Density matrix theory of transport and gain in quantum cascade lasers in a magnetic field

A density matrix theory of electron transport and optical gain in quantum cascade lasers in an external magnetic field is formulated. Starting from a general quantum kinetic treatment, we describe the intraperiod and interperiod electron dynamics at the non-Markovian, Markovian, and Boltzmann approximation levels. Interactions of electrons with longitudinal optical phonons and classical light fields are included in the present description. The non-Markovian calculation for a prototype structure reveals a significantly different gain spectra in terms of linewidth and additional polaronic features in comparison to the Markovian and Boltzmann ones. Despite strongly controversial interpretations of the origin of the transport processes in the non- Markovian or Markovian and the Boltzmann approaches, they yield comparable values of the current densities

Photoinduced suppression of the ferroelectric instability in PbTe

The interactions between electrons and phonons drive a large array of technologically relevant material properties including ferroelectricity, thermoelectricity, and phase-change behaviour. In the case of many group IV-VI, V, and related materials, these interactions are strong and the materials exist near electronic and structural phase transitions. Their close proximity to phase instability produces a fragile balance among the various properties. The prototypical example is PbTe whose incipient ferroelectric behaviour has been associated with large phonon anharmonicity and thermoelectricity. Experimental measurements on PbTe reveal anomalous lattice dynamics, especially in the soft transverse optical phonon branch. This has been interpreted in terms of both giant anharmonicity and local symmetry breaking due to off-centering of the Pb ions. The observed anomalies have prompted renewed theoretical and computational interest, which has in turn revived focus on the extent that electron-phonon interactions drive lattice instabilities in PbTe and related materials. Here, we use Fourier-transform inelastic x-ray scattering (FT-IXS) to show that photo-injection of free carriers stabilizes the paraelectric state. With support from constrained density functional theory (CDFT) calculations, we find that photoexcitation weakens the long-range forces along the cubic direction tied to resonant bonding and incipient ferroelectricity. This demonstrates the importance of electronic states near the band edges in determining the equilibrium structure.Comment: 9 page, 3 figure

Real-time chest-wall-motion tracking by a single optical fibre grating:a prospective method for ventilator triggering

Objective: The ventilators involved in non-invasive mechanical ventilation commonly provide ventilator support via a facemask. The interface of the mask with a patient promotes air leaks that cause errors in the feedback information provided by a pneumatic sensor and hence patient-ventilator asynchrony with multiple negative consequences. Our objective is to test the possibility of using chest-wall motion measured by an optical fibre-grating sensor as a more accurate non-invasive ventilator triggering mechanism. Approach: The basic premise of our approach is that the measurement accuracy can be improved by using a triggering signal that precedes pneumatic triggering in the neuro-ventilatory coupling sequence. We propose a technique that uses the measurement of chest-wall curvature by a long-period fibre-grating sensor. The sensor was applied externally to the rib-cage and interrogated in the lateral (edge) filtering scheme. The study was performed on 34 healthy volunteers. Statistical data analysis of the time lag between the fibre-grating sensor and the reference pneumotachograph was preceded by the removal of the unwanted heartbeat signal by wavelet transform processing. Main results: The results show a consistent fibre-grating signal advance with respect to the standard pneumatic signal by (230  ±  100) ms in both the inspiratory and expiratory phases. We further show that heart activity removal yields a tremendous improvement in sensor accuracy by reducing it from 60 ml to 0.3 ml. Significance: The results indicate that the proposed measurement technique may lead to a more reliable triggering decision. Its imperviousness to air leaks, non-invasiveness, low-cost and ease of implementation offer good prospects for applications in both clinical and homecare ventilation

Supplementary data for the article: Savić, T. D.; Ćomor, M. I.; Abazović, N. D.; Šaponjić, Z. V.; Marinović-Cincović, M. T.; Veljković, D. Ž.; Zarić, S. D.; Janković, I. A. Anatase Nanoparticles Surface Modified with Fused Ring Salicylate-Type Ligands (1-Hydroxy-2-Naphthoic Acids): A Combined DFT and Experimental Study. Journal of Alloys and Compounds 2015, 630, 226–235. https://doi.org/10.1016/j.jallcom.2015.01.041

Supplementary material for: [https://doi.org/10.1016/j.jallcom.2015.01.041]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/1661

