Meromorphic extensions of regular holonomic distributions

In this paper we consider distributions of the form 1/P and dy/P(x,y), whereP is a polynomial. Using results by Kashiwara and Kawai we give fairly accessible proofs that these expressions can be defined as regular holonomic distributions by utilising a meromorphic parameter. We also discuss distributions of the form /P and their direct image , when one knows that is a regular holonomic distribution. All these distributions are relevant to the study of renormalised Feynman integrals.     

Influence of Ga/(Ga + In) grading on deep‐defect states of Cu(In,Ga)Se2 solar cells

The benefits of gallium (Ga) grading on Cu(In,Ga)Se₂ (CIGS) solar cell performance are demonstrated by comparing with ungraded CIGS cells. Using drive‐level capacitance profiling (DLCP) and admittance spectroscopy (AS) analyses, we show the influence of Ga grading on the spatial variation of deep defects, free‐carrier densities in the CIGS absorber, and their impact on the cell's open‐circuit voltage V_oc. The parameter most constraining the cell's V_oc is found to be the deep‐defect density close to the space charge region (SCR). In ungraded devices, high deep‐defect concentrations (4.2 × 10¹⁶cm^–3) were observed near the SCR, offering a source for Shockley–Read–Hall recombination, reducing the cell's V_oc. In graded devices, the deep‐defect densities near the SCR decreased by one order of magnitude (2.5 × 10¹⁵ cm^–3) for back surface graded devices, and almost two orders of magnitude (8.6 × 10¹⁴ cm^–3) for double surface graded devices, enhancing the cell's V_oc. In compositionally graded devices, the free‐carrier density in the absorber's bulk decreased in tandem with the ratio of gallium to gallium plus indium ratio GGI = Ga/(Ga + In), increasing the activation energy, hindering the ionization of the defect states at room temperature and enhancing their role as recombination centers within the energy band. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

A sublogarithmic convex hull algorithm

We present a parallel algorithm for finding the convex hull of a sorted set of points in the plane. Our algorithm runs inO(logn/log logn) time usingO(n log logn/logn) processors in theCommon crcw pram computational model, which is shown to be time and cost optimal. The algorithm is based onn ^1/3 divide-and-conquer and uses a simple pointer-based data structure.Part of this work was done when the last three authors were at the Department of Computer and Information Science, Linköping University. The research of the second author was supported by the Academy of Finland.     

Potential‐induced optimization of ultra‐thin rear surface passivated CIGS solar cells

Ultra‐thin Cu(In,Ga)Se₂ (CIGS) solar cells with an Al₂O₃ rear surface passivation layer between the rear contact and absorber layer frequently show a “roll‐over” effect in the J–V curve, lowering the open circuit voltage (V_OC), short circuit current (J_SC) and fill factor (FF), similar to what is observed for Na‐deficient devices. Since Al₂O₃ is a well‐known barrier for Na, this behaviour can indeed be interpreted as due to lack of Na in the CIGS absorber layer. In this work, applying an electric field between the backside of the soda lime glass (SLG) substrate and the SLG/rear‐contact interface is investi‐gated as potential treatment for such Na‐deficient rear surface passivated CIGS solar cells. First, an electrical field of +50 V is applied at 85 °C, which increases the Na concentration in the CIGS absorber layer and the CdS buffer layer as measured by glow discharge optical emission spectroscopy (GDOES). Subsequently, the field polarity is reversed and part of the previously added Na is removed. This way, the J –V curve roll‐over related to Na deficiency disappears and the V_OC (+25 mV), J_SC(+2.3 mA/cm²) and FF (+13.5% absolute) of the rear surface passivated CIGS solar cells are optimized. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Zwei Beispiele ganzer Funktionen mit algebraischem Höchstindex einer Stellensorte

Ohne Zusammenfassung     

Very high crystalline quality of thick 4H‐SiC epilayers grown from methyltrichlorosilane (MTS)

200 µm thick 4H‐SiC epilayers have been grown by chloride‐based chemical‐vapor deposition using methyltrichlorosilane (MTS) as single precursor. The very high crystalline quality of the grown epilayer is demonstrated by high resolution X‐Ray Diffraction rocking curve with a full‐width‐half‐maximum value of only 9 arcsec. The high quality of the epilayer is further shown by low temperature photoluminescence showing strong free exciton and nitrogen bound exciton lines. The very high crystalline quality achieved for the thick epilayer grown in just two hours at 1600 °C suggests that MTS is a suitable precursor molecule for SiC bulk growth. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Laser generated and recorded transient bending waves in composite tubes

Propagating bending waves are studied in three different composite tubes by holographic interferometry. A conical mirror is placed axially inside the tubes. Axial illumination and observation directions make it possible to view the circumference of the tube, with a high sensitivity to radial deformation. It is shown how the deformation field can be numerically evaluated using a phase stepping and unwrapping technique. Transient bending waves in the tubes are both generated and recorded by the same pulsed laser, which makes the experiments easy to perform. Finite element simulations of the impacted tubes are compared to corresponding experiments. Both the geometry and the material properties of the tubes affect the wave propagation. For unidirectional composite tubes, the 0-deg and 90-deg directions have different dynamic behavior. The proposed method could be used in nondestructive testing of tubes.     

Mechanistic insights into the phosphine-free RuCp*-diamine-catalyzed hydrogenation of aryl ketones: experimental and theoretical evidence for an alcohol-mediated dihydrogen activation

The commercially available chiral diamine quincorine-amine, originally derived from quinine, was found to be a highly active catalyst for ruthenium-catalyzed hydrogenation of ketones. The complex formed between the quincorine-amine, containing both a primary and a quinuclidine amino function, and RuCp*Cl catalyzes the hydrogenation of aromatic and aliphatic ketones in up to 90% ee approximately 24 times faster than previously reported Ru-diamine complexes. The pseudo-enantiomer of the quincorine-amine, i.e., quincoridine-amine, also showed high activity; however, the enantioselectivities obtained with this catalyst were lower. The reason for the lower, but opposite stereoselectivity seen with the quincoridine-amine, as compared to the quincorine-amine, was rationalized by a kinetic and computational study of the mechanism of the reaction. The theoretical calculations also revealed a significantly lower activation barrier for the alcohol-mediated split of dihydrogen, as compared to the nonalcohol-mediated process, a finding of utmost implication also for the diphosphine/diamine-mediated enantioselective hydrogenation of ketones.     

Asymmetric split-vacancy defects in SiC polytypes: a combined theoretical and electron spin resonance study

Transition metal defects were studied in different polytypes of silicon carbide (SiC) by ab initio supercell calculations. We found asymmetric split-vacancy (ASV) complexes for these defects that preferentially form at only one site in hexagonal polytypes, and they may not be detectable at all in cubic polytype. Electron spin resonance study demonstrates the existence of ASV complex in niobium doped 4H polytype of SiC.