1,720,971 research outputs found
From space flights to osteoporosis.
No full textSpace missions (microgravity) alter the balance between bone formation/resorption and induce bone loss. This effect represents a major limiting step in the realization of
long-term space missions. A similar picture is induced by prolonged immobilization in bed (bed rest). The Osteoporosis and Muscular Atrophy project (OSMA) was a research program sponsored by the Italian Space Agency which included 35-day bed rest experiments in healthy young men. Anthropometric data of these experiments indicated the expected bone mass reduction in some segments of the leg and body mass redistribution
from non-fat mass to fat mass. According to the current view, the bone mass reduction due to microgravity/bed rest is associated with the release of calcium from the bone into the bloodstream (hypercalcemia) which, in turn, lowers the secretion of parathyroid hormone and increases urinary calcium excretion. One of the main unsolved issues
in this view is that hypercalcemia is mild and transient during microgravity/bed rest whereas parathyroid hormone reduction is sustained. Bone mass reduction could also
be dependent on parathyroid hormone reduction as this hormone affects both formation and resorption of bone tissue. The research on the mechanisms underlying bone
mass loss during microgravity/bed rest could be of help, not only to space medicine, but hopefully also for prevention and control of bone ageing and osteoporosis
In-Vivo Measurement of Muscle Tension: Dynamic Properties of the MC Sensor during Isometric Muscle Contraction
Get PDFSkeletal muscle is the largest tissue structure in our body and plays an essential role for producing motion through integrated action with bones, tendons, ligaments and joints, for stabilizing body position, for generation of heat through cell respiration and for blood glucose disposal. A key function of skeletal muscle is force generation. Non-invasive and selective measurement of muscle contraction force in the field and in clinical settings has always been challenging. The aim of our work has been to develop a sensor that can overcome these difficulties and therefore enable measurement of muscle force during different contraction conditions. In this study, we tested the mechanical properties of a “Muscle Contraction” (MC) sensor during isometric muscle contraction in different length/tension conditions. The MC sensor is attached so that it indents the skin overlying a muscle group and detects varying degrees of tension during muscular contraction. We compared MC sensor readings over the biceps brachii (BB) muscle to dynamometric measurements of force of elbow flexion, together with recordings of surface EMG signal of BB during isometric contractions at 15° and 90° of elbow flexion. Statistical correlation between MC signal and force was very high at 15° (r = 0.976) and 90° (r = 0.966) across the complete time domain. Normalized SD or σN = σ/max(FMC) was used as a measure of linearity of MC signal and elbow flexion force in dynamic conditions. The average was 8.24% for an elbow angle of 90° and 10.01% for an elbow of angle 15°, which indicates high linearity and good dynamic properties of MC sensor signal when compared to elbow flexion force. The next step of testing MC sensor potential will be to measure tension of muscle-tendon complex in conditions when length and tension change simultaneously during human motion
From space flights to osteoporosis
No full textSpace missions (microgravity) alter the balance between bone formation/resorption and induce bone loss. This effect represents a major limiting step in the realization of
long-term space missions. A similar picture is induced by prolonged immobilization in bed (bed rest). The Osteoporosis and Muscular Atrophy project (OSMA) was a research program sponsored by the Italian Space Agency which included 35-day bed rest experiments in healthy young men. Anthropometric data of these experiments indicated the expected bone mass reduction in some segments of the leg and body mass redistribution
from non-fat mass to fat mass. According to the current view, the bone mass reduction due to microgravity/bed rest is associated with the release of calcium from the bone into the bloodstream (hypercalcemia) which, in turn, lowers the secretion of parathyroid hormone and increases urinary calcium excretion. One of the main unsolved issues
in this view is that hypercalcemia is mild and transient during microgravity/bed rest whereas parathyroid hormone reduction is sustained. Bone mass reduction could also
be dependent on parathyroid hormone reduction as this hormone affects both formation and resorption of bone tissue. The research on the mechanisms underlying bone
mass loss during microgravity/bed rest could be of help, not only to space medicine, but hopefully also for prevention and control of bone ageing and osteoporosis
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
Differences between skeletal muscle contractile parameters estimated from transversal tensiomyographic and longitudinal torque twitch response
Get PDFContractile properties of skeletal muscle are studied for various purposes and mainly by means of force or torque twitch responses. This study compared contractile properties estimated from isometric longitudinal and transversal vastus lateralis twitch mechanical actions using torque and tensiomyography (TMG) as assessment methods, respectively. We calculated delay, contraction, sustain, half relaxation time and peak amplitude from the maximal twitch response obtained by both methods in 19 healthy males (age 46.1±17.8 years). Results indicated a shorter delay (Δ=-23.4%;
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
- …
