6,531 research outputs found
Reduced density matrix hybrid approach: An efficient and accurate method for adiabatic and non-adiabatic quantum dynamics
We present a new approach to calculate real-time quantum dynamics in complex
systems. The formalism is based on the partitioning of a system's environment
into "core" and "reservoir" modes, with the former to be treated quantum
mechanically and the latter classically. The presented method only requires the
calculation of the system's reduced density matrix averaged over the quantum
core degrees of freedom which is then coupled to a classically evolved
reservoir to treat the remaining modes. We demonstrate our approach by applying
it to the spin-boson problem using the noninteracting blip approximation to
treat the system and core, and Ehrenfest dynamics to treat the reservoir. The
resulting hybrid methodology is accurate for both fast and slow baths, since it
naturally reduces to its composite methods in their respective regimes of
validity. In addition, our combined method is shown to yield good results in
intermediate regimes where neither approximation alone is accurate and to
perform equally well for both strong and weak system-bath coupling. Our
approach therefore provides an accurate and efficient methodology for
calculating quantum dynamics in complex systems.Comment: 10 pages, 7 figure
A Test of Kangaroo Care on Preterm Infant Breastfeeding
To test the effects of kangaroo care (KC) on breastfeeding outcomes in preterm infants compared to two control groups and to explore whether maternal-infant characteristics and the mother’s choice to use KC were related to breastfeeding measures
Keck/LRIS Spectroscopic Confirmation of Coma Cluster Dwarf Galaxy Membership Assignments
Keck/LRIS multi-object spectroscopy has been carried out on 140 of some of
the lowest and highest surface brightness faint (19 < R < 22) dwarf galaxy
candidates in the core region of the Coma Cluster. These spectra are used to
measure redshifts and establish membership for these faint dwarf populations.
The primary goal of the low surface brightness sample is to test our ability to
use morphological and surface brightness criteria to distinguish between Coma
Cluster members and background galaxies using high resolution HST/ACS images.
Candidates were rated as expected members, uncertain, or expected background.
From 93 spectra, 51 dwarf galaxy members and 20 background galaxies are
identified. Our morphological membership estimation success rate is ~100% for
objects expected to be members and better than ~90% for galaxies expected to be
in the background. We confirm that low surface brightness is a very good
indicator of cluster membership. High surface brightness galaxies are almost
always background with confusion arising only from the cases of the rare
compact elliptical galaxies. The more problematic cases occur at intermediate
surface brightness. Many of these galaxies are given uncertain membership
ratings, and these were found to be members about half of the time. Including
color information will improve membership determination but will fail for some
of the same objects that are already mis-identified when using only surface
brightness and morphology criteria. Compact elliptical galaxies with B-V colors
~0.2 magnitudes redward of the red sequence in particular require spectroscopic
follow-up. In a sample of 47 high surface brightness, UCD candidates, 19
objects have redshifts which place them in the Coma Cluster. Redshift
measurements are presented and the use of indirect means for establishing
cluster membership is discussed.Comment: Accepted for publication in ApJ, 25 pages, 15 figure
Development and clinical performance of high throughput loop-mediated isothermal amplification for detection of malaria.
BACKGROUND: Accurate and efficient detection of sub-microscopic malaria infections is crucial for enabling rapid treatment and interruption of transmission. Commercially available malaria LAMP kits have excellent diagnostic performance, though throughput is limited by the need to prepare samples individually. Here, we evaluate the clinical performance of a newly developed high throughput (HTP) sample processing system for use in conjunction with the Eiken malaria LAMP kit. METHODS: The HTP system utilised dried blood spots (DBS) and liquid whole blood (WB), with parallel sample processing of 94 samples per run. The system was evaluated using 699 samples of known infection status pre-determined by gold standard nested PCR. RESULTS: The sensitivity and specificity of WB-HTP-LAMP was 98.6% (95% CI, 95.7-100), and 99.7% (95% CI, 99.2-100); sensitivity of DBS-HTP-LAMP was 97.1% (95% CI, 93.1-100), and specificity 100% against PCR. At parasite densities greater or equal to 2 parasites/μL, WB and DBS HTP-LAMP showed 100% sensitivity and specificity against PCR. At densities less than 2 p/μL, WB-HTP-LAMP sensitivity was 88.9% (95% CI, 77.1-100) and specificity was 99.7% (95% CI, 99.2-100); sensitivity and specificity of DBS-HTP-LAMP was 77.8% (95% CI, 54.3-99.5) and 100% respectively. CONCLUSIONS: The HTP-LAMP system is a highly sensitive diagnostic test, with the potential to allow large scale population screening in malaria elimination campaigns
The Halo Occupation Distribution: Towards an Empirical Determination of the Relation Between Galaxies and Mass
We investigate galaxy bias in the framework of the ``Halo Occupation
Distribution'' (HOD), which defines the bias of a population of galaxies by the
conditional probability P(N|M) that a dark matter halo of virial mass M
contains N galaxies, together with prescriptions that specify the relative
spatial and velocity distributions of galaxies and dark matter within halos. By
populating the halos of a cosmological N-body simulation using a variety of HOD
models, we examine the sensitivity of different galaxy clustering statistics to
properties of the HOD. The galaxy correlation function responds to different
aspects of P(N|M) on different scales. Obtaining the observed power-law form of
xi(r) requires rather specific combinations of HOD parameters, implying a
strong constraint on the physics of galaxy formation; the success of numerical
and semi-analytic models in reproducing this form is entirely non-trivial.
