104,928 research outputs found
Examples of groups in abstract Algebra Course Books
No full textThis study has been conducted with the aim to examine the examples of Abelian and non-Abelian groups given in the abstract algebra course books in the university level. The non-examples of Abelian groups serve as examples of non-Abelian groups. Examples with solutions in the course books are trusted by the students and hence miscellaneous of those are required to clarify the subject in enough detail. The results of the current study show that the examples of Abelian groups are about the same among three course books, including number sets only with known operations. The examples of non-Abelian groups are rare in comparison and encapsulate the nonnumeric sets which are novel to students. The current study shows the mentioned examples are not sufficiently examined in the course books. Suggestions for the book writers are given in the study. Mainly it is suggested that more and various examples of Abelian and especially non-Abelian groups should be included in the course books
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Surface modification of the Co-free LiNi0.5 Mn1.5O4-δ positive electrode material for high-voltage lithium-ion batteries
No full textThe aim of this thesis was to modify the surface of the LNMO powder to improve
its electrochemical performance as a high-voltage lithium-ion battery positive
electrode material. Different types of LNMO powders, synthesis routes and surface
modification materials were explored to achieve this target.
The Ti-containing surface modification materials were shown to be effective in
improving the LNMO electrochemical performance:
Ti surface doped LNMO nanopowders synthesized via the hydrolysiscondensation approach improved the LNMO cyclic stability, Coulombic
efficiency and rate performance compared to bare LNMO
Amorphous-LTO surface modified LNMO micron-powders synthesized via the
solution-gel approach improved the LNMO rate performance, reduced the cell
impedance during cycling and improved the cyclic stability
Returning to the questions introduced in the scope of the thesis in Section 1.12:
A too high LNMO surface area results in low capacities due to a high amount
of side reactions for the LNMO commercial nanopowders, as in Chapter 2. A
micron-sized LNMO composed of large, irregular aggregates is not ideal either,
as in Chapter 3. Optimizing the pre-calcination conditions during the aqueous
solution-gel synthesis route in Chapter 3 enabled synthesis of an optimum
LNMO particle size and morphology with good electrochemical performance.
To reach an optimum electrode preparation protocol and electrochemical
performance with a specific powder, the solvent concentration and slurry
mixture viscosity, therefore the electrode morphology, should be optimized.
Several electrode preparation parameters were studied in Chapter 4 and an
optimum preparation protocol is obtained.
Materials of strong metal-oxygen bonds are interesting candidates for surface
modification, to improve the LNMO surface stability at high voltages. Surface
doping occurs instead of surface coating, especially if high synthesis
temperatures are used. The surface doping approach is an effective way to
improve the electrochemical performance. Interesting candidates also include
amorphous oxides. The amorphous oxides seem to increase the side reactions
at the beginning of cycling. However, as the cycling continues, they might be
providing a more stable, compact CEI layer, since the cell resistance drops
and cycle life improves.
Two different synthesis approaches provide successful surface modifications
for the nano/micron-sized LNMO powders and improve the electrochemical
performance: The hydrolysis-condensation approach (Section 1.9.3.2) coupled with
LNMO nanopowders in Chapter 2. It provides uniformly doped LNMO
nanopowder surfaces. An electrostatic adsorption mechanism is
proposed to take place during synthesis. Electrically charged LNMO
surfaces apply electrostatic forces to ions/nanoparticles in the solution
over large distances and loosely bind them to their surface.
o The solution-gel approach (Section 1.9.4) coupled with LNMO micronpowders in Chapter 5. The solution-gel approach allows synthesis of
multi-metal ion surface modification materials with controlled
stoichiometry. It provides coatings/islands or surface dopants on
LNMO micron-powders. A surface complex formation mechanism is
proposed to take place during synthesis.
Possible reasons for the electrochemical performance improvements with the
Ti-based surface modification materials are:
o Surface structure stabilization by incorporation of the strong Ti-O
bonds
o Increased LNMO surface area after the surface modification leading to
lower polarization and improved rate performance
o A more favorable CEI layer formation on the electrode during cycling
The findings of this thesis are summarized below in further detail:
The thesis started with the use of commercial, nano-sized LiNi0.5Mn1.5O4-δ powder
in Chapter 2. A hydrolysis-condensation approach was used for surface
modification, followed by annealing. The surface of the LNMO powder was
modified by Ti cation doping over 2-4 nm depth, while maintaining the initial spinel
structure, using a hydrolysis-condensation approach followed by 500oC anneal.
