The Gaussian Plasma Lens in Astrophysics. Refraction

We consider the geometrical optics for refraction of a distant radio source by an interstellar plasma lens, with application to a lens with a Gaussian electron column density profile. The refractive properties of the lens are specified completely by a dimensionless parameter, alpha, which is a function of the wavelength of observation, the lens' electron column density, the lens-observer distance, and the transverse diameter of the lens. Relative motion of the observer and lens produces modulations in the source's light curve. Plasma lenses are diverging so the light curve displays a minimum, when the lens is on-axis, surrounded by enhancements above the unlensed flux density. Lensing can also produce caustics, multiple imaging, and angular position wander of the background source. If caustics are formed, the separation of the outer caustics can constrain alpha, while the separation of the inner caustics can constrain the size of the lens. We apply our analysis to 0954+654, a source for which we can identify caustics in its light curve, and 1741-038, for which polarization observations were obtained during and after the scattering event. We find general agreement between modelled and observed light curves at 2.25 GHz, but poor agreement at 8.1 GHz. The discrepancies may result from a combination of lens substructure or anisotropic shape, a lens that only grazes the source, or unresolved source substructure. Our analysis places the following constraints on the lenses: Toward 0954+654 (1741-038) the lens was 0.38 AU (0.065 AU) in diameter, with a peak column density of 0.24 pc cm^{-3} (1E-4 pc cm^{-3}) and an electron density of 1E5 cm^{-3} (300 cm^{-3}). The angular wander caused by the lens was 250 mas (0.4 mas) at 2.25 GHz. For 1741-038, we place an upper limit of 100 mG on the lens' magnetic field.Comment: 26 pages, LaTeX2e using AASTeX macro aaspp4, 11 PostScript figures; to be published in Ap

Extended Hydrogen-Bonded Molybdenum Arrays Derived from Carboxylic Acids and Dianilines: ROP Capability of the Complexes and Parent Acids and Dianilines

From reactions involving sodium molybdate and dianilines [2,2′ -(NH2 )C6H4 ]2 (CH2 )n (n = 0, 1, 2) and amino-functionalized carboxylic acids 1,2-(NH2 )(CO2H)C6H4 or 2-H2NC6H3 -1,4-(CO2H)2 , in the presence of Et3N and Me3SiCl, products adopting H-bonded networks have been characterized. In particular, the reaction of 2,2′ -diaminobiphenyl, [2,2′ -NH2 (C6H4 )]2 , and 2-aminoterephthalic acid, H2NC6H3 -1,4-(CO2H)2 , led to the isolation of [(MoCl3 [2,2′ -N(C6H4 )]2 }{HNC6H3 -1-(CO2 ),4- (CO2H)]\ub72[2,2′ -NH2 (C6H4 )]2 \ub73.5MeCN (1\ub73.5MeCN), which contains intra-molecular N–H\ub7\ub7\ub7Cl Hbonds and slipped π\ub7\ub7\ub7π interactions. Similar use of 2,2′ -methylenedianiline, [2,2′ -(NH2 )C6H4 ]2CH2 , in combination with 2-aminoterephthalic acid led to the isolation of [MoCl2 (O2CC6H3NHCO2SiMe3 ) (NC6H4CH2C6H4NH2 )]\ub73MeCN(2\ub73MeCN). Complex 2 contains extensive H-bonds between pairs of centrosymmetrically-related molecules. In the case of 2,2′ ethylenedianiline, [2,2′ -(NH2 )C6H4 ]2CH2CH2 , and anthranilic acid, 1,2-(NH2 )(CO2H)C6H4 , reaction with Na2MoO4 in the presence of Et3N and Me3SiCl in refluxing 1,2-dimethoxyethane afforded the complex [MoCl3 {1,2-(NH)(CO2 )C6H4 }{NC6H4 CH2CH2C6H4NH3 }]\ub7MeCN (3\ub7MeCN). In 3, there are intra-molecular bifurcated H-bonds between NH3 H atoms and chlorides, whilst pairs of molecules H-bond further via the NH3 groups to the non-coordinated carboxylate oxygen, resulting in H-bonded chains. Complexes 1 to 3 have been screened for the ring opening polymerization (ROP) of both ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) using solvent-free conditions under N2 and air. The products were of moderate to high molecular weight, with wide 0 values, and comprised several types of polymer families, including OH-terminated, OBn-terminated (for PCL only), and cyclic polymers. The results of metal-free ROP using the dianilines [2,2′ -(NH2 )C6H4 ]2 (CH2 )n (n = 0, 1, 2) and the amino-functionalized carboxylic acids 1,2-(NH2 )(CO2H)C6H4 or 2-H2NC6H3 -1,4-(CO2H)2 under similar conditions (no BnOH) are also reported. The dianilines were found to be capable of the ROP of δ-VL (but not ε-CL), whilst anthranilic acid outperformed 2-aminoterephthalic acid for both ε-Cl and δ-VL

