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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Neural Correlates of Birth: Labor Contractions Induce C-Fos Expression In Newborn Rat Brain

At birth, the newborn mammal must make rapid adaptations to the extrauterine environment to survive. We have previously shown that labor contractions augment the appearance of adaptive responses at birth, viz., postpartum breathing and the onset of suckling. Since neuronal activity has been shown to upregulate the activity of immediate early genes (IEGs) in the brain, we analyzed the neural distribution of c-Fos protein expression in newborn rats using immunohistochemistry. Previous studies have reported a burst of c-Fos mRNA expression in mouse and rat brain at birth however relationships to labor and delivery have not been examined. In the present study, we exposed near-term rat fetuses to elements of the vaginal birth process: 1) Simulated labor contractions. 2) Postpartum cooling (22 deg C). 3) Umbilical cord occlusion. and 4) Stroking to mimic postpartum licking by the dam. Cardinally delivered newborns (VG) were compared with those delivered by cesarean section following either prenatal exposure to compressions (C) [simulated labor contractions], or no compressions (NC) [no labor contractions]. Similar patterns of c-fos activation were observed throughout hypothalamic and thalamic nuclei, hippocampus and cerebral cortex in VG and C newborns that were not apparent in NC newborns. Our results indicate that labor contractions play a role in the induction of widespread neural activation in the newborn brain.

Ronca, A. E.↗
NASA NTRS1981

Oxidation-induced contraction and strengthening of boron fibers

An investigation of the physical and mechanical effects of thermal treatment in a controlled oxygen-argon atmosphere on boron fibers is reported, with attention to the optimization of such treatment as a secondary processing method for improvement of fiber strength. The strengthening mechanism is comprised of an oxidation-induced axial contraction of the fiber, accompanied by axial compression of strength-limiting flaws within the fiber's tungsten boride core. It was found that after an oxidation contraction of 0.3% near 900 C, and a slight surface etch near 100 C, the average tensile strength of 203-micron fibers increased from 500 to 800 ksi. Various physical observations are used to develop mechanistic models of oxidation, contraction, and the formation of new flaws in the boron sheath at contractions greater than 0.3%.

Dicarlo, J. A.↗
NASA NTRS1983

Rapid distortion of small-scale turbulence by an axisymmetric contraction

The rapid distortion of small-scale turbulence by an axisymmetric internal contracting flow has been investigated. The analysis is an example of the modern version of rapid distortion theory in that the effects of vortex bending and tilting are included. On the axis of symmetry, the classical results are recovered. The longitudinal and lateral velocity components are suppressed and amplified, respectively, with increasing contraction ratio. These effects are enhanced with increasing radial position. The numerical calculations also show that the correlation between the streamwise and radial velocity components increases monotonically with respect to both the radial location and the contraction ratio. The longitudinal and lateral one-dimensional spectra show a shift towards higher and lower wavenumbers, respectively, as the contraction ratio increases. Here, these effects become less pronounced for larger radii. These results also show that the downstream longitudinal integral length scale based on the streamwise velocity as well as the one based on the transverse velocity increase with the radial coordinate.

Hultgren, L. S.↗
NASA NTRS1985

The effect of contraction on a homogeneous turbulent shear flow

In the present study, a homogeneous flow was generated and allowed to reach its asymptotic state. A two-dimensional contraction was inserted a short distance downstream. Both mean velocity and turbulence-stress profiles (normal and shear) were measured at several points along the flow direction. The pressure-strain terms were evaluated from the energy balance made along the wind-tunnel axis. On the basis of the obtained results, it is concluded that a uniformly sheared turbulent flow with approximate transverse homogeneity remains in its condition at all stages of its development through a two-dimensional contraction. Small deviations from homogeneity observed upstream of contraction become much less visible towards the end of contraction. The mean-flow development can be predicted adequately by the Bernoulli equation.

Sreenivasan, K. R.↗
NASA NTRS1985

The application of contraction theory to an iterative formulation of electromagnetic scattering

Contraction theory is applied to an iterative formulation of electromagnetic scattering from periodic structures and a computational method for insuring convergence is developed. A short history of spectral (or k-space) formulation is presented with an emphasis on application to periodic surfaces. To insure a convergent solution of the iterative equation, a process called the contraction corrector method is developed. Convergence properties of previously presented iterative solutions to one-dimensional problems are examined utilizing contraction theory and the general conditions for achieving a convergent solution are explored. The contraction corrector method is then applied to several scattering problems including an infinite grating of thin wires with the solution data compared to previous works.

