Constraining white dwarf viscosity through tidal heating in detached binary systems

Although the internal structure of white dwarfs is considered to be generally well understood, the source and entity of viscosity is still very uncertain. We propose here to study white dwarf viscous properties using short period (< 1 hr), detached white dwarf binaries, such as the newly discovered ~12.8 min system. These binaries are wide enough that mass transfer has not yet started but close enough that the least massive component is subject to a measurable tidal deformation. The associated tidal torque transfers orbital energy, which is partially converted into heat by the action of viscosity within the deformed star. As a consequence, its outer non-degenerate layers expand, and the star puffs up. We self-consistently calculate the fractional change in radius, and the degree of asynchronism (ratio of stellar to orbital spin) as a function of the viscous time. Specializing our calculations to J0651, we find that the discrepancy between the measured radius of the secondary star and He white dwarf model predictions can be interpreted as tidal inflation if the viscous timescale is either ~2 10^5 yr or ~10^4 yr. Such values point to a non-microscopic viscosity, possibly given by tidally induced turbulence, or by magnetic field stresses with a magnetic field strength of 10-100 Gauss. Fortunately, these two timescales produce very different degree of asynchronism, with the shortest one, bringing the system much closer to synchronisation. A measurement of the stellar spin can thus univocally determined the mean viscosity. Extrapolating the secondary's radial expansion, we predict that the star will fill is Roche lobe at a separation which is 1.2-1.3 smaller than the current one. Applying this method to a future sample of systems can allow us to learn whether viscosity changes with mass and/or nuclear composition.Comment: 7 pages, 6 figures, MNRAS submitte

Seismic Behaviour and Ductility Evaluation of multi-storey Light timber-frame Buildings by Means of analytical Formulations and numerical Modelling

The research activity is focused on the study of both the linear and nonlinear behaviour of light timber-frame shear-walls buildings (called Platform Frame); in the first part the analysis of the linear-elastic behaviour is presented, whereas in the second part the non-linear behaviour is considered. After a short introduction on the state of the art of timber buildings both from the constructive and from the legislative point of view, the linear-elastic behaviour of single timber shear-wall is presented. The analysis of a single timber shear-wall allows to develop an analytical equation and simplified numerical macro-model (called UniTn-Model) which are able to represent the behaviour of a wall both in terms of displacement capacity and, much more important, in terms of stiffness. In fact, the evaluation of the correct walls stiffness constitutes a fundamental step in the seismic analysis of the timber buildings. The later section is based on what stated about the single-wall and it deals firstly with the elastic behaviour of systems composed by single-storey coupled walls and then it analyses systems of multi-storey single-walls. Theses analyses highlighted the influence of the vertical loads on the external force distribution within the shear walls, as well as the changing of the system stiffness caused by the hold-downs state variation. Both these aspects allow to develop some analytical formulations through which the stiffness matrix of full-scale buildings can be determined. Three iterative methods for the application of the Modal Response Spectrum Analysis are also presented; the differences between the methods, from the computational point of view as well as from the analytical one, are emphasized by means of a case study. The second part illustrates the non-linear analysis of a single shear-wall in order to identify the influence of the base components features on the wall ductility, both from the qualitative and the quantitative point of view; the UniTn-Model is hence extended to the non-linear field. It is also determined that the contribution of the nail deformation is not dependent on the nails spacing but it is only dependent on the geometry ratio of the sheathing-panels themselves. This property, analytically determined, is demonstrated on the basis of numerical and experimental analyses, by means of some non-linear F.E.M. analysis and some ad-hoc laboratory tests respectively. In the following section, using what developed for the single shear-wall, the non-linear analysis of single and multi-storey full-scale buildings is performed. The analyses are performed in order to assess the ductility level achievable by the buildings varying the ductility of the base components as well as the failure mechanism. In order to get generalized results and provide reliable values of ductility for the constructive system analysed, a large set of non-linear analysis has been performed through the use of a Matlab code specifically developed. This allowed to determine the ductility level that light timber-frame buildings can reach and to propose a new set of values for the behaviour factor q to be used in the seismic design. In the last section the study of the applicability of the capacity design to the light timber-frame buildings is presented. This study assesses the conditions that make the capacity design physically feasible and economically viable in comparison to the elastic design. The analyses have been conducted by varying both the geometry of the buildings that the seismic force level

