6,632 research outputs found
Process for purification of solids
A process for purifying solids, especially silicon, by melting and subsequent resolidification, is described. Silicon used in solar cell manufacturing is processed more efficiently and cost effectively
Process for purification of silicon
The purification of metallurgically pure silicon having a silicon content of more than 95% by weight is accomplished by leaching with an acidic solution which substantially does not attack silicon. A mechanical treatment leading to continuous particle size reduction of the granulated silicon to be purified is combined with the chemical purification step
First look analysis of geologic ground patterns on ERTS-1 imagery of Missouri
Examination of ERTS-1 data for selected areas of Missouri revealed not only many of the known geologic features but also a number of unknown linear, circular and arcuate ground patterns. The number of new geologic elements that have been brought to light as well as the sharp definition and probable extensions of several known geologic features point out the importance of multispectral imagery via satellite and the synoptic views which they provide. To date, analysis and interpretations have been a first-look visual examination of the unenhanced projected images
Diamond Integrated Optomechanical Circuits
Diamond offers unique material advantages for the realization of micro- and
nanomechanical resonators due to its high Young's modulus, compatibility with
harsh environments and superior thermal properties. At the same time, the wide
electronic bandgap of 5.45eV makes diamond a suitable material for integrated
optics because of broadband transparency and the absence of free-carrier
absorption commonly encountered in silicon photonics. Here we take advantage of
both to engineer full-scale optomechanical circuits in diamond thin films. We
show that polycrystalline diamond films fabricated by chemical vapour
deposition provide a convenient waferscale substrate for the realization of
high quality nanophotonic devices. Using free-standing nanomechanical
resonators embedded in on-chip Mach-Zehnder interferometers, we demonstrate
efficient optomechanical transduction via gradient optical forces. Fabricated
diamond resonators reproducibly show high mechanical quality factors up to
11,200. Our low cost, wideband, carrier-free photonic circuits hold promise for
all-optical sensing and optomechanical signal processing at ultra-high
frequencies
Chemoenzymatic Synthesis of Cryptophycin Anticancer Agents by an Ester Bond-Forming Non-ribosomal Peptide Synthetase Module
Cryptophycins (Crp) are a group of cyanobacterial
depsipeptides with activity against drug-resistant tumors. Although they have been shown to be promising, further efforts are required to return these highly potent compounds to the clinic through a new generation of
analogues with improved medicinal properties. Herein,
we report a chemosynthetic route relying on themultifunctional enzyme CrpD-M2 that incorporates a 2-hydroxy acid moiety (unit D) into Crp analogues. CrpD-M2 is a unique nonribosomal peptide synthetase (NRPS) module comprised of condensation-adenylation-ketoreduction-thiolation (C-A-KR-T) domains. We interrogated A-domain 2-keto and 2-hydroxy acid activation and loading, and KR domain activity in the presence of NADPH and NADH. The
resulting 2-hydroxy acid was elongated with three synthetic
Crp chain elongation intermediate analogues through ester
bond formation catalyzed by CrpD-M2 C domain. Finally, the
enzyme-bound seco-Crp products were macrolactonized by
the Crp thioesterase. Analysis of these sequential steps was
enabled through LC-FTICR-MS of enzyme-bound intermediates
and products. This novel chemoenzymatic synthesis of
Crp involves four sequential catalytic steps leading to the
incorporation of a 2-hydroxy acid moiety in the final chain
elongation intermediate. The presented work constitutes the
first example where a NRPS-embedded KR domain is employed
for assembly of a fully elaborated natural product, and
serves as a proof-of-principle for chemoenzymatic synthesis of new Crp analogues
Does market structure matter?Trading costs and return volatility around exchange listings
We document that bid-ask spreads decrease substantially for stocks that moved from Nasdaq to the NYSE between 1996 and 2000, and that spread reductions continued to be observed after the 1997 market reforms. Somewhat surprising in light of these reforms, the largest spread reductions are for stocks where Nasdaq liquidity providers round quotations most often. We extend the analysis to document that average return volatility also decreases substantially after exchange listing. However, spreads, volatility, and trading activity are determined jointly in equilibrium, implying that simple before versus after comparisons may not reveal structural effects. The results of simultaneous equation estimation indicate that decreases in average bid-ask spreads are attributable to market structure, while reductions in volatility and trading volume can be attributed to changes in other endogenous and exogenous variables, including the spread reduction
Summary of an integrated ERTS-1 project and its results at the Missouri Geological Survey
Use of the ERTS imagery involved the recognition and interpretation of various ground patterns. Analysis and application are tied to ongoing programs. Specific studies utilizing the imagery and NASA aircraft photography are: a statewide lake and dam inventory; assessment of flooding and floodprone areas along the Missouri portion of the Mississippi and Missouri Rivers; land-use classification for several counties; structural features in selected areas; and Pleistocene features in northern Missouri. Though it has been suggested that repetitive coverage is not necessary for geologic studies, it is this specific feature along with the synoptic view of large portions of the State that provided the potential for the utilization of the ERTS imagery in Missouri. Other State agencies, Departments of Conservation, Agriculture, and Community Affairs, have expressed interest in the potential application of ERTS data in their respective fields
A framework for efficient ab initio electronic structure with Gaussian Process States
We present a general framework for the efficient simulation of realistic
fermionic systems with modern machine learning inspired representations of
quantum many-body states, towards a universal tool for ab initio electronic
structure. These machine learning inspired ansatzes have recently come to the
fore in both a (first quantized) continuum and discrete Fock space
representations, where however the inherent scaling of the latter approach for
realistic interactions has so far limited practical applications. With
application to the 'Gaussian Process State', a recently introduced ansatz
inspired by systematically improvable kernel models in machine learning, we
discuss different choices to define the representation of the computational
Fock space. We show how local representations are particularly suited for
stochastic sampling of expectation values, while also indicating a route to
overcome the discrepancy in the scaling compared to continuum formulated
models. We are able to show competitive accuracy for systems with up to 64
electrons, including a simplified (yet fully ab initio) model of the Mott
transition in three-dimensional hydrogen, indicating a significant improvement
over similar approaches, even for moderate numbers of configurational samples.Comment: 15 pages, 5 figure
Advanced gastrointestinal endoscopic imaging for inflammatory bowel diseases
Gastrointestinal luminal endoscopy is of paramount importance for diagnosis, monitoring and dysplasia surveillance in patients with both, Crohn's disease and ulcerative colitis. Moreover, with the recent recognition that mucosal healing is directly linked to the clinical outcome of patients with inflammatory bowel disorders, a growing demand exists for the precise, timely and detailed endoscopic assessment of superficial mucosal layer. Further, the novel field of molecular imaging has tremendously expanded the clinical utility and applications of modern endoscopy, now encompassing not only diagnosis, surveillance, and treatment but also the prediction of individual therapeutic responses. Within this review, we describe how novel endoscopic approaches and advanced endoscopic imaging methods such as high definition and high magnification endoscopy, dye-based and dye-less chromoendoscopy, confocal laser endomicroscopy, endocytoscopy and molecular imaging now allow for the precise and ultrastructural assessment of mucosal inflammation and describe the potential of these techniques for dysplasia detection
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