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All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Modeling plasma-induced surface charge effects on CO 2 activation by single atom catalysts supported on reducible and irreducible metal oxides

Abstract The accumulation of negative surface charge on catalytic surfaces in the presence of low-temperature plasma (LTP) could influence catalytic performance. However, it is difficult to disentangle the role of surface charging and other LTP catalytic effects in experiment. Herein, we use density functional theory (DFT) modeling to understand the effect of plasma-induced surface charging on CO 2 activation by atomically dispersed single atom (SA) catalysts on both reducible and irreducible metal oxide supports. We model CO 2 adsorption strength and CO 2 dissociation barriers for Co 1 , Ni 1 , Cu 1 , Rh 1 , Pd 1 , and Ag 1 SAs on both reducible and irreducible supports, namely, CeO 2 (100), TiO 2 (101), and γ -Al 2 O 3 (110), to elucidate trends. We find that accumulated surface charge on the SA increases the CO 2 adsorption strength and decreases the CO 2 dissociation barrier for all studied SA/support combinations. For both charged and uncharged (neutral) systems, SAs on the reducible CeO 2 (100) support generally adsorb CO 2 more weakly compared to when on irreducible supports like γ -Al 2 O 3 (110). SAs on γ -Al 2 O 3 (110) typically have larger barriers for CO 2 dissociation for both charged and uncharged systems compared to TiO 2 (101) and CeO 2 (100). The magnitude of surface charging effects on CO 2 binding energies and dissociation barriers depends sensitively on both the SA and the support. In some cases, the CO 2 activation trends qualitatively change between neutral and charged systems for a fixed SA across different supports. This DFT modeling study demonstrates that surface charging should be considered in strong electric fields because it can have a large effect on molecule adsorption and bond-breaking on catalytic surfaces.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Low- Z polymer sample supports for fixed-target serial femtosecond X-ray crystallography

X-ray free-electron lasers (XFELs) offer a new avenue to the structural probing of complex materials, including biomolecules. Delivery of precious sample to the XFEL beam is a key consideration, as the sample of interest must be serially replaced after each destructive pulse. The fixed-target approach to sample delivery involves depositing samples on a thin-film support and subsequent serial introduction via a translating stage. Some classes of biological materials, including two-dimensional protein crystals, must be introduced on fixed-target supports, as they require a flat surface to prevent sample wrinkling. A series of wafer and transmission electron microscopy (TEM)-style grid supports constructed of low- Z plastic have been custom-designed and produced. Aluminium TEM grid holders were engineered, capable of delivering up to 20 different conventional or plastic TEM grids using fixed-target stages available at the Linac Coherent Light Source (LCLS). As proof-of-principle, X-ray diffraction has been demonstrated from two-dimensional crystals of bacteriorhodopsin and three-dimensional crystals of anthrax toxin protective antigen mounted on these supports at the LCLS. In conclusion, the benefits and limitations of these low- Z fixed-target supports are discussed; it is the authors' belief that they represent a viable and efficient alternative to previously reported fixed-target supports for conducting diffraction studies with XFELs.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

An algorithm to estimate the object support in truncated images

Purpose: Truncation artifacts in CT occur if the object to be imaged extends past the scanner field of view (SFOV). These artifacts impede diagnosis and could possibly introduce errors in dose plans for radiation therapy. Several approaches exist for correcting truncation artifacts, but existing correction algorithms do not accurately recover the skin line (or support) of the patient, which is important in some dose planning methods. The purpose of this paper was to develop an iterative algorithm that recovers the support of the object. Methods: The authors assume that the truncated portion of the image is made up of soft tissue of uniform CT number and attempt to find a shape consistent with the measured data. Each known measurement in the sinogram is interpreted as an estimate of missing mass along a line. An initial estimate of the object support is generated by thresholding a reconstruction made using a previous truncation artifact correction algorithm (e.g., water cylinder extrapolation). This object support is iteratively deformed to reduce the inconsistency with the measured data. The missing data are estimated using this object support to complete the dataset. The method was tested on simulated and experimentally truncated CT data. Results: The proposed algorithm produces a better defined skin line than water cylinder extrapolation. On the experimental data, the RMS error of the skin line is reduced by about 60%. For moderately truncated images, some soft tissue contrast is retained near the SFOV. As the extent of truncation increases, the soft tissue contrast outside the SFOV becomes unusable although the skin line remains clearly defined, and in reformatted images it varies smoothly from slice to slice as expected. Conclusions: The support recovery algorithm provides a more accurate estimate of the patient outline than thresholded, basic water cylinder extrapolation, and may be preferred in some radiation therapy applications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-T-237: The Imaging and Radiation Oncology Core (IROC) Cooperatives Activities Supporting the NCI’s National Clinical Trial Network

