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A detailed analysis of the vibrational spectra of CH3, CH2D, and CD3 adsorbed on Ni(111) and the products of their reactions is presented. The synthesis of adsorbed methyl radicals from CH4, CH3D, or CD4 is effected by molecular beam techniques. The ability to measure these spectra by high-resolution electron energy loss spectroscopy (HREELS) at higher resolution (35 cm-1) and higher sensitivity (5×106 counts/s) has allowed new features to be observed and a symmetry analysis to be carried out. It is concluded that the CH3 radical is adsorbed with C3v symmetry on a threefold hollow site. The symmetric C–H stretch mode of CH3 and the overtone of the antisymmetric deformation mode are observed to be in Fermi resonance. At temperatures above 150 K, CH3 dissociates to form adsorbed CH. Confirmation for the assignment to a CH species is found in the observation that the spectrum measured after thermal decomposition of CH2D is a superposition of those from the decomposition of CH3 and CD3. The adsorption site of the CH species is concluded to be a threefold hollow site and the geometry of the Ni3–C–H is concluded to be pyramidal. At temperatures above 250 K, carbon–carbon bond formation between the CH species is observed to yield C2H2. Low coverages of C2H2 are shown to dehydrogenate at 400 K. High coverages of C2H2 are shown conclusively to trimerize to form adsorbed benzene in contrast to a literature report of C2H2 dissociation to adsorbed CH at these temperatures. The relative stabilities of the hydrocarbon species on Ni(111) are determined to be CH3

During the last two decades, several land surface schemes for use in climate, regional and/or mesoscale, hydrological and ecological models have been designed. Incorrect parametrization of land-surface processes and prescription of the surface parameters in atmospheric modeling, can result in artificial changes of the horizontal gradient of the sensible heat flux. Thus, an error in horizontal temperature gradient within the lower atmosphere may be introduced. The reliability of the model depends on the quality of boundary layer scheme implemented and its sensitivity to the bare soil and vegetation parameters. In this study, a series of sensitivity experiments has been conducted over broad time scales, using a version of the ARPEGE Climate Model coupled to the ISBA land surface scheme in order to investigate model sensitivity to separate changes in land surface parameters over Africa. Effects of perturbing vegetation cover, distribution of soil depth, albedo of vegetation, roughness length, leaf area index and minimum stomatal resistance were explored by using a simple statistical analysis. Identifying which parameters are important in controlling turbulent energy fluxes, temperature and soil moisture is dependent on which variables are used to determine sensibility, which type of vegetation and climate regime is being simulated and the magnitude and sign of the parameter change. This study does not argue that a particular parameter is important in ISBA, rather it shows that no general ranking of parameters is possible. So, it is essential to specify all land surface parameters with greater precision when attempting to determine the climate response to modification of the land surface. The implication of ISBA being sensitive to parameters that cannot be validated suggests that there will always be considerable doubt over the predictive quality of land-surface schemes. [ABSTRACT FROM AUTHOR]

The primary goal of this investigation is to focus on a “realistic” scenario for simulating impacts on regional African climate of future deforestation in a greenhouse-warmed world. Combined effects of plausible land-cover change and greenhouse warming are assessed by ‘time-slice’ simulations with an atmospheric general circulation model (AGCM) for the middle of the twenty first century. Three “time-slice” integrations have been performed with the ARPEGE-Climat AGCM incorporating a zooming technique to achieve a resolution of about 100 km over Africa. A control run for the current climate is forced by observed climatological sea surface temperatures (SSTs) and the observed vegetation distribution is specified from a new vegetation database, in order to improve the geographical distribution and properties of the vegetation cover. Future SST changes are derived from a transient coupled atmosphere–ocean simulation for scenario B2 of the International Panel on Climate Change (IPCC). Future vegetation changes are specified from a simulation of scenario B2 with the Integrated Model to Assess the Global Environment (IMAGE) developed at the National Institute of Public Health and the Environment in the Netherlands (RIVM). The results show that land surface processes can locally modulate greenhouse warming effects for African climate, with reductions of surface transpiration and small increases of surface temperature. Deforestation of tropical Africa has overall only a marginal effect on precipitation because of a compensatory increase in moisture convergence. Energy budget analyses show that increases in surface temperature are produced both by increases of greenhouse gases (GHG) concentration from the increase in downward atmospheric longwave radiation, and by African tropical deforestation from the resulting reduction in transpiration. This study indicates that realistic land-use changes, though of smaller amplitude than greenhouse gas forcing, may have a small regional effect in projections of future climate. [ABSTRACT FROM AUTHOR]

