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Zinc oxide thin films have been grown via metalorganic vapor phase epitaxy at 450°C and 250 Torr total pressure on O-terminated areas and micro-regions of native oxide formed on GaN(0 0 0 1) epilayers during exposure to the oxygen reactant. Analyses of the Ga3d core level spectra acquired from films grown for progressively longer times and comparisons of these data with both thermodynamic models of growth processes and associated atomic force micrographs revealed that the ZnO nucleated and grew via the Stranski–Krastanov mode. Considerations of (1) differences in surface energetics of the polar (0 0 0 1) surfaces of ZnO and GaN and that of the Ga-based oxide as well as (2) the relatively low stress generated by the moderate lattice mismatches in the a -axis lattice parameters of these compounds supported the observed growth mode. The shifts in the position of the Ga3d core level with increasing deposition time and decreasing peak intensity were caused by surface charging and increasing sampling volumes of the Ga-based oxide as well as the growing ZnO layer. The island/ocean morphology of the Ga-based oxide controlled the morphology of the initial ZnO layer, which, in turn controlled the locations and the morphologies of the subsequently nucleated ZnO islands. Scanning electron microscopy of thicker ZnO films revealed a highly textured microstructure.

Background. As the incidences of type 2 diabetes (non-insulin dependent diabetes mellitus; NIDDM) and associated nephropathy increase worldwide at epidemic rates, the occurrence of serious renal outcomes such as end-stage renal disease has become a critical burden to patients and health care systems. Methods. The Irbesartan Diabetic Nephropathy Trial (IDNT), Reduction of Endpoints in NIDDM with the Angiotensin II Antagonist Losartan (RENAAL), and Losartan Intervention For Endpoint reduction in hypertension (LIFE) trials are reviewed. Results. In the IDNT trial, treatment with irbesartan significantly reduced the composite primary endpoint [doubling of serum creatinine (SCr), end-stage renal disease (ESRD; dialysis, transplantation, or SCr ≥ 6 mg/dl), or death] by 20% compared with placebo (P = 0.02), and by 23% compared with amlodipine (P = 0.006). In the RENAAL study, treatment with losartan resulted in a significant risk reduction of 16% in the primary composite endpoint [doubling of SCr, ESRD (dialysis or transplantation), or death]; P = 0.02. In the diabetic subgroup of LIFE, losartan reduced the risk of the primary composite endpoint of cardiovascular morbidity and mortality by 24% (P = 0.031). The risk of cardiovascular mortality was 37% lower in the losartan group than in the atenolol group (P = 0.028). These benefits in IDNT, RENAAL, and LIFE appeared to be beyond the blood pressure effect. Conclusions. The findings from recent clinical trials support the use of angiotensin receptor antagonists in patients with nephropathy due to type 2 diabetes, and have shown a significant reduction in the progression towards ESRD (losartan) and proteinuria (losartan, irbesartan), effects that were independent of blood pressure lowering achieved with these agents. Reduction in cardiovascular morbidity and mortality have also been shown in a trial with losartan in diabetics. Collectively, these studies will have worldwide beneficial impact on the treatment of this devastating disease.

PURPOSE: The aim of this study was to determine the effects of a 4-wk individualized training program using Vmax as the exercise intensity and utilizing between 60 and 75% of a subject's Tmax as the exercise duration. METHODS: Five male, middle-distance, trained subjects with the following characteristics (mean +/- SD): age, 22.8 +/- 4.5 yr; height, 181 +/- 4.7 cm; weight, 74.1 +/- 3.2 kg; skinfolds based on five areas, 35.9 +/- 3.9; and VO2max, 61.5 +/- 6.1 mL O2 x kg min(-1) volunteered to participate in this study. Before the training program, the subjects completed a 3000-m time trial, and three each of VO2max/Vmax and Tmax tests. Subjects then completed a 4-wk training program on the treadmill and were then retested on the VO2max/Vmax and Tmax tests. RESULTS: Pretraining versus posttraining results showed significant (P < 0.05) increases in average Vmax (20.5 km x h(-1) vs 21.3 km x h(-1) posttraining), Tmax (225.5 s vs 300.9 s posttraining), and VO2max (61.5 mL O2 x kg x min(-1) vs 64.5 mL O2 x kg x min(-1)). The 3000-m time trial decreased significantly from a pretraining value of 616.6 s to a posttraining value of 599.6 s (P < 0.05). CONCLUSIONS: The results of this study indicate that by utilizing between 60 and 75% of Tmax as an exercise duration and using Vmax as an exercise intensity that these two parameters can be extremely valuable in the prescription of exercise programs for athletes.

