Calculated elastic constants of dilute alloys based on bcc metals

The elastic constants of dilute alloys based on bcc metals have been calculated using the Green’s function method obtaining explicit expressions for change in elastic constants in terms oft-matrix. The crystal impurity problem is discussed within an impurity model containing central and non-central force constant changes extended up to second neighbours of the impurity. The effect of volume change on elastic constants and a contribution from electron pressure term are considered. Numerical results for changes in three elastic moduli have been presented for a number of dilute alloys based on Mo, Nb, W, Ta and V.     

Coherence vs. decoherence in (some) problems of condensed matter physics

We present an ‘overview’ of coherence-to-decoherence transition in certain selected problems of condensed matter physics. Our treatment is based on a subsystem-plus-environment approach. All the examples chosen in this paper have one thing in common — the environmental degrees of freedom are taken to be bosonic and their spectral density of excitations is assumed to be ‘ohmic’. The examples are drawn from a variety of phenomena in condensed matter physics involving, for instance, quantum diffusion of hydrogen in metals, Landau diamagnetism and c-axis transport in high T _c superconductors.     

Contribution of electron-nuclear interaction to the residual resistivity of metals

In nonmagnetic metals the spin-spin interaction of the electrons and nuclei makes a strongly magnetic field and temperature T dependent contribution to the residual resistivity. The nuclei act as magnetic impurities. For magnetic metals (Tb, Ho, Dy) with a high internal magnetic field, the nuclear contribution to the resistivity vanishes at low temperatures T, where the nuclear spins are ordered, and saturates at high temperatures T, where the nuclear spins are disordered—the analog of the Schottky effect for the nuclear specific heat. The electron-nuclear interaction can destroy superconductivity in metals with low critical magnetic fields under conditions of ferromagnetic ordering of the nuclear spins. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 3, 193–197 (10 August 1996)     

Half-shellT matrix for Coulomb-modified Graz separable potential

We construct a closed form expression for the off-shell Jost function for scattering by the Coulomb-distorted Graz separable potential and express it in the ‘maximal reduced form’. Our result is particularly suitable for numerical computation. We present a case study in support of this and examine the role of Coulomb interaction in thep — p half-shell scattering in the¹ S ₀ channel.     

Lattice mechanical properties of noble and transition metals

A model pseudopotential depending on an effective core radius but otherwise parameter free is used to study the interatomic interactions, phonon dispersion curves (inq and r-space analysis), phonon density of states, mode Grüneisen parameters, dynamical elastic constants (C ₁₁,C ₁₂ andC ₄₄), bulk modulus (B), shear modulus (C′), deviation from Cauchy relation (C ₁₂–C ₄₄), Poisson’s ratio (σ), Young’s modulus (Y), behavior of phonon frequencies in the elastic limit independent of the direction (Y ₁), limiting value in the [110] direction (Y ₂), degree of elastic anisotropy (A), maximum frequencyω _max, mean frequency 〈ω〉, 〈ω ²〉^1/2=(〈ω〉/〈ω ⁻¹〉)^1/2, fundamental frequency 〈ω ²〉, and propagation velocities of the elastic constants in Cu, Ag, Au, Ni, Pd, and Pt. The contribution of s-like electrons is calculated in the second-order perturbation theory for the model potential while that of d-like electrons is taken into account by introducing repulsive short-range Born-Mayer like term. Very recently proposed screening function due to Sarkar et al. has been used to obtain the screened form factor. The theoretical results are compared with experimental findings wherever possible. A good agreement between theoretical investigations and experimental findings has proved the ability of our model potential for predicting a large number of physical properties of transition metals.     

Ultrasonic wave propagation in rare-earth monochalcogenides

The ultrasonic attenuation in thulium monochalcogenides TmX (X=S, Se and Te) has been studied theoretically with a modified Mason’s approach in the temperature and range 100 K to 300 K along 〈100〉, 〈110〉 〈111〉 crystallographic directions. The thulium monochalcogenides have attracted a lot of interest due to their complex physical and chemical characteristics. TmS, TmSe and TmTe are trivalent metal, mixed valence state, and divalent semiconductor, respectively. Coulomb and Born-Mayer potential is applied to evaluate the second- and third-order elastic constants. These elastic constants are used to compute ultrasonic parameters such as ultrasonic velocities, thermal relaxation time, and acoustic coupling constants that, in turn, are used to evaluate ultrasonic attenuation. A comparison of calculated ultrasonic parameters with available theoretical/experimental physical parameters gives information about classification of these materials.      

