Design of a neutron microscope based on Wolter mirrors Hussey, D.S.; Abir, M.; Cook, J.C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2021, Letnik:
987
Journal Article
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The predominant geometry for a neutron imaging experiment is that of a pinhole camera. This is primarily due to the difficulty in focusing neutrons due to the weak refractive index, which is also ...strongly chromatic. Proof of concept experiments demonstrated that neutron image forming lenses based on reflective Wolter mirrors can produce quantitative, high spatial resolution neutron images while also increasing the time resolution compared to the conventional pinhole camera geometry. Motivated by these results, we report the design of a neutron microscope where two Wolter mirrors replace condensing and objective lenses, in direct analogy with typical visible light microscopes. Ray tracing results indicate that this system will yield 3μm spatial resolution images with an acquisition time of order <1 s (104 faster than currently possible at this spatial resolution) with a field of view of about 5 mm in diameter.
The ancestral Bacillus subtilis strain 3610 contains an 84-kb plasmid called pBS32 that was lost during domestication of commonly used laboratory derivatives. Here we demonstrate that pBS32, normally ...present at 1 or 2 copies per cell, increases in copy number nearly 100-fold when cells are treated with the DNA-damaging agent mitomycin C. Mitomycin C treatment also caused cell lysis dependent on pBS32-borne prophage genes. ZpdN, a sigma factor homolog encoded by pBS32, was required for the plasmid response to DNA damage, and artificial expression of ZpdN was sufficient to induce pBS32 hyperreplication and cell death. Plasmid DNA released by cell death was protected by the capsid protein ZpbH, suggesting that the plasmid was packaged into a phagelike particle. The putative particles were further indicated by CsCl sedimentation but were not observed by electron microscopy and were incapable of killing B. subtilis cells extracellularly. We hypothesize that pBS32-mediated cell death releases a phagelike particle that is defective and unstable.
Prophages are phage genomes stably integrated into the host bacterium's chromosome and less frequently are maintained as extrachromosomal plasmids. Here we report that the extrachromosomal plasmid pBS32 of Bacillus subtilis encodes a prophage that, when activated, kills the host. pBS32 also encodes both the sigma factor homolog ZpdN that is necessary and sufficient for prophage induction and the protein ComI, which is a potent inhibitor of DNA uptake by natural transformation. We provide evidence that the entire pBS32 sequence may be part of the prophage and thus that competence inhibition may be linked to lysogeny.
We present an updated catalog of sources detected by the Mikhail Pavlinsky ART-XC telescope aboard the Spektrum-Roentgen-Gamma (SRG) observatory during its all-sky survey. It is based on the data of ...the first four and the partially completed fifth scans of the sky (ARTSS1-5). The catalog comprises 1545 sources detected in the 4–12 keV energy band. The achieved sensitivity ranges between ~4 × 10 −12 erg s −1 cm −2 near the ecliptic plane and ~7 × 10 −13 erg s −1 cm −2 near the ecliptic poles, which is a ~30–50% improvement over the previous version of the catalog based on the first two all-sky scans (ARTSS12). There are ~130 objects, excluding the expected contribution of spurious detections, that were not known as X-ray sources before the SRG/ART-XC all-sky survey. We provide information, partly based on our ongoing follow-up optical spectroscopy program, on the identification and classification of the majority of the ARTSS1-5 sources (1463), of which 173 are tentative at the moment. The majority of the classified objects (964) are extragalactic, a small fraction (30) are located in the Local Group of galaxies, and 469 are Galactic. The dominant classes of objects in the catalog are active galactic nuclei (911) and cataclysmic variables (192).
We demonstrate neutron beam focusing by axisymmetric mirror systems based on a pair of mirrors consisting of a confocal ellipsoid and hyperboloid. Such a system, known as a Wolter mirror ...configuration, is commonly used in X-ray telescopes. The axisymmetric Wolter geometry allows nesting of several mirror pairs to increase collection efficiency. We implemented a system containing four nested Ni mirror pairs, which was tested by the focusing of a polychromatic neutron beam at the MIT Reactor. In addition, we have carried out extensive ray-tracing simulations of the mirrors and their performance in different situations. The major advantages of the Wolter mirrors are nesting for large angular collection and aberration-free performance. We discuss how these advantages can be utilized to benefit various neutron scattering methods, such as imaging, SANS, and time-of-flight spectroscopy.
Due to be launched in late 2021, the Imaging X-ray Polarimetry Explorer (IXPE) is a NASA Small Explorer mission designed to perform polarization measurements in the 2–8 keV band, complemented with ...imaging, spectroscopy and timing capabilities. At the heart of the focal plane is a set of three polarization-sensitive Gas Pixel Detectors (GPD), each based on a custom ASIC acting as a charge-collecting anode.
In this paper we shall review the design, manufacturing, and test of the IXPE focal-plane detectors, with particular emphasis on the connection between the science drivers, the performance metrics and the operational aspects. We shall present a thorough characterization of the GPDs in terms of effective noise, trigger efficiency, dead time, uniformity of response, and spectral and polarimetric performance. In addition, we shall discuss in detail a number of instrumental effects that are relevant for high-level science analysis—particularly as far as the response to unpolarized radiation and the stability in time are concerned.
We propose and design novel axisymmetric focusing mirrors, known as Wolter optics, for small-angle neutron scattering instruments. Ray-tracing simulations show that using the mirrors can result in ...more than an order-of-magnitude increase in the neutron flux reaching detectors, while decreasing the minimum wave vector transfer. Such mirrors are made of Ni using a mature technology. They can be coated with neutron supermirror multilayers, and multiple mirrors can be nested to improve their flux-collection ability. Thus, these mirrors offer simple and flexible means of significantly improving existing and future SANS instruments. In addition, short SANS instruments might become possible, especially at compact neutron sources, when high-resolution detectors are combined with Wolter optics.
► Improved optical design for small-angle neutron scattering instruments is proposed. ► The use of Wolter mirrors, axisymmetric grazing-incident optics, is analyzed. ► Simulations show that mirrors can increase signal rates by factors of 50 or more.
Drug overdoses have tripled in the United States over the last two decades. With the increasing demand for donor organs, one potential consequence of the opioid epidemic may be an increase in ...suitable donor organs. Unfortunately, organs from donors dying of drug overdose have poorer utilization rates than other groups of brain‐dead donors, largely due to physician and recipient concerns about viral disease transmission. During the study period of 2011 to 2016, drug overdose donors (DODs) account for an increasingly greater proportion of the national donor pool. We show that a novel model of donor care, known as specialized donor care facility (SDCF), is associated with an increase in organ utilization from DODs compared to the conventional model of hospital‐based donor care. This is likely related to the close relationship of the SDCF with the transplant centers, leading to improved communication and highly efficient donor care.
Cigarette smokers with past major depressive disorder (MDD) received 8 group sessions of standard, cognitive-behavioral smoking cessation treatment (ST;
n
= 93) or standard, cognitive-behavioral ...smoking cessation treatment plus cognitive-behavioral treatment for depression (CBT-D;
n
= 86). Although abstinence rates were high in both conditions (ST, 24.7%; CBT-D, 32.5%, at 1 year) for these nonpharmacological treatments, no main effect of treatment was found. However, secondary analyses revealed significant interactions between treatment condition and both recurrent depression history and heavy smoking (≥25 cigarettes a day) at baseline. Smokers with recurrent MDD and heavy smokers who received CBT-D were significantly more likely to be abstinent than those receiving ST (odds ratios = 2.3 and 2.6, respectively). Results suggest that CBT-D provides specific benefits for some, but not all, smokers with a history of MDD.
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