Dynamical Characterization and Stabilization of Large Gravity-Tractor Designs

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76167/1/AIAA-32554-693.pd

Paving the pathways towards sustainable future? A critical review of STI policy roadmaps as policy instruments enabling sustainability transitions

Roadmaps and roadmapping techniques receive increasing attention in the Science, Technology and Innovation policy community, notably for the development of strategies and policies to address societal challenges and ambitious goals such as the SDGs. STI policy roadmaps are used to evoke future visions, align actor expectations and formulate, document, plan and implement public policies for long-term, ambitious sustainability goals. As a sophisticated strategic planning process, roadmapping seems appropriate for policy support aiming to foster sustainability transitions. Nevertheless, there is little research on the role and limitations of roadmaps as a policy instrument to support innovation for sustainability transitions. This paper critically assesses selected national and international policy and sectoral roadmaps that focus on technology areas and societal challenges relevant to sustainability and energy transitions. The assessment of the objectives, design features and embeddedness of roadmaps in policy processes shows that current policy roadmaps have several shortfalls. The paper outlines knowledge gaps and research priorities to understand how such limitations might be overcome and draws tentative lessons for future applications of roadmaps as policy instruments for sustainability transitions

Seasonal and interannual variations in ice melange and its impact on terminus stability, Jakobshavn Isbræ, Greenland

We used satellite-derived surface temperatures and time-lapse photography to infer temporal variations in the proglacial ice melange at Jakobshavn Isbræ, a large and rapidly retreating outlet glacier in Greenland.We used satellite-derived surface temperatures and time-lapse photography to infer temporal variations in the proglacial ice melange at Jakobshavn Isbræ, a large and rapidly retreating outlet glacier in Greenland. Freezing of the melange-covered fjord surface during winter is indicated by a decrease in fjord surface temperatures and is associated with (1) a decrease in ice melange mobility and (2) a drastic reduction in iceberg production. Vigorous calving resumes in spring, typically abruptly, following the steady up-fjord retreat of the sea-ice/ice-melange margin. An analysis of pixel displacement from time-lapse imagery demonstrates that melange motion increases prior to calving and subsequently decreases following several events. We find that secular changes in ice melange extent, character and persistence can influence iceberg calving, and therefore glacier dynamics over daily-to-monthly timescales, which, if sustained, will influence the mass balance of an ice sheet.This research was supported by funds from the Gordon and Betty Moore Foundation (GBMF2627), NASA (NNX08AN74G), the US National Science Foundation (ANT0944193 and ANS0909552) and the New Hampshire Space Grant Consortium (NNX10AL97H). We thank CH2M HILL Polar Services and Air Greenland for logistics support, and PASSCAL (Program for the Array Seismic Studies of theContinental Lithosphere) for the use of seismic instrumentation. Ian Joughin derived TerraSAR-X velocities and terminus positions from images provided by the German (DLR) space agency under NASA grant NNX08AL98A. We acknowledgethe use of Rapid Response imagery from the Land Atmosphere Near-real time Capability for EOS (LANCE) system operated by the NASA/GSFC/Earth Science Data and Information System (ESDIS) with funding provided by NASA HQ. Glacier surface elevations were provided by CReSIS, and bed elevations by CReSIS and Mathieu Morlighem. The manuscript was significantly improved by comments from Tim Bartholomaus and an anonymous reviewer.Ye

Decreased mTOR signaling pathway in human idiopathic autism and in rats exposed to valproic acid

