We present a theoretical study of the acoustic properties of graphene-semiconductor layered structures. The transmission coefficient for longitudinal acoustic waves through the structure is evaluated by using the usua...We present a theoretical study of the acoustic properties of graphene-semiconductor layered structures. The transmission coefficient for longitudinal acoustic waves through the structure is evaluated by using the usual transfer matrix method. We find that the finite thickness of the graphene layer can affect significantly the transmission spectrum of the proposed structure. The features of the sound transmittance depend strongly on the number of the graphene layers. For mul-ti-layer graphene-semiconductor structures, the sound transmission spectrum looks very similar to that for an ideal superlattice. For such structures, terahertz acoustic forbidden gap can be observed even when a thick semiconductor layer is considered. These results are the consequence of the Bragg’s condition for sound waves. This study is relevant to the exploration of the acoustic properties of graphene-based layered structures and to the application of graphene as high-frequency acoustic devices.展开更多
Machine learning(ML) has been widely applied to the upper layers of wireless communication systems for various purposes, such as deployment of cognitive radio and communication network. However, its application to the...Machine learning(ML) has been widely applied to the upper layers of wireless communication systems for various purposes, such as deployment of cognitive radio and communication network. However, its application to the physical layer is hampered by sophisticated channel environments and limited learning ability of conventional ML algorithms. Deep learning(DL) has been recently applied for many fields, such as computer vision and natural language processing, given its expressive capacity and convenient optimization capability. The potential application of DL to the physical layer has also been increasingly recognized because of the new features for future communications, such as complex scenarios with unknown channel models, high speed and accurate processing requirements; these features challenge conventional communication theories. This paper presents a comprehensive overview of the emerging studies on DL-based physical layer processing, including leveraging DL to redesign a module of the conventional communication system(for modulation recognition, channel decoding, and detection) and replace the communication system with a radically new architecture based on an autoencoder. These DL-based methods show promising performance improvements but have certain limitations, such as lack of solid analytical tools and use of architectures that are specifically designed for communication and implementation research, thereby motivating future research in this field.展开更多
Transpiration element is included in the integrated stomatal conductance photosynthesis model by considering gaseous transfer processes, so the present model is capable to simulate the influence of boundary layer con...Transpiration element is included in the integrated stomatal conductance photosynthesis model by considering gaseous transfer processes, so the present model is capable to simulate the influence of boundary layer conductance. Leuning in his revised Ball's model replaced relative humidity with VPD s (the vapor pressure deficit from stomatal pore to leaf surface) and thereby made the relation with transpiration more straightforward, and made it possible for the regulation of transpiration and the influence of boundary layer conductance to be integrated into the combined model. If the differences in water vapor and CO 2 concentration between leaf and ambient air are considered, VPD s , the evaporative demand, is influenced by stomatal and boundary layer conductance. The physiological responses of photosynthesis, transpiration, and stomatal function, and the changes of intercellular CO 2 and water use efficiency to environmental factors, such as wind speed, photon flux density, leaf temperature and ambient CO 2, are analyzed. It is shown that if the boundary layer conductance drops to a level comparable with stomatal conductance, the results of simulation by the model presented here differ significantly from those by the previous model, and, in some cases, are more realistic than the latter.展开更多
A field experiment was conducted in Tianjin, China from September 9-30, 2010, focused on the evolution of Planetary Boundary Layer （PBL） and its impact on surface air pollutants. The experiment used three remote sen...A field experiment was conducted in Tianjin, China from September 9-30, 2010, focused on the evolution of Planetary Boundary Layer （PBL） and its impact on surface air pollutants. The experiment used three remote sensing instruments, wind profile radar （WPR）, microwave radiometer （MWR） and micro-pulse lidar （MPL）, to detect the vertical profiles of winds, temperature, and aerosol backscattering coefficient and to measure the vertical profiles of surface pollutants （aerosol, CO, SO2, NOx）, and also collected sonic anemometers data from a 255-m meteorological tower. Based on these measurements, the evolution of the PBL was estimated. The averaged PBL height was about 1000-1300 m during noon/afternoon-time, and 200-300 m during night-time. The PBL height and the aerosol concentrations were anti-correlated during clear and haze conditions. The averaged maximum PBL heights were 1.08 and 1.70 km while the averaged aerosol concentrations were 52 and 17 μg/m＆3 under haze and clear sky conditions, respectively, The influence of aerosols and clouds on solar radiation was observed based on sonic anemometers data collected from the 255-m meteorological tower. The heat flux was found significantly decreased by haze （heavy pollution） or cloud, which tended to depress the development of PBL, while the repressed structure of PBL further weakened the diffusion of pollutants, leading to heavy pollution. This possible positive feedback cycle （more aerosols→lower PBL height → more aerosols） would induce an acceleration process for heavy ground pollution in megacities.展开更多
