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181.
Hidetsugu Horikawa Earl H. Dowell Francis C. Moon 《International Journal of Solids and Structures》1978,14(10):821-839
This study examines the possibility of controlling through feedback a thin cantilevered beam subjected to a nonconservative follower force. A converging frequency flutter instability which occurs in this model is similar to classical bending-torsion flutter of an aircraft wing. Because of the similar nature of the instabilities, the beam under the follower force can be a useful vehicle for investigating the fundamental aspects of stabilization of wing flutter by feedback control. A modal approach is used for obtaining the mathematical model and control laws. A standard root locus technique for simple analytical models is also used to understand and explain the control of the beam. Experiments are carried out to verify the validity of this theoretical model. Good correlation is shown between theoretically and experimentally determined stability boundaries as well as for modal frequency and damping variation with follower force. 相似文献
182.
Alexander Aerts Dr. Mohamed Haouas Dr. Tom P. Caremans Lana R. A. Follens Dr. Titus S. van Erp Dr. Francis Taulelle Dr. Jan Vermant Prof. Johan A. Martens Prof. Christine E. A. Kirschhock Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(9):2764-2774
Colloidal silicalite‐1 zeolite was crystallized from a concentrated clear sol prepared from tetraethylorthosilicate (TEOS) and aqueous tetrapropylammonium hydroxide (TPAOH) solution at 95 °C. The silicate speciation was monitored by using dynamic light scattering (DLS), synchrotron small‐angle X‐ray scattering (SAXS), and quantitative liquid‐state 29Si NMR spectroscopy. The silicon atoms were present in dissolved oligomers, two discrete nanoparticle populations approximately 2 and 6 nm in size, and crystals. On the basis of new insight into the evolution of the different nanoparticle populations and of the silicate connectivity in the nanoparticles, a refined crystallization mechanism was derived. Upon combining the reagents, different types of nanoparticles (ca. 2 nm) are formed. A fraction of these nanoparticles with the least condensed silicate structure does not participate in the crystallization process. After completion of the crystallization, they represent the residual silicon atoms. Nanoparticles with a more condensed silicate network grow until approximately 6 nm and evolve into building blocks for nucleation and growth of the silicalite‐1 crystals. The silicate network connectivity of nanoparticles suitable for nucleation and growth increasingly resembles that of the final zeolite. This new insight into the two classes of nanoparticles will be useful to tune the syntheses of silicalite‐1 for maximum yield. 相似文献
183.
The rhombohedral modification of the thiospinel, CuZr1.86(1)S4, has been synthesized by the reaction of the constituent elements in an alkali metal halide flux and structurally characterized by single crystal X-ray diffraction techniques. The title compound crystallizes in the rhombohedral space group (#166, a=7.3552(2) Å, c=35.832(2) Å, V=1678.76(13) Å3, Z=12, and R/wR=0.0239/0.0624). The structure is composed of close packed S layers, with a stacking order of ?ABCBCABABCACAB?·along the c axis. The Zr and Cu atoms occupy the octahedral and tetrahedral holes between S layers, respectively. Three different kinds of S-M-S layers exist in the structure: layer I has fully occupied Zr and Cu sites, layer II has fully occupied Zr sites but no Cu, and layer III has partially occupied Zr and fully occupied Cu sites. Transport and optical properties indicate that the title compound is a small band gap (1.26 eV) n-type semiconductor. 相似文献
184.
Mika Mahosenaho Felice Caprio Laura Micheli Adama M. Sesay Giuseppe Palleschi Vesa Virtanen 《Mikrochimica acta》2010,170(3-4):243-249
A disposable tri-enzymatic biosensor is presented for the determination of α-amylase in human saliva. It is based on the quantity of maltose generated by hydrolysis of maltopentose in the presence of salivary α-amylase. The biosensor is fabricated by co-immobilization of the enzymes α-glucosidase, glucose oxidase, and mutarotase on screen-printed electrodes modified with Prussian Blue. The assay can be performed with a “drop” of sample, this allowing for ease and simplicity. A linear relationship is found for the range from 5 to 250 units per mL, with an LOD of 5 units per mL. The biosensor is stable for at least one month and over this time retains 80% of its original activity. The system was then evaluated for matrix effects of human saliva and compared to a spectrometric method using a commercially available kit. 相似文献
185.
