Analytical and numerical study of photocurrent transients in organic polymer solar cells

This article is an attempt to provide a self consistent picture, including existence analysis and numerical solution algorithms, of the mathematical problems arising from modeling photocurrent transients in organic polymer solar cells (OSCs). The mathematical model for OSCs consists of a system of nonlinear diffusion–reaction partial differential equations (PDEs) with electrostatic convection, coupled to a kinetic ordinary differential equation (ODE). We propose a suitable reformulation of the model that allows us to prove the existence of a solution in both stationary and transient conditions and to better highlight the role of exciton dynamics in determining the device turn-on time. For the numerical treatment of the problem, we carry out a temporal semi-discretization using an implicit adaptive method, and the resulting sequence of differential subproblems is linearized using the Newton–Raphson method with inexact evaluation of the Jacobian. Then, we use exponentially fitted finite elements for the spatial discretization, and we carry out a thorough validation of the computational model by extensively investigating the impact of the model parameters on photocurrent transient times.     

Differential Evolution as a viable tool for satellite image registration

A software system grounded on Differential Evolution to automatically register multiview and multitemporal images is designed, implemented and tested through a set of 2D satellite images on two problems, i.e. mosaicking and changes in time. Registration is effected by looking for the best affine transformation in terms of maximization of the mutual information between the first image and the transformation of the second one, and no control points are needed in this approach. This method is compared against five widely available tools, and its effectiveness is shown.     

The Finely Coordinated Action of SSB and NurA/HerA Complex Strictly Regulates the DNA End Resection Process in Saccharolobus solfataricus

Generation of the 3′ overhang is a critical step during homologous recombination (HR) and replication fork rescue processes. This event is usually performed by a series of DNA nucleases and/or helicases. The nuclease NurA and the ATPase HerA, together with the highly conserved MRE11/RAD50 proteins, play an important role in generating 3′ single-stranded DNA during archaeal HR. Little is known, however, about HerA-NurA function and activation of this fundamental and complicated DNA repair process. Herein, we analyze the functional relationship among NurA, HerA and the single-strand binding protein SSB from Saccharolubus solfataricus. We demonstrate that SSB clearly inhibits NurA endonuclease activity and its exonuclease activities also when in combination with HerA. Moreover, we show that SSB binding to DNA is greatly stimulated by the presence of either NurA or NurA/HerA. In addition, if on the one hand NurA binding is not influenced, on the other hand, HerA binding is reduced when SSB is present in the reaction. In accordance with what has been observed, we have shown that HerA helicase activity is not stimulated by SSB. These data suggest that, in archaea, the DNA end resection process is governed by the strictly combined action of NurA, HerA and SSB.     

Universal multifractal scaling of synthetic aperture radar imagesof sea-ice

Multifrequency, multipolarization imaging radar scattering coefficient data sets, acquired by synthetic aperture radar (SAR) over sea-ice, were studied in order to reveal their scale-invariant properties. Two distinct scenes were acquired at C-band (5.6 cm) and L-band (25 cm) wavelengths for three different linear polarizations (HH, VV, and HV). These sea-ice radar scattering coefficient fields were investigated by applying both Fourier and multifractal analysis techniques. The (multi) scaling of the data is clearly exhibited in both scenes for all three polarizations at L-band and for the HV polarization at C-band. The fields presenting this symmetry were found to be well described by universal multifractals. The corresponding parameters α, C₁, and H were determined for all these fields and were found to vary little with only the parameter H (characterizing the degree of nonconservation) displaying some systematic sensitivity to polarization. The values found for the universal multifractal parameters are α≈1.85±0.05, C₁≈0.0086±0.0041, and H≈-0.15±0.05     

Some integrals involving Heidler’s lightning return stroke current expression

This paper deals with the analytical evaluation of the definite integral and Fourier transform of Heidlers lightning return stroke current expression. This expression is commonly used to represent the return stroke channel base current in international standards.

Reformer and membrane modules plant powered by a nuclear reactor or by a solar heated molten salts: Assessment of the design variables and production cost evaluation

The application of hydrogen selective membranes in steam reforming plants may play an important role in converting natural gas or heavy hydrocarbons into hydrogen in a very efficient way. Providing the reaction heat by sources as solar heated molten salts or a fluid heated in a nuclear reactor may further increase the overall energy efficiency of the system and pave the way for producing large amount of hydrogen with minimum environmental impact. The new architecture proposed in this paper consists of a heat exchanger where air is heated up by molten salts or other fluids as helium, a post-combustion chamber, a reforming-membrane system based on three reaction/separation steps, a retentate recirculator, a hydrogen cooler and compressor, and a final PSA.     

Determination of anthocyanin concentration in whole grape skins using hyperspectral imaging and adaptive boosting neural networks

This paper reports a novel application of a type of neural network committee, called AdaBoost, to the estimation of grape anthocyanin concentration using hyperspectral data. The inputs from the neural networks were the principal components of the grapes’ spectra. Hyperspectral data were collected in the reflectance mode for 46 individual whole grapes of the Cabernet Sauvignon variety, using a hyperspectral camera that operates with wavelengths ranging from 400 to 1000 nm at an approximate 0.6 nm resolution. The hyperspectral camera was positioned a few tens of centimetres away from the grapes. The grapes were harvested on five dates between August 28th and September 23rd in 2009 and presented average sugar content values between 14.6 and 20.2 Brix. They were kept frozen until January 2010, when they were thawed and the hyperspectral data collected at ambient temperature. The anthocyanin concentration values obtained by our calibrations exhibited a squared correlation coefficient value of 0.65 compared to the values measured using conventional laboratory techniques. This correlation value is better than the value reported in another recent scientific work which estimated anthocyanin values in individual whole grapes of Cabernet Sauvignon.