Co-Existent Biphasic Region of Nematic and Columnar Smectic Phases in Binary Mixture of Berberine and Alizarin Dye

We report the results of our studies on the optical and thermal properties of binary mixture of two compounds viz., berberine and alizarin dye. The mixture shows a very interesting co-existent biphasic region of nematic N + I and smectic C + I phases, sequentially when the specimen is cooled from its isotropic phase respectively at different concentrations of Alizarin dye in berberine molecule. The temperature variations of optical anisotropy, optical textures, and electrical conductivity have also been discussed. Aggregated molecular size has been confirmed by X-ray studies.     

Enhanced x-ray emissions from low-density high-Z mixture plasmas generated with intense nanosecond laser

Enhancement of x-ray emissions from laser-produced plasmas is imperative for various applications. Low-density Au–Gd mixture was proposed to enhance the x-ray emissions. X-ray emissions were simulated for the laser-irradiated gold and Au–Gd mixtures with different initial densities. It was shown that 1.34 times conversion efficiency has been achieved for the 0.05 g/cm³$0.05\text{g}/{\text{cm}}^3$ Au–Gd (6/4)$(6/4)$ mixture comparing with the 10 g/cm³$10\text{g}/{\text{cm}}^3$ gold. The enhancement is attributed to higher Rosseland mean opacities of the mixture and reduction of the ion kinetic energy caused by the lower initial density.     

Stochastic sensitivity analysis of periodic attractors in non-autonomous nonlinear dynamical systems based on stroboscopic map

To apply stochastic sensitivity function method, which can estimate the probabilistic distribution of stochastic attractors, to non-autonomous dynamical systems, a 1/N$1/N$-period stroboscopic map for a periodic motion is constructed in order to discretize the continuous cycle into a discrete one. In this way, the sensitivity analysis of a cycle for discrete map can be utilized and a numerical algorithm for the stochastic sensitivity analysis of periodic solutions of non-autonomous nonlinear dynamical systems under stochastic disturbances is devised. An external excited Duffing oscillator and a parametric excited laser system are studied as examples to show the validity of the proposed method.     

Stochastic sensitivity analysis of the attractors for the randomly forced Ricker model with delay

Stochastically forced regular attractors (equilibria, cycles, closed invariant curves) of the discrete-time nonlinear systems are studied. For the analysis of noisy attractors, a unified approach based on the stochastic sensitivity function technique is suggested and discussed. Potentialities of the elaborated theory are demonstrated in the parametric analysis of the stochastic Ricker model with delay nearby Neimark–Sacker bifurcation.     

Deconvolution of Raman spectra for the quantification of ternary high‐pressure phase equilibria composed of carbon dioxide,water and organic solvent

The paper reports on a routine to extract the composition of multi‐component mixtures from their Raman spectra at elevated pressures. The strategy is based on fitting weighted Raman spectra of the pure compounds to the measured Raman spectrum of the mixture, also considering the effects of intermolecular interactions onto the Raman spectra by applying Gaussian and Voigt profile deconvolution of the Raman peaks. Thereby, an improved accuracy compared to previous evaluation strategies could be obtained. The more accurate data of the ternary mixtures of carbon dioxide, water and organic solvents are presented. Copyright © 2014 John Wiley & Sons, Ltd.     

Enhancement of the molecular nitrogen dissociation and ionization levels by argon mixture in flue nitrogen plasma

In this work, the nitrogen molecular dissociation and ionization levels in Ar/N₂ flue plasma are evaluated as functions of plasma parameters such as Ar mixture quantity and N₂ flux in order to obtain the best condition for various applications such as thin film deposition and material surface modification. This plasma is operated at 10 kV and the nitrogen dissociation rate is determined by analyzing the optical emission of the nitrogen band. For different operating conditions, the dissociation rate [N] of N₂ molecules was enhanced, as the mixture quantity of Ar increased from 0.06 m³/h to 0.9 m³/h and the max of enhancement factor is 4.3. This factor becomes bigger when the N₂ flux becomes bigger. Moreover, the molecular nitrogen ionization density is calculated from the current intensity of the plasma. The ionization density was also enhanced, as the mixture quantity of Ar increased from 0.1 m³/h to 1.5 m³/h, under three different voltages. The max of enhancement factor of 1.96 is much smaller than the factor of the dissociation rate. These results are discussed in terms of the kinetics of the electrons, nitrogen ions, atoms and molecules.     

