266 research outputs found
Micellar Catalysis and Concept in Apolar Media
The active interest aroused by catalytically affected reactions
in apolar surfactant solutions requires one to look for a relation to
micelle formation and solubilization in an effort to attain a more
unified description of phenomena peculiar to apolar surfactant
systems.
Since these catalytic phenomena are usually summarized by
the notion »micellar catalysis« the present paper wants to contribute
towards a sound abstraction of this concept. This was done by
analyzing a particular catalyzed reaction (the catalyzed hydrolysis
of p-nitrophenylacetate in the presence of dodecylammoniumpropionate
in cyclohexane) in the frequently investigated apolar solutions
of cationic surfactants. A quantitative description of the
overall reaction was obtained which was found in satisfactory agreement
with experimental details. It was concluded that micellar and
multiple association patterns are reflected also in the relationships
obtained by examining catalytically influenced reactions in these
systems
Resolution of Racemic Guaifenesin Applying a Coupled Preferential Crystallization-Selective Dissolution Process: Rational Process Development
Preferential
crystallization is a cost efficient method to provide
pure enantiomers from a racemic mixture of a conglomerate forming
system. Exploiting small amounts of pure crystals of both enantiomers,
several batch or continuous processes were developed, capable of providing
both species. However, an intermediate production step has to be used
when pure enantiomers are not available. In such cases, partially
selective synthesis, chromatography, or crystallization processes
utilizing chiral auxiliaries have to be used to provide the initial
seed material. Recently, it was shown that a coupled Preferential
Crystallization-selective Dissolution process (CPCD) in two coupled
crystallizers can be applied if at least one pure enantiomer is available
to produce both antipodes within one batch. The corresponding process
is carried out in one reactor (crystallization tank) by seeding a
racemic supersaturated solution with the available enantiomer at a
certain temperature. The second reactor (dissolution tank) contains
a saturated racemic suspension at a higher temperature. Both reactors
are coupled via the fluid phase, allowing for a selective dissolution
of the preferentially crystallizing enantiomer from the solid racemic
feed provided in the dissolution vessel. The dissolution and crystallization
processes continue until the solid racemic material is completely
resolved and becomes enantiopure. At this point, both enantiomers
can be harvested in their pure crystalline form. For a specific pharmaceutically
relevant case study, a rational process design and the applied empirical
optimization procedure will be described. The achieved productivities
after optimization show the great potential of this approach also
for industrial applications. Also, a strategy to control this process
based on inline turbidity measurement will be presented
Comprehensive Comparison of Various Techniques for the Analysis of Elemental Distributions in Thin Films
The present work shows results on elemental distribution analyses in Cu(In,Ga)Se2 thin films for solar cells performed by use of wavelength-dispersive and energy-dispersive X-ray spectrometry (EDX) in a scanning electron microscope, EDX in a transmission electron microscope, X-ray photoelectron, angle-dependent soft X-ray emission, secondary ion-mass (SIMS), time-of-flight SIMS, sputtered neutral mass, glow-discharge optical emission and glow-discharge mass, Auger electron, and Rutherford backscattering spectrometry, by use of scanning Auger electron microscopy, Raman depth profiling, and Raman mapping, as well as by use of elastic recoil detection analysis, grazing-incidence X-ray and electron backscatter diffraction, and grazing-incidence X-ray fluorescence analysis. The Cu(In,Ga)Se2 thin films used for the present comparison were produced during the same identical deposition run and exhibit thicknesses of about 2 μm. The analysis techniques were compared with respect to their spatial and depth resolutions, measuring speeds, availabilities, and detection limit
Determination of nutrient salts by automatic methods both in seawater and brackish water: the phosphate blank
9 páginas, 2 tablas, 2 figurasThe main inconvenience in determining nutrients in seawater by automatic methods is simply solved:
the preparation of a suitable blank which corrects the effect of the refractive index change on the recorded
signal. Two procedures are proposed, one physical (a simple equation to estimate the effect) and the other
chemical (removal of the dissolved phosphorus with ferric hydroxide).Support for this work came from CICYT (MAR88-0245 project) and
Conselleria de Pesca de la Xunta de GaliciaPeer reviewe
Measuring Tax Attractiveness Across Countries
This paper develops a new tax measure - the Tax Attractiveness Index - reflecting the attractiveness of a country's tax environment and the tax planning opportunities that are offered. Specifically, the Tax Attractiveness Index covers 16 different components of real-world tax systems, such as the statutory tax rate, the taxation of dividends and capital gains, withholding taxes, the existence of a group taxation regime, loss offset provision, the double tax treaty network, thin capitalization rules, and controlled foreign company (CFC) rules. We develop methods to quantify each tax factor. The Tax Attractiveness Index is constructed for 100 countries over the 2005 to 2009 period. Regional clusters in the index as well as in the application of certain tax rules can be observed. The evaluation of individual countries based on the index corresponds - but is not totally identical - with the OECD's black respectively grey list. By comparing the Tax Attractiveness Index with the statutory tax rate, we reveal that even high tax countries offer favorable tax condi-tions. Hence, the statutory tax rate is not a suitable proxy for a country's tax climate in any case since countries may set other incentives to attract firms and investments
- …