25,904 research outputs found
Incompatibility of different customary kaon phase convention
The conventions that Wu and Yang assumed for the kaon phases in the context
of symmetrical two-pion decay channels fix the relative kaon phase. This
fact, apparently not emphasized sufficiently in the past, has recently been
overlooked by Hayakawa and Sanda. In particular, Wu and Yang fix the relative
phase to a different value than the one resulting from the convention
. The difference between the two
values is made up of possible contributions from - and direct
-violations during the decay of a kaon into a two-pion state of isospin
zero.Comment: 5 pages, LaTe
Raman spectroscopy with ultrashort coherent excitation. Narrowing of spectral lines beyond the dephasing linewidth
Spectroscopists are constantly faced with the task of improved spectral resolution. Two points are of major interest: (i) The precise frequency of the quantized transition and (ii) the detection of new neighboring transitions. Besides experimental factors the ultimate spectral resolution is determined by the inherent linewidth of the transition. Optical spectroscopists have to deal with different line-broadening processes; for instance with the Doppler effect or with collision broadening in gases, with dephasing processes in condensed systems and with the population relaxation which results in the natural linewidth. In recent years, different novel techniques have been devised which provide spectral resolution beyond the transition linewidth. For instance, Doppler broadening can be eliminated by saturation spectroscopy or by two counter-propagating beams for two-photon transitions/I/. Even measurements beyond the natural linewidth have been performed taking biased signals from the fluorescent decay /2-5/. Techniques have been proposed where the difference between the decay rates of the two states rather than their sum determines the linewidth /6,7/, and narrowing of the natural linewidth by decaying-pulse excitation has been discussed /8/. Very recently, we have demonstrated substantial line narrowing of Raman type transitions in condensed phases /9-11/. The lines were broadened by vibrational dephasing. New information was obtained in congestedspectral regions
The Minispiral in the Galactic Center revisited
We present the results of a re-examination of a [Ne II] line emission data
cube (\lambda 12.8 \mu m) and discuss the kinematic structure of the inner \sim
3 \times 4 pc of the Galaxy. The quality of [Ne II] as a tracer of ionized gas
is examined by comparing it to radio data. A three dimensional representation
of the data cube allows us to disentangle features which are projected onto the
same location on the sky. A model of gas streams in different planes is fitted
to the data. We find that most of the material is located in a main plane which
itself is defined by the inner edge of the Circum-Nuclear Disk in the Galactic
Center. Finally, we present a possible three dimensional model of the gas
streams.Comment: 12 pages, 18 figures; submitted to New Astronomy; higher resolution
version and two animations available via anonymous ftp
ftp://ftp.ita.uni-heidelberg.de/pub/ITA/wjd/Minispira
Redundancy of minimal weight expansions in Pisot bases
Motivated by multiplication algorithms based on redundant number
representations, we study representations of an integer as a sum , where the digits are taken from a finite alphabet
and is a linear recurrent sequence of Pisot type with
. The most prominent example of a base sequence is the
sequence of Fibonacci numbers. We prove that the representations of minimal
weight are recognised by a finite automaton and obtain an
asymptotic formula for the average number of representations of minimal weight.
Furthermore, we relate the maximal order of magnitude of the number of
representations of a given integer to the joint spectral radius of a certain
set of matrices
Using abundance data to assess the relative role of sampling biases and evolutionary radiations in Upper Muschelkalk ammonoids
The Middle Triassic ammonoid genus Ceratites diversified spectacularly within the Germanic Muschelkalk Basin during the Anisian/Ladian (244–232 Mya). Previous studies have interpreted this diversification as a sequence of rapid, endemic radiations from a few immigrant taxa. Here we investigate the possibility that geological and sampling biases, rather than ecological and evolutionary processes, are responsible for this pattern. A new specimen based dataset of Ceratites species-richness and abundance was assembled. This dataset was combined with 1:200000 geological maps in a geodatabase to facilitate geospatial analyses. One set of analyses compared species richness per geological map with the number of occurrences and localities per map. Per-map change in the amount of rock available to sample for fossils was also included as a variable. Of these three variables, number of occurrences is the most strongly correlated with richness. Variation in the amount of rock is not a strong determinant of species-richness. However, rarefaction of basin-wide species/abundance data demonstrates that differences in species-richness through time are not attributable to sample size differences. The average percent similarity among sites remained close to 50% throughout the Upper Muschelkalk. The rank abundance distribution (RAD) of species from the first interval of the Upper Muschelkalk is consistent with colonization of a disturbed environment, while the other two intervals have RADs consistent with more stable ecosystems. These results indicate that genuine ecological and evolutionary events are partly responsible for the observed differences in richness and abundance. Although changes in the RADs through time support changes in the ammonoid assemblage structure, the processes underlying increasing richness and change in RADS cannot be explained by increasing geographic distinctiveness or isolation among the ammonoid assemblages present at different localities
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