Condensed phases in flame spectrometry: an equilibrium model of the acetylene flame

An equilibrium model for a wet acetylene flame has been used for the calculation of the distribution of carbon, aluminium and silicon between gaseous and condensed phases. Calculated values of free atom vapour fractions are in agreement with published experimental data. It is thermodynamically probable that the formation of condensed phases limits atom vapour formation. There is a relationship between the position of an element in the Periodic Table and the nature of the condensed phase.     

Suppression factors in diffractive photoproduction of dijets

Now that new publications of H1 data for the diffractive photoproduction of dijets, which overlap with the earlier published H1 data and the recently published data of the ZEUS collaboration, have appeared, we have recalculated the cross sections for this process in next-to-leading order (NLO) of perturbative QCD to see whether they can be interpreted consistently. The results of these calculations are compared to the data of both collaborations. We find that the NLO cross sections disagree with the data, showing that factorization breaking occurs at that order. If direct and resolved contributions are both suppressed by the same amount, the global suppression factor depends on the transverse-energy cut. However, by suppressing only the resolved contribution, also reasonably good agreement with all the data is found with a suppression factor independent of the transverse-energy cut.     

Eine neue Laboratoriums-Vakuumpumpe

Ohne Zusammenfassung     

On the Distinctness of Chemistry

Chemistry is concerned with all aspects of the changing of one kind of matter into another. It has many parts and all but one of these are so different from all the adjacent sciences that their distinctness is obvious; the exception is physical chemistry. The activities of its practitioners resemble prima facie those of physicists. These however deal with unchanging matter that retains its chemical identity, and virtually all their experimental information is numerical. The physical chemist's concerns are the nature, extent, and rate of chemical changes, and on these much information may be gathered by the observer's unaided senses.A fundamental feature or chemistry with few parallels in other sciences is that the variables determining chemical behaviour include the purity of reaction vessels, reagents, and the gas-phase in contact with these, as well as the exact experimental procedures when bringing about the chemical changes. For this reason, when encountering ostensibly new chemical phenomena, it is even more important than in other areas to distinguish between repeatability (of phenomena, e.g. explosions) and reproducibility (of quantities, e.g. reduction potentials). The distinction is not always clear, as differences of degree may develop into differences of kind. Unrepeatability may be of great heuristic significance, but irreproducibility is often of trivial origin. Examples from the author's researches illustrate how chemical behaviour, e.g. electrochemical conductivity or the nature of a product, such as the shape of a polymer molecule, can be altered profoundly by very small changes of experimental conditions, which is uncommon in other sciences.     

Radial segregation due to weak convection in a floating zone

The influence of weak convection, caused by surface tension forces, on radial dopant segregation occurring in crystals grown under microgravity conditions is studied numerically. The geometry considered corresponds to a floating-zone configuration with partially coated melt surfaces consisting of small evenly distributed spots of free surfaces. In order to distinguish dopant distribution due to weak convection clearly from distribution due to diffusion the spots only cover one quarter of the periphery. Thus, surface tension-driven convection is allowed only over one quarter of the floating-zone configuration resulting in an asymmetric dopant distribution. The percentage of free surfaces present is varied in order to alter the Marangoni flow rates. The maximum dopant concentration due to radial segregation is plotted as a function of a certain convection level. The results of the present numerical study are supposed to be used to design corresponding space experiments launched at the end of the year 2000.     

Multiple equilibria and indifference-threshold points in a rational addiction model

Becker and Murphy (J Polit Econ 96(4):675–700, 1988) have established the existence of unstable steady states leading to threshold behavior for optimal consumption rates in intertemporal rational addiction models. In the present paper a simple linear-quadratic optimal control model is used to illustrate how their approach fits into the framework of multiple equilibria and indifference-threshold points. By changing the degree of addiction and the level of harmfulness we obtain a variety of behavioral patterns. In particular we show that when the good is harmful as well as very addictive, an indifference-threshold point, also known in the literature as a Skiba point, separates patterns converging to either zero or maximal consumption, where the latter occurs in the case of a high level of past consumption. This implicitly shows that an individual needs to be aware in time of these characteristics of the good. Otherwise, he/she may start consuming so much that in the end he/she is totally addicted.     

Asymmetric Information in a Capital Accumulation Differential Game with Spillover and Learning Effects

Journal of Optimization Theory and Applications - This paper considers a capital accumulation game where the installation costs of investments are lowered by the firm’s own capital stock...     

Persistent oscillations in a threshold adjustment model

In this paper we present a simple time-continuous behavioural model of habit formation. Addictive behaviour is damped by a threshold which adapts itself to the habit. This adaptive behaviour of the threshold may lead to periodic fluctuations of the consumption rate, the habit and the threshold. It turns out that both a low adjustment rate of the threshold as well as a steep consumption function favour oscillatory patterns.