926 research outputs found
The development of adaptive conformity in young children : effects of uncertainty and consensus
Human culture relies on extensive use of social transmission, which must be integrated with independently acquired (i.e. asocial) information for effective decision-making. Formal evolutionary theory predicts that natural selection should favor adaptive learning strategies, including a bias to copy when uncertain, and a bias to disproportionately copy the majority (known as conformist transmission'). Although the function and causation of these evolved strategies has been comparatively well studied, little is known of their development. We experimentally investigated the development of the bias to copy-when-uncertain and conformist transmission in children from the ages of 3 to 7, testing predictions derived from theoretical models. Children first attempted to solve a binary-choice quantity discrimination task themselves using asocial information, but were then given the decisions of informants, and an opportunity to revise their answer. We investigated whether children's revised judgments were adaptively contingent on (i) the difficulty of the trial and (ii) the degree of consensus amongst informants. As predicted, older but not younger children copied others more on more difficult trials than on easier trials, even though older children also showed a tendency to stick with their initial, asocial decision. We also found that older children, like adults, were disproportionately receptive to non-total majorities (i.e. were conformist) whereas younger children were receptive only to total (i.e. unanimous) majorities. We conclude that, whilst the mechanism for incorporating social information into decision-making is initially very blunt, across the course of early childhood it converges on the adaptive learning mechanisms observed in adults and predicted by cultural evolutionary theory. A video abstract of this article can be viewed at http://youtu.be/Qb6JINGYqVkPostprintPeer reviewe
Managing cow dung with a low tech, cheap plastic digester
In this report, the management and
disinfection of manure with a low-tech, cheap, plastic
digester is described. The efficacy of disinfection was
monitored by carrying out microscopy and culture analysis
of the raw and treated manure slurries to establish the
microbial presence in both
Generalized contact process on random environments
Spreading from a seed is studied by Monte Carlo simulation on a square
lattice with two types of sites affecting the rates of birth and death. These
systems exhibit a critical transition between survival and extinction. For
time- dependent background, this transition is equivalent to those found in
homogeneous systems (i.e. to directed percolation). For frozen backgrounds, the
appearance of Griffiths phase prevents the accurate analysis of this
transition. For long times in the subcritical region, spreading remains
localized in compact (rather than ramified) patches, and the average number of
occupied sites increases logarithmically in the surviving trials.Comment: 6 pages, 7 figure
Humor and preschoolers’ trust: Sensitivity to changing intentions
This research demonstrates that preschoolers (a) avoid trusting informants with humorous intentions when learning novel information and (b) flexibly consider current intentions rather than initial intentions when determining who to trust. In Study 1 (N = 61), 3- and 4-year-olds based their trust on intentions or intentional cues alone, trusting a sincere informant over a joker, even when no prior accuracy or inaccuracy was displayed. In Study 2 (N = 32), 3- and 4-year-olds flexibly based their trust on the informants’ current intentions or intentional cues rather than their initial ones. Children trusted a sincere informant, who originally joked, over a joker, who was originally sincere. In Study 3 (N = 89), 3-, 4-, and 5-year-olds tracked changing intentions, and not just intentional cues, in determining who to trust. Children trusted an informant who joked during training trials but was sincere during test trials over an informant who was ignorant during training trials and was sincere during test trials. However, if the ignorant informant became knowledgeable and the joker continued to joke, the pattern reversed. This is the first study to show that preschoolers consider intentions to joke when learning information. This is also the first study to show that preschoolers do not see trust as stable but rather see it as a function of changing intentions
Ultrahigh sensitivity of slow-light gyroscope
Slow light generated by Electromagnetically Induced Transparency is extremely
susceptible with respect to Doppler detuning. Consequently, slow-light
gyroscopes should have ultrahigh sensitivity
Mitochondrial function and oxygen supply in normal and in chronically ischemic muscle: A combined 31P magnetic resonance spectroscopy and near infrared spectroscopy study in vivo
AbstractPurpose: We used 31P magnetic resonance spectroscopy (MRS) and near-infrared spectroscopy (NIRS) as a means of quantifying abnormalities in calf muscle oxygenation and adenosine triphosphate (ATP) turnover in peripheral vascular disease (PVD). Methods: Eleven male patients with PVD (mean age, 65 years; range, 55-76 years) and nine male control subjects of similar age were observed in a case-control study in vascular outpatients. Inclusion criteria were more than 6 months' calf claudication (median, 1.5 years; range, 0.6-18 years); proven femoropopliteal or iliofemoral occlusive or stenotic disease; maximum treadmill walking distance (2 km/h, 10° gradient) of 50 to 230 m (mean, 112 m); ankle-brachial pressure index of 0.8 or less during exercise (mean, 0.47; range, 0.29-0.60). Exclusion criteria included diabetes mellitus, anemia, and magnet contraindications. Simultaneous 31P MRS and NIRS of lateral gastrocnemius was conducted during 2 to 4 minutes of voluntary 0.5 Hz isometric plantarflexion at 50% and 75% maximum voluntary contraction force (MVC), followed by 5 minutes recovery. Each subject was studied three times, and the results were combined. Results: Compared with control subjects, patients with PVD showed (1) normal muscle cross-sectional area, MVC, ATP turnover, and contractile efficiency (ATP turnover per force/area); (2) larger phosphocreatine (PCr) changes during exercise (ie, increased shortfall of oxidative ATP synthesis) and slower PCr recovery (47% ± 7% [mean ± SEM] decrease in functional capacity for oxidative ATP synthesis, P =.001); (3) faster deoxygenation during exercise and slower postexercise reoxygenation (59% ± 7% decrease in rate constant, P =.0009), despite reduced oxidative ATP synthesis; (4) correlation between PCr and NIRS recovery rate constants (P <.02); and (5) correlations between smaller walking distance, slower PCr recovery, and reduced MVC (P <.001). The precision of the key measurements (rate constants and contractile efficiency) was 12% to 18% interstudy and 30% to 40% intersubject. Conclusion: The primary lesion in oxygen supply dominates muscle metabolism. Reduced force-generation in patients who are affected more may protect muscle from metabolic stress. (J Vasc Surg 2001;34:1103-10.
