Evidence for p-f mixing in U3P4 and U3As4 from optical spectroscopy

The near normal incidence reflectivity of the ferromagnets U₃P₄ and U₃As₄ and the isostructural but diamagnetic compounds Th₃P₄ and Th₃As₄ has been measured from 0.03 to 12 eV. Trithorium tetraphosphide and tetraarsenide are shown to be indirect gap semiconductors with gap energies of 0.43 and 0.39 eV, respectively. U₃P₄ and U₃As₄ display similar sets of p→d transitions than the corresponding thorium compounds, however, they are shifted by 0.85 eV to lower photon energies. It is concluded that the uranium compounds are metals due to a merging of the valence p band into the 6d conduction band giving direct experimental evidence for a p-f mixing effect of the same size. Energy level schemes are derived.     

Magnetic properties of the uranium sesquichalcogenides

Magnetic measurements on the orthorhombic uranium sesquichalcogenides and orthorhombic U₃Te₄ were performed in the temperature range 4.2–1000 K and in magnetic fields up to 140 kOe. The temperature dependence of the reciprocal susceptibility was found to be curvilinear for all the investigated compounds. At low temperatures U₂Te₃ and U₃Te appeared to be antiferromagnetic below 106 K. U₂Se₃ and U₂S₃ seem to have a more considerable ferromagnetic contribution below 60 and 80 K, respectively. The magnetic properties are discussed in terms of crystal structure and related properties of the investigated compounds.     

Nonstandard U q(so3) and U q(so4): tensor products of representations, oscillator realizations and roots of unity

Nonstandard q-deformed algebras U _q(so₃) and U _q(so₄), which can be embedded into U _q(sl₃) and U _q(sl₄) and are coideals in them, are considered. It is shown how to multiply finite dimensional representations of U _q(so₃) when q is positive. Homomorphisms from U _q(so₃) and U _q(so₄) to the q-oscillator algebras are given. By making use of these homomorphisms, irreducible representations of U _q(so₃) and U _q(so₄) for q equal to a root of unity are obtained.     

Non-stoichiometry in uranium sesquinitride

A statistical model is proposed for analyzing thermodynamic properties of non-stoichiometric uranium sesquinitride. It consists of the combination of the site exclusion mechanism and cluster formation reactions. The model was applied to the three ionic possibilities of U_3/2⁴⁺U_1/2⁶⁺N₃^3?, U⁴⁺U⁵⁺N₃^3? and U₂³⁺N₃^2?. By fitting the theoretical equations to the experimentally observed data, it was found that the set U_3/2⁴⁺U_1/2⁶⁺U₃^3?, β=2, 1:2 cluster gave the most satisfactory results. From β=2, the upper limit of non-stoichiometry is expected to be N/U=1·75. The result that the 1:2 clusters predominantly exist in U₂N_3+x suggests the existence of UN_1·75 phase. The energy required for nitrogen atom for occupying the lattice site of the crystal, E, was calculated to be ?120·5 kcal/mole, and the interaction energy to form clusters, E_c, was ?11·07 kcal/mole.     

Enhanced superhyperfine structure of the EPR spectra of a U<Superscript>3+</Superscript> ion introduced into the Van Vleck paramagnet LiTmF<Subscript>4</Subscript>

The observation of the superhyperfine structure (SHFS) in EPR spectra due to enhanced nuclear magnetism is reported. The X-band spectrum of a U³⁺ ion introduced into the Van Vleck paramagnet LiTmF₄ is measured in the temperature range of 5–20 K and compared with the spectra of LiLuF₄:U³⁺ and LiYF₄:U³⁺ single crystals. The spectra reveal well-resolved and strikingly different SHFS. The SHFS of Li(Lu, Y)F₄:U³⁺ is due to the fluorine ions forming the nearest surroundings of the U³⁺ ion. The main contribution to the SHFS of the U³⁺ spectrum in LiTmF₄ comes from the Tm³⁺ ions with a highly enhanced nuclear gyromagnetic tensor. The text was submitted by the authors in English.     

