Crystallization of ZBLAN Glass

The glass transition, onset crystallization, solidus, and liquidus temperatures of a ZBLAN glass have been measured by differential thermal analysis in a sealed Pt ampoule. The onset crystallization was observed at 335°C for a powdered glass, while for a monolithic glass, prepared by in situ quenching in the Pt capsule, the onset crystallization was observed at 395°C, 135°C higher than T _g. Surface-induced heterogeneous nucleation is therefore proposed to be important for the crystallization of ZBLAN glasses. The solidus temperature was observed at 452°C, about 10°C lower than reported for the subsystem ZrF₄–BaF₂–NaF.     

4‐Alkylated Silver–N‐Heterocyclic Carbene (NHC) Complexes with Cytotoxic Effects in Leukemia Cells

Computational chemistry has shown that backbone‐alkylated imidazoles ought to be efficient ligands for transition metal catalysts with improved carbene‐to‐metal donation. In this work, such alkylated imidazoles were synthesized and complexed with silver(I) by means of an eight/nine‐step synthetic pathway we devised to access a new class of biologically active silver complexes. The synthesis involves selective iodination of the imidazole backbone, followed by Sonogashira coupling to replace the backbone iodine. The installed alkyne moiety is then subjected to reductive hydrogenation with Pearlman’s catalyst. The imidazole N1 atom is arylated by the palladium‐catalyzed Buchwald N‐arylation method. The imidazole N3 position was then methylated with methyl iodine, whereupon the synthesis was terminated by complexation of the imidazolium salt with silver(I) oxide. The synthetic pathway provided an overall yield of ≈20 %. The resulting complexes were tested in vitro against HL60 and MOLM‐13 leukemic cells, two human‐derived cell lines that model acute myeloid leukemia. The most active compounds exhibiting low IC₅₀ values of 14 and 27 μM , against HL60 and MOLM‐13 cells, respectively. The imidazole side chain was found to be essential for high cytotoxicity, as the imidazole complex bearing a C₇ side chain at the 4‐position was four‐ to sixfold more potent than the corresponding imidazole elaborated with a methyl group.     

Eliciting security requirements and tracing them to design: an integration of Common Criteria, heuristics, and UMLsec

Building secure systems is difficult for many reasons. This paper deals with two of the main challenges: (i) the lack of security expertise in development teams and (ii) the inadequacy of existing methodologies to support developers who are not security experts. The security standard ISO 14508 Common Criteria (CC) together with secure design techniques such as UMLsec can provide the security expertise, knowledge, and guidelines that are needed. However, security expertise and guidelines are not stated explicitly in the CC. They are rather phrased in security domain terminology and difficult to understand for developers. This means that some general security and secure design expertise are required to fully take advantage of the CC and UMLsec. In addition, there is the problem of tracing security requirements and objectives into solution design, which is needed for proof of requirements fulfilment. This paper describes a security requirements engineering methodology called SecReq. SecReq combines three techniques: the CC, the heuristic requirements editor HeRA, and UMLsec. SecReq makes systematic use of the security engineering knowledge contained in the CC and UMLsec, as well as security-related heuristics in the HeRA tool. The integrated SecReq method supports early detection of security-related issues (HeRA), their systematic refinement guided by the CC, and the ability to trace security requirements into UML design models. A feedback loop helps reusing experience within SecReq and turns the approach into an iterative process for the secure system life-cycle, also in the presence of system evolution.     

Subcritical drying of silica gels

Silica aerogel is a sol-gel prepared material characterized by high porosity and large inner surface area. Aerogels can be prepared with a high transparency and low thermal conductivity, giving a material excellent for application as transparent thermal insulator. The traditional route to prepare silica aerogels is by formation of an alcogel by hydrolysis and condensation of silicon alkoxides followed by supercritical drying in an autoclave at high pressure (–100 atm). Unfortunately, this process is expensive and might be dangerous, so drying methods have been developed that operate under ambient conditions. In previous work, we have shown that gels can be strengthened and stiffened by providing new monomers to the alcogel giving xerogels with similar properties as aerogels by drying at ambient pressure (porosity up to 90%). This method of obtaining ambient pressure dried aerogels will be described and special emphasis will be given on the effect of the initial gel structure on the preparation of the xerogels.     

Enhancing security requirements engineering by organizational learning

More and more software projects today are security-related in one way or the other. Requirements engineers without expertise in security are at risk of overlooking security requirements, which often leads to security vulnerabilities that can later be exploited in practice. Identifying security-relevant requirements is labor-intensive and error-prone. In order to facilitate the security requirements elicitation process, we present an approach supporting organizational learning on security requirements by establishing company-wide experience resources and a socio-technical network to benefit from them. The approach is based on modeling the flow of requirements and related experiences. Based on those models, we enable people to exchange experiences about security-relevant requirements while they write and discuss project requirements. At the same time, the approach enables participating stakeholders to learn while they write requirements. This can increase security awareness and facilitate learning on both individual and organizational levels. As a basis for our approach, we introduce heuristic assistant tools. They support reuse of existing experiences that are relevant for security. In particular, they include Bayesian classifiers that issue a warning automatically when new requirements seem to be security-relevant. Our results indicate that this is feasible, in particular if the classifier is trained with domain-specific data and documents from previous projects. We show how the ability to identify security-relevant requirements can be improved using this approach. We illustrate our approach by providing a step-by-step example of how we improved the security requirements engineering process at the European Telecommunications Standards Institute (ETSI) and report on experiences made in this application.     

Groundwater Contamination from Rural Pit Latrines: Examples from Siberia and Kosova

New hydrogeochemical data from Kosova and southern Siberia agree with previous studies from Botswana and Moldova in suggesting that high densities of pit latrines (and other domestic pollution sources) in rural villages can result in contamination of potable groundwater supplies by microbes and nitrate. Concentrations in excess of 100 mg/l nitrate have been recorded in each of these areas, at which levels small children may be endangered by methaemoglobinaemia. The sanitation and water-supply conditions are believed to be typical of large areas of Eastern Europe and the former Soviet Union. It is likely that poor sanitation and conflict with potable-water supplies are among the main sources of environmental risk to populations in these areas, rather than the industrial and military contamination upon which so many international collaborative programmes have focused.     

Stability of SrFeO3-Based Materials in H2O/CO2-Containing Atmospheres at High Temperatures and Pressures

The chemical stability of SrFeO₃-based perovskites in H₂O- and CO₂-containing atmospheres at high temperatures and pressures has been examined. The extent of reaction as a function of p CO₂, p H₂O, temperature, and time has been determined. Either strontium carbonate or Sr(OH)₂·H₂O was observed on sample surfaces after exposure. Observation of two different reaction-rate behaviors could be explained by the formation of different products. The stability of the perovskite has been found to increase when the activity of Sr is decreased. Chemical stability in H₂O/CO₂ is important to understand in order to use these membrane materials for syngas production.