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Topic: Attenuation

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	Topics: Natural Attenuation
		This makes the sites where the investigations are conducted ideally suited to assessing potential long-term impacts, evaluating the potential and the limitations of remediation by monitored natural attenuation, and designing systems to monitor the performance of remediation where monitored natural attenuation is being relied upon.
		The scientists are withdrawing water with a syringe from a core encased in polycarbonate tubing.
		The sample was used to study the natural attenuation of hydrocarbon vapors in the unsaturated zone.
	toxics.usgs.gov /topics/attenuation.html (521 words)

	Stress Attenuation Study -- patient_2264 (Site not responding. Last check: )
		When the attenuation study is acquired simultaneously with the emission study.
		The patient was absolutely still during and between the two attenuation studies.
		Perhaps an explanation of why the inferior wall is hot in the 2/27 scan and is not in the 4/23 scan can be found by comparing overlays of the stress scans from the 2 studies on top of their respective (resting) attenuation scans.
	www.emory.edu /CRL/abb/stress_shift (416 words)

	DACT Attenuation Curve Calculator
		Please observe that the ACC assumes that the output impedance of the equipment feeding the attenuator is zero (or at least much lower than the attenuator resistance).
		If the attenuator is used as a volume control in an active preamplifier, the entered value should be the input resistance of the amplifier stage that follows the attenuator.
		Usually it is the capacitance of the cables on the attenuator output plus the input capacitance of the connected amplifier or amplifier stage.
	www.dact.com /html/ac_calculator.html (1108 words)

	Attenuation Correction
		Attenuation is the loss of detection of true coincidence events because of their absorption in the body or due to their scattering out of the detector field of view.
		Without attenuation correction, significant artifacts which may occur on whole-body PET scans include: (1) prominent activity at body surface edges due to relative lack of attenuation at the surfaces compared to deeper structures, (2) distorted appearance of areas of intense activity (e.g.
		The attenuation correction process essentially “adds counts back” into areas that are more attenuated due to their being deeper or being surrounded by relatively dense structures.
	www.med-ed.virginia.edu /courses/rad/PETCT/Attenuation.html (697 words)

	Attenuation
		In biology, attenuation is a mechanism in the regulation of gene expression 2.
		In physical oceanography, light attenuation is the decrease in light intensity with depth in the water column due to absorption (by water molecules) and scattering (by suspended particulates).
		In telecommunication, attenuation is the decrease in intensity of a signal, beam, or wave as a result of absorption of energy and of scattering out of the path to the detector, but not including the reduction due to geometric spreading.
	www.abacci.com /wikipedia/topic.aspx?cur_title=Attenuation (309 words)

	Attenuation Information
		Attenuation is an important property in fibre optics and ultrasound applications because of its importance in determining signal strength as a function of distance.
		Attenuation is usually measured in units of decibels per centimetre of medium (dB/cm) and is represented by the attenuation coefficient of the medium in question.
		Attenuation is an important factor limiting the transmission of a light pulse across far distances, and as a result much research has gone into both limiting the attenuation and maximizing the amplification of the fibre optic light beam.
	www.bookrags.com /wiki/Attenuation (446 words)

	Kids.Net.Au - Encyclopedia > Attenuation (Site not responding. Last check: )
		In biology, attenuation is a mechanism in the regulation of gene expression
		In ecology and geochemistry, attenuation is the ability to withhold contaminants in soils and groundwaters by various mechanisms like adsorption, dilution[?], dispersion or biological degradation, causing a lower toxicity compared to the total amount of the contaminant.
		Note 2: "Attenuation" is often used as a misnomer for "attenuation coefficient[?], " which is expressed in dB per kilometer.
	www.kids.net.au /encyclopedia-wiki/at/Attenuation (182 words)

	News \| Gainesville.com \| The Gainesville Sun \| Gainesville, Fla. (Site not responding. Last check: )
		Attenuation is the decrease in intensity of electromagnetic radiation due to absorption or scattering of photons.
		Attenuation is an important consideration in the modern world of wireless telecommunication.
		Here, attenuation is the decrease in light intensity with depth due to absorption (by water molecules) and scattering (by suspended particulates).
	www.gainesville.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=attenuation_(electromagnetic_radiation) (267 words)

