Synthesis of Strontium Borophosphate,SrBPO5 by Solid State and Hydrothermal Methods and Characterisation

SrBPO₅ was synthesized by a solid‐state reaction reported and by a new solid state reaction using BPO4 as a phosphating agent. It was also obtained by a hydrothermal method. The structure of the compound was solved by Rietveld analysis before. The examination of X‐ray powder diffraction data showed that, SrBPO5 is isostructural with CaBPO₅ and BaBPO₅. It crystallizes in the trigonal system in P3₁21 and the refined unit cell parameters are a = 6.8488(1), c = 6.8159(2) Å, Z=3 and D_m 3.77 g/cm³.     

FTIR studies of vitamin E-cholesterol-DPPC membrane interactions in CH 2 region

Binary and ternary mixtures of -tocopherol (T), cholesterol and dipalmitoyl phosphatidylcholine (DPPC) in the form of multilamellar liposomes have been investigated by Fourier Transform Infrared Spectroscopy (FTIR). Investigation of frequencies, bandwidths and band shapes of CH₂ stretching and scissoring bands indicate that the effect of T is dominant in comparison with cholesterol and T decreases the interaction of cholesterol with phospholipid membranes.     

Sonochemical synthesis and chracterization of Mn3O4 nanoparticles

We report on the synthesis of Mn₃O₄ nanoparticles (NPs) using a novel sonochemical method without requiring any pH adjustment. Synthesized material was identified as tetragonal hausmannite crystal structure model of Mn₃O₄ from XRD analysis. Crystallite size was estimated from x-ray line profile fitting to be 17±5 nm. FTIR analysis revealed stretching vibrations of metal ions in tetrahedral and octahedral coordination confirming the crystal structure. TEM analysis revealed a dominantly cubic morphology of NPs with an average size of ∼20 nm. Magnetic evaluation revealed a blocking temperature, T _B of 40 K above which the material behaves paramagnetic. Asymmetric coercive field is attributed to the interaction between ferromagnetic Mn₃O₄ and antiferromagnetic Mn oxide at the surface of nanoparticles.      

Dynamics of compressible air flow with friction in a variable-area duct

An adiabatic compressible air flow with friction in a variable-area duct is investigated. A nozzle-flow apparatus is built in which compressed air flows in a frictional diverging conical duct. According to the experimental investigation together with the numerical solution of the governing differential equations it is colligated that the dominance of either factor, friction or variation of area effect, depends upon the product of the inequality .

---

Dynamik einer kompressiblen Luftströmung mit Reibung in einem Kanal veränderlichen Querschnitts

Zusammenfassung Es wurde eine adiabate kompressible Luftströmung mit Reibung in einem Kanal veränderlichen Querschnitts untersucht. Dazu wurde ein düsenförmiger Kanal gebaut, in dem die komprimierte Luft im erweiterten Teil strömt. Sowohl die Versuche als auch die numerische Lösung der beschreibenden Differentialgleichungen ergaben, daß entweder der Reibungsbeiwert oder die Änderung des Strömungsquerschnittes von dem Produkt abhängen.

---

Nomenclature A cross-sectional area of the duct - A _in inlet cross-sectional area of the duct - D diameter of a cross-sectional area - f friction coefficient - M Mach number - /D relative surface roughness of the duct wall - P local static pressure at any axial location - P₀ stagnation pressure at any location - P_{0 in} inlet stagnation pressure - mass flow rate - T static temperature - T_o stagnation temperature - R air gas constant - Re Reynolds number - ratio of specific heats - x measured from the duct inlet     

Partially coherent elegant Hermite–Gaussian beams

Elegant Hermite–Gaussian beams (EHGBs) are extended to the partially coherent case. An explicit and analytical formula is derived for the cross-spectral density of a partially coherent EHGB propagating through an aligned or misaligned paraxial ABCD optical system. The propagation properties of a partially coherent EHGB in free space and its focusing properties through a thin lens are studied numerically, and are compared to those of a partially coherent standard Hermite–Gaussian beam (SHGB). It is found that the propagation and focusing properties of a partially coherent EHGB are closely related to its initial coherence. A partially coherent EHGB spreads slower than a partially coherent SHGB in free-space propagation. A partially coherent EHGB can be focused more tightly than a partially coherent SHGB.     

Convergence of general beams into Gaussian intensity profiles after propagation in turbulent atmosphere

It is shown that a general shaped laser beam will eventually approach a Gaussian average intensity profile after propagation in turbulent atmosphere. In our formulation, source field at the exit plane of the laser is taken as the product of arbitrary functions of source transverse coordinates with Gaussian exponential modulations. Following the expansion of the arbitrary functions in terms of Hermite polynomials, the average receiver intensity expression is derived using the extended Huygens-Fresnel principle and the conditions for the intensity profile to assume a Gaussian shape are stated. The results are illustrated by simulating various source field distributions.     

Effect of spatial coherence on the scintillation properties of a dark hollow beam in turbulent atmosphere

With the help of a tensor method, we derive an explicit expression for the on-axis scintillation index of a circular partially coherent dark hollow (DH) beam in weakly turbulent atmosphere. The derived formula can be applied to study the scintillation properties of a partially coherent Gaussian beam and a partially coherent flat-topped (FT) beam. The effect of spatial coherence on the scintillation properties of DH beam, FT beam and Gaussian beam is studied numerically and comparatively. Our results show that the advantage of a DH beam over a FT beam and a Gaussian beam for reducing turbulence-induced scintillation increases particularly at long propagation distances with the decrease of spatial coherence or the increase of the atmospheric turbulence, which will be useful for long-distance free-space optical communications.     

Paraxial propagation of a partially coherent flattened Gaussian beam through apertured ABCD optical systems

By expanding the hard aperture function into a finite sum of complex Gaussian functions, some approximate analytical formulae for the cross-spectral density of a partially coherent flattened Gaussian beam (FGB) propagating through apertured aligned and misaligned ABCD optical systems are derived based on the generalized Collins formula. The results obtained by using the approximate analytical formula are in good agreement with those obtained by using the numerical integral calculation. As a numerical example, the focusing properties (including average irradiance distribution and focal shift) of a partially coherent FGB focused by an apertured thin lens are studied, and it is found that the focusing properties of a partially coherent FGB are closely related to its initial coherence and the aperture width. Our results provide an effective and fast way for studying the paraxial propagation of a partially coherent FGB through apertured ABCD optical systems.     

Equivalence of structure constants in non-Kolmogorov and Kolmogorov spectra

We find the equivalence of the structure constants in non-Kolmogorov and Kolmogorov spectra in a turbulent atmosphere. As the reference point, the spherical wave scintillation index in a non-Kolmogorov medium is used. Relations of the structure constants are found to be functions of the power law of the turbulence spectrum and the Fresnel zone. It will be useful to employ the equivalence of the structure constants in making performance comparisons found with non-Kolmogorov and Kolmogorov spectra.     

Minimization of scintillation index against displacement parameters

For sinusoidal beams, minimization of scintillation index is carried out against the displacements parameters. It is found that x-y asymmetric cosh-Gaussian beam fulfills the requirements of such optimum beam. Our minimization procedure reveals that the optimum beam is achieved by continually focusing it at the chosen propagation length and by further adjusting displacements parameters to be propagation distance dependent. Scintillation index of thus constructed optimum beam is formulated and numerically evaluated. Our graphical comparisons entailing collimated and focused versions of cos-, cosh-Gaussian, annular-Gaussian and Gaussian beams show that the optimum beam yields the lowest scintillations provided that propagation range is less than or equal to the focusing distance.