141 research outputs found
The Carnegie Supernova Project: The Low-Redshift Survey
Supernovae are essential to understanding the chemical evolution of the
Universe. Type Ia supernovae also provide the most powerful observational tool
currently available for studying the expansion history of the Universe and the
nature of dark energy. Our basic knowledge of supernovae comes from the study
of their photometric and spectroscopic properties. However, the presently
available data sets of optical and near-infrared light curves of supernovae are
rather small and/or heterogeneous, and employ photometric systems that are
poorly characterized. Similarly, there are relatively few supernovae whose
spectral evolution has been well sampled, both in wavelength and phase, with
precise spectrophotometric observations. The low-redshift portion of the
Carnegie Supernova Project (CSP) seeks to remedy this situation by providing
photometry and spectrophotometry of a large sample of supernovae taken on
telescope/filter/detector systems that are well understood and well
characterized. During a five-year program which began in September 2004, we
expect to obtain high-precision u'g'r'i'BVYJHKs light curves and optical
spectrophotometry for about 250 supernovae of all types. In this paper we
provide a detailed description of the CSP survey observing and data reduction
methodology. In addition, we present preliminary photometry and spectra
obtained for a few representative supernovae during the first observing
campaign.Comment: 45 pages, 13 figures, 3 tables, accepted by PAS
The Carnegie Supernova Project: Analysis of the First Sample of Low-Redshift Type-Ia Supernovae
We present the analysis of the first set of low-redshift Type Ia supernovae
(SNe Ia) by the Carnegie Supernova Project. Well-sampled, high-precision
optical (ugriBV) and near-infrared (NIR; YJHKs) light curves obtained in a
well-understood photometric system are used to provide light-curve parameters,
and ugriBVYJH template light curves. The intrinsic colors at maximum light are
calibrated to compute optical--NIR color excesses for the full sample, thus
allowing the properties of the reddening law in the host galaxies to be
studied. A low value of Rv~1.7, is derived when using the entire sample of SNe.
However, when the two highly reddened SNe in the sample are excluded, a value
Galactic standard of Rv~3.2 is obtained. The colors of these two events are
well matched by a reddening model due to circumstellar dust. The peak
luminosities are calibrated using a two-parameter linear fit to the decline
rates and the colors, or alternatively, the color excesses. In both cases,
dispersions in absolute magnitude of 0.12--0.16 mag are obtained, depending on
the filter-color combination. In contrast to the results obtained from color
excesses, these fits give Rv~1--2, even when the two highly reddened SNe are
excluded. This discrepancy suggests that, beyond the "normal" interstellar
reddening produced in the host galaxies, there is an intrinsic dispersion in
the colors of SNe Ia which is correlated with luminosity but independent of the
decline rate. Finally, a Hubble diagram is produced by combining the results of
the fits for each filter. The resulting scatter of 0.12 mag appears to be
limited by peculiar velocities as evidenced by the strong correlation between
the distance-modulus residuals among the different filters. The implication is
that the actual precision of SN Ia distances is 3--4%.Comment: 76 pages, 20 figures, accepted for publication in A
The Carnegie Supernova Project: First Photometry Data Release of Low-Redshift Type Ia Supernovae
The Carnegie Supernova Project (CSP) is a five-year survey being carried out
at the Las Campanas Observatory to obtain high-quality light curves of ~100
low-redshift Type Ia supernovae in a well-defined photometric system. Here we
present the first release of photometric data that contains the optical light
curves of 35 Type Ia supernovae, and near-infrared light curves for a subset of
25 events. The data comprise 5559 optical (ugriBV) and 1043 near-infrared
(YJHKs) data points in the natural system of the Swope telescope. Twenty-eight
supernovae have pre-maximum data, and for 15 of these, the observations begin
at least 5 days before B maximum. This is one of the most accurate datasets of
low-redshift Type Ia supernovae published to date. When completed, the CSP
dataset will constitute a fundamental reference for precise determinations of
cosmological parameters, and serve as a rich resource for comparison with
models of Type Ia supernovae.Comment: 93 pages, 8 figures, accepted for publication in A
The Peculiar SN 2005hk: Do Some Type Ia Supernovae Explode as Deflagrations?
