Dominant Heat Source Research Articles

Thermal Analysis of High-Energy Railgun Tests

This paper describes temperature measurements made on the high-energy medium-caliber launcher at the Institute for Advanced Technology. Simulations performed in Maxwell 3-D and E-Physics showed that Joule heating from current diffusing into the rails accounts for most of the temperature rise in the conductors. Temporal skin effects increase thermal dissipation significantly over what would be expected by the ohmic losses under fully diffused conditions. Based on this analysis, Joule heating is the overwhelmingly dominant source of heating in low-speed tests. As the velocity of the armature increases, Joule heating remains the dominant source of heat; however, additional mechanisms-which may include frictional heating, arcing energy, aluminum deposition, and temperature-dependent properties-are required to more satisfactorily explain the temperature profile obtained.

Temperature Variations of Cold Dust in the Triangulum Galaxy M 33

We present wide-field 1.1 mm continuum imaging of the nearby spiral galaxy M 33, conducted with the AzTEC bolometer camera on ASTE. We show that the 1.1 mm flux traces the distribution of dust with $T$$\sim$ 20 K. Combined with far-infrared imaging at 160$\ \mu$m, we derived the dust temperature distribution out to a galactic radius of $\sim$ 7 kpc with a spatial resolution of $\sim$ 150 pc. Although the 1.1 mm flux was observed predominantly near star-forming regions, we found a smooth radial temperature gradient declining from $\sim$ 20 K to $\sim$ 13 K consistent with recent results from the Herschel satellite. Further comparisons of individual regions show a strong correlation between the cold dust temperature and the $K_{\rm S}$ band brightness, but not with the ionizing flux. The observed results imply that the dominant heating source of cold dust at few hundred parsec scales is due to non-OB stars, even when associated with star-forming regions.

Time-of-Flight Mass Measurements for Nuclear Processes in Neutron Star Crusts

We present results from time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory that are relevant for neutron star crust models. The masses of 16 neutron-rich nuclei in the scandium-nickel range were determined simultaneously, with the masses of (61)V, (63)Cr, (66)Mn, and (74)Ni measured for the first time with mass excesses of -30.510(890) MeV, -35.280(650) MeV, -36.900(790) MeV, and -49.210(990) MeV, respectively. With these results the locations of the dominant electron capture heat sources in the outer crust of accreting neutron stars that exhibit super bursts are now experimentally constrained. We find the experimental Q value for the (66)Fe→(66)Mn electron capture to be 2.1 MeV (2.6σ) smaller than predicted, resulting in the transition occurring significantly closer to the neutron star surface.

X-RAY EMISSION FROM THE SOMBRERO GALAXY: A GALACTIC-SCALE OUTFLOW

Based on new and archival Chandra observations of the Sombrero galaxy (M 104), we study the diffuse X-ray emission in and around its massive stellar bulge. The 2-6 keV unresolved emission from the bulge region closely follows the K-band star light and most likely arises from unresolved stellar sources. At lower energies, however, the unresolved emission reaches a galactocentric radius of at least 23 kpc, significantly beyond the extent of the starlight, clearly indicating the presence of diffuse hot gas. We isolate the emission of the gas by properly accounting for the emission from unresolved stellar sources, predominantly cataclysmic variables and coronally active binaries, whose quasi-universal X-ray emissivity is recently established. We find a gas temperature of ~0.6 keV with little variation across the field of view, except for a lower temperature of ~0.3 keV along the stellar disk. We measure a total intrinsic 0.3-2 keV luminosity of ~2e39 erg/s, which is comparable to the prediction by the latest galaxy formation models for disk galaxies as massive as Sombrero. However, such numerical models do not fully account for internal feedback processes, such as nuclear feedback and stellar feedback, against accretion from the intergalactic medium. On the other hand, we find no evidence for either the nucleus or the very modest star-forming activities in the disk to be a dominant heating source for the diffuse gas. We also show that neither the expected energy released by Type Ia supernovae nor the expected mass returned by evolved stars is recovered by observations. We argue that in Sombrero a galactic-scale subsonic outflow of hot gas continuously removes much of the "missing" energy and mass input from the bulge region. The observed density and temperature distributions of such an outflow, however, continues to pose challenges to theoretical studies.

