558 research outputs found
Entangled Quantum States of Magnetic Dipoles
Free magnetic moments usually manifest themselves in Curie Laws, where weak
external magnetic fields produce magnetizations diverging as the reciprocal 1/T
of the temperature. for a variety of materials that do not disply static
magnetism, including doped semiconductors and certain rare earth
intermetallics, the 1/T law is changed to a power law T^-a with a<1. We report
here that a considerably simpler material, namely an insulating magneticsalt
can also display such a power law, and show via comparison to specific heat
data and numerical simulations that quantum mechanics is crucial for its
formation. Two quantum mechanical phenomena are needed, namely level splitting
- which affects the spectrum of excited states - and entanglement - where the
wavefunction of a system with several degrees of freedom cannot be written as a
product of wavefunctions for each degree of freedom. Entanglement effects
become visible for remarkably small tunnelling terms, and are turned on well
before tunnelling has visible effects on the spectrum. Our work is significant
because it illustrates that entanglement is at the very heart of a very simple
experimental observation for an insulating quantum spin system.Comment: 17 pages, 4 figure
Intrinsic activity in the fly brain gates visual information during behavioral choices
The small insect brain is often described as an input/output system that executes reflex-like behaviors. It can also initiate neural activity and behaviors intrinsically, seen as spontaneous behaviors, different arousal states and sleep. However, less is known about how intrinsic activity in neural circuits affects sensory information processing in the insect brain and variability in behavior. Here, by simultaneously monitoring Drosophila's behavioral choices and brain activity in a flight simulator system, we identify intrinsic activity that is associated with the act of selecting between visual stimuli. We recorded neural output (multiunit action potentials and local field potentials) in the left and right optic lobes of a tethered flying Drosophila, while its attempts to follow visual motion (yaw torque) were measured by a torque meter. We show that when facing competing motion stimuli on its left and right, Drosophila typically generate large torque responses that flip from side to side. The delayed onset (0.1-1 s) and spontaneous switch-like dynamics of these responses, and the fact that the flies sometimes oppose the stimuli by flying straight, make this behavior different from the classic steering reflexes. Drosophila, thus, seem to choose one stimulus at a time and attempt to rotate toward its direction. With this behavior, the neural output of the optic lobes alternates; being augmented on the side chosen for body rotation and suppressed on the opposite side, even though the visual input to the fly eyes stays the same. Thus, the flow of information from the fly eyes is gated intrinsically. Such modulation can be noise-induced or intentional; with one possibility being that the fly brain highlights chosen information while ignoring the irrelevant, similar to what we know to occur in higher animals
Design principles for riboswitch function
Scientific and technological advances that enable the tuning of integrated regulatory components to match network and system requirements are critical to reliably control the function of biological systems. RNA provides a promising building block for the construction of tunable regulatory components based on its rich regulatory capacity and our current understanding of the sequence–function relationship. One prominent example of RNA-based regulatory components is riboswitches, genetic elements that mediate ligand control of gene expression through diverse regulatory mechanisms. While characterization of natural and synthetic riboswitches has revealed that riboswitch function can be modulated through sequence alteration, no quantitative frameworks exist to investigate or guide riboswitch tuning. Here, we combined mathematical modeling and experimental approaches to investigate the relationship between riboswitch function and performance. Model results demonstrated that the competition between reversible and irreversible rate constants dictates performance for different regulatory mechanisms. We also found that practical system restrictions, such as an upper limit on ligand concentration, can significantly alter the requirements for riboswitch performance, necessitating alternative tuning strategies. Previous experimental data for natural and synthetic riboswitches as well as experiments conducted in this work support model predictions. From our results, we developed a set of general design principles for synthetic riboswitches. Our results also provide a foundation from which to investigate how natural riboswitches are tuned to meet systems-level regulatory demands
Numerical instability of the Akhmediev breather and a finite-gap model of it
In this paper we study the numerical instabilities of the NLS Akhmediev
breather, the simplest space periodic, one-mode perturbation of the unstable
background, limiting our considerations to the simplest case of one unstable
mode. In agreement with recent theoretical findings of the authors, in the
situation in which the round-off errors are negligible with respect to the
perturbations due to the discrete scheme used in the numerical experiments, the
split-step Fourier method (SSFM), the numerical output is well-described by a
suitable genus 2 finite-gap solution of NLS. This solution can be written in
terms of different elementary functions in different time regions and,
ultimately, it shows an exact recurrence of rogue waves described, at each
appearance, by the Akhmediev breather. We discover a remarkable empirical
formula connecting the recurrence time with the number of time steps used in
the SSFM and, via our recent theoretical findings, we establish that the SSFM
opens up a vertical unstable gap whose length can be computed with high
accuracy, and is proportional to the inverse of the square of the number of
time steps used in the SSFM. This neat picture essentially changes when the
round-off error is sufficiently large. Indeed experiments in standard double
precision show serious instabilities in both the periods and phases of the
recurrence. In contrast with it, as predicted by the theory, replacing the
exact Akhmediev Cauchy datum by its first harmonic approximation, we only
slightly modify the numerical output. Let us also remark, that the first rogue
wave appearance is completely stable in all experiments and is in perfect
agreement with the Akhmediev formula and with the theoretical prediction in
terms of the Cauchy data.Comment: 27 pages, 8 figures, Formula (30) at page 11 was corrected, arXiv
admin note: text overlap with arXiv:1707.0565
Grouping practices in the primary school: what influences change?
