23,560 research outputs found

    Laboratory experiments on cohesive soil bed fluidization by water waves

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    Part I. Relationships between the rate of bed fluidization and the rate of wave energy dissipation, by Jingzhi Feng and Ashish J. Mehta and Part II. In-situ rheometry for determining the dynamic response of bed, by David J.A. Williams and P. Rhodri Williams. A series of preliminary laboratory flume experiments were carried out to examine the time-dependent behavior of a cohesive soil bed subjected to progressive, monochromatic waves. The bed was an aqueous, 50/50 (by weight) mixture of a kaolinite and an attapulgite placed in a plexiglass trench. The nominal bed thickness was 16 cm with density ranging from 1170 to 1380 kg/m 3, and water above was 16 to 20 cm deep. Waves of design height ranging from 2 to 8 cm and a nominal frequency of 1 Hz were run for durations up to 2970 min. Part I of this report describes experiments meant to examine the rate at which the bed became fluidized, and its relation to the rate of wave energy dissipation. Part II gives results on in-situ rheometry used to track the associated changes in bed rigidity. Temporal and spatial changes of the effective stress were measured during the course of wave action, and from these changes the bed fluidization rate was calculated. A wave-mud interaction model developed in a companion study was employed to calculate the rate of wave energy dissipation. The dependence of the rate of fluidization on the rate of energy dissipation was then explored. Fluidization, which seemingly proceeded down from the bed surface, occurred as a result of the loss of structural integrity of the soil matrix through a buildup of the excess pore pressure and the associated loss of effective stress. The rate of fluidization was typically greater at the beginning of wave action and apparently approached zero with time. This trend coincided with the approach of the rate of energy dissipation to a constant value. In general it was also observed that, for a given wave frequency, the larger the wave height the faster the rate of fluidization and thicker the fluid mud layer formed. On the other hand, increasing the time of bed consolidation prior to wave action decreased the fluidization rate due to greater bed rigidity. Upon cessation of wave action structural recovery followed. Dynamic rigidity was measured by specially designed, in situ shearometers placed in the bed at appropriate elevations to determine the time-dependence of the storage and loss moduli, G' and G", of the viscoelastic clay mixture under 1 Hz waves. As the inter-particle bonds of the space-filling, bed material matrix weakened, the shear propagation velocity decreased measurably. Consequently, G' decreased and G" increased as a transition from dynamically more elastic to more viscous response occurred. These preliminary experiments have demonstrated the validity of the particular rheometric technique used, and the critical need for synchronous, in-situ measurements of pore pressures and moduli characterizing bed rheology in studies on mud fluidization. This study was supported by WES contract DACW39-90-K-0010. (This document contains 151 pages.

    Time-resolved velocity map imaging of methyl elimination from photoexcited anisole

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    To date, H-atom elimination from heteroaromatic molecules following UV excitation has been extensively studied, with the focus on key biological molecules such as chromophores of DNA bases and amino acids. Extending these studies to look at elimination of other non-hydride photoproducts is essential in creating a more complete picture of the photochemistry of these biomolecules in the gas-phase. To this effect, CH3 elimination in anisole has been studied using time resolved velocity map imaging (TR-VMI) for the first time, providing both time and energy information on the dynamics following photoexcitation at 200 nm. The extra dimension of energy afforded by these measurements has enabled us to address the role of πσ* states in the excited state dynamics of anisole as compared to the hydride counterpart (phenol), providing strong evidence to suggest that only CH3 fragments eliminated with high kinetic energy are due to direct dissociation involving a 1πσ* state. These measurements also suggest that indirect mechanisms such as statistical unimolecular decay could be contributing to the dynamics at much longer times

