4,645 research outputs found
Backward Diffusion Methods for Digital Halftoning
We examine using discrete backward diffusion to produce digital halftones.
The noise introduced by the discrete approximation to backwards diffusion forces
the intensity away from uniform values, so that rounding each pixel to black or
white can produce a pleasing halftone. We formulate our method by considering
the Human Visual System norm and approximating the inverse of the blurring
operator. We also investigate several possible mobility functions for use in a
nonlinear backward diffusion equation for higher quality results
The Chemical Compositions of the SRd Variable Stars-- II. WY Andromedae, VW Eridani, and UW Librae
Chemical compositions are derived from high-resolution spectra for three
stars classed as SRd variables in the General Catalogue of Variable Stars.
These stars are shown to be metal-poor supergiants: WY And with [Fe/H] = -1.0,
VW Eri with [Fe/H] = -1.8, and UW Lib with [Fe/H] = -1.2. Their compositions
are identical to within the measurement errors with the compositions of
subdwarfs, subgiants, and less evolved giants of the same FeH. The stars are at
the tip of the first giant branch or in the early stages of evolution along the
asymptotic giant branch (AGB). There is no convincing evidence that these SRd
variables are experiencing thermal pulsing and the third dredge-up on the AGB.
The SRds appear to be the cool limit of the sequence of RV Tauri variables.Comment: 14 pages, 1 figure, 4 table
An Abundance Analysis for Five Red Horizontal Branch Stars in the Extremely Metal Rich Globular Cluster NGC 6553
We provide a high dispersion line-by-line abundance analysis of five red HB
stars in the extremely metal rich galactic globular cluster NGC 6553. These red
HB stars are significantly hotter than the very cool stars near the tip of the
giant branch in such a metal rich globular cluster and hence their spectra are
much more amenable to an abundance analysis than would be the case for red
giants.
We find that the mean [Fe/H] for NGC 6553 is -0.16 dex, comparable to the
mean abundance in the galactic bulge found by McWilliam & Rich (1994) and
considerably higher than that obtained from an analysis of two red giants in
this cluster by Barbuy etal (1999). The relative abundance for the best
determined alpha process element (Ca) indicates an excess of alpha process
elements of about a factor of two. The metallicity of NGC 6553 reaches the
average of the Galactic bulge and of the solar neighborhood.Comment: 29 pages, 6 figures, accepted for publication in the Ap
Gaia: The Astrometry Revolution
The power of micro-arcsecond (as) astrometry is about to be unleashed.
ESA's Gaia mission, now headed towards the end of the first year of routine
science operations, will soon fulfil its promise for revolutionary science in
countless aspects of Galactic astronomy and astrophysics. The potential of Gaia
position measurements for important contributions to the astrophysics of
planetary systems is huge. We focus here on the expectations for detection and
improved characterization of 'young' planetary systems in the neighborhood of
the Sun using a combination of Gaia as astrometry and direct imaging
techniques.Comment: 6 pages, 3 figures, to appear in the Proceedings of IAU Symposium 314
'Young Stars & Planets Near the Sun', held on May 11-15 2015 in Atlanta (GA),
USA (J. H. Kastner, B. Stelzer, & S. A. Metchev, eds.
Nucleosynthesis in Type II supernovae and the abundances in metal-poor stars
We explore the effects on nucleosynthesis in Type II supernovae of various
parameters (mass cut, neutron excess, explosion energy, progenitor mass) in
order to explain the observed trends of the iron-peak element abundance ratios
([Cr/Fe], [Mn/Fe], [Co/Fe] and [Ni/Fe]) in halo stars as a function of
metallicity for the range [Fe/H] . [Cr/Fe] and [Mn/Fe]
decrease with decreasing [Fe/H], while [Co/Fe] behaves the opposite way and
increases. We show that such a behavior can be explained by a variation of mass
cuts in Type II supernovae as a function of progenitor mass, which provides a
changing mix of nucleosynthesis from an alpha-rich freeze-out of Si-burning and
incomplete Si-burning. This explanation is consistent with the amount of
ejected Ni determined from modeling the early light curves of individual
supernovae. We also suggest that the ratio [H/Fe] of halo stars is mainly
determined by the mass of interstellar hydrogen mixed with the ejecta of a
single supernova which is larger for larger explosion energy and the larger
Str\"omgren radius of the progenitor.Comment: 17 pages, LaTeX, Accepted for publication in the Astrophysical
Journal, more discussion on the Galactic chemical evolutio
Two-photon imaging of cancer cell extravasation in live mice
Abstract
