Large Energy Fluxes Research Articles

Classical scalar fields and the generalized second law

It has been shown that classical non-minimally coupled scalar fields can violate all of the standard energy conditions in general relativity. Violations of the null and averaged null energy conditions obtainable with such fields have been suggested as possible exotic matter candidates required for the maintenance of traversable wormholes. In this paper, we explore the possibility that if such fields exist, they might be used to produce large negative energy fluxes and macroscopic violations of the generalized second law (GSL) of thermodynamics. We find that it appears to be very easy to produce large magnitude negative energy fluxes in flat spacetime. However we also find, somewhat surprisingly, that these same types of fluxes injected into a black hole do {\it not} produce violations of the GSL. This is true even in cases where the flux results in a decrease in the area of the horizon. We demonstrate that two effects are responsible for the rescue of the GSL: the acausal behavior of the horizon and the modification of the usual black hole entropy formula by an additional term which depends on the scalar field.

The Energetics and Tidally Induced Reverse Renewal in a Two-Silled Fjord

A laterally integrated, two-dimensional numerical model is used to examine the influence of the M2 tide on the circulation in the Saguenay Fjord, a two-silled fjord (with a “large” inner and a “small” outer basin) located on the north shore of the St. Lawrence Estuary. It is found that the M2 tide is more vigorous in the outer than in the inner basin and that more vertical mixing occurs in the outer basin. Therefore, the density at depth in the outer basin decreases faster than it does in the inner basin, and the resulting horizontal pressure gradient causes a bottom flow of water from the inner to the outer basin across the inner sill. This “reverse renewal” is evident in both the available observations and the simulation. According to the model, much of the M2 energy withdrawn from the surface tide is fed into the internal tide. Significant tidal energy is also advected by the mean flow velocity. Approximately 25% of the net energy flux into the fjord is dissipated within 2 km of the outer sill. Because of the baroclinic pressure (i.e., the total pressure but with the influence of the surface displacement removed) the subtidal circulation is associated with very large energy fluxes within the fjord. These fluxes are much larger than the net rate at which tidal energy enters the fjord and they are greater than the subtidal, advective energy flux. They represent a large redistribution of energy within the fjord and their horizontal divergence along the fjord is almost in balance with the time rate of change of potential energy. When a flux Richardson number is calculated for the inner basin below sill depth, a value of 0.075 is obtained, which is close to values found for other fjords.

Observations of plasmas in the Io torus with the Galileo spacecraft

On December 7, 1995, the Galileo spacecraft passed through the Io torus near the magnetic equatorial plane of Jupiter. High– resolution measurements of positive ions and electrons in the energy/charge (E/Q) range of 0.9 V to 52 kV were acquired over the jovicentric radial distances of 5.6 to 7.8 Rj. At radial distances beyond Io's orbit at 5.9 Rj the plasma instrument (PLS) observed intense magnetically field‐aligned beams of electrons with average energies of hundreds of eV to several keV. The directional energy fluxes at the spacecraft position ranged from ∼1.5 to 90 erg cm−2S−1sr−1 in directions parallel and antiparallel to the magnetic field. The corresponding range of energy fluxes into Jupiter's ionosphere was ∼9 to 560 erg Cm−2s−1, sufficient for the production of auroral emissions at far‐ultraviolet wavelengths with brightnesses in the range of 0.06 to 3 mega‐Rayleighs. The largest energy fluxes were observed at ∼7.8 Rj and were comparable to those observed during the close flyby of Io. The torus plasmas were observed to rigidly corotate with Jupiter out to a radial distance of ∼7 Rj and are slower at greater radial distances. Fluctuations of the bulk ion speeds and densities were found to be superposed upon the general pattern of corotation and are suggestive of interchange of magnetic flux tubes in the plasma torus. For an isolated field‐aligned electron beam, the radial component of plasma flow was directed toward Jupiter at a speed of ∼4 km s−1. The other electron beams also occurred coincidentally with the fluctuations in the radial component of flow. The observations of these low‐energy electron beams are consistent with the absence of magnetically field‐aligned acceleration of electrons into Jupiter's ionosphere. The electron acceleration appears to be due to intense heating of the ionospheric plasmas associated with large currents driven by the interchange motions in the torus plasmas.

