Complex permittivity,complex permeability and microwave absorption properties of ferrite–polymer composites

The complex permittivity (ε′–jε″), complex permeability (μ′–jμ″) and microwave absorption properties of ferrite–polymer composites prepared with different ferrite ratios of 50%, 60%, 70% and 80% in polyurethane (PU) matrix have been investigated in X-band (8.2–12.4 GHz) frequency range. The M-type hexaferrite composition BaCo⁺²_0.9Fe⁺²_0.05Si⁺⁴_0.95Fe⁺³_10.1O₁₉ was prepared by solid-state reaction technique, whereas commercial PU was used to prepare the composites. At higher GHz frequencies, ferrite's permeabilities are drastically reduced, however, the forced conversion of Fe⁺³ to Fe⁺² ions that involves electron hopping, could have increased the dielectric losses in the chosen composition. We have measured complex permittivity and permeability using a vector network analyzer (HP/Agilent model PNA E8364B) and software module 85071. All the parameters ε′, ε″, μ′ and μ″ are found to increase with increased ferrite contents. Measured values of these parameters were used to determine the reflection loss at various sample thicknesses, based on a model of a single-layered plane wave absorber backed by a perfect conductor. The composite with 80% ferrite content has shown a minimum reflection loss of −24.5 dB (>99% power absorption) at 12 GHz with the −20 dB bandwidth over the extended frequency range of 11–13 GHz for an absorber thickness of 1.6 mm. The prepared composites can fruitfully be utilized for suppression of electromagnetic interference (EMI) and reduction of radar signatures (stealth technology).     

Effects of phase duration and electrode separation on loudness growth in cochlear implant listeners

Loudness estimates were obtained in a group of four adult subjects implanted with the Nucleus-22 multielectrode cochlear implant device, for a range of pulse amplitudes and different fixed phase durations and electrode separations. The stimulus was a 200-ms long train of biphasic pulses presented at 500 pulses/s. Subjects estimated loudness as a number from 0 ("don't hear it") to 100 ("uncomfortably loud"). Loudness was found to grow exponentially with pulse amplitude, at a rate that was dependent upon the phase duration as well as the electrode separation. An equation of the form L = e(lambda + gamma M)(D theta)I, where L is the estimated loudness, M is the separation between electrodes of a stimulating pair, D is the phase duration, I is current amplitude, and lambda, gamma, and theta are constants, appears to describe the observed data adequately. The findings are remarkably consistent across subjects.     

Enhancement of second harmonic generation by double-pass configuration in barium borate

Double-pass type-I second harmonic generation (SHG) external to a laser cavity is reported for the first time in a BBO crystal resulting in an enhancement of the generated harmonic intensity by a factor of 3.4 from that obtained in the single-pass generation.     

Characterization of biaxial crystals for tangentially phase-matched frequency conversion

Ultraviolet radiation has been generated by tangentially phase-matched sum-frequency mixing in biaxial L-arginine phosphate (LAP) crystal for the first time using Nd:YAG output at 1064 nm and Rh 6G dye laser output at 560 nm as the two input sources. Characterization has also been made of such a cheap, biaxial crystal for its possible use in devices for tangentially phase-matched short wavelength generation. If the crystal is of proper cut, thickness and quality so that its maximum capability can be exploited it can replace the potassium dihydrogen phosphate (KDP) group of crystals for various applications.     

Thermogravimetric analysis of cellulose

An application of TGA technique to elucidate the chain reaction mechanism of cellulose pyrolysis is discussed. The mathematical expressions for isothermal kinetics are modified for use with temperature-programmed kinetics. It is shown that in temperature-programmed kinetics, the initial reaction should theoretically be a pseudo zero-order type, whereas the latter part should be a pseudo first-order type. Experimental data from the present study and from the literature are in good agreement with the theory. Energies of activation for the initiation and the propagation steps of cellulose pyrolytic reactions are analyzed from TG data. Various cellulose samples, such as adsorbent cotton, vibratory ball-milled absorbent cotton, mercerized commercial yarn, mercerized and treated commercial yarn, dewaxed-kiered cotton, and microcrystalline cellulose are included in this study. A basic problem which is associated with all thermogravimetric kinetic expressions is also discussed.     

Absorption of sodium lauryl sulphate at the benzene-water interface

Summary The interfacial tension of benzene-water interface was measured as a function of sodium lauryl sulphate concentration in presence of 0, 0,1 and 1 M sodium chloride. Analysis of pressure-area curves constructed from these data indicated qualitatively the validity of the onekT and twokT forms of theGibbs equation respectively for the presence and absence of neutral salt. The proposed dimerisation of lauryl sulphate ions in the bulk was shown not to affect the- A curves to a large extent in the high pressure region. The limiting area per adsorbed ion was evaluated from an empirical plot. The experimental pressure was found to deviate significantly from that expected theoretically from theGouy model of the electrical double layer. This deviation was explained on the basis of the discrete-ion-effect proposed byBell, Levine andPethica. Based in part, upon the thesis submittedby A. K. Chatterjee (Chattopadhyay) for Ph. D. degree of the Jadavpur University, 1966.The authors are grateful to Dr.G. M. Bell and Dr.B. A. Pethica for the interpretation of several points of their theory in a private communication. Thanks are also due to the Council of Scientific and Industrial Research. India for the financial assistance.     

Spectrophotometric determination of lanthanum, thorium and iron(III) with chromotropic acid azo dyes of the pyridine series

Highly sensitive methods for the determination of lan thanum, thorium and iron(III) have been developed with the sodium salts of 2-(pyridyl-2-azo)chromotropic acid, 2-(pyridyl-3-azo)chromotropic acid and 2-(2-carboxypyridyl-3-azo)chromotropic acid. Optimum concentration ranges are of the order 1-20 ppm. The effect of diverse ions (cations and anions) including those of rare-earths are reported. The nature of the complexes has been investigated and values for the instability constants are given.     

Effect of hydrogen bonding on the acid character of some synthetic copolymers

A copolymer of p-hydroxybenzoic acid, formaldehyde, and p-bromoaniline was prepared in the presence of acid catalyst, and five fractions have been separated from it. Br content of each of the fractions was determined by chemical analysis, and on the basis of mole ratio of repeating units present in the copolymer chain, the total amounts of acidic and basic groups in a given weight of the copolymer were calculated. Nonaqueous titrations of all the fractions have been carried out in acidic and basic medium with suitable titrants. An excellent correlation was observed between the calculated and observed values of functional groups. The features of the titration curves were interpreted in terms of intramolecular hydrogen bonding and homoconjugation.     

Synthetic studies on alkaloids. Part 2. Stereospecific synthesis of 1β-methyl-13α-acetoxy-8,11-dioxotetracyclo[7:2:2:05,11:05,12]tridec-Δ6,7-ene; model reactions on the construction of aconitine skeleton

The title compound (2), an advanced relay towards the well-appreciated aconitine skeleton (1) of the C₁₉-norditerpene alkaloids, has been synthesised $\text{via}$ regiospecific intramolecular oxocarbenedo CH σ-bond insertion as the key step and this intermediate has the full potential for further elaboration to the intact skeleton.