Improving the SMAC atmospheric correction code by analysis of Meteosat Second Generation NDVI and surface reflectance data

In order to obtain high quality data, the correction of atmospheric perturbations acting upon land surface reflectance measurements recorded by a space-based sensor is an important topic within remote sensing. For many years the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) radiative transfer model and the Simplified Method for Atmospheric Correction (SMAC) codes have been used for this atmospheric correction, but previous studies have shown that in a number of situations the quality of correction provided by the SMAC is low. This paper describes a method designed to improve the quality of the SMAC atmospheric correction algorithm through a slight increase in its computational complexity. Data gathered from the SEVIRI aboard Meteosat Second Generation (MSG) is used to validate the additions to SMAC, both by comparison to simulated data corrected using the highly accurate 6S method and by comparison to in-situ and 6S corrected SEVIRI data gathered for two field sites in Africa. The additions to the SMAC are found to greatly increase the quality of atmospheric correction performed, as well as broaden the range of atmospheric conditions under which the SMAC can be applied. When examining the Normalised Difference Vegetation Index (NDVI), the relative difference between SMAC and in-situ values decreases by 1.5% with the improvements in place. Similarly, the mean relative difference between SMAC and 6S reflectance values decreases by a mean of 13, 14.5 and 8.5% for Channels 1, 2 and 3 respectively. Furthermore, the processing speed of the SMAC is found to remain largely unaffected, with only a small increase in the time taken to process a full SEVIRI scene. Whilst the method described within this paper is only applicable to SEVIRI data, a similar approach can be applied to other data sources than SEVIRI, and should result in a similar accuracy improvement no matter which instrument supplies the original data.     

无线传感器SMAC协议的自适应占空比调整机制研究

针对无线传感器SMAC协议无法适应网络负载的动态变化而导致网络丢包和时延抖动的情况,设计了DSMAC协议.该协议依据数据包在发送队列中等待时间的平均值来预测当前网络的负载情况,并动态地调整节点的占空比,从而在实现能量有效利用的同时保证数据的及时可靠传输.仿真实验表明,改进后的协议能有效地利用了节点能量,同时增加了网络吞吐量,降低了数据端到端的时延.     

无线传感器网络动态节能信道接入协议

为了使无线传感器网络移动节点加入时能快速地建立连接并且能量消耗较低,提出一种动态、节能的信道接入控制协议DEE-MAC.该协议以一种新颖的方式在TDMA的基础上叠加了动态分簇和优先级竞争簇头机制,在移动和静止场景中,既有最低性能保障,又有较高信道利用率.仿真结果表明,有移动节点加入时,DEE-MAC协议在数据吞吐量、延时以及丢包率方面比SMAC协议都有明显改善.     

DIRECT NUMERICAL SIMULATION OF BLUFF BODY FLOWS USING NON-STAGGERED GRIDS

The present authors pointed out in the previous paper [1] that the implicit SMAC scheme is quite efficient and non-staggered grid arrangement can decrease the computational effort and save the storage memory which is very important to the direct numerical simulation (DNS) of complicated 3-D flow fields. But using non-staggered grid arrangement, the pressure field oscillation (PFO) ordinarily occurs and also, the pressure on the solid walls including sharp corners need to be prescribed directly as the pressure boundary conditions.

In this paper, a new interpolation method, which is a modification to Cheng and Armfield's interpolation formulation, is presented in order to completely prevent PFO from occurring, Moreover, a more accurate specification method of wall pressures and special treatment of pressures at sharp corners are proposed. To test the new methods proposed, the DNS of flow past a square cylinder and flows over backward-facing steps, which are typical of the flow fields with sharp corners, is made using the implicit SMAC scheme combined with these methods. The calculated results are compared with the previous experimental and numerical data and show good agreement with them.     

