1,720,961 research outputs found
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
The Physical Mechanism of Unilateral Cytokinesis
No full textCell division is well known to be accomplished by the constriction of a contractile ring. However, many exceptions exist in which a cell is divided with an incomplete ring or contractile band that has loose ends and generates contractile forces while extending around the cell. This type of cell division is present in unilaterally cleaving embryos and therefore underlies development in many different species, from jellyfish, over lizards to platypus. In the early embryos of these species, the cells are attached to yolk, which prevents the formation of a complete ring. However, the physical mechanisms of how a contractile band with loose ends can be stable and ingress, rather than collapse under tension, remains elusive.
In this thesis work, I investigate the division mechanism by combining laser severing of the contractile band with rheological measurements of the cytoplasm in vivo. I show that gelation of the bulk cytoplasm during the presence of an interphase microtubule network is an essential anchoring mechanism that allows the band to be stable during growth. Moreover, when the cell progresses to the M-phase of the second cycle, the cytoplasm fluidises, thereby reducing the anchoring of the band to the cytoplasm, causing the band to shrink but also allowing it to ingress. This balance between stability and growth versus instability and ingression repeats for several cell cycles until the division is complete, resulting in a mechanical ratchet that drives cell division without a complete actin ring. This study underscores the role of temporal control over cytoplasm rheology as a fundamental factor driving unilateral cytokinesis.:I Introduction
1 Cell division
1.1 The cytokinetic ring
1.2 Unilateral cytokinesis
2 The material properties of cells
2.1 The cytoskeleton
2.2 Measuring material properties in cells
2.2.1 Laser ablation
2.2.2 Magnetic tweezers
2.2.3 Ferrofluid droplet deformation
3 This work – aim and scope
II Results
4 The anchoring mechanism of the contractile band
4.1 Live-imaging of the first cell division in zebrafish embryos
4.2 Laser ablation of the contractile band shows local anchoring
4.3 The contractile band is anchored to microtubules
5 The bulk microtubule network in band stabilisation
5.1 The contractile band is stable in interphase
6 The material properties of the cytoplasm
6.1 Interphase microtubule asters drive a sol-to-gel transition
6.1.1 Model-independent analysis of magnetic tweezers data
6.1.2 Jeffrey’s model analysis of magnetic tweezers data
6.1.3 A gap between the microtubule asters remains fluid in interphase
6.2 Ferrofluid droplets for measuring cytoplasm mechanics
7 A ratchet mechanism of cell division
7.1 Contractile band ingression velocity
7.2 Computational model
7.3 A temporal ratchet mechanism prevents the band from collapsing
8 Ongoing work and open questions
8.1 The embryo operating near an instability
8.1.1 Cytoskeletal instability in cytoplasmic partitioning
8.1.2 Phase separation in the actin cortex
8.2 Membrane domains along the cleavage furrow
8.3 Membrane deformation during subsequent divisions
8.4 Transition to the contractile ring mechanism
III Discussion
9 Summary of main results
10 Discussion
IV Methods
11 Materials and methods for zebrafish experiments
11.1 Ethics statement
11.2 Transgenic zebrafish lines
11.3 Zebrafish husbandry and crossing
11.4 Zebrafish sample collection
11.5 Zebrafish embryo micro-injection
11.6 Zebrafish sample mounting for microscopy
11.6.1 Mounting for confocal imaging with refractive index matching
