Efficiency in public schools: a case study in non-parametric measurement

This study illustrates the problem of efficiency measurement in stochastic input-output systems when market price data are unavailable. Efficiency comparisons by non-parametric methods are attempted for selected public elementary schools in California for 1976-77 and 1977-78. A suitable linear programming model is developed for the efficiency frontier in the input-output space, which is found to be significantly different from an average relation. This is shown to have important policy implications for improving input performance for better efficiency.     

A theory of portfolio revision: robustness and truncation problems

A set of decision criteria, different from bayesian methods is developed here, which is useful for making optimal portfolio decisions in a mean variance framework, These criteria which emphasize robustness and sensitivity to outliers are applied to revise a given size portfolio by including new securities or excluding old ones. A set of theorems is utilized to characterize situations when revisions are unnecessary due to the original portfolio being robust in some sense     

Portfolio performance of mutual funds: efficiency and robustness

Empirical analysis often mutual funds randomly selected from Jensen's study over a twenty-year period (1945-64) is used to test (l) the risk-return efficiency frontiers, and (2) the robustness in terms of minimax levels of variance. The statistical tests confirm that balanced funds and balanced portfolios are more robust than the so-called growth funds and growth portfolios. Tests on optimal ordering and selection of the best population also show that the mutual fund with the highest sample mean return has a very low probability of identifying the best population distribution, i.e. with a highest mean return     

On the optimality of output inventory decisions of a firm under imperfect stochastic markets

A class of suboptimal strategies in price, output and inventories is proposed for a firm in imperfectly competitive stochastic markets. When the demand faced is incompletely known and inventories are held partly as a buffer against fluctuations in demand, and partly as active decision variables, the solution is characterized by maximizing expected profits over two periods with an additive error in the demand function having a known prior density. Simulations of the solution profiles show that for the two-period moving horizon model proposed here, the variance of profits and revenues are sharply reduced, a feature that is most attractive for a risk averse firm.     

On the two-level planning procedure under a Dantzig-Wolfe decomposition†

In this paper a modified Dantzig-Wolfe decomposition algorithm is interpreted as a. decontralized planning process. The main objective is to provide some extensions of the pricing and allocation rules of the original algorithm to make the solution process more efficient. A simple numerical example is included.     

Data envelopment analysis: a new tool for improving managerial efficiency

Two new applications of the recently developed tool of ‘data envelopment analysis’ are focused on here. One develops the concept of systematic efficiency, and the other the concept of dynamic efficiency. An empirical application shows the tremendous usefulness of this new managerial technique for measuring and improving industrial productivity     

The effects of market power on the stocks and prices of world coffee

The objective of this study is to explore the consequences of market power for optimal stockholding and price variations in the world coffee economy. Optimal storage decision rules which incorporate risk aversion under several market scenarios are considered. These generate a set of price and quantity series that can be compared with the historical data and to test the hypothesis proposed by Newbery that a monopolistic producer tends to undertake more storage than a competitive producer and hence price stability may increase in proportion to the dominant role played by the monopolist. Our study reveals that the world coffee market has been rather close to the competitive regime since the 1960s. As far as price variations are concerned, results are not always consistent with the Newbery hypothesis.     

Informetric analysis of dynamic decision rules in applied economic models: a selective survey

The characteristics of various information structures underlying a class of control theoretic applications to economic models known as linear decision rules are analysed here through a set of illustrative applications. The implications of departure from the two assumptions of normality and certainty equivalence are emphasized in particular, with reference to Cournot-type market models and stabilization policy in an econometric framework     

Analysis,design and implementation of sensorless <Emphasis Type="Italic">V/f</Emphasis> control in a surface-mounted PMSM without damper winding

This paper presents a novel, reliable and efficient V/f control implementation on a 8-pole, 750 rpm, 5 kW surface-mounted permanent magnet synchronous motor (PMSM) without damper winding. In the absence of a damper winding, open loop V/f control of SM is inherently unstable, particularly at high speeds. Stabilisation can be done with proper stator frequency modulation in accordance with the change in rotor speed to provide for effect of damping. This has been implemented here without use of any shaft-mounted encoder. The change in rotor speed is observed from power perturbation, thereby eliminating the need for using a speed sensor in the drive. The efficiency of the drive is further increased with appropriate control of the power factor, irrespective of load and frequency variations. Simulated and experimental results are presented for both open-loop and the proposed V/f control. These results establish the accuracy of the design of the proposed V/f control strategy and the precision of hardware implementation. A comparative study between the proposed V/f control method and standard vector control method, as implemented on this PMSM, has also been presented here to establish the advantages of the proposed scheme. The PMSM itself was designed and fabricated in the laboratory.