4,542 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
A direct-sequence spread-spectrum communication system for integrated sensor microsystems
Some of the most important challenges in health-care technologies have been identified to be development of noninvasive systems and miniaturization. In developing the core technologies, progress is required in pushing the limits of miniaturization, minimizing the costs and power consumption of microsystems components, developing mobile/wireless communication infrastructures and computing technologies that are reliable. The implementation of such miniaturized systems has become feasible by the advent of system-on-chip technology, which enables us to integrate most of the components of a system on to a single chip. One of the most important tasks in such a system is to convey information reliably on a multiple-access-based environment. When considering the design of telecommunication system for such a network, the receiver is the key performance critical block. The paper describes the application environment, the choice of the communication protocol, the implementation of the transmitter and receiver circuitry, and research work carried out on studying the impact of input data characteristics and internal data path complexity on area and power performance of the receiver. We provide results using a test data recorded from a pH sensor. The results demonstrate satisfying functionality, area, and power constraints even when a degree of programmability is incorporated in the system
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&
Superbursts at near-Eddington mass accretion rates
Models for superbursts from neutron stars involving carbon shell flashes
predict that the mass accretion rate should be anywhere in excess of one tenth
of the Eddington limit. Yet, superbursts have so far only been detected in
systems for which the accretion rate is limited between 0.1 and 0.25 times that
limit. The question arises whether this is a selection effect or an intrinsic
property. Therefore, we have undertaken a systematic study of data from the
BeppoSAX Wide Field Cameras on the luminous source GX 17+2, comprising 10 Msec
of effective observing time on superbursts. GX 17+2 contains a neutron star
with regular Type-I X-ray bursts and accretes matter within a few tens of
percents of the Eddington limit. We find four hours-long flares which
reasonably match superburst characteristics. Two show a sudden rise (i.e.,
faster than 10 s), and two show a smooth decay combined with spectral
softening. The implied superburst recurrence time, carbon ignition column and
quenching time for ordinary bursts are close to the predicted values. However,
the flare decay time, fluence and the implied energy production of (2-4) x
10^17 erg/g are larger than expected from current theory.Comment: Accepted for publication in Astronomy & Astrophysic
\u3ci\u3ePhyllium (Phyllium) letiranti\u3c/i\u3e sp. nov. (Phasmida: Phylliidae) a new leaf insect from Peleng Island, Indonesia
A new species of leaf insect, Phyllium (Phyllium) letiranti Cumming and Teemsma, new species (Phasmida: Phylliidae), is described from a series of males, females, and eggs from Peleng Island, Indonesia. This new species is the first record of the family Phylliidae on the island and is here differentiated from congeners. Keys to males, females, and eggs of the Phyllium species of Sulawesi and Peleng islands are included within
SPATIAL AND TEMPORAL DISTRIBUTION OF THE FORENSICALLY SIGNIFICANT BLOW FLIES OF LOS ANGELES COUNTY, CALIFORNIA, UNITED STATES (DIPTERA: CALLIPHORIDAE)
Forensic entomology although not a commonly used discipline in the forensic sciences, does have its niche and when used by investigators is respected in crinimolegal investigations (Greenberg and Kunich, 2005). With many species of forensically significant insects being regionally specific, it is often difficult for forensic entomologists to as confidently translate regionally specific studies across drastically differing geographic regions (Brundage, et al., 2011).
The purpose of this study is to help create a better temporal and geographic distributional understanding of the blow fly species present in Los Angeles County, California, United States. Twenty-five locations from four ecoregions (coastal mountains, urban, interior mountains, and desert) were regularly surveyed using baited traps for forensically significant blow flies throughout Los Angeles County from July, 2017 through January, 2018.
In total 10,875 arthropod specimens were collected, of which 4,933 were the target family Calliphoridae. Six genera and twelve forensically significant species were recorded from the county during this time period. In addition to the current survey, all specimens from the Los Angeles Museum of Natural History and from select literature were included revealing an additional three species not collected during this current survey. Chrysomya rufifacies and Lucilia sericata comprised most the specimens recorded [collectively 87.9% (61.3% and 26.6% respectively)].
Several species define two ecoregions, Lucilia cuprina was only recorded below 1,000 feet elevation in urban disturbed environments, and Calliphora livida and Calliphora vomitoria define the San Gabriel Mountains having only been found there above about 4,000 feet elevation. Temporally, with Los Angeles having a rather Mediterranean climate year-round it is not surprising that most species have wide temporal distributions with only Calliphora terraenovae significantly restricted to only May-June.
