9,600 research outputs found
A Compact Codimension Two Braneworld with Precisely One Brane
Building on earlier work on football shaped extra dimensions, we construct a
compact codimension two braneworld with precisely one brane. The two extra
dimensions topologically represent a 2-torus which is stabilized by a bulk
cosmological constant and magnetic flux. The torus has positive constant
curvature almost everywhere, except for a single conical singularity at the
location of the brane. In contradistinction to the football shaped case, there
is no fine-tuning required for the brane tension. We also present some
plausibility arguments why the model should not suffer from serious stability
issues.Comment: 13 pages, 2 figures; references added, typos fixes; essentially the
version published in PR
Study of fluoride corrosion of nickel alloys
Report contains the results of an investigation of the corrosion resistance of nickel and nickel alloys exposed to fluorine, uranium hexafluoride, and volatile fission product fluorides at high temperatures. Survey of the unclassified literature on the subject is included
Derivatives Usage in Risk Management by US and German Non-Financial Firms: A Comparative Survey
This paper is a comparative study of the responses to the 1995 Wharton School survey of derivative usage among US non-financial firms and a 1997 companion survey on German non-financial firms. It is not a mere comparison of the results of both studies, but a comparative study, drawing a comparable subsample of firms from the US study to match the sample of German firms on both size and industry composition. We find that German firms are more likely to use derivatives than US firms, with 78% of German firms using derivatives compared to 57% of US firms. Aside from this higher overall usage, the general pattern of usage across industry and size groupings is comparable across the two countries. In both countries, foreign currency derivative usage is most common, followed closely by interest rate derivatives, with commodity derivatives a distant third. In contrast to the similarities, firms in the two countries differ notably on issues such as the primary goal of hedging, their choice of instruments, and the influence of their market view when taking derivative positions. These differences appear to be driven by the greater importance of financial accounting statements in Germany than the US and stricter German corporate policies of control over derivative activities within the firm.
Decline in extinction rates and scale invariance in the fossil record
We show that the decline in the extinction rate during the Phanerozoic can be
accurately parameterized by a logarithmic fit to the cumulative total
extinction. This implies that extinction intensity is falling off approximately
as the reciprocal of time. We demonstrate that this observation alone is
sufficient to explain the existence of the proposed power-law forms in the
distribution of the sizes of extinction events and in the power spectrum of
Phanerozoic extinction, results which previously have been explained by
appealing to self-organized critical theories of evolutionary dynamics.Comment: 11 pages including 3 postscript figures, typeset in LaTeX 2e using
the Elsevier macro package elsart.cl
Dynamic order submission strategies with competition between a dealer market and a crossing network.
Ks- and Lp-band polarimetry on stellar and bow-shock sources in the Galactic center
Infrared observations of the Galactic center (GC) provide a unique
opportunity to study stellar and bow-shock polarization effects in a dusty
environment. The goals of this work are to present new Ks- and Lp-band
polarimetry on an unprecedented number of sources in the central parsec of the
GC, thereby expanding our previous results in the H- and Ks-bands. We use
AO-assisted Ks- and Lp-band observations, obtained at the ESO VLT. High
precision photometry and the new polarimetric calibration method for NACO allow
us to map the polarization in a region of 8" x 25" (Ks) resp. 26" x 28" (Lp).
These are the first polarimetric observations of the GC in the Lp-band in 30
years, with vastly improved spatial resolution compared to previous results.
This allows resolved polarimetry on bright bow-shock sources in this area for
the first time at this wavelength. We find foreground polarization to be
largely parallel to the Galactic plane (Ks-band: 6.1% at 20 degrees, Lp-band:
4.5% at 20 degrees, in good agreement with our previous findings and with older
results. The previously described Lp-band excess in the foregound polarization
towards the GC could be confirmed here for a much larger number of sources. The
bow-shock sources contained in the FOV seem to show a different relation
between the polarization in the observed wavelength bands than what was
determined for the foreground. This points to the different relevant
polarization mechanisms. The resolved polarization patterns of IRS 5 and 10W
match the findings we presented earlier for IRS~1W. Additionally, intrinsic
Lp-band polarization was measured for IRS 1W and 21, as well as for other, less
prominent MIR-excess sources (IRS 2S, 2L, 5NE). The new data offer support for
the presumed bow-shock nature of several of these sources (1W, 5, 5NE, 10W, 21)
and for the model of bow-shock polarization presented in our last work.Comment: 19 pages, 18 figure
Circadian variation of the atropine effect on the running performance of mice treated with 1,2,2-trimethylpropylmethylphosphonofluoridate (soman)
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