11.6.2 Mounting for magnetic tweezer experiments
11.6.3 Mounting for optical tweezer experiments
11.6.4 Mounting for confocal imaging with multiple conditions
11.6.5 Mounting embryos without confinement in agarose
11.7 Chemical treatments
11.8 Membrane labelling
12 Image Acquisition and Analysis
12.1 Confocal microscopy
12.2 Light sheet microscopy
12.3 Laser ablation experiments
12.4 Laser ablation analysis
12.5 Magnetic tweezer experiments
12.6 Magnetic tweezer analysis
12.7 Analysis of band growth and ingression velocity
12.8 Contractile band retraction
V Appendix
A Appendix
A.1 Supplementary figures
A.2 Computational model of the contractile band
BibliographyUm eine Zelle in zwei zu teilen, muss nach der Aufteilung der Erbinformation auf beide Seiten eine physikalische Teilung auftreten, sodass die zwei Zellen von jeweils eigenen Membranen umgeben sind. In der Regel wird die Membran mithilfe eines kontraktilen Rings geteilt. Er bildet sich um die Zelle herum und schnürt sie ein. Es gibt allerdings Ausnahmen, in denen solch ein Ring nicht gebildet werden kann, da die Zelle zum Beispiel zu groß ist oder andere geometrische Faktoren die Ringbildung verhindern. Vor allem Zellen von Embryos sind oftmals mit einem Dotter verbunden, der nicht geteilt wird. In diesen Fällen bildet sich nur ein halber Ring, beziehungsweise ein Band, das nur einen Teil der Zelle umrundet. Das Band hat lose Enden und kontrahiert, während es eine Hälfte der Zelle umschließt. Diese Art der Zellteilung kommt bei unilateralen Teilungen von Embryonen vor und bildet somit die Grundlage für die Entwicklung vieler verschiedener Arten, von Quallen über Eidechsen bis hin zu Schnabeltieren. Die physikalischen Mechanismen, die erlauben, dass ein kontraktiles Band mit losen Enden stabil bleibt und die Zelle einschnüren kann, anstatt unter Spannung zu kollabieren, blieben bislang jedoch unklar.
In dieser Arbeit kombiniere ich Laserablationen am kontraktilen Band mit rheologischen Messungen des Zytoplasmas, um den Zellteilungs-mechanismus zu untersuchen. Dadurch lässt sich zeigen, dass die Gelierung des Zytoplasmas durch das Interphasen-Mikrotubuli-Netzwerk ein wesentlicher Verankerungsmechanismus ist. Dieser ermöglicht dem Band während seines Wachstums stabil zu bleiben, sodass es wächst, bis es den Rand des Zytoplasmas beziehungsweise den Dotter erreicht. Wenn die Zelle dann in die M-Phase des zweiten Zyklus übergeht, verflüssigt sich das Zytoplasma, wodurch die Verankerung des Bandes im Zytoplasma reduziert wird, was jedoch gleichzeitig die Beweglichkeit und Einschnürung des Bandes ermöglicht. Bevor das Band während der Einschnürung zu instabil wird und kollabiert, beginnt der nächste Zellzyklus, und mit dem Beginn der zweiten Zellteilung wird auch die erste Teilung wieder stabilisiert. Dieses Gleichgewicht zwischen Stabilität und Wachstum einerseits und Instabilität aber Einschnürung andererseits wiederholt sich über mehrere Zellzyklen, bis die erste Teilung abgeschlossen ist. Das führt zu einem mechanischen Ratschen-Mechanismus, der die Zellteilung ohne einen vollständigen Ring vorantreibt.:I Introduction
1 Cell division
1.1 The cytokinetic ring
1.2 Unilateral cytokinesis
2 The material properties of cells
2.1 The cytoskeleton
2.2 Measuring material properties in cells
2.2.1 Laser ablation
2.2.2 Magnetic tweezers
2.2.3 Ferrofluid droplet deformation
3 This work – aim and scope
II Results
4 The anchoring mechanism of the contractile band
4.1 Live-imaging of the first cell division in zebrafish embryos
4.2 Laser ablation of the contractile band shows local anchoring
4.3 The contractile band is anchored to microtubules
5 The bulk microtubule network in band stabilisation
5.1 The contractile band is stable in interphase
