基于傅里叶基的自适应压缩感知重构算法

在压缩感知中,为了提高含噪信号的重构精度,提出了基于傅里叶基的稀疏度自适应匹配追踪算法.该算法在重构过程中采用相关系数作为匹配准则的基础上,创新性地利用傅里叶变换的共轭对称性,进一步严格控制索引值加入支撑集的过程;同时利用余量能量和余量能量变化率双门限作为停止迭代的依据;最后将估计的傅里叶域中的信号逆变换得到时域的重构信号.仿真实验表明,在同等噪声污染的情况下,该算法与同类算法相比有较高的重构精度.

基于改进傅里叶基的压缩感知频谱测量

提出一种由对称频点原子构成的改进傅里叶稀疏基,通过共轭原子与观测向量的相关累加,提高压缩感知在频谱重构中的抗噪性能,减少重构算法的计算量。在研究多频带信号频谱检测的基础上,提出频域子带表示字典,阐明字典原子间满足正交性并通过计算验证字典与观测矩阵的不相干性。实验结果表明,在多频带信号频谱测量的抗噪性能与检测性能上,基于频谱子带字典的压缩频谱感知方法优于传统的小波边缘检测方法。

航空重力傅里叶基追踪低通滤波方法研究

航空重力测量受到各种各样的高频噪声干扰,因此,低通滤波是提取重力信号的重要环节,其关键在于设计性能优越的低通滤波器.目前航空重力测量中常用FIR(Finite Impulse Response)低通滤波方法存在明显的滤波边缘效应,导致不得不舍弃边缘部分数据.针对这一问题,本文引入一种可以有效抑制边缘效应的新方法——傅里叶基追踪低通滤波方法(Fourier Basis Pursuit Low Pass Filter,FBPLPF).该方法通过基追踪准则,选择全局优化,采用凸优化中的内点算法,将低频信号挤压在低频上,实现低频信号与高频信号的有效分离,能够有效减少有限时间序列造成的谱污染和谱泄漏.最后利用仿真实验和实测数据对该方法进行了验证,均方根误差(RMS)东西测线为0.7×10^(-5) m·s^(-2),南北测线为1.4×10^(-5) m·s^(-2),与FIR低通滤波方法舍弃边缘数据后统计的均方根误差相当.表明该方法可以不舍弃或者舍弃少量边缘数据,提高航空重力数据的利用率.

基于非正交傅里叶基的冗余字典设计

在压缩感知理论的稀疏表示过程中,通常选择正交完备字典实现信号稀疏表示.冗余字典比完备字典表现出对信号更好的适应性,常见的冗余字典直接由两个或多个正交完备字典级联而成.为了设计对信号具有更好适应性的冗余字典,改变原有正交完备字典,通过对正交傅里叶完备字典中的原子进行扩展、延时、混叠等一系列变换,设计出一种新的非正交完备字典.在此基础上,将该完备字典与单位矩阵级联构造了新的非正交冗余字典.以一维信号作为测试信号,研究了冗余字典的性能.仿真实验结果表明提出的非正交冗余字典比正交傅里叶完备字典具有更好的稀疏性能和重构性能.

基于聚类和傅里叶基PSO-Elman谐波检测研究

谐波检测算法是有源电力滤波器(APF)动态响应速度和稳态精度的重要保障,针对传统检测算法易产生频谱泄漏和实时性较差的问题,将拥有全局优化能力的粒子群优化算法(PSO)与动态性能良好的Elman神经网络相结合,并重置激励函数构造一种基于傅里叶基(FB)的神经网络用于谐波检测。首先对谐波采样并聚类集成,聚类后同类别的数据作为网络的训练数据;再利用粒子群优化算法的寻优能力将最优权值和阈值赋予神经网络;最后利用训练好的模型对谐波参数进行预测。仿真结果表明,使用8万组k-means聚类集成数据训练的傅里叶基PSO-Elman网络比单纯的Elman神经网络拥有更高的参数辨识精度,谐波电流幅值与相位估计准确,验证了该检测方法的可靠性。

基于压缩感知的ISAR像目标旁瓣抑制新方法

在ISAR成像中,基于脉冲压缩的处理方法不可避免地会产生目标旁瓣现象。为了有效的抑制目标旁瓣,提高目标识别能力,文中提出了一种基于压缩感知理论的ISAR成像方法,该方法根据雷达原始回波信号与参考信号作差频处理后所得信号的稀疏特性,构造合理的傅里叶基矩阵实现雷达数据的稀疏表征,然后利用正交匹配追踪算法重构目标谱图,并得到目标旁瓣被有效抑制的目标ISAR像。最后,通过仿真实验验证了文中方法的有效性和可行性。