ΛN Space-exchange effects in thes-shell hypernuclei and Λ 9 Be

Variational Monte Carlo calculations of the ground state separation energiesB _Λ of thes-shell hypernuclei and also of _Λ ⁹ Be have been made for an Urbana-type central space-exchange ΛN potential consistent with Λp scattering, and also including three-body ΛNN forces. Thes-shell hypernuclei are treated asA-body systems (A = baryon number), and _Λ ⁹ Be is analysed as a partially nine-body problem in the Λ — 2α model. The reduction ofB _Λ due to the space-exchange ΛN potential has been calculated for thes-shell hypernuclei for a range of interactions: both ΛN and ΛN + ΛNN forces. ForA = 3,4,5 the exchange energy is approximately, 0.04, 0.15 and 0.50 MeV, respectively. For _Λ ⁹ Be a much more limited study gives ≅ 1.3 MeV. These values are much larger than that for ‘soft’ ΛN +NN potentials when the correlations are weak. Preliminary results were presented at the DAE Symp. on ‘Nuclear Physics’ Vol. 32B (1989).     

Wei Hua’s four-parameter potential: Comments and computation of molecular constants αe and εeXe

The value of adjustable parameterC in the four-parameter potentialU(r) =D _e [(1 - exp[-b(r -r _e)])/(1 -C exp[-b(r -r _e)])]² has been expressed in terms of molecular parameters and its significance has been brought out. The potential so constructed, withC derived from the molecular parameters, has been applied to ten electronic states in addition to the states studied by Wei Hua. Average mean deviation for these 25 states has been found to be 3.47 as compared to 6.93, 6.95 and 9.72 obtained from Levine, Varshni and Morse potentials, respectively. Also Dunham’s method has been used to express rotation-vibration interaction constant (α_e) and anharmonicity constant (ω_ex_e) in terms ofC and other molecular constants. These relations have been employed to determine these quantities for 37 electronic states. For α_e, the average mean deviation is 7.2% compared to 19.7% for Lippincott’s potential which is known to be the best to predict these values. Average mean deviation for (ω_ex_e) turns out to be 17.4% which is almost the same as found from Lippincott’s potential function.     

Of heat capacity at homologous temperatures for metals showing h.c.p. ⇄ b.c.c. transformation

Some interesting aspects of the temperature dependence of the Planck’s functionφ and heat capacities of metals exhibiting the h.c.p. ⇄ b.c.c. transformation have been brought to light by the use of reduced temperature (T*) and Planck’s function (-φ T*). It has been shown that tangents drawn to the -φ T* vsT* plots of these metals at any chosen value ofT* intersect at a point whose coordinates are defined by the slope and intercept ofφ vs entropy plots at any homologous temperature and the selectedT* value. A generalized expression obtained for the temperature dependence ofφ has been used to demonstrate that the heat capacity of these metals may be visualized to have structural and material components.     

A Study of the Interaction Between Malachite Green and Lysozyme by Steady-State Fluorescence

The interaction of a N-methylated diaminotriphenylmethane dye, malachite green, with lysozyme was investigated by fluorescence spectroscopic techniques under physiological conditions. The binding parameters have been evaluated by fluorescence quenching methods. The results revealed that malachite green caused the fluorescence quenching of lysozyme through a static quenching procedure. The thermodynamic parameters like ΔH and ΔS were calculated to be −15.33 kJ mol⁻¹ and 19.47 J mol⁻¹ K⁻¹ according to van’t Hoff equation, respectively, which proves main interaction between malachite green and lysozyme is hydrophobic forces and hydrogen bond contact. The distance r between donor (lysozyme) and acceptor (malachite green) was obtained to be 3.82 nm according to Fӧrster’s theory. The results of synchronous fluorescence, UV/vis and three-dimensional fluorescence spectra showed that binding of malachite green with lysozyme can induce conformational changes in lysozyme. In addition, the effects of common ions on the constants of lysozyme-malachite green complex were also discussed.     

Third-order elastic moduli of single-layer graphene

In the framework of the Keating model with allowance made for the anharmonic constant of the central interaction between the nearest neighbors μ, analytical expressions have been obtained for three third-order independent elastic constants c _ijk (μ, ζ) of single-layer graphene, where ζ = (2α − β)/(4α + β) is the Kleinman internal displacement parameter and α and β are the harmonic constants of the central interaction between the nearest neighbors and the noncentral interaction between the next-nearest neighbors, respectively. The dependences of the second-order elastic constants on the pressure p have been determined. It has been shown that the moduli c ₁₁ and c ₂₂ differently respond to the pressure. Therefore, graphene is isotropic in the harmonic approximation, whereas the inclusion of anharmonicity leads to the appearance of the anisotropy.     

