Anomalous X-ray scattering studies on superionic glassy (As2Se3)-(AgX) systems (X = halides)

Anomalous X-ray scattering experiments for glassy room-temperature superionic conductors (As₂Se₃)_0.4 (AgI)_0.6 and (As₂Se₃)_0.4(AgBr)_0.6 were performed close to the As, Se, Ag, and Br K edges using a third-generation synchrotron radiation facility, ESRF. The differential structure factors, Δ_iS(Q), were obtained from detailed analyses, indicating that Δ_AsS(Q) and Δ_SeS(Q) of both the glassy superionic semiconductors are similar to those of glassy As₂ Se₃ except the prepeak in Δ_SeS(Q). The Δ_AgS(Q) spectrum of (As₂Se₃)_0.4 (AgI)_0.6 looks molten salt-like. However, the Δ_Ag S(Q) of (As₂Se₃)_0.4(AgBr)_0.6 glass have quite different features from that of (As₂Se₃)_0.4 (AgI)_0.6 glass in the low Q range, and the Δ_BrS(Q) has even a pre-shoulder around 13 nm^? 1 unlike molten salts. In the differential pair distribution functions Δ_ig(r) obtained from the Fourier transforms of Δ_iS(Q), the first peaks of Δ_Asg(r) and Δ_Seg(r) show no correlation with those of Δ_Agg(r) and Δ_Brg(r), and vice versa. From these results, it can be concluded that a pseudo-binary mixture of the As₂Se₃ network matrix and AgX-related ionic conduction pathways is a good structural model for these superionic glasses. Differences between the AgBr- and AgI mixtures were found in the second-neighbor structures around the Ag atoms, which may reflect those in the crystal structures of the AgX salts.     

The current-induced effect on the Jahn-Teller distortion in the La0.5Ca0.5MnO3 manganite

The influence of dc current on the resistivity ρ and the Young's modulus E of La_0.5Ca_0.5MnO₃ compound has been investigated by means of an in situ measuring method. At low temperatures, both the resistivity ρ and the relative modulus ΔE increase with the current. A relaxation behavior of ρ to the higher resistive state is observed at a fixed temperature and a constant current. After storing the sample for a few days, ρ decreases with the current, accompanying a slight drop of ΔE at low temperatures. Current-induced effects on ρ and ΔE are interpreted according to the current-induced interwinning of Mn³⁺O₆ octahedral distortion modes between Q₂- and Q₃-types, which is suggested to contribute to the variation of the resistivity.     

Deep-inelastic scattering in κ factorization and the anatomy of the differential gluon structure function of the proton

The differential gluon structure function of the proton, ?(x, Q ²), introduced by Fadin, Kuraev, and Lipatov in 1975 is extensively used in small-x QCD. We report here the first determination of ?(x, Q ²) from experimental data on the small-x proton structure function F _2p (x, Q ²). We give convenient parametrizations for ?(x, Q ²) based partly on the available DGLAP evolution fits (GRV, CTEQ, and MRS) to parton distribution functions and on realistic extrapolations into the soft region. We discuss the impact of soft gluons on various observables. The x dependence of the so-determined ?(x, Q ²) varies strongly with Q ² and does not exhibit simple Regge properties. Nonetheless, the hard-to-soft diffusion is found to give rise to a viable approximation of the proton structure function F _2p (x, Q ²) by the soft and hard Regge components with intercepts Δ_soft=0 and Δ_hard ～ 0.4.     