AIM: To investigate potential therapeutic recommendations for endoscopic and surgical resection of T1a/ T1b esophageal neoplasms. METHODS: A thorough search of electronic databases MEDLINE, Embase, Pubmed and Cochrane...AIM: To investigate potential therapeutic recommendations for endoscopic and surgical resection of T1a/ T1b esophageal neoplasms. METHODS: A thorough search of electronic databases MEDLINE, Embase, Pubmed and Cochrane Library, from 1997 up to January 2011 was performed. An analysis was carried out, pooling the effects of outcomes of 4241 patients enrolled in 80 retrospective studies. For comparisons across studies, each reporting on only one endoscopic method, we used a random effects meta-regression of the log-odds of the outcome of treatment in each study. "Neural networks" as a data mining technique was employed in order to establish a prediction model of lymph node status in superficial submucosal esophageal carcinoma. Another data mining technique, the "feature selection and root cause analysis", was used to identify the most impor-tant predictors of local recurrence and metachronous cancer development in endoscopically resected patients, and lymph node positivity in squamous carcinoma (SCC) and adenocarcinoma (ADC) separately in surgically resected patients. RESULTS: Endoscopically resected patients: Low grade dysplasia was observed in 4% of patients, high grade dysplasia in 14.6%, carcinoma in situ in 19%, mucosal cancer in 54%, and submucosal cancer in 16% of patients. There were no significant differences between endoscopic mucosal resection and endoscopic submucosal dissection (ESD) for the following parameters: complications, patients submitted to surgery, positive margins, lymph node positivity, local recurrence and metachronous cancer. With regard to piecemeal resection, ESD performed better since the number of cases was significantly less [coefficient: -7.709438, 95%CI: (-11.03803, -4.380844), P < 0.001]; hence local recurrence rates were significantly lower [coefficient: -4.033528, 95%CI: (-6.151498, -1.915559),P < 0.01]. A higher rate of esophageal stenosis was observed following ESD [coefficient: 7.322266, 95%CI: (3.810146, 10.83439), P < 0.001]. A significantly greater number of SCC patients wer展开更多
文摘We present a theoretical study of the acoustic properties of graphene-semiconductor layered structures. The transmission coefficient for longitudinal acoustic waves through the structure is evaluated by using the usual transfer matrix method. We find that the finite thickness of the graphene layer can affect significantly the transmission spectrum of the proposed structure. The features of the sound transmittance depend strongly on the number of the graphene layers. For mul-ti-layer graphene-semiconductor structures, the sound transmission spectrum looks very similar to that for an ideal superlattice. For such structures, terahertz acoustic forbidden gap can be observed even when a thick semiconductor layer is considered. These results are the consequence of the Bragg’s condition for sound waves. This study is relevant to the exploration of the acoustic properties of graphene-based layered structures and to the application of graphene as high-frequency acoustic devices.
文摘Machine learning(ML) has been widely applied to the upper layers of wireless communication systems for various purposes, such as deployment of cognitive radio and communication network. However, its application to the physical layer is hampered by sophisticated channel environments and limited learning ability of conventional ML algorithms. Deep learning(DL) has been recently applied for many fields, such as computer vision and natural language processing, given its expressive capacity and convenient optimization capability. The potential application of DL to the physical layer has also been increasingly recognized because of the new features for future communications, such as complex scenarios with unknown channel models, high speed and accurate processing requirements; these features challenge conventional communication theories. This paper presents a comprehensive overview of the emerging studies on DL-based physical layer processing, including leveraging DL to redesign a module of the conventional communication system(for modulation recognition, channel decoding, and detection) and replace the communication system with a radically new architecture based on an autoencoder. These DL-based methods show promising performance improvements but have certain limitations, such as lack of solid analytical tools and use of architectures that are specifically designed for communication and implementation research, thereby motivating future research in this field.
