57 research outputs found
Highway Guide: Teaching lnternet Skills
No doubt about it, library users are feeling the weight and stress of
information overload. In addition to the sheer enormity of the amount of
information "out there," the tools used to archive, categorize, and access .
information are becoming increasingly complex. No group understands this
overload better than those of us who work in libraries. Like our users, we
struggle daily to keep up with our reading, wade through all our e-mail, and
identify and learn to use new sources of information, and new access tools.
Unlike our users, however, we are obligated by dejinition, to provide what I
call "information guidance" - the best access to quality information. Library
staff members must proactively rise to the challenge and must provide
guidance through the infomation glut. I watch the users in our library. What
do they state that they need? What do they need that they do not know they
need? How can we use new technologies to improve their access to information?
How can we best point them toward the most accurate, timely, and
useful information? As the complexity of the tools increases, the need for
training in the use of the tools increases. If we are to guide, we must educate.
In the case of the library where I work, the Clarian Health Partners Medical
Library, we are part of the Educational Services Department, and so, specifically
charged with educating users
Spectral similarity measures for in vivo human tissue discrimination based on hyperspectral imaging
Problem: Similarity measures are widely used as an approved method for spectral discrimination or identification with their applications in different areas of scientific research. Even though a range of works have been presented, only a few showed slightly promising results for human tissue, and these were mostly focused on pathological and non-pathological tissue classification. Methods: In this work, several spectral similarity measures on hyperspectral (HS) images of in vivo human tissue were evaluated for tissue discrimination purposes. Moreover, we introduced two new hybrid spectral measures, called SID-JM-TAN(SAM) and SID-JM-TAN(SCA). We analyzed spectral signatures obtained from 13 different human tissue types and two different materials (gauze, instruments), collected from HS images of 100 patients during surgeries. Results: The quantitative results showed the reliable performance of the different similarity measures and the proposed hybrid measures for tissue discrimination purposes. The latter produced higher discrimination values, up to 6.7 times more than the classical spectral similarity measures. Moreover, an application of the similarity measures was presented to support the annotations of the HS images. We showed that the automatic checking of tissue-annotated thyroid and colon tissues was successful in 73% and 60% of the total spectra, respectively. The hybrid measures showed the highest performance. Furthermore, the automatic labeling of wrongly annotated tissues was similar for all measures, with an accuracy of up to 90%. Conclusion: In future work, the proposed spectral similarity measures will be integrated with tools to support physicians in annotations and tissue labeling of HS images
The MOSDEF survey: a stellar mass-SFR-metallicity relation exists at
We investigate the nature of the relation among stellar mass, star-formation
rate, and gas-phase metallicity (the M-SFR-Z relation) at high redshifts
using a sample of 260 star-forming galaxies at from the MOSDEF
survey. We present an analysis of the high-redshift M-SFR-Z relation based
on several emission-line ratios for the first time. We show that a M-SFR-Z
relation clearly exists at . The strength of this relation is similar
to predictions from cosmological hydrodynamical simulations. By performing a
direct comparison of stacks of and galaxies, we find that
galaxies have dex lower metallicity at fixed M and
SFR. In the context of chemical evolution models, this evolution of the
M-SFR-Z relation suggests an increase with redshift of the mass-loading
factor at fixed M, as well as a decrease in the metallicity of infalling
gas that is likely due to a lower importance of gas recycling relative to
accretion from the intergalactic medium at high redshifts. Performing this
analysis simultaneously with multiple metallicity-sensitive line ratios allows
us to rule out the evolution in physical conditions (e.g., N/O ratio,
ionization parameter, and hardness of the ionizing spectrum) at fixed
metallicity as the source of the observed trends with redshift and with SFR at
fixed M at . While this study highlights the promise of
performing high-order tests of chemical evolution models at high redshifts,
detailed quantitative comparisons ultimately await a full understanding of the
evolution of metallicity calibrations with redshift.Comment: 19 pages, 8 figures, accepted to Ap
The MOSDEF Survey: Kinematic and Structural Evolution of Star-Forming Galaxies at
We present ionized gas kinematics for 681 galaxies at from
the MOSFIRE Deep Evolution Field survey, measured using models which account
for random galaxy-slit misalignments together with structural parameters
derived from CANDELS Hubble Space Telescope (HST) imaging. Kinematics and sizes
are used to derive dynamical masses. Baryonic masses are estimated from stellar
masses and inferred gas masses from dust-corrected star formation rates (SFRs)
and the Kennicutt-Schmidt relation. We measure resolved rotation for 105
galaxies. For the remaining 576 galaxies we use models based on HST imaging
structural parameters together with integrated velocity dispersions and
baryonic masses to statistically constrain the median ratio of intrinsic
ordered to disordered motion, . We find that
increases with increasing stellar mass and decreasing specific SFR (sSFR).
