Search NASA⌕ Search

SEARCH · Search NASA

Results for “Transient Expression”

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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Parathyroid hormone induces c-fos and c-jun messenger RNA in rat osteoblastic cells

PTH is a potent regulator of osteoblast gene expression, yet the nuclear events that mediate PTH action are poorly understood. We were interested in identifying immediate early genes which may regulate PTH-altered gene expression in the osteoblast. Therefore, we examined the effects of PTH on c-fos and c-jun gene expression in a rat osteoblastic cell line (UMR 106-01). Under control conditions, c-fos and c-jun mRNAs were present at low basal levels. After PTH treatment, c-fos mRNA abundance dramatically increased, with a maximal and transient response at 30 min. PTH also stimulated an increase in c-jun mRNA, but in a biphasic manner, with maximal levels at 30 min and 2 h. These responses were dose dependent, not altered by cotreatment with the protein synthesis inhibitor cycloheximide, and preceded PTH-induced expression of matrix metallo-proteinase-1 mRNA. Nuclear run-on assays demonstrated an increased rate of c-fos and c-jun transcription after PTH exposure. To determine the signal transduction pathways involved, second messenger analogs were tested for their ability to mimic the effects of PTH. 8-Bromo-cAMP and phorbol 12-myristate 13-acetate (PMA) caused increases in the abundance of c-fos and c-jun transcripts. Ionomycin had no effect on the expression of these genes. Pretreatment of the cells with PMA resulted in a decrease in basal c-jun expression, but did not alter the PTH-mediated increase in c-fos, c-jun, or matrix metalloproteinase-1 mRNAs.(ABSTRACT TRUNCATED AT 250 WORDS).

Non-NASA Center↗
NASA NTRS2001

TP53-dependent chromosome instability is associated with transient reductions in telomere length in immortal telomerase-positive cell lines

Telomere shortening in telomerase-negative somatic cells leads to the activation of the TP53 protein and the elimination of potentially unstable cells. We examined the effect of TP53 gene expression on both telomere metabolism and chromosome stability in immortal, telomerase-positive cell lines. Telomere length, telomerase activity, and chromosome instability were measured in multiple clones isolated from three related human B-lymphoblast cell lines that vary in TP53 expression; TK6 cells express wild-type TP53, WTK1 cells overexpress a mutant form of TP53, and NH32 cells express no TP53 protein. Clonal variations in both telomere length and chromosome stability were observed, and shorter telomeres were associated with higher levels of chromosome instability. The shortest telomeres were found in WTK1- and NH32-derived cells, and these cells had 5- to 10-fold higher levels of chromosome instability. The primary marker of instability was the presence of dicentric chromosomes. Aneuploidy and other stable chromosome alterations were also found in clones showing high levels of dicentrics. Polyploidy was found only in WTK1-derived cells. Both telomere length and chromosome instability fluctuated in the different cell populations with time in culture, presumably as unstable cells and cells with short telomeres were eliminated from the growing population. Our results suggest that transient reductions in telomere lengths may be common in immortal cell lines and that these alterations in telomere metabolism can have a profound effect on chromosome stability. Copyright 2000 Wiley-Liss, Inc.

Non-NASA Center↗
DOE OSTI2020

Geometry-Dependent Solidification Regimes in Metal Additive Manufacturing

Recent modeling and experimental work in additive manufacturing has suggested that cross-sectional geometry may play a significant role in the local development of the solidification structure through its influence on the heat source path. This effect has been rationalized as the transition from a quasi-static point heat source regime, to a regime dominated by the quasi-static motion of an equivalent line source. This work provides a simple analytical framework for determining the conditions under which a system transitions between these regimes. Here, a transient semi-analytical heat transfer model is used to examine a wide range of process conditions and material properties. A simple analytical expression is derived and shown to accurately predict the transition between solidification regimes over these conditions. The functional form of this expression is then used to help understand the importance of various material properties, process parameters, and geometric factors on the characteristics of the solidification conditions. This approach may be used as a simple guideline for optimizing process conditions in response to variations in cross-sectional geometry to produce more consistent microstructural distributions in additively manufactured components.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Combined influence of unsteady free stream velocity and free stream turbulence on stagnation point heat transfer

