COMPARISON OF ISODOSE DISTRIBUTIONS IN CANINE BRAIN IN HETEROGENEITY-CORRECTED VERSUS UNCORRECTED TREATMENT PLANS USING 6 MV PHOTONS     

J. LYONS  D.E. THRALL  A.F. PRUITT 《Veterinary radiology & ultrasound》2007,48(3):292-296

Magnetic resonance (MR) images may be useful for radiation planning due to greater contrast resolution. One disadvantage of MR images for radiation planning is the inability to incorporate electron density information into the dose calculation algorithm. To assess the magnitude of this problem, we evaluated radiation dose distribution in canine brain by comparing computed tomography (CT)-based radiotherapy plans with and without electron density correction. Computerized radiotherapy plans were generated for 13 dogs with brain tumors using 6 MV photons. A tissue-contouring program was used to outline the gross tumor volume (GTV) and the planning target volume (PTV) for each patient. Two treatment plans were generated for each dog. First, the plan was optimized without heterogeneity correction. Then the heterogeneity correction was implemented without changing any other plan parameters. Isodose distributions and dose volume histograms (DVHs) were used to compare the two plans. The D95 (dose delivered to 95% of the volume) within the PTV was calculated for each treatment plan and differences in the D95s were compared. The mean D95s without and with heterogeneity correction were 49.1 +/- 0.7 and 48.9 +/- 1.0Gy, respectively. The absolute mean percent dose difference without and with heterogeneity correction was 1.0 - 0.9% (-1.3-3.2%) and was not considered to be clinically significant. We found no clinically significant difference between CT-based radiotherapy plans without and with heterogeneity correction for brain tumors in small animals, which supports the use of MR-based treatment planning for radiotherapy of small animal brain tumors.  相似文献   

Simulation of transpiration, drainage, N uptake, nitrate leaching, and N uptake concentration in tomato grown in open substrate   总被引：3，自引：0，他引：3  

M. Gallardo  J.S. Rodríguez  M.D. Fernández  J.J. Magán 《Agricultural Water Management》2009,96(12):1773-1784

Free-drainage or “open” substrate system used for vegetable production in greenhouses is associated with appreciable NO₃⁻ leaching losses and drainage volumes. Simulation models of crop N uptake, N leaching, water use and drainage of crops in these systems will be useful for crop and water resource management, and environmental assessment. This work (i) modified the TOMGRO model to simulate N uptake for tomato grown in greenhouses in SE Spain, (ii) modified the PrHo model to simulate transpiration of tomato grown in substrate and (iii) developed an aggregated model combining TOMGRO and PrHo to calculate N uptake concentrations and drainage NO₃⁻ concentration. The component models simulate NO₃⁻-N leached by subtracting simulated N uptake from measured applied N, and drainage by subtracting simulated transpiration from measured irrigation. Three tomato crops grown sequentially in free-draining rock wool in a plastic greenhouse were used for calibration and validation. Measured daily transpiration was determined by the water balance method from daily measurements of irrigation and drainage. Measured N uptake was determined by N balance, using data of volumes and of concentrations of NO₃⁻ and NH₄⁺ in applied nutrient solution and drainage. Accuracy of the two modified component models and aggregated model was assessed by comparing simulated to measured values using linear regression analysis, comparison of slope and intercept values of regression equations, and root mean squared error (RMSE) values. For the three crops, the modified TOMGRO provided accurate simulations of cumulative crop N uptake, (RMSE = 6.4, 1.9 and 2.6% of total N uptake) and NO₃⁻-N leached (RMSE = 11.0, 10.3, and 6.1% of total NO₃⁻-N leached). The modified PrHo provided accurate simulation of cumulative transpiration (RMSE = 4.3, 1.7 and 2.4% of total transpiration) and cumulative drainage (RMSE = 13.8, 6.9, 7.4% of total drainage). For the four cumulative parameters, slopes and intercepts of the linear regressions were mostly not statistically significant (P < 0.05) from one and zero, respectively, and coefficient of determination (r²) values were 0.96-0.98. Simulated values of total drainage volumes for the three crops were +21, +1 and −13% of measured total drainage volumes. The aggregated TOMGRO-PrHo model generally provided accurate simulation of crop N uptake concentration after 30-40 days of transplanting, with an average RMSE of approximately 2 mmol L⁻¹. Simulated values of average NO₃⁻ concentration in drainage, obtained with the aggregated model, were −7, +18 and +31% of measured values.  相似文献   

