Excitons dressed by a sea of excitons

We here consider an exciton i embedded in a sea of N identical excitons 0. If the excitons are taken as true bosons, a bosonic enhancement factor N is found for i=0. If the exciton composite nature is kept, this enhancement not only exists for i=0, but also for any exciton having a center of mass momentum equal to the sea exciton momentum. This physically comes from the fact that an exciton with such a momentum can be transformed into a sea exciton by Pauli scattering, i.e., carrier exchange with the sea, making this exciton i not so much different from a sea exciton. This possible scattering, directly linked to the composite nature of the excitons, is irretrievably lost when the excitons are bosonized. The underlying interest of this work is in fact the calculation of the scalar products of N-exciton states, which turns out to be quite tricky, due to possible carrier exchanges between excitons. This work actually constitutes a crucial piece of our many-body theory for interacting composite bosons, because all physical effects involving composite bosons ultimately end by the calculation of such scalar products. The skeleton diagrams we here introduce to represent them, allow to visualize many-body effects linked to carrier exchanges in an easy way. They are conceptually different from Feynman diagrams, because of the special feature of the Pauli scatterings which originate from boson statistics departure.     

A Schematic Calculation of the ββ-Decay Matrix Element Within the Green Function Approach

The time integral representation of the many-body Green function describing the two-neutrino double-beta-decay (2-decay) matrix element is used in schematic calculations within the proton-neutron Lipkin model. The two-body Hamiltonian considered includes a quadratic polynomial in bosons to describe the motion of the selected degrees of freedom. The beta-transition operators also include higher-order terms in the boson expansion. They have been shown to be of crucial importance in the determination of the 2-decay matrix element M _F. We have found that in the standard QRPA approach, which exploits the form of M _F with denominator, there is a dominant unphysical contribution to M _F arising from the non-orthogonality of the initial and final quasiparticle ground states. The physical part of M _F is negligible for small values of the particle-particle interaction strength, i.e., it exhibits a different behavior as that known from the QRPA approaches.     

Lyapunov Modes of Two-Dimensional Many-Body Systems; Soft Disks, Hard Disks, and Rotors

The dynamical instability of many-body systems can best be characterized through the local Lyapunov spectrum {}, its associated eigenvectors {}, and the time-averaged spectrum {}. Each local Lyapunov exponent describes the degree of instability associated with a well-defined direction—given by the associated unit vector —in the full many-body phase space. For a variety of hard-particle systems it is by now well-established that several of the vectors, all with relatively-small values of the time-averaged exponent , correspond to quite well-defined long-wavelength modes. We investigate soft particles from the same viewpoint here, and find no convincing evidence for corresponding modes. The situation is similar—no firm evidence for modes—in a simple two-dimensional lattice-rotor model. We believe that these differences are related to the form of the time-averaged Lyapunov spectrum near =0.     

The distribution of neutron density in the vicinity of a partly inserted black rod in two-group approximation

The neutron density in the vicinity of a black cylindrical rod partly inserted in a bare reactor is calculated and illustrated by a numerical example. The starting point is a two-group diffusion theory approximation. While the dependence of the effect of the rod on the insertion depth can be calculated simply by means of perturbation theory, the question of the neutron density estimate in the vicinity of the rod is considerably more difficult and in some considerations the estimate of the neutron density caused by the presence of the rod is indispensable. The method makes it possible to determine the reactivity value of the rod in dependence on the insertion depth and especially the neutron density deformation in the vicinity of the rod.

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In conclusion the author thanks J. Svato for help in carrying out the numerical calculations.     

Die Abhängigkeit der Banddurchbiegung von der Lage der Stufenversetzung

Zusammenfassung Es wird die Lösung des Spanungszustandes im unendlichen Band mit einer lotrecht zur Bandebene stehenden Stufenversetzung und mit einem Burgerschen Vektor, der parallel mit der Bandachse verläuft, unter der Voraussetzung der klassischen mathematischen Elastizitätstheorie wiedergegeben. Weiter wird der Ausdruck für die Gesamtdurchbiegung des Bandes in Abhängigkeit von der Lage der Versetzung und für die Durchbiegung bei einer allgemeinen Verteilung der Versetzungen, die durch eine kontinuierliche Verteilung approximiert ist, abgeleitet.

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Für die wertvolle Diskussion und einige Hinweise danke ich dem Kollegen Jan Kaczér, für das Lektorieren der Arbeit dem Kollegen Bohdan esták.     

