Attenuation, defined

Natural antioxidants, 12 60-61 Natural attenuation, defined, 3 759t Natural boric acid, 4 133t Natural cements, 5 502 Natural colors, 12 51 Natural color system (NCS), 7 309 Natural convection, 13 245 Natural defenses, against silver, 22 655, 681... 

This leads naturally to the concept of X-ray attenuation, defined as the natural logarithm of the transmitted intensity fraction ... 

Since any DAC is defined by its coordinates P (Ai,S ) and the instrument sensitivity Gg f (reference gain) during DAC recording, any recalculation of the curve including the consideration of individual corrections (transfer loss, sound attenuation, etc.) is an easy task for modern PC based flaw detectors and does no longer burden the operator. 

The echo amplitude Ar of a reference reflector depends on the type, size (diameter) d f, and distance Sr,., of the reference reflector, and additionally on a possible attenuation in the reference block and finally the absolute gain setting of the instrument G f. In a combined DAC/DGS evaluation program we define the following ... 

For optical transmission, tire parameters of greatest importance are attenuation (i.e. loss) and material dispersion. In effect tliey define tire limits of tire optical communication system. Loss, due to absorjDtion and scattering, limits tire lengtlis between tire transmission nodes. In transmission quality fibre, tire loss is in units of decibels per kilometre. 

The attenuation of electromagnetic radiation as it passes through a sample is described quantitatively by two separate, but related terms transmittance and absorbance. Transmittance is defined as the ratio of the electromagnetic radiation s power exiting the sample, to that incident on the sample from the source, Pq, (Figure 10.20a). 

An alternative method for expressing the attenuation of electromagnetic radiation is absorbance. A, which is defined as... 

Amplifier bandwidth. The range of signal frequencies over which an amplifier is capable of undistorted or unattenuated transmission. An operational amplifier should transmit DC voltage accurately the upper (bandwidth) limit is defined as the 3-dB point (attenuation factor of two). Because bandwidth can vary with gain, the product of gain x bandwidth can be a more useful parameter. 

Safety Standards. Protection from laser beams involves not allowing laser radiation at a level higher than a maximum permissible exposure level to strike the human body. Maximum permissible exposure levels for both eyes and skin have been defined (55—57). One of the most common safety measures is the use of protective eyewear. Manufacturers of laser safety eyewear commonly specify the attenuation at various laser wavelengths. Under some conditions safety eyewear has been known to shatter or to be burned through (58), and it is not adequate to protect a wearer staring directly into the beam. 

The transducers on most ultrasound imaging systems operate at a frequency between 1 and 20 MH2. The attenuation, of ultrasound by tissues is both frequency and tissue dependent. The attenuation coefficient, a, of a tissue is defined by equation 5 ... 

Lihou and Maund (1982) define attenuation constants for hydrocarbon flames through the atmosphere, which can vary from 4 x 10 m (for a clear day) to 10 m (for a hazy day). The mean value suggested by the authors is 7 x 10 m , which gives a transmissivity of ... 

Cos W is used as an indicator to determine the frequency ranges of attenuation and transmission. Transmission regions are defined as those wherein cos W has a value of +1 and — 1. Values of a higher order indicate regions in which attenuation will occur. Cos W should be plotted as shown in Figures 13-19A and 13-19B. 

No single method is perfect and common problems include the difficulty of defining peak boundaries accurately, operator dependence on precision and the need for a finite time to make each measurement. A major disadvantage of manual measurements is the necessity that all peaks of Interest must be completely contained on the chart paper (or adjusted to remain on the chart paper by varying the detector attenuation during the... 

Airway hyperresponsiveness is defined as the exaggerated ability of the airways to narrow in response to a variety of stimuli. Although AHR exists in patients without asthma, it is a characteristic feature of asthma and appears to be directly related to airway inflammation and the severity of asthma.1,3 Treatment of airway inflammation with inhaled corticosteroids attenuates AHR in asthma but does not eliminate it.1 Clinically, AHR manifests as increased variability of airway function. Although not commonly used to diagnose asthma, AHR can be evaluated clinically using a methacholine or histamine bronchoprovocation test. 

Filter specifications are matched to the response times of the process. For example, a given process has a time constant of 5 minutes. That means that it can respond over the frequency range of 0 to 1/20 of a cycle per minute. Higher frequencies are attenuated naturally by the process. Thus, if the data contain components beyond 0.05 cycles per minute, then those components are likely to be unwanted interferences. The linear filter would pass the frequencies between 0 and 1/20 and reject frequencies outside this range. The filter should attenuate frequencies higher than one decade above the break-point frequency. Process measurements processed by this filter are transformed to a new sequence with less interference than the original data. In this way, an input mapping has been defined. 

U.S. EPA defines MNA as the reliance on natural processes, within the context of a carefully controlled and monitored site cleanup approach, to achieve site-specific remediation objectives within a time frame that is reasonable compared to that offered by other more active methods. The natural processes include biodegradation, dispersion, dilution, sorption, volatilization, stabilization, and transformation. These processes reduce site risk by transforming contaminants to less toxic forms, reducing contaminant concentrations, and reducing contaminant mobility and bioavailability. Other terms for natural attenuation in the literature include intrinsic remediation, intrinsic bio-remediation, passive bioremediation natural recovery, and natural assimilation. 30... 

The well-defined large bimetallic Au—Ag cluster as [(Ph3P)i2AuigAg2oCli4] can achieve nearly two orders of magnitude of attenuation of high-intensity laser power and, consequently opens the door to a new class of optical materials based on nanosized metal clusters 3269... 

Protection of the Detector. With all direct calibration methods the primary beam intensity must be measured. If the primary beam itself is attenuated, shape of the beam and spectral composition of the radiation may be altered. This problem is avoided if the load of the detector is reduced by scanning the beam using a slit or a perforated disc. On the other hand, in order to be useful at a powerful synchrotron beamline these devices should have very tiny and well-defined slits or holes. 

For example, when = 200 mW is attenuated to / ml = 20 mW, then the attenuator indicates an output power P = -10 dB (see also Table 2.2). And when / ml = 2 mW, then P = -20 dB. Every additional attenuation by a factor of 10 gives another -10 dB in P. This type of device is usable to 50-60 dB attenuation, which also corresponds to the lower power limit at which the spectrometer is still operable. Note that, in addition to the relative dB scale, microwave engineers also use an absolute dBm scale. The m in dBm is shorthand for milliwatt and defines the reference point of this scale ... 

We have previously defined the relative dB scale in Equation 2.11. The power in EPR is expressed in decibels (dB) attenuation (or alternatively in -dB amplification) of a maximum value. X-band microwave sources (either klystrons or Gunn diodes) have a constant output that is usually leveled off at 200 mW. This value then corresponds... 

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