GaN films have been grown on 6H-SiC substrates employing a new form of selective lateral epitaxy, namely pendeo-epitaxy. This technique forces regrowth to start exclusively on sidewalls of GaN seed structures. Both discrete pendeo-epitaxial microstructures and coalesced single crystal layers of GaN have been achieved. SEM and TEM analysis are used to evaluate the morphology of the resulting GaN films. Process routes leading to GaN pendeo-epitaxial growth using silicon substrates have also been achieved and the preliminary results are discussed.

C CLARKE, CG BRENNAN, K RODGERS, RM DWYER, PPA SMYTH ENDOCRINE LABORATORY, DEPARTMENT OF MEDICINE AND THERAPEUTICS, UNIVERSITY COLLEGE DUBLIN, IRELAND he demonstration in extrathyroidal human tissues of the sodium iodide symporter (NIS) has raised the possibility that 1311, commonly used as a systemic therapeutic ablative agent in hyperthyroidism and thyroid cancer, might be applied in the treatment of tumours in other NISexpressing tissues such as human breast cancer. Thyroidal transport of 1311 is known to be proportional to circulating stable I and the aim of this study was to determine how stable I (KI) would effect such transport in human breast cancer cell lines MDA-MB-231, MCF-7 and in FRTL-5 thyroid cells. All cells were incubated with KI (01 00mM) for 72 hours after which 1Th I was added . Incubation and uptake of 'l by cells was counted every four hours. Timed efflux of '^I was measured every five minutes. KI in the incubation medium blocked 1251 uptake in a dose-dependent manner in the E receptor positive MCF7 cell line. The effect was less marked in the E receptor negative MDA-MB-231 with significant uptake being maintained even at an I concentration of 50mM. A similar blockade was seen in the FRTL-5 cells with maximum uptake blockade of 25mM I. The rate of efflux of 15I was similar in both MCF-7 and MDA-MB-231 cell lines with a tin of 35 and 40 minutes respectively. In contrast, efflux from the FRTL-5 cells was faster (tire=15 mins). As the human breast has a much lower avidity for I than the thyroid, control of dietary intake would assume even greater importance in radioactive iodine treatment of breast tumours or their metastases.

The present study tested the hypothesis that nitric oxide production in coronary resistance vessels is an important mechanism affecting the regulation of myocardial perfusion in unanesthetized dogs. We inhibited nitric oxide synthesis with the arginine analogue N omega-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg) and maintained the compressive determinants of myocardial blood flow constant by ventricular pacing. L-NAME did not affect resting coronary blood flow and reduced the receptor-mediated increase in flow to intracoronary acetylcholine (100 micrograms/min IC) from 143 +/- 20% (mean +/- SEM) under control conditions to 31 +/- 10% after L-NAME (P < .001). Coronary autoregulatory relations were determined as steady-state coronary pressure was reduced by inflating a hydraulic occluder. Initial resistance adjustments over the autoregulatory plateau were not affected by L-NAME. Closed-loop autoregulatory gain was 0.84 +/- 0.09 under control conditions versus 0.78 +/- 0.07 after L-NAME (P = NS). As coronary pressure was reduced further, however, the critical pressure at which myocardial ischemia began (lower autoregulatory break point) increased from 45 +/- 3 mm Hg under control conditions to 61 +/- 2 mm Hg (P < .001) after L-NAME. In addition, the slope of the coronary pressure-flow relation below the autoregulatory break point was reduced (1.0 +/- 0.2 versus 0.58 +/- 0.09 mL.min-1.mm Hg-1 after L-NAME, P < .05), reflecting a reduction in the maximal conductance recruitable during ischemia. In concert with the effects of L-NAME on autoregulatory responses during ischemia, peak reactive hyperemic flow to a 30-second coronary occlusion was also reduced (from 200 +/- 22 to 166 +/- 24 mL/min after L-NAME, P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Eighteen patients underwent stenting for symptomatic basilar artery stenosis. There were three major periprocedural complications (16.7%) without fatality. At a mean 26.7 ± 12.1-month follow-up, 15 patients (83.3%) had an excellent long-term outcome. Only one patient (5.6%) had moderate disability from recurrent stroke, and two patients died of medical illness at 30 and 36 months after stenting. In this uncontrolled study, stenting appeared to be effective in reducing stroke risk and death and worthy of further scrupulous trial.

Industry is the largest consumer for engineering and science doctorates, and doctorate-level training is thus a main link between the U.S. economy and education. Recent pressures on federal research and development funding, and the widening gap between the needs of industry and the expertise of academia, pose several challenges for the nature of graduate training. Fellowships, off-campus research, and opportunities for teaching should be emphasized in graduate schools, versus research assistant support.

