77 research outputs found
Measurements of the neutron-proton and neutron-carbon total cross section from 150 to 800 keV
No full textThere have been very few measurements of the total cross section for np scattering below 500 keV. To differentiate among NN potential models, improved cross section data between 20 and 600 keV are required. We measured the np and nC total cross sections in this energy region by transmission; a collimated neutron beam was passed through CH[subscript 2] and C samples and transmitted neutrons were detected by a BC-501A liquid scintillator. Cross sections were obtained with a precision of 1.1–2.0% between 150 and 800 keV using ratios of normalized neutron yields measured with and without the scattering samples in the beam. In energy regions where they overlap, the present results are consistent with existing precision measurements and fill in a significant gap in the data between E[subscript n]=150 and 500 keV
Evidence for a "Wattle and Daub" Model of the Cyst Wall of Entamoeba
No full textThe cyst wall of Entamoeba invadens (Ei), a model for the human pathogen Entamoeba histolytica, is composed of fibrils of chitin and three chitin-binding lectins called Jacob, Jessie3, and chitinase. Here we show chitin, which was detected with wheat germ agglutinin, is made in secretory vesicles prior to its deposition on the surface of encysting Ei. Jacob lectins, which have tandemly arrayed chitin-binding domains (CBDs), and chitinase, which has an N-terminal CBD, were each made early during encystation. These results are consistent with their hypothesized roles in cross-linking chitin fibrils (Jacob lectins) and remodeling the cyst wall (chitinase). Jessie3 lectins likely form the mortar or daub of the cyst wall, because 1) Jessie lectins were made late during encystation; 2) the addition to Jessie lectins to the cyst wall correlated with a marked decrease in the permeability of cysts to nucleic acid stains (DAPI) and actin-binding heptapeptide (phalloidin); and 3) recombinant Jessie lectins, expressed as a maltose-binding proteins in the periplasm of Escherichia coli, caused transformed bacteria to agglutinate in suspension and form a hard pellet that did not dissociate after centrifugation. Jessie3 appeared as linear forms and rosettes by negative staining of secreted recombinant proteins. These findings provide evidence for a "wattle and daub" model of the Entamoeba cyst wall, where the wattle or sticks (chitin fibrils likely cross-linked by Jacob lectins) is constructed prior to the addition of the mortar or daub (Jessie3 lectins). Author SummaryParasitic protists, which are spread by the fecal-oral route, have cyst walls that resist environmental insults (e.g. desiccation, stomach acids, bile, etc.). Entamoeba histolytica, the cause of amebic dysentery and liver abscess, is the only protist characterized to date that has chitin in its cyst wall. We have previously characterized Entamoeba chitin synthases, chitinases, and multivalent chitin-binding lectins called Jacob. Here we present evidence that the Entamoeba Jessie3 lectin contributes to the mortar or daub, which makes the cyst wall impenetrable to small molecules. First, the Jessie3 lectin was made after chitin and Jacob lectins had already been deposited onto the surface of encysting Entamoeba. Second, cysts became impenetrable to small molecules at the same time that Jessie3 was deposited into the wall. Third, recombinant Jessie3 lectins self-aggregated and caused transfected bacteria to agglutinate. These results suggest a "wattle and daub" model of the Ei cyst wall, where the wattle or sticks (chitin fibrils likely cross-linked by Jacob lectins) is constructed prior to the addition of the mortar or daub (Jessie3 lectins).National Institutes of Health (AI44070, GM31318); Council for Scientific and Industrial Research, Government of Indi
Detecting sub-MeV neutrons in solid plastic scintillator with gamma-ray discrimination
No full textWe report on recent efforts to design a solid plastic scintillation hodoscope to measure neutron production cross sections at low energies. Our program includes not only the development of the detector itself, but also a set of auxiliary measurements which will help characterize its low-energy response. A novel scintillation counter has been developed to detect sub-MeV neutrons while rejecting gamma-ray backgrounds with good efficiency. The detector uses multiple layers of thin solid scintillator, with optical isolation between the adjacent layers. Incident low-energy neutrons produce ionizing recoil particles which remain within just one of the scintillator layers, while background gamma rays create electrons which most often cross the boundary between layers. By observing the trigger pattern within the layers, most gamma-ray backgrounds can be distinguished from the low-energy neutrons of interest. We report on the results of our Monte Carlo studies of this design, as well as on the operation of a prototype detector unit. We also have undertaken a new measurement of the neutron-proton total cross section below 1 MeV. Calculations of the efficiency for detecting low energy neutrons in plastic scintillator rely on accurate low energy n-p cross sections, yet surprisingly few such data currently exist. New measurements which span the region from 150 to 800 keV neutron (lab) energy are reported and discussed. Additionally, we have measured the light response of BC 418 scintillator for recoil proton energies as low as 100 keV. Recoil protons are produced at a known energy in the scintillator by placing it in a neutron beam and detecting in coincidence the elastically scattered neutrons at fixed angle. Our new results extend the energy range of previous measurements of the light response of solid organic scintillators, and may indicate a significantly modified response at the lowest observed energies.United States. Dept. of Energy (Grant No. DE-FG52-10NA29651
Low energy neutron-proton interactions
