Magnetotransport and superconductivity of α-uranium

We have measured the electrical resistivity, magnetoresistance and Hall effect on several new single-crystal samples and one polycrystalline sample of α-U. The residual resistivity ratios of these samples vary from 13 to 315. Matthiessen's law appears to hold above the onset of the charge-density wave phase transitions that begin near 43?K, but not below this temperature. Sharp features at all three charge-density wave transitions are observed and the effects of high magnetic fields on them are presented and discussed. The magnetoresistance is anisotropic, reaches 1000% at 2?K and 18?T and does not exhibit Kohler scaling. The Hall coefficient is positive, independent of magnetic field and slightly temperature dependent above about 40?K in agreement with earlier studies. Below 40?K the Hall coefficient changes sign as the temperature falls, varies with field and becomes much more strongly negative at the lowest temperatures than has been reported. Some of our results suggest that a spin-density wave may coexist with the charge-density wave states. Superconductivity is observed in two of our samples; we argue that it is intrinsic to α-U and suggest that it is consistent with a two-band model. Several parameters characterizing the transport and superconductivity of α-U are estimated.     

α-Decay half-lives, α-capture cross sections, and α-nucleous interaction

The expression for the α-nuclear potential was found. This potential describes the α-decay half-lives for the ground states of nuclei and the α-particle capture cross sections for ⁴⁰Ca, ⁴⁴Ca, ⁵⁹Co, ²⁰⁸Pb, and ²⁰⁹Bi nuclei well. The potential was used to calculate the probabilities of α-transitions from the ground states of parent nuclei to different excited states of daughter nuclei. Simple analytical relations for calculating α-decay half-lives for transitions between the ground states of nuclei are determined.     

Processing and characterization of α-elastin electrospun membranes

Elastin isolated from fresh bovine ligaments was dissolved in a mixture of 1,1,1,3,3,3-Hexafluoro-2-propanol and water were electrospun into fiber membranes under different processing conditions. Fiber mats of randomly and aligned fibers were obtained with fixed and rotating ground collectors and fibrils were composed by thin ribbons whose width depends on electrospinning conditions; fibrils with 721 nm up to 2.12 μm width were achieved. After cross-linking with glutaraldehyde, α-elastin can uptake as much as 1700 % of PBS solution and a slight increase on fiber thickness was observed. The glass transition temperature of electrospun fiber mats was found to occur at ～80 °C. Moreover, α-Elastin showed to be a perfect elastomeric material, and no mechanical hysteresis was found in cycle mechanical measurements. The elastic modulus obtained for random and aligned fibers mats in a PBS solution was 330±10 kPa and 732±165 kPa, respectively. Finally, the electrospinning and cross-linking process does not inhibit MC-3T3-E1 cell adhesion. Cell culture results showed good cell adhesion and proliferation in the cross-linked elastin fiber mats.     

SIA energetic and structural morphology of α-iron

In this paper, the stability of various atomic configurations containing a self-interstitial atom (SIA) in a model representing α-iron is investigated. From the energy panorama maps of the SIA located in possible non-equivalent interstitial sites, six relatively stable self-interstitial sites are found, whose structures and formation energies have been described and calculated using the modified analytical embedded atom method and molecular dynamics. The simulation results indicate that the [110] dumbbell interstitial is the energetically most favorable configuration, which is in good agreement with the experimental and ab initio results, and the distances between two displaced atoms that compose the [100], [110] and [111] direction dumbbells have been computed to be 0.68a, 0.65a and 0.29a, respectively, not all being about 0.75a apart. The relaxed displacements up to the fifth-nearest-neighbor atoms around the SIA in O interstitial position are also calculated.     

Microwave spectra and internal rotation in α-angelicalactone

The rotational spectrum of α-angelicalactone has been analyzed in the frequency range 18.0–40.0 GHz. The internal rotation barrier of the methyl group has been determined in the ground and four vibrationally excited states from the A-E splittings. The results indicate a possible rotational between the methyl torsion and the ring puckering mode. The ground state rotational parameters are consistent with a planar ring skeleton. The dipole moment components obtained from Stark displacements are μ_a = 3.16(1) D and μ_b = 2.59(2) D with a total value of 4.08(2) D.     

Competition between α-decay and β-decay for heavy and superheavy nuclei

In this work, the β-stable region for Z 90 is proposed based on a successful binding energy formula.The calculated β-stable nuclei in the β-stable region are in good agreement with the ones obtained by Mo¨ller et al. The half-lives of the nuclei close to the β-stable region are calculated and the competition between α-decay andβ-decay is systematically investigated. The calculated half-lives and the suggested decay modes are well in line with the experimental results. The decay modes are mostly β--decay above the β-stable region. Especially for Z 111,all the decay modes are β--decay. Regarding the nuclei above the β-stable region, α-decay and β--decay(α+β-)can occur simultaneously when Z 112. This is a very interesting phenomenon. The competition between α-decay and β-decay is very complex and drastic below the β-stable region. The predictions for half-lives and decay modes of the nuclei with Z =107–110 are presented in detail.     