Brand, J. C.↗
NASA NTRS1987

Experimental evaluation of honeycomb/screen configurations and short contraction section for NASA Lewis Research Center's altitude wind tunnel

An experimental investigation was conducted in the high speed leg of the 0.1 scale model of the proposed Altitude Wind Tunnel to evaluate flow conditioner configurations in the settling chamber and their effect on the flow through the short contraction section. The lowest longitudinal turbulence intensity measured at the contraction-section entrance, 1.2%, was achieved with a honeycomb plus three fine-mesh screens. Turbulence intensity in the test section was estimated to be between 0.1 and 0.2% with the honeycomb plus three fine mesh screens in the settling chamber. Adding screens, however, adversely affected the total pressure profile, causing a small defect near the centerline at the contraction section entrance. No significant boundary layer separation was evident in the short contraction section.

Burley, Richard R.↗
NASA NTRS1994

An analysis of cost overruns on defense acquisition contracts

This article examines the history of cost overruns reported on 64 completed defense contracts. Its purpose is to formally test the observation of the Under Secretary. Results confirm the observation at the 95 percent level of confidence, and were generally insensitive to the contract type (price, cost), the contract phase (development, production), the type of weapon system (air, ground, sea), and the armed forces service (Air Force, Army, Navy) that managed the contract. After a review of terminology, concepts, and related research for those unfamiliar with the area, the methodology, results, and managerial implications are described.

Christensen, David S.↗
NASA NTRS1995

Observational and numerical studies of extreme frontal scale contraction

The general objective of this effort is to increase understanding of how frontal scale contraction processes may create and sustain intense mesoscale precipitation along intensifying cold fronts. The five-part project (an expansion of the originally proposed two-part project) employed conventional meteorological data, special mesoscale data, remote sensing measurements, and various numerical models. First an idealized hydrostatic modeling study of the scale contraction effects of differential cloud cover on low-level frontal structure and dynamics was completed and published in a peer-reviewed journal. The second objective was to complete and publish the results from a three dimensional numerical model simulation of a cold front in which differential sensible heating related to cloud coverage patterns was apparently crucial in the formation of a severe frontal squall line. The third objective was to use a nonhydrostatic model to examine the nonlinear interactions between the transverse circulation arising from inhomogeneous cloud cover, the adiabatic frontal circulation related to semi-geostrophic forcing, and diabatic effects related to precipitation processes, in the development of a density current-like microstructure at the leading edge of cold fronts. Although the development of a frontal model that could be used to initialize such a primitive equation model was begun, we decided to focus our efforts instead on a project that could be successfully completed in this short time, due to the lack of prospects for continued NASA funding beyond this first year (our proposal was not accepted for future funding). Thus, a fourth task was added, which was to use the nonhydrostatic model to test tentative hypotheses developed from the most detailed observations ever obtained on a density current (primarily sodar and wind profiler data). These simulations were successfully completed, the findings were reported at a scientific conference, and the results have recently been submitted to a peer-reviewed journal. The fifth objective was to complete the analysis of data collected during the Cooperative Oklahoma Profiler Studies (COPS-91) field project, which was supported by NASA. The analysis of the mesoscale surface and sounding data, Doppler radar imagery, and other remote sensing data from multi frequency wind profiler, microwave radiometer, and the Radio Acoustic Sounding System has been completed. This study is a unique investigation of processes that caused the contraction of a cold front to a microscale zone exhibiting an undular bore-like structure. Results were reported at a scientific conference and are being prepared for publication. In summary, considerable progress has been achieved under NASA funding in furthering our understanding of frontal scale contraction and density current - gravity wave interaction processes, and in utilizing models and remotely sensed data in such studies.

Koch, Steven E.↗
NASA NTRS2000

Effects of Adrenergic Blockade on Postpartum Adaptive Responses Induced by Labor Contractions

Prenatal exposure to labor contractions augments the expression of postnatal adaptive responses in newborn rats. Near-term rat fetuses exposed prenatally to simulated labor contractions and delivered by cesarean section breath and attach to nipples at greater frequencies than non-stimulated fetuses. Plasma NE (norepinephrine) and EPI (epinephrine) was significantly elevated in newborn rats exposed to vaginal birth or simulated labor contractions (compressions) with cesarean delivery as compared to non-compressed fetuses. In the present study, we investigated adrenergic mechanisms underlying labor-induced postnatal adaptive responses. Following spinal transection of late pregnant rat dams, fetuses were administered neurogenic or non-neurogenic adrenergic blockade: 1) bretylium (10 mg/kg sc) to prevent sympathetic neuronal release, 2) hexamethonium (30 mg/kg) to produce ganglionic blockade, 3) phenoxybenzanune (10mg/kg sc), an a- adrenergic receptor antagonist, 4) ICI-118551, 10 mg/kg sc), a b receptor antagonist, or 5) vehicle alone. Fetuses were either compressed (C) or non-compressed (NC) prior to cesarean delivery. a- and b- adrenergic antagonists reduced respiration and nipple attachment rates while sympathetic and vehicle alone did not. These results provide additional support for the hypothesis that adaptive neonatal effects of labor contractions are mediated by adrenal and extra-adrenal catecholamines.

