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Search Results: 1 - 10 of 50939 matches for " Kunlin Wei "
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Uncertainty of feedback and state estimation determines the speed of motor adaptation
Kunlin Wei,Konrad K?rding
Frontiers in Computational Neuroscience , 2010, DOI: 10.3389/fncom.2010.00011
Abstract: Humans can adapt their motor behaviors to deal with ongoing changes. To achieve this, the nervous system needs to estimate central variables for our movement based on past knowledge and new feedback, both of which are uncertain. In the Bayesian framework, rates of adaptation characterize how noisy feedback is in comparison to the uncertainty of the state estimate. The predictions of Bayesian models are intuitive: the nervous system should adapt slower when sensory feedback is more noisy and faster when its state estimate is more uncertain. Here we want to quantitatively understand how uncertainty in these two factors affects motor adaptation. In a hand reaching experiment we measured trial-by-trial adaptation to a randomly changing visual perturbation to characterize the way the nervous system handles uncertainty in state estimation and feedback. We found both qualitative predictions of Bayesian models confirmed. Our study provides evidence that the nervous system represents and uses uncertainty in state estimate and feedback during motor adaptation.
Credit Assignment during Movement Reinforcement Learning
Gregory Dam, Konrad Kording, Kunlin Wei
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0055352
Abstract: We often need to learn how to move based on a single performance measure that reflects the overall success of our movements. However, movements have many properties, such as their trajectories, speeds and timing of end-points, thus the brain needs to decide which properties of movements should be improved; it needs to solve the credit assignment problem. Currently, little is known about how humans solve credit assignment problems in the context of reinforcement learning. Here we tested how human participants solve such problems during a trajectory-learning task. Without an explicitly-defined target movement, participants made hand reaches and received monetary rewards as feedback on a trial-by-trial basis. The curvature and direction of the attempted reach trajectories determined the monetary rewards received in a manner that can be manipulated experimentally. Based on the history of action-reward pairs, participants quickly solved the credit assignment problem and learned the implicit payoff function. A Bayesian credit-assignment model with built-in forgetting accurately predicts their trial-by-trial learning.
Lower Limb Wearable Capacitive Sensing and Its Applications to Recognizing Human Gaits
Enhao Zheng,Baojun Chen,Kunlin Wei,Qining Wang
Sensors , 2013, DOI: 10.3390/s131013334
Abstract: In this paper, we present an approach to sense human body capacitance and apply it to recognize lower limb locomotion modes. The proposed wearable sensing system includes sensing bands, a signal processing circuit and a gait event detection module. Experiments on long-term working stability, adaptability to disturbance and locomotion mode recognition are carried out to validate the effectiveness of the proposed approach. Twelve able-bodied subjects are recruited, and eleven normal gait modes are investigated. With an event-dependent linear discriminant analysis classifier and feature selection procedure, four time-domain features are used for pattern recognition and satisfactory recognition accuracies (97:3% ± 0:5%, 97:0% ± 0:4%, 95:6% ± 0:9% and 97:0% ± 0:4% for four phases of one gait cycle respectively) are obtained. The accuracies are comparable with that from electromyography-based systems and inertial-based systems. The results validate the effectiveness of the proposed lower limb capacitive sensing approach in recognizing human normal gaits.
Bayesian Integration and Non-Linear Feedback Control in a Full-Body Motor Task
Ian H. Stevenson ,Hugo L. Fernandes,Iris Vilares,Kunlin Wei,Konrad P. K?rding
PLOS Computational Biology , 2009, DOI: 10.1371/journal.pcbi.1000629
Abstract: A large number of experiments have asked to what degree human reaching movements can be understood as being close to optimal in a statistical sense. However, little is known about whether these principles are relevant for other classes of movements. Here we analyzed movement in a task that is similar to surfing or snowboarding. Human subjects stand on a force plate that measures their center of pressure. This center of pressure affects the acceleration of a cursor that is displayed in a noisy fashion (as a cloud of dots) on a projection screen while the subject is incentivized to keep the cursor close to a fixed position. We find that salient aspects of observed behavior are well-described by optimal control models where a Bayesian estimation model (Kalman filter) is combined with an optimal controller (either a Linear-Quadratic-Regulator or Bang-bang controller). We find evidence that subjects integrate information over time taking into account uncertainty. However, behavior in this continuous steering task appears to be a highly non-linear function of the visual feedback. While the nervous system appears to implement Bayes-like mechanisms for a full-body, dynamic task, it may additionally take into account the specific costs and constraints of the task.