A first direct measurement of the intergalactic medium temperature around a quasar at z= 6

The thermal state of the intergalactic medium (IGM) provides an indirect probe of both the HI and HeII reionisation epochs. Current constraints on the IGM temperature from the Lya forest are restricted to the redshift range 2<z<4.5, limiting the ability to probe the thermal memory of HI reionisation toward higher redshift. In this work, we present the first direct measurement of the IGM temperature around a z=6 quasar by analysing the Doppler widths of Lya absorption lines in the proximity zone of SDSS J0818+1722. We use a high resolution (R= 40000) Keck/HIRES spectrum in combination with detailed numerical modelling to obtain the temperature at mean density, T_0=23600\pm^5000_6900K (\pm^9200_9300K) at 68 (95) per cent confidence assuming a prior probability 13500K<T_0<38500 K following HI and HeII reionisation. This enables us to place an upper limit on the redshift of HI reionisation, z_H, within 33 comoving Mpc of SDSS J0818+1722. If the quasar reionises the HeII in its vicinity, then in the limit of instantaneous reionisation we infer z_H<9.0 (11.0) at 68 (95) per cent confidence assuming photoheating is the dominant heat source and that HI reionisation is driven by ionising sources with soft spectra, typical of population II stars. If the HI and HeII in the IGM around SDSS J0818+1722 are instead reionised simultaneously by a population of massive metal-free stars, characterised by very hard ionising spectra, we obtain a tighter upper limit of z_H<8.4 (9.4). Initiating reionisation at higher redshifts produces temperatures which are too low with respect to our constraint unless the HI ionising sources or the quasar itself have spectra significantly harder than typically assumed.

On the origin of selectivity and anisotropy loss during microstructure release etch

The origin of the loss of Si anisotropy and selectivity to barrier metals during the release etch process of a CMOS-MEMS fabrication flow is investigated experimentally using in situ infrared imaging. The release etch is performed in an inductively coupled plasma etch chamber fitted with a CaF2 window to maximize IR transmission. Suspended disk test structures of varying plan area, thickness, transverse suspension cross-section and suspension length are etched at various bias voltages using a SF6/O2/C4F8 time-multiplexed, Bosch-type, anisotropic DRIE process followed by an O2 polymer removal process and an isotropic SF6 process. Temperatures up to 150 °C are reported for suspended disk test structures during the isotropic SF6 process while the temperature rise during the anisotropic DRIE and polymer removal processes is less than 7 °C. A physical model based on the power balance of the suspended disk test structures is developed and used to extract the proportion of etch heat absorbed by the structures, which is determined to be 0.26. The model predicts that exothermic heat of reaction of Si with neutral F species is the dominant source of heat and is supported by the observed temperature trends.

Meteorological and ablation features of Potanin Glacier, Mongolian Altai

An observational study was conducted for the first time at the ablation area of Potanin glacier, Tavan Bogd region, in western Mongolia in 2007-2008 in order to understand the meteorological and glaciological features. In the study, annual meteorological data and summer surface ablation data were obtained. It was found that the annual mean temperature was -8.8°C on the glacier, and the surface albedo exhibited altitude dependence. Further, the precipitation measured near the glacier during summer was much larger than that measured at Ulgii. Surface energy balance was calculated by a gradient method; it revealed that shortwave radiation was the dominant heat source of surface ablation, whereas the contribution rate of turbulent heat flux was small. The ablation calculated by an equation constructed using the measured radiation showed fairly good correlations with the observed daily ablation, whereas the degree-day method showed good correlations for cumulative ablation. This study revealed the certain uniqueness of the glacio-climate in this region, and showed the further necessity of analysis on the relation of meteorological conditions and the mass balance of the glacier.

