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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.

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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Local Discontinuous Galerkin Methods for Partial Differential Equations with Higher Order Derivatives

In this paper we review the existing and develop new continuous Galerkin methods for solving time dependent partial differential equations with higher order derivatives in one and multiple space dimensions. We review local discontinuous Galerkin methods for convection diffusion equations involving second derivatives and for KdV type equations involving third derivatives. We then develop new local discontinuous Galerkin methods for the time dependent bi-harmonic type equations involving fourth derivatives, and partial differential equations involving fifth derivatives. For these new methods we present correct interface numerical fluxes and prove L(exp 2) stability for general nonlinear problems. Preliminary numerical examples are shown to illustrate these methods. Finally, we present new results on a post-processing technique, originally designed for methods with good negative-order error estimates, on the local discontinuous Galerkin methods applied to equations with higher derivatives. Numerical experiments show that this technique works as well for the new higher derivative cases, in effectively doubling the rate of convergence with negligible additional computational cost, for linear as well as some nonlinear problems, with a local uniform mesh.

Yan, Jue↗
NASA NTRS2002

Osteoblast Differentiation Decreases Hypergravity-Stimulated Release of PGE(sub 2)

We determined if progressive differentiation of osteoblasts influences their sensitivity to gravitational loading. Osteoblasts were cultured for 4 days (confluent monolayer), 6 days (prenodules), 9 days (nodules) and 19 days (mineralized nodules), then centrifuged at 10 times gravity (g) or 50-g for 3 hours using the NASA Ames 1-ft. Diameter Centrifuge. Stationary controls were placed in an adjacent incubator. Following centrifugation, conditioned media were collected and analyzed for PGE, by ELISA. Microtubules were fluorescently labeled and analyzed by confocal microscopy to determine microtubule network morphology and height. Centrifugation at 10-g reduced microtubule network height by 15% on d4 and 10% on d6, with variable changes in more mature cultures. No major changes in microtubule morphology were observed. PGE(sub 2) release by d4 cultures increased in a dose-dependent fashion (3-fold at 10-g and 6-fold at 50-g relative to controls). D6 cultures produced a 5-fold increase for both 10-g and 50-g. PGE(sub 2) increased only 1.5-fold by d9, and by d19, PGE(sub 2) was not delectable in either the control or hypergravity-stimulated cells. Thus, as osteoblasts differentiate in culture, responsiveness of the microtubule cytoskeleton and the PGE(sub 2) pathway to hypergravity declines.

Searby, Nancy D.↗
NASA NTRS2003

Dual reporter transgene driven by 2.3Col1a1 promoter is active in differentiated osteoblasts

AIM: As quantitative and spatial analyses of promoter reporter constructs are not easily performed in intact bone, we designed a reporter gene specific to bone, which could be analyzed both visually and quantitatively by using chloramphenicol acetyltransferase (CAT) and a cyan version of green fluorescent protein (GFPcyan), driven by a 2.3-kb fragment of the rat collagen promoter (Col2.3). METHODS: The construct Col2.3CATiresGFPcyan was used for generating transgenic mice. Quantitative measurement of promoter activity was performed by CAT analysis of different tissues derived from transgenic animals; localization was performed by visualized GFP in frozen bone sections. To assess transgene expression during in vitro differentiation, marrow stromal cell and neonatal calvarial osteoblast cultures were analyzed for CAT and GFP activity. RESULTS: In mice, CAT activity was detected in the calvaria, long bone, teeth, and tendon, whereas histology showed that GFP expression was limited to osteoblasts and osteocytes. In cell culture, increased activity of CAT correlated with increased differentiation, and GFP activity was restricted to mineralized nodules. CONCLUSION: The concept of a dual reporter allows a simultaneous visual and quantitative analysis of transgene activity in bone.

