In location-based services, a density query re- turns the regions with high concentrations of moving objects （MOs）. The use of density queries can help users identify crowded regions so as to avoid congestion. Most ...In location-based services, a density query re- turns the regions with high concentrations of moving objects （MOs）. The use of density queries can help users identify crowded regions so as to avoid congestion. Most of the exist- ing methods try very hard to improve the accuracy of query results, but ignore query efficiency. However, response time is also an important concern in query processing and may have an impact on user experience. In order to address this issue, we present a new definition of continuous density queries. Our approach for processing continuous density queries is based on the new notion of a safe interval, using which the states of both dense and sparse regions are dynamically main- tained. Two indexing structures are also used to index candi- date regions for accelerating query processing and improving the quality of results. The efficiency and accuracy of our approach are shown through an experimental comparison with snapshot density queries.展开更多
The mode-2 internal solitary wave(ISW)propagating independently in the stratified ocean is a high-mode internal wave(IW),and its complex wave-flow field will cause the harm to the safe operation of marine engineering ...The mode-2 internal solitary wave(ISW)propagating independently in the stratified ocean is a high-mode internal wave(IW),and its complex wave-flow field will cause the harm to the safe operation of marine engineering structures.In this paper,a fluid environment with a continuous density pycnocline was prepared in a large experimental stratified fluid flume.Based on the principle of ISWs generated by the fluid gravity collapse,a physical experimental method for exciting the“oval”mode-2 ISW solitons by bidirectional fluid gravity collapse in a continuous density pycnocline was proposed.The experimental results showed that the evolution of the upper and lower double vortices near the center of pycnocline is a special generation mechanism of the generation process of mode-2 ISW generated by the gravity collapse of the stratified fluid.The number of generated mode-2 ISW internal solitons depends on the geometric size of fluid gravity collapse region and the geometric thickness ratio of the upper and lower layers of the fluid.The wave evolution process,wave-flow structure,wave-flow characteristics of the“oval”mode-2 ISW in the continuous density pycnocline and its stratified environment effect were obtained.The results showed that the wave speed of the mode-2 ISW increases with the increasing wave amplitude,and the wavelength increases first and then decreases with the increasing wave amplitude.Under the experimental conditions with same wave amplitude,the increase of the thickness ratio of the upper and lower layers of the fluid,the density difference and the thickness of the middle fluid layer would lead to the increase of the wavelength and wave speed of the mode-2 ISW.The velocity range of the mode-2 ISW is positively correlated with the wave amplitude.The increase of the thickness ratio of the upper and lower fluid layers,the density difference and the thickness of the middle fluid layer will lead to the enhancement of the horizontal and vertical flow field of the mode-2 ISW.展开更多
As a kind of statistical method, the technique of Hidden Markov Model （HMM） is widely used for speech recognition. In order to train the HMM to be more effective with much less amount of data, the Subspace Distribut...As a kind of statistical method, the technique of Hidden Markov Model （HMM） is widely used for speech recognition. In order to train the HMM to be more effective with much less amount of data, the Subspace Distribution Clustering Hidden Markov Model （SDCHMM）, derived from the Continuous Density Hidden Markov Model （CDHMM）, is introduced. With parameter tying, a new method to train SDCHMMs is described. Compared with the conventional training method, an SDCHMM recognizer trained by means of the new method achieves higher accuracy and speed. Experiment results show that the SDCHMM recognizer outperforms the CDHMM recognizer on speech recognition of Chinese digits.展开更多
文摘In location-based services, a density query re- turns the regions with high concentrations of moving objects （MOs）. The use of density queries can help users identify crowded regions so as to avoid congestion. Most of the exist- ing methods try very hard to improve the accuracy of query results, but ignore query efficiency. However, response time is also an important concern in query processing and may have an impact on user experience. In order to address this issue, we present a new definition of continuous density queries. Our approach for processing continuous density queries is based on the new notion of a safe interval, using which the states of both dense and sparse regions are dynamically main- tained. Two indexing structures are also used to index candi- date regions for accelerating query processing and improving the quality of results. The efficiency and accuracy of our approach are shown through an experimental comparison with snapshot density queries.
基金supported by the National Natural Science Foundation of China(Grant No.12472247)supported by the Natural Science Foundation of Hunan Province(Grant No.2025JJ60027)+1 种基金the Innovation Research Foundation of National University of Defense Technology(Grant No.ZK24-51)the Science and Technology Innovation Program of Hunan Province(Grant No.2023RC3005).
文摘The mode-2 internal solitary wave(ISW)propagating independently in the stratified ocean is a high-mode internal wave(IW),and its complex wave-flow field will cause the harm to the safe operation of marine engineering structures.In this paper,a fluid environment with a continuous density pycnocline was prepared in a large experimental stratified fluid flume.Based on the principle of ISWs generated by the fluid gravity collapse,a physical experimental method for exciting the“oval”mode-2 ISW solitons by bidirectional fluid gravity collapse in a continuous density pycnocline was proposed.The experimental results showed that the evolution of the upper and lower double vortices near the center of pycnocline is a special generation mechanism of the generation process of mode-2 ISW generated by the gravity collapse of the stratified fluid.The number of generated mode-2 ISW internal solitons depends on the geometric size of fluid gravity collapse region and the geometric thickness ratio of the upper and lower layers of the fluid.The wave evolution process,wave-flow structure,wave-flow characteristics of the“oval”mode-2 ISW in the continuous density pycnocline and its stratified environment effect were obtained.The results showed that the wave speed of the mode-2 ISW increases with the increasing wave amplitude,and the wavelength increases first and then decreases with the increasing wave amplitude.Under the experimental conditions with same wave amplitude,the increase of the thickness ratio of the upper and lower layers of the fluid,the density difference and the thickness of the middle fluid layer would lead to the increase of the wavelength and wave speed of the mode-2 ISW.The velocity range of the mode-2 ISW is positively correlated with the wave amplitude.The increase of the thickness ratio of the upper and lower fluid layers,the density difference and the thickness of the middle fluid layer will lead to the enhancement of the horizontal and vertical flow field of the mode-2 ISW.
基金Supported by the National Natural Science Foundation of China (No.60172048)
文摘As a kind of statistical method, the technique of Hidden Markov Model （HMM） is widely used for speech recognition. In order to train the HMM to be more effective with much less amount of data, the Subspace Distribution Clustering Hidden Markov Model （SDCHMM）, derived from the Continuous Density Hidden Markov Model （CDHMM）, is introduced. With parameter tying, a new method to train SDCHMMs is described. Compared with the conventional training method, an SDCHMM recognizer trained by means of the new method achieves higher accuracy and speed. Experiment results show that the SDCHMM recognizer outperforms the CDHMM recognizer on speech recognition of Chinese digits.
