A performance measure for manual control systems

A new performance measure is introduced for multivariable closed loop experiments with a human operator. The essential feature of the phase margin performance measure (PMPM) is that the performance of each control loop can be determined independently, with prescribed disturbance and error levels. A variable filter parameter is used as the PMPM within the loop and it assures a high workload at the same time. There is a straightforward relationship between the PMPM and the inner loop feedback augmentation that can be utilized in trade-off studies. An adjustment scheme that seeks the PMPM automatically is described as employed in a single loop control task. This task applies directly to the experimental study of displays for helicopters and VTOL aircraft

On the Generalised Random Energy Model

The Generalised Random Energy Model is a generalisation of the Random Energy Model introduced by Derrida to mimic the ultrametric structure of the Parisi solution of the Sherrington-Kirkpatrick model of a spin glass. It was solved exactly in two special cases by Derrida and Gardner. A rigorous analysis by Capocaccia et al. claimed to give a complete solution for the thermodynamics of the model in the general case. Here we use Large Deviation Theory to analyse the model along the lines followed by Dorlas and Wedagedera for the Random Energy Model. The resulting variational expression for the free energy is the same as that found by Capocaccia et al. We show that it can be evaluated in a very simple way. We find that the answer given by Capocaccia et al. is incorrect

Sources of Capital and Debt Structure in Small Firms

In this paper we examine the relationship between ownership differences and small firms’ financial policies using a survey of U.S. companies. The study finds that financial policies differ according to the type of ownership (private versus public) and by the ownership differences (family-owned, closely-held, or widely-held) within the private firms. The differences are in the ownership concentration, relative importance of various sources of capital, debt characteristics (sources of debt financing, debt maturity, and debt cost). A multiple regression equation estimated in the paper provides evidence relating to cross-sectional variations in debt ratios of small firms. The paper offers information asymmetry, illiquidity, and agency cost explanations for the observed differences in ownership and financial policies of small firms

Use of Debt Covenants in Small Firms

This paper examines the structure of debt covenants in small firms, with emphasis on privately owned firms. It is based on a survey of a large sample of firms drawn from the S&P Register of Corporations. The findings show that debt covenants imposed on small firms differ according to the firm type (privately owned or publicly owned), debt level, the borrowing cost, and the source of financing (bank or other sources). The evidence is generally consistent with the arguments relating to stockholder-bondholder agency cost conflicts and the Costly Contracting Hypothesis of Smith and Warner (1979)

Corporate Governance, Illiquidity, and Valuation Issues in Privately-Owned Corporations

Investors in private corporations face unique problems relating to corporate control, illiquidity and valuation of securities. In this research, we survey a large sample of US corporations. Our sample includes both private and public firms. Major findings of our research are as follows: Private firms use written shareholder agreements for safeguarding ownership interests and dividend payments. Family owned firms dominate the ownership structure of private firms. Insiders of private firms own a much larger proportion of common stock than insiders in public firms, and the CEOs of private firms often happen to be the largest stockholders

The Role of Solar Wind Hydrogen in Space Weathering: Insights from Laboratory-Irradiated Northwest Africa 12008

Micrometeoroid impacts, solar wind plasma interactions, and regolith gardening drive the complicated and nuanced mechanism of space weathering (or optical maturation); a process by which a materials optical properties are changed as a result of chemical and physical alterations at the surface of grains on airless bodies. Reddened slopes, attenuated absorption bands, and an overall reduction in albedo in the visible and near-IR wavelength ranges are primarily the result of native iron nanoparticle (npFe0) production within glassy rims that form from sputtering and vaporization. The sizes and abundance of these particles provide information about the relative surface exposure age of a particular grain. In addition, many studies have indicated that composition greatly affects the rate at which optical maturation occurs. Despite our understanding of how npFe0 affects optical signatures, the relative roles of micrometeoroid bombardment and solar wind interactions remains undetermined. To simulate the early effects of weathering by the solar wind and to determine thresholds for optical change with respect to a given mineral phase, we irradiated a fine-grained lunar basalt with 1 keV H+ to a fluence of 6.4 x 1016 H+ per sq.cm. Surface alterations within four phases have been evaluated using transmission electron microscopy (TEM). We found that for a given fluence of H+, the extent of damage acquired by each grain was dependent on its composition. No npFe(0) was produced in any of the phases evaluated in this study. These results are consistent with many previous studies conducted using ions of similar energy, but they also provide valuable information about the onset of space weathering and the role of the solar wind during the early stages of optical maturation