An Improved Prediction Method for Noise Generated by Conventional Profile Coaxial Jets

A semiempirical model for predicting the noise generated by conventional velocity profile jets exhausting from coaxial nozzles is presented and compared with small scale static and simulated flight data. Improvements to the basic circular jet noise prediction are developed which improve the accuracy, especially at high jet velocity and near the jet axis

Une épitaphe aux discours d’austérité? Une approche expérimentale des évolutions de l’opinion publique et des dynamiques de classe pendant la crise de la Covid-19

The Covid-19 pandemic is disrupting the international political economy context unlike any event since World War II. As a consequence, the French government has, at least momentarily, reversed decades of fiscal consolidation policies sedimented around austerity narratives by instating a costly emergency furlough scheme for a third of the workforce. This crisis provides a natural setting to investigate the relations among an emerging “critical juncture” in political economy, public preferences, and the salience of austerity narratives. We collected panel data and administered two experiments to test if citizens’ viewpoints are sensitive to the trade-off between health and economics, still receptive to austerity narratives, and conditioned by socioeconomic status in supporting them. We find public viewpoints were highly swayable between health and economic concerns at the first peak of the epidemic outbreak in April 2020, but they were not influenced by the austerity narratives during the phase-out of the lockdown in June, with the exception of the upper class. Overall, public support is shifting in favor of increased social spending, and austerity might no longer inhabit the majority’s “common sense.” We conclude with further implications for the study of class and conflict in a post-pandemic world.La pandémie de Covid-19 bouleverse le contexte de l’économie politique internationale comme aucun événement ne l’a fait depuis la Seconde Guerre mondiale. En conséquence, le gouvernement français a, au moins momentanément, foulé au pied des décennies de politiques d’assainissement budgétaire appuyées sur des discours d’austérité, en mettant en place une aide d’urgence onéreuse à destination d’un tiers de la population active. Cette crise offre donc un cadre naturel pour enquêter sur les relations entre ce «moment critique» émergent de l’économie politique, l’opinion publique et la prépondérance du récit justifiant les mesures d’austérité. Nous avons collecté des données auprès d’un panel et mené deux expériences pour tester si les points de vue exprimés par les citoyens sont sensibles au compromis entre mesures privilégiant la santé ou l’économie, s’ils se montrent toujours réceptifs aux récits d’austérité et si leur soutien est conditionné par leur statut socio-économique. Nous avons pu constater que si les points de vue exprimés lors du premier pic épidémique d’avril 2020 oscillaient aisément des préoccupations sanitaires aux préoccupations économiques, ils n’étaient plus perméables aux discours d’austérité lors de la sortie progressive du confinement en juin, à l’exception de la classe supérieure. Dans l’ensemble, le soutien du public semble basculer en faveur d’une augmentation des dépenses sociales et l’austérité ne plus appartenir au «sens commun» de la majorité de la population. Nous concluons avec des implications pour l’étude des classes sociales et des conflits dans un monde post-pandémique.1 Introduction 2 Contextualizing public opinion shifts in political economy 3 Measuring public preferences and their manipulability 4 Moving away from austerity narratives? For the many, not the few 5 Concluding remarks 6 Data and methodological note Reference

Evidence of a new low field cross-over in the vortex critical velocity of type-II superconducting thin films

We measure current-voltage characteristics as function of magnetic field and temperature in Nb strips of different thickness and width. The instability voltage of the flux flow state related to the vortex critical velocity v* is studied and compared with the Larkin-Ovchinnikov theory. Beside the usual power-law dependence v* ~ B^-1/2, in the low field range a new cross-over field, Bcr1, is observed below which v* decreases by further lowering the external magnetic field B. We ascribe this unexpected cross-over to vortex channeling due to a fan-like penetration of the applied magnetic field as confirmed by magneto-optic imaging. The observation of Bcr1 becomes a direct evidence of a general feature in type-II superconducting films at low fields, that is a channel-like vortex motion induced by the inhomogeneous magnetic state caused by the relatively strong pinning

