1,720,973 research outputs found
The Effect of a DC Magnetic Field on the AC Magnetic Properties of Oleic Acid-Coated Fe3O4 Nanoparticles
No full textThe AC magnetic properties of a sample of Fe3O4 nanoparticles coated with oleic acid have been investigated with the help of AC susceptibility measurements. In particular, several DC magnetic fields have been superimposed on the AC field, and their effect on the magnetic response of the sample has been analysed. The results show the presence of a double peak structure in the imaginary component of the complex AC susceptibility measured as a function of the temperature. A preliminary evaluation of the Mydosh parameter for both peaks gives the information that each one of them is associated with a different state of interaction between nanoparticles. The two peaks evolve both in amplitude and position when the intensity of the DC field is changed. The field dependence of the peak position shows two different trends, and it is possible to study them in the framework of the currently existing theoretical models. In particular, a model of non-interacting magnetic nanoparticles has been used to describe the behaviour of the peak at lower temperatures, whereas the behaviour of the peak at higher temperatures has been analysed in the framework of a spin-glass-like model. The proposed analysis technique can be useful for the characterisation of magnetic nanoparticles used in several types of applications, such as biomedical and magnetic fluids
The Vortex Glass-Liquid Transition In Fe1.02Se Crystal
No full textThe vortex-glass (VG) to vortex-liquid (VL) transition is studied in flux-grown Fe1.02Se crystal with nanosized hexagonal phase inclusions. These non-superconducting impurities effectively pin the vortices and shift lightly the irreversibility line to higher fields and temperatures in comparison with single crystal. It is shown that the interplay between vortex pinning and thermal fluctuations enable the observation of VG-VL transition. The existence of this transition was proved by the scaling presentation of current-voltage characteristics at two different magnetic fields. The obtained scaling parameters are practically field independent. The values of the dynamic z exponent are in the range predicted by the VG model, while the values of static ν exponent are a little smaller. This is not considered as a lack of the universality of the model, but rather as a consequence of the type of pinning and special domain morphology of the crystal resembling the granularity in polycrystalline sample
DC magnetic characterization and pinning analysis on Nd1.85Ce0.15CuO4 cuprate superconductor
No full textWe report the analysis of the magnetic response detected on the cuprate superconductor Nd1.85Ce0.15CuO4. In particular the magnetic behavior of the sample has been studied by means of DC magnetization measurements as a function of the temperature (T) and DC magnetic field (H). The superconducting critical temperature Tc has been obtained by analyzing the m(T) curve performed in Zero Field Cooling-Field Cooling conditions. Moreover, the m(T) curve shows the presence of a magnetic background for temperatures above Tc. By considering the superconducting m(H) hysteresis loop at different temperatures, it can be noted that the width of the curves appears narrow corresponding to a weak superconductivity. This is confirmed by the field dependence of the critical current densities Jc extracted from the superconducting hysteresis loops m(H) at different temperatures within the Bean critical state model. In fact, at the lowest measurement temperature, Jc is close to zero already at low magnetic fields. Nevertheless, by means of the temperature dependence of Jc, the sample shows a strong pinning behavior that can open perspectives for future improvement in the fabrication of this material
Evaluation of the intragrain critical current density in a multidomain FeSe crystal by means of dc magnetic measurements
No full textThe magnetic behavior of an iron-based FeSe crystal sample has been studied by means of dc magnetization measurements as a function of the temperature (T), the dc magnetic field (H) and the time (t). The M(T) curves show a discrepancy in the determination of the onset of the critical temperature T C with respect to what is observed in the superconducting M(H) measurements obtained by subtracting the ferromagnetic background from the curves measured at various temperatures. By using magnetic relaxation measurements M(t), the correct value of T C has been obtained. Moreover, the superconducting M(H) loops show the presence of a noisy signal up to an anomalous 'peak effect' only found for positive and negative increasing fields. These features have been analyzed by fitting the temperature dependence of the critical current density J c(T), extracted from the M(H) loops, with the help of the J c(T) dependencies governing an S-N-S junction network. This analysis has allowed us to interpret the behavior found in the M(H) loops and to obtain the value of the intrinsic critical current density J 0 which is not influenced by the presence of the junctions
Critical current and flux dynamics in Ag-doped FeSe superconductor
No full textThe measurements of DC magnetization as a function of the temperature M(T), magnetic field M(H), and time M(t) have been performed in order to compare the superconducting and pinning properties of an undoped FeSe0.94 sample and a silver doped FeSe0.94 + 6 wt% Ag sample. The M(T) curves indicate an improvement of the superconducting critical temperature and a reduction of the non-superconducting phase Fe7Se8 due to the silver doping. This is confirmed by the field and temperature dependent critical current density Jc(H,T) extracted from the superconducting hysteresis loops at different temperatures within the Bean critical state model. Moreover, the combined analysis of the Jc(T) and of the pinning force Fp(H/Hirr) indicate that the pinning mechanisms in both samples can be described in the framework of the collective pinning theory. The U∗(T, J) curves show a pinning crossover from an elastic creep regime of intermediate size flux bundles, for low temperatures, to a plastic creep regime at higher temperatures for both the samples. Finally, the vortex hopping attempt time has been evaluated for both samples and the results are comparable with the values reported in the literature for high Tc materials
Effect of Magnetite Nanoparticles Content on the Magnetic Properties of Polylactide and Polystyrene Composites
No full textThe effect of magnetite nanoparticles (NPs) content on the magnetic properties of polylactide (PLA) and polystyrene (PS) matrix has been investigated by means of DC magnetization measurements as a function of temperature (T) and magnetic field (H). Previous to the dispersion by melt-compounding into PLA and PS, the magnetite NPs have been reactively surface treated with 3% polymethylhydrogensiloxane (MHX) in order to make them hydrophobic and more stable to the action of oxygen and moisture. The magnetic analysis of the properties has been performed by measuring the Zero Field Cooling (ZFC) magnetization curve as a function of the temperature, at 0.1 Tesla applied field. In this framework, a superparamagnetic shape like has been noted for all the samples with the possibility to individuate the blocking temperature (TB) of the NPs. Moreover, the magnetization as a function of the field has been measured at room temperature (in particular above TB) investigating the coercive field and the magnetization values finding potentially interesting results. In particular, the very low values obtained for the coercive field at room temperature, together with the maximum found in the ZFC curve, have confirmed the superparamagnetic behavior of the PLA and PS - magnetite filled samples. Finally, a table with the fundamental magnetic features values of the samples has been reported for understanding if the obtained results for this kind of surface treated NPs and the afferent nanocomposites could be suitable for being used in applications requiring superparamagnetic properties (protection of environment, magnetic microcarriers, magnetic separation of stem cells, other biomedical purposes)
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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