基于高度分集技术的低仰角测高影响因素分析

米波三坐标雷达有重要的军事价值,尽管目前有很多种测高技术包括高分辨技术、空间谱估计技术、复角技术、偏差补偿技术、频率捷变技术等,但其低仰角测高精度不高,因此有必要分析影响测高因素。本文利用高度分集测高技术,仿真分析了不同介质以及极化方式对反射系数的影响;信噪比,幅相特性不一致对测高精度的影响。     

非规则全分集LDPC码的构造方法

提出一种基于渐进边增长（Progressive Edge．Growth,PEG）算法的非规则全分集低密度奇偶校验（Low—Density Parity—Check,LDPC）码的构造方法。首先根据度分布和码率,对非规则全分集LDPC码中的节点进行度分配;然后对PEG算法中校验节点的选择标准加以约束,生成消除短环的非规则全分集LDPC码;进一步,通过改变局部校验节点剩余度的方法,解决在特殊度分布下算法失效的问题。仿真结果表明,构造的非规则全分集LDPC码在瑞利块衰落信道下能够实现全分集;在码长、码率相同的情况下与规则全分集LDPC码相比,非规则全分集LD—PC码能够获得更高的编码增益。     

Improving the Reception Performance of Legacy T‐DMB/DAB Receivers in a Single‐Frequency Network with Delay Diversity

This paper describes a simple delay diversity technique for terrestrial digital multimedia broadcasting (T‐DMB) and digital audio broadcasting in a single‐frequency network (SFN). For the diversity technique, a delay diversity scheme is adopted. In the delay diversity scheme, a non‐delayed signal is transmitted in the first antenna, and delayed versions of the signal are transmitted in each additional antenna. For an SFN environment with multiple transmitters, delay diversity can be executed by controlling the emission times of the transmitters. This SFN delay diversity scheme does not require any hardware changes in either the transmitter or receiver, and perfect backward compatibility can be acquired. To evaluate the performance improvement, laboratory tests are executed with various types of commercial T‐DMB receivers as well as a measurement receiver. The improvement in the bit error rate performance is evaluated using a measurement receiver, and an improvement of the threshold of visibility value is evaluated for commercial receivers. Test results show that the T‐DMB system can obtain diversity gain using the described technique.     

丘陵地区城镇设计初探

随着社会经济和城乡统筹的发展,城镇化迅速推进,丘陵地区中小城镇的开发建设也不例外。阐述了丘陵地区中小城镇开发建设的特点,以及当前所面临的主要问题,并指出了丘陵地区城镇设计的重要意义。最后从整体性与发展性,多样性和地域性,人性化和宜居性等角度对丘陵地区城镇设计做了初步探析。     

多用户协作分集方案研究

多用户协作分集是一种在无需基础控制设施的无线传输环境中获得类似多天线传输性能的分布式多天线技术。由于其能够提高频谱、时间、空间的有效复用。改善网络覆盖性能,多用户协作分集将对未来无线通信发展产生重大的影响。本文从协作用户中转方式的角度。介绍了协作分集的由来、特征和关键技术,并对部分研究成果作了进一步探讨。     

Genotype and environment effects on nitrate accumulation in a diversity set of lettuce accessions at commercial maturity: the influence of nitrate uptake and assimilation, osmotic interactions and shoot weight and development

BACKGROUND: The causes of the natural variation in nitrate accumulation and associated traits are studied using a diverse population of 48 mature lettuce accessions grown hydroponically in winter and summer seasons. Information on the effects of genotype, environment and their interactions will inform future selection strategies for the production of low‐nitrate varieties more suited to meeting EU requirements for harvested produce. RESULTS: The effects of genotype (G), environment (E) and G × E interactions were all significant, with nitrate concentrations lower but covering a wider range in summer. Concentrations of nitrate‐N were positively correlated with those of water and total‐N and negatively with assimilated‐C in the shoot in both seasons, with all relationships partitioned according to morphotype and/or seasonal type. Corresponding relationships between nitrate‐N and assimilated‐N or with shoot fresh or dry weight were generally weak or inconsistent. Nitrate concentrations at an early growth stage were strongly related to those at maturity in winter, but not in summer when light levels were less variable. CONCLUSION: The effects of genotype and environment on nitrate accumulation in lettuce are strongly influenced by morphotype, with most G × E interactions between accessions within the same morphotype predominantly of the non‐crossover type. All low‐nitrate‐accumulating genotypes have increased concentrations of organic solutes (concentration regulation) and reduced water (volume regulation) to help stabilise osmotic potential within the shoots. Variability in nitrate accumulation arises more from differences in uptake than in efficiency of its chemical reduction. Genotypic differences in nitrate accumulation can be masked by changes in head morphology during maturation, provided that they are not confounded by substantial changes in intercepted light. Recent selection strategies do not appear to have produced lower‐nitrate‐accumulating cultivars. Copyright © 2011 Society of Chemical Industry     

