Mars Dogs: Biomimetic Robots for the Exploration of Mars, from its Rugged Surface to its Hidden Caves
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Agha-mohammadi, Ali-akbar↗
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Mapping Pawprints with Dog Whistles on MSFC’s Flat Floor
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Tom Bryan↗
Hybrid accelerator magnets based on dog bone shaped CORC® wire inserts for operation beyond 20 T
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van der Laan, Danko↗
Fault tolerant hypercube computer system architecture
A fault-tolerant multiprocessor computer system of the hypercube type comprising a hierarchy of computers of like kind which can be functionally substituted for one another as necessary is disclosed. Communication between the working nodes is via one communications network while communications between the working nodes and watch dog nodes and load balancing nodes higher in the structure is via another communications network separate from the first. A typical branch of the hierarchy reporting to a master node or host computer comprises, a plurality of first computing nodes; a first network of message conducting paths for interconnecting the first computing nodes as a hypercube. The first network provides a path for message transfer between the first computing nodes; a first watch dog node; and a second network of message connecting paths for connecting the first computing nodes to the first watch dog node independent from the first network, the second network provides an independent path for test message and reconfiguration affecting transfers between the first computing nodes and the first switch watch dog node. There is additionally, a plurality of second computing nodes; a third network of message conducting paths for interconnecting the second computing nodes as a hypercube. The third network provides a path for message transfer between the second computing nodes; a fourth network of message conducting paths for connecting the second computing nodes to the first watch dog node independent from the third network. The fourth network provides an independent path for test message and reconfiguration affecting transfers between the second computing nodes and the first watch dog node; and a first multiplexer disposed between the first watch dog node and the second and fourth networks for allowing the first watch dog node to selectively communicate with individual ones of the computing nodes through the second and fourth networks; as well as, a second watch dog node operably connected to the first multiplexer whereby the second watch dog node can selectively communicate with individual ones of the computing nodes through the second and fourth networks. The branch is completed by a first load balancing node; and a second multiplexer connected between the first load balancing node and the first and second watch dog nodes, allowing the first load balancing node to selectively communicate with the first and second watch dog nodes.
Madan, Herb S.↗
Vasopressin and angiotensin II in reflex regulation of ACTH, glucocorticoids, and renin: effect of water deprivation
Angiotensin II (ANG II) and vasopressin participate in baroreflex regulation of adrenocorticotropic hormone (ACTH), glucocorticoid, and renin secretion. The purpose of this study was to determine whether this participation is enhanced in water-deprived dogs, with chronically elevated plasma ANG II and vasopressin levels, compared with water-replete dogs. The baroreflex was assessed by infusing increasing doses of nitroprusside (0.3, 0.6, 1.5, and 3.0 micrograms.kg-1.min-1) in both groups of animals. To quantitate the participation of ANG II and vasopressin, the dogs were untreated or pretreated with the competitive ANG II antagonist saralasin, a V1-vasopressin antagonist, or combined V1/V2-vasopressin antagonist, either alone or in combination. The findings were as follows. 1) Larger reflex increases in ANG II, vasopressin, and glucocorticoids, but not ACTH, were produced in water-deprived dogs compared with water-replete dogs. 2) ANG II blockade blunted the glucocorticoid and ACTH responses to hypotension in water-deprived dogs, but not water-replete dogs. In contrast, vasopressin blockade reduced the ACTH response only in water-replete dogs. 3) Vasopressin or combined vasopressin and ANG II blockade reduced the plasma level of glucocorticoids related either to the fall in arterial pressure or to the increase in plasma ACTH concentration in water-replete dogs, and this effect was enhanced in water-deprived dogs. 4) In both water-deprived and water-replete animals, saralasin and/or a V1-antagonist increased the renin response to hypotension, but a combined V1/V2-antagonist did not. These results reemphasize the importance of endogenous ANG II and vasopressin in the regulation of ACTH, glucocorticoid, and renin secretion.(ABSTRACT TRUNCATED AT 250 WORDS).
