Binary Axis Research Articles

Temperature dependence of the far infrared spectrum of oriented phenanthrene single crystals

The far infrared absorption spectra (150—40 cm −1) of oriented phenathrene single crystals were recorded on a Fourier transform interferometer at several temperatures in the range 77 to 368 K where the melting point of phenanthrene is 373 K. Strong polarization effects were observed by placing the sample in the position with the binary axis parallel or perpendicular to the beamsplitter plane (or perpendicular and parallel to the plane of incidence). Since the factor group of phenathrene is C 2, the comparison of the observed spectra with earlier observed Raman spectra allowed the assignment of the observed bands to symmetry species A or B. The observed far-infrared spectrum made it possible to complete the assignments proposed from the earlier Raman measurements and to improve the precision of the temperature dependence determinations.

Far-Infrared Magneto-Plasma Wave Transmission and the Dielectric Constant in Bismuth under High Magnetic Fields

Far-infrared magneto-plasma wave transmission in Bi was observed in pulsed high magnetic fields up to 40 T using an HCN laser (337 µm wavelength). The Fabry-Perot interferograms due to the propagation of the Alfven wave were observed as well as the cyclotron resonance, the combined resonance, and the Shubnikov-de Haas effect. The mass densities were obtained for the magnetic field parallel to the binary axis and electric field parallel to the bisectrix and trigonal axis. The lattice dielectric constant e // was obtained as e // =48. As for e ⊥ , however, an anomalously large increase of e ⊥ was observed as the magnetic field was increased above 14 T. The large field-dependence of e ⊥ was explained semi-quantitatively by the interband coupling between the lowest Landau levels of the conduction and valence bands for light electrons.

Magnetostriction of Bismuth and Graphite in Fields up to 40 Tesla

Longitudinal magnetostriction has been measured in bismuth along the binary axis and in graphite along the c -axis in pulsed magnetic fields up to 40 T. The field dependence of the magnetostriction of bismuth is compared with theoretical calculations based on a model proposed by Vecchi et al. for the lowest quantum number Landau levels. A better correspondence with the experimental result is obtained by using a set of parameter values recently given by Hiruma et al. rather than the original Vecchi et al. 's values. For graphite, a large and field-superlinear magnetostriction has been found.

Refinement of the structure of bovine seminal ribonuclease.

AbstractWe report here the refinement at 2.5‐Å resolution of the x‐ray crystal structure of bovine seminal ribonuclease, a dimeric covalent enzyme. The protein, which crystallizes with one molecule in the asymmetric unit, consists of two subunits of identical chemical sequences, related by an almost exact binary axis. The tertiary structure of the subunits is similar to that of the pancreatic enzyme, which shows similar catalytic properties. The refinement was carried out using the restrained least‐squares procedure both in the reciprocal and real spaces. The assemblage of the subunits in the dimer is described and discussed.

Observation of the Magnetic-Field-Induced Semimetal-Semiconductor Transition in Bi under Megagauss Fields

The magnetic-field-induced semimetal-semiconductor transition has been observed in Bi under very high magnetic fields parallel to the binary axis. The transition was observed at 88 T as a change of the transmission of the far-infrared radiation at 337-\ensuremath{\mu}m wavelength at low temperature. The field position of the transition as well as the positions of absorption peaks arising from the Shubnikov-de Haas effect were analyzed in terms of newly determined band parameters.

Pressure-dependent magnetoreflection studies of Bi andBi1−xSbxalloys

Pressure-dependent magnetoreflection results for Bi and ${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}$ ($x=0.05,0.15$) alloys are reported for pressures up to 3 kbar at 77 K, for $\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$ parallel to the binary axis and using a C${\mathrm{O}}_{2}$ laser source operating at 10.6 \ensuremath{\mu}m. The results are interpreted to yield values for the pressure dependence of the $L$-point energy gap and the band-edge cyclotron effective mass. The analysis shows that the pressure dependence of $\frac{{E}_{g}}{{{m}_{c}}^{*}}$ dominates the pressure-dependent magnetoreflection spectra, a result of significance because previous pressure-dependent Fermi-surface studies have assumed $\frac{{E}_{g}}{{{m}_{c}}^{*}}$ to be pressure independent. Furthermore, the analysis shows that the magnitudes of the individual pressure derivatives $\frac{d{E}_{g}}{\mathrm{dp}}$ and $\frac{d{{m}_{c}}^{*}}{\mathrm{dp}}$ are very sensitive to $\frac{d(\frac{{E}_{g}}{{{m}_{c}}^{*}})}{\mathrm{dp}}$ for these materials.

