Extent of thermal ablation suffered by model organic microparticles during aerogel capture at hypervelocities

Abstract— New model organic microparticles are used to assess the thermal ablation that occurs during aerogel capture at speeds from 1 to 6 km s^?1. Commercial polystyrene particles (20 μm diameter) were coated with an ultrathin 20 nm overlayer of an organic conducting polymer, polypyrrole. This overlayer comprises only 0.8% by mass of the projectile but has a very strong Raman signature, hence its survival or destruction is a sensitive measure of the extent of chemical degradation suffered. After aerogel capture, microparticles were located via optical microscopy and their composition was analyzed in situ using Raman microscopy. The ultrathin polypyrrole overlayer survived essentially intact for impacts at ～1 km s^?1, but significant surface carbonization was found at 2 km s^?1, and major particle mass loss at ≥3 km s^?1. Particles impacting at ～6.1 km s^?1 (the speed at which cometary dust was collected in the NASA Stardust mission) were reduced to approximately half their original diameter during aerogel capture (i.e., a mass loss of 84%). Thus significant thermal ablation occurs at speeds above a few km s^?1. This suggests that during the Stardust mission the thermal history of the terminal dust grains during capture in aerogel may be sufficient to cause significant processing or loss of organic materials. Further, while Raman D and G bands of carbon can be obtained from captured grains, they may well reflect the thermal processing during capture rather than the pre‐impact particle's thermal history.     

Organic matter from comet 81P/Wild 2, IDPs,and carbonaceous meteorites; similarities and differences

Abstract— During preliminary examination of 81P/Wild 2 particles collected by the NASA Stardust spacecraft, we analyzed seven, sulfur embedded and ultramicrotomed particles extracted from five different tracks. Sections were analyzed using a scanning transmission X‐ray microscope (SXTM) and carbon X‐ray absorption near edge structure (XANES) spectra were collected. We compared the carbon XANES spectra of these Wild 2 samples with a database of spectra on thirty‐four interplanetary dust particles (IDPs) and with several meteorites. Two of the particles analyzed are iron sulfides and there is evidence that an aliphatic compound associated with these particles can survive high temperatures. An iron sulfide from an IDP demonstrates the same phenomenon. Another, mostly carbon free containing particle radiation damaged, something we have not observed in any IDPs we have analyzed or any indigenous organic matter from the carbonaceous meteorites, Tagish Lake, Orgueil, Bells and Murchison. The carbonaceous material associated with this particle showed no mass loss during the initial analysis but chemically changed over a period of two months. The carbon XANES spectra of the other four particles varied more than spectra from IDPs and indigenous organic matter from meteorites. Comparison of the carbon XANES spectra from these particles with 1. the carbon XANES spectra from thirty‐four IDPs (<15 micron in size) and 2. the carbon XANES spectra from carbonaceous material from the Tagish Lake, Orgueil, Bells, and Murchison meteorites show that 81P/Wild 2 carbon XANES spectra are more similar to IDP carbon XANES spectra then to the carbon XANES spectra of meteorites.     

Early bronze in two Holocene archaeological sites in Gansu, NW China

Understanding of the origin and development of bronze technology in eastern Asia remains unresolved. Here we report on the distribution of copper and associated cations in sediments from Huoshiliang in northwestern Gansu, China, strontium and lead isotope analyses of ore and slag samples, and some artifact fragments at archaeological sites at Ganggangwa and Huoshiliang in the Black River valley.We conclude that bronze production began perhaps as early as 2135 BC and that the Baishantang modern mine site at Dingxin was a possible source of copper ore. There was at least one other, but currently unidentified, source of ore. The Bronze Age people were also farmers and planted cereals such as wheat, and they may have abandoned the region when wood was exhausted and desertification took over.     

