100kHz高频逆变式CO＿2激光电源的研制

本文描述高频逆变式ＣＯ＿２激光电源，逆变频率为１００ｋＨｚ。该电源在升压高频变压器次级端去掉滤波高压电容和限流电阻的条件下能长期稳定工作，工作电流变化量小于０．１ｍＡ，抗网路波动范围为１６０～２５０Ｖ，调节范围宽，转换效率高。它具有适应性强、稳定性好，以及体积小、质量轻、便携等优点，是一种新型的激光器电源。     

工业级卡托辛成分分析及其双核二茂铁制备工艺

2,2-双(乙基二茂铁)丙烷(卡托辛)因其优异的催化活性和制药工艺性,成为当前复合固体推进剂中主要的燃速催化剂之一.由于卡托辛合成工艺复杂,工业级产品成分也很复杂,使得其相关产品的性能难以得到保证.利用气相色谱-质谱联用技术和高效液相色谱技术,对工业级卡托辛的成分进行了分析;依据各成分结构特性及其极性、溶解度差异,通过...     

Sequential packing algorithm for channel assignment under cochanneland adjacent-channel interference constraint

Generally, the channel-assignment problem (CAP) for mobile cellular systems is solved by graph-coloring algorithms. These algorithms, though sometimes can yield an optimal solution, do not supply any information on whether an optimal solution has been found or bow far away it is from the optimum. In view of these undesirable features, two relevant results are presented. First, a lower bound for the minimum number of channels required to satisfy a given call-traffic demand is derived. This lower bound is tighter than the existing ones under certain conditions and can be used as a supplement for other approximate algorithms. Second, we propose an efficient heuristic algorithm to solve this problem. Although the CAP is nondeterministic polynomial (NP) complete in general, our algorithm provides an optimal solution for a special class of network topologies. For the general case, promising results are obtained, and numerical examples show that our algorithm has a better performance than many existing algorithms     

Ion implantation doping of OMCVD grown GaN

Doping by ion implantation using Si, O, Mg, and Ca has been studied in single crystal semi-insulating and n-type GaN grown on a-sapphire substrates. The n-and p-type dopants used in this study are Si and O; Mg and Ca, respectively. Room temperature activation of Si and O donors has been achieved after 1150°C annealing for 120 s. The activation of Mg and Ca acceptors is too low to measure at both room temperature and 300°C. Using higher doses to achieve a measurable p-type conduction increases the amount of damage created by the implantation. Rutherford back scattering measurements on this material indicate that the damage is still present even after the maximum possible heat treatment. Secondary ion mass spectrometry measurements have indicated a redistribution in the measured profiles of Mg due to annealing.     

三值TTL施密特电路的研究

本文通过对施密特电路的跳阈分析,指出在二值TTL施密特电路中实现该一功能的核心部件为阈值可控的差动电流开关。根据三值TTL电路有两个信号检测阈值的特点,本文设计了有二次跳阈反应的三值TTL施密特电路。PSPICE模拟证明了设计的电路具有理想的施密特电路功能。     

A location‐aware peer‐to‐peer overlay network

This work describes a novel location‐aware, self‐organizing, fault‐tolerant peer‐to‐peer (P2P) overlay network, referred to as Laptop. Network locality‐aware considerations are a very important metric for designing a P2P overlay network. Several network proximity schemes have been proposed to enhance the routing efficiency of existing DHT‐based overlay networks. However, these schemes have some drawbacks such as high overlay network and routing table maintenance overhead, or not being completely self‐organizing. As a result, they may result in poor scalability as the number of nodes in the system grows. Laptop constructs a location‐aware overlay network without pre‐determined landmarks and adopts a routing cache scheme to avoid maintaining the routing table periodically. In addition, Laptop significantly reduces the overlay maintenance overhead by making each node maintain only the connectivity between parent and itself. Mathematical analysis and simulations are conducted to evaluate the efficiency, scalability, and robustness of Laptop. Our mathematical analysis shows that the routing path length is bounded by log_d N, and the joining and leaving overhead is bounded by d log_d N, where N is the number of nodes in the system, and d is the maximum degree of each node on the overlay tree. Our simulation results show that the average latency stretch is 1.6 and the average routing path length is only about three in 10 000 Laptop nodes, and the maximum degree of a node is bounded by 32. Copyright © 2006 John Wiley & Sons, Ltd.     

