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The effective migration of amoeboid cells requires a fine regulation of cell-substratum adhesion. These entwined processes have been shown to be regulated by a host of biophysical and biochemical cues. Here, we reveal the pivotal role played by calcium-based mechanosensation in the active regulation of adhesion resulting in a high migratory adaptability. Using mechanotactically driven Dictyostelium discoideum amoebae, we uncover the existence of optimal mechanosensitive conditions—corresponding to specific levels of extracellular calcium—for persistent directional migration over physicochemically different substrates. When these optimal mechanosensitive conditions are met, noticeable enhancement in cell migration directionality and speed is achieved, yet with significant differences among the different substrates. In the same narrow range of calcium concentrations that yields optimal cellular mechanosensory activity, we uncovered an absolute minimum in cell-substratum adhesion activity, for all considered substrates, with differences in adhesion strength among them amplified. The blocking of the mechanosensitive ion channels with gadolinium—i.e., the inhibition of the primary mechanosensory apparatus—hampers the active reduction in substrate adhesion, thereby leading to the same undifferentiated and drastically reduced directed migratory response. The adaptive behavioral responses of Dictyostelium cells sensitive to substrates with varying physicochemical properties suggest the possibility of novel surface analyses based on the mechanobiological ability of mechanosensitive and guidable cells to probe substrates at the nanometer-to-micrometer level. 相似文献
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Scott Dick Omolbanin Yazdanbaksh Xiuli Tang Toan Huynh James Miller 《Information processing & management》2014
Several studies of Web server workloads have hypothesized that these workloads are self-similar. The explanation commonly advanced for this phenomenon is that the distribution of Web server requests may be heavy-tailed. However, there is another possible explanation: self-similarity can also arise from deterministic, chaotic processes. To our knowledge, this possibility has not previously been investigated, and so existing studies on Web workloads lack an adequate comparison against this alternative. We conduct an empirical study of workloads from two different Web sites: one public university, and one private company, using the largest datasets that have been described in the literature. Our study employs methods from nonlinear time series analysis to search for chaotic behavior in the web logs of these two sites. While we do find that the deterministic components (i.e. the well-known “weekend effect”) are significant components in these time series, we do not find evidence of chaotic behavior. Predictive modeling experiments contrasting heavy-tailed with deterministic models showed that both approaches were equally effective in modeling our datasets. 相似文献
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In earlier studies, the Breastfeeding Attrition Prediction Tool (BAPT) demonstrated predictive validity in the postpartum period. The purpose of this study was to compare the effectiveness of a modified version of the BAPT when given in the last trimester (BAPT1) and following delivery (BAPT2) in predicting breastfeeding attrition among 117 women who planned to breastfeed for at least 8 weeks. Subjects completed the BAPT during a prenatal breastfeeding class and again at delivery, and they received a phone call at 8 weeks to determine breastfeeding status. In this study, neither of the two administrations of the BAPT was predictive of breastfeeding status at 8 weeks. Findings here may differ because subjects in the current study were all committed enough to attend breastfeeding class and, thus, varied less on commitment than women in earlier studies. Significant associations were found with level of education and having a close relative who breastfed. To assist the perinatal educator in identifying women most at risk for early cessation of breastfeeding, the use of three questions regarding level of education, family support, and breastfeeding preparation is suggested. 相似文献
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This paper explores the Westernization of academic quality within the Papua New Guinea higher education system and the hybridity of the university sector where different actors force knowledge to be created for the needs of a small, formal economy, rather than for the development needs of the country. The country has yet to find a system that best responds to its educational needs; several models have been put into practice but without significant results. The approach that the PNG higher education institutes have taken, continuing the colonial tradition, builds on and is reinforced by the new international trends in higher education that follow the market needs, giving a false guarantee that HE is contributing to the economic growth of the country. Colonial legacies and neo‐colonial practices provide the conceptual framework. 相似文献