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51.
52.
In this paper we report the syntheses and study of a number of oxo- and sulphido-bridged tungsten(V) complexes with morpholine dithiocarbamate and piperidine dithiocarbamate as ligands. We assign the following formulae to the complexes: W2O3(Rdtc)4, W2O4(Rdtc)2, W2O2S2(Rdtc)2 and W2O3S(Rdtc)2 (where R = morpholine and piperidine), based on the analytical data. We have studied the complexes by IR and electronic spectra, and magnetic susceptibility measurements. We assign in the IR spectra the following bands: W=O (νs=939–948 cm?1), W-Ob(νa=813–819 cm?1, νs = 431–448 cm?1), W-Sb (νa=470–476 cm?1, νs = 368–370 cm?1, C-N (β = 1511–1519 cm?1) and C-S (ν = 1090–1113 cm?1). The low values of the magnetic moments (0.03–0.60 B.M.) are in accordance with a dimeric species of tungsten(V). 相似文献
53.
Summary A nonlinear approximation technique for the numerical solution of certain free boundary problems is proposed. The method is shown for a degenerate one-dimensional Stefan problem. For this problem, an error estimate, which is independent of the used algorithm, is derived. Numerical examples are discussed.This paper was written when the author held a 1 1/2 year postdoctoral position at the Department of Mathematics and Applied Mathematics Institute of the University of Delaware 相似文献
54.
J. Grannec L. Lozano P. Sobre J. Portier P. Hagenmuller 《Journal of fluorine chemistry》1975,6(3):267-274
The action of 70 bar of fluorine at 500°C on a mixture of lithium and nickel +II fluorides leads to a Li3NiF6 phase isostructural with α-Li3AlF6. The magnetic measurements characterize at low temperature the low spin configuration of nickel +III (d7), which tends to a high spin configuration with increasing temperature. 相似文献
55.
Canales A Angulo J Ojeda R Bruix M Fayos R Lozano R Giménez-Gallego G Martín-Lomas M Nieto PM Jiménez-Barbero J 《Journal of the American Chemical Society》2005,127(16):5778-5779
The first direct NMR determination of the conformation of a conformationally flexible heparin-like hexasaccharide bound to a key receptor, FGF-1, is described. The determination has been based on the use of a 13C-labeled protein and a regular 12C sugar. FGF-1 recognizes several conformations of the iduronic moieties of the hexasaccharide. Therefore, this case is different than that described for the controversial recognition of heparin-like saccharides by AT-III, which seems to recognize just one conformation of the iduronic acid residues. 相似文献
56.
In data envelopment analysis (DEA) an inefficient unit can be projected onto an efficient target that is far away, i.e. reaching
the target may demand large reductions in inputs and increases in outputs. When the inputs and outputs modifications planned
are large, it may be troublesome to carry them out all at once. In order to help an inefficient unit reach a distant target,
a strategy of gradual improvements with successive, intermediate targets has been proposed. This paper extends such approach
to the variable returns to scale (VRS) case. In the VRS scenario we distinguish between units that are technical efficient
and those that are not. On the one hand, for those units that are not technical efficient the proposed approach determines
successive intermediate targets leading to the technical efficiency frontier, i.e. the priority for those units is to attain
technical efficiency. On the other hand, for those units that are technical efficient but not scale efficient the proposed
approach computes a sequence of targets ending in the global efficiency frontier, i.e. when technical efficiency is guaranteed
the goal is then to attain global efficiency. In both cases, the successive targets are obtained by iteratively solving specific
DEA models that take into account given bounds on the rates of change in inputs and outputs that the unit can implement in
each step. 相似文献
57.
Taguchi method is the usual strategy in robust design and involves conducting experiments using orthogonal arrays and estimating the combination of factor levels that optimizes a given performance measure, typically a signal-to-noise ratio. The problem is more complex in the case of multiple responses since the combinations of factor levels that optimize the different responses usually differ. In this paper, an Artificial Neural Network, trained with the experiments results, is used to estimate the responses for all factor level combinations. After that, Data Envelopment Analysis (DEA) is used first to select the efficient (i.e. non-dominated) factor level combinations and then for choosing among them the one which leads to a most robust quality loss penalization. Mean Square Deviations of the quality characteristics are used as DEA inputs. Among the advantages of the proposed approach over traditional Taguchi method are the non-parametric, non-linear way of estimating quality loss measures for unobserved factor combinations and the non-parametric character of the performance evaluation of all the factor combinations. The proposed approach is applied to a number of case studies from the literature and compared with existing approaches. 相似文献
58.