Systematic evaluation of genome-wide methylated DNA enrichment using a CpG island array
Liu Yang, Kunlin Zhang, Wei Dai, Ximiao He, Qian Zhao, Jing Wang, Zhong Sun
BMC Genomics , 2011, DOI: 10.1186/1471-2164-12-10
Abstract: In order to evaluate the sensitivity and accuracy of methylated DNA enrichment, we investigated and optimized a number of important parameters to improve the performance of several enrichment assays, including differential methylation hybridization (DMH), microarray-based methylation assessment of single samples (MMASS), and methylated DNA immunoprecipitation (MeDIP). With advantages and disadvantages unique to each approach, we found that assays based on methylation-sensitive enzyme digestion and those based on immunoprecipitation detected different methylated DNA fragments, indicating that they are complementary in their relative ability to detect methylation differences.Our study provides the first comprehensive evaluation for widely used methodologies for methylated DNA enrichment, and could be helpful for developing a cost effective approach for DNA methylation profiling.The most widely studied epigenetic modification in humans is cytosine methylation at CpG dinucleotides. Computational analysis predictions have indicated there are about 29,000 CpG islands in the human genome [1,2]. Approximately 70% of CpG dinucleotides in mammals are methylated and found in repetitive elements [3] whereas most CpG islands with relative high densities of unmehylated CpG dinucleotides are located at the promoter region of house-keeping genes and tumor suppressor genes and play important roles in gene expression regulation and cellular differentiation [4]. Additionally, researchers have found that DNA methylation changes occur in human cancers [5], and researches in this area have established that hypermethylation of CpG islands tends to silence tumor suppressor genes and that hypomethylation activates oncogenes [6-8].Many approaches for detecting DNA methylation are done in a gene-specific manner, such as bisulfite treatment of DNA combined with sequencing, amplification by methylation-specific PCR, or restriction enzyme-based digestion. These techniques are limited to study kn
Chemical Doping and Enhanced Solar Energy Conversion of Graphene/Silicon Junctions
Xinming Li,Hongwei Zhu,Kunlin Wang,Jinquan Wei,Guifeng Fan,Xiao Li,Dehai Wu
Physics , 2010,
Abstract: The effect of chemical doping of graphene films on the photovoltaic properties of the graphene/silicon Schottky junction solar cells was investigated. Thionyl chloride modification greatly enhanced the conductivity of graphene film, resulting in a significant improvement in cell performance with a 3-fold increase in conversion efficiency (up to 3.9%) and good short-term stability.
Luminescence of carbon nanotube bulbs
ChuanGang Li,KunLin Wang,JinQuan Wei,BingQing Wei,HongWei Zhu,ZhiCheng Wang,JianBin Luo,WenJin Liu,MingXin Zheng,DeHai Wu
Chinese Science Bulletin , 2007, DOI: 10.1007/s11434-007-2211-8
Abstract: Carbon nanotube (CNT) bulbs made of decimeter-scale double-walled carbon nanotube (DWCNT) strands and films were fabricated and their luminescence properties, including the lighting efficiency, voltage-current relation and thermal stability were investigated. The results show that the DWCNT bulb has a comparable spectrum of visible light with tungsten bulb and its average efficiency is 40% higher than that of a tungsten filament at the same temperature (1400–2300 K). The nanotube filaments show both resistance and thermal stability over a large temperature region. No obvious damage was found for a nanotube bulb illuminating at 2300 K for more than 24 hours in vacuum.
Spread of double-walled carbon nanotube membrane
Yi Jia,JinQuan Wei,QinKe Shu,JianGuo Chang,KunLin Wang,ZhiCheng Wang,JianBin Luo,WenJin Liu,MingXin Zheng,DeHai Wu
Chinese Science Bulletin , 2007, DOI: 10.1007/s11434-007-0068-5
Abstract: A single-layer double-walled carbon nanotube (DWNT) membrane, with 100 cm2 in area, 50 nm in thickness, was spread by adding a few drops of ethanol (or acetone) on the purified DWNTs. Compared with acetone, ethanol is more efficient in spreading DWNT films. The spreading rate of DWNT membrane increases with the ethanol concentration, and it also first increases with temperature (below 60°C), then decreases as the temperature rises to above 60°C.
Neurogenesis in the aging brain
Veronica Galvan,Kunlin Jin
Clinical Interventions in Aging , 2007,
Abstract: Veronica Galvan, Kunlin JinBuck Institute for Age Research, 8001 Redwood Blvd. Novato, CA, USAAbstract: Neurogenesis, or the birth of new neural cells, was thought to occur only in the developing nervous system and a fixed neuronal population in the adult brain was believed to be necessary to maintain the functional stability of adult brain circuitry. However, recent studies have demonstrated that neurogenesis does indeed continue into and throughout adult life in discrete regions of the central nervous systems (CNS) of all mammals, including humans. Although neurogenesis may contribute to the ability of the adult brain to function normally and be induced in response to cerebral diseases for self-repair, this nevertheless declines with advancing age. Understanding the basic biology of neural stem cells and the molecular and cellular regulation mechanisms of neurogenesis in young and aged brain will allow us to modulate cell replacement processes in the adult brain for the maintenance of healthy brain tissues and for repair of disease states in the elderly.Keywords: neurogenesis, aging, brain, neural stem cells, subgranular zone, subventricular zone
Luminescence of carbon nanotube bulbs
LI ChuanGang,
LI
,ChuanGang,WANG,KunLin,WEI,JinQuan,WEI,BingQing,ZHU,HongWei,WANG,ZhiCheng,LUO,JianBin,LIU,WenJin,ZHENG,MingXin,WU,DeHai

科学通报(英文版) , 2007,
Abstract: Carbon nanotube (CNT) bulbs made of decimeter-scale double-walled carbon nanotube (DWCNT) strands and films were fabricated and their luminescence properties, including the lighting efficiency, voltage-current relation and thermal stability were investigated. The results show that the DWCNT bulb has a comparable spectrum of visible light with tungsten bulb and its average efficiency is 40% higher than that of a tungsten filament at the same temperature (1400–2300 K). The nanotube filaments show both resistance and thermal stability over a large temperature region. No obvious damage was found for a nanotube bulb illuminating at 2300 K for more than 24 hours in vacuum. Supported by the National Center for Nanoscience and Technology, China
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