Behaviour of the proton-proton total cross section at ISR energies in the reggeon calculus

We study the behaviour of σ^pp_T at ISR energies in the Reggeon calculus with a bare triple Pomeron coupling non vanishing at q² = 0. The parameters are determined from elastic and inclusive data. A sizable increase of σ_T with s can only be obtained when the bare Pomeron intercept is such that the renormalized Pomeron singularity is above one, in the forward direction.     

Determination of the longitudinal and transverse cross section in resonance electroproduction

Using all relevant data we determine σ_L/σ_T for 1.1<W<1.8 GeV, 0.1<Q ²<2.0 (GeV/c)². New results, emerging in the region of the second and third resonance, are mainly due to our recently published very low ε-data. σ_L/σ_T is found to be small but different from zero.     

Change in the size dependences of the surface properties of nanodiamond upon variation in the isotope composition

The isothermal-isomorphic dependences of the specific surface energy (σ), its isochoric temperature derivative (σ′), and surface pressure (P _sf) on the size of nanodiamonds ¹²C and ¹³C at 100 and 4300 K are calculated. It is shown that the ratio σ(¹²C)/σ(¹³C) decreases with decreasing size along both isotherms, and σ′(¹²C)/σ′(¹³C) increases with decreasing size, and this effect is higher at lower temperatures. The ratio P _sf(¹²C)/P _sf(¹³C) increases with decreasing size. The effect is stronger at higher temperatures.     

Thermal conductivity of high-porosity biocarbon precursors of white pine wood

This paper reports on measurements of the thermal conductivity κ and the electrical conductivity σ of high-porosity (cellular pores) biocarbon precursors of white pine tree wood in the temperature range 5–300 K, which were prepared by pyrolysis of the wood at carbonization temperatures (T _carb) of 1000 and 2400°C. The x-ray structural analysis has permitted the determination of the sizes of the nanocrystallites contained in the carbon framework of the biocarbon precursors. The sizes of the nanocrystallites revealed in the samples prepared at T _carb = 1000 and 2400°C are within the ranges 12–35 and 25–70 Å, respectively. The dependences κ(T) and σ(T) are obtained for samples cut along the tree growth direction. As follows from σ(T) measurements, the biocarbon precursors studied are semiconducting. The values of κ and σ increase with increasing carbonization temperature of the samples. Thermal conductivity measurements have revealed that samples of both types exhibit a temperature dependence of the phonon thermal conductivity κ_ph, which is not typical of amorphous (and amorphous to x-rays) materials. As the temperature increases, κ_ph first varies proportional to T, to scale subsequently as ～T ^1.7. The results obtained are analyzed.     

Magnetic anisotropy and saturation of LaFe12O19 and some related compounds

The saturation magnetization σ_s and uniaxial anisotropy constants K₁ and K₂ are measured on a polycrystalline, crystal-oriented sample of LaFe₁₂O₁₉ contaminated with known amounts of Fe₃O₄ and LaFeO₃. K₁ and K₂ increase strongly with decreasing temperature and the value of K₁ = (19–24) × 10⁵ erg/g at T = 0 shows that the substance is considerably more anisotropic than BaFe₁₂O₁₉ (K₁ ? 8·5 × 10⁵ erg/g) at low temperatures. The σ_s-T curve is more convex than that of BaFe₁₂O₁₉, so that σ_s is 11 per cent higher at room temperature but lower at T = 0. The value σ_s(T = 0) = 96·2 G cm³/g (19·2 μ_B/molecule) and the anisotropic behaviour are attributed to the presence of 1 Fe²⁺/molecule occupying the octahedral 2a sites in the magnetoplumbite lattice and having a uniaxial anisotropy of 10–15 cm^?1/ion.From measurements on polycrystalline, crystal-oriented samples of BaFe_10·8Fe²⁺_0·6Ti⁴⁺_0·6O₁₉ and BaFe_10·5Fe²⁺_1·0Sb⁵⁺_0·5O₁₉ it was found that, in comparison with LaFe₁₁Fe²⁺O₁₉, σ_s (T = 0) is smaller and K₁ is much smaller and much less temperature-dependent. The difference in anisotropic behaviour is attributed to a different distribution of the Fe²⁺ ions among the lattice sites due to the effective positive charge of the Ti⁴⁺ and Sb⁵⁺ ions.     