Non-NASA Center↗
NASA NTRS2001

Proliferation, differentiation and apoptosis in connexin43-null osteoblasts

Osteoblasts are highly coupled by gap junctions formed primarily by connexin43 (Cx43). We have shown that interference with Cx43 expression or function disrupts transcriptional regulation of osteoblast genes, and that deletion of Cx43 in the mouse causes skeletal malformations, delayed mineralization, and osteoblast dysfunction. Here, we studied the mechanisms by which genetic deficiency of Cx43 alters osteoblast development. While cell proliferation rates were similar in osteoblastic cells derived from calvaria of Cx43-null and wild type mice, camptothecin-induced apoptosis was 3-fold higher in mutant compared to wild type osteoblasts. When grown in mineralizing medium, Cx43-null cells were able to produce mineralized matrix but it took one week longer to reach the same mineralization levels as in normal cells. Likewise, expression of alkaline phosphatase activity per cell--a marker of osteoblast differentiation--was maximal only 2 weeks later in Cx43-null relative to wild-type cells. These observations suggest that Cx43 is important for a normal and timely development of the osteoblastic phenotype. Delayed differentiation and increase programmed cell death may explain the skeletal phenotype of Cx43-null mice.

NASA Discipline Cell Biology↗
NASA NTRS2002

Differential effects of intermittent and continuous administration of parathyroid hormone on bone histomorphometry and gene expression

A mechanism explaining the differential skeletal effects of intermittent and continuous elevation of serum parathyroid hormone (PTH) remains elusive. Intermittent PTH increases bone formation and bone mass and is being investigated as a therapy for osteoporosis. By contrast, chronic hyperparathyroidism results in the metabolic bone disease osteitis fibrosa characterized by osteomalacia, focal bone resorption, and peritrabecular bone marrow fibrosis. Intermittent and continuous PTH have similar effects on the number of osteoblasts and bone-forming activity. Many of the beneficial as well as detrimental effects of the hormone appear to be mediated by osteoblast-derived growth factors. This hypothesis was tested using cDNA microgene arrays to compare gene expression in tibia of rats treated with continuous and pulsatile administration of PTH. These treatments result in differential expression of many genes, including growth factors. One of the genes whose steady-state mRNA levels was increased by continuous but not pulsatile administration was platelet-derived growth factor-A (PDGF-A). Administration of a PDGF-A antagonist greatly reduced bone resorption, osteomalacia, and bone marrow fibrosis in a rat model for hyperparathyroidism, suggesting that PDGF-A is a causative agent for this disease. These findings suggest that profiling changes in gene expression can help identify the metabolic pathways responsible for the skeletal responses to the hormone.

Review↗
NASA NTRS2000

Two distinct regions of response drive differential growth in Vigna root electrotropism

Although exogenous electric fields have been reported to influence the orientation of plant root growth, reports of the ultimate direction of differential growth have been contradictory. Using a high-resolution image analysis approach, the kinetics of electrotropic curvature in Vigna mungo L. roots were investigated. It was found that curvature occurred in the same root toward both the anode and cathode. However, these two responses occurred in two different regions of the root, the central elongation zone (CEZ) and distal elongation zone (DEZ), respectively. These oppositely directed responses could be reproduced individually by a localized electric field application to the region of response. This indicates that both are true responses to the electric field, rather than one being a secondary response to an induced gravitropic stimulation. The individual responses differed in the type of differential growth giving rise to curvature. In the CEZ, curvature was driven by inhibition of elongation, whereas curvature in the DEZ was primarily due to stimulation of elongation. This stimulation of elongation is consistent with the growth response of the DEZ to other environmental stimuli.

Non-NASA Center↗
NASA NTRS2001

Differential expression of decorin and biglycan genes during mouse tooth development

Small leucine-rich proteoglycans (SLRPs) have a number of biological functions and some of them are thought to regulate collagen mineralizaton in bone and tooth. We have previously identified and immunolocalized two members of the SLRPs family, decorin and biglycan, in bovine tooth/periodontium. To investigate their potential roles in tooth development, we examined the mRNA expression patterns of decorin, biglycan and type I collagen in newborn (day 19) mice tooth germs by in situ hybridization. At this developmental stage, the first maxillary and mandibular molars include stages before and after secretion of the predentin matrix, respectively. The expression of decorin mRNA coincided with that of type I collagen mRNA and was mostly observed in secretory odontoblasts, while the biglycan mRNA was expressed throughout the tooth germ, including pre-secretory odontoblasts/ameloblasts, dental papilla and stellate reticulum. However, its signal in secretory odontoblasts was not as evident as that of decorin. In mandibular incisors, where a significant amount of predentin matrix and a small amount of enamel matrix were already secreted, a similar differential expression pattern was observed. In secretory ameloblasts the biglycan mRNA expression was apparent, while that of decorin was not. These differential expression patterns suggest the distinct roles of biglycan and decorin in the process of tooth development.

