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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Product energy distributions and energy partitioning in O atom reactions on surfaces

Surface reactions involving O atoms are likely to be highly exoergic, with different consequences if energy is channeled mostly to product molecules or surface modes. Thus the surface may become a source of excited species which can react elsewhere, or a sink for localized heat deposition which may disrupt the surface. The vibrational energy distribution of the product molecule contains strong clues about the flow of released energy. Two instructive examples of energy partitioning at surfaces are the Pt catalyzed oxidations: (1) C(ads) + O(ads) yields CO* (T is greater than 1000 K); and (2) CO(ads) + O(gas) yields CO2* (T is approx. 300 K). The infrared emission spectra of the excited product molecules were recorded and the vibrational population distributions were determined. In reaction 1, energy appeared to be statistically partitioned between the product CO and several Pt atoms. In reaction 2, partitioning was non-statistical; the CO2 asymmetric stretch distribution was inverted. In gas reactions these results would indicate a long lived and short lived activated complex. The requirement that Pt be heated in O atoms to promote reaction of atomic O and CO at room temperature is specifically addressed. Finally, the fraction of released energy that is deposited in the catalyst is estimated.

Halpern, Bret↗
NASA NTRS2020

Tidal Disruptions of Main-sequence Stars. IV. Relativistic Effects and Dependence on Black Hole Mass

Using a suite of fully relativistic hydrodynamic simulations applied to main-sequence stars with realistic internal density profiles, we examine full and partial tidal disruptions across a wide range of black hole mass( MM105 105BH7)and stellar mass (MM0.33) as larger MBH leads to stronger relativistic effects. For fixed Må, as MBH increases, the ratio of the maximum pericenter distance yielding full disruptions (t) to its Newtonian prediction rises rapidly, becoming triple the Newtonian value for= ́MM510BH7, while the ratio of the energy width of the stellar debris for full disruptions to the Newtonian prediction decreases steeply, resulting in a factor of 2 correction at= ́MM510BH7. We provide approximate formulae that express the relativistic corrections of both t and the energy width relative to their Newtonian approximate estimates. For partial disruptions, we find that the fractional remnant mass for a given ratio of the pericenter to t is higher for larger MBH. These results have several implications. As MBH increases above~M107, the cross section for complete disruptions is suppressed by competition with direct capture. However, the cross-section ratio for partial to complete disruptions depends only weakly on MBH. The relativistic correction to the debris energy width delays the time of peak mass-return rate and diminishes the magnitude of the peak return rate. ForMM10BH7, the MBH-dependence of the full disruption cross section and the peak mass-return rate and time is influenced more by relativistic effects than by Newtonian dynamics.

Taeho Ryu↗
NASA NTRS2003

Cognitive deficits induced by 56Fe radiation exposure

Exposing rats to particles of high energy and charge (e.g., 56Fe) disrupts neuronal systems and the behaviors mediated by them; these adverse behavioral and neuronal effects are similar to those seen in aged animals. Because cognition declines with age, and our previous study showed that radiation disrupted Morris water maze spatial learning and memory performance, the present study used an 8-arm radial maze (RAM) to further test the cognitive behavioral consequences of radiation exposure. Control rats or rats exposed to whole-body irradiation with 1.0 Gy of 1 GeV/n high-energy 56Fe particles (delivered at the alternating gradient synchrotron at Brookhaven National Laboratory) were tested nine months following exposure. Radiation adversely affected RAM performance, and the changes seen parallel those of aging. Irradiated animals entered baited arms during the first 4 choices significantly less than did controls, produced their first error sooner, and also tended to make more errors as measured by re-entries into non-baited arms. These results show that irradiation with high-energy particles produces age-like decrements in cognitive behavior that may impair the ability of astronauts to perform critical tasks during long-term space travel beyond the magnetosphere. Published by Elsevier Science Ltd on behalf of COSPAR.

Non-NASA Center↗
NASA NTRS1982

Fragmentation of ice by low velocity impact

Low-velocity impact experiments (0.14 to 1 km/s) carried out in polycrystalline water ice targets at 257 and 81 K reveal interactions which are assigned to four fragmentation classes: cratering, erosion, disruption, and total fragmentation. The specific kinetic energies for the transitions between these classes are found to be about one to two orders of magnitude below those for silicate rocks. The mass vs. cumulative number distribution of fragments in the experiments is described by a simple power law, similar to that observed in fragmented rocks both in the laboratory and in nature. The logarithmic slopes of cumulative number vs. fragment weight range from -0.9 to -1.8; they decrease with increasing projectile energy and are approximately independent of target temperature. The shapes of fragments resulting from erosion and disruption of ice targets are found to be significantly less spherical for 257 K targets than for 81 K targets. Fragment sphericity increases with increasing projectile energy at 257 K; however, no similar trend is observed for 81 K ice.

