47 results on '"Dongwen Zhang"'
Search Results
2. GoDetector: Detecting Concurrent Bug in Go
- Author
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Dongwen Zhang, Penghao Qi, and Yang Zhang
- Subjects
Concurrency bugs ,channel ,WaitGroup ,static analysis ,pushdown automaton ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
Go provides a new concurrency mechanism based on message-passing, which brings a series of new concurrency bugs. The existing tools are highly dependent on model-checking methods in which they take the source program as the input of model-checking tools to detect the potential concurrent bugs. However, these methods can only qualitatively obtain the concurrency of the program but not obtain the exact number of concurrency bugs in the program. Meanwhile, these approaches are not sensitive to dead codes, which are prone to false negatives. Furthermore, few works have been done on detecting WaitGroup-related bugs in Go concurrent programming, which may cause deadlock. To this end, this paper proposes a novel approach GoDetector to detect concurrent bugs. GoDetector uses a detecting algorithm and a pushdown automaton to verify the channel-related concurrent bugs and WaitGroup-related concurrent bugs separately. To support the evaluation of the tool, 30 benchmarks are collected from the existing tools. GoDetector reports 2 channel safety errors, 29 deadlocks, and 11 WaitGroup-related errors. Compared with the existing tool Godel, GoDetector has the capacity to report more concurrency bugs and fewer false positives. GoDetector also offers additional support for the detection of WaitGroup variables. The experimental results indicate that GoDetector is more efficient at detecting the concurrency in regards to accuracy and diversity.
- Published
- 2021
- Full Text
- View/download PDF
3. Enhanced Terahertz Generation From the Lithium Niobate Metasurface
- Author
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Yanyun Tu, Xu Sun, Haizhong Wu, Xiaolei Zan, Yan Yang, Ning Liu, Xiaowei Wang, Congsen Meng, Zhihui Lyu, Zhihong Zhu, Ken Liu, Dongwen Zhang, and Zengxiu Zhao
- Subjects
terahertz ,lithium niobate ,metasurface ,guided-mode resonance ,optical rectification ,Physics ,QC1-999 - Abstract
The lithium niobate (LiNbO3) metasurface is an attractive platform for nonlinear frequency conversion due to its excellent nonlinearity, high damage threshold, and strong enhancement of the driving field. Here, we demonstrated the nonlinear metasurface for terahertz (THz) generation from LiNbO3 on an insulator. The THz electric field from the LiNbO3 metasurface of 300 nm thickness is enhanced by more than one order of magnitude compared to the unstructured sample. The enhanced terahertz electric field is very selective in the excitation wavelength due to its resonant feature and is highly anisotropic with respect to the excitation polarization. The polarization direction of the THz electric field can be controlled by rotating the optical axis of the LiNbO3 metasurface. By combining the nanofabrication technology of the LiNbO3 metasurface and ultrafast nonlinear optics, our work paves the way for the design of new compact terahertz photonic devices that integrate THz emitters into LiNbO3-based chips with multifaceted capabilities.
- Published
- 2022
- Full Text
- View/download PDF
4. Deep Learning-Based Object Detection Improvement for Tomato Disease
- Author
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Yang Zhang, Chenglong Song, and Dongwen Zhang
- Subjects
Faster RCNN ,disease recognition ,deep residual network ,K-means clustering ,disease diagnosis ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
To improve the recognition model accuracy of crop disease leaves and locating diseased leaves, this paper proposes an improved Faster RCNN to detect healthy tomato leaves and four diseases: powdery mildew, blight, leaf mold fungus and ToMV. First, we use a depth residual network to replace VGG16 for image feature extraction so we can obtain deeper disease features. Second, the k-means clustering algorithm is used to cluster the bounding boxes. We improve the anchoring according to the clustering results. The improved anchor frame tends toward the real bounding box of the dataset. Finally, we carry out a k-means experiment with three kinds of different feature extraction networks. The experimental results show that the improved method for crop leaf disease detection had 2.71% higher recognition accuracy and a faster detection speed than the original Faster RCNN.
- Published
- 2020
- Full Text
- View/download PDF
5. Traffic Resource Allocation for Multi-Layer Networks
- Author
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Changfeng Du, Jinlong Ma, and Dongwen Zhang
- Subjects
Multi-layer networks ,traffic capacity ,coupling correlation ,betweenness centrality ,resource allocation ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
Traffic dynamics on multi-layer networks are of great importance to alleviate traffic congestion of real networks. In this work, we focus on information transport in multi-layer networks comprised of two coupled subnetworks. We investigate the relationship between correlated inter-layer couplings and resource allocation strategies on the traffic dynamics of multi-layer networks. Simulation results show that assortative coupling (AC) structure can improve the multi-layer networks traffic capacity more better than disassortative coupling (DC) and random coupling (RC) with degree-based (DE) efficient resources allocation strategy, and DC structure is better in enhancing the traffic capacity with the simplest average resources allocation (SA) strategy. Our work may shed some light on the traffic dynamics on multi-layer networks.
- Published
- 2020
- Full Text
- View/download PDF
6. Non-symmetry and symmetry of syzygies of a system of Cauchy functional equations with a homomorphism
- Author
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Dongwen Zhang, John Michael Rassias, Qi Liu, and Yongjin Li
- Subjects
Symmetry ,functional equations ,new computation techniques ,the alienation phenomenon ,the Cauchy equation ,Mathematics ,QA1-939 - Abstract
Two entirely different Cauchy functional equations have been investigated in the literature with a couple of unknown operators f and g mapping a unitary ring X into a domain of integrity Y satisfying the elimination law and keeping the operations of addition about operator f and multiplication about operator g, respectively. A total of four studying syzygies achieved by multiplying these two fundamental Cauchy functional equations side by side are investigated. The novelty of the literature is to find out sufficient conditions upon [Formula: see text] deriving the model to be produced a strongly alienation phenomenon by using some new computation techniques.
