Varactor controlled frequency and polarization reconfigurable microstrip antenna

A single feed compact microstrip antenna achieving frequency and polarization diversity using a varactor is presented. A simple patch antenna with an X‐slot constitutes the fundamental structure. The frequency and polarization agility is realized by varying the reactance of an embedded varactor at the center of the X‐slot with respect to the biasing from 0 to 25 V. The prototype fabricated on a substrate of dielectric constant (ε_r) 4.4 and height (h) 1.6 mm is fed by a proximity feed fabricated using the same substrate. By controlling the bias voltage of the varactor, the polarization of the antenna can be switched between linear and circular polarization. Furthermore, the proposed antenna offers stable broadside radiation characteristics without any extra impedance matching circuit. The frequency and polarization diversities of this design could potentially improve the reliability of wireless communication systems. The details of the antenna are presented and discussed. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2011.     

Natural and synthetic antioxidants: Influence on the oxidative stability of biodiesel synthesized from non-edible oil

According to the proposed National Mission on Biodiesel in India, we have undertaken studies on the oxidative stability of biodiesel synthesized from tree borne non-edible oil seeds jatropha. Neat jatropha biodiesel exhibited oxidation stability of 3.95 h and research was conducted to investigate the influence of natural and synthetic antioxidants on the oxidation stability of jatropha methyl ester. Antioxidants namely α-tocopherol, tert-butylated hydroxytoluene, tert-butylated phenol derivative, octylated butylated diphenyl amine, and tert-butylhydroxquinone were doped to improve the oxidation stability. It was found that both types of antioxidants showed beneficial effects in increasing the oxidation stability of jatropha methyl ester, but comparatively, the synthetic antioxidants were found to be more effective.     

Constitution of scheffleroside: a spermicidal saponin from Schefflera capitata

While screening Indian plants for biological activities, it was observed that a 2% aqueous solution of the crude 70% aqueous ethanolic extract of Schefflera capitata showed significant activity against both rat and human spermatozoa. The new saponin, melting point 230-232 degrees, gives on acid hydrolysis D(+)-fucose (1 mole), D(+)-galactose (1 mole), D(+)-glucoronic acid (1 mole) and echinocystic acid (1 mole). Its structure has been tentatively assigned to scheffleroside.     

Cu-Zr and Cu-Zr-Cr alloys produced from rapidly quenched powders

The production of alloys by means of ingot technology leads to micro-and macrosegregation, separation of phases and impurities, often into large, brittle particles, and coarse grain size. Alloy development is frequently restricted because of the coarseness of the structure and the resultant imposed limitations on hot and cold plasticity. One ready means of avoiding these problems is to produce the alloy in powder or pellet form; this permits attainment of high cooling rates in the liquid and solid, minimizes segregation, alters phase separation and distribution advantageously, and results in significantly finer structures. The powders utilized to produce wrought shapes may be much coarser than press-and-sinter powders, leading to important processing economies without sacrifice of structure refinement. The alloy systems Cu-Zr and Cu-Zr-Cr were selected for the present study; these are high conductivity, high strength alloys of commercial interest. Cooling rates for these specific powders using nitrogen atomization varied from about 10³ to 10⁴°CJsec. Powders were cleaned, canned, and hot extruded to produce bar stock; mechanical testing was performed on both as-extruded and thermomechanically-worked samples, with highly beneficial improvements in strength, ductility, and high-temperature structural stability. V. K. SARIN, formerly Research Assistant, Department of Metallurgy and Materials Science, Massachusetts Institute of Technology, Cambridge, Mass.     

