Showing papers by "University of Rochester published in 1968"

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.

A Theory of the Calculus of Voting

Abstract: Much recent theorizing about the utility of voting concludes that voting is an irrational act in that it usually costs more to vote than one can expect to get in return.1 This conclusion is doubtless disconcerting ideologically to democrats; but ideological embarrassment is not our interest here. Rather we are concerned with an apparent paradox in the theory. The writers who constructed these analyses were engaged in an endeavor to explain political behavior with a calculus of rational choice; yet they were led by their argument to the conclusion that voting, the fundamental political act, is typically irrational. We find this conflict between purpose and conclusion bizarre but not nearly so bizarre as a non-explanatory theory: The function of theory is to explain behavior and it is certainly no explanation to assign a sizeable part of politics to the mysterious and inexplicable world of the irrational.2 This essay is, therefore, an effort to reinterpret the voting calculus so that it can fit comfortably into a rationalistic theory of political behavior. We describe a calculus of voting from which one infers that it is reasonable for those who vote to do so and also that it is equally reasonable for those who do not vote not to do so. Furthermore we present empirical evidence that citizens actually behave as if they employed this calculus.3

Equations-of-Motion Method and the Extended Shell Model

Abstract: This paper presents the equations-of-motion method as a useful and flexible tool in the study of nuclear spectroscopy. It is partly a review, but also it introduces a new and much more powerful equations-of-motion technique which supercedes the older linearization methods. The older methods worked with operator equations. To obtain closed expressions they had to be linearized in a rather arbitrary manner. The present approach works with the ground-state expectation of operator equations and thereby avoids all problems of linearization. Thus, like the Green's function method, the equations-of-motion method becomes potentially exact. It has many advantages over Green's function methods, however, among which are its greater compactness, simplicity, and the physical insight it yields.The method is first applied to rederive the random phase approximation (RPA) and the quasi-particle RPA (QRPA) and to show precisely what terms they neglect. It is demonstrated that some of these terms have coherent phases. A higher RPA and QRPA are then derived to include these terms. The corrections have some interesting effects: notably, there is a reduction of the effective interaction strength and a stabilization of the nucleus against sudden phase transitions. The equations-of-motion method is also used to generalize, in a very simple and natural way, the Hartree-Fock (HF) and Hartree-Bogolyubov (HB) concepts of independent particles and quasi-particles to nonsimple ground states.The equations-of-motion method is presented as a simple extension of the shell model to the treatment of excitationg of a correlated ground state. By concentrating on the quantities of direct physical interest, the complexity of workins with correlated wavefunctions is avoided.

The value of hyposensitization therapy for bronchial asthma in children—a 14-year study

Abstract: The clinical course of 210 children with perennial bronchial asthma was followed in a prospective controlled study in which one half of the children received placebo injections while the other half received conventional hyposensitization therapy. Of the 130 children still under observation at the time of their sixteenth birthday, 22% of the placebo-treated children were free of asthma compared to 72% of the treated children. In the treated group the rate of loss of asthma may be related to the dose of antigen received in hyposensitization therapy. Whereas 66% of the "1/5,000" group were free of asthma at the end of the study, 78% of the "highest tolerated dose" group were symptom free in their sixteenth year. The likelihood of a child outgrowing asthma was not significantly influenced by his sex, age of onset, or severity of his symptoms when first seen. A previous history of hay fever increased the likelihood of a child9s asthma persisting into adolescence.

Evidence that there are two forms of fluoride in human serum.

Abstract: IT has been assumed that there is only one form of fluoride in serum, the inorganic F ion. It would therefore seem that either the value for serum fluoride which I found (1 µM) (refs. 1 and 2) or that found by Singer and Armstrong (7.5 µM) (ref. 3) must be in error. While the diffusion method of Singer and Armstrong has been shown to produce erroneous values, the same cannot be said for their ashing and distillation procedure. The evidence that the serum fluoride is about 1 µM in a fluoridated community does not rule out the possibility that more fluoride could be made available from serum by ashing; it only indicates that the fluoride in serum able to exchange with added radioactive fluoride can be measured and is 1 µM.

Origin and Evolution

Abstract: Discussants have been asked to synthesize and prophecy rather than to summarize. The variety of models and views expressed here warn that any report is only another opinion. Blessing to the reader.

