Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “CaGe”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Structural Integrity of a Wind Tunnel Balance

The National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) has been designing strain-gage balances for utilization in wind tunnels since its inception. The utilization of balances span over a wide variety of aerodynamic tests. A force balance is an inherently critically stressed component due to the requirements of measurement sensitivity. Research and analyses are done in order to investigate the structural integrity of the balances as well as developing an understanding of their performance in order to enhance their capability. Maximum loading occurs when all 6 components of the loads are applied simultaneously with their maximum value allowed (limit load). This circumstance normally does not occur in the wind tunnel. However, if it occurs, is the balance capable of handling the loads with an acceptable factor of safety? LaRC Balance 1621 was modeled and meshed in PATRAN for analysis in NASTRAN. For a complete analysis, it is necessary to consider all the load cases as well as use dense mesh near all the edges. Because of computer limitations, it is not possible to have one model with the dense mesh near all edges. In the present study, a dense mesh is limited to the surface corners where the cage and axial sections meet. Four different load combinations are used for the current analysis. Linear analysis is performed for each load case. In the case where the stress value is above linear elastic region, it is necessary to perform nonlinear analysis. It is also important to investigate the variables limiting the structural integrity of the balances. In order to investigate the possibility of modifying the existing balances to enhance the structural integrity, some modifications are done on this balance. The structural integrity of the balance after modification is investigated.

Karkehabadi, R.↗
NASA NTRS2004

Electrochemical Reconstitution of Biomolecules for Applications as Electrocatalysts for the Bionanofuel Cell

Platinum-cored ferritins were synthesized as electrocatalysts by electrochemical biomineralization of immobilized apoferritin with platinum. The platinum cored ferritin was fabricated by exposing the immobilized apoferritin to platinum ions at a reduction potential. On the platinum-cored ferritin, oxygen is reduced to water with four protons and four electrons generated from the anode. The ferritin acts as a nano-scale template, a biocompatible cage, and a separator between the nanoparticles. This results in a smaller catalyst loading of the electrodes for fuel cells or other electrochemical devices. In addition, the catalytic activity of the ferritin-stabilized platinum nanoparticles is enhanced by the large surface area and particle size phenomena. The work presented herein details the immobilization of ferritin with various surface modifications, the electrochemical biomineralization of ferritin with different inorganic cores, and the fabrication of self-assembled 2-D arrays with thiolated ferritin.

Kim, Jae-Woo↗
NASA NTRS2004

Space Technology 5: Pathfinder for Future Micro-Sat Constellations

The Space Technology 5 (ST-5) Project, currently in the implementation phase, is part of the National Aeronautics and Space Administration (NASA) s New Millennium Program (NMP). ST-5 will consist of a constellation of three miniature satellites, each with mass less than 25 kg and size approximately 60 cm by 30 cm. ST-5 addresses technology challenges, as well as fabrication, assembly, test and operations strategies for future micro-satellite missions. ST-5 will be deployed into a highly eccentric, geo-transfer orbit (GTO). This will expose the spacecraft to a high radiation environment as well as provide a low level magnetic background. A three-month flight demonstration phase is planned to validate the technologies and demonstrate concepts for future missions. Each ST-5 spacecraft incorporates NMP competitively-selected breakthrough technologies. These include Cold Gas Micro-Thrusters for propulsion and attitude control, miniature X-band transponder for space-ground communications, Variable Emittance Coatings for dynamic thermal control, and CULPRiT ultra low power logic chip used for Reed-Solomon encoding. The ST-5 spacecraft itself is a technology that can be infused into future missions. It is a fully functional micro-spacecraft built within tight volume and mass constraints. It is built to withstand a high radiation environment, large thermal variations, and high launch loads. The spacecraft power system is low-power and low-voltage, and is designed to turn on after separation &om the launch vehicle. Some of the innovations that are included in the ST-5 design are a custom spacecraft deployment structure, magnetometer deployment boom, nutation damper, X-band antenna, miniature spinning sun sensor, solar array with triple junction solar cells, integral card cage assembly containing single card Command and Data Handling and Power System Electronics, miniature magnetometer, and lithium ion battery. ST-5 will demonstrate the ability of a micro satellite to perform research-quality science. Each ST-5 spacecraft will deploy a precision magnetometer to be used both for attitude determination and as a representative science instrument. The spacecraft has been developed with a low magnetic signature to avoid interference with the magnetometer. The spacecraft will be able to detect and respond autonomously to science events, i.e. significant changes in the magnetic field measurements. The three spacecraft will be a pathfinder for future constellation missions. They will be deployed to demonstrate an appropriate geometry for scientific measurements as a constellation. They will be operationally managed as a constellation, demonstrating automation and communication strategies that will be useful for future missions. The technologies and future mission concepts will be validated both on the ground and in space. Technologies will be validated on the ground by a combination of component level and system level testing of the flight hardware in a thermal vacuum environment. In flight, specific validation runs are planned for each of the technologies. Each validation run consists of one or more orbits with a specific validation objective. This paper will describe the ST-5 mission, and the applicability of the NMP technologies, spacecraft, and mission concepts to future missions. It will also discuss the validation approach for the ST-5 technologies and mission concepts.

