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Using spectroscopic ellipsometry, the temperature-dependence of the dielectric functions of a series of Hg1−xCdxSe thin films deposited on both ZnTe/Si(112) and GaSb(112) substrates were investigated. Initially, for each sample, room-temperature ellipsometric spectra were obtained from 35 meV to 6 eV using two different ellipsometers. Subsequently, ellipsometry spectra were obtained from 10 K to 300 K by incorporating a cryostat to the ellipsometer. Using a standard inversion technique, the spectroscopic ellipsometric data were modeled in order to obtain the temperature-dependent dielectric functions of each of the Hg1−xCdxSe thin films. The results indicate that the E1 critical point blue-shifts as a function of Cd-alloy concentration. The temperature-dependence of E1 was fitted to a Bose-Einstein occupation distribution function, which consequently allowed us to determine the electron-phonon coupling of Hg1−xCdxSe alloys. From the fitting results, we obtain a value of 17 ± 2 meV for the strength of the electron-phonon coupling for Hg1−xCdxSe alloy system, which compares nominally with the binary systems, such as CdSe and CdTe, which have values around 38 meV and 16 meV, respectively. This implies that the addition of Hg into the CdSe binary system does not significantly alter its electron-phonon coupling strength. Raman spectroscopy measurements performed on all the samples show the HgSe-like transverse optic (TO) and longitudinal optic (LO) phonons (∼ 130 cm−1 and ∼ 160 cm−1, respectively) for all the samples. While there is a slight red-shift of the HgSe-like TO peak as a function of the Cd-concentration, HgSe-like LO peak does not significantly change with the alloy concentration. [ABSTRACT FROM AUTHOR]

Iodine-doped CdTe and CdMgTe layers were grown by molecular beam epitaxy. Secondary ion mass spectrometry characterization was used to measure dopant concentration, while Hall measurement was used for determining carrier concentration. Photoluminescence intensity and time-resolved photoluminescence techniques were used for optical characterization. Maximum n-typ e carrier concentrations of 7.4 × 10 cm for CdTe and 3 × 10 cm for CdMgTe were achieved. Studies suggest that electrically active doping with iodine is limited with dopant concentration much above these values. Dopant activation of about 80% was observed in most of the CdTe samples. The estimated activation energy is about 6 meV for CdTe and the value for CdMgTe is about 58 meV. Iodine-doped samples exhibit long lifetimes with no evidence of photoluminescence degradation with doping as high as 2 × 10 cm, while indium shows substantial non-radiative recombination at carrier concentrations above 5 × 10 cm. Iodine was shown to be thermally stable in CdTe at temperatures up to 600°C. Results suggest iodine may be a preferred n-type dopant compared to indium in achieving heavily doped n-type CdTe. [ABSTRACT FROM AUTHOR]

The relationships between Mg composition, band gap, and lattice characteristics are investigated for CdMgTe barrier layers using a combination of cathodoluminescence, energy dispersive x-ray spectroscopy, variable angle spectral ellipsometry, and atom probe tomography. The use of a simplified, yet accurate, variable angle spectral ellipsometry analysis is shown to be appropriate for fast determination of composition in thin CdMgTe layers. The validity of using high-resolution x-ray diffraction for CdTe/CdMgTe double heterostructures is discussed. The stability of CdTe/CdMgTe heterostructures are investigated with respect to thermal processing. [ABSTRACT FROM AUTHOR]

Iodine-doped CdMgTe/CdSeTe double heterostructures (DHs) have been grown by molecular beam epitaxy and studied using time-resolved photoluminescence (PL), focusing on absorber layer thickness of 2 μm. The n-type free carrier concentration was varied to ∼7 × 10 cm, 8.4 × 10 cm, and 8.4 × 10 cm using iodine as dopant in DHs. Optical injection at 1 × 10 photons/pulse/cm to 3 × 10 photons/pulse/cm, corresponding to initial injection of photocarriers up to ∼8 × 10 cm, was applied to examine the effects of excess carrier concentration on the PL lifetimes. Iodine-doped DHs exhibited an initial rapid decay followed by a slower decay at free carrier concentration of 7 × 10 cm and 8.4 × 10 cm. The optical injection dependence of the carrier lifetimes for DHs was interpreted based on the Shockley-Read-Hall model. The observed decrease in lifetime with increasing n is consistent with growing importance of radiative recombination. [ABSTRACT FROM AUTHOR]

A four compartment model of the cardiovascular system is developed. To allow for easy interpretation and to minimise the number of parameters, an effort was made to keep the model as simple as possible. Using a standard method (Matlab function fminsearch) to calculate the parameter values led to unacceptable run times or non-convergence. Consequently we developed an algorithm which first finds the most important model parameters and uses these as a basis for a four stage process which accurately determines all parameter values. This process is then applied to data from three ICU patients. Good agreement between the model and measured arterial pressure is demonstrated in all cases. [ABSTRACT FROM AUTHOR]

