Pulsar radio emission

Radio emission by pulsars is calculated from first principles. In an almost current-free magnetosphere, the two charged components (of the unsteadily escaping pair plasma) have different (and varying) bulk Lorentz factors. Curvature radiation emitted by the more energetic component is thus locally coherent, (so-called antenna mechanism). Strong enough seed signals cause the relativistically streaming charges to enhance their radiation, via an induced drift that can largely exceed the curvature drift. This amplification mechanism is similar to - but different from - that of a maser; we call it a MAIDER. Maximal amplification occurs at an (emission) altitude where the two components have sufficiently separated in energy though not yet separated too strongly in space.     

On measuring low-degree p-mode frequency splitting with full-disc integrated data

The standard method of measuring rotational splitting from solar full-disc oscillation data, based on maximum-likelihood fitting of multi-Lorentzian profiles to oscillation power spectra, systematically overestimates the splitting. One of the reasons is that the maximum likelihood estimators (MLE) become unbiased only asymptotically as the number of data tends to infinity; for a finite data set they are often biased, inducing a systematic error. In this paper we assess by Monte Carlo simulations the amount of systematic error in the splitting measurement, using artificially generated power spectra. The simulations are carried out for multiplets of degree     2 and 3 with various signal-to-noise ratios, linewidths and observing times. We address the possible use of non-MLE estimators that could provide a smaller or negligible systematic error. The implication for asteroseismology is also discussed.     

Laboratory studies on the sputtering contribution to the sodium atmospheres of Mercury and the Moon

To ascertain the importance of sputtering by solar wind ions on the formation of a sodium exosphere around Mercury and the Moon, we have irradiated with 4 keV He ions, the Na bearing tectosilicates: albite, labradorite, and anorthoclase, as well as adsorbed Na layers deposited on albite and on olivine (a neosilicate that does not contain Na). Sodium at the surface and near surface (<40 Å) was quantified with X-ray photoelectron spectroscopy before and after each irradiation to determine the depletion cross section. We measured a cross section for sputtering of Na adsorbed on mineral surfaces, σ_s ≈ 1 × 10^?15 cm² atom^?1. In addition, mass spectrometric analyses of the sputtered flux show that a large fraction of the Na is sputtered as ions rather than as neutral atoms. These results have strong implications for modeling the sodium population within the mercurian and the lunar exospheres.     

Nitrogen utilisation by size‐fractionated phytoplankton assemblages associated with an upwelling event off Westland,New Zealand

Abstract

Uptake rates of ammonium (NH₄ ⁺ ), nitrate (NO₃ ^? ), and urea by three subgroups of phytoplankton (< 200, < 20, < 2 μm) off Westland, were measured using ¹⁵ N tracer techniques in midwinter 1988, after a recent upwelling. For all size fractions at surface irradiance (I₁₀₀), nitrogen (N) was taken up primarily as NO₃ ^?. This accounted for 67–85% of total N uptake (SρN), whereas at 40 and 7% of surface irradiance, the regenerated N (NH₄ ⁺ ) and urea) made up 31–72% of SρN. Depth profile experiments for all three size components showed that uptake of NO₃ ^? was most light‐sensitive, followed by that of NH₄ ⁺ and urea. The irradiance and nutrient availability plot indicated that light was substantially more important than the nutrient concentrations in controlling the assimilation of N by microplankton (20–200 μm). Nano‐ (2–20 μm) and picoplankton (< 2 μm) however, were not as sensitive to either light or nutrient concentrations. High winds and the resulting deep mixing, combined with offshore and alongshore advection in the midwinter, were suggested to be the major cause of the low biomass and N productivity.     

半球形多向波聚合波道振荡水柱气室优化设计

为了解决振动水柱式波浪能转换装置收集多向波浪问题,本文设计了半球形多向聚合波道振荡水柱气室结构,以适合远海单点波浪能采集和发电。在规则波正向入射条件下,基于流体仿真分析软件(FLUENT)、流体动力学连续性假设和粘性不可压缩流体动量守恒的运动方程(Navier-Stokes方程)建立半球形振荡气室和三维数值波浪水槽模型。仿真结果表明:增设气室后壁,合理设计波道开口角度实现多向迎波捕获波浪能,优化前壁形状可降低波浪触底反射带来的能量耗散,同时提高了气室内空气压强和出气口速度,有效提升波浪能俘获效率,为后续发电的二次能量转换提供高效的空气动力。     

Characteristics of sea ice kinematics from the marginal ice zone to the packed ice zone observed by buoys deployed during the 9th Chinese Arctic Expedition