The thermoelectric properties of Pb0.5Sn0.5Te doped with In at 1.0, 2.0, and 3.0×1019/cm3 and sintered at a high pressure and high temperature (HPHT) of 4.0 GPa and 800 or 900 °C, respectively, have been studied. All samples show p-type semiconducting behavior with positive thermopower. We find that HPHT sintering of conventionally synthesized materials improves their thermoelectric properties. The highest power factor is obtained for In doping of 2.0×1019/cm3 with 13.5 μW/cm K2 at 230 °C. The corresponding figure of merit is 1.43×10−3/K. This represents a twofold improvement in thermoelectric figure of merit, compared to the conventionally sintered materials reported in the literature. When exposed to 400 °C for 10 days, samples sintered at 900 °C exhibit more stable thermoelectric properties, while the properties of those sintered at 800 °C deteriorated. These results demonstrate that HPHT sintering is a viable and controllable way of tuning the thermoelectric properties of PbTe-based materials. 相似文献
186.
Jean-Daniel Compain Anne Dolbecq Jérôme Marrot Pierre Mialane Francis Sécheresse 《Comptes Rendus Chimie》2010,13(3):329-335
The reactivity of the [MoV2O4]2+ dinuclear unit with the [O3P(C(CH3)(OH))PO3]4? etidronate ligand has been investigated. Three complexes have been isolated and characterized by IR spectroscopy, elemental analysis and single crystal X-Ray diffraction studies. Structural determination of the tetranuclear compound (CN3H6)6[(MoV2O4)2(O3P(C(CH3)O)PO3)2]·12H2O (1) revealed that the hydroxo group of the etidronate ligand can be deprotonated in presence of MoV even in acidic media. It follows that its coordination mode thus differs from that of the methylenediphosphonate ligand [O3P(CH2)PO3]4?, which reactivity with MoV has been previously widely studied. In contrast, no such deprotonation of the hydroxo group is observed in the (NH4)18[(MoV2O4)6(OH)6(O3P(C(CH3)(OH))PO3)6]·35H2O complex 2. This species contains a dodecanuclear core analogous to the one previously found in the [(MoV2O4)6(OH)6(O3PCH2PO3)6]18? methylenediphosphonato polyanion. In 2, six interconnected {(MoV2O4)(O3P(C(CH3)(OH))PO3)} units form a cyclohexane-like ring in a chair conformation. In the (CN3H6)18Na3[(MoV2O4)7(O3P(C(CH3)(OH))PO3)7(CH3COO)7]·5CH3COONa 52H2O compound 3, seven {(MoV2O4)(O3P(C(CH3)(OH))PO3)(CH3COO)} units are connected, forming an almost planar tetradecanuclear wheel. This compound represents the largest homometallic MoV polyoxometalate cyclic system reported to date. Finally, 31P NMR studies revealed that only complex 1 is stable in aqueous solution. 相似文献
187.
This paper investigates the synchronization of complex systems with delay that are impulsively coupled at discrete instants only. Based on the comparison theorem of impulsive differential system, a distributed impulsive control scheme is proposed to achieve the synchronization for systems with delay. In the control strategy, the influence of all nodes to network synchronization relies on its weight. The proposed control scheme is applied to the chaotic delayed Hopfield neural networks and numerical simulations are presented to demonstrate the effectiveness of the proposed scheme. 相似文献
188.
189.
We investigate the impact of nanoparticles (NP) on the fragility and cooperative stringlike motion in a model glass-forming polymer melt by molecular dynamics simulation. The NP cause significant changes to both the fragility and the average length of stringlike motion, where the effect depends on the NP-polymer interaction and NP concentration. We interpret these changes via the Adam-Gibbs (AG) theory, assuming the strings can be directly identified with the abstract "cooperatively rearranging regions" of AG. Our findings indicate that fragility is primarily a measure of the temperature dependence of the cooperativity of molecular motion. 相似文献
190.
Martineau C Engelke F Taulelle F 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,212(2):311-319
The effects of multiple-resonance heteronuclear decoupling under magic angle spinning (MAS) on the resolution of one-dimensional 19F and 31P and various two-dimensional MAS NMR spectra and on the residual non-refocusable coherence lifetimes in fluorinated aluminophosphate AlPO4-CJ2, i.e. a compound that contains numerous highly abundant nuclei but no homonuclear spin bath, has been investigated. The design of the four-channel (1H, 19F, 27Al, 31P) MAS probe used for this study is first described. 1H and 1H–27Al double-resonance decouplings allows lengthening the optimized transverse relaxation and increasing the resolution in the 19F and 31P dimensions. Under the application of multi-nuclear decoupling, a two-dimensional 19F–31P CP-HETCOR correlation spectrum for AlPO4-CJ2 is recorded with unprecedented high-resolution in the two dimensions. Moreover, because 1H-decoupling increases the 19F , it has been applied during the entire duration of the 2D NMR experiments, allowing the direct use of residual small interactions to generate 19F–19F and 19F–27Al 2D NMR correlation spectra in AlPO4-CJ2. 相似文献