Super <Emphasis Type="Italic">D</Emphasis>-Differentiation for <Emphasis Type="Italic">R</Emphasis><Superscript> ∞ </Superscript>-Supermanifolds

The concept of ‘D-Differentiation’, which, in the context of smooth manifolds, generalises Lie and covariant differentiation, is extended to R ^∞-supermanifolds under the name of ‘Super D-Differentiation’. This is done by defining new (non-linear) mappings, called ‘μ-mappings’ and by relating their non-linearity to the Leibniz rule that a derivation must satisfy when it acts on a tensor product. The resulting axiomatics, which is basis-independent and coordinate-free, is then expressed in a general basis (not necessarily holonomic). Super Lie and Super covariant differentiation are, amongst others, special cases of Super D-Differentiation. In particular, the transformation rules for the connection coefficients and the commutation coefficients of non-holonomic bases are obtained. These special cases are found to be in agreement with the DeWitt Super covariant and Super Lie derivatives.      

Fluid structure and molecular interaction of acetophenone derivatives

Dielectric constants of the binary mixtures of acetophenone,p-chloroaceto-phenone,p-methylacetophenone ando-hydroxyacetophenone in dilute solutions of benzene and 1,4-dioxane were measured at 303 K and at frequency 100 kHz. The low frequency molecular dynamics of acetophenone and its derivatives have been studied by evaluating the Kirkwood correlation factorg, molar polarizationP ₂, excess correlation factor δg and excess free energy ΔG. The dipolar contribution to excess free energy of mixing arising from long-range electrostatic interaction and short-range interaction between identical molecules has been assessed separately. The presence of α- and β-multimers in the above systems was identified. The results have been used to interpret the fluid structure in such mixtures.     

Pressure-volume calculation in bcc metals using Born stability criteria

A simple analytical two-body potential φ(r) = −Ar ⁻ⁿ + B exp(−pr ^m) is considered for P-V calculations in bcc metals using Born stability criteria. It is shown that the stability of bcc metals can be expressed uniquely as a function of a parameter q (discussed in the text). The P-V calculations are done in ten bcc metals. The calculations are compared with the experimental data of shock-wave measurements and also with other potential available. It is found out that the present potential is better than the other two-body potentials in case of bcc metals. Further, the calculations done for TOEC and the first pressure derivative of SOEC are found in good agreement with the reported results.     

Conformational analysis of allyl halides from the calculation of indirect spin-spin coupling

A theoretical study on the conformation of allyl halides from the calculation of nuclear spin-spin coupling constants by adopting the finite perturbation theory (FPT), is carried out in terms of the self-consistent, semi-empirical INDO (intermediate neglect of differential overlap) approximation of molecular orbital theory. Results of the calculations performed using ‘s’ and ‘p’ valence orbitals alone (‘sp’ basis) at INDO level approximation seem to replicate the experimental trend quite satisfactorily. Despite the overall agreement of the theoretical values with the experimental ones, the uncertainties in the INDO parametrization scheme lead to overestimation of certain coupling constants. The calculations also show that the orientation of the coupled protons with respect to the substituent halogen atom is an important factor to be considered.     

Structural and electrical properties of tantalum nitride thin films fabricated by using reactive radio-frequency magnetron sputtering

TaN thin film is an attractive interlayer as well as a diffusion barrier layer in [FeN/TaN]_n multilayers for the application as potential write-head materials in high-density magnetic recording. We synthesized two series of TaN films on glass and Si substrates by using reactive radio-frequency sputtering under 5-mtorr Ar/N₂ processing pressure with varied N₂ partial pressure, and carried out systematic characterization analyses of the films. We observed clear changes of phases in the films from metallic bcc Ta to a mixture of bcc Ta(N) and hexagonal Ta₂N, then sequentially to fcc TaN and a mixture of TaN with N-rich phases when the N₂ partial pressure increased from 0.0% to 30%. The changes were associated with changes in the grain shapes as well as in the preferred crystalline orientation of the films from bcc Ta [100] to [110], then to random and finally to fcc TaN [111], correspondingly. They were also associated with a change in film resistivity from metallic to semiconductor-like behavior in the range of 77–295 K. The films showed a typical polycrystalline textured structure with small, crystallized domains and irregular grain shapes. Clear preferred (111) stacks parallel to the substrate surface with embedded amorphous regions were observed in the film. TaN film with [111]-preferred orientation and a resistivity of 6.0 mΩ cm was obtained at 25% N₂ partial pressure, which may be suitable for the interlayer in [FeN/TaN]_n multilayers. Received: 6 December 1999 / Accepted: 24 July 2000 / Published online: 9 November 2000     

