58,876 research outputs found
An experimental evaluation of cattail (Typha spp.) cutting depths on subsequent regrowth
Citation: Moorberg, C. & Ahlers, A. (2020). An experimental evaluation of cattail (Typha spp.) cutting depths on subsequent regrowth.Cattail (Typha spp.) expansions can negatively affect both native wetland flora and fauna diversity, and active management is often needed to maintain wetland habitat quality. Cattail removal is often non-permanent, requiring repeated treatments to retard reestablishment. Mechanically cutting cattails is a common management technique, but it is unclear what cutting depths are optimal. We conducted an experiment at Cheyenne Bottoms Wildlife Area (Kansas, USA) during 2017-2019 to address this question. We established a randomized complete block design experiment with four blocks and three cutting treatments in July 2017, including cattail cut above water, cut below water, and an uncut control. We hypothesized that cattails cut below water would have reduced gas-exchange capabilities due to flooded aerenchyma. We quantified emergent stem densities in each plot in September 2017 to assess the effectiveness of simulated management actions. The above water treatment had significantly fewer total stems than both the control (p = 0.0003) and the below water treatments (p = 0.0203). The above water treatment also had significantly fewer stems than the control treatment (p = 0.0032). Our results suggest that management efforts focused on cutting cattails below water slow cattail reestablishment
Integrable subsystem of Yang--Mills dilaton theory
With the help of the Cho-Faddeev-Niemi-Shabanov decomposition of the SU(2)
Yang-Mills field, we find an integrable subsystem of SU(2) Yang-Mills theory
coupled to the dilaton. Here integrability means the existence of infinitely
many symmetries and infinitely many conserved currents. Further, we construct
infinitely many static solutions of this integrable subsystem. These solutions
can be identified with certain limiting solutions of the full system, which
have been found previously in the context of numerical investigations of the
Yang-Mills dilaton theory. In addition, we derive a Bogomolny bound for the
integrable subsystem and show that our static solutions are, in fact, Bogomolny
solutions. This explains the linear growth of their energies with the
topological charge, which has been observed previously. Finally, we discuss
some generalisations.Comment: 25 pages, LaTex. Version 3: appendix added where the equivalence of
the field equations for the full model and the submodel is demonstrated;
references and some comments adde
Integrability from an abelian subgroup of the diffeomorphism group
It has been known for some time that for a large class of non-linear field
theories in Minkowski space with two-dimensional target space the complex
eikonal equation defines integrable submodels with infinitely many conservation
laws. These conservation laws are related to the area-preserving
diffeomorphisms on target space. Here we demonstrate that for all these
theories there exists, in fact, a weaker integrability condition which again
defines submodels with infinitely many conservation laws. These conservation
laws will be related to an abelian subgroup of the group of area-preserving
diffeomorphisms. As this weaker integrability condition is much easier to
fulfil, it should be useful in the study of those non-linear field theories.Comment: 13 pages, Latex fil
BPS submodels of the Skyrme model
We show that the standard Skyrme model without pion mass term can be
expressed as a sum of two BPS submodels, i.e., of two models whose static field
equations, independently, can be reduced to first order equations. Further,
these first order (BPS) equations have nontrivial solutions, at least locally.
These two submodels, however, cannot have common solutions. Our findings also
shed some light on the rational map approximation. Finally, we consider certain
generalisations of the BPS submodels.Comment: Latex, 12 page
k-defects as compactons
We argue that topological compactons (solitons with compact support) may be
quite common objects if -fields, i.e., fields with nonstandard kinetic term,
are considered, by showing that even for models with well-behaved potentials
the unusual kinetic part may lead to a power-like approach to the vacuum, which
is a typical signal for the existence of compactons. The related approximate
scaling symmetry as well as the existence of self-similar solutions are also
discussed. As an example, we discuss domain walls in a potential Skyrme model
with an additional quartic term, which is just the standard quadratic term to
the power two. We show that in the critical case, when the quadratic term is
neglected, we get the so-called quartic model, and the corresponding
topological defect becomes a compacton. Similarly, the quartic sine-Gordon
compacton is also derived. Finally, we establish the existence of topological
half-compactons and study their properties.Comment: the stability proof of Section 4.4 corrected, some references adde
Investigation of the Nicole model
We study soliton solutions of the Nicole model - a non-linear
four-dimensional field theory consisting of the CP^1 Lagrangian density to the
non-integer power 3/2 - using an ansatz within toroidal coordinates, which is
indicated by the conformal symmetry of the static equations of motion. We
calculate the soliton energies numerically and find that they grow linearly
with the topological charge (Hopf index). Further we prove this behaviour to
hold exactly for the ansatz. On the other hand, for the full three-dimensional
system without symmetry reduction we prove a sub-linear upper bound,
analogously to the case of the Faddeev-Niemi model. It follows that symmetric
solitons cannot be true minimizers of the energy for sufficiently large Hopf
index, again in analogy to the Faddeev-Niemi model.Comment: Latex, 35 pages, 1 figur
Discovery of a Second L Subdwarf in the Two Micron All Sky Survey
I report the discovery of the second L subdwarf identified in the Two Micron
All Sky Survey, 2MASS J16262034+3925190. This high proper motion object (mu =
1.27+/-0.03 "/yr) exhibits near-infrared spectral features indicative of a
subsolar metallicity L dwarf, including strong metal hydride and H2O absorption
bands, pressure-broadened alkali lines, and blue near-infrared colors caused by
enhanced collision-induced H2 absorption. This object is of later type than any
of the known M subdwarfs, but does not appear to be as cool as the apparently
late-type sdL 2MASS 0532+8246. The radial velocity (Vrad = -260+/-35 km/s) and
estimated tangential velocity (Vtan ~ 90-210 km/s) of 2MASS 1626+3925 indicate
membership in the Galactic halo, and this source is likely near or below the
hydrogen burning minimum mass for a metal-poor star. L subdwarfs such as 2MASS
1626+3925 are useful probes of gas and condensate chemistry in low-temperature
stellar and brown dwarf atmospheres, but more examples are needed to study
these objects as a population as well as to define a rigorous classification
scheme.Comment: 11 pages, 3 figures, accepted for publication ApJ Letters, v. 614
October 200
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