Detecting feature points on the human body in video frames is a key step for tracking human movements. There have been methods developed that leverage models of human pose and classification of pixels of the body imag...Detecting feature points on the human body in video frames is a key step for tracking human movements. There have been methods developed that leverage models of human pose and classification of pixels of the body image. Yet, occlusion and robustness are still open challenges. In this paper, we present an automatic, model-free feature point detection and action tracking method using a time-of-flight camera. Our method automatically detects feature points for movement abstraction. To overcome errors caused by miss-detection and occlusion, a refinement method is devised that uses the trajectory of the feature points to correct the erroneous detections. Experiments were conducted using videos acquired with a Microsoft Kinect camera and a publicly available video set and comparisons were conducted with the state-of-the-art methods. The results demonstrated that our proposed method delivered improved and reliable performance with an average accuracy in the range of 90 %.The trajectorybased refinement also demonstrated satisfactory effectiveness that recovers the detection with a success rate of 93.7 %. Our method processed a frame in an average time of 71.1 ms.展开更多
目的:探讨压缩感知技术在头颅时间飞跃法磁共振血管造影(TOF-MRA)中的应用价值,并比较不同加速因子对成像的影响。方法:选取在医院同时行头颅并行采集(PI)TOF-MRA和压缩感知(CS)TOF-MRA扫描的21例受试者,根据CS采用的加速因子系数(AF)4....目的:探讨压缩感知技术在头颅时间飞跃法磁共振血管造影(TOF-MRA)中的应用价值,并比较不同加速因子对成像的影响。方法:选取在医院同时行头颅并行采集(PI)TOF-MRA和压缩感知(CS)TOF-MRA扫描的21例受试者,根据CS采用的加速因子系数(AF)4.6和10.3,分别设CS5和CS10,每例患者获得PI、CS5和CS10的3组TOF-MRA图像。定性分析3组图像的诊断质量,分支小血管显示能力,定量分析3组图像的信噪比(SNR)、对比噪声比(CNR)和血管边缘锐利度。结果:PI、CS5和CS10扫描时间分别为4 min 48 s、5 min 4 s和2 min 31 s。图像质量定性评价中CS5优于PI,差异有统计学意义(t=3.062,P<0.05),CS10与PI相当(P=0.086)。图像SNR和CNR定量评估中CS5优于CS10,差异有统计学意义(t=2.744,t=2.428;P<0.05);PI与CS差异无统计学意义。CS图像血管边缘锐利度优于PI,且CS5优于CS10,差异有统计学意义(t=3.729,P<0.05);CS5对分支小血管显示能力最佳。结论:CS技术可缩短头颅TOF-MRA扫描时间,提供与常规PI-TOF相当或更高质量的图像,具有很高的临床应用价值。展开更多
An ionic liquid(IL)electrospray thruster was developed for application in micro-nano satellites or gravitational wave detectors.The thruster employed a porous ceramic emitter with seven emitter strips located on its e...An ionic liquid(IL)electrospray thruster was developed for application in micro-nano satellites or gravitational wave detectors.The thruster employed a porous ceramic emitter with seven emitter strips located on its emission surface.Without any liquid-supply device,IL was delivered through porous media to emitter strips via capillary effect.Multiple emission sites then formed at the tip of each strip.A charged beam of up to 350μA(with a current density of 540μA cm^(-2))was stably produced in the negative mode.However,in the positive mode,a corona was observed which could prevent the thruster from emitting larger current.A time-of-flight mass spectrometer with significantly improved signal-to-noise ratio was built,which was used to obtain the mass distribution of the beam of the thruster.A retarding potential analysis was also performed.The test results showed that the thruster worked in the pure-ion regime,and delivered a maximum thrust of 67.1μN with specific impulses of 3952 s and 3117 s in the positive and negative modes,respectively.展开更多
Constant fraction discriminator （CFD） is one of theoretic method which can locate timing point at same fraction of echo pulse in pulsed time-of-flight （TOF） laser rangefinding. In this paper, the theory of CFD met...Constant fraction discriminator （CFD） is one of theoretic method which can locate timing point at same fraction of echo pulse in pulsed time-of-flight （TOF） laser rangefinding. In this paper, the theory of CFD method was analyzed in reality condition. The design, simulation and printed-circuit-board （PCB） performance of CFD circuit were shown. Finally, an over amplified method was introduced, by which the influence of direct-current （DC） bias error could be reduced. The experimental results showed that timing discriminator could set the timing point to a certain point on echo pulse, which did not depend on the amplitude of echo pulse.展开更多