Locomotor system of pigs as a health problem in sows and boars

The problems with the musculoskeletal system in all categories of pigs are common at industrial swine farms representing one of the major issues leading to exclusion of sows and boars from the production process. Topographic-anatomic relationships of bone and joint system of pigs make the diagnosis diffi cult in cases of illness affecting the upper parts of the limbs, pelvis and spine. In most cases, the presenting clinical sign is lameness, the cause of which can be determined only by a careful clinical examination. Lameness is a multifactorial problem that includes nutrition, poor horn quality, trauma, infection scale of housing and walking surface. At two industrial swine farms, presence of disease of locomotor systems was monitored in sows and boars. Occurrence of mechanical lesions in distal parts of limbs that are probably incurred as a result of inadequate storage space was established. Occurrence of arthritis in large number of animals was also established. The appearance of aseptic pododermatitis was also represented. Disorders of the locomotion system in the boars imported from the European Union were also followed at the farm. Of the 40 imported boars, annually between 6 and 7 boars develop acropodial problems. Over a year 3-4 boars are excluded from the reproduction due to the above problems. In most of boars problems occur after the fi rst jump as result of weak cartilage ossifi cation of the femoral bone, as a condition resulting from disturbed calcium, phosphorous and vitamin D ratio. Locomotion system diseases in sows and boars cause economic losses at pig farms.Proceeding

Hydrogen Evolution on Pyrolytic Graphite

The hydrogen evolution reaction from acid solutions was studied on highly oriented pyrolytic graphite at different surfaces obtained by cutting graphite under the various angles in respect to the basal plane. The experiments were done galvanostatically on the polished samples of desired orientation, in a cell which enabled the pretreatment of graphite at 1000° C in argon and use of prepurified Na2S04 + H2S04 solutions. Tafel lines with 2 RT/F slopes were obtained in all the experiments with i 0 varying from ca 10-9A/cm2 for cleavage plane to ca 10-8A/cm~ for edge plane. The transients show the considerable pseudo-capacitances of 250--500 μF/cm2 being larger at more negative potentials and edge surfaces. The experimental data are consistent with the slow discharge - electrochemical desorption mechanism with the limited number of sites of H adsorption but also with the coupled discharge - recombination reaction for hydrogen evolution

Anderson Localization of Thermal Phonons Leads to a Thermal Conductivity Maximum

Our elastic model of ErAs disordered GaAs/AlAs superlattices exhibits a local thermal conductivity maximum as a function of length due to exponentially suppressed Anderson-localized phonons. By analyzing the sample-to-sample fluctuations in the dimensionless conductance, g, the transition from diffusive to localized transport is identified as the crossover from the multichannel to single-channel transport regime g ≈ 1. Single parameter scaling is shown to hold in this crossover regime through the universality of the probability distribution of g that is independent of system size and disorder strength.Solid-State Solar-Thermal Energy Conversion Center (Award DE-FG02-09ER46577

Cuticular chemoprofile of the fruit fly Drosophila Subobscura (Diptera, drosophilidae)

In insects, cuticular hydrocarbon (CHC) profile is involved in many important biological functions and may vary in different conditions. Among fruit fly species, Drosophila subobscura is one of the most frequently used in genetic, ecological and evolutionary research, because of its rich chromosomal polymorphism, specific behavioral repertoires and habitat preferences. In this work, we identified and quantified cuticular chemoprofile of D. subobscura. Using gas chromatography (GC) and gas chromatography coupled with mass spectrometry (GC-MS), 25 chemical compounds were found in males and 23 compounds were found in females. Further, ANOVA confirmed significant sexual dimorphism in cuticular chemoprofile amounts. Knowledge of cuticular chemistry could contribute to further research in D. subobscura, starting from behavioral, up to ecological, since this species is recognized as an important model system for the study and monitoring of global climate changes. © 2018, Pakistan Agricultural Scientists Forum. All rights reserved

Far infrared properties of sintered PbTe doped with boron

Far infrared spectra of sintered PbTe doped with boron were analyzed. The measured infrared spectra were fitted using a modified plasmon-phonnon interaction model with two additional oscillators (at about 195 cm-1 and 285 cm-1) representing local B-impurity modes. The obtained results were compared with previously published data for a single crystal PbTe sample doped with boron