In summary, summer was the most species rich season with all 15 species recorded, and the San Gabriel Mountains had the highest diversity with 13 of the 15 species occurring there.
Advisor: Leon Higle
What makes the Crab pulsar shine?
Our high time resolution observations of individual pulses from the Crab
pulsar show that the main pulse and interpulse differ in temporal behavior,
spectral behavior, polarization and dispersion. The main pulse properties are
consistent with one current model of pulsar radio emission, namely, soliton
collapse in strong plasma turbulence. The high-frequency interpulse is quite
another story. Its dynamic spectrum cannot easily be explained by any current
emission model; its excess dispersion must come from propagation through the
star's magnetosphere. We suspect the high-frequency interpulse does not follow
the ``standard model'', but rather comes from some unexpected region within the
star's magnetosphere. Similar observations of other pulsars will reveal whether
the radio emission mechanisms operating in the Crab pulsar are unique to that
star, or can be identified in the general population.Comment: 5 pages, 2 figures, to appear in proceedings of meeting "Forty Years
of Pulsars: Millisecond Pulsars, Magnetars and More", Montreal, August 200
A Bayesian multi-region radial composite reservoir model for deconvolution in well test analysis
In petroleum well test analysis, deconvolution is used to obtain information about the reservoir system. This information is contained in the response function, which can be estimated by solving an inverse problem in the pressure and flow rate measurements. Our Bayesian approach to this problem is based upon a parametric physical model of reservoir behaviour, derived from the solution for fluid flow in a general class of reservoirs. This permits joint parametric Bayesian inference for both the reservoir parameters and the true pressure and rate values, which is essential due to the typical levels of observation error. Using a set of flexible priors for the reservoir parameters to restrict the solution space to physical behaviours, samples from the posterior are generated using MCMC. Summaries and visualisations of the reservoir parameters' posterior, response, and true pressure and rate values can be produced, interpreted, and model selection can be performed. The method is validated through a synthetic application, and applied to a field data set. The results are comparable to the state of the art solution, but through our method we gain access to system parameters, we can incorporate prior knowledge that excludes non-physical results, and we can quantify parameter uncertainty
Equity crowdfunding and governance : Toward an integrative model and research agenda
This is the author accepted manuscript. The final version is available
from the Academy of Management via the DOI in this recordEquity crowdfunding markets have grown exponentially over the last few years. Despite this impressive growth, significant informational asymmetry problems may plague these markets, making them susceptible to difficulties and even market failure. In this paper, we depart from current equity crowdfunding research that focuses almost exclusively on the funding success and funding dynamics on platforms to study the effective governance of equity-crowdfunded (ECF) firms and how it relates to these firms’ success. We propose a conceptual model that identifies a multitude of governance mechanisms (e.g., internal or external and formal or informal) that potentially operate in equity crowdfunding markets to reduce adverse selection and moral hazard problems. Further, building on this framework, we offer a roadmap for future research that examines how different governance mechanisms may help in the selection and development of successful ECF firms.Research Foundation—Flander
The Subpulse Modulation Properties of Pulsars and its Frequency Dependence
A large sample of about two hundred pulsars have been observed to study their
subpulse modulation at an observing wavelength of (when achievable) both 21 and
92 cm using the Westerbork Synthesis Radio Telescope. For 57 pulsars drifting
subpulses are discovered for the first time and are confirmed for many others.
This leads to the conclusion that it could well be that the drifting subpulse
mechanism is an intrinsic property of the emission mechanism itself, although
for some pulsars it is difficult or impossible to detect. It appears that the
youngest pulsars have the most disordered subpulses and the subpulses become
more and more organized into drifting subpulses as the pulsar ages. Drifting
subpulses are in general found at both frequencies and the measured values of
P3 at the two frequencies are highly correlated, showing the broadband nature
of this phenomenon. Also the modulation indices measured at the two frequencies
are clearly correlated, although at 92 cm they are on average possibly higher.
The correlations with the modulation indices are argued to be consistent with
the picture in which the radio emission is composed out of a drifting subpulse
signal plus a quasi-steady signal which becomes, on average, stronger at high
observing frequencies. There is no obvious correlation found between P3 and the
pulsar age (or any other pulsar parameter) contrary to reports in the past.Comment: Proceedings of the 40 Years of Pulsars: Millisecond Pulsars,
Magnetars and More conference in Montrea
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