1,453 research outputs found
Rigidity transitions and constraint counting in amorphous networks: beyond the mean-field approach
Subj-class: Disordered Systems and Neural NetworksComment: 12 pages, revtex, 3 figure
Confirmation of the planet around HD 95086 by direct imaging
VLT/NaCo angular differential imaging at L' (3.8 microns) revealed a probable
giant planet comoving with the young and early-type HD 95086 also known to
harbor an extended debris disk. The discovery was based on the proper motion
analysis of two datasets spanning 15 months. However, the second dataset
suffered from bad atmospheric conditions, which limited the significance of the
redetection at the 3 sigma level. In this Letter, we report new VLT/NaCo
observations of HD 95086 obtained on 2013 June 26-27 at L' to recover the
planet candidate. We unambiguously redetect the companion HD 95086 b with
multiple independent pipelines at a signal-to-noise ratio greater than or equal
to 5. Combined with previously reported measurements, our astrometry decisively
shows that the planet is comoving with HD 95086 and inconsistent with a
background object. With a revised mass of 5 pm 2 Jupiter masses, estimated from
its L' photometry and "hot-start" models at 17 pm 4 Myr, HD 95086 b becomes a
new benchmark for further physical and orbital characterization of young giant
planets.Comment: accepted for publication to AP
VLT/NACO astrometry of the HR8799 planetary system. L'-band observations of the three outer planets
HR8799 is so far the only directly imaged multiple exoplanet system. The
orbital configuration would, if better known, provide valuable insight into the
formation and dynamical evolution of wide-orbit planetary systems. We present
L'-band observations of the HR8799 system obtained with NACO at VLT, adding to
the astrometric monitoring of the planets HR8799b, c and d. We investigate how
well the two simple cases of (i) a circular orbit and (ii) a face-on orbit fit
the astrometric data for HR8799d over a total time baseline of ~2 years. The
results indicate that the orbit of HR8799d is inclined with respect to our line
of sight, and suggest that the orbit is slightly eccentric or non-coplanar with
the outer planets and debris disk.Comment: 5 pages, 4 figures, 1 table, accepted for publication in A\&A.
Updated version includes minor changes made in the proof
POTENTIATION OF T-CELL-MEDIATED IMMUNITY BY SELECTIVE SUPPRESSION OF ANTIBODY FORMATION WITH CYCLOPHOSPHAMIDE
Delayed-type hypersensitivity (DTH) appears in mice immunized with less than an optimal immunogenic dose of sheep red blood cells (SRBC), but is blocked progressively as antibody production increases in response to larger doses of SRBC. Treatment with cyclophosphamide (CY) was shown to release T cells from this inhibitory influence of the humoral response, and cause enhancement of DTH. The magnitude of this enhancing effect on T-cell activity was markedly dependent on the time of treatment relative to the time of immunization, and on the time chosen for measuring DTH. The reasons for these pronounced effects of timing are threefold: (a) CY given before antigenic stimulation has a long-lasting effect on antibody formation, but no apparent effect on the precursors of activated T cells. (b) After antigenic stimulation, T cells also become susceptible to CY. (c) The production of a nonspecific participant (monocyte) in the DTH reaction is also suppressed by CY, though the supply of circulating monocytes is not immediately affected by the drug. The differential effect of CY on T and B lymphocytes depends on the differing physiological states of the majority of cells that make up these two populations. The former are resting cells that are insensitive to CY until exposed to specific antigen, while the latter are drawn from a rapidly replicating precursor pool and are susceptible to CY at all times
Principles and Implementation of an Ultrafast Transmission Electron Microscope
Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 - August 2, 201
Constraining the orbit of the possible companion to Beta Pictoris: New deep imaging observations
We recently reported on the detection of a possible planetary-mass companion
to Beta Pictoris at a projected separation of 8 AU from the star, using data
taken in November 2003 with NaCo, the adaptive-optics system installed on the
Very Large Telescope UT4. Eventhough no second epoch detection was available,
there are strong arguments to favor a gravitationally bound companion rather
than a background object. If confirmed and located at a physical separation of
8 AU, this young, hot (~1500 K), massive Jovian companion (~8 Mjup) would be
the closest planet to its star ever imaged, could be formed via core-accretion,
and could explain the main morphological and dynamical properties of the dust
disk. Our goal was to return to Beta Pic five years later to obtain a
second-epoch observation of the companion or, in case of a non-detection,
constrain its orbit. Deep adaptive-optics L'-band direct images of Beta Pic and
Ks-band Four-Quadrant-Phase-Mask (4QPM) coronagraphic images were recorded with
NaCo in January and February 2009. We also use 4QPM data taken in November
2004. No point-like signal with the brightness of the companion candidate
(apparent magnitudes L'=11.2 or Ks ~ 12.5) is detected at projected distances
down to 6.5 AU from the star in the 2009 data. As expected, the non-detection
does not allow to rule out a background object; however, we show that it is
consistent with the orbital motion of a bound companion that got closer to the
star since first observed in 2003 and that is just emerging from behind the
star at the present epoch. We place strong constraints on the possible orbits
of the companion and discuss future observing prospects.Comment: 8 pages, 8 figures, 1 table, accepted for publication in Astronomy
and Astrophysic
Volume 13, Number 2, June 1993 OLAC Newsletter
Digitized June 1993 issue of the OLAC Newsletter
On Virtual Displacement and Virtual Work in Lagrangian Dynamics
The confusion and ambiguity encountered by students, in understanding virtual
displacement and virtual work, is discussed in this article. A definition of
virtual displacement is presented that allows one to express them explicitly
for holonomic (velocity independent), non-holonomic (velocity dependent),
scleronomous (time independent) and rheonomous (time dependent) constraints. It
is observed that for holonomic, scleronomous constraints, the virtual
displacements are the displacements allowed by the constraints. However, this
is not so for a general class of constraints. For simple physical systems, it
is shown that, the work done by the constraint forces on virtual displacements
is zero. This motivates Lagrange's extension of d'Alembert's principle to
system of particles in constrained motion. However a similar zero work
principle does not hold for the allowed displacements. It is also demonstrated
that d'Alembert's principle of zero virtual work is necessary for the
solvability of a constrained mechanical problem. We identify this special class
of constraints, physically realized and solvable, as {\it the ideal
constraints}. The concept of virtual displacement and the principle of zero
virtual work by constraint forces are central to both Lagrange's method of
undetermined multipliers, and Lagrange's equations in generalized coordinates.Comment: 12 pages, 10 figures. This article is based on an earlier article
physics/0410123. It includes new figures, equations and logical conten
- …