Study and suppression of anomalous fast events in inorganic scintillators for dark matter searches

The status of dark matter searches with inorganic scintillator detectors at Boulby mine is reviewed and the results of tests with a CsI(Tl) crystal are presented. The objectives of the latter experiment were to study anomalous fast events previously observed and to identify ways to remove this background. Clear indications were found that these events were due to surface contamination of crystals by alphas, probably from radon decay. A new array of unencapsulated NaI(Tl) crystals immersed either in liquid paraffin or pure nitrogen atmosphere is under construction at Boulby. Such an approach allows complete control of the surface of the crystals and the ability to remove any surface contamination. First data from the unencapsulated NaI(Tl) do not show the presence of anomalous fast events.     

脉冲型近断层地震动作用单自由度体系响应分析

近断层前方向性效应地震动含有高幅值,短持时的速度脉冲,与远场地震动相比存在显著差异。本文根据所选取的40条近断层地震波记录,用小波分析方法将原始记录分解为脉冲波部分和高频波部分,对弹性和非弹性单自由度体系进行分析,得出了以下结论:对于弹性体系,大约0.484倍的速度脉冲周期可以作为临界周期,脉冲波部分将对固有周期大于临界周期的结构的响应起主导作用,反之,高频波部分将会产生显著影响;对于非弹性体系,仅仅用等效速度脉冲方法模拟近断层地震动的计算精度将会受到延性系数?的影响,随着延性系数的增加,脉冲波部分满足精度要求的结构固有周期范围将明显缩小,并且向较低周期范围偏移;仅用等效速度脉冲模型来模拟近断层地震动具有一定的局限性。     

Shelf currents,lee-trapped and transient eddies on the inshore boundary of the Agulhas Current,South Africa: their relevance to the KwaZulu-Natal sardine run

The existence and strength of the annual KwaZulu-Natal (KZN) sardine run has long been a conundrum to fishers and scientists alike ― particularly that the sardine Sardinops sagax migrate along the narrow Transkei shelf against the powerful, warm Agulhas Current. However, examination of ship-borne acoustic Doppler current profiler (S–ADCP) data collected during two research surveys in 2005 indicated that northward-flowing coastal countercurrents exist at times between the Agulhas Bank and the KZN Bight, near Port Alfred, East London, Port St Johns and Durban. The countercurrent near Port Alfred extended as far east as the Keiskamma River, within an upwelling zone known to exist there. An ADCP mooring at a depth of 32 m off Port Alfred indicated that the countercurrent typically lasted a few days, but at times remained in the same direction for as long as 10 days. Velocities ranged between 20 and 60 cm s^?1 with maximum values of ～80 cm s^?1. The S–ADCP data also highlighted the existence of cyclonic flow in the Port St Johns–Waterfall Bluff coastal inset, with a northward coastal current similarly ranging in velocity between 20 and 60 cm s^?1. CTD data indicated that this was associated with shelf-edge upwelling, with surface temperatures 2–4 °C cooler than the adjacent core temperature (24–26 °C) of the Agulhas Current. Vertical profiles of the S–ADCP data showed that the countercurrent, about 7 km wide, extends down the slope to at least 600 m, where it appeared to link with the deep Agulhas Undercurrent at 800 m. S–ADCP and sea surface temperature (SST) satellite data confirmed the existence of the semi-permanent, lee-trapped, cyclonic eddy off Durban, associated with a well-defined northward coastal current between Park Rynie and Balito Bay. Analysis of three months (May–July 2005) of satellite SST and ocean colour data showed the shoreward core-boundary of the Agulhas Current (24 °C isotherm) to commonly be close to the coast along the KZN south coast, as well as between the Kei and Mbhashe rivers on the Transkei shelf. The Port St Johns–Waterfall Bluff cyclonic eddy was also frequently visible in these satellite data. Transient cyclonic eddies, which spanned 150–200 km of shelf, appeared to move downstream in the shoreward boundary of the Agulhas Current at a frequency of about once a month. These seemed to be break-away Durban eddies. Data collected by ADCP moorings deployed off Port Edward in 2005 showed that these break-away eddies and the well-known Natal Pulse are associated with temporary northward countercurrents on the shelf, which can last up to six days. It is proposed that these countercurrents off Port Alfred, East London and Port St Johns assist sardine to swim northwards along the Transkei shelf against the Agulhas Current, but that their progress north of Waterfall Bluff is dependent on the arrival of a transient, southward-moving, break-away Durban cyclonic eddy, which apparently sheds every 4–6 weeks, or on the generation of a Natal Pulse. This passage control mechanism has been coined the ‘Waterfall Bluff gateway’ hypothesis. The sardine run survey in June–July 2005 was undertaken in the absence of a cyclonic eddy on the KZN south coast, i.e. when the ‘gate’ was closed.     