    The Spectral Correlation Function -- A New Tool for Analyzing Spectral-Line Maps

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    The "spectral correlation function" analysis we introduce in this paper is a new tool for analyzing spectral-line data cubes. Our initial tests, carried out on a suite of observed and simulated data cubes, indicate that the spectral correlation function [SCF] is likely to be a more discriminating statistic than other statistical methods normally applied. The SCF is a measure of similarity between neighboring spectra in the data cube. When the SCF is used to compare a data cube consisting of spectral-line observations of the ISM with a data cube derived from MHD simulations of molecular clouds, it can find differences that are not found by other analyses. The initial results presented here suggest that the inclusion of self-gravity in numerical simulations is critical for reproducing the correlation behavior of spectra in star-forming molecular clouds.Comment: 29 pages, including 4 figures (tar file submitted as source) See also: http://cfa-www.harvard.edu/~agoodman/scf/velocity_methods.htm

    Metabolic Processes Preserved as Biosignatures in Iron-Oxidizing Microorganisms: Implications for Biosignature Detection on Mars

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    Iron-oxidizing bacteria occupy a distinct environmental niche. These chemolithoautotrophic organisms require very little oxygen (when neutrophilic) or outcompete oxygen for access to Fe(II) (when acidophilic). The utilization of Fe(II) as an electron donor makes them strong analog organisms for any potential life that could be found on Mars. Despite their importance to the elucidation of early life on, and potentially beyond, Earth, many details of their metabolism remain unknown. By using on-line thermochemolysis and gas chromatography?mass spectrometry (GC-MS), a distinct signal for a low-molecular-weight molecule was discovered in multiple iron-oxidizing isolates as well as several iron-dominated environmental samples, from freshwater and marine environments and in both modern and older iron rock samples. This GC-MS signal was neither detected in organisms that did not use Fe(II) as an electron donor nor present in iron mats in which organic carbon was destroyed by heating. Mass spectral analysis indicates that the molecule bears the hallmarks of a pterin-bearing molecule. Genomic analysis has previously identified a molybdopterin that could be part of the electron transport chain in a number of lithotrophic iron-oxidizing bacteria, suggesting one possible source for this signal is the pterin component of this protein. The rock samples indicate the possibility that the molecule can be preserved within lithified sedimentary rocks. The specificity of the signal to organisms requiring iron in their metabolism makes this a novel biosignature with which to investigate both the evolution of life on ancient Earth and potential life on Mars

    SWAS and Arecibo observations of H2O and OH in a diffuse cloud along the line-of-sight to W51

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    Observations of W51 with the Submillimeter Wave Astronomy Satellite (SWAS) have yielded the first detection of water vapor in a diffuse molecular cloud. The water vapor lies in a foreground cloud that gives rise to an absorption feature at an LSR velocity of 6 km/s. The inferred H2O column density is 2.5E+13 cm-2. Observations with the Arecibo radio telescope of hydroxyl molecules at ten positions in W51 imply an OH column density of 8E+13 cm-2 in the same diffuse cloud. The observed H2O/OH ratio of ~ 0.3 is significantly larger than an upper limit derived previously from ultraviolet observations of the similar diffuse molecular cloud lying in front of HD 154368. The observed variation in H2O/OH likely points to the presence in one or both of these clouds of a warm (T > 400) gas component in which neutral-neutral reactions are important sources of OH and/or H2O.Comment: 15 pages (AASTeX) including 4 (eps) figures. To appear in the Astrophysical Journa

    Raman scattering mediated by neighboring molecules

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    Raman scattering is most commonly associated with a change in vibrational state within individual molecules, the corresponding frequency shift in the scattered light affording a key way of identifying material structures. In theories where both matter and light are treated quantum mechanically, the fundamental scattering process is represented as the concurrent annihilation of a photon from one radiation mode and creation of another in a different mode. Developing this quantum electrodynamical formulation, the focus of the present work is on the spectroscopic consequences of electrodynamic coupling between neighboring molecules or other kinds of optical center. To encompass these nanoscale interactions, through which the molecular states evolve under the dual influence of the input light and local fields, this work identifies and determines two major mechanisms for each of which different selection rules apply. The constituent optical centers are considered to be chemically different and held in a fixed orientation with respect to each other, either as two components of a larger molecule or a molecular assembly that can undergo free rotation in a fluid medium or as parts of a larger, solid material. The two centers are considered to be separated beyond wavefunction overlap but close enough together to fall within an optical near-field limit, which leads to high inverse power dependences on their local separation. In this investigation, individual centers undergo a Stokes transition, whilst each neighbor of a different species remains in its original electronic and vibrational state. Analogous principles are applicable for the anti-Stokes case. The analysis concludes by considering the experimental consequences of applying this spectroscopic interpretation to fluid media; explicitly, the selection rules and the impact of pressure on the radiant intensity of this process

