55,922 research outputs found
Device for mechanically stabilizing web ribbon buttons during growth initiation
The invention relates to a stabilization device for stabilizing dendritic web seed buttons during initiation of crystal growth from a float melt zone. The invention includes angular maintenance means for maintaining a constant angular orientation between the axis of a growth initiation seed and the upper surface of a web button during withdrawal of the web button from the melt. In the preferred embodiment, the angular means includes an adjustable elevation tube which surrounds the seed, the weight of which may be selectively supported by the seed button during web button withdrawal
Recurrent Acceleration in Dilaton-Axion Cosmology
A class of Einstein-dilaton-axion models is found for which almost all flat
expanding homogeneous and isotropic universes undergo recurrent periods of
acceleration. We also extend recent results on eternally accelerating open
universes.Comment: 8 pages, 7 figures. minor changes. Version 4 corrects a figure
captio
Simple examples of distinct Liouville-type symplectic structures
We discuss some examples of open manifolds which admit non-isomorphic
symplectic structures of Liouville type.Comment: v2: one remark added, minor change
BPS Bounds for Worldvolume Branes
The worldvolume field equations of M-branes and D-branes are known to admit
p-brane soliton solutions. These solitons are shown to saturate a BPS-type
bound on their p-volume tensions, which are expressed in terms of central
charges that are expected to appear in the worldvolume supertranslation
algebra. The cases we consider include vortices, `BIons', instantons and dyons
(both abelian and non-abelian), and the string boundaries of M-2-branes in the
M-5-brane.Comment: Latex, 20 pages. References added, minor change
The Magnetic Field of L1544: I. Near-Infrared Polarimetry and the Non-Uniform Envelope
The magnetic field (B-field) of the starless dark cloud L1544 has been
studied using near-infrared (NIR) background starlight polarimetry (BSP) and
archival data in order to characterize the properties of the plane-of-sky
B-field. NIR linear polarization measurements of over 1,700 stars were obtained
in the H-band and 201 of these were also measured in the K-band. The NIR BSP
properties are correlated with reddening, as traced using the RJCE (H-M)
method, and with thermal dust emission from the L1544 cloud and envelope seen
in Herschel maps. The NIR polarization position angles change at the location
of the cloud and exhibit their lowest dispersion of position angles there,
offering strong evidence that NIR polarization traces the plane-of-sky B-field
of L1544. In this paper, the uniformity of the plane-of-sky B-field in the
envelope region of L1544 is quantitatively assessed. This allowed evaluating
the approach of assuming uniform field geometry when measuring relative
mass-to-flux ratios in the cloud envelope and core based on averaging of the
envelope radio Zeeman observations, as in Crutcher et al. (2009). In L1544, the
NIR BSP shows the envelope B-field to be significantly non-uniform and likely
not suitable for averaging Zeeman properties without treating intrinsic
variations. Deeper analyses of the NIR BSP and related data sets, including
estimates of the B-field strength and testing how it varies with position and
gas density, are the subjects of later papers in this series.Comment: 16 pages, 9 figures; accepted for publication in The Astrophysical
Journa
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