Quantum mechanics of layers with a finite number of point perturbations

We study spectral and scattering properties of a spinless quantum particle confined to an infinite planar layer with hard walls containing a finite number of point perturbations. A solvable character of the model follows from the explicit form of the Hamiltonian resolvent obtained by means of Krein's formula. We prove the existence of bound states, demonstrate their properties, and find the on-shell scattering operator. Furthermore, we analyze the situation when the system is put into a homogeneous magnetic field perpendicular to the layer; in that case the point interactions generate eigenvalues of a finite multiplicity in the gaps of the free Hamiltonian essential spectrum.Comment: LateX 2e, 48 pages, with 3 ps and 3 eps figure

Navigating institutional pressure in state-socialist and democratic regimes: The case of movement brontosaurus

Using the case of Movement Brontosaurus, a Czech organization founded in state socialist times, this article investigates how civic associations and nongovernmental organizations seeking to promote alternatives to the status quo respond to institutional pressures in different political and social contexts. The case shows that under state socialism, Brontosaurus appeared to conform to state mandates and societal expectations. However, its formal structure was decoupled from many activities to obscure its oppositional intent.After the transition to democracy, the organization was only able to maintain its place in society after it aligned its structure and practices with each other and openly expressed its alternative agenda. The findings demonstrate how social change and alternative lifestyle organizations vary their responses to institutional pressure in ways that enable them to realize their values and pursue their missions while accounting for the political and social contexts in which they are embedded

ECG Signal Compression Based on Fractals and RLE

Compression of ECG signal is up to date challenge. There are many methods for ECG compression. This paper focuses on fractal based compression method. The method is implemented in MATLAB and compared with results in source article. New single cycle method for ECG signal compression that combines fractals and run length encoding (RLE) is created. Both methods are compared with method based on wavelet transform (WT) and RLE and up to date wavelet based Set Partitioning in Hierarchical Trees (SPIHT) algorithm

Effect of sulphate impurity in chromic acid anodizing of aluminium

AbstractThe formation of porous anodic alumina during potentiostatic anodizing of aluminium for times up to 900s has been investigated using two grades of chromic oxide reagent. The anodic films were examined by ion beam analysis and scanning and transmission electron microscopies. Sulphate impurity in the chromic acid led to incorporation of sulphate into the anodic film, a lower current density, a smaller cell size and less feathering of the pore walls. In addition, the efficiency of film formation was increased. The sulphate concentration in the film was greatly enhanced relative to the electrolyte