In this paper, we study the melting of a spherical nanoparticle. The model differs from previous ones in that a number of features have been incorporated to match experimental observations. These include the size dependence of the latent heat and a cooling condition at the boundary (as opposed to the fixed temperature condition used in previous studies). Melt temperature variation and density change are also included. The density variation drives the flow of the outer fluid layer. The latent heat variation is modelled by a new relation, which matches experimental data better than previous models. A novel form of Stefan condition is used to determine the position of the melt front. This condition takes into account the latent heat variation, the energy required to create new surface and the kinetic energy of the displaced fluid layer. Results show that melting times can be significantly faster than predicted by previous theoretical models; for smaller particles, this can be around a factor 3. This is primarily due to the latent heat variation. The previously used fixed temperature boundary condition had two opposing effects on melt times: the implied infinite heat transfer led to faster melting but also artificially magnified the effect of kinetic energy, which slowed down the process. We conclude that any future models of nanoparticle melting must be based on the new Stefan condition and account for latent heat variation. [ABSTRACT FROM AUTHOR]

The melting process of a spherical nanoparticle is analysed using a mathematical model derived from continuum theory. The standard model for macro-scale melting is modified to include melting point depression using the Gibbs-Thomson equation. The key difference between the current and previous work in the melting of nanoparticles is that the difference in densities between the solid and liquid phases is accounted for. This modifies the energy balance at the phase change interface to include a kinetic energy term, which then changes the form of the equation, and it also requires an advection term in the heat equation for the liquid phase. Approximate analytical and numerical solutions are presented for the melting of particles in the range 10-100 nm. It is shown that when the density difference is included in the model, melting is significantly slower than when density is assumed constant throughout the process. This is attributed to the flowing liquid providing a sink term, namely kinetic energy, in the energy balance. The difference in results is greatest for small particles; however, it is concluded that the varying density model will never reduce to the constant density model resulting in a difference of around 15 % even at the macro-scale. [ABSTRACT FROM AUTHOR]

A theoretical model for nanofluid flow, including Brownian motion and thermophoresis, is developed and analysed. Standard boundary layer theory is used to evaluate the heat transfer coefficient near a flat surface. The model is almost identical to previous models for nanofluid flow which have predicted an increase in the heat transfer with increasing particle concentration. In contrast our work shows a marked decrease indicating that under the assumptions of the model (and similar ones) nanofluids do not enhance heat transfer. It is proposed that the discrepancy between our results and previous ones is due to a loose definition of the heat transfer coefficient and various ad hoc assumptions. [ABSTRACT FROM AUTHOR]

In this paper, we analyse the melting of a spherically symmetric nanoparticle, using a continuum model which is valid down to a few nanometres. Melting point depression is accounted for by a generalised Gibbs–Thomson relation. The system of governing equations involves heat equations in the liquid and solid, a Stefan condition to determine the position of the melt boundary and the Gibbs-Thomson equation. This system is simplified systematically to a pair of first-order ordinary differential equations. Comparison with the solution of the full system shows excellent agreement. The reduced system highlights the effects that dominate the melting process and specifically that rapid melting is expected in the final stages, as the radius tends to zero. The results agree qualitatively with limited available experimental data. [ABSTRACT FROM AUTHOR]

Cross-section electron micrographs, cathodoluminescence images, and confocal photoluminescence (cPL) images have been acquired for ZnTe layers deposited to various thicknesses on GaSb substrates with (211)B and (100) orientations. The critical thickness of ZnTe on GaSb is predicted to range between 115 nm and 329 nm, depending on the theoretical approach chosen. For ZnTe layers grown on (211)B GaSb with thickness exceeding 150 nm, dark spots and lines are present in all images. We associate these with dislocations generated at the ZnTe/GaSb interface. The discrepancy between this thickness value and a critical thickness value (350 nm to 375 nm) obtained for the (211)B orientation in a previous study is related to the distinction between the onset of misfit dislocations and the onset of significant plastic deformation. The former requires a direct imaging technique, as strain-related measurements such as x-ray diffraction do not have the resolution to detect the effects of small numbers of dislocations. For ZnTe layers on (100) GaSb, x-ray diffraction measurements indicate an abrupt change characteristic of dislocation multiplication at a thickness value in the range from 250 nm to 275 nm. High-resolution electron micrographs of the ZnTe/GaSb interface indicate that deoxidation using atomic hydrogen produces GaSb surfaces suitable for ZnTe epitaxy. cPL images of a 1.2- μm-thick lattice-matched ZnTeSe layer grown on a 150-nm-thick ZnTe buffer layer on a (211)B GaSb substrate yield a threading dislocation density of ∼7 × 10 cm. [ABSTRACT FROM AUTHOR]

In this paper, we analyse the time-dependent heat equations over a finite domain to determine expressions for the thermal diffusivity and conductivity of a nanofluid (where a nanofluid is a fluid containing nanoparticles with average size below 100 nm). Due to the complexity of the standard mathematical analysis of this problem, we employ a well-known approximate solution technique known as the heat balance integral method. This allows us to derive simple analytical expressions for the thermal properties, which appear to depend primarily on the volume fraction and liquid properties. The model is shown to compare well with experimental data taken from the literature even up to relatively high concentrations and predicts significantly higher values than the Maxwell model for volume fractions approximately >1 %. The results suggest that the difficulty in reproducing the high values of conductivity observed experimentally may stem from the use of a static heat flow model applied over an infinite domain rather than applying a dynamic model over a finite domain. [ABSTRACT FROM AUTHOR]

