1,720,983 research outputs found
Cardiovascular adaptations during sustained acceleration in a short-arm human centrifuge Increases in heart rate, and total peripheral resistance are the main counter-measures during consecutive +g-force exposure
No full textIntroduction: During exposure to hyper gravity (+Gz), a massive strain on the cardiovascular system takes place, via blood sequestration in the lower extremities and splanchnic vessels of the pelvis. This blood sequestration leads to a substantial decline in cardiac output (CO) and stroke volume (SV). In order to maintain adequate mean arterial pressure (MAP) , upsurges in heart rate (HR) and total peripheral resistance (TPR) occur as physiologic counter-measures. The objective of this study was to examine how these counter measures react during 2 consecutive rounds of +Gz in a short arm human centrifuge (SAHC).
Methods: 20 non-pilot G-force test subjects were exposed to 9 phases of alternating +Gz in an SAHC To measure hemodynamics during the +Gz profile, cardiac output (CO),heart rate (HR), left ventricular ejection time (LVET), mean arterial pressure (MAP), pulse interval (PI), stroke volume (SV), and total peripheral resistance (TPR) were continuously monitored.
Results: Out of 20 G-Force test subjects, 14 accomplished all 9 phases of shifting sustained acceleration. The hemodynamics of these 14 successfully maintained a stabile mean arterial pressure (MAP) (13% above baseline values) under conditions of +Gz . This was accomplished via increases in heart rate (HR) (35% above baseline) and total peripheral resistance (TPR) (50% above baseline). Decreases in left ventricular ejection time (LVET) & pulse interval (PI) (24% below baseline) were also significant factors in maintaining MAP.
Discussion: The results from this study show that the cardiovascular system can adapt to consecutive +Gz via alternating increases in HR and TPR, as well as decreases in LVET and PI. Through this orchestration of physiologic countermeasures, MAP can be sufficiently maintained, thereby retaining adequate perfusion throughout continued hyper gravitational stress
Phase shifts of circadian core body temperature profiles during Mars500
No full textA growing body of research indicates that a misalignment of circadian rhythms can be detrimental
to mental and physical health. Long-term space missions may also potentially alter circadian rhythms,
and pose a critical risk to crew health and safety. The long-term impact of isolation and confinement on
circadian rhythms has not been fully characterized. We here assessed the impact of the Mars500 study
on the circadian phase of core body temperature (CBT). CBT was recorded continuously for 24 h at
the forehead using a recently proposed heat-flux technique (Double Sensor) [1] before (BDC) and during
(ISO-20, ISO-60, ISO-140, ISO-200, ISO-260, ISO-320, ISO-400, ISO-460) the mission. Each recording
was then subjected to cosinor analysis to determine acrophase for each subject and session. A linear mixed
model treating “Time” as fixed e↵ect was fit to phase, including random e↵ects (intercepts and slopes) to
account for individual subject variation. To analyze whether the rate of change in CBT was characterized
by nonlinear changes over time, quadratic and cubic models were also considered. In spite of substantial
inter-individual variation, visual inspection of the data indicated a phase advance during the first half of
the mission (+1.4 h), after which phase returned to baseline again (phase delay of about -1.2 h relative
to first mission half). At ISO-460 phase sharply advanced again to similar levels observed during the first
half of the mission. This pattern was confirmed by significant linear, quadratic and cubic components of
the mixed model (P<0.05). This third degree polynomial trend is well in line with recent data, showing
substantial di↵erences for sleep-wake cycles between the first and last the part of the 520-d mission [2].
We suggest that this specific pattern is related to a highly controlled diet, which was administered during
the first half of the mission. This diet required very strict meal times, which are well known to be strong
nonphotic cues for circadian entrainment [3]. In contrast, we speculate that the sudden phase advance
after 400 mission days could be related to the exposure of blue light, which was exclusively employed
during days 439-499 only. In conclusion, the present results indicate that long-term isolation can induce
significant changes in the circadian timing system, which might be attributed to specific nonphotic and
photic cues of the Mars500 experiment.
[1] Respir Physiol Neurobiol, 169 (2009) S63-S68 [2] PNAS, 110 (2013) 2635-2640 [3] Science, 320
(2008) 1074–107
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
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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