10,000 publications from this institution
It has been established that microelectromechanical systems created from polycrystalline silicon thin films are subject to cyclic fatigue. Prior work by the authors has suggested that although bulk silicon is not susceptible to fatigue failure in ambient air, fatigue in micron-scale silicon is a result of a "reaction-layer" process, whereby high stresses induce a thickening of the post-release oxide at stress concentrations such as notches, which subsequently undergoing moisture-assisted cracking. However, there exists some controversy regarding the post-release oxide thickness of the samples used in the prior study. In this letter, we present data from devices from a more recent fabrication run that confirm our prior observations. Additionally, new data from tests in high vacuum show that these devices do not fatigue when oxidation and moisture are suppressed. Each of these observations lends credence to the "reaction-layer" mechanism.
The rational camera model recently introduced in [18] provides a general methodology for studying abstract nonlinear imaging systems and their multi-view geometry. This paper builds on this framework to study physical realizations of rational cameras. More precisely, we give an explicit account of the mapping between between physical visual rays and image points (missing in the original description), which allows us to give simple analytical expressions for direct and inverse projections. We also consider primitive camera models, that are orbits under the action of various projective transformations, and lead to a general notion of intrinsic parameters. The methodology is general, but it is illustrated concretely by an in-depth study of two-slit cameras, that we model using pairs of linear projections. This simple analytical form allows us to describe models for the corresponding primitive cameras, to introduce intrinsic parameters with a clear geometric meaning, and to define an epipolar tensor characterizing two-view correspondences. In turn, this leads to new algorithms for structure from motion and self-calibration.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Approaching a Holy Grail? A regioselective functionalization of alkanes occurs with commercially available rhenium catalysts and borane reagents under photochemical conditions [Eq. (1)]. Mechanistic studies indicate that the regioselectivity results from a direct thermal reaction of a photochemically generated 16-electron boryl complex with alkane.
Electrocatalysts supporting the oxygen electrode reaction are commonly covered with thin oxide films that may have a profound influence over the kinetics of the reaction. Little is currently known about the role of oxide films on electrocatalysts, particularly with regard to the role of the defect structure. In this work, the physical and defect structures of the oxide film that forms on platinum in under steady-state conditions have been investigated using electrochemical impedance spectroscopy (EIS) and ARXPS (angle-resolved X-ray photoelectron spectroscopy). Mott-Schottky analysis shows that the film is n-type, indicating that the defects in the film are either platinum interstitials or oxygen vacancies, or both. ARXPS analysis shows that, for potentials between 1.0 and , a single-layer film develops, with the principal oxidation state for Pt (in the film) being . However, a bi-layer structure was observed for films formed at potentials greater than and ARXPS analysis shows that these bilayer films comprise an inner layer containing and an outer layer containing . Optimization of the point defect model on the EIS data yields values for various kinetic parameters that are then used to predict the steady-state thickness and current. Good agreement with experiment is obtained.
Associate Professor of Health Education, School of Public Health, University of California, Berkeley, California
Reduced cell proliferation is associated with lower cancer risk. Alternate-day fasting (ADF), defined as alternating 24-h periods of ad libitum feeding and fasting, decreases cell proliferation. The effect of modified regimens of ADF on cell proliferation, however, has not been examined. This study measured the effects of modified ADF regimens on prostate and splenic T-cell proliferation and circulating insulin-like growth factor-1 (IGF-1) levels in mice. In a 4-wk study, 24 male C57BL/6J mice were randomized to one of four interventions: 1) ADF-25% [25% calorie restriction (CR) on fast day], 2) ADF-50% (50% CR on fast day), 3) ADF-100% (100% CR on fast day), and 4) control. Body weight of the ADF-100% group was less ( P < 0.005) than that of the ADF-25% and ADF-50% groups posttreatment. On the feast day, the ADF-100% and ADF-50% groups ate 85% and 45% more food, respectively, than controls, indicating a hyperphagic response to fasting. Proliferation rates of T-cells were 6% and 30% lower ( P < 0.05) in the ADF-50% and ADF-100% groups, respectively, relative to controls. Prostate cell proliferation was reduced ( P < 0.05) by 49% in the ADF-100% group, relative to controls, but did not change in the other groups. IGF-1 levels were reduced ( P < 0.05) by 40%, relative to controls, in the ADF-100% group. These findings confirm the beneficial effects of ADF-100% on cancer risk by decreasing cell proliferation and IGF-1 levels and suggest that modified ADF regimens comprising 25–50% CR on the fast day do not replicate these effects.
The authors used a modified Stroop task to study how people with posttraumatic stress disorder (PTSD) process threatening information. Participants were motor vehicle accident (MVA) survivors with either PTSD (n = 15), simple phobia of driving (n = 15), or low anxiety (n = 15). Participants named colors of 4 types of words: strong threat words (MVA related), mild threat words (MVA related), positive words, and neutral words. Participants with PTSD demonstrated greater interference on strong threat words than those with simple phobia or low anxiety. Contrary to expectation, participants with simple phobia did not display an interference effect. Findings suggest that individuals with PTSD and simple phobia may process threatening information differently. The nature of attentional bias in different anxiety conditions following trauma is discussed.
Probing is a common operation employed to reduce the position uncertainty of objects. This paper demonstrates a technique for constructing provably near-optimal probing strategies for precisely localizing polygonal parts. This problem is shown to be dual to the well-studied grasping problem of computing optimal finger placements as defined by B. Mishra and others. A useful quality metric of any given probing strategy can easily be computed from simple geometric constructions in the displacement space of the polygon. The approach will always find a minimal set of probes that is guaranteed to be near optimal for constraining the position of the polygon. The size of the resulting set of probes is within O(1) of the optimal number of probes and can be computed in O(n log 2 n) time, whereas the exact optimal solution is in NP-hard. The result of this work is a probing strategy useful in practice for refining part poses.
Abstract The environment of the east central Great Plains of North America can be very extreme during the course of a growing season. A field study was thus conducted during the summer of 1979 to examine the exchange of mass and energy between the atmosphere and a soybean canopy [ Glycine max (L.) Merrill] for various environmental conditions experienced in the east central Great Plants of North America. The crop was planted in a Typic Argiudoll (Sharpsburg silty, clay loam) soil. Measurements of mass and energy exchange rates were made using the Bowen‐ratio energy balance technique. Hot, clear days dominated by sensible heat advection limited CO 2 exchange but increased latent heat flux. As a result, the CO 2 ‐water flux ratio (CWFR), a measure of water‐use efficiency, was low. Cloudy days suppressed both CO 2 and latent heat flux. This effect caused CWFR to be greater. Optimal conditions for photosynthesis and CWFR occurred in the absence of sensible heat advection on clear days with moderate temperatures. Our measurements indicate that a developed soybean canopy (LAI of 4.1) did not become light saturated at photosynthetically active radiation (PAR) levels exceeding 400 Wm −2 . Optimal air temperatures for CO 2 exchange ranged between 29 and 32 C. Higher temperatures led to a reduction in CO 2 , exchange. The CWFR was found to be dependent on both net radiation and sensible heat advection.
