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A correlação entre irreversibilidade magnética e resistência elétrica nula em monocristais de YBa2Cu3O7-δ dopados quimicamente
No full textAt this work is conducted an experimental study of dc magnetometry and
ac electrical resistivity about the effects of substitution of Y for Ca up to 10% in
YBa
2
Cu
3
O
7-δ
structure on the magnetic irreversibility, T
(H) and zero electric
resistance, T
0
(H) temperatures. The Y
1-x
Ca
x
Ba
2
Cu
3
O
7-δ
irr
(x = 0, 0,01 e 0,1) single
crystals were prepared by self flux technique and the dc magnetization and
magnetoresistance measurements were conducted respectively with a SQUID
and a PPMS measurement systems. Magnetic fields up to 50kOe were applied
parallel to the c axis of single crystals. The magnetoresistance transition of the
McCa1% sample displayed a strong inhomogeneous character which was not
reproduced to the McCa10% sample. The observation of this particular
character to the McCa1% sample was attributed to the possible underdoped
oxygen level of its structure. The magnetic irreversibility line (MIL) behavior of
doped samples at the H-T diagram was characterized by predominance of the
Josephson vortices dynamic to H ≤ 1kOe and to H > 1kOe the MIL was ruled by
the Abrikosov vortices dynamic. In this scenario the MIL behavior to H ≤ 1kOe is
interpreted by the superconducting glass model take into account the spin glass
magnetic irreversibility analogy. In contrast, the MIL behavior to H > 1kOe is
described by the giant flux creep (gfc) model. The gfc model was applied to the
MIL interpretation of the YBa
2
Cu
3
O
(McY) singlecrystal in its H-T diagram
entirety. In the doped samples the T
7-δ
irr
(H) and T
(H) correlation has been shown
discordant to H ≤ 5kOe. This particular behavior suggests that these
temperatures depend of different parts of sample as could be expected to a
granular superconductor when the T
irr
0
(H) is ruled by the interconnectivity
established between the superconducting regions (grains) of the sample and
the T
(H) is ruled by the percolation of superconducting grains arrays over of
cross section area of the sample. In contrast, the T
0
irr
(H) and T
(H) are identical
to H > 5kOe what agrees to Abrikosov vortices dynamics preponderance on the
high magnetic field regime.A presente dissertação consiste na realização um estudo experimental
de magnetometria DC e resistividade elétrica AC sobre os efeitos da
substituição de até 10% do Y por Ca no sistema YBa
2
Cu
sobre a
correlação entre as temperaturas de irreversibilidade magnética, T
(H) e
resistência elétrica nula, T
0
(H). Os monocristais de Y
1-x
Ca
x
Ba
2
3
O
Cu
(x = 0,
0,01 e 0,1) foram crescidos pela técnica de auto-fluxo e as medidas de
magnetização DC e magnetoresistência AC foram realizadas com os auxílios
de um SQUID e de um PPMS onde H ≤ 50kOe foram aplicados paralelamente
ao eixo cristalográfico c dos monocristais. A transição magnetoresistiva da
amostra McCa1% exibiu um caráter fortemente inomogêneo o qual não se
mostrou tão intenso para a amostra McCa10%, sendo esta diferença atribuída
ao caráter subdopado em oxigênio da amostra McCa1%. A linha de
irreversibilidade magnética (LIM) das amostras dopadas mostraram-se
dominadas pela dinâmica de vórtices de Josephson para H ≤ 1kOe e pela
dinâmica de vórtices de Abrikosov quando H > 1kOe foram aplicados. Desta
forma, o comportamento da LIM para H ≤ 1kOe é interpretado pelo modelo de
vidro supercondutor levando em consideração a analogia com a
irreversibilidade magnética dos vidro de spin. Por outro lado, para H > 1kOe o
comportamento da LIM passa a ser descrito pelo modelo “flux creep” gigante
comportamento esse que foi reproduzido de todo o diagrama H-T do
monocristal de YBa
2
Cu
3
O
(McY). Nas amostras dopadas a correlação entre
T
irr
(H) e T
0
7-δ
(H) mostrou-se discordante para H ≤ 5kOe. Este comportamento
sugere que estas temperaturas dependam de diferentes partes da amostra, ou
seja, enquanto T
(H) depende da interconectividade dos anéis de regiões
supercondutoras, T
irr
(H), por sua vez, depende da percolação das estruturas
anteriores ao longo da seção transversal dos monocristais. Por outro lado,
T
irr
(H) e T
0
0
(H) mostram-se coincidentes para H > 5kOe o que está de acordo
com a preponderância da dinâmica de Abrikosov para este patamar de campo
magnético aplicado