基于P-IFourier观测矩阵的宽带压缩感知方法

针对压缩感知理论在宽带频谱感知领域应用时重构精度差的问题,根据平稳信号在频域所表现出的稀疏特性,提出了一种基于P-IFourier(partial-inverse Fourier)观测矩阵的宽带压缩频谱感知方法。新方法首先将频谱感知问题建模为一个典型的压缩感知问题,利用相关性能优良的标准正交傅里叶基构造观测矩阵,使观测矩阵具有良好的重构性能和重构精度。仿真结果表明,相比于高斯随机观测矩阵和嵌入式混沌序列—循环Toeplitz结构观测矩阵,该方法在较低信噪比环境下能够明显降低信号重构的均方误差,并且在相同条件下的重构概率得到了明显改善。

基于电热耦合模型的功率器件热可靠性仿真分析

功率器件是现代电力电子技术的核心,分析和解决功率器件热可靠性问题是提高功率器件可靠性的重要课题。文中围绕功率器件在高温和温度变化下的可靠性这一主题,提出从仿真分析的角度对功率器件进行热可靠性分析评价,通过综合考虑电应力、热应力对器件电学特性、传热特性的影响,运用傅里叶基方法和Cauer网络模型建立器件的电热耦合模型,结合失效物理模型对器件进行寿命预测和薄弱环节分析,相比可靠性试验方法具有显著的周期和成本优势。

基于复指数基扩展方法的快时变信道模型

研究基于复指数基扩展方法的快时变信道模型,以一组傅里叶基作为模型的基函数,将信道的冲激响应展开成这一组傅里叶基的线性叠加。文章给出综合考虑NMMSE(归一化最小均方误差)和复杂度的算法,并且分析不同模型阶数、不同信道估计时间间隔以及不同移动台速度对信道模型的影响。该信道模型可以运用于未来第五代高速移动通信系统(例如高铁通信)的信道估计中,为系统设计提供重要的依据。

经典启发式量子计算整数分解问题

大整数分解是破解RSA加密算法的基本途径之一,由于计算量过大,经典计算机难以有效解决大整数分解问题.量子叠加和纠缠的特性,使得量子计算可以对经典问题求解起到并行加速的作用.Shor算法是一个能够高效快速对大整数分解的量子算法.然而,Shor算法需要进行模幂运算,使得电路设计极其复杂,时间复杂度也高.为了解决该问题,基于经典计算的启发,提出一种启发式算法:利用量子计算的并行性,设计相关Oracle去计算2个奇数叠加态a和b的乘积,再将叠加态乘积的负相位加在大整数N的傅里叶基上,当结果为0时,利用多控制门便能够将满足pq=N的一个质因子p给提取出来.该文提出的算法最低仅需要2n个量子比特,时间复杂度也达到指数级加速.另外,该文在QISKit框架上实现了该算法,证明了算法的可行性和通用性.

Hermiticity of Hamiltonian Matrix using the Fourier Basis Sets in Bond-Bond-Angle and Radau Coordinates

In quantum calculations a transformed Hamiltonian is often used to avoid singularities in a certain basis set or to reduce computation time. We demonstrate for the Fourier basis set that the Hamiltonian can not be arbitrarily transformed. Otherwise, the Hamiltonian matrix becomes non-hermitian, which may lead to numerical problems. Methods for cor- rectly constructing the Hamiltonian operators are discussed. Specific examples involving the Fourier basis functions for a triatomic molecular Hamiltonian （J=0） in bond-bond angle and Radau coordinates are presented. For illustration, absorption spectra are calculated for the OC10 molecule using the time-dependent wavepacket method. Numerical results indicate that the non-hermiticity of the Hamiltonian matrix may also result from integration errors. The conclusion drawn here is generally useful for quantum calculation using basis expansion method using quadrature scheme.

Microwave radiation one-pot synthesis of chloropropyl-functionalized mesoporous MCM-41

Chloropropyl-functionalized mesoporous MCM-41（MCM-41-（CH2）3Cl） was synthesized in alkaline medium by the microwave radiation one-pot method, using cetyltrimethy-lammoniumbromide （CTAB） as novel template, tetraethoxysilane （TEOS） as silica source, and chloropropyltriethoxysilane （C1PTES） as the coupling agent. The microstructure of MCM-41-（CH2）3Cl was characterized by the means of X-ray diffraction （XRD）, nitrogen absorption-desorption, Fourier transform infrared spectroscopy （FT-IR）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. The results show that a successful synthesis of MCM-41-（CH2）3Cl with well structure is obtained. The optimal microwave power is 120 W and the best microwave time is 50 rain. The dosage of chloropropyltriethoxysilane on the structure of chloropropyl-functionalzed MCM-41 was also investigated. It is found that the chloropropyltriethoxysilane volume between 0.8 mL and 1.6 mL is favorable for the formation of highly ordered MCM-41-（CH2）3Cl mesostructure.

