9,573 research outputs found
Two loop detection mechanisms: a comparison
In order to compare two loop detection mechanisms we describe two calculi for theorem proving in intuitionistic propositional logic. We call them both MJ Hist, and distinguish between them by description as `Swiss' or `Scottish'. These calculi combine in different ways the ideas on focused proof search of Herbelin and Dyckhoff & Pinto with the work of Heuerding emphet al on loop detection. The Scottish calculus detects loops earlier than the Swiss calculus but at the expense of modest extra storage in the history. A comparison of the two approaches is then given, both on a theoretic and on an implementational level
Superheated Droplet Detectors as CDM Detectors: The SIMPLE Experiment
Superheated Droplet Detectors (SDDs) are becoming commonplace in neutron
personnel dosimetry. Their total insensitivity to minimum ionizing radiation
(while responsive to nuclear recoils of energies ~ few keV), together with
their low cost, ease of production, and operation at room temperature and 1 atm
makes them ideal for Cold Dark Matter (CDM) searches. SDD's are optimal for the
exploration of the spin-dependent neutralino coupling due to their high
fluorine content. The status of SIMPLE (Superheated Instrument for Massive
ParticLe Experiments) is presented. Under realistic background considerations,
we expect an improvement in the present Cold Dark Matter sensitivity of 2-3
orders of magnitude after ~1 kg-y of data acquisition.Comment: 6 pages, including 4 figures. To appear in the Proceedings of the
Intl. Workshop on the Identification of Dark Matter (Sheffield, Sept. 96
Polarization state of the optical near-field
The polarization state of the optical electromagnetic field lying several
nanometers above complex dielectric structures reveals the intricate
light-matter interaction that occurs in this near-field zone. This information
can only be extracted from an analysis of the polarization state of the
detected light in the near-field. These polarization states can be calculated
by different numerical methods well-suited to near--field optics. In this
paper, we apply two different techniques (Localized Green Function Method and
Differential Theory of Gratings) to separate each polarisation component
associated with both electric and magnetic optical near-fields produced by
nanometer sized objects. The analysis is carried out in two stages: in the
first stage, we use a simple dipolar model to achieve insight into the physical
origin of the near-field polarization state. In the second stage, we calculate
accurate numerical field maps, simulating experimental near-field light
detection, to supplement the data produced by analytical models. We conclude
this study by demonstrating the role played by the near-field polarization in
the formation of the local density of states.Comment: 9 pages, 11 figures, accepted for publication in Phys. Rev.
Evidence for a circumplanetary disk around protoplanet PDS 70 b
We present the first observational evidence for a circumplanetary disk around
the protoplanet PDS~70~b, based on a new spectrum in the band acquired with
VLT/SINFONI. We tested three hypotheses to explain the spectrum: Atmospheric
emission from the planet with either (1) a single value of extinction or (2)
variable extinction, and (3) a combined atmospheric and circumplanetary disk
model. Goodness-of-fit indicators favour the third option, suggesting
circumplanetary material contributing excess thermal emission --- most
prominent at m. Inferred accretion rates (-- yr) are compatible with observational
constraints based on the H and Br lines. For the planet, we
derive an effective temperature of 1500--1600 K, surface gravity , radius , mass , and possible thick clouds.
Models with variable extinction lead to slightly worse fits. However, the
amplitude (mag) and timescale of variation
(~years) required for the extinction would also suggest
circumplanetary material.Comment: 8 pages, 2 figures, 1 table. This is a pre-copyedited,
author-produced PDF of an article accepted for publication in ApJL on 2019
May 1
beta Pic b position relative to the Debris Disk
Context. We detected in 2009 a giant, close-by planet orbiting {\beta} Pic, a
young star surrounded with a disk, extensively studied for more than 20 years.
We showed that if located on an inclined orbit, the planet could explain
several peculiarities of {\beta} Pictoris system. However, the available data
did not permit to measure the inclination of {\beta} Pic b with respect to the
disk, and in particular to establish in which component of the disk - the main,
extended disk or the inner inclined component/disk-, the planet was located.
