SiC-faserverstärkte Titanlegierung Ti 6 Al4 V. Einfluß von TiC- und TiN-Zwischenschichten auf die Reaktionszone

SiC-Fiber Reinforced Ti 6 Al4 V Alloy: Effect of TiC and TiN Interlayers on the Reaction Zone . Processing and properties of SiC-fiber reinforced Ti 6 Al4 V alloys are briefly summarized. In order to avoid the degradation of the SiC-fibers caused by interfacial reactions, TiC and TiN interlayers were incorporated and their influence on the formation of the reaction zone was investigated. The reaction fiber-matrix was determinated by high temperature X-ray diffraction and Auger electron depth profiling. Coating with TiC and TiN cannot completely avoid fiber damage and interfacial reactions. However, due to the low reaction rate, at short process times (ca. < 1 h) the formation of titanium silicides can be prevented. Based on these results, the coating of the SiC-fibers by TiN, but especially TiC, gives positive aspects for further improving these composites.     

Respiratory virus infections during anticancer treatment in children

To evaluate the occurrence and clinical significance of respiratory virus infections in children during anticancer treatment, we studied 75 consecutive episodes of febrile infection in 32 children during 17 months. Viral antigen detection for 7 respiratory viruses, viral culture for rhinoviruses and enzyme immunoassay serology were used. Evidence for respiratory virus infection was found in 28 (37%) cases. Rhinovirus was the most common virus detected in 13 (17%) episodes. The other etiologic agents were respiratory syncytial virus (6 episodes), parainfluenza virus type 3 (5 episodes), adenovirus (4 episodes), influenza A virus (3 episodes), and influenza B virus (1 episode). Respiratory virus infections were diagnosed as often in leukopenic as in non-leukopenic patients (37% vs. 38%). In 4 cases bacteremic infection was diagnosed. We found no difference in serum C-reactive protein values when episodes positive for respiratory viruses were compared with virus-negative episodes. Our observations show that respiratory virus infections are common in febrile children receiving anticancer treatment. Diagnostic tests for respiratory viruses should be used more often in evaluation of fever in these patients.     

Verification and optimization of a PLC control schedule

We report on the use of model checking techniques for both the verification of a process control program and the derivation of optimal control schedules. Most of this work has been carried out as part of a case study for the EU VHS project (Verification of Hybrid Systems), in which the program for a Programmable Logic Controller (PLC) of an experimental chemical plant had to be designed and verified. The original intention of our approach was to see how much could be achieved here using the standard model checking environment of SPIN/Promela. As the symbolic calculations of real-time model checkers can be quite expensive it is interesting to try and exploit the efficiency of established non-real-time model checkers like SPIN in those cases where promising work-arounds seem to exist. In our case we handled the relevant real-time properties of the PLC controller using a time-abstraction technique; for the scheduling we implemented in Promela a so-called variable time advance procedure . To compare and interpret the results we carried out the same case study with the aid of the real-time model checker Uppaal, enhanced with facilities for cost-guided state space exploration. Both approaches proved sufficiently powerful to verify the design of the controller and/or derive (time-)optimal schedules within reasonable time and space requirements. Published online: 2 October 2002 The work reported here was carried out while the second and third authors were employed by the Computer Science Department of the University of Nijmegen, Netherlands. The second author was supported by an NWO postdoc grant, the third author by an NWO PhD grant, and both were supported by the EU LTR project VHS (Project No. 26270).     

The NIRVANA code: Parallel computational MHD with adaptive mesh refinement

I report on a new version of the magnetohydrodynamics code NIRVANA¹ which is targeted at the study of astrophysical problems. The new version allows for distributed-memory simulations supporting adaptive mesh refinement. Numerical algorithms include dissipative terms (viscosity, Ohmic diffusion, thermal heat conduction) in a conservative form. Domain decomposition is preferably block-wise in case of unigrid applications but adopts space-filling curve techniques for adaptive mesh applications with a hierarchical block-structured mesh. The code architecture facilitates workload balancing among processors for arbitrary mesh refinement depths maintaining intra-level data locality via space-filling curve mappings and, at the same time, ensuring inter-level data locality by applying a novel technique called block sharing. This way, it is demonstrated that comparable performance can be achieved for problems with locally highly refined grid. The data transfer between processors extensively utilizes the coarse-granularity concept of parallel computing and makes use of the MPI library. Conservation properties of the numerical method carry over to the parallel framework. In particular, the solenoidality condition for the magnetic field is preserved to roundoff precision applying the constrained transport machinery. This paper has its focus of discussion on implementation details related to the parallelization and on a code performance analysis.     

