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In this review we discuss recent work and progress in the modelling of photospheres of stars of spectral types F and later. Special emphasis is laid on advances as regards the consideration of atomic and molecular blanketing, non-LTE and convection and other dynamic processes. In a special chapter we discuss the possibilities of semi-empirical modelling of late-type photospheres. In the conclusions we find that much important work remains in this field, but that a considerable part of this work may in fact be carried out in a near future.

This paper presents simultaneous observations made near the magnetic equator during counter electrojet events using a coherent VHF backscattcr radar, magnetometer and digital ionosonde to understand the physical processes that generate the counter electrojet conditions. The VHF backscatter radar gives the height structure of the drift velocity or the ionization irregularities, the equatorial electrojet current variations are obtained from the magnetometer and the digital ionosonde provides the presence of blanketing E-layers at the F-region heights which give rise to the backscatter signals. These observations have provided direct experimental evidence for the theoretically predicted distortions in the height structure of the polarization electric field in the equatorial electrojet due to the local effects of shearing zonal neutral winds.

This paper investigates the equilibrium behavior during the dead-ended anode (DEA) operation of a proton exchange membrane fuel cell. A reduced order model is developed focusing on the species molar fraction in the anode channel. At equilibrium, hydrogen is present only in a partial region in the anode, and the remaining region is deactivated by the accumulation of water and nitrogen. Simulation results are analysed to study the influences of certain controllable inputs and system parameters on the nitrogen front location and steady-state cell voltage. The simulation results are consistent with the initial experimental observations. The results in this paper suggest that it is possible to coat only the active portion of the membrane, along the channel length, with catalyst.

“A huge mountain took apart from the others, and traveled through the entire valley to join the other peaks on the opposite side, so blanketing the villages with earth and stones.” So a Polish monk describes the disaster of the Mount Grainer landslide in Savoy, France, 1248. The Alps have been several times the place of deadly large rock failures. Dante Alighieri in his Divine Comedy describes the scar of the Lavini di Marco landslides in Italy, speculating on the possible role of an earthquake or lack of support as a possible cause. Large deposits of much older landslides, historical and pre-historical, remind us that huge rock avalanches are an actual threat for mountain communities.

We undertake a new test of the metallicity sensitivity of the Leavitt Law for Classical Cepheids. We derive an empirical calibration of the apparent luminosities of Cepheids as measured from the optical through the mid-infrared (0.45-8.0um) as a function of spectroscopic [Fe/H] abundances of individual Cepheids in the Large Magellanic Cloud from Romaniello et al. (2008). The cumulative trend over the entire wavelength range shows a nearly monotonic behavior. The sense of the trend is consistent with differential line-blanketing in the optical, leading to stars of high metallicity being fainter in the optical. This is followed by a reversal in the trend at longer wavelengths, with the cross-over occurring near the K band at about 2.2um, consistent with a subsequent redistribution of energy resulting in a mild brightening of Cepheids (with increased metallicity) at mid-infrared wavelengths. This conclusion agrees with that of Romaniello et al. based on a differential comparison of the mean V- and K-band Leavitt Laws for the Galaxy, SMC and LMC, but is opposite in sign to most other empirical tests of the sensitivity of Cepheid distances to mean [O/H] HII region abundances. We also search for a correlation of Cepheid host-galaxy metallicity with deviations of the galaxy's Cepheid distance from that predicted from a pure Hubble flow. Based on Cepheid distances to 26 nearby galaxies in the local flow, only a very weak signal is detected giving Dmu_o = -0.17 (+/- 0.31) ([O/H] - 8.80) - 0.21 (+/-0.10). This is in agreement with previous determinations, but statistically inconclusive., Comment: Accepted to the Astrophysical Journal. 8 pages, 5 figures, 1 table

Several arguments that justify establishing a revised abundance calibration for DDO photometry of population I red giants are presented. The components of the blanketing vector in the DDOC(45–48) vsC(42–45) diagram are determined for late-type dwarfs and giants. We have redefined the DDO cyanogen anomaly and calibrated it against metallicity. The sample of field giants now available with abundances derived from high dispersion spectroscopy is substantially larger than previously available, leading to a more accurate abundance calibration. Iso-abundance lines in theC(41–42) vsC(42–45) diagram have been determined for population IG and K giants and an iterative method for deriving abundances of these stars is described. We show that the new DDO abundances are in very good agreement with those derived from high dispersion spectroscopy. The new method improves by about 0.1 dex the DDO abundances derived for early G and/or late K giants, with respect to the δCN method of Janes (1975).

The Bribie Island HF radar array (27°S, 153° E) can be set up to make angle of arrival and Doppler shift measurements throughout the range of spread-Es, layers. Results of this experiment show that the range spread seen on ionograms is not due to multiple reflection with varying obliquity, but rather a genuine height spread exists. Where velocity measurements can be reliably made, reflector velocity appears to be a slowly varying function of height. Spread-Es, can be blanketing or non-blanketing, sequential or non-sequential and at first impression it seems that the chief difference between spread-Es, and normal Es, is a small scale, partially transparent structure in lower regions that allows higher regions to be observed. It is suggested that on occasion spread-Es, irregularities are further modulated by the passage of gravity waves.