NASA Discipline Cardiopulmonary↗
Targeted metabolomic analysis identifies increased serum levels of GABA and branched chain amino acids in canine diabetes
Introduction Dogs with naturally occurring diabetes mellitus represent a potential model for human type 1 diabetes, yet signifcant knowledge voids exist in terms of the pathogenic mechanisms underlying the canine disorder. Untargeted metabolomic studies from a limited number of diabetic dogs identifed similarities to humans with the disease. Objective To expand and validate earlier metabolomic studies, identify metabolites that difer consistently between diabetic and healthy dogs, and address whether certain metabolites might serve as disease biomarkers. Methods Untargeted metabolomic analysis via liquid chromatography-mass spectrometry was performed on serum from diabetic (n=15) and control (n=15) dogs. Results were combined with those of our previously published studies using identical methods (12 diabetic and 12 control dogs) to identify metabolites consistently diferent between the groups in all 54 dogs. Thirty-two candidate biomarkers were quantifed using targeted metabolomics. Biomarker concentrations were compared between the groups using multiple linear regression (corrected P<0.0051 considered signifcant). Results Untargeted metabolomics identifed multiple persistent diferences in serum metabolites in diabetic dogs compared with previous studies. Therefore, targeted metabolomics showed increases in gamma amino butyric acid, valine, leucine, isoleucine, citramalate, and 2-hydroxyisobutyric acid in diabetic versus control dogs while indoxyl sulfate, N-acetyl-L-aspartic acid, kynurenine, anthranilic acid, tyrosine, glutamine, and tauroursodeoxycholic acid were decreased. Conclusion Several of these fndings parallel metabolomic studies in both human diabetes and other animal models of this disease. Given recent studies on the role of GABA and branched chain amino acids in human diabetes, the increase in serum concentrations in canine diabetes warrants further study of these metabolites as potential biomarkers, and to identify similarity in mechanisms underlying this disease in humans and dogs.
59 BASIC BIOLOGICAL SCIENCES↗
Is Mini Beam Ready for Human Trials? Results of Randomized Study of Treating De-Novo Brain Tumors in Canines Using Linear Accelerator Generated Mini Beams
The main challenge in treating malignant brain neoplasms lies in eradicating the tumor while minimizing treatmentrelated damage. Conventional radiation treatments are associated with considerable side effects. Synchrotron generated micro-beam radiation (SMBRT) has shown to preserve brain architecture while killing tumor cells, however physical characteristics and limited facility access restrict its use. We have created a new clinical device which produces mini beams on a linear accelerator, to provide a new type of treatment called mini-beam radiation therapy (MBRT). The objective of this study is to compare the treatment outcomes of linear accelerator based MBRT versus standard radiation treatment (SRT), to evaluate the tumor response and the treatment-related changes in the normal brain with respect to each treatment type. Pet dogs with de-novo brain tumors were accrued for treatment. Dogs were randomized between standard fractionated stereotactic (9 Gy in 3 fractions) radiation treatment vs. a single fraction of MBRT (26 Gy mean dose). Dogs were monitored after treatment for clinical assessment and imaging. When the dogs were euthanized, a veterinary pathologist assessed the radiation changes and tumor response. We accrued 16 dogs, 8 dogs in each treatment arm. In the MBRT arm, 71% dogs achieved complete pathological remission. The radiation-related changes were all confined to the target region. Structural damage was not observed in the beam path outside of the target region. In contrast, none of the dogs in control group achieved remission and the treatment related damage was more extensive. Therapeutic superiority was observed with MBRT, including both tumor control and the normal structural preservation. The MBRT findings are suggestive of an immune related mechanism which is absent in standard treatment. These findings together with the widespread availability of clinical linear accelerators make MBRT a promising research topic to explore further treatment and clinical trial opportunities.
