Magnetic linear dichroism of an antiferromagnetic MnF<Subscript>2</Subscript> crystal: Oddness in two different antiferromagnetic states

Dichroism of linearly polarized light propagating along the tetragonal C ₄ axis, induced by a longitudinal magnetic field, has been revealed in a tetragonal antiferromagnetic manganese fluoride crystal in the region of optical transitions. The magnetic linear dichroism observed is proportional to the magnetic field strength and odd with respect to the field sign. The value of the effect is sufficient for optical observation of antiferromagnetic domains in MnF₂ crystals.     

Efficient kinetic bioresolution of 2-nitrocyclohexanol

The kinetic bioresolution of 2-nitrocyclohexanol 1 was investigated by screening a range of hydrolases both for enantioselective transesterification and for enantioselective hydrolysis of the corresponding acetate. By appropriate choice of biocatalyst and conditions, both enantiomers of cis and trans 2-nitrocyclohexanol 1 can be accessed in enantiopure form.     

Pressure induced self-oxidation of Fe(OH)2

M?ssbauer spectroscopy, x-ray diffraction, and electrical resistance [R(P,T)] studies in Fe(OH)(2) to 40 GPa revealed an unforeseen process by which a gradual Fe2+ oxidation takes place, starting at approximately 8 GPa reaching 70% Fe3+ abundance at 40 GPa. The nonreversible process Fe2+-->Fe3++e(-) occurs with no structural transition. The "ejected" electrons form a deep band within the high-pressure electronic manifold becoming weakly localized at P>50 GPa. This process is attributed to an effective ionization potential created by the pressure induced orientationally deformed (OH) dipoles and the unusual small binding energy of the valence electron in Fe2+(OH)(2).     

A novel three-dimensional system to study interactions between endothelial cells and neural cells of the developing central nervous system

Background  

During angiogenesis in the developing central nervous system (CNS), endothelial cells (EC) detach from blood vessels growing on the brain surface, and migrate into the expanding brain parenchyma. Brain angiogenesis is regulated by growth factors and extracellular matrix (ECM) proteins secreted by cells of the developing CNS. In addition, recent evidence suggests that EC play an important role in establishing the neural stem cell (NSC) niche. Therefore, two-way communication between EC and neural cells is of fundamental importance in the developing CNS. To study the interactions between brain EC and neural cells of the developing CNS, a novel three-dimensional (3-D) murine co-culture system was developed. Fluorescent-labelled brain EC were seeded onto neurospheres; floating cellular aggregates that contain NSC/neural precursor cells (NPC) and smaller numbers of differentiated cells. Using this system, brain EC attachment, survival and migration into neurospheres was evaluated and the role of integrins in mediating the early adhesive events addressed.     

Speaking rate of adventitiously deaf male cochlear implant candidates

No objective group data on speaking rate or speaking duration have been reported on the speech of adventitiously profoundly hearing-impaired adults. Results of the present study showed that speaking rate, i.e., number of syllables per second, was significantly slower and speaking duration was significantly longer for 25 adventitiously profoundly hearing-impaired adult male cochlear implant candidates than for 10 normal-hearing control subjects. The factors of length of time since onset of profound hearing loss and hearing aid use did not significantly affect speaking rate. Based on these objective data, a rationale and method are presented for aural rehabilitation of the profoundly hearing-impaired who exhibit speaking rate abnormalities.     

A finite element method for a two-sex model of population dynamics

A finite element scheme is described to approximate the solution of a nonlinear and non-local system of integro-differential equations that models the dynamics of a two-sex population. Crank-Nicolson time discretization is used and error estimates are derived for the appoximation.     

The analysis of plutonium uranium carbide-iron cermets by electrochemical method

Summary Electrochemical methods have been developed for the direct determination of the main metallic constituents of 15 w/o (Pu, U) C — 10 w/o Fe cermets. Samples are dissolved in nitric acid, followed by wet oxidation with a mixture of sulphuric and nitric acids to destroy organic matter. Plutonium is determined by a potentiometric titration procedure based upon the reduction of Pu^VI to Pu^IV with ferrous iron added in slight excess, followed by the titration of this excess with ceric sulphate. The precision of this determination on 4 mg amounts of plutonium is 0.1%. Both uranium and iron are determined by controlled-potential coulometry, but the method for iron includes a contribution from plutonium and allowance has to be made for this. The precision of the uranium determination on 10 mg amounts is 0.25%, and the value for iron on 1 mg amounts is also 0.25%. Results for the complete analysis of typical cermet samples are given.

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Zusammenfassung Elektrochemische Verfahren wurden ausgearbeitet zur direkten Bestimmung der metallischen Hauptbestandteile in Metall-keramischen Materialien (Cermets) der Zusammensetzung 15% (Pu,U)C-10% Fe. Hierbei wird die Probe in Salpetersäure aufgelöst und anschließend zur Zerstörung organischer Substanz einer nassen Oxydation mit einem Gemisch von Schwefel- und Salpetersäure unterworfen. Plutonium wird mit Hilfe eines potentiometrischen Verfahrens bestimmt, das auf der Reduktion von Pu^VI zu Pu^IV mit Fe^II in geringem Überschluß und nachfolgender Titration des Überschusses mit Cer^IV-sulfatlösung beruht. Die Genauigkeit beträgt hierbei 0,1% bei Mengen von 4 mg Pu. Uran und Eisen werden durch Coulometrie mit Potentialkontrolle bestimmt; jedoch wird bei der Eisenbestimmung Plutonium miterfaßt und muß bei der Berechnung berücksichtigt werden. Die Genauigkeit der Uranbestimmung beträgt 0,25% bei 10 mg U, die der Eisenbestimmung 0,25% bei 1 mg Fe. Ergebnisse von vollständigen Analysen typischer Cermetproben werden angeführt.

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Dedicated to Prof. Dr. M. von Stackelberg on his 70th birthday.