3,147 research outputs found
Star Formation and Tidal Encounters with the Low Surface Brightness Galaxy UGC 12695 and Companions
We present VLA H I observations of the low surface brightness galaxy UGC
12695 and its two companions, UGC 12687 and a newly discovered dwarf galaxy
2333+1234. UGC 12695 shows solid body rotation but has a very lopsided
morphology of the H I disk, with the majority of the H I lying in the southern
arm of the galaxy. The H I column density distribution of this very blue, LSB
galaxy coincides in detail with its light distribution. Comparing the H I
column density of UGC 12695 with the empirical (but not well understood) value
of Sigma_c = 10E21 atoms/cm^2 found in, i.e., Skillman's 1986 paper shows the
star formation to be a local affair, occurring only in those regions where the
column density is above this star formation threshold. The low surface
brightness nature of this galaxy could thus be attributed to an insufficient
gas surface density, inhibiting star formation on a more global scale.
Significantly, though, the Toomre criterion places a much lower critical
density on the galaxy (+/-10E20 atoms/cm^2), which is shown by the galaxy's low
SFR to not be applicable.
Within a projected distance of 300kpc/30kms of UGC 12695 lie two companion
galaxies - UGC 12687, a high surface brightness barred spiral galaxy, and
2333+1234, a dwarf galaxy discovered during this investigation. The close
proximity of the three galaxies, combined with UGC 12695's extremely blue color
and regions of localized starburst and UGC 12687's UV excess bring to mind
mutually induced star formation through tidal activity.Comment: 14 pages, 8 figures (2 color), To be published in A.J., May 2000
From Model Checking to Runtime Verification and Back
We describe a novel approach for adapting an existing software model checker
to perform precise runtime verification. The software under test is allowed to
communicate with the wider environment (including the file system and network).
The modifications to the model checker are small and self-contained, making
this a viable strategy for re-using existing model checking tools in a new
context.
Additionally, from the data that is gathered during a single execution in the
runtime verification mode, we automatically re-construct a description of the
execution environment which can then be used in the standard, full-blown model
checker. This additional verification step can further improve coverage,
especially in the case of parallel programs, without introducing substantial
overhead into the process of runtime verification
Point vortices and classical orthogonal polynomials
Stationary equilibria of point vortices with arbitrary choice of circulations
in a background flow are studied. Differential equations satisfied by
generating polynomials of vortex configurations are derived. It is shown that
these equations can be reduced to a single one. It is found that polynomials
that are Wronskians of classical orthogonal polynomials solve the latter
equation. As a consequence vortex equilibria at a certain choice of background
flows can be described with the help of Wronskians of classical orthogonal
polynomials.Comment: 20 pages, 12 figure
Spitzer Observations of Low Luminosity Isolated and Low Surface Brightness Galaxies
We examine the infrared properties of five low surface brightness galaxies
(LSBGs) and compare them with related but higher surface brightness galaxies,
using Spitzer Space Telescope images and spectra. All the LSBGs are detected in
the 3.6 and 4.5um bands, representing the stellar population. All but one are
detected at 5.8 and 8.0um, revealing emission from hot dust and aromatic
molecules, though many are faint or point-like at these wavelengths. Detections
of LSBGs at the far-infrared wavelengths, 24, 70, and 160um, are varied in
morphology and brightness, with only two detections at 160um, resulting in
highly varied spectral energy distributions. Consistent with previous
expectations for these galaxies, we find that detectable dust components exist
for only some LSBGs, with the strength of dust emission dependent on the
existence of bright star forming regions. However, the far-infrared emission
may be relatively weak compared with normal star-forming galaxies.Comment: 20 pages, 8 figures, accepted to Ap
Accessing monomers, surfactants, and the queen bee substance by acrylate cross-metathesis of long-chain alkenones
Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Journal of the American Oil Chemists' Society 94 (2017): 831-840, doi: 10.1007/s11746-017-2997-8.Polyunsaturated long-chain alkenones are a unique class of lipids biosynthesized in
significant quantities (up to 20% of cell carbon) by several algae including the industrially grown
marine microalgae Isochrysis. Alkenone structures are characterized by a long linear carbon-chain
(35-40 carbons) with one to four trans-double bonds and terminating in a methyl or ethyl ketone.