Gluon multiple scattering and the transverse momentum dependence of J/ψ production in nucleus-nucleus collisions

A J/ψ meson is mainly formed by gluon fusion for 200 GeV pp collisions. In reactions with nuclei the gluons (g) scatter off other nucleons (N) before fusing to a J/ψ, which thenshows additional transverse momentum p_T. Fitting the value of the parameter σ_gN〈p²_T〉_gN to describe the gluon multiple scattering effect in proton-nucleus data, we can reproduce the p_T distribution of J/ψ production in 200 GeV/A nucleus-nucleus collisions. The origin of the p_T distribution is traced to soft gluon radiation via the Sudakov form factor.     

Surface tension of pure liquid helium isotopes

The effects caused by vapor inhomogeneity over liquid helium are considered. Both pure isotopes have surface levels, whose population increases with temperature T. We separated their contribution to the temperature dependence of surface tension σ₃(T) and σ₄(T) and compared our theoretical results with the results of Japanese experimental works [1–3]. For liquid He³, one has σ₃(T)=σ₃(0)?σ ₃ ^∞ T² at 0.2 K<T<1 K and σ₃(T)=σ₃(0)?α ₃ ⁰ T²exp(?Δ₃/T) at T<0.2 K, with Δ₃≈0.25 K. For liquid He⁴, σ₄(T)=σ₄(0)?AT^7/3? α ₄ ⁰ T²exp(?Δ₄/T) at T<2 K, where A is the Atkins constant and Δ₄≈4 K. The parameters α ₃ ⁰ , α ₃ ^∞ , and α ₄ ⁰ depend on the fluid properties.     

Giant forced volume magnetostriction of Fe-rich iron-cobalt-zirconium amorphous alloys

The forced volume magnetostriction has been measured as a function of composition and temperature in amorphous (Fe_1?xCo_x)₉₀Zr₁₀ alloys. The maximum value of $\text{δω}\text{δH}$ (T = 0 K), equal to 285 × 10^-10 Oe^-1, has been observed for Fe₉₀Zr₁₀ alloys. The effect of pressure on the magnetization σ₀ at T = 0 K was calculated from $\text{δω}\text{δH}$ data. The pressure dependence of the Curie temperature T_c and σ₀ behaves in a similar way as those observed for crystalline NiPd and NiRh alloys.     

Resolution of theK-factor ambiguity in QCD

The previously presented relations between inclusive cross sections for nucleus-nucleus, nucleon-nucleus and nucleon-nucleon scatterings with largep _T production were generalized to include effects of large momentum tail of nucleons inside the nucleus. Simple numerical estimations show that these effects are likely to dominate the inclusive cross section for nucleus-nucleus collisions at very largep _T.     

Effect of the disorder parameter on the magnetic,electrical, galvanomagnetic,elastic, and magnetoelastic properties of <Emphasis Type="Italic">R</Emphasis><Subscript>0.55</Subscript>Sr<Subscript>0.45</Subscript>MnO<Subscript>3</Subscript> manganites

This paper reports on a study of the magnetic, transport, magnetotransport, elastic, and magnetoelastic properties of the R_0.55Sr_0.45MnO₃ ceramics (R=Sm, Eu_0.40Nd_0.15, Tb_0.25Nd_0.30) with the same carrier concentration and identical tolerance factor but which differ in the cation disorder parameter σ². It was found that the Curie temperature T_C decreases linearly with increasing σ². An increase in σ² results in an increase in the maximum electrical resistivity and an increased jump in the temperature dependence of linear thermal expansion near T_C, as well as in a decrease in magnetoresistance and magnetostriction. For T>T_C, one observes an abrupt increase in magnetostriction, magnetization, and magnetoresistance in a critical FIeld H_C1 which grows with increasing temperature. The value of H_C1 determined at fixed T/T_C decreases with increasing σ².     

