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排序方式: 共有195条查询结果,搜索用时 15 毫秒
191.
Colin D. MacLeod Laura Mandleberg Caroline Schweder Sarah M. Bannon Graham J. Pierce 《Hydrobiologia》2008,612(1):21-32
Approaches for modelling the distribution of animals in relation to their environment can be divided into two basic types,
those which use records of absence as well as records of presence and those which use only presence records. For terrestrial
species, presence–absence approaches have been found to produce models with greater predictive ability than presence-only
approaches. This study compared the predictive ability of both approaches for a marine animal, the harbour porpoise (Phoceoena phocoena). Using data on the occurrence of harbour porpoises in the Sea of Hebrides, Scotland, the predictive abilities of one presence–absence
approach (generalised linear modelling—GLM) and three presence-only approaches (Principal component analysis—PCA, ecological
niche factor analysis—ENFA and genetic algorithm for rule-set prediction—GARP) were compared. When the predictive ability
of the models was assessed using receiver operating characteristic (ROC) plots, the presence–absence approach (GLM) was found
to have the greatest predictive ability. However, all approaches were found to produce models that predicted occurrence significantly
better than a random model and the GLM model did not perform significantly better than ENFA and GARP. The PCA had a significantly
lower predictive ability than GLM but not the other approaches. In addition, all models predicted a similar spatial distribution.
Therefore, while models constructed using presence–absence approaches are likely to provide the best understanding of species
distribution within a surveyed area, presence-only models can perform almost as well. However, careful consideration of the
potential limitations and biases in the data, especially with regards to representativeness, is needed if the results of presence-only
models are to be used for conservation and/or management purposes.
Guest editor: V. D. Valavanis
Essential Habitat Mapping in the Mediterranean 相似文献
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194.
Cyclins are indispensable elements of the cell cycle and derangement of their function can lead to cancer formation. Recent studies have also revealed more mechanisms through which cyclins can express their oncogenic potential. This review focuses on the aberrant expression of G1/S cyclins and especially cyclin D and cyclin E; the pathways through which they lead to tumour formation and their involvement in different types of cancer. These elements indicate the mechanisms that could act as targets for cancer therapy. 相似文献
195.
Annemijn Vis Jan CAM Lammers Roel de Vroege Martijn MJ van Nieuwburg Marlijn S Jansen Joyce MJ Visser Bart Meuris Paul F Gründeman Jolanda Kluin 《Comparative medicine》2021,71(3):235
Sheep are a commonly used and validated model for cardiovascular research and, more specifically, for heart valve research. Implanting a heart valve on the arrested heart in sheep is complex and is often complicated by difficulties in restarting the heart, causing significant on-table mortality. Therefore, optimal cardioprotective management during heart valve implantation in sheep is essential. However, little is known about successful cardioprotective management techniques in sheep. This article reports our experience in the cardioprotective management of 20 female sheep that underwent surgical aortic valve replacement with a stented tissue-engineered heart valve prosthesis. During this series of experiments, we modified our cardioprotection protocol to improve survival. We emphasize the importance of total body hypothermia and external cooling of the heart. Furthermore, we recommend repeated cardioplegia administration at 20 min intervals during surgery, with the final dosage of cardioplegia given immediately before the de-clamping of the aorta. To reduce the number of defibrillator shocks during a state of ventricular fibrillation (VF), we have learned to restart the heart by reclamping the aorta, administering cardioplegia until cardiac arrest, and de-clamping the aorta thereafter. Despite these encouraging results, more research is needed to finalize a protocol for this procedure.Sheep are a commonly used and well-validated model for cardiovascular research, particularly for heart valve research, as blood pressure, heart rate, cardiac output, and intracardiac pressures are similar between sheep and humans. Sheep are particularly useful for heart valve research because observable changes in implanted heart valve bioprostheses that would take several years to develop in humans are apparent after only a few months in sheep.3,11 This feature allows the ovine model to provide relevant and important information about heart valve prostheses in a relatively short time span. The first preclinical step in developing novel heart valves is to test the valve in the pulmonary position in sheep. This surgical technique is relatively easy, as the procedure can be performed on a beating heart in a low-pressure circulation. However, aortic valve surgery is the most frequently performed valvular surgical intervention in human patients.12 Thus, an important next step is to prove the clinical applicability of a new valve by testing the valve in-vivo in the aortic position in an animal model. In contrast to pulmonary valve replacement, aortic valve replacement must be performed on an arrested heart, which makes the surgical procedure significantly more complex. The sheep is a difficult model for aortic valve replacements due to its narrow annulus, short distance between the annulus and coronary ostia, a short ascending aorta, and difficulty in de-airing of the heart prior to suturing the aortotomy.19 Consequently, high on-table mortality rates, ranging from 9% to 33%, have been reported.1,18,21,24 Furthermore, the incidence of mortality during the first 30 d after surgery, directly related to the surgical procedure, is often high, ranging from 17% to 50%.1,2,16,18,21 Therefore, optimizing cardioprotective strategies during surgery would improve postoperative survival. However, little is known about protective strategies in sheep. In the current series of experiments, we implanted stented, tissue engineered, aortic heart valve prostheses in 20 adult domestic sheep and developed cardioprotective techniques to increase survival rates. In this observational study, we share our experience and insights regarding cardioprotective management to potentially improve the outcome of future surgeries that require an arrested heart in sheep. 相似文献