Effects of decision-making on the transport costs across complex networks

We analyze the effects of agents' decisions on the creation of congestion on a centralized network with ring-and-hub topology. We show that there are two classes of agents each displaying a distinct set of behaviours. The dynamics of the system are driven by an interplay between the formation of, and transition between, unique stable states that arise as the network is varied. We show how the flow of objects across the network can be understood in terms of the ordering and allocation of strategies. Our results show that the existence of congestion in a network is a dynamic process that is as much dependent on the agents' decisions as it is on the structure of the network itself.Comment: Special Issue on Complex Networks, edited by Dirk Helbin

Constraining the Solution to the Last Parsec Problem with Pulsar Timing

The detection of a stochastic gravitational-wave signal from the superposition of many inspiraling supermassive black holes with pulsar timing arrays (PTAs) is likely to occur within the next decade. With this detection will come the opportunity to learn about the processes that drive black-hole-binary systems toward merger through their effects on the gravitational-wave spectrum. We use Bayesian methods to investigate the extent to which effects other than gravitational-wave emission can be distinguished using PTA observations. We show that, even in the absence of a detection, it is possible to place interesting constraints on these dynamical effects for conservative predictions of the population of tightly bound supermassive black-hole binaries. For instance, if we assume a relatively weak signal consistent with a low number of bound binaries and a low black-hole-mass to galaxy-mass correlation, we still find that a non-detection by a simulated array, with a sensitivity that should be reached in practice within a few years, disfavors gravitational-wave-dominated evolution with an odds ratio of $\sim$30:1. Such a finding would suggest either that all existing astrophysical models for the population of tightly bound binaries are overly optimistic, or else that some dynamical effect other than gravitational-wave emission is actually dominating binary evolution even at the relatively high frequencies/small orbital separations probed by PTAs.Comment: 14 pages, 8 figure

Development of molecular tools for honeybee virus research: the South African contribution

Increasing knowledge of the association of honeybee viruses with other honeybee parasites, primarily the ectoparasitic mite Varroa destructor, and their implication in the mass mortality of honeybee colonies has resulted in increasing awareness and interest in honeybee viruses. In addition the identification, monitoring and prevention of spread of bee viruses is of considerable importance, particularly when considering the lack of information on the natural incidence of virus infections in honeybee populations worldwide. A total of eighteen honeybee viruses have been identified and physically characterized. Most of them have physical features resembling picornaviruses, and are referred to as picorna-like viruses. The complete genome sequences of four picorna-like honeybee viruses, namely Acute Bee Paralysis Virus (ABPV), Black Queen Cell Virus (BQCV), Sacbrood Virus (SBV) and Deformed Wing Virus (DWV) have been determined. The availability of this sequence data has lead to great advances in the studies on honeybee viruses. In particular, the development of a reverse genetics system for BQCV, will open new opportunities for studies directed at understanding the molecular biology, persistence, pathogenesis, and interaction of these bee viruses with other parasites. This review focuses on the contribution of the Honeybee Virus Research Group (HBVRG), from the University of the Western Cape of South Africa, in the development of molecular tools for the study of molecular biology and pathology of these viruses

Remote-sensing Characterisation of Major Solar System Bodies with the Twinkle Space Telescope

Remote-sensing observations of Solar System objects with a space telescope offer a key method of understanding celestial bodies and contributing to planetary formation and evolution theories. The capabilities of Twinkle, a space telescope in a low Earth orbit with a 0.45m mirror, to acquire spectroscopic data of Solar System targets in the visible and infrared are assessed. Twinkle is a general observatory that provides on demand observations of a wide variety of targets within wavelength ranges that are currently not accessible using other space telescopes or that are accessible only to oversubscribed observatories in the short-term future. We determine the periods for which numerous Solar System objects could be observed and find that Solar System objects are regularly observable. The photon flux of major bodies is determined for comparison to the sensitivity and saturation limits of Twinkle's instrumentation and we find that the satellite's capability varies across the three spectral bands (0.4-1, 1.3-2.42, and 2.42-4.5{\mu}m). We find that for a number of targets, including the outer planets, their large moons, and bright asteroids, the model created predicts that with short exposure times, high-resolution spectra (R~250, {\lambda} 2.42{\mu}m) could be obtained with signal-to-noise ratio (SNR) of >100 with exposure times of <300s

Small Bodies Science with Twinkle

Twinkle is an upcoming 0.45m space-based telescope equipped with a visible and two near-infrared spectrometers covering the spectral range 0.4 to 4.5{\mu}m with a resolving power R~250 ({\lambda}<2.42{\mu}m) and R~60 ({\lambda}>2.42{\mu}m). We explore Twinkle's capabilities for small bodies science and find that, given Twinkle's sensitivity, pointing stability, and spectral range, the mission can observe a large number of small bodies. The sensitivity of Twinkle is calculated and compared to the flux from an object of a given visible magnitude. The number, and brightness, of asteroids and comets that enter Twinkle's field of regard is studied over three time periods of up to a decade. We find that, over a decade, several thousand asteroids enter Twinkle's field of regard with a brightness and non-sidereal rate that will allow Twinkle to characterise them at the instrumentation's native resolution with SNR > 100. Hundreds of comets can also be observed. Therefore, Twinkle offers researchers the opportunity to contribute significantly to the field of Solar System small bodies research.Comment: Published in JATI

