东北黑土区农业生态景观格局及变化研究——以德惠市为例

目的 以德惠市为黑土区代表,研究其农业生态景观格局及其动态,为黑土区农业生态建设提供依据.方法 根据影像解译的土地利用图上各类斑块的分布特点,应用地理信息系统方法和景观生态学方法进行研究.结果 德惠市的农业景观主要以旱地和水田构成,形成以旱地为基质,水田为斑块镶嵌于其上的格局.水田较多沿松花江分布在东北部分,居民地基本上呈东北一西南走向且平行排列.其土地利用变化主要体现为各类用地向水田转化.结论 自然和社会因素共同作用形成了德惠市的农业生态景观格局.德惠市农业属于扩大耕地面积的"外延式"发展,甚至仍然存在开垦林、草地为耕地的现象,很大程度上影响了德惠市土地可持续利用.发展生态农业,在耕地资源总量减少的情况下,提高农村收入,促进黑土区农村社会经济的全面发展是今后农村生态建设的重点问题.     

Computer simulation on reliability of retention index with FDG–PET and optimization of dual-time-point imaging protocol

The inherent noise in positron emission tomography (PET) leads to the instability of quantitative indicators, which may affct the diagnostic accuracy for diffrentiating malignant and benign lesions in the management of lung cancer. In this paper, the reliability of retention index (RI) is systematically investigated by using computer simulation for the dual-time-point imaging protocol. The area under the receiver operating characteristic (ROC) curve is used to evaluate the optimal protocol. Results demonstrate that the reliability of RI is a?ected by several factors including noise level, lesion type, and imaging schedule. The RIs with small absolute values su?er from worse reliability than those larger ones. The results of ROC curves show that over delayed second scan cannot help to improve the diagnostic performance further, while an early ?rst scan is expected. The method of optimization based on ROC analysis can be easily extended to comprise as many lesions as possible.     

Temperature Distribution in a Long-Span Aircraft Hangar

Long-span aircraft hangars have features which differ from other large structural systems. The temperature stresses due to temperature variations often greatly impact the mechanical performance of the structure. The paper presents an analysis of the heat transfer processes and factors which influence the temperature distribution. The AMECO-A380 aircraft hangar at the Beijing Capital International Airport was selected as a practical example to illustrate the use of finite volume analysis to calculate the temperature field taking into account meteorological conditions, solar radiation, heat convection, etc. The temperature distribution and the variation of the length of the upper and lower chords of the grid structure roof were analyzed to develop guidelines for the temperature distributions in very large aircraft hangars. The results show that the temperature effect will be large for long-span hangars, and the temperature stresses due to nonuniform temperatures should be analyzed to guarantee the structural safety of large aircraft hangars.     

Magnetic rotation imaging method to measure the geomagnetic field

A new imaging method for measuring the geomagnetic field based on the magnetic rotation effect is put forward. With the help of polarization property of the sunlight reflected from the ground and the magnetic rotation of the atmosphere, the geomagnetic field can be measured by an optical system installed on a satellite. According to its principle, the three-dimensional image of the geomagnetic field can be obtained. The measuring speed of this method is very high, and there is no blind spot and distortion. In this paper, the principle of this method is presented, and some key problems are discussed.     

基于平衡的微型燃气轮机回热循环效率分析

对采用回热循环的微型燃气轮机进行了正、反平衡效率分析,推导了正、反平衡效率一致性的数学模型.结合微型燃气轮机实例,计算了正、反平衡的效率,并进行了分析的可靠性检验,检验结果表明,实例中的正、反平衡效率偏差和偏差率都很小,分析结果可靠.通过反平衡效率分析,得出了微型燃气轮机的主要损部位,提高微型燃气轮机效率可主要从改进燃烧室和回热器入手,对于排气中的损失可采用结合余热利用装置加以利用.     

农村教师队伍建设面临的问题透视——农村教师专业化发展视角

我国农村教师队伍建设取得了很大新成就,但是依然面临着诸多问题与挑战,主要是农村教师保障难、补充难和农村教师教育难。就问题及其原因分析,相应的对策建议是：加强教育执法,确保农村教师待遇;增加教师编制,有序补充农村教师;师范毕业生定向分配当农村教师,落实有编有岗,激活农村教师教育。对于农村代课教师,不是简单地说“清退”,而是要妥善“安置”。     

Sr_4Al_(14)O_(25)∶Eu~(2 ),Dy~(3 )长余辉发光材料的合成及正交实验设计法

研究了燃烧温度、Eu2 和Dy3 的搀杂量、助熔剂硼酸的加入量、尿素加入量及Al/Sr的比例对Sr4Al14O25∶Eu2 ,Dy3 长余辉发光材料发光性能的影响,从而确定了长余辉发光材料Sr4Al14O25∶Eu2 ,Dy3 的最佳合成工艺.对所得产物分别进行了XRD、TEM、荧光测试和亮度测试.结果表明:磷光体存在403和482 nm 2个发射峰,分别对应于Eu2 在基质中2种不同的存在方式,与传统的高温固相法相比发射主峰出现了蓝移;亮度测试找到了最佳的原料配比及合成条件.     

一种改进的快速车牌定位算法

文章提出了一种基于纹理特征和颜色特征的车牌定位算法.算法首先利用车牌的纹理特征对车牌进行了初步定位,其中主要有图像预处理、边缘检测、数学形态学处理等步骤.最后利用车牌区域的颜色特征对车牌区域进行精确定位,主要包括空间转换、边界确定等步骤.对80张相片进行测试的结果表明,该方法准确率高、速度快.     

Novel Waterborne Fluorinated Polyurethane Containing Fluoroalkyl Side Chain:Synthesis,Characterization and Application on Cotton Fabric

A polyether diol poly[3-bromomethyl-3-tridecafluorooctyloxymethyloxetane]glycol(PFBOX 3) was prepared in 91% yield from ring opening polymerization of 3-bromomethyl-3-tridecafluorooctyloxymethyloxetane 2 which was derived from 3,3-dibromomethyloxetane 1 and 1H,1H,2H,2H-perfluorooctanol.The waterborne fluorinated polyurethane FPU was thus obtained by condensed polymerization of PFBOX 3 with isophoronediisocyanate(IPDI).The structure of FPU was characterized by Fourier transform infrared spectrometer(FTIR).FP...     

浅表性骨肉瘤病理分析及其微血管密度

目的 探讨浅表性骨肉瘤的临床病理学特征及其微血管密度.方法 选取经手术病理证实的13例浅表性骨肉瘤患者,对其临床及病理资料进行回顾性分析,采用免疫组化SP法检测患者CD105及CD105-MVD的表达情况,并与13例良性骨肿瘤患者资料进行对照分析.结果 患者膝关节会出现屈曲活动受限,可伴有不同程度疼痛、肿胀、压痛、缓慢性增大肿块、皮温增高等症状.肿瘤的部位、大小与周围组织关系以及骨皮质侵蚀情况均可在影像学上清晰显示.在浅表性骨肉瘤中CD105阳性表达率和CD105-MVD均明显高于良性骨肿瘤,两者比较差异具有统计学意义(P<0.05).结论 浅表性骨肉瘤诊断主要依靠临床、影像学以及病理学等多方面综合诊断,浅表性骨肉瘤中CD105-MVD明显升高,CD105-MVD很可能参与肿瘤性血管的生成,从而影响浅表性骨肉瘤的发生、发展以及预后.