Thermal shields for heat loss reduction in Siemens-type CVD reactors

The use of thermal shields to reduce radiation heat loss in Siemens-type CVD reactors is analyzed, both theoretically and experimentally. The potential savings from the use of the thermal shields is first explored using a radiation heat model that takes emissivity variations with wavelength into account, which is important for materials that do not behave as grey bodies. The theoretical calculations confirm that materials with lower surface emissivity lead to higher radiation savings. Assuming that radiation heat loss is responsible for around 50% of the total power consumption, a reduction of 32.9% and 15.5% is obtained if thermal shields with constant emissivities of 0.3 and 0.7 are considered, respectively. Experiments considering different thermal shields are conducted in a laboratory CVD reactor, confirming that the real materials do not behave as grey bodies, and proving that significant energy savings in the polysilicon deposition process are obtained. Using silicon as a thermal shield leads to energy savings of between 26.5-28.5%. For wavelength-dependent emissivities, the model shows that there are significant differences in radiation heat loss, of around 25%, when compared to that of constant emissivity. The results of the model highlight the importance of having reliable data on the emissivities within the relevant range of wavelengths, and at deposition temperatures, which remains a pending issue.

The imprint of the crustal magnetic field on the thermal spectra and pulse profiles of isolated neutron stars

Isolated neutron stars (NSs) show a bewildering variety of astrophysical manifestations, presumably shaped by the magnetic field strength and topology at birth. Here, using state-of-the-art calculations of the coupled magnetic and thermal evolution of NSs, we compute the thermal spectra and pulse profiles expected for a variety of initial magnetic field configurations. In particular, we contrast models with purely poloidal magnetic fields to models dominated by a strong internal toroidal component. We find that, while the former displays double-peaked profiles and very low pulsed fractions, in the latter, the anisotropy in the surface temperature produced by the toroidal field often results in a single pulse profile, with pulsed fractions that can exceed the 50–60 per cent level even for perfectly isotropic local emission. We further use our theoretical results to generate simulated ‘observed’ spectra, and show that blackbody (BB) fits result in inferred radii that can be significantly smaller than the actual NS radius, even as low as ∼1–2 km for old NSs with strong internal toroidal fields and a high absorption column density along their line of sight. We compute the size of the inferred BB radius for a few representative magnetic field configurations, NS ages and magnitudes of the column density. Our theoretical results are of direct relevance to the interpretation of X-ray observations of isolated NSs, as well as to the constraints on the equation of state of dense matter through radius measurements.

Spectral features in isolated neutron stars induced by inhomogeneous surface temperatures

The thermal X-ray spectra of several isolated neutron stars display deviations from a pure blackbody. The accurate physical interpretation of these spectral features bears profound implications for our understanding of the atmospheric composition, magnetic field strength and topology, and equation of state of dense matter. With specific details varying from source to source, common explanations for the features have ranged from atomic transitions in the magnetized atmospheres or condensed surface, to cyclotron lines generated in a hot ionized layer near the surface. Here, we quantitatively evaluate the X-ray spectral distortions induced by inhomogeneous temperature distributions of the neutron star surface. To this aim, we explore several surface temperature distributions, we simulate their corresponding general relativistic X-ray spectra (assuming an isotropic, blackbody emission), and fit the latter with a single blackbody model. We find that, in some cases, the presence of a spurious ‘spectral line’ is required at a high significance level in order to obtain statistically acceptable fits, with central energy and equivalent width similar to the values typically observed. We also perform a fit to a specific object, RX J0806.4−4123, finding several surface temperature distributions able to model the observed spectrum. The explored effect is unlikely to work in all sources with detected lines, but in some cases it can indeed be responsible for the appearance of such lines. Our results enforce the idea that surface temperature anisotropy can be an important factor that should be considered and explored also in combination with more sophisticated emission models like atmospheres.