- Published
- 2022
- Full Text
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7. Probing Ultrafast Dynamics of Ferroelectrics by Time‐Resolved Pump‐Probe Spectroscopy
- Author
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Yuan Zhang, Junfeng Dai, Xiangli Zhong, Dongwen Zhang, Gaokuo Zhong, and Jiangyu Li
- Subjects
ferroeletrics ,time‐resolved pump‐probe spectroscopy ,ultrafast dynamics ,Science - Abstract
Abstract Ferroelectric materials have been a key research topic owing to their wide variety of modern electronic and photonic applications. For the quick exploration of higher operating speed, smaller size, and superior efficiencies of novel ferroelectric devices, the ultrafast dynamics of ferroelectrics that directly reflect their respond time and lifetimes have drawn considerable attention. Driven by time‐resolved pump‐probe spectroscopy that allows for probing, controlling, and modulating dynamic processes of ferroelectrics in real‐time, much research efforts have been made to understand and exploit the ultrafast dynamics of ferroelectric. Herein, the current state of ultrafast dynamic features of ferroelectrics tracked by time‐resolved pump‐probe spectroscopy is reviewed, which includes ferroelectrics order parameters of polarization, lattice, spin, electronic excitation, and their coupling. Several potential perspectives and possible further applications combining ultrafast pump‐probe spectroscopy and ferroelectrics are also presented. This review offers a clear guidance of ultrafast dynamics of ferroelectric orders, which may promote the rapid development of next‐generation devices.
- Published
- 2021
- Full Text
- View/download PDF
8. A Note on the Stability of Functional Equations via a Celebrated Direct Method
- Author
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Dongwen Zhang, John Michael Rassias, Qi Liu, and Yongjin Li
- Subjects
Analysis ,QA299.6-433 ,Applied mathematics. Quantitative methods ,T57-57.97 - Abstract
More than ten years after Justyna Sikorska [8] attempted to solve the Heyers-Ulam stability of a single variable equation by using direct method. In this paper, we will improve the results of Justyna Sikorska by using a more efficient approach. Relations between the generalized functional equation, the dependence of their different parameters and several properties are also further explored. To achieve the problem, we try to develop some new techniques to overcome the fundamental difficulties caused by the different properties of the function and the presence of several variables in the equation. Furthermore, we continue to construct and study a couple of functional equations by making a new direct method.
- Published
- 2022
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- View/download PDF
9. Refactoring Java Programs for Customizable Locks Based on Bytecode Transformation
- Author
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Yang Zhang, Shuai Shao, Huan Liu, Jing Qiu, Dongwen Zhang, and Guanghua Zhang
- Subjects
Software refactoring ,synchronization ,consistency ,locks ,program analysis ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
Developers of parallel programming are faced with choices of using various Java locks. Choosing the best lock is a challenging task because a multithreaded application implemented using different locks may end up with uncertain performance. There is a strong need for automated tool support that helps Java programmers choose the best lock for each specific application. This paper presents an automated transformation approach to convert an implementation using a synchronized lock to a ReentrantLock or a ReentrantReadWriteLock at the bytecode level. For the ReentrantLock, our approach runs analysis for global monitors using the visitor pattern in the Joeq compiler. For the ReentrantReadWriteLock, a read or write lock is chosen after a side-effect analysis. Then, the proposed system validates the consistency of the analysis results to ensure a correct sequence of lock usage. Finally, lock operations and related thread communication operations are transformed into a ReentrantLock or a ReentrantReadWriteLock using a bytecode transformation framework Javassist. We validate our approach on several benchmarks including RBTree, PC, SPECjbb2005, and HSQLDB. The experimental results show that the proposed automated transformation approach can transform these benchmarks successfully in a timely fashion.
- Published
- 2019
- Full Text
- View/download PDF
10. Automated Refactoring for Stampedlock
- Author
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Yang Zhang, Shicheng Dong, Xiangyu Zhang, Huan Liu, and Dongwen Zhang
- Subjects
Automated refactoring ,StampedLock ,reentrance analysis ,optimistic read lock ,upgrading/downgrading lock ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
StampedLock, proposed in JDK 1.8, provides many interesting features, such as optimistic read locks and upgrading/downgrading locks to improve the design of concurrent programs instead of employing pure read/write locks. Existing refactorings have proposed algorithms to convert locks, but there are a few refactorings that use these promising features of StampedLock. To illustrate a possible refactoring, this paper first shows three code transformations based on StampedLock. Then, this paper presents CLOCK, an automated refactoring tool that helps developers convert the synchronized lock into the StampedLock. An algorithm for reentrance analysis is proposed for the precondition validation. The write lock, read lock, optimistic read lock, and upgrading/downgrading lock are inferred and refactored. CLOCK is evaluated with the SPECjbb2005 benchmark and two real-world applications, Xalan and FOP. A total of 66 classes are modified by searching approximately 395KSLOC and applying the refactoring, achieving an average of 22 classes per benchmark. The experimental results show that CLOCK can help developers with refactoring for StampedLock and save developer effort.
- Published
- 2019
- Full Text
- View/download PDF
11. Ultrafast Hole Deformation Revealed by Molecular Attosecond Interferometry
- Author
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Yindong Huang, Jing Zhao, Zheng Shu, Yalei Zhu, Jinlei Liu, Wenpu Dong, Xiaowei Wang, Zhihui Lü, Dongwen Zhang, Jianmin Yuan, Jing Chen, and Zengxiu Zhao
- Subjects
Physics ,QC1-999 ,Applied optics. Photonics ,TA1501-1820 - Abstract
Understanding the evolution of molecular electronic structures is the key to explore and control photochemical reactions and photobiological processes. Subjected to strong laser fields, electronic holes are formed upon ionization and evolve in the attosecond timescale. It is crucial to probe the electronic dynamics in real time with attosecond-temporal and atomic-spatial precision. Here, we present molecular attosecond interferometry that enables the in situ manipulation of holes in carbon dioxide molecules via the interferometry of the phase-locked electrons (propagating in opposite directions) of a laser-triggered rotational wave packet. The joint measurement on high-harmonic and terahertz spectroscopy (HATS) provides a unique tool for understanding electron dynamics from picoseconds to attoseconds. The optimum phases of two-color pulses for controlling the electron wave packet are precisely determined owing to the robust reference provided with the terahertz pulse generation. It is noteworthy that the contribution of HOMO-1 and HOMO-2 increases reflecting the deformation of the hole as the harmonic order increases. Our method can be applied to study hole dynamics of complex molecules and electron correlations during the strong-field process. The threefold control through molecular alignment, laser polarization, and the two-color pulse phase delay allows the precise manipulation of the transient hole paving the way for new advances in attochemistry.
