58,215 research outputs found
Thermoelectric properties of AgGaTe and related chalcopyrite structure materials
We present an analysis of the potential thermoelectric performance of p-type
AgGaTe, which has already shown a of 0.8 with partial optimization,
and observe that the same band structure features, such as a mixture of light
and heavy bands and isotropic transport, that lead to this good performance are
present in certain other ternary chalcopyrite structure semiconductors. We find
that optimal performance of AgGaTe will be found for hole concentrations
between 4 and 2 cm at 900 K, and 2
and 10 cm at 700 K, and that certain other
chalcopyrite semiconductors might show good thermoelectric performance at
similar doping ranges and temperatures if not for higher lattice thermal
conductivity
GIOTTO's antenna de-spin mechanism: Ots lubrication and thermal vacuum performance
Except in the near Earth phase of GIOTTO's mission to Comet Halley, the HGA (high gain antenna) on board GIOTTO was the only designed means of up/down communications. The spacecraft spin stabilization required that the HGA be despun at the same rotational rate of nominally 15 rpm in order to keep the HGA pointing accurately to a Earth. A dual servomotor despin mechanism was designed and built by SEP of France for this purpose. The expected thermal environment suggested that dry lubrication was preferable to wet for the ball bearings but there existed no relevant data on the torque noise spectrum of candidate solid lubricants. Therefore ad hoc torque noise tests were run with two solid lubricants: ion plated lead film plus lead bronze cage (retainer) and a PTFE composite cage only. The lead lubrication showed the better spectrum up to the mission lifetime point so it was selected for continued test over some 20 times the Halley mission life, with periodic torque spectrum monitoring. The spectrum remained well within the pointing error budget over the 100 million revolutions covered
Increasing throughput in IEEE 802.11 by optimal selection of backoff parameters
Engineering and Physical Sciences Research Council. Grant Number: EP/G012628/
Transparent polymeric laminates
Laminate prepared from epoxy-boroxine and phenolphthalein polycarbonate has high mechanical strength at elevated temperature and is resistant to impact, fire, and high-energy thermal radiation. Polycarbonate is prepared by reaction of phenolphthalein with phosgene in presence of amine catalyst and immiscible organic solvent phase
Barriers to the utilization of synthetic fuels for transportation
The principal types of engines for transportation uses are reviewed and the specifications for conventional fuels are compared with specifications for synthetic fuels. Synfuel processes nearing the commercialization phase are reviewed. The barriers to using synfuels can be classified into four groups: technical, such as the uncertainty that a new engine design can satisfy the desired performance criteria; environmental, such as the risk that the engine emissions cannot meet the applicable environmental standards; economic, including the cost of using a synfuel relative to conventional transportation fuels; and market, involving market penetration by offering new engines, establishing new distribution systems and/or changing user expectations
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