Atmospheric energy for subsurface life on Mars?

The location and density of biologically useful energy sources on Mars will limit the biomass, spatial distribution, and organism size of any biota. Subsurface Martian organisms could be supplied with a large energy flux from the oxidation of photochemically produced atmospheric H(2) and CO diffusing into the regolith. However, surface abundance measurements of these gases demonstrate that no more than a few percent of this available flux is actually being consumed, suggesting that biological activity driven by atmospheric H(2) and CO is limited in the top few hundred meters of the subsurface. This is significant because the available but unused energy is extremely large: for organisms at 30-m depth, it is 2,000 times previous estimates of hydrothermal and chemical weathering energy and far exceeds the energy derivable from other atmospheric gases. This also implies that the apparent scarcity of life on Mars is not attributable to lack of energy. Instead, the availability of liquid water may be a more important factor limiting biological activity because the photochemical energy flux can only penetrate to 100- to 1,000-m depth, where most H(2)O is probably frozen. Because both atmospheric and Viking lander soil data provide little evidence for biological activity, the detection of short-lived trace gases will probably be a better indicator of any extant Martian life.

Transport of intense LH pulses into a tokamak plasma

Application of lower-hybrid (LH) power in short, intense pulses in the 5–10 GW range should overcome the limiting effects of Landau damping, and thereby permit the penetration of LH power into the interior of large-scale plasmas. We show that, under such very intense LH pulses, wave coupling may deteriorate because of nonlinear density changes due to the ponderomotive force effects in front of the grill. Ponderomotive forces are also likely to induce strong plasma bias and consequent poloidal and toroidal plasma rotation. Although backward electric currents, created in the plasma by intense LH pulses, dissipate a large portion of the radio frequency power absorbed, the current drive efficiency is acceptable. We use a numerical simulation of wave–particle interactions to analyse the applicability of standard quasilinear theory to the case of large energy flux densities. The initial results indicate the existence of important restrictions on the use of the quasilinear approximation. The results of the present paper also indicate that some of the effects considerably alter some ideas of Cohen et al.

An energy-efficient submarine desalination plant

The socio-economical development of many regions lacking a sufficient supply of fresh water (FW) may at times be planned with the help of desalination technologies for sea and brackish water (SW and BW). Since these technologies require large energy fluxes in the form of heat or electricity and produce sizable salt fluxes in the form of brines (B), relevant environmental problems have to be duly taken into account. One of the most energy-efficient industrial desalination technologies, reverse osmosis (RO) requires ∼3–10 kWh of electric energy per cubic meter of FW produced from SW.AtENEL Research Division (Polo Idraulico e Strutturale, Milano), this desalination technology has been made the object of system design analyses which have brought out three novel, highly efficient schemes (submarine, underground, and ground-based) for FW production from SW. The present report concerns the submarine RO scheme RODSS (reverse osmosis deep sea system) which has been designed in collaboration among ENEL-Research (Milano), ETA (Firenze), JRC (Ispra), and WIP (Muenchen), under the auspices of the European Commission. RODSS has its RO desalinating units sited offshore at a suitable operative depth and achieves a remarkable energy efficiency through the free exploitation of the hydrostatic pressure of SW.RODSS will be described in sufficient detail to demonstrate that it requires much less electric energy than any conventional (ground-based) desalination plant of comparable FW production capacity. The discussion will clarify the main operative and maintenance features of the proposed submarine desalination technology which seems to have a promising technico-economical potential also vis-à-vis advantageous couplings with renewable energy sources.

