Charge symmetrical pairing correlations for Even-Even nuclei withN=Z

The temperature dependence of the critical heat currentQ _c in He II has been measured in the temperature region 3 · 10^?5 (?K)<T _λ?T<1.2 · 10^?2 (?K). The result Q_c∫ (T _λ?T)^1.07±0.01is consistent with a divergent mutual friction nearT _λ proposed recently byAhlers.     

High efficiency second-harmonic generation in KNbO3 crystals

Second-harmonic generation in KNbO₃ crystals has been studied with CW and pulsed Al_xGa_1?xAs and dye lasers. High conversion efficiencies were obtained by noncritical Type I phase-matching at room temperature for the wavelength λ_PM = (860±2) nm using the nonlinear optical coefficient d₃₂ = 21 pm/V. The measured peak power was P_2ω=13.6 μW for a fundamental power P_ω=21 mW with a crystal of l = 8.97 mm in length. The phase-matching wavelength in the orthorhombic phase of KNbO₃ can be temperature tuned between 838 nm (for T = -36°C) and 950 nm (for T = +180°C).     

Continuous measures in one dimension

Families of unimodal maps satisfying

1. T _λ: [?1,1]?[?1,1] withT(±1)=?1 and |T _λ ^′ (1)|>1.
2. T _λ(x) isC ² inx ² and λ, and symmetric inx.
3. T ₀(0)=0,T ₁(0)=1 with \(\frac{d}{{d\lambda }}\) T _λ(0)>0

are considered. The results of Guckenheimer (1982) are extended to show that there is a positive measure of λ for whichT _λ has a finite absolutely continuous invariant measure. The appendix contains general theorems for the existence of such measures for some markov maps of the interval.     

Thermal conductivity of the amorphous and nanocrystalline phases of the beech wood biocarbon nanocomposite

Natural composites (biocarbons) obtained by carbonization of beech wood at different carbonization temperatures T _carb in the range of 800–2400°C have been studied using X-ray diffraction. The composites consist of an amorphous matrix and nanocrystallites of graphite and graphene. The volume fractions of the amorphous and nanocrystalline phases as functions of T _carb have been determined. Temperature dependences of the phonon thermal conductivity κ(T) of the biocarbons with different temperatures T _carb (1000 and 2400°C) have been analyzed in the range of 5–300 K. It has been shown that the behavior of κ(T) of the biocarbon with T _carb = 1000°C is controlled by the amorphous phase in the range of 5–50 K and by the nanocrystalline phase in the range of 100–300 K. The character of κ(T) of the biocarbon with T _carb = 2400°C is determined by the heat transfer (scattering) in the nanocrystalline phase over the entire temperature range of 5–300 K.     

Light-induced light absorption changes in AsSe and GeSe2 thin films

Reversible transmittance (T) changes for λ = 6328 Å light were observed in stabilized AsSe and GeSe₂ thin films when irradiated by λ = 5145 Å and λ = 4880 Å wavelength exciting light pulses. During photodarkening, T reaches a steady state value obeying a T ∝ t^-1 relationship then approaches its starting value exponentially when the light is switched off. Both of these processes develop in a few seconds. The transmittance changes are explained by variations in the absorption coefficients with temperature, controlled by the absorption and loss of energy.     

Br NQR relaxation and successive phase transitions of CH3NH3HgBr3

The measurement of ⁸¹Br NQR in CH₃NH₃HgBr₃ has been carried out in the temperature range between 80 and 300 K using a pulse NQR method. The temperature dependence of ⁸¹Br NQR frequencies in CH₃NH₃HgBr₃ has revealed that it undergoes three characteristic successive phase transitions at T?=?123, 184 and 239 K. The phase transition temperature at T?=?239 K is the second-order type, whereas those at T?=?184 and 123 K are the first-order nature of the phase transitions. Each phase transition seems to be closely related to the motions of methyl ammonium cation as a partial or whole. The enhancement of 1/T ₁ at T?=?239 K indicates the onset of the molecular motion of the cation as a whole with increasing temperatures.     

Study of the K − → μ − νπ 0 decay

The decay K ^? → μ ^? νπ ⁰ has been studied using in-flight decays detected with the ISTRA+ setup operating in the 25-GeV negative secondary beam of the U-70 PS. About 112K events were used for the analysis. The λ ₊ and λ ₀ slope parameters of the decay form factors f ₊(t) and f ₀(t) have been measured: λ ₊=0.0321±0.004(stat.)±0.002(syst.), λ ₀=0.0209±0.004(stat.)±0.002(syst.); the correlation dλ ₀/dλ ₊=?0.46. The limits on the possible tensor and scalar couplings have been derived: f _T/f ₊(0)=?0.021±0.028(stat.)±0.014(theor.), f _S/f ₊(0)=0.004±0.005(stat.)±0.005(theor.).     

