The d(7Li,p)8Li cross section near E cm = 0.61 MeV

The absolute cross section σ of the d(⁷Li, p)⁸Li reaction near the E_cm = 0.61 MeV resonance has been measured using a ⁷Li ion beam and a windowless gas target system filled with D₂ gas. The proton yield of the reaction and the β-delayed α-activity of the residual nuclides ⁸Li were observed both concurrently with the elastic scattering yield, relating σ to the Rutherford scattering cross section σ_R. The resulting values, σ (from p) = 143.6 ± 8.9 mb and σ (from ⁸Li) = 151 ± 20 mb, lead to a weighted mean value of σ = 153 ± 6 mb (χ² = 2.26) including all available values and σ = 146 ± 5 mb (χ² = 0.05) removing some values from the data set. The consequences for the expected flux of high-energy solar neutrinos are discussed.     

Study of the possibility to measure the root-mean-square roughness of a shaded rough surface

The estimate of the root-mean-square roughness of a rough surface σ₁ is studied experimentally as a function of the angle of incidence. A surface with σ=1.3 μm is illuminated by laser radiation with a wavelength of 0.633 μm. The angle of incidence of radiation on the surface under study is varied from 85° to 87.5°. σ₁ is estimated under the assumption that the regime of a slightly rough surface is fulfilled for the surface studied. Theoretical estimates of σ₁ are calculated in the Kirchhoff approximation with rough surface shadowing taken into account. The greatest relative difference between experimental and theoretical estimates of σ ₁ does not exceed 0.07. The effect of rough surface shadowing on the estimate of σ is analyzed, and the possibility for exact measurement of σ₁ of a shaded rough surface is demonstrated in the case of a priori knowledge of the angle of incidence, for which this measurement is possible. A method that makes it possible to determine the angle of incidence, for which a good agreement between the measured value and the true value of σ of a shaded rough surface is possible, is proposed.     

Fe deep level optical spectroscopy in InP

The optical cross-section σ_n⁰(hv) and σ_p⁰(hv) associated with the (Fe³⁺ ? Fe²⁺) deep level have been measured by Deep Level Optical Spectroscopy in n-type Fe doped samples of InP. Optical transitions are interpreted as transitions from the Fe²⁺ ground state to the Γ and L point minima of the conduction band for σ_n⁰(hv) and from the valence band to the ground and excited state for Fe²⁺ for σ_p(hv). A theoretical model which accounts for the main features of the experimental data is proposed.     

Measurements of the probability for 1 sσ excitation in very heavy ion-atom-collisions and determination of the binding energy of the 1 σ molecular orbital

Using particle x-ray coincidence techniques, the probability to produceK-shell vacancies in 4.7 MeV/u Pb+Z₂ (42≦Z ₂≦92) collisions for impact parametersb<100 fm was measured. For these impact parameters, the 1sσ excitation probability is greater than 1 σ 10^?2 and the 2p _1/2 σ excitation probability is greater than 1 σ 10^?1. Binding energies of the 1sσ state derived from the measured probabilities agree well with theoretical calculations.     

Relationship between σxx and σyx - integral quantum hall effect

The possibility of a Kramers-Kronig relation between the longitudinal and transverse conductivities of a 2-D electron gas in the presence of a magnetic field is investigated. The longitudinal (σ_xx) and the transverse (σ_yx) conductivities are expressed as the real and imaginary part of a complex conductivity (σ). A formal expression is derived for σ within the independent particle approximation. In the classical limit, σ is analytic in the upper complex ω_c plane, where ω_c is the cyclotron frequency. Hence the usual Kramers-Kronig relation holds for σ^c. We modeled a quantum correction (σ^q) to σ and found that σ^q is non-analytic in the upper half plane, hence the total σ does not satisfy a Kramers-Kronig relation.     