Electrode Dependence of Tunneling Electroresistance and Switching Stability in Organic Ferroelectric P(VDF‐TrFE)‐Based Tunnel Junctions

Ferroelectric tunnel junctions (FTJs) are promising candidates for nonvolatile memories and memristor‐based computing circuits. Thus far, most research has focused on FTJs with a perovskite oxide ferroelectric tunnel barrier. As the need for high‐temperature epitaxial film growth challenges the technological application of such inorganic junctions, more easily processable organic ferroelectrics can serve as alternative if large tunneling electroresistance (TER) and good switching durability would persist. This study reports on the performance of FTJs with a spin‐coated ferroelectric P(VDF‐TrFE) copolymer tunnel barrier. The use of three different bottom electrodes, indium tin oxide (ITO), La_0.67Sr_0.33MnO₃, (LSMO), and Nb‐doped SrTiO₃ (STO) are compared and it is shown that the polarity and magnitude of the TER effect depend on their conductivity. The largest TER of up to 10⁷% at room temperature is measured on FTJs with a semiconducting Nb‐doped STO electrode. This large switching effect is attributed to the formation of an extra barrier over the space charge region in the substrate. The organic FTJs exhibit good resistance retention and switching endurance up to 380 K, which is just below the ferroelectric Curie temperature of the P(VDF‐TrFE) barrier.     

Functionalization of Graphene Oxide Films with Au and MoOx Nanoparticles as Efficient p‐Contact Electrodes for Inverted Planar Perovskite Solar Cells

A graphene oxide (GO) film is functionalized with metal (Au) and metal‐oxide (MoO_x) nanoparticles (NPs) as a hole‐extraction layer for high‐performance inverted planar‐heterojunction perovskite solar cells (PSCs). These NPs can increase the work function of GO, which is confirmed with X‐ray photoelectron spectra, Kelvin probe force microscopy, and ultraviolet photoelectron spectra measurements. The down‐shifts of work functions lead to a decreased level of potential energy and hence increased V_oc of the PSC devices. Although the GO‐AuNP film shows rapid hole extraction and increased V_oc, a J_sc improvement is not observed because of localization of the extracted holes inside the AuNP that leads to rapid charge recombination, which is confirmed with transient photoelectric measurements. The power conversion efficiency (PCE) of the GO‐AuNP device attains 14.6%, which is comparable with that of the GO‐based device (14.4%). In contrast, the rapid hole extraction from perovskite to the GO‐MoO_x layer does not cause trapping of holes and delocalization of holes in the GO film accelerates rapid charge transfer to the indium tin oxide substrate; charge recombination in the perovskite/GO‐MoO_x interface is hence significantly retarded. The GO‐MoO_x device consequently shows significantly enhanced V_oc and J_sc, for which its device performance attains PCE of 16.7% with great reproducibility and enduring stability.     

Constructing a novel single-layer white organic light-emitting device through a new sky-blue fluorescent bipolar host

A novel device concept was realized for simple single-layer small-molecule white organic light emitting devices. The single organic active layer here is simply comprised of a newly synthesized sky-blue fluorescent bipolar host (TPASO) and a common orange phosphorescent dopant. Suppressed singlet Föster energy transfer induced by a low-concentration doping and spontaneous high- to low-lying triplet energy transfer, respectively, lead to sky-blue fluorescence from TPASO and orange phosphorescence from the dopant. The resulting two-organic-component device exhibits a low turn-on voltage of 2.4 V, maximum current/power efficiencies up to 11.27 ± 0.02 cd A⁻¹ and 14.15 ± 0.03 lm W⁻¹, and a warm-white CIE coordinate of (0.42, 0.45) at 1000 cd m⁻².     

Helical‐Like 3D Ultrathin Piezoelectric Element for Complicated Ultrasonic Field

The developments of personalized medicine, ultrasound imaging, and contactless “microscopic handle” techniques are pushing ultrasonic transducers toward features of high frequency, device miniaturization, and even novel function. However, the conventional ultrasonic transducer has severely limited the development of novel ideas for applications due to its ordinary ultrasonic field. Although transducer arrays and monolithic acoustic holograms are capable of producing the complicated ultrasonic field, it is still difficult to achieve high frequency, device miniaturization, and novel function simultaneously. Here, a simple but effective approach is introduced that aims at reconstructing the complicated and high‐frequency ultrasonic field via a compact single‐element ultrasonic transducer. The 3D ultrathin piezoelectric element with a complex configuration is demonstrated theoretically and experimentally to produce the desired complicated ultrasonic field. With helical‐like configuration, the single‐element ultrasonic transducer offers efficient noncontact trapping and manipulation of suspended microparticles and biological cells. Moreover, its strong trapping capability leads to the 3D stacking of microparticles, which is a novel and interesting phenomenon achieved by a single‐element ultrasonic transducer. This work brings the possibility of a complicated ultrasonic field for achieving novel high‐frequency ultrasound applications through the design of smart structure ultrathin piezoelectric materials.