Green's functions technique for calculating the emission spectrum in a quantum dot-cavity system

We introduce the Green's functions technique as an alternative theory to the quantum regression theorem formalism for calculating the two-time correlation functions in open quantum systems. In particular, we investigate the potential of this theoretical approach by its application to compute the emission spectrum of a dissipative system composed by a single quantum dot inside of a semiconductor cavity. We also describe a simple algorithm based on the Green's functions technique for calculating the emission spectrum of the quantum dot as well as of the cavity which can easily be implemented in any numerical linear algebra package. We find that the Green's functions technique demonstrates a better accuracy and efficiency in the calculation of the emission spectrum and it allows to overcome the inherent theoretical difficulties associated to the direct application of the quantum regression theorem approach

A Correlational Study of the Personality Inventory for Children, the Piers-Harris Children\u27s Self-Concept Scale and the Devereux Child Behavior Rating Scale

U radu je predstavljena nova metoda određivanja ekvivalentnih elektromagnetskih parametara vodljivih materijala s obzirom na gubitke uslijed izmjeničnog magnetskog polja. Metoda povezuje evolucijski optimizacijski algoritam diferencijalnu evoluciju i proračun metodom konačnih elemenata. Diferencijalnom evolucijom određuju se parametri materijala koji će u proračunu metodom konačnih elemenata dati gubitke jednake izmjerenima u volumenu tog materijala. Napravljeni su torusi s masivnom nelaminiranom jezgrom i štapovi za mjerenje statičkih krivulja magnetiziranja i specifične električne vodljivosti nemagnetskog i magnetskog čelika. Izmjereni parametri materijala upotrijebljeni su za određivanje njihovih graničnih vrijednosti prilikom proračuna ekvivalentnih parametara materijala diferencijalnom evolucijom. Napravljena je prigušnica za direktno mjerenje dodatnih gubitaka, te je proveden niz mjerenja na različitim uzorcima od različitih materijala. Prigušnica je modelirana u programu za 3D proračun metodom konačnih elemenata te su diferencijalnom evolucijom određeni ekvivalentni parametri materijala uzoraka. Proračun je uspoređen s mjerenjima. Pomoću 2D rotacijsko simetričnog modela pločice debljine 10 mm analizirano je kako parametri materijala utječu na iznos gubitaka u uzorku u sinusnom magnetskom polju izvora konstantne amplitude. Pokazano je da gubici imaju zvonoliku ovisnost o parametrima materijala što je posljedica činjenice da gubici teže k nuli kada vodljivost materijala teži k nuli ili u beskonačno. Diferencijalnom evolucijom određeni su parametri materijala pri kojima gubici postižu svoj maksimum. Napravljena su tri modela transformatora, na njima su primijenjeni ekvivalentni parametri materijala određeni na prigušnici te je metodom konačnih elemenata određen udio histereznih u ukupnim gubicima u konstrukcijskim dijelovima transformatora. Također su određeni najveći mogući gubici u konstrukcijskim dijelovima transformatora koje je moguće dobiti proračunom metodom konačnih elemenata, uspoređeni su s mjerenim vrijednostima i objašnjeni su razlozi odstupanja.The thesis introduces a new method for determination of equivalent electromagnetic parameters of conducting materials considering the losses due to alternating magnetic field. The method combines evolutionary optimization algorithm and calculation by finite element method. The differential evolution determines the equivalent parameters of the material which in finite element calculation yield the same losses in the volume of that material as the measured ones. The toroidal solid cores and rods were made for measurement of static magnetization curve and specific electrical conductivity of nonmagnetic and magnetic steel. Thus obtained material parameters were used for determination of their boundary values for calculation of the equivalent material parameters by differential evolution. The coil for direct measurement of additional losses was made. A series of measurements on various samples of different materials were conducted. The 3D model of the coil was made in finite element software and using the differential evolution method, the equivalent material parameters were determined. The calculation was compared with measurement. Using a 2D rotational symmetric model of the plate with the thickness of 10 mm it was analyzed how the material parameters affect the amount of losses in the sample placed in the sinusoidal magnetic field of constant amplitude. It was shown that losses have the bell-shaped dependence on material parameters due to the fact that losses tend to zero when the conductivity of material tends to zero or infinity. Using differential evolution the material parameters for which losses have a maximum value were determined. Three models of transformers were made. The equivalent material parameters determined for the coil were applied on those models in order to determine using finite element method the share of hysteresis losses in the total amount of losses in structural parts of a transformer. The largest possible losses in structural parts of transformers that can be calculated using finite element method were also determined. The results were compared with the measurement and the reasons for discrepancies were explained