AN ANALYTIC MODEL FOR THE EVOLUTION OF A VISCOUS, IRRADIATED DISK

We describe an analytic model for the evolution of a protoplanetary disk heated by viscous accretion and radiation from the central star. The disk is assumed to be flared and viscosity is assumed to follow an alpha model, where viscosity is proportional to the local sound speed and scale height. In the inner disk, the midplane temperature is mainly determined by the energy released by the viscous accretion of material through the disk and onto the star. In the outer disk, stellar irradiation is the dominant heat source. A third regime is present in the innermost part of the disk, where viscous heating dominates but the opacity declines rapidly with increasing temperature due to dust grain sublimation. Changes in the protostellar radius and luminosity over time are readily incorporated into the model, although these have a relatively minor effect on the disk evolution. The model yields the surface density and midplane temperature at any point in space and time during the lifetime of the disk. It is especially suited to studies of planet formation that require a self-consistent model of disk evolution with minimal computational expense.

An investigation of urban heat island intensity (UHII) as an indicator of urban heating

The objective of this paper is to evaluate the reliability of urban heat island intensity (UHII) as an indicator of urban heating. The diurnal patterns of air and surface-temperature based UHII and variations in urban and rural area heating were analyzed and discussed. The detailed air-temperature based UHII patterns were determined in one urban and four suburban areas of Hong Kong. UHII was determined as spatially-averaged air-temperature difference between an urban/suburban area and its surrounding rural area. Additionally, reported air and surface-temperature based UHII patterns were integrated in the discussion to carry out a comprehensive analysis. The urban and rural area heating variations (i.e., the diurnal variations in net radiation, sensible heat flux, latent heat flux, and heat stored by an area) were examined in the light of UHII patterns to validate UHII as an indicator for urban heating. It is noted that the air-temperature based UHIIs were higher and positive in the night-time but lower and negative during the daytime. On the other hand, most of the surface-temperature based UHIIs, investigated through satellite data were positive during both the daytime and night-time. It is revealed that UHII can well reflect urban heating during night-time and early morning. However, the lower and negative UHII during solar peak time (daytime when solar radiation is the dominant source of heating) has seemingly not been representing urban heating.

Constraints from diffusion profiles on the duration of high-strain deformation in thickened crust

Diffusion profiles in garnet are used to determine the duration of movement on shear zones. In the Musgrave Block, central Australia, Grenville age granulites were overprinted at depths of ~40 km by high-strain zones during the intracratonic Petermann orogeny (ca. 550 Ma ago). In these zones, quartzofeldspathic mylonites contain garnet from the early granulite facies event that developed compositional gradients during the high-pressure overprint. The diffusion of Ca into garnet is linked with the release of Ca in plagioclase (the only calcic mineral in the rock) during neocrystallization of sodic feldspar during high-strain deformation. Available diffusion data on garnet directly define the duration of high-strain deformation at eclogite facies. Our results indicate that the integrated time scales of movement in individual high-strain zones were short lived (between 0.07 Ma and 1.4 Ma), and that wide shear zones were active longer than narrow ones. In addition, we find that relict K-feldspar in one of the narrow eclogite facies shear zones yields a 40 Ar- 39 Ar age that is partially reset, indicating that the thermal event was also short lived. These short time scales support the hypothesis that shear heating was the dominant source of heat for the eclogite facies overprint.

Role of the upper ocean in the energy budget of Arctic sea ice during SHEBA

As part of the 1997–1998 Surface Heat Budget of the Arctic Experiment (SHEBA), a nearly yearlong record of upper ocean observations was obtained below a drifting ice camp in the Beaufort Gyre. A combination of observational and numerical modeling techniques are used to estimate heat fluxes across the under‐ice ocean boundary layer. Over the Canada Basin, the upper pycnocline contained moderate heat, but strong stratification effectively insulated it from mixed layer turbulence. Average resulting heat fluxes at the base of the mixed layer (Fpyc) and at the ocean‐ice interface (F0) were small (0.3–1.2 and 0.2 W m−2, respectively). Over the Chukchi Borderlands, the presence of relatively warm and salty Pacific origin water increased upper pycnocline heat content and reduced stratification, which permitted moderate Fpyc and F0 (2.1–3.7 and 3.5 W m−2, respectively). Solar insolation was the dominant heat source during the final, summertime portion of the drift. During the heating period, Fpyc was relatively small (0.4–1.5 W m−2) while F0 was large (16.3 W m−2). The drift‐averaged value of F0 was 7.6 W m−2. Energy budgets for the ice cover were constructed. The oceanic contribution to the budget during the portion of the drift over the Chukchi Borderlands, supported by entrainment of heat stored in the upper pycnocline, was responsible for a 15% reduction in ice growth. During the summer heating season, the F0 estimates were larger than the latent energy changes associated with basal melting.

