Physical Principles of the Amplification of Electromagnetic Radiation Due to Negative Electron Masses in a Semiconductor Superlattice

In a superlattice placed in crossed electric and magnetic fields, under certain conditions, the inversion of electron population can appear at which the average energy of electrons is above the middle of the miniband and the effective mass of the electron is negative. This is the implementation of the negative effective mass amplifier and generator (NEMAG) in the superlattice. It can result in the amplification and generation of terahertz radiation even in the absence of negative differential conductivity.Comment: 5 pages, 3 figure

Mössbauer study of the process of the room-temperature aging of the alloy Cu79Ni14Fe7

Mössbauer spectroscopy was used to investigate the initial stage of the phase separation in the quasi-binary system Cu79Ni 14Fe7 and the subsequent transformation of the alloy structures as a result of prolonged aging at room temperature. For describing the Mössbauer spectra of ferromagnetic particles, which appear upon the spinodal decomposition in a paramagnetic matrix, a model was proposed and approved, which uses particle-size distribution in the approximation of the generalized Lifshitz-Slezov-Wagner (LSW) model and of the linear decrease of the hyperfine field at the 57Fe nuclei in the near-surface layers of spherical particles. © 2011 Pleiades Publishing, Ltd

Mössbauer study of the surface of core-shell type nanoparticles

© 2016, Pleiades Publishing, Ltd.The properties of the surface layer of core-shell nanoparticles incorporated into the matrix of macromolecules of 3,4-bis(decyloxybenzoyl) poly(propylene imine) derivative of the second generation are studied by Mössbauer spectroscopy at low temperatures. The spin states, the details of the phonon spectrum and the Debye temperature of surface layer atoms discussed

Magnetic Properties of Novel Dendrimeric Iron(III) Complexes of the First Generation: EPR and Mössbauer Study

© 2016, Springer-Verlag Wien.The magnetic properties of novel liquid-crystalline dendrimeric iron(III) complexes of the first generation, [Fe(L2)]+X−, where L = 3,4,5-tri(tetradecyloxy) benzoyloxy-4-salicyliden-N′-ethyl-N-ethylenediamine and X = Cl, NO3 have been investigated for the first time by electron paramagnetic resonance (EPR) and Mössbauer spectroscopy in the wide (4–300 K) temperature range. It has been shown that each compound consists of two types of iron centers: low-spin (LS, S = 1/2) and high-spin (HS, S = 5/2). A partial thermally driven spin transition (S = 5/2 ↔ 1/2) was observed in these complexes. EPR showed that the LS and HS iron centers are coupled by weak antiferromagnetic interactions and most probably form a chain in the column. Mössbauer spectroscopy confirmed the existence of the LS and HS Fe(III) centers in the compounds, a partial spin crossover of approximately 2–8 % of the Fe(III) molecules and showed that the HS Fe(III) centers demonstrate the antiferromagnetc type of ordering at 5 K

Mössbauer studies of Cu1-xNi xFeMnO4 spinel ferrites

Nickel copper ferromanganites Cu1-xNi xFeMnO4 with the composition (0≤x≤1) have been prepared using a ceramic technique. A single phase of these compounds was confirmed by X-ray powder diffraction measurements. Mössbauer spectra were recorded in 20-628 K temperature range. The spectra of all samples showed two well-resolved Zeeman patterns corresponding to A- and B-sites. At room temperature the hyperfine field increases with decreasing Cu concentration. The cation distribution obtained from analysis of Mössbauer spectra revealed a partially inverse spinel structure. The Curie temperature (TC) increased with the increase of the composition parameters (x). The specific heat Cp for nucleus 57Fe was calculated from Mössbauer data for Cu0.5Ni0.5FeMnO4, and NiFeMnO 4. The temperature dependence of the hyperfine parameters was studied, for these samples. The sublattice magnetization H(T) obeys the one-third power law in the range 0.47<T/TC<0.92. © 2004 Elsevier B.V. All rights reserved

