Individual extraction constants of some dicarbollylcobaltate anions in the water-nitrobenzene system

Individual extraction constants of nine dicarbollylcobaltate anions in the two-phase water-nitrobenzene system were determined radiometrically assuming that the changes of Gibbs energy of the transfer of the tetraphenylarsonium cation, Ph₄As⁺, and of the tetraphenylborate anion, BPh ₄ ^– , from the aqueous into the nitrobenzene phase are equal. The constants obtained by this method were correlated with Hansch's constants of hydrophobity.     

A new convenient method for the synthesis of mixed-ligand β-diketonato Tc(III) complexes

A new convenient method has been proposed to synthesize mixed-ligand -diketonato Tc(III) complexes, using the ligand exchange reaction [Tc(acac)₂(CH₃CN)₂]⁺+L^–[Tc(acac)₂L]+ +2CH₃CN where L is bza, dpm or dbm. The yield was about 30–40%. UV-visible and IR spectra of these complexes were measured. Characteristic features of the compounds were compared with those of the corresponding complexes of ruthenium.     

Enzyme and microbial sensors for phosphate, phenols, pesticides and peroxides

Biosensors employing a biocatalyst on a different level of integration have been developed for monitoring environmental pollution. These probes range from laboratory specimen to commercial detectors applied to analyzers. Recent developments on amperometric enzyme and microbial biosensors are presented here. A monoenzymatic bulk-type carbon electrode is described for biosensing organic hydroperoxides in aqueous solutions; peroxidase is immobilized within the electrode body and the direct electron transfer between electrode and enzyme is measured. Both, reversible and irreversible inhibitors of acetylcholinesterase have been quantified by using a kinetically controlled acetylcholine enzyme sequence electrode. The inhibitory effect of pesticides such as butoxycarboxime, dimethoate, and trichlorfon could be quantified within 6 min in molar concentrations. Different multi-enzyme electrodes have been developed for the determination of inorganic phosphate. These sensors represent examples of sequentially acting enzymes in combination with enzymatic analyte recycling. Using this type of amplification nanomolar concentrations can be measured.     

Boundary layers in finite thermoelasticity

In this paper, we study inhomogeneous deformations within the context of finite thermoelasticity with a view towards highlighting the developments of boundary layer like structures. We find that such structures manifest themselves by virtue of the material's ability to shear soften or shear stiffen. When the material moduli depend both on the temperature and the stretch, their effects can either reinforce or mitigate one another, thereby leading to the accentuation or annihilation of the boundary layer structure.     

Atomic absorption spectrophotometric determination of gold with preconcentration by Donnan dialysis

Donnan dialysis enrichment with tubular cation-exchange membrane was used as a preconcentration method prior to determination of gold by flame atomic absorption spectrometry (FAAS). The value of enrichment factor can be controlled for a particular application through adjustment of the membrane tuning length, dialysis time, carrier flow rate, composition of the receiver solution and by addition of complexing ligand to the receiver or the sample solution. For 10 min dialysis enrichment factor above 3 can be achieved. The detection limit (signal-to-noise ratio = 3) of 35 ng/ml was obtained. RSD at 0.2 mug/ml level was 4.7% (n = 6). The results of dialysis of noble metals mixtures are demonstrated.     

Brownian motion with restoring drift: The petit and micro-canonical ensembles

Letf(Q) be odd and positive near +∞. Then the non-linear wave equation ?² Q/?t ²??² Q/?x ²?f(Q)=0, considered on the circle 0≤x<L, can be written in Hamiltonian formQ ^⊙ =?H/?P, P ^⊙ =??H/?Q with $$P = Q^\cdot and H = \tfrac{1}{2}\mathop \smallint \limits_0^L (Q')^2 + \mathop \smallint \limits_0^L F(Q) + \tfrac{1}{2}\mathop \smallint \limits_0^L P^2 ;$$ the corresponding flow preserves the (suitably interpreted) “petit ensemble”e ^?H d ^∞ Qd ^∞ P; and forL↓∞,Q settles down to the stationary diffusion with infinitesimal operator 1/2 ?²/?Q ²+m(Q)?/?Q,m being the logarithmic derivative of the ground state of ?d ²/dQ ² ‖F(Q). This diffusion is the “Brownian motion with restoring drift”; see McKean-Vaninsky [1993(1)]. For reasons suggested by the paper of Lebowitz-Rose-Speer [1988] on NLS, it is interesting to study the “micro-canonical ensemble” obtained by restricting to the sphere $\int\limits_0^L {Q^2 } = N$ and makingL↓∞ with fixedD=N/L. Now, forF(Q)/Q ²→∞, the same type of diffusion appears, but with drift arising from the modified potentialF(Q)+cQ ²,c being chosen so that the mean ofQ ² is the assigned numberD. The proof employs Döblin's method of “loops” [1937] and steepest descent. The same is true forF(Q)=m ² Q ², only now the proof is elementary. The outcome is also the same ifF(Q)/Q ²→0, providedD is smaller than the petit canonical mean ofQ ²; forD larger than this mean, the matter is more subtle and the outcome is unknown.     

AES-depth-profiling of thin annealed Pt-films on Si(100)

Thin PtSi films can be grown by evaporating Pt on Si(100) at RT and subsequent annealing of the system at 600–700 K. Contaminants like oxygen are known to have a strong influence on this reaction. In the present study we concentrate on the effect of oxygen partial pressure during the annealing on the silicide growth process. Under proper vacuum conditions annealing at 500 K leads to a homogeneous Pt₂Si film which reacts around 600 K completely to PtSi. A substantial oxygen partial pressure ( 0.1 mbar) in contrast results in an incomplete reaction in the same temperature range: unreacted platinum remains at the surface separated from the silicide by an oxygen enriched layer.Presented at the Seminar on Secondary Electrons in Electron Spectroscopy, Microscopy, and Microanalysis, Chlum (The Czech Republic), 21–24 September, 1993.This work was supported by Deutsche Forschungsgemeinschaft (DFG) through Sonderforschungsbereich 292.We thank Dr. W. Platz (Deutsche Aerospace AG, Ottobrunn) for providing us with Pt evaporated Si-wafers and Th. Hierl (Lehrstuhl für Angewandte Physik, University of Erlangen-Nürnberg), who performed the RBS measurements for AES calibration.