Effects of Activation Atmospheres on Structure and Activity of Mo-based Catalyst for Synthesis of Higher Alcohols

Activated carbon supported Mo-based catalysts were prepared and reduced under different activation atmospheres, including pure H2, syngas （H2/CO=2/1）, and pure CO. The cat- alysts structures were characterized by X-ray diffraction , X-ray absorption fine structure, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The catalytic per- formance for the higher alcohol synthesis from syngas was tested. The pure H2 treatment showed a high reduction capacity. The presence of a large amount of metallic CoO and low valence state Mo^φ＋ （0〈φ〈2） on the surface suggested a super activity for the CO dissoci- ation and hydrogenation, which promoted hydrocarbons formation and reduced the alcohol selectivity. In contrast, the pure CO-reduced catalyst had a low reduction degree. The Mo and Co species at the catalyst mainly existed in the form of Mo^4＋ and Co^2＋. The syngas- reduced catalyst showed the highest activity and selectivity for the higher alcohols synthesis. We suggest that the syngas treatment had an appropriate reduction capacity that is between those of pure H2 and pure CO and led to the coexistence of multivalent Co species as well as the enrichment of Mo~＋ on the catalyst＇s surface. The synergistic effects between these active species provided a better cooperativity and equilibrium between the CO dissociation, hydrogenation and CO insertion and thus contributed beneficially to the formation of higher alcohols.

Digital Channelization Technology for HF Communication Base on Fast Filter Bank

Channelization typically realized by digital filter banks is an important topic in high frequency(HF) communication and software defined radios(SDR) areas. Channelization has a rigorous requirement for the characteristic of frequency response, e.g., steep transitional band and sharp decay. To address this issue, we investigated the feasibility and implementation of applying fast filter bank(FFB) in channelization in this paper. We analyzed the butterfly structure of FFB similar with fast Fourier transform(FFT), in which prototype sub-filters are cascaded to achieve a low complexity. Hence, it is suitable for designing filter bank with steep transitional band and sharp decay in stop-band. Moreover, we designed a pipelined structure of FFB to achieve a balance between area and performance. Design example shows that FFB has lower computational complexity compared with the other filter banks.

Polyhydroxyl-aluminum pillaring improved adsorption capacities of Pb^(2+) and Cd^(2+) onto diatomite

In order to greatly improve adsorption capacity, the diatomite was pillared by polyhydroxyl-aluminum.A series of adsorption tests were conducted to obtain the optimum condition for pillared diatomite synthesis. The scanning electron microscopy （SEM）, Fourier transform infrared spectroscopy （FTIR）, surface area and porosity analyzer and micro-electrophoresis were used to determine pore structure and surface property.The pillared diatomite attaining the optimal adsorption densities （qe） of Pb^2＋ and Cd^2＋ was synthesized with the following conditions： Addition of pillaring solution containing Al3＋-oligomers with a concentration range of 0.1-0.2 mol/L to a suspension containing Na＋-diatomite to obtain the required Al/diatomite ratio of 10 mmol/g; synthesis temperature of 80 ℃ for 120 min; aging at a temperature of 105 ℃ for 16 h. The adsorption capacities of Pb^2＋ and Cd^2＋ on pillared diatomite increase by 23.79% and 27.36% compared with natural diatomite, respectively. The surface property of pillared diatomite is more favorable for ion adsorption than natural diatomite. The result suggests that diatomite can be modified by pillaring with polyhydroxyl-aluminum to improve its adsorption properties greatly.

Characterization of calcium deposition induced by Synechocystis sp. PCC6803 in BG11 culture medium

Calcium carbonate （CaCO3） crystals in their preferred orientation were obtained in BG11 culture media inoculated with Synechocystis sp. PCC6803 （inoculated BG11）. In this study, the features of calcium carbonate deposition were investigated. Inoculated BGll in different calcium ion concentrations was used for the experimental group, while the BGll culture medium was used for the control group. The surface morphologies of the calcium carbonate deposits in the experimental and control groups were determined by scanning and transmission electron microscopy. The deposits were analyzed by electronic probe micro-analysis, Fourier transform infrared spectrum, X-ray diffraction, thermal gravimetric analysis and differential scanning calorimetry. The results show that the surfaces of the crystals in the experimental group were hexahedral in a scaly pattern. The particle sizes were micrometer-sized and larger than those in the control group. The deposits of the control group contained calcium （Ca）, carbon （C）, oxygen （O）, phosphorus （P）, iron （Fe）, copper （Cu）, zinc （Zn）, and other elements. The deposits in the experimental group contained Ca, C, and O only. The deposits of both groups contained calcite. The thermal decomposition temperature of the deposits in the control group was lower than those in the experimental group. It showed that the CaCO3 deposits of the experimental group had higher thermal stability than those of the control group. This may be due to the secondary metabolites produced by the algae cells, which affect the carbonate crystal structure and result in a close-packed structure. The algae cells that remained after thermal weight loss were heavier in higher calcium concentrations in BGll culture media. There may be more calcium- containing crystals inside and outside of these cells. These results shall be beneficial for understanding the formation mechanism of carbonate minerals.

