8,246 research outputs found
Anderson localization of pairs in bichromatic optical lattices
We investigate the formation of bound states made of two interacting atoms
moving in a one dimensional (1D) quasi-periodic optical lattice. We derive the
quantum phase diagram for Anderson localization of both attractively and
repulsively bound pairs. We calculate the pair binding energy and show
analytically that its behavior as a function of the interaction strength
depends crucially on the nature -extended, multi-fractal, localized- of the
single-particle atomic states. Experimental implications of our results are
discussed.Comment: final revised version with more explanations, 4 pages, 3 figure
Ligula intestinalis (Cestoda: Pseudophyllidea): an ideal fish-metazoan parasite model?
Since its use as a model to study metazoan parasite culture and in vitro development, the plerocercoid of the tapeworm, Ligula intestinalis, has served as a useful scientific tool to study a range of biological factors, particularly within its fish intermediate host. From the extensive long-term ecological studies on the interactions between the parasite and cyprinid hosts, to the recent advances made using molecular technology on parasite diversity and speciation, studies on the parasite have, over the last 60 years, led to significant advances in knowledge on host-parasite interactions. The parasite has served as a useful model to study pollution, immunology and parasite ecology and genetics, as well has being the archetypal endocrine disruptor
Stability control of nonlinear micromechanical resonators under simultaneous primary and superharmonic resonances
Fast effects of a slow excitation on the main resonance of a nonlinear micromechanical resonator are analytically and experimentally investigated. We show, in particular, how the bifurcation topology of an undesirable unstable behavior is modified when the resonator is simultaneously actuated at its primary and superharmonic resonances. A stabilization mechanism is proposed and demonstrated by increasing the superharmonic excitation
âNext-Generationâ surveillance: an epidemiologistsâ perspective on the use of molecular information in food safety and animal health decision-making
Advances in the availability and affordability of molecular and genomic data are transforming human health care. Surveillance aimed at supporting and improving food safety and animal health is likely to undergo a similar transformation. We propose a definition of âmolecular surveillanceâ in this context and argue that molecular data are an adjunct to rather than a substitute for sound epidemiological study and surveillance design. Specific considerations with regard to sample collection are raised, as is the importance of the relation between the molecular clock speed of genetic markers and the spatiotemporal scale of the surveillance activity, which can be control- or strategy-focused. Development of standards for study design and assessment of molecular surveillance system attributes is needed, together with development of an interdisciplinary skills base covering both molecular and epidemiological principles
Limits of feedback control in bacterial chemotaxis
Inputs to signaling pathways can have complex statistics that depend on the
environment and on the behavioral response to previous stimuli. Such behavioral
feedback is particularly important in navigation. Successful navigation relies
on proper coupling between sensors, which gather information during motion, and
actuators, which control behavior. Because reorientation conditions future
inputs, behavioral feedback can place sensors and actuators in an operational
regime different from the resting state. How then can organisms maintain proper
information transfer through the pathway while navigating diverse environments?
In bacterial chemotaxis, robust performance is often attributed to the zero
integral feedback control of the sensor, which guarantees that activity returns
to resting state when the input remains constant. While this property provides
sensitivity over a wide range of signal intensities, it remains unclear how
other parameters affect chemotactic performance, especially when considering
that the swimming behavior of the cell determines the input signal. Using
analytical models and simulations that incorporate recent experimental
evidences about behavioral feedback and flagellar motor adaptation we identify
an operational regime of the pathway that maximizes drift velocity for various
environments and sensor adaptation rates. This optimal regime is outside the
dynamic range of the motor response, but maximizes the contrast between run
duration up and down gradients. In steep gradients, the feedback from
chemotactic drift can push the system through a bifurcation. This creates a
non-chemotactic state that traps cells unless the motor is allowed to adapt.
Although motor adaptation helps, we find that as the strength of the feedback
increases individual phenotypes cannot maintain the optimal operational regime
in all environments, suggesting that diversity could be beneficial.Comment: Corrected one typo. First two authors contributed equally. Notably,
there were various typos in the values of the parameters in the model of
motor adaptation. The results remain unchange
Quantum ballistic experiment on antihydrogen fall
We study an interferometric approach to measure gravitational mass of
antihydrogen. The method consists of preparing a coherent superposition of
antihydrogen quantum state localized near a material surface in the
gravitational field of the Earth, and then observing the time distribution of
annihilation events followed after the free fall of an initially prepared
superposition from a given height to the detector plate. We show that a
corresponding time distribution is related to the momentum distribution in the
initial state that allows its precise measurement. This approach is combined
with a method of production of a coherent superposition of gravitational states
by inducing a resonant transition using oscillating gradient magnetic field. We
estimate an accuracy of measuring the gravitational mass of antihydrogen atom
which could be deduced from such a measurement.Comment: arXiv admin note: text overlap with arXiv:1403.478
Casimir-Polder shifts on quantum levitation states
An ultracold atom above a horizontal mirror experiences quantum reflection
from the attractive Casimir-Polder interaction, which holds it against gravity
and leads to quantum levitation states. We analyze this system by using a
Liouville transformation of the Schr\"odinger equation and a Langer coordinate
adapted to problems with a classical turning point. Reflection on the
Casimir-Polder attractive well is replaced by reflection on a repulsive wall
and the problem is then viewed as an ultracold atom trapped inside a cavity
with gravity and Casimir-Polder potentials acting respectively as top and
bottom mirrors. We calculate numerically Casimir-Polder shifts of the energies
of the cavity resonances and propose a new approximate treatment which is
precise enough to discuss spectroscopy experiments aiming at tests of the weak
equivalence principle on antihydrogen. We also discuss the lifetimes by
calculating complex energies associated with cavity resonances.Comment: Accepted in PR
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