110 resultados para Voronoi Diagram
Resumo:
This paper proposes compact adders that are based on non-binary redundant number systems and single-electron (SE) devices. The adders use the number of single electrons to represent discrete multiple-valued logic state and manipulate single electrons to perform arithmetic operations. These adders have fast speed and are referred as fast adders. We develop a family of SE transfer circuits based on MOSFET-based SE turnstile. The fast adder circuit can be easily designed by directly mapping the graphical counter tree diagram (CTD) representation of the addition algorithm to SE devices and circuits. We propose two design approaches to implement fast adders using SE transfer circuits the threshold approach and the periodic approach. The periodic approach uses the voltage-controlled single-electron transfer characteristics to efficiently achieve periodic arithmetic functions. We use HSPICE simulator to verify fast adders operations. The speeds of the proposed adders are fast. The numbers of transistors of the adders are much smaller than conventional approaches. The power dissipations are much lower than CMOS and multiple-valued current-mode fast adders. (C) 2009 Elsevier Ltd. All rights reserved.
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We demonstrate theoretically that electric field can drive a quantum phase transition between band insulator to topological insulator in CdTe/HgCdTe/CdTe quantum wells. The numerical results suggest that the electric field could be used as a switch to turn on or off the topological insulator phase, and temperature can affect significantly the phase diagram for different gate voltage and compositions. Our theoretical results provide us an efficient way to manipulate the quantum phase of HgTe quantum wells.
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A distributed-feedback (DFB) laser and a high-speed electroabsorption (EA) modulator are integrated, on the basis of the selective area MOVPE growth (SAG) technique and the ridge waveguide structure, for a 10 Gbit s(-1) optical transmission system. The integrated DFB laser/EA modulator device is packaged in a compact module with a 20% optical coupling efficiency to the single-mode fibre. The typical threshold current is 15 mA, and the side-mode suppression ratio is over 40 dB with the single-mode operation at 1550 nm. The module exhibits 1.2 mW fibre output power at a laser gain current of 70 mA and a modulator bias voltage of 0 V. The 3 dB bandwidth is 12 GHz. A dynamic extinction ratio of over 10 dB has been successfully achieved under 10 Gbit s(-1) non-return to zero (NRZ) operation, and a clearly open eye diagram is obtained.
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A two-dimensional (2D) photonic crystal waveguide in the Gamma-K direction with triangular lattice on a silicon-on insulator (SOI) substrate in the near-infrared band is fabricated by the combination of electron beam lithography and inductively coupled plasma etching. Its transmission characteristics are analysed from the stimulated band diagram by the effective index and the 2D plane wave expansion (PWE) methods. In the experiment, the transmission band edge in a longer wavelength of the photonic crystal waveguide is about 1590 nm, which is in good qualitative agreement with the simulated value. However, there is a disagreement between the experimental and the simulated results when the wavelength ranges from 1607 to 1630 nm, which can be considered as due to the unpolarized source used in the transmission measurement.
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A differential recursive scheme for suppression of Peak to average power ratio (PAPR) for Orthogonal frequency division multiplexing (OFDM) signal is proposed in this thesis. The pseudo-randomized modulating vector for the subcarrier series is differentially phase-encoded between successive components in frequency domain first, and recursion manipulates several samples of Inverse fast Fourier transformation (IFFT) output in time domain. Theoretical analysis and experimental result exhibit advantage of differential recursive scheme over direct output scheme in PAPR suppression. And the overall block diagram of the scheme is also given.
Resumo:
In this work, a novel light source of strained InGaAsP/InGaAsP MQW EAM monolithically integrated with DFB laser is fabricated by ultra-low-pressure (22 x 10(2) Pa) selective area growth ( SAG) MOCVD technique. Superior device performances have been obtained, sue h as low threshold current of 19 mA, output light power of about 7 mW, and over 16 dB extinction ratio at 5 V applied voltage when coupled into a single mode fiber. Over 10 GHz 3 dB bandwidth in EAM part is developed with a driving voltage of 3 V. After the chip is packaged into a 7-pin butterfly compact module, 10-Gb/s NRZ transmission experiments are successfully performed in standard fiber. A clearly-open eye diagram is achieved in the module output with over 8.3 dB dynamic extinction ratio. Power penalty less than 1.5 dB has been obtained after transmission through 53.3 km of standard fiber, which demonstrates that high-speed, low chirp EAM/DFB integrated light source can be obtained by ultra-low-pressure (22 x 102 Pa) SAG method.
