K4,4,p的点可区别的IE-全染色(p≥1008)

该文利用色集事先分配法、构造染色法、反证法探讨了完全三部图K_4,4,p (p≥1008)的点可区别IE-全染色问题，确定了K_4,4,p (p≥1008)的点可区别IE-全染色数。     

双添加剂低浓度水系硫酸盐电解液用于2V碳-碳超级电容器

为了解决水系电解液在超级电容器中电压窗口低、能量密度小的问题,研究了含有0.5 mol/L硫酸钾(K₂SO₄)以及聚乙二醇(PEG)和碱金属碘化物(AMI)双添加剂的低浓度中性水系电解液在碳-碳超级电容器中的应用。首先在0.5 mol/L K₂SO₄中添加PEG,由于H₂O-PEG之间的相互作用,3%质量分数的PEG添加剂使得0.5 mol/L K₂SO₄电解液的电化学稳定窗口达到4.70 V。该0.5 mol/L K₂SO₄+3%PEG电解液应用于以商业活性炭YP-50F作为电极材料的碳-碳超级电容器中,可在2V条件下稳定循环10 000次。进一步添加AMI(LiI、NaI或KI)氧化还原添加剂来增大比电容和能量密度,使法拉第反应的比电容进一步提高到400 F·g^-1以上,是原始0.5 mol/L K₂SO₄+3%PEG电解...     

聚合物钝化钙钛矿量子点的红光放大自发辐射性能

全无机CsPbX₃(X=Cl、Br、I)钙钛矿量子点具有优异的发光性能,是一种极具应用潜力的新型显示材料及激光增益介质。本文制备了发光峰位于640 nm的CsPbBr_1.2I_1.8红光量子点,在该量子点薄膜表面分别涂覆聚甲基丙烯酸甲酯(PMMA)、聚甲基丙烯酸异丁酯(PIBMA)、聚苯乙烯(PS)3种带不同功能基团的聚合物,制备了CsPbBr_1.2I_1.8/PMMA、CsPbBr_1.2I_1.8/PIBMA、CsPbBr_1.2I_1.8/PS复合薄膜,研究它们的放大自发辐射性能。结果表明,聚合物钝化一方面提升了量子点的水稳定性,另一方面,PMMA和PIBMA中的C=O钝化了量子点表面未配位的Pb²⁺,增强了量子点薄膜的光致发光强度。进一步的,在532 nm的纳秒激光泵浦下,CsPbBr_1.2I_1.8/PIBMA薄膜放大自发辐射阈值...     

原位环境透射电镜研究SnO2纳米线作为K-O2电池空气正极的放电行为

本文使用先进的球差校正环境透射电子显微镜(AC-ETEM)与原位电化学测试平台,在环境透射电镜中以SnO₂纳米线作为空气正极,构建起一纳米K-O₂金属空气电池,原位观测该电池在氧还原反应(ORR)过程中的微观变化行为。实验结果表明:在ORR过程中,SnO₂纳米线首先转化为Sn单质颗粒与K₂O;因纳米尺度的Sn单质颗粒具有优异的催化活性,在O₂氛围中纳米线的表面生成了大量的KO₂。但由于KO₂不能稳定存在,会迅速分解成K₂O₂并释放O₂,导致材料发生巨大的体积膨胀。相关实验结果为宏观K-O₂电池的设计与改性提供了直观的实验证据。     

K3B6O10Br紫外非线性光学晶体研究进展(特邀)

利用非线性光学晶体实现激光频率转换是拓展激光波长的有效手段之一,非线性光学晶体也成为全固态激光系统中的核心器件。硼酸盐由于其丰富的结构多样性和优异的光学性能,已成为开发可用于紫外激光输出的非线性光学晶体的重要体系。K₃B₆O₁₀Br晶体具有短的紫外截止边(182 nm)、较大的非线性光学系数(d₂₂为0.83 pm/V)、适中的双折射率(0.046@1064 nm),在激光二倍频、三倍频激光输出领域具有潜在应用。本文简要介绍了K₃B₆O₁₀Br晶体生长及基本性能,对晶体倍频与和频实现可见/紫外激光及光参量啁啾脉冲放大方面的研究进展进行了总结,并对K₃B₆O₁₀Br晶体未来发展及应用前景进行了简要分析。     

