The perception and measurement of contrast: the influence of gaps between display elements

The influence of the luminance of the gap between display elements of flat panel displays (FPDs) on perceived contrast was investigated. Twelve black-on-white FPDs, differing systematically with respect to foreground, background, and gap luminance, were simulated in an experiment. Twelve subjects rated each simulation on u scale, measuring several aspects of image quality, and performed a search task with each simulated FPD. The aims of the research were (a) to validate and assess the reliability of the rating scale items concerning contrast; (b) to relate subjective to objective measures; (c) to find out if ratings improve if raters perform a task with the rated objects; and (d) to evaluate a metric for expressing FPD contrast that we recently proposed. It is concluded that (a) the scale items are reliable if the rated objects vary on the property under concern; several items consistently measured subjective contrast; (b) subjective and objective contrast were strongly related in a linear fashion; (c) without actually using the stimuli in a working task, raters were capable of producing reliable and valid ratings; and (d) the proposed effective luminance modulation (M_r) metric did, but ordinary luminance modulation did not correspond to perceived contrast. Based on this latter finding we recommend that an alternative contrast measurement procedure based on the (M_r) metric is further validated for wide gaps and negative polarity displays.     

Efficient CPU‐based Volume Ray Tracing Techniques

Recent research on high‐performance ray tracing has achieved real‐time performance even for highly complex surface models already on a single PC. In this report, we provide an overview of techniques for extending real‐time ray tracing also to interactive volume rendering. We review fast rendering techniques for different volume representations and rendering modes in a variety of computing environments. The physically‐based rendering approach of ray tracing enables high image quality and allows for easily mixing surface, volume and other primitives in a scene, while fully accounting for all of their optical interactions. We present optimized implementations and discuss the use of upcoming high‐performance processors for volume ray tracing.     

Limitations of the Tauc Plot Method

The Tauc plot is a method originally developed to derive the optical gap of amorphous semiconductors such as amorphous germanium or silicon. By measuring the absorption coefficient α(hν) and plotting ${(\alpha hv)}^{\frac{1}{2}}$ versus photon energy hν, a value for the optical gap (Tauc gap) is determined. In this way non-direct optical transitions between approximately parabolic bands can be examined. In the last decades, a modification of this method for (poly-) crystalline semiconductors has become popular to study direct and indirect interband transitions. For this purpose, (ahν)ⁿ (n = $\frac{1}{2}$, 2) is plotted against hν to determine a value of the electronic bandgap. Due to the ease of performing UV–vis measurements, this method has nowadays become a standard to analyze various (poly-) crystalline solids, regardless of their different electronic structure. Although this leads partially to widely varying values of the respective bandgap of nominally identical materials, there is still no study that critically questions which peculiarities in the electronic structure prevent a use of the Tauc plot for (poly-) crystalline solids and to which material classes this applies. This study aims to close this gap by discussing the Tauc plot and its limiting factors for exemplary (poly-) crystalline solids with different electronic structures.     

Kupfer,Silber, Gold; fixiert in metallorganischen π-Pinzetten

Alkinyl functionalized titanocenes of general type RC≡C-[Ti]-C≡CR and Cl-[Ti]-C≡CR {[Ti] = (η⁵-C₅H₄-SiMe₃)₂Ti}; R = singly bonded organic ligand} can successfully be used as organometallic π-tweezers to stabilize numerous mononuclear MX/R¹ species (M = Cu, Ag, Au; X = singly bonded inorganic group; R¹ = singly bonded organic ligand). The synthesis, manifold reaction chemistry as well as bonding and spectroscopy of {[Ti](C≡CR)₂}MX/R¹ and {[Ti] (C≡CR)(Cl)}CuX complexes is described     

Bestimmung von Gamma-Hydroxybuttersäure und Gamma- Hydroxybuttersäure- Metaboliten im Haar und deren forensische Bedeutung

