基于CCD的高精度水管倾斜仪研制

CCD技术近年来已发展的非常成熟,应用范围广泛.本文介绍了利用CCD技术实现的高精度水管倾斜仪测量系统,其采用非接触式测量方法降低了测量过程中浮子干扰对测量精度的影响,体积小,安装简单,可用于流动观测中.     

循环往复加载的地下结构Pushover分析方法及其在地震损伤分析中的应用

考虑到地震作用下地下结构往往受到双向往复荷载作用,本文提出了循环往复加载的地下结构Pushover分析方法.介绍了该方法的实施步骤、基本功能与特点.该方法考虑了地震作用下地下结构双向受力的特点,利用多点位移控制的推覆分析算法进行地震作用下正向加载-卸载-反向再加载的全过程分析.该方法将一次循环加载过程近似看作一次地震作用过程,提出了基于循环往复加载Pushover分析的损伤模型,避免了对土-结构整体模型进行复杂的动力相互作用分析;通过一次循环往复加载的Pushover分析,根据结构构件刚度的改变对结构损伤进行有效评估.结合实际工程进行算例分析初步验证了循环往复加载Pushover分析及地震损伤模型的有效性.     

Titanium- and water-rich metamorphic olivine in high-pressure serpentinites from the Voltri Massif (Ligurian Alps,Italy): evidence for deep subduction of high-field strength and fluid-mobile elements

Titanium- and water-rich metamorphic olivine (Fo 86–88) is reported from partially dehydrated serpentinites from the Voltri complex, Ligurian Alps. The rocks are composed of mostly antigorite and olivine in addition to magnetite, chlorite, clinopyroxene and Ti-clinohumite. In situ secondary ion mass spectrometry (SIMS) data show that metamorphic olivine has very high and strongly correlated H₂O (up to 0.7 wt%) and TiO₂ contents (up to 0.85 wt%). Ti-rich olivine shows colourless to yellow pleochroism. Olivine associated with Ti-clinohumite contains low Ti, suggesting that Ti-rich olivine is not the breakdown product of Ti-clinohumite. Fourier transform infrared spectroscopy (FTIR) absorption spectra show peaks of serpentine, Ti-clinohumite and OH-related Si vacancies. Combining FTIR and SIMS data, we suggest the presence of clustered planar defects or nanoscale exsolutions of Ti-clinohumite in olivine. These defects or exsolutions contain more H₂O (x ~ 0.1 in the formula 4Mg₂SiO₄·(1?x)Mg(OH,F)₂·xTiO₂) than Ti-clinohumite in the sample matrix (x = 0.34–0.46). In addition to TiO₂ and H₂O, secondary olivine contains significant Li (2–60 ppm), B (10–20 ppm), F (10–130 ppm) and Zr (0.9–2.1 ppm). It is enriched in ¹¹B (δ¹¹B = +17 to +23 ‰). Our data indicate that secondary olivine may play a significant role in transporting water, high-field strength and fluid-mobile elements into the deeper mantle as well as introduce significant B isotope anomalies. Release of hydrogen from H₂O-rich olivine subducted into the deep mantle may result in strongly reduced mantle domains.     

Oxygen isotopes composition of sapphires from the French Massif Central: implications for the origin of gem corundum in basaltic fields

Alluvial and colluvial gem sapphires are common in the basaltic fields of the French Massif Central (FMC) but sapphire-bearing xenoliths are very rare, found only in the Menet trachytic cone in Cantal. The O-isotope composition of the sapphires ranges between 4.4 and 13.9‰. Two distinct groups have been defined: the first with a restricted isotopic range between 4.4 and 6.8‰ (n = 22; mean δ¹⁸O = 5.6 ± 0.7‰), falls within the worldwide range defined for blue-green-yellow sapphires related to basaltic gem fields (3.0 < δ¹⁸O < 8.2‰, n = 150), and overlaps the ranges defined for magmatic sapphires in syenite (4.4 < δ¹⁸O < 8.3‰, n = 29). A second group, with an isotopic range between 7.6 and 13.9‰ (n = 9), suggests a metamorphic sapphire source such as biotite schist in gneisses or skarns. The δ¹⁸O values of 4.4–4.5‰ for the blue sapphire-bearing anorthoclasite xenolith from Menet is lower than the δ¹⁸O values obtained for anorthoclase (7.7–7.9‰), but suggest that these sapphires were derived from an igneous reservoir in the subcontinental spinel lherzolitic mantle of the FMC. The presence of inclusions of columbite-group minerals, pyrochlore, Nb-bearing rutile, and thorite in these sapphires provides an additional argument for a magmatic origin. In the FMC lithospheric mantle, felsic melts crystallized to form anorthoclasites, the most evolved peraluminous variant of the alkaline basaltic melt. The O-isotopic compositions of the first group suggests that these sapphires crystallized from felsic magmas under upper mantle conditions. The second group of isotopic values, typified for example by the Le Bras sapphire with a δ¹⁸O of 13.9‰, indicates that metamorphic sapphires from granulites were transported to the surface by basaltic magma.     

