Adjustment to climate change is constrained by arrival date in a long-distance migrant bird

Spring temperatures in temperate regions have increased over the past 20 years, and many organisms have responded to this increase by advancing the date of their growth and reproduction. Here we show that adaptation to climate change in a long-distance migrant is constrained by the timing of its migratory journey. For long-distance migrants climate change may advance the phenology of their breeding areas, but the timing of some species' spring migration relies on endogenous rhythms that are not affected by climate change. Thus, the spring migration of these species will not advance even though they need to arrive earlier on their breeding grounds to breed at the appropriate time. We show that the migratory pied flycatcher Ficedula hypoleuca has advanced its laying date over the past 20 years. This temporal shift has been insufficient, however, as indicated by increased selection for earlier breeding over the same period. The shift is hampered by its spring arrival date, which has not advanced. Some of the numerous long-distance migrants will suffer from climate change, because either their migration strategy is unaffected by climate change, or the climate in breeding and wintering areas are changing at different speeds, preventing adequate adaptation.     

The buffer effect and large-scale population regulation in migratory birds

Buffer effects occur when sites vary in quality and fluctuations in population size are mirrored by large changes in animal numbers in poor-quality sites but only small changes in good-quality sites. Hence, the poor sites 'buffer' the good sites, a mechanism that can potentially drive population regulation if there are demographic costs of inhabiting poor sites. Here we show that for a migratory bird this process can apply on a country-wide scale with consequences for both survival and timing of arrival on the breeding grounds (an indicator of reproductive success). The Icelandic population of the black-tailed godwit, Limosa limosa islandica, wintering in Britain has increased fourfold since the 1970s (ref. 5) but rates of change within individual estuaries have varied from zero to sixfold increases. In accordance with the buffer effect, rates of increase are greater on estuaries with low initial numbers, and godwits on these sites have lower prey-intake rates, lower survival rates and arrive later in Iceland than godwits on sites with stable populations. The buffer effect can therefore be a major process influencing large-scale population regulation of migratory species.     

基于中心对称圆阵的不相关源和相干源的DOA估计

基于中心对称的圆阵,提出了一种针对不相关源和成对相干源的波达方向(DOA)估计方法.这是一种分两步估计的方法,首先利用阵列流形的唯一性条件估计出不相关源;然后通过构造中心对称的阵列流形来去除不相关源的干扰,同时达到去除成对相干源相干性的目的.这种方法简单有效,由于直接在阵元空间进行估计而不需要进行波束变换,因此具有较高的估计精度.仿真实验结果验证了该方法的有效性.     

近场源频率、二维到达角和距离的联合估计

文章基于四阶累积量提出了一种多个独立非高斯窄带近场源频率、二维到达角和距离的联合估计算法。该算法首先构造六个四阶累积量矩阵,由它们组成五个矩阵对,然后对五个矩阵对进行广义值分解并对广义特征值进行配对,由配对后的广义特征值求得中间参数,最后由中间参数解出各个近场源的参数。该算法无需任何搜索,而且只需五个阵元放置在固定的位置,对阵列的其它阵元并无要求。由于采用四阶累积量,所以该算法适用于任意高斯噪声环境。计算机仿真结果证实了该算法的有效性。     

优化迁移共享的自适应令牌协议

针对写作废的一致性协议在处理迁移特征时需要2次访问的特征，提出了一种自适应的令牌协议，根据数据的读/写处理器和数据的令牌信息判断数据是否具有迁移特征.如果数据具有迁移特征，则请求者的状态变为可以避免迁移访问序列中出现写访问的状态MG，从而消除了迁移特征中的写作废次数.结果表明，所提出的自适应令牌协议在读访问时获取了数据所有权，避免了部分写失效的产生，从而使得平均失效延迟降低5%，通信量平均降低9%.
     

一种简单的三维空间声源定位方法

为了简化使用话筒阵列对空间声源的定位，文中提出了一种简单的三维空间声源定位方法．该方法在直角坐标轴上放置4个麦克风，声源到达麦克风对之间的时间差可以由测量接收信号的互相关函数得到．由到达时间差和一个近似的锥模型可以很容易得到声源相对于3个坐标轴的方位角，从而转换成极坐标系中的方位角和仰角．相比较已有方法：该方法具有简单易行、计算量小的显著优点．     

Predicting heartbeat arrival time for failure detection over internet using auto-regressive exogenous model

Predicting heartbeat message arrival time is crucial for the quality of failure detection service over internet. However, internet dynamic characteristics make it very difficult to understand message behavior and accurately predict heartbeat arrival time. To solve this problem, a novel black-box model is proposed to predict the next heartbeat arrival time. Heartbeat arrival time is modeled as auto-regressive process, heartbeat sending time is modeled as exogenous variable, the model's coefficients are estimated based on the sliding window of observations and this result is used to predict the next heartbeat arrival time. Simulation shows that this adaptive auto-regressive exogenous (ARX) model can accurately capture heartbeat arrival dynamics and minimize prediction error in different network environments.     

