3,888 research outputs found
Syzygies of torsion bundles and the geometry of the level l modular variety over M_g
We formulate, and in some cases prove, three statements concerning the purity
or, more generally the naturality of the resolution of various rings one can
attach to a generic curve of genus g and a torsion point of order l in its
Jacobian. These statements can be viewed an analogues of Green's Conjecture and
we verify them computationally for bounded genus. We then compute the
cohomology class of the corresponding non-vanishing locus in the moduli space
R_{g,l} of twisted level l curves of genus g and use this to derive results
about the birational geometry of R_{g, l}. For instance, we prove that R_{g,3}
is a variety of general type when g>11 and the Kodaira dimension of R_{11,3} is
greater than or equal to 19. In the last section we explain probabilistically
the unexpected failure of the Prym-Green conjecture in genus 8 and level 2.Comment: 35 pages, appeared in Invent Math. We correct an inaccuracy in the
statement of Prop 2.
Magnetic field control of cycloidal domains and electric polarization in multiferroic BiFeO
The magnetic field induced rearrangement of the cycloidal spin structure in
ferroelectric mono-domain single crystals of the room-temperature multiferroic
BiFeO is studied using small-angle neutron scattering (SANS). The cycloid
propagation vectors are observed to rotate when magnetic fields applied
perpendicular to the rhombohedral (polar) axis exceed a pinning threshold value
of 5\,T. In light of these experimental results, a phenomenological model
is proposed that captures the rearrangement of the cycloidal domains, and we
revisit the microscopic origin of the magnetoelectric effect. A new coupling
between the magnetic anisotropy and the polarization is proposed that explains
the recently discovered magnetoelectric polarization to the rhombohedral axis
Unfolded Description of Kerr Black Hole
It is shown that Kerr black hole is a solution of simple unfolded
differential equations that form a deformation of the zero-curvature
description of empty space-time. Our construction uses the Killing
symmetries of the Kerr solution. All known and some new algebraic properties of
the Kerr-Schild solution result from the obtained black hole unfolded system in
the coordinate-independent way. Kerr Schild type solutions of free equations in
for massless fields of any spin, associated to the proposed black hole
unfolded system, are found.Comment: 18 page
Alpha-induced reactions for the astrophysical p-process: the case of 151Eu
The cross sections of 151Eu(alpha,gamma)155Tb and 151Eu(alpha,n)154Tb
reactions have been measured with the activation method. Some aspects of the
measurement are presented here to illustrate the requirements of experimental
techniques needed to obtain nuclear data for the astrophysical p-process
nucleosynthesis. Preliminary cross section results are also presented and
compared with the predictions of statistical model calculations.Comment: Accepted for publication in Journal of Physics Conference Series,
proceeding of the Nuclear Physics in Astrophysics IV. conferenc
Exploring context dependency in eco‐evolutionary patterns with the stick insect Timema cristinae
Rapid evolution can influence the ecology of populations, communities, and ecosystems, but the importance of evolution for ecological dynamics remains unclear, largely because the contexts in which evolution is powerful are poorly resolved. Here, we carry out a large observational study to test hypotheses about context dependency of eco‐evolutionary patterns previously identified on the stick insect Timema cristinae . Experiments and observations conducted in 2011 and 2012 documented predator‐mediated negative effects of camouflage maladaptation (i.e., evolutionary dynamics) on: (a) T. cristinae abundance and, (b) species richness and abundance of other arthropods. Here we show that camouflage maladaptation does not correlate with T. cristinae abundance and, instead, is associated with increased abundance and species richness of cohabitating arthropods. We furthermore find that plants with high levels of Timema maladaptation tend to have higher foliar nitrogen, that is, higher nutritional value, and more positive mass‐abundance slopes in the coexisting arthropod communities. We propose explanations for the observed contrasting results, such as negative density‐ and frequency‐dependent selection, feedbacks between herbivore abundance and plant nutritional quality, and common effects of predation pressure on selection and prey abundance. Our results demonstrate the utility of observational studies to assess the context dependency of eco‐evolutionary dynamics patterns and provide testable hypotheses for future work
Steady states in a structured epidemic model with Wentzell boundary condition
We introduce a nonlinear structured population model with diffusion in the
state space. Individuals are structured with respect to a continuous variable
which represents a pathogen load. The class of uninfected individuals
constitutes a special compartment that carries mass, hence the model is
equipped with generalized Wentzell (or dynamic) boundary conditions. Our model
is intended to describe the spread of infection of a vertically transmitted
disease, for example Wolbachia in a mosquito population. Therefore the
(infinite dimensional) nonlinearity arises in the recruitment term. First we
establish global existence of solutions and the Principle of Linearised
Stability for our model. Then, in our main result, we formulate simple
conditions, which guarantee the existence of non-trivial steady states of the
model. Our method utilizes an operator theoretic framework combined with a
fixed point approach. Finally, in the last section we establish a sufficient
condition for the local asymptotic stability of the positive steady state
Remarks on the analytic structure of supersymmetric effective actions
We study the effective superpotential of N=1 supersymmetric gauge theories
with a mass gap, whose analytic properties are encoded in an algebraic curve.
We propose that the degree of the curve equals the number of semiclassical
branches of the gauge theory. This is true for supersymmetric QCD with one
adjoint and polynomial superpotential, where the two sheets of its
hyperelliptic curve correspond to the gauge theory pseudoconfining and higgs
branches. We verify this proposal in the new case of supersymmetric QCD with
two adjoints and superpotential V(X)+XY^2, which is the confining phase
deformation of the D_{n+2} SCFT. This theory has three kinds of classical vacua
and its curve is cubic. Each of the three sheets of the curve corresponds to
one of the three semiclassical branches of the gauge theory. We show that one
can continuously interpolate between these branches by varying the couplings
along the moduli space.Comment: 49 pages, 3 figures, harvmac; typos correcte
Precise half-life measurement of the 10 h isomer in 154Tb
The precise knowledge of the half-life of the reaction product is of crucial
importance for a nuclear reaction cross section measurement carried out with
the activation technique. The cross section of the 151Eu(alpha,n)154Tb reaction
has been measured recently using the activation method, however, the half-life
of the 10 h isomer in 154Tb has a relatively high uncertainty and ambiguous
values can be found in the literature. Therefore, the precise half-life of the
isomeric state has been measured and found to be 9.994 h +- 0.039 h. With
careful analysis of the systematic errors, the uncertainty of this half-life
value has been significantly reduced.Comment: Accepted for publication in Nuclear Physics
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