3,024 research outputs found
Noncommutative gauge theory using covariant star product defined between Lie-valued differential forms
We develop an internal gauge theory using a covariant star product. The
space-time is a symplectic manifold endowed only with torsion but no curvature.
It is shown that, in order to assure the restrictions imposed by the
associativity property of the star product, the torsion of the space-time has
to be covariant constant. An illustrative example is given and it is concluded
that in this case the conditions necessary to define a covariant star product
on a symplectic manifold completely determine its connection.Comment: AMS-LaTeX 19 pages. v2: corrections in language and equations
(typos), expanded sections 3-5, added references. v3: minor presentational
and grammatical corrections, completed, corrected and reordered some
references
Covariant star product on symplectic and Poisson spacetime manifolds
A covariant Poisson bracket and an associated covariant star product in the
sense of deformation quantization are defined on the algebra of tensor-valued
differential forms on a symplectic manifold, as a generalization of similar
structures that were recently defined on the algebra of (scalar-valued)
differential forms. A covariant star product of arbitrary smooth tensor fields
is obtained as a special case. Finally, we study covariant star products on a
more general Poisson manifold with a linear connection, first for smooth
functions and then for smooth tensor fields of any type. Some observations on
possible applications of the covariant star products to gravity and gauge
theory are made.Comment: AMS-LaTeX, 27 pages. v2: minor corrections in presentation and
language, added one referenc
The paradox of searching efficiency or why are violent population cycles so uncommon in terrestrial ecosystem
The searching efficiency of predators depends on the balance between the adaptations
of the predator and the counter-adaptations of the prey. In this evolutionary race,
the prey should normally have the upper hand, as it can perform tradeoffs between
efficiency in resource use and ability to avoid predators. In terrestrial predator–herbivore systems, however, the huge difference in food quality between prey and predators
seems to give predators an advantage. In productive terrestrial ecosystems, predators
thus chronically overexploit herbivores, i.e. regulate them at densities far below the
point of maximum sustainable yield. Assuming type II functional response, this should
result in violent limit cycle dynamics. In reality, however, such cycles are only common
at high latitudes, whereas the herbivory-based food webs of species-rich ecosystems at
middle and low latitudes are characterized by asymptotic dynamics, where numerical
changes only occur in response to external forcing. One way or another, diversity thus
seems to beget stability in terrestrial grazing webs. We propose that strong, donorcontrolled energy flows from the detritus web and directly from plants to predators are
the key for the prevalence of asymptotic dynamics at middle and low latitudes. These
flows support generalists with type III functional response and, therefore, a capacity to
curb budding outbreaks at an early stage. The ongoing extinction wave could critically
weaken these stabilizing interactions, which could destabilize currently stable food
webs. and result in violent limit cycle dynamics in ecosystems, where the dominating
species have evolved under asymptotic dynamics. This could cause secondary extinctions and inflict large economic losses
Keeping it cool: Soil sample cold pack storage and DNA shipment up to 1 month does not impact metabarcoding results
A grant from the One-University Open Access Fund at the University of Kansas was used to defray the author's publication fees in this Open Access journal. The Open Access Fund, administered by librarians from the KU, KU Law, and KUMC libraries, is made possible by contributions from the offices of KU Provost, KU Vice Chancellor for Research & Graduate Studies, and KUMC Vice Chancellor for Research. For more information about the Open Access Fund, please see http://library.kumc.edu/authors-fund.xml.With the advances of sequencing tools, the fields of environmental microbiology and soil ecology have been transformed. Today, the unculturable majority of soil microbes can be sequenced. Although these tools give us tremendous power and open many doors to answer important questions, we must understand how sample processing may impact our results and interpretations. Here, we test the impacts of four soil storage methods on downstream amplicon metabarcoding and qPCR analyses for fungi and bacteria. We further investigate the impact of thaw time on extracted DNA to determine a safe length of time during which this can occur with minimal impact on study results. Overall, we find that storage using standard cold packs with subsequent storage at −20°C is little different than immediate storage in liquid nitrogen, suggesting that the historical and current method is adequate. We further find evidence that storage at room temperature or with aid of RNAlater can lead to changes in community composition and in the case of RNAlater, lower gene copies. We therefore advise against these storage methods for metabarcoding analyses. Finally, we show that over 1 month, DNA extract thaw time does not impact diversity or qPCR metrics. We hope that this work will help researchers working with soil bacteria and fungi make informed decisions about soil storage and transport to ensure repeatability and accuracy of results and interpretations.National Science Foundation (DEB- 1738041, OIA 1656006)National Geographic Society (WW-036ER-17
Effects of multidisciplinary inpatient rehabilitation for chronic back or neck pain: a register-linkage study of sickness absences and analgesic purchases in an occupational cohort
Three Phages from a Boreal Lake during Ice Cover Infecting Xylophilus, Caulobacter, and Polaromonas Species
Although the important role of microbes in freshwater is well understood, studies on phage–host systems in such environments during ice cover are completely lacking. Here, we describe the isolation and characterization of three new bacteriophages infecting Xylophilus sp., Caudobacter sp., and Polaromonas sp. from freshwater samples taken under the ice cover of Lake Konnevesi, Finland. Lumi, Kuura, and Tiera bacteriophages have tailed icosahedral virions and double-stranded DNA. Lumi is a siphophage with a genome of 80,496 bp, and Kuura and Tiera are podophages, and their genomes are 43,205 and 45,327 bp in length, resembling viruses in the class Caudoviricetes. Their host ranges were very limited among the winter-isolated bacterial strains from Konnevesi, each infecting only their own hosts. They can infect efficiently at 4 °C, showing that they are adapted to living in lake water under ice cover. Analysis of the viral genome sequences showed that a significant number of the gene products of each virus are unique, indicating that there is unexplored viral diversity in freshwaters. To our knowledge, Lumi and Tiera are the first phages isolated on the Xylophilus sp. and Polaromonas sp. strains, allowing their exploitation in further studies of freshwater bacterial–phage interactions
Seiberg-Witten map with Lorentz-invariance and gauge-covariant star product
We develop the Seiberg-Witten map using the gauge-covariant star product with the noncommutativity tensor theta(mu v)(x). The latter guarantees the Lorentz invariance of the theory. The usual form of this map and its other recent generalizations do not consider such a covariant star product. We construct the Seiberg-Witten map for the gauge parameter, the gauge field and the strength tensor to the first order in the noncommutativity parameter theta(mu v)(x). Prescription for the generalization of the map to higher orders is also given. Interestingly, the associativity of the covariant star product both in the first and second orders requires the same constraints, namely, on the theta(mu v)(x) and on the space-time connection. This fact suggests that the same constraints could be enough to ensure the associativity in all orders. The resulting Seiberg-Witten map applies both to the internal and space-time gauge theories. Comparisons with the Seiberg-Witten map based on other (non-covariant) star products are given and some characteristic properties are also presented. As an application, we consider the GL(2, C) noncommutative gauge theory of gravitation, in which it is shown that the connection determines a space-time with symplectic structure (as proposed by Zumino et al [33]). This example shows that the constraints required for the associativity of the gauge-covariant star product can be satisfied. The presented GL(2, C) noncommutative gauge theory of gravitation is also compared to the one (given by Chamseddine [44]) with non-covariant star product. (C) 2022 The Author(s). Published by Elsevier B.V.Peer reviewe
- …