Controlling information behaviour: the case for access control

Intentional dissemination of information is a key role of information systems. Yet methods for controlling access to information – as opposed to data – are still in their infancy, especially in relation to the key ‘decision points' that need to be made regarding what information users can access when, and under what conditions. This paper presents the case for access control to be explicitly integrated into models of information behaviour, especially as they relate to information access on the relatively unregulated internet. An observational case study relating to information access in Indonesia – which is a highly regulated society – is presented, through advertising on rogue websites – in this case, behaviour which is strictly regulated in the physical world (such as the promotion of gambling) is relatively unchecked online; the absence of effective controls, as suggested by situational crime prevention theory [Clarke, R. V. G., ed. 1997. Situational Crime Prevention. Criminal Justice Press] is reflected in the high levels of offending seen online. The extent to which information systems can manage information-seeking behaviour in a way that is consistent with regulatory or policy requirements in the online environment is discussed, with a view to establishing a foundation and terminology to modify information behaviour theory for the online environment.     

Dermatoglyphics in type 1 diabetes mellitus

Although fingerprints and handprints are widely used in criminology, it is only recently that this approach has been applied to the field of medical and genetic diagnoses. In order to investigate dermatoglyphics in Type 1 diabetes mellitus, quantitative characteristics of fingers and palms (ridge count and main line indices) as well as qualitative parameters such as digital and interdigital patterns, the position of the palmar axial triradii and main line courses were analysed in 88 male and 108 female Type 1 diabetic patients and compared with data from 100 male and 99 female normal controls. Type 1 diabetic patients show a lower third finger ridge count (p < 0.05) and a-b ridge count (p < 0.001) and higher transversality of the main lines as indicated by the main line index value (p < 0.001) or the ending of the main line A in a specific sector 5, 5', and 5" (p < 0.001) compared with controls. In addition, diabetic patients show higher frequency of palmar axial t' and t" triradii (p < 0.001) and a lower frequency of 'true' patterns in the fourth interdigital and thenar area (p < 0.001) than controls. By multivariate analysis of quantitative and qualitative variables a predictive value of 78.6% and 77.3%, respectively, for male, and 81.4% and 82.2%, respectively, for female Type 1 diabetic patients was found. In conclusion, dermatoglyphics seem to be an interesting tool for genetic studies related to Type 1 diabetes.     

Atomic Resolution Transmission Electron Microscopy of the Intergranular Structure of a Y2O3-Containing Silicon Nitride Ceramic

High-resolution transmission electron microscopy (HRTEM) employing focus-variation phase-reconstruction methods is used to image the atomic structure of grain boundaries in a silicon nitride ceramic at subangstrom resolution. Complementary energy-dispersive X-ray emission spectroscopy experiments revealed the presence of yttrium ions segregated to the 0.5–0.7-nm thin amorphous boundary layers that separate individual grains. Our objective here is probing if yttrium ions attach to the prismatic planes of the Si₃N₄ at the interface toward the amorphous layer, using Scherzer and phase-reconstruction imaging, as well as image simulation. Crystal structure images of grain boundaries in thin sample (<100 Å) areas do not reveal the attachment of yttrium at these positions, although lattice images from thicker areas do suggest the presence of yttrium at these sites. It is concluded that most of the yttrium atoms are located in the amorphous phase and only a few atoms may attach to the terminating prism plane. In this case, the line concentrations of such yttrium in the latter location are estimated to be at most one yttrium atom every 17 Å.     

Formation of Mullite from Filled Siloxanes

Monolithic mullite with low sintering shrinkage was synthesized from polymer/filler blendsMthat is, siloxane/alumina (siloxane/Al₂O₃) (and siloxane/aluminum (siloxane/Al)) mixtures. The synthesis was based on a reaction-bonding process of amorphous silica, which formed when the siloxane was oxidized, with Al₂O₃ (or oxidized aluminum filler) at temperatures >1250°C. Thermodynamic calculations were used to calculate the phase composition at equilibrium. Thermoanalytical, infrared-spectroscopic, and microscopic techniques were applied to reveal the microstructural evolution. The corresponding volume changes were used to evaluate the linear shrinkage, based on the quantitative phase assemblage.