3,999 research outputs found

    High B test of a commercial step-down Point of Load for LHC experiments

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    The performance in magnetic field (B-field) of the commercial DC-DC converter LTM8033, from Linear Technology, has been evaluated. The tests have been carried out at the Laboratorio Acceleratori e Superconduttivit\ue0 Applicata (LASA), in Milan (Italy), on December 2013 and the experimental results are here presented and discussed. Their ability to operate in hostile environment is particularly interesting for physics experiments where the presence of radiation and strong B field make electronic devices challenged to function . In particular, in this article the operation in high B-field environment will be investigated and discussed

    A Molecular Dynamics Study of Noncovalent Interactions between Rubber and Fullerenes

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    The percolation and networking of filler particles is an important issue in the field of rubber reinforcement, and much effort is given to clarify the true nature of the reinforcement mechanism and the viscoelastic behavior. The concentration of nanofillers also in the presence of large amounts of carbon black is a parameter that can influence the macroscopic rubber behavior. In this paper, noncovalent interactions between C60 fullerenes with poly-1,4-cis-isoprene (PI) either as such or modified are studied through atomistic simulations based on molecular mechanics (MM) and molecular dynamics (MD) methods. At first, the conformational properties of a single chain and of 12 PI chains in a periodic simulation box are studied. Afterwards, the conformational properties of a single PI chain polymer terminated with a -COOH group, and then a bulk system formed by chains of unmodified and some PI modified chains are considered. Then, the systems formed by adding fullerenes to these two different bulk systems are studied. Relatively small interaction energy between rubber and fullerenes being well dispersed in the sample is found. The simulations showed a preferential tendency of fullerenes to display self-aggregation, in the presence of even a small fraction of modified polymer chains

    Radiation and magnetic field effects on new semiconductor power devices for HL-LHC experiments

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    The radiation hardness of commercial Silicon Carbide and Gallium Nitride power MOSFETs is presented in this paper, for Total Ionizing Dose effects and Single Event Effects, under gamma, neutrons, protons and heavy ions. Similar tests are discussed for commercial DC-DC converters, also tested in operation under magnetic field

    Mechanical transients initiated by ramp stretch and release to P0 in frog muscle fibers

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    Single fibers from the tibialis muscle of Rana temporaria were subjected to ramp stretches during tetanic stimulation at a sarcomere length of ~2 \u3bcm. Immediately after the stretch, or after different time delays, the active fiber was released against a constant force equal to the isometric force (P0) exerted immediately before the stretch. Four phases were detected after release: 1) an elastic recoil of the fiber's undamped elements, 2) a transient rapid shortening, 3) a marked reduction in the velocity of shortening (often to 0), and 4) an apparently steady shortening (sometimes absent). Increasing the amplitude of the stretch from ~2 to 10% of the fiber rest length led to an increase in phase 2 shortening from ~5 to 10 nm per half-sarcomere. Phase 2 shortening increased further (up to 14 nm per half-sarcomere) if a time interval of 5-10 ms was left between the end of large ramp stretches and release to P0. After 50- to 100-ms time intervals, shortening occurred in two steps of ~5 nm per half-sarcomere each. These findings suggest that phase 2 is due to charging, during and after the stretch, of a damped element, which can then shorten against P0 in at least two steps of ~5 nm/half sarcomere each

    Polyether from a biobased Janus molecule as surfactant for carbon nanotubes

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    A new polyether (PE) was prepared from a biobased Janus molecule, 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3- propanediol (serinol pyrrole, SP). SP was synthesized with very high yield (about 96%) and high atom efficiency (about 80%) by reacting a biosourced molecule, such as serinol, with 2,5-hexanedione in the absence of solvent or catalyst. The reaction of SP with 1,6-dibromohexane led to PE oligomers, that were used as surfactants for multiwalled carbon nanotubes (MWCNT), in ecofriendly polar solvents such as acetone and ethyl acetate. The synergic interaction of aromatic rings and oxyalkylene sequences with the carbon allotrope led to dramatic improvement of surfactant efficiency: only 24% of SP based PE was extracted with ethyl acetate from the adduct with MWCNT, versus 98% of a typical pluronic surfactant. Suspensions of MWCNT-PE adducts in ethyl acetate were stable for months. High resolution transmission electron microscopy revealed a film of oligomers tightly adhered to MWCNT surface

    Advances and Perspectives in Genetics of Congenital Thyroid Disorders

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    Congenital hypothyroidism (CH) is the most frequent endocrine disease in infants, affects about 1 in 3,000 newborns and is characterized by elevated levels of thyroidstimulating hormone (TSH) as a consequence of reduced thyroid function. It is also one of the most common preventable causes of cognitive and motor deficits. Prevention of CH is based on carrier identification, genetic counseling and prenatal diagnosis. In neonates a complete diagnosis of CH should include clinical examination, biochemical thyroid tests, thyroid ultrasound, radioiodine or technetium scintigraphy and perchlorate discharge test (PDT). In the last two decades, considerable progress has been made in identifying the genetic and molecular causes of CH. Knowing the prevalence of mutations in each population will facilitate greatly the molecular genetic testing. The classification based on the genetic alterations divides CH into two main categories caused: (a) by disorders of thyroid gland development (dysembriogenesis or thyroid dysgenesis group) or (b) by defects in any of the steps of thyroid hormone synthesis (dyshormonogenesis group) [1]. The dysembryogenesis or thyroid dysgenesis group, which accounts for the 80-85% of the cases, results from a thyroid gland that is completely absent in orthotopic or ectopic location (agenesis or athyreosis), severely reduced in size but in the proper position in the neck (orthotopic hypoplasia) or located in an unusual position (thyroid ectopy) at the base of the tongue or along the thyroglossal tract [1]. In only 5% of the patients, the CH is associated with mutations in genes responsible for the development or growth of thyroid cells: NKX2.1 (also known as TTF1 or T/EBP), FOXE1 (also known as TTF2 or FKHL15), paired box transcription factor 8 (PAX-8), NKX2.5, and TSHR genes [1]. Consequently, the genetic mechanisms underlying the defects in thyroid organogenesis in the majority of the cases remain to be elucidated. Epigenetic mechanisms leading to stochastic variations in the expression of multiple loci could be responsible for the sporadic characteristic of thyroid dysgenesis
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