3D dependence of the dielectric dispersion in a BaTiO3 single crystal

The 3D dependences ?′(log f, T) and tanδ(logf, T) of a perfect BaTiO₃ single crystal grown by the Remeika method have been studied in the ranges f = 1–2 × 10⁷ Hz and T = ?80–130°C. These dependences characterize a transition from the paraelectric phase (121.5°C) as a near-antiferroelectric transition followed by the transition to the tetragonal phase at ～79.5°C. According to a number of signs, the range 121.5–79.5°C corresponds to a metastable phase typical of first-order phase transitions. The unexpected result of this work has been discussed with invoking the hypothesis on the BaTiO₃ structure in the paraelectric phase, according to which it consists of three antiferroelectric states oriented along the crystallographic axes. Using the dielectric properties of BaTiO₃ as an example, the method of direct correct determination of the temperatures of the structural transformations from the anomaly of tanδ(logf, T) has also been demonstrated.     

Critical behavior of a ferroelectric studied by nuclear spin-lattice relaxation

Nuclear spin-lattice relaxation measurements have been performed on ¹¹B nuclei in colemanite CaB₃O₄(OH)₃·H₂O in the ferroelectric and paraelectric phases. Results obtained with a temperature accuracy of 0.01° C show a logarithmic behavior of T₁^?1 in the very vicinity of T_c.     

The critical behaviour of spontaneous magnetization in the antiferromagnetic NiO

The spontaneous magnetization of the sublattice vs temperature in the antiferromagnetic NiO was measured by the neutron diffraction method. Temperature changes of the Bragg peaks (111), (222), (333) and (444) with the wavelengths of neutrons $\text{λ}{}_{\mathrm{I}}\text{= 4.16}\text{A}\text{?}$, $\text{λ}{}_{\mathrm{II}}\text{= 2.08}\text{A}\text{?}$, $\text{λ}{}_{\mathrm{III}}\text{= 1.39}\text{A}\text{?}$ and $\text{λ}{}_{\mathrm{IV}}\text{= 1.04}\text{A}\text{?}$, respectively were simultaneously investigated by the neutron time-of-flight spectrometer. On the basis of these measurements, the transition temperature from the antiferromagnetic into the paramagnetic phase was determined, T_N = (523 ± 1)°K. The temperature function of the (111) magnetic peak intensity has been accepted to be I ～ (T_N?T)^2β. According to the present measurements the critical point exponent is 0.33 ± ^0.02_0.04.     

Self-organization of the structure in the Cu60Fe40 composite during deformation-thermal treatment

The deformation-thermal stability of a clusterized amorphous-crystalline structure prepared from a Cu₆₀Fe₄₀ powder mixture at a logarithmic strain e = 4.6 and subjected to isochronous (40 min) annealings at T _a = 200–800°C has been investigated. Periodic changes (ΔT = 300°C) in the order and disorder with a maximum ordering at T _a = 300 and 600°C and a maximum disordering at T _a = 400 and 700°C have been observed. The periodicity of the dominant crystallographic order with a period ΔT = 400°C in the annealing temperature has been revealed for face-centered cubic copper phase planes separated by a singular point at T = 500°C characterized by the dominant body-centered cubic iron phase ordering. It has been shown that the sawtooth shape of the size distribution of strain clusters formed within the crystal structure of deformed samples slowly changes with increasing annealing temperature from exponential (T _a = 200–700°C) to linear (T _a = 800°C). This indicates a high density of internal local distortions in structural units.     

Magnetic phase transition in Heisenberg antiferromagnetic films with easy-axis single-ion anisotropy

The staggered susceptibility of spin-1 and spin-3/2 Heisenberg antiferromagnet with easy-axis single-ion anisotropy on the cubic lattice films consisting of n=2, 3, 4, 5 and 6 interacting square lattice layers is studied by high-temperature series expansions. Sixth order series in J/k_BT have been obtained for free-surface boundary conditions. The dependence of the Néel temperature on film thickness n and easy-axis anisotropy D has been investigated. The shifts of the Néel temperature from the bulk value can be described by a power law n^−λ with a shift exponent λ, where λ is the inverse of the bulk correlation length exponent. The effect of easy-axis single-ion anisotropy on shift exponent of antiferromagnetic films has been studied. A comparison is made with related works. The results obtained are qualitatively consistent with the predictions of finite-size scaling theory.     

A law of corresponding states for the superfluid fraction of He II

The superfluid fraction ?_s/? in He II has been accurately measured at more than 400 points throughout the P-T plane above 1.2 K and is found to be a universal function of the reduced temperature T/T_λ(P).     

