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.

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.

Chlorine isotope fractionation in the stratosphere.

Chlorinated organic compounds are important contributors to the anthropogenic enhancement of stratospheric ozone depletion. We report measurements of stratospheric isotope fractionation in such a compound. Stratospheric and tropospheric difluorodichloromethane (CF2Cl2) were found to have the largest relative 37Cl/35Cl isotope ratio difference ever measured for a natural compound. The increase of the relative isotope ratio difference with altitude was tightly correlated to the corresponding decrease in the CF2Cl2 mixing ratio. The observed relationship has a high potential to provide new insights into atmospheric chemistry and transport processes.

General and visceral adiposity in black and white adolescents and their relation with reported physical activity and diet.

BACKGROUND: Excess body fat accumulation may begin in youth and is linked with increased risk of cardiovascular disease. Examination of physical activity (PA) and diet behaviours predictive of adiposity may help target efforts to reduce chronic disease risk. OBJECTIVE: We hypothesized that energy intake (EI) from fat, vigorous PA (VPA), and their interaction would predict body fat percentage (%BF) and visceral adipose tissue (VAT) in youth and that sedentary behaviours and intake of dairy, fruit, vegetable and whole grain foods would be related to adiposity. DESIGN: A cross-sectional, observational study of reported PA and diet behaviours and objective adiposity measures. SUBJECTS: Six-hundred sixty-one healthy black and white adolescents aged 14-18 years. MEASUREMENTS: Diet by 24-h recalls using Nutrition Data Systems for Research (Minneapolis, MN, USA), VPA by previous day physical activity recalls (PAR), and %BF with dual-energy X-ray absorptiometry. VAT by magnetic resonance imaging for 434 subjects. RESULTS: Reported EI and VPA were positively correlated with each other and were negative predictors of %BF. Time spent watching television or movies and %EI from protein were positive predictors of %BF. Adjusted for EI, none of the independent variables predictive of %BF retained their significance. %BF and VAT were highly correlated (r=0.73, P<0.0001). EI was the sole and negative predictor of VAT. CONCLUSIONS: Higher energy 'throughput', not energy restriction, characterize leaner youths. Youths should be advised to engage in VPA so that they can eat sufficient calories to obtain the nutrients required for optimal health while remaining lean.

Nourishing the body through use of process prescriptions in group therapy.

OBJECTIVE: This clinical report describes a creative process for developing between-session prescriptions which sustain and strengthen the momentum of change occurring in group treatment sessions. METHOD: Therapists in this model use words and phrases depicting the group as a body in order to guide the treatment process and develop between-session prescriptions. Maintaining a perspective of the treatment group as a body facilitates development of member commitment to the well-being of a physical and psychological body, and between-session assignments employ the developmental phases of the therapy for illuminating the disorder and effecting its resolution. This approach was developed in an ongoing, open-ended treatment group provided at a community mental health center for 14 years. RESULTS: Examples are presented of process prescriptions which simultaneously address several dynamic levels: (a) the theme of interactions between the individuals in each session; (b) the particular stage of the group's development, and the ways this level of maturation determines how interactions arise and themes are selected; and (c) the underlying functions of the eating disorder. DISCUSSION: Using the metaphor of the body to guide the language of between-session prescriptions links developmental group treatment process with members' day-to-day engagement with the eating disorder. By participating directly in the development of the treatment experience, the group members become committed to a developmental process that engages them in accountability and caring for a body, and, by extension, their own bodies.

Why group therapy for bulimia?

Many treatment approaches for bulimia rely on the use of a group format. However, descriptions of the treatments do not reveal that the powers of group process are curative in themselves. The dynamics of the group parallel and are metaphorical for the dynamics of the disorder. Therefore, group therapy can be facilitated so that the members resolve the physical, psychological, and social aspects of their disorder through attending to these aspects of the group system. Case material is offered to illustrate symptomatic expressions and therapeutic responses.

[Case of old uterine perforation after abortus mens II/III]. / Ein Fall einer alten Uterusperforation nach Abortus mens II/III

We can point out a rare case of an old, covered perforation of the uterus after abortus mens II-III and report the method of treatment carried out.

PIP: A case of old, hidden uterine perforation resulting from induced abortion in a 23-year-old woman is reported. The patient presented with incomplete abortion after 2 months of amenorrhea. The patient was released 3 days after uncomplicated evacuation of the uterus. She was readmitted 2 months later for acute abdominal symptoms. At operation, liquid and clotted blood was found in the abdominal cavity, originating from a large hematoma of the fundus uteri (between the perimetrium and the myometrium). The resected part consisted of uterine wall and placental polyp, with clotted blood. Recovery was uncomplicated, and the internal genitalia were normal at laparotomy (for intestinal torsion) 10 months later.