Micro Insert: A Prototype Full-Ring PET Device for Improving the Image Resolution of a Small-Animal PET Scanner

A full-ring PET insert device should be able to enhance the image resolution of existing small-animal PET scanners. Methods: The device consists of 18 high-resolution PET detectors in a cylindric enclosure. Each detector contains a cerium-doped lutetium oxyorthosilicate array (12 x 12 crystals, 0.72 x 1.51 x 3.75 mm each) coupled to a position-sensitive photomultiplier tube via an optical fiber bundle made of 8 x 16 square multiclad fibers. Signals from the insert detectors are connected to the scanner through the electronics of the disabled first ring of detectors, which permits coincidence detection between the 2 systems. Energy resolution of a detector was measured using a Ge-68 point source, and a calibrated 68Ge point source stepped across the axial field of view (FOV) provided the sensitivity profile of the system. A Na-22 point source imaged at different offsets from the center characterized the in-plane resolution of the insert system. Imaging was then performed with a Derenzo phantom filled with 19.5 MBq of F-18-fluoride and imaged for 2 h; a 24.3-g mouse injected with 129.5 MBq of F-18-fluoride and imaged in 5 bed positions at 3.5 h after injection; and a 22.8-g mouse injected with 14.3 MBq of F-18-FDG and imaged for 2 h with electrocardiogram gating. Results: The energy resolution of a typical detector module at 511 keV is 19.0% +/- 3.1 %. The peak sensitivity of the system is approximately 2.67%. The image resolution of the system ranges from 1.0- to 1.8-mm full width at half maximum near the center of the FOV, depending on the type of coincidence events used for image reconstruction. Derenzo phantom and mouse bone images showed significant improvement in transaxial image resolution using the insert device. Mouse heart images demonstrated the gated imaging capability of the device. Conclusion: We have built a prototype full-ring insert device for a small-animal PET scanner to provide higher-resolution PET images within a reduced imaging FOV. Development of additional correction techniques are needed to achieve quantitative imaging with such an insert.

A Particle-in-cell scheme of the RFQ in the SSC-Linac

A 52 MHz Radio Frequency Quadrupole (RFQ) linear accelerator (linac) is designed to serve as an initial structure for the SSC-Linac system (injector into Separated Sector Cyclotron). The designed injection and output energy are 3.5 keV/u and 143 keV/u, respectively. The beam dynamics in this RFQ have been studied using a three-dimensional Particle-In-Cell (PIC) code BEAMPATH. Simulation results show that this R,FQ structure is characterized by stable values of beam transmission efficiency (at least 95%) for both zero-current mode and the space charge dominated regime. The beam accelerated in the RFQ has good quality in both transverse and longitudinal directions, and could easily be accepted by Drift Tube Linac (DTL). The effect of the vane error and that of the space charge on the beam parameters have been studied as well to define the engineering tolerance for RFQ vane machining and alignment.

长白山北坡土壤动物群落物种共有度的海拔梯度变化

群落间各生活型土壤动物科及所有土壤动物科的共有度,一定程度上反映了群落间的相关性及沿环境梯度的物种替代关系.应用梯度格局法在长白山北坡海拔550～2 650 m地段,每隔100 m海拔高度设置一块样地,共计22块样地,并应用Jaccard指数,对各海拔不同土壤动物群落问物种共有度的海拔梯度变化进行了分析.结果表明,不同海拔土壤动物群落间物种的共有度,无论以哪一生活层的土壤动物科来表达,基本都以与其最相邻的群落间为最高.群落间物种共有度峰值与谷点反映了群落类型随海拔具有间断性变化.线虫、甲螨、弹尾等各生活型土壤动物的共有度以及所有土壤动物科的共有度,均随着海拔差的增加呈下降趋势,但并非与植被情况完全吻合.

基于MODIS数据的草地生物量估算模型比较

准确估算草地生物量对合理规划区域畜牧业、评估草地植被的生态效益有重要意义。目前,在常用的遥感估算模型中,采用的植被指数和模型函数形式多样。本文根据野外生物量调查结果和MODIS数据,分别采用归一化植被指数(NDVI)、增强植被指数(EVI)和修正的土壤调节植被指数(MSAVI)建立了内蒙古科尔沁左翼后旗草地地上生物量和地上地下总生物量估测的3种(线性、乘幂和指数)模型,并进行了比较。结果表明:3种模型能够对草地生物量进行较好的模拟,其中指数模型效果最佳;3个植被指数(NDVI,EVI和MSAVI)与草地生物量均有较高的相关性,可用于该草地产量估测,其中MSAVI对地上生物量拟合效果最好(R2=0.900);NDVI和EVI的线性模型对总生物量的模拟明显好于对地上生物量的模拟。

