Electron-phonon vertex in the two-dimensional one-band Hubbard model

Using quantum Monte Carlo techniques, we study the effects of electronic correlations on the effective electron-phonon (el-ph) coupling in a two-dimensional one-band Hubbard model. We consider a momentum-independent bare ionic el-ph coupling. In the weak- and intermediate-correlation regimes, we find that the on-site Coulomb interaction $U$ acts to effectively suppress the ionic el-ph coupling at all electron- and phonon- momenta. In this regime, our numerical simulations are in good agreement with the results of perturbation theory to order $U^2$. However, entering the strong-correlation regime, we find that the forward scattering process stops decreasing and begins to substantially increase as a function of $U$, leading to an effective el-ph coupling which is peaked in the forward direction. Whereas at weak and intermediate Coulomb interactions, screening is the dominant correlation effect suppressing the el-ph coupling, at larger $U$ values irreducible vertex corrections become more important and give rise to this increase. These vertex corrections depend crucially on the renormalized electronic structure of the strongly correlated system.Comment: 5 pages, 4 eps-figures, minor change

Semiclassical approach to calculating the influence of local lattice fluctuations on electronic properties of metals

We propose a new semiclassical approach based on the dynamical mean field theory to treat the interactions of electrons with local lattice fluctuations. In this approach the classical (static) phonon modes are treated exactly whereas the quantum (dynamical) modes are expanded to second order and give rise to an effective semiclassical potential. We determine the limits of validity of the approximation, and demonstrate its usefulness by calculating the temperature dependent resistivity in the Fermi liquid to polaron crossover regime (leading to `saturation behavior') and also isotope effects on electronic properties including the spectral function, resistivity, and optical conductivity, problems beyond the scope of conventional diagrammatic perturbation theories.Comment: 11 pages, 7 figure

Novi analitički pristup sa smanjenom potrošnjom organskih otapala u spektrofotometrijskoj analizi temeljenoj na prijenosu naboja: Primjena u analizi nekih antihipertenziva

The present study describes the development of a novel analytical approach that can reduce by 50-fold the consumption of organic solvents in the charge transfer (CT)-based spectrophotometric analysis. The proposed approach employed 96-microwell assay plates for carrying out the reaction. The CT reaction between the electron-donating analyte and electron-accepting reagent was performed in microwells (200-µL of organic solvent) and the color signals were measured with a microwell-plate reader. Optimum conditions for the proposed approach were established for two antihypertensive drugs, namely ramipril (RML) and lisinopril (LSL) as model compounds for the electron-donating analytes, and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as a -electron acceptor. Under the optimum conditions, Beer’s law was obeyed in the concentration range of 6–100 and 6–60 g mL1 for RML and LSL, respectively. The limits of detection were 0.97 and 1.10 g mL1 for RML and LSL, respectively. The precision of the methods was satisfactory; the values of relative standard deviations did not exceed 1.1 %. The proposed approach was successfully applied to the analysis of pharmaceutical dosage forms with good accuracy and precision. The results were comparable with those of the reported methods. The approach described herein is of great practical value in pharmaceutical analysis because it reduces the exposure of analysts to the toxic effects of organic solvents, lowers the analysis cost by 50-fold, and it has a high throughput property. Although the approach was validated for RML and LSL, the same methodology could be used for any electron-donating analyte for which a CT-reaction can be performed.U radu je opisan razvoj novog analitičkog pristupa koji 50 puta smanjuje potrošnju organskih otapala u spektrofotometrijskoj analizi na bazi prijenosa naboja (CT). Predložena metoda koristi ploče s 96 jažica za izvođenje analize. CT reakcije između elektron-donora i elektron-akceptora izvodi se u jažicama s 200-µL organskog otapala. Promjene boje mjere se pomoću posebnog mikročitača za ploče s jažicama. Određeni su optimalni uvjeti za dva antihipertenzivna lijeka, ramipril (RML) i lizinopril (LSL) koji su upotrebljeni kao modelni spojevi za elektron-donorske analite, i 2,3-diklor-5,6-dicijano-1,4-benzokinon (DDQ) kao -elektronski akceptor. U optimalnim uvjetima Beerov zakon je vrijedio u koncentracijskom području 6–100 i 6–60 g mL1 za RML, odnosno LSL. Granice detekcije bile su 0,97 i 1,1 g mL1 za RML, odnosno LSL. Preciznost metode bila je zadovoljavajuća, a relativna standardna devijacija bila je manja od 1,1 %. Predložena metoda uspješno je primijenjena za analizu doziranih farmaceutskih pripravaka koji sadrže ispitivane lijekove, uz dobru točnost i preciznost. Rezultati predložene metode usporedivi su s rezultatima poznatih metoda. Postupak opisan u ovom radu vrlo je praktičan: analitičari su manje izloženi toksičnim učincima organskih otapala, troškovi analize smanjeni su 50 puta, a također ju odlikuje visoka propusnost. Iako je postupak validiran za RML i LSL, ista metoda može se upotrijebiti za elektron-donirajući analit koji ulazi u CT reakciju

Aquaponics: alternative types and approaches

Whilst aquaponics may be considered in the mid-stage of development, there are a number of allied, novel methods of food production that are aligning alongside aquaponics and also which can be merged with aquaponics to deliver food efficiently and productively. These technologies include algaeponics, aeroponics, aeroaquaponics, maraponics, haloponics, biofloc technology and vertical aquaponics. Although some of these systems have undergone many years of trials and research, in most cases, much more scientific research is required to understand intrinsic processes within the systems, efficiency, design aspects, etc., apart from the capacity, capabilities and benefits of conjoining these systems with aquaponics

Phytoplankton responses to marine climate change – an introduction

Phytoplankton are one of the key players in the ocean and contribute approximately 50% to global primary production. They serve as the basis for marine food webs, drive chemical composition of the global atmosphere and thereby climate. Seasonal environmental changes and nutrient availability naturally influence phytoplankton species composition. Since the industrial era, anthropogenic climatic influences have increased noticeably – also within the ocean. Our changing climate, however, affects the composition of phytoplankton species composition on a long-term basis and requires the organisms to adapt to this changing environment, influencing micronutrient bioavailability and other biogeochemical parameters. At the same time, phytoplankton themselves can influence the climate with their responses to environmental changes. Due to its key role, phytoplankton has been of interest in marine sciences for quite some time and there are several methodical approaches implemented in oceanographic sciences. There are ongoing attempts to improve predictions and to close gaps in the understanding of this sensitive ecological system and its responses