干湿循环条件下压实黄土变形特性试验研究

由于降雨及蒸发的周期性变化等原因,压实地基土经常处于干湿交替状态,这种干湿循环作用会影响路基及地基的长期稳定性。通过气压式固结仪测试压实黄土试样经过不同次数干湿循环作用后的侧限压缩应变与垂直压力( - )曲线,研究干湿循环作用对压实黄土变形特性的影响,同时利用已有模型对实测曲线进行拟合,并基于割线模量法分析了割线模量与初始压实度及干湿循环次数的关系。结果表明：初始压实度对黄土的压缩变形有显著影响,不同初始压实度的试样其各级压力下的侧限压缩应变均随着干湿循环次数的增大逐渐增加,之后趋于稳定;初始压实度越高,干湿循环作用影响效应越显著;干湿循环作用并不改变土体 - 曲线的形式;割线模量与干湿循环次数及初始压实度的关系均呈指数关系。     

非饱和土增湿变形的实用计算方法

非饱和土力学研究目前还未进入实用阶段,主要原因在于吸力量测困难。本文提出了用等效吸力代替真实吸力的试验方法。首先以常规静三轴试验得到的原状饱和土以及非饱和土的应力-应变曲线为基础,根据变形等效的原则确定与某一饱和度相当的围压即为等效吸力;然后建立饱和度与等效吸力之间的非线性关系,并验证了该数学公式的正确性;再根据试验结果分析含水量对非饱和土强度的影响,建立了非饱和土的实用抗剪强度公式;最后按照邓肯-张模型的参数整理方法得到了不同饱和度非饱和土的模型参数,探索这些参数随饱和度的变化规律,建立了引入饱和度的非饱和黄土实用非线性模型,并进行了降雨入渗情况下非饱和土增湿变形的计算。结果表明,饱和度最大值为95%,等效吸力最大值为160 kPa,最大水平位移与竖向位移分别为0.6 cm和20.0 cm,均出现在浸水位置。计算结果合理地反映了非饱和土变形的分布趋势,验证了方法的合理性。     

地形模型的多分辨率简化与压缩

在地形的三维表达中 ,海量的三维数据在显示、存储、传输等方面存在着很多困难。为了解决这些困难 ,本文提出了一种基于渐进简化的多分辨率几何简化与压缩方法。通过该种方法 ,复杂的地形模型能够很好的被简化成适于LOD连续表达的方式 ,并且在简化基础上的数据压缩可使地形模型的存储量减少、绘制速度增加、网络传输效率提高 ,其结果能够胜任地形模型在网络上的渐进传输     

Research on the imaging of concrete defect based on the pulse compression technique

When the synthetic aperture focusing technology (SAFT) is used for the detection of the concrete, the signal-to-noise ratio (SNR) and detection depth are not satisfactory. Therefore, the application of SAFT is usually limited. In this paper, we propose an improved SAFT technique for the detection of concrete based on the pulse compression technique used in the Radar domain. The proposed method first transmits a linear frequency modulation (LFM) signal, and then compresses the echo signal using the matched filtering method, after which a compressed signal with a narrower main lobe and higher SNR is obtained. With our improved SAFT, the compressed signals are manipulated in the imaging process and the image contrast is improved. Results show that the SNR is improved and the imaging resolution is guaranteed compared with the conventional short-pulse method. From theoretical and experimental results, we show that the proposed method can suppress noise and improve imaging contrast, and can also be used to detect multiple defects in concrete.     

The biaxial compression mechanical properties of crushed rock

Crushed rock subgrade, as one of the roadbed-cooling methods, has been widely used in the Qinghai-Tibet Railway. Much attention has been paid on the cooling effect of crushed rock; however, the mechanical properties of crushed rock are somehow neglected. Based on the discrete element method, biaxial compression test condition for crushed rock is compiled in FISH language in PFC^2D, and the natural shape of crushed rock is simulated with super particle "cluster". The effect of particle size, crushed rock strength and confining pressure level on overall mechanical properties of the crushed rock aggregate are respectively analyzed. Results show that crushed rock of large particle size plays an essential framework role, which is mainly responsible for the deformation of crushed rock aggregate. The strength of gravel has a great influence on overall mechanical properties which means that strength attenuation caused by the freeze thaw cycles cannot be ignored. The stress-strain curves can be divided into two stages including shear contraction and shear expansion at different confining pressures.     

一种抗压缩的等高线数据盲水印算法

根据等高线数据的特点,提出了一种抗压缩的等高线数据盲水印算法。首先采用逐点前进法对等高线数据进行数据压缩,提取特征点,然后基于量化思想将水印信息嵌入在特征点的小数部分。实验结果表明,该算法具有较好的抗压缩效果。     

Multi-threaded compression of Earth observation time-series data

ABSTRACT

Earth observation data are typically compressed using general-purpose single-threaded compression algorithms that operate at a fraction of the bandwidth of modern storage and processing systems. We present evidence that recently developed multi-threaded compression codecs offer substantial benefits over widely used single-threaded codecs in terms of compression efficiency when applied to a selection of moderate resolution imaging spectroradiometer (MODIS) datasets stored in the HDF5 format. Compression codecs from the LZ77 and Rice families are shown to vary in efficacy when applied to different MODIS data products, highlighting the need for compression strategies to be tailored to different classes of data. We also introduce LPC-Rice, a new multi-threaded codec, that performs particularly well when applied to time-series data.     

Effects of lossy compression on remote sensing image classification of forest areas

Lossy compression is being increasingly used in remote sensing; however, its effects on classification have scarcely been studied. This paper studies the implications of JPEG (JPG) and JPEG 2000 (J2K) lossy compression for image classification of forests in Mediterranean areas. Results explore the impact of the compression on the images themselves as well as on the obtained classification. The results indicate that classifications made with previously compressed radiometrically corrected images and topoclimatic variables are not negatively affected by compression, even at quite high compression ratios. Indeed, JPG compression can be applied to images at a compression ratio (CR, ratio between the size of the original file and the size of the compressed file) of 10:1 or even 20:1 (for both JPG and J2K). Nevertheless, the fragmentation of the study area must be taken into account: in less fragmented zones, high CR are possible for both JPG and J2K, but in fragmented zones, JPG is not advisable, and when J2K is used, only a medium CR is recommended (3.33:1 to 5:1). Taking into account that J2K produces fewer artefacts at higher CR, the study not only contributes with optimum CR recommendations, but also found that the J2K compression standard (ISO 15444-1) is better than the JPG (ISO 10918-1) when applied to image classification. Although J2K is computationally more expensive, this is no longer a critical issue with current computer technology.     

Steim2压缩算法的优点和缺点

基于SEED卷格式的Steim2压缩算法, 是目前国际国内的地震数据传输和本地存储中普遍采用的压缩算法, 该算法优点突出, 缺点明显. 其优点是:摸准了地震事件"长期平静"和"长期无震"的特点, 是专门符合该特点量身定做的数据压缩算法, 有显著的独到之处. 其缺点是:在地震事件"活跃期"或"突发期", 即对数据压缩需求...     

三轴压缩条件下基于CT实时监测的冻结兰州黄土细观损伤变化研究

在IMPa围压下,对不同温度条件下的冻结兰州黄土三轴压缩试验过程进行CT动态扫描,获得了由CT数表示的土体损伤量表达式．结果表明：冻结兰州黄土最初在围压作用下,试样沿径向方向被压缩,导致试样轴向伸长;低温冻结试样的弹性变形持续时间长于高温试样,如-2．3℃试样在应变达到0．32％时即开始屈服进入塑性变形,而-7℃试样的...