Far-infrared magnetoreflection in bismuth and bismuth-antimony alloys in high magnetic fields

Cyclotron resonances of electrons and holes were observed in Bi and BiSb alloys (containing 0.5, 4.4 at .% Sb) in the magnetoreflection at far-infrared region in pulsed high magnetic fields up to 40 T. The observed magnetoreflection lineshape was compared with the calculated one for the magnetic field parallel to the binary axis for Bi. Cyclotron effective masses of electrons and holes were obtained for Bi and BiSb in the high field range. It was confirmed in Bi that the hole band ( T - 45 band) shows a remarkable non-parabolicity at high magnetic fields. It was also found in BiSb alloys that the cyclotron effective masses of electrons become smaller with increasing Sb concentrations, while the cyclotron effective masses of holes are almost independent of Sb concentration.

ChemInform Abstract: GENERAL MODELS FOR HELICENES

Several geometrical characteristics of 6-, 7-, 10-, 11- helicene have been studied: accuracy of the binary axis, distribution of atoms over three helices, bond distances and angles, planarity and interplanar angles of benzene rings, existence of new planar groups. Two types of general models are suggested and discussed: the triple helix and the staircase model.

Thermoelectric properties and phase transition in Sb2Te3 under hydrostatic pressure up to 9 GPa

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X-ray crystallographic analysis of a progesterone-binding protein. The C222 1 crystal form of oxidized uteroglobin at 2.2 Å resolution

Oxidized uteroglobin, in the C222 1 crystal form, has been analyzed by X-ray diffraction at a resolution of 2.2 Å. Uteroglobin is a dimer, possessing in this crystal form a true binary axis symmetry. It is built from two identical polypeptidic chains of 70 residues each, held together by antiparallel (Cys3—Cys69′, Cys3′—Cys69) disulfide bridges. The observed structure is in agreement with one of the amino acid sequence determinations previously described. It is a monodomain globular protein which contains a high proportion (~70%) of α helix and no β sheets. An oblong hydrophobic pocket is located in a central position around the binary axis. This cavity has the features expected from a progesterone-binding site. The possible mechanisms of hormone binding to uteroglobin are discussed.

Shubnikov-de Haas effect and semimetal-semiconductor transition in bismuth-antimony alloys in high magnetic fields

Shubnikov-de Haas effect is observed in Bi and BiSb alloys (containing 0.1−4.4 at.% Sb) in pulsed high magnetic fields up to 420 kG. It is found that the amplitude of the quantum oscillation remarkably increases by mixing a small amount of Sb in Bi, and that the magnitude of the Hall electric field in BiSb alloy (0.1 at.% Sb) is much larger than that in pure Bi. These observations demonstrate the difference in the scattering mechanism of carriers between Bi and BiSb alloys. The magnetic field induced semimetal to semiconductor transition is observed in BiSb alloy with 4.4 at.% Sb. From the analysis of the Shubnikov-de Haas oscillation in BiSb, the field at which the semimetal to semiconductor transition will occur in Bi is estimated as about 1 MG for the field direction parallel to the binary axis.

Shubnikov-de Haas effect in Bismuth in high magnetic fields

Abstract Shubnikov-de Haas effect in Bi was observed in pulsed high magnetic fields up to 420 kG. Hole resonances were observed up to the second ( N = 1) and the third ( N = 2) peaks for the magnetic fields along the bisectrix and the binary axes, respectively. From the analysis of the resonant magnetic fields, changes of the Fermi level and the carrier concentration were calculated. The field at which the semimetal to semiconductor transition will occur was estimated as 850 kG ∽ 1 MG for the field direction parallel to the binary axis. Anomalously large decrease of the magnetoresistance was observed above 300 kG.

Interdomain phase transition in hematite single crystal

Abstract A simultaneous action of magnetic field and pressure along the binary axis of a hematite single crystal below the Morin point may induce a first order phase transition between two types of domains. This phase transition can be observed by means of elastic coherent scattering of neutrons at new phase “germs”.

General models for helicenes

AbstractSeveral geometrical characteristics of 6‐, 7‐, 10‐, 11‐ helicene have been studied: accuracy of the binary axis, distribution of atoms over three helices, bond distances and angles, planarity and interplanar angles of benzene rings, existence of new planar groups. Two types of general models are suggested and discussed: the triple helix and the staircase model.

Infrared dispersion of lead phosphate at room temperature

Infrared reflection spectra [15–4000 cm -1] along the b (binary axis) and c axes ( A u and B u -type modes) are reported at room temperature as obtained with a Fourier-transform scanning interferometer. The spectra are analyzed with the factorized form of the dielectric function and the infrared-active mode parameters are reported.

Far infrared absorption spectrum of a pyroelectric saccharose single crystal

The far infrared spectrum of a saccharose single crystal shows the polarisation of the vibrational modes. The low frequency mode (49.5 cm-1) polarised along the binary axis, has allowed the authors to explain the temperature dependence of the pyroelectric coefficient.