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In this paper we report the applicability of the density matrix renormalization group (DMRG) approach to the cylindrical single wall carbon nanotube (SWCN) for the purpose of its correlation effect. By applying the DMRG approach to the t+U+V model, with t and V being the hopping and Coulomb energies between the nearest neighboring sites, respectively, and U the on-site Coulomb energy, we calculate the phase diagram for the SWCN with chiral numbers (n(1)=3, n(2)=2), which reflects the competition between the correlation energy U and V. Within reasonable parameter ranges, we investigate possible correlated ground states, the lowest excitations, and the corresponding correlation functions in which the connection with the excitonic insulator is particularly addressed.
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We have obtained the parameter-phase diagram, which unambiguously defines the parameter region for the use of InAs/GaAs quantum dot as two-level quantum system in quantum computation in the framework of the effective-mass envelope function theory. Moreover, static electric field is found to efficiently prolong decoherence time. As a result, decoherence time may reach the order of magnitude of milli-seconds as external static electric field goes beyond 20 kV/cm if only vacuum fluctuation is taken as the main source for decoherence. Our calculated results are useful for guiding the solid-state implementation of quantum computing.
Resumo:
The time evolution of the quantum mechanical state of an electron is calculated in the framework of the effective-mass envelope function theory for an InAs/GaAs quantum dot. The results indicate that the superposition state electron density oscillates in the quantum dot, with a period on the order of femtoseconds. The interaction energy E-ij between two electrons located in different quantum dots is calculated for one electron in the ith pure quantum state and another in the jth pure quantum state. We find that E-11]E-12]E-22, and E-ij decreases as the distance between the two quantum dots increases. We present a parameter-phase diagram which defines the parameter region for the use of an InAs/GaAs quantum dot as a two-level quantum system in quantum computation. A static electric field is found to efficiently prolong the decoherence time. Our results should be useful for designing the solid-state implementation of quantum computing. (C) 2001 American Institute of Physics.
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We investigate the electronic structures of the inhomogeneous quantum dots within the framework of the effective mass theory. The results show that the energies of electron and hole states depend sensitively on the relative magnitude 77 of the core radius to the capped quantum dot radius. The spatial distribution of the electrons and holes vary significantly when the ratio eta changes. A quantum-confinement-driven type-II-type-I transition is found in GaAs/AlxGa1-xAs-capped quantum dot structures. The phase diagram is obtained for different capped quantum dot radii. The ground-state exciton binding energy shows a highly nonlinear dependence on the innner structures of inhomogeneous quantum dots, which originates from the redistribution of the electron and hole wave functions.
Resumo:
Comparing with the conventional CCFL (Cold Cathode Fluorescent Lamp) backlight, three-basic-color LEDs backlight has some advantages such as good color reproduction, long life and lead free etc. Theoretically, the color gamut is determined by x, y coordinates of the three basic colors in CIE chromaticity diagram, and the x, y coordinates of each basic color can derived from the relative spectrum distribution (RSD) of the LED. In this paper, the red, green and blue LEDs' RSD models are established to calculate and analyze the color gamut of a backlight. By simulating those models, the relationships that the color gamut of a LED backlight varies with each color are analyzed, and the optimum combination of three colors is obtained within the given wavelengths ranges. Moreover, the combinations of three colors for the gamut of 115% NTSC and 110% NTSC are plotted in pictures, respectively.
Resumo:
Wavelength tunable electro-absorption modulated distributed Bragg reflector lasers (TEMLs) are promising light source in dense wavelength division multiplexing (DWDM) optical fiber communication system due to high modulation speed, small chirp, low drive voltage, compactness and fast wavelength tuning ability. Thus, increased the transmission capacity, the functionality and the flexibility are provided. Materials with bandgap difference as large as 250nm have been integrated on the same wafer by a combined technique of selective area growth (SAG) and quantum well intermixing (QWI), which supplies a flexible and controllable platform for the need of photonic integrated circuits (PIC). A TEML has been fabricated by this technique for the first time. The component has superior characteristics as following: threshold current of 37mA, output power of 3.5mW at 100mA injection and 0V modulator bias voltage, extinction ratio of more than 20 dB with modulator reverse voltage from 0V to 2V when coupled into a single mode fiber, and wavelength tuning range of 4.4nm covering 6 100-GHz WDM channels. A clearly open eye diagram is observed when the integrated EAM is driven with a 10-Gb/s electrical NRZ signal. A good transmission characteristic is exhibited with power penalties less than 2.2 dB at a bit error ratio (BER) of 10(-10) after 44.4 km standard fiber transmission.
