Visualizing certainty of extrapolations from models of land change   总被引：2，自引：0，他引：2  

Robert Gilmore Pontius Jr.  Anna J. Versluis  Nicholas R. Malizia 《Landscape Ecology》2006,21(7):1151-1166

This article presents a method to estimate and to visualize the certainty of land change models as they extrapolate beyond the time interval for which empirical data exist. The method to project the certainty relies on measurements of model performance during a validation run with historic data and on the assumption that the model’s accuracy approaches randomness as it predicts farther into the future. A land change model typically predicts each pixel as exactly one category for each year. This article presents a technique to convert those predictions into conditional probabilities. As an example, we use the model Geomod to extrapolate forest change over a century for the Plum Island Ecosystems, which is a Long Term Ecological Research site of the United States’ National Science Foundation. Geomod uses calibration information between 1971 and 1985 in order to predict the changes from 1985 to 1999, at which point the validation procedure measures the model’s predictive accuracy. Then the model is re-calibrated with information from 1985 to 1999 in order to extrapolate into the future, assuming a business as usual scenario. As time progresses, the expected accuracy approaches 0.5, which is the probability at which the model’s prediction is as accurate as a random prediction, since the application involves two categories. The extrapolated accuracy of the prediction for the entire study area in the year 2097 is 68%. The method is designed to work with any number of categories so it can be used with a variety of land change models.  相似文献   

Systematic Review and Meta‐Analysis of Diagnostic Accuracy of Serum Refractometry and Brix Refractometry for the Diagnosis of Inadequate Transfer of Passive Immunity in Calves          下载免费PDF全文

S. Buczinski  E. Gicquel  G. Fecteau  Y. Takwoingi  M. Chigerwe  J.M. Vandeweerd 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2018,32(1):474-483

Background

Transfer of passive immunity in calves can be assessed by direct measurement of immunoglobulin G (IgG) by methods such as radial immunodiffusion (RID) or turbidimetric immunoassay (TIA). IgG can also be measured indirectly by methods such as serum refractometry (REF) or Brix refractometry (BRIX).

Objectives

To determine the accuracy of REF and BRIX for assessment of inadequate transfer of passive immunity (ITPI) in calves.

Design

Systematic review and meta‐analysis of diagnostic accuracy studies.

Methods

Databases (PubMed and CAB Abstract, Searchable Proceedings of Animal Science) and Google Scholar were searched for relevant studies. Studies were eligible if the accuracy (sensitivity and specificity) of REF or BRIX was determined using direct measurement of IgG by RID or turbidimetry as the reference standard. The study population included calves <14 days old that were fed with natural colostrum (colostrum replacement products were excluded). Quality assessment was performed by the QUADAS‐2 tool. Hierarchical models were used for meta‐analysis.

Results

From 1,291 references identified, 13 studies of 3,788 calves were included. Of these, 11 studies evaluated REF and 5 studies evaluated BRIX. The median (range) prevalence of ITPI (defined as calves with IgG <10 g/L by RID or TIA) was 21% (1.3–56%). Risk of bias and applicability concerns were generally low or unclear. For REF, summary estimates were obtained for 2 different cutoffs: 5.2 g/dL (6 studies) and 5.5 g/dL (5 studies). For the 5.2 g/dL cutoff, the summary sensitivity (95% CI) and specificity (95% CI) were 76.1% (63.8–85.2%) and 89.3% (82.3–93.7%), and 88.2% (80.2–93.3%) and 77.9% (74.5–81.0%) for the 5.5 g/dL cutoff. Due to the low number of studies using the same cutoffs, summary estimates could not be obtained for BRIX.

Conclusions and Clinical Importance

Despite their widespread use on dairy farms, evidence about the optimal strategy for using refractometry, including the optimal cutoff, are sparse (especially for BRIX). When using REF to rule out ITPI in herds, the 5.5 g/dL cutoff may be used whereas for ruling in ITPI, the 5.2 g/dL cutoff may be used.  相似文献   

Evaluation of the Accutrend for lactate measurement in dogs     

Stevenson CK  Kidney BA  Duke T  Snead EC  Jackson ML 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》2007,36(3):261-266