胶州湾东北部海域生态环境污染状况研究

根据2004年5月和2005年5月两次对胶州湾东北部海域海水的盐度、pH、溶解氧、化学需氧量、无机氮、活性磷酸盐、铜、铅、锌、镉、多环芳烃和有机氯农药以及表层沉积物中有机碳、石油烃、硫化物、铜、铅、镉、汞、多环芳烃和有机氯农药测定结果,并结合2001年以来历史资料,对胶州湾东北部海域生态环境质量历史变化趋势进行了分析,该海域生态环境中除个别要素如活性磷酸盐、铅、镉、汞等重金属含量有所增加外,其他污染要素含量相对稳定且有下降趋势,2001—2005年该海域生态环境质量相对稳定,仅部分要素有加重趋势。     

Numerical simulation of the shear behavior of rockfills

A strain hardening model is proposed for simulation of the shear behavior of rockfills, including the non-linear stress–strain relationship, stress-dependence of stiffness, non-linear strength envelope, and particularly the shearing contraction and dilatancy. This model utilizes the Mohr–Coulomb yield criterion, which is defined by the mobilized friction angle varying with plastic octahedral shear strain. The development of Rowe’s stress dilatancy theory is reviewed, with its limitation for rockfills highlighted. A modified solution is then proposed to derive the mobilized dilatancy angle of rockfills. Compared with large-scale triaxial testing results, it has been demonstrated that this simple model is capable of predicting the shear behavior of rockfills with fair accuracy.     

基于海洋细菌为受试生物的海洋防污剂快速筛选方法

本文研究探索了一种快速简单易行的海洋防污剂室内评价筛选方法。将待测防污剂均匀分散于凝胶溶液中,然后均匀涂布到一定面积的玻璃板上,固化得到含防污剂凝胶测试板,将其置于接种有三种分离自舟山以东海域的优势海洋菌种(编号为Y-16,W-1和F-6)的人工加富海水中,连续培养24h后显微镜下可发现凝胶板表面上细菌菌落,将凝胶板表面细菌淋洗、定容,测定其光密度(optical density,OD)值,计算平均抑菌率,得到吡啶硫酮锌(ZPT)为38.87%,吡啶硫酮铜(CPT)为41.24%,三甲基氧化锡(TBTO)为65.19%,N,N-二甲基-3,4-二氯苄胺(DCDMA)为30.88%,敌草隆(Diuron)仅为15.29%,抑菌性大小为TBTOCPTZPTDCDMADiuron。实验结果表明5种受试防污剂的抑菌性大小为TBTOCPTZPTDCDMADiuron。采用绘制OD-t生长曲线法,分别得到5种防污剂对3种海洋细菌的最小抑制浓度(minimum inhibitory concentration,MIC),TBTO对三种菌的MIC均为0.5×10–3mg/mL;CPT对W-1和F-6的MIC为0.97×10–3mg/mL,对Y-16的MIC为1.93×10–3mg/mL;ZPT对W-1和Y-16的MIC为1.91×10–3mg/mL,对F-6的MIC为0.96×10–3mg/mL;DCDMA对W-1和F-6的MIC为8.46×10–3mg/mL,对Y-16的MIC为×10–342.29mg/mL。其中,Diuron对细菌的生长几乎没有抑制作用。其抑菌性与室内短期挂板结果具有一致性,表明经OD-t生长曲线得到的MIC可作为溶剂可溶型防污剂评价的辅助方法。另外,将本文中室内短期挂板方法应用于不同粒径的氧化亚铜的防污评价,也取得了与文献一致的结果。     

作物病虫害高光谱遥感进展与展望

作物病虫害作为影响农作物品质、产量及威胁粮食安全的主要因素,仅依靠人工田间调查对其进行监测已不能满足当下农业生产精准高效的需求。高光谱遥感作为能够获取地表物体连续波谱信息的遥感技术,已经成为当下作物病虫害监测识别的重要手段。本文对作物病虫害高光谱遥感监测识别的研究进展进行综述,通过对该领域发表文献的统计以及对主要机构、团队、数据源的分析,明确了病虫害高光谱遥感监测的研究热点和趋势;在此基础上,分析高光谱技术及其作物病虫害的监测识别机理,从病虫害胁迫探测、分类识别、危害严重度定量分析及早期检测四个方面综述相关技术及研究现状;通过探讨当下高光谱遥感病虫害监测识别面临的挑战,提出作物病虫害标准图谱库的建立、星载高光谱传感器的完善以及星空地一体化监测平台的搭建是当前作物病虫害高光谱遥感监测识别技 术落到实处的关键,也是未来发展的重点方向。     