Structure and magnetic properties of flower-like α-NiS nanostructures

In this paper we report the structure and magnetic properties of flower-like α-NiS nanostructure prepared by a facile one-step hydrothermal method. The flowers consist of polycrystalline nanoflakes, and the nanoflakes are composed of single crystalline nanocrystals with an average size of about 15 nm. The α-NiS flowers exhibit the transition from paramagnetism to ferromagnetism with the blocking temperature of about 12 K. The field dependences of the magnetization prove that these flowers demonstrate a coexistence of antiferromagnetism and ferromagnetism at 5 K, and exhibit a strong paramagnetic response at temperature higher than 100 K.     

Conformational and Electronic Interaction Studies of P-Substituted α-Phenoxyacetones

The v_co analysis of p-substituted α-phenoxy-acetones X-θ-O-CH₂-C(O)-Me (1-6) indicates the existence of the cislgauche rotational isomerism. The nearly constant increase in the cislgauche population ratios for the whole series, on going from carbon tetrachloride to acetonitrile, and the small sensitivity of the carbonyl frequency shifts (Δv_c) for the cis rotamer, on going from electron-attracting to electron-donating substituents, are interpreted as an interplay of the Field (F) and the Inductive (-I) Effects, which originates an almost constant carbonyl bond order, and suggests that the cis rotamers have almost the same energy in the whole series. The decrease in the cislgauche population ratios, in all solvents, and the deshielding effects on the carbonyl carbon atom, and on the methylene carbon atom in a weaker extent, observed in the ¹³C NMR spectra, on going from electron-attracting to electron-donating substituents, are discussed in terms of φ*CO/ⁿO orbital and Ar^δ+ -O^δ- — C^δ+ =O^δ- Coulombic interactions, which stabilize the gauche rotamers of the investigated compounds.     

Inelastic α-scattering from 90Zr and 96Zr

The ⁹⁰Zr and ⁹⁶Zr(α, α') reactions have been studied at 35.4 MeV with an energy resolution of 35–50 keV. Angular distributions were measured between 10 and 50 degrees for an E_x range of 1.5 to 6.0 MeV. Spin assignments have been made on the basis of the shapes of the differential cross sections and by comparison with collective DWBA calculations. For ⁹⁶Zr discrepancies in spin assignments have been removed for several levels. Within the framework of the vibrational model isoscalar transition rates have been derived.     

Deuteron chemical shift and EFG tensors in α-glycine

By computer fitting of resonance lines in deuteron spectra of perdeuterated crystals, deuteron chemical shifts in crystals are measured with an accuracy of ±0.3 ppm. Second-order quadrupole shifts must be taken into account. An important advantage of the method is that the measured chemical shifts and the shift tensors are automatically related to EFG tensors which can be assigned easily. The method is applied to α-glycine for which a shift anisotropy Δσ = 21 ± 9 ppm has been reported for the methylene protons. Full EFG and chemical-shift tensors are reported at both methylene deuteron sites, and motionally averaged tensors are reported for the ND₃⁺ sites. The shift anisotropies Δσ for the methylene deuterons are 4.7 and 9.4 ppm, respectively. Significant differences of the isotropic shifts and quadrupole coupling constants are also observed for these two deuterons. They are interpreted as evidence for the formation of a weak CH … O hydrogen bond in α-glycine.     

Electronic structure and magnetic susceptibility of monoclinic α-plutonium

The electronic structure of the α-phase of plutonium has been calculated by the band methods with allowance for the spin-orbit interaction and Coulomb correlations in the complete matrix form (the LDA + U + SO method). The strong spin-orbit interaction of the 5 f electrons is manifested in the splitting of the calculated density of the 5f states, which makes a small contribution at the Fermi level on the order of the contribution from the 6d states. Using the results of the ab initio calculations, the spin and orbit contributions to the magnetic susceptibility of α-plutonium have been determined. Along with the impurity contribution, they describe well the experimental data on the susceptibility of this plutonium phase to a temperature of 300 K.     

Rotational Inhibition and Magnetization Transfer in α-Crystallin Solutions

The magnetic field dependence (dispersion profile) of 1/T₁ of solvent water protons of solutions of the mammalian eye lens protein α-crystallin has a reversible nonlinear dependence on concentration which, as protein concentration increases above ∼20 wt.%, changes rapidly from a profile characteristic of mobile protein solute to a profile characteristic of rotationally immobilized protein (e.g., chemically cross-linked). From quantitative comparisons of new measurements of K at 200.1 MHz, the rate of water-to-protein interfacial magnetization transfer, with earlier data for α-crystallin and bovine serum albumin (BSA), we conclude, for α-crystallin, that: (i) Brownian rotation is slowed by intermolecular interactions at unexpectedly low concentrations; (ii) K is mediated by the newly reported, long-lived, protein hydration sites with the same surface density as BSA; and (iii) ¹⁴N peaks seen in solvent 1/T₁ arise from interfacial magnetization transfer plus diffusion to protein NH magnetization sinks.     

