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排序方式: 共有1118条查询结果,搜索用时 15 毫秒
41.
《Chronobiology international》2013,30(4):397-407
The purpose was to assess age-related circadian changes of blood pressure profile (BPP) employing a truncated Fourier series with four harmonics (tFs) in patients with essential hypertension. The study was performed on 32 patients with essential hypertension divided in two groups: (A) 15 patients younger than 55 years and (B) 17 patients older than 60 years. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were monitored every 20 minutes for 24h with a noninvasive portable device (SpaceLabs 90202). To evaluate the existence of SBP and DBP circadian rhythms a one-sample runs-test was performed and the mesor, amplitude, and acrophase from the overall curve of each patient were obtained by tFs. In both groups, SBP and DBP profiles showed a first peak in the late morning and a second peak in the early evening around the same hours. The two peaks in the SBP profile were higher and the two peaks in the DBP profile were lower in older patients than in younger ones (p. 01, p <. 05, p>. 3, p>. 05). The truncated Fourier series with four harmonics evidences different age-related BP profiles characterized by two peaks with higher SBP and lower DBP in elderly patients. These changes of BPP are in accordance with the reported higher risk of cardiovascular events observed around the same hours. (Chronobiology International, 14(4), 397–407, 1997) 相似文献
42.
基于多种方法的景观格局动态变化综合分析——以辽宁省铁岭市为例 总被引:2,自引:0,他引:2
景观格局变化一直是景观生态学研究的核心问题之一,也是相关生态和环境过程研究的基础.本文应用3S技术,综合传统的空间统计分析、转移矩阵、景观指数和景观动态指数、Kappa指数系列,并引入模糊Kappa指数方法,以铁岭市2002-2011年间景观格局变化为例进行了综合研究.结果表明:铁岭市景观空间格局在研究时段内发生一定程度的变化.旱地面积大幅增加,水田面积明显减少,各景观类型之间均有相互转化.景观格局总体的变化趋势是形状趋于复杂、异质性增加、破碎化加剧,人为干扰的影响较明显.研究区域2002-2007年综合景观动态度指数明显高于2007-2011年,景观动态总体呈现放缓趋势.通过Kappa指数系列可知,研究时段内研究区景观变化由景观类型之间变化为主逐渐转变为各类斑块位置上的变化为主.应用多种方法进行综合分析更能全面有效地反映景观格局变化. 相似文献
43.
Frequently, vital rates are driven by directional, long‐term environmental changes. Many of these are of great importance, such as land degradation, climate change, and succession. Traditional demographic methods assume a constant or stationary environment, and thus are inappropriate to analyze populations subject to these changes. They also require repeat surveys of the individuals as change unfolds. Methods for reconstructing such lengthy processes are needed. We present a model that, based on a time series of population size structures and densities, reconstructs the impact of directional environmental changes on vital rates. The model uses integral projection models and maximum likelihood to identify the rates that best reconstructs the time series. The procedure was validated with artificial and real data. The former involved simulated species with widely different demographic behaviors. The latter used a chronosequence of populations of an endangered cactus subject to increasing anthropogenic disturbance. In our simulations, the vital rates and their change were always reconstructed accurately. Nevertheless, the model frequently produced alternative results. The use of coarse knowledge of the species' biology (whether vital rates increase or decrease with size or their plausible values) allowed the correct rates to be identified with a 90% success rate. With real data, the model correctly reconstructed the effects of disturbance on vital rates. These effects were previously known from two populations for which demographic data were available. Our procedure seems robust, as the data violated several of the model's assumptions. Thus, time series of size structures and densities contain the necessary information to reconstruct changing vital rates. However, additional biological knowledge may be required to provide reliable results. Because time series of size structures and densities are available for many species or can be rapidly generated, our model can contribute to understand populations that face highly pressing environmental problems. 相似文献
44.
Jeanne D. Mihail 《Fungal biology》2013,117(3):202-210
Bioluminescence is well known among white-spored species of Basidiomycota including several species of the white-rot wood decay genus Armillaria. Previous work demonstrated consistent differences among A. gallica, A. mellea, and A. tabescens in luminescence magnitude and in luminescence expression relative to environmental stimuli. In the present studies, temporal fluctuations in mycelial luminescence were quantitatively characterized using genets matched for geographical location. All genets derived from rhizomorphs or basdiomata were constitutively luminescent while six of 13 genets originating from mycelial fans were inconsistently luminescent. Using time series of 1000 consecutive measurements over 800 ms intervals, fluctuation patterns had significantly quantifiable structure and were not simply ‘white noise’. Fluctuation patterns were qualitatively similar with alternating periods of rapid fluctuation and relative stability, regardless of luminescence magnitude. Anomalous spikes or shifts in luminescence were recorded for several genets suggesting further work to identify the transient stimuli which elicited these altered luminescence patterns. 相似文献
45.
