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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Repurposing the θ (Al 2 Cu) phase to simultaneously increase the strength and ductility of an additively manufactured Al–Cu alloy

The Al–Cu–Mn–Zr (ACMZ) cast family of alloys offers unique properties and value propositions for higher strength, higher temperature lightweight components of future vehicles. Earlier research has demonstrated trade-offs in the selection of the alloy chemistry in which an increase in Cu content from 6 up to 9 wt% improves hot tear resistance but lowers ductility. However, a recent study has demonstrated that higher-Cu (9Cu) ACMZ fabricated with laser powder bed fusion additive manufacturing (AM) results in an increase in both ductility and strength when compared to as-aged microstructure of cast 9Cu alloys. The mechanisms of differing mechanical performance of the cast and AM ACMZ alloys are elucidated in the current paper through the utilization of in situ high energy x-ray diffraction (HEXRD) tensile testing wherein lattice strains of different phases are calculated and correlated to their stresses. The ACMZ alloys consisted of theta (θ) and theta prime (θ') phases (both Al 2 Cu in nominal composition) within an aluminum matrix. The larger micron-size θ phase which decorated the grain boundaries in 9Cu ACMZ cast alloys recorded small lattice strains, while the submicron, homogeneously distributed θ phase in the 9Cu ACMZ AM alloy recorded considerably higher lattice strains. The maximum stress reached in the θ phase for the cast 9Cu alloy was found to be ~280 MPa, which was lower than the AM 9Cu alloy which registered a maximum stress of ~1.4 GPa. These measurements indicate that delayed fracture of the finer intermetallic phases simultaneously improves the ductility and strength of AM 9Cu alloy relative to the cast 9Cu alloy, which exhibits early fracture of the larger intermetallic particles.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Amidination of ligands for chemical and field-effect passivation stabilizes perovskite solar cells

Surface passivation has driven the rapid increase in the power conversion efficiency (PCE) of perovskite solar cells (PSCs). However, state-of-the-art surface passivation techniques rely on ammonium ligands that suffer deprotonation under light and thermal stress. We developed a library of amidinium ligands, of interest for their resonance effect–enhanced N–H bonds that may resist deprotonation, to increase the thermal stability of passivation layers on perovskite surfaces. This strategy resulted in a >10-fold reduction in the ligand deprotonation equilibrium constant and a twofold increase in the maintenance of photoluminescence quantum yield after aging at 85°C under illumination in air. Here, implementing this approach, we achieved a certified quasi–steady-state PCE of 26.3% for inverted PSCs; and we report retention of ≥90% PCE after 1100 hours of continuous 1-sun maximum power point operation at 85°C.

Yang, Yi↗
DOE OSTI2022

Interplay of Electrode Heterogeneity and Lithium Plating

Lateral microstructure heterogeneity in anodes is known to induce nonuniform current density, state of charge, and lithium plating. This means that such electrode heterogeneity can limit the fast charging of lithium-ion batteries. In this work, a combination of experiments and simulation is employed to understand the effect of mm scale lateral heterogeneity on cell aging. A previously developed model was extended to efficiently simulate SEI formation and Li plating for independent regions of an electrode. The model consists of three parallel regions each described under a P2D framework and with a distinct ionic resistance and possibly active material loading. The results suggest that during fast charge when the active material is uniformly distributed across the three regions, the region with the highest resistance reaches the end of life sooner than the other regions. There is also positive feedback from Li metal filling the pores near the separator interface that further accelerates lithium plating. Lastly, when there is a non-uniform active material distribution associated with the ionic resistance heterogeneity, tight competition between regions can occur, leading to less overall lithium plating and plating that is more uniform between regions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2011

Prognostics of Power MOSFET

This paper demonstrates how to apply prognostics to power MOSFETs (metal oxide field effect transistor). The methodology uses thermal cycling to age devices and Gaussian process regression to perform prognostics. The approach is validated with experiments on 100V power MOSFETs. The failure mechanism for the stress conditions is determined to be die-attachment degradation. Change in ON-state resistance is used as a precursor of failure due to its dependence on junction temperature. The experimental data is augmented with a finite element analysis simulation that is based on a two-transistor model. The simulation assists in the interpretation of the degradation phenomena and SOA (safe operation area) change.

