对山西应县木塔采用纳米复合纤维加固的建议

山西应县木塔是古人留给我们的稀世珍宝，如何妥善地保护好这一珍贵的遗产，使之在加固时尽量保持原有的风貌，是一项复杂而艰巨的任务。根据长期的研究成果和实际工作的经验，提出了用纳米复合纤维加固应县木塔的建议，介绍了纳米复合纤维材料的特点，分析讨论了加固时的一些具体技术问题。     

中国西北地区季节性积雪的性质与结构

中国内陆地区积雪分布十分广泛。根据西北地区大陆性气候条件下形成的“干寒型”积雪的特征 ,对中国天山和阿尔泰山山区的季节性积雪进行了观测与分析。结果表明 ,该区最大积雪深度达 15 2cm(1997) ,积雪层一般由新雪 (或表层凝结霜 )、细粒雪、中粒雪、粗粒雪、松散深霜、聚合深霜层和薄融冻冰层组成。与“湿暖型”积雪相比 ,“干寒型”积雪的性质具有密度小 (新雪的最小密度为 0 .0 4 g/cm3 )、含水率少 (隆冬期 <1% )、温度梯度大(最大可达 - 0 .5 2℃ /cm)、深霜发育层厚等特点 ,并且变质作用以热量交换和雪层压力变质作用为主。据中国科学院天山积雪与雪崩研究站 (43°2 0N ,84°2 9E ,海拔 1776m)的观测资料 ,中国内陆干旱区冬季积雪期雪面太阳辐射通量以负平衡为主 ,新雪雪面反射率达 96 % ,短波辐射在干寒型积雪中的穿透厚度达 2 8cm。春季积雪消融期 ,深霜层厚度可占整个积雪层厚度的 80 %。随着气温的升高 ,雪粒间的键链首先融化 ,使积雪变得松散 ,内聚力、抗压、抗拉和抗剪强度降低 ,积雪含水率也随之增大 ,整个积雪层趋于接近 0℃的等温现象 ,因此 ,春季天山、阿尔泰山等山地全层性湿雪崩频繁发生     

论区域的最佳结构与最佳发展——提出“点-轴系统”和“T”型结构以来的回顾与再分析

通过阐述各种型式空间结构与发展之间的关系及如何通过区域的最佳组织使其达到最佳发展 ,从理论和实践的结合上论证了社会经济空间组织的客观过程和“点 -轴系统”的形成 ,说明“点 -轴系统”理论可以导致区域或国家的最佳发展 ,因而该系统是最有效的区域开发模式。根据对十多年来我国区域发展实践效果的分析 ,指出“T”型结构的战略对我国发展起到了巨大作用。     

Pitfalls in Nonlinear Inversion

— We discuss and illustrate graphically with simple 2-D problems, four common pitfalls in geophysical nonlinear inversion. The first one establishes that the Lagrange multiplier, used to incorporate a priori information in the geophysical inverse problem, should be the largest value still compatible with a reasonable data fitting. This procedure should be used only when the interpreter is sure about the importance of the a priori information used to stabilize the inverse problem relative to the geophysical observations. Because this is rarely the case, the user should use the smallest Lagrange multiplier still producing stable solutions. The second pitfall is an attempt to automatically estimate the Lagrange multiplier by decreasing it along the iterative process used to solve the nonlinear optimization problem. Consequently, at the last iteration, the Lagrange multiplier may be so small that the problem may become ill-posed and any computed solution in this case is meaningless. The third pitfall is related to the incorporation of a priori information by a technique known as “Jumping.” This formulation, from the viewpoint of the class of Acceptable Gradient Methods, is incomplete and may lead to a premature halt in the iteration, and, consequently, to solutions far from the true one. Finally, the fourth pitfall is an inadequate convergence criterion which stops the iteration when the data misfit drops just below the noise level, irrespective of the fact that the functional to be minimized may not have attained its minimum. This means that the a priori information has not been completely incorporated, so that this stopping criterion partially neutralizes the effect of the stabilizing functional, and opens the possibility of obtaining unstable, meaningless estimates.     

赣东加里东变质混合岩带金地球化学特征和地球化学行为

赣东加里东变质混合岩带 ,是以混合岩体为主体 ,受韧性剪切带控制的多相、多型、递增变质带 ,是受区域深构造控制的热变质带。该带产有茅排式金矿。通过对该带金地球化学特征和地球化学行为研究 ,认为带中金丰度 0 .83× 10 - 9,呈峰式分布 ,为对数及双对数正态分布型式 ,Au与主元素成分无关 ,与微量元素组合是Au -Zn -Li-Pb -Cs ,在韧性剪切过程中Au具活化迁移富集特点     

