4,411 research outputs found
The Dust Mantle of Comet 9P/Tempel 1: Dynamical Constraints on Physical Properties
The trajectories of dust particles ejected from a comet are affected by solar
radiation pressure as a function of their ratios of radiation pressure cross
section to mass. Therefore, a study on the orbital evolution of the particles
caused by the radiation pressure reveals the physical properties of dust on the
surface of the comet nucleus. In the course of NASA's Deep Impact mission, the
ejecta plume evolved under the influence of the radiation pressure. From the
evolution and shape of the plume, we have succeeded in obtaining , where is the ratio of the radiation pressure to the solar
gravity. Taking into account as well as the observational
constraints of a high color temperature and a small silicate-feature strength,
dust particles ejected from the surface of comet 9P/Tempel 1 are likely compact
dust aggregates of sizes m (mass \,g). This is
comparable to the major dust on the surface of comet 1P/Halley (m)
inferred from in-situ measurements and theoretical considerations. Since such
dust aggregates with must have survived on the surface
against jets due to ice sublimation, the temperature of ice in the nucleus must
be kept below 145\,K, which is much lower than equilibrium temperature
determined by solar irradiation and thermal emission. These facts indicate that
9P/Tempel 1 has a dust mantle composed of m-sized dust aggregates with
low thermal conductivities .Comment: 4 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
Virological aspects of Epstein-Barr virus infections.
Epstein-Barr virus (EBV) is usually maintained in an asymptomatic and latent form by the host immune system, and primarily by EBV-specific cytotoxic T cells (CTLs). However, EBV has been linked to several refractory diseases such as EBV-associated hemophagocytic syndrome(EBV-AHS) and chronic active EBV infection (CAEBV). In these ectopic diseases, EBV infects T/NK cells, causing severe immunodeficiency with a very high EBV load. In recent years, the laboratory procedure to assess these types of EBV infections has been improved. In particular, real-time polymerase chain reaction (PCR) has been used to quantify the EBV load, and the MHC: peptide tetramer assay has been used to quantitate EBV-specific CTLs; these tests have been employed for the management of the illnesses associated with EBV infection. Here, we have reviewed the recent progress in the clinical application of these assays. The pathogenesis of EBV-infected T/NK cells, and the host immune response to infection, including the roles carried out by innate immunity and inflammatory cytokines, are likely to be revealed in the future.</p
Sublimation Temperature of Circumstellar Dust Particles and Its Importance for Dust Ring Formation
Dust particles in orbit around a star drift toward the central star by the
Poynting-Robertson effect and pile up by sublimation. We analytically derive
the pile-up magnitude, adopting a simple model for optical cross sections. As a
result, we find that the sublimation temperature of drifting dust particles
plays the most important role in the pile-up rather than their optical property
does. Dust particles with high sublimation temperature form a significant dust
ring, which could be found in the vicinity of the sun through in-situ
spacecraft measurements. While the existence of such a ring in a debris disk
could not be identified in the spectral energy distribution (SED), the size of
a dust-free zone shapes the SED. Since we analytically obtain the location and
temperature of sublimation, these analytical formulae are useful to find such
sublimation evidences.Comment: 9 pages, 5 figures, to be published in Earth Planets Spac
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