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991.
Fernández de Luis R Mesa JL Urtiaga MK Larrea ES Rojo T Arriortua MI 《Inorganic chemistry》2012,51(4):2130-2139
The hydrothermal treatment of Ni(NO(3))(2)·6H(2)O, NaVO(3), and Bpa (1,2-Di(pyridyl)ethane) (C(12)H(12)N(2)) at 120 °C during 3 days leads to green single crystals of the title compound. The single crystal X-ray diffraction reveals that [{Ni(3)(H(2)O)(3)(Bpa)(4)}(V(6)O(18))]·8H(2)O crystallizes in the monoclinic system, P2(1)/c space group, with a = 13.5536 (2), b = 19.0463 (2), c = 27.7435 (3) ?, β = 112.3880 (10)°, V = 6622(3) ?(3), with R1(obs) = 0.0558, wR2(obs) = 0.1359, for 10278 observed reflections. The complexity of the crystal structure is based on different points, as the existence of: both "gauche" and "trans" conformations of the organic ligand, the [V(12)O(36)](-12) cycles, formed by 12 corner-sharing VO(4) tetrahedra, and, finally, the combination of both three-dimensional metal-organic and inorganic substructures, giving rise to a self-catenated highly connected net. The crystallization water molecules are semi-encapsulated in the channels along the [100] direction, and their loss gives rise to a dynamical and reversible structural contraction. Moreover, after the removal of the crystallization water molecules, the compound exhibits a negative thermal behavior in the 85-155 °C temperature range, and irreversible structural transformation due to the loss of coordinated water molecules up to 200 °C. The IR and UV-vis spectra were determined for the as-synthesized sample, after the removal of crystallization water molecules and after the irreversible transformation due to the loss of coordinated water molecules. The thermal evolution of χ(m) was adjusted to a magnetic model considering an isotropic dimer plus two Ni(II) d(8) isolated octahedra. 相似文献
992.
Rodrigo Carareto Fernando M. Orsatti José Roberto C. Piqueira 《Communications in Nonlinear Science & Numerical Simulation》2012,17(12):4672-4682
Synchronous telecommunication networks, distributed control systems and integrated circuits have its accuracy of operation dependent on the existence of a reliable time basis signal extracted from the line data stream and acquirable to each node. In this sense, the existence of a sub-network (inside the main network) dedicated to the distribution of the clock signals is crucially important. There are different solutions for the architecture of the time distribution sub-network and choosing one of them depends on cost, precision, reliability and operational security. In this work we expose: (i) the possible time distribution networks and their usual topologies and arrangements. (ii) How parameters of the network nodes can affect the reachability and stability of the synchronous state of a network. (iii) Optimizations methods for synchronous networks which can provide low cost architectures with operational precision, reliability and security. 相似文献
993.
Pedro Larra?aga Hossein Karshenas Concha Bielza Roberto Santana 《Journal of Heuristics》2012,18(5):795-819
Thanks to their inherent properties, probabilistic graphical models are one of the prime candidates for machine learning and decision making tasks especially in uncertain domains. Their capabilities, like representation, inference and learning, if used effectively, can greatly help to build intelligent systems that are able to act accordingly in different problem domains. Evolutionary algorithms is one such discipline that has employed probabilistic graphical models to improve the search for optimal solutions in complex problems. This paper shows how probabilistic graphical models have been used in evolutionary algorithms to improve their performance in solving complex problems. Specifically, we give a survey of probabilistic model building-based evolutionary algorithms, called estimation of distribution algorithms, and compare different methods for probabilistic modeling in these algorithms. 相似文献
994.
