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排序方式: 共有1289条查询结果,搜索用时 15 毫秒
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Pavel Strunz Debashis Mukherji Přemysl Beran Ralph Gilles Lukas Karge Michael Hofmann Markus Hoelzel Joachim Rösler Gergely Farkas 《Metals and Materials International》2018,24(5):934-944
An addition of boron largely increases the ductility in polycrystalline high-temperature Co–Re alloys. Therefore, the effect of boron on the alloy structural characteristics is of high importance for the stability of the matrix at operational temperatures. Volume fractions of ε (hexagonal close-packed—hcp), γ (face-centered cubic—fcc) and σ (Cr2Re3 type) phases were measured at ambient and high temperatures (up to 1500 °C) for a boron-containing Co–17Re–23Cr alloy using neutron diffraction. The matrix phase undergoes an allotropic transformation from ε to γ structure at high temperatures, similar to pure cobalt and to the previously investigated, more complex Co–17Re–23Cr–1.2Ta–2.6C alloy. It was determined in this study that the transformation temperature depends on the boron content (0–1000 wt. ppm). Nevertheless, the transformation temperature did not change monotonically with the increase in the boron content but reached a minimum at approximately 200 ppm of boron. A probable reason is the interplay between the amount of boron in the matrix and the amount of σ phase, which binds hcp-stabilizing elements (Cr and Re). Moreover, borides were identified in alloys with high boron content. 相似文献
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5.
Jiři Gregor 《Mathematics of Control, Signals, and Systems (MCSS)》1991,4(2):205-215
A significant part of the theory of one-dimensional linear shift-invariant systems is based on the concept of weighting function
(or impulse response): the output is the convolution of the weighting function with the input. This paper introduces the concept
of linear translation-invariant systems and uses this notion in studying impulse response, z-transforms, and transfer functions
for multidimensional systems. 相似文献
6.
Jiří Polívka 《Journal of Infrared, Millimeter and Terahertz Waves》1996,17(10):1779-1788
In his earlier paper on Active Microwave Radiometry, the author indicated that microwave noise can be used to map field density distribution inside radiators and in antenna systems, without the need for anechoic chambers. The presented paper gives details and results of such experiment. The method is described, details of equipment are given and results are presented with a concluding commentary. 相似文献
7.
M. Kohl M. Odehnal V. Petříěek R. Tichý S. Šafrata 《Journal of Low Temperature Physics》1988,72(3-4):319-343
We describe an apparatus allowing the observation of the NMR static longitudinal component of nuclear magnetizationM
z
by a SQUID at low magnetic fields and atT=4.2 K in Plexiglas, Teflon, and CaF2. The higher order NMR Larmor lines at 2f
0, 3f
0, and 4f
0, wheref
0 is the Larmor frequency of the allowed NMR line, were measured. These lines correspond to a flip of two, three, and four spins, respectively, by one photon. The amplitudes of 2f
0 and 3f
0 lines and their field dependences show that the common assertion that the forbidden lines at 2f
0 and 3f
0 appear in the same order of perturbation theory and that their intensity decreases with static magnetic fieldB
0 asB
0
–2
is wrong. In fact, the third Larmor line 3f
0 appears at higher order than the second Larmor line 2f
0 and its intensity decreases asB
0
–4
. This is also shown by a theoretical calculation of its intensity. For the first time the NMR SQUID technique allowed the detection of the 4f
0 line, corresponding to the simultaneous flip of four spins by one photon. 相似文献
8.
Summary The effect of tert-butyl chloride in the polymerizations of isobutylene carried out in the presence of SnCl4 in dichloromethane at temperatures-20°C and-78°C was investigated. Synthesized polyisobutylene samples showed a bimodal molecular
weight distribution (MWD) and it was found that the weight content of the lowermolecular weight (LMW) fraction increased with
increasing t-BuCl concentration in the polymerization mixture. The effect of ageing of the initiation mixture t-BuCl/SnCl4 in CH2Cl2 prepared in advance on MWD of the PIB samples was also studied. Ageing of the initiation system supports the formation of
the LMW fraction and this oily PIB is the only product of the polymerization at-20°C,
. 相似文献
9.
The paper deals with state estimation of the nonlinear stochastic systems by means of the unscented Kalman filter with a focus on specification of the σ-points. Their position is influenced by two design parameters—the scaling parameter determining the spread of the σ-points and a covariance matrix decomposition determining rotation of the σ-points. In this paper, a choice of the scaling parameter is analyzed. It is shown that considering other values than the standard choice may lead to increased quality of the estimate, especially if the scaling parameter is adapted. Several different criteria for the adaptation are proposed and techniques to reduce computational costs of the adaptation are developed. The proposed algorithm of the unscented Kalman filter with advanced adaptation of the scaling parameter is illustrated in a numerical example. 相似文献
10.
Martin Saska Tomáš Krajník Vojtěch Vonásek Zdeněk Kasl Vojtěch Spurný Libor Přeučil 《Journal of Intelligent and Robotic Systems》2014,73(1-4):603-622
A fault-tolerant method for stabilization and navigation of 3D heterogeneous formations is proposed in this paper. The presented Model Predictive Control (MPC) based approach enables to deploy compact formations of closely cooperating autonomous aerial and ground robots in surveillance scenarios without the necessity of a precise external localization. Instead, the proposed method relies on a top-view visual relative localization provided by the micro aerial vehicles flying above the ground robots and on a simple yet stable visual based navigation using images from an onboard monocular camera. The MPC based schema together with a fault detection and recovery mechanism provide a robust solution applicable in complex environments with static and dynamic obstacles. The core of the proposed leader-follower based formation driving method consists in a representation of the entire 3D formation as a convex hull projected along a desired path that has to be followed by the group. Such an approach provides non-collision solution and respects requirements of the direct visibility between the team members. The uninterrupted visibility is crucial for the employed top-view localization and therefore for the stabilization of the group. The proposed formation driving method and the fault recovery mechanisms are verified by simulations and hardware experiments presented in the paper. 相似文献