In this paper, an analytical and numerical study of the three-dimensional equations describing the motion through the air of a spinning ball is presented. The initial analysis involves constant drag coefficients, but is later extended to involve drag varying with the spin ratio. Excellent agreement is demonstrated between numerical, analytical and experimental results. The analytical solution shows explicitly how the ball's motion depends on parameters such as ball roughness, velocity and atmospheric conditions. The importance of applying three-dimensional models, rather than two-dimensional approximations, is demonstrated. [ABSTRACT FROM AUTHOR]

A mathematical model is developed to analyse the combined flow and solidification of a liquid in a small pipe or two-dimensional channel. In either case, the problem reduces to solving a single equation for the position of the solidification front. Results show that for a large range of flow rates the closure time is approximately constant, and the value depends primarily on the wall temperature and channel width. However, the solid shape at closure will be very different for low and high fluxes. As the flow rate increases the closure time starts to depend on the flow rate until the closure time increases dramatically, subsequently the pipe will never close. [ABSTRACT FROM AUTHOR]

There remains considerable interest in the behavior of acceptors in ZnO, the ultimate goal being the realization of device grade p-type material. Silver is a candidate acceptor, and, in this study, in situ doping of silver was performed during plasma-assisted molecular beam epitaxy. Silver concentrations, as determined by ion beam analysis, ranged between 1018 cm−3and 1020 cm−3, with as much as 94% incorporated substitutionally on Zn lattice sites. Variable magnetic field Hall effect measurements detected no evidence of holes, and 4 K photoluminescence was dominated by donor bound excitons. Transient capacitance measurements, however, suggested that incorporated silver had led to the formation of an acceptor, located approximately 320 meV above the valence band edge, indicating that compensation remains a significant issue in determining the conductivity of ZnO. [ABSTRACT FROM AUTHOR]

In-situ cathodoluminescence (CL) measurement during growth of gallium nitride (GaN) by molecular beam epitaxy (MBE) was investigated for determining substrate temperature. Cathodoluminescence was easily observed from room temperature up to and beyond typical temperatures used during growth. Determination of the peak energy of the CL spectrum allows unambiguous determination of the substrate temperature. Temperature drift and reproducibility issues during growth of GaN were observed using the in-situ CL measurement. [ABSTRACT FROM AUTHOR]

We calculate the radiative, Auger, and the Shockley-Read-Hall recombination rates with Fermi-Dirac statistics and accurate band structures to explain the measured temperature dependence and doping dependence of minority carrier lifetimes in three n- and one p-type sample. We show that a trap state tracking the conduction band edge with very small activation energy can explain the lifetimes in the n-doped samples considered here. Similarly, for moderately p-doped HgCdTe alloy, a trap level at 75 meV is needed to explain the observed lifetimes. In either case, movement of Fermi level with respect to the trap level explains the temperature dependence of the lifetimes. [ABSTRACT FROM AUTHOR]

We have initiated a joint effort to better elucidate the fundamental mechanisms underlying As-doping in molecular beam epitaxy (MBE)-grown HgCdTe. We have greatly increased the As incorporation rate by using an As cracker cell. With a cracker temperature of 700°C, As incorporation as high as 4 x 1020 cm-3 has been achieved by using an As-reservoir temperature of only 175°C. This allows the growth of highly doped layers with high quality as measured by low dislocation density. Annealing experiments show higher As-activation efficiency with higher anneal temperatures for longer time and higher Hg overpressures. Data are presented for layers with a wide range of doping levels and for layer composition from 0.2 to 0.6. [ABSTRACT FROM AUTHOR]

Variable magnetic-field Hall and transient photoconductance-lifetime measurements were performed on a series of undoped, In-doped, and As-doped HgCdTe samples grown by molecular beam epitaxy (MBE). Use of quantitative mobility-spectrum analysis (QMSA) combined with multiple carrier-fitting (MCF) techniques indicates that the majority of samples contain an interfacial n-type layer that significantly influences the interpretation of the electrical measurements. This n-type layer completely masks the high-quality electrical properties of undoped or low n-type In-doped HgCdTe, as well as complicating the interpretation of activation in As-doped p-type HgCdTe. Introduction of an intentional n-type background, typically created through doping with In to "recover" high mobility, is actually shown to increase the "bulk" layer conductivity to a level comparable to the interface layer conductivity. Photoconductance-lifetime measurements suggest that In-doping may introduce Shockley-Read-Hall (SRH) recombination centers. Variable-field Hall analysis is shown to be essential for characterizing p-type material. Photoconductance-lifetime measurements suggest that trapping states may be introduced during the incorporation and activation of As. Two distinctly different types of temperature dependencies were observed for the lifetimes of As-doped samples. [ABSTRACT FROM AUTHOR]