Non-NASA Center↗
NASA NTRS1985

Polyamine levels as related to growth, differentiation and senescence in protoplast-derived cultures of Vigna aconitifolia and Avena sativa

We have previously reported that aseptically cultured mesophyll protoplasts of Vigna divide rapidly and regenerate into complete plants, while mesophyll protoplasts of Avena divide only sporadically and senesce rapidly after isolation. We measured polyamine titers in such cultures of Vigna and Avena, to study possible correlations between polyamines and cellular behavior. We also deliberately altered polyamine titer by the use of selective inhibitors of polyamine biosynthesis, noting the effects on internal polyamine titer, cell division activity and regenerative events. In Vigna cultures, levels of free and bound putrescine and spermidine increased dramatically as cell division and differentiation progressed. The increase in bound polyamines was largest in embryoid-forming callus tissue while free polyamine titer was highest in root-forming callus. In Avena cultures, the levels of total polyamines decreased as the protoplast senesced. The presence of the inhibitors alpha-difluoromethyl-arginine (specific inhibitor of arginine decarboxylase), alpha-difluoromethylornithine (specific inhibitor of ornithine decarboxylase) and dicyclohexylamine (inhibitor of spermidine synthase) reduced cell division and organogenesis in Vigna cultures. Addition of low concentration of polyamines to such cultures containing inhibitors or removal of inhibitors from the culture medium restored the progress of growth and differentiation with concomitant increase in polyamine levels.

NASA Program Space Biology↗
NASA NTRS1987

Measurement of differential proton spectra onboard the Space Shuttle using a thermoluminescent dosimetry system

An experimental technique that permits the extraction of orbit-averaged, differential energy spectra of trapped radiation belt protons using simple passive detectors is described. An inversion technique is used for the data analysis. The basic principle of the described system is measurement of the energy deposited in six thermoluminescent (TLD) detector assemblies behind various spherical absorbers. The technique has been applied to a detector assembly flown on four Shuttle flights. Although severe restraints were placed on the flight package, the differential energy spectra derived from these measurements are in good agreement with analytical results using a modified trapped proton environment model. The technique shows good promise for measuring the spectra in low inclination orbits where the flux of high energy galactic cosmic rays protons is small. Modifications to the detector assembly to improve the accuracy and to extend the range of the system to higher energies are suggested.

STS-51J Shuttle Project↗
NASA NTRS1995

Integrin-extracellular matrix interactions in connective tissue remodeling and osteoblast differentiation

The differentiaton of bone cells is a complex multistep process. Bone is somewhat unusual in that it is very actively and continually remodeled in the adult and that maintenance of its mass in the mature organism is exquisitely sensitive to mechanical as well as chemical signals. Bone is also unique because it consists of a very large amount of extracellular matrix (ECM) that is mineralized. The integrin family of ECM receptors has been shown to play an important role in tissue morphogenesis in several systems. Our studies on the regulation of matrix remodeling enzymes by integrins in rabbit synovial fibroblasts show that two b1 integrin fibronectin (FN) receptor complexes (alpha 5 beta 1 and alpha 4 beta 1) cooperate in detecting subtle changes in the composition of the ECM. As a result of signal transduction by these integrins, the levels of mRNA and protein for several members of the metalloproteinase family are regulated in these cells. We have also used antibody and RGD peptide perturbation studies to determine the significance of cell/ECM interactions to normal osteogenesis. We found that interactions between the cell binding domain of FN and integrins are required for both normal morphogenesis and gene expression in cultured osteoblasts that differentiate to form bone-like tissue in culture. These data lead us to propose that beta 1 integrins play an important role in osteoblast differentiation as well as in bone remodeling.

NASA Discipline Number 26-10↗
NASA NTRS1988

Hormonal induction and antihormonal inhibition of tracheary element differentiation in Zinnia cell cultures

Mechanically isolated mesophyll cells of Zinnia elegans L. cv Envy differentiate to tracheary elements when cultured in inductive medium containing sufficient auxin and cytokinin. Tracheary element differentiation was induced by the three auxins (alpha-naphthaleneacetic acid, indole-3-acetic acid, and 2,4-dichlorophenoxyacetic acid) and four cytokinins (6-benzyladenine, kinetin, 2-isopentenyladenine and zeatin) tested. Tracheary element formation is inhibited or delayed if the inductive medium is supplemented with an anticytokinin, antiauxin, or inhibitor of auxin transport.

