Synthesis of elastic structures with controlled forces

An analytical model is presented for synthesis of elastic structural systems under external loads and desired “controlled forces”. In the first stage, the optimal force distribution and the final cross sectional dimensions are chosen, solving an optimization problem with elastic compatibility temporarily excluded. In the second stage, the force due to the external loads is determined for the optimal structure by elastic analysis, and the desired controlled force needed for the optimal cross sections and force distribution is obtained by subtracting the above result from the optimal force of the first stage. The final design which has been determined in the first stage, satisfies both conditions of equilibrium and compatibility. It is a lower-bound solution for a similar incontrolled elastic system. In some cases the first-stage optimization problem may be cast in linear programming form. Numerical examples of continuous beam and indeterminate truss demonstrate application of the proposed method.     

On the Pressure Distribution in Uncharged Membranes During Osmotic Plow

Experiments indicated that adsorptive forces lower the potential energy of water inside uncharged cellulose acetate membranes. As a result it is postulated that the steady-state pressure distribution during osmosis is affected. In particular, a sudden rise in pressure should occur across the water-membrane interface. Thus, in this region, water may flow against a pressure gradient.     

Smooth approximation and forecasting of load duration curves

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.     

The demand for electrical energy by agriculture in the USA

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.     

Global Implications of the Information Society

"As with life itself, the prognosis for an information society is mixed, the remedy inconclusive."     

A bounding procedure for synthesis of prestressed systems

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.     

A mixed approach to forecasting peak system load

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.     

Planning available capacity in electrical power generation

In planning for the utilisation of available capacity, an electrical company needs to know the power requirements of the system. The load versus duration curve provides information on past demand patterns and thus forms a basis for planning future supply needs. Since electrical supply is discrete by nature, the load versus duration curve only approximates to the true supply requirements. This paper develops an algorithm for finding an optimal step function approximation to the load versus duration curve. It is based on the minimisation of a total penalty function.     

Some Aspects of Thermal and Photochemical Autoxidation

Following an outline of the pioneering work of Haber's School, emphasis is placed on a critical review of the most important recent achievements. These embrace, in the area of thermal autoxidation: the concept of critical antioxidant concentration, the multiple effects of heavy metals (including catalyst-inhibitor conversion), the development of new synergistic antioxidant combinations composed of free radical acceptor and peroxide decomposer and, finally, Denisov's direct experimental evidence for the reaction of heavy metals with molecular oxygen in organic media in support of Uri's trace metal hypothesis of the general mechanism of the initiation of autoxidation. The following recent advances in the field of photochemical autoxidation are described: photosensitized initiation by trace metals and its inhibition, the singlet oxygen hypothesis, the inadequacy of phenolic antioxidants and the reliance on UV absorbers, the importance of energy transfer in photochemical protection leading to new stabilizers. A very recent innovation which is relevant to both thermal and photochemical autoxidation is highlighted, i.e., the development of new α-dithidiketone chelates, particularly bis (stilbenedithiolate) nickel (= NiS₄C₄Ph₄or, abbreviated, NiSDT) as antioxidants which combine in a unique way the properties of free radical acceptors, peroxide decomposers and UV stabilizers. They were then found to be the most powerful antioxidants for polyethylene and polypropylene.