534 research outputs found
Experimental comparison of model-free and model-based dark hole algorithms for future space telescopes
Coronagraphic instruments provide a great chance of enabling high contrast
spectroscopy for the pursuit of finding a habitable world. Future space
telescope coronagraph instruments require high performing focal plane masks in
combination with precise wavefront sensing and control techniques to achieve
dark holes for planet detection. Several wavefront control algorithms have been
developed in recent years that might vary in performance depending on the
coronagraph they are paired with. This study compares 3 model-free and
model-based algorithms when coupled with either a Vector (VVC) or a Scalar
(SVC) Vortex Coronagraph mask in the same laboratory conditions: Pairwise
Probing with Electric Field Conjugation, the Self-Coherent Camera with Electric
Field Conjugation, and Implicit Electric Field Conjugation. We present
experimental results from the In-Air Coronagraph Testbed (IACT) at JPL in
narrowband and broadband light, comparing the pros and cons of each of these
wavefront sensing and control algorithms with respect to their potential for
future space telescopes.Comment: Conference Proceedings of SPIE: Techniques and Instrumentation for
Detection of Exoplanets XI, vol. 12680 (2023
A crop yield change emulator for use in GCAM and similar models: Persephone v1.0
Future changes in Earth system state will impact agricultural yields and,
through these changed yields, can have profound impacts on the global
economy. Global gridded crop models estimate the influence of these Earth
system changes on future crop yields but are often too computationally
intensive to dynamically couple into global multi-sector economic models,
such as the Global Change Assessment Model (GCAM) and other similar-in-scale models. Yet, generalizing a faster
site-specific crop model's results to be used globally will introduce
inaccuracies, and the question of which model to use is unclear given the
wide variation in yield response across crop models. To examine the feedback
loop among socioeconomics, Earth system changes, and crop yield changes,
rapidly generated yield responses with some quantification of crop response
uncertainty are desirable. The Persephone v1.0 response functions presented
in this work are based on the Agricultural Model Intercomparison and
Improvement Project (AgMIP) Coordinated Climate-Crop Modeling Project (C3MP)
sensitivity test data set and are focused on providing GCAM and similar models with a tractable number of rapid
to evaluate dynamic yield response functions corresponding to a range of the
yield response sensitivities seen in the C3MP data set. With the Persephone
response functions, a new variety of agricultural impact experiments will be
open to GCAM and other economic models: for example, examining the economic
impacts of a multi-year drought in a key agricultural region and how economic
changes in response to the drought can, in turn, impact the drought.</p
Dilatation in the femoral vascular bed does not cause retrograde relaxation of the iliac artery in the anaesthetized pig
Aim: We tested the hypothesis that dilatation of a feeding artery may be elicited by transmission of a signal through the tissue of the arterial wall from a vasodilated peripheral vascular bed. Methods: In eight pentobarbital anaesthetized pigs, acetylcholine (ACh, an endothelium-dependent vasodilator) was injected intra-arterially above (upstream) and below (downstream) a test segment of the left iliac artery, the diameter of which was measured continuously by sonomicrometry. Results: Under control conditions, ACh injections upstream and downstream of the test segment caused dilatation. Downstream injection dilated the peripheral arterioles, resulting in increased blood flow and proximal dilatation. This is a shear stress, nitric oxide (NO)-dependent response. The experiment was then repeated after applying a stenosis to prevent the increased flow caused by downstream injection of ACh; the stenosis was placed either above the site of diameter measurement to allow retrograde conduction, or below that site to prevent distally injected ACh reaching the measurement site. Under these conditions, downstream injection of ACh had a minimal effect on the shear stress of the test segment with no increase in test segment diameter. This was not due to endothelial damage or dysfunction as injection of ACh upstream still caused a large increase in test segment diameter. Conclusions: Our results indicate that dilatation of the feeding artery of a vasodilated bed is caused by increased shear stress within the feeding artery and not via a signal transmitted through the arterial wall from below
Broadband Vector Vortex Coronagraph Testing at NASA's High Contrast Imaging Testbed Facility
The unparalleled theoretical performance of an ideal vector vortex
coronagraph makes it one of the most promising technologies for directly
imaging exoplanets with a future, off-axis space telescope. However, the image
contrast required for observing the light reflected from Earth-sized planets
() has yet to be demonstrated in a laboratory setting. With
recent advances in the manufacturing of liquid crystal vector vortex waveplates
as well as system-level performance improvements on our testbeds, we have
achieved raw contrast of 1.6 and 5.9 in 10% and
20% optical bandwidths, respectively, averaged over 3-10 separations
on one side of the pseudo-star. The former represents a factor of 10
improvement over the previously reported performance. We show experimental
comparisons of the contrast achieved as a function of spectral bandwidth. We
provide estimates of the limiting error terms and discuss the improvements
needed to close the gap in contrast performance required for future exoplanet
imaging space telescopes.Comment: To appear in the Proceedings of the SPI
Review of high-contrast imaging systems for current and future ground- and space-based telescopes I. Coronagraph design methods and optical performance metrics
The Optimal Optical Coronagraph (OOC) Workshop at the Lorentz Center in
September 2017 in Leiden, the Netherlands gathered a diverse group of 25
researchers working on exoplanet instrumentation to stimulate the emergence and
sharing of new ideas. In this first installment of a series of three papers
summarizing the outcomes of the OOC workshop, we present an overview of design
methods and optical performance metrics developed for coronagraph instruments.
