Showing papers in "Czechoslovak Journal of Physics in 1992"

The Jülich hyperon-nucleon interaction models

Abstract: Hyperon-nucleon interaction models (A, B), which have been developed in the meson-exchange framework by the Julich group, are reviewed, with some emphasis on characteristic conceptual differences compared to corresponding interactions constructed by the Nijmegen group. We report on two new versionsA and\(\tilde B\) in which the explicit energydependence of the original models A and B is removed in order to simplify application in nuclear structure calculations. As a byproduct of our analysis we find that the resulting SU(3)-parameters likeF/(F+D) ratios do depend on the specific model used an on approximations applied. While all models provide a reasonable description of the scarce cross-section data, sizeable differences occur in the, so far unmeasured, spin observables, especially between our models and the Nijmegen soft-core model NSC. This demonstrates clearly that a measurement of such observables can easily discriminate between present models and thus shed some light on various aspects of the hyperon-nucleon interactions like e.g. the proper choice of parameter constraints. In addition, the results obtained with the energy-independent potentials (A,\(\tilde B\)) in a conventional first-order Brueckner calculation for a λ-hyperon in nuclear matter are presented. The binding energy BΛ(∞) of a λ-hyperon in nuclear matter was found to be 29.8 MeV (32.0 MeV) for model A(\(\tilde B\).

Inhomogeneous quantum groups

Abstract: Inhomogeneous quantum groups corresponding to the homogeneous quantum groupsUq(N), SOq(N) and theq-deformed Lorentz group acting on affine quantum spaces are constructed.

Hypernuclear properties derived from the Jülich hyperon-nucleon interaction (in comparison with the Nijmegen interactions)

Abstract: TheG-matrix interactions are derived from the Julich YN interaction models A and B, and compared with those from the Nijmegen models. The DDHF calculations for heavy A hypernuclei and the shell-model analysis for spin-doublet states of light hypernuclei are performed by use of theG-matrix interactions. It is demonstrated that the OBE models can be tested by the hypernuclear calculations.

Iodine photodissociation laser system Perun II

Abstract: A construction and exploitation of a medium size iodine photodissociation laser system Perun II is reported. This laser produced pulses of infrared light (λ=1.315μm) up to 50 J in energy and 300 ps in duration. The diameter of the beam is 82 mm. The beam divergence is about 4×10−4 rad. The laser beam can be focused in a focal spot of a power density exceeding 1014 W/cm2. The resuls of measurements of basic plasma parameters on an Al foil target are also presented. A recent improvement of the system includes a conversion to the second harmonic by a DKDP crystal.

Extended number state basis and number-phase intelligent states of light field II. The reduced number-sine intelligent and Jackiw states

Abstract: The number-sine intelligent state is introduced for the extended Hilbert space and reduced to serve as an approximation to the Jackiw number-sine intelligent state. Usual and modified statistical and uncertainty characteristics of these states are determined and compared. A new technique is used for reconstructing the crescent state of Kitagawa and Yamamoto and studying the properties of the reduced number-sine intelligent state.

Thermodynamics of partially open systems

Abstract: The concept of partially open thermodynamic systems (consisting of components of two distinct categories: free and conservative components) is studied to suggest an adequate way of their description and analysis. Quasimolar fractions and quasimolar quotients are introduced to describe macroscopic composition of the systems and quasimolar thermodynamic quantities are suggested to substitute molar quantities usual with closed systems. New thermodynamic potential (called hyperfree energy), suitable as a function whose minimum expresses the equilibrium condition of partially open systems, is introduced using Legendre transformation. To assemble the hyperfree energy function, shortened thermodynamic quantities and quasimolar phase fractions are useful. Thermodynamics of partially open systems is applied to analyze the behavior of these systems at equilibrium transitions (e.g. decomposition of simple oxide) under a dynamic atmosphere. As a result, new Clapeyron-like equations are derived.

Ultraviolet and infrared aspects of the axial anomaly I

Abstract: This is the first part of a brief review of some perturbative aspects of the Adler-Bell-Jackiw axial anomaly, described in terms of ultraviolet and infrared behaviour of the famous VVA triangle graph. Apart from a general overview of the diversified role played by the anomaly in quantum field theory and particle physics, we present here an elementary introduction to the subject of the anomaly, which hopefully should be comprehensible to an uninitiated reader with only a basic background in quantum field theory. In this article we stress the ultraviolet aspects of the anomaly and the topics covered here are the following: Vector and axial-vector Ward identities for the VVA triangle graph, the anomaly and several ways to derive it, namely the symmetric momentum cut-off and shifting the integration variables in linearly divergent integrals, the Adler-Rosenberg argument, the Pauli-Villars method and dimensional regularization.