We present extensive u'g'r'i'BVRIYJHKs photometry and optical spectroscopy of
SN 2005hk. These data reveal that SN 2005hk was nearly identical in its
observed properties to SN 2002cx, which has been called ``the most peculiar
known type Ia supernova.'' Both supernovae exhibited high ionization SN
1991T-like pre-maximum spectra, yet low peak luminosities like SN 1991bg. The
spectra reveal that SN 2005hk, like SN 2002cx, exhibited expansion velocities
that were roughly half those of typical type Ia supernovae. The R and I light
curves of both supernovae were also peculiar in not displaying the secondary
maximum observed for normal type Ia supernovae. Our YJH photometry of SN 2005hk
reveals the same peculiarity in the near-infrared. By combining our optical and
near-infrared photometry of SN 2005hk with published ultraviolet light curves
obtained with the Swift satellite, we are able to construct a bolometric light
curve from ~10 days before to ~60 days after B maximum. The shape and unusually
low peak luminosity of this light curve, plus the low expansion velocities and
absence of a secondary maximum at red and near-infrared wavelengths, are all in
reasonable agreement with model calculations of a 3D deflagration which
produces ~0.25 M_sun of 56Ni.Comment: Accepted by PASP, to appear in April 2007 issue, 63 pages, 16
figures, 11 table
Additional Saturday rehabilitation improves functional independence and quality of life and reduces length of stay: a randomised controlled trial
Background Many inpatients receive little or no rehabilitation on weekends. Our aim was to determine what effect providing additional Saturday rehabilitation during inpatient rehabilitation had on functional independence, quality of life and length of stay compared to 5 days per week of rehabilitation.MethodsThis was a multicenter, single-blind (assessors) randomized controlled trial with concealed allocation and 12-month follow-up conducted in two publically funded metropolitan inpatient rehabilitation facilities in Melbourne, Australia. Patients were eligible if they were adults (aged ≥18 years) admitted for rehabilitation for any orthopedic, neurological or other disabling conditions excluding those admitted for slow stream rehabilitation/geriatric evaluation and management. Participants were randomly allocated to usual care Monday to Friday rehabilitation (control) or to Monday to Saturday rehabilitation (intervention). The additional Saturday rehabilitation comprised physiotherapy and occupational therapy. The primary outcomes were functional independence (functional independence measure (FIM); measured on an 18 to 126 point scale), health-related quality of life (EQ-5D utility index; measured on a 0 to 1 scale, and EQ-5D visual analog scale; measured on a 0 to 100 scale), and patient length of stay. Outcome measures were assessed on admission, discharge (primary endpoint), and at 6 and 12 months post discharge.ResultsWe randomly assigned 996 adults (mean (SD) age 74 (13) years) to Monday to Saturday rehabilitation (n = 496) or usual care Monday to Friday rehabilitation (n = 500). Relative to admission scores, intervention group participants had higher functional independence (mean difference (MD) 2.3, 95% confidence interval (CI) 0.5 to 4.1, P = 0.01) and health-related quality of life (MD 0.04, 95% CI 0.01 to 0.07, P = 0.009) on discharge and may have had a shorter length of stay by 2 days (95% CI 0 to 4, P = 0.1) when compared to control group participants. Intervention group participants were 17% more likely to have achieved a clinically significant change in functional independence of 22 FIM points or more (risk ratio (RR) 1.17, 95% CI 1.03 to 1.34) and 18% more likely to have achieved a clinically significant change in health-related quality of life (RR 1.18, 95% CI 1.04 to 1.34) on discharge compared to the control group. There was some maintenance of effect for functional independence and health-related quality of life at 6-month follow-up but not at 12-month follow-up. There was no difference in the number of adverse events between the groups (incidence rate ratio = 0.81, 95% CI 0.61 to 1.08).ConclusionsProviding an additional day of rehabilitation improved functional independence and health-related quality of life at discharge and may have reduced length of stay for patients receiving inpatient rehabilitation. </p
First-principles flocculation as the key to low energy algal biofuels processing.
