Search

National Society for Clean Air Publications: NSCA Reference Book £10-95 NSCA Environmental Glossary £4-85 (available from NSCA, 136 North St., Brighton BN1 1RG, U.K.)Aerosols: An Industrial and Environmental Science G.M. Hidy, Academic Press, 1984

A system for obtaining anatomical cross-sections for treatment planning using a radiotherapy simulator is described. A fluorescent screen is viewed by a low light level Isocon television camera and the video signal is digitized and stored. Many projections of the phantom are obtained by rotating the simulator gantry. A convolution algorithm has been used to reconstruct chest sections in which skin and lung outlines are visible. The technique could also be used to make corrections to radiotherapy dose distributions where irradiation of lung tissue is involved.

We report the synthesis of (cyclobutadiene)cyclopentadienylcobalt derivatives, C4R4−Co−C5Y5, where R is a rigid arm capable of linear coupling through its para position and the tentacle Y carries a functionality with a large affinity for the surface of mercury. The compounds are needed for a proposed synthesis of a square-grid polymer by 2-dimensional cross-linking polymerization, which calls for cross-shaped star connector modules mounted horizontally on a flat pedestal with a large affinity to a liquid interface. The substituents are R = 4-pyridyl, 4-iodophenyl, 4-bromophenyl, 4-(ethoxycarbonyl)phenyl, 4-(1,12-dicarba-closo-dodecaboran-1-yl)phenyl, 4-carboxyphenyl, 4−[(triethylsilyl)ethynyl]phenyl, Y = H; R = phenyl, Y = (trifluoroacetoxy)mercurio, iodo; R = 4-bromophenyl, Y = (trifluoroacetoxy)mercurio; R = 4-(ethoxycarbonyl)phenyl, Y = [(2-hydroxyethyl)thio]mercurio. Single-crystal X-ray diffraction structures are reported for R = 4-pyridyl, 4-(1,12-dicarba-closo-dodecaboran-1-yl)−phenyl, 4-(ethoxycarbonyl)phenyl with Y = H, R = phenyl with Y = (trifluoroacetoxy)mercurio, and bis[4-(1,12-dicarba-closo-dodecaboran-1-yl)phenyl]acetylene and phenyl[4−(1,12-dicarba-closo-dodecaboran-1-yl)phenyl]acetylene.

A collaborative survey between the National Radiological Protection Board and the Hospital Physicists' Association has been conducted to ascertain current levels of exposure for patients undergoing 10 routine types of X-ray examination in England. The main part of this study consisted of measurements on nearly 3200 patients attending 20 randomly selected English hospitals. The energy imparted to each patient was determined from a measurement of the total exposure–area product for the examination. In addition, thermoluminescent dosemeters were attached to the patient's skin to enable the derivation of doses to the major radiosensitive organs, either directly or using appropriate conversion factors calculated for a mathematical phantom by a Monte Carlo technique. Histograms are presented showing the wide distributions often observed in the doses for each type of examination. Mean values of exposure–area product, energy imparted to the patient, entrance skin dose per film and organ dose are reported, together with coefficients of variation. Comparison of the results with those from similar surveys in the UK and abroad is complicated by inconsistencies in the reporting of such data, but substantial differences are sometimes apparent, particularly for the estimates of organ doses. The present measurements will provide a useful baseline for future measurements and will be used to evaluate the collective dose to the population from medical exposures and the radiation risks from the various radiological procedures.

