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1.
Self-consistent solutions of the nonlinear Ginzburg-Landau (GL) equations are investigated numerically for a superconducting (SC) cylinder, placed in an axial magnetic field, with a single vortex on the axis (m=1). Two modes, which show the original state of the cylinder, SC or normal (s 0 andn 0), are studied. The field increase (FI) and the field decrease (FD) regimes are studied. The critical fields destroying the SC state withm=1 are found in both regimes. It is shown that in a cylinder of radiusR and GL-parameter ϰ, there exist a number of solutions depending only on the radial co-ordinater corresponding to different states such as M,e, d, p,i, n, ,n *, and the state diagram on the plane of the variables (ϰ,R) is described. The critical fields corresponding to intrastate transitions and the onset of hysteresis are obtained. The critical fieldH 0(R) dividing the paramagnetic and diamagnetic states of the cylinder withm=1 is determined. The limiting fields of supercooling or superheating of the normal state at which the restoration of the SC state occurs are established. It is shown, that (in both casesm=1,0) there exist two critical parameters, and , which divide bulk SC into three groups (with and ), in accordance with the behavior in a magnetic field. The parameters and mark the boundary for the existence of a supercooled normal -state in FD-regime and a superheated SC M-state in FI-regime respectively. It is shown, that the value , which was claimed in a number of papers as related to type-I superconductors, is illusory. We regret to inform that Professor Gely Zharkov passed away on 9th July 2004.  相似文献   

2.
The maximum number of non-vanishing and independent second order photoelastic coefficients required by the seven pentagonal and the two icosahedral point groups 5(C5), (S10), (C5h ), m2(D5h ), 52(D5), 5m(C5v ), 2m(D5d ); 235(I), 2/m (I h )—that describe the quasicrystals symmetry groups in two and three dimensions—is obtained. The schemes of non-vanishing and independent coefficients have been calculated and listed. Finally the results of this group-theoretical study are briefly discussed.  相似文献   

3.
Let δ be a quasi-free derivation of the CAR algebra, and let be a closed *-derivation which is an extension of δ. We use Price's techniques from [6] to show that if the polynomials in the linear field operators a(f)→a * (f) in D( ) is a core for , then is quasi-free.  相似文献   

4.
The decay time τl ofo-Ps by the electron pickoff process has been measured in polystyrene as a function of molecular weight. For samples below their glass transition temperature τl is essentially independent of . In the low molecular weight region, , τl increased with decreasing in line with earlier theoretical predictions. The overall behaviour reflects closely the dependence of free volume on . The effects of molecular motion on τl are examined and it is concluded that the decay time is insensitive to such motions in polystyrene below the melting point, in contrast to what is observed in polytetrafluoroethylene.  相似文献   

5.
KN sigma commutator has been calculated in the framework of the (6, )+( , 6) model. It is found that though this model could not be discarded in favour of the (3, )+( , 3) or (8, 8) model, a very large value forKN sigma term is required to get a positive value ofπN sigma term.  相似文献   

6.
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 −12 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   

7.
A natural supersymmetric extension is defined of the current (= affine Kac-Moody Lie) algebra ; it corresponds to a superconformal and chiral invariant 2-dimensional quantum field theory (QFT), and hence appears as an ingredient in superstring models. All unitary irreducible positive energy representations of are constructed. They extend to unitary representations of the semidirect sumS (G) of with the superconformal algebra of Neveu-Schwarz, for , or of Ramond, for =0.On leave of absence from the Institute for Nuclear Research and Nuclear Energy of the Bulgarian Academy of Sciences, BG-1184 Sofia, Bulgaria  相似文献   

8.
A K Giri  L Maharana  R Mohanta 《Pramana》1996,46(1):41-50
An estimation of the mass difference of system with heavy quark symmetry formalism is presented. The effective Hamiltonian describing the transition (whereh=b forB d 0 -system) is considered in a manifest left right symmetric (MLRS) model along with contribution from neutral Higgs boson. We use the spin and flavor symmetry for heavy quarks to obtain the transition matrix element 〈B d 0 |ℋeff(x)| d 0 〉 in terms of Isgur-Wise function. Assuming thatB d 0 and states are at rest, we find that Isgur-Wise function turns out to be unity. However using the experimental values of ΔM K and as input, we find thatM R=835 GeV andM H⩾2·9 TeV.  相似文献   