6 The material properties of the cytoplasm
6.1 Interphase microtubule asters drive a sol-to-gel transition
6.1.1 Model-independent analysis of magnetic tweezers data
6.1.2 Jeffrey’s model analysis of magnetic tweezers data
6.1.3 A gap between the microtubule asters remains fluid in interphase
6.2 Ferrofluid droplets for measuring cytoplasm mechanics
7 A ratchet mechanism of cell division
7.1 Contractile band ingression velocity
7.2 Computational model
7.3 A temporal ratchet mechanism prevents the band from collapsing
8 Ongoing work and open questions
8.1 The embryo operating near an instability
8.1.1 Cytoskeletal instability in cytoplasmic partitioning
8.1.2 Phase separation in the actin cortex
8.2 Membrane domains along the cleavage furrow
8.3 Membrane deformation during subsequent divisions
8.4 Transition to the contractile ring mechanism
III Discussion
9 Summary of main results
10 Discussion
IV Methods
11 Materials and methods for zebrafish experiments
11.1 Ethics statement
11.2 Transgenic zebrafish lines
11.3 Zebrafish husbandry and crossing
11.4 Zebrafish sample collection
11.5 Zebrafish embryo micro-injection
11.6 Zebrafish sample mounting for microscopy
11.6.1 Mounting for confocal imaging with refractive index matching
11.6.2 Mounting for magnetic tweezer experiments
11.6.3 Mounting for optical tweezer experiments
11.6.4 Mounting for confocal imaging with multiple conditions
11.6.5 Mounting embryos without confinement in agarose
11.7 Chemical treatments
11.8 Membrane labelling
12 Image Acquisition and Analysis
12.1 Confocal microscopy
12.2 Light sheet microscopy
12.3 Laser ablation experiments
12.4 Laser ablation analysis
12.5 Magnetic tweezer experiments
12.6 Magnetic tweezer analysis
12.7 Analysis of band growth and ingression velocity
12.8 Contractile band retraction
V Appendix
A Appendix
A.1 Supplementary figures
A.2 Computational model of the contractile band
Bibliograph
The Physical Mechanism of Unilateral Cytokinesis
No full textCell division is well known to be accomplished by the constriction of a contractile ring. However, many exceptions exist in which a cell is divided with an incomplete ring or contractile band that has loose ends and generates contractile forces while extending around the cell. This type of cell division is present in unilaterally cleaving embryos and therefore underlies development in many different species, from jellyfish, over lizards to platypus. In the early embryos of these species, the cells are attached to yolk, which prevents the formation of a complete ring. However, the physical mechanisms of how a contractile band with loose ends can be stable and ingress, rather than collapse under tension, remains elusive.
In this thesis work, I investigate the division mechanism by combining laser severing of the contractile band with rheological measurements of the cytoplasm in vivo. I show that gelation of the bulk cytoplasm during the presence of an interphase microtubule network is an essential anchoring mechanism that allows the band to be stable during growth. Moreover, when the cell progresses to the M-phase of the second cycle, the cytoplasm fluidises, thereby reducing the anchoring of the band to the cytoplasm, causing the band to shrink but also allowing it to ingress. This balance between stability and growth versus instability and ingression repeats for several cell cycles until the division is complete, resulting in a mechanical ratchet that drives cell division without a complete actin ring. This study underscores the role of temporal control over cytoplasm rheology as a fundamental factor driving unilateral cytokinesis.:I Introduction
1 Cell division
1.1 The cytokinetic ring
