7,266 research outputs found
Multiple traffic signal control using a genetic algorithm
Optimising traffic signal timings for a multiple-junction road network is a difficult but important problem. The essential difficulty of this problem is that the traffic signals need to coordinate their behaviours to achieve the common goal of optimising overall network delay. This paper discusses a novel approach towards the generation of optimal signalling strategies, based on the use of a genetic algorithm (GA). This GA optimises the set of signal timings for all junctions in network. The different efficient red and green times for all the signals are determined by genetic algorithm as well as the offset time for each junction. Previous attempts to do this rely on a fixed cycle time, whereas the algorithm described here attempts to optimise cycle time for each junction as well as proportion of green times. The fitness function is a measure of the overall delay of the network. The resulting optimised signalling strategies were compared against a well-known civil engineering technique, and conclusions drawn
Tranching in the Syndicated Loan Market
We use data comprising over 100,000 loans from 115 countries during 1995-2009 to examine factors that affect the extent of loan tranching, and the range of tranche spreads. The data show five factors that drive them: asymmetric information, borrower risk, transaction costs, the presence of institutional investors, and the legal system. Tranching is more extensive and generates greater differences in spreads between tranches of a same loan when asymmetric information and risk are more pronounced. Economic and institutional factors driving tranching are more directly applicable to non-investment grade loans. For developing countries, the data highlight factors that affect the extent of tranching but such factors show little sensitivity to the pricing of the relative spreads.Loan;Debt finance;Tranche;Law and finance
Multi-channel GaAs-based planar gunn diodes
We present a multi-channel GaAs-based planar Gunn
diode. By introducing extra channels, the output RF power has
been significantly improved compared to single-channel GaAsbased
planar Gunn diodes. For a 1.14 μm length and 60 μm wide
device, the highest power achieved was approximately -4 dBm
operating in fundamental mode at 109 GHz, and -26.6 dBm at its
second-harmonic at 218 GHz
The cooling rate of neutron stars after thermonuclear shell flashes
Thermonuclear shell flashes on neutron stars are detected as bright X-ray
bursts. Traditionally, their decay is modeled with an exponential function.
However, this is not what theory predicts. The expected functional form for
luminosities below the Eddington limit, at times when there is no significant
nuclear burning, is a power law. We tested the exponential and power-law
functional forms against the best data available: bursts measured with the
high-throughput Proportional Counter Array (PCA) on board the Rossi X-ray
Timing Explorer. We selected a sample of 35 'clean' and ordinary (i.e., shorter
than a few minutes) bursts from 14 different neutron stars that 1) show a large
dynamic range in luminosity, 2) are the least affected by disturbances by the
accretion disk and 3) lack prolonged nuclear burning through the rp-process. We
find indeed that for every burst a power law is a better description than an
exponential function. We also find that the decay index is steep, 1.8 on
average, and different for every burst. This may be explained by contributions
from degenerate electrons and photons to the specific heat capacity of the
ignited layer and by deviations from the Stefan-Boltzmann law due to changes in
the opacity with density and temperature. Detailed verification of this
explanation yields inconclusive results. While the values for the decay index
are consistent, changes of it with the burst time scale, as a proxy of ignition
depth, and with time are not supported by model calculations.Comment: 10 pages, 7 figures, recommended for publication in A&
A wideband CPW ring power combiner with low insertion loss and high port isolation
In this paper we present a coplanar waveguide (CPW)-based ring power combiner that exhibits less than 0.8 dB insertion loss, better than 15 dB port match and higher than 22 dB isolation loss over the frequency range from 50 GHz to 100 GHz. Compared with the conventional 2-way Wilkinson combiner, the proposed ring power combiner replaces the resistor between the two input ports with two quasi quarter-wave CPWs, a 180º CPW phase inverter, and two resistors that lead to frequency-insensitive port isolation and wideband port match. The power combiner is realized using an electron beam-based GaAs MMIC process along with simple electron beam airbridge technology. These results agree well with 3D full-wave simulations
Fabrication of submicron planar Gunn diode
We present, for the first time, the fabrication
process for a submicron planar Gunn diode in In<sub>0.53</sub>Ga<sub>0.47</sub>As on an InP substrate operating at 265 GHz. A novel two stage lift off method has been developed to achieve a submicron gaps between
contacts down to 135 nm with widths up to 120 μm
- …