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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Shifting Sands: Modulating Interactions and Outputs of the CHIP‐Hsp70/HOP‐Hsp70 Protein Quality Control Complexes

The 70‐kilodalton heat shock protein (Hsp70) interacts with tetratricopeptide repeat (TPR) domains of CHIP (C‐terminus of Hsp70 Interacting Protein) and HOP (Hsp Organizing Protein) using a two‐carboxylate clamp binding mechanism. Differential affinity for the TPR domains of CHIP and HOP are achieved through interactions with the six residues preceding the carboxy‐terminal Asp 641 of Hsp70. In particular, phosphorylation of Hsp70 Thr 636 produces a dramatic swing in binding affinities that shift preferential formation of CHIP/Hsp70 complexes to preferential formation of HOP/Hsp70 complexes. Given that CHIP‐Hsp70 complexes promote ubiquitin‐mediated degradation of Hsp70‐chaperoned clients while HOP‐Hsp70 complexes promote refolding of Hsp70‐chaperoned clients, phosphorylation of Hsp70 Thr 636 acts as a switch that directs the output and function of cellular protein quality control. Herein, through biophysical assays and new structures of CHIP‐Hsp70 and Hop‐Hsp70 we identify the molecular mechanism that enables phosphorylation‐driven switching that directs interactions within the CHIP‐Hsp70/HOP‐Hsp70 protein quality control complexes. We also present a structure‐guided mutation of Hsp70 that bypasses Thr 636 phosphorylation‐driven switching by recovering affinity of CHIP for phosphorylated Hsp70, thereby redirecting Hsp70 to preferentially bind to CHIP. This structure‐guided mutation corrects a binding defect present in wild type CHIP and provides a system for studying the effect of shifting output of the CHIP‐Hsp70/HOP‐Hsp70 protein quality control complexes toward chaperoned ubiquitination via the CHIP‐Hsp70 complex. Support or Funding Information The authors acknowledge financial support from the US National Science Foundation (Award No. MCB 1552113 to RCP), the American Heart Association (Award No. 16SDG26960000 to RCP), the Burroughs Wellcome Fund (Award No. 1014031 to RCP), and institutional support from Miami University through the Robert H. and Nancy J. Blayney Professorship (to RCP). The Advanced Light Source is supported by the US Department of Energy under contract number DE‐AC03‐76SF00098 at Lawrence Berkeley National Laboratory.

Page, Richard C.↗
DOE OSTI2013

Design, testing and emplacement of sand-bentonite for the construction of a gas-permeable seal test (gast)

The main aim of a gas-permeable seal is to increase the gas transport capacity of the backfilled underground structures without compromising the radionuclide retention capacity of the engineered barrier system or the host rock. Such a seal, proposed by NAGRA as part of the 'Engineered Gas Transport System' in a L/ILW repository, considers specially designed backfill and sealing materials such as sand/bentonite (S/B) mixtures with a bentonite content of 20- 30%. NAGRA's RD and D plan foresees demonstrating the construction and performance of repository seals and improving the understanding and the database for reliably predicting water and gas transport through these systems. The fluid flow and gas transport properties of these backfills have been determined at the laboratory scale and through modelling the maximum gas pressures in the near field of a repository system and the gas flow rates have been evaluated. Within this context, the Gas-permeable Seal Test (GAST) was constructed at Grimsel Test Site (GTS) to validate the effective functioning of gas-permeable seals at realistic scale. The intrinsic permeability of such seals should be in the order of 10-18 m2. Because the construction of S/B seals is not common practice for construction companies, a stepwise approach was followed to evaluate different construction and quality assurance methods. As a first step, an investigation campaign with simple tests in the laboratory and in the field followed by 1:1 scale pre-tests at GTS was performed. Through this gradual increase of the degree of complexity, practical experience was gained and confidence in the methods and procedures to be used was built, which allowed reliably producing and working with S/B mixtures at a realistic scale. During the whole pre-testing phase, a quality assurance (QA) programme for S/B mixtures was developed and different methods were assessed. They helped to evaluate and choose appropriate emplacement techniques and methodologies to achieve the target S/B dry density of 1.70 g/cm{sup 3}, which results in the desired intrinsic permeability throughout the experiment. The final QA methodology was targeted at engineering measures to decide if the work can proceed, and at producing high resolution material properties database for future water and gas transport modelling activities. The different applied QA techniques included standard core cutter tests, the application of neutron-gamma (Troxler) probes and two mass balance methods (2D and 3D). The methods, looking at different representative scales, have provided only slightly different results and showed that the average density of the emplaced S/B plug was between 1.65 and 1.73 g/cm{sup 3}. Spatial variability of dry densities was observed at decimeter scale. Overall, the pre-testing and QA programme performed for the GAST project demonstrated how the given design criteria and requirements can be met by appropriately planning and designing the material emplacement. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Detection of uranyl fluoride and sand surface contamination on metal substrates by hand-held laser-induced breakdown spectroscopy

Here, a hand-held device for laser-induced breakdown spectroscopy has been investigated for the determination of uranyl fluoride surface contamination. This research demonstrates the ability to successfully detect uranium on surfaces when using a low resolving power (λ/Δλ=4000) spectrograph, with a 5 mJ energy per 1 ns pulsed laser radiation, available as a commercially packaged hand-held system. Sand/uranyl fluoride mixtures are prepared to simulate residue likely encountered during decontamination efforts at facilities that handle uranium hexafluoride. Detection limits are described for four uranium lines with one revealing the capability to detect uranium at a level of 250 parts per million. Lastly, advantages of the studied compact device include that location specific information can be obtained on-site to augment contamination identification.

36 MATERIALS SCIENCE↗