9.
We consider an inhomogeneous contact process on a tree of degreek, where the infection rate at any site isλ, the death rate at any site in isδ (with 0 <δ ⩽ 1) and that at any site in is 1. Denote by the critical value for thehomogeneous model (i.e.,δ=1) on and byϑ(δ, λ) the survival probability of the inhomogeneous model on . We prove that whenk > 4, if , a subtree embedded in , with 1 ⩽σ ⩽ √k, then three existsδ c σ strictly between ( ) and 1 such that ( ) whenδ >δ c σ andϑ(δ, λ c( ) > 0 whenδ <δ c σ ; ifS={o}, the origin of , then for anyδ ε (0, 1).  相似文献   

10.
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.
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   

11.
Explicit evaluation of the following parameters has been carried out in the extraU (1) superstring inspired model: (i) As Mz2 varies from 555 GeV to 620 GeV and (m t) CDF = 175.6 ± 5.7 GeV (Table 1): (a) SNew varies from -0.100 ± 0.089 to -0.130 ± 0.090, (b) TNew varies from -0.098 ± 0.097 to -0.129 ± 0.098, (c) UNew varies from -0.229 ± 0.177 to -0.253 ± 0.206, (d) Τz varies from 2.487 ± 0.027 to 2.486 ± 0.027, (e) ALR varies from 0.0125 ± 0.0003 to 0.0126 ± 0.0003, (f) A FB b remains constant at 0.0080 ± 0.0007. Almost identical values are obtained for (m t)D0 = 169 GeV (see table 2). (ii) Triple gauge boson vertices (TGV) contributions: AsMz 2 varies from 555 GeV to 620 GeV and (m t) CDF = 175.6 ±5.7 GeV. (a)√s = 500 GeV, asymptotic case: varies from -0.301 to -0.179; varies from -0.622 to -0.379; varies from +0.0061 to 0.0056; varies from -3.691 to -2.186. varies from +0.270 to +0.118; varies from +0.552 to 0.238; varies from +0.0004 to +0.0002; remains constant at -0.110. (b)√s = 700 GeV, asymptotic case: varies from -0.297 to -0.176; varies from -0.609 to -0.370; varies from -0.0082 to -0.0078; varies from -3.680 to -2.171.√s = 700 GeV, nonasymptotic case: varies from -0.173 to -0.299; varies from-0.343 to -0.591; varies from -0.005 to -0.011; remains constant at -0.110. The pattern of form factors values for√s = 1000, 1200 GeV is almost identical to that of√s= 700 GeV. Further the values of the form factors for (m t)D0 (=169 GeV) follow identical pattern as that of (m t) CDF form factors values (see tables 5, 6, 9, 10). We conclude that the values of all the form factors with the exception of these of , are comparable or larger than theS, T values and therefore the TGV contributions are important while deciding the use of extraU (1) model for doing physics beyond standard model.  相似文献   

12.
Let be a finite-dimensional complex simple Lie algebra and Uq( ) the associated quantum group (q is a nonzero complex number which we assume is transcendental). IfV is a finitedimensional irreducible representation of Uq( ), an affinization ofV is an irreducible representationVV of the quantum affine algebra Uq( ) which containsV with multiplicity one and is such that all other irreducible Uq( )-components ofV have highest weight strictly smaller than the highest weight ofV. There is a natural partial order on the set of Uq( ) classes of affinizations, and we look for the minimal one(s). In earlier papers, we showed that (i) if is of typeA, B, C, F orG, the minimal affinization is unique up to Uq( )-isomorphism; (ii) if is of typeD orE and is not orthogonal to the triple node of the Dynkin diagram of , there are either one or three minimal affinizations (depending on ). In this paper, we show, in contrast to the regular case, that if Uq( ) is of typeD 4 and is orthogonal to the triple node, the number of minimal affinizations has no upper bound independent of .As a by-product of our methods, we disprove a conjecture according to which, if is of typeA n,every affinization is isomorphic to a tensor product of representations of Uq( ) which are irreducible under Uq( ) (in an earlier paper, we proved this conjecture whenn=1).Both authors were partially supported by the NSF, DMS-9207701.  相似文献   

