Measurement of decoherence of electron waves and visualization of the quantum-classical transition

Controlled decoherence of free electrons due to Coulomb interaction with a truly macroscopic environment, the electron (and phonon) gas inside a semiconducting plate, is studied experimentally. The quantitative results are compared with different theoretical models. The experiment confirms the main features of the theory of decoherence and can be interpreted in terms of which-path information. In contrast to previous model experiments on decoherence, the obtained interferograms directly visualize the transition from quantum to classical.     

Preferred conformations of enol ethers in solution: Detection of an equilibrium by kinetic nuclear overhauser effects

n.O.e. difference spectra reveal that the preferred solution conformation of methyl enol ethers has the methyl group $\text{syn}$-periplanar to the double bond; n.O.e kinetics in a methoxy—heptatriene demonstrate the presence of both possible periplanar conformations, the energy difference being $\text{ca}$ 1 kcal/mole.     

Prediction of the three-dimensional structure of the enzymatic domain of t-PA

Summary Tissue plasminogen activator (t-PA), an enzyme of the fibrinolytic system, is responsible for lysis of fibrin via activation of plasminogen, and therefore for degradation of blood clots. There are currently no X-ray crystal structure data of the t-PA molecule available either in whole or in part. We therefore predicted the three-dimensional structure of the protease domain by means of computer-graphical methods.The model obtained forms a basis for understanding the binding of plasminogen to the active site of t-PA. In addition, the interactions of various inhibitors with t-PA were studied by modeling them into the active site. The model also yields an explanation for the observed amidolytic activity of t-PA in the single chain form.     

A host-guest optical sensor for aliphatic amines based on lipophilic cyclodextrin

A host-guest optical sensor for the determination of aliphatic amines as exemplified by octylamine is proposed. It is based on the reversible fluorescence enhancement of heptakis(2,6-di-O-isobutyl)-β-cyclodextrin(DOB-β-CD) hosting tetraphenylporphyrin (TPP) immobilized in poly(vinyl chloride) (PVC) membrane by aliphatic amine extracted from aqueous phase into membrane phase. The optimum membrane contained 1.15 wt % TPP, 6.15 wt % DOB-β-CD as sensing reagent and other membrane materials. The fluorescence enhancement of the membrane resulted from the formation of a stable three-component complex among DOB-β-CD, TPP, and aliphatic amines. With the optimum conditions described, the fluorescence response of the sensor to octylamine shows a good correlation with the theoretically derived equation in the range 1.0 × 10^–6 to 8.0 × 10^–4 mol/L. The response characteristics including reversibility, response time, reproducibility and lifetime and selectivity of this optical device are also discussed in detail. This sensor has also been applied for the determination of octylamine in water samples containing interferents with satisfactory recovery. Received: 21 November 1999 / Revised: 10 January 2000 / Accepted: 15 January 2000     

Visibility spectroscopy with electron waves using a Wien filter: higher order corrections

Fourier spectroscopy, one of the most precise spectrometry methods in light optics, has been realized in the past years with electron waves by including a crossed-field analyzer (Wien filter) as a wave packet shifting device into a biprism interferometer. To fully exploit the high precision of this method of determining the energy spectrum, higher order corrections stemming from the Wien filter's focusing action are necessary in the evaluation of the measurement. We show that these can be taken into account by using a transformation variable being proportional to the quotient of electric field strength of the Wien capacitor over fringe spacing. Finally, we make some remarks about the possibility of interference of inelastically scattered electrons.     

Emissionsmikroskopische Messung der Ortsverteilung von 20 keV-Elektronen nach Streuung in dünnen Al- und Ge-Aufdampfschichten

Electrons incident on a thin film are displaced laterally when leaving the target by elastic and inelastic scattering. The widening of the current density distribution of an electron beam with an initial energy of 19.5 keV and an initial Gaussian distribution with a half width of about 0.6 microns by plural and multiple scattering as well as in the region of complete diffusion (corresponding to mass thicknesses ranging from 40–500 µg/cm²) is measured for evaporated films of Al and Ge. From these results the increase in half width of an infinitely fine primary electron beam (δ-function response) is computed and plotted. In order to measure the current density distribution of the scattered electrons it is converted to an equivalent distribution of secondaries using a cathode lens image converter. These distributions are magnified and scanned electronically or recorded photographically.