Carlisle, Candace↗
NASA NTRS2004

Microscale Investigation of Thermo-Fluid Transport in the Transition FIL, Region of an Evaporating Capillary Meniscus Using a Microgravity Environment

In order to enhance the fundamental understanding of thin film evaporation and thereby improve the critical design concept for two-phase heat transfer devices, microscale heat and mass transport is to be investigated for the transition film region using state-of-the-art optical diagnostic techniques. By utilizing a microgravity environment, the length scales of the transition film region can be extended sufficiently, from submicron to micron, to probe and measure the microscale transport fields which are affected by intermolecular forces. Extension of the thin film dimensions under microgravity will be achieved by using a conical evaporator made of a thin silicon substrate under which concentric and individually controlled micro-heaters are vapor-deposited to maintain either a constant surface temperature or a controlled temperature variation. Local heat transfer rates, required to maintain the desired wall temperature boundary condition, will be measured and recorded by the concentric thermoresistance heaters controlled by a Wheatstone bridge circuit, The proposed experiment employs a novel technique to maintain a constant liquid volume and liquid pressure in the capillary region of the evaporating meniscus so as to maintain quasi-stationary conditions during measurements on the transition film region. Alternating use of Fizeau interferometry via white and monochromatic light sources will measure the thin film slope and thickness variation, respectively. Molecular Fluorescence Tracking Velocimetry (MFTV), utilizing caged fluorophores of approximately 10-nm in size as seeding particles, will be used to measure the velocity profiles in the thin film region. An optical sectioning technique using confocal microscopy will allow submicron depthwise resolution for the velocity measurements within the film for thicknesses on the order of a few microns. Digital analysis of the fluorescence image-displacement PDFs, as described in the main proposal, can further enhance the depthwise resolution.

Kihm, K. D.↗
NASA NTRS2002

Alteration of gene expression profiles in skeletal muscle of rats exposed to microgravity during a spaceflight

To clarify the mechanism of skeletal muscle wasting during spaceflights, we investigated whether intramuscular gene expression profiles are affected, by using DNA microarray methods. Male rats sent on the 17-day NASA STS-90 Neurolab spaceflight were sacrificed 24 hours after return to earth (MG group). Ground control rats were maintained for 17 days in flight-simulated cages (CS group). Spaceflight induced a 19% and 23% loss of tibialis anterior and gastrocnemius muscle mass, respectively, as compared to ground controls. Muscle RNA was analyzed by the Clontech Atlas DNA expression array in four rats, with two MG/ CS pairs for the tibialis anterior, and one pair for the gastrocnemius. Alterations in gene expression were verified for selected genes by reverse-transcription PCR. In both muscles of MG rats, mRNAs for 12 genes were up-regulated by over 2-fold, and 38 were down-regulated compared to controls. There was inhibition of genes for cell proliferation and growth factor cascades, including cell cycle genes and signal transduction proteins, such as p21 Cip1, retinoblastoma (Rb), cyclins G1/S, -E and -D3, MAP kinase 3, MAD3, and ras related protein RAB2. These data indicate that following exposure to microgravity, there is downregulation of genes involved in regulation of muscle satellite cell replication.

