Poopćena metoda razvoja po jacobijevim eliptičkim funkcijama i primjene na nelinearne valne jednadžbe

In this work an extended Jacobian elliptic function expansion method is applied to construct the exact periodic solutions of two nonlinear wave equations. The periodic solutions obtained by this method can be reduced to the solitary wave solutions under certain limiting conditions.Primijenili smo proširenu metodu razvoja po Jacobijevim eliptičkim funkcijama za izvod točnih periodičnih rješenja dviju nelinearnih valnih jednadžbi. Periodična rješenja koja smo izveli tom metodom svode se na solitonska rješenja u određenim graničnim uvjetima

Poopćena metoda razvoja po jacobijevim eliptičkim funkcijama i primjene na nelinearne valne jednadžbe

In this work an extended Jacobian elliptic function expansion method is applied to construct the exact periodic solutions of two nonlinear wave equations. The periodic solutions obtained by this method can be reduced to the solitary wave solutions under certain limiting conditions.Primijenili smo proširenu metodu razvoja po Jacobijevim eliptičkim funkcijama za izvod točnih periodičnih rješenja dviju nelinearnih valnih jednadžbi. Periodična rješenja koja smo izveli tom metodom svode se na solitonska rješenja u određenim graničnim uvjetima

Experimental and numerical study on a novel dual-resonance wave energy converter with a built-in power take-off system

A new concept of point-absorber wave energy converter (WEC) with a waterproof outer-floater and a built-in power take-off (BI-PTO) mechanism, named Dual-Resonance WEC (DR-WEC), is put forward and investigated by experiments and numerical simulations. The BI-PTO mechanism includes spring, sliding-mass and damping systems, where the spring system is the most complicated and should be designed specially. A 1:10 scale model is designed. The mechanical performance of the BI-PTO system is investigated by a bench test. The results have shown that the design is feasible, and the added inertia effect of the BI-PTO has a negative influence on the power output. The average mechanical efficiency of the BI-PTO is 65.8% with maximum up to 80.0%. The motion and power responses of the DR-WEC are studied by a wave tank experiment and a linear numerical model with corrected mechanical added mass and viscosity. The viscous added mass and damping correction coefficients are obtained by a free decay test. The good agreement between the experimental measurements and numerical simulations has indicated that the present numerical model with corrections is of enough accuracy and the effects of mooring system and other degree of freedoms on the heave motion and power responses can be ignored. (C) 2018 Elsevier Ltd. All rights reserved

Spatiotemporal Variation in Avian Migration Phenology: Citizen Science Reveals Effects of Climate Change

A growing number of studies have documented shifts in avian migratory phenology in response to climate change, and yet there is a large amount of unexplained variation in the magnitude of those responses across species and geographic regions. We use a database of citizen science bird observations to explore spatiotemporal variation in mean arrival dates across an unprecedented geographic extent for 18 common species in North America over the past decade, relating arrival dates to mean minimum spring temperature. Across all species and geographic locations, species shifted arrival dates 0.8 days earlier for every °C of warming of spring temperature, but it was common for some species in some locations to shift as much as 3–6 days earlier per °C. Species that advanced arrival dates the earliest in response to warming were those that migrate more slowly, short distance migrants, and species with broader climatic niches. These three variables explained 63% of the interspecific variation in phenological response. We also identify a latitudinal gradient in the average strength of phenological response, with species shifting arrival earlier at southern latitudes than northern latitudes for the same degree of warming. This observation is consistent with the idea that species must be more phenologically sensitive in less seasonal environments to maintain the same degree of precision in phenological timing

A model of increased temperature sensitivity in low seasonality environments.

<p>Seasonal variation in average monthly temperatures from January to June in Atlanta (solid) and Montreal (dashed) based on long term averages from weather.com (black) and under a seasonally uniform warming scenario of +2°C (gray). Dotted lines indicate the predicted arrival dates of a hypothetical species that based its arrival on an average temperature of 19°C under each of the four scenarios. The same degree of warming would result in a greater shift in arrival date in Atlanta.</p

Explaining interspecific variation in phenological response.

<p>(A) Mean arrival date (averaged over both year and longitude) as a function of latitude for 18 bird species, depicting the rate at which various species advance northward during migration. (B) Boxplots showing the variation in the slope of the trend in arrival date with minimum spring temperature for each species, with more negative values reflecting earlier arrival. +, p<0.10; *, p<0.05; **, p<0.01. (C) Relationship between migration time (from (A)) and the median phenological response of arrival date to temperature. (D) Residuals of the phenological response to temperature after controlling for migration time and migration distance as a function of niche breadth. Species codes are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031662#pone-0031662-t001" target="_blank">Table 1</a>.</p

Geographical variation in the community-level phenological response.

<p>Mean shift in arrival date per °C change in minimum spring temperature for all grid cells with at least two species trends.</p

Most supported models explaining interspecific variation in shifts in arrival date in response to temperature change.

<p>Top 5 models out of 63 as ranked by AIC_c, including model weights and relative importance weights of each of the 6 variables considered. The variable importance weights represent the sum of the model weights for all models in which a particular variable is entered (Burnham and Anderson 2002). na, not applicable.</p

The species analyzed in this study, along with species abbreviations, migration class, foraging guild, number of lat-long blocks analysed, and the median slope of mean arrival date (MAD) as a function of minimum spring temperature over all lat-long blocks.

1<p>Technically, all of these species may be considered Neotropical migrants, but here we define those that winter at least partially in the U.S. as short distance migrants.</p>2<p>A - aerial insectivore, F - foliage gleaner, G - ground gleaner.</p

Geographic variation in phenological response and example trajectories of temperature and arrival date.

<p>Geographic variation in the mean shift in arrival date per °C change in minimum spring temperature for four bird species (right-hand column). The left-hand column depicts changes in both minimum spring temperature (solid line) and arrival date (dashed line) through time for one example region (indicated by arrow) for each species. Note that the arrival date axis increases towards the bottom. Photo credits: red-eyed vireo, Dario Sanches; scarlet tanager, Steve Maslowski; great-crested flycatcher, Matt Ward; indigo bunting, Kevin Bolton.</p