共查询到20条相似文献，搜索用时 15 毫秒
1.
The calibration of a high resolution gamma-ray density probe and a simple experiment comparing the probe with an earlier, lower resolution version are described. An assessment is made of the performance of the probe in three experiments investigating compaction by tractor wheels, two of which were in the field and the third in an indoor soil tank. A linear calibration relationship was obtained, although the addition of a quadratic term improved the fit of the curve slightly. The probe was found to be much more accurate than the earlier version within 100 mm of the soil surface where treatment effects were largest and most numerous in the field experiments, and thin layers of high density could be detected. Over the 15 month period of the experiments, the stability of the system was found to be satisfactory. 相似文献
2.
Continuous Time-Varying Kriging for Spatial Prediction of Functional Data: An Environmental Application 总被引：2，自引：0，他引：2
R. Giraldo P. Delicado J. Mateu 《Journal of Agricultural, Biological & Environmental Statistics》2010,15(1):66-82
Spatially correlated functional data are present in a wide range of environmental disciplines and, in this context, efficient
prediction of curves is a key issue. We present an approach for spatial prediction based on the functional linear pointwise
model adapted to the case of spatially correlated curves. First, a smoothing process is applied to the curves by expanding
the curves and the functional parameters in terms of a set of basis functions. The number of basis functions is chosen by
cross-validation. Then, the spatial prediction of a curve is obtained as a pointwise linear combination of the smoothed data.
The prediction problem is solved by estimating a linear model of coregionalization to set the spatial dependence among the
fitted coefficients. We extend an optimization criterion used in multivariable geostatistics to the functional context. The
method is illustrated by smoothing and predicting temperature curves measured at 35 Canadian weather stations. 相似文献
3.
质粒制备绝对定量PCR标准曲线方法的建立 总被引：5，自引：2，他引：5
用质粒制备绝对定量PCR标准曲线存在着作为标准品的双链环状质粒分子与待测样品单链线性cDNA分子结构不一致的问题.为了消除二者之间的差异,确保绝对定量PCR测定方法的准确性,我们在用质粒制备标准曲线和测定未知样品中特定基因mRNA分子拷贝数时进行了两个改进:1)用酶切的方法使环状质粒线性化,用线性质粒制备标准曲线;2)将未知样品cDNA扩增出一条正义链,再与作为标准曲线的质粒标准品同时开始荧光定量PCR循环.实验结果表明,1)具有相同拷贝数的环状和线性质粒在一起进行定量PCR测定时,环状质粒所得的Ct值大于线性质粒所得的Ct值(P＜0.05);2)本研究测定的cDNA样品中先扩增一次测出的起始拷贝数均大于未先扩增一次的测定结果.样品起始拷贝数两次测定结果的差异分析表明5个样品中有3个样品的测定差异达到了显著水平(P＜0.05).应用该方法改进的鸡GATA5基因绝对定量PCR的标准曲线能够准确地反应目的产物扩增.经改进的质粒制备绝对定量PCR标准曲线的方法更为简便易行,并提高了测定的准确性. 相似文献
4.
花岗岩风化土物理特征曲线间的相关性研究 总被引：2，自引：0，他引：2
花岗岩风化壳水分及收缩特性的研究是花岗岩土体稳定性评价及侵蚀机理研究的基础。通过Van Genuchten(VG)模型对不同风化程度的花岗岩土壤的颗粒累积分布、土水特征曲线和收缩特征曲线进行拟合,分析曲线拟合参数间以及这些参数与基本物理性质间的线性及非线性相关关系。结果表明:VG模型可以很好地用于不同风化程度花岗岩风化土的颗粒组成、土水特征与收缩特征的拟合与预测;曲线拟合参数间具有一定的线性相关关系;曲线拟合参数与基本物理性质间具有一定的线性相关关系,其中土水特征曲线参数与土壤质地以及容重线性相关性较高,收缩特征曲线物理参数与基本物理性质间的线性相关性较收缩特征曲线其他参数高。此外,曲线拟合参数间以及这些参数与基本物理性质间具有一定的非线性相关关系,而关系多为二次、三次非线性相关。根据花岗岩风化土颗粒组成状况及其基本物理性质对其水分特征曲线及收缩特征曲线进行预测具有一定的可行性。 相似文献
5.