Two‐dimensional Hydrodynamics of Pre–Core Collapse: Oxygen Shell Burning

By direct hydrodynamic simulation, using the Piecewise Parabolic Method (PPM) code PROMETHEUS, we study the properties of a convective oxygen burning shell in a SN 1987A progenitor star prior to collapse. The convection is too heterogeneous and dynamic to be well approximated by one-dimensional diffusion-like algorithms which have previously been used for this epoch. Qualitatively new phenomena are seen. The simulations are two-dimensional, with good resolution in radius and angle, and use a large (90-degree) slice centered at the equator. The microphysics and the initial model were carefully treated. Many of the qualitative features of previous multi-dimensional simulations of convection are seen, including large kinetic and acoustic energy fluxes, which are not accounted for by mixing length theory. Small but significant amounts of carbon-12 are mixed non-uniformly into the oxygen burning convection zone, resulting in hot spots of nuclear energy production which are more than an order of magnitude more energetic than the oxygen flame itself. Density perturbations (up to 8%) occur at the `edges' of the convective zone and are the result of gravity waves generated by interaction of penetrating flows into the stable region. Perturbations of temperature and electron fraction at the base of the convective zone are of sufficient magnitude to create angular inhomogeneities in explosive nucleosynthesis products, and need to be included in quantitative estimates of yields. Combined with the plume-like velocity structure arising from convection, the perturbations will contribute to the mixing of nickel-56 throughout supernovae envelopes. Runs of different resolution, and angular extent, were performed to test the robustness of these

Interpretation and modeling of the high‐latitude electromagnetic energy flux

An interpretation of the electromagnetic energy flux at high latitudes under steady state conditions is presented and analyzed through modeling of the large‐scale coupling between the high‐latitude ionosphere and magnetosphere. In this paper we elucidate the steady state relationship between the electromagnetic energy flux (divergence of the dc Poynting flux), the Joule heating rate, and the mechanical energy transfer rate in the high‐latitude ionosphere. We also demonstrate the important role of the neutral wind and its conductivity‐weighted distribution with altitude in determining the resultant exchange of electromagnetic energy at high latitudes. Because the Poynting flux approach accounts for the neutral wind implicitly and describes the net electromagnetic energy flux between the magnetosphere and ionosphere, it is a fundamental measure of energy transfer in the system. A significant portion of this energy transfer results in Joule heating; however, the conversion of electromagnetic energy flux into mechanical energy of the neutrals is also considerable and can in some regions exceed the Joule heating rate. We will show that neglect of the neutral dynamics in calculations of the Joule heating rate can be misleading. To evaluate and interpret the electromagnetic energy flux at high latitudes, we employ the vector spherical harmonic model, which is based on the National Center for Atmospheric Research thermosphere‐ionosphere general circulation model, to provide the steady state properties of the thermosphere‐ionosphere system under moderate to quiet geomagnetic activity. For the specific geophysical conditions modeled we conclude that (1) the electromagnetic energy flux is predominantly directed into the high‐latitude ionosphere with greater input in the morning sector than in the evening sector, as supported by DE 2 observations. (2) The Joule heating rate accounts for much of the electromagnetic energy deposited in the ionosphere with the conductivity‐weighted neutral wind contributing significantly to the Joule heating rate and thus affecting the net electromagnetic energy flux in the ionosphere. (3) On average, the mechanical energy transfer rate amounts to about 10% to 30% of the net electromagnetic energy flux in the auroral dawn, dusk, and polar cap regions, acting as a sink of electromagnetic energy flux in the dawn and dusk sectors and a source in the polar cap. (4) Weak regions of upward electromagnetic energy flux are found near the convection reversal boundaries where the mechanical energy transfer rate exceeds the Joule heating rate. In general, large upward electromagnetic energy fluxes may be rare, as the always positive Joule heating rate increases irrespective of the source of electromagnetic energy flux; that is, neutral dynamics contribute directly to the Joule heating rate.

