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61.
62.
The finite zeros of the open-loop transfer function matrix of the optimal controller of the multiinput time-invariant regulator problem are found to be the eigenvalues of a negative real matrix. The infinite zeros of the transfer function matrix are all real. Using the root loci technique recently developed for multivariable systems, these properties of the zeros provide means of designing stable, not necessarily optimal, high feedback gain systems under significant parameter uncertainty.  相似文献   
63.
Some approximation concepts for efficient synthesis of structural geometry are presented. Using the force method of analysis and neglecting temporarily the implicit compatibility conditions, an approximate explicit problem (AEP) is introduced. Solving the AEP, a lower bound of the optimum is efficiently obtained. To evaluate the true optimum of the implicit problem, the compatibility conditions are considered for the final geometry of the AEP.Choosing the geometric variables as the independent ones, multilevel solution procedures are proposed. To improve the solution efficiency, the number of independent variables is reduced by geometric variable linking. Also, the number of trial geometries is reduced by introducing a coarse grid in the independent variables space.Several approximation concepts are proposed for efficient solution of the explicit fixed geometry problem. Linear programming models and approximate treatment of the displacement constraints are presented. The proposed solution procedures do not involve multiple implicit analyses of the structure.Numerical examples show that in a variety of structures, where the optimal geometry is not appreciably affected by the compatibility conditions, a single exact analysis is sufficient to evaluate the final optimum. The efficiency of the solution process and the quality of the approximations used are demonstrated.  相似文献   
64.
65.
The purpose of this paper is to develop a methodology for forecasting a load duration curve. The approach adopted in the development is to estimate a load duration curve as a combined linear-exponential function and relate the coefficients of this function to a set of economic and weather related variables. This relationship allows one to forecast the coefficients which are in turn used to provide a forecast of the coefficients of interest.The model presented, for a specific set of data, forecasts well and presents a substantial improvement over existing approaches to obtaining future load duration curves.  相似文献   
66.
This paper examines the responsiveness of US agriculture to changes in the price of electricity. Price and demand equations for electricity are estimated using data for 48 American states over the period 1975–1977. Price elasticity is then estimated and found to be of sufficient magnitude to dispel doubts about the market mechanism in curtailing demand.  相似文献   
67.
"As with life itself, the prognosis for an information society is mixed, the remedy inconclusive."  相似文献   
68.
Optimal design of indeterminate prestressed concrete systems is stated in a nonlinear programming form. The design variables are the concrete dimensions, tendon coordinates, and prestressing force. The constraints are related to various behaviour and design requirements and the objective function represents the overall cost. On the basis of the transitivity property, a lower bound on the concrete volume is determined by solving a reduced problem. The corresponding minimum prestressing force, calculated by linear programming, is an upper bound. Similarly, a lower bound on the prestressing force is determined by assuming the maximum concrete dimensions. Based on the two bounding solutions a lower bound on the objective function is evaluated. An efficient design procedure is proposed. The best of the bounding solutions is first checked for optimality. The search is then continued, if necessary, in the reduced space of the concrete variables using a feasible directions technique. For any assumed concrete dimensions a reduced linear programming problem is solved. It is shown that the potentially critical constraints at the optimum of the latter problem can be identified a priori. The solution methodology and the efficiency of the proposed procedure are illustrated by some examples.  相似文献   
69.
Realizing that Box-Jenkins time series analysis lacks any basis in economic theory but at the same time wanting to take advantage of the excellent forecasting accuracy of the approach, in the first part of this paper the author takes the basic Box-Jenkins structure and integrates it into an econometric system. Relating Box-Jenkins parameters to economic and weather variables allows these parameters to be forecast. The forecast parameters can in turn be used in a Box-Jenkins model to provide a forecast of the series of interest. The result, for a specific example, proves to be clearly superior to a pure Box-Jenkins model.An alternative approach is suggested whereby an econometric model is estimated, the residual errors analyzed and forecast using a Box-Jenkins time series model, and then the results of both these models combined. The result, for the same example, proved to be an improvement over a simple Box-Jenkins model or the econometric model.When the two hybrid models are compared, the first model is the best, judged on forecasting accuracy. An important feature to consider when using the approaches, however, is the ease of use. On this basis, the alternative approach is best.  相似文献   
70.
Semiconductor tetrapods are three-dimensional (3D) branched nanostructures, representing a new class of materials for electrical conduction. We employ the single-electron transistor approach to investigate how charge carriers migrate through single nanoscale branch points of tetrapods. We find that carriers can delocalize across the branches or localize and hop between arms depending on their coupling strength. In addition, we demonstrate a new single-electron transistor operation scheme enabled by the multiple branched arms of a tetrapod: one arm can be used as a sensitive arm-gate to control the electrical transport through the whole system.  相似文献   
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