Quantum Tunneling of D(H) Atoms and 2 – in Solid Hydrogen

This paper contains three results. First, the rate constants for the tunneling reaction HD + D H + D ₂ in solid HD increase steeply with increasing temperature above 5 K, while they are almost independent of temperature below 5 K. A mechanism of a vacancy–assisted tunneling reaction is proposed to account for this temperature dependence. Second, a hydrogen atom and a hydrogen molecule form a van der Waals complex in the Ar matrix at 20 K, where the tunneling reaction HD + D H + D ₂ takes place in this complex. The analysis of well–resolved ESR spectra of the complex determined the distance between a hydrogen atom and a hydrogen molecule as 2.3 – 2.5 Å. Third, the decay rate constants of anions in solid parahydrogen decrease with decreasing temperature below 6.6 K, attain the minimum value at 5 K, and then increase with decreasing temperature in the range of 5 2.7 K. The abnormal temperature dependence of the decay rate constants below 5 K is ascribed to a phonon–scattering process of quantum diffusion.     

Distribution of the Impurity Resonance Energy in Bi2Sr2CaCu2O8+δ Observed by Scanning Tunneling Spectroscopy

Using scanning tunneling microscopy and spectroscopy (STM/STS) at 4.2 K, we observed Zn impurity resonance states in single crystals of Zn substituted Bi₂Sr₂Ca(Cu_1?x Zn _x )₂O_8+δ . Zn impurity resonances were characterized by the peak structure in the local density of states (LDOS). The peaks were appeared near the E _F on each of Zn impurity sites. The peak energy showed a wide distribution from ?7 to 5 meV. The average peak energy was ?1.5 meV and the variance was 1.8 meV. We investigated the correlation between the peak energy at a Zn site and the energy gap value in the region where the Zn site is embedded. Although we observed about hundred Zn sites, no correlation between the local energy gap and the peak energy was observed.     

Effect of γ-radiation on optical properties of Eu2+ ions in the KCl: Eu2+ system

Emission spectra and luminescence time decay of Eu²⁺ ions in KCl crystals annealed at 873 K and quenched to room temperature before irradiation were measured at 80 K after -irradiation which was performed at 295 and 200 K. The results are consistent with radiation-induced aggregation of the original isolated europium dipoles.     

Mechanism on the Effect of Al upon the γ→ε Martensite Transformation in the Fe-Mn Alloys

The structure of the solid solution treated and deformed Fe-25Mn-(0-3.11)Al-0.15C alloys was examined by means of metallograph and X-ray diffraction, which has confirmed that Al restrains the γ→ε transformation in the Fe-Mn alloys. The mechanism on the restraining effect of Al has been discussed on the basis of the efFect of Al upon the stacking fault energy in the Fe-Mn alloys.Aluminium increases thermodynamically the stability of the Fe-Mn austenite and the driving force limit necessitated to be overcome for the γ→ε transformation, because the thermodynamicalcalculation indicates that Al increases the stacking fault energy in the Fe-Mn alloys at 300 K.Al will decrease the number and the size for the ε-martensite nucleus according to the stacking fault mechanism of the ε-martensite nucleation     

Effect of oxygen on short-range order in the Ba1−xBixF2+x solid solution

Various compositions within the range of the fluorite-type solid solution in the BaF₂–BiF₃–BiO_l.5 system are investigated by impedance spectroscopy. This study is carried out along two lines of compositions: δ₁, corresponding to the Ba_l−2z/3Bi_2z/3F_2+4z/3O_z solid solution, where z is the oxygen rate; and δ₂, corresponding to the Ba_l−xBi_xF_2+x−0.30O_0.15 solid solution, where x is the bismuth rate. An approach to the nature of the fluorine–oxygen order is proposed which derives from the clustering process in the Ba_l−xBi_xF_2+x fluoride solid solution.     

Size Effect in the Phase Separation of Cr–W Solid Solutions

Size effects in phase transformations of nanoscale systems show up as significant changes in their phase diagram. Here, using a thermodynamic approach we demonstrate how the immiscibility region of Cr–W solid solutions is influenced by their particle size. For 40- and 70-nm-diameter particles, we consider two thermodynamically stable states with a core–shell configuration, differing in the composition of the core phase. It is shown that, in the nanometer range, one of these states becomes metastable and that the phase diagrams of the stable and metastable states differ significantly. Reducing the particle size leads to a decrease in the upper critical dissolution temperature (UCDP) by 300–400 K and marked changes in the mutual solubility of the components at temperatures comparable to the UCDP.     

