77 research outputs found
Optimal Control with a Cost of Changing Control
No full textIn this paper, we consider a class of optimal control problems where the variation of the control variable is appended as a penalty term into the cost function to reduce the fluctuation of the control. A new computational approach is developed for solving this type of problems, based on control parametrization technique used in conjunction with the time scaling transform, the constraint transcription method and a smoothing technique. This computational method is supported by rigorous convergence analysis
A dual-frequency antenna based on substrate integrated waveguide (SIW) in millimeter-wave range
No full text
Expansion and equality in Chinese higher education
No full textWhat is the relationship between the fast expansion of higher education and the equality of college enrollment opportunity in China? Based on the data from four large-scale surveys on college graduates in China, this paper explores this question by conducting empirical analysis on the family occupational, educational, regional, and economic status through descriptive and regression analyses. The result shows: Firstly, quantitatively speaking, enrollment opportunities have equalized in some aspects as well as unequalized in some others. The percentage of students from medium and inferior occupational families and the percentage of female students have increased, while the percentage of students from families with low academic qualification has not changed much more; but the percentage of students from county and below has obviously decreased. Secondly, qualitatively speaking, enrollment opportunity inequality has deepened continuously. Students with better family occupational, educational, regional, and economic status and male students have more chances to enter elite universities, and those groups have become more and more advantaged with the passing of time. (C) 2014 Elsevier Ltd. All rights reserved.Education & Educational [email protected]
Optical singularity assisted method for accurate parameter detection of step-shaped nanostructure in coherent Fourier scatterometry
No full textAccurate determination of the physical parameters of nanostructures from optical far-field scattering is an important and challenging topic in the semiconductor industry. Here, we propose a novel metrology method to determine simultaneously the height and side-wall angle of a step-shaped silicon nanostructure. By employing an optical singular beam into a typical coherent Fourier scatterometry system, both parameters can be retrieved through analyzing the intensity profile of the far-field scattering pattern. The use of singular beam is shown to be sensitive to slight changes of the parameters of the step. By changing the relative direction between the singularity and structure, the height and side-wall angle can both be retrieved with high precision. This new method is robust, simple, and can provide valuable means for micro-and-nano- metrologies.ImPhys/Optic
Safety and security of oil and gas pipeline transportation : a systematic analysis of research trends and future needs using WoS
No full textAbstract: The terrorist attack on the Abqaiq oil plant in Saudi Arabia on September 14, 2019 attracted global attention to the significant role of safety and security in the sustainable oil and gas supply chain and the vulnerability of supply infrastructures subject to intentional and unintentional damages. Different from other oil and gas supply infrastructures, oil and gas pipelines may be more vulnerable to accidental, natural and intentional threats due to their widespread distribution. Therefore a systematic and thorough review is carried out to investigate safety and security of oil and gas pipelines based on bibliometric analysis. First, a total of 598 publications between 1970 and 2019 related to safety and security of oil and natural gas pipelines was retrieved and refined from the database of Web of Science (WoS). The 598 publications are analyzed by the bibliometric software VOSviewer to obtain the temporal and regional distribution of publications, to identify \u201cproductive institutions\u201d and \u201cproductive authors\u201d, and create the cooperation networks between institutions and authors. Besides, the evolution of research topics and research methods are identified based on keywords and bibliographic analysis. Moreover, the main research topics and research methods are analyzed to obtain insight into the research evolutions and trends. Risk assessment, leakage, and corrosion are the main topics while QRA, fuzzy theory and the Bayesian network are the most frequently used research methods. To further improve the sustainability of oil and gas pipelines, this study provides and discusses future research needs such as pipeline security, environmental sustainability, pipeline system resilience. According to these results, the research on risk assessment based on Bayesian network and consequence analysis using CFD may increase in the future. Besides, more research and guidelines on pipeline security, resilience, and environmental impacts to better protect pipelines, are expected
A new exact penalty function method for continuous inequality constrained optimization problems
No full textpublisher-authenticated version online. Alternate Location: Permanent Link: The attached document may provide the author's accepted version of a published work. See Citation for details of the published work
Transversal optical singularity induced precision measurement of step-nanostructures
No full textOptical singularities indicate zero-intensity points in space where parameters, such as phase, polarization, are undetermined. Vortex beams such as the Laguerre–Gaussian modes are characterized by a phase factor eilθ, and contain a phase singularity in the middle of its beam. In the case of a transversal optical singularity (TOS), it occurs perpendicular to the propagation, and its phase integral is 2π in nature. Since it emerges within a nano-size range, one expects that TOSs could be sensitive in the light-matter interaction process and could provide a great possibility for accurate determination of certain parameters of nanostructure. Here, we propose to use TOSs generated by a three-wave interference to illuminate a step nanostructure. After interaction with the nanostructure, the TOS is scattered into the far field. The scattering direction can have a relation with the physical parameters of the nanostructure. We show that by monitoring the spatial coordinates of the scattered TOS, its propagation direction can be determined, and as consequence, certain physical parameters of the step nanostructure can be retrieved with high precision.ImPhys/Pereira grou
Determination of steep sidewall angle using polarization-sensitive asymmetric scattering
No full textThe sidewall angle (SWA) of a nanostructure exerts influence on the performance of the nanostructure and plays an important role in processing nano-structural chips. It is still a great challenge to determine steep SWAs from far field measurements especially when the SWAs are close to 90°. Here, we propose a far-field detection system to determine steep SWA of a cliff-shape step structure on a silicon substrate by combining a split detector with a scanning method. The far-field radiation field is asymmetric due to the scattering of the step structure, and further numerical analysis demonstrates the reliability of this far-field measurement method. In the simulations, two key variables, i.e. the polarization state and the focus position of the incident laser beam, are considered to explore their impacts. By scanning over the structure laterally and longitudinally with both TE and TM polarizations, polarization effects on the far-field occur. These effects show higher sensitivity to steep SWA variation for TM polarization as compared to TE. Furthermore, with a comprehensive longitudinal scanning analysis for the TM polarization case, a feasible focus interval can be optimized to retrieve the steep SWA. As the proposed method is fast, highly sensitive and easy to implement, it provides a powerful approach to investigate the scattering behavior of nanostructures. </p
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