Gravitational Wave Bursts from Collisions of Primordial Black Holes in Clusters

The rate of gravitational wave bursts from the mergers of massive primordial black holes in clusters is calculated. Such clusters of black holes can be formed through phase transitions in the early Universe. The central black holes in clusters can serve as the seeds of supermassive black holes in galactic nuclei. The expected burst detection rate by the LISA gravitational wave detector is estimated.Comment: 10 pages, 2 figure

Power Capacity Expansion Planning Considering Endogenous Technology Cost Learning

We present an power systems optimisation model for national-scale power supply capacity expansion considering endogenous technology cost reduction (ESO-XEL). The mixed-integer linear program minimises total system cost while complying with operational constraints, carbon emission targets, and ancillary service requirements. A data clustering technique and the relaxation of integer scheduling constraints is evaluated and applied to decrease the model solution time. Two cost learning curves for the different power technologies are derived: one assuming local learning effects, the other accounting for global knowledge spill-over. A piece-wise linear formulation allows the integration of the exponential learning curves into the ESO-XEL model. The model is applied to the UK power system in the time frame of 2015 to 2050. The consideration of cost learning effects moves optimal investment timings to earlier planning years and influences the competitiveness of technologies. In addition, the maximum capacity build rate parameter influences the share of power generation significantly; the possibility of rapid capacity build-up is more important for total system cost reduction by 2050 than accounting for technology cost reduction

The Burst and Transient Source Experiment Earth Occultation Technique

An Earth orbiting detector sensitive to gamma ray photons will see step-like occultation features in its counting rate when a gamma ray point source crosses the Earth's limb. This is due to the change in atmospheric attenuation of the gamma rays along the line of sight. In an uncollimated detector, these occultation features can be used to locate and monitor astrophysical sources provided their signals can be individually separated from the detector background. We show that the Earth occultation technique applied to the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) is a viable and flexible all-sky monitor in the low energy gamma ray and hard X-ray energy range (20 keV - 1 MeV). The method is an alternative to more sophisticated photon imaging devices for astronomy, and can serve well as a cost-effective science capability for monitoring the high energy sky. Here we describe the Earth occultation technique for locating new sources and for measuring source intensity and spectra without the use of complex background models. Examples of transform imaging, step searches, spectra, and light curves are presented. Systematic uncertainties due to source confusion, detector response, and contamination from rapid background fluctuations are discussed and analyzed for their effect on intensity measurements. A sky location-dependent average systematic error is derived as a function of galactic coordinates. The sensitivity of the technique is derived as a function of incident photon energy and also as a function of angle between the source and the normal to the detector entrance window. Occultations of the Crab Nebula by the Moon are used to calibrate Earth occultation flux measurements independent of possible atmospheric scattering effects.Comment: 39 pages, 24 figures. Accepted for publication in the Astrophysical Journal Supplement

Fault and magmatic interaction within Iceland's western rift over the last 9kyr

We present high-resolution 'Chirp' sub-bottom profiler data from Thingvallavatn, a lake in Iceland's western rift zone. These data are combined with stratigraphic constraints from sediment cores to show that movement on normal faults since 9 ka are temporally correlated with magmatic events, indicating that movements were controlled by episodic dyke intrusion. Sediment depo-centres and the focus of subsidence migrated westwards over 3-4 kyr towards the locus of subsequent brittle failure. We interpret this subsidence as related to dyke intrusion a few km along strike, originating from the Hengill volcanic system, which occurred prior to major dyking, faulting and subsidence within the lake at 1.9 ka

A Quantitative and Qualitative Exploration of Photoaversion in Achromatopsia

Purpose: Photoaversion (PA) is a disabling and ubiquitous feature of achromatopsia (ACHM). We aimed to help define the characteristics of this important symptom, and present the first published assessment of its impact on patients' lives, as well as quantitative and qualitative PA assessments. Methods: Molecularly confirmed ACHM subjects were assessed for PA using four tasks: structured survey of patient experience, novel quantitative subjective measurement of PA, visual acuities in differing ambient lighting, and objective palpebral aperture-related PA testing. Results: Photoaversion in ACHM was found to be the most significant symptom for a substantial proportion (38%) of patients. A novel subjective PA measurement technique was developed and demonstrated fidelity with more invasive paradigms without exposing often very photosensitive patients to brighter light intensities used elsewhere. An objective PA measurement was also refined for use in trials, indicating that higher light intensities than previously published are likely to be needed. Monocular testing, as required for trials, was also validated for the first time. Conclusions: This study offers new insights into PA in ACHM. It provides the first structured evidence of the great significance of this symptom to patients, suggesting that PA should be considered as an additional outcome measure in therapeutic trials. It also offers new insights into the characteristics of PA in ACHM, and describes both subjective and objective measures of PA that could be employed in clinical trials

