Improved all-sky search method for continuous gravitational waves from unknown neutron stars in binary systems

Continuous gravitational waves from spinning deformed neutron stars have not been detected yet, and are one of the most promising signals for future detection. All-sky searches for continuous gravitational waves from unknown neutron stars in binary systems are the most computationally challenging search type. Consequently, very few search algorithms and implementations exist for these sources, and only a handful of such searches have been performed so far. In this paper, we present a new all-sky binary search method, BinarySkyHou$\mathcal{F}$, which extends and improves upon the earlier BinarySkyHough method, and which was the basis for a recent search (Covas et al. [1]). We compare the sensitivity and computational cost to previous methods, showing that it is both more sensitive and computationally efficient, which allows for broader and more sensitive searches. <br

Improved short-segment detection statistic for continuous gravitational waves

Continuous gravitational waves represent one of the long-sought types of signals that have yet to be detected. Due to their small amplitude, long observational datasets (months-years) have to be analyzed together, thereby vastly increasing the computational cost of these searches. All-sky searches face the most severe computational obstacles, especially searches for sources in unknown binary systems, which need to break the data into very short segments in order to be computationally feasible. In this paper, we present a new detection statistic that improves sensitivity by up to 19% compared to the standard $\mathcal{F}$-statistic for segments shorter than a few hours

Study of solids conveying in single screw extruders based on flow dynamics and structure of solid pellets

Flow of granular matter is presently a subject of extensive research, due to the characteristics of this type of systems (e.g., dilatancy, segregation, arching, clustering) and relevance to various application areas, such as civil construction, agriculture, food processing, geophysics, pharmacology [1, 2]. The plasticating process in single screw polymer extrusion is one of the areas where this research can help to increase the existing knowledge. In the initial turns of an Archimedes-type screw, loose pellets are conveyed forward. However, traditional analyses assume the movement of an elastic solid plug at constant velocity. This work follows previous efforts to predict the characteristics of this flow using the Discrete Element Method (DEM) [3, 4]. Two boundary conditions are considered: a) open-discharge, implying that no compaction of the solids occurs and b) close-discharge, leading to a pressure increase. The dynamics and the structure of the flow were studied by computing the cross- and down channel velocity profiles, the coordination number distribution, the output rate, the residence time distribution and the density profile, as a function of the friction force grain-wall, screw speed and pellet size. The model is able to capture the process of plug formation towards the discharge, and its predictions provide an insight into possible flow fluctuations

Flow dynamics and structure of solid pellets along the channel of a single screw extruder

Plasticating single screw extrusion involves the progressive compaction and heating of loose solid pellets that eventually melt, form a relatively homogenous stream and are subsequently pumped through a shaping tool. Traditional analyses of the solids conveying stage assume the sliding of an elastic solid plug due to differential wall friction coefficients. However, not only the corresponding predictions may fail considerably, but it is also well known that, at least in the initial screw turns, pellets are far from compact. This work follows previous efforts to model the flow of solids in the hopper and initial screw turns using the Discrete Element Method (DEM). The model considers the development of normal and tangential forces resulting from the inelastic collisions between the pellets and between them and the neighbouring metallic surfaces. As an example of the capability of the model to capture detailed features of granular flow, the effect of pellet size on flow is discussed.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BPD/39381/2007

Structure and Evolution of Giant Cells in Global Models of Solar Convection

The global scales of solar convection are studied through three-dimensional simulations of compressible convection carried out in spherical shells of rotating fluid which extend from the base of the convection zone to within 15 Mm of the photosphere. Such modelling at the highest spatial resolution to date allows study of distinctly turbulent convection, revealing that coherent downflow structures associated with giant cells continue to play a significant role in maintaining the strong differential rotation that is achieved. These giant cells at lower latitudes exhibit prograde propagation relative to the mean zonal flow, or differential rotation, that they establish, and retrograde propagation of more isotropic structures with vortical character at mid and high latitudes. The interstices of the downflow networks often possess strong and compact cyclonic flows. The evolving giant-cell downflow systems can be partly masked by the intense smaller scales of convection driven closer to the surface, yet they are likely to be detectable with the helioseismic probing that is now becoming available. Indeed, the meandering streams and varying cellular subsurface flows revealed by helioseismology must be sampling contributions from the giant cells, yet it is difficult to separate out these signals from those attributed to the faster horizontal flows of supergranulation. To aid in such detection, we use our simulations to describe how the properties of giant cells may be expected to vary with depth, how their patterns evolve in time, and analyze the statistical features of correlations within these complex flow fields.Comment: 22 pages, 16 figures (color figures are low res), uses emulateapj.cls Latex class file, Results shown during a Press release at the AAS meeting in June 2007. Submitted to Ap

Constraints on r-modes and mountains on millisecond neutron stars in binary systems

Continuous gravitational waves are nearly monochromatic signals emitted by asymmetries in rotating neutron stars. These signals have not yet been detected. Deep all-sky searches for continuous gravitational waves from isolated neutron stars require significant computational expense. Deep searches for neutron stars in binary systems are even more expensive, but potentially these targets are more promising emitters, especially in the hundreds-Hz region, where ground-based gravitational wave detectors are most sensitive. We present here an all-sky search for continuous signals with frequency between 300 and 500 Hz, from neutron stars in binary systems with orbital period between 15 and 60 days, and projected semi-major axis between 10 and 40 light-seconds. This is the only binary search on Advanced-LIGO data that probes this frequency range. Compared to previous results, our search is over an order of magnitude more sensitive. We do not detect any signals, but our results exclude plausible and unexplored neutron star configurations, for example, neutron stars with relative deformations greater than 3e-6 within 1 kpc from Earth and r-mode emission at the level of alpha ~ few 1e-4 within the same distance.Comment: Accepted for publication in The Astrophysical Journal Letter

Optimization of single screw extrusion

Multi-objective evolutionary optimization algorithms (MOEA) are used for the optimization of plasticating single screw extrusion. For this purpose, a specific MOEA is linked to available process modelling routines. The methodology is used to set the operating conditions and identify the screw geometry for a specific case study, thus demonstrating the practical utility of this approach.Project H2020-MSCA-RISE-2016-734205info:eu-repo/semantics/publishedVersio