3,933 research outputs found
Population of the Scattered Kuiper Belt
We present the discovery of three new Scattered Kuiper Belt Objects (SKBOs)
from a wide-field survey of the ecliptic. This continuing survey has to date
covered 20.2 square degrees to a limiting red magnitude of 23.6. We combine the
data from this new survey with an existing survey conducted at the University
of Hawaii 2.2m telescope to constrain the number and mass of the SKBOs. The
SKBOs are characterized by large eccentricities, perihelia near 35 AU, and
semi-major axes > 50 AU. Using a maximum-likelihood model, we estimate the
total number of SKBOs larger than 100 km in diameter to be N = 3.1 (+1.9/-1.3)
x 10^4 (1 sigma) and the total mass of SKBOs to be about 0.05 Earth masses,
demonstrating that the SKBOs are similar in number and mass to the Kuiper Belt
inside 50 AU.Comment: 15 pages, 3 figure
Discovery of a planetary-sized object in the scattered Kuiper belt
We present the discovery and initial physical and dynamical characterization
of the object 2003 UB313. The object is sufficiently bright that for all
reasonable values of the albedo it is certain to be larger than Pluto.
Pre-discovery observations back to 1989 are used to obtain an orbit with
extremely small errors. The object is currently at aphelion in what appears to
be a typical orbit for a scattered Kuiper belt object except that it is
inclined by about 44 degrees from the ecliptic. The presence of such a large
object at this extreme inclination suggests that high inclination Kuiper belt
objects formed preferentially closer to the sun. Observations from Gemini
Observatory show that the infrared spectrum is, like that of Pluto, dominated
by the presence of frozen methane, though visible photometry shows that the
object is almost neutral in color compared to Pluto's extremely red color. 2003
UB313 is likely to undergo substantial seasonal change over the large range of
heliocentric distances that it travels; Pluto at its current distance is likely
to prove a useful analog for better understanding the range of seasonal changes
on this body.Comment: 9 pages, 1 figur
Putting hydrodynamic interactions to work: tagged particle separation
Separation of magnetically tagged cells is performed by attaching markers to
a subset of cells in suspension and applying fields to pull from them in a
variety of ways. The magnetic force is proportional to the field gradient, and
the hydrodynamic interactions play only a passive, adverse role. Here we
propose using a homogeneous rotating magnetic field only to make tagged
particles rotate, and then performing the actual separation by means of
hydrodynamic interactions, which thus play an active role. The method, which we
explore here theoretically and by means of numerical simulations, lends itself
naturally to sorting on large scales.Comment: Version accepted for publication - Europhysics Letter
Shared Antigenic Epitopes on the V3 Loop of HIV-1 gp120 and Proteins on Activated Human T Cells
AbstractProliferation of HIV-1 in the infected host is characterized by a progressive loss of CD4+T lymphocytes and consequent dysregulation of the immune system. Both direct and indirect mechanisms have been proposed. We show here that proteins with molecular weights 35, 48, and 110 kDa on stimulated primary human T cells are recognized by neutralizing antibodies against the V3 loop of HIV-1 gp120. Recognition is specific since it can be blocked by a recombinant HIV-1 gp120. Furthermore, these V3 monoclonal antibodies, as well as sera from AIDS patients that recognized these V3-like proteins, induced killing of HIV-1-infected as well as uninfected T cells. This killing was also inhibited by HIV-1 gp120 V3 peptides. These results indicate that the V3 loop shares epitopes with proteins on stimulated T cells. This may be an additional autoimmune mechanism contributing to CD4+T cell disappearance in AIDS. V3 antibodies have been proposed as potential prophylactic agents. However, if such vaccines were based on certain epitopes, they might induce cross-reacting immune responses with cellular proteins. Vaccine candidates should be evaluated for such potential effects
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