Variable magnetic-field Hall-effect measurements were performed on two thick GaN samples grown by hydride vapor-phase epitaxy (HVPE), one freestanding and one attached to the sapphire substrate. Results are compared to those obtained using the more standard, single magnetic-field Hall measurements. In both samples, a second low-mobility electron was indicated that significantly influenced interpretation of single-field Hall measurements, particularly at low temperatures. Extraction of the bulk carrier using fits to the variable-field Hall data allowed a more accurate determination of the temperature dependence of the bulk electrical properties and, hence, basic physical parameters. In addition, the quantitative mobility-spectrum analysis (QMSA) technique, reported here for the first time on GaN, indicated a continuous and significant spread in mobility for the bulk electron, likely with sample thickness. Thus, even the "improved" results, based on modeling the multiple-carrier fitting (MCF) analysis, obtained in this study should be viewed with some suspicion, as they clearly represent an average over an electrically inhomogeneous sample. [ABSTRACT FROM AUTHOR]

Background: There are an estimated 40,000 to 90,000 injection opiate users in Canada. The social, economic and health consequences of opiate addiction have been well documented. However, there are no data on the self-perceived health status of opiate users in Canada. Therefore, the goal of this research is to gain an understanding of the self-perceived health status of opiate users by comparing the health-related quality of life of opiate users to chronic disease populations and to the general population.Methods: The SF-36 was administered to a nonrandom sample of 143 opiate users entering low-threshold methadone treatment. Two sample t-tests were performed to assess statistical differences, at a 5% level of significance, between population scores across SF-36 dimensions.Results: Opiate users perceived both their mental and physical health as worse than the general population and individuals with minor and serious medical problems, but comparable to those with diagnosed psychiatric illnesses.Conclusions: Methadone treatment services should incorporate both primary care and psychiatric care into their programs, or at the very least secure appropriate referral mechanisms to ancillary services to ensure that the health concerns of opiate users are dealt with in the context of their treatment program. [ABSTRACT FROM AUTHOR]

Epitaxial ZnSe layers were grown by molecular beam epitaxy (MBE) to study Cr incorporation with the long-term goal of demonstrating an alternate route for achieving transition-metal-doped lasers. Concentrations between 1015 atoms cm−3 and 4×1020 atoms cm−3 were achieved. Secondary ion-mass spectroscopy (SIMS) concentration profiles strongly suggest that surface segregation and accumulation of Cr occurs during growth. Photoluminescence (PL) measurements indicate Cr is incorporated in the optically active Cr2+ state up to levels of ∼1019 cm−3. Electron paramagnetic resonance (EPR) studies suggest that the Cr atoms exhibit collective magnetic behavior even at these levels. X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED) indicate high structural quality is maintained for Cr incorporation for levels up to ∼1019 atoms cm−3. [ABSTRACT FROM AUTHOR]

Electron irradiation during reflection high-energy electron diffraction is shown to affect the growth of ZnSe and ZnMgSe by molecular beam epitaxy. The high-energy electrons produce an electron stimulated desorption effect during growth of ZnSe which primarily affects adsorbed Se. Se desorption rates under electron irradiation are shown to be significantly larger than thermal desorption rates. Electron irradiation also decreases ZnSe growth rates under Zn-rich conditions. The decrease in growth rate can be suppressed by either growth under Se-rich conditions or by using high-index substrate orientations, in this case (211)B. High-energy electron irradiation does not alter composition during the growth of ZnMgSe. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy has been used to study the low-temperature (<80°C) preparation of HgCdTe surfaces with atomic hydrogen for the purpose of CdTe passivation. Atomic hydrogen was used to etch overlayers and surfaces of liquid phase epitaxy and molecular beam epitaxy HgCdTe, CdTe, HgTe, and Te. Oxide layers were easily removed, while carbon overlayers were resistant to atomic hydrogen etching at low temperature. Both Te and HgTe are etched by atomic hydrogen, with the HgTe etch rate about twice that of Te, while CdTe and ZnTe are not etched. Chemi-mechanical polishing of liquid phase epitaxy HgCdTe left a 10 to 20Å Te overlayer that could be removed with atomic hydrogen. In all cases, exposure of HgCdTe to atomic hydrogen led to surface composition shifts to higher x-value, with an x-value plateau near x∼0.6. All observations could be explained in terms of the formation of a 15Å surface layer of CdTe which blocks further etching. [ABSTRACT FROM AUTHOR]

Atomic hydrogen is shown to be particularly efficacious for the preparation of substrates for subsequent growth of II-VI compounds by molecular beam epitaxy. A commercial thermal cracker was used to produce atomic hydrogen in the molecular beam epitaxy growth chamber for in-situ cleaning. This paper discusses the use of atomic hydrogen for both oxide removal from GaAs prior to ZnSe and CdTe growth, and for low-temperature oxide removal from CdTe and HgCdTe. Reflection high energy electron diffraction, ultra violet fluorescence microscopy, Nomarski interference contrast microscopy, and atomic force microscopy were used to characterize the growths. [ABSTRACT FROM AUTHOR]

