Low Frequency Gravitational Waves from Black Hole MACHO Binaries

Nakamura, Sasaki, Tanaka, and Thorne have recently estimated the initial distribution of binary MACHOs in the galactic halo assuming that the MACHOs are primordial half solar mass black holes, and considered their coalescence as a possible source for ground-based interferometer gravitational wave detectors such as LIGO. Evolving their binary distribution forward in time to the present, the low-frequency (10^{-5} < f < 10^{-1} Hz) spectrum of gravitational waves associated with such a population of compact binaries is calculated. The resulting gravitational waves would form a strong stochastic background in proposed space interferometers such as LISA and OMEGA. Low frequency gravitational waves are likely to become a key tool for determining the properties of binaries within the dark MACHO population.Comment: 8 pages + 2 ps figures; AASTe

Wet Ontologies, Fluid Spaces: Giving Depth to Volume through Oceanic Thinking

This paper expands on recent attempts to destabilise the static, bordered, and linear framings that typify human geographical studies of place, territory, and time. In a world conceptualised as open, immanent, and ever-becoming, scholars have turned away from notions of fixity towards fluidity and flow, and, in so doing, have developed networked, ‘flat’ ontologies. Recent attempts have gone further, challenging the horizontalism inherent in such approaches by opening up a vertical world of volume. In this paper we contend that such approaches are still somewhat lacking. The vertical element of volume is all too often abstract and dematerialised; the emphasis on materiality that is typically used to rectify this excess of abstraction tends to reproduce a sense of matter as fixed and grounded; and the temporality that is employed to reintroduce ‘motion’ to matter has the unintended effect of signalling a periodised sense of time that minimises the chaotic underpinnings and experiences of place. We argue that the ocean is an ideal spatial foundation for addressing these challenges since it is indisputably voluminous, stubbornly material, and unmistakably undergoing continual reformation, and that a ‘wet ontology’ can reinvigorate, redirect, and reshape debates that are all too often restricted by terrestrial limits

The Shape of Dark Matter Haloes IV. The Structure of Stellar Discs in Edge-on Galaxies

We present optical and near-infrared archival observations of eight edge-on galaxies. These observations are used to model the stellar content of each galaxy using the FitSKIRT software package. Using FitSKIRT, we can self-consistently model a galaxy in each band simultaneously while treating for dust. This allows us to accurately measure both the scale length and scale height of the stellar disc, plus the shape parameters of the bulge. By combining this data with the previously reported integrated magnitudes of each galaxy, we can infer their true luminosities. We have successfully modelled seven out of the eight galaxies in our sample. We find that stellar discs can be modelled correctly, but have not been able to model the stellar bulge reliably. Our sample consists for the most part of slow rotating galaxies, and we find that the average dust layer is much thicker than what is reported for faster rotating galaxies.Comment: Accepted for publication by Monthly Notices RAS. Hi-res. version available at www.astro.rug.nl/~vdkruit/Petersetal-IV.pd

The Shape of Dark Matter Haloes II. The Galactus HI Modelling & Fitting Tool

We present a new HI modelling tool called \textsc{Galactus}. The program has been designed to perform automated fits of disc-galaxy models to observations. It includes a treatment for the self-absorption of the gas. The software has been released into the public domain. We describe the design philosophy and inner workings of the program. After this, we model the face-on galaxy NGC2403, using both self-absorption and optically thin models, showing that self-absorption occurs even in face-on galaxies. It is shown that the maximum surface brightness plateaus seen in Paper I of this series are indeed signs of self-absorption. The apparent HI mass of an edge-on galaxy can be drastically lower compared to that same galaxy seen face-on. The Tully-Fisher relation is found to be relatively free from self-absorption issues.Comment: Accepted for publication by Monthly Notices RAS. Hi-res. version available at www.astro.rug.nl/~vdkruit/Petersetal-II.pd

Unconventional carrier-mediated ferromagnetism above room temperature in ion-implanted (Ga, Mn)P:C

Ion implantation of Mn ions into hole-doped GaP has been used to induce ferromagnetic behavior above room temperature for optimized Mn concentrations near 3 at.%. The magnetism is suppressed when the Mn dose is increased or decreased away from the 3 at.% value, or when n-type GaP substrates are used. At low temperatures the saturated moment is on the order of one Bohr magneton, and the spin wave stiffness inferred from the Bloch-law T^3/2 dependence of the magnetization provides an estimate Tc = 385K of the Curie temperature that exceeds the experimental value, Tc = 270K. The presence of ferromagnetic clusters and hysteresis to temperatures of at least 330K is attributed to disorder and proximity to a metal-insulating transition.Comment: 4 pages, 4 figures (RevTex4

