Short-wavelength free-electron lasers with their ultrashort pulses at high intensities have originated new approaches for tracking molecular dynamics from the vista of specific sites. X-ray pump ...X-ray probe schemes even allow to address individual atomic constituents with a 'trigger'-event that preludes the subsequent molecular dynamics while being able to selectively probe the evolving structure with a time-delayed second X-ray pulse. Here, we use a linearly polarized X-ray photon to trigger the photolysis of a prototypical chiral molecule, namely trifluoromethyloxirane (C\(_3\)H\(_3\)F\(_3\)O), at the fluorine K-edge at around 700 eV. The evolving fluorine-containing fragments are then probed by a second, circularly polarized X-ray pulse of higher photon energy in order to investigate the chemically shifted inner-shell electrons of the ionic motherfragment for their stereochemical sensitivity. We experimentally demonstrate and theoretically support how two-color X-ray pump X-ray probe experiments with polarization control enable XFELs as tools for chiral recognition.
We have found a class of circular radio objects in the Evolutionary Map of the Universe Pilot Survey, using the Australian Square Kilometre Array Pathfinder telescope. The objects appear in radio ...images as circular edge-brightened discs, about one arcmin diameter, that are unlike other objects previously reported in the literature. We explore several possible mechanisms that might cause these objects, but none seems to be a compelling explanation.
A True Autoactivating Enzyme Gál, Péter; Harmat, Veronika; Kocsis, Andrea ...
Journal of biological chemistry/The Journal of biological chemistry,
09/2005, Letnik:
280, Številka:
39
Journal Article
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Few reports have described in detail a true autoactivation process, where no extrinsic cleavage factors are required to initiate the autoactivation of a zymogen. Herein, we provide structural and ...mechanistic insight into the autoactivation of a multidomain serine protease: mannose-binding lectin-associated serine protease-2 (MASP-2), the first enzymatic component in the lectin pathway of complement activation. We characterized the proenzyme form of a MASP-2 catalytic fragment encompassing its C-terminal three domains and solved its crystal structure at 2.4 Å resolution. Surprisingly, zymogen MASP-2 is capable of cleaving its natural substrate C4, with an efficiency about 10% that of active MASP-2. Comparison of the zymogen and active structures of MASP-2 reveals that, in addition to the activation domain, other loops of the serine protease domain undergo significant conformational changes. This additional flexibility could play a key role in the transition of zymogen MASP-2 into a proteolytically active form. Based on the three-dimensional structures of proenzyme and active MASP-2 catalytic fragments, we present model for the active zymogen MASP-2 complex and propose a mechanism for the autoactivation process.
We report on the coherent timing analysis of the 182 Hz accreting millisecond X-ray pulsar Swift J1756.9\(-\)2508 during its 2018 outburst as observed with the Neutron Star Interior Composition ...Explorer (NICER). Combining our NICER observations with Rossi X-ray Timing Explorer observations of the 2007 and 2009 outbursts, we also studied the long-term spin and orbital evolution of this source. We find that the binary system is well described by a constant orbital period model, with an upper limit on the orbital period derivative of \(|\dot P_b| < 7.4\times 10^{-13}\) s s\(^{-1}\). Additionally, we improve upon the source coordinates through astrometric analysis of the pulse arrival times, finding R.A. = \(17^{\rm h}56^{\rm m}57.18^{\rm s}\pm0.08^{\rm s}\) and Decl. = \(-25^{\circ}06'27.8''\pm3.5''\), while simultaneously measuring the long-term spin frequency derivative as \(\dot\nu = -7.3\times 10^{-16}\) Hz s\(^{-1}\). We briefly discuss the implications of these measurements in the context of the wider population of accreting millisecond pulsars.
We present the data and initial results from the first Pilot Survey of the Evolutionary Map of the Universe (EMU), observed at 944 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP) ...telescope. The survey covers 270 \sqdeg of an area covered by the Dark Energy Survey, reaching a depth of 25--30 \ujybm\ rms at a spatial resolution of \(\sim\) 11--18 arcsec, resulting in a catalogue of \(\sim\) 220,000 sources, of which \(\sim\) 180,000 are single-component sources. Here we present the catalogue of single-component sources, together with (where available) optical and infrared cross-identifications, classifications, and redshifts. This survey explores a new region of parameter space compared to previous surveys. Specifically, the EMU Pilot Survey has a high density of sources, and also a high sensitivity to low surface-brightness emission. These properties result in the detection of types of sources that were rarely seen in or absent from previous surveys. We present some of these new results here.
