131,193 research outputs found
Ascites in chickens : oxygen consumption and requirement related to its occurrence
No full textThe present thesis describes the etiology of heart failure syndrome (HFS) and ascites in broiler chickens.In The Netherlands, ascites, as a cause of mortality in broiler chickens, is increasing steadily. Rates of mortality in broiler flocks in practice, related to HFS and ascites, during a growth period of approximately six weeks, nowadays vary between 2 and 10 percent. This depends on a genetically predisposition of the flock and on effects of environmental factors which can differ between different farms.The occurrence of ascites at high altitudes and its relation to the low oxygen pressure in the air is well documented (chapter 1). Hypoxia (a low oxygen tension in the inspired air) causes an increase in pulmonary arterial pressure in humans and in animals. The consensus of all studies on hypoxic pulmonary pressor response is that besides an increased heart rate, pulmonary vasoconstriction is an eminently important component in a control system that matches ventilation and perfusion and that preserves arterial P 02 . A reduction of the oxygen tension in the air stimulates a recruitment of reserve capillaries in the pulmonary vascular bed which previously were not perfused. Vasoconstriction of arterioles in the main pulmonary blood stream increases the local resistance to flow and causes a redistribution of blood towards reserve capillaries.The increased total resistance to flow by the use of more small tubes distributing the blood to all regions of the lungs (by vasoconstriction) increases distinctly the work-load of the right ventricle of the heart (chapter 1). Increased blood pressure in the lungs and failure of the right heart ventricle causing an increased blood pressure in the veins of the systemic circulation results in edema in different parts of the body (lung edema, hydropericard and ascites).Now the same symptoms of edema and right ventricle hypertrophy and failure, known from high altitudes, are found in modern broiler-chicken breeds in non hypobaric conditions at sea level.Experimental results obtained with different species of animals at high altitudes and at sea level showed that at both locations at least partly the same initial conditions are responsible for the development of HFS and ascites.Hypoxia in the sense of a low oxygen tension in the airways appears not to be directly responsible for the pulmonary pressure response. More important is the result of hypoxia which can be measured as low values for oxygen tension in the blood (hypoxemia) and which directly can affect pulmonary arterioles. Hypoxemia leads to tissue oxygen deprivation or anoxia which directly can influence oxidative phosphorylation and which can induce vasoconstriction of pulmonary arterioles.Experimental results obtained with hypoxic chickens at high altitudes and with normoxic fast growing chickens at sea level indicate that in both cases hypoxemia and anoxia can be the initiating factors leading to an inhibited oxidative phosphorylation inducing vasoconstriction of pulmonary arterioles. The subsequent increased pulmonary blood pressure results in hypertrophy and failure of the right heart ventricle and in edema including ascites. From this point of view a hypothesis was formulated that changes in metabolizable energy intake (MEi) and in energy partitioning in the body affecting oxidative phosphorylation quantitatively and thus oxygen requirements could be initial factors in the development of ascites. In accompaniment with changes in oxygen supply these factors could be responsible for pathophysiological processes in the body inducing HFS and ascites. Thyroid hormones initiating and stimulating oxidative phosphorylation therefore could interfere in those pathophysiological processes.Experiments with different populations of broiler chickens combined with effects of different environmental factors described in chapters 2, 3, 4, 5 and 6 were carried out. The aim was to explore the impact of changes in MEi, together with changes in energy partitioning into deposited protein and fat and into heat, and of changes in oxygen consumption on indices of susceptibility for ascites in chickens. Differences in MEi, in deposition of energy (RE) and in heat production (HP) between populations of chickens in experiments were obtained by using following experimental factors:1 . Different genetic groups of chickens obtained by differences in selection pressure on a fast growth rate and on a low feed conversion ratio (FCR) affecting MEi, energy partitioning, and energy efficiency for growth (RE/MEi).2. Different dietary compositions, differences in energy density affecting MEi and nutrient composition affecting deposition of energy (RE), deposition of protein (RIP), deposition of fat (RF), and heat production per body weight gain (HP/BWG).3. Different ambient temperatures affecting mainly MEi, HP/BWG, and oxygen consumption per deposition of protein (OXc/RP).4. Supplementation of exogenous thyroxine (T4) in diets affecting MEi, and directly OXc followed by