Spherical clustering of users navigating 360{\deg} content

In Virtual Reality (VR) applications, understanding how users explore the omnidirectional content is important to optimize content creation, to develop user-centric services, or even to detect disorders in medical applications. Clustering users based on their common navigation patterns is a first direction to understand users behaviour. However, classical clustering techniques fail in identifying these common paths, since they are usually focused on minimizing a simple distance metric. In this paper, we argue that minimizing the distance metric does not necessarily guarantee to identify users that experience similar navigation path in the VR domain. Therefore, we propose a graph-based method to identify clusters of users who are attending the same portion of the spherical content over time. The proposed solution takes into account the spherical geometry of the content and aims at clustering users based on the actual overlap of displayed content among users. Our method is tested on real VR user navigation patterns. Results show that our solution leads to clusters in which at least 85% of the content displayed by one user is shared among the other users belonging to the same cluster.Comment: 5 pages, conference (Published in: ICASSP 2019 - 2019 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)

Midfrontal theta transcranial alternating current stimulation modulates behavioural adjustment after error execution

Cognitive control during conflict monitoring, error processing, and post-error adjustment appear to be associated with the occurrence of midfrontal theta (MFϴ). While this association is supported by correlational EEG studies, much less is known about the possible causal link between MFϴ and error and conflict processing. In the present study, we aimed to explore the role of band-specific effects in modulating the error system during a conflict resolution. In turn, we delivered transcranial alternating current stimulation (tACS) at different frequency bands (delta δ, theta θ, alpha α, beta β, gamma γ) and sham stimulation over the medial frontal cortex (MFC) in 36 healthy participants performing a modified version of the Flanker task. Task performance and reports about the sensations (e.g. visual flickering, cutaneous burning) induced by the different frequency bands, were also recorded. We found that online θ-tACS increased the response speed to congruent stimuli after error execution with respect to sham stimulation. Importantly, the accuracy following the errors did not decrease because of speed-accuracy trade off. Moreover, tACS evoked visual and somatosensory sensations were significantly stronger at α-tACS and β-tACS compared to other frequencies. Our findings suggest that theta activity plays a causative role in modulating behavioural adjustments during perceptual choices in a stimulus-response conflict task. © 2018 Federation of European Neuroscience Societies and John Wiley &amp; Sons Lt

Use of Remote Sensing for the Assessment of Farmland Biodiversity

In many countries farmland represent the most relevant type of land use. The conservation and the enhancement of biodiversity within these areas is primary objective for the achievement of sustainable management of agro-ecosystems and the level of biodiversity can be used as agri-environmental indicator. The measure of biodiversity over larger territories however, can be very expensive and time consuming. Earth observations have a rich history in characterizing and monitoring biodiversity and ecosystems. The possibility to use remotely sensed data for monitoring biodiversity was identified at the dawn of Earth observations and has been widely used for decades. Remotely sensed data can cost-effectively track changes in ecosystem distribution and status. The new generation of high-spatial and spectral resolution offers more hope for more direct monitoring of habitats and species. Recent developments in satellite remote sensing and in geographic information system (GIS) combined with user oriented computer programs allow us to use ecological principles for biodiversity characterization at landscape level more efficiently. This paper presents an approach for biodiversity characterization at landscape level using geospatial techniques. The present study hypothesizes that the complexity of the landscape is related to biological phytodiversity, and in turn phytodiversity can be considered a proxy of the overall biodiversity. The aim of the study is to estimate the farmland landscape complexity by using a remote sensing based approach. The approach has been validated in a Northern Italian agricultural area (Emilia-Romagna region). The proposed approach can provide policy makers and land use planners valuable, updated and low cost information on farmland landscape complexity and an estimate of its biodiversity.JRC.DDG.H.7 - Land management and natural hazard

PULP-HD: Accelerating Brain-Inspired High-Dimensional Computing on a Parallel Ultra-Low Power Platform

Computing with high-dimensional (HD) vectors, also referred to as $\textit{hypervectors}$, is a brain-inspired alternative to computing with scalars. Key properties of HD computing include a well-defined set of arithmetic operations on hypervectors, generality, scalability, robustness, fast learning, and ubiquitous parallel operations. HD computing is about manipulating and comparing large patterns-binary hypervectors with 10,000 dimensions-making its efficient realization on minimalistic ultra-low-power platforms challenging. This paper describes HD computing's acceleration and its optimization of memory accesses and operations on a silicon prototype of the PULPv3 4-core platform (1.5mm$^2$, 2mW), surpassing the state-of-the-art classification accuracy (on average 92.4%) with simultaneous 3.7$\times$ end-to-end speed-up and 2$\times$ energy saving compared to its single-core execution. We further explore the scalability of our accelerator by increasing the number of inputs and classification window on a new generation of the PULP architecture featuring bit-manipulation instruction extensions and larger number of 8 cores. These together enable a near ideal speed-up of 18.4$\times$ compared to the single-core PULPv3