Implicit numerical scheme based on SMAC method for unsteady incompressible Navier-Stokes equations

An implicit numerical scheme is developed based on the simplified marker and cell （SMAC） method to solve Reynolds-averaged equations in general curvilinear coordinates for three-dimensional （3-D） unsteady incompressible turbulent flow. The governing equations include the Reynolds-averaged momentum equations, in which contravariant velocities are unknown variables, pressure-correction Poisson equation and k- s turbulent equations. The governing equations are discretized in a 3-D MAC staggered grid system. To improve the numerical stability of the implicit SMAC scheme, the higherorder high-resolution Chakravarthy-Osher total variation diminishing （TVD） scheme is used to discretize the convective terms in momentum equations and k- e equations. The discretized algebraic momentum equations and k- s equations are solved by the time-diversion multiple access （CTDMA） method. The algebraic Poisson equations are solved by the Tschebyscheff SLOR （successive linear over relaxation） method with alternating computational directions. At the end of the paper, the unsteady flow at high Reynolds numbers through a simplified cascade made up of NACA65-410 blade are simulated with the program written according to the implicit numerical scheme. The reliability and accuracy of the implicit numerical scheme are verified through the satisfactory agreement between the numerical results of the surface pressure coefficient and experimental data. The numerical results indicate that Reynolds number and angle of attack are two primary factors affecting the characteristics of unsteady flow.     

GPU加速的二维流体实时流动仿真

Stable Fluids是计算机图形学领域标准的流体仿真技术,但其存在一定的数值耗散.针对这一问题,将计算流体动力学领域(CFD)成熟的SMAC法移植到计算机图形学领域,结合CFD领域合理的边界条件处理及其相关技术进行二维流体的实时流动模拟.基于2种技术在可编程图形硬件(GPU)上进行Kárman漩涡以及叶轮机械叶片尾流等算例仿真,试验表明SMAC法具有更强的视觉真实感和物理真实感,是纯CFD技术的移植和加速,因而具有一定的工程价值;所采用的噪声纹理混合技术能够准确反映流体流动的物理细节,适用于计算机图形学领域,并可应用于矢量场的数据可视化.     

无线传感器网络MAC协议研究与实现

一直以来,能量有效都是无线传感器网络MAC协议的研究重点。其中能量有效性比较好的如SMAC协议,采用周期性的睡眠机制可以很好的节约能量。然而,在SMAC协议中可能会由于一些节点遵守多个睡眠时间表,这就造成他们比其他节点更高的唤醒频率。因此,修改了原来的SMAC协议,使得所有节点尽可能的遵守一个时间表。修改后的协议延长网络的生存时间。通过仿真实验证明,该协议明显的提高网络寿命。     

An unstructured SMAC algorithm for thermal non-equilibrium two-phase flows

The SMAC (Simplified Marker And Cell) algorithm is extended for an application to thermal non-equilibrium two-phase flows in light water nuclear reactors (LWRs). A two-fluid three-field model is adopted and a multi-dimensional unstructured grid is used for complicated geometries. The phase change and the time derivative terms appearing in the continuity equations are implemented implicitly in the pressure correction step. The energy equations are decoupled from the momentum equations for faster convergence. The verification of the present numerical method was carried out against a set of test problems which includes the single and the two-phase flows. The results are also compared to those of the semi-implicit ICE method, where the energy equations are coupled with the momentum equation for pressure correction.     

无线传感器网络SMAC协议的节能改进

分析SMAC协议的工作过程以及自适应侦听的原理,针对该机制存在的无谓侦听问题提出改进方案。在协议中引入上下节点表,使节点自行判断是否应当被唤醒,避免无谓侦听,减少能量损耗,同时对该改进方案进行仿真。实验结果表明,该方案是有效的。     

Bivalent SMAC Mimetics for Treating Cancer by Antagonizing Inhibitor of Apoptosis Proteins

Inhibitors of apoptosis proteins (IAPs) inhibit caspase activity, allowing various cancers to reduce programmed cell death (apoptosis) and resist drug treatment. The second mitochondrial-derived activator of caspases (SMAC) protein is an endogenous IAP antagonist, which can be considered as a potential anticancer therapy. Small-molecule SMAC mimetics based on the Ala-Val-Pro-Ile motif have been validated as potent IAP antagonists. In particular, most bivalent SMAC mimetics, which target both the baculovirus IAP repeat 2 (BIR2) and BIR3 domains in X-linked IAP (XIAP), antagonize IAPs better than the corresponding monovalent mimetics. Here we focus on strategies for designing bivalent small-molecule SMAC mimetics and progress in using them to antagonize IAPs. We also consider their clinical potential. Our discussion will hopefully help guide further study of these interesting mimetics.