关于Coates图的1-因子的算法

本文是作者1982年一文的继续,根据该文使用星积产生1-因子的定理,我们先讨论了一类特殊图,阐明星积和求排列的关系,然后推广到一般情况。最后,给出求Coates图的1-因子的算法。     

LDPC编码MC-LDS系统联合因子图的改进PEG设计

作为非正交多址(Non-orthogonal Multiple Access,NOMA)技术之一,基于稀疏因子图的多载波低密度序列(Multi-carrier Low-density Signature,MC-LDS)技术由于其译码复杂度较低,可以与同样基于稀疏因子图的低密度奇偶校验码(Low Density Parity Check Code,LDPC)同时使用。MC-LDS技术的检测算法和LDPC的译码算法都是基于稀疏因子图上的消息传递算法(Message Passing Algorithm,MPA),但现有研究中,对于MC-LDS和LDPC稀疏因子图的设计一般独立进行,得到的结果往往不是最优的。为此,提出一种将LDPC与MC-LDS稀疏因子图进行联合分析设计的方法,采用改进的渐进边增长(Progressive Edge Growth,PEG)方法,消除了MC-LDS与LDPC联合因子图中各自的因子图之间互相耦合导致的短环,构建了性能良好的联合稀疏因子图。仿真结果表明,对于不同的LDPC码长,所提方案获得了0.5~0.6 dB的性能增益。     

三维荧光光谱技术及平行因子分析法在绿茶分析及种类鉴别中的应用

提出了一种绿茶成分分析和种类鉴别的新方法。利用FS920荧光光谱仪测量得到国内生产的26个绿茶样品的三维荧光光谱矩阵(EEMs),建立了不同种类绿茶在特定范围内(激发波长为300～550 nm,发射波长为310～750 nm)的三维荧光光谱图和等高线光谱图。采用平行因子分析法(PARAFAC)计算得到绿茶的3因子激发-发射光谱轮廓图和样品因子投影得分图。通过因子光谱特征分析确定绿茶的三种主要成分(茶多酚、黄酮醇及叶绿素);通过三维荧光光谱图和等高线光谱图的图谱特征和样品因子投影得分图的分析,证实三维荧光光谱技术和平行因子分析法对绿茶进行成分分析和种类鉴别,是一种高效、精确的方法。     

利用图的完全1-因子分解构造双容错数据布局

本文介绍了一种full-2码的虚拟顶点简单图表示法，简化了双容错数据布局判定定理，最优冗余数据布局定理和双容错数据布局的构造．本文还提出了一种基于完全二部图（对应二维奇偶校验码）的完全1-因子分解的双容错数据布局构造方法，可构造高扩展性双容错数据布局BG-HEDP．与B-CODE等同类双容错数据布局相比，BG-HEDP同样具有更新代价最优、高可靠性和低编码／解码复杂度的优点，冗余率接近最优，而扩展性更好．     

由-5V产生1A、3.3V的简单电路

图1所示的电路,利用脉冲频率调制(PFM)结构从-5V电源产生+3.3V输出,不需要任何外部变压器。当有一个稳定的-5V电源,并且不要求隔离时,这是一个非常实用的电路。开关模式调节器(IC1)采用传统的升压电路配置,工作在非自举模式。利用相关IC可以实现+5V到+8.3V的转换,但是,图1所示连接(GND和AGND连接到-5V,V+连接到系统地)使电路产生了一个相对于系统地的3.3V输出。转换效率在1A负载下可以达到90%,对于小于10mA的轻负载,效率可以达到84%(图2)。图3示出输出电压(由外部电阻设定)与负载电流的关系曲线。对于3.3V输出,当负载电流小于500m…     

关于FFT算法流图的记忆方法

数字信号课中要求熟练掌握有关按时间抽取(DIT)的FFT算法(库里-图基算法)和按频率抽取(DIF)的FFT算法(桑德-图基算法),本文从这两个方面总结整理了这两种算法的记忆方法,帮助读者在学习FFT的算法流图后快速熟练记忆此流程图.     