Spin-dependent parton distributions in polarized deep inelastic lepton nucleon scattering

We analyze the recently measured first moment Г ^p (Q ²) of the structure functiong ₁ ^p (x,Q ²) obtained in deep inelastic scattering of polarized electrons from polarized protons. It is shown that the recent experimental result Г ^p (〈Q ²〉?10 GeV²)? 0.113 implies a polarized strange quark sea whose total polarization Δs(μ²)??0.22 is comparable to Δμ(μ²)?0.74 and Δd(μ²)??0.50 already at a typically hadronic scale μ=0(1 GeV). Most remarkably, the total polarization due to quark distributions Δμ(μ²)+Δd(μ²)+Δs(μ²) practically vanishes which implies that the spin of the proton is carried by the gluons, ΔG(μ²), and/or the angular momentum of the partons. This surprising conjecture can be experimentally tested with heavy quark production in longitudinally polarized lepton-nucleon scattering. In particular the (real) photon-gluon fusion process γg→Q \(\bar Q\) provides a rather unique measure of ΔG(x,Q ²).     

Influence of uniaxial stress on the Mössbauer spectrum of α-iron

The Mössbauer spectrum of a 20 μm rolled foil of α-iron has been studied as a function of an applied tensile stress. A constant velocity spectrometer was used in transmission geometry. A method involving three-point observations on single lines combined with chopping between two absorbers was used to minimize and evaluate effects of drift. Line displacements amount to approximately one percent of the line width and vary reversibly and linearly with stress. They can be interpreted in terms of changes in isomer shift ΔI, magnetic splitting ΔH and quadrupole shift ΔQ. Comparison with data from hydrostatic pressure experiments indicate that ΔI and ΔH are mainly influenced by volume changes. Observed variations in the area ratio of lines 6 and 5 amount to a few percent and reflect that changes in the magnetization direction are caused by stress. The complicated, irreversible behaviour is interpreted in terms of magnetization rotation and domain wall motion.     

Heavy fermion contributions to the anomalous magnetic dipole and quadrupole moments of theW-boson

The contribution of a massivet-quark to the anomalous magnetic moment (Δκ) and the quadrupole moment (ΔQ) of theW-boson is calculated. An upper bound of Δκ=1.5×10^?2 and ΔQ=2.5×10^?3 for the standard model is obtained. Additional contributions from extraE ₆ fermions is also discussed.     

Investigation of slow surface states on a real germanium surface by the optical excitation technique

The slow states (SS) charging ΔQ_s under the action of light quanta of different energy (2 ? hv ? 4.6 eV) has been investigated on a real germanium surface. The considerable influence on the optical SS charging of the preparation method as well as of adsorption-desorption processes has been revealed. On the basis of the spectral dependencies ΔQ_s(hv) the conclusion has been made about the existence of the adsorption-sensitive system of “fluctuation” electron states near the edges of energy bands of the oxide layer. The photocharging method has been shown the construction of the whole energy scheme of the semiconductor-dielectric heterojunction (including the band gap of the dielectric layer). The possible origin of the deep traps in oxide layer which are responsible for the optical charging of a real germanium surface, has been discussed.     

Excitations in a quantum Hall ferromagnet with strong Coulomb interaction

A quantum Hall ferromagnet is considered at integer fillings ν, provided typical Coulomb interaction energy E _c is large compared to the cyclotron energy ω_H. Low-energy collective modes consist of a magnetoplasmon exciton and a gapless spin exciton. All charged excitations have a gap. The activation energy gap for a pair of charged topological excitations—skyrmion and antiskyrmion—is small, i.e., Δ< vω_H. The electric charge of a skyrmion is the multiple q=eνQ, where Q is the integer topological charge.     

Variation Angulaire,Transitions Interdites Dans Le Spectre De R.P.E. Des Ions Mn2+ Dans L'alumine α

The spin Hamiltonian with trigonal symmetry for Mn²⁺ in Al₂O₃ has been derived. The line positions have been calculated using perturbation theory up to third order. Three groups of forbidden transitions ΔM = ± 1 Δm = ± 1 have been investigated. Q′ and γ have been deduced from for forbidden hyperfine doublets. The two evaluations of the spin Hamiltonian parameters from allowed (Δm = 0) and forbidden lines (Δm = 1) are discussed.     

