Radiative E1 decay of the1P1 level of charmonium in the sum rules of quantum chromodynamics

An analysis of the radiative decay¹P₁ ¹S₀ + of charmonium is performed by using the sum rules of quantum chromodynamics (QCD). A sum rule that allows for luon power corrections is obtained, and the decay width _c + is computed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 80–84, November, 1991.Finally, the author express thanks to professor R. N. Faustov for valuable advice and useful discussion of the resulting work.     

Large-Deviation Principle for One-Dimensional Vector Spin Models with Kac Potentials

We consider the one-dimensional planar rotator and classical Heisenberg models with a ferromagnetic Kac potential J (r)=J(yr), J with compact support. Below the Lebowitz-Penrose critical temperature the limit (mean-field) theory exhibits a phase transition with a continuum of equilibrium states, indexed by the magnetization vectors m s, s any unit vector and m the Curie–Weiss spontaneous magnetization. We prove a large-deviation principle for the associated Gibbs measures. Then we study the system in the limit 0 below the above critical temperature. We prove that the norm of the empirical spin average in blocks of order ^–1 converges to m , uniformly in intervals of order ^–p , for any p 1. We also give a lower bound to the scale on which the change of phase occurs, by showing that the empirical spin average is approximately constant on intervals having length of order ^-1-with (0,1) small enough.     

The effects of inkomogeneous center structure on the shape of the ESR spectra of alkali-rich glasses

The paper considers the effect of nonuniform structure in the centers on the ESR spectrum for the case of axial anisotropy in the g factor; it is shown that if (² >² , _¦ >), the model enables one to describe fairly completely the spectrum of a glass containing 33% Na₂O and 67% SiO₂. Good agreement with all experimental evidence is not obtained for potassium silicate glasses.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 86–90, June, 1971.     

Instability in degenerate two-photon running wave laser with detuning

The previous stability analysis of the degenerate two-photon running wave laser is extended to the inclusion of detuning between frequencies of cavity and atoms. We derive the analytical equation for the critical pumping and prove analytically that for the special case ofr (/) being unity, there is no Hopf bifurcation instability for the bad cavity. The good cavity case is analysed numerically. The role played by detuning is to raise the critical pumping. In the case ofk (or <K) where there is no Hopf bifurcation instability for the perfect tuning case, the large detuning can give rise to self-pulsing instability.     

Generalized Stefan-Boltzmann law

Thermodynamics arguments have been employed to derive how the energy density depends on the temperatureT for a fluid whose pressurep obeys the equation of statep = ( –1), where is a constant. Three different methods, among them the one considered by Boltzmann (Carnot cycle), lead to the expression = T/( –1), where is a constant. This result also appears naturally in the framework of general relativity for spacetimes with constant spatial curvature. Some particular cases are vacuum (p = –), cosmic strings (p= –1/3), radiation (p = 1/3), and stiff matter (p = ). It is also shown that such results can be adapted for blackbody radiation inN spatial dimensions.     

Investigation of the (n, γf) process on a235U nucleus

The fluctuations of uranium X-rays yield in coincidence with fission of the²³⁵U nucleus were observed at several neutron resonances. The results show the dependence ofK ₁ yield on fission width _f. This dependence is explained by the (n, f) process which is the result of competition between fission and -decay during the deexcitation of the²³⁶U compound nucleus. The mean width _f was determined to be equal to (2·1 _–1·7 ^+1·5 ) meV. The mean energy of prefission-rays was found to be (750 _–130 ⁺⁴⁰⁰ ) keV. It seems that the -transitions taking place before fission of the²³⁶U compound nucleus are mostly of the magnetic dipole.It is a great pleasure to express our gratitude to Yu. I. Kolgin for considerable help in all the experimental work, to L. B. Pikelner and Yu. P. Popov for many useful discussions, I. M. Salamatin, A. Mateeva for the programme supply of the experiment, to A. A. Bogdzel and V. G. Tishin for taking part in different steps of the work.     

