Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99


Any time

2020 ( 4 )

2019 ( 195 )

2018 ( 1241 )

2017 ( 1090 )

Custom range...

Search Results: 1 - 10 of 90009 matches for " Chen X "
All listed articles are free for downloading (OA Articles)
Page 1 /90009
Display every page Item
An ARX-Based PID-Sliding Mode Control on Velocity Tracking Control of a Stick-Slip Pi-ezoelectric-Driven Actuator  [PDF]
Y. Cao, X. B. Chen
Modern Mechanical Engineering (MME) , 2015, DOI: 10.4236/mme.2015.51002
Abstract: Piezoelectric-driven stick slip actuators have been drawn more and more attention in the nano- positioning application due to the high accuracy and theoretical unlimited displacement. However, the hysteresis of piezoelectric actuator (PEA) and the nonlinear friction force between the end- effector and the stage make control of piezoelectric-driven stick slip actuator challenge. This paper presents the development of an autoregressive exogenous (ARX)-based proportional-integral-derive (PID)-sliding mode control (SMC) for the velocity tracking control of the piezoelectric-driven stick slip actuator. Stability is guaranteed by rigorously choosing the appropriate PID parameters and the zero steady state error is achieved. To verify the effectiveness of the proposed method, experiments were carried out on a commercially-available piezoelectric-driven stick slip actuator. The tracking errors were compared with the traditional PID controller, illustrating that in spite of existing of modeling error, the ARX-based PID-SMC is able to better improve the velocity tracking performance of piezoelectric-driven stick slip actuator, compared with the traditional PID controller.
On K?hler manifolds with positive orthogonal bisectional curvature
X. X. Chen
Mathematics , 2006,
Abstract: In this paper, we study any K\"ahler manifold where the positive orthogonal bisectional curvature is preserved on the K\"ahler Ricci flow. Naturally, we always assume that the first Chern class $C_1$ is positive. In particular, we prove that any irreducible K\"ahler manifold with such property must be biholomorphic to $\mathbb{C}\mathbb{P}^n. $ This can be viewed as a generalization of Siu-Yau\cite{Siuy80}, Morri's solution \cite{Mori79} of the Frankel conjecture. According to [8], note that any K\"ahler manifold with 2-positive traceless bisectional curvature operator is preserved under Kahler Ricci flow; which in turns implies the positivity of orthogonal bisectional curvature under the flow.
Space of K?hler metrics III--On the lower bound of the Calabi energy and geodesic distance
X. X. Chen
Mathematics , 2006,
Abstract: In this paper, we first prove a folklore conjecture on a greatest lower bound of the Calabi energy in all K\"ahler manifold. Similar result in algebriac setting was obtained by S. K. Donaldson. Secondly, we give an upper/lower bound estimate of the K energy in terms of the geodesic distance and the Calabi energy. This is used to prove a theorem on convergence of K\"ahler metrics in holomorphic coordinates, with uniform bound on the Ricci curvature and the diameter. Thirdly, we set up a framework for the existence of geodesic rays when an asymptotic direction is given. I
Synthetic Pattern of Fish Diversity in Alabama, USA
Chen, X.
Wildlife Biology in Practice , 2006,
Abstract: The state of Alabama has a rich fish fauna. Analyzing the current distributional patterns of fish diversity by synthesizing information and integrating different spatial and temporal scales is important for understanding the underlying mechanisms of diversity and making strategies for fish conservation. Basing the study on long-term intensive samples (9,244 collections) of fish species at 3,716 field stations across Alabama from 1845 to 1994, I analyzed the general pattern of fish diversity in Alabama at the county level. The results indicate that more than half the area of Alabama has high fish diversity, including fish species endemic to the USA. Most of the counties with the highest fish diversity are in southwestern Alabama. Nonnative fish species occurred mainly in the southernmost counties, such as Mobile and Baldwin. Twelve counties have the rare species which has only one occurence location in each country, with Lauderdale County having the most (10 rare species); the counties with the rare species are generally distributed at the four corner areas of the state boundaries, particularly on the northern and southern boundaries. A high positive correlation exists between species diversity and endemic species, but there is no significant correlation between species diversity and diversification. Both Power-law and logarithmic relationships exist between class of species diversity and its frequency; counties with higher fish diversity tend to have low human-population densities, and are located at or nearby the Alluvial-deltaic Plain and Gulf Coast floodplain.
Topological properties in the spatial distribution of amphibians in Alabama USA for the use of large scale conservation
X. Chen
Animal Biodiversity and Conservation , 2008,
Abstract: Large-scale biodiversity conservation is urgently needed due to increasing habitat loss and fragmentation. Understanding topological perspectives of species' distribution patterns can provide useful information for linking conservation studies at larger scales. We studied topological properties of localities in Alabama where 60 species of 12 families of amphibians were present. Analysis included a clustering coefficient which measures the strength of a population group, the relationship between occurrence localities and species number, the fractal dimension of occurrence localities (which emphasizes spatial irregularity), and distance to nearest-neighbor. The results indicate that the clustering coefficients of most amphibian species were low, but were higher for species with few occurrence localities, such as Rana sylvatica and Limnaoedus ocularis. The general relationship between species number and occurrence localities was that the majority of species held few localities in their distribution, while the remaining species occupied a greater number of localities. The fractal dimension (FD) for all amphibian localities was about 1.58, although FD was low for most individual species. We identified four relationships in the distribution of distance to nearest-neighbor: linear, logarithmic, power and polynomial. These topological properties may indicate intrinsic features about amphibians in Alabama and provide useful information for regional planning. Enhancing landscape linkages across a large area using undisturbed areas, such as 300-500 km in diameter may be a good approach to conservation practice in this region. Steps needed for biodiversity conservation planning in Alabama include creating or conserving small habitats across agricultural and urban land, and maintaining suitable spatial complexity and distance to nearest neighbors.
A Legacy System Encapsulation Strategy Based on Web Service  [PDF]
D. J. Chen, X. Y. Li
Creative Education (CE) , 2012, DOI: 10.4236/ce.2012.37B014

