Search

The impacts of human-driven environmental changes on the stability of natural grasslands have been assessed by comparing differences between manipulative warming and grazing plots and reference plots. However, little is known about whether or how ambient climate regulates the effects of manipulative treatments. A 36-year observational dataset shows that there is a nonlinear response of community stability to ambient climate. Manipulative warming and grazing decrease community stability with experiment duration through an increase in legume coverage and/or decrease in species asynchrony, due to exceeding the threshold of background annual mean air temperature with decreasing background annual mean air temperature through time during the 10-year experiment period. Moreover, the temperature sensitivity of community stability is more sensitive under the ambient treatment than under the manipulative treatments. Therefore, our study emphasizes the importance of the context dependency of the response of community stability to human-driven environmental changes.

Changes in ecological processes over time in ambient treatments are often larger than the responses to manipulative treatments in climate change experiments. However, the impacts of human-driven environmental changes on the stability of natural grasslands have been typically assessed by comparing differences between manipulative plots and reference plots. Little is known about whether or how ambient climate regulates the effects of manipulative treatments and their underlying mechanisms. We collected two datasets, one a 36-year long-term observational dataset from 1983 to 2018, and the other a 10-year manipulative asymmetric warming and grazing experiment using infrared heaters with moderate grazing from 2006 to 2015 in an alpine meadow on the Tibetan Plateau. The 36-year observational dataset shows that there was a nonlinear response of community stability to ambient temperature with a positive relationship between them due to an increase in ambient temperature in the first 25-years and then a decrease in ambient temperature thereafter. Warming and grazing decreased community stability with experiment duration through an increase in legume cover and a decrease in species asynchrony, which was due to the decreasing background temperature through time during the 10-year experiment period. Moreover, the temperature sensitivity of community stability was higher under the ambient treatment than under the manipulative treatments. Therefore, our results suggested that ambient climate may control the directional trend of community stability, while manipulative treatments may determine the temperature sensitivity of the response of community stability to climate relative to the ambient treatment. Our study emphasizes the importance of the context dependency of the response of community stability to human-driven environmental changes.

The effect of interface roughness on exchange bias for NiFe/FeMn bilayers is investigated for polycrystalline films and epitaxial films. Three different systems were investigated: polycrystalline Ta (10 nm)/Ni80Fe20 (10nm)/Fe50Mn50 (20 nm) films on oxygen plasma-etched Si(100) or Cu/H–Si(100) and epitaxial Ni80Fe20 (10nm)/Fe60Mn40 (20 nm) films on Cu/H–Si(110). For films grown on plasma-etched substrates, as the etching time is increased, film roughness increases up to 12 nm. For the polycrystalline films grown on ultrathin Cu underlayers, x-ray diffraction shows the fcc (111) texture is greatly reduced as the thickness is increased. The epitaxial Cu/Si(110) buffer layer induces fcc (111) epitaxial growth and modifies the interface morphology. The dependence of exchange bias on roughness for each set of samples is explained in terms of a competition between the interfacial exchange coupling and the af uniaxial anisotropy.

The electrodeposition of Co–Fe–Ni films from electrolytes without additives and their magnetic and structural properties in the as-deposited and vacuum annealed states are reported. Co52Fe26Ni22 alloy films exhibit a saturation magnetization Bs of 20 kG, coercivity Hc around 1 Oe, resistivity of 22 μΩ cm and saturation magnetostriction of about 10−6. Crystalline structure from bcc to fcc changes with increasing Ni content; films with best soft magnetic properties are obtained when bcc and fcc structures coexist. Varying electrolyte formulation or using pulse plating, the deposition parameters which yield optimum soft magnetic properties vary, but alloy composition and crystalline structure of optimum films are unchanged. dc plated films exhibit Ni enrichment at the interface in a region of about 1 μm thickness. Easy axis annealing in a vacuum of 10−7 Torr at 200–280 °C for 30 min decreases Hc and slightly decreases the anisotropy field. Annealing, however, does not change Bs, crystalline structure or latt...