To increase spatial resolution and signal-to-noise ratio in PET imaging,we present in this paper the design and performance evaluation of a PET detector module combining both depth-of-interaction(DOI) and time-offligh...To increase spatial resolution and signal-to-noise ratio in PET imaging,we present in this paper the design and performance evaluation of a PET detector module combining both depth-of-interaction(DOI) and time-offlight(TOF) capabilities.The detector module consists of a staggered dual-layer LYSO block with2 mm × 2 mm × 7 mm crystals.MR-compatible SiPM sensors(MicroFJ-30035-TSV,SensL) are assembled into an 8× 8 array.SiPM signals from both fast and slow outputs are read out by a 128-channel ASIC chip.To test its performance,a flood histogram is acquired with a ^(22)Na point source on top of the detector,and the energy resolution and the coincidence resolving time(CRT) value for each individual crystal are measured.The flood histogram shows excellent crystal separation in both layers.The average energy resolution at 511 keV is 14.0 and 12.7%at the bottom and top layers,respectively.The average CRT of a single crystal is 635 and 565 ps at the bottom and top layers,respectively.In conclusion,the compact DOI-TOF PET detector module is of excellent crystal identification capability,good energy resolution and reasonable time resolution and has promising application prospective in clinical TOF PET,PET/MRI,and brain PET systems.展开更多
The photoneutron source （PNS, phase 1）, an electron linear accelerator （linac）-based pulsed neutron facility that uses the time-of-flight （TOF） technique, was constructed for the acquisition of nuclear data from...The photoneutron source （PNS, phase 1）, an electron linear accelerator （linac）-based pulsed neutron facility that uses the time-of-flight （TOF） technique, was constructed for the acquisition of nuclear data from the Thorium Molten Salt Reactor （TMSR） at the Shanghai Institute of Applied Physics （SINAP）. The neutron detector signal used for TOF calculation, with information on the pulse arrival time, pulse shape, and pulse height, was recorded by using a waveform digitizer （WFD）. By using the pulse height and pulse-shape discrimination （PSD） analysis to identify neutrons and ＂y-rays, the neutron TOF spectrum was obtained by employing a simple electronic design, and a new WFD-based DAQ system was developed and tested in this commissioning experiment. The DAQ system developed is characterized by a very high efficiency with respect to millisecond neutron TOF spectroscopy.展开更多
文摘Detecting feature points on the human body in video frames is a key step for tracking human movements. There have been methods developed that leverage models of human pose and classification of pixels of the body image. Yet, occlusion and robustness are still open challenges. In this paper, we present an automatic, model-free feature point detection and action tracking method using a time-of-flight camera. Our method automatically detects feature points for movement abstraction. To overcome errors caused by miss-detection and occlusion, a refinement method is devised that uses the trajectory of the feature points to correct the erroneous detections. Experiments were conducted using videos acquired with a Microsoft Kinect camera and a publicly available video set and comparisons were conducted with the state-of-the-art methods. The results demonstrated that our proposed method delivered improved and reliable performance with an average accuracy in the range of 90 %.The trajectorybased refinement also demonstrated satisfactory effectiveness that recovers the detection with a success rate of 93.7 %. Our method processed a frame in an average time of 71.1 ms.
