4,642 research outputs found
MC: Subaru and Hubble Space Telescope Weak-Lensing Analysis of the Double Radio Relic Galaxy Cluster PLCK G287.0+32.9
The second most significant detection of the Planck Sunyaev Zel'dovich
survey, PLCK~G287.0+32.9 () boasts two similarly bright radio relics
and a radio halo. One radio relic is located kpc northwest of the
X-ray peak and the other Mpc to the southeast. This large difference
suggests that a complex merging scenario is required. A key missing puzzle for
the merging scenario reconstruction is the underlying dark matter distribution
in high resolution. We present a joint Subaru Telescope and {\it Hubble Space
Telescope} weak-lensing analysis of the cluster. Our analysis shows that the
mass distribution features four significant substructures. Of the
substructures, a primary cluster of mass
$M_{200\text{c}}=1.59^{+0.25}_{-0.22}\times 10^{15} \ h^{-1}_{70} \
\text{M}_{\odot}M_{200\text{c}}=1.16^{+0.15}_{-0.13}\times 10^{14} \ h^{-1}_{70} \
\text{M}_{\odot}\sim 400\sim 2M_{200\text{c}}=1.68^{+0.22}_{-0.20}\times
10^{14} \ h^{-1}_{70} \ \text{M}_{\odot}M_{200\text{c}}=1.87^{+0.24}_{-0.22}\times 10^{14} \ h^{-1}_{70} \
\text{M}_{\odot}$, is northwest of the X-ray peak and beyond the NW radio
relic.Comment: 19 pages, 14 figures; Accepted to Ap
A New Method for Finding Vacua in String Phenomenology
One of the central problems of string-phenomenology is to find stable vacua
in the four dimensional effective theories which result from compactification.
We present an algorithmic method to find all of the vacua of any given
string-phenomenological system in a huge class. In particular, this paper
reviews and then extends hep-th/0606122 to include various non-perturbative
effects. These include gaugino condensation and instantonic contributions to
the superpotential.Comment: 27 pages, 5 .eps figures. V2: Minor corrections, reference adde
Modeling and Correcting the Time-Dependent ACS PSF
The ability to accurately measure the shapes of faint objects in images taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) depends upon detailed knowledge of the Point Spread Function (PSF). We show that thermal fluctuations cause the PSF of the ACS Wide Field Camera (WFC) to vary over time. We describe a modified version of the TinyTim PSF modeling software to create artificial grids of stars across the ACS field of view at a range of telescope focus values. These models closely resemble the stars in real ACS images. Using 10 bright stars in a real image, we have been able to measure HST s apparent focus at the time of the exposure. TinyTim can then be used to model the PSF at any position on the ACS field of view. This obviates the need for images of dense stellar fields at different focus values, or interpolation between the few observed stars. We show that residual differences between our TinyTim models and real data are likely due to the effects of Charge Transfer Efficiency (CTE) degradation. Furthermore, we discuss stochastic noise that is added to the shape of point sources when distortion is removed, and we present MultiDrizzle parameters that are optimal for weak lensing science. Specifically, we find that reducing the MultiDrizzle output pixel scale and choosing a Gaussian kernel significantly stabilizes the resulting PSF after image combination, while still eliminating cosmic rays/bad pixels, and correcting the large geometric distortion in the ACS. We discuss future plans, which include more detailed study of the effects of CTE degradation on object shapes and releasing our TinyTim models to the astronomical community
CANDELS: The Contribution of the Observed Galaxy Population to Cosmic Reionization
We present measurements of the specific ultraviolet luminosity density from a
sample of 483 galaxies at 6<z<8. These galaxies were selected from new deep
near-infrared HST imaging from the CANDELS, HUDF09 and ERS programs. In
contrast to the majority of previous analyses, which assume that the
distribution of galaxy ultraviolet (UV) luminosities follows a Schechter
distribution, and that the distribution continues to luminosities far below our
observable limit, we investigate the contribution to reionization from galaxies
which we can observe, free from these assumptions. We find that the observable
population of galaxies can sustain a fully reionized IGM at z=6, if the average
ionizing photon escape fraction (f_esc) is ~30%. A number of previous studies
have measured UV luminosity densities at these redshifts that vary by 5X, with
many concluding that galaxies could not complete reionization by z=6 unless a
large population of galaxies fainter than the detection limit were invoked, or
extremely high values of f_esc were present. The observed UV luminosity density
from our observed galaxy samples at z=7-8 is not sufficient to maintain a fully
reionized IGM unless f_esc>50%. Combining our observations with constraints on
the emission rate of ionizing photons from Ly-alpha forest observations at z=6,
we can constrain f_esc<34% (2-sigma) if the observed galaxies are the only
contributors to reionization, or <13% (2-sigma) if the luminosity function
extends to M_UV = -13. These escape fractions are sufficient to complete
reionization by z=6. These constraints imply that the volume ionized fraction
of the IGM becomes less than unity at z>7, consistent with a number of
complementary reionization probes. If faint galaxies dominate reionization,
future JWST observations will probe deep enough to see them, providing an
indirect constraint on the ionizing photon escape fraction [abridged].Comment: 16 pages, 7 figures, Submitted to the Astrophysical Journa
Breaking the Curve with CANDELS: A Bayesian Approach to Reveal the Non-Universality of the Dust-Attenuation Law at High Redshift
Dust attenuation affects nearly all observational aspects of galaxy
evolution, yet very little is known about the form of the dust-attenuation law
in the distant Universe. Here, we model the spectral energy distributions
(SEDs) of galaxies at z = 1.5--3 from CANDELS with rest-frame UV to near-IR
imaging under different assumptions about the dust law, and compare the amount
of inferred attenuated light with the observed infrared (IR) luminosities. Some
individual galaxies show strong Bayesian evidence in preference of one dust law
over another, and this preference agrees with their observed location on the