Magnetic anisotropy,magnetostriction and intermediate range order in Co-P alloys

Coercivity, magnetostriction and saturation field as a measure of magnetic ansitropy energy have been investigated in Co_100-xP_x with 5 ? x ? 26. According to their magnetization curves and coercivities crystalline alloys (5 ? x ? 11) contain hcp-inclusions whereas amorphous material (12 ? x ? 26) is magnetically soft. The saturation magnetization is mainly determined by the nearest neighbour shell but magnetostriction is also correlated with the further environment of the cobalt atoms. The abrupt breakdown of the value |λ_s| of the saturation magnetostriction with increasing phosphorus content of the crystalline alloys points to a growing structural disorder. λ_s of the amorphous material depends on the saturation magnetization alone (λ_s ≈ σ₀²) which decreases with increasing phosphorus content. The small value of λ_s suggests that angular correlations do not exceed the second coordination shell.     

Microwave electrophysical properties of superionic crystals Ag2HgI4

The paper concerns itself with the investigation results of temperature dependencies of electric conduction and dielectric properties of Ag₂Hgl₄ crystals in the frequency range of 10⁷–7,8·10¹⁰ Hz. The obtained data have shown that in α-phase at T=326 K, the electric conductivity σ is proportional v^0,28 in the frequency range of 10⁷–10⁹ Hz and σ is proporti onal v^0,5 in the range of (1,1–78)·10⁹ Hz. The dependence σ(v) in the range of (1,1–78)·10⁹ Hz may be conditioned by the jumping mechanism of the conductivity and low frequency oscillations of the crystal lattice. It is believed, tha in the σ-phase of Ag₂Hgl₄ a condition of the existence of the ionic polaron is satisfied. The activation energy of the polaron is ΔE_p=0,09 eV.     

Be9(d,p),(d,t),(d,a)反应研究

本文在E_d=0.1—2.5MeV能量范围内,研究了Be⁹(d,p₀)Be¹⁰(0),Be⁹(d,p₁)Be¹⁰(3.368MeV),Be⁹(d,t₀)Be⁸(0),Be⁹(d,α₀)Li⁷(0)及Be⁹(d,α₁)Li⁷(0.478MeV)诸反应。在E_d=0.150,0.220,0.401,0.706,1.005,1.301,1.484,1.750,2.000,2.250和2.500MeV共十一个能量上分别测量了这五群出射粒子在θ_L=10—155°区间的角分布。在θ_L=135°,E_d=0.1—2.5MeV,在θ_L=95°,E_d=0.1—2.2MeV,和在θ_L=112.5°,E_d=0.5—2.5MeV测量了Be⁹(d,p₀)Be¹⁰的激发函数。在θ_L=135°和112.5°,E_d=1.2MeV,用较厚靶(100—300μg/cm²)测量了Be⁹(d,p₀)Be¹⁰(0)反应的截面绝对值,结果为σ_(p0)(θ_L=135°)=1.60mb/sr,σ_(p0)(θ_L=112.5°)=1.55mb/sr。这样就得到了在此能区内,这五群出射粒子的截面情况。对所得结果进行了一些讨论。     

SU(2) ⊗ U(1) gauge theories of the generalized σ model for π0, η, η' → γγ decays

By embedding the chiral current-mixing gauge theories in the SU(2)_L ? SU(2)_R generalized σ model, it is shown that the correct sign and magnitude for π⁰ → γγ decay, as well as the SU(3) relation of π⁰, η, η' → γγ decays can be obtained within the framework of SU(2) ? U(1) gauge theories of weak and electromagnetic interactions.     

Current-conducting properties of paper consisting of multiwall carbon nanotubes

Electrical conductivity σ(T) of the paper consisting of multiwalled carbon nanotubes (MWCNTs) is studied in the temperature range 4.2-295 K, and its magnetoresistivity ρ(B) at various temperatures in magnetic fields up to 9 T is analyzed. The temperature dependence of the paper electrical conductivity σ(T) exhibits two-dimensional quantum corrections to the conductivity below 10 K. The dependences of negative magnetoresistivity ρ(B) measured at various temperatures are used to estimate the wavefunction phase breakdown length L _φ of conduction electrons and to obtain the temperature dependence L _φ = constT ^?p/2, where p ≈ 1/3. Similar dependences of electrical conductivity σ(T), magnetoresistivity ρ(B), and phase breakdown length L _φ(T) are detected for the initial MWCNTs used to prepare the paper.     