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 265-270).There have been few measurements of cross sections for neutron-proton scattering and radiative capture below 1 MeV. Those measurements which do exist are at a small number of energies and are often inconsistent with theoretical models and with each other. We have conducted several experiments with the goal of obtaining improved data on these cross sections at the University of Kentucky (UKY) and the Los Alamos Neutron Science Center (LANSCE). Feasibility studies for measuring the low energy cross section for np radiative capture have been conducted at both UKY and LANSCE, culminating in a measurement of the cross section at 0.5, 0.9, 1.5, 2.0, and 2.5 MeV at UKY, using a plastic scintillator to detect recoiling deuterons and two BGO scintillators to detect the [gamma]-ray yields at 64.6° and 106.6°. We also performed measurements of the response of BC418 plastic scintillator to low energy protons during these studies, and conducted several additional measurements of the scintillator response at LANSCE and UKY, yielding very precise results from 100 keV to 3.6 MeV. The total cross section for np scattering was measured at UKY from 150 to 800 keV by neutron transmission, measuring the neutron yields in a liquid scintillator with various targets in the beam. The cross section was determined by taking ratios of neutron yields with and without the target, giving cross sections which are independent of detector efficiency and dead time. These results fill a significant gap in the available data below 500 keV.by Brian Daub.Ph.D
Author Correction: Considerations in the search for epistasis
No full textFollowing publication of the original article [1], the authors identified that two author affiliations were incorrect. Joséphine Daub is affiliated with Utrecht University (21) and not affiliation 9. Sanne Abeln is affiliated with Utrecht University only (21) and not affiliation 1. The original article [1] has been corrected.</p
Correction to: Considerations in the search for epistasis (Genome Biology, (2024), 25, 1, (296), 10.1186/s13059-024-03427-z)
No full textFollowing publication of the original article [1], the authors identified that two author affiliations were incorrect. Joséphine Daub is affiliated with Utrecht University (21) and not affiliation 9. Sanne Abeln is affiliated with Utrecht University only (21) and not affiliation 1. The original article [1] has been corrected
THE CONTINUITY OF THE ULTRAVIOLET BANDS OF BENZENE WITH THOSE OF ITS DERIVATIVES. APPLICATION TO TRISUBSTITUTED DERIVATIVES.
No full textAuthor Institution: Parke, Davis, and CompanyPrevious work has supported the thesis that the bands of benzene are displaced and occur in the spectra of its simple monosubstituted and disubstituted derivatives. The wavelength position of the bands of these derivatives is roughly predictable. The concepts evolved have now been applied to certain types of trisubstituted benzene compounds containing one electron attracting and two electron releasing substituents. The spectra of these trisubstituted derivatives have been compared with the spectrum of each of the possible disubstituted compounds containing the same substituent groups in the same relative positions in the benzene ring. It has been found that a striking similarity frequently exists between the spectrum of a trisubstituted derivative and that of the most displaced of the corresponding disubstituted compounds. This applies both to the general appearance of the spectrum and to the wavelength position of the bands. The correspondence in position is particularly good with the first primary band (the ca. band in benzene itself). Certain limitations and consequences of this generalization will be discussed
Author Correction: Considerations in the search for epistasis
No full textBalvert M, Cooper-Knock J, Stamp J, et al. Author Correction: Considerations in the search for epistasis. Genome Biology . 2025;26(1): 12
Draft genome of the filarial nematode parasite Brugia malayi
No full textParasitic nematodes that cause elephantiasis and river blindness threaten hundreds of millions of people in the developing world. We have sequenced the approximately 90 megabase (Mb) genome of the human filarial parasite Brugia malayi and predict approximately 11,500 protein coding genes in 71 Mb of robustly assembled sequence. Comparative analysis with the free-living, model nematode Caenorhabditis elegans revealed that, despite these genes having maintained little conservation of local synteny during approximately 350 million years of evolution, they largely remain in linkage on chromosomal units. More than 100 conserved operons were identified. Analysis of the predicted proteome provides evidence for adaptations of B. malayi to niches in its human and vector hosts and insights into the molecular basis of a mutualistic relationship with its Wolbachia endosymbiont. These findings offer a foundation for rational drug design
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Archaeological Excavations of a Late Bronze to Early Iron Age Settlement and Romano-British Enclosures at Eye Quarry, Peterborough
No full textThe report is to provides an assessment of the stratigraphic, artefactual and environmental data from the archaeological excavations at Eye Quarry, Peterborough in terms of their potential for analysis. A general summary of the fieldwork results, integrated with the specialists findings are given in the main body of the report and followed by a statement of the potential and recommendation for analysis. The various components of the site archive have been evaluated by the author of this report and qualified specialists. The total pottery assemblage was scanned by the Iron Age & Roman ceramic specialists with the primary aim of determining its date and character. Quantity was recorded by sherd count and weight. Flint was recorded by count and weight. The other materials such as daub, slag and metalwork have been catalogued with preliminary comments. The faunal and environmental components were sampled according to varying criteria
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