In situ electron paramagnetic resonance (EPR) study of surface oxygen species on Au/ZnO catalyst for low-temperature carbon monoxide oxidation

Some paramagnetic superoxide ions detectable by electron paramagnetic resonance (EPR) can be generated on Au/ZnO catalyst by oxygen adsorption at room temperature as well as at 553 K. In both the cases, the O-2(-) ions are present on the catalyst surface. The disappearance of the O-2(-) signal by the introduction of carbon monoxide over the catalyst surface implies that the O-2(-) ions are either the active oxygen species or the precursors of the active oxygen species. The CO3- species produced are also detected by EPR. (C) 2001 Elsevier Science B.V. All rights reserved.

Apoptotic deletion of Th cells specific for the 19-kDa carboxyl-terminal fragment of merozoite surface protein 1 during malaria infection

Immunity induced by the 19-kDa fragment of merozoite surface protein 1 is dependent on CD4(+) Th cells. However, we found that adoptively transferred CFSE-labeled Th cells specific for an epitope on Plasmodium yoelii 19-kDa fragment of merozoite surface protein 1 (peptide (p)24), but not OVA-specific T cells, were deleted as a result of P. yoelii infection. As a result of infection, spleen cells recovered from infected p24-specific T cell-transfused mice demonstrated reduced response to specific Ag. A higher percentage of CFSE-labeled p24-specific T cells stained positive with annexin and anti-active caspase-3 in infected compared with uninfected mice, suggesting that apoptosis contributed to deletion of p24-specific T cells during infection. Apoptosis correlated with increased percentages of p24-specific T cells that stained positive for Fas from infected mice, suggesting that P. yoelii-induced apoptosis is, at least in part, mediated by Fas. However, bystander cells of other specificities also showed increased Fas expression during infection, suggesting that Fas expression alone is not sufficient for apoptosis. These data have implications for the development of immunity in the face of endemic parasite exposure.

Deep and superficial fibers of the lumbar multifidus muscle are differentially active during voluntary arm movements

AB Study Design. A cross-sectional study was conducted. Objective. To determine the activity of the deep and superficial fibers of the lumbar multifidus during voluntary movement of the arm. Summary of Background Data. The multifidus contributes to stability of the lumbar spine. Because the deep and superficial parts of the multifidus are near the center of lumbar joint rotation, the superficial fibers are well suited to control spine orientation, and the deep fibers to control intervertebral movement. However, there currently are limited in vivo data to support this distinction. Methods. Electromyographic activity was recorded in both the deep and superficial multifidus, transversus abdominis, erector spinae, and deltoid using selective intramuscular electrodes and surface electrodes during single and repetitive arm movements. The latency of electromyographic onset in each muscle during single movements and the pattern of electromyographic activity during repetitive movements were compared between muscles. Results. With single arm movements, the onset of electromyography in the erector spinae and superficial multifidus relative to the deltoid was dependent on the direction of movement, but the onset in the deep multifidus and transversus abdominis was not. With repetitive arm movements, peaks in superficial multifidus and erector spinae electromyography occurred only during flexion for most subjects, whereas peaks in deep multifidus electromyography occurred during movement in both directions. Conclusions. The deep and superficial fibers of the multifidus are differentially active during single and repetitive movements of the arm. The data from this study support the hypothesis that the superficial multifidus contributes to the control of spine orientation, and that the deep multifidus has a role in controlling intersegmental motion. (C) 2002 Lippincott Williams & Wilkins, Inc.

Nature and specificity of the required protective immune response that develops postchallenge in mice vaccinated with the 19-kilodalton fragment of Plasmodium yoelii merozoite surface protein 1

Immunity induced by the 19-kDa fragment of Plasmodium yoelii merozoite surface protein 1 (MSP1(19)) is dependent on high titers of specific antibodies present at the time of challenge and a continuing active immune response postinfection. However, the specificity of the active immune response postinfection has not been defined. In particular, it is not known whether anti-MSP1(19) antibodies that arise following infection alone are sufficient for protection. We developed systems to investigate whether an MSP1(19)-specific antibody response alone both prechallenge and postchallenge is sufficient for protection. We were able to exclude antibodies with other specificities, as well as any contribution of MSP1(19)-specific CD4(+) T cells acting independent of antibody, and we concluded that an immune response focused solely on MSP1(19)-specific antibodies is sufficient for protection. The data imply that the ability of natural infection to boost an MSPI,g-specific antibody response should greatly improve vaccine efficacy.

Analysis of service stress corrosion cracking in a natural gas transmission pipeline, active or dormant?