The extensive academic and commercial development of CT in the last decade has resulted in the emergence of sophisticated and expensive instruments capable of carrying out whole-body section scans at high spatial and density resolutions. Where such equipment is installed, it is normally in heavy demand for diagnostic work, and, as a result, only a small proportion of patients who might benefit from a CT scan for the purposes of radiotherapy treatment planning can be accommodated. A need persists, therefore, for less costly and more convenient alternative forms of CT scanner for use in radiotherapy treatment planning, where one of the requirements is merely the delineation of large anatomical features, such as the lungs and spine. High spatial and density resolution are not essential. The clear advantages of using an existing piece of treatment planning equipment, the radiotherapy simulator, to obtain low-resolution cross-sectional images, have been pointed out by a number of authors. Webb and Leach (1980) employ radiographic film as an X-ray detector, while Smith et al (1980) use a bolt-on ionisation chamber array. Harrison and Farmer (1978) carried out a feasibility study on a simulator CT system using TV fluoroscopy. The system described below is a practical development of this work.The simulator upon which the CT system is based is a modified TEM “Ximatron” with a novel viewing system (Thompson, 1979). A 48.5 × 48.5 cm fluorescent screen is viewed by a low-light-level Intensifier Isocon television camera (English Electric Valve Co. Ltd. Type P4150/2).

Techniques for the determination of radiation doses to patients in diagnostic radiology are briefly reviewed. Attention is focused upon indirect methods in which measurements of X-ray output are made prior to the actual examination, thereby enabling the entrance skin dose to be calculated if radiographic factors are known. Indirect methods are compared with direct methods which involve TLD measurements on the patient. For certain examinations involving automatic exposure control, and in fluoroscopy, retrospective simulations of the examination or direct methods may be used to supplement the calculations.In order to appreciate the significance of inter-hospital variations, the “speed” of an X-ray imaging system is quantified in terms of the “speeds” of individual components of the imaging chain such as tube potential, film-screen speed, grid attenuation and the performance of the automatic film processor. These “system speed factors” (SSF) may be multiplied together to give a combined SSF which indicates the relative efficiency with which a particular X-ray imaging system utilises the X-ray flux incident upon the patient.

Nitrification of NH4‐N, added as (NH4)2HPO4to acid soils representative of three southeastern physiographic regions, was studied under controlled conditions at 6 and 32C following amendments to minimize differences among soils in reaction and certain major elements. At 32C, nitrification of the applied NH4approached completion in all soils, except the Tifton, by the 10th day irrespective of the region of origin. At 6C, however, patterns of nitrate accumulation were comparable among soils within a defined physiographic region but distinctly different to that of soils from other regions. Since these data were suggestive of variation in microbial adaptation, soils representative of regions of contrasting climate and elevation were further studied. Results from various treatments, such as cross inoculation, sterilization, and stimulation of initial nitrifying population, in either whole or “synthetic soil,” provide evidence that the activity of a soil nitrifying flora subjected to wide temperature variation, is a function of the metabolic adaptation of the organisms to the climate of origin.

A simplified soil extraction procedure was evaluated for the recovery of trifluralin (a,a,a,‐trifluoro‐2,6‐dinitro‐N,N‐dipropyl‐p‐toluidine). Soil recovery values for the herbicide compared favorably with those reported in the literature. Recoveries of 90 to 93% of soil‐incorporated trifluralin were obtained over a 7‐day period, regardless of soil moisture conditions, ranging from 0 to 200% of field capacity, and whether treated soils were exposed to the atmosphere or maintained under airtight conditions. After 14 days, herbicide recovery for all treatments was approximately 64%. Trifluralin in methanol or N‐hexane solution was rapidly degraded by ultraviolet light. In a 24‐hour U.V. exposure study, seven degradation products were observed using gas‐liquid chromatography (GLC). Under laboratory conditions trifluralin solutions were maintained in the dark for 30 days without degradation but exhibited a 1.4% loss per day when maintained under laboratory light conditions. Linear electron capture detector response was shown to be related to injection volume of trifluralin solutions when analyzed quantitatively.

Molecular nitrogen, nitrous oxide (N2O), nitric oxide (NO), and CO2were identified in the gases formed by reacting NO2‐with soils, humic and fulvic acids, lignins, lignin‐building units, and polyphenols in aqueous buffer solutions of pH 6 and 7 in the absence of oxygen. The composition of the mixture of gases was dependent upon the nature of the material examined, with relatively larger amounts of N2being produced from the humic and fulvic acids. Compounds containing methoxyl groups failed to yield detectable amounts of methyl nitrite (CH3ONO) at the pH levels found in most soils. The reaction of NO with humic substances in the absence of oxygen led to the production of N2O and CO2.

