The GRavitational lEnsing Accuracy Testing 3 (GREAT3) challenge is the third in a series of image analysis challenges, with a goal of testing and facilitating the development of methods for analyzing ...astronomical images that will be used to measure weak gravitational lensing. This measurement requires extremely precise estimation of very small galaxy shape distortions, in the presence of far larger intrinsic galaxy shapes and distortions due to the blurring kernel caused by the atmosphere, telescope optics, and instrumental effects. Uie GREAT3 challenge is posed to the astronomy, machine learning, and statistics communities, and includes tests of three specific effects that are of immediate relevance to upcoming weak lensing surveys, two of which have never been tested in a community challenge before. These effects include many novel aspects including realistically complex galaxy models based on high-resolution imaging from space; a spatially varying, physically motivated blurring kernel; and a combination of multiple different exposures. To facilitate entry by people new to the field, and for use as a diagnostic tool, the simulation software for the challenge is publicly available, though the exact parameters used for the challenge are blinded. Sample scripts to analyze the challenge data using existing methods will also be provided. See http://great3challenge.info and http://great3.projects.phys.ucl.ac.uk/leaderboard/ for more information.
The LSST DESC DC2 Simulated Sky Survey Abolfathi, Bela; Alonso, David; Armstrong, Robert ...
The Astrophysical journal. Supplement series,
03/2021, Letnik:
253, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
We describe the simulated sky survey underlying the second data challenge (DC2) carried out in preparation for analysis of the Vera C. Rubin Observatory Legacy Survey of Space and Time ...(LSST) by the LSST Dark Energy Science Collaboration (LSST DESC). Significant connections across multiple science domains will be a hallmark of LSST; the DC2 program represents a unique modeling effort that stresses this interconnectivity in a way that has not been attempted before. This effort encompasses a full end-to-end approach: starting from a large
N
-body simulation, through setting up LSST-like observations including realistic cadences, through image simulations, and finally processing with Rubin’s LSST Science Pipelines. This last step ensures that we generate data products resembling those to be delivered by the Rubin Observatory as closely as is currently possible. The simulated DC2 sky survey covers six optical bands in a wide-fast-deep area of approximately 300 deg
2
, as well as a deep drilling field of approximately 1 deg
2
. We simulate 5 yr of the planned 10 yr survey. The DC2 sky survey has multiple purposes. First, the LSST DESC working groups can use the data set to develop a range of DESC analysis pipelines to prepare for the advent of actual data. Second, it serves as a realistic test bed for the image processing software under development for LSST by the Rubin Observatory. In particular, simulated data provide a controlled way to investigate certain image-level systematic effects. Finally, the DC2 sky survey enables the exploration of new scientific ideas in both static and time domain cosmology.
Highly crystalline oriented Halocynthia roretzi cellulose Iβ films were investigated by IR-spectroscopy between −180 and +10 °C. Changes in the IR-spectra induced by temperature were compared to ...published changes induced by mechanical stretching. This made it possible to conclude that frequency shifts in the O–H stretching region of the IR-spectra due to temperature were not predominantly an indirect effect of thermal expansion leading to greater O–O distances, but were due directly to the effect of temperature on the O–H···O hydrogen bonds. Temperature induced frequency shifts of C–H stretching bands were consistent with the presence of weak inter-sheet C–H···O bonds. Furthermore, no phase transition in cellulose Iβ was found between −180 and +10 °C.
We perform a cosmological parameter analysis of the 75 deg super(2) CTIO lensing survey in conjunction with cosmic microwave background (CMB) and Type Ia supernovae data. For CDM cosmologies, we find ...+ 0.15 that the amplitude of the power spectrum at low redshift is given by s sub(8) = 0.81 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(1) sub(1) super(5) sub(0) (95% confidence level), where the error bound includes both statistical and systematic errors. The total of all systematic errors is smaller than the statistical errors, but they do make up a significant fraction of the error budget. We find that weak lensing improves the constraints on dark energy as well. The (constant) dark energy equation of state parameter, w, is measured to be -0.89 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(1) sub(2) super(6) sub(1) (95% c.l.). Marginalizing over a constant w slightly changes the estimate of s sub(8) to 0.79 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(1) sub(1) super(7) sub(4) (95% c.l.). We also investigate variable w cosmologies but find that the constraints weaken considerably; next-generation surveys are needed to obtain meaningful constraints on the possible time evolution of dark energy.
Cellulose stacks up Jarvis, Mike
Nature (London),
12/2003, Letnik:
426, Številka:
6967
Journal Article
Recenzirano
The long chains of cellulose pack laterally into microfibrils of two crystalline forms. Comparison of the structures of these two forms reveals unexpected patterns of bonding that tie the chains ...together.
Summary
The irregular xylem 2 (irx2) mutant of Arabidopsis thaliana exhibits a cellulose deficiency in the secondary cell wall, which is brought about by a point mutation in the KORRIGAN (KOR) β,1‐4 ...endoglucanase (β,1‐4 EGase) gene. Measurement of the total crystalline cellulose in the inflorescence stem indicates that the irx2 mutant contains approximately 30% of the level present in the wild type (WT). Fourier–Transform Infra Red (FTIR) analysis, however, indicates that there is no decrease in cellulose in primary cell walls of the cortical and epidermal cells of the stem. KOR expression is correlated with cellulose synthesis and is highly expressed in cells synthesising a secondary cell wall. Co‐precipitation experiments, using either an epitope‐tagged form of KOR or IRX3 (AtCesA7), suggest that KOR is not an integral part of the cellulose synthase complex. These data are supported by immunolocalisation of KOR that suggests that KOR does not localise to sites of secondary cell wall deposition in the developing xylem. The defect in irx2 plant is consistent with a role for KOR in the later stages of secondary cell wall formation, suggesting a role in processing of the growing microfibrils or release of the cellulose synthase complex.
In grasses, leaf cells divide and expand within the sheaths of older leaves, where the micro-environment differs from the open atmosphere. By the time epidermal cells are displaced into the ...atmosphere, they must have a functional cuticle to minimize uncontrolled water loss. In the present study, gas chromatography and scanning electron microscopy were used to follow cuticular wax deposition along the growing leaf three of barley (Hordeum vulgare L.). 1-Hexacosanol (C26 alcohol) comprised more than 75% of extractable cuticular wax and was used as a marker for wax deposition. There was no detectable wax along the first 20 mm from the point of leaf insertion. Deposition started within the distal portion of the elongation zone (23—45 mm) and continued beyond the point of leaf emergence from the sheath of leaf two. The region where wax deposition commenced shifted towards more proximal (basal) positions when the point of leaf emergence was lowered by stripping back part of the sheath. When relative humidity in the shoot environment was elevated from 70% (standard growth conditions) to 92—96% for up to 4 days prior to analysis, wax deposition did not change significantly. The results show that cuticular waxes are deposited along the growing grass leaf independent of cell age or developmental stage. Instead, the reference point for wax deposition appears to be the point of emergence of cells into the atmosphere. The possibility of changes in relative humidity between enclosed and emerged leaf regions triggering wax deposition is discussed.
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