1.2 Unilateral cytokinesis
2 The material properties of cells
2.1 The cytoskeleton
2.2 Measuring material properties in cells
2.2.1 Laser ablation
2.2.2 Magnetic tweezers
2.2.3 Ferrofluid droplet deformation
3 This work – aim and scope
II Results
4 The anchoring mechanism of the contractile band
4.1 Live-imaging of the first cell division in zebrafish embryos
4.2 Laser ablation of the contractile band shows local anchoring
4.3 The contractile band is anchored to microtubules
5 The bulk microtubule network in band stabilisation
5.1 The contractile band is stable in interphase
6 The material properties of the cytoplasm
6.1 Interphase microtubule asters drive a sol-to-gel transition
6.1.1 Model-independent analysis of magnetic tweezers data
6.1.2 Jeffrey’s model analysis of magnetic tweezers data
6.1.3 A gap between the microtubule asters remains fluid in interphase
6.2 Ferrofluid droplets for measuring cytoplasm mechanics
7 A ratchet mechanism of cell division
7.1 Contractile band ingression velocity
7.2 Computational model
7.3 A temporal ratchet mechanism prevents the band from collapsing
8 Ongoing work and open questions
8.1 The embryo operating near an instability
8.1.1 Cytoskeletal instability in cytoplasmic partitioning
8.1.2 Phase separation in the actin cortex
8.2 Membrane domains along the cleavage furrow
8.3 Membrane deformation during subsequent divisions
8.4 Transition to the contractile ring mechanism
III Discussion
9 Summary of main results
10 Discussion
IV Methods
11 Materials and methods for zebrafish experiments
11.1 Ethics statement
11.2 Transgenic zebrafish lines
11.3 Zebrafish husbandry and crossing
11.4 Zebrafish sample collection
11.5 Zebrafish embryo micro-injection
11.6 Zebrafish sample mounting for microscopy
11.6.1 Mounting for confocal imaging with refractive index matching
11.6.2 Mounting for magnetic tweezer experiments
11.6.3 Mounting for optical tweezer experiments
11.6.4 Mounting for confocal imaging with multiple conditions
11.6.5 Mounting embryos without confinement in agarose
11.7 Chemical treatments
11.8 Membrane labelling
12 Image Acquisition and Analysis
12.1 Confocal microscopy
12.2 Light sheet microscopy
12.3 Laser ablation experiments
12.4 Laser ablation analysis
12.5 Magnetic tweezer experiments
12.6 Magnetic tweezer analysis
12.7 Analysis of band growth and ingression velocity
12.8 Contractile band retraction
V Appendix
A Appendix
A.1 Supplementary figures
A.2 Computational model of the contractile band
BibliographyUm eine Zelle in zwei zu teilen, muss nach der Aufteilung der Erbinformation auf beide Seiten eine physikalische Teilung auftreten, sodass die zwei Zellen von jeweils eigenen Membranen umgeben sind. In der Regel wird die Membran mithilfe eines kontraktilen Rings geteilt. Er bildet sich um die Zelle herum und schnürt sie ein. Es gibt allerdings Ausnahmen, in denen solch ein Ring nicht gebildet werden kann, da die Zelle zum Beispiel zu groß ist oder andere geometrische Faktoren die Ringbildung verhindern. Vor allem Zellen von Embryos sind oftmals mit einem Dotter verbunden, der nicht geteilt wird. In diesen Fällen bildet sich nur ein halber Ring, beziehungsweise ein Band, das nur einen Teil der Zelle umrundet. Das Band hat lose Enden und kontrahiert, während es eine Hälfte der Zelle umschließt. Diese Art der Zellteilung kommt bei unilateralen Teilungen von Embryonen vor und bildet somit die Grundlage für die Entwicklung vieler verschiedener Arten, von Quallen über Eidechsen bis hin zu Schnabeltieren. Die physikalischen Mechanismen, die erlauben, dass ein kontraktiles Band mit losen Enden stabil bleibt und die Zelle einschnüren kann, anstatt unter Spannung zu kollabieren, blieben bislang jedoch unklar.