垂直圆盘式气吸排种器种子着地点原始误差数学模型的建立     

张旭  刘哲良  刘刚  班春华 《农业科技与装备》2012,(4):31-32

使用气吸式播种机进行播种可大大提高作业效率,减轻劳动强度。针对目前垂直圆盘式气吸播种机在作业时存在种子着地误差较大的问题,分析其误差形成的原因与过程,建立相应的数学模型,为播种机具性能的改进提供理论依据。  相似文献   

The fallacy of the missing middle: physics →…→ fisheries     

MICHAEL BAUMANN 《Fisheries Oceanography》1998,7(1):63-65

In this paper I discuss some of the shortcomings of today's marine science in response to a recently published paper by Ann Gargett (1997). Three problem areas have been identified in the field linking climate forcing and fish production: First, the yet-to-be established observational proof for a relationship between the two; Second, the strongly neglected biology of organisms at evolutionary and ecological time scales; and thrird, the disregard for spatial and temporal scales in the discussion of mechanisms and supporting data.  相似文献   

CORRECTION OF ANGULAR DEFORMITY BY ASYMMETRIC PHYSEAL GROWTH AND BONE REMODELLING     

Terje O.  Fjeld  DVM  Harald  Steen  MD 《Veterinary radiology & ultrasound》1986,27(2):58-64

Angular deformities of 25 or 37 degrees valgus were created by transverse wedge osteotomies in the diaphysis of the radius in 3-month-old Cocker Spaniels. Spontaneous correction was judged from radiographs until skeletal maturity. The magnitude of correction was estimated, using the opposite normal leg as a control. Asymmetrical physeal growth corrected the induced angulation between the proximal and distal radial joint plane surfaces (joint plane angle). The average correction of the joint plane angle was 80% in the 25 degree group, and 72% in the 37 degree group. Bone remodeling of the radial shaft corrected the induced diaphyseal angulation by 50% in both groups during the study.  相似文献   

Evaluating Modified Atmospheric Correction Methods for Landsat Imagery: Image‐Based and Model‐Based Calibration Methods     

《Communications in Soil Science and Plant Analysis》2012,43(9-10):1532-1545

Abstract

To increase the accuracy of remotely sensed data for agricultural forecasting, pixel values must be corrected for atmospheric effects and converted to spectral reflectance. The objective of this research was to compare two atmospheric correction methods of Landsat imagery under a range of atmospheric conditions. Ground‐based dark‐object subtraction (GDOS) is an image‐based calibration method that used in situ ground data that the dark‐object subtraction (DOS) method did not use, whereas atmospheric calibration (AC) is a model‐based calibration method that required a standard atmospheric profile refined with the use of in situ atmospheric data. GDOS and AC methods improved the reflectance values and had relationships with measured bands, which were approximately 1 to 1 in all bands. However, the GDOS generally had lower root‐mean‐square errors (RMSE) than AC. Data from this study suggest that at the present time the GDOS method may be more accurate than the AC method.  相似文献   

一种恢复渠道中线测量的快捷方法     

杨中利 《安徽农业科学》2009,35(19):9140-9141

渠道是农田水利建设的一个重要工程，渠道测量在渠道兴、改、扩建中具有重要的地位和作用。仅就施工过程中如何快捷恢复渠道中线的测量方法作了探讨，并对恢复中线的精度作了相应分析。  相似文献   

农业机器人的超声波测距系统设计   总被引：6，自引：2，他引：4  

高云 《农机化研究》2009,31(4)

设计了一种用于农业机器人的超声波测距系统;分析了系统的硬件组成和工作原理;提出了采用声速温度补偿及针对湿度、气压和硬件电路的精度等其他影响因素的误差修正因子补偿来提高测距精度的方法.实验证明:该系统能够实现对农作物的精确测距和定位, 在一定程度上辅助农业机器人的视觉系统,使其提高精度.  相似文献   

吉林省农村居民消费与收入的关系分析和政策建议   总被引：1，自引：1，他引：0  

刘子玉  杨印生  肖静 《农机化研究》2008,(3):12-15

消费是国民经济的重要组成部分.为此,通过对吉林省1985～2005年农村居民消费支出与农村收入的关系进行协整检验并建立误差修正模型,验证了两者之间存在的长期协整关系和短期修正关系.同时,根据分析的结果给出了提高吉林省居民消费水平的相关政策建议.  相似文献   

霍尔效应测量中的系统误差及其处理     

么强  赵保利 《内蒙古农业大学学报(自然科学版)》2008,29(1):211-214

本文对霍尔效应测量中的热能流引起的不等位电势误差提出了自己的见解,然后着重研究消除系统误差的方法,并对实验结果进行了评述.  相似文献