Kullback-Leibler-Quadratic Optimal Control

This paper presents advances in Kullback-Leibler-Quadratic (KLQ) optimal control: a stochastic control framework for Markovian models. The motivation is distributed control of large networks. As in prior work, the objective function is composed of a state cost in the form of Kullback-Leibler divergence plus a quadratic control cost. With this choice of objective function, the optimal probability distribution of a population of agents over a finite time horizon is shown to be an exponential tilting of the nominal probability distribution. The same is true for the controlled transition matrices that induce the optimal probability distribution. However, one limitation of the previous work is that randomness can only be introduced via the control policy; all uncontrolled (natural) processes must be modeled as deterministic to render them immutable under an exponential tilting. In this work, only the controlled dynamics are subject to tilting, allowing for more general probabilistic models. Another advancement is a reduction in complexity based on lossy compression using transform techniques. This is motivated by the need to consider time horizons that are much longer than the inter-sampling times required for reliable control. Numerical experiments are performed in a power network setting. The results show that the KLQ method enables the aggregate power consumption of a collection of flexible loads to track a time-varying reference signal, while simultaneously ensuring each individual load satisfies its own quality of service constraints

Deceptive Affectionate Messages: Mate Retention Deployed Under the Threat of Partner Infidelity

Deceptive affectionate messages (DAMs) have been proposed to act as relational maintenance techniques and, as such, might be part of a greater repertoire of mate retention behaviors. We analyzed data from 1,993 Mechanical Turk participants to examine the relations between DAMs and mate retention, and whether these relations were mediated by the perceived risk of partner infidelity. In line with predictions, frequency of DAMs positively predicted general mate retention and cost-inflicting mate retention through the perceived risk of partner infidelity. In line with our nondirectional prediction, we also found that frequency of DAMs negatively predicted benefit-provisioning mate retention behaviors. In an exploratory mediation analysis of DAMs on benefit-provisioning mate retention via perceived partner infidelity, we surprisingly found that DAMs negatively predicted benefit-provisioning behavior due to the perceived risk of partner infidelity, suggesting that DAMs—but not benefit-provisioning mate retention—are deployed under the threat of partner infidelity. Overall, these findings suggest that DAMs might belong to a greater repertoire of mate retention (especially cost-inflicting) behaviors to thwart the possibility of partner infidelity

Optimising the analysis of transcript data using high density oligonucleotide arrays and genomic DNA-based probe selection

Background: Affymetrix GeneChip arrays are widely used for transcriptomic studies in a diverse range of species. Each gene is represented on a GeneChip array by a probe-set, consisting of up to 16 probe-pairs. Signal intensities across probe-pairs within a probe-set vary in part due to different physical hybridisation characteristics of individual probes with their target labelled transcripts. We have previously developed a technique to study the transcriptomes of heterologous species based on hybridising genomic DNA (gDNA) to a GeneChip array designed for a different species, and subsequently using only those probes with good homology. Results: Here we have investigated the effects of hybridising homologous species gDNA to study the transcriptomes of species for which the arrays have been designed. Genomic DNA from Arabidopsis thaliana and rice (Oryza sativa) were hybridised to the Affymetrix Arabidopsis ATH1 and Rice Genome GeneChip arrays respectively. Probe selection based on gDNA hybridisation intensity increased the number of genes identified as significantly differentially expressed in two published studies of Arabidopsis development, and optimised the analysis of technical replicates obtained from pooled samples of RNA from rice. Conclusion: This mixed physical and bioinformatics approach can be used to optimise estimates of gene expression when using GeneChip arrays

Detection of three honeybee viruses simultaneously by a single Multiplex Reverse Transcriptase PCR

A single multiplex reverse transcriptase (RT) polymerase chain reaction (PCR) assay was developed for the simultaneous detection of three honeybee viruses: acute bee paralysis virus (ABPV), sacbrood virus (SBV) and black queen cell virus (BQCV). Unique PCR primers were designed from the complete genome sequence to amplify fragments of 900 bp from ABPV, 434 bp from SBV and 316 bp from BQCV. Individual bee pupae homogenates or total RNA extracted from these crude extracts were used in the RT-PCR amplification. Sequence analysis of the fragments amplified revealed nucleotide sequence identities between 97 and 98% for each virus against its reference strain. In a blind test, samples containing various combinations of ABPV, SBV and BQCV were successfully identified. Furthermore, field samples of honeybee pupae were screened for viral infections, and evidence of virus inapparent infection as well as virus co-infection were found. Key words: Multiplex, RT-PCR, virus, honeybee, varroa. African Journal of Biotechnology Vol. 4 (8), pp. 763-767, August 200