QCD Corrections to Electroweak Vector Boson Scattering at Small Scattering Angles

We investigate the role of a certain class of QCD corrections to electroweak vector boson scattering at small scattering angles and large energies. These are present since, from the perturbative analysis, the vector bosons may dissociate into quark-antiquark pairs giving rise to colour dipoles interacting through gluon exchanges. After the computation of the vector boson impact factors, we present expressions for the lowest order QCD scattering amplitude and for the leading logarithmic BFKL amplitude. Particularly we discuss numerical results for the process $\gamma\gamma\to ZZ$. The QCD corrections to the cross section resulting from the interference with the electroweak ones are estimated and compared with the leading pure electroweak part. Corrections resulting from the leading log BFKL amplitude are of the order of few percent already at the $0.5 - 1$ TeV energy range.Comment: 21 pages,9 figures, discussion on the helicity-flip impact factors added, typos correcte

Mathematical modelling of ethanol metabolism in normal subjects and chronic alcohol misusers

The time course of ethanol disappearance from the blood has been examined in normal males and females and in alcohol misusers. Blood alcohol estimations were made over a period of 3 hr, following an oral dose of ethanol (0.8 g/kg body weight) administered in the form of whisky. Attempts were made to fit the data to zero order, first order and mixed zero + first order kinetics. In the majority (75%) of normal females the blood ethanol concentration was still increasing at 30 min. This was only seen in 50% of normal males and in 50% of non-dependent alcohol misusers, but not in dependent alcohol misusers. In all of the normal females the disappearance of ethanol could be adequately described by zero order kinetics. However, in the normal male group only 20% could be described by zero order kinetics, 10% fitted first order kinetics and the remainder required a mixed model of zero + first order. The rate constant for the zero order component of the control male group was identical to zero order rate constant obtained for the female control group. In the female alcohol misuser group, 40% of the curves could not be described by zero order kinetics and fitted best to a mixed model. The zero order component of the entire group was significantly increased (by 35%) compared to that obtained for the female control group. In the male dependent and non-dependent alcohol misuser groups, all blood alcohol concentration curves fitted best to mixed zero and first order kinetics. However, no significant differences were noted in the values of the kinetic parameters when compared with the male control group. It is suggested that the zero order component of the blood alcohol concentration curves is due to the action of liver alcohol dehydrogenase and the first order component represents redistribution to the tissues. The presence or absence of a first order component is attributed to differences in absorption rates from the gut

A compact and robust diode laser system for atom interferometry on a sounding rocket

We present a diode laser system optimized for laser cooling and atom interferometry with ultra-cold rubidium atoms aboard sounding rockets as an important milestone towards space-borne quantum sensors. Design, assembly and qualification of the system, combing micro-integrated distributed feedback (DFB) diode laser modules and free space optical bench technology is presented in the context of the MAIUS (Matter-wave Interferometry in Microgravity) mission. This laser system, with a volume of 21 liters and total mass of 27 kg, passed all qualification tests for operation on sounding rockets and is currently used in the integrated MAIUS flight system producing Bose-Einstein condensates and performing atom interferometry based on Bragg diffraction. The MAIUS payload is being prepared for launch in fall 2016. We further report on a reference laser system, comprising a rubidium stabilized DFB laser, which was operated successfully on the TEXUS 51 mission in April 2015. The system demonstrated a high level of technological maturity by remaining frequency stabilized throughout the mission including the rocket's boost phase

PIPPS: Flexible model-based policy search robust to the curse of chaos

Previously, the exploding gradient problem has been explained to be central in deep learning and model-based reinforcement learning, because it causes numerical issues and instability in optimization. Our experiments in model-based reinforcement learning imply that the problem is not just a numerical issue, but it may be caused by a fundamental chaos-like nature of long chains of nonlinear computations. Not only do the magnitudes of the gradients become large, the direction of the gradients becomes essentially random. We show that reparameterization gradients suffer from the problem, while likelihood ratio gradients are robust. Using our insights, we develop a model-based policy search framework, Probabilistic Inference for Particle-Based Policy Search (PIPPS), which is easily extensible, and allows for almost arbitrary models and policies, while simultaneously matching the performance of previous data-efficient learning algorithms. Finally, we invent the total propagation algorithm, which efficiently computes a union over all pathwise derivative depths during a single backwards pass, automatically giving greater weight to estimators with lower variance, sometimes improving over reparameterization gradients by 10^6 times