2,397 research outputs found
Intravenous conscious sedation in patients under 16 years of age. Fact or fiction?
Recently published guidelines on the use of conscious sedation in dentistry have published varying recommendations on the lower age limit for the use of intravenous conscious sedation. There are a large number of dentists currently providing dental treatment for paediatric patients under intravenous conscious sedation. The 18 cases reported here (age range 11-15 years), were successfully managed with intravenous conscious sedation. The experience in this paper is not sufficient evidence to recommend the wholesale use of intravenous conscious sedation in patients who are under 16 years. The fact that a range of operators can use these techniques on paediatric patients would suggest that further study should be carried out in this population. The guidance should be modified to say there is insufficient evidence to support the use of intravenous conscious sedation in children, rather than arbitrarily selecting a cut off point at age 16 years
Gene Sampling Strategies for Multi-Locus Population Estimates of Genetic Diversity (θ)
BACKGROUND: Theoretical work suggests that data from multiple nuclear loci provide better estimates of population genetic parameters than do single loci, but just how many loci are needed and how much sequence is required from each has been little explored. METHODOLOGY/PRINCIPLE FINDINGS: To investigate how much data is required to estimate the population genetic parameter θ (4N(e)μ) accurately under ideal circumstances, we simulated datasets of DNA sequences under three values of θ per site (0.1, 0.01, 0.001), varying in both the total number of base pairs sequenced per individual and the number of equal-length loci. From these datasets we estimated θ using the maximum likelihood coalescent framework implemented in the computer program Migrate. Our results corroborated the theoretical expectation that increasing the number of loci impacted the accuracy of the estimate more than increasing the sequence length at single loci. However, when the value of θ was low (0.001), the per-locus sequence length was also important for estimating θ accurately, something that has not been emphasized in previous work. CONCLUSIONS/SIGNIFICANCE: Accurate estimation of θ required data from at least 25 independently evolving loci. Beyond this, there was little added benefit in terms of decreasing the squared coefficient of variation of the coalescent estimates relative to the extra effort required to sample more loci
Two-stream instability in quasi-one-dimensional Bose-Einstein condensates
We apply a kinetic model to predict the existence of an instability mechanism in elongated Bose-Einstein condensates. Our kinetic description, based on the Wigner formalism, is employed to highlight the existence of unstable Bogoliubov waves that may be excited in the counterpropagation configuration. We identify a dimensionless parameter, the Mach number at T=0, that tunes different regimes of stability. We also estimate the magnitude of the main parameters at which two-stream instability is expected to be observed under typical experimental conditions
Historical divergence and gene flow: Coalescent analyses of mitochondrial, autosomal and sex-linked loci in passerina buntings
Quantifying the role of gene flow during the divergence of closely related species is crucial to understanding the process of speciation. We collected DNA sequence data from 20 loci (one mitochondrial, 13 autosomal, and six sex-linked) for population samples of Lazuli Buntings (Passerina amoena) and Indigo Buntings (Passerina cyanea) (Aves: Cardinalidae) to test explicitly between a strict allopatric speciation model and a model in which divergence occurred despite postdivergence gene flow. Likelihood ratio tests of coalescent-based population genetic parameter estimates indicated a strong signal of postdivergence gene flow and a strict allopatric speciation model was rejected. Analyses of partitioned datasets (mitochondrial, autosomal, and sex-linked) suggest the overall gene flow patterns are driven primarily by autosomal gene flow, as there is no evidence of mitochondrial gene flow and we were unable to reject an allopatric speciation model for the sex-linked data. This pattern is consistent with either a parapatric divergence model or repeated periods of allopatry with gene flow occurring via secondary contact. These results are consistent with the low fitness of female avian hybrids under Haldane\u27s rule and demonstrate that sex-linked loci likely are important in the initial generation of reproductive isolation, not just its maintenance. © 2010 The Author(s). Journal compilation © 2010 The Society for the Study of Evolution
Evidence for a dynamic phase transition in [Co/Pt]_3 magnetic multilayers
A dynamic phase transition (DPT) with respect to the period P of an applied
alternating magnetic field has been observed previously in numerical
simulations of magnetic systems. However, experimental evidence for this DPT
has thus far been limited to qualitative observations of hysteresis loop
collapse in studies of hysteresis loop area scaling. Here, we present
significantly stronger evidence for the experimental observation of this DPT,
in a [Co(4 A)/Pt(7 A)]_3-multilayer system with strong perpendicular
anisotropy. We applied an out-of-plane, time-varying (sawtooth) field to the
[Co/Pt]_3 multilayer, in the presence of a small additional constant field,
H_b. We then measured the resulting out-of-plane magnetization time series to
produce nonequilibrium phase diagrams (NEPDs) of the cycle-averaged
magnetization, Q, and its variance, Var(Q), as functions of P and H_b. The
experimental NEPDs are found to strongly resemble those calculated from
simulations of a kinetic Ising model under analagous conditions. The similarity
of the experimental and simulated NEPDs, in particular the presence of a
localized peak in the variance Var(Q) in the experimental results, constitutes
strong evidence for the presence of this DPT in our magnetic multilayer
samples. Technical challenges related to the hysteretic nature and response
time of the electromagnet used to generate the time-varying applied field
precluded us from extracting meaningful critical scaling exponents from the
current data. However, based on our results, we propose refinements to the
experimental procedure which could potentially enable the determination of
critical exponents in the future.Comment: substantial revision; 26 pages, 9 figures; to appear in Phys. Rev.
Conjugate field and fluctuation-dissipation relation for the dynamic phase transition in the two-dimensional kinetic Ising model
The two-dimensional kinetic Ising model, when exposed to an oscillating
applied magnetic field, has been shown to exhibit a nonequilibrium,
second-order dynamic phase transition (DPT), whose order parameter Q is the
period-averaged magnetization. It has been established that this DPT falls in
the same universality class as the equilibrium phase transition in the
two-dimensional Ising model in zero applied field. Here we study for the first
time the scaling of the dynamic order parameter with respect to a nonzero,
period-averaged, magnetic `bias' field, H_b, for a DPT produced by a
square-wave applied field. We find evidence that the scaling exponent,
\delta_d, of H_b at the critical period of the DPT is equal to the exponent for
the critical isotherm, \delta_e, in the equilibrium Ising model. This implies
that H_b is a significant component of the field conjugate to Q. A finite-size
scaling analysis of the dynamic order parameter above the critical period
provides further support for this result. We also demonstrate numerically that,
for a range of periods and values of H_b in the critical region, a
fluctuation-dissipation relation (FDR), with an effective temperature
T_{eff}(T, P, H_0) depending on the period, and possibly the temperature and
field amplitude, holds for the variables Q and H_b. This FDR justifies the use
of the scaled variance of Q as a proxy for the nonequilibrium susceptibility,
\partial / \partial H_b, in the critical region.Comment: revised version; 31 pages, 12 figures; accepted by Phys. Rev.
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