University of Rochester

About: University of Rochester is a education organization based out in Rochester, New York, United States. It is known for research contribution in the topics: Population & Laser. The organization has 63915 authors who have published 112762 publications receiving 5484122 citations. The organization is also known as: Rochester University.

Coherence Properties of Optical Fields

Abstract: This article presents a review of coherence properties of electromagnetic fields and their measurements, with special emphasis on the optical region of the spectrum. Analyses based on both the classical and quantum theories are described. After a brief historical introduction, the elementary concepts which are frequently employed in the discussion of interference phenomena are summarized. The measure of second-order coherence is then introduced in connection with the analysis of a simple interference experiment and some of the more important second-order coherence effects are studied. Their uses in stellar interferometry and interference spectroscopy are described. Analysis of partial polarization from the standpoint of correlation theory is also outlined. The general statistical description of the field is discussed in some detail. The recently discovered universal "diagonal" representation of the density operator for free fields is also considered and it is shown how, with the help of the associated generalized phase-space distribution function, the quantum-mechanical correlation functions may be expressed in the same form as the classical ones. The sections which follow deal with the statistical properties of thermal and nonthermal light, and with the temporal and spatial coherence of blackbody radiation. Later sections, dealing with fourth- and higher-order coherence effects include a discussion of the photoelectric detection process. Among the fourth-order effects described in detail are bunching phenomena, the Hanbury Brown-Twiss effect and its application to astronomy. The article concludes with a discussion of various transient superposition effects, such as light beats and interference fringes produced by independent light beams.

The Performance of Mutual Funds in the Period 1945-1964

Abstract: In this paper I derive a risk-adjusted measure of portfolio performance (now known as Jensen's Alpha) that estimates how much a manager's forecasting ability contributes to the fund's returns. The measure is based on the theory of the pricing of capital assets by Sharpe (1964), Lintner (1965a) and Treynor (Undated). I apply the measure to estimate the predictive ability of 115 mutual fund managers in the period 1945-1964 - that is their ability to earn returns which are higher than those we would expect given the level of risk of each of the portfolios. The foundations of the model and the properties of the performance measure suggested here are discussed in Section II. The evidence on mutual fund performance indicates not only that these 115 mutual funds were on average not able to predict security prices well enough to outperform a buy-the-market-and-hold policy, but also that there is very little evidence that any individual fund was able to do significantly better than that which we expected from mere random chance. It is also important to note that these conclusions hold even when we measure the fund returns gross of management expenses (that is assume their bookkeeping, research, and other expenses except brokerage commissions were obtained free). Thus on average the funds apparently were not quite successful enough in their trading activities to recoup even their brokerage expenses.

Cellulase, Clostridia, and Ethanol

Abstract: Biomass conversion to ethanol as a liquid fuel by the thermophilic and anaerobic clostridia offers a potential partial solution to the problem of the world's dependence on petroleum for energy. Coculture of a cellulolytic strain and a saccharolytic strain of Clostridium on agricultural resources, as well as on urban and industrial cellulosic wastes, is a promising approach to an alternate energy source from an economic viewpoint. This review discusses the need for such a process, the cellulases of clostridia, their presence in extracellular complexes or organelles (the cellulosomes), the binding of the cellulosomes to cellulose and to the cell surface, cellulase genetics, regulation of their synthesis, cocultures, ethanol tolerance, and metabolic pathway engineering for maximizing ethanol yield.

Intrinsic motivation, extrinsic reinforcement, and inequity

Abstract: If a person who is intrinsically motivated to perform an activity begins to receive external reinforcement for the activity, what will happen to his intrinsic motivation? Previous studies and the present study indicate that money decreases intrinsic motivation, while verbal reinforcements tend to enhance intrinsic motivation. The beginning of a cognitive evaluation theory is discussed, and an apparently discrepant prediction between this theory and inequity theory is pointed out. It is argued, however, that the theories are not conceptually discrepant, and the present study gives support for this argument. It is possible to distinguish between two broad classes of motivation to perform an activity: intrinsic motivation and extrinsic motivation. A person is intrinsically motivated if he performs an activity for no apparent reward except the activity itself (cf. Berlyne, 1966; Hunt, 1965; White, 1959). Extrinsic motivation, on the other hand, refers to the performance of an activity because it leads to external rewards (e.g., status, approval, or passing grades). The question of interest in this study is whether there will be changes in a person's intrinsic motivation for an activity when he receives external rewards for performing that activity. Deci (1971) reported that external reinforcements do affect intrinsic motivation, and he suggested the initial elements of a cognitive evaluation theory to account for the changes in intrinsic motivation following an experience with extrinsic rewards. The theory focuses on a person's cognitive evaluation of an activity and the reasons for his engaging in the activity. It suggests that distinctions should be made among different kinds of external rewards, since a person's evaluation of different rewards may be different. In turn, this would 1 The author would like to thank Wayne Cascio for serving as the first experimenter and for helping with the data analysis; Victor Vroom for making helpful comments on an earlier draft of the manuscript; and Larry Coff for being the second experimenter.

Disparities in Health Care by Race, Ethnicity, and Language Among the Insured:Findings From a National Sample

Abstract: BACKGROUND: Racial and ethnic disparities in health care have been well documented, but poorly explained. OBJECTIVE: To examine the effect of access barriers, including English fluency, on racial and ethnic disparities in health care. RESEARCH DESIGN: Cross-sectional analysis of the Community Tracking Survey (1996 –1997). SUBJECTS: Adults 18 to 64 years with private or Medicaid health insurance. MEASURES: Independent variables included race, ethnicity, and English fluency. Dependent variables included having had a physician or mental health visit, influenza vaccination, or mammogram during the past year. RESULTS: The health care use pattern for English-speaking Hispanic patients was not significantly different than for non-Hispanic white patients in the crude or multivariate models. In contrast, Spanish-speaking Hispanic patients were significantly less likely than non-Hispanic white patients to have had a physician visit (RR, 0.77; 95% CI, 0.72– 0.83), mental health visit (RR, 0.50; 95% CI, 0.32–0.76), or influenza vaccination (RR, 0.30; 95% CI, 0.15– 0.52). After adjustment for predisposing,need, and enabling factors, Spanish-speaking Hispanic patients showed significantly lower use than non-Hispanic white patients across all four measures. Black patients had a significantly lower crude relative risk of having received an influenza vaccination(RR, 0.73; 95% CI, 0.58–0.87). Adjustment for additional factors had little impact on this effect, but resulted in black patients being significantly less likely than non-Hispanic white patients to have had a visit with a mental health professional (RR, 0.46; 95% CI,0.37– 0.55). CONCLUSIONS: Among insured nonelderly adults, there are appreciable disparities in health-care use by race and Hispanic ethnicity. Ethnic disparities in care are largely explained by differences in English fluency, but racial disparities in care are not explained by commonly used access factors.