Lange, M. A.↗
NASA NTRS2020

Tidal Disruptions of Main-sequence Stars. IV. Relativistic Effects and Dependence on Black Hole Mass

Using a suite of fully relativistic hydrodynamic simulations applied to main-sequence stars with realistic internal density profiles, we examine full and partial tidal disruptions across a wide range of black hole mass (10(exp 5)≤M(BH)/M(ʘ)≤5 x 10(exp 7) and stellar mass (0.3≤M(*)/M(ʘ)≤3) as larger M(BH) leads to stronger relativistic effects. For fixed M( ), as M(BH) increases, the ratio of the maximum pericenter distance yielding full disruptions ( ) to its Newtonian prediction rises rapidly, becoming triple the Newtonian value for M(BH)=5 x 10(exp 7)M(ʘ), while the ratio of the energy width of the stellar debris for full disruptions to the Newtonian prediction decreases steeply, resulting in a factor of 2 correction at M(BH)=5 x 10(exp 7)M(ʘ). We provide approximate formulae that express the relativistic corrections of both R(t) and the energy width relative to their Newtonian approximate estimates. For partial disruptions, we find that the fractional remnant mass for a given ratio of the pericenter to R(t) is higher for larger M(BH). These results have several implications. As M(BH) increases above ~10(exp 7)M(ʘ), the cross section for complete disruptions is suppressed by competition with direct capture. However, the cross-section ratio for partial to complete disruptions depends only weakly on M(BH). The relativistic correction to the debris energy width delays the time of peak mass-return rate and diminishes the magnitude of the peak return rate. For M(BH)≳10(exp 7)M(ʘ), the M(BH)-dependence of the full disruption cross section and the peak mass-return rate and time is influenced more by relativistic effects than by Newtonian dynamics.

Taeho Ryu↗
NASA NTRS1993

Collisions and close encounters between massive main-sequence stars

Smooth-particle hydrodynamics is used to investigate collisions and close encounters between two massive main-sequence stars. Approximate scaling relations and fitting formulas are given for the amount of mass loss and for the critical impact parameters for capture or merging. The more massive stars, which have smaller ratios of specific binding energy to the square of escape velocity, are more easily disrupted in collisions. As the relative velocity increases, the orbital energy of the colliding stars can only be dissipated by shock heating, and the critical capture radius decreases much faster than predicted by linear theory. The average fractional mass loss per collision in a cluster is found not to depend sensitively on the stellar velocity dispersion.

Lai, Dong↗
NASA NTRS1984

Mechanical models of close approaches and collisions of large protoplanets

In models of lunar origin by great impact, attention is usually paid to the hydrodynamic expansion resulting from the great amount of thermal energy. However, the source of this disruption is inevitably significant in a close approach between large bodies, it is to be expected that significant departures from simple hyperbolic orbits would occur even before impact. These departures could arise from mechanical effects, and hence purely mechanical models are worth pursuing. The most interesting results obtained for approach offsets are small multiples of the planet radius and approach velocities of a few kilometers/second. In an interaction between Mars and Earth sized protoplanets, most of the material ends in collision, but a few percent end in elliptic orbits and a few percent escape. Another model considered is an offset collision, arising from a wide range of approach velocities and offsets.

Kaula, W. M.↗
NASA NTRS1986

Hyper-resistivity produced by tearing mode turbulence

Tearing mode turbulence produces a hyperresistivity or effective anomalous electron viscosity. The hyperresistivity is calculated for the mean magnetic field quasi-linearly, and for long-wavelength modes using the direct interaction approximation. The hyperresistivity accounts for current relaxation in reversed-field pinch experiments, and gives a magnetic fluctuation scaling of S to the -1/3. It causes enhanced tearing mode growth rates in the turbulent phase of tokamak disruptions. In astrophysics, it limits magnetic energy growth because of the dynamo effect, and may explain rapid reconnection phenomena such as solar flares.

