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1.
Tracer counting of beta emitters in aqueous solution was performed with a detector fabricated from a plastic scintillator capillary. The detector exhibits low gamma background and reproducible detection efficiency, and it requires minimum sample preparation. Counting efficiencies were determined for aqueous solutions of P(32), Na(22), and C(14) and for C(14)O(2) gas. 相似文献
2.
Lipid films as transducers for detection of antigen-antibody and enzyme-substrate reactions 总被引：5，自引：0，他引：5
The transverse electrical impedance of thin lipid films separating two aqueous saline solutions containing a small concentration of antibodies or enzymes decreases markedly and reversibly after immunological and enzymatic reactions involving such protein molecules, which presumably are adsorbed to the lipid-water interface. 相似文献
3.
Illumination of aqueous solutions containing ferric ions and hydrogen peroxide leads to evolution of 0(2) by way of a chain reaction. The photochemically active intermediate is the complex between Fe(3) and HO(2)-. The effects of pH and concentration of the reagent on the quantum yield (chain length) are reported. 相似文献
4.
The addition of quercetin, an organic flavone (C(15)H(10)O(7)), to aqueous solutions containing silica and aluminum and adjusted to final pH's from 6.5 to 8.5 produced a 1 : 1 alumninosilicate precipitate which, after 6 to 16 months of aging in solution at 25 degrees C, contained as much as 5 percent well-formed kaolinite plates. Similar solutions containing no organic material produced relatively amorphous precipitates with the same composition and stability (standard free energy of formation = -897+/-1 kilocalories per mole) but with substantially smaller amounts of crystaline material even after 2 years of aging. 相似文献
5.
本文介绍了用Polybren作滴定剂 ,铬黑T作滴定终点指示剂 ,使用光学自动滴定仪 (Phototitrator)测定水溶液中微量聚阴离子的新方法。在试验条件下 ,通常浓度的一价或二价离子不干扰本法测定 相似文献
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7.
Divalent phosphate ion activities can be measured in dilute aqueous solutions in the physiological pH range (7.0 to 7.5) with a liquid ionexchange membrane electrode system; the organic ion exchanger consists of an amine chloride membrane. Reference solutions may be either aqueous chloride or bicarbonate solutions. An essentially Nernstian slope is obtained. 相似文献
8.
Very long threadlike micelles observed in aqueous solutions of some surfactants have attracted much attention because of the peculiar rheological properties of these systems. Molecular dynamics simulations have suggested that branched threadlike micelles should exist in concentrated solutions of dimeric surfactants. Here experimental evidence, obtained from transmission electron microscopy at cryogenic temperature, is presented of branched threadlike micelles in aqueous solutions of a triquaternary ammonium (trimeric) surfactant made up of three amphiphilic moieties connected at the level of the head-groups by two propanediyl spacers. 相似文献
9.
We report here the self-assembly of macroscopic sacs and membranes at the interface between two aqueous solutions, one containing a megadalton polymer and the other, small self-assembling molecules bearing opposite charge. The resulting structures have a highly ordered architecture in which nanofiber bundles align and reorient by nearly 90 degrees as the membrane grows. The formation of a diffusion barrier upon contact between the two liquids prevents their chaotic mixing. We hypothesize that growth of the membrane is then driven by a dynamic synergy between osmotic pressure of ions and static self-assembly. These robust, self-sealing macroscopic structures offer opportunities in many areas, including the formation of privileged environments for cells, immune barriers, new biological assays, and self-assembly of ordered thick membranes for diverse applications. 相似文献
10.
以广东第二师范学院图书馆为例,主要围绕如何做好图书清点工作,论叙了从图书清点的必要性、准备工作、方法、清点过程中的问题和解决办法以及馆藏书目数据库建设维护等方面。 相似文献
11.
【目的】探索桑蚕一代杂交种成品卵质量检验新方法,提高成品卵质量检验的准确性、高效性及可操作性。【方法】分别采用直接计数蚁蚕法、称量计算蚁蚕法、直接计数良卵法,进行蚕种孵化率和良卵数调查,并比较3种方法的调查效率。【结果】采用称量法计算蚁蚕头数与直接计数蚁蚕头数的结果无显著性差异,采用直接计数良卵数与实际良卵孵化值误差达到极显著水平;在效率方面,直接计数良卵法耗时是直接计数蚁蚕法的56.75%,而称量计算蚁蚕法耗时仅是直接计数蚁蚕法的21.83%,节省约4/5的调查时间,工作效率极大提高。【结论】将称量计算蚁蚕法应用于良卵数和孵化率调查是可行的,且具有操作性好、省时、省工、效率高,准确性高等优点。 相似文献
12.
Kahlweit M 《Science (New York, N.Y.)》1988,240(4852):617-621
Water and oil can be made completely miscible by adding a sufficient amount of an amphiphilic compound, such as soap or a detergent. For historical reasons, such stable homogeneous solutions are called "microemulsions." In this article the term microemulsion is used in a more restrictive manner; at low concentrations of the amphiphile, mixtures of water, nonpolar solvents, and amphiphiles may separate into three coexisting liquid layers, namely, an aqueous phase, an amphiphile-rich phase, and an oil-rich phase. In the amphiphile-rich phase, which is the microemulsion in the narrower sense, one finds for thermodynamic reasons a maximum of the mutual solubility between water and oil, combined with a minimum of the interfacial tension between the aqueous and the oil-rich phase, properties that are of interest for both theory and application. The present state of art in this rapidly growing field of science is reviewed. 相似文献
13.
