2,316 research outputs found
The Gemini NICI Planet-Finding Campaign
Our team is carrying out a multi-year observing program to directly image and
characterize young extrasolar planets using the Near-Infrared Coronagraphic
Imager (NICI) on the Gemini-South 8.1-meter telescope. NICI is the first
instrument on a large telescope designed from the outset for high-contrast
imaging, comprising a high-performance curvature adaptive optics system with a
simultaneous dual-channel coronagraphic imager. Combined with state-of-the-art
observing methods and data processing, NICI typically achieves ~2 magnitudes
better contrast compared to previous ground-based or space-based programs, at
separations inside of ~2 arcsec. In preparation for the Campaign, we carried
out efforts to identify previously unrecognized young stars, to rigorously
construct our observing strategy, and to optimize the combination of angular
and spectral differential imaging. The Planet-Finding Campaign is in its second
year, with first-epoch imaging of 174 stars already obtained out of a total
sample of 300 stars. We describe the Campaign's goals, design, implementation,
performance, and preliminary results. The NICI Campaign represents the largest
and most sensitive imaging survey to date for massive (~1 Mjup) planets around
other stars. Upon completion, the Campaign will establish the best measurements
to date on the properties of young gas-giant planets at ~5-10 AU separations.
Finally, Campaign discoveries will be well-suited to long-term orbital
monitoring and detailed spectrophotometric followup with next-generation
planet-finding instruments.Comment: Proceedings of the SPIE, vol 7736 (Advances in Adaptive Optics, San
Diego, CA, June 2010 meeting), in pres
The Gemini NICI Planet-Finding Campaign: The Frequency of Giant Planets Around Debris Disk Stars
We have completed a high-contrast direct imaging survey for giant planets
around 57 debris disk stars as part of the Gemini NICI Planet-Finding Campaign.
We achieved median H-band contrasts of 12.4 mag at 0.5" and 14.1 mag at 1"
separation. Follow-up observations of the 66 candidates with projected
separation < 500 AU show that all of them are background objects. To establish
statistical constraints on the underlying giant planet population based on our
imaging data, we have developed a new Bayesian formalism that incorporates (1)
non-detections, (2) single-epoch candidates, (3) astrometric and (4)
photometric information, and (5) the possibility of multiple planets per star
to constrain the planet population. Our formalism allows us to include in our
analysis the previously known Beta Pictoris and the HR 8799 planets. Our
results show at 95% confidence that 5MJup
planet beyond 80 AU, and 3MJup planet outside
of 40 AU, based on hot-start evolutionary models. We model the population of
directly-imaged planets as d^2N/dMda ~ m^alpha a^beta, where m is planet mass
and a is orbital semi-major axis (with a maximum value of amax). We find that
beta 1.7. Likewise, we find that beta < -0.8 and/or amax
< 200 AU. If we ignore the Beta Pic and HR 8799 planets (should they belong to
a rare and distinct group), we find that
3MJup planet beyond 10 AU, and beta < -0.8 and/or alpha < -1.5. Our Bayesian
constraints are not strong enough to reveal any dependence of the planet
frequency on stellar host mass. Studies of transition disks have suggested that
about 20% of stars are undergoing planet formation; our non-detections at large
separations show that planets with orbital separation > 40 AU and planet masses
> 3 MJup do not carve the central holes in these disks.Comment: Accepted to ApJ on June 24, 2013. 67 pages, 17 figures, 12 table
Merging Galaxies in the SDSS EDR
We present a new catalog of merging galaxies obtained through an automated
systematic search routine. The 1479 new pairs of merging galaxies were found in
approximately 462 sq deg of the Sloan Digital Sky Survey Early Data Release
(SDSS EDR; Stoughton et al. 2002) photometric data, and the pair catalog is
complete for galaxies in the magnitude range 16.0 <= g* <= 20.
The selection algorithm, implementing a variation on the original
Karachentsev (1972) criteria, proved to be very efficient and fast. Merging
galaxies were selected such that the inter-galaxy separations were less than
the sum of the component galaxies' radii.
We discuss the characteristics of the sample in terms of completeness, pair
separation, and the Holmberg effect. We also present an online atlas of images
for the SDSS EDR pairs obtained using the corrected frames from the SDSS EDR
database. The atlas images also include the relevant data for each pair member.