Growth of rough surfaces

Abstract: The growth of objects with rough surfaces is a common phenomenon. We describe several models used in the study of the temporal evolution of fluctuating interfaces and then we explain the dynamical scaling in this class of growth models with self-affine surfaces. The recent progress in this field is reviewed. Much emphasis is put on roughness properties and in particular on a possible kinetic roughening transition — a nonequilibrium analog of the thermal roughening transition. Both analytical and numerical results for scaling exponents are summarized and indications of a phase transition in some models are discussed.

Numerical modeling of the streamer-cathode interaction in a short positive point-plane corona gap

Abstract: The development of the streamer-cathode interface has been studied by computer simulation of the discharge in a short positive point-plane gap in N2 at 267 kPa Special emphasis was given to the transition from a streamer head structure to an abnormal glow discharge fall and to the identification of the cathode current signal corresponding to the streamer arrival at the cathode The signal, taking the form of a sharp spike due to the displacement current, was found to be relatively insensitive to changes in the cathode secondary photoemission The conduction current due to the collection of positive ions by the cathode begins to become significant in a time of some 20 ns after the streamer arrival, resulting in subsequent gradual rise in the cathode current

The instability of streaming fluids with fine dust in porous medium

Abstract: The instability of the plane interface between two uniform, superposed, and streaming fluids permeated with suspended particles through porous medium is considered. The effect of a uniform horizontal magnetic field on the problem is also studied. In the absence of surface tension, perturbations transverse to the direction of streaming are found to be unaffected by the presence of streaming if perturbations in the direction of streaming are ignored, whereas for perturbations in all other directions there exists instability for a certain wavenumber range. The instability of the system is postponed by the presence of magnetic field. The magnetic field and surface tension are able to suppress this Kelvin-Helmholtz instability for small wavelength perturbations and the medium porosity reduces the stability range given in terms of a difference in streaming velocities and the Alfven velocity. The suspended particles do not affect the above results.

Sensitivity of approximate formulas for determining optical constants of thin films

Abstract: The sensitivity of approximate formulas for determining the optical constants of thin films using measurement of reflectancesR and transmittancesT at normal incidence have been investigated theoretically. The ranges of refractive indexn, absorption indexk,2nk (=ɛ2) andn 2−k 2(=ɛ1) within relative errors of 5%, 10%, and 20% may be obtained. Selected signs of (ɛ1)+ or (ɛ1)− have been determined. Validity of the condition n0 A′=n s A has been also evaluated (A=1−R −T andA′=1−R′−T).

Electroproduction of strangeness

Abstract: Formalism for the electroproduction of strange particles based on the one photon exchange approximation and the Feynman diagrams representation of hadron current is reviewed Different photoproduction models are compared with available photo and electroproduction data New experiments are proposed that may resolve existing uncertainties and inconsistencies The formation of hypernuclei via kaon electroproduction is investigated theoretically and compared with other reactions involving purely hadronic processes

Chiral perturbation theory in the Extended Nambu-Jona-Lasinio model

Abstract: The chiral perturbation theory is developed at the quark level within the Extended Nambu-Jona-Lasinio model which we used for the low-energy approximation of QCD in the leading order of the large N expansion. In terms of constituent-quark-loop diagrams we analyse all of the main low-energy effects caused by the first order corrections in the current quark mass expansions. For the correct description of theη →3π decays we confirm the important role of the final-state-interaction quoted by Gasser and Leutwyler.

Models of Q algebra representations

Abstract: This article gives a review of various straightforward models ofQ algebra representations. This is done using one and two variable function space models of theq-analogues of Lie enveloping algebras. The algebras considered are the quantum algebraU q (su 2 ) and aq analogue of the oscillator algebra. We present only the general framework and refer the reader to references of the joint work of the author and Willard Miller, Jr.

