Heterogeneity in hedonic modelling of house prices: looking at buyers’ household profiles

This paper introduces household-level data into hedonic models in order to measure the heterogeneity of implicit prices regarding household type, age, educational attainment, income, and the previous tenure status of the buyers. Two methods are used for this purpose: a first series of models uses expansion terms, whereas a second series applies Geographically Weighted Regressions. Both methods yield conclusive results, showing that the marginal value given to certain property specifics and location attributes do vary regarding the characteristics of the buyer’s household. Particularly, major findings concern the significant effect of income on the location rent as well as the premium paid by highly-educated households in order to fulfil social homogeneity.     

A spectral barotropic model of the wind-driven world ocean

A global spectral barotropic ocean model is introduced to describe the depth-averaged flow. The equations are based on vorticity and divergence (instead of horizontal momentum); continents exert a nearly infinite drag on the fluid. The coding follows that of spectral atmospheric general circulation models using triangular truncation and implicit time integration to provide a first step for seamless coupling to spectral atmospheric global circulation models and an efficient method for filtering of ocean wave dynamics. Five experiments demonstrate the model performance: (i) Bounded by an idealized basin geometry and driven by a zonally uniform wind stress, the ocean circulation shows close similarity with Munk’s analytical solution. (ii) With a real land–sea mask the model is capable of reproducing the spin-up, location and magnitudes of depth-averaged barotropic ocean currents. (iii) The ocean wave-dynamics of equatorial waves, excited by a height perturbation at the equator, shows wave dispersion and reflection at eastern and western coastal boundaries. (iv) The model reproduces propagation times of observed surface gravity waves in the Pacific with real bathymetry. (v) Advection of tracers can be simulated reasonably by the spectral method or a semi-Langrangian transport scheme. This spectral barotropic model may serve as a first step towards an intermediate complexity spectral atmosphere–ocean model for studying atmosphere–ocean interactions in idealized setups and long term climate variability beyond millennia.     

一种基于反距离加权方法的层状三维地质界面拟合算法

三维空间中地质曲面模拟是矿产勘查、大比例尺成矿预测等地学领域的重要研究内容之一.与地球化学、地球物理数据的曲面拟合相比,地质界面拟合更加复杂且具有一般性.从功能需求角度出发,地质界面拟合需要处理层状地层、不整合地层以及存在构造的地层等多种情况;从算法实现角度讲,该拟合过程不同于物化探数据通过某一属性值进行曲面拟合的情况,因为在地质界面模拟过程中,不存在这样的特征值进行曲面拟合,因此不能直接使用物化探数据等值面提取的思想模拟地质接触界面.针对上述问题,提出了一种基于反距离加权法移动立方格算法的层状地层曲面拟合算法.该方法模型适合绝大多数层状地学三维曲面模拟.     

一阶Rytov近似有限频走时层析

传统的波动方程走时核函数（或走时Fréchet导数）多基于互相关时差测量方式及地震波场的一阶Born近似导出,其成立条件非常苛刻.然而,地震波走时与大尺度的速度结构具有良好的线性关系,对于小角度的前向散射波场,Rytov近似优于Born近似.因此,本文基于Rytov近似和互相关时差测量方式,导出了基于Rytov近似的有限频走时敏感度核函数的两种等价形式：频率积分和时间积分表达式.在此基础之上,本文提出了一种隐式矩阵向量乘方法,可以直接计算Hessian矩阵或者核函数与向量的乘积,而无需显式计算和存储核函数及Hessian矩阵.基于隐式矩阵向量乘方法,本文利用共轭梯度法求解法方程实现了一种高效的Gauss-Newton反演算法求解走时层析反问题.与传统的敏感度核函数反演方法相比,本文方法在每次迭代过程中,无需显式计算和存储核函数,极大降低了存储需求.与基于Born近似的伴随状态方法走时层析相比,本文方法具有准二阶的收敛速度,且适用范围更广.数值试验证明了本文方法的有效性.

