Improved (1s)<Superscript>2</Superscript> variational model for helium

The ground-state energy of neutral helium is estimated variationally with a trial wavefunction of the form ϕ≈e ^−γ(rA/a _o)ⁿe^−γ(rB/a _o)ⁿ. This model represents a modification of traditional textbook examinations of this problem via inclusion of the power “n” as a second nonlinear variational parameter in addition to the usual effective nuclear charge γ and leads to an upper-limit on the ground state energy of −2.86107 E _h (E _h =1 hartree) in comparison with the traditional (n=1) result of −2.84766 E _h . This result represents a reduction of the percentage overestimate from the true ground-state energy (−2.90373 E _h ) of from 1.93 to 1.47. In comparison with the maximum accuracy obtainable from an uncorrelated trial wavefunction, −2.86168 E _h , the present trial wavefunction reduces the percentage overestimate from 0.49 (n=1) to 0.021. The optimum values of (n, γ) are determined to be ≈(0.897, 1.825).     

Electronic structure of silicon nitride according to ab initio quantum-chemical calculations and experimental data

Charge transfer ΔQ = 0.35e at the Si-N bond in silicon nitride is determined experimentally using photoelectron spectroscopy, and the ionic formula of silicon nitride Si₃^+1.4N₄^−1.05 is derived. The electronic structure of α-Si₃N₄ is studied ab initio using the density functional method. The results of calculations (partial density of states) are compared with experimental data on X-ray emission spectroscopy of amorphous Si₃N₄. The electronic structure of the valence band of amorphous Si₃N₄ is studied using synchrotron radiation at different excitation energies. The electron and hole effective masses m _e ^* ≈ m _h ^* ≈ 0.5m _e are estimated theoretically. The calculated values correspond to experimental results on injection of electrons and holes into silicon nitride.     

Some consequences of global horizontal symmetry

It is pointed out that the present SU(3) _c ×SU(2) _L ×U(1) gauge interactions with three families have a global horizontal symmetry (denoted hereby SU(3) _H ) which is broken only by the weak charged hadron currentJ _h. Also, with (u, c), (d, s), (v _e, {ie437-1}) and (e ⁻,μ ⁻) as doublets of SU(2) _H (subgroup of SU(3) _H ),J _h has simple transformation properties under this subgroup. Amplitude relations, using SU(2) _H symmetry, for hadronic leptonic and semileptonic decays are given.     

Minimum-wear characteristics for boundary friction between solids

A new parameter is proposed for characterizing boundary friction between solids—the probability Q that some contact spot will be converted to a wear particle as the real contact area shifts by one mean contact-spot diameter. A method is proposed for the phenomenological detection of optimum regimes of boundary friction, which are characterized by the minimum wear intensity of the sample material, and for measuring the corresponding quantity Q=Q ^opt. For babbitt, one of the most frictionless materials, the value of Q ^opt is found to be ≈2×10⁻¹⁰. When data on the linear wear intensity I _h , the contact pressure p _n , and the hardness H are available, Q can be calculated for the given test conditions. Deviations of Q from the value Q ^opt (for a given material) can serve as a criterion for how closely a prepared surface structure approaches the optimal. Zh. Tekh. Fiz. 68, 48–52 (April 1998)     

Strange quarks in the nucleon sea

The HAPPEX Collaboration measured parity-violating electron scattering from ⁴He$(e, e)$and H(e, e) in 2004 and 2005 for Q ²≤0.11GeV^2. Results for the strange-quark contributions to the electromagnetic form factors of the nucleon from the 2004 data will be reviewed. Preliminary results from the 2005 data, which have significantly greater statistical precision, are G _E ^s = 0.004±0.014_stat±0.013_syst for Q ² = 0.0772GeV^2 from the helium data and G _E ^s +0.088G _M ^s = 0.004±0.011_stat±0.005_syst±0.004_FF for Q ² = 0.1089GeV^2 from the hydrogen data.     

Pseudovector heavy quarkonia in e + e −2 collisions

It is shown that BR(χ _b1(1 P)→e ⁺ e ⁻)≃3.3· 10⁻⁷ and BR(χ _c1(1 P)→e ⁺ e ⁻)≃10⁻⁸. This gives realistic possibilities for searching for the production of χ _b1(1 P) and ξ _c1(1 P) states in e ⁺ e ⁻ collisions, even on the present-day colliders, to say nothing of b and c-τ factories. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 569–574 (25 April 1996)     

Inelastic x-ray scattering measurements of dynamical cross-over in liquid As2Se3 at high temperature and high pressure

Liquid As₂Se₃ undergoes the semiconductor-metal transition with increasing temperature when pressure is applied to avoid evaporation of the liquid. To investigate the atomic dynamics of liquid As₂Se₃, we have carried out inelastic x-ray scattering experiments of this system at 1073 K and 6 MPa and obtained the dynamic structure factor S(Q,E), from approximately 1.6 nm⁻¹ to 11 nm⁻¹, where Q and E are momentum and energy transfer, respectively. The excitation energy in the semiconducting state at 1073 K disperses as fast as the ultrasonic sound velocity at Q < 2.5 nm⁻¹ but at Q > 2.9 nm⁻¹ it disperses approximately 1.8 times faster. We analyzed S(Q,E) at 1073 K using a simple viscoelastic model and discussed Q dependence of the propagation of the acoustic mode.     

