The Possibility of Forming Two-Lobe Vortex Light Fields Using a Modified Liquid-Crystal Focusator

Optics and Spectroscopy - The possibilities of forming light fields with intensity distribution in the form of two maxima rotating during propagation using a liquid-crystal modal device are...     

The interference enhancement of light polarization conversion from structures with a quantum well

The optical activity of crystals leads to the occurrence of ellipticity at the reflection of light which is linearly polarized in the interface plane or normally to it. The effect experimentally discovered in the investigated structures with quantum wells is due to a spin-orbit interaction and birefringence. The qualitative dependence of the effect on the change in the orientation of the linear polarization of the incident light has been revealed. A sharp increase in the degree of the polarization conversion in a narrow range of incidence angles for light polarized in the incidence plane has been detected. The latter is due to the influence of the interference of the reflected wave on the structure thickness.     

Phase formation in the Ag<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-MgMoO<Subscript>4</Subscript>-Al<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> system

The subsolidus region of the Ag₂MoO₄-MgMoO₄-Al₂(MoO₄)₃ ternary salt system has been studied by X-ray phase analysis. The formation of new compounds Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.4) and AgMg₃Al(MoO₄)₅ has been determined. The Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ variable-composition phase is related to the NASICON type structure (space group R \(\bar 3\) c). AgMg₃Al(MoO₄)₅ is isostructural to sodium magnesium indium molybdate of the same formula unit and crystallizes in triclinic system (space group P \(\bar 1\), Z = 2) with the following unit cell parameters: a = 9.295(7) Å, b = 17.619(2) Å, c = 6.8570(7) Å, α = 87.420(9)°, β = 101.109(9)°, γ = 91.847(9)°. The compounds Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ and AgMg₃Al(MoO₄)₅ are thermally stable up to 790 and 820°C, respectively.     

Phase formation in the system involving silver, magnesium, and indium molybdates

The subsolidus region of the Ag₂MoO₄-MgMoO₄-In₂(MoO₄)₃ ternary salt system has been studied by X-ray powder diffraction. The formation of new compounds Ag_{1 ? x} Mg_{1 ? x} In_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.6) and AgMg₃In(MoO₄)₅ has been established. The unit cell parameters of solid-solution samples have been determined. The Ag_{1 ? x} Mg_{1 ? x} In_{1 + x} (MoO₄)₃ phase of variable composition has a NASICON-type structure (space group R $ \bar 3 $ c) AgMg₃In(MoO₄)₅ is isostructural to sodium magnesium indium molybdate of the same formula unit and crystallizes in triclinic system (space group P $ \bar 1 $ , Z = 2) with the following unit cell parameters: a = 7.0374(5) Å, b = 17.932(1) Å, c = 6.9822(4) Å, α = 87.309(6)°, β = 100.832(6)°, γ = 92.358(6)°. The compounds Ag_{1 ? x} Mg_{1 ? x} In_{1 + x} (MoO₄)₃ and AgMg3In(MoO₄)₅ are thermally stable up to 960 and 1030°C, respectively.     

Thermodynamic properties of Ni-Ga melts

The partial mixing enthalpies of the components (Δ_m $ \bar H $ \bar H _i ) of the Ni-Ga melts were measured using the high-temperature isoperibolic calorimetry at 1770 ± 5 K in wide concentration interval. The limiting partial mixing enthalpy of gallium in a liquid nickel (Δ_m $ \bar H $ \bar H _Ga^∞) is −95.5 ± 19.8 kJ mol⁻¹, and similar function of nickel in liquid gallium (Δ_m $ \bar H $ \bar H _Ni^∞) is −74.5 ± 16.4 kJ mol⁻¹. The integral mixing enthalpy of liquid alloys of this system was calculated from partial enthalpies for the whole concentration area (Δ_m H _min = −32.1 ± 2.7 kJ mol⁻¹ at x _Ni = 0.5). The Δ_m H value of liquid nickel-gallium alloys independence of the temperature is confirmed. Enthalpies of formation of liquid (Δ_m H) phases of Ni-Ga system were compared with ones for solid (Δ_f H) phases of this system. An analysis of d-metals influence on formation energy of Ga-d-Me melts was made using the values of Δ_f H for intermediate phases of these systems. The article was translated by the authors.     