     

中国地质灾害气象预警模型研究

地质灾害气象预警是指对气象因素(主要为降雨)引发的地质灾害发生可能性大小的预测预报。中国大陆的地质灾害气象预警工作始于2003年, 逐步形成了国家级、省级、市县级的分级运行业务模式, 预警模型及可靠性问题是这项工作的核心科学技术问题和研究难点。考虑到各级地质灾害气象预警的时空尺度与预警时效, 形成了两代预警模型并行运算、相互校验与补充的运行模式。第一代隐式统计预警模型, 也称为临界降雨判据法, 基于不同地质环境区域引发地质灾害的临界雨量不同, 分区建立临界降雨判据, 该模型2003年起在预警业务中使用, 因其只涉及一个或一类参数, 使用广泛, 近年来又在模型参数、判据修正等方面不断完善。但单一的临界雨量指标很难准确反映地质环境的变化以及地质灾害的成生规律, 且预警区划、判据更新与准确性提高等也限制了其进一步发展。第二代显式统计预警模型, 耦合了地质环境变化与降雨参数等多因素建立预警判据, 地质环境指标在模型中显式表达, 在模型原理、空间精度、升级能力等方面表现了其优越性, 显著提高了预警精细度和准确度, 2008年开始在国家级预警业务使用, 并逐步向省级推广。两代预警模型均是基于统计方法建立, 一定程度上均受到统计样本的选择、地质环境条件的精细程度、实况降雨数据的精确匹配等因素控制和影响。多年来, 两代预警模型在中国地质灾害气象预警业务中成功运行并不断升级完善, 为中国大陆的地质灾害防灾减灾工作做出了重要贡献。     

一种求解黏弹塑性介质流动的全隐格式算法

在岩石圈动力学数值模拟中,现有的黏弹塑性数值模型通常在每个时间步先使用迎风间断Galerkin方法对偏应力张量进行旋转,然后使用Particle-In-Cell（PIC）方法或场方法求解对流方程,所构成的时间离散格式为显格式或半隐格式.我们将黏弹塑性介质的经典数值模型和非牛顿流体力学领域的黏弹性流体问题计算方法相结合,提出了一种基于有限单元法的求解黏弹塑性介质流动的全隐格式算法.本文通过数值实验将这种全隐格式算法与PIC方法和半隐格式算法进行了详细的对比,实验结果表明全隐格式算法的数值稳定性优于PIC方法,而当Deborah数较高时精度优于半隐格式算法.同时,我们在应力场引入三阶WENO（Weighted Essentially Non-Oscillatory）限制器,可以在保留数值解精度的同时有效消除应力集中引起的数值振荡.

     

Evaluation of stochastic reservoir operation optimization models

This paper investigates the performance of seven stochastic models used to define optimal reservoir operating policies. The models are based on implicit (ISO) and explicit stochastic optimization (ESO) as well as on the parameterization–simulation–optimization (PSO) approach. The ISO models include multiple regression, two-dimensional surface modeling and a neuro-fuzzy strategy. The ESO model is the well-known and widely used stochastic dynamic programming (SDP) technique. The PSO models comprise a variant of the standard operating policy (SOP), reservoir zoning, and a two-dimensional hedging rule. The models are applied to the operation of a single reservoir damming an intermittent river in northeastern Brazil. The standard operating policy is also included in the comparison and operational results provided by deterministic optimization based on perfect forecasts are used as a benchmark. In general, the ISO and PSO models performed better than SDP and the SOP. In addition, the proposed ISO-based surface modeling procedure and the PSO-based two-dimensional hedging rule showed superior overall performance as compared with the neuro-fuzzy approach.     

Ore-structure relationships at Sishen Mine,Northern Cape,Republic of South Africa,based on fully-constrained implicit 3D modelling

A fully-constrained, implicit, 3D geological model of Sishen Mine reveals the original, pre-mining geometry of ore bodies, host rocks to mineralization and major structures. There are several overlapping controls, at a variety of scales, on the position, depth and geometry of laminated and conglomeratic ore. Most of these controls are structural or may be reconciled with the kinematic history of this part of the Maremane Dome. A series of near-horizontal sections, through the entire 3D model, demonstrates the manner in which these controls overlap and interact. First-order or large-scale controls comprise broad domes, which show preservation of laminated ore around their rims, outside of which conglomeratic ore occurs. Second-order controls comprise grabens and half-grabens, which are often bounded by strike-persistent normal faults, which show fault drag on their western flanks due to inversion, along with preservation of BIF-related supergene ore and conglomeratic ore. A type example is the thick, deep, linear ore to the west of the Sloep Fault. Third-order controls on the preservation of mineralization comprise downthrown blocks to the north of reactivated E-W, SE/ESE- or NE/ENE-trending conjugate faults. Upthrow to the south could be attributed to the 1.15–1.0 Ga NNW-directed Lomanian (Namaqua-Natal) Orogeny. Palaeosinkholes comprise fourth-order controls, which are superimposed on higher-order controls. Palaeosinkholes, which form the bulk of current mining, comprise deep, conical depressions with anomalous thicknesses of chert, chert breccia and haematite. Due to their limited size, the steepness of all units and the often chaotic nature of detached and slumped blocks in their centres, these volumes reflect longstanding models on palaeosinkhole development and very local ore control.