	CommsDesign - Performing Fiber-Optic Cable Attenuation Measurements: A Tutorial (Site not responding. Last check: )
		Measuring attenuation in a fiber-optic cable is a vital ingredient to obtaining the maximum performance from a system designs.
		Because attenuation features are incorporated in every fiber, they also increase their effect with the length of that fiber.
		Light is attenuated in the ratio dB/km, and we can measure the difference between two configurations; one where the length or bending is minimal, compared (measured) against one where the length or bending is extensive.
	www.commsdesign.com /design_center/opticalnetworking/design_corner/OEG20030812S0010 (2385 words)

	Attenuation Relationships
		The results of this study were compared with several attenuation relationships developed for the Central and Eastern U.S. The comparisons with Atkinson and Boore (1997) and Toro et al.
		The attenuation relationships for soil were compared with the results of the Uplands (Pleistocene-age) and Lowlands (Holocene-age) profiles.
		Figure 4 Comparison of attenuation relationships and calculated rock spectral accelerations for a period of 0.2 second and a moment magnitude of 6.5.
	www.ce.gatech.edu /~sromero/maecenter/Attenuation.html (951 words)

	Attenuation of Sound Waves
		Attenuation often serves as a measurement tool that leads to the formation of theories to explain physical or chemical phenomenon that decreases the ultrasonic intensity.
		Attenuation is generally proportional to the square of sound frequency.
		Attenuation can be determined by evaluating the multiple backwall reflections seen in a typical A-scan display like the one shown in the image at the top of the page.
	www.ndt-ed.org /EducationResources/CommunityCollege/Ultrasonics/Physics/attenuation.htm (429 words)

	Attenuation
		The notion of attenuation is not the familiar notion of temporal increase in the extension of a relation.
		Ultimately attenuation includes the introduction of uses of the vocable which, though n-adic, are not relational (that is, joining nominals) but rather connectival (that is, joining main clauses).
		What attenuation and its eventual outcomes require is more radical than this, since attenuated R begins to acquire n-tuples of vocables of different semantic types.
	www.cecm.sfu.ca /~thalie/PhD/node45.html (281 words)

	Beating Signal Loss in WLANs
		Attenuation is simply a reduction of signal strength during transmission.
		You represent attenuation in decibels (dB), which is ten times the logarithm of the signal power at a particular input divided by the signal power at an output of a specified medium.
		Excessive attenuation causes the network's throughput to decrease because of operation at a lower data rate and the additional overhead necessary to retransmit the frames.
	www.wi-fiplanet.com /tutorials/article.php/1431101 (1347 words)

	National Stakeholders' Forum on Monitored Natural Attenuation (Site not responding. Last check: )
		The people who design and approve a natural attenuation strategy for a groundwater plume will be long gone by the date at which remedial objectives are expected to be reached, but most of the residents or their descendants will still have to live with the results.
		Because natural attenuation is frequently much less costly than other approaches, they expressed concern that budgets built on the assumption that natural attenuation will do the job may actually lock it in as a remedy, even when it doesn't work.
		Many believed the non- destructive forms of attenuation should not be acceptable, and one tried to pin that down by asking what share of attenuation should be attributable to degradation for it to be considered the principal process.
	www.cpeo.org /pubs/narpt.html (2384 words)

	Sound Wave Attenuation
		A sound wave in air has an attenuation factor due to a transfer of kinetic energy from the systematic mean molecular velocity of the wave, to random molecular motion (i.e.
		The actual attenuation in air is complicated, due to the mixture of various gases and water vapor.
		The classical method for calculating sound attenuation, developed by Stokes and Rayleigh, is to add terms to the wave equation representing viscosity and thermal conduction.
	www.silcom.com /~aludwig/Physics/Main/Wave_attenuation.htm (1399 words)

	Commonly Asked Questions - Natural Attenuation - Petroleum Contaminated Sites (Site not responding. Last check: )
		The truth is that natural attenuation is a proactive approach that focuses on the verification and monitoring of natural remediation processes rather than relying totally on "engineered" processes.
		Before natural attenuation should be proposed for any site, significant soil and groundwater data must be collected and evaluated to document that natural attenuation is occurring and to estimate the effectiveness of natural processes in reducing contaminant concentrations over time.
		Although natural attenuation is not a default option or a "presumptive remedy," it is recognized by the EPA as a viable method of remediation for soil and groundwater that can be evaluated and compared to other methods of achieving site remediation as a part of the remedy selection process.
	www.mmr.org /cleanup/tech/brochure/nabroc2.htm (1575 words)