Preliminary results on the operation of a 2270 kg cryogenic gravitational-wave antenna with a resonant capacitive transducer and a d.c. SQUID amplifier

Summary In November 1985 the gravitational-wave antenna of the Rome group, installed at CERN, has started operating. It consists of a 5056 aluminium cilinder 3 m long, 2270 kg heavy, cooled at 4.2 K. The antenna vibrations are detected by means of a resonant capacitive transducer that together with the bar makes a two-coupled-oscillator system. The low-noise amplification is obtained with a d.c. SQUID amplifier. The frequencies of the two resonant modes are:v _-=907.116 Hz andv ₊=923.083 Hz, with merit factorsQ ₋=3.2·10⁶ andQ ₊=5.6·10⁶. The sensitivity to short gravitational bursts, expressed in terms of effective noise temperature, is 18 mK. This corresponds to a change in the metric tensor whose Fourier transform isH=1.1·10⁻²¹ Hz⁻¹. For monochromatic waves the antenna is sensitive (SNR=1) toh∼2·10⁻²⁵ in a band width of about 1/3 Hz, with a three months integration time.

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Riassunto Nel novembre 1985 è stata messa in funzione l'antenna gravitazionale del gruppo di Roma, installata al CERN. Questa consiste di un cilindro d'alluminio 5056 lungo 3 m e pesante 2270 kg, raffeeddato a 4.2 K. Le vibrazioni dell'antenna vengono rivelate mediante un transduttore capacitivo risonante, che assieme alla sbarra forma un sistema di due oscillatori accoppiati. L'amplificazione a basso rumore è ottenuta con un amplificatore a d.c.-SQUID. Le frequenze dei due modi risonanti sono:v _-=907.116 Hz ev ₊=923.083 Hz, con fattori di meritoQ ₋=3.2·10⁶ eQ ₊ =5.6·10⁶. La sensibilità per brevi fiotti di onde gravitazionali, espressa in termini di temperatura efficace di numore, è 18 mK. Questa corrisponde a una variazione di tensore metrico con trasformata di Fourier:H=1.1·10⁻²¹ Hz. Per le onde monocromatiche l'antenna è sensibile (SNR=1) ah∼2·10⁻²⁵ in una banda di circa 1/3 Hz, con tempo d'integrazione di tre mesi.

     

Electron screening in backward elastic scattering

Abstact: The elastic scattering cross sections, σ (E,θ), for the systems He+Ta and He+W have been measured at θ_lab=165° and E _lab=76.1 keV to 3.988 MeV using targets with a thickness of a few atomic layers. The results are smaller than the results given by the Rutherford scattering law, σ_R(E,θ), due to the effects of electron screening and can be described by σ(E,θ)/σ_R(E,θ)=(1+U_e/E)⁻¹, where U _e is an atomic screening potential energy. The deduced average value, U _e=28 ± 3 keV, is consistent with the Moliére- and Lenz-Jensen-models as well as electron binding energies. Received: 25 May 1998     

Vortex pinning in YBa2Cu3O7?x films

Evidence that pinning on linear or planar defects dominates the vortex dynamics in YBa₂Cu₃O_7−x (YBCO) films is provided by complex impedance measurements at temperature 8 K<T<T _c and magnetic field 0<B<6 T. Below the vortex lattice melting transition B_g(T) but above a threshold field B_p≈8(1-T/T _c ) T, the inductance of vortices increases as B², much less rapidly than predicted for collective pinning of vortices by point defects. Above the vortex melting line, critical scaling persists over the region B_g(T<B<B^*(T) where the vortex correlation length ξ exceeds a characteristic length scale ξ^*≡ξ(B=B^*)≈450?. The value of ξ^* is not sensitive to Al-doping in the Cu sites in the lattice and is close to the size of twin domains in the film. The nature of the observed crossovers is discussed in terms of available theoretical models for a glass-liquid transition at B_g.     

