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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Cytogenetic Biodosimetry Using the Blood Lymphocytes of Astronauts

Cytogenetic analysis of blood lymphocytes remains the most sensitive and reliable method available for in vivo assessment of the biological effects of exposure to radiation and provides the most informative measurement of radiation induced health risks. To date chromosome damage has been assessed in lymphocytes from more than 30 astronauts before and after they participated in long-duration space missions of three months or more on board the International Space Station. For all individuals, the frequency of chromosome damage measured within a month of return from space was higher than their prefight yield and biodosimetry estimates lie within the range expected from physical dosimetry. Biodosimetry data provides a direct measurement of space radiation damage, which takes into account individual radiosensitivity in the presence of confounding factors such as microgravity and other stress conditions. In contrast to physical measurements, which are external to body and require multiple devices to detect all radiation types all of which have poor sensitivity to neutrons, biodosimetry is internal and includes the effects of shielding provided by the body itself plus chromosome damage shows excellent sensitivity to protons, heavy ions, and neutrons. In addition, chromosome damage is reflective of cancer risk and biodosimetry values can therefore be used to validate and develop risk assessment models that can be used to characterize excess health risk incurred by crewmembers. A review of astronaut biodosimetry data will be presented along with recent findings on the persistence of space radiation induced chromosome damage and the cytogenetic effects of repeat long duration missions

George, Kerry↗
NASA NTRSDate not supplied

Active and Passive Storage Solutions for Low Temperature Lunar Sample Return

Active and passive thermal storage solutions to return lunar biological, physical science and/or geology samples to the Earth are under development. Temperature requirements for biological/physical science sample conditioning range from -100˚C to -153˚C and possibly down to -253˚C for geological samples. The lower limit for geological samples is derived from the temperature of permanently shadowed regions on the lunar surface and the sublimation temperature of specific volatiles of interest (i.e., H2O, NH3 and CH4). Individual samples for the lunar application are expected to be less than 50 kg with a 700 kg allowance for the container and refrigeration. Requiring no electrical power or heat rejection, passive approaches, comprised of high performance insulation and consumable Joule-Thompson cooling, may be preferred for shorter duration missions (< 30 days) to provide significant mass savings. Active storage approaches with cryogenic cooling may be necessary to preserve samples for longer periods of time. A notional passive storage concept with an internal vapor cooled shield is shown below. The vapor cooled shield contains the sample and is isolated from the outer container with concentric reflective rigid shields and conventional multi-layer and/or aerogel insulation on the outer layer. A special removable, insulating end cap to stow or retrieve the sample is included.

Lunar Sample Return↗
DOE OSTI2020

Uncertainty analysis of Resource Demand Model for Covid-19

As part of the Department of Energy response to the novel coronavirus pandemic of 2020, a modeling effort was sponsored by the DOE Office of Science. One task of this modeling effort at Sandia was to develop a model to predict medical resource needs given various patient arrival scenarios. Resources needed include personnel resources (nurses, ICU nurses, physicians, respiratory therapists), fixed resources (regular or ICU beds and ventilators), and consumable resources (masks, gowns, gloves, face shields, sedatives). This report documents the uncertainty analysis that was performed on the resource model. The uncertainty analysis involved sampling 26 input parameters to the model. The sampling was performed conditional on the patient arrival streams that also were inputs to the model. These patient arrival streams were derived from various epidemiology models and had a significant effect on the projected resource needs. In this report, we document the sampling approach, the parameter ranges used, and the computational workflow necessary to perform large-scale uncertainty studies for every county and state in the United States.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Virion glycosylation influences mycobacteriophage immune recognition

