Many recent observations have shown that resonances have a wide variety of effects in planetary rings: spiral waves, gaps, confinement, sharp edges, arcs. While resonances are known to be associated with such structures, the role of inter-particle collisions is still poorly understood, although necessary to explain the long term evolution of the rings.
In an effort to better understand the associated dynamics, we have performed numerical simulations of colliding particles orbiting a massive central planet. The code simulates the 3-D motion of 100 identical spherical particles orbiting a massive cental body and suffering inelastic collisions while being perturbed by one or more satellites.
We used this code to explore in more details the dynamics of are rings, and to explain in particular the reeent observations of are structures around Neptune. Clusters of particles at a satellite’s Lagrangian point {L4 or L5) are shown to be dispersed by dissipative effects. However, a second satellite can stabilize the system by providing sufficient energy through a Lindblaďs
resonance m±l:m. Other dynamically equivalent configurations (e.g. only one satellite, but with an eccentric orbit) can also stabilize are sytems, in accord with current analytical models.
We examine the roles of collisions at Lindblad and corotation resonances in various cases. Arcs remain at the potential maxima created by the corotations. However, stability requires that the satellites’ masses be within a limited range: small satellites cannot provide enough energy while large ones give too much, so the arc can disperse.
We report on detailed studies of the absorption line spectrum and spectroscopic orbit of the binary BN2.5Ib star HD 235679. We also give ao preliminary report on our study of the Hα emission line profiles from this perplexing system. Hipparcos and Tycho2 astrometric data allow us to place limits on the distance to the system. The lack of a measurable reflection effect in the Hipparcos photometry allows us to rule out the possibility that the massive invisible star is cool and fills its Roche lobe. Thus, by process of elimination, the invisible star must be hot or a black hole. The properties of the Hα profiles suggest that the invisible star is somewhat hotter, and has a stronger wind than HD235679.
This article discusses the issues raised by James M. Robertson in his review of Joseph Grim Feinberg’s The Paradox of Authenticity: Folklore Performance in Post-Communist Slovakia, which appeared in Contradictions (2019, no. 2). Focusing on the nature and form of a re-politicized folklore, the article argues that to make full sense of the question of authenticity in a modern folkloric movement, authenticity must be seen against the broader backdrop of the alienation inherent to consumer capitalist society. Folklore, it concludes, can become re-politicized by emphasizing people’s participation in art as part of a broader countercultural movement that challenges the consumerist paradigm.
Th e article reads the Czech literary canon during the period from 1948 to 1989 not from a consciously feminist standpoint, but from a gender perspective. Following works of Michel Foucault, Judith Butler, and Wendy Brown, the article’s primary focus is on fi ction written by dissent and alternative writers, with an emphasis on their role in what the author calls “dispositives of silence,” consisting of the discursive emergence of silencing and the aff ective dimension of “injurious attachments.” Th e article holds that while the dissident and alternative literary scene’s opposition to the then-offi cial regime made the need for political opposition clearly visible to it, other issues, such as the drive towards gender equality, became invisible to it, which represents a case of injurious attachments. In the article’s interpretative part, it reads literary works by writers Iva Pekárková, Tereza Boučková, and Pavel Kohout as examples that illustrate the issue of injurious attachments. In the article’s fi nal part, it supplements its thesis on dissident and alternative literature of the 1948–1989 period with a brief sketch of the literary evolution during the period, and it presents an overview of fi ve major – and partly contradictory – tendencies that can be identifi ed in the four decades in question.
The scholarly attention paid to Anna Katharina SweertsSporck has so far focused on the phase of her youth when she was engaged in translating books chosen by her father count Franz Anton Sporck for publishing. The article explores her interest in the book culture in the later stage of her life after her forced entrance into marriage in 1712. Anna Katharina initiated a large program of publishing and spreading devotional literature. The project was realized in cooperation with the Servite friar Wilhelm M. Löhrer and it aimed to cultivate internal, affective piety as a newly appraised type of religiosity which was increasingly popular across the confessional boundaries in the eighteenth century., Veronika Čapská., and Obsahuje bibliografické odkazy
We have computed the following physical parameters for the atmosphere of Titan, usinge Voyager´s measurements:
1) Temperature, 2) Pressure, 3) Density, 4 Speed of sound, 5) Density scale, 6) Number density, 7) Mean free path, 8) Viscosity, 9) Pressure scale, 10) Mean particle velocity, 11) Mean collisional frequency, 12) Columnar mass.
The present-day mass function (PDMF) of field stars in the solar neighborhood is discussed. Major uncertainties in the derivation exist, in partlcular the luminosity-mass relation and the bolometric corrections. Consequently, It is not clear whether the PDMF turns over at very low masses (M < 0.3 Mq), and the slope at the
high-mass end (M > 10 Mq) is more uncertain than usually assumed. The reality of two features in the PDMF (at M = 1.2 Mq and M = 3 Mq respectively) is an open question. Next, the concept of a bimodal IMF is critically examined. Both Gůsten and Mezger's (1983) and Larson's (1986) bimodal models may run into problems. If the effects of high-mass stars prevent low-mass stars from forming, the term "biassed IMF" is a better
description of the situation than "bimodal IMF". The IMF is probably not universal; reported IMF variations in open clusters and globular clusters are unlikely to be spurious. Finally the physics of the IMF is discussed. The. fact that the mass of a star in the making depends on many random-valued (multlplicative) input parameters
suggests a stochastic rather than a deterministic approach for the origin of the IMF.