共查询到20条相似文献，搜索用时 15 毫秒
1.
N. Tamura G. J. Murray P. Luke C. Blackburn D. J. Robertson N. A. Dipper R. M. Sharples J. R. Allington-Smith 《Experimental Astronomy》2003,15(1):1-12
We present results from cryogenic tests of a Volume-Phase Holographic(VPH) grating at 200 K measured at near-infrared wavelengths.
The aims of these tests were to see whether the diffraction efficiency and angular dispersion of a VPH grating are significantly
different at a low temperature from those at a room temperature, and to see how many cooling and heating cycles the grating
can withstand. We have completed 5 cycles between room temperature and 200 K, and find that the performance is nearly independent
of temperature, at least over the temperature range which we are investigating. In future, we will not only try more cycles
between these temperatures but also perform measurements at a much lower temperature (e.g., ∼80 K). 相似文献
2.
Evaluations are presented of the time-average heating at different latitudes and heights due to energy flux divergence of the equinox diurnal and semidiurnal tides calculated by Forbes (1982a,h)from 0 to 400 km.It is found that diurnal tidal heating maximizes in the region of 80 km and semidiurnal has a sharp maximum at 108 km. Thermospheric diurnal oscillations give rise to a second region of heating that maximizes at 200 km and effectively transports energy from low to high latitudes.Global means are evaluated for the time-averaged vertical energy fluxes and heating rates: below 130 km, the results for the diurnal tide agree with those for the (1,1) mode alone, and for the semidiurnal tide, heating rates below 130 km are the same as those that would he obtained without the thermospheric semidiurnal excitation.Comparisons are made from 90 to 170 km between the combined diurnal and semidiurnal heating rates and previously reported rates due to e.u.v. radiation, Sq currents and gravity waves. 相似文献
3.
Douglas C. Hunt 《Planetary and Space Science》1970,18(12):1745-1751
The transfer of energy from an ionizing photon to the atoms and molecules of the neutral gas in the F-region of the atmosphere is investigated. It is found that photoionization heating should be divided into two parts: (1) photoelectron heating associated with the slowing down of the fast photoelectrons formed by photoionization; and (2) reaction heating associated with the chemical reactions undergone by the ions formed in the photoionization process. The photoelectron heating will take place near the time and place of photoionization while the reaction heating will occur at the time and place of the ionic reactions.
Photoelectron and reaction heating rates per unit column are computed for the daytime, and reaction heating rates per unit column are computed for the nighttime. It is concluded that: (1) chemical reactions at night lead to a small but significant amount of F-region heating; and (2) reaction heating during the day is nearly proportional to the cosine of the solar zenith angle except near sunrise and sunset. 相似文献
4.
5.
S. J. Morden 《Meteoritics & planetary science》1992,27(5):560-567
Abstract— The magnetic properties of the Millbillillie eucrite have been intensively studied using mutually oriented samples. The magnetic carrier has been identified as single domain/pseudo-single domain kamacite. It is believed that due to clast-rich/clast-poor layering, the rock has been subjected to minimum shock since formation. This is supported by the presence of a stable, unidirectional remanence. Three separate palaeointensity tests (IRM/NRM, ARM-NRM, and Thellier heating) have been used to determine the strength of the palaeofield. The criteria for the suitability of samples to be used in such tests are discussed, as are the three methods; IRM/NRM is deemed the least accurate. The results obtained (IRM/NRM: 6 μT and 25 μT; ARM-NRM: 31 μT, 28 μT, and 15 μT; Thellier: 30 μT, 37 μT, 15 μT) indicate that the rock cooled in a strong magnetic field. Modes of formation, given that Millbillillie has a layered structure, and the nature of the HED parent body, are discussed. A volcanic genesis is preferred over formation in an impact melt. An internal dynamo field is favoured for dynamical reasons, and calculations based on the assumption that 4 Vesta is a possible HED parent body indicate that an iron core may be present in such a body. 相似文献
6.