62 RADIOLOGY AND NUCLEAR MEDICINE↗
Advanced Electrocardiography Can Identify Occult Cardiomyopathy in Doberman Pinschers
Recently, multiple advanced resting electrocardiographic (A-ECG) techniques have improved the diagnostic value of short-duration ECG in detection of dilated cardiomyopathy (DCM) in humans. This study investigated whether 12-lead A-ECG recordings could accurately identify the occult phase of DCM in dogs. Short-duration (3-5 min) high-fidelity 12-lead ECG recordings were obtained from 31 privately-owned, clinically healthy Doberman Pinschers (5.4 +/- 1.7 years, 11/20 males/females). Dogs were divided into 2 groups: 1) 19 healthy dogs with normal echocardiographic M-mode measurements: left ventricular internal diameter in diastole (LVIDd . 47mm) and in systole (LVIDs . 38mm) and normal 24-hour ECG recordings (<50 ventricular premature complexes, VPCs); and 2) 12 dogs with occult DCM: 11/12 dogs had increased M-mode measurements (LVIDd . 49mm and/or LVIDs . 40mm) and 5/11 dogs had also >100 VPCs/24h; 1/12 dogs had only abnormal 24-hour ECG recordings (>100 VPCs/24h). ECG recordings were evaluated via custom software programs to calculate multiple parameters of high-frequency (HF) QRS ECG, heart rate variability, QT variability, waveform complexity and 3-D ECG. Student's t-tests determined 19 ECG parameters that were significantly different (P < 0.05) between groups. Principal component factor analysis identified a 5-factor model with 81.4% explained variance. QRS dipolar and non-dipolar voltages, Cornell voltage criteria and QRS waveform residuum were increased significantly (P < 0.05), whereas mean HF QRS amplitude was decreased significantly (P < 0.05) in dogs with occult DCM. For the 5 selected parameters the prediction of occult DCM was performed using a binary logistic regression model with Chi-square tested significance (P < 0.01). ROC analyses showed that the five selected ECG parameters could identify occult ECG with sensitivity 89% and specificity 83%. Results suggest that 12-lead A-ECG might improve diagnostic value of short-duration ECG in earlier detection of canine DCM as five selected ECG parameters can with reasonable accuracy identify occult DCM in Doberman Pinschers. Future extensive clinical studies need to clarify if 12-lead A-ECG could be useful as an additional screening test for canine DCM.
Spiljak, M.↗
NuSTAR Observations of WISE J1036+0449, A Galaxy at Z Approx. 1 Obscured by Hot Dust
Hot dust-obscured galaxies (hot DOGs), selected from Wide-Field Infrared Survey Explorer's all-sky infrared survey, host some of the most powerful active galactic nuclei known and may represent an important stage in the evolution of galaxies. Most known hot DOGs are located at z > 1.5, due in part to a strong bias against identifying them at lower redshift related to the selection criteria. We present a new selection method that identifies 153 hot DOG candidates at z approx. 1, where they are significantly brighter and easier to study. We validate this approach by measuring a redshift z = 1.009 and finding a spectral energy distribution similar to that of higher-redshift hot DOGs for one of these objects, WISE J1036+0449 (L(BOL) approx. = 8 x 10(exp 46) erg/s). We find evidence of a broadened component in Mg II, which would imply a black hole mass of M(BH) approx. = 2 x 10(exp 8) Stellar Mass and an Eddington ratio of lambda(Edd) approx. = 2.7. WISE J1036+0449 is the first hot DOG detected by the Nuclear Spectroscopic Telescope Array, and observations show that the source is heavily obscured, with a column density of N(H) approx. = (2-15) x 10(exp 23)/sq cm. The source has an intrinsic 2-10 keV luminosity of approx. 6 x 10(exp 44) erg/s, a value significantly lower than that expected from the mid-infrared X-ray correlation. We also find that other hot DOGs observed by X-ray facilities show a similar deficiency of X-ray flux. We discuss the origin of the X-ray weakness and the absorption properties of hot DOGs. Hot DOGs at z < or approx. 1 could be excellent laboratories to probe the characteristics of the accretion flow and of the X-ray emitting plasma at extreme values of the Eddington ratio.