Celaya, Jose Ramon↗
DOE OSTI2024

Thermal aging effects on crosslinked polyethylene cable insulation with decabromodiphenyl ether flame retardant alternative

Decabromodiphenyl ether (decaBDE) has been extensively used as a flame retardant in several applications, including nuclear electrical cable insulation. However, decaBDE has been identified as a persistent, bioaccumulative and toxic (PBT) substance, leading to regulatory scrutiny. The Environmental Protection Agency (EPA) published a regulation on January 6, 2021, aimed at phasing out the manufacturing, processing, and distribution of decaBDE. This rule set a compliance deadline of March 8, 2021, for the manufacture and processing of decaBDE, and an extended deadline of January 6, 2023, for specific applications including wire and cable insulation in nuclear power generation facilities. In response to such regulations, RSCC, a major supplier of safety-related electrical cables and associated products to the U.S. nuclear industry updated the formula of their crosslinked polyethylene (XLPE) insulation to replace the historically used decaBDE flame retardant with an acceptable alternative. This change from the previous decaBDE-containing XLPE prompted interest in comparative performance of the two material formulations, especially with respect to characteristics relevant to safety-related function such as thermal and radiation resistance. RSCC graciously provided samples of wire insulated with the decaBDE-containing XLPE formulation and corresponding wire insulated with XLPE of the new formulation, containing a decaBDE alternative. In this work we compare characteristics of the two formulations and a previously produced commercial version of the RSCC decaBDE-containing XLPE insulation subjected to thermal aging at 150 °C and 165 °C. The comparison was focused on mechanical durability, thermal stability in the oxidative environment, and chemical structures. Briefly, • Tensile elongation at break (EAB) results showed loss of mechanical elasticity with longer aging time, as expected. Aging time dependence of EAB did not differ between the decaBDE-containing and decaBDE-alternative samples. • Subtle differences between the two materials can be detected from Fourier-transform infrared spectroscopy (FTIR) absorbance spectra in the range below 1700 cm -1 , are assumed to be related to decomposition of flame retardant additives during thermal aging. • The oxidation induction time (OIT) data seemed to show that the unaged decaBDE-containing XLPE material is more thermally stable than the unaged decaBDE-alternative material, but the discrepancy in OIT decreased with aging time and the OIT values of the two materials became similar starting with the 4 th day of aging at 165 °C. This thermal aging investigation confirmed that the mechanical durability, a key property monitored for cable qualification, was not significantly affected by the modification of the formulation with a decaBDE alternative flame-retardant system in the investigated thermal aging conditions. Further studies on the same sets of materials exposed to thermal and gamma radiation aging would further inform comparison of the materials safety-related function.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Impact of Laboratory-Accelerated Aging Methods to Study Alkali–Silica Reaction and Reinforcement Corrosion on the Properties of Concrete

This study focuses on two separate investigations of the main aging mechanisms: alkali–silica reactivity (ASR) and the corrosion of reinforcing steel (rebar) concrete, both of which may result in a premature failure to meet the serviceability or strength requirements of a concrete structure. However, these processes occur very slowly, spanning decades. The impact of direct chemical additives to fresh concrete to accelerate ASR and the corrosion of reinforcing steel on the fresh and hardened properties of the ensuing material are investigated to inform the potential use of chemicals in large-scale studies. The deterioration of reinforced concrete (RC) is determined by means of expansion, cracking, bulk diffusivity and surface resistivity measurements, and compressive, split tensile and flexural strength tests. The results indicate that the addition of sodium hydroxide and calcium chloride can effectively accelerate the crack formation and propagation in concrete due to ASR and the corrosion of rebar, respectively. The ASR-induced cracks maintained a constant crack width from 0.05 mm to 0.1 mm over the measurement period regardless of the intensity of aging acceleration. Adding 4% chloride by weight of cement for accelerating rebar corrosion resulted in an average crack that was 82% larger than in the case of ASR accelerated with the addition of sodium hydroxide. The addition of alkali resulted in an increase in early-age (7-day) strength. At a total alkali loading of 2.98 kg/m3, 3.84 kg/m3 and 5.57 kg/m3, the 28-day compressive strength of concrete decreased by 3%, 10% and 24%, respectively. Similarly, a higher early-age strength and a lower later-age strength was observed for the concrete in the presence of corrosive calcium chloride. The results from this research are expected to inform future studies on the long-term performance of RC structures under accelerated ASR and corrosion.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Forecasting battery capacity and power degradation with multi-task learning