Stress corrosion cracks (SCC) had been found in a natural gas transmission pipeline during a dig-up and inspection program. The question was raised as to whether the SCC was active or dormant. This paper describes the resultant investigation to determine if a particular service crack was actively growing. The strategy adopted was to assess the appearance of the fracture surface of the service crack and to compare with expectations from laboratory specimens with active SCC. The conclusions from this study are as follows. To judge whether a crack in the service pipe is active or dormant, it is reasonable to compare the very crack tip of the service crack and a fresh crack in a laboratory sample. If the crack tip of the active laboratory sample is similar to that of the service pipe, it means the crack in the service pipe is likely to be active. From the comparison of the crack tip between the service pipe and the laboratory samples, it appears likely that the cracks in the samples extracted from service were most likely to have been active intergranular stress corrosion cracks. (C) 2003 Elsevier Ltd. All rights reserved.

Patch and whole of surface mass-transfer rate measurements on a stepped rotating cylinder electrode

A recently developed whole of surface electroplating technique was used to obtain mass-transfer rates in the separated flow region of a stepped rotating cylinder electrode. These data are compared with previously reported mass-transfer rates obtained with a patch electrode. It was found that the two methods yield different results, where at lower Reynolds numbers, the mass-transfer rate enhancement was noticeably higher for the whole of the surface electrode than for the patch electrode. The location of the peak mass transfer behind the step, as measured with a patch electrode, was reported to be independent of the Reynolds number in previous studies, whereas the whole of the surface electrode shows a definite Reynolds number dependence. Large eddy simulation results for the recirculating region behind a step are used in this work to show that this difference in behavior is related to the existence of a much thinner fluid layer at the wall for which the velocity is a linear junction of distance from the wall. Consequently, the diffusion layer no longer lies well within a laminar sublayer. It is concluded that the patch electrode responds to the wall shear stress for smooth wall flow as well as for the disturbed flow region behind the step. When the whole of the surface is electro-active, the response is to mass transfer even when this is not a sole function of wall shear stress. The results demonstrate that the choice of the mass-transfer measurement technique in corrosion studies can have a significant effect on the results obtained from empirical data.

A study on transition of iron from active into passive state

An investigation was carried out on the transition of an iron electrode from active to passive state in a sulphuric acid solution. It was found that the active-passive transition was an auto-catalytic process in which a pre-passive film grew on the electrode surface. The growing pre-passive film had a fractal edge whose dimension was affected by the applied passivating potential and the presence of chlorides in the solution. Applying a more positive passivating potential led to a faster active-passive transition and resulted in a more irregular pre-passive film. If chlorides were introduced into the sulphuric acid solution, the active-passive transition became more rapid and the pre-passive film more irregular. Apart from the influence on the growth of the pre-passive film, the presence of chlorides in the passivating solution was found to deteriorate the stability of the final passive film. All these phenomena can be understood if the passivating iron electrode is regarded as a dissipative system. To explain these results, a fractal pre-film model is proposed in this paper. (C) 2004 Elsevier Ltd. All rights reserved.

The influence of natural body sway on neuromuscular responses to an unpredictable surface translation

Previous research has shown that the postural configuration adopted by a subject, such as active leaning, influences the postural response to an unpredictable support surface translation. While those studies have examined large differences in postural conditions, it is of additional interest to examine the effects of naturally occurring changes in standing posture. Thus, it was hypothesized that the normal postural sway observed during quiet standing would affect the responses to an unpredictable support surface translation. Seventeen young adults stood quietly on a moveable platform and were perturbed in either the forward or backward direction when the location of the center of pressure (COP) was either 1.5 standard deviations anterior or posterior to the mean baseline COP signal. Postural responses, in the form of electromyographic (EMG) latencies and amplitudes, were recorded from lower limb and trunk muscles. When the location of the COP at the time of the translation was in the opposite, as compared to the same, direction as the upcoming translation, there was a significantly earlier onset of the antagonists (10-23%, i.e. 15-45 ms) and a greater EMG amplitude (14-39%) in four of the six recorded muscles. Stepping responses were most frequently observed during trials where the position of the COP was opposite to the direction of the translation. The results support the hypothesis that postural responses to unpredictable support surface translations are influenced by the normal movements of postural sway. The results may help to explain the large variability of postural responses found between past studies.

Free-Surface Aeration and Momentum Exchange at a Bottom Outlet

This study aims to provide some new understanding of the air-water flow properties in high-velocity water jets discharging past an abrupt drop. Such a setup has been little studied to date despite the relevance to bottom outlets. Downstream of the step brink, the free-jet entrains air at both upper and lower air-water interfaces, as well as along the sides. An air-water shear layer develops at the lower nappe interface. At the lower nappe, the velocity redistribution was successfully modelled and the velocity field was found to be similar to that in two-dimensional wake flow. The results highlighted further two distinct flow regions. Close to the brink (Wex < 5000), the flow was dominated by momentum transfer. Further downstream (Wex > 5000), a strong competition between air bubble diffusion and momentum exchanges took place.

