4,238 research outputs found
A measurement system for vertical seawater profiles close to the airāsea interface
This paper describes a near-surface ocean profiler, which has been designed to precisely measure vertical gradients in the top 10āÆm of the ocean. Variations in the depth of seawater collection are minimized when using the profiler compared to conventional CTD/rosette deployments. The profiler consists of a remotely operated winch mounted on a tethered yet free-floating buoy, which is used to raise and lower a small frame housing sensors and inlet tubing. Seawater at the inlet depth is pumped back to the ship for analysis. The profiler can be used to make continuous vertical profiles or to target a series of discrete depths. The profiler has been successfully deployed during wind speeds up to 10āÆmāÆsā1 and significant wave heights up to 2āÆm. We demonstrate the potential of the profiler by presenting measured vertical profiles of the trace gases carbon dioxide and dimethylsulfide. Trace gas measurements use an efficient microporous membrane equilibrator to minimize the system response time. The example profiles show vertical gradients in the upper 5āÆm for temperature, carbon dioxide and dimethylsulfide of 0.15āÆĀ°C, 4āÆĀµatm and 0.4āÆnM respectively
An Extended Variational Principle for the SK Spin-Glass Model
The recent proof by F. Guerra that the Parisi ansatz provides a lower bound
on the free energy of the SK spin-glass model could have been taken as offering
some support to the validity of the purported solution. In this work we present
a broader variational principle, in which the lower bound, as well as the
actual value, are obtained through an optimization procedure for which
ultrametic/hierarchal structures form only a subset of the variational class.
The validity of Parisi's ansatz for the SK model is still in question. The new
variational principle may be of help in critical review of the issue.Comment: 4 pages, Revtex
Peptidyltransferase activity of ribosomes and a ribosome precursor from a mutant of Escherichia coli
Creativity and Autonomy in Swarm Intelligence Systems
This work introduces two swarm intelligence algorithms -- one mimicking the behaviour of one species of ants (\emph{Leptothorax acervorum}) foraging (a `Stochastic Diffusion Search', SDS) and the other algorithm mimicking the behaviour of birds flocking (a `Particle Swarm Optimiser', PSO) -- and outlines a novel integration strategy exploiting the local search properties of the PSO with global SDS behaviour. The resulting hybrid algorithm is used to sketch novel drawings of an input image, exploliting an artistic tension between the local behaviour of the `birds flocking' - as they seek to follow the input sketch - and the global behaviour of the `ants foraging' - as they seek to encourage the flock to explore novel regions of the canvas. The paper concludes by exploring the putative `creativity' of this hybrid swarm system in the philosophical light of the `rhizome' and Deleuze's well known `Orchid and Wasp' metaphor
Developing an On-Line Interactive Health Psychology Module.
On-line teaching material in health psychology was developed which ensured a range of students could access appropriate material for their course and level of study. This material has been developed around the concept of smaller 'content chunks' which can be combined into whole units of learning (topics), and ultimately, a module. On the basis of the underlying philosophy that the medium is part of the message, we considered interactivity to be a key element in engaging the student with the material. Consequently, the key aim of this development was to stimulate and engage students, promoting better involvement with the academic material, and hence better learning. It was hoped that this was achieved through the development of material including linked programmes and supporting material, small Java Scripts and basic email, forms and HTML additions. This material is outlined as are some of the interactive activities introduced, and the preliminary student and tutor experience described
Exploring the Subtle Effect of Aliphatic Ring Size on Minor Actinide-Extraction Properties and Metal Ion Speciation in Bis-1,2,4-Triazine Ligands
Calling all actinides! Bis-1,2,4-triazine ligands bearing five-membered rings were synthesized and evaluated as actinide-selective extractants. Tuning the size of the aliphatic ring leads to subtle changes in actinide-extraction properties. The origins of these changes were elucidated at the molecular level, paving the way for the rational design of improved actinide-selective extractants for reprocessing of spent nuclear fuel.,