Clinical radiation pathology as applied to curative radiotherapy

Abstract: The value of radiation pathology in understanding the radiation effects in normal tissues and tumors is stressed in developing curative radiotherapy. A theory of cell radiosensitivity is presented based on cellular proliferation, differentiation and life span. From this base, concepts of tissue and organ radiosensitivity are developed utilizing the knowledge of tissue organization, cell kinetics and microcirculation. Through a series of paradigmatic charts and drawings an attempt is made to explain different clinical manifestations of radiation reactions on the basis of similar histopathologic changes. Possible future directions for radiation research to explore are outlined.

Inverse Diffraction and a New Reciprocity Theorem

Abstract: A solution is obtained to the inverse diffraction problem for a monochromatic scalar wave field propagated into the half space z>0. It is shown how to determine the field distribution throughout the region 0≤z 0. The solution takes a particularly simple form when the spatial-frequency spectrum of the distribution in the plane z=z1 (or in any other plane z=const>0) is bandlimited to a circle whose radius is equal to the wavenumber of the field. In this case, the solution to the inverse diffraction problem may be expressed in a form strictly similar to that for the direct-propagation problem (exterior boundary-value problem), given by Rayleigh’s diffraction formula of the first kind. A comparison of these two solutions leads to the formulation of a new reciprocity theorem, valid for a wide class of wave fields.

Studies on the developing cerebellums. Ultrastructure of the growth cones

Abstract: The fine structure of the cerebellar cortex in rats was examined between the first and forty-fifth post-natal day The formation and growth of axon and dendrites are reported here As inferred from these observations, the process starts under the cell membrane as a local accumulation of vesicles without any visible content, about 1,100 A in size This is followed by an outward bulging of the membrane which then becomes filled with vesicles and is known as the primary growth cone In axons the synaptic and growth cone vesicles coexist until the third week or longer In dendrites secondary growth cones exist at the tip of the branching dendrites and spines Variations in the shape of the growth cone vesicles related to the age of the animal are described, and the importance of attempting to isolate the growth cones and the vesicles is emphasized

Coherent Soft-Photon States and Infrared Divergences. II. Mass-Shell Singularities of Green's Functions

Abstract: This is the second in a series of four papers in which a new, field-theoretic approach to the problem of the infrared divergences of quantum electrodynamics is presented. The primary aim of the present paper is the study of the mass-shell singularities of the Green's functions, which are branch points rather than simple poles. This is an essential preliminary to the discussion of asymptotic states and scattering matrix elements in subsequent papers. A conventional separation is introduced between hard- and soft-photon regions of momentum space. It is shown that the soft-photon contribution to an arbitrary Green's function may be isolated in a single function of the external momenta, independent of the spins of the particles involved. An explicit expression for this function is obtained and its mass-shell singularities are studied in detail. In particular, it is shown that, in contrast to the case where there are no massless particles, the mass-shell singularities in different momenta are not independent, but depend on the order in which the various momenta are allowed to approach their mass shells.

Vision: The Additivity Law Made To Work for Heterochromatic Photometry with Bipartite Fields

Abstract: Additivity failures are common in heterochromatic photometry when the usual criterion of equal brightness is used. Using instead the criterion of a minimally distinct border between two precisely juxtaposed fields, we found that the additivity law holds.

Salt-induced contraction of bacterial cell walls.

Abstract: Intact Bacillus megaterium cells were found to contract as much as 26% in terms of dextran-impermeable volume when transferred from water to unbuffered, non-plasmolyzing NaCl solutions. This shrinkage appeared to be primarily due to electrostatic wall contraction rather than to any osmotic response of the cells. A variety of salts (but not sucrose) added to water suspensions of isolated cell walls caused protons to be released from the walls with resultant lowering of suspension pH and contraction of the structures. In effect, B. megaterium walls behaved as flexible, amphoteric polyelectrolytes, and their compactness in aqueous suspensions was affected by changes in environmental ionic strength and pH. Isolated walls were most compact in low ionic strength media with a pH of about 4, a value close to the apparent isoelectric pH of wall peptidoglycan. Electrostatic attractions appeared to play a major role in determining the compactness of highly contracted walls, and the walls responded to increased environmental ionic strength by expanding. In contrast, electrostatic repulsions were dominant in highly expanded walls, and increased environmental ionic strength induced wall contraction. Walls of whole bacteria also shrank when the cells were plasmolyzed. This second type of contraction seemed to result from relief of wall tension during plasmolysis, and it could be induced with nonionic solutes. Thus, cell wall tone in B. megaterium appeared to be set both by mechanical tension and by electrostatic interactions among wall ions.

