Far infrared measurements of bulk and surface phonons in GaAs/AlAs superlattices

We have used far-infrared oblique-incidence reflection spectroscopy to study bulk phonon polaritons, and attenuated total reflection (ATR) spectroscopy to study surface phonon polaritons, in long-period GaAs/Al_xGa_1?xAs and short-period GaAs/AlAs superlattices. Results on the former are in good agreement with an effective-medium bulk-slab model of the dielectric tensor of the superlattice; results on the latter are analysed in terms of a model that contains dielectric-tensor contributions from the confined optic phonons.     

高性能大带宽存储器--DDR SDRAM DIMM设计指南

DDR SDRAM的功能 SDR和DDR SDRAM都是同步存储器,所有的命令和数据都与时钟上升沿同步.通过同时利用数据选通脉冲的上升和下降沿,DDR SDRAM数据的传输速率能够达到SDR SDRAM的两倍.SDR和DDR内部都采用四组结构,并且具有同样的寻址方式和刷新速率.DDR的关键优势在于源同步数据获取,两倍预取结构以及2.5V的稳定SSTL_2接口.DDR还采用了差分时钟(CK,CK#),以及新的数据选通(DQS)和数据屏蔽(DM)/时钟使能(CKE)信号.     

Broadcasting info-pages to sensors: efficiency versus energy conservation

In sensor networks applied to monitoring applications, individual sensors may perform preassigned or on-demand tasks, or missions. Data updates (info-pages) may be sent to sensors from a command center, via a time-division broadcast channel. Sensors are normally put in sleep mode when not actively listening, in order to conserve energy in their batteries. Hence, a schedule is required that specifies when sensors should listen for updates and when they should sleep. The performance of such a schedule is evaluated based on data-related costs and sensor-related costs. Data-related costs reflect the obsoleteness of current sensor data, or the delay while sensors wait for updated instructions. Sensor-related costs reflect the energy that sensors consume while accessing the broadcast channel and while switching between the active and sleeping modes (rebooting). Our goal is a schedule with the minimum total cost. Previous related work has explored data-related costs, but listening cost has been addressed only under the assumption that the rebooting operation is free. This paper formulates a new cost model, which recognizes the cost of sensor rebooting. We derive an optimal schedule for the single-sensor setting. We proceed to consider schedules of multiple sensors; we formulate a mathematical program to find an optimal fractional schedule for this setting and provide a solution to the lower bound. Several heuristics for scheduling multiple sensors are introduced and analyzed, and various tradeoffs among the cost factors are demonstrated.     

Orthorhombic Ti2O3: A Polymorph‐Dependent Narrow‐Bandgap Ferromagnetic Oxide

Magnetic semiconductors are highly sought in spintronics, which allow not only the control of charge carriers like in traditional electronics, but also the control of spin states. However, almost all known magnetic semiconductors are featured with bandgaps larger than 1 eV, which limits their applications in long‐wavelength regimes. In this work, the discovery of orthorhombic‐structured Ti₂O₃ films is reported as a unique narrow‐bandgap (≈0.1 eV) ferromagnetic oxide semiconductor. In contrast, the well‐known corundum‐structured Ti₂O₃ polymorph has an antiferromagnetic ground state. This comprehensive study on epitaxial Ti₂O₃ thin films reveals strong correlations between structure, electrical, and magnetic properties. The new orthorhombic Ti₂O₃ polymorph is found to be n‐type with a very high electron concentration, while the bulk‐type trigonal‐structured Ti₂O₃ is p‐type. More interestingly, in contrast to the antiferromagnetic ground state of trigonal bulk Ti₂O₃, unexpected ferromagnetism with a transition temperature well above room temperature is observed in the orthorhombic Ti₂O₃, which is confirmed by X‐ray magnetic circular dichroism measurements. Using first‐principles calculations, the ferromagnetism is attributed to a particular type of oxygen vacancies in the orthorhombic Ti₂O₃. The room‐temperature ferromagnetism observed in orthorhombic‐structured Ti₂O₃, demonstrates a new route toward controlling magnetism in epitaxial oxide films through selective stabilization of polymorph phases.     

Fiber-optic confocal reflectance microscope with miniature objective for in vivo imaging of human tissues

We have built a fiber-optic confocal reflectance microscope capable of imaging human tissues in near real time. Miniaturization of the objective lens and the mechanical components for positioning and axially scanning the objective enables the device to be used in inner organs of the human body. The lateral resolution is 2 micrometers and axial resolution is 10 micrometers. Confocal images of fixed tissue biopsies and the human lip in vivo have been obtained at 15 frames/s without any fluorescent stains. Both cell morphology and tissue architecture can be appreciated from images obtained with this microscope.     

IC设计复杂化加剧：先进验证方式重要性倍增

虽然目前的IC设计持续以惊人的速度复杂化,但设计者仍然希望可以通过先进的验证工作提高工作效率.所谓的先进验证工作便是将测试平台自动化(Test-Bench Automation)和正式属性检测(Formal Property Checking)两功能添加到功能验证(Functional Verification)的流程之中.本文将主要探讨其中的基本概念、价值以及使用方法,进而帮助读者了解.     

