698 research outputs found
Hexabromocyclododecane and hexachlorocyclohexane: How lessons learnt have led to improved regulation
This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2014 Taylor & Francis.The use of chemicals by society has many benefits but contamination of the environment is an unintended consequence. One example is the organochlorine compound hexachlorocyclohexane (HCH). During the 1980s, when HCH was banned in many countries, the brominated flame retardant, hexabromocyclododecane (HBCD), found increasing use. The persistent, bioaccumulative, and toxic characteristics of HBCD are, 30 years later, likely to warrant global action on production and use under the Stockholm Convention on persistent organic pollutants. Historical lessons have taught us that we need to control the use of chemicals and programs are in place worldwide in an attempt to do so.Tertiary Education Trust Fund, Nigeri
Existence and Stability of Symmetric Periodic Simultaneous Binary Collision Orbits in the Planar Pairwise Symmetric Four-Body Problem
We extend our previous analytic existence of a symmetric periodic
simultaneous binary collision orbit in a regularized fully symmetric equal mass
four-body problem to the analytic existence of a symmetric periodic
simultaneous binary collision orbit in a regularized planar pairwise symmetric
equal mass four-body problem. We then use a continuation method to numerically
find symmetric periodic simultaneous binary collision orbits in a regularized
planar pairwise symmetric 1, m, 1, m four-body problem for between 0 and 1.
Numerical estimates of the the characteristic multipliers show that these
periodic orbits are linearly stability when , and are
linearly unstable when .Comment: 6 figure
Promoting physical activity among native american youth: A systematic review of the methodology and current evidence of physical activity interventions and community-wide initiatives
Promoting physical activity using environmental, policy, and systems approaches could potentially address persistent health disparities faced by American Indian and Alaska Native children and adolescents. To address research gaps and help inform tribally led community changes that promote physical activity, this review examined the methodology and current evidence of physical activity interventions and community-wide initiatives among Native youth. A keyword-guided search was conducted in multiple databases to identify peer-reviewed research articles that reported on physical activity among Native youth. Ultimately, 20 unique interventions (described in 76 articles) and 13 unique community-wide initiatives (described in 16 articles) met the study criteria. Four interventions noted positive changes in knowledge and attitude relating to physical activity but none of the interventions examined reported statistically significant improvements on weight-related outcomes. Only six interventions reported implementing environmental, policy, and system approaches relating to promoting physical activity and generally only shared anecdotal information about the approaches tried. Using community-based participatory research or tribally driven research models strengthened the tribal-research partnerships and improved the cultural and contextual sensitivity of the intervention or community-wide initiative. Few interventions or community-wide initiatives examined multi-level, multi-sector interventions to promote physical activity among Native youth, families, and communities. More research is needed to measure and monitor physical activity within this understudied, high risk group. Future research could also focus on the unique authority and opportunity of tribal leaders and other key stakeholders to use environmental, policy, and systems approaches to raise a healthier generation of Native youth
Relative Equilibria in the Four-Vortex Problem with Two Pairs of Equal Vorticities
We examine in detail the relative equilibria in the four-vortex problem where
two pairs of vortices have equal strength, that is, \Gamma_1 = \Gamma_2 = 1 and
\Gamma_3 = \Gamma_4 = m where m is a nonzero real parameter. One main result is
that for m > 0, the convex configurations all contain a line of symmetry,
forming a rhombus or an isosceles trapezoid. The rhombus solutions exist for
all m but the isosceles trapezoid case exists only when m is positive. In fact,
there exist asymmetric convex configurations when m < 0. In contrast to the
Newtonian four-body problem with two equal pairs of masses, where the symmetry
of all convex central configurations is unproven, the equations in the vortex
case are easier to handle, allowing for a complete classification of all
solutions. Precise counts on the number and type of solutions (equivalence
classes) for different values of m, as well as a description of some of the
bifurcations that occur, are provided. Our techniques involve a combination of
analysis and modern and computational algebraic geometry
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Libraries and open society; Popper, Soros and digital information
This paper examines the role of libraries and information services, in promoting the âopen societyâ espoused by Karl Popper and George Soros. After a brief discussion of the nature of an âopen societyâ, the paper covers the role played by provision of knowledge and information, of new technology, particularly the Internet, and of critical thinking and digital literacy in the development of this form of society. Conclusions are drawn for the role of libraries and librarians, with seven general principles suggested:
âą provision of access to a wide variety of sources without ânegativeâ restriction or censorship
âą provision of âpositiveâ guidance on sources, based on open and objective criteria
âą a recognition that a âfree flow of informationâ though essential, is not sufficient
âą a recognition that provision of factual information, while valuable, is not enough
âą a need for a specific concern for the effect of new ICTs, and the Internet in particular
âą promotion of critical thinking and digital literacy
âą a need for explicit consideration of the ethical values of librarie
Comparison of Gadoterate Meglumine and Gadobutrol in the MRI Diagnosis of Primary Brain Tumors: A Double-Blind Randomized Controlled Intraindividual Crossover Study (the REMIND Study)
ABSTRACT BACKGROUNDANDPURPOSE: Effective management of patients with brain tumors depends on accurate detection and characterization of lesions. This study aimed to demonstrate the noninferiority of gadoterate meglumine versus gadobutrol for overall visualization and characterization of primary brain tumors.