- Published
- 2021
- Full Text
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12. The Stability of Functional Equations with a New Direct Method
- Author
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Dongwen Zhang, Qi Liu, John Michael Rassias, and Yongjin Li
- Subjects
Hyers–Ulam stability ,functional equations ,approximation ,the direct method ,the convergence series ,Mathematics ,QA1-939 - Abstract
We investigate the Hyers–Ulam stability of an equation involving a single variable of the form ∥f(x)−αf(kn(x))−βf(kn+1(x))∥⩽u(x) where f is an unknown operator from a nonempty set X into a Banach space Y, and it preserves the addition operation, besides other certain conditions. The theory is employed and stability theorems are proven for various functional equations involving several variables. By comparing this method with the available techniques, it was noticed that this method does not require any restriction on the parity, on the domain, and on the range of the function. Our findings suggest that it is very much easy and more appropriate to apply the proposed method while investigating the stability of functional equations, in particular for several variables.
- Published
- 2022
- Full Text
- View/download PDF
13. A consistency-guaranteed approach for Internet of Things
- Author
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Yang Zhang, Shixin Sun, Dongwen Zhang, Jing Qiu, and Zhihong Tian
- Subjects
Electronic computers. Computer science ,QA75.5-76.95 - Abstract
The software architecture of Internet of Things defines the component model and interconnection topology of Internet of Things systems. Refactoring is a systematic practice of improving a software structure without altering its external behaviors. When the Internet of Things software is refactored, it is necessary to detect the correctness of Internet of Things software to ensure its security. To this end, this article proposes a novel refactoring correction detection approach to ensure software security. Control flow analysis and data flow analysis are used to detect code changes before and after refactoring, and synchronization dependency analysis is used to detect changes in synchronization dependency. Three detection algorithms are designed to detect refactoring correctness. Four real-world benchmark applications are used to evaluate our approach. The experimental results show that our proposed approach can ensure correctness of Internet of Things software refactoring.
- Published
- 2020
- Full Text
- View/download PDF
14. The suppression of pump-to-signal phase distortion transformation for optical parametric amplifiers in both temporal and spatial domains
- Author
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Guobao Jiang, Ying Chen, Dongwen Zhang, and Yuan Zhou
- Subjects
Physics ,QC1-999 - Abstract
During the OPA (optical parametric amplifier) processes pumped by a high-energy laser, the phase distortion of pump light will transmit to the signal light inevitably. As a result, the beam quality of amplified signal will become poor. In this article, a hybrid seeding scheme with a paired two-stage OPA system is used, where the first and second stages used the signal and the idler as seed sources, respectively. The numerical results show that the hybrid seeding OPA scheme can suppress the phase distortion transformation from pump to signal in both spatial and temporal domains. Consequently, the phase of output signal is well restored to its input state. Because of the restriction removal of beam quality for pump light under the conventional birefringent phase-matching method, this scheme had a good application prospect in high-energy OPA or optical parametric chirped pulse amplification systems.
- Published
- 2019
- Full Text
- View/download PDF
15. Numerical study on the characteristics of hybrid seeded femtosecond optical parametric amplifier at mid-infrared wavelength
- Author
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Yuan Zhou, Ying Chen, Dongwen Zhang, Guobao Jiang, Lulu Wang, and Fangrong Hu
- Subjects
Physics ,QC1-999 - Abstract
In the optical parametric amplifier (OPA) process, the phase of the pump is transmitted to the amplified signal due to the spatial walk-off effect and/or a temporal group velocity mismatch (GVM) effect between coherent light waves. As a result, the quality of amplified signal will be reduced by the phase distortion and variation of beam equality of the pump pulse. By using a pair of OPAs, the signal and idler are chosen as seeding lights in the front and back stages, respectively, so that the phase of the amplified signal can be restored, and the influence of phase distortion and beam equality deterioration of pump pulse can be eliminated. The present article also reports other characteristics of this hybrid seeded scheme, including accepted bandwidth, spectral purity, and conversion efficiency.
- Published
- 2019
- Full Text
- View/download PDF
16. Using Trust to Establish a Secure Routing Model in Cognitive Radio Network.
- Author
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Guanghua Zhang, Zhenguo Chen, Liqin Tian, and Dongwen Zhang
- Subjects
Medicine ,Science - Abstract
Specific to the selective forwarding attack on routing in cognitive radio network, this paper proposes a trust-based secure routing model. Through monitoring nodes' forwarding behaviors, trusts of nodes are constructed to identify malicious nodes. In consideration of that routing selection-based model must be closely collaborative with spectrum allocation, a route request piggybacking available spectrum opportunities is sent to non-malicious nodes. In the routing decision phase, nodes' trusts are used to construct available path trusts and delay measurement is combined for making routing decisions. At the same time, according to the trust classification, different responses are made specific to their service requests. By adopting stricter punishment on malicious behaviors from non-trusted nodes, the cooperation of nodes in routing can be stimulated. Simulation results and analysis indicate that this model has good performance in network throughput and end-to-end delay under the selective forwarding attack.
- Published
- 2015
- Full Text
- View/download PDF
17. Probing Ultrafast Dynamics of Ferroelectrics by Time‐Resolved Pump‐Probe Spectroscopy
- Author
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Dongwen Zhang, Gaokuo Zhong, Xiangli Zhong, Yuan Zhang, Jiangyu Li, and Junfeng Dai
- Subjects
Materials science ,General Chemical Engineering ,Science ,General Physics and Astronomy ,Medicine (miscellaneous) ,Physics::Optics ,Reviews ,Review ,Biochemistry, Genetics and Molecular Biology (miscellaneous) ,ferroeletrics ,Condensed Matter::Materials Science ,General Materials Science ,Spectroscopy ,time‐resolved pump‐probe spectroscopy ,Spin-½ ,business.industry ,General Engineering ,Polarization (waves) ,Ferroelectricity ,Coupling (physics) ,ultrafast dynamics ,Optoelectronics ,Photonics ,business ,Ultrashort pulse ,Excitation - Abstract
Ferroelectric materials have been a key research topic owing to their wide variety of modern electronic and photonic applications. For the quick exploration of higher operating speed, smaller size, and superior efficiencies of novel ferroelectric devices, the ultrafast dynamics of ferroelectrics that directly reflect their respond time and lifetimes have drawn considerable attention. Driven by time‐resolved pump‐probe spectroscopy that allows for probing, controlling, and modulating dynamic processes of ferroelectrics in real‐time, much research efforts have been made to understand and exploit the ultrafast dynamics of ferroelectric. Herein, the current state of ultrafast dynamic features of ferroelectrics tracked by time‐resolved pump‐probe spectroscopy is reviewed, which includes ferroelectrics order parameters of polarization, lattice, spin, electronic excitation, and their coupling. Several potential perspectives and possible further applications combining ultrafast pump‐probe spectroscopy and ferroelectrics are also presented. This review offers a clear guidance of ultrafast dynamics of ferroelectric orders, which may promote the rapid development of next‐generation devices., In this review, the ultrafast dynamic features of ferroelectrics, including polarization, lattice, spin, electronic excitation, and their coupling, tracing by time‐resolved pump‐probe spectroscopy are systematically discussed and summarized. The various potential perspectives on ultrafast pump‐probe spectroscopy and the additional nondestructive functionality for ultrafast ferroelectric device design are also presented.
