Conversion of supramolecular clusters to macromolecular objects

In a reaction proceeding within a nanoscopic volume, supramolecular clusters were transformed to polymer objects while retaining their shape and size. Spatial isolation of the cross-linkable blocks of oligobutadiene that were involved in this stitching reaction was achieved by self-assembly of the molecules that made up the clusters. Thermal activation of cross-linking yielded macromolecules (molecular weight of 70,000) with a narrow size distribution that was similar to that of the supramolecular clusters. The macromolecules obtained have an anisotropic shape (2 nanometers by 8 nanometers), as determined by electron microscopy and small-angle x-ray scattering, and form materials that exhibit a liquid crystalline state.     

水氮耦合对棉花干物质积累及产量的影响

[目的]研究水氮耦合对棉花干物质积累及产量影响.[方法]大田试验采用裂区试验设计,设置灌溉量与施肥量2个调控因子,其中灌溉量为主区,施肥量为副区,均设置3个梯度,灌溉量依次为2250(低灌量)、3450(中灌量,传统经验灌溉量CK)、4650 m3/hm2,(高灌溉量)分别以W1、W2和W3表示;施肥量(折合纯氮)依次...     

Hydrogen radicals, nitrogen radicals, and the production of O3 in the upper troposphere

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.     

The Current State of Solar Modeling

Data from the Global Oscillation Network Group (GONG) project and other helioseismic experiments provide a test for models of stellar interiors and for the thermodynamic and radiative properties, on which the models depend, of matter under the extreme conditions found in the sun. Current models are in agreement with the helioseismic inferences, which suggests, for example, that the disagreement between the predicted and observed fluxes of neutrinos from the sun is not caused by errors in the models. However, the GONG data reveal subtle errors in the models, such as an excess in sound speed just beneath the convection zone. These discrepancies indicate effects that have so far not been correctly accounted for; for example, it is plausible that the sound-speed differences reflect weak mixing in stellar interiors, of potential importance to the overall evolution of stars and ultimately to estimates of the age of the galaxy based on stellar evolution calculations.     

Fertility and whelping complications in bitches following correction of vaginal abnormalities

The fertility and whelping complications of normal bitches and of bitches that had had surgery to correct a vaginal abnormality of varying severities were compared retrospectively. Reproductive performance and whelping statistics were compared between 37 bitches that had been diagnosed with a vaginal abnormality and 37 age- and breed-matched bitches with no history of vaginal abnormalities. There were no significant differences in reproductive performance between the affected and control bitches. When analysed by the severity of the abnormality, pregnancy rates were significantly lower for the group of bitches with the most severe abnormalities compared with the group of bitches that had mild vaginal abnormalities. Furthermore, the bitches that had severe abnormalities were significantly more likely to require a caesarean section than those with mild abnormalities.     

森林采伐限额制度存在的问题及建议

森林采伐限额是采伐消耗森林、林木蓄积的最大限量。实行森林采伐限额管理是《森林法》确定的一项重要法律制度,是控制森林资源过量消耗的核心措施和加强森林可持续经营的关键手段。本文阐述了森林采伐限额的概念,分析了当前采伐制度存在的一些问题,提出了改进措施及具体做法,以寻求最佳的森林采伐管理制度,保护好国家珍贵而有限的森林资源,达到科学经营的目的。