An experimental study on the kinetics of leaching for the preparation of a Raney-silver catalyst

A Raney-Ag catalyst was prepared by leaching out aluminium from a Raney Ag-Al alloy with NaOH solution. The kinetics of leaching has been investigated in a stirred-batch-reactor at various temperatures by using alloy particles of different sizes. The kinetic model best fitting the experimental results has been determined. This revised version was published online in June 2006 with corrections to the Cover Date.     

On the Physical Origin of Long-Ranged Fluctuations in Fluids in Thermal Nonequilibrium States

Thermodynamic fluctuations in systems that are in nonequilibrium steady states are always spatially long ranged, in contrast to fluctuations in thermodynamic equilibrium. In the present paper we consider a fluid subjected to a stationary temperature gradient. Two different physical mechanisms have been identified by which the temperature gradient causes long-ranged fluctuations. One cause is the presence of couplings between fluctuating fields. Secondly, spatial variation of the strength of random forces, resulting from the local version of the fluctuation-dissipation theorem, has also been shown to generate long-ranged fluctuations. We evaluate the contributions to the long-ranged temperature fluctuations due to both mechanisms. While the inhomogeneously correlated Langevin noise does lead to long-ranged fluctuations, in practice, they turn out to be negligible as compared to nonequilibrium temperature fluctuations resulting from the coupling between temperature and velocity fluctuations.     

Resolution of Some Open Problems Concerning Multiple Zeta Evaluations of Arbitrary Depth

We prove some new evaluations for multiple polylogarithms of arbitrary depth. The simplest of our results is a multiple zeta evaluation one order of complexity beyond the well-known Broadhurst–Zagier formula. Other results we provide settle three of the remaining outstanding conjectures of Borwein, Bradley, and Broadhurst. A complete treatment of a certain arbitrary depth class of periodic alternating unit Euler sums is also given.     

Separating Classical and Quantum Correlations

We examine to what extent the correlation between two quantum observables at a mixed state can be separated into a classical and a quantum term. The nonunique decomposition of quantum mixed states into pure states makes such a separation ambiguous. We outline this fact by a simple example, which also shows that classical and quantum correlations may cancel each other out.     

Modification of Paving Asphalts with Sulfur

Sulfur dissolved in oil components of asphalt is a binder, filler, and chemical co-reagent at once. The structure of sulfur-extended asphalt depends on its formula and heating temperature. Road pavement based on sulfur-extended asphalt demonstrates higher durability as compared to that with the conventional binders.     

New insights on amorphous silicon-nitride microcavities

All amorphous silicon-nitride planar optical microcavities operating in the visible range have been grown by plasma enhanced chemical vapor deposition. The luminescence intensity of the N-rich silicon-nitride layer from a microcavity with 6 period distributed Bragg reflectors (DBRs) is two order of magnitude higher than that of the luminescent layer without the cavity. Moreover, a strong directionality of the microcavities emission can be observed. Such results can be ascribed to the anisotropic optical density of states induced in the Fabry–Perot structure. The quality factors of the resonators are strictly correlated to the number of periods of the DBRs.     

Study of removal processes of <Superscript>7</Superscript>Be and <Superscript>137</Superscript>Cs from the atmosphere

In order to understand better the way in which radioactive contamination may be transferred from the atmosphere to other ecological compartments it is necessary to obtain information of the deposition mechanisms of radionuclides. Concentration and speciation of ¹³⁷Cs and ⁷Be in the atmospheric aerosol and deposition were studied. The mixed deposition velocities of water-soluble and insoluble ¹³⁷Cs and ⁷Be were determined. The relation between activity concentrations of insoluble ⁷Be in the atmosphere and its amount in deposition was observed. It is supposed that in the deposition process of radiocesium the precipitation plays an important role in scavenging of water-soluble radiocesium by falling raindrops, in contrast to insoluble ¹³⁷Cs where the dry deposition becomes predominant.     

Comment on: “Confined states in two-dimensional flat elliptic quantum dots and elliptic quantum wires” [Physica E 11 (2001) 345]

We argue that the two-dimensional elliptic quantum dot problem with finite barrier cannot be exactly solved, contrary to a recent assertion (van den Broek and Peeters, Physica E 11 (2001) 345. We also prove it explicitly by numerically calculating the correct energy spectrum.     

Microcalorimetric measurements of the metabolic activity by bacteria and fungi in some Brazilian soils amended with different organic matter

The effect of bacterial and fungal activities on organic matter degradation in Brazilian soils was studied by a microcalorimetric method. Bacteria and fungi isolated from tropical soils and added to: Rhodic eutrudox (R), Typic eutrudox (V) and Quartzipsamment (Q) soils amended separately with moisture (control) (A) and 25% of cattle manure (E), municipal refuse compost (L), earthworm casts (H) or 23 μg of trifluralin (T) were investigated. The number of colony forming units in soil suspension was quantified by microscopy and inoculated in respective soil. All processes were measured at intervals of 7 days over a period of 35 days. The exothermic thermal effect (μJ) per cm³ of bacteria or fungi per gram of dry soil, respectively, for each substrate was: [(9±1), (4±1)] RA; [(478±24), (105±5)] RE; [(121±6), (71±4)] RL; [(121±6), (71±4)] RH; [(8±1); (3±1)] RT; [(10±1), (9±1] VA; [(347±17), (261±13)] VE; [(71±4), (28±1)] VL; [(22±1), (33±2)] VH; [(7±1), (10±1)] VT; [(19±1), (12±1)] QA; [(1301±65), (46±2)] QE; [(89±4), (9±1)] QL; [(130±7), (11±1)] QH; [(32±2), (8±1)] QT. The calorimetric values are higher for bacteria than for fungi. In general, the results showed higher activities in the soil amended with cattle manure than with other additives.