Author Response to the Comment by Popov on “Contact Mechanics for Randomly Rough Surfaces: On the Validity of the Method of Reduction of Dimensionality”

Tribology Letters - In a recent paper, Persson (Tribol Lett, 2015. doi: 10.1007/s11249-015-0498-1 ) has criticized the validity of the method of dimensionality reduction in contact mechanics....     

Time trends of selected persistent organic pollutants in lake sediments from Greenland

Sediments from seven lakes in West Greenland were used as natural archives to study past and present levels of PCBs (polychlorinated biphenyls, tri- to decachlorinated), tetra-BDE #47 (2,2',4,4'-bromodiphenyl ether), chlordane (cis- and trans-octachlordane) and HxCBz (hexachlorobenzene). The concentrations found are lower than or comparable to concentrations found in sediments from other Arctic regions and one to 2 orders of magnitude lower than concentrations typically found in sediments at lower latitudes. The observed temporal trends (direct and indirect dating) show a decreasing total PCB concentration. Even though local contamination sources exist, the POP deposition in the studied area is most likely a result from long-range transport. The hypothesis about "cold condensation" suggests a latitudinal fractionation to occur between different volatile compounds during the transport toward the pole. In this study a time delay in the deposition for the low-chlorinated PCBs (tri- and tetrachlorinated), compared to their emission histories and compared to higher chlorinated PCBs, was indicated. Although very low tetra-BDE #47 concentrations are observed in this study, there are indications for an increasing concentration in recent sediment layers that may reflect increasing environmental concentrations at lower latitudes. The investigated pesticides are still in use at lower latitudes, however neither chlordane nor HxCBz show any distinct temporal trend of increasing or decreasing concentration toward the sediment surface.     

Chemical images

Chemical sensors can be used to generate a vast amount of information about the emissions from bio- and chemical processes, from food and bacteria and from a number of products. These emissions are either wanted or should be avoided. Wolfgang Göpel was one of those who recognized early the large potential of chemical sensor arrays and different modes of operation of a given sensor. We describe how large area field effect devices, with catalytic metal gates, can be used for the construction of a response image of a gaseous emission. More specifically, we discuss the new possibilities obtained through the use of catalytic metals with a gradient in thickness. Some basic features of such sensing surfaces are demonstrated and, finally, time-dependent response images from aging meat are used to demonstrate the potential of the method used. It is based on a scanning light pulse technique (SLPT) which measures local polarization or work function changes in two dimensions and, e.g. a sensing surface consisting of bands of different catalytic metals with a gradient in thickness.     

HOT TEST OF A TALSPEAK PROCEDURE FOR SEPARATION OF ACTINIDES AND LANTHANIDES USING RECIRCULATING DTPA-LACTIC ACID SOLUTION

Abstract

Results are reported from a hot test of a TALSPEAK type process for separation of higher actinides (Am, Cm) from lanthanides. Actinides and lanthanides are extracted by 1 M HDEHP and separated by selective strip of the actinides, using a mixture of DTPA and lactic acid (reversed TALSPEAK process). In order to minimize the generation of secondary waste, a procedure using recirculating DTPA-Lactic acid solution has been developed. A separation factor between Am and Eu of 132 was achieved. In regard to separations of Am and Cm from commercial HLLW, this corresponds to 1.5 % of the lanthanide group remaining with the actlnldes. The loss of Am was about 0.2 %.     

Supporting the discovery and labeling of non-taxonomic relationships in ontology learning

Ontology learning (OL) from texts has been suggested as a technology that helps to reduce the bottleneck of knowledge acquisition in the construction of domain ontologies. In this learning process, the discovery, and possibly also labeling, of non-taxonomic relationships has been identified as one of the most difficult and often neglected problems. In this paper, we propose a technique that addresses this issue by analyzing a domain text corpus to extract verbs frequently applied for linking certain pairs of concepts. Integrated in an ontology building process, this technique aims to reduce the work-load of knowledge engineers and domain experts by suggesting candidate relationships that might become part of the ontology as well as prospective labels for them.     

The first mover and the challenger: The relationship between two journals in organization research

Many new journals are started in response to increasing specialization and limited space in existing journals. In this study two journals in organization research are studied,Administrative Science Quarterly as the first mover in the field andOrganization Studies as the challenger. It is shown that the new journal gradually differ from the old in terms of the national origin of its authors as well as the documents cited. It is concluded that the scientific journal market may not mirror the copy-cat behaviour found among newspapers or companies in other markets.     

