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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Janus: A Python Package for Agent-Based Modeling of Land Use and Land Cover Change

Janus is an open source Python package for agent-based modeling (ABM) of land use and land cover change (LULCC). Many ABMs of LULCC have been created across platforms, some of which are not ideal for large scale, high resolution scenarios. This model provides a simple object-oriented framework for creating ABMs specific to LULCC. The organizational philosophy of the modeling framework is to create software objects (agents) that are associated with specific and contextual attributes which are isolated from where those agents exist in the spatial setting of the model, yet provide clear linkages between the agent, their environment, and other agents in the simulation. In this way, the framework allows for assembly of LULCC ABMs with low (programmatic) overhead, making the models extensible and providing clear mechanisms for integrating them with process-oriented biophysical models. Provided with Janus is a suite of geospatial data preprocessing tools that can use arbitrary land cover products as an input. Crop choice decisions are based on potential crop prices, these can be created synthetically, or drawn from integrated human-Earth systems models such as the GCAM. Janus is publicly accessible through GitHub and provides an example dataset for testing.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRSDate not supplied

Revisiting the Soyuz-1 Parachute Failure in the Context of Safety in the Modern Era

The Soyuz‑1 accident remains one of the most consequential parachute related failures in human spaceflight history and provides enduring lessons for modern Entry, Descent, and Landing (EDL) system design. Occurring during the height of the Cold War and the Space Race, the mission unfolded under extraordinary political and schedule pressure as the Soviet Union sought to maintain its early leadership in space achievements following the death of chief designer Sergei Korolev. Despite unresolved propulsion, electrical, and parachute system deficiencies, Soyuz‑1 proceeded to launch and immediately encountered critical inflight anomalies, including a failed solar panel deployment, attitude control issues, and communication dropouts. Upon reentry, a malfunction in the parachute system, driven by a primary main canopy that failed to deploy, and subsequent entanglement of the reserve main canopy with the primary drogue parachute, resulted in insufficient deceleration and the fatal crash of cosmonaut Vladimir Komarov. Subsequent investigations revealed deep rooted cultural and organizational issues within the Soviet space program, including inadequate testing, suppression of dissent, undocumented last minute design changes, and the absence of integrated parachute system verification. More than 200 design flaws were identified after the accident, and firsthand accounts, including those from Yuri Gagarin, highlighted widespread concern prior to launch. Over time, the Soviet program implemented substantial reforms: systematic design corrections, rigorous process documentation, and an extensive series of drop tests that ultimately transformed the Soyuz system into one of the world’s most reliable human-rated return vehicles. This paper examines the technical architecture of the Soyuz‑1 parachute system, reconstructs the likely deployment sequence and failure mechanism, and analyzes the cultural contributors that shaped the accident. The study draws parallels to modern spacecraft parachute development, emphasizing the critical importance of integrated system testing, transparent engineering culture, and continuous hardware surveillance. These lessons remain directly relevant to today’s NASA and Commercial Crew Programs (CCP), where the Government continues to refine its understanding of aggregate risk and strengthen overall astronaut safety in the face of increasingly complex parachute systems.