plane of infrared excess (IRX, ) and UV slope
(). We generalize the shape of the dust law with an empirical model,
where
is the dust law of Calzetti et al. (2000), and show that there
exists a correlation between the color excess and tilt with
+ . Galaxies with high
color excess have a shallower, starburst-like law, and those with low color
excess have a steeper, SMC-like law. Surprisingly, the galaxies in our sample
show no correlation between the shape of the dust law and stellar mass,
star-formation rate, or . The change in the dust law with color excess
is consistent with a model where attenuation is caused by by scattering, a
mixed star-dust geometry, and/or trends with stellar population age,
metallicity, and dust grain size. This rest-frame UV-to-near-IR method shows
potential to constrain the dust law at even higher () redshifts.Comment: 20 pages, 18 figures, resubmitted to Ap
Revealing Charge Carrier Mobility and Defect Densities in Metal Halide Perovskites via Space-Charge-Limited Current Measurements
Space-charge-limited current (SCLC) measurements have been widely used to study the charge carrier mobility and trap density in semiconductors. However, their applicability to metal halide perovskites is not straightforward, due to the mixed ionic and electronic nature of these materials. Here, we discuss the pitfalls of SCLC for perovskite semiconductors, and especially the effect of mobile ions. We show, using drift-diffusion (DD) simulations, that the ions strongly affect the measurement and that the usual analysis and interpretation of SCLC need to be refined. We highlight that the trap density and mobility cannot be directly quantified using classical methods. We discuss the advantages of pulsed SCLC for obtaining reliable data with minimal influence of the ionic motion. We then show that fitting the pulsed SCLC with DD modeling is a reliable method for extracting mobility, trap, and ion densities simultaneously. As a proof of concept, we obtain a trap density of 1.3 × 1013 cm-3, an ion density of 1.1 × 1013 cm-3, and a mobility of 13 cm2 V-1 s-1 for a MAPbBr3 single crystal
Hybrid organic-inorganic nanoparticles: controlled incorporation of gold nanoparticles into virus-like particles and application in surface-enhanced Raman spectroscopy.
A capsid is the protein coat surrounding a virus' genome that ensures its protection and transport. The capsid of murine polyomavirus (muPy) consists of one major (VP1) and two minor (VP2/3) proteins, from which just VP1 is sufficient to form the capsid when expressed recombinantly (1). From a material engineering point of view, viral capsids are of interest because they present a paradigm for complex self-assembly on the nanometer scale. Understanding and controlling these assembly dynamics will allow the construction of nanoscale structures using a self-assembly process. The first step in this direction was the discovery that capsids of several viruses can be reversibly disassembled into their building blocks and reassembled using the same building blocks by simply changing the buffer conditions (2, 3). Such capsids already find applications as targeted in vivo delivery vectors for genes, proteins or small molecular drugs (4, 5), as optical probes for biomedical imaging and sensing purposes with unprecedented resolution and sensitivity and can potentially be used as templates for nanoelectronics (6, 7)
New compound sets identified from high throughput phenotypic screening against three kinetoplastid parasites:an open resource
Using whole-cell phenotypic assays, the GlaxoSmithKline high-throughput screening (HTS) diversity set of 1.8 million compounds was screened against the three kinetoplastids most relevant to human disease, i.e. Leishmania donovani, Trypanosoma cruzi and Trypanosoma brucei. Secondary confirmatory and orthogonal intracellular anti-parasiticidal assays were conducted, and the potential for non-specific cytotoxicity determined. Hit compounds were chemically clustered and triaged for desirable physicochemical properties. The hypothetical biological target space covered by these diversity sets was investigated through bioinformatics methodologies. Consequently, three anti-kinetoplastid chemical boxes of ~200 compounds each were assembled. Functional analyses of these compounds suggest a wide array of potential modes of action against kinetoplastid kinases, proteases and cytochromes as well as potential host–pathogen targets. This is the first published parallel high throughput screening of a pharma compound collection against kinetoplastids. The compound sets are provided as an open resource for future lead discovery programs, and to address important research questions.The support and funding of Tres Cantos Open Lab Foundation is gratefully acknowledgedPeer reviewe
Techniques for visualization of carbohydrate molecules
Standard molecular visualizations, such as the classic ball-and-stick model, are not suitable for large, complex molecules because the overall molecular structure is obscured by the atomic detail. For proteins, the more abstract ribbon and cartoon representations are instead used to reveal large scale molecular conformation and connectivity. However, there is currently no accepted convention for simplifying oligo- and polysaccharide structures.
We introduce two novel visualization algorithms for carbohydrates, incorporated into a visualization package, CarboHydra. Both algorithms highlight the sugar rings and backbone conformation of the carbohydrate chain, ignoring ring substituents. The first algorithm, termed PaperChain, emphasizes the type and conformation of the carbohydrate rings. The second, Twister, emphasizes the relative orientation of the rings. We further include two rendering enhancements to augment these visualizations: silhouettes edges and a translucent overlay of the ball-and-stick atomic representation.
To demonstrate their utility, the algorithms and visualization enhancements are here applied to a variety of carbohydrate molecules. User evaluations indicate that they present a more useful view of carbohydrate structure than the standard ball-and-stick representation. The algorithms were found to be complementary, with PaperChain particularly effective for smaller carbohydrates and Twister useful at larger scales for highlighting the backbone twist of polysaccharides
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