to the wavelength and taking account of large-scale permittivity fluctuations in the layer. The condition under which p cannot be small when
i
2
2 is specified. In particular, it is shown that if the scattering is only at the upper boundary of the layer (when 1 0, 2 = = 0), then this condition is
, where m, n=0, 1,.... The potential of the layered medium sounding methods based on the relations obtained is estimated.Institute of Physics, State University, Rostov-on-Don. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 7, pp. 619–630, July, 1995. 相似文献
9.
Self-diffusion coefficients of vanadium in the FeV -phase and in the corresponding -solid solution (Fe-47 wt.% V) measured in the temperature ranges 1002–1115 °C (-phase) and 1230–1320 °C are reported. The found results differ fundamentally and significantly from the relations in ordered and disordered solid solutions [9]. The diffusivity in -phase at the transition temperature (T
/=1200 °C) is cca 14 times lower than the diffusivity in the b.c.c. solid solution, the chemical composition of which is the same. The lowering is caused by the different values of frequency factors,D
O=0.11 cm2/s andD
O=45 cm2/s. The effect of the corresponding activation enthalpiesH
=252 kJ/mole andH
=293 kJ/mole is small and quite opposite. The occurence of higher activation enthalpyH
in the -solid solution at temperaturesT>T
/ may be attributed to a certain amount of the f.c.c. phase coexisting in the b.c.c. matrix at concentrationsc
v>27 wt.% at sufficiently high temperatures [7]. A comparison of vanadium self-diffusion characteristics measured in the -phase to the extrapolated values obtained on the basis of the previous measurements [1] in the Fe-V primary solid solutions 1 shows that the diffusivity ratioD
1/D
(1473 K)=33 and that the activation enthalpyH
is by about 3% higher than the valuesH
1 (eq. (5)) measured in the uniphase b.c.c. solid solutions. 相似文献
10.
We present exact explicit expressions for the row spin-spin correlation functions
00
n0 in the isotropicd= 2 Ising model, in terms of elliptic integrals, forn 5. We also give a general structural formula for
00
n0. 相似文献
11.
Th. Frommhold F. Steiper W. Henkel U. Kneissl J. Ahrens R. Beck J. Peise M. Schmitz I. Anthony J. D. Kellie S. J. Hall G. J. Miller 《Zeitschrift für Physik A Hadrons and Nuclei》1994,350(3):249-261
The total photofission cross section ,F
for235U and238U has been measured in the energy range 50E
800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 4 arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section F
, which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections ,F
normalized to the atomic numberA for both isotopes coincide, and agree in the-resonance region, within the systematic errors, with the socalledUniversal Curve ,T
/A of the total photon absorption cross section ,T
. At higher energies the cross sections exhibit a smooth behaviour. In particular, it is shown for the first time that there isno resonance-like shape near the D13 resonance (at 710 MeV) as observed for the free proton. This complete suppression of the D13 resonance in complex nuclei is not yet understood on a microscopic level. The fragment mass distributions show a predominantly mass symmetric fission. However, contributions from mass asymmetric fission at some photon energies may give a hint of an increased mass asymmetric fission after the onset of the pion and two pion channels.Excerpt from D26 Supported by the Deutsche Forschungsgemeinschaft, SFB 201 Mainz 相似文献
12.
The non-linear distribution of lattice strain
310vs sin2
observed on the surface of a polished steel specimen can be interpreted by tri-axial stress state with surface components of stress tensor
11(0)=
22(0) and gradientsg
11=
11/T, g
33=
33/T. The distribution of experimental values
is duscussed from the viewpoint of various ways of calculating
11.The authors would like to thank Dr. J. Musil, D. Sc. of the Institute of Physics of Czechoslovak Academy of Sciences for kindly providing the samples which made possible this study. 相似文献
13.
The couplings of conventional and hybrid mesons to (real and virtual) and their production amplitudes in M are described in a unified manner. Existing results for heavy quarks are recovered, extensions to light quarks and to virtual couplings are made and phenomenological applications discussed. In particular we discuss relativistic corrections to 0+, 1+, 2+ for both real and virtual photons and offer a resolution to a long standing puzzle in perturbative QCD concerning the helicity structure of 2++. We suggest that the production off
2 (1720) involves gluons in an essential way or that this meson hasJ2. 相似文献
14.
Orlin Stoytchev 《Letters in Mathematical Physics》1993,27(1):43-50
Every normal, faithful, self-adjoint functional on a von Neumann algebraA canonically determines a one-parameter-weakly continuous *-automorphism group
(the analog of the modular group) and a canonical 2 grading onA, commuting with
. We show that the functional satisfies the weak super-KMS property with respect to
and Furthermore, we prove that
and are the unique pair of a-weakly continuous one-parameter *-automorphism group and a grading of the algebra, commuting with each other, with respect to which is weakly super-KMS. The above results thus provide a complete extension of the theory of Tomita and Takesaki to the nonpositive case.Supported in part by the National Science Foundation under Grant DMS-8922002. 相似文献
15.
