Point detectors

AMD 1 Components of automatic fire detection systems. Part 5 Heat sensitive detectors point detectors containing a static element (AMD 5762) dated 31 August 1988. Superseded BS 3116 Part 1 1970... 

Depending on the type of detector pointed at the sky and the wavelength region to which it is sensitive, the objects revealed may exhibit different levels of... 

Effect of minimizing detector point-spread function... 

The ELS detector was previously also referred to as a mass detector, pointing to the fact that the response is (mainly) determined by the mass of the sample rather than by its chemical structure. Van der Meeren et al., though, demonstrated that the ELSD calibration curves of phospholipid classes were also dependent on the fatty acid composition (52). The dependence on the fatty acid composition is, however, completely different in nature and much less pronounced than for UV detection. The reason for this behavior is to be found in the partial resolution of molecular species, even during normal-phase chromatography. Thus, the peak shape depends not only on the chromatographic system but also on the fatty acid composition and molecular species distribution of the PL sample (47). Because it was shown before, based on both theoretical considerations and practical experiments, that the ELS detector response is generally inversely proportional to peak width (62,104), it follows that the molecular species distribution of the PL standards used should be similar to the sample components to be quantified. It was shown that up to 20% error may be induced if an inappropriate standard is used (52). 

One-channel feedback has been first applied to control meandering spiral waves in experiments with the light-sensitive BZ medinm [21]. Later a theory of this control method has been elaborated for rigidly rotating [40, 43] and for meandering [30] spiral waves. In accordance with this control algorithm, the wave activity (e.g. the value of the variable v in Eq. (9.1)) is measured at a particular detection point as a function of time. This value oscillates with time and exceeds the value Ve every time instant ti, when a wave front touches the detector point. A short perturbation is applied to the system immediately at ti or after some time delay r, i.e. at instances = ti + r. The frequency of the periodic sequence of generated... 

Let us assume that the drift is slow and determine its direction. Obviously, the phase of the pulse sequence depends on the spiral location. Indeed, if the spiral wave center is placed at the point z = x + iy, the wave front specified by Eq. (9.5) crosses the detector point located at the origin of the coordinate system each time ti satisfying the following equation ... 

This drift velocity field is shown in Fig. 9.2 corresponding to r = 0. The constant ip is taken as (/> == —1.8 in accordance with the chosen parameters for the Oregonator model (9.1). The field has rotational symmetry, but the drift angle 7 monotonously increases with the distance z from the detector point. Hence, there is a discrete set of sites along any radial direction, where the drift direction is orthogonal to the radial one i.e. 

These results have been verified experimentally. Figure 9.11 shows measured tip trajectories of spiral waves in the light-sensitive BZ medium starting from six different initial locations of the spiral center. The feedback signal is determined as the sum of the intensities of the transmitted light measured at two detector points located at the distance dp = A. As pre-... 

Measurement of particle velocity with optic fibers is based on traversing a distance / by a particle between two known points over a transit time (or the time lag) t or the velocity V = l/t. However, the instantaneous velocity can be obtained only when the measuring distance between the two detector points is short enough to avoid interference. The diameters of the optic fiber and of the particle can both fit in the same range, and the response of probe against light signals is almost without time lag. Thus this kind of probes is very suitable for the measurement of instantaneous particle velocity. 

The longer half-lives of these reactor-produced tracers facilitated their availability and decreased their cost compared to cyclotron-produced radionuclides. Carbon-14 and tritium emitted oifly beta particles with a very short range in tissue, so they could not be used to examine regional biochemistry with radiation detectors pointed at the human body. Three decades were to elapse before physicians and scientists returned to the cyclotron as an important, indeed essential, tool in molecular imaging. 

Two diseases that were defined half a century ago can illustrate a molecular theory of mental disease. The rate of accumulation of radioactive iodine by the thyroid could be measured by radiation detectors pointed at the neck. Patients, who had a disease subsequently called hyperthyroidism were found to have an increased accumulation of radioactive iodine, whereas radioiodine uptake was low in patients with hypothyroidism. Patients with hyperthyroidism were nervousness and anxious, and suffered from weight loss, whereas hypothyroid patients were lethargic and had impaired mental functions. These two diseases illustrate the fundamental principle that if one can measure a chemical process in some part of the body, there will be patients in which the chemical process is abnormally slow, and others in which it is abnormally fast (Fig. 19.1). 

Table 1. Values of some relevant parameters used for the numerical simulations of the telescope. Em represents the logarithmic mean energy ( ZSi ) A jj is the efficient area, i.e the geometric area (367.2 cm ) times the detector efficiency BKG is the total (cosmic plus hadronic) background PSF is the width (FWHM) of the detector point spread function...

Initial alignment of the testbed was achieved with a continuous wave green laser mounted on the optical axis between the beam combiner and the detector, pointing in the direction of the source. The detector position was then set to provide maximum signal with the MAL source with the spectral arm a long way from the ZPD. 

To avoid dust, it is better to locate the detector at a suitable location with the detector pointing downward. 

Suppose that a neutron detector is placed on the opposite side from the face exposed to the incident beam and that this detector registers a count only when a neutron reaches it by a path normal to the slab surface. Thus, neutrons that are scattered about inside the slab and eventually emerge at face x = a traveling in some random direction are not counted. It is possible that some of these neutrons might still leave the surface with a trajectory normal to the surface and at a point directly opposite the detector (point A in Fig. 2.6) however, these are few in number, and most of them can be eliminated by using very thin slabs (i.e., by requiring that aS< 1). The number of neutrons which survive... 

Single element detector Point-by-point analysis Line and area infrared maps Ante) or manual control ATR and grazing angle Visible image capture 2D and 3D graphics... 

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