Leithem SM Lavarello RJ O'Brien WD Oelze ML 《The Journal of the Acoustical Society of America》2012,131(3):2295-2305
Ultrasound contrast agents (UCAs) have been explored as a means to enhance therapeutic techniques. Because the effectiveness of these techniques relies on the UCA concentration at a target site, it would be beneficial to estimate UCA concentration noninvasively. In this study, a noninvasive method for estimating UCA concentration was developed in vitro. Backscatter coefficients (BSCs) estimated from measurements of Definity(?) UCAs were fitted to a theoretical scattering model in the 15-25 MHz range using a Levenberg-Marquardt regression technique. The model was defined by the UCA size distribution and concentration, and therefore concentration estimates were extracted directly from the fit. Calculation of the BSC was accomplished using planar reference measurements from the back wall of a Plexiglas(?) chamber and an average of 500 snapshots of ultrasonic backscatter from UCAs flowing through the chamber. In order to verify the ultrasonically derived UCA concentration estimates, a sample of the UCAs was extracted from the flow path and the concentration was estimated with a hemacytometer. UCA concentrations of 1, 2, and 5 times the dose recommended by the manufacturer were used in experiments. All BSC-based estimates were within one standard deviation of hemacytometer based estimates for peak rarefactional pressures of 100-400 kPa. 相似文献
995.
The control of sound transmission through panels is an important noise control problem in the aerospace, aeronautical, and automotive industries. The trend towards using lightweight composite materials that have lower sound insulation performance is a negative factor regarding low frequency transmission loss. Double-panel partitions with the gap filled with sound absorption materials are often employed to improve the sound insulation performance with reduced added weight penalty. However, in the low frequency range, the strong coupling between the panels through the air cavity and mechanical paths may greatly reduce the sound transmission performance, making it even lower than the performance of a single panel in some frequency ranges. In this work, an experimental investigation of a new kind of hybrid (active/passive) acoustic actuator is presented. The idea consists of replacing the acoustic absorption material by a hybrid actuator aiming at improving the transmission loss at low frequencies without altering the passive attenuation. A prototype of the system is tested in a plane wave acoustic tube setup. Different kinds of SISO feedforward control implementations were used to attenuate the sound power transmitted through the hybrid active–passive panel using an error microphone or a particle velocity sensor placed downstream with respect to the sample panel. Measurement results of the transmission loss with active and hybrid attenuation are presented and discussed. 相似文献
996.
997.
Computer simulations based on Discrete Element Method have been performed in order to investigate the influence of interparticle interactions on the kinetics of self-assembly and the mechanical strength of nanoparticle aggregates.Three different systems have been considered.In the first system the interaction between particles has been simulated using the JKR (Johnson,Kendall and Roberts) contact theory,while in the second and third systems the interaction between particles has been simulated using van der Waals and electrostatic forces respectively.In order to compare the mechanical behaviour of the three systems,the magnitude of the maximum attractive force between particles has been kept the same in all cases.However,the relationship between force and separation distance differs from case to case and thus,the range of the interparticle force.The results clearly indicate that as the range of the interparticle force increases,the self-assembly process is faster and the work required to produce the mechanical failure of the assemblies increases by more than one order of magnitude. 相似文献
998.
The effect of the number of blades on wake evolution was investigated on three propellers having the same blade geometry but
different numbers of blades. The experiments concerned velocity measurements along nine transversal planes of the wake by
LDV phase-sampling techniques. The study was performed with all the propellers having the same tip vortex intensity. In addition,
high-speed visualizations were carried out to analyze the main features of propeller wake evolution in the transition and
in the far wake. Aspects concerning wake evolution were pointed out, with particular emphasis on the instability mechanism
of the propeller slipstream and on its correlation with the blade-to-blade interaction phenomenon. 相似文献
999.
1000.
Although the formulation of the nonlinear theory of H
∞ control has been well developed, solving the Hamilton–Jacobi–Isaacs equation remains a challenge and is the major bottleneck
for practical application of the theory. Several numerical methods have been proposed for its solution. In this paper, results
on convergence and stability for a successive Galerkin approximation approach for nonlinear H
∞ control via output feedback are presented. An example is presented illustrating the application of the algorithm. 相似文献