On design of physical random access channel in high-speed railway LTE systems

For the uplink in the long-term evolution （LTE） systems, the physical random access channel （PRACH） adopts Zadoff-Chu （ZC） sequences as preamble sequences, and each user can choose a unique cyclic shift for user identification. In high-mobility scenario, the Doppler fre- quency shift raises up the false alarm probability by inducing the correlation peak offsetting at the receiver side. Traditional detection method utilizes multiple search win- dows for searching the potential uplink users. When the Doppler frequency shift is larger than the subcarrier spac- ing, the energy of correlation peak leaks outside the search window and increases the false alarm probability. In this paper, we present a novel design for PRACH preamble sequence for high-speed railway scenario. Through numerical observation, we find out that the offset of the correlation peaks only depends on the initial root sequence number and the length of ZC sequences. Therefore, the root number of ZC sequences should be carefully designed to generate a preamble sequence to fight against the Doppler frequency shift. Consequently, those offsets of the corre- lation peaks are concentrated within a single search win- dow, resulting in lower complexity of detection and lower probability of false alarm for random access in LTE uplink.     

Spatiotemporal characteristics of freezing and thawing of the active layer in the source areas of the Yellow River （SAYR）

Based on the analysis of data on temperatures and moisture of soils in the active layer at four different permafrost sites in the source areas of the Yellow River(SAYR)in 2010–2012,the freeze–thaw processes of soils in the active layer were compared and contrasted for understanding the spatiotemporal variations.At the four studied sites,the thickness and mean annual temperature of permafrost are different.The temperatures at the top of permafrost(TTOP),i.e.,the maximum depth(s)of seasonal frost and/or thaw penetration,are-1.9°C at the Chalaping site(CLP),-0.9°C at the site on the southern bank of the Zhaling Lake(ZLH),-0.4°C at the Maduo Town site(MDX),and 1.1°C at the site on the northern bank of the Eling Lake(ELH).Differences in the mean annual ground temperature of permafrost and TTOPs may be responsible for the differentiations in the freeze–thaw processes of soils in the active layer.With rising TTOPs,the ground thawing started earlier:CLP in early June,ZLH in late May,MDX in early May,and ELH in mid-April,while the freezing began later:CLP in early October,ZLH in early to midOctober,MDX in mid-October,and ELH in the mid-to late October.With increasing TTOPs,the freeze-up periods for permafrost sites were shortened:202 days at CLP,130 days at ZLH,100 days at MDX,and the period of complete thaw was 89 days at ELH.At the CLP and ZLH sites,the two-directional ground freezing(downwards from ground surfaces and upwards from the permafrost table)and thawing finished in the same year,but the ground freezing at the MDX continued to the end of the nextJanuary,with very slow freezing rates in the end.At the ELH site,ground freezing kept on until early May when thawing began on the surface,and upward and downward thawing became increasingly stable in late June to early July.At each site,with rising TTOPs,the downward freezing accelerated in comparison with the upward freezing,and with an increasing proportion of downward frozen depth,and with the larger ratios of freezing to thawing duration.In summary,the patterns of thawing and freezing processes in the active layer in the SAYR differ from those in other parts of the Qinghai–Tibet Plateau to a noticeable extent.     

破产准则下修正Heston波动的最优再保-投资决策

为了研究修正Heston随机波动率下保险公司最优再保-投资策略问题,在盈余水平服从扩散过程的假设下,运用随机动态规划原理,建立最小化破产概率准则的HJB方程,通过求解方程得到最优再保-投资策略和最小化破产概率的显式解,并分析了随机波动率对最优投资决策,最优比例再保险策略和最小破产概率的影响。     

植被—土壤—水文相互作用及生态水文模型参数的动态表述

植被与土壤、水文之间存在复杂的相互作用,是生态水文模型和植被变化生态水文效应评估研究的重点.虽然陆面植被指数等动态变化对流域截留、蒸散发等水量、能量平衡项影响已有较多研究,但植被地下生物量变化如何改变土壤结构和水力特性,进而影响入渗和径流等水文过程研究相对缺乏.本文综述国内外植被变化对土壤、水文动态变化特征研究成果基础上,分析植被变化水文响应的阈值效应和尺度效应、植被变化下的土壤水力参数时变特征定量表述及其与植被、土壤类型以及气候条件的关系.在生态水文模型中,考虑植被因子对土壤水力参数影响的动态表达可以提高植被变化下水文效应模拟和预测的可靠性.     

非目标因素对AVO属性叠加的影响

除了泊松比外,有不少非目标因素会引起振幅随炮检距变化,在AVO属性叠加图上能直观看到它们的影响.AVO的抗干扰性能远低于水平叠加,那些振幅或时差随炮检距单调变化的因素会引起严重的假AVO异常,因此利用AVO方法时,需要作特别精细的叠前处理.地震数据处理,AVO属性盛加.非目标因素;随机嗓声,剩余时差     

非齐次泊松过程中向量参数极大似然估计的重对数律

对于具有向量参数的非齐次泊松过程的一般模型,论证了向量参数极大似然估计每个分量的收敛速度符合重对数律。     

烧结助剂和工艺对RBSN性能的影响

本文介绍了新型非金属材料Si3N4利用反应烧结方法（简称RBSN）的制取过程,并以MgO、AlO3、Y2O3和ZrO2为助剂,探讨烧结助剂和成型工艺对制品性能的影响;温度和助剂对氨化率的影响;ZrO2含量、烧结时间和气氛对制品烧结性能的影响。为提高制品的致密度和机械强度等方面做了一定的工作。     

光滑经验分布函数的随机加权逼近

利用样条函数将分布函数光滑化,得到光滑经验分布函数,在一定的条件下,证明了光没经验分布函数随机加权逼近的相合性。     

关于半紧随机1-集压缩映射的随机不动点定理

利用随机ｋ（ｗ）－集压缩集值映射的随机不动点定理,建立了若干半紧随机１－集压缩集值映射的随机不动点定理,推广了已知的相应结果。     

Stage characteristics for the development of late Quaternary paleosols in the Yangtze Delta area

The late Quaternary paleosols in the Yangtze Delta area developed in the period of 25 000-12 000 aBP. Phytolith ratios (value A) of contents of fan, square and rectangle types indicating the warm and humid climate to those of bar, hat and point types indicating cold and dry climates decrease upwards overall on profiles of the paleosols, suggesting that the climates turned from warm and humid to cold and dry. So, the paleosols developed mainly during the regression before the last glacial maximum. Changes of value A indicate no trend of warming, suggesting that the transgression was rapid after the last glacial maximum. The development of the paleosols exhibited obvious stages, which were controlled remarkably by transgression and regression : Ⅰ . Period of alternation of deposition and pedogenesis, which was from the occurrence of regresson before the last glacial maximum to the time when sea levels fell close to the lowest; Ⅱ . Exposure period with continual pedogenesis, which was terminated when the paleosols were drown in the post-glacial transgression; Ⅲ . Period of being drown and buried, the paleosols were buried by marine sediments, and reworked by early diagenesis.