Aaron L Morris↗
NASA NTRS1999

In-Situ Production of Solar Power Systems for Exploration

Current proposals for developing an extended human presence, beyond space stations, on the Moon and Mars increasingly consider the processing of non-terrestrial materials essential for keeping the Earth launch burden reasonable. Utilization of in-situ resources for construction of lunar and Mars bases will initially require assessment of resource availability followed by the development of economically acceptable and technically feasible extractive processes. In regard to materials processing and fabrication the lower gravity level on the Moon (0.125 g) and Mars (0.367 g) will dramatically change the presently accepted hierarchy of materials in terms of specific properties, a factor which must be understood and exploited. Furthermore, significant changes are expected in the behavior of liquid materials during processing. In casting, for example, mold filling and associated solidification processes have to be reevaluated. Finally microstructural development and therefore material properties, presently being documented through on-going research in microgravity science and applications, needs to be understood and scaled to the reduced gravity environments. One of the most important elements of a human planetary base is power production. Lunar samples and geophysical measurements returned by the Apollo missions provide detailed data on the composition and physical characteristics of the lunar materials and environment. Based on this knowledge and extrapolations of terrestrial industrial experience it is clear that several types of solar-to-electric converters can be manufactured on the Moon. It is conceivable that well over 90% of a solar-to- electric power system could be made from lunar materials. Production and utilization of photovoltaic devices for solar energy production on Earth is primarily driven by the market economy. On Earth a production plant for photovoltaic devices is intimately linked to the planets massive industrial base. A selection of off the shelf refined materials are available as well as cheap fast transportation on demand. The processes takes place (except for the few seconds reprieve in shot towers etc.) under one gravity, with solar radiation significantly modulated by weather, and under conditions where one atmosphere is free and high vacuum is cumbersome and expensive. Off Earth, on lunar or Mars bases, the cost of photovoltaic power is driven by transport costs - Earth launch, deep space transport, landing on the planetary surface. Thus there is a premium for processes that are materials self-sufficient or for closed loop in-situ processes. The lack of differentiated ores on the Moon, and lack of explored minerals on Mars and interplanetary space give a premium to universal/non-ore-specific mineral extractive processes. Initially a semiconductor/photovoltaic production facility will build on no conveniently located industrial base, further increasing the premium on closed loop self sufficient processes.

Curreri, Peter A.↗
DOE OSTI2020

DPSIR-ESA Vulnerability Assessment (DEVA) Framework: Synthesis, Foundational Overview, and Expert Case Studies

Land resources are central to understanding the relationship between humans and their environment. We broadly define a land resource to include all the ecological resources of climate, water, soil, landforms, flora, and fauna, and all the socioeconomic systems that interact with agriculture, forestry, and other land uses within some system boundary. Understanding the vulnerability of land resources to changes in land management or climate forcing is critical to developing sustainable land management strategies. Vulnerability assessments are complex given the multiple uses of the assessments, the multi-disciplinary nature of the problem, limited understanding, the dynamic structure of vulnerability, scale issues, and problems with identifying effective vulnerability indicators. Here, we propose a novel conceptual framework for vulnerability assessments of land resources that combines the driver– pressure–state–impact–response (DPSIR) framework adopted by the European Environment Agency to describe interactions between society and the environment, and the exposure-sensitivity-adaptive capacity (ESA) framework used by the Intergovernmental Panel on Climate Change to assess impacts of climate change. The DPSIR-ESA Vulnerability Assessment (DEVA) framework operationalizes the process of assessing the vulnerability of a target system to external stressors. The DEVA framework includes the following elements: 1) Definition of the target system (Land resource), 2) Description of internal characteristics of the target system (State), 3) Description of target system vulnerability indicators (Adaptive capacity, Sensitivity), 4) Description of stressor characteristics (Drivers, Pressures), 5) Description of stressor vulnerability indicators (Exposure), 6) Description of target system response to stressors (Impacts), and 7) Description of modifications to target systems or stressors (Responses). In stating that they have “applied the DEVA framework”, analysts acknowledge that they have (a) considered the full breadth of each DEVA element, (b) have made conscious decisions to limit the scope and complexity of certain elements, and (c) can communicate both the rationale for these decisions and the impact of these decisions on the vulnerability assessment results and recommendations. The DEVA framework was refined during invited presentations and follow-up discussions from a series of Special Sessions with leading experts at two successive ASABE Annual International Meetings. Six case studies drawn from the sessions elaborate upon the DEVA framework and provide concrete examples of the key concepts. The DEVA approach gives engineers, planners, and analysts a new, flexible framework to apply a broad array of useful tools toward assessment of land resource system vulnerability.