Lithium-ion batteries degrade due to usage and exposure to environmental conditions, which affects their capability to store energy and supply power. Accurately predicting the capacity and power fade of lithium-ion battery cells is challenging due to intrinsic manufacturing variances and coupled nonlinear ageing mechanisms. In this paper, we propose a data-driven prognostics framework to predict both capacity and power fade simultaneously with multi-task learning. The model is able to predict the degradation trajectory of both capacity and internal resistance together with knee-points and end-of-life points accurately at early-life stage. The validation shows an average percentage error of 2.37% and 1.24% for the prediction of capacity fade and resistance rise, respectively. The model's ability to accurately predict the degradation, facing capacity and resistance estimation errors, further demonstrates the model's robustness and generalizability. Compared with single-task learning models for forecasting capacity and power degradation, the model shows a significant prediction accuracy improvement and computational cost reduction. This work presents the highlights of multi-task learning in the degradation prognostics for lithium-ion batteries.

25 ENERGY STORAGE↗
NASA NTRS1973

Cyclic debonding of adhesive joints

Bonded lap joints were manufactured and tested under static and fatigue loading. Specimens were designed to fail in the bondline, and all fatigue tests included monitoring the crack growth to failure. Test specimens included aluminum details joined by two different adhesives. Specimens also included titanium and boron-epoxy details joined by an epoxy laminating resin. Additonal program variables included bondline thickness, adherend and spice plate thickness, specimen width, and specimen fabrication procedure. Adhesive aging was found to be generally detrimental to the lives of most of the specimens bonded with one adhesive system. Adhesive material was found to have a major influence on debond rate. Co-cured titanium/boron-epoxy specimens were found to resist debonding better than specimens fabricated with a sequential cure. Splice plate thickness and test section width were found to have little effect on debond rate. The data also suggested the existence of an optimum bondline thickness.

Hoffman, D. J.↗
NASA NTRS1998

Autoregulation of cerebral blood flow in orthostatic hypotension

BACKGROUND AND PURPOSE: We sought to evaluate cerebral autoregulation in patients with orthostatic hypotension (OH). METHODS: We studied 21 patients (aged 52 to 78 years) with neurogenic OH during 80 degrees head-up tilt. Blood flow velocities (BFV) from the middle cerebral artery were continuously monitored with transcranial Doppler sonography, as were heart rate, blood pressure (BP), cardiac output, stroke volume, CO2, total peripheral resistance, and cerebrovascular resistance. RESULTS: All OH patients had lower BP (P<.0001), BFV_diastolic (P<.05), CVR (P<.007), and TPR (P<.02) during head-up tilt than control subjects. In control subjects, no correlations between BFV and BP were found during head-up tilt, suggesting normal autoregulation. OH patients could be separated into those with normal or expanded autoregulation (OH_NA; n=16) and those with autoregulatory failure (OH_AF; n=5). The OH_NA group showed either no correlation between BFV and BP (n=8) or had a positive BFV/BP correlation (R2>.75) but with a flat slope. An expansion of the "autoregulated" range was seen in some patients. The OH_AF group was characterized by a profound fall in BFV in response to a small reduction in BP (mean deltaBP <40 mm Hg; R2>.75). CONCLUSIONS: The most common patterns of cerebral response to OH are autoregulatory failure with a flat flow-pressure relationship or intact autoregulation with an expanded autoregulated range. The least common pattern is autoregulatory failure with a steep flow-pressure relationship. Patients with patterns 1 and 2 have an enhanced capacity to cope with OH, while those with pattern 3 have reduced capacity.

Non-NASA Center↗
DOE OSTI2022

Electrochemical Aging and Halogen Oxides Formation on Multiwalled Carbon Nanotubes and Fe 3 O 4 @g-C 3 N 4 Coated Conductive Membranes

Electrochemical membrane filtration is widely reported to enhance water contaminants' degradation or rejection via anodic oxidation or cathodic repulsion. Despite their advances, electrochemical membranes or electrocatalysts often suffer from corrosion or passivation, especially under strong electrode potentials or reactions. Moreover, the formation of toxic byproducts, such as chlorinated organic compounds and oxyhalides (e.g., ClO 4 - ) is another major concern. This study investigated the membrane aging processes of two types of conductive membranes, multiwalled carbon nanotubes (MWCNTs) and ferrite/graphitic carbon nitride hybrids (Fe 3 O 4 @g-C 3 N 4 ) coated on ceramic membranes. Under high current densities (~ 20 mA∙cm -2 ) with anodic potentials (~10 V), MWCNTs and Fe 3 O 4 @g-C 3 N 4 catalysts underwent evident oxidation as indicated by an increase of the intensity ratio of the Raman spectral bands (I D /I G ) and charge transfer resistance (R ct ) of two electrochemical membranes. Under variations of electrode potentials, chloride or bromide were shown to be oxidized to bromate (BrO 3 - ) and chlorate (ClO 3 - ) at levels of 1-10 mmol∙L -1 . The formation of BrO 3 - and ClO 3 - was dependent on the solution pH, current densities (1-20 mA∙cm -2 ), and initial concentrations of Br or Cl ions. Finally, to warrant a safe and rational design and operation of electrochemically reactive membrane processes, membrane aging and toxic byproduct's formation deserve careful characterization under relevant water filtration environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2012

