10,113 research outputs found
Prepontine non-giant neurons drive flexible escape behavior in zebrafish
Many species execute ballistic escape reactions to avoid imminent danger. Despite fast reaction times, responses are often highly regulated, reflecting a trade-off between costly motor actions and perceived threat level. However, how sensory cues are integrated within premotor escape circuits remains poorly understood. Here, we show that in zebrafish, less precipitous threats elicit a delayed escape, characterized by flexible trajectories, which are driven by a cluster of 38 prepontine neurons that are completely separate from the fast escape pathway. Whereas neurons that initiate rapid escapes receive direct auditory input and drive motor neurons, input and output pathways for delayed escapes are indirect, facilitating integration of cross-modal sensory information. These results show that rapid decision-making in the escape system is enabled by parallel pathways for ballistic responses and flexible delayed actions and defines a neuronal substrate for hierarchical choice in the vertebrate nervous system
Industrial wastewater treatment using hydrodynamic cavitation and heterogeneous advanced Fenton processing
A combination of hydrodynamic cavitation and heterogeneous advanced Fenton process (AFP) based on the use of zero valent iron as the catalyst has been investigated for the treatment of real industrial wastewater. The effect of various operating parameters such as inlet pressure, temperature, and the presence of copper windings on the extent of mineralization as measured by total organic carbon (TOC) content have been studied with the aim of maximizing the extent of degradation. It has been observed that increased pressures, higher operating temperature and the absence of copper windings are more favourable for a rapid TOC mineralization. A new approach of latent remediation has also been investigated where hydrodynamic cavitation is only used as a pre-treatment with an aim of reducing the overall cost of pollutant degradation. It has been observed that approach of latent remediation works quite well with about 50–60% removal of TOC using only minimal initial treatment by hydrodynamic cavitation
Intensification of hydroxyl radical production in sonochemical reactors
The efficacy of sonochemical reactors in chemical processing applications has been well established in the laboratory scale of operation though at a given set of operating parameters and no efforts have been directed in terms of maximizing the free radical production. In the present work, the effect of different operating parameters viz. pH, power dissipation into the system, effect of additives such as air, haloalkanes, titanium dioxide, iron and oxygen on the extent of hydroxyl radical formation in a sonochemical reactor have been investigated using salicylic acid dosimetry. Possible mechanisms for oxidation of salicylic acid in the presence of different additives have also been established. It has been observed that acidic conditions under optimized power dissipation in the presence of iron powder and oxygen result in maximum liberation of hydroxyl radicals as quantified by the kinetic rate constant for production of 2,5- and 2,3-dihydroxybenzoic acid. The study has enabled the optimization of the conditions for maximum efficacy of sonochemical reactors where free radical attack is the controlling mechanism for the chemical processing applications
The high partial wave phenomenon of spin changing atomic transitions
The collisional transition between two highly excited atomic states with different spin is investigated theoretically. Taking helium-like n1S − n3P as an example, it is found that the transition is driven in the highly ion-ized Fe ion purely by exchange, and the cross section becomes increasingly dominated by partial waves of high orbital angular momentum as the scattering energy increases. Whereas for the near-neutral Li ion the transition is dominated by channel coupling in low partial waves. Analytical bench-marks and numerical methods are developed for the accurate calculation of the exchange integral at high angular momentum. It is shown how the partial wave and energy dependence of the collision strength for high n spin changing transitions in the highly ionized ion is related to the overlap of the extended atomic orbitals.</p
Assessing reference conditions and ecological status for lakes using subfossil diatoms
This is the final report to the Environment Agency under an extension to the project, ‘Development of a phytobenthos classification tool for lakes and lochs of UK (DALES– Diatom Assessment of lake and loch ecological status)’ (contract no. SC030103), funded by the Environment Agency (EA).This project forms part of the strategy for the implementation of the European Council Water Framework Directive (WFD), which requires reference conditions to be determined for all water body types including lakes
Quasiperpendicular high Mach number Shocks
Shock waves exist throughout the universe and are fundamental to
understanding the nature of collisionless plasmas. Reformation is a process,
driven by microphysics, which typically occurs at high Mach number
supercritical shocks. While ongoing studies have investigated this process
extensively both theoretically and via simulations, their observations remain
few and far between. In this letter we present a study of very high Mach number
shocks in a parameter space that has been poorly explored and we identify
reformation using in situ magnetic field observations from the Cassini
spacecraft at 10 AU. This has given us an insight into quasi-perpendicular
shocks across two orders of magnitude in Alfven Mach number (MA) which could
potentially bridge the gap between modest terrestrial shocks and more exotic
astrophysical shocks. For the first time, we show evidence for cyclic
reformation controlled by specular ion reflection occurring at the predicted
timescale of ~0.3 {\tau}c, where {\tau}c is the ion gyroperiod. In addition, we
experimentally reveal the relationship between reformation and MA and focus on
the magnetic structure of such shocks to further show that for the same MA, a
reforming shock exhibits stronger magnetic field amplification than a shock
that is not reforming.Comment: Accepted and Published in Physical Review Letters (2015
Effective Actions, Boundaries and Precision Calculations of Casimir Energies
We perform the matching required to compute the leading effective boundary
contribution to the QED lagrangian in the presence of a conducting surface,
once the electron is integrated out. Our result resolves a confusion in the
literature concerning the interpretation of the leading such correction to the
Casimir energy. It also provides a useful theoretical laboratory for
brane-world calculations in which kinetic terms are generated on the brane,
since a lot is known about QED near boundaries.Comment: 5 pages. revtex; Added paragraphs describing finite-conductivity
effects and effects due to curvatur
Color, Spin and Flavor Diffusion in Quark-Gluon Plasmas
In weakly interacting quark-gluon plasmas diffusion of color is found to be
much slower than the diffusion of spin and flavor because color is easily
exchanged by the gluons in the very singular forward scattering processes. If
the infrared divergence is cut off by a magnetic mass, ,
the color diffusion is , a
factor smaller than spin and flavor diffusion. A similar effect is
expected in electroweak plasmas above due to exchanges. The color
conductivity in quark-gluon plasmas and the electrical conductivity in
electroweak plasmas are correspondingly small in relativistic heavy ion
collisions and the very early universe.Comment: 5 pages, no figure
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