Short-range hunters: exploring the function and constraints of water shooting in dwarf gouramis

Ballistic predation is a rare foraging adaptation: in fishes, most attention has focused on a single genus, the archerfish, known to manipulate water to shoot down prey above the water surface. However, several gourami species also exhibit apparently similar ‘shooting’ behaviour, spitting water up to 5 cm above the surface. In a series of experiments, we explored the shooting behaviour and aspects of its significance as a foraging ability in the dwarf gourami (Trichogaster lalius). We investigated sex differences in shooting abilities to determine whether gourami shooting is related to the sex-specific bubble nest manufacture where males mix air and water at the surface to form bubbles. We found that, actually, both sexes were equally able to shoot and could learn to shoot a novel target. In a second experiment, we presented untrained gouramis with opportunities to shoot at live prey and found they successfully shot down both fruit flies and crickets. Finally, we explored the effect of target height on shooting performance to establish potential constraints of shooting as a foraging ability. The frequency of attempted shots and success of hitting targets decreased with height, whereas latency to shoot increased. We also observed that repeatable individual differences account for variation in these measures of shooting performance. Together, our results provide evidence that gourami shooting has a foraging function analogous to that of archerfish. Gourami shooting may serve as an example of convergent evolution and provide opportunities for comparative studies into the, as yet unexplored, ecology and evolution of shooting in fishes.Peer reviewe

Spin polarization and spin-dependent scattering of holes observed in transverse magnetic focusing

In two-dimensional systems with a spin-orbit interaction, magnetic focusing can be used to create a spatial separation of particles with different spin. Here we measure hole magnetic focusing for two different magnitudes of the Rashba spin-orbit interaction. We find that when the Rashba spin-orbit magnitude is large there is significant attenuation of one of the focusing peaks, which is conventionally associated with a change in the spin polarization. We instead show that in hole systems with a k3 spin-orbit interaction, this peak suppression is due to a change in the scattering of one spin state, not a change in spin polarization. We also show that the change in scattering length extracted from magnetic focusing is consistent with results obtained from measurements of Shubnikov-de Haas oscillations. This result suggests that scattering must be considered when relating focusing peak amplitude to spin polarization in hole systems

On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

The Rate-equation for Biogenic Silica Dissolution in Seawater – New Hypotheses

This paper investigates the kinetics of biogenic silica dissolution in seawater, through batch dissolution, where the reaction is observed as the increase in dissolved silicic acid concentration with time. It utilises new data from dissolution of the marine diatom Cyclotella cryptica, and the freshwater diatom C. meneghiniana, as well as literature results. The sum of exponentials form:, is hypothesised as the most general rate equation, with the single exponential form occurring in a minority of cases. The consistency of this behaviour with a near-exponential decay of surface area with time, an appropriate mathematical integration, and surface heterogeneity, is discussed. (Serious errors in some existing integrations are identified.) The rate of dissolution at constant surface area is shown to decrease non-linearly as the ambient concentration of silicic acid increases. A fractional order with respect to silicic acid in the back reaction, close to 0.5, leads to a mechanism in which an intermediate is formed from the surface and an, as yet, unidentified molecule, probably water. Good preliminary fits are found between the model and literature results found using entirely different methods. A parallel treatment of hydrogen ion dependency is suggested. The likely distortion of full reaction curves from exponential behaviour imposed by the back reaction, is considered in detail. [KEYWORDS: biogenic silica ; dissolution kinetics ; diatom frustules ; silica cycling]

Cultural Transmission

The term “cultural transmission” is widely and often imprecisely used in the scientific literature to refer to various forms and outcomes of social learning. This entry considers cultural transmission to refer to the specific forms of social transmission where knowledge is passed between individuals, through some form of social learning, resulting in persistent increases in behavioral homogeneity in a population or group. In this way, cultural transmission allows different populations or groups of animals to show distinct differences in behavior. As described in the social learning section (“Social Learning”), social transmission occurs when the performance of a behavior by one individual (directly or indirectly) causes a lasting influence on the rate at which a second individual acquires and or performs that same behavior. While social transmission can allow behaviors or knowledge to persist at individual level, only those behaviors or knowledge which persist long enoug

In vitro, batch-dissolution of biogenic silica in seawater – the application of recent modelling to real data

Abstract Both for straight-forward oceanographic needs as well as application to climate-change amelioration, there is a need for quantitative description of the spatial and temporal variability in the recycled flux of silicic acid in the ocean water column in terms of governing processes. As part of that, the need for a fuller chemical kinetics treatment of biogenic silica dissolution, involving laboratory rate measurements, rate equations and mechanisms, is stressed. Advantage is taken of recent modell [KEYWORDS: Silica dissolution ; Biogenic silica ; In vitro dissolution ; Chemical kinetics ; Batch dissolutions ; Mineral dissolution]

Toward an understanding of biogenic-silica dissolution in seawater – An initial rate approach applied between 40 and 90°C

The kinetics of phytoplankton frustule dissolution has generally been studied as the appearance of silicic acid in a batch reactor. Unfortunately, this approach, though often illuminating, has not so far been successful because of the difficulty of parameterising the full reaction curve. This current study shows how the initial rate approach to chemical kinetics offers a way around this bottleneck, thereby allowing much chemical kinetics information about frustule dissolution to be collected. The technique is shown to be flexible and suited to short reaction times which facilitate detailed quantitative kinetics investigation, indeed, as would be expected in a solution phase, kinetics study. The technique is exemplified by a dissolution study of uncleaned frustules of Cyclotella crypticaat 40°C and above. The frustules were found to yield the same dissolution rate after 5weeks dark storage, at 4°C. Meanwhile, log dissolution rate was found to vary linearly with pH, with gradient 0.38±0.01 (r2=0.990). Linearity was upheld even at pHs as high as 14. Finally, a robust Arrhenius plot was established between 40 and 90°C yielding an activation energy for dissolution of 84±3kJmol–1. Follow through with the Eyring equation yielded an activation enthalpy, H, and an activation entropy, S, of 81 and 85Jmol–1K–1, respectively. The discussion brings salient aspects of existing knowledge about diatom frustule dissolution kinetics into the wider context of silicate mineral dissolution. [KEYWORDS: biogenic silica ; dissolution kinetics ; initial rate]