Purpose: The Imaging and Radiation Oncology Core (IROC) Cooperative has been active for the past two years supporting the National Clinical Trial Network and the details of that support are reported. Methods: There are six QA centers (Houston, Ohio, Philadelphia-RT, Philadelphia-DI, Rhode Island, St. Louis) providing an integrated RT and DI quality control program in support of the NCI’s clinical trials. The QA Center’s efforts are focused on assuring high quality data for clinical trials designed to improve the clinical outcomes for cancer patients worldwide. This program is administered through five core services: site qualification, trial design support, credentialing, data management, and case review. Results: IROC currently provides core support for 172 NCTN trials with RT, DI and RT/DI components. Many of these trials were legacy trial from the previous cooperative group program. IROC monitors nearly 1800 RT photon and 20 proton institutions. Over 28,000 beams outputs were monitored with 8% of the sites requiring repeat audits due to beam out of criteria. As part of credentialing, 950 QA phantoms have been irradiated, 515 imaging modalities evaluated and almost 4000 credentialing letters have been issued. In just year 2, 5290 RT and 4934 DI patient datasets were received (many using TRIAD) by IROC QA Centers to be prepared for review. During the past 2 years, a total of 6300 RT cases and 19,000 DI image sets were reviewed by IROC technical staff. To date, IROC has published 36 manuscripts. Conclusion: The QA services provided by IROC are numerous and are continually being evaluated for effectiveness, harmonized across all NCTN Groups and administered in an efficient and timely manner to enhance accurate and per protocol trial data submission. These efforts increase each NCTN Group’s ability to derive meaningful outcomes from their clinical trials. This work was supported by DHHS NIH grant 5U24CA180803.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

WE-H-201-00: Opportunities for Physicists to Support Low and Mid-Income Countries

The desperate need for radiotherapy in low and mid-income countries (LMICs) has been well documented. Roughly 60 % of the worldwide incidence of cancer occurs in these resource-limited settings and the international community alongside governmental and non-profit agencies have begun publishing reports and seeking help from qualified volunteers. However, the focus of several reports has been on how dire the situation is and the magnitude of the problem, leaving most to feel overwhelmed and unsure as to how to help and why to get involved. This session will help to explain the specific ways that Medical Physicists can uniquely assist in this grand effort to help bring radiotherapy to grossly-underserved areas. Not only can these experts fulfill an important purpose, they also can benefit professionally, academically, emotionally and socially from the endeavor. By assisting others worldwide with their skillset, Medical Physicists can end up helping themselves. Learning Objectives: Understand the need for radiotherapy in LMICs. Understand which agencies are seeking Medical Physicists for help in LMICs. Understand the potential research funding mechanisms are available to establish academic collaborations with LMIC researchers/physicians. Understand the potential social and emotional benefits for both the physicist and the LMIC partners when collaborations are made. Understand the potential for collaboration with other high-income scientists that can develop as the physicist partners with other large institutions to assist LMICs. Wil Ngwa - A recent United Nations Study reports that in developing countries more people have access to cell phones than toilets. In Africa, only 63% of the population has access to piped water, yet, 93% of Africans have cell phone service. Today, these cell phones, Skype, WhatsApp and other information and communication technologies (ICTs) connect us in unprecedented ways and are increasingly recognized as powerful, indispensable to global health. Thanks to ICTs, there are growing opportunities for Medical Physicists to reach out beyond the bunker and impact the world far beyond, without even having to travel. These growing opportunities in global health for Medical Physicists, powered by ICTs, will be highlighted in this presentation, illustrated by high impact examples/models across the globe that are improving patient safety and healthcare outcomes, saving lives. Learning Objectives: Published definitions of global health and the emerging field of global radiation oncology Learn about the transformative potential of ICTs in global radiation oncology care, research and education with focus on Medical Physics Learn about high impact examples of ICT-powered global radiation oncology and the increasing opportunities for participation by Medical Physicists. Yakov Pipman - The number and scope of volunteer Medical Physics activities in support of low-to-middle income countries has been increasing gradually. This happens through a variety of formal channels and to some extent through less formal but personal initiatives. A good deal of effort is dedicated by many, but many more could be recruited through a structured framework to volunteer. We will look into typical volunteer activities and how they fit with organizations already involved in advancing Medical Physics in LMIC. We will identify the range of these organizational activities and their scope to reveal areas of further need. We will point to a few key features of MPWB ( http://www.mpwb.org ) as a volunteering and collaborating structure and how members can get involved and contribute to these efforts at the grass roots level. The goal is that scarce resources can thus be channeled to complement rather than compete with those already in place. Learning Objectives: Understand the strengths and limitations of various organizations that support Medical Physics efforts in LMIC. Learn about ways to volunteer and contribute to Global Health through a grass roots organization focused on Medical Physics in LMIC. Perry Sprawls - With the growing capability and complexity of medical imaging methods in all countries of the world, the expanding role of medical physicists includes optimizing imaging procedures with respect to image quality, radiation dose, and other conflicting factors. With access to appropriate educational resources local medical physicists in all countries can provide direct clinical support and educational for other medical professionals. This is being supported through the process of Collaborative Teaching that combines the capabilities and experience of medical physicists in countries spanning the spectrum of economic, technological, and clinical development. The supporting resources are on the web at: http://www.sprawls.org/resources . Learning Objectives: Identify the medical physics educational needs to support effective and optimized medical imaging procedures. Use collaborative teaching resources to enhance the role of medical physicists in all countries of the world.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2011