The energy distribution of the Am stars are affected by the line blanketing, which appears as a deviation in the behaviour of color indices with reference to the normal stars. In this paper we study the various color indices along with the data from IRAS and try to identify a realistic representative of the effective temperature. An excess in the IR also becomes apparent in some cases.

We present the first non-LTE time-dependent radiative-transfer simulations of supernovae (SNe) II-Plateau (II-P) covering both the photospheric and nebular phases, from similar to 10 to greater than or similar to 1000 d after the explosion, and based on 1.2 B piston-driven ejecta produced from a 15 M-circle dot and a 25 M-circle dot non-rotating solar-metallicity star. The radial expansion of the gradually cooling photosphere gives rise to a near-constant luminosity up to greater than or similar to 100 d after the explosion. The photosphere remains in the outer 0.5 M-circle dot of the ejecta for up to similar to 50 d after the explosion. As the photosphere reaches the edge of the helium core, the SN luminosity drops by an amount mitigated by the progenitor radius and the 56Ni mass. Synthetic light curves exhibit a bell-shaped morphology, evolving faster for more compact progenitors, and with an earlier peak and narrower width in bluer filters. UV and U-band fluxes are very sensitive to line blanketing, the metallicity and the adopted model atoms. During the recombination epoch synthetic spectra are dominated by H i and metal lines, and are largely insensitive to the differing H/He/C/N/O composition of our two progenitor stars. In contrast, synthetic nebular-phase spectra reveal a broader/stronger O i doublet line in the higher-mass progenitor model, reflecting the larger masses of oxygen and nickel that are ejected. Our simulations overestimate the typical luminosity and the visual rise time of standard SNe II-P, most likely a consequence of our progenitor stars being too big and/or too hydrogen rich. Comparison of our simulations with photospheric-phase observations of SN1999em of the same colour is satisfactory. Our neglect of non-thermal excitation/ionization leads to a fast disappearance of continuum radiation and Balmer-line emission at the end of the plateau phase. With the exception of H i lines, our nebular spectra show a striking similarity to contemporaneous observations of SN1999em.

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a survey of all Galactic stellar populations that will employ an R=30,000 spectrograph operating in the near-infrared (1.5-1.7μm) wavelength range. The fiber-fed spectrograph is housed in a large (1.4m x 2.3m x 1.3m) stainless steel cryostat or Dewar that is LN2-cooled and will be located in a building near the 2.5m Sloan Digital Sky Survey (SDSS) telescope to which it will be coupled. The choice of shell material and configuration was an optimization among optics packaging, weight, strength, external dimensions, rigging and transportation, the available integration and testing room, and the ultimate instrument room at APO. Internals are fabricated of more traditional 6061-T6 aluminum which is well proven in cryogenic applications. An active thermal shield with MLI blanketing yields an extremely low thermal load of 45-50 watts for this ~3000 liter instrument. Cryostat design details are discussed with applicable constraints and trade decisions. APOGEE is one of four experiments that are part of Sloan Digital Sky Survey III (SDSS-III).

The evaluation of the anti-jamming capability is one of the important aspects of the operational effectiveness evaluation of the netted radar system. The main work of this paper consists of three parts: firstly, a new evaluation framework of anti-jamming capability of netted radar system is constructed; secondly, the dynamic evaluation index system is created for anti-blanket jamming capability of netted radar system; thirdly, the dynamic simulation analysis and evaluation of anti-jamming capability are fulfilled under the four netting schemes by means of the method based on degree of gray incidence. The simulating results prove that the proposed evaluation framework and index system are correct and feasible.

We discuss a new one-dimensional non-LTE time-dependent radiative-transfer technique for the simulation of supernova (SN) spectra and light curves. Starting from a hydrodynamical input characterizing the homologously-expanding ejecta at a chosen post-explosion time, we model the evolution of the entire ejecta, including gas and radiation. Non-LTE, which holds in all regions at and above the photosphere, is accounted for. The effects of line blanketing on the radiation field are explicitly included, using complex model atoms and solving for all ion level populations appearing in the statistical-equilibrium equations. Here, we present results for SN1987A, evolving the model "lm18a7Ad" of Woosley from 0.27 to 20.8d. The fastest evolution occurs prior to day 1, with a spectral energy distribution peaking in the range 300-2000A, subject to line blanketing from highly ionized metal and CNO species. After day 1, our synthetic multi-band light curve and spectra reproduce the observations to within 10-20% in flux in the optical, with a greater mismatch for the faint UV flux. We do not encounter any of the former discrepancies associated with the HeI and HI lines in the optical, which can be fitted well with a standard Blue-supergiant-star surface composition and no contribution from radioactive decay. The effects of time dependence on the ionization structure, discussed in Dessart & Hillier, are recovered, and thus nicely integrated in this new scheme. Despite the 1D nature of our approach, its high physical consistency and accuracy will allow reliable inferences to be made on explosion properties and pre-SN star evolution.

Extreme helium stars are hydrogen‐deficient supergiants of spectral type A and B. They are believed to result from mergers in double degenerate systems, if one white dwarf is of C/O‐type and the other of He‐type. We calculate a new grid of model atmospheres accounting for metal line blanketing with ATLAS12 and compare it to the benchmark code STERNE. Synthetic spectra are calculated accounting for NLTE effects for many ions and applied to high‐quality optical spectra of the prototype extreme helium star BD+10°2179.