Darren M. O'Brien Paulo J.V. Garcia Jonathan Ferreira Sylvie Cabrit Luc Binette 《Astrophysics and Space Science》2004,292(1-4):609-617
The effects of phenomenological heating functions on the flow thermodynamics of cold T-Tauri disk winds are examined. Turbulent dissipation (mechanical) heating and a warm disk corona are invoked to heat the wind. The temperature and ionization evolution are solved for along the flow. The results allow the construction of synthetic observations; emission maps, forbidden line ratios, line fluxes and line profiles; and successfully reproduce a number of observed trends. Mechanical heating produces line ratios and fluxes that fit very well with observations. Invoking a warm disk corona successfully reproduces forbidden line profile low velocity components. 相似文献
7.
Hα and HeI emission in the jets of pre-main sequence stars – implications for the heating mechanisms
M. Takami A. Chrysostomou J. Bailey T.M. Gledhill M. Tamura H. Terada 《Astrophysics and Space Science》2003,287(1-4):143-146
Jets and winds in pre-main sequence (PMS) stars are often heated and ionized, and understanding their heating mechanism is desired to compare UV-to-IR spectral signatures with models and thus investigate their driving mechanism. We review our results of long-slit spectroscopy and spectro-astrometry for He I 1.083 μm and Hα emission, and investigate the heating mechanisms in the jet in the outer (>10 AU) and inner (<10 AU) regions, respectively. 相似文献
8.
Recent observations show that the cooling flows in the central regions of galaxy clusters are highly suppressed. Observed active galactic nuclei (AGN)-induced cavities/bubbles are a leading candidate for suppressing cooling, usually via some form of mechanical heating. At the same time, observed X-ray cavities and synchrotron emission point towards a significant non-thermal particle population. Previous studies have focused on the dynamical effects of cosmic ray pressure support, but none has built successful models in which cosmic ray heating is significant. Here, we investigate a new model of AGN heating, in which the intracluster medium is efficiently heated by cosmic rays, which are injected into the intra-cluster medium (ICM) through diffusion or the shredding of the bubbles by Rayleigh–Taylor or Kelvin–Helmholtz instabilities. We include thermal conduction as well. Using numerical simulations, we show that the cooling catastrophe is efficiently suppressed. The cluster quickly relaxes to a quasi-equilibrium state with a highly reduced accretion rate and temperature and density profiles which match observations. Unlike the conduction-only case, no fine-tuning of the Spitzer conduction suppression factor f is needed. The cosmic ray pressure, P c / P g ≲ 0.1 and ∇ P c ≲ 0.1ρ g , is well within observational bounds. Cosmic ray heating is a very attractive alternative to mechanical heating, and may become particularly compelling if Gamma-ray Large Array Space Telescope ( GLAST ) detects the γ-ray signature of cosmic rays in clusters. 相似文献
9.
Abstract— We report the discovery of four large (>50 μm) cosmic spherules (CSs) and a single scoriaceous micrometeorite (SMM) that contain evidence for the separation of immiscible Fe-Ni-S liquids during atmospheric entry heating. The particles contain segregated Fe-rich regions dominated by either Ni-S-bearing Fe-oxides or iron sulphides and have textural relations that suggest these separated from the silicate portions of the particles as metallic liquids. The oxides, which may be hydrous, are thought to result from alteration of metal and sulphide. The compositions of the silicate portions of the CSs are equivalent to spherules without Fe-rich regions, implying that metallic liquids are exsolved during the heating of most spherules, but completely separate. The single SMM has a very different composition from other scoriaceous particles, and the occurrence of an exsolved metallic liquid probably indicates extreme reduction during entry heating. The pyrolysis of carbonaceous materials is the most likely explanation for reduction and suggests that the precursor material of this particle was unusually C-rich. This SMM might be, therefore, an appropriate candidate for a large melted anhydrous or smectite interplanetary dust particle (IDP). The exsolution of immiscible Fe-Ni-S liquids during entry heating will result in systematic changes in the compositions of the remaining silicate melt. 相似文献
10.
Despite great advances in observations and modelling, the problem of solar and stellar heating still remains one of the most challenging problems of space physics. To find a definite answer to what sort of mechanisms act to heat the plasma to a few million degrees requires a collaborative effort of small scales observations, large capacity numerical modelling and complicated theoretical approaches. A unique theory should incorporate aspects such as the generation of energy, its transport and dissipation. Up to now, the first two problems are rather clarified. However, the modality of transfer of magnetic or kinetic energy into heat is a question still awaiting for an answer. In the present paper we review the various popular heating mechanisms put forward in the existing extensive literature. The heating processes are, somewhat arbitrarily, classified as hydrodynamic, magnetohydrodynamic or kinetic based on the characteristics of the model medium. These mechanisms are further divided based on the time scales of the ultimate dissipation involved (i.e. AC and DC heating, turbulent heating). In particular, special attention is paid to discuss shock dissipation, mode coupling, resonant absorption, phase mixing, and, reconnection. Finally, we briefly review the various heating mechanisms proposed to heat other stars. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
11.
