Image states on beryllium surfaces with low indices

Using the self-consistent pseudopotential method, we have calculated the binding energy of the image states for the (0001) , and surfaces of beryllium. It is shown for the (0001) face that there exists a pronounced resonance image state with n=1 and energy −0.95 eV at the point of the surface Brillouin zone. In the surface, which has a wide band gap in the vicinity of the vacuum level, the calculated image state with n=1 at the point has energy −1.2 eV and is a surface state of gap type. For the face in the vicinity of the point band gaps are absent. However, the symmetry of the bulk states near the vacuum level enables the existence of a resonance image state with n=1 and energy −0.6 eV. Fiz. Tverd. Tela (St. Petersburg) 41, 935–940 (June 1999)     

Present and future experiments in nonequilibrium reactor antineutrino energy spectrum

Considerable efforts that have been undertaken in recent years in low-energy antineutrino experiments require further systematic investigations in line of reactor antineutrino spectroscopy as a metrological basis of these experiments. We consider some effects associated with the nonequilibrium of reactor radiation and residual emission from spent reactor fuel in contemporary experiments. The text was submitted by the authors in English.     

Atomic structure of silver clusters on silicon

The atomic structure of silver clusters formed on a Si(111)-7×7 single crystal surface by annealing a silver thin film condensed at room temperature is investigated by the diffraction of medium-energy quasielastically scattered electrons. Simulation of the diffraction pattern obtained within a nearly complete electron reflection hemisphere shows that the silver islands formed on the silicon have an ordered structure and a fixed orientation relative to the substrate. Close-packed Ag(111) monolayers, which form a face-centered cubic structure, are arranged parallel to the surface, the direction of these microcrystals being antiparallel to the axis of the substrate. Zh. Tekh. Fiz. 67, 62–66 (December 1997)     

Model for the shock actuation of a wedge-shaped nozzle with allowance for detachment of the flow

The motion of the starting gasdynamic discontinuities and of the detached flow arising upon the shock actuation of a wedge-shaped nozzle is examined in the framework of the problem of the decay of an arbitrary discontinuity at a jump in the cross-sectional area of the channel. The results of the calculation are compared with experimental measurements of the spatial and time dependence of the starting discontinuities upon the shock actuation of submerged jets over a wide range of variation of the parameters governing the flow: at pressure ratios and sound velocities of the issuing and immersing gases, for issuing gas species with 1.16<γ<1.67, and for various combinations of these parameters. The possibility of using this model to determine the relaxation time to an undetached supersonic flow in a wedge-shaped nozzle upon the shock actuation of slightly underexpanded and overexpanded jet flows is analyzed. Zh. Tekh. Fiz. 67, 1–4 (June 1997)     

Photoelasticity in quasicrystals

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), (C_5h ), m2(D_5h ), 52(D₅), 5m(C_5v ), 2m(D_5d ); 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.     

Antihydrogen at sub-Kelvin temperatures

We discuss the behavior of magnetically trapped antihydrogen ( ) at temperatures relevant for gravity and spectroscopy experiments (well below 1 K) and the possibilities of attaining these temperatures. Two possible options are considered. In the discussion of the first one, i.e. as admixture in cold H gas, we develop the quantum-mechanical theory of -H (and also -H) elastic and rearrangement collisions at ultra-low (sub-Kelvin) energies, when s-wave scattering in the incoming channel dominates. The rate constant of rearrangement leading to decay turns out to be large, which makes the possibilities for collisional cooling in H gas and -H coexistence rather limited. As we show, the most promising is the other option, i.e. atoms in the collisionless regime. For this regime the possibility of one-dimensional adiabatic cooling of is demonstrated by using the example of the Ioffe trap. This phenomenon, interesting from the fundamental point of view, offers the opportunity to cool below 1 mK.     

A remark on extensions of quasi-free derivations on the CAR-algebra

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.     