Glycosylation of eukaryotic virus particles is common and influences their uptake, trafficking, and immune recognition. In contrast, glycosylation of bacteriophage particles has not been reported; phage virions typically do not enter the cytoplasm upon infection, and they do not generally inhabit eukaryotic systems. We show here that several genomically distinct phages of Mycobacteria are modified with glycans attached to the C terminus of capsid and tail tube protein subunits. These O-linked glycans influence antibody production and recognition, shielding viral particles from antibody binding and reducing production of neutralizing antibodies. Glycosylation is mediated by phage-encoded glycosyltransferases, and genomic analysis suggests that they are relatively common among mycobacteriophages. Putative glycosyltransferases are also encoded by some Gordonia and Streptomyces phages, but there is little evidence of glycosylation among the broader phage population. The immune response to glycosylated phage virions in mice suggests that glycosylation may be an advantageous property for phage therapy of Mycobacterium infections.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Structural adaptation of fungal cell wall in hypersaline environment

Abstract Halophilic fungi thrive in hypersaline habitats and face a range of extreme conditions. These fungal species have gained considerable attention due to their potential applications in harsh industrial processes, such as bioremediation and fermentation under unfavorable conditions of hypersalinity, low water activity, and extreme pH. However, the role of the cell wall in surviving these environmental conditions remains unclear. Here we employ solid-state NMR spectroscopy to compare the cell wall architecture of Aspergillus sydowii across salinity gradients. Analyses of intact cells reveal that A. sydowii cell walls contain a rigid core comprising chitin, β-glucan, and chitosan, shielded by a surface shell composed of galactomannan and galactosaminogalactan. When exposed to hypersaline conditions, A. sydowii enhances chitin biosynthesis and incorporates α-glucan to create thick, stiff, and hydrophobic cell walls. Such structural rearrangements enable the fungus to adapt to both hypersaline and salt-deprived conditions, providing a robust mechanism for withstanding external stress. These molecular principles can aid in the optimization of halophilic strains for biotechnology applications.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Decoupling of particles and dissolved iron downstream of Greenlandic glacier outflows

Glaciers can be a significant and locally dominant source of iron (Fe), a biologically essential micronutrient, in high latitude coastal seas. The vast majority of this glacial Fe delivery is associated with particles, yet the speciation of the solid-phase Fe and specifically the relationships that govern exchange between particulate and dissolved Fe phases in these environments are poorly described. Here, in this work, we performed measurements of in situ dissolved Fe (dFe) along meltwater and particle plumes in three transects around Disko Bay and Ameralik Fjord (West Greenland). Measurements of dFe were combined with Fe K-edge X-ray absorption spectroscopy analysis of ~40 suspended sediment samples obtained from the same transects and from select depth profiles down to 300 m. We observed relatively constant dFe levels (4 to 10 nM for nearly all dFe measurements) across fjords with widely varying particulate Fe(II) contents (from 20 to 90% Fe(II)), indicating that dFe concentrations had little dependence on the oxidation state of Fe in the suspended sediment. Particulate Fe data were grouped by underlying bedrock geology, with suspended sediment consisting of 80-90% biotite-like Fe(II) in fjords with Precambrian shield geology and poorly-ordered Fe(III) particles (<20-30% Fe(II)) in one fjord with suspended sediments derived from tertiary basalts. Our characterization data indicated no significant change in the average Fe oxidation state and bonding environment of particles along the fjord transects, implying that Fe(II) in biotite-like coordination is not a readily labile Fe form on this spatial scale. Finally, our results suggest that dFe in these glacially-modified coastal waters is buffered at a relatively constant low nM concentration due to factors other than particle Fe mineralogy and that glacier-derived Fe phases are relatively inert on this spatial scale.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

PE5–PPE4–EspG 3 heterotrimer structure from mycobacterial ESX-3 secretion system gives insight into cognate substrate recognition by ESX systems