- Published
- 2021
18. Free-Standing Titanium Nitride Films as Carbon-Free Sulfur Hosts for Flexible Lithium-Sulfur Batteries.
- Author
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Cheng Wang, Ruiqing Liu, Yanan Fang, Weiwei Yang, Feng Jin, Min Gu, Dongwen Zhang, Lulu He, Wenxiu Liu, Jianyu Chen, Xiujing Lin, Xiaomiao Feng, and Yanwen Ma
- Abstract
To achieve the commercialization of lithium-sulfur (Li-S) batteries, there is a big challenge to improve the sulfur content and sulfur loading of sulfur cathodes. Although carbonaceous materials can improve the sulfur content and sulfur loading, the addition of binders and conductive agents limits the increase in energy density to a great extent. Here, carbon-free titanium nitride nanobelt (TiN-NB) thin films with flexible, conductive, hierarchically porous, and free-standing structures have been successfully developed to construct high-sulfur-loading and high-energy-density sulfur electrodes. In addition, macroscopically intertwined 3D nanobelt networks can provide an effective transport path for lithium ions and electrons, and a microscopically high specific surface area and porosity provide a necessary guarantee for the adsorption and catalytic transformation of polysulfides. At a sulfur loading of 1.0 mg cm
-2 , the TiN-900@S electrode delivers an initial capacity of 1436.7 mAh g-1 . After 150 cycles, the reversible capacity still remains at 1032.6 mAh g-1 at 0.5C. Precisely, at a high sulfur loading of 7.1 mg cm-2 , the discharge capacity of the TiN-900@S electrode is maintained at 403.1 mAh g-1 after 50 cycles at 0.1C. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
19. Numerical study on the characteristics of hybrid seeded femtosecond optical parametric amplifier at mid-infrared wavelength
- Author
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Ying Chen, Fangrong Hu, Lulu Wang, Dongwen Zhang, Guobao Jiang, and Yuan Zhou
- Subjects
010302 applied physics ,Materials science ,business.industry ,Energy conversion efficiency ,Bandwidth (signal processing) ,Phase distortion ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Optical parametric amplifier ,lcsh:QC1-999 ,Wavelength ,Optics ,0103 physical sciences ,Femtosecond ,Group velocity ,0210 nano-technology ,business ,lcsh:Physics ,Spectral purity - Abstract
In the optical parametric amplifier (OPA) process, the phase of the pump is transmitted to the amplified signal due to the spatial walk-off effect and/or a temporal group velocity mismatch (GVM) effect between coherent light waves. As a result, the quality of amplified signal will be reduced by the phase distortion and variation of beam equality of the pump pulse. By using a pair of OPAs, the signal and idler are chosen as seeding lights in the front and back stages, respectively, so that the phase of the amplified signal can be restored, and the influence of phase distortion and beam equality deterioration of pump pulse can be eliminated. The present article also reports other characteristics of this hybrid seeded scheme, including accepted bandwidth, spectral purity, and conversion efficiency.
- Published
- 2019
20. The reduction of CuO by Si during ball milling
- Author
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Shengqi, Xi, Jingen, Zhou, Xiaotian, Wang, and Dongwen, Zhang
- Published
- 1996
- Full Text
- View/download PDF
21. Using Trust to Establish a Secure Routing Model in Cognitive Radio Network
- Author
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Liqin Tian, Dongwen Zhang, Guanghua Zhang, and Zhen Guo Chen
- Subjects
Routing protocol ,Virtual routing and forwarding ,Dynamic Source Routing ,Computer science ,Equal-cost multi-path routing ,Routing table ,Enhanced Interior Gateway Routing Protocol ,IP forwarding ,Wireless Routing Protocol ,lcsh:Medicine ,Geographic routing ,Throughput ,Trust ,Frequency allocation ,Computer Communication Networks ,Cognition ,Computer Simulation ,Destination-Sequenced Distance Vector routing ,lcsh:Science ,Static routing ,Multidisciplinary ,business.industry ,Policy-based routing ,lcsh:R ,Packet forwarding ,Models, Theoretical ,Radio ,Cognitive radio ,Link-state routing protocol ,Routing domain ,Optimized Link State Routing Protocol ,Multipath routing ,lcsh:Q ,business ,Wireless Technology ,Wireless sensor network ,Research Article ,Computer network - Abstract
Specific to the selective forwarding attack on routing in cognitive radio network, this paper proposes a trust-based secure routing model. Through monitoring nodes’ forwarding behaviors, trusts of nodes are constructed to identify malicious nodes. In consideration of that routing selection-based model must be closely collaborative with spectrum allocation, a route request piggybacking available spectrum opportunities is sent to non-malicious nodes. In the routing decision phase, nodes’ trusts are used to construct available path trusts and delay measurement is combined for making routing decisions. At the same time, according to the trust classification, different responses are made specific to their service requests. By adopting stricter punishment on malicious behaviors from non-trusted nodes, the cooperation of nodes in routing can be stimulated. Simulation results and analysis indicate that this model has good performance in network throughput and end-to-end delay under the selective forwarding attack.
- Published
- 2015
22. Constrained robust model predictive control for time-delay descriptor systems with linear fractional uncertainty
- Author
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Dongwen Zhang
- Subjects
descriptor system ,model predictive control ,linear matrix inequality ,linear fractional uncertainty ,input constrain - Abstract
This paper addresses the robust model predictive control (MPC) for a class of time delay descriptor systems with linear fractional uncertainty and input constrains. The systems are transferred to the piecewise continuous descriptor systems and a piecewise constant control sequence is calculated by minimizing the worst-case quadratic objective function. At each sampling internal, by means of Lyapunov theory and optimization theory, the optimal problem with infinite horizon objective function is reduced to a convex optimization problem involving linear matrix inequalities. The sufficient conditions for the existence of the state feedback control are derived and expressed as linear matrix inequalities. Further, an iterative model predictive control algorithm is proposed for the on-line synthesis of state feedback controllers with the conditions guaranteeing that the closed-loop descriptor systems are regular, impulse-free and robust stable. Finally, a numerical example is presented to show the efficiency of the proposed approach.