Particle size and surface area of the bare and surface modified LNMO remained
similar after 500oC anneal and the Ti doped surface remained intact. Although the
initial discharge capacity was slightly reduced, cycle life, Coulombic efficiency and
rate performance were improved for Ti surface doped LNMO annealed at 500oC
compared to bare LNMO also annealed at 500oC. The improvement is probably
due to surface structure stabilization by the stronger Ti-O bonds, which reduces
the manganese dissolution. On the other hand, during an 800oC anneal, Ti diffused
from the surface towards the core of LNMO, causing a secondary LiNi0.5-xMn1.5-
yTizO4 phase formation and particle size growth. Mn-Ni ordering in the lattice
increased with 800oC annealing in oxygen for both bare and surface modified
LNMO samples, compared to 500oC annealed samples in oxygen. However, no
significant improvement was observed in cycle life or Coulombic efficiency of Ti
surface modified LNMO annealed at 800oC compared to bare LNMO also annealed
at 800oC. This is probably because the Ti doped surface layer of LNMO was in this
case not well preserved during Ti diffusion and particle size growth. The Ti surfacedoped LNMO annealed at 500oC, having a well preserved spinel surface structure
and a disordered Mn-Ni distribution, could be an interesting candidate as a
cathode material for lithium-ion battery applications requiring both good cycle life
and rate performance. The thesis continued with the synthesis of LNMO powders to achieve an optimum
particle size, morphology and electrochemical performance in Chapter 3. The
LNMO particle size and morphology were controlled using aqueous solution-gel
synthesis with different pre-calcination temperatures, times and oven types.
Crystalline LNMO powder morphology and particle sizes were shown to depend on
the organic residue in the LNMO precursor powder before the 900oC calcination
step. Calcining the LNMO precursor gel at 200oC for 40 h in a forced convection
oven (LNMO-4) started a vigorous decomposition reaction and resulted in a
voluminous, foam-like precursor powder morphology. The amount of organic
residues before crystallization was minimized in the LNMO-4 precursor powder,
enabling a small particle size after the 900oC calcination step with well-defined
facets. LNMO-4 provided the highest initial discharge capacity of 121 mAh/g at
0.2 C compared to other LNMO powders. On the other hand, organic removal was
probably incomplete with 170oC, 24 h, natural-convection oven pre-calcination
during LNMO-1 precursor powder synthesis, resulting in large aggregates with
non-uniform size distribution and poor electrochemical performance. The
carboxylates or carbonaceous residues present in LNMO-1 precursor powder
possibly adsorb on the surface of small metal oxide nuclei cause agglomeration
and prevent formation of well-defined facets during the 900oC calcination step.
Ball-milling of crystalline LNMO powder (LNMO-3) reduced the agglomeration and
particle size, increased the disordering, Mn3+ concentration and lattice parameter.
However, the initial discharge capacities of LNMO-3 were lower compared to
LNMO-4, which was linked to the increased surface area, Mn3+ concentration and
side-reactions. LNMO particle size optimization via controlling the pre-calcination
conditions is more advantageous compared to size reduction via ball-milling, in
terms of preserving well-defined facets, a high capacity and high Coulombic
efficiency.
The synthesized LNMO powders in Chapter 3 were used to optimize the electrode
properties in Chapter 4, which also has an important influence on the
electrochemical properties. An optimized electrode preparation protocol was
proposed for the synthesized LNMO active material of ~30 μm average aggregate
and ~3.5 μm average primary particle size, after individually examining the
effects of composite electrode processing parameters on the electrochemical
performance of the Li|LNMO cells. A good rate performance was obtained for
LNMO electrodes made using a 150 μm wet thickness, 3 wt. % PVDF-NMP mixture
and C65 carbon black. The use of C45 carbon black can improve the initial
discharge capacity, reduce the amount of parasitic side reactions and improve the
cyclability compared to C65. However, the application of C65 should be preferred,
if a higher rate performance is desired. Thinky planetary mixing method coupled
with a LNMO-carbon black dry mixing step could be preferred over ball-milling to
homogeneously distribute the carbon black particles and increase porosity while
eliminating LNMO particle size, crystalline structure or morphology changes. A
calendering step should be applied to optimize the porosity, improve the electrical
contact and reduce the cell impedance. However, LNMO particle size and shape
should be considered while calendering and excessive forces should be avoided
since LNMO particles could break apart during calendering resulting in a lower
capacity.