Precise Quadrupole Moment of the Doubly Closed Shell Plus One Proton Nucleus 41Sc

In order to precisely determine the |eqQ(⁴¹Sc)/h| of ⁴¹Sc(I ^π=7/2⁻, T _1/2=0.596 s) implanted in a TiO₂ single crystal the electric field gradient tensor and anisotropic chemical shift were determined by detecting the Fourier Transformed Pulse-NMR of ⁴⁵Sc(I ^π=7/2⁻, stable) in the crystal at a high field of 7.0 T and 9.4 T. Combining the new |eqQ(⁴¹Sc)/h| value with the Q(⁴⁵Sc)=−(23.6±0.2) fm², also renewed by using the known atomic hyperfine interaction constants and Sternheimer polarization effect, the |Q(⁴¹Sc;I ^π=7/2⁻,T _1/2=0.596 s)|=(15.6±0.3) fm² has been precisely determined. The value is compared with the theoretical Q(⁴¹Sc) given by a shell model code. This revised version was published online in September 2006 with corrections to the Cover Date.     

Dielectric nonlinearity of crystalline Li2−x NaxGe4O9 (x≈0.23)

The dielectric nonlinearity of ferroelectric Li_2−x Na_xGe₄O₉ (x≈0.23) crystals is measured in the neighborhood of the phase transition temperatures. The magnitude of the nonlinear coefficient β is estimated from the shift in T _c and the reduction in ɛ _max under the influence of E ₌, from the dielectric nonlinearity in the paraphase, and from the temperature dependence of P _s in crystalline Li_2−x Na_xGe₄O₉ (x≈0.23). The resulting values of β are 1.87, 1.26, 2.17, and 1.17×10⁻⁹ (CGSE cm²)⁻², respectively. The mechanism for the phase transition in crystalline Li_2−x Na_xGe₄O₉ (x≈0.23) is discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 1070–1072 (June 1999)     

铁磁/反铁磁双层膜中冷却场对交换偏置场的影响

用铁磁畴壁模型研究了非补偿界面铁磁/反铁磁双层膜中冷却场（包括大小及其方向）对交换偏置场h_E的影响.结果表明：当冷却场的方向与反铁磁层磁易轴一致时,h_E大小与冷却场大小无关.当冷却场的方向偏离磁易轴时,h_E的大小随偏离角度的增大有缓慢的改变,但当冷却场的方向偏离到临界角度γ_c处,h_E的大小发生突变,其γ_c的大小随冷却场的增大而增大.特别是当冷却场的偏离角度大于γ_c后,h_E出现由负转正的现象,其转变点还与冷却场的大小有关.另外,h_E与铁磁层原子层数N_F的关系会发生由h_E∝N^-1_F向h_E∝N^-λ_F的转变,其中λ>1.其发生转变的条件与N_F、冷却场大小和方向密切相关. 关键词： 铁磁/反铁磁双层膜 交换偏置 冷却场     

Perturbation theory of polar hard Gaussian overlap fluid mixtures

A perturbation theory of polar hard Gaussian overlap fluid mixture is discussed. Explicit analytic expressions for the second and third varial coefficients are given. Numerical results are estimated for the thermodynamic properties of quadrupolar hard Gaussian overlap fluid and fluid mixture. It is found that the excess free energy and internal energy depend on concentrationsc ₁,c ₂, molecular diameter ratioR, shape parameterK and the quadrupole momentsQ*₁,Q*₂.     

Nuclear spin lattice relaxation and electric field gradient in liquid indium

We have measured the nuclear spin lattice relaxation time in liquid indium from 130°C to 300°C to be: 1/T ₁=(1.98 × 0.0082T) × 10³ sec^-1. The relaxation rate consists of two significant parts: (1/T ₁) _K from the nuclear magnetic hyperfine interaction, and (1/T ₁) _Q from the nuclear quadrupole interaction. We calculate (1/T ₁) _K from the the modified Korringa relation using a correction factor of order unity for electron-electron interactions. The hyperfine term is linear in T and accounts for the second term in 1/T ₁. Within experimental error the remaining rate, (1/T ₁) _Q , is temperature independent, and theoretically varies as the product of the square of the electric field gradient, q, and τ_c, a typical time between field gradient fluctuations. Making use of the x-ray RDF, we construct a simple model for liquid indium and calculate the ionic and electronic contributions, q _I and q _E, to the electric field gradient, to be q _I=1.4 × 10²⁴/cm³ and q _E=8.5 × 10²⁴/cm³. The calculation of q _E assumes covalent bonding between nearest neighbours. Taking q _I and q _E to be of opposite sign, we find that the correlation time τ_c is 1.6 × 10^-13 sec. When we further identify τ _c with the correlation time for diffusion in a three-dimensional random walk, we are able to calculate the r.m.s. jump distance, Δr _D, involved in self-diffusion, Δr _D=0.38 Å. This value is consistent with the x-ray peak width of 0.38 Å which we used earlier to calculate the electric field gradient.     