A modified discrete random pore model allowing for different initial surface reactivity

We investigate here a modification of the discrete random pore model [Bhatia SK, Vartak BJ, Carbon 1996;34:1383], by including an additional rate constant which takes into account the different reactivity of the initial pore surface having attached functional groups and hydrogens, relative to the subsequently exposed surface. It is observed that the relative initial reactivity has a significant effect on the conversion and structural evolution, underscoring the importance of initial surface chemistry. The model is tested against experimental data on chemically controlled char oxidation and steam gasification at various temperatures. It is seen that the variations of the reaction rate and surface area with conversion are better represented by the present approach than earlier random pore models. The results clearly indicate the improvement of model predictions in the low conversion region, where the effect of the initially attached functional groups and hydrogens is more significant, particularly for char oxidation. It is also seen that, for the data examined, the initial surface chemistry is less important for steam gasification as compared to the oxidation reaction. Further development of the approach must also incorporate the dynamics of surface complexation, which is not considered here.

Changes in neutrophil surface receptor expression, degranulation, and respiratory burst activity following moderate and high intensity exercise

Intense exercise stimulates the systemic release of a variety of factors that alter neutrophil surface receptor expression and functional activity. These alterations may influence resistance to infection after intense exercise. The aim of this study was to examine the influence of exercise intensity on neutrophil receptor expression, degranulation (measured by plasma and intracellular myeloperoxidase concentrations), and respiratory burst activity. Ten well-trained male runners ran on a treadmill for 60 min at 60% [moderate-intensity exercise (MI)] and 85% maximal oxygen consumption [high-intensity exercise (HI)]. Blood was drawn immediately before and after exercise and at 1 h postexercise. Immediately after HI, the expression of the neutrophil receptor CD16 was significantly below preexercise values (P < 0.01), whereas MI significantly reduced CD35 expression below preexercise values (P < 0.05). One hour after exercise at both intensities, there was a significant decline in CD11b expression (P < 0.05) and a further decrease in CD16 expression compared with preexercise values (P < 0.01). CD16 expression was lower 1 h after HI than 1 h after MI (P < 0.01). Immediately after HI, intracellular myeloperoxidase concentration was less than preexercise values (P < 0.01), whereas plasma myeloperoxidase concentration was greater (P < 0.01), indicating that HI stimulated neutrophil degranulation. Plasma myeloperoxidase concentration was higher immediately after HI than after MI (P < 0.01). Neutrophil respiratory burst activity increased after HI (P < 0.01). In summary, both MI and HI reduced neutrophil surface receptor expression. Although CD16 expression was reduced to a greater extent after HI, this reduction did not impair neutrophil degranulation and respiratory burst activity.

Inorganic surface passivation of PbS nanocrystals resulting in strong photoluminescent emission

Strong photoluminescent emission has been obtained from 3 nm PbS nanocrystals in aqueous colloidal solution, following treatment with CdS precursors. The observed emission can extend across the entire visible spectrum and usually includes a peak near 1.95 eV. We show that much of the visible emission results from absorption by higher-lying excited states above 3.0 eV with subsequent relaxation to and emission from states lying above the observed band-edge of the PbS nanocrystals. The fluorescent lifetimes for this emission are in the nanosecond regime, characteristic of exciton recombination.

Polarized photoluminescence from surface-passivated lead sulfide nanocrystals

Effective surface passivation of lead sulfide (PbS) nanocrystals (NCs) in an aqueous colloidal solution has been achieved following treatment with CdS precursors. The resultant photoluminescent emission displays two distinct components, one originating from the absorption band edge and the other from above the absorption band edge. We show that both of these components are strongly polarized but display distinctly different behaviours. The polarization arising from the band edge shows little dependence on the excitation energy while the polarization of the above-band-edge component is strongly dependent on the excitation energy. In addition, time-resolved polarization spectroscopy reveals that the above-band-edge polarization is restricted to the first couple of nanoseconds, while the band edge polarization is nearly constant over hundreds of nanoseconds. We recognize an incompatibility between the two different polarization behaviours, which enables us to identify two distinct types of surface-passivated PbS NC.

Investigation of the role of cadmium sulfide in the surface passivation of lead sulfide quantum dots

Surface passivation of PbS nanocrystals (NC), resulting in strong photoluminescence, can be achieved by the introduction of CdS precursors. The role of CdS in the surface passivation of PbS NCs is uncertain, as the crystalline structure of CdS and PbS are different, which should impede effective epitaxial overgrowth. Absorption spectroscopy is used to show that the CdS precursors strongly interact with the PbS NC surface. Electron microscopy reveals that the introduction of CdS precursors results in an increased particle size, consistent with overcoating. However, we also find the process to be highly non-uniform. Nevertheless, evidence for epitaxial growth is found, suggesting that effective surface passivation may be possible.