Dye solar cells efficiency maps: a parametric study

In this work we present a numerical simulation of a dye solar cell efficiency using a drift-diffusion model for the complete cell. The physical parameters such as the active layer thickness, the electron mobility and the dye spectrum are varied systematically in a range of values individuated experimentally, in order to obtain efficiency maps that reveal interesting features in this kind of devices.     

Atomistic simulation of InGaN/GaN quantum disk LEDs

In this work electronic and optoelectronic properties of InGaN/GaN nanocolumn quantum disk LEDs have been studied with the multiscale simulation tool tiberCAD. Calculations have been performed with an atomistic tight-binding model. Results shows that emission energies have a minor dependence on the nanocolumn dimension while In concentration in the active region is a critical parameter.     

Computation of weak steady shock reflections by means of an unstructured shock-fitting solver

Weak steady Mach reflections are numerically simulated using unstructured grids by means of either “shock-fitting” or “shock-capturing” techniques. It is shown that shock-fitting allows using coarser meshes than those required by shock-capturing, since the latter needs mesh refinement in the direction normal to the discontinuities, which is not needed using the former approach. The shock-fitted solution is also free from the numerical disturbances that arise along the captured discontinuities and pollute the captured solution in the smooth flowfield region. Finally, the shock-fitting solutions show the presence of a small region next to the Mach stem and the reflected shock downstream of the triple point, characterized by very high gradients.     

Bias in modal parameters using the direct and iterative RFP identification procedures

In the rational fraction polynomial method [1] the identification of modal parameters is obtained through a direct linear least-square optimization technique but a particular form of fitting error is minimized. An iterative algorithm has been recently developed which uses the true fitting error [2]. In this paper a statistical analysis is developed to estimate the bias effects on the identified parameters when the data are polluted with noise. Both the direct and iterative procedures are considered. Numerical simulations are used to validate the results predicted by the theoretical analysis, which shows that the iterative approach is by far more efficient than the direct method.A first version of this paper was presented at 17th Int. Seminar on Modal Analysis, Leuven (Belgium), 23–25 September 1992, and preprinted in the Proceedings.     

Hilbert-Kunz function of monomial ideals and binomial hypersurfaces

The aim of this note is to determine the Hilbert-Kunz functions of rings defined by monomial ideals and of rings defined by a single binomial equationX ^a−X^b with gcd(X ^a, X^b)=1.     

Block Renormalization Group Approach for Correlation Functions of Interacting Fermions

Inspired by a decomposition of the lattice Laplacian operator into massive terms (coming from the use of the block renormalization group transformation for bosonic systems), we establish a telescopic decomposition of the Dirac operator into massive terms, with a property named orthogonality between scales. Making a change of Grassmann variables and writing the initial fields in terms of the eigenfunctions of the operators related to this decomposition, we propose a multiscale structure for the generating function of interacting fermions. Due to the orthogonality property we obtain simple formulas, establishing a trivial link between the correlation functions and the effective potential theories. In particular, for the infrared analysis of some asymptotically free models, the two point correlation function is written as a dominant term (decaying at large distances as the free propagator) plus a correction with faster decay, and the study of both terms is straightforward once the effective potential theory is controlled.     

Chromatographic purification and HPLC assay with electrochemical detection of diethylstilboestrol residues in meat

Summary A rapid, reliable and sensitive procedure is reported for the detection of residues of total diethylstilboestrol (DES) (free and conjugated) in bovine muscle samples. Prior to analysis, the DES in the sample was enzymatically deconjugated. Subsequently the sample was subjected to a clean-up procedure using a two-trap system composed of a first cartridge of non-specific adsorbing material (C 18) and of a second cartridge containing a sulphonic acid type silica-based anion exchanger. The determination was performed by HPLC with electrochemical detection. Analytical variables such as efficiency of hydrolysis, enzyme purification, hydrodynamic voltammetric studies and variation in the DES trans/cis ratio were investigated. Mean recovery of total DES was 87.3%. The precision of the procedure was 7.2% for DES levels of 0.5 ng/g and 2.1% for levels of 5 ng/g.     

High-performance liquid chromatographic-electrospray mass spectrometric analysis of phenolic acids and aldehydes

The present work describes the development of an HPLC-electrospray mass spectrometric method for the analysis of phenolic acids and aldehydes. These compounds are important for the quality of foods and feeds, such as dietary fiber supplements, wine and lignicellulose by-products. Good separation was obtained with a phenyl column (3 μm particle size, 150 mm×3.9 mm I.D.), using McOH-H₂O (30:70, v/v) as the mobile phase with 0.01% CH,COOH and 0.2 mM tetraethyl ammonium iodide as the ion pairing agent, at a flow-rate of 0.3 ml/min. This system permits post column splitting of the eluate for analysis by electrospray mass spectrometry with a flow-rate of 11 μl/min. This new method is extremely sensitive and less than 6 pg/inj of the studied phenols can be identified and quantified. This method was applied to standard compounds as well as to components of high-fiber dietary supplements (primarily wheat bran), cornmeal, and oat bran.