ΔT-window neutron spectrometer

A high resolution neutron spectrometer making use of a ΔT-window filter for the analyser and time-of-flight technique for analysing incident neutron energy has been designed. The spectrometer will provide a continuously variable energy resolution ΔE from 40–50μeV at ∼ 5230μeV. The range of energy transfer allowed is −1450μeV to +2950μeV and the range of wavevector transferQ allowed is 0·82–3·06 ?⁻¹. Depending on the resolution used, the counting rates are expected to vary from 28–60 × 10³ counts/hr if one assumes 10% isotropic elastic scattering from the sample.     

The ground state of an antiferromagnetic superconductor in the presence of a homogeneous magnetic field

The effect of a homogeneous magnetic field, H₀. on the ground state of an antiferromagnetic superconductor has been investigated. Assuming a one-dimensional like half-filled band, we have found a new state having gapless superconductivity and H₀-dependent order parameter. This state exists for H_Q/Δ₀>0.22 and when ∣Δ ? H_Q∣?H₀ < Δ + H_Q (H_Q is the staggered magnetic field, Δ is the superconducting order parameter and Δ₀ is Δ in the absence of H_Q and H₀).     

Quadrupole splitting of Fe(II) spin crossover compounds study of temperature and pressure dependence and the implication for the interaction mechanism

The temperature and pressure dependence of the quadrupole splitting ΔE _Q of the 3/2→1/2 nuclear Mössbauer transition of⁵⁷Fe in the spin crossover compounds [Fe _x Zn_1?x (2-pic)₃]Cl₂?EtOH and the deuterated analog [Fe _x Zn_1?x (2-pic-ND₂)₃] Cl₂?EtOD (2-pic=2-picolylamine) have been studied. The change of ΔE _Q can be linearly related to the defomation of the lattice as observed by X-ray measurements. The dependence of ΔE _Q on temperatureT, pressurep, and the fraction γ of molecules in the electronic high spin state in the pure iron (x=1) compounds is therefore interpreted as a result of the change of the lattice contribution to the electric field gradient (EFG) at the nucleus only. The intrinsic EFGs of the molecules remain unchanged under the cooperative interaction of the spin crossover complex molecules. This fact is consistent with a simple elastic interaction between the complexes rather than a Jahn-Teller-type of interaction also discussed in the literature.     

Relation between the EPR linewidths and the exchange integrals in ACrO2 (A = Li, NaandK)

The temperature dependence of the peak-to-peak EPR linewidth (ΔH_p-p) of the ACrO₂ (A = Li, Na, K) compounds in the X-band is typical for the previously observed antiferromagnetic interactions. All three oxides show a single absorption line with a lorentzian shape. As expected the room temperature values of ΔH_p-p in the Q-band are very close to those obtained in the X-band. Using the Anderson-Weiss model for exchange-narrowed Lorentzian lines and the high-temperature limit values for ΔH_p-p 's of all three oxides it was possible to estimate the coefficient relating the exchange integrals between the adjacent Cr³⁺-ions in the cationic sublattice to the corresponding exchange fields and the coefficient relating the crystal-field parameters of Cr³⁺-ions to the second moments of the spectral lines.     

Polarized leptoproduction and dynamically generated spin-dependent parton distributions

The first moment of the polarized parton distributions of the proton is evaluated dynamically using the assumption that at some low resolution scale the proton consists of valence quarks only. The spin carried by gluons, ΔG, at the EMC resolution scaleQ ₀ ² =10 GeV² ispredicted to be ΔG/s _p ?5 withs _p=1/2 denoting the spin of the proton. This result furthermoreexplains the dynamical origin of the recent EMC measurement of the first moment of the polarized structure functiong ₁ ^P (x, Q ²).     