We analyze Ca ii K-line profiles of one flare and EUV continuum observations of two other flares in order to infer values for the temperature enhancements (over active region values) produced in the upper photosphere around and above the temperature minimum region. The results, obtained through a partial redistribution calculation of the Ca ii K-line profiles and an LTE approach to the continuum observations, show that the flare temperature minimum is depressed some two scale heights below its preflare level, and that substantial temperature enhancements are produced even at this depth. Estimates for the energy release in these photospheric layers are given, and are found to be comparable with that released in chromospheric H and L emission.We then turn our attention to the investigation of possible heating mechanisms which might be responsible for the observed enhancements. Bombardment by both electrons and protons, and irradiation by soft X-rays, are each considered and found to be largely ineffective, due to the large attenuation of flux by photospheric depths, unless new ideas on the precise nature of these mechanisms are invoked, particularly if the same mechanism is also to explain the observed chromospheric emissions. We therefore conclude that it is most likely that some other mechanism must be advocated in order to explain the observed heating. Possibilities for this are (a) heating by EUV radiation, (b) proton beams with low dispersion energy spectra centered around 10–20 MeV, and (c) localized heating at temperature minimum levels.On leave from: Department of Astronomy, The University, Glasgow G12 8QQ, Scotland, United Kingdom. 相似文献
12.
Radiative-convective equilibrium models for Jupiter and Saturn have been produced in a study centered primarily on the stratospheric energy balance and the possible role of aerosol heating. These models are compared directly to the thermal structure profiles obtained from Voyager radio occultation measurements. The method is based on a straightforward flux divergence formulation derived from earlier work (J. S. Hogan, S. I. Rasool, and T. Encrenaz 1969, J. Atmos. Sci.26, 898–905). The balance between absorbed and emitted energies is computed iteratively at each level in the atmosphere, assuming local thermodynamic equilibrium and employing a standard treatment of opacities. Results for Jupiter indicate that a dust-free model (no aerosol heating) furnishes a good mean thermal profile for the stratosphere when compared with the Voyager 1 radio occultation (RSS) measurements. These observations of the equatorial region (0° and 12°S, respectively) exhibit periodic vertical structure. Of course, among many possible complications, the Voyager profiles may not represent typical excursions from the mean. The aerosol heat depositions required to match these profiles exactly, relative to the nominal dust-free model, are reasonably consistent with independent estimates for “continuum” absorbers. Other interpretations are discussed, along with a survey of problems encountered in intercomparing the lower portions (P ? 300 mb) of the models, the RSS profiles, and a recent IRIS equatorial profile. Although aerosol heating cannot be ruled out at low latitudes on Jupiter, our results indicate that it may not be required to reproduce the Voyager 1 RSS profiles. On the other hand, heating by aerosols or some other absorber seems necessary in order to match the high-latitude Voyager 2 RSS temperature profile. The Saturn models are relatively simple and in good-to-excellent agreement with the Voyager 2 RSS profiles at all levels. Our comparisons indicate that aerosol heating played a minor role in Saturn's midlatitude stratospheric energy balance at the time of the Voyager 2 encounter. These models, however, may need to be reassessed once the hydrocarbon concentrations have been more precisely determined. 相似文献
13.
One way of revealing the nature of the coronal heating mechanism is by comparing simple theoretical one-dimensional hydrostatic
loop models with observations at the temperature and/or density structure along these features. The most well-known method
for dealing with comparisons like that is the χ
2 approach. In this paper we consider the restrictions imposed by this approach and present an alternative way for making model
comparisons using Bayesian statistics. In order to quantify our beliefs we use Bayes factors and information criteria such
as AIC and BIC. Two datasets (Ugarte-Urra et al.
2005; Priest et al.