responses of HP and RE.In the experiments was shown that populations which combined a low FCR with a fast growth rate exhibited low values for HP/BWG and OXc/RP and high values for RE/MEi and were more susceptible to ascites relative to other populations (chapters 2, 3, 4, 5, and 6). These results indicated that in fast growing stocks, showing low FCR values as a result of high RE/MEi values, a fast protein accretion was achieved together with a reduced ability to convert chemical energy to metabolic heat. A low rate of HIP and thus of OXc, which is not matched to high oxygen requirements, for synthesis and maintenance of protein in tissues, will lead to hypoxemia, heart failure and ascites.Fast growing birds with a low FCR showed less flexibility in metabolic adaptation to a changed environment such as a high fat content in diets and a low ambient temperature. Especially a low ambient temperature will demand a high rate of HP and OXc (chapter 2, 3, 4, and 6). An environment demanding a high level of OXc can induce an imbalance between oxygen supply and requirement in birds. A low FCR can be due to an inability to increase OXc above a certain level. This can reduce the transformation of dietary energy in heat energy.The same fast growing stocks exhibiting a low FCR, if exposed to a low temperature, showed distinctly lower oxygen tension values in venous blood relative to other stocks. The metabolic inability of birds to respond sufficiently to a low temperature by a higher rate of oxygen consumption, inducing hypoxemia and pulmonary hypertension, again can be responsible for the development of ascites. Experimental results described in chapters 3 and 4 support the hypothesis that hypothyroidism reducing HIP and OXc might be one of correlated responses to a selection for a low FCR.Results described in chapter 5 show that supplementation of exogenous thyroxine (T4) to chickens susceptible for ascites can have positive effects on initial conditions responsible for the development of ascites in birds. Supplementation of T4 resulted, only in a population which was susceptible for ascites, in lower haematocrits and haemoglobin contents in blood. High values of both blood parameters are indices of susceptibility for ascites. T4 added to diets also increased adaptive responses of birds, which were susceptible for ascites, to a low ambient temperature, with respect to oxygen consumption. The experimental results reveal that a low thyroid hormone activity might cause impaired adaptive responses of birds to an unfavourable environment which can induce ascites.From the results is concluded that selection procedures and environmental factors which result in decreased values for heat production per gram of body weight gain and in decreased values for oxygen consumption per gram of deposited protein (both of them are related to a decreased feed conversion ratio) will increase the susceptibility for ascites in populations of broiler chickens
Politik und Geschlechterverhältnis
No full textScheele A. Politik und Geschlechterverhältnis. In: Berg-Schlosser D, Quenter S, eds. Literaturführer Politikwissenschaft. Eine kritische Einführung in die Standardwerke und "Klassiker" der Gegenwart. Stuttgart: Kohlhammer; 1999: 217-245
Fragile Sorge: Zumutungen und Konflikte während der COVID-19-Pandemie
No full textScheele A, Schiffbänker H, Walker D, Wienkamp G. Fragile Sorge: Zumutungen und Konflikte während der COVID-19-Pandemie. Femina Politica. 2023;32(1):38-53
Gender
No full textScheele A. Gender. In: Badie B, Berg-Schlosser D, Morlino L, eds. International Encyclopedia of Political Science. Vol 4. Thousand Oaks: Sage Publications; 2011: 961-966
Geometric Spanners of Bounded Tree-Width
No full textGiven a point set P in the Euclidean space, a geometric t-spanner G is a graph on P such that for every pair of points, the shortest path in G between those points is at most a factor t longer than the Euclidean distance between those points. The value t ≥ 1 is called the dilation of G. Commonly, the aim is to construct a t-spanner with additional desirable properties. In graph theory, a powerful tool to admit efficient algorithms is bounded tree-width. We therefore investigate the problem of computing geometric spanners with bounded tree-width and small dilation t.
Let d be a fixed integer and P ⊂ ℝ^d be a point set with n points. We give a first algorithm to compute an (n/k^{d/(d-1)})-spanner on P with tree-width at most k. The dilation obtained by the algorithm is asymptotically worst-case optimal for graphs with tree-width k: We show that there is a set of n points such that every spanner of tree-width k has dilation (n/k^{d/(d-1)}). We further prove a tight dependency between tree-width and the number of edges in sparse connected planar graphs, which admits, for point sets in ℝ², a plane spanner with tree-width at most k and small maximum vertex degree.
Finally, we show an almost tight bound on the minimum dilation of a spanning tree of n equally spaced points on a circle
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
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