Computer model for magnetic fields in electrolytic cells including the effect of steel parts

The computer model described in this paper calculates magnetic fields in electrolytic cells from an input of constructional data and known current distribution. Conventional formulas are used for the magnetic field from the current carrying system of the cell and its surroundings. A special method has been developed for the representation of steel parts in the model, in order to include their magnetic effect with reasonable accuracy. Principles are described and examples of calculations are given.     

Homochiral glycerol derivatives by lipase-catalysed racemate resolution

Various aspects of enzyme-catalysed racemate resolution arediscussed by using examples from hydrolysis of butanoates ofglycerol derivatives. Primary esters of various 1,2-ketals gavelow enantioselectivity (E). The results with secondary estersvaried. The highest E value (> 100) was obtained when theprimary ether groups were methyl and phenylethyl. For the correspondingmethyl, phenyl diether E was observed to increase as the hydrolysisproceeded. The stereochemistry of the products agree with aproposed model for lipases.     

Arsenolipids in marine oils and fats: A review of occurrence,chemistry and future research needs

Numerous studies have focused on arsenic in marine organisms, and relatively high natural levels of the element have been reported in marine samples. Despite their seemingly consistent presence in marine oils and fats, there is currently only limited knowledge available on arsenic compounds that exhibit lipid soluble characteristics, the arsenolipids, in contrast to the water-soluble arsenic species. The development of analytical techniques has, however, renewed the interest in these arsenic species and significant novel findings have been published in the last couple of years. The aim of this review is to present current knowledge on the occurrence and chemistry of arsenolipids in marine oils, and to identify future research needs. The occurrence of arsenolipids and their relevance in marine organisms will be discussed, in addition to their relevance for consumers and industry, with respect to feed and food safety and legislative issues. Analytical techniques, including techniques in the early work on arsenolipids in addition to methods employed today, and relevant sample preparation will be discussed.     

Separation of polypeptides by isoelectric point focusing in electrospray-friendly solution using a multiple-junction capillary fractionator

We introduce an online multiple-junction capillary isoelectric focusing fractionator (OMJ-CIEF) for separation of biological molecules in solution by pI. In OMJ-CIEF, the separation capillary is divided into seven equal sections joined with each other via tubular Nafion membrane insertions. Each junction is communicated with its own external electrolytic buffer which is used both to supply electrical contact and for solvent exchange. The performance of the fractionator was explored using protein and peptide samples covering broad pI range. Separation was achieved in ionic and ampholytic buffers, including ammonium formate, ammonium hydroxide, histidine, and arginine. By maintaining electric potential across upstream segments of the capillary after the focusing stage, selective release of downstream analyte fractions could be achieved. The selective release mode circumvents the problem of peak broadening during mobilization and enables convenient comprehensive sampling for orthogonal separation methods. Using single-component ampholyte buffers with well-defined pI cutoff values, controlled separation of protein mixture into basic and acidic fractions was demonstrated. The device is cheap and easy to fabricate in-house, simple in operation, and straightforward in interfacing to hyphened analytical platforms. OMJ-CIEF has a potential of becoming a practical add-on unit in a wide range of bioanalytical setups, in particular as a first-dimension separation in mass spectrometry based proteomics or as a preparative tool for analyte purification, fractionation, and preconcentration.     

Regioselective lipase-catalyzed transesterification of tributyrin. Influence of salt hydrates on acyl migration

The influence of the nature of solid salt hydrates on the rate of hexanoic acid catalyzed acyl migration in 1,2-dibutyrin has been examined in hexane. The results show that the rate of acyl migration is faster when hydrogen phosphate salts are included compared to sulfate salts. The rate is essentially the same in the presence of sulfate salts and without salts. In regioselective lipase-catalyzed acidolysis of tributyrin with hexanoic acid, the use of hydrogen phosphate salts to control water activity leads to a higher rate of migration than the use of sulfate salts. Minor differences are observed in interesterification with ethyl hexanoate.     

Instabilities of the metal surface in electrolytic alumina reduction cells

Transient waves on the metal surface in electrolytic cells are studied by simulation on a computer model. The model used is a semidynamic modification of a model for stationary flow and surface calculation. The simulation results clearly show that any wave once started by some disturbance, will turn into a transient wave rotating along the edge of the cell cavity, resulting in a tilting movement of the whole metal surface. The mechanism of the rotating wave is explained. It is further demonstrated that there exists a stability limit above which the rotating waves are amplified instead of being damped, leading to an unstable situation known as “shaky pot”. A simple empirical stability formula is presented, showing the interrelation of the decisive cell parameters. General estimation curves for typical cells are also given.     

Computation of electric and magnetic stimulation in human head using the 3-D impedance method

A comparative, computational study of the modeling of transcranial magnetic stimulation (TMS) and electroconvulsive therapy (ECT) is presented using a human head model. The magnetic fields from a typical TMS coil of figure-eight type is modeled using the Biot-Savart law. The TMS coil is placed in a position used clinically for treatment of depression. Induced current densities and electric field distributions are calculated in the model using the impedance method. The calculations are made using driving currents and wave forms typical in the clinical setting. The obtained results are compared and contrasted with the corresponding ECT results. In the ECT case, a uniform current density is injected on one side of the head and extracted from the equal area on the opposite side of the head. The area of the injected currents corresponds to the electrode placement used in the clinic. The currents and electric fields, thus, produced within the model are computed using the same three-dimensional impedance method as used for the TMS case. The ECT calculations are made using currents and wave forms typical in the clinic. The electrical tissue properties are obtained from a 4-Cole-Cole model. The numerical results obtained are shown on a two-dimenaional cross section of the model. In this study, we find that the current densities and electric fields in the ECT case are stronger and deeper penetrating than the corresponding TMS quantities but both methods show biologically interesting current levels deep inside the brain.     

部分大型运营商ARPU值与劳动生产率的对标分析

本文从ARPU值和每员工用户数两项指标对全球16家大型运营商进行了对标分析。ARPU值表征了它们运营的区域的富裕程度,而每员工用户数则代表了运营商的劳动生产率。通过对标分析表明,这些大运营商没有一家能够同时具有高的ARPU值和劳动生产率。在高ARPU值的市场上并处于高端地位的运营商似乎“臃肿而懒散”,而处在低ARPU值的市场上的运营商则“被迫”提高了劳动生产率。中国和印度的运营商都带有“大本土市场综合征”的特征,即ARPU值和劳动生产率均很低,但它们的规模效益带来了丰厚利润。非洲运营商具有极高的劳动生产率,使之能在极低ARPU值的市场上生存。文章最后还指出了处于高劳动生产率、低ARPU值区的运营商更容易通过并购进入高ARPU值、低劳动生产率的市场。