The optimized LNMO synthesis and electrode making routes in Chapters 3 and 4
were used to explore the influence of amorphous LTO surface modification of
LNMO on the electrochemical performance in Chapter 5. LNMO surface was
modified with amorphous LTO material (LNMO@LTO-200oC) via a solution-gel
route, resulting in Ti-rich amorphous coatings/islands or Ti-rich spinel surfaces
mostly on the {001} surfaces of LNMO. Transition metal ions on LNMO powder
surfaces partly dissolved into the aqueous, citric acid LTO precursor solution
during the LNMO@LTO-200oC synthesis. The dissolved TM ions precipitated
together with the Ti ions in the LTO precursor solution during the water removal
step and formed the Ti-Ni-Mn-O containing amorphous nanoparticles inside the
LNMO@LTO-200oC powder. Upon 500oC annealing in dry air flow (LNMO@LTO500oC), the amorphous matter crystallized into spinel or rock salt nanoparticles
depending on the composition. Amorphous LTO surface modification slightly
increased the Mn3+ concentration in LNMO based on the capacity curve
measurements and dQ/dV plots, but the electronic or bulk ionic conductivities
were not improved. Amorphous LTO surface modification increased the LNMO
surface area by ~4 times. The rate performance and cyclability were improved for
LNMO@LTO-200oC compared to bare LNMO, while crystallized LNMO@LTO-500oC
showed similar rate performance and cyclabilites compared to its bare
counterpart. The cell impedance increased more rapidly for the bare LNMO
compared to LNMO@LTO-200oC, while the dry air annealed samples had similar
impedances after 1000 cycles. Amorphous coating-HF scavenging reactions might
be occuring slowly on the LNMO@LTO-200oC powder surfaces during cycling,
providing a more favorable CEI layer formation on the electrode surface compared
to bare LNMO.
ZrO2-SiO2 surface modification materials were explored for LNMO in Chapter 6 via
the hydrolysis-condensation approach. ZrO2 surface modified LNMO was
synthesized using different ZrO2 loadings. A too thick, tetragonal ZrO2 coating
layer was probably synthesized on LNMO using 0.2 mL NH3 (25 wt. %) and 4 h
annealing time, which impedes the Li+ transport and causes a large capacity drop.
ZrO2 coating made using 0.1 mL NH3 (25 wt. %) and 4 h annealing time on the
other hand provided probably a more optimum coating thickness, a slightly
improved initial capacity but a deteriorated cyclic stability. The cyclic stability was
improved using a longer anneal time of 10 h, which probably promotes Zr ion
doping into the LNMO surface structure and improves the CEI layer stability during
cycling at room temperature. Cycling temperature was increased to 55oC to
increase the amount of side-reactions and to observe the influence of the ZrO2
surface modification layer better. Improved Coulombic efficiency values were
recorded for the surface modified LNMO compared to the bare LNMO. This could
be explained by a HF-scavengering mechanism where Zr cations react with HF to
form a more stable, ZrF4 containing CEI layer.
