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排序方式: 共有1219条查询结果,搜索用时 15 毫秒
11.
Tholén EA Platz D Forchheimer D Schuler V Tholén MO Hutter C Haviland DB 《The Review of scientific instruments》2011,82(2):026109
Nonlinear systems can be probed by driving them with two or more pure tones while measuring the intermodulation products of the drive tones in the response. We describe a digital lockin analyzer which is designed explicitly for this purpose. The analyzer is implemented on a field-programmable gate array, providing speed in analysis, real-time feedback, and stability in operation. The use of the analyzer is demonstrated for intermodulation atomic force microscopy. A generalization of the intermodulation spectral technique to arbitrary drive waveforms is discussed. 相似文献
12.
Multiscale approaches require the coupling of models on different spatial scales. In this paper, a coupling using neural networks is proposed. Based on a set of mesoscale simulations of concrete a system of neural networks is trained to approximate the response. A macroscale constitutive model is obtained by homogenizing the mesoscale response. Special focus is put on the mesh sensitivity, since the mesoscale model includes softening and consequently the width of the localization zone compared to the dimension of the mesoscale model is an additional parameter in the model. 相似文献
13.
A multi-objective controller synthesis problem is considered in which an output is to be regulated approximately by assuring a bound on the steady-state peak amplification in response to an infinite-energy disturbance, while also guaranteeing a desired level of performance measured in terms of the worst-case energy gain from a finite-energy input to a performance output. Relying on a characterization of the controllers with which almost asymptotic regulation is accomplished, the problem of guaranteeing the desired level of performance is reduced to solving a system of linear matrix inequalities subject to a set of linear equality constraints. Based on the solution of this system, a procedure is outlined for the construction of a suitable controller whose order is equal to the order of the plant plus the order of the exogenous system. 相似文献
14.
A collaborative filtering framework based on both local user similarity and global user similarity 总被引:1,自引:0,他引:1
Collaborative filtering as a classical method of information retrieval has been widely used in helping people to deal with
information overload. In this paper, we introduce the concept of local user similarity and global user similarity, based on
surprisal-based vector similarity and the application of the concept of maximin distance in graph theory. Surprisal-based
vector similarity expresses the relationship between any two users based on the quantities of information (called surprisal) contained in their ratings. Global user similarity defines two users being similar if they can be connected through their
locally similar neighbors. Based on both of Local User Similarity and Global User Similarity, we develop a collaborative filtering
framework called LS&GS. An empirical study using the MovieLens dataset shows that our proposed framework outperforms other
state-of-the-art collaborative filtering algorithms. 相似文献
15.
Andreas Petlund Paul Beskow Jon Pedersen Espen Søgård Paaby Carsten Griwodz Pål Halvorsen 《Multimedia Tools and Applications》2009,45(1-3):33-60
A large number of network services rely on IP and reliable transport protocols. For applications that provide abundant data for transmission, loss is usually handled satisfactorily, even if the application is latency-sensitive (Wang et al. 2004). For data streams where small packets are sent intermittently, however, applications can occasionally experience extreme latencies (Griwodz and Halvorsen 2006). As it is not uncommon that such thin-stream applications are time-dependent, any unnecessarily induced delay can have severe consequences for the service provided. Massively Multiplayer Online Games (MMOGs) are a defining example of thin streams. Many MMOGs (like World of Warcraft and Age of Conan) use TCP for the benefits of reliability, in-order delivery and NAT/firewall traversal. It has been shown that TCP has several shortcomings with respect to the latency requirements of thin streams because of the way it handles retransmissions (Griwodz and Halvorsen 2006). As such, an alternative to TCP may be SCTP (Stewart et al. 2000), which was originally developed to meet the requirements of signaling transport. In this paper, we evaluate the Linux-kernel SCTP implementation in the context of thin streams. To address the identified latency challenges, we propose sender-side only enhancements that reduce the application-layer latency in a manner that is compatible with unmodified receivers. These enhancements can be switched on by applications and are used only when the system identifies the stream as thin. To evaluate the latency performance, we have performed several tests over various real networks and over an emulated network, varying parameters like RTT, packet loss and amount of competing cross traffic. When comparing our modifications with SCTP on Linux and FreeBSD and TCP New Reno, our results show great latency improvements and indicate the need for a separate handling of thin and thick streams. 相似文献
16.
For robustness analysis with integral quadratic constraints, we formulate a new positivity condition on the solution of the corresponding linear matrix inequality which is necessary and sufficient for nominal stability of the underlying system. The application of this technical result is illustrated by a complete solution of the L2-gain and robust H2-estimator design problems if the uncertainties are characterized by dynamic integral quadratic constraints. 相似文献
17.
In this work we examine the influence of the diffusive motion of vortices in highly anisotropic high-Tc superconductors near the Berezinskii-Kosterlitz-Thouless (BKT) transition temperature T
bkt
on the spin-lattice relaxation rate T
1
–1
.We find a jump in T
1
–1
at the temperature T
bkt
. 相似文献
18.
Carsten Behn 《Multibody System Dynamics》2011,26(3):213-243
In this paper we consider an adaptive control problem of finite DoF worm-like locomotion systems (WLLS) which contact the
ground with Coulomb dry friction. Using a rough mathematical friction law the system is shown to belong to a system class
that allows adaptive control. Gaits from the kinematic theory can be tracked by means of adaptive controllers. For this we
introduce two different adaptive controllers for λ-tracking and focus on that one which is not based on the derivative of the output. We pay attention to the analysis of such
systems and present some theoretical control investigations including proofs. Numerical simulations of tracking different
reference signals under arbitrary choice of the system parameters demonstrate and illustrate that the introduced simple adaptive
controllers work successfully and effectively. Current experiments are aimed at the justification of theoretical results. 相似文献
19.
Rule cubes for causal investigations 总被引:1,自引:1,他引:0
Axel Blumenstock Franz Schweiggert Markus Müller Carsten Lanquillon 《Knowledge and Information Systems》2009,18(1):109-132
With the complexity of modern vehicles tremendously increasing, quality engineers play a key role within today’s automotive
industry. Field data analysis supports corrective actions in development, production and after sales support. We decompose
the requirements and show that association rules, being a popular approach to generating explanative models, still exhibit
shortcomings. Interactive rule cubes, which have been proposed recently, are a promising alternative. We extend this work
by introducing a way of intuitively visualizing and meaningfully ranking them. Moreover, we present methods to interactively
factorize a problem and validate hypotheses by ranking patterns based on expectations, and by browsing a cube-based network
of related influences. All this is currently in use as an interactive tool for warranty data analysis in the automotive industry.
A real-world case study shows how engineers successfully use it in identifying root causes of quality issues.
相似文献
Axel BlumenstockEmail: |
20.
Nils Hasler Carsten Stoll Bodo Rosenhahn Thorsten Thormhlen Hans-Peter Seidel 《Computers & Graphics》2009,33(3):211
The paper presents a method to estimate the detailed 3D body shape of a person even if heavy or loose clothing is worn. The approach is based on a space of human shapes, learned from a large database of registered body scans. Together with this database we use as input a 3D scan or model of the person wearing clothes and apply a fitting method, based on ICP (iterated closest point) registration and Laplacian mesh deformation. The statistical model of human body shapes enforces that the model stays within the space of human shapes. The method therefore allows us to compute the most likely shape and pose of the subject, even if it is heavily occluded or body parts are not visible. Several experiments demonstrate the applicability and accuracy of our approach to recover occluded or missing body parts from 3D laser scans. 相似文献