Strauss, H. R.↗
NASA NTRS2003

Coordination of Lower Limb Joints During Locomotion: The Effects of Vestibulo-Ocular Reflex Adaptation

Controlling locomotion while maintaining a stable gaze requires precise coordination between several, interdependent full-body sensorimotor subsystems (Bloomberg and Mulavara, 2003; McDonald, et al., 1997). The overall goal of this study is to determine how this full-body gaze stabilization system responds to adaptive changes in vestibuloocular reflex (VOR) function. Locomotion involves cyclical physical interactions (impacts) with the environment. Hence, focusing on a target and maintaining visual acuity during this activity may require mechanisms to manage the energy flow, so it does not disrupt the visual and vestibular sensory information processing that stabilizes gaze. It has been shown that increasing the difficulty of a gaze task (reading numbers on a screen as opposed to simply focusing on a central dot pattern) resulted in an increase in the amount of knee flexion movement during the critical phase immediately following the heel strike event (Mulavara and Bloomberg, 2003). The increase in knee flexion during the stance phase of the gait cycle has been suggested to function as a shock absorbing mechanism associated with the rapid weight transfer from the trailing to the leading leg during walking. To understand this full-body coordination, the relative contributions of each component and the resulting effects should be assessed. In this study, we hypothesized that VOR adaptation would result in a reorganization of the lower limb joint coordination during treadmill walking in a manner to facilitate the gaze stabilization task and preserve locomotor function.

Miller, Chris↗
NASA NTRS2014

Misconceptions of Electric Propulsion Aircraft and Their Emergent Aviation Markets

Over the past several years there have been aircraft conceptual design and system studies that have reached conflicting conclusions relating to the feasibility of full and hybrid electric aircraft. Some studies and propulsion discipline experts have claimed that battery technologies will need to improve by 10 to 20 times before electric aircraft can effectively compete with reciprocating or turbine engines. However, such studies have approached comparative assessments without understanding the compelling differences that electric propulsion offers, how these technologies will fundamentally alter the way propulsion integration is approached, or how these new technologies can not only compete but far exceed existing propulsion solutions in many ways at battery specific energy densities of only 400 watt hours per kilogram. Electric propulsion characteristics offer the opportunity to achieve 4 to 8 time improvements in energy costs with dramatically lower total operating costs, while dramatically improving efficiency, community noise, propulsion system reliability and safety through redundancy, as well as life cycle Green House Gas emissions. Integration of electric propulsion will involve far greater degrees of distribution than existing propulsion solutions due to their compact and scale-free nature to achieve multi-disciplinary coupling and synergistic integration with the aerodynamics, highlift system, acoustics, vehicle control, balance, and aeroelasticity. Appropriate metrics of comparison and differences in analysis/design tools are discussed while comparing electric propulsion to other disruptive technologies. For several initial applications, battery energy density is already sufficient for competitive products, and for many additional markets energy densities will likely be adequate within the next 7 years for vibrant introduction. Market evolution and early adopter markets are discussed, along with the investment areas that will fill technology gaps and create opportunities for the effective, near-term electric aircraft products. Without understanding both the context of how electric propulsion will integrate into the vehicle system, and evolve into the market place it is likely that electric propulsion will continue to be misunderstood.

Moore, Mark D.↗
NASA NTRS1994

Cosmic bullets as particle accelerators and radio sources

We have simulated in two dimensions the dynamical evolution of dense gas clouds(`cosmic bullets') moving supersonically through a uniform low-density medium. The diffusive shock acceleration of relativistic protons (cosmic rays) and their dynamical feedback on the background flow are included by the two-fluid model for this process. The acceleration of relativistic electrons is approximated by a test-particle model, and a passive magnetic field is followed by a simple advection scheme. Strong bow shocks, with Mach numbers similar to that of a bullet's motion, are the most important particle accelerators in the flow, while tail shocks and shocks inside the bullets do not play generally significant roles in this regard. For our simulation parameters, approximately greater than 10% of the initial bullet kinetic energy is converted to a combination of internal energy of gas and cosmic-ray protons by the time the bullets begin to be disrupted. Characteristically, the cosmic rays gain several percent of the available kinetic energy. Bullet destruction on timescales only a little larger than the ram pressure bullet crushing time begins in response to Kelvin-Helmholtz and especially to Rayleigh-Taylor instabilities along the forward bullet surface. For dense bullets this happens before the bullet is stopped by ram pressure. According to our simple model for synchrotron emission from relativistic electrons accelerated and transported within the flows, that emission increases rapidly as the bullet begins to fragment, when it is strongly dominated by field enhancement in sheared flows. Synchrotron emission from the acceleration region within the bow shock is, by contrast, much weaker.

Jones, T. W.↗
NASA NTRS1982

Recent progress on molecular hydrogen in Orion

The H2 emission from the Orion Molecular Cloud is, by an order of magnitude, the brightest known example of H2 emission, offering a means by which to estimate quantities connected with the mass flow. The size, temperature, velocity, and intensity of the lines can be used to infer the mass loss rate, the rate at which momentum is yielded to the cloud through masss loss, and the energy dissipation rate as the cloud is disrupted internally. Attention is accordingly given to the most recent observational results, with respect to morphology, extinction, level populations, and excitation temperature. The estimates concerning the mass loss phenomenon derived from H2 observations yield approximately the same numbers of those inferred from CO and H2O maser observations.