Coherent Soft-Photon States and Infrared Divergences. III. Asymptotic States and Reduction Formulas

Abstract: In paper II of this series, the mass-shell singularities of the Green's functions of quantum electrodynamics were investigated. In this paper, the relationship between these singularities and the asymptotic states of the theory is studied by considering the nature of the intermediate states that can contribute to the corresponding discontinuity functions. The basic principle underlying this work is that the asymptotic states of the theory should not be specified a priori but should be determined from the structure of the Green's functions themselves. The pure soft-photon asymptotic states, which can be created from the vacuum by operators constructed from the soft-photon part of the electromagnetic field, are studied first. These states are defined by appropriate weak limits and are shown to span a space with the same structure as in the noninteracting case. Next, states containing a single particle (massive particle or hard photon), together with soft photons, are investigated. These states can appear as intermediate states in the two-point function. They are again defined by weak limits, and are shown to be stable in the absence of external currents. It is demonstrated that the near-mass-shell components of the field operator, acting on the vacuum or on a soft-photon coherent state, yield a state containing one particle and a soft-photon coherent state. Finally, the analysis is extended to two-particle and multiparticle states. The only essentially new feature here is the appearance of factors related to the "Coulomb phases." General reduction formulas are obtained that permit matrix elements between arbitrary asymptotic states to be extracted from the Green's functions. In effect, these matrix elements may be identified with the coefficients not of poles but of branch-point singularities.

Coherent Soft-Photon States and Infrared Divergences. IV. The Scattering Operator

Abstract: In Paper III of this series, the asymptotic states of quantum electrodynamics were defined in terms of the mass-shell singularity structure of the Green's functions. In this paper the reduction formulas obtained are used to derive simple expressions for the matrix elements of the scattering operator. This operator is defined on the space of asymptotic states, which is the direct product of the Fock space of the particles (massive particles and hard photons) with the nonseparable Hilbert space, defined in Paper I, which is spanned by the soft-photon coherent states. It is shown that the scattering operator so defined is gauge-invariant, Lorentz-invariant, unitary, crossing-symmetric, and independent of the choice of the small parameter that defines the separation between hard and soft photons. For a given initial state, the only nonvanishing scattering matrix elements are those to final states in a specific equivalence class, and conditions for states to be equivalent in this sense are obtained. The relationship between these matrix elements and physically measurable cross sections is discussed. In this way, results obtained by conventional methods are reproduced, but in addition questions inaccessible to such methods, such as the effect of an infinite number of soft photons in the initial state, may be investigated.

Tetraploid DNA content of Purkinje neurons of human cerebellar cortex.

Abstract: Microspectrophotometric analysis of single cells in Feulgen preparations revealed tetraploid amounts of DNA in Purkinje neurons of human cerebellar cortex.

Perturbation Approach to Spatial Brightness Interaction in Human Vision

Abstract: The tools of Fourier analysis can be used to explain visual phenomena of spatial brightness interaction, provided that attention is confined to small perturbations of spatially uniform fields. A perturbation approach is outlined here, and a transfer function is presented which is appropriate for small perturbations. The transfer function was obtained from human subjects with psychophysical methods, for the case of briefly flashed, achromatic fields at photopic levels of illumination. For the frequency range of 0.005 to 0.15 cycles per minute of arc, the transfer function is roughly proportional to spatial frequency, thus reflecting, in large part, nonoptical properties of the system. A simple mechanism of lateral inhibition could underlie this transfer function.

Effect of lattice disorder on the superconducting transition temperature.

Abstract: A theory is presented to explain the dependence of the superconducting transition temperature ${T}_{c}$ on the changes in the phonon frequency spectrum and electronic density of states which result from lattice disorder. Numerical calculations of ${T}_{c}$ are presented for films composed of crystalline granules, for films composed of amorphous granules, and for homogeneous amorphous metals. The calculations are in good agreement with experimental values of ${T}_{c}$.

Extensions of griffin's statistical model for medium-energy nuclear reactions.

Abstract: The new statistical model due to Griffin has been extended to include charged-particle emission by evaluation of the transition matrix in terms of a relative velocity and scattering cross section. Additionally a quite different formulation is derived for the equilibrium emission probability, whereas the precompound emission probability is similar to Griffin's result.