4,001 research outputs found
A Physical Model-based Correction for Charge Traps in the Hubble Space Telescope's Wide Field Camera 3 Near-IR Detector and Applications to Transiting Exoplanets and Brown Dwarfs
The Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) near-IR channel
is extensively used in time-resolved observations, especially for transiting
exoplanet spectroscopy and brown dwarf and directly imaged exoplanet rotational
phase mapping. The ramp effect is the dominant source of systematics in the
WFC3 for time-resolved observations, which limits its photometric precision.
Current mitigation strategies are based on empirical fits and require
additional orbits "to help the telescope reach a thermal equilibrium". We show
that the ramp effect profiles can be explained and corrected with high fidelity
using charge trapping theories. We also present a model for this process that
can be used to predict and to correct charge trap systematics. Our model is
based on a very small number of parameters that are intrinsic to the detector.
We find that these parameters are very stable between the different datasets,
and we provide best-fit values. Our model is tested with more than 120 orbits
( visits) of WFC3 observations and is proved to be able to provide near
photon noise limited corrections for observations made with both staring and
scanning modes of transiting exoplanets as well as for starting-mode
observations of brown dwarfs. After our model correction, the light curve of
the first orbit in each visit has the same photometric precision as subsequent
orbits, so data from the first orbit need no longer be discarded. Near IR
arrays with the same physical characteristics (e.g., JWST/NIRCam) may also
benefit from the extension of this model, if similar systematic profiles are
observed.Comment: 16 pages, 13 figures, accepted to Astronomical Journa
An Overview of Variational Integrators
The purpose of this paper is to survey some recent advances in variational
integrators for both finite dimensional mechanical systems as well as continuum
mechanics. These advances include the general development of discrete
mechanics, applications to dissipative systems, collisions, spacetime integration algorithms,
AVI’s (Asynchronous Variational Integrators), as well as reduction for
discrete mechanical systems. To keep the article within the set limits, we will only
treat each topic briefly and will not attempt to develop any particular topic in
any depth. We hope, nonetheless, that this paper serves as a useful guide to the
literature as well as to future directions and open problems in the subject
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Dynamic Behavior of Precast Concrete Beam-Column Sub-Assemblages with High Performance Connections Subjected to Sudden Column Removal Scenario
Unbonded posttensioned precast concrete (UPPC) structure has shown its excellent aseismic performance in laboratory tests and earthquake investigation. However, the progressive collapse behavior of UPPC subjected to column removal scenario is still unclear. To fill this knowledge gap, two 1/2 scaled UPPC beam-column sub-assemblages were tested under a penultimate column removal scenario. The dynamic test results indicated that UPPC sub-assemblages have desirable load redistribution capacity to mitigate progressive collapse. The failure modes of the sub-assemblages observed in dynamic test were quite similar to that in static counterparts
The Midpoint Rule as a Variational--Symplectic Integrator. I. Hamiltonian Systems
Numerical algorithms based on variational and symplectic integrators exhibit
special features that make them promising candidates for application to general
relativity and other constrained Hamiltonian systems. This paper lays part of
the foundation for such applications. The midpoint rule for Hamilton's
equations is examined from the perspectives of variational and symplectic
integrators. It is shown that the midpoint rule preserves the symplectic form,
conserves Noether charges, and exhibits excellent long--term energy behavior.
The energy behavior is explained by the result, shown here, that the midpoint
rule exactly conserves a phase space function that is close to the Hamiltonian.
The presentation includes several examples.Comment: 11 pages, 8 figures, REVTe
Antimicrobial Peptide Exposure and Reduced Susceptibility to Daptomycin: Insights Into a Complex Genetic Puzzle
Adequate antibiotic treatment of bacteri-al infections is one of the most impor-tant problems of our time, not only because of the incessant development of antibiotic resistance, but also because of diminished development of novel anti-bacterial products. Attention has been focused on this problem by the recent United Nations World Health Day in April 2011, which highlighted antibiotic resistance and issued calls for urgent action by expert scientific panels tasked to establish priorities and solutions [1]. Among the proposals is a call for enhanced understanding of resistance, includin
Serotonin Syndrome after Concomitant Treatment with Linezolid and Citalopram
Linezolid, a new synthetic antimicrobial, is an important weapon against methicillin-resistant Staphylococcus aureus (MRSA). Although there are reports of serotonin syndrome developing after concomitant use of linezolid and the selective serotonin reuptake inhibitor paroxitene, this report concerns a patient receiving citalopram who developed thrombocytopenia, serotonin syndrome, and lactic acidosis and died following long-term linezolid therap
A new web-based genomics resource for bioinformatics analysis of Rhipicephalus (Boophilus) microplus: CattleTickBase
No abstract availabl
Individuals, communities, and sound change:An introduction
Do individual differences affect sound change? Traditional approaches to phonetic and phonological change typically downplay differences between the individuals who make up a speech community that is undergoing change, but this has been questioned in recent years in a number of ways from within several distinct traditions of research. The articles in the Glossa Special Collection to which this article is an introduction consider the extent to which individual differences (at a psychological, sociological, physiological, genetic and/or behavioral level) between the members of a speech community might or might not be important in explaining the general properties of sound change. This introduction places these articles in context, considers what we might mean by ‘sound change’ and ‘individual differences’, and aims to build a synthesis of the current research landscape in the area
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