    Concise Review: Mind the Gap: Challenges in Characterizing and Quantifying Cell- and Tissue-Based Therapies for Clinical Translation

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    There are many challenges associated with characterizing and quantifying cells for use in cell- and tissue-based therapies. From a regulatory perspective, these advanced treatments must not only be safe and effective but also be made by high-quality manufacturing processes that allow for on-time delivery of viable products. Although sterility assays can be adapted from conventional bioprocessing, cell- and tissue-based therapies require more stringent safety assessments, especially in relation to use of animal products, immune reaction, and potential instability due to extended culture times. Furthermore, cell manufacturers who plan to use human embryonic stem cells in their therapies need to be particularly stringent in their final purification steps, due to the unrestricted growth potential of these cells. This review summarizes the current issues in characterization and quantification for cell- and tissue-based therapies, dividing these challenges into the regulatory themes of safety, potency, and manufacturing quality. It outlines current assays in use, as well as highlights the limits of many of these product release tests. Mode of action is discussed, with particular reference to in vitro surrogate assays that can be used to provide information to correlate with proposed in vivo patient efficacy. Importantly, this review highlights the requirement for basic research to improve current knowledge on the in vivo fate of these treatments; as well as an improved stakeholder negotiation process to identify the measurement requirements that will ensure the manufacture of the best possible cell- and tissue-based therapies within the shortest timeframe for the most patient benefit

    Geology of the Kentucky Geological Survey Marvin Blan No. 1 Well, East-Central Hancock County, Kentucky