galaxies↗
Cytoskeletal role in the transition from compensated to decompensated hypertrophy during adult canine left ventricular pressure overloading
Increased microtubule density causes cardiocyte contractile dysfunction in right ventricular (RV) pressure-overload hypertrophy, and these linked phenotypic and contractile abnormalities persist and progress during the transition to failure. Although more severe in cells from failing than hypertrophied RVs, the mechanical defects are normalized in each case by microtubule depolymerization. To define the role of increased microtubule density in left ventricular (LV) pressure-overload hypertrophy and failure, in a given LV we examined ventricular mechanics, sarcomere mechanics, and free tubulin and microtubule levels in control dogs and in dogs with aortic stenosis both with LV hypertrophy alone and with initially compensated hypertrophy that had progressed to LV muscle failure. In comparing initial values with those at study 8 weeks later, dogs with hypertrophy alone had a very substantial increase in LV mass but preservation of a normal ejection fraction and mean systolic wall stress. Dogs with hypertrophy and associated failure had a substantial but lesser increase in LV mass and a reduction in ejection fraction, as well as a marked increase in mean systolic wall stress. Cardiocyte contractile function was equivalent, and unaffected by microtubule depolymerization, in cells from control LVs and those with compensated hypertrophy. In contrast, cardiocyte contractile function in cells from failing LVs was quite depressed but was normalized by microtubule depolymerization. Microtubules were increased only in failing LVs. These contractile and cytoskeletal changes, when assayed longitudinally in a given dog by biopsy, appeared in failing ventricles only when wall stress began to increase and function began to decrease. Thus, the microtubule-based cardiocyte contractile dysfunction characteristic of pressure-hypertrophied myocardium, originally described in the RV, obtains equally in the LV but is shown here to have a specific association with increased wall stress.
Non-NASA Center↗
Design of potent substrate-analogue inhibitors of canine renin
Through a systematic study of structure-activity relationships, we designed potent renin inhibitors for use in dog models. In assays against dog plasma renin at neutral pH, we found that, as in previous studies of rat renin inhibitors, the structure at the P2 position appears to be important for potency. The substitution of Val for His at this position increases potency by one order of magnitude. At the P3 position, potency appears to depend on a hydrophobic side chain that does not necessarily have to be aromatic. Our results also support the approach of optimizing potency in a renin inhibitor by introducing a moiety that promotes aqueous solubility (an amino group) at the C-terminus of the substrate analogue. In the design of potent dog plasma renin inhibitors, the influence of the transition-state residue 4(S)-amino-3(S)-hydroxy-5-cyclohexylpentanoic acid (ACHPA)-commonly used as a substitute for the scissile-bond dipeptide to boost potency-is not obvious, and appears to be sequence dependent. The canine renin inhibitor Ac-paF-Pro-Phe-Val-statine-Leu-Phe-paF-NH2 (compound 15; IC50 of 1.7 nM against dog plasma renin at pH 7.4; statine, 4(S)-amino-3(S)-hydroxy-6-methylheptanoic acid; paF, para-aminophenylalanine) had a potent hypotensive effect when infused intravenously into conscious, sodium-depleted, normotensive dogs. Also, compound 15 concurrently inhibited plasma renin activity and had a profound diuretic effect.
Non-NASA Center↗
Premorbid determinants of left ventricular dysfunction in a novel model of gradually induced pressure overload in the adult canine
BACKGROUND: When a pressure overload is placed on the left ventricle, some patients develop relatively modest hypertrophy whereas others develop extensive hypertrophy. Likewise, the occurrence of contractile dysfunction also is variable. The cause of this heterogeneity is not well understood. METHODS AND RESULTS: We recently developed a model of gradual proximal aortic constriction in the adult canine that mimicked the heterogeneity of the hypertrophic response seen in humans. We hypothesized that differences in outcome were related to differences present before banding. Fifteen animals were studied initially. Ten developed left ventricular dysfunction (dys group). Five dogs maintained normal function (nl group). At baseline, the nl group had a lower mean systolic wall stress (96 +/- 9 kdyne/cm2; dys group, 156 +/- 7 kdyne/cm2; P < .0002) and greater relative left ventricular mass (left ventricular weight [g]/body wt [kg], 5.1 +/- 0.36; dys group, 3.9 +/- 0.26; P < .02). On the basis of differences in mean systolic wall stress at baseline, we predicted outcome in the next 28 dogs by using a cutoff of 115 kdyne/cm2. Eighteen of 20 dogs with baseline mean systolic stress > 115 kdyne/cm2 developed dysfunction whereas 6 of 8 dogs with resting stress < or = 115 kdyne/cm2 maintained normal function. CONCLUSIONS: We conclude that this canine model mimicked the heterogeneous hypertrophic response seen in humans. In the group that eventually developed dysfunction there was less cardiac mass despite 60% higher wall stress at baseline, suggesting a different set point for regulating myocardial growth in the two groups.
