Subacute neuropathological effects of microplanar beams of x-rays from a synchrotron wiggler.

Microplanar beam radiation therapy has been proposed to treat brain tumors by using a series of rapid exposures to an array of parallel x-ray beams, each beam having uniform microscopic thickness and macroscopic breadth (i.e., microplanar). Thirty-six rats were exposed head-on either to an upright 4-mm-high, 20- or 37-microns-wide beam or to a horizontal 7-mm-wide, 42-microns-high beam of mostly 32- to 126-keV, minimally divergent x-rays from the X17 wiggler at the National Synchrotron Light Source at Brookhaven National Laboratory. Parallel slices of the head, separated at either 75 or 200 microns on center, were exposed sequentially at 310-650 grays (Gy) per second until each skin-entrance absorbed dose reached 312, 625, 1250, 2500, 5000, or 10,000 Gy. The rats were euthanized 2 weeks or 1 month later. Two rats with 10,000-Gy-entrance slices developed brain tissue necrosis. All the other 10,000- and 5000-Gy-entrance slices and some of the 2500- and 1250-Gy-entrance slices showed loss of neuronal and astrocytic nuclei and their perikarya. No other kind of brain damage was evident histologically in any rat with entrance absorbed doses < or = 5000 Gy. Brain tissues in and between all the 312- and 625-Gy-entrance slices appeared normal. This unusual resistance to necrosis is central to the rationale of microplanar beam radiation therapy for brain tumors.

Carbon nanotube-supported Ni–CeO2 catalysts. Effect of the support on the catalytic performance in the low-temperature WGS reaction

The low temperature water-gas shift (WGS) reaction has been studied over two commercial multiwall carbon nanotubes-supported nickel catalysts promoted by ceria. For comparison purposes, activated carbon-supported catalysts have also been studied. The catalytic performance and the characterization by N2 adsorption analysis, powder X-ray diffraction (XRD), temperature-programmed reduction with H2 (TPR-H2), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analysis showed that the surface chemistry has an important effect on the dispersion of ceria. As a result, ceria was successfully dispersed over the carbon nanotubes (CNTs) with less graphitic character, and the catalyst afforded better activity in WGS than the catalyst prepared over massive ceria. Moreover, a 20 wt.% CeO2 loading over this support was more active than the analogous catalyst with a 40 wt.% loading. The ceria nanoparticles were smaller when the support was previously oxidized, however this resulted in a decrease of the activity.

Effect of carbohydrate supplementation on walking performance in peripheral arterial disease: A preliminary physiologic study

Objective: In this preliminary study we tested the effect of short-term carbohydrate supplementation on carbohydrate oxidation and walking performance in peripheral arterial disease. Methods: Eleven patients with peripheral arterial disease and intermittent claudication and 8 healthy control subjects completed several weeks of baseline exercise testing, then were given supplementation for 3 days with a carbohydrate solution and placebo. Maximal walking time was assessed with a graded treadmill test. Carbohydrate oxidation during a submaximal phase of this test was measured with indirect calorimetry. At the end of baseline testing a biopsy specimen was taken from the gastrocnemius muscle, and the active fraction of pyruvate dehydrogenase complex activity was determined. Results: Carbohydrate supplementation resulted in a significant increase in body weight and carbohydrate oxidation during exercise in patients with intermittent claudication and control subjects. Maximal walking time decreased by 3% in control subjects, whereas it increased by 6% in patients with intermittent claudication (group X treatment interaction, P < .05). There was a wide range of performance responses to carbohydrate supplementation among patients with claudication (-3%-37%). This effect was greater in poorer performers, and was negatively correlated (P < .05) with muscle pyruvate dehydrogenase complex activity. Conclusion: Preliminary data suggest that carbohydrate oxidation during exercise might contribute to exercise intolerance in more dysfunctional patients with intermittent claudication and that carbohydrate supplementation might be an effective therapeutic intervention in these patients.

Effect of granule morphology on breakage behaviour during compression

In the area of dry particle breakage, Discrete Element Method (DEM) simulations have been widely used to analyse the sensitivity of various physical parameters to the behaviour of agglomerates during breakage. This paper looks at the effect of agglomerate shape and structure on the mechanisms and extent of breakage of dry agglomerates under compressive load using DEM simulations. In the simulations, a spherical-shaped agglomerate produced within the DEM code is compared with an irregularly shaped agglomerate, whose structure is that of an actual granule that was characterised with X-ray microtomography (muCT). Both agglomerates have identical particle size distribution, coordination number and surface energy values, with only the agglomerate shape and structure differing between the two. The work here details the breakage behaviour with a number of traditional DEM output parameters (i.e., contact/cluster distributions) with showing vastly different behaviour between the two agglomerates. (C) 2004 Elsevier B.V. All rights reserved.

