1,721,039 research outputs found
Pairing state in the ruthenocuprate superconductor RuSr2GdCu2O8: A point-contact Andreev reflection spectroscopy study
No full textThe results of point contact Andreev reflection spectroscopy on polycrystalline RuSr2GdCu2O8 pellets are presented. The wide variety of the measured spectra are all explained in terms of a modified Blonder–Tinkham–Klapwijk model considering a d-wave symmetry of the superconducting order parameter. Remarkably low values of the energy gap Δ=(2.8±0.2) meV and of the 2Δ∕kBTc≃2 ratio are inferred. From the temperature evolution of the dI∕dV vs V characteristics we extract a sublinear temperature dependence of the superconducting energy gap. The magnetic field dependence of the conductance spectra at low temperatures is also reported. From the Δ vs H evolution, a critical magnetic field Hc2≃30 T is inferred. To properly explain the curves showing gap-like features at higher voltages, we consider the formation of a Josephson junction in series with the point contact junction, as a consequence of the granularity of the sample
A tunneling spectroscopy study of the pairing symmetry in the electron-doped Pr1−xLaCexCuO4−y
No full textWe have performed scanning tunneling spectroscopy and point contact spectroscopy
measurements on the electron-doped superconductor Pr1−xLaCexCuO4−y (x = 0.12,
Tc ? 25 K). We address the question of the symmetry of the order parameter and of the
amplitude of the energy gap. We compare three possible scenarios, i.e. isotropic s-wave,‘anisotropic’ s-wave, and d-wave. Evidence for a d-wave symmetry of the order parameter is given. From the temperature evolution of the dI/dV versus V characteristics we extract a
BCS-like temperature dependence of the superconducting energy gap ?. Despite the variety of measured spectra we give a consistent explanation for the whole set of data, indicating ? = (3.6 ± 0.2) meV and a ratio 2?/KBTC ? 3.5 ± 0.2. In particular, point contact characteristics showing gap-like features at higher voltages have been interpreted by considering the formation of an intergrain Josephson junction in series with the point contact junction. Further confirm..
Andreev reflection in ferrimagnetic CoFe_{2}O_{4} spin filters
No full textWe have performed point-contact spectroscopy measurements on a sample constituted by a metallic ferromagnetic oxide (SrRuO3) bottom electrode and a tunnel ferrimagnetic (CoFe2O4) barrier. Andreev reflection is observed across the tunnel barrier. From the comparison of Andreev reflection in SrRuO3 and across the CoFe2O4 barrier we infer that the ferrimagnetic barrier has a spin filter efficiency not larger than +13%. The observation of a moderate and positive spin filtering is discussed in the context of the microstructure of the barriers and symmetry-related spin-filtering effects
Tellurium-Poly(methyl methacrylate) nanocomposite materials
No full textFine powders composed of tellurium grains of average size less than 10 nm were produced by dry vibration milling combined with liquid-phase sedimentation techniques, starting from polycrystalline powders with average grain diameter of ca. 30 μm. A novel nanocomposite material was obtained by binding the nanosized tellurium grains with poly(methyl methacrylate) (PMMA), using a solvent mediated method. The morphological, structural and electrical properties of Te/PMMA nanocomposite films were investigated. The Raman spectroscopy points out that the prepared material was composed of Te and TeO2 crystalline phases. Infrared spectroscopy analysis indicates that the milled powder contained an increased amount of tellurium oxide as compared to the “as received” powder. The electrical properties of the films were studied in dark condition and under white light illumination turning on and off the light cyclically. Te/PMMA nanocomposite films show a linear behavior of the photocurrent under white light illumination varying the optical power density of about three order of magnitude (2-1,608 mW/cm2). The observed photoconductivity properties [1-3] make the fabricated Te/PMMA material exploitable for plastic electronic applications [4]
Carbon Nanorods Synthesized by Graphite Oxide Thermal Reduction with Microwaves
No full textRecently, carbon nano-rods (CNRs) have been investigated for potential applications as support for catalytic metal nanoparticles, in gas storage, electrochemical energy storage, etc. [1]. The CNRs consist of stacked graphene sheets with aspect ratios ranging from 3 to 5 and their functional properties arise from quantum-confinement and surface effects [1]. These materials have been produced by different techniques, like for example arc discharge, plasma torch, CVD, nanocasting, etc. [1]. In this work, CNRs have been obtained as byproduct of the graphene synthesis made by thermal reduction of graphite oxide (GO), using microwave heating [2]. In particular, water solutions of GO have been synthetized according to the Hummers method and dried to give GO paper. This solid material has been dissolved in N-methyl-2-pyrrolydone (NMP) by a prolonged ultrasound treatment and the achieved GO/NMP solution has been heated to the solvent boiling point (202°C) in a microwave oven. In a few minutes the solution turned into a black graphene/NMP suspension and by a filtering procedure a graphite/NMP gel and a reddish CNRs/NMP solution have been obtained. The CNRs have been recovered by solvent removal and purified by washing with ethanol. The purified product has been morphologically characterized by transmission electron microscopy (TEM). According to the TEM micrographs shown in Figure 1, CNRs have length of several hundred nanometers (300-600 nm) and height less than 100 nm. The excitation-emission properties of these nanostructures were investigated by florescence spectroscopy
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
Low density polyethylene coated by graphene nanoplatelets
No full textAn advantageous micromechanical technique to deposit large area graphene nanoplatelet (GNP) thin films on a low-density polyethylene substrate is proposed. This method, based on the application of shear-stress and friction forces to a graphite platelets/ethanol paste on the surface of a polymeric substrate, allows to obtain films of overlapped nanoplatelets mainly made of 13-30 graphene layers. X-ray diffraction (XRD), atomic force and transmission electron microscopy (TEM) measurements support the occurrence of a partial exfoliation of the graphite platelets due to shear-stress and friction forces applied during film formation. Scanning electron microscopy (SEM) observations point out that the surface of the polymer is uniformly coated by GNP unities, and the TEM analysis reveals the tendency of the nanoplatelets to align parallel to the interfacial plane. It has been found that the deposited samples, under white light illumination, exhibit a negative photoconductivity and a linear photoresponse as a function of the applied voltage and the optical power density in the -120÷120 mV and 20.9÷286.2 mWcm-2 ranges, respectively. These structural and electrical characteristics will be compared to those of LDPE films coated with thin layers deposited by spraying a commercial graphite-based product
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
- …
