Chemical analyses of water emanating from Fossil Springs in Central Arizona were conducted to predict changes in travertine deposition related to changes in stream discharge caused by diversion for ...hydroelectric power generation. During spring of 1996, water was sampled at 15 locations during normal seepage flow in a 6.7 km reach below Fossil Springs and at full baseflow during turbine maintenance. Analyses resulted in a rate of 11,923 kg d
−1 of CaCO
3 precipitated from 1218 l s
−1 of water emanating from the springs, while flows of 5.6 l s
−1 that seep past a diversion dam produced 46 kg d
−1 of CaCO
3 precipitation. Active travertine dams currently occur predominantly below the Irving hydroelectric powerplant with partial return of diverted flow back into the natural channel. The lower reach resulted in 519 kg d
−1 of CaCO
3 precipitated from the return of 56.6 l s
−1 with a reduced rate of precipitation during surface runoff conditions due to a dilution effect. Artificial substrates were located at sites in the lower reach for comparison with mass transfer rates derived from changes in water chemistry. Comparison between actual precipitation rates and overall mass transfer rates suggested preferential deposition was occurring at dam locations. Rates of mass transfer for high flow were greater than lower flow. Overall, mass transfer rates for the upper reach were proportional to the flow velocities with total mass transfers for both flows being approximately equal.
The phase transfer-catalyzed addition of cyclohexyl bromide to cyclopentadiene under basic conditions yields 2,3,5,5′-tetracyclohexylcyclopentadiene as the sole tetra-substituted isomer. An X-ray ...crystal structure reveals that some angle distortion exists around the quaternary carbon, including a compressed C5 ring angle (99.4(5)°). The reason for the production of only the 2,3,5,5′ isomer from the seven possible for tetracyclohexylcyclopentadiene was probed with molecular mechanical and semiempirical MO calculations. The 2,3,5,5′ form was determined to be the lowest in strain energy, although not in the heat of formation. Close intramolecular H…H contacts are present in the cyclohexyl-substituted cyclopentadienes that are absent in isopropyl analogs.
On February 17, 2009, the United States will complete the transition to digital television. The FCC is in the process of establishing rules to allow unlicensed secondary use of the TV "white space" ...that this transition creates. This television white space (TVWS) opens vital new portions of limited radio spectrum and enables delivery of new communication services, particularly wireless broadband, to millions of underserved Americans. In some rural markets, up to 250 MHz of spectrum could be utilized. Expected initial system deployments in TVWS include wireless Internet service providers (WISPs) and broadband coverage systems for business enterprises. It is critical that these early services are successful, both technically in protecting incumbent licensed users as well as financially in being commercially viable. Cognitive radio technologies are available that enable radio systems operating in the TVWS spectrum to reliably protect the incumbent licensed users. These technologies include geolocation, augmented by sensing, and beaconing. Existing protocols, such as WiMax, WiFi, and proprietary protocols, rebanded to the UHF frequency ranges, will provide broadband data throughput at adequate ranges to allow practical services. It is important to develop and deploy early viable solutions into this band that protect incumbent licensed users so that cycles of learning can start. Lessons from these early systems will allow the industry to accept more aggressive cognitive radio technologies and services, will offer greater comfort to critics of the technology, and will provide regulatory agencies worldwide with data for future rulemaking.
The cross section of atomic electron Compton scattering \(\gamma + e \rightarrow \gamma^\prime + e^\prime \) was measured in the 4.40--5.475 GeV photon beam energy region by the {\em PrimEx} ...collaboration at Jefferson Lab with an accuracy of 2\% and less. The results are consistent with theoretical predictions that include next-to-leading order radiative corrections. The measurements provide the first high precision test of this elementary QED process at beam energies greater than 0.1 GeV.
PDF