NASA Program Space Biology↗
NASA NTRS2000

Shape-dependent control of cell growth, differentiation, and apoptosis: switching between attractors in cell regulatory networks

Development of characteristic tissue patterns requires that individual cells be switched locally between different phenotypes or "fates;" while one cell may proliferate, its neighbors may differentiate or die. Recent studies have revealed that local switching between these different gene programs is controlled through interplay between soluble growth factors, insoluble extracellular matrix molecules, and mechanical forces which produce cell shape distortion. Although the precise molecular basis remains unknown, shape-dependent control of cell growth and function appears to be mediated by tension-dependent changes in the actin cytoskeleton. However, the question remains: how can a generalized physical stimulus, such as cell distortion, activate the same set of genes and signaling proteins that are triggered by molecules which bind to specific cell surface receptors. In this article, we use computer simulations based on dynamic Boolean networks to show that the different cell fates that a particular cell can exhibit may represent a preprogrammed set of common end programs or "attractors" which self-organize within the cell's regulatory networks. In this type of dynamic network model of information processing, generalized stimuli (e.g., mechanical forces) and specific molecular cues elicit signals which follow different trajectories, but eventually converge onto one of a small set of common end programs (growth, quiescence, differentiation, apoptosis, etc.). In other words, if cells use this type of information processing system, then control of cell function would involve selection of preexisting (latent) behavioral modes of the cell, rather than instruction by specific binding molecules. Importantly, the results of the computer simulation closely mimic experimental data obtained with living endothelial cells. The major implication of this finding is that current methods used for analysis of cell function that rely on characterization of linear signaling pathways or clusters of genes with common activity profiles may overlook the most critical features of cellular information processing which normally determine how signal specificity is established and maintained in living cells. Copyright 2000 Academic Press.

Review↗
NASA NTRS1994

Parallel Calculation of Sensitivity Derivatives for Aircraft Design using Automatic Differentiation

Sensitivity derivative (SD) calculation via automatic differentiation (AD) typical of that required for the aerodynamic design of a transport-type aircraft is considered. Two ways of computing SD via code generated by the ADIFOR automatic differentiation tool are compared for efficiency and applicability to problems involving large numbers of design variables. A vector implementation on a Cray Y-MP computer is compared with a coarse-grained parallel implementation on an IBM SP1 computer, employing a Fortran M wrapper. The SD are computed for a swept transport wing in turbulent, transonic flow; the number of geometric design variables varies from 1 to 60 with coupling between a wing grid generation program and a state-of-the-art, 3-D computational fluid dynamics program, both augmented for derivative computation via AD. For a small number of design variables, the Cray Y-MP implementation is much faster. As the number of design variables grows, however, the IBM SP1 becomes an attractive alternative in terms of compute speed, job turnaround time, and total memory available for solutions with large numbers of design variables. The coarse-grained parallel implementation also can be moved easily to a network of workstations.

Bischof, c. H.↗
NASA NTRS2004

The Nature of Low T/|W| Dynamical Instabilities in Differentially Rotating Stars

Recent numerical simulations indicate the presence of dynamical instabilities of the f-mode in differentially rotating stars even at very low values of T/|W|, the ratio of kinetic to potential energy. In this Letter we argue that these are shear instabilities which occur when the degree of differential rotation exceeds a critical value and the f-mode develops a corotation point associated with the presence of a continuous spectrum. Our explanation, which is supported by detailed studies of a simple shell model, offers a straightforward way of understanding all of the key features of these instabilities.

