The period structure of the ZZ Ceti variables

The current observational status of the period structure of ZZ Ceti stars is reviewed, and in particular those features which appear to be the most important for theory to explain, or which may be relevant to the directions of theoretical development are discussed. Mechanisms to explain the broad range of period structure are suggested. Multiple nonradial modes, probably corresponding to different radial overtones, may be simultaneously excited in each star. The excitation energy of individual stars is distributed among permitted modes by nonlinear resonant coupling. In addition, rotational splitting of the nonradial modes can produce closely spaced periods which results in modulation of the light curve. Amplitude/spectral complexity correlation results from the appearance in the power spectrum of harmonics and cross-frequencies which are the effects brought on by increasing nonlinearity of the pulsations

The High Speed Water Tunnel three-component balance

An experimental program was initiated in the High Speed Water Tunnel to measure force coefficients for hydrofoils under cavitating conditions. This program necessitated either a new force balance or a major modification of the existing one. Various balance configurations and pressure seal designs which were considered are described. A balance modification design was selected which consists of an appendage bolted between the existing balance and the water tunnel working section. This appendage alters the basic geometry of the force balance so that the model is now mounted on a parallelogram linkage instead of on a simple pivoted lever. The addition of the parallelogram force table suspension to the old balance renders the modified balance unresponsive to moments which in the old balance, interacted with forces and resulted in errors in the force readings. This modification which is described in detail was accomplished and resulted in a successful force balance capable of accurate measurement of forces on cavitating and noncavitating hydrofoils; and, in fact, it is expected to replace the old force balance for all force measurement work in the High Speed Water Tunnel. The cost and construction time for the balance modification were considerably less than would have been required for an entirely new force balance of comparable accuracy and sensitivity

Functional evidence for cone-specific connectivity in the human retina

NoPhysiological studies of colour vision have not yet resolved the controversial issue of how chromatic opponency is constructed at a neuronal level. Two competing theories, the cone-selective hypothesis and the random-wiring hypothesis, are currently equivocal to the architecture of the primate retina. In central vision, both schemes are capable of producing colour opponency due to the fact that receptive field centres receive input from a single bipolar cell ¿ the so called `private line arrangement¿. However, in peripheral vision this single-cone input to the receptive field centre is lost, so that any random cone connectivity would result in a predictable reduction in the quality of colour vision. Behavioural studies thus far have indeed suggested a selective loss of chromatic sensitivity in peripheral vision. We investigated chromatic sensitivity as a function of eccentricity for the cardinal chromatic (L/M and S/(L + M)) and achromatic (L + M) pathways, adopting stimulus size as the critical variable. Results show that performance can be equated across the visual field simply by a change of scale (size). In other words, there exists no qualitative loss of chromatic sensitivity across the visual field. Critically, however, the quantitative nature of size dependency for each of the cardinal chromatic and achromatic mechanisms is very specific, reinforcing their independence in terms of anatomy and genetics. Our data provide clear evidence for a physiological model of primate colour vision that retains chromatic quality in peripheral vision, thus supporting the cone-selective hypothesis

Luminance cues constrain chromatic blur discrimination in natural scene stimuli

Introducing blur into the color components of a natural scene has very little effect on its percept, whereas blur introduced into the luminance component is very noticeable. Here we quantify the dominance of luminance information in blur detection and examine a number of potential causes. We show that the interaction between chromatic and luminance information is not explained by reduced acuity or spatial resolution limitations for chromatic cues, the effective contrast of the luminance cue, or chromatic and achromatic statistical regularities in the images. Regardless of the quality of chromatic information, the visual system gives primacy to luminance signals when determining edge location. In natural viewing, luminance information appears to be specialized for detecting object boundaries while chromatic information may be used to determine surface properties

Relationship between Allan variances and Kalman Filter parameters

A relationship was constructed between the Allan variance parameters (H sub z, H sub 1, H sub 0, H sub -1 and H sub -2) and a Kalman Filter model that would be used to estimate and predict clock phase, frequency and frequency drift. To start with the meaning of those Allan Variance parameters and how they are arrived at for a given frequency source is reviewed. Although a subset of these parameters is arrived at by measuring phase as a function of time rather than as a spectral density, they all represent phase noise spectral density coefficients, though not necessarily that of a rational spectral density. The phase noise spectral density is then transformed into a time domain covariance model which can then be used to derive the Kalman Filter model parameters. Simulation results of that covariance model are presented and compared to clock uncertainties predicted by Allan variance parameters. A two state Kalman Filter model is then derived and the significance of each state is explained

The Golden Staph: Medicine's Response to the Challenge of the Resistant Staphylococci in the Mid-Twentieth Century

During ttie first two decades of the antibiotic era the problem of microbia! resistance to antibiotic therapy was discovered, challenged and, iri part, the battle was wori. The chemotherapeutic agents, antibiotics, werc often touted as ((miracle drugs)), but were not without severe tests arid riot unconinion lost skirmishes. The refractory resistance of one particular pathogen, Staphylococcus aureus, the Golden Staph, was to cause corisidcrable difficulties for the new medicine of the 1940s and 1950s. It secarried that rio sooner had penicillin become available than Charles Rarrinielkarrip (b. 191 l), one of the first phvsicians to employ it, discovcred resistarice to its antimicrobial abilities (1)

Controversial issues concerning the treatment of hyperactive children with behavior-modifying drugs: a critical review

In the light of these stated areas of controversy, it was the purpose of this paper to review the literature of hyperactivity and drug therapy and to clarify some of the issues. Particular attention was paid to the description and classification and etiology of the hyperactive child; and the specific drugs presently being used to treat hyperactivity

Automobile Insurance Rates: Promulgation, Regulation, and Equal Protection

T HE INTEREST in the price one pays for automobile insurance continues to grow at a rapid pace. The reason for this growing consumer interest may be attributed to the equally increasing need for automobiles, the price paid for them, and consequently, the need for insurance protection. This insurance protection has developed into a matter of major economic consequence to the auto owner.....The key to improved and efficient rate-watching is in the good faith efforts and perseverance of the policyholders themselves. Accordingly, an examination of the effects of consumerism along with a discussion of modern rate and regulatory developments is offered to show the present relationships and interactions of the groups involved