Showing papers by "Northwestern University published in 1968"

Behavior of Current Divergences under SU 3 × SU 3

Abstract: We investigate the behavior under SU3×SU3 of the hadron energy density and the closely related question of how the divergences of the axial-vector currents and the strangeness-changing vector currents transform under SU3×SU3. We assume that two terms in the energy density break SU3×SU3 symmetry; under SU3 one transforms as a singlet, the other as the member of an octet. The simplest possible behavior of these terms under chiral transformations is proposed: They are assigned to a single (3,3*)+(3*,3) representation of SU3×SU3 and parity together with the current divergences. The commutators of charges and current divergences are derived in terms of a single constant c that describes the strength of the SU3-breaking term relative to the chiral symmetry-breaking term. The constant c is found not to be small, as suggested earlier, but instead close to the value (-sqrt[2]) corresponding to an SU2×SU2 symmetry, realized mainly by massless pions rather than parity doubling. Some applications of the proposed commutation relations are given, mainly to the pseudoscalar mesons, and other applications are indicated.

The two-arousal hypothesis: reticular formation and limbic system.

Abstract: It is postulated that there are 2 major systems in the brain that maintain the ongoing behavior of the vertebrate organism. Arousal System 1 is related to the reticular activating system. It maintains the arousal of the organism, and provides the organization for responses. Arousal System II is related to the limbic system, and provides control of responses through incentive-related stimuli. The organization of these 2 mechanisms is postulated to be mutually inhibitory. It is shown how such an organization is of value in understanding reinforcement as part of a reciprocal relation between drive (Arousal System I) and incentive (Arousal System II). Memory is viewed as a consequence of this reciprocity. The present paper grew out of an attempt to understand the relation between two recent major findings in neurobiology. The first was described by Moruzzi and Magoun (1949) and concerned itself with a medial core primarily in midbrain and hindbrain whjch was capable of activating or arousing the cerebral cortex. This system has often been referred to as the Ascending Reticular Activating System (ARAS). The second finding concerned the discovery (Olds & Milner, 1954) of a series of points primarily within the forebrain which when stimulated prpduced effects similar to "normal" reward. The proposal offered here is that these two discoveries represent the description of two major brain mechanisms that are critical to the organism for the execution of appropriate behavior sequences. Because the two systems operate in such an intimate 1 The author wishes to thank Stanley A. Lorens and Benton J. Underwood for reading a preliminary draft of the manuscript, an4 tp acknowledge his debt to P. Milner, S. Glickman, and J. Olds. During the preparation of the manuscript the author was supported by United States Public Health Service contract MH11991. fashion, much confusion has occurred in the analysis of certain data related to these systems. It is the purpose of the paper to show that an analysis of brain function assuming two arousal systems may be of value in the future to help correct this confusion. A second purpose is to organize a sufficient amount of information to point out where empirical facts appear necessary, and to stress certain special issues which have arisen in considering the information relevant to the two-arousal hypothesis.

Size-detecting mechanisms in human vision.

Abstract: Inspecting a pattern of alternating dark and light bars makes it difficult to see a similar pattern presented afterward. This phenomenon can be used to isolate mechanisms responsive to bars of a given width. Our results suggest that the human visual system contains several different classes of size detectors, each maximally sensitive to visual targets with sizes in a particular range.

Non-linear capillary instability of a liquid jet

Abstract: A third-order theory has been developed to study capillary instability of a liquid jet. The result shows that the asymmetrical development of an initially sinusoidal wave is a non-linear effect with generation of higher harmonics as well as feedback into the fundamental. The growth of the surface wave is found to depend explicitly on the dimensionless initial amplitude of the disturbance and the dimensionless wave-number k of the wave. For the same initial disturbance, the wave is found to have a maximum growth rate at k = 0·7 in agreement with the linearized theory. For the same wave-number, the growth is proportional to the initial amplitude of the disturbance. The cut-off wave-number and the fundamental frequency (or growth rate for the unstable case) of the wave for a given k are found to be different from the linearized theory. Furthermore, at the cut-off wave-number, the present theory shows the disturbance experiences a growth which is proportional to t2. The excellent agreement between Donnelly & Glaberson's experiment and Rayleigh's linearized theory is found to be due to their method of measurement.

