A 60-GHz push-push InGaP HBT VCO with dynamic frequency divider

We present a 60-GHz push-push voltage-controlled oscillator (VCO) with dynamic frequency divider, which is implemented in an InGaP/GaAs heterojunction bipolar transistor technology. A common-base inductive feedback topology is used in the push-push VCO, which generates a pair of 30GHz differential outputs and a single-ended 60GHz push-push output. The 30GHz differential outputs are followed by the proposed dynamic frequency divider. The proposed dynamic frequency divider incorporates active loads with inductive peaking to achieve the higher bandwidth. The maximum operating frequency of the divider was found to be much higher than f/sub T//2 of transistor. To the best of our knowledge, this is the first report demonstrating the extended bandwidth performance of the dynamic frequency divider with active loads and inductive peaking.     

Wideband probe-fed circularly polarised circular loop antenna

A wideband probe-fed circularly polarised circular loop antenna is presented. The wideband performance is achieved by introducing a parasitic loop inside the original loop that is driven by a feed probe. It is found that the 2 dB axial ratio bandwidth can be increased from 6% for a single circular loop to 16% by the introduction of a parasitic loop.     

High indium content graded channel GainAs/AlinAs pseudomorphic MODFETs

We report on the electrical and microstructural properties of InP/Ga_xIn ₁ -xAs/Al_0.48In_0.52As modulation doped layers having compositionally graded active channels with different channel thicknesses. The layers were grown by solid source molecular beam epitaxy on Fe-doped InP substrates. The undoped GaInAs two dimensional electron gas channel layers were grown having indium compositions graded fromx = 0.53 at the substrate buffer tox= 0.65 at the heterointerface by varying the Ga cell temperature during growth. Active channel thicknesses of 20 nm and 30 nm were compared with lattice matched layers. Transmission electron microscope image analysis indicates no misfit dislocations in these structures. Hall-effect measurements at 300 K show an increase in the mobility from 8,380 cm²/Vs for the lattice matched layer to 12,500 cm²/Vs for the 30 nm pseudomorphic layer. Small gate-length, 0.25 μn, MODFETs were fabricated to determine effective velocity values from transconductance (g _m ) and current gain (h ₂₁ ) measurements. The peak dc extrinsicg _m increased from 367 mS/mm for the lattice matched layer to 668 mS/mm for the 30 nm pseudomorphic layer. The effective electron carrier velocity increased from 1.57 × 10⁷ cm/s for the lattice matched layer to 1.88 × 10⁷ cm/s for the 30 nm pseudomorphic layer. Our results show that compositional grading is a useful technique to obtain thick pseudomorphic layers with good transport properties.     

Comment on “On the speed and noise performance of direction-implanted GaAs MESFET's”

Moll comments on the original paper (see ibid., vol.40, pp. 9-17, 1993), stating that the large values of ν_Feng are an artifact of an incorrect analysis and do not represent any physical velocity in the transistor. Most probably, a careful analysis of data for their typical transistors would lead to the notion that the electron velocity is on the order of 1.6 10⁷ cm/s at the drain end of the gated channel. In reply, Feng and Laskar probe the current issues regarding these equations and seek to clarify and validate the equations with 1) The question of velocity overshoot or enhancement in the GaAs channel of HEMT's and MESFET's and its impact upon high speed operation and 2) The delay time analysis technique applied to average velocity extraction     

A detailed study on the antioxidant activity of the stem bark of Dalbergia sissoo Roxb., an Indian medicinal plant

A detailed study was performed on the antioxidant activity of the aqueous and methanol extracts (AED and MED respectively) of the stem bark of the plant, Dalbergia sissoo Roxb. (Fam. Fabaceae), also known as Indian Rosewood. The antioxidant activity of the extracts was measured by in vitro chemical analyses involving the assays of (1) 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (2) ferric ion reducing power (3) ferrous ion chelating activity and (4) Au nanoparticle formation potential. A simplified method was developed based on Au nanoparticles formation to assess the antioxidant activity of any plant extract, and was used for the first time to assay the antioxidant activity of AED and MED. In all the assays, AED showed significantly greater activity over MED. This work provides a scientific support for the high antioxidant activity of this plant and thus it may find potential applications in the treatment of the diseases caused by ROS.     

Experimental investigation on high conversion free-radical polymerization of behenyl acrylate

An experimental investigation on the kinetics of free-radical polymerization of behenyl (a mixture of 14.8% n-octadecyl, 15.1% n-docosyl) acrylate initiated with benzoyl peroxide was conducted at 70°C using a HAAKE rotational viscometer. Molecular weight measurements and differential scanning calorimetric studies of the samples are also described and the results are compared with those obtained by batch reactions conducted under a nitrogen atmosphere. A high monomer order of 1.61±0.11 and a low initiator order of 0.35±0.04 was obtained. The role played by the long methylene chain in behenyl acrylate is also discussed. © 1994 John Wiley & Sons, Inc.     

Cryogenic microwave performance of 0.5-μm InGaAs MESFET's

Microwave and DC properties of 0.5-μm InGaAs MESFETs were measured at 300 and 125 K. The authors have measured approximately 30% increases in RF g_m|ext and f_T when cooling from 300 to 125 K. The authors also observe a 0.06-V increase in gate built-in voltage at 125 K that results in smaller gate leakage currents. The improved gate characteristic at 125 K leads to better RF properties at higher gate bias     

Isolation and chemical investigation of teak (Tectona grandis linn) seed proteins

Proteins were extracted from the deoiled seeds ofTectona grandis Linn., Fam. Verbenaceae, a quality lumber source, in aqueous solutions of various pH’s or by different concentrations of NaCl at pH 8.0. Chemical analysis of isolated protein identified 15 amino acids, of which eight were essential. Gel filtration on Sephadex G-200 revealed the presence of six components, whose molecular weights were determined by two comparable standard methods. Seven components were resolved electrophoretically (SDS-PAG electrophoresis) and their molecular weights were found to be 118,900, 92,300, 72,400, 62,400, 43,600, 39,800 and 32,400.     

Biocidal polymers active by contact. I. Synthesis of polybutadiene with pendant quaternary ammonium groups

Hydroxytelechelic polybutadienes carrying covalently bound quaternary ammonium salts were successfully synthesized in three steps. The first one was the preparation of 1-(N, N-dimethylaminopropyl) 1,1,3,3-tetramethyldisiloxane (M′₂A) by hydrosilylation. The addition occurred mainly in the terminal position of the double bond, but isomers were formed in small proportion (an isomer resulting from an inverse addition and an isomer resulting from an isomerization of the double bond). The proportion of these isomers increased with the concentration of catalyst (H₂PtCl₆). Similar results were obtained with a Pt (0)-di-vinyltetramethyldisiloxane complex (Pt,DVDS). The second step was the grafting of M′₂A onto the 1,2-units of a hydroxytelechelic polybutadiene by hydrosilylation. The yield of the reaction was higher than 90% and the OH functionality decreased slightly. Here again, different platinum catalysts were compared: initial rates were higher with Pt,DVDS, but the final yields were better with H₂PtCl₆. The last step was the quaternization of the pendant tertiary amino groups in methanol with alkyl bromides from C₈H₁₇Br to C₁₆H₃₃Br. The yield of the reaction was higher than 90% and the OH functionality was not modified. © 1993 John Wiley & Sons, Inc.