NASA Program Fundamental Space Biology↗
NASA NTRS2003

Mammalian development in space

Life on Earth, and thus the reproductive and ontogenetic processes of all extant species and their ancestors, evolved under the constant influence of the Earth's l g gravitational field. These considerations raise important questions about the ability of mammals to reproduce and develop in space. In this chapter, I review the current state of our knowledge of spaceflight effects on developing mammals. Recent studies are revealing the first insights into how the space environment affects critical phases of mammalian reproduction and development, viz., those events surrounding fertilization, embryogenesis, pregnancy, birth, postnatal maturation and parental care. This review emphasizes fetal and early postnatal life, the developmental epochs for which the greatest amounts of mammalian spaceflight data have been amassed. The maternal-offspring system, the coordinated aggregate of mother and young comprising mammalian development, is of primary importance during these early, formative developmental phases. The existing research supports the view that biologically meaningful interactions between mothers and offspring are changed in the weightlessness of space. These changes may, in turn, cloud interpretations of spaceflight effects on developing offspring. Whereas studies of mid-pregnant rats in space have been extraordinarily successful, studies of young rat litters launched at 9 days of postnatal age or earlier, have been encumbered with problems related to the design of in-flight caging and compromised maternal-offspring interactions. Possibilities for mammalian birth in space, an event that has not yet transpired, are considered. In the aggregate, the results indicate a strong need for new studies of mammalian reproduction and development in space. Habitat development and systematic ground-based testing are important prerequisites to future research with young postnatal rodents in space. Together, the findings support the view that the environment within which young mammals develop, comprised of its mother and siblings, is of paramount importance in interpreting spaceflight effects.

Review↗
NASA NTRS2000

Disuse bone loss in hindquarter suspended rats: partial weightbearing, exercise and ibandronate treatment as countermeasures

The purpose of this study was to evaluate potential countermeasures for bone loss during long-term space missions in the hindquarter suspended rat, including partial weight bearing (surrogate for artificial gravity) episodic full weight bearing (2 hour/day full weight bearing) and treatment with the third generation bisphosphonate ibandronate (Roche). Graded mechanical loading was studied by housing the animals on a novel servo controlled force plate system which permitted the titration of mechanical force at varying frequency and amplitude and different levels of weight bearing. The force plate, which forms the cage floor, is a glass platform supported by an 18" diameter speaker cone filled with expanding polyurethane foam. An infrared optical sensor attached to the speaker cone yields a voltage linearly related to vertical displacement of the glass platform. The dynamic force on the paw was computed as a product of the apparent mass of the animal on the platform at rest and the acceleration of the platform determined from the second derivative of the optical sensor output. The mass of the animal on the platform was varied by adjusting tension on the tether suspending the animal. Mechanical impact loading was titrated with the force plate resonating at different frequencies, including 3 Hz and 16 Hz.

