80 research outputs found
Eta invariants for flat manifolds
Using H. Donnelly result from the article "Eta Invariants for G-Spaces" we
calculate the eta invariants of the signature operator for almost all
7-dimensional flat manifolds with cyclic holonomy group. In all cases this eta
invariants are an integer numbers. The article was motivated by D. D. Long and
A. Reid article "On the geometric boundaries of hyperbolic 4-manifolds, Geom.
Topology 4, 2000, 171-178Comment: 18 pages, a new version with referees comment
Does the Red Queen reign in the kingdom of digital organisms?
In competition experiments between two RNA viruses of equal or almost equal
fitness, often both strains gain in fitness before one eventually excludes the
other. This observation has been linked to the Red Queen effect, which
describes a situation in which organisms have to constantly adapt just to keep
their status quo. I carried out experiments with digital organisms
(self-replicating computer programs) in order to clarify how the competing
strains' location in fitness space influences the Red-Queen effect. I found
that gains in fitness during competition were prevalent for organisms that were
taken from the base of a fitness peak, but absent or rare for organisms that
were taken from the top of a peak or from a considerable distance away from the
nearest peak. In the latter two cases, either neutral drift and loss of the
fittest mutants or the waiting time to the first beneficial mutation were more
important factors. Moreover, I found that the Red-Queen dynamic in general led
to faster exclusion than the other two mechanisms.Comment: 10 pages, 5 eps figure
The sensitivity of the vortex filament method to different reconnection models
We present a detailed analysis on the effect of using different algorithms to
model the reconnection of vortices in quantum turbulence, using the
thin-filament approach. We examine differences between four main algorithms for
the case of turbulence driven by a counterflow. In calculating the velocity
field we use both the local induction approximation (LIA) and the full
Biot-Savart integral. We show that results of Biot-Savart simulations are not
sensitive to the particular reconnection method used, but LIA results are.Comment: 9 pages, 9 figure
Tree method for quantum vortex dynamics
We present a numerical method to compute the evolution of vortex filaments in
superfluid helium. The method is based on a tree algorithm which considerably
speeds up the calculation of Biot-Savart integrals. We show that the
computational cost scales as Nlog{(N) rather than N squared, where is the
number of discretization points. We test the method and its properties for a
variety of vortex configurations, ranging from simple vortex rings to a
counterflow vortex tangle, and compare results against the Local Induction
Approximation and the exact Biot-Savart law.Comment: 12 pages, 10 figure
Search for heavy neutrinos mixing with tau neutrinos
We report on a search for heavy neutrinos (\nus) produced in the decay
D_s\to \tau \nus at the SPS proton target followed by the decay \nudecay in
the NOMAD detector. Both decays are expected to occur if \nus is a component
of .\
From the analysis of the data collected during the 1996-1998 runs with
protons on target, a single candidate event consistent with
background expectations was found. This allows to derive an upper limit on the
mixing strength between the heavy neutrino and the tau neutrino in the \nus
mass range from 10 to 190 . Windows between the SN1987a and Big Bang
Nucleosynthesis lower limits and our result are still open for future
experimental searches. The results obtained are used to constrain an
interpretation of the time anomaly observed in the KARMEN1 detector.\Comment: 20 pages, 7 figures, a few comments adde
Surface state atoms and their contribution to the surface tension of quantum liquids
We investigate the new type of excitations on the surface of liquid helium.
These excitations, called surfons, appear because helium atoms have discrete
energy level at the liquid surface, being attracted to the surface by the van
der Waals force and repulsed at a hard-core interatomic distance. The
concentration of the surfons increases with temperature. The surfons propagate
along the surface and form a two-dimensional gas. Basing on the simple model of
the surfon microscopic structure, we estimate the surfon activation energy and
effective mass for both helium isotopes. We also calculate the contribution of
the surfons to the temperature dependence of the surface tension. This
contribution explains the great and long-standing discrepancy between theory
and experiment on this temperature dependence in both helium isotopes. The
achieved agreement between our theory and experiment is extremely high. The
comparison with experiment allows to extract the surfon activation energy and
effective mass. The values of these surfon microscopic parameters are in a
reasonable agreement with the calculated from the proposed simple model of
surfon structure.Comment: 10 pages, 6 figure
The NOMAD Experiment at the CERN SPS
The NOMAD experiment is a short base-line search for ν<sub>μ</sub> − ν<sub>τ</sub> oscillations in the CERN neutrino beam. The ν<sub>τ</sub>'s are searched for through their charged current interactions followed by the observation of the resulting τ− through its electronic, muonic or hadronic decays. These decays are recognized using kinematical criteria necessitating the use of a light target which enables the reconstruction of individual particles produced in the neutrino interactions. This paper describes the various components of the NOMAD detector: the target and muon drift chambers, the electromagnetic and hadronic calorimeters, the preshower and transition radiation detectors and the veto and trigger scintillation counters. The beam and data acquisition system are also described. The quality of the reconstruction and individual particles is demonstrated through the ability of NOMAD to observe K<sub>s</sub><sup>0</sup>'s, Λ<sup>0</sup>'s and π<sup>0</sup>'s. Finally, the observation of τ− through its electronic decay being one of the most promising channels in the search, the identification of electrons in NOMAD is discussed
Cross-ancestry genome-wide association analysis of corneal thickness strengthens link between complex and Mendelian eye diseases
Central corneal thickness (CCT) is a highly heritable trait associated with complex eye diseases such as keratoconus and glaucoma. We perform a genome-wide association meta-analysis of CCT and identify 19 novel regions. In addition to adding support for known connective tissue-related pathways, pathway analyses uncover previously unreported gene sets. Remarkably, >20% of the CCT-loci are near or within Mendelian disorder genes. These included FBN1, ADAMTS2 and TGFB2 which associate with connective tissue disorders (Marfan, Ehlers-Danlos and Loeys-Dietz syndromes), and the LUM-DCN-KERA gene complex involved in myopia, corneal dystrophies and cornea plana. Using index CCT-increasing variants, we find a significant inverse correlation in effect sizes between CCT and keratoconus (r =-0.62, P = 5.30 × 10-5) but not between CCT and primary open-angle glaucoma (r =-0.17, P = 0.2). Our findings provide evidence for shared genetic influences between CCT and keratoconus, and implicate candidate genes acting in collagen and extracellular matrix regulation
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