498 research outputs found
Cloud phase detection based on short-wave infrared polarized multi-angle imager onboard FY-3G
No full text<p>This dataset contains the observation data of the shortwave infrared multi-angle polarization imager and the medium-resolution spectral imager on the same platform of Fengyun satellite, where the multi-angle polarization imager contains 1.03 μm, 1.37 μm and 1.64 μm polarization channels. These data provide important support for cloud phase identification.</p>
The implied cost of capital: accounting for growth
No full textThis paper involves a critique of the Implied Cost of Capital (ICC) that leads to an alternative measure which, like the ICC, is extracted from accounting data. The critique deals with how the ICC handles the accounting involved. First, the ICC fails an accounting consistency condition. Second, expected earnings growth conveys risk and return, but this is not recognized when a growth rate is inserted in the reverse engineering exercise. Empirical tests so confirm. An alternative accounting-based measure accommodates these points and validates on criteria indicating risk and return. The resulting measure is a yield to maturity for equities, much like that for a bond
Towards the fabrication of suspended superconductor-graphene-superconductor Josephson junctions
No full textThesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 61-63).Graphene, a newly discovered material. has been the subject of much experimental and theoretical study due to its unique electronic behavior. In this thesis, I present, my work with graduate student Joel Wang to design and fabricate Josephson junctions on high quality graphene samples. Using niobium, with its high critical magnetic field., as the superconducting contact metal, along with high mobility suspended graphene samples, we hope to measure the behavior of graphene Josephson junctions in the quantum Hall regime. However, difficulties involved in the suspension and annealing processes of fabricating suspended graphene Josephson junctions have made it necessary for us to to develop a new fabrication process for making suspended Josephson devices. Over the course of this project, we have developed a fabrication process which uses a flip-chip bonder and graphene deposited on PMMA films to make suspended graphene samples. With these suspended flakes, we have produced niobium-graphene-niobiun Josephson junctions which exhibit multiple Andreev reflection at temperatures of 4 K. and a Dirac peak near -0.4 V, all without any annealing of the graphene. We have also developed an annealing and lithography process which can clean graphene and preserve its cleaness during the rest of the fabrication process. This annealing process has yielded suspended graphene samples with mobility upwards of 200, 000 cm 2 V-i s-1 comparable with high mobility flakes presented in literature.by Haofei Wei.S.B
Comparison of two models on simulating electric field in HVDC cable insulation
No full textSpace charge accumulation in cable insulation is one of the major technical problems in the further development of HVDC cables. A conductivity model and a bipolar charge transport model are developed to respectively calculate the space charge and electric field distribution in polymeric insulation. In this paper, both models are employed to simulate the field distribution in a medium voltage polymeric cable. Comparisons are made between theoretical and simulation results. The limitations of the conductivity model which is widely used in HVDC cable design are presented, and the results of the bipolar charge transport model are more consistent with the experimental observations. Moreover, transient current in the cable is simulated to anticipate the field distribution within the insulation when subjected to a thermal transient. The results suggest that the thermal transient can affect the space charge and electric field distribution significantly. A field inversion can only take place with higher temperature and larger temperature gradient, and this can be maintained even with temperature decreasing
Study of DC breakdown in multilayered insulation systems
No full textMultilayer insulation systems have been widely used in both high voltage alternating current (HVAC) and high voltage direct current (HVDC) power systems. A well designed multilayer insulation structure could benefit the performances and reliability of the overall insulation system and as well as costs reduction. In this present work, DC breakdown strengths of various combinations of multilayer polyethylene terephthalate (PET) films (from one to four layers) with a same total thickness were investigated. It has been found that multilayer symmetrical structures can enhance the breakdown strength of the insulation system. Space charge characteristics of these various configurations have been initially studied, in order to understand the results of the DC breakdown tests. The space charge results indicate that large amount of fast moving charges presences immediately after the voltage application, which can be partially blocked and trapped by the interfaces between film layers. The trapped charges could further distort the electric field distributions in the insulation system, and resulting field enhancement in thin layers, particularly in unsymmetrical configurations. However, more evidences and investigations are required for better understanding the mechanisms of breakdown in multilayer insulation system.</p
Modelling space charge in HVDC cable insulation