Mycobacterium tuberculosis has evolved numerous type VII secretion (ESX) systems to secrete multiple factors important for both growth and virulence across their cell envelope. ESX-1, ESX-3, and ESX-5 systems have been shown to each secrete a distinct set of substrates, including PE and PPE families of proteins, named for conserved Pro-Glu and Pro-Pro-Glu motifs in their N termini. Proper secretion of the PE–PPE proteins requires the presence of EspG, with each system encoding its own unique copy. There is no cross-talk between any of the ESX systems, and how each EspG recognizes its subset of PE–PPE proteins is currently unknown. The only current structural characterization of PE–PPE–EspG heterotrimers is from the ESX-5 system. Here we present the crystal structure of the PE5 mt –PPE4 mt –EspG 3mm heterotrimer from the ESX-3 system. Our heterotrimer reveals that EspG 3mm interacts exclusively with PPE4 mt in a similar manner to EspG 5 , shielding the hydrophobic tip of PPE4 mt from solvent. The C-terminal helical domain of EspG 3mm is dynamic, alternating between “open” and “closed” forms, and this movement is likely functionally relevant in the unloading of PE–PPE heterodimers at the secretion machinery. In contrast to the previously solved ESX-5 heterotrimers, the PE–PPE heterodimer of our ESX-3 heterotrimer is interacting with its chaperone at a drastically different angle and presents different faces of the PPE protein to the chaperone. We conclude that the PPE–EspG interface from each ESX system has a unique shape complementarity that allows each EspG to discriminate among noncognate PE–PPE pairs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

AI-driven multiscale simulations illuminate mechanisms of SARS-CoV-2 spike dynamics

We develop a generalizable AI-driven workflow that leverages heterogeneous HPC resources to explore the time-dependent dynamics of molecular systems. We use this workflow to investigate the mechanisms of infectivity of the SARS-CoV-2 spike protein, the main viral infection machinery. Our workflow enables more efficient investigation of spike dynamics in a variety of complex environments, including within a complete SARS-CoV-2 viral envelope simulation, which contains 305 million atoms and shows strong scaling on ORNL Summit using NAMD. We present several novel scientific discoveries, including the elucidation of the spike’s full glycan shield, the role of spike glycans in modulating the infectivity of the virus, and the characterization of the flexible interactions between the spike and the human ACE2 receptor. We also demonstrate how AI can accelerate conformational sampling across different systems and pave the way for the future application of such methods to additional studies in SARS-CoV-2 and other molecular systems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

A Mobile Hot Cell for Conditioning Disused Sealed Radioactive Sources for Storage or Transportation

An innovative Mobile Hot Cell (MHC) has been developed for conditioning Disused Sealed Radioactive Sources (DSRS) category 1 and 2 for storage or transportation. The MHC is designed to provide both Radiological and Biological containment with a maximum capacity of 1000 Ci Co60 or 5000Ci Cs137 source and can be transported via standard cargo containers. This project has been supported through the National Nuclear Safety Administration (NNSA) Offsite Source Recovery Program (OSRP). The project is intended for the international community rather than domestic although domestic use is a possibility. Many countries have significant stockpiles of these devices that are often stored in less-than-optimal circumstances. This necessitates that these devices be addressed expeditiously, and the sources secured. The MHC utilizes robotics, automation, and other non-traditional methods for disassembling, characterizing, and packaging these sources that have reached end of life or are otherwise not needed. These innovative approaches are necessary to facilitate an expedited timeline to efficiently and safely secure these sources in a non-proliferation effort. Conditioning efforts include disassembling the device such as a teletherapy head used for cancer treatment, or blood/research irradiators such that the radioactive sources may be removed safely. The sources are then characterized. Leak checks are performed, dimensions are verified, and serial numbers are confirmed. Upon completion, the sources are typically placed into a Standard Forms Capsule which is seal welded closed. It is leak tested and placed into a Long-Term Storage Shield (LTSS) which can either be secured for storage directly or loaded into an appropriate cask for transportation. Further innovations include multiple deployment scenarios that include a full deployment of MHC components, deployment of the MHC automation internal components to an existing hot cell, deployment of minimally required MHC components and incorporation of sand for shielding, and integration of the MHC for Silo Storage, or Bore Hole Storage efforts. The MHC has evolved from a very specific use case to a “Swiss Army Knife” type of a tool in that it can be readily adapted to a large variety of situations. Innovative approaches such as the use of robotics, Computer Numeric Control (CNC) machining centers, automated welding equipment, HDMI Cameras, and LED lighting are some of the developed technologies incorporated into the MHC design. Shielding is accomplished with a steel walled Base Box which is surrounded by four nesting doll shield shells which when combined limits the external dose rate to 5mr/hr when a 1000 Ci Co60 source is exposed inside.

