Measurement historical background

The historical background is presented for the asteroid-impact theory that is based on the iridium anomaly found in rocks frm the Cretaceous-Tertiary boundary. Recent measurements of Ir, Pt, and Au abundances from such rocks in Denmark have shown that the element abundance ratios are different from mantle-derived sources and agree with values for chondritic meteorites within one standard deviation of the measurement errors (7-10%). Rare-earth patterns for these rocks are... 

B. Experimental Determination of Detonation Velocity. Historical background for development of methods for exptl determination of deton velocities is already given in Vol 3 of this Encycl (Ref 75), pp C310-R and C311-L, under Chronographs and Other Devices Used for Measuring Detonation Velocities of Explosives. 

Enzymes are the catalysts evolved in nature to achieve the speed and coordination of a multitude of chemical reaction necessary to develop and maintain life. Chemical reactions are far too slow to be effective under the conditions prevalent in normal living systems - aqueous environments with neutral pH values and temperatures between 20 and 40 °C. Even catalysts developed in the chemical industry fall short enzymes in comparison achieve up to 107 - fold faster reaction rates. Mankind has utilized enzymes empirically since ancient times for the conservation or production of food, e. g. in cheese making or brewing. A historical background is given in Table 1-1. The catalytic properties of enzymes were recognized long before their chemical nature was known. We stil. use acceleration of reaction rate to search for unknown enzymes as well as to measure and quantify enzyme activity. 

The following sections of this chapter present some examples of applications of AE/MS measurement in rock structures of different extension. Sections 11.2 to 11.4 deal with monitoring of parts of mines with typical dimensions of 100 to 250 m. After a list of various applications found in the literature (in Subsection 11.2.1) and the historical background of AE/MS measurement (in Subsection 11.2.2), examples on monitoring in granite and rock salt are given in Section 11.3 and 11.4, respectively. 

Hu and Chao [7] performed two-dimensional numerical simulation on the performance of an electroosmotic pump for planar channels. The model is able to handle the case with the dimensions comparable to the EDL thickness. Also no Debye-Huckle approximation and symmetric conditions are required. But the results show considerable deviation from the experimentally measured ones. Yao and Santiago [8] provided useful review on the historical background of the development of EO pumps. They considered different molar conductivities for cations (A+) and anions (A ) in calculating the electric current caused by electromigration. They predicted that A+ is almost twice A for sodium ions. 

THIS article is an overview of time and frequency technology. It introduces basic time and frequency concepts and describes the devices that produce time and frequency signals and information. It explains how these devices work and how they are measured. Section I introduces the basic concepts of time and frequency and provides some historical background. Section II discusses time and frequency measurements and the specifications used to state the measurement results. Section III discusses time and frequency standards. These devices are grouped into two categories quartz and atomic oscillators. Section IV discusses time and frequency transfer, or the process of using a clock or frequency standard to measure or set a device at another location. 

Empirical—statistical models ate based on estabUshing a relationship between historically observed air quaUty and the corresponding emissions. The linear rollback model is simple to use and requites few data, and for these reasons has been widely appHed (3,4). Linear rollback models assume that the highest measured pollutant concentration is proportional to the basinwide emission rate, plus the background value that is,... 

The phenomenon of fluorescence has been synonymous with ultraviolet (UV) and visible spectroscopy rather than near-infrared (near-IR) spectroscopy from the beginning of the subject. This fact is evidenced in definitive texts which also provide useful background information for this volume (see, e.g., Refs. 1-6). Consequently, our understanding of the many molecular phenomena which can be studied with fluorescence techniques, e.g., excimer formation, energy transfer, diffusion, and rotation, is based on measurements made in the UV/visible. Historically, this emphasis was undoubtedly due to the spectral response of the eye and the availability of suitable sources and detectors for the UV/visible in contrast to the lack of equivalent instrumentation for the IR. Nevertheless, there are a few notable exceptions to the prevalence of UV/visible techniques in fluorescence such as the near-IR study of chlorophyll(7) and singlet oxygen,<8) which have been ongoing for some years. 

Three reviews describing applications of diffusion denuders have been published. The doctoral dissertation of Ferm (31) reflects considerable experience with single-tube denuders for the measurement of a variety of species. The review by Ali et al. (32) is extensive it provides an excellent historical and theoretical background and summarizes the literature based on the type of analyte gas determined. The focus of the most recent review, by Cheng (19), is diffusion batteries used for size discrimination of aerosols as well as diffusion denuders. Various physical designs are discussed in some detail in that review. 

Figure 2.3 Globally averaged profiles of historic sediment contamination by trace metals, in industrialised countries, providing a general idea of the evolution of contamination versus time (years). 100% represents the maximum value reached in cored sediments and 0% the lowest value measured. These values are rough estimates, extrapolated from results reported in the literature to 1990. Section (a) represents a background or low contamination period, section (b) corresponds to the increase in sediment contamination around World War I. Section (c) visualises the rapid increases occurring after World War II that reach a maximum in the mid-1970s. Section (d) represents the recent decrease observed in concentrations of many trace metals (after Valette-Silver, 1993).

Historically, the sulfosalicylic acid test was used as a crude measure of proteinuria. This test can be performed by adding five drops of 20% sulfosalicylic acid to 3 mL of urine in one test mbe. The specimen tube is then visually compared with a mbe of untreated urine held against a dark background, with the presence of turbidity indicating proteinuria. 

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