•A dynamic Bayesian network (DBN) model with only speed condition data for crash prediction is proposed.•Several intervals traffic data are used to capture dynamic state transition.•Two approaches ...are applied to identify different traffic state combinations.•The DBN model with nine state combinations has better prediction performance.
Traffic crashes occurring on freeways/expressways are considered to relate closely to previous traffic conditions, which are time-varying. Meanwhile, most studies use volume/occupancy/speed parameters to predict the likelihood of crashes, which are invalid for roads where the traffic conditions are estimated using speed data extracted from sampled floating cars or smart phones. Therefore, a dynamic Bayesian network (DBN) model of time sequence traffic data has been proposed to investigate the relationship between crash occurrence and dynamic speed condition data. Moreover, the traffic conditions near the crash site were identified as several state combinations according to the level of congestion and included in the DBN model. Based on 551 crashes and corresponding speed information collected on expressways in Shanghai, China, DBN models were built with time series speed condition data and different state combinations. A comparative analysis of the DBN model using flow detector data and a static Bayesian network model was also conducted. The results show that, with only speed condition data and nine traffic state combinations, the DBN model can achieve a crash prediction accuracy of 76.4% with a false alarm rate of 23.7%. In addition, the results of transferability testing imply that the DBN models are applicable to other similar expressways with 67.0% crash prediction accuracy.
Cardiac disease has become a severe threat to public health according to the government report. In China, there are 0.29 billion cardiac patients and early diagnosis will greatly reduce mortality and ...improve life quality. Electrocardiogram (ECG) signal is a priority tool in the diagnosis of heart diseases because it is non‐invasive and easily available with a simple diagnostic tool of low cost. The paper proposes an automatic classification model by combing convolutional neural network (CNN) and recurrent neural network (RNN) to distinguish different types of cardiac arrhythmias. Morphology features of the raw ECG signals are extracted by CNN blocks and fed into a bidirectional gated recurrent unit (GRU) network. Attention mechanism is used to highlight specific features of the input sequence and contribute to the performance improvement of classification. The model is evaluated with two datasets considering the class imbalance problem constructed with records from MIT‐BIH arrhythmia database and China Physiological Signal Challenge 2018 database. Experimental results show that this model achieves good performance with an average F1 score of 0.9110 on public dataset and 0.9082 on subject‐specific dataset, which may have potential practical applications.
Large―scale nanophotonic phased array JIE SUN; TIMURDOGAN, Erman; YAACOBI, Ami ...
Nature (London),
01/2013, Volume:
493, Issue:
7431
Journal Article
Peer reviewed
Electromagnetic phased arrays at radio frequencies are well known and have enabled applications ranging from communications to radar, broadcasting and astronomy. The ability to generate arbitrary ...radiation patterns with large-scale phased arrays has long been pursued. Although it is extremely expensive and cumbersome to deploy large-scale radiofrequency phased arrays, optical phased arrays have a unique advantage in that the much shorter optical wavelength holds promise for large-scale integration. However, the short optical wavelength also imposes stringent requirements on fabrication. As a consequence, although optical phased arrays have been studied with various platforms and recently with chip-scale nanophotonics, all of the demonstrations so far are restricted to one-dimensional or small-scale two-dimensional arrays. Here we report the demonstration of a large-scale two-dimensional nanophotonic phased array (NPA), in which 64 × 64 (4,096) optical nanoantennas are densely integrated on a silicon chip within a footprint of 576 μm × 576 μm with all of the nanoantennas precisely balanced in power and aligned in phase to generate a designed, sophisticated radiation pattern in the far field. We also show that active phase tunability can be realized in the proposed NPA by demonstrating dynamic beam steering and shaping with an 8 × 8 array. This work demonstrates that a robust design, together with state-of-the-art complementary metal-oxide-semiconductor technology, allows large-scale NPAs to be implemented on compact and inexpensive nanophotonic chips. In turn, this enables arbitrary radiation pattern generation using NPAs and therefore extends the functionalities of phased arrays beyond conventional beam focusing and steering, opening up possibilities for large-scale deployment in applications such as communication, laser detection and ranging, three-dimensional holography and biomedical sciences, to name just a few.
