958 research outputs found
A comparison of the growth kinetics of six marine heterotrophic nanoflagellates fed with one bacterial species.
Animal suffering calls for more than a bigger cage
Ng (2016) argues for incremental welfare biology partly because it would be impossible to demonstrate conclusively that animals are sentient. He argues that low cost changes in industrial practices and working collaboratively may be more effective in advancing animal welfare than more adversarial approaches. There is merit in some of Ng’s recommendations but a number of his arguments are, in my view, misdirected. The fact that nonhuman animals feel has already been adequately demonstrated. Cruelty to animals is intrinsic to some industries, so the only way to oppose it is to oppose the industry
Semiclassical description of resonant tunneling
We derive a semiclassical formula for the tunneling current of electrons
trapped in a potential well which can tunnel into and across a wide quantum
well. The calculations idealize an experimental situation where a strong
magnetic field tilted with respect to an electric field is used. The resulting
semiclassical expression is written as the sum over special periodic orbits
which hit both walls of the quantum well and are perpendicular to the first
wall.Comment: LaTeX, 8 page
Filter-feeding, near-field flows, and the morphologies of colonial choanoflagellates
Efficient uptake of prey and nutrients from the environment is an important component in the fitness of all microorganisms, and its dependence on size may reveal clues to the origins of evolutionary transitions to multicellularity. Because potential benefits in uptake rates must be viewed in the context of other costs and benefits of size, such as varying predation rates and the increased metabolic costs associated with larger and more complex body plans, the uptake rate itself is not necessarily that which is optimized by evolution. Uptake rates can be strongly dependent on local organism geometry and its swimming speed, providing selective pressure for particular arrangements. Here we examine these issues for choanoflagellates, filter-feeding microorganisms that are the closest relatives of the animals. We explore the different morphological variations of the choanoflagellate , which can exist as a swimming cell, as a sessile thecate cell, and as colonies of cells in various shapes. In the absence of other requirements and in a homogeneously nutritious environment, we find that the optimal strategy to maximize filter-feeding by the collar of microvilli is to swim fast, which favors swimming unicells. In large external flows, the sessile thecate cell becomes advantageous. Effects of prey diffusion are discussed and also found to be to the advantage of the swimming unicell.This work was supported in part by the Engineering and Physical Sciences Research Council and St. Johns College (J.B.K.) and Wellcome Trust Senior Investigator Award 097855MA (R.E.G.)
Magnetic Quantum Dot: A Magnetic Transmission Barrier and Resonator
We study the ballistic edge-channel transport in quantum wires with a
magnetic quantum dot, which is formed by two different magnetic fields B^* and
B_0 inside and outside the dot, respectively. We find that the electron states
located near the dot and the scattering of edge channels by the dot strongly
depend on whether B^* is parallel or antiparallel to B_0. For parallel fields,
two-terminal conductance as a function of channel energy is quantized except
for resonances, while, for antiparallel fields, it is not quantized and all
channels can be completely reflected in some energy ranges. All these features
are attributed to the characteristic magnetic confinements caused by nonuniform
fields.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
Phonon-mediated thermal conductance of mesoscopic wires with rough edges
We present an analysis of acoustic phonon propagation through long,
free-standing, insulating wires with rough surfaces. Due to a crossover from
ballistic propagation of the lowest-frequency phonon mode at to a diffusive (or even localized) behavior upon the increase of
phonon frequency, followed by re-entrance into the quasi-ballistic regime, the
heat conductance of a wire acquires an intermediate tendency to saturate within
the temperature range .Comment: 4 pages, 3 figures included; minor changes and corrections, figures 1
and 2 replaced by better versions; to appear in PRB Brief Report
Unbroken supersymmetry in the Aharonov-Casher effect
We consider the problem of the bound states of a spin 1/2 chargless particle
in a given Aharonov-Casher configuration. To this end we recast the description
of the system in a supersymmetric form. Then the basic physical requirements
for unbroken supersymmetry are established. We comment on the possibility of
neutron confinement in this system
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