Prognostics Approach for Power MOSFET Under Thermal-Stress

The prognostic technique for a power MOSFET presented in this paper is based on accelerated aging of MOSFET IRF520Npbf in a TO-220 package. The methodology utilizes thermal and power cycling to accelerate the life of the devices. The major failure mechanism for the stress conditions is dieattachment degradation, typical for discrete devices with leadfree solder die attachment. It has been determined that dieattach degradation results in an increase in ON-state resistance due to its dependence on junction temperature. Increasing resistance, thus, can be used as a precursor of failure for the die-attach failure mechanism under thermal stress. A feature based on normalized ON-resistance is computed from in-situ measurements of the electro-thermal response. An Extended Kalman filter is used as a model-based prognostics techniques based on the Bayesian tracking framework. The proposed prognostics technique reports on preliminary work that serves as a case study on the prediction of remaining life of power MOSFETs and builds upon the work presented in [1]. The algorithm considered in this study had been used as prognostics algorithm in different applications and is regarded as suitable candidate for component level prognostics. This work attempts to further the validation of such algorithm by presenting it with real degradation data including measurements from real sensors, which include all the complications (noise, bias, etc.) that are regularly not captured on simulated degradation data. The algorithm is developed and tested on the accelerated aging test timescale. In real world operation, the timescale of the degradation process and therefore the RUL predictions will be considerable larger. It is hypothesized that even though the timescale will be larger, it remains constant through the degradation process and the algorithm and model would still apply under the slower degradation process. By using accelerated aging data with actual device measurements and real sensors (no simulated behavior), we are attempting to assess how such algorithm behaves under realistic conditions.

Power MOSFET PHM↗
NASA NTRS1977

Investigation of test methods, material properties and processes for solar cell encapsulants

The potentially useful encapsulating materials for Task 3 of the Low-Cost Silicon Solar Array project were studied to identify, evaluate, and recommend encapsulant materials and processes for the production of cost-effective, long-life solar cell modules. Materials for study were chosen on the basis of existing knowledge of generic chemical types having high resistance to environmental weathering. The materials varied from rubbers to thermoplastics and presented a broad range of mechanical properties and processing requirements. Basic physical and optical properties were measured on the polymers and were redetermined after exposure to indoor artificial accelerated aging conditions covering four time periods. Strengths and weaknesses of the various materials were revealed and data was accumulated for the development of predictive methodologies. To date, silicone rubbers, fluorocarbons, and acrylic polymers appear to have the most promising combination of characteristics. The fluorocarbons may be used only as films, however, because of their high cost.

Willis, P. B.↗
DOE OSTI2021

Long-Term Thermal Aging Effect Evaluation for Grade 92 and 316L at The LWR Relevant Temperature

Life extension of the existing nuclear reactors imposes accumulated damages, such as higher fluences and longer periods of corrosion, to structural materials, which would result in significant challenges to the traditional reactor materials such as type 304 and 316 stainless steels. Advanced alloys with superior radiation resistance will increase safety margins, design flexibility, and economics for not only the life extension of the existing fleet but also new builds with advanced reactor designs. The Electric Power Research Institute (EPRI) initiated a collaboration with the Department of Energy (DOE) Light Water Reactor Sustainability (LWRS) Program on the Advanced Radiation Resistant Materials (ARRM) program, focused on developing and test degradation resistant alloys for light water reactor (LWR)- relevant environments. Based on a comprehensive microstructure and property screening, the ARRM program selected a total of five alloys (i.e., Grade 92, 310, 690, 718A, and 725), together with 316L and X-750 as references, for further investigations.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Thermal stability of anisotropic bonded magnets prepared by additive manufacturing