Sea ice growth and consolidation play a significant role in heat and momentum exchange between the atmosphere and the ocean. However, few in situ observations of sea ice kinematics have been reported owing to difficulties of deployment of buoys in the marginal ice zone (MIZ). To investigate the characteristics of sea ice kinematics from MIZ to packed ice zone (PIZ), eight drifting buoys designed by Taiyuan University of Technology were deployed in the open water at the ice edge of the Canadian Basin. Sea ice near the buoy constantly increased as the buoy drifted, and the kinematics of the buoy changed as the buoy was frozen into the ice. This process can be determined using sea ice concentration, sea skin temperature, and drift speed of buoy together. Sea ice concentration data showed that buoys entered the PIZ in mid-October as the ice grew and consolidated around the buoys, with high amplitude, high frequency buoy motions almost ceasing. Our results confirmed that good correlation coefficient in monthly scale between buoy drift and the wind only happened in the ice zone. The correlation coefficient between buoys and wind was below 0.3 while the buoys were in open water. As buoys entered the ice zone, the buoy speed was normally distributed at wind speeds above 6 m/s. The buoy drifted mainly to the right of the wind within 45° at wind speeds above 8 m/s. During further consolidation of the ice in MIZ, the direct forcing on the ice through winds will be lessened. The correlation coefficient value increased to 0.9 in November, and gradually decreased to 0.7 in April.     

30ka以来南海东北部陆坡坡底沉积有机质的长链正构烷烃特征及其古植被意义

为探寻南海深海平原区的有机质组成特征、来源及其所反映的古气候/环境演化信息, 对南海东北部深水区的ZSQD289沉积柱状样品进行了正构烷烃组成及其单体稳定碳同位素的相关分析, 结合孢粉鉴定结果, 重点探讨该沉积区末次冰期以来陆源输入变化、源区的古植被演化及其气候响应因素。结果表明:30ka以来, 南海东北部深海陆坡坡底的沉积有机质以洋/陆混源为特征, 且以海洋自生生产力贡献为主, 其生源贡献存在明显的冰期/间冰期旋回变化特征, 冰期时陆源有机质输入明显高于全新世间冰期; 其陆源有机质应该主要由台湾南部河流输入, 在低海平面时通过海底峡谷搬运至此, 其过程中可能受到西太平洋底流和黑潮的影响。该沉积源区植被演化经历了C3/C4植物互为消长的变化过程, 但30ka以来主要还是以C3植物占优势, 由此推测末次冰期以来源区(台湾岛南部)不存在明显的干旱化, 冰期虽然温度较低但气候比较湿润。     

无锡马山抽水蓄能电站地面厂房边坡稳定性分析

以无锡马山抽水蓄能电站地面厂房建筑过程中形成的人工边坡为例,在对其工程地质剖面分析并找出可能的滑动模式后,利用极限平衡法和有限元法分析了4个典型地质剖面的稳定性安全系数以及应力应变关系。结果表明,通过对该边坡的极限平衡法得到了2-2剖面的安全系数和通过有限元法得到的计算结果比较接近,且都满足相关规范的要求;坡体的最大位移发生在高程为－20 m和－5.0 m附近,其值为－22 mm;最大主应力位于高程－45.0 m处,值为0.134 MPa;最小主应力位于坡内深处,其值为－6.22 MPa。同时,提出了下一阶段应考虑时间效应,对边坡的变形进行分析。     

城镇化与区域工程地质学发展机遇

城镇化是我国现代化进程中的最伟大工程,2001年诺贝尔经济学奖获得者J.Stiglitse把中国的城镇化与美国的高科技并列为影响21世纪人类发展进程的两大关键因素。协调好城市化进程中强大的人类工程活动同复杂的地质环境变化间的关系是我国工程地质工作者的责任与义务,也是工程地质学发展的机遇。充分学习、借鉴地球科学相关学科领域的新观念、新成果、新资料,开展区域工程地质研究,探寻我国区域工程地质环境的形成演化和工程建设与地质环境间的相互作用规律,实现城镇化与地质环境的和谐。     

猪毛菜在不同降水条件下的水分来源差异研究

通过测定大柴旦与都兰地区猪毛菜木质部水分及其不同潜在水源的稳定性氢氧同位素值,利用多源线性混合模型分析不同水分来源对猪毛菜的贡献率.研究结果表明:大柴旦地区大气降水线为y=7.565x+4.796(R²=0.908),都兰地区大气降水线为y=6.005x-7.856(R²=0.7391),说明两个地区都存在较强的蒸发作用.但是,都兰地区较大柴旦风速大,温度高,雨水蒸发速度快,造成雨水δ¹⁸O偏高,形成比大柴旦地区斜率更小的当地大气降水线.大柴旦和都兰地区的猪毛菜,在两个样地的用水策略上存在显著差异.在降水较少的大柴旦地区,猪毛菜以土壤水为主要水源.在降水较多的都兰地区,则以降水为主要水源.就其对土壤水的使用情况来看,大柴旦的猪毛菜多利用深层土壤水,而都兰地区的猪毛菜却对表层土壤水利用比例较大.两地猪毛菜在生长季的不同时期都存在对利用水源的转换现象.为适应不同地区降水量的变化,猪毛菜根据不同水源调节利用比例.降水格局的改变将导致猪毛菜的水分利用策略发生适应性的变化.