Chalk River Laboratories

About: Chalk River Laboratories is a based out in . It is known for research contribution in the topics: Neutron diffraction & Neutron scattering. The organization has 2297 authors who have published 2700 publications receiving 73287 citations.

Time Patterns of Peromyscus Activity and Their Correlations with Weather

Abstract: The activity of Peromyscus maniculatus in an Ontario forest and Peromyscus truei and Peromyscus californicus in California chaparral was observed directly and monitored electronically. The activity of all three species outside the burrow was pulsed through the night, with different individuals not in tight synchrony and a depression in overall activity in the middle of the night. Activity of P. californicus was similar to that of P. truei , but P. californicus had in addition a pronounced burst of activity before dawn. As summer progressed, the amount of activity of P. maniculatus diminished and was compressed into the early part of the night. Wind and moonlight had no strong effect upon activity within a night. From night to night, P. truei had conspicuous fluctuations in total nightly activity (at a period of about 4 days), the entire population usually being in synchrony. Night-to-night fluctuations in P. californicus activity were in phase with those of P. truei . Night-to-night fluctuations in vole tracks in Quebec (unpublished data from R. Bider) had low correlations with P. maniculatus tracks in the same area. Night-to-night fluctuations in P. truei activity had a positive correlation with barometric pressure and a negative correlation with low pressure weather variables (humidity, temperature). There was no correlation with wind or cloud cover. None of the weather variables had a strong periodicity at 4 days, but P. truei activity was in phase with the 4-day-component of barometric pressure, out of phase with temperature, and leading humidity. The evidence suggested that sundown temperature was the key variable. Fluctuations in tracks of P. maniculatus (Quebec) had similar properties, except they were in-phase with low pressure weather variables. Vole tracks ( Microtus pennsylvanicus and Clethrionomys gapperi ) showed the same periodicities as weather and were tightly correlated with weather.

Tritium Sampling and Measurement

Abstract: Current methods for sampling and measuring tritium are described. Although the basic techniques have not changed significantly over the last 10 y, there have been several notable improvements in tritium measurement instrumentation. The design and quality of commercial ion-chamber-based and gas-flow-proportional-counter-based tritium monitors for tritium-in-air have improved, an indirect result of fusion-related research in the 1980s. For tritium-in-water analysis, commercial low-level liquid scintillation spectrometers capable of detecting tritium-in-water concentrations as low as 0.65 Bq L-1 for counting times of 500 min are available. The most sensitive method for tritium-in-water analysis is still 3He mass spectrometry. Concentrations as low as 0.35 mBq L-1 can be detected with current equipment. Passive tritium-oxide-in-air samplers are now being used for workplace monitoring and even in some environmental sampling applications. The reliability, convenience, and low cost of passive tritium-oxide-in-air samplers make them attractive options for many monitoring applications. Airflow proportional counters currently under development look promising for measuring tritium-in-air in the presence of high gamma and/or noble gas backgrounds. However, these detectors are currently limited by their poor performance in humidities over 30%.

Modulation of the polymorphism of the palmitic acid/ cholesterol system by the pH

Abstract: Differential scanning calorimetry, infrared spectroscopy, solid-state 13C and 2H NMR spectroscopy, and X-ray diffraction were used to characterize hydrated mixtures of palmitic acid (PA) and cholesterol (chol), at low (5.4) and high (8.5−9.0) pH. The pH affects the ionization state of the fatty acid, and it was found to modulate its interaction with cholesterol, and the architecture of the resulting complexes. At low pH, this system undergoes a transition from a phase-separated crystalline state to a lamellar liquid-ordered (lo) phase, in agreement with previous results (Langmuir 2001, 17, 5587−5594). The apparent pKa of PA in these conditions is found to be about 8.2. At high pH, when the fatty acid is deprotonated and consequently negatively charged, both components participate in the formation of an lo lamellar structure that was found to be stable over a large temperature range (20−70 °C). For 50/50 PA/chol mixtures, only this phase, with a d spacing of approximately 49 A, is detected. These fluid bil...