1,006 research outputs found
Separation of Blood Mixtures Using Fluorescently Labeled Antibodies
Identifying and analyzing biological mixture samples at a crime scene are of paramount concern for forensic scientists, especially if that type of evidence contains only one cell type. The presence of multiple contributors in a biological evidence sample reduces the probative value of DNA evidence and can sometimes lead to its eventual loss of value. As such, this study was performed in an attempt to examine and evaluate flow cytometry analysis as a means to separate blood mixture samples labeled with fluorescent antibodies. Fluorescein Isothiocyanate (FITC) antibodies were specifically targeted and bound to HLA (Human Leukocyte Antigens) markers present on nucleated cells in the blood, after which they were isolated from the blood mixture utilizing Fluorescent Activated Cell Sorting (FACS) - A high throughput technique that separates cell populations based on their optical activity, followed by STR analysis. This approach was tested on fresh blood mixtures containing two contributors, where one contributor possessed an HLA A*02 allele that was not shared with the other contributor. We hypothesize that HLA A*02 positive samples would exhibit fluorescence when bound with the fluorescently labeled antibodies while the HLA A*02 samples would not. As such, we would be able to separate both cell populations using FACS followed by STR analysis. Such a work flow is believed to yield discriminant STR profiles unique to each contributor thus increasing the probative value of the evidence at hand. Results supported our hypothesis and yielded discriminant STR profiles for both contributors, with minor peaks from the A*02 negative contributor being observed in A*02 positive contributor sample. We can then conclude that HLA-A*02 antibodies coupled to FACS is a suitable method that can be utilized to evaluate and separate blood mixture samples in an attempt to yield discriminant STR profiles.https://scholarscompass.vcu.edu/uresposters/1264/thumbnail.jp
CCD PHOTOMETRY OF RR LYRAE STARS IN M5 AS A TEST FOR THE PULSATIONAL SCENARIO
In this paper we present new CCD investigations of RR Lyrae pulsators in the
Oo.I globular cluster M5. B V curves of light for 15 RR Lyrae are presented.
With the addition of further 11 curves of light by Storm, Carney and Beck
(1991) one is dealing with a sample of 26 well studied cluster pulsators whose
properties have been implemented with similar data for RR Lyrae in clusters M3,
M15, M68 to allow a comparison with the theoretical scenario recently presented
by Bono and Stellingwerf (1994). On this basis, we discuss the distribution of
stars in the period amplitude diagram, disclosing a substantial reduction of
Sandage's period shift. We suggest that theoretical constraints concerning
periods and amplitudes could allow information on masses and luminosity of the
pulsators directly from Bailey's diagram only. Static temperatures have been
derived for all stars in the sample, discussing the dependence on the
temperature of the observed pulsational properties.Comment: postscript file of 17 pages of text plus 7 figures and 2 tables. For
any problem please write to [email protected]
Stellar models for very low mass main sequence stars: the role of model atmospheres
We present Very Low Mass stellar models as computed including non-grey model
atmospheres for selected assumptions about the star metallicities. The role of
atmospheres is discussed and the models are compared with models based on the
Eddington approximation and with similar models appeared in the recent
literature. Theoretical predictions concerning both the HR diagram location and
the mass-luminosity relation are presented and discussed in terms of
expectations in selected photometric bands. Comparison with available
observational data concerning both galactic globular clusters and dwarfs in the
solar neighborhood reveals a satisfactory agreement together with the existence
of some residual mismatches.Comment: 10 pages including 13 figures, gzip postscript file, To be published
in MNRA
Predicted HST FOC and broad band colours for young and intermediate Simple Stellar Populations
This paper presents theoretical HST and broad band colours from population
synthesis models based on an homogeneous set of stellar evolutionary tracks as
computed under canonical (no overshooting) assumptions, covering the range of
cluster ages from t=8 Myr to t=5 Gyr for three different metallicities (Z=0.02,
0.006, and 0.001). Statistical fluctuations in the cluster population have been
investigated, assessing the predicted fluctuations of the various colours as a
function of the cluster integrated absolute magnitude. We show that the red
leak in HST UV filters deeply affects the predicted fluxes and colours.
