Scattering of electromagnetic waves by static wormholes

Scattering of electromagnetic waves by static and traversable wormholes is discussed. Based on the fact that these spacetimes have no horizon, and regarding their non-trivial topology, we have developed the perturbation theory of scattering and the Born approximation for obtaining the differential scattering cross section. Some of the zeros of the scattering pattern at long wavelengths are determined which can be used for estimating the radius of the throat. The known result that in scattering by static spacetimes the linear polarization remains unchanged is verified here.     

Accurate radial basis function based neural network approach for analysis of photonic crystal fibers

In this paper, a new and an accurate artificial neural network approach (ANN) is presented for the analysis and design of photonic crystal fibers (PCFs). The new ANN approach is based on the radial basis functions which offer a very quick convergence and high efficiency during the ANN learning. The accuracy of the suggested approach is demonstrated via the excellent agreement between the results obtained using the presented approach and the results of the full vectorial finite difference method (FVFDM). In addition, a new design of highly birefringence PCF with low losses for the two polarized modes is presented using the proposed approach.     

Effect of the laser axial modes on the coherence length of the laser beam

The effect of the presence of the axial modes within the spectral halfwidth of a laser spectral line on the visibility of its interference fringes is represented. It is found in case of axial modes with equal spectral halfwidths that the dominant factor in determining the coherence length of the laser beam is the spectral halfwidth of its axial mode and not the spectral halfwidth of the laser line. For the case of a laser beam with axial modes of different spectral halfwidths, the calculation shows a coherence length, closer to the mode with the smaller halfwidth.     

Antibacterial sphingolipid and steroids from the black coral Antipathes dichotoma

From the black coral Antipathies dichotoma, a sphingolipid (2S*,3S*,4E,8E)-2N-[tetradecanoyl]-4(E),8(E)-icosadiene-1,3-diol (1) and a steroid (22E)-methylcholesta-5,22-diene-1α,3β,7α-triol (2) were isolated. Other known compounds, 3β,7α-dihydroxy-cholest-5-ene (3), (22E,24S),5α,8α-epidioxy-24-methylcholesta-6,22-dien-3β-ol (4) and (22E,24S),5α,8α-epidioxy-24-methylcholesta-6,9(11),22-trien-3β-ol (5). The structures were established on the basis of NMR spectroscopic analysis and comparison with literature. The antibacterial activity of five compounds was evaluated.     

Spin Fidelity for Three-Qubit Greenberger-Horne-Zeilinger and W States Under Lorentz Transformations

Constructing the reduced density matrix for a system of three massive spin- \frac12\frac{1}{2} particles described by a wave packet with Gaussian momentum distribution and a spin part in the form of GHZ or W state, the fidelity for the spin part of the system is investigated from the viewpoint of moving observers in the jargon of special relativity. Using a numerical approach, it turns out that by increasing the boost speed, the spin fidelity decreases and reaches to a non-zero asymptotic value that depends on the momentum distribution and the amount of momentum entanglement.     

Reduction of Ozonides by Means of Polymeric Triphenylphosphine: Simplified Synthesis of Carbonyl Compounds from Alkenes

A classical system for the preparation of carbonyl compounds from alkenes relies upon ozonolysis of the double bond, followed by reductive cleavage of the ozonide so formed. Among the reagents of choice for such a reduction, triphenylphosphine certainly has enjoyed a widespread use.¹ However, in spite of the simplicity of the method, often one can face problems in the purification of the carbonyl compound from unreacted triphenylphosphine, especially if the polarities of both products are very similar. We have encountered such a problem during the preparation of the (20 S)-6β -ethoxy-3 α, 5-cyclo-5α -pregnane-20-carbaldehyde 4 from the suitably protected stigmasterol3². In this case, when triphenylphosphine was used for reduction of ozonide we never could isolate the aldehyde 2 uncontaninated by tripherylphosphine.     

Two parallel plane jets: mean flow and effects of acoustic excitation

 The flow field generated by unventilated two parallel jets has been investigated using LDA. The two nozzles each with an aspect ratio of 24 were separated by 4.25 nozzle widths. Results show that a recirculation zone with sub-atmospheric static pressure was bounded by the inner shear layers of the individual jets and the nozzles plate. It was shown that the two-dimensionality of the flow was greatly enhanced by the installation of side plates and that the flow was independent of Reynolds number between 8300 and 19300. Acoustic excitation introduced at the outer shear layer mode has been shown to reduce the size of the potential core, recirculation zone, merging length and combined length but enhance jet spreading, streamwise velocity decay and volume entrainment. Received: 18 November 1994/Accepted: 26 July 1996     

Analytical Model for The Capillary Pressure Gradient in Oil–Water–Rock System

A simplified analytical expression for the capillary pressure gradient in homogeneous porous media is proposed. Basic assumptions are: (1) the three phase contact angle between two fluids and porous rock is finite, (2) the surface area of contact between two fluids is small in comparison with contact surface areas between each fluid and porous rock in the unit volume of the system under consideration, (3) the model corresponds to conditions when both phases are continuous.     

Characterization of currently marketed heparin products: key tests for quality assurance

During the 2007–2008 heparin crisis, it was found that the United States Pharmacopeia (USP) testing monograph for unfractionated heparin sodium (UFH) did not detect the presence of the contaminant, oversulfated chondroitin sulfate (OSCS) in heparin. In response to this concern, new tests and specifications were developed by the Food and Drug Administration (FDA) and USP and put in place to not only detect the contaminant OSCS but also to improve assurance of quality and purity of the drug product. Additional tests were also developed to monitor the heparin supply chain for other possible economically motivated additives or impurities. In 2009, a new USP monograph was put in place that includes 500 MHz ¹H NMR, SAX-HPLC, %galactosamine in total hexosamine, and anticoagulation time assays with purified factor IIa or factor Xa. These tests represent orthogonal approaches for UFH identification, measurement of bioactivity, and for detection of process impurities or contaminants in UFH. The FDA has applied these analytical approaches to the study of UFH active pharmaceutical ingredients in the marketplace. Here, we describe results from a comprehensive survey of UFH collected from seven different sources after the 2009 monograph revision and compare these data with results obtained on other heparin samples collected during the 2007–2008 crisis.