An analysis is presented to study the combined effects of transient free stream velocity and free stream turbulence on heat transfer at a stagnation point over a cylinder situated in a crossflow. An expression for the eddy diffusivity has been formulated and the governing momentum and energy equations are integrated by means of the steepest descent method. The numerical results for the heat transfer rate are correlated by a turbulence parameter. It has been found that the stagnation point heat transfer rate increases with increasing free stream turbulence intensity.

Gorla, R. S. R.↗
NASA NTRS2017

Imaging of Earthquake Faults Using Small UAVs as a Pathfinder for Air and Space Observations

Large earthquakes cause billions of dollars in damage and extensive loss of life and property. Geodetic and topographic imaging provide measurements of transient and long-term crustal deformation needed to monitor fault zones and understand earthquakes. Earthquake-induced strain and rupture characteristics are expressed in topographic features imprinted on the landscapes of fault zones. Small UAVs provide an efficient and flexible means to collect multi-angle imagery to reconstruct fine scale fault zone topography and provide surrogate data to determine requirements for and to simulate future platforms for air- and space-based multi-angle imaging.

Donnellan, Andrea↗
NASA NTRS1940

Transient Effects of the Wing Wake on the Horizontal Tail

An investigation was made of the effect of the wing wake on the lift of the horizontal tail surfaces. In the development of expressions for this effect, the growth of wing circulation and wing wake, the time interval represented by the tail length, and the development of lift by the rail were considered. The theory has been applied to a specific case to show the magnitude of the effect to be expected. It is shown that, for motions below a certain frequency, the development of lift by the tail may be represented by a simple lag function. The lag is, however, somewhat greater than that indicated by the rail length.

Jones, Robert T↗
DOE OSTI2024

Transient Stability Analysis of Direct Droop-Controlled Grid-Forming Inverter with Current Clipping as Current Limiting Control

This paper investigates the transient stability of the direct droop-controlled grid-forming (GFM) inverter which employs the current clipping-based approach for overcurrent limitation. An equivalent circuit model of the direct-droop GFM inverter with current clipping is developed for this purpose. It is shown that during overcurrent conditions, the GFM inverter with current clipping acts as a voltage source with a virtual resistance behind the inverter filters. To compute the parameters of this virtual resistance an analytical expression is given in the paper. Then utilizing the developed circuit, a criteria to exit current limiting during post-fault conditions is given. The developed analytical approaches are then validated through electromagnetic transient (EMT) simulation results in PSCAD software and finally concluding remarks are drawn.

Mohiuddin, Sheik Mohammad↗
NASA NTRS1999

Developmental regulation of the gene for chimeric calcium/calmodulin-dependent protein kinase in anthers

Chimeric Ca(2+)/calmodulin-dependent protein kinase (CCaMK) was cloned from developing anthers of lily (Lilium longiflorum Thumb. cv. Nellie White) and tobacco (Nicotiana tabacum L. cv. Xanthi). Previous biochemical characterization and structure/function studies had revealed that CCaMK has dual modes of regulation by Ca(2+) and Ca(2+)/calmodulin. The unique structural features of CCaMK include a catalytic domain, a calmodulin-binding domain, and a neural visinin-like Ca(2+)-binding domain. The existence of these three features in a single polypeptide distinguishes it from other kinases. Western analysis revealed that CCaMK is expressed in a stage-specific manner in developing anthers. Expression of CCaMK was first detected in pollen mother cells and continued to increase, reaching a peak around the tetrad stage of meiosis. Following microsporogenesis, CCaMK expression rapidly decreased and at later stages of microspore development, no expression was detected. A tobacco genomic clone of CCaMK was isolated and transgenic tobacco plants were produced carrying the CCaMK promoter fused to the beta-glucuronidase reporter gene. Both CCaMK mRNA and protein were detected in the pollen sac and their localizations were restricted to the pollen mother cells and tapetal cells. Consistent results showing a stage-specific expression pattern were obtained by beta-glucuronidase analysis, in-situ hybridization and immunolocalization. The stage- and tissue-specific appearance of CCaMK in anthers suggests that it could play a role in sensing transient changes in free Ca(2+) concentration in target cells, thereby controlling developmental events in the anther.

