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To understand the evolution and morphology of planetary nebulae, a detailed knowledge of their central stars is required. Central stars that exhibit emission lines in their spectra, indicating stellar mass-loss allow to study the evolution of planetary nebulae in action. Emission line central stars constitute about 10 % of all central stars. Half of them are practically hydrogen-free Wolf-Rayet type central stars of the carbon sequence, [WC], that show strong emission lines of carbon and oxygen in their spectra. In this contribution we address the weak emission-lines central stars (wels). These stars are poorly analyzed and their hydrogen content is mostly unknown. We obtained optical spectra, that include the important Balmer lines of hydrogen, for four weak emission line central stars. We present the results of our analysis, provide spectral classification and discuss possible explanations for their formation and evolution.
The main thread of this review article is to identify the reasons of how to account for the trajectory of American power in the region. Leaving behind the vast amount of highly politicised and hastily compiled volumes of recent years (notwithstanding valuable exceptions), the monographs composed by Lawrence Freedman, Trita Parsi and Oliver Roy attempt to subtly disentangle the intricacies of US involvement in the region from highly distinct perspectives. One caveat for International Relations theorists is that none of the
aforementioned authors intends to provide theoretical frameworks for his examination. However, since IR theory has damagingly neglected history in the last decades, the works under review here, at least in part, compensate for this disciplinary and intellectual failure. In conclusion, Freedman’s in-depth approach as a diplomatic historian, with its under-lying reference to the various traditions in US foreign policy thinking, is most illuminating, while Parsi’s contestable account focuses too narrowly on the Iran-Israel relationship. Roy’s explications fail to show how and why the ‘ideological’ element in US foreign policy came to carry exceedingly more weight after 2001 than it did in the 1990s.
We study pattern-forming instabilities in reaction-advection-diffusion systems. We develop an approach based on Lyapunov-Bloch exponents to figure out the impact of a spatially periodic mixing flow on the stability of a spatially homogeneous state. We deal with the flows periodic in space that may have arbitrary time dependence. We propose a discrete in time model, where reaction, advection, and diffusion act as successive operators, and show that a mixing advection can lead to a pattern-forming instability in a two-component system where only one of the species is advected. Physically, this can be explained as crossing a threshold of Turing instability due to effective increase of one of the diffusion constants.
Saccades move objects of interest into the center of the visual field for high-acuity visual analysis. White, Stritzke, and Gegenfurtner (Current Biology, 18, 124–128, 2008) have shown that saccadic latencies in the context of a structured background are much shorter than those with an unstructured background at equal levels of visibility. This effect has been explained by possible preactivation of the saccadic circuitry whenever a structured background acts as a mask for potential saccade targets. Here, we show that background textures modulate rates of microsaccades during visual fixation. First, after a display change, structured backgrounds induce a stronger decrease of microsaccade rates than do uniform backgrounds. Second, we demonstrate that the occurrence of a microsaccade in a critical time window can delay a subsequent saccadic response. Taken together, our findings suggest that microsaccades contribute to the saccadic facilitation effect, due to a modulation of microsaccade rates by properties of the background.
We asked whether invariant phonetic indices for syllable structure can be identified in a language where word-initial consonant clusters, regardless of their sonority profile, are claimed to be parsed heterosyllabically. Four speakers of Moroccan Arabic were recorded, using Electromagnetic Articulography. Pursuing previous work, we employed temporal diagnostics for syllable structure, consisting of static correspondences between any given phonological organisation and its presumed phonetic indices. We show that such correspondences offer only a partial understanding of the relation between syllabic organisation and continuous indices of that organisation. We analyse the failure of the diagnostics and put forth a new approach in which different phonological organisations prescribe different ways in which phonetic indices change as phonetic parameters are scaled. The main finding is that invariance is found in these patterns of change, rather than in static correspondences between phonological constructs and fixed values for their phonetic indices.
