Isolated Cu2+ ions: active sites for selective catalytic reduction of NO

Cu chabazite catalysts show remarkable low temperature activity in selective catalytic reduction (SCR) of NO. This high activity is due to the unique character of the zeolite framework that allows only the presence of one type of isolated mononuclear Cu(2+) species. These Cu(2+) species are the active sites for SCR.     

Lactose oxidation kinetics with oxygen in catalyst-solution-gas three-phase system with simultaneous electrical potential measurement of supported gold catalyst

Lactose oxidation kinetics was studied on an supported gold catalyst with simultaneous control of catalyst potential. The experimental data were described well by the suggested mechanism and kinetic model of this reaction.     

Characterization of Transfer Functions of Pritchard–Salamon or Other Realizations with a Bounded Input or Output Operator

We show that the transfer functions that have a (continuoustime) well-posed realization with a bounded input operator are exactly those that are strong-H² (plus constant feedthrough) over some right half-plane. The dual condition holds iff the transfer function has a realization with a bounded output operator. Both conditions hold iff the transfer function has a Pritchard–Salamon (PS) realization. A state-space variant of the PS result was proved already in [3], under the additional assumption that the weighting pattern (or impulse response) is a function (whose values are bounded operators). We illustrate by an example that this does not cover all PS systems, not even if the input and output spaces are separable.     

Behavior of thin rectangular ANCF shell elements in various mesh configurations

The absolute nodal coordinate formulation (ANCF) is characterized by being developed specifically for dynamic analysis of large deformation problems. The objective of the study is to investigate how the shape of the initial mesh configuration influences the obtained numerical solution. After a thorough review of three available formulations, they are used in three different convergence studies. Initially a reference study is conducted to determine how the ANCF performs in an uniform and rectangular mesh. Subsequently, the ANCF methods sensitivity to irregular mesh is investigated and finally, the ability of the ANCF method to describe curved structures is evaluated. This study concludes that thin ANCF shell elements are sensitive to both the initial shape and their loading condition. Furthermore, both the initial configuration and the loading condition affect how the ANCF-based models converge. It is suggested that models containing thin ANCF shell elements are subjected to extensive validation studies, before they are used in a design process.     

A study of contact methods in the application of large deformation dynamics in self-contact beam

Nonlinear Dynamics - This paper introduces a procedure in the field of computational contact mechanics to analyze contact dynamics of beams undergoing large overall motion with large deformations...     

Ultrastructural element localization by EDXS in Empetrum nigrum

Empetrum nigrum L. is one of the few species growing on highly polluted areas in the northern boreal forests and it accumulates considerable amounts of heavy metals especially in its older stems. Previous-year stems of Empetrum nigrum were collected from two different sites located at distances of 0.5km (highly contaminated) and 8km (low contaminated) from a Cu--Ni smelter at Harjavalta, SW Finland. The element (Al, As, Cu, Fe, Mn, Zn, Ca, K, P, S, Mg, Na) localization was performed by energy-dispersive X-ray spectroscopy (EDXS) after cryofixation, freeze-drying and pressure infiltration of the material. The results showed higher levels of Cu, As and Fe in cell compartments of E. nigrum close to the smelter than at further distance. The Al and Zn levels, in contrast, showed no clear differences between the sites. Cu was distributed homogeneously in the tissue and occurred in vacuoles, cytoplasm, cell walls as well as in lumens of the vascular tissue. The higher amounts of As were localized in the outer regions of the stem cross-section and the amounts were higher in the primary cell walls of living (ray cells, phloem) than dead cells (xylem, sclereids). Ray cells, phloem and sclereids had elevated Fe amounts compared to the other tissues in the contaminated stem samples but owing to the high variation between the replicates, no significant differences were found. Based on the rather homogeneous localization of Cu, As and Fe in the living tissue and increased levels of Cu, As and Fe in vacuoles, cell walls and cytoplasm near the smelter, it seems that more than one specific mechanism contribute to the heavy metal tolerance of E. nigrum. Macronutrients did not show clear differences between the two distances or connection to heavy metal localization. Neither the role of complexing agents in heavy metal tolerance in the cytoplasm or vacuoles could be shown by this study. Because of the more frequent localization of electron dense phenolic material in the polluted samples, it might also have a function in the heavy metal tolerance of E. nigrum.     

New bonding modes of gas-phase deposited gamma-aminopropyltriethoxysilane on silica studied by 29Si CP/MAS NMR

Besides the well-known reaction between the ethoxy groups of the silane end of the gamma-aminopropyltriethoxysilane (APTS) molecule and the silanols of silica, the amino ends of APTS molecules were observed to react in the gas phase with ethoxy groups of other APTS molecules and silanols of silica at elevated temperatures on the silica surface, dehydroxylated at 600 degrees C, forming Si-N linkages, as established by 29Si CP/MAS NMR.     

Iron Atoms in Cr–Mn Antiferromagnetic Matrix

Hyperfine Interactions - The results of the Mössbauer effect measurements on bcc Cr rich Cr-Fe-Mn alloys in temperature range 12–296 K in zero- and in applied magnetic fields are...     

Influence of Additives on Capillary Absorption of Aqueous Solutions into Asymmetric Porous Ceramic Substrate

The effect of divalent and trivalent salts (CaCl(2), CaBr(2), MgCl(2), MgBr(2), LaCl(3), CeCl(3), La(NO(3))(3), and Ce(NO(3))(3)) on the micelle formation in C(8)-lecithin solutions was investigated using the techniques of static and dynamic light scattering. The critical micelle concentration (cmc), mean hydrodynamic radius (R(h)), gyration radius (R(g)), and weight-average molecular weight of the micelles were measured as functions of salt identity and concentration, amphiphile concentration, and temperature. It was found that the micelles in solutions of magnesium are less likely to form and less stable; their standard enthalpy is less exothermic as the ionic strength increases. On the contrary, the micelles in solutions of calcium and trivalent salts form easily, and are more stable; their standard enthalpy is also more exothermic as the ionic strength increases. Based on our model of the Gibb's free energy for the salt-added solutions, we obtained the following formula for the effect of salts on cmc: ln(cmc)'=ln(cmc)+k(1) I(1/2)+k(2)I, where (cmc)' and (cmc) are the critical micelle concentrations in salt-added and salt-free solutions, respectively, I is the ionic strength, and k(1) and k(2) are the salt effect parameters. The agreement between the formula and the experimental data for all the systems under study shows that the formula is more satisfactory than those suggested previously by other authors in describing the effect of salts on the cmc in the micellar solutions of not only zwitterionic but also nonionic surfactants. Copyright 2001 Academic Press.