A. CHANZY J. CHADOEUF J. C. GAUDU D. MOHRATH G. RICHARD L. BRUCKLER 《European Journal of Soil Science》1998,49(4):637-648
The capacitance probe is an attractive device for monitoring soil moisture automatically. However, its sphere of influence is rather small (a few cubic centimetres only). We have analysed the possibility of monitoring moisture at the field scale using only a few probes (≤3). We calibrated each probe by establishing a direct relation between the field average soil moisture θf and the signal given by the probe. As in earlier studies, we found that a linear relation is generally suitable. A classical statistical analysis was performed to assess the error of a single probe. When replicate probes were installed, we obtained replicate estimates of θf. We proposed an estimator θf that combines all replications optimally. Three experiments each lasting several months were carried out on bare tilled fields to evaluate the probe against gravimetric measurements. Our results show that the calibrations differ significantly from one probe to another. Once calibrated, the capacitance probe provided accurate soil moisture measurements (70% of the calibration relations had residual standard deviations < 0.02m3m?3), but it is advisable to have at least two replicate probes. Soil water storage was well estimated by combining four to seven probes to establish the moisture profile, despite the error induced by each probe. Moreover, the temporal variations in water storage were accurately measured by the probes. We found an error of 0.6 mm day?1 (standard deviation) in daily variation of the water storage, which partly involved the error made on the reference measurements (gravimetric method). 相似文献
6.
基于实测甩负荷的水轮机力矩特性曲线拟合 总被引：1，自引：1，他引：0
水电站过渡过程计算中,水轮机特性曲线对计算结果有着十分重要的影响。由于水轮机模型试验得到的综合特性曲线仅包含了水轮机工作的相对高效率区、导叶大开度下水轮机特性,无法满足甩负荷过渡过程计算的要求,需要对特性曲线进行拓展得到水轮机在导叶小开度区、低效率区及制动工况区的特性。目前对于水轮机特性曲线的处理主要根据经验和数学方法对力矩特性进行拓展和拟合,其仿真结果与实测结果存在较大的差异,无法满足对甩负荷过渡过程精确仿真的要求。虽然通过内特性或CFD的方法能够增加水轮机特性的仿真精度,但是需要能够获得详细及准确的水轮机结构及尺寸参数,实际情况中这些参数往往无法准确获取,不利于工程应用。该文基于真机甩负荷实测结果对水轮机力矩特性曲线的拟合进行了研究,通过甩负荷实测数据得到导叶零开度线下的水轮机力矩特性,结合最小二乘法对整个力矩特性曲线进行拓展和拟合。将利用该处理方法得到的水轮机力矩特性曲线与传统处理方法得到的结果进行对比,结果表明,在导叶大开度、高效率区及水轮机正常运行范围内2种特性曲线基本重合,而在导叶小开度下2种特性曲线存在较大的差异,原因在于本文中零导叶开度线上的力矩特性通过甩负荷实测结果得出其更加精确,零导叶开度线力矩特性的差异导致了特性曲线拟合中边界条件的不同。利用本文处理方法得到的特性曲线对不同调速器参数下的甩负荷过渡过程进行了计算,并分析了调速器参数对甩负荷过渡过程的影响,计算结果表明,调速器参数对甩负荷中导叶开度的快关过程和机组转速的上升下降过程无影响,其主要影响机组转速接近稳态后的调节过程,调速器参数设置不当会造成调节系统的调节品质变差,甚至会导致水轮机调节过程失稳。分别采用2种特性曲线对水电机组甩负荷过渡过程进行仿真,并将仿真结果与实测结果进行对比,结果表明,相比传统处理方法得到的特性曲线,本文处理方法得到的特性曲线能更准确反映机组在导叶小开度下的力矩特性,机组频率仿真结果中,传统特性曲线计算结果与实测结果最大偏差达到了15.74%,本文特性曲线计算结果与实测结果最大偏差为1.05%;导叶开度仿真结果中,传统特性曲线计算结果与实测结果最大偏差为36.07%,本文特性曲线计算结果与实测结果最大偏差为9.74%。通过对比可以看出,本文所提出的特性曲线拟合方法可大大提高甩负荷过渡过程计算精度,能够有效指导水电机组的安全运行。 相似文献
7.
