Direct 3D Printing of Ultralight Graphene Oxide Aerogel Microlattices

Graphene aerogel microlattices (GAMs) hold great prospects for many multifunctional applications due to their low density, high porosity, designed lattice structures, good elasticity, and tunable electrical conductivity. Previous 3D printing approaches to fabricate GAMs require either high content of additives or complex processes, limiting their wide applications. Here, a facile ion‐induced gelation method is demonstrated to directly print GAMs from graphene oxide (GO) based ink. With trace addition of Ca²⁺ ions as gelators, aqueous GO sol converts to printable gel ink. Self‐standing 3D structures with programmable microlattices are directly printed just in air at room temperature. The rich hierarchical pores and high electrical conductivity of GAMs bring admirable capacitive performance for supercapacitors. The gravimetric capacitance (C_s) of GAMs is 213 F g^?1 at 0.5 A g^?1 and 183 F g^?1 at 100 A g^?1, and retains over 90% after 50 000 cycles. The facile, direct 3D printing of neat graphene oxide can promote wide applications of GAMs from energy storage to tissue engineering scaffolds.     

Mobility Enhancement Technology for Scaling of CMOS Devices: Overview and Status

The aggressive downscaling of complementary metal–oxide–semiconductor (CMOS) technology to the sub-21-nm technology node is facing great challenges. Innovative technologies such as metal gate/high-k dielectric integration, source/drain engineering, mobility enhancement technology, new device architectures, and enhanced quasiballistic transport channels serve as possible solutions for nanoscaled CMOS. Among them, mobility enhancement technology is one of the most promising solutions for improving device performance. Technologies such as global and process-induced strain technology, hybrid-orientation channels, and new high-mobility channels are thoroughly discussed from the perspective of technological innovation and achievement. Uniaxial strain is superior to biaxial strain in extending metal–oxide–semiconductor field-effect transistor (MOSFET) scaling for various reasons. Typical uniaxial technologies, such as embedded or raised SiGe or SiC source/drains, Ge pre-amorphization source/drain extension technology, the stress memorization technique (SMT), and tensile or comprehensive capping layers, stress liners, and contact etch-stop layers (CESLs) are discussed in detail. The initial integration of these technologies and the associated reliability issues are also addressed. The hybrid-orientation channel is challenging due to the complicated process flow and the generation of defects. Applying new high-mobility channels is an attractive method for increasing carrier mobility; however, it is also challenging due to the introduction of new material systems. New processes with new substrates either based on hybrid orientation or composed of group III–V semiconductors must be simplified, and costs should be reduced. Different mobility enhancement technologies will have to be combined to boost device performance, but they must be compatible with each other. The high mobility offered by mobility enhancement technologies makes these technologies promising and an active area of device research down to the 21-nm technology node and beyond.     

全球数据中心发展趋势和特点

云计算的出现,改变了传统IT基础设施的使用方式和软件部署模式,并带来了大型云计算数据中心的建设热潮。本文阐述了全球数据中心的发展趋势,总结了数据中心发展的特点,并对我国数据中心发展的情况做了分析。     

Fabrication of biomimic GaAs subwavelength grating structures for broadband and angular-independent antireflection

We combine interferometric lithography and inductively coupled plasma etching to fabricate GaAs subwavelength grating (SWG) which mimics the moth eye structures. Through the modification of morphology parameters, including profile, height and packing fraction, tapered, high-aspect-ratio and closely-packed GaAs SWGs are obtained. The measurement of spectral reflectance of the fabricated SWGs shows that reflection has been dramatically reduced compared to the polished GaAs surface. Particularly, the optimized SWG structures exhibit an average reflection below 5% in the wavelengths ranging from 350 to 900 nm. Furthermore, the angular-independent property is demonstrated by measuring the reflectance versus varying angles of incidence at 532 and 632.8 nm wavelengths.     