2000) are reanalyzed using the method described above. For the dataset of Ugarte-Urra et al. (2005), we conclude to apex dominant heating as the likely heating candidate, whereas the dataset of Priest et al. (2000) implies basal heating. Note that these new results are different from those obtained using the chi-squared statistic. For
this we suggest that proper usage of Classical and Bayesian statistics should be applied in order to make safe assumptions
about the nature of the coronal heating mechanisms. 相似文献
14.
Many coronal heating mechanisms have been suggested to balance the losses from this tenuous medium by radiation, conduction, and plasma mass flows. A previous paper (Walsh, Bell, and Hood, 1995) considered a time-dependent heating supply where the plasma evolved isobarically along the loop length. The validity of this assumption is investigated by including the inertial terms in the fluid equations making it necessary to track the sound waves propagating in a coronal loop structure due to changes in the heating rate with time. It is found that the temperature changes along the loop are mainly governed by the variations in the heating so that the thermal evolution can be approximated to a high degree by the simple isobaric case. A typical isobaric evolution of the plasma properties is reproduced when the acoustic time scale is short enough. However, the cooling of a hot temperature equilibrium to a cool one creates supersonic flows which are not allowed for in this model. 相似文献
15.
Characteristic times for heating and cooling of the thermal X-ray plasma in solar flares are estimated from the time profile of the thermal X-ray burst and from the temperature, emission measure and over-all length scale of the flare-heated plasma at thermal X-ray maximum. The heating is assumed to be due to magnetic field reconnection, and the cooling is assumed to be due to heat conduction and radiation. Temperatures and emission measures derived from UCSD OSO-7 X-ray flare observations are used, and length scales are obtained from Big Bear large-scale Hα filtergrams for 17 small (subflare to Class 1) flares. The empirical values obtained for the characteristic times imply (1) that flares are produced by magnetic field reconnection, (2) that conduction cooling of the thermal X-ray plasma dominates radiative cooling and (3) that reconnection heating and conduction cooling of the thermal X-ray plasma are approximately in balance at thermal X-ray maximum. This model in combination with the data gives estimates for the electron number density (1010–1011 cm?3) and the magnetic field strength (10–100 G) in the thermal X-ray plasma and for the total thermal energy generated in a subflare (≈ 1030 erg for an Hα area ≈ 1 square degree) which agree with previous observational and theoretical estimates obtained by others. 相似文献
16.
A. Gordon Emslie 《Solar physics》1985,98(2):281-291
We solve the energy equation for the high-temperature (coronal) component of flare plasma for two models of energy input: (i) direct collisional heating by a beam of suprathermal electrons, and (ii) ohmic heating by the beam-neutralizing reverse current. We discuss the regimes where each case is applicable, and solve for the differential emission measure distribution of the coronal plasma in each case. Scaling laws between loop temperatures and injected electron fluxes are derived for both models; these are testable observationally through coordinated soft X-ray and hard X-ray observations, thus providing a method of discriminating between the two cases. We also readdress the question of the energetic importance of a return current which is below the instability threshold for generation of ion-acoustic plasma turbulence. We find that unless the ambient coronal density is very low ( 109 cm –3), collisional heating will always dominate there, in agreement with the findings of previous authors. However, in the chromosphere/corona transition region, the relatively low temperature and correspondingly high plasma resistivity imply that reverse current ohmic heating can predominate the flare energetics, by up to an order of magnitude.Presidential Young Investigator. 相似文献
17.
Darren O'Brien Paulo Garcia Jonathan Ferreira Sylvie Cabrit Luc Binette 《Astrophysics and Space Science》2003,287(1-4):129-134
Following the work of Garcia et al. (2001a) (GFCB), we compute the thermal properties and ionization structure of magnetically-driven disk winds. The original model's dominant heating function along the jet, ambipolar diffusion, is augmented by a mechanical heating term supposed to arise from weak shocks, as used by (Shang et al., 2002). We add this mechanical heating function to a cold disk wind model and calculate its effect on the jet as a whole. The temperature and ionization of the flow are calculated in the case of cold jet solutions consistent with the underlying accretion disk (Ferreira, 1997). These solutions are compared to those of (GFCB) in order to quantitatively determine the effect of the mechanical heating on the flow. We then use the computed thermal and ionization structures to calculate jet synthetic observations. We find that the addition of mechanical heating leads to higher electron fractions, in turn leading to increased line fluxes and line ratios approaching observed values. 相似文献
18.