NASA Discipline Plant Biology↗
NASA NTRS2016

Gene Expression and Structural Skeletal Responses to Long-Duration Simulated Microgravity in Rats

Spaceflight has deleterious effects on skeletal structure and function, specifically causingprofound loss in bone mass, density, and strength, as well as changes in expression levels of genes related to oxidative stress [Hyeon et al., Smith et al.]. It is known that bone resorption remains elevated after spaceflight and that bone density and strength fail to recover completely even years following spaceflight [Smith et al., Carpenter et al.]. However, our current understanding of the signaling pathways and molecular mechanisms that control bone loss and that link oxidative stress, bone resorption, and mechanical unloading of skeletal tissue is incomplete. Here, we aim to examine skeletal responses to simulated long-duration spaceflight on bone loss using the ground-based hindlimb unloading (HU) model in adult (9 months old) male rats. We hypothesized that simulated microgravity leads to the temporal regulation of oxidative-defense genes and pro-osteoclastogenic factors, showing progression and eventual plateau during long-term unloading, and that transient changes at early timepoints in these pathways precede skeletal adaptations to long-duration unloading. We will identify oxidativestress and bone resorption-related changes using global gene expression analysis (Affymetrix arrays) for both acute (within 14 days) and long-term timepoints (90 days). We will also use quantitative PCR to examine changes in expression of genes related to oxidative metabolism (e.g. Nrf2, SOD-1), bone turnover (resorption and formation markers, e.g. TRAP, osteocalcin respectively, SOST), and osteoclastogenesis (e.g. RANKL, OPG) at both early and late timepoints. We will then use detailed microarchitectural and structural analysis through microcomputed tomography to relate gene expression changes with structural changes in bone, expecting that plateaus in gene expression correlate with long-term changes in bone microarchitecture.

Rael, Victoria E.↗
NASA NTRS2000

Effects of orbital spaceflight on human osteoblastic cell physiology and gene expression

During long-term spaceflight, astronauts lose bone, in part due to a reduction in bone formation. It is not clear, however, whether the force imparted by gravity has direct effects on bone cells. To examine the response of bone forming cells to weightlessness, human fetal osteoblastic (hFOB) cells were cultured during the 17 day STS-80 space shuttle mission. Fractions of conditioned media were collected during flight and shortly after landing for analyses of glucose utilization and accumulation of type I collagen and prostaglandin E(2) (PGE(2)). Total cellular RNA was isolated from flight and ground control cultures after landing. Measurement of glucose levels in conditioned media indicated that glucose utilization occurred at a similar rate in flight and ground control cultures. Furthermore, the levels of type I collagen and PGE(2) accumulation in the flight and control conditioned media were indistinguishable. The steady-state levels of osteonectin, alkaline phosphatase, and osteocalcin messenger RNA (mRNA) were not significantly changed following spaceflight. Gene-specific reductions in mRNA levels for cytokines and skeletal growth factors were detected in the flight cultures using RNase protection assays. Steady-state mRNA levels for interleukin (IL)-1alpha and IL-6 were decreased 8 h following the flight and returned to control levels at 24 h postflight. Also, transforming growth factor (TGF)-beta(2) and TGF-beta(1) message levels were modestly reduced at 8 h and 24 h postflight, although the change was not statistically significant at 8 h. These data suggest that spaceflight did not significantly affect hFOB cell proliferation, expression of type I collagen, or PGE(2) production, further suggesting that the removal of osteoblastic cells from the context of the bone tissue results in a reduced ability to respond to weightlessness. However, spaceflight followed by return to earth significantly impacted the expression of cytokines and skeletal growth factors, which have been implicated as mediators of the bone remodeling cycle. It is not yet clear whether these latter changes were due to weightlessness or to the transient increase in loading resulting from reentry.

