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Results for “adiabatic approximation”

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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Measuring the Redshift Dependence of The Cosmic Microwave Background Monopole Temperature With Planck Data

We study the capability of Planck data to constrain deviations of the cosmic microwave background (CMB) blackbody temperature from adiabatic evolution using the thermal Sunyaev-Zeldovich anisotropy induced by clusters of galaxies. We consider two types of data sets depending on how the cosmological signal is removed: using a CMB template or using the 217 GHz map. We apply two different statistical estimators, based on the ratio of temperature anisotropies at two different frequencies and on a fit to the spectral variation of the cluster signal with frequency. The ratio method is biased if CMB residuals with amplitude approximately 1 microK or larger are present in the data, while residuals are not so critical for the fit method. To test for systematics, we construct a template from clusters drawn from a hydro-simulation included in the pre-launch Planck Sky Model. We demonstrate that, using a proprietary catalog of X-ray-selected clusters with measured redshifts, electron densities, and X-ray temperatures, we can constrain deviations of adiabatic evolution, measured by the parameter α in the redshift scaling T (z) = T0(1 + z)(sup 1−alpha), with an accuracy of sigma(sub alpha) = 0.011 in the most optimal case and with sigma alpha = 0.018 for a less optimal case. These results represent a factor of 2-3 improvement over similar measurements carried out using quasar spectral lines and a factor 6-20 with respect to earlier results using smaller cluster samples.

cosmic background radiation↗
NASA NTRS1971

The propagation of solar cosmic-ray bursts.

Description of a model showing analytically the three phases of anisotropy which occur during solar cosmic-ray events in the 7.5 to 21 MeV kinetic-energy interval and reported by McCracken et al. (1971): (1) a highly anisotropic, near field-aligned, initial phase, (2) a convective phase, and (3) a late-time phase in which the anisotropy is approximately perpendicular to the mean interplanetary magnetic field. The model is based on the cosmic-ray particles being convectively transported out from the sun, undergoing anisotropic diffusion along the interplanetary magnetic-field lines, and losing energy by adiabatic deceleration or by collision processes. The event is seen simply as a pulse moving outward from the sun after a cosmic-ray burst with a negative density-gradient in front of it and a positive gradient behind.

Ng, C. K.↗
NASA NTRS1978

Design and performance of a 427-meter-per-second-tip-speed two-stage fan having a 2.40 pressure ratio

The aerodynamic design and the overall and blade-element performances are presented of a 427-meter-per-second-tip-speed two-stage fan designed with axially spaced blade rows to reduce noise transmitted upstream of the fan. At design speed the highest recorded adiabatic efficiency was 0.796 at a pressure of 2.30. Peak efficiency was not established at design speed because of a damper failure which terminated testing prematurely. The overall efficiencies, at 60 and 80 percent of design speed, peaked at approximately 0.83.

Cunnan, W. S.↗
NASA NTRS1974

Shock compression and adiabatic release of lunar fines from Apollo 17

An experimental investigation was conducted with the objective to obtain quantitative bounds, in terms of shock pressure and hence meteoroid impact velocity, concerning the conditions required to compact and lithify lunar fines. The measured pressure-particle velocity release states provide a basis for the determination of the approximate values of shock pressure associated with various postshock volumes and temperatures concomitant with solid-state vitrification and thermal melting. The implications of the obtained results for the study of regolith evolution are discussed.

Ahrens, T. J.↗
NASA NTRS2005

Support of NASA ADR/ Cross-Enterprise NRA Advanced Adiabatic Demagnetization Refrigerators for Continuous Cooling from 10K to 50mK, Development of a Heat Switch

Mechanical heat switches are used in conjunction with sorption refrigerators, adiabatic demagnetization refrigerators and for other cryogenic tasks including the pre-cooling cryogenic systems. They use a mechanical actuator which closes Au plated Cu jaws on an Au plated Cu bar. The thermal conductance in the closed position is essentially independent of the area of the jaws and proportional to the force applied. It varies linearly with T. It is approximately 10mW/K for 200 N at 1.5K. In some applications, the heat switch can be driven from outside the cryostat by a rotating rod and a screw. Such heat switches are available commercially from several sources. In other applications, including systems for space, it is desirable to drive the switch using a cold linear motor, or solenoid. Superconducting windings are used at temperatures s 4.2K to minimize power dissipation, but are not appropriate for pre-cooling a system at higher temperatures. This project was intended to improve the design of solenoid activated mechanical heat switches and to provide such switches as required to support the development of Advanced Adiabatic Demagnetization Refrigerators for Continuous Cooling from 10 K to 50 mK at GSFC. By the time funding began in 5/1/01, the immediate need for mechanical heat switches at GSFC had subsided but, at the same time, the opportunity had arisen to improve the design of mechanical heat switching by incorporating a "latching solenoid". In this device, the solenoid current is required only for changing the state of the switch and not during the whole time that the switch is closed.