非圆锥齿轮球面齿廓数值计算方法 总被引：1，自引：0，他引：1
非圆锥齿轮传动是宽窄行分插机构实现空间插秧轨迹的重要组成部分,而满足不同机型的宽窄行分插机构需要设计不同参数的非圆锥齿轮。针对目前设计不同非圆锥齿轮需建立不同齿廓计算模型的问题,该文开展了基于样条曲线拟合封闭球面曲线的非圆锥齿轮大端齿廓数值计算方法研究,利用三次Nurbs曲线拟合方法建立了球面节曲线的统一表达式;根据齿形法线法和球面三角形性质建立了大端齿廓和齿根过渡曲线的数值计算模型,编写了基于Matlab的非圆锥齿轮大端齿廓计算程序;以一种步行式宽窄行分插机构的传动齿轮为例,当节点数取720时,齿槽齿厚差值可达到0.0037 mm,可以满足加工要求;并在ADAMS软件中采用齿间加载接触力的方式得到了与理论计算结果相吻合的齿轮传动比,验证了该齿廓计算方法的正确性,从而实现了非圆锥齿轮的通用化设计,为行星轮系式的宽窄行分插机构、取苗机构、植苗机构等种植机械关键部件实现期望运动轨迹提供技术支持。 相似文献
8.
A nongravimetric acetyl bromide lignin (ABL) method was evaluated to quantify lignin concentration in a variety of plant materials. The traditional approach to lignin quantification required extraction of lignin with acidic dioxane and its isolation from each plant sample to construct a standard curve via spectrophotometric analysis. Lignin concentration was then measured in pre-extracted plant cell walls. However, this presented a methodological complexity because extraction and isolation procedures are lengthy and tedious, particularly if there are many samples involved. This work was targeted to simplify lignin quantification. Our hypothesis was that any lignin, regardless of its botanical origin, could be used to construct a standard curve for the purpose of determining lignin concentration in a variety of plants. To test our hypothesis, lignins were isolated from a range of diverse plants and, along with three commercial lignins, standard curves were built and compared among them. Slopes and intercepts derived from these standard curves were close enough to allow utilization of a mean extinction coefficient in the regression equation to estimate lignin concentration in any plant, independent of its botanical origin. Lignin quantification by use of a common regression equation obviates the steps of lignin extraction, isolation, and standard curve construction, which substantially expedites the ABL method. Acetyl bromide lignin method is a fast, convenient analytical procedure that may routinely be used to quantify lignin. 相似文献
9.
A high-performance liquid chromatography (HPLC) method was developed to quantitatively analyze oleocanthal in extra virgin olive oils. Oleocanthal, a deacetoxy ligstroside aglycone, is known to be responsible for the back of the throat irritation of olive oils and to have probated antiinflamatory activity. Oleocanthal was isolated from small amounts of olive oil sample (1 g) by liquid-liquid extraction. Hexane-acetonitrile was found to be the best solvent system to extract oleocanthal from the oil matrix. The solvent extract was analyzed by reversed-phase HPLC with UV detection at 278 nm. Chromatogaphic separation of oleocanthal from other extracted compounds and of the two geometric isomers of oleocanthal was achieved by an elution gradient with acetonitrile and water. Both the external standard calibration curve and the internal standard calibration curve were established, and quantitation using both calibration curves gave essentially the same result. The reproducibility (RSD = 4.7%), recovery (> 95%), and limit of quantitation (< 1 microg/g) were also determined. Concentrations of oleacanthal in 10 selected throat-burning extra virgin olive oils were determined using the method (ranged from 22 to 190 microg/g) with external standard calibration. 相似文献
10.
