Wave propagation in quasi-one-dimensional quantum plasma in a magnetic field

A cold electron gas fills the lowest Landau level for high enough magnetic fields and for low enough densities. Such a situation is expected to occur for the Malmberg-O'Neil experiment and also for pulsar crusts and atmospheres. Such plasmas behave as a quasi-one-dimensional system and exhibit some peculiarities in their wave structure. We study the dispersion and damping of the low frequencies, i.e., the whistler mode, and the extraordinary mode for zero temperature. The behavior of the whistler mode depends critically on the filling number _Fc=_F/ , where _F is the Fermi energy and is the cyclotron frequency. The one-dimensional character of the system affects the pair excitation spectrum and thus the decay of modes. We find that, in contrast to the three-dimensional situation, the plasma mode and the extraordinary mode remain undamped, while the whistler mode is undamped for all but very highk values.     

The search for top quarks at hadron colliders: a realistic appraisal

We study means of identifying top quarks of mass in the range 70–120 GeV at the CERN and FNAL \(\bar pp\) colliders. We show that “W+dijet” production presents a serious background to the conventional “isolated electron+dijet” signature of top. We study an improved signature, calculate the expected event rates, and discuss the determination of the mass of the top quark.     

On the origin of additional peaks in the photoelectron spectra of yttrium

Ultraviolet Photoemission analysis of yttrium metal reveals well defined features far below the conduction band. In order to elucidate their origin, we have used X-ray/Ultra violet photoelectron spectroscopy together with inverse photoemission. The comparison of the spectra of clean yttrium and of H exposed yttrium suggests that these structures are most probably due to hydrogen bands, hydrogen being either in a stable surface hydride form or as subsurface H.     

Macroscopic persistent currents in YBa2Cu3O7

Persistent currents in polycrystalline YBa₂Cu₃O₇ rings have been investigated by measuring the spatial distribution of the magnetic flux trapped in field-cooled samples. The results unambiguously show that macroscopic persistent ring currents exist. The critical current density depends very sensitively on the sample quality, reachingj _c 250 A/cm² at 77 K for our best samples.     

Searching for optimal configurations by simulated tunneling

Optimization theory deals with algorithms finding the lowest cost (energy) configuration in a minimal number of steps. When the cost function has many local minima, the deterministic algorithms become easily trapped in suboptimal solutions. The simulated annealing method tries to overcome this difficulty by introducting thermal noise in the problem. Here we explore the possibility of implementing search procedures analogous to the quantum tunneling effect. The suggested dynamics is a guided diffusion process of an interactingpopulation of configurations. Different dynamical aspects of the search process are formulated first in a simple one-dimensional tight-binding model with a hierarchical potential. The new algorithm is then applied to the Traveling Salesman Problem. It is demonstrated that the use of interacting, evolving populations of tours representing our wave packet leads to systematic improvements and possibly, to the optimal tour. In addition, the structure of the cost function landscape for a given instance becomes locally accessible. The performance of the algorithm and its implications for parallel computing and genetic programming are briefly discussed.     

Synthesis of 24-epiteasterone

Starting from ergosterol, the synthesis of the brassinosteroid 24-epiteasterone has been achieved by the use of a new scheme for introducing a 3-hydroxy-6-keto group as the result of the Birch reduction of the corresponding 5-hydroxy-⁷-3,6-dione.Institute of Bioorganic Chemistry, Belorussian Academy of Sciences, Minsk. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 224–227, March–April, 1992.     

Behavior of large nucleic acids in reversed-phase high-performance liquid chromatography.

Large nucleic acids can be separated by reversed-phase high-performance liquid chromatography. Analysis shows that the retention time depends not only on the chain length but also on the base composition and the secondary structure of the molecule. A model is proposed to interpret their behavior. This model, called "multiple-point interaction theory" is based on the observation that macromolecules are flexible and very large compared to the hydrophobic phase (octadecylsilane) of the column. It explains the behavior of large nucleic acids in terms of an equilibrium of the macromolecule between the two phases through a multiple-point attachment to the chromatographic matrix, the parameters of the equilibrium being both the hydrophobicity of the base and the number of attachment points. This model fits the experimental data and can be applied to all types of flexible macromolecules, especially proteins and nucleic acids, when they are chromatographed on reversed-phase columns. The model is used to explain the separation of nucleic acids of importance in molecular biology.     

Base-atom recognition in protein adsorption to alkyl agaroses.

The three proteins phosphorylase b, calmodulin and fibrinogen are adsorbed onto thioalkyl derivatives of Sepharose much more strongly than onto gels carrying the same alkyl residue coupled via a carbamate linkage. This enhancement of binding onto alkyl-S-Sepharoses compared with alkyl-N-agaroses is not primarily due to an increase in the extent of conformational changes of the proteins occurring on the gel surface. This can be shown in experiments with the tripeptide Trp-Trp-Trp. The Trp tripeptide is also adsorbed with a much higher affinity to butyl-S-Sepharose than to butyl-N-Sepharose, showing that the primary interaction between the immobilized alkyl residue and the amino acids of the protein is decisive for adsorption. A model stressing the strong influence of an atom or a group of atoms at the base of an immobilized alkyl residue is described as "base-atom recognition".     

Determination of gallium by anodic stripping square-wave voltammetry Detection of a GaZn intermetallic compound and its destruction by Sb in an NaSCNNaClO(4) supporting electrolyte

Reproducibility for successive determinations with a hanging mercury drop electrode is assessed in relation to solution stirring, drop size and back-diffusion to the mercury thread. The effect of experimental parameters such as drop size, deposition time and gallium concentration on the observed stripping current is investigated. The interference of zinc present in a 0.5M NaSCN + 4.2M NaClO(4) supporting electrolyte on the gallium detection limit and calibration plots is described. Formation of an intermetallic compound with a Zn:Ga ratio of 2:3 and its destruction by co-deposition of zinc with Sb are reported. A detection limit of 10(-8)M gallium was obtained in the presence of 10(-5)M Sb(III).