Investigations of the electron paramagnetic resonance parameters and defect structures for Ni ions in CdX2 (X=Cl,Br) crystals

The high-order perturbation formulas of electron paramagnetic resonance (EPR) parameters (g factors g_∥,g_⊥ and zero-field splitting D) for 3d⁸ ions in trigonal octahedral clusters are established. These formulas contain the contributions not only from the crystal-field (CF) mechanism, but also from the charge-transfer (CT) mechanism (which is not considered in the widely used CF theory). From these formulas, the EPR parameters and the impurity-induced defect structures for Ni²⁺ ions in CdX₂ (X=Cl, Br) crystals are studied. The calculated EPR parameters are coincident with the experimental values, and the defect structure of Ni²⁺ impurity center obtained from the calculation is different from the corresponding structure in the host crystal. The sign of Q^CT (Q=Δg_∥, Δg_⊥, or D) due to CT mechanism agrees with that of the corresponding Q^CF due to CF mechanism and the relative importance of CT mechanism (characterized by Q^CT/Q^CF) increases with increasing covalence of 3d⁸ clusters and hence with raising atomic number of ligand X. So, in the explanations of the EPR parameters of 3d⁸ (or other 3dⁿ) ions in crystals with the heavy-element ligand ion (e.g., Br⁻), the calculated formulas based on the two-mechanism (CF and CT mechanisms) model are preferable to those based on only the CF mechanism in the CF theory.     

Free energy of (PO4)2Pb3 around the transition point

The structures of α and β(PO₄)₂Pb₃ show that there is a condensation of an Au type soft mode at the ferroelastic transition point (180°C). Since only the C₁₁ elastic constant has a strong discontinuity at the transition point, the interaction term in the free energy is ΔW₃=2b?₁₁Q². The calculated discontinuities of the spontaneous deformations are in good accordance with the experimental results.     

A new theoretical approach to study the effects of active molecules on lipid bilayer properties: The cholesterol problem

A model to study phospholipid bilayers with active molecules that greatly disturb molecular conformations of their neighboring lipids is proposed. In the particular case of cholesterol in DPPC bilayers, this method allows us to use the spin 1 Ising hamiltonian as a natural extension of the two state model of chain melting transition. Physical processes responsible for the decreasing of the total transition enthalpy Δ_tQ and temperature T_c, and for the phase separation, both below and above T_c, when cholesterol is added, are easily identified. From the details of the phase separation, the two peak specific heat data are explained. Similar models for the addition of other binding molecules to lipid bilayers are discussed.     

Spin structure of hadrons in supersymmetric quantum chromodynamics at short distances

We study the short-distance spin structure of nucleons in supersymmetric QCD. We calculate the Altarelli-Parisi spin transition coefficients ΔP _ba and corresponding anomalous Δ γ _ab ⁿ fora, b=quarks, gluons, gluinos and squarks and present the supersymmetric relations between them. Further analysis is divided into two parts: the parity conserving case and parity violating case, both following from the mass mixing in the squark sector. Solving theQ ²-evolution equations we determine the quark, gluon, gluino and squark spin distribution at variousQ ² above the threshold for production of supersymmetric partners. We also show the analytic solutions for the first moments in the nonsinglet and singlet sector. In particular the spin carried by the valence quarks turn out to vanish asymptotically except of one particular case of squark mixing.     

High-resolution inverse Raman spectroscopy of the ν1 band of 28SiH4

A near-Doppler-limited isotropic Raman spectrum of the symmetric stretching fundamental ν₁ of ²⁸SiH₄ has been recorded between 2182.8 and 2187.0 cm^?1 using high-sensitivity “quasi-cw” inverse Raman spectroscopy. The band exhibits compact, nonoverlapping J manifolds, which were measured from Q(0) through Q(13), plus a portion of Q(14). Since ν₁ is in resonance with the nearby infrared-active stretch ν₃, these two bands were analyzed simultaneously using the infrared frequencies of ν₃ reported by Cabana, Gray, Robiette, and Pierre. The results confirm their analysis, in which several perturbation-allowed ν₁ transitions were identified in the infrared, but the molecular constants for the v₁ = 1 state are much better determined with the inclusion of the Raman data. At higher J, ν₁ exhibits significant intensity perturbations due to a breakdown of the selection rule ΔN = 0; these have been quantitatively accounted for.