Photo-luminescence and growth defects in ZnS: Cu monocrystals

The paper describes microscopic investigation into the spectral distribution of photo-luminescence and its polarization on hexagonal ZnS monocrystals in relation to the structural defects of such crystals. These observations, as well as birefringent observations, show that the values of the birefringence and the degree of polarization in different stripes of the same crystal are the same within the limits of observational errors.

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ZnS: Cu

ZnS . , , , .

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In conclusion the author would like to thank K. Pátek, L. Souková and M. Mokonová for providing the monocrystals and for fruitful discussions.     

Absence of asymptotic-time symmetry breaking in zero-bias spin-boson model with partial relaxation

The symmetric spin-boson model without external field is treated for any type of coupling to the boson bath and any initial bath density matrix. With initially fully aligned spin (_z (0)= =1), the proof is given that a partial relaxation (_z (+) t1<) implies that there is no asymptotic-time (up-and-down) symmetry breaking (i.e. that _z (+)=0). For the problem of a particle (interacting with free bosons) in a symmetric double well without spatial symmetry breaking before the infinite time limit, this means that att + the particle distribution becomes symmetric (irrespective of the full initial asymmetry) unless the particle fully remains (att + ) in Ihe starting well.     

Radiative decays of the Z boson

We calculate the Stokes parameters of the photons produced in the decays of neutral vector bosons Z, Z 1+¯1+ and Z q+¯q+, wherel=e, , or , and q is a quark. In the decays of unpolarized Z bosons (with the production of unpolarized leptons or quarks) the nonzero Stokes parameters for ₂ (circularly polarized photons) and ₃ (linearly polarized photons). The magnitude of ₃ does not depend on the parameters of the netural weak current of the leptons and the quarks (if their mass is neglected). The anomalous magnetic moment of the Z boson is studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 38–43, February, 1986.     

The crystal structure of meta-zeunerite Cu(UO2)2(AsO4)2⋅8 H2O

The structure of the mineral zeunerite (deposits at Rotava near Kraslice, Ore Mountains) was determined. The tetragonal unit cell, having the dimensionsa=7.10₅Å andc=17.70₄Å, contains two structure units of Cu(UO₂)₂(AsO₄)₂8H₂O. The space group isP4₂/nmc. The distribution of the atoms in the unit cell was determined from the Patterson projectionP(vw) and by means of (F ₀-F _c) synthesis. Meta-Zeunerite has a layer type structure. The sheets [(UO₂)(AsO₄)] are separated by layers containing the cations (Cu(H₂O)₄)²⁺ and molecules of water. The uranium is coordinated octahedrally with six oxygen atoms at distances: U-O₁ 1.94 Å, U-O₂ 1.78 Å, U-O₃₍₄₎ 2.18 Å (4×). The uranyl radical O₁-U-O₂ is linear. In the tetrahedron AsO₄ the interatomic distances are As-O 1.77 Å and the bond angles 102°, 102°, 113° and 113°. Each oxygen atom of the tetrahedron AsO₄ is simultaneously bonded to the uranium atom. The bond angle As-O-U is 137°. The layers [(UO₂)₂(AsO₄)] are bonded together by the cations (Cu(H₂O)₄)²⁺. The distances Cu-O₁ and Cu-O₂ are 2.55 and 2.58Å respectively. The structural changes during hydration and dehydration are explaned.

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- Cu(UO₂)₂(AsO₄)₂8 H₂O

( , ). =7,10₅ Å,=17,70₄ Å Cu(UO₂)₂(AsO₄)₂8 ₂O. P4₂/nmc. P(v w) (F ₀-F _c) . . , [(UO₂)(AsO₄)], , [u(₂)₄]²⁺ . : U-O₁ 1,94 Å, U-O₂ 1,78 Å, U-O₃₍₄₎ 2,18 Å ( ). ₁-U-₂. AsO₄ As- 1,77 Å -102°, 102°, 113° 113°. AsO₄ . As--U 137°. [(UO₂)₂(AsO₄)] [u(₂O)₄]²⁺. u-O₁ 2,55 Å, u-O₂ 2,58 Å. .

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In conclusion the author thanks T. Veselská for assistance in the calculations and workers of the National Museum in Prague, and primarily Dr. ípek, for supplying the sample. The experimental work was carried out at the Department of Physics of the Natural Science Faculty of Komenský University.     

