211 research outputs found
Estimation of genetic parameters for height using spatial analysis in Tsuga heterophylla full-sibling family trials in British Columbia
Non-spatial and spatial analyses were carried out to study the effects on genetic parameters in ten-year height growth data across two series of 10 large second-generation full-sib progeny trials of western hemlock [Tsuga heterophylla (Raf.) Sarg.] in British Columbia. To account for different and complex patterns of environmental heterogeneity, spatial single trial analyses were conducted using an individual-tree mixed model with a two-dimensional smoothing surface with tensor product of B-spline bases. The spatial single trial analysis, in all cases, showed sizeable lower Deviance Information Criterion values relative to the non-spatial analysis. Also, fitting a surface displayed a consistent reduction in the posterior mean as well as a decrease in the standard deviations of error variance, no appreciable changes in the additive variance, an increase of individual narrow-sense heritability, and accuracy of breeding values. The tensor product of cubic basis functions of B-spline based on a mixed model framework does provide a useful new alternative to model different and complex patterns of spatial variability within sites in forest genetic trials. Individual narrow-sense heritabilities estimates from the spatial single trial analyses were low (average of 0.06), but typical of this species. Estimated dominance relative to additive variances were unstable across sites (from 0.00 to 1.59). The implications of these estimations will be discussed with respect to the western hemlock genetic improvement program in British Columbia.Fil: Cappa, Eduardo Pablo. British Columbia Ministry of Forests and Range; Canadá. University of British Columbia; Canadá. Instituto Nacional de TecnologĂa Agropecuaria. Centro de InvestigaciĂłn de Recursos Naturales. Instituto de Recursos BiolĂłgicos; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Yanchuk, A. D.. British Columbia Ministry of Forests and Range; CanadáFil: Cartwright, C. V.. British Columbia Ministry of Forests and Range; Canad
On the stability of periodic orbits in delay equations with large delay
We prove a necessary and sufficient criterion for the exponential stability
of periodic solutions of delay differential equations with large delay. We show
that for sufficiently large delay the Floquet spectrum near criticality is
characterized by a set of curves, which we call asymptotic continuous spectrum,
that is independent on the delay.Comment: postprint versio
Noise enhanced coupling between two oscillators with long-term plasticity
Spike time-dependent plasticity is a fundamental adaptation mechanism of the nervous system. It induces structural changes of synaptic connectivity by regulation of coupling strengths between individual cells depending on their spiking behavior. As a biophysical process its functioning is constantly subjected to natural fluctuations. We study theoretically the influence of noise on a microscopic level by considering only two coupled neurons. Adopting a phase description for the neurons we derive a two-dimensional system which describes the averaged dynamics of the coupling strengths. We show that a multistability of several coupling configurations is possible, where some configurations are not found in systems without noise. Intriguingly, it is possible that a strong bidirectional coupling, which is not present in the noise-free situation, can be stabilized by the noise. This means that increased noise, which is normally expected to desynchronize the neurons, can be the reason for an antagonistic response of the system, which organizes itself into a state of stronger coupling and counteracts the impact of noise. This mechanism, as well as a high potential for multistability, is also demonstrated numerically for a coupled pair of Hodgkin-Huxley neurons
Frequency locking by external forcing in systems with rotational symmetry
We study locking of the modulation frequency of a relative periodic orbit in
a general -equivariant system of ordinary differential equations under an
external forcing of modulated wave type. Our main result describes the shape of
the locking region in the three-dimensional space of the forcing parameters:
intensity, wave frequency, and modulation frequency. The difference of the wave
frequencies of the relative periodic orbit and the forcing is assumed to be
large and differences of modulation frequencies to be small. The intensity of
the forcing is small in the generic case and can be large in the degenerate
case, when the first order averaging vanishes. Applications are external
electrical and/or optical forcing of selfpulsating states of lasers.Comment: 5 figure
Rate and memory effects in bifurcation-induced tipping
A variation in the environment of a system, such as the temperature, the
concentration of a chemical solution or the appearance of a magnetic field, may
lead to a drift in one of the parameters. If the parameter crosses a
bifurcation point, the system can tip from one attractor to another
(bifurcation-induced tipping). Typically, this stability exchange occurs at a
parameter value beyond the bifurcation value. This is what we call here the
stability exchange shift. We study systematically how the shift is affected by
the initial parameter value and its change rate. To that end, we present
numerical and analytical results for different types of bifurcations and
different paradigmatic systems. Finally, we deduce the scaling laws governing
this phenomenon. We show that increasing the change rate and starting the drift
further from the bifurcation can delay the tipping process. Furthermore, if the
change rate is sufficiently small, the shift becomes independent of the initial
condition (no memory) and the shift tends to zero as the square root of the
change rate. Thus, the bifurcation diagram for the system with fixed parameters
is recovered
Mathematical simulation of package delivery optimization using a combination of carriers
A variety of goods and services in the contemporary world requires permanent
improvement of services e-commerce platform performance. Modern society is so
deeply integrated with mail deliveries, purchasing of goods and services
online, that makes competition between service and good providers a key
selection factor. As long as logistic, timely, and cost-effective delivery
plays important part authors decided to analyze possible ways of improvements
in the current field, especially for regions distantly located from popular
distribution centers. Considering both: fast and lazy delivery the factor of
costs is playing an important role for each end-user. Given work proposes a
simulation that analyses the current cost of delivery for e-commerce orders in
the context of delivery by the Supplier Fleet, World-Wide delivery service
fleet, and possible vendor drop-ship and checks of the alternative ways can be
used to minimize the costs. The main object of investigation is focused around
mid and small businesses living far from big distribution centers (except edge
cases like lighthouses, edge rocks with very limited accessibility) but
actively using e-commerce solutions for daily activities fulfillment. Authors
analyzed and proposed a solution for the problem of cost optimization for
packages delivery for long-distance deliveries using a combination of paths
delivered by supplier fleets, worldwide and local carriers. Data models and
Add-ons of contemporary Enterprise Resource Planning systems were used, and
additional development is proposed in the perspective of the flow selection
change. The experiment is based on data sources of the United States companies
using a wide range of carriers for delivery services and uses the data sources
of the real companies; however, it applies repetitive simulations to analyze
variances in obtained solutions
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