The space missions Voyager and Cassini together with earthbound observations re-vealed a wealth of structures in Saturn’s rings. There are, for example, waves being excited at ring positions which are in orbital resonance with Saturn’s moons. Other structures can be assigned to embedded moons like empty gaps, moon induced wakes or S-shaped propeller features. Further-more, irregular radial structures are observed in the range from 10 meters until kilometers. Here some of these structures will be discussed in the frame of hydrodynamical modeling of Saturn’s dense rings. For this purpose we will characterize the physical properties of the ring particle ensemble by mean field quantities and point to the special behavior of the transport coefficients. We show that unperturbed rings can become unstable and how diffusion acts in the rings. Additionally, the alternative streamline formalism is introduced to describe perturbed regions of dense rings with applications to the wake damping and the dispersion relation of the density waves.
X-ray observations of young Planetary Nebulæ (PNe) have revealed diffuse emission in extended regions around both H-rich and H-deficient central stars. In order to also repro-duce physical properties of H-deficient objects, we have, at first, extended our time-dependent radiation-hydrodynamic models with heat conduction for such conditions. Here we present some of the important physical concepts, which determine how and when a hot wind-blown bubble forms. In this study we have had to consider the, largely unknown, evolution of the CSPN, the slow (AGB) wind, the fast hot-CSPN wind, and the chemical composition. The main conclusion of our work is that heat conduction is needed to explain X-ray properties of wind-blown bubbles also in H-deficient objects.
Neues deutsches Gedenken?
(2011)
Bedarf es eines neuen Gedenktages der Vertriebenen in Deutschland? Die deutsche Regierung meint Ja. Auf ihre Initiative hin wurde die Entschließung "60 Jahre Charta der deutschen Heimatvertriebenen – Aussöhnung vollenden" im Februar 2011 angenommen. Dieser Gedenktag soll der 5. August sein, also jener Tag, an dem 1950 die "Charta der deutschen Heimatvertriebenen" in Stuttgart angenommen wurde. Der Entschluss traf im Bundestag auf den Widerstand der Opposition – aber auch auf scharfe Kritik in Polen.
The selection of ‘good’ pictures has increasingly become a crucial factor when transmitting news to the recipients. Every day thousands of events are happening and millions of pictures are taken. By choosing photographs for newspapers and magazines, photographic editorial departments want to attract the recipients’ attention, evoke emotions and get them to read their stories. But what exactly is a good picture that meets these expectations? Which criteria are decisive for selecting pictures and what effects of this selection can be measured on the recipients’ side? This article presents the results of a research project carried out at the University of Erfurt in 2008 and conducted in collaboration with the German weekly magazine stern. It deals with the selection and impact of press photography by introducing the concept ‘photo news factors’. Applying the traditional news value theory to pictures, photo news factors are defined as selection criteria that, on the part of the communicator, decide whether the press photos are worth publishing. Furthermore, they are assumed to exert an influence on the intensity of attention that a picture arouses.
Following up on research suggesting an age-related reduction in the rightward extent of the perceptual span during reading (Rayner, Castelhano, & Yang, 2009), we compared old and young adults in an N+2-boundary paradigm in which a nonword preview of word N+2 or word N+2 itself is replaced by the target word once the eyes cross an invisible boundary located after word N. The intermediate word N+1 was always three letters long. Gaze durations on word N+2 were significantly shorter for identical than nonword N+2 preview both for young and for old adults with no significant difference in this preview benefit. Young adults, however, did modulate their gaze duration on word N more strongly than old adults in response to the difficulty of the parafoveal word N+1. Taken together, the results suggest a dissociation of preview benefit and parafoveal-on-foveal effect. Results are discussed in terms of age-related decline in resilience towards distributed processing while simultaneously preserving the ability to integrate parafoveal information into foveal processing. As such, the present results relate to proposals of regulatory compensation strategies older adults use to secure an overall reading speed very similar to that of young adults.