文摘Transpiration element is included in the integrated stomatal conductance photosynthesis model by considering gaseous transfer processes, so the present model is capable to simulate the influence of boundary layer conductance. Leuning in his revised Ball's model replaced relative humidity with VPD s (the vapor pressure deficit from stomatal pore to leaf surface) and thereby made the relation with transpiration more straightforward, and made it possible for the regulation of transpiration and the influence of boundary layer conductance to be integrated into the combined model. If the differences in water vapor and CO 2 concentration between leaf and ambient air are considered, VPD s , the evaporative demand, is influenced by stomatal and boundary layer conductance. The physiological responses of photosynthesis, transpiration, and stomatal function, and the changes of intercellular CO 2 and water use efficiency to environmental factors, such as wind speed, photon flux density, leaf temperature and ambient CO 2, are analyzed. It is shown that if the boundary layer conductance drops to a level comparable with stomatal conductance, the results of simulation by the model presented here differ significantly from those by the previous model, and, in some cases, are more realistic than the latter.
基金supported by National Natural Science Foundation of China(NSFC) under Grant Nos.41175007 and 40905060the Project of Scientific and Technological New Star of Beijing under Grant No.2010B029+1 种基金the National Basic Research Program of China(2011CB403401)China Meteorological Administration (CMA) under Grant No.GYHY200806001-4
文摘A field experiment was conducted in Tianjin, China from September 9-30, 2010, focused on the evolution of Planetary Boundary Layer （PBL） and its impact on surface air pollutants. The experiment used three remote sensing instruments, wind profile radar （WPR）, microwave radiometer （MWR） and micro-pulse lidar （MPL）, to detect the vertical profiles of winds, temperature, and aerosol backscattering coefficient and to measure the vertical profiles of surface pollutants （aerosol, CO, SO2, NOx）, and also collected sonic anemometers data from a 255-m meteorological tower. Based on these measurements, the evolution of the PBL was estimated. The averaged PBL height was about 1000-1300 m during noon/afternoon-time, and 200-300 m during night-time. The PBL height and the aerosol concentrations were anti-correlated during clear and haze conditions. The averaged maximum PBL heights were 1.08 and 1.70 km while the averaged aerosol concentrations were 52 and 17 μg/m＆3 under haze and clear sky conditions, respectively, The influence of aerosols and clouds on solar radiation was observed based on sonic anemometers data collected from the 255-m meteorological tower. The heat flux was found significantly decreased by haze （heavy pollution） or cloud, which tended to depress the development of PBL, while the repressed structure of PBL further weakened the diffusion of pollutants, leading to heavy pollution. This possible positive feedback cycle （more aerosols→lower PBL height → more aerosols） would induce an acceleration process for heavy ground pollution in megacities.
文摘AIM: To investigate potential therapeutic recommendations for endoscopic and surgical resection of T1a/ T1b esophageal neoplasms. METHODS: A thorough search of electronic databases MEDLINE, Embase, Pubmed and Cochrane Library, from 1997 up to January 2011 was performed. An analysis was carried out, pooling the effects of outcomes of 4241 patients enrolled in 80 retrospective studies. For comparisons across studies, each reporting on only one endoscopic method, we used a random effects meta-regression of the log-odds of the outcome of treatment in each study. "Neural networks" as a data mining technique was employed in order to establish a prediction model of lymph node status in superficial submucosal esophageal carcinoma. Another data mining technique, the "feature selection and root cause analysis", was used to identify the most impor-tant predictors of local recurrence and metachronous cancer development in endoscopically resected patients, and lymph node positivity in squamous carcinoma (SCC) and adenocarcinoma (ADC) separately in surgically resected patients. RESULTS: Endoscopically resected patients: Low grade dysplasia was observed in 4% of patients, high grade dysplasia in 14.6%, carcinoma in situ in 19%, mucosal cancer in 54%, and submucosal cancer in 16% of patients. There were no significant differences between endoscopic mucosal resection and endoscopic submucosal dissection (ESD) for the following parameters: complications, patients submitted to surgery, positive margins, lymph node positivity, local recurrence and metachronous cancer. With regard to piecemeal resection, ESD performed better since the number of cases was significantly less [coefficient: -7.709438, 95%CI: (-11.03803, -4.380844), P < 0.001]; hence local recurrence rates were significantly lower [coefficient: -4.033528, 95%CI: (-6.151498, -1.915559),P < 0.01]. A higher rate of esophageal stenosis was observed following ESD [coefficient: 7.322266, 95%CI: (3.810146, 10.83439), P < 0.001]. A significantly greater number of SCC patients wer