区域大气加权平均温度模型的构建及其精度分析

大气加权平均温度(T_m)可通过模型计算得到,针对一些常用的T_m模型在中国区域研究中存在精度较低的问题,提出一种顾及地表温度(T_s)和T_m年周期、半年周期、日周期的T_m模型——BGT_m模型。利用2017—2019年欧洲中期天气预报中心(ECMWF)提供的ERA5再分析数据建立适用于中国区域的区域T_m模型,使用2020年ERA5数据和探空数据对模型精度进行评估。实验结果表明,与GPT3、UNB3和Bevis模型相比,BGT_m模型在研究区域内具有更好的适用性。BGT_m模型可为中国区域提供精确的T_m值,为该区域水汽反演提供水汽信息的参考。     

Sb2Te3量子点的制备、结构及红外性质研究

碲化锑（Sb₂Te₃）是一种新型二维层状材料,采用“自上而下”的超声剥离法,以碲化锑粉末为原料,以N-甲基吡咯烷酮（NMP）为分散剂,首次成功制备出碲化锑量子点（Sb₂Te₃ QDs）,并采用多种手段（SEM,TEM,AFM,XPS,XRD等）对所制备Sb₂Te₃ QDs的形貌和结构进行了表征,同时还采用UV-Vis、PL及PLE探究了Sb₂Te₃ QDs的光学性质。研究表明:所制备的Sb₂Te₃ QDs平均粒径为2.3 nm,平均高度为1.9 nm,颗粒大小均匀、具有良好的分散性,PL与PLE峰位有明显的红移现象,研究还发现Sb₂Te₃ QDs在红外波段有明显的吸收与光致发光。研究表明:超声剥离法制备Sb₂Te₃ QDs是切实可行的,该量子点的PL与PLE对波长具有依赖性,其在红外波段的特性表明:它有望成为一种新型的红外探测材料。     

CoTe2量子点的制备、结构及光学性质研究（特邀）

近年来,过渡金属碲化物（TMTs）以其独特的晶体结构和优异的物化特性引起了科学界的广泛关注和研究。本文采用超声法制备CoTe₂量子点（QDs）,通过TEM、AFM、EDS、XPS、XRD、FTIR等技术手段对制备的CoTe₂ QDs进行了形貌和结构的表征,同时使用分光光度计(UV-Vis)、光致发光谱(PL)和光致发光激发光谱(PLE)研究了CoTe₂ QDs的光学性质。结果表明,制备得到的CoTe₂ QDs分散性良好、粒径均匀、呈现球形形貌,晶粒的平均直径约为3.1 nm,平均高度约为2.9 nm;CoTe₂ QDs在红外波段存在明显的吸收,吸收值随稀释浓度的增加而降低;当激发光波长和发射光波长依次增加时,PL和PLE峰出现红移,具有明显的Stokes位移效应,表明CoTe₂ QDs的光致发光具有激发波长依赖性;CoTe₂ QDs具有光致多色发光特性,不同激发光波长可发出不同颜色的光;荧光量子产率可达62.6%。CoTe₂ QDs优异的光学特性尤其是在红外波段的吸收和发光特性,表明其在红外探测、激光防护涂层、荧光成像、多色发光和纳米光子器件等研究领域中具有重要的潜在应用价值,有望成为一种新型红外探测材料。     

铌酸钾钠基无铅压电陶瓷烧结及极化工艺优化

采用传统固相法在烧结温度1 110～1 150℃内成功制备了(K_0.5Na_0.5)_0.98Li_0.02Nb_0.77Ta_0.18Sb_0.05O₃(LTS-KNN)无铅压电陶瓷,所有样品结晶性良好,无第二相产生。在1 130℃下烧结的压电陶瓷致密度良好,陶瓷表现出较好的压电性能。通过调节极化电场与极化温度可改善陶瓷的极化程度,进而优化陶瓷的压电性能。实验结果表明,在烧结温度为1 130℃,极化电场为3 kV/mm,极化温度为60℃时,陶瓷的压电性能达到最佳,即压电常数d₃₃ =310 pC/N,机电耦合系数k_p =48%。     

非相干叠加光束携带C点偶极子的演化特性

为了探讨非相干叠加光束携带C点偶极子的演化特性,推导了携带C点偶极子的高斯光束非相干叠加传输表达式,并进行了数值模拟研究。结果表明,构成C点偶极子的两个C点的位置和偏振度会随着相关参数的变化而改变;在旁轴情形下,没有C点产生和湮灭,并且这两个C点连线的斜率随着传输距离的增加而单调增加;在非旁轴情形下,当光束传输到z=0.01z_R时,有多个C点偶极子产生,在z=10.39z_R时又出现C点偶极子的湮灭;在瑞利距离z_R处,光腰半径增加到0.222μm和0.56μm时分别出现C点偶极子的产生和湮灭;随着离轴距离和光束波长的变化,也出现C点的产生和湮灭。研究结果对深入理解偏振奇点矢量光束和寻找奇点光学潜在应用具有一定参考价值。     

