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21.
Multipliers are often used to find conditions for the absolute stability of Lur’e systems. They can be used either in conjunction with passivity theory or within the more recent framework of integral quadratic constraints (IQCs). We compare the use of multipliers in both approaches. Passivity theory requires that the multipliers have a canonical factorization and it has been suggested in the literature that this represents an advantage of the IQC theory. We consider sufficient conditions on the nonlinearity class for the associated multipliers to have a canonical factorization. 相似文献
22.
Multiple-input multiple-output (MIMO) wireless systems can achieve significant diversity and array gain by using transmit beamforming and receive combining techniques. In the absence of full channel knowledge at the transmitter, the transmit beamforming vector can be quantized at the receiver and sent to the transmitter using a low-rate feedback channel. In the literature, quantization algorithms for the beamforming vector are designed and optimized for a particular channel distribution, commonly the uncorrelated Rayleigh distribution. When the channel is not uncorrelated Rayleigh, however, these quantization strategies result in a degradation of the receive signal-to-noise ratio (SNR). In this paper, switched codebook quantization is proposed where the codebook is dynamically chosen based on the channel distribution. The codebook adaptation enables the quantization to exploit the spatial and temporal correlation inherent in the channel. The convergence properties of the codebook selection algorithm are studied assuming a block-stationary model for the channel. In the case of a nonstationary channel, it is shown using simulations that the selected codebook tracks the distribution of the channel resulting in improvements in SNR. Simulation results show that in the case of correlated channels, the SNR performance of the link can be significantly improved by adaptation, compared with nonadaptive quantization strategies designed for uncorrelated Rayleigh-fading channels 相似文献
23.
Maximum G Edge-Packing (EPack
G
) is the problem of finding the maximum number of edge-disjoint isomorphic copies of a fixed guest graph G in a host graph H . This paper investigates the computational complexity of edge-packing for planar guests and planar hosts. Edge-packing is
solvable in polynomial time when both G and H are trees. Edge-packing is solvable in linear time when H is outerplanar and G is either a 3-cycle or a k -star (a graph isomorphic to K
1,k
). Edge-packing is NP-complete when H is planar and G is either a cycle or a tree with edges. A strategy for developing polynomial-time approximation algorithms for planar hosts is exemplified by a linear-time
approximation algorithm that finds a k -star edge-packing of size at least half the optimal.
Received May 1995, and in revised form November 1995, and in final form December 1997. 相似文献
24.
Andrew C. Heath Juan M. Pestana John T. Harvey Manuel O. Bejerano 《Canadian Metallurgical Quarterly》2004,130(9):896-904
One of the important components of a flexible pavement structure is granular material layers. Unsaturated granular pavement materials (UGPMs) in these layers influence stresses and strains throughout the pavement structure, and have a large effect on asphalt concrete fatigue and pavement rutting (two of the primary failure mechanisms for flexible pavements). The behavior of UGPMs is dependent on water content, but this effect has been traditionally difficult to quantify using either empirical or mechanistic methods. This paper presents a practical mechanistic framework for determining the behavior of UGPMs within the range of water contents, densities, and stress states likely to be encountered under field conditions. Both soil suction and generated pore pressures are determined and compared to confinement under typical field loading conditions. The framework utilizes a simple soil suction model that has three density-independent parameters, and can be determined using conventional triaxial equipment that is available in many pavement engineering laboratories. 相似文献
25.
26.
Continuous hydrogen production using upflow anaerobic sludge blanket reactors: effect of organic loading rate on microbial dynamics and H2 metabolism 下载免费PDF全文
27.
Noori M. Cata Saady Subba Rao Chaganti Jerald A. Lalman Sathyanarayanan S. Veeravalli Saravanan R. Shanmugam Daniel D. Heath 《International Journal of Hydrogen Energy》2012
The effects of lauric (LUA), myristic (MA), palmitic (PA), and a mixture of myristic:palmitic (MA:PA) acids on hydrogen (H2) production from glucose degradation using anaerobic mixed cultures were assessed at 37 °C with an initial pH set at 5.0 and 7.131 mM of each acid. The maximum H2 yield (2.53 ± 0.18 mol mol−1 glucose) was observed in cultures treated with PA. A principal component analysis (PCA) of the by-products and the microbial population data sets detected similarities between the controls and PA treated cultures; however, differences were observed between the controls and PA treated cultures in comparison to the MA and LUA treated cultures. The flux balance analysis (FBA) showed that PA decreased the quantity of H2 consumed via homoacetogenesis compared to the other LCFAs. The control culture was dominated by Thermoanaerovibrio acidaminovorans (60%), Geobacillus sp. and Eubacterium sp. (28%), while Clostridium sp. was less than 1%. Treatment with PA, MA, MA:PA, or LUA increased the H2 producers (Clostridium sp. and Bacillus sp.) population by approximately 48, 67, 86, and 86%, respectively. 相似文献
28.
Noori M. Cata Saady Subba Rao Chaganti Jerald A. Lalman Daniel Heath 《International Journal of Hydrogen Energy》2012
Genomic and statistical methods were used to demonstrate the effects of linoleic acid (LA) on hydrogen (H2) production in mixed anaerobic cultures from two sources (designated as A and B). The microbial composition of the control cultures CA and CB were statistically different. Bacteroidaceae (26%) and Clostridiaceae (10%) dominated CA whereas Clostridiaceae (33%) and Bacteroidaceae (10%) dominated CB. Homoacetogens directed 42% of the electron equivalents to acetate production and decreased the H2 yield by 50% in CA compared to CB. The maximum H2 yields (3.11 ± 0.02 and 3.11 ± 0.07 mol H2 mol−1 glucose in LA-treated cultures ALA and BLA, respectively) were statistically the same. Cultures ALA and BLA followed the acetate-butyrate pathway while CA and CB followed propionate and homoacetogenic pathways. LA-treated and control cultures were statistically different based on the type and quantity of metabolites; the differences were also confirmed by principal component analysis (PCA). 相似文献
29.
Heath H. Himstedt Mark S. Huberty Alon V. McCormick Lanny D. Schmidt E. L. Cussler 《American Institute of Chemical Engineers》2015,61(4):1364-1371
Conversion to ammonia with Haber–Bosch catalysts can be increased above 95% by selective absorption of ammonia by MgCl2. The maximum conversion depends on reaction and absorption equilibria. At very short times, the measured conversion rate is the same with and without absorption by the MgCl2 salt; the overall rate constants are comparable to those in the literature. At larger times, conversion to ammonia can be over seven times greater with MgCl2 than without. However, the overall rate constants can be over 10 times slower because they are controlled by ammonia diffusion in the solid salt. An approximate, pseudosteady state theory consistent with these results provides a strategy for improving the overall rate while keeping the conversion over 90%. For example, the absorption rates might be increased using smaller particles of absorbent on a porous inert absorbent support. The results provide part of the basis for designing small scale ammonia plants. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1364–1371, 2015 相似文献
30.
2D Materials: The Influence of Water on the Optical Properties of Single‐Layer Molybdenum Disulfide (Adv. Mater. 17/2015) 下载免费PDF全文