Fermilab top mass and modified Fritzsch mass matrices

Fritzsch like mass matrices with non-zero 22-elements both in U sector and D sector have been investigated in the context of latest data regardingm _t ^phys , |V _ub|, |V _cb|, |V _td| and |V _ts|. Unlike several other phenomenological models, the present model not only accommodates the value ofm _t ^phys in the range 150–240 GeV, encompassing the CDF and D0 values, but is also able to reproduce |V _cb| ≊0.040 and |V _ub/V_cb| = 0.08±0.02 and |V _td| is predicted to lie in the range 0.005–0.014. Further, the angles of the unitarity triangle, related to the CP-violating asymmetries, are calculated to be in the ranges −1.0⩽sin2α⩽−0.1, 0.6 ⩽sin2α⩽1.0 and 0.48⩽sin2β⩽0.56, which are in agreement with other recent calculations.     

Measurement ofL-shell photoelectric cross-sections in lower intermediateZ elements at 6 keV

L-shell photoelectric cross-sections have been measured at 6 keV for eight elements in the range 40⩽Z⩽53. The measurements agree with theoretical calculations.     

Effect of constant-energy surface anisotropy on the thermoelectric figure-of-merit of the n-Bi2 (Te,Se,S)3 solid solutions

A study is reported of the thermoelectric and galvanomagnetic properties of n-Bi₂Te_3−x−y Se_xSe_y solid solutions for 0.12⩽x⩽0.36 and 0.12⩽y⩽0.21 within the 80–300 K temperature region. The thermoelectric figure-of-merit Z has been found to correlate with the parameters of the many-valley energy-band model including anisotropic carrier scattering. It is shown that a decrease in the constant-energy surface anisotropy and scattering anisotropy results in a growth of Z for optimum carrier concentrations in the solid solution. Fiz. Tverd. Tela (St. Petersburg) 41, 187–192 (February 1999)     

The parity violation A4 experiment at forward and backward angles

The A4 Collaboration at the MAMI accelerator in Mainz measures the parity-violating asymmetry in the cross-section of elastic scattering of longitudinally polarized electrons off unpolarized protons from which the contribution of strange sea quarks to the vector form factors of the proton can be derived. Measurements at forward angles 30^° ⩽ θ ⩽ 40^° and two different momentum transfers Q² of 0.23 (GeV/c)² and 0.11 (GeV/c)² have been performed in the past. Measurements at backward angles 140^° ⩽ θ ⩽ 150^° are underway for a separate determination of the strange electric and the strange magnetic form factor at Q ² = 0.23(GeV/c)² .     

Energy dependence of photon-inducedL shell x-ray intensity ratios in Ta and W

TheL shell x-ray intensity ratios have been measured for the elements Ta and W by photoionization ofL shell electrons in the photon energy region 14⩽E⩽44 keV. The experimental results are compared with those calculated at the photon energies used in the present measurements. The measured values show fairly good agreement with the calculated values within the experimental uncertainties.     

Nuclear structure of <Superscript>128–140</Superscript>Nd in IBM

We determined the most appropriate Hamiltonian that is needed for calculations of nuclei in the A ≅ 130 region from the viewpoint of the interacting boson model (IBM). Using the best-fitted values of parameters in the Hamiltonian, we have calculated energy levels and B(E2) values for a number of transitions in some doubly even Nd nuclei of 128 ⩽ N ⩽ 140. The results were compared with the previous experimental and theoretical data, and it is observed that they are in good agreement. The calculations have been extended to Nd isotopes for which some B(E2) values are still not known. The text was submitted by the author in English.     

Anomalous behavior of the interlayer resistance of a BSCCO-2212 crystal in a parallel magnetic field

The electrical resistance across the Cu-O layers of a BSCCO-2212 single crystal is investigated in the range of angles 0°⩽φ⩽90° between the magnetic field H⩽15 T and the ab plane. It is found that the temperature dependence R(T) at the transition into the mixed state is much sharper for φ≃0° than for 1°≲φ≲90°, where R is determined by the perpendicular component of the magnetic field and is described by the Arrhenius law R∼exp(−U/T). For H∥ ab hysteretic jumps in R(T, H), which vanish as the current increases, are observed at fields in the range 5.5⩽H⩽11 T. This effect can be attributed to a commensurate phase transition in a lattice of Josephson vortices. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 123–128 (25 January 1996)     

Infinite nuclear matter model and a new mass formula for atomic nuclei

The ground-state energy of an atomic nucleus with asymmetryβ is considered to be equivalent to the energy of a perfect sphere made up of the infinite nuclear matter of the same asymmetry plus a residual energyη called the local energy,η represents the energy due to shell, deformation, diffuseness and exchange Coulomb effect etc. Using this picture and the generalized Hugenholtz- Van Hove theorem of many-body theory a new mass formula has been developed. Based on this, a mass table containing the mass excesses of 3481 nuclei in the range 18 ⩽A ⩽ 267 has been made. This mass formula is compared with other mass models.     