	Attenuation
		Attenuation in an optical fiber is caused by absorption, scattering, and bending losses.
		Attenuation is the loss of optical power as light travels along the fiber.
		Fiber attenuation caused by extrinsic absorption is affected by the level of impurities (OH) present in the fiber.
	www.tpub.com /neets/tm/106-14.htm (1423 words)

	Commonly Asked Questions Regarding the Use of Natural Attenuation for Chlorinated Solvent Spills at Federal Facilities
		Natural attenuation is recognized by the EPA as a viable method of remediation for soil and groundwater that can be evaluated and compared to other methods of achieving site remediation as a part of the remedy selection process.
		Before natural attenuation can be proposed for any site, significant soil and groundwater data must be collected and evaluated to document that natural attenuation is occurring and to estimate the effectiveness of natural processes in reducing contaminant concentrations over time.
		If natural attenuation is selected as the preferred site remedy, the party responsible for site cleanup must commit to long-term monitoring to verify that the contaminants pose no risk to human health or the environment and that natural processes are reducing contaminant levels and risk as predicted.
	www.p2pays.org /ref/02/01675.htm (1915 words)

	Natural Attenuation
		Natural attenuation occurs [in situ] and is used to reduce the mass, mobility, [toxicity], volume, or concentration of contaminants to acceptable levels.
		Natural attenuation does not generate wastes and the compounds that are the most toxic and most mobile are generally the most susceptible to biodegradation (Wiedemeier, et al, 1996).
		The key factor in terms of a compound applicability to natural attenuation is that the biodegradation rate of the contaminant of concern must be fast enough to allow in situ biodegradation before contaminant migration.
	www.glue.umd.edu /~eseagren/intrinsic.htm (2843 words)

	What is attenuation? - a definition from Whatis.com
		Attenuation is a general term that refers to any reduction in the strength of a signal.
		The extent of attenuation is usually expressed in units called decibels (dBs).
		In conventional and fiber optic cables, attenuation is specified in terms of the number of decibels per foot, 1,000 feet, kilometer, or mile.
	searchnetworking.techtarget.com /sDefinition/0,,sid7_gci211613,00.html (382 words)

	Natural Attenuation(OB/OD)
		In studying the natural attenuation of chlorinated solvents, other contaminants likely to be present in plumes should also be included in the investigation and remedy selection.
		Although immobilization is the primary attenuation process operative for arsenic and metals, it is not fully understood; this uncertainty makes it very difficult to apply MNA to arsenic and metals.
		MNA may be appropriate for some metals, when natural attenuation processes result in a change in the valence state of the metal that results in immobilization (e.g., chromium).
	www.cpeo.org /techtree/ttdescript/natatt.htm (1131 words)

	Fiber Attenuation- Developer Zone - National Instruments
		To calculate total attenuation using fractions, you must convert both absorption figures to the fractions of power transmitted, then multiply them, and convert that number from the fraction of light transmitted to the fraction attenuated.
		As we saw before, fiber attenuation is the sum of absorption and scattering, both of which vary with wavelength.
		Attenuation generally is higher in commercial graded-index multimode fibers, with typical values about 2.5 dB/km at 850 nm, 0.8 dB/km at 1310 nn, and no more than 3 dB/km at the 1380 nm water peak.
	zone.ni.com /devzone/cda/ph/p/id/88 (2155 words)

	DACT Attenuation Curve Calculator
		Please observe that the ACC assumes that the output impedance of the equipment feeding the attenuator is zero (or at least much lower than the attenuator resistance).
		If the attenuator is used as a volume control in an active preamplifier, the entered value should be the input resistance of the amplifier stage that follows the attenuator.
		Usually it is the capacitance of the cables on the attenuator output plus the input capacitance of the connected amplifier or amplifier stage.
	dact.com /html/ac_calculator.html (1108 words)

	Natural Attenuation
		Use of monitored natural attenuation as a remediation strategy involves filing a formal regulatory application to allow natural biological, chemical, and physical processes to treat groundwater contaminants, and conducting ongoing monitoring to verify that these processes are effective.
		In many cases, the feasibility of a natural attenuation strategy depends on whether the regulatory goal is to clean up the plume to drinking water standards or whether a less stringent, risk-based goal applies, such as preventing the plume from expanding.
		Although natural attenuation in the aquifer and stream decreased metal transport, the size of the plume and the longevity of the source of contamination at Pinal Creek Basin have overwhelmed the intrinsic remediation capacity of the aquifer.
	www.eas.slu.edu /People/DJCrossley/scomm/ass7text.html (2966 words)

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