关于连续映射半群拓扑熵的一点注记

本文研究了度量空间中连续映射构成半群的拓扑熵.利用Patr′ao~([8])的方法,给出了度量空间中两种有限个连续映射构成的半群的拓扑d-熵的定义,比较了两种拓扑d-熵的大小.证明了局部紧致可分度量空间上有限个真映射构成的半群的拓扑d-熵和它的一点紧化空间上对应的拓扑熵相等.上面结果推广了Patr′ao的相应结论.     

Narrow Band Gap and Roomtemperature Ferromagnetism in KNb1-xFexO3-δ

We have investigated the structure, optical and magnetic properties of ferroelectric KNb_1-xFe_xO_3-δ (X=0, 0.01, 0.03, 0.05, 0.10, 0.15, 0.20, 0.25) synthesized by a traditional solid-state reaction method. According to the X-ray diffraction and the results of Rietveld refinement, all the samples maintain orthorhombic distorted perovskite structures with Amm2 space group without any secondary phase, suggesting the well incorporation of Fe ions into the KNbO₃ matrix. With the increase of Fe concentration, the band gap of each sample is decreased gradually, which is much smaller than the 3.18 eV band gap of pure KNbO₃. Through X-ray photoelectron spectrum analysis, the increased density of oxygen vacancy and Fe ions may be responsible for the observed decrease in band gap. Compared with the pure KNbO₃, Fe doped samples exhibit room-temperature weak ferromagnetism. The ferromagnetism in KNb_1-xFe_xO_3-δ with low-concentration dopants (x=0.01-0.10) can be attributed to the bound magnetic polaron mediated exchange. The enhancement of magnetism for the high-concentration (x=0.10-0.20) doped samples may arise from the further increase of magnetic Fe ions.     

Metal‐Borohydride‐Modified Zr(BH4)4⋅8 NH3: Low‐Temperature Dehydrogenation Yielding Highly Pure Hydrogen

Due to its high hydrogen density (14.8 wt %) and low dehydrogenation peak temperature (130 °C), Zr(BH₄)₄ ? 8 NH₃ is considered to be one of the most promising hydrogen‐storage materials. To further decrease its dehydrogenation temperature and suppress its ammonia release, a strategy of introducing LiBH₄ and Mg(BH₄)₂ was applied to this system. Zr(BH₄)₄ ? 8 NH₃–4 LiBH₄ and Zr(BH₄)₄ ? 8 NH₃–2 Mg(BH₄)₂ composites showed main dehydrogenation peaks centered at 81 and 106 °C as well as high hydrogen purities of 99.3 and 99.8 mol % H₂, respectively. Isothermal measurements showed that 6.6 wt % (within 60 min) and 5.5 wt % (within 360 min) of hydrogen were released at 100 °C from Zr(BH₄)₄ ? 8 NH₃–4 LiBH₄ and Zr(BH₄)₄ ? 8 NH₃–2 Mg(BH₄)₂, respectively. The lower dehydrogenation temperatures and improved hydrogen purities could be attributed to the formation of the diammoniate of diborane for Zr(BH₄)₄ ? 8 NH₃–4 LiBH₄, and the partial transfer of NH₃ groups from Zr(BH₄)₄ ? 8 NH₃ to Mg(BH₄)₂ for Zr(BH₄)₄ ? 8 NH₃–2 Mg(BH₄)₂, which result in balanced numbers of BH₄ and NH₃ groups and a more active H^δ+ ??? ^?δH interaction. These advanced dehydrogenation properties make these two composites promising candidates as hydrogen‐storage materials.     

BLOCK H-MATRICES AND SPECTRUM OF BLOCK MATRICES

ＩｎｔｒｏｄｕｃｔｉｏｎＬｅｔＡ ∈Ｃｎ ,ｎ,ａｎｄｂｅｐａｒｔｉｔｉｏｎｅｄａｓｆｏｌｌｏｗｓ:Ａ =Ａ11Ａ12 …Ａ1ｋＡ2 1Ａ2 2 …Ａ2ｋ…………Ａｋ1Ａｋ2 …Ａｋｋ,( 1 )ｗｈｅｒｅＡｉｉ∈Ｃｎｉ,ｎｉ,1 ≤ｉ≤ｋ ,∑ｋｉ=1ｎｉ=ｎ ,Ａｉｉ( 1 ≤ｉ≤ｋ)ａｒｅｎｏｎｓｉｎｇｕｌａｒ.Ｉｎｍｏｓｔｐｒａｃｔｉｃａｌａｐｐｌｉｃａｔｉｏｎｓ,ｔｈｅｍａｔｒｉｃｅｓＡｉｊａｒｅｓｐａｒｓｅａｎｄｍａｎｙｏｆｔｈｅｂｌｏｃｋｍａｔｒｉｃｅｓａｒｅｚｅｒｏ .Ｄｅｆｉｎｉｔｉｏｎ 1　ＩｆＢ =(ｂｉｊ) =(‖Ａｉｊ‖ ) ｋ×…     

