1,065 research outputs found
Time of Flight system to investigate positronium cooling
No full textA positronium Time of Flight (TOF) apparatus, conceived to work with continuous positron beams of intensity up to ∼10 6 positrons/s, was developed. The geometry of the TOF chamber and the acquisition chain are described in detail. The performances of the set up were preliminary tested with a laboratory positron beam of ∼5 × 10 3 positrons/s by measuring the Time of Flight of Ps emitted from oxidized nanochannels produced in a Si single crystal. A TOF spectrum of ∼10 4 events was collected in 9 days with a time resolution of 8 ns. The analysis of the TOF spectrum is discussed. This apparatus is going to be assembled at the intense positron source NEPOMUC at FRM-II reactor, where the measurement time of each spectrum will be reduced to less than 2 h, making this TOF system appropriate to investigate positronium emission after cooling in porous materials held at cryogenic temperature. © The Author(s) 2012
Can CSR classification be generally applied outside Britain?
No full textThe general applicability of CSR classification (a methodology for applying CSR theory) has not been tested outside Britain. We hypothesised that principal axes of trait variation for plant species native to southern European continental, sub-alpine and alpine bioclimatic zones correlate with CSR classification scores. Functional traits were quantified in situ for 506 species of 57 families. Multivariate analysis revealed three main modes in which plants invested biomass: (1) architectural extension of individual ramets (tall canopies, large leaves), (2) durable tissues (high leaf dry matter contents and carbon contents, low specific leaf areas) or (3) regenerative development (early, extensive flowering with delicate, nitrogen-rich leaves). These were highly significantly correlated with the extent of competitive ability (C), stress-tolerance (S) and ruderalism (R), respectively, determined by CSR classification. Despite being calibrated using only 43 British species, CSR classification is consistent with trait variation in a phylogenetically broader sample of species native to a wider range of bioclimatic zones
Collisional cooled Ps emitted into vacuum from silica-based porous materials: Experiment to measure the Ps cooling time
No full textIn recent experiments on positronium time of flight (Ps-TOF) we have studied emission of cooled and thermalized Ps into vacuum from oxidized nanochannels synthetized in silicon. Ps cools down through collisions with the walls of the channels before exiting into vacuum. An important unknown parameter in the Ps-TOF measurements is the permanence time in the medium, i.e. the Ps cooling time before emission into vacuum. In this paper we describe an experiment that allows us to estimate the cooling time of Ps by analyzing the Ps-TOF spectra of cool Ps at three different distances from the sample
Positronium cooling at cryogenic temperature for advanced experiments
No full textNew Ps spectroscopy measurements, formation of antihydrogen for antimatter-matter comparison experiments, production of Ps beams require the efficient production of cooled positronium in vacuum. At present the most efficient positron-positronium converters are silica based ordered or disordered porous materials, in which formed Ps decreases its kinetic energy by collisional cooling. Recently new positron-positronium converters based on oxidized nanochannels in silicon were found to be very promising because of the tunability of the nanochannel size, which allows to overcome the limits imposed to the Ps cooling by the quantum confinement. With these converters, Ps with temperatures as low as 150 K was detected in vacuum by a TOF apparatus. The Ps formation, quantum confinement, collisional cooling and emission into vacuum from nanochanneled silicon will be discussed in light of recent results. © Published under licence by IOP Publishing Ltd
Influence of microinclusion in life of rolling elements: Experimental, microstructural, analytical and numerical investigation
No full textRolling contact fatigue is the main cause of failure in bearings. Among other factors, damage phenomena are related to material properties and manufacturing processes. The damage evolution might be affected by microinclusions present in the material. This influence is related to composition, dimension, shape and location of microinclusions. The relation between microinclusions and fatigue life is investigated for both specimens undergoing
rotating bending fatigue and balls undergoing Hertzian pressure fatigue for 100Cr6. A life model for balls, involving microinclusions effect and actual ball rotation movements is proposed. Failures are analyzed to relate life of rolling elements to the microinclusion parameters
Can CSR classification be generally applied outside Britain?