Comparative Assessment of Adaptive Body-Bias SOI Pass-Transistor Logic

A very low voltage transconductor for video frequency range applications and compatible with standard CMOS technology is described. In the proposed transconductor, except the DC level shifter circuit (DCLS), the whole transconductor uses the main supply voltage [which can be as low as 1.5 V in a standard 0.6 μm CMOS technology] while the DCLS uses a simple charge-pump circuit as its supply voltage and has a very low current consumption. In addition, proper common-mode sense and charge-pump circuits are developed for this low-voltage application. Meanwhile, some techniques to improve the frequency response, linearity, and noise performance of the proposed transconductor are described. In a standard 0.6 μm CMOS technology and single 1.5 V supply, simulations show that the proposed transconductor futures a THD of −50 dB for 1.4 V_pp and 10 MHz input signal and −60 dB for 1.4 V_pp and 1 MHz signal where the threshold voltage of MOS transistors could be as high as 1 V. Based on the proposed transconductor, a lowpass filter with 700 kHz to 8 MHz programmable cutoff frequency and a bandpass 10.7 MHz second order filter were implemented. Armin Tajalli received the B.Sc. from Sharif University of Technology (SUT), Tehran, Iran, in 1997, and M.Sc. from Tehran Polytechnic University, Tehran, Iran, in 1999. From 1998 he has joint Emad Co. as a senior design engineer were he has worked on several industrial and R&D projects on analog and mixed-mode ICs. He received the award of the Best Design Engineer from Emad Co., 2001, the Kharazmi Award of Industrial Research and Development, Iran, 2002, and Presidential Award of the Best Iranian Researchers, in 2003. He is now working toward his PhD degree at SUT. His current interests are design of high speed circuits for telecommunication systems. Mojtaba Atarodi received the B.S.E.E. from Amir Kabir University of Technology (Tehran Polytechnic) in 1985, and M.Sc. degree in electrical engineering from the University of California, Irvine, in 1987. He received the Ph.D. degree from the University of Southern California (USC) on the subject of analog IC design in 1993. From 1993 to 1996 he worked with Linear Technology Corporation as a senior analog design engineer. Since then, he has been consulting with different IC companies. He is currently a visiting professor at Sharif University of Technology. He has published more than 30 technical papers in the area of analog and mixed-signal integrated circuit design as well as analog CAD tools.     

Considerations for Synchronization in Body Area Networks for Human Activity Monitoring

In this paper, we highlight considerations for synchronization issues in body area networks. Requirements for the synchronization accuracy in body area networks depend on the application at hand. Synchronization may be needed for power management, sample ordering, calculation of stimulus responses and for sensor fusion. This paper provides a theoretical exercise to help understand the accuracy required for typical human motion sensing. It gives an overview of various synchronisation strategies used and implemented in prototype systems. Lessons learnt from practical implementations using Bluetooth, an IEEE 802.15.4 proprietary network and Nanonet are presented to illustrate the principles involved. The discussion provides some considerations and the requirements for typical WBAN applications.     

X‐Ray Spectroscopic Investigation of Chlorinated Graphene: Surface Structure and Electronic Effects

Chemical doping of graphene represents a powerful means of tailoring its electronic properties. Synchrotron‐based X‐ray spectroscopy offers an effective route to investigate the surface electronic and chemical states of functionalizing dopants. In this work, a suite of X‐ray techniques is used, including near edge X‐ray absorption fine structure spectroscopy, X‐ray photoemission spectroscopy, and photoemission threshold measurements, to systematically study plasma‐based chlorinated graphene on different substrates, with special focus on its dopant concentration, surface binding energy, bonding configuration, and work function shift. Detailed spectroscopic evidence of C–Cl bond formation at the surface of single layer graphene and correlation of the magnitude of p‐type doping with the surface coverage of adsorbed chlorine is demonstrated for the first time. It is shown that the chlorination process is a highly nonintrusive doping technology, which can effectively produce strongly p‐doped graphene with the 2D nature and long‐range periodicity of the electronic structure of graphene intact. The measurements also reveal that the interaction between graphene and chlorine atoms shows strong substrate effects in terms of both surface coverage and work function shift.     

A 0D Lead‐Free Hybrid Crystal with Ultralow Thermal Conductivity

Organic–inorganic hybrid materials are of significant interest owing to their diverse applications ranging from photovoltaics and electronics to catalysis. Control over the organic and inorganic components offers flexibility through tuning their chemical and physical properties. Herein, it is reported that a new organic–inorganic hybrid, [Mn(C₂H₆OS)₆]I₄, with linear tetraiodide anions exhibit an ultralow thermal conductivity of 0.15 ± 0.01 W m^?1 K^?1 at room temperature, which is among the lowest values reported for organic–inorganic hybrid materials. Interestingly, the hybrid compound has a unique 0D structure, which extends into 3D supramolecular frameworks through nonclassical hydrogen bonding. Phonon band structure calculations reveal that low group velocities and localization of vibrational energy underlie the observed ultralow thermal conductivity, which could serve as a general principle to design novel thermal management materials.