Single-pixel imaging uses a single-pixel detector, rather than a focal plane detector array, to image a scene. It provides advantages for applications such as multi-wavelength, three-dimensional ...imaging. However, low frame rates have been a major obstacle inhibiting the use of computational ghost imaging technique in wider applications since its invention one decade ago. To address this problem, a computational ghost imaging scheme, which utilizes an LED-based, high-speed illumination module is presented in this work. At 32 × 32 pixel resolution, the proof-of-principle system achieved continuous imaging with 1000 fps frame rate, approximately two orders larger than those of other existing ghost imaging systems. The proposed scheme provides a cost-effective and high-speed imaging technique for dynamic imaging applications.
•The most cited journal is Journal of Consumer Research in business and Tourism Management in hospitality/tourism.•The four theoretical pillars in business are WOM and sales, WOM and social media ...marketing, WOM and social influence, and Internet and online WOM. The four pillars in hospitality/tourism are online reviews and behavior, online reviews and eWOM, information technology and UGC, and research methodology.•The seven themes of keywords are defined as Foundation, Platform, Content, Business Sector, Managerial Application, Methodology, and Emerging Trend.•Four differences between the two fields are observed: different research foundations, business sector foci, methodological supports, and emerging trends.•A future research agenda is proposed in three aspects: WOM based on social theories, big data using text mining methods, and diverse research designs.
This study combined two bibliometric analysis methods to provide a systematic and holistic review of social media-related academic literature. A total of 406 publications related to social media between 2007 and 2016 were identified from 16 business and hospitality/tourism journals. Co-citation analysis identified Word-of-Mouth as the major theoretical foundation of social media research in business, while the hospitality/tourism field presented a diverse theoretical foundation. The study then employed co-word analysis to identify the evolution of research themes over time in both fields. The comparison of social media research between the two fields highlighted four similarities, including the growth of research over time, the term “social media” gaining popularity, the new trend of social networking sites, and managerial applications as research focus. Finally, the study called for a future research agenda on social media research in the hospitality/tourism field.
Time-of-flight three-dimensional imaging is an important tool for applications such as object recognition and remote sensing. Conventional time-of-flight three-dimensional imaging systems frequently ...use a raster scanned laser to measure the range of each pixel in the scene sequentially. Here we show a modified time-of-flight three-dimensional imaging system, which can use compressed sensing techniques to reduce acquisition times, whilst distributing the optical illumination over the full field of view. Our system is based on a single-pixel camera using short-pulsed structured illumination and a high-speed photodiode, and is capable of reconstructing 128 × 128-pixel resolution three-dimensional scenes to an accuracy of ∼3 mm at a range of ∼5 m. Furthermore, by using a compressive sampling strategy, we demonstrate continuous real-time three-dimensional video with a frame-rate up to 12 Hz. The simplicity of the system hardware could enable low-cost three-dimensional imaging devices for precision ranging at wavelengths beyond the visible spectrum.
Wing polymorphism is an evolutionary feature found in a wide variety of insects, which offers a model system for studying the evolutionary significance of dispersal. In the wing-dimorphic planthopper ...Nilaparvata lugens, the insulin/insulin-like growth factor signaling (IIS) pathway acts as a 'master signal' that directs the development of either long-winged (LW) or short-winged (SW) morphs via regulation of the activity of Forkhead transcription factor subgroup O (NlFoxO). However, downstream effectors of the IIS-FoxO signaling cascade that mediate alternative wing morphs are unclear. Here we found that vestigial (Nlvg), a key wing-patterning gene, is selectively and temporally regulated by the IIS-FoxO signaling cascade during the wing-morph decision stage (fifth-instar stage). RNA interference (RNAi)-mediated silencing of Nlfoxo increase Nlvg expression in the fifth-instar stage (the last nymphal stage), thereby inducing LW development. Conversely, silencing of Nlvg can antagonize the effects of IIS activity on LW development, redirecting wing commitment from LW to the morph with intermediate wing size. In vitro and in vivo binding assays indicated that NlFoxO protein may suppress Nlvg expression by directly binding to the first intron region of the Nlvg locus. Our findings provide a first glimpse of the link connecting the IIS pathway to the wing-patterning network on the developmental plasticity of wings in insects, and help us understanding how phenotypic diversity is generated by the modification of a common set of pattern elements.