6Li与核弹性散射的微观光学势

从基本的Dirac-Brueckner-Hartree-Fock微观理论出发,得到同时包含实部和虚部的核子-核散射的微观光学势,并利用折叠模型直接获得了核-核散射参数无关的整体微观光学势.考虑到核-核散射去弹过程高级项的贡献和⁶Li的碎裂效应,在微观光学势的实部和虚部中引入了修正因子N_R,N_I.系统研究了入射粒子⁶Li与靶核¹²C,²⁸Si,关键词： 弹性散射 Dirac-Brueckner-Hartree-Fock方法 折叠模型 微观光学势     

Transport and magnetic properties of multiwall carbon nanotubes before and after bromination

Bulk samples of oriented carbon nanotubes were prepared by electric arc evaporation of graphite in a helium environment. The temperature dependence of the conductivity σ(T), as well as the temperature and field dependences of the magnetic susceptibility χ(T, B) and magnetoresistance ρ(B, T), was measured for both the pristine and brominated samples. The pristine samples exhibit an anisotropy in the conductivity σ_∥(T)/σ_⊥>50, which disappears in the brominated samples. The χ(T, B) data were used to estimate the carrier concentration n ₀ in the samples: n _0ini ～3×10¹⁰ cm^?2 for the pristine sample, and n _0Br～10¹¹ cm^\t—2 for the brominated sample. Estimation of the total carrier concentration n=n _e+n _p from the data on ρ(B, T) yields n _ini=4×10¹⁷ cm^?3 (or 1.3×10¹⁰ cm^?2) and n _Br=2×10¹⁸ cm^?3 (or 6.7×10¹⁰ cm^?2). These estimates are in good agreement with one another and indicate an approximately fourfold increase in carrier concentration in samples after bromination.     

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.     

Spin relaxation of charged centers in silicon in the presence of photocarriers (Si: Cr+, [Cr+−B−])

Spin relaxation of deep charged centers Cr⁺ and of donor-acceptor pairs (Cr⁺?B^?)⁰ in silicon is studied by nonstationary EPR spectroscopy at liquid-helium temperatures. We observed the effect of an increase in the spin-lattice relaxation rate under band-to-band sample illumination; the magnitude of the effect is proportional to the photoelectron concentration. The spin-dependent carrier trapping is shown to play a dominant role in spin relaxation under illumination for centers of both types. Coupled rate equations describing the interaction of various subsystems with one another and with the bath are solved. A comparison of experimental data with theory yielded the electron trapping cross sections σ_r(Cr⁺)?4.9×10^?12 cm² and σ_r(Cr⁺?B^?)?1.6×10^?12 cm² at T=4.2 K. The results obtained are discussed in terms of the theory of trapping by attractive centers.     

Static and high-frequency hole transport in <Emphasis Type="Italic">p</Emphasis>-Si/SiGe heterostructures in the extreme quantum limit

Complex high-frequency (HF), σ^AC = σ₁ ? iσ₂, and static, σ^DC, conductivities, as well as current-voltage characteristics, have been measured in p-Si/SiGe heterostructures with a low hole density (p = 8.2 × 10¹⁰ cm^?2) at temperatures T = 0.3–4.2 K in the ultraquantum limit, when the filling factor is v < 1. In order to determine the components of the HF conductivity, the acoustic contactless method in the “hybrid configuration” is used, when the surface acoustic wave propagates on the surface of the LiNbO₃ piezoelectric and the heterostructure is pressed to the surface by a spring. The conductivities σ₁ and σ₂ are determined from the damping and velocity of the surface acoustic waves that are measured simultaneously with varying the magnetic field. The revealed HF conductivity features—σ₁ ? |σ₂|, the negative sign of σ₂, the threshold behavior of the current-voltage characteristic, and the dependence I ∝ exp(-A/V ^0.3) in the subthreshold region—indicate the formation of a pinned Wigner crystal (glass) in the ultraquantum limit (T = 0.3–0.8 K, B > 14 T).     

