The Denver Universal Microspectroradiometer (DUM)

Abstract

SUMMARY This paper discusses the design and describes the construction of an accurate digital microspectrophotometer, microspectrofluorimeter and microrefractometer known as the ‘Denver Universal Microspectroradiometer’ (DUM). The instrument operates in the spectral range of between 428.3 and 1303.4 THz (700–230 nm). Microscopic objects are scanned digitally in two dimensions and absolute digital spectra of various kinds are obtained automatically. Optical path differences can be measured automatically in the same microdomains in which absorbance, fluorescence and bioluminescence are studied. Measurements on solutions in standard cuvettes, and other macroscopic objects, can be made without altering the alignment of the optical components used in microanalysis. The multi‐detector radiometric system is based on the principle of synchronous single photoelectron counting. The operation of the entire system is controlled by an integral computer which is also used for on‐line data‐processing, reduction and analysis. Automatic multiparametric and multicomponent analyses can be carried out with relative ease. The quality of the images obtained is largely diffraction‐limited, and the instrumental uncertainty of measurement is essentially that imposed by the quantum statistics of the radiation captured by the detectors. The linear dynamic range is about 108. The limit of detectability of absorbance is of the order of 0.0001. The system is sensitive enough to measure paucimolecular photoemissive events, such as cellular bioluminescence, yielding about 0.1s−1 photoelectrons (equivalent photocathode current ≃3 times 10−22 A). The absolute accuracy of the system is limited principally by uncertainties inherent in currently available methods of calibrating the spectral response of detectors.

Trying to Turn up the Turnout: Youth Wings and the Youth Vote in the 2015 General Election

“…24 David Denver argues that four interconnected social factors are associated with low turnout: being young (the most important one), being unmarried, living in privately rented accommodation, and being residentially mobile. 25 Higher levels of non-voting by these groups can be explained in terms of isolation from personal and community networks, which are characteristic of stable communities that encourage conformity or the norm of voting. 26 Varying political participation rates can be understood in terms of cost and benefit, 27 hence some young people might not see the point (or the value) of making the effort to vote.…”

“…42 Membership of political parties has decreased considerably in Britain over the past two generations. 43 In 2015, a tiny proportion of the population is a member of a political party:…”

Microspectrophotometric studies of Romanowsky stained blood cells

“…Spectra were obtained by photon counting, using the Denver Universal Microspectroradiometer (DUM) (David & Galbraith, 1975;Galbraith et al, 1975). A stabilized 450 W xenon arc was used, and further stabilization was introduced by diverting a small fraction of the light beam near the source to a 'Monitor' photon counter, attenuating to 1 million photons s-l, and using the resulting signal as the 1 MHz external clock signal to the photon counting electronics (David & Galbraith, 1975).…”

“…The monochromators are driven in wavelength by stepping motors under computer control. They are calibrated directly from the emission lines of a mercury arc, both in order to determine the relationship between stepping motor drive and wavelength transmitted, as described in David & Galbraith (1975), and also to zero the drive during the daily setting up procedure.…”

Measurement of reflectance of coal macerals: its automation and significance

“…A new development in reflectance measurement may result from research into radiometric systems~ David and Galbraith (1975) have described the design of the Denver Universal Micrqspectroradiometer (DUM) which uses direct photoelectron counting for precise optical measurements on biological materials. As noted by these authors, advantages of photon counting include the precision _resulting from a digitized signal, and minimization of errors attributable to the analoq components of the system.…”