During the 1990s, there was considerable emphasis on promoting particular kinds of pupil grouping as a means of raising educational standards. This survey of 2000 primary schools explored the extent to which schools had changed their grouping practices in responses to this, the nature of the changes made and the reasons for those changes. Forty eight percent of responding schools reported that they had made no change. Twenty two percent reported changes because of the literacy hour, 2% because of the numeracy hour, 7% because of a combination of these and 21% for other reasons. Important influences on decisions about the types of grouping adopted were related to pupil learning and differentiation, teaching, the implementation of the national literacy strategy, practical issues and school self-evaluation
Lambda and Antilambda polarization from deep inelastic muon scattering
We report results of the first measurements of Lambda and Antilambda
polarization produced in deep inelastic polarized muon scattering on the
nucleon. The results are consistent with an expected trend towards positive
polarization with increasing x_F. The polarizations of Lambda and Antilambda
appear to have opposite signs. A large negative polarization for Lambda at low
positive x_F is observed and is not explained by existing models.A possible
interpretation is presented.Comment: 9 pages, 2 figure
Change in First Graders’ Science-Related Competence Beliefs During Digitally Intensive Science Workshops
The aim of this research was to examine if a set of three science and technology workshops would promote first-grade pupils’ science-related competence beliefs. The first workshop dealt with electric circuits and related handicraft tasks. The second workshop involved programming with Lego Mindstorms robots. The third workshop was related to computer-based data logging. Fifty-nine Finnish first graders (age 7–8 years) participated in the digitally intensive science workshops, and 38 pupils served as a control group. The data were analysed using a paired samples t-test. The analysis results reveal that the set of three workshops increased the pupils’ science and technology-related competence beliefs.Peer reviewe
Large-Range Movements of Neotropical Orchid Bees Observed via Radio Telemetry
Neotropical orchid bees (Euglossini) are often cited as classic examples of trapline-foragers with potentially extensive foraging ranges. If long-distance movements are habitual, rare plants in widely scattered locations may benefit from euglossine pollination services. Here we report the first successful use of micro radio telemetry to track the movement of an insect pollinator in a complex and forested environment. Our results indicate that individual male orchid bees (Exaerete frontalis) habitually use large rainforest areas (at least 42–115 ha) on a daily basis. Aerial telemetry located individuals up to 5 km away from their core areas, and bees were often stationary, for variable periods, between flights to successive localities. These data suggest a higher degree of site fidelity than what may be expected in a free living male bee, and has implications for our understanding of biological activity patterns and the evolution of forest pollinators
Natural polymorphisms in C. elegans HECW-1 E3 ligase affect pathogen avoidance behaviour
available in PMC 2012 June 22.Heritable variation in behavioural traits generally has a complex genetic basis1, and thus naturally
occurring polymorphisms that influence behaviour have been defined in only rare instances2,3.
The isolation of wild strains of Caenorhabditis elegans has facilitated the study of natural genetic
variation in this species4 and provided insights into its diverse microbial ecology5. C. elegans
responds to bacterial infection with conserved innate immune responses6-8 and, while lacking the
immunological memory of vertebrate adaptive immunity, exhibits an aversive learning response to
pathogenic bacteria9. Here, we report the molecular characterization of naturally occurring coding
polymorphisms in a C. elegans gene encoding a conserved HECT domain-containing E3 ubiquitin
ligase, HECW-1. We show that two distinct polymorphisms in neighbouring residues of HECW-1
each affect C. elegans behavioural avoidance of a lawn of Pseudomonas aeruginosa. Neuronspecific
rescue and ablation experiments, and genetic interaction analysis suggest that HECW-1
functions in a pair of sensory neurons to inhibit P. aeruginosa lawn avoidance behaviour through
inhibition of the neuropeptide receptor NPR-110, which we have previously shown promotes P.
aeruginosa lawn avoidance behaviour11. Our data establish a molecular basis for natural variation
in a C. elegans behaviour that may undergo adaptive changes in response to microbial pathogens.National Institutes of Health (U.S.) (NIH Grant GM084477
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