1,720,988 research outputs found
Magnetoresistance of RuO2-based thick film resistors
No full textIn a series of samples whose composition was systematically changed, we have studied the magnetoresistance (Delta R/R = [R(B)-R]/R) of RuO2-based thick film resistors (TFR's) in magnetic fields (B) up to 20 Tesla and in a temperature range (1.2K<T<40K) in which their resistance exhibits insulating behavior at the boundary between rite strong and the weak localization. At the higher temperatures, Delta R/R exhibits a positive bump, that does not depend on the RuO2 concentration but it changes with the concentration of magnetic Mn impurities diluted in the glassy matrix. For T less than or equal to 20 K magnetoresistance is entirely negative and it has a quadratic magnetic field dependence at low field. We use the weak localization theory to relate these features of the high temperature magnetoresistance to the composition of TFR's. At low temperature (T<4.2K) the negative magnetoresistance shows some peculiarities. The quadratic term shrinks, within a vanishing magnetic field range and the magnetoresistance linearly increases in a wide range of B. Ar the strongest fields and the lowest temperature Delta R/R shows a tendency to saturation. Although these results do not enable to discriminate among different mechanisms, we note that the low temperature (T<4.2 K) behavior is essentially consistent,with recent theory of Nguen et al
Magnetic and electronic properties of Mn4Si7
No full textWe present a systematic study of the magnetization, Hall effect and specific heat on single crystals of Mn4Si7. Curie-Weiss law is observed above 43 K. At low-temperature moments order in an anisotropic helical state and are aligned above 1 T. We observe an anomalous Hall effect in both rho(H) vs. B and in R-H vs. T curves and a field dependence of the low T specific heat due to spin fluctuations. The magnetic moments (p(eff) and p(sat)) are the lowest reported for similar itinerant magnetic systems, this suggests that Mn4Si7 is a good candidate to observe critical quantum fluctuations expected for a marginal Fermi liquid
Electronic properties of TiSi2 single crystals at low temperatures
No full textWe report measurements of Hall effect, transverse magnetoresistance, and specific heat on high-quality TiSi2 (C54 phase) single crystals at low temperatures. We used crystals with low residual resistivity (typically rho(4.2 K)=0.15 mu Omega cm) and magnetic fields (B) up to 20 T. These facts allowed us to study the electronic properties from the low (omega(c) tau much less than 1) to the high field regime (omega(c) tau>1, omega(c)=eB/m* being the cyclotron frequency and tau the electron relaxation time) as a function of magnetic-field strength and temperature. The low field Hall coefficient R(H) is negative, almost constant R(H)=-(0.5+/-0.1)x10(-10) m(3)/C between 100 and 300 K and it changes sign at similar to 30 K. The angular dependence of magnetoresistance shows either minima or maxima when the magnetic field is parallel to the principal crystallographic axes. These structures are, however, less pronounced than in other silicides, such as PdSi2 and NbSi2, and this suggests only a weak anisotropy of the TiSi2 Fermi surface. The galvanomagnetic properties behave consistently with band-structure calculations of Mattheiss and Hensel [Phys. Rev. B 39, 7754 (1989)] who found that TiSi2 is a compensated metal with only closed orbits for the Fermi electrons. Using a simple two-band model we estimated, from the low field magnetoresistance, carrier density n(e)=n(h)=(0.45-0.52)x10(22) cm(-3) assuming equal concentration of electrons and holes. Low temperatures (1.6<22 K) specific-heat (C-p) measurements fit a linear C-p/T=gamma+beta T-2 dependence, with gamma=3.35+/-0.05 mJ/K-2 mol and beta=0.0201+/-0.0005 mJ/K-4 mel. From these parameters we estimated the Debye temperature Theta(D)=662+/-4 K and the renormalized electronic density of states at the Fermi surface N(epsilon(F))(1+lambda)=2.85 states/eV cell
Some properties of the phonon spectra of transition metal disilicides VSi2, NbSi2, and TaSi2
No full textThe phonon spectra of metallic disilicides VSi2, NbSi2, and TaSi2 have been studied in detail by inelastic neutron scattering at 300 K and specific heat measurements between 10 K and 250 K. The specific heat calculated from the generalised phonon density of states extracted from neutron measurements is in good agreement with the measured lattice contribution to the specific heat. The properties of the phonon spectra are discussed in relation with other data reported for these isostructural and isoelectronic disilicides. (C) 2003 Elsevier Science Ltd. All rights reserved
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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