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(1998)Journal ArticleThe first results obtained using a SOI device for microdosimetry applications are presented. Microbeam and broadbeam spectroscopy methods are used for determining minority carrier lifetime and radiation damage constants. A spectroscopy model is presented which includes the majority of effects that impact spectral resolution. Charge collection statistics were found to substantially affect spectral resolution. Lateral diffusion effects significantly complicate charge collection
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(1996)Journal ArticleThe passivated emitter, rear locally diffused (PERL) cells, fabricated in our laboratory, reach an efficiency of 24.0%, the highest value for any silicon-based solar cell under terrestrial illumination. In an attempt to improve the rear surface passivation, which is usually obtained by a thermally grown oxide, we add a floating (i.e., noncontacted) p-n junction at the rear surface, resulting in the passivated emitter, rear floating p-n junction (PERF) cell design. Although these cells exhibit record 1-sun open-circuit voltages of up to 720 mV, their efficiency is degraded by nonlinearities ("shoulders") in the logarithmic I-V curves. In order to understand and manipulate such nonlinearities, this paper presents a detailed investigation of the internal operation of PERF cells by means of numerical modelling based on experimentally determined device parameters. From the model, we derive design rules for optimum cell performance and develop a generalized argumentation that is suitable to compare the passivation properties of different surface structures. For example, the oxidized rear surface of the PERL cell is treated as an electrostatically induced floating junction in this approach and analogies to the diffused floating p-n junction are drawn. Our simulations indicate that optimum rear surface passivation can be obtained in three different ways. (i) The floating junction of the PERF cell should be very lightly doped, resulting in a sheet resistivity of 5000 Omega/[D'Alembertian], and losses due to shunt leaking paths between the p-n junction and the rear metal contacts must be avoided. (ii) The rear surface of the PERL cell should be passivated by chemical vapor deposition of a silicon nitride film containing a larger positive interface charge density than exists in thermally grown oxides. (iii) An external gate can be added at the rear with low leakage currents and gate voltages of around 15 V.
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Freezing-Induced Hydration Forces Between Phospatidylcholine Bilayers-The Effect of Osmotic Pressure(1997)Journal ArticleQuantitative nuclear magnetic resonance was used to measure the freezing behaviour of lamellar phases of phosphatidylcholine in water and in solutions of sorbitol. Both solute and solvent were deuterated in different series of experiments to allow the calculation of the partitioning of solute and solvent molecules between the lamellar phase and unfrozen bulk solution. Sorbitol, as well as water, was found to redistribute between these phases as a function of temperature. The results show a strong, repulsive, interlamellar force which decreases approximately exponentially with hydration. Compared to measurements on lipid/water systems and solute/water systems, the hydration of the lamellar phase containing solutes is slightly less than the sum of the hydrations of lipid and solute at any given chemical potential of water. For a lamellar phase with a given quantity of lipid, interlamellar sorbitol and water, reduction of chemical potential of water is greater than that due to lipid acting alone plus that due to solute acting alone.
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(1997)Journal ArticleAcoustic resonances of the vocal tract give rise to formants (broad bands of acoustic power) in the speech signal when the vocal tract is excited by a periodic signal from the vocal folds. This paper reports a novel instrument which uses a real-time, non-invasive technique to measure these resonances accurately during phonation. A broadband acoustic current source is located just outside the mouth of the subject and the resulting acoustic pressure is measured near the lips. The contribution of the speech signal in the pressure spectrum is then digitally suppressed and the resonances are calculated from the input impedance of the vocal tract as a function of frequency. The external excitation signal has a much smaller harmonic spacing than the periodic signal from the vocal folds and consequently the resonances are determined much more accurately due to the closer sampling. This is particularly important for higher pitched voices and we demonstrate that this technique can be markedly superior to the curve-fitting technique of linear prediction. The superior frequency resolution of this instrument which results from external vocal tract excitation can provide the precise, stable, effective, articulatory feedback considered essential for some language-learning and speech therapy applications.
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(2008)Journal ArticleObjectives: This study assesses interest in genetic testing for gene variations associated with bipolar disorder and associated information needs. Methods: Two hundred individuals (95 unaffected and 105 affected with either bipolar disorder, schizoaffective disorder-manic type, or recurrent major depression) from families with multiple cases of bipolar disorder were assessed, using mailed, self-administered questionnaires. Results: The percentage of participants reporting interest in genetic testing was associated with the degree of certainty with which any test would indicate the development of bipolar disorder. Interest in genetic testing, given a 25% lifetime risk scenario, was lowest (with 77% of participants indicating interest), and highest for the 100% lifetime risk scenario (92%). Eighty percent of participants indicated interest in genetic testing of their own children; of these 30% reported wanting their children tested at birth, and 33% in early childhood. Forty-one percent of participants reported that they would be interested in preimplantation genetic diagnosis, and 54% in prenatal testing. Limitations: The possibility of ascertainment bias cannot be ruled out. Interest in hypothetical genetic testing for bipolar disorder may not necessarily translate into actual utilization. Conclusions: These results indicate that uptake of genetic testing for genotyping for low-risk alleles related to bipolar disorder is likely to be lower than for testing for high-penetrance gene mutations that follow Mendelian inheritance. The discrepancy between the desired age of testing children and the accepted current practice may be a source of distress and conflict for parents and health professionals alike.
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(1995)Journal ArticleThe scaling behaviour of vortex-glass superconductivity is studied, by measuring the resistive transition as well as the I-V curve under a variety of magnetic fields, in a series of V doped YBa2Cu307_y samples with different grain sizes. The equilibrium phase boundary line between the normal and superconducting phases in the H-T plane obtained by fitting the resistive transition is consistent with that obtained by the I-V curve measurements. As the magnetic field is lower than a certain value, Hs, the scaling exponents are magnetic-field independent, but at H = H s, they begin to increase with the magnetic field and gradually get saturation. The switch field, Hs, decreases with decreasing the grain size in the samples. The results show that the magnetic-field-dependent scaling behaviour of the I-V curve observed in weak-link containing systems originates from the transition of a "weak" vortex-glass state to a "strong" vortex-glass state.
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(1995)Journal ArticleTwo types of Bi-2212 single crystals, one type having a low T c and the other having a high T¢ were annealed in air at different temperatures over the range 450°C to 750°C followed by furnace cooling. The transition temperature of the crystals with low T c (~ 56 K) increased with increase of annealing temperature, while the crystals with high Tc (~ 91 K) had just the opposite behaviour under the same annealing conditions. It is indicated that the quality of as-grown crystal has a significant effect on the superconducting properties of the annealed crystal. The c-axis values for both types of crystals decreased with increase of annealing temperature. According to the relationship between c-axis values and the oxygen content, our results confirmed the existence of a dome-shaped curve of T¢ with carrier concentration in Bi-2212 single crystal similar to that in Bi-2212 compound reported previously by Groen and de Leeuw [Physica C 159 (1989) 417]. By studying the increase of annealing time at a fixed temperature of 650°C, T¢ and ATe were found to change very little for both types of crystals. Thus, T c and AT~ were more sensitive to annealing temperature than to annealing time. XRD, SEM and EDS revealed that a small quantity of powder phase appeared after annealing at temperatures above 500°C for both types of crystals. This powder phase had the Bi-2212 composition, which indicated that the integrity of the Bi-2212 single crystals was significantly degraded by the annealing process.