Gyrotron coaxial cylindrical resonators with corrugated innerconductor: Theory and experiment

Gyrotron coaxial resonators with a longitudinally slotted inner cylinder are examined analytically using a surface impedance model, from which expressions for the electromagnetic field, ohmic quality (Q) factor, and characteristic equation of the transverse eigenvalues χ _m,p are obtained. The major attributes of such resonators are expressed by the dependence of χ_m,p on the parameter C-defined as the ratio of the outer to inner radii of the coaxial structure. In that connection, the effect of the corrugation parameters on χ_m,p is particularly investigated on the basis of an expression derived for the slope function dχ_m,p,p/dC. It is shown that the χ_m,p(C) curve may either exhibit oscillatory behavior or present a flat portion over a wide range of C depending on the corrugation parameters chosen. The theory is checked against experiment in which resonant frequencies and total Q factors were measured for TE modes operating in the range of 8-16 GHz in a coaxial cavity with 40 slots. Good agreement is found in that the magnitude of the relative error in frequency is less than 0.5%. Corrugated coaxial resonators prove to be relevant to megawatt gyrotrons where highly selective cavities are required to ensure high conversion efficiency     

A model for the multipath delay profile of fixed wireless channels

This paper deals with the measurement and modeling of multipath delay on fixed wireless paths at 1.9 GHz in suburban environments. The primary focus is on the delay profile, which is the normalized plot of received power versus delay in response to an RT “impulse.” We describe measurement campaigns in the western suburbs of Chicago, IL, and in suburban north-central New Jersey. Our analysis of the data suggests to us that, for directive terminal antennas, the delay profile can be modeled as having a “spike-plus-exponential” shape, i.e., a strong return (“spike”) at the lowest delay, plus a set of returns whose mean powers decay exponentially with delay. This delay profile can be characterized by just two parameters (both variable over the terrain), namely, the ratio (K₀) of the average powers in the “spike” and “exponential” components and the decay time constant (τ₀) of the “exponential” component. No such simple structure appears to apply for delay profiles using omnidirectional antennas. For a directive antenna with a 32° beamwidth, we find that: (1) the statistical correlation between the profile parameters K₀ and τ₀ is negligible; (2) these parameters are relatively insensitive to antenna height and path length; and (3) over each measured region (Illinois and New Jersey), K₀ and τ₀ have median values close to 8 dB and just below 0.2 μs, respectively. Moreover, we have found simple probability distributions that accurately portray the variability of K₀ and τ₀ over the terrain     

快速响应的共面转换型液晶显示器

共面转换液晶显示器(IPS-LCD)由于其具有可视角度大、色彩真实、画质出色等优点,在平板显示器中得到了广泛应用,然而响应速度慢限制了其在高端显示器中的应用。本文中,首先通过采用正性液晶,对IPS类型中的边缘场转换型(FFS)和边缘场共面转换型(FIS)的液晶显示器,不同摩擦角度下的电光特性和响应时间进行了模拟计算。然后从预倾角度、电极尺寸以及弹性常数出发,对FIS液晶盒结构参数进行了优化,提出了一种快速响应的液晶显示器。我们通过计算机模拟发现,在FFS液晶盒中,摩擦角度对工作电压具有较大影响,小摩擦角度可实现高透过率、低工作电压;而在FIS液晶盒中,摩擦角度对响应时间具有较大影响,大于10°时与2°时相比,响应速度可提高82.7%以上。并且,不同摩擦角度下,弹性常数对FIS液晶显示器的响应速度影响不同,摩擦角度为2°时,响应速度与弹性常数K11、K22、K33都有关,而摩擦角度为12°时,响应速度只与K22有关,这个原因导致了12°与2°时相比,响应速度提高了84.2%。     

Modulator driver and photoreceiver for 20 Gb/s optic-fiber links

Two integrated circuits, a modulator driver and a photoreceiver integrating a metal-semiconductor-metal (MSM) photodetector, a differential transimpedance amplifier and two limiting amplifier stages for high-speed optical-fiber links are presented. The IC's were manufactured in a 0.2 μm gate-length AlGaAs-GaAs high-electron mobility transistor (HEMT) technology with a f_T of 60 GHz. The modulator driver IC operates up to 25 Gb/s with an output voltage swing of 3.3 V_p-p at each output. The 1.3-1.55 μm wavelength monolithically integrated photoreceiver optoelectronic integrated circuit (OEIC) has a bandwidth of 17 GHz with a high transimpedance gain of 12 kΩ. Eye diagrams are demonstrated at 20 Gb/s with an output voltage of 1 V_p.p     