This catalog will be useful for conducting studies of the general
characteristics of merging galaxies, their environments, and their component
galaxies. The redshifts for a subset of the interacting and merging galaxies
and the distribution of angular sizes for these systems indicate the SDSS
provides a much deeper sample than almost any other wide-area catalog to date.Comment: 58 pages, which includes 15 figures and 6 tables. Figures 2, 8, 9,
10, 11, 13, and 14 are provided as JPEG files. For online atlas, see
http://home.fnal.gov/~sallam/MergePair/ . Accepted for publication in A
Relationship Between Dispersion Metric and Properties of PMMA/SWNT Nanocomposites
Particle spatial dispersion is a crucial characteristic of polymer composite materials and this property is recognized as especially important in nanocomposite materials due to the general tendency of nanoparticles to aggregate under processing conditions. We introduce dispersion metrics along with a specified dispersion scale over which material homogeneity is measured and consider how the dispersion metrics correlate quantitatively with the variation of basic nanocomposite properties. We then address the general problem of quantifying nanoparticle spatial dispersion in model nanocomposites of single wall carbon nanotubes (SWNT) dispersed in poly(methyl methacrylate) (PMMA) at a fixed SWNT concentration of 0.5 % using a \u27coagulation\u27 fabrication method. Two methods are utilized to measure dispersion, UV-Vis spectroscopy and optical confocal microscopy. Quantitative spatial dispersion levels were obtained through image analysis to obtain a \u27relative dispersion index\u27 (RDI) representing the uniformity of the dispersion of SWNTs in the samples and through absorbance. We find that the storage modulus, electrical conductivity, and flammability containing the same amount of SWNTs, the relationships between the quantified dispersion levels and physical properties show about four orders of magnitude variation in storage modulus, almost eight orders of magnitude variation in electric conductivity, and about 70 % reduction in peak mass loss rate at the highest dispersion level used in this study. The observation of such a profound effect of SWNT dispersion indicates the need for objective dispersion metrics for correlating and understanding how the properties of nanocomposites are determined by the concentration, shape and size of the nanotubes
D-branes as GMS Solitons in Vacuum String Field Theory
In this paper we map the D-brane projector states in the vacuum string field
theory to the noncommutative GMS solitons based on the recently proposed map of
Witten's star to Moyal's star. We find that the singular geometry conditions of
Moore and Taylor are associated with the commutative modes of these projector
states in our framework. The properties of the candidate closed string state
and the wedge state are also discussed, and the possibility of the non-GMS
soliton in VSFT is commented.Comment: 19 pages, LaTex; revised version, typos corrected; third version, a
new subsection about the midpoint singulariy regularization added;fourth
edition, arguments improve
Cubic String Field Theory in pp-wave Background and Background Independent Moyal Structure
We study Witten open string field theory in the pp-wave background in the
tensionless limit, and construct the N-string vertex in the basis which
diagonalizes the string perturbative spectrum. We found that the Witten
*-product can be viewed as infinite copies of the Moyal product with the same
noncommutativity parameter . Moreover, we show that this Moyal
structure is universal in the sense that, written in the string bit basis,
Witten's *-product for any background can always be given in terms of the
above-mentioned Moyal structure. We identify some projective operators in this
algebra that we argue to correspond to D-branes of the theory.Comment: Latex, 23 pages, reference adde
Isospin Multiplet Structure in Ultra--Heavy Fermion Bound States
The coupled Bethe--Salpeter bound state equations for a system,
where is a degenerate, fourth generation, super--heavy quark doublet,
are solved in several ladder approximation models. The exchanges of gluon,
Higgs and Goldstone modes in the standard model are calculated in the
ultra--heavy quark limit where weak and contributions are
negligible. A natural and multiplet pattern is found, with large
splittings occuring between the different weak iso--spin states when , the
quark masses, are larger than values in the range ,
depending on which model is used. Consideration of ultra--heavy quark lifetime
constraints and mass splitting constraints are reviewed to establish the
plausibility of lifetime and mass degeneracy requirements assumed for this
paper.Comment: 20 pages, 7 figures (hard copy available upon request), report#
KU-HEP-93-2
Projection methods in conic optimization
There exist efficient algorithms to project a point onto the intersection of
a convex cone and an affine subspace. Those conic projections are in turn the
work-horse of a range of algorithms in conic optimization, having a variety of
applications in science, finance and engineering. This chapter reviews some of
these algorithms, emphasizing the so-called regularization algorithms for
linear conic optimization, and applications in polynomial optimization. This is
a presentation of the material of several recent research articles; we aim here
at clarifying the ideas, presenting them in a general framework, and pointing
out important techniques
Noncommutative Electromagnetism As A Large N Gauge Theory
We map noncommutative (NC) U(1) gauge theory on R^d_C X R^{2n}_{NC} to U(N ->
\infty) Yang-Mills theory on R^d_C, where R^d_C is a d-dimensional commutative
spacetime while R^{2n}_{NC} is a 2n-dimensional NC space. The resulting U(N)
Yang-Mills theory on R^d_C is equivalent to that obtained by the dimensional
reduction of (d+2n)-dimensional U(N) Yang-Mills theory onto R^d_C. We show that
the gauge-Higgs system (A_\mu,\Phi^a) in the U(N -> \infty) Yang-Mills theory
on R^d_C leads to an emergent geometry in the (d+2n)-dimensional spacetime
whose metric was determined by Ward a long time ago. In particular, the
10-dimensional gravity for d=4 and n=3 corresponds to the emergent geometry
arising from the 4-dimensional N=4 vector multiplet in the AdS/CFT duality. We
further elucidate the emergent gravity by showing that the gauge-Higgs system
(A_\mu,\Phi^a) in half-BPS configurations describes self-dual Einstein gravity.Comment: 25 pages; More clarifications, to appear in Eur. Phys. J.
Cosmological and black hole brane-world Universes in higher derivative gravity
General model of multidimensional -gravity including Riemann tensor
square term (non-zero case) is considered. The number of brane-worlds in
such model is constructed (mainly in five dimensions) and their properties are
discussed. Thermodynamics of S-AdS BH (with boundary) is presented when
perturbation on is used. The entropy, free energy and energy are
calculated. For non-zero the entropy (energy) is not proportional to the
area (mass). The equation of motion of brane in BH background is presented as
FRW equation. Using dual CFT description it is shown that dual field theory is
not conformal one when is not zero. In this case the holographic entropy
does not coincide with BH entropy (they coincide for Einstein gravity or
HD gravity where AdS/CFT description is well applied).
Asymmetrically warped background (analog of charged AdS BH) where Lorentz
invariance violation occurs is found. The cosmological 4d dS brane connecting
two dS bulk spaces is formulated in terms of parameters of -gravity.
Within proposed dS/CFT correspondence the holographic conformal anomaly from
five-dimensional higher derivative gravity in de Sitter background is
evaluated.Comment: LaTeX file 40 pages, references added, version to appear in PR
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