Non-NASA Center↗
Effect of solution concentration on ethylene propylene diene monomer (EPDM) nonmetallic components used in caustic liquid waste transfer lines
The hose-in-hose transfer lines (HIHTL) used to transfer waste at the United States Department of Energy’s Hanford Site Tank Farm are fabricated from an ethylene propylene diene monomer (EPDM) synthetic rubber. During waste transport, these hoses are exposed to several stressors including caustic solutions at high temperatures and high pressures, as well as β and γ radiation. The aging behavior of HIHTL and dog-bone shaped EPDM specimens were evaluated by exposure to solutions at 77 °C containing 0.00, 6.25, 12.50, and 25.00 % (v/v) sodium hydroxide (NaOH) for 12-months. After the exposure, the material properties of the specimens were measured and compared to the unaged samples. The material properties evaluated included the tensile strength of the EPDM dog-bone samples and the burst pressure of the HIHTL. Both the tensile strength of the EPDM dog-bone samples and the burst pressure of the HIHTL specimens exposed to the 6.25 % NaOH solution exhibited the most significant deterioration and those exposed to 25.00 % NaOH solution had the least deterioration. Finally, examination of the HIHTL and the EPDM dog-bone specimens with scanning electron microscopy showed that the deterioration for the specimens exposed to 6.25 % NaOH solution were the most severe and the samples exposed to 25.00 % NaOH solution had the least deterioration.
42 ENGINEERING↗
Elimination of human rabies in Goa, India through an integrated One Health approach
Dog-mediated rabies kills tens of thousands of people each year in India, representing one third of the estimated global rabies burden. Whilst the World Health Organization (WHO), World Organization for Animal Health (OIE) and the Food and Agriculture Organization of the United Nations (FAO) have set a target for global dog-mediated human rabies elimination by 2030, examples of large-scale dog vaccination programs demonstrating elimination remain limited in Africa and Asia. We describe the development of a data-driven rabies elimination program from 2013 to 2019 in Goa State, India, culminating in human rabies elimination and a 92% reduction in monthly canine rabies cases. Smartphone technology enabled systematic spatial direction of remote teams to vaccinate over 95,000 dogs at 70% vaccination coverage, and rabies education teams to reach 150,000 children annually. An estimated 2249 disability-adjusted life years (DALYs) were averted over the program period at 526 USD per DALY, making the intervention ‘very cost-effective’ by WHO definitions. This One Health program demonstrates that human rabies elimination is achievable at the state level in India.
60 APPLIED LIFE SCIENCES↗
From wolves to humans: oral microbiome resistance to transfer across mammalian hosts
The mammalian mouth is colonized by complex microbial communities, adapted to specific niches, and in homeostasis with the host. Individual microbes interact metabolically and rely primarily on nutrients provided by the host, with which they have potentially co-evolved along the mammalian lineages. The oral environment is similar across mammals, but the diversity, specificity, and evolution of community structure in related or interacting mammals are little understood. Here, we compared the oral microbiomes of dogs with those of wild wolves and humans. In dogs, we found an increased microbial diversity relative to wolves, possibly related to the transition to omnivorous nutrition following domestication. This includes a larger diversity of Patescibacteria than previously reported in any other oral microbiota. The oral microbes are most distinct at bacterial species or strain levels, with few if any shared between humans and canids, while the close evolutionary relationship between wolves and dogs is reflected by numerous shared taxa. More taxa are shared at higher taxonomic levels including with humans, supporting their more ancestral common mammalian colonization followed by diversification. Phylogenies of selected oral bacterial lineages do not support stable human-dog microbial transfers but suggest diversification along mammalian lineages (apes and canids). Therefore, despite millennia of cohabitation and close interaction, the host and its native community controls and limits the assimilation of new microbes, even if closely related. Higher resolution metagenomic and microbial physiological studies, covering a larger mammalian diversity, should help understand how oral communities assemble, adapt, and interact with their hosts.