Ronca, April E.↗
NASA NTRS2002

Labor Contractions Enhance Oxygenation and Behavioral Activity of Newborn Rat Pups

Labor contractions help instigate behavioral responses at birth (viz., breathing and suckling) that are vital for the newborn's adaptation to the extrauterine world (Ronca et al., 1996). In the present study, we analyzed the role of labor contractions in postpartum oxygenation and behavioral activity of newborn rat pups. Newborns were observed following either vaginal (V) or cesarean delivery. For cesarean delivery, day 21 pregnant dams' were administered a spinal transaction to eliminate lower body sensation, a laparotomy was performed and the uterus was maintained in a heated (37.5 C) bath. Four rat fetuses in one of the dams' paired uterine horn were compressed (C) to Simulate labor contractions (20 sec/min for 10 min) while four fetuses in the opposite horn were not compressed (NC). Fetuses were surgically removed from the uterus, stroked with a soft brush to mimic postnatal licking by the dam, the umbilical cord occluded. Pups were exposed to room temperature (22 C) for one hr, then nest temperature (33 C) for one hr. PO2, CO2, and O2, saturation were determined at 0, 30, 60, or 120 min post delivery using a blood gas analyzer. V and C delivered neonates showed comparable rates of PO2, CO2 and O2 saturation whereas NC neonates showed depressed levels at all time points (p<0.05). Respiratory rates of V, C and NC neonates increased significantly (p<0.05) over the first two postpartum hrs and did not differ across groups. Postpartum behavioral activity was significantly greater in V and C conditions and positively correlated with postnatal oxygenation. These findings provide further evidence for importance of labor contractions in early postpartum adaptation.

Mills, N. A.↗
NASA NTRS2016

Magnetic-Island Contraction and Particle Acceleration in Simulated Eruptive Solar Flares

The mechanism that accelerates particles to the energies required to produce the observed high-energy impulsive emission in solar flares is not well understood. Drake et al. proposed a mechanism for accelerating electrons in contracting magnetic islands formed by kinetic reconnection in multi-layered current sheets (CSs). We apply these ideas to sunward-moving flux ropes (2.5D magnetic islands) formed during fast reconnection in a simulated eruptive flare. A simple analytic model is used to calculate the energy gain of particles orbiting the field lines of the contracting magnetic islands in our ultrahigh-resolution 2.5D numerical simulation. We find that the estimated energy gains in a single island range up to a factor of five. This is higher than that found by Drake et al. for islands in the terrestrial magnetosphere and at the heliopause, due to strong plasma compression that occurs at the flare CS. In order to increase their energy by two orders of magnitude and plausibly account for the observed high-energy flare emission, the electrons must visit multiple contracting islands. This mechanism should produce sporadic emission because island formation is intermittent. Moreover, a large number of particles could be accelerated in each magneto hydro dynamic-scale island, which may explain the inferred rates of energetic-electron production in flares. We conclude that island contraction in the flare CS is a promising candidate for electron acceleration in solar eruptions.

Guidoni, S. E.↗
NASA NTRS1976

The formation of Saturn's satellites and rings, as influenced by Saturn's contraction history

The paper investigates constraints imposed on the ice content of Saturn's satellites and rings by the planet's high luminosity during the early part of its quasi-equilibrium contraction phase. It is assumed that the addition of ices to the satellites was not completed until after the start of the quasi-equilibrium contraction and that the condensation of ices ceased at the same time within the primordial nebulae of Jupiter and Saturn. Using previously derived limits on the time of condensation cessation for Jupiter's system, the following tentative conclusions are made: (1) Titan is the innermost satellite at whose position a methane-containing ice could condense; (2) water ice could have condensed at the positions of all the satellites; (3) the systematic decrease in the mass of the regular satellites with decreasing distance from the planet may have been caused, in part, by the larger time intervals, for the closer satellites, between the start of contraction and the first condensation of ices at their positions; and (4) ammonia ices, primarily NH4SH, were able to condense at the positions of all but the innermost satellites. It is also shown that water ice could have condensed in the region of the rings near the end of the condensation period.

