Liquid-crystalline behaviour of some carboxylic acids

Summary A series of 4--carboxyalkoxyphenyl-4-methoxybenzoates 2 has been prepared. Compounds with a spacer length of n=3 and n=5 show liquid crystalline behaviour. The products were characterized by IR and ¹HNMR-spectroscopy, mass spectrometry, optical microscopy and DSC-measurements. The compounds are potentially useful as side-groups in liquid-crystalline polymers.     

Accessing the spoken word

Spoken-word audio collections cover many domains, including radio and television broadcasts, oral narratives, governmental proceedings, lectures, and telephone conversations. The collection, access, and preservation of such data is stimulated by political, economic, cultural, and educational needs. This paper outlines the major issues in the field, reviews the current state of technology, examines the rapidly changing policy issues relating to privacy and copyright, and presents issues relating to the collection and preservation of spoken audio content .     

Electrochemical behaviour of the antimony electrode in sulphuric acid solutions—II. Formation and properties of the primary anodic layer

The formation of an anodic layer during the oxidation of antimony in sulphuric acid solutions as well as the structure and properties of the layer have been studied using linear sweep voltammetry, potentiostatic oxidation, ac impedance measurements, X-ray diffraction analysis and scanning electron microscopy. The electrochemical investigations as well as the shape of the impedance spectra during electrode passivation indicate that the surface layer probably has a complicated structure. Under the conditions of these experiments the passivating film is mainly amorphous, gel-like, exhibiting good ionic conductivity and a relatively high dissolution rate. Assuming that the anodic layer consists mainly of antimony hydroxide a reaction scheme for the growth and dissolution of this film is presented.     

Current distribution measurements with a free-breathing direct methanol fuel cell using PVDF-g-PSSA and Nafion 117 membranes

The methanol crossover and other mass transfer phenomena have been investigated in a free-breathing direct methanol fuel cell (DMFC). The current distribution profile along the MeOH flow channel was measured and information of local concentrations of the reacting species was obtained. The DMFC with a segmented cathode was found to be very useful for a detailed analysis of the interrelated parameters, which cause the local variations of the cell current. The connections between different operating parameters were clarified in detail for two different membranes. The measurements were done for both an experimental poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid) (PVDF-g-PSSA) membrane and the commercial Nafion^® 117 membrane, which have different methanol permeabilities. The MeOH concentration and the flow rate were varied in a wide range in order to determine their optimum values. The deviations from an even current density distribution were observed to increase as a function of MeOH concentration and decrease as a function of temperature. The power production of a free-breathing DMFC was observed to be proportional to the local oxygen concentration at the cathode side and inadequate air convection together with the MeOH crossover phenomenon was observed to decrease the cell performance locally.     

A numerical Hartree-Fock program for diatomic molecules

This paper describes an algorithm and a computer program which solves numerically (virtually exactly) equations of the restricted open-shell Hartree-Fock and Hartree-Fock-Slater model for diatomic molecules     

A solid-state 13C nuclear magnetic resonance study of cured,unsaturated polyester resins

The styrene sequence distributions and amount of reacted fumarate units in cured, unsaturated polyester resins were studied by solid-state ¹³C nuclear magnetic resonance. Increasing the styrene content and molar ratio of styrene to the double bonds in the polyester chain increased the amount of diad and n-ad sequences and decreased the amount of monad sequences. At the same time, the amount of reacted fumarate units increased. The glass transition temperature was almost constant for resins with the same composition but different styrene contents. Changing the composition affected the glass transition temperature, which could not be detected for highly crosslinked resins. The mechanical properties were improved with increasing styrene content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 563–571, 1999     

Influence of thiourea and thiourea ageing on the electrodeposition of copper from acid sulfate solutions studied by the ring-disc technique

