313 research outputs found
Discovery of Reflection Nebulosity Around Five Vega-like Stars
Coronagraphic optical observations of six Vega-like stars reveal reflection
nebulosities, five of which were previously unknown. The nebulosities
illuminated by HD 4881, HD 23362, HD 23680, HD 26676, and HD 49662 resemble
that of the Pleiades, indicating an interstellar origin for dust grains. The
reflection nebulosity around HD 123160 has a double-arm morphology, but no
disk-like feature is seen as close as 2.5 arcsec from the star in K-band
adaptive optics data. We demonstrate that uniform density dust clouds
surrounding HD 23362, HD 23680 and HD 123160 can account for the observed
12-100 micron spectral energy distributions. For HD 4881, HD 26676, and HD
49662 an additional emission source, such as from a circumstellar disk or
non-equilibrium grain heating, is required to fit the 12-25 micron data. These
results indicate that in some cases, particularly for Vega-like stars located
beyond the Local Bubble (>100 pc), the dust responsible for excess thermal
emission may originate from the interstellar medium rather than from a
planetary debris system.Comment: The Astrophysical Journal, in press for March, 2002 (32 pages, 13
figures
Structure-based discovery of glycomimetic FmlH ligands as inhibitors of bacterial adhesion during urinary tract infection
Significance
The emergence of multidrug-resistant bacteria, including uropathogenic
Escherichia coli
(UPEC), makes the development of targeted antivirulence therapeutics a critical focus of research. During urinary tract infections (UTIs), UPEC uses chaperone–usher pathway pili tipped with an array of adhesins that recognize distinct receptors with sterochemical specificity to facilitate persistence in various tissues and habitats. We used an interdisciplinary approach driven by structural biology and synthetic glycoside chemistry to design and optimize glycomimetic inhibitors of the UPEC adhesin FmlH. These inhibitors competitively blocked FmlH in vitro, in in vivo mouse UTI models, and in ex vivo healthy human kidney tissue. This work demonstrates the utility of structure-driven drug design in the effort to develop antivirulence therapeutic compounds.
</jats:p
mAb Das-1 recognizes 3\u27-Sulfated Lewis A/C, which is aberrantly expressed during metaplastic and oncogenic transformation of several gastrointestinal epithelia
INTRODUCTION: Multiple previous studies have shown the monoclonal antibody Das-1 (formerly called 7E12H12) is specifically reactive towards metaplastic and carcinomatous lesions in multiple organs of the gastrointestinal system (e.g. Barrett\u27s esophagus, intestinal-type metaplasia of the stomach, gastric adenocarcinoma, high-grade pancreatic intraepithelial neoplasm, and pancreatic ductal adenocarcinoma) as well as in other organs (bladder and lung carcinomas). Beyond being a useful biomarker in tissue, mAb Das-1 has recently proven to be more accurate than current paradigms for identifying cysts harboring advanced neoplasia. Though this antibody has been used extensively for clinical, basic science, and translational applications for decades, its epitope has remained elusive.
METHODS: In this study, we chemically deglycosylated a standard source of antigen, which resulted in near complete loss of the signal as measured by western blot analysis. The epitope recognized by mAb Das-1 was determined by affinity to a comprehensive glycan array and validated by inhibition of a direct ELISA.
RESULTS: The epitope recognized by mAb Das-1 is 3\u27-Sulfo-Lewis A/C (3\u27-Sulfo-LeA/C). 3\u27-Sulfo-LeA/C is broadly reexpressed across numerous GI epithelia and elsewhere during metaplastic and carcinomatous transformation.