Non-NASA Center↗
NASA NTRS1974

Theoretical investigations on plasma processes in the Kaufman thruster

An analysis of the sputtering of metal surfaces and grids by ions of medium energies is given and it is shown that an exact, nonlinear, hyperbolic wave equation for the temperature field describes the transient transport of heat in metals. Quantum statistical and perturbation theoretical analysis of surface sputtering by low energy ions are used to develop the same expression for the sputtering rate. A transport model is formulated for the deposition of sputtered atoms on system components. Theoretical efforts in determining the potential distribution and the particle velocity distributions in low pressure discharges are briefly discussed.

Wilhelm, H. E.↗
NASA NTRS1992

The effect of severe storms on the ice cover of the northern Tatarskiy Strait

Passive microwave images from the Special Sensor Microwave Imager are used to study the volume of ice and sea-bottom water in the Japan Sea as affected by winds and severe storms. The data set comprises brightness temperatures gridded on a polar stereographic projection, and the processing is accomplished with a linear algorithm by Cavalieri et al. (1983) based on the vertically polarized 37-GHz channel. The expressions for calculating heat fluxes and downwelling radiation are given, and ice-cover fluctuations are correlated with severe storm events. The storms generate large transient polynya that occur simultaneously with the strongest heat fluxes, and severe storms are found to contribute about 25 percent of the annual introduction of 25 cu km of ice in the region. The ice production could lead to the renewal of enough sea-bottom water to account for the C-14 data provided, and the generation of Japan Sea bottom water is found to vary directly with storm activity.

Martin, Seelye↗
NASA NTRS1998

Calcium signals and calcium channels in osteoblastic cells

Calcium (Ca2+) channels are present in non-excitable as well as in excitable cells. In bone cells of the osteoblast lineage, Ca2+ channels play fundamental roles in cellular responses to external stimuli including both mechanical forces and hormonal signals. They are also proposed to modulate paracrine signaling between bone-forming osteoblasts and bone-resorbing osteoclasts at local sites of bone remodeling. Calcium signals are characterized by transient increases in intracellular Ca2+ levels that are associated with activation of intracellular signaling pathways that control cell behavior and phenotype, including patterns of gene expression. Development of Ca2+ signals is a tightly regulated cellular process that involves the concerted actions of plasma membrane and intracellular Ca2+ channels, along with Ca2+ pumps and exchangers. This review summarizes the current state of knowledge concerning the structure, function, and role of Ca2+ channels and Ca2+ signals in bone cells, focusing on the osteoblast.

Non-NASA Center↗
NASA NTRS2008

Numerical Determination of Critical Conditions for Thermal Ignition

The determination of ignition or thermal explosion in an oxidizing porous body of material, as described by a dimensionless reaction-diffusion equation of the form .tu = .2u + .e-1/u over the bounded region O, is critically reexamined from a modern perspective using numerical methodologies. First, the classic stationary model is revisited to establish the proper reference frame for the steady-state solution space, and it is demonstrated how the resulting nonlinear two-point boundary value problem can be reexpressed as an initial value problem for a system of first-order differential equations, which may be readily solved using standard algorithms. Then, the numerical procedure is implemented and thoroughly validated against previous computational results based on sophisticated path-following techniques. Next, the transient nonstationary model is attacked, and the full nonlinear form of the reaction-diffusion equation, including a generalized convective boundary condition, is discretized and expressed as a system of linear algebraic equations. The numerical methodology is implemented as a computer algorithm, and validation computations are carried out as a prelude to a broad-ranging evaluation of the assembly problem and identification of the watershed critical initial temperature conditions for thermal ignition. This numerical methodology is then used as the basis for studying the relationship between the shape of the critical initial temperature distribution and the corresponding spatial moments of its energy content integral and an attempt to forge a fundamental conjecture governing this relation. Finally, the effects of dynamic boundary conditions on the classic storage problem are investigated and the groundwork is laid for the development of an approximate solution methodology based on adaptation of the standard stationary model.