Magnetization of Fe2+-Cr-Ti spinels

Measurements of magnetization σ in fields up to 14 kOe on four sintered samples of Fe²⁺-Cr-Ti spinels reveal σ-temperature curves which exhibit in part compensation points (T_co). The magnetic moments are low, indicating non Néel spin configuration. Close to T_co viscose magnetic effects have been detected.     

Electrode reaction at Pt,O2(g)/stabilized zirconia interfaces. Part I: Theoretical consideration of reaction model

This study aims to make clear the reaction kinetics at Pt, O₂(g)/zirconia electrodes in the oxygen partial pressure, P_O2, of ∼ 10⁻⁴ − 1 atm at ∼ 400–∼800°C. By a critical review on the preceding studies, problems were pointed out in the application of the Langmuir adsorption isotherm to the P_O2 dependence of electrode conductance, in the assumption of electric double layer at the electrode interface, and of the inconsistency between the recent reaction model of surface diffusion controlled kinetics and the absolute rate theory. It was shown that the charge transfer kinetics cannot be the rate determining step (RDS) of the electrode reaction. The possible RDS was concluded to be either (i) dissociative adsorption of oxygen molecules on the Pt surface or (ii) surface diffusion of O_ad atoms on the Pt surface to the Pt/zirconia contact. The diffusion of O_ad atoms on the Pt surface was considered to be proportional to θ(1−θ)(∂μ_O/∂x), where θ is the occupancy of O_ad atoms on Pt and μ_O is the oxygen chemical potential on the Pt surface. The rate equation, current-potential relationship, and the electrode conductivity, σ_E, were calculated for the cases the RDS is (i) and (ii), respectively. By comparing the calculated σ_E versus log P_O2 relationship with the reported ones, it was shown that the RDS is (i) for T ≲ 500°C and is (ii) for T ≳ 600°C. In the former case, σ_E is essentially constant irrespective to P_O2, and in the latter case, σ_E maximum appears on the σ_E versus log P_O2 relations.     

A note on the induced pseudo-scalar coupling constant in μ− + 12C(g.s)→ 12B(1+,g.s+ ν μ

The sum of the induce pseudo-scalar g_P and the second-class induced tensor g_T couplings in muon capture is found to be (g_P + g_T)g_A= (13.3 + 1.8) by comparing with recent data on the recoil polarization of ¹²B(1⁺) in the μ^? + ¹²C→¹²B+ ν_μ process, even aaking into account the corrections due to the gamma decay of the excited states of ¹²B to ¹²B(1⁺;g.s.). With the canonical value for g_P and in the absence of meson exchange effects, our results indicate a large positive value for g_T which is in strong contradiction with the conclusion of the Louvain-Saclay—ETH experiment.     

(γ, p) cross sections and isospin splitting of the giant dipole resonance in N = 50 nuclei

The differential (e, e'p) cross sections of ⁸⁸Sr, ⁸⁹Y, ⁹⁰Zr and ⁹²Mo have been measured at θ = 90°. The results are used to obtain the (γ, p) cross sections by correcting with the angular distribution data. The (γ, p) cross sections are compared with the (γ, n) cross sections. A resonance corresponding to the T_< GDR is found and another resonance is separated by fitting a Lorentz line with a width equal to that of the (γ, n) GDR. The ratios σ(γ, p)/σ(γ, n) and σ(γ, p₀)/σ(γ, p) show differences between the two resonances. The two GDR resonances are studied from the isospin splitting point of view. The sum rule and splitting energy of the (γ, p) GDR agree well with theory. However, when the sum of the (γ, p) and (γ, n) experimental data is taken, the results are too large to be explained by the T_> GDR.