1,720,979 research outputs found
Measurement of the longitudinal relaxation time by continuous-wave, nonlinear electron spin resonance spectroscopies
No full textWe characterize a continuous-wave, nonlinear electron spin resonance spectroscopy which detects the longitudinal component of the magnetization, It is demonstrated that the signal is proportional to the Laplace transform of a relaxation function with decay time equal to the longitudinal relaxation time T-1. The conclusion is reached by comparing T-1 to the effective time T-1((eff)) being drawn by progressive saturation for a nitroxide radical dissolved in supercooled o-terphenyl. (C) 1998 Academic Press
EVIDENCE OF LARGE-ANGLE REORIENTATION IN SUPERCOOLED O-TERPHENYL
No full textWe study the reorientation process of a paramagnetic radical dissolved in supercooled o-terphenyl around and below T-g via the Electron Spin Resonance spectroscopy. The experimental results are at variance with the hypothesis of diffusive reorientation of the radical. Instead, the ESR lineshapes are fairly well reproduced by assuming that the radical reorientates via large angular jumps with a width Delta phi = 80 degrees(-5 degrees)(+10 degrees). The results are compared with previous H-2 NMR studies
Rotational dynamics of a molecular probe in tri-cresyl phosphate: from 'stick' to 'slip' boundary conditions
No full textThe rotational dynamics of a molecular probe dissolved in the glass-former tri-cresyl phospate has been studied by linear and non-linear Electron Spin Resonance spectroscopy. At the highest temperatures the Debye-Stokes-Einstein (DSE) law with stick boundary conditions holds. On cooling, a transition region is crossed and then a new regime sets in Which is accounted for by the DSE law provided that slip boundary conditions are assumed. At the lowest temperatures the rotational diffusion and the shear viscosity are decoupled. The onset of the decoupling takes place close to T-c, the critical temperature predicted by the Mode Coupling Theory
Debye-Stokes-Einstein fractional law in a polymeric liquid crystal: A non-linear ESR study by using spin probes with different symmetries
No full textThe reorientation of spin probes with very different aspect ratios, dissolved in a polymeric liquid crystal, is studied by non-linear Electron Spin Resonance. A scaling law between the rotational correlation time tau and the macroscopic viscosity, as measured via the dynamic shift factor a(T), is found. A discussion on the current interpretations of the scaling, which takes the form tau proportional to a(T)(xi) with 0 less than or equal to xi less than or equal to 1, is given
Jump reorientation of a molecular probe in the glass transition region of o-terphenyl
No full textThe reorientation process of a molecular probe dissolved in the fragile glass former o-terphenyl is studied via electron spin-resonance spectroscopy. Owing to the good resolution of the ESR lineshape in the so-called slow-motion regime, we are able to discriminate between diffusive and jump rotations. In the region of the glass transition (T-g - 31 K < T ( T-g + 17 K) the results are at variance with the diffusion models and are fairly well reproduced by assuming that the probe jumps with steps phi = 80 degrees(-5 degrees)(+10 degrees). The temperature dependence of the correlation time is well described, in the temperature range investigated, by a double Arrhenius law broken at T-g. The findings are compared with previous NMR, dielectric, fluorescence and molecular dynamics studies
An experimental investigation on OBD II techniques for fuel injection system monitoring in a common rail passenger car diesel engine
No full textDifferent diagnostic techniques were experimentally tested on a common rail automotive 4 cylinder diesel engine in order to evaluate their capabilities to fulfill the California Air Resources Board (CARB) requirements concerning the monitoring of fuel injected quantity and timing. First, a comprehensive investigation on the sensitivity of pollutant emissions to fuel injection quantity and timing variations was carried out over 9 different engine operating points, representative of the FTP75 driving cycle: fuel injected quantity and injection timing were varied on a single cylinder at a time, until OBD thresholds were exceeded, while monitoring engine emissions, in-cylinder pressures and instantaneous crankshaft revolution speed. Afterwards, the different diagnostic algorithms under investigation, based both on crankshaft revolution speed sensor signal and on in-cylinder pressure sensor signal, were tested under steady state operating conditions in order to detect their fault rate detection capabilities. Finally, the more promising diagnostic algorithms, which were selected through the above mentioned process, were tested on transient conditions in order to assess their capabilities to detect both injection quantity and timing errors
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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