燕麦种质资源农艺性状的遗传多样性分析--测试文章

分析了国内外54份燕麦种质资源的遗传多样性,归纳其遗传亲缘关系,为合理利用燕麦品种(系)资源提供理论依据。结果表明：(1) 54份种质资源农艺性状间存在广泛的遗传多样性,5个质量性状(粒色、粒型、穗型、小穗型、抗病性)以抗病性的多样性指数最高,粒色的遗传多样性指数最低;8个数量性状(单株分蘖数、株高、穗长、小穗数、轮层数、单株粒数、单株粒重、千粒重)以单株粒重的遗传多样性指数最高,变异系数最大。(2)聚类分析将54份种质资源的8个数量性状分为4大类群,类群Ⅰ为高秆、大粒型育种目标亲本材料;类群Ⅱ为矮秆育种目标亲本材料,类群Ⅲ的有益性状不明显,为多目标性状育种的亲本材料,类群Ⅳ为增加轮层数、小穗数等育种目标的优良材料。     

网印艺术可拓展性初探

丝网版画相对于木版、铜版、石版,其产生的时间较短,艺术形式不够鲜明.传统的印刷材料属于工业油墨,污染较重,阻碍了网印艺术的发展.在采用了丝网版画新材料专用水性油墨和专用版画纸张后,使丝网版画艺术焕发了新的艺术活力.当代丝网版画已更具多样性、可开放性,对于可以融入大量现代科技手段和先进技术的丝网版画,恰恰能够把握和紧跟时代节拍,充分调动丝网版画多元性、开放性和不确定性的特点,运用不同的手段、不同的表达方式来创作个人的优秀的艺术作品.     

基于高通量测序技术分析菜心切口处微生物多样性

研究菜心冷藏期间的腐败微生物,使用高通量测序技术,对冷藏菜心切口处微生物的多样性进行分析,探究冷藏期间微生物菌群相对丰度的动态变化。以4 ℃冷藏菜心为研究对象,分析贮藏早期0 d、中期7 d、后期14 d的菜心切口处细菌的16S rRNA和真菌的ITS序列,比较各组菌群组成和丰度。通过物种注释评估和物种组成分析,明确菜心贮藏过程中切口处的优势菌群。在贮藏早、中、后期,真菌优势菌群均为担子菌门（Basidiomycota）、子囊菌门（Ascomycota）和unclassified Fungi。在贮藏早期,细菌优势菌群为厚壁菌门（Firmicutes）和变形菌门（Proteobacteria）,而在贮藏中、后期,细菌优势菌群转变为厚壁菌门、变形菌门、放线菌门（Actinobacteria）和拟杆菌门（Bacteroidetes）。微生物多样性结果显示,真菌的多样性要高于细菌。本研究明确了菜心冷藏期间的微生物多样性发生规律,为后续菜心保鲜剂和保鲜技术的研究提供了理论支撑。     

宜宾地区不同性状窖泥的细菌群落结构解析及代谢功能预测

该研究基于16S rRNA V3-V4区基因序列,采用高通量测序技术对宜宾地区不同性状窖泥（新窖泥、老熟窖泥、老化窖泥）的细菌群落结构差异进行分析,并采用PICRUSt预测不同性状窖泥微生物的代谢功能,解析宜宾地区不同性状窖泥的代谢功能差异。结果表明,该地区三种性状窖泥的细菌群落结构存在显著差异,老熟窖泥和老化窖泥细菌群落的丰富度高于新窖泥,而多样性相反。己酸菌属（Caproiciproducens）在老熟窖泥中的相对丰度较高,可能是该地区窖泥老熟的标志,该菌对浓香型白酒的风味物质形成具有重要的作用;乳酸杆菌（Lactobacillus）则在新窖泥中的相对丰度较高,可能是该地区新窖泥的标志。窖泥的碳水化合物代谢和氨基酸代谢功能最强,且其相对丰度同样呈现出老熟窖泥＞老化窖泥＞新窖泥的变化规律,说明老熟窖泥的细菌群落结构对浓香型白酒风味物质的形成最有利。