Heat transfer performance of a double-loop separate-type heat pipe: Measurement results

An experimental study is presented for the heat transfer performance of a rectangular double-loop natural circulation system, in which the condensers are made of double tubes with water-steam as the working fluid. Detailed temperature measurements of the core fluid and the wall are made, from which overall heat transfer coefficients for the evaporator, condensers, and entire system are obtained. Parametric studies of the liquid charge level, fluid properties, and heating or cooling conditions on the heat transfer performance are presented and correlation equations are given. The results show that the overall heat transfer coefficients for the evaporator, condensers, and entire loop are all increasing with decreasing liquid charge level. Overhead phenomena at low liquid charge level and thermal oscillation at some situations are also observed and discussed.     

High strain rate compression behavior for Sn-37Pb eutectic alloy, lead-free Sn-1Ag-0.5Cu and Sn-3Ag-0.5Cu alloys

This paper emphasized on studying the high strain-rate compression behavior of the unleaded Sn-3Ag-0.5Cu (SAC305), Sn-1Ag-0.5Cu (SAC105) solders and the traditional Sn-37Pb eutectic solder. The split Hopkinson pressure bar (SHPB) apparatus was used to conduct high strain rate tests in order to characterize the associated high rate mechanical response of these alloys. Specimens were tested at strain rates ranging from 380 to 3030 s⁻¹ to obtain the dynamic stress-strain relationship for the Sn-37Pb, SAC305 and SAC105 alloys. The tested soft and ductile samples experienced a large amount of elastoplastic deformation due to impact test. In the high strain rate range studied, limited strain rate hardening effect was observed for SAC305, SAC105 and Sn-37Pb alloys studied. The strain rate sensitivity parameter (m) related to the power law creep equation was also calculated for the present solder materials at specific strain values. In addition, the saturation stresses for the leaded and lead-free solders at the strain rate range studied are also reported.     

Photoactive Electro-Controlled Visual Perception Memory for Emulating Synaptic Metaplasticity and Hebbian Learning

In bionic technology, it has become an innovative process imitating the functionality and structuralism of human biological systems to exploit advanced artificial intelligent machines. Bionics plays a significant role in environmental protection, especially for its low energy loss. By fusing the concept of receptor-like sensing component and synapse-like memory, the photoactive electro-controlled optical sensory memory (PE-SM) is proposed and realized in a single device, which endows a simple methodology of reducing power consumption by photoactive electro-control. The PE-SM is the system built with the stacked atomically thick materials, in which rhenium diselenide serves as a robust photosensor, hexagonal boron nitride serves as a tunneling dielectric, and graphene serves as a charge-storage layer. With the features of the PE-SM, it performs synaptic metaplasticities under optical spikes. In addition, a simulated spiking neural network composed of 24 × 24 PE-SMs is further presented in an unsupervised machine learning environment, performing image recognition via the Hebbian rule. The PE-SM not only improves the neuromorphic computing efficiency but also simplifies the circuit-size structure. Eventually, the concept of photoactive electro-control can extend to other photosensitive 2D materials and provide a new approach of constructing either visual perception memory or photonic synaptic devices.     

A Fundamental 90-GHz CMOS VCO Using New Ring-Coupled Quad

A new circuit topology, named ring-coupled quad for millimeter-wave voltage controlled oscillator (VCO) design, is proposed. The proposed circuit topology provides higher open loop voltage gain than conventional cross-coupled pair. The layout of the proposed ring-coupled quad is fully symmetric without additional interconnection lines. A 90-GHz VCO using 90-nm CMOS process is implemented with this ring-coupled quad. This 90-GHz oscillator demonstrates a 2.5-GHz tuning range and higher than -20dBm output power. The proposed ring-coupled quad is suitable for the realization of high frequency VCOs     

