Crystal and molecular structure, and P N.M.R. characteristics of di-μ-chlorodi(propionyl)bis(dimethylphenylphosphine)diplatinum(III). Trans-influence of ligands in binuclear complexes

The known complex, $\text{trans}$-(η-C₅H₅)₂Rh₂(CO)₂(CF₃C₂CF₃) is formed in high yield from (η-C₅H₅)Rh(CO)₂ and CF₃FCCF₃ at 100°. The less stable $\text{cis}$-isomer of the complex is obtained in low yield from the same reaction. The infrared, ¹H, ¹⁹F and ¹³C NMR spectra of the two isomers are compared. The $\text{trans}$-isomer undergoes CO scrambling in solution at room temperature, and the variable temperature ¹³C NMR spectra are consistent with a pairwise bridge opening and closing mechanism. The mechanism is extended to account for the isomerization of $\text{cis}$ to $\text{trans}$ isomer, whihc has a half-life of 12 h at room temperature. The ¹³C spectrum indicates that the $\text{cis}$-isomer is static in solution at room temperature. The $\text{trans}$-isomer is reversibly protonated by protonic acids, and BF₄^? and PF₆^? salts of the protonated species can be isolated. The spectroscopic properties of these salts are consistent with protonation at one of the alkynyl-carbons, but it is not possible to distinguish between two alternative structures for the complex cation.Treatment of (η-C₅H₅)₂Rh₂(CO)₂(CF₃C₂CF₃) with (η-C₅H₅)Rh(CO)₂ gives the trinuclear complex (η-C₅H₅)₃Rh₃(CO)(CF₃C₂CF₃) in 80% yield. The analogoug but-2-yne complex is formed from (η-C₅H₅)₃Rh₃(CO)₃ and MeCCMe. The infrared, ¹H, ¹⁹F and ¹³C NMR spectra indicate that the hexafluorobut-2-yne complex exists in two different structural arrangements in solution. One has an edge bridging, and the other a face bridging carbonyl. The proportion of the isomers is affected by the solvent polarity. The spectra of the but-2-yne complex indicate it is fluxional at room temperature, and has a face bridging structure in solution regardless of the polarity of the solvent. Reversible protonation of the hexafluorobut-2-yne complex occurs in protonic acids, and the salt [(η-C₅H₅)₃Rh₃(CO)(CF₃C₂CF₃)H]⁺[BF₄]^?,H₂O can be isolated. The spectroscopic properties of this complex are consistent with a structure incorporating an edge-bridging carbonyl, and probably, an edge-bridging hydride ligand.     

Stable isotope composition of the meteoric precipitation in Croatia

The precipitation is the input into the water system. Its stable isotope composition has to be known for the proper use and management of water resources. Croatia is not well represented in the Global Network of Isotopes in Precipitation (GNIP) database, and the geomorphology of the country causes specific local conditions. Therefore, at the Stable Isotope Laboratory (SILab), Rijeka, we monitor the stable isotope composition (δ¹⁸O, δ²H) of precipitation. Since δ¹⁸O and δ²H are well correlated, we concentrate the discussion on the δ¹⁸O distribution. Together with GNIP, our database contains 40 stations in Croatia and in the neighbouring countries. Their different latitudes, longitudes and altitudes give information of great detail, including the influence of the topographic structure on the precipitation in the south-eastern part of Europe, as well as the complex interplay of the different climate conditions in the area. Within a few hundred kilometres, the stable isotope values display a significant change from the maritime character in the south (mean δ¹⁸O around?6 to?8%‰) to the continental behaviour in the north (mean δ¹⁸O around?8 to?11%‰). Depending on the location, the mean δ¹⁸O values vary with altitude at a rate of approximately?0.2%‰/100 m and?0.4%‰/100 m, respectively. Also the deuterium excess has been found to depend on location and altitude. The data are being used to construct a δ¹⁸O map for the entire area.     

Raman Spectroscopic Signature of Ectoine Conformations in Bulk Solution and Crystalline State

Recent crystallographic results revealed conformational changes of zwitterionic ectoine upon hydration. By means of confocal Raman spectroscopy and density functional theory calculations, we present a detailed study of this transformation process as part of a Fermi resonance analysis. The corresponding findings highlight that all resonant couplings are lifted upon exposure to water vapor as a consequence of molecular binding processes. The importance of the involved molecular groups for water binding and conformational changes upon hydration is discussed. Our approach further shows that the underlying rapid process can be reversed by carbon dioxide saturated atmospheres. For the first time, we also confirm that the conformational state of ectoine in aqueous bulk solution coincides with crystalline ectoine in its dihydrate state, thereby highlighting the important role of a few bound water molecules.     

