Mass Transport in the Presence of Internal Defect Reactions—Concept of Conservative Ensembles: II, Evaluation of Electrochemical Transport Measurements

It is shown that in the general case of a defective solid, where the ionic point defects can change their valence states, the evaluation formulas of well-known electrochemical techniques (such as concentration cell experiments, Wagner-Hebb method, chemical and electrochemical polarization and relaxation) have to be modified. The generalized relationships are derived.     

Analysis of process dynamics in bioreactors

The dynamic behaviour of bioreactors was analysed by means of experimental process identification using correlation analysis with pseudo-random binary input signals (PRBS) for excitation of the process. Agitation speed and airflow were used as input signals. The correlation with oxygen partial pressure in the liquid and oxygen and carbon dioxide concentrations in the exhaust gas were calculated. Results of the computation are: degree of a linear differential equation and coefficients of the equation, which can then be used to design adaptive controllers. The dead time of the system can be found by comparing the least squares of different models. The variation of the parameters during process time are shown for a low order adaptive controller.     

On the theory of superconductors containing magnetic impurities: Crystalline field effects

We extend to finite concentrations a previous calculation of crystalline field effects in superconductors containing rare-earth impurities. The computations, which have to be done numerically, apply to non-Kramers ions as well as Kramers ions. A comparison between theory and available experimental data is made.The computer time used was supported in part by the Computer Science Center of the University of Maryland.     

Derivation of variational principles for rigid-plastic solids obeying non-associated flow laws—I: Further development of the nonlinear method of adding the adjoint operator,prescribed jumps

In this paper several variational functionals have been derived for a perfectly plastic solid obeying non-associated flow rule. The nonlinear method of adding the adjoint operator has been applied. Making use of the method a basic variational functional is obtained, from which others, with a reduced number of independent fields, are derived. In the first part of the paper discontinuities of stress and velocity fields are prescribed. Also further results concerning the method of adding the adjoint operator are presented.     

Hochfeld-13C-kernresonanz an acrylnitril/vinylchlorid-copolymeren

Copolymers of acrylonitrile and vinylchloride (molar ratio ACN : VC = 44.5 : 55.5) were synthesized by continuous emulsion polymerization. Their sequence distribution was studied by ¹³C-NMR-spectra at 90.52 MHz. Three different methylene carbon regions were attributed to diads of the type ? VC? VC? ,? VC? ACN? and ? ACN? ACN? . The experimentally determined diad distribution was in good agreement with the calculated diad distribution, using reactivity ratios of r_ACN = 3.6 and r_VC = 0.05.     

Equation of motion approach to the Hubbard model in infinite dimensions

We consider the Hubbard model on the Bethe lattice with infinite Coordination number and construct (i) a systematic series of self-consistent approximations to the one-particle Green's function, G⁽ⁿ⁾(), n = 2,3,... and (ii) conduct an exact diagonalization study of the Hubbard star and the star of the stars. We present analytic and numerical results for the Mott-Hubbard transition at half filling. We find consistently (i) a critical U_c 2.5 and (ii) that the gap opens like (U-U_c)^3/2.     

Thermodynamic analysis of the δ ferrite in the systems Fe-Cr-N and Fe-Cr-Mn-N

The solubility of nitrogen in ferritic iron-chromium alloys with mass contents of between 6.08 to 23.94 % chromium was measured in the temperature range 1523 to 1773 K. Combining the results with published data for the nitrogen solubility in iron-chromium, improved parameters describing the chromium-nitrogen interaction were derived. The Gibbs free excess energy can be described by . Calculations of the nitrogen solubility using this equation and calculations using parameters published by the Swedish Institute of Metals Research differ the more the higher the temperature. A repeated analysis of measurements of the nitrogen solubility in ferritic Fe-Cr-Mn alloys using the Gibbs free excess energy derived in this investigation for the chromium-nitrogen interaction leads to the manganese-nitrogen interaction energy .     

Knowledge construction in an outsider community: Extending the communities of practice concept

We present an empirical analysis of a web forum in which followers of a health-related community exchange information and opinions in order to pass on and develop relevant knowledge. We analyzed how knowledge construction takes place in such a community that represents an outsider position which is not accepted by majority society. For this purpose we applied the Community of Practice (CoP) concept as a guideline for our analysis and found that many well-known activities of CoPs were true of the Urkost community. The social network analysis findings also supported interpreting this community as a CoP. But we found as well that this community had a variety of structural characteristics that the CoP literature deals with insufficiently. We identified the structure of goals, roles, and communication as relevant features that are typical of this outsider CoP. For example, the attitude of the core members towards people of a ‘different faith’ was characterized by strong hostility and rejection. These features provided an effective basis for the development and maintenance of a shared identity in the community. Our findings are discussed against the background of the necessity for further development of the CoP concept.