Attenuation depth

UV transparency of natural waters can be described empirically by two measures that are wavelength-specific and inter-related the downwelling diffuse attenuation coefficient, K, and the percent attenuation depth, Z o/ . A downwelling diffuse attenuation coefficient is nominally proportional to the concentration of substances in the water that absorb or scatter UVR [17,42]. It is typically calculated for specific wavelengths (A) from measurements of downwelling irradiance ( d,A) by fitting the following equation (in units of m ) [8] to irradiance versus depth data ... 

Figure 3. Maximum 37% attenuation depths for 320 nm (depth where irradiance is attenuated to 37% of the value just beneath the surface, computed as l/Kd32o)- Values have been calculated for the lowest K s reported for each category from Table 1.

Figure 3. Relationship between the attenuation depth (depth to which 1 % of surface 320 nm UV-B radiation penetrates the water column) and dissolved organic carbon (DOC) concentrations in 65 glacial lakes in North and South America [2,15]. Note the rapid increase in the depth of penetration of UV below DOC concentrations of 1-2 mg 1. [Modified from [2] with permission.]...

UV levels. For example, lakes that one of us has sampled (C.E.W.) in the Beartooth Mountains of Wyoming and Montana, USA at about 3000 m, include meadow lakes with DOC concentrations in the 2-4 mg 1 range, and UV attenuation depths at 320 nm of less than 0.2 m. 

ZEph depth of the euphotic zone Z %, percent attenuation depth ZuML> depth of the upper mixed layer... 

Figure 3.3 shows the increasing attenuation for cracks in a depth between 5 and 30 mm, using the optimised excitation frequency for each depth. The coils (circular, double-D) have a current density of lOWm. In case of circular and double-D coil, this corresponds to an... 

In most ultrasonic tests, the significant echo signal often is the one having the maximum ampHtude. This ampHtude is affected by the selection of the beam angle, and the position and direction from which it interrogates the flaw. The depth of flaws is often deterrnined to considerable precision by the transit time of the pulses within the test material. The relative reflecting power of discontinuities is deterrnined by comparison of the test signal with echoes from artificial discontinuities such as flat-bottomed holes, side-drilled holes, and notches in reference test blocks. This technique provides some standardized tests for sound beam attenuation and ultrasonic equipment beam spread. 

The attenuation of the pressure waves increases with depth and with the mud pressure wave velocity. More attenuation is observed with oil-base muds, which are mostly used in deep or very deep holes, and can be calculated with the mud and pipe characteristics [108] according to the equations... 

Figure 4-254. Attenuation of electromagnetic signals for 1 and 0 n m average earth resistivity (a) attenuation as a function of frequency (b) maximum depth reached versus frequency. (Courtesy Geoservices [109]. ...

For the average pressure wave velocity in the pipe, compute the distance at which the amplitude falls to 1/e of its original value, the distance at which it falls at one-half of its original value (half depth) and the attenuation in dB/1,000 ft. Compute also the amplitude at surface. Bottomhole amplitude peak to peak 200 psi frequencies 0.2, 12 and 24 Hz. 

While electron or ion beam techniques can only be applied under ultra-high vacuum, optical techniques have no specific requirements concerning sample environment and are generally easier to use. The surface information which can be obtained is, however, quite different and mostly does not contain direct chemical information. While with infra-red attenuated total reflection spectroscopy (IR-ATR) a deep surface area with a typical depth of some micrometers is investigated, other techniques like phase-measurement interference microscopy (PMIM) have, due to interference effects, a much better surface sensitivity. PMIM is a very quick technique for surface roughness and homogeneity inspection with subnanometer resolution. 

Surface composition and morphology of copolymeric systems and blends are usually studied by contact angle (wettability) and surface tension measurements and more recently by x-ray photoelectron spectroscopy (XPS or ESCA). Other techniques that are also used include surface sensitive FT-IR (e.g., Attenuated Total Reflectance, ATR, and Diffuse Reflectance, DR) and EDAX. Due to the nature of each of these techniques, they provide information on varying surface thicknesses, ranging from 5 to 50 A (contact angle and ESCA) to 20,000-30,000 A (ATR-IR and EDAX). Therefore, they can be used together to complement each other in studying the depth profiles of polymer surfaces. 

Curves showing the cnrrent densities as functions of x are presented for two val-nes of electrode thickness in Fig. 18.5. The parameter L has the dimensions of length it is called the characteristic length of the ohmic process. It corresponds approximately to the depth x at which the local current density has fallen by a factor of e (approximately 2.72). Therefore, this parameter can be nsed as a convenient characteristic of attenuation of the process inside the electrode. 

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