Hierarchical Annealing for Synthesis of Binary Images

This paper introduces a hierarchical annealing algorithm which addresses the very large computational costs associated with simulated annealing for the synthesis of binary images. In real-world examples, the large configuration space of such models has led to the disappointing performance of annealing approaches. Our method essentially approaches different natural scales in the image separately and in a hierarchical manner. We demonstrate orders-of-magnitude improvement compared to existing results, and discuss the inherent computational difficulties encountered with these types of approaches.     

分形介质与分形地层

由于地层的二元特征,对地层和地下介质有两种不同的认识倾向,即旋回性(准周期性)和随机性。实际的地下介质物性参数的变化以及地层的分布在一般意义上更具有分形和多重分形的特征,而准周期性和随机性只是其中的两种特别情况。与之类似,地层的过渡也不应该是简单的阶梯函数,而应该是由更具有一般意义的启动函数来描述。通过分析一套实际的多重分形碳酸盐岩沉积层序并对其可能指示的古环境和古海平面的变化进行了初步探讨。     

复杂介质有限元法2.5维可控源音频大地电磁法数值模拟

利用有限元2.5维可控源音频大地电磁法（简称CSAMT）数值模拟方法,对100Ωm均匀半空间介质中有限长度的电偶极源产生的电场、磁场及视电阻率、相位特征进行了数值模拟,研究了场的空间变化规律. 在一个象限中,场的特征存在双叶现象,当收发距大于4个趋肤深度时,电阻率较接近介质真实的电阻率,这些结果为观测系统和收发距的选择提供了依据. 波数域场的特征表明,低波数对源的贡献占较大的比例. 有限元法2.5维CSAMT数值模拟的优势在于能较准确地获得复杂介质结构的波场特征. 本文结合直立异常体、倾斜异常体及断陷模型对CSAMT电阻率、相位剖面特征及频率曲线特征的可靠性进行了研究. 数值模拟结果直观地给出了异常体的剖面异常形态. 通过对比研究异常体的剖面异常形态和半空间场的特征进一步说明本文方法和软件在模拟复杂介质结构场特征时是可靠的. 这为认识观测数据,指导反演解释提供了较好的依据.     

TI介质双参数速度分析

TI介质是常见的介质类型．当道集的排列长度远大于勘探目的层的深度时,P波走时资料包含的信息可以用来确定TI介质的各向异性参数．TI介质的CMP道集中,速度随炮检距而变化,可以从这种变化中求出Vnmo和η。通过模型试验说明,从TI介质P波资料的CMP道集求取Vnmo和η的方法是可取的．     

Re-creating Wilderness 2.0: Or getting back to work in a virtual nature

Camping on Twitter, trekking in Google Street View, mountaineering on Snapchat. Wilderness is dead. Long live Wilderness 2.0. In this paper, the term “Wilderness 2.0” refers to the articulation of new media technologies, including mobile digital devices, web 2.0 and locative media, with the practice of wilderness recreation. In this new era of virtual nature, outdoor recreation occurs as much in the statusphere and blogosphere as it does in the biosphere. While much public and academic debate about Wilderness 2.0 has focused on the extent to which new media technologies connect people to, or disconnect them from, nature, this paper argues that wilderness is not a static and essential reality that can simply be connected to or disconnected from, but a social construct that is continually re-created in different cultural contexts. In this sense, Wilderness 2.0 reflects the re-creation of a new ontology of wilderness as DigiPlace: an augmented reality that blurs the lines between the “actual” and the “virtual.” Moreover, Wilderness 2.0 does not simply refer to the creation of a new ontology of wilderness, but the incorporation of outdoor recreation into the political economy of the web 2.0. In the context of Wilderness 2.0, outdoor recreation is increasingly exploited as a form of virtual labour. Thus, despite being associated with a discourse of “sharing” and “connecting to nature,” Wilderness 2.0 is, above all else, a nature that capital can see.     

Sensitivity of incipient particle motion to fluid flow penetration depth within a packed bed

A discrete element method is applied to a three‐dimensional analysis related to sediment entrainment on a micro‐scale. Sediment entrainment is the process by which a fluid medium accelerates particles from rest and advects them upward until they are either transported as bedload or suspended by the flow. Modelling of the entrainment process is a critically important aspect for studies of erosion, pollutant resuspension and transport, and formation of bedforms in environmental flows. Previous discrete element method studies of sediment entrainment have assumed the flow within the particle bed to be negligible and have only allowed for the motion of the topmost particles. At the same time, micro‐scale experimental studies indicate that there is a small slip of the fluid flow at the top of the bed, indicating the presence of non‐vanishing fluid velocity within the topmost bed layers. The current study demonstrates that the onset of particle incipient motion, which immediately precedes particle entrainment, is highly sensitive to this small fluid flow within the topmost bed layers. Using an exponential decay profile for the inner‐bed fluid flow, the discrete element method calculations are repeated with different fluid penetration depths within the bed for several small particle Reynolds numbers. For cases with slip velocity corresponding to that observed in previous experiments with natural sediment, the predicted particle velocity is found to be a few percent of the fluid velocity at the top of the viscous wall layer, which is a reasonable range of velocities for observation of incipient particle motion. This method for prescribing the fluid flow within the particle bed allows for the current discrete element method to be extended in future studies to the analysis of sediment entrainment under the influence of events such as turbulent bursting. Additionally, predictions for the slip velocities and fluid flow profile within the bed suggest the need for further experimental studies to provide the data necessary for additional improvement of the discrete element method models.     

用最小二乘配点法解地下水稳定流问题

最小二乘配点无网格法是一种新型高效的无网格法。该方法除节点外又在研究域内引入辅助点,近似函数仍然只通过节点构造,微分方程在所有节点和辅助点上满足。本文将最小二乘配点无网格法应用于非均质多孔介质中的二维地下水稳定流问题,推导了计算格式、编制了相应的计算程序。算例结果表明,最小二乘配点无网格法算法简单,有较高的精度且节省计算量。     

垃圾渗滤液污染地下环境介质岩性对pH缓冲能力的影响

通过模拟实验研究垃圾渗滤液污染地下环境介质岩性对pH缓冲能力变化的影响。亚黏土和砂土的pH缓冲容量的本底值分别为440.20和324.93mmol/(kg·pH),其中阳离子交换缓冲、碳酸钙缓冲、硅酸盐缓冲和次级缓冲的本底值分别为206.18、88.43、75.79和69.80mmol/(kg·pH),149.31、86.53、47.33和41.77mmol/(kg·pH)。污染的亚黏土和砂土的交换性阳离子(CEC)和交换性盐基离子(BEC)均小于本底值;盐基饱和度随离污染源距离的增加呈先升高后降低的变化趋势。     

可控力源激发EDA介质中横波分裂现象正演模拟研究

在研究了各向异性介质中波动方程的正演模拟现状的基础上,对波动理论进行了总结,并采用FCT有限差分法对EDA介质中的波动方程进行了数值模拟,得到了EDA介质中横波分裂的波场快照,并对波场特性进行了分析。     

与图像内容相关的色域映射算法研究

通过对经典色域映射算法的调查分析,总结归纳了映射执行中影响图像质量的各个相关因素,在分析其影响权重的基础上建立了一个最佳的映射模型,设计实现了一个与图像内容相关的色域映射算法。测试实验验证,新算法优于ICC推荐的HPMINDE和SGCK算法,确保转换图像的视觉效果最佳。