Use of variable p(H) interface to a mass spectrometer for the measurement of dissolved volatile compounds

A wide variety of dissolved chemicals can be measured continuously with some specificity by directly interfacing a relatively inexpensive mass spectrometer to a solution. Specifically, we describe the construction and initial use of a membrane interace to a mass spectrometer which allows the continuous measurement of the concentration of dissolved volatile compounds in buffered aqueous solution. In addition to volatile compounds that do not dissociate appreciably at p(H) 7 (e.g., ethanol, ethylene glycol), volatile acids and bases, such as acetic acid or ammonia, can be measured with the interface is operated within the range 1相似文献   

Debunking myths about self-quitting: Evidence from 10 prospective studies of persons who attempt to quit smoking by themselves.

This article examines data from 10 long-term prospective studies (N?>?5,000) in relation to key issues about the self-quitting of smoking, especially those discussed by S. Schachter (see PA, Vols 58:7407 and 68:10809). When a single attempt to quit was evaluated, self-quitters' success rates were no better than those reported for formal treatment programs. Light smokers (20 or less cigarettes per day) were 2.2 times more likely to quit than heavy smokers. The cyclical nature of quitting was also examined. There was a moderate rate (mdn?=?2.7%) of long-term quitting initiated after the early months (expected quitting window) of these studies, but also a high rate (mdn?=?24%) of relapsing for persons abstinent for six months. The number of previous unsuccessful quit attempts was unrelated to success in quitting. Finally, there were few occasional smokers (slips) among successful long-term quitters. We argue that quitting smoking is a dynamic process, not a discrete event. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stark-induced three-wave mixing in molecular gases--Part I: Theory

Application of dc electric field to a gaseous system destroys the basic inversion symmetry and allows three-wave mixing processes to occur. A theoretical derivation of this effect under conditions of resonantly enhanced nonlinearities is given for a three-level system. Calculations are presented for mixing of a CO2laser with 4-GHz microwaves in the molecule NH2D, producing single lower sideband radiation.     

A variable 10.6-µ attenuator

A variable CO2laser attenuator with a dynamic range of 33 dB, large power handling capability, and reproducible attenuation has been constructed.     

Precipitation studies of lead and selenium in single-crystal PbSe

The kinetics of precipitation in PbSe was studied as a function of the species precipitating and the precipitation temperature. This was accomplished by performing Hall effect measurements as a function of time and temperature. According to Ham's theory of diffusion-limited precipitation, the kinetics are described by: $$f(t) = 1 - \exp [ - (t/\tau )]^n $$ where the time constant τ and the power dependencen provide useful information about the rate-limiting process involved and the size, shape, and density of the precipitate particles. For the initial stage of precipitation of lead in PbSe an average value ofn=1.12 was experimentally determined. This value is indicative of spheroidally shaped precipitate particles, especially if preprecipitation exists. After approximately 50 pct of the lead precipitates, a longer τ process becomes rate-controlling andn in the above equation equzls 1/3. With respect to the size, which was on the order of 1000Å in radius, and the shape of the lead precipitates, the kinetic predictions were found to be in good agreement with evidence provided by extraction replica techniques and electron microscopy. For the precipitation of selenium in PbSe an average value ofn=0.9 was experimentally determined. This value is indicative of cylindrically shaped precipitate particles, especially if preprecipitation exists. Utilizing the experimentally determined value for τ, an approximate size for the precipitate particles at equilibrium was calculated as being about 40Å in radius and 3000Å in length. Values obtained for the activation energy of precipitation, 0.84 ev for Pb, 1.23 ev for Se, agree very closely with those for the activation energy of diffusion, 0.83 ev for Pb, 1.20 ev for Se. This indicates that diffusion plays an important role in the precipitation of lead and selenium in PbSe.