Spontaneous vesicle formation in aqueous mixtures of single-tailed surfactants

Spontaneous, single-walled, equilibrium vesicles can be prepared from aqueous mixtures of simple, commercially available, single-tailed cationic and anionic surfactants. Vesicle size, surface charge, or permeability can be readily adjusted by varying the ratio of anionic to cationic surfactant. Vesicle formation apparently results from the production of anion-cation surfactant pairs that then act as double-tailed zwitterionic surfactants. These vesicles are quite stable in comparison to conventional vesicles prepared by mechanical disruption of insoluble liquid crystalline dispersions.     

阴阳离子交换纤维柱联合法制备医药级蔗糖

采用ZB-1强酸性阳离子交换纤维柱和ZB-2强碱性阴离子交换纤维柱联合法制备医药级蔗糖.用石墨炉原子吸收光谱法测定医药级蔗糖痕量的铅,测定其比旋光度及电导率.结果表明,当ZB-1强酸性阳离子交换纤维和ZB-2强碱性阴离子交换纤维为2.0 g和3.5 g,上柱液质量浓度为0.30 g/mL,pH为7.0,流速为5.0 BV/h时,可有效除去蔗糖中的各种杂质.该法制备的医药级蔗糖指标符合英国药典2000版标准,收率高达92.63％.     

Carotenoid cation formation and the regulation of photosynthetic light harvesting

Photosynthetic light harvesting in excess light is regulated by a process known as feedback deexcitation. Femtosecond transient absorption measurements on thylakoid membranes show selective formation of a carotenoid radical cation upon excitation of chlorophyll under conditions of maximum, steady-state feedback deexcitation. Studies on transgenic Arabidopsis thaliana plants confirmed that this carotenoid radical cation formation is correlated with feedback deexcitation and requires the presence of zeaxanthin, the specific carotenoid synthesized during high light exposure. These results indicate that energy transfer from chlorophyll molecules to a chlorophyllzeaxanthin heterodimer, which then undergoes charge separation, is the mechanism for excess energy dissipation during feedback deexcitation.     

Tactoid formation in montmorillionite: effect on ion exchange kinetics

Exchange between calcium from montmorillonite and hydrogen from resin is much slower than exchange between sodium from montmorillonite and hydrogen from resin. Film kinetics are prevailing in both cases, but the location of the rate-determining step is shifted from the Nernst films of the resin particles in the sodium-hydrogen exchange to the Nernst films of the clay particles in the calcium-hydrogen exchange. The increased particle size of the montmorillonite in the calcium state, caused by tactoid formation, appears to be the main reason for the shift.     

皖南山区不同类型森林土壤阳离子交换性能差异

为了解皖南山区不同类型森林土壤阳离子交换性能差异,为该区合理营林提供参考,选取皖南山区6种不同类型森林土壤（杉木林、马尾松林、栓皮栎林、外松林、天然阔叶林和杉木-栓皮栎混交林）为研究对象,比较森林土壤阳离子交换性能的差异。结果表明：（1）研究区土壤呈强酸性,土壤有机质含量为33.84～91.50 g·kg^-1,总氮含量为0.94～3.37 g·kg^-1,碱解氮含量为131.58～203.62 mg·kg^-1,总磷含量为0.22～0.77 g·kg^-1,有效磷含量为0.17～ 0.32 mg·kg^-1;土壤主要缺乏速效磷养分。（2）阳离子交换量在8.09～12.57 cmol·kg^-1之间,排序为：天然阔叶林 ＞ 外松林 ＞ 马尾松林 ＞ 混交林 ＞ 杉木林 ＞ 栓皮栎林,不同森林土壤间阳离子交换量的差异主要由其土壤有机质的差异引起。（3）交换性盐基总量在1.74～2.72 cmol·kg^-1g之间,排序为：马尾松林 ＞ 外松林 ＞ 杉木林 ＞ 栓皮栎林 ＞ 混交林 ＞ 天然阔叶林,Ca²⁺和 Mg²⁺是主要的盐基离子,是成土过程中Ca、Mg优先固持形成的。（4）盐基饱和度在13.97%～28.98% 之间,排序为：马尾松林 ＞ 杉木林 ＞ 栓皮栎林 ＞ 外松林 ＞ 混交林 ＞ 天然阔叶林,该差异是由淋溶作用和树木对盐基离子的吸收共同作用形成的差异。综上,研究区土壤保肥和缓冲性能较低且供肥能力较差,尤其是土壤速效磷供应能力差。其中松林的供肥保肥能力及缓冲性能明显优于其他树种森林,混交林的速效养分含量更高,故可通过营造松类混交林以及施肥来提高森林土壤供肥保肥能力和缓冲性能。     

Species formation through punctuated gradualism in planktonic foraminifera

Detailed analysis of evolutionary changes in a 10-million-year long Late Neogene lineage of planktonic foraminifera has revealed a pattern that is not consistent with either the gradualistic or the punctuational model of evolution. The lineage was in stasis over a considerable part of its total duration but underwent relatively rapid, but not geologically instantaneous, gradual morphologic change that did not lead to lineage splitting. The term punctuated gradualism is suggested for this evolutionary modality.     