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A photovoltaic quantum dot infrared photodetector with InAs/GaAs/AlGaAs structures is reported. The detector is sensitive to normal incident light. At zero bias and 78 K, a clear spectral response in the range of 2 -7 mu m has been obtained with peaks at 3.1, 4.8 and 5.7 mu m. The bandgap energies of GaAs and Al0.2Ga0.8As at 78K are calculated and the energy diagram of the transitions in the Quantum-Dot Infrared Photodetector (QDIP) is given out. The photocurrent signals can be detected up to 110 K, which is state-of-the-art for photovoltaic QDIP. The photovoltaic effect in our detector is a result of the enhanced band asymmetry as we design in the structure.
Resumo:
在发布/订阅系统中,订阅者向系统注册其对某一个或某一类事件的兴趣,发布者将生成的事件发布到系统中,发布/订阅系统负责将事件与订阅进行匹配,并向对事件感兴趣的订阅者发出事件通知。发布者和订阅者在时间、空间和控制流上完全解耦合,能很好地满足大型分布式应用对松耦合交互的需求。发布/订阅系统在金融服务、新闻服务、物流等领域有着很大的实际应用价值。随着传感器技术的发展和普适应用的增长, 发布/订阅系统应用于传感器网络和 RFID应用等普适环境下的研究方兴未艾。在普适环境下,分布式大规模多种类事件给发布/订阅系统带来了更多的系统效率和可伸缩性问题。 来自传感器或RFID设备的原子事件数据被采集获取后即被发送到功能更为强大的代理服务器上处理。当传感器节点很多、传感数据规模很大时,大量收集到的数据容易造成网络拥塞以及某些代理服务器负载过重,从而成为性能瓶颈。因此,需要设计有效的代理部署算法,选取代理服务器的最佳位置,构建数据收集网络的拓扑结构,以高效地利用代理服务器的处理能力和网络带宽,提高数据的采集效率,从而支持发布/订阅系统更高效地处理大量事件和订阅。 在基于内容的发布/订阅系统中,基于内容的订阅是高度多样化的,不同的事件可能满足大量的感兴趣的订阅者。 系统中, 大规模的订阅信息和事件的到达,可能造成某些代理服务器负载过重,网络消息流量也过大,使得事件不能及时送达订阅者。因此,需要设计一个有效的消息路由策略,将发布者发布的事件消息高效地传递给订阅者,并且将事件匹配的责任分派到网络中不同的代理服务器上,使得网络中各代理服务器的负载分布相对均衡。 本文围绕发布/订阅系统的可伸缩性,对原子事件数据收集中的代理服务器部署问题,以及原子事件/订阅的路由问题展开研究。本文针对一般部署问题,即存在禁止部署区域的情形,提出了基于栅格化和爬山法的代理部署算法;对于无禁止区域的部署问题, 提出了更优的基于 Voronoi 图和Steiner 树的代理部署算法。本文实现了上述两个算法,实验表明,算法能获得在部署代价、通信开销和负载均衡度方面均较优的部署方案。在原子事件/订阅的路由上,本文提出了基于事件空间划分的渠道路由算法。算法将事件空间划分为多个事件渠道,每个事件渠道分配给单个代理服务器负责。代理服务器对到达的事件或订阅,根据其所属的渠道,决定转发或在本地处理。算法还通过实时监控代理服务器的负载,在负载较重时,分割渠道,在负载较轻时,合并渠道,从而达到动态负载均衡的效果。本文在OncePubSub系统上实现了上述算法,实验表明,算法能够有效地降低事件和订阅的传递开销,减小事件处理延迟,并能均衡代理服务器的负载。
Resumo:
GaSb layers are grown on GaSb substrates; the effects of input partial pressure of trimethylantimony and the V/III ratio are studied. A model of the MOVPE phase diagram for the growth of GaSb and GaAsxSb1-x is developed which assumes thermodynamic equilibrium to be established at the solid-vapor interface.