ASME Code Efforts Supporting HTGRs

In 1999, an international collaborative initiative for the development of advanced (Generation IV) reactors was started. The idea behind this effort was to bring nuclear energy closer to the needs of sustainability, to increase proliferation resistance, and to support concepts able to produce energy (both electricity and process heat) at competitive costs. The U.S. Department of Energy has supported this effort by pursuing the development of the Next Generation Nuclear Plant, a high temperature gas-cooled reactor. This support has included research and development of pertinent data, initial regulatory discussions, and engineering support of various codes and standards development. This report discusses the various applicable American Society of Mechanical Engineers (ASME) codes and standards that are being developed to support these high temperature gascooled reactors during construction and operation. ASME is aggressively pursuing these codes and standards to support an international effort to build the next generation of advanced reactors so that all can benefit.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2012

Technical Support Document for Version 3.9.1 of the COM check Software

COM check provides an optional way to demonstrate compliance with commercial and high-rise residential building energy codes. Commercial buildings include all use groups except single family and multifamily not over three stories in height. COM check was originally based on ANSI/ASHRAE/IES Standard 90.1-1989 (Standard 90.1-1989) requirements and is intended for use with various codes based on Standard 90.1, including the Codification of ASHRAE/IES Standard 90.1-1989 (90.1-1989 Code) (ASHRAE 1989a, 1993b) and ASHRAE/IESNA Standard 90.1-1999 (Standard 90.1-1999). This includes jurisdictions that have adopted the 90.1-1989 Code, Standard 90.1-1989, Standard 90.1-1999, or their own code based on one of these. We view Standard 90.1-1989 and the 90.1-1989 Code as having equivalent technical content and have used both as source documents in developing COM check . This technical support document (TSD) is designed to explain the technical basis for the COM check software as originally developed based on the ANSI/ASHRAE/IES Standard 90.1-1989 (Standard 90.1-1989). Documentation for other national model codes and standards and specific state energy codes supported in COM check has been added to this report as appendices. These appendices are intended to provide technical documentation for features specific to the supported codes and for any changes made for state-specific codes that differ from the standard features that support compliance with the national model codes and standards. Beginning with COM check version 3.8.0, support for 90.1-1989, 90.1-1999, and the 1998 IECC and version 3.9.0 support for 2000 and 2001 IECC are no longer included, but those sections remain in this document for reference purposes.