BACKGROUND: Lactate concentrations are increasingly quantified in dogs using point-of-care instruments, but often without canine-specific method evaluation and instrument-specific reference intervals. OBJECTIVES: The objectives of this study were to 1) determine the precision of the Accutrend (Roche Diagnostics) for lactate determination in dogs, 2) determine the accuracy of the Accutrend using the Rapidlab 865 (Bayer Diagnostics) as the reference method, and 3) establish and compare reference intervals for lactate concentration in clinically healthy dogs for both instruments. METHODS: Precision was evaluated using low and high control materials, and variable (1 drop) and fixed (25 microL) sample volumes. Accuracy was determined by comparing lactate concentrations obtained with the Accutrend with those from the Rapidlab 865 in 273 heparinized canine jugular venous blood samples from 100 clinically healthy dogs and 107 systemically ill dogs (173 samples). Lactate reference intervals were established for both analyzers using data from the 100 clinically healthy dogs. RESULTS: The precision of the Accutrend was good (coefficients of variation, < or = 5.3%) for 25-microL samples but not when a drop was used. Lactate concentrations obtained on the Accutrend correlated poorly with those from the Rapidlab 865 (r = 0.864, mean bias = 0.66 mmol/L, 95% confidence interval [CI] = 0.57-0.76 with 95% limits of agreement = -0.87 (lower limit, 95% CI = -1.03 to -0.71) and 2.20 (upper limit, 95% CI = 2.04 to 2.36). The reference interval for canine lactate concentration on the Accutrend was 1.2-3.1 mmol/L compared with 0.46-2.31 mmol/L on the Rapidlab. CONCLUSION: Although precision was good with fixed sample volumes, blood lactate concentrations obtained on the Accutrend were significantly different than those on the Rapidlab 865, with systematic and random errors resulting in a positive bias. Further evaluation of the Accutrend is required before its use in dogs can be recommended.  相似文献   

基于不同玉米品种叶片高光谱的SPAD值估测模型研究   总被引：2，自引：0，他引：2  

高鑫  高聚林  于晓芳  王志刚  张宝林  胡树平  谢岷  孙继颖  罗瑞林  吕福虎  陈广庭  王富贵 《玉米科学》2016,24(2):108-114

通过研究不同玉米品种叶片SPAD值与高光谱参数的关系,建立玉米叶片SPAD值估测模型,并对模型进行品种间精度检验。通过两年试验,测定不同玉米品种的叶片SPAD值及其高光谱数据,综合分析叶片SPAD值与高光谱反射率、反射率一阶导数及其光谱参数的相关关系,对玉米叶片SPAD值估测模型进行构建。玉米叶片SPAD值与高光谱反射率最敏感波段在550和710 nm附近,反射率一阶导数最敏感波段出现在500~750 nm范围内。叶片SPAD值与单波段反射率的相关性要高于其一阶导数,以550 nm附近光谱反射率构建的模型对大多数品种的叶片SPAD预测值平均误差最小。  相似文献   

旱涝时空水污染监测失灵与低碳高值化方法学研究——以湘乡县域污染监测水土气数据相关性试验为例     

李劲松  李林杰 《安徽农业科学》2011,39(31):19156-19161

基于化学生态学及化学信息学的低碳高值化方法学,坚持理论与方法相结合,以节约、环保、低碳、高产、高值、循环为价值理念与旨归,以人地关系为基础,以生态系统为中心,以整体调控为目标,以农业生态工程为手段,首先致力于破解农产品与粮食安全问题的瓶颈之一——环境污染监测;通过近两年（2009～2010年）旱涝频发、以旱为主的枯水年份的实地调查,以及典型小流域地表水流量监测与水质测定,发现县域局地水、土、气数据的相关性以及监测重点由水环境转移到大气环境的可能性与必要性。该研究推进了水、土、气数据相关性的定量研究,其阶段性成果与相关研究的结论相符合。  相似文献   

中英文摘要在结构、内容和表达上的常见问题分析     

谷春 《大麦与谷类科学》2019,36(2):58-62

中英文摘要的质量直接影响论文的研究成果在国内外的影响力,但不少中英文摘要在结构、内容或表达上有明显不足,从而严重削弱了它们的科学价值。为提高作者和读者的摘要写作技巧,本文阐明了摘要应具备的结构整体性、内容具体性和表达准确性,举例分析了有些摘要在这3个方面的缺陷。首先,有些摘要对研究目的不加陈述,导致结构不完整。其次,很多基于田间试验的摘要在主体部分具体性严重不足,比如田间试验的时间地点不详,试验对照未被定义,以及杀菌剂的施用剂量和防效数值不明确等。再者,有些英文摘要用词不当,导致句意不清。本文通过分析多个摘要实例,阐述了写作的基本规则,这有利于作者和读者提升中英文摘要写作质量,从而增强其研究成果在国内外的交流成效。  相似文献   

