Optically controlled switching of the charge state of a single nitrogen-vacancy center in diamond at cryogenic temperatures.

In this Letter, the photoinduced switching of the single nitrogen-vacancy (NV) center between two different charge states, negative (NV(-)) and neutral (NV(0)), is studied under resonant excitation at liquid helium temperature. We show that resonant conversion of NV(0) to NV(-) significantly improves spectral stability of the NV(-) defect and allows high fidelity initialization of the spin qubit. Based on density functional theory calculations a novel mechanism involving an Auger ionization of NV(-) and charge transfer of an electron from the valence band to NV(0) is discussed. This study provides further insight into the charge dynamics of the NV center, which is relevant for quantum information processing based on an NV(-) defect in diamond.

High-pressure core structures of Si nanoparticles for solar energy conversion.

We present density functional and many body perturbation theory calculations of the electronic, optical, and impact ionization properties of Si nanoparticles (NPs) with core structures based on high-pressure bulk Si phases. Si particles with a BC8 core structure exhibit significantly lower optical gaps and multiple exciton generation (MEG) thresholds, and an order of magnitude higher MEG rate than diamondlike ones of the same size. Several mechanisms are discussed to further reduce the gap, including surface reconstruction and chemistry, excitonic effects, and embedding pressure. Experiments reported the formation of BC8 NPs embedded in amorphous Si and in amorphous regions of femtosecond-laser doped "black silicon." For all these reasons, BC8 nanoparticles may be promising candidates for MEG-based solar energy conversion.

Fluoroscopically-guided manipulation of malfunctioning peritoneal dialysis catheters.

OBJECTIVE: To review our experience with fluoroscopic evaluation and manipulation of malpositioned, malfunctioning, peritoneal dialysis (PD) catheters. MATERIALS AND METHODS: Thirty-one patients, over a 5-year period (1 May 1992 to 30 April 1997) with malfunctioning PD catheters, who had fluoroscopically-guided manipulation were reviewed. Catheters were manipulated using a malleable aluminum bar and, if necessary, guide wires or other stiffeners. Technical success was assessed on the basis of adequate, fluoroscopically verified, catheter placement at the time of the procedure and improved flows. A functional PD catheter at 30 days post manipulation was considered to be a clinically successful manipulation. RESULTS: There were 41 manipulations [33 initial (IM) and 8 remanipulations (RM)] for malpositioned or kinked catheters. In 31 (19 male, 12 female) patients ranging in age from 31 to 76 years (mean age 60 years), the initial technical success rate was 85% for IM (n = 28/33) and 63% (n = 5/8) for RM. The overall clinical success rate, or 30-day primary patency, was 55% for IM (n = 18/33) and 63% for RM. Catheter function (combined IM and RM) continued for a median 869 days (95% CI: 118, 1620). No early complications were noted. CONCLUSIONS: Fluoroscopic manipulation, including attempts at remanipulation, of PD catheters is a safe procedure. The technique is a simple, inexpensive, and effective way of prolonging PD catheter life, thereby reducing the number of surgical interventions.

[Unusual cases of maternal death caused by amniotic fluid embolism]. / Rendkívüli gestatiós anyai halálesetek, magzatvíz embolia miatt.

Five cases of amnion fluid embolism are reported. In the first case the cause of the death was the obstruction of the lung-vessels. In the lung tissue calcium embolia could also been detected. In the second case embolization started--at unruptured amnionsac--with ecclampsia-like convulsions, later it was followed by coagulopathia. In the third case amnion fluid embolism was complicated by coagulopathia. In the fourth case in addition to amnion fluid embolism endometritis purulenta complicated by endotoxinaemia and coagulopathia were also present. In all four cases rupture of the uterus was revealed. In the fifth case amnion fluid embolism developed without the rupture of the uterus. At the autopsy of cases of maternal death the possibility of amnion fluid embolism should always be considered. Although macroscopic changes seen at amnion fluid embolism are not pathognomic, when clinical and pathological symptoms of haemorrhagic diathesis are present, there always arises the suspicion of amnion fluid embolism. Since lungs are relatively resistant to putrefaction amnion fluid embolism in optimal cases can be diagnosed histologically even in exhumated lung specimen. Reliable diagnosis of amnion fluid embolism in cases of sudden maternal death gives possibility to exclude medical negligence.