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排序方式: 共有1659条查询结果,搜索用时 31 毫秒
1.
Linda J. Barton DVM Jennifer J. Devey DVM Steven Gorski BSt Louis Mainiero MSt Daniel DeBehnke MD FACEP 《Journal of Veterinary Emergency and Critical Care》1996,6(1):21-28
Ten, anesthetized dogs were instrumented with three pulse oximeter probes; two lingual transmittance probes and one rectal reflective probe. Arterial oxygen desaturation was produced by decreasing the inspired oxygen concentration. Hypotension was produced with an infusion of nitroprusside. Simultaneous pulse oximeter readings (SpO2 ) were compared to co-oximeter measured arterial saturation (SaO2 ) collected over a range of SaO2 (50–100%) and mean arterial pressures (40–100mmHg). Each of the monitors and means of evaluating SpO2 studied provided accurate SpO2 measurements over a range of mean arterial pressure from 40–100mmHg. All of the monitors tested tended to overestimate the SaO2 when the arterial saturation was less than 70%. 相似文献
2.
Existing spatial patterns of a forest are in part a product of its disturbance history. Using laser altimetry and field measures
of canopy top height to represent pre- and post-hurricane canopy topography, respectively, we measured changes in spatial
patterns of stand structure of a United States southern mixed coniferous-deciduous for est. Autocorrelative and fractal properties
were measured in this opportunistic study to quantify changes in canopy architecture along twelve, 190-250 m transects that
were subjected to moderate to high levels of wind disturbance. Prior to the hurricane, canopy heights were autocorrelated
at scales <40 m with an average fractal dimension of 1.71. After the disturbance, autocorrelation disappeared; the average
fractal dimension rose to 1.94. This shift towards spatial randomness illustrates part of the cyclical nature of ecosystem
development. It shows how a catastrophic collapse of biomass accumulation corresponds to a decrease in ecosystem organization
across a landscape.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
4.
Prediction of chemical composition and peroxide value in unground pet foods by near‐infrared spectroscopy
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M. De Marchi F. Righi M. Meneghesso D. Manfrin R. Ricci 《Journal of animal physiology and animal nutrition》2018,102(1):337-342
The massive development of the pet food industry in recent years has lead to the formulation of hundreds of canine and feline complete extruded foods with the objective of meeting both the needs of the animals and numerous demands from pet owners. In the meantime, highly variable raw material compositions and the industry's new production techniques oblige manufacturers to monitor all phases of the extrusion process closely in order to ensure the targeted composition and quality of the products. This study aimed at evaluating the potential of infrared technology (visible and near‐infrared spectrophotometer; 570–1842 nm) in predicting the chemical composition and peroxide value (PV) of unground commercial extruded dog foods. Six hundred and forty‐nine commercial extruded dog foods were collected. For each product, an unground aliquot was analysed by infrared instrument while a second aliquot was sent to a laboratory for proximate analysis and PV quantification. The wide range of extruded dog food typologies included in the study was responsible for the wide variability observed within each nutritional trait, especially crude fibre and ash. The mean value of the 208 pet foods sampled for PV quantification was 17.49 mEq O2/kg fat (min 2.2 and max 94.10 mEq O2/kg fat). The coefficients of determination in cross‐validation of NIRS prediction models were 0.77, 0.97, 0.83, 0.86, 0.78 and 0.94 for moisture, crude protein, crude fat, crude fibre, ash and nitrogen‐free extract (NFE) respectively. PV prediction was less precise, as demonstrated by the coefficient of determination in cross‐validation (0.66). The results demonstrated the potential of NIRS in predicting chemical composition in unground samples, with lower accuracy for moisture and ash, while PV prediction models suggest use for screening purposes only. 相似文献
5.
Pedotransfer functions to assess adsorbed phosphate using iron oxide content and magnetic susceptibility in an Oxisol
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L. A. Camargo J. Marques Jr. G. T. Pereira L. R. F. Alleoni A. S. R. de S. Bahia D. De B. Teixeira 《Soil Use and Management》2016,32(2):172-182
Adsorbed phosphate in soils can be chemically extracted; however, this process is both time‐consuming and not cost‐effective if large numbers of samples have to be analysed. Indirect assessment of adsorbed phosphate by pedotransfer functions (PTFs) can help optimize fertilizer strategies. This study aimed to evaluate the spatial variability of adsorbed phosphate (Pads), iron oxides and magnetic susceptibility (MS) in oxisols and to calibrate PTFs to predict Pads. A total of 308 soil samples were collected from Hapludox and Eutrudox soils formed from sandstone in Brazil. The contents of clay (196–607 g/kg), iron oxides (40–165 g/kg), MS (1.2–29 × 10?6 m3/kg) and Pads (327–842 mg/kg) were in the range of typical values for these highly weathered soils. This study showed that the attributes studied were spatially dependent. Geomorphic surfaces enabled understanding of spatial variability and helped to develop a more efficient sampling scheme to calibrate PTFs. Moreover, the adsorbed phosphate in these oxisols could be predicted by a PTF using iron oxides and MS as predictors. The MS attribute enabled the most accurate prediction (concordance coefficient = 0.95, root‐mean‐square error = 46 mg/kg and relative improvement in root‐mean‐square error = ?4.12) of spatial variability through PTF compared to other predictors. 相似文献
6.