In dieser Arbeit kombiniere ich Laserablationen am kontraktilen Band mit rheologischen Messungen des Zytoplasmas, um den Zellteilungs-mechanismus zu untersuchen. Dadurch lässt sich zeigen, dass die Gelierung des Zytoplasmas durch das Interphasen-Mikrotubuli-Netzwerk ein wesentlicher Verankerungsmechanismus ist. Dieser ermöglicht dem Band während seines Wachstums stabil zu bleiben, sodass es wächst, bis es den Rand des Zytoplasmas beziehungsweise den Dotter erreicht. Wenn die Zelle dann in die M-Phase des zweiten Zyklus übergeht, verflüssigt sich das Zytoplasma, wodurch die Verankerung des Bandes im Zytoplasma reduziert wird, was jedoch gleichzeitig die Beweglichkeit und Einschnürung des Bandes ermöglicht. Bevor das Band während der Einschnürung zu instabil wird und kollabiert, beginnt der nächste Zellzyklus, und mit dem Beginn der zweiten Zellteilung wird auch die erste Teilung wieder stabilisiert. Dieses Gleichgewicht zwischen Stabilität und Wachstum einerseits und Instabilität aber Einschnürung andererseits wiederholt sich über mehrere Zellzyklen, bis die erste Teilung abgeschlossen ist. Das führt zu einem mechanischen Ratschen-Mechanismus, der die Zellteilung ohne einen vollständigen Ring vorantreibt.:I Introduction
1 Cell division
1.1 The cytokinetic ring
1.2 Unilateral cytokinesis
2 The material properties of cells
2.1 The cytoskeleton
2.2 Measuring material properties in cells
2.2.1 Laser ablation
2.2.2 Magnetic tweezers
2.2.3 Ferrofluid droplet deformation
3 This work – aim and scope
II Results
4 The anchoring mechanism of the contractile band
4.1 Live-imaging of the first cell division in zebrafish embryos
4.2 Laser ablation of the contractile band shows local anchoring
4.3 The contractile band is anchored to microtubules
5 The bulk microtubule network in band stabilisation
5.1 The contractile band is stable in interphase
6 The material properties of the cytoplasm
6.1 Interphase microtubule asters drive a sol-to-gel transition
6.1.1 Model-independent analysis of magnetic tweezers data
6.1.2 Jeffrey’s model analysis of magnetic tweezers data
6.1.3 A gap between the microtubule asters remains fluid in interphase
6.2 Ferrofluid droplets for measuring cytoplasm mechanics
7 A ratchet mechanism of cell division
7.1 Contractile band ingression velocity
7.2 Computational model
7.3 A temporal ratchet mechanism prevents the band from collapsing
8 Ongoing work and open questions
8.1 The embryo operating near an instability
8.1.1 Cytoskeletal instability in cytoplasmic partitioning
8.1.2 Phase separation in the actin cortex
8.2 Membrane domains along the cleavage furrow
8.3 Membrane deformation during subsequent divisions
8.4 Transition to the contractile ring mechanism
III Discussion
9 Summary of main results
10 Discussion
IV Methods
11 Materials and methods for zebrafish experiments
11.1 Ethics statement
11.2 Transgenic zebrafish lines
11.3 Zebrafish husbandry and crossing
11.4 Zebrafish sample collection
11.5 Zebrafish embryo micro-injection
11.6 Zebrafish sample mounting for microscopy
11.6.1 Mounting for confocal imaging with refractive index matching
11.6.2 Mounting for magnetic tweezer experiments
11.6.3 Mounting for optical tweezer experiments
11.6.4 Mounting for confocal imaging with multiple conditions
11.6.5 Mounting embryos without confinement in agarose
11.7 Chemical treatments
11.8 Membrane labelling
12 Image Acquisition and Analysis
12.1 Confocal microscopy
12.2 Light sheet microscopy
12.3 Laser ablation experiments
12.4 Laser ablation analysis
12.5 Magnetic tweezer experiments
12.6 Magnetic tweezer analysis
12.7 Analysis of band growth and ingression velocity
12.8 Contractile band retraction
V Appendix
A Appendix
A.1 Supplementary figures
A.2 Computational model of the contractile band
Bibliograph
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
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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