Observed variability in the Fraunhofer line spectrum of solar flux, 1975 - 1980

Over the five years double-pass spectrometer observations of the Sun-as-a-star revealed significant changes in line intensities. The photospheric component weakened linearly with time 0 to 2.3%. From a lack of correlation between these line weakenings and solar activity indicators like sunspots and plage, a global variation of surface properties is inferred. Model-atmosphere analysis suggests a slight reduction in the lower-photospheric temperature gradient corresponding to a 15% increase in the mixing length within the granulation layer. Chromospheric lines such as Ca II H and K, Ca II 8543 and the CN band head weaken synchronously with solar activity. Thus, the behavior of photospheric and chromospheric lines is markedly different, with the possibility of secular change for the former

Teaching Ethics Without Confusing Questions: Illustrated by the Example of Schopenhauer's Ethics

Like many other philosophical disciplines, ethics is sometimes highly abstract. And many key notions of the discipline are vague, ambiguous or both. Abstractness, vagueness, and ambiguity invite confusion. My objective in this paper is to draw attention to a serious problem that, despite being widespread, has so far remained largely unrecognized: the confusion of different questions in teaching ethics. This confusion occurs, for example, when a philosopher’s viewpoint is presented as an answer to one question, but in fact, the philosopher is addressing a different question with that viewpoint. In the first part of this paper, I will present and clarify several ethical questions that are often confused, and point out damaging consequences that the confusion of such questions entails. In the second part, I will demonstrate the confusion of ethical questions by drawing attention to cases of confused teaching of Schopenhauer’s ethics. Finally, for those interested, I outline how Schopenhauer’s ethics could be taught without confusion

Novel Predictors for Friction and Wear in Drivetrain Applications

Reliability in a drivetrain is given by the life of its constituents, e.g., gears, clutches, and bearings. Lubrication contributes to the life cycle, preventing wear, friction, and environmental impacts. As lubricants and their additives are chemicals with an expected reactivity in a tribological contact, it comes to the question how surface fatigue phenomena due to loading may be influenced by the reactivity of functional additives and how this might be embedded in construction guidelines. A very basic study based on an elementary gear test rig presents the result that pitting life of a gear is substantially influenced by the chemical structure of wear-preventing additives. Even under appropriate loading conditions, the lubricant structure comes as a life-limiting factor. A molecular model shows how the release and the approach of the additives toward a surface is essential and related to the reaction processes that occur during the loading

Characterization of Sentinel Butte Petrified Wood and Host Lithology Associations

Large quantities of petrified wood occur in the Paleocene Sentinel Butte Formation in western North Dakota. An examination of this petrified wood has provided information about modes and degrees of fossilization, silica phases present, organic structure preservation, and parent tree type. In the study site, fossilized tree stumps were concentrated along one continuous clay horizon. Twenty petrified wood samples were obtained. Five representative samples were chosen for thin section characterization. Microscopic analyses revealed well preserved plant structures including rays, tracheids, and growth rings. These structures were suitable for identifying parent tree type, which was determined to be a gymnosperm. Silica phases involved in the petrification, include microcrystalline quartz (chert), fibrous chalcedony and megaquartz. Silica fills tracheids and also pervasively replaces organic material. Permineralization is the dominant mode of fossilization observed, with silica filling tracheids and other plant voids. Replacement of original plant material by silica is also seen. Larger fractures or veins are filled gradually with microcrystalline quartz, chalcedony, and megaquartz. Loss on ignition data supports the interpretation that observed plant structure retaining an organic composition. Variability observed in hand samples caused by differences in degree and types of fossilization. Laboratory analyses were conducted to determine if the continuous clay horizon containing the petrified stumps is a bentonite

Numerical simulation of the three-dimensional structure and dynamics of the non-magnetic solar chromosphere

Three-dimensional numerical simulations with CO5BOLD, a new radiation hydrodynamics code, result in a dynamic, thermally bifurcated model of the non-magnetic chromosphere of the quiet Sun. The 3-D model includes the middle and low chromosphere, the photosphere, and the top of the convection zone, where acoustic waves are excited by convective motions. While the waves propagate upwards, they steepen into shocks, dissipate, and deposit their mechanical energy as heat in the chromosphere. Our numerical simulations show for the first time a complex 3-D structure of the chromospheric layers, formed by the interaction of shock waves. Horizontal temperature cross-sections of the model chromosphere exhibit a network of hot filaments and enclosed cool regions. The horizontal pattern evolves on short time-scales of the order of typically 20 - 25 seconds, and has spatial scales comparable to those of the underlying granulation. The resulting thermal bifurcation, i.e., the co-existence of cold and hot regions, provides temperatures high enough to produce the observed chromospheric UV emission and -- at the same time -- temperatures cold enough to allow the formation of molecules (e.g., carbon monoxide). Our 3-D model corroborates the finding by Carlsson & Stein (1994) that the chromospheric temperature rise of semi-empirical models does not necessarily imply an increase in the average gas temperature but can be explained by the presence of substantial spatial and temporal temperature inhomogeneities.Comment: 18 pages, 13 figures, accepted by Astronomy & Astrophysics (30/10/03

Line formation in convective stellar atmospheres. I. Granulation corrections for solar photospheric abundances

In an effort to estimate the largely unknown effects of photospheric temperature fluctuations on spectroscopic abundance determinations, we have studied the problem of LTE line formation in the inhomogeneous solar photosphere based on detailed 2-dimensional radiation hydrodynamics simulations of the convective surface layers of the Sun. By means of a strictly differential 1D/2D comparison of the emergent equivalent widths, we have derived "granulation abundance corrections" for individual lines, which have to be applied to standard abundance determinations based on homogeneous 1D model atmospheres in order to correct for the influence of the photospheric temperature fluctuations. In general, we find a line strengthening in the presence of temperature inhomogeneities as a consequence of the non-linear temperature dependence of the line opacity. For many lines of practical relevance, the magnitude of the abundance correction may be estimated from interpolation in the tables and graphs provided with this paper. The application of abundance corrections may often be an acceptable alternative to a detailed fitting of individual line profiles based on hydrodynamical simulations. The present study should be helpful in providing upper bounds for possible errors of spectroscopic abundance analyses, and for identifying spectral lines which are least sensitive to the influence of photospheric temperature inhomogeneities.Comment: Accepted by A&