Multiple ocean layering models and mode trapping in sublayers for high frequency propagation

It is possible for sublayers in a layered ocean to have pronounced effects on the propagating modes in the water column. For example, atypical effects occur for sound speeds less than the overlaying water column or some overlying sublayers. In some cases one predicts the concentration of a large energy flux in that layer even at model eigenvalues that prohibit propagation in the water column while supporting propagating modes in the sublayer. Since some data suggest the possibility of underlying gaseous regions that support low sound speeds, this is a practical problem. This allows for the possibility that for a layer thick enough to absorb energy before arriving in a higher speed sublayer, the number of propagation modes in the water column can be reduced with increasing frequency. Since this is a frequency-dependent effect [effective (absorbing) thickness of layers is inversely proportional to wavelength or directly proportional to frequency], absorption into the overlying sublayers becomes more pronounced with increased frequency thus reducing the possibility of ‘‘tunnelling’’ which leads to a reduction in propagating modes in the water column. This effect is the converse of the usual case for ocean bottom layering and can be directly measured. Some interesting effects are studied and compared with available data using the high frequency mode model SWAMP. [Work sponsored by the Office of Naval Research.]

Erosion processes in plasma-wall interactions

During plasma-wall interactions in fusion experiments large energy and particle fluxes are deposited predominantly onto limiter and divertor structures. Besides good thermomechanical properties, plasma facing materials must exhibit low erosion yields. Under normal operation conditions, the main erosion mechanisms are physical sputtering, chemical sputtering, radiation enhanced sublimation and thermal sublimation. High-Z materials, such as W, show low effective sputtering yields at low plasma temperatures and a favourable redeposition behaviour, and may be suited for divertor plates for these plasma conditions. For higher plasma temperatures low-Z materials such as CFC materials and Ti-doped graphites, which enable high power removal, are preferable. In the other wall areas a low-Z material with reduced chemical erosion, e.g. B 4C coatings, could be appropriate.

Universal multifractal indices for the ocean surface at far red wavelengths

For some time, ocean wave breaking has been conceptualized as a cascade process in which the large scale wind energy flux driving the system is dissipated by wave breaking at small scales, the two seperated by the “equilibrium” scaling range. Cascades are now known to generically lead to multifractals; with special “universal” multifractals theoretically predicted. In this paper we use far red (0.95 μm) radiances at 1m resolution obtained from aircraft to test the multifractal behavior of the ocean surface and estimate the corresponding universal multifractal parameters of the radiance field.

Heat load material studies: simulated tokamak disruptions

It is clear that an improved understanding of the effects of tokamak disruptions on plasma facing component materials is needed for the ITER program. Very large energy fluxes are predicted to be deposited in ITER and could be very damaging to the machine. During 1991, Sandia National Laboratories and the University of New Mexico conducted cooperative tokamak disruption simulation experiments at several Soviet facilities. These facilities were located at the Efremov Institute in Leningrad, the Kurchatov Atomic Energy Institute (Troisk and Moscow) and the Institute for Physicial Chemistry of the Soviet Academy of Sciences in Moscow. Erosion of graphite from plasma stream impact is seen to be much less than that observed with laser or electron beams with similar energy fluxes. This, along with other data obtained, seem to suggest that the “vapor shielding” effect is a very important phenomenon in the study of graphite erosion during tokamak disruption.

Alfv�n wave-driving mechanism of late-type stellar wind

Because late-type stellar wind has low temperature, massive outflow, and high terminal velocity, theoretical models of thermal pressure or radiation pressure cannot explain the acceleration of late-type stellar wind. Energy damping of Alfven wave in stellar winds is small, and Alfven wave is perhaps the driving force of late-type stellar wind if the wave energy-flux is large enough. After theoretical analysis and numerical calculation, we get various velocity distributions by taking various wave energy-fluxes in reliable range, the terminal velocities accord with observations. If late-type stellar winds are driven by thermal pressure, the temperature is higher than acceptable. The results of Alfven wave driving winds also indicate that massive stellar winds need large energy flux and acceleration is closely related with gravity. In discussion we think that Alfven wave accelerating late-type stellar wind is feasible and the initial energy-flux, damping of Alfven wave in stellar winds need further study.

