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.     

A Complete Separation of Hexane Isomers by a Functionalized Flexible Metal Organic Framework

The separation ability of branched alkane isomers (nHEX, 3MP, 22DMB) of the flexible and functionalized microporous iron(III) dicarboxylate MIL‐53(Fe)‐(CF₃)₂ solid is evaluated through a combination of breakthrough experiments (binary or ternary mixtures), adsorption isotherms, X‐ray diffraction temperature analysis, quasi‐elastic neutron scattering measurements and molecular dynamics simulations. A kinetically controlled molecular sieve separation between the di‐branched isomer of hexane 22DMB from a mixture of paraffins is achieved. The reported total separation between mono‐ and di‐branched alkanes which was neither predicted nor observed so far in any class of porous solids is spectacular and paves the way towards a potential unprecedented upgrading of the RON of gasoline.     

OC-48、OC-192芯片和系统设计师面临挑战

当今，从事OC-48、OC-192技术的设计师在设计基于因特网协议(IP协议)的下一代系统时，因系统含有诸如ASIC、网络处理器(NP)、高速跟踪器等元件，以及分组SONET物理层(PoS-PHY)接口规范等的演变，而一直面临挑战。抖动和扭斜失真等现象的存在给诸如系统分组接口第4层(SPI-4)和通用交换接口(CSIX)等总线结构本已拥挤的时序容限，以及四元数据率静态RAM传送表访问时间带来极大混乱。再加上诸如低压差分信号(LVDS)、高速收发逻辑和短线串行终端逻辑等超低电压峰-峰信号技术的引入，使数据出错的可能性变得异常之高。而利用仿真技…     

Engineering Gold Nanotubes with Controlled Length and Near‐Infrared Absorption for Theranostic Applications

Important aspects in engineering gold nanoparticles for theranostic applications include the control of size, optical properties, cytotoxicity, biodistribution, and clearance. In this study, gold nanotubes with controlled length and tunable absorption in the near‐infrared (NIR) region have been exploited for applications as photothermal conversion agents and in vivo photoacoustic imaging contrast agents. A length‐controlled synthesis has been developed to fabricate gold nanotubes (NTs) with well‐defined shape (i.e., inner void and open ends), high crystallinity, and tunable NIR surface plasmon resonance. A coating of poly(sodium 4‐styrenesulfonate) (PSS) endows the nanotubes with colloidal stability and low cytotoxicity. The PSS‐coated Au NTs have the following characteristics: i) cellular uptake by colorectal cancer cells and macrophage cells, ii) photothermal ablation of cancer cells using single wavelength pulse laser irradiation, iii) excellent in vivo photoacoustic signal generation capability and accumulation at the tumor site, iv) hepatobiliary clearance within 72 h postintravenous injection. These results demonstrate that these PSS‐coated Au NTs have the ideal attributes to develop their potential as effective and safe in vivo imaging nanoprobes, photothermal conversion agents, and drug delivery vehicles. To the best of knowledge, this is the first in vitro and in vivo study of gold nanotubes.     

Determination of total glucosinolates in oilseed rape by X-ray spectrometric analysis for oxidised sulphur (S6+)

A rapid X-ray spectrometric (XRS) method has been developed for the determination of the total glucosinolate content of oilseed rape and other Brassica oilseeds. The method is based on analysis for fully oxidised sulphur (S⁶⁺), which includes half the sulphur (S) in the glucosinolate molecule, and the S in sulphate. Results are highly correlated with glucosinolate content determined by glucose release, a standard method widely used in Australia. The relationship is total glucosinolates = (23·97 S⁶⁺ -9·43) r² = 0·987, where the glucosinolate content is expressed as μmol g^?1 and the S⁶⁺ content in mg g^?1. The relationship is applicable to seed of any glucosinolate content and to meal, and is unaffected by changes in protein sulphur content. The correlation of glucosinolates with S⁶⁺ is shown to be closer than the correlation with total S. The latter correlation forms the basis of the existing XRS method, used within the European Community in recent years. The advantages of S⁶⁺ derive from the linearity of the regression and the elimination of errors caused by variation in protein content. The method should be valuable to the Australian oilseed industry because it allows the rapid screening of breeding lines to ensure low glucosinolate content and the assessment of deliveries for crushing and of meal.     

Surface copper enrichment by reduction of copper chromite catalyst employed for carbon monoxide oxidation

The effect of prereduction on CO oxidation activity of unsupported copper-chromite oxide catalysts was examined. Results were found to be in good agreement with two mechanisms for a surface copper enrichment due to CO prereduction which produced an activity increase in the copper-chromite catalyst.     

Ultrastructural alterations during embryonic rats' lung development caused by ozone

Ozone (O3) is an oxidizing agent that acts on phospholipids, proteins and sugars of cellular membranes producing free radicals, which cause oxidative damages. The O3 exposure has been used as a model to study oxidative stress, in which the respiratory airways represent the entrance to the organism. In this study, ultrastructural alterations were identified at the bronchiolar level during the intra-uterine lung development, using an O3 exposure model in pregnant rats during 18, 20 and 21 days of gestation. Twelve pregnant Wistar rats, six controls and six exposed to 1 ppm O3 inhalation during 12 h per day, were used. The rats were sacrificed at gestational days 18, 20 and 21; the fetuses were obtained and their lungs dissected. The ultrastructural analysis evidenced swollen mitochondria, cytoplasmic vacuolization of the epithelial cells and structural disorder caused by the oxidative stress. At gestation day 20, flake-off epithelial cells and laminar bodies in the bronchiolar lumen were observed. In the 21-gestation-day group, the mitochondria were edematous and their cristae were disrupted by the damage caused in mitochondrial membranes.     

Diketopyrrolopyrrole Organic Thin‐Film Transistors: Impact of Alkyl Substituents and Tolerance of Ethylhexyl Stereoisomers

Bis(thiophen‐2‐yl)‐diketopyrrolopyrrole (DPP) dyes bearing various alkyl substituents at the amide positions (n‐butyl, n‐pentyl, n‐hexyl, n‐heptyl, n‐octyl, 2‐ethylhexyl) and chlorine (Cl), bromine (Br), or cyano (CN) substituents at the thiophene positions have been synthesized and investigated with regard to their molecular and semiconducting properties. Intense absorption, strong fluorescence, and reversible oxidation and reduction processes are common to all of these dyes. Their characterization as organic semiconductors in vacuum‐processed thin‐film transistors reveals p‐channel operation with field‐effect mobilities ranging from 0.01 to 0.7 cm² V^?1 s^?1. The highest mobility is found for the DPP dyes bearing the 2‐ethylhexyl substituents, which is surprising, considering that as a result of the chiral substituents, this material is a mixture of (R,R), (S,S), and (R,S) stereoisomers. The high carrier mobility in the films of the DPPs bearing stereoisomerically inhomogeneous ethylhexyl groups is rationalized here by single‐crystal X‐ray diffraction (XRD) analysis in combination with XRD and atomic force microscopy studies on thin films, which reveal the presence of slightly different 2D layer arrangements for the n‐alkyl and the 2‐ethylhexyl derivatives. For the cyano‐substituted DPPs possessing the lowest LUMO levels, ambipolar transport characteristics are observed.