Origin of garnet in the basic granulites around Saltora,W. Bengal,India

Garnetiferous basic granulites occur, as parts of hornblende-pyroxene- and pyroxene granulites, in a Precambrian terrain around Saltora. The chemistry of the garnetiferous basic granulites is broadly similar to that of the hornblende-pyroxene granulites, their immediate precursors, but in detail they have distinctly higher Fe/Mg ratios. The compositions of the major mafic silicates of the garnetiferous varieties do not reflect higher pressures of formation: the Jd/Ts ratios in calcic pyroxenes are similar to those from the non-garnetiferous varieties, and the pyrope contents of garnets are low. Exchange equilibrium in respect of major elements was established among the mafic silicates in spite of garnets being late overprints. The orthopyroxene — calcic pyroxene pairs from the garnetiferous granulites show lower values of K _D(Mg-Fe) ^opx-cpx than those from the non-garnetiferous granulites, pointing to lower temperature of equilibration. The K _D(Mg-Fe) ^opx-hbl K _D(Mg-Fe) ^cpx-hbl relations show that the more magnesian triads equilibrated at lower temperatures; viewed against experimental data regarding the effect of Mg/Fe ratios on the appearance of garnets in basic rocks, formation of garnets by cooling is strongly indicated. Several intergrowth textures, especially garnet-ilmenite and garnet-quartz (±albite) symplectites, and modal relations argue in favour of composite reactions of the type hornblende+ quartz-→calcic pyroxene+garnet+albite+H₂O, which couple hornblende breakdown reactions with orthopyroxene+anorthite→garnet reactions. The approximate range of pressure and temperature conditions, estimated from experimental data, are 6–8.5 kb and 750–830° C. Since garnets formed by cooling in iron-rich granulites, the garnetiferous granulites do not represent higher pressure subfacies of the granulite facies.     

EVIDENCE FOR ABRUPT CLIMATIC CHANGES ONNORTHWESTERN MARGIN OF EAST ASIAN MONSOON REGION DURING LAST DEGLACIATION

Based on investigations of the Zhongwei Nanshan aeolian section situated in the southeastern margin of Tengger Dcsert, carbon-14 and TL (thermoluminescence) dating results and paleoclimatic proxies such as magnetic susceptibility and grain size, we inferred that the northwestern margin of East Asian monsoon region experienced abrupt climatic changes during the last deglaciation. Six oscillation events were identified: Oldest Dryas, Belling, Older Dryas, AllerФd, lntra-AllerФd Cold Period (1ACP) and Younger Dryas (YD). The summer monsoon was weaker during Oldest Dryas and Younger Dryas when the winter monsoon was stronger. However, during the B/A (BФlling/AllerФd) period, the summer monsoon strengthened, reflected by magnetic susceptibility, when the winter monsoon also became strong, which is different from the paleoclimatic pattern established in the East Asian monsoon region. Furthermore,the summer monsoon was nearly in phase with the climate changes inferred from the oxygen isotopic records of Greenland ice cores. It could be speculated that the variations of the sea ice cover in the high latitudes of the North Hemisphere affected the high pressure of Asian continent and the changes of the winter monsoon inland. On the other hand,the sea ice cover variations might have indirectly caused the occurrence of ENSO events that has tightly been related to the summer monsoon in northwest margin of East Asian monsoon region.     

水力停留时间对硫自养还原高氯酸盐和硝酸盐性能的影响

以填充单质硫颗粒(S0)的生物膜反应器作为研究对象,研究了水力停留时间(HRT)变化对硫自养还原高氯酸盐(ClO-4)和硝酸盐(NO-3)性能的影响。研究结果表明,在进水NO-3-N和ClO-4分别为20mg/L和100μg/L时,在HRT从16h逐渐缩短到0.5h过程中,NO-3-N去除率能在较短时间内达到99%以上。与硫自养还原NO-3-N相比,HRT的缩短导致ClO-4去除率趋于稳定所需时间增加,说明硫自养还原NO-3-N过程先于硫自养还原ClO-4的过程。在不同HRT下未发现中间产物ClO-3和ClO-2的积累,ClO-4摩尔数减少量与Cl-摩尔数增加量比约为1∶1,出水中SO2-4的实际产生量远大于理论产生量,出水pH值范围为6.8~7.1。通过PCR-DGGE图谱和测序结果分析可知,属于α-proteobacteria菌群在反应器中占优势地位,β-proteobacteria菌群次之。其中,具有NO-3和ClO-4还原能力的Denitromonas sp.和Azospirillumsp.存在于反应器的底部、中部和上部的生物膜,能还原ClO-4的Dechloromonas sp.MissR被发现存在于反应器中部和上部的生物膜。     

基于卷积神经网络的无人机影像违章建筑检测应用

无人机航拍影像具有分辨率高、回访周期短等特点,利用无人机遥感技术手段对城市范围的建设进行动态监测,可及时、有效地发现涉嫌违法的建设活动。本文结合实际项目需求,研究通过卷积神经网络方法进行违章建筑的自动检测,替代过去靠大量人力检查的模式,目前测试区域无人机影像试验取得了较好的效果,在样本数据不足5000份的情况下,准确率和召回率分别达到了71%和88%。随着样本数据的不断增多,基于该深度学习方法将较大程度上持续提升检测准确率和召回率,能够更精准地发现违法活动,具有较大的实际应用价值及潜力。     