DISCUSSION: 3\u27-Sulfo-LeA/C is a clinically important antigen that can be detected both intracellularly in tissue using immunohistochemistry and extracellularly in cyst fluid and serum by ELISA. The results open new avenues for tumorigenic risk stratification of various gastrointestinal lesions
The Molecular Gas Environment around Two Herbig Ae/Be Stars: Resolving the Outflows of LkHa 198 and LkHa 225S
Observations of outflows associated with pre-main-sequence stars reveal
details about morphology, binarity and evolutionary states of young stellar
objects. We present molecular line data from the Berkeley-Illinois-Maryland
Association array and Five Colleges Radio Astronomical Observatory toward the
regions containing the Herbig Ae/Be stars LkHa 198 and LkHa 225S. Single dish
observations of 12CO 1-0, 13CO 1-0, N2H+ 1-0 and CS 2-1 were made over a field
of 4.3' x 4.3' for each species. 12CO data from FCRAO were combined with high
resolution BIMA array data to achieve a naturally-weighted synthesized beam of
6.75'' x 5.5'' toward LkHa 198 and 5.7'' x 3.95'' toward LkHa 225S,
representing resolution improvements of factors of approximately 10 and 5 over
existing data. By using uniform weighting, we achieved another factor of two
improvement. The outflow around LkHa 198 resolves into at least four outflows,
none of which are centered on LkHa 198-IR, but even at our resolution, we
cannot exclude the possibility of an outflow associated with this source. In
the LkHa 225S region, we find evidence for two outflows associated with LkHa
225S itself and a third outflow is likely driven by this source. Identification
of the driving sources is still resolution-limited and is also complicated by
the presence of three clouds along the line of sight toward the Cygnus
molecular cloud. 13CO is present in the environments of both stars along with
cold, dense gas as traced by CS and (in LkHa 225S) N2H+. No 2.6 mm continuum is
detected in either region in relatively shallow maps compared to existing
continuum observations.Comment: 14 pages, 10 figures (5 color), accepted for publication in Ap
Collisional Cascades in Planetesimal Disks I. Stellar Flybys
We use a new multiannulus planetesimal accretion code to investigate the
evolution of a planetesimal disk following a moderately close encounter with a
passing star. The calculations include fragmentation, gas and
Poynting-Robertson drag, and velocity evolution from dynamical friction and
viscous stirring. We assume that the stellar encounter increases planetesimal
velocities to the shattering velocity, initiating a collisional cascade in the
disk. During the early stages of our calculations, erosive collisions damp
particle velocities and produce substantial amounts of dust. For a wide range
of initial conditions and input parameters, the time evolution of the dust
luminosity follows a simple relation, L_d/L_{\star} = L_0 / [alpha +
(t/t_d)^{beta}]. The maximum dust luminosity L_0 and the damping time t_d
depend on the disk mass, with L_0 proportional to M_d and t_d proportional to
M_d^{-1}. For disks with dust masses of 1% to 100% of the `minimum mass solar
nebula' (1--100 earth masses at 30--150 AU), our calculations yield t_d approx
1--10 Myr, alpha approx 1--2, beta = 1, and dust luminosities similar to the
range observed in known `debris disk' systems, L_0 approx 10^{-3} to 10^{-5}.
Less massive disks produce smaller dust luminosities and damp on longer
timescales. Because encounters with field stars are rare, these results imply
that moderately close stellar flybys cannot explain collisional cascades in
debris disk systems with stellar ages of 100 Myr or longer.Comment: 33 pages of text, 12 figures, and an animation. The paper will appear
in the March 2002 issue of the Astronmomical Journal. The animation and a
copy of the paper with full resolution figures are at S. Kenyon's planet
formation website: http://cfa-www.harvard.edu/~kenyon/p
A white-light trap for Bose-Einstein condensates
We propose a novel method for trapping Bose-condensed atoms using a
white-light interference fringe. Confinement frequencies of tens of kHz can be
achieved in conjunction with trap depths of only a few micro-K. We estimate
that lifetimes on the order of 10 s can be achieved for small numbers of atoms.
The tight confinement and shallow depth permit tunneling processes to be used
for studying interaction effects and for applications in quantum information.Comment: 10 pages with 3 figure
Multi-Wavelength Modelling of the Beta Leo Debris Disc: 1, 2 or 3 planetesimal populations?