A study of the Barkhausen effect in U3P4 single crystal

The present work is the study of the amplitude distribution and the course of the power spectra of the Barkhausen impulses during the magnetization reversal of U₃P₄ single-crystal. On the basis of the obtained results the dynamics of the magnetization processes is discussed. In agreement with some preceding experimental papers it is shown that U₃P₄ has a large anisotropy of initial susceptibility.     

On a general analytic formula for U q(su(3)) Clebsch-Gordan coefficients

We present the projection operator method in combination with the Wigner-Racah calculus of the subalgebra U _q(su(2)) for calculation of Clebsch-Gordan coefficients (CGCs) of the quantum algebra U _q(su(3)). The key formulas of the method are couplings of the tensor and projection operators and also a tensor form for the projection operator of U _q(su(3)). We obtain a very compact general analytic formula for the U _q(su(3)) CGCs in terms of the U _q(su(2)) Wigner 3nj symbols.     

Calculations of the vibrational frequency and isotopic shift of UF6 and U2F6

Molecular structure, vibrational frequency and infrared intensity of UF6 are investigated by using the revised Perdew Burke-Enzerhof function with the triple-zeta polarized basis set. The calculation results are in good agreement with the experimental values and indicate the existence of a stable U2F6 molecule with a multiple bonded U2 unit. The calculation results also predict that the D3d symmetry of U2F6 is more stable than D3h. The optimized geometries, vibrational frequencies, and infrared intensities are also reported for U2F6 molecules in D3d symmetry. In addition, the isotopic shift of vibrational frequencies of the two molecules under isotopic substitution of uranium atom are also investigated with the same method. The U2F6 molecule is predicted to be better than UF6 for laser uranic isotope separation.     

A model for electroweak interactions based on the left-right symmetric gauge group UL(2) UR(2)

The left-right symmetric gauge group U_L(2) U_R(2) is considered as the unifying electroweak gauge group. It is shown that it has the merit of fixing the mixing parameter sin²θ_W of the standard model at 0.25.     

Analysis of irreducible representations of the group U (4) Up(2) × Un(2)

The general method of projection operators is used to construct the noncanonical nonorthogonal basis of arbitrary irreducible representation of the group U (4) in the reduction U (4) U_p(2) × U_n(2), where U_p(2)(U_n(2)) is the transformation group in the proton (neutron) spin space. The completeness of this basis is proved and the matrices of the U (4) group generators and of the Bargmann-Moshinsky operator Ω in this basis are obtained. The matrix Ω exhibits a nondegenerate spectrum of the eigenvalues which may be used as the missing quantum number.     

Electronic structure of YMn2O5 studied by EELS and first-principles calculations

The electronic structure of multiferroic YMn₂O₅ material has been studied by use of the generalized gradient approximation (GGA). The results demonstrate that the oxygen 2p and manganese 3d orbitals are strongly hybridized. Considering the on-site Coulomb interaction U, we performed the GGA+U calculations for 0 < U ? 8 eV, and it is found that the increase of U could enlarge the band gap and, on the other hand, weaken the Mn-O hybridization. The experimental measurements of the electron energy-loss spectrometry (EELS) exhibit a rich variety of structural features in both O-K edge and Mn-L edges. A theoretical and experimental analysis on the O-K edge suggests that the on-site Coulomb interaction (U) in YMn₂ O₅ could be less than 4 eV. Certain electronic structural features of LaMn₂O₅ have been discussed in comparison with those of YMn₂O₅.     

Effect of moisture content on ultrasonic velocity and attenuation in woods

Ultrasonic velocity and attenuation are measured at 1 MHz in several kinds of wood as a function of the moisture content U. The results are interpreted in terms of water absorption mechanism of woods. The velocity decreases rapidly with increasing U up to a critical value U₁ at which the curve shows a sharp bend, and the decrease is very slow for U>U₁. This critical point U₁ is in the range 20–50% depending on the species of wood and is regarded as the fibre saturation point of the wood, the moisture content at which the wood substance is saturated with absorbed water. Ultrasonic measurements thus provide us with an accurate way to determine the fibre saturation point. The attenuation curve also shows a critical change at U = U₂, which is slightly lower than U₁. The attenuation shows no change from U = 0 up to U₂, but begins to increase rapidly thereafter. This point U₂ indicates the moisture content at which free water begins to enter the vacant space of wood cells.     