A correlação entre irreversibilidade magnética e resistência elétrica nula em monocristais de YBa2Cu3O7-δ dopados quimicamente
No full textAt this work is conducted an experimental study of dc magnetometry and
ac electrical resistivity about the effects of substitution of Y for Ca up to 10% in
YBa
2
Cu
3
O
7-δ
structure on the magnetic irreversibility, T
(H) and zero electric
resistance, T
0
(H) temperatures. The Y
1-x
Ca
x
Ba
2
Cu
3
O
7-δ
irr
(x = 0, 0,01 e 0,1) single
crystals were prepared by self flux technique and the dc magnetization and
magnetoresistance measurements were conducted respectively with a SQUID
and a PPMS measurement systems. Magnetic fields up to 50kOe were applied
parallel to the c axis of single crystals. The magnetoresistance transition of the
McCa1% sample displayed a strong inhomogeneous character which was not
reproduced to the McCa10% sample. The observation of this particular
character to the McCa1% sample was attributed to the possible underdoped
oxygen level of its structure. The magnetic irreversibility line (MIL) behavior of
doped samples at the H-T diagram was characterized by predominance of the
Josephson vortices dynamic to H ≤ 1kOe and to H > 1kOe the MIL was ruled by
the Abrikosov vortices dynamic. In this scenario the MIL behavior to H ≤ 1kOe is
interpreted by the superconducting glass model take into account the spin glass
magnetic irreversibility analogy. In contrast, the MIL behavior to H > 1kOe is
described by the giant flux creep (gfc) model. The gfc model was applied to the
MIL interpretation of the YBa
2
Cu
3
O
(McY) singlecrystal in its H-T diagram
entirety. In the doped samples the T
7-δ
irr
(H) and T
(H) correlation has been shown
discordant to H ≤ 5kOe. This particular behavior suggests that these
temperatures depend of different parts of sample as could be expected to a
granular superconductor when the T
irr
0
(H) is ruled by the interconnectivity
established between the superconducting regions (grains) of the sample and
the T
(H) is ruled by the percolation of superconducting grains arrays over of
cross section area of the sample. In contrast, the T
0
irr
(H) and T
(H) are identical
to H > 5kOe what agrees to Abrikosov vortices dynamics preponderance on the
high magnetic field regime.A presente dissertação consiste na realização um estudo experimental
de magnetometria DC e resistividade elétrica AC sobre os efeitos da
substituição de até 10% do Y por Ca no sistema YBa
2
Cu
sobre a
correlação entre as temperaturas de irreversibilidade magnética, T
(H) e
resistência elétrica nula, T
0
(H). Os monocristais de Y
1-x
Ca
x
Ba
2
3
O
Cu
(x = 0,
0,01 e 0,1) foram crescidos pela técnica de auto-fluxo e as medidas de
magnetização DC e magnetoresistência AC foram realizadas com os auxílios
de um SQUID e de um PPMS onde H ≤ 50kOe foram aplicados paralelamente
ao eixo cristalográfico c dos monocristais. A transição magnetoresistiva da
amostra McCa1% exibiu um caráter fortemente inomogêneo o qual não se
mostrou tão intenso para a amostra McCa10%, sendo esta diferença atribuída
ao caráter subdopado em oxigênio da amostra McCa1%. A linha de
irreversibilidade magnética (LIM) das amostras dopadas mostraram-se
dominadas pela dinâmica de vórtices de Josephson para H ≤ 1kOe e pela
dinâmica de vórtices de Abrikosov quando H > 1kOe foram aplicados. Desta
forma, o comportamento da LIM para H ≤ 1kOe é interpretado pelo modelo de
vidro supercondutor levando em consideração a analogia com a
irreversibilidade magnética dos vidro de spin. Por outro lado, para H > 1kOe o
comportamento da LIM passa a ser descrito pelo modelo “flux creep” gigante
comportamento esse que foi reproduzido de todo o diagrama H-T do
monocristal de YBa
2
Cu
3
O
(McY). Nas amostras dopadas a correlação entre
T
irr
(H) e T
0
7-δ
(H) mostrou-se discordante para H ≤ 5kOe. Este comportamento
sugere que estas temperaturas dependam de diferentes partes da amostra, ou
seja, enquanto T
(H) depende da interconectividade dos anéis de regiões
supercondutoras, T
irr
(H), por sua vez, depende da percolação das estruturas
anteriores ao longo da seção transversal dos monocristais. Por outro lado,
T
irr
(H) e T
0
0
(H) mostram-se coincidentes para H > 5kOe o que está de acordo
com a preponderância da dinâmica de Abrikosov para este patamar de campo
magnético aplicado
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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