Hybrid Resonance in a Quantizing Magnetic Field in BiSb

AbstractHybrid resonances are investigated in a quantizing magnetic field in semiconductive BiSb alloys. The measurements are carried out at 1.6 K at frequencies ranging between 120 and 70 GHz with the magnetic field being parallel to the binary axis. It is found that above a definite measuring frequency hybrid resonances can be detected, the occurrences and the field location of which are in effect determined by the redistribution of charge carriers between the component surfaces of the parted Fermi surface in the quantizing magnetic field. The discussion of the results allows the determination of the spin splitting parameter, which is found to be G2 = 0.9. A quadratic relation between energy and momentum gives good agreement between theory and experiment.

Piezospectroscopy of the Raman spectrum ofα-quartz

The first-order Raman spectrum of $\ensuremath{\alpha}$-quartz, consisting of four totally symmetric ${A}_{1}$ lines, four $E$ lines with unresolved LO-TO components, and four LO-TO split $E$ doublets, have been investigated under uniaxial stress. A compressive force $\stackrel{\ensuremath{\rightarrow}}{\mathrm{F}}$ was applied along the trigonal axis $\stackrel{^}{z}$, along the binary axis $\stackrel{^}{x}$, or along ${\stackrel{^}{z}}^{\ensuremath{'}}=(\frac{1}{\ensuremath{\surd}2})(\ensuremath{-}\stackrel{^}{y}+\stackrel{^}{z})$. All splittings and/or shifts were found to be linear in stress and hence describable in terms of a linear-deformation-potential theory. From measurements using these three force directions the two deformation-potential constants characterizing each ${A}_{1}$ and the four constants characterizing each $E$ line have been deduced. The extreme sharpness of the 128-${\mathrm{cm}}^{\ensuremath{-}1}$ $E$ line at liquid-helium temperature allowed a Fabry-Perot interferometer to be used in the study of its behavior. The LO-TO splittings of the $E$ lines at 263, 695, and 1160 ${\mathrm{cm}}^{\ensuremath{-}1}$ were measured to be 1.25 \ifmmode\pm\else\textpm\fi{} 0.09, 2.39 \ifmmode\pm\else\textpm\fi{} 0.10, and -3.02 \ifmmode\pm\else\textpm\fi{} 0.45 ${\mathrm{cm}}^{\ensuremath{-}1}$, respectively, for the phonon wave vector, $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}$ along $\stackrel{^}{y}$; the LO-TO splittings are comparable to the observed linewidths at liquid-helium temperature and were deduced from the zero-stress intercepts of the least-squares fits characterizing the stress dependence of the components. The LO-TO splittings of the 695- and 1160-${\mathrm{cm}}^{\ensuremath{-}1}$ lines were just resolved at liquid-helium temperature for $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}\ensuremath{\parallel}\stackrel{^}{y}$. The LO-TO splittings calculated from the reststrahlen spectra for all eight $E$ lines are in satisfactory agreement with those measured in the present Raman study, even as to the unusual negative sign for the splitting of the 1160-${\mathrm{cm}}^{\ensuremath{-}1}$ line.

Alfvén Wave Propagation in Antimony

The Alfven wave transmission in a thin slab of antimony has been observed at 22–26 GHz and 1.27 K by using high magnetic fields up to 15 Tesla and a carbon film bolometer having a quick response. The experiments were carried out in the Faraday configuration with the magnetic field applied along the principal axis of the crystal (the binary, bisectrix and trigonal axes). The measured mass densities are in agreement with the theoretical values calculated from the previously reported band parameters. The mean collision time of electrons and holes is obtained as 0.8-2.0×10 -10 sec.

Anomalies in the magnetoreflection spectrum of bismuth in the low-quantum-number limit

We report here anomalies observed at high magnetic fields in the magnetoreflection line shape of bismuth $\stackrel{\ensuremath{\rightarrow}}{H}$ parallel to binary, bisectrix axes) and bismuth-antimony alloys $\stackrel{\ensuremath{\rightarrow}}{H}$ parallel to binary axis) and associated with Landau-level transitions originating from the lowest-quantum-number $j=0$ levels of the valence and conduction bands. Also reported are the corresponding Shubnikov-de Haas measurements made in steady magnetic fields up to 220 kG. To interpret these anomalous magnetoreflection line shapes an accurate model for the dispersion relations of the two coupled $j=0$ magnetic energy levels is developed, including the dependence of the magnetic energy levels on the magnetic field and on the wave-vector component parallel to $\stackrel{\ensuremath{\rightarrow}}{H}$. This model is applied to the interpretation of the Shubnikov-de Haas data and to a magnetoreflection line-shape calculation for the experimental conditions under which these anomalies are observed. The calculated line shapes successfully reproduce the large variety of observed line-shape anomalies as well as their relative intensities, thereby providing strong support for this description of the dispersion relations for the $j=0$ magnetic energy levels.