Richards, Paul L.↗
NASA NTRS1973

The early evolution of the solar system

The problems of relating collapse conditions in an interstellar cloud to a model of the primitive solar nebula are discussed. In such a nebula there is a radial force balance between gravity, the pressure gradient, and centrifugal forces due to the rotation. Approximate values are given for the combinations of temperature and density throughout the nebula, from a maximum of about 2000 K near the center to less than 200 K in the outer portion. These conditions are based upon the compression adiabats in the terminal stages of the collapse of an interstellar cloud. One general conclusion, of great importance for accumulation of bodies within the solar system, is that interstellar grains should not be completely evaporated at distances in the nebula beyond about one or more astronomical units.

Cameron, A. G. W.↗
NASA NTRS2006

Skin Friction at Very High Reynolds Numbers in the National Transonic Facility

Skin friction coefficients were derived from measurements using standard measurement technologies on an axisymmetric cylinder in the NASA Langley National Transonic Facility (NTF) at Mach numbers from 0.2 to 0.85. The pressure gradient was nominally zero, the wall temperature was nominally adiabatic, and the ratio of boundary layer thickness to model diameter within the measurement region was 0.10 to 0.14, varying with distance along the model. Reynolds numbers based on momentum thicknesses ranged from 37,000 to 605,000. The measurements approximately doubled the range of available data for flat plate skin friction coefficients. Three different techniques were used to measure surface shear. The maximum error of Preston tube measurements was estimated to be 2.5 percent, while that of Clauser derived measurements was estimated to be approximately 5 percent. Direct measurements by skin friction balance proved to be subject to large errors and were not considered reliable.

Watson, Ralph D.↗
NASA NTRS1993

Mass loading and velocity diffusion models for heavy pickup ions at comet Grigg-Skjellerup

We compare model predictions of cometary water group ion densities and the solar wind slow down with measurements made by the Giotto Johnstone plasma analyzer implanted ion sensor at the encounter with comet Grigg-Skjellerup (G-S) on July 10, 1992. The observed slope of the ion density profile on approach to the comet is unexpectedly steep. Possible explanations for this are discussed. We present also a preliminary investigation of the quasilinear velocity-space diffusion of the implanted heavy ion population at G-S using a transport equation including souce, convection, adiabatic compression, and velocity diffusion terms. Resulting distributions are anisotropic, in agreement with observations. We consider theoretically the waves that may be generated by the diffusion process for the observed solar wind conditions. At initial ion injections, waves are generated at omega approximately Omega(sub i) the ion gyrofrequency, and lower frequencies are predicted for diffusion toward a bispherical shell.

Huddleston, D. E.↗
NASA NTRS2003

On the Critical Behaviour, Crossover Point and Complexity of the Exact Cover Problem

Research into quantum algorithms for NP-complete problems has rekindled interest in the detailed study a broad class of combinatorial problems. A recent paper applied the quantum adiabatic evolution algorithm to the Exact Cover problem for 3-sets (EC3), and provided an empirical evidence that the algorithm was polynomial. In this paper we provide a detailed study of the characteristics of the exact cover problem. We present the annealing approximation applied to EC3, which gives an over-estimate of the phase transition point. We also identify empirically the phase transition point. We also study the complexity of two classical algorithms on this problem: Davis-Putnam and Simulated Annealing. For these algorithms, EC3 is significantly easier than 3-SAT.

