11,077 research outputs found
No slices on the space of generalized connections
On a fiber bundle without structure group the action of the gauge group (the
group of all fiber respecting diffeomorphisms) on the space of (generalized)
connections is shown not to admit slices.Comment: AmSTeX, diag.tex, 7 page
Transport functions of nitrogen up to 26,000 K
The current field strength characteristic, E(1), and a large number of radial temperature distributions, T(r,I), measured in a 5 mm N2 cascade arc at normal pressure are used to evaluate the transport properties of nitrogen up to 26,000 K. The electrical conductivity sigma (T) and the Coulomb cross section are determined directly from the E(I) and several T(r,I) curves. Between 10,000 and 15,000 K the radiative energy flux for different arc current, the thermal conductivity, and from this the charge exchange cross section are determined in a good approximation utilizing the large number of measured temperature distributions. It turns out, that at the highest measured arc current, i.e., 570 A, in the axial region of the arc about 95% of the supplied energy is carried off by radiation
Nitrous oxide in coastal waters
We determined atmospheric and dissolved nitrous oxide (N2O) in the surface waters of the central North Sea, the German Bight, and the Gironde estuary. The mean saturations were 104 ± 1% (central North Sea, September 1991), 101 ± 2% (German Bight, September 1991), 99 ± 1% (German Bight September 1992), and 132% (Gironde estuary, November 1991). To evaluate the contribution of coastal areas and estuaries to the oceanic emissions we assembled a compilation of literature data. We conclude that the mean saturations in coastal regions (with the exception of estuaries and regions with upwelling phenomena) are only slightly higher than in the open ocean. However, when estuarine and coastal upwelling regions are included, a computation of the global oceanic N2O flux indicates that a considerable portion (approximately 60%) of this flux is from coastal regions, mainly due to high emissions from estuaries. We estimate, using two different parameterizations of the air-sea exchange process, an annual global sea-to-air flux of 11–17 Tg N2O. Our results suggest a serious underestimation of the flux from coastal regions in widely used previous estimates
Diemethlsulfide (DMS) and Dimethylsulfoniopropionate (DMSP) in the Mauritanian Upwelling (NW Africa)
On the Imaginary Simple Roots of the Borcherds Algebra
In a recent paper (hep-th/9703084) it was conjectured that the imaginary
simple roots of the Borcherds algebra at level 1 are its only
ones. We here propose an independent test of this conjecture, establishing its
validity for all roots of norm . However, the conjecture fails for
roots of norm -10 and beyond, as we show by computing the simple multiplicities
down to norm -24, which turn out to be remakably small in comparison with the
corresponding multiplicities. Our derivation is based on a modified
denominator formula combining the denominator formulas for and
, and provides an efficient method for determining the imaginary
simple roots. In addition, we compute the multiplicities of all roots
up to height 231, including levels up to and norms -42.Comment: 14 pages, LaTeX2e, packages amsmath, amsfonts, amssymb, amsthm,
xspace, pstricks, longtable; substantially extended, appendix with new
root multiplicities adde
ECG baseline wander reduction using linear phase filters
The continuous real time reduction of baseline wander is a considerable problem in electrocardiography during exercises. Our solution consists of spectral filtering. The legitimacy of high-pass filtering of the ECG by means of digital linear phase filters with a low cut-off frequency as high as the heart rate is shown. The specifications of these filters are derived from experimental results. Special hardware is presented that simultaneously performs the desired real-time filter operation in four ECG leads
Cherenkov Telescope Array: The next-generation ground-based gamma-ray observatory
High energy gamma-ray astronomy is a newly emerging and very successful
branch of astronomy and astrophysics. Exciting results have been obtained by
the current generation Cherenkov telescope systems such as H.E.S.S., MAGIC,
VERITAS and CANGAROO. The H.E.S.S. survey of the galactic plane has revealed a
large number of sources and addresses issues such as the question about the
origin of cosmic rays. The detection of very high energy emission from
extragalactic sources at large distances has provided insights in the star
formation during the history of the universe and in the understanding of active
galactic nuclei. The development of the very large Cherenkov telescope array
system (CTA) with a sensitivity about an order of magnitude better than current
instruments and significantly improved sensitivity is under intense discussion.
This observatory will reveal an order of magnitude more sources and due to its
higher sensitivity and angular resolution it will be able to detect new classes
of objects and phenomena that have not been visible until now. A combination of
different telescope types will provide the sensitivity needed in different
energy ranges.Comment: 4 pages, 3 figures, to appear in the proceedings of the 30th
International Cosmic Ray Conference, Merida, July 200
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