Searching for the parallel growth of cities

Three urban growth theories predict parallel growth of cities. The endogenous growth theory predicts deterministic parallel growth; the random growth theory implies that city growth follows Gibrat’s law with a steady-state distribution; and the hybrid growth theory suggests the co-movement of random city growth. This paper uses the Chinese city size data from 1984-2006 and time series econometric techniques to test for parallel growth. The results from various types of stationarity tests on pooled heterogeneous cities show that city growth is random. However, once growth trend and structural change are taken into account, certain groups of cities with common group characteristics, such as similar natural resource endowment or policy regime, grow parallel.Urban growth; Parallel growth; Zipf’s law; Unit root; Structural change

Conversion of sugarcane bagasse to carboxylic acids under thermophilic conditions

With the inevitable depletion of the petroleum supply and increasing energy demands in the world, interest has been growing in bioconversion of lignocellulosic biomass (e.g., sugarcane bagasse). Lignocellulosic biomass is an abundant, inexpensive, and renewable resource. Most of current conversion technologies require expensive enzymes and sterility. In contrast, the patented MixAlco process requires no enzymes or sterility, making it attractive to convert lignocellulosic biomass to transportation fuels and valuable chemicals. This study focuses on pretreatment and thermophilic fermentation in the MixAlco process. Ammonium bicarbonate (NH4HCO3) was discovered to be a better pH buffer than previously widely used calcium carbonate (CaCO3) in anaerobic fermentations under thermophilic conditions (55°C). The desired pH should be controlled within 6.5 to 7.5. Over 85% acetate content in the product was found in paper fermentations and bagasse fermentations. Hot-lime-water-treated bagasse countercurrent fermentations buffered by ammonium bicarbonate achieved 50–60% higher total product concentrations than those using calcium carbonate. It was nearly double in paper batch fermentations if the pH was controlled around 7.0. Ammonium bicarbonate is a “weak” methane inhibitor, so a strong methane inhibitor (e.g., iodoform) is still required in ammonium bicarbonate buffered fermentations. Residual calcium salts did not show significant effects on ammonium bicarbonate buffered fermentations. Lake inocula from the Great Salt Lake, Utah, proved to be feasible in ammonium bicarbonate buffered fermentations. Under mesophilic conditions (40°C), the inoculum from the Great Salt Lake increased the total product concentration about 30%, compared to the marine inoculum. No significant fermentation performance difference, however, was found under thermophilic conditions. The Continuum Particle Distribution Model (CPDM) is a powerful tool to predict product concentrations and conversions for long-term countercurrent fermentations, based on batch fermentation data. The experimental acid concentrations and conversions agree well with the CPDM predictions (average absolute error < 15%). Aqueous ammonia treatment proved feasible for bagasse. Air-lime-treated bagasse had the highest acid concentration among the three treated bagasse. Air-lime treatment coupled with ammonium bicarbonate buffered fermentations is preferred for a “crop-tofuel” process. Aqueous ammonia treatment combined with ammonium bicarbonate buffered fermentations is a viable modification of the MixAlco process, if “ammonia recycle” is deployed

LA CROISSANCE URBAINE CHINOISE RECONSIDÉRÉE

Over the last decade, many researchers have focused on the study of different urban hierarchies and their evolution over time. These studies may or may not confirm Zipf’s law and emphasize the characteristics of urban growth. The question is then whether urban growth depends upon city-size or not, which is a main issue in modern regional economics. Using data on Chinese cities for the period 1960-2000, this paper aims to provide some answers to this question which has led to a recent passionate debate between the random growth theories and the endogenous growth theories.CROISSANCE URBAINE, HIÉRARCHIES URBAINES, LOI DE ZIPF, URBANISATION CHINOISE, AGGLOMÉRATION, LOI DE GIBRAT

Towards Integrated Optical Quantum Networks in Diamond

We demonstrate coupling between the zero phonon line (ZPL) of nitrogen-vacancy centers in diamond and the modes of optical micro-resonators fabricated in single crystal diamond membranes sitting on a silicon dioxide substrate. A more than ten-fold enhancement of the ZPL is estimated by measuring the modification of the spontaneous emission lifetime. The cavity-coupled ZPL emission was further coupled into on-chip waveguides thus demonstrating the potential to build optical quantum networks in this diamond on insulator platform

Mechanical properties and structural health monitoring performance of carbon nanotube-modified FRP composites:A review

This article provides an extensive review of key publications covering topics of fabrication methods, enhancement of mechanical properties, and applications of CNT-modified FRP materials in structural health monitorin

Searching for the Parallel Growth of Cities

Based on the parallel growth implications of the four urban growth theories (endogenous growth theory, random growth theory, hybrid growth theory, and locational fundamentals theory), this paper uses the Chinese city size data from 1984-2006 and time series econometric techniques to test for parallel growth. The results from various types of stationarity tests show that city growth is generally random. Conditioning on growth trend and structural change, certain groups of cities with common location specific characteristics, such as similar natural resource endowment or policy regime, grow parallel in the long run, suggesting that locational fundamentals may have persistent impacts on city growth

Searching for the parallel growth of cities

Three urban growth theories predict parallel growth of cities. The endogenous growth theory predicts deterministic parallel growth; the random growth theory implies that city growth follows Gibrat’s law with a steady-state distribution; and the hybrid growth theory suggests the co-movement of random city growth. This paper uses the Chinese city size data from 1984-2006 and time series econometric techniques to test for parallel growth. The results from various types of stationarity tests on pooled heterogeneous cities show that city growth is random. However, once growth trend and structural change are taken into account, certain groups of cities with common group characteristics, such as similar natural resource endowment or policy regime, grow parallel

Identification of Cbp1, a c-di-GMP Binding Chemoreceptor in Azorhizobium caulinodans ORS571 Involved in Chemotaxis and Nodulation of the Host Plant

Cbp1, a chemoreceptor containing a PilZ domain was identified in Azorhizobium caulinodans ORS571, a nitrogen-fixing free-living soil bacterium that induces nodule formation in both the roots and stems of the host legume Sesbania rostrata. Chemoreceptors are responsible for sensing signals in the chemotaxis pathway, which guides motile bacteria to beneficial niches and plays an important role in the establishment of rhizobia-legume symbiosis. PilZ domain proteins are known to bind the second messenger c-di-GMP, an important regulator of motility, biofilm formation and virulence. Cbp1 was shown to bind c-di-GMP through the conserved RxxxR motif of its PilZ domain. A mutant strain carrying a cbp1 deletion was impaired in chemotaxis, a feature that could be restored by genetic complementation. Compared with the wild type strain, the Δcbp1 mutant displayed enhanced aggregation and biofilm formation. The Δcbp1 mutant induced functional nodules when inoculated individually. However, the Δcbp1 mutant was less competitive than the wild type in competitive root colonization and nodulation. These data are in agreement with the hypothesis that the c-di-GMP binding chemoreceptor Cbp1 in A. caulinodans is involved in chemotaxis and nodulation