Adsorption behavior of heptyl xanthate on surface of ZnO and Cu(Ⅱ) activated ZnO using continuous online in situ ATR-FTIR technology

A continuous online in situ attenuated total reflection Fourier-transform infrared(ATR-FTIR)spectroscopic technique was used to investigate the adsorption and desorption kinetics of heptyl xanthate(KHX)on the surface of ZnO and Cu(Ⅱ)activated ZnO.The results showed that Cu(Ⅱ)facilitated the xanthate adsorption process on the surface,and led to the formation of cuprous xanthate(CuX),dixanthogen(X_(2))and xanthate aggregates.The adsorption of xanthate on the surface of ZnO and Cu(Ⅱ)activated ZnO was found to both follow the pseudo-first-order kinetic model.When the NaOH solution was used as a desorption agent,the adsorbed xanthate can largely be removed due to the competition between OH^(−)and HX−.However,for Cu(Ⅱ)activated ZnO,the peak intensities at 1197 and 1082 cm^(−1) had no obvious weakening,and the absorption intensities at 1261 and 1026 cm^(−1) increased in the first 5 min,indicating an ion-exchange reaction between OH^(−)and surface zinc bonded xanthate HX−and the reorganization of adsorbed xanthate.

Time evolution of coal structure during low temperature air oxidation

The time evolution of coal structure during low temperature oxidation was investigated by oxidizing coal samples in air at 120℃ for periods of up to 14 days. The structure of the oxidized coal samples was char- acterized by Fourier transform infrared spectroscopy （FFIR） and curve fitting analysis. The results show that carboxyl and ether groups are the main oxygen containing moieties in oxidized coal. Ethers are most abundant during the first 3 days of oxidation, thereafter carboxyl groups predominate. The content of carboxyl and ester functionality increases with oxidation time. The other oxygen containing groups vary in concentration over time. The amount of hydroxyl groups first decreases then increases and finally decrease again during the oxidation. The aliphatic structure and the degree of branching of the aliphatic chains is reduced as the oxidation proceeds. The proportion of aromatic structure increases with oxida- tion time. Obvious decomposition of aromatic rings occurs after about 9 days of oxidation. The aryl ester bands and the CH3/CH2 ratio both have a good linear relationship to oxidation time.

Pervaporation of Aqueous Solution of Acetaldehyde Through ZSM-5 Filled PDMS Composite Membrane

Hydrophobic ZSM-5 zeolite filled polydimethylsiloxane （PDMS） composite membranes with Nylon micro-filtration membrane as the support layer were prepared to separate acetaldehyde from its aqueous solution. The composite membranes were characterized by Fourier transform infrared spectroscopy and X-ray diffraction. Their structural morphology and thermal stability were also examined. The swelling study showed that the composite membranes presented higher degree of swelling in aqueous solution of acetaldehyde than in pure water at 25℃,

Preparation and characterization of sulfated TiO_2 with rhodium modification used in esterification reaction and decomposition of methyl orange

A unique Rh/TiO2 solid acid catalyst modified with H2S04 was synthesized and evaluated in the esterification reaction of propylene glycol methyl ether and decomposition of methyl orange （MO） in aqueous phase under halogen lamp irradiation. For this purpose, rhodium （Rh） nanoparticles were loaded on S02-/Ti02 via the photo-deposition method. It was found that S024-/Rh-Ti02 exhibited stronger catalytic activity than S02-/ Ti02. The new catalysts were characterized by X-ray powder diffraction （XRD）, Brunauer-Emmett-Teller （BET）, Transmission electron microscopy （TEM） and high-resolution （HRTEM）, X-ray photoelectron spec- troscopy （XPS） and Fourier Transform infrared spectroscopy （FrlR）. Results from XRD and BET show that S02-/Rh-Ti02 has higher specific surface area and smaller pore size than S02-fri02. The distribution of loaded Rh was found to be uniform with a particle size of 2-4 nm. Data from XPS reveal that Rh primarily exists as Rh~ and Rh3 ＋ in Rh-Ti02 and SO^-/Rh-TiO~. These valence forms of Rh likely contribute to the en- hanced catalytic activity. Furthermore, FT-IR spectra of the catalysts show an abundance of surface hydroxyl groups, which help the formation of hydroxyl radicals and the enhancement of surface acid density. The results show that more acid sites are formed on the sulfated Rh-Ti02, and these acidic sites are largely responsible for improving the catalytic performance. This superior SO]-/Rh-Ti02 catalyst has potential applications in reactions reouirinz efficient acid catalysts, includinz esterification reactions and waste water treatment.