- Published
- 2015
23. SRD: Static Data Race Detection for Concurrent Programs.
- Author
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Yang Zhang, Yanan Liang, and Dongwen Zhang
- Subjects
METHODOLOGY ,GRAPHIC methods ,COMPUTER storage devices ,CLOUD storage ,COMPUTER memory management - Abstract
Data race probably occurs when many threads concurrently access the same memory location and at least one is a write thread. Data race detection suffers from false negatives and false positives. How to detect data race and avoid false negatives and false positives has become a hot topic. This paper proposes a static data race detection methodology to eliminate false negatives and false positives. We use Soot to conduct intra-thread and inter-thread analysis. Our data race detection focuses on variable access events that are collected from call graphs. Several program analysis technologies, such as alias variable analysis, alias lock analysis, happens-before analysis, constraint graph, and slicing analysis, are used to improve the coverage and precision of the detection results. In the experimentation, several benchmarks, such as raytracer, sor, and mergesort, have been selected to evaluate our methodology. Experimental results show that SRD can not only eliminate fake races but also identify potential races. Furthermore, SRD can detect more positive races than the existing tool RVPredict. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
24. Application of dual-source CT perfusion imaging and MRI for the diagnosis of primary liver cancer.
- Author
-
DONGWEN ZHANG and AIXIA XU
- Subjects
- *
LIVER cancer , *LIVER , *HEMODYNAMICS , *MEDICAL statistics , *BLOOD flow , *MAGNETIC resonance imaging - Abstract
The objective of the present study was to evaluate the application of dual-source CT perfusion imaging and MRI for the diagnosis of primary liver cancer. Sixty-three patients with primary liver cancer were selected between February 2015 and May 2016. All patients underwent examinations by dual-source CT perfusion imaging and MRI. The perfusion parameters of the focus center and normal liver parenchyma by CT examination and the hemodynamic parameters of the focus center and normal liver parenchyma by MRI examination were analyzed. The accuracy rates of the three detection methods (CT perfusion imaging, MRI, and combined examination) were analyzed and compared by ROC curves. Dual-source CT perfusion imaging revealed that blood flow and blood volume of the focus center were significantly higher than those of normal liver parenchyma (P<0.05). MRI examination showed that hepatic arterial perfusion and hepatic perfusion index of the focus center were significantly higher than those of normal liver parenchyma; portal venous perfusion of the focus center was significantly lower than that of normal liver parenchyma (P<0.05); the difference in total liver perfusion between the focus center and normal liver parenchyma was not significant (P>0.05); the accuracy rates of CT perfusion imaging, MRI, and combined examination were 76.19, 85.71, and 95.24% respectively; the area under the curve of CT perfusion imaging was 0.753 (P<0.05), the sensitivity was 79.2% and the specificity was 74.7%; the area under the curve of MRI was 0.846 (P<0.05), the sensitivity was 84.6%, and the specificity was 80.5%; the area under the curve of CT combined with MRI was 0.947 (P<0.05), the sensitivity was 94.6%, and the specificity was 86.5%. In conclusion, the effect of dual-source CT perfusion imaging combined with MRI for examination of primary liver cancer is superior to that of single use of CT or MRI, and has high clinical application and popularization value. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
25. Filament characterization via resonance absorption of terahertz wave.
- Author
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Zhigang Zheng, Yindong Huang, Quan Guo, Chao Meng, Zhihui Lü, Xiaowei Wang, Jing Zhao, Congsen Meng, Dongwen Zhang, Jianmin Yuan, and Zengxiu Zhao
- Subjects
ELECTRON density ,PHASE shift (Nuclear physics) ,PLASMA waves ,PLASMA gases ,TERAHERTZ spectroscopy - Abstract
In this work, we characterize the transmission properties of the focusing-laser-induced filament by using terahertz (THz) time domain spectroscopy. Significant resonance absorption of the THz wave is identified, which is attributed to the dynamic screening of the ionized electrons. The polarization and intensity of the filament-generated pulse have been varied to study their influences on the resonance absorption. Our results suggest that the electron density of the filament can be determined by fitting the phase shifts and absorption properties around the absorption. This method provides not only an alternative to the plasma diagnostics with plasma frequency at the THz range, but also a supplement to the existing generation theory of THz waves from plasma. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
26. Lock-Free Binary Search Tree Based on Leaf Search.
- Author
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Yang Zhang, Xin Yu, Dongwen Zhang, Mengmeng Wei, and Yanan Liang
- Published
- 2017
- Full Text
- View/download PDF
27. Enhancement of terahertz radiation by using circularly polarized two-color laser fields.
- Author
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Chao Meng, Wenbo Chen, Xiaowei Wang, Zhihui Lü, Yindong Huang, Jinlei Liu, Dongwen Zhang, Zengxiu Zhao, and Jianmin Yuan
- Subjects
SUBMILLIMETER waves ,LASER arrays ,OPTICAL polarization ,IONIZING radiation ,HELICITY of nuclear particles - Abstract
Terahertz radiation from tunneling ionization of gaseous atoms and molecules in the two-color laser fields with various polarizations has been investigated. We experimentally demonstrate that the efficiency of terahertz emission in the circularly polarized laser fields with the same helicity is 5 times higher than that with linearly polarized two-color femtosecond pulses in high laser intensity. By solving time-dependent Schrödinger equation, this enhancement is well explained based on the analysis of electron tunneling ionization and subsequent dynamics. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
28. Research of automatic needle locating based on stereo visual servoing.
- Author
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Sheng Lv, Dongwen Zhang, and Jia Gu
- Published
- 2010
- Full Text
- View/download PDF
29. Implementing and Testing Producer-Consumer Problem Using Aspect-Oriented Programming.
- Author
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Yang Zhang, Jingjun Zhang, and Dongwen Zhang
- Published
- 2009
- Full Text
- View/download PDF
30. Robot-assisted light dose evaluation for endoscopically guided photodynamic therapy: A preliminary study.
- Author
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Dongwen Zhang, Lei Wang, Jia Gu, and Zhen Zheng
- Published
- 2009
- Full Text
- View/download PDF
31. A Novel Gridding Algorithm Using NUFFT with Applications to Ultrasound Diffraction Tomography.
- Author
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Dongwen Zhang, Jinxu Tao, and Hairong Zheng
