A simple method to construct Flat Band lattices

We develop a simple and general method to construct arbitrary Flat Band lattices. We identify the basic ingredients behind zero-dispersion bands and develop a method to construct extended lattices based on a consecutive repetition of a given mini-array. The number of degenerated localized states is defined by the number of connected mini-arrays times the number of modes preserving the symmetry at a given connector site. In this way, we create one or more (depending on the lattice geometry) complete degenerated Flat Bands for quasi-one and two-dimensional systems. We probe our method by studying several examples, and discuss the effect of additional interactions like anisotropy or nonlinearity. At the end, we test our method by studying numerically a ribbon lattice using a continuous description.Comment: 11 pages, 11 figure

Quantum localized states in photonic flat-band lattices

The localization of light in flat-band lattices has been recently proposed and experimentally demonstrated in several configurations, assuming a classical description of light. Here, we study the problem of light localization in the quantum regime. We focus on quasi one-dimensional and two-dimensional lattices which exhibit a perfect flat-band inside their linear spectrum. Localized quantum states are constructed as eigenstates of the interaction Hamiltonian with a vanishing eigenvalue and a well defined total photon number. These are superpositions of Fock states with probability amplitudes given by positive as well as negative square roots of multinomial coefficients. The classical picture can be recovered by considering poissonian superpositions of localized quantum states with different total photon number. We also study the separability properties of flat band quantum states and apply them to the transmission of information via multi-core fibers, where these states allow for the total passive suppression of photon crosstalk and exhibit robustness against photon losses. At the end, we propose a novel on-chip setup for the experimental preparation of localized quantum states of light for any number of photons.Comment: 12 pages, 5 figure

Key Parameters for Urban Heat Island Assessment in A Mediterranean Context: A Sensitivity Analysis Using the Urban Weather Generator Model

Although Urban Heat Island (UHI) is a fundamental effect modifying the urban climate, being widely studied, the relative weight of the parameters involved in its generation is still not clear. This paper investigates the hierarchy of importance of eight parameters responsible for UHI intensity in the Mediterranean context. Sensitivity analyses have been carried out using the Urban Weather Generator model, considering the range of variability of: 1) city radius, 2) urban morphology, 3) tree coverage, 4) anthropogenic heat from vehicles, 5) building’s cooling set point, 6) heat released to canyon from HVAC systems, 7) wall construction properties and 8) albedo of vertical and horizontal surfaces. Results show a clear hierarchy of significance among the considered parameters; the urban morphology is the most important variable, causing a relative change up to 120% of the annual average UHI intensity in the Mediterranean context. The impact of anthropogenic sources of heat such as cooling systems and vehicles is also significant. These results suggest that urban morphology parameters can be used as descriptors of the climatic performance of different urban areas, easing the work of urban planners and designers in understanding a complex physical phenomenon, such as the UHI