Non-NASA Center↗
NASA NTRS2003

Hindlimb unloading has a greater effect on cortical compared with cancellous bone in mature female rats

This study was designed to determine the effects of 28 days of hindlimb unloading (HU) on the mature female rat skeleton. In vivo proximal tibia bone mineral density and geometry of HU and cage control (CC) rats were measured with peripheral quantitative computed tomography (pQCT) on days 0 and 28. Postmortem pQCT, histomorphometry, and mechanical testing were performed on tibiae and femora. After 28 days, HU animals had significantly higher daily food consumption (+39%) and lower serum estradiol levels (-49%, P = 0.079) compared with CC. Proximal tibia bone mineral content and cortical bone area significantly declined over 28 days in HU animals (-4.0 and 4.8%, respectively), whereas total and cancellous bone mineral densities were unchanged. HU animals had lower cortical bone formation rates and mineralizing surface at tibial midshaft, whereas differences in similar properties were not detected in cancellous bone of the distal femur. These results suggest that cortical bone, rather than cancellous bone, is more prominently affected by unloading in skeletally mature retired breeder female rats.

NASA Discipline Musculoskeletal↗
NASA NTRS2001

Space flight affects magnocellular supraoptic neurons of young prepuberal rats: transient and permanent effects

Effects of microgravity on postural control and volume of extracellular fluids as well as stress associated with space flight may affect the function of hypothalamic neurosecretory neurons. Since environmental modifications in young animals may result in permanent alterations in neuroendocrine function, the present study was designed to determine the effect of a space flight on oxytocinergic and vasopressinergic magnocellular hypothalamic neurons of prepuberal rats. Fifteen-day-old Sprague-Dawley female rats were flown aboard the Space Shuttle Columbia (STS-90, Neurolab mission, experiment 150) for 16 days. Age-matched litters remained on the ground in cages similar to those of the flight animals. Six animals from each group were killed on the day of landing and eight animals from each group were maintained under standard vivarium conditions and killed 18 weeks after landing. Several signs of enhanced transcriptional and biosynthetic activity were observed in magnocellular supraoptic neurons of flight animals on the day of landing compared to control animals. These include increased c-Fos expression, larger nucleoli and cytoplasm, and higher volume occupied in the neuronal perikaryon by mitochondriae, endoplasmic reticulum, Golgi apparatus, lysosomes and cytoplasmic inclusions known as nematosomes. In contrast, the volume occupied by neurosecretory vesicles in the supraoptic neuronal perikarya was significantly decreased in flight rats. This decrease was associated with a significant decrease in oxytocin and vasopressin immunoreactive levels, suggestive of an increased hormonal release. Vasopressin levels, cytoplasmic volume and c-Fos expression returned to control levels by 18 weeks after landing. These reversible effects were probably associated to osmotic stimuli resulting from modifications in the volume and distribution of extracellular fluids and plasma during flight and landing. However, oxytocin levels were still reduced at 18 weeks after landing in flight animals compared to controls. This indicates that space flight during prepuberal age may induce irreversible modifications in the regulation of oxytocinergic neurons, which in turn may result in permanent endocrine and behavioral impairments.

NASA Experiment Number 9301150↗
NASA NTRS1988

The effects of feedback lighting on the circadian rhythm of locomotor activity and the reproductive maturation of the male Djungarian hamster (Phodopus sungorus)