Low-temperature mobility of surface electrons and ripplon-phonon interaction in liquid helium

The low-temperature dc mobility of the two-dimensional electron system localized above the surface of superfluid helium is determined by the slowest stage of the longitudinal momentum transfer to the bulk liquid, namely, by the interaction between the surface and volume excitations of liquid helium, which decreases rapidly with the temperature. Thus, the temperature dependence of the low-frequency mobility is μ_dc ≈ 8.4 × 10⁻¹¹ n _e T ^−20/3 cm⁴ K^20/3/(V s), where n _e is the surface electron density. The relation T ^20/3 E_⊥⁻³ ≪ 2 × 10⁻⁷ between the pressing electric field (in kilovolts per centimeter) and temperature (in Kelvins) and the value ω ≲ 10⁸ T ⁵ K⁻⁵ s⁻¹ of the driving-field frequency have been obtained, at which the above effect can be observed. In particular, E _⊥ ≃ 1 kV/cm corresponds to T ≲ 70 mK and ω/2π ≲ 30 Hz.     

Internal friction in directed-crystallization (Cu-Sn)-Nb alloys

The distinctive features of the low-frequency internal friction Q ⁻¹(T) of (Cu-Sn)-Nb composites at high temperatures (up to 400°C) are investigated for strains in the range 10⁻⁵–10⁻⁴. Considerable hysteresis of Q ⁻¹(T) in the heating-cooling cycle is recorded, including the presence of a minimum at ∼175°C when the sample is heated to 400°C and two peaks P ₂ (at 280°C) and P ₁ (at ∼100°C) when the sample is cooled from 400°C. The activation energy of the anomalous internal friction background (up to 175°C), the oxygen diffusion parameters, and the oxygen concentration in the niobium fibers (all of which govern the peak P ₂) are calculated, and the value and temperature dependence of the yield point of the bronze matrix (which govern the peak P ₁) are estimated. Zh. Tekh. Fiz. 68, 114–117 (November 1998)     

Kinetics of radiation cooling of fullerenes

Emission from fullerene molecules excited by means of electron impact in crossed beams under conditions of single collisions between electrons and C₆₀ molecules in a kinetic energy range E _e from 25 to 100 eV was studied experimentally. Emission spectra in a wavelength range from 300 to 800 nm; the emission excitation functions and the temperature of emitting molecules as a function of E _e were measured with a resolution of 1.6–3.2 nm. The contribution to emission from ionized C ₆₀ ^+* molecules has been determined and data on the emissivity of the C ₆₀ ^+* ion have been obtained. It has been shown that the emission spectra can be well approximated with the spectral distribution of thermal emission from a black body (Planck’s formula), taking into account the lowering of emissivity for a small particle. The emission can be observed starting with electron energy of about 27 eV; the emission excitation function is of a nonresonant form, peaking at an energy of E _e ≈70 eV. As E _e is increased, the temperature of emitting particles rises and reaches its maximum value of 3100–3200 K at E _e ≈47 eV.     

Electromagnetic mass splittings of heavier hadrons in quantum chromodynamics

The electromagnetic mass splittings of heavier hadrons are estimated in the framework of gauge theory model where ligher quarks are taken to behave relativistically and the spatial wave functions are described by the spin-spin interaction affected relative distances between quarks. The predictions for (Ξ⁻-Ξ⁰), (Σ*⁰−Σ*⁺), (Ξ^*−-Ξ^*0), (D _c ⁺−D _c ⁰) and (D _c ^*+ −D _c ^*0 ) are in fair agreement with the experimental data available whereas those for (D _b ⁻ −D _b ⁰ ) and (D _b ^*− −D _b ^*0 ) are in qualitative agreement with other theoretical estimates.     

Determination of the partition coefficients of the nonionic detergent C12E7 between lipid-detergent mixed membranes and water by means of Laurdan fluorescence spectroscopy

The membrane-water partition coefficient of the detergent C₁₂E₇ between water and C₁₂E₇/POPC mixed membranes has been determined by means of steady-state fluorescence spectroscopy. The emission spectra of the fluorescent probe Laurdan were used as an indicator of membrane composition at different membrane concentrations in the sample. The partition coefficient expressed as the ratio of the mole fractions of the detergent in the membrane and water phases is about 6^*10⁵ at low molar ratios of C₁₂E₇/POPC (R _c ) and decreases rapidly with increasingR _c . The limiting detergent content of the lamellar phase (R _c ^* >0.8) is indicated by a minimum ofP(R _c ).