The physical volcanology of the 1600 eruption of Huaynaputina, southern Peru

Volcán Huaynaputina is a group of four vents located at 16°36'S, 70°51'W in southern Peru that produced one of the largest eruptions of historical times when ~11 km³ of magma was erupted during the period 19 February to 6 March 1600. The main eruptive vents are located at 4200 m within an erosion-modified amphitheater of a significantly older stratovolcano. The eruption proceeded in three stages. Stage I was an ~20-h sustained plinian eruption on 19-20 February that produced an extensive dacite pumice fall deposit (magma volume ~2.6 km³). Throughout medial-distal and distal parts of the dispersal area, a fine-grained plinian ashfall unit overlies the pumice fall deposit. This very widespread ash (magma volume ~6.2 km³) has been recognized in Antarctic ice cores. A short period of quiescence allowed local erosion of the uppermost stage-I deposits and was followed by renewed but intermittent explosive activity between 22 and 26 February (stage II). This activity resulted in intercalated pyroclastic flow and pumice fall deposits (~1 km³). The flow deposits are valley confined, whereas associated co-ignimbrite ash fall is found overlying the plinian ash deposit. Following another period of quiescence, vulcanian-type explosions of stage III commenced on 28 February and produced crudely bedded ash, lapilli, and bombs of dense dacite (~1 km³). Activity ceased on 6 March. Compositions erupted are predominantly high-K dacites with a phenocryst assemblage of plagioclase>hornblende>biotite>Fe-Ti oxides-apatite. Major elements are broadly similar in all three stages, but there are a few important differences. Stage-I pumice has less evolved glass compositions (~73% SiO₂), lower crystal contents (17-20%), lower density (1.0-1.3 g/cm³), and phase equilibria suggest higher temperature and volatile contents. Stage-II and stage-III juvenile clasts have more evolved glass (~76% SiO₂) compositions, higher crystal contents (25-35%), higher densities (up to 2.2 g/cm³), and lower temperature and volatile contents. All juvenile clasts show mineralogical evidence for thermal disequilibrium. Inflections on a plot of log thickness vs area^1/2 for the fall deposits suggest that the pumice fall and the plinian ash fall were dispersed under different conditions and may have been derived from different parts of the eruption column system. The ash appears to have been dispersed mainly from the uppermost parts of the umbrella cloud by upper-level winds, whereas the pumice fall may have been derived from the lower parts of the umbrella cloud and vertical part of the eruption column and transported by a lower-altitude wind field. Thickness half distances and clast half distances for the pumice fall deposit suggests a column neutral buoyancy height of 24-32 km and a total column height of 34-46 km. The estimated mass discharge rate for the ~20-h-long stage-I eruption is 2.4᎒⁸ kg/s and the volumetric discharge rate is ~3.6᎒⁵ m³/s. The pumice fall deposit has a dispersal index (Hildreth and Drake 1992) of 4.4, and its index of fragmentation is at least 89%, reflecting the dominant volume of fines produced. Of the 11 km³ total volume of dacite magma erupted in 1600, approximately 85% was evacuated during stage 1. The three main vents range in size from ~70 to ~400 m. Alignment of these vents and a late-stage dyke parallel to the NNW-SSE trend defined by older volcanics suggest that the eruption initiated along a fissure that developed along pre-existing weaknesses. During stage I this fissure evolved into a large flared vent, vent 2, with a diameter of approximately 400 m. This vent was active throughout stage II, at the end of which a dome was emplaced within it. During stage III this dome was eviscerated forming the youngest vent in the group, vent 3. A minor extra-amphitheater vent was produced during the final event of the eruptive sequence. Recharge may have induced magma to rise away from a deep zone of magma generation and storage. Subsequently, vesiculation in the rising magma batch, possibly enhanced by interaction with an ancient hydrothermal system, triggered and fueled the sustained Plinian eruption of stage I. A lower volatile content in the stage-II and stage-III magma led to transitional column behavior and pyroclastic flow generation in stage II. Continued magma uprise led to emplacement of a dome which was subsequently destroyed during stage III. No caldera collapse occurred because no shallow magma chamber developed beneath this volcano.     

Two Brazilian archaeological sites investigated by GPR: Serrano and Morro Grande

The application of the ground penetrating radar (GPR) at two archaeological sites, Serrano and Morro Grande, situated in Araruama County, Rio de Janeiro, Brazil, aids the study of a prehistoric indigenous culture, associated with the “Tupinambá” that inhabited the region during prehistoric times.The archaeological remains of the study area are mainly characterized by pottery artifacts for several uses, including funerary urns, which were buried within layers of sand and clay. Several profiles were acquired using a RAMAC system, with a 200 and 400 MHz frequency antennae. At the Serrano site, the profiles were acquired around some partially exposed pottery shards, due to sand exploitation. The resultant profiles provided a response model to guide the interpretation of new profiles acquired at other sites in the area, which present similar characteristics.The results showed the great importance of the dielectric permittivity contrast which exists between the targets and the host media, in order for possibly significant features to be identified in radar data.     

