An equation of state of a carbon-fibre epoxy composite under shock loading

An anisotropic equation of state (EOS) is proposed for the accurate extrapolation of high-pressure shock Hugoniot (anisotropic and isotropic) states to other thermodynamic (anisotropic and isotropic) states for a shocked carbon-fibre epoxy composite (CFC) of any symmetry. The proposed EOS, using a generalised decomposition of a stress tensor [A.A. Lukyanov, Int. J. Plasticity 24, 140 (2008)], represents a mathematical and physical generalisation of the Mie-Grüneisen EOS for isotropic material and reduces to this equation in the limit of isotropy. Although a linear relation between the generalised anisotropic bulk shock velocity U_s ^A and particle velocity u_p was adequate in the through-thickness orientation, damage softening process produces discontinuities both in value and slope in the U_s ^A-u_p relation. Therefore, the two-wave structure (non-linear anisotropic and isotropic elastic waves) that accompanies damage softening process was proposed for describing CFC behaviour under shock loading. The linear relationship U_s ^A-u_p over the range of measurements corresponding to non-linear anisotropic elastic wave shows a value of c₀ ^A (the intercept of the U_s ^A-u_p curve) that is in the range between first and second generalised anisotropic bulk speed of sound [A.A. Lukyanov, Eur. Phys. J. B 64, 159 (2008)]. An analytical calculation showed that Hugoniot Stress Levels (HSLs) in different directions for a CFC composite subject to the two-wave structure (non-linear anisotropic elastic and isotropic elastic waves) agree with experimental measurements at low and at high shock intensities. The results are presented, discussed and future studies are outlined.     

Compaction of cereal grain

Abstract

We report on simple shaking experiments to measure the compaction of a column of Firth oat grain. Such grains are elongated anisotropic particles with a bimodal polydispersity. In these experiments, the particle configurations start from an initially disordered, low-packing-fraction state and under vertical shaking evolve to a dense state with evidence of nematic-like structure at the surface of the confining tube. This is accompanied by an increase in the packing fraction of the grain.     

Phosphorescence from the two triplet states of p-benzoquinone and toluquinone vapour

Molecular formulae for the isotropic and anisotropic scattering are derived by considering the internal field acting upon a molecule within a dense medium and its fluctuation caused by density fluctuations. The anisotropic scattering formula of classical theory is retained but modified by the factors of the internal field. The new formula for the isotropic scattering depends sensitively on the principal values of the optical polarizability tensor and on the parameters describing the anisotropic internal field. Assuming the internal field to be given by the semimacroscopic approach of the Onsager-Scholte model with an ellipsoidal cavity, comparison of the calculated isotropic Rayleigh factor with the experimental value allows a prediction of the degree of the cavity anisotropy for different liquid densities.     

Perturbation theory for equilibrium properties of molecular fluids

Perturbation theory for the angular pair correlation function g(r₁₂ ω ₁ ω ₂), using a fluid with isotropic intermolecular forces as the reference system, is applied to the calculation of a variety of macroscopic properties. Comparisons with experiment are made for methane, oxygen and nitrogen (and carbon monoxide for infra-red and Raman band moments) in the dense fluid and liquid states. Theoretical expressions are given and calculations made for thermodynamic properties (isothermal compressibility, pressure, configurational energy, entropy and specific heat) both along and away from the vapour-liquid co-existence curve, for infra-red and Raman band moments, and for neutron scattering cross sections. Excellent agreement with experiment is obtained for all properties, except for the infra-red and Raman band moments; this latter comparison is inconclusive because of large experimental uncertainties. The anisotropic intermolecular forces are found to have very little effect on the liquid isothermal compressibility, in agreement with the first-order theory. Molecular anisotropy has a relatively small effect on the configurational energy and on the Helmholtz free energy, but the effect is large for pressure and specific heat. The pressure is more sensitive to short-range anisotropic forces than the other properties, whereas the specific heat is particularly sensitive to the long-range anisotropic forces. Mean squared torques (derived from infra-red and Raman band moments) are very sensitive to the strengths of the anisotropic forces, and are more sensitive to higher terms in the multipole series than are the other properties. The structure factors for oxygen and nitrogen are found to be little affected by the anisotropic forces.     

