Conduction electrons localized by charged magneto-acceptors A2−^{2-} in GaAs/GaAlAs quantum wells

A variational theory is presented of A$^{1-}$ and A$^{2-}$ centers, i.e. of a negative acceptor ion localizing one and two conduction electrons, respectively, in a GaAs/GaAlAs quantum well in the presence of a magnetic field parallel to the growth direction. A combined effect of the well and magnetic field confines conduction electrons to the proximity of the ion, resulting in discrete repulsive energies above the corresponding Landau levels. The theory is motivated by our experimental magneto-transport results which indicate that, in a heterostructure doped in the GaAs well with Be acceptors, one observes a boil-off effect in which the conduction electrons in the crossed-field configuration are pushed by the Hall electric field from the delocalized Landau states to the localized acceptor states and cease to conduct. A detailed analysis of the transport data shows that, at high magnetic fields, there are almost no conducting electrons left in the sample. It is concluded that one negative acceptor ion localizes up to four conduction electrons.Comment: 8 pages, 5 figure

Photoluminescence investigations of 2D hole Landau levels in p-type single Al_{x}Ga_{1-x}As/GaAs heterostructures

We study the energy structure of two-dimensional holes in p-type single Al_{1-x}Ga_{x}As/GaAs heterojunctions under a perpendicular magnetic field. Photoluminescence measurments with low densities of excitation power reveal rich spectra containing both free and bound-carrier transitions. The experimental results are compared with energies of valence-subband Landau levels calculated using a new numerical procedure and a good agreement is achieved. Additional lines observed in the energy range of free-carrier recombinations are attributed to excitonic transitions. We also consider the role of many-body effects in photoluminescence spectra.Comment: 13 pages, 10 figures, accepted to Physical Review

Landauer Conductance of Generalized Fibonacci-Type Semiconductor Superlattices

The quantum model of quasi-one-dimensional generalized Fibonacci semiconductor superlattice with the mass of charge carriers depending on the position in superlattice is formulated. The Landauer electrical conductance σ$\text{}_{L}$ of generalized Fibonacci semiconductor superlattice is studied analytically and numerically. The dynamical maps allowing us to calculate σ$\text{}_{L}$ of the studied systems are presented. It is shown that σ$\text{}_{L}$ as a function of incident energy E of charge carriers oscillates strongly and exhibits the resonant character. We have verified numerically that σ$\text{}_{L}$(E) reaches its local maximum for energies E corresponding to energy eigenvalues of charges in superlattice

Adverse outcomes after percutaneous dilatational tracheostomy versus surgical tracheostomy in intensive care patients: case series and literature review

Konrad Jarosz,1 Bartosz Kubisa,2 Agata Andrzejewska,3 Katarzyna Mrówczyńska,3 Zbigniew Hamerlak,4 Alicja Bartkowska-Śniatkowska5 1Department of Clinical Nursing, Pomeranian Medical University, 2Thoracic Surgery and Transplantation Department, Pomeranian Medical University, 3Anaesthesiology and Intensive Care Department, Pomeranian Medical University, 4Stomatology Department, Pomeranian Medical University, 5Anaesthesiology and Pediatric Intensive Care Department, Poznan University of Medical Sciences, Szczecin, Poland Abstract: Tracheostomy is a routinely done procedure in the setting of intensive care unit (ICU) in patients requiring prolonged mechanical ventilation. There are two ways of making a tracheostomy: an open surgical tracheostomy and percutaneous dilatational tracheostomy. Percutaneous dilatational tracheostomy is associated with fewer complications than open tracheostomy. In this study, we would like to compare both techniques of performing a tracheostomy in ICU patients and to present possible complications, methods of diagnosing and treating and minimizing their risk. Keywords: tracheostomy, percutaneous tracheostomy, percutaneous dilatational tracheostomy, bronchoscopy, surgical tracheostomy, tracheoesophageal fistula, tracheostomy complication