Grazing by the Copepod Parvocalanus crassirostris on Picochlorum sp. at Harmful Bloom Densities and the Role of Particle Size

Harmful blooms of nanophytoplankton (2–20 μm) are increasingly common and sometimes severe, but requirements and controls of such blooms (e.g., water quality constraints, requirements for nutrients, and the presence of different guilds of grazers) are poorly understood. Laboratory grazing experiments were conducted to evaluate the potential for top-down control by the copepod Parvocalanus crassirostris on a small harmful algal species (an unidentified chlorophyte Picochlorum, 1–4 μm) and to test the effects of cell sizes on grazing rates. The Picochlorum sp. is a strain isolated from a long-lasting harmful algal bloom in the Indian River Lagoon that reached high densities (>1 × 106 cells ml–1). Experiments contrasted grazing on Picochlorum sp. with grazing on the palatable prymnesiophyte Isochrysis galbana (4–6 μm) in monocultures and mixed cultures. When presented in monocultures, grazing rates on Picochlorum sp. were lower than grazing rates on the palatable alternative. When Picochlorum sp. were presented alongside I. galbana, copepods essentially ceased feeding on the former. In additional experiments, P. crassirostris were fed plastic beads with diameters of 2.0–17.9 μm to control for differences in taste, toxicity, production of mucilage and shape of potential food. Paracalanus crassirostris fed most efficiently on beads with diameters of 7.0–7.9 μm. Results revealed that P. crassirostris can consume Picochlorum sp., but small size and the presence of palatable cells reduces the likelihood of top-down control of blooms of Picochlorum sp.

A conceptual framework of drought legacies in grasslands

<p>As a consequence of climate change, extreme climatic events such as droughts will become more frequent and severe, affecting ecosystem structure and functioning, with implications for humans and society. While concurrent effects of drought events are comparatively well studied, the short- and longer-term changes in ecosystem structure and functioning triggered by drought (i.e. drought legacies) are far less understood. Furthermore, it has rarely been analysed how drought legacies alter the resistance to and recovery from subsequent drought events. To assess the overall impact of drought events on ecosystems and emerging cascading effects on societies, we need to advance the understanding of drought legacies and their long-lasting impacts on ecosystems. Based on a review of the literature on above- and belowground mechanisms underlying drought legacies in grasslands, we propose a conceptual framework, which identifies the factors determining the shape of potential legacy trajectories during recovery and post-recovery phases and synthesize the mechanisms leading to legacy responses to subsequent drought events.</p>

The Noether–Bessel-Hagen symmetry approach for dynamical systems

The Noether–Bessel-Hagen theorem can be considered a natural extension of Noether Theorem to search for symmetries. Here, we develop the approach for dynamical systems introducing the basic foundations of the method. Specifically, we establish the Noether–Bessel-Hagen analysis of mechanical systems where external forces are present. In the second part of the paper, the approach is adopted to select symmetries for a given systems. In particular, we focus on the case of harmonic oscillator as a testbed for the theory, and on a cosmological system derived from scalar–tensor gravity with unknown scalar-field potential [Formula: see text]. We show that the shape of potential is selected by the presence of symmetries. The approach results particularly useful as soon as the Lagrangian of a given system is not immediately identifiable or it is not a Lagrangian system.

DIRAC QUASINORMAL MODES OF CHARGED BRANEWORLD BLACK HOLE

We study the quasinormal modes (QNMs) of charged braneworld black hole, which carry two types of "charge". In this paper, the six-order Wentzel–Kramers–Brillouin (WKB) approximation is applied to calculate the quasinormal frequencies (QNF), and then two types of charges affecting the shape of potential function, and oscillation frequency increases with increasing β while the damping of QMNs is slower as β is smaller.

ACCELERATION OF DIFFUSION IN SUBCRITICALLY TILTED PERIODIC POTENTIALS

We study the enhancement of effective diffusion coefficient of an overdamped Brownian particle in tilted periodical potential profile. For analysis we use the model piece-wise linear potential, where independent variation of the potential profile parameters (such as height and width of potential barriers, width of potential wells and period of potential profile) is possible. This approach allows to investigate the influence of potential profile shape on the conditions for the diffusion acceleration, maximal value of the diffusion coefficient, values of noise intensity and the tilt for which the maximum occurs. For the large barriers and subcritical tilt the results are generalized for arbitrary shape of potential profile.

2-D resistivity modeling: An approach to arrays parallel to the strike direction

An algorithm for two‐dimensional electrical resistivity modeling using the finite‐element method with mixed boundary conditions can calculate the electrical potential along any arbitrary direction. In the particular case of the direction parallel to the strike of the structure, a numerical singularity occurs. We resolved it by calculating the potential near the singularity and improving the involved interpolation of the transformed potential. Investigating the shape of potential in the Fourier transformed space, we conclude that this interpolation may combine logarithmic and exponential functions.