Development of metal borohydrides for hydrogen storage

A metal borohydride M(BH₄)_n is a potential candidate for hydrogen storage materials because of its high gravimetric hydrogen density. The important research issues for M(BH₄)_n are to control the thermodynamic stability and to achieve the faster reaction kinetics. To clarify the thermodynamic stability, M(BH₄)_n (M=Mg, Ca∼Mn, Zn, Al, Y, Zr and Hf; n=2-4) were synthesized by mechanical milling and its thermal desorption properties were investigated. The hydrogen desorption temperature T_d of M(BH₄)_n decreases with increasing Pauling's electronegativities χ_P of M. Because Mn, Zn, and Al borohydrides (χ_P?1.5) desorb borane, they are too unstable for hydrogen storage applications. The enthalpy changes of desorption reaction ΔH_des can be estimated by using our predicted heat of formation of M(BH₄)_n ΔH_boro and reported data for decomposed products ΔH_prod, which are useful indicators for searching M(BH₄)_n with appropriate stability for hydrogen storage material. In the latter case, microwave processing was adopted for achieving fast reaction kinetics. Among metal borohydrides, LiBH₄ was rapidly heated above 380 K by microwave irradiation, 13.7 mass% of hydrogen was desorbed by microwave irradiation. The composites of LiBH₄ with B or C desorbed hydrogen within 3 min. Microwave heating aids in realizing faster kinetics of the hydrogen desorption reaction.     

Fission-fragment energy correlation measurements for 252Cf(sf) and structures in far-out asymmetric fission

Fragment-mass and kinetic-energy distribution measurements for ²⁵²Cf(sf) have been extended to the far-out asymmetric low-yield fission region of M_H = 190 compared with the existing data that go up to M_H ≈ 168. The mass yield Y(m) shows a shoulder for M_H ≈ 163 and an important enhancement for M_H ? 176. The 〈E_K〉(m), σ_EK(m) and, to a lesser extent, Y(m) distributions show strong and correlated amplitude fluctuations for M_H ? 170. These data indicate strong and rapid changes in deformation of the nascent fragments and the coexistence of more than one deformed-shell stabilized scission configuration for the same mass splits. These structures and those present in the relatively high-yield regions are discussed in terms of the static macro-microscopic potential-energy calculations.     

The N2-broadened water vapor absorption line shape and infrared continuum absorption—II. Implementation of the line shape

The total line shape model of the previous paper is tested using a set of experimental room temperature H₂O continuum measurements of high quality. Parameters of the far wing component of the total line shape are determined from near band experimental data. Grating spectrometer measurements from 300 to 650 cm^?1 are used to determine unknown far wing parameters of the pure rotational band of H₂O. CO and HF laser measurements taken in the 5 and 3 μm regions are used to determine the far wing parameters of the ν₂ and ν₁, ν₃ fundamental bands, respectively.The total line shape model is applied to the 10 and 4 μm transmission windows with encouraging success. A significant increase in the self-broadening ability of H₂O over N₂ is predicted in the far wing. This procedure allows the proper modeling of the absorption coefficient vs H₂O partial pressure dependence in all window regions. A negative temperature is predicted by the model in the continuum. The observed rate of the temperature decrease is not predicted by the model; however, this limitation is related to the approximations made on the interaction potentials and the perturbation expansion of the Hamiltonians. Although the total line shape has limitations, it does demonstrate the importance of considering far wings of absorption lines in continuum absorption.     

Model-independent determination on <Emphasis Type="Italic">H</Emphasis><Subscript>0</Subscript> using the latest cosmic chronometer data

We perform the updated constraints on the Hubble constant H ₀ by using the model-independent method, Gaussian processes. Utilizing the latest 30 cosmic chronometer measurements, we obtain H ₀ = 67.38 ± 4.72 km s^?1 Mpc^?1, which is consistent with the Planck 2015 and Riess et al. analysis at 1σ confidence level. Different from the results of Busti et al. by only using 19 H(z) measurements, our reconstruction results of H(z) and the derived values of H ₀ are insensitive to the concrete choice of covariance functions of Matérn family.     

