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91.
Ryan P. North Rebecca L. North David M. Livingstone Oliver Köster Rolf Kipfer 《Global Change Biology》2014,20(3):811-823
The (Lower) Lake of Zurich provides an ideal system for studying the long‐term impact of environmental change on deep‐water hypoxia because of its sensitivity to climatic forcing, its history of eutrophication and subsequent oligotrophication, and the quality and length of its data set. Based on 39 years (1972–2010) of measured profiles of temperature, oxygen concentration and phosphorus (P) concentration, the potentially confounding effects of oligotrophication and climatic forcing on the occurrence and extent of deep‐water hypoxia in the lake were investigated. The time‐series of Nürnberg's hypoxic factor (HF) for the lake can be divided into three distinct segments: (i) a segment of consistently low HF from 1972 to the late‐1980s climate regime shift (CRS); (ii) a transitional segment between the late‐1980s CRS and approximately 2000 within which the HF was highly variable; and (iii) a segment of consistently high HF thereafter. The increase in hypoxia during the study period was not a consequence of a change in trophic status, as the lake underwent oligotrophication as a result of reduced external P loading during this time. Instead, wavelet analysis suggests that changes in the lake's mixing regime, initiated by the late‐1980s CRS, ultimately led to a delayed but abrupt decrease in the deep‐water oxygen concentration, resulting in a general expansion of the hypoxic zone in autumn. Even after detrending to remove long‐term effects, the concentration of soluble reactive P in the bottom water of the lake was highly correlated with various measures of hypoxia, providing quantitative evidence supporting the probable effect of hypoxia on internal P loading. Such climate‐induced, ecosystem‐scale changes, which may result in undesirable effects such as a decline in water quality and a reduction in coldwater fish habitats, provide further evidence for the vulnerability of large temperate lakes to predicted increases in global air temperature. 相似文献
92.
In this paper a new enzymatic process direction is described for obtaining machine washable wool with acceptable quality. In general, application of protease enzyme technology in wool processing results in considerable loss of tensile strength by diffusion of the enzyme into the interior of wool fibers. To overcome this disadvantage enzymatic activity has been more targeted to the outer surface of the scales by improving the susceptibility of the outer surface scale protein for proteolytic degradation. This has been realized by a pretreatment of wool with hydrogen peroxide at alkaline pH in the presence of high concentrations of salt. 相似文献
93.
Sam Subbey Kathrine Michalsen Geir Kjetil Nilsen 《Reviews in Fish Biology and Fisheries》2008,18(3):301-312
Electronic Data Storage Tags (DSTs) have the potential of providing long term, high-resolution observation data of individual
fish in the ecosystem. However, traditional time series analysis methods are limited in extracting the required information
from DSTs. The continuous wavelet transform (CWT) is a tool for decomposing a time series into instantaneous frequency versus
time characteristics. This allows data signals, which are restricted to specific frequencies (localized frequencies), or frequency
components, which are restricted to specific time intervals (time localized) to be extracted and displayed in a highly intuitive
way. The aim of this short communication is to present the CWT as a tool for extracting information from DST data. In the
first case, synthetically generated data is used to demonstrate how the methodology captures different time–frequency dependent
patterns in the time series data. The relevance of the methodology to real field data is demonstrated by an analysis of DST
depth data from tagged Barents Sea coastal cod.
This work has also enjoyed partial funding from the EU-FP5-Q5RS200200813 CODYSSEY project. 相似文献
94.
1 Introduction Iris recognition technology is based on the stableand distinctive iris patterns, and has attracted a lot ofattention recently. Nowadays it has become a most im-portant biometric solution for personal identification. Since the 1990s, much work on iris recognition hasbeen done and great progress has been made. Some pre-dominant algorithms for iris recognition have beenproposed. Daugman generated an iris code by quantizingthe local phase angle using a set of 2-D Gabor f… 相似文献
95.
96.
Polymerization shrinkage of dental resin composites can lead to restoration debonding or cracked tooth tissues in composite-restored teeth. In order to understand where and how shrinkage strain and stress develop in such restored teeth, Digital Image Correlation (DIC) was used to provide a comprehensive view of the displacement and strain distributions within model restorations that had undergone polymerization shrinkage.Specimens with model cavities were made of cylindrical glass rods with both diameter and length being 10 mm. The dimensions of the mesial-occlusal-distal (MOD) cavity prepared in each specimen measured 3 mm and 2 mm in width and depth, respectively. After filling the cavity with resin composite, the surface under observation was sprayed with first a thin layer of white paint and then fine black charcoal powder to create high-contrast speckles. Pictures of that surface were then taken before curing and 5 min after. Finally, the two pictures were correlated using DIC software to calculate the displacement and strain distributions.The resin composite shrunk vertically towards the bottom of the cavity, with the top center portion of the restoration having the largest downward displacement. At the same time, it shrunk horizontally towards its vertical midline. Shrinkage of the composite stretched the material in the vicinity of the “tooth-restoration” interface, resulting in cuspal deflections and high tensile strains around the restoration. Material close to the cavity walls or floor had direct strains mostly in the directions perpendicular to the interfaces. Summation of the two direct strain components showed a relatively uniform distribution around the restoration and its magnitude equaled approximately to the volumetric shrinkage strain of the material. 相似文献
97.
