Photochemistry of Halogens in the Marine Atmosphere

Diatomic halogen molecules diffusing into the marine atmosphere are photodissociated to atoms in daylight more rapidly than they undergo other fates. The geochemistry of ‘gaseous halogens’ is considered in terms of photolysis rates and the secondary reactions of the atoms produced. Diatomic halogens could be photolyzed predominantly by day and adsorbed on aerosol by night without yielding diurnal variations in currently measurable variables. Halogen atoms in the marine atmosphere react with ozone more rapidly than with other marine tropospheric constituents, this reaction yielding haloxy radicals that are also reactive.

The new concepts and new developments in hte theory of polymer crystallization

Recently a debate about the initial crystallization process which has not been the hotspot for a long time since the theory proposed by Hoffman- Lauritzen (LH) dominated the field arose again. For a long time the Hoffman-Lauritzen model was always confronted by criticism,and some of the points were taken up and led to modifications, but the foundation remained unchanged which deemed that before the nucleation and crystallization the system was uniform. In this article the classical nucleation and growth theory of polymer crystallization was reviewed, and the confusion of the explanations to the polymer crystallization phenomenon was pointed out. LH theory assumes that the growth of lamellae is by the direct attachment of chain sequences from the melt onto smooth lateral sides.

Tip-induced dynamic characterization of multilayers and variable morphologies of cytochrome c molecules on highly oriented pyrolytic graphite revealed by in-situ scanning tunnelling microscopy

The dynamic states of cytochrome c multilayers on electrochemically pretreated highly oriented pyrolytic graphite (HOPG) have been studied by in-situ scanning tunnelling microscopy (STM) under potential control of both the tip and the substrate in cytochrome c and phosphate buffer solution. The dynamic characterization of cytochrome c multilayers and relatively stable adsorbed single cytochrome c molecules scattered on HOPG imply that physically adsorbed multilayers were more easily influenced by the STM tip than those of chemically adsorbed single molecules. In-situ STM images of chemically adsorbed cytochrome c molecules with discernible internal structures on HOPG revealed that morphologies of cytochrome c molecules also suffered tip influence; possible tip-sample-substrate interactions have been discussed.

STUDIES ON STATES OF CYTOCHROME-C MOLECULES IN AQUOUS SOLUTIONS USING SYNCHRONOUS FLUORESCENCE SPECTROSCOPY

The states of cytochrome C molecules in aquous solution were studied with synchronous fluorescence spectroscopy, It was found that the synchronous fluorescent spectra of cytochrome C were contributed by tyrosine and tryptophan residues separately at Delta lambda = 20 nm and Delta lambda = 80 nm, The peak position in synchronous fluorescent spectra of tyrosine residues in cytochrome C molecule does not change with its concentration, but that of tryptophan residue changes with its concentration, Only one peak at 340.0 nm was observed in the dilute solution of cytochrome C, With increasing the concentration of cytochrome C, a new peak at 304. 0 nm appeared. The peak at 340.0 nm disappeared and only one peak at 304.0 nm was observed at a higher concentration of cytochrome C, It may originate from the change of aggregation states of cytochrome C molecules and it was considered that the peak at 340.0 nm was attributed to the monomer and peak at 304.0 nm was due to the dimmer or oligomers. When urea was added into cytochrome C solution in which both monomer and dimmer or oligomers exist, cytochrome C molecules do not denature in the range of the specific concentrations of urea. The concentration of monomer of cytochrome C molecules increased and that of aggregation slates decreased by adding urea, Therefore, the synchronous fluorescence spectroscopy can be used to identify monomer and aggregation states of cytochrome C molecules.

