338 research outputs found
Correlation functions by Cluster Variation Method for Ising model with NN, NNN and Plaquette interactions
We consider the procedure for calculating the pair correlation function in
the context of the Cluster Variation Methods. As specific cases, we study the
pair correlation function in the paramagnetic phase of the Ising model with
nearest neighbors, next to the nearest neighbors and plaquette interactions in
two and three dimensions. In presence of competing interactions, the so called
disorder line separates in the paramagnetic phase a region where the
correlation function has the usual exponential behavior from a region where the
correlation has an oscillating exponentially damped behavior. In two
dimensions, using the plaquette as the maximal cluster of the CVM
approximation, we calculate the phase diagram and the disorder line for a case
where a comparison is possible with results known in literature for the
eight-vertex model. In three dimensions, in the CVM cube approximation, we
calculate the phase diagram and the disorder line in some cases of particular
interest. The relevance of our results for experimental systems like mixtures
of oil, water and surfactant is also discussed.Comment: 31 pages, LaTeX file, 7 figure
An approach for the estimation of the aggregated photovoltaic power generated in several European countries from meteorological data
Classical approaches to the calculation of the photovoltaic (PV) power generated in a region from meteorological data require the knowledge of the detailed characteristics of the plants, which are most often not publicly available. An approach is proposed with the objective to obtain the best possible assessment of power generated in any region without having to collect detailed information on PV plants. The proposed approach is based on a model of PV plant coupled with a statistical distribution of the prominent characteristics of the configuration of the plant and is tested over Europe. The generated PV power is first calculated for each of the plant configurations frequently found in a given region and then aggregated taking into account the probability of occurrence of each configuration. A statistical distribution has been constructed from detailed information obtained for several thousands of PV plants representing approximately 2 % of the total number of PV plants in Germany and was then adapted to other European countries by taking into account changes in the optimal PV tilt angle as a function of the latitude and meteorological conditions. The model has been run with bias-adjusted ERA-interim data as meteorological inputs. The results have been compared to estimates of the total PV power generated in two countries: France and Germany, as provided by the corresponding transmission system operators. Relative RMSE of 4.2 and 3.8 % and relative biases of −2.4 and 0.1 % were found with three-hourly data for France and Germany. A validation against estimates of the country-wide PV-power generation provided by the ENTSO-E for 16 European countries has also been conducted. This evaluation is made difficult by the uncertainty on the installed capacity corresponding to the ENTSO-E data but it nevertheless allows demonstrating that the model output and TSO data are highly correlated in most countries. Given the simplicity of the proposed approach these results are very encouraging. The approach is particularly suited to climatic timescales, both historical and future climates, as demonstrated here
Fabrication methods for a quantum cascade photonic crystal surface emitting laser
Conventional quantum cascade (QC) lasers are intrinsically edge-emitting devices with mode confinement achieved via a standard mesa stripe configuration. Surface emission in edge emitting QC lasers has therefore necessitated redirecting the waveguided laser emission using a second order grating. This paper describes the methods used to fabricate a 2D photonic crystal (PC) structure with or without a central defect superimposed on an electrically pumped QC laser structure with the goal of achieving direct surface emission. A successful systematic study of PC hole radius and spacing was performed using e-beam lithography. This PC method offers the promise of a number of interesting applications, including miniaturization and integration of QC lasers
Scoping the potential usefulness of seasonal climate forecasts for solar power management
Solar photovoltaic energy is widespread worldwide and particularly in Europe, which became in 2016 the first region in the world to pass the 100 GW of installed capacity. As with all the renewable energy sources, for an effective management of solar power, it is essential to have reliable and accurate information about weather/climate conditions that affect the production of electricity. Operations in the solar energy industry are normally based on daily (or intra-daily) forecasts. Nevertheless, information about the incoming months can be relevant to support and inform operational and maintenance activities.