Fine Adjustment of Large Scale Air-Sea Energy Flux Parameterizations by Direct Estimates of Ocean Heat Transport

An inverse technique is used to adjust uncertain coefficients and parameters in the bulk formulae of climatological air-sea energy fluxes in order to obtain an agreement of indirect estimates of meridional heat transport with direct estimates in the North Atlantic Ocean. Three oceanographic estimates of ocean heat transport at the equator, at 25°N, and 32°N are compatible with meteorological evidence provided that the uncertainties of both direct and indirect estimates are taken into account. The transport coefficient CE for estimation of the latent heat flux is the major contributor to the overall uncertainty in estimates of ocean heat transport. The constraint of 1 PW northward transport across 25°N leads to a set of parameterizations for which the parameter adjustments are only less than half as large as the estimated uncertainties. Based on this set of constrained parameterizations monthly climatological fields of the individual fluxes in the North Atlantic Ocean are computed which are consistent with direct transport estimates. With a larger set of heat transport observations this method will provide a possibility to discriminate between various bulk formulations, and to obtain more accurate estimates of the air-sea energy flux.

Fate of the companion stars of ultra-rapid pulsars

A millisecond pulsar that is formed by spin-up 'recycling'1,2 in a binary system will, once the mass transfer becomes temporarily interrupted, start to evaporate its companion star as a consequence of the large impinging pulsar energy flux. This evaporation is easiest if the pulsar has a short pulse period, the companion star has a relatively large radius and is therefore hydrogen-rich, and the orbital period is short. Evaporation of companion stars induced by millisecond pulsars could account for the lack of low-mass X-ray binaries with short orbital periods below the period gap of the cataclysmic variables, and for the statistics of new-born radio pulsars and their space velocities.

Chromospheric evaporation velocities in solar flares

view Abstract Citations (49) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Chromospheric evaporation velocities in solar flares Fisher, G. H. ; Canfield, R. C. ; McClymont, A. N. Abstract It is shown that the upper limit to chromospheric evaporation velocities in solar flare loops is 2.35 Cs, where Cs is the sound speed in the evaporated material. Upward velocities greater than this limit would imply the existence of additional nonhydrodynamic forces. Several hydrodynamic calculations are made of collisional heat produced by nonthermal energetic electrons, and upward velocities are found which are at the upper limit of large (less than 3 x 10 to the 10th ergs/sec/sq cm) energy flux values. At more modest fluxes (10 to the 10th or 10 to the 9th ergs/sec/sq cm) both thermal and thick target models yield upward velocities which are within 10 to 20 percent of the upper limit. When both temperature and velocity of the evaporated plasma are considered, the thermal model is found to be the most consistent with recent observational data. Publication: The Astrophysical Journal Pub Date: June 1984 DOI: 10.1086/184290 Bibcode: 1984ApJ...281L..79F Keywords: Chromosphere; Evaporation Rate; Solar Flares; Solar X-Rays; Constraints; Hydrodynamics; Solar Physics full text sources ADS |