Quiescent thermal emission from neutron stars in low-mass X-ray binaries

Context. We monitored the quiescent thermal emission from neutron stars in low-mass X-ray binaries after active periods of intense activity in X-rays (outbursts). Aims. The theoretical modeling of the thermal relaxation of the neutron star crust may be used to establish constraints on the crust composition and transport properties, depending on the astrophysical scenarios assumed. Methods. We numerically simulated the thermal evolution of the neutron star crust and compared them with inferred surface temperatures for five sources: MXB 1659−29, KS 1731−260, XTE J1701−462, EXO 0748−676  and IGR J17480−2446. Results. We find that the evolution of MXB 1659−29, KS 1731−260 and EXO 0748−676 can be well described within a deep crustal cooling scenario. Conversely, we find that the other two sources can only be explained with models beyond crustal cooling. For the peculiar emission of XTE J1701−462 we propose alternative scenarios such as residual accretion during quiescence, additional heat sources in the outer crust, and/or thermal isolation of the inner crust due to a buried magnetic field. We also explain the very recent reported temperature of IGR J17480−2446 with an additional heat deposition in the outer crust from shallow sources.

Sea-surface temperature reconstruction for sediment core GeoB1023-5

Sediment core GeoB 1023-5 from the eastern South Atlantic was investigated at high temporal resolution for variations of sea-surface temperature (SST) during the past 22 kyr, using the alkenone (UK'37) method. SSTs increased by 3.5°C from about 18°C during the Last Ice Age (21±2 cal kyr BP) to about 21.5°C at 14.5 cal kyr BP. This warming trend associated with the deglaciation phase was followed by a cooling event with lowest SSTs near 20°C, persisting for about 1000 years between 13 and 12 cal kyr BP. The SSTs then continued to increase to about 22.5°C at the Holocene climatic optimum at 7 cal kyr BP, and decreased again during the Late Holocene to a core-top value of 19.8°C that is comparable to modern annual mean SST values. When compared with alkenone SST records from the eastern North Atlantic, our SST record indicates continuous warming throughout the deglaciation phase in the Benguela Current, while its northern counterpart, the Canary Current, experienced prominent cooling during 'Heinrich Event 1' (H1). On the other hand, for the time period corresponding to the 'Younger Dryas' (YD) cooling event, the Benguela SST record exhibits a cold-temperature interval that corresponds to that observed in the eastern North Atlantic SST records. This observation suggests that interhemispheric climate response in Atlantic eastern boundary current systems was different with respect to the two abrupt climate events associated with Termination I. For the H1, the eastern South Atlantic SST record strongly supports the hypothesis that an 'anti-phase' thermal behavior in South Atlantic surface waters was forced by the slowdown of the North Atlantic Deep Water formation during cold spells in the North Atlantic. In contrast, the abrupt cooling in the eastern South Atlantic coincident with the YD period was probably induced by more vigorous global atmospheric circulation, enhancing the upwelling intensity in both eastern boundary current systems. This atmospheric control may have overridden any effect caused by changes in thermohaline circulation on the South Atlantic SSTs during the YD, which leads to the assumption that the thermohaline circulation was already much closer to its interglacial mode during the YD than during the H1.

Stable isotope record, Mg/Ca ratios and sea surface reconstruction for sediment core MD06-3067

We present sea surface, upper thermocline, and benthic d18O data, as well as temperature and paleoproductivity proxy data, from the International Marine Global Change Study Program (IMAGES) Core MD06-3067 (6°31'N, 126°30'E, 1575 m water depth), located in the western equatorial Pacific Ocean within the flow path of the Mindanao Current. Our records reveal considerable glacial-interglacial and suborbital variability in the Mindanao Dome upwelling over the last 160 kyr. Dome activity generally intensified during glacial intervals resulting in cooler thermocline waters, whereas it substantially declined during interglacials, in particular in the early Holocene and early marine oxygen isotope stage (MIS) 5e, when upwelling waters did not reach the thermocline. During MIS 3 and MIS 2, enhanced surface productivity together with remarkably low SST and low upper ocean thermal contrast provide evidence for episodic glacial upwelling to the surface, whereas transient surface warming marks periodic collapses of the Mindanao Dome upwelling during Heinrich events. We attribute the high variability during MIS 3 and MIS 2 to changes in the El Niño Southern Oscillation state that affected boreal winter monsoonal winds and upper ocean circulation. Glacial upwelling intensified when a strong cyclonic gyre became established, whereas El Niño-like conditions during Heinrich events tended to suppress the cyclonic circulation, reducing Ekman transport. Thus, our findings demonstrate that variations in the Mindanao Dome upwelling are closely linked to the position and intensity of the tropical convection and also reflect far-field influences from the high latitudes.