Comments on the electric modulus formalism model and superior alternatives to it for the analysis of the frequency response of ionic conductors

Because of the past and continuing wide usage of the 1973 original modulus formalism (OMF) model for analyzing dispersive frequency-response data of ion-conducting materials, it is important to discuss and demonstrate its theoretical and experimental inadequacies to help avoid its future use and to describe and illustrate important alternatives to it. The OMF fits data with a K1 response model alone, one indirectly derived from stretched-exponential temporal behavior, while the corrected modulus formalism (CMF) involves the composite CK1 model, one that includes in addition a separate free, parallel bulk dielectric parameter, ε_D∞. The crucial error of the OMF approach is its identification of a high-frequency-limiting dielectric constant intrinsic to K1 response and associated entirely with conductive effects, with the full high-frequency-limiting dielectric constant of the material, ε_∞, one that must include the non-ionic, primarily dipolar quantity ε_D∞. Comparison here of OMF fitting results with those of the CMF CK1 model for both an experimental data set and an exact one derived from it demonstrate the incorrectness of the OMF and the virtues of the CK1 alternative. The OMF fitting approach, but not the CMF one, leads to crucial inconsistency between the estimates of its β shape parameter for fits of the data expressed at all immittance levels except those of σ′ and ε″, where it yields the same results as the CK1. Its incorrect β estimates, extensively used in the Ngai coupling model and interpreted as being associated with ion–ion correlations, also lead to erroneous “excess wing” effects in plots of the imaginary part of the data and fit at the modulus level. Further, OMF modulus-level fits yield non-physical estimated values of the characteristic relaxation time of the K1 model. Finally, some possible alternatives to the CK1 model are discussed for situations involving dielectric-system dispersion.     

Magnetic sub-state population cross sections in inelastic alpha-nucleus scattering

Properties of the sub-state population cross sections σ_M for inelastic α-nucleus scattering are explored within the deformed collective nuclear model. The interference between the nuclear and Coulomb parts of the inelastic transition potential is calculated with the DWBA. The effect on the M = ?2 sub-state cross section is substantially more pronounced than that for the usual inelastic differential cross section Σ_mσ_m. The effect of re-orientation terms is calculated by means of a coupled channel formalism for small values of the quadrupole deformation parameter β₂. It is found to shift the angular position of the minima of the σ_M relative to the DWBA result, in a way which depends on the sign of β₂. A spin orbit potential has only a small effect on the σ_M. The calculations refer to 15 MeV α-particles incident on a nucleus of the size and charge of Ca.     

Effect of magnesium substitution on dielectric and magnetic properties of Ni-Zn ferrite

The dielectric and magnetic properties of Mg incorporated Ni-Zn spinel ferrites have been investigated. Ni_0.5−xZn_0.5Mg_xFe₂O₄ ferrites have been prepared by sol-gel auto-combustion technique. The as prepared ferrites were annealed at 673, 873 and 1073 K. The X-ray diffraction studies reveal the spinel structure of annealed ferrites. The TEM results are in agreement with XRD results. FTIR study has also been carried out to get insight into the structure of these ferrites. The dielectric measurements show that the dielectric constant (ε′), dielectric loss (tan δ) and conductivity (σ_ac) increase on incorporation of Mg in the Ni-Zn ferrite. ε′, tan δ and σ_ac also show dependence on temperature, frequency of external applied electric field and microstructure of the samples. The magnetic moment measurements reveal that the saturation magnetization (M_s) increases and coercivity (H_c) decreases with the increase in concentration of Mg²⁺ ions. M_s and H_c also show dependence on the annealing temperature.     

Low-energy dilation

We study consequences of scale symmetry breaking in the QCD effective SU(2)×SU(2) chiral model. The mass of a pseudo-Goldstone boson dilation is estimated to be M_σ≅1 GeV and the upper bound to its lifetime τ_σ⩽4×10⁻²⁸ s. We also show that the dilation gives a considerable contribution to the pion scalar radius.     