This document summarizes a three year Laboratory Directed Research and Development (LDRD) program effort to improve our understanding of algal flocculation with a key to overcoming harvesting as a techno-economic barrier to algal biofuels. Flocculation is limited by the concentrations of deprotonated functional groups on the algal cell surface. Favorable charged groups on the surfaces of precipitates that form in solution and the interaction of both with ions in the water can favor flocculation. Measurements of algae cell-surface functional groups are reported and related to the quantity of flocculant required. Deprotonation of surface groups and complexation of surface groups with ions from the growth media are predicted in the context of PHREEQC. The understanding of surface chemistry is linked to boundaries of effective flocculation. We show that the phase-space of effective flocculation can be expanded by more frequent alga-alga or floc-floc collisions. The collision frequency is dependent on the floc structure, described in the fractal sense. The fractal floc structure is shown to depend on the rate of shear mixing. We present both experimental measurements of the floc structure variation and simulations using LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). Both show a densification of the flocs with increasing shear. The LAMMPS results show a combined change in the fractal dimension and a change in the coordination number leading to stronger flocs
Dendritic Spikes Amplify the Synaptic Signal to Enhance Detection of Motion in a Simulation of the Direction-Selective Ganglion Cell
The On-Off direction-selective ganglion cell (DSGC) in mammalian retinas responds most strongly to a stimulus moving in a specific direction. The DSGC initiates spikes in its dendritic tree, which are thought to propagate to the soma with high probability. Both dendritic and somatic spikes in the DSGC display strong directional tuning, whereas somatic PSPs (postsynaptic potentials) are only weakly directional, indicating that spike generation includes marked enhancement of the directional signal. We used a realistic computational model based on anatomical and physiological measurements to determine the source of the enhancement. Our results indicate that the DSGC dendritic tree is partitioned into separate electrotonic regions, each summing its local excitatory and inhibitory synaptic inputs to initiate spikes. Within each local region the local spike threshold nonlinearly amplifies the preferred response over the null response on the basis of PSP amplitude. Using inhibitory conductances previously measured in DSGCs, the simulation results showed that inhibition is only sufficient to prevent spike initiation and cannot affect spike propagation. Therefore, inhibition will only act locally within the dendritic arbor. We identified the role of three mechanisms that generate directional selectivity (DS) in the local dendritic regions. First, a mechanism for DS intrinsic to the dendritic structure of the DSGC enhances DS on the null side of the cell's dendritic tree and weakens it on the preferred side. Second, spatially offset postsynaptic inhibition generates robust DS in the isolated dendritic tips but weak DS near the soma. Third, presynaptic DS is apparently necessary because it is more robust across the dendritic tree. The pre- and postsynaptic mechanisms together can overcome the local intrinsic DS. These local dendritic mechanisms can perform independent nonlinear computations to make a decision, and there could be analogous mechanisms within cortical circuitry
Recommended from our members
Multiscale models of nuclear waste reprocessing : from the mesoscale to the plant-scale.
Custom Integrated Circuits
Contains table of contents for Part III, table of contents for Section 1 and reports on eleven research projects.IBM CorporationMIT School of EngineeringNational Science Foundation Grant MIP 94-23221Defense Advanced Research Projects Agency/U.S. Army Intelligence Center Contract DABT63-94-C-0053Mitsubishi CorporationNational Science Foundation Young Investigator Award Fellowship MIP 92-58376Joint Industry Program on Offshore Structure AnalysisAnalog DevicesDefense Advanced Research Projects AgencyCadence Design SystemsMAFET ConsortiumConsortium for Superconducting ElectronicsNational Defense Science and Engineering Graduate FellowshipDigital Equipment CorporationMIT Lincoln LaboratorySemiconductor Research CorporationMultiuniversity Research IntiativeNational Science Foundatio
- …