超模序及其在离散排队系统中的应用

总结了超模序的一些性质,这些性质充分地说明了超模序能刻划随机向量的正相关性的强度.并证明了一个新的性质.最后给出了超模序在有正相关到达的离散时间排队系统中的应用,得到了队长的一些随机比较结果,并分析了有Bernoulli相关到达和消息长度相关的N源消息到达2个具体的模型.     

基于公交运行数据的到站时间填充方法

公交实时到站数据是乘客出行行为分析的基础,但是现有公交运行数据存在到站时间缺失问题。以公交实时到站数据为基础,结合公交车辆的运行特性以及拥堵传播特性,建立考虑多因素加权的多项式插值方法,对公交车辆的到站缺失数据进行填补。填补后的到站时间能够更详细地描述车辆运行过程,得到更精确的车辆到站间隔。应用该方法对北京市地面公交运行数据进行补全,得到了修正的时刻表,并对公交运行间隔与串车现象进行分析。     

一种改进的声发射P波到时自动提取算法

岩石破裂过程中的声发射(AE)监测技术已广泛应用于岩石工程领域,声发射信号的到时提取是深入开展岩石力学声发射研究的基础和关键.为了获取更为准确的声发射信号P波到时,在前人研究的基础上,提出了一种改进的Pphase-Picker声发射P波到时自动提取算法并对其原理进行详细描述.选取1000个典型声发射波形,对比分析了几种到时自动提取算法的计算结果,表明改进的算法不仅可以获取更为精确的P波到时,还可以获取到时提取误差的估计值.     

基于公交运行数据的到站时间填充方法

公交实时到站数据是乘客出行行为分析的基础,但是现有公交运行数据存在到站时间缺失问题。以公交实时到站数据为基础,结合公交车辆的运行特性以及拥堵传播特性,建立考虑多因素加权的多项式插值方法,对公交车辆的到站缺失数据进行填补。填补后的到站时间能够更详细地描述车辆运行过程,得到更精确的车辆到站间隔。应用该方法对北京市地面公交运行数据进行补全,得到了修正的时刻表,并对公交运行间隔与串车现象进行分析。     

T cells become licensed in the lung to enter the central nervous system

The blood–brain barrier (BBB) and the environment of the central nervous system (CNS) guard the nervous tissue from peripheral immune cells. In the autoimmune disease multiple sclerosis, myelin-reactive T-cell blasts are thought to transgress the BBB and create a pro-inflammatory environment in the CNS, thereby making possible a second autoimmune attack that starts from the leptomeningeal vessels and progresses into the parenchyma. Using a Lewis rat model of experimental autoimmune encephalomyelitis, we show here that contrary to the expectations of this concept, T-cell blasts do not efficiently enter the CNS and are not required to prepare the BBB for immune-cell recruitment. Instead, intravenously transferred T-cell blasts gain the capacity to enter the CNS after residing transiently within the lung tissues. Inside the lung tissues, they move along and within the airways to bronchus-associated lymphoid tissues and lung-draining mediastinal lymph nodes before they enter the blood circulation from where they reach the CNS. Effector T cells transferred directly into the airways showed a similar migratory pattern and retained their full pathogenicity. On their way the T cells fundamentally reprogrammed their gene-expression profile, characterized by downregulation of their activation program and upregulation of cellular locomotion molecules together with chemokine and adhesion receptors. The adhesion receptors include ninjurin 1, which participates in T-cell intravascular crawling on cerebral blood vessels. We detected that the lung constitutes a niche not only for activated T cells but also for resting myelin-reactive memory T cells. After local stimulation in the lung, these cells strongly proliferate and, after assuming migratory properties, enter the CNS and induce paralytic disease. The lung could therefore contribute to the activation of potentially autoaggressive T cells and their transition to a migratory mode as a prerequisite to entering their target tissues and inducing autoimmune disease.     

基于网络环境下学习资源的整合与应用

信息化时代的到来,不仅为人们开辟了新的视野,也为人们的生产生活、工作和学习带来了方便。然而,丰富的数字化资源在给人们带来方便的同时,也给人们选择带来了一些意料之外的麻烦。尤其是高校数字化教学资源,这就需要对高校数字化资源进行整合,并以此为依据采取有效的资源整合策略,有效地实现高校数字化资源共享,使数字化资源在教学应用中更好地发挥其作用。文中通过对数字化资源概况和数字化资源整合必要性的分析,提出了基于数字化资源整合的应用策略。     

