Self-avoiding walks on strongly diluted lattices: Chain-growth simulations vs. exact enumeration

We discuss and compare two different methods that can be used to investigate self-avoiding walks on lattices with random site dilution. One is the so-called pruned-enriched Rosenbluth method (PERM), a chain-growth Monte Carlo algorithm, the other is a recently developed exact enumeration technique. While the latter is highly efficient for systems close to the critical concentration, it cannot be used for less dilute systems. PERM is more versatile but appears to have difficulties coping with strong confinement.     

Critical amplitude ratios of the Baxter–Wu model

A Monte Carlo simulation study of the critical and off-critical behavior of the Baxter–Wu model, which belongs to the universality class of the 4-state Potts model, was performed. We estimate the critical temperature window using known analytical results for the specific heat and magnetization. This helps us to extract reliable values of universal combinations of critical amplitudes with reasonable accuracy. Comparisons with approximate analytical predictions and other numerical results are discussed.     

On the existence of primary methods of measurement

 There is much discussion in chemical metrology about the definition of primary methods of measurement, just as a couple of years ago there was debate about its predecessors, absolute methods and definitive methods. It is argued in this paper that the designation of certain methods as being primary only makes sense if there is an outstanding property identified that is common to all primary methods, and not present for all non-primary methods. The aim to identify primary methods should not blur our notion that it is the good practice of analytical chemistry that produces good results, not a particular method of analysis.     

The wrong kind of gravity

The KPZ formula [V.G. Knizhnik, A.M. Polyakov, and A.B. Zamolodchikov, Mod. Phys. Lett. A 3 (1988) 819] shows that coupling central charge c≤1 spin models to 2D quantum gravity dresses the conformal weights to get new critical exponents, where the relation between the original and dressed weights depends only on c. At the discrete level the coupling to 2D gravity is effected by putting the spin models on annealed ensembles of Φ³ planar random graphs or their dual triangulations, where the connectivity fluctuates on the same time-scale as the spins.Since the sole determining factor in the dressing is the central charge, one could contemplate putting a spin model on a quenched ensemble of 2D gravity graphs with the “wrong” c value. We might then expect to see the critical exponents appropriate to the c value used in generating the graphs. In such cases the KPZ formula could be interpreted as giving a continuous line of critical exponents which depend on this central charge. We note that rational exponents other than the KPZ values can be generated using this procedure for the Ising, tricritical Ising and 3-state Potts models.     

Recognizing heterogeneous distribution of platinum group elements (PGE) in geological materials by means of the Re–Os isotope system

The identification of uncertainties caused by sample inhomogeneity, as distinct from those caused by sample preparation and measurement, is a challenging task. Use of chemometric methods to separate and estimate these contributions to the combined standard uncertainty of a measurement (u _c ) of an analytical result requires complex experiments. The difficulty of platinum group element measurement makes this task even more complex. But unless it can be demonstrated that sample inhomogeneity is the major contributor to the high variability of an analytical result one should be careful not to mistakenly attribute this to a nugget effect. In this contribution we are able to demonstrate in two special cases that irreproducible results (up to 90% RSD) for analysis of Os and Re in the pg g^–1 to ng g^–1 range are truly caused by a nugget effect and not by inadequacies of the analytical method.     

X-ray fluorescence raw intensities vs. concentration data for multivariate classification of hungarian coal

A set of coal samples was examined by routine methods of coal analysis (density, calorific value, sulfur content, etc.) and by trace element determinations on the coal ash. Both data sets gave satisfactory clustering of samples from similar geological zones. X-ray fluorescence spectra were evaluated in order to identify the significant data-reduction steps in the sequence raw spectra/net intensities/trace element concentrations that is commonly used in x-ray spectrometry. The deconvolution yielding net intensities from spectra was identified as the most significant step. This was explained by the decorrelation effect of geochemically dissimilar elements.     

Qualitative and quantitative determination of micro-inclusions by automated SEM/EDX analysis

With the help of an automated SEM/EDX analysis system non-metallic micro-inclusions in steel can be detected on a metallographically prepared surface area. The system makes it possible to determine position, size, shape and composition of each particle. Usually more than 1000 inclusions are found on one scan area. Therefore a new offline evaluation method has been developed to classify the large amount of inclusions and calculate specific size and shape data. A summary sheet is created to show the area contents and the mean values of all important properties for each class. Size and XY distributions as well as binary and ternary phase diagrams are drawn to depict the results. The strengths of this analytical technique are demonstrated by evaluation of an LC (low-carbon) steel. Alumina, common spinel, sulfide and oxisulfide inclusions could be identified as dominant inclusion types in LC steel.     

The determination of arsenic at ng/g- andμg/g-levels in organic and biological matrices

Summary Three independent decomposition methods for organic matter are compared for use in the determination of arsenic by the hydride-AAS method. Matrix interferences in the arsine evolution cause systematic errors.

---

Bestimmung von Arsen im ng/g- und g/g-Bereich in organischem und biologischem Material

Zusammenfassung Drei unabhängige Aufschlußmethoden zwecks Arsenbestimmung nach der Hydrid-Atomabsorptionsmethode wurden verglichen. Störungen seitens der Matrix bei der AsH₃-Entwicklung sind eine der Ursachen für systematische Fehler.