基于CompactRIO的多通道强震动数据采集器FPGA的实现

提出以Compact RIO作为硬件平台,用Lab VIEW FPGA技术实现48通道强震动数据采集器底层数据采集功能。详细阐述了设计要点及从技术上实现了时钟同步、数据采集、标定信号输出、量程设置、状态显示、外触发信号接入等功能。结果表明,数据采集器的噪声、动态范围、幅频响应等主要技术指标满足国内地震行业标准DB/T 10-2001的要求,数据采集器的线性度误差满足DB/T 22-2007的要求。实现的阶段成果能为人们利用NI产品进行强震动数据采集器开发提供重要参考。     

微脉冲激光雷达反演半干旱区气溶胶消光系数方法

利用位于甘肃省榆中县兰州大学半干旱区气候与环境观测站的微脉冲激光雷达2008年春季的有效观测数据,对微脉冲激光雷达在半干旱区应用时不同反演方法的差别、参数的选取以及反演结果的差异及可能出现的原因进行了讨论。认为Klett法和Fernald法均能反映出大气气溶胶垂直分布的空间和时间特征,且结果较为一致。在晴朗无云及沙尘天气时,两种方法对于低层大气气溶胶消光系数反演结果基本相同,在接近实际探测高度时结果差异较大。有云天气下,Fernald法对于低层气溶胶的消光系数的反演结果同Klett法相比较小,在接近实际探测高度时差异较大。实际应用中,在半干旱地区利用微脉冲激光雷达对气溶胶消光系数进行反演时,对于高层气溶胶的信息获取,采用Klett法更为合理。     

CINRAD/SC雷达观测参数合理配置问题研究

中国产CINRAD/SC新一代天气雷达的脉冲重复频率、脉冲采样数和天线扫描转速这3个观测参数均可由雷达使用者自行配置。雷达观测实践表明,这3个观测参数配置得正确、合理与否,将直接影响到雷达获取的基数据资料质量的优劣,进而可影响到雷达导出产品的质量。通过理论分析,得到了天气雷达脉冲重复频率、脉冲采样数和天线转速这3个可配置观测参数科学合理的配置规律。以此作为CINRAD/SC天气雷达相关参数的配置依据,获取的基数据质量可以得到提高。     

浅海声信道中脉位信息检测的抗多途研究

简述了浅海声信道中多途干扰的主要特征及其对脉位信息检测的影响,探讨克服多途干扰的几种可能途径,并提出了一种有效的抗多途方法,以实现浅海声信道中脉位信息的可靠、精确检测。     

Products and Kinetics of the OH‐radical‐induced Dealkylation of Atrazine

Hydroxyl radicals, generated radiolytically in N₂O/O₂‐saturated solutions, yield in their reaction with atrazine equal amounts of deethylatrazine and acetaldehyde (40% of OH radical yield) and deisopropylatrazine and acetone (16%), respectively. The precursors of deethylatrazine and acetaldehyde is their Schiff base which hydrolyzes slowly (OH^–‐catalyzed: k = 5.2 dm³ mol^–1 s^–1). The hydrolysis of the Schiff base of deisopropylatrazine and acetone is too fast to be detected. In a pulse radiolysis experiment, the intermediate formed upon OH‐radical attack (k = 3·10⁹ dm³ mol^–1 s^–1) has a strong absorption at 440 nm. It decays in the presence of oxygen (k = 1.3·10⁹ dm³ mol^–1 s^–1), and upon deprotonation [pK_a(peroxyl radicals) ≈ 10.5] the peroxyl radicals thus‐formed eliminate superoxide radicals (k = 2.9·10⁵ s^–1). s‐Triazine itself reacts much more slowly with OH radicals (k = 9.7·10⁷ dm³ mol^–1 s^–1). This can explain, why in the case of atrazine in comparison to other aromatic compounds, e.g. toluene, the addition of the OH radical to the ring (estimated at ca. 40%) is of relatively little importance as compared to an H‐abstraction from (activated) positions of the side groups.     

介绍一种多功能时号灯电源

利用家用石英钟步进电机的驱动信号、整点报时触点或数字钟时分秒号脉冲控制时号灯的开启,具有可靠性高和有效工作年限长的特点。本文介绍了电路的工作原理。     

CCD十三位巴格码脉冲压缩器

CCD肪冲压缩器与数字式脉冲压缩器相比,具有体积小,功耗低,可靠性高,并可省去昂贵的高速、高精密的A/D、D/A变换器等优点。但一般使用在数微秒子码宽的量极上。现代雷达距离分辨要求窄脉冲、高时钟驱动下工作的CCD脉冲压缩器。本文简单扼要地介绍了用CCD分裂电极横向滤波器或CCD抽头延迟线作的13位巴格码脉冲压缩器,其码宽从0.4μS到1.6μS可变或0.7μS到2μS可变。当工作频率提高时,输出的主副瓣比逐渐下降,达不到理论值(22.3dB)。作者从理论上对影响主副瓣比下降的主要因素作了探讨,给出了试验结果,对进一步改进CCD脉冲压缩器性能提出自己的看法。