In order to migrate the enterprise legacy system to the web, a multi-agent based legacy system encapsulation model is proposed.  Firstly, the characteristics of legacy system are analyzed, and then the data and functions that need to be published are confirmed. Secondly the legacy system is wrapped into web components with common interface, and these components are managed by the application server. Thirdly, the clients can send requests to the application server, and receive the return result from the application server.  Due to adoption of wrapping technology for legacy system, original security and stability of legacy system are guaranteed in the web components. Finally, the validity and practicability of the migration technology are verified through the application in the encapsulation of Matlab as web components.

Real-Time Timing Channel Detection in a Software-Defined Networking Virtual Environment  [PDF]
Anyi Liu, Jim X. Chen, Harry Wechsler
Intelligent Information Management (IIM) , 2015, DOI: 10.4236/iim.2015.76023
Abstract: Despite extensive research, timing channels (TCs) are still known as a principal category of threats that aim to leak and transmit information by perturbing the timing or ordering of events. Existing TC detection approaches use either signature-based approaches to detect known TCs or anomaly-based approach by modeling the legitimate network traffic in order to detect unknown TCs. Un-fortunately, in a software-defined networking (SDN) environment, most existing TC detection approaches would fail due to factors such as volatile network traffic, imprecise timekeeping mechanisms, and dynamic network topology. Furthermore, stealthy TCs can be designed to mimic the legitimate traffic pattern and thus evade anomalous TC detection. In this paper, we overcome the above challenges by presenting a novel framework that harnesses the advantages of elastic re-sources in the cloud. In particular, our framework dynamically configures SDN to enable/disable differential analysis against outbound network flows of different virtual machines (VMs). Our framework is tightly coupled with a new metric that first decomposes the timing data of network flows into a number of using the discrete wavelet-based multi-resolution transform (DWMT). It then applies the Kullback-Leibler divergence (KLD) to measure the variance among flow pairs. The appealing feature of our approach is that, compared with the existing anomaly detection approaches, it can detect most existing and some new stealthy TCs without legitimate traffic for modeling, even with the presence of noise and imprecise timekeeping mechanism in an SDN virtual environment. We implement our framework as a prototype system, OBSERVER, which can be dynamically deployed in an SDN environment. Empirical evaluation shows that our approach can efficiently detect TCs with a higher detection rate, lower latency, and negligible performance overhead compared to existing approaches.
The Space of K?hler metrics (II)
E. Calabi,X. X. Chen
Mathematics , 2001,
Abstract: This paper, the second of a series, deals with the function space of all smooth K\"ahler metrics in any given closed complex manifold $M$ in a fixed cohomology class. The previous result of the second author \cite{chen991} showed that the space is a path length space and it is geodesically convex in the sense that any two points are joined by a unique path, which is always length minimizing and of class C^{1,1}. This already confirms one of Donaldson's conjecture completely and verifies another one partially. In the present paper, we show first of all, that the space is, as expected, a path length space of non-positive curvature in the sense of A. D. Alexanderov. The second result is related to the theory of extremal K\"ahler metrics, namely that the gradient flow of the K energy is strictly length decreasing on all paths except those induced by a path of holomorphic automorphisms of $M$. This result, in particular, implies that extremal K\"ahler metric is unique up to holomorphic transformations, provided that Donaldson's conjecture on the regularity of geodesic is true.
Ricci flow on K?hler-Einstein manifolds
X. X. Chen,G. Tian
Mathematics , 2001, DOI: 10.1007/s002220100181
Abstract: In our previous paper math.DG/0010008, we develop some new techniques in attacking the convergence problems for the K\"ahler Ricci flow. The one of main ideas is to find a set of new functionals on curvature tensors such that the Ricci flow is the gradient like flow of these functionals. We successfully find such functionals in case of Kaehler manifolds. On K\"ahler-Einstein manifold with positive scalar curvature, if the initial metric has positive bisectional curvature, we prove that these functionals have a uniform lower bound, via the effective use of Tian's inequality. Consequently, we prove the following theorem: Let $M$ be a K\"ahler-Einstein manifold with positive scalar curvature. If the initial metric has nonnegative bisectional curvature and positive at least at one point, then the K\"ahler Ricci flow will converge exponentially fast to a K\"ahler-Einstein metric with constant bisectional curvature. Such a result holds for K\"ahler-Einstein orbifolds.
The K?hler-Ricci flow on K?hler manifolds with 2 traceless bisectional curvature operator
X. X. Chen,H. Li
Mathematics , 2005,
Abstract: It was proved by H. Chen earlier that the property of the sum of any two eigenvalues of the curvature operator is positive is preserved under the ricci flow in all dimensional. By a recent result of Phong-Sturm, a similar notion of positive 2-traceless bisectional curvature positive is preserved on complex surface. We prove that this holds in all dimensional K\"ahler manifold. Moreover, the scalar curvature controls full curvature for this type of metrics.
Page 1 /90009
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.