Hall Effect in the coma of 67P/Churyumov-Gerasimenko

Magnetohydrodynamics simulations have been carried out in studying the solar wind and cometary plasma interactions for decades. Various plasma boundaries have been simulated and compared well with observations for comet 1P/Halley. The Rosetta mission, which studies comet 67P/Churyumov-Gerasimenko, challenges our understanding of the solar wind and comet interactions. The Rosetta Plasma Consortium observed regions of very weak magnetic field outside the predicted diamagnetic cavity. In this paper, we simulate the inner coma with the Hall magnetohydrodynamics equations and show that the Hall effect is important in the inner coma environment. The magnetic field topology becomes complex and magnetic reconnection occurs on the dayside when the Hall effect is taken into account. The magnetic reconnection on the dayside can generate weak magnetic filed regions outside the global diamagnetic cavity, which may explain the Rosetta Plasma Consortium observations. We conclude that the substantial change in the inner coma environment is due to the fact that the ion inertial length (or gyro radius) is not much smaller than the size of the diamagnetic cavity.Comment: 23 pages, 6 figur

Severe Loss of Tritan Color Discrimination in RPE65 Associated Leber Congenital Amaurosis

Purpose: RPE65-associated Leber congenital amaurosis (RPE65-LCA) is a progressive severe retinal dystrophy with early profound dysfunction of rod photoreceptors followed by progressive cone photoreceptor degeneration. We aim to provide detailed information about how cone dysfunction affects color discrimination. Methods: Seven adults (aged 16-21) with RPE65-LCA underwent monocular color discrimination assessment using the Trivector and Ellipse versions of three computerized tests: Cambridge Colour Test (CCT), low vision version of the Cambridge Colour Test (lvvCCT), and the Universal Colour Discrimination Test (UCDT). For comparison, subjects were also tested using the American Optical Hardy Rand Rittler (AO-HRR) plates. Each assessment was repeated three times. Results: The Trivector version of the tests demonstrated that color discrimination along the tritan axis was undetectable in four subjects, and severely reduced in three subjects. These findings were confirmed by the Ellipse version of the tests. Color discrimination along the protan and deutan axes was evident but reduced in six of seven subjects. Four of seven subjects were unable to read any of the HRR plates. Conclusions: The computerized color vision tests adopted in this study provide detailed information about color discrimination in adult RPE65-LCA patients. The condition is associated with severe impairment of color discrimination, particularly along the tritan axis indicating possible early involvement of S-cones, with additional protan and deutan loss to a lesser extent. This psychophysical assessment strategy is likely to be valuable in measuring the impact of therapeutic intervention on cone function

Confidence Intervals for the Area Under the Receiver Operating Characteristic Curve in the Presence of Ignorable Missing Data

Receiver operating characteristic curves are widely used as a measure of accuracy of diagnostic tests and can be summarised using the area under the receiver operating characteristic curve (AUC). Often, it is useful to construct a confidence interval for the AUC; however, because there are a number of different proposed methods to measure variance of the AUC, there are thus many different resulting methods for constructing these intervals. In this article, we compare different methods of constructing Wald‐type confidence interval in the presence of missing data where the missingness mechanism is ignorable. We find that constructing confidence intervals using multiple imputation based on logistic regression gives the most robust coverage probability and the choice of confidence interval method is less important. However, when missingness rate is less severe (e.g. less than 70%), we recommend using Newcombe\u27s Wald method for constructing confidence intervals along with multiple imputation using predictive mean matching

Equilibrium Properties of Temporally Asymmetric Hebbian Plasticity

A theory of temporally asymmetric Hebb (TAH) rules which depress or potentiate synapses depending upon whether the postsynaptic cell fires before or after the presynaptic one is presented. Using the Fokker-Planck formalism, we show that the equilibrium synaptic distribution induced by such rules is highly sensitive to the manner in which bounds on the allowed range of synaptic values are imposed. In a biologically plausible multiplicative model, we find that the synapses in asynchronous networks reach a distribution that is invariant to the firing rates of either the pre- or post-synaptic cells. When these cells are temporally correlated, the synaptic strength varies smoothly with the degree and phase of synchrony between the cells.Comment: 3 figures, minor corrections of equations and tex

A Sequence of Declining Outbursts from GX339-4

The flux and spectrum of the black hole candidate GX339-4 has been monitored by the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-ray Observatory (CGRO) since the observatory became operational in May 1991. Between the summer of 1991 and the fall of 1996, eight outbursts from GX339-4 were observed. The history of these outbursts is one of declining fluence or total energy release, as well as a shortening of the time between outbursts. A rough linear correlation exists between the fluence emitted during an outburst and the time elapsed between the end of the previous outburst and the beginning of the current one. The peak flux is also roughly linearly correlated with outburst fluence. The lightcurves of the earlier, more intense, outbursts (except for the second one) can be modeled by a fast exponential (time constant ~ 10 days) followed by a slower exponential (~ 100 days) on the rise and a fast exponential decay (~ 5 days) on the fall. The later, weaker, outbursts are modeled with a single rising time constant (~ 20 days) and a longer decay on the fall (~ 50 days). An exponential model gives a marginally better fit than a power law to the rise/decay profiles. GX339-4 is a unique source in having more frequent outbursts than other low mass x-ray binary black hole candidates. These observations can be used to constrain models of the behavior of the accretion disk surrounding the compact object.Comment: Accepted for Publication in the Astrophysical Journal Letters, AASTE