Fano resonances in a three-terminal nanodevice

The electron transport through a quantum sphere with three one-dimensional wires attached to it is investigated. An explicit form for the transmission coefficient as a function of the electron energy is found from the first principles. The asymmetric Fano resonances are detected in transmission of the system. The collapse of the resonances is shown to appear under certain conditions. A two-terminal nanodevice with an additional gate lead is studied using the developed approach. Additional resonances and minima of transmission are indicated in the device.Comment: 11 pages, 5 figures, 2 equations are added, misprints in 5 equations are removed, published in Journal of Physics: Condensed Matte

Electrophysiological Parameters of Sinus Node Function in Patients with Paroxysmal Tachyarrhythmias

to analyze the indicators of the function of the sinus node in patients of young age with paroxysmal tachycardia. Methods: study included 11 patients with suspected paroxysmal tachycardia, with an average age of 17±28. The basis for holding transesophageal electrophysiological study (TE EPS) was the clinical and electrophysiological characteristics of paroxysmal tachycardia. According to the results of Holter monitoring ECG (HM ECG) analyzed the minimum and maximum heart rate, number of ventricular and supraventricular arrhythmias, presence of pauses, rhythm and episodes of paroxysmal tachycardia. According to CHP, EFI estimated the initial heart rate (HR), recovery time of sinus node function (RTSNF), corrected recovery time of sinus node function (CRTSNF), point of Wenkebach (p. W), duration of the effective refractory period of the atrioventricular connections, presence of aberrant complexes and episodes of paroxysmal tachycardias before and after administration of atropine at a dose of 0.02 mg/kg. Results: Complaints characteristic of the tachyarrhythmia was diagnosed in 9 patients, episodes of heart rate more than 150 beats per minute in 7 patients. When conducting TE EPS obtained the following results: episodes of supraventricular tachycardia provoked in 8 patients (in two cases of paroxysmal tachycardia managed to provoke only after administration of atropine). Three of them have shimmer and atrial flutter episodes reciprocal tachycardia in five. Three patients provoke paroxysmal tachycardia failed, but they showed a shortening of the PQ interval and the appearance of aberrant QRS complexes when stimulated. In patients with paroxysmal SVT signs of sinus node dysfunction was detected in 6 patients, in the form of episodes of sinus arrhythmia (4 patients), migration pacemaker the atria (4 patients), sinoatrial blockade of II degree (3 patients), blockade of legs of bunch of gisa (2 patients), atrioventricular block degree II-III (1 patient), RTSNF more than 1500 MS in 1 patient, CRTSNF greater than 500 msec in 3 patients. Conclusion: in 6 of 9 patients with supraventricular paroxysmal tachycardia revealed signs of sinus node dysfunction, probably has a vagotonic in nature

Blue shift in optical absorption, magnetism and light-induced superparamagnetism in γ-Fe2O3 nanoparticles formed in dendrimer

© 2015, Springer Science+Business Media Dordrecht. Abstract: We are presenting the investigation of the optical, magnetic, and photoinduced superparamagnetic properties of single-domain γ-Fe2O3 nanoparticles (NPs) with diameters of about 2.5 nm formed in second-generation poly(propylene imine) dendrimer. The optical absorption studies indicated direct allowed transition with the band gap (4.5 eV), which is blue shift with respect to the value of the bulk material. Low-temperature blocking of the NPs magnetic moments at 18 K is determined by SQUID measurements. The influence of pulsed laser irradiation on the superparamagnetic properties of γ-Fe2O3 NPs was studied by EPR spectroscopy. It has been shown that irradiation of the sample held in vacuo and cooled in zero magnetic field to 6.9 K leads to the appearance of a new EPR signal, which decays immediately after the irradiation is stopped. The appearance and disappearance of this new signal can be repeated many times at 6.9 K when we turn on/turn off the laser. We suppose that the generation of conduction band electrons by irradiation into the band gap of the γ-Fe2O3 changes the superparamagnetic properties of NPs. Graphical Abstract: [Figure not available: see fulltext.]Features of the behavior of single-domain γ-Fe2O3 nanoparticles formed in dendrimer were found by UV-Vis and EPR spectroscopy: “blue” shift in optical absorption, a significant increase in the band gap width and variation of superparamagnetic properties under light irradiation