Orientation relationship between α-Fe precipitate and α-Al2O3 matrix in iron-implanted sapphire

Fe ions were implanted into α-Al₂O₃ single crystals (sapphire) at room temperature and annealed in a reducing atmosphere. The orientation relationships (ORs) between α-Fe particles and sapphire matrix were investigated using transmission electron microscopy (TEM). All the α-Fe particles have the orientation relationship (OR) of (1 1 1)_α-Fe || (0 0 0 1)_sapphire and ${[1\overline{1}0]}_{\alpha \text{-Fe}}\left|\right|{[11\overline{2}0]}_{\text{sapphire}}$ with sapphire. This OR is predicted precisely by the coincidence of reciprocal lattice points (CRLP) method. The other OR of (1 1 0)_α-Fe || (0 0 0 1)_sapphire and ${[111]}_{\alpha \text{-Fe}}\left|\right|{[5\overline{1}\overline{4}0]}_{\text{sapphire}}$ reported before is confirmed by the same method to be one of the secondary preferred orientation relationships in the α-Fe/sapphire system.     

The α-decay energies and halflives of 195g,mAt and 199Fr

The α-decay energy and halflife of ^195mAt were determined to be 6960±20 keV and 385⁺⁶⁹ ₋₅₁ ms respectively, on the basis of genetic correlations in the ¹⁶⁹Tm(³⁶Ar, α6n)¹⁹⁵At reaction, while those of ^195gAt measured simultaneously were 7105±30 keV and 146⁺²¹ ₋₁₇ ms respectively, reconfirming the previously reported values. A new isotope ¹⁹⁹Fr was also produced and identified in the same way in the ¹⁶⁹Tm(³⁶Ar, 6n)¹⁹⁹Fr reaction, yielding E_α= 7655±40 keV and T_1/2= 12⁺¹⁰ ₋₄ ms. Received: 26 March 1999     

Model of grain-boundary self-diffusion in α- and β-phases of titanium and zirconium

A model of the grain-boundary self-diffusion process in metals undergoing phase transitions in the solid state is proposed. The model is based on the ideas and approaches of the theory of nonequilibrium grain boundaries. It is shown that the range of application of basic relations of this theory can be extended, and they can be used to calculate the parameters of grain-boundary self-diffusion in high-temperature and low-temperature phases of metals with phase transition. Based on the constructed model, activation energies of grainboundary self-diffusion in titanium and zirconium are calculated, and their anomalously low values in the low-temperature phase are explained. The calculated activation energies of grain-boundary self-diffusion are in good agreement with experimental data.     

The α-efficiency of corals and its importance for ESR-dating

The uncertainty in an ESR age results almost completely from the error in the evaluation of the annual dose. In the case of corals, α-efficiency has a high influence on D_E (Paleodose). The published k_α-values vary from 0.05 to 0.2, so the correct determination of k_α is crucial. In this experiment, based on direct irradiation with an ²⁴¹Am-source, we used seven samples (20 aliquots for each sample) with different ages. The first aim was to improve the measurement conditions to reach a reliable data base for the α-efficiency calculation and the second was the question of age dependency of k_α. With respect to the results of our experiments we propose an α-efficiency value for corals of 0.06–0.07 which leads to younger ages of about 7–10% less than with the k_α factor of 0.05 we used in previous studies.     

Antioxidative and α-glucosidase inhibitory constituents of Polyscias guilfoylei: experimental and computational assessments

Molecular Diversity - Searching for bioactive agents from medicinal plants, eleven constituents were isolated from Polyscias guilfoylei stem for the first time, including a nucleoside uracil (1),...     

Atomic positions and diffusion paths of h and he in the α-Ti lattice

The solution energy of H and He in various interstitial and substitution positions in the hcp lattice of α-Ti has been calculated based on the method of electron density functional. The lowest solution energy of He corresponds to the basal octahedral position and that of H corresponds to the octahedral position (next in energy is the tetrahedral position). The calculated vibration frequencies of H in various positions are used for identification of lines in the vibration spectrum obtained by the method of neutron inelastic scattering. Taking into account these spectra, it can be concluded that hydrogen atoms occupy in the hcp lattice of Ti both the octahedral and tetrahedral positions even at 600 K. The available experimental data do not contradict the conclusion that the octahedral position is more preferable in α-Ti. The energy barriers are estimated for various diffusion paths of H and He.     

gem-Difunctionalization of α-diazoarylketones with diaryldiselenides and N-halosuccinimides: facile synthesis of α-halo-α-arylseleno ketones

Molecular Diversity - An efficient synthesis of α-halo-α-arylseleno ketones has been developed via gem-difunctionalization of α-diazoarylketones with diaryldiselenides and...     

Vibrational Spectra of α-Pyrazinamide and 15N-α-Pyrazinamide

α-Pyrazinamide and its α-Pyrazinamide-d² as well as the ¹⁵N-isotopic derivative were synthesized with an isotopic content of 99.4% and their Raman and infrared spectra were recorded and assigned on the basis of isotopic shifts.