Pollack, J. B.↗
NASA NTRS1977

Earth resources-regional transfer activity contracts review

A regional transfer activity contracts review held by the Earth Resources Office was summarized. Contracts in the earth resources field primarily directed toward applications of satellite data and technology in solution of state and regional problems were reviewed. A summary of the progress of each contract was given in order to share experiences of researchers across a seven state region. The region included Missouri, Kentucky, Tennessee, Mississippi, Alabama, Georgia, and North Carolina. Research in several earth science disciplines included forestry, limnology, water resources, land use, geology, and mathematical modeling. The use of computers for establishment of information retrieval systems was also emphasized.

Bensko, J., Jr.↗
NASA NTRS1978

Steady flow of a non-Newtonian fluid through a contraction

A steady-state analysis is conducted to examine the basic flow structure of a non-Newtonian fluid in a domain including an inflow region, a contraction region, and an outflow region. A Cartesian grid system is used throughout the entire flow domain, including the contraction region, thus creating an irregular grid cell structure adjacent to the curved boundary. At node points adjacent to the curved boundary symmetry conditions are derived for the different flow variables in order to solve the governing difference equations. Attention is given to the motion and non-Newtonian constitutive equations, the boundary conditions, the numerical modeling of the non-Newtonian equations, the stream function contour lines for the non-Newtonian fluid, the vorticity contour lines for the non-Newtonian fluid, the velocity profile across the contraction, and the shear stress contour lines for the non-Newtonian fluid.

Gatski, T. B.↗
NASA NTRS1979

Generalized disks of contractivity for explicit and implicit Runge-Kutta methods

The A-contractivity of Runge-Kutta methods with respect to an inner product norm was investigated thoroughly by Butcher and Burrage (who used the term B-stability). Their theory is extended to contractivity in a region bounded by a circle through the origin. The largest possible circle is calculated for many known explicit Runge-Kutta methods. As a rule it is considerably smaller than the stability region, and in several cases it degenerates to a point. It is shown that an explicit Runge-Kutta method cannot be contractive in any circle of this class if it is more than fourth order accurate.

Dahlquist, G.↗
NASA NTRS1981

Guidelines for cost control and analysis of cost-type research and development contracts

The cost information which should be obtained from a contractor(s) on a major, cost type research and development contract(s), and the analyses and effective use of these data are discussed. Specific type(s) of information which should be required, methods for analyzing such information, and methods for effectively using the results of such analyses to enhance NASA contract and project management are included. The material presented is based primarily on the principal methods which have been effectively used in the management of major cost type research and development contracts.

Sibbers, C. W.↗
NASA NTRS1985

Role of muscle mass and mode of contraction in circulatory responses to exercise

The roles of the mode of contraction (dynamic or static) and active muscle mass in determining the cardiovascular response to exercise has been investigated experimentally in six normal men. Exercise consisted of static handgrip and dynamic handgrip exercise, and static and dynamic knee extension for a period of six minutes. Observed increases in mean arterial pressure after exercise were similar for each mode of contraction, but larger for knee extension than handgrip exercise. Cardiac output increased more for dynamic than for static exercise and for each mode more for knee exercise than for handgrip exercise. Systemic resistance was found to be lower for dynamic than for static exercise, and to decrease from resisting levels by about one third during dynamic knee extension. It is shown that the magnitude of cardiovascular response is related to active muscle mass, but is independent of the contraction mode. Equalization of cardiovascular response was achieved by proportionately larger increases in cardiac output during dynamic exercise. The complete experimental results are given in a table.

Lewis, S. F.↗
NASA NTRS1986

Short time Fourier analysis of the electromyogram - Fast movements and constant contraction

Short-time Fourier analysis was applied to surface electromyograms (EMG) recorded during rapid movements, and during isometric contractions at constant forces. A portion of the data to be transformed by multiplying the signal by a Hamming window was selected, and then the discrete Fourier transform was computed. Shifting the window along the data record, a new spectrum was computed each 10 ms. The transformed data were displayed in spectograms or 'voiceprints'. This short-time technique made it possible to see time-dependencies in the EMG that are normally averaged in the Fourier analysis of these signals. Spectra of EMGs during isometric contractions at constant force vary in the short (10-20 ms) term. Short-time spectra from EMGs recorded during rapid movements were much less variable. The windowing technique picked out the typical 'three-burst pattern' in EMG's from both wrist and head movements. Spectra during the bursts were more consistent than those during isometric contractions. Furthermore, there was a consistent shift in spectral statistics in the course of the three bursts. Both the center frequency and the variance of the spectral energy distribution grew from the first burst to the second burst in the same muscle. The analogy between EMGs and speech signals is extended to argue for future applicability of short-time spectral analysis of EMG.

Hannaford, Blake↗