Anandhi, Aauvadi↗
DOE OSTI2023

Joint Analysis of the Epidemic Evolution and Human Mobility During the First Wave of COVID-19 in Spain: Retrospective Study

Background The initial wave of the COVID-19 pandemic placed a tremendous strain on health care systems worldwide. To mitigate the spread of the virus, many countries implemented stringent nonpharmaceutical interventions (NPIs), which significantly altered human behavior both before and after their enactment. Despite these efforts, a precise assessment of the impact and efficacy of these NPIs, as well as the extent of human behavioral changes, remained elusive. Objective In this study, we conducted a retrospective analysis of the initial wave of COVID-19 in Spain to better comprehend the influence of NPIs and their interaction with human behavior. Such investigations are vital for devising future mitigation strategies to combat COVID-19 and enhance epidemic preparedness more broadly. Methods We used a combination of national and regional retrospective analyses of pandemic incidence alongside large-scale mobility data to assess the impact and timing of government-implemented NPIs in combating COVID-19. Additionally, we compared these findings with a model-based inference of hospitalizations and fatalities. This model-based approach enabled us to construct counterfactual scenarios that gauged the consequences of delayed initiation of epidemic response measures. Results Our analysis demonstrated that the pre–national lockdown epidemic response, encompassing regional measures and heightened individual awareness, significantly contributed to reducing the disease burden in Spain. The mobility data indicated that people adjusted their behavior in response to the regional epidemiological situation before the nationwide lockdown was implemented. Counterfactual scenarios suggested that without this early epidemic response, there would have been an estimated 45,400 (95% CI 37,400-58,000) fatalities and 182,600 (95% CI 150,400-233,800) hospitalizations compared to the reported figures of 27,800 fatalities and 107,600 hospitalizations, respectively. Conclusions Our findings underscore the significance of self-implemented prevention measures by the population and regional NPIs before the national lockdown in Spain. The study also emphasizes the necessity for prompt and precise data quantification prior to enacting enforced measures. This highlights the critical interplay between NPIs, epidemic progression, and human behavior. This interdependence presents a challenge in predicting the impact of NPIs before they are implemented.

Public, Environmental & Occupational Health↗
NASA NTRS2001

Neurophysiology Summary

The terrestrial gravitational field serves as an important orientation reference for human perception and movement, being continually monitored by sensory receptors in the skin, muscles, joints, and vestibular otolith organs. Cues from these graviceptors are used by the brain to estimate spatial orientation and to control balance and movement. Changes in these cues associated with the tonic changes in gravity (gravito-inertial force),during the launch and entry phases of space flight missions result in altered perceptions, degraded motor control performance, and in some cases, "motion" sickness during, and for a period of time after, the g-transitions. In response to these transitions, however, physiological and behavioral response mechanisms are triggered to compensate for altered graviceptor cues and/or to adapt to the new sensory environment. Basic research in the neurophysiology discipline is focused on understanding the characteristic features of and the underlying mechanisms for the normal human response to tonic changes in the gravito-inertial force environment. These studies address fundamental questions regarding the role of graviceptors in orientation and movement in the terrestrial environment, as well as the capacity, specificity, and modes for neural plasticity in the sensory-motor and perceptual systems of the brain. At the 2001 workshop basic research studies were presented addressing: neuroanatomical responses to altered gravity environments, the neural mechanisms for resolving the ambiguity between tilting and translational stimuli in otolith organ sensory input, interactions between the vestibular system and the autonomic nervous system , the roles of haptic and visual cues in spatial orientation, mechanisms for training environment-appropriate sensorimotor responses triggered by environment-specific context cues, and studies of sensori-motor control of posture and locomotion in the terrestrial environment with and without recent exposure to space flight. Building on these basic research studies are more applied studies focused on the development of countermeasures to the untoward neurophysiological responses to space flight. At the 2001 workshop, applied research studies were presented addressing issues related to the use of rotational artificial gravity (centripetal acceleration) as a multisystem (bone, muscle, cardiovascular, and, perhaps, neurovestibular) countermeasure. Also presented was a clinical study reporting on a new rating system for clinical evaluation of postflight functional neurological status.