The influence of the additive thiourea in freshly made and aged solutions on copper deposition from acid sulfate solutions was studied using a Pt/Pt rotating ring-disc electrode. In fresh thiourea solutions copper deposition is retarded, but the most distinct effect of thiourea is seen during dissolution of the deposits. The intermediate in copper dissolution, Cu⁺, is partly complexed with adsorbed thiourea. Thus Cu⁺ is adsorbed at the electrode surface and the current peak at the ring due to dissolving Cu⁺ becomes very small. The small peak indicates that active additive is present in the deposit. Thiourea containing solutions aged for only a few days have a distinct effect on the electrode reactions. At low concentrations of thiourea (1 mg dm^–3 ) a correlation between ageing and growth of the Cu⁺ peak at the ring is clearly seen. At high thiourea concentrations (100 mg dm^–3) a small growth of the Cu⁺ peak is seen during the first few days but upon further ageing of the thiourea solution copper deposition becomes strongly inhibited. The ring current can be used as a qualitative diagnostic criterion for the concentration and state of thiourea in copper sulfate solutions.     

Preliminary investigations of scaling and corrosion in high enthalpy geothermal wells in Hungary

A solubility equilibrium program GEOPROF was applied to the determination of the bubble-point depth, pressure and temperature, as well as the partial pressure profiles of the gases CO₂, CH₄ and N₂ between the bubble-point depth and the wellhead, in two high enthalpy geothermal wells, NSZ-2 and FAB-4 in southern Hungary. The pH, alkalinity, total carbonates, and equilibrium solubility for CaCO₃, CaSO₄, BaSO₄, and SrSO₄ along the well depth profile in the Na–K–Mg–Ca–H–Ba–Sr–Cl–Br–SO₄–OH–HCO₃–CO₃–CO₂–H₂O system were also determined and the concentrations of Ca²⁺, Ba²⁺, Sr²⁺, H⁺, OH⁻, HCO₃⁻, CO₃²⁻, and H₂CO₃* were computed at the actual temperature and CO₂ pressure using the Davies and Pitzer activity calculation methods. The calculated amounts of CaCO₃ scaling along the wells and at the surface were used in estimating service life. The results for well FAB-4 contain high uncertainties because of the estimated gas separation analysis data.     

Implicit Epistemic Aspects of Constructive Logic

In the present paper I wish to regard constructivelogic as a self-contained system for the treatment ofepistemological issues; the explanations of theconstructivist logical notions are cast in anepistemological mold already from the outset. Thediscussion offered here intends to make explicit thisimplicit epistemic character of constructivism.Particular attention will be given to the intendedinterpretation laid down by Heyting. This interpretation, especially as refined in the type-theoretical work of Per Martin-Löf, puts thesystem on par with the early efforts of Frege andWhitehead-Russell. This quite recent work, however,has proved valuable not only in the philosophy andfoundations of mathematics, but has also foundpractical application in computer science, where thelanguage of constructivism serves as an implementableprogramming language, and within the philosophy oflanguage.\footnote{Nordstr\"{o}m et al. (1990) give an overview of the work in computerscience, whereas Ranta (1995) provides an impressiveconstructivist alternative to Montague Grammar usingthe richer type structure of Martin-L\"{o}f in placeof the simple classical type theory of Church.} Mypresentation will be carried out through a contrastwith standard metamathematical work.\footnote{Troelstra and van Dalen (1988) give an encyclopedictreatment of the metamathematics of constructivism.}In the course of the development I have occasion tooffer some novel considerations (in Sections~6 and 8) on thenature of proof and inference(-acts).     

Electrochemical characterization of radiation-grafted ion-exchange membranes based on different matrix polymers

Seven proton conducting membranes based on different commercial fluoropolymer films were prepared by radiation grafting with styrene followed by sulfonation. These membranes were studied as candidates for fuel cell electrolyte membranes and compared to Nafion^® 105 and 117 with respect to conductivity, oxygen and hydrogen permeability, kinetics of the oxygen reduction reaction (ORR) and performance in a fuel cell. The dependence of the conductivity of the membranes on the relative humidity (RH) and temperature was also determined. The conductivity was observed to depend on the membrane thickness and the water uptake. The dependence of the conductivity on the temperature and the RH was the same for all of the experimental membranes. Reactant gas permeabilities appeared to depend only slightly on the matrix material and no major differences in the Tafel slopes and exchange current densities of the ORR were observed. Membranes with high water uptakes appeared to be less durable in the fuel cell than membranes with low water uptakes. Thus to prepare a membrane that is durable under the fuel cell conditions, the water uptake must remain low even at the expense of the conductivity.