No full textThe design of high-voltage direct-current extruded cable is one of the most challenging issues in the cable industry, as the electric field distribution across the insulation can be strongly affected by the presence of space charge, which can subsequently affect its long-term reliability and life expectancy. In this study, the bipolar charge transport model was utilized to calculate space charge and field distribution in a polymeric cable insulation, and the result was compared with the one obtained by the conductivity model which is commonly used in the cable industry. It is shown that the simulation results of the bipolar charge transport model are more comparable with the previous experimental work, and the shortcomings of the conductivity model are presented. At last, the feasibility and potential issues of the new method are discussed for further development
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What Affects the Number of Non-Work Stops Made During Commute Tours? A Study Based on the 2009 US National Household Travel Survey in Large Metropolitan Areas
No full textTrip chaining is an important aspect of travel behavior, yet is less well understood than direct trips generated. Using a negative binomial regression model to fit data from the 2009 National Household Travel Survey (NHTS) and the 2010 US Census, this study focuses on the association between the complexity of commute tours (i.e. the number of non-work intervening stops) and the characteristics of commuters, households, and their neighborhoods and regions. The results from the 51 largest metropolitan areas confirm the saliency of household responsibilities, gender, flexibility of work schedule, and household auto ownership, but do not show any strong effect of socio-economic status, the regional and local built environment, or gasoline price. The findings of this study demonstrate the need for travel demand modeling to take into account the effect of trip chaining
Axons-on-a-chip for mimicking non-disruptive diffuse axonal injury underlying traumatic brain injury
No full textDiffuse axonal injury (DAI) is the most severe pathological feature of traumatic brain injury (TBI). However, how primary axonal injury is induced by transient mechanical impacts remains unknown, mainly due to the low temporal and spatial resolution of medical imaging approaches. Here we established an axon-on-achip (AoC) model for mimicking DAI and monitoring instant cellular responses. Integrating computational fluid dynamics and microfluidic techniques, DAI was induced by injecting a precisely controlled micro-flux in the transverse direction. The clear correlation between the flow speed of injecting flux and the severity of DAI was elucidated. We next used the AoC to investigate the instant intracellular responses underlying DAI and found that the dynamic formation of focal axonal swellings (FAS) accompanied by Ca2+ surge occurs during the flux. Surprisingly, periodic axonal cytoskeleton disruption also occurs rapidly after the flux. These instant injury responses are spatially restricted to the fluxed axon, not affecting the overall viability of the neuron in the acute stage. Compatible with high-resolution live microscopy, the AoC provides a versatile system to identify early mechanisms underlying DAI, offering a platform for screening effective treatments to alleviate TBI.Xiaorong Pan, Jie Li, Wei Li, Haofei Wang, Nela Durisic, Zhenyu Li, Yu Feng, Yifan Liu, Chun-Xia Zhao and Tong Wan
IDENTIFICATION OF ESSENTIAL CIS-REGULATROY ELEMENTS FOR PLURIPOTENCY BY CRISPR SCREEN
No full textPh.DDOCTOR OF PHILOSOPHY (FOS
Hybrid interface for human robot interaction
No full textTo better interact with robots, human robot interfaces should decode human intent reliably. There are multiple possible communication channels for such interfaces. In this thesis, we seek to develop hybrid interfaces for human-robot interaction, focusing on integrating cues from electroencephalography (EEG), eye gaze, force, and the environment. First, we describe a hybrid EEG/gaze-based brain computer interaction system. Past work has shown that it is possible to use motor imagery to decode the subject's voluntary intent. However, system accuracy is limited by the low signal-to-noise ratio of EEG signals. We investigated combining motor imagery with eye gaze to improve system performance. We demonstrated a hybrid interface for a robot arm that enables subjects to perform a pick and place task. We found that the integration of EEG with eye gaze significantly improved system performance over either cue in isolation. Second, we addressed the problem of estimating 3D gaze location in a world-centric coordinate system. The key challenge in 3D gaze tracking is to estimate the depth along the line of sight. We solved this problem by integrating the gaze estimates with information about the environmental structure represented by a point-cloud representation from an RGBD camera. We implemented the algorithm on both remote and head-mounted eye trackers. We tested the proposed system in a human-human collaborative assembly task. Next, we developed a gaze-based upper limb rehabilitation system. Unlike previous works focusing mainly on the mechanical design, we proposed a gaze-modulated admittance control strategy that integrates gaze estimates with force estimates. Our system has the flexibility to be configured into different working modes to fit patient needs at different injury stages: a passive mode for the acute phase, an assistive mode for the sub-acute phase, and an active mode for the chronic phase. To keep the patient engaged, we designed a fishing game and implemented the algorithm on a planar robot. We also developed an immersive gaze-controlled painting task in virtual reality. Finally, we investigated using single-trial EEG signal to distinguish between target and non-target faces presented in a rapid serial visual presentation paradigm. Unlike the past work on event-related-potentials (ERP) detection, which averaged multiple trials, here we focused on the more challenging task of detecting the target using a single-trial EEG signal. We used a convolutional neural network for classification, resulting in performance surpassing that of the support vector machine (SVM) algorithm, which has been commonly used in ERP detection tasks.</p
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