Solvent dependent study of carbonyl vibrations of 3‐phenoxybenzaldehyde and 4‐ethoxybenzaldehyde by Raman spectroscopy and ab initio calculations

A Raman spectroscopy investigation of the carbonyl stretching vibrations of 3‐phenoxybenzaldehye (3Phbz) and 4‐ethoxybenzaldeheyde (4Etob) was carried out in binary mixtures with different polar and nonpolar solvents. The purpose of this study was twofold: firstly, to describe the interaction of the carbonyl groups of two solute molecules in terms of a splitting in the isotropic and anisotropic components and secondly, to analyze their spectroscopic signatures in a binary mixture. Changes in wavenumber position, variation in the anisotropic shift and full width half maximum were investigated for binary mixtures with different mole fractions of the reference systems. In binary mixtures, the observed increase in wavenumber with solvent concentration does not show linearity, indicating the significant role of molecular interactions on the occurrence of breaking of the self‐association of the solute. In all the solvents, a gradual decrease in the anisotropic shift reflects the progressive separation of the coupled oscillators with dilution. Γ_i(η_c), 3Phbz—solvent mixtures, exhibit a gradual decrease with decrease in the concentration of the solute which is an evidence on the influence of micro viscosity on linewidth. For 4Etob, the carbonyl stretching vibration shows two well‐resolved components in the Raman spectra, attributed to the presence of two distinct carbonyl groups: hydrogen‐bonded and free carbonyl groups. The intensity ratio of the carbonyl stretching vibration of these two types of carbonyl groups is studied to understand the dynamics of solute/solvent molecules owing to hydrogen bond interactions. Ab initio calculations were employed for predicting relevant molecular structures in the binary mixtures arising from intermolecular interactions, and are related to the experimental results. Copyright © 2009 John Wiley & Sons, Ltd.     

Nonlinear refractive index and light scattering due to fluctuations of molecular multipole electric fields

Statistical fluctuations of multipolar electric molecular fields, leading to variations of isotropic and anisotropic light scattering, are moreover shown to give rise to a temperature-dependent nonlinear refractive index of dense fluids. Some selected models of dipolar and quadrupolar molecules, linearly and nonlinearly polarizable and correlated in binary as well as ternary assemblages, are discussed. The formulae derived for the isotropic and anisotropic scattering constants are applicable to one-and many-component fluids, consisting of atoms and polar molecules, and provide the basis for a deeper interpretation of the latest experimental results.     

Thermodynamic fluctuations in two-dimensional degenerate antiferromagnetic structures

A model of a two-dimensional antiferromagnet with an arbitrary anisotropic interaction that allows for degeneracy of the ground state is proposed. The lifting of degeneracy by thermodynamic fluctuations and the accompanying effects are studied by a method of self-consistent calculations of Gaussian angular fluctuations that is asymptotically exact at low temperatures. Fluctuations are shown to lead to collinear ordering of the orientations of magnetic sublattices, an effect that initiates long-range orientational order in systems with anisotropic interaction but retains only short-range order in systems with isotropic short-range interaction. The temperature patterns of the orientational correlators are given for the particular cases of dipole and isotropic short-range interaction models. The nature of the Ising-like behavior of the system is discussed for the case of a strong anisotropy of the correlators, which corresponds to quasi-one-dimensional behavior. Zh. éksp. Teor. Fiz. 111, 669–680 (February 1997)     

Qualitative theory of amplitude and phase fluctuations in a medium with anisotropic turbulent irregularities

Abstract

Wave propagation in an anisotropic turbulent medium is studied assuming that the anisotropy coefficient η is constant for all scales of inhomogeneities. A qualitative method of studying the amplitude and phase fluctuations is developed. Formulae have been obtained for the phase structure functions and scintillation index for the medium with spectrum power index 3<μ<5 and anisotropy coefficient η≥1. Two particular cases have been studied in detail—propagation along and across the axis of the stretching of irregularities. During propagation along a short axis of inhomogeneities the fluctuations are decreasing and the phase structure function and scintillation index turn out to be η^μ?2 times smaller as compared with isotropic case. At the same time, during propagation along the long axis of inhomogeneities the phase structure function in vertical plane and the scintillation index are η times greater than in the isotropic medium.     

Analysis of anisotropic spin-label motion in saturation-transfer ESR spectra of spin-labeled cowpea chlorotic mottle virus

A saturation-transfer ESR study is carried out on maleimide spin-labeled cowpea chlorotic mottle virus dissolved in various glycerol-water systems. The saturation-transfer ESR spectra were analyzed by comparing them with reference spectra of isotropically reorienting spin labels. The results are interpreted in terms of the overall motion of the virus particle, described by an isotropic rotational correlation time τ_R, and a local anisotropic spin-label motion with rotational correlation times τ_| and τ_⊥.     

