228 research outputs found
Exploratory development and services for preparing and examining ultrathin polished sections of lunar rocks and particulates, part 1
Development of improved procedures is reported for three classes of lunar materials: dense rocks, breccias, and particulates. High quality ultrathin sections of these materials are obtained. Lists of equipment and supplies, procedures, photomicrographic documentation, and training are provided. Advantages of ultrathin polished sections for conventional and unconventional optical microscopy methods are described. Recommendations are provided for use of ultrathin sections in lunar rock studies, for further refinement of ultrathinning procedures, and for additional training efforts to establish a capability at the Manned Space Center. For Part 2, See N72-50754
Experimental Verification of a Cracked Fuel Mechanical Model
This report describes the results of a series of laboratory experiments conducted to independently verify a model that describes the nonlinear mechanical behavior of cracked fuel in pelletized UO{sub 2}/Zircaloy nuclear fuel rods under normal operating conditions. After a brief description of the analytical model, each experiment is discussed in detail. Experiments were conducted to verify the general behavior and numerical values for the three primary independent modelling parameters (effective crack roughness, effective gap roughness, and total crack length), and to verify the model predictions that the effective Young's moduli for cracked fuel systems were substantially less than those for solid UO{sub 2} pellets. In general, the model parameters and predictions were confirmed, and new insight was gained concerning the complexities of cracked fuel mechanics
Intrinsic point defects and volume swelling in ZrSiO4 under irradiation
The effects of high concentration of point defects in crystalline ZrSiO4 as
originated by exposure to radiation, have been simulated using first principles
density functional calculations. Structural relaxation and vibrational studies
were performed for a catalogue of intrinsic point defects, with different
charge states and concentrations. The experimental evidence of a large
anisotropic volume swelling in natural and artificially irradiated samples is
used to select the subset of defects that give similar lattice swelling for the
concentrations studied, namely interstitials of O and Si, and the anti-site
Zr(Si), Calculated vibrational spectra for the interstitials show additional
evidence for the presence of high concentrations of some of these defects in
irradiated zircon.Comment: 9 pages, 7 (color) figure
Data Report for the NRC/PNL Halden Assembly IFA-432: April 1978-May 1980
This report presents the in-reactor data collected from the U.S. Nuclear Regulatory Commission (NRC)/Pacific Northwest Laboratory (PNL) Halden test assembly IFA-432 for the period from April 1978 through May 1980. The irradiation test is part of an experimental program entitled 11 Experimental Support and Development of Single-Rod Fuel Codes" sponsored by the Fuel Behavior Research Branch of the NRC. The purpose of this program is to reduce the uncertainties of predicting the thermal and mechanical behavior of an operating nuclear fuel rod, Fuel centerline temperatures, cladding elongation, internal fuel rod pressures, and local powers at the thermocouple (TC) positions are shown as a function of time. The local powers were derived from neutron detector readings while the other variables were measured directly. Detailed analysis of the data is not made, but topical reports discussing certain aspects of the data are referenced. Descriptions of the assembly, instrumentation and calibration, and data processing methods are also presented
High Burnup Effects Program A State-of-the-Technology Assessment
Various analytical models and empirical correlations describing the fission gas release phenomenon were examined. An evaluation was made of the current pertinent experimental data on the subject of high burnup fission gas release. Data reported by individual investigators were compared and evaluated in relation to their applicability to the content and scope of the High Burnup Effects Program. These evaluations then form the bases for defining the data needs, and the selection of variables to be studied in this program
Self-Adjusting Biofeedback with a Dynamic Feedback Signal Set (DyFSS)
A lack of control over their autonomic nervous system presents a major challenge for many children with Autism Spectrum Disorder (ASD). Autonomic biofeedback training is a promising treatment for managing anxiety and ASD symptoms more generally. We describe software that tunes four autonomic measurements to the best abilities and needs of each individual patient. Using this dynamic feedback signal set (DyFSS), a strength-based, self-customizing algorithm, we aim to address the autonomic heterogeneity of youth with ASD. The DyFSS may improve autonomic biofeedback training for the user by making it more understandable and easier to accomplish. Because it is self-adjusting, it may also ease the integration of autonomic biofeedback training into clinical work. Initial feasibility testing of this algorithm in youth with ASD with a five-session autonomic biofeedback training protocol showed improved behavior in relation to ASD symptoms Initial reactions show that youth with ASD are readily engaged through technological interventions such as autonomic biofeedback. Keywords— autism spectrum disorder; autonomi