The synthesis and evaluation of three novel bis-1,2,4-triazine ligands containing five-membered aliphatic rings are reported. Compared to the more hydrophobic ligands 1ā3 containing six-membered aliphatic rings, the distribution ratios for relevant f-block metal ions were approximately one order of magnitude lower in each case. Ligand 10 showed an efficient, selective and rapid separation of AmIII and CmIII from nitric acid. The speciation of the ligands with trivalent f-block metal ions was probed using NMR titrations and competition experiments, time-resolved laser fluorescence spectroscopy and X-ray crystallography. While the tetradentate ligands 8 and 10 formed Ln complexes of the same stoichiometry as their more hydrophobic analogues 2 and 3, significant differences in speciation were observed between the two classes of ligand, with a lower percentage of the extracted 1:2 complexes being formed for ligands 8 and 10. The structures of the solid state 1:1 and 1:2 complexes formed by 8 and 10 with Y, Lu and Pr are very similar to those formed by 2 and 3 with Ln. Ligand 10 forms Cm and Eu 1:2 complexes that are thermodynamically less stable than those formed by ligand 3, suggesting that less hydrophobic ligands form less stable An complexes. Thus, it has been shown for the first time how tuning the cyclic aliphatic part of these ligands leads to subtle changes in their metal ion speciation, complex stability and metal extraction affinity
The inverse resonance problem for perturbations of algebro-geometric potentials
We prove that a compactly supported perturbation of a rational or simply
periodic algebro-geometric potential of the one-dimensional Schr\"odinger
equation on the half line is uniquely determined by the location of its
Dirichlet eigenvalues and resonances.Comment: 14 page
A translational research experience in Argentina.
Background: The Argentinean programwas initiatedmore than a decade ago as the first experience of systematic
translational research focused on NCL in Latin America. The aim was to overcome misdiagnoses and
underdiagnoses in the region.
Subjects: 216 NCL suspected individuals from 8 different countries and their direct family members.
Methods: Clinical assessment, enzyme testing, electron microscopy, and DNA screening.
Results and discussion: 1) The study confirmed NCL disease in 122 subjects. Phenotypic studies comprised
epileptic seizures and movement disorders, ophthalmology, neurophysiology, image analysis, rating scales,
enzyme testing, and electron microscopy, carried out under a consensus algorithm; 2) DNA screening and
validation of mutations in genes PPT1 (CLN1), TPP1 (CLN2), CLN3, CLN5, CLN6, MFSD8 (CLN7), and CLN8:
characterization of variant types, novel/knownmutations and polymorphisms; 3) Progress of the epidemiological
picture in Latin America; and 4) NCL-like pathology studies in progress. The Translational Research Program was
highly efficient in addressing the misdiagnosis/underdiagnosis in the NCL disorders. The study of āorphan
diseasesā in a public administrated hospital should be adopted by the health systems, as it positively impacts
upon the family's quality of life, the collection of epidemiological data, and triggers research advances. This article
is part of a Special Issue entitled: āCurrent Research on the Neuronal Ceroid Lipofuscinoses (Batten Disease)āpublishedVersio
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Beagle 2: Mission to Mars ā current status
Beagle 2, developed in the UK, was launched on June 2, 2003. It landed on Mars on December 25th, 2003 in Isidis Planitia, a large sedimentary basin. To date, the team is awaiting signals from the Beagle 2 lander. Current status of the mission will be reported
Two--Electron Atoms in Short Intense Laser Pulses
We discuss a method of solving the time dependent Schrodinger equation for
atoms with two active electrons in a strong laser field, which we used in a
previous paper [A. Scrinzi and B. Piraux, Phys. Rev. A 56, R13 (1997)] to
calculate ionization, double excitation and harmonic generation in Helium by
short laser pulses. The method employs complex scaling and an expansion in an
explicitly correlated basis. Convergence of the calculations is documented and
error estimates are provided. The results for Helium at peak intensities up to
10^15 W/cm^2 and wave length 248 nm are accurate to at least 10 %. Similarly
accurate calculations are presented for electron detachment and double
excitation of the negative hydrogen ion.Comment: 14 pages, including figure
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