Morris, Robin D.↗
DOE OSTI2022

Conformer-Specific Dissociation Dynamics in Dimethyl Methylphosphonate Radical Cation

The dynamics of the dimethyl methylphosphonate (DMMP) radical cation after production by strong field adiabatic ionization have been investigated. Pump-probe experiments using strong field 1300 nm pulses to adiabatically ionize DMMP and a 800 nm non-ionizing probe induce coherent oscillations of the parent ion yield with a period of about 45 fs. The yields of two fragments, PO 2 C 2 H 7 + and PO 2 CH 4 + , oscillate approximately out of phase with the parent ion, but with a slight phase shift relative to each other. We use electronic structure theory and nonadiabatic surface hopping dynamics to understand the underlying dynamics. The results show that while the cation oscillates on the ground state along the P=O bond stretch coordinate, the probe excites population to higher electronic states that can lead to fragments PO 2 C 2 H 7 + and PO 2 CH 4 + . The computational results combined with the experimental observations indicate that the two conformers of DMMP that are populated under experimental conditions exhibit different dynamics after being excited to the higher electronic states of the cation leading to different dissociation products. These results highlight the potential usefulness of these pump-probe measurements as a tool to study conformer-specific dynamics in molecules of biological interest.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1972

Diffusion models for Jupiter's radiation belt

Solutions are given for the diffusion of trapped particles in a planetary magnetic field in which the first and second adiabatic invariants are preserved but the third is not, using as boundary conditions a fixed density at the outer boundary (the magnetopause) and a zero density at an inner boundary (the planetary surface). Losses to an orbiting natural satellite are included and an approximate evaluation is made of the effects of the synchrotron radiation on the energy of relativistic electrons. Choosing parameters appropriate to Jupiter, the electrons required to produce the observed synchrotron radiation are explained. If a speculative mechanism in which the diffusion is driven by ionospheric wind is the true explanation of the electrons producing the synchrotron emission it can be concluded that Jupiter's inner magnetosphere is occupied by an energetic proton flux that would be a serious hazard to spacecraft.

Jacques, S. A.↗
NASA NTRS2011

Evolution of the Equatorial Oscillation in Saturn's Stratosphere Between 2005 and 2010 from Cassini/CIRS Limb Data Analysis

We present an analysis of thermal infrared spectra acquired in limb viewing geometry by Cassini/CIRS in February 2010. We retrieve vertical profiles of Saturn's stratospheric temperature from 20 hPa to 10 (exp -2) hPa, at 9 latitudes between 20 deg N and 20 deg S. Using the gradient thermal wind equation, we derive a map of the zonal wind field. Both the temperature and the zonal wind vertical profiles exhibit an oscillation in the equatorial region. These results are compared to the temperature and zonal wind maps obtained from 2005-2006 CIRS limb data, when this oscillation was first reported. In both epochs, strong temperature anomalies at the equator (up to 20K) are consistent with adiabatic heating (cooling) due to a sinking (rising) motion at a speed of 0.1 - 0.2 mm/s. Finally, we show that the altitude of the maximum eastward wind has moved downwards by 1.3 scale heights in 4.2 years, hence with a 'phase' speed of approximately 0.5 mm/s. This rate is consistent with the estimated period of 14.7 years for the equatorial oscillation, and requires a local zonal acceleration of 1.1 x 10(exp -6) m.s(exp -2) at the 2.5 hPa pressure level. This downward propagation of the oscillation is consistent with it being driven by absorption of upwardly propagating waves.

Guerlet, S.↗
DOE OSTI2024

Lattice holography on a quantum computer

We explore the potential application of quantum computers to the examination of lattice holography, which extends to the strongly coupled bulk theory regime. With adiabatic evolution, we compute the ground state of a spin system on a ( 2 + 1 )-dimensional hyperbolic lattice, and measure the spin-spin correlation function on the boundary. Notably, we observe that with achievable resources for coming quantum devices, the correlation function demonstrates an approximate scale-invariant behavior, aligning with the pivotal theoretical predictions of the anti–de Sitter/conformal field theory correspondence. Published by the American Physical Society 2024

