Apsidal motion in massive close binary systems. I. HD 165052 an extreme case?

We present a new set of radial-velocity measurements of the spectroscopic binary HD 165052 obtained by disentangling of high-resolution optical spectra. The longitude of the periastron (60 +- 2 degrees) shows a variation with respect to previous studies. We have determined the apsidal motion rate of the system (12.1 +- 0.3 degree/yr), which was used to calculate the absolute masses of the binary components: M_1 = 22.5 +- 1.0 and M_2 = 20.5 +- 0.9 solar masses. Analysing the separated spectra we have re-classified the components as O7Vz and O7.5Vz stars

Optical phase-locked loop for coherent detection optical receiver

Lette

Data-Driven Aeroacoustic Modelling: Trailing-Edge Noise

Broadband noise emitted at the trailing edge of an airfoil represents a significant contribu- tion to the noise emission in rotors, wind turbine and fan blades, in low Mach number flows. High-fidelity calculations are out of the scope when fast parametric calculations are needed. In these cases it is necessary to resort to analytical models and the most popular one is the model proposed by Amiet. In the model, the knowledge of the wall pressure spectrum allows to define an equivalent point source located at the trailing edge. The description of the turbulent wall pressure spectrum is of major importance for the correct noise prediction. Proposed empirical laws of wall pressure spectra in presence of adverse pressure gradients are limited to cases which are not too far from the test cases employed for their calibration. Recently, the development of machine learning techniques make it possible to analyze large amounts of experimental data in order to automatically extract modeling knowledge. However measurements of pressure fluctuations near a trailing edge are difficult. An alternative solution is to measure the far-field trailing-edge noise at each condition. The measures are comparatively simpler and contain all the information about the source. In this work a deep learning algorithm, based on a standard feed-forward Artificial Neural Network (ANN) and a Random Forest (RF) algorithm are applied to far-field directivity data sets. The motivation of the present work is to evaluate the prediction ability of the ANN and RF models. The proposed approach allows to build a general model which can potentially be trained on experimental data and so it is not limited by the simplifying assumptions required by analytical models or empirical wall pressure spectrum. The prediction capabilities of ANN and RF are investigated by considering data not included in the training database. The potential of RF regression for the evaluation of the prediction uncertainty is also addressed. The proposed models are based on a splitting in sub models: the ANN or the RF algorithm is used to describe the noise directivity while a polynomial model is introduced for the prediction of the emitted acoustic power. This splitting, which improves significantly the training performance, can be seen as a possible way to introduce a physical constraint to the machine learning model which is forced to satisfy a constraint on the emitted power. The proposed procedure is tested on an artificial database generated by the Amiet model. However, it can be directly applied to experimental data or high-fidelity calculations

Governing bodies or managing freedom? Subcultural struggles, national sport systems and the glocalised institutionalisation of parkour

Whilst being the world’s fastest growing informal sport, parkour is also undergoing a gradual institutionalisation which is shaped differently by each national context’s specific sport system. We investigate this glocalised process by examining the subcultural tensions and power struggles it generates within the Italian parkour community. Whilst in other countries parkour practitioners (the so-called traceurs/traceuses) have managed to gain public recognition by forming a specific and independent national governing body, in Italy they are gradually affiliating with different Sport Promotion Bodies (Enti di Promozione Sportiva), the distinctive umbrella organisations which compete for the provision of sport-for-all within the country. Through a qualitative mixed-method approach based on focus groups, individual interviews and the analysis of ethnographic and documentary material, we explore the institutionalisation of Italian parkour by focusing on the controversies surrounding the introduction of teaching standards and qualifications, which is becoming a battlefield between competing authenticity claims based on different visions and interpretations of parkour. Our analysis shows how sport policymakers become influential agents in this authentication process by (often unwittingly) favouring certain forms and meanings of the practice and thereby contributing to legitimising certain practitioners over others, distributing subcultural reputations and shaping hierarchies in the field. Moreover, by highlighting how the specific characteristics of the Italian sport system contribute to increasing tensions amongst traceurs but also stimulate discussion and pluralism, this study calls for future comparative analysis of the role of policymakers in the local re-contextualisation of highly globalised practices

Photometric and spectroscopic variations of the Be star HD 112999

Be objects are stars of B spectral type showing lines of the Balmer series in emission. The presence of these lines is attributed to the existence of an extended envelope, disk type, around them. Some stars are observed in both the Be and normal B-type spectroscopic states and they are known as transient Be stars. In this paper we show the analysis carried out on a new possible transient Be star, labelled HD 112999, using spectroscopic optical observations and photometric data.Comment: 10 pages, 5 figures, accepted for publication in IBV

Estimation of displacement for internet of things applications with kalman filter

In the vision of the Internet of Things, an object embedded in the physical world is recognizable and becomes smart by communicating data about itself and by accessing aggregate information from other devices. One of the most useful types of information for interactions among objects regards their movement. Mobile devices can infer their position by exploiting an embedded accelerometer. However, the double integration of the acceleration may not guarantee a reliable estimation of the displacement of the device (i.e., the difference in the new location). In fact, noise and measurement errors dramatically affect the assessment. This paper investigates the benefits and drawbacks of the use of the Kalman filter as a correction technique to achieve more precise estimation of displacement. The approach is evaluated with two accelerometers embedded in commercial devices: A smartphone and a sensor platform. The results show that the technique based on the Kalman filter dramatically reduces the percentage error, in comparison to the assessment made by double integration of the acceleration data; in particular, the precision is improved by up to 72%. At the same time, the computational overhead due to the Kalman filter can be assumed to be negligible in almost all application scenarios

Numerical Tool Optimization for Advanced Rocket Nozzle Performance Prediction

A number of Altitude-Compensating Nozzle concepts have been developed through the years, to reduce nozzle performance losses. One of the most promising concepts is the dual- bell nozzle, where the flow is capable of auto-adapting at low and high altitude without the use of mechanical devices. This paper focuses on the optimization and validation of an in- house solver for the prediction of the flow field in advanced rocket nozzles, with emphasis on dual-bell rocket nozzles. Numerical efforts are concentrated on predicting transition from one operating mode to the other, since low and high altitude operating modes are both well known stable conditions. Both steady state and transient problems are considered and the performances of different numerical schemes are investigated

Characterization of multilayer stack parameters from X-ray reflectivity data using the PPM program: measurements and comparison with TEM results

Future hard (10 -100 keV) X-ray telescopes (SIMBOL-X, Con-X, HEXIT-SAT, XEUS) will implement focusing optics with multilayer coatings: in view of the production of these optics we are exploring several deposition techniques for the reflective coatings. In order to evaluate the achievable optical performance X-Ray Reflectivity (XRR) measurements are performed, which are powerful tools for the in-depth characterization of multilayer properties (roughness, thickness and density distribution). An exact extraction of the stack parameters is however difficult because the XRR scans depend on them in a complex way. The PPM code, developed at ERSF in the past years, is able to derive the layer-by-layer properties of multilayer structures from semi-automatic XRR scan fittings by means of a global minimization procedure in the parameters space. In this work we will present the PPM modeling of some multilayer stacks (Pt/C and Ni/C) deposited by simple e-beam evaporation. Moreover, in order to verify the predictions of PPM, the obtained results are compared with TEM profiles taken on the same set of samples. As we will show, PPM results are in good agreement with the TEM findings. In addition, we show that the accurate fitting returns a physically correct evaluation of the variation of layers thickness through the stack, whereas the thickness trend derived from TEM profiles can be altered by the superposition of roughness profiles in the sample image