Reverse undercompressive shock structures in driven thin film flow

We show experimental evidence of a new structure involving an undercompressive and reverse undercompressive shock for draining films driven by a surface tension gradient against gravity. The reverse undercompressive shock is unstable to transverse perturbations while the leading undercompressive shock is stable. Depending on the pinch-off film thickness, as controlled by the meniscus, either a trailing rarefaction wave or a compressive shock separates from the reverse undercompressive shock

Vicious Geography: The Spatial Organization of Prostitution in Twentieth Century Philadelphia

This study analyzes the geography of prostitution in twentieth-century Philadelphia. Specifically, it addresses how the spatial organization of the sex trade has changed over this time period and considers possible explanations for this change. The author evaluates the influence of market economics, police repression and moral stigmatization on prostitution’s geography in Philadelphia. The author relies on records of prostitution-related arrests, vice complaints, law enforcement testimony, press coverage, and governmental reports to determine the location of vice since the early 1900s. The author concludes that Philadelphia’s case study complicates the narrative of spatial change put forth by the existing scholarship, which argues that prostitution has dispersed over the twentieth century. Rather, Philadelphia\u27 sex trade has consistently intensified in clusters or along packed corridors, while the location of these hubs has oscillated between the City’s downtown core and its peripheries. This geography has resulted from a dialectical process involving prostitutes’ own agency and the imposition of police repression

What happens to students with an immigrant background in the transition to higher education? Evidence from Italy

As shown by the international literature on educational attainment, in most European countries participation rates of students with a migrant background are usually lower compared to natives, particularly in tertiary education. In Italy, the focus of the debate is mainly on secondary school, while little or no attention has been paid to immigrant students attending universities. This paper tries to fill the gap by providing new and extensive empirical evidence on this phenomenon and by discussing some of the main issues related to it. The results show that, first, ethnic background matters. East European and Russian students are more likely to continue their studies, as found in other European countries. Second and contrary to what is expected on the basis of the existing Italian literature, the specific secondary school track is not important for the transition choice. However, while this is true for immigrant students, it does not hold for the native population. For Italian secondary school graduates, the attainment of a liceo diploma increases the probability of enrolling in tertiary education. Third, local labour markets affect the incentive to invest in human capital. High youth unemployment rates have a negative impact on educational attainment for both immigrant and native students. Lastly, the average education level of the local immigrant population has a positive influence on transition choice

"Marginal pinching" in soap films

We discuss the behaviour of a thin soap film facing a frame element: the pressure in the Plateau border around the frame is lower than the film pressure, and the film thins out over a certain distance lambda(t), due to the formation of a well-localized pinched region of thickness h(t) and extension w(t). We construct a hydrodynamic theory for this thinning process, assuming a constant surface tension: Marangoni effects are probably important only at late stages, where instabilitites set in. We find lambda(t) ~ t^{1/4}, and for the pinch dimensions h(t) ~ t^{-1/2}$ and w(t) ~ t^{-1/4}. These results may play a useful role for the discussion of later instabilitites leading to a global film thinning and drainage, as first discussed by K. Mysels under the name ``marginal regeneration''.Comment: 7 pages, 2 figure

Functional Self-Assembling Bolaamphiphilic Polydiacetylenes as Colorimetric Sensor Scaffolds

Conjugated polymers capable of responding to external stimuli by changes in optical, electrical, or electrochemical properties can be used for the construction of direct sensing devices. Polydiacetylene-based systems are attractive for sensing applications due to their colorimetric response to changes in the local environment. Here we present the design, preparation, and characterization of self-assembling functional bolaamphiphilic polydiacetylenes (BPDAs) inspired by nature\u27s strategy for membrane stabilization. We show that by placing polar headgroups on both ends of the diacetylene lipids in a transmembranic fashion and by altering the chemical nature of the polar surface residues, the conjugated polymers can be engineered to display a range of radiation-, thermal-, and pH-induced colorimetric responses. We observed dramatic nanoscopic morphological transformations accompanying charge-induced chromatic transitions, suggesting that both side-chain disordering and main-chain rearrangement play important roles in altering the effective conjugation lengths of the poly(ene-yne). These results establish the foundation for further development of BPDA-based colorimetric sensors

Experiments on crack propagation and threshold at defects in press-fits of railway axles

Fatigue strength under fretting fatigue is one of the open problems in the area of fatigue. In the case of railway wheel-axle press-fits, there are no records of recent failures because design rules are today based on making the shape of geometrical transitions the most stressed point. However, it is important to analyze correctly the acceptability of defects and micro-cracks at press-fits. In this paper, after a preliminary presentation of the results obtained by a new criterion for predicting the non-propagation of cracks under rolling contact fatigue conditions, a new series of experiments on full-scale axle press-fits containing artificial defects is presented and discussed. Results show the modified Dang Van criterion is adequate for describing the development of natural cracks and cracks from artificial defects. The latter, characterized by a depth of 250 350 m, are competitors of fretting cracks naturally developed from surface scars and surface damage