Paloski, William H.↗
NASA NTRS2010

Propulsion Design With Freeform Fabrication (PDFF)

The nation is challenged to decrease the cost and schedule to develop new space transportation propulsion systems for commercial, scientific, and military purposes. Better design criteria and manufacturing techniques for small thrusters are needed to meet current applications in missile defense, space, and satellite propulsion. The requirements of these systems present size, performance, and environmental demands on these thrusters that have posed significant challenges to the current designers and manufacturers. Designers are limited by manufacturing processes, which are complex, costly, and time consuming, and ultimately limited in their capabilities. The PDFF innovation vastly extends the design opportunities of rocket engine components and systems by making use of the unique manufacturing freedom of solid freeform rapid prototype manufacturing technology combined with the benefits of ceramic materials. The unique features of PDFF are developing and implementing a design methodology that uses solid freeform fabrication (SFF) techniques to make propulsion components with significantly improved performance, thermal management, power density, and stability, while reducing development and production costs. PDFF extends the design process envelope beyond conventional constraints by leveraging the key feature of the SFF technique with the capability to form objects with nearly any geometric complexity without the need for elaborate machine setup. The marriage of SFF technology to propulsion components allows an evolution of design practice to harmonize material properties with functional design efficiency. Reduced density of materials when coupled with the capability to honeycomb structure used in the injector will have significant impact on overall mass reduction. Typical thrusters in use for attitude control have 60 90 percent of its mass in the valve and injector, which is typically made from titanium. The combination of material and structure envisioned for use in an SFF thruster design could reduce thruster weight by a factor of two or more. The thrust-to-weight ratios for such designs can achieve 1,000:1 or more, depending on chamber pressure. The potential exists for continued development in materials, size, speed, accuracy of SFF techniques, which can lead to speculative developments of PDFF processes such as fabrication of custom human interface devices like masks, chairs, and clothing, and advanced biomedical application to human organ reconstruction. Other potential applications are: higher fidelity lower cost test fixtures for probes and inspection, disposable thrusters, and ISRU (in situ resource utilization) for component production in space or on Lunar and Martian missions, and application for embedding MEMS (microelectromechanical systems) during construction process of form changing aerostructure/dynamic structures.

Barnes, Daudi↗
NASA NTRS2015

Numerical Modeling of Ophthalmic Response to Space

To investigate ophthalmic changes in spaceflight, we would like to predict the impact of blood dysregulation and elevated intracranial pressure (ICP) on Intraocular Pressure (IOP). Unlike other physiological systems, there are very few lumped parameter models of the eye. The eye model described here is novel in its inclusion of the human choroid and retrobulbar subarachnoid space (rSAS), which are key elements in investigating the impact of increased ICP and ocular blood volume. Some ingenuity was required in modeling the blood and rSAS compartments due to the lack of quantitative data on essential hydrodynamic quantities, such as net choroidal volume and blood flowrate, inlet and exit pressures, and material properties, such as compliances between compartments.

intracranial pressure↗
NASA NTRSDate not supplied

NASA’s Global Change Master Directory (GCMD) Keyword Viewer Beta

The Global Change Master Directory (GCMD) Keyword Viewer is a web-based client that allows metadata curators and ontologists to search for and navigate the GCMD keywords in a user-friendly and human-readable tree structure. The Keyword Viewer is built on top of the Keyword Management Systems (KMS) API, which provides machine-to-machine access to the keywords.

Tyler B Stevens↗
NASA NTRSDate not supplied

Spaceflight Food System Impacts to Nutritional Adequacy, Health, Performance, and Resources in Space Exploration

Despite high physical standards and training protocols, physiological and behavioral decrements have been documented in astronauts on both short (1-2 weeks) and long (6+ month) missions in spaceflight, including dysregulation of the immune system, cardiovascular and musculoskeletal deconditioning, ophthalmic changes, weight loss, and increased stress and fatigue. Optimizing food and nutrition intakes are key underpinnings for the proper function and performance of all physiological systems and the resulting physical and behavioral health and performance outcomes of astronauts. Much has been learned about the role of nutrition in human health on Earth over the past hundred years, from the identity and role of specific vitamins to the importance of the quantities of some nutrients to immune function. The requirements for providing adequate nutrition to astronauts seem obvious. However, providing a safe, reliable, and nutritious food system for space exploration missions remains a challenge. In fact, food is one of the greatest resource and logistical challenges, which is part of why it remains a “red” risk for Mars missions.