Wave normal directions of chorus near the equatorial source region

Wave propagation directions of post‐midnight chorus in the near‐equatorial region at L shells of 6 to 7 have been determined from OGO 5 triaxial search coil magnetometer data. Several methods were used to estimate the wave normal directions: minimum variance, imaginary part of cross‐spectral matrix, eigenvector of Hermitian cross‐spectral matrix, and fit of dispersion relations for one‐wave and two‐wave models to cross‐spectral matrix. Comparisons of the methods and results are discussed in detail. Wave propagation at all frequencies within chorus tones was found to occur most frequently along the magnetic field with median and average cone angles of 9.1° and 12.2°, respectively. All methods of analysis gave similar results. It is concluded that the wave growth is maximum for waves propagating parallel to B. Our results are consistent with emission in a narrow beam but not as a broad angular distribution. The two wave propagation model typically resulted in negligible improvements in the residual beyond that obtained by assuming that only one wave was present. In only a few cases did substantial improvement result. These cases were unusual periods when it was obvious that simultaneous rising and falling tone emissions were present and crossing. It is concluded that in most cases only one chorus wave was present. In some cases the two‐wave model gives misleading indications of waves with large energy fluxes propagating at very oblique angles near the resonance cone. This is because the wave group velocity goes to zero near the resonance cone, and if electric field data are not used, then a small amount of magnetic noise is modeled with a large wave energy flux. Some examples have been found of a lower frequency burst propagating almost exactly along the magnetic field followed by a higher frequency burst travelling at large angles to the magnetic field. These paired bursts are quasi‐periodic with a delay of about 6 s between pairs of bursts; the phenomenon is presumed to be associated with pulsating auroral patches. The physical implications are discussed.

Alfv�nic resonant cavities in the solar atmosphere: Simple aspects

We investigate the propagation of Alfven waves in a simple medium consisting of three uniform layers; each layer is characterized by a different value for the Alfven speed, υA. We show how the central layer can act as a resonant cavity under quite general conditions. If the cavity is driven externally, by an incident wave in one of the outer layers, there result resonant transmission peaks, which allow large energy fluxes to enter the cavity from outside. The transmission peaks result from the destructive interference between a wave which leaks out of the cavity, and a directly reflected wave. We show that there are two types of resonances. The first type occurs when the cavity has the largest (or smallest) of the three Alfven speeds; this situation occurs on coronal loops. The second type occurs when the cavity Alfven speed is intermediate between the other two values of υA; this situation may occur on solar spicules. Significant heating of the cavity can occur if the waves are damped. We show that if the energy lost to heat greatly exceeds the energy lost by leakage out of the cavity, then the cavity heating can be independent of the damping rate. This conclusion is shown to apply to coronal resonances and to the spicule resonances. This conclusion agrees with a point made by Ionson (1982) in connection with the coronal resonances. Except for a numerical factor of order unity, we recover Ionson's expression for the coronal heating rate. However, Ionson's qualities are much too large. For solar parameters, the maximum quality is of the order of 100, but the heating is independent of the damping rate only when dissipation reduces the quality to less than about 10.

Electron heating by fast mode magnetohydrodynamic waves in the solar wind emanating from coronal holes

It is shown that fast mode magnetohydrodynamic waves, propagating outwards from the sun in coronal hole regions, will dissipate primarily through collisionless interaction with electrons rather than with protons. This dissipation can lead to higher electron than proton temperatures in the accelerating region of the solar wind, provided the waves carry a sufficiently large energy flux.

Heat flux induced wave fronts

The thermalization of a large energy flux W in a medium of density ρ leads to heat waves consisting of compression and expansion fronts, associated with substantial bulk motion. Particles can enter or leave the thermalization front at subsonic, sonic, or supersonic speed, allowing for a wide variety of wave modes. The wave mode depends on power input, thermodynamic response of the medium, and the boundary conditions. The intake Mach number mainly determines the degree of compression achieved across the front. Using macroscopic conservation equations the thermodynamic properties of the wave fronts are discussed in a pressure–density diagram and compared to other thermodynamic processes. The fluid dynamic properties are shown as a function of the absorbed power input W/ρ. Finally, the hydrodynamic properties of the entire two front heat wave are presented for specified boundary conditions in the response plane h–W/ρ, showing the enthalpy h of the heated target material as a function of an external energy flux W/ρ. Examples of the boundary conditions of free and retarded flow and heat transport due to inverse bremsstrahlung are discussed.