1,720,964 research outputs found
Plasma vitamin K1 levels in Italian patients receiving oral anticoagulant therapy for mechanical heart prosthesis: a case-control study
No full textBackground
Oral anticoagulant therapy (OAT) with a vitamin K antagonist (VKA) is the choice of treatment for preventing thromboembolism in patients with mechanical heart valve prosthesis (MHP). The percentage of time in the therapeutic range (TTR%) expresses the OAT quality. We planned a case-control study in order to determine vitamin K1 plasmatic concentrations in MHP patients and to correlate these with TTR%.
Materials and Methods
Of 756 MHP patients receiving OAT, 125 patients (61 younger than 65 years, and 64 older than 65 years) and 120 healthy blood donors, matched for sex and age, were enrolled in the study. All subjects completed a living questionnaire regarding diet, and underwent blood collection. Vegetable and fruit intake was categorized as optimal or suboptimal, and the high-performance liquid chromatography method was used to determine vitamin K1 levels.
Results
Neither the patients nor controls had been taking vitamin supplements prior to the start of the study. The median vitamin K1 level was 290 pg/L in 72 controls with optimal intake, and 274 pg/L in 48 controls with suboptimal intake, while the median vitamin K1 level in MHP patients with optimal intake was 409 pg/L, significantly higher (p < 0.001) than the 133.5 pg/L in patients with suboptimal intake. Vitamin K1 concentration in MHP patients appears to be linked to an agerelated threshold: in patients younger than 65 years of age, the median vitamin K1 level was 431 pg/L, significantly higher (p < 0.05) than the 290 pg/L in patients older than 65 years of age. No clear relation was found between vitamin K1 levels and TTR% (Pearson = 0.14). However, patients with vitamin K1 > 160 pg/L showed a TTR% > 60 %. Among patients younger than 65 years, subjects with vitamin K1 > 160 pg/L showed a median TTR of 66 %, this being significantly higher (p < 0.001) than the 46 % level shown by patients with vitamin K1 > 160 pg/L.
Conclusions
Vitamin K1 concentrations in MHP patients seem to be related to both diet and age. © Springer International Publishing Switzerland 2016
Vitamin K concentration and cognitive status in elderly patients on anticoagulant therapy: a pilot study
Full text linkObjectives. Recent studies have suggested that vitamin K may exert significant effects on the central nervous system. The present study investigates the relationship between vitamin K plasmatic levels and cognitive functions in elderly patients on oral anticoagulant therapy (OAT). Design. At the Thrombosis Centre of Haematology, "Sapienza" University of Rome, 85 patients on OAT, aged between 75 and 92, were randomly enrolled in the study. Patients were on OAT with vitamin K antagonists (VKAs). Vitamin K1 concentrations were determined using standardized High-Performance Liquid Chromatography (HPLC). Cognitive functions were assessed using the Milan Overall Dementia Assessment (MODA). Results. MODA scores are positively correlated to vitamin K1 concentration. Patients with vitamin K1 below 0.100 μg/L and between 0.100 and 0.400 μg/L showed a mean MODA score of 79 ± 5 and 82 ± 3, respectively. Patients with vitamin K1 above 0.400 μg/L had a significantly greater MODA score (89 ± 1). After binning the data into bicentiles, MODA scores are shown to be linearly dependent on vitamin K1 concentrations (p<0.001). Even long-term OAT (>10 years) does not affect MODA scores. Education seems to exert a greater role on the cognitive status in comparison with aging. Conclusions. The study shows a positive association between vitamin K1 concentration and cognitive status in elderly patients (≥75 years) on OAT. The relationship between vitamin K1 concentration and MODA scores is described by a linear model. Cognitive status is not influenced by the duration of OAT but by the years of education. © 2020 Ludovico Alisi et al
Lubricated friction at the nano and mesoscale
Full text linkFriction is central to numerous natural processes and technological applications, from the motion of synovial joints to car engines and wind turbines. Despite its ubiquitous relevance, a comprehensive picture is still lacking and current models are largely semi-empirical. Experiments conducted at the atomic scale have shed light on the fundamental origins of friction, but linking findings on the single atom or molecule level to macroscale observations involving countless tribological contacts remains a considerable challenge. To bridge this gap, results are needed at the mesoscale, typically between 1 nm and 1 m, where atomistic information is still tractable but macroscopic behaviour begins to emerge.
The problem becomes even more complex when considering the presence of a fluid lubricant confined in a nanogap between the two sliding surfaces.
This thesis aims at bridging the current gap between atomistic models for lubricated friction and larger scale observations. This is done mainly using atomic force microscopy (AFM) which allows investigations of both the molecular level details and the mesoscale picture within the same experiment. Wherever possible, AFM measurements have been complemented by other experimental and computational techniques. Using a variety of model systems, the thesis studies the organisation and dynamics of lubricants under nanoconfinement at the solid/liquid interface. The investigations lead to some novel insights. First, polar and non-polar lubricants are shown to experience a structural transition under nanoconfinement, with the solid-like characteristics of the boundary layer being responsible for an increase in lubricated friction. Second, the lubricant molecular ordering can be modulated by surface singularities that limit the configurational entropy of the fluid molecules. This suggests surface defects indirectly influence the lubricant properties by inducing local molecular rearrangement. External factors, such as humidity and temperature, are also investigated. Some common threads in the different model systems suggest that atomistic models can be adapted at the mesoscale to describe lubricated friction based on a thermally activated process
Local probing of the nanoscale hydration landscape of kaolinite basal facets in the presence of ions
Full text linkThe interface between aqueous solutions and the facets of kaolinite plays an important role in a wide range of technological applications including tribology, paper production, oil recovery, waste water treatment and medical devices. This is made possible by kaolinite's layered structure, with its two basal surfaces -aluminol and siloxane-exhibiting different properties and reactivity. Using a combination of high-resolution atomic force microscopy (AFM) and atomistic molecular dynamics (MD) simulations, we probe in situ the hydration structure over both facets, in water and in the presence of added NaCl. The AFM images reflect the facets' first hydration layer, as confirmed from simulations. Complementary AFM spectroscopy measurements show an excellent agreement between the conservative component and MD's water density profiles, with discrete hydration layers on both facets and little sensitivity to added ions. The dissipative component of the measured tip-sample interactions is more sensitive to the presence of ions, with MD suggesting a link with the local water dynamics and transient instabilities between stable hydration layers. These effects are facet-dependant and more pronounced on the aluminol facet where the first water layer is better defined. Increasing the salt concentration allows hydrated ions to form more stable layers, with hints of organised ionic domains. The results provide unique insights into both the equilibrium molecular structure and dynamics of the kaolinite facets, potentially informing applications involving interfacial processes
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
- …