SiO2 was incorporated on the LNMO surface together with the ZrO2. Lower or
higher temperatures were used to synthesize ZrO2-SiO2 coated or Zr-Si doped
LNMO surfaces. Neither showed an important improvement in the rate
performance. However, when also coupled with different cooling rates, important
variations in the Ni/Mn disordering were observed for the bare/ZrO2-SiO2 coated
LNMO powders, which greatly influenced the electrochemical performances. The
700oC annealed, slow cooled (1oC/min) bare/ZrO2-SiO2 surface modified LNMO
powders showed a drastic increase in the Ni/Mn ordering and better
electrochemical performance compared to the 500oC annealed, furnace cooled
bare/surface modified LNMO powders. Increased ordering is probably caused by
the slower cooling rate in oxygen flow. The higher temperature used on the other
hand could be introducing more oxygen vacancies in the structures, because of
the temperature dependent O2 evolution reaction. As a result, a more optimum
amount of oxygen vacancies and Ni/Mn ordering were probably achieved in the
bare/ZrO2-SiO2 surface modified LNMO powders with the 700oC annealing and
1°C/min heating/cooling rates, which helped improve the electrochemical
performance
Surface modification of the Co-free LiNi0.5 Mn1.5O4-δ positive electrode material for high-voltage lithium-ion batteries
No full textThe aim of this thesis was to modify the surface of the LNMO powder to improve
its electrochemical performance as a high-voltage lithium-ion battery positive
electrode material. Different types of LNMO powders, synthesis routes and surface
modification materials were explored to achieve this target.
The Ti-containing surface modification materials were shown to be effective in
improving the LNMO electrochemical performance:
Ti surface doped LNMO nanopowders synthesized via the hydrolysiscondensation approach improved the LNMO cyclic stability, Coulombic
efficiency and rate performance compared to bare LNMO
Amorphous-LTO surface modified LNMO micron-powders synthesized via the
solution-gel approach improved the LNMO rate performance, reduced the cell
impedance during cycling and improved the cyclic stability
Returning to the questions introduced in the scope of the thesis in Section 1.12:
A too high LNMO surface area results in low capacities due to a high amount
of side reactions for the LNMO commercial nanopowders, as in Chapter 2. A
micron-sized LNMO composed of large, irregular aggregates is not ideal either,
as in Chapter 3. Optimizing the pre-calcination conditions during the aqueous
solution-gel synthesis route in Chapter 3 enabled synthesis of an optimum
LNMO particle size and morphology with good electrochemical performance.
To reach an optimum electrode preparation protocol and electrochemical
performance with a specific powder, the solvent concentration and slurry
mixture viscosity, therefore the electrode morphology, should be optimized.
Several electrode preparation parameters were studied in Chapter 4 and an
optimum preparation protocol is obtained.
Materials of strong metal-oxygen bonds are interesting candidates for surface
modification, to improve the LNMO surface stability at high voltages. Surface
doping occurs instead of surface coating, especially if high synthesis
temperatures are used. The surface doping approach is an effective way to
improve the electrochemical performance. Interesting candidates also include
amorphous oxides. The amorphous oxides seem to increase the side reactions
at the beginning of cycling. However, as the cycling continues, they might be
providing a more stable, compact CEI layer, since the cell resistance drops
and cycle life improves.
Two different synthesis approaches provide successful surface modifications
for the nano/micron-sized LNMO powders and improve the electrochemical
performance: The hydrolysis-condensation approach (Section 1.9.3.2) coupled with
LNMO nanopowders in Chapter 2. It provides uniformly doped LNMO
nanopowder surfaces. An electrostatic adsorption mechanism is
proposed to take place during synthesis. Electrically charged LNMO
surfaces apply electrostatic forces to ions/nanoparticles in the solution
over large distances and loosely bind them to their surface.
o The solution-gel approach (Section 1.9.4) coupled with LNMO micronpowders in Chapter 5. The solution-gel approach allows synthesis of
multi-metal ion surface modification materials with controlled
stoichiometry. It provides coatings/islands or surface dopants on
LNMO micron-powders. A surface complex formation mechanism is
proposed to take place during synthesis.
Possible reasons for the electrochemical performance improvements with the
Ti-based surface modification materials are:
o Surface structure stabilization by incorporation of the strong Ti-O
bonds
o Increased LNMO surface area after the surface modification leading to
lower polarization and improved rate performance
o A more favorable CEI layer formation on the electrode during cycling
The findings of this thesis are summarized below in further detail:
The thesis started with the use of commercial, nano-sized LiNi0.5Mn1.5O4-δ powder
in Chapter 2. A hydrolysis-condensation approach was used for surface
modification, followed by annealing. The surface of the LNMO powder was
modified by Ti cation doping over 2-4 nm depth, while maintaining the initial spinel
structure, using a hydrolysis-condensation approach followed by 500oC anneal.
