X-ray measurements of growth rates at a gas interface accelerated by shock waves

A new experimental technique to measure the density of a high atomic number gas at a shock-accelerated interface has been developed and demonstrated. It is based on the absorption of x rays by the high atomic number gas, and it was implemented in a vertical square shock tube. The object of the study was the turbulent entrainment and mixing of shock-accelerated air/xenon interfaces prepared by retracting a metal plate, initially separating the two gases, prior to the release of the shock wave. Interfaces of two types, quasi-sinusoidal and nominally flat, were examined. The amplitude of large wavelength (25–100 mm) perturbations on the interface, and the thickness of the interface were measured. An integral definition for the interface mean line was adopted, making it possible to study and time evolution of the individual Fourier modes of the perturbations. A new integral definition for the interface thickness was proposed, making it feasible to study for the first time the time evolution of the thickness of quasi-sinusoidal interfaces. Images of interfaces after interacting with a series of weak waves reverberating between the interface and the shock tube end wall were obtained. The perturbations are studied at the late stages of their evolution, when their amplitude is no longer small compared to their wavelength. Consequently, the measured growth rates of the modal amplitudes are smaller than those predicted by the impulsive model based on the small amplitude approximation. In the case of nominally flat interfaces, the thickness is observed to grow linearly at rates comparable to values previously reported

Locating L2 English writing centers in German universities

As L2 English writing support services, including writing centers, expand into different linguistic and national contexts, it becomes imperative for literacy brokers (Lillis and Curry 2006) and literacy managers (Bräuer 2012) to reflect on the uses and limitations of existing writing support models and teaching approaches. This paper presents the findings from a project that tracked the growth of L2 English writing centers in German universities from 2013-2015, locating their emergence within changes in the German academic landscape. Using data taken from questionnaires and interviews, this paper locates and explores ten L2 English writing centers in Germany, focusing on their aims; organizational models and teaching approaches; staffing and funding; key university partnerships; offers; and reflections on the future. It is hoped that these collated experiences could be of interest to other L2 English centers developing in different countries and language contexts

Coaxial cable connector

A coaxial cable connector is provided, which resists radio frequency breakdown in coaxial cables used in the vacuum of outer space. The connector body surrounds an insulator which includes an easily compressible elastomeric portion. An insulated coaxial cable is prepared so that its insulation projects beyond the outer conductor and compresses the elastomeric portion of the connector insulator

Locating L2 English Writing Centers in German Universities

 As L2 English writing support services, including writing centers, expand into different linguistic and national contexts, it becomes imperative for literacy brokers (Lillis and Curry 2006) and literacy managers (Bräuer 2012) to reflect on the uses and limitations of existing writing support models and teaching approaches. This paper presents the findings from a project that tracked the growth of L2 English writing centers in German universities from 2013-2015, locating their emergence within changes in the German academic landscape. Using data taken from questionnaires and interviews, this paper locates and explores ten L2 English writing centers in Germany, focusing on their aims; organizational models and teaching approaches; staffing and funding; key university partnerships; offers; and reflections on the future. It is hoped that these collated experiences could be of interest to other L2 English centers developing in different countries and language contexts

Slavery in the Mediterranean

This chapter focuses on slavery in the Mediterranean region from the sixteenth to the nineteenth century, and especially in the Northern Mediterranean basin, including the Italian states, France, Spain, and Portugal. Comparing the situation in Southern European states to that in the Ottoman Empire and its satellite states enables an analysis of the forms of reciprocity and the commonalities inherent in slave trade practices around the Mediterranean. The Mediterranean was at the center of larger slave trading networks whose slaves originated from all over the world. More specifically, this chapter examines various forms of enslavement and types of work performed by slaves, along with the different levels of coercion involved in them. In its conclusion, the chapter details some of the exit strategies that enabled slaves to become free—both in socio-economic terms and from a legal perspective

Locating L2 English Writing Centers in German Universities

 As L2 English writing support services, including writing centers, expand into different linguistic and national contexts, it becomes imperative for literacy brokers (Lillis and Curry 2006) and literacy managers (Bräuer 2012) to reflect on the uses and limitations of existing writing support models and teaching approaches. This paper presents the findings from a project that tracked the growth of L2 English writing centers in German universities from 2013-2015, locating their emergence within changes in the German academic landscape. Using data taken from questionnaires and interviews, this paper locates and explores ten L2 English writing centers in Germany, focusing on their aims; organizational models and teaching approaches; staffing and funding; key university partnerships; offers; and reflections on the future. It is hoped that these collated experiences could be of interest to other L2 English centers developing in different countries and language contexts