Particle size dependence of exchange-bias and coercivity in CuO nanoparticles

For CuO nanocrystals of size 6.6-37 nm, the exchange bias H_eb and coercivity H_c are measured at 5 K in zero-field-cooled (ZFC) and field-cooled (FC at 50 kOe) samples and their variations investigated as a function of particle size D. The similar 1/D variations observed for the difference coercivity ΔH_c=H_c(FC)−H_c(ZFC) and the interfacial exchange energy Δσ=H_ebM_fD are discussed in terms of the ferromagnetic magnetization M_f being produced by the uncompensated surface Cu²⁺ spins in the otherwise antiferromagnetically ordered CuO nanoparticles. This leads to the observation that the experimentally measured ΔH_c provides a good measure of Δσ in nanoparticle systems, with H_eb/ΔH_c varying as 1/M_fD.     

Commensurate and incommensurate states of a spin density wave in a quasi-two-dimensional system with an anisotropic energy spectrum in an external magnetic field of arbitrary direction relative to magnetization

A theory of thermodynamic properties of a spin density wave (SDW) in a quasi-two-dimensional system (with a preset impurity concentration x) is constructed. We choose an anisotropic dispersion relation for the electron energy and assume that external magnetic field H has an arbitrary direction relative to magnetic moment M _Q . The system of equations defining order parameters M _Q ^z , M _Q ^σ , M _z , and M ^σ is constructed and transformed with allowance for the Umklapp processes. Special cases when H ‖ M _Q and H ⊥ M _Q (H _Z H ^σ = 0) are considered in detail as well as cases of weak fields H of arbitrary direction. The condition for the transition of the system to the commensurate and incommensurate states of the SDW is analyzed. The concentration dependence of magnetic transition temperature T _M is calculated, and the components of the order parameter for the incommensurate phase are determined. The phase diagram (T,~x) is constructed. The effect of the magnetic field on magnetic transition temperature T _M is analyzed for H _Z H ^σ = 0, and longitudinal magnetic susceptibility χ‖ is calculated; this quantity demonstrates the temperature dependence corresponding to a system with a gap for x < x _c and to a gapless state for x > x _c . In the immediate vicinity of the critical impurity concentration (x ～ x _c ), the temperature dependence of the magnetic susceptibility acquires a local maximum. The effect of anisotropy of the electron energy spectrum on the investigated physical quantities is also analyzed.     

On the use of a noncentral velocity dependent potential for the interpretation of the nucleon-nucleon scattering data

A phenomenological nucleon-nucleon potential containing a noncentral velocity dependent term of the form (σ ₁ ·p)(σ ₂ ·p) is used to fit the solutions YLAM and YLAN 3 M of the phaseshift analysis ofBreit et al. andHull et al. for protonproton and neutron-proton scattering respectively. The potential contains altogether 20 parameters. The fit is carried through in the range from 10 to 300 MeV laboratory energy. While the results for thep-p phase parameters are useful only in some cases the results for then-p phase parameters are in general quite satisfactory.     

Is the peak value of σ xx at the quantum Hall transition universal?

The question of the universality of the longitudinal peak conductivity at the integer quantum Hall transition is considered. For this purpose, a system of 2D Dirac fermions with random mass characterised by variance g is proposed as a model which undergoes a quantum Hall transition. Whilst for some specific models the longitudinal peak conductivity σ _xx was found to be universal (in agreement with the conjecture of Lee et al. as well as with some numerical work), we find that σ _xx is reduced by a factor (1 + g/2π)^?1, at least for small g. This provides some theoretical evidence for the non-universality of σ _xx , as observed in a number of experiments.     