On the Long Time Behavior of Infinitely Extended Systems of Particles Interacting via Kac Potentials

We analyze the long time behavior of an infinitely extended system of particles in one dimension, evolving according to the Newton laws and interacting via a non-negative superstable Kac potential (x)=(x), (0, 1]. We first prove that the velocity of a particle grows at most linearly in time, with rate of order . We next study the motion of a fast particle interacting with a background of slow particles, and we prove that its velocity remains almost unchanged for a very long time (at least proportional to ^–1 times the velocity itself). Finally we shortly discuss the so called Vlasov limit, when time and space are scaled by a factor .     

Ultra-high piezoelectric response in 〈<Emphasis Type="Bold">110</Emphasis>〉- oriented polydomain Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>- PbTiO<Subscript>3</Subscript> single crystals

The piezoelectric constant and electromechanical coupling coefficients of 110-oriented polydomain0.71Pb(Mg_1/3Nb_2/3)O₃-0.29PbTiO₃ single crystals were determined experimentally by using resonance methods. It was confirmed that the single-crystal system has large electromechanical coupling coefficients k₃₃ (91%), k₃₃ (83%), and k₃₁ (81%), and piezoelectric constant d₃₃ (1400 pC/N), which are comparable to those of 001-oriented crystals, and we also found that the values of k₃₃ and k₃₁ are sensitive to the cuts of the crystals. X-ray-diffraction measurements on 110-oriented crystals have shown that the origin of the high piezoelectric response should be attributed to the orthorhombic distortion. Our results show that the 110-oriented crystals are also promising for a wide range of electromechanical transducer applications, since the 110-oriented crystals can be grown from 110-oriented seed crystals in the modified Bridgman technique. PACS 77.80.Bh; 77.84.Dy; 77.65.Bn     

An Invariant Formulation of Special Relativity, or the “True Transformations Relativity,” and Comparison with Experiments

Different formulations of special relativity (SR) are briefly theoretically discussed. In the first formulation SR is understood as the theory of a four-dimensional (4D) spacetime with the pseudo-Euclidean geometry. It is an invariant formulation of SR, which we call the true transformations (TT) relativity. There a physical quantity in the 4D spacetime is mathematically represented either by a true tensor (when no basis has been introduced) or equivalently by a coordinate-based geometric quantity comprising both components and a basis (when some basis has been introduced). This invariant formulation is compared with the usual covariant formulation, which mainly deals with the basis components of tensors in a specific, i.e., Einstein's coordinatization of the chosen inertial frame of reference. The third formulation is the usual noncovariant approach to SR in which some quantities are not tensor quantities, but rather quantities from 3+1 space and time, e.g., the synchronously determined spatial length. This formulation is called the apparent transformations (AT) relativity. Some of the well-known experiments: the muon experiment, the Michelson–Morley type experiments, the Kennedy–Thorndike type experiments, and the Ives–Stilwell type experiments are analyzed using the nonrelativistic theory and the mentioned different formulations of SR. It is shown that all the experiments (when they are complete from the TT relativity viewpoint) are in agreement with the TT relativity but not always with the AT relativity.     

High energy electrons in the earth's radiation belts

Special experiments performed aboard the space stations Salyut-6-SoyuzProgress, Salyut-7-Soyuz T-13-Kosmos-1669, and the artificial earth satellite IK Bolgariya-1300 discovered, significant electron and positron fluxes with energies of more than decades of MeV in the earth's radiation belts. Spatial and angular characteristics of these fluxes have been studied. Study of the charge ratio of the electron-positron component has shown that it is electron-based. This indicates that in outer space near the earth some efficient mechanism capable of accelerating electrons to energies of more than decades of MeV exists.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 38–43, September, 1986.The authors consider it their pleasant duty to express gratitude to V. M. Gracev, S. V. Koldashov, A. V. Popov, and S. E. Ulin for their preparation of the equipment and conduct of the experiments.     

РЕАКЦИЯ (γ, р) НА КОБАЛЬ ТЕ

- , Li(, ) ( =17,6. 14,8 MeV). , u . , gQ=0,74+-0,16 MeV ⁵⁸Fe E ^* : 6,76; 6,44; 5,90; 5,47; 4,98; 4,35; 3,50; 3,20 MeV. , .     