科尔沁沙地南缘樟子松人工林地下水埋深季节变化

于2005年5—10月,在未经过度人为干扰(大面积人工造林及农田开发)的大青沟地区(42°52′N,122°55′E)和自20世纪50年代大面积人工造林并相应开发农田的章古台地区(42°43′N,122°22′E)分别选择了樟子松疏林草地和草地(撂荒地)、樟子松衰退后皆伐地(皆伐地)及不同年龄沙地樟子松人工纯林设置固定标准地,监测了一个生长季的地下水埋深动态变化。结果表明:生长季内地下水埋深呈现出4种类型:平稳型、"V"型、"N"型和"M"型。大青沟地区的疏林草地地下水埋深在生长季变化不大,平均地下水埋深为1.88 m;章古台地区的草地和皆伐地呈现5—7月升高,之后下降;林龄较小(23年)樟子松纯林变化幅度较大,生长季地下水埋深相差4.30 m;林龄较大(33、42、45年)樟子松人工纯林生长季地下水埋深波动变化,且变幅不一。总体上,地下水埋深表现为疏林草地(大青沟地区)<(章古台地区)衰退后皆伐地和草地<林龄较小樟子松人工纯林<林龄较大樟子松人工纯林。上述结果表明,大面积造林及农田开发是造成大青沟与章古台两地地下水埋深差别的主要原因;在章古台地区,不同植被覆盖与林龄也直接影响地下水埋深。

绿色食品的态势

<正> "绿色食品"系指经"中国绿色食品发展中心"认定,许可使用"绿色食品"标志的无污染、安全、优质、营养类食品。它具有三个显著的特点:1.出自良好的生态环境; 2.有规范的"从土地到餐桌"全程质量控制措施和标准;3.其标志受法律保护,是集社会效益、环境效益和经济效益为一体的产物,赋予极强的时代特征和浓厚的食品文化内涵.1.绿色食品的开发是社会与经济发展的必然产物,有重要的现实意义现代大工业和城市的发展和进

受干扰长白山阔叶红松林林分结构组成特征及健康距离评估

通过样地调查对不同干扰方式产生的过伐天然林、次生白桦林和人工落叶松林等群落的结构组成进行分析和分类探讨 ,并选取能够表征结构完整性和稳定性的一些指标因子 ,利用健康距离法对长白山阔叶红松林区的森林生态系统健康进行了评估实践 ,结果按顺序依次为 :原始阔叶类 0 14 <结构转换型0 2 3<结构保留型 0 32 <结构破坏型 0 33<严重干扰类型 0 4 4 <次生白桦林 0 5 3<人工落叶松林0 6 8.以期对阔叶红松林生态系统的恢复和区域林业可持续发展提供参考 .

Relating the molecular structure and crystallization behavior of polypropylene

The crystallization behavior of two polypropylene (PP) resins as used for biaxially oriented polypropylene (BOPP) and general injection mold applications, respectively, has been intensively investigated and compared by means of polarized light optical micrography (POM), differential scanning calorimetry (DSC), conventional transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM). It is found that both molecular weight distribution and isotacticity of polypropylene strongly affect its crystallization characteristics, e.g., the number of crystal nuclei at the initial stage, crystallization dynamics, the morphology, size and perfection of crystals in the final product, and so on. The results indicate an appropriate molecular structure is vital in producing high-quality BOPP film.

Electrochemical behavior of 3,4-dihydroxybenzoic acid in self-assembled monolayer electrode system

The self-assembled monolayer of cystamine was prepared on gold electrode and 3,4-dihydroxybenzoic acid (DHBA) was electrochemically deposited on cystamine surface as a functional group by electrostatic adsorption, namely, molecular deposition. It shows that the MD/SAM structure has a higher stability, and E-1/2 of the DBAH in MD/SAM shifts more negative than that of on naked gold electrode, The n-decanethiol was also used to fill defects in MD/SAM, it results in much better cyclic voltermmetric behavior.