The stress F due to friction forces in copper-based solid solutions was determined. Under the conditions of the procedure used to measure F, on the basis of the half-wave hysteresis with polycrystalline samples, the value of d: F = F0 + KFd–(1/2) where F0 is the resistance to dislocation motion in an alloy having an infinite grain size, and KF is a constant. It is shown that F0 is governed by the interaction of moving dislocations with impurity atoms in the case of a statistically disordered atomic distribution. A study was made of the effects of various factors on F and of the nature of the changes in F0 caused by alloying.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No.3, pp. 18–23, March, 1971. 相似文献
16.
M. A. Afifi H. H. Labib M. H. El-Fazary M. Fadel 《Applied Physics A: Materials Science & Processing》1992,55(2):167-169
The dc and thermal conductivities of five different compositions of the chalcogenide glass system Se75Ge25–x
Sb
x
have been studied in a temperature range below T
g. The dc conductivity results indicate that each composition has a single activation energy in the considered temperature range. The coefficient of thermal conductivity increased linearly with temperature below T
g for the compositions investigated. The increase of Sb content in the chalcogenide glass system leads to an increased coefficient of electrical conductivity , an increased coefficient of thermal conductivity , and to a decreased activation energy E
and pre-exponential factor 0. The observed compositional dependencies of and E
have been correlated with the increase of weak bond density and the decrease of covalent bond density in the structure of the compositions investigated with increasing Sb content at the expense of Ge content. The decrease in 0 and the increase in has been, respectively, correlated with the decrease in mobility and the increase in phonon velocity. 相似文献
17.
An expression for the heat conductivity
xx
is derived in the effective medium approximation. Mott type formulas are obtained for
xx
and the Peltier coefficient
xx
. Using percolation theory in a three-dimensional system the Wiedemann-Franz ratio was found to depend on the temperature like
. The Mott type formulas were evaluated in a similar way for a two-dimensional system in the quantum Hall regime within the high-field percolation model. In contrast to previous calculations of the high field hopping conductivity
xx
, the results are fully consistent with the experimental data on
xx
and the density of states at the Fermi level. Finally,
xx
is estimated which together with
xx
and
xy
=ie
2/h(i=0,1,2,...), determines both thermopower coefficients
xx
and
xy
.Dedicated to Professor W. Brenig on the occasion of his 60th birthday 相似文献
18.
A. Möbius 《Zeitschrift für Physik B Condensed Matter》1990,79(2):265-273
A detailed phenomenological re-analysis of previously published conductivity data, (T, x), is presented. It is based on the investigation of differences, (T, x
1)–(T, x
2). In this way, the cusp-like low-temperature term is amplified against the other temperature dependent contributions. This term can be described by
wherep=0.19±0.03. It is present, if (4.2 K,x) exceeds 260 –1 cm–1, at least up to (4.2 K,x)1350 –1 cm–1 and forT60 K. But it is absent, if (4.2 K,x)180 –1 cm–1. The disappearance of this contribution should be related to the metal-semiconductor transition, taking place atx
c
0.14. On the other hand, the presence of a term proportional toT
1/2, as predicted by Altshuler and Aronov, seems unlikely.It is argued that the term
should be related to the interplay of electron-electron interaction and disorder. The comparison with data from the literature shows that this contribution might also be present in heavily doped crystalline semiconductors. 相似文献
19.
Elliott H. Lieb 《Communications in Mathematical Physics》1980,77(2):127-135
A general formulation is given of Simon's Ising model inequality:
whereB is any set of spins separating from . We show that
b
can be replaced by
b
A
whereA is the spin system insideB containing . An advantage of this is that a finite algorithm can be given to compute the transition temperature to any desired accuracy. The analogous inequality for plane rotors is shown to hold if a certain conjecture can be proved. This conjecture is indeed verified in the simplest case, and leads to an upper bound on the critical temperature. (The conjecture has been proved in general by Rivasseau. See notes added in proof.)Work partially supported by U.S. National Science Foundation grant PHY-7825390 A01 相似文献
20.
We consider the 4 quantum field theory in two and three spacetime dimensions. In the single phase region the physical mass (inverse correlation length)m() decreases continuously to zero as the bare mass parameter approaches a critical value
c
from above. In three dimensions the critical point
c
is in the single phase region and the physical mass vanishes there,m(
c
)=0.A consequence of our results is that the critical exponentv governing the approach to infinite correlations is bounded below (rigorously) by its classical value, 1/2.Supported in part by the National Science Foundation under Grant MPS74-13252 相似文献