An achromatic shearing phase sensor is proposed as a phasing technique for the alignment of segmented telescopes. The sensor is based upon a shearing interferometer using two-wavelength ...interferometry methods. The two beams are created with a diffraction grating. The diffracted orders are re-imaged such that the pupil plane is focused onto a CCD array with a shear displacing the two orders. The amount of shear is equal to the size of the re-imaged segments. The sensor was measured to have a capture range of at least 5 μm, and an accuracy of 0.3 μm or better. The repeatability was 0.1 vm. The sensor is very sensitive to field dependent aberrations in its optical design but the resulting errors can be calibrated. The sensor is an improvement over similar technologies because it can measure and compensate for segment aberrations with tilt and piston adjustments. The sensor is compatible with many mature interferometry techniques and can be used with extended and broadband sources.
The James Webb Space Telescope (JWST) is a large, infrared space telescope that has recently started its science program which will enable breakthroughs in astrophysics and planetary science. ...Notably, JWST will provide the very first observations of the earliest luminous objects in the Universe and start a new era of exoplanet atmospheric characterization. This transformative science is enabled by a 6.6 m telescope that is passively cooled with a 5-layer sunshield. The primary mirror is comprised of 18 controllable, low areal density hexagonal segments, that were aligned and phased relative to each other in orbit using innovative image-based wavefront sensing and control algorithms. This revolutionary telescope took more than two decades to develop with a widely distributed team across engineering disciplines. We present an overview of the telescope requirements, architecture, development, superb on-orbit performance, and lessons learned. JWST successfully demonstrates a segmented aperture space telescope and establishes a path to building even larger space telescopes.
An achromatic shearing phase sensor is proposed as a phasing technique for the alignment of segmented telescopes. The sensor is based upon a shearing interferometer using two-wavelength ...interferometry methods. The two beams are created with a diffraction grating. The diffracted orders are re-imaged such that the pupil plane is focused onto a CCD array with a shear displacing the two orders. The amount of shear is equal to the size of the re-imaged segments. The sensor was measured to have a capture range of at least 5 μm, and an accuracy of 0.3 μm or better. The repeatability was 0.1 μm. The sensor is very sensitive to field dependent aberrations in its optical design but the resulting errors can be calibrated. The sensor is an improvement over similar technologies because it can measure and compensate for segment aberrations with tilt and piston adjustments. The sensor is compatible with many mature interferometry techniques and can be used with extended and broadband sources.
In 2014, the Optical Ground Support Equipment was integrated into the large cryo vacuum chamber at Johnson Space Center (JSC) and an initial Chamber Commissioning Test was completed. This insured ...that the support equipment was ready for the three Pathfinder telescope cryo tests. The Pathfinder telescope which consists of two primary mirror segment assemblies and the secondary mirror was delivered to JSC in February 2015 in support of this critical risk reduction test program prior to the flight hardware. This paper will detail the Chamber Commissioning and first optical test of the JWST Pathfinder telescope.
Normal differentiation and induced reprogramming require the activation of target cell programs and silencing of donor cell programs. In reprogramming, the same factors are often used to reprogram ...many different donor cell types. As most developmental repressors, such as RE1-silencing transcription factor (REST) and Groucho (also known as TLE), are considered lineage-specific repressors, it remains unclear how identical combinations of transcription factors can silence so many different donor programs. Distinct lineage repressors would have to be induced in different donor cell types. Here, by studying the reprogramming of mouse fibroblasts to neurons, we found that the pan neuron-specific transcription factor Myt1-like (Myt1l) exerts its pro-neuronal function by direct repression of many different somatic lineage programs except the neuronal program. The repressive function of Myt1l is mediated via recruitment of a complex containing Sin3b by binding to a previously uncharacterized N-terminal domain. In agreement with its repressive function, the genomic binding sites of Myt1l are similar in neurons and fibroblasts and are preferentially in an open chromatin configuration. The Notch signalling pathway is repressed by Myt1l through silencing of several members, including Hes1. Acute knockdown of Myt1l in the developing mouse brain mimicked a Notch gain-of-function phenotype, suggesting that Myt1l allows newborn neurons to escape Notch activation during normal development. Depletion of Myt1l in primary postmitotic neurons de-repressed non-neuronal programs and impaired neuronal gene expression and function, indicating that many somatic lineage programs are actively and persistently repressed by Myt1l to maintain neuronal identity. It is now tempting to speculate that similar 'many-but-one' lineage repressors exist for other cell fates; such repressors, in combination with lineage-specific activators, would be prime candidates for use in reprogramming additional cell types.
Reported COVID-19 cases and associated mortality remain low in many sub-Saharan countries relative to global averages, but true impact is difficult to estimate given limitations around surveillance ...and mortality registration. In Lusaka, Zambia, burial registration and SARS-CoV-2 prevalence data during 2020 allow estimation of excess mortality and transmission. Relative to pre-pandemic patterns, we estimate age-dependent mortality increases, totalling 3212 excess deaths (95% CrI: 2104-4591), representing an 18.5% (95% CrI: 13.0-25.2%) increase relative to pre-pandemic levels. Using a dynamical model-based inferential framework, we find that these mortality patterns and SARS-CoV-2 prevalence data are in agreement with established COVID-19 severity estimates. Our results support hypotheses that COVID-19 impact in Lusaka during 2020 was consistent with COVID-19 epidemics elsewhere, without requiring exceptional explanations for low reported figures. For more equitable decision-making during future pandemics, barriers to ascertaining attributable mortality in low-income settings must be addressed and factored into discourse around reported impact differences.
The cyanobacterial metabolite apratoxin A (1) demonstrates potent cytotoxicity against tumor cell lines by a hitherto unknown mechanism. We have used functional genomics to elucidate the molecular ...basis for this activity. Gene expression profiling and DNA content analysis showed that apratoxin A induces G1-phase cell cycle arrest and apoptosis. Cell-based functional assays with a genome-wide collection of expression cDNAs showed that ectopic induction of fibroblast growth factor receptor (FGFR) signaling attenuates the apoptotic activity of apratoxin A. This natural product inhibited phosphorylation and activation of STAT3, a downstream effector of FGFR signaling. It also caused defects in FGF-dependent processes during zebrafish development, with concomitant reductions in expression levels of the FGF target gene mkp3. We conclude that apratoxin A mediates its antiproliferative activity through the induction of G1 cell cycle arrest and an apoptotic cascade, which is at least partially initiated through antagonism of FGF signaling via STAT3.
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