医疗红外线热影像应用于辅助临床冠状动脉血管阻塞率分析

红外线数位热影像非常适合显示受测物体曲面所发射红外线辐射之二维温度分佈,因此红外线心脏热影像又被称为冠状动脉热像血管造影。在本研究中,提出了一种数位影像处理之演算法,以定位血栓阻塞或颈缩狭窄之位置。本演算法包含四个连续之处理过程;首先,针对红外线数位热影像之二维温度灰阶像素进行二值化处理,利用多阈值适性分割来区分心脏(背景)或冠状动脉(前景)像素。接著第二处理过程将分割所得原始动脉像素,经过一连串之胡椒状像素去除(pepper-like pixels removing)、外围像素侵蚀(erosion)、与原区域相减(subtraction)、递迴式邻域探访(recursive neighborhood visiting)、动脉轮廓点串链(point linked list)建立以及短边删除等处理之后,提取出冠状动脉之候选轮廓。在第三个处理过程中,由医生自主点选一冠状动脉分支,利用形态学细化(morphological thinning)以及临域分析(neighborhood analysis),以便计算最长之中心轴曲线。在最后一个处理过程中,在沿著有向中心轴曲线上移动,将每一个中心轴像素至最近之左右边动脉血管轮廓相加起来,成为该中心轴像素之可变血管管径,并沿此弯曲之中心轴绘製出矫直哩程管径图,以提供医生有用之狭窄处生理资讯。接著本研究定义一血管阻塞率公式,以区域阻塞率最小值来预估未来动脉阻塞最可能发生之位置。     

High-speed Modulation of InGaAs: Sb-GaAs-GaAsP quantum-well vertical-cavity surface-emitting lasers with 1.27-/spl mu/m emission wavelength

1.27-/spl mu/m InGaAs: Sb-GaAs-GaAsP vertical-cavity surface-emitting lasers (VCSELs) were grown by metal-organic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current changes from 1.8 to 1.1 mA and the slope efficiency falls less than /spl sim/35% as the temperature raised from room temperature to 70/spl deg/C. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is measured to be 10.7 GHz with modulation current efficiency factor (MCEF) of /spl sim/5.25 GHz/(mA)/sup 1/2/. These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25/spl deg/C to 70/spl deg/C.     

A novel ultracompact two-mode-interference wavelength division multiplexer for 1.5-/spl mu/m operation

A novel ultracompact 2/spl times/2 wavelength division multiplexer (WDM) for 1.55-/spl mu/m operation based on highly dispersive two-mode interference (TMI) was designed, theoretically modeled, and verified using a finite-difference-time-domain (FDTD) method. A two-moded waveguide assisted with a dispersive tooth-shaped grating provided a mode-dependent reflection band of central wavelength at 1.55 /spl mu/m. The wavelengths of 1538 and 1572 nm that were at the band edges and had the lowest reflection losses and relatively high dispersion were selected for wavelength multiplexing. The result showed that the wavelengths were separated by grating dispersion in a coupler length of 75 /spl mu/m which was much shorter than the required length of 1.1 mm in a regular TMI multiplexer of no grating. Insertion loss of about 1.7 dB and channel contrast of about 12 dB were achieved.     

Reliability evaluation of class-E and class-a power amplifiers with nanoscaled CMOS technology

Circuit reliability of class-E and class-A power amplifiers is investigated based on a newly developed degradation subcircuit model. Measured degradation characteristics on the fabricated circuits agree well with the simulation predictions. Using this model, we have found that the class-E amplifier degrades faster than a class-A amplifier, due to a much higher stress level during switching. With a drastic decrease of PAE, a shorter lifetime is expected for a class-E amplifier.     

Nanomechanical characterization of polymer using atomic force microscopy and nanoindentation

The nanomechanical characteristics of polycarbonate (PC) polymer were investigated by atomic force microscope (AFM) and nanoindentation. Scratching, wear properties, hardness and Young's modulus were obtained. The relationships between scribing feed and speed, surface depth and roughness and applied load were also investigated. The results indicated that as the applied load was increased, the furrow depth and the surface roughness increased. When the scribing feed was increased, the depth and roughness decreased. Increasing the furrow speed also decreased the surface roughness. The applied load is more significant than the scribing speed on the material removal rate. In addition, the Young's modulus and hardness of the polycarbonate material were 1.8 and 0.2 GPa, respectively.     

A Cost-Effective Design for MPEG-2 Audio Decoder with Embedded RISC Core

MPEG-2 audio decoding algorithms are involved of several complex coding techniques and therefore difficult to be implemented by an efficient dedicated architecture design. In this paper, we present an effective architecture for the MPEG-2 audio decoder. The MPEG-2 audio algorithms can be roughly divided into two types of operations. The first type is regular but computation-intensive such as filtering, matrixing, degrouping, and transformation operations. The second type is not regular but computation-intensive such as parsing bitstream, setting operation mode and controlling of all system operations. A RISC core with variable instruction length is designed for the decision-making part, and the dedicated hardware such as special divider, and synthesis filterbank is designed for the computation-intensive part. Based on the standard cell design technique, the VLSI chip consists of 27000 gate counts with the chip size of 6.4 × 6.4 mm². The chip can run at maximum 43.5 MHz clock rate, with the power dissipation of 150 mW at 3 V power supply.