ENSLAVED LABOUR AND IM/MOBILITY IN THE MEDITERRANEAN: THE ITALIAN CASE (1752-1885)

The objective of this article is to illustrate the tension between mobility and immobility that existed in the slave labour market in the Mediterranean during the 18th and 19th centuries, focusing mainly on the Italian case, but it also considers the issue in a wider European sense. The skin colour, age, physical appearance, and ethnic origin (as described by the sources) of captives, enslaved people and formerly enslaved people affected their mobility before and after the legal abolition of slavery between 1752 and 1885. I will analyse the correlation between the legal end of slavery and the im/mobility of enslaved and ex-enslaved based on the characteristics and qualities assigned to them. The juridical abolitions of slavery in the 19th century did not change this correlation in geographical spaces characterised by accelerating mobility of persons of colour with different juridical statuses. My case studies are based in Florence, Venice, Livorno, Rome and Civitavecchia

Collective and Individual Experiences of Slaves in Leghorn, Pisa and Florence, 1702-1826

This article presents a group portrait of captives and slaves and a picture of some individual slaves’ lives in the Bagno of Leghorn and Pisa and in the House of Catechumens of Florence in the Grand Duchy of Tuscany during the period 1702-1826. This research is based on Leghorn government papers, the archive of Florence’s Ginori family and the records of the Magistrato del Bigallo. The study follows two lines of inquiry corresponding to two different scales of analysis. The first draws a group portrait from a list of slaves living at the Bagno of Leghorn and released in 1747. This portrait reveals a uniform and collective life and provides quantitative information on the latter, particularly concerning the question of the time of their captivity or their enslavement. The second line of investigation explores the experiences and individual trajectories of several slaves between Livorno, Pisa and Florence and raises questions about conclusive interpretations concerning the level of homogeneity in their living and working conditions. The presence of slaves and captives in galleys or prisons has been the subject of much research based on the many documents produced in these places, including lists of slaves that allow scholars to build a group portrait. The realization of this type of portrait requires, however, consideration of individual trajectories and differences. This is made possible by sources such as the supplications of slaves living in these places of detention as well as those resident in the House of Catechumens of Florence. The petitions of slaves, in both Pisa and Livorno, reveal the diversity of living conditions in the same place of detention. While historiography has emphasized a standardization of conditions in different environments—such as galleys and prisons—the study sheds light on how differences in physical qualities (health, physical strength, skin colour), geographical origin, professional skills or religion of captives and slaves had an impact on access to freedom, their agency, and their treatment by their owners. In addition, the sources of the Magistrato del Bigallo allow for a very subtle approach, making it possible to show for example the different experiences of a brother and a sister, both slaves and from Sub-Saharan Africa, in the House of Catechumens of Florence. These sources, less explored, bring to light formerly invisible stories of enslaved people from the Mediterranean and outside with singular trajectories that complicate existing interpretations. The two approaches, that of the group portrait and that concentrating on the individual experiences of the captives and slaves, are fundamental to developing a comprehensive understanding of the phenomenon of slavery in Tuscany

Shock accelerated vortex ring

The interaction of a shock wave with a spherical density inhomogeneity leads to the development of a vortex ring through the impulsive deposition of baroclinic vorticity. The present fluid dynamics videos display this phenomenon and were experimentally investigated at the Wisconsin Shock Tube Laboratory's (WiSTL) 9.2 m, downward firing shock tube. The tube has a square internal cross-section (0.25 m x 0.25 m) with multiple fused silica windows for optical access. The spherical soap bubble is generated by means of a pneumatically retracted injector and released into free-fall 200 ms prior to initial shock acceleration. The downward moving, M = 2.07 shock wave impulsively accelerates the bubble and reflects off the tube end wall. The reflected shock wave re-accelerates the bubble (reshock), which has now developed into a vortex ring, depositing additional vorticity. In the absence of any flow disturbances, the flow behind the reflected shock wave is stationary. As a result, any observed motion of the vortex ring is due to circulation. The shocked vortex ring is imaged at 12,500 fps with planar Mie scattering.Comment: For Gallery of Fluid Motion 200