Основные соотношени я длн построения механических селект оров нейтронов

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Spin manifolds,killing spinors and universality of the Hijazi inequality

In terms of the Dirac operator P, we introduce on any field a first-order operator D and show that the operator (–) on the spinors (=(n/4(n–1))R; dim W=n) is positive. By means of a universal formula, we show that, on a compact spin manifold of dimension 3, the Hijazi inequality [8] holds for every spinor field such that (P, P) = ²(, ) (=const.). In the limiting case, the manifold admits a Killing spinor which can be evaluated in terms of . Different properties of spin manifolds admitting Killing spinors are proved. D is nothing but the twistor operator.     

Continuously Varying Exponents in a Sandpile Model with Dissipation Near Surface

We consider the directed Abelian sandpile model in the presence of sink sites whose density f_t at depth t below the top surface varies as ct^–. For >1 the disorder is irrelevant. For <1, it is relevant and the model is no longer critical for any nonzero c. For =1 the exponents of the avalanche distributions depend continuously on the amplitude c of the disorder. We calculate this dependence exactly, and verify the results with simulations.     

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.     

Propagation of elastoplastic waves in thin rods

The problem of the propagation of a perturbation in a thin rod is solved using the dynamic gauge theory of crystalline media with dislocations. When a shock is applied to the rod an elastic forerunner is generated with propagates with a velocity of (where E is Young's modulus and is the density of the medium) and, in addition, unclamping of the end of the rod occurs. Depending on the parameters of the medium, this unclamping may take the form of both purely viscous flow and wave flow. There is no volume elastic compression wave in the rod characteristic of an unbounded medium.Institute of Physics of the Strength and Study of Materials, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 39–42, June, 1994.     

Development of an electrical discharge in strongly overstressed gaps with a low air pressure

The time of switching, step length and delay time of a discharge were investigated in this present project, under the following experimental conditions: plain brass electrodes, two- to 20-fold overvoltage and air pressure 30 mm Hg. In addition, the relative intensity of bremsstrahlung from the anode was measured and the-quanta energy was determined by the radiation attenuation method in aluminum plates. It is suggested that such short delay times obtained can be explained first of all by the accelerated motion of electrons and secondly by the bremsstrahlung from the anode.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 61–65, January, 1973.     

Properties of a weak link with tunable strength in a quasi-one-dimensional superconductor

In a superconducting whisker a region of weakened superconductivity (weak link) has been induced by a second crystal carrying a control current and crossing the first one. By varying the control current the grade of weakness could be continuously adjusted and its influence on the voltage-current characteristics of the weak link could be investigated.     

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.     

Surface channeling of protons and electrons on reflection by a single crystal

Computer modeling is used to investigate the reflection of 0.67-MeV protons and 1-MeV electrons by the (110) face of an Au single crystal for angles of divergence < _cr of the incident beam with the direction 110 lying in the surface. The angular distributions and reflection coefficients of protons and electrons are compared. Several maxima are found in the angular distributions. In additon to the specular-reflection maximum at = there is a maximum at > for protons and a maximum at < for electrons. The maxima in the angular distributions are attributed to multiple scattering at atomic chains of the crystal surface. An analytic approximation of the reflection coefficient for protons K_cor() is given. The great contribution to the reflected flux from particles channeled in the surface layer allows it to be used for structural analysis of crystal surfaces.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 85–90, March, 1979.     

A new high frequency “relaxation window” for measuring molecular field fluctuations

We report a new Mössbauer relaxation window which allows the fluctuation rate of a molecular field acting on an impurity in a strongly correlated spin system to be obtained. For a molecular field of 1 T, the fluctuation rate can be measured up to 10 THz, which is three orders of magnitude higher than for the classical relaxation window. The calculated line shapes show that Ising-like fluctuations of the molecular field can be distinguished from other types of fluctuations (in-plane or in space). An application and some other possible uses of this new relaxation window are discussed.     

Der Einfluss der Metallbedeckung auf die Supraleitenden Eigenschaften von Dünnen Zylindern

The critical parameters (upper critical field, critical temperature) of a thin type II superconducting cylinders are considerably changed by coating with normal metal. Below a minimum cylinder radius, the superconductivity can no longer exist. The oscillations of the critical temperature with magnetic field are also modified. For good conductive metals, only an aperiodic effect appears. The decrease of the critical temperature produced by coating is given. The thin-film quantization effects the existence of jumps in the field dependence of the critical temperature.     

