Eksitonska stanja u kvantnoj točki

The exciton binding energies in finite-potential quantum dot discs of GaAs are obtained and the eigenstates and the eigenvalues of the exciton are calculated. We present the exciton binding energy for different values of the disc radius (R) and the disc half-width (L/2). The exciton-state stability for large and small sizes of the dot is discussed. We compare our results with the existing theoretical and experimental results. Our results give good estimates for the optimal quantum dot disc geometry, and represent useful data in studies of the optical properties of quantum dots in nano-scale devices.Izračunali smo energiju vezanja, svojstvena stanja i svojstvene vrijednosti eksitona u kvantnoj točki s konačnim potencijalom. Opisujemo energiju vezanja eksitona za više vrijednosti polumjera (R) i poluširine (L/2) diska. Raspravljamo stabilnost eksitona za male i veće dimenzije diska. Uspoređujemo naše rezultate s poznatim drugim teorijskim i eksperimentalnim rezultatima. Naši rezultati daju dobre ocjene za povoljnu veličinu diska kvantne točke, i predstavljaju korisne podatke za proučavanje optičkih svojstava kvantnih točaka u napravama nano veličine

Une xpected large benign thymoma on myocardial scintigraphy, a case report

Myocardial perfusion imaging (MPI) by 99mTc-sestamibi constitutes a major part of nuclear medicine studies. Incidental detection of extracardiac abnormalities occurs not infrequently. These can include benign and malignant lesions and their detection can be of great value in patient's future. We present a 60 year-old man who underwent MPI to evaluate coronary artery disease as the possible cause of his chest discomfort. The images revealed a large area of intense increased tracer uptake in the antero- inferior mediastinum that further evaluation confirmed to be a benign thymoma. © 2015 The Authors

Effect of taurine supplementation on hyperhomocysteinemia and markers of oxidative stress in high fructose diet induced insulin resistance

<p>Abstract</p> <p>Background</p> <p>High intake of dietary fructose is accused of being responsible for the development of the insulin resistance (IR) syndrome. Concern has arisen because of the realization that fructose, at elevated concentrations, can promote metabolic changes that are potentially deleterious. Among these changes is IR which manifests as a decreased biological response to normal levels of plasma insulin.</p> <p>Methods</p> <p>Oral glucose tolerance tests (OGTT) were carried out, homeostasis model assessment of insulin resistance (HOMA) was calculated, homocysteine (Hcy), lipid concentrations and markers of oxidative stress were measured in male <it>Wistar </it>rats weighing 170-190 g. The rats were divided into four groups, kept on either control diet or high fructose diet (HFD), and simultaneously supplemented with 300 mg/kg/day taurine via intra-peritoneal (i.p.) route for 35 days.</p> <p>Results</p> <p>Fructose-fed rats showed significantly impaired glucose tolerance, impaired insulin sensitivity, hypertriglyceridemia, hypercholesterolemia, hyperhomocysteinemia (HHcy), lower total antioxidant capacity (TAC), lower paraoxonase (PON) activity, and higher nitric oxide metabolites (NOx) concentration, when compared to rats fed on control diet. Supplementing the fructose-fed rats with taurine has ameliorated the rise in HOMA by 56%, triglycerides (TGs) by 22.5%, total cholesterol (T-Chol) by 11%, and low density lipoprotein cholesterol (LDL-C) by 21.4%. Taurine also abolished any significant difference of TAC, PON activity and NOx concentration among treated and control groups. TAC positively correlated with PON in both rats fed on the HFD and those received taurine in addition to the HFD. Fructose-fed rats showed 34.7% increase in Hcy level. Taurine administration failed to prevent the observed HHcy in the current dosage and duration.</p> <p>Conclusion</p> <p>Our results indicate that HFD could induce IR which could further result in metabolic syndrome (MS), and that taurine has a protective role against the metabolic abnormalities induced by this diet model except for HHcy.</p

Narrow-band injection seeding of a terahertz frequency quantum cascade laser: Selection and suppression of longitudinal modes

A periodically poled lithium niobate (PPLN) crystal with multiple poling periods is used to generate tunable narrow-bandwidth THz pulses for injection seeding a quantum cascade laser (QCL). We demonstrate that longitudinal modes of the quantum cascade laser close to the gain maximum can be selected or suppressed according to the seed spectrum. The QCL emission spectra obtained by electro-optic sampling from the quantum cascade laser, in the most favorable case, shows high selectivity and amplification of the longitudinal modes that overlap the frequency of the narrow-band seed. Proper selection of the narrow-band THz seed from the PPLN crystal discretely tunes the longitudinal mode emission of the quantum cascade laser. Moreover, the THz wave build-up within the laser cavity is studied as a function of the round-trip time. When the seed frequency is outside the maximum of the gain spectrum the laser emission shifts to the preferential longitudinal mode

Worm Epidemics in Wireless Adhoc Networks

A dramatic increase in the number of computing devices with wireless communication capability has resulted in the emergence of a new class of computer worms which specifically target such devices. The most striking feature of these worms is that they do not require Internet connectivity for their propagation but can spread directly from device to device using a short-range radio communication technology, such as WiFi or Bluetooth. In this paper, we develop a new model for epidemic spreading of these worms and investigate their spreading in wireless ad hoc networks via extensive Monte Carlo simulations. Our studies show that the threshold behaviour and dynamics of worm epidemics in these networks are greatly affected by a combination of spatial and temporal correlations which characterize these networks, and are significantly different from the previously studied epidemics in the Internet

Investigation of time-resolved gain dynamics in an injection seeded terahertz quantum cascade laser

The evolution of the gain of terahertz quantum cascade laser during injection seeding is probed as a function of time. Oscillations of the gain are commensurate with the variations of the field envelope

Observation of Time-resolved Gain Dynamics in a Terahertz Quantum Cascade Laser

The dynamic response of a terahertz quantum cascade laser is probed as a function of time. The gain of the THz QCL is saturated by injection seeding the laser with an initial THz seed pulse. The time-resolved gain of the injection seeded laser is then probed with a second THz pulse

Selection of longitudinal modes in a terahertz quantum cascade laser via narrow-band injection seeding

A terahertz quantum cascade laser is injection seeded with narrow-band seed pulses generated from a periodically poled lithium niobate crystal. The spectral emission of the quantum cascade laser is controlled by the seed spectra