Analysis of experiments on energetic ions from laser produced plasmas with reference to hot electrons and pulsation

Abstract: The need for highly charged heavy ions from projected particle accelerators has recently led to a re-evaluation of the complex processes of ion production in laser generated plasmas. Possible mechanisms for the production of intense beams of high charge state ions are investigated as is the experimental evidence for these mechanisms. The hypothesis that 20 keV ions are driven by “hot electrons” is not supported by experimental work to date. This work, on the other hand, suggests that 30ps pulsation is the basic mechanism for the acceleration of tantalum ions up to charge state 8+ whose energy increases linearly with charge state up to 24keV. For long pulses and charge states between 8+ and 18+, it appears that there is a secondary mechanism of electron impact ionisation by plasma electrons of approximately 200 eV in the plasma in front of the target, resulting in ions whose energy of around 24 keV is independent of charge state.

Two-nucleon production of hyperons and the search for strange dibaryons

Abstract: The double charge exchange reaction3He(K−,π +)Xn was studied at 870 MeV/c. In the X missing mass range below the sigma-nucleon production threshold (2130 MeV/c2), events were detected which can be attributed to the two-nucleon process pp(K−,π +)λn. This reaction and mass range also offers good prospects for finding theI=1/2,l=1 (1 P1) spin-singlet dibaryon Ds suggested as the lowest massS=−1 dibaryon in the MIT Bag Model. Although the existence of the Ds is not ruled out by the present data, there is no need to invoke such an object to account for the observed events below σ production threshold. We show that the cross section level for these events is compatible with a dominant two-nucleon mechanism K−p→π 0λ,π 0p →π +n. We also offer an interpretation of the recent (K−,K+) data on nuclear targets from Iijimaet al., which display a broad peak centered around a K+ momentum of 600 MeV/c. We find that the two-nucleon mechanism K−N →πY,πN→K+Y produces cross sections which are at least an order of magnitude smaller than those observed, and we suggest that the one nucleon process K−p →Φλ, followed by the decayΦ → K+K−, accounts for the data.

Baryonic decay and 1p-shell hypernuclear spectroscopy

Abstract: The detailed discussion of baryonic decay channels is presented Levels built on sλp−1, PλP−1 and sλs−1 configurations are considered The results presented are obtained in the calculations based on the Translationally Invariant Shell Model which automatically includes some intruder states through the kinematic correlations The role of the intruder states in the proton decay is discussed The evolution of the baryonic decay width with increasing nucleon number A in the 1p-shell hypernuclei is traced Hypernuclear decays into the bound excited states either of secondary hypernuclei or nuclei are revealed Information which could be extracted from the de-excitation of the baryonic decay products whenever they were measured is discussed From the suggested new set of theλN interaction parameters for the sλp−1 configuration some new information on the proton decay of the Λ 12 C hypernucleus pλp−1 low-lying levels is given

Separation of charge and spin degrees of freedom in the Hubbard model

Abstract: The representation of the electron field operators separating charge from spin and providing transmutations between spin and isospin quantum numbers has been derived for any dimension. In this representation the interaction term in the Hubbard model is expressed in a bilinear form of quasiparticle field operators. The quasiparticles are spinless fermions with the electron electric charge. The consequence of this representation is that superconductivity in the strong coupling Hubbard model is due to odd wave pairings of electrons.

Why and how to avoid standard kinetic equations II. Time-convolution or convolutionless equations and hopping

Abstract: Review of ideas questioning applicability of standard approximate kinetic equations derived from Generalized Master Equations (GME) with time-independent projector, in particular in the long-time (low-frequency) domain except for special situations, is given. Attention is concentrated on the time-convolutionless GME for systems interacting with a reservoir with applications to the phonon-assisted hopping problem. As compared to the previous work of the series, the treatment is extended to any power of the external field. Inapplicability of mathematical methods justifying standard markovian treatments in the Van Hove limit is found to be owing to finite coupling constants encountered in nature. It is argued that performing (for finite coupling constants usually necessary) approximations in a consistent way (preserving some exact identities derived here) means, in fact, avoiding the approximate kinetic equation method. The existence of an alternative stemming from GME is argued.

Thin layers of gallium-arsenide: A molecular orbital study

Abstract: The quasirelativistic INDO/1 method has been used to generate molecular orbitals for some {GaAs}n clusters up to 160 atoms. On the basis of these one-electron energy levels the density of states (DOS) and density of hole functions have been calculated. Various projections of DOS functions are discussed. The calculations are compared with those generated by periodic crystal orbitals of the EHT quality and with experimental ESCA spectra on thin layers of GaAs.