Prediction of the effective elastic moduli of materials with irregularly-shaped pores based on the pore projected areas

Statistical modeling is used to correlate geometric parameters of pores with their contributions to the overall Young’s moduli of linearly elastic solids. The statistical model is based on individual pore contribution parameters evaluated by finite element simulations for a small pore subset selected using the design of experiments approach, so there is no need to solve the elasticity problem for all pores in the material. A polynomial relating pore geometric parameters to the contribution parameters is then fitted to the results of the simulations. We found a good correlation between normalized projected areas of the pores on three coordinate planes and their contributions to the corresponding effective Young’s moduli. The model is applied and validated for two large sets of pore geometries obtained by X-ray microcomputed tomography of a carbon/carbon and a 3D woven carbon/epoxy composite specimens.     

A numerical study on the deformation and fracture modes of steel projectiles during Taylor bar impact tests

A heterogeneous material model based on macro-mechanical observations is proposed for simulation of fracture in steel projectiles during impact. A previous experimental study on the deformation and fracture of steel projectiles during Taylor bar impact tests resulted in a variety of failure modes. The accompanying material investigation showed that the materials used in the impact tests were heterogeneous on scales ranging from microstructure as investigated with SEM to variation in fracture strains from tensile tests. A normal distribution is employed to achieve a heterogeneous numerical model with respect to the fracture properties. The proposed material model is calibrated based on the tensile tests, and then used to independently simulate the Taylor bar impact tests. A preliminary investigation showed that the simulations are sensitive to assumptions regarding the anvil behaviour and friction properties. A flexible anvil and a yield-limited friction law are shown to be necessary to correctly reproduce the experimental behaviour. The proposed model is then shown to be capable of correctly reproducing all fracture modes but one, and also predict critical impact velocities for projectile fracture with reasonable accuracy. Fragmentation at velocities above the critical velocity is not well reproduced due to excessive element erosion. Measures to make the element erosion process more physical are proposed and discussed with their respective drawbacks. The use of a simple fracture criterion in combination with an element erosion technique accentuates the effect of distributing the fracture parameter.     

Study on the operational safety of high-speed trains exposed to stochastic winds

The characteristic wind curve （CWC） was com- monly used in the previous work to evaluate the operational safety of the high-speed trains exposed to crosswinds. How- ever, the CWC only provide the dividing line between safety state and failure state of high-speed trains, which can not evaluate the risk of derailment of high-speed trains when ex- posed to natural winds. In the present paper, a more realistic approach taking into account the stochastic characteristics of natural winds is proposed, which can give a reasonable and effective assessment of the operational safety of high-speed trains under stochastic winds. In this approach, the longitudi- nal and lateral components of stochastic winds are simulated based on the Cooper theory and harmonic superposition. An algorithm is set up for calculating the unsteady aerody- namic forces （moments） of the high-speed trains exposed to stochastic winds. A multi-body dynamic model of the rail vehicle is established to compute the vehicle system dynamic response subjected to the unsteady aerodynamic forces （mo- ments） input. Then the statistical method is used to get the mean characteristic wind curve （MCWC） and spread range of the high-speed trains exposed to stochastic winds. It is found that the CWC provided by the previous analyticalmethod produces over-conservative limits. The methodol- ogy proposed in the present paper can provide more signif- icant reference for the safety operation of high-speed trains exposed to stochastic winds.     

Constructing transient response probability density of non-linear system through complex fractional moments

The probability density function for transient response of non-linear stochastic system is investigated through the stochastic averaging and Mellin transform. The stochastic averaging based on the generalized harmonic functions is adopted to reduce the system dimension and derive the one-dimensional Itô stochastic differential equation with respect to amplitude response. To solve the Fokker–Plank–Kolmogorov equation governing the amplitude response probability density, the Mellin transform is first implemented to obtain the differential relation of complex fractional moments. Combining the expansion form of transient probability density with respect to complex fractional moments and the differential relations at different transform parameters yields a set of closed-form first-order ordinary differential equations. The complex fractional moments which are determined by the solution of the above equations can be used to directly construct the probability density function of system response. Numerical results for a van der Pol oscillator subject to stochastically external and parametric excitations are given to illustrate the application, the convergence and the precision of the proposed procedure.