Bartlett, Rosemarie↗
DOE OSTI2015

Preliminary Results of Ancillary Safety Analyses Supporting TREAT LEU Conversion Activities

The Transient Reactor Test Facility (TREAT), located at Idaho National Laboratory (INL), is a test facility designed to evaluate the performance of reactor fuels and materials under transient accident conditions. The facility, an air-cooled, graphite-moderated reactor designed to utilize fuel containing high-enriched uranium (HEU), has been in non-operational standby status since 1994. Currently, in support of the missions of the Department of Energy (DOE) National Nuclear Security Administration (NNSA) Material Management and Minimization (M3) Reactor Conversion Program, a new core design is being developed for TREAT that will utilize low-enriched uranium (LEU). The primary objective of this conversion effort is to design an LEU core that is capable of meeting the performance characteristics of the existing HEU core. Minimal, if any, changes are anticipated for the supporting systems (e.g. reactor trip system, filtration/cooling system, etc.); therefore, the LEU core must also be able to function with the existing supporting systems, and must also satisfy acceptable safety limits. In support of the LEU conversion effort, a range of ancillary safety analyses are required to evaluate the LEU core operation relative to that of the existing facility. These analyses cover neutronics, shielding, and thermal hydraulic topics that have been identified as having the potential to have reduced safety margins due to conversion to LEU fuel, or are required to support the required safety analyses documentation. The majority of these ancillary tasks have been identified in [1] and [2]. The purpose of this report is to document the ancillary safety analyses that have been performed at Argonne National Laboratory during the early stages of the LEU design effort, and to describe ongoing and anticipated analyses. For all analyses presented in this report, methodologies are utilized that are consistent with, or improved from, those used in analyses for the HEU Final Safety Analysis Report (FSAR) [3]. Depending on the availability of historical data derived from HEU TREAT operation, results calculated for the LEU core are compared to measurements obtained from HEU TREAT operation. While all analyses in this report are largely considered complete and have been reviewed for technical content, it is important to note that all topics will be revisited once the LEU design approaches its final stages of maturity. For most safety significant issues, it is expected that the analyses presented here will be bounding, but additional calculations will be performed as necessary to support safety analyses and safety documentation. It should also be noted that these analyses were completed as the LEU design evolved, and therefore utilized different LEU reference designs. Preliminary shielding, neutronic, and thermal hydraulic analyses have been completed and have generally demonstrated that the various LEU core designs will satisfy existing safety limits and standards also satisfied by the existing HEU core. These analyses include the assessment of the dose rate in the hodoscope room, near a loaded fuel transfer cask, above the fuel storage area, and near the HEPA filters. The potential change in the concentration of tramp uranium and change in neutron flux reaching instrumentation has also been assessed. Safety-significant thermal hydraulic items addressed in this report include thermally-induced mechanical distortion of the grid plate, and heating in the radial reflector.

Brunett, A. J.↗
DOE OSTI2024

Support of US Burning Plasma Organization (Final Technical Report)

The objective of the project described here was to support and increase the effectiveness of the US Burning Plasma Organization. This a national organization of scientists and engineers in magnetic fusion energy, established in 2005 at the request of the DOE Office of Fusion Energy Sciences, which serves to “Advance the scientific understanding of burning plasmas and ensure the greatest benefit from a burning plasma experiment by coordinating relevant U.S. fusion research with broad community participation.” It has grown to over 420 members from over 70 institutions, primarily across the US but with some associate members from other countries. The project was divided into two tasks. The first supported leadership activities in the USBPO by the Deputy Director, Dr. Amanda Hubbard. Responsibilities included chairing regular meetings of the USBPO Research Committee, communicating with the USBPO membership via emails and web seminars, forming and overseeing activities of Task Groups, and ensuring good communication about activities of the International Tokamak Physics Activity. A task group report on ‘Recommendations for ITER Experimental Operation, U.S. Team Formation and Participation’ was completed. Hubbard organized a series of highly popular web seminars for the burning plasma community, on a range of topics attracting a large number of participants from diverse institutions. Hubbard ended her term as Deputy Director in May, 2020. She subsequently received the Secretary of Energy’s Appreciation award for her service to USBPO. The second task supported the communications functions of the USBPO, led by Communications Coordinator, Mark London. Communications are critical for the effective operation of the USBPO, given it consists of members at many widely scattered institutions, and conducts its business almost entirely using remote tools. MIT has hosted and maintained the USBPO website, mailing lists, and discussion forums and provided member support, and videoconferencing support. MIT has continued this support following this grant, with funding incorporated into a broader Cooperative Agreement.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Support Effect Studied on Thin-Film Perovskites