Fill Factor Losses in Cu2ZnSn(SxSe1−x)4 Solar Cells: Insights from Physical and Electrical Characterization of Devices and Exfoliated Films 下载免费PDF全文
Kong Fai Tai Oki Gunawan Masaru Kuwahara Shi Chen Subodh Gautam Mhaisalkar Cheng Hon Alfred Huan David B. Mitzi 《Liver Transplantation》2016,6(3)
Besides the open circuit voltage (VOC) deficit, fill factor (FF) is the second most significant parameter deficit for earth‐abundant kesterite solar cell technology. Here, various pathways for FF loss are discussed, with focus on the series resistance issue and its various contributing factors. Electrical and physical characterizations of the full range of bandgap (Eg = 1.0–1.5 eV) Cu2ZnSn(SxSe1?x)4 (CZTSSe) devices, as well as bare and exfoliated films with various S/(S + Se) ratios, are performed. High intensity Suns‐VOC measurement indicates a nonohmic junction developing in high bandgap CZTSSe. Grazing incidence X‐ray diffraction, Raman mapping, field emission scanning electron microscopy, and X‐ray photoelectron spectroscopy indicate the formation of Sn(S,Se)2, Mo(S,Se)2, and Zn(S,Se) at the high bandgap CZTSSe/Mo interface, contributing to the increased series resistance (RS) and nonohmic back contact characteristics. This study offers some clues as to why the record‐CZTSSe solar cells occur within a bandgap range centered around 1.15 eV and offers some direction for further optimization. 相似文献
46.
An improved neutral landscape model for recreating real landscapes and generating landscape series for spatial ecological simulations 总被引:1,自引:0,他引:1 下载免费PDF全文
Maarten J. van Strien Cornelis T. J. Slager Bauke de Vries Adrienne Grêt‐Regamey 《Ecology and evolution》2016,6(11):3808-3821
Many studies have assessed the effect of landscape patterns on spatial ecological processes by simulating these processes in computer‐generated landscapes with varying composition and configuration. To generate such landscapes, various neutral landscape models have been developed. However, the limited set of landscape‐level pattern variables included in these models is often inadequate to generate landscapes that reflect real landscapes. In order to achieve more flexibility and variability in the generated landscapes patterns, a more complete set of class‐ and patch‐level pattern variables should be implemented in these models. These enhancements have been implemented in Landscape Generator (LG), which is a software that uses optimization algorithms to generate landscapes that match user‐defined target values. Developed for participatory spatial planning at small scale, we enhanced the usability of LG and demonstrated how it can be used for larger scale ecological studies. First, we used LG to recreate landscape patterns from a real landscape (i.e., a mountainous region in Switzerland). Second, we generated landscape series with incrementally changing pattern variables, which could be used in ecological simulation studies. We found that LG was able to recreate landscape patterns that approximate those of real landscapes. Furthermore, we successfully generated landscape series that would not have been possible with traditional neutral landscape models. LG is a promising novel approach for generating neutral landscapes and enables testing of new hypotheses regarding the influence of landscape patterns on ecological processes. LG is freely available online. 相似文献
47.
48.
Fabian Alperth Božena Mitić Stefanie Mayer Željan Maleš Olaf Kunert Dario Hruševar 《Plant biosystems》2019,153(2):317-324
Iris adriatica Trinajsti? ex Miti? (Iridaceae L.) is a strictly endemic taxon from Croatia. It is a rhizomatous dwarf plant from the I. pumila complex with a distribution area limited to the Croatian part of the Mediterranean area, mainly central Dalmatia. The genus Iris is known for its richness in isoflavonoids which also play a significant role in chemotaxonomy and biological activity. Hence, in the current study, different plant batches of I. adriatica collected in early spring of 2016 were analysed for their phytochemical profiles and qualitatively compared. UHPLC-PDA-ESI-MS analyses of methanolic rhizome extracts were performed. Altogether, 36 compounds, representing isoflavonoids (including 6,7-methylendioxy derivatives), benzophenones and xanthones were found as aglycones or in glycosidically bound form to be the main constituent groups of I. adriatica rhizomes. Qualitative results were identical between different batches of plant material from collection sites in central Dalmatia, they differed only in quantity. For some phenolic compounds of I. adriatica, chemotaxonomic relevance was detected. 相似文献
49.
50.
Chrysantus Mbi Tanga Samira Abuelgasim Mohamed Govender Prem Daisy Salifu Sunday Ekesi 《Biocontrol Science and Technology》2019,29(4):325-349
Damage caused by invasive downey snow line mealybug, Rastrococcus iceryoides Green (Hemiptera: Pseudococcidae) has been reported to vary between 30% to complete crop loss where no control measure is applied. The current studies seek to determine factors influencing R. iceryoides population outbreaks, parasitoid – host and predator–prey relationships as well as predict optimal management strategies through weather modelling over a period of 28 months from 2008 to 2010 in Tanzania. The highest incidence of R. iceryoides was recorded during the dry season coinciding with the major mango fruiting season. The relationship between R. iceryoides and the parasitoid was positive but not significant, which implies the influence on outbreaks was negligible probably due to low percent parasitism (<12%). However, the predator abundance was directly and significantly related to that of R. iceryoides. Average temperature, average relative humidity, rainfall, and R. iceryoides abundance were autocorrelated to each other. Cross-correlation coef?cients vary significantly from ?0.286 to 0.589 for the pair-variable between R. iceryoides, temperature, relative humidity, rainfall, parasitism and predators. Our findings showed that temperature was the key climatic variable that significantly influenced R. iceryoides outbreaks while rainfall was significantly negatively associated with the pest. Time series analyses show R. iceryoides population increased 4 months after an increase in average temperature in all the sites, 11 months after rainfall and 11 months after relative humidity in Kibaha and Dar es Salaam, respectively. Our findings revealed that R. iceryoides is an excellent target for classical biological control. Thus, the importation of promising co-evolved parasitoid specific to R. iceryoides from the aboriginal home is crucial in formulating an efficient and sustainable management approaches against the invasive mealybug pest in mango agro-ecosystems. 相似文献