Study of the Cosmic-Ray Modulation During the Passage of ICMEs and CIRs

We compare the cosmic-ray response to interplanetary coronal mass ejections (ICMEs) and corotating interaction regions (CIRs) during their passage in near-Earth space. We study the relative importance of various structures/features identified during the passage of the ICMEs and CIRs observed during Cycle 23 (1995?–?2009). The identified ICME structures are the shock front, the sheath, and the CME ejecta. We isolate the shock arrival time, the passage of the sheath region, the arrival of ejecta, and the end time of their passage. Similarly, we isolate the CIR arrival, the associated forward shock, the stream interface, and the reverse shock during the passage of a CIR. For the cosmic-ray intensity, we utilize the data from high counting rate neutron monitors. In addition to neutron monitor data, we utilize near-simultaneous and same time-resolution data of interplanetary plasma and field, namely the solar-wind velocity, the interplanetary magnetic field (IMF) vector, and its variance. Further, we also utilize some derived interplanetary parameters. We apply the method of the superposed-epoch analysis. As the plasma and field properties are different during the passage of different structures, both in ICMEs and CIRs, we systematically vary the epoch time in our superposed-epoch analysis one by one. In this way, we study the role and effects of each of the identified individual structures/features during the passage of the ICMEs and CIRs. Relating the properties of various structures and the corresponding variations in plasma and field parameters with changes of the cosmic-ray intensity, we identify the relative importance of the plasma/field parameters in influencing the amplitude and time profiles of the cosmic-ray intensity variations during the passage of the ICMEs and CIRs.     

Fish assemblage stability over fifty years in the Lake Pontchartrain estuary; Comparisons among habitats using canonical correspondence analysis

We assessed fish assemblage stability over the last half century in Lake Pontchartrain, an environmentally degraded oligohaline estuary in southeastern Louisiana. Because assemblage instability over time has been consistently associated with severe habitat degradation, we attempted to determine whether fish assemblages in demersal, nearshore, and pelagic habitats exhibited change that was unrelated to natural fluctuations in environmental variables (e.g., assemblage changes between wet and dry periods). Collection data from three gear types (trawl, beach seine, and gill nets) and monthly environmental data (salinity, temperature, and Secchi depth) were compared for four collecting periods: 1954 (dry period), 1978 (wet period), 1996–1998 (wet period), and 1998–2000 (dry period). Canonical correspondence analysis (CCA) revealed that although the three environmental variables were significantly associated with the distribution and abundance patterns of fish assemblages in all habitats (with the exception of Secchi depth for pelagic samples), most fish assemblage change occurred among sampling periods (i.e., along a temporal gradient unrelated to changing environmental variables). Assemblage instability was the most pronounced for fishes collected by trawls from demersal habitats. A marked lack of cyclicity in the trawl data CCA diagram indicated a shift away from a baseline demersal assemblage of 50 yr ago. Centroid positions for the five most collected species indicated that three benthic fishes, Atlantic croaker (Micropogonias undulatus), spot (Leiostomus xanthurus), and hardhead catfish (Arius felis), were more dominant in past demersal assemblages (1954 and 1978). A different situation was shown for planktivorous species collected by trawls with bay anchovy (Anchoa mitchilli) becoming more dominant in recent assemblage and Gulf menhaden (Brevoortia patromus) remaining equally represented in assemblages over time. Changes in fish assemblages from nearshore (beach seine) and pelagic (gill net) habitats were more closely related to environmental fluctuations, though the CCA for beach seine data also indicated a decrease in the dominance ofM. undulatus and an increase in the proportion ofA. mitchilli over time. The reduced assemblage role of benthic fishes and the marked assemblage change indicated by trawl data suggest that over the last half century demersal habitats in Lake Pontchartrain have been impacted more by multiple anthropogenic stressors than nearshore or pelagic habitats.     