Molecular dynamics studies of slow dynamics in random media: Type A-B and reentrant transitions

Molecular dynamics simulations of mobile particles confined in disordered immobile particles are carried out. Slow dynamics in random media are characterized by two types of dynamics: Type B dynamics for large mobile particle density and Type A dynamics for small mobile particle density. The crossover from Type A to B dynamics is studied by the mean square displacement and the density correlation function. Our results are qualitatively consistent with the results of recent numerical and theoretical studies on relevant spatially heterogeneous systems. We also investigate the effect of random matrix generation on the dynamics of mobile particles in order to examine the reentrant transition predicted by the recent mode-coupling theory. Our simulations demonstrate that the diffusion of the mobile particles largely depends on the protocol of the random matrix generation and that the reentrant transition is observed for a particular protocol.     

Nematic-wetted colloids in the isotropic phase: pairwise interaction, biaxiality, and defects

We calculate the interaction between two spherical colloidal particles embedded in the isotropic phase of a nematogenic liquid. The surface of the particles induces wetting nematic coronas that mediate an elastic interaction. In the weak wetting regime, we obtain exact results for the interaction energy and the texture, showing that defects and biaxiality arise, although they are not topologically required. We evidence rich behaviors, including the possibility of reversible colloidal aggregation and dispersion. Complex anisotropic self-assembled phases might be formed in dense suspensions.     

Lateral transport in quasiperiodically ordered layered media with isotropic randomness

Abstract

We investigate the lateral wave transport in quasiperiodically ordered layer media with isotropic randomness. As an example, we consider the case of the Fibonacci sequence and study the ergodic properties in such systems. From the results of the channel occupation number of nine generations, we find that the wave transport in such systems falls between the transport of anisotropic hopping systems and that of randomly layered media and can be associated with a fractal dimension that can be tuned according to the strength of the layer coupling. The origin of this fractal dimensionality is attributed to the interplay between the quasiperiodic ordering in the layer direction and the presence of isotropic randomness in the system.     

Evaluation of anisotropic small-angle neutron scattering data from metastable β-Ti alloy

ABSTRACT

Small-angle neutron scattering (SANS) data from single-crystal metastable β-Ti alloys exhibit an anisotropic character with interparticle interference maxima due to ordering of the dense system of ω particles. For an evaluation of such data, the program NOC (previously used for evaluation of data from dense ordered γ′ precipitate system in single-crystal nickel-based superalloys) was well suited. Nevertheless, an improvement of this evaluation program was necessary in its model-forming part. A further change of the evaluation program concerned the mode in which the size distribution was calculated. This upgrade is presented. The improved NOC program was employed for the evaluation of SANS data of annealed metastable single-crystal β-Ti alloy containing ω particles. 3D fit in reciprocal space was successfully used. A model of ellipsoids did not lead to a better fit than a model of particles with the spherical shape. The microstructural parameters of ω particles were determined.     

Intracavity Electronic Absorption Spectra of MoO and WO Molecules in the Visible Region

Absorption electronic spectra of MoO and WO molecules have been investigated by a intracavity laser technique in the region 550–800 run. New features have been discovered.

As for MoO molecule the rotational analysis of the four bands have been carried out for the first time. Two of these bands were referred to 0–0 transitions arisen from the new (probable triplet) low-lying electronic state, two other bands were referred to transitions arisen from excited components of X⁵II ground state.

As for WO molecule the rotational analysis of 0–0 and 1–0 bands represented A-X and B-X systems have been carried out for the first time. The new band has been discovered which has been referred to new electronic transition.

Molecular constants of new states of both molecules studied have been evaluated.     

