Nonlinear refraction and photoinduced birefringence in chlorophosphonazo I doped polymer thin films

The nonlinear refraction and photoinduced birefringence of chlorophosphonazo I (CPA I ) doped PVA thin films were investigated. The single-beam Z-scan measurement showed that CPA I doped PVA thin film possessed a large value of nonlinear refractive index (n₂=1.82×10⁻¹² cm²/W) under a pulse 532 nm excitation, and the mechanism accounting for the process of nonlinear refraction was discussed in term of resonant electronic effect. Moreover, fast and stable molecular reorientation was observed when investigating the photoinduced birefringence of CPA I doped PVA thin film with a CW 532 nm laser as pump light and a CW 650 nm laser as probe light.     

Depletion interactions between colloidal particles in polymer solutions: density functional approach

A density functional theory for colloid–polymer mixtures based on the weighted-density approximation has been developed to investigate the depletion effects acting between two colloids immersed in a bath of polymers and the depletion effects for a colloid near a planar hard wall. The theoretical results for the polymer-induced depletion interactions and the local polymer density distributions are in good agreement with the computer simulations. The calculation shows that the depletion interaction for a colloid near a planar hard wall is much stronger than that between two colloids in a polymer solution because of the strong confinement effect. The behaviour of the depletion interactions has been analysed as a function of the polymer density, the polymer chain length, and the colloid/polymer size ratio. Strong depletion effects appear in short-chain systems and with large colloid/polymer size ratios.     

Simultaneous birefringence,small‐ and wide‐angle X‐ray scattering to detect precursors and characterize morphology development during flow‐induced crystallization of polymers

An experimental configuration that combines the powerful capabilities of a short‐term shearing apparatus with simultaneous optical and X‐ray scattering techniques is demonstrated, connecting the earliest events that occur during shear‐induced crystallization of a polymer melt with the subsequent kinetics and morphology development. Oriented precursors are at the heart of the great effects that flow can produce on polymer crystallization (strongly enhanced kinetics and formation of highly oriented crystallites), and their creation is highly dependent on material properties and the level of stress applied. The sensitivity of rheo‐optics enables the detection of these dilute shear‐induced precursors as they form during flow, before X‐ray techniques are able to reveal them. Then, as crystallization occurs from these precursors, X‐ray scattering allows detailed quantification of the characteristics and kinetics of growth of the crystallites nucleated by the flow‐induced precursors. This simultaneous combination of techniques allows unambiguous correlation between the early events that occur during shear and the evolution of crystallization after flow has stopped, eliminating uncertainties that result from the extreme sensitivity of flow‐induced crystallization to small changes in the imposed stress and the material. Experimental data on a bimodal blend of isotactic polypropylenes are presented.     

Correlation between randomly varying birefringence and random dispersion map in a dispersion-managed soliton system

The correlation between perturbations caused by randomly varying birefringence and a random dispersion map is considered in a dispersion-managed soliton system, and their effects on soliton propagation and interaction are investigated numerically. These perturbations lead to the disintegration of a soliton, and enhance the interaction between solitons. The correlation plays an important role, and reinforces these effects. Furthermore, there is a stochastic resonance between two perturbations in the system; here the effect is the largest, and the corresponding distance until disintegration is the shortest. Finally, nonlinear gain and a filter are introduced to effectively suppress these effects.     

Fluorescence and solvatochromism of a merocyanine dye with a high quadratic polarizability in solutions and polymer films

The influence of medium polarity on the spectroscopic and photophysical properties of 2-[(2E,4E)-6-(1,3,3-trimethyl-2,3-dihydro-1H-2-indolyliden)-2,4-hexadienyliden]malononitrile (THDM) in solutions and polymer matrices is studied at room temperature and 77 K under conditions of steady-state and pulsed laser excitation. A large bathochromic shift of the absorption spectra observed upon an increase in the solvent polarity is caused by a strong increase of the dipole moment in the ground state () on going to an excited Franck-Condon state (). Based on the solvatochromic data, the quadratic polarizability was calculated to be , which is close to the experimentally determined value . A strong narrowing of the fluorescence spectra in comparison with the absorption spectra at room temperature is observed upon an increase in the solvent polarity caused by a decrease in the bond length alternation parameter and by weakening of vibronic interactions in the singlet excited state. The mirror symmetry of the absorption and fluorescence spectra of THDM in ethanol at 77 K is explained by the increase of the electrostatic interactions between the solvent and merocyanine molecules. The dynamic fluorosolvatochromism of THDM in the picosecond range is caused by molecules reorientations of the polar environment occurring during a time period consistent with the dielectric relaxation time of these molecules.     