Beckwith, S.↗
NASA NTRS1989

Microwave evidence for large-scale changes associated with a filament eruption

VLA observations at 6 and 20 cm wavelengths taken on August 3, 1985 are presented, showing an eruptive filament event in which microwave emission originated in two widely separated regions during the disintegration of the filament. The amount of heat required for the enhancement is estimated. Near-simultaneous changes in intensity and polarization were observed in the western components of the northern and southern regions. It is suggested that large-scale magnetic interconnections permitted the two regions to respond similarly to an external energy or mass source involved in the disruption of the filament.

Kundu, M. R.↗
NASA NTRS1999

Major Optical Outburst of Two Blazars: 3C66A and OJ287

Differential CCD photometric observations of 3C66A and OJ287 were carried out on 16 and 35 nights between December 1995 and March 1996, at the Vainu Bappu Observatory, India, as part of the blazar monitoring program. During this period we detected major optical outbursts (brightness of 3C66A and OJ287 increased by 0.8 and 1 mag, respectively) of these two blazars on timescales of two months. Integrating the outburst profiles we find that both the blazars released around 10(exp 53) erg. Such large amount of energy may come from the release of binding energy of a compact star when tidally disrupted by a super-massive black hole at the center of these blazars. Also we extend this model to explain the observed multifrequency (radio through gamma-ray) outburst of these two blazars and show that this model will be able to explain the outburst phenomena of other blazars. These new results will be presented with a detailed discussion of the suggested model.

Ghosh, K. K.↗
NASA NTRS2010

Sources and Losses of Ring Current Ions

During geomagnetic quiet times, in-situ measurements of ring current energetic ions (few to few tens of keVs) from THEMIS spacecraft often exhibit multiple ion populations at discrete energies that extend from the inner magnetosphere to the magnetopause at dayside or plasma sheet at nightside. During geomagnetic storm times, the levels of fluxes as well as the mean energies of these ions elevated dramatically and the more smooth distributions in energies and distances during quiet times are disrupted into clusters of ion populations with more confined spatial extends. This reveals local plasma heating processes that might have come into play. Several processes have been proposed. Magnetotail dipolarization, sudden enhancement of field-aligned current, local current disruptions, and plasma waves are possible mechanisms to heat the ions locally as well as strong convections of energetic ions directly from the magnetotail due to reconnections. We will examine two geomagnetic storms on October 11, 2008 and July 22, 2009 to reveal possible heating mechanisms. We will analyze in-situ plasma and magnetic field measurements from THEMIS, GOES, and DMSP for the events to study the ion pitch angle distributions and magnetic field perturbations in the auroral ionosphere and inner magnetosphere where the plasma heating processes occur.

Chen, Sheng-Hsien↗
NASA NTRS1996

Geologic signatures of atmospheric effects on impact cratering on Venus

Highlights of the research include geologic signatures of impact energy and atmospheric response to crater formation. Laboratory experiments were performed at the NASA Ames Vertical Gun Range (AVGR) to assess the interaction between disrupted impactor and atmosphere during entry, and to assess the energy coupling between impacts and the surrounding atmosphere. The Schlieren imaging at the AVGR was used in combination with Magellan imaging and theoretical studies to study the evolution of the impactor following impact. The Schlieren imaging documented the downrange blast front created by vaporization during oblique impacts. Laboratory experiments allowed assessing the effect of impact angle on coupling efficiency with an atmosphere. And the impact angle's effect on surface blasts and run-out flows allowed the distinction of crater clusters created by simultaneous impacts from those created by isolated regions of older age.

Source record↗
NASA NTRS1986

Effects of high-energy neutrino production and interactions on stars in close X-ray binaries

Limits are discussed that may be placed on binary systems in which a compact partner is a strong source of high-energy particles that produce photons, neutrinos, and other secondary particles in the companion star. The highest energy neutrinos are absorbed deep in the companion and the associated energy deposition may be large enough to affect its structure or lead to its ultimate disruption. This neutrino heating is evaluated, starting with a detailed numerical calculation of the hadronic cascade induced in the atmosphere of the companion star. For some theoretical models, the resulting energy deposition from neutrino absorption may be so great as to disrupt the companion star over a time scale of 10,000-100,000 yr. Even if the energy deposition is smaller, it may still be high enough to alter the system substantially.

Gaisser, T. K.↗