African Urbanization as Flight? Some Policy Implications of Geography

The mystery of the lack of a positive relationship between growth and urbanization in sub-Saharan Africa has been raised in a number of studies. A recent paper by Barrios et al. (Journal of Urban Economics 60:357–371, 2006) provides a compelling explanation for why this occurs. Exploiting a new data source, they show how climate change, specifically the reduction in rainfall, has driven people from the increasingly impoverished countryside to the city. They also show that while this is an important factor explaining urbanization in sub-Saharan African countries it does not affect urbanization elsewhere. Their explanation for this important difference is differences in the patterns of rainfall, as well as the composition of soil in most sub-Saharan countries. In a word, geographical factors have dominated the unusual pattern observed in the world’s most rapidly urbanizing continent. In this paper, we extend the work done by Barrios et al. to include more observations and more detailed geographic variables. We first replicate their results and extend the number of observations to more recent periods. Then we consider the effects of a range of specific country geographical characteristics, relying on data developed by other researchers. After discussing our results, we focus on the implications of our findings for policy formulation, particularly for sub-Saharan African countries. The results indicate that geographical circumstances place significantly more important constraints on maximization processes. In other words, urbanization in these countries takes place in a profoundly “second-best” world. We consider what this kind of context implies for the sequencing and implementation of economic reforms which would allow for an urbanization process that would be more conducive to economic growth.     

Starch determination in horticultural plant material by an enzymic-colorimetric procedure

The starch content of horticultural plant material (including leaves and woody tissues such as roots, stems, twigs, trunks and bark) was determined by an enzymic procedure. A heat-stable α-amylase and amyloglucosidase were used to hydrolyse the starch in the finely ground plant material to glucose. The glucose produced was measured colorimetrically using a coupled glucose oxidase/peroxidase reaction. Conditions necessary for maximum glucose recovery were established. Plant material analysed included samples from macadamia (Macadamia integrifolia Maiden and Betche, trunk and bark), mango (Mangifera indica L; stems and roots), lychee (Litchi chinensis Sonn; leaves, stems, twigs and roots), pineapple (Ananas comosus (L) Merrill; leaves, stems and roots) and nectarine (Prunus persica (L) Batsch var nucipersica (Suckow) C K Schneid; twigs, shoots, branches, limbs, roots and trunk). Starch values ranged from less than 14% to greater than 30%. The method allows assessment of variations in the starch content of perennial plants and may be used in crop management.     

Structural Orientation and Anisotropy in Biological Materials: Functional Designs and Mechanics

Biological materials exhibit anisotropic characteristics because of the anisometric nature of their constituents and their preferred alignment within interfacial matrices. The regulation of structural orientations is the basis for material designs in nature and may offer inspiration for man‐made materials. Here, how structural orientation and anisotropy are designed into biological materials to achieve diverse functionalities is revisited. The orientation dependencies of differing mechanical properties are introduced based on a 2D composite model with wood and bone as examples; as such, anisotropic architectures and their roles in property optimization in biological systems are elucidated. Biological structural orientations are designed to achieve extrinsic toughening via complicated cracking paths, robust and releasable adhesion from anisotropic contact, programmable dynamic response by controlled expansion, enhanced contact damage resistance from varying orientations, and simultaneous optimization of multiple properties by adaptive structural reorientation. The underlying mechanics and material‐design principles that could be reproduced in man‐made systems are highlighted. Finally, the potential and challenges in developing a better understanding to implement such natural designs of structural orientation and anisotropy are discussed in light of current advances. The translation of these biological design principles can promote the creation of new synthetic materials with unprecedented properties and functionalities.     

符合RoHS的产品的向下兼容性

向RoHS(<关于在电气电子设备中禁止使用某些有害物质指令>)转换看起来是值得称颂的现代电子制造界的大事.对于符合RoHS的新型产品的需求不断地困扰着元件供应商,而同时另外一些用户则要求继续供应传统锡/铅型元件.对于那些未直接受到RoHS影响的电子制造商,元件供应链的惯性肯定要影响到锡/铅元件的可用性,同时元件供应商需要减少不符合RoHS的产品的库存;因此,向无铅型转换的时间期限日益加快.如果你必须购买无铅的商用现成产品,那么在您目前的锡/铅制造实践中会使用这些无铅的商用现成产品吗?     