99 - GENERAL AND MISCELLANEOUS↗
DOE OSTI2023

Structure of a ribonucleotide reductase R2 protein radical

Aerobic ribonucleotide reductases (RNRs) initiate synthesis of DNA building blocks by generating a free radical within the R2 subunit; the radical is subsequently shuttled to the catalytic R1 subunit through proton-coupled electron transfer (PCET). Here we present a high-resolution room temperature structure of the class Ie R2 protein radical captured by x-ray free electron laser serial femtosecond crystallography. The structure reveals conformational reorganization to shield the radical and connect it to the translocation path, with structural changes propagating to the surface where the protein interacts with the catalytic R1 subunit. Restructuring of the hydrogen bond network, including a notably short O–O interaction of 2.41 angstroms, likely tunes and gates the radical during PCET. These structural results help explain radical handling and mobilization in RNR and have general implications for radical transfer in proteins.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Deinococcus radiodurans UWO298 Dependence on Background Radiation for Optimal Growth

Ionizing radiation is a major environmental variable for cells on Earth, and so organisms have adapted to either prevent or to repair damages caused by it, primarily from the appearance and accumulation of reactive oxygen species (ROS). In this study, we measured the differential gene expression in Deinococcus radiodurans UWO298 cultures deprived of background ionizing radiation (IR) while growing 605 m underground at the Waste Isolation Pilot Plant (WIPP), reducing the dose rate from 72.1 to 0.9 nGy h –1 from control to treatment, respectively. This reduction in IR dose rate delayed the entry into the exponential phase of the IR-shielded cultures, resulting in a lower biomass accumulation for the duration of the experiment. The RNASeq-based transcriptome analysis showed the differential expression of 0.2 and 2.7% of the D. radiodurans genome after 24 and 34 h of growth in liquid culture, respectively. Gene expression regulation after 34 h was characterized by the downregulation of genes involved in folding newly synthesized and denatured/misfolded proteins, in the assimilation of nitrogen for amino acid synthesis and in the control of copper transport and homeostasis to prevent oxidative stress. We also observed the upregulation of genes coding for proteins with transport and cell wall assembly roles. These results show that D. radiodurans is sensitive to the absence of background levels of ionizing radiation and suggest that its transcriptional response is insufficient to maintain optimal growth.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Structural insights into the modulation of coronavirus spike tilting and infectivity by hinge glycans

Abstract Coronavirus spike glycoproteins presented on the virion surface mediate receptor binding, and membrane fusion during virus entry and constitute the primary target for vaccine and drug development. How the structure dynamics of the full-length spikes incorporated in viral lipid envelope correlates with the virus infectivity remains poorly understood. Here we present structures and distributions of native spike conformations on vitrified human coronavirus NL63 (HCoV-NL63) virions without chemical fixation by cryogenic electron tomography (cryoET) and subtomogram averaging, along with site-specific glycan composition and occupancy determined by mass spectrometry. The higher oligomannose glycan shield on HCoV-NL63 spikes than on SARS-CoV-2 spikes correlates with stronger immune evasion of HCoV-NL63. Incorporation of cryoET-derived native spike conformations into all-atom molecular dynamic simulations elucidate the conformational landscape of the glycosylated, full-length spike that reveals a role of hinge glycans in modulating spike bending. We show that glycosylation at N1242 at the upper portion of the stalk is responsible for the extensive orientational freedom of the spike crown. Subsequent infectivity assays implicated involvement of N1242-glyan in virus entry. Our results suggest a potential therapeutic target site for HCoV-NL63.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRSDate not supplied