Uncertainty propagation in orbital mechanics via tensor decomposition

Uncertainty forecasting in orbital mechanics is an essential but difficult task, primarily because the underlying Fokker–Planck equation (FPE) is defined on a relatively high dimensional (6-D) state–space and is driven by the nonlinear perturbed Keplerian dynamics. In addition, an enormously large solution domain is required for numerical solution of this FPE (e.g. encompassing the entire orbit in the \(x-y-z\) subspace), of which the state probability density function (pdf) occupies a tiny fraction at any given time. This coupling of large size, high dimensionality and nonlinearity makes for a formidable computational task, and has caused the FPE for orbital uncertainty propagation to remain an unsolved problem. To the best of the authors’ knowledge, this paper presents the first successful direct solution of the FPE for perturbed Keplerian mechanics. To tackle the dimensionality issue, the time-varying state pdf is approximated in the CANDECOMP/PARAFAC decomposition tensor form where all the six spatial dimensions as well as the time dimension are separated from one other. The pdf approximation for all times is obtained simultaneously via the alternating least squares algorithm. Chebyshev spectral differentiation is employed for discretization on account of its spectral (“super-fast”) convergence rate. To facilitate the tensor decomposition and control the solution domain size, system dynamics is expressed using spherical coordinates in a noninertial reference frame. Numerical results obtained on a regular personal computer are compared with Monte Carlo simulations.     

Cosmology and Astrophysics using the Post-Reionization HI

We discuss the prospects of using the redshifted 21-cm emission from neutral hydrogen in the post-reionization epoch to study our Universe. The main aim of the article is to highlight the efforts of Indian scientists in this area with the SKA in mind. It turns out that the intensity mapping surveys from SKA can be instrumental in obtaining tighter constraints on the dark energy models. Cross-correlation of the HI intensity maps with the Ly α forest data can also be useful in measuring the BAO scale.     

A multi-proxy reconstruction of spatial and temporal variations in Asian summer temperatures over the last millennium

To investigate climate variability in Asia during the last millennium, the spatial and temporal evolution of summer (June–July–August; JJA) temperature in eastern and south-central Asia is reconstructed using multi-proxy records and the regularized expectation maximization (RegEM) algorithm with truncated total least squares (TTLS), under a point-by-point regression (PPR) framework. The temperature index reconstructions show that the late 20th century was the warmest period in Asia over the past millennium. The temperature field reconstructions illustrate that temperatures in central, eastern, and southern China during the 11th and 13th centuries, and in western Asia during the 12th century, were significantly higher than those in other regions, and comparable to levels in the 20th century. Except for the most recent warming, all identified warm events showed distinct regional expressions and none were uniform over the entire reconstruction area. The main finding of the study is that spatial temperature patterns have, on centennial time-scales, varied greatly over the last millennium. Moreover, seven climate model simulations, from the Coupled Model Intercomparison Project Phase 5 (CMIP5), over the same region of Asia, are all consistent with the temperature index reconstruction at the 99 % confidence level. Only spatial temperature patterns extracted as the first empirical orthogonal function (EOF) from the GISS-E2-R and MPI-ESM-P model simulations are significant and consistent with the temperature field reconstruction over the past millennium in Asia at the 90 % confidence level. This indicates that both the reconstruction and the simulations depict the temporal climate variability well over the past millennium. However, the spatial simulation or reconstruction capability of climate variability over the past millennium could be still limited. For reconstruction, some grid points do not pass validation tests and reveal the need for more proxies with high temporal resolution, accurate dating, and sensitive temperature signals, especially in central Asia and before AD 1400.     

太阳目标哈特曼波前探测研究

分别对Hinode光学望远镜SOT观测太阳黑子的本影和半影图像以及太阳米粒组织图像进行了空间频谱计算和相关计算,分析了太阳不同结构区域图像的时域和空域特性对哈特曼波前探测精度的影响。计算和分析结果表明,在子孔径波面倾斜小于0.25″情况下,米粒组织图像采样时间在2 min内、本影和半影采样时间在4 min内,对子孔径波面倾斜探测精度的影响极小;并且由太阳目标特性引起的哈特曼波面探测误差随波面畸变量的增大而增大。这些研究结果可为太阳望远镜哈特曼波前探测器研制和应用提供依据和参考。     

兴隆1m光学望远镜杂散光效应研究

兴隆1m光学望远镜采取了加装挡板等基于经验和定性分析的杂散光抑制措施。用Tracepro光学分析软件对圆顶内1m望远镜的杂散光传播路径做了计算和分析,提出了对1m望远镜的杂散光抑制的改进措施,通过在Tracepro中计算的系统杂散光"归一化点源辐照度透过率(PSNIT)"函数对改进措施进行了评价。计算结果表明:对于有效视场外30°范围的杂散源,改进措施可使得1m望远镜的PSNIT全部下降到10-10;模拟1m望远镜在满月条件下对偏月25°的天体观测(R波段、15等星、t=15~150s),1m望远镜观测信噪比可提高约147%。