溶胶-凝胶法制备外延Ba1-xSrxTiO3薄膜及其结构与性能研究

应用溶胶-凝胶技术在Pt/MgO(100)衬底上成功地制备了Ba0.65Sr0.35TiO3外延薄膜.XRD和SEM分析结果表明该薄膜在O2气氛中650℃热处理1h后,其(001)面是沿着Pt(100)和MgO(100)面外延取向生长的;薄膜表面均匀致密,厚度为260nm,平均晶粒大小为48.5nm.当测试频率为10kHz时,BST薄膜的介电常数和损耗因子分别为480和0.02.介电常数-温度关系测试结果表明sol-gel工艺制备的Ba0.65Sr0.35TiO3薄膜其居里温度在35℃左右,且在该温度下Ba0.65Sr0.35TiO3薄膜存在扩散铁电相变特征.当外加偏置电压为3V时,BST薄膜的漏电流密度为1.5×10-7A/cm2.该薄膜可作为制备新型非制冷红外焦平面阵列和先进非制冷红外热像仪的优选材料.     

1-丁基-3-甲基咪唑离子液体在超级电容器中的应用

两步法合成了1-丁基-3-甲基咪唑三氟乙酸盐(BMI-CF3CO2)、1-丁基-3-甲基咪唑六氟磷酸盐(BMI-PF6)及1-丁基-3-甲基咪唑四氟硼酸盐(BMI-BF4)三种离子液体,研究了这三种离子液体所制超级电容器的电化学性能。结果表明:BMI-CF3CO2在电化学稳定性及充放电效率等方面优于BMI-PF6和BMI-BF4;BMI-CF3CO2离子液体电解液电势窗口达到4.0V,所制备的超级电容器在3.6V电压下循环寿命超过1000次。     

基于因子图的自适应波束形成

图模型具有广泛的应用,它为许多问题提供了一种新的表达方式和研究思路。因子图作为一类重要的图模型,尤其适用于多变量的复杂统计模型。因子图的引入可以使复杂的多变量问题得到简化。因子图理论在系统建模以及信号检测和估计算法中有着重要的应用。国内外不少学者将因子图理论应用于复杂的通信信号处理,但目前很少见到将因子图理论应用在雷达信号处理中。为了将因子图理论作为一种有效的工具应用于雷达信号处理,提出了用因子图理论实现雷达信号处理中的自适应波束形成技术（ADBF）的方法,这为用图模型研究雷达信号处理提供了一个很好的思路。     

平行因子法因子数目选择流程改进设计与验证

针对平行因子算法在分解三维荧光光谱中存在的模型因子数目选择流程不明确的问题,提出了核心对角矩阵-核一致函数-恒波长残差图这一改进因子数目选择流程.自行编写改进平行因子分析算法,以腐植酸作为检测物质验证该因子数目选择流程的准确性.结果 表明,结合改进流程,在激发光和发射光分别在350～450nm/350 ～620nm、因子数为4时,核心对角矩阵分布满足需求,核一致函数为52％,在标准区间内,拟合图残差最小,分解效果最优.相较于使用单一方法进行判断,上述组合选择流程逻辑性更强,准确性更高,在实际应用中可以快速确定因子数目.4个因子分别是两个位于为360～370nm/450～500nm和350～360nm/450～500nm的类腐植酸A类因子、一个位于365～375nm/475～525nm的类腐植酸C类因子、一个位于380～390nm/475～525nm处的土壤富里酸因子,同时通过分析不同浓度腐植酸的溶液,发现当浓度由20 mg/L增至200 mg/L时,因子的组成和贡献率差别不大,即浓度变化并未改变溶液性质.     

关于无重复分解产生树的定理

本文定义了一种二分图,称之为互补划分图。利用此图容易证明有关互补划分的定理,并可得到一个判别是否是本性互补划分的较弱的条件。     

Constellations matched to the Rayleigh fading channel

We introduce a new technique for designing signal sets matched to the Rayleigh fading channel, In particular, we look for n-dimensional (n⩾2) lattices whose structure provides nth-order diversity. Our approach is based on a geometric formulation of the design problem which in turn can be solved by using a number-geometric approach. Specifically, a suitable upper bound on the pairwise error probability makes the design problem tantamount to the determination of what is called a critical lattice of the body S={x=(x₁, ···, x_n)∈Rⁿ, |Π_i=1ⁿx_i|⩽1}. The lattices among which we search for an optimal solution are the standard embeddings in R ⁿ of the number ring of some totally real number field of degree n over Q. Simulation results confirm that this approach yields lattices with considerable coding gains     