Some functional oxides exhibit strong support effects but typically have low surface areas and stabilities that negate the promotional effects. The primary goal of our work in the past three years was to develop high-surface-area versions of these supports by Atomic Layer Deposition onto stable supports, then use these to understand how the oxide supports affect the metal catalytic properties. The primary application targeted for these materials was methane oxidation and related reactions for emissions control. Systems of particular interest were supported, precious metals on thin-film perovskites in order to develop “intelligent” catalysts in which the metal can reversibly ex-solve from perovskite lattices. This following report lists the papers that were published with the support of this DOE grant, together with a brief summary of the results from each paper.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Clear Sky Toolkit: Decision Support User Guide

The Clear Sky Decision Support Template is a Microsoft Excel-based resource that enables users to screen and prioritize critical facilities for the addition of solar + storage. The Decision Support Template consolidates and streamlines the most relevant resources from the emergency management discipline, the electric utility sector, and national energy research institutions to assist in further site analysis and decision-making. The Decision Support Template is intended for use by local government and private sector decision-makers who aim to mitigate the effects of power outages on critical infrastructure, understand the potential for deploying photovoltaic (PV) and storage solutions on critical facilities, and align emergency management planning processes and utility needs with community resilience objectives. The Decision Support Template is divided into five modules that provide a structured, step-by-step approach users can follow and apply to unique circumstances. This process guides a more thorough and accurate assessment of a site's potential to accommodate a solar + storage system, provide grid benefits to utilities, and support community resilience and disaster mitigation for the broader region. After identifying potentially viable and preferred sites for solar + storage using the Decision Support Template, users should conduct a more detailed evaluation and consultation with a solar professional.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2024

Sulfur-Doped Carbon Support Boosts CO2RR Activity of Ag Electrocatalysts

For presentation at the 70th AVS International Symposium and Exhibition. In this work, we show that the activity of Ag electrocatalysts for electrochemical CO2 to CO conversion is improved when supported on sulfur-doped (S-doped) carbon materials. S-doped carbon support was created by treating the heavily sputtered, highly oriented pyrolytic graphite (HOPG) in H2S at elevated temperatures, as confirmed by the S 2p X-ray photoelectron spectroscopy (XPS) peak. Scanning tunneling microscopy (STM) images indicated that Ag nanoparticles supported on S-doped HOPG had similar size distributions as those supported on sulfur-free (S-free) HOPG. While both catalysts reached > 90% CO Faradaic efficiency (FECO) at E = -1.3 V vs. the reversible hydrogen electrode (RHE) in the CO2 reduction reaction (CO2RR), Ag catalysts supported on S-doped HOPG demonstrated 70% higher CO turnover frequency (TOFCO = 3.4 CO/atomAg/s) than those supported on S-free HOPG (TOFCO = 2.0 CO/atomAg/s). Preliminary calculations based on density functional theory (DFT) indicated a more favorable energetic pathway of CO2-to-CO at the C-S-Ag interface, tentatively consistent with experiments. These results hint at a new approach to design active and selective electrocatalysts for CO2 conversion.

Deng, Xingyi↗
NASA NTRS1974

MSFC Skylab operations support summary

A summary of the actions and problems involved in preparing the Skylab-one vehicle is presented. The subjects discussed are: (1) flight operations support functions and organization, (2) launch operations and booster flight support functions and organization, (3) Skylab launch vehicle support teams, (4) Skylab orbital operations support performance analysis, (5) support manning and procedures, and (6) data support and facilities.