Spectral Analysis of Pulse Frequency Modulation in the Nervous Systems

Abstract: Spectral analysis is one of the more important design and evaluation tools available to the communications engineer and it could also be a key to increased understanding of the nervous system. Some results of an analysis of the spectrum of the frequency modulated pulses of the nervous system show that 1) change in average pulse frequency is the likely information-carrying parameter of a neural pulse train, since distortion-free recovery of this variable is possible by simple low-pass filtering, and 2) phase relationships existing between signal components and distortion components of a neural pulse train imply unusual distortion attenuating properties of multiple or duplicate information channels. These results are discussed in light of some known nervous system structures.

Dynamic Warehouse Location Analysis

Abstract: In a rapidly changing economy, warehouse location is a dynamic decision problem. Yet most existing location models used to solve the problem are static. In this article, solutions from these static...

Causes of death among anesthesiologists: a 20-year survey.

Abstract: During the years 1947–1966, there were 441 deaths among junior, active and retired members of the American Society of Anesthesiologists living in the United States or Canada. A cause of death was found for each member and death rates calculated for this group. Comparisons of these rates with those for U. S. males and with male policyholders of the Metropolitan Life Insurance Company were made. Anesthesiologists appear to have a low incidence of lung cancer, a somewhat lower than average incidence of coronary artery disease in recent years, and a high death rate from suicide and malignancies of the lymphoid and reticuloendothelial tissues. These data only suggest trends and point to the need for a prospective study of this subject.

Antenatal detection of hereditary disorders.

Abstract: Amniotic fluid cells obtained by transabdominal amniocentesis at various stages of pregnancy were successfully cultivated The intra-uterine detection of Down9s syndrome, galactosemia, and mucopolysaccharidosis was established utilizing the cultivated amniotic fluid cells The use of this procedure increases the precision of genetic counseling and should stimulate the development of new approaches for the intra-uterine management of genetic defects However, until considerably more experience is gained with these techniques, these procedures should be considered experimental in nature

An Income-Net Worth Approach to Measuring Economic Welfare

Abstract: Economists and public policy-makers alike have long been concerned with the relative and absolute economic welfare of various segments of the population. This interest reflects an underlying concern both about the equity of the existing distribution and about our ability to explainand forecast more effectively the behavior of producers and consumers.' But given the many possible dimensions of a comprehensive measure of economic welfare, the single-dimensional, money-income measure so commonly used leaves much to be desired. The concern of this paper is with the development of an approach for measuring current economic welfare which is operationally feasible and broader in scope than the traditional money-income measure. The measure proposed is based on a combination of current income and current net worth (assets minus liabilities). These are made commensurable by converting net worth into an annuity value, which is added to current income. While this proposed measure stops well short of an "ideal"measure, we show that even this change leads to policy prescriptions rather different from those generated by the current income measure of economic welfare.

The development of the female Drosophila reproductive system.

Abstract: Light and electron microscopical studies allow a descriptive account to be given of the preadult development of the ovary of Drosophila melanogaster. The lineage of the cell groups which contribute to the tissues of the adult ovary has been determined. The earliest morphologically detectable event in the differeentiation of each ovariole is the formation during the larval period of its terminal filament. Oogonia play no role in the induction of terminal filaments. The developmental events which transform a spherical mass of ovarian cells into a collection of multicellular cylinders is described. The importance in morphogenesis of acellular membranes secreted at the interface separting cells of different prospective significances is stressed. Such membranes may serve to regulate the future migration of cell populations or as sites of attachment for monolayers of cells which later fuse to form multinucleated muscle sheaths. The transformation of oogonia to cystoblasts coincides with and presumably depends upon the same hormonal stimulus which causes metamorphosis. The first oocytes to undergo crossing over do so between 24 and 36 hours after puparium formation.