In Situ Topochemical Transformation of ZnIn2S4 for Efficient Photocatalytic Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran

Photocatalytic selective oxidation of 5-hydroxymethylfurfural (HMF) coupled H₂ production offers a promising approach to producing valuable chemicals. Herein, an efficient in situ topological transformation tactic is developed for producing porous O-doped ZnIn₂S₄ nanosheets for HMF oxidation cooperative with H₂ evolution. Aberration-corrected high-angle annular dark-field scanning TEM images show that the hierarchical porous O-ZIS-120 possesses abundant atomic scale edge steps and lattice defects, which is beneficial for electron accumulation and molecule adsorption. The optimal catalyst (O-ZIS-120) exhibits remarkable performance with 2,5-diformylfuran (DFF) yields of 1624 µmol h⁻¹ g⁻¹ and the selectivity of >97%, simultaneously with the H₂ evolution rate of 1522 µmol h⁻¹ g⁻¹. Mechanistic investigations through theoretical calculations show that O in the O-ZIS-120 lattice can reduce the oxidation energy barrier of hydroxyl groups of HMF. In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) results reveal that DFF^* (C₄H₂(CHO)₂O^*) intermediate has a weak interaction with O-ZIS-120 and desorb as the final product. This study elucidates the topotactic structural transitions of 2D materials simultaneously with electronic structure modulation for efficient photocatalytic DFF production.     

End-to-end data paths: quickest or most reliable?

Let N=(V,E,c,l,p) be a network where V is the set of n vertices, E is the set of m edges, c(u,v)⩾0 is the capacity of edge {u,v}, l(u,v)⩾0 is the delay of edge {u,v}, p(u,v)∈[0,1] is the operational probability of edge {u,v}. In this letter, we present O(rm+rnlog n) time algorithms for the most reliable quickest path problem and the quickest most reliable path problem, where r is the number of different capacity values in the network     

On the stability of real exponential polynomials with interval-valued delays

We consider the family ? of exponential polynomials. $$f_T (z): = f_0 (z) + f_1 (z)e^{ - zT_1 } + f_2 (z)e^{ - T_2 } + \cdots + f_n (z)e^{ - zT_n } ,T : = T_1 \times T_2 \times \cdots \times T_n ,$$ where thef _k(z),k=0(1)n, are real polynomials under the degree restriction deg(f ₀)>deg(f _k),k=1(1)n, and theT _k,k=1(1)n, are intervals inR ₊. The functions in ? are characteristic functions of linear, retarded dynamical systems with constant coefficients and finitely many interval-valued discrete delays. A stability criterion for ? is expounded; ? is stable if (a) ? contains a stable member and (b) a certain functionalT:S(y) →; {0, 1} vanishes fory in a compact interval inR ₊. Here,S(y) is the boundary of a circular are regionS(y) in the complex plane derived fromf _T. Tools needed for a computer implementation are compiled.     

Minimal distance lexicographic codes over an infinite alphabet

The author investigates the properties of minimal distance lexicographic codes, or lexicode, over the ordered infinite alphabet N={0,1,2…}. The author presents a method for computing the basis of such a code. It is shown that any lexicographic code S with minimal distance d has a unique basis where each basis vector is a one followed by a string of zeros, followed by d-1 nonzero digits a_ij. Furthermore, the matrix A=(a_ij) has no singular minors over the nim-field. The dual code when S has finite length is also computed. The author develops a systematic approach to determine which words belong to these lexicodes     

Low-noise solar-blind AlxGa1-xN-based metal-semiconductor-metal ultraviolet photodetectors

We report the growth, fabrication, and characterization of high performance Schottky metal-semiconductor-metal solar-blind photodetectors fabricated on epitaxial Al_0.4Ga_0.6N layers grown by metalorganic chemical vapor deposition. The devices exhibited low dark current (<2 pA at 30 V) and a gain-enhanced ultraviolet (UV) photocurrent for bias voltages >40 V. The gain was corroborated by external quantum efficiency measurements reflecting a quantum efficiency as high as 49% (at=272 nm) at 90 V bias, with a corresponding responsivity R=107 mA/W. A visible-to-UV rejection factor of more than three orders of magnitude was demonstrated. Time-domain and frequency-domain speed measurements show a 3-dB bandwidth of ∼100 MHz. Low-frequency noise measurements have determined a detectivity (D^*) as high as 3.3 10¹⁰ cm·Hz^1/2/W for a 500 Hz bandwidth at 37 V bias.     