In conventional 200 mm wafer processing, backside defects are not considered to be of much concern because they are obscured by wafer backside topography. However, in current 300 mm wafer processing where both sides of a wafer are polished, backside defects require more consideration. In the beginning, backside defect inspection examined particle contamination because particle contamination adversely influences the depth of field in lithography. Recently, metal contamination is of concern because backside metal contamination causes cross‐contamination in a process line, and backside metals easily transfer to the front surface. As the industry strives to yield more devices from the area around the wafer edge, edge exclusion requirements have also become more important. The current International Technology Roadmap for Semiconductors [1] requires a 2 mm edge exclusion. Therefore, metal contamination must be controlled to less than 2 mm from the edge because metal contamination easily diffuses in silicon wafers. To meet these current semiconductor processing requirements, newly developed zero edge exclusion TXRF (ZEE‐TXRF) and backside measurement TXRF (BAC‐TXRF) are effective metrology methods.

We describe recent experiments in which we attempted the initial steps for fabricating twodimensional arrays of metal nanocrystals. We use a commercial pulsed-laser deposition system in concert with a focused ion beam to attempt control over both lateral and vertical dimensions at the nanometer length scale. In our experiments, regular arrays of holes typically 80 nm in diameter were drilled in Si substrates using the focused ion beam. Silver atoms were then deposited onto these substrates by pulsed laser evaporation from a metallic target in high vacuum. Under certain conditions of substrate temperature, laser pulse repetition rate, and fluence, small silver nanoclusters form preferentially around the structures previously etched in the silicon surfaces by the focused ion beam.

The problem of the formation of molecular hydrogen is certainly the most important one in astrophysical environments, and in interstellar clouds in particular, because H2 is the most abundant molecule in space and, as such, it is the most frequent collisional partner of all other particles in the gas phase. This relevant peculiarity makes of H2 what has been called (Duley and Williams, 1984) the “seminal molecule”, the mother of all other molecular species; it, in fact once ionized by UV photons in diffuse clouds and by cosmic rays in dense, initiates ion-molecule reactions (the only ones that can efficiently take place in the cold interstellar medium because characterized by low energy activation barriers) chains that have been succesfully proposed to synthesize most of observed species in space. Furthermore molecular hydrogen, together with the other species, provides a very efficient mechanism for cooling clouds. Molecules, in fact, once are collisionally excited, deexcite in cascade through rotovibrational transitions emitting photons to which the cloud itself is transparent. This cooling mechanism helps the gravitational collapse of interstellar clouds, increases the formation rate of stars and has great impact in the structure and evolution of galaxies. In this note we report on measurements of molecular hydrogen synthesis for the first time performed in conditions and on materials close to interstellar reality (Pirronello et al., 1997a,b).

We report on laboratory measurements of molecular hydrogen formation and recombination on an olivine slab as a function of surface temperature under conditions relevant to those encountered in the interstellar medium. On the basis of our experimental evidence, we recognize that there are two main regimes of H coverage that are of astrophysical importance; for each of them we provide an expression giving the production rate of molecular hydrogen in interstellar clouds., Comment: Accepted for publications in: Astrophysical Journal Letters. Corresponding author: Gianfranco Vidali: gvidali@syr.edu (http://physics.syr.edu/research/surface_physics/)

We report on experimental investigations of HD production on low temperature surfaces of silicates under conditions relevant to hydrogen recombination on dust grain surfaces in the interstellar medium. Following adsorption of H and D at thermal energies on a silicate surface (olivine) in the 5–15 K range, flash desorption experiments were conducted to yield desorption energies and order of desorption kinetics. We find that significant recombination occurs only at the lowest temperatures. Current models of diffusion and recombination of H on cold surfaces, developed to explain interstellar recombination processes, will be discussed and appraised in the light of the new results.

We report on the first results of experiments to measure the recombination rate of hydrogen on surfaces of astrophysical interest. Our measurements give lower values for the recombination efficiency (sticking probability S x probability of recombination upon H-H encounter $\gamma$) than model-based estimates. We propose that our results can be reconciled with average estimates of the recombination rate (1/2 n(H) n(g) v(H)A S $\gamma$) from astronomical observations, if the actual surface of an average grain is rougher, and its area bigger, than the one considered in models., Comment: 13 pages plus 5 figures (only change: this version has 5 figures included); this paper is to appear in Astrophysical Journal Letters.