On the multistage nature of deformation of the microcrystalline aluminum-lithium alloy 1420 under superplasticity conditions

The constant-rate tensile deformation and creep of aluminum-lithium alloy 1420 with a grain size of 3 µm (obtained by equal-channel angular extrusion) exhibiting superplasticity at temperatures of 600–670 K and relative-deformation rates of 10^?2–10^?3 s^?1 are considered. It is shown that, upon tension at a constant rate V _m, a steady-state segment appears in the true stress σ_t-true strain ?_t dependence, which is described by the expression $\dot \varepsilon _t \sim \sigma _t^n \exp ( - U/kT)$ with constant coefficients, and that the rate of deformation $\dot \varepsilon _t$ is close to the creep rate at comparable stresses and strains. The conclusion is made that, upon deformation under superplasticity conditions, an equilibrium structure is formed, which remains unaltered in the process of further deformation until the sample goes over (because of geometrical conditions) to a prefracture state.     

Conductivity of a periodic two-component system of rhombic type

The conductivity and the distribution of electric field, current, and charge density in a periodic two-component system composed of rhombs with an arbitrary vertex angle of 2α are investigated. The effective conductivity of such a medium is represented by a tensor with components σ _eff ¹¹ (α) and σ _eff ²² (α) in the principal axes that satisfy the Dykhne relation σ _eff ¹¹ (α) σ _eff ²² (α)=σ ₁σ₂, where σ₁, σ₂ are the isotropic conductivities of media 1 and 2. In addition, the relation σ _eff ²² (α)=σ _eff ¹¹ (π/2?α) is satisfied. The principal axes are directed along the diagonals of the rhombs. It is shown that there are three lines in the rectangle 0<α ≤π/2,?1<Z<1((Z=σ₁?σ₂)/(σ ₁+σ₂)) on which the charge density is expressed in terms elliptic functions. An explicit expression is obtained for all physical quantities on these lines.     

Effect of zinc salt on transport,structural, and thermal properties of PEG-based polymer electrolytes for battery application

Solid polymer polyethylene glycol (PEG)-based electrolytes composed with zinc acetate Zn(CH₃COO)₂ have been prepared by using solution blending. We proposed a scheme of PEG–zinc acetate for battery application. The structure confirmation was done by using X-ray diffraction studies detecting the phase variation. The thermal properties demonstrate the optimization of melting point (T _m) as a function of loading zinc acetate. The impedance analysis reveals that the role of ionic conductivity depends on the controlled concentration of Zn(CH₃COO)₂. Optimum ionic conductivity σ?~?1.55?×?10^?6 S?cm^?1 at room temperature (303 K) was observed for 70:30 composition. The linear variation in log σ vs 1000/T plot is based on the Arrhenius-type thermally activated process. The simultaneous discharge profile was confirmed by the solid-state electrochemical cell. Hence, the PEG–zinc acetate composition was suggested for polymer electrolyte battery application.     

Creep mechanism of gas-pressure-sintered silicon nitride polycrystals II. Deformation mechanism

As reported in the companion paper, part I, the creep behaviour of two silicon nitride ceramics is governed by a stress exponent n?=?0.6?±?0.1. It is known that, under certain conditions, silicon nitride ceramics may undergo a transition n?=?1?→?n<1 (the ‘shear-thickening transition’) at a well-defined stress σ*. This transition has not been observed, which, together with considerations regarding the value of the transition stress σ*, leads us to reject the shear-thickening phenomenon as an explanation for the creep behaviour of the materials investigated. Instead, it may be understood in terms of a particular grain boundary sliding mechanism accommodated by solution–precipitation.     