到达率和飞机流结构对终端区排序的影响研究

为了找出终端区平均到达率和飞机流结构与优化排序结果之间的关系,通过选取平均到达率和飞机流结构的不同组合,再使用循环排序找出最优结果。在此基础上,分别研究和分析了平均到达率和飞机流结构对飞机流总体,重型飞机、大型飞机和小型飞机优化结果的影响程度。经过大量数据仿真和统计表明：当终端区有10架待降飞机时,与先到先服务原则相比,平均可以减小延误达30%左右;重型飞机和大型飞机的延误对平均到达率的变化较为敏感,而小型飞机则非常有限;从飞机流结构变化的角度看,随着大型飞机和小型飞机所占比例的逐渐减少,重型飞机和大型飞机延误可以得到明显的缩减,而小型飞机延误的缩减程度变化较小。研究结果可以为终端区飞机的着陆调度提供借鉴和参考,同时为进一步研究跑道容量与来流飞机的关系打下基础。     

利用小波变换提高地震波初至拾取的精确度

众所周知,折射静校正是中国西北地区地震资料处理中十分重要的环节,而准确地拾取初至又是折射静校正的基础.然而,这些地区的地震记录中,初至波却常常受到各种干扰的影响,使得其波形发生畸变,从而导致初至拾取不准确.文章首先分析了最常见的引起初至波难以准确拾取的情况,并提出了初至拾取预处理的方法.具体采用小波阈值去噪并结合连续小波变换的方法,恢复初至波的最大振幅波形,并突出初至波的起跳时刻,从而提高初至拾取的准确度.通过理论模型研究和实际资料试算表明,该方法具有很好的应用前景,它对于目前常用的拾取初至起跳时刻和拾取初至波最大峰值时刻的两类拾取方法,都具有非常重要的意义.     

机场选址对候鸟影响评价研究-以大连为例

在机场建设及运营过程中,不可避免地会对周围环境产生一定的影响,尤其是对候鸟迁徙、栖息等活动造成的生态损失更为明显。目前有关此类研究多为在机场运营时如何驱赶鸟类,较少考虑在机场建设选址初期如何规避对鸟类的影响。针对这一问题,根据候鸟的迁徙规律,通过对大连现有机场及迁建机场周边候鸟的调查,建立了评价指标体系,开展了机场建设选址的不同方案对候鸟迁徒影响的评价对比研究。结果显示,大连扩建机场选址对候鸟种群影响的评价分值为11.33,海上机场选址为8.87,相对减少了21%,说明海上机场方案对候鸟迁徙的影响小于扩建现有机场方案,因而从减少对鸟类影响角度出发应为首选。本文思路和评价方法可为机场选址论证提供借鉴。     

干线关键断面的到车率分布预测

干线协调控制需要了解交通量在干线上下游的传递和变化关系,传统的行程时间预测或到达分布预测无法提供足够的参考信息.根据干线的道路条件,界定干线上若干个关键断面;统计实际的车辆检测数据或仿真实验数据,按较小的时间间隔汇总和统计不同周期在对应间隔内的到达分布,绘制得到关键断面的到车率分布图.分析路段离散和信号控制对到车率分布的影响;以车速的累积概率分布图为基础计算转移矩阵,提出了考虑路段离散的到车率分布预测方法;分析红灯排队、绿灯放行的车流离散过程,提出了考虑信号控制的到车率预测方法.仿真案例分析表明,预测的到车率分布相对误差较小,验证了预测方法的有效性.     

首达时间依分布最优模型与风险最小模型

研究了离散时间首达时间依分布（随机序）最优模型与风险最小模型。给出存在最优策略的若干充要条件及重要性质，证明最优方程序列存在唯一解，给出寻优的算法。证明了ｍ时段风险最小Ｅ最优策略必定存在。     

出口箱随机入港下的箱区选择与箱位分配协调调度

针对出口箱随机入港下的分散堆放与随机选位对集装箱卡车行驶和场桥取箱作业的影响,提出了出口箱的箱区选择与箱位分配协调调度问题,并以箱区位置、箱量分配、箱位分配为决策变量,以集装箱卡车接运单位TEU平均作业时间最少、场桥作业成本最低为目标,构建了出口箱箱区选择与箱位分配两阶段非线性整数规划模型.设计了基于遗传算法的双层启发式算法,上层用于箱区搜索,确定出口箱堆放箱区及箱量分配;下层用于箱位搜寻,并依据场桥取箱顺序规则,确定具体堆放箱位或重选堆放箱区.通过算例分析结果表明:与集中入港下集中堆放相比,对出口箱随机入港下分散堆放的箱区选择与箱位分配进行协调调度同步优化,可以减少单位TEU平均装卸时间5.46%,并显著降低堆场作业成本,模型与算法可行有效.     

列车运行调整与到发线运用的协同优化研究

在列车运行的过程中,受到各种不确定性因素的影响,列车可能会偏离图定运行计划,同时也会对车站的到发线运用造成干扰。针对列车运行调整与到发线运用协同的优化问题,本文兼顾列车运行调整约束与到发线运用约束,建立了多目标的整数规划模型,并设计了适用于求解该模型的分层序列鸽群优化算法。算例分析表明,模型对列车运行计划进行调整的同时,还能得到满意的到发线运用方案,并且分层序列鸽群优化算法可以快速求解列车加权总到发晚点最少和到发线占用总消耗最小的目标函数。