Squeezing Molecularly Thin Alkane Lubrication Films: Layering Transitions and Wear

The properties of alkane lubricants confined between two approaching solids are investigated by a model that accounts for the curvature and the elastic properties of the solid surfaces. We consider linear alkane molecules of different chain lengths, C₃H₈, C₄H₁₀, C₈H₁₈, C₉H₂₀, C₁₀H₂₂, C₁₂H₂₆, and C₁₄H₃₀ confined between smooth gold surfaces. We observe well-defined molecular layers develop in the lubricant film when the width of the film is of the order of a few atomic diameters. An external squeezing-pressure induces discontinuous changes in the number n of lubricant layers. We find that with increasing alkane chain length, the transition from n to n - 1 layers occurs at higher pressure, as expected based on the increasing wettability with increasing chain length. We obtain good correlation between our theoretical results and wear experiments.     

Boron implantation and epitaxial regrowth studies of 6H SiC

Implantation of B has been performed into an epitaxially grown layer of 6H SiC, at two different B concentrations, 2×10¹⁶ cm⁻³ and 2×10¹⁸ cm⁻³. Subsequently, an epitaxial layer was regrown on the B implanted layer. The samples were investigated by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS). In the highly B-doped layers plate-like defects were found, associated with large strain fields, and an increased B concentration. These defects were stable at the originally implanted region during regrowth and at anneal temperatures up to 1700°C. In the samples implanted with the lower B concentration, no crystal defects could be detected by TEM. No threading dislocations or other defects were observed in the regrown epitaxial layer, which shows the possibility to grow a layer with high crystalline quality on B implanted 6H SiC. By SIMS, it was found that B piles up at the interface to the regrown layer, which could be explained by enhanced diffusion from an increased concentration of point defects created by implantation damage in the region. B is also spread out into the original crystal and in the regrown layer at a concentration of below 2×10¹⁶ cm⁻³, with a diffusion constant estimated to 1.3×10⁻¹² cm²s⁻¹. This diffusion is most probably not driven by implantation damage, but by intrinsic defects in the grown crystal. Our investigation shows that the combination of implantation and subsequent regrowth techniques could be used in SiC for building advanced device structures, with the crystal quality in the regrown layer not being deteriorated by crystal defects in the implanted region. A device process using B implantation and subsequent regrowth could on the other hand be limited by the diffusion of B.     

Major oil exporters may profit rather than lose, in a carbon-constrained world

The Organization of Petroleum Exporting Countries (OPEC) claims compensation for losses in expected oil export revenues due to CO₂ mitigation measures in developing countries. These losses are expected for two primary reasons: a reduction in the consumption of oil in importing countries and a reduction in the producer price of oil (taxation in an importing country implies a transfer of rents from producers to consumers). So far, most studies have focused on these two mechanisms and corroborated that revenue losses for OPEC are to be expected. However, there are also mechanisms that may be expected to raise the price of oil products. In a cost-effective regime for dealing with climate change, i.e., a regime in which all or most countries participate and in which the same carbon price is applied on all carbon-emitting activities, the cost of using unconventional oil, or synthetic diesel from coal, will increase even more than the cost of using conventional oil. Given that reserves of conventional oil are expected to dwindle over time, heavy oils and coal to liquids might set the long-run price for liquid fuels, which means that the price of oil would increase beyond the carbon fee; i.e., the rent on conventional oil would increase. We use an energy-economic optimization model to analyze these three mechanisms. We find that the net present value of OPEC revenue from conventional oil increases slightly (at most by 4 percent) with a global CO₂ restriction regime. We also consider conditions under which this result does not hold.     

Molecular ordering of interfacially localized tryptophan analogs in ester- and ether-lipid bilayers studied by 2H-NMR

Perdeuterated indole-d6 and N-methylated indole-d6 were solubilized in lamellar liquid crystalline phases composed of either 1,2-diacyl-glycero-3-phosphocholine (14:0)/water or 1,2-dialkyl-glycero-3-phosphocholine(14:0/water. The molecular ordering of the tryptophan analogs was determined from deuteron quadrupole splittings observed in 2H-NMR spectra on macroscopically aligned lipid bilayers. NMR spectra were recorded with the bilayers oriented perpendicular to or parallel with the external magnetic field, and the values of the splittings differed by a factor of 2 between these distinct orientations, indicating fast rotational motion of the molecules about an axis parallel to the bilayer normal. In all cases the splittings were found to decrease with increasing temperature. Relatively large splittings were observed in all systems, demonstrating that the tryptophans partition into a highly anisotropic environment. Solubilization most likely occurs at the lipid/water interface, as indicated by 1H-NMR chemical shift studies. The 2H-NMR spectra obtained for each analog were found to be rather similar in ester and ether lipids, but with smaller splittings in the ether lipid under similar conditions. The difference was slightly less for the indole molecule. Furthermore, in both lipid systems the positions of the splittings from indole were different from those of N-methyl indole. The results suggest that 1) the tryptophan analogs are solubilized in the interfacial region of the lipid bilayer, 2) the behavior may be modulated by hydrogen bonding in the case of indole, and 3) hydrogen bonding with the lipid carbonyl groups is not likely to play a major role in the solubilization of single indole molecules in the ester lipid bilayer interface.