DNA molecule as an elastic Heisenberg chain

A DNA molecule is simulated by an anisotropic elastic fiber which defines the configuration of the molecule central line and is supplemented with a chain of quantum two-level systems imitating hydrogen bonds between two polynucleotide chains in the DNA double helix. The system Hamiltonian consists of Kirchhoff’s classical elastic energy and the energy of a quantum anisotropic chain of “spins” 1/2. The two-level systems and macroscopic vector variables which determine the conformation of the central line are coupled by a classical vector field q, which is introduced to take into account the existence of two polynucleotide strands. Averaging over fast (microscopic) variables yields an effective potential U(q). In the approximation of weak coupling between the systems, the spectrum of elementary excitations and effective potential U(q) have been calculated in explicit form. The relation between elementary excitations in the “magnetic” subsystem and so-called breathing modes [C. Mandel, N. R. Kallenbach, and S. W. Englander, J. Mol. Biol. 135, 391 (1980); G. Manning, Biopolymers 22, 689 (1983)] corresponding to low-frequency excitations in DNA molecules is discussed. Zh. éksp. Teor. Fiz. 111, 1833–1844 (May 1997)     

Librational effects on carbon-13 N.M.R. spin-lattice relaxation times of tricyclic condensed molecules

A general method is described for calculating the effect of internal librational motion on the correlation times in tricyclic molecules having a folded structure about the central hetero-ring. The relaxation equations have been derived for isotropic as well as anisotropic models of overall molecular re-orientation. In the case of the isotropic model of motion, the parameter which determines the effective relaxation times is the librational amplitude; for the anisotropic model a somewhat more complicated correlation function is found. The present treatment provides a tool for interpreting in a quantitative way the spin-lattice relaxation times of hydrogen bearing carbons in pharmacologically important tricyclic systems where internal conformational flexibility could be exclusively monitored by using such a non conventional N.M.R. spectroscopic approach. Application of the method and its limitations are discussed briefly.     

Role of different polarization mechanisms in the self-organization of the director of a thin layer of nematic liquid crystal

A theoretical analysis of the processes occurring in a symmetric metal-liquid-crystal-metal structure is carried out to obtain the dependence of the anisotropic component of the surface free energy on the angle of deviation of the director from the direction of easy orientation. The differences between the angular dependence of the surface energy obtained in this paper from the form described by the Rapini potential are discussed. The coordinate dependence of the ionic and dipolar polarization are calculated, as is the order parameter characterizing the ordering of the dipole moments of the liquid-crystal molecules. The interrelationships of the the boundary polarization with the equilibrium orientation of the director near the surface bounding the liquid crystal and with the value of the internal electric field in the volume of the mesophase are discussed. Zh. Tekh. Fiz. 67, 23–28 (May 1997)     

A CNDO CI Study of the Electronic Structure of Nitrome Thane

Abstract

Molecular orbital calculations in the well-known CNDO/2 approximation [1–5] have been carried out for a number of polyatomic molecules, with generally good agreement for bond lengths, bond angles, bending force constants and dipole moments, but the original parametrization has not given satisfactory energy results. J. Del Bene and H. H. Jaffé [6–7] suggested therefore on the basis of spectroscopic calculations a number of changes in the parametrization     

The influence of interparticle interaction on magnetization curves of nano-and microcrystal ensembles

Reconstruction of magnetization curves for real close-packed systems of highly anisotropic ferrimagnetic BaFe₁₂O₁₉ single-domain nano-and microcrystals is carried out on the basis of the results of a study of interparticle magnetic interaction. These curves allowed us to distinguish general laws of magnetization of ensembles of randomly oriented single-domain particles predicted by the Stoner-Wohlfarth theory and to discuss special features found for microcrystals.     

Second- and third-harmonic generations for a nondilute suspension of coated particles with radial dielectric anisotropy

We derive expressions for the effective nonlinear susceptibility tensors for both the second harmonic generation (SHG) and induced third harmonic generation (THG) of nonlinear composite materials, in which nondilute coated particles with radial dielectric anisotropy are randomly embedded in the linear host. Two types of coated particles are considered. The first is that the core possesses a second order nonlinear susceptibility and the shell is linear and radially anisotropic, while the second is that the core is linear with radial anisotropy and the shell has a second order nonlinear susceptibility. We observe greatly enhanced SHG and THG susceptibilities at several surface plasmon resonant frequencies. For the second model, due to the coating material being metallic, there exists two fundamental resonant frequencies ω_c1 and ω_c2, whose difference ω_c2-ω_c1 is strongly dependent on the interfacial parameter and the radial dielectric anisotropy. Furthermore, in both systems, the adjustment of the dielectric anisotropy results in larger enhancement of both SHG and induced THG susceptibilities at surface plasmon resonant frequencies than the corresponding isotropic systems. Therefore, both the core-shell structure and the dielectric anisotropy play important roles in determining the nonlinear enhancement and the surface resonant frequencies.