Bounds on the order of cross characteristic subgroups of the finite simple groups of Lie type

Let and be finite groups of Lie type and and be coprime. If is embedded in , then the Landazuri-Seitz-Zalesskii theorem implies that is small relative to . We formalize this observation and illustrate how it can be used with some applications.

     

Indirect optical crosstalk reduction by highly-doped backside layer in single-photon avalanche diode arrays

A method of reducing indirect optical crosstalk in single-photon avalanche diode arrays is investigated by TCAD simulations. The reduction is accomplished by taking advantage of an enhanced optical absorption in a highly-doped Si layer on the backside of the wafer. A simulation environment was developed to give information about optical crosstalk by incorporating the experimental optical constants of the materials constituting the crosstalk-reduction layer. It is shown that the indirect optical crosstalk is greatly reduced by increasing the thickness and doping of the layer. A crosstalk reduction of 5 orders of magnitude is gained with addition of 1-μm-thick \(\hbox {PureB}/\upalpha \hbox {-Si}\) stack for the array processed on a p-type substrate, while the same reduction is achieved with a 1-μm-thick highly-doped Si layer (As, \(1.1\times 10^{20}\, \hbox {cm}^{-3}\)) for an array processed on an n-type substrate.     

Quick method for determination of equilibrium temperature of calcium carbonate dissociation

A quick method for determination of equilibrium temperature of high temperature reactions, which is inexpensive and suitable for small industrial laboratories, is reported. Reaction of high temperature dissociation of calcium carbonate is used as example for quick method application. The method is based on calorimetric measurement, Hess Law, and thermodynamic calculations. The calibrated calorimeter is used to determine enthalpy change for reactions CaCO₃(s)?+?HCl(l), Ca(s)?+?2HCl(l), and CaO(s)?+?2HCl(l). By application of Hess??s energy cycle, enthalpies of formation of calcium carbonate and calcium oxide were determined. Acquired results were used to calculate enthalpy change for carbonate dissociation reaction. Calculated enthalpy change value was used for free energy change in dependence of temperature and also for equilibrium constant in dependence of temperature calculation using equations derived from basic thermodynamic equations. Using this method, equilibrium temperature for calcium carbonate dissociation reaction is found to be equal to 1154.14?K, which confirms accuracy of the method.     

Thermal characterization of biomass smoke particles

In this paper we present results on characterization of filter-collected redwood (Sequoia sempevirens)-needle and eucalyptus smoke particles by thermal, optical, and solvent extraction methods. Our results show that black carbon and a significant fraction of organic carbon in biomass smoke particles have similar volatility and combustion temperatures. Combustion temperatures of both black carbon and this organic fraction critically depend on the concentrations of common constituents of biomass smoke such as Na and K. These species are also known to catalyze the combustion and therefore lower the combustion temperatures by more than 100 °C. Consequently, thermal methods that rely on a specific temperature to separate organic from black carbon may either underestimate or overestimate the black and organic carbon concentrations, depending on the amounts of Na and K and on the composition and concentration of organic material present in a sample. These results suggest that more than one method must be used to accurately determine the organic and black carbon concentrations in biomass smoke particles.     

Unramified cohomology of alternating groups

We prove vanishing results for the unramified stable cohomology of alternating groups.     

Prioritization of e-learning forms: a multicriteria methodology

Strategic planning of e-learning implementation includes decision making about the most suitable form of implementing e-learning on different levels in an institution. Decision making about e-learning implementation has been covered as consisting of four phases: (1) intelligence, (2) design, (3) choice and (4) implementation. During the Intelligence phase we have precisely identified our central decision problem and have conducted situation analysis. In the Design phase we have developed alternatives and established criteria and subcriteria. The questionnaire about the importance of the advantages and goals of e-learning implementation and about criteria and subcriteria significant for decision making was created. Essential for the survey was use of Croatian e-learning experts that are familiar with higher education (HE) environment. Further, we connected these findings with the results of the factor analysis which was performed on the survey. The results of the factor analysis have served as input in the multicriteria decision model (AHP) that we have developed in the Choice phase. In the implementation phase we have solved the problem of prioritisation of e-learning options with the help of multi-criteria modelling in the process of group decision making. In this article, firstly we will present and analyze the results of the survey. Secondly, the outputs of factor analysis will be stated and compared with the model used in the questionnaire. Finally, the structure of AHP model will be given and the results of the quantitative evaluation of the model will be presented.