The Cosmic Radiation Symphony: Soundtrack for a Journey to Mars

Space radiation (SR) is a constant threat to astronauts who journey away from the Earth’s protective magnetosphere. Galactic cosmic rays (GCR) are atomic nuclei from remnants of supernovae and are omnipresent in outer space. These ionized particles travel close to the speed of light and when they traverse biological material,they leave behind a path of damage. Another space radiation threat is from our sun when solar particle events (SPEs), or bursts of energetic protons,occur. Exposure to space radiation can lead to cancer, cardiovascular disease,immune dysfunction, and cognitive and behavioral decrements. Yet humans cannot see, smell, taste, hear,or feel radiation, making it less tangible than other health threats and much more difficult to describe.This is an important gap in risk communication that the Space Radiation Element is working to close within NASA’s Human Research Program. Music and art are powerful means of communicating human emotions and feelings and are effective and creative ways to convey other types of information. In this work, the sonification process was used to transcribe or translate the physical nature of the SR environment on a 3-year mission to Mars into sound, a format perceptible to the human ear. A visual representation for the journey was also developed so the audience can both hear and envision the chronic presence of GCR and the acute and large bursts of energy present in SPEs. Data for this project were derived from the Radiation Assessment Detector on the NASA Curiosity Rover during its outbound cruise to Mars and on the Martian surface, as well as from models of the space radiation environment behind spacecraft shielding. Our data-driven audiovisual composition was realized using custom programmed digital signal processing and graphic design in the programming languages Pure Data and Processing. The data sonification was contextualized in time and space by calculating and visualizing the location of the spacecraft in relation to the other planets during the Mars mission. The finished work is a unique and powerful means of communicating the presence and risk of space radiation, accessible by people of all ages and scientific backgrounds

Richard Snow↗
NASA NTRS2002

Behavioral consequences of radiation exposure to simulated space radiation in the C57BL/6 mouse: open field, rotorod, and acoustic startle

Two experiments were carried out to investigate the consequences of exposure to proton radiation, such as might occur for astronauts during space flight. C57BL/6 mice were exposed, either with or without 15-g/cm2 aluminum shielding, to 0-, 3-, or 4-Gy proton irradiation mimicking features of a solar particle event. Irradiation produced transient direct deficits in open-field exploratory behavior and acoustic startle habituation. Rotorod performance at 18 rpm was impaired by exposure to proton radiation and was impaired at 26 rpm, but only for mice irradiated with shielding and at the 4-Gy dose. Long-term (>2 weeks) indirect deficits in open-field activity appeared as a result of impaired experiential encoding immediately following exposure. A 2-week recovery prior to testing decreased most of the direct effects of exposure, with only rotorod performance at 26 rpm being impaired. These results suggest that the performance deficits may have been mediated by radiation damage to hippocampal, cerebellar, and possibly, forebrain dopaminergic function.

Non-NASA Center↗
DOE OSTI2025

Efficient 15 N hyperpolarization of [ 15 N 3 ]metronidazole antibiotic via spin-relayed pulsed SABRE-SHEATH