We present an analysis of a series of observations of the auroral/polar regions of Jupiter, carried out between September 8 and 11, 1998, making use of the high-resolution spectrometer, CSHELL, on the NASA InfraRed Telescope Facility (IRTF), Mauna Kea, Hawaii; these observations spanned an “auroral heating event.” This analysis combines the measured line intensities and ion velocities with a one-dimensional model vertical profile of the jovian thermosphere/ionosphere. We compute the model line intensities both assuming local thermodynamic equilibrium (LTE) and, relaxing this condition (non-LTE), through detailed balance calculations, in order to compare with the observations. Taking the model parameters derived, we calculate the changes in heating rate required to account for the modelled temperature profiles that are consistent with the measured line intensities. We compute the electron precipitation rates required to give the modelled ion densities that are consistent with the measured line intensities, and derive the corresponding Pedersen conductivities. We compute the changes in heating due to Joule heating and ion drag derived from the measured ion velocities, and modelled conductivities, making use of ion-neutral coupling coefficients derived from a 3-D global circulation model. Finally, we compute the cooling due to the downward conduction of heat and the radiation-to-space from the molecular ion and hydrocarbons. Comparison of the various heating and cooling terms enables us to investigate the balance of energy inputs into the auroral/polar atmosphere. Increases in Joule heating and ion drag are sufficient to explain the observed heating of the atmosphere; increased particle precipitation makes only a minor heating contribution. But local cooling effects—predominantly radiation-to-space—are shown to be too inefficient to allow the atmosphere to relax back to pre-event thermal conditions. Thus we conclude that this event provides observational, i.e. empirical, evidence that heat must be transported away from the auroral/polar regions by thermally or mechanically driven winds. 相似文献
19.
G. C. Pande G. A. Georgantopoulos C. N. Douskos C. L. Goudas 《Astrophysics and Space Science》1978,57(1):113-118
Unsteady hydromagnetic thermal boundary layer flow of an electrically conducting, viscous, incompressible fluid near a harmonically oscillating limiting surface (e.g. in stellar atmospheres) is considered when the viscous dissipation and the Joule heating terms are retained in the energy equation. Exact solution of the problem, with the aid of the Laplace transform technique, is obtained when the magnetic Prandtl number is unity. For the purpose of application and discussion of the results, the variations of the temperature and the rate of heat transfer (expressed in the form of the Nusselt number) are presented for different sets of values of the magnetic parameter for the case of two particular fluids — air and water — when the limiting surface is under the condition of either cooling or heating. 相似文献
20.
Queenie H. S. Chan Aiko Nakato Yoko Kebukawa Michael E. Zolensky Tomoki Nakamura Jessica A. Maisano Matthew W. Colbert James E. Martinez A. L. David Kilcoyne Hiroki Suga Yoshio Takahashi Yasuo Takeichi Kazuhiko Mase Ian P. Wright 《Meteoritics & planetary science》2019,54(1):104-125
We present in this study the effects of short‐term heating on organics in the Tagish Lake meteorite and how the difference in the heating conditions can modify the organic matter (OM) in a way that complicates the interpretation of a parent body's heating extent with common cosmothermometers. The kinetics of short‐term heating and its influence on the organic structure are not well understood, and any study of OM is further complicated by the complex alteration processes of the thermally metamorphosed carbonaceous chondrites—potential analogues of the target asteroid Ryugu of the Hayabusa2 mission—which had experienced posthydration, short‐duration local heating. In an attempt to understand the effects of short‐term heating on chondritic OM, we investigated the change in the OM contents of the experimentally heated Tagish Lake meteorite samples using Raman spectroscopy, scanning transmission X‐ray microscopy utilizing X‐ray absorption near edge structure spectroscopy, and ultraperformance liquid chromatography fluorescence detection and quadrupole time of flight hybrid mass spectrometry. Our experiment suggests that graphitization of OM did not take place despite the samples being heated to 900 °C for 96 h, as the OM maturity trend was influenced by the heating conditions, kinetics, and the nature of the OM precursor, such as the presence of abundant oxygenated moieties. Although both the intensity of the 1s?σ* exciton cannot be used to accurately interpret the peak metamorphic temperature of the experimentally heated Tagish Lake sample, the Raman graphite band widths of the heated products significantly differ from that of chondritic OM modified by long‐term internal heating. 相似文献