However, we find that for F152M-F307M < 0.5 and for F170M-F278M < 0.5 (which
means ages lower than 1 Gyr) the HST UV colours can still be used to infer
reliable indications on the age of distant clusters. Moreover, one finds that
the age calibration of these colours is scarcely affected by the amount of
original helium or by the assumed IMF. On this basis, we present a calibration
of the HST UV two-colours (F152M-F307M vs F170M-F278M) in terms of cluster ages
for the three above quoted metallicities. We suggest the combined use of HST UV
colours and IR colours (V-K in particular) to disentangle the metallicity-age
effect in integrated colours of young stellar populations (t< 1 Gyr).Comment: Latex 18 pages, 16 encapsulated figures, 6 tables, A&ASS accepte
On the impact of Helium abundance on the Cepheid Period-Luminosity and Wesenheit relations and the Distance Ladder
This work analyses the effect of the Helium content on synthetic
Period-Luminosity Relations (PLRs) and Period-Wesenheit Relations (PWRs) of
Cepheids and the systematic uncertainties on the derived distances that a
hidden population of He-enhanced Cepheids may generate. We use new stellar and
pulsation models to build a homogeneous and consistent framework to derive the
Cepheid features. The Cepheid populations expected in synthetic color-magnitude
diagrams of young stellar systems (from 20 Myr to 250 Myr) are computed in
several photometric bands for Y = 0.25 and Y = 0.35, at a fixed metallicity (Z
= 0.008). The PLRs appear to be very similar in the two cases, with negligible
effects (few %) on distances, while PWRs differ somewhat, with systematic
uncertainties in deriving distances as high as about 7% at log P < 1.5.
Statistical effects due to the number of variables used to determine the
relations contribute to a distance systematic error of the order of few
percent, with values decreasing from optical to near-infrared bands. The
empirical PWRs derived from multi-wavelength datasets for the Large Magellanic
Cloud (LMC) is in a very good agreement with our theoretical PWRs obtained with
a standard He content, supporting the evidence that LMC Cepheids do not show
any He effect
Surface Brightness Fluctuations: a theoretical point of view
We present new theoretical evaluations of optical and near-IR Surface
Brightness Fluctuations (SBF) magnitudes for single-burst stellar populations
in the age range t=5-15 Gyr and metallicity from Z_{\sun}/200 to 2Z_{\sun}.
Our theoretical predictions can be successfully used to derive reliable
distance evaluations. They also appear to be a new and valuable tool to trace
the properties of unresolved stellar populations.Comment: 2 pages, incl. 1 figure, uses newpasp.sty, to be published in ``New
Horizons in Globular Cluster Astronomy'', ASP Conference Series, 2002; Eds.:
G. Piotto, G. Meylan, G. Djorgowski and M. Riello, in pres
Synthetic Stellar Clusters for Pop III
We present preliminary results of an incoming theoretical work concerning the
integrated properties of the Population III clusters of stars. On the basis of
synthetic Color-Magnitude Diagrams, we provide a grid of optical and near-IR
colors of Simple Stellar Populations with very low metallicity (Z=10
and Z=10) and age which spans from 10 Myr to 15 Gyr. A comparison with
higher metallicities up to 0.006 is also shown, disclosing sizable differences
in the CMD morphology, integrated colors and Spectral Energy Distribution
(SED).Comment: 2 pages, incl. 2 figures, "The First Stars", Proceedings of the
second MPA/ESO workshop, Eds.: Weiss, Abel, Hill, Springer, Heidelberg, 200
Distances and Stellar Population properties using the SBF method
We present some results on the study of stellar population properties and
distances of galaxies using the SBF technique. The applications summarized here
show that the Surface Brightness Fluctuations (SBF) method is able to i)
provide accurate distances of resolved and unresolved stellar systems from ~10
Kpc to ~150 Mpc, and ii) to reliably constrain the physical properties (e.g.
age and metallicity) of unresolved stellar systems.Comment: 4 page
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