We present our new grids of NLTE model atmospheres for hot subdwarf O (sdO) stars computed with the public codes TLUSTY and SYNSPEC and including the effects of metal line blanketing. Until recently, large grids of NLTE models could not be practically computed over reasonable timescales, and have remained unavailable for quantitative spectroscopic analyses of this category of hot stars. We solved the problem by adapting TLUSTY and SYNSPEC to run in parallel mode on a small dedicated cluster of 80 fast processors. We present a comparison of three different NLTE grids including different elements. By fitting synthetic spectra from a given grid with another one, we obtain “maps” showing the line blanketing effects of metals, i.e., the differences between the real atmospheric parameters (Teff and log g) and the ones inferred by the fitting procedure. Finally, we present the results of the spectral analysis of SDSS J1600+0748, this unique pulsating sdO star, using our different grids of NLTE model atmospheres.

We use a sample of 121 spectroscopically normal Type Ia supernovae (SNe Ia) to show that their intrinsic color is correlated with their ejecta velocity, as measured from the blueshift of the Si II 6355 feature near maximum brightness, v_Si. The SN Ia sample was originally used by Wang et al. (2009) to show that the relationship between color excess and peak magnitude, which in the absence of intrinsic color differences describes a reddening law, was different for two subsamples split by v_Si (defined as "Normal" and "High-Velocity"). We verify this result, but find that the two subsamples have the same reddening law when extremely reddened events (E(B-V) > 0.35 mag) are excluded. We also show that (1) the High-Velocity subsample is offset by ~0.06 mag to the red from the Normal subsample in the (B_max - V_max) - M_V plane, (2) the B_max - V_max cumulative distribution functions of the two subsamples have nearly identical shapes, but the High-Velocity subsample is offset by ~0.07 mag to the red in B_max - V_max, and (3) the bluest High-Velocity SNe Ia are ~0.10 mag redder than the bluest Normal SNe Ia. Together, this evidence indicates a difference in intrinsic color for the subsamples. Accounting for this intrinsic color difference reduces the scatter in Hubble residuals from 0.190 mag to 0.130 mag for SNe Ia with A_V < 0.7 mag. The scatter can be further reduced to 0.109 mag by exclusively using SNe Ia from the Normal subsample. Additionally, this result can at least partially explain the anomalously low values of R_V found in large SN Ia samples. We explain the correlation between ejecta velocity and color as increased line blanketing in the High-Velocity SNe Ia, causing them to become redder. We discuss some implications of this result, and stress the importance of spectroscopy for future SN Ia cosmology surveys, with particular focus on the design of WFIRST., 9 pages, 8 figures, submitted to ApJ

An analytical model for small-scale single drop fuel coolant interaction based on fragmentation caused by the Taylor instability and transient heat transfer during collapse and bounce period is developed. According to our previous analysis, pressure in the vapor film blanketing hot surface increases transiently more than 10 MPa, when thickness of the vapor film decreases less than 10 μm. The transient high pressure makes vapor-liquid interface bounce and causes the Taylor instabilities at both sides of the vapor-liquid interfaces by the large acceleration. As the growth time of the interface instability is enough short compared with the bouncing time, the instabilities result to fragmentation and mixing of both liquids. In the proposed model, the fragmentation time and fragmented particle size were estimated from the growth rate and the wave length of the instability. The analytical model composed of a set of time dependent differential equations was numerically calculated by the Runge-Kutta-Gill...

To help resolve unknowns regarding consequences of air-ingress accidents in uranium beds, a series of experiments was conducted at Ontario Hydro Research Division with the participation of Princeton Plasma Physics Laboratory and the Idaho National Engineering Laboratory. These experiments involved exposure of uranium beds of various sizes to air, oxygen in helium, argon and Nitrogen. Beds of 5-gram to 3-kg uranium capacity were tested. Starting temperatures ranged from 294 K to 824 K. Results of these experiments showed that in every test the reaction was restrained with modest temperature excursions. Either surface films or gas blanketing may be responsible for quenching the reaction with air. In these tests the reaction appears to be stopped by a diffusive barrier film of reaction products that grows on the surface of the uranium grains. The only tritium emissions appeared to be due to thermal oscillation-driven gas expansion. Our conclusion is that the hazard associated with an air-ingress acci...

This study has used ionospheric and magnetic observational data obtained at a meridional chain of stations during the high latitude geophysical experiment ‘Taimir-82’ in the winter of 1982–1983. Mean statistical latitude-time distributions of the occurrence probability of various types of E s , their blanketing frequency and of the amplitude of geomagnetic field H -variations have been constructed. Based on these distributions and taking the E s properties into account, an analysis is made of the mutual correspondence of large-scale structures of the auroral ionosphere and ionospheric currents. Ionospheric currents flow mainly in the region of high E -layer ionization. With increasing magnetic activity, the zone of currents and the zone of ionization expand simultaneously toward lower latitudes. The evening eastward electrojet and the morning westward electrojet are localized inside the zone of diffuse auroral precipitation which is responsible for the formation of E s type r . The equatorial part of the midnight westward electrojet is also located in the zone of diffuse precipitation which coincides also with the region of maximum ionization of the E -layer. The polar part of this electrojet, which extends far into the dusk sector, is located in the zone of discrete auroral precipitation ( a type E s ). Whereas there exists in the meridional cross-section quite a definite relationship between the Harang discontinuity and ionospheric parameters, such a relationship is not manifested in the zonal cross-section of the Harang discontinuity.