Gas chromatographic techniques were developed for separating and determining inorganic gases in experimental systems dealing with losses of soil N. A single column, consisting of acid‐washed chromatographic‐grade coconut charcoal, gave excellent resolution of H2, N2, CO, CO2, N2O, and NO (or O2). The sensitivity of the method for NO and CO was improved considerably by blocking sorption sites responsible for irreversible retention of these gases. Alkyl nitrites did not interfere with the separations.

An in-vitrosystem for the fertilization of superovulated rabbit ova recovered from the ovarian surface and from the oviducts was used to study uterine-oviducal relationships in connection with sperm capacitation. Spermatozoa recovered from ligated uterine horns as early as 8 hr after mating were capacitated although they fertilized periovarian ova at a lower level than spermatozoa from control uteri.In the last decade, a number of factors have been found which aid an in-vitrofertilization system. Replacement of serum by bovine serum albumin (BSA) (Brackett, 1966) and the maintenance of high humidity and prevention of evaporation from culture dishes (Brackett & Williams, 1965) have augmented the earlier work of Chang (1955, 1959) and Bedford & Chang (1962). Using the techniques first described by these workers and some new

Molybdenum (Mo) is a key cofactor in enzymes used for nitrogen (N) fixation and nitrate reduction, and the low availability of Mo can constrain N inputs, affecting ecosystem productivity. Natural atmospheric Mo aerosolization and deposition from sources such as desert dust, sea‐salt spray, and volcanoes can affect ecosystem function across long timescales, but anthropogenic activities such as combustion, motor vehicles, and agricultural dust have accelerated the natural Mo cycle. Here we combined a synthesis of global atmospheric concentration observations and modeling to identify and estimate anthropogenic sources of atmospheric Mo. To project the impact of atmospheric Mo on terrestrial ecosystems, we synthesized soil Mo data and estimated the global distribution of soil Mo using two approaches to calculate turnover times. We estimated global emissions of atmospheric Mo in aerosols (<10 μm in diameter) to be 23 Gg Mo yr−1, with 40%–75% from anthropogenic sources. We approximated that for the top meter of soil, Mo turnover times range between 1,000 and 1,000,000 years. In some industrialized regions, anthropogenic inputs have enhanced Mo deposition 100‐fold, lowering the soil Mo turnover time considerably. Our synthesis of global observational data, modeling, and a mass balance comparison with riverine Mo exports suggest that anthropogenic activity has greatly accelerated the Mo cycle, with potential to influence N‐limited ecosystems. Molybdenum (Mo) is an essential trace element that is, important for terrestrial and aquatic ecosystems, as it is required for biological nitrogen fixation and uptake. Mo is carried in particles to the atmosphere from sources such as desert dust, sea spray, and volcanoes resulting in losses and sources to different ecosystems. Atmospheric Mo deposition is essential on long time scales for soils which have lost Mo due to soil weathering, with consequences for nitrogen cycling. Anthropogenic changes to the Mo cycle from combustion, motor vehicles, and agricultural dust, are likely to be large, and have more than doubled sources of Mo to the atmosphere. Locally, anthropogenic changes to Mo in industrialized regions can represent a 100‐fold increase in deposition, and may affect nitrogen cycling in nitrogen‐limited ecosystems. We compiled atmospheric molybdenum (Mo) concentration data and compared observations to a three‐dimensional global atmospheric aerosol modelAnthropogenic activity has likely doubled atmospheric Mo globally, but with regional variationMo turnover time in soils ranges between 1,000 and 1,000,000 years, with the shortest times in dust source regions and industrialized areas We compiled atmospheric molybdenum (Mo) concentration data and compared observations to a three‐dimensional global atmospheric aerosol model Anthropogenic activity has likely doubled atmospheric Mo globally, but with regional variation Mo turnover time in soils ranges between 1,000 and 1,000,000 years, with the shortest times in dust source regions and industrialized areas