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1993

Stormtime transport of ring current and radiation belt ions

This is an investigation of stormtime particle transport that leads to formation of the ring current. Our method is to trace the guiding-center motion of representative ions (having selected first adiabatic invariants mu) in response to model substorm-associated impulses in the convection electric field. We compare our simulation results qualitatively with existing analytically tractable idealizations of particle transport (direct convective access and radial diffusion) in order to assess the limits of validity of these approximations. For mu approximately less than 10 MeV/G (E approximately less than 10 keV at L equivalent to 3) the ion drift period on the final (ring-current) drift shell of interest (L equivalent to 3) exceeds the duration of the main phase of our model storm, and we find that the transport of ions to this drift shell is appropriately idealized as direct convective access, typically from open drift paths. Ion transport to a final closed drift path from an open (plasma-sheet) drift trajectory is possible for those portions of that drift path that lie outside the mean stormtime separatrix between closed and open drift trajectories, For mu approximately 10-25 MeV/G (110 keV approximately less than E approximately less than 280 keV at L equivalent to 3) the drift period at L equivalent to 3 is comparable to the postulated 3-hr duration of the storm, and the mode of transport is transitional between direct convective access and transport that resembles radial diffusion. (This particle population is transitional between the ring current and radiation belt). For mu approximately greater than 25 MeV/G (radiation-belt ions having E approximately greater than 280 keV at L equivalent to 3) the ion drift period is considerably shorter than the main phase of a typical storm, and ions gain access to the ring-current region essentially via radial diffusion. By computing the mean and mean-square cumulative changes in 1/L among (in this case) 12 representative ions equally spaced in drift time around the steady-state drift shell of interest (L equivalent to 3), we have estimated (from both our forward and our time-reversed simulations) the time-integrated radial-diffusion coefficients D(sup sim)(sub LL) for particles having selected values of mu approximately greater than 15 MeV/G. The results agree surprisingly well with the predictions (D(sup ql)(sub LL)) of quasilinear radial diffusion theory, despite the rather brief duration (approximately 3 hrs) of our model storm and despite the extreme variability (with frequency) of the spectral-density function that characterizes the applied electric field during our model storm. As expected, the values of D(sup sim)(sub LL) deduced (respectively) from our forward and time-reversed simulations agree even better with each other and with D(sup sim)(sub LL) when the impulse amplitudes which characterize the individual substorms of our model storm are systematically reduced.

Chen, Margaret W.↗
NASA NTRS1994

Explosions of infalling comets in Jupiter's atmosphere

In view of the expected collision of comet Shoemaker-Levy 9 (1993e) with Jupiter in 1994 July, we calculate basic properties of the initial interaction for a simplified Jovian atmosphere. The comet is expected to impact Jupiter at 60 km/sec and at an angle of 45 deg to the zenith. The shock wave generated by the bolide should be optically thick once it has penetrated to an atmospheric density approximately 10(exp -6) gr/cm(exp 3), and we calculate the post-shock conditions assuming local thermodynamic equilibrium (LTE) for shock velocities v(sub sh) in the range 10 to 60 km/sec and preshock densities rho(sub a) = 10(exp -6) to 10(exp -2) gr/cm(exp 3). Our shock calculations include molecular hydrogen, atomic hydrogen, ionized hydrogen, neutral helium, and singly ionized helium. Even at the highest shock velocity, the gas is only partially ionized and the postshock temperature rises with preshock density in order to maintain the ionization. The value of the effective shock adiabatic index gamma(sub sh) varies from 1.17 (at low v(sub sh) and rho(sub a) to 1.40 (at high v(sub sh) and rho(sub a). The ablation rate is limited by the radiative flux that reaches the bolide surface. We argue that the ablated gas does not efficiently transfer its kinetic energy to the atmosphere, and it ultimately slows in a similar fashion to the comet material. As the bolide initially falls through the atmosphere, the character of the shock emission changes. At rho(sub a) approximately 10(exp -8) gr/cm (exp 3), the gas is optically thin and we expect line emission; in the optical spectrum, Balmer emission is expected from the shocked atmosphere and low-ionization metal lines from ablated cometary material. At rho(sub a) approximately 10(exp -6) gr/m(exp 3), the shocked gas is optically thick and the shock front near the bolide produces a blackbody spectrum. The temperature is favorable for ultraviolet (1000 to 3000 A) emission and the luminosity may be approximately 5 x 10(exp 23) ergs/sec for approximately 0.6 sec for a bolide 1 km in radius. At rho(sub a) approximately 10(exp -4) gr/cm(exp 3), the bolide has passed below the ultraviolet photosphere. The shock front emits considerable ionizing radiation, but it is absorbed in a narrow preshock region. The bolometric correction for the optical luminosity is large and we expect a 3000 to 8000 A luminosity of approximately 3 x 10(exp 23) ergs/sec for approximately 1 sec. The optical emission is strongly peaked in the vicinity of the bolide. The bolide does have a somewhat less luminous, optically thick trail extending greater than or equal to 10 km, but the radiation is characterized by a temperature of 4000 to 5000 K. From the fragmentation model of Chyba, Thomas, & Zahnle (1993), the bolide deposits most of its kinetic energy at rho(sub a) approximately 10(exp -3) gr/cm(exp 3) and this is the effective explosion site. The shock wave from such an explosion can move up about one density scale height. We examine the breakout of the shock front from the Jovian atmosphere and find that the shock acceleration in the decreasing density region is slow, so that the energy flux in the shock front is small. Higher velocities might be generated by shock acceleration along the channel left by the bolide if the shock motion can occur before the channel closes off as a result of radiative cooling. Hot gas created by the explosion ultimately rises due to buoyancy on a timescale of a minute. The luminosity is highest when the bubble first rises into the optically thin part of the atmosphere and may be approximately 1 x 10(exp 25) ergs/sec in the near-infrared. Roughly 1% of the initial bolide energy may be radiated in this way; the rest of the energy is lost to sound waves from the initial explosion and to work done by the bubble on the surrounding atmosphere.