基于移动用户上下文相似度的协同过滤推荐算法

该文面向移动通信网络领域的个性化服务推荐问题,通过将移动用户上下文信息引入协同过滤推荐过程,提出一种基于移动用户上下文相似度的改进协同过滤推荐算法。该算法首先计算基于移动用户的上下文相似度,以构造目标用户当前上下文的相似上下文集合,然后采用上下文预过滤推荐方法对移动用户-移动服务-上下文3维模型进行降维得到移动用户-移动服务2维模型,最后结合传统2维协同过滤算法进行偏好预测和推荐。仿真数据集和公开数据集实验表明,该算法能够用于移动网络服务环境下的用户偏好预测,并且与传统协同过滤相比具有更高的推荐精确度。     

InGaAs近红外探测器高可靠封装技术

对256元和512元InGaAs线列探测器进行了气密封装,对封装结构和工艺中的几个关键技术进行了分析,包括热电致冷器的热负载性能、温度烘烤性能、组件密封性.研究结果表明:在室温条件下,热电致冷器的致冷温差可以达到55K以上,热负载每增加50 mW,致冷温差下降约0.51 K,能够满足组件的使用要求.经过120℃、500...     

Materialized view selection as constrained evolutionary optimization

One of the important issues in data warehouse development is the selection of a set of views to materialize in order to accelerate a large number of on-line analytical processing (OLAP) queries. The maintenance-cost view-selection problem is to select a set of materialized views under certain resource constraints for the purpose of minimizing the total query processing cost. However, the search space for possible materialized views may be exponentially large. A heuristic algorithm often has to be used to find a near optimal solution. In this paper, for the maintenance-cost view-selection problem, we propose a new constrained evolutionary algorithm. Constraints are incorporated into the algorithm through a stochastic ranking procedure. No penalty functions are used. Our experimental results show that the constraint handling technique, i.e., stochastic ranking, can deal with constraints effectively. Our algorithm is able to find a near-optimal feasible solution and scales with the problem size well.     

High power mid-infrared optically pumped PbSe/PbSrSe multiple-quantum-well vertical-cavity surface-emitting laser operation at 325 K

A high power, mid-infrared (/spl lambda/=3.8 /spl mu/m) lead-salt vertical-cavity surface-emitting laser (VCSEL) operating at 325 K is demonstrated. The laser emission is generated in a half-wavelength microcavity consisting of seven pairs of PbSe/PbSrSe multiple-quantum-wells embedded in two mirrors and optically pumped with 5 ns laser pulses.     

A 1.8-V 6/9-GHz reconfigurable dual-band quadrature LC VCO in SiGe BiCMOS technology

This paper presents a dual-band voltage-controlled oscillator (VCO) that can be reconfigured between 6- and 9-GHz frequency bands. It comprises a 6-GHz LC-tuned VCO, two 1/2 dividers, two mixers, and two 3-GHz notch filters. The 9-GHz output is generated based on the analog frequency multiplication method by mixing the 6-GHz VCO output with its divide-by-two signal. The VCO, implemented in a 0.18-/spl mu/m SiGe BiCMOS technology, achieves a fast reconfiguration time of 3.6 ns. The measured VCO phase noises are -106 and -104 dBc/Hz at 1-MHz offset for 6- and 9-GHz modes, respectively, while draining 10.8 mA from a 1.8-V supply.     

Microwave imaging via space-time beamforming for early detection of breast cancer

A method of microwave imaging via space-time (MIST) beamforming is proposed for detecting early-stage breast cancer. An array of antennas is located near the surface of the breast and an ultrawideband (UWB) signal is transmitted sequentially from each antenna. The received backscattered signals are passed through a space-time beamformer that is designed to image backscattered signal energy as a function of location. The beamformer spatially focuses the backscattered signals to discriminate against clutter and noise while compensating for frequency-dependent propagation effects. As a consequence of the significant dielectric-properties contrast between normal and malignant tissue, localized regions of large backscatter energy levels in the image correspond to malignant tumors. A data-adaptive algorithm for removing artifacts in the received signals due to backscatter from the skin-breast interface is also presented. The effectiveness of these algorithms is demonstrated using a variety of numerical breast phantoms based on anatomically realistic MRI-derived FDTD models of the breast. Very small (2 mm) malignant tumors embedded within the complex fibroglandular structure of the breast are easily detected above the background clutter. The MIST approach is shown to offer significant improvement in performance over previous UWB microwave breast cancer detection techniques based on simpler focusing schemes.