无线传感器网络中基于时钟漂移补偿的时间同步技术

在分析和总结现有时间同步算法的特点及其存在问题的基础上,提出了一种在无线传感器网络的时间同步协议（TPSN）中同时考虑节点时钟偏移和频率漂移率的改进算法。该算法利用连续两次同步过程中所记录的时间信息来估算节点时钟的偏移和频率漂移率,并进行补偿。同传统算法相比,此算法通讯成本较低、精度较高。最后通过数学分析和仿真的方法对所提出的改进算法进行了验证。     

水深对软刚臂单点系泊FPSO动力响应的影响

系泊系统的定位能力是浅水油田作业的软刚臂式单点系泊FPSO安全作业的重要保障,为研究不同水深/吃水比下单点系泊系统的受力性能,针对一艘16万吨级软刚臂单点系泊FPSO,在线性三维势流理论的基础上,基于多体动力学方法,建立FPSO-系泊腿-软刚臂的耦合模型,采用Newman近似法和Pinkster近似法分析了FPSO所受二阶波浪力,在时域内计算了不同水深/吃水比对系泊系统动力响应性能的影响。结果表明,随着水深/吃水比的增加,Newman近似法计算得到二阶波浪力先增大后减小,引起单点系泊系统载荷先增大后减小;而Pinkster近似法计算得到的二阶波浪力逐渐减下,引起单点载荷逐渐减下。在浅水条件下,Pinkster近似法具有较好的适用性,Newman近似法严重低估了FPSO所受的二阶波浪力;在深水条件下,Newman近似法能满足工程计算的要求;适用两种方法的临界水深/吃水比为1.64。     

某海底沉管隧道风塔及下部结构抗震性能分析

为研究某海底隧道风塔及下部结构体系在塑性阶段的损伤破坏形态及特点,探讨在多重荷载作用下弹塑性静动力响应对结构的影响,建立了沉管隧道风塔及下部结构的大型三维有限元模型。采用基于能量原理的混凝土塑性及损伤本构模型,借助大型有限元软件ANSYS及ABAQUS分别对结构进行不同地震条件下的动力时程分析,对比分析振型、层间位移角及较为完整的塑性损伤破坏系数曲线。结果表明:不同设防地震下,结构整体性良好,振型及层间位移角满足规范要求;不同罕遇地震下,该结构的混凝土塑性拉压损伤最大时刻均发生在20 s,主要破坏区域在风塔与人防井及下部立柱的接触位置,且拉伸破坏系数明显高于压缩破坏。本文的研究成果可以为类似近海沉管隧道工程抗震设计提供一定的依据与指导。     

Decameter Type III-Like Bursts

We report the first observations of Type III-like bursts at frequencies 10 – 30 MHz. More than 1000 such bursts during 2002 – 2004 have been analyzed. The frequency drift of these bursts is several times that of decameter Type III bursts. A typical duration of the Type III-like bursts is 1 – 2 s. These bursts are mainly observed when the source active region is located within a few days from the central meridian. The drift rate of the Type III-like bursts can take a large value by considering the velocity of Type III electrons and the group velocity of generated electromagnetic waves.     

Bimodality of anomalous pulsars?

At present, it is widely believed that anomalous X-ray pulsars (AXPs), soft gamma-ray repeaters (SGRs), rotational radio transients (RRATs), compact central objects (CCOs) in supernova remnants, and X-ray dim isolated neutron stars (XDINSs) belong to different classes of anomalous objects in which the central bodies are isolated neutron stars. Previously, we have shown that AXPs and SGRs can be described in terms of the drift model for parameters of the central neutron star typical of radio pulsars (rotation periods P ～ 0.1–1 s and surface magnetic fields B ～ 10¹¹–10¹³ G). Here, we show that some of the peculiarities of the sources under consideration can be explained by their geometry (in particular, by the angle β between the rotation axis and the magnetic moment). If β ? 10° (an aligned rotator), the drift waves in the outer layers of the neutron star magnetosphere can account for the observed periodicity in the radiation. For large β (a nearly orthogonal rotator), the observed modulation of the radiation and its short bursts can be explained by mass accretion from the ambient medium (e.g., a relic disk).     

Effect of NOAA satellite orbital drift on AVHRR-derived phenological metrics

The U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center routinely produces and distributes a remote sensing phenology (RSP) dataset derived from the Advanced Very High Resolution Radiometer (AVHRR) 1-km data compiled from a series of National Oceanic and Atmospheric Administration (NOAA) satellites (NOAA-11, −14, −16, −17, −18, and −19). Each NOAA satellite experienced orbital drift during its duty period, which influenced the AVHRR reflectance measurements. To understand the effect of the orbital drift on the AVHRR-derived RSP dataset, we analyzed the impact of solar zenith angle (SZA) on the RSP metrics in the conterminous United States (CONUS). The AVHRR weekly composites were used to calculate the growing-season median SZA at the pixel level for each year from 1989 to 2014. The results showed that the SZA increased towards the end of each NOAA satellite mission with the highest increasing rate occurring during NOAA-11 (1989–1994) and NOAA-14 (1995–2000) missions. The growing-season median SZA values (44°–60°) in 1992, 1993, 1994, 1999, and 2000 were substantially higher than those in other years (28°–40°). The high SZA in those years caused negative trends in the SZA time series, that were statistically significant (at α = 0.05 level) in 76.9% of the CONUS area. A pixel-based temporal correlation analysis showed that the phenological metrics and SZA were significantly correlated (at α = 0.05 level) in 4.1–20.4% of the CONUS area. After excluding the 5 years with high SZA (>40°) from the analysis, the temporal SZA trend was largely reduced, significantly affecting less than 2% of the study area. Additionally, significant correlation between the phenological metrics and SZA was observed in less than 7% of the study area. Our study concluded that the NOAA satellite orbital drift increased SZA, and in turn, influenced the phenological metrics. Elimination of the years with high median SZA reduced the influence of orbital drift on the RSP time series.     