Effect of nitrogen supply on leaf appearance, leaf growth, leaf nitrogen economy and photosynthetic capacity in maize (Zea mays L.)

Leaf area growth and nitrogen concentration per unit leaf area, N-a (g m(-2) N) are two options plants can use to adapt to nitrogen limitation. Previous work indicated that potato (Solanum tuberosum L.) adapts the size of leaves to maintain Na and photosynthetic capacity per unit leaf area. This paper reports on the effect of N limitation on leaf area production and photosynthetic capacity in maize, a C4 cereal. Maize was grown in two experiments in pots in glasshouses with three (0.84-6.0 g N pot(-1)) and five rates (0.5-6.0 g pot(-1)) of N. Leaf tip and ligule appearance were monitored and final individual leaf area was determined. Changes with leaf age in leaf area, leaf N content and light-saturated photosynthetic capacity, P a,, were measured on two leaves per plant in each experiment. The final area of the largest leaf and total plant leaf area differed by 16 and 29% from the lowest to highest N supply, but leaf appearance rate and the duration of leaf expansion were unaffected. The N concentration of expanding leaves (N-a or %N in dry matter) differed by at least a factor 2 from the lowest to highest N supply. A hyperbolic function described the relation between P-max and N-a. The results confirm the 'maize strategy': leaf N content, photosynthetic capacity, and ultimately radiation use efficiency is more sensitive to nitrogen limitation than are leaf area expansion and light interception. The generality of the findings is discussed and it is suggested that at canopy level species showing the 'potato strategy' can be recognized from little effect of nitrogen supply on radiation use efficiency, while the reverse is true for species showing the 'maize strategy' for adaptation to N limitation. (c) 2004 Elsevier B.V. All rights reserved.

The effect of high temperature on the insecticidal properties of Bt Cotton

Bt transgenic cotton has not shown the same level of resistance to bollworm in China, as in other major Bt cotton growing areas of the world. The objective of this study was to investigate the effects of high temperature on the CryIA insecticidal protein content and nitrogen metabolism, in the leaf of Bt transgenic cotton. The study was undertaken on two transgenic cotton cultivars, one conventional (Xinyang 822) and the other a hybrid (Kumian No. 1), during the 2001 and 2002 growing seasons at the Yangzhou University Farm, Yangzhou, China. In the 2001 study, potted cotton plants were exposed to 37 C for 24 h under glasshouse conditions at three growth stages peak square, peak flowering and peak boll developing periods. Based on the 2001 results, in 2002 the same two cultivars were exposed to the same temperature for 48 h at two growth stages-peak flowering and boll developing periods. The results of the study indicated that the insecticidal protein content of the leaf was not significantly affected by the stress during the square and flowering periods. However, exposure to high temperature for 24h during the boll period reduced the CryIA protein content by approximately 51% in the cultivar Kumian No 1, and 30% in Xinyang 822 in the 2001 study, and by approximately 73 and 63% for 48 h with the same cultivars, respectively, in the 2002 study. Glutamic-pyruvic transaminase (GPT) activity, total free amino acid and soluble protein content, and the activity of protease in the leaf, showed relatively little change in response to high temperature in the flowering period. However, exposure to high temperature in the boll period resulted in the following changes - a reduction of GPT activity, a sharp increase in free amino acid content, a significant decrease in soluble protein content, and significant increases in the activity of protease. The results suggest that high temperature may result in the degradation of soluble protein in the leaf, with a resulting decline in the level of the toxin CryIA. It is believed that this may be the cause of the reduced efficacy of Bt cotton in growing conditions in China, where temperatures during the boll period often reach 36-40&DEG; C. © 2004 Elsevier B.V All rights reserved.