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    The Kentucky Geological Survey’s Marvin Blan No. 1 well was drilled in east-central Hancock County, Ky., about 4 mi southwest of the Ohio River, to demonstrate CO2 injection in the Western Kentucky Coal Field, following the mandate and partial funding from Kentucky’s House Bill 1, August 2007. Installation of a groundwater monitoring well was required as a condition of obtaining a U.S. Environmental Protection Agency Underground Injection Control Class V Permit prior to drilling the Blan well; however, no groundwater was encountered under the Blan well site. The groundwater monitoring well was immediately plugged and abandoned in accordance with State regulations, and the UIC permit was amended to require monitoring of two domestic water wells and two developed springs within approximately 2 mi of the Blan well site. Drilling of the Blan well commenced in April 2009 and was completed in June 2009. Testing CO2 injection and storage was completed in two phases during 2009 and 2010. The Blan well penetrated an unfaulted Early Pennsylvanian through Neoproterozoic stratigraphic section characteristic of western Kentucky north of the Rough Creek Graben. Minor hydrocarbon shows were encountered during drilling. Whole-diameter 4-in. cores were recovered from the Late Devonian New Albany Shale, Late Ordovician Maquoketa Shale and Black River Group, Middle Cambrian–Lower Ordovician Knox Group (Beekmantown Dolomite, Gunter Sandstone, and Copper Ridge Dolomite), and Precambrian Middle Run Sandstone. Electric logs recorded in the Marvin Blan No. 1 can serve as type logs for western Kentucky. Structural dip in the well was found to be homoclinal, dipping approximately 0.5° west above the Knox unconformity, 1° west in the Knox Group and Eau Claire Formation, and about 3.5° north in the Middle Run. The Knox Group, the target interval of the well, has a complex lithology including fabric-preserving primary dolomite and fabric-destructive secondary dolomite, vugfilling saddle dolomite, vug-lining chert, chert nodules and fracture fills, and nodular to disseminated pyrite in the Beekmantown, Gunter, and Copper Ridge dolomite facies, and fine-grained quartz sand with dolomite cement in the sandstone facies of the Gunter. CO2 storage capacity of the Knox was evidenced by reservoir properties of porosity and permeability and the injection testing programs. Reservoir seals were evaluated in the Knox and overlying strata. Within the Knox, permeabilities measured in vertical core plugs from the Beekmantown and Copper Ridge Dolomites suggest that intraformational seals may be problematic. Three stratigraphic intervals overlying the Knox in the Marvin Blan No. 1 well may provide seals for potential CO2 storage reservoirs in western Kentucky: the Wells Creek Formation, Black River Group, and Maquoketa Shale. The Wells Creek and Black River had permeabilities suggesting that these intervals may act as secondary sealing strata. The primary reservoir seal for the Knox, however, is the Maquoketa. The Maquoketa is a dark gray, calcareous, silty, fissile shale. Maximum seal capacity calculated from permeabilities measured in vertical core plugs from the Maquoketa exceeded the net reservoir height in the Knox by about two orders of magnitude. Rock strength measured in core plugs from the Maquoketa suggests that any CO2 migrating from the Knox would likely have sufficient pressure to fracture the Maquoketa. Phase 1 injection testing used 18,454 bbl of synthetic brine and 323 tons of CO2 (equivalent to 1,765 bbl of fluid or 5,646 mcf of gaseous CO2), and phase 2 injection testing used a total of 4,265 bbl of synthetic brine and 367 tons of CO2 (2,000 bbl of liquid or 6,415 mcf of gaseous CO2). Calculating the reservoir volume required to store a volume of supercritical CO2 used data provided by wireline electric logs, analysis of whole and sidewall cores, wireline temperature and pressure surveys, and analysis of formation waters collected prior to injection tests. The most likely storage capacities calculated in the Knox in the Marvin Blan No. 1 ranges from 450 tons per surface acre in the phase 2 Gunter interval to 3,190 tons per surface acre for the entire Knox section. At the completion of testing, the injection zone in the Marvin Blan No. 1 well was permanently abandoned with cement plugs in accordance with Kentucky and U.S. Environmental Protection Agency regulations. Regional extrapolation of CO2 storage potential based on the results of a single well test can be problematic unless corroborating evidence can be demonstrated. Core analysis from the Knox is not available from wells in the region surrounding the Marvin Blan No. 1 well, although indirect evidence of porosity and permeability can be demonstrated in the form of active saltwater-disposal and gas-storage wells injecting into the Knox. This preliminary regional evaluation suggests that the Knox reservoir may be found throughout much of western Kentucky. The western Kentucky region suitable for CO2 storage in the Knox is limited updip, to the east and south, by the depth at which the base of the Maquoketa lies above the depth required to ensure storage of CO2 storage in its supercritical state and the deepest a commercial well might be drilled for CO2 storage. The resulting prospective region has an area of approximately 6,000 mi2, beyond which it is unlikely that suitable Knox reservoirs may be developed. Faults in the subsurface, which serve as conduits for CO2 migration and compromise sealing strata, may mitigate the area with Knox reservoirs suitable for CO2 storage. The data from the Marvin Blan No. 1 well make an important contribution to understanding the subsurface strata in western Kentucky, and clarify relationships between electric-log responses, lithology, and rock properties, and effectively demonstrate the CO2 storage potential of the Knox and sealing capacity of the Maquoketa. The results of the injection tests in the Blan well, however, provide a basis for evaluating supercritical CO2 storage in Cambrian-Ordovician carbonate reservoirs throughout the Midcontinent

    Optical vortex generation from molecular chromophore arrays

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    The generation of light endowed with orbital angular momentum, frequently termed optical vortex light, is commonly achieved by passing a conventional beam through suitably constructed optical elements. This Letter shows that the necessary phase structure for vortex propagation can be directly produced through the creation of twisted light from the vacuum. The mechanism is based on optical emission from a family of chromophore nanoarrays that satisfy specific geometric and symmetry constraints. Each such array can support pairs of electronically delocalized doubly degenerate excitons whose azimuthal phase progression is responsible for the helical wave front of the emitted radiation. The exciton symmetry dictates the maximum magnitude of topological charge; detailed analysis secures the conditions necessary to deliver optical vortices of arbitrary order
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