Assessment of the illumination dependency of Al2O3 and SiO2 rear‐passivated p‐type silicon solar cells

This Letter discusses an important difference between positively charged SiO₂ and negatively charged Al₂O₃ rear‐passivated p‐type Si solar cells: their illumination level dependency. For positively charged SiO₂ rear‐passivated p‐type Si solar cells, a loss in short circuit current (J_SC) and open circuit voltage (V_OC) as a function of illumination level is mainly caused by parasitic shunting and a decrease in surface recombination, respectively. Hence, the relative loss in cell conversion efficiency, J_SC, and V_OC as a function of the illumination level for SiO₂ compared to Al₂O₃ rear‐passivated p‐type Si solar cells has been measured and discussed. Subsequently, an exponential decay fit of the loss in cell efficiency is applied in order to estimate the difference in the energy output for both cell types in three different territories: Belgium (EU), Seattle and Austin (US). The observed trends in the difference in energy output between both cells, as a function of time of the year and region, are as expected and discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of CO<Subscript>2</Subscript> Compressibility on CO<Subscript>2</Subscript> Storage in Deep Saline Aquifers

The injection of supercritical CO₂ in deep saline aquifers leads to the formation of a CO₂ plume that tends to float above the formation brine. As pressure builds up, CO₂ properties, i.e. density and viscosity, can vary significantly. Current analytical solutions do not account for CO₂ compressibility. In this article, we investigate numerically and analytically the effect of this variability on the position of the interface between the CO₂-rich phase and the formation brine. We introduce a correction to account for CO₂ compressibility (density variations) and viscosity variations in current analytical solutions. We find that the error in the interface position caused by neglecting CO₂ compressibility is relatively small when viscous forces dominate. However, it can become significant when gravity forces dominate, which is likely to occur at late times of injection.     

[13C]Dynamic NMR and Molecular Modeling of 2,4-Bis(N-Pyrrolidinyl)-6-chloro-s-triazine

The room temperature [¹³C]NMR spectrum of 2,4-bis(N-pyrrolidinyl)-6-chloro-s-triazine shows doubled signals for the pyrrolidine rings, which suggests restricted rotation about the Ar-C—N bond. The rotational barrier around this bond was determined by [¹³C]dynamic NMR (DNMR) spectra run at different increasing temperatures and also by the PM3 Hamiltonian contained in the MOPAC package. The values thus obtained, 16.6 and 13.6 kcal mol^–1, respectively, are in good agreement.     

Sparse direct factorizations through unassembled hyper-matrices

We set out to efficiently compute the solution of a sequence of linear systems A_ix_i = b_i, where the matrix A_i is tightly related to matrix A_{i –1}. In the setting of an hp -adaptive Finite Element Method, the sequence of matrices A_i results from successive local refinements of the problem domain. At any step i > 1, a factorization already exists and it is the updated linear system relative to the refined mesh for which a factorization must be computed in the least amount of time. This observation holds the promise of a tremendous reduction in the cost of an individual refinement step. We argue that traditional matrix storage schemes, whether dense or sparse, are a bottleneck, limiting the potential efficiency of the solvers. We propose a new hierarchical data structure, the Unassembled Hyper-Matrix (UHM), which allows the matrix to be stored as a tree of unassembled element matrices, hierarchically ordered to mirror the refinement history of the physical domain. The factorization of such an UHM proceeds in terms of element matrices, only assembling nodes when they need to be eliminated. Efficiency comes in terms of both performance and space requirements. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optimization in constrained crack problems

Following the optimization approach to brittle fracture, we consider the evolution of a crack in a domain as solution of the global problem of constrained minimization of the total potential energy with respect to both state variables (the displacement vector) and shape variables (parameters of the crack shape). This formulation describes the initiation of a crack in a homogeneous body and its stable as well as unstable propagation, which allows also a kink (topology change) of the crack during the evolution process. By this we assume that contact can occurs between the opposite crack faces. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Existence of solutions for motion equations for an objective model of viscoelastic medium

We consider the Dirichlet initial-boundary value problem for the equations of motion of incompressible viscoelastic medium with objective rheological constitutive laws of Maxwell and Jeffreys kind. Several types of existence results are presented. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Michael Addition of Sulfur Anions to β,β-Substituted Nα-Formyl-α, β-Dehydroamino Acid Esters

The addition of lithium benzylthiolates to N^α,-formyl-α,β-dehydro-α-amino acid esters gave protected N^α-formyl-β-S-benzyl-β,β-dialkylcysteine esters. Hydrolysis and N^α-protection produced β,β-dialkyl-cysteines which can be used for peptide synthesis.     

Three-component diastereoselective cascade synthesis of thiohydantoins

A new three-component cascade reaction for the synthesis of thiohydantoins is reported. The reaction between α-amino esters, nitrostyrenes, and aromatic isothiocyanates is efficiently promoted by organic bases to afford highly substituted thiohydantoins in moderate to good yields and diastereoselectivities.     

Facility Update: The Center for Advanced Microstructures and Devices: A Status Report

The progress in the field of high resolution X-ray microscopy is caused in particular by the rapid developments of synchrotron radiation sources and X-ray optical elements, by the extension of the energy range, improved designs of X-ray microscopes and scanning X-ray microscopes, the use of CCD detectors with high detective quantum efficiency, the introduction of new imaging techniques, and the development of new fields of application.