Radially polarized 3 kW beam from a CO2 laser with an intracavity resonant grating mirror

A 3 kW radially polarized beam is generated from a CO(2) laser by means of a resonant grating mirror. The design results and spectral characterization of a broadband polarizing mirror are presented as well as the mirror's operation in a CO(2) laser resonator. In a long-term experiment a radially polarized beam with a power of 2.7 kW was observed for several hours, proving the high stability of this polarizing scheme.     

Enantioselective CD analysis of amino acids based on chiral amplification with a stereodynamic probe

The condensation between stereolabile 1,8-bis(3′-formyl-4′-hydroxyphenyl)naphthalene, 1, and two amino acid molecules results in the formation of chiral diimines exhibiting strong CD signals. This reaction has been used to develop a chiroptical sensing method for the determination of the absolute configuration and enantiomeric composition of unprotected amino acids. This sensing approach is based on distinctive chiral amplification due to central-to-axial chirality induction within the diimine scaffold formed and does not require the use of an enantiopure ligand or metal complex.     

Comment on “Stochastic analysis of recurrence plots with applications to the detection of deterministic signals” by Rohde et al. [Physica D 237 (2008) 619-629]

In the recent article “Stochastic analysis of recurrence plots with applications to the detection of deterministic signals” (Physica D 237 (2008) 619-629), Rohde et al. stated that the performance of RQA in order to detect deterministic signals would be below traditional and well-known detectors. However, we have concerns about such a general statement. Based on our own studies we cannot confirm their conclusions. Our findings suggest that the measures of complexity provided by RQA are useful detectors outperforming well-known traditional detectors, in particular for the detection of signals of complex systems, with phase differences or signals modified due to the measurement process.Nevertheless, we also clearly assert that an uncritical application of RQA may lead to wrong conclusions.     

Complex networks in climate dynamics

Complex network theory provides a powerful framework to statistically investigate the topology of local and non-local statistical interrelationships, i.e. teleconnections, in the climate system. Climate networks constructed from the same global climatological data set using the linear Pearson correlation coefficient or the nonlinear mutual information as a measure of dynamical similarity between regions, are compared systematically on local, mesoscopic and global topological scales. A high degree of similarity is observed on the local and mesoscopic topological scales for surface air temperature fields taken from AOGCM and reanalysis data sets. We find larger differences on the global scale, particularly in the betweenness centrality field. The global scale view on climate networks obtained using mutual information offers promising new perspectives for detecting network structures based on nonlinear physical processes in the climate system.     

Relations between structure, acidity, and activity of WOx/TiO2: influence of the initial state of the support, titanium oxyhydroxide, or titanium oxide

Two series of WO(x)/TiO(2) catalysts, containing W surface densities up to 4.4 W atoms/nm(2), were prepared by pore volume impregnation of two different supports, titanium oxyhydroxide (amorphous) or titanium oxide (crystallized, 100% anatase). The influence of W surface density and the nature of the support on the surface structure, development of the acidity, and catalytic performances were examined. The texture and structure of the catalysts were investigated by Brunauer-Emmett-Teller measurements, X-ray diffraction (XRD), and Raman and infrared spectroscopy. The catalytic activity was tested for 2-propanol dehydration and n-hexane isomerization. For catalysts obtained by impregnation of titanium oxide, XRD and Raman results showed that W was present as a surface phase. Infrared spectra indicated an increase in the degree of polymerization of W species with increasing W surface density. CO and lutidine adsorption, followed by infrared spectroscopy, showed an increase in the strength and abundance of Br?nsted acid sites (measured after lutidine desorption at 573 K) with the W surface density above a threshold of 1.3 W atoms/nm(2). The development of Br?nsted acidity correlated with the evolution of the infrared bands attributed to polymerized W species. A direct relationship was observed between the concentration of Br?nsted acid sites and the catalytic activity for 2-propanol dehydration. Catalytic activity, for n-hexane isomerization, appears to be associated with the presence of highly condensed W species. The catalysts synthesized by impregnation of titanium oxyhydroxide exhibited a comparable behavior. Hence, for a given W surface density, the W surface structure, concentration of Br?nsted acid sites, and catalytic performances were similar. Thus, no significant effect of the initial form of the support (titanium oxyhydroxide versus titanium oxide; 100% anatase) was evidenced.     

A New and Elegant Approach for Solving $$\varvec{n \times n}$$-Order Linear Fractional Differential Equations

The application of fractional differential equations (FDEs) in the fields of science and engineering are gradually increasing day by day during the last two decades. The solutions of linear systems of FDEs are of great importance. Several investigations are carried out on such systems using eigenvalue analysis or Laplace transform method. But both the methods have limitations, and as of now there are no methods for solving \(n \times n\)-order linear FDEs. In the present investigation, the issues of such difficulties are addressed, and the exact solutions of linear \(2 \times 2\)-order linear FDEs are presented by Laplace transform. We are unable to provide the exact solutions of such system of order \(n \times n\) by Laplace transform. To overcome this, we provide a new and elegant approach to find the approximate solutions of \(n \times n\)-order linear FDEs with the help of residual power series (RPS) method. The results thus obtained are verified by providing numerous examples.     

Investigating the topology of interacting networks

Network theory provides various tools for investigating the structural or functional topology of many complex systems found in nature, technology and society. Nevertheless, it has recently been realised that a considerable number of systems of interest should be treated, more appropriately, as interacting networks or networks of networks. Here we introduce a novel graph-theoretical framework for studying the interaction structure between subnetworks embedded within a complex network of networks. This framework allows us to quantify the structural role of single vertices or whole subnetworks with respect to the interaction of a pair of subnetworks on local, mesoscopic and global topological scales. Climate networks have recently been shown to be a powerful tool for the analysis of climatological data. Applying the general framework for studying interacting networks, we introduce coupled climate subnetworks to represent and investigate the topology of statistical relationships between the fields of distinct climatological variables. Using coupled climate subnetworks to investigate the terrestrial atmosphere’s three-dimensional geopotential height field uncovers known as well as interesting novel features of the atmosphere’s vertical stratification and general circulation. Specifically, the new measure “cross-betweenness” identifies regions which are particularly important for mediating vertical wind field interactions. The promising results obtained by following the coupled climate subnetwork approach present a first step towards an improved understanding of the Earth system and its complex interacting components from a network perspective.     

Surface modification and characterization of Jordanian kaolinite: Application for lead removal from aqueous solutions

Kaolinite clay was tested for removal of lead ions from aqueous solution. This clay was washed with sulfuric acid solution followed by chemical surface modification using 3-chloropropyltriethoxysilane and sodium hydroxide. XRF results showed that silica to alumina ratio was 2.8:1 for the treated sample compared to 1.6:1 for the raw one.XRD analysis displayed different distinct kaolinite and quartz peaks before treatment while kaolinite peaks were diminished after the treatment. SEM morphology indicated that the raw kaolinite appears as plate structure with no local pores on the plates. However, after treatment the surface was found to have micropores.Different adsorption isotherm models were applied to the experimental data and found that Shawabkeh-Tutunji equation best fit these data adequately. It was also found that chemisorption took place at the surface of the modified kaolinite with maximum adsorption capacity of 54.35 mg/g.