We show that variations of the E1 reflectance peak in Hg-based superlattices can be used to probe low-temperature interdiffusion by monitoring the shift of the E1 peak with time over extended periods. Little evidence of interdiffusion was detected for a number of HgTe/CdTe and HgCdTe/CdTe superlattices stored at room temperature for approximately two years. Two HgTe/CdTe superlattices and one HgCdTe/CdTe superlattice were subsequently annealed in a dry nitrogen atmosphere at 100°C for approximately six months, and then at 150°C for 24 days. During these intervals, the superlattices were periodically removed from the anneal for reflectance measurements to assess the extent of the interdiffusion. Comparison of these results with calculations of superlattice bandgaps and interdiffusion profiles has led to an evaluation of the low temperature interdiffusion coefficients. These extend previous results to lower temperatures and confirm that the degradation of Hg-based superlattices devices due to thermal interdiffusion under normal processing, storage, and operating conditions should not be an issue of concern. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) studies of nitrogen doped ZnSe epilayers grown by molecular beam epitaxy have been performed as a function of excitation wavelength, power density, and temperature. The broad emission from heavily doped ZnSe:N is composed of two distinct bands which we label as NI and NII. The dominant band NI appears at 2.54 eV, while the NII band position is sensitive to excitation power and occurs between 2.55 and 2.61 eV. The NI emission energy is insensitive to incident power or temperature over the ranges studied. Further, a 69 meV localized phonon of the NI band is observed. We propose that the NI band is related to transitions within a (Vse+-Zn-Nse-)0 close-associate pair. The NII band displays characteristics consistent with the conventional donor acceptor pair model. A third band NIII at 2.65 eV is observed under high-power pulsed excitation. Previous studies of heavily doped ZnSe:N had suggested that the broad emission band was described by a modified donor-acceptor pair model. Our PL study does not support this previous model. In addition, our data suggests that singly ionized selenium vacancy complexes form in heavily doped ZnSe:N and play a role in compensation. [ABSTRACT FROM AUTHOR]

Nitrogen doping in CdTe epilayers grown by photo-assisted molecular beam epitaxy was demonstrated using an rf plasma source. The effect of the presence of atomic hydrogen during growth of undoped and nitrogen-doped CdTe was investigated. The layers were characterized using photoluminescence spectros-copy (PL), Hall effect, secondary ion mass spectroscopy (SIMS), Fourier transform infrared spectroscopy, and atomic force microscopy. PL confirmed the incorporation of nitrogen as acceptors. While p-type carrier concentrations greater than 10 cm were easily obtained, SIMS measurements indicated that nitrogen was concentrated near the undoped-doped and epilayer-substrate interfaces which complicates interpretation of activation efficiency. Hydrogen incorporation was found to be enhanced by the presence of nitrogen. Infrared absorption measurements strongly suggested the formation of N-H complexes. Hall measurements indicated that complexes are formed which are donor-like in nature. The presence of atomic hydrogen during growth radically changed the low temperature photoluminescence in both undoped and nitrogen-doped layers. Exciton-related luminescence was quenched at low temperature. Nitrogenrelated donor-acceptor pair luminescence was also absent from the N-doped hydrogenated layers, consistent with complex formation. Copper (a cation-site acceptor) donor-acceptor pair luminescence appeared to be enhanced by hydrogenation. [ABSTRACT FROM AUTHOR]

In order to form HgTe-CdTe superlattice diode arrays, a well-controlled etch process must be developed to form mesa structures on HgTe-CdTe superlattice layers. Wet etch processes result in nonuniform, isotropic etch profiles, making it difficult to control etch depth and diode size. In addition, surface films such as a Te-rich layer may result after wet etching, degrading diode performance. Recently, a dry etch process for HgTe-CdTe superlattice materials has been developed at Martin Marietta using an electron cyclotron resonance plasma reactor to form mesa diode structures. This process results in uniform, anisotropic etch characteristics, and therefore may be a better choice for etching superlattice materials than standard wet etch processes. In this paper, we will present a comparison of etch processes for HgTe-CdTe superlattice materials using electron microscopy, scanning tunneling microscopy, surface profilometry, and infrared photoluminescence spectroscopy to characterize both wet and dry etch processes. [ABSTRACT FROM AUTHOR]

Epitaxial growth of Hg-based semiconductors by molecular beam epitaxy (MBE) and metalorganic MBE (MOMBE) has progressed sufficiently to shift emphasis to the control of factors limiting the yield of both materials and devices. This paper reports on an ex-situ study to evaluate the suitability of reflectance and photoreflectance (PR) as in-situ characterization techniques for the growth of CdTe and HgCdTe. Photoreflectance yields information about CdTe layers, with largest utility for doped and multi-layer structures. However, caution must be taken in interpretation of the spectra since the near-bandedge PR spectra consists of multiple transitions and the E transition energy is very sensitive to the sample history. Photoreflectance appears to be of limited utility for HgCdTe single layer growth with x<0.4. However, reflectance measurements of the E peak can be used to determine composition in HgCdTe single layers with an accuracy Δx = ±0.01, which can be useful for growth control. A tight binding model was used to calculate the E peak energy as a function of bandgap for HgCdTe and HgTe/CdTe superlattices. Comparisons are made with experimental observations. Surface interdiffusion in HgTe-CdTe superlattices was probed using reflectance measurements. [ABSTRACT FROM AUTHOR]