The design and optimization of coronagraphs for future telescopes has
progressed rapidly over the past several years in the context of space mission
studies for Exo-C, WFIRST, HabEx, and LUVOIR as well as ground-based
telescopes. Design tools have been developed at several institutions to
optimize a variety of coronagraph mask types. We aim to give a broad overview
of the approaches used, examples of their utility, and provide the optimization
tools to the community. Though it is clear that the basic function of
coronagraphs is to suppress starlight while maintaining light from off-axis
sources, our community lacks a general set of standard performance metrics that
apply to both detecting and characterizing exoplanets. The attendees of the OOC
workshop agreed that it would benefit our community to clearly define
quantities for comparing the performance of coronagraph designs and systems.
Therefore, we also present a set of metrics that may be applied to theoretical
designs, testbeds, and deployed instruments. We show how these quantities may
be used to easily relate the basic properties of the optical instrument to the
detection significance of the given point source in the presence of realistic
noise.Comment: To appear in Proceedings of the SPIE, vol. 1069
A Framework for the Cross-Sectoral Integration of Multi-Model Impact Projections: Land Use Decisions Under Climate Impacts Uncertainties
Climate change and its impacts already pose considerable challenges for societies that will further increase with global warming (IPCC, 2014a, b). Uncertainties of the climatic response to greenhouse gas emissions include the potential passing of large-scale tipping points (e.g. Lenton et al., 2008; Levermann et al., 2012; Schellnhuber, 2010) and changes in extreme meteorological events (Field et al., 2012) with complex impacts on societies (Hallegatte et al., 2013). Thus climate change mitigation is considered a necessary societal response for avoiding uncontrollable impacts (Conference of the Parties, 2010). On the other hand, large-scale climate change mitigation itself implies fundamental changes in, for example, the global energy system. The associated challenges come on top of others that derive from equally important ethical imperatives like the fulfilment of increasing food demand that may draw on the same resources. For example, ensuring food security for a growing population may require an expansion of cropland, thereby reducing natural carbon sinks or the area available for bio-energy production. So far, available studies addressing this problem have relied on individual impact models, ignoring uncertainty in crop model and biome model projections. Here, we propose a probabilistic decision framework that allows for an evaluation of agricultural management and mitigation options in a multi-impactmodel setting. Based on simulations generated within the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP), we outline how cross-sectorally consistent multi-model impact simulations could be used to generate the information required for robust decision making. Using an illustrative future land use pattern, we discuss the trade-off between potential gains in crop production and associated losses in natural carbon sinks in the new multiple crop- and biome-model setting. In addition, crop and water model simulations are combined to explore irrigation increases as one possible measure of agricultural intensification that could limit the expansion of cropland required in response to climate change and growing food demand. This example shows that current impact model uncertainties pose an important challenge to long-term mitigation planning and must not be ignored in long-term strategic decision makin
Construction and Cost Analysis of BladeBridges Made from Decommissioned FRP Wind Turbine Blades
This paper describes repurposing projects using decommissioned wind turbine blades in bridges conducted under a multinational research project entitled “Re-Wind”. Repurposing is defined by the Re-Wind Network as the re-engineering, redesigning, and remanufacturing of a wind blade that has reached the end of its life on a turbine and taken out of service and then reused as a load-bearing structural element in a new structure (e.g., bridge, transmission pole, sound barrier, seawall, shelter). The issue of end-of-life of wind turbine blades is becoming a significant sustainability concern for wind turbine manufacturers, many of whom have committed to the 2030 or 2040 sustainability goals that include zero-waste for their products. Repurposing is the most sustainable end-of-life solution for wind turbine blades from an environmental, economic, and social perspective. The Network has designed and constructed two full-size pedestrian/cycle bridges—one on a greenway in Cork, Ireland and the other in a quarry in Draperstown, Northern Ireland, UK. The paper describes the design, testing, and construction of the two bridges and provides cost data for the bridges. Two additional bridges that are currently being designed for construction in Atlanta, GA, USA are also described. The paper also presents a step-by-step procedure for designing and building civil structures using decommissioned wind turbine blades. The steps are: project planning and funding, blade sourcing, blade geometric characterization, material testing, structural testing, designing, cost estimating, and construction
