Cyclotron Resonance Study of the Two-Dimensional Electron Layers and Double-Layers in Tilted Magnetic Fields

The far-infrared absorption in two-dimensional electron layers subject to magnetic field of general orientation was studied theoretically. The Kubo formula is employed to derive diagonal components of the magneto-conductivity tensor of two-dimensional electron single-layers and double-layers. The parabolic quantum well is used to model a simple single-layer system. Both single-layer and double-layer systems can be realized in a pair of tunnel-coupled, strictly two-dimensional quantum wells. Obtained results are compared to experimental data.Comment: 4 pages, 6 figures, elsart/PHYEAUTH macros; presented on the EP2DS-15 Conference in Nara, Japan. To be published in Physica

Multivariate calibration approach for quantitative determination of cell-line cross contamination by intact cell mass spectrometry and artificial neural networks

Cross-contamination of eukaryotic cell lines used in biomedical research represents a highly relevant problem. Analysis of repetitive DNA sequences, such as Short Tandem Repeats (STR), or Simple Sequence Repeats (SSR), is a widely accepted, simple, and commercially available technique to authenticate cell lines. However, it provides only qualitative information that depends on the extent of reference databases for interpretation. In this work, we developed and validated a rapid and routinely applicable method for evaluation of cell culture cross-contamination levels based on mass spectrometric fingerprints of intact mammalian cells coupled with artificial neural networks (ANNs). We used human embryonic stem cells (hESCs) contaminated by either mouse embryonic stem cells (mESCs) or mouse embryonic fibroblasts (MEFs) as a model. We determined the contamination level using a mass spectra database of known calibration mixtures that served as training input for an ANN. The ANN was then capable of correct quantification of the level of contamination of hESCs by mESCs or MEFs. We demonstrate that MS analysis, when linked to proper mathematical instruments, is a tangible tool for unraveling and quantifying heterogeneity in cell cultures. The analysis is applicable in routine scenarios for cell authentication and/or cell phenotyping in general

Electronic Structure of Three-Dimensional Superlattices Subject to Tilted Magnetic Fields

Full quantum-mechanical description of electrons moving in 3D structures with unidirectional periodic modulation subject to tilted magnetic fields requires an extensive numerical calculation. To understand magneto-oscillations in such systems it is in many cases sufficient to use the quasi-classical approach, in which the zero-magnetic-field Fermi surface is considered as a magnetic-field-independent rigid body in k-space and periods of oscillations are related to extremal cross-sections of the Fermi surface cut by planes perpendicular to the magnetic-field direction. We point out cases where the quasi-classical treatment fails and propose a simple tight-binding fully-quantum-mechanical model of the superlattice electronic structure.Comment: 8 pages, 7 figures, RevTex, submitted to Phys. Rev.

Magneto crystalline anisotropies in (Ga,Mn)As: A systematic theoretical study and comparison with experiment

We present a theoretical survey of magnetocrystalline anisotropies in (Ga,Mn)As epilayers and compare the calculations to available experimental data. Our model is based on an envelope function description of the valence band holes and a spin representation for their kinetic-exchange interaction with localised electrons on Mn ions, treated in the mean-field approximation. For epilayers with growth induced lattice-matching strains we study in-plane to out-of-plane easy-axis reorientations as a function of Mn local-moment concentration, hole concentration, and temperature. Next we focus on the competition of in-plane cubic and uniaxial anisotropies. We add an in-plane shear strain to the effective Hamiltonian in order to capture measured data in bare, unpatterned epilayers, and we provide microscopic justification for this approach. The model is then extended by an in-plane uniaxial strain and used to directly describe experiments with strains controlled by postgrowth lithography or attaching a piezo stressor. The calculated easy-axis directions and anisotropy fields are in semiquantitative agreement with experiment in a wide parameter range

On computing fixpoints in well-structured regular model checking, with applications to lossy channel systems

We prove a general finite convergence theorem for "upward-guarded" fixpoint expressions over a well-quasi-ordered set. This has immediate applications in regular model checking of well-structured systems, where a main issue is the eventual convergence of fixpoint computations. In particular, we are able to directly obtain several new decidability results on lossy channel systems.Comment: 16 page

Nuclear physics for cultural heritage

We report about the expert review, published by the Nuclear Physics Division of the European Physical Society (NPD EPS), which aims to provide the public with a popular and accessible account of the latest developments in the field of nuclear physics application for cultural heritage. The contributions from a range of leading specialists explain how applied atomic and nuclear techniques can be used to obtain information that can help us to understand the way of life in ancient times and how they can be used to conserve cultural heritage treasures. This topical review draws heavily on European work and is extensively illustrated with important discoveries and examples from archaeology, pre-history, history, geography, culture, religion and curation. It outlines key advances in a wide range of cross-disciplinary techniques and has been written with the minimum of technical detail so as to be accessible by as wide as possible audience. The large number of groups and laboratories working in the study and preservation of cultural heritage using mainly nuclear physics methods across Europe indicates the enormous effort and importance paid by society to this activity

Functional Text Dimensions for the annotation of web corpora

This paper presents an approach to classifying large web corpora into genres by means of Functional Text Dimensions (FTDs). This offers a topological approach to text typology in which the texts are described in terms of their similarity to prototype genres. The suggested set of categories is designed to be applicable to any text on the web and to be reliable in annotation practice. Interannotator agreement results show that the suggested categories produce Krippendorff's α at above 0.76. In addition to the functional space of eighteen dimensions, similarity between annotated documents can be described visually within a space of reduced dimensions obtained through t-distributed Statistical Neighbour Embedding. Reliably annotated texts also provide the basis for automatic genre classification, which can be done in each FTD, as well as as within the space of reduced dimensions. An example comparing texts from the Brown Corpus, the BNC and ukWac, a large web corpus, is provided