Anti-photon

It should be apparent from the title of this article that the author does not like the use of the word photon, which dates from 1926. In his view, there is no such thing as a photon. Only a comedy of errors and historical accidents led to its popularity among physicists and optical scientists. I admit that the word is short and convenient. Its use is also habit forming. Similarly, one might find it convenient to speak of the aether or vacuum to stand for empty space, even if no such thing existed. There are very good substitute words for photon, (e.g., radiation or light), and for photonics (e.g., optics or quantum optics). Similar objections are possible to use of the word phonon, which dates from 1932. Objects like electrons, neutrinos of finite rest mass, or helium atoms can, under suitable conditions, be considered to be particles, since their theories then have viable non-relativistic and non-quantum limits. This paper outlines the main features of the quantum theory of radiation and indicates how they can be used to treat problems in quantum optics.It is a pleasure to join in the 60th birthday celebration of the Director, Herbert Walther, of the Max-Planck-Institute for Quantum Optics at Garching, and wish him much happiness and many more years of his very great scientific creativity.     

Усовершенствование рентгенометрическо го метода определения дефекто в решетки третьего ро да в поликристаллическ их и порошкообразных материалах

, . .     

The rotation of bloch walls

A Bloch wall has an integral magnetic moment which is due to the spatial distribution of the magnetic moments of the spin. The external magnetic field thus acts on the wall with a torque, which leads to the rotation of the sub-domains and therefore to deformation of the walls. A theory of this rotation is given and from it a microphysical model of the undulatory surface structure in uniaxial ferromagnets is derived. Experiments performed on magnetoplumbite single crystals fully confirm the theoretical assumptions.

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Our thanks go to J. Fousek and Z. Málek who by reading this paper contributed greatly to the clarity of its presentation.     

On discontinuity of the pressure

A class of one-dimensional classical lattice gas models with translationally invariant, stable and strongly tempered many-body interactions, is constructed for which the limiting thermodynamic pressure is a discontinuous function of the density (at fixed temperature). This demonstrates that an apparently mild restriction on the potential (supersummability) employed by Griffiths and Ruelle in proving the continuity of the pressure in lattice systems, plays, in fact, a crucial role.     

Pairing correlations: II. Exact model ground-state results for generalised ladders

In this series of papers, the so-called ground-state version of the [exp(S) or] coupled-cluster formalism (CCF) of quantum many-body theory is applied to the general problem of pairing correlations within a many-body system of identical fermions. In this second work in the series we restrict ourselves to exact calculations and concentrate on analytic solutions to the generalised ladder approximations formulated in the first paper. We focus attention on the particular model case of a general (non-local) separable potential, and work within the so-called complete ladder (CLAD) approximation which was shown in the earlier paper to be the CCF formulation of the well-known Galitskii approximation. We show how the CLAD approximation reduces in this case to a highly non-trivial pair of coupled nonlinear integral equations for the four-point correlation function,S ₂, which provides a measure of the two-particle/two-hole component in the true ground-state wave-function. In the further derivation of exact analytic solutions for bothS ₂ and the corresponding ground-state energy, we also see how various types of composite pairs within the many-body medium manifest themselves as virtual (de-)excitations. We thus show how our CCF provides an efficient and unified framework in which to describe all aspects of pairing, such as: (i) a possible free bound pair and its gradual approach to dissolution as the density is increased; (ii) the possible appearance of a second bound pair of predominantly hole-like quasi-particles above some lower critical density (which depends on the total momentum of the pair); (iii) the unstable but bound resonant pairs that can exist for densities above a comparable upper critical density at which the two previous types of real bound pairs have dissolved; and (iv) Cooper pairs. Even though each of these composite pairs leads to a new condensed-pair phase of lower energy, we further show that our so-called ground-state CCF leads only to the fluid-like state of uncondensed particles. In a third paper in this series we use the solutions obtained here as input to the analogous excited-state version of the CCF, and show how these various composite pairs materialise as negative energy (de-)excitations.     

О ЗАТУХАНИИ ФАЗОВЫХ К ОЛЕБАНИЙ В СИНХРОТРОНЕ СО СЛАБ ОЙ ФОКУСИРОВКОЙ

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On the damping of phase oscillations in a weak-focusing synchroton

An equation of the phase oscillations in a weak-focusing synchroton is derived for the case that an arbitrary high-frequency field of sinusoidal time dependence is distributed on the circumference of the accelerator. It is shown that the damping of phase oscillations is practically independent of the shape of the high-frequency field. From this we get the special case that any adjustments to the accelerator gaps, considered for example in [1], are useless.