In this article, the stabilization is addressed for the continuous‐time nonhomogeneous nonlinear Markovian jump system (MJS) with parameter uncertainty and stochastic disturbance via sliding mode ...control (SMC) technique. By using a piecewise homogeneous Markov chain to describe its time‐varying characteristics, the considered nonhomogeneous MJS is established by two kinds of piecewise homogeneous MJSs. After that, an integral sliding mode function is constructed. Then, by applying the SMC theory, two control schemes are proposed to force the states of the piecewise homogeneous MJSs onto the designed sliding surface. Sufficient conditions are given to assure the stochastic stability of the sliding mode dynamics. In addition, the reachability of the system states under the developed SMC law is discussed via Lyapunov stability theory. Lastly, some simulation results are provided to show the effectiveness of the presented SMC methods.
Tremendous demands for renewable hydrogen generated from water splitting have stimulated intensive research on developing earth‐abundant, non‐noble, and versatile metal catalysts toward the hydrogen ...evolution reactions (HER). Here, self‐supported Cu‐Ni‐Al hybrid electrodes that are composed of electroactive Al7Cu4Ni@Cu4Ni core/shell nanocrystals seamlessly integrated in self‐supported 3D bimodal nanoporous Cu skeleton (Bi‐NP Cu/Al7Cu4Ni@Cu4Ni) as robust HER electrocatalysts in alkaline electrolyte are reported. As a result of the proper architecture, in which the Bi‐NP Cu skeleton not only facilitates both electron and electrolyte transports but also provides high specific surface areas to fully use high electrocatalytic activity of Al7Cu4Ni@Cu4Ni core/shell nanocrystals, the Bi‐NP Cu/Al7Cu4Ni@Cu4Ni hybrid catalysts exhibit a low onset overpotential of 60 mV and a small Tafel slope of 110 mV dec−1, enabling the catalytic current density of 10 mA cm−2 at a low overpotential of 139 mV. The highly stable electrochemical performance makes them promising candidates as cathode catalysts in alkaline‐based devices.
Self‐supported bimodal nanoporous Cu‐Ni‐Al catalytic electrodes are successfully developed as robust hydrogen evolution reaction (HER) electrocatalysts in alkaline electrolyte. These hybrid electrodes that are composed of electroactive Al7Cu4Ni@Cu4Ni core/shell nanocrystals seamlessly integrated in a 3D bimodal nanoporous Cu skeleton (Bi‐NP Cu/Al7Cu4Ni@Cu4Ni) exhibit exceptional HER performance as a result of enhanced electrolyte accessibility and electron transport as well as HER catalytic activity.
This study investigates the compressive mechanical properties and energy absorption characteristics of three types of triply periodic minimal surface (TPMS) Ti6Al4V cellular structures fabricated by ...selective laser melting (SLM). Based on the SEM observation, the morphology of Ti6Al4V alloy sheet-based TPMS structures was observed, and imperfections of SLM-fabricated cellular structures were investigated. The quasi-static uniaxial compression tests were carried out, and the deformation behavior was recorded by a camera. The result indicated that the compressive mechanical properties had an approximately positive relationship with the relative density of TPMS structures. In addition, the revised Gibson-Ashby prediction models of three sheet-based TPMS structures were established by fitting the compression test results. Furthermore, finite element analysis (FEA) of the compression process was also conducted to facilitate analysis and understanding of the deformation mechanism for TPMS structures. The results also revealed that the energy absorption capacity of TPMS structures increased with the increase in the actual relative density. The mechanical properties, energy absorption, and relative density diagram of sheet-based Ti6Al4V alloy TPMS structures were established to systematically obtain the optimal relative densities of TPMS structures for specific load-bearing and energy absorption applications.
•The mechanical properties and deformation mechanisms of three types of TPMS sheet-based structures were investigated.•The Gibson and Ashby's models for the cellular structure were modified by re-fitting the compression results.•The energy absorption characteristics of Ti6Al4V alloy sheet-based TPMS cellular structures were studied.•Numerical simulations were conducted to calculate the strength and deformation mechanisms of sheet-based TPMS structures.
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