Full quantum solutions to the resonant four-wave mixing of two single-photon wave packets
We analyze both analytically and numerically the resonant four-wave mixing of
two co-propagating single-photon wave packets. We present analytic expressions
for the two-photon wave function and show that soliton-type quantum solutions
exist which display a shape-preserving oscillatory exchange of excitations
between the modes. Potential applications including quantum information
processing are discussed.Comment: 7 pages, 3 figure
The N-methyl-d-aspartate receptor antagonist CPP alters synapse and spine structure and impairs long-term potentiation and long-term depression induced morphological plasticity in dentate gyrus of the awake rat
Long-term morphological synaptic changes associated with homosynaptic long-term potentiation (LTP) and heterosynaptic long-term depression (LTD) in vivo, in awake adult rats were analyzed using three-dimensional (3-D) reconstructions of electron microscope images of ultrathin serial sections from the molecular layer of the dentate gyrus. For the first time in morphological studies, the specificity of the effects of LTP and LTD on both spine and synapse ultrastructure was determined using an N-methyl-d-aspartate (NMDA) receptor antagonist CPP (3-[(R)-2-carboxypiperazin-4-yl]-propyl-1-phosphonic acid). There were no differences in synaptic density 24 h after LTP or LTD induction, and CPP alone had no effect on synaptic density. LTP increased significantly the proportion of mushroom spines, whereas LTD increased the proportion of thin spines, and both LTP and LTD decreased stubby spine number. Both LTP and LTD increased significantly spine head evaginations (spinules) into synaptic boutons and CPP blocked these changes. Synaptic boutons were smaller after LTD, indicating a pre-synaptic effect. Interestingly, CPP alone decreased bouton and mushroom spine volumes, as well as post-synaptic density (PSD) volume of mushroom spines.These data show similarities, but also some clear differences, between the effects of LTP and LTD on spine and synaptic morphology. Although CPP blocks both LTP and LTD, and impairs most morphological changes in spines and synapses, CPP alone was shown to exert effects on aspects of spine and synaptic structure
Evidence for geometry-dependent universal fluctuations of the Kardar-Parisi-Zhang interfaces in liquid-crystal turbulence
We provide a comprehensive report on scale-invariant fluctuations of growing
interfaces in liquid-crystal turbulence, for which we recently found evidence
that they belong to the Kardar-Parisi-Zhang (KPZ) universality class for 1+1
dimensions [Phys. Rev. Lett. 104, 230601 (2010); Sci. Rep. 1, 34 (2011)]. Here
we investigate both circular and flat interfaces and report their statistics in
detail. First we demonstrate that their fluctuations show not only the KPZ
scaling exponents but beyond: they asymptotically share even the precise forms
of the distribution function and the spatial correlation function in common
with solvable models of the KPZ class, demonstrating also an intimate relation
to random matrix theory. We then determine other statistical properties for
which no exact theoretical predictions were made, in particular the temporal
correlation function and the persistence probabilities. Experimental results on
finite-time effects and extreme-value statistics are also presented. Throughout
the paper, emphasis is put on how the universal statistical properties depend
on the global geometry of the interfaces, i.e., whether the interfaces are
circular or flat. We thereby corroborate the powerful yet geometry-dependent
universality of the KPZ class, which governs growing interfaces driven out of
equilibrium.Comment: 31 pages, 21 figures, 1 table; references updated (v2,v3); Fig.19
updated & minor changes in text (v3); final version (v4); J. Stat. Phys.
Online First (2012
Application of time-dependent density functional theory to optical activity
As part of a general study of the time-dependent local density approximation
(TDLDA), we here report calculations of optical activity of chiral molecules.
The theory automatically satisfies sum rules and the Kramers-Kronig relation
between circular dichroism and optical rotatory power. We find that the theory
describes the measured circular dichroism of the lowest states in methyloxirane
with an accuracy of about a factor of two. In the chiral fullerene C_76 the
TDLDA provides a consistent description of the optical absorption spectrum, the
circular dichroism spectrum, and the optical rotatory power, except for an
overall shift of the theoretical spectrum.Comment: 17 pages and 13 PostScript figure
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