1,720,985 research outputs found
Hydration and nanomechanical changes in collagen fibrils bearing advanced glycation end-products
Full text linkAccumulation of advanced glycation end-products (AGEs) in biological tissues occurs as a consequence of normal ageing and pathology. Most biological tissues are composed of considerable amounts of collagen, with collagen fibrils being the most abundant form. Collagen fibrils are the smallest discernible structural elements of load-bearing tissues and as such, they are of high biomechanical importance. The low turnover of collagen cause AGEs to accumulate within the collagen fibrils with normal ageing as well as in pathologies. We hypothesized that collagen fibrils bearing AGEs have altered hydration and mechanical properties. To this end, we employed atomic force and Brillouin light scattering microscopy to measure the extent of hydration as well as the transverse elastic properties of collagen fibrils treated with ribose. We find that hydration is different in collagen fibrils bearing AGEs and this is directly related to their mechanical properties. Collagen fibrils treated with ribose showed increased hydration levels and decreased transverse stiffness compared to controlled samples. Our results show that BLS and AFM yield complementary evidence on the effect of hydration on the nanomechanical properties of collagen fibrils.</p
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
Entwicklung einer Zugprüfmaschine für einzelne Kollagenfibrillen und andere nanoskalige Fasern
Full text linkCollagens constitute approximately 30 % of the total protein mass in the human body and serve as the primary structural proteins. They provide tensile strength and toughness to tissues such as tendons, ligaments, vessels, and bones. Collagens are also abundant in the extracellular matrix (ECM) of almost all tissue types, providing sites for cell attachment and playing a crucial role in cellular processes. The unique mechanical properties of these collagen rich tissues are achieved through their complex nano- and microstructure, in which they form collagen fibrils. Collagen fibrils are nanoscale fibers, formed by fibril-forming collagen molecules in a self-assembly process. They are the smallest discernable structural unit of collagenous tissue that can be visualized with high-power microscopes. Collagen fibrils have diameters ranging from tens to hundreds of nanometers and lengths of up to several millimeters. It is debated, whether altered mechanical properties of collagen fibrils contribute to ageing and disease progression (or vice versa). In this context, there is increasing evidence that understanding changes in the viscoelasticity of collagenous tissues is paramount to gaining a better knowledge of disease progression and altered cell behavior. However, current methods for conducting tensile tests on collagen fibrils are very time-consuming and/or lack the capability to precisely determine their viscoelastic properties.The first objective of this thesis was to provide a novel method to overcome current technical limitations and achieve higher sample throughput. This was accomplished by developing the NanoTens, a nano tensile testing instrument that uses a 3D-printed gripper attached to a fiber-optic force probe. Reversible sample attachment to the force probe was achieved through magnetic manipulation. This increases sample throughput at least 25-fold. The NanoTens was utilized to explore the mechanical behavior of collagen fibrils from a mouse model of osteogenesis imperfecta, or brittle bone disease, manifested by a genetic defect that affects the synthesis of collagen molecules. As a result, the synthesized collagen molecules have an impaired structure. The study, surprisingly, revealed that collagen fibrils from the osteogenesis imperfecta mouse model have superior mechanical properties compared to collagen fibrils from wild-type mice, despite the defective collagen molecules. Fibrils from the tail tendons of the osteogenesis mouse model exhibited the characteristics of densely cross-linked collagen fibrils, which hints at elevated cross-linking in the osteogenesis imperfecta mouse model.The second objective was to enhance NanoTens with the capability to perform force-controlled tensile tests. This was done to quantify viscoelastic material properties. Following successful implementation, force-controlled tensile tests were utilized in two studies. The first study compared the viscoelastic properties of collagen fibrils to those of individual electrospun nanofibers. These nanofibers are used in tissue grafts that mimic the mechanical properties of native tendons. It was discovered that collagen fibrils exhibit lower energy dissipation while demonstrating similar elastic properties. In the second study, collagen fibrils were artificially cross-linked using methylglyoxal (MGO), a fast-reacting sugar. Subsequently, creep experiments were performed at relatively low fibril strains (below 10 %) to determine the effect of advanced glycation endproducts (AGEs), i.e. cross-links (and adducts), on viscoelasticity in the physiological strain range. It appears that AGE cross-links reduce molecular sliding even at physiological strains, as determined by reduced creep and residual strain in the MGO cross-linked fibrils. Interestingly, the same fibrils do not display significant differences in transient viscoelasticity
Safety monitoring for functional magnetic stimulation
No full textIn the recent years the use of Functional Magnetic Stimulation (FMS) has gained growing importance as a complementary method to Functional Electrical Stimulation (FES). Unlike electrical stimulation, FMS relies on induction of a magnetic field with rapid intensity changes which bypass the skin¿s impedance and induce eddy currents in deeper tissues. Thereby they evoke action potentials on targeted nerve fibers whilst avoiding unpleasant perception in less conductive skin and subcutaneous areas. Their magnetic fields are applied via coils that are optimized to concentrate the field to specific anatomical structures. While the main design parameter of the coil is the shape of their magnetic field it is also important to consider the electrical characteristics of the target tissue and in particular the possible presence of metal implants which have significant influence on magnetic impedance and field distribution. Induction of eddy currents in metal implants (e.g. joint prostheses like artificial hip or osteosynthesis components) can lead to strong heat development which can lead to serious tissue damage and a severe health risk. In this investigation the electrical characteristics of three different FMS stimulation coils - one with a laminated magnetic iron core and two air coils - are examined and compared by recording the frequency dependency of their impedance. Further the coils were inserted into a parallel resonance circuit using an appropriate parallel capacitance. The deviation of the operating points were analysed when various standard orthopaedic implant components (e.g. Cobalt-Chrome hip implant sphere or Titanium cup of a hip implant) were placed along the coil¿s central axis with varying distances. Resonance frequencies for different set-ups range from 3kHz to 100kHz. Depending on the coil type results show a characteristic frequency range where the resonance frequency and voltage drop of the LC circuit was most affected by an implant insertion. Based on these results a metal detector was designed to identify potentially hazardous conductive materials within the magnetic field of an FMS stimulation device during application. The results also indicate a 3-fold increase of the resistance when the resonance frequency is increased from 3kHz to 10kHz, and a further increase of frequency leads to an exponential growth of the stimulation coil¿s resistance. These results have to be taken into consideration when designing an FMS stimulation system as the resistance leads to power losses and excessive heating of the stimulation coil
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
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