994 research outputs found
Improved alkaline electrochemical cell
Addition of lead ions to electrolyte suppresses zinc dendrite formation during charging cycle. A soluble lead salt can be added directly or metallic lead can be incorporated in the zinc electrode and allowed to dissolve into the electrolyte
Experimentally estimated dead space for GaAs and InP based planar Gunn diodes
The authors would like to thank the staff of the James Watt Nanofabrication Centre at the University of Glasgow for help in fabricating the devices which is reported in this paper. âPart of this work was supported by ESPRC through EP/H011862/ 1, and EP/H012966/1.Peer reviewedPublisher PD
Investigation of contact edge effects in the channel of planar Gunn diodes
The effect of the edge of the channel on the operation of Planar Gunn diodes has been examined using Monte Carlo simulations. High fields at the corner of the anode contact are known to cause impact ionization and consequent electroluminescence, but our simulations show that the Gunn domains are attracted to these corners, perturbing the formation of the domains which can lead to chaotic dynamics within the rest of the channel leading to uneven heating and reduced RF output power. We show how novel shaping of the electrical contacts at the ends of the channel reduces the attraction and restores the domain wave-fronts for good device operation
Micro-cooler Enhancements by Barrier Interface Analysis
Peer reviewedPublisher PD
The EBEX Experiment
EBEX is a balloon-borne polarimeter designed to measure the intensity and
polarization of the cosmic microwave background radiation. The measurements
would probe the inflationary epoch that took place shortly after the big bang
and would significantly improve constraints on the values of several
cosmological parameters. EBEX is unique in its broad frequency coverage and in
its ability to provide critical information about the level of polarized
Galactic foregrounds which will be necessary for all future CMB polarization
experiments. EBEX consists of a 1.5 m Dragone-type telescope that provides a
resolution of less than 8 arcminutes over four focal planes each of 4 degree
diffraction limited field of view at frequencies up to 450 GHz. The experiment
is designed to accommodate 330 transition edge bolometric detectors per focal
plane, for a total of up to 1320 detectors. EBEX will operate with frequency
bands centered at 150, 250, 350, and 450 GHz. Polarimetry is achieved with a
rotating achromatic half-wave plate. EBEX is currently in the design and
construction phase, and first light is scheduled for 2008.Comment: 13 pages, 10 figures. Figure 1 is changed from the one which appeared
in the Proceedings of the SPI
Terahertz oscillations in an In<sub>0.53</sub>Ga<sub>0.47</sub>As submicron planar gunn diode
The length of the transit region of a Gunn diode determines the natural frequency at which it operates in fundamental mode â the shorter the device, the higher the frequency of operation. The long-held view on Gunn diode design is that for a functioning device the minimum length of the transit region is about 1.5ÎŒm, limiting the devices to fundamental mode operation at frequencies of roughly 60 GHz. Study of these devices by more advanced Monte Carlo techniques that simulate the ballistic transport and electron-phonon interactions that govern device behaviour, offers a new lower bound of 0.5ÎŒm, which is already being approached by the experimental evidence that has shown planar and vertical devices exhibiting Gunn operation at 600nm and 700nm, respectively. The paper presents results of the first ever THz submicron planar Gunn diode fabricated in In<sub>0.53</sub>Ga<sub>0.47</sub>A on an InP substrate, operating at a fundamental frequency above 300 GHz. Experimentally measured rf power of 28 ”W was obtained from a 600 nm long Ă120 ”m wide device. At this new length, operation in fundamental mode at much higher frequencies becomes possible â the Monte Carlo model used predicts power output at frequencies over 300 GHz
Self-avoiding walks crossing a square
We study a restricted class of self-avoiding walks (SAW) which start at the
origin (0, 0), end at , and are entirely contained in the square on the square lattice . The number of distinct
walks is known to grow as . We estimate as well as obtaining strict upper and lower bounds,
We give exact results for the number of SAW of
length for and asymptotic results for .
We also consider the model in which a weight or {\em fugacity} is
associated with each step of the walk. This gives rise to a canonical model of
a phase transition. For the average length of a SAW grows as ,
while for it grows as
. Here is the growth constant of unconstrained SAW in . For we provide numerical evidence, but no proof, that the
average walk length grows as .
We also consider Hamiltonian walks under the same restriction. They are known
to grow as on the same lattice. We give
precise estimates for as well as upper and lower bounds, and prove that
Comment: 27 pages, 9 figures. Paper updated and reorganised following
refereein
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