文摘目的:探讨压缩感知技术在头颅时间飞跃法磁共振血管造影(TOF-MRA)中的应用价值,并比较不同加速因子对成像的影响。方法:选取在医院同时行头颅并行采集(PI)TOF-MRA和压缩感知(CS)TOF-MRA扫描的21例受试者,根据CS采用的加速因子系数(AF)4.6和10.3,分别设CS5和CS10,每例患者获得PI、CS5和CS10的3组TOF-MRA图像。定性分析3组图像的诊断质量,分支小血管显示能力,定量分析3组图像的信噪比(SNR)、对比噪声比(CNR)和血管边缘锐利度。结果:PI、CS5和CS10扫描时间分别为4 min 48 s、5 min 4 s和2 min 31 s。图像质量定性评价中CS5优于PI,差异有统计学意义(t=3.062,P<0.05),CS10与PI相当(P=0.086)。图像SNR和CNR定量评估中CS5优于CS10,差异有统计学意义(t=2.744,t=2.428;P<0.05);PI与CS差异无统计学意义。CS图像血管边缘锐利度优于PI,且CS5优于CS10,差异有统计学意义(t=3.729,P<0.05);CS5对分支小血管显示能力最佳。结论:CS技术可缩短头颅TOF-MRA扫描时间,提供与常规PI-TOF相当或更高质量的图像,具有很高的临床应用价值。
文摘An ionic liquid(IL)electrospray thruster was developed for application in micro-nano satellites or gravitational wave detectors.The thruster employed a porous ceramic emitter with seven emitter strips located on its emission surface.Without any liquid-supply device,IL was delivered through porous media to emitter strips via capillary effect.Multiple emission sites then formed at the tip of each strip.A charged beam of up to 350μA(with a current density of 540μA cm^(-2))was stably produced in the negative mode.However,in the positive mode,a corona was observed which could prevent the thruster from emitting larger current.A time-of-flight mass spectrometer with significantly improved signal-to-noise ratio was built,which was used to obtain the mass distribution of the beam of the thruster.A retarding potential analysis was also performed.The test results showed that the thruster worked in the pure-ion regime,and delivered a maximum thrust of 67.1μN with specific impulses of 3952 s and 3117 s in the positive and negative modes,respectively.
基金This work was sponsored by the National Natural Science Foundation of China （Grant No. 40801123）.
文摘Constant fraction discriminator （CFD） is one of theoretic method which can locate timing point at same fraction of echo pulse in pulsed time-of-flight （TOF） laser rangefinding. In this paper, the theory of CFD method was analyzed in reality condition. The design, simulation and printed-circuit-board （PCB） performance of CFD circuit were shown. Finally, an over amplified method was introduced, by which the influence of direct-current （DC） bias error could be reduced. The experimental results showed that timing discriminator could set the timing point to a certain point on echo pulse, which did not depend on the amplitude of echo pulse.
基金supported in part by Fundamental Research Funds for the Central Universities(No.FRF-TP-15-114A1)National Natural Science Foundation of China(Nos.11375096,11505300)Tsinghua University Initiative Scientific Research Program(No.20131089289)
文摘To increase spatial resolution and signal-to-noise ratio in PET imaging,we present in this paper the design and performance evaluation of a PET detector module combining both depth-of-interaction(DOI) and time-offlight(TOF) capabilities.The detector module consists of a staggered dual-layer LYSO block with2 mm × 2 mm × 7 mm crystals.MR-compatible SiPM sensors(MicroFJ-30035-TSV,SensL) are assembled into an 8× 8 array.SiPM signals from both fast and slow outputs are read out by a 128-channel ASIC chip.To test its performance,a flood histogram is acquired with a ^(22)Na point source on top of the detector,and the energy resolution and the coincidence resolving time(CRT) value for each individual crystal are measured.The flood histogram shows excellent crystal separation in both layers.The average energy resolution at 511 keV is 14.0 and 12.7%at the bottom and top layers,respectively.The average CRT of a single crystal is 635 and 565 ps at the bottom and top layers,respectively.In conclusion,the compact DOI-TOF PET detector module is of excellent crystal identification capability,good energy resolution and reasonable time resolution and has promising application prospective in clinical TOF PET,PET/MRI,and brain PET systems.
基金Supported by Strategic Priority Research Program of the Chinese Academy of Science(TMSR)(XDA02010100)National Natural Science Foundation of China(NSFC)(11475245,No.11305239)Shanghai Key Laboratory of Particle Physics and Cosmology(11DZ2260700)
文摘The photoneutron source （PNS, phase 1）, an electron linear accelerator （linac）-based pulsed neutron facility that uses the time-of-flight （TOF） technique, was constructed for the acquisition of nuclear data from the Thorium Molten Salt Reactor （TMSR） at the Shanghai Institute of Applied Physics （SINAP）. The neutron detector signal used for TOF calculation, with information on the pulse arrival time, pulse shape, and pulse height, was recorded by using a waveform digitizer （WFD）. By using the pulse height and pulse-shape discrimination （PSD） analysis to identify neutrons and ＂y-rays, the neutron TOF spectrum was obtained by employing a simple electronic design, and a new WFD-based DAQ system was developed and tested in this commissioning experiment. The DAQ system developed is characterized by a very high efficiency with respect to millisecond neutron TOF spectroscopy.