Tropical monsoon circulations exhibit substantial interannual variability. Establishing clear links between this variability and the slowly varying boundary forcing (sea surface temperatures, SSTs, and land surface conditions) has proved difficult. For example, no clear relationships have been found between SST anomalies associated with El Nino/La Nina events and monsoon rainfall. Despite much research over the past 50 years, there are still questions regarding how different components of the land–atmosphere–ocean system contribute to tropical monsoon variability. This study examines the question of land-surface–atmosphere interactions in large-scale tropical convection and their role in rainfall interannual variability. The analysis method is based on a conceptual model of convection energetics applied every day of the simulation at the grid points within the region of interest. This allows for a distinction between the frequency and the characteristic energy and water cycle of these events. With two ensembles of five and three experiments in which different land-surface schemes are used, the relation between land-surface processes and variation of the frequency of convection is studied. It has been found in this modeling study that the formulation of land surface schemes may be important for both the simulation of mean tropical precipitation and its interannual variability by way of the frequency of convective events. Linked to this is an increased response of hydrological cycle over land to SSTAs. Numerous studies have suggested that large-scale factors, such as SST, are the dominant control. However the influence of surface processes depends on the areal extent and distance that separates the region from the ocean. The fact that differences between tropical regions decreases as convection intensifies strengthens this hypothesis. The conclusion is that it is inappropriate to separate the causes of interannual variability between SSTAs and land-surface anomalies to explain precipitation variations as land surface processes play a significant mediating role in the relationship between SSTs and monsoon strength. However there remains the possibility that a substantial portion of variability is due to dynamical processes internal to the atmosphere. Determining the relative roles of internal and lower boundary forcing processes in producing interannual variations in the tropical climate is a major objective of future research. [ABSTRACT FROM AUTHOR]

The Interstellar Boundary Explorer (IBEX) Science Operations Center is responsible for supporting analysis of IBEX data, generating special payload command procedures, delivering the IBEX data products, and building the global heliospheric maps of energetic neutral atoms (ENAs) in collaboration with the IBEX team. We describe here the data products and flow, the sensor responses to ENA fluxes, the heliospheric transmission of ENAs (from 100 AU to 1 AU), and the process of building global maps of the heliosphere. The vast majority of IBEX Science Operations Center (ISOC) tools are complete, and the ISOC is in a remarkable state of readiness due to extensive reviews, tests, rehearsals, long hours, and support from the payload teams. The software has been designed specifically to support considerable flexibility in the process of building global flux maps. Therefore, as we discover the fundamental properties of the interstellar interaction, the ISOC will iteratively improve its pipeline software, and, subsequently, the heliospheric flux maps that will provide a keystone for our global understanding of the solar wind’s interaction with the interstellar medium. The ISOC looks forward to the next chapter of the IBEX mission, as the tools we have developed will be used in partnership with the IBEX team and the scientific community over the coming years to define our global understanding of the solar wind’s interaction with the local interstellar medium. [ABSTRACT FROM AUTHOR]

Abstract: Real-time, accurate assessment of islet viability is critical for avoiding transplantation of nontherapeutic preparations. Measurements of the intracellular ADP/ATP ratio have been recently proposed as useful prospective estimates of islet cell viability and potency. However, dead cells may be rapidly depleted of both ATP and ADP, which would render the ratio incapable of accounting for dead cells. Since the DNA of dead cells is expected to remain stable over prolonged periods of time (days), we hypothesized that use of the ATP/DNA ratio would take into account dead cells and may be a better indicator of islet cell viability than the ADP/ATP ratio. We tested this hypothesis using mixtures of healthy and lethally heat-treated (HT) rat insulinoma cells and human islets. Measurements of ATP/DNA and ADP/ATP from the known mixtures of healthy and HT cells and islets were used to evaluate how well these parameters correlated with viability. The results indicated that ATP and ADP were rapidly (within 1 hour) depleted in HT cells. The fraction of HT cells in a mixture correlated linearly with the ATP/DNA ratio, whereas the ADP/ADP ratio was highly scattered, remaining effectively unchanged. Despite similar limitations in both ADP/ADP and ATP/DNA ratios, in that ATP levels may fluctuate significantly and reversibly with metabolic stress, the results indicated that ATP/DNA was a better measure of islet viability than the ADP/ATP ratio. [Copyright &y& Elsevier]

Pump shafts used for power generation are susceptible to fatigue cracking while often in near-continuous operation. Technology based on torsional vibration is under development for condition-based assessment of shaft health. The focus of this paper is on the relationship between a crack, which propagated due to bending loads, and the torsional stiffness of the shaft. An analytical method to determine the compliance associated with a crack has been implemented for a semi-elliptical surface crack. A 3-D finite element model of a shaft section with a crack has also been used to predict the effect of a crack on stiffness. Fatigue cracks were seeded in shafts on a three-point bend apparatus. A benchtop test rig was constructed to evaluate the torsional natural frequencies of a cracked shaft system. Quasistatic torsional stiffness tests indicated that crack closure has an effect on the results. A torsional finite element model of the benchtop test rig indicates that the first torsional natural frequency is reduced by the propagation of a crack. The reduction in torsional stiffness of the shaft inferred from the natural frequency results is in reasonable agreement with the quasistatic results and the model predictions. [ABSTRACT FROM AUTHOR]