查询词典 approximation method

Based on the conservation law, applying appropriate rezone methods for meshes we modify the 9-point method to reduce computation error due to poor regularity of the meshes and low precision due to the approximation to vertices values by an average of neighboring cell values. The nonlinear system obtained is a different system from the 9-point scheme.

该方法从守恒方程出发，将九点差分格式应用于按某种合适的方式进行重分之后的网格上，减少由于网格正则性差以及网格节点上的物理量采用周围网格量的加权平均等原因所引起的计算误差，得到一个新的但其解仍然逼近原来网格上的物理量的方程组。

The paper investigates both block-type pilot linear minimum mean square error algorithm and IEEE802.16 OFDM channel estimation analysis. Simulation results confirm the block-type pilot structure is more suitable for IEEE802.16 system. An optimal pilot setting algorithm, based on space frequency domain, is explored and the pilot chart is presented. The proposed algorithm finds its application in MIMO-OFDM. Simulation results show the algorithm presents a good approximation to the perfect channel state information curve, with about 2dB difference in SNR. The simulation results also demonstrate the algorithm achieves fairly high stability in the environment of fast fading, performance of the proposed algorithm is better that of pilot training channel estimation.3. Taking into account the characteristics of IEEE802.16 OFDM system, OFDM system simulation platform is constructed in Matlab, exploiting simulink as a tool. OFDM modulation and demodulation simulation system are configured on LabVIEW platform. All the system signal processing is simulated, including defining system parameters, designing modulation model, and verifying all the proposed algorithms under different environments, such as white Gaussian noise, multi-path fading, with or without guard interval etc. Bit error performance is evaluated. The research provides valid theoretical basis for practical OFDM system performance evaluation.4. Taking advantage of software radio, the paper designs a hardware platform with both 256-IFFT/FFT and 512-IFFT/FFT OFDM schemes co-existing in one platform. You can predetermine one from the two schemes to carry out almost the same model function with different system performance and parameter setting.5. Referring to IEEE802.16 standard, the paper proposes a design method for generating signals and frames suitable for laboratory investigations implemented in laboratory environment.6. Based on 6701evm digital evaluation card, combined with analogy front-end, the paper designs a DSP software model to deal with baseband signal processing. An overall OFDM scheme, with modulation and demodulation function, is accomplished.

讨论分析了MIMO-OFDM中一种基于空频域的最优导频设置算法，给出了导频图案，通过仿真实验表明，该算法与理想的信道状态信息曲线非常接近，信噪比差距约在2dB左右，并且在快衰落条件下具有较好的稳定性，其性能要优于基于前导训练的信道估计方法。3、根据IEEE802.16OFDM系统特点，论文分别在Matlab中应用Simulink工具构建OFDM系统仿真平台、在LabVIEW平台上实现了OFDM调制解调仿真系统，模拟了整个系统的信号流程，进行了OFDM仿真系统参数的选择和调制模块的仿真设计、论证各算法性能，并根据各种不同的条件：例如高斯噪声、多径衰落、有无保护间隔等，对系统的误码特性进行了评估，为正确评价实际OFDM系统的性能提供了有效的理论依据。4、论文以软件无线电思想作为指导，提出了以256点IFFT／FFT为核心和以512点IFFT／FFT为核心的两种OFDM算法模式并存于同一个硬件平台、且可预选的方案，它们在参数选取和性能指标上有所差异，均实现了相似的模块和功能。5、论文参考IEEE 802.16无线网络标准的参数设置，针对本设计系统的应用环境和系统硬件的性能速率，提出了一种应用于实验室环境的信号结构、帧格式等参数设计。6、论文基于TI公司的6701evm数字评估板卡，结合模拟前端搭建数字中频平台，设计了基带处理的DSP软件模块并进行系统调试，基本实现了一套完整的OFDM调制解调方案。

In order to study the changing process of Barium strontium titanate Ba(subscript xSr(subscript 1-x) TiO3, BST from cubic phase to the tetragonal phase with Ba doping and the ferroelectric characteristic of BST, the total energy of BST with different mole ratio of Ba/Sr when Ba doped was calculated and the fine structure determined, based on general gradient approximation, by means of ultrasoft pseudopotentials plane wave method.

为了研究钛酸锶(SrTiO3， ST)中随Ba的掺入，其晶体从顺电相到铁电相的变化过程及四方相钛酸锶钡Ba(下标 xSr(下标 1-x)TiO3， BST的铁电性。在广义梯度近似下，利用超软赝势平面波方法计算了不同Ba/Sr摩尔比BST的总能量，确定了BST的精细结构。

There are few equivalent circuit modeling methods for UWB antennas. This thesis compares the characteristic of some existing modeling methods and presents a general and precise modeling method for UWB antennas. Firstly, establish the narrowband model of the antenna, and compute the difference between input admittances of the antenna and its narrowband model. Secondly, implement rational approximation of the difference to build the macromodel, and convert it into SPICE equivalent circuits. Lastly, combine the narrowband model and the macromodel to form the ultimate equivalent circuit model of the antenna.

本论文针对目前UWB天线等效电路建模方法比较少的现状，结合现有的天线建模方法的一些特点，研究了一种系统通用、模型精度高的新建模方法：首先建立超宽带天线的窄带模型，计算天线及其窄带模型导纳的差值；接着对差值进行有理多项式拟合，得到相应的宏模型，并转化为SPICE等效电路；最后合并窄带模型与宏模型电路，得到天线等效电路模型。

We used different methods to calculate luminosity in order to assure its reliability. Structure function method is adopted to derive the radiatively corrected cross section whose accuracy is up to 1%. The corrections from vacuum polarization and effect of energy spread are also studied. The final analytical approximation formulaes of the observed cross sections are worked out. Different fitting methods are carried out to fit the resonances according to different requests.

模拟的分布图的仔细对比，并兼顾实验的要求，得到每种事例对应的选择条件，特别是在处理积分亮度时，更是采用了不同的方法，以保证亮度计算的可靠性；采用结构函数的方法推导出截面的辐射修正公式，精确度达到了1％的水平，研究了真空极化给拟合公式带来的修正，并考虑了束流能散的影响，计算出最终的观测截面的解析近似式；对于三个共振态的拟合，针对不同的要求，采用了不同的拟合方法；同时在M.C。

The results show that for SiO〓 and GeO〓 glasses, the Rayleigh scatterings arise mainly from the disorders of the densities of atoms, consistent with the assumption of the fictive temperature approximation which is the usual method used in the existing optical fiber theory to calculate Rayleigh scatterings in glasses.

计算结果表明：对SiO〓和GeO〓玻璃，现有光纤理论的瑞利散射处理方法——虚温度近似所作关于玻璃中瑞利散射主要来自玻璃的原子密度无序的假设能很好成立。

The split between the two groups can hardly be papered over.

这两个团体间的分歧难以掩饰。

This approach not only encourages a greater number of responses, but minimizes the likelihood of stale groupthink.

这种做法不仅鼓励了更多的反应，而且减少跟风的可能性。