Chevalier, Roger A.↗
NASA NTRS1991

The Uranian system - An overview

Results of many years of observations from the ground and from the Voyager encounter with Venus are presented which clarify a number of issues that were subjects of speculation or partial information. The new issues that the encounter brought to light are outlined. The encounter revealed additional rings, extensive dust associated with them, and complexities, including azimuthal asymmetries. Uranus possesses a strong (about 1 gauss) magnetic field with a bizarre geometry that can be described as a dipole offset 0.3 RU from the center of the planet and tilted approximately 60 deg with respect to the axis of rotation. It is argued that it is produced by a magnetohydrodynamic dynamo at about 0.4 RU from the planet's center. It is inferred from this that at least part of the interior is a convective fluid, indicating an adiabatic temperature profile and a warm interior. The magnetic field produces a magnetosphere with some peculiar characteristics, owing to the unique orientation of the dipole axis with respect to the direction of the solar wind flow.

Bergstralh, Jay T.↗
NASA NTRS1992

Quasi-linear regime of gravitational instability as a clue to understanding the large-scale structure in the Universe

In the late seventies, an image of the large-scale structure in the Universe began to emerge as a result of the accumulation of the galaxy redshifts. Most of the galaxies are found to concentrate in large filaments and perhaps sheets leaving most of the volume empty. Similar structures were predicted theoretically in the frame of the adiabatic theory of galaxy formation (Zeldovich) and later in the hot dark matter cosmology. However, both scenarios have been ruled out by the observations. With these scenarios the dynamical part of the scenario was also erroneously rejected by many as well. In this talk, I derive the Zeldovich approximation from the exact dynamic equations and show that it is always better than the standard linear approximation. The advantage of the Zeldovich approximation is the greatest in the quasi-linear regime when delta(sub rms) is less than 1 (delta identical to delta(rho)/rho), but the displacement of the matter is essential. The range of scales in the quasi-linear regime depends upon the slope of the initial spectrum and increases with decreasing n, where n is the exponent, if the initial spectrum is approximated by a simple power law P(k) varies as k(exp n).

Shandarin, Sergei F.↗
NASA NTRS2005

An Expanding Radio Nebula Produced by a Giant Flare from the Magnetar SGR 1806-20

Soft gamma repeaters (SGRs) are "magnetars", a small class of slowly spinning neutron stars with extreme surface magnetic fields, B approx. 10(sup 15) gauss. On 2004 December 27, a giant flare was detected from the magnetar SGR 1806-20, the third such event ever recorded. This burst of energy, which resulted in the highest flux of gamma-rays ever measured from a celestial object, was detected by a variety of instruments and even caused an ionospheric disturbance in the Earth's upper atmosphere recorded around the globe. Here we report the detection of a very bright but rapidly-fading radio source at the position of SGR 1806-20 following this outburst. From day 6 to day 19 after the flare, we see a resolved, linearly polarized, radio nebula, expanding at a velocity of approximately 0.3c. To create this nebula, at least 4 x 10(exp 43) ergs of energy must have been emitted by the giant flare in the form of magnetic fields and relativistic particles. The steep decline of the radio flux may indicate episodic particle acceleration followed by adiabatic expansion, as could occur if the ejecta have energized a thin shell surrounding a preexisting cavity.

Gaensler, B. M.↗