MATERIALS AND METHODS: This multicenter, double-blind, randomized, controlled intraindividual, crossover, noninferiority study included279patients.Bothcontrastagents(dose=0.1mmol/kgofbodyweight)wereassessedwith2identicalMRIsatatimeintervalof 2â14 days. The primary end point was overall lesion visualization and characterization, scored independently by 3 off-site readers on a 4-point scale, ranging from âpoorâ to âexcellent.â Secondary end points were qualitative assessments (lesion border delineation, internal morphology, degree of contrast enhancement, diagnostic conïŹdence), quantitative measurements (signal intensity), and safety (adverse events). All qualitative assessments were also performed on-site.
RESULTS: Forall3readers,imagesofmostpatients(>90%)werescoredgoodorexcellentforoveralllesionvisualizationandcharacterizationwitheithercontrastagent;andthenoninferiorityofgadoteratemeglumineversusgadobutrolwasstatisticallydemonstrated.No signiïŹcant differences were observed between the 2 contrast agents regarding qualitative end points despite quantitative mean lesion percentageenhancementbeinghigherwithgadobutrol(P81%ofthe patientswithbothcontrastagents.Similarpercentagesofpatientswithadverseeventsrelatedtothecontrastagentswereobservedwith gadoterate meglumine (7.8%) and gadobutrol (7.3%), mainly injection site pain.
CONCLUSIONS: Thenoninferiorityofgadoteratemeglumineversusgadobutrolforoverallvisualizationandcharacterizationofprimary brain tumors was demonstrated
An Alternative Method to Deduce Bubble Dynamics in Single Bubble Sonoluminescence Experiments
In this paper we present an experimental approach that allows to deduce the
important dynamical parameters of single sonoluminescing bubbles (pressure
amplitude, ambient radius, radius-time curve) The technique is based on a few
previously confirmed theoretical assumptions and requires the knowledge of
quantities such as the amplitude of the electric excitation and the phase of
the flashes in the acoustic period. These quantities are easily measurable by a
digital oscilloscope, avoiding the cost of expensive lasers, or ultrafast
cameras of previous methods. We show the technique on a particular example and
compare the results with conventional Mie scattering. We find that within the
experimental uncertainties these two techniques provide similar results.Comment: 8 pages, 5 figures, submitted to Phys. Rev.
The structure of the cysteine protease and lectin-like domains of Cwp84, a surface layer-associated protein from <em>Clostridium</em> <em>difficile</em>
Clostridium difficile is a major problem as an aetiological agent for antibiotic-associated diarrhoea. The mechanism by which the bacterium colonizes the gut during infection is poorly understood, but undoubtedly involves a myriad of components present on the bacterial surface. The mechanism of C. difficile surface-layer (S-layer) biogenesis is also largely unknown but involves the post-translational cleavage of a single polypeptide (surface-layer protein A; SlpA) into low- and high-molecular-weight subunits by Cwp84, a surface-located cysteine protease. Here, the first crystal structure of the surface protein Cwp84 is described at 1.4â
Ă
resolution and the key structural components are identified. The truncated Cwp84 active-site mutant (amino-acid residues 33â497; C116A) exhibits three regions: a cleavable propeptide and a cysteine protease domain which exhibits a cathepsin L-like fold followed by a newly identified putative carbohydrate-binding domain with a bound calcium ion, which is referred to here as a lectin-like domain. This study thus provides the first structural insights into Cwp84 and a strong base to elucidate its role in the C. difficile S-layer maturation mechanism
The structure of the cysteine protease and lectin-like domains of Cwp84, a surface layer-associated protein from <em>Clostridium</em> <em>difficile</em>
Magnetohydrodynamic Waves in an Asymmetric Magnetic Slab
Analytical models of solar atmospheric magnetic structures have been crucial for our understanding of magnetohydrodynamic (MHD) wave behaviour and in the development of the field of solar magneto-seismology. Here, an analytical approach is used to derive the dispersion relation for MHD waves in a magnetic slab of homogeneous plasma enclosed on its two sides by non-magnetic, semi-infinite plasma with different densities and temperatures. This generalises the classic magnetic slab model, which is symmetric about the slab. The dispersion relation, unlike that governing a symmetric slab, cannot be decoupled into the well-known sausage and kink modes, i.e. the modes have mixed properties. The eigenmodes of an asymmetric magnetic slab are better labelled as quasi-sausage and quasi-kink modes. Given that the solar atmosphere is highly inhomogeneous, this has implications for MHD mode identification in a range of solar structures. AÂ parametric analysis of how the mode properties (in particular the phase speed, eigenfrequencies, and amplitudes) vary in terms of the introduced asymmetry is conducted. In particular, avoided crossings occur between quasi-sausage and quasi-kink surface modes, allowing modes to adopt different properties for different parameters in the external region
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