A comprehensive study of the properties of undoped and iodine-doped CdTe structures by photoluminescence (PL) and photoreflectance (PR) is reported. Undoped bulk CdTe and iodine-doped CdTe layers grown by metalorganic molecular beam epitaxy on (lOO)-oriented CdTe and (211)B-oriented GaAs substrates with electron concentrations ranging from 10 to mid-10 cm were included in this study. Lineshape modeling of 80KPL and PR spectra indicated the presence of both free exciton and donor-hole transitions at the higher doping levels. Strong PL and PR signals were also observed at room temperature. If only a single transition is considered for the analysis of the 300K spectra, the PL emission peak and the PR transition energy both exhibit a strong dependence on electron concentration for doped layers. However, lineshape modeling of the room-temperature spectra indicated the presence of multiple transitions consisting of free exciton and direct band-to-band transitions. The use of two transitions resulted in a constant value of bandgap over the entire range of conductivities studied. A strong correlation remained between the broadening of the PR and PL spectra and excess carrier concentration N-N. In addition, the E transition energy measured by PR was found to vary dramatically with growth conditions. [ABSTRACT FROM AUTHOR]

In this paper the effects of changing the ion concentration in and around a sample of soft tissue are investigated. The triphasic theory developed by Lai et al. (1990, Biomechanics of Diarthrodial Joints, Vol. 1, Berlin, Springer-Verlag) is reduced to two coupled partial differential equations involving fluid ion concentration and tissue solid deformation. These equations are given in general form for Cartesian, cylindrical and spherical geometries. After solving the two equations quantities such as fluid velocity, fluid pressure, chemical potentials and chemical expansion stress may be easily calculated. In the Cartesian geometry comparison is made with the experimental and theoretical work of Myers et al. (1984, ASME J. biomech. Engng, 106, 151-158). This dealt with changing the ion concentration of a salt shower on a strip of bovine articular cartilage. Results were obtained in both free swelling and isometric tension states, using an empirical formula to acount for ion induced deformation. The present theory predicts lower ion concentrations inside the tissue than this earlier work. A spherical sample of tissue subjected to a change in salt bath ion concentration is also considered. Numerical results are obtained for both hypertonic and hypotonic bathing solutions. Of particular interest is the finding that tissue may contract internally before reaching a final swollen equilibrium state or swell internally before finally contracting. By considering the relative magnitude, and also variation throughout the time course of terms in the governing equations, an even simpler system is deduced. As well as being linear the concentration equation in the new system is uncoupled. Results obtained from the linear system compare well with those from the spherical section. Thus, biological swelling situations may be modelled by a simple system of equations with the possibility, of approximate analytic solutions in certain cases. [ABSTRACT FROM AUTHOR]

Avian rotavirus isolates were used to infect normal chicken spleen cells, lymphoblastoid T cell lines transformed by Marke's disease virus, an avian leukosis virus-transformed B cell line, and a reticuloendotheliosis virus-transformed line, which is a pre-B, pre-T cell line. All five isolates tested were able to infect spleen cells and the three types of lymphoblastoid cell lines, suggesting that avian rotaviruses can infect both B and T cells. Splenic lymphocytes were considerably less susceptible to infection than chick kidney cells. Lymphoblastoid cell lines remained virus-positive during a 10-day culture period. Virus was neutralized by the addition of low dilutions of normal chicken serum and high dilutions of chicken anti-rotavirus serum. [ABSTRACT FROM AUTHOR]

Two material properties important to the application of HgTe/CdTe superlattices for device fabrication are band gap uniformity and thermal stability. In this paper, we present the results of an infrared photoluminescence study of (211)B HgTe/CdTe superlattices grown by photon-assisted molecular beam epitaxy which show that cut-off wavelength uniformity can be controlled to a level commensurate with the demands of advanced infrared detector fabrication. Infrared photoluminescence and transmission electron microscopy were also employed to demonstrate that (211)B HgTe/CdTe superlattices are less prone to interdiffusion than previously believed. [ABSTRACT FROM AUTHOR]