BackgroundThe molecular mechanisms underlying autistic behaviors remain to be elucidated. Mutations in genes linked to autism adversely affect molecules regulating dendritic spine formation, function and plasticity, and some increase the mammalian target of rapamycin, mTOR, a regulator of protein synthesis at spines. Here, we investigated whether the Akt/mTOR pathway is disrupted in idiopathic autism and in rats exposed to valproic acid, an animal model exhibiting autistic-like behavior.MethodsComponents of the mTOR pathway were assayed by Western blotting in postmortem fusiform gyrus samples from 11 subjects with idiopathic autism and 13 controls and in valproic acid versus saline-exposed rat neocortex. Additionally, protein levels of brain-derived neurotrophic factor receptor (TrkB) isoforms and the postsynaptic organizing molecule PSD-95 were measured in autistic versus control subjects.ResultsFull-length TrkB, PI3K, Akt, phosphorylated and total mTOR, p70S6 kinase, eIF4B and PSD-95 were reduced in autistic versus control fusiform gyrus. Similarly, phosphorylated and total Akt, mTOR and 4E-BP1 and phosphorylated S6 protein were decreased in valproic acid- versus saline-exposed rats. However, no changes in 4E-BP1 or eIF4E were found in autistic brains.ConclusionsIn contrast to some monogenic disorders with high rates of autism, our data demonstrate down-regulation of the Akt/mTOR pathway, specifically via p70S6K/eIF4B, in idiopathic autism. These findings suggest that disruption of this pathway in either direction is widespread in autism and can have adverse consequences for synaptic function. The use of valproic acid, a histone deacetylase inhibitor, in rats successfully modeled these changes, implicating an epigenetic mechanism in these pathway disruptions

Molecular corridors and kinetic regimes in the multiphase chemical evolution of secondary organic aerosol

The dominant component of atmospheric, organic aerosol is that derived from the oxidation of volatile organic compounds (VOCs), so-called secondary organic aerosol (SOA). SOA consists of a multitude of organic compounds, only a small fraction of which has historically been identified. Formation and evolution of SOA is a complex process involving coupled chemical reaction and mass transport in the gas and particle phases. Current SOA models do not embody the full spectrum of reaction and transport processes, nor do they identify the dominant rate-limiting steps in SOA formation. Based on molecular identification of SOA oxidation products, we show here that the chemical evolution of SOA from a variety of VOC precursors adheres to characteristic "molecular corridors" with a tight inverse correlation between volatility and molar mass. The slope of these corridors corresponds to the increase in molar mass required to decrease volatility by one order of magnitude (-dM / dlogC_0). It varies in the range of 10–30 g mol^(−1), depending on the molecular size of the SOA precursor and the O : C ratio of the reaction products. Sequential and parallel reaction pathways of oxidation and dimerization or oligomerization progressing along these corridors pass through characteristic regimes of reaction-, diffusion-, or accommodation-limited multiphase chemical kinetics that can be classified according to reaction location, degree of saturation, and extent of heterogeneity of gas and particle phases. The molecular corridors and kinetic regimes help to constrain and describe the properties of the products, pathways, and rates of SOA evolution, thereby facilitating the further development of aerosol models for air quality and climate

Model of Double Asteroid Redirection Test Impact Ejecta Plume Observations

The Double Asteroid Redirection Test (DART) spacecraft will impact the moon Dimorphos of the [65803] Didymos binary in order to demonstrate asteroid deflection by a kinetic impactor. DART will measure the deflection by using ground-based telescopic observations of the orbital period change of Didymos and will carry the Light Italian CubeSat for Imaging of Asteroids (LICIACube) cubesat, which will perform a flyby of Didymos about 167 s after the DART impact, obtaining images of the DART impact ejecta plume. LICIACube images showing the ejecta plume spatial structure and temporal evolution will help determine the vector momentum transfer from the DART impact. A model is developed for the impact ejecta plume optical depth, using a pointsource scaling model of the DART impact. The model is applied to expected LICIACube plume images and shows how plume images enable characterization of the ejecta mass versus velocity distribution. The ejecta plume structure, as it evolves over time, is determined by the amount of ejecta that has reached a given altitude at a given time. The evolution of the plume optical depth profiles determined from LICIACube images can distinguish between strength-controlled and gravity-controlled impacts, by distinguishing the respective mass versus velocity distributions. LICIACube plume images discriminate the differences in plume structure and evolution that result from different target physical properties, mainly the strength and porosity, thereby allowing inference of these properties to improve the determination of DART impact momentum transfer