The Nyquist frequency for time series with slight deviations from regular spacing

The paper is based on the notion that the Nyquist frequency  ν_N  is a symmetry point of the periodogram of a time series: the power spectrum at frequencies above  ν_N  is a mirror image of that below  ν_N  . Koen showed that the sum     (where   t_k   and   t _ℓ  range over the time points of observation) is zero when the frequency  ν=ν_N  . This property is used to investigate the Nyquist frequency for data which are almost regularly spaced in time. For some configurations, there are deep minima of SS at frequencies  ν_P≪ν_N  ; such  ν_P  are dubbed 'pseudo-Nyquist' frequencies: the implication is that most of the information about the frequency content of the data is available in the spectrum over  (0, ν_P)  . Systematic simulation results are presented for two configurations – small random variations in respectively the time points of observation and the lengths of the intervals between successive observations. A few real examples of CCD time series photometry obtained over several hours are also discussed.     

Relict sand wedges in soliflucted London Clay at Wimbledon, London, UK

Exposures on Wimbledon Hill, SW London, in the Palaeogene London Clay Formation, are described. The 3° slopes are mantled by clayey solifluction (head) deposits, comprising two superimposed sheets, each around 1.2 m thick. The lower sheet exhibits relict sand wedges forming polygons 1.0-1.5 m across, up to 50 mm wide and 1.25 m deep. These have no surface expression. The wedges are sand-filled and modify significantly the hydrogeology and properties of the solifluction mantle. There are no sand wedges in the upper solifluction sheet.The mechanics of emplacement of the lower solifluction sheet are explored and the high initial water content estimated. Subsequent desiccation and consolidation have reduced the thickness of this sheet by at least 35%, thus distorting contained features such as the wedges. An active layer about 0.4 m thick is inferred to have formed in the top of the lower solifluction sheet. No direct dating was undertaken but, by analogy with relevant dated sites in southern Britain and the Netherlands it is inferred that the lower solifluction sheet was emplaced during the first part of the Loch Lomond Stadial and frost-cracked during a subsequent, colder and more arid part. On this basis, following filling of the cracks by sand, emplacement of the upper solifluction sheet would have occurred in the later part of the Loch Lomond Stadial.     

云南武定荒箐铁铜多金属矿矿床成因

矿床产于断层破碎带中,受断层和地层层位控制,与迤纳厂矿床具有一定的相似性。铁矿为中低温热液裂隙充填型脉状矿床,而铜矿床应为沉积——变质型。     

昆明海口头石山尾矿库工程地质问题及处理

头石山尾矿库存在坝址地基土稳定性差和库址渗漏等地质问题,认真研究处理,以确保尾矿库设计合理和坝体安全及投入使用后运行正常。     

DR-150型全液压履带取样钻机的研究

为解决区域地质、环境地质及农业地质填图工作,特别是在钻探验证工程中孔位浅,分布散等问题,设计一款新型的适合于工地常搬迁、快速迁移的集成化、模块化轻便取样钻机,其需具有能更好的解决工程施工中存在的问题、提高钻探施工质量和效率、实现钻探设备的整体搬迁和多种钻探工艺组合配套施工工艺等优点。     

运用H、O同位素资料分析地下热水的补给来源——以鲁西北阳谷-齐河凸起为例

通过对阳谷-齐河凸起地下热水的化学成分、同位素及其地热地质条件的分析,对这一地区的地下热水的补给来源进行了研究。本区地下热水的δD为-65‰～-80.67‰,δ18O为-9.2‰～-10.2‰,均分布在全球雨水线的附近,说明该区地下热水主要为大气降水成因。济南北地热田地下热水的补给高程为256m,此范围大致相当于济南南部山区及其以南的泰山北麓;聊城东地热田地下热水的补给高程为411m,此范围大致相当于泰山山脉及其周边的中山区。聊城东地热田地下热水的2H过量参数d明显低于济南北地热田,说明聊城东地热田地下热水的补给区比后者更远。     

新显色剂四-(3-磺基-4-氯苯基)卟啉分光光度法测定微量铜

研究了新显色剂四-(3-磺基-4-氯苯基)卟啉在微酸性介质中,表面活性剂OP与CPC存在下测定微量铜的显色反应。络合物在波长420 nm处有最大吸收峰,摩尔吸光度系数为3.44×105L·mol-1cm-1,用双峰双波长光度法测定摩尔吸光系数为6.72×105L·mol-1·cm-1,铜含量在0.5~4.5μg/25 m L范围内符合比耳定律。方法应用于矿样中微量铜的测定,结果令人满意。     

芜湖高铁建设对居民出游行为影响调查及对策研究

从居民旅游交通决策行为、居民出游空间、居民出游行为预期影响3个角度分析芜湖市高铁建设对城市居民出游的影响.结果表明：（1）旅游交通是影响居民旅游决策的重要因素.（2）居民出游市场以近程为主,空间分布主要集中在100-400 km范围内,且东向出游特征明显,目的地以长三角地区为主.（3）高速铁路开通将增加芜湖居民出游交通工具的选择,改变原有的旅游市场空间,中远程出游比例增加,同时也会影响居民出游次数与天数以及景区的选择.最后,依据国内外学者对高铁旅游研究成果,结合本次问卷调查实际情况,初步探讨高速化背景下,芜湖市旅游的发展对策.