Sb2(SxSe1−x)3 sensitized solar cells prepared by solution deposition methods

Solid state semiconductor sensitized solar cells are a very active research subject in emerging photovoltaic technologies. In this work, heterojunctions of antimony sulfide-selenide (Sb₂(S_xSe_1−x)₃) solid solution as the absorbing material and cadmium sulfide coated titanium dioxide (TiO₂/CdS) as the electron conductor have been developed with solution deposition methods such as spin-coating, successive ionic layer adsorption and reaction (SILAR), and chemical bath deposition. In particular, CdS has been deposited on mesoporous TiO₂ layers by SILAR deposition, followed by the chemical deposition of Sb₂(S_xSe_1−x)₃. It was found that by increasing the number of CdS SILAR deposition, both the open circuit voltage V_oc and the short circuit current density J_sc of the Sb₂(S_xSe_1−x)₃ sensitized solar cells had been increased from 153 to 434 mV and 0.77–9.73 mA/cm², respectively. This improvement was attributed to the fact that the presence of the CdS on TiO₂ surface reduces the formation of undesired Sb₂O₃ and promotes a better nucleation of the Sb₂(S_xSe_1−x)₃ during the chemical bath deposition. The best result was obtained for the solar cell with 30 cycles of CdS which produced a V_oc of 434 mV, a J_sc of 9.73 mA/cm², and a power conversion efficiency of 1.69% under AM1.5 G solar radiation.     

A novel analytical model of the vertical breakdown voltage on impurity concentration in top silicon layer for SOI high voltage devices

A novel analytical model of the vertical breakdown voltage (V_{B , V} ) on impurity concentration (N_d ) in top silicon layer for silicon on insulator high voltage devices is first presented in this article. Based on an effective ionisation rate considering the multiplication of threshold energy ε_T in the electron, a new formula of silicon critical electric field E_{S , C} on N_d is derived by solving a 2D Poisson equation, which increases with the increase in N_d especially at higher impurity concentration, and reaches up to 68.8?V/µm with N_d  = 1 × 10¹⁷?cm^?3 and 157.2?V/µm with N_d  = 1 × 10¹⁸?cm^?3 from the conventional about 30?V/µm, respectively. A new physical concept of critical energy ε_B is introduced to explain the mechanism of variable high E_{S , C} with heavy impurity concentration. From the E_{S , C} , the expression of V_{B , V} is obtained, which is improved with the increasing N_d due to the enhanced E_{S , C}. V_{B , V} with a dielectric buried layer thickness (t_I ) of 2?µm increases from 428?V of 1 × 10¹⁷?cm^?3 to 951?V of 1 × 10¹⁸?cm^?3. The dependence of N_d and top silicon layer thickness (t_S ) for an optimised device is discussed. 2D simulations and some experimental results are in good agreement with the analytical results.     

Covalent Furan-Benzimidazole-Linked Polymer Hollow Fiber Membrane for Clean and Efficient Photosynthesis of Hydrogen Peroxide

Photocatalytic H₂O₂ production by conversion of O₂ in aqueous solution is often challenged by the use of sacrificial agents, the separation of powdery photocatalysts, solution, and contaminants, and low activity of photocatalyst. Herein, a membrane of covalent furan-benzimidazole-linked polymer (Furan-BILP) with both O- and N-containing heterocycles bonded via O C CN is reported for the first time as a photocatalyst to harvest clean H₂O₂ in pure water with high-performance. A coordination-polymer hard template strategy is developed to produce Furan-BILP hollow microfibers that can be further assembled into membranes with desired sizes. The resultant Furan-BILP membrane directly delivers clean H₂O₂ solution as the product with a high H₂O₂ production rate of 2200 µmol g⁻¹ h⁻¹ in pure water. Density functional theory calculations and experiment results indicate that the C atom from Furan ring on the linkage binds to the adsorbed OOH^*, the H atom of OOH^* forms a hydrogen bond with the N atom in the benzimidazole ring, thus the intermediate six-membered ring structure stabilizes the OOH^* and favors 2e-ORR. The strategy using both molecular engineering to tune the electronic structure and macrostructural engineering to shape the morphology may be applied to design other coordination organic polymer photocatalysts with further improved performance.