Watts, A. L.↗
NASA NTRS1995

Fibronectin gene expression, synthesis and accumulation during in vitro differentiation of chicken osteoblasts

A well-defined chicken osteoblast culture system(18) has been used to examine fibronectin (FN) mRNA levels, synthesis, and accumulation during in vitro differentiation and matrix mineralization. Immunofluorescent staining of cells after 6 or 18 days in culture revealed that FN was initially associated with the cell surface and in partial coalignment with cytoskeletal elements while at the latter time most FN was associated with the extracellular matrix as a ubiquitous fibrillar network. Western blot analysis of total cell-associated proteins also detected FN at all culture times. However, when results were normalized to cellular DNA, FN levels increased until 12-16 and remained relatively constant thereafter. Similarly, FN synthesis as measured by [35S]-methionine labeling, and immunoprecipitation was greatest in early cultures (culture day 3) and then declined such that synthesis decreased 60% at day 18 and 94% after 24-31 days. FN mRNA levels as measured by Northern blot analysis were well correlated with FN synthesis. These results clearly show that FN is made by primary osteoblasts during their in vitro maturation. In contrast to other osteoblast markers such as alkaline phosphatase, osteocalcin, and osteopontin, whose expression increases as cells differentiate, FN accumulates in the matrix during periods of early cell growth and attachment and then remains proportional to cell number. Results with FN differ from those obtained with collagen which continues to accumulate in the extracellular matrix during osteoblast maturation. These results are consistent with FN being important for the initial attachment of early osteoblasts or osteoblast precursors to the pericellular matrix.

NASA Discipline Musculoskeletal↗
NASA NTRS1994

Effects of extracellular matrix proteins on macrophage differentiation, growth, and function: comparison of liquid and agar culture systems

Both spaceflight and skeletal unloading suppress the haematopoietic differentiation of macrophages (Sonnenfeld et al., Aviat. Space Environ. Med., 61:648-653, 1990; Armstrong et al., J. Appl. Physiol., 75:2734-2739, 1993). The mechanism behind this reduction in haematopoiesis has yet to be elucidated. However, changes in bone marrow extracellular matrix (ECM) may be involved. To further understand the role of ECM products in macrophage differentiation, we have performed experiments evaluating the effects of fibronectin, laminin, collagen type I, and collagen type IV on macrophage development and function. Bone marrow-derived macrophages cultured on four different ECM substrates in liquid culture medium showed less growth than those cultured on plastic. Significant morphological differences were seen on each of the substrates used. Phenotypically and functionally, as measured by class II major histocompatibility molecule (MHCII) expression, MAC-2 expression, and the secretion of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha), these macrophages were similar. In contrast, bone marrow-derived macrophages cultured in suspension, using agar, showed no difference in growth when exposed to ECM proteins. However, IL-6 and TNF-alpha secretion was affected by fibronectin, laminin, collagen type I, and collagen type IV in a concentration-dependent manner. We conclude that the ECM products fibronectin, laminin, collagen type I, and collagen type IV have profound effects on macrophage development and function. Additionally, we suggest that an ECM-supplemented agar culture system provides an environment more analogous to in vivo bone marrow than does a traditional liquid culture system.

Non-NASA Center↗
NASA NTRS1993

Utilization of microgravity bioreactors for differentiation of mammalian skeletal tissue

Bioreactor cell and tissue culture vessels can be used to study bone development in a simulated microgravity environment. These vessels will also provide an advantageous, low maintenance culture system on space station Freedom. Although many types of cells and tissues can potentially utilize this system, our particular interest is in developing bone tissue. We have characterized an organ culture system utilizing embryonic mouse pre-metatarsal mesenchyme, documenting morphogenesis and differentiation as cartilage rods are formed, with subsequent terminal chondrocyte differentiation to hypertrophied cells. Further development to form bone tissue is achieved by supplementation of the culture medium. Research using pre-metatarsal tissue, combined with the bioreactor culture hardware, could give insight into the advantages and/or disadvantages of conditions experienced in microgravity. Studies such as these have the potential to enhance understanding of bone development and adult bone physiology, and may help define the processes of bone demineralization experienced in space and in pathological conditions here on earth.

Non-NASA Center↗
NASA NTRS2001

End-to-End QoS for Differentiated Services and ATM Internetworking

The Internet was initially design for non real-time data communications and hence does not provide any Quality of Service (QoS). The next generation Internet will be characterized by high speed and QoS guarantee. The aim of this paper is to develop a prioritized early packet discard (PEPD) scheme for ATM switches to provide service differentiation and QoS guarantee to end applications running over next generation Internet. The proposed PEPD scheme differs from previous schemes by taking into account the priority of packets generated from different application. We develop a Markov chain model for the proposed scheme and verify the model with simulation. Numerical results show that the results from the model and computer simulation are in close agreement. Our PEPD scheme provides service differentiation to the end-to-end applications.

Su, Hongjun↗