419 research outputs found
A hot compact dust disk around a massive young stellar object
No full textCircumstellar disks are an essential ingredient of the formation1 of low-mass stars. It is unclear, however, whether the accretion-disk paradigm can also account for the formation of stars more massive than about 10 solar masses2, in which strong radiation pressure might halt mass infall3, 4. Massive stars may form by stellar merging5, although more recent theoretical investigations suggest that the radiative-pressure limit may be overcome by considering more complex, non-spherical infall geometries6, 7. Clear observational evidence, such as the detection of compact dusty disks8 around massive young stellar objects, is needed to identify unambiguously the formation mode of the most massive stars. Here we report near-infrared interferometric observations that spatially resolve the astronomical-unit-scale distribution of hot material around a high-mass (~20 solar masses) young stellar object. The image shows an elongated structure with a size of ~13 × 19 astronomical units, consistent with a disk seen at an inclination angle of ~45°. Using geometric and detailed physical models, we found a radial temperature gradient in the disk, with a dust-free region less than 9.5 astronomical units from the star, qualitatively and quantitatively similar to the disks observed in low-mass star formation. Perpendicular to the disk plane we observed a molecular outflow and two bow shocks, indicating that a bipolar outflow emanates from the inner regions of the system
Glial contribution to cyclodextrin-mediated reversal of cholesterol accumulation in murine NPC1-deficient neurons in vivo
No full textNiemann-Pick type C disease is a rare and fatal lysosomal storage disorder presenting severe neurovisceral symptoms. Disease-causing mutations in genes encoding either NPC1 or NPC2 protein provoke accumulation of cholesterol and other lipids in specific structures of the endosomal-lysosomal system and degeneration of specific cells, notably neurons in the central nervous system (CNS). 2-hydroxypropyl-beta-cyclodextrin (CD) emerged as potential therapeutic approach based on animal studies and clinical data, but the mechanism of action in neurons has remained unclear. To address this topic in vivo, we took advantage of the retina as highly accessible part of the CNS and intravitreal injections as mode of drug administration. Coupling CD to gold nanoparticles allowed us to trace its intracellular location. We report that CD enters the endosomal-lysosomal system of neurons in vivo and enables the release of lipid-laden lamellar inclusions, which are then removed from the extracellular space by specific types of glial cells. Our data suggest that CD induces a concerted action of neurons and glial cells to restore lipid homeostasis in the central nervous system
The inner rim of 51 HAeBe protoplanetary disks. A VLTI-Pionier survey
No full textWe establish the following results:
(a) Dust Tsub ~1800K.
(b) Ring structure.
(c) 1.65µm emission region is wide (Delta_r/r~0.5), favoring recent physical rim models.
(d) Disk thickness z/h~0.2, larger than hydrostatic scaleheight
(e) Extended (>>1AU) flux component; correlated with disk flaring indicators and group status.
(f) Confirm and extend the size-luminosity relationship.
(1) Authorship:
B. Lazareff, J.-P. Berger , J. Kluska, J.-B. Le Bouquin, C. Pinte, W.-F. Thi, and 15 more co-authors.Presented by Jean-Philippe Berger ||
J.-P. Berger, J. Kluska, J.-B. Le Bouquin, M. Benisty, F. Malbet, C. Koen, C. Pinte, W.-F. Thi, O. Absil, F. Baron, A. Delboulbé, G. Duvert, A. Isella, L. Jocou, A. Juhasz, S. Kraus, R. Lachaume, F. Ménard, R. Millan-Gabet, J. Monnier, K. Perraut, F. Soulez, M. Tallon, E. Thiébaut, W. Traub and G. Zin
Mass-loss of hot stars studied with spectro-polarimetric interferometry (SPIN)
No full textAstronomical Telescopes and Instrumentation, Polarimetry in Astronomy, Fineschi, S., Proc. SPIE 4843, pp. 484-1491 (2003)International audienc
Alternating bursts of low energy ions and electrons near the substorm onset
No full textInternational audienceThe substorm associated behavior of the low energy particles (30 eV?28.5 keV) near the earthward edge of the plasma sheet is examined using data from CRRES during the late growth and early expansion phases of a substorm on 12 March 1991 and their significance for the substorm onset mechanism is discussed. In this substorm, the CRRES was located on L ~6.3 and ~20° westward of the substorm onset and observed the sequence of the alternating bursts of the low energy ions and electrons. The bursts of the 0.633?9.6 keV ions occurred 1?2 min before the (7.31?21.7 keV) electron bursts. The first ion burst happened 2min before the substorm onset, at the moment of weak brightening of the most equatorial pre-breakup arc near the latitude ~62°. The alternation of the ion and electron bursts may be a signature of a drift-Alfvén ballooning instability on the inner edge of the plasma sheet near substorm onset
Electromagnetic fluctuations in the vicinity of the magnetopause
No full textInternational audienceA detailed analysis of electromagnetic fluctuations recorded during several magnetopause and boundary layer crossings by the ESA GEOS-2 geostationary spacecraft is presented. A high level of electromagnetic fluctuations in the ULF (0 - 10 Hz) range is observed for each such crossing. The obtained frequency spectra are shown to fit with a power law f exp -alpha. The distribution of these alpha indexes is found to be narrow, with a peak value of about 2.5 which does not depend on the direction with respect to the magnetic field. Data suggest that the magnetopause boundary layer is the source of these intense fluctuations
He+ dominance in the plasmasphere during geomagnetically disturbed periods: 1. Observational results