Signal Processing Methodology of Response Data from a Historical Arch Bridge toward Reliable Modal Identification

The paper is part of a case study concerning the structural assessment of a historical infrastructure in the local territory, a road three-span reinforced concrete arch bridge over a river, built by the end of World War I (1917). The purpose of the paper is twofold: first, in-situ acquired response data are systematically analysed by specific signal processing techniques, to form a devoted methodological procedure and to extract useful information toward possible interpretation of the current structural conditions; second, the deciphered information is elaborated, in view of obtaining peculiar conceptualisations of detailed features of the structural response, as meant to achieve quantitative descriptions and modelling, for final Structural Health Monitoring (SHM) and intervention purposes. The proposed methodology, integrating self-implemented and adapted classical signal processing methods, and refined techniques, such as Wavelet analysis and ARMA models, assembles a rather general, systematic methodological approach to signal processing, highlighting the capability to extract useful and fundamental information from acquired response data, also endowed of a non-stationary character, toward final structural interpretation, identification and modelling, thus enabling for developing a reliable and effective SHM platform, on strategic ageing infrastructures. For the present case study, non-stationary characteristics of the response signals are revealed and flattened out, to identify the underlying fundamental frequencies of the infrastructure and to advance particular interpretations of its current structural behaviour, in forming an enlarging structural consciousness of the bridge at hand

Study of coupling loss on bi-columnar BSCCO/Ag tapes by a.c. susceptibility measurements

Coupling losses were studied in composite tapes containing superconducting material in the form of two separate stacks of densely packed filaments embedded in a metallic matrix of Ag or Ag alloy. This kind of sample geometry is quite favorable for studying the coupling currents and in particular the role of superconducting bridges between filaments. By using a.c. susceptibility technique, the electromagnetic losses as function of a.c. magnetic field amplitude and frequency were measured at the temperature T = 77 K for two tapes with different matrix composition. The length of samples was varied by subsequent cutting in order to investigate its influence on the dynamics of magnetic flux penetration. The geometrical factor $\chi_0$ which takes into account the demagnetizing effects was established from a.c. susceptibility data at low amplitudes. Losses vs frequency dependencies have been found to agree nicely with the theoretical model developed for round multifilamentary wires. Applying this model, the effective resistivity of the matrix was determined for each tape, by using only measured quantities. For the tape with pure silver matrix its value was found to be larger than what predicted by the theory for given metal resistivity and filamentary architecture. On the contrary, in the sample with a Ag/Mg alloy matrix, an effective resistivity much lower than expected was determined. We explain these discrepancies by taking into account the properties of the electrical contact of the interface between the superconducting filaments and the normal matrix. In the case of soft matrix of pure Ag, this is of poor quality, while the properties of alloy matrix seem to provoke an extensive creation of intergrowths which can be actually observed in this kind of samples.Comment: 20 pages 11 figure, submitted to Superconductor Science and Technolog

An Optical Study of BG Geminorum: An Ellipsoidal Binary with an Unseen Primar Star

We describe optical photometric and spectroscopic observations of the bright variable BG Geminorum. Optical photometry shows a pronounced ellipsoidal variation of the K0 I secondary, with amplitudes of ~0.5 mag at VRI and a period of 91.645 days. A deep primary eclipse is visible for wavelengths < 4400A; a shallower secondary eclipse is present at longer wavelengths. Eclipse timings and the radial velocity curve of the K0 secondary star indicate an interacting binary where a lobe-filling secondary, M_2 ~ 0.5 Msun, transfers material into a extended disk around a massive primary, M_1 ~ 4.5 Msun. The primary star is either an early B-type star or a black hole. If it did contain a black hole, BG Gem would be the longest period black hole binary known by a factor of 10, as well as the only eclipsing black hole binary system.Comment: 27 pages, includes 8 figures and 5 tables, accepted to A