Comparison between the observed planet position and the disk orientation
measured on previous imaging data was not an option because of potential biases
in the measurements. Aims. Our aim is to measure precisely the planet location
with respect to the dust disk using a single high resolution image, and
correcting for systematics or errors that degrades the precision of the disk
and planet relative position measurements. Methods. We gathered new NaCo data
at Ks band, with a set-up optimized to derive simultaneously the orientation(s)
of the disk(s) and that of the planet. Results. We show that the projected
position of {\beta} Pic b is above the midplane of the main disk. With the
current data and knowledge on the system, this implies that {\beta} Pic b
cannot be located in the main disk. The data rather suggest the planet being
located in the inclined component.Comment: 13 pages, 6 figures, to appear in Astronomy and Astrophysic
Sparse aperture masking at the VLT II. Detection limits for the eight debris disks stars Pic, AU Mic, 49 Cet, Tel, Fomalhaut, g Lup, HD181327 and HR8799
Context. The formation of planetary systems is a common, yet complex
mechanism. Numerous stars have been identified to possess a debris disk, a
proto-planetary disk or a planetary system. The understanding of such formation
process requires the study of debris disks. These targets are substantial and
particularly suitable for optical and infrared observations. Sparse Aperture
masking (SAM) is a high angular resolution technique strongly contributing to
probe the region from 30 to 200 mas around the stars. This area is usually
unreachable with classical imaging, and the technique also remains highly
competitive compared to vortex coronagraphy. Aims. We aim to study debris disks
with aperture masking to probe the close environment of the stars. Our goal is
either to find low mass companions, or to set detection limits. Methods. We
observed eight stars presenting debris disks ( Pictoris, AU
Microscopii, 49 Ceti, Telescopii, Fomalhaut, g Lupi, HD181327 and
HR8799) with SAM technique on the NaCo instrument at the VLT. Results. No close
companions were detected using closure phase information under 0.5 of
separation from the parent stars. We obtained magnitude detection limits that
we converted to Jupiter masses detection limits using theoretical isochrones
from evolutionary models. Conclusions. We derived upper mass limits on the
presence of companions in the area of few times the diffraction limit of the
telescope around each target star.Comment: 7 pages, All magnitude detection limits maps are only available in
electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5
Atomic diffraction from nanostructured optical potentials
We develop a versatile theoretical approach to the study of cold-atom
diffractive scattering from light-field gratings by combining calculations of
the optical near-field, generated by evanescent waves close to the surface of
periodic nanostructured arrays, together with advanced atom wavepacket
propagation on this optical potential.Comment: 8 figures, 10 pages, submitted to Phys. Rev.
KMOS LENsing Survey (KLENS) : morpho-kinematic analysis of star-forming galaxies at
We present results from the KMOS lensing survey-KLENS which is exploiting
gravitational lensing to study the kinematics of 24 star forming galaxies at
with a median mass of and median
star formation rate (SFR) of . We find that 25% of
these low-mass/low-SFR galaxies are rotation dominated, while the majority of
our sample shows no velocity gradient. When combining our data with other
surveys, we find that the fraction of rotation dominated galaxies increases
with the stellar mass, and decreases for galaxies with a positive offset from
the main sequence. We also investigate the evolution of the intrinsic velocity
dispersion, , as a function of the redshift, , and stellar mass,
, assuming galaxies in quasi-equilibrium (Toomre Q parameter equal
to 1). From the relation, we find that the redshift evolution of
the velocity dispersion is mostly expected for massive galaxies (). We derive a relation, using
the Tully-Fisher relation, which highlights that a different evolution of the
velocity dispersion is expected depending on the stellar mass, with lower
velocity dispersions for lower masses, and an increase for higher masses,
stronger at higher redshift. The observed velocity dispersions from this work
and from comparison samples spanning appear to follow this relation,
except at higher redshift (), where we observe higher velocity dispersions
for low masses () and lower velocity
dispersions for high masses () than
expected. This discrepancy could, for instance, suggest that galaxies at
high- do not satisfy the stability criterion, or that the adopted
parametrisation of the specific star formation rate and molecular properties
fail at high redshift.Comment: Accepted for publication in A&A, 21 pages, 10 figure
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