No full textObservations made by the DMSP 1710 satellite during the recovery phase from geomagnetic disturbances in June 1991 show regions of He+ dominance around 830 km altitude at 09:00 MLT. These regions are co-located with a trough in ionisation observed around 55degrees in the winter hemisphere. Plasma temperature and concentration observations made during the severe geomagnetic storm of 24 March 1991 are used as a case study to determine the effects of geomagnetic disturbances along the orbit of the F10 satellite. Previous explanations for He+ dominance in this trough region relate to the part of the respective flux tubes that is in darkness. Such conditions are not relevant for this study, since the whole of the respective flux tubes are sunlit. A new mechanism is proposed to explain the He+ dominance in the trough region. This mechanism is based on plasma transport and chemical reaction effects in the F-region and topside ionosphere, and on the time scales for such chemical reactions. Flux tubes previously depleted by geomagnetic storm effects refill during the recovery phase from the ionosphere as a result of pressure differences along the flux tubes. Following a geomagnetic disturbance, the He+ ion recovers quickly via the rapid photoionisation of neutral helium, in the F-region and the topside. The recovery of the O+ and H+ ions is less rapid. This is proposed as a result of the respective charge exchange reactions with neutral atomic hydrogen and oxygen. Preliminary model calculations support the proposed mechanism
Magnetic reconnection in the Jovian tail : X-line evolution and consequent plasma sheet structures
No full textMagnetic reconnection in planetary magnetospheres plays important roles in energy and mass transfer in the steady state, and also possibly in transient large-scale disturbances. In this paper we report observations of a reconnection event in the Jovian magnetotail by the Galileo spacecraft on 17 June 1997. In addition to the tailward retreat of a main X-line, signatures of recurrent X-line formations are found by close examination of energetic particle anisotropies. Furthermore, detailed analyses of multi-instrumental data for this period provide various spatiotemporal features in the plasma sheet. A significant density decrease was detected in the central plasma sheet, indicative of the transition to lobe (open field line) reconnection from plasma sheet (closed field line) reconnection. When Galileo vertically swept through the plasma sheet, a velocity layer structure was observed. We also analyze a strong southward magnetic field which is similar to dipolarization fronts observed in the terrestrial magnetotail: the ion flow (∼450 km s−1) was observed behind the magnetic front, whose thickness of 10000–20000 km was of the order of ion inertial length. The electron anisotropy in this period suggests an anomalously high-speed electron jet, implying ion-electron decoupling behind the magnetic front. Particle energization was also seen associated with these structures. These observations suggest that X-line evolution and consequent plasma sheet structures are similar to those in the terrestrial magnetosphere, whereas their generality in the Jovian magnetosphere and influence on the magnetospheric/ionospheric dynamics including transient auroral events need to be further investigated with more events
Limited antigenic diversity of Plasmodium falciparumapical membrane antigen 1 supports the development of effective multi-allele vaccines
No full textBackground: Polymorphism in antigens is a common mechanism for immune evasion used by many important pathogens, and presents major challenges in vaccine development. In malaria, many key immune targets and vaccine candidates show substantial polymorphism. However, knowledge on antigenic diversity of key antigens, the impact of polymorphism on potential vaccine escape, and how sequence polymorphism relates to antigenic differences is very limited, yet crucial for vaccine development. Plasmodium falciparum apical membrane antigen 1 (AMA1) is an important target of naturally-acquired antibodies in malaria immunity and a leading vaccine candidate. However, AMA1 has extensive allelic diversity with more than 60 polymorphic amino acid residues and more than 200 haplotypes in a single population. Therefore, AMA1 serves as an excellent model to assess antigenic diversity in malaria vaccine antigens and the feasibility of multi-allele vaccine approaches. While most previous research has focused on sequence diversity and antibody responses in laboratory animals, little has been done on the cross-reactivity of human antibodies. Methods: We aimed to determine the extent of antigenic diversity of AMA1, defined by reactivity with human antibodies, and to aid the identification of specific alleles for potential inclusion in a multi-allele vaccine. We developed an approach using a multiple-antigen-competition enzyme-linked immunosorbent assay (ELISA) to examine cross-reactivity of naturally-acquired antibodies in Papua New Guinea and Kenya, and related this to differences in AMA1 sequence. Results: We found that adults had greater cross-reactivity of antibodies than children, although the patterns of cross-reactivity to alleles were the same. Patterns of antibody cross-reactivity were very similar between populations (Papua New Guinea and Kenya), and over time. Further, our results show that antigenic diversity of AMA1 alleles is surprisingly restricted, despite extensive sequence polymorphism. Our findings suggest that a combination of three different alleles, if selected appropriately, may be sufficient to cover the majority of antigenic diversity in polymorphic AMA1 antigens. Antigenic properties were not strongly related to existing haplotype groupings based on sequence analysis. Conclusions: Antigenic diversity of AMA1 is limited and a vaccine including a small number of alleles might be sufficient for coverage against naturally-circulating strains, supporting a multi-allele approach for developing polymorphic antigens as malaria vaccines
- …