Signal Amplification by Reversible Exchange in SHield Enables Alignment Transfer to Heteronuclei (SABRE-SHEATH) is an NMR hyperpolarization technique that relies of the simultaneous exchange of parahydrogen and a to-be-hyperpolarized molecule on the metal center of a polarization-transfer catalyst in a microtesla magnetic field. Until recently, this method has been understood to perform hyperpolarization by establishing level anti-crossings between the nuclear spins of the parahydrogen derived hydrides (acting as a source of hyperpolarization) and those of the substrate. Recently, the application of highly non-intuitive pulse sequences (comprising pulses of microtesla DC fields) was predicted to hyperpolarize nuclear spins more efficiently than the canonical (static-field) SABRE-SHEATH approach. Here we show that by employing a basic “on-off” pulse sequence of rectangular microtesla pulses, it is possible to improve the hyperpolarization efficiency for SABRE-SHEATH of [ 15 N 3 ]metronidazole, an FDA-approved antibiotic (in non-enriched and non-hyperpolarized form) and potential hypoxia sensing molecule. Specifically, we demonstrate that 15N polarization of 18.5 % can be obtained in 80 s of parahydrogen bubbling parahydrogen through a solution containing 20 mM [ 15 N 3 ]metronidazole. In practice, (1.32 ± 0.14)-fold improvements in P 15N was obtained with the pulsed method described here compared to static field technique variant. These results show that pulsed SABRE-SHEATH was successfully applied to 15 N-labeled biologically relevant molecule. Moreover, we also demonstrate that although the pulsed SABRE-SHEATH sequence was designed for polarization transfer from parahydrogen derived hydrides to the metronidazole’s 15 N catalyst-binding site, all three 15 N sites of [ 15 N 3 ]metronidazole attained the hyperpolarized state. This spin-relayed polarization transfer becomes possible due to the 15 N relay network established by their spin-spin J-couplings. The feasibility of the spin-relayed polarization transfer is demonstrated here for the first time for pulsed SABRE-SHEATH (as opposed to the static-field SABRE-SHEATH reported previously) and it paves the way to broad applicability of the technique.

Hyperpolarization↗
DOE OSTI2020

Challenges and Solutions in Operation and Lay-Up of the Modular Caustic- Side Solvent Extraction Unit - 20078

The Modular Caustic-Side Solvent Extraction (CSSX) Unit (MCU) was designed and constructed to provide interim salt waste processing so that the Liquid Waste Disposition Program (LWDP) could continue waste removal and tank closure until start-up of the Salt Waste Processing Facility (SWPF). MCU processes Clarified Salt Solution (CSS), or salt solution (SS) that has undergone actinide removal/filtration, to produce two waste streams: the cesium laden Strip Effluent (SE), which is incorporated into glass at the Defense Waste Processing Facility (DWPF), and the cesium depleted Decontaminated SS (DSS), which is incorporated into grout at the Saltstone Production Facility (SPF). MCU completed start-up in 2008 with an initial operating life of 3 years and design life of 5 years. Prior to reaching the end of the design life, multiple critical components were upgraded and/or replaced to mitigate risks associated with any delays in SWPF start-up. During the remainder of operation (until June 2019), MCU was challenged to maximize processing with minimal additional modifications to repair/improve aging infrastructure, while maintaining low levels of risk to workers and the environment. Notable challenges during the extended operating life of the facility involved both mechanical and operational issues. Two of the most significant issues were the increased frequency of Process Vessel Ventilation (PVV) High Efficiency Particulate Air (HEPA) filter change-outs and the biofouling of the SE coalescer (SEC). The major impacts of both issues were that replacement of these components 1) resulted in high exposure to workers, and 2) required substantial downtime, thus hindering achievement of processing goals. PVV HEPA filter replacements are required based on dose rate and differential pressure (dP) limits. After introducing a higher-curie feed to MCU, the operating time between change outs was reduced by approximately half. SEC replacements are required based on dP limits. After restarting from an extended outage, the operating life of the SEC was significantly reduced by more than half due to biofouling. As a result of extensive troubleshooting and process improvements, the facility was able to recover performance and extend the operating life of the PVV HEPA filters and the SEC media. Through troubleshooting both of these issues, the facility was also able to learn from prior experience and adapt in order to minimize down time and maintain throughput. Although the facility took advantage of short periods of downtime to perform nonintrusive troubleshooting and minor corrective/preventative maintenance activities, longer outages were periodically required for corrective maintenance involving process cell entry. During these outages, remote tools and specialized shield plates were employed to minimize dose to workers. Mock-ups of non-routine maintenance activities were critical to early identification of potential issues and improvements, which shortened outage duration. Consistent with the facility's operational strategy, evolutions needed for MCU layup were identified and sequenced to ensure safe conditions within the facility, meet pre-defined criteria for lay-up configuration, and protect workers, while minimizing the impact to SWPF integration. De-inventory and flushing of process areas was prioritized so that the total residual inventory was reduced as efficiently as possible. This paper discusses lessons learned and best practices from troubleshooting unique issues, performing complex maintenance activities, and implementing a layup strategy that best supports the overall system mission. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS2002

