5,253 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.
Revisiting the stability of spatially heterogeneous predator-prey systems under eutrophication
We employ partial integro-differential equations to model trophic interaction
in a spatially extended heterogeneous environment. Compared to classical
reaction-diffusion models, this framework allows us to more realistically
describe the situation where movement of individuals occurs on a faster time
scale than the demographic (population) time scale, and we cannot determine
population growth based on local density. However, most of the results reported
so far for such systems have only been verified numerically and for a
particular choice of model functions, which obviously casts doubts about these
findings. In this paper, we analyse a class of integro-differential
predator-prey models with a highly mobile predator in a heterogeneous
environment, and we reveal the main factors stabilizing such systems. In
particular, we explore an ecologically relevant case of interactions in a
highly eutrophic environment, where the prey carrying capacity can be formally
set to 'infinity'. We investigate two main scenarios: (i) the spatial gradient
of the growth rate is due to abiotic factors only, and (ii) the local growth
rate depends on the global density distribution across the environment (e.g.
due to non-local self-shading). For an arbitrary spatial gradient of the prey
growth rate, we analytically investigate the possibility of the predator-prey
equilibrium in such systems and we explore the conditions of stability of this
equilibrium. In particular, we demonstrate that for a Holling type I (linear)
functional response, the predator can stabilize the system at low prey density
even for an 'unlimited' carrying capacity. We conclude that the interplay
between spatial heterogeneity in the prey growth and fast displacement of the
predator across the habitat works as an efficient stabilizing mechanism.Comment: 2 figures; appendices available on request. To appear in the Bulletin
of Mathematical Biolog
Thermal measurement and modeling of multi-die packages
Thermal measurement and modeling of multi-die packages became a hot topic
recently in different fields like RAM chip packaging or LEDs / LED assemblies,
resulting in vertical (stacked) and lateral arrangement. In our present study
we show results for a mixed arrangement: an opto-coupler device has been
investigated with 4 chips in lateral as well as vertical arrangement. In this
paper we give an overview of measurement and modeling techniques and results
for stacked and MCM structures, describe our present measurement results
together with our structure function based methodology of validating the
detailed model of the package being studied. Also, we show how to derive
junction-to-pin thermal resistances with a technique using structure functions.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Electrical, thermal and optical characterization of power LED assemblies
Besides their electrical properties the optical parameters of LEDs also
depend on junction temperature. For this reason thermal characterization and
thermal management play important role in case of power LEDs, necessitating
both physical measurements and simulation tools. The focus of this paper is a
combined electrical, thermal and optical characterization of power LED
assemblies. In terms of simulation a method for board-level electro-thermal
simulation is presented, for measurements a combined thermal and radiometric
characterization system of power LEDs and LED assemblies is discussed.
Comparison of measurement and simulation results is presented in a case study.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
An extremal effective survey about extremal effective cycles in moduli spaces of curves
We survey recent developments and open problems about extremal effective
divisors and higher codimension cycles in moduli spaces of curves.Comment: Submitted to the Proceedings of the Abel Symposium 2017. Comments are
welcom
Production Technology and Competitiveness In the Hungarian Manufacturing Industry
Following the big transformations of the 1990s, enterprise structure and technological level seem to
have become stabilised in Hungary. Under these circumstances it is especially interesting to identify
the elements responsible for competitiveness in general, and the role technology plays in development
in particular, according to managers experienced in production and marketing. This empirical
study – based on in-depth interviews and field research – summarises characteristics of the technological
level in the sectors examined, role of technology and labour in production, effects of foreign
direct investment, relations between competition and firm-level factors determining competitiveness,
and concludes by summing up those most frequently mentioned proposals that should be incorporated
into economic policy according to managers. Main findings indicate that more qualified,
more intensive and cheaper labour can be substituted for high technology. The competitiveness of an
enterprise is not determined by technology alone, but rather by a combination of technology, the parameters
of available labour and the costs of investment increasing productivity. The insufficiency
of inter-company relations, together with a shortage of available assets necessary for investment
constitute the major threat undermining the competitiveness of enterprises in present-day Hungary
On the uniqueness of -gonal automorphisms of Riemann surfaces
Let be a compact Riemann surface of genus . A cyclic subgroup of
prime order of is called properly -gonal if it has a fixed
point and the quotient surface has genus . We show that if , then a
properly -gonal subgroup of is unique. We also discuss some
related results.Comment: final version, 9 pages, minor improvements, added 2 reference
Incorporating model uncertainty into optimal insurance contract design
In stochastic optimization models, the optimal solution heavily depends on the selected probability model for the scenarios. However, the scenario models are typically chosen on the basis of statistical estimates and are therefore subject to model error. We demonstrate here how the model uncertainty can be incorporated into the decision making process. We use a nonparametric approach for quantifying the model uncertainty and a minimax setup to find model-robust solutions. The method is illustrated by a risk management problem involving the optimal design of an insurance contract
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