Sea-surface temperature reconstruction in the Southwest Pacific

Uniquely in the Southern Hemisphere the New Zealand micro-continent spans the interface between a subtropical gyre and the Subantarctic Circumpolar Current. Its 20° latitudinal extent includes a complex of submerged plateaux, ridges, saddles and basins which, in the present interglacial, are partial barriers to circulation and steer the Subtropical (STF) and Subantarctic (SAF) fronts. This configuration offers a singular opportunity to assess the influence of bottom topography on oceanic circulation through Pleistocene glacial - interglacial (G/I) cycles, its effect on the location and strength of the fronts, and its ability to generate significant differences in mixed layer thermal history over short distances. For this study we use new planktic foraminiferal based sea-surface temperature (SST) estimates spanning the past 1 million years from a latitudinal transect of four deep ocean drilling sites. We conclude that: 1. the effect of the New Zealand landmass was to deflect the water masses south around the bathymetric impediments; 2. the effect of a shallow submerged ridge on the down-current side (Chatham Rise), was to dynamically trap the STF along its crest, in stark contrast to the usual glacial-interglacial (G-I) meridional migration that occurs in the open ocean; 3. the effect of more deeply submerged, downstream plateaux (Campbell, Bounty) was to dynamically trap the SAF along its steep southeastern margin; 4. the effects of saddles across the submarine plateaux was to facilitate the development of jets of subtropical and subantarctic surface water through the fronts, forming localized downstream gyres or eddies during different phases in the G-I climate cycles; 5. the deep Pukaki Saddle across the Campbell-Bounty Plateaux guided a branch of the SAF to flow northwards during each glacial, to form a strong gyre of circumpolar surface water in the Bounty Trough, especially during the mid-Pleistocene Climate Transition (MIS 22-16) when exceptionally high SST gradients existed across the STF; 6. the shallower Mernoo Saddle, at the western end of the Chatham Rise, provided a conduit for subtropical water to jet southwards across the STF in the warmest interglacial peaks (MIS 11, 5.5) and for subantarctic water to flow northwards during glacials; 7. although subtropical or subantarctic drivers can prevail at a particular phase of a G-I cycles, it appears that the Antarctic Circumpolar Current is the main influence on the regional hydrography. Thus complex submarine topography can affect distinct differences in the climate records over short distances with implications for using such records in interpreting global or regional trends. Conversely, the local topography can amplify the paleoclimate record in different ways in different places, thus enhancing its value for the study of more minor paleoceanographic influences that elsewhere are more difficult to detect. Such sites include DSDP 594, which like some other Southern Ocean sites, has the typical late Pleistocene asymmetrical saw-tooth G-I climate pattern transformed to a gap-tooth pattern of quasi-symmetrical interglacial spikes that interrupt extended periods of minimum glacial temperatures.

Planktonic foraminiferal assemblages of the Paleocene-Eocene Thermal Maximum of ODP Hole 113-690B

High-resolution study of Antarctic planktonic foraminiferal assemblages (Ocean Drilling Program Site 690, Weddell Sea) shows that these microplankton underwent a stepwise series of changes during the Paleocene-Eocene thermal maximum (PETM). Initiation of this response coincides with the onset of the carbon isotope excursion (CIE) but precedes the benthic foraminiferal mass extinction. The "top-to-bottom" succession in the biotic response indicates that the surface ocean/atmosphere was affected before the deep sea. The earliest stage of the faunal response entailed a conspicuous turnover within the shallow-dwelling genus Acarinina and a succession of stratigraphic first appearances. The genus Morozovella, large (>180 µm) biserial planktonics, and A. wilcoxensis are all restricted to the lower CIE within this PETM section. Acarininid populations crashed as the ocean/climate system ameliorated during the CIE recovery, reflecting atypical surface water conditions. This transient decline in acarininids is paralleled by a marked increase in carbonate content of sediments. It is postulated that this interval of carbonate enrichment, and its unusual microfauna, reflects enhanced carbon storage within reservoirs of the global carbon cycle other than the marine carbonate system (sensu Broecker et al., 1993, doi:10.1029/93PA00423; Ravizza et al., 2001, doi:10.1029/2000PA000541).