APPLICATION OF ULTRAMICROELECTRODES IN STUDIES OF HOMOGENEOUS CATALYTIC REACTIONS .2. A THEORY OF QUASI-1ST AND 2ND-ORDER HOMOGENEOUS CATALYTIC REACTIONS

The analytical expressions of quasi-first and second order homogeneous catalytic reactions with different diffusion coefficients at ultramicrodisk electrodes under steady state conditions are obtained by using the reaction layer concept. The method of treatment is simple and its physical meaning is clear. The relationship between the diffusion layer, reaction layer, the electrode dimension and the kinetic rate constant at an ultramicroelectrode is discussed and the factor effect on the reaction order is described. The order of a catalytic reaction at an ultramicroelectrode under steady state conditions is related not only to C(Z)*/C(O)* but also to the kinetic rate constant and the dimension of the ultramicroelectrode; thus the order of reaction can be controlled by the dimension of the ultramicroelectrode. The steady state voltammetry of the ultramicroelectrode is one of the most simple methods available to study the kinetics of fast catalytic reactions.

A theory of nonlinear AC response in coated composites

A method for determining effective dielectric responses of Kerr-like coated nonlinear composites under the alternating current (AC) electric field is proposed by using perturbation approach. As an example, we have investigated the composite with coated cylindrical inclusions randomly embedded in a host under an external sinusoidal field with finite frequency omega. The local field and potential of composites in general consists of components with all harmonic frequencies. The effective nonlinear AC responses at all harmonics are induced by the coated nonlinear composites because of the nonlinear constitutive relation. Moreover, we have derived the formulae of effective nonlinear AC responses at the fundamental frequency and the third harmonic in the dilute limit.

Characterization of iron atoms in the framework of MFI-type zeolites by UV resonance Raman spectroscopy

Silicalite-I, ZSM-5, and Fe-ZSM-5 zeolites prepared from two different silicon sources are characterized by UV resonance Raman (UVRR) spectroscopy, X-ray diffraction (XRD), electron spin resonance (ESR), and UV/visible diffuse reflectance spectroscopy (UV/Vis DRS). A new technique for investigating zeolitic structure, UV resonance Raman spectroscopy selectively enhances the Raman bands associated with framework iron atoms incorporated into MFI-type zeolites, and it is very sensitive in identifying the iron atoms in the framework of zeolites, while other techniques such as XRD, ESR, and UV/Vis DRS have failed in uncovering trace amounts of iron atoms in the framework of zeolites. (C) 2000 Academic Press.

Towards a Computational Theory of Definite Anaphora Comprehension in English Discourse

This report investigates the process of focussing as a description and explanation of the comprehension of certain anaphoric expressions in English discourse. The investigation centers on the interpretation of definite anaphora, that is, on the personal pronouns, and noun phrases used with a definite article the, this or that. Focussing is formalized as a process in which a speaker centers attention on a particular aspect of the discourse. An algorithmic description specifies what the speaker can focus on and how the speaker may change the focus of the discourse as the discourse unfolds. The algorithm allows for a simple focussing mechanism to be constructed: and element in focus, an ordered collection of alternate foci, and a stack of old foci. The data structure for the element in focus is a representation which encodes a limted set of associations between it and other elements from teh discourse as well as from general knowledge.

Choices of approaches in e-moderation: conclusions from a grounded theory study

Much has been published in recent years about the desirable nature of facilitated interactions in on-line discussions with educational purposes. However little has been reported about the roles which tutors actually adopt in real life learning contexts, how these range between ‘tutoring, ‘managing’ and ‘facilitating’, and what the distinctions between these three roles may be. In this paper choices of priorities in e-moderation, which were made in three naturalistic (real life) case studies by three higher education practitioners, are identified and discussed. These contrasting approaches were captured and analysed using grounded theory principles. The paper also discusses these occasions when the facilitation was less effective than might have been desired. It finally summarises the potential of various approaches within e-moderation – and some of the attendant risks. The finding is that principles and practices developed for face-to-face support of student-directed learning were found equally applicable in e-moderated online group work, despite several significant differences between the two types of setting. Keywords: higher education, e-learning, e-moderation, asynchronous discussions, learning outcomes, grounded theory