Grace L Douglas↗
NASA NTRSDate not supplied

Extending the Duration of Crewed Stays on the Lunar Surface

NASA’s Artemis missions aim to return humans to the Moon for the first time since the Apollo Program. Unlike the Apollo missions, Artemis missions will take advantage of pre-emplaced assets on the lunar surface to support crewed exploration, science, and utilization. Although the initial Artemis surface missions are intended to keep crew on the lunar surface for durations ranging from several days to several weeks, crewed stays of longer periods may provide additional support toward NASA’s Moon to Mars Objectives, including long-term exploration and continuous human lunar presence. If mission durations are extended beyond the expected few weeks, the elements and concepts of operation for the lunar architecture will need to be capable of supporting that extension. This paper uses an integrated systems analysis perspective to examine the architectural considerations of extending the duration of human missions on the lunar surface. By identifying these key architectural considerations, this paper offers insight into how elements and operations might meet the demands of potential future mission concepts. This paper does not recommend changes to NASA’s lunar architecture, and it does not evaluate whether any mission concepts affect the relative satisfaction of the Moon to Mars Objectives. However, if crew do remain on the surface for progressively longer periods of time, the functions and capabilities provided by the assets supporting the crew may need to adjust to support the needs of those missions. The functions and capabilities identified as key to enable such extended duration missions include power generation and storage, logistics delivery, radiation mitigation, provision of medical and exercise capability, abort from the lunar surface, maintenance, and the provision of pressurized volume. For example, the medical capabilities available to the crew may become more extensive, and habitable elements may need to change to support longer crewed periods (and shorter quiescent periods). In some cases, these changes may be accomplished through alterations to use cases, operational changes, or the evolution of lunar surface elements, but in other cases, new elements may be preferable. By identifying key considerations for the functions and capabilities of notional lunar surface elements as the length of each crewed mission is extended from several days to continuous human presence on the Moon, this paper assesses how the elements of NASA’s lunar architecture might support the extension of mission durations. In addition, this analysis can help inform future evaluation of whether such extended duration missions improve NASA’s ability to address its Moon to Mars Objectives.

Garrett M. Carman↗
NASA NTRS2003

National Aeronautics and Space Administration 2003 Strategic Plan

Imagine knowing that we are not alone, but that life is abundant in our solar system and throughout the universe. Imagine a world where we can safely travel anywhere, anytime, on our home planet, and in space. Imagine a world in which long-term weather forecasts are reliable, and natural disasters are predictable and perhaps even preventable. NASA is changing our understanding of the world, exploring the unknown, and creating new awareness about who we are and what our place is in the cosmos. For the first time in history, we have the tools, the insight and ability to seek answers to some of humanity's most profound questions: 1) How did we get here? 2) Where are we going? 3) Are we alone? In addition to pursuing these compelling questions, NASA helps the Nation to meet its challenges and address its urgent national needs. Among these are the requirements to improve the security and safety of our air transportation system and counter the looming shortage of U.S. scientists and engineers in our next generation of Americans.

Source record↗
NASA NTRS1999

Is skeletal muscle ready for long-term spaceflight and return to gravity?