Pegmatite Emplacement in the Seridó Belt, Northeastern Brazil: Late Stage Kinematics of the Brasiliano Orogen

Geometric and kinematic analysis was performed in an area located in the central part of the Seridó Belt (NE Brazil), where supracrustal rocks affected by polyphase deformation are well exposed. The first event recognized in this area (and regionally known as the D₂ deformation) is characterized by top to the south thrust tectonics while a second one (D₃ deformation) is marked by upright folds, strike-slip or transpressive shear zones and the development of flower structures. Major pegmatite swarms were emplaced during and late as regards the second event (dated ca. 580 Ma), being part of the Brasiliano orogeny; similar dyke swarms are known from the Nigerian Shield. These pegmatite swarms provide reliable kinematic markers of the late evolutionary stage of the Neoproterozoic Trans-Sahara-Borborema collisional belt. Mineralogical, geometric and kinematic features support two stages of pegmatite emplacement during the strike-slip event: (i) older, syn-D₃ homogeneous pegmatites intruded mostly along lithological and structural discontinuities, such as foliation surfaces; (ii) late, D₃ heterogeneous pegmatites were emplaced along tension gashes and other dilation structures. The heterogeneous pegmatites are economically more important, being exploited for precious metals and stones, as well as industrial minerals.     

Fine sediment transport and accumulations at the mouth of the Seine estuary (France)

A comprehensive study of fine sediment transport in the macrotidal Seine estuary has been conducted, including observations of suspended particulate matter (SPM), surficial sediment, and bathymetric data, as well as use of a three dimensional mathematical model. Tide, river regime, wind, and wave forcings are accounted. The simulated turbidity maximum (TM) is described in terms of concentration and location according to tidal amplitude and the discharge of the Seine River. The TM is mainly generated by tidal pumping, but can be concentrated or stretched by the salinity front. The computed deposition patterns depend on the TM location and are seasonally dependent. The agreement with observations is reasonable, although resuspension by waves may be overestimated. Although wave resuspension is likely to increase the TM mass, it generally occurs simultaneously with westerly winds that induce a transverse circulation at the mouth of the estuary and then disperse the suspended material. The resulting effect is an output of material related to wind and wave events, more than to high river discharge. The mass of the computed TM remains stable over 6 months and independent of the river regime, depending mainly on the spring tide amplitude. Computed fluxes at different cross-sections of the lower estuary show the shift to the TM according to the river flow and point out the rapidity of the TM adjustment to any change of river discharge. The time for renewing the TM by riverine particles has been estimated to be one year.     

Late- to post-orogenic basins of the Pan-African – Brasiliano collision orogen in southern Africa and southern Brazil

Late- to post-orogenic basins formed on both sides of the Pan-African – Brasiliano orogen when the Congo and Kalahari Cratons collided with the Rio de la Plata Craton during the formation of western Gondwana. Trace fossil evidence and radiometric age dating indicate that deposits on both sides are coeval and span the Cambrian–Precambrian boundary. A peripheral foreland basin, the Nama Basin, developed on the subducting southern African plate. Lower, craton-derived fluviomarine clastics are overlain by marine platform carbonates and deltaic flysch derived in part from the rising subduction complex along the northern (Damara Belt) and western (Gariep Belt) orogenic margins. Rare, thin volcanic ash layers (tuffs and cherts) are present. Upper sediments consist of unconformable red molasse related to collisional orogenesis. Orogenic loading from the north and west led to crustal flexure and the formation of a remnant ocean that drained to the south and closed progressively from north to south. During final collision SE-, E- and NE-verging nappes overrode the active basin margins. Although younger than most of the post-orogenic magmatism, its setting on the cratonic edge of the subducting plate precluded marked volcanism or granitic intrusion, the only exception being the youngest intrusions of the Kuboos-Bremen Suite dated at 521±6 Ma to 491±8 Ma. Two foreland-type basins, perhaps faulted remnants of a much larger NE–SW elongated retroarc foreland basin, are found west of the Dom Feliciano Belt on the edge of the Rio de la Plata Craton in southern Brazil. In the southern Camaqua Basin, basal fluvial deposits are followed by cyclical marine and coarsening-up deltaic deposits with a notable volcanic and volcaniclastic component. This lower deformed succession, comprising mainly red beds, contain stratabound Cu and Pb–Zn deposits and is overlain unconformably by a fluviodeltaic to aeolian succession of sandstones and conglomerates (with minor andesitic volcanics), derived primarily from an eastern orogenic source and showing southerly longitudinal transport. In the northern Itajaí Basin, sediments range from basal fluvial and platform sediments to fining-up submarine fan and turbidite deposits with intercalated acid tuffs. The Brazilian basins had faulted margins off which alluvial fans were shed. They also overlie parts of the Ribeira Belt. Thrust deformation along the orogenic margin bordering the Dom Feliciano Belt was directed westward in the Camaqua and Itajaí basins, but reactivated strike-slip and normal faults are also present. Late- to post-orogenic granitoids and volcanics of the Dom Feliciano Belt, ranging in age from 568±6 Ma to 529±4 Ma, occur in the foreland basins and are geochemically related to some of the synsedimentary volcanics.