7,644 research outputs found

    On a photon-counting array using the Fairchild CCD-201

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    The evaluation of certain performance parameters of the Fairchild CCD 201 and the proposed method of operation of an electron bombarded charge coupled device are described. Work in progress on the evaluation of the parameters relevant to remote, low noise operation is reported. These tests have been conducted using light input. The video data from the CCD are amplified, digitized, stored in a minicomputer memory, and then recorded on magnetic tape for analyzing. The device will be used in an array of sensors in the aperture plane of a telescope to discriminate between photoelectron events, and in the focal plane operating at single photoelectron sensitivity at a minimum of blooming and lag

    Laser beam pointing tests

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    Laser beam pointing tests for lunar communication and rangefinding and tracking using Surveyor 7 vidicon camer

    An evaluation of an ICCD imager of dynamic range expansion technique and application of insitu procedures for life-time extension

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    Research toward practical implementation of the Intensified Charge Coupled Device (ICCD) as a photon-counting array detector for astronomy is reported. The first area of concentration was to determine the rate and extent of the lifetime limiting damage to the CCD caused by the impact of high energy electrons, and to find whether various methods of annealing the damage were productive. The second effort was to determine the performance of the ICCD in a photon-counting mode to produce extended dynamic range measurements. There are two main effects that appear as the practical results of the electron damage to the CCD. One is an increase in the leakage current, i.e., the normal thermal generation of charge carriers in the silicon that provides a background dark signal that adds to the light produced image. In an undamaged CCD, the leakage current is usually fairly uniform across the photosensitive area of the silicon chip, with the exception of various bright pixels which have an anomalous leakage current well above the overall level

    Research concerning the geophysical causes and measurement accuracies related to the irregularities in the rotation of the earth

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    The primary objective of this effort consisted of a detailed study of the history of the motion of the moon. Several analyses were developed which are related to the determination of the effect of various refractive phenomena on the accuracy of measurements made through the earth's atmosphere

    Socioeconomic inequalities in childhood exposure to secondhand smoke before and after smoke-free legislation in three UK countries

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    Background: Secondhand smoke (SHS) exposure is higher among lower socioeconomic status (SES) children. Legislation restricting smoking in public places has been associated with reduced childhood SHS exposure and increased smoke-free homes. This paper examines socioeconomic patterning in these changes.<p></p> Methods: Repeated cross-sectional survey of 10 867 schoolchildren in 304 primary schools in Scotland, Wales and Northern Ireland. Children provided saliva for cotinine assay, completing questionnaires before and 12 months after legislation.<p></p> Results: SHS exposure was highest, and private smoking restrictions least frequently reported, among lower SES children. Proportions of saliva samples containing <0.1 ng/ml (i.e. undetectable) cotinine increased from 31.0 to 41.0%. Although across the whole SES spectrum, there was no evidence of displacement of smoking into the home or increased SHS exposure, socioeconomic inequality in the likelihood of samples containing detectable levels of cotinine increased. Among children from the poorest families, 96.9% of post-legislation samples contained detectable cotinine, compared with 38.2% among the most affluent. Socioeconomic gradients at higher exposure levels remained unchanged. Among children from the poorest families, one in three samples contained > 3 ng/ml cotinine. Smoking restrictions in homes and cars increased, although socioeconomic patterning remained.<p></p> Conclusions Urgent action is needed to reduce inequalities in SHS exposure. Such action should include emphasis on reducing smoking in cars and homes

    Tumour specific immunogenicity of methylcholanthrene-induced sarcoma cells after incubation in neuraminidase.

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    IT was previously suggested (Currie and Bagshawe, 1967) that effective antigenic expression by some types of tumour cell may be inhibited by the presence of sialic (N-acetylneuraminic) acid in the cell periphery. Treatment of the cells from several " non-specific " transplantable mouse tumours with neuraminidase results in a marked increase in their immunogenicity when subsequently injected into intact host mice and leads to a powerful anti-tumour immunity in these animals. So far this phenomenon has been reported using the Ehrlich (Lindenmann and- Klein, 1967), Landschuitz (Currie, 1967), and TA3 (Sanford, 1967) ascitic tumours. The antigenic discrepancies between these tumours and their respective host mice are probably related to strain-specific histocompatibility differences, i.e. these tumours are malignant allografts. Little of the information obtained from the study of such tumours is of immediate relevance to the growth and development of autochthonous tumours where the only tumour-host antigen discrepancy (if any) is specific to the tumour. The purpose of this paper is to report studies of the effects of incubation i

    The far field diffraction pattern for corner reflectors with complex reflection coefficients

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    The far field diffraction pattern of a geometrically perfect corner reflector is examined analytically for normally incident monochromatic light. The states of polarization and the complex amplitudes of the emerging light are expressed through transformation matrices in terms of those of the original incident light for each sextant of the face in a single coordinate system. The analytic expression of the total diffraction pattern is obtained for a circular face. This expression consists of three component functions in addition to the basic Airy function. The coefficient of each function is expressed in terms of complex coefficients of reflectance of the reflecting surface. Some numerical results for different reflecting surfaces, including total internal reflection, are presented. The iso-intensity contours of the diffraction pattern evaluated from the analytical expressions for an uncoated solid corner reflector are also presented along with the photographs of the pattern
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