Economics of the oxidative coupling of methane as an add-on unit for naphtha cracking

The feasibility of methane coupling as an add-on unit to a naphtha cracker was studied. The existing cold box was used for separation of ethylene and unconverted methane, but arrangements were made for separation of the coupling by-products. The cracker's methane was used as a feedstock. The concept is technically and economically feasible at spring 1992 prices, provided the catalyst meets the assumed 30% conversion and 80% C₂ selectivity.     

Evaluation of the Premi Test Salmonella, a commercial low-density DNA microarray system intended for routine identification and typing of Salmonella enterica

A new commercial system based on genetic profiling and aimed at identifying Salmonella enterica serovars was evaluated by comparing its performance with classical serotyping on 443 strains. Within 62 serovars represented, 60 gave unique genetic profiles while 2 were undistinguishable. Results were obtained within 8 h, were reproducible and clear-cut. The system allowed single-tube processing of the samples and required no peculiar technical skill. It showed interesting potential for routine laboratory testing.     

From thickness dependent exit waves to projected potential: Thickness derivative approach

In HREM, due to multiple scattering, the exit wave of the object is nonlinear thickness dependent so that there is no one-to-one relation between object structure and the exit wave. This feature hampers the direct retrieval of structural information from exit waves. In this paper we discuss the possibility to restore the object structure in a direct way using exit waves of different thicknesses. It is theoretically shown that the amplitude of the thickness derivative exit wave |∂ψ/∂z| may directly reflect the project potential in a simple way. Image simulations show that it can be applied to restore the projected potential.     

Ion beam nitriding of high purity iron surfaces

Ion beam nitriding of iron by N₂⁺ ions of medium energy (1–10 keV) was investigated. This nitriding technique leads to the formation of layer structures quite similar to those obtained by other methods but compared with these the nitride layers obtained are pore free. Results consisting of the surface topography of the samples, the stages of nitride coverage, the formation of different nitrides and their precipitation depth as well as microhardness and electrochemical corrosive behaviour are presented and discussed.     

Preparation of hard coatings by ion beam methods

The activated growth of surface coatings under the influence of impinging ionized species has been investigated by beam techniques operating in high vacuum. A brief survey of the operating parameters using one or several beam bundles of ions or neutrals is given. Some results and problems are discussed in connection with the following processes: (1) nitriding of iron by low energy ion bombardment; (2) dual beam synthesis of silicon nitride and of hard carbon; (3) preparation of chromium-carbon and of hard carbon layers by ion beam plating from organic vapours. It is concluded that beam techniques can contribute to a better understanding of activated film growth at high rates of deposition. Moreover, ion beam methods offer interesting prospects for the preparation of special layer structures, particularly unusual film phases such as the hard i-carbon.     

Distortion of DNA Origami on Graphene Imaged with Advanced TEM Techniques

While graphene may appear to be the ultimate support membrane for transmission electron microscopy (TEM) imaging of DNA nanostructures, very little is known if it poses an advantage over conventional carbon supports in terms of resolution and contrast. Microscopic investigations are carried out on DNA origami nanoplates that are supported onto freestanding graphene, using advanced TEM techniques, including a new dark‐field technique that is recently developed in our lab. TEM images of stained and unstained DNA origami are presented with high contrast on both graphene and amorphous carbon membranes. On graphene, the images of the origami plates show severe unwanted distortions, where the rectangular shape of the nanoplates is significantly distorted. From a number of comparative control experiments, it is demonstrated that neither staining agents, nor screening ions, nor the level of electron‐beam irradiation cause this distortion. Instead, it is suggested that origami nanoplates are distorted due to hydrophobic interaction of the DNA bases with graphene upon adsorption of the DNA origami nanoplates.     

Fostering transfer of websearchers’ evaluation skills: A field test of two transfer theories

Transfer of complex cognitive skills is important when stimulating students to become life long learners. An example of a complex cognitive skill is the skill of evaluating results, information and source while solving information problems using the WWW. Especially the knowledge and use of evaluation criteria is crucial in this matter. Two educational programs to foster this skill in students were designed and evaluated. The programs were based on two different transfer theories. The first program was based on the theory that transfer of complex cognitive skills is fostered through the development of a rich knowledge structure. The second program is based on the theory that transfer is fostered by paying explicit attention to the various steps that have to be taken in a problem solving process. Effects of the two programs on increase in knowledge and use of criteria and degree of transfer were determined. Results show that both programs enable transfer.     

Checking Finite Traces using Alternating Automata

We present three algorithms to check at runtime whether a reactive program satisfies a temporal specification, expressed by a future linear-time temporal logic formula. The three methods are all based on alternating automata, but traverse the automaton in different ways: depth-first, breadth-first, and backwards, respectively. All three methods have been implemented and experimental results are presented. We outline an extension to these algorithms that is applicable to LTL formulas containing both past and future operators.     

Cross-section transmission electron microscopy characterization of the near-surface structure of medical Nitinol superelastic tubing

The application of Nitinol in a wide variety of medical implants is progressively increasing because of its unique mechanical properties, durability and biocompatibility. However, as Nitinol consists of about 50 at.% of toxic Ni, certain applications are still hindered by the concern of free Ni release in the surrounding tissue. The latter is controlled by the structure of near-surface layers and can be strongly affected by various surface treatments. A proper application of advanced cross-section sample preparation techniques allows us to characterize the Nitinol near-surface structure down to the nanoscale by means of transmission electron microscopy (TEM). Elemental maps of the Ti, O and Ni distribution, concentration profiles, quantification of composition as well as atomic resolution images at the surface of a Nitinol tubing are presented and the results obtained with different sample preparation and analytical characterization techniques are compared. In addition to a strong decrease of Ni towards the surface of the oxide layer and a Ti depleted layer underneath the oxide, also a possible transformation from TiO to TiO₂ is documented.     

Local Knowledge Spillovers and Development: An Exploration of the Software Cluster in Uruguay

The paper contributes to the understanding of the nature of local knowledge spillovers and their importance for innovation in clusters in developing countries. Using detailed primary data about a cluster of software firms in Montevideo, Uruguay, the paper finds plenty of evidence of the existence of pure unintentional knowledge spillovers. In addition, it supports previous theoretical studies that have contended that there are also many knowledge flows that are to some degree produced purposively by local parties—these flows can be placed somewhere in between pure spillovers and pure market transactions. While the respondents themselves place most value on knowledge flows that are more or less purposively co-produced with customer transactions, a more objective statistical analysis shows that good product/service-innovation performance is associated with intensive use of flows with more pronounced spillover characteristics. The respondents possibly underrate the latter because of their invisibility and spontaneous nature. Heavy use of knowledge flows lying close to the market-transaction side of the spectrum is found to be associated with relatively advanced organizational capability, but not with product innovation. Overall, the findings point towards the relevance of cluster-based policies to promote innovation in a less developed country context. Various policy measures to stimulate the local circulation of knowledge are suggested.