Finite element analysis for cooling effect of magnetic fluid with alternating magnetic field

We present a fully coupled finite element method (FEM) for analyzing a cooling effect of magnetic fluid with an alternating magnetic field driven with the power frequency, 60 Hz. There are two different heat sources with an alternating magnetic field such as the Joule’s loss in coils excited with electric input and the power dissipation corresponding to Neel and Brownian relaxation. Because the input frequency is relatively low, the Joule’s loss in coil is a dominant heat source. The heat, therefore, transfers from the coil to the magnetic fluid and the natural convection phenomena arise on the coil surfaces. To consider the natural convection phenomena, the buoyant force density was considered in a magnetic fluid. Additionally, the forced convection, magnetoconvection, results from the magnetic body force density with the magnetization as a function of magnetic field intensity and temperature. These two convection phenomena play a key role for cooling effect of magnetic fluid with an alternating magnetic field. To derive the magnetic body force density, we, here, numerically employed the continuous approach of Kelvin force density, which has been derived by introducing the virtual air-gap scheme incorporating with the FEM. The Langevin function was employed to consider the nonlinear magnetic susceptibility for evaluating the Kelvin force density and the power dissipations due to the Neel relaxation and Brownian relaxation.

Surface-induced heating of cold polar molecules

We study the rotational and vibrational heating of diatomic molecules placed near a surface at finite temperature on the basis of macroscopic quantum electrodynamics. The internal molecular evolution is governed by transition rates that depend on both temperature and position. Analytical and numerical methods are used to investigate the heating of several relevant molecules near various surfaces. We determine the critical distances at which the surface itself becomes the dominant source of heating and we investigate the transition between the long-range and short-range behavior of the heating rates. A simple formula is presented that can be used to estimate the surface-induced heating rates of other molecules of interest. We also consider how the heating depends on the thickness and composition of the surface.

Heating Titan's upper atmosphere

A detailed analysis of the mechanisms heating Titan's neutral atmosphere is provided. Two primary sources of incoming energy, the solar photons and the energetic electrons from Saturn's magnetosphere, are taken into account. The processes studied include the excitation of atmospheric molecules by electron impact, suprathermal electron heating, and the energy release through ion and neutral exothermic chemistry. The redistribution of heat by suprathermal particles throughout the atmosphere is also considered and calculated using a two‐stream model. Local time‐dependent heating rate profiles are presented. Exothermic chemistry is found to be the dominant source of heat, with electron‐impact excitation and suprathermal electron heating becoming significant at high altitudes. Large variations in local peak amplitudes were found, varying between ≃3 × 10−10 erg cm−3s−1 at 990 km and zenith angle 62° and ≃7 × 10−12 erg cm−3s−1 at 940 km and zenith angle 165°. Neutral heating efficiency profiles averaged with respect to local time at the fixed latitudes of 38.8° N and 73.7° N are presented, with mean values of ≃25 ± 15% and 23 ± 19%, respectively.

Spatially Resolved Imaging at 350 μm of Cold Dust in Nearby Elliptical Galaxies

Continuum observations at 350 μm of seven nearby elliptical galaxies for which CO gas disks have recently been resolved with interferometry mapping are presented. These SHARC II mapping results provide the first clearly resolved far-infrared (FIR)-to-submillimeter continuum emission from cold dust (with temperatures 31 K T 23 K ) of any elliptical galaxy at a distance >40 Mpc. The measured FIR excess shows that the most likely and dominant heating source of this dust is not dilute stellar radiation or cooling flows, but rather star formation that could have been triggered by an accretion or merger event and fueled by dust-rich material that has settled in a dense region cospatial with the central CO gas disks. The dust is detected even in two cluster ellipticals that are deficient in H I, showing that, unlike H I, cold dust and CO in ellipticals can survive in the presence of hot X-ray gas, even in galaxy clusters. No dust cooler than 20 K, either distributed outside the CO disks or cospatial with and heated by the entire dilute stellar optical galaxy (or very extended H I), is currently evident.