Astrophysics spans an enormous range of questions on scales from individual planets to the entire cosmos. To address the richness of 21st century astrophysics requires a corresponding richness of ...telescopes spanning all bands and all messengers. Much scientific benefit comes from having the multi-wavelength capability available at the same time. Most of these bands,or measurement sensitivities, require space-based missions. Historically, NASA has addressed this need for breadth with a small number of flagship-class missions and a larger number of Explorer missions. While the Explorer program continues to flourish, there is a large gap between Explorers and strategic missions. A fortunate combination of new astrophysics technologies with new, high capacity, low dollar-per-kg to orbit launchers, and new satellite buses allow for cheaper missions with capabilities approaching strategic mission levels. NASA has recognized these developments by calling for Probe-class mission ideas for mission studies, spanning most of the electromagnetic spectrum from GeV gamma-rays to the far infrared, and the new messengers of neutrinos and ultra-high energy cosmic rays. The key insight from the Probes exercise is that order-of-magnitude advances in science performance metrics are possible across the board for initial total cost estimates in the range 500M-1B dollars.
We introduce Codex, a GPT language model fine-tuned on publicly available code from GitHub, and study its Python code-writing capabilities. A distinct production version of Codex powers GitHub ...Copilot. On HumanEval, a new evaluation set we release to measure functional correctness for synthesizing programs from docstrings, our model solves 28.8% of the problems, while GPT-3 solves 0% and GPT-J solves 11.4%. Furthermore, we find that repeated sampling from the model is a surprisingly effective strategy for producing working solutions to difficult prompts. Using this method, we solve 70.2% of our problems with 100 samples per problem. Careful investigation of our model reveals its limitations, including difficulty with docstrings describing long chains of operations and with binding operations to variables. Finally, we discuss the potential broader impacts of deploying powerful code generation technologies, covering safety, security, and economics.
Switched reluctance (SR) drives offer the advantages of simple and robust motor construction, high speeds, high overall efficiencies over a wide operating range of torque and speed, simple power ...converter circuits with a reduced number of switches, and excellent controllability. The basis of these claims is explained. The history of the SR system, in particular the extensive research at Nottingham and Leeds Universities, and the basic operating principles and design considerations for motors and power converters are reviewed. Alternative configurations are discussed. The difficulties of establishing a simple mathematical model for the motor and of calculating torque and inverter VA requirements are examined. A comparison of the VA requirements for SR and pulsewidth modulation (PWM) is given for a 7.85-kW system. Measured drive performance is discussed in terms of efficiency over an operating envelope, specific output, controllability, and power converter ratings. Earlier traction drives, incorporating a constant power range and including regeneration, are reported together with the constant torque industrial drives and more recent traction extensions. The long-term potential of the drive is discussed for a wide range of applications. A comprehensive list of references is provided.
The Bergman Minimal Model enables estimation of two key indices of glucose/insulin dynamics: glucose effectiveness and insulin sensitivity. In this paper we describe MINMOD Millennium, the latest ...Windows-based version of minimal model software. Extensive beta testing of MINMOD Millennium has shown that it is user-friendly, fully automatic, fast, accurate, reproducible, repeatable, and highly concordant with past versions of MINMOD. It has a simple interface, a comprehensive help system, an input file editor, a file converter, an intelligent processing kernel, and a file exporter. It provides publication-quality charts of glucose and insulin and a table of all minimal model parameters and their error estimates. In contrast to earlier versions of MINMOD and some other minimal model programs, Millennium provides identified estimates of insulin sensitivity and glucose effectiveness for almost every subject.
Mapping of the EVI2 gene between the translocation breakpoints of two patients with neurofibromatosis type 1 (NF1), combined with the likely role of its murine homolog in neoplastic disease, ...implicates EVI2 as a possible candidate for the NF1 gene. We report here the expression of a 1.6-kb EVI2 transcript in normal human brain and peripheral blood mononuclear cells. Sequencing studies predict an EVI2 protein of 232 amino acids that contains an N-terminal signal peptide, an extracellular domain with five potential glycosylation sites, a single hydrophobic transmembrane domain with a leucine zipper, and a hydrophilic cytoplasmic domain. These features are all well-conserved with respect to the mouse Evi-2 protein and are consistent with the hypothesis that EVI2 is a membrane protein that may complex with itself and/or other proteins within the membrane, perhaps to function as part of a cell-surface receptor. In the course of these studies we have also identified three other transcripts (classes of cDNAs) from the NF1 region. Two of these transcripts map between the NF1 translocation breakpoints; the remaining transcript maps just outside this region.
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