The nature of dislocation motion in quasicrystals

Calculations in a hydrodynamic model of quasicrystal dynamics show that dislocation motion in these systems is impeded by a drag far greater than that in crystals.     

Novel AB crosslinked polymer networks based on 1‐vinylimidazole‐ terminated polyurethane and poly(methyl methacrylate)

1‐Vinylimidazole‐terminated telechelic polyurethanes were prepared from 1‐vinylimidazole and bromine‐terminated polyurethane. This vinyl‐terminated telechelic polyurethane (VTPU) and methyl methacrylate were polymerized in the presence of benzoyl peroxide to prepare novel AB crosslinked polymer networks (ABCPs). These were characterized by spectral, thermal and mechanical studies. The absence of the characteristic peak of vinyl group in infrared spectra of ABCP films confirms the occurrence of crosslinking. Static mechanical testing showed that the tensile strength of ABCP increases with increasing poly(methyl methacrylate) content. Dynamic mechanical studies revealed that ABCPs, at equal compositions of VTPU and methyl methacrylate, show good damping properties. Copyright © 2006 Society of Chemical Industry     

Slow relaxation in spin glasses

The remarkable remanence effects observed in spin glasses are discussed. Some theoretical approaches and results are reviewed. Invited talk given at the Indian Academy of Sciences, Bangalore, Academy discussion meeting on phase transitions, June 21st, 1978.     

Discrete-Time Analysis of Integrated Voice/Data Multiplexers With and Without Speech Activity Detectors

Discrete-time analysis of two schemes for multiplexing voice and data is presented. In each scheme voice and data are multiplexed using the movable boundary frame allocation scheme. In the first scheme, speech activity detectors (SAD's) are not used, and hence, the variations in the voice traffic are only due to the on/off characteristics of voice. In the second scheme, SAD's are employed so that talker silences can he utilized for transmission of additional voice and/or data. In this scheme, the multiplexer performs digital speech interpolation as well as movable boundary frame allocation. The performance measures considered are probability of loss for voice calls, probability of speech clipping, speech packet rejection ratio, and the expected data message delay. In the case of the multiplexer with SAD, a tradeoff exists between data message delay and speech interpolation advantage. Some numerical examples are presented which illustrate the performance of the two multiplexers.     

Dynamics of flexible-link mechanisms

Dynamic response of flexible-link mechanism (structure) when subjected to external dynamic load is analyzed. The non-linear equations of motion are discretized using the finite element method (FEM) and Newmark time integration method combined with Newton-Raphson iterative technique is used for solution. From the dynamic response of the structure, the required kinematic characteristics are derived. Typical examples are worked out for illustration.     

Stress corrosion cracking of carbon steel in caustic aluminate solutions—crack propagation studies

Stress corrosion cracking of a commercial 0.19 pct C steel (SA-516 Grade 70) was studied in hot (92 ‡C) caustic solutions of NaOH and NaOH plus aluminate (AlO⁻ ₂) species. Potentiostatically controlled tests were conducted near the active-passive transition, using fracture mechanics testing techniques and fatigue precracked double cantilever beam specimens. Crack propagation rates (Ν) were determined for a range of stress intensities (K _l). In simple NaOH solutions, Region I (K₁-dependent) and Region II (K ₁-independent) cracking behavior were observed. Increasing the concentration of NaOH from2m to8m decreasedK _ISCC and displaced Region I and the onset of Region II to lowerK ₁ levels. The presence of AlO⁻ ₂ produced a comparable effect, with Region II being extended to lowerK _I -Ν levels relative to simple NaOH solutions of similar hydroxyl anion concentration. The overallK _I -Νv behavior and fractography were consistent with a dissolution mechanism of crack advance based on the general principles of the film rupture-dissolution model. The effect of environment composition uponK _I — Ν behavior was attributed to changes in repassivation kinetics. Formerly Graduate Student at the University of British Columbia     

Nanocolumnar Preferentially Oriented PSZT Thin Films Deposited on Thermally Grown Silicon Dioxide

We report the first instance of deposition of preferentially oriented, nanocrystalline, and nanocolumnar strontium-doped lead zirconate titanate (PSZT) ferroelectric thin films directly on thermal silicon dioxide. No intermediate seed or activation layers were used between PSZT and silicon dioxide. The deposited thin films have been characterised using a combination of diffraction and microscopy techniques.     

Long‐Term Electrical and Mechanical Function Monitoring of a Human‐on‐a‐Chip System

The goal of human‐on‐a‐chip systems is to capture multiorgan complexity and predict the human response to compounds within physiologically relevant platforms. The generation and characterization of such systems is currently a focal point of research given the long‐standing inadequacies of conventional techniques for predicting human outcome. Functional systems can measure and quantify key cellular mechanisms that correlate with the physiological status of a tissue, and can be used to evaluate therapeutic challenges utilizing many of the same endpoints used in animal experiments or clinical trials. Culturing multiple organ compartments in a platform creates a more physiologic environment (organ–organ communication). Here is reported a human 4‐organ system composed of heart, liver, skeletal muscle, and nervous system modules that maintains cellular viability and function over 28 days in serum‐free conditions using a pumpless system. The integration of noninvasive electrical evaluation of neurons and cardiac cells and mechanical determination of cardiac and skeletal muscle contraction allows the monitoring of cellular function, especially for chronic toxicity studies in vitro. The 28‐day period is the minimum timeframe for animal studies to evaluate repeat dose toxicity. This technology can be a relevant alternative to animal testing by monitoring multiorgan function upon long‐term chemical exposure.     

Miniaturization of monopole antenna using high refractive index metamaterial loading

In this article, miniaturization of the wire monopole antenna with the help of high refractive index (HRI) metamaterial is presented. For the first time, HRI medium is realized by using the array of single ring split ring resonator. By surrounding the wire monopole with the array of SR‐SRRs, the effective wavelength is squeezed in the vicinity of the near field dominance. By the loading of the monopole with such an HRI medium, the size of the antenna is reduced from 29.5 to 16 mm, without any deformation in the current distribution and radiation pattern corresponding to the fundamental resonance. The simulated and measured results are agreed to the same.     

Coaxial‐fed high‐gain triple‐band zeroth‐order circularly polarized antenna using pseudo‐open termination and asymmetric unit cells

A coaxial‐fed tri‐band zeroth‐order resonance (ZOR) circularly polarized antenna with higher gains for all the excited ZORs is designed and analyzed in this paper. Epsilon negative transmission line (ENG TL) and pseudo‐open termination (P‐OT) unit cells with different series capacitances (C_S and C_S1 ) resonate shunt ZOR (f_sh ) and two series ZORs (f_se and f_se1 ), respectively. Asymmetric unit cell concept is applied to ENG‐TL and P‐OT unit cells to create vertical and horizontal components, and the 90° phase shift is provided by the ZOR, resulting in circular polarization (CP). Left‐hand CP (LHCP) is achieved by creating two 90° right bends to the extended stubs in ENG TL and P‐OT unit cells. Higher gains for all the excited ZORs are achieved by shifting the shorting pins of ENG TL and P‐OT unit cells far away from the center position. After fabrication, the measured resonances occur at 4.64 GHz (f_sh ), 4.04 GHz (f_se ), and 3.86 GHz (f_se1 ) with fractional bandwidths of 1.62%, 1.73%, and 1.6%, respectively. The measured LHCP peak gains are 4.05 dBic (f_sh ), 3.85 dBic (f_se ), and 3.94 dBic (f_se1 ). The average axial ratio obtained is less than 3‐dB in the 10‐dB fractional bandwidth of the proposed antenna.