Electrical resistivities of the uranium carbides

Electrical resistivities of arc-melted uranium carbides, UC, UC₂, U₂C₃ and UC + UC₂, were measured over the temperature range between 4 and 1900 K. The monocarbide, dicarbide and the mixture of carbides showed metallic character in their resistivity dependence on temperature above 30 K, while below this the resistivities were constant. U₂C₃ showed a knee in the resistivity curve at 54.0 K corresponding to a magnetic transition. Above 1100 K, the resistivity of U₂C₃ did not vary with temperature. The resistivity of the mixture (UC + UC₂ with U₂C₃ precipitates) showed an arrest between 800 and 950 K.     

Non-colinear magnetic structure of U3P4 and U3As4

Neutron diffraction experiments have been performed on single crystal samples of U₃P₄ and U₃As₄. The magnetic ordering is found to be a non-collinear three axial structure in which magnetic moments of U⁴⁺ ions are tilted from the [111] axis by an angle of about twenty degrees within (110) planes.     

The structural and spectroscopic properties for uranium oxides

The equilibrium structures, the charge population, and the spectroscopic properties of UO, UO 2 , UO 3 , and U 2 O 3 molecules are systematically investigated using the density functional theory (DFT) with the method of generalized gradient approximation (GGA). The bond lengths and the vibrational frequencies of the ground states of UO, UO 2 , and UO 3 molecules are all in agreement with available experimental data. For U 2 O 3 molecules, our calculations indicate that the ground state of the U 2 O 3 molecule is an X 7 A ′ 1 state with D 3h (trigonal bipyramid) symmetry (R 1 (U–O)=0.2113 nm, R 2 (U 1 –U 2 )=0.2921 nm, ∠U 1 OU 2 = 87.5 , dihedral angle Θ(U,O 1 ,O 2 ,O 3 )=62.40 ). The harmonic frequency, the IR intensity and the spin density of the U 2 O 3 molecule are all obtained for the first time in theory. For the ground state of U 2 O 3 molecules, the vibrational frequencies are 178.46 (A ′ 1 ), 276.79 (E ′′ 1 ), 310.77 (E ′ 1 ), 396.63 (A ′′ 2 ), 579.15 (E ′ 1 ), and 614.98 (A ′ 1 ) cm 1 . The vibrational modes corresponding to the IR maximum peaks are worked out for UO 3 and U 2 O 3 molecules. Besides, the results of Gophinatan–Jug bond order indicate that UO, UO 2 , and UO 3 molecules possess U=O double bonds and that the U 2 O 3 molecule possesses U–O single bonds and a U–U single bond.     

Nuclear vibron model with 2 and 3 clusters for heavy nuclear molecules

An algebraic vibron model for two- and three-cluster nuclear molecules is presented, where all clusters are deformed. It is shown that if the clusters are deformed a minimum can be obtained for r ≠ 0, even in the relative vibrational limit U _R (4) ? U _R (3) for the case of two clusters, and U _R (7) ? U _R (3) ? U _R (3) for three clusters. By using coherent states, the geometrical mapping is discussed.     

On Gell-Mann's λ-matrices,d- andf-tensors,octets, and parametrizations ofS U (3)

The algebra ofS U (3) is developed on the basis of the matrices _i ofGell-Mann, and identities involving the tensorsd _{i j k} andf _{i j k} occurring in their multiplication law are derived. Octets and the tensor analysis of the adjoint groupS U (3)/Z(3) ofS U (3) are discussed. Various explicit parametrizations ofS U (3) are presented as generalizations of familiarS U (2) results.     

Striking and Running Voltages in a Glow Discharge for Combinations Fe/Ne with and without Hg

An experimental investigation of striking U_s and running U_r voltages in a glow discharge for the combinations cathode material Fe—gas filling Ne with and without Hg has been carried out. It has been shown that Hg addings increase running voltage U_r in the whole pressure range p under investigation. At the same time striking voltage U_s is decreased in the whole investigated range of Paschen curve. The additional effects, which occur in the discharge with Hg addings, have been discussed. A qualitative explanation of the obtained results is adduced.