743 research outputs found
Hegel's Criticism of Newton's Physics: A Reconsideration"
The persisting conception of Hegel's criticism of Newton's physics as an irrational or at least hopelessly exaggerated one partly has its roots mainly in Hegel's terminology and in his style. This does not mean that a mere translation of Hegel's arguments into any contemporary philosophical language be sufficient to immediately convince every Newtonian scientist. However, a non-Hegelian way of rephrasing the core of Hegel's anti-Newtonian philosophy of nature can help to understand to which extent the latter does satisfy any scientist's criteria for a rational and self-consistent theory. To demonstrate this is the central aim of my talk, which is structured as follows: In the first part, I'm trying to highlight basic features of Hegel's criticism of Newton's optics and celestial mechanics, eventually focussing on his concept of a "sense of nature". This part has the character of a review. Second - and that is supposed to be the "reconsideration" part of my paper - I'll try to highlight the fundamental difference between Newton's and Hegel's ideas of natural laws and of the relation between mathematics and physics. Third, the metaphysical background of this difference will be analyzed. It is by the analysis of this metaphysical background that I hope to render Hegel's criticism of Newton's scientific revolution more understandable
Optical constants of refractory oxides at high temperatures
Many cosmic dust species, among them refractory oxides, form at temperatures
higher than 300 K. Nevertheless, most astrophysical studies are based on the
room-temperature optical constants of solids, such as corundum and spinel. A
more realistic approach is needed for these materials, especially in the
context of modeling late-type stars. We aimed at deriving sets of optical
constants of selected, astrophysically relevant oxide dust species with high
melting points. A high-temperature-high-pressure-cell and a Fourier-transform
spectrometer were used to measure reflectance spectra of polished samples. For
corundum (alpha-AlO), spinel (MgAlO), and alpha-quartz
(SiO), temperature-dependent optical constants were measured from 300 K up
to more than 900 K. Small particle spectra were also calculated from these
data. All three examined oxides show a significant temperature dependence of
their mid-IR bands. For the case of corundum, we find that the 13m
emission feature - seen in the IR spectra of many AGB stars - can very well be
assigned to this mineral species. The best fit of the feature is achieved with
oblate corundum grains at mean temperatures around 550 K. Spinel remains a
viable carrier of the 13m feature as well, but only for T < 300 K and
nearly spherical grain shapes. Under such circumstances, spinel grains may also
account for the 31.8m band that is frequently seen in sources of the
13m feature and which has not yet been identified with certainty.Comment: Astronomy & Astrophysics, accepted, 26 February 2013. Article with 18
pages and 15 figure
Reconsidering the origin of the 21 micron feature: Oxides in carbon-rich PPNe?
The origin of the so-called "21 micron" feature which is especially prominent
in the spectra of some carbon-rich protoplanetary nebulae (PPNe}) is the matter
of a lively debate. A large number of potential band carriers have been
presented and discarded within the past decade. The present paper gives an
overview of the problems related to the hitherto proposed feature
identifications, including the recently suggested candidate carrier silicon
carbide. We also discuss the case for spectroscopically promising oxides.
SiC is shown to produce a strong resonance band at 20-21 micron if coated by
a layer of silicon dioxide. At low temperatures, core-mantle particles composed
of SiC and amorphous SiO indeed have their strongest spectral signature at
a position of 20.1 micron, which coincides with the position of the "21 micron"
emission band.
The optical constants of another candidate carrier that has been relatively
neglected so far -- iron monoxide -- are proven to permit a fairly accurate
reproduction of the "21 micron" feature profile as well, especially when
low-temperature measurements of the infrared properties of FeO are taken into
account. As candidate carrier of the "21 micron" emission band, FeO has the
advantage of being stable against further oxidation and reduction only in a
narrow range of chemical and physical conditions, coinciding with the fact that
the feature, too, is detected in a small group of objects only. However, it is
unclear how FeO should form or survive particularly in carbon-rich PPNe.Comment: 28 pages, 15 figures, accepted for publication in ApJ (December
Adaptive Survival Trials
Mid-study design modifications are becoming increasingly accepted in
confirmatory clinical trials, so long as appropriate methods are applied such
that error rates are controlled. It is therefore unfortunate that the important
case of time-to-event endpoints is not easily handled by the standard theory.
We analyze current methods that allow design modifications to be based on the
full interim data, i.e., not only the observed event times but also secondary
endpoint and safety data from patients who are yet to have an event. We show
that the final test statistic may ignore a substantial subset of the observed
event times. Since it is the data corresponding to the earliest recruited
patients that is ignored, this neglect becomes egregious when there is specific
interest in learning about long-term survival. An alternative test
incorporating all event times is proposed, where a conservative assumption is
made in order to guarantee type I error control. We examine the properties of
our proposed approach using the example of a clinical trial comparing two
cancer therapies.Comment: 22 pages, 7 figure
Recent Results of Solid-State Spectroscopy
Solid state spectroscopy continues to be an important source of information
on the mineralogical composition and physical properties of dust grains both in
space and on planetary surfaces. With only a few exceptions, artificially
produced or natural terrestrial analog materials, rather than 'real' cosmic
dust grains, are the subject of solid state astrophysics. The Jena laboratory
has provided a large number of data sets characterizing the UV, optical and
infrared properties of such cosmic dust analogs. The present paper highlights
recent developments and results achieved in this context, focussing on
'non-standard conditions' such as very low temperatures, very high temperatures
and very long wavelengths.Comment: 15 pages, 10 figures. Contribution to an IAU Conference "The
Molecular Universe" held in Toledo in June 201
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