In this paper we have carried out an analysis of the predictions of the radiatively driven stellar winds theories on 63 stars belonging to clusters or associations. The spectral types in our sample range from O3 to B0 and all classes of luminosity are considered. The study has been carried out starting from the relationship between the stellar-wind velocity (v edge) obtained from the resonance doublet ofCIV for stars observed with the IUE, and the escape velocity. The stellar masses have been obtained from the evolutionary tracks of Maeder and Meynet. Results from recent NLTE analyses with blanketing of lines and winds have been used for the effective temperature.

A model using photochemistry and transport due to electric fields and gravity wave winds has been used to explain the formation of ionisation layers observed over an equatorial station Thumba (dip 0°47′S) with rocket-borne Langmuir probes during two daytime counter-electrojet periods. These layers were seen as blanketing E s -layers with an ionosonde at Thumba. Convergence of the metallic ions due to three-dimensional gravity wave winds and a westward electric field appears to be mainly responsible for the observed ionisation layer over the equator.

Field Strengths of video signals by Transequatorial propagation between Kokavil (Sri Lanka) & Madras (India); and Pidurutalagala (Sri Lanka) & Madras (India) were recorded daring March 1982 to June 1983 on VHF band III channels 5 and 8 ie picture carriers frequencies of 175.25 MHz and 196.25 MHz respectively. The observed signal strength on both of these channels indicated strong dependence on the occurrence of blanketing sporadic E layers (Es-b) of the ionosphere near the magnetic equator. A comparison between the video field strengths and critical frequency blanketing sporadic-E, fbEs, led to the conclusion that the transequatorial propagation is mainly due to the presence of sporadic-E rather than the actual values of fbEs The observed video signal strengths plotted vs foEs, critical frequency of sporadic E show better correlation in distinct frequency ranges 3–5 MHz and 7–11 MHz. On the otherhand, there is no evidence of the influence of the F-region (foF2, the critical frequency of the F2 layer and s...

Summary A brief review of plutonium oxidation literature was conducted. The purpose of the review was to ascertain the effect of oxidation conditions on oxide morphology to support the design and operation of the PDCF direct metal oxidation (DMO) furnace. The interest in the review was due to a new furnace design that resulted in oxide characteristics that are different than those of the original furnace. Very little of the published literature is directly relevant to the DMO furnace operation, which makes assimilation of the literature data with operating conditions and data a convoluted task. The oxidation behavior can be distilled into three regimes, a low temperature regime (RT to 350°C) with a relatively slow oxidation rate that is influenced by moisture, a moderate temperature regime (350 – 450°C) that is temperature dependent and relies on more or less conventional oxidation growth of a partially protective oxide scale, and high temperature oxidation (> 500°C) where the metal autocatalytically combusts and oxidizes. The particle sizes obtained from these three regimes vary with the finest being from the lowest temperature. It is surmised that the slow growth rate permits significant stress levels to be achieved that help break up the oxides. The intermediate temperatures result in a fairly compact scale that is partially protective and that grows to critical thickness prior to fracturing. The growth rate in this regime may be parabolic or paralinear, depending on the oxidation time and consequently the oxide thickness. The high temperature oxidation is invariant in quiescent or nearly quiescent conditions due to gas blanketing while it accelerates with temperature under flowing conditions. The oxide morphology will generally consist of fine particles ( 250 µm). The particle size ratio is expected to be < 5%, 25%, and 70% for fine, medium and large particles, respectively, for metal temperatures in the 500-600°C range.

The blanketing process consists of creating and maintaining an inert atmosphere inside a closed equipment to prevent the contained product from mixing with oxygen. This technique is widely used in chemical, pharmaceutical and food industries operations, to avoid the ignition, degradation or evaporation losses of their products. This work deals with the design process of an optimal blanketing system in terms of cost, safety and environmental issues, for a multiple-tank storage facility. With this objective, the feasibility of installing a manifold in the system as an alternative to the traditional approach of an individual component in each tank has been technically studied by means of statistical analysis and fluid flow simulation. Moreover, economical, environmental and safety analyses have been performed. The reported results shed light to a more economical solution, which entails a decrease in atmospheric emissions and offers an even higher reliability than traditional systems.

This paper provides insight into the complicated issue of launch vehicle resonate cavity effects that has applicability outside of the space industry. Radiation from spacecraft or launch vehicle antennas located within the enclosures of a launch vehicle generates an electromagnetic environment that is difficult to predict accurately. This paper discusses the test results of power levels produced by a transmitter within a representative scaled vehicle fairing model and provides preliminary modeling results at critical frequencies using a commercial tool. Initially, fairing walls are aluminum and are then layered with materials to simulate acoustic blanketing structures that are typical in payload fairings. The effects of these blanketing materials on the power levels within the fairing are examined. Industry data is also reviewed for comparison purposes.