The non-parametric model of entrainment suggests that brief pulses of light, delivered between dusk and dawn can simulate the phasing effects of full photoperiods or even constant light (LL). Feedback lighting (LDFB) is a lighting condition where individual animals, otherwise in constant darkness (DD), are exposed to light in response to a monitored behavior. The specific purpose of this type of illumination is to expose the circadian cycle to light only during the subjective night. LDFB has been used to support this hypothesis in several species of nocturnal rodents and one species of diurnal primate by producing similar free-running periods in LDFB as in LL. This lighting condition has also been used to test the hypothesis that exposing the subjective night to even short duration light pulses will maintain reproductive function in long day breeders. In the Syrian hamster (Mesocricetus auratus), however, LDFB is not as photostimulatory as LL despite extensive light exposure during the subjective night. In the experiments presented here, a group of immature male Djungarian hamsters (Phodopus sungorus) were placed in individual light-tight sound attenuated chambers where they had free access to food, water and an activity wheel. The animals were exposed to one of four lighting conditions [DD, LL, LDFB or a neighbor control of feedback lighting (LDFB NC)] for approximately 30 days shortly after weaning. LDFB NC is a lighting condition where a neighbor control hamster receives the identical lighting regime as a paired animal exposing itself to LDFB, yet the neighbor has no control over it. A fifth group was exposed to a light-dark cycle of 16 hours of light and 8 hours of dark (LD16:8). This group was housed in cages in a colony room and did not have access to a running wheel. The free-running periods of the locomotor activity rhythms for hamsters exposed to LDFB and LL were not similar, unlike the results for rats, Syrian hamsters, mice, monkeys and even mature Djungarian hamsters. Immature hamsters exposed to DD and LDFB NC developed more slowly than animals exposed to LL or LD16:8, while hamsters in LDFB developed at an intermediate rate. Thus, it appears that LDFB, although capable of inducing reproductive function in immature Djungarian hamsters, is not as photostimulatory as may have been expected from current photoperiodic models, despite substantial light exposure during the subjective night. Furthermore, this data may suggest that the circadian system of 18-48 day old Djungarian hamsters are still undergoing organizational maturation.

NASA Program Space Biology↗
NASA NTRS1994

Cardiopulmonary adaptation to weightlessness

The lung is profoundly affected by gravity. The absence of gravity (microgravity) removes the mechanical stresses acting on the lung paranchyma itself, resulting in a reduction in the deformation of the lung due to its own weight, and consequently altering the distribution of fresh gas ventilation within the lung. There are also changes in the mechanical forces acting on the rib cage and abdomen, which alters the manner in which the lung expands. The other way in which microgravity affects the lung is through the removal of the gravitationally induced hydrostatic gradients in vascular pressures, both within the lung itself, and within the entire body. The abolition of a pressure gradient within the pulmonary circulation would be expected to result in a greater degree of uniformity of blood flow within the lung, while the removal of the hydrostatic gradient within the body should result in an increase in venous return and intra-thoracic blood volume, with attendant changes in cardiac output, stroke volume, and pulmonary diffusing capacity. During the 9 day flight of Spacelab Life Sciences-1 (SLS-1) we collected pulmonary function test data on the crew of the mission. We compared the results obtained in microgravity with those obtained on the ground in both the standing and supine positions, preflight and in the week immediately following the mission. A number of the tests in the package were aimed at studying the anticipated changes in cardiopulmonary function, and we report those in this communication.

short duration↗
NASA NTRS1987

Air ion exposure system for plants

A system was developed for subjecting plants to elevated air ion levels. This system consisted of a rectangular Plexiglas chamber lined with a Faraday cage. Air ions were generated by corona discharge from frayed stainless steel fibers placed at one end of the chamber. This source was capable of producing varying levels of either positive or negative air ions. During plant exposures, environmental conditions were controlled by operating the unit in a growth chamber.

NASA Discipline Number 61-10↗
NASA NTRS1992

Investigations of rhesus monkey video-task performance: evidence for enrichment

We have developed the Language Research Center's Computerized Test System (LRC-CTS) for psychological research. Basically, the LRC-CTS is a battery of software tasks--computerized versions of many of the classic testing paradigms of cognitive and comparative psychology--and the hardware required to administer them. An XT- or 386-compatible computer is connected to a color monitor, onto which computer-generated stimuli are presented. Sound feedback is delivered through an external speaker/amplifier, and a joystick is used as an input device. The animals reach through the mesh of their home cages to manipulate the joystick, which causes isomorphic movements of a cursor on the screen thereby allowing animals to respond according to the varied demands of the tasks. Correct responses are rewarded with a fruit-flavored chow pellet. Using this technology, we have trained and tested rhesus monkeys, a variety of apes, human adults, and normally developing or mentally retarded human children. Other labs using the LRC-CTS are beginning to report encouraging results with other monkey species as well. From this research, a number of interesting and important psychological findings have resulted. In the present paper, however, evidence will be reviewed which suggests that the LRC-CTS is an effective means of providing environmental enrichment to singly housed rhesus monkeys.