Efficient Coupling of Solar Energy to Catalytic Hydrogenation by Using Well‐Designed Palladium Nanostructures

A Ru³⁺‐mediated synthesis for the unique Pd concave nanostructures, which can directly harvest UV‐to‐visible light for styrene hydrogenation, is described. The catalytic efficiency under 100 mW cm^?2 full‐spectrum irradiation at room temperature turns out to be comparable to that of thermally (70 °C) driven reactions. The yields obtained with other Pd nanocrystals, such as nanocubes and octahedrons, are lower. The nanostructures reported here have sufficient plasmonic cross‐sections for light harvesting in a broad spectral range owing to the reduced shape symmetry, which increases the solution temperature for the reaction by the photothermal effect. They possess a large quantity of atoms at corners and edges where local heat is more efficiently generated, thus providing active sites for the reaction. Taken together, these factors drastically enhance the hydrogenation reaction by light illumination.     

Photovoltage analysis of a heterojunction solar cell

According to the p-n junction model of Shockley,the relationship between the equilibrium carrier concentrations of n-type and p-type semiconductors on the edges of the depletion region of a p-n junction solar cell is analysed.The calculation results show that the photovoltage can exceed the built-in voltage for a special kind of heterojunction solar cell.When the photovoltage exceeds the built-in voltage under illumination,the dark current and the photocurrent are impeded by the peak of voltage barrier at the interface and the expression of the total I-V characteristic is given.     

基于N-对甲氧苯基咔唑-2-乙烯基-8-羟基喹啉锌的白色和黄色有机电致发光器件的性能

通过研究新型荧光染料N-对甲氧苯基咔唑-2-乙烯基-8-羟基喹啉锌(MoBCzHQZn)的电致发光(EL)特性, 发现MoBCzHQZn具有较强的发光特性和空穴传输特性, 利用此特性制备了非掺杂型的有机电致白光器件和掺杂型的有机电致黄光器件. 白光器件的结构为ITO/2T-NATA(20 nm)/MoBCzHQZn(25 nm)/NPBX(13 nm)/BCP(8nm)/Alq3(34 nm)/LiF(0.5 nm)/Al, 器件在15 V电压下实现了白光发射, 色坐标为(0.3719, 0.3275), 最大发光亮度为3414 cd·m-2, 在14 V 电压下的最大发光效率为1.69 cd·A-1、黄光器件的结构为ITO/2T-NATA(20 nm)/CBP:6%Ir(ppy)3:10%MoBCzHQZn(25 nm)/TPBi:6%Ir(ppy)3(47 nm)/LiF(0.5 nm)/Al, 器件在15 V电压下实现了黄绿光发射, 色坐标为(0.3590, 0.5787), 最大发光亮度为11073 cd·m-2, 在9 V电压下的最大发光效率为2.51 cd·A-1.     

人工头近场头相关传输函数及其特性

采用球形正十二面体声源及其空间定位系统,测量并建立了KEMAR人工头的近场头相关传输函数(HRTF)数据库。基于数据库分析了近场HRTF在频域和时域随声源距离变化的规律;讨论了用近场HRTF算得的双耳声级差(TLD)和双耳时间差(ITD)所包含的声源距离定位信息。结果表明,测量系统和所得数据具有较好的重复性和准确性,保留了1 kHz以下的低频定位信息。并且,近场HRTF幅度谱和ILD随声源距离的变化明显;用相关法算得2 kHz以下频段的ITD随声源距离略有变化。本文数据库及其分析结果将为声源距离定位的应用提供基础。      

One-way hash function construction based on the spatiotemporal chaotic system

Based on the spatiotemporal chaotic system,a novel algorithm for constructing a one-way hash function is proposed and analysed.The message is divided into fixed length blocks.Each message block is processed by the hash compression function in parallel.The hash compression is constructed based on the spatiotemporal chaos.In each message block,the ASCII code and its position in the whole message block chain constitute the initial conditions and the key of the hash compression function.The final hash value is generated by further compressing the mixed result of all the hash compression values.Theoretic analyses and numerical simulations show that the proposed algorithm presents high sensitivity to the message and key,good statistical properties,and strong collision resistance.     

Period of the discrete Arnold cat map and general cat map

The paper first studies the period of the discrete Arnold cat map. When the modulo is composite, the formulae are developed to calculate the minimal period. When the modulo is prime, the formulae calculating the period are given and an algorithm is proposed in order to determine the minimal period. Then the paper explores the relationship between the period of the discrete general cat map and its modulo for different parameters a and b. Some period formulae are given and some properties about the period are obtained. In addition, the paper also expands the period formulae of the corresponding a-Fibonacci sequence taken the modulo for more new parameters.