Effect of Ni+2-substituted Fe2TiO5 on the H2-reduction and CO2 Catalytic Decomposition Reactions at 500℃

CO2 is a major component of the greenhouse gases, which causes the global warming. To reduce CO2 gas, high activity nanosized Ni＋2 substituted Fe2TiO5 samples were synthesized by conventional ceramic method. The effect of the composition of the synthesized ferrite on the H2-reduction and CO2-catalytic decomposition was investigated. Fe2TiO5 （iron titanate） phase that has a nanocrystallite size of -80 nm is formed as a result of heating Fe2O3 and TiO2 while the addition of NiO leads to the formation of new phases （-80 nm） NiTiO3 and NiFe2O4, but the mixed solid of NiO and Fe2O3 results in the formation of NiFe2O4 only. Samples with Ni^＋2=0 shows the lowest reduction extent （20%）; as the extent of Ni＋2 increases, the extent of reduction increases. The increase in the reduction percent is attributed to the presence of NiTiO3 and NiFe2O4 phases, which are more reducible phases than Fe2TiO5. The CO2 decomposition reactions were monitored by thermogravimetric analysis （TGA） experiments. The oxidation of the H2-reduced Ni＋2 substituted Fe2TiO5 at 500℃ was investigated. As Ni^＋2 increases, the rate of reoxidation increases. Samples with the highest reduction extents gave the highest reoxidation extent, which is attributed to the highly porous nature and deficiency in oxygen due to the presence of metallic Fe, Ni and/or FeNi alloy. X-ray diffraction （XRD） and transmission electron microscopy （TEM） of oxidized samples show also the presence of carbon in the sample containing Ni＋2〉0, which appears in the form of nanotubes （25 nm）.     

Tunneling Conductance in Strained Graphene-Based Superconductor: Effect of Asymmetric Weyl–Dirac Fermions

Based on the BTK theory, we investigate the tunneling conductance in uniaxially strained graphene-based normal metal (NG)/barrier (I)/superconductor (SG) junctions. In the present model, we assume that by depositing the conventional superconductor on the top of the uniaxially strained graphene, normal graphene may turn to superconducting graphene with the Cooper pairs formed by the asymmetric Weyl–Dirac electrons, the massless fermions with direction-dependent velocity. The highly asymmetrical velocity, v _y /v _x ≫1, may be created by strain in the zigzag direction near the transition point between gapless and gapped graphene. In the case of highly asymmetrical velocity, we find that the Andreev reflection strongly depends on the direction of strain, and the current perpendicular to the direction of strain can flow through the junction as if there were no barrier. Also, the current parallel to the direction of strain anomalously oscillates as a function of the gate voltage with very high frequency. Our predicted result is quite different from the feature of the quasiparticle tunneling in the unstrained graphene-based NG/I/SG conventional junction. This is because of the presence of the direction-dependent-velocity quasiparticles in the highly strained graphene system.     

Effect of Hydrogen on the Structure and Magnetic Properties of (Sm1–xErx)2Fe17 (x = 0.1, 0.4) Solid Solutions

Inorganic Materials - (Sm1–xErx)2Fe17 (x = 0.1, 0.4) solid solutions have been prepared by induction melting and then hydrided to give high hydrogen content materials: Sm1.8Er0.2Fe17H4.4 and...     

Specific Features of the Magnetoelectric Effect in Permendur–Quartz–Permendur Structures in the Region of Electromechanical Resonance

Technical Physics Letters - The experimental frequency and field dependences of the magnetoelectric effect in three-layer permendur–quartz–permendur structures in the region of...     

Effect of Dissipation on Quantum Tunneling of Vortices in Tl2Ba2Ca2Cu3O10+δSuperconductors

The temperature and magnetic field dependence of the magnetic relaxation rate has been investigated at low temperatures (1.8 < T < 10 K) on two Tl₂Ba₂Ca₂Cu₃O₁₀₊ samples (epitaxial thin film and sintered pellet). The temperature dependence gives evidence of a crossover in the mechanism of vortex motion, from classical thermal activation to quantum tunneling as temperature decreases. The field dependence of the relaxation rate indicates a crossover in the dimensionality of vortices, from three-dimensional flux lines to two-dimensional pancake vortices as field increases. For the thin film, the temperature dependence of the rate has been fitted to the theoretically predicted expressions for finite-temperature enhancement of the quantum rate in different regimes of dissipation. In spite of the similarity of the fits, the estimate of the ratio of Hall to viscous drag terms in the equation of motion indicates that quantum tunneling in this system occurs in an intermediate dissipative regime, where both terms contribute to the motion of vortices.     

Effect of glycerol on the preparation of phosphogypsum-based CaSO4·0.5H2O whiskers

Phosphogypsum-based CaSO₄·0.5H₂O whiskers were successfully prepared in the presence of glycerol by hydrothermal method. The action mechanism of glycerol on the morphology of CaSO₄·0.5H₂O whiskers was investigated and discussed in detail. The as-prepared products were characterized by X-ray powder diffraction spectrometer, scanning electron microscopy, Fourier transform infrared spectrometer, and thermal analyzer. The main phase of the as-prepared products was CaSO₄·0.5H₂O, and the morphology was uniform fiber. Moreover, the aspect ratio and productivity of the as-prepared CaSO₄·0.5H₂O whiskers increased with the concentration of glycerol. Even whiskers with mean length of 38–83 μm, mean width of 1.33–0.73 μm, aspect ratio of 29–118, and productivity of 89–96 % were obtained under the condition of glycerol/water volume ratio of 10–100 %. As far as mechanism was concerned, the hydroxyl groups of glycerol adsorbed and occupied the vacancies of Ca sites on (001) plane of CaSO₄·0.5H₂O whiskers, and however, on (100) plane, hydroxyl groups of glycerol adsorbed mainly on Ca sites and formed hydrogen bond layered structure on both sides of that, which should be the reason that CaSO₄·0.5H₂O whiskers grew along the c-axis observed in this study.     