CNT Metamaterial Fabrication 3D Printing Mask Process

The demand for clean energy is rising with the global population. Renewable energy sources, such as solar, will play a key role in the years ahead. Solar energy has a key problem with energy storage as the energy produced during peak solar hours must be used immediately or stored. Carbon Nanotubes (CNTs) have unique electrostatic properties, similar to metals, capable of producing and storing electric energy in the form of a capacitor. The CNTs are to be arranged in a pattern using 3D printing to generate a Split Ring Resonator (SRR) metamaterial. Past research has shown generating CNT SRR patterns is possible using a Focused Ion Beam (FIB). FIB allows for limited sample size to be patterned for CNT growth. On the other hand, 3D printed shadow masks enable SRR patterns on a larger sample size. Today’s 3D printing technology cannot achieve the same resolution as FIB patterning yet are capable of producing larger samples. In the present research, a 3D model of a shadow mask with the desired SRR pattern was created using Fusion 360 and printed using Phrozen Sonic Mini 8K 3D printer. For the CNT synthesis process, first, heat-treated Silicon Oxide substrate was placed into a RF magnetic sputtering to deposit the first catalyst film of Aluminum Oxide using Argon plasma. The sample then was removed from the chamber to place the mask on and placed back in to sputter an Iron catalyst layer. The sample was then taken to a thermal catalytic chemical vapor deposition (CVD) chamber in which it was annealed to 730° C and afterwards exposed to acetylene gas to generate CNTs

The dollarization process in Mexico: 1983-1997

The purpose of this study is to analyze the extent of dollarization in the Mexican economy during the period 1983-1997. Dollarization is defined as the replacement of domestic currency for dollars as a store of value or for transaction purposes. In this study, a narrow definition of dollarization will be used as an estimate of the amount of dollars circulating in the Mexican economy. This measure includes only the dollar-denominated demand deposits held by businesses in Mexican banks, since the public is no longer allowed to hold this type of accounts and a better measure for the exact amount of dollars circulating in the Mexican economy is not available. This study will emphasize the effects of expected peso depreciations, peso devaluations, and political changes on the dollarization process

Livestock heat stress risk in response to the extreme heat event (heatwave) of July 2022 in the UK

On the 18th and 19th of July 2022, the UK experienced a record-breaking extreme heat event. For the first time, temperatures exceeding 40C were recorded. Whilst this may seem exceptional or unprecedented, the progression of climate change is expected to increase both the likelihood and severity of such events. Livestock are vulnerable to heat stress, which manifests as losses to health and welfare, productivity, and sustainability. Here, we characterize the heatwave of July 2022 in the context of livestock heat-stress risk, with a focus on cattle. Meteorological data was obtained from 85 weather stations and the Comprehensive Climate Index (CCI) was calculated, hourly, for each station. The CCI was mapped across the UK for 18/07/22 and 19/07/22 and compared against heat stress risk thresholds. Across both days, >25% of sites experienced 'severe' heat stress risk. On 19/07/22 there was an 'extreme' risk across >5% of sites. The site that experienced the highest risk was near Rugby, in the West Midlands. Across all sites, night-time temperatures fell below risk thresholds and may have mitigated some of the heat stress risk. Whilst there was some evidence of productivity losses, this was not conclusive. The impacts of this event on livestock were not just direct, but indirect through negative impacts on water and forage availability. The heatwave of July 2022 must serve as a warning for the UK livestock industry and these results may act as a case study of what the sector may be increasingly likely to experience in the future