Calibration graphs for steels by IR laser ablation inductively coupled plasma atomic emission spectrometry

Infrared laser ablation (IRLA) was studied as a sample-introduction technique for the analysis of steels by inductively coupled plasma atomic emission spectrometry (ICP-AES). A comparison of two IRLA-ICP-AES systems based on Q-switched nanosecond Nd: YAG lasers was performed. The beam of the LINA-Spark atomizer (LSA Sarl, Cully, Switzerland) based on the Surelite 1-20 laser (Continuum, USA) was moved along a circle. A Perkin-Elmer Optima 3000 DV ICP system was used both with lateral and axial viewing modes. A laboratory-made ablation system based on the Brilliant laser (Quantel) was coupled to a Jobin-Yvon 170 Ultrace ICP (lateral viewing, polychromator part employed). A sample was rotated along a circle during ablation. Linearity of calibration plots was verified at least up to 19% Cr and 12% Ni without internal standardization for both LA-ICP-AES systems. Other elements examined were Mo up to 3%, Mn up 1.5%, Si up to 1.7%, and Cu up to 0.15%. The reproducibility was in the range 5-1 %RSD for a mass percentage 0.5-20% of steel constituents. The relative uncertainty of the centroids of the calibration lines was in the range from +/- 4% to +/- 12% for Cr, Ni, Mn, Mo, and Si, and from +/- 8% to +/- 19% for Cu. The lowest determinable quantities were calculated for calibration dependencies. Performances of both the IR-LA-ICP-AES were comparable.     

Noncommutative field theory and Lorentz violation

The role of Lorentz symmetry in noncommutative field theory is considered. Any realistic noncommutative theory is found to be physically equivalent to a subset of a general Lorentz-violating standard-model extension involving ordinary fields. Some theoretical consequences are discussed. Existing experiments bound the scale of the noncommutativity parameter to (10 TeV)(-2).     

Regularity of Flow of Anisotropic Fluid

We study the steady flow of an anisotropic generalised Newtonian fluid under Dirichlet boundary conditions in a bounded domain . The fluid is characterised by a nonlinear dependence of the stress tensor on the symmetric gradient of the velocity vector field. We prove the existence of a C ^1,α-solution of this problem under certain assumptions on the growth of the elliptic term. The result is global: we prove the regularity up to the boundary of the domain Ω. This research was supported by the grant GACR 201/03/0934; partially also by the grants MSM 0021620839 and GAUK 262/2002/B-MAT/MFF.     

Counterexample to lower semicontinuity in Calculus of Variations

An example is shown of a functional which is not lower semicontinuous with respect to -convergence. The function f is lower semicontinuous, convex in the second variable and linearly coercive. Application to nonexistence of minimizers in BV-setting is also given. Received: 2 May 2000 / Published online: 4 May 2001     

Ground-state properties of the Falicov-Kimball model in one and two dimensions

A new numerical method is used to study the ground-state properties of the spinless Falicov-Kimball model in one and two dimensions. The resultant solutions are used to examine the phase diagram of the model as well as possibilities for valence and metal-insulator transitions. In one dimension a comprehensive phase diagram of the model is presented. On the base of this phase diagram, the complete picture of valence and metal-insulator transitions is discussed. In two dimensions the structure of ground-state configurations is described for intermediate interactions between f and d electrons. In this region the phase separation and metal-insulator transitions are found at low f-electron concentrations. It is shown that valence transitions exhibit a staircase structure. Received 20 October 2000     

Coexistence of Partially Disordered/Ordered Phases in an Extended Potts Model

We consider a generalization of the standard Potts model in which there are q=r+s states with an interaction that distinguishes the two subspecies. We develop a graphical representation (of the FK type) for the system and show that this representation may be incorporated directly into reflection positivity arguments. Using combinations of these techniques, we establish detailed properties of the phase diagram including the existence of sharp triple points. Whenever relevant, the phases are characterized by the percolation properties of the underlying representation.     

Cost Benefit Ratio of Industrial Tracer Applications

Simple relations are given, which could help to estimate the expected annual savings resulting from the application of radioisotope methods for the mixing time, segregation effect or residence time distribution determination. Criteria for estimation of benefit at optimum transition of the continuous production from one quality to another, criteria for estimate the benefits on basis of known holdup and for estimate of benefits resulting from knowledge of the distribution function of residence time and of the kinetics of chemical reaction are presented. Further are demonstrated two examples of evaluation of the economic effect of the results of a system analysis in chemical industry where beside the measurements od residence time distribution by help of radiotracers are used also results of other experimental methods and that practically without increasing production cost.     

Shock elasticities and impulse responses

We construct shock elasticities that are pricing counterparts to impulse response functions. Recall that impulse response functions measure the importance of next-period shocks for future values of a time series. Shock elasticities measure the contributions to the price and to the expected future cash flow from changes in the exposure to a shock in the next period. They are elasticities because their measurements compute proportionate changes. We show a particularly close link between these objects in environments with Brownian information structures.     

The discrete maximum principle for Galerkin solutions of elliptic problems

This paper provides an equivalent characterization of the discrete maximum principle for Galerkin solutions of general linear elliptic problems. The characterization is formulated in terms of the discrete Green’s function and the elliptic projection of the boundary data. This general concept is applied to the analysis of the discrete maximum principle for the higher-order finite elements in one-dimension and to the lowest-order finite elements on simplices of arbitrary dimension. The paper surveys the state of the art in the field of the discrete maximum principle and provides new generalizations of several results.