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排序方式: 共有208条查询结果,搜索用时 15 毫秒
1.
Dov Katz Arun Venkatraman Moslem Kazemi J. Andrew Bagnell Anthony Stentz 《Autonomous Robots》2014,37(4):369-382
Autonomous manipulation in unstructured environments will enable a large variety of exciting and important applications. Despite its promise, autonomous manipulation remains largely unsolved. Even the most rudimentary manipulation task—such as removing objects from a pile—remains challenging for robots. We identify three major challenges that must be addressed to enable autonomous manipulation: object segmentation, action selection, and motion generation. These challenges become more pronounced when unknown man-made or natural objects are cluttered together in a pile. We present a system capable of manipulating unknown objects in such an environment. Our robot is tasked with clearing a table by removing objects from a pile and placing them into a bin. To that end, we address the three aforementioned challenges. Our robot perceives the environment with an RGB-D sensor, segmenting the pile into object hypotheses using non-parametric surface models. Our system then computes the affordances of each object, and selects the best affordance and its associated action to execute. Finally, our robot instantiates the proper compliant motion primitive to safely execute the desired action. For efficient and reliable action selection, we developed a framework for supervised learning of manipulation expertise. To verify the performance of our system, we conducted dozens of trials and report on several hours of experiments involving more than 1,500 interactions. The results show that our learning-based approach for pile manipulation outperforms a common sense heuristic as well as a random strategy, and is on par with human action selection. 相似文献
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Electrospinning of protein‐loaded fibers faces many challenges, e.g. burst release owing to segregation of the protein on the fiber surface, loss of activity due to electrospinning conditions, limitation of loading capacity etc. Core–shell electrospinning provides an effective way to electrospin fibers wherein the core can be loaded with bioactive molecules in friendly conditions of a compatible polymer solution, thereby protecting the molecules from the electrostatic field and organic solvent of shell solutions. The shell polymer, after the electrospinning, acts as a barrier to control the release of the loaded molecules. However, the limitation of loading capacity still remains due the prerequisite of using an additional polymer as additive to achieve the minimum viscosity of the core solution required for viscous drag by the shell solution being drawn by the electrostatic force. The work reported here aims to alleviate the need of a polymer additive by using aqueous protein solutions of very high concentration. High concentrations of protein solutions were successfully electrospun as the core of the protein–poly(lactide‐co‐glycolic acid) core–shell fibers. A partitioning effect was seen in the controlled release of hydrophilic proteins as they were retained in the aqueous core for longer times. Using lysozyme as a model protein, it was shown that the activity is significantly retained after electrospinning, compared with electrospinning in monolithic fibers. Moreover, the lysozyme activity was also comparable with the lysozyme released from core–shell fibers spun using poly(vinyl acetate) as additive in the core. Copyright © 2012 Society of Chemical Industry 相似文献
5.
Sandeep Kumar Tiwari Subbu S. Venkatraman 《Materials science & engineering. C, Materials for biological applications》2012,32(5):1037-1042
Electrospun polymeric fibers are attractive candidates in the development of scaffolds for the tissue engineering and for providing new systems for delivery of bioactive molecules. Co-axial fibers have emerged as an efficient tool to protect the core material from the adverse conditions of electrospinning process, to spin difficult-to-process fluids and to generate fibers with much more control of the delivery of encapsulated bioactive molecules. Currently, there is very little reported work on the optimization of the processing parameters of electrospinning, especially core–shell electrospinning. This study extends the understanding of the role of solution viscosity as a vital material parameter for electrospinning of fibers. The spinning solutions were characterized for viscosity and optical imaging of the compound Taylor cone for spinnability, and the fibers were imaged by Scanning Electron Microscopy (SEM). Our experimental results, using PLGA as the model polymer, confirm that the solution concentration be above the entanglement concentration (Ce) to obtain uniform beadless monolithic fibers; for core–shell fibers, the shell solution must fulfill the above criterion for spinnability and, further, the ratio of the viscosities of core and shell solutions (ηcore/ηshell) has to be greater than a threshold value to get a stable compound Taylor cone and therefore to obtain uniform beadless core–shell fibers. Addition of surfactant led to reduction of the threshold ηcore/ηshell (from 0.55 to 0.18) for the PVA–PLGA system. 相似文献
