10B Conformal Doping for Highly Efficient Thermal Neutron Detectors.

This paper reports a simple and novel conformal doping strategy for microstructured silicon diodes using enriched 10B for sidewall doping while enabling enhanced neutron sensitivity. Monte-Carlo nuclear particle (MCNP) code simulations were initially used to calculate the neutron detection efficiency in the microstructured diodes as a function of geometry and pitch. A high-temperature anneal in 10B-filled diodes results in a conformal silicon p+ layer along the side walls of the trenches in the diodes. This results in large neutron detection areas and enhanced neutron detection efficiency when compared with planar detectors. With the method discussed here, a thermal neutron detection of ∼21% efficiency is achieved, which is significantly higher than the efficiency achieved in planar detectors (∼3.5%). The higher efficiency is enabled by the 10B acting as a source for conformal doping in the trenches, resulting in lower leakage current while also enabling neutron sensitivity in the microstructured diodes.

Effects of caffeine on linear and nonlinear measures of heart rate variability before and after exercise.

Caffeine intake is associated with an increase in heart rate (HR) variability. This study sought to examine the effects of caffeine on HR variability measures before and during progressive exercise in 11 healthy volunteers in a double-blind randomized and counterbalanced placebo-controlled paradigm. As expected, there were significant increases in HR and decreases in HR variability after exercise during both placebo and caffeine conditions; however, pre-exercise caffeine condition was associated with a significant increase of HR variability, especially in the high-frequency range (0.15-0.5 Hz), and also approximate entropy (APEN), which is usually attributed to cardiac vagal function. But during progressive exercise, caffeine intake resulted in a greater decrease of HF power as well as HR APEN. Caffeine also was associated with significantly higher LF power during exercise compared to the placebo condition. These results suggest that caffeine may have different effects on HR variability at rest, compared to exercise. These findings may have implications for patients with cardiac illness and anxiety, depression, and psychotic disorders who use beverages containing excessive caffeine.