Alkenones were extracted and isolated from commercially obtained Isochrysis biomass and then
subjected to cross-metathesis (CM) with methyl acrylate or acrylic acid using the Hoveyda-Grubbs
metathesis initiator. Within 1 h at room temperature alkenones were consumed, however complete
fragmentation (i.e. conversion to the smallest subunits by double bond cleavage) required up to 16
h. Analysis of the reaction mixture by gas chromatography and comprehensive two-dimensional
gas chromatography revealed a predictable product mixture consisting primarily of long-chain
(mostly C17) acids (or methyl esters from CM with methyl acrylate) and diacids (or diesters), along with smaller amounts (~5%) of the honey bee âqueen substanceâ (E)-9-oxo-decenoic acid.
Together, these compounds comprise a diverse mixture of valuable chemicals that includes
surfactants, monomers, and an agriculturally relevant bee pheromone.This work was supported by the National Science Foundation (CHE-
1151492) and through a private donation from friends of WHOI
Optical microrheology using rotating laser-trapped particles
We demonstrate an optical system that can apply and accurately measure the
torque exerted by the trapping beam on a rotating birefringent probe particle.
This allows the viscosity and surface effects within liquid media to be
measured quantitatively on a micron-size scale using a trapped rotating
spherical probe particle. We use the system to measure the viscosity inside a
prototype cellular structure.Comment: 5 pages, 4 figures. v2: bibliographic details, minor text correction
Academic freedom in Europe: reviewing UNESCOâs recommendation
This paper examines the compliance of universities in the European Union with the UNESCO Recommendation concerning the Status of HigherâEducation Teaching Personnel, which deals primarily with protection for academic freedom. The paper briefly surveys the European genesis of the modern research university and academic freedom, before evaluating compliance with the UNESCO recommendation on institutional autonomy, academic freedom, university governance and tenure. Following from this, the paper examines the reasons for the generally low level of compliance with the UNESCO Recommendation within the EU states, and considers how such compliance could be improved
Implementation of Multidimensional Databases with Document-Oriented NoSQL
International audienceNoSQL (Not Only SQL) systems are becoming popular due to known advantages such as horizontal scalability and elasticity. In this paper, we study the implementation of data warehouses with document-oriented NoSQL systems. We propose mapping rules that transform the multidimensional data model to logical document-oriented models. We consider three different logical models and we use them to instantiate data warehouses. We focus on data loading, model-to-model conversion and OLAP cuboid computation
On the Mean-Field Limit of Bosons with Coulomb Two-Body Interaction
In the mean-field limit the dynamics of a quantum Bose gas is described by a
Hartree equation. We present a simple method for proving the convergence of the
microscopic quantum dynamics to the Hartree dynamics when the number of
particles becomes large and the strength of the two-body potential tends to 0
like the inverse of the particle number. Our method is applicable for a class
of singular interaction potentials including the Coulomb potential. We prove
and state our main result for the Heisenberg-picture dynamics of "observables",
thus avoiding the use of coherent states. Our formulation shows that the
mean-field limit is a "semi-classical" limit.Comment: Corrected typos and included an elementary proof of the Kato
smoothing estimate (Lemma 6.1
UGC 7388: a galaxy with two tidal loops
We present the results of spectroscopic and morphological studies of the
galaxy UGC7388 with the 8.1-m Gemini North telescope. Judging by its observed
characteristics, UGC7388 is a giant late-type spiral galaxy seen almost
edge-on. The main body of the galaxy is surrounded by two faint (\mu(B) ~ 24
and \mu(B) ~ 25.5) extended (~20-30 kpc) loop-like structures. A large-scale
rotation of the brighter loop about the main galaxy has been detected. We
discuss the assumption that the tidal disruption of a relatively massive
companion is observed in the case of UGC7388. A detailed study and modeling of
the observed structure of this unique galaxy can give important information
about the influence of the absorption of massive companions on the galactic
disks and about the structure of the dark halo around UGC7388.Comment: 8 pages, 5 figure
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