It has long been recognized that limitations exist in the analytical methodology for amylose determination. This study was conducted to evaluate various amylose determination methods. Purified amylose and amylopectin fractions were obtained from corn, rice, wheat, and potato and then mixed in proportion to make 10, 20, 30, 50, and 80% amylose content starch samples for each source. These samples, considered amylose standards, were analyzed using differential scanning calorimetry (DSC), high-performance size-exclusion chromatography (HPSEC), and iodine binding procedures to generate standard curves for each of the methods. A single DSC standard equation for cereal starches was developed. The standard curve of potato starch was significantly different. Amylose standard curves prepared using the iodine binding method were also similar for the cereal starches, but different for potato starch. An iodine binding procedure using wavelengths at 620 nm and 510 nm increased the precision of the method. When HPSEC was used to determine % amylose, calculations based on dividing the injected starch mass by amylose peak mass, rather than calculations based on the apparent amylose/amylopectin ratio, decreased the inaccuracies associated with sample dispersion and made the generation of a cereal amylose standard curve possible. Amylose contents of pure starch, starch mixtures from different sources with different amylose ranges, and tortillas were measured using DSC, HPSEC, iodine binding, and the Megazyme amylose/amylopectin kit. All the methods were reproducible (±3.0%). Amylose contents measured by these methods were significantly different (P < 0.05). Amylose measurements using iodine binding, DSC, and Megazyme procedures were highly correlated (correlation coefficient >0.95). DSC and traditional iodine binding procedures likely overestimated true amylose contents as residual butanol in the amylose standards caused interference. The modified two-wavelength iodine binding procedure seemed to be the most precise and generally applicable method. Each amylose determination method has its benefits and limitations. 相似文献
11.
The Q/I curves for Na in the Na–Ca system in some salt-affected soils of Malaprabha and Ghataprabha river valleys lacked the curvature commonly seen in the Q/I curve for potassium. The Malaprabha soils showed lower AR0 Na , NaL and BC0 Na values and higher energies of replacement of calcium by sodium than the Ghataprabha soils; the latter showed a higher affinity for Na than Ca. Two distinct linear parts of the quantity/ potential curves, with different slopes, indicated that Na is held in these soils in two characteristic types of exchange sites having different affinities for sodium. The intersection of the two linear parts corresponded to ESP values in the range of 13 to 64%. The change in the affinity at such a high degree of Na saturation was attributed to the presence of chloritized smectitic clays and sodium-selective zeolite, such as analcite, reported in these soils. 相似文献
12.
玉米丸粒化种子刚制成后其含水率比较大，必须及时干燥。其干燥工艺的合理选择对提高干燥效率，减少能耗，保证质量非常重要。采用正交试验的方法，对玉米丸粒化种子进行了3因素3水平的干燥试验，得出其干燥曲线为指数曲线，并分析各试验因素对干燥特性的影响。同时对不同风温下的干燥曲线进行了模型比较，采用多元线性回归分析程序，经拟合得出适合于玉米丸粒化种子的数学模型为Page模型。玉米丸粒化种子干燥特性不同于非丸粒化种子，丸粒化种子有其特定的薄层干燥方程。该模型能较好地预测各干燥阶段的干燥速率及含湿量，确定合理的干燥工艺以便调控干燥环境，达到高效低耗的目的。 相似文献
13.
J L Casterline J A Bradlaw B J Puma Y Ku 《Journal of the Association of Official Analytical Chemists》1983,66(5):1136-1139
A sensitive biological test to detect the presence of certain contaminants, such as highly toxic halogenated dioxins, dibenzofurans, and biphenyls in foods, was applied to extracts of fresh water fish that had been prepared by a food extraction-cleanup procedure developed by the Food and Drug Administration for pesticides and industrial chemicals. Aryl hydrocarbon hydroxylase (AHH) activity in a rat hepatoma cell line was used as the biological detection system for residues that induce enzyme activity. The induction of AHH activity by the extracts was compared with a standard AHH-induction curve for the most active compound known, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and results were computed as TCDD equivalents. Several dilutions of fish extracts were used to produce AHH-induction curves from which an optimal dose-response range was determined and used to estimate TCDD equivalents. Cleaned-up extracts of fish obtained from different water bodies in the United States were examined for AHH activity. The samples which had low levels of polyhalogenated contaminants produced low biological activity, while a higher activity was obtained from fish that contained higher levels of polyhalogenated contaminants. The results suggest that the fish extracts can be screened for AHH inducers before chemical analysis. 相似文献
14.