Nucleation and growth of combustion flame deposited diamond on silicon nitride

The effect of substrate temperature (T_s) on the nucleation and growth of diamond on silicon nitride (Si₃N₄) based substrates deposited via the oxy-acetylene combustion flame technique was investigated. The diamond deposits were characterized via scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The nucleation density of the resulting deposits, which was of the order 10⁵ nuclei/cm², was used to approximate the activation energy for heterogeneous nucleation of diamond as32 – 40 kcal/mol. An Arrhenius plot of particle growth rate was used to calculate the activation energy for diamond growth as9.4 and 8.3 kcal/mol in the center and outside annulus of the deposit, respectively. These results suggest that the heterogeneous nucleation of diamond is a highly energetic process and may in fact be responsible for the observed low nucleation density of diamond on Si₃N₄. Thermodynamic analysis of gas/substrate reactions under conventional process conditions predicted that SiC formation, which is known to be a necessary precursor to diamond nucleation on Si, is energetically forbidden. Via kinetic and thermodynamic considerations, a patented in situ multistage deposition technique was developed which yielded continuous diamond coatings on Si₃N₄ substrates without extensive substrate preparation.     

Varactor Controlled Gunn Oscillator at W-Band

This paper describes the experimental circuit and measured performance of varactor tuned Gunn oscillator at W-band. The power output of 12.5 dBm has been achieved when packaged GaAs Gunn diode is used. Linear frequency excursion of 150 MHz with power variation of 1 dB has been observed when varactor was given reverse bias from 0 to 20 volts. GaAs hyperabrupt varactor is used in parallel to gunn diode at a distance of odd multiple of λg/2 in waveguide channel.     

Detailed characterisation of polyalphaolefins and their branched structures using multi-pulse NMR techniques

The present work describes some structural investigations carried out on commercial and laboratory synthesised polyalphaolefin (PAO) samples. A number of structures having different branched groups along the chain have been identified in the hydrogenated dimer product of 1-decene, using multi-pulse ¹³C-NMR DEPT techniques. These branched structures have been further confirmed by correlating methyl and methine group resonance in the ¹³C-NMR spectra, using a CALMOD computer program. An insight into the molecular mobility and dynamics of various structures has been obtained through spin lattice relaxation measurement. The study aims to provide a better understanding of the structure—performance relationships in PAOs. A probable mechanism of oligomerisation responsible for the formation of the identified structures is proposed.     

Beitr?ge zur Kenntnis des russischen Kochsalzes

Ohne Zusammenfassung     

Temporal trends in atmospheric PM₂.₅, PM₁₀, elemental carbon, organic carbon, water-soluble organic carbon, and optical properties: impact of biomass burning emissions in the Indo-Gangetic Plain

The first simultaneous measurements and analytical data on atmospheric concentrations of PM(2.5), PM(10), inorganic constituents, carbonaceous species, and their optical properties (aerosol optical depth, AOD; absorption coefficient, b(abs); mass absorption efficiency, σ(abs); and single scattering albedo, SSA) from an urban site (Kanpur) in the Indo-Gangetic Plain are reported here. Significantly high aerosol mass concentration (>100 μg m(-3)) and AOD (> 0.3) are seen as a characteristic feature throughout the sampling period, from October 2008 to April 2009. The temporal variability in the mass fractions of carbonaceous species (EC, OC, and WSOC) is pronounced during October-January when emissions from biomass burning are dominant and OC is a major constituent (～30%) of PM(2.5) mass. The WSOC/OC ratio varies from 0.21 to 0.65, suggesting significant contribution from secondary organic aerosols (SOAs). The mass fraction of SO(4)(2-) in PM(2.5) (Av: 12.5%) exceeds that of NO(3)(-) and NH(4)(+). Aerosol absorption coefficient (@ 678 nm) decreases from 90 Mm(-1) (in December) to 20 Mm(-1) (in April), and a linear regression analysis of the data for b(abs) and EC (n = 54) provides a measure of the mass absorption efficiency of EC (9.6 m(2) g(-1)). In contrast, scattering coefficient (@ 678 nm) increases from 98 Mm(-1) (in January) to 1056 Mm(-1) (in April) and an average mass scattering efficiency of 3.0 ± 0.9 m(2) g(-1) is obtained for PM(10) samples. The highest b(scat) was associated with the dust storm event (April 17, 2009) over northern Iraq, eastern Syria, and southern Turkey; thus, resulting in high SSA (0.93 ± 0.02) during March-April compared to 0.82 ± 0.04 in October-February. These results have implications to large temporal variability in the atmospheric radiative forcing due to aerosols over northern India.