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排序方式: 共有3390条查询结果,搜索用时 31 毫秒
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Rosana A. DiasAuthor Vitae Edmond CretuAuthor VitaeReinoud WolffenbuttelAuthor Vitae Luis A. RochaAuthor Vitae 《Sensors and actuators. A, Physical》2011,172(1):47-53
The pull-in time (tpi) of electrostatically actuated parallel-plate microstructures enables the realization of a high-sensitivity accelerometer that uses time measurement as the transduction mechanism. The key feature is the existence of a metastable region that dominates pull-in behavior, thus making pull-in time very sensitive to external accelerations. Parallel-plate MEMS structures have been designed and fabricated using a SOI micromachining process (SOIMUMPS) for the implementation of the accelerometer. This paper presents the experimental characterization of the microdevices, validating the concept and the analytical models used. The accelerometer has a measured sensitivity of 0.25 μs/μg and a bandwidth that is directly related to the pull-in time, BW = 1/2tpi ≈ 50 Hz. These specifications place this sensor between the state of the art accelerometers found both in the literature and commercially. More importantly, the resolution of the measurement method used is very high, making the mechanical-thermal noise the only factor limiting the resolution. The in-depth noise analysis to the system supports these conclusions. The total measured noise floor of 400 μg (100 μs) is mainly due to the contribution of the environmental noise, due to lack of isolation of the experimental setup from the building vibrations (estimated mechanical thermal noise of 2.8 μg/√Hz). The low requirements of the electronic readout circuit makes this an interesting approach for high-resolution accelerometers. 相似文献
95.
Sergio F. León-LuisAuthor VitaeUlises R. Rodríguez-MendozaAuthor Vitae Emmanuel LallaAuthor VitaeVíctor LavínAuthor Vitae 《Sensors and actuators. B, Chemical》2011,158(1):208-213
The temperature dependence of the green upconverted emission from the two thermally coupled 2H11/2 and 4S3/2 levels of the Er3+ ion in a fluorotellurite glass has been analyzed as a function of the optically active ion concentration in order to check its availability as a temperature sensor. The infrared-to-green upconverted emission have been observed by the naked eyes after a cw laser diode excitation at 800 nm. The fluorescence intensity ratio between the thermally coupled emitting levels as well as the temperature sensitivity has been experimentally obtained up to 540 K. A better behaviour as a temperature sensor has been obtained for the less Er3+ concentrated glass with a maximum sensitivity of 54 × 10−4 K−1 at 540 K, one of the highest found in rare-earth doped transparent materials. 相似文献
96.
Chvátal-Gomory cuts are among the most well-known classes of cutting planes for general integer linear programs (ILPs). In
case the constraint multipliers are either 0 or
, such cuts are known as
-cuts. It has been proven by Caprara and Fischetti (Math. Program. 74:221–235, 1996) that separation of
-cuts is
-hard.
In this paper, we study ways to separate
-cuts effectively in practice. We propose a range of preprocessing rules to reduce the size of the separation problem. The
core of the preprocessing builds a Gaussian elimination-like procedure. To separate the most violated
-cut, we formulate the (reduced) problem as integer linear program. Some simple heuristic separation routines complete the
algorithmic framework.
Computational experiments on benchmark instances show that the combination of preprocessing with exact and/or heuristic separation
is a very vital idea to generate strong generic cutting planes for integer linear programs and to reduce the overall computation
times of state-of-the-art ILP-solvers. 相似文献
97.
Matthew R. Graham Author Vitae Author Vitae Raymond A. de Callafon Author Vitae 《Automatica》2009,45(6):1489-1496
This paper introduces an alternative formulation of the Kalman-Yakubovich-Popov (KYP) Lemma, relating an infinite dimensional Frequency Domain Inequality (FDI) to a pair of finite dimensional Linear Matrix Inequalities (LMI). It is shown that this new formulation encompasses previous generalizations of the KYP Lemma which hold in the case the coefficient matrix of the FDI does not depend on frequency. In addition, it allows the coefficient matrix of the frequency domain inequality to vary affinely with the frequency parameter. One application of this results is illustrated in an example of computing upper bounds to the structured singular value with frequency-dependent scalings. 相似文献
98.
The paper is devoted to developing methods for control of ecological-economic systems consisting of three hierarchically subordinate subjects of control. In describing the dynamics of a system state, equations in partial derivatives that are solved numerically according to a semi-implicit scheme of the finite-difference method are used. To achieve its main goal (maintenance of an ecological subsystem in stable state), the subject of control of the upper level applies different control methods. Methods of hierarchical control (motivation, enforcement, and persuasion) that differ in the direction of action (on the objective function or domain of admissible controls) are proposed; examples of their use are represented and a comparative analysis of the obtained results is made. 相似文献
99.
We propose a visualization based approach for digital signature authentication. Using our method, the speed and pressure aspects of a digital signature process can be clearly and intuitively conveyed to the user for digital signature authentication. Our design takes into account both the expressiveness and aesthetics of the derived visual patterns. With the visual aid provided by our method, digital signatures can be authenticated with better accuracy than using existing methods—even novices can examine the authenticity of a digital signature in most situations using our method. To validate the effectiveness of our method, we conducted a comprehensive user study which confirms positively the advantages of our approach. Our method can be employed as a new security enhancement measure for a range of business and legal applications in reality which involve digital signature authorization and authentication. 相似文献
100.