Effect of O2, H2O2, and HNO2 on the stability of Np(III–VII) in aqueous solutions

Published data on reactions of Np ions with O₂, H₂O₂, HNO₂, and HNO₃ in solutions of various compositions in a wide pH range are considered. O₂ oxidizes Np(III) in acid solution and Np(IV) and Np(V) in alkaline solutions. H₂O₂ exhibits dual behavior. In weakly acidic solutions, it converts Np(III) and (IV) to Np(V), in 0.75?C1 M NaHCO₃ it oxidizes Np(V) to Np(VI), whereas in dilute HClO₄ and HNO₃ and in carbonate and alkali solutions it reduces Np(VI), and in alkali solutions it reduces Np(VII). The first step of reduction in most cases is the formation of the Np(VI) peroxide complex, and the next step is the intramolecular charge transfer. In concentrated HNO₃ solutions, H₂O₂ converts Np(V) to Np(IV) and Np(VI) and then reduces Np(VI). Some radiation-, photo-, and sonochemical reactions occur via formation of excimers, i.e., of dimers arising from excited and unexcited Np ions. The excimer decomposes into two ions with higher and lower oxidation states. In reduction reactions, the excimer eliminates H₂O₂ (in addition to the H₂O₂ arising as primary product of water radiolysis). In HNO₃ solutions, oxidation of Np ions occurs only in the presence of HNO₂ arising as reaction product or upon radiolysis, photolysis, or sonolysis. The active species are NO ₂ ^? , NO₂, and NO⁺ present in equilibrium with HNO₂.     

Effect of Liquid–Solid Extrusion on the High-Temperature Compressive Properties of Csf/Mg Composites

Short carbon fiber reinforced Mg matrix composites (C_sf/Mg) were prepared by an infiltration–extrusion integrated technique in which pressure infiltration and liquid–solid extrusion are performed continuously. Their compressive properties were evaluated in the temperature range 20–300°C, and compared with C_sf/Mg composites fabricated by only pressure infiltration technique. The results show that after liquid–solid extrusion, the fiber tended to align along the extrusion direction, and a refined-grain microstructure was obtained, thereby contributing to a significant increase in both compressive strength and yield strength up to 200°C, but they are abnormally lower than those of the infiltrated composite at 300°C due to fiber rotation and a different deformation mechanism related to the finer grain structures.     

Effect of Solid Solution Supersaturation on Precipitation of γ'''' in Rapidly Quenched Ni-Al Binary Alloys

The effect of solid solution supersaturation on the precipitation of γ' in rapidly quenched Ni-Al binary alloys containing 11.6, 14.2 and 16.5 at. Pct Al was investigated. The samples were solutioned at 1250℃, quenched in iced brine, and then analyzed by electron microscopy and XRD (X-ray diffraction) techniques. In Ni-11.6 at. Pct Al alloy, ordering and phase separation took place simultaneously, resulting in a uniform distribution of γ'. A transition from uniform to bimodal γ' phase distribution occurred in the composition range between 14.2 and 16.5 at. Pct Al. This transition was accompanied by changes in the morphology of γ' precipitates. The microstructural observations were discussed in view of both kinetics and crystallographic considerations.     

Effect of the LIII Absorption Edge of Uranium on Chemical Shifts of the Lβ1 Line of Uranium in UO2+x

The effect of intraatomic absorption of the L₁ X-ray emission line of uranium was studied. To eliminate the effect of the L _{I I I} absorption edge on the chemical shift () of the L₁ line, the dependence of L₁ on the oxygen index x in oxide systems of variable composition UO_{2 + x} was determined indirectly. It was shown that, in the absence of the effect of the L _{I I I} absorption edge, the dependence of L₁ on x is ordinary and, as in the case of other hard emission lines of the uranium L series, can be described by a second-order polynomial. The abnormal dependence of L₁ on x is explained.     

Mechanism of Inelastic Phonon Scattering on the Quadrupolar o–H2 Impurity in p–H2 Matrix

A quantum–mechanical problem on inelastic phonon scattering by a quadrupolar pair defect is discussed. As an example of the physical system, where this mechanism is of great concern, the solution of o–H ₂ molecules in p–H ₂ matrix is considered. The effective relaxation time _p of a phonon collision with a pair defect as a function of the phonon frequency is calculated. Due to intrinsic degrees of freedom, pair defects give rise to the resonance phonon scattering above a certain temperature T ₀ , which for o–H ₂ —p–H ₂ mixtures is approximately 6 ÷ 7 K.