It is now clear that prevention of muscle debilitation during spaceflight will require a broader approach than simple exercise aimed at strengthening of the muscle fibers. The levels of several hormones and receptors are altered by unloading and must be returned to homeostasis. Pharmacotherapy and gene transfer strategies to raise the relative level of structural proteins may minimize the problems faced by astronauts in readapting to Earth-gravity. Up to now, we have only minimally exploited microgravity for advancing our understanding of muscle biology. A research laboratory in the space station with a centrifuge facility (gravity control) is essential for conducting basic research in this field. Microgravity has proven an excellent tool for noninvasively perturbing the synthesis of muscle proteins in the search for molecular signals and gene regulatory factors influencing differentiation, growth, maintenance and atrophy of muscle. Understanding the relation between blood flow and interstitial edema and between workload and subsequent structural failure are but two important problems that require serious attention. The roles of hormones and growth factors in regulating gene expression and their microgravity-induced altered production are other urgent issues to pursue. These types of studies will yield information that advances basic knowledge of muscle biology and offers insights into countermeasure design. This knowledge is likely to assist rehabilitation of diseased or injured muscles in humans on Earth, especially individuals in the more vulnerable aging population and persons participating in strenuous sports. Will the skeletal muscle system be prepared for the increased exposure to microgravity and the return to gravity loading without injury when space station is operational? The answer depends in large part on continued access to space and funding of ground-based models and flight experiments. The previous two decades of spaceflight research have described the effects of microgravity on multiple systems. The next generation of experiments promises to be even more exciting as we are challenged to define the cellular and molecular mechanisms of microgravity-induced changes.

manned↗
DOE OSTI2022

Demonstration and Evaluation of the Human-Technology Integration Guidance for Plant Modernization

The significance of nuclear power in its role producing carbon-free electricity to the U.S. cannot be overstated. However, with changes in the energy market coupled with changes in incentives given to certain resources like solar and wind, the operating and maintenance costs for these sources have seen a significant reduction, which has consequently negatively impacted the economic viability of the existing U.S. nuclear power plant fleet. Digital instrumentation and control (I&C) and control room modernization is a major critical work domain to reduce operating and maintenance costs. Existing nuclear power plants are commonly configured with mostly legacy analog I&C as well as isolated pockets of digital I&C (a plant process computer, digital recorders, etc.). One challenge with this analog I&C is that replacement parts are becoming prohibitively more expensive and difficult to obtain. Moreover, a significant challenge with the existing analog I&C is that the way in which plants are currently operated and maintained is no longer competitive with other electricity generating sources, like natural gas, where advanced digital I&C technologies are commonplace. This gap between the waynuclear power plants are operated compared to other electricity generating sources significantly challenges the economic viability of the nuclear industry. Indeed, digital I&C systems can fundamentally change the way the plant is operated (i.e., the concept of operation). The introduction of digital I&C technologies offers a wealth of benefits to the nuclear industry. However, it is important to emphasize that, to realize these benefits, a careful understanding of how to integrate technology in a collaborative way that leverages the capabilities of people and technologies is necessary. Human-technology integration applies human factors engineering methods and tools to ensure the safe and reliable use of these technologies while ensuring that the inherent features of the technologies that provide economic value are not missed. The scope of this work documents the demonstration of the recently developed human and technology integration methodology, as applied to developing a new vision and concept of operations for a major U.S. nuclear power plant fleet. This report focuses on the methodological aspects of developing a vision and concept of operations. This report shares the tools, activities, and lessons learned during a modernization currently underway for industry as a whole to consider when planning any significant digital modification and developing a new vision and concept of operations.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1998