1957-2014年库布齐沙漠地面风场特征

风对沙漠化过程具有重要影响,起沙风是塑造沙漠地貌格局的主要动力。根据1957-2014年库布齐沙漠周边4个基准气象站的地面风资料,从风速、风向和输沙势等方面分析库布齐沙漠的地面风场特征。结果显示：（1）库布齐沙漠的起沙风频率与平均风速有很高的相关性;（2）年平均风速为2.7 m·s^-1,全年盛行风向为WNW-NW,为中等变率锐双峰风况,合成输沙风向约为310°。4月风速最大,为中等变率环境;8月风速较小,为高变率环境;1月风速最小,为低变率环境。3-6月风速最大,风向集中度一般;11月至翌年2月风速较大,风向集中度高;7-10月风速最小,风向集中度差;（3）20世纪80年代中后期和2007年前后风速、起沙风频率和输沙势发生了较大变化,尤其是2007年前后由减小向增大发展;（4）大气环流和地表粗糙度的改变是库布齐沙漠地面风场变化的重要原因。     

策勒沙漠-绿洲输沙及动力环境特征

利用2012年4月9日—5月9日策勒沙漠和绿洲内部测点的输沙及气象资料,分析了沙漠与绿洲内部沙尘传输的差异性,并从风动力环境上揭示了成因。结果表明:(1)观测期间,通过沙漠测点100 cm(宽)×200 cm(高)断面的沙尘总量为117.5 kg,通过绿洲内部棉田相同断面的沙尘总量为15.1 kg,比沙漠测点减少了87.1%;(2)过渡带和防护林带对风速的消减作用明显,观测期间,沙漠测点起沙风的持续时间为97.4 h,棉田测点仅为18.9 h;(3)观测期间,沙漠测点的总输沙势为114.2 VU,合成输沙势为72.8 VU,合成输沙方向为65.5°;棉田测点的总输沙势为16.1 VU,合成输沙势为15.1 VU,合成输沙方向为104.5°。荒漠过渡带和绿洲防护林通过降低绿洲内部的风速,改变动力环境,削弱沙尘在绿洲区的传输。     

An analysis of horizontal dispersion due to the drift current with an Ekman layer

An analytical method for describing horizontal matter dispersion in shear currents is presented using a tensor expression from the point of view that matter dispersion due to the shear effect should be one of the principal mixing dilution processes. Although the behavior of horizontal dispersion is considerably more complicated than common longitudinal dispersion, the present study elucidates the vertical structure of dispersion and the dispersing process from the initial to the stationary stage, besides the usual depth-averaged dispersion coefficient at the stationary stage. As one of the typical applications of horizontal dispersion, dispersion due to the pure drift current with an Ekman layer is examined theoretically using the present method. This examination reveals that the displacement of the centroid and the major axis of dispersion are twisted in the vertical direction more than the direction of the current vector forming the Ekman spiral; that the variance increases in proportion to the third power of the elapsed time; and that the dispersion coefficient at the stationary stage remains constant, independent of the depth normalized by an Ekman layer thickness. Such dependence of the dispersion coefficient in the steady current is shown to be different from that in the oscillatory current, which is inversely proportional to the depth normalized by a Stokes layer thickness. This is considered to be induced by the difference of the vertical profiles of the first order moment in both currents, that is, the shear region of the first order moment is restricted around the floor by the alternation of the current shear in the oscillatory current while it is diffused in the whole depth in the steady current.     

长时效的正压原始方程能量完全守恒(拟)谱模式

遵循误差反演补偿新计算原理,对正压原始方程传统气象全球拟谱模式方案进行了改造,构造了正压原始方程能量完全守恒全球拟增模式新计算方案,解决了正压原始方程的（非线性）计算稳定性问题和能量守恒整体性质保持问题,改进了相应正压原始方程传统气象全球拟谱模式方案的计算效能。新方案的数值试验表明：在计算实践上,新方案在解决能量守恒问题的同时,可解决（非线性）计算稳定性问题,并在一定条件下可解决非线性计算收敛性问题。进一步的比较数值试验还表明：在计算实践上,新方案具有在提高相应传统气象方案的计算精度,减少其计算量的同时,延长其计算时效,解决其中一类特定“气候漂移”问题方面的效用。本工作原理也适用于斜压原始方程情形。