The effect of microsegregation on the generation of dislocations in zinc single crystals

The applicability of Tiller's considerations on the production of dislocations is proved. The density of dislocations appearing during impurity microsegregation increases with increasing rate of growth as a consequence of the corresponding change in the effective distribution coefficient. The real value of C at the microsegregation boundaries is at least twice as great as the average value of the concentration of impurities in the crystal in question.

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A hollow cathode bismuth ion laser

cw laser oscillations of Bi II at 680.9, 660.0, and 571.9 nm have been achieved for the first time by using a bismuth hollow cathode discharge. In addition, laser oscillations of Bi I at 1.1711 m in the afterglow were observed. The ionic laser lines are excited by Penning ionization. The atomic line is produced by recombination of the bismuth ions and lowenergy electrons in the afterglow.     

Final dt stickingω s using the “survived moun method”

A new direct measurement of the final dt sticking probability _s using a special data analysis called the survived muon method is presented. The data were obtained at PSI using a high pressure ionization chamber with H/D/T gas mixtures. The method can provide information on final sticking dt +n independent of theoretical models of stripping and initial sticking. It was found: _s=(0.57±0.07±0.02)%. The experiment and the analysis method are discussed in detail.     

Металлографические методы определепия нлотности дислокаци й В монокристаллах германия

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The quasilinear theory of two-stream cyclotron instability of electron beams

The paper is devoted to a study of cyclotron instability ( _e) of two opposite beams of electrons from the aspect of the quasilinear effects. For this case of instability the authors evolve the diffusion equation in the velocity space for an averaged distribution function. They estimate the relaxation times , _z of the spreading of the distribution function in the velocity space. At the end of the paper, they compare their results with an experiment described by M. Seidl and P. unka [Phys. Letters11 (1964), 31].     

Superconducting surface resistance of thin amorphous Ga films on metallic substrates

The surface resistance of a metal coated with amorphous superconducting films is investigated. With an improved microwave cryostat and a two layer model considering the influence of the substrate, much thinner films can be used than previously. As an example the surface resistance of amorphous Ga is determined. A set of parameters ₀/k _BT_c=2,27; _L=13,4 nm; ₀=223 nm andl=1,0 nm describes the temperature dependence independent of thickness. As expected a model of free electrons is in agreement with the experimental results. For crystalline-Ga ₀/k _B T _c =1,91; _L=24 nm; ₀=163 nm and a much larger mean free pathl=22 nm is found.     

Experimental survey of the sticking problem in muon catalyzed dt fusion

The sticking process dt + n, which constitutes the most severe limit to the number of fusions which a muon can catalyze, is reviewed. Many attempts were made to determine by calculations and measurements the probability for initial sticking _s ⁰ (immediately after dt fusion) and for final sticking _s (after the came to rest). Previous results based on neutron disappearance rates and on the observation of -X-rays were controversial and also in some disagreement with theory. New data are reported from PSI on direct observation of final sticking, using a setup with the St. Petersburg ionization chamber. These data mark a significant improvement in reliability and may clarify questions concerning previous discrepancies. The new results is _s(0.56±0.04)%, lower than the theory prediction _s=(0.65±0.03)%, at medium density.     

Corner transfer matrices of the eight-vertex model. I. Low-temperature expansions and conjectured properties

A corner transfer matrix (CTM) is defined for the zero-field, eight-vertex model on the square lattice. Its logarithm and its diagonal form are obtained to second order in a perturbation expansion of low-temperature type. They turn out to have a very simple form, apart from certain remainder contributions that can be ignored in the limit of a large lattice. It is conjectured that in this limit the operators have these simple forms for all temperatures less than the critical temperatureT _c. The spontaneous magnetization can then easily be obtained, and agrees with the expression previously proposed. It is intended to prove some of the conjectures in subsequent papers.     

Making Sense of a World of Clicks

In a recent article, O. Ulfbeck and A. Bohr [Found. Phys. 31, 757 (2001)] have stressed the genuine fortuitousness of detector clicks, which has also been pointed out, in different terms, by the present author [Am. J. Phys. 68, 728 (2000)]. In spite of this basic agreement, the present article raises objections to the presuppositions and conclusions of Ulfbeck and Bohr, in particular their rejection of the terminology of indefinite variables, their identification of reality with the world of experience, their identification of experience with what takes place on the spacetime scene, and the claim that their interpretation of quantum mechanics is entirely liberated from classical notions. An alternative way of making sense of a world of uncaused clicks is presented. This does not invoke experience but deals with a free-standing reality, is not fettered by classical conceptions of space and time but introduces adequate ways of thinking about the spatiotemporal aspects of the quantum world, and does not reject indefinite variables but clarifies the implications of their existence.