5,545 research outputs found
Computational Complexity Results for Genetic Programming and the Sorting Problem
Genetic Programming (GP) has found various applications. Understanding this
type of algorithm from a theoretical point of view is a challenging task. The
first results on the computational complexity of GP have been obtained for
problems with isolated program semantics. With this paper, we push forward the
computational complexity analysis of GP on a problem with dependent program
semantics. We study the well-known sorting problem in this context and analyze
rigorously how GP can deal with different measures of sortedness.Comment: 12 page
Slug grazing effects on seedling and adult life stages of North American Prairie plants used in designed urban landscapes
Designed vegetation is a major contributor to ecosystem service provision incities, and as such the study of how herbivory and other ecological factors determine its
capacity to deliver such services, is long overdue. This study investigated the effect of slug grazing on the establishment and development of 26 species of North American prairie forbs and grasses used in sown or planted naturalistic communities in urban greenspace. The experiment was designed to provide slugs with the opportunity to choose between the plant species used, to mirror the situation that prevails in public greenspace. Slug density was manipulated through baiting with metaldehyde at different frequencies. Seedlings of prairie species were more palatable to slugs than adults.
Seedling establishment was significantly reduced in most species by slug grazing, with only seven species showing no significant increase in establishment in response to
baiting with metaldehyde. In many species successful establishment was based on moderate-high unpalatability and large or fast growing seedlings. Adult prairie plants
were typically more able to withstand slug damage, and once their shoots reached a certain size, grazing declined. This was not true of the most palatable species, which
even as adults were eventually eliminated by grazing in the absence of baiting. Phenology plays an important role in the survival of adults, with early emerging species
potentially subject to severe damage due to the limited availability of alternate food plants. As a group, prairie forbs are typically palatable to slugs, and unlikely to be
persistent in the most slug-rich urban situations
Efficient Algorithms for Distributed Detection of Holes and Boundaries in Wireless Networks
We propose two novel algorithms for distributed and location-free boundary
recognition in wireless sensor networks. Both approaches enable a node to
decide autonomously whether it is a boundary node, based solely on connectivity
information of a small neighborhood. This makes our algorithms highly
applicable for dynamic networks where nodes can move or become inoperative.
We compare our algorithms qualitatively and quantitatively with several
previous approaches. In extensive simulations, we consider various models and
scenarios. Although our algorithms use less information than most other
approaches, they produce significantly better results. They are very robust
against variations in node degree and do not rely on simplified assumptions of
the communication model. Moreover, they are much easier to implement on real
sensor nodes than most existing approaches.Comment: extended version of accepted submission to SEA 201
Electrical switching of antiferromagnetic MnAu and the role of thermal activation
Electrical manipulation of antiferromagnets with specific symmetries offers
the prospect of creating novel, antiferromagnetic spintronic devices. Such
devices aim to make use of the insensitivity to external magnetic fields and
the ultrafast dynamics at the picosecond timescale intrinsic to
antiferromagnets. The possibility to electrically switch antiferromagnets was
first predicted for Mn2Au and then experimentally observed in tetragonal
CuMnAs. Here, we report on the electrical switching and detection of the Neel
order in epitaxial films of Mn2Au. The exponential dependences of the switching
amplitude on the current density and the temperature are explained by a
macroscopic thermal activation model taking into account the effect of the
Joule heating in Hall cross devices and we observe that the thermal activation
plays a key role in the reorientation process of the Neel order. Our model
analysis shows that the electrically set Neel-state is long-term stable at room
temperature, paving the way for practical applications in memory devices.Comment: 8 pages, 6 figure
Nonlinear Term Structure Dependence: Copula Functions, Empirics, and Risk Implications
This paper documents nonlinear cross-sectional dependence in the term structure of U.S. Treasury yields and points out risk management implications. The analysis is based on a Kalman filter estimation of a two-factor affine model which specifies the yield curve dynamics. We then apply a broad class of copula functions for modeling dependence in factors spanning the yield curve. Our sample of monthly yields in the 1982 to 2001 period provides evidence of upper tail dependence in yield innovations; i.e., large positive interest rate shocks tend to occur under increased dependence. In contrast, the best fitting copula model coincides with zero lower tail dependence. This asymmetry has substantial risk management implications. We give an example in estimating bond portfolio loss quantiles and report the biases which result from an application of the normal dependence model.affine term structure models, nonlinear dependence, copula functions, tail dependence, value-at-risk
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