Sea surface temperature (Mg/Ca) from ODP Hole 161-977A

Mg/Ca, Sr/Ca, and stable isotope measurements have been performed on tests from the planktonic foraminifers Globigerinoides ruber (white), Globigerina bulloides, and Neogloboquadrina pachyderma (right coiling) in samples from Ocean Drilling Program site 977A in the Alboran Sea (Western Mediterranean). The evolution of different water masses between 250 and 150 ka is described. Warm substages were characterized by strong seasonality and thermal stratification of the water column. By contrast, less pronounced seasonality and basin stratification seem to prevail during cold substages. Several periods of stratification due to the low salinity of the upper water mass occurred during the formation of organic-rich layers and also during a possible Heinrich-like event at 220 ka. The three foraminifer species studied show a common and large shell Sr/Ca variability in short timescales, suggesting changes in the global ocean Sr/Ca ratio as one of the main causes of variations in shell composition.

Ice rafted debris, planktic foraminifera and reconstructed sea surface temperatures from site GIK23414

Planktic foraminiferal census data, faunal sea surface temperatures (SSTs) and oxygen isotopic and lithic records from a site in the northeast Atlantic were analyzed to study the interglacial dynamics of Marine Isotope Stage (MIS) 11, a period thought to closely resemble the Holocene on the basis of orbital forcing. Interglacial conditions during MIS 11 persisted for approximately 26 ka. After the main deglacial meltwater processes ceased, a 10- to 12-ka-long transitional period marked by significant water mass circulation changes occurred before surface waters finally reached their thermal maximum. This SST peak occurred between 400 and 397 ka, inferred from the abundance of the most thermophilic foraminiferal species and was coincident with lowest sea level according to benthic isotope values. The ensuing stepwise SST decrease characterizes the overall climate deterioration preceding the increase in global ice volume by ab. 3 ka. This cooling trend was followed by a more pronounced cold event that began at 388 ka, and that terminated in the recurrence of icebergs at the site around 382 ka. Because the water mass configuration of early MIS 11 evolved quite differently from that of the early Holocene, there is little evidence that MIS 11 can serve as an appropriate analogue for a future Holocene climate, despite the similarity in some orbital parameters.

Analog network to convert surface temperature to heat flux.

Mode of access: Internet.

Nonlinear analog network to convert surface temperature to heat flux.

Mode of access: Internet.

Analysis of adsorption of gases and vapors on nonporous graphitized thermal carbon black

In this paper we analyzed the adsorption of a large number of gases and vapors on graphitized thermal carbon black. The Henry constant was used to determine the adsorbate-adsorbent interaction energy, which is found to be a modest decreasing function of temperature. Analysis of the complete adsorption isotherm over a wider range of pressure yields information on the monolayer coverage concentration and the adsorbate-adsorbate interaction energy. Among the various equations tested, the Hill-de Boer equation accounting for BET-postulated multilayer formation describes well the adsorption isotherms of all adsorbates. On average, the adsorbate-adsorbate interaction energy in the adsorbed phase is less than that in the bulk phase, suggesting that the distance between adsorbed molecules in the first layer of the adsorbed phase is slightly less than the equilibrium distance between two adsorbate molecules in the bulk phase. This suggests that the first layer is in a compressed state, which is due to the attraction of the adsorbent surface. The monolayer concentration as determined from the fitting of the Hill-de Boer equation with experimental data is slightly larger than the values calculated from the molecular projection area, suggesting that molecules can be oriented such that a larger number of molecules can be accommodated on the carbon black surface. This further supports the shorter distance between adsorbate molecules in the adsorbed phase.

Adsorption of Supercritical fluids on graphitised thermal carbon black: Molecular layer structure theory versus grand canonical Monte Carlo simulation

This paper presents a detailed analysis of adsorption of supercritical fluids on nonporous graphitized thermal carbon black. Two methods are employed in the analysis. One is the molecular layer structure theory (MLST), proposed recently by our group, and the other is the grand canonical Monte Carlo (GCMC) simulation. They were applied to describe the adsorption of argon, krypton, methane, ethylene, and sulfur hexafluoride on graphitized thermal carbon black. It was found that the MLST describes all the experimental data at various temperatures well. Results from GCMC simulations describe well the data at low pressure but show some deviations at higher pressures for all the adsorbates tested. The question of negative surface excess is also discussed in this paper.