Damage mechanism of nickel-based creep-resistant alloys strengthened by the Laves phase at the grain boundary

ABSTRACT

This study proposes a design guideline for polycrystal Ni-based model alloys with high ductility and 100-MPa creep rupture strength beyond 800°C and 10^5?h. These alloys are strengthened by both the precipitation of fine γ′ particles inside the grain and the Laves phase at the grain boundary. For investigating the damage mechanism, transformation from the non-equilibrium Laves phase to the σ phase at the grain boundary and formation of the equilibrium needle-like Laves phase inside the grain are promoted by increasing the Fe concentration. The rupture time of Fe-free alloys significantly increases because of the equilibrium Laves phase at the grain boundary owing to a suitable Mo equivalent. In particular, W addition can help achieve high-temperature creep strength. The precipitate-free zone (PFZ) is predominantly formed by prior migration at the grain boundary without precipitation. Creep rupture occurs at the precipitation/matrix interface in the PFZ. Therefore, transformation control from the Laves to the σ phase at the grain boundary suppresses creep degradation. Consequently, a Ni-based alloy with strength >100?MPa and rupture elongation >20% at 800°C and 10^5?h is fabricated using Larson–Miller parameter conversion, and the alloy design guideline’s validity is confirmed.     

Simulation studies of gas-liquid transitions in two dimensions via a subsystem-block-density distribution analysis

The finite-size scaling analysis of the density distribution function of subsystems of a system studied at constant total density is studied by a comparative investigation of two models: (i) the nearest-neighbor lattice gas model on the square lattice, choosing a total lattice size of 64×64 sites. (ii) The two-dimensional off-lattice Lennard-Jones system (truncated at a distance of 2.5 σ, σ being the range parameter of the interaction) withN=4096 particles, applying the NVT ensemble. In both models, the density distribution functionP _L (ρ) is obtained forL×L subsystems for a wide range of temperaturesT, subblock linear dimensionsL and average densities <ρ>. Particular attention is paid to the question whether accurate estimates of critical temperatureT _c and critical density ρ _c can be obtained. In the lattice gas model these critical parameters are known exactly and the limitations of the approach can thus be definitively asserted. The final estimates for the Lennard Jones problem areT _c =0.47±0.01 (in units of the Lennard Jones energy ε) and ρ _c (in units of σ²), a comparison with previous estimates is made.     

Frequency response of the low-temperature ionic conductivity of single crystals R 1 − y M y F3 − y (R = La-Er; M = Ca, Sr, Ba, Cd)

The frequency response (10^?1–10^?7 Hz) of the ionic conductivity σ of R _{1 ? y} M _y F_{3 ? y} single crystals (R is a rare-earth element, and M stands for an alkaline-earth element and Cd) with a tysonite structure is studied over a wide temperature range (114–410 K), which includes (for the first time for these phases) the interval below room temperature. The dependences σ(ν) obtained are discussed within the hopping relaxation model. The characteristics of the relaxation and migration processes and the carrier concentration and mobility are determined.     

Interaction de l'oxygène aux basses pressions avec la solution solide niobium-oxygène à haute température: I. Èquilibre de segrégation — chimisorption

Interactions between oxygen under low pressure and a niobium-oxygen solid solution had been studied, in the regime where adsorption is the rate-determining step, from 1000 to 1700 K. It is shown that at saturation of solid solution, there exists a constant limiting value Θ_l of superficial coverage, comparable to a limiting bulk concentration c_l. The ratios θ = Θ/Θ_l and ? = c/c_l are called “relative ratio of occupation” (superficial and bulk). $\text{K}$_SV is the equilibrium constant of segregation between adsorbed and dissolved oxygen atoms: (O_diss^?v) + σ ? (O_chim?σ) + v (σ and v being respectively surface and bulk sites), $\text{K}$_SV = [(1 ? θ)/θ] [?/(1 ? ?)]. The experimentally determined expression: $\text{K}$_SV = 5.7 exp[?(22.1 ? 12.1 θ)/ RT] shows that lateral superficial interactions have a large influence on the enthalpy of transfer between the bulk and the surface of the sample. Adsorption is direct and non activated. At the solubility limit, only a fraction of the superficial sites is occupied. We estimate it to be one half. The sticking probability b of oxygen on a niobium oxygen solid solution is given by b = (1 ? θ/2)², its value at zero coverage being estimated as unity.