Luo, W.↗
DOE OSTI2022

CsbZIP2-miR9748-CsNPF4.4 Module Mediates High Temperature Tolerance of Cucumber Through Jasmonic Acid Pathway

High temperature stress seriously affects the growth of cucumber seedlings, and even leads to a decline in yield and quality. miRNAs have been shown to be involved in regulating the response to stress in plants, but little is known about its effects on cucumber high temperature stress tolerance. Here, we found that high temperature stress induced the expression of miR9748 in cucumber. Overexpression of cucumber miR9748 in Arabidopsis improved high temperature tolerance. Transcriptome analysis revealed that miR9748 might mediate high temperature tolerance through plant hormone signal pathway. 5′ RNA ligase-mediated rapid amplification of cDNA ends (5′ RLM-RACE) and transient transformation technology demonstrated that CsNPF4.4 was the target gene of miR9748. CsNPF4.4 overexpression plants decreased high temperature tolerance accompanied by reducing the content of jasmonic acid (JA), but alleviated by foliar application of methyl jasmonate, indicating that CsNPF4.4 negatively regulated high temperature stress tolerance through inhibition JA signal pathway. Furthermore, high temperature stress also increased the expression level of CsbZIP2 . Yeast one-hybrid and dual-luciferase assays showed that CsbZIP2 directly bound to the promoter of MIR9748 to induce its expression. Taken together, our results indicated that CsbZIP2 directly regulated miR9748 expression to cleave CsNPF4.4 to mediate high temperature tolerance through JA pathway.

Li, Lan↗
DOE OSTI2022

Noise-Resilient Quantum Machine Learning for Stability Assessment of Power Systems

Transient stability assessment (TSA) is a cornerstone for resilient operations of todays interconnected power grids. This paper is a confluence of quantum computing, data science and machine learning to potentially address the power system TSA issue. Here, we devise a quantum TSA (QTSA) method to enable scalable and efficient data-driven transient stability prediction for bulk power systems, which is the first attempt to tackle the TSA issue with quantum computing. Our contributions are three-fold: 1) A high expressibility, low-depth (HELD) quantum circuit is designed for accurate and noise-resilient TSA; 2) A quantum natural gradient descent algorithm is developed for efficient HELD circuit training; 3) A systematical analysis on QTSAs performance under various quantum factors is per-formed. QTSA underpins a foundation of quantum-enabled and data-driven power grid stability analytics. It renders the intractable TSA straightforward and effortless in the Hilbert space, and therefore provides stability information for power system operations. Extensive experiments on quantum simulators and real quantum computers verify the accuracy, noise-resilience, scalability and universality of QTSA.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
NASA NTRS1973

Quantum theory of an optical maser. VI - Transient behavior.

The transient behavior of a laser is discussed using the quantum theory as did Scully and Lamb. The formal solution of the density-matrix equation is expressed in terms of exponentially decaying eigenmodes. Some of the lower decay constants are obtained numerically. The equations for the moments of the density matrix are then derived and solved by a truncation method. The equations of motion are integrated numerically for the case where the average number of photons in a laser cavity has the realistically large value 1.3 x 100,000. An alternative Fokker-Planck-equation approach is discussed.

Wang, Y. K.↗
NASA NTRS1975

An approximation technique for predicting the transient response of a second order nonlinear equation

An approximation technique has been developed for determining the transient response of a nonlinear dynamic system. The nonlinearities in the system which has been considered appear in the system's dissipation function. This function was expressed as a second order polynomial in the system's velocity. The developed approximation is an extension of the classic Kryloff-Bogoliuboff technique. Two examples of the developed approximation are presented for comparative purposes with other approximation methods.

Laurenson, R. M.↗