The definition of mesoscale selective forecast error covariances for a limited area variational analysis

Summary ?The paper deals with an alternative formulation of the so-called NMC (National Meteorological Center, now National Centers for Environmental Prediction) statistics to compute the background error covariance matrix to be used in a mesoscale variational analysis. While the standard method uses differences of forecasts valid for the same time, but starting from different analysis times, the new formulation required the recomputation of the short-term forecast with the initial and lateral boundary data that come from the long-term run. In the frame of a limited-area model, this approach forces the error variances at large scales to decrease drastically, because those scales are controlled by the (constant data) lateral boundary coupling. As a result, the background cost function acts more scale selectively, with an emphasis on medium scales. The analysis increments obtained from the 3D-VAR system show that the analysis increments are sharper and more concentrated with the new formulation, both in single observation and in full observation experiments. This work is part of a wider project for building a variational assimilation system inside the ALADIN model. The complete system should concentrate on mesoscale features and it should not reanalyse those scales that were already treated by the global model (ARPEGE). Some difficulties and perspectives are drawn in the concluding discussion. Received February 12, 2001; revised July 24, 2001     

Estimation of rock physicomechanical properties using hardness methods

The purpose of this study is to investigate the statistical relationship between hardness value and physicomechanical properties of constructional and cover rocks. The definition, measurement of hardness and classification of the rocks used are very important in construction sector. From this point of view, rock hardness is one of the most important parameters for the determination of rock properties. In this study, the determination of hardness and the physicomechanical properties of constructional and cover rocks in Çukurova region was accomplished using various methods in the laboratory. Statistical relations between physicomechanical properties and hardness of rocks were also determined. High correlations were found between the hardness methods (Shore Scleroscope, Schmidt hammer hardness), which are cheap and easy to use, and other physical and mechanical properties. It was found that physicomechanical properties can be estimated using hardness methods and compared with the calculated value from different empirical equations.     

新疆东天山地区构造控水机制及找水意义

极端干旱缺水的哈密东天山地区地下水的赋存、分布和富水性主要受地质构造的控制。由地质构造分割或圈闭的规模不同、类型不同的各类蓄水构造，可分为断块型蓄水构造、压性、压扭性逆断裂型蓄水构造、张性、张扭性断裂蓄水构造和大面积花岗岩分布地区小型岩脉型蓄水构造。不同的蓄水构造可以满足不同规模矿山的需求。采用遥感释译。地面测绘、物探和钻探等多种手段，进行综合分析，就近选择找水靶区，确定供水方向是解决该地区矿山供水的重要途径。     

新疆退耕还林工程关键问题与对策

退耕还林工程在新疆自2000年开始试点和2002年开始全面实施以来，虽然其效益尚未明显地显现．但可以肯定韵是，它将使新疆绿洲生态系统的结构得到改善，减小沙尘暴的发生频率与强度．延缓和削弱局部土地沙化和盐碱化过程。本文介绍了新疆退耕还林工程的实施原则与措施以及新疆的退耕还林模式，分析了退耕还林工程的实施状况和由此带来的生态效益、社会效益和经济效益，同时也分析了退耕还林工程实施中尚存在的问题，并就解决这些问题提出了一些建议和措施。     

Interaction of Weak Shock Waves with Current Sheets in an Active Region to Produce Nanoflares and Chains of Type I Radio Bursts

Interaction of weak shock waves with a current sheet is investigated by a two-dimensional numerical magnetohydrodynamic model. In accordance with solar coronal conditions, a ratio of thermal to magnetic pressures of 0.1 and a shock Alfvén Mach number slightly above 1 are considered. It is found that even weak shock waves trigger magnetic field reconnection in current sheets. Based on this result, it is suggested that drifting chains of type I radio bursts are radio manifestations of the interactions of weakly super-Alfvénic shock waves with pre-existing current sheets distributed in an active region. This model of type I noise storms is then discussed in connection with the concept of nanoflares (localized reconnections) and the heating of the solar corona.     

Fe-C合金扩散型相变的计算机模拟

以扩散规律和成核－长大机制为基础，论述了Fe-C合金的扩散型相变数学模型的建立，采用计算机模拟技术来研究TTT曲线及合金元素对它的影响。结果表明，模拟曲线与实际曲线吻合良好，且能动态描述合金元素对TTT曲线的影响。钢的TTT曲线在钢的热处理中极为重要，因此相变的计算机模拟具有广阔的应用前景及实际推广价值。     

Na2CO3-Na2B4O7-H2O三元体系288K相平衡研究

采用等温溶解平衡法研究了三元体系 Na2 CO3- Na2 B4 O7- H2 O 2 88K时的相平衡及平衡液相的主要物化性质 (密度 ,电导率 ,p H)。研究发现 :该三元体系为简单共饱和型 ,无复盐及固溶体形成 ,根据溶解度数据绘制出相图 ,相图中单变量曲线所对应的平衡固相分别为 :Na2 CO3· 10 H2 O,Na2 B4 O7· 10 H2 O。并简要讨论了物化性质的变化规律。     

中国中-新生代陆相沉积中的遗迹群落

中国中新生代陆相沉积地层中的遗迹化石已知七大生态类型近40种，按其形成的沉积环境可大致划分为三大遗迹群落，即（1）Scoyenia遗迹群落，代表冲积平原或三角洲平原至滨湖环境；（2）Macaronichnus-Planolites遗传群落，主要产生于浅湖环境及水下砂扇（扇三角洲、冲积扇）沉积环境；（3）Mermoides-Neonereites遗迹群落，属典型半深-深湖环境的产物。     

黄河上游末次冰盛期古洪水事件的初步研究

洪水的发生规律是洪灾预报的前提，已有的人类洪水记录时间尺度，不足以认识和把握洪水的出现规律。因此，利用地质记录延长洪水序列，探讨地球特征气候期的洪水特点，就显得非常重要的必要。黄河上游兰州－银川段的洪水地质记录表明，在末次冰盛期的20－18ka，该区共发生了106次大洪水漫滩事件，其中有18次为多次洪峰叠加的复合型大洪水，洪水的发生频率达53次/ka。发生于末次冰盛期的大洪水可能属冰凌洪水，与末次冰盛期强烈的气候波动和不稳定有关。这些大洪水的频发与中国西部的末次冰盛期出现的高湖面相对应，既不符合一般的季风气候理论，也不同于我国东部广大地区末次冰盛期以冷干为主的气候特点，表明中国西部气候的独特性和复杂性。