[1] The crater population of asteroid 433 Eros exhibits a deficit in small crater diameters that has been suggested to result from impact-induced seismic shaking initiating downslope movements of regolith material, covering these small craters. As in lunar maria, saturation equilibrium was expected to characterize the crater population of Eros, but was surprisingly not shown by the data set. The surface of Eros displays evidence of burial by regolith especially for boulders, suggesting that ejecta coverage erases the craters in addition to seismic shaking erasure. In this work we investigate the production and erasure of craters by impact ejecta and compare derived crater size distributions with those measured for Eros. We simulate a bombardment of Eros by an impactor population derived from the Main Asteroid Belt and estimate the crater and ejecta characteristics with a scaling law, allowing ejecta to progressively create a regolith blanket. Assuming the contribution of the ejecta blanketing process only, we find a good agreement between the simulated and the observed population of 250 m to 4 km diameter craters for exposure times of 600 Ma and 400 Ma. This suggests a major impact or breakup that occurred about 500 Ma ago, inducing a surface reset. A mismatch for craters with a diameter smaller than ∼100 m remains, indicating that seismic shaking (or another erasure process) is still necessary to explain their low number. Our simulations emphasize the importance of an accurate modeling of both processes to fully understand and interpret the small body size-frequency crater curves.

The FUSE flux calibration is defined by synthetic spectra of six DA white dwarfs with effective temperatures Teff ranging from 32,800 K to 61,200 K. The LWRS observations of these stars were reprocessed using the final calibration, and the results compared against synthetic spectra. Discrepancies were generally 5% or less, apart from the well‐known “worm” feature in LiF1B. Discrepancies for GD 246 were significant for the Teff used previously (53,000 K), but are comparable to those for the other stars for a model computed at Teff = 58,700 K. The effects of quasi‐molecular satellite features are significant for the coolest star in this sample, and appear to modify the Lyman line profiles at all Teff. Blanketing by weak metal lines in G 191‐B2B make use of this star problematic for calibrations accurate to a few percent or better in the FUV.

International audience; Early in the STEREO mission observers noted that the white-light instruments of the SECCHI suite were detecting significantly more spacecraft-related ``debris'' than any previously flown coronagraphic instruments. Comparison of SECCHI ``debris storms'' with S/WAVES indicates that almost all are coincident with the most intense transient emissions observed by the radio and plasma waves instrument. We believe the debris is endogenous ( i.e., from the spacecraft thermal blanketing), and the storms appear to be caused by impacts of large interplanetary dust grains that are detected by S/WAVES. Here we report the observations, compare them to interplanetary dust distributions, and document a reminder for future spacebased coronagraphic instrument builders.

The flexural rigidity of the oceanic lithosphere is strongly dependent on its temperature structure at the time of loading. It is commonly assumed that the depth to the 450°C isotherm defines the effective elastic thickness Te of the lithosphere. However, recent gravity studies across the Baltimore Canyon and Nova Scotian margins suggest that temperature may play a more complicated role in controlling the mechanical strength of extended continental lithosphere. For example, the flexural strength of the Baltimore Canyon margin (with sediment thicknesses of ≅ 15 km) appears to be controlled by the depth to the 150°C isotherm whereas the strength of the Nova Scotian margin (with sediment thicknesses cf ≅ 10 km) is controlled by the depth to the 250°C isotherm. The apparent correlation between sediment thickness and controlling isotherm suggests that sediment blanketing may play a role in modifying the flexural strength of extended continental lithosphere. This hypothesis was investigated by simulating the sedimentation history of a margin as a Gaussian function in which sedimentation peak and rate are determined by the mean and standard deviation of the function. The temperature structure of the lithosphere is continually modified as sediments are deposited on, and incorporated into the temperature structure of, the underlying lithosphere. Given a ‘starting’ value of Te defined by the degree of extension of the lithosphere, the modification of Te appears to be directly proportional to the sedimentation rate and cumulative sediment thickness, and inversely proportional to the time at which the sedimentation rate is a maximum. The first-order consequence of sediment blanketing is to reduce the cooling rate of the lithosphere relative to cooling in the absence of sediments. At thermal equilibrium, the initial value of Te is reduced by the cumulative sediment thickness. Local isostatic conditions (i. e. Te≅ 0) can only be approached when the sedimentation rate is unrealistically high (> 1000 m/Myr) during the rift or early post-rift phase of basin development. However, while these early loads may be locally compensated, any subsequent loads will be regionally compensated. Thus, it is unlikely that the low present-day flexural strengths interpreted from the Baltimore Canyon and Nova Scotian passive continental margins are a consequence of sediment blanketing.

Recent studies are leading to a better understanding of the formation of the earth's metal core. This new information includes: better knowledge of the physics of metal segregation, improved geochemical data on the abundance of siderophile and chalcophile elements in the silicate part of the earth, and experimental data on the partitioning behavior of siderophile and chalcophile elements. Extensive melting of the earth as a result of giant impacts, accretion, or the presence of a dense blanketing atmosphere is thought to have led to the formation of the core. Collision between a planet-sized body and the earth may have also produced the moon. Near the end of accretion, core formation evidently ceased as upper mantle conditions became oxidizing. The accumulation of the oceans is a consequence of the change to oxidizing conditions.

The information content of (photospheric) stellar spectra and the accuracy of abundance determinations are discussed. Besides the physical properties of the line spectra, the spectral resolution, the signal-to-noise ratio, but also the incompleteness of the knowledge of the contributing blends limit the abundance information. For a perfect model atmosphere the main factors determining the accuracy of the abundances are S/N, the line saturation, and the location of the continuum (or, in a synthetic spectrum, the background of numerous lines). In addition systematic errors introduced by missing atomic data and an imperfect model atmosphere (non-LTE, line blanketing, hydrodynamics) are important. The typical accuracy of abundance determinations is discussed for main sequence stars for which the most reliable data are available, and for a few selected other stellar types.

