Retardation of Tricalcium Aluminate Hydration by Calcium Sulfate

The influence of calcium sulfate on the hydration of 3CaO· Al₂O₃ in the presence of Ca(OH)₂ was studied using conduction calorimetry, differential thermogravimetry, and X-ray diffraction. Sodium sulfate was also used instead of calcium sulfate. A substantial retardation of tricalcium aluminate hydration in the presence of sulfate occurs only when calcium sulfate is used and enough ettringite is formed. When ettringite disappears due to the consumption of gypsum, tricalcium aluminate hydration is renewed. Sodium sulfate does not significantly retard this hydration. The results confirm the hypothesis that ettringite formation is essential for coating 3CaO·Al₂O₃ grains and then retarding their hydration.     

Expression Cassettes for Formaldehyde and Fluoroacetate Resistance,Two Dominant Markers in Saccharomyces cerevisiae

We employed two genes in constructing yeast expression cassettes for dominant, selectable markers. The Saccharomyces cerevisiae gene SFA1, encoding formaldehyde dehydrogenase, was placed under the control of the GPD1 promoter and CYC1 terminator. The Moraxella sp. strain B gene dehH1, encoding fluoroacetate dehalogenase, was placed under the control of both the GPD1 and CYC1 promoters. With these constructs it was possible to select directly for yeast strains resistant to either formaldehyde or fluoroacetate. Both selective agents are completely metabolized and inexpensive, making them very useful in the pursuit of yeast gene functions and for industrial applications. An additional advantage of the formaldehyde dehydrogenase marker is that it is an S. cerevisiae gene, thus allowing ‘all yeast’ constructs. © 1997 John Wiley & Sons, Ltd.     

On a circuit representation of the Hodgkin and Huxley nerve axon membrane equations

A circuit representation of the nerve axon membrane equations proposed by Hodgkin and Huxley is presented and discussed. In contrast with the usual circuit formulation found in the literature and based on ‘time-varying conductances’, all the elements of the present circuit are time-invariant and the whole structure is sufficiently detailed to become suitable for both theoretical and numerical investigations. In particular, this ‘change of perspective’ makes it possible to reproduce all the ‘classical’ results through the use of computer circuit analysis programmes and leads to some new considerations about the basic aspects of pulse generation mechanisms in the axon membrane. © 1997 by John Wiley & Sons, Ltd.     

ST已经做好部署,准备挖掘GaN的全部潜力

1 看好哪类GaN功率器件市场 凡是对开关频率有较高要求的应用和其他半导体技术无法实现的拓扑结构, GaN(氮化镓)均适用.在汽车市场,我们最看好的应用是开关频率兆赫级别的低压DC-DC(直流-直流)转换器和车载充电机(OBC),在这个应用领域,GaN在能效与功率密度之间取得了最佳平衡.汽车48 V轻混系统中的皮带传动...     

3-VINYL-1,2,5-THIADIAZOLE-METHACRYLIC ACID COPOLYMERS AS pH CONTROLLED FLOCCULANTS FOR FINELY DIVIDED COPPER MINERALS

ABSTRACT

Good selective flocculants for chalcocite. which may be transformed into dispersants by a slight change in pH, have been prepared by copolymerization of mixtures of 3-vinyl-1,2,5-thiadiazole and methacrylic acid. Their average osmometric molecular weight is no higher than 200,000 dalton. They are virtually insoluble in water and fairly soluble in 0.1N NaOH; they do not flocculate gangue minerals like quartz and calcite, but tend to act as dispersants for them.

I.R. spectra confirm a chemical interaction between thiadiazole units and the particle surface, an interaction that probably takes place through the coordination of nitrogen atoms with surface copper atoms. The formation of the complex, the stability of which depends on pH, ensures to a certain extent the interposition of the copolymer between the particle surface and the solvent. Thus the copolymer partly controls the particle-solvent relations and regulates flocculation or dispersion, as the case may be.     

Technological Evolution, System Architecture and the Obsolescence of Firm Capabilities

We present a historical study of technological evolution inthe mainframe computer industry. We show that the pattern ofinnovation in the industry is not well characterized by existingmodels. The incremental evolution of mainframe system performanceas seen by the customer was the result of an aggregation thatmasked substantial discontinuities at the component level. Newtechnological concepts led to the frequent obsolescence of existingcapabilities, despite the stability of customer needs and thepersistence of a dominant design. The nature of our observationsis captured in a simple critical path model of technologicalevolution. Our conceptualization sheds light on the dynamicsof the evolution of the capability base of firms in an environmentcharacterized by complex products and rapid technological change.