In this paper we present a model of the Beta Leo debris disc, with an
emphasis on modelling the resolved PACS images obtained as part of the Herschel
key programme DEBRIS. We also present new SPIRE images of the disc at 250
microns, as well as new constraints on the disc from SCUBA-2, mid-IR and
scattered light imaging. Combining all available observational constraints, we
find three possible models for the Beta Leo (HD102647) debris disc: (i) A 2
component model, comprised of a hot component at 2 AU and a cold component from
15-70 AU. (ii) A 3 component model with hot dust at 2 AU, warm dust at 9 AU,
and a cold component from 30-70 AU, is equally valid since the cold emission is
not resolved within 30 AU. (iii) A somewhat less likely possibility is that the
system consists of a single very eccentric planetesimal population, with
pericentres at 2 AU and apocentres at 65 AU. Thus, despite the wealth of
observational constraints significant ambiguities remain; deep mid-IR and
scattered light imaging of the dust distribution within 30 AU seems the most
promising method to resolve the degeneracy. We discuss the implications for the
possible planetary system architecture; e.g., the 2 component model suggests
planets may exist at 2-15 AU, while the 3 component model suggests planets
between 2-30 AU with a stable region containing the dust belt at 9 AU, and
there should be no planets between 2-65 AU in the eccentric planetesimal model.
We suggest that the hot dust may originate in the disintegration of comets
scattered in from the cold disc, and examine all A stars known to harbour both
hot and cold dust to consider the possibility that the ratio of hot and cold
dust luminosities is indicative of the intervening planetary system
architecture.Comment: 20 pages, 14 figures. Accepted to MNRA
Multi-density model of the ionised gas in NGC 253 using radio recombination lines
We have imaged the H92alpha (8.3 GHz), H75alpha (15 GHz), and H166alpha (1.4
GHz) Radio Recombination Lines (RRLs) from NGC 253 at resolutions of 4.5 pc
(0.4"), 2.5 pc (0.2") and 53 pc (4.5") respectively. The H92alpha line arises
from individual compact sources, most of which possess radio continuum
counterparts. The line widths range from ~200 km/s for the sources near the
radio nucleus to 70-100 km/s for the extranuclear ones. These lines are emitted
by gas at a density ~10000 /cc. The remainder of the cm-wave RRLs arise in
lower density gas (~500 /cc) with a higher area filling factor and with ten
times highermass. A third component of higher density gas (>10000 /cc) is
required to explain the mm-wave RRLs.Comment: Accepted by A&A; Changed to fit all figures within pag
99 Herculis: Host to a Circumbinary Polar-ring Debris Disk
We present resolved Herschel images of a circumbinary debris disk in the 99
Herculis system. The primary is a late F-type star. The binary orbit is well
characterised and we conclude that the disk is misaligned with the binary
plane. Two different models can explain the observed structure. The first model
is a ring of polar orbits that move in a plane perpendicular to the binary
pericenter direction. We favour this interpretation because it includes the
effect of secular perturbations and the disk can survive for Gyr timescales.
The second model is a misaligned ring. Because there is an ambiguity in the
orientation of the ring, which could be reflected in the sky plane, this ring
either has near-polar orbits similar to the first model, or has a 30 degree
misalignment. The misaligned ring, interpreted as the result of a recent
collision, is shown to be implausible from constraints on the collisional and
dynamical evolution. Because disk+star systems with separations similar to 99
Herculis should form coplanar, possible formation scenarios involve either a
close stellar encounter or binary exchange in the presence of circumstellar
and/or circumbinary disks. Discovery and characterisation of systems like 99
Herculis will help understand processes that result in planetary system
misalignment around both single and multiple stars.Comment: accepted to MNRA
Optical and structural characterization of Ge clusters embedded in ZrO2
The change of optical and structural properties of Ge nanoclusters in ZrO2 matrix have been investigated by spectroscopic ellipsometry versus annealing temperatures. Radio-frequency top-down magnetron sputtering approach was used to produce the samples of different types, i.e. single-layers of pure Ge, pure ZrO2 and Ge-rich-ZrO2 as well as multi-layers stacked of 40 periods of 5-nm-Ge-rich-ZrO2 layers alternated by 5-nm-ZrO2 ones. Germanium nanoclusters in ZrO2 host were formed by rapid-thermal annealing at 600-800 ∘C during 30 s in nitrogen atmosphere. Reference optical properties for pure ZrO2 and pure Ge have been extracted using single-layer samples. As-deposited multi-layer structures can be perfectly modeled using the effective medium theory. However, annealed multi-layers demonstrated a significant diffusion of elements that was confirmed by medium energy ion scattering measurements. This fact prevents fitting of such annealed structure either by homogeneous or by periodic multi-layer model
- …