Nonlinear dynamics and solitons in spin glasses

Institute of Theoretical Physics, Ukrainian SSR Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 83, No. 2, pp. 163–174, May, 1990     

Nonequilibrium thermodynamics of a gas of solitons of kink type in quasione-dimensional systems

Institute of Metal Physics, Ukrainian SSR Academy of Sciences, Kiev. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 74, No. 1, pp. 46–60, January, 1988.     

Three-dimensional solitons in ferrites and their stability

The study is made of soliton solution of nonlinear equations describing dynamics of some magnets as well as the field theory models. Three-dimensional solitons are analysed to which non-uniform magnetization precession corresponds.Necessary and sufficient conditions for soliton stability according to Lyapunov are obtained. The soliton without nodes is proved to be stable over a wide range of the precission frequencies and unstable beyond this range. Solitons with nodes are unstable at all frequencies.     

Cetyl‐alcohol‐reinforced hollow fiber solid/liquid‐phase microextraction and HPLC–DAD analysis of ezetimibe and simvastatin in human plasma and urine

A new cetyl‐alcohol‐reinforced hollow fiber solid/liquid‐phase microextraction (CA–HF–SLPME) followed by high‐performance liquid chromatography–diode array detection (HPLC–DAD) method was developed for simultaneous determination of ezetimibe and simvastatin in human plasma and urine samples. To prepare the CA–HF–SLPME device, the cetyl‐alcohol was immobilized into the pores of a 2.5 cm hollow fiber micro‐tube and the lumen of the micro‐tube was filled with 1‐octanol with the two ends sealed. Afterwards, the prepared device was introduced into 10 mL of the sample solution containing the analytes with agitation. Under optimized conditions, calibration curves plotted in spiked plasma and urine samples were linear in the ranges of 0.363–25/0.49–25 μg L^?1 for ezetimibe/simvastatin and 0.193–25/0.312–25 μg L^?1 for ezetimibe/simvastatin in plasma and urine samples, respectively. The limit of detection was 0.109/0.174 μg L^?1 for ezetimibe/simvastatin in plasma and 0.058/0.093 μg L^?1 for ezetimibe/simvastatin in urine. As a potential application, the proposed method was applied to determine the concentration of selected analytes in patient plasma and urine samples after medication and satisfactory results were achieved. In comparison with reference methods, the CA–HF–SLPME–HPLC–DAD method demonstrates considerable potential in the biopharmaceutical analysis of selected drugs.     

Chitosan loaded with silver nanoparticles,CS‐AgNPs,using thymus syriacus,wild mint,and rosemary essential oil extracts as reducing and capping agents

The present study describes the green method for the preparation of chitosan loaded with silver nanoparticles (CS‐AgNPs) in the presence of 3 different extracted essential oils. The essential oils play dual roles as reductant and capping agents. The reducing power and DPPH (2,2‐diphenyl‐1‐picrylhydrazyl) assay for the 3 essential oils—Thymus syriacus (T), wild mint (M), and rosemary (R)—have been reported. The preparation of CS‐AgNPs was performed by 2 steps. The 3 previously extracted essential oils have been used as reducing and capping agent in the first step, while in the second step, silver nanoparticles were integrated in chitosan. The integration of AgNPs in the structure of chitosan was confirmed by ultraviolet‐visible, Fourier transform infrared spectroscopy, scanning electron microscopy techniques, and energy dispersive X‐ray. Surface plasmon resonance confirmed the formation of CS‐AgNPs with maximum absorbance at λ_max between 405 ‐ 410 and 410 ‐ 430 nm for colloidal and films of CS‐AgNPs, respectively. The intensity of bands at 3408 cm^?1 in the fourier transform infrared spectroscopy measurements was decreased substantially and shifted slightly to lower frequency (?υ = 43 cm^?1). Scanning electron microscopy shows a spherical morphology of AgNPs with size of 62 nm for both colloidal and film samples, and energy dispersive X‐ray analysis shows peaks confirming AgNPs formation.     

Enantioselective determination of modafinil in pharmaceutical formulations by capillary electrophoresis, and computational calculation of their inclusion complexes

A fast capillary electrophoretic method is described for the separation and determination of the enantiomers of the novel wake-promoting agent, modafinil. Several parameters affecting the separation were studied, including the type and concentration of chiral selector, buffer pH, buffer concentration, voltage and temperature. Good chiral separation of the racemic mixture was achieved in less than 5 min with resolution factor Rs?=?2.51, using a bare fused-silica capillary and a background electrolyte (BGE) of 25 mM H₃PO₄?1 M tris solution; pH 8.0; containing 30 mg mL^?1 of sulfated-β-cyclodextrin (S-β-CD). The separation was carried out in normal polarity mode at 25 ^?C, 18 kV and using hydrostatic injection. Acceptable validation criteria for selectivity, linearity, precision, and accuracy were included. The developed method was successfully applied to the assay of enantiomers of modafinil in pharmaceutical formulations. The computational calculations for the enantiomeric inclusion complexes rationalized the reasons for the different migration times between the modafinil enantiomers.     

Magnetooptical properties of a ferromagnetic superlattice

Transmission and reflection of a normally incident wave from a magnetic superlattice consisting of 2N ferromagnetic layers with alternating orientation of the magnetization vector are considered. The characteristic matrix of a superlattice relating wave amplitudes at the entrance to the system and at the exit from it is calculated in the closed form and Jones matrices determining all the basic magnetooptical characteristics of the structure (transmission and reflection coefficients, the degree of polarization of transmitted and reflected waves, and so on) are constructed. A significant dependence of these characteristics on the number of layers is demonstrated.     

Dynamics of domain walls in ultrathin magnetic films

The domain walls in ultrathin ferromagnetic films with uniaxial magnetic anisotropy are investigated theoretically. It is shown that taking account of the magnetodipole and magnetoelastic interactions leads to the appearance of an effective anisotropy with respect to the direction of the normal to the plane of the wall. The existence of a new type of domain walls—“corner” walls, at which the magnetization vector is rotated in the plane making a certain angle, which depends on the film parameters, with the plane of the domain wall and the static and dynamic properties of these walls are investigated. The dependence of the limiting velocity of the domain walls on the film thickness is found. Zh. éksp. Teor. Fiz. 112, 1476–1489 (October 1997)     

Propagation of light in a structure with a regular magnetic inhomogeneity

The reflection and transmission of a light wave normally incident on a layer with a regular magnetic inhomogeneity described by a harmonic function are investigated. Solutions to the Maxwell equations for such a medium and the Jones matrices determining the magneto-optical characteristics of the structure under consideration (the coefficients of transmission and reflection and the degrees of polarization of transmitted and reflected waves) are obtained.