151 research outputs found
The UV/X-ray emission of the symbiotic star AG Draconis during quiescence and the 1994/1995 outbursts
No full textWe present the results of an extensive campaign of coordinated X-ray (ROSAT) and UV (IUE) observations of the symbiotic star AG Dra during a long period of quiescence followed recently by a remarkable phase of activity characterized by two optical outbursts. The major optical outburst in June 1994 and the secondary outburst in July 1995 were covered by a number of target of opportunity observations (TOO) with both satellites. Optical photometry is used to establish the state of evolution along the outburst. Our outburst observations are supplemented by a substantial number of X-ray observations of AG Dra during its quiescent phase between 1990-1393. Near-simultaneous IUE observations at the end of 1992 are used to derive the spectral energy distribution from the optical to the X-ray range. The X-ray flux remained constant over this three year quiescent phase. The hot component (i.e. X-ray emitting compact object) turns out to be very luminous: a blackbody fit to the X-ray data in quiescence with an absorbing column equal to the total galactic NH in this direction gives (9.5 +/- 1.5) x 10(36) (D/2.5 kpc)(2) erg/s. This suggests that the compact object is burning hydrogen-rich matter on its surface even in the quiescent (as defined optically) state at a rate of (3.2 +/- 0.5) x 10(-8) (D/2.5 kpc)(2) M./yr. Assuming a steady state, i.e. burning at precisely the accretion supply rate. this high rate suggests a Roche lobe filling cool companion though Bondi-Hoyle accretion from the companion wind cannot be excluded. With ROSAT observations we have discovered a remarkable decrease of the X-ray flux during both optical maxima, followed by a gradual recovering to the pre-outburst flux, In the UV these events were characterized by a large increase of the emission line and continuum fluxes, comparable to the behaviour of AC Dra during the 1980-81 active phase. The anticorrelation of X-ray/UV flux and optical brightness evolution is very likely due to a temperature decrease of the hot component. Such a temperature decrease could be the result of an increased mass transfer to the burning compact object, causing it to slowly expand to about twice its original size during each optical outburst
Cold cracking in DC-cast high strength aluminum alloy ingots: An intrinsic problem intensified by casting process parameters
No full textFor almost half a century the catastrophic failure of direct chill (DC) cast high strength aluminum alloys has been challenging the production of sound ingots. To overcome this problem, a criterion is required that can assist the researchers in predicting the critical conditions which facilitate the catastrophic failure of the ingots. This could be achieved at first glance by application of computer simulations to assess the level and distribution of residual thermal stresses. However, the simulation results are only able to show the critical locations and conditions where and when high stresses may appear in the ingots. The prediction of critical void/crack size requires simultaneous application of fracture mechanics. In this paper, we present the thermo-mechanical simulation results that indicate the critical crack size distribution in several DC-cast billets cast at various casting conditions. The simulation results were validated upon experimental DC-casting trials and revealed that the existence of voids/cracks with a considerable size is required for cold cracking to occur.Materials Science & EngineeringMechanical, Maritime and Materials Engineerin
Benthic stable carbon and oxygen isotopes of Cibicidoides wuellerstorfi from ODP Hole 130-806B 0-4 m.y
No full textODP Leg 130 - Site 806B benthic stable carbon and oxygen isotopes have been measured using the epibenthic foraminifer species Cibicidoides wuellerstorfi in cores cores 1H to 11H of Hole B, only. Stratigraphy is based on correlation to the benthic oxygen isotope stack of Lisiecki and Raymo 2005 (Paleoceanography vol 20, PA1003, doi:10.1029/2004PA001071)
UV and X-Ray Monitoring of AG Draconis During the 1994/1995 Outbursts
No full textThe recent 1994-1995 active phase of AG Draconis has given us for the first time the opportunity to follow the full X-ray behaviour of a symbiotic star during two successive outbursts and to compare with its quiescence X-ray emission. With \ros observations we have discovered a remarkable decrease of the X-ray flux during both optical maxima, followed by a gradual recovering to the pre-outburst flux. In the UV the events were characterized by a large increase of the emission line and continuum fluxes, comparable to the behaviour of AG Dra during the 1980-81 active phase. The anticorrelation of X-ray/UV flux and optical brightness evolution is shown to very likely be due to a temperature decrease of the hot component. Such a temperature decrease could be produced by an increased mass transfer to the burning compact object, causing it to slowly expand to about twice its original size
A Study of Customer Relationship Management in Mobile Phone Service Providing Companies in the State of Gujarat
No full textNot availabl
Coccoliths in sediment traps from the Norwegian Sea
No full textThe fine fraction of surface sediment samples in the Norwegian Sea shows an unexpectedly high amount of calcareous nannoplankton. Investigations, using time-series sediment traps in the Lofoten Basin (69°N, 1983/84), near Bear Island (75°N, 1984/85) and in the Fram Strait (78°N, 1984/85) provided information about the accumulation of this material in relation to the strong seasonality of biological production.
Coccolith identification and counting, by means of a scanning electron microscope, indicated that the coccolith assemblages in the traps consist almost entirely of the two speciesEmiliania huxleyi andCoccolithus pelagicus. These species dominated the flux rate of the nannoplankton carbonate. A further eight species only made minor contributions to the flux.
In the Lofoten Basin a distinct seasonality could be recognized in both standing crop and carbonate flux. Also the relationship between the two main species and the proportion of intact coccospheres showed an annual cycle. In the sample series of the two northerly traps the seasonality was less distinct. In general, the coccolith flux decreases towards the North. This was particularly evident for the smaller speciesE. huxleyi, while the number of massiveC. pelagicus coccoliths — and so the coccolith carbonate flux — diminished only slightly.
Additional investigations on water samples from the Norwegian Sea revealed species compositions that differed greatly from those in the sediment traps. This suggests that selective processes change the relative species proportions during sedimentation
oxLDL downregulates the dendritic cell homing factors CCR7 and CCL21
No full textDendritic cells (DCs) and oxLDL play an important role in the atherosclerotic process with DCs accumulating in the plaques during plaque progression. Our aim was to investigate the role of oxLDL in the modulation of the DC homing-receptor CCR7 and endothelial-ligand CCL21. Methods and Results. The expression of the DC homing-receptor CCR7 and its endothelial-ligand CCL21 was examined on atherosclerotic carotic plaques of 47 patients via qRT-PCR and immunofluorescence. In vitro, we studied the expression of CCR7 on DCs and CCL21 on human microvascular endothelial cells (HMECs) in response to oxLDL. CCL21- and CCR7-mRNA levels were significantly downregulated in atherosclerotic plaques versus non-atherosclerotic controls [90% for CCL21 and 81% for CCR7 (P<0.01)]. In vitro, oxLDL reduced CCR7 mRNA levels on DCs by 30% and protein levels by 46%. Furthermore, mRNA expression of CCL21 was significantly reduced by 50% (P<0.05) and protein expression by 24% in HMECs by oxLDL (P<0.05). Conclusions. The accumulation of DCs in atherosclerotic plaques appears to be related to a downregulation of chemokines and their ligands, which are known to regulate DC migration. oxLDL induces an in vitro downregulation of CCR7 and CCL21, which may play a role in the reduction of DC migration from the plaques
(Table A5) Isotope stratigraphy of ODP Hole 130-806B
No full text(Table A5) Isotope stratigraphy of ODP Hole 130-806
(Table A2) Stable oxygen isotope ratio of Globigerinoides sacculifer from sediment core RNDB74
No full text(Table A2) Stable oxygen isotope ratio of Globigerinoides sacculifer from sediment core RNDB7
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