13.
Let be aC*-algebra and be an opposite algebra. Notions of exact andj-positive states of are introduced. It is shown, that any factor state of can be extended to a pure exactj-positive state of . The correspondence generalizes the notion of the purifications map introduced by Powers and Størmer. The factor states 1 and 2 are quasi-equivalent if and only if their purifications and are equivalent.  相似文献   

14.
15.
The surface electronic band structure of the Pb (001) was calculated using the self-consistent, first-principles linear-augmented-plane-wave method and the norm-conserving pseudopotentiai method. In the nonrelativistic case, forbidden gaps appear above and below the Fermi levelin the bulk projected band structure of lead. An occupied surface state at the point and two surface states in a wide forbidden gap above EF are found. A characteristic feature of the electronic structure of the Pb (001) surface is the absence of a surface state within the forbidden S-P gap in the vicinity of the point. The inclusion of scalar-relativistic effects leads to the merger of several S-P gaps into one wide gap extending throughout the entire Brillouin zone. At the same time, the occupied state at point extends to point and its energy decreases by 2 eV. New, relatively weak surface states in the direction and unoccupied states in the vicinity of the point appear. An unoccupied surface state is found at the bottom of the forbidden gap at point . Including the contribution of the spinorbit pseudopotentiai leads to the appearance of two-spin orbit gas; however, the surface level structure is practically unchanged (except for the disappearance of the unoccupied surface state of Pz-symmetry at point ).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 47–53, October, 1991.  相似文献   

16.
Starting from aC*-algebra and a locally compact groupT of automorphisms of we construct a covariance algebra with the property that the corresponding *-representations are in one-to-one correspondence with covariant representations of i.e. *-representations of in which the automorphisms are continuously unitarily implemented. We further construct for relativistic field theory an algebra yielding the *-representations of in which the space time translations have their spectrum contained inV. The problem of denumerable occurence of superselection sectors is formulated as a condition on the spectrum of . Finally we consider the covariance algebra built with space translations alone and show its relevance for the discussion of equilibrium states in statistical mechanics, namely we restore in this framework the equivalence of uniqueness of the vacuum, irreducibility and a weak clustering property.On leave of absence from Istituto di Fisica G. Marconi — Roma.  相似文献   

17.
Summary Frequency distributions of energy deposition in microscopic tissue volumes determined by means of a ?Rossi type? proportional counter for 31, 12 and 8 MeV proton beams and, dose response curves for mortality and chromosome aberrations in cultured human cells exposed to the same beams are analysed with a view to determining suitable parameters to specify radiation quality. The behaviour of quantities LET,Z *22 and the microdosimetric parameter as a function of energy are compared with the corresponding behaviour of the most significant radiobiological parameters as mean lethal dose per targetD 0, mean inactivation dose , intensity of chromosome aberrations, and dicentrics. It is shown that is the most suitable physical parameter to characterize the relative effectiveness of protons in the (8÷31) MeV range. Work partially supported by grant No. 8000165896 for the Finalized Project ?Tumor Growth Control?.  相似文献   

18.
The equilibrium shape ofhcp 4He crystals has been studied at temperatures 0.05≤T≤0.7 K by means of a high precision optical interferometer. We find that the profile of the interfacial boundary, close to an almost horizontal c-facet, has a well-defined slope discontinuity separating two angular regions with different behavior of the surface stiffness. For surfaces tilted by an angle ϕ≤100 μrad with respect to the c-facet, we obtain, contrary to the linear angular dependence predicted by current theories.  相似文献   

19.
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   

20.
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   

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