Other clustering statistics such as the galaxy-mass correlation function, the
bispectrum, the void probability function, the pairwise velocity dispersion,
and the group multiplicity function are sensitive to different combinations of
HOD parameters and thus provide complementary information about galaxy bias. We
outline a strategy for determining the HOD empirically from redshift survey
data. This method starts from an assumed cosmological model, but we argue that
cosmological and HOD parameters will have non-degenerate effects on galaxy
clustering, so that a substantially incorrect cosmological model will not
reproduce the observations for any choice of HOD. Empirical determinations of
the HOD as a function of galaxy type from the 2dF and SDSS redshift surveys
will provide a detailed target for theories of galaxy formation, insight into
the origin of galaxy properties, and sharper tests of cosmological models.Comment: 60 pages + 21 eps figures. Replaced with accepted ApJ version. Minor
changes + added reference
The Incidence of Highly-Obscured Star-Forming Regions in SINGS Galaxies
Using the new capabilities of the Spitzer Space Telescope and extensive
multiwavelength data from the Spitzer Infrared Nearby Galaxies Survey (SINGS),
it is now possible to study the infrared properties of star formation in nearby
galaxies down to scales equivalent to large HII regions. We are therefore able
to determine what fraction of large, infrared-selected star-forming regions in
normal galaxies are highly obscured and address how much of the star formation
we miss by relying solely on the optical portion of the spectrum. Employing a
new empirical method for deriving attenuations of infrared-selected
star-forming regions we investigate the statistics of obscured star formation
on 500pc scales in a sample of 38 nearby galaxies. We find that the median
attenuation is 1.4 magnitudes in H-alpha and that there is no evidence for a
substantial sub-population of uniformly highly-obscured star-forming regions.
The regions in the highly-obscured tail of the attenuation distribution
(A_H-alpha > 3) make up only ~4% of the sample of nearly 1800 regions, though
very embedded infrared sources on the much smaller scales and lower
luminosities of compact and ultracompact HII regions are almost certainly
present in greater numbers. The highly-obscured cases in our sample are
generally the bright, central regions of galaxies with high overall attenuation
but are not otherwise remarkable. We also find that a majority of the galaxies
show decreasing radial trends in H-alpha attenuation. The small fraction of
highly-obscured regions seen in this sample of normal, star-forming galaxies
suggests that on 500pc scales the timescale for significant dispersal or break
up of nearby, optically-thick dust clouds is short relative to the lifetime of
a typical star-forming region.Comment: Accepted for publication in ApJ; emulateapj style, 30 pages, 18
figures (compressed versions), 3 table
The Tully-Fisher Relation in Cluster Cl0024+1654 at z=0.4
Using moderate-resolution Keck spectra, we have examined the velocity
profiles of 15 members of cluster Cl0024+1654 at z=0.4. WFPC2 images of the
cluster members have been used to determine structural parameters, including
disk sizes, orientations, and inclinations. We compare two methods of optical
rotation curve analysis for kinematic measurements. Both methods take seeing,
slit size and orientation, and instrumental effects into account and yield
similar rotation velocity measurements. Four of the galaxies in our sample
exhibit unusual kinematic signatures, such as non-circular motions. Our key
result is that the Cl0024 galaxies are marginally underluminous (0.50 +/- 0.23
mag), given their rotation velocities, as compared to the local Tully-Fisher
relation. In this analysis, we assume no slope evolution, and take into account
systematic differences between local and distant velocity and luminosity
measurements. Our result is particularly striking considering the Cl0024
members have very strong emission lines, and local galaxies with similar Halpha
equivalent widths tend to be overluminous on the Tully-Fisher relation. Cl0024
Tully-Fisher residuals appear to be correlated most strongly with galaxy
rotation velocities, indicating a possible change in the slope of the
Tully-Fisher relation. However, we caution that this result may be strongly
affected by magnitude selection and by the original slope assumed for the
analysis. Cl0024 residuals also depend weakly on color, emission line strength
and extent, and photometric asymmetry. In a comparison of stellar and gas
motions in two Cl0024 members, we find no evidence for counter-rotating stars
and gas, an expected signature of mergers.Comment: 38 pages, 10 figures, accepted for publication in ApJ; version with
full-resolution figures can be downloaded from
http://www.ucolick.org/~anne/recent_pubs.htm
Optical Rotation Curves of Distant Field Galaxies: Sub-L* Systems
Moderate-resolution spectroscopic observations from the Keck 10m telescope
are used to derive internal kinematics for eight faint disk galaxies in the
fields flanking the Hubble Deep Field. The spectroscopic data are combined with
high-resolution F814W WFPC2 images from the Hubble Space Telescope which
provide morphologies and scale-lengths, inclinations and orientations. The
eight galaxies have redshifts 0.15 < z < 0.75, magnitudes 18.6 < I_814 < 22.1
and luminosities -21.8 < M_B < -19.0 (H_0 = 75 and q_0 = 0.05). Terminal disk
velocities are derived from the spatially-resolved velocity profiles by
modeling the effects of seeing, slit width, slit misalignment with galaxy major
axis, and inclination for each source. These data are combined with the sample
of Vogt et al. (1996) to provide a high-redshift Tully-Fisher relation that
spans three magnitudes. This sample was selected primarily by morphology and
magnitude, rather than color or spectral features. We find no obvious change in
the shape or slope of the relation with respect to the local Tully-Fisher
relation. The small offset of < 0.4 B mag with respect to the local relation is
presumably caused by luminosity evolution in the field galaxy population, and
does not correlate with galaxy mass. A comparison of disk surface brightness
between local and high-redshift samples yields a similar offset, ~0.6 mag.
These results provide further evidence for only a modest increase in luminosity
with lookback time.Comment: Text is 9 pages (13 with figures, images in JPG format here for
brevity). Full text and postscript figures are available at
http://www.ucolick.org/~nicole/pubs/pubs.html#vfp2 and
http://tarkus.pha.jhu.edu/deep/publications.html . Accepted for publication
by The Astrophysical Journal Letter
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