树木茎干半径变化记录仪(Dendrometer)监测的高精度数据不仅包括木质部的年内径向生长过程, 还包含由茎干水分的消耗和补充引起的可逆变化。然而, 不同的年内生长去趋势方法获得的茎干水分波动之间的差异性仍缺乏对比研究。基于芦芽山北坡针叶林下限白扦(Picea meyeri) 2015年生长季的茎干半径变化和环境因子的实时监测数据, 使用Gompertz生长模型(GPZ)、线性生长模型(LG)、零生长模型(ZG)、日值法(D)和茎干循环法(SC)模拟并去除茎干年内的生长趋势, 然后提取5种不同类型树木水分缺乏引起的茎干收缩(TWDGPZ、TWDLG、TWDZG、TWDD和TWDSC)以表征茎干水分亏缺, 并进一步对比分析了不同茎干水分亏缺序列对环境中水分状况的响应特征。研究发现: (1)不同去趋势方法计算的茎干水分亏缺的趋势和幅度有所差异, 可聚类为3组: TWDLG和TWDZG、TWDGPZ以及TWDD和TWDSC。同组或聚类距离接近的序列在生长季内每个月份都展现出显著的相关性。然而, TWDLG、TWDZG和TWDGPZ与TWDD和TWDSC在8月份相关性较弱。(2) TWDD和TWDSC与空气饱和水汽压差(VPD)的正相关关系比TWDGPZ、TWDLG和TWDZG更加稳定, 且具有更大的相关系数。5种茎干水分亏缺序列和土壤含水量(SWC)的关系在生长季内变化很大。(3)不同去趋势方法的茎干水分亏缺都随着水分胁迫程度(VPD/SWC)升高而显著增长。当胁迫程度较低时, TWDSC对VPD/SWC的变化最为敏感(R2 = 0.39, p < 0.001), 但是与TWDZG差别不大(R 2 = 0.37, p < 0.001); 当胁迫程度较高时, TWDZG对VPD/SWC的敏感性最高(R 2 = 0.59, p < 0.001)。综合对比来看, 零生长模型是比较适合研究区白扦生长季内茎干水分波动的去趋势方法, 其可为干旱胁迫条件下预测研究区树木的茎干水分动态及特征提供科学 依据。 相似文献
98.
Many modern genomic data analyses require implementing regressions where the number of parameters (p, e.g., the number of marker effects) exceeds sample size (n). Implementing these large-p-with-small-n regressions poses several statistical and computational challenges, some of which can be confronted using Bayesian methods. This approach allows integrating various parametric and nonparametric shrinkage and variable selection procedures in a unified and consistent manner. The BGLR R-package implements a large collection of Bayesian regression models, including parametric variable selection and shrinkage methods and semiparametric procedures (Bayesian reproducing kernel Hilbert spaces regressions, RKHS). The software was originally developed for genomic applications; however, the methods implemented are useful for many nongenomic applications as well. The response can be continuous (censored or not) or categorical (either binary or ordinal). The algorithm is based on a Gibbs sampler with scalar updates and the implementation takes advantage of efficient compiled C and Fortran routines. In this article we describe the methods implemented in BGLR, present examples of the use of the package, and discuss practical issues emerging in real-data analysis. 相似文献
99.
100.
Precipitation variability and fire influence the temporal dynamics of soil CO2 efflux in an arid grassland 总被引:1,自引:0,他引:1
Rodrigo Vargas Scott L. Collins Michell L. Thomey Jennifer E. Johnson Renee F. Brown Donald O. Natvig Michael T. Friggens 《Global Change Biology》2012,18(4):1401-1411
Climate models suggest that extreme rainfall events will become more common with increased atmospheric warming. Consequently, changes in the size and frequency of rainfall will influence biophysical drivers that regulate the strength and timing of soil CO2 efflux – a major source of terrestrial carbon flux. We used a rainfall manipulation experiment during the summer monsoon season (July–September) to vary both the size and frequency of precipitation in an arid grassland 2 years before and 2 years after a lightning‐caused wildfire. Soil CO2 efflux rates were always higher under increased rainfall event size than under increased rainfall event frequency, or ambient precipitation. Although fire reduced soil CO2 efflux rates by nearly 70%, the overall responses to rainfall variability were consistent before and after the fire. The overall sensitivity of soil CO2 efflux to temperature (Q10) converged to 1.4, but this value differed somewhat among treatments especially before the fire. Changes in rainfall patterns resulted in differences in the periodicity of soil CO2 efflux with strong signals at 1, 8, and 30 days. Increased rainfall event size enhanced the synchrony between photosynthetically active radiation and soil CO2 efflux over the growing season before and after fire, suggesting a change in the temporal availability of substrate pools that regulate the temporal dynamics and magnitude of soil CO2 efflux. We conclude that arid grasslands are capable of rapidly increasing and maintaining high soil CO2 efflux rates in response to increased rainfall event size more than increased rainfall event frequency both before and after a fire. Therefore, the amount and pattern of multiple rain pulses over the growing season are crucial for understanding CO2 dynamics in burned and unburned water‐limited ecosystems. 相似文献