These trends may reflect marginal disk stability, where systems with higher gas
fractions have thicker disks. For galaxies with detected rotation we assess
trends between their kinematics and mass, sSFR, and baryon surface density
(). Intrinsic dispersion correlates most with
and velocity correlates most with mass. By comparing
dynamical and baryonic masses, we find that galaxies at are
baryon dominated within their effective radii (), with Mdyn/Mbaryon
increasing over time. The inferred baryon fractions within ,
, decrease over time, even at fixed mass, size, or surface
density. At fixed redshift, does not appear to vary with
stellar mass but increases with decreasing and increasing
. For galaxies at , the median inferred baryon
fractions generally exceed 100%. We discuss possible explanations and future
avenues to resolve this tension.Comment: Accepted to ApJ. Added Figure 9, corrected sample size (main results
unchanged). 28 pages, 13 figure
The MOSDEF Survey: An Improved Voronoi Binning Technique on Spatially Resolved Stellar Populations at z~2
We use a sample of 350 star-forming galaxies at from the
MOSFIRE Deep Evolution Field survey to demonstrate an improved Voronoi binning
technique that we use to study the properties of resolved stellar populations
in galaxies. Stellar population and dust maps are constructed from the
high-resolution CANDELS/3D-HST multi-band imaging. Rather than constructing the
layout of resolved elements (i.e., Voronoi bins) from the S/N distribution of
the -band alone, we introduce a modified Voronoi binning method that
additionally incorporates the S/N distribution of several resolved filters. The
SED-derived resolved E(B-V), stellar population ages, SFRs,
and stellar masses that are inferred from the Voronoi bins constructed from
multiple filters are generally consistent with the properties inferred from the
integrated photometry within the uncertainties, with the exception of the
inferred E(B-V) from our sample due to their UV
slopes being unconstrained by the resolved photometry. The results from our
multi-filter Voronoi binning technique are compared to those derived from a
"traditional" single-filter Voronoi binning approach. We find that
single-filter binning produces inferred E(B-V) that are
systematically redder by 0.02 mag on average, but could differ by up to 0.20
mag, and could be attributed to poorly constrained resolved photometry covering
the UV slope. Overall, we advocate that our methodology produces more reliable
SED-derived parameters due to the best-fit resolved SEDs being better
constrained at all resolved wavelengths--particularly those covering the UV
slope.Comment: 23 pages, 15 figures, accepted for publication in MNRA
The MOSDEF Survey: the Variation of the Dust Attenuation Curve with Metallicity
We derive the UV-optical stellar dust attenuation curve of galaxies at
z=1.4-2.6 as a function of gas-phase metallicity. We use a sample of 218
star-forming galaxies, excluding those with very young or heavily obscured star
formation, from the MOSFIRE Deep Evolution Field (MOSDEF) survey with
H, H, and [NII] spectroscopic measurements. We
constrain the shape of the attenuation curve by comparing the average flux
densities of galaxies sorted into bins of dust obscuration using Balmer
decrements, i.e., H-to-H luminosities. The average attenuation
curve for the high-metallicity sample (12+log(O/H)>8.5, corresponding to
) has a shallow slope, identical to that of the
Calzetti local starburst curve, and a significant UV 2175A extinction bump that
is the strength of the Milky Way bump. On the other hand, the
average attenuation curve of the low-metallicity sample (12+log(O/H) ) has a steeper slope similar to that of the SMC curve, only consistent
with the Calzetti slope at the level. The UV bump is not detected in
the low-metallicity curve, indicating the relative lack of the small dust
grains causing the bump at low metallicities. Furthermore, we find that on
average the nebular reddening (E(B-V)) is a factor of 2 times larger than that
of the stellar continuum for galaxies with low metallicities, while the nebular
and stellar reddening are similar for galaxies with higher metallicities. The
latter is likely due to a high surface density of dusty clouds embedding the
star forming regions but also reddening the continuum in the high-metallicity
galaxies.Comment: 20 pages and 9 figures and 1 appendix, accepted for publication in
Ap
The MOSDEF Survey: [SIII] as a New Probe of Evolving ISM Conditions
We present measurements of [SIII]9069,9531 for a sample of
star-forming galaxies, the first sample with measurements of these
lines at z>0.1. We employ the line ratio
S[SIII]9069,9531/[SII]6716,6731
as a novel probe of evolving ISM conditions. Since this ratio includes the
low-ionization line [SII], it is crucial that the effects of diffuse ionized
gas (DIG) on emission-line ratios be accounted for in integrated
galaxy spectra, or else that comparisons be made to samples of local HII
regions in which DIG emission is not present. We find that S decreases
with increasing stellar mass at both and , but that the
dependence is weak suggesting S has a very shallow anticorrelation with
metallicity, in contrast with O that displays a strong metallicity
dependence. As a result, S only mildly evolves with redshift at fixed
stellar mass. The sample is systematicallty offset towards lower
S and higher [SII]/H at fixed [OIII]/H relative to
HII regions. By comparing to photoionization model grids, we find that such
trends can be explained by a scenario in which the ionizing spectrum is harder
at fixed O/H with increasing redshift, but are inconsistent with an increase in
ionization parameter at fixed O/H. This analysis demonstrates the advantages of
expanding beyond the strongest rest-optical lines for evolutionary studies, and
the particular utility of [SIII] for characterizing evolving ISM conditions and
stellar compositions. These measurements provide a basis for estimating [SIII]
line strengths for high-redshift galaxies, a line that the James Webb Space
Telescope will measure out to z~5.5
The MOSDEF Survey: Differences in SFR and Metallicity for Morphologically-Selected Mergers at z~2
We study the properties of 55 morphologically-identified merging galaxy
systems at z~2. These systems are flagged as mergers based on features such as
tidal tails, double nuclei, and asymmetry. Our sample is drawn from the MOSFIRE
Deep Evolution Field (MOSDEF) survey, along with a control sample of isolated
galaxies at the same redshift. We consider the relationships between stellar
mass, star formation rate (SFR), and gas-phase metallicity for both merging and
non-merging systems. In the local universe, merging systems are characterized
by an elevated SFR and depressed metallicity compared to isolated systems at a
given mass. Our results indicate SFR enhancement and metallicity deficit for
merging systems relative to non-merging systems for a fixed stellar mass at
z~2, though larger samples are required to establish these preliminary results
with higher statistical significance. In future work, it will be important to
establish if the enhanced SFR and depressed metallicity in high-redshift
mergers deviate from the "fundamental metallicity relation," as is observed in
mergers in the local universe, and therefore shed light on gas flows during
galaxy interactions.Comment: 9 pages, 5 figures, 5 figures, accepted to MNRA
- …