ACTIVIDAD ANTIOXIDANTE DE Tropaeolum tuberosum RUIZ & PAVÓN (MASHUA) Y SU APLICACIÓN COMO COLORANTE PARA YOGUR

The objective of the study was to evaluate the antioxidant activity and use of ethanol extract of Tropaeolum tuberosum Ruiz & Pavón (mashua) as colorant for yogurt. The antioxidant activity was evaluated using DPPH and ABTS methods. The total content of anthocyanins (TA) and polyphenols (TP) was determined by the method of differential pH and Folin-Ciocalteu, respectively. Parameters of CIEL*a*b* system were used to measure the purple color and concentration of pigment used to color natural yogurt "3500", comparing with yogurt commercial blackberry "6224" which was taken as a reference. Both yogurt samples were stored under refrigeration (4°C ± 1) for 28 days and color and pH were measured every 4 days. For sensory analysis the acceptance test was applied (p<0,05). The contents of TA and TP in the extracts analyzed were 192,63 ± 1,28 mg of cyanidin-3-glucoside/100g fresh weight (FW) and 314,12 ± 1,23 mg of gallic acid/100 g FW, respectively. The antioxidant capacity trolox equivalent obtained was 15,8 ± 0,2 µmol/g FW, using the DPPH assay, and 17,0 ± 0,2 µmol/g FW with ABTS, the extract was added to plain yogurt (1,2 mg/ 100 g) imparting the purple similar to commercial yogurt blackberry color with minimal changes that were not visually apparent; yogurt "3500" was significantly preferred by judges against the yogurt "6224". It is concluded that the extracted pigments tuber Tropaeolum tuberosum Ruiz & Pavon, possess antioxidant activity, appearing as an alternative of colorant aplicable intermediate acidity foods like yogurt.El objetivo del estudio fue evaluar la actividad antioxidante y uso del extracto etanólico de Tropaeolum tuberosum Ruiz & Pavón (mashua) como colorante para yogur. La actividad antioxidante se determinó por los métodos DPPH y ABTS. El contenido total de antocianinas (AT) y polifenoles (PT) fue determinado por el método de pH diferencial y Folin-Ciocalteu, respectivamente. Los parámetros del sistema CIEL*a*b* se utilizaron para medir el color morado y la concentración de pigmento empleado para colorear el yogur natural “3500”, comparándose con yogur comercial de mora “6224”, que fue tomado como referencia. Ambas muestras de yogur se almacenaron bajo condiciones de refrigeración (4°C ± 1) durante 28 días; se les midió color y pH cada 4 días. Para el análisis sensorial se aplicó la prueba de aceptación (p<0,05). El contenido de AT y PT en los extractos analizados fueron 192,63 ± 1,28 mg de cianidina-3-glucósido/100g peso fresco (PF) y de 314,12 ± 1,23 mg de ácido gálico/100g PF, respectivamente. La capacidad antioxidante equivalente al trolox obtenida fue de 15,8 ± 0,2 µmol/g PF, aplicando el ensayo DPPH, y 17,0 ± 0,2 µmol/g PF con ABTS. El extracto se adicionó al yogur natural (1,2 mg/100 g) impartiendo un color morado similar al del yogur comercial de mora con mínimos cambios del color que no fueron visualmente evidentes; el yogur “3500” fue significativamente el preferido por los jueces frente al yogur “6224”. Se concluye que los pigmentos extraídos del tubérculo de Tropaeolum tuberosum Ruiz & Pavón, poseen actividad antioxidante, presentándose como una alternativa de colorante aplicable en alimentos de acidez intermedia como el yogur

Solar photovoltaic technology in isolated rural communities in Latin America and the Caribbean

The main characteristics of photovoltaic (PV) energy and its current development in Latin American and Caribbean countries (LAC); its impact on the electrification of homes, health institutions, and schools in isolated or difficult-to-access communities; and, the advantages thereof are presented and discussed by replacing the use of traditional fuels such as firewood and kerosene in order to improve inhabitants ’health as well as reducing CO2 emissions. Countries like Nicaragua, Peru, Brazil, Argentina, and Chile stand out for their growing PV energy development in the region. A case study of the electrification process by PV systems shows very positive changes are manifested in terms of improving the quality of life of the inhabitants, and especially their physical and mental health state. In addition, CO2 emission reductions from electrifying 216 houses in the nine communities reach an annual amount of 2,164.19 t/yr, reducing firewood consumption by 2,123.39 t/yr and kerosene consumption by 40.80 t/yr However, LAC countries must adopt laws and regulations that regulate the use of PV energy, with an emphasis on recycling systems at the end of their life cycle

Urban Heat Island Effect on the Energy Consumption of Institutional Buildings in Rome

The urban heat island (UHI) effect is constantly increasing the energy consumption of buildings, especially in summer periods. The energy gap between the estimated energy performance - often simulated without considering UHI - and the real operational consumption is especially relevant for institutional buildings, where the cooling needs are in general higher than in other kind of buildings, due to more internal gains (people, appliances) and different architectural design (more transparent façades and light walls). This paper presents a calculation of the energy penalty due to UHI in two institutional buildings in Rome. Urban Weather Generator (UWG) is used to generate a modified weather file, taking into account the UHI phenomenon. Then, two building performance simulations are done for each case: the first simulation uses a standard weather file and the second uses the modified one. Results shows how is it necessary to re-develop mitigation strategies and a new energy retrofit approach, in order to include urbanization ad UHI effect, especially in this kind of buildings, characterized by very poor conditions of comfort during summer, taking into account users and occupant-driven demand