A New Direction for the NASA Materials Science Research Using the International Space Station

In 2001 NASA created a fifth Strategic Enterprise, the Office of Biological and Physical Research (OBPR), to bring together physics, chemistry, biology, and engineering to foster interdisciplinary research. The Materials Science Program is one of five Microgravity Research disciplines within this new Enterprise's Division of Physical Sciences Research. The Materials Science Program will participate within this new enterprise structure in order to facilitate effective use of ISS facilities, target scientific and technology questions and transfer results for Earth benefits. The Materials Science research will use a low gravity environment for flight and ground-based research in crystallization, fundamental processing, properties characterization, and biomaterials in order to obtain fundamental understanding of various phenomena effects and relationships to the structures, processing, and properties of materials. Completion of the International Space Station's (ISS) first major assembly, during the past year, provides new opportunities for on-orbit research and scientific utilization. The Enterprise has recently completed an assessment of the science prioritization from which the future materials science ISS type payloads will be implemented. Science accommodations will support a variety of Materials Science payload hardware both in the US and international partner modules with emphasis on early use of Express Rack and Glovebox facilities. This paper addresses the current scope of the flight and ground investigator program. These investigators will use the various capabilities of the ISS lab facilities to achieve their research objectives. The type of research and classification of materials being studied will be addressed. This includes the recent emphasis being placed on radiation shielding, nanomaterials, propulsion materials, and biomaterials type research. The Materials Science Program will pursue a new, interdisciplinary approach, which contributes, to Human Space Flight Exploration research. The Materials Science Research Facility (MSRF) and other related American and International experiment modules will serve as the foundation for the flight research environment. A summary will explain the concept for materials science research processing capabilities aboard the ISS along with the various ground facilities necessary to support the program.

Schlagheck, Ronald A.↗
DOE OSTI2024

Selective consolidation of learning and memory via recall-gated plasticity

In a variety of species and behavioral contexts, learning and memory formation recruits two neural systems, with initial plasticity in one system being consolidated into the other over time. Moreover, consolidation is known to be selective; that is, some experiences are more likely to be consolidated into long-term memory than others. Here, we propose and analyze a model that captures common computational principles underlying such phenomena. The key component of this model is a mechanism by which a long-term learning and memory system prioritizes the storage of synaptic changes that are consistent with prior updates to the short-term system. This mechanism, which we refer to as recall-gated consolidation, has the effect of shielding long-term memory from spurious synaptic changes, enabling it to focus on reliable signals in the environment. We describe neural circuit implementations of this model for different types of learning problems, including supervised learning, reinforcement learning, and autoassociative memory storage. These implementations involve synaptic plasticity rules modulated by factors such as prediction accuracy, decision confidence, or familiarity. We then develop an analytical theory of the learning and memory performance of the model, in comparison to alternatives relying only on synapse-local consolidation mechanisms. We find that recall-gated consolidation provides significant advantages, substantially amplifying the signal-to-noise ratio with which memories can be stored in noisy environments. We show that recall-gated consolidation gives rise to a number of phenomena that are present in behavioral learning paradigms, including spaced learning effects, task-dependent rates of consolidation, and differing neural representations in short- and long-term pathways.

59 BASIC BIOLOGICAL SCIENCES↗