Towards automated design of quantum cascade lasers

We present an advanced technique for the design and optimization of GaAs/AlGaAs quantum cascade laser structures. It is based on the implementation of the simulated annealing algorithm with the purpose of determining a set of design parameters that satisfy predefined conditions, leading to an enhancement of the device output characteristics. Two important design aspects have been addressed: improved thermal behavior, achieved by the use of higher conduction band offset materials, and a more efficient extraction mechanism, realized via a ladder of three lower laser states, with subsequent pairs separated by the optical phonon energy. A detailed analysis of performance of the obtained structures is carried out within a full self-consistent rate equations model of the carrier dynamics. The latter uses wave functions calculated by the transfer matrix method, and evaluates all relevant carrier–phonon and carrier–carrier scattering rates from each quantized state to all others within the same and neighboring periods of the cascade. These values are then used to form a set of rate equations for the carrier density in each state, enabling further calculation of the current density and gain as a function of the applied field and temperature. This paper addresses the application of the described procedure to the design of lambda~9 µm GaAs-based mid-infrared quantum cascade lasers and presents the output characteristics of some of the designed optimized structures. © 2005 American Institute of Physic

Inter-Landau Level Scattering Processes in Magnetic Field Assisted THz Quantum Cascade Laser

We present a detailed analysis of GaAs/AlGaAs terahertz quantum cascade laser in the presence of an intense external magnetic field. One of the objectives in further development of THz quantum cascade laser is the realization of structures operating at higher temperatures. This is difficult to obtain as the operating photon emission energy is smaller than the longitudinal-optical phonon energy in the semiconductor material. With increased temperature, electrons in the upper radiative state gain sufficient in-plane energy to emit an longitudinal-optical phonon, which represents a non-radiative scattering and reduces the optical gain. By applying strong magnetic field, two-dimensional continuous energy subbands become split into series of discrete Landau levels, and at particular values of B it is possible to quench these non-radiative channels. Numerical simulations are performed on two-well design quantum cascade laser operating at 4.6 THz, implemented in CaAs/Al(0.15)Ga(0.85)As, and the magnetic field is perpendicular to the epitaxial layers. Strong oscillations of carrier lifetimes for the upper state of the laser transition, as a function of magnetic field are observed, which can be attributed to interface roughness scattering and longitudinal-optical phonon scattering between Landau levels.12th Annual YUCOMAT Conference, Sep 06-10, 2010, Herceg Novi, Montenegr

Effect of dietary supplementation with medium chain fatty acids on growth performance, intestinal histomorphology, lipid profile and intestinal microflora of broiler chickens

The aim of the present study was to assess the effects of medium-chain fatty acid (MCFA) diet supplementation on growth performance, intestinal histomorphology, serum biochemistry and intestinal microflora of broiler chickens. The study was performed on 180 one-day-old broilers of the same origin (Cobb 500 hybrid), over a 42-day period. They were fed diets supplemented with three treatments: control group (basal diet without supplementation); group with MCFA supplementation; and group with MCFA and coccidiostat supplementation. Broiler chickens fed diets supplemented with MCFAs had a significantly greater final bodyweight. The weights of carcass cuts (breast, drumsticks with thighs and wings) were greater in broilers receiving MCFAs than in control broilers. The addition of MCFAs to broiler diet significantly increased villus length and crypt depth in the duodenum and caecum, and significantly decreased villus width in the duodenum and ileum. Additionally, serum HDL-cholesterol and triglyceride concentrations were increased significantly in broilers with MCFA dietary supplementation. The results indicated that the MCFA diet supplementation had a beneficial effect on the performance of broiler chickens, their intestinal histomorphology and microflora