On the diffusion-driven growth: the perturbed sphere problem revisited

Abstract: A growth process driven by stationary diffusion field is considered to be a consequence of the mass conservation law. A correct expression for the growth velocity is derived and applied to a specific model of the perturbed sphere. It is studied in the linear regime, for which all corrections are consequently taken into account and graphically demonstrated. A critical discussion and confrontation with some statements in the literature is carried out.

Optical properties of stannous oxide thin films

Abstract: Thin films of stannous oxide (SnO) have been prepared by the electron-beam evaporation method. Film properties, such as refractive indexn, extinction indexk, and absorption coefficientα, were studied in the wavelength range between 200 nm and 2 000 nm with different methods. The surface roughness of SnO thin films has been found to depend linearly on the film thickness in the range 400

Perturbation theory and nonperturbative effects: A happy marriage ?

Abstract: Perturbation expansions in renormalized quantum field theories are reformulated in a way that permits a straightforward handling of situations when in the conventional approach, i.e. in fixed renormalization scheme, these expansions are factorially divergent and even of asymptotically constant sign. The result takes the form of convergent (under certain circumstances) expansions in a set of functionsZk(a,χ) of the couplant and the free parameterχ which specifies the procedure involved. The value ofχ is shown to be correlated to the basic properties of nonperturbative effects as embodied in power corrections. Close connection of this procedure to Borel summation technique is demonstrated and its relation to conventional perturbation theory in fixed renormalization schemes elucidated.

Optical bremsstrahlung of relativistic particles in a transparent medium and its relation to the Vavilov-čerenkov radiation

Abstract: The classical formula for the intensity of the optical bremsstrahlung (OB) emitted by a charged particle moving in a transparent medium with a velocity above the Vavilov-cerenkov radiation (VCR) threshold is analysed in the paper.

The double duals and gauges of the lanczos tensor

Abstract: It is shown that: i) the Weyl tensor can be expressed in terms of the sum of a tensor and its double dual, where the tensor is constructed from the covariant derivatives of the Lanczos tensor, ii) a similar expression does not exist for the Riemann tensor in electromagnetic theory, iii) the electromagnetic field cannot be identified with the differential gauge freedom of the Lanczos tensor, iv) the symmetries of Einstein Maxwell theory and the Lanczos tensor do not prohibit the identification of the electromagnetic field with the algebraic gauge freedom of the Lanczos tensor, these symmetries require a differential equation relating the electromagnetic field tensor to the algebraic gauge vector and this is given.

On the use of large pixel PIN diode array in plasma diagnostics

Abstract: Silicon PIN diodes tailored for x-ray diagnostics of high-temperature plasmas were investigated. Their spectral responsivity was determined from the direct calibration of the diodes by x-rays and indirectly through the bombardment by monoenergetic electrons, the accuracy of the calibration amounts to 11.5 %. The single diodes are used in combination with an absorption foil technique, the large pixel PIN diode array was utilized in a compact spectrometer for monitoring the electron temperature and density of laser produced plasma. The construction of the spectrometer and an example of experimental results are presented.

A-dependence of inclusive Φ-meson production in neutron-nucleus interactions at 30–70 GeV

Abstract: The production of Φ-mesons on nuclear targets (carbon, aluminium and copper) by high-energy neutrons has been analysed. The dependence of the Φ-production cross section ratios on the nuclear mass numberA was parametrized by the power lawA α withα=0.81±0.06. Within the sensitive kinematic rangex F>0 andp T<1 GeV/c we have not observed any dependence of the exponentα on the longitudinal or transverse momentum. A possible interpretation of the measuredA-dependence is discussed in the Appendix.

Chiral properties of low-energy matrix elements of local four-quark operators

Abstract: The chiral properties of low-energy matrix elements of four-quark operators describing the weak vertices in the effective Lagrangian of weak interactions are investigated. A constituent quark diagram technique for the derivation of “soft” pion low-energy theorems is proposed. The technique is applied to the calculation of the⌆-term operator correlator in the low-energy theorem of the penguin-operator matrix elements.

Molecular orbital study of germanium, germanium-gallium and germanium-arsenic clusters

Abstract: The quasirelativistic INDO/1 method has been used to generate molecular orbitals for some {Gex}, doped {GexGay} and {GexAsy} clusters. These one-electron energy levels predefine the density of states (DOS) and/or hole functions. The effect of the cluster size (x=24, 56, 92) and that of dopants on the DOS profiles are discussed. The calculations are compared with those generated by periodic crystal orbitals of the EHT quality.