Dissociative attachment of low-energy electrons to vibrationally excited molecules using a photoelectron source

The process of dissociative attachment (DA) of low-energy electrons ) to vibrationally excited sodium dimer molecules is studied with high electron energy resolution () in a supersonic molecular beam. A novel photoelectron source, based on two-step photoionization of the sodium atoms in the beam, may deliver a current of up to 1 nA and has been used with a current of typically 0.2 nA in this experiment. The energy dependence of the rate of sodium anion formation is determined by ion detection based on a time-of-flight analysis. The molecules are selectively excited to levels using the technique of coherent population transfer by delayed pulses (STIRAP). The comparison of the experimental data with recent resonance model calculations based on improved potential curves reveals generally good agreement for levels v ”>12. For some distinct differences between theoretical and experimental results persist. Received: 21 November 1998 / Received in final form: 7 April 1999     

Modeling of three-dimensional pressure fields in sonochemical reactors with an inhomogeneous density distribution of cavitation bubbles. Comparison of theoretical and experimental results

During the last 50 years extensive experimental investigation has been carried out on the chemical effects of ultrasound, but limited work has been reported on modeling. This paper presents a new model in which a numerical calculation of the three-dimensional linear sound pressure field distribution in a commonly used sonoreactor containing three transducers is carried out. In this model the inhomogeneous three-dimensional time-dependent wave equation was solved using the finite difference approach. The modeled results are then compared with the experimentally measured values, and the agreement, in general, is found to be good. Further, our modeling studies have an advantage, since they clearly describe the continuous sound pressure field structure, unlike previously reported results in which some information is missing due to limited intermittent measured points.     

Spektrophotometrische Bestimmung von Gallium durch Extraktion des 8-Hydroxychinolinkomplexes

Analytical and Bioanalytical Chemistry - Durch Benutzung eines pH-Wertes von 2,5 und Anwendung verschiedener Maskierungsmittel kann die extraktive spektralphotometrische Bestimmung von Ga mit...     

Investigations of the microscopic structure of poly(vinyl alcohol) hydrogels by confocal laser scanning microscopy

The fluorescence mode confocal laser scanning microscopy (CLSM) is introduced as an alternative method to investigate the bulk structure of poly(vinyl alcohol) (PVA) hydrogel. Investigations of the bulk structure of hydrogel samples, prepared by freezing and controlled thawing of aqueous PVA solutions followed by fluorochrome conjugation, were possible in the native state because with this technique water does not need to be removed prior to examination. This is of advantage to other methods, such as scanning electron microscopy, requiring dehydration by critical-point drying or freeze-etching, because both may result in a significant alteration of the gel structure. CLSM images of the hydrogel bulk structure were taken at several successive intervals from the surface into the hydrogel (up to 60 μm) without freeze-fracturing or cutting the sample. Detailed morphological characterization is achievable by superimposing series of images taken at successive intervals and by magnifying special regions of interest. Images of hydrogel bulk structures revealed a continuous, three-dimensional network that originates from phase-separation (spinodal decomposition) during the freezing period. The pore or mesh size in the cryogel increased, from about 2–7 μm, with decreasing PVA concentration. The surface layer was only a few microns thick, and the bulk structure underneath showed neither porosity gradients nor structural orientations. Received: 29 April 2000/Accepted: 18 August 2000     

Classical analogue of displaced Fock states and quantum correlations in Glauber-Fock photonic lattices

Coherent states and their generalizations, displaced Fock states, are of fundamental importance to quantum optics. Here we present a direct observation of a classical analogue for the emergence of these states from the eigenstates of the harmonic oscillator. To this end, the light propagation in a Glauber-Fock waveguide lattice serves as equivalent for the displacement of Fock states in phase space. Theoretical calculations and analogue classical experiments show that the square-root distribution of the coupling parameter in such lattices supports a new family of intriguing quantum correlations not encountered in uniform arrays. Because of the broken shift invariance of the lattice, these correlations strongly depend on the transverse position. Consequently, quantum random walks with this extra degree of freedom may be realized in Glauber-Fock lattices.     

Solitons in geometric potentials

We show that the geometrically induced potential existing in undulated slab waveguides dramatically affects the properties of solitons. In particular, whereas solitons residing in the potential maxima do not feature power thresholds and are stable, their counterparts residing in the potential minima are unstable and may exhibit a power threshold for their existence. Additionally, the geometric potential is shown to support stable multipole solitons that cannot be supported by straight waveguides. Finally, the geometric potential results in the appearance of the effective barriers that prevent transverse soliton motion.     

Multifunctional nanoparticles as simulants for a gravimetric immunoassay

Immunoassays are important tools for the rapid detection and identification of pathogens, both clinically and in the research laboratory. An immunoassay with the potential for the detection of influenza was developed and tested using hemagglutinin (HA), a commonly studied glycoprotein found on the surface of influenza virions. Gold nanoparticles were synthesized, which present multiple peptide epitopes, including the HA epitope, in order to increase the gravimetric response achieved with the use of a QCM immunosensor for influenza. Specifically, epitopes associated with HA and FLAG peptides were affixed to gold nanoparticles by a six-mer PEG spacer between the epitope and the terminal cysteine. The PEG spacer was shown to enhance the probability for interaction with antibodies by increasing the distance the epitope extends from the gold surface. These nanoparticles were characterized using thermogravimetric analysis, transmission electron microscopy, matrix-assisted laser desorption/ionization-time of flight, and ¹H nuclear magnetic resonance analysis. Anti-FLAG and anti-HA antibodies were adhered to the surface of a QCM, and the response of each antibody upon exposure to HA, FLAG, and dual functionalized nanoparticles was compared with binding of Au–tiopronin nanoparticles and H5 HA proteins from influenza virus (H5N1). Results demonstrate that the immunoassay was capable of differentiating between nanoparticles presenting orthogonal epitopes in real-time with minimal nonspecific binding. The detection of H5 HA protein demonstrates the logical extension of using these nanoparticle mimics as a safe positive control in the detection of influenza, making this a vital step in improving influenza detection methodology.     

Ultrafast electrical signal generation,propagation and detection

Short-pulse optical sources have allowed the study of ultrafast electrical phenomena in the circuits and devices which will become future electronic systems. In this paper techniques for the generation, propagation and detection of electrical signals in the femtosecond regime are presented.     

Theoretical rate constant calculations for O(3P) with saturated hydrocarbons

Theoretical rate constants have been calculated for O(³P) with five saturated hydrocarbons, CH₄, C₂H₆, C₃H₈, iso-C₄H₁₀, and neo-C₅H₁₂. The method of choice is bond energy–bond order (BEBO) with activated complex theory (ACT). Because the BEBO method is empirical, O(³P) + CH₄ is evaluated first, and the theoretical results are compared to more rigorous calculations and to the empirical transition state method. Comparisons are also made between predictions and experimental results. All of these comparisons show that the BEBO-ACT method gives results which are consistent with experiment and other theory. Because the method is successful, the other four cases are then considered. Ambiguity arises for the higher hydrocarbons from the problem of internal rotations in the activated complexes, and three cases are evaluated. Best agreement with experiment is obtained if the primary rotor(s) in the complexes are considered to be free. Predictions of rate constants are made from 500 to 2500 K. Throughout the discussion issues of theory which are common to any ACT calculation from any method of potential energy evaluation (LEP, LEPS, or ab initio quantum mechanics) are featured.