693 research outputs found
Monopoles from Rational Maps
The moduli space of charge k SU(2) BPS monopoles is diffeomorphic to the
moduli space of degree k rational maps between Riemann spheres. In this note we
describe a numerical algorithm to compute the monopole fields and energy
density from the rational map. The results for some symmetric examples are
presented.Comment: 8 pages, 2 figures. To appear in Phys. Lett.
The Role of Electrode Catalyst Interactions in Enabling Efficient CO2 Reduction with Mo(bpy)(CO)(4) As Revealed by Vibrational Sum-Frequency Generation Spectroscopy
Group 6 metal carbonyl complexes ([M(bpy)(CO)4], M = Cr, Mo, W) are potentially promising CO2 reduction electrocatalysts. However, catalytic activity onsets at prohibitively negative potentials and is highly dependent on the nature of the working electrode. Here we report in situ vibrational SFG (VSFG) measurements of the electrocatalyst [Mo(bpy)(CO)4] at platinum and gold electrodes. The greatly improved onset potential for electrocatalytic CO2 reduction at gold electrodes is due to the formation of the catalytically active species [Mo(bpy)(CO)3]2– via a second pathway at more positive potentials, likely avoiding the need for the generation of [Mo(bpy)(CO)4]2–. VSFG studies demonstrate that the strength of the interaction between initially generated [Mo(bpy)(CO)4]•– and the electrode is critical in enabling the formation of the active catalyst via the low energy pathway. By careful control of electrode material, solvent and electrolyte salt, it should therefore be possible to attain levels of activity with group 6 complexes equivalent to their much more widely studied group 7 analogues
iRefScape. A Cytoscape plug-in for visualization and data mining of protein interaction data from iRefIndex
<p>Abstract</p> <p>Background</p> <p>The iRefIndex consolidates protein interaction data from ten databases in a rigorous manner using sequence-based hash keys. Working with consolidated interaction data comes with distinct challenges: data are redundant, overlapping, highly interconnected and may be collected and represented using different curation practices. These phenomena were quantified in our previous studies.</p> <p>Results</p> <p>The iRefScape plug-in for the Cytoscape graphical viewer addresses these challenges. We show how these factors impact on data-mining tasks and how our solutions resolve them in a simple and efficient manner. A uniform accession space is used to limit redundancy and support search expansion and searching on multiple accession types. Multiple node and edge features support data filtering and mining. Node colours and features supply information about search result provenance. Overlapping evidence is presented using a multi-graph and a bi-partite representation is used to distinguish binary and n-ary source data. Searching for interactions between sets of proteins is supported and specifically includes searches on disease-related genes found in OMIM. Finally, a synchronized adjacency-matrix view facilitates visualization of relationships between sets of user defined groups.</p> <p>Conclusions</p> <p>The iRefScape plug-in will be of interest to advanced users of interaction data. The plug-in provides access to a consolidated data set in a uniform accession space while remaining faithful to the underlying source data. Tools are provided to facilitate a range of tasks from a simple search to knowledge discovery. The plug-in uses a number of strategies that will be of interest to other plug-in developers.</p
Ultrafast 2D-IR spectroscopy of intensely optically scattering pelleted solid catalysts
ACKNOWLEDGMENTS This work was supported by a UKRI Future Leaders Fellowship grant (Grant No. MR/S015574/1), STFC-UKRI program access to CLF-ULTRA (Grant No. LSF1828), direct access to CLF-ULTRA (Grant Nos. Apps 17330043 and 19130012), and a group residency in the Research Complex at Harwell (RCaH). The authors are grateful to Kathryn Welsby, Ivalina Minova, and Santhosh Matam for support early in the project with samples and the Linkam cell. Mr. John Still of the School of Geosciences, University of Aberdeen is thanked for the SEM images, and Kieran Farrell/Martin Zanni is thanked for the discussion about the polarizations of the beams creating the thermal transientsPeer reviewedPublisher PD
GPUVerify: A Verifier for GPU Kernels
We present a technique for verifying race- and divergence-freedom of GPU kernels that are written in mainstream ker-nel programming languages such as OpenCL and CUDA. Our approach is founded on a novel formal operational se-mantics for GPU programming termed synchronous, delayed visibility (SDV) semantics. The SDV semantics provides a precise definition of barrier divergence in GPU kernels and allows kernel verification to be reduced to analysis of a sequential program, thereby completely avoiding the need to reason about thread interleavings, and allowing existing modular techniques for program verification to be leveraged. We describe an efficient encoding for data race detection and propose a method for automatically inferring loop invari-ants required for verification. We have implemented these techniques as a practical verification tool, GPUVerify, which can be applied directly to OpenCL and CUDA source code. We evaluate GPUVerify with respect to a set of 163 kernels drawn from public and commercial sources. Our evaluation demonstrates that GPUVerify is capable of efficient, auto-matic verification of a large number of real-world kernels
