Structural parameters effect on the electrical and electroluminescence properties of silicon nanocrystals/SiO2 superlattices.

The effect of the oxide barrier thickness (tSiO2) reduction and the Si excess ([Si]exc) increase on the electrical and electroluminescence (EL) properties of Si-rich oxynitride (SRON)/SiO2 superlattices (SLs) is investigated. The active layers of the metal-oxide-semiconductor devices were fabricated by alternated deposition of SRON and SiO2 layers on top of a Si substrate. The precipitation of the Si excess and thus formation of Si nanocrystals (NCs) within the SRON layers was achieved after an annealing treatment at 1150 °C. A structural characterization revealed a high crystalline quality of the SLs for all devices, and the evaluated NC crystalline size is in agreement with a good deposition and annealing control. We found a dramatic conductivity enhancement when the Si content is increased or the SiO2 barrier thickness is decreased, due to a larger interaction of the carrier wavefunctions from adjacent layers. EL recombination dynamics were studied, revealing radiative recombination decay times of the order of tens of microseconds. Lower lifetimes were found at higher [Si]exc, attributed to exciton confinement delocalization, whereas intermediate barrier thicknesses present the slowest decay. The electrical-to-light conversion efficiency increases monotonously at thicker barriers and smaller Si contents. We ascribe these effects mainly to free carriers, which enhance carrier transport through the SLs while strongly quenching light emission. Finally, the combination of the different results led us to conclude that tSiO2 âˆ¼ 2 nm and [Si]exc from 12 to 15 at% are the ideal structure parameters for a balanced electro-optical response of Si NC-based SLs.

Nearly perfect near-infrared luminescence efficiency of Si nanocrystals: A comprehensive quantum yield study employing the Purcell effect.

Thin layers of silicon nanocrystals (SiNC) in oxide matrix with optimized parameters are fabricated by the plasma-enhanced chemical vapor deposition. These materials with SiNC sizes of about 4.5 nm and the SiO2 barrier thickness of 3 nm reveal external quantum yield (QY) close to 50% which is near to the best chemically synthetized colloidal SiNC. Internal QY is determined using the Purcell effect, i.e. modifying radiative decay rate by the proximity of a high index medium in a special wedge-shape sample. For the first time we performed these experiments at variable temperatures. The complete optical characterization and knowledge of both internal and external QY allow to estimate the spectral distribution of the dark and bright NC populations within the SiNC ensemble. We show that SiNCs emitting at around 1.2-1.3 eV are mostly bright with internal QY reaching 80% at room temperature and being reduced by thermally activated non-radiative processes (below 100 K internal QY approaches 100%). The mechanisms of non-radiative decay are discussed based on their temperature dependence.

Interplay of bimolecular and Auger recombination in photoexcited carrier dynamics in silicon nanocrystal/silicon dioxide superlattices.

We report results of investigating carrier recombination in silicon nanocrystal/silicon dioxide superlattices. The superlattices prepared by nitrogen-free plasma enhanced chemical vapour deposition contained layers of silicon nanocrystals. Femtosecond transient transmission optical spectroscopy was used to monitor carrier mechanisms in the samples. The three-particle Auger recombination was observed in accord with previous reports. However, under high pump intensities (high photoexcited carrier densities) the bimolecular process dominated the recombination. Detailed analysis of measured data and fitting procedure made it possible to follow and quantify the interplay between the two recombination processes. The bimolecular recombination was interpreted in terms of the trap-assisted Auger recombination.

Microcirculatory functions in systemic sclerosis: additional parameters for therapeutic concepts?

To study the functional reactivity of the cutaneous microcirculation in progressive systemic sclerosis (PSS), hyperemic responses after arterial occlusion (3 min) and during local heating (42 degrees C) were investigated with simultaneous measurements of red blood cell flux and cutaneous oxygen tension (pcuO2) of the skin in female patients (n = 19) with PSS and in healthy female controls (n = 15). Additionally, serum levels of 6-keto-prostaglandin 1 alpha (PGF1 alpha), a stable metabolite of prostacyclin, were compared to the microcirculatory data, and both were used to evaluate further a standardized therapy with 10-d intravenous calcitonin (100 IU/d) infusion in six PSS patients. In PSS, the initial mean pcuO2 value was significantly reduced and was inversely proportional to flux and to PGF1 alpha levels, whereas the flux and pcuO2 responses to the above hyperemic stimuli showed significant reductions, revealing a pattern of "hyperemic hypoxia" probably due to exhausted functional reserves of cutaneous perfusion. During calcitonin infusion significant rises in pcuO2 and temporarily in PGF1 alpha and flux were found. After 10 d of therapy, increased pcuO2 was associated significantly with decreased flux, indicating a shifting of blood from deeper regulatory vessels to the subepidermal capillaries. Both clinical improvement and the results of microcirculatory measurements demonstrate a beneficial effect of calcitonin on the cutaneous microcirculation in PSS patients, possibly due in part to a short-term increase in release of endogenous prostacyclin from the vascular endothelium during the infusion. The disturbed reactivity of the dermal vessels in PSS is important for the evaluation of therapeutic concepts and stresses, together with the elevated PGF1 alpha plasma levels, vascular factors in the pathogenesis of PSS.