Abstract In this research, anisotropic NdFeB + SmFeN hybrid and NdFeB bonded magnets are additively printed in a polyphenylene sulfide (PPS) polymer binder. Printed NdFeB + SmFeN PPS bonded magnets displayed excellent magnetic properties ( B r [remanence] = 6.9 kG [0.69 T], H cj [coercivity] = 8.3 kOe [660 kA/m], and BH max [energy product] = 9.9 MGOe [79 kJ/m 3 ]) with superior corrosion resistance and thermal stability. The anisotropic NdFeB bonded magnet shows a high coercivity of 14.6 kOe (1162 kA/m) with a BH max of 8.7 MGOe (69 kJ/m 3 ). The coercivity and remanence temperature coefficients for NdFeB + SmFeN hybrid bonded magnets are −0.10%/K and −0.46%/K, and for NdFeB bonded magnets are −0.14%/K and −0.53%/K in the range of 300–400 K, indicating that the hybrid bonded magnets are thermally stable. The average flux aging loss for hybrid magnets was also determined to be very stable over 2000 h at 448 K (175°C) in air with 2.04% compared to that of NdFeB magnets with 3.62%.

thermal stability↗
NASA NTRS2012

Paleo-Environment and C-14 Dating: The Key to the Depositional Age of the Tha Chang and Related Sand Pits, Northeastern Thailand

Tha Chang sand pits, Nakhon Ratchasima Province and many other sand pits in the area adjacent to the Mun River are characterized by their fluviatile environment in association with mass wasting deposits, along the paleo-river channel and the flood plain of the Mun River. Sediments of these deposits are characterized by clasts of various rock types especially the resistant ones with frequent big tree trunks, logs and wood fragments in different sizes and various stages of transformation from moldering stage to lignification and petrification. Widespread pyritization of the lower horizon suggests strongly reducing environment during burial. The Tha Chang deposits have been received much attention from geoscientists especially paleontologist communities, as they contain fragments of some distinct vertebrate species such as Stegadon sp., hominoid primate, rhinoceros Aceratherium and others. Based on the associated mammal fauna and hominoid fossils, the late Miocene ( 9 - 6 Ma) was given for the time of deposition of this sand and gravel unit. Some other reports believed that sediments and materials of these sand and gravel quarries (pits) were deposited by high-energy flood pulses contemporaneous with the tektites forming event during mid-Pleistocene at c. 0.8 Ma. Interpretation from Palynostratigraphical study suggested that the lower horizon of Tha Chang sand pit was deposited during Pliocene/Pleistocene period and the upper horizons are Pleistoncene/Holocene. It is crystal clear that all the fluviatile sediments including tektites and almost all fossil fragments being deposited in these sand pits were, likely a multiple times reworked materials. Only some old bamboo trees, some old crowling trees and fossils grasses observed on the old river bank are considered in situ. C-14 dating of 5 old wood specimens from Tha Chang Sand Pits, 15 old wood specimens from Chumpuang Sand Pits and one sample of old pottery from a Chumpuang Sand Pit were carried out in the NSF- Arizona AMS Laboratory. Although, there is no sharp boundary between the unconsolidated sedimentary horizons in the pits, C-14 ages obtained from the Tha Chang vary from 34,340 BP at the middle horizon (approx 10 m below ground zero) to >49,900 BP at the lower horizon with unknown basal formation (highly pyritized zone approx 20 - 25 m below ground zero). The ages for the Chumpuang vary from 41,700 BP, >45,900 BP and >49,900 BP from the upper most to the lower most of a broad horizon (approx 8 m to approx 12 m below ground zero). The C-14 age of the pottery collected from layer approximately 5 m below ground zero is 2,514 BP. The nature of fluviatile together with occasional mass wasting characteristics of all sand pits studies suggest the relatively faster depositional rate of the lower horizon which involved more flooding and mass wasting deposits than those of the upper horizons. The apparent of some mixing of the wood ages may indicate reworking and lag deposits nature of the area. The depositional rate of the upper most sand and soil horizon (5 m thick) is approximately 1 m per 500 years which mean both erosion and deposition had played a significant role during that time period. In term of the true age of the formation, we argue that since most of the materials deposited are reworked materials, all ages obtained from fossil fragments could not be the age of sand and gravel formation. Furthermore, the maximum age of all the tektite bearing horizons cannot be older than 0.8 Ma. The oldest C-14 age of 49,900 BP is interpreted as the minimum age of the Tha Chang and related sand pits formation when geomorphology of the area was a lot more hilly and much higher gradient than that of the present day.