Thermal comfort range of a military cold protection glove: database by thermophysiological simulation

The thermal insulation properties of a military wet/cold protection glove of the German Bundeswehr were investigated using the thermophysiological simulation device CYBOR with a heated full-scale hand model. The aim of this study was the physiology related and more reliable estimation of a database for the thermal comfort range of the glove in terms of environmental limit temperatures and maximum safe wearing times (limit times). For that purpose the simulation device CYBOR is equipped with a control feature allowing the simulation of the physiological effect that the blood flow into the hands as the dominant heat source is reduced with decreasing skin temperature (vasoconstriction effect). In the simulation test, the criterion defining the thermal comfort range of the glove was the maintenance of a minimum hand phantom skin temperature of 15 degrees C. For various assumed metabolic rates between 50 and 175 W m(-2) and environmental temperatures down to -22 degrees C, the maximum safe wearing times within the thermal comfort range of the military glove were estimated between only 20 min and almost 1 h. The used simulation scenario for the prediction of environmental limit temperatures, however, tends to deliver too low values in correlation to the estimated limit times and needs further critical consideration. The estimated data concerning the thermal comfort range of the wet/cold protection glove of the German Bundeswehr leads to the recommendation for a use of this model in mild cold climatic regions. The presented thermophysiological simulation procedure for the evaluation of the cold protection properties of gloves in terms of maximum safe wearing times within the thermal comfort range can be a useful tool to establish practical operating instructions for soldiers or civilians acting in cold environments.

Heating of blue compact dwarf galaxies: gas distribution and photoionization by stars in I Zw 18

Photoionization models so far are unable to account for the high electron temperature Te([O III]) implied by the line ratio [O III]4363A/[O III]5007A in low-metallicity blue compact dwarf galaxies, casting doubts on the assumption of photoionization by hot stars as the dominant source of heating of the gas in these objects. Combinations of runs of the 1-D photoionization code NEBU are used to explore alternative models for the giant H II region shell I Zw 18 NW. Acceptable models are obtained, which represent schematically an incomplete shell comprising radiation-bounded condensations embedded in a low-density matter-bounded diffuse medium. The thermal pressure contrast between gas components is about a factor 7. The diffuse phase can be in pressure balance with the hot superbubble fed by mechanical energy from the inner massive star cluster. The failure of previous modellings is ascribed to (1) the adoption of an inadequate small-scale gas density distribution, which proves critical when the collisional excitation of hydrogen contributes significantly to the cooling of the gas, and possibly (2) a too restrictive implementation of Wolf-Rayet stars in synthetic stellar cluster spectral energy distributions. A neutral gas component heated by soft X-rays, whose power is less than 1% of the star cluster luminosity and consistent with CHANDRA data, can explain the low-ionization fine-structure lines detected by SPITZER. [O/Fe] is slightly smaller in I Zw 18 NW than in Galactic Halo stars of similar metallicity and [C/O] is correlatively large. Extra heating by, e.g., dissipation of mechanical energy is not required to explain Te([O III]) in I Zw 18. Important astrophysical developments are at stakes in the 5% uncertainty attached to [O III] collision strengths.