Particle size and surface area of the bare and surface modified LNMO remained
similar after 500oC anneal and the Ti doped surface remained intact. Although the
initial discharge capacity was slightly reduced, cycle life, Coulombic efficiency and
rate performance were improved for Ti surface doped LNMO annealed at 500oC
compared to bare LNMO also annealed at 500oC. The improvement is probably
due to surface structure stabilization by the stronger Ti-O bonds, which reduces
the manganese dissolution. On the other hand, during an 800oC anneal, Ti diffused
from the surface towards the core of LNMO, causing a secondary LiNi0.5-xMn1.5-
yTizO4 phase formation and particle size growth. Mn-Ni ordering in the lattice
increased with 800oC annealing in oxygen for both bare and surface modified
LNMO samples, compared to 500oC annealed samples in oxygen. However, no
significant improvement was observed in cycle life or Coulombic efficiency of Ti
surface modified LNMO annealed at 800oC compared to bare LNMO also annealed
at 800oC. This is probably because the Ti doped surface layer of LNMO was in this
case not well preserved during Ti diffusion and particle size growth. The Ti surfacedoped LNMO annealed at 500oC, having a well preserved spinel surface structure
and a disordered Mn-Ni distribution, could be an interesting candidate as a
cathode material for lithium-ion battery applications requiring both good cycle life
and rate performance. The thesis continued with the synthesis of LNMO powders to achieve an optimum
particle size, morphology and electrochemical performance in Chapter 3. The
LNMO particle size and morphology were controlled using aqueous solution-gel
synthesis with different pre-calcination temperatures, times and oven types.
Crystalline LNMO powder morphology and particle sizes were shown to depend on
the organic residue in the LNMO precursor powder before the 900oC calcination
step. Calcining the LNMO precursor gel at 200oC for 40 h in a forced convection
oven (LNMO-4) started a vigorous decomposition reaction and resulted in a
voluminous, foam-like precursor powder morphology. The amount of organic
residues before crystallization was minimized in the LNMO-4 precursor powder,
enabling a small particle size after the 900oC calcination step with well-defined
facets. LNMO-4 provided the highest initial discharge capacity of 121 mAh/g at
0.2 C compared to other LNMO powders. On the other hand, organic removal was
probably incomplete with 170oC, 24 h, natural-convection oven pre-calcination
during LNMO-1 precursor powder synthesis, resulting in large aggregates with
non-uniform size distribution and poor electrochemical performance. The
carboxylates or carbonaceous residues present in LNMO-1 precursor powder
possibly adsorb on the surface of small metal oxide nuclei cause agglomeration
and prevent formation of well-defined facets during the 900oC calcination step.
Ball-milling of crystalline LNMO powder (LNMO-3) reduced the agglomeration and
particle size, increased the disordering, Mn3+ concentration and lattice parameter.
However, the initial discharge capacities of LNMO-3 were lower compared to
LNMO-4, which was linked to the increased surface area, Mn3+ concentration and
side-reactions. LNMO particle size optimization via controlling the pre-calcination
conditions is more advantageous compared to size reduction via ball-milling, in
terms of preserving well-defined facets, a high capacity and high Coulombic
efficiency.
The synthesized LNMO powders in Chapter 3 were used to optimize the electrode
properties in Chapter 4, which also has an important influence on the
electrochemical properties. An optimized electrode preparation protocol was
proposed for the synthesized LNMO active material of ~30 μm average aggregate
and ~3.5 μm average primary particle size, after individually examining the
effects of composite electrode processing parameters on the electrochemical
performance of the Li|LNMO cells. A good rate performance was obtained for
LNMO electrodes made using a 150 μm wet thickness, 3 wt. % PVDF-NMP mixture
and C65 carbon black. The use of C45 carbon black can improve the initial
discharge capacity, reduce the amount of parasitic side reactions and improve the
cyclability compared to C65. However, the application of C65 should be preferred,
if a higher rate performance is desired. Thinky planetary mixing method coupled
with a LNMO-carbon black dry mixing step could be preferred over ball-milling to
homogeneously distribute the carbon black particles and increase porosity while
eliminating LNMO particle size, crystalline structure or morphology changes. A
calendering step should be applied to optimize the porosity, improve the electrical
contact and reduce the cell impedance. However, LNMO particle size and shape
should be considered while calendering and excessive forces should be avoided
since LNMO particles could break apart during calendering resulting in a lower
capacity.