Martin, J. R.↗
NASA NTRS1974

Orbiter ECLSS support of Shuttle payloads

The orbiter ECLSS (Environmental Control and Life Support System) provides the functions of atmosphere revitalization, crew life support, and active thermal control. This paper describes these functions as they relate to the support of Shuttle payloads, including automated spacecraft, Spacelab and Department of Defense missions. Functional and performance requirements for the orbiter ECLSS which affect payload support are presented for the atmosphere revitalization subsystem, the food, water and waste subsystem, and the active thermal control subsystem. Schematics for these subsystems are also described. Finally, based on the selected orbiter configuration, preliminary design and off-design thermodynamic data are presented to quantify the baseline orbiter capability; to quantify the payload chargeable penalties for increasing this support; and to identify the significant limits of orbiter ECLSS support available to Shuttle payloads.

Jaax, J. R.↗
NASA NTRS1975

Stability and transient motion of a plain journal mounted in flexible damped supports

Results are presented for an extensive study of the influence of damped flexible supports on the stability-threshold speed of a symmetric rotor mounted in nonlinear fluid-film bearings. A stability analysis is conducted by applying the Routh criteria and calculating the damped eigenvalues of the system. Stability maps are given in dimensionless form for a range of support stiffness, damping, and mass ratios. The effect of rotor imbalance on the stability of rotor systems is examined, and it is shown that time transient orbits of shaft and support motions clearly indicate their dynamic behavior for both stable and unstable operating speeds. Simple design criteria are proposed for choosing the support stiffness and damping on the basis of rotor weight and journal clearance to promote optimum stability. It is concluded that the use of a flexible damped support system may increase the stability threshold of a plain journal bearing and that damper supports should promote smoother and quieter machine operation by suppressing oil whirl and attenuating unbalanced rotational forces.

Kirk, R. G.↗
NASA NTRS1985

BLSS: A Contribution to Future Life Support

The problem of the supply of basic life supporting ingredients was analyzed. Storage volume and launch weight of water, oxygen and food in a conventional nonregenerable life support system are directly proportional to the crew size and the length of the mission. Because of spacecraft payload limitations this requires that the carbon, or food, recycling loop, the third and final part in the life support system, be closed to further reduce logistics cost. Advanced life support systems need to be developed in which metabolic waste products are regenerated and food is produced. Biological life support systems (BLSS) satisfy the space station environmental control functions and close the food cycle. Numerous scientific space experiments were delineated, the results of which are applicable to the support of BLSS concepts. Requirements and concepts are defined and the feasibility of BLSS for space application are analyzed. The BLSS energy mass relation, and the possibilities to influence it to achieve advantages for the BLSS are determined. A program for the development of BLSS is proposed.

Skoog, A. I.↗
NASA NTRS1988

The GSFC Flight Support System for on-orbit satellite servicing

To plan and execute a successful on-orbit satellite servicing mission, space support hardware, a serviceable spacecraft design, and flexible ground operations are required. This paper addresses space support hardware and in particular the Goddard Space Flight Center (GSFC) Satellite Servicing Project's (SSP) Flight Support System (FSS). The FSS is designed to be compatible with the Space Transportation System Orbiter and to support on-orbit servicing of Multimission Modular Spacecraft. It provides mechanical, electrical, and thermal support to the spacecraft during the servicing mission. Standardization of spacecraft design, components, and interfaces is required to make a satellite serviceable. Spacecraft ground operation capabilities must accommodate servicing mission requirements. Space support tools and equipment, such as the Power Ratchet Tool, assists the astronaut during time critical EVA operations to more efficiently perform the servicing mission.

Griffin, Thomas J.↗
NASA NTRS1986

Space station Ada runtime support for nested atomic transactions

The Space Station Data Management System (DMS), associated computing subsystems, and applications have varying degrees of reliability associated with their operation. A model has been developed (McKay '86) which allows the DMS runtime environment to appear as an Ada virtual machine to applications executing within it. This model is modular, flexible, and dynamically configurable to allow for evolution and growth over time. Support for Fault-tolerant computing is included within this model. The basic primitive involved in this support is based on atomic actions (Grey '78). An atomic action possesses two fundamental properties: (1) it is indivisible with respect to concurrent actions, and (2) it is indivisible with respect to failure. A transaction is a collection of atomic actions which collectively appear to be one action. Transactions may be nested, providing even more powerful support for reliability. A proposed approach is described for providing support for nested atomic transactions within the Ada runtime model developed for the Space Station environment. The level of support is modular, flexible and dynamically configurable just like the overall runtime support environment.

Monteiro, Edward J.↗