Entropy functionals of Kolmogorov-Sinai type and their limit theorems

Two functionals and are introduced forC ^*-dynamical systems with invariant states and stationary channels. It is shown that the Kolmogorov-Sinai-type theorems hold for these functionals and . Our functionals and are set within the framework of quantum information theory and generalize a quantum KS entropy by CNT and the mutual entropy by Ohya.     

The nature of the {\bar p} metastability in helium

A new interpretation of the nature of the metastable states of antiprotons in helium is proposed. The first step is the formation of an ion ( ), which shall be called “ioncule”. After its decay a neutral “atomcule” ( ) is formed which was observed in the experiments on metastable antiprotonic helium. This model explains the experiments in a natural way, in particular the quenching by atomic and molecular admixtures and the pressure dependence of quenching in pure helium. At high helium densities the ioncule creates a vacuum bubble in helium. It is shown that the annihilation of slowed-down can be suppressed at helium pressures of ∼ 10 000 bar. This revised version was published online in August 2006 with corrections to the Cover Date.     

Theoretical analysis of collisional shift and broadening of antiprotonic helium spectral lines

Effect of medium density on shift and broadening of ( ) spectral lines is considered in the framework of binary-collision approximation with an effective ( )–He potential including the long-range attraction and short-range repulsion. Quantum calculations of the scattering phase shifts at reasonable values of the potential parameters allow to explain the main features of the observed density effect on the shape of ( ) spectral lines in low-temperature helium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Do the fundamental physical constants have the same values in different regions of space-time?

An analysis of quasar spectra yields highly reliable constraints on the possible variation of the fine-structure constant a and the proton-to-electron mass ratio μ during cosmological evolution from the epoch corresponding to a cosmological red shift z≈2.8 (i.e., ∼10¹⁰ years ago) to the current epoch and . Zh. Tekh. Fiz. 69, 1–5 (September 1999)     

Grain growth in ice

Summary Grain growth is studied in polycrystalline ice, consisting of elongated grains, of (200÷300) μm mean width and (2÷3) mm mean length . The samples are annealed at different temperatures, between 0°C and −10°C. It is found that is not affected by annealing, while increases with the annealing time. Below the melting point, (t) tends to a limit value . This behaviour is related to the pinning action of air bubbles, which would be similar to that found for solid inclusions in metals. By assuming where is the mean bubble diameter andf is the volume fraction of air dissolved in water, reasonable values are found for . The activation energy of the phenomenon is evaluated on the basis of the present and of Jellinek and Gouda's results. It is foundQ=0.6 eV, which value approximately coincides with that for bulk self-diffusion as it occurs for metals, several degrees below the melting point. This coincidence suggests that, for ice, grain growth would be controlled by bulk impurity diffusion up to the very melting point. Instituto de Matemática, Astronomía y Física, Universidad Nacional de Córdoba and CONICET.     

Chiral symmetry breaking andKN sigma commutator

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.     

Quark-gluon string-model description of baryon production in <Emphasis Type="Italic">K</Emphasis><Superscript>±</Superscript><Emphasis Type="Italic">N</Emphasis> interactions

The process of baryon production in Kp collisions at high energies is considered in the framework of the quark-gluon string model. The contribution of the string-junction mechanism to the strange-baryon production is analyzed. The results of numerical calculations are in reasonable agreement with the data on inclusive spectra of p, Λ, and on the /Λ asymmetry. The predictions for inclusive spectra and production asymmetry of Ξ and Ω baryons are presented. The text was submitted by the authors in English.     

EELS cross-section of surface phonons on Ag(001)

Summary We present EELS cross-section data of surface phonons on Ag(001) along . The inelastic intensity is due to the contribution of different modes which are not solved by the EEL spectrometer. However, the shape of the inelastic intensity shows a strong dependence on impact energy for all wave vectors, which allows tuning the EELS on the different modes. The dependence of the loss frequency on impact energy is at variance with the one reported previously for , leading to the conclusion that other modes contribute to the inelastic intensity besidesS ₁ andL ₁ which dominate at . In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching.     