P nuclear magnetic resonance spectroscopy (NMRS) measurements were made on human T2 and T3 vertebral bodies. The bone mineral content (BMC) of isolated vertebral bodies minus the posterior elements and disks was measured using (1) NMRS on a 3.5 T, 85 mm bore GE Medical Systems NT-150 superconducting spectrometer, (2) a Lunar Corporation DPX-L dual-energy X-ray absorptiometry (DXA) scanner in an anterior-posterior (AP) orientation, (3) a Norland Corporation XR26 DXA scanner, also in an AP direction, and (4) a Norland Corporation model 2600 dual-photon absorptiometry (DPA) densitometer in both the AP and superior-inferior (SI) directions. Vertebral body volumes were measured using a water displacement technique to determine volume bone mineral densities (VBMD). They were then compressed to failure using an electrohydraulic testing device, followed by ashing in a muffle furnace at 700 °C for 18 h. Correlations of BMC between NMRS and DPA, DXA and ashing were excellent (0.96⩽ r⩽0.99); in a one-way analysis of variance (ANOVA) test, means were not statistically different at a p level of 0.757. The correlations of VBMD between NMRS and the other methods were not as good (0.83⩽ r⩽0.95); in a one-way ANOVA test, means were not statistically different at a p level of 0.089. BMC was a better predictor of ultimate compressive failure than VBMD for all six methods. For NMRS, the regression coefficient for BMC was r=0.806, compared with r=0.505 for VBMD. NMRS may prove an alternative to present methods of determing bone mineral. [ABSTRACT FROM AUTHOR]

The algal flora was sampled in 15 intertidal rock pools, selected for habitat uniformity within a limited area. The distribution of species agreed closely with that expected at random, whether examined by the distribution of associations, by nesting, by chequerboarding or by incidence functions. The simplest explanation is that differences in specific composition between the pools are caused by chance. [ABSTRACT FROM AUTHOR]

Variable magnetic field Hall and transient photoconductance lifetime measurements were performed on a series of undoped, In-doped, and As-doped HgCdTe samples grown by molecular beam epitaxy and metalorganic chemical vapor deposition. Temperature variation and, in the case of Hall, magnetic-field variation are needed to give a more complete picture of the mechanisms that control lifetimes in HgCdTe samples. Recent predictions of recombination lifetimes from full band structure calculations were compared to experimental lifetimes at various doping levels at long-wave infrared (LWIR) and mid-wave infrared (MWIR) compositions. For n-type material, lifetimes from low doping levels fall well below the predictions, implying that Shockley-Read-Hall (SRH) recombination is still dominant. MWIR samples have a lifetime that increases somewhat with carrier concentration, suggesting that In doping passivates the SRH defects for that composition. Lifetimes in p-type MWIR material appear to be well-explained by recent theoretical calculations. In p-type material, trapping states may be introduced during the incorporation and activation of As, since some samples with unusually long lifetimes had a distinctly different type of temperature dependence. [ABSTRACT FROM AUTHOR]

The dependence of characteristics of plasma-assisted molecular beam epitaxy-grown ZnO thin films on different postgrowth annealing conditions was investigated. It was found that, under oxygen atmosphere, annealing temperature can profoundly affect the morphological, electrical, and optical properties of ZnO thin films. In particular, the surface morphology changed from a relatively smooth surface before annealing to various island morphologies after annealing above 800° C for samples grown directly on sapphire without a buffer layer. It is speculated that intrinsic stress due to lattice mismatch drives the island formation and the high temperature provides the energy needed for this surface rearrangement. Single-field Hall-effect measurement showed that the carrier concentration improved by an order of magnitude and the mobility increased from about 30 cm²/Vs to ∼ 70 cm² /Vs by annealing at 750°C. Variable-field Hall effect shows that a model with two carriers, one a degenerate low-mobility electron and the other a higher mobility non-degenerate electron, is needed to explain the transport properties of the thin film. Analysis indicates that annealing at 750°C decreased the carrier concentration and increased the mobility for the high-mobility carrier. Annealing also led to a significant improvement in photoluminescence, with temperatures of ∼ 750-850°C yielding the best results. [ABSTRACT FROM AUTHOR]

Objectives: To measure HIV prevalence, risk behaviours, and further service needs in needle exchange programs throughout Ontario, and to conduct regional comparisons., Methods: Injection drug users (IDU) recruited through the efforts of needle exchange programme (NEP) staff in 9 Ontario cities during 1997-98 completed questionnaires about their drug use and behaviours and provided saliva and/or dried blood samples for anonymous unlinked HIV testing., Results: Demographic and drug use characteristics of participants showed great regional variation. HIV prevalence by region ranged from 1.4% to 14.7%. In addition to region, HIV positivity was associated with injecting for more than 5 years, use of (powder) cocaine, use of crack, binge injection (10 or more times per day at least once in the previous 6 months), and being a longer-term NEP user. Sharing of injection equipment, and especially of other drug injection materials such as water and cookers, remain important issues, although much of the sharing reported is with only one other person. Unmet demand for methadone treatment was identified despite changes in regulation of methadone provision designed to make it more accessible., Conclusions: This study suggested significant further HIV prevention needs among IDU throughout Ontario. There is also evidence of potential to provide additional services such as methadone at NEPs if the required resources are invested. NEPs that have succeeded in gaining the trust of high-risk IDU offer a means to provide access to needed services.

