9,915 research outputs found
A point mass in an isotropic universe: III. The region
McVittie's solution of Einstein's field equations, representing a point mass
embedded into an isotropic universe, possesses a scalar curvature singularity
at proper radius . The singularity is space-like and precedes, in the
expanding case, all other events in the space-time. It is shown here that this
singularity is gravitationally weak, and the possible structure of the region
is investigated. A characterization of this solution which does not
involve asymptotics is given.Comment: Revtex, 11pp. To appear in Class.Quant.Grav. Paper II appeared as
Class. Quant. Grav. 16 (1999) 122
Disorder in DNA-Linked Gold Nanoparticle Assemblies
We report experimental observations on the effect of disorder on the phase
behavior of DNA-linked nanoparticle assemblies. Variation in DNA linker lengths
results in different melting temperatures of the DNA-linked nanoparticle
assemblies. We observed an unusual trend of a non-monotonic ``zigzag'' pattern
in the melting temperature as a function of DNAlinker length. Linker DNA
resulting in unequal DNA duplex lengths introduces disorder and lowers the
melting temperature of the nanoparticle system. Comparison with free DNA
thermodynamics shows that such an anomalous zigzag pattern does not exist for
free DNA duplex melting, which suggests that the disorder introduced by unequal
DNA duplex lengths results in this unusual collective behavior of DNA-linked
nanoparticle assemblies.Comment: 4 pages, 4 figures, Phys.Rev.Lett. (2005), to appea
Photometric identification of the periods of the first candidate extragalactic magnetic massive stars
Galactic stars belonging to the Of?p category are all strongly magnetic
objects exhibiting rotationally modulated spectral and photometric changes on
timescales of weeks to years. Five candidate Of?p stars in the Magellanic
Clouds have been discovered, notably in the context of ongoing surveys of their
massive star populations. Here we describe an investigation of their
photometric behaviour, revealing significant variability in all studied objects
on timescales of one week to more than four years, including clearly periodic
variations for three of them. Their spectral characteristics along with these
photometric changes provide further support for the hypothesis that these are
strongly magnetized O stars, analogous to the Of?p stars in the Galaxy.Comment: 9pages, accepted by A&
Sampling the progression of domain-initial denasalization in Seoul Korean
Word-initial nasals in Korean are known to exhibit prosody-sensitive denasalization. The
literature on the subject is still scarce and even the basic description of the process is debated.
This study tested the speculation that inconsistencies in the literature may be explained if
certain features of denasalization have developed relatively recently as part of an ongoing
sound change. Based on apparent-time data from thirty-two speakers of Seoul Korean, the
study explored the development of denasalization over a fifty-year period. The phonetic
manifestations of domain-initial nasals were examined, along with the effects of prosodic
position, place of articulation, and the height of the following vowel. The results revealed
that denasalization has advanced rapidly over time, acquiring more plosive-like features of
devoicing as well as a complete lack of nasality. Alveolar nasals before a high vowel were
most likely to show denasalization and devoicing. Interestingly, the cumulative effect of
prosody became weakest and partial denasalization was least likely for the younger group.
Based on these results, we speculate that Korean denasalization is in the process of being
stabilized into a discrete phrase-level process from a more general, gradient phenomenon of
domain-initial strengthening, consistent with the theory of the life cycle of phonological
processes.
Keywords: denasalization; domain-initial strengthening; articulatory strengthening; fortition;
Korean; sound change; rule scattering; life cycle of phonological processes; apparent tim
A note on behaviour at an isotropic singularity
The behaviour of Jacobi fields along a time-like geodesic running into an
isotropic singularity is studied. It is shown that the Jacobi fields are
crushed to zero length at a rate which is the same in every direction
orthogonal to the geodesic. We show by means of a counter-example that this
crushing effect depends crucially on a technicality of the definition of
isotropic singularities, and not just on the uniform degeneracy of the metric
at the singularity.Comment: 13 pp. plain latex. To appear in Classical and Quantum Gravit
Aircraft noise prediction program propeller analysis system IBM-PC version user's manual version 2.0
The IBM-PC version of the Aircraft Noise Prediction Program (ANOPP) Propeller Analysis System (PAS) is a set of computational programs for predicting the aerodynamics, performance, and noise of propellers. The ANOPP-PAS is a subset of a larger version of ANOPP which can be executed on CDC or VAX computers. This manual provides a description of the IBM-PC version of the ANOPP-PAS and its prediction capabilities, and instructions on how to use the system on an IBM-XT or IBM-AT personal computer. Sections within the manual document installation, system design, ANOPP-PAS usage, data entry preprocessors, and ANOPP-PAS functional modules and procedures. Appendices to the manual include a glossary of ANOPP terms and information on error diagnostics and recovery techniques
Status and plans for the ANOPP/HSR prediction system
ANOPP is a comprehensive prediction system which was developed and validated by NASA. Because ANOPP is a system prediction program, it allows aerospace industry researchers to create trade-off studies with a variety of aircraft noise problems. The extensive validation of ANOPP allows the program results to be used as a benchmark for testing other prediction codes
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