Numerical model for small-signal modulation response in vertical-cavity surface-emitting lasers

We present a numerical model allowing for simulations of small-signal modulation (SSM) response of vertical-cavity surface-emitting lasers (VCSELs). The model of SSM response utilizes only the data provided by a static model of continuous-wave operation for a given bias voltage. Thus the fitting of dynamic measurement parameters is not needed nor used. The validity of this model has been verified by comparing experimental SSM characteristics of a VCSEL with the results of simulations. A good agreement between experiment and simulations has been observed. Based on the results obtained in the simulations of the existing laser, the impact of the number of quantum wells in the active region on the modulation properties has been calculated and analyzed

Threat of allergenic airborne grass pollen in Szczecin, NW Poland: the dynamics of pollen seasons, effect of meteorological variables and air pollution

The dynamics of Poaceae pollen season, in particularly that of the Secale genus, in Szczecin (western Poland) 2004–2008 was analysed to establish a relationship between the meteorological variables, air pollution and the pollen count of the taxa studied. Consecutive phases during the pollen season were defined for each taxon (1, 2.5, 5, 25, 50, 75, 95, 97.5, 99% of annual total), and duration of the season was determined using the 98% method. On the basis of this analysis, the temporary differences in the dynamics of the seasons were most evident for Secale in 2005 and 2006 with the longest main pollen season (90% total pollen). The pollen season of Poaceae started the earliest in 2007, when thermal conditions were the most favourable. Correlation analysis with meteorological factors demonstrated that the relative humidity, mean and maximum air temperature, and rainfall were the factors influencing the average daily pollen concentrations in the atmosphere; also, the presence of air pollutants such as ozone, PM10 and SO2 was statistically related to the pollen count in the air. However, multiple regression models explained little part of the total variance. Atmospheric pollution induces aggravation of symptoms of grass pollen allergy

Rodzaje ryzyk w procesie inwestowania w odnawialne źródła energii elektrycznej

The development of renewable power engineering is inevitable. Administrative, financial, political, social, environmental or technical/technological barriers are and must be minimized. They determine the scale of risk borne by the investor. Risk due to the special character of investments is high and is intensified by difficulties associated with the growing liberalization and deregulation of the power market. In the process of investing in RES, several phases are enumerated. Each of them is divided into stages, with hazards visible in them. Types of the renewable energy sources, despite differences in their obtaining and processing into usable energy, are characterized by many common elements as to the kinds of risk. The article presents an attempt to specify them and assign them a rank importance for the project.Rozwój energetyki odnawialnej jest nieunikniony. Bariery administracyjne, finansowe, polityczne, społeczne, środowiskowe czy techniczno-technologiczne są i muszą być minimalizowane. Stanowią one o skali ryzyka ponoszonego przez inwestora. Ryzyko ze względu na specyfikę inwestycji jest wysokie i potęgują je trudności związane z postępującą liberalizacją oraz deregulacją rynku energii. W procesie inwestowania w OZE wyróżnia się kilka faz. Każda z nich dzieli się na etapy, a w nich uwidaczniają się zagrożenia. Rodzaje źródeł odnawialnej energii, mimo różnic w ich pozyskiwaniu i przetwarzaniu na energię użytkową, cechuje wiele elementów wspólnych w zakresie rodzajów ryzyka. W artykule podjęto próbę ich wyspecyfikowania oraz nadania im rangi istotności dla projektu

Impact of the active area position in a nitride tunnel junction vertical-cavity surface-emitting laser on its emission characteristics

This paper presents results of numerical simulations of a nitride semiconductor vertical-cavity surface-emitting laser (VCSEL) with a tunnel junction. The modeled laser is based on a structure created at the University of California in Santa Barbara. The analysis concerns the impact of the position of laser’s active area on the emitted power. Both small detunings from the standing waveanti-node, and positioning of the active area at different anti-nodes are considered

First Principles Calculations of the Formation Energy of the Neutral Vacancy in Germanium

score: 0collation: 241-24