Role of Activator and Vacancy Centers in the Decay of the Gamma Scintillators of CsI–Na Crystals

The influence of the concentration of an activator (C _NaI) and of plastic deformation on a change in the contribution of a slow component to the decay of the -scintillations of CsI–Na crystals was investigated, as well as the influence of C _NaI on a change in the shape of the luminescence excitation spectrum in the region of absorption of activator centers (AC) and of vacancy-related centers (VRC) and also on a change in the intercenter time of deexcitation of the centers indicated. It is shown that AC and VRC participate in the photoluminescence and -scintillations of CsI–Na crystals. In the -scintillations, AC are responsible for the component ₁ = 370 nsec, whereas the components ₁ = 460 nsec and ₂ 2 sec are associated with VRC. The reduction of ₁ from 770 to 560 nsec with an increase in C _NaI from 2·10^–3 to 3·10^–2 mole% and from 570 to 470 nsec after plastic deformation of the crystals ( = 5%) along the 111 axis is caused by a decrease in the number of VRC. The mechanisms underlying the -scintillations of the CaI–Na crystals containing AC and VRC and also the decrease in the number of VRC are discussed.     

Computational study of propagating fronts in a Lattice-gas model

Velocities and other features of propagating fronts in the lattice-gas model analyzed by Bramsonet al. are computed by Monte Carlo simulation. The propagation velocity() is found to converge slowly to its asymptotic dependence on the exchange-rate parameter. The number density of occupied sites in the interaction zone (extending from the forwardmost occupied to the rearmost unoccupied site) appears to converge to 2/3 for large. Spatial profiles of site occupancy and interface number density for finite are compared to the profiles originally computed by Fisher using the differential equation obeyed in the large- limit. Several significant features inferred from the computations have not yet been explained analytically.     

Interpretation of the a0(980) meson as a four-quark system

Quantum chromodynamics methods are used to calculate the section of the reaction a₀ ⁰ with formation as an intermediate state of the meson a₀(980), which is interpreted as a bound state of two quark-antiquark pairs, formed upon dissociation of two virtual photons, with which an electron and positron are exchanged in incident e^–- and e⁺-beams. It is shown that the a₀ 2⁰ decay is significantly more suppressed than the a₀ ⁰ decay.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 19–23, July, 1991.     

Structural stability properties of friedman cosmology

A dynamical system with Robertson-Walker symmetries and the equation of the statep=, 01, considered both as a conservative and nonconservative system, is studied with respect to its structural stability properties. Different cases are shown and analyzed on the phase space (x=R ^D , y=x).     

Baryon decays and gamma-spectroscopy of hypernuclei

The applicability of (K ^–,^–) - and (K ^–,^– N)-reactions on^13,14C and^14,15N nuclei to the study of -transitions in primary and daughter -hypernuclei is discussed. The intensity of -deexcitation of ¹³C state |S ¹²C(15·11 MeV; 1⁺1): 1/2⁺ has been shown to be comparable with the intensity of baryon decay. Isospin selection rules are used to distinguish excitation energy ranges of primary hypernuclei, where the identification of the secondary -lines is probable.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

High-spin isomer in 93Mo

The high-spin states of ⁹³Mo have been studied by a ⁸²Se( ¹⁶O, 5n) ⁹³Mo reaction at a beam energy of 100 MeV using techniques of in-beam -ray spectroscopy. Measurements of -t, --t coincidences, -ray angular distributions and -ray linear polarizations were performed. The high-spin isomer was found as a (39/2^-) state at about 9.7 MeV. The near-yrast states in ⁹³Mo were interpreted using the weak-coupling picture of a d_5/2 neutron to a neutron magic core nucleus ⁹²Mo.     

Electrovac fields with geodesic eigenrays

The stationary states of electrovac fields for which the geodesic eigenrays of both the Maxwell and gravitational field coincide are investigated. The fact that the Kerr-Newman solutions belong to this class lends physical interest to the fields considered here. Particular attention is devoted to fields with shearing eigenrays since principal null congruences do not coincide with eigenrays in this case, and so earlier approaches to the problem fail. By the generalisation of a theorem on the corresponding vacuum case, it is proven that no spherical solutions exist in the shearing class, with the exception of the fields with ²¦G_O¦²-¦H_O¦²=O.The metrics with O, admitted by the theorem, can either be calculated from the corresponding vacuum solutions by a relatively simple procedure, or, if not, we list them explicitly in this paper.     