Porphyrin effect on the surface morphology of amphiphilic polymers as observed by atomic force microscopy

Complexes of porphyrin photosensitizers (PPS) with triblock copolymers of ethylene- and propylene oxide – Pluronics^® – exhibit markedly increased activity in the generation of singlet oxygen in aqueous media, as compared to pure porphyrins. Pluronics are amphiphilic polymers with surfactant properties suitable for a number of medical applications. PPS–Pluronic systems are considered as promising agents for photodynamic therapy which implies generation of singlet oxygen in the water-based human tissue.Importantly, Pluronics are capable of solubilization of not only water-soluble, but also hydrophobic PPS providing their transfer into the aqueous phase. It has been shown earlier that specific interactions of PPS with Pluronics must play a primary role for the photocatalytic properties of PPS–Pluronic systems. In the process of solubilization of a hydrophobic porphyrin by a Pluronic, both components are dissolved in an organic solvent, which is then removed, and the dry film is re-dissolved in water. Apparently, the initial binding between the porphyrin and the lipophilic part of the polymer takes place already at the stage of the film formation.We applied atomic force microscopy (AFM) to visualize structures formed by Pluronics upon their interactions with meso-tetraphenylporphyrin (TPP). We studied the surface structure of Pluronics^® F87, F108 and F127 crystallized alone or together with TPP on silicon substrates from chloroform solutions. We found Pluronics to form similar dendritic structures independently of their molecular weight and degree of hydrophobicity. In the presence of TPP, though, we observed formation of distinct convex structures on top of the Pluronic dendrites. These structures appeared to consist of multiple flat layers placed on top of each other. Their sizes varied among the three Pluronics. We believe that TPP aggregates interact with the hydrophobic units of Pluronics causing the polymer chains to pack themselves in a distinct manner around those TPP-containing “cores”. These interactions apparently direct formation of complexes between the porphyrin and the polymer upon their dissolution in water, thus resulting in the encapsulation of TPP aggregates inside a Pluronic micelle. A single mechanism for the TPP solubilization by Pluronics is consistent with the same catalytic activity of the three TPP–Pluronic systems observed in the photooxidation of tryptophan.     

Optical tweezers technique for the study of red blood cells deformation ability

The presented here technique is developed for in vitro estimation of the influence of external conditions on the deformation ability of human red blood cells. The method is based on the use of single-beam laser trap for capturing of erythrocytes fixed to the bottom of the liquid cell by the adhesion force. The approach is suitable for evaluation of the properties of individual cells as well as for real-time acquisition of the data on ensemble of erythrocytes large enough for subsequent statistical analysis. It is shown that both a change in the saline solution concentration and presence of certain stabilizing agents lead to measurable shift of the maximum of the cells distribution by their deformability.     

Effect of charge memory in organic composites

The effect of charge memory in composites based on polymer molecules has been investigated. Resistive switchings in sandwich samples prepared by lamination from commercially available polymers (polystyrene and poly(2,3-dihydrothieno-1,4-dioxine)-poly(styrene sulphonate) are analyzed. It is shown that the characteristic switching times in the composite samples reach several nanoseconds and the number of switchings exceeds 10⁶. Switchings are observed in electric fields much below the breakdown threshold, which indicates the absence of destructive processes in the polymer.     

Thermodynamic properties of Al-Y system melts

The thermochemical properties of Al-Y melts were determined by isoperibolic calorimetry. It was established that the minimal value of integral mixing enthalpies is equal to −40.8 + 0.4 kJ/mol at 1770 K and x _Y = 0.41. The thermodynamic properties of liquid alloys were modeled by the developed procedure using the coordinates of a liquidus line in the phase diagram of the Al-Y system, and by the theory of ideal associated solutions. The component activities exhibit high negative deviations from the Raoult law. The Gibbs energies of mixing of Al-Y melts have a minimum of −30.6 kJ/mol at x _Y = 0.48.