Traditional knowledge about milkiness of domestic animals in Pirot district

Mnoge knjige koje obrađuju ovu problematiku sa razlogom počinju sličnim citatima kao što je ovaj: “Lekovito bilje je najstariji lek svih naroda, na svim kontinentima i u svim epohama”. Cilj ovog velikog istraživanja je bio da se sakupi narodno bogatstvo u vezi lečenja životinja u regionima Srbije. Ovo bogatstvo je raznovrsno i mudro osmišljeno, a preti mu zaborav, zbog toga što novo vreme nosi nove savremene metode lečenja. Namera je takođe bila, da se utvrdi šta je u narodnim receptima ispravno a nedovoljno primenjivano. U cilju sakupljanja podataka vezanih za zdravlje stoke i domaćih životinja, napravljen je upitnik (28 pitanja) i na toj osnovi su obrađeni podaci u vezi mlečnosti. Anketiranja su najčešće vršena lično i direktno od ispitanika, najstarijih osoba iz obuhvaćenih sela i zaseoka. Ispitivani su takođe travari i potkivači stoke koji su se ujedno bavili i lečenjem. Baza ovog terenskog istraživanja je bila u ataru zaseoka Lužnica, opstina Babušnica. Najčešće pomenute biljke za spravljanje receptura (sa ili bez dodatih neorganskih sastojaka) bile su trubelj, zdravac, pelin, ovas, reska trava, lubeničan, djurdjevac, bokvica i trava Svetog Jovanča. Nedovoljno primenjivani narodni recepti mogli bi se nakon naučnih ispitivanja primeniti u savremenoj veterinarskoj praksi. Treba dati veći značaj biljkama iz nezagađenih područja čiji se aktivni sastojci još uvek nedovoljno koriste u veterinarskoj farmakologiji što može predstavljati zahvalnu oblast za istraživanja

Modeling of electron relaxation processes and the optical gain in a magnet-field assisted THz quantum cascade laser

III International School and Conference on Photonics : PHOTONICA2011 : book of abstracts; August 29- September 2, 2011; Belgrad

Spin-dependent dwell times of electron tunneling through double- and triple-barrier structures

We have analyzed the influence of Dresselhaus and Rashba spin-orbit couplings (caused by the bulk inversion asymmetry and the structural asymmetry, respectively) on electron tunneling through a double- and triple-barrier structures, with and without an externally applied electric field. The results indicate that the degree of structural asymmetry and external electric field can greatly affect the dwell times of electrons with opposite spin orientation. This opens up the possibilities of obtaining efficient spin separation in the time domain. The material system of choice is AlxGa1-xSb, and the presented model takes into account the position dependence of material parameters, as well as the effects of band nonparabolicity. (C) 2008 American Institute of Physics

Pulmonary sequestration mimicring lun cancer: A case report

Introduction. Pulmonary sequestration is a rare congenital anomaly and most intralobar sequestrations were located in lower lobes. Case report. We reported an unusual 28-yearold female patient with intralobar pulmonary sequestration on the left lower lobe, successfully treated with lobectomy. Computed tomography (CT) of the chest with intravenous contrast revealed multiple clustered cystic lesions in the left lower lobe with aberrant artery from descedenting aorta. Additional aortography showed an aberrant artery (3 mm in diameter) arising from the abdominal aorta and flowing into the lesion. Conclusion. Standard therapy regimen for pulmonary sequestration includes surgery. CT scan of thorax with intravenous contrast and aortography represent the gold standard for its diagnosis. Tumor-like shadows seen on the chest radiography or CT scans should not be always suspected on malignant lesions

The influence of sociodemographic factors on the use of antihypertensive drugs among adults in Serbia: Cross-sectional study

Background: Despite the knowledge that they have high blood pressure, which can be controlled with medicines, one portion of the patients still ignores doctor's advice. The aim of the research was to examine the impact of socio-demographic factors for treatment of hypertension among adults in Serbia. Subjects and methods: In the study, we used data from the National Health Survey of the Republic of Serbia in 2013. The sample consisted of respondents who had diagnosed hypertension, 5073 of them. The dependent variable in the study was binary (treatment, or no treatment of hypertension) and independent was socio-demographic characteristics of respondents. Logistic regression was used to determine sociodemographic predictors associated with blood pressure control. Results: From a total of 5073 diagnosed hypertensive patients, 91.3% of them cures high blood pressure. Women, older, medium rich patients, those who follow health topics on television and those who do not follow them on the Internet, who, in the past year, have been hospitalized or used the services of daily care significantly more often treat hypertension. The results of binary logistic regression in which the dependent variable is the treatment of high blood pressure, showed that a statistically significantly predictors are: age, gender, the wealth index and monitoring topics related to health through television and the Internet. In the treatment of hypertension, the strongest predictor was the index of well-being. Thus, people who are medium rich are almost three times more likely to treat high blood pressure compared to the richest (OR=2.94, 95%CI=1.54-5.59). A statistically significant difference in treatment is not recorded between the richest and the poorest (p> 0.05). Men are 1.5 times more likely to treat their tension as compared to women (OR=1.54, 95%CI=1.02-2.32). People following itopics related to the health via the internet are1.7 times more likely to treat hypertension in comparison to subjects who do not follow these topics via the Internet (OR=1.72, 95%CI=1.07-2.76). Conclusion: Analysis of the impact of sociodemographic characteristics on the awareness of patients about the importance of treatment of hypertension is an important step in defining the strategies for treatment of patients