Plutonium stabilization in zircon: Effects of self-radiation
Zircon (ZrSiO4)(ZrSiO4) is the most thoroughly studied of all candidate ceramic phases for the stabilization of plutonium. Self-radiation damage from α-decay of the 239Pu,239Pu, which releases a 5.16 MeV α-particle and a 0.086 MeV 235U235U recoil nucleus, can significantly affect the structure and properties of zircon. Recent computer simulations using energy minimization techniques indicate that the lowest energy configuration occurs for a defect cluster composed of two near-neighbor Pu3+Pu3+ substitutions on Zr4+Zr4+ sites and a neighboring charge-compensating oxygen vacancy. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87571/2/18_1.pd
Precharacterization Report for Instrumented Fuel Assembly (IFA)-527
This report is a resource document covering the rationale, design, fabrication, and preirradiation characterization of instrumented fuel assembly (IFA)-527. This assembly is being irradiated in the Halden Boiling Water Reactor (HBWR) in Norway as part of the Experimental Support and Development of Single-Rod Fuel Codes Program conducted by Pacific Northwest laboratory (PNL) and sponsored by the Fuel Behavior Research Branch of the U.S. Nuclear Regulatory Commission (NRC). Data from this assembly will be used to better understand light water reactor (LWR) fuel behavior under normal operating conditions
Evolutionary pathways to NS5A inhibitor resistance in genotype 1 hepatitis C virus
Direct-acting antivirals (DAAs) targeting NS5A are broadly effective against hepatitis C virus (HCV) infections, but sustained virological response rates are generally lower in patients infected with genotype (gt)-1a than gt-1b viruses. The explanation for this remains uncertain. Here, we adopted a highly accurate, ultra-deep primer ID sequencing approach to intensively study serial changes in the NS5A-coding region of HCV in gt-1a- and gt-1b-infected subjects receiving a short course of monotherapy with the NS5A inhibitor, elbasvir. Low or undetectable levels of viremia precluded on-treatment analysis in gt-1b-infected subjects, but variants with the resistance-associated substitution (RAS) Y93H in NS5A dominated rebounding virus populations following cessation of treatment. These variants persisted until the end of the study, two months later. In contrast, while Y93H emerged in multiple lineages and became dominant in subjects with gt-1a virus, these haplotypes rapidly decreased in frequency off therapy. Substitutions at Q30 and L31 emerged in distinctly independent lineages at later time points, ultimately coming to dominate the virus population off therapy. Consistent with this, cell culture studies with gt-1a and gt-1b reporter viruses and replicons demonstrated that Y93H confers a much greater loss of replicative fitness in gt-1a than gt-1b virus, and that L31M/V both compensates for the loss of fitness associated with Q30R (but not Y93H) and also boosts drug resistance. These observations show how differences in the impact of RASs on drug resistance and replicative fitness influence the evolution of gt-1a and gt-1b viruses during monotherapy with an antiviral targeting NS5A. © 2018 Elsevier B.V
Kinetic analyses reveal potent and early blockade of hepatitis C virus assembly by NS5A inhibitors
Background & Aims All-oral regimens combining different classes of direct-acting antivirals (DAA) are highly effective for treatment of patients with chronic hepatitis C. NS5A inhibitors will likely form a component of future interferon-sparing treatment regimens. However, despite their potential, the detailed mechanism of action of NS5A inhibitors is unclear. To study their mechanisms, we compared their kinetics of antiviral suppression with those of other classes of DAA, using the hepatitis C virus genotype 1a cell culture-infectious virus H77S.3. Methods We performed detailed kinetic analyses of specific steps in the hepatitis C virus life cycle using cell cultures incubated with protease inhibitors, polymerase inhibitors, or NS5A inhibitors. Assays were designed to measure active viral RNA synthesis and steady-state RNA abundance, polyprotein synthesis, virion assembly, and infectious virus production. Results Despite their high potency, NS5A inhibitors were slow to inhibit viral RNA synthesis compared with protease or polymerase inhibitors. By 24 hours after addition of an NS5A inhibitor, polyprotein synthesis was reduced <50%, even at micromolar concentrations. In contrast, inhibition of virus release by NS5A inhibitors was potent and rapid, with onset of inhibition as early as 2 hours. Cells incubated with NS5A inhibitors were rapidly depleted of intracellular infectious virus and RNA-containing hepatitis C virus particles, indicating a block in virus assembly. Conclusions DAAs that target NS5A rapidly inhibit intracellular assembly of genotype 1a virions. They also inhibit formation of functional replicase complexes, but have no activity against preformed replicase, thereby resulting in slow shut-off of viral RNA synthesis
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