Putthapiban, P.↗
DOE OSTI2024

Investigation of ion irradiation effects on mineral analogues of concrete aggregates

Irradiation can cause prominent damage to reactor concrete aggregates leading to amorphization, strength and modulus decrease, radiation induced volume expansion (RIVE) and micro-cracking, which limits their long-term performance. Here, to develop an improved understanding of irradiation effects in concrete, three mineral analogues of concrete aggregates (limestone, marble and quartzite) were irradiated by 5.5 MeV He ions and 13 MeV Ni ions to surface doses of 0.011 displacements per atom (dpa) and 0.23 dpa, respectively, at room temperature. The two different ion species allow irradiation spectrum effects (ionizing and displacive) to be examined. Irradiation induced cracks were observed in He irradiated limestone and marble, and Ni irradiated quartzite. Full amorphization was observed in Ni irradiated quartzite with 14.3 % RIVE, and ∼25 % hardness and modulus decrease, while almost no change was observed in He irradiated quartzite except 4.35 % RIVE, revealing a possible ionization enhanced diffusion effect for high energy light ions. Furthermore, partial amorphization was observed in Ni irradiated marble and limestone matrix with a 12 % hardness decrease in marble while no amorphization was observed for He irradiation with a 20 % hardness increase in limestone matrix. The role of knock-on damage and irradiation spectrum on amorphization, volumetric expansion and mechanical property changes are discussed. Moreover, the onset and critical doses for amorphization and RIVE in quartz are obtained for ion irradiations at room temperature. The dose dependence of RIVE exhibits a delay compared to the amorphization behavior. The superior irradiation resistance of calcite phase compared to quartz phase implies there could be advantages to using calcareous aggregates and lowering the usage of siliceous aggregates for concrete in nuclear power plants for extended operation beyond 60 years. However, other effects such as corrosion, aging and reactions during severe accidents should also be considered, and further investigations are needed.

Amorphous↗
NASA NTRS1989

Determinants of bone density among athletes engaged in weight-bearing and non-weight-bearing activity

The effect of weight bearing activity on the bone density was investigated in athletes by comparing the measures of bone density of athletes engaged in weight-training programs with those of polo players and nonexercising subjects. All subjects had measurements of spinal trabecular and integral bone density by quantitative tomography, as well as determinations of hip bone density by dual photon absorptiometry. Results confirmed previous findings by Block et al. (1987) of significantly greater bone density among highly trained athletes compared with nonexercising subjects of similar age. Results also indicated that athletes engaged in non-weight-bearing forms of rigorous exercise had greater levels of bone density. However, as the participants in this study were exceptional athletes, engaged in a strenuous sport with both aerobic and heavy resistance components, a confirmation of these data is needed, using larger samples of individuals.

Block, Jon E.↗
NASA NTRS1992

Magnetic Resonance Imaging (MRI) of skeletal muscles in astronauts after 9 days of space flight

Skylab data indicated that prolonged exposure of human subjects to microgravity environment causes significant muscle atrophy accompanied by reduced muscle strength and fatigue resistance. The objective of this study was to determine decrements in muscle size, if any, in the soleus and gastrocnemius muscles of male and female astronauts after 9 days of space flight. Methods: Eight astronauts, one female and seven male, between the ages of 31 and 59 years 59-84 kg in body weight were examined by MRI 2-3 times preflight within 16 days before launch, and 2 days, (n=6) and seven days (n=3) after landing. The right leg muscles (gastroc-soleus) were imaged with a lower extremity coil in magnets operating at 1.0 or 1.5 Tsela. The imaging protocol consisted of spin echo with a Tr of 0.70 - 1.5 sec. Thirty to forty 3-5 mm thick slices were acquired in 256 x 128 or 256 x 256 matrices. Acquisition time lasted 20-40 minutes. Multiple slices were measured by computerized planimetry. Results: Compared to the preflight, the cross-sectoral areas (CSA) of the soleus, gastrocnemius, and the leg, at 2 days after landing were reduced (at least p less than 0.05) 8.9 percent, 13.2 percent, and 9.5 percent respectively. The soleus and the leg of three astronauts evaluated at 7 days postflight did not show full recovery compared to the preflight values. Conclusions: It is concluded that l9-days of space flight may cause significant decreases in CSA of the leg muscles. The factors responsible for this loss need further determination.

Jaweed, M.↗