Spin-Correlation Coefficients and Phase-Shift Analysis for p+3^3He Elastic Scattering

Angular Distributions for the target spin-dependent observables A$_{0y}$, A$_{xx}$, and A$_{yy}$ have been measured using polarized proton beams at several energies between 2 and 6 MeV and a spin-exchange optical pumping polarized $^3$He target. These measurements have been included in a global phase-shift analysis following that of George and Knutson, who reported two best-fit phase-shift solutions to the previous global p+$^3$He elastic scattering database below 12 MeV. These new measurements, along with measurements of cross-section and beam-analyzing power made over a similar energy range by Fisher \textit{et al.}, allowed a single, unique solution to be obtained. The new measurements and phase-shifts are compared with theoretical calculations using realistic nucleon-nucleon potential models.Comment: Submitted to Phys. Rev.

Effects of Thermal Shock on Mechanical Behaviour of Kevlar Fibre Composites

The development of composite technology represents one of the most significant advances in materials science since 1940s. The major advantages of composite materials are their high strength and stiffness, light weight, corrosion resistance, crack and fatigue resistance and design flexibility as compared to metallic materials. Because of the attractive properties. the use of composite materials has been increasing steadily in recent years. Unfortunately, there are disadvantages in composite materials as compared with metals. They include brittleness, vulnerability to stress concentration, inflexibility for localised multidirectional stresses, sensitivity to environmental effects, and poor damage tolerance to impact. These factors must be critically considered in designing a composite system. The aramid keviar family of fibres have been accepted as reinforcement for composites and finds wider and newer applications in various industrial and aerospace sectors. The interfacial bond strength between aramid fibres and epoxy resins is normally lower than what is experienced with carbon fibre composites. This weakness with kevlar necessitates investigation and evaluation of the interlaminar shear strength (ILSS) and modulus under some realistic environmental conditions. The present work has been taken up to evaluate the variation of ILS S and modulus values after being given the extreme thermal shock of 160°C thermal gradient. The thermal shock is given in two separate ways, firstly, one series of kevlar/ epoxy and kevlar/polyester short beam shear (SBS) specimens are kept in a oven at 80°C for different time intervals and then immersed in a liquid bath at -80`'C temperature. The other experiment is done in reverse way i.e. first kept at -80°C and then exposed to 80°C temperature. The interesting variations of ELSS and modulus values have generated some ideas for assessment in this area. The thermal shock, positive temperature and cryogenic temperature affect the kevlar/epoxy and kevlar/polyester composites in a very complex way. The wide fluctuation in results necessitates further investigation and depth analysis of this interaction, It may be hypothesised that the extreme thermal shock may introduce some decohesion between fibre/matrix interface especially when the gradient is positive in thermal shock

A New Look At Carbon Abundances In Planetary Nebulae. III. DDDM1, IC 3568, IC4593, NGC 6210, NGC 6720, NGC 6826, & NGC 7009