Spontaneous cell polarization through actomyosin-based delivery of the Cdc42 GTPase

Cell polarization can occur in the absence of any spatial cues. To investigate the mechanism of spontaneous cell polarization, we used an assay in yeast where expression of an activated form of Cdc42, a Rho-type guanosine triphosphatase (GTPase) required for cell polarization, could generate cell polarity without any recourse to a preestablished physical cue. The polar distribution of Cdc42 in this assay required targeted secretion directed by the actin cytoskeleton. A mathematical simulation showed that a stable polarity axis could be generated through a positive feedback loop in which a stochastic increase in the local concentration of activated Cdc42 on the plasma membrane enhanced the probability of actin polymerization and increased the probability of further Cdc42 accumulation to that site.     

Spontaneous formation of macroscopic chiral domains in a fluid smectic phase of achiral molecules

A smectic liquid-crystal phase made from achiral molecules with bent cores was found to have fluid layers that exhibit two spontaneous symmetry-breaking instabilities: polar molecular orientational ordering about the layer normal and molecular tilt. These instabilities combine to form a chiral layer structure with a handedness that depends on the sign of the tilt. The bulk states are either antiferroelectric-racemic, with the layer polar direction and handedness alternating in sign from layer to layer, or antiferroelectric-chiral, which is of uniform layer handedness. Both states exhibit an electric field-induced transition from antiferroelectric to ferroelectric.     

外源镧的吸附对红壤阳离子交换量和溶液组成的影响

采用不同用量外源锋土镧,研究其在红壤上的吸附及对红壤阳离子交换量和溶液组成的影响。结果表明,红壤对Ｌａ＾３＋具有较大的吸附容量和具有较高的可解吸性。当外源Ｌａ＾３＋浓度小于４００ｇｍ／ｋｇ时,被吸附的Ｌａ＾３＋具有较高的非交换性。阳离子交换量受外源镧的影响不显著;当外源镧浓度大于３００ｍｇ／ｋｇ时,土壤盐基饱和度与有效阳离子交换量显著降低,而交换性酸和交换性铝显著增加。浸出液中的盐基离子浓度随外源     

盐度和硬度对001×7 Na型阳离子交换树脂性能的影响

通过调整原水和再生剂中的盐度和硬度,研究了不同盐度和硬度组合对001×7 Na型阳离子交换树脂软化性能的影响,并用海水作为再生剂进行了试验。结果表明:盐度较高时,对软化和再生过程影响较大;海水不适合直接用作再生剂,并提出了理论依据。本试验结果可为实际工程中软化除盐设计的参数选取和运行提供参考。     

Ceramic thin-film formation on functionalized interfaces through biomimetic processing

Processing routes have been developed for the production of thin ceramic films through precipitation from aqueous solutions. The techniques are based on crystal nucleation and growth onto functionalized interfaces. Surface functionalization routes have been developed by the mimicking of schemes used by organisms to produce complex ceramic composites such as teeth, bones, and shells. High-quality, dense polycrystalline films of oxides, hydroxides, and sulfides have now been prepared from "biomimetic" synthesis techniques. Ceramic films can be synthesized on plastics and other materials at temperatures below 100 degrees C. As a low-temperature process in which water rather than organic solvents is used, this synthesis is environmentally benign. Nanocrystalline ceramics can be produced, sometimes with preferred crystallite orientation. The direct deposition of high-resolution patterned films has also been demonstrated. The process is well suited to the production of organic-inorganic composites.     

汇率变化对我国农业产业的影响——基于农业部门局部均衡模型

为研究汇率浮动与中国农产品市场波动之间的关系,采用全球农产品市场局部均衡模型,设定5种货币贬值和升值的情景方案,通过静态模拟方法,评估不同货币的汇率变化对中国农业产业的影响。结果显示,人民币贬值时,进口商品变的更加昂贵,进口减少,国内产品的需求增加,刺激国内产出增加。从具体产品来看,人民币贬值对稻谷、小麦、玉米、牛肉、猪肉和奶粉产量的影响较大。当人民币升值,中国农业受到的影响与贬值情况相反。主要农业贸易伙伴国货币汇率变动则首先影响该国产品的进出口量,进而影响产品的世界价格,再通过进出口将价格传导到中国,最终引起中国相关产品的生产、消费和贸易量的变动。中国受到较大影响的是从这些国家进口份额较大的产品,其中欧元、澳元、新西兰元和巴西雷亚尔汇率变动将主要引起中国牛肉、猪肉、奶粉、小麦和大豆进口量和产量的变化。     