The effect of copper toxicity on the growth and root morphology of Rhodes grass (Chloris gayana Knuth.) in resin buffered solution culture

A solution culture experiment was conducted to examine the effect of Cu toxicity on Rhodes grass (Chloris gayana Knuth.), a pasture species used in mine-site rehabilitation. The experiment used dilute, solution culture to achieve external nutrient concentrations, which were representative of the soil solution, and an ion exchange resin to maintain stable concentrations of Cu in solution. Copper toxicity was damaging to plant roots, with symptoms ranging from disruption of the root cuticle and reduced root hair proliferation, to severe deformation of root structure. A reduction in root growth was observed at an external Cu concentration of < 1 mu M, with damage evident from an external concentration of 0.2 mu M. Critical to the success of this experiment, in quantitatively examining the relationship between external Cu concentration and plant response, was the use of ion exchange resin to buffer the concentration of Cu in solution. After some initial difficulty with pH control, stable concentrations of Cu in solution were maintained for the major period of plant growth. The development of this technique will facilitate future investigations of the effect of heavy metals on plants.

A modelling approach to estimate the effect of exotic pollinators on exotic weed population dynamics: bumblebees and broom in Australia

The role of mutualisms in contributing to species invasions is rarely considered, inhibiting effective risk analysis and management options. Potential ecological consequences of invasion of non-native pollinators include increased pollination and seed set of invasive plants, with subsequent impacts on population growth rates and rates of spread. We outline a quantitative approach for evaluating the impact of a proposed introduction of an invasive pollinator on existing weed population dynamics and demonstrate the use of this approach on a relatively data-rich case study: the impacts on Cytisus scoparius (Scotch broom) from proposed introduction of Bombus terrestris. Three models have been used to assess population growth (matrix model), spread speed (integrodifference equation), and equilibrium occupancy (lattice model) for C. scoparius. We use available demographic data for an Australian population to parameterize two of these models. Increased seed set due to more efficient pollination resulted in a higher population growth rate in the density-independent matrix model, whereas simulations of enhanced pollination scenarios had a negligible effect on equilibrium weed occupancy in the lattice model. This is attributed to strong microsite limitation of recruitment in invasive C. scoparius populations observed in Australia and incorporated in the lattice model. A lack of information regarding secondary ant dispersal of C. scoparius prevents us from parameterizing the integrodifference equation model for Australia, but studies of invasive populations in California suggest that spread speed will also increase with higher seed set. For microsite-limited C. scoparius populations, increased seed set has minimal effects on equilibrium site occupancy. However, for density-independent rapidly invading populations, increased seed set is likely to lead to higher growth rates and spread speeds. The impacts of introduced pollinators on native flora and fauna and the potential for promoting range expansion in pollinator-limited 'sleeper weeds' also remain substantial risks.

Effect of deposition conditions on mechanical properties of low-temperature PECVD silicon nitride films

The effect of deposition conditions on characteristic mechanical properties - elastic modulus and hardness - of low-temperature PECVD silicon nitrides is investigated using nanoindentation. lt is found that increase in substrate temperature, increase in plasma power and decrease in chamber gas pressure all result in increases in elastic modulus and hardness. Strong correlations between the mechanical properties and film density are demonstrated. The silicon nitride density in turn is shown to be related to the chemical composition of the films, particularly the silicon/nitrogen ratio. (c) 2006 Elsevier B.V. All rights reserved.

Effect of uncorrected astigmatism on vision

PURPOSE: To examine the effect of uncorrected astigmatism in older adults. SETTING: University Vision Clinic METHOD: Twenty-one healthy presbyopes, aged 58.9±2.8 years, had astigmatism of 0.0 to -4.0 x 90?DC and -3.0DC of cylinder at 90?, 180? and 45? induced with spectacle lenses, with the mean spherical equivalent compensated to plano, in random order. Visual acuity was assessed binocularly using a computerised test chart at 95%, 50% and 10% contrast. Near acuity and reading speed were measured using standardised reading texts. Light scatter was quantified with the cQuant and driving reaction times with a computer simulator. Finally visual clarity of a mobile phone and computer screen was subjectively rated. RESULTS: Distance visual acuity decreased with increasing uncorrected astigmatic power (F=174.50, p<0.001) and was reduced at lower contrasts (F=170.77, p<0.001). Near visual acuity and reading speed also decreased with increasing uncorrected astigmatism power (p<0.001). Light scatter was not significantly affected by uncorrected astigmatism (p>0.05), but the reliability and variability of measurements decreased with increasing uncorrected astigmatic power (p<0.05). Driving simulator performance was also unaffected by uncorrected astigmatism (p>0.05), but subjective rating of clarity decreased with increasing uncorrected astigmatic power (p<0.001). Uncorrected astigmatism at 45? or 180? orientation resulted in a worse distance and near visual acuity, and subjective rated clarity than 90? orientation (p<0.05). CONCLUSION: Uncorrected astigmatism, even as low as 1.0DC, causes a significant burden on a patient’s vision. If left uncorrected, this could impact significantly on their independence, quality of life and wellbeing.