- Published
- 2008
- Full Text
- View/download PDF
32. Robust Stability of Uncertain Neutral Systems with Time-Varying and Distributed Delays.
- Author
-
Jiqing Qiu, Jinhui Zhang, Yan Shi, Dongwen Zhang, and Peng Shi
- Published
- 2006
- Full Text
- View/download PDF
33. Terahertz electro-optic properties of PbZr0.52Ti0.48O3 and BaTiO3 ferroelectric thin films.
- Author
-
Lei Chen, Yuan Zhang, Quan Guo, Dongwen Zhang, Xiangli Zhong, and Jianmin Yuan
- Subjects
TERAHERTZ materials ,LEAD compounds ,ELECTRIC properties of metals ,OPTICAL properties of metals ,FERROELECTRIC thin films ,BARIUM compounds ,SPECTROMETRY - Abstract
Electro-optic effects of PbZr
0.52 Ti0.48 O3 (PZT) and BaTiO3 (BTO) ferroelectric thin films in the terahertz frequency range are studied with high-sensitive terahertz time-domain spectroscopy. A linear response of PZT film with the linear electro-optic coefficient rc = 6.73 × 10−11 m/V and a quadratic response of BTO film with the second-order electro-optic coefficient Rc = 1.42 × 10−17 m2 /V2 are observed at the frequency of 1 terahertz under the applied static electric field less than 80 kV/cm. The calculation of rc and Rc based on the Landau-Devonshire free energy theory explains the different electro-optic effects of PZT and BTO well. [ABSTRACT FROM AUTHOR]- Published
- 2014
- Full Text
- View/download PDF
34. Dynamic virtual fixture on the Euclidean group for admittance-type manipulator in deforming environments.
- Author
-
Dongwen Zhang, Qingsong Zhu, Jing Xiong, and Lei Wang
- Subjects
- *
DEFORMATIONS (Mechanics) , *EUCLIDEAN domains , *GEOMETRICAL constructions , *MEDICAL robotics , *QUANTITATIVE research , *DEGREES of freedom - Abstract
Background In a deforming anatomic environment, the motion of an instrument suffers from complex geometrical and dynamic constraints, robot assisted minimally invasive surgery therefore requires more sophisticated skills for surgeons. This paper proposes a novel dynamic virtual fixture (DVF) to enhance the surgical operation accuracy of admittance-type medical robotics in the deforming environment. Methods A framework for DVF on the Euclidean Group SE(3) is presented, which unites rotation and translation in a compact form. First, we constructed the holonomic/ non-holonomic constraints, and then searched for the corresponded reference to make a distinction between preferred and non-preferred directions. Second, different control strategies are employed to deal with the tasks along the distinguished directions. The desired spatial compliance matrix is synthesized from an allowable motion screw set to filter out the task unrelated components from manual input, the operator has complete control over the preferred directions; while the relative motion between the surgical instrument and the anatomy structures is actively tracked and cancelled, the deviation relative to the reference is compensated jointly by the operator and DVF controllers. The operator, haptic device, admittance-type proxy and virtual deforming environment are involved in a hardware-in-the-loop experiment, human-robot cooperation with the assistance of DVF controller is carried out on a deforming sphere to simulate beating heart surgery, performance of the proposed DVF on admittance-type proxy is evaluated, and both human factors and control parameters are analyzed. Results The DVF can improve the dynamic properties of human-robot cooperation in a low-frequency (0 ~ 40 rad/sec) deforming environment, and maintain synergy of orientation and translation during the operation. Statistical analysis reveals that the operator has intuitive control over the preferred directions, human and the DVF controller jointly control the motion along the non-preferred directions, the target deformation is tracked activly. Conclusions The proposed DVF for an admittance-type manipulator is capable of assisting the operator to deal with skilled operations in a deforming environment. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
35. Attosecond synchronization of terahertz wave and high-harmonics.
- Author
-
Zhihui Lü, Dongwen Zhang, Chao Meng, Xiyu Du, Zhaoyan Zhou, Yindong Huang, Zengxiu Zhao, and Jianmin Yuan
- Subjects
- *
ATTOSECOND pulses , *SUBMILLIMETER waves , *ELECTRICAL harmonics , *WAVE packets , *ARGON , *IONIZATION (Atomic physics) - Abstract
Argon atom ionizing in the ultrafast two-colour field has been used to investigate the physical mechanism of terahertz (THz) generation. We measured simultaneously pulse energies of THz and high-harmonics as the phase delay between the fundamental and its second harmonic was varied. The optimal phase delay of THz generation is determined according to the inherent attochirp of the emitted high-harmonics. The dynamic analysis of the tunnelling electron wave packet driven by the Coulomb-laser coupling shows that laser-assisted soft collisions of the electron wave packet with the atomic core play a key role. it is demonstrated that the rescattering process, being indispensable in high-harmonic generation processes, dominates THz wave generation as well in a more elaborate way. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
36. An optical tracker based robot registration and servoing method for ultrasound guided percutaneous renal access.
- Author
-
Dongwen Zhang, Zhicheng Li, Ken Chen, Jing Xiong, Xuping Zhang, and Lei Wang
- Subjects
- *
KIDNEY diseases , *ROBOTICS , *MEDICAL imaging systems , *MEDICAL technology , *MEDICAL innovations - Abstract
Background: Robot-assisted needle steering facilitates the percutaneous renal access (PRA) for their accuracy and consistency over manual operation. However, inaccurate image-robot correspondence and uncertainties in robot parameters make the needle track deviate from the intrarenal target. This paper aims to simplify the image-tracker -robot registration procedure and improves the accuracy of needle alignment for robot assisted ultrasound-guided PRA. Methods: First, a semi-automatic rigid registration is used for the alignment of the preoperative MR volume and the intraoperative orthogonal US slices. Passive markers are mounted both on US probe and robot end-effector, the planned puncture path is transferred from the MR volume frame into optical tracker frame. Tracker-robot correspondence and robot calibration are performed iteratively using a simplified scheme, both position and orientation information are incorporated to estimate the transformation matrix, only several key structural robot parameters and joint zeropositions are calibrated for simplicity in solving the inverse kinematic. Furthermore, an optical tracker feedback control is designed for compensating inaccuracies in robot parameters and tracker-robot correspondence, and improving the accuracy of needle alignment. The intervention procedure was implemented by a telemanipulated 5R1P robot, two experiments were conducted to validate the efficiency of robot-tracker registration method and the optical tracker feedback control, robot assisted needle insertion experiment was conducted on kidney phantom to evaluate the system performance. Results: The relative positioning accuracy of needle alignment is 0.24±0.08 mm, the directional accuracy is 6.78±1.65 × 10-4rad; the needle-target distance of needle insertion is 2.15±0. 17 mm. The optical tracker feedback control method performs stable against wide range of angular disturbance over (0 ∼ 0.4) radians, and the length disturbance over (0 ∼ 100) mm. Conclusions: The proposed optical tracker based robot registration and servoing method is capable of accurate three dimension needle operation for PRA procedure with improved precision and shortened time. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