The relationship between amount of a nutrient in soil and its concentration in solution, the buffer curve, is usually non‐linear. However, most models that calculate nutrient transport in the soil and nutrient uptake by the plant often assume a linear buffer curve because of simpler programming. In this paper a model is presented that uses the Freundlich function to describe the non‐linear buffer curve in the soil. It has been shown that calculated uptake and depletion curves were not influenced by the shape of the buffer curve. In a sensitivity analysis the buffer capacity, soil solution concentration, soil water content, soil impedance factor, maximum influx and the curvature of the Freundlich function were varied and the influence on calculated uptake was studied. The buffer capacity in general had a minor influence and the linearity or non‐linearity of the buffer capacity had under no circumstances an influence on calculated uptake. Thus, the use of a linear buffer curve in transport models does not lead to a significant error in the results. 相似文献
15.
《Communications in Soil Science and Plant Analysis》2012,43(15-16):1333-1345
Abstract Accurate and rapid methods for in situ measurement of soil water content of field soils are required for assessment of plant growth conditions, crop water balance, and irrigation scheduling. Advances in electronics have made possible the recent development of a commercially available non‐nuclear resonant frequency capacitance probe (Troxler Sentry 200‐AP) for measuring water content of various materials. However, the performance of this probe to measure soil water content of the field soils in situ has not been widely reported. This study was undertaken to identify the need for field calibration and to understand the calibration process and evaluate the performance of the capacitance probe. A field calibration curve for a Uchee loamy sand was made for the Sentry 200‐AP probe. In situ volumetric soil water content obtained using this calibration curve differed markedly from those obtained using the factory calibration provided with the probe. The capacitance probe was found to be more sensitive at the lower range (<40%) of soil volumetric water content. However it appears to be reliable and to give reproducible results. 相似文献
16.
The rheological properties of wheat doughs prepared from different flour types, water contents, and mixing times for a total of 20 dough systems were studied. The results were compared with the results of standard baking tests with the same factors. Water and flour type had a significant effect on storage modulus (G′) or phase angle measured by an oscillatory test both in the linear viscoelastic region and as a function of stress, and on compressional force measured as a function of time. The correlation of maximum force of dough in compression and G′ of dough measured within the linear viscoelastic region was r = 0.80. Correlation between the compression and oscillation test improved when all measuring points of the G′ stress curve were included (r = 0.88). The baking performance of the different doughs varied greatly; loaf volumes ranged from 2.9 to 4.7 mL/g. Although the water content of the dough correlated with the rheological measurements, the correlation of G′measured in the linear viscoelastic region or maximum force from stress‐time curve during compression was poor for bread loaf volumes. Mixing time from 4.5 to 15.5 min did not affect the rheological measurements. No correlation was observed with the maximum force of compression or G′ of dough measured in the linear viscoelastic region and baking performance. Good correlation of rheological measurements of doughs and baking performance was obtained when all the data points from force‐time curve and whole stress sweep (G′ as a function of stress) were evaluated with multivariate partial least squares regression. Correlation of all data points with loaf volume was r = 0.81 and 0.72, respectively, in compression and shear oscillation. 相似文献
17.
基于土壤中溶质运移的对流 弥散方程 (CDE)提出了溶质运移参数估计的图解方法。根据土柱溶质运移“穿透曲线”(BTC)数据计算通量浓度随时间变化 (dc/dt)。应用绘图软件 ,例如MicrosoftExcel,绘制出t1 5dc/dt和dc/dt相对于时间的变化曲线。这两条曲线都是单峰曲线 ,并被用于估计CDE中延迟因子(R)和弥散系数 (D0 )。设计算例和穿透实验数据被用于校正图解法估计参数的精度和稳定性。参数估计的稳定性由估计参数对它们平均值的标准差评价 ;参数的估计精度与CXTFIT法和等斜率法比较。结果表明图解法具有较高的精度和较好的稳定性 ,特别是对于运移参数R的估值。图解法是一个确定性方法 ,它具备确定性方法中估计参数唯一性特点 ,克服了统计方法中需要给定参数初值的缺点。因此 ,这个方法是土壤溶质运移参数估计的可选方法之一。 相似文献
18.