[1] A number of puzzling features have been observed that occur during the day in the vicinity of the equatorial electrojet (EEJ). They include (1) an equatorial belt, essentially collocated with the EEJ, that is virtually devoid of blanketing sporadic E (Esb); (2) appearances of Esb within that “forbidden” belt but only when the EEJ is weak or reversed (i.e., a counterelectrojet); (3) occasional appearances of a secondary current layer above the EEJ; and (4) observations at 4.3°N dip latitude of a latitudinal tilt in the bottomside E layer on one occasion and an unexpectedly large electron drift velocity on another. These features are shown to be accountable if the usual framework for electrodynamics in this region is modified to include the following: (1) transport of Esb that is controlled by a shear in the neutral wind with a crucial contribution from the polarization electric field of the EEJ; (2) the formation of an equatorward boundary for Esb by a dynamical balance between the neutral wind and the polarization electric field; (3) a buildup in conductivity within a band-like region, just poleward of the Esb boundary, from an accumulation of metallic ions; and (4) the appearance of a secondary polarization electric field across the band of enhanced conductivity and current flow throughout the region pervaded by that secondary electric field.

[1] Recent P wave velocity compilations of the oceanic crust indicate that the velocity of the uppermost layer 2A doubles or reaches ∼4.3 km/s found in mature crust in

We have constructed a grid of about 10,000 spherically symmetric and plane-parallel models with the MARCS program, and make it available for public use. Parameter ranges are: Teff=2500 to 8000 K, log g =log(GM/R2)= -1 to 5 (cgs) with various masses and radii, [Me/H]=-5 to +1, with [Alpha/Fe] = 0.0 and 0.4 and different choices of C and N abundances to also represent stars of types R, S and N, and with microturbulence parameters from 1 to 5 km/s. We also list fluxes in approximately 108,000 wavelength points. Underlying assumptions in addition to 1D stratification include hydrostatic equilibrium, MLT convection and LTE. A number of general properties of the models are discussed, in relation to the effects of changing blanketing and sphericity. Models are compared with other available grids and excellent agreement is found with plane-parallel models of Castelli and Kurucz within the overlapping parameter range. Although there are departures from the spherically symmetric NextGen models, the agreement with more recent PHOENIX models is gratifying. The models of the grid show regularities, but some interesting departures from general patterns occur for the coolest models due to the molecular opacities. We have tested rules of thumb concerning effects of blanketing and sphericity and found them to often be astonishingly accurate. Some interesting new phenomena have been discovered, such as the intricate coupling between blanketing and sphericity, and the strong effects of carbon enhancement on metal-poor models. We give further details of models and comparisons with observations in subsequent papers., 20 pages, 20 figures, to be published in Astronomy & Astrophysics

A grid of NLTE model atmospheres for early-type stars is presented. Model atoms of eleven different elements with various abundances and, for a subset of the models, effects of wind blanketing, are taken into account. These model atmospheres supply realistic emergent fluxes which can be used in ionization calculations for circum- and interstellar gas. The dependence of the ionizing radiation of these stars on spectral type, luminosity class, evolutionary state and stellar environment is discussed.

Continuum and line blanketing models for the photospheres of novae in the early stages of their outbursts are presented. The expanding envelopes are characterized by a very slow increase of density with decreasing radius which leads to very large geometrical extensions and large temperature differences between the inner and outer parts. The spectra show a large IR excess and a small Balmer jump which may be either in absorption or in emission. For the parameters considered (T eff = 104,1.5 x 104, 2 x 104K, R = 1011 cm, solar composition), most lines are in absorption. The effects of both modifications in the temperature structure (e.g. by heating from shock fronts) and changes in the abundances of the heavy elements on the emergent spectra are briefly discussed.

This paper describes experimental analyses using the SIMMER-III computer code, which were precedently carried out to give boundary conditions for the integral verification of the new COMPASS code, which is based on MPS method. Two topics of key phenomena in core disruptive accidents were presented in this paper: molten fuel freezing and dispersion; and boiling behavior of molten fuel pool. Related experimental database are reviewed to select appropriate experiments. To analyze the fuel freezing behavior, the GEYSER out-of-pile and the CABRI-EFM1 in-pile experiments were selected. The SIMMER-III calculations were in good agreement with fuel penetration lengths measured in a series of the GEYSER experiments. The fuel freezing behavior in the CABRI-EFM1 experiment was also reasonably simulated by SIMMER-III. The boiling pool consisting principally of molten fuel/steel mixtures is characterized by the heat transfer between fuel and steel. The CABRI-TPA2 experiment has suggested low transient heat flux from fuel to steel due to a steel vapor blanketing around a steel droplet. SIMMER-III well simulated the steel boiling behavior observed in the CABRI-TPA2 experiment by applying reduced heat transfer coefficients between fuel and steel. These experimental analyses by SIMMER-III have also identified key processes to be clarified by mesoscopic simulations using the COMPASS code.