μSR in oxygen deficient YBa2Cu3O x (6.5⩽x⩽7.0)

A systematic μSR study of the local magnetic field distribution in a series of oxygen deficient YBa₂Cu₃O _x samples with 6.5⩽x⩽7.0 is reported. Special attention was given to perform the experiments under the same conditions, so that the oxygen content of the measured samples was the only parameter varied. The behavior of the depolarization rate σ as a function of the oxygen contentx was found to have strong similarities with the behavior of the critical temperatureT _c as a function ofx. In particular, two step-like increases of σ were observed abovex=6.7 and 6.9. The temperature dependence of the normalized depolarization rate σ(T)/σ(0) is well described by the two-fluid model forx⩾6.781(1) and clearly deviates from this behavior forx⩽6.704(1). Our results are compared to those obtained by other groups.     

The search for cosmic strangelets with the supersonic concorde and with JACEE's circumpolar balloon flight in Antarctica

The search for cosmic strangelet nuclei was carried out by two experiments with emulsion chambers. A balloon-borne JACEE emulsion chamber was flown at 3.5 g/cm² for 200 h in Antarctica (JACEE-10 experiment) and the Concorde flights were made by ECHOS at an atmospheric depth of 110 g/cm² between Paris and New York. No nuclei withZ⩾30 survived after traversing 60–120 g/cm² of the detector materials in the JACEE instruments. No evidence for a long mean free path were found in the zenith angle distribution forZ/β⩾26 nuclei. The exposure factor used by the JACEE was 72 m²hsr. The intensity upperbounds,I⩽(2.2–9.7)×10⁻²/m²h sr, were obtained for strangelets having an atmospheric attenuation length of 220−50 g/cm², which corresponds to the case for mass numberA=100–10000 andZ/β > 13. Concorde experiments (ECHOS) used both a thin and a thick emulsion chamber. The total exposure was 209 m² h sr and no candidates with chargeZ⩾30 were found. The largest track hadZ/β=28.6±1.29 withβ ∼ 1. Nuclei observed with charge 13⩽Z⩽30 were consistent with the survival intensity of ordinary nuclei. The flux bounds from the ECHOS experiments were I⩽(2.1–5.0) x 10⁻²/m²h for strangelets with mass number 100⩽A⩽1000.     

Electron transport in Chevrel phase superconductors,Cu1.8Mo6S8−y Se y , 0⩽y⩽8 and Cu1.8Mo6S8−y Te y , 0⩽y⩽4—Fit to Cote-Meisel theory

Normal state electrical resistivity of the Chevrel phase compounds of the type Cu_1.8Mo₆S_8−y Se _y , 0⩽y⩽8 and Cu_1.8Mo₆S_8−y Te _y , 0⩽y⩽4 is analysed on the basis of the generalized diffraction model which incorporates a postulate on electron-phonon interaction,viz phonons with wavelength exceeding the electron mean-free path are ineffective electron scatterers. Fit obtained by this model was found to be superior to other models based on the interbands-d scattering of electrons.     

Nuclear magnetic relaxation in ferrimagnetic Y3Fe5−x SixO12 films

The effect of silicon impurities on the damping of spin-echo signals from the ⁵⁷Fe nuclei of tetrahedral Fe³⁺ ions in epitaxial yttrium-iron-garnet films was investigated. It was found that for silicon concentrations 0.015⩽x⩽0.037 the damping of the spin echo is a two-component process, which made it possible to separate nuclei into two types, differing by both the longitudinal and transverse magnetic relaxation times. For silicon concentrations 0.044⩽x⩽0.073 the decay of the echo can be described by one exponential and all nuclei in the sample have the same transverse relaxation times and the same longitudinal relaxation times. The experimental results are interpreted on the basis of the supposition that impurity “macromolecules” form around the Si⁴⁺ ions. The relaxation times of the iron nuclei in a “macromolecule” are much shorter than the relaxation times of iron nuclei belonging to the matrix ions. The radius of a “macromolecule” is estimated on the basis of percolation theory. Fiz. Tverd. Tela (St. Petersburg) 40, 1494–1497 (August 1998)     

Direct observation of phase separation in La1−x CaxMnO3

In a study of the infrared optical absorption spectra of polycrystalline La_1−x Ca_xMnO₃ (0.1⩽x⩽0.8), a contribution from free charge carriers is observed below the Curie temperature for compositions with x⩽0.4. The existence of this contribution for samples with a high resistivity is a direct proof of the existence of “metallic” drops in an insulating matrix. The relative volume of the “metallic” phase is estimated. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 89–92 (10 July 1998)     