基于图像特征的收获前籽棉品级聚类融合分析   总被引：1，自引：0，他引：1  

王玲  姬长英  陈兵林  刘善军 《作物学报》2007,33(7):1162-1167

为客观评价收获前籽棉品级,依据籽棉品级国家标准,基于机器视觉在3个颜色空间中选取棉棉瓣大小、色泽特征用K-均值、竞争学习网络方法对7个品级的样本进行聚类融合分析。结果表明,亮度修正后特征之间极显著相关,Hunter颜色空间较好。肉眼对第1、2、7品级的识别率为73%~100%,3~6品级为26%~46%,总计47.7%;聚类融合对各品级的识别率为65%~100%,总计78.6%。聚类融合方法基于人类的先验知识,在更宽的视觉范围内更均衡所有特征,可克服个体聚类器的过度训练,能够客观地识别收获前籽棉品级,提高其采摘、收购质量。  相似文献   

Land use and land cover classification in the irrigated Indus Basin using growth phenology information from satellite data to support water management analysis   总被引：1，自引：0，他引：1  

M.J.M. Cheema  W.G.M. Bastiaanssen 《Agricultural Water Management》2010,97(10):1541-149

Water resources planning and management is fundamental for food security, environmental conservation, economic development and livelihoods. In complex basins like the Indus Basin, water is utilized by different land cover and land uses. Up to date information about these Land Use and Land Cover (LULC) classes provide essential information on the water flow path. Traditionally, landscapes are described by cover type. For water management analysis, the information on land use is vital. To this end, a classification of LULC in the Indus Basin (covering 116.2 million hectares of Pakistan, India, China and Afghanistan) has been made. Vegetation index images freely available from SPOT-Vegetation satellite were used to describe the phenological cycle of all agro-ecosystems at a spatial resolution of 1 km × 1 km. An unsupervised clustering technique was adapted to classify 27 land use classes. Ground information and expert knowledge on the growing patterns of crops was used to label the resulting LULC classes. This helped to discern specific crops and crop rotations. An error matrix was prepared using ground truthing data to evaluate the classification accuracy. Existing global, regional and local studies were also considered for validation. The results show an overall accuracy of 77%, with the producer's accuracy being 78% and user's accuracy 83%. The Kappa coefficient (0.73) shows moderate agreement between on ground and satellite derived map. This is deemed sufficient for supporting water management analysis. The availability of major crop rotation statistics and types of forests and savanna is key information for the input data in hydrological models and water accounting frameworks.  相似文献   

内燃机工作过程模拟计算结果的准确性分析及应用     

康红  刘胜吉 《拖拉机与农用运输车》2008,35(3):53-56

介绍了目前国内外常用的内燃机工作过程模拟计算软件,初步分析了各种软件在使用过程中误差产生的原因。利用AVL BOOST软件,基于一台缸径为95 mm的小缸径增压中冷柴油机,计算了两种不同平均机械损失压力经验公式和燃烧过程参数m值、燃烧持续期对发动机性能的影响,并模拟了三种不同燃烧组织方案。通过计算结果分析,探讨了使用工程模拟软件过程中如何提高计算结果准确性等相关问题。  相似文献   

基于APSIM的旱地小麦籽粒蛋白质含量模型精度检验及应用     

聂志刚  李广  王钧  董莉霞  逯玉兰  雒翠萍  马维伟 《中国生态农业学报》2020,28(1):86-95

:籽粒蛋白质积累过程的准确模拟对黄土丘陵区旱地小麦优质生产的有效调控有重要意义。利用甘肃省定西市安定区凤翔镇安家沟村2016—2017年大田试验数据及定西市安定区1971—2017年气象资料,建立基于APSIM(agricultural production systems simulator)的旱地小麦籽粒蛋白质含量模型,采用相关性分析方法检验,并定量分析了耕作方式(传统耕作、传统耕作+秸秆覆盖、免耕及免耕+秸秆覆盖)和播期(正常播期、早播、晚播)对小麦籽粒蛋白质含量的影响。结果表明:3个播期处理和4种耕作方式下,产量和籽粒蛋白质含量模拟值和观测值之间的均方根误差(RMSE)分别为66.4～121.9 kg·hm-2和0.2%～1.1%;归一化均方根误差(NRMSE)分别为1.23%～9.66%和1.31%～9.94%,模型模拟精度较高。播期对旱地小麦籽粒蛋白质含量的影响显著,正常播期的蛋白质含量最高,晚播明显降低了蛋白质含量。4种耕作方式的小麦产量与籽粒蛋白质含量均呈开口向下的二次曲线关系,随着蛋白质含量的升高,产量呈先增加后减少的态势,经过秸秆覆盖的耕作方式(传统耕作+秸秆覆盖和免耕+秸秆覆盖)比不覆盖的耕作方式(传统耕作和免耕)更利于小麦籽粒蛋白质含量的提高。  相似文献