球体城市

文章试图以德国哲学家彼得·斯洛特戴克在《空间》三部曲中提出的"球体"和"气泡"概念来理解当代全球城市所面临的复杂空间状况,并挑战以往建筑学中占主导的水平主义。同时,文章追溯了现代主义的发展历史中曾出现过的"球体城市"实践,特别是俄国构成主义、20世纪中期以米歇尔·拉贡为主的国际前瞻建筑团体、库哈斯的"囚禁中的城市",以及全球化背景下,"球体策略"在上海、深圳这类城市中的进一步运用。     

利用电压基准产生稳定流入电流源

正无源元件长期测试用模拟电路,比如0.1%公差电阻或高强度白光LED,经常需要恒流。利用两个运算放大器和一个电压基准,你就能开发出一种提供恒定流入电流源,其可变设定范围是0mA至0.99A。图1所示电路使稳定电     

Electrochemical nitrite nanosensor developed with amine- and sulphate-functionalised polystyrene latex beads self-assembled on polyaniline

Aniline doped with polyvinyl sulphonate (PV-SO₃⁻) was electropolymerised on screen printed carbon (SPCE) and glassy carbon (GCE) electrodes. Then nano-structured polystyrene (PS_NP) latex beads functionalised with amine (PS_NP-NH₂) and sulphate (PS_NP-OSO₃⁻) were self-assembled on the modified SPCE and GCE. The resultant polyaniline nanocomposites (PANI|PS_NP-NH₂ or PANI|PS_NP-OSO₃⁻) were characterised by cyclic voltammetry (CV), UV-vis spectroscopy and scanning electron microscopy (SEM). Brown-Anson analysis of the multi-scan rate CV responses of the various PANI films gave surface concentrations of the order of 10⁻⁸ mol cm⁻². UV-vis spectra of the PANI films dissolved in dimethyl sulphoxide showed typical strong absorbance maxima at 480 and 740 nm associated with benzenoid π-π* transition and quinoid excitons of polyaniline, respectively. The SEM images of the PANI nanocomposite films showed cauliflower-like structures that are <100 nm in diameter. When applied as electrochemical nitrite sensor, sensitivity values of 60, 40 and 30 μA/mM were obtained for electrode systems containing PANI|PS_NP-NH₂, PANI and PANI|PS_NP-SO₃⁻, respectively. The corresponding limits of detection of the sensors were 7.4, 9.2 and 38.2 μM NO₂⁻.     

Nitrogen balances in farmers fields under alternative uses of a cover crop legume: a case study from Nicaragua

Canavalia brasiliensis (canavalia), a drought tolerant legume, was introduced into the smallholder traditional crop-livestock production system of the Nicaraguan hillsides as green manure to improve soil fertility or as forage during the dry season for improving milk production. Since nitrogen (N) is considered the most limiting nutrient for agricultural production in the target area, the objective of this study was to quantify the soil surface N budgets at plot level in farmers fields over two cropping years for the traditional maize/bean rotation and the alternative maize/canavalia rotation. Mineral fertilizer N, seed N and symbiotically fixed N were summed up as N input to the system. Symbiotic N₂ fixation was assessed using the ¹⁵N natural abundance method. Nitrogen output was quantified as N export via harvested products. Canavalia derived in average 69% of its N from the atmosphere. The amount of N fixed per hectare varied highly according to the biomass production, which ranged from 0 to 5,700 kg ha^?1. When used as green manure, canavalia increased the N balance of the maize/canavalia rotation but had no effect on the N uptake of the following maize crop. When used as forage, it bears the risk of a soil N depletion up to 41 kg N ha^?1 unless N would be recycled to the plot by animal manure. Without N mineral fertilizer application, the N budget remains negative even if canavalia was used as green manure. Therefore, the replenishment of soil N stocks by using canavalia may need a few years, during which the application of mineral N fertilizer needs to be maintained to sustain agricultural production.     

Modeling nitrate fluxes at the catchment scale using the integrated tool CAWAQS

Nitrates fluxes in the Grand Morin basin (1200 km(2)), that is subjected to intense agricultural pressure, are considered using in-stream observations (around 250 sampling days over 5 years) and physically based simulations using the CAWAQS model (CAtchment WAter Quality Simulator). In-stream nitrate concentration averaged 6 mg N L(-1), increasing by approximately 0.2 mg N L(-1) yr(-1) around this value (period 1991-1996). Our results show that, over the period of 1991-1996, the differences between in-stream observed nitrate concentrations and simulated nitrate concentrations result from nitrate losses at the basin scale. These losses are due to denitrification by transfer through wetlands, alluvial plains, the hyporheic zone, and by benthic processes in rivers. A mean annual mass balance at the basin scale indicates that 40% of the infiltration flux (3360 kg N km(-2) yr(-1)) is removed from the system via the river network, 40% is stored in aquifers and 20% is lost by denitrification (period 1991-1996).     