Objective: Examine the challenges of four service delivery models (i.e., fixed, mobile, satellite and home visits) and how service delivery may impact on NEP HIV prevention efforts., Methods: Using a modified ethnographic approach, semi-structured interviews concerning policies and procedures were conducted with staff (n = 59) of NEPs (n = 15) in Ontario. An iterative, inductive analytic process was used., Results: According to workers and managers, effectiveness of NEP prevention efforts depend on client development and retention and service design. Fixed and satellite sites, home visits and mobile services provide varied levels of temporal and spatial accessibility. Combining modes of delivery can offset the disadvantages of individual modes., Discussion: NEP evaluations that do not consider service and resource factors run the risk of concluding that NEPs are ineffective when it may be that the program works for a small proportion of IDUs whom the NEP has the resources to serve.

Objective: To examine the contribution of patterns of sexual partnering to the spread of HIV/STD infection between communities., Methods: 651 randomly selected Aboriginals from 11 reserve communities in Ontario were interviewed. This analysis included those who had sex in the previous 12 months. Descriptive statistics and multivariate analyses identified associations with patterns of sexual partnering., Results: 22% reported having partners from both within and outside the community, 51% from within only, and 27% from outside only. Those with partners from both within and outside were more likely to be male, unmarried, from a remote community, have more sexual partners and perceive that their behaviour placed them at higher risk of HIV/STD infection. They were least likely to perceive their community to be at risk from their behaviour., Conclusions: Findings suggest that Aboriginal communities are not insulated and that HIV could spread rapidly if introduced.

Purpose: To explore group variations in sexual risk-taking among different sexual orientations of men who have sex with men (MSM)., Method: A convenience sample of men was recruited in gay-identified venues. An analysis was conducted to determine the independence of sexual orientation (gay, gay-previously heterosexual, currently bisexual), age and risk-taking., Results: Bisexual men were younger, lived outside metropolitan areas and socialized more in bathhouses. In general, bisexuals reported the safest sexual practices and previously heterosexual men the most unprotected., Conclusions: Among MSM, variation in sexual orientations was associated with differences in unprotected sex for older age groups. For the youngest age group, a similar level of risk-taking of the different orientation groups suggests uniform sociocultural influences.

During 1989-90, interviews were conducted with 582 current injection drug users in the City of Toronto, 535 of whom also provided blood and/or saliva for anonymous unlinked HIV antibody testing. The rate of seropositivity identified was 4.3% (95% CI 3-6). The subjects were predominantly male, with a mean age of 28.3. The commonest drug of choice was cocaine (70%). Forty-six percent of the subjects reported using someone else's needle in the preceding six months, 60% of these indicating that they always cleaned it first. Eighty-one percent of those interviewed had been in jail at some time since they began injecting; 25% of these had injected while in custody, and of these 61% had shared injection equipment. Eighty-two percent of the men and 85.4% of the women reported opposite sex partners in the previous six months. Only about 20% of men reported consistent condom use, while 22% of females reported condom use at least 75% of the time.

Objective: This paper presents a preliminary analysis of the determinants of selected behavioural predispositions toward HIV prevention among injection drug users., Method: An exploratory factor analysis was used to group attitudinal, behavioural intention and change statements into five predisposing factors and the correlates with these were examined using general linear regression., Results: The analysis demonstrates that many IDUs have responded to AIDS and highlights the characteristics of those who are predisposed to unsafe practices. Predispositions toward safer sex appear to be contextually determined, and needle-sharing determined by socio-behavioural history., Conclusions: The data emphasize the need for prevention programs in educational and correctional systems along with community-wide harm reduction and HIV prevention strategies, especially for younger persons. For older drug users, there may be a need for more intensive rehabilitation programs. Some evidence suggest that greater attention be given to the type of drug dependence when focusing programs.

Introduction: This paper analyzes differences between heterosexual male and female college students' behaviour, attitudes and knowledge about condom use., Method: A convenience sample of 707 students were recruited at sexual health displays to complete an anonymous questionnaire., Results: Based on reported sexual partners in the previous year, 486 students (51.2% male and 48.8% female) were classified as heterosexual. No significant differences were found between the sexes in reported risk behaviour. Females reported more appropriate condom use techniques than males, and more positive attitudes toward condoms. Males rated sexual enjoyment to be more important. A greater proportion of males than females gave reasons for not using condoms., Conclusion: Differences between male and female attitudes and behaviour are important to address in AIDS prevention. Along with an emphasis on the improvement of condom use techniques, it is critical to focus on gender issues of assertiveness, power and trust.

The Talking Sex Project is an HIV risk reduction education project for gay and bisexual men. It was developed to evaluate two types of small discussion groups using a randomized control study design. This paper reports on the baseline measures of knowledge, attitudes and sexual practices. The 612 subjects had a mean age of 32 years, were all English speaking and were relatively highly educated. Bivariate analyses found that younger men, those in a relationship, those reporting bisexual activity and those with higher levels of substance use were significantly more likely to have unprotected anal intercourse. While overall knowledge was not associated with sexual behaviour, a significant relationship was found with knowledge of risk of anal sex. Attitudes, in particular, the belief in the efficacy of condoms and the enjoyment of safer sex were found to have the strongest associations with protected anal intercourse. The paper provides an understanding of some of the factors which may be important to behaviour change and clues for the targeting of programs.