10,079 research outputs found
Renewing solar science: The solar maximum repair mission
The purpose of the Solar Maximum Repair Mission is to restore the operational capacity of the satellite by replacing the attitude control system module and servicing two of the scientific instruments on board. The mission will demonstrate the satellite servicing capacity of the Space Shuttle for the first time
The Advanced X-Ray Astrophysics Facility. Observing the Universe in X-Rays
An overview of the Advanced X ray Astronophysics Facility (AXAF) program is presented. Beginning with a brief introduction to X ray astrophysics, the AXAF observatory is described including the onboard instrumentation and system capabilities. Possible X ray sources suitable for AXAF observation are identified and defined
Assembly, Structure, and Reactivity of Cu\u3csub\u3e4\u3c/sub\u3eS and Cu\u3csub\u3e3\u3c/sub\u3eS Models for the Nitrous Oxide Reductase Active Site, Cu\u3csub\u3eZ\u3c/sub\u3e*
Bridging diphosphine ligands were used to facilitate the assembly of copper clusters with single sulfur atom bridges that model the structure of the CuZ* active site of nitrous oxide reductase. Using bis(diphenylphosphino)amine (dppa), a [CuI4(Ī¼4-S)] cluster with NāH hydrogen bond donors in the secondary coordination sphere was assembled. Solvent and anion guests were found docking to the NāH sites in the solid state and in the solution phase, highlighting a kinetically viable pathway for substrate introduction to the inorganic core. Using bis(dicyclohexylphosphino)methane (dcpm), a [CuI3(Ī¼3-S)] cluster was assembled preferentially. Both complexes exhibited reversible oxidation events in their cyclic voltammograms, making them functionally relevant to the CuZ* active site that is capable of catalyzing a multielectron redox transformation, unlike the previously known [CuI4(Ī¼4-S)] complex from Yam and co-workers supported by bis(diphenylphosphino)methane (dppm). The dppa-supported [CuI4(Ī¼4-S)] cluster reacted with N3ā, a linear triatomic substrate isoelectronic to N2O, in preference to NO2ā, a bent triatomic. This [CuI4(Ī¼4-S)] cluster also bound Iā, a known inhibitor of CuZ*. Consistent with previous observations for nitrous oxide reductase, the tetracopper model complex bound the Iā inhibitor much more strongly and rapidly than the substrate isoelectronic to N2O, producing unreactive Ī¼3-iodide clusters including a [Cu3(Ī¼3-S)(Ī¼3-I)] complex related to the [Cu4(Ī¼4-S)(Ī¼2-I)] form of the inhibited enzyme
Book Review: The Slow Undoing: The Federal Courts and the Long Struggle for Civil Rights in South Carolina
Sherry Neal reviews The Slow Undoing: The Federal Courts and the Long Struggle for Civil Rights in South Carolina, written by Stephen H. Lowe
Design and Fabrication of a Micromechanical Pressure Sensor
A Microelectromechanical (MEMS) pressure sensor was designed, fabricated, and tested. Photomasks were designed for the project and built in house at RIT. The masks included designs for three separate device designs: devices to be fabricated with a KOH bulk etch, devices to be fabricated with an Surface Technology Systems (STS) Deep Reactive Ion Etch (DRIE), and a third set of scaled device designs for use with the STS DRIE process. Devices were tested in house, and the ideal design was determined. The most sensitive device, which had a resistor L/W of 10, demonstrated a voltage differential of 39 mV
A Cu\u3csub\u3e4\u3c/sub\u3eS Model for the Nitrous Oxide Reductase Active Sites Supported Only by Nitrogen Ligands
To model the (His)7Cu4Sn (n = 1 or 2) active sites of nitrous oxide reductase, the first Cu4(Ī¼4-S) cluster supported only by nitrogen donors has been prepared using amidinate supporting ligands. Structural, magnetic, spectroscopic, and computational characterization is reported. Electrochemical data indicates that the 2-hole model complex can be reduced reversibly to the 1-hole state and irreversibly to the fully reduced state
Using multiple reference ontologies: Managing composite annotations
There are a growing number of reference ontologies available across a variety of biomedical domains and current research focuses on their construction, organization and use. An important use case for these ontologies is annotationāwhere users create metadata that access concepts and terms in reference ontologies. We draw on our experience in physiological modeling to present a compelling use case that demonstrates the potential complexity of such annotations. In the domain of physiological biosimulation, we argue that most annotations require the use of multiple reference ontologies. We suggest that these ācompositeā annotations should be retained as a repository of knowledge about post-coordination that promotes sharing and interoperation across biosimulation models
Orienting Graphs to Optimize Reachability
The paper focuses on two problems: (i) how to orient the edges of an
undirected graph in order to maximize the number of ordered vertex pairs (x,y)
such that there is a directed path from x to y, and (ii) how to orient the
edges so as to minimize the number of such pairs. The paper describes a
quadratic-time algorithm for the first problem, and a proof that the second
problem is NP-hard to approximate within some constant 1+epsilon > 1. The
latter proof also shows that the second problem is equivalent to
``comparability graph completion''; neither problem was previously known to be
NP-hard
Stability of adversarial Markov chains, with an application to adaptive MCMC algorithms
We consider whether ergodic Markov chains with bounded step size remain
bounded in probability when their transitions are modified by an adversary on a
bounded subset. We provide counterexamples to show that the answer is no in
general, and prove theorems to show that the answer is yes under various
additional assumptions. We then use our results to prove convergence of various
adaptive Markov chain Monte Carlo algorithms.Comment: Published at http://dx.doi.org/10.1214/14-AAP1083 in the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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