Strong localization in conducting Langmuir-Blodgett films of quasi-one-dimensional charge-transfer complexes

The temperature dependence of intragrain conductivity of the Langmuir-Blodgett (LB) films of (C₁₆H₃₃-TCNQ)_0.4(C₁₇H₃₅-DMTTF)_0.6 has been studied by means of measuring the surface acoustic waves (SAW) attenuation in a piezocrystal resonator covered by the LB film. [(C₁₆H₃₃-TCNQ)_0.4(C₁₇H₃₅-DMTTF)_0.6 denotes the surface-active charge-transfer complex of hexadecyltetracyanoquinodimethane (C₁₆H₃₃-TCNQ) and heptadecyldimethyltetrathiofulvalene (C₁₇H₃₅-DMTTF)]. We have found that the intragrain conductivity decreases with decreasing temperature, following σ∝exp(−1/T^1/2) law. According to the theory of electron transport in quasi-one-dimensional disordered systems (Q1D DS) proposed by E.P. Nakhmedov et al. [Sov. Phys. Solid State 31 (1989) 368] and developed by Z.H. Wang et al. [Phys. Rev. B 43 (1991) 4373], this temperature behaviour of the conductivity points to the disorder-induced electron localization within the film grains. Fitting our experimental data to the relations proposed in these references, allowed us to evaluate the electron relaxation times due to scattering by phonons and impurities. Based on structural parameters of the conducting bilayer, we have also estimated the Fermi velocity and density of states at the Fermi level, which enabled us to determine the mean free path and localization length in the film studied.     

Radiative gauge symmetry breaking in supersymmetric flipped SU(5)

The radiative breaking of the SU(5)×U(1) symmetry in the flipped SU(5) model recently proposed by Antoniadis et al. is studied using renormalization group techniques. It is shown that gaugino masses can only be the dominant source of supersymmetry breaking at the Planck scale if the U(1) gaugino mass M₁ is at least 10 times larger than the SU(5) gaugino mass M₅. If M₁≅M₅ at the Planck scale, non-vanishing trilinear soft breaking terms (“A-terms”) are needed already at the Planck scale. In both cases consequences for the sparticle spectrum at the weak scale are discussed.     

Wing profile measurements of the resonance emission lines of Na (5890/96Å) and Sr (4607Å) in flames

The blue and red wing intensity distributions of the Na 5890Åand 5896Åresonance lines were measured in emission in a pre-mixed, laminar, shielded H₂/O₂ flame at 1 atm with Ar or N₂ as diluent gases (T≈2000 K). The wavelength range scanned amounted to about 20Åfrom line center. In addition, we measured the wing intensity distributions of the resonance line of Sr (4607Å) in CO/N₂O flames at 1 atm (T≈2800 K) in a wavelength range of about 10Åfrom line center. The scanning monochromator used in these emission experiments had a spectral bandwidth of 0.30±0.04Å.For the resonance lines of Na and of Sr, the wavelength dependence of each wing was derived from 25 repeated scans and found to differ from theoretical predictions based on binary quasistatic theory.The red wing of the D₁ line of Na was investigated for the occurrence of satellites. We discovered a structure resembling a “smoothed” satellite at about 12Åfrom line centre. A satellite-like structure was also found in the blue wing of the resonance emission line of Sr at about 5Åfrom line center.     

Measurement of L X-ray fluorescence cross sections and relative intensities for some elements in the atomic range 78 ≤ Z ≤ 92

The L X-ray fluorescence cross sections (σ_Ll, σ_Lα, σ_Lη, σ_Lβ, σ_Lβ6, σ_Lβ2,₄, σ_Lβ1,₃, σ_Lβ9,10, σ_Lγ, σ_Lγ1, σ_Lγ2,3, σ_Lγ4 and σ_Lγ5) and relative intensities (I_Lα, I_Ll, I_Lη, I_Lβ, I_Lβ6, I_Lβ2,4, I_Lβ1,3, I_Lβ9,10, I_Lγ, I_Lγ1, I_Lγ2,3, I_Lγ4 and I_Lγ5) for some elements in the atomic range 78 ≤ Z ≤ 92 have been measured at 59.54 keV photons energies from an Am-241 point source. The L X-rays emitted by samples have been counted by a Si(Li) detector. The L X-ray fluorescence cross sections and relative intensities have been also calculated theoretically by using atomic parameters. The measured values have been compared with the theoretical values.     