Non-NASA Center↗
NASA NTRS1990

Nocturnal illumination maintains reproductive function and simulates the period-lengthening effect of constant light in the mature male Djungarian hamster (Phodopus sungorus)

Mature male Djungarian hamsters (Phodopus sungorus) were placed in individual light-tight, sound attenuated chambers and exposed to one of four lighting conditions for a duration of approximately seven weeks. The four lighting conditions were: constant light (LL); constant dark (DD); feedback lighting (LDFB; a condition that illuminates the cage in response to locomotor activity); or a feedback lighting neighbor control (LDFB NC; the animal receives the same light pattern as a paired animal in feedback lighting, but has no control over it). Exposure of hamsters to LL or LDFB produced significantly and similarly longer free-running periods of the locomotor activity rhythm than exposure of animals to DD. Hamsters exposed to LDFB NC did not free-run or entrain, but rather displayed "relative coordination". The paired testes and sex accessory glands weights suggest that in the Djungarian hamster, LL and LDFB exposed animals maintained reproductive function, whereas DD exposed animals did not. Animals exposed to LDFB NC had intermediate paired testes weights. Since several previous studies have demonstrated that short pulses of light, which are coincident with the subjective night, are photostimulatory, it is not surprising that LDFB maintained reproductive function in the mature Djungarian hamster. Feedback lighting, however, has been shown to be an insufficient stimulus to maintain reproductive function of mature male and female Syrian hamsters, and to the reproductive maturation of immature Djungarian hamsters. The results suggest that there may be slight, but significant differences in the way these two species interpret photoperiod, as well as a developmental change in the photoperiodic response of Djungarian hamsters.

NASA Program Space Biology↗
NASA NTRS2002

Peripheral vascular responses to heat stress after hindlimb suspension

PURPOSE: The purpose of this study was to determine whether hindlimb suspension (which simulates the effects of microgravity) results in impaired hemodynamic responses to heat stress or alterations in mesenteric small artery sympathetic nerve innervation. METHODS: Over 28 d, 16 male Sprague-Dawley rats were hindlimb-suspended, and 13 control rats were housed in the same type of cage. After the treatment, mean arterial pressure (MAP), colonic temperature (Tcol), and superior mesenteric and iliac artery resistances (using Doppler flowmetry) were measured during heat stress [exposure to 42 degrees C until the endpoint of 80 mm Hg blood pressure was reached (75 +/- 9 min); endpoint Tcore = 43.6 +/- 0.2] while rats were anesthetized (sodium pentobarbital, 50 mg x kg(-1) BW). RESULTS: Hindlimb-suspended and control rats exhibited similar increases in Tcol, MAP, and superior mesenteric artery resistance, and similar decreases in iliac resistance during heat stress (endpoint was a fall in MAP below 80 mm Hg). Tyrosine hydroxylase immunostaining indicated similar sympathetic nerve innervation in small mesenteric arteries from both groups. CONCLUSION: Hindlimb suspension does not alter the hemodynamic or thermoregulatory responses to heat stress in the anesthetized rat or mesenteric sympathetic nerve innervation, suggesting that this sympathetic pathway is intact.