The optimized LNMO synthesis and electrode making routes in Chapters 3 and 4
were used to explore the influence of amorphous LTO surface modification of
LNMO on the electrochemical performance in Chapter 5. LNMO surface was
modified with amorphous LTO material (LNMO@LTO-200oC) via a solution-gel
route, resulting in Ti-rich amorphous coatings/islands or Ti-rich spinel surfaces
mostly on the {001} surfaces of LNMO. Transition metal ions on LNMO powder
surfaces partly dissolved into the aqueous, citric acid LTO precursor solution
during the LNMO@LTO-200oC synthesis. The dissolved TM ions precipitated
together with the Ti ions in the LTO precursor solution during the water removal
step and formed the Ti-Ni-Mn-O containing amorphous nanoparticles inside the
LNMO@LTO-200oC powder. Upon 500oC annealing in dry air flow (LNMO@LTO500oC), the amorphous matter crystallized into spinel or rock salt nanoparticles
depending on the composition. Amorphous LTO surface modification slightly
increased the Mn3+ concentration in LNMO based on the capacity curve
measurements and dQ/dV plots, but the electronic or bulk ionic conductivities
were not improved. Amorphous LTO surface modification increased the LNMO
surface area by ~4 times. The rate performance and cyclability were improved for
LNMO@LTO-200oC compared to bare LNMO, while crystallized LNMO@LTO-500oC
showed similar rate performance and cyclabilites compared to its bare
counterpart. The cell impedance increased more rapidly for the bare LNMO
compared to LNMO@LTO-200oC, while the dry air annealed samples had similar
impedances after 1000 cycles. Amorphous coating-HF scavenging reactions might
be occuring slowly on the LNMO@LTO-200oC powder surfaces during cycling,
providing a more favorable CEI layer formation on the electrode surface compared
to bare LNMO.
ZrO2-SiO2 surface modification materials were explored for LNMO in Chapter 6 via
the hydrolysis-condensation approach. ZrO2 surface modified LNMO was
synthesized using different ZrO2 loadings. A too thick, tetragonal ZrO2 coating
layer was probably synthesized on LNMO using 0.2 mL NH3 (25 wt. %) and 4 h
annealing time, which impedes the Li+ transport and causes a large capacity drop.
ZrO2 coating made using 0.1 mL NH3 (25 wt. %) and 4 h annealing time on the
other hand provided probably a more optimum coating thickness, a slightly
improved initial capacity but a deteriorated cyclic stability. The cyclic stability was
improved using a longer anneal time of 10 h, which probably promotes Zr ion
doping into the LNMO surface structure and improves the CEI layer stability during
cycling at room temperature. Cycling temperature was increased to 55oC to
increase the amount of side-reactions and to observe the influence of the ZrO2
surface modification layer better. Improved Coulombic efficiency values were
recorded for the surface modified LNMO compared to the bare LNMO. This could
be explained by a HF-scavengering mechanism where Zr cations react with HF to
form a more stable, ZrF4 containing CEI layer.