37. Synchronizing Terahertz Wave Generation with Attosecond Bursts.
- Author
-
Dongwen Zhang, Zhihui Lü, Chao Meng, Xiyu Du, Zhaoyan Zhou, Zengxiu Zhao, and Jianmin Yuan
- Subjects
- *
SUBMILLIMETER waves , *ELECTRIC waves , *ELECTRICAL harmonics , *ARGON , *LASER pulses - Abstract
We perform a joint measurement of terahertz waves and high-harmonics generated from argon atoms driven by a fundamental laser pulse and its second harmonic. By correlating their dependence on the phase delay between the two pulses, we determine the generation of THz waves in tens of attoseconds precision. Compared with simulations and models, we find that the laser-assisted soft collision of the electron wave packet with the atomic core plays a key role. It is demonstrated that the rescattering process, being indispensable in high-harmonic generation processes, dominates THz wave generation as well in a more elaborate way. The new finding might be helpful for the full characterization of the rescattering dynamics. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
38. Coherently controlled terahertz source for a time domain spectroscopy system via injection current in bulk ZnSe.
- Author
-
Zhihui Lu, Dongwen Zhang, Zhaoyan Zhou, Lin Sun, Zengxiu Zhao, and Jianmin Yuan
- Published
- 2012
- Full Text
- View/download PDF
39. Generation of 88 as Isolated Attosecond Pulses with Double Optical Gating*.
- Author
-
Xiaowei Wang, Li Wang, Fan Xiao, Dongwen Zhang, Zhihui Lü, Jianmin Yuan, and Zengxiu Zhao
- Subjects
ATTOSECOND pulses ,LASER pulses - Abstract
Isolated attosecond pulses with a duration of 88 as are generated in the spectral range of 29–72 eV using double optical gating technique. The gate width is set to be shorter than half the optical cycle to avoid carrier envelop phase stabilization of the 4.2 fs driving laser pulses centered at 800 nm. The attosecond pulse duration is measured with the technique of frequency resolved optical gating for complete reconstruction of attosecond bursts. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
40. Single-scan detection of arbitrary polarized terahertz wave.
- Author
-
Lu, Zhihui, Dongwen Zhang, Cao Meng, Zengxiu Zhao, and Jianmin Yuan
- Abstract
A polarization sensitive scheme of air-biases-coherent-detection (ABCD) is presented for THz-TDS to directly measure the amplitude and polarization angle of the THz filed, which provides a broad bandwidth coverage from 0.3 to 30 THz. All of the information of arbitrary polarized THz wave can be achieved with just single-scan detection. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
- Full Text
- View/download PDF
41. Controlling the birth of terahertz radiation ticked with attosecond pulses.
- Author
-
Dongwen Zhang, Lv, Zhihui, Xiyu Du, Meng, Chao, Zhaoyan Zhou, Zengxiu Zhao, and Yuan, Jianmin
- Abstract
We perform a joint measurement of terahertz waves and high-order harmonics generated from Argon atoms driven by a fundamental laser pulse and its second harmonic. By correlating their dependence on the phase-delay of the two pulses, we determine the generation of THz waves in tens of attoseconds precision. Compared with simulations and models, we find that the laser-assisted soft-collision of the electron wave packet with the atomic core plays a key role. It is demonstrated that the rescattering process, being indispensable in HHG processes, dominant THz wave generation as well but in a more elaborate way. The new finding might be helpful for the full characterization of the rescattering dynamics. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
- Full Text
- View/download PDF
42. Terahertz radiation from free-free transitions of an atom in strong superposing laser fields.
- Author
-
Dongwen Zhang, Zhaoyan Zhou, Zhihui Lv, Lin Sun, and Jianmin Yuan
- Published
- 2009
- Full Text
- View/download PDF
43. Dynamic virtual fixture on the Euclidean group for admittance-type manipulator in deforming environments
- Author
-
Qingsong Zhu, Dongwen Zhang, Jing Xiong, and Lei Wang
- Subjects
Engineering ,Biomedical Engineering ,Translation (geometry) ,Feedback ,Biomaterials ,Motion ,Control theory ,Virtual fixture ,Humans ,Minimally Invasive Surgical Procedures ,Radiology, Nuclear Medicine and imaging ,Computer vision ,Cooperative Behavior ,Simulation ,Haptic technology ,ComputingMethodologies_COMPUTERGRAPHICS ,Radiological and Ultrasound Technology ,business.industry ,Research ,Robotics ,General Medicine ,Surgery, Computer-Assisted ,Surgical instrument ,Robot ,Artificial intelligence ,business ,Rotation (mathematics) - Abstract
Background In a deforming anatomic environment, the motion of an instrument suffers from complex geometrical and dynamic constraints, robot assisted minimally invasive surgery therefore requires more sophisticated skills for surgeons. This paper proposes a novel dynamic virtual fixture (DVF) to enhance the surgical operation accuracy of admittance-type medical robotics in the deforming environment. Methods A framework for DVF on the Euclidean Group SE(3) is presented, which unites rotation and translation in a compact form. First, we constructed the holonomic/non-holonomic constraints, and then searched for the corresponded reference to make a distinction between preferred and non-preferred directions. Second, different control strategies are employed to deal with the tasks along the distinguished directions. The desired spatial compliance matrix is synthesized from an allowable motion screw set to filter out the task unrelated components from manual input, the operator has complete control over the preferred directions; while the relative motion between the surgical instrument and the anatomy structures is actively tracked and cancelled, the deviation relative to the reference is compensated jointly by the operator and DVF controllers. The operator, haptic device, admittance-type proxy and virtual deforming environment are involved in a hardware-in-the-loop experiment, human-robot cooperation with the assistance of DVF controller is carried out on a deforming sphere to simulate beating heart surgery, performance of the proposed DVF on admittance-type proxy is evaluated, and both human factors and control parameters are analyzed. Results The DVF can improve the dynamic properties of human-robot cooperation in a low-frequency (0 ~ 40 rad/sec) deforming environment, and maintain synergy of orientation and translation during the operation. Statistical analysis reveals that the operator has intuitive control over the preferred directions, human and the DVF controller jointly control the motion along the non-preferred directions, the target deformation is tracked actively. Conclusions The proposed DVF for an admittance-type manipulator is capable of assisting the operator to deal with skilled operations in a deforming environment.