Molecular Hydrogen Emission from Protoplanetary Disks. II. Effects of X‐Ray Irradiation and Dust Evolution

Detailed models for the density and temperature profiles of gas and dust in protoplanetary disks are constructed by taking into account X-ray and UV irradiation from a central T Tauri star, as well as dust size growth and settling toward the disk midplane. The spatial and size distributions of dust grains are numerically computed by solving the coagulation equation for settling dust particles, with the result that the mass and total surface area of dust grains per unit volume of the gas in the disks are very small, except at the midplane. The H2 level populations and line emission are calculated using the derived physical structure of the disks. X-ray irradiation is the dominant heating source of the gas in the inner disk and in the surface layer, while the UV heating dominates otherwise. If the central star has strong X-ray and weak UV radiation, the H2 level populations are controlled by X-ray pumping, and the X-ray-induced transition lines could be observable. If the UV irradiation is strong, the level populations are controlled by thermal collisions or UV pumping, depending on the dust properties. As the dust particles evolve in the disks, the gas temperature at the disk surface drops because the grain photoelectric heating becomes less efficient. This makes the level populations change from LTE to non-LTE distributions, which results in changes to the line ratios. Our results suggest that dust evolution in protoplanetary disks could be observable through the H2 line ratios. The emission lines are strong from disks irradiated by strong UV and X-rays and possessing small dust grains; such disks will be good targets in which to observe H2 emission.

The False Lucre of Low-Pressure SAGD

Abstract The recent trend in SAGD is towards low-pressure steam injection. The intention is to be more thermally efficient: steam at lower pressures has a greater proportion of its heat as latent heat, which is the dominant source of heat released to the cold reservoir. The oil sand then warms up to the steam temperature, thus mobilizing the bitumen. The SAGD process must be thermally efficient for optimal economic viability. However, a more rigorous examination of the SAGD process presented here, inclusive of surface processes, reveals that there are fewer thermal benefits in operating at lower pressures. In addition, SAGD will be hindered by low-pressure injection due to higher viscosities and the inhibited dilation of the unconsolidated sandstone reservoir. This paper demonstrates that a complete analysis of the SAGD process favours operation at high pressures, and that SAGD at low pressures will be less effective. Introduction Steam assisted gravity drainage (SAGD) has been successfully applied to the in-situ thermal recovery of bitumen beginning with AOSTRA's Underground Test Facility laboratory-scale pilot project, Phase A (1987 – 1991)(1), and the subsequent commercialscale pilot, Phase B (1991 – present)(2). Since then, a large number of commercial SAGD projects have emulated their success. The current trend in operating philosophy is towards low-pressure SAGD: LPSAGD. This is based on the fact that at lower pressures, a larger percentage of steam's total heat is latent heat. Attractiveness of Low-Pressure SAGD SAGD Process In SAGD, most of the heat transferred to the cold oil sands formation is by the condensation of steam into the periphery of the steam chamber. The latent heat released from the steam is transferred to the colder formation mainly by conduction. Therefore, along the slopes of the steam chamber, the predominant flow of condensed steam (i.e. hot water) and mobilized hot bitumen is perpendicular to the direction of conductive heat flow. Steam quality is the mass fraction of water converted from liquid to steam. In SAGD, the injection of less than 100% quality steam is counterproductive, since the injected liquid water fraction just falls from the injector well to the producer well under gravitational forces within the isobaric steam chamber. This adds to the water recycling costs while contributing neither to the release of energy to the formation nor to bitumen recovery. Steam Properties The energy in steam at constant pressure consists of sensible heat and latent heat. The sensible heat is the energy required to raise the temperature of the water from an initial source temperature to the steam temperature; the latent heat is the energy required for the phase change from that hot water to steam. It is this latent heat that provides the dominant source of heat for the SAGD process. While the enthalpy of steam over the pressure range of 1,000 to 3,500 kPa is relatively uniform (see Figures 1 and 2), at lower pressures the proportion of heat as latent heat is higher. Since latent heat is the dominant form of heat transfer to the formation, one can see the attraction of low-pressure injection, solely from a steam energy viewpoint.

Electron heating mode transitions in dual frequency capacitive discharges

The authors consider electron heating in the sheath regions of capacitive discharges excited by a combination of two frequencies, one much higher than the other. There is a common supposition that in such discharges the higher frequency is the dominant source of electron heating. In this letter, the authors discuss closed analytic expressions quantifying the Ohmic and collisionless electron heating in a dual frequency discharge. In both cases, the authors show that the lower frequency parameters strongly influence the heating effect. Moreover, this influence is parametrically different, so that the dominant heating mechanism may be changed by varying the low frequency current density.