Effective Lagrangian for quantum black holes

We discuss the most general effective Lagrangian obtained from the assumption that the degrees of freedom to be quantized, in a black hole, are on the horizon. The effective Lagrangian depends only on the induced metric and the extrinsic curvature of the (fluctuating) horizon, and the possible operators can be arranged in an expansion in powers of M_P1/M, where M_P1 is the Planck mass and M the black hole mass. We perform a semiclassical expansion of the action with a formalism which preserves general covariance explicitly. Quantum fluctuations over the classical solutions are described by a single scalar field living in the (2 + 1)-dimensional world-volume swept by the horizon, with a given coupling to the background geometry. We discuss the resulting field theory and we compute the black hole entropy with our formalism.     

Photo-induced bias of the hysteresis loop in ferrites at room temperature with long-time memory

New photo-magnetic effects with an indefinitely long-time memory are found at room temperature in the epitaxial Mg_0.75Mn_0.21Co_0.04Fe₂O₄ ferrite film. Illumination of the ferrimagnetic material with low-intensity (0.4 W cm⁻²) circularly polarized light with or without a static magnetic field in the Faraday effect geometry results in a number of nonlinear effects in both space and time. In a uniform crystal with cubic symmetry, the long-lived photo-induced magnetization (PIM) with a unidirectional anisotropy appears along the direction of the incoming light. The effects depend on a combination of magnetic field H and the helicity of circularly polarized light σ. Two combinations H⁺,σ⁺ and H⁻,σ⁻ lead to a photo-induced unidirectional anisotropy with a shift of the hysteresis loop along an applied field and a change in loop parameters. The loop contracts by a factor of two, the shift of the mid-point H_sh increases by factor of five surpassing the coercivity H_c, the coercivity H_c1 and remanence M_r1 (for decreasing applied field) reverse the sign, increasing by 9 Oe and reducing by a factor of 4.5, respectively. The effects cannot be erased by a conventional demagnetization (using an AC current that is reduced to zero amplitude), but can be removed using an illumination with two other combinations (H⁺,σ⁻ and H⁻,σ⁺) as well as by heating at temperatures higher than the Curie temperature. This long-lived room-temperature memory effect may arise from the formation of complex photo-induced defects including photo-induced magnetic polarons. The possible mechanisms responsible for the appearance of a room-temperature photo-induced unidirectional anisotropy with a long-lived memory are discussed. These new photo-magnetic effects may find an application in magneto-optical memory devices.     

Higher orders in N−1 in the Gross-Neveu model

We study higher-order terms in the N expansion of the two-dimensional model field theory of Gross and Neveu. The quantity $\text{M}{}_{\mathrm{\sigma }}\text{2M}{}_{\mathrm{<mtext>F</mtext><mtext>?1</mtext>}}$ (M_F is the fermion mass, M_σ is the scalar bound-state mass), is conjectured to deviate from zero in O(N^?4). Order N^?1 corrections are found to leave unchanged both the symmetry-breaking, and the absence of zeros of the Callan-Symanzik function β for real non-zero coupling constant. Behavior of β for complex coupling constant is altered considerably by the corrections; consequences are discussed.We obtain the following additional results: proof that the model is renormalizable without the necessity of additional interactions; construction of a perturbation theory in the asymmetric vacuum; proof of a lemma on fermion-antifermion thresholds in two-dimensional space-time; derivation of closed formulae for arbitrary one-loop integrals in two-dimensional space-time.     

An investigation of the phase structure of the two-dimensional O(2) and O(4) symmetric nonlinear sigma-models

We investigate the phase structure of the two-dimensional O(2) and O(4) lattice σ-models by means of a Monte Carlo simulation using Binder's phenomenological renormalization group. For the O(2) model the transition temperature β_c⁻¹ is estimated and the expected line of critical points is found. For the O(4) model no signal of a phase transition is found in the range of couplings considered. This is in contradiction to a recent claim that the O(4) model has a critical point at finite β.