228 research outputs found
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Tracking and change of orientation of the child or the stimulus in preschoolers\u27 spatial localization.
Charge Violation and Alice Behavior in Global and Textured Strings
Spontaneous breaking of global symmetries can produce ``Alice'' strings: line
defects which make unbroken symmetries multivalued, induce apparent charge
violation via Aharonov-Bohm interactions, and form point defects when twisted
into loops. We demonstrate this behavior for both divergent and textured global
Alice strings. Both adiabatically scatter charged particles via effective
Wilson lines. For textured Alice strings, such Wilson lines occur at all radii,
and are multivalued only inside the string. This produces measurable effects,
including path-dependent charge violation.Comment: 32 pages, 2 epsfigs, Revte
Topologically Alice Strings and Monopoles
Symmetry breaking can produce ``Alice'' strings, which alter scattered
charges and carry monopole number and charge when twisted into loops. Alice
behavior arises algebraically, when strings obstruct unbroken symmetries -- a
fragile criterion. We give a topological criterion, compelling Alice behavior
or deforming it away. Our criterion, that \pi_o(H) acts nontrivially on
\pi_1(H), links topologically Alice strings to topological monopoles. We twist
topologically Alice loops to form monopoles. We show that Alice strings of
condensed matter systems (nematic liquid crystals, helium 3A, and related
non-chiral Bose condensates and amorphous chiral superconductors) are
topologically Alice, and support fundamental monopole charge when twisted into
loops. Thus they might be observed indirectly, not as strings, but as loop-like
point defects. We describe other models, showing Alice strings failing our
topological criterion; and twisted Alice loops supporting deposited, but not
fundamental, monopole number.Comment: 2 figures; this paper consolidates preprints hep-th/0304161 and
hep-th/0304162, to appear in Phys. Rev.
Data Sharing: How Much Doesn't Get Submitted to GenBank?
Funding agencies and journals require researchers to deposit DNA sequences in public databases such as GenBank when the paper is published, but how often do authors fail to do so
Confining Flux Tubes in a Current Algebra Approach
We describe flux tubes and their interactions in a low energy sigma model
induced by flavor symmetry breaking in
QCD. Unlike standard QCD, this model allows gauge confinement to
manifest itself in the low energy theory, which has unscreened spinor color
sources and global flux tubes. We construct the flux tubes and show how
they mediate the confinement of spinor sources. We further examine the flux
tubes' quantum stability, spectrum and interactions. We find that flux tubes
are Alice strings, despite ambiguities in defining parallel transport.
Furthermore, twisted loops of flux tube support skyrmion number, just as gauged
Alice strings form loops that support monopole charge. This model, while
phenomenologically nonviable, thus affords a perspective on both the dynamics
of confinement and on subtleties which arise for global Alice strings.Comment: 29 pages (REVTEX) plus 6 figures, two corrections in the final
section and added reference
A universe in a global monopole
We investigate brane physics in a universe with an extra dimensional global
monopole and negative bulk cosmological constant. The graviton zero mode is
naturally divergent; we thus invoke a physical cut-off to induce four
dimensional gravity on a brane at the monopole core. Independently, the massive
Kaluza-Klein modes have naturally compactified extra dimensions, inducing a
discrete spectrum. This spectrum remains consistent with four dimensional
gravity on the brane, even for small mass gap. Extra dimensional matter fields
also induce four dimensional matter fields on the brane, with the same
Kaluza-Klein spectrum of excited states. We choose parameters to solve the
hierarchy problem; that is, to induce the observed hierarchy between particle
and Planck scales in the effective four dimensional universe.Comment: 22 pages, 2 eps figures, revte
The Astropy Problem
The Astropy Project (http://astropy.org) is, in its own words, "a community
effort to develop a single core package for Astronomy in Python and foster
interoperability between Python astronomy packages." For five years this
project has been managed, written, and operated as a grassroots,
self-organized, almost entirely volunteer effort while the software is used by
the majority of the astronomical community. Despite this, the project has
always been and remains to this day effectively unfunded. Further, contributors
receive little or no formal recognition for creating and supporting what is now
critical software. This paper explores the problem in detail, outlines possible
solutions to correct this, and presents a few suggestions on how to address the
sustainability of general purpose astronomical software
Comparative Analysis of Teleost Genome Sequences Reveals an Ancient Intron Size Expansion in the Zebrafish Lineage
We have developed a bioinformatics pipeline for the comparative evolutionary analysis of Ensembl genomes and have used it to analyze the introns of the five available teleost fish genomes. We show our pipeline to be a powerful tool for revealing variation between genomes that may otherwise be overlooked with simple summary statistics. We identify that the zebrafish, Danio rerio, has an unusual distribution of intron sizes, with a greater number of larger introns in general and a notable peak in the frequency of introns of approximately 500 to 2,000 bp compared with the monotonically decreasing frequency distributions of the other fish. We determine that 47% of D. rerio introns are composed of repetitive sequences, although the remainder, over 331 Mb, is not. Because repetitive elements may be the origin of the majority of all noncoding DNA, it is likely that the remaining D. rerio intronic sequence has an ancient repetitive origin and has since accumulated so many mutations that it can no longer be recognized as such. To study such an ancient expansion of repeats in the Danio, lineage will require further comparative analysis of fish genomes incorporating a broader distribution of teleost lineages
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