土壤温度对作物的生长发育具有很强的调控作用。在全球气候变化背景下,根区土壤温度对玉米生长的影响及其调控机制已成为当前研究的一个热点。结合目前农业生产中土壤低温和高温对玉米造成危害的现状,从土壤温度对作物根区土壤环境以及玉米根系生长、冠层发育与产量形成的影响方面,综述土壤温度对玉米生长发育调控作用的研究进展,介绍改变土壤温度的措施以及对玉米土壤温度研究的发展方向进行展望,为今后的研究提供参考。 相似文献
7.
The estimation of crop nitrogen status in fresh vegetation leaf using field spectroscopy is challenging due to the weak responses on leaf/canopy reflectance and the overlapping with the absorption features of other compounds. Although the spectral indices were proposed in the literature to predict leaf nitrogen content (LNC), the performance of selected spectral indices to estimate the LNC is often inconsistent. Moreover, the models for nitrogen content estimation changed with the growth stage. The goal of this study was to evaluate the performance of published indices, ratio of data difference index (RDDI) and ratio of data index (RDI) developed by band iterative-optimization algorithm in LNC estimation. The correlation analysis, linear regression and cross validation were used to analyze the relationship between spectral data and LNC and construct the best performed estimation model. The study was conducted by the data of five growing seasons of litchi from the orchards in Guangdong Province of China. Results showed that the relationship between chlorophyll (Chl) related spectral indices and LNC varied with the growth stage. Even in flower bud morphological differentiation stage and autumn shoot maturation stage, there were not significant correlations between the proposed spectral indices and LNC. Besides it is difficult to estimate the LNC by the general model across the growth stages due to the integrated effects of cultivar, biochemical, canopy structure, etc. The band iterative-optimization algorithm can improve the sensitivity of spectral data to LNC to some extent. The optimal RDDI performed better than other indices for the synthetic dataset and the dataset in each growth stage. And the sensitive bands selected in the optimal indices at each growth stage are not consistent, which are not only related to the Chl absorption but also other biochemical components, such as starch, lignin, cellulose, protein, etc. In general, the LNC can be estimated by the optimized CR-based RDDI indices in autumn shoot maturation stage, flower spike stage, fruit maturation stage, and flowering stage with the R2 > 0.50 and RMSE < 0.14. Although there were the significant relationship between RDIs and RDDIs in flower bud morphological differentiation stage, the highest R2s of the model developed by RDDIs and RDIs were less than 0.50 in cross validation. This study indicated that the applicability of canopy reflectance to estimate litchi LNC was closely related to the growth stage of litchi. Growth stage-specific models will be preferred for estimating litchi LNC estimation. 相似文献
8.
《Communications in Soil Science and Plant Analysis》2012,43(19):2330-2339
This study evaluates the effect of soil particle size (SPS) on the measurement of exchangeable sodium (Na) (EXC-Na) by near-infrared reflectance (NIR) spectroscopy. Three hundred thirty-two (n = 332) top soil samples (0–10 cm) were taken from different locations across Uruguay, analyzed by EXC-Na using emission spectrometry, and scanned in reflectance using a NIR spectrophotometer (1100–2500 nm). Partial least squares (PLS) and principal component regression (PCR) models between reference chemical data and NIR data were developed using cross validation (leaving one out). The coefficient of determination in calibration (R2) and the root mean square of the standard error of cross validation (RMSECV) for EXC-Na concentration were 0.44 (RMSECV: 0.12 mg kg–1) for soil with small particle size (SPS-0.053) and 0.77 (RMSECV: 0.09 mg kg–1) for soils with particle sizes greater than 0.212 mm (SPS-0.212), using the NIR region after second derivative as mathematical transformation. The R2 and RMSECV for EXC-Na concentration using PCR were 0.54 (RMSECV: 0.07 mg kg–1) and 0.80 (RMSECV: 0.03 mg kg–1) for SPS-0.053 and SPS-0.212 samples, respectively. 相似文献
9.
笔者以7年生-10年生壶瓶枣树为试材,研究了遮雨棚栽培与大田栽培条件下温湿度变化规律和差异。结果表明:遮雨棚在晴天高温时有降温的作用,而阴雨天温度较低时则有保温的作用;遮雨棚阻碍了水分蒸发,使得相同条件下棚内湿度高于棚外;雨后棚内与棚外温度变化趋势基本一致,棚外湿度变化剧烈,棚内较为缓和。 相似文献
10.
探索近红外光谱法测定紫花苜蓿品质的可行性,采用近红外光谱法与常规方法对8个紫花苜蓿品种(系)的粗蛋白、粗脂肪、粗灰分、酸性洗涤纤维、中性洗涤纤维、钙、磷和干物质等8项指标进行测定。利用配对T检验、多重比较和回归分析等方法检验近红外光谱法测定结果的可行性,运用灰色关联度分析对苜蓿品质进行综合评价。结果表明,粗蛋白、粗灰分、中性洗涤纤维、酸性洗涤纤维、磷和干物质等6项指标用近红外光谱法测定可信度较高。紫花苜蓿品质评价指标可简化为粗蛋白、粗灰分、中性洗涤纤维、酸性洗涤纤维和干物质等5项。灰色关联度分析综合表现较好的苜蓿品种(系)有WL358、WL440HQ、WL656HQ和WL366HQ。 相似文献