Effect of propionic acid on kinetics of acetate and oleate and on plasma and milk fatty acid composition of goats

Entry rates of acetate and oleate and their incorporation into lipids of blood plasma and fatty acids of milk were studied in lactating goats fed a concentrate-roughage ration with propionic acid infused intraruminally at 0, 5.52, and 13.74 g/h by primed constant intravenous infusion of [1-carbon-14] acetate and [9, 10-hydrogen-3] oleate. Means for infusion rates were acetate, 60, 52, and 39 micrograms/ml blood plasma; propionate 9, 12, and 22 micrograms/ml; oleate, 19, 14, and 12 micrograms/ml; acetate entry rate, 3.9, 2.7, and 1.8 mmol/h per kg bodyweight; oleate entry rate, 47, 29, and 19 mumol/h per kg bodyweight; acetate oxidation rate, 2.0, 1.7, and 1.4 mmol/h per kg, and its contribution to the total carbon dioxide production, 16, 14, and 11%. Propionic acid increased incorporation of carbon-14 and hydrogen-3 into plasma lipids, elevated proportions of 7:0, 9:0, 11:0, 13:0, 15:0, and 17:0 fatty acids in milk, and tended to lower others. Specific radioactivities of milk fatty acids during infusion of propionic acid were elevated by 1.8 to 2.8 times, and total fatty acids in milk and plasma were lowered by 22 and 38%. Data support the glucogenic theory that propionic acid either directly or through gluconeogenesis stimulates insulin secretion, which in turn inhibits release of fatty acids from adipose tissue, resulting in milk fat depression.     

Changes in lipid content and composition during germination of groundnuts

The cotyledons of two varieties of germinating groundnut seeds (Runner and Bunch) were analysed periodically for their lipid content and fatty acid composition over a period of 132 h. The lipid content decreased drastically during germination. More drastic changes in lipid constituents were observed for light-grown seedlings than for dark-grown ones. In general, the non-polar lipids (NPL) were metabolised faster than the polar ones (P > 0.05) especially in those seeds grown in the dark. The rate of decrease in NPL content almost paralleled that of increase in glycolipid (GL) content. Triacyl glycerol content decreased noticeably during germination while other NPL tended to increase. Among the GL, sterylglucoside increased rapidly during early germination under darkness, only to decrease steadily thereafter. A converse effect was observed for acyl sterylglucoside which, in the dark, decreased rapidly at early germination only to increase equally rapidly later on. Among the phospholipids (PL), only phosphatidic acid showed a marked increase during germination, under both growth conditions, while others tended to decrease in varying degrees. The changing patterns of GL and PL during germination seem to follow the pattern of the formation of photosynthetic tissues and the metabolic conversion of PL. The major fatty acids of the three lipid groups, which more or less decreased or increased in varying degrees with germination in light-grown seeds were oleic, linoleic, palmitic, stearic, arachidic and lignoceric acids in decreasing order of prominence at early germination.     

Solution-processable graphene linked to 3,5-dinitrobenzoyl as an electron acceptor in organic bulk heterojunction photovoltaic devices

3,5-Dinitrobenzoyl chloride was covalently linked to graphene oxide (GO) nanosheets prepared by a modified Hummers’ method, using ethylenediamine as a spacer. The linkage of the GO with the small molecule was confirmed by spectroscopic (e.g., Fourier transform infrared, Raman) and microscopic analyses. The resultant GO-ethylene-dinitro-benzoyl (GO-EDNB) consists of a controlled scale of different graphene structures and is highly dispersable in common organic solvents. The GO-EDNB was used as the electron acceptor material in poly-(3-hexylthiophene) (P3HT) bulk heterojunction photovoltaic devices to significantly improve the performance, yielding a power conversion efficiency improvement of two orders and one order of magnitude compared with the pristine P3HT and the P3HT-GO devices respectively.     

Contextual correlates of adolescents' self-efficacy after smoking cessation.

Recent research has shown that daily changes in self-efficacy predict lapses and relapse into smoking after quitting among adolescent daily smokers, but it is not known if and how momentary self-efficacy is associated with affect-motivational states and external contexts. In the present study, 134 adolescent daily smokers were monitored daily during 1 week prior to and 3 weeks after they began their quit attempt. Participants completed questions on smoking, self-efficacy, affect-motivational states (craving and negative affect), and external contexts (seeing others smoke, experiencing a stressful event, and alcohol and coffee consumption) three times a day. Affect-motivational states as well as all external contexts (except for coffee consumption) were associated with lower self-efficacy when participants were still abstinent, but also after they had lapsed. Associations between the situational contexts and self-efficacy did not largely depend on individual characteristics such as baseline self-efficacy and age. Among girls, however, the negative associations between self-efficacy and negative affect and drinking alcohol were found to be stronger. These results show that adolescents' self-efficacy during a quit attempt may be responsive to affect-motivational states and external contexts, both before and after lapsing. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

SOLVENT EXTRACTION WITH ORGANOPHOSPHONIC MONO-ACIDIC ESTERS

Mono-acidic liquid ion exchangers (extractants) containing the phosphonyl functional group arc reviewed.