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Hexagonal boron nitride nanomechanical resonators with spatially visualized motion

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Microsystems & Nanoengineering 2017年第1期3卷 196-203页

作者： Xu-Qian Zheng jaesung lee Philip X.-L.Feng Department of Electrical Engineering&Computer Science Case School of EngineeringCase Western Reserve University10900 Euclid AvenueClevelandOH 44106USA

Atomic layers of hexagonal boron nitride(h-BN)crystal are excellent candidates for structural materials as enabling ultrathin,two-dimensional(2D)nanoelectromechanical systems(NEMS)due to the outstanding mechanical properties and very wide bandgap(5.9 eV)of *** this work,we report the experimental demonstration of h-BN 2D nanomechanical resonators vibrating at high and very high frequencies(from~5 to~70 MHz),and investigations of the elastic properties of h-BN by measuring the multimode resonant behavior of these ***,we demonstrate a dry-transferred doubly clamped h-BN membrane with~6.7 nm thickness,the thinnest h-BN resonator known to *** addition,we fabricate circular drumhead h-BN resonators with thicknesses ranging from~9 to 292 nm,from which we measure up to eight resonance modes in the range of~18 to 35 *** measurements and modeling of the rich multimode resonances,we resolve h-BN’s elastic behavior,including the transition from membrane to disk regime,with built-in tension ranging from 0.02 to 2 N m−*** Young’s modulus of h-BN is determined to be EY≈392 GPa from the measured *** ultrasensitive measurements further reveal subtle structural characteristics and mechanical properties of the suspended h-BN diaphragms,including anisotropic built-in tension and bulging,thus suggesting guidelines on how these effects can be exploited for engineering multimode resonant functions in 2D NEMS transducers.

关键词： Hexagonal boron nitride(h-BN) multimode resonances nanoelectromechanical systems(NEMS) resonators spatial mapping Young’s modulus

Productivity Growth in the Transportation Industries in the United States: An Application of the DEA Malmquist Productivity Index

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American Journal of Operations Research 2015年第1期5卷 1-20页

作者： jaesung Choi David C. Roberts EunSu lee Transportation and Logistics Program North Dakota State University Fargo ND USA Department of Agribusiness & Applied Economics North Dakota State University Fargo ND USA Upper Great Plains Transportation Institute North Dakota State University Fargo ND USA

This study reviews productivity growth in the five major transportation industries in the United States (airline, truck, rail, pipeline, and water) and the pooled transportation industry from 2004 to 2011. We measure the average productivity for these eight years by state in each transportation industry and the annual average productivity by transportation industry. The major findings are that the U.S. transportation industry shows strong and positive productivity growth except that in the years of the global financial crisis in 2007, 2008, and 2010, and among the five transportation industries, the rail and water sectors show the highest productivity growth in 2011.

关键词： DEA Malmquist Productivity Index Productivity Growth U.S. Transportation Industry

Reshaping Tribal Road Network Using Public Information

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Journal of Geographic Information System 2014年第6期6卷 594-604页

作者： jaesung Choi EunSu lee David C. Roberts Transportation and Logistics Program North Dakota State University Fargo USA Upper Great Plains Transportation Institute North Dakota State University Fargo USA Department of Agribusiness & Applied Economics North Dakota State University Fargo USA

The area with the fastest growing Native American population in North Dakota is the Fort Berthold Reservation. State and federal road information available to the public is not identical in terms of the number of physical road segments or in the attribute information provided for the road network. In this study we develop: 1) a navigable road network achieved by improving connectivity among road segments, updating road information, and making a comprehensive network;and 2) a standard process for integrating the state and federal local road information. The standard process broadly consists of three Parts: 1) combining road segments from each source;2) providing legitimacy to snapping distance;and 3) performing a snapping based on the result of Part 2 to connect those road segments, which remained unconnected from Part 1. The findings show that data on local roads on the Fort Berthold Reservation from the two different sources are joined through the standard process, and the process saves considerable time and resources required for fixing the road network. The standard process that has been developed here can be applied to a variety of other Indian road information integration projects to join not only physical road segments, but also plural attribute information. The process will also be useful for a variety of other projects integrating road information, which is available to the public, in order to overcome financial and time limitations.

关键词： GIS Standard Process Tribal Roads Geoprocessing Topology Error Error Inspection

Forecasting Oil Production in North Dakota Using the Seasonal Autoregressive Integrated Moving Average (S-ARIMA)

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Natural Resources 2015年第1期6卷 16-26页

作者： jaesung Choi David C. Roberts EunSu lee Transportation and Logistics Program North Dakota State University Fargo USA Department of Agribusiness & Applied Economics North Dakota State University Fargo USA Upper Great Plains Transportation Institute North Dakota State University Fargo USA

North Dakota’s oil production has been rapidly increasing during the past several years. The state’s oil production in March 2013 even increased to more than twice the quantity produced in March 2011, and the estimated Bakken Formation reserves were reported very large compared with those of the United Arab Emirates. It eventually makes a question to us of how much oil will be able to be actually extracted with currently available technologies. To answer this question, this paper forecasts future oil development trend in North Dakota using the Seasonal Autoregressive Integrated Moving Average (S-ARIMA) model. Nonstationarity derived from a stochastic trend and the abrupt structural change of oil industry was a big potential problem, but through the Quandt Likelihood Ratio test, we found break points, which allowed us to select a model fitting period suitable for the S-ARIMA method to provide accurate statistical inference for the historical period. The seven major oil producing counties were investigated to determine whether the current oil boom was consistent across all oil fields in North Dakota. Empirical estimates show that North Dakota’s oil production will be more than double in the next five years. What we can predict with great certainty is that North Dakota’s influence over domestic and global oil supply systems will increase in the near future, especially over the next five to six years. This is good news for those who are concerned about domestic energy security in the USA.

关键词： Bakken Formation Forecasting North Dakota Oil S-ARIMA