Trapping dust particles in the outer regions of protoplanetary disks

Aims. We attempt to explain grain growth to mm sized particles and their retention in the outer regions of protoplanetary disks, as observed at sub-mm and mm wavelengths, by investigating whether strong inhomogeneities in the gas density profiles can decelerate excessive radial drift and help the dust particles to grow. Methods. We use coagulation/fragmentation and disk-structure models, to simulate the evolution of dust in a bumpy surface density profile, which we mimic with a sinusoidal disturbance. For different values of the amplitude and length scale of the bumps, we investigate the ability of this model to produce and retain large particles on million-year timescales. In addition, we compare the pressure inhomogeneities considered in this work with the pressure profiles that come from magnetorotational instability. Using the Common Astronomy Software Applications ALMA simulator, we study whether there are observational signatures of these pressure inhomogeneities that can be seen with ALMA. Results. We present the conditions required to trap dust particles and the corresponding calculations predicting the spectral slope in the mm-wavelength range, to compare with current observations. Finally, we present simulated images using different antenna configurations of ALMA at different frequencies, to show that the ring structures will be detectable at the distances of either the Taurus Auriga or Ophiucus star-forming regions

Voluntary Environmental Agreements in Developing Countries: The Colombian Experience

According to proponents, voluntary agreements (VAs) negotiated with polluters sidestep weak institutions and other barriers to conventional environmental regulation in developing countries. Yet little is known about their effectiveness. We examine VAs in Colombia, a global leader in the use of these policies. We find that the main motive for using VAs has been to build capacity needed for broader environmental regulatory reform. Their additional effect on environmental performance has been questionable. These findings suggest that in developing countries, VAs may be best suited to capacity building, not environmental management per se.voluntary environmental agreement, pollution, Colombia

Mass fluctuation kinetics: analysis and computation of equilibria and local dynamics

The mass fluctuation kinetics (MFK) model is a set of coupled ordinary differential equations approximating the time evolution of means and covariances of species concentrations in chemical reaction networks. It generalises classical mass action kinetics (MAK), in which fluctuations around the mean are ignored. MFK may be used to approximate stochasticity in system trajectories when stochastic simulation methods are prohibitively expensive computationally. This study presents a set of tools to aid in the analysis of systems within the MFK framework. A closed-form expression for the MFK Jacobian matrix is derived. This expression facilitates the computation of MFK equilibria and the characterisation of the dynamics of small deviations from the equilibria (i.e. local dynamics). Software developed in MATLAB to analyse systems within the MFK framework is also presented. The authors outline a homotopy continuation method that employs the Jacobian for bifurcation analysis, that is, to generate a locus of steady-state Jacobian eigenvalues corresponding to changing a chosen MFK parameter such as system volume or a rate constant. This method is applied to study the effect of small-volume stochasticity on local dynamics at equilibria in a pair of example systems, namely the formation and dissociation of an enzyme-substrate complex and a genetic oscillator. For both systems, this study reveals volume regimes where MFK provides a quantitatively and/or qualitatively correct description of system behaviour, and regimes where the MFK approximation is inaccurate. Moreover, our analysis provides evidence that decreasing volume from the MAK regime (infinite volume) has a destabilising effect on system dynamics

Neuroimaging of rapid eye movement sleep behavior disorder and its relation to Parkinson's disease

Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia characterized by polysomnography-confirmed REM sleep without atonia and dream-enacting behaviors. This disorder is considered a prodromal syndrome of alpha-synucleinopathies like Parkinson's disease (PD), where it affects more than 50% of PD patients. The underlying pathology of RBD has been generally understood to involve the pontine nuclei within the brainstem. However, the complete pathophysiology beyond the brainstem remains unclear as does its relationship with PD pathology. Therefore, this review aims to survey the neuroimaging literature involving PET, SPECT, and MR imaging techniques to provide an updated understanding of the neuro-chemical, structural, and functional changes in both RBD and PD patients comorbid with RBD. This review found neuroimaging evidence that indicate alterations to the dopaminergic and cholinergic system, blood perfusion, and glucose metabolism in both RBD patients and PD patients with RBD. Beyond the brainstem, structural and functional changes were found to involve the nigrostriatal system, limbic system, and the cortex-suggesting that RBD is a multi-systemic neurodegenerative process. Future investigations are encouraged to follow RBD patients longitudinally using multimodal imaging techniques to enhance our understanding of this parasomnia disorder. Uncovering which individuals are most likely to develop an alpha-synuclein disorder in the prodromal phase will improve patient outcomes and potentially aid in the development of novel treatments for patients affected by RBD

Preformed metal crowns may last longer than fillings

Copyright: Copyright 2007 Elsevier B.V., All rights reserved.Data sources: Searches were made using the Cochrane Central Register of Controlled Trials (CENTRAL), Medline, Embase and the System for Information on Grey Literature in Europe (SIGLE). Study selection: Randomised controlled trials (RCT) were chosen that assessed the effectiveness of PMC, compared with filling materials or in children where there had been no treatment of tooth decay in one or more primary molar teeth. Data extraction and synthesis: Forty-seven records were retrieved by the search strategies, some of which proved to be duplicates. Ultimately, 14 studies were scrutinised. None met the inclusion criteria and six studies were excluded from the review because they were either retrospective in design or they reported prospective outcomes but were not randomised. Conclusions: No RCT were available for appraisal. Although the use of PMC is recommended in clinical practice by the British Society of Paediatric Dentistry (BSPD), the evidence to support this is not strong, consisting mainly of case reports and uncontrolled studies. The lower quality levels of evidence that have been produced nevertheless have some strength, since clinical outcomes are consistently in favour of PMC even though many studies analyse casts placed on the most damaged of the pair of teeth. It is important that the absence of evidence for PMC is not misinterpreted as evidence for their lack of efficacy.publishersversionPeer reviewe