Stochastic Schrödinger operators and Jacobi matrices on the strip

We discuss stochastic Schrödinger operators and Jacobi matrices with wave functions, taking values in ^l so there are 2l Lyaponov exponents ₁..._l0 _l+1..._2l =–₁. Our results include the fact that if ₁=0 on a set positive measure, thenV is deterministic and one that says that {E|exactly 2j 's are zero} is the essential support of the a.c. spectrum of multiplicity 2j.Research partially supported by USNSF under grant DMS-8416049     

The magnetic moment of103Ru

The nuclear magnetic moment of¹⁰³Ru has been determined using the technique of low-temperature nuclear orientation on¹⁰³Ru as a dilute impurity in Fe. The Fe lattice was cooled to 1.7 mK using a PrNi₅ enhanced nuclear demagnetisation stage precooled with a³He–⁴He dilution refrigerator. The¹⁰³RuFe system was observed to have a long nuclear spin-lattice relaxation time, but analysis of the relaxation indicates that the¹⁰³Ru nuclei are close to thermal equilibrium with the Fe lattice at times>200 min after demagnetising. From the near thermal equilibrium anisotropy of the 497 keV -ray in¹⁰³Rh we have deduced the nuclear magnetic moment as |(¹⁰³Ru)|=0.18(2)_N. This value is almost independent of the choice of spinI=3/2 or 5/2 for the nucleus, but is only consistent with systematics ifI(¹⁰³Ru)=3/2 and <0. UsingI=3/2 we obtain the E2/M1 mixing ratio of the 497 keV -ray as =–0.42(4). The sign of the anisotropy of the 610 keV -ray from the 650 keV level in¹⁰³Rh is only consistent with an allowed -decay to the state ifI(650 keV,¹⁰³Rh)=5/2. The E2/M1 mixing ratio of the 610 keV -ray is then =+0.15(3) or +60( _–40 ⁺ ), <–80. From the initial rise in -ray anisotropy following demagnetisation we determine the Korringa constant for¹⁰³RuFe to beC=5.7(5) K·s.     

Note on the susceptibility exponent for two-dimensional percolation

Analyses of mean site content, mean bond content, mean perimeter and related quantities give a susceptibility diverging as (p _c –p)^–, with 2.41±0.025. This exponent disagrees with some earlier estimates but it is consistent with the (p _c –p)^–2.388... divergence predicted by the formulas of den Nijs, Nienhuis et al. and Pearson.     

Prompt gamma-ray emission from fission of239Pu by resonance neutrons I

Gamma-ray spectra from²³⁹Pu(n,f) reaction were measured with the gamma spectrometer on the pulsed reactor IBR-30. The fast 19-section ionization chamber with 1.6 g of²³⁹Pu targets was used. The fission gamma-rays within the 32 ns time window were measured using a Ge(Li) detector. Based on the measured gamma-ray spectrum in the (0.1–1.8) MeV interval, the total number of emitted-quanta-multiplicity N ^tot and total energy of -quanta per fission event, E ^tot , were calculated. The results were 7.0±0.6/fission and 6.8±0.5 MeV/fission respectively.This work is supported in part by the Grant Agency of the Slovak Academy of Science under grant GA-SAV 517/1992.     

Electric field gradient at the Hf site and the phase transition in HfV2

The electric quadrupole interaction at the Hf site in the cubic HfV₂ compound, which shows lattice instability when cooled below 120 K, has been studied using the 482 keV (5/2⁺) state in¹⁸¹Ta. The time differential perturbed angular correlation (TDPAC) studies involving (133+136)-482 keV - cascade at room temperature show that only a fraction of¹⁸¹Ta nuclei see a cubic symmetry while the remaining experience a weak, randomly oriented, electric quadrupole interaction described by a Gaussian frequency distribution with _Q=6.1±1.0 Mrad/sec and the relative width =0.5. There is a dramatic change in TDPAC pattern indicating a phase transition when the compound is cooled down to 77 K. At this temperature the quadrupole interaction frequency is found to be _Q=40.6±3.0 Mrad/sec with =0.35. The experimentally observed EFG both at the Hf and the V sites are compared to the theoretical estimates based on point charge model.     

Some critical exponent inequalities for percolation

For a large class of independent (site or bond, short- or long-range) percolation models, we show the following: (1) If the percolation densityP (p) is discontinuous atp _c , then the critical exponent (defined by the divergence of expected cluster size, nP _n (p) (P _c –P)^– asp p _c ) must satisfy 2. (2) or (defined analogously to, but asp p _c ) and [P _n (p _c ) (n ^–1–1/) asn ] must satisfy, 2(1 – 1/). These inequalities for improve the previously known bound 1(Aizenman and Newman), since 2 (Aizenman and Barsky). Additionally, result 1may be useful, in standardd-dimensional percolation, for proving rigorously (ind>2) that, as expected,P _x has no discontinuity atp _c .