A methodology for the screening of tetracyclines (TCs), including tetracycline (TC), oxytetracycline (OTC), and chlorotetracycline (CTC), in different fish muscle matrices has been proposed. This method was based on in situ fluorescent derivation of TCs, transferring weakly fluorescing TCs to highly fluorescent species, on alkaline-activated solid silica gel G plates (SGGPs). By coupling solid-surface fluorescence (SSF) with charge-coupled device (CCD) camera imaging, a CCD camera-based SSF (CCD-SSF) methodology has been developed. Calibration curve, repeatability, selectivity, limit of detection (LOD), and limit of quantification (LOQ) have been explored for evaluating the performance of the method itself. Linear calibration curves were obtained over a range of 0.20-1.0 ng/spot for all three TCs. The LODs, defined as 3sigma, for TC, OTC, and CTC were 0.14, 0.15, and 0.16 ng/spot, respectively. The trueness of method was validated by HPLC, and no significant difference between CCD-SSF and HPLC was found, on a basis of 95% confidence level. By spiked recovery studies, a linear calibration curve ranging from 20 to 300 microg/kg of TC in fish muscle samples with a correlation coefficient (R 2) equal to 0.994 was obtained. The total average recovery for TC in fish muscle samples from six different fish matrices, fortified with TC at 50, 100, and 200 microg/kg levels, was 75.7% with average relative standard deviations (RSDs) ranging from 2.0 to 7.7%. RSDs ranged from 2.5 to 5.8% and from 5.2 to 7.6% for in-day and interday repeatability, respectively. The detection and quantification limits in fish muscle matrices were 16 and 53 microg/kg of TCs, respectively. The newly developed CCD-SSF method has been applied to the screening of the TC residues in fish muscle samples. The method has been demonstrated to bear some advantages, such as its simplicity, high throughput, low cost, use of fewer pollutants, and reasonable sensitivity. 相似文献
19.
T Dolan L Legette J McNeal A J Malanoski 《Journal of the Association of Official Analytical Chemists》1978,61(4):982-985
A rapid analytical procedure was investigated for measuring the fluoride content of deboned meat, using a specific ion electrode. The method involves a defatting procedure followed by chelation with EDTA before final solubilization and measurement. Fluoride content is determined by comparison to a standard curve on 2-cycle semi-logarithmic graph paper of fluoride ion vs. millivolt readings. The method is applicable to hand and mechanically deboned pork, beef, and poultry within a range of from 0.7 to 25.0 ppm fluoride. Higher concentrations may be measured by analyzing additional standards and extending the curve into a third cycle. The curve is not linear below 0.7 ppm. Samples less than 0.7 ppm may be estimated by extrapolation. Studies with fortified samples indicate average recoveries of 92 +/- 4.2%. The standard deviation of duplicates within the laboratory is 0.5 ppm in the range stated above. 相似文献
20.
Virgilio A Raposo JL Cardoso AA Nóbrega JA Gomes Neto JA 《Journal of agricultural and food chemistry》2011,59(6):2197-2201
The usefulness of molecular absorption was investigated for the determination of total sulfur (S) in agricultural samples by high-resolution continuum source flame molecular absorption spectrometry. The lines for CS at 257.595, 257.958, and 258.056 nm and for SH at 323.658, 324.064, and 327.990 nm were evaluated. Figures of merit, such as linear dynamic range, sensitivity, linear correlation, characteristic concentration, limit of detection, and precision, were established. For selected CS lines, wavelength-integrated absorbance equivalent to 3 pixels, analytical curves in the 100-2500 mg L(-1) (257.595 nm), 250-2000 mg L(-1) (257.958 nm), and 250-5000 mg L(-1) (258.056 nm) ranges with a linear correlation coefficient better than 0.9980 were obtained. Results were in agreement at a 95% confidence level (paired t test) with those obtained by gravimetry. Recoveries of S in fungicide and fertilizer samples were within the 84-109% range, and the relative standard deviation (n=12) was typically <5%. 相似文献