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The polar mesopause region (80-100 km) is the coldest region of the Earth's atmosphere and is expected to be sensitive to global change. Reported increases in observations of polar mesospheric clouds over the last 100 years have been postulated to be related to decreased temperatures (associated with tropospheric warming) and increased water vapour at mesospheric altitudes (a result of increased methane concentrations in the troposphere). The temperature of this region can be monitored by spectroscopic techniques utilising hydroxyl (OH) emissions which originate near 87 km. The Australian Antarctic Division, Atmospheric and Space Physics group has been analyzing OH (6-2) band spectra recorded with a Czerny—Turner scanning spectrometer at Davis Station, Antarctica (68.6° S, 78.0° E) to optimise temperature determinations for climate change studies. A number of difficulties were encountered, some of which have been overcome and all of which can be overcome. The mid-winter average temperature of the OH layer for May-July 1990 has been measured as 224 ±2 K. The equivalent value for 1996 is 215±2 K. Possible reasons for the difference are discussed.
This article describes recent studies of the chemistry of adhesion between thin (d ≥ 11 Å) polyimide films and silver and copper substrates, and the structural changes in the polymer when polyamic acid is imidized to polyimide. The thin polyamic acid films were formed by vapor phase deposition of 1,2,4,5-benzenetetracarboxylic anhydride (PMDA) and 4,4-oxydianiline (ODA) under high vacuum conditions and subsequent imidization by heating in vacuum. Both ODA and PMDA are at least partially dissociated upon adsorption onto clean copper and silver and with increasing film thicknesses react to form the polyimide precursor, polyamic acid. Heating to T ≥ 425 K leads to polymerization to form polyimide films which are thermally stable to about 700 K. Polyimide films with mean thicknesses as small as 1.1 nm have been fabricated in this way and their bonding to the substrate as determined by x-ray photoemission studies is su marized. Infrared reflection absorption data gives further evidence that the polyimide bonds to the substrate via fragmented PMDA. Changes in the surface topography and molecular structure of the films during imidization are demonstrated by scanning tunneling micrographs and infrared reflection absorption data.
J. P. Singh, Diagnostics Instrumentation and Analysis Laboratory (DIAL), Mississippi State University, USA,
F. Y. Yueh, Diagnostics Instrumentation and Analysis Laboratory (DIAL), Mississippi State University, USA,
V. N. Rai, Diagnostics Instrumentation and Analysis Laboratory (DIAL), Mississippi State University, USA,
R. Harmon, US Army Research Laboratory, Research Triangle Park, USA,
S. Beaton, ADA Technologies, Inc., USA,
P. French, ADA Technologies, Inc., USA,
F. C. DeLucia, US Army Research Laboratory, Aberdeen Proving Ground, USA,
B. Peterson, US Army Research Laboratory, Aberdeen Proving Ground, USA,
K. L. McNesby, US Army Research Laboratory, Aberdeen Proving Ground, USA,
A. W. Miziolek, US Army Research Laboratory, Aberdeen Proving Ground, USA
Laser-induced breakdown spectroscopy (LIBS) has demonstrated its capability in quantitative determination of elemental composition in various samples in laboratories for decades. Recently, the interest in applying LIBS to detect various hazardous materials in the environment has grown rapidly. This chapter reviews some recent work related to environmental contamination studies using LIBS. Two portable LIBS instruments developed for field application are described in this chapter. The first instrument has been used by the US Army Research Laboratory to analyze the contaminated soil from Army sites and also for other geological applications. The other system was used by Mississippi State University to detect the resources conservation and recovery act (RCRA) metals in the off-gas of industrial plants and in liquids. The practical problems with LIBS application in environmental application such as calibration and sensitivity are also discussed in this chapter. The concept of using a new generation of broadband spectrometers to improve LIBS' capability in monitoring multiple emission lines of the same element to improve the detection limit and other signal enhancement techniques is addressed. The initial result of LIBS application in environmental problems is encouraging. We believe that the performance of LIBS in environmental application will continuously improve with the commercial development of various components in LIBS detection system.
LIBS is a chemical sensor technology with a capability for real-time in situ analysis that was first demonstrated in the laboratory over two decades ago and is now at the threshold of widespread commercialization.
Clostridium perfringens isolates are currently classified into one of five biotypes on the basis of
the differential production of α-, β-, ε- and ι-toxins. Different biotypes are associated with
different diseases of man and animals. In this study a multiple PCR assay was developed to
detect the genes encoding these toxins. In addition, detection of the genes encoding the C.
perfringens enterotoxin and β2-toxin allowed subtyping of the bacteria. C. perfringens isolates
taken from a variety of animals, including foals, piglets or lambs, were genotyped using this
assay. Most of the isolates were found to be genotype A and the gene encoding β-toxin was
present in 50% of the isolates genotyped. A significant association between C. perfringens
possessing the β2-toxin gene and diarrhoea in piglets was identified, suggesting that β2-toxin
may play a key role in the pathogenesis of the disease.
Twelve male subjects took part in a study to investigate the effects of overfeeding a high-fat diet (19·17 MJ/d; 58% energy from fat) for 2 weeks on plasma cholecystokinin (CCK) levels, food intake, and subjective feelings of hunger and fullness. Before and after the diet, subjects completed a 2-week weighed dietary inventory, formal measurements of food intake from a pre-selected appetizing evening meal were carried out, and blood samples were taken after a standard breakfast for measurement of CCK. Hunger and fullness were rated on visual analogue scales before and after each of these meals and at evening meals during the diet period. Following the high-fat diet there was a small non-significant increase in food intake from the pre-selected meal (6919 (SE 615) kJ ν 6405 (SE 540) kJ; P = 0·1) and a significant increase in the average daily food consumption measured from the diaries (10·25 (SE 0·49) MJ/d ν. 9·59 (SE 0·62) MJ/d; P = 0·05). Corresponding trends of increasing feelings of hunger and declining fullness also occurred over the study period. Plasma CCK responses to the standard breakfast were raised following the diet (1285 (SE 153) ν. 897 (SE 78) pM min; 3h integrated CCK production post ν. pre diet; P < ·01) with the major differences observed at 90 and 120 min following the meal. These results suggest that the increase in food intake may be related to a down-regulation in putative CCK receptors responsible for food intake. Elevated CCK levels might suggest a corresponding down-regulation in CCK receptors responsible for feedback inhibition of CCK release.
Cytomegalovirus (CMV) is a common opportunistic infection in both iatrogenic and HIV-induced immunosuppression. The usual sites of involvement are the gastro-intestinal tract, retina and lung. We present three cases of CMV ulceration of the oropharynx. All three patients presented with symptoms localized to the oropharynx and in each case the diagnosis was only made on histological examination of ulcer biopsy specimens. The patients all responded well to ganciclovir treatment and at writing none have required maintenance therapy (7–11 months post diagnosis).
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