Concentration dependences of the elastic constants of the two-dimensional graphene-silicene system

The concentration dependences of the elastic constants of the two-dimensional Si _x C_{1 − x} system have been investigated with the use of the Harrison bonding-orbital method and the Keating model. The central and non-central force constants and the Grüneisen parameter have been considered by means of the bonding-orbital method. All quantities under consideration have been shown to exhibit a nonlinear behavior during the transition from graphene to silicene. A nontrivial role of the short-range repulsion has been discussed. The second-order and third-order elastic constants, the pressure dependences of the second-order elastic constants, as well as the Poisson’s ratio and Young’s modulus have been investigated in the Keating model. It has been found that the elastic constants and Young’s modulus change almost linearly upon the transition from graphene to silicene, whereas the other quantities under consideration exhibit nonlinearity.     

Field theoretic calculation of energy cascade rates in non-helical magnetohydrodynamic turbulence

Energy cascade rates and Kolmogorov’s constant for non-helical steady magnetohydrodynamic turbulence have been calculated by solving the flux equations to the first order in perturbation. For zero cross helicity and space dimensiond = 3, magnetic energy cascades from large length-scales to small length-scales (forward cascade). In addition, there are energy fluxes from large-scale magnetic field to small-scale velocity field, large-scale velocity field to small-scale magnetic field, and large-scale velocity field to large-scale magnetic field. Kolmogorov’s constant for magnetohydrodynamics is approximately equal to that for fluid turbulence (≈ 1.6) for Alfvén ratio 05 ≤r _A ≤ ∞. For higher space-dimensions, the energy fluxes are qualitatively similar, and Kolmogorov’s constant varies asd ^1/3. For the normalized cross helicity σ_c →1, the cascade rates are proportional to (1 − σ_c)/(1 + σ_c , and the Kolmogorov’s constants vary significantly with σ_cc.     

Biophysical Studies on the Interactions of a Classic Mitochondrial Uncoupler with Bovine Serum Albumin by Spectroscopic,Isothermal Titration Calorimetric and Molecular Modeling Methods

The interaction between a classic uncoupler (2,4-dinitrophenol, DNP) and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy under the physiological conditions. The fluorescence quenching constants were calculated by the Stern-Volmer equation, and based upon the temperature dependence of quenching constants, it was proved that DNP caused a static quenching of the intrinsic fluorescence of BSA. Owing to the static quenching mechanism, different associative binding constants at various temperatures were determined and thus the thermodynamic parameters, namely enthalpy (ΔH = −21.12 kJ mol⁻¹) and entropy changes (ΔS = 23.51 J mol⁻¹ K⁻¹) could be calculated based on the binding constants. Moreover, the enthalpy and entropy changes are consistent with the “Enthalpy-Entropy Compensation” equation obtained from our previous work. The negative enthalpy and positive entropy indicated that the electrostatic interactions played a major role in DNP-BSA binding process. Site marker competitive displacement experiments were carried out by using fluorescence and isothermal titration calorimetry (ITC) methods. These results showed that DNP bound with high affinity to Sudlow’s site I (subdomain IIA) of BSA. The distance (r = 3.78 nm) between donor (BSA) and acceptor (DNP) was obtained according to the mechanism of fluorescence resonance energy transfer (FRET). Furthermore, the results of synchronous fluorescence and circular dichroism (CD) spectroscopic studies indicated that the microenvironment and the secondary conformation of BSA were altered. The above results were supported by theoretical molecular modeling methods.     

Equilibrium properties of the cubic phases of cobalt

Lattice constants and magnetic moments of face-centered cubic (fcc) and body-centered cubic (bcc) phases of cobalt obtained from self-consistent spin-polarized total-energy calculations by the augmented spherical wave method are compared to measurements. The calculated lattice constants fit the measured values of both phases to about 1%, but favor one of the two reported results on the newly-synthesized bcc phase. However the reported magnetic moments are substantially lower than the theoretical value for the bcc phase. We show that bcc cobalt is metastable up to 400 kbars pressure and, like fcc cobalt, is a strong ferromagnet. The magnetic moment of fcc cobalt is shown to collapse at a 5% lattice compression.