Single‐crystal silicon has been implanted with nitrogen ions at MeV energies, to fluences between 0.25×1018 and 1.65×1018 ions/cm2 at a substrate temperature of 700 °C. Infrared transmission and reflection spectra in the range of 1.25–40 μm were measured and interference fringes were observed which are produced by the interference of light which has been multiply reflected between the front surface and the buried layers. By detailed theoretical analyses of the interference fringes we obtain refractive‐index profiles, which, under suitable interpretation, provide accurate measurements of the range and straggling of the implanted ions. Rutherford backscattering measurements on the same samples confirm this interpretation. Between the energies of 0.67 and 3.17 MeV, the measured values of the projected range agree with theory after adjusting the electronic stopping power, but the straggling measurements are lower by ∼30%. It is demonstrated that the asymmetry of the range distribution can be measured with thi...

Electron cyclotron resonance and radio frequency reactive ion etching have been used to fabricate narrow n+‐GaAs wires employing CCl2F2/He as the etch gas. A comparison of the induced sidewall damage is made using room‐temperature conductivity measurements of the etched structures and the effect of overetching is investigated. In addition, preliminary analysis of low‐temperature transport reveals that the amplitude of universal conductance fluctuations is extremely sensitive to sidewall damage.

Fabrication of metal‐epitaxial insulator‐semiconductor field‐effect transistors by molecular beam epitaxial growth of CaF2 on Si is reported for the first time. These devices have a room‐temperature electron mobility of 300 cm2/Vs and a threshold voltage of 0.5 V. The breakdown voltage of the films ranges from ≳105 to ≳106 V/cm in different regions of the film. These devices will be important for the characterization and improvement of the interface transport properties of the CaF2/Si system.

We describe how the unique capabilities of molecular beam epitaxy together with the electron-beam lithography and reactive-ion etching can be utilized to realize novel quasi-one- and zero-dimensional electron systems. We also present the results of capacitive and tunneling studies on these quantum systems.

We have devised and demonstrated a novel technique for fabricating structures with nanometer scale features in semiconductor heterostructures. The technique is based on definition of nanometer scale patterns by submicron trenches in a GaAs‐AlGaAs heterostructure. The depletion of free carriers below the trenches gives rise to very strong electrostatic confinement. This technique avoids the complications associated with the use of negative resist materials and lift‐off techniques while minimizing the time required to expose densely packed patterns. Aharonov–Bohm rings fabricated using this technique exhibit interference oscillation larger than any reported previously.

We show that post anneals of short duration at high temperature can markedly improve the quality of CaF2 films grown by molecular beam epitaxy (MBE) on Si (100). Anneals at 1100°C for 20 sec in an Ar ambient improved χmin, the ratio of backscattered 1.8 MeV He4 ions in the aligned to random direction, from as-grown values of .07 to .26, to post post-anneal values of .03 to .045. This is the best χmin yet reported for the CaF2:Si system. The post-annealed films also show improved resistance to chemical etching and mechanical stress, and increased dielectric breakdown voltages.

Rapid thermal annealing (RTA) has been shown to be a useful technique for improving the epitaxial quality of CaF2 films grown on Si(100) by molecular beam epitaxy. We have modified the annealing procedure to prevent crack formation, while still maintaining high film quality. Our work also shows RTA to be useful for improving the crystalline quality, chemical stability, and electrical characteristics of CaF2 films grown on Si(111). After RTA, the crystallinity of CaF2 films on Si(111), as measured by electron channeling, is indistinguishable from bulk single crystal CaF2, and the interface state density is reduced by nearly two orders of magnitude from that found in as-grown films.

The characterization of electronic devices using epitaxial CaF2 on Si is described. In addition, the growth and annealing techniques used to obtain high quality epitaxial films are discussed. In particular, the results of using rapid thermal annealing to improve the epitaxial quality of CaF2 films are presented in detail.The electronic and electrical properties of these structures are very promising. Epitaxial CaF2 films with breakdown fields as high as 3 × 106 V/cm and interface trap densities as low as 7 × 1010cm-2eV-1 have been fabricated. In addition, minority carrier dominated trapping has been observed at the CaF2 /Si interface. Finally, the material properties of these structures, as determined by Rutherford backscattering, channeling, and electron microscopy, are discussed and correlated with their electronic properties.

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We use picosecond optics techniques to generate and detect acoustic pulses in an epitaxially grown film of AlAs. From the round trip time of the acoustic pulse we find a sound velocity in the [100] direction of 6.4×105 cm s−1. We also show how measurements of this type can be used to determine the refractive index.

This paper demonstrates a submicron trenching technique for defining low‐dimensional electron systems in GaAs/GaAlAs heterostructures for transport measurements. A variety of electron systems can be defined between trenches as narrow as 200 nm etched into a suitable heterostructure. The use of narrow trenches gives the advantages of high resolution, simplicity, and flexibility, and also avoids the complications associated with negative resists and lift‐off techniques. Using the trenching technique, we have fabricated Aharonov–Bohm ring devices with a Schottky gate over the entire ring. At 0.4 K, these devices exhibit clear interference effects which are dependent on the gate bias.