59 BASIC BIOLOGICAL SCIENCES↗
Organic Iodide Sorption from Dilute Gas Streams
Reprocessing used nuclear fuel releases volatile radionuclides, including 129 iodine (I), into the off-gas of a processing plant. Volatile radioiodine could be present in several forms, depending on the chemistry of the process used and the off-gas stream. Inorganic I 2 is expected to be the predominant I species in the dissolver off-gas (DOG), with minor organic iodides present. The bulk of the I is expected to volatilize into the DOG in parts-per-million-level (ppm) concentrations. In contrast, in the vessel off-gas (VOG), most of the volatile I is expected to be found as organic iodides, such as CH 3 I, C 4 H 9 I, and C 12 H 25 I. These species are expected to be present in parts-per-billion-level (ppb) concentrations but require abatement, even at low expected concentrations, to meet regulatory emissions limits in the United States. Historically, studies of I abatement by Ag-functionalized sorbents have focused on inorganic I in the DOG, but in the last few years, more research attention has been given to organic iodides, especially longer chain species, such as C 4 H 9 I, and C 12 H 25 I. This report has three main goals: (1) to present new data generated at Oak Ridge National Laboratory (ORNL) in FY21 on the sorption behavior of organic iodides on AgZ, (2) to summarize and synthesize organic iodide data produced by ORNL and Idaho National Laboratory (INL) over the last 4 years to answer questions on organic iodides behavior outlined in the 2018 joint test plan (Jubin et al. 2018), and (3) to propose a VOG abatement system design that can provide the capture efficiencies required to meet I emission limits. The 2021 ORNL experimental campaign tested the effects of organic iodide speciation and concentration in the off-gas, superficial velocity of the off-gas, and effects of aging on AgZ sorbent capacity. These studies found that the sorption rate of organic iodides by AgZ depends on the hydrocarbon chain length and the concentration in the off-gas. Higher molecular weight organic iodides adsorb to AgZ more slowly than I. At a concentration of 50 ppm concentration in the off-gas, CH 3 I loads 8% slower, C 4 H 9 I loads 20% slower, and C 12 H 25 I loads 40% slower than I. The lowest concentration loading rates calculated were in 5 ppm organic iodide gas streams in which AgZ gained on average 0.14 mg I/g sorbent/hour in the bench scale test system. Thus, longer sorbent beds might be needed to accommodate slower loading rates onto AgZ in lower concentration gas streams. Although sorption rate varies as a function of hydrocarbon chain length, the saturation concentration of the sorbent for these I-bearing species does not vary. Aging AgZ in a humid air stream for 9 months drops the overall sorbent capacity by ~35% for CH 3 I, ~50% for C 4 H 9 I, and ~40% for C 12 H 25 I. This results in a saturation capacity between 35 and 70 mg I/g sorbent for the aged AgZ. In conjunction with recent data produced by INL, these data are used to estimate the mass transfer zone (MTZ) and decontamination factor (DF) for sorbent beds of AgZ. Sorption tests performed with iodide gas concentrations of about 1 ppm and higher at a superficial gas velocity of 10 m/min, indicate that MTZ depths for these conditions tend to range between about 8-20 cm. Tests performed at lower concentrations between 50-90 ppb and at gas superficial velocities of 1, 10, and 20 m/min indicate that the MTZ depth increases with increasing superficial gas velocity. The 20 m/min test indicates that the MTZ for those conditions was at least 22 cm, and doubling the superficial gas velocity from 10 to 20 m/min could roughly double or triple the MTZ depth. Doubling and tripling the bounding MTZ depth of 20 cm for the body of MTZ estimates made at with 10 m/min superficial velocity would extend the MTZ for a superficial velocity of 20 m/min to 40-60 cm. This bounding limit applies to all of the organic iodides that have been tested. These results also indicate that the sorption rate-limiting step is not sensitive to the superficial gas velocity; otherwise the MTZ depth would not have increased approximately in proportion to the increase in the gas superficial velocity. This further suggests that the rate limiting step is not associated with mass transfer of the sorbate to the sorbent surface, or mass transfer of the reaction byproducts from the sorbent surface, but is associated with sorption or chemical reactions on the sorbent