Distribution of the extracellular space during postnatal maturation of rat cerebral cortex

Abstract: The cerebral cortices of young adult and immature Sprague-Dawley rats, 10, 14, and 21 days of age, were rapidly frozen in situ and substituted at –78.5°C with a 1% solution of osmium tetroxide in acetone. In random electron micrographs of each animal, each representing 42 μ2 of cerebral cortical molecular layer, the extracellular space was evaluated stereologically. In all cases the extracellular space was found to be distributed as large extracellular lakes of variable dimension. Where no extracellular space was apparent adjacent cell processes were joined by 5-membered complexes, which appeared to represent fusion of immediately adjacent plasma membranes. In 10-day old animals an extracellular space of 40.5% was found. This diminished progressively to 31.8% at 14 days and 26.3% at 21 days, which approached the adult value of 21.7%. These data were consonant with measurements of the maturing extracellular space based on uptake studies of tracers, water and electrolyte determinations and impedance measurements. They appear to represent accurately the changing distribution of extracellular water in rapidly maturing cerebral cortex.

Statistical Mechanics of Hard‐Particle Systems

Abstract: The concept of the equivalence of a hard particle (depending on the number of dimensions: hard sphere, disk, or rod, with no attractive interaction) of diameter a in a system of hard particles, and a spherical cavity of radius at least a, is extended to define distribution functions, γn(r1, ···rn), for sets of n cavities in a hard‐particle system. A new theorem, relating the excess chemical potential of a hard‐particle system to the distribution function of two cavities at zero separation, γ2(r12)|τ12–0, as well as corresponding theorems for higher‐order distributions, are derived. The theorems for γ2(r12) and γ3(r1, r2, r3), and some simple physical arguments are used to obtain an approximation to the exact Born–Green–Yvon equation for γ2(r12), the “pair stress approximation” (PSA). The resulting simple equation of state yields very good approximate values for the fourth and fifth virial coefficients for hard disks, and for the fourth virial coefficient for hard spheres. The corresponding zero‐separation...

Space filling curves and mathematical programming

Abstract: The problem of finding {if314-1} in n dimensional Euclidean space such that {if314-2}, i = 1, 2, ···, N , is considered. The only assumption on the f i is that a solution exists in the quantized unit hypercube. Implicitly exhaustive solution procedures, which obtain solutions by implicitly considering every point in the quantized space without making computations at each point, are studied. The implicitly exhaustive feature is made possible by adapting “space filling curves≓ to discrete spaces of general dimensionality. Several space filling curves are surveyed, and Peano's continuous mapping from the unit interval onto the unit square is used as a basis for defining a mapping from the unit quantized interval onto the unit quantized hypercube, and inversely. Ternary arithmetic is the basis for the required functional relationships in the discrete mapping. The discrete mapping has attributes of quasi-continuity, and specific numerical bounds are derived in this respect. It is shown that these bounds are of optimal order dependence on the relevant variables. It is shown how to use knowledge of first and second order properties of the f i to obtain solutions on a digital computer using space filling curves as a basis for the concept of implicitly exhaustive search. The only global properties assumed are bounds on first, or possibly second, order variations. Concluding remarks bear on the ultimate practicality of the method, and present a limited amount of experimental data.

Monetary Returns to College Education, Student Ability, and College Quality

Abstract: This paper attempts to shed new light on the extent to which college education brings financial returns. It recognizes the existence of a number of variables that are likely to affect the financial returns that education produces for a given person -particularly the student's "ability" and "motivation," and the "quality" of his schooling. It attempts to isolate returns to education from returns to these other related variables.

A Goal Programming Model for Media Planning

Abstract: A goal programming model for selecting media is presented which alters the objective and extends previous media models by accounting for cumulative duplicating audiences over a variety of time periods. This permits detailed control of the distribution of message frequencies directed at each of numerous marketing targets over a sequence of interrelated periods. This is accomplished via a new logarithmic non-reach device and a continuous lognormal generation of the discrete message frequencies.