Performance of CMORPH,TMPA, and PERSIANN rainfall datasets over plain,mountainous, and glacial regions of Pakistan

The present study aims at the assessment of six satellite rainfall estimates (SREs) in Pakistan. For each assessed products, both real-time (RT) and post adjusted (Adj) versions are considered to highlight their potential benefits in the rainfall estimation at annual, monthly, and daily temporal scales. Three geomorphological climatic zones, i.e., plain, mountainous, and glacial are taken under considerations for the determination of relative potentials of these SREs over Pakistan at global and regional scales. All SREs, in general, have well captured the annual north-south rainfall decreasing patterns and rainfall amounts over the typical arid regions of the country. Regarding the zonal approach, the performance of all SREs has remained good over mountainous region comparative to arid regions. This poor performance in accurate rainfall estimation of all the six SREs over arid regions has made their use questionable in these regions. Over glacier region, all SREs have highly overestimated the rainfall. One possible cause of this overestimation may be due to the low surface temperature and radiation absorption over snow and ice cover, resulting in their misidentification with rainy clouds as daily false alarm ratio has increased from mountainous to glacial regions. Among RT products, CMORPH-RT is the most biased product. The Bias was almost removed on CMORPH-Adj thanks to the gauge adjustment. On a general way, all Adj versions outperformed their respective RT versions at all considered temporal scales and have confirmed the positive effects of gauge adjustment. CMORPH-Adj and TMPA-Adj have shown the best agreement with in situ data in terms of Bias, RMSE, and CC over the entire study area.     

Using Two-Point Set Statistics to Estimate the Diameter Distribution in Boolean Models with Circular Grains

This paper deals with the counting and measuring of overlapping circular objects in binary images, a problem that arises in the mineral processing industry when estimating the distribution of bubble diameters in flotation cells in order to predict the geometallurgical performance of the flotation process. By viewing the images as realizations of a stationary planar Boolean model with circular grains and by using two-point set statistics, it is possible to jointly estimate the average number of objects per unit area and their diameter distribution. When applied to real and simulated images, this method is shown to give accurate estimates, to be robust to the presence of noise contaminating the images and of moderate drifts in the number of objects per unit area, and to speed up the processing time with respect to currently used methods. Combined, these properties serve to make the method suitable for an on-line monitoring of the flotation process.     

‘Surface Drag in the Arctic Marginal Sea-ice Zone: A Comparison of Different Parameterisation Concepts’

Two parameterisation schemes for the turbulent surface fluxes and drag coefficients over the Arctic marginal sea-ice zone (MIZ) are (further) developed, and their results are compared with each other. Although the schemes are based on different principles (flux averaging and parameter averaging), the resulting drag coefficients differ only slightly in the case of neutral and stable stratification. For unstable stratification and sea-ice conditions being typical for the north-eastern Fram Strait, the drag coefficients resulting from the parameter-averaging concept are 5–10% larger than those of the flux-averaging concept. At a sea-ice concentration of 45%, the parameter-averaging method overestimates the heat fluxes by a factor of 1.2. An inclusion in the schemes of form drag caused by floe edges and ridges has a much larger effect on the drag coefficient, and on the momentum fluxes, than the choice between the parameter-averaging or flux-averaging methods. Based on sensitivity studies with the flux-averaging scheme, a simple formula for the effective drag coefficient above the Arctic MIZ is derived. It reduces the computational costs of the more complex parameterisations and could also be used in larger scale models. With this simple formula, the effective drag coefficient can be calculated as a function of the sea-ice concentration and skin drag coefficients for water and ice floes. The results obtained with this parameterisation differ only slightly from those using the more complex schemes. Finally, it is shown that in the MIZ, drag coefficients for sea-ice models may differ significantly from the effective drag coefficients used in atmospheric models.     

Contemporary Deposition and Long-Term Accumulation of Sediment and Nutrients by Tidal Freshwater Forested Wetlands Impacted by Sea Level Rise

Contemporary deposition (artificial marker horizon, 3.5 years) and long-term accumulation rates (²¹⁰Pb profiles, ~150 years) of sediment and associated carbon (C), nitrogen (N), and phosphorus (P) were measured in wetlands along the tidal Savannah and Waccamaw rivers in the southeastern USA. Four sites along each river spanned an upstream-to-downstream salinification gradient, from upriver tidal freshwater forested wetland (TFFW), through moderately and highly salt-impacted forested wetlands, to oligohaline marsh downriver. Contemporary deposition rates (sediment, C, N, and P) were greatest in oligohaline marsh and lowest in TFFW along both rivers. Greater rates of deposition in oligohaline and salt-stressed forested wetlands were associated with a shift to greater clay and metal content that is likely associated with a change from low availability of watershed-derived sediment to TFFW and to greater availability of a coastal sediment source to oligohaline wetlands. Long-term accumulation rates along the Waccamaw River had the opposite spatial pattern compared to contemporary deposition, with greater rates in TFFW that declined to oligohaline marsh. Long-term sediment and elemental mass accumulation rates also were 3–9× lower than contemporary deposition rates. In comparison to other studies, sediment and associated nutrient accumulation in TFFW are lower than downriver/estuarine freshwater, oligohaline, and salt marshes, suggesting a reduced capacity for surface sedimentation (short-term) as well as shallow soil processes (long-term sedimentation) to offset sea level rise in TFFW. Nonetheless, their potentially large spatial extent suggests that TFFW have a large impact on the transport and fate of sediment and nutrients in tidal rivers and estuaries.