SiO2 was incorporated on the LNMO surface together with the ZrO2. Lower or
higher temperatures were used to synthesize ZrO2-SiO2 coated or Zr-Si doped
LNMO surfaces. Neither showed an important improvement in the rate
performance. However, when also coupled with different cooling rates, important
variations in the Ni/Mn disordering were observed for the bare/ZrO2-SiO2 coated
LNMO powders, which greatly influenced the electrochemical performances. The
700oC annealed, slow cooled (1oC/min) bare/ZrO2-SiO2 surface modified LNMO
powders showed a drastic increase in the Ni/Mn ordering and better
electrochemical performance compared to the 500oC annealed, furnace cooled
bare/surface modified LNMO powders. Increased ordering is probably caused by
the slower cooling rate in oxygen flow. The higher temperature used on the other
hand could be introducing more oxygen vacancies in the structures, because of
the temperature dependent O2 evolution reaction. As a result, a more optimum
amount of oxygen vacancies and Ni/Mn ordering were probably achieved in the
bare/ZrO2-SiO2 surface modified LNMO powders with the 700oC annealing and
1°C/min heating/cooling rates, which helped improve the electrochemical
performance
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
No full textWe 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
Further investigation of intramolecular H-bonding in benzimidazole and EDOT containing monomer
No full textDensity functional theory (OFT) calculations of the relative stabilities and harmonic vibrational spectra of four different conformers of 4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2-phenyl-1H-benzo[d] imidazole (BlmBEd) are presented and compared with experimental IR data. BlmBEd, containing phenyl substituted benzimidazole as the acceptor and 3,4-ethylenedioxythiophene (EDOT) as the donor unit, was electrochemically polymerized in different pH media earlier. Electronic states of nitrogen in benzimidazole unit of synthesized polymeric films were analyzed via X-ray photoelectron spectroscopy. Both DFT and XPS results suggest the presence of an intramolecular H-bond between the amine of the imidazole and the oxygen of the EDOT molecules. Additionally, the quantity of the H-bond can be controlled via treatment of an acid (trifloroacetic acid) and a base (sodium hydroxide) as we stated in our previous study
The construction of Karen Karnak: The multi-author-function
No full textThis thesis is situated within the comparatively recent developments of Web 2.0 and the emergence of interactive WikiMedia, and explores the mode of authorship within a Read/Write culture compared to that of a Read/Only tradition. The hypothesis of this study is that the role of the audience has become merged with the author, and as such, represents new functions and attributes, distinct from a more conventional concept of authorship, in which the roles of audience and author are more separate. Read/Write and participatory culture, as defined by this study, is focused on collaboration, and includes the influences of D.I.Y. culture, Open-Source practices and the production of text by multiple authors. Multi-authorship presents a re-thinking of several concepts which support the notion of the individual author, since the focus of multi-authorship is not on attribution and ownership of a finished text, but on the continued malleability of a text. Modes of multi-authorship, demonstrated in the use of the pseudonyms Alan Smithee and Karen Eliot, represent declarative authors whose names signify multiple origins, whilst concurrently indicating a distinct body of work. The function of these names form an important context to this study, since primary research involves the construction of an experimental mode of multi-authorship utilising WikiMedia technology and the interaction of thirty nine participants, who are invited to create a body of work under the collective pseudonym Karen Karnak. The data generated by this experiment is analysed using aspects of Michel Foucault's author-function to identify and determine power structures inherent in the WikiMedia context. The interplay of power structures, including concepts such as identity, ownership and the body of work, affect the resulting mode of authorship and contribute to the construction of Karen Karnak, suggesting further areas of research into the emerging multi-author
Contribution of Information and Communication Technology (ICT) in Country’S H-Index
No full textThe aim of this study is to examine the effect of Information and Communication Technology (ICT) development on country’s scientific ranking as measured by H-index. Moreover, this study applies ICT development sub-indices including ICT Use, ICT Access and ICT skill to find the distinct effect of these sub-indices on country’s H-index. To this purpose, required data for the panel of 14 Middle East countries over the period 1995 to 2009 is collected. Findings of the current study show that ICT development increases the H-index of the sample countries. The results also indicate that ICT Use and ICT Skill sub-indices positively contribute to higher H-index but the effect of ICT access on country’s H-index is not clear
Fully Turbulent Mean Velocity Profile for Purely Viscous non-Newtonian Fluids
No full textThe characteristic near wall behavior of turbulent flow of purely-viscous non-Newtonian fluids is discussed for both power-law (P.-L.) and Herschel-Bulkley (H.-B.) rheological models. A proper scaling is presented for H.-B. fluids to establish an analogy with power-law fluids with same flow index. To provide reference data for turbulent flow of non-Newtonian fluids, DNS simulations of power-law fluids are conducted in a rectangular channel for a large range of power-law indices ( = 0.5, 0.69, 0.75, 0.9, 1, 1.2). The DNS data show that the mean velocity profile in the viscous and logarithmic layers follow expressions of the form and respectively, where shows a logarithmic dependency on the flow index.Comparison with some experimental data shows the above formulation to be valid for Reynolds numbers (based on shear velocity) as high as 1000
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