Gamma-Hydroxybutyrate (GHB) has been subject of scientific research due to its endogenous occurrence in humans and at the same time sedating effect after exogenous uptake, whether intentional or not. Of particular interest in this context is the distinction between possible endogenous GHB-concentrations and those that were in hair after a (single) exogenous uptake. In the present study, methods of extraction and quantification by LC-MS/MS for GHB and its metabolites glycolic acid, 2,4-dihydroxybutanoic acid (2,4-DHB), 3,4-dihydroxybutanoic acid (3,4-DHB) and 4-(sulfooxy)butanoic acid (GHB-sulf) were established. After validation of those methods, hair samples of persons without known exogenous GHB uptake were analysed to define an endogenous reference range for each substance. Subsequently hair samples were analysed after single or regular uptake of GHB. GHB-concentrations of 928 hair samples from persons without known uptake of GHB were between < 0.1 and 6.3 ng/mg. Only 29 samples showed concentrations higher than 3.0 ng/mg. Interestingly, hair samples that were stored for two to eight years showed significantly higher GHB-concentrations between 1.5 and 130 ng/mg, with 48 of 52 analysed segments showing concentrations above 3.0 ng/mg. Thus, storing seems to have a greater effect on the observed GHB-concentration than the quantity of GHB taken. In accordance with that, of 136 analysed hair samples of persons with a daily uptake of 3 to 9 g GHB, only 25 of the measured concentrations were above 3.0 ng/mg and only three outside of the prior defined endogenous reference range. The association between the quantity of exogenous GHB-uptake and the observed GHB-concentration in hair was found to be very weak. In agreement with those results, no raise in GHB-concentration was observed in hair samples after a single uptake of GHB. All concentrations were in the lower range of the prior defined endogenous reference range. Regarding the four analysed GHB-metabolites, the following endogenous reference ranges (including outliers) were defined: glycolic acid 0.39 - 11 (24) ng/mg, GHB-sulf < 0.40 - 1.7 (12) ng/mg, 3,4-DHB < 0.10 - 0.63 (4.7) ng/mg and 2,4-DHB < 0.20 - 0.45 (0.65) ng/mg. In hair samples from persons with regular uptake of GHB, at least one metabolite was found to be elevated (i.e., above the prior defined endogenous reference range) in the average of each hair strand, in contrast to the observed GHB-concentrations. In four of eleven hair strands even all four metabolites were above their endogenous reference range. Nevertheless, no statistically significant association between the quantity of GHB-uptake and the observed concentration in hair was found. Hair strands examined after a single GHB-uptake partially showed elevated concentrations of GHB-metabolites. The elevated segments, however, were not in each case those one would expect assuming the average hair growth rate of 1 cm/month. In the present study, it was shown that the exogenous uptake of GHB does not necessarily result in an elevated GHB-concentration in hair. Thus, the sole quantification of GHB will most likely not allow a clear decision whether or not GHB has been taken up exogenously. Thus, the here developed analytical methods do not yield legal certainty. However, in combination with the detection of one or more elevated GHB-metabolite concentrations, a better evaluation of this issue seems possible.     

Chemical Recycling of Polyolefinic Waste to Light Olefins by Catalytic Pyrolysis

Catalytic pyrolysis of post-industrial and post-consumer waste is studied in an auger-type reactor at pilot scale by applying two different zeolites and an amorphous silica-alumina catalyst in-situ at 400–550 °C. Contrary to thermal pyrolysis, of polyolefin-rich waste, high gaseous pyrolysis product yields of approx. 85 wt % are achieved with C₂–C₄ olefin contents of up to 67 wt %. After deactivation by coke deposition catalyst regeneration is proved feasible for maintaining the gaseous product yield and composition. Waste feedstocks with significant nitrogen and halogen heteroatom content are not suitable for in-situ catalytic pyrolysis.     

Hexaazapolycyclen durch selektive Multimethylenierungen mit Dichlormethan und Base oder mit Urotropin

Hexaazapolycycles by Selective Multimethylenations with Dichloromethane and Base or with Hexamethylenetetramine Multiple methylenations of 2-aminomethylbenzimidazole with dichloromethane and methylamine or ammonia or with hexamethylenetetramine lead to highly selective formations of 6 new single bonds to give only a polycyclic bis-spiro-1,5-diazocine 2 or only a polycyclic spiro-1,3,6-triazonine 4 or only a polycyclic 1,3,6,8-tetrazecine derivative 6 . 4 and 6 may be equally well obtained starting with 2-chloromethyl-benzimidazole. All of these selectively formed products are concave cryptands with 6 amino nitrogen atoms. No template metals are used in their syntheses. The reasons for the unusual changes in selectivity are investigated using semi-empirical PM3 calculations and mechanistic considerations. Experimental and spectroscopic details are given.     

Photochemische Reaktionen von Pyrazolidon-(3)-betainen. VII. Photochemische Dimerisierung von Pyrazolidon-(3)-azomethiniminen

Photochemical Reactions of 3-Pyrazolidone Betains. VII. Photochemical Dimerization of 3-Pyrazolidone Azomethinimines UV irradiation of 3-pyrazolidone azomethinimines 1 in methanol results in low yields in photochemical head-tail-dimerization of 1 to the hexahydrotetrazines 3 . The structure of 3 is elucidated by chemical and spectroscopic methods (IR, ¹H-, ¹³NMR).