Algorithm for tissue ischemia estimation based on electrical impedance spectroscopy

The purpose of this paper is to present an algorithm developed for real-time estimation of skeletal muscle ischemia, based on parameters extracted from in vivo obtained electrical impedance spectra. A custom impedance spectrometer was used to acquire data sets: complex impedance spectra measured at 27 frequencies in the range of 100 Hz-1 MHz, and tissue pH. Twenty-nine in vivo animal studies on rabbit anterior tibialis muscle were performed to gather data on the behavior of tissue impedance during ischemia. An artificial neural network (ANN) was used to quantitatively describe the relationship between the parameters of complex tissue impedance spectra and tissue ischemia via pH. The ANN was trained on 1249, and tested on 946 ischemic tissue impedance data sets. A correlation of 94.5% and a standard deviation of 0.15 pH units was achieved between the ANN estimated pH and measured tissue pH values.     

3G基站的两个关键部件--高速数据转换器和放大器

第三代移动电话主要依靠宽带码分多址(WCDMA)技术,信号处理技术的发展、体系结构的进步以及新开发的高速数据转换器和运算放大器正在使无线基础结构的设计师们降低成本,更好地实现第三代无线通信系统的目标。     

基于CMOS工艺的高性能射频滤波器:体声波滤波器(BAW)

过去几年中,随着射频集成电路技术和系统结构的发展,移动电话中射频部分的很多分立器件已被替换。最为明显的就是接收机中分立的低噪声放大器(LNA)和中频(IF)滤波器已经被集成到射频集成电路中。可以预期各射频模块将逐步被集成到标准BiCMOS或CMOS集成电路中,但还是有几类射频元件的集成不太容易做到,其中就包括射频滤波器。所有的移动电话都需要射频滤波器以保护敏感的接收(Rx)信道,使之免受其他用户的发送(Tx)信号及各种射频源产生的噪声干扰。移动电话可能要求当Rx信号比干扰信号强度低120dB时仍能工作。而前置放大器无法提供足够小的互调以满足这种要求。     

Free-Space Optical Communications for Next-generation Military Networks

There is a continuing need for increased capacity for military applications, especially in network-centric operational concepts that promote the use of information as fundamental for gaining superiority on the battlefield. As an example, the access to, and distribution of, sensor data is a major tenet of network-centric warfare and yet radio frequency (RF) links will struggle to provide the needed capacity. Free-space optical communications (FSOC) has the potential to meet these emerging military needs by offering dramatic increases in capacity. However, there are many technical challenges al multiple layers of the communications protocol stack. This article describes these challenges and discusses some mitigation approaches to provide a path to realizing this capability on the battlefield     

A linear 60 GHz 65 nm-CMOS power amplifier realization and characterization for OFDM signal

A millimeter-wave Power Amplifier (PA) based on a 65nm CMOS technology from STMicroelectronics has been designed. The targeted feature is the unlicensed band around 60 GHz suitable for wireless personal area network application (WPAN). To optimize the linearity, the PA is designed under class A biasing to have an output compression point (OCP₁) close to its saturated Power (P _sat). S-parameters and large signal measurement results are demonstrated and compared with electromagnetic simulations. The PA offers a P _sat of 8.3 dBm, an OCP₁ of 6 dBm and a gain of 6.7 dB. The die area is 0.29 mm² with pads. Considering those results, one-tone simulations are not sufficient to characterize the linearity performances of the PA in its real conditions of use. Consequently, two-tone simulations are firstly performed. After, linearity figures of merit (FoM) are discussed applying an orthogonal frequency-division multiplexing (OFDM) modulated signal. The PA offers an adjacent channel power ratio (ACPR) of 15 dB and an error vector magnitude (EVM) of 20% at PA compression operating mode.     

密集传感器的设计

随着微处理器与传感器价格的不断下滑,自动系统与半自动系统都可以包含更多的智能,根据对自身内部状况以及当时外部环境的更好了解,作出更优化的决策。为一个设计增加传感器,并将所有这些传感器的数据作智能关联处理,这些都会带来更多的设计时间成本与复杂性,但各个设计团队仍在日益接受这种成本,因为权衡的结果可以是一个差异化的系统,它能更有效地提供更多功能,而价格则与前代设计不相上下。