Effects of microgravity on osteoblast growth

Studies from space flights over the past two decades have demonstrated that basic physiological changes occur in humans during space flight. These changes include cephalic fluid shifts, loss of fluid and electrolytes, loss of muscle mass, space motion sickness, anemia, reduced immune response, and loss of calcium and mineralized bone. The cause of most of these manifestations is not known and until recently, the general approach was to investigate general systemic changes, not basic cellular responses to microgravity. Recently analyzed data from the 1973-1974 Skylabs disclose that there is a rise in the systemic hormone, cortisol, which may play a role in bone loss in flight. In two flights where bone growth was measured (Skylabs 3 and 4), the crew members had a significant loss of calcium accompanied by a rise in 24 hour urinary cortisol during the entire flight period. In ground-based work on osteoblasts, we have demonstrated that equivalent amounts of glucocorticoids can inhibit osteoblast cell growth. In addition, this laboratory has recently studied gene growth and activation of mouse osteoblasts (MC3T3-E1) during spaceflight. Osteoblast cells were grown on glass coverslips, loaded in the Biorack plunger boxes 18 hours before launch and activated 19 hours after launch in the Biorack incubator under microgravity conditions. The osteoblasts were launched in a serum deprived state, activated and collected in microgravity. Samples were collected at 29 hours after sera activation (0-g, n=4; 1-g, n=4). The osteoblasts were examined for changes in gene expression and cell morphology. Approximately one day after growth activation, remarkable differences were observed in gene expression in 0-g and 1-g flight samples. The 0-g activated cells had increased c-fos mRNA when compared to flight 1-g controls. The message of immediate early growth gene, cox-2 was decreased in the microgravity activated cells when compared to ground or 1-g flight controls. Cox-1 was not detected in any of the samples. There were no significant differences in the expression of actin mRNA between the 0-g and 1-g samples. These data indicate that quiescent osteoblasts are slower to enter the cell cycle in microgravity, suggesting that the force of gravity itself may be a significant factor in bone loss in spaceflight. Preliminary data from our STS 76 flight experiment support our hypothesis that a basic biological response occurs at the tissue, cellular, and molecular level in 0-g. Here we examine ground-based and space flown data on osteoblast growth in ground-based experiments mimicking space flight conditions and in microgravity to simulate lack of gravity stress to help us understand the mechanism of bone loss by experiments.

NASA Experiment Number 9403056↗
NASA NTRS1993

Mathematical modelling of the human cardiovascular system in the presence of stenosis

This paper reports a theoretical study on the distribution of blood flow in the human cardiovascular system when one or more blood vessels are affected by stenosis. The analysis employs a mathematical model of the entire system based on the finite element method. The arterial-venous network is represented by a large number of interconnected segments in the model. Values for the model parameters are based upon the published data on the physiological and rheological properties of blood. Computational results show how blood flow through various parts of the cardiovascular system is affected by stenosis in different blood vessels. No significant changes in the flow parameters of the cardiovascular system were found to occur when the reduction in the lumen diameter of the stenosed vessels was less than 65%.

NASA Program Data Analysis↗
NASA NTRS1996

Gravitational physiology of human immune cells: a review of in vivo, ex vivo and in vitro studies

The study of the function of immune cells in microgravity has been studied for more than 20 years in several laboratories. It is clear today that the immune system is depressed in more than 50% of the astronauts during and after space flight and that the activation of T lymphocytes by mitogens in vitro changes dramatically. This article gives an overview of the gravitational studies conducted by our laboratory in Spacelab, in MIR station, in sounding rockets and on the ground in the clinostat and the centrifuge. Three experimental approaches are followed in our work: (i) Ex vivo studies are performed with blood samples drawn from astronauts; (ii) in vivo studies are based on the application of seven antigens to the skin of the astronauts; (iii) in vitro studies are carried out with immune cells purified from the blood of healthy donors (not astronauts). The data from our in vivo and ex vivo studies are in agreement with those of other laboratories and show that the immunological function is depressed in the majority of astronauts as a consequence of the stress of space flight rather than by a direct influence of gravity on the cell. Immune depression may become a critical hazard on long duration flights on space stations or to other planets. In vitro experiments show that cultures of free-floating lymphocytes and monocytes undergo a dramatic depression of activation by the mitogen concanavalin A, while activation is more than doubled when the cells are attached to microcarrier beads. Such effects may be attributed to both direct and indirect effects of gravitational unloading on basic biological mechanisms of the cell. While the in vitro data are very important to clarify certain aspects of the biological mechanism of T cells activation, they are not descriptive of the changes of the immunological function of the astronauts.

Review↗
NASA NTRS1975

Operational calm and the optimum regulation of human working capacity

Muscle hardness measurements in a squeezing dynamometer test are interpreted for expressions of adjustment effects of the central nervous system in rapid response to a starting signal. It is shown that preliminary muscle tension leads to the transmission of inhibiting proprioceptive impulses to the nervous system centers and that the degree of pre-working changes depends on the individual's typological personality characteristics. Concentration of attention during the pre-working adjustment is considered the primary emotional factor that controls sensorimotor performance.

Ilin, Y. P.↗