Optimized acquisition time and image sampling for dynamic SPECT ofTl-201

With the recent development in scatter and attenuation correction algorithms, dynamic single photon emission computerized tomography (SPECT) can potentially yield physiological parameters, with tracers exhibiting suitable kinetics such as thallium-201 (Tl-201). A systematic way is proposed to investigate the minimum data acquisition times and sampling requirements for estimating physiological parameters with quantitative dynamic SPECT. Two different sampling schemes were investigated with Monte Carlo simulations: (1) Continuous data collection for total study duration ranging from 30-240 min. (2) Continuous data collection for first 10-45 min followed by a delayed study at approximately 3 h. Tissue time activity curves with realistic noise were generated from a mean plasma time activity curve and rate constants (K₁-k₄) derived from Tl-201 kinetic studies in 16 dogs. Full dynamic sampling schedules (DynSS) were compared to optimum sampling schedules (OSS). The authors found that OSS can reliably estimate the blood flow related K₁ and V_d comparable to DynSS. A 30-min continuous collection was sufficient if only K₁ was of interest. A split session schedule of a 30-min dynamic followed by a static study at 3 h allowed reliable estimation of both K₁ and V_d avoiding the need for a prolonged (>60-min) continuous dynamic acquisition. The methodology developed should also be applicable to optimizing sampling schedules for other SPECT tracers     

Microwave Hall effect in a TE11p cylindrical cavity

A microwave Hall effect signal produced by a TE_11p degenerate cylindrical cavity is considered. The analysis presented identifies the cavity end walls as the source of the Hall signal, and a formula relating the Hall output power to the dimensions of the cavity is derived. Experimental results from the measurement of the empty cavity signal at 9.5 GHz are reported     

向列相液晶弹性各向异性诱导液晶盒产生漏光的研究

为了阐述具有体缺陷结构的向列相液晶盒在暗态出现漏光的原因,以及边界锚定条件对漏光的影响,首先,建立了3个向列相液晶盒模型,它们具有不同的初始指向矢排布。接着,基于Landau-de Gennes理论,通过对指向矢场的缺陷动力学计算,得到液晶盒截面内平衡态的指向矢分布。最后,使用琼斯矩阵法将该截面内的指向矢分布以透过率的形式表示出来。模拟结果显示,在无外场条件下,当向列相液晶的弹性常数满足L2/L1≥1(K22/K11≤2/3)时,具有体缺陷结构的液晶盒展现出了自发的扭曲结构,导致了漏光的出现。且漏光强度随着缺陷结构和边界条件的不同而不同。本文模型很好地解释了体缺陷造成液晶盒在暗态出现漏光的原因,且模拟结果与工业生产过程中观察到的现象是一致的。     

Performance limits for channelized cellular telephone systems

Studies the performance of channel assignment algorithms for “channelized” (e.g., FDMA or TDMA) cellular telephone systems, via mathematical models, each of which is characterized by a pair (H,p), where H is a hypergraph describing the channel reuse restrictions, and p is a probability vector describing the variation of traffic intensity from cell to cell. For a given channel assignment algorithm, the authors define T(r) to be the amount of carried traffic, as a function of the offered traffic, where both r and T(r) are measured in Erlangs per channel. They show that for a given H and p, there exists a function T_H,p(r), which can be computed by linear programming, such that for every channel assignment algorithm, T(r)⩽T_H,p(r). Moreover, they show that there exist channel assignment algorithms whose performance approaches T_H,p (r) arbitrarily closely as the number of channels increases. As a corollary, they show that for a given (H,p) there is a number r₀ , which also can be computed by linear programming, such that if the offered traffic exceeds r₀, then for any channel assignment algorithm, a positive fraction of all call requests must be blocked, whereas if the offered traffic is less than r₀, all call requests can be honored, if the number of channels is sufficiently large. The authors call r₀, whose units are Erlangs per channel, the capacity of the cellular system     

(k,l)-递归极大平面图的结构

对于一个平面图G实施扩3-轮运算是指在G的某个三角形面xyz内添加一个新顶点v,使v与x, y, z均相邻,最后得到一个阶为|V(G)|+1的平面图的过程。一个递归极大平面图是指从平面图K₄出发,逐次实施扩3-轮运算而得到的极大平面图。 所谓一个(k,l)-递归极大平面图是指一个递归极大平面图,它恰好有k个度为3的顶点,并且任意两个3度顶点之间的距离均为l。该文对(k,l)-递归极大平面图的存在性问题做了探讨,刻画了(3,2)-及(2,3)-递归极大平面图的结构。