Parity anomaly in a \mathcal{P}\mathcal{T}-symmetric quartic Hamiltonian

In this paper, two independent methods are used to show that the non-Hermitian -symmetric wrong-sign quartic Hamiltonian H = (1/2m)p ² − gx ⁴ is exactly equivalent to the conventional Hermitian Hamiltonian . First, this equivalence is demonstrated by using elementary differential-equation techniques and second, it is demonstrated by using functional-integration methods. As the linear term in the Hermitian Hamiltonian is proportional to ℏ, this term is anomalous; that is, the linear term in the potential has no classical analog. The anomaly is a consequence of the broken parity symmetry of the original non-Hermitian -symmetric Hamiltonian. The anomaly term in remains unchanged if an x ² term is introduced into H. When such a quadratic term is present in H, this Hamiltonian possesses bound states. The corresponding bound states in are a direct physical measure of the anomaly. If there were no anomaly term, there would be no bound states.     

BV Structure of the Cohomology of Nilpotent Subalgebras and the Geometry of(W) Strings

Given a simple, simply laced, complex Lie algebra corresponding to the Lie group G, let be thesubalgebra generated by the positive roots. In this Letter we construct aBV algebra whose underlying graded commutative algebra is given by the cohomology, with respect to , of the algebra of regular functions on G with values in . We conjecture that describes the algebra of allphysical (i.e., BRST invariant) operators of the noncritical string. The conjecture is verified in the two explicitly known cases, ₂ (the Virasoro string) and ₃ (the string).     

The CPT Group of the Dirac Field

Using the standard representation of the Dirac equation, we show that, up to signs, there exist only two sets of consistent solutions for the matrices of charge conjugation (C), parity (P), and time reversal (T), which give the transformation of fields , and , where and . These sets are given by , , and , , . Then , and two successive applications of the parity transformation to fermion fields necessarily amount to a 2 rotation. Each of these sets generates a non abelian group of 16 elements, respectively, and , which are non isomorphic subgroups of the Dirac algebra, which, being a Clifford algebra, gives a geometric nature to the generators, in particular to charge conjugation. It turns out that and , where is the dihedral group of eight elements, the group of symmetries of the square, and 16E is a non trivial extension of by , isomorphic to a semidirect product of these groups; S₆ and S₈ are the symmetric groups of six and eight elements. The matrices are also given in the Weyl representation, suitable for taking the massless limit, and in the Majorana representation, describing self-conjugate fields. Instead, the quantum operators C, P and T, acting on the Hilbert space, generate a unique group , which we call the CPT group of the Dirac field. This group, however, is compatible only with the second of the above two matrix solutions, namely with , which is then called the matrix CPT group. It turns out that , where is the dicyclic group of 8 elements and S₁₀ is the symmetric group of 10 elements. Since , the quaternion group, and , the 0-sphere, then .     

Effect of a magnetic field on the yield point of NaCl crystals

A constant magnetic field is found to have a substantial effect on the macroplasticity of NaCl crystals when they are being actively strained at a constant rate during magnetic treatment. We have measured the dependence of the yield point σ _y on the magnetic induction B=0–0.48 T and the strain rate . It is shown that this magnetic effect has a threshold character and is observed only for B>B _c , where B _c grows with increasing as . The lower the strain rate , the larger the relative decrease in the yield point σ _y (B)/σ _y (0) at fixed field B>B _c . At small enough strain rates the threshold field B _c ceases to depend on and goes constant. A theoretical model is proposed which is in good agreement with the observed regularities. The model is based on the competition between thermally activated and magnetically stimulated depinning of dislocations from paramagnetic impurity centers. Zh. éksp. Teor. Fiz. 115, 951–958 (March 1999)