Relationship between elastic anisotropy and texture in metal-matrix composites

The relationship between elastic anisotropy and texture in two-phase metal-matrix composites has been developed under certain conditions. Using measurements of the six independent ultrasonic velocities V_ij in samples of the aluminium alloys 8091 and 7064 containing up to 20% SiC particles and the formulation given by Bunge, the fourt-order expansion coefficients of the orientation distribution function are determined. The Young's moduli in different directions are also obtained from ultrasonic velocity measurements. Linear correlations between anisotropy described by Young's moduli and texture determined by orientation distribution function expansion coefficients are obtained, and confirm developed relationships for two-phase metal-matrix composites. This result shows that ultrasonic measurements provide a technique for the characterization of texture and elastic anisotropy in these materials.     

似稳场中的涡旋电场和电流源的关系

推导了涡旋电场与它的电流源之间的关系，利用此关系和磁场矢势计算了球形线圈内外的磁感应强度，并证明了两个闭合回路之间的互感系数相符。     

Stochastic persistence and stationary distribution in a Holling-Tanner type prey-predator model

In this paper, we study a stochastic predator-prey model with Beddington-DeAngelis type functional response and logistic growth for predators. The deterministic model is already well-studied and we recall some important results here. We construct the stochastic model from the deterministic model by introducing multiplicative noise terms into the growth equations of prey and predator populations. For the stochastic model, we show that the system admits unique positive global solution starting from the positive initial value. Then we prove that the system is strongly persistent in mean when the intensity of environmental forcing is less than some threshold magnitudes. Finally, we show that the system has a stationary distribution under certain parametric restrictions. Numerical simulations are carried out to substantiate the analytical results.     

The difference in noise property between the Autler-Townes splitting medium and the electromagnetically induced transparent medium

The quantum noise of squeezed probe light passing through an atomic system with different electromagnetically induced transparency and Autler-Townes splitting effects is investigated theoretically.It is found that the optimal squeezing preservation of the outgoing probe beam occurs in the strong-coupling-field regime rather than in the weakcoupling-field regime.In the weak-coupling-field regime,which was recently recognized as the electromagnetically induced transparency regime(Abi-Salloum T Y 2010 Phys.Rev.A 81 053836),the output amplitude noise is affected mainly by the atomic noise originating from the random decay process of atoms.While in the strong-coupling-field regime,defined as the Autler-Townes splitting regime,the output amplitude noise is affected mainly by the phase-toamplitude conversion noise.This is useful in improving the quality of the experiment for efficient quantum memory,and hence has an application in quantum information processing.     

The difference in noise property between the Autlerben Townes splitting medium and the electromagnetically induced transparent medium

The quantum noise of squeezed probe light passing through an atomic system with different electromagnetically induced transparency and Autler-Townes splitting effects is investigated theoretically. It is found that the optimal squeezing preservation of the outgoing probe beam occurs in the strong-coupling-field regime rather than in the weak-coupling-field regime. In the weak-coupling-field regime, which was recently recognized as the electromagnetically induced transparency regime (Abi-Salloum T Y 2010 Phys. Rev. A bf81 053836), the output amplitude noise is affected mainly by the atomic noise originating from the random decay process of atoms. While in the strong-coupling-field regime, defined as the Autler-Townes splitting regime, the output amplitude noise is affected mainly by the phase-to-amplitude conversion noise. This is useful in improving the quality of the experiment for efficient quantum memory, and hence has an application in quantum information processing.     

Relationship between the diffusion rate constant and rate constant of triplet-triplet annihilation for porphyrins in liquid solutions

Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70. F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 63, No. 4, pp. 613–621, July–August, 1996.