Less hairy leaf 1, an RNaseH-like protein,regulates trichome formation in rice through auxin

The trichomes of rice leaves are formed by the differentiation and development of epidermal cells. Plant trichomes play an important role in stress resistance and protection against direct ultraviolet irradiation. However, the development of rice trichomes remains poorly understood. In this study, we conducted ethylmethane sulfonate (EMS)-mediated mutagenesis on the wild-type (WT) indica rice ‘Xida 1B’. Phenotypic analysis led to the screening of a mutant that is defective in trichome development, designated lhl1 (less hairy leaf 1). We performed map-based cloning and localized the mutated gene to the 70-kb interval between the molecular markers V-9 and V-10 on chromosome 2. The locus LOC_Os02g25230 was identified as the candidate gene by sequencing. We constructed RNA interference (LHL1-RNAi) and overexpression lines (LHL1-OE) to verity the candidate gene. The leaves of the LHL1-RNAi lines showed the same trichome developmental defects as the lhl1 mutant, whereas the trichome morphology on the leaf surface of the LHL1-OE lines was similar to that of the WT, although the number of trichomes was significantly higher. Quantitative real-time PCR (RT-qPCR) analysis revealed that the expression levels of auxin-related genes and positive regulators of trichome development in the lhl1 mutant were down-regulated compared with the WT. Hormone response analysis revealed that LHL1 expression was affected by auxin. The results indicate that the influence of LHL1 on trichome development in rice leaves may be associated with an auxin pathway.     

Spontaneous occurrence of chromosome abnormality in cats

A syndrome in male cats analogous to chromatin-positive Klinefelter's syndrome in human males has been demonstrated. The physical characteristics which suggested an abnormality of chromosome number in cats were "calico" or "tortoise-shell" coat colors in a male. Buccal mucosal smears were found to have "female-type" patterns in two out of 12 such male cats screened, and these two were found to have a diploid chromosome number of 39 rather than the normal 38. Testicular biopsy performed on one revealed an abnormal pattern; no gonadal tissue was found in the other cat with an abnormal chromosome number. These findings indicate that the cat, in addition to the mouse, is available for experimental study of chromosome number abnormalities.     

Cation exchange reactions in ionic nanocrystals

Cation exchange has been investigated in a wide range of nanocrystals of varying composition, size, and shape. Complete and fully reversible exchange occurs, and the rates of the reactions are much faster than in bulk cation exchange processes. A critical size has been identified below which the shapes of complex nanocrystals evolve toward the equilibrium shape with lowest energy during the exchange reaction. Above the critical size, the anion sublattice remains intact and the basic shapes of the initial nanocrystals are retained throughout the cation exchange. The size-dependent shape change can also be used to infer features of the microscopic mechanism.     

Regulation of erythrocyte cation and water content in sickle cell anemia

The pathophysiological events in sickle cell disease are critically dependent on the intracellular concentration of hemoglobin S, which varies inversely with cell cation and water content. Erythrocytes of SS homozygotes exposed to oxygen or carbon monoxide decrease their potassium and water content through a pathway for potassium transport that is activated by both cell swelling and decrease in internal pH. This pathway is not inhibited by ouabain either with or without bumetanide. When SS erythrocytes were separated according to density, the pH- and volume-dependent potassium transport was greatest in the least dense fraction and was reduced in the densest cells. This pathway, which does not depend on polymerization of sickle hemoglobin, may be important in regulating the cation and water content of SS erythrocytes.     

Spontaneous emission spectrum in double quantum dot devices

A double quantum dot device is a tunable two-level system for electronic energy states. A dc electron current was used to directly measure the rates for elastic and inelastic transitions between the two levels. For inelastic transitions, energy is exchanged with bosonic degrees of freedom in the environment. The inelastic transition rates are well described by the Einstein coefficients, relating absorption with stimulated and spontaneous emission. The most effectively coupled bosons in the specific environment of the semiconductor device used here were acoustic phonons. The experiments demonstrate the importance of vacuum fluctuations in the environment for quantum dot devices and potential design constraints for their use for preparing long-lived quantum states.     

Spontaneous Electrical Activity in the Brains of Diapausing Insects

The spontaneous electrical activity in cerebral ganglia of several insect species does not disappear during diapause. Some recordings of electrical activity in pupae of the cecropia silkworm (in which the brain is considered to be electrically "silent" during diapause) suggest that at least some activity is maintained, but possibly it is restricted to certain regions of the brain.