Geophysical Surveys Across the Boise Hydrogeophysical Research Site to Determine Geophysical Parameters of a Shallow, Alluvial Aquifer
At the Boise Hydrogeophysical Research Site (BHRS), we are characterizing the hydrogeophysical parameters of a cobble-and-sand, unconfined aquifer using a wide variety of geophysical methods. Our goal is to develop methods for mapping variations in permeability by combining non-invasive geophysical data with hydrologic measurements. We are using seismic, ground penetrating radar, and electrical methods in a variety of configurations to provide images of and parameter distributions at the BHRS. Issues such as resolution, depth of penetration, and the ability to image the desired parameters will help determine the most effective methods. Supporting data sets from the BHRS include core analyses and geophysical logs from 18 wells at the site. We will use these data to verify our geophysical interpretations. The various geophysical methods and acquisition geometries, combined with the well control, will provide an outstanding data set to characterize the heterogeneity of the subsurface beneath this alluvial aquifer, and find ways to map permeability with geophysical information
The non-abelian D-brane effective action through order
Requiring the existence of certain BPS solutions to the equations of motion,
we determine the bosonic part of the non-abelian D-brane effective action
through order . We also propose an economic organizational
principle for the effective action.Comment: 12 pages, 2 figures, JHEP styl
Breaking Barriers in Ultrafast Spectroscopy and Imaging Using 100 kHz Amplified Yb-Laser Systems
Ultrafast spectroscopy and imaging have become tools utilized by a broad
range of scientists involved in materials, energy, biological, and chemical
sciences. Commercialization of ultrafast spectrometers including transient
absorption spectrometers, vibrational sum frequency generation spectrometers,
and even multidimensional spectrometers have put these advanced spectroscopy
measurements into the hands of practitioners originally outside the field of
ultrafast spectroscopy. There is a technology shift occurring in ultrafast
spectroscopy, made possible by new Yb-based lasers, that is opening exciting
new experiments in the chemical and physical sciences. Amplified Yb-based
lasers operate at many times the repetition rate of the previous generation of
Ti:Sapphire amplifier technology, enabling improvements to long-standing
techniques, new experiments, and the transformation of spectroscopies to
microscopies. The impact of this technology will be felt across a great swath
of the scientific communities. This review focuses on amplified Yb-based laser
systems used in conjunction with 100 kHz spectrometers operating with
shot-to-shot pulse shaping and detection. The shift to 100 kHz lasers is a
transformative step in nonlinear spectroscopy and imaging, much like the
dramatic expansion that occurred with the commercialization of Ti:Sapphire
laser systems in the 1990s
Femtosecond to Microsecond Observation of the Photochemical Reaction of 1,2-di(quinolin-2-yl)disulfide with Methyl Methacrylate
Multiple radical reaction steps have been observed in a continuous sequence with sub-picosecond to microsecond transient absorption spectroscopy.</p
2D-infrared spectroscopy of proteins in water : using the solvent thermal response as an internal standard
Ultrafast two-dimensional infrared (2D-IR) spectra can now be obtained in a matter of seconds, opening up the possibility of high-throughput screening applications of relevance to the biomedical and pharmaceutical sectors. Determining quantitative information from 2D-IR spectra recorded on different samples and different instruments is however made difficult by variations in beam alignment, laser intensity, and sample conditions. Recently, we demonstrated that 2D-IR spectroscopy of the protein amide I band can be performed in aqueous (H2O) rather than deuterated (D2O) solvents, and we now report a method that uses the magnitude of the associated thermal response of H2O as an internal normalization standard for 2D-IR spectra. Using the water response, which is temporally separated from the protein signal, to normalize the spectra allows significant reduction of the impact of measurement-to-measurement fluctuations on the data. We demonstrate that this normalization method enables creation of calibration curves for measurement of absolute protein concentrations and facilitates reproducible difference spectroscopy methodologies. These advances make significant progress toward the robust data handling strategies that will be essential for the realization of automated spectral analysis tools for large scale 2D-IR screening studies of protein-containing solutions and biofluids
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