MDA-MB-231 breast cancer cells were engineered to express cytoplasmic paxillin-GFP and nuclear H2B-mCherry. In order to image extravasation, the cancer cells were injected in the blood stream of nude mice. Using 2-photon excitation microscopy we can simultaneously excite the two probes and also visualize the autofluorescence of tissues. A skin flap was opened to visualize blood vessels and recognize the position of the cancer cells. Two-photon imaging showed that after an initial phase in which the cells are non-adherent, some cells spread on the internal surface of the capillaries. Days later some cells started to appear on the external side of the capillary. The extravasated cells extend very long protrusions into the tissue. The goal was to determine if at the end of the long protrusion, if it is possible to observe the formation of focal adhesions by imaging paxillin-GFP. Preliminary results show that when cells start to adhere to the blood vessel wall they form focal adhesions as determined by the characteristic elongated features observed in the paxillin-GFP channel. New approaches will allow the tracking of the tip of the protrusion to determine if focal adhesions are forming there as the cells extravasate. This is important in establishing the mechanism of cell extravasation and migration in tissues.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1412. doi:10.1158/1538-7445.AM2011-141
Photometric and spectroscopic study of the intermediate age open cluster NGC 3960
We present CCD UBVI photometry and high-resolution spectroscopy of the
intermediate age open cluster NGC 3960. The colour - magnitude diagrams (CMDs)
derived from the photometric data and interpreted with the synthetic CMD method
allow us to estimate the cluster parameters. We derive: age = 0.9 or 0.6 Gyr
(depending on whether or not overshooting from convective regions is included
in the adopted stellar models), distance (m-M)0 = 11.6 +/- 0.1, reddening
E(B-V) = 0.29 +/- 0.02, differential reddening Delta E(B-V) = 0.05 and
approximate metallicity between solar and half of solar. We obtained high
resolution spectra of three clump stars, and derived an average [Fe/H] = -0.12
(rms 0.04 dex), in very good agreement with the photometric determination. We
also obtained abundances of alpha-elements, Fe-peak elements, and of Ba. The
reddenings toward individual stars derived from the spectroscopic temperatures
and the Alonso et al. calibrations give further support to the existence of
significative variations across the cluster.Comment: Accepted for publication on MNRAS; fig. 3, 4, 5, 6 at degraded
resolutio
The Spectra of Main Sequence Stars in Galactic Globular Clusters II. CH and CN Bands in M71
Spectra with a high signal-to-noise ratio of 79 stars which are just below
the main sequence turnoff of M71 are presented. They yield indices for the
strength of the G band of CH and the ultraviolet CN band at 3885 \AA. These
indices are each to first order bimodal and they are anti-correlated. There are
approximately equal numbers of CN weak/CH strong and CN strong/CH weak main
sequence stars in M71. It is not yet clear whether these star-to-star
variations arise from primordial variations or from mixing within a fraction of
individual stars as they evolve.Comment: Accepted for publication in the AJ to appear back to back with paper
I. 14 pages with 5 figure
The dynamics of liquid slugs forced by a syringe pump
Microfluidic processes for chemical synthesis have become popular in recent years. The small scale of the chemical reactions promise greater control over reaction conditions and more timely creation of products. The small scale of microfluidics poses its own set of problems, however. At the microscale, the dominant fluid forces are viscous resistance and surface tension. The effects of viscosity and scale reduce the Reynolds number and make mixing difficult. Much work has been done to control mixing at the microscale.
This problem is concerned with a different microfluidic problem: delivering reactants to the site of reaction. A common setup is to attach syringes full of reactant to a reaction chamber by narrow hydrophobic tubing. Using a stepper motor, a controlled dose of liquid may be injected into the tube. The hydrophobosity causes the dose to curve outward on the sides, becoming a "slug" of reactant with air in front and behind. The syringe at the rear is then switched for one full of air, and air pressure is used to drive the slug to the reaction site.
If too much pressure is applied, the slug will arrive with a significant back pressure that will be relieved through bubbling in the reaction site. This causes the formation of a foam and is highly undesirable. We present a simple model based on Boyleâs law for the motion of a slug through a tube. We then extend this model for trains of slugs separated by air bubbles. Last, we consider the case of a flooded reaction site, where the forward air bubble must be pushed through the flooding liquid.
In conclusion, we have determined the dynamics of a single slug moving towards an empty reaction chamber giving the final equilibrium position of the slug. A phase-plane analysis then determined a condition on the size of the slug needed to ensure that it comes to rest without oscillating about the equilibrium position. The effect of a flooded reaction chamber was then considered. In this case it is impossible to avoid bubbling due to the design of the device. We found that it is possible, however, to reduce the bubbling by minimising the back pressure behind the slug. Finally, the dynamics of multiple slugs with or without a flooded reaction chamber has been investigated
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