- Full Text
- View/download PDF
44. An optical tracker based robot registration and servoing method for ultrasound guided percutaneous renal access
- Author
-
Ken Chen, Jing Xiong, Lei Wang, Zhicheng Li, Xuping Zhang, and Dongwen Zhang
- Subjects
Engineering ,Optical Phenomena ,Robot calibration ,Biomedical Engineering ,Kinematics ,Kidney ,Imaging phantom ,Feedback ,Biomaterials ,Image Processing, Computer-Assisted ,Calibration ,Humans ,Minimally Invasive Surgical Procedures ,Radiology, Nuclear Medicine and imaging ,Computer vision ,Skin ,Ultrasonography ,Radiological and Ultrasound Technology ,business.industry ,Orientation (computer vision) ,Research ,Frame (networking) ,Robotics ,General Medicine ,Surgery, Computer-Assisted ,Needles ,Robot ,Artificial intelligence ,business - Abstract
Background Robot-assisted needle steering facilitates the percutaneous renal access (PRA) for their accuracy and consistency over manual operation. However, inaccurate image-robot correspondence and uncertainties in robot parameters make the needle track deviate from the intrarenal target. This paper aims to simplify the image-tracker-robot registration procedure and improves the accuracy of needle alignment for robot assisted ultrasound-guided PRA. Methods First, a semi-automatic rigid registration is used for the alignment of the preoperative MR volume and the intraoperative orthogonal US slices. Passive markers are mounted both on US probe and robot end-effector, the planned puncture path is transferred from the MR volume frame into optical tracker frame. Tracker-robot correspondence and robot calibration are performed iteratively using a simplified scheme, both position and orientation information are incorporated to estimate the transformation matrix, only several key structural robot parameters and joint zero-positions are calibrated for simplicity in solving the inverse kinematic. Furthermore, an optical tracker feedback control is designed for compensating inaccuracies in robot parameters and tracker-robot correspondence, and improving the accuracy of needle alignment. The intervention procedure was implemented by a telemanipulated 5R1P robot, two experiments were conducted to validate the efficiency of robot-tracker registration method and the optical tracker feedback control, robot assisted needle insertion experiment was conducted on kidney phantom to evaluate the system performance. Results The relative positioning accuracy of needle alignment is 0.24 ± 0.08 mm, the directional accuracy is 6.78 ± 1.65 × 10-4rad; the needle-target distance of needle insertion is 2.15 ± 0. 17 mm. The optical tracker feedback control method performs stable against wide range of angular disturbance over (0 ~ 0.4) radians, and the length disturbance over (0 ~ 100) mm. Conclusions The proposed optical tracker based robot registration and servoing method is capable of accurate three dimension needle operation for PRA procedure with improved precision and shortened time.
- Full Text
- View/download PDF
45. High-harmonic and terahertz wave spectroscopy (HATS) for aligned molecules.
- Author
-
Yindong Huang, Chao Meng, Jing Zhao, Xiaowei Wang, Zhihui Lü, Dongwen Zhang, Zengxiu Zhao, and Jianmin Yuan
- Subjects
HARMONIC generation ,SUBMILLIMETER wave generation - Abstract
We present the experimental and theoretical details of our recent published letter Huang et al (2015 Phys. Rev. Lett.115 123002) on synchronized high-harmonic and terahertz-wave spectroscopy (HATS) from nonadiabatically aligned nitrogen molecules in dual-color laser fields. By associating alignment-angle dependent terahertz wave generation (TWG) with high harmonic generation (HHG), the angular differential photoionization cross section (PICS) for molecules can be reconstructed. The angles at which the PICS’s minima are located show great convergence between the theoretical predictions and the experimentally deduced results when choosing a suitable internuclear distance. We also show the optimal relative phase between the dual-color laser fields for TWG does not change with the alignment angle at a precision of about 50 attoseconds. This all-optical method provides an alternative for investigating molecular structures and dynamics. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
46. Joint Measurements of Terahertz Wave Generation and High-Harmonic Generation from Aligned Nitrogen Molecules Reveal Angle-Resolved Molecular Structures.
- Author
-
Yindong Huang, Chao Meng, Xiaowei Wang, Zhihui Liü, Dongwen Zhang, Wenbo Chen, Jing Zhao, Jianmin Yuan, and Zengxiu Zhao
- Subjects
- *
SUBMILLIMETER waves , *NITROGEN , *MOLECULAR physics , *MOLECULAR structure , *PHOTOIONIZATION - Abstract
We report the synchronized measurements of terahertz wave generation and high-harmonic generation from aligned nitrogen molecules in dual-color laser fields. Both yields are found to be alignment dependent, showing the importance of molecular structures in the generation processes. By calibrating the angular ionization rates with the terahertz yields, we present a new way of retrieving the angular differential photoionization cross section (PICS) from the harmonic signals which avoids specific model calculations or separate measurements of the alignment-dependent ionization rates. The measured PICS is found to be consistent with theoretical predications, although some discrepancies exist. This all-optical method provides a new alternative for investigating molecular structures. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
47. Theoretical study of terahertz generation from atoms and aligned molecules driven by two-color laser fields.
- Author
-
Wenbo Chen, Yindong Huang, Chao Meng, Jinlei Liu, Zhaoyan Zhou, Dongwen Zhang, Jianmin Yuan, and Zengxiu Zhao
- Subjects
- *
RADIATION , *THERMOCHROMISM , *ATOMS , *COMPUTER simulation , *WAVELENGTHS - Abstract
We study the generation of terahertz radiation from atoms and molecules driven by an ultrashort fundamental laser and its second-harmonic field by solving the time-dependent Schrödinger equation (TDSE). The comparisons between one-, two-, and three-dimensional TDSE numerical simulations show that the initial ionized wave packet and its subsequent acceleration in the laser field and rescattering with long-range Coulomb potential play key roles. We also present the dependence of the optimum phase delay and yield of terahertz radiation on the laser intensity, wavelength, duration, and ratio of two-color laser components. Terahertz wave generation from model hydrogen molecules is further investigated by comparing with high harmonic emission. It is found that the terahertz yield follows the alignment dependence of the ionization rate, while the optimal two-color phase delays vary by a small amount when the alignment angle changes from 0 to 90 degrees, which reflects the alignment dependence of attosecond electron dynamics. Finally, we show that terahertz emission might be used to clarify the origin of interference in high harmonic generation from aligned molecules by coincidentally measuring the alignment-dependent THz yields. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
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