Intensity scintillations of 40 MHz, 140 MHz and 360 MHz radio beacons on board the geostationary satellite ATS-6, (at 34°E longitude), recorded at Ootacamund (magnetic dip latitude 3°N) during the ATS-6 phase II (1975–1976) are described. The scintillation index S4, which is the normalised RMS value of the intensity fluctuations, is found to be very large at 2100-0200 h associated with equatorial spread-F, and in the forenoon and afternoon hours associated with a blanketing type of sporadic E-layer. At 40 MHz there seems to be a weak scintillation (S4 The frequency exponent, n, (with S 4 ∝ ƒ −1 , whereƒ is the signal frequency), was found to decrease monotonically with increasing intensity of scintillations, approaching a value of zero for saturated scintillations. The relationship between the frequency exponent and the scintillation index was found to be independent of the time of the day or the season, in spite of different kinds of irregularities being involved in the scintillation processes.

AA Tau was observed for about 5h per XMM orbit (2 days) over 8 successive orbits, which covers two optical eclipse periods (8.2 days). The XMM optical/UV monitor simultaneously provided UV photometry with a ~15 min sampling rate. Some V-band photometry was also obtained from the ground during this period in order to determine the dates of the eclipses. Two X-ray and UV measurements were secured close to the center of the eclipse. The UV flux is the highest just before the eclipse starts and the lowest towards the end of it. We model the UV flux variations with a weekly modulation (inner disk eclipse), plus a daily modulation, which suggests a non-steady accretion. No eclipses are detected in X-rays. For one measurement, the X-ray count rate was nearly 50 times stronger than the minimum observed level, and the plasma temperature reached 60 MK, i.e., a factor of 2-3 higher than in the other observations. This X-ray event, observed close to the center of the optical eclipse, is interpreted as an X-ray flare. We identify the variable column density with the low-density accretion funnel flows blanketing the magnetosphere. The lack of X-ray eclipses indicates that X-ray emitting regions are located at high latitudes. Furthermore, the occurrence of a strong X-ray flare near the center of the optical eclipse suggests that the magnetically active areas are closely associated with the base of the high-density accretion funnel flow. We speculate that the impact of this free falling accretion flow onto the strong magnetic field of the stellar corona may boost the X-ray emission (abridged)., 17 pages and 9 Figures. Accepted by A&A

[1] The role of the molecular and metallic ions in the formation of sporadic E layers (Es layers) has been an active area of research for many years. Ionosonde data of the Es layer parameter, fbEs (the blanketing frequency of sporadic layer), and ftEs (the top frequency of Es trace), obtained over the Brazilian sites, Fortaleza, and Sao Luis, show that the diurnal variations of these parameters often present a disruption that is coincident with the evening prereversal electric field/vertical drift enhancement, to reappear after about 2 hours. In this work we have developed a model of the E region with the objective to describe all the phases of the life cycle of the sporadic layer and its relation to the evening vertical electric field enhancement that is associated with the development of the prereversal zonal electric field enhancement. The model calculates the densities of NO + , O + 2 , O + , N + 2 , and Fe + in the height region 86-140 km by simultaneously solving the continuity and momentum equations for each of the species. For low latitudes this model shows that winds and electric fields each play distinct roles in the vertical transport of plasma leading to Es layer formation. The results of our numerical simulation confirm the dominant role of the vertical electric field as the cause of the inhibition/disruption of the sporadic layer in the evening. More specifically, the results reveal that an upward directed (positive) vertical electric field is capable of disrupting an ongoing sporadic layer, whereas a downward (negative) electric field favors its formation or even intensification, thus corroborating the conclusions of the recent study by Abdu et al. (2003).

Jamming and clutter must be effectively suppressed for moving target detection. A method of detecting slow-moving ground targets based on three-aperture synthetic aperture radar (SAR) in the presence of blanketing jamming is presented. It uses two-aperture cancellation method to suppress SAR jamming to target then to detect the moving ground targets. Firstly, spatial geometry model and echo signal model of three-antenna SAR were built, then an algorithm of SAR moving target detection based on clutter suppression interferometer (CSI) was derived, and the realization steps were presented. Finally, computer simulation results validate its effectiveness.

HF-induced fine-scale electron density variations and/or enhanced airglow in the ionosphere were investigated. These irregularities appear to trap waves and cause them to "self-focus." Knowing what irregularities exist is important for improving communications and for pure discovery research on wave-particle interactions in the lower ionosphere at high latitudes. To develop accurate models of its behavior, lower ionospheric structure must be known. Under this grant, we conducted telescopic imaging of heater-induced airglow at HAARP to optically measure fine structure in the ionosphere and to study airglow sources. In the presence of aurora and a strong blanketing E layer, HAARP was modulated at intervals of several seconds. For several cycles, small bright airglow spots were observed whenever HAARP was on. These spots are elongated horizontally, indicating drift motion, and are the same order of brightness as the aurora. Such bright artificial airglow was never recorded previously. These results were published in the journal Nature.

