863 research outputs found
Lie group weight multiplicities from conformal field theory
Dominant weight multiplicities of simple Lie groups are expressed in terms of
the modular matrices of Wess-Zumino-Witten conformal field theories, and
related objects. Symmetries of the modular matrices give rise to new relations
among multiplicities. At least for some Lie groups, these new relations are
strong enough to completely fix all multiplicities.Comment: 12 pages, Plain TeX, no figure
Compact Three Dimensional Black Hole: Topology Change and Closed Timelike Curve (minor changes)
We present a compactified version of the 3-dimensional black hole recently
found by considering extra identifications and determine the analytical
continuation of the solution beyond its coordinate singularity by extending the
identifications to the extended region of the spacetime. In the extended region
of the spacetime, we find a topology change and non-trivial closed timelike
curves both in the ordinary 3-dimensional black hole and in the compactified
one. Especially, in the case of the compactified 3-dimensional black hole, we
show an example of topology change from one double torus to eight spheres with
three punctures.Comment: 20 pages revtex.sty 8 figures contained, TIT/HEP-245/COSMO-4
The Cosmic Censor Forbids Naked Topology
For any asymptotically flat spacetime with a suitable causal structure
obeying (a weak form of) Penrose's cosmic censorship conjecture and satisfying
conditions guaranteeing focusing of complete null geodesics, we prove that
active topological censorship holds. We do not assume global hyperbolicity, and
therefore make no use of Cauchy surfaces and their topology. Instead, we
replace this with two underlying assumptions concerning the causal structure:
that no compact set can signal to arbitrarily small neighbourhoods of spatial
infinity (``-avoidance''), and that no future incomplete null geodesic is
visible from future null infinity. We show that these and the focusing
condition together imply that the domain of outer communications is simply
connected. Furthermore, we prove lemmas which have as a consequence that if a
future incomplete null geodesic were visible from infinity, then given our
-avoidance assumption, it would also be visible from points of spacetime
that can communicate with infinity, and so would signify a true naked
singularity.Comment: To appear in CQG, this improved version contains minor revisions to
incorporate referee's suggestions. Two revised references. Plain TeX, 12
page
Field studies on coliphages and coliforms as indicators of airborne animal viral contamination from wastewater treatment facilities
The occurrence of animal viruses in the aerosol emissions of wastewater treatment facilities was evaluated by direct assay and by the use of coliforms and coliphages as indicator organisms. Coliforms and coliphages were compared and evaluated with regard to their suitability as indicators of airborne animal viral contamination from wastewater treatment facilities. Two plants, one with treatment by activated sludge and the other by trickling filtration, were studied. Field air sampling procedures used large-volume air samplers, with recirculation devices, and Andersen samplers. Airborne viruses were enumerated by a most probable number (MPN) procedure. Partially treated liquid sewage contained about 1.0 x 102 pfu l-1 of animal viruses assayed on Buffalo Green Monkey (BGM) cells, 3.6 x 105 and 5.0 x 105 pfu l-1 of coliphages, depending upon the E. coli host strain used for assay, and 2.0 x 109 colonies l-1 of coliform bacteria. No airborne animal viruses were recovered, airborne coliphage levels averaged 2.3 x 10-1 and 3.0 x 10-1 MPN m-3, coliforms from aerosol emissions were 2.1 x 102 colonies m-3. Ratios of coliphages to animal viruses indicate that wastewater treatment plants may be continuous sources of low level concentrations of animal virus aerosols. Evidence shows coliforms to be much less stable than coliphages in the airborne state. Coliphages may be a more acceptable indicator of airborne animal viral contamination than coliforms.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23037/1/0000608.pd
Generalized Weyl Solutions
It was shown by Weyl that the general static axisymmetric solution of the
vacuum Einstein equations in four dimensions is given in terms of a single
axisymmetric solution of the Laplace equation in three-dimensional flat space.