Silva GA Czeisler C Niece KL Beniash E Harrington DA Kessler JA Stupp SI 《Science (New York, N.Y.)》2004,303(5662):1352-1355
Neural progenitor cells were encapsulated in vitro within a three-dimensional network of nanofibers formed by self-assembly of peptide amphiphile molecules. The self-assembly is triggered by mixing cell suspensions in media with dilute aqueous solutions of the molecules, and cells survive the growth of the nanofibers around them. These nanofibers were designed to present to cells the neurite-promoting laminin epitope IKVAV at nearly van der Waals density. Relative to laminin or soluble peptide, the artificial nanofiber scaffold induced very rapid differentiation of cells into neurons, while discouraging the development of astrocytes. This rapid selective differentiation is linked to the amplification of bioactive epitope presentation to cells by the nanofibers. 相似文献
14.
Singlet oxygen (1O2) is a highly reactive species formed through solar irradiation of organic matter in environmental waters. Implicated in a range of reactions, it has proven difficult to quantify its spatial distribution in natural waters. We assessed the microheterogeneous distribution of 1O2 in irradiated solutions containing chromophoric dissolved organic matter (CDOM) by using molecular probes of varying hydrophobicity. The apparent 1O2 concentrations ([1O2]app), measured by recently developed hydrophobic trap-and-trigger chemiluminescent probe molecules, were orders of magnitude higher than those measured by the conventional hydrophilic probe molecule furfuryl alcohol. The differential [1O2]app values measured by these probes reflect a steep concentration gradient between the CDOM macromolecules and the aqueous phase. A detailed kinetic model based on the data predicts probabilistic 1O2 distributions under different solvent conditions. 相似文献
15.
为解决含锰工业废水对环境、土壤及生物带来的危害,研究采用热电厂废弃物粉煤灰作为吸附剂,希望能找到最佳吸附条件,同时为粉煤灰的综合利用提供更多机会;采用EDTA滴定法,对含锰废液进行了吸附研究,模拟测定了影响粉煤灰吸附特性的几种因素:重金属离子浓度、吸附时间、粉煤灰颗粒度以及待吸附液的pH等;结果表明:在其它条件相同的情况下,随着废液Mn2 浓度的增大,去除率逐渐降低;在吸附中60min为最佳震荡时间;随着粉煤灰粒度的减小,去除率增加;pH值应控制在中性偏碱性(pH值约为8.0最好)范围;可见,采用粉煤灰吸附含锰工业废水在适当工艺条件下可以有很好的处理效果,这种方法较简便,成本低廉,能达到以废治废的目的。 相似文献
16.
Number words that, in principle, allow all kinds of objects to be counted ad infinitum are one basic requirement for complex numerical cognition. Accordingly, short or object-specific counting sequences in a language are often regarded as earlier steps in the evolution from premathematical conceptions to greater abstraction. We present some instances from Melanesia and Polynesia, whose short or object-specific sequences originated from the same extensive and abstract sequence. Furthermore, the object-specific sequences can be shown to be cognitively advantageous for calculations without notation because they use larger counting units, thereby abbreviating higher numbers, enhancing the counting process, and extending the limits of counting. These results expand our knowledge both regarding numerical cognition and regarding the evolution of numeration systems. 相似文献
17.
Galun M Keller P Malki D Feldstein H Galun E Siegel SM Siegel BZ 《Science (New York, N.Y.)》1983,219(4582):285-286
Penicillium digitatum mycelium can accumulate uranium from aqueous solutions of uranyl chloride. Azide present during the uptake tests does not inhibit the process. Killing the fungal biomass in boiling water or by treatment with alcohols, dimethyl sulfoxide, or potassium hydroxide increases the uptake capability to about 10,000 parts per million (dry weight). Formaldehyde killing does not enhance the uranium uptake. The inference that wall-binding sites were involved led to the testing of uranium uptake by chitin, cellulose, and cellulose derivatives in microcolumns. All were active, especially chitin. 相似文献
18.
利用共沉淀水热法制备镁铝阴离子黏土材料,研究了其水溶液对砷酸根[As（V）]离子的吸附热力学及其机理。结果表明：在303～333 K和试验浓度范围内,阴离子黏土对水中As（V）的吸附平衡数据符合Langmuir和Freundlich吸附等温方程。阴离子黏土对水中As（V）的吸附是吸热过程;根据热力学函数关系计算出As（V）在阴离子黏土上的吸附焓为2.85 kJ/mol,吉布斯吸附自由能改变量为-6.64～-5.90 kJ/mol,吸附自由能的变小是As（V）在阴离子黏土上吸附的推动力,吸附熵变为29.38 J/（mol.K）。 相似文献
19.
Truesdell AH 《Science (New York, N.Y.)》1968,161(3844):884-886
Values of the mean activity coefficient of sodium chloride at 15 degrees , 250, 380 and 50 degrees C were determined for aqueous NaCl solutions of 0.01 to 1.0 molal from electromotive force measurements on the cell: (sodium-sensitive glass electrode, aqueous sodium chloride, silver chloride-silver). 相似文献