No full textThe general applicability of CSR classification (a methodology for applying CSR theory) has not been tested outside Britain. We hypothesised that principal axes of trait variation for plant species native to southern European continental, sub-alpine and alpine bioclimatic zones correlate with CSR classification scores. Functional traits were quantified in situ for 506 species of 57 families. Multivariate analysis revealed three main modes in which plants invested biomass: (1) architectural extension of individual ramets (tall canopies, large leaves), (2) durable tissues (high leaf dry matter contents and carbon contents, low specific leaf areas) or (3) regenerative development (early, extensive flowering with delicate, nitrogen-rich leaves). These were highly significantly correlated with the extent of competitive ability (C), stress-tolerance (S) and ruderalism (R), respectively, determined by CSR classification. Despite being calibrated using only 43 British species, CSR classification is consistent with trait variation in a phylogenetically broader sample of species native to a wider range of bioclimatic zones
CO2 Laser irradiation of GeO2 planar waveguide fabricated by rf-sputtering
No full textGeO2 transparent glass ceramic planar waveguides were fabricated by a RF-sputtering technique and then irradiated by a pulsed CO2 laser. The effects of CO2 laser processing on the optical and structural properties of the waveguides were evaluated by different techniques including m-line, micro-Raman spectroscopy, atomic force microscopy, and positron annihilation spectroscopy. After laser annealing, an increase of the refractive index of approximately 0.04 at 1.5 μm and a decrease of the attenuation coefficient from 0.9 to 0.5 db/cm at 1.5 μm was observed. Raman spectroscopy and microscopy results put in evidence that the system embeds GeO2 nanocrystals and their phase varies with the irradiation time. Moreover, positron annihilation spectroscopy was used to study the depth profiling of the as prepared and laser annealed samples. The obtained results yielded information on the structural changes produced after the irradiation process inside the waveguiding films of approximately 1 μm thickness. In addition, a density value of the amorphous GeO2 samples was evaluated.Fil: Chiasera, A.. Consiglio Nazionale delle Ricerche. Istituto di Fotonica e Nanotecnologie; ItaliaFil: Macchi, Carlos Eugenio. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física de Materiales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; ArgentinaFil: Mariazzi, C.. Università di Trento. Dipartimento di Fisica; ItaliaFil: Valligatla, S.. Consiglio Nazionale delle Ricerche. Istituto di Fotonica e Nanotecnologie; Italia. University of Hyderabad. School of Physics; India. Università di Trento. Dipartimento di Fisica; ItaliaFil: Lunelli, L.. Bruno Kessler Foundation; Italia. National Research Council Institute of Biophysics; ItaliaFil: Pederzolli, C.. Bruno Kessler Foundation; ItaliaFil: Rao, D. N.. University of Hyderabad. School of Physics; IndiaFil: Somoza, Alberto Horacio. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física de Materiales; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; ArgentinaFil: Brusa, R. S.. Università di Trento. Dipartimento di Fisica; ItaliaFil: Ferrari, M.. Consiglio Nazionale delle Ricerche. Istituto di Fotonica e Nanotecnologie; Itali
La familiarità e lo stile cognitivo influenzano l’acquisizione della mappa mentale di una città?
No full textThe intimacy between sexual traits and Grime’s CSR strategies for orchids coexisting in semi-natural calcareous grassland at the Olive Lawn
No full textThe diversity of orchid species in semi-natural calcareous grassland is thought to depend on floral variability. However, differences in primary life-history strategy, or the overall suite of functional traits, could also affect coexistence. Both primary strategy (affecting day-to-day survival) and reproductive traits (representing periodic events) have been hypothesized to contribute to a general mechanism regulating the local persistence and relative abundance of species. We recorded species identity at 8,000 points at the centimetre scale along sixteen 5-m long transects at the Olive Lawn, a xeric sand calcareous grassland near Lecco, Italy. Transects allowed the relative abundance and spatial aggregation of Grime's competitor, stress-tolerator, ruderal (CSR) strategies to be quantified. Orchid flowering and fruiting phenology was recorded alongside the phenology of graminoid growth. Seven orchid species were present and exhibited a spectrum of strategies spanning two extremes, (1) small early-flowering ruderals (R/CR-selected), and (2) larger-leaved competitors (C/CR) flowering later as dominant graminoids attained maximum height. These orchids, and other subordinate species in the community, exhibited random spatial distributions amongst dominant graminoids that exhibited a high degree of spatial aggregation and similar, but non-identical, stress-tolerator (S) strategies. The reproductive phenology of meadow orchids is an intimate component of their CSR strategies, and appears to promote coexistence by allowing segregation between temporal niches and the exploitation of opportunities between clumps of dominant species. Only for closely related species with identical CSR strategies, such as Ophrys benacensis and Ophrys sphegodes, could specific floral differences alone explain coexistence
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