Site response studies in Agartala Urban agglomeration

A systematic investigation using digital microearthquake recorders with short period SS-1 seismometers, covering 76 sites in and around Agartala city, has been carried out for site response (SR) studies in the area. In the northern part of the area, SR varies from 1.15 to 1.85 corresponding to peak frequency 0.76 to 0.93 Hz where soil is mostly semi-consolidated and stiffer than recent Quaternary deposits (Haora River formation). In the southern part of the area, SR varies from 1.12 to 2.42 corresponding to peak frequency from 0.71 to 0.85 Hz within the Dupitila formation (early Quaternary). It is observed that estimated SR from H/V increases from edges to middle of the Haora River valley and impedance contrast fallows the similar trend. This reflects that site response by H/V is influenced by impedance contrast, whereas computed amplification from 1-D model shows opposite trend. The maximum amplification at fundamental frequency of resonance, 1.04 Hz estimated from H/V by near to BH-7, is 2.5 times greater than the impedance contrast/ratio derived from 1-D model for same location. Relationship between resonance frequency and depth was obtained by applying quarter wavelength and Bard (2000) methodologies, which shows linearity, whereas H/V shows its nonlinearity characteristic in soil across the valley part of Haora River. Shear wave velocities, and subsequently, SPT index and factor of safety (by cyclic stress approach) were estimated from geotechnical parameters. Vs30 and site response data were used in this study for getting a first hand information about soil stiffness condition in the area. The estimation of SPT index and factor of safety could be a useful tool for delineating liquefied and none liquefied zones at various depth levels, especially where water table exists at a very shallow level. The expected liquefiable zone was observed at depths varying from 6–25 m beneath the soil bearing zones where percentage of fines is estimated to be more than 35% for the area. This knowledge about subsurface soil characteristics will be useful for the civil engineers/city planners, which can be taken into account at the time of constructing earthquake-resistant structures in the area.     

Isotope composition of neodymium in neo-Archean banded iron formations of Karelia and Kola Peninsula

Studies of three deposits of neo-Archean banded iron formations from the West Karelian domain (the Kostomuksha deposit) and from the Central Kola block (the Olenegorsk and Kirovogorsk deposits) showed a pronounced difference in the isotope compositions of Nd from quartz and magnetite–hematite interlayers. The less radiogenic Nd of iron-containing layers compared to that of the quartz component may be considered as an indication of the formation mechanism of the treated banded iron formations. Thus, silicon-containing layers are related to submarine volcanism and iron was supplied to the sedimentation zone from other sources.     

优秀教师评价学生学业的策略与技巧

学业评价是教师教育教学中的重要环节,不仅关系到对学生的评价,也关系到学生对学习的情感态度和努力投入,以及师生关系的质量。优秀的中小学教师在评定学生学业成绩时,能够从学生长远发展角度考虑评价对学生的全面影响,重视评分的发展性评价目的;在具体评分实践中,能充分考虑学生对分数的认识、理解和感受,评分目的明确;能够运用多种评价方式,从多个来源对学生多个方面的表现实施多元综合评价;能够根据评分目的和条件合理恰当地选择评分标准,评分灵活可靠,又不失评价原则。这些理念和策略作法,确保了他们的评分能够真正发挥鼓励学生学习,促进学生成长的广阔而深远的目的。     

Ecological controls on biogeochemical lfuxes in the western Antarctic Peninsula studied with an inverse foodweb model

Sea ice in the western Antarctic Peninsula (WAP) region is both highly variable and rapidly changing. In the Palmer Station region, the ice season duration has decreased by 92 d since 1978. The sea-ice...     

Dynamic responses of two buildings connected by viscoelastic dampers under bidirectional earthquake excitations

In this study,dynamic responses of two buildings connected by viscoelastic dampers under bidirectional excitations are extensively investigated.The two buildings are a 10-story building and a 16-story building,with the shorter building on the left.Viscoelastic dampers are installed at all fl oors of the shorter building.Equations of motion are formulated using a fractional derivative model to represent the viscoelastic dampers.Three cases are considered with mass eccentricities at 0,10% and-10% with respect to the dimensions of the buildings.The responses of the buildings are numerically predicted at different damper properties.The simulation results indicated that the maximum horizontal responses of the buildings without eccentricities are signifi cantly mitigated.However,torsional effects are adversely increased.For asymmetric buildings,the effectiveness of the connecting dampers is affected by building eccentricities.As a result,mass eccentricities must be taken into account in damper selection.When compared with vibrations induced by unidirectional excitations,bidirectional excitations can increase the responses of coupled asymmetric buildings.In addition,installing dampers only at the top fl oor of the shorter building may cause a sudden change in lateral stiffness of the taller building.Consequently,the story shear envelopes of the taller building are changed.