This paper discusses a methodology to assess whether a seasonal climate forecast can provide a useful prediction for a specific sector, in this paper the European solar power industry. After evaluating the quality of the forecasts in providing probabilistic information for solar radiation, we describe how to assess their potential usefulness for a generic user by proposing an approach that takes into account not only their accuracy but also other potentially relevant factors. This approach is called index of opportunity and is then illustrated by presenting an example for the European solar power sector. The index of opportunity provides indications about where and when seasonal climate forecasts can benefit the decision-making in the photovoltaic sector. Even more importantly, it suggests an approach on how to evaluate their usefulness for the user's decision-making. This approach has the advantage of not limiting the definition of the usefulness only to the quality of the forecasts but rather considering, in an explicit way, all the factors that must be combined with the forecast's quality to define what is useful or not for the user
Quantum cascade photonic crystal surface emitting injection laser
A surface emitting quantum cascade injection laser is presented. Direct surface emission is obtained by using a 2D photonic-band-gap structure that simultaneously acts as a microcavity. The approach may allow miniaturization and on-chip-integration of the devices
Fabrication technologies for quantum cascade photonic-crystal microlasers
In this paper we describe the technological and fabrication methods necessary to incorporate both photonic and electronic-band engineering in order to create novel surface-emitting quantum cascade microcavity laser sources. This technology offers the promise of several innovative applications such as the miniaturization of QC lasers, and multi-wavelength two-dimensional laser arrays for spectroscopy, gas-sensing and imaging. This approach is not limited to light-emitting devices, and may be efficiently applied to the development of mid- and far-infrared normal-incidence detectors
Using ERA-Interim reanalysis for creating datasets of energy-relevant climate variables
The construction of a bias-adjusted dataset of climate variables at the near surface using ERA-Interim reanalysis is presented. A number of different, variable-dependent, bias-adjustment approaches have been proposed. Here we modify the parameters of different distributions (depending on the variable), adjusting ERA-Interim based on gridded station or direct station observations. The variables are air temperature, dewpoint temperature, precipitation (daily only), solar radiation, wind speed, and relative humidity. These are available on either 3 or 6 h timescales over the period 1979–2016. The resulting bias-adjusted dataset is available through the Climate Data Store (CDS) of the Copernicus Climate Change Data Store (C3S) and can be accessed at present from ftp://ecem.climate.copernicus.eu. The benefit of performing bias adjustment is demonstrated by comparinginitial and bias-adjusted ERA-Interim data against gridded observational fields
Lasing mode pattern of a quantum cascade photonic crystal surface-emitting microcavity laser
The identification of the lasing mode within a quantum cascade photonic crystal microcavity laser emitting at λ ~8 µm is presented. The symmetry of the lasing mode is determined by the position of nodal lines within micro-bolometer camera measurements of its polarized spatial distribution. Full three-dimensional finite-difference time-domain simulations are also performed, and the resulting vertically emitted radiation field pattern is seen to follow the experimental results closely
Trace-Metal Concentrations in Coastal Marshes of the Lower Parana River and the Rio-de-La-Plata Estuary
Fil: Villar, Carlos Alberto. Instituto de Limnología Dr. Raúl A. Ringuelet (ILPLA). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Stripeikis, J.. INQUlMAE. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires; ArgentinaFil: Tudino, M.. INQUlMAE. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires; ArgentinaFil: Dhuicque, L.. INQUlMAE. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires; ArgentinaFil: Troccoli, O.. INQUlMAE. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires; ArgentinaFil: Bonetto, Carlos Alberto. Instituto de Limnología Dr. Raúl A. Ringuelet (ILPLA). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; Argentin
Ecología trófica del lenguado patagónico Paralichthys patagonicus (Jordan, 1889) en el Ecosistema Costero Argentino-Uruguayo
Food habits and diet composition of Patagonian flounder Paralichthys patagonicus (Jordan, 1889) were studied on the basis of stomach content analyses from 828 specimens (512 females, 304 males, 12 unsexed) collected during 16 commercial cruises between February 2009 and April 2010 in the Argentine-Uruguayan Coastal Ecosystem (34° S-41° S). A total of 272 stomachs (32.9%) contained food (184 females and 84 males), among which 20 prey taxa were identified. The most important prey category was pelagic fish, primarily Argentine anchovy (Engraulis anchoita), followed by rough scad (Trachurus lathami). Evidence showed that females consumed a higher total wet weight of prey compared to males. Results also suggested a specialised diet over E. anchoita, across all sex and size groups. The estimated trophic level for the population of P. patagonicus was 4.16. This study suggests that P. patagonicus is a tertiary piscivorous consumer of the trophic food web in the region, and reveals changes in the prey consumption compared with previous studies.Se estudiaron los hábitos alimentarios y la composición de la dieta del lenguado patagónico Paralichthys patagonicus (Jordan, 1889) sobre la base del análisis del contenido estomacal de 828 especímenes (512 hembras, 304 machos, 12 indeterminados) recolectados durante 16 cruceros comerciales entre febrero de 2009 y abril de 2010 en el Ecosistema Costero Argentino-Uruguayo (34° S-41° S). Un total de 272 estómagos (32,9%) contenían alimento (184 hembras y 84 machos), entre los que se identificaron 20 taxones de presas. La categoría de presa más importante fue los peces pelágicos, principalmente la anchoíta argentina (Engraulis anchoita), seguida por el surel (Trachurus lathami). La evidencia mostró que las hembras consumieron un mayor peso húmedo total de presa en comparación con los machos. Los resultados también sugirieron una dieta especializada sobre E. anchoita para todos los sexos y tamaños. El nivel trófico estimado para toda la población de P. patagonicus fue 4,16. Este estudio sugiere que P. patagonicus es un consumidor piscívoro terciario de la trama trófica en la región, y revela cambios importantes en el consumo de presas en comparación con estudios previos.
- …