Construction and Cost Analysis of BladeBridges Made from Decommissioned FRP Wind Turbine Blades
This paper describes repurposing projects using decommissioned wind turbine blades in bridges conducted under a multinational research project entitled “Re-Wind”. Repurposing is defined by the Re-Wind Network as the re-engineering, redesigning, and remanufacturing of a wind blade that has reached the end of its life on a turbine and taken out of service and then reused as a load-bearing structural element in a new structure (e.g., bridge, transmission pole, sound barrier, seawall, shelter). The issue of end-of-life of wind turbine blades is becoming a significant sustainability concern for wind turbine manufacturers, many of whom have committed to the 2030 or 2040 sustainability goals that include zero-waste for their products. Repurposing is the most sustainable end-of-life solution for wind turbine blades from an environmental, economic, and social perspective. The Network has designed and constructed two full-size pedestrian/cycle bridges—one on a greenway in Cork, Ireland and the other in a quarry in Draperstown, Northern Ireland, UK. The paper describes the design, testing, and construction of the two bridges and provides cost data for the bridges. Two additional bridges that are currently being designed for construction in Atlanta, GA, USA are also described. The paper also presents a step-by-step procedure for designing and building civil structures using decommissioned wind turbine blades. The steps are: project planning and funding, blade sourcing, blade geometric characterization, material testing, structural testing, designing, cost estimating, and construction
Creative Product Problem-solving Game
Creativity is a talent that undergirds invention and innovation, making it an important skill in today’s society. Although students are often told to “be creative,” they many times do not know how and have little practice in this skill. This document presents an analysis of 33 creative products made by adult participants at a state conference for educators working with preK-12 gifted students or their teachers as a model for what teachers can do in their classrooms to allow students to practice creative thinking. During the conference presentation, Torrance’s creative strengths were reviewed with photographic examples, definitions, and suggestions printed on handouts. For the problem-solving game, each participant was given an identical set of recycled/craft materials, and about 30 minutes to create an object or scene fitting with a given theme. This presentation was delivered each of the two days of the conference with a different theme each day: “under water” was the theme the first day and “cool space” was the theme for the products on the second day. Participants each created an object that exhibited creative strengths and followed game-rules using the additional tools of scissors, glue, markers, and thread. Photographs of the final products are shown with their creative strengths identified. Most participants were successful in developing products that showed five creative strengths as required by the game rules. The most common approach to making a creative product that exhibited creative strengths was to tell an original story involving some motion that was detailed, artistically appealing, or humorous, and contained characters with emotional expressions. Because of the success and enthusiasm of participants for the game, the authors recommend it for students, clubs, and recreational activities. [7 Tables, 33 Figures, 6 References
High-contrast spectroscopy testbed for Segmented Telescopes: instrument overview and development progress
The High Contrast spectroscopy testbed for Segmented Telescopes (HCST) is being developed at Caltech. It aims at addressing the technology gap for future exoplanet imagers and providing the U.S. community with an academic facility to test components and techniques for high contrast imaging, focusing on segmented apertures proposed for future ground-based (TMT, ELT) and space-based telescopes (HabEx, LUVOIR). We present an overview of the design of the instrument and a detailed look at the testbed build and initial alignment. We offer insights into stumbling blocks encountered along the path and show that the testbed is now operational and open for business. We aim to use the testbed in the future for testing of high contrast imaging techniques and technologies with amongst with thing, a TMT-like pupil
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