Theoretical study of superconducting state parameters of binary metallic glasses by a pseudopotential method

The theoretical investigations of the superconducting state parameters (SSP) viz. electron–phonon coupling strength λ, Coulomb pseudopotential μ¹, transition temperature T_C, isotope effect exponent α and effective interaction strength N₀V of binary metallic glasses have been reported using Ashcroft’s empty core (EMC) model potential for the first time. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. It is observed that λ and T_C are quite sensitive to the selection of the local field correction functions in comparisons with μ¹, α and N₀V. The T_C obtained from H-local field correction function is found in qualitative agreement with available experimental data and show linear nature with the concentration (C). A linear T_C equation is proposed by fitting the present outcomes for H-local field correction function, which is in conformity with other results for the experimental data. Also, the present results are found in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in the metallic glasses.     

McMillan Tc公式的解析推导(Ⅱ)——μ*≠0情形

本文把文献[1]的理论以及所得到的T_c公式推广到μ^*≠0情形,得到T_c=(2γ)/πω_log·(ω_log/ω_c)^{(μ*/(λ-μ*))}·exp{-(1+λ)/(λ-μ^*)}. Inγ=C=0.5772是Euler常数。 关键词：     

Pseudogap and metal-insulator transitions in doped semiconductors

The electronic spectrum of a doped semiconductor described by the Anderson-Holstein impurity model and its conductivity derived from the Kubo linear response theory are calculated. Two characteristic temperatures depending on the doping level x are found in the phase diagram, T _PG and T _λ(x). The pseudogap that opens in the single-particle spectrum at low doping levels and temperatures closes at the lower one, T _PG. The pseudogap state of an insulator is attributed to spin fluctuations in a doped compound. At the higher characteristic temperature T _λ(x),, spin fluctuations vanish and the doped compound becomes a paramagnetic poor metal. Two distinct metal-insulator crossovers between semiconductor-like and metallic temperature dependence of resistivity are found. An insulator-to-poor-metal transition occurs at T ^*(x) ≈ T _λ(x). A poor-metal-to-insulator transition at a lower temperature is attributed to the temperature dependence of density of states in the pseudogap. It is shown that both transitions are observed in La_2?x Sr_xCUO₄.     

Electron spin resonance and longitudinal relaxation around phase transition in La0.9Ca0.1 MnO3

With original modulation technique, the longitudinal electron spin-relaxation timeT ₁ has been measured in the La_1-xCa_xMnO₃ manganite (x = 0.1) both in the paramagnetic state and around the temperature (T _c) of the ferromagnetic ordering. The data are compared with the evolution of the transverse relaxation time T₂ as determined from the electron spin resonance (ESR) linewidth. Well above T_c, theT ₁ =T ₂ equality was confirmed, whereas a steep slowing down ofT ₂ was observed asT _c was approached (theT ₁/T₂ ratio increased by two orders of magnitude). The temperature dependence ofT ₁ within the whole temperature range was found to be consistent with that ofT · χ(T), where χ(T) is the electron-spin susceptibility obtained from the ESR absorption area. The interpretation suggests that both the longitudinal and transverse electron-spin relaxation rates are governed by strong exchange interaction between the Mn ions, the ESR linewidth being inhomogeneously broadened in the vicinity of the phase transition.     

On the hydrodynamics of condensed Bose-systems

A microscopic theory of superfluidity is developed, which is shown to be fully compatible with the phenomenological two-fluid model. The obtained connection between the densities of the condensate and the supercomponent is velocity dependent and has the correct limiting behaviour for T=0K and T_λ.     

Study of the K − → e − νπ 0 decay

The decay K ^? → e ^? νπ ⁰ has been studied using in-flight decays detected with the ISTRA₊ setup working at the 25-GeV negative secondary beam of the U-70 PS. About 130K events were used for the analysis. The λ ₊ parameter of the vector form factor has been measured: λ ₊=0.0293±0.0015(stat.)±0.002(syst.). The limits on the possible tensor and scalar couplings have been derived: f _T/f ₊(0)=?0.045±0.060(stat.) and f _S/f ₊(0)=?0.019 _?0.016 ^+0.025 (stat.).     

Radiative width of the first T = 2 state in 8Be

The lowest T = 2 state (J^π = 0⁺) in ⁸Be was observed as a resonance at E_d = 6962.8 ± 3.0 keV (E_X = 27495.8 ± 2.4 keV, λ_c.m. = 5.5 ± 2.0 keV) in the ⁶Li(d, γ)⁸Be reaction. The resonant capture yield to the 17.6 MeV J^π = 1⁺, T = 1 state gives λ_γ = 23 ± 4 eV (1.14 ± 0.20 W.u.), in good agreement with the intermediate coupling model.