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Viswanath Venkatesh Tracy Ann Sykes Srinivasan Venkatraman 《Information Systems Journal》2014,24(3):249-269
Electronic government (e‐Government) is one of the most important ways to bridge the digital divide in developing countries. We develop a model of e‐Government portal use. We use various individual characteristics, namely demographics and personality, as predictors of e‐Government portal use. Specifically, our predictors were (1) gender, age, income and education; (2) the Big Five personality characteristics, i.e. extraversion, neuroticism, conscientiousness, agreeableness and openness to experience; and (3) personal innovativeness with information technology. We conducted a field study in a village in India. We collected data from over 300 heads of household. We found support for our model, with most variables being significant and explaining 40% of the variance in e‐Government portal use. 相似文献
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Infrared Thermography is one of the advanced NDE methods that is becoming attractive due to its ability to inspect non invasively large areas in short times and provide full field images in a non contact nature. While initially the method started as a qualitative technique for defect detection alone, with the advent of lock in and pulsed techniques, quantitative defect detection was made possible. While these techniques have been applied in case of ceramics and composites for defect quantification, defect sizing and quantification using these methods have not been systematically attempted in case of stainless steels. A systematic study has been undertaken to evaluate the accuracy of these empirical Pulsed Thermography (PT) techniques for defect size and depth estimation in type 316 L austenitic stainless steels. Theoretical modelling based on finite difference analysis using Thermo Calc 6L software has also been done and the results compared. 相似文献
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The synthesis, morphological characterization and cyclic deformation behaviour of a double crystalline triblock copolymer containing crystalline poly(l-lactide) (PLLA) or random copolymer of poly(l-lactide) and polycaprolactone (PCL) hard segment and a random copolymer of polycaprolactone and poly(trimethylene carbonate) (PTMC) soft segment are presented. The hard segment content was varied via the CL/LLA molar ratio to produce copolymer with distinct morphologies. Differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS) and atomic force microscopy (AFM) measurements confirmed the existence of a microphase-separated structure and the domain size was largely affected by the hard segment PCL content. Furthermore, combined measurements of WAXD and stress - strain curves revealed the molecular mechanism responsible for the superior strain recovery behaviour. It was formed that the permanent set can be largely reduced by incorporating PCL into PLLA hard segment and the strain recovery is enhanced by the ease of PCL crystal rotation upon retraction. 相似文献
10.
Madhu K. Shankarapani Subbu Ramamoorthy Ram S. Movva Srinivas Mukkamala 《Journal in Computer Virology》2011,7(2):107-119
One of the major problems concerning information assurance is malicious code. To evade detection, malware has also been encrypted
or obfuscated to produce variants that continue to plague properly defended and patched networks with zero day exploits. With
malware and malware authors using obfuscation techniques to generate automated polymorphic and metamorphic versions, anti-virus
software must always keep up with their samples and create a signature that can recognize the new variants. Creating a signature
for each variant in a timely fashion is a problem that anti-virus companies face all the time. In this paper we present detection
algorithms that can help the anti-virus community to ensure a variant of a known malware can still be detected without the
need of creating a signature; a similarity analysis (based on specific quantitative measures) is performed to produce a matrix
of similarity scores that can be utilized to determine the likelihood that a piece of code under inspection contains a particular
malware. Two general malware detection methods presented in this paper are: Static Analyzer for Vicious Executables (SAVE)
and Malware Examiner using Disassembled Code (MEDiC). MEDiC uses assembly calls for analysis and SAVE uses API calls (Static
API call sequence and Static API call set) for analysis. We show where Assembly can be superior to API calls in that it allows
a more detailed comparison of executables. API calls, on the other hand, can be superior to Assembly for its speed and its
smaller signature. Our two proposed techniques are implemented in SAVE) and MEDiC. We present experimental results that indicate
that both of our proposed techniques can provide a better detection performance against obfuscated malware. We also found
a few false positives, such as those programs that use network functions (e.g. PuTTY) and encrypted programs (no API calls
or assembly functions are found in the source code) when the thresholds are set 50% similarity measure. However, these false
positives can be minimized, for example by changing the threshold value to 70% that determines whether a program falls in
the malicious category or not. 相似文献