Weyl's construction is generalized here to arbitrary dimension . The
general solution of the D-dimensional vacuum Einstein equations that admits D-2
orthogonal commuting non-null Killing vector fields is given either in terms of
D-3 independent axisymmetric solutions of Laplace's equation in
three-dimensional flat space or by D-4 independent solutions of Laplace's
equation in two-dimensional flat space. Explicit examples of new solutions are
given. These include a five-dimensional asymptotically flat ``black ring'' with
an event horizon of topology S^1 x S^2 held in equilibrium by a conical
singularity in the form of a disc.Comment: 50 pages, 10 figures; v2: minor improvement
Ringholes and closed timelike curves
It is shown that in a classical spacetime with multiply connected space
slices having the topology of a torus, closed timelike curves are also formed.
We call these spacetime ringholes. Two regions on the torus surface can be
distinguished which are separated by angular horizons. On one of such regions
(that which surrounds the maximum circumference of the torus) everything
happens like in spherical wormholes, but the other region (the rest of the
torus surface), while still possessing a chronology horizon and non-chronal
region, behaves like a coverging, rather than diverging, lens and corresponds
to an energy density which is always positive for large speeds at or near the
throat. It is speculated that a ringhole could be converted into a time machine
to perform time travels by an observer who would never encounter any matter
that violates the classical averaged weak energy condition. Based on a
calculation of vacuum fluctuations, it is also seen that the angular horizons
can prevent the emergence of quantum instabilities near the throat.Comment: 11 pages, RevTex, 4 figures available upon reques
Investigating the Information Systems Heterarchy
This article assesses how one IS organization is changing in response to the increased globalization of software development and posits the emergence of a new form of multi-national enterprise (MNE)—the heterarchy. Data from two projects create new insights into the structures and behaviors of ISMNEs as they adapt to global systems development. The article identifies four primary dimensions of impact—cultural, economic, operational, and organizational—and suggests how such organizations are evolvin
The CMS Tracker Readout Front End Driver
The Front End Driver, FED, is a 9U 400mm VME64x card designed for reading out
the Compact Muon Solenoid, CMS, silicon tracker signals transmitted by the
APV25 analogue pipeline Application Specific Integrated Circuits. The FED
receives the signals via 96 optical fibers at a total input rate of 3.4 GB/sec.
The signals are digitized and processed by applying algorithms for pedestal and
common mode noise subtraction. Algorithms that search for clusters of hits are
used to further reduce the input rate. Only the cluster data along with trigger
information of the event are transmitted to the CMS data acquisition system
using the S-LINK64 protocol at a maximum rate of 400 MB/sec. All data
processing algorithms on the FED are executed in large on-board Field
Programmable Gate Arrays. Results on the design, performance, testing and
quality control of the FED are presented and discussed
On the complete classification of the unitary N=2 minimal superconformal field theories
Aiming at a complete classification of unitary N=2 minimal models (where the
assumption of space-time supersymmetry has been dropped), it is shown that each
modular invariant candidate of a partition function for such a theory is indeed
the partition function of a minimal model. A family of models constructed via
orbifoldings of either the diagonal model or of the space-time supersymmetric
exceptional models demonstrates that there exists a unitary N=2 minimal model
for every one of the allowed partition functions in the list obtained from
Gannon's work.
Kreuzer and Schellekens' conjecture that all simple current invariants can be
obtained as orbifolds of the diagonal model, even when the extra assumption of
higher-genus modular invariance is dropped, is confirmed in the case of the
unitary N=2 minimal models by simple counting arguments.Comment: 53 pages; Latex; minor changes in v2: intro expanded, references
added, typos corrected, footnote added on p31; renumbering of sections; main
theorem reformulated for clarity, but contents unchanged. Minor revisions in
v3: typos corrected, footnotes 5, 6 added, lemma 1 and section 3.3.2
rewritten for greater generality, section 3.3 review removed. To appear in
Comm. Math. Phy
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