NASA Discipline Cardiopulmonary↗
NASA NTRS2001

Effect of short-term microgravity and long-term hindlimb unloading on rat cardiac mass and function

The purpose of this study was to test the hypothesis that exposure to short-term microgravity or long-term hindlimb unloading induces cardiac atrophy in male Sprague-Dawley rats. For the microgravity study, rats were subdivided into four groups: preflight (PF, n = 12); flight (Fl, n = 7); flight cage simulation (Sim, n = 6), and vivarium control (Viv, n = 7). Animals in the Fl group were exposed to 7 days of microgravity during the Spacelab 3 mission. Animals in the hindlimb-unloading study were subdivided into three groups: control (Con, n = 20), 7-day hindlimb-unloaded (7HU, n = 10), and 28-day hindlimb-unloaded (28HU, n = 19). Heart mass was unchanged in adult animals exposed to 7 days of actual microgravity (PF 1.33 +/- 0.03 g; Fl 1.32 +/- 0.02 g; Sim 1.28 +/- 0.04 g; Viv 1.35 +/- 0.04 g). Similarly, heart mass was unaltered with hindlimb unloading (Con 1.40 +/- 0.04 g; 7HU 1.35 +/- 0.06 g; 28HU 1.42 +/- 0.03 g). Hindlimb unloading also had no effect on the peak rate of rise in left ventricular pressure, an estimate of myocardial contractility (Con 8,055 +/- 385 mmHg/s; 28HU 8,545 +/- 755 mmHg/s). These data suggest that cardiac atrophy does not occur after short-term exposure to microgravity and that neither short- nor long-term simulated microgravity alters cardiac mass or function.

manned↗
NASA NTRS2001

Expression of heat shock protein 72 in atrophied rat skeletal muscles

Changes in the expression of heat shock protein 72 (HSP72) in response to atrophic-inducing perturbations of muscle involving chronic mechanical unloading and denervation were determined. Adult male Wistar rats were assigned randomly to a sedentary cage control (CON), hind limb unloading (HU, via tail suspension), HU plus tenotomy (HU + TEN), HU plus denervation (HU + DEN), or HU + TEN + DEN group. Tenotomy and DEN involved cutting the Achilles tendon and removing a segment of the sciatic nerve, respectively. After 5 days, HSP72 levels in the soleus of the HU + DEN and HU + TEN + DEN groups were 42 (P < 0.05) and 53% (P < 0.01) less than CON, respectively. Soleus weight decreased in both groups. Heat shock protein 72 levels in the plantaris of the HU + TEN, HU + DEN, and HU + TEN + DEN groups were 31, 25, and 30% lower than CON, respectively (P < 0.05). Plantaris weight decreased in the HU + DEN and HU + TEN + DEN, but not in the HU + TEN group. Hind limb unloading alone had little effect on the HSP72 level in either muscle. Reduced levels of HSP72 were associated with a decreased soleus (r=0.62, P < 0.01) and plantaris (r=0.78, P < 0.001) weight. These results indicate that the levels of HSP72 in both a slow and a fast rat plantarflexor are responsive to a chronic decrease in the levels of loading and/or activation and suggest that the neuromuscular activity level and the presence of innervation of a muscle are important factors that induce HSP72 expression.

NASA Discipline Musculoskeletal↗
NASA NTRS2001

Changes in root cap pH are required for the gravity response of the Arabidopsis root

Although the columella cells of the root cap have been identified as the site of gravity perception, the cellular events that mediate gravity signaling remain poorly understood. To determine if cytoplasmic and/or wall pH mediates the initial stages of root gravitropism, we combined a novel cell wall pH sensor (a cellulose binding domain peptide-Oregon green conjugate) and a cytoplasmic pH sensor (plants expressing pH-sensitive green fluorescent protein) to monitor pH dynamics throughout the graviresponding Arabidopsis root. The root cap apoplast acidified from pH 5.5 to 4.5 within 2 min of gravistimulation. Concomitantly, cytoplasmic pH increased in columella cells from 7.2 to 7.6 but was unchanged elsewhere in the root. These changes in cap pH preceded detectable tropic growth or growth-related pH changes in the elongation zone cell wall by 10 min. Altering the gravity-related columella cytoplasmic pH shift with caged protons delayed the gravitropic response. Together, these results suggest that alterations in root cap pH likely are involved in the initial events that mediate root gravity perception or signal transduction.

NASA Discipline Plant Biology↗