This paper is the third in a series reporting on a study of carbon abundances in a carefully chosen sample of planetary nebulae representing a large range in progenitor mass and metallicity. We make use of the IUE Final Archive database containing consistently-reduced spectra to measure line strengths of C III] 1909 along with numerous other UV lines for the planetary nebulae DDDM1, IC 3568, IC 4593, NGC 6210, NGC 6720, NGC 6826, & NGC 7009. We combine the IUE data with line strengths from optical spectra obtained specifically to match the IUE slit positions as closely as possible, to determine values for the abundance ratios He/H, O/H, C/O, N/O, and Ne/O. The ratio of C III] 1909/C II 4267 is found to be effective for merging UV and optical spectra when He II 1640/4686 is unavailable. Our abundance determination method includes a 5-level program whose results are fine-tuned by corrections derived from detailed photoionization models constrained by the same set of emission lines. All objects appear to have subsolar levels of O/H, and all but one show N/O levels above solar. In addition, the seven planetary nebulae span a broad range in C/O values. We infer that many of our objects are matter bounded, and thus the standard ionization correction factor for N/O may be inappropriate for these PNe. Finally, we estimate C/O using both collisionally-excited and recombination lines associated with C+2 and find the well established result that abundances from recombination lines usually exceed those from collisionally-excited lines by several times.Comment: 36 pages, 7 tables, 2 figures, latex. Tables and figures supplied as two separate postscript files. Accepted for publication in Ap

Colloid-stabilized emulsions: behaviour as the interfacial tension is reduced

We present confocal microscopy studies of novel particle-stabilized emulsions. The novelty arises because the immiscible fluids have an accessible upper critical solution temperature. The emulsions have been created by beginning with particles dispersed in the single-fluid phase. On cooling, regions of the minority phase nucleate. While coarsening these nuclei become coated with particles due to the associated reduction in interfacial energy. The resulting emulsion is arrested, and the particle-coated interfaces have intriguing properties. Having made use of the binary-fluid phase diagram to create the emulsion we then make use of it to study the properties of the interfaces. As the emulsion is re-heated toward the single-fluid phase the interfacial tension falls and the volume of the dispersed phase drops. Crumpling, fracture or coalescence can follow. The results show that the elasticity of the interfaces has a controlling influence over the emulsion behaviour.Comment: Submitted for the proceedings of the 6th Liquid Matter Conference, held in Utrecht (NL) in July 200

Studies of a Lacustrine-Volcanic Mars Analog Field Site with Mars-2020-like Instruments

On the upcoming Mars‐2020 rover two remote sensing instruments, Mastcam‐Z and SuperCam, and two microscopic proximity science instruments, SHERLOC and PIXL, will collect compositional (mineralogy, chemistry, and organics) data essential for paleoenvironmental reconstruction. The synergies between and limitations of these instruments were evaluated via study of a Mars analog field site in the Mojave Desert, using instruments approximating the data that will be returned by Mars‐2020. A ground truth dataset was generated for comparison to validate the results. The site consists of a succession of clay‐rich mudstones of lacustrine origin, interbedded tuffs, a carbonate‐silica travertine deposit, and gypsiferous mudstone strata. The major geological units were mapped successfully using simulated Mars‐2020 data. Simulated Mastcam‐Z data identified unit boundaries and Fe‐bearing weathering products. Simulated SuperCam passive shortwave infrared and green Raman data were essential in identifying major mineralogical composition and changes in lacustrine facies at distance; this was possible even with spectrally downsampled passive IR data. LIBS and simulated PIXL data discriminated and mapped major element chemistry. Simulated PIXL revealed mm‐scale zones enriched in zirconium, of interest for age dating. SHERLOC‐like data mapped sulfate and carbonate at sub‐mm scale; silicates were identified with increased laser pulses/spot or by averaging of hundreds of spectra. Fluorescence scans detected and mapped varied classes of organics in all samples, characterized further with follow‐on spatially targeted deep‐UV Raman spectra. Development of dedicated organics spectral libraries is needed to aid interpretation. Given these observations, the important units in the outcrop would be sampled and cached for sample return

Observations of rotationally resolved C3 in translucent sight lines

The rotationally resolved spectrum of the A ^1Pi_u <- X ^1Sigma^+_g 000-000 transition of C3, centered at 4051.6A, has been observed along 10 translucent lines of sight. To interpret these spectra, a new method for the determination of column densities and analysis of excitation profiles involving the simulation and fitting of observed spectra has been developed. The populations of lower rotational levels (J<14) in C3 are best fit by thermal distributions that are consistent with the kinetic temperatures determined from the excitation profile of C2. Just as in the case of C2, higher rotational levels (J>14) of C3 show increased nonthermal population distributions in clouds which have been determined to have total gas densities below ~500 cm-3.Comment: 12 pages, 4 figures, accepted for publication in The Astrophysical Journa