Environmental dependence of stellar mass,SFR, and SSFR for the Luminous Red Galaxy (LRG) sample of the SDSS DR7

Using the Luminous Red Galaxy (LRG) sample of the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we investigate the environmental dependence of stellar mass, star formation rate (SFR) and specific star formation rate (SSFR) of LRGs. It is found that stellar mass of LRGs nearly is independent of local environments, and that the environmental dependence of SFR and SSFR in the LRG sample is much weaker than the one in the Main galaxy sample. One possible explanation is that galaxy color and morphology are a pair of galaxy properties most predictive of local environments, while LRGs are a group of galaxies that are likely to be luminous, red and of early types (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mg isotopic heterogeneity,Al‐Mg isochrons,and canonical 26Al/27Al in the early solar system

There is variability in the Mg isotopic composition that is a reflection of the widespread heterogeneity in the isotopic composition of the elements in the solar system at approximately 100 ppm. Measurements on a single calcium‐aluminum‐rich inclusion (CAI) gave a good correlation of ²⁶Mg/²⁴Mg with ²⁷Al/²⁴Mg, yielding an isochron corresponding to an initial (²⁶Al/²⁷Al)_o = (5.27 ± 0.18) × 10^?5 and an initial (²⁶Mg/²⁴Mg)_o = ?0.127 ± 0.032‰ relative to the standard. This isochron is parallel to that obtained by Jacobsen et al. (2008) , but is distinctively offset. This demonstrates that there are different initial Mg isotopic compositions in different samples with the same ²⁶Al/²⁷Al. No inference about uniformity/heterogeneity of ²⁶Al/²⁷Al on a macro scale can be based on the initial (²⁶Mg/²⁴Mg)_o values. Different values of ²⁶Al/²⁷Al for samples representing the same point in time would prove heterogeneity of ²⁶Al/²⁷Al. The important issue is whether the bulk solar inventory of ²⁶Al/²⁷Al was approximately 5 × 10^?5 at some point in the early solar system. We discuss ultra refractory phases of solar type oxygen isotope composition with ²⁶Al/²⁷Al from approximately 5 × 10^?5 to below 0.2 × 10^?5. We argue that the real issues are: intrinsic heterogeneity in the parent cloud; mechanism and timing for the later production of ¹⁶O‐poor material; and the relationship to earlier formed ¹⁶O‐rich material in the disk. ²⁶Al‐free refractories can be produced at a later time by late infall, if there is an adequate heat source, or from original heterogeneities in the placental molecular cloud from which the solar system formed.     

Experimental determination of photostability and fluorescence‐based detection of PAHs on the Martian surface

Abstract– Even in the absence of any biosphere on Mars, organic molecules, including polycyclic aromatic hydrocarbons (PAHs), are expected on its surface due to delivery by comets and meteorites of extraterrestrial organics synthesized by astrochemistry, or perhaps in situ synthesis in ancient prebiotic chemistry. Any organic compounds exposed to the unfiltered solar ultraviolet spectrum or oxidizing surface conditions would have been readily destroyed, but discoverable caches of Martian organics may remain shielded in the subsurface or within surface rocks. We have studied the stability of three representative polycyclic aromatic hydrocarbons (PAHs) in a Mars chamber, emulating the ultraviolet spectrum of unfiltered sunlight under temperature and pressure conditions of the Martian surface. Fluorescence spectroscopy is used as a sensitive indicator of remaining PAH concentration for laboratory quantification of molecular degradation rates once exposed on the Martian surface. Fluorescence‐based instrumentation has also been proposed as an effective surveying method for prebiotic organics on the Martian surface. We find the representative PAHs, anthracene, pyrene, and perylene, to have persistence half‐lives once exposed on the Martian surface of between 25 and 60 h of noontime summer UV irradiation, as measured by fluorescence at their peak excitation wavelength. This equates to between 4 and 9.6 sols when the diurnal cycle of UV light intensity on the Martian surface is taken into account, giving a substantial window of opportunity for detection of organic fluorescence before photodegradation. This study thus supports the use of fluorescence‐based instrumentation for surveying recently exposed material (such as from cores or drill tailings) for native Martian organic molecules in rover missions.