Effect of pulsed current on the electrodeposition of chromium and copper

This research was concerned with the effects of pulsed current on the electrodeposition of chromium and copper. In the case of the latter metal, a novel application has been studied and a theory proposed for the ability to improve throwing power by the joint use of organic additives and pulsed reverse current. During the course of the research, several improvements were made to the pulse plating unit.Chromium. A study was made of the effect of square wave pulsed current on various physical properties of deposits from three hard chromium plating electrolytes. The effect of varying frequency at a duty cycle of 50% on the mean bulk internal stress, visual appearance, hardness, crack characteristics and surface topography of the electrodeposits was determined. X-ray diffraction techniques were used to study the phases present in the deposits. The effect of varying frequency on the cathodic efficiencies of the electrolytes was also determined. It was found that pulsed current reduced the internal stress of deposits from the sulphate catalysed electrolyte. It also reduced or eliminated cracking of deposits and reduced deposit brightness. Under certain conditions, pulsed current was found to induce the co-deposition of hydrides of chromium. Deposit hardness was found to be reduced by the use of pulsed current. Cathodic efficiencies of the high efficiency electrolytes were reduced by use of pulsed current although this effect was minimised at high frequencies. The sulphate catalysed electrolyte showed an increase in efficiency over the frequency range where hydrides were co-deposited.Copper. The polarisation behaviour of acid copper solutions containing polyethers, sulphopropyl sulphides and chloride ions was studied using both direct and pulse reverse current. The effect of these additives on the rest potentials of copper deposits immersed in the electrolyte was also studied. Hole Throwing Power on printed circuit boards was determined using a specially designed test cell. The effect of pulsed reverse current on the hole throwing power of commercially produced printed circuit boards was also studied. Polyethers were found to have an inhibiting effect on the deposition of copper whereas the sulphopropyl sulphides produced a stimulating (i.e. depolarising) effect. Studies of rest potentials made when both additives were present indicated that the sulphopropyl sulphide was preferentially adsorbed. The use of pulsed reverse current in solutions containing both polyether and sulphopropyl sulphide was found to cause desorption of the sulphopropyl sulphide at the cathode surface. Thus, at higher current densities, the inhibiting effect of the polyether produced an increase in the cathodic polarisation potential. At lower current densities, the depolarisation effect of the sulphopropyl sulphide could still occur. On printed circuit boards, this effect was found to produce an increase in the `hole throwing power' due to depolarisation of the holes relative to the surface of the boards. Typically, using direct current, hole/surface thickness ratios of 40% were obtained when plating 0.6 mm holes in a 3.2 mm thick board at a current density of 3 A/dm2 whereas using pulsed reverse current, ratios of 80% could be obtained at an equivalent rate of deposition. This was observed both in laboratory tests and on commercially plated boards.

The effect of elevated temperature on the wear of stainless steel in contact with tungsten carbide

The bearings in the air motors of modern jet aircraft engines must operate dry in hostile conditions at temperatures up to 500° C, where the thrust races in the actuators operate at temperatures up to 300° C. One of the few metallurgical combinations which can function efficiently under these conditions is martensitic stainless steel on tungsten carbide. The work described was initiated to isolate the wear mechanisms of two such steels in contact with tungsten carbide at temperatures up to 500° C. Experiments were carried out on angular contact bearings similar to these used in service, where both rolling and sliding is present and also for pure sliding conditions using a pin-on-disc apparatus. Wear measurements of the bearings were obtained with wear rates, friction and surface temperatures from the pin-on-disc machine for a series of loads and speeds. Extensive X-ray diffraction analysis was carried out on the wear debris, with also S.E.M. analysis and hardness tests on the worn surfaces along with profilometry measurements of the disc. The oxidational parameters of the steel were obtained from measurements of oxide growth rates by ellipsometry. Three distinct mechanisms of wear were established and the latter two were found to be present in both configurations. These involve an oxidational-abrasive mechanism at loads below 40 N with pin surface temperatures up to about 300 °C, with the mechanism changing to severe wear for higher loads. As the temperature increases a third wear mechanism appears due to transfer of relatively soft oxide films to the steel surface reducing the wear rate. Theoretical K factors were derived and compared with experimental values which were found to be in good agreement for the severe wear mechanism. The pin-on-disc experiments may be useful as a screening test for material selection, without the considerable cost of producing the angular contact bearings.