We present the XMM-Newton discovery of X-ray emission from the planetary nebula (PN) A78, the second born-again PN detected in X-rays apart from A30. These two PNe share similar spectral and morphological characteristics: They harbor diffuse soft X-ray emission associated with the interaction between the H-poor ejecta and the current fast stellar wind, and a point-like source at the position of the central star (CSPN). We present the spectral analysis of the CSPN, using for the first time a NLTE code for expanding atmospheres which takes line blanketing into account for the UV and optical spectra. The wind abundances are used for the X-ray spectral analysis of the CSPN and the diffuse emission. The X-ray emission from the CSPN in A78 can be modeled by a single C VI emission line, while the X-ray emission from its diffuse component is better described by an optically thin plasma emission model with temperature $kT$=0.088 keV ($T\approx$1.0$\times$10${^6}$ K). We estimate X-ray luminosities in the 0.2--2.0 keV energy band of $L_{\mathrm{X,CSPN}}$=(1.2$\pm$0.3)$\times$10$^{31}$ erg~s$^{-1}$ and $L_{\mathrm{X,DIFF}}$=(9.2$\pm$2.3)$\times$10$^{30}$ erg~s$^{-1}$ for the CSPN and diffuse components, respectively., 12 pages, 10 figures, 2 tables; Accepted to Astrophysical Journal

CONTEXT: Very massive stars pass through the Wolf-Rayet (WR) stage before they finally explode. Details of their evolution have not yet been safely established, and their physics are not well understood. Their spectral analysis requires adequate model atmospheres, which have been developed step by step during the past decades and account in their recent version for line blanketing by the millions of lines from iron and iron-group elements. However, only very few WN stars have been re-analyzed by means of line-blanketed models yet. AIMS: The quantitative spectral analysis of a large sample of Galactic WN stars with the most advanced generation of model atmospheres should provide an empirical basis for various studies about the origin, evolution, and physics of the Wolf-Rayet stars and their powerful winds. METHODS: We analyze a large sample of Galactic WN stars by means of the Potsdam Wolf-Rayet (PoWR) model atmospheres, which account for iron line blanketing and clumping. The results are compared with a synthetic population, generated from the Geneva tracks for massive star evolution. RESULTS: We obtain a homogeneous set of stellar and atmospheric parameters for the Galactic WN stars, partly revising earlier results. CONCLUSIONS: Comparing the results of our spectral analyses of the Galactic WN stars with the predictions of the Geneva evolutionary calculations, we conclude that there is rough qualitative agreement. However, the quantitative discrepancies are still severe, and there is no preference for the tracks that account for the effects of rotation. It seems that the evolution of massive stars is still not satisfactorily understood., 19 pages, 11 figures, A&A, in press, additional Online-material on http://www.astro.physik.uni-potsdam.de/abstracts/galwn.html

The progress over the last years in modelling the atmospheres and winds of PN central stars is reviewed. We discuss the effect of the inclusion of the blanketing by millions of metal lines in NLTE on the diagnostics of photospheric and stellar wind lines, which can be used to determine stellar parameters such as effective temperature, gravity, radius, mass loss rate and distance. We also refer to recent work on the winds of massive O-type stars, which indicates that their winds are possibly inhomogeneous and clumped. We investigate implications from this work on the spectral diagnostics of PN central stars and introduce a method to determine wind clumping factors from the relative strengths of Halpha and HeII 4686. Based on new results we discuss the wind properties of CSPN., 8 pages, 12 figures; Proceedings, IAU Symposium No. 234, 2006, "Planetary Nebulae in our Galaxy and Beyond", M.J. Barlow and R.H. Mendez, eds

The possibility of air objects location in bistatic radars employing as illumination the signals of broadcast SB stations is considered in this paper. The spectrums of illumination signal are investigated experimentally. The requirements to the direct signal blanketing degree for the location assurance at given distances. The possibility of building of bistatic systems complex employing broadcast SB stations and providing location of acquiring object employing the information of Doppler frequency translation of signal receiving from object is considered.

Inert Gas blanketing as used by FPSOs for crude storage tanks results in significant VOC emissions to the atmosphere. The HC blanketing system shows significant reduction in emissions compared to the Inert Blanketing system. The Carbon Costing methodology and the CAPEX estimates show the comparable savings vs. investments, excluding the potential positive effects on reputation management. The HC blanketing option therefore presents a serious environmental emissions reduction opportunity, that warrants a dedicated effort to make it work on future FPSOs.

The parameters of ten supersoft X-ray sources (RX J0439.8-6809, RX J0513.9-6951, RX J0527.8-6954, CAL 87, CAL 83, 1E 0035.4-7230, RX J0048.4-7332, 1E 0056.8-7154, RX J0019.8 +2156, RX J0925.7-4758) observed by ROSAT obtained using blanketing LTE model atmospheres are analyzed. The consistency of the resulting parameters with a model with stable/recurrent burning on the surface of the white dwarf is studied. The luminosity and sizes of seven of the sources are in good agreement with this model. The masses of the white dwarfs in these sources are estimated. A formula that can be used to estimate the masses of white dwarfs in classical supersoft sources based on their effective temperatures is presented., 8 pages, 2 tables, 4 figures

ROSAT spectra of 11 supersoft X-ray sources (RX J0439.8-6809, RX J0513.9-6951, RX J0527.8-6954, CAL 87, CAL 83, 1E 0035.4-7230, RX J0048.4-7332, 1E 0056.8-7154, RX J0019.8 +2156, RX J0925.7-4758, AG Draconis) are approximated with theoretical spectra obtained in LTE models for the atmospheres of hot white dwarfs with line blanketing. The confidence intervals of parameters derived from these approximations $ T_{\rm eff}$, $\log g$, $N_H$, and $R^2/d^2$ are determined. The results are compared with predictions for a model with stable/recurrent thermonuclear burning on the white-dwarf surface., Comment: 7 pages, 6 tables, 5 figures