3,4-二羟基苯甲酸在自组装结构中的电化学行为

电极与有确定取向的电活性基团之间的电子传递是电化学领域的研究热点．利用二维有序薄膜固定电活性官能团是一个成熟的方法［１］，主要包括ＬＢ技术和自组装技术，这两者都存在着样品合成困难的问题．近年来，通过表面逐层反应来固定电活性官能团已有研究，但是反应过程…

聚乙烯膜辐照接枝丙烯酸的XPS表征

用辐照方法,使亲水单体在聚烯烃类高分子材料表面接枝聚合,从而改善这些材料的亲水性,同时也可用这种方法来制备具有所需性能的膜材料(作离子交换膜、反渗透膜等),是一个较热门的研究课题。

Three tetraspanins from Chinese shrimp, Fenneropenaeus chinensis, may play important roles in WSSV infection

Three members of the tetraspanin/TM4SF superfamily were cloned from Chinese shrimp, Fenneropenaeus chinensis. The deduced amino acid sequences of the three proteins have typical motifs of the tetraspanin/TM4SF superfamily. Phylogenetic analysis of the proteins, together with the known tetraspanins of invertebrates and vertebrates, revealed that they belong to different tetraspanin subfamilies: CD9, CD63 and tetraspanin-3. The three cloned genes of CD9, CD63 and tetraspanin-3 showed apparently different tissue distributions. The CD9 gene (FcCD9) was specifically expressed in the hepatopancreas. While for the CD63 gene (FcCD63), the highest expression was detected in nerves, epidermis and heart, with low expression in haemocytes, ovary, gill, hepatopancreas and stomach and no expression in intestine, muscle and lymphoid organ. Compared with FcCD9 and FcCD63, the tetraspanin-3 gene (FcTetraspanin-3) was more broadly expressed and its highest expression was detected in the intestine. Its expression in nerves was lower than in the intestine, but was higher than in other tissues. Expression in haemocytes, ovary and muscle was much lower than in other tissues. The expression profiles of FcCD9, FcCD63 and FcTetraspanin-3 in different tissues, including haemocytes, lymphoid organ and hepatopancreas, were compared by real-time PCR when shrimp were challenged by live white spot syndrome virus (WSSV) and heat-inactivated WSSV. All three tetraspanins were markedly up-regulated in the live WSSV-challenged shrimp tissues. The data suggested that the three cloned members of TM4SF superfamily in Chinese shrimp may play a key role in the route of WSSV infection.

一种无解析解的运动学逆问题的数值一解析解法

本文提出用数值—解析法求解一种无解析解的6R机器人的运动学逆问题。该方法不同于一般的数值解法,首先建立起目标函数,并把θ_6与θ_1～θ_5的求解分离开,先用数值迭代法求出θ_6,然后用解析法直接得出θ_1～θ_5并在有轨迹端点约束条件下给出了迭代算法,并证明了算法的收敛性及稳定性,仿真结果表明该方法可靠,精度高,速度快,便于实际应用

冰期间冰期转换过程中陆地碳库的演化规律研究

Terrestrial carbon pool mainly consists of three parts: the active carbon pool of the vegetation，soil carbon pools and the lithosphere carbon pool of less activity. Under natural conditions，vegetation carbon pools，soil carbon exchange with atmospheric carbon pool directly，the lithosphere participate in the global carbon cycle by weathering Our research have coverd the soil organic carbon density，plant biomass (carbon density)，plant net primary productivity of past 40 ka，and the magnetic susceptibility，grain size，weathering of silicate carbon consumption of past 140 ka. This study has achieved a number of conclusions as shown below. 1 Silicate weathering CO2 consumption in the long-term fluctuations with a similar deep-sea δ18O record，demonstate that it not only can be used as one of the instructions of terrestrial carbon pool，even can be used as indicators of global environmental change; silicate weathering CO2 consumption and susceptibility shown a clear relationship between lag or lead at different times，it maybe lies on how the climate change. 2 Soil carbon pools in line with the global climate on long-term，but the relationship between soil carbon density and climate change was not obvious in short-term change，generally lags behind the changes in other climatic proxies. 3 Carbon density of vegetation and other proxy indicators of climate have good consistency. In the study period，perform the cycle of glacial and interglacial completely，but because of the ancient vegetation of accurate information is difficult to obtain，it did not reflect rapid response to climate change. 4 Cooling events is conducive to soil organic carbon accumulation but not conducive to weathering and vegetation growth. High temperature environment is not conducive to the accumulation of soil organic carbon. 5 In the deglacial time from the last glacial maximum to the Holocene，weathering carbon consumption seems earlier than vegetation and soil organic carbon in the fluctuant increase.Does it imply that the effects of silicate weathering is an important factor to the global carbon cycle and global climate change? It is worth further research.