Naian Liu Qiong Liu Jesse S. Lozano Linhe Zhang Zhihua Deng Bin Yao Jiping Zhu Kohyu Satoh 《Proceedings of the Combustion Institute》2013,34(2):2555-2564
This paper presents the first effort to explore the spatial distributions of the burning rates in group fires consisting of a large number of fire points, by analyzing burn-out time data from experimental square fire arrays ranging from 3 × 3 to 15 × 15. A new concept termed fire layer is introduced and defined to characterize the spatial locations of fire points by which the complex spatial variations of burning rates, under different conditions, are analyzed and physically interpreted. Analysis shows that the fire layer burning rates vary from outer to inner in definite nonlinear modes. This indicates that the two fire interaction effects, heat feedback enhancement and air supply restriction, involve distinct spatial fluctuations in fire arrays. The spatial fluctuations of the two interaction effects are significantly affected by the two major parameters, fire spacing and fire array size. Definite spatial regions and parameter ranges for the spatial fluctuations and high competitions of the two interaction effects are clearly distinguished. It is demonstrated that the average burning rates of all fire layers involve consistent variations versus fire spacing or fire array size, especially with high comparability to the entire fire array. It is found that by varying fire spacing, the average burning rates for all fire layers vary linearly versus the fire area ratio, within the same ranges as the entire fire array, while there exist different fluctuation modes of fire layer burning rates with respect to fire array size. Furthermore, analysis shows that the burning rates of all fire layers will be significantly affected by fire merging when it occurs. Finally, a new approach is presented to simulate fire propagation among discrete fuel sources, by which the positive effect of the surrounding new fire points on the burning rates of the original ones is definitely indicated. 相似文献
59.
Jiao Lei Naian Liu Jesse S. Lozano Linhe Zhang Zhihua Deng Kohyu Satoh 《Proceedings of the Combustion Institute》2013,34(2):2607-2615
This paper presents the first experimental effort to explore the large scale 3-D flame instabilities of fire whirls, including the inclined flame revolution during the transition from a general pool fire to fire whirl, and the swirling flame precession in a quasi-steady fire whirl. The experimental medium-scale fire whirls were produced by a fixed-frame facility. Experimental observations indicate that flame revolution is an important flame instability during the formation of fire whirl, showing that the entire flame is inclined and revolves around the geometrical axis of symmetry with increasing angular velocity until the critical point, without the self-rotation of the flame. It is found that the inlet velocity fluctuates synchronously with the flame revolution. As soon as the fire whirl forms, the erect swirling flame starts to precess around the geometrical axis of symmetry. Analysis indicates that during flame precession the periodic fluctuations of inlet velocity disappear and a local annular external recirculation zone (ERZ) is produced outside the flame (vortex core), while the flow is upward inside. It is found that the inlet velocities are nearly constant within the continuous flame in order to maintain a stable generating eddy. A good linear correlation exists between the average inlet velocities and average ambient circulations for all fuel pan sizes. The precession frequency is relatively stable during one test. The frequencies of flame revolution and precession are both proportional to the average inlet velocity, and the corresponding Strouhal numbers are constants of 0.42 and 0.80, respectively. The flame revolves and precesses in the same direction as the self-rotation of the fire whirl flame in all tests. The flame revolution is related to the periodical fluctuations of inlet flow, while the flame precession is considered to be linked to the occurrence of ERZ in fire whirls. 相似文献
60.
In this paper, a directional distance approach is proposed to deal with network DEA problems in which the processes may generate not only desirable final outputs but also undesirable outputs. The proposed approach is applied to the problem of modelling and benchmarking airport operations. The corresponding network DEA model considers two process (Aircraft Movement and Aircraft Loading) with two final outputs (Annual Passenger Movement and Annual Cargo handled), one intermediate product (Aircraft Traffic Movements) and two undesirable outputs (Number of Delayed Flights and Accumulated Flight Delays). The proposed approach has been applied to Spanish airports data for year 2008 comparing the computed directional distance efficiency scores with those obtained using a conventional, single-process directional distance function approach. From this comparison, it can be concluded that the proposed network DEA approach has more discriminatory power than its single-process counterpart, uncovering more inefficiencies and providing more valid results. 相似文献