surface or in sorbent pores. Deep bed testing at INL has established DFs of >2,000 for I, CH 3 I, and C 4 H 9 I under a range of conditions (Soelberg et al. 2021, Bruffey et al. 2019). DF does not seem to be affected by the concentration of the organic iodide in the gas stream over the range of 1 to 50 ppm. Thus, if the MTZ is accommodated in sorbent bed design for the DOG and VOG, then regulatory DFs will be met. To meet the third objective outlined in this report, these experimental data were used to update an engineering evaluation of the VOG first completed in 2016. The updated VOG design can be found in an accompanying document (Welty et al., 2021; INL- LTD-21-64587). This report finds that the VOG will decrease in both size and complexity, relative to previous designs, and will still meet regulatory requirements for all iodine forms.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
Exercise hyperthermia as a factor limiting physical performance - Temperature effect on muscle metabolism
The effect of trunk cooling on the muscle contents of ATP, ADP, AMP, creatine phosphate (CrP), and creatine, as well as of glycogen, some glycolytic intermediates, pyruvate, and lactate were assessed in 11 fasted dogs exercised at 20 C on treadmill to exhaustion. Without cooling, dogs were able to run 57 min, and their rectal (Tre) and muscle (Tm) temperatures increased to 41.8 and 43.0 C, respectively. Cooling with ice packs prolonged the ability to run by 45 percent, and resulted in lower Tre (by 1.1 C) and Tm (by 1.2 C). Depletion of muscle content of total high-energy phosphates (ATP + CrP) and glycogen, and increases in contents of AMP, pyruvate, and lactate were lower in cooled dogs than in non-cooled dogs. The muscle content of lactiate correlated positively with TM. These results indicate that hypothermia accelerates glycolysis, and shifts the equilibrium between high- and low-energy phosphates in favor of the latter. The adverse effect of hypothermia on muscle metabolism may be relevant to the limitation of endurance.
Kozlowski, S.↗
Analysis of Factors Affecting the Performance of RLV Thrust Cell Liners
The reusable launch vehicle (RLV) thrust cell liner, or thrust chamber, is a critical component of the Space Shuttle Main Engine (SSME). It is designed to operate in some of the most severe conditions seen in engineering practice. This requirement, in conjunction with experimentally observed 'dog-house' failure modes characterized by bulging and thinning of the cooling channel wall, provides the motivation to study the factors that influence RLV thrust cell liner performance. Factors or parameters believed to be directly related to the observed characteristic deformation modes leading to failure under in-service loading conditions are identified, and subsequently investigated using the cylindrical version of the higher-order theory for functionally graded materials in conjunction with the Robinson's unified viscoplasticity theory and the power-law creep model for modeling the response of the liner s constituents. Configurations are analyzed in which specific modifications in cooling channel wall thickness or constituent materials are made to determine the influence of these parameters on the deformations resulting in the observed failure modes in the outer walls of the cooling channel. The application of thermal barrier coatings and functional grading are also investigated within this context. Comparison of the higher-order theory results based on the Robinson and power-law creep model predictions has demonstrated that, using the available material parameters, the power-law creep model predicts more precisely the experimentally observed deformation leading to the 'dog-house' failure mode for multiple short cycles, while also providing much improved computational efficiency. However, for a single long cycle, both models predict virtually identical deformations. Increasing the power-law creep model coefficients produces appreciable deformations after just one long cycle that would normally be obtained after multiple cycles, thereby enhancing the efficiency of the analysis. This provides a basis for the development of an accelerated modeling procedure to further characterize dog-house deformation modes in RLV thrust cell liners. Additionally, the results presented herein have demonstrated that the mechanism responsible for deformation leading to 'dog-house' failure modes is driven by pressure, creep/relaxation and geometric effects.
Arnold, Steven M.↗