Multiconfiguration Dirac-Fock results for forbidden transitions in the 2<Emphasis Type="Italic">p</Emphasis><Superscript>4</Superscript> configuration

Relativistic configuration interaction calculations with the inclusion of the Breit interaction, quantum electrodynamics and finite nuclear mass corrections have been carried out in the extended optimal level scheme using multiconfiguration Dirac-Fock wavefunctions on the forbidden transition probabilities for the 2p ⁴ ground state configuration of the oxygen isoelectronic sequence for 8 ⩽ Z ⩽ 42. Electric quadrupole and magnetic dipole transition probabilities are reported for transitions between several of these levels. Our results are compared with those from other theories and experiments. Our energy levels are in better agreement with experiment than other theories.     

Levels in74As from the74Ge(p,nγe)74As reaction

The low-lying levels in⁷⁴As have been studied by means ofγ-ray and internal conversion electron spectroscopy following the⁷⁴Ge(p,n)⁷⁴As reaction. New levels at 372.7, 532.8, 632.1, 731.6, 752.7, 758.3, 801.6, 902.9 and 1128.5 keV, not observed in earlier studies, have been established.J ^π assignments have been made to several low-lying levels. An earlier ambiguity regarding the identification of an isomeric level has been clarified. The half-life of a level at 271.4 keV has been measured to be 1.0±0.1 nsec; in addition, limits on half-lives of levels at 182.7, 277.5 and 425.4 keV have been assigned. The level structure is discussed on the basis of available nuclear models.     

Dependence of the superconducting transition parameters on the solid-solution composition and Te excess in Sn1−z PbzTe:In

A low-temperature (0.4–4.2 K) measurement of the temperature dependences of the resistivity of two series of samples, SnTe_1+y and Sn_0.8Pb_0.2Te_1+y solid solution, doped with 5 at.% In, is reported. The parameters of the superconducting transition, namely, the critical temperatures T _c and the second critical magnetic field H _c2, and their dependences on tellurium excess (0⩽y⩽0.06) have been determined. The observed variation of the critical parameters with increasing tellurium excess in the samples is associated with a change in the filling by holes of the indium-impurity resonance states. Fiz. Tverd. Tela (St. Petersburg) 41, 2132–2134 (December 1999)     

Phase transitions and magnetic-transport phenomena in the system La2/3Ba1/3(Mn1−x Cox)O3

A study is performed of the crystalline structure, magnetization, and magnetotransport properties of the system La_2/3Ba_1/3(Mn_1−x Co_x)O₃ with perovskite structure. It is shown that cubic solid solutions exist over the entire range of cobalt concentrations 0⩽x⩽1. Compositions with x⩽0.2 are ferromagnets with maximum resistance near T _C . Compositions with 0.2<x<0.4 manifest properties of inhomogeneous ferromagnets. Measurements of magnetic properties indicate the absence of long-range magnetic order in compositions with 0.5⩽x⩽0.9, which are probably spin glasses. The spontaneous magnetization of cobaltate (2μ _B per formula unit) corresponds to ferromagnetic ordering of the moments of the Co³⁺ and Co⁴⁺ ions found in the intermediate spin state. It is conjectured that the magnetoresistance consists of an extrinsic and an intrinsic contribution. The first arises as a result of intergrain transport of spin-polarized charge carriers, and the second, as a result of magnetic ordering near T _C . The magnetoresistance is essentially independent of the spontaneous magnetization and decreases abruptly as the cobalt concentration is increased with a corresponding transition from long-range to short-range magnetic order. Zh. éksp. Teor. Fiz. 116, 604–610 (August 1999)     

Spin-glass like behaviors in La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Tb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> perovskite

A series of samples of La_1−x Tb _x MnO₃ (0⩽x⩽0.15) are prepared. The static and dynamic magnetizations of La_1−x Tb _x MnO₃ have been investigated. The results indicate that the spins with the short-range order are frozen into random direction at low enough temperatures which leads to the samples exhibiting the spin-glass like behavior. It is considered that the spin-glass like behavior originates from the competition between ferromagnetic double exchange among Mn³⁺ and Mn²⁺ and antiferromagnetic superexchange among Mn³⁺ and Mn³⁺, as well as Tb³⁺ and Tb³⁺.     

The ratioR i for nondissociative ionization of molecular hydrogen by antiproton/proton impact

The theoretical ratioR _i of antiproton/proton cross sections for nondissociative ionization of hydrogen molecule has been obtained as a function of the impact energyE in the range 30⩽E⩽2500 KeV lab. The required cross sections were computed in the close-coupling formulation of the semiclassical impact parameter theory using a simple one-active electron model for the molecular target. The ratioR _i is important for the analysis of the recent experimental data of Andersen et al. on antiproton scattering and the understanding of the collisional mechanisms in the KeV range.