Changes in serum lipids when fluvastatin is substituted for lovastatin in the same doses.

This study evaluated changes in serum lipids when fluvastatin was substituted for lovastatin using equivalent doses. Results showed that serum lipids, especially low-density lipoprotein cholesterol, significantly increase with this substitution.

Effect of atorvastatin 15 mg/week on serum lipids in patients with hypercholesterolemia.

Atorvastatin 15 mg/week was administered to 21 patients with hypercholesterolemia for 2 months. The mean low-density lipoprotein concentration decreased by 20% after treatment.

A comparison of fluvastatin 40 mg every other day versus 20 mg every day in patients with hypercholesterolemia.

STUDY OBJECTIVE: To assess the efficacy of fluvastatin administered every other day versus an equivalent dose given daily in patients with hypercholesterolemia. DESIGN: Randomized, nonblinded, crossover study. SETTING: Veterans Affairs Medical Center. PATIENTS: Twenty-three patients with low-density lipoprotein (LDL) levels above 160 mg/dl despite diet therapy INTERVENTION: Patients received fluvastatin 40 mg every other day or 20 mg/day, all doses taken at bedtime. Each treatment arm was 6 weeks in duration. MEASUREMENTS AND MAIN RESULTS: A lipid profile was determined at baseline and after each regimen. Both regimens significantly lowered total cholesterol and LDL versus baseline. The LDL levels were lowered by 24% and 21% by fluvastatin 20 mg/day and 40 mg every other day, respectively. There was no statistically significant difference in lipid components between regimens. CONCLUSION: Fluvastatin 40 mg every other day is effective in lowering total cholesterol and LDL in patients with hypercholesterolemia.

Quantitation and localization of 204thallium in the central and peripheral nervous system of adult and young rats.

A single dose of 204Tl, representing about 2-3 ng 204Tl per gm/wt was injected into young and adult rats. Rats were killed daily over a period of 10 days and the levels of Tl were estimated in nervous and other tissues. The greatest concentrations of Tl (peak concentration time - PCT) in all tissues in the adult rat occurred 24 hours after injection. In the young rat PCT in the sciatic nerve and spinal cord were 48 hours after injection whereas it occurred 24 hours after injection in the brain and somatic organs. There were differences in biological half-lives of the organs in the young as compared to the adult rats. Tl level in all organs except the kidney, were about 2 pg/mg of tissue. It was concentrated in the cytoplasm of most cells examined. Tl levels then fell rapidly during the few days following the injection, and slowly afterwards. Thirty days after the injection, tracts of 204Tl were present in the cytoplasm of nervous and somatic cells.

The ultraendurance triathlete: a physiological profile.

To better characterize the athletes who participate in ultraendurance triathlons, 14 triathletes in training for the Hawaii IRONMAN triathlon were studied. A physical and physiological profile was developed from anthropometric measurements and oxygen uptake during maximal exercise on a treadmill, cycle ergometer, and arm ergometer. A comparison of the maximal values among exercise modes and between males and females was made. A comparison of height, weight, and percent body fat of these triathletes with elite athletes from the sports of swimming, cycling, and running showed the physique of triathletes to be most similar to that of cyclists. Oxygen uptake at maximal exercise was, for males and females, respectively: 68.8 ml X kg-1 X min-1, 65.9 ml X kg-1 X min-1 on the treadmill; 66.7 ml X kg-1 X min-1, 61.6 ml X kg-1 X min-1 on the cycle ergometer; and 49.1 ml X kg-1 X min-1, 39.7 ml X kg-1 X min-1 on the arm ergometer. When comparing the highest oxygen uptake attained at maximal exercise in any one of the three exercise modes, the male triathletes are comparable to swimmers, but have a lower aerobic capacity than cyclists or distance runners. The female triathletes studied were able to attain oxygen uptake values greater than those previously reported for female athletes.

Issues and outcomes in integrated treatment programs for dual disorders.

In an integrated, dual disorder treatment program delivered at two sites, the authors address numerous barriers to delivering services to dually diagnosed consumers and employ a set of multidimensional indicators to assess outcome. Consumers who received services through the well-implemented, integrated services program for 12 months were functioning better in the community. There was a cost shifting from mental health to drug and alcohol services, as well as a one-third increase in the total costs of care by the end of the first year of treatment. Program implementation issues are described and the clinical management implications for more effectively serving dually diagnosed consumers through integrated treatment programs are discussed.