A hierarchical approach to simulate the packing density of particle mixtures on a computer

In many fields of materials science it is important to know how densely a particle mixture can be packed. The “packing density” is the ratio of the particle volume and the volume of the surrounding container needed for a random close packing of the particles. We present a method for estimating the packing density for spherical particles based on computer simulations only, i.e. without the need for additional experiments. Our method is particularly suited for particle mixtures with an extremely wide range of particle diameters as they occur e.g. in modern concrete mixtures. A single representative sample from such mixtures would be much larger than can be handled on present standard computers. In our hierarchical approach the diameter range is therefore divided into smaller intervals. Samples from these limited diameter intervals are drawn and their packing density is estimated from a simulated packing. The results are used to “fill” the interstices in the sample from the next larger particle interval. To account for the interaction between particles of different sizes we include larger particles into the sample of smaller ones. The larger ones act as part of the boundary during the packing. Thus we obtain more realistic estimates of how dense a fraction of particles can be packed within the whole mixture. The focus of this paper is on the divide-and-conquer approach and on how the simulation results from the fractions can be collected into an overall estimate of the packing density. We do not go into details of the simulation technique for the single packing. We compare our results to some experimental data to show that our method works at least as good as the classical analytical models like CPM without the need for any experiments.     

Airborne Microbes and Endotoxins in the Work Environment of Two Sanitary Landfills in Finland

The Andersen sampler was used to study the occurrence of bacteria and fungi in the working air of two large, intensively used landfills in Finland. Endotoxins were also determined. The concentrations of airborne microbes were high in summer in warm windy weather. Mesophilic bacteria exceeded 10⁵ colony-forming units (cfu)/m³ and mesophilic fungi 10⁴ cfu/m³. In 67% of the samples, the concentrations of gram-negative bacteria exceeded 10³/m³, which has been suggested to be the threshold limit value (TLV). The endotoxin levels were all below 0.1 μg/m³. A large part of the colony-forming particles were within the respirable size range, about 40% of the bacteria and about 80% of the fungi. The commonly isolated airborne bacteria were Pseudomonas, Enterobacter, and Bacillus spp. The landfill workers should try to work upwind. There are also grounds for using a mask and irrigating the refuse terrace with leachate in dry weather. It is suggested that the traffic on the refuse terrace be decreased by arranging for the private cars to be emptied in the reception area.     

Valorization of Beef Tallow by Lipase-Catalyzed Interesterification with High Oleic Sunflower Oil

Although beef tallow (BT) has been considered a hard low-trans fat convenient to be used in several bakery applications, it has some undesirable characteristics like fatty acid composition, crystallization behavior, graininess formation and poor plastic range. This work studied the modification of BT by blending at different percentages with high oleic sunflower oil (HOSFO) followed by the enzyme-catalyzed interesterification of the blends. The reduction in the solid fat content achieved by the simple blending was enhanced by the interesterification process, as a result of the increase in the concentration of the diunsaturated monosaturated type triacylglycerols. Interesterification strongly impacted too on the crystallization behavior of the blends, since products showed more homogeneous and regular crystals than the starting mixture. Results show that lipase catalyzed interesterification of BT with HOSFO offers a useful tool for the design of fats with adjustable physicochemical properties, improved with respect to that of the starting fats.     

The ELPI Response and Data Reduction II: Properties of Kernels and Data Inversion

The first part of this article reports the analytical form of the Electrical Low Pressure Impactor (ELPI) kernel functions. In this latter part, the numerical quality of ELPI response matrices is studied and an example of an inversion algorithm is given. The ELPI assemblies with and without an electrical filter stage and with smooth or sintered impaction plates are studied and compared with basic impactor kernels and the kernels for the calculation of the aerosol mass distribution. It is shown that the ELPI assembly with the electrical filter stage and smooth impaction plates should be the best choice for the inversion of data if no bounce occurs. The comparison to a mass impactor shows that the devices are on par in data inversion. The inversion ELPI data is studied with a Bayesian algorithm assuming a bimodal lognormal size distribution of the aerosol. The algorithm includes a novel procedure for obtaining an initial guess of the distribution parameters. To our knowledge, it is also the first algorithm to use ELPI current readings as its input. Simulations and diesel emission measurements show that the proposed algorithm is a useful tool in the study of ELPI data.     

In‐Depth Study of Mass Transfer in Nanoporous Materials by Micro‐Imaging

The first application of interference microscopy to monitoring mass transfer in nanoporous materials dates back to late 1970s when Caro and colleagues reported results of investigations of water uptake by LTA type zeolites. It was, however, not before the beginning of the new millennium that the developments in both the measuring technique and computational power have enabled the recording of transient guest profiles during molecular uptake and release under well‐defined conditions, leading to the establishment of a novel access to diffusion studies, now referred to as micro‐imaging. In the present contribution, the thus accessible novel type of information is illustrated by an in‐depth analysis of the uptake kinetics of methanol in an all‐silica ferrierite. In particular, two remarkable experimental findings are reported, which may be tracked back to their microstructural and/or microdynamic origin, namely a pronounced asymmetry in the transient concentration profiles and a slowing down of guest uptake with increasing temperature.     

Einsatz von Faserstoffen aus chemo-thermo-mechanisch (CTMP) aufgeschlossenen, gebrauchten Span- und Faserplatten zur Herstellung von mitteldichten Faserplatten (MDF)

Ohne Zusammenfassung     

Geometry-driven-diffusion filtering of magnetic resonance images using model-based conductance

The paper deals with the problems of staircase artifacts and low-contrast boundary smoothing in filtering (magnetic resonance MR) brain tomograms that is based on geometry-driven diffusion (GDD). A novel method of the model-based GDD filtering of MR brain tomograms is proposed to tackle these problems. It is based on a local adaptation of the conductance that is defined for each diffusion iteration within the variable limits. The local adaptation uses a neighborhood inhomogeneity measure, pixel dissimilarity, while gradient histograms of MR brain template regions are used as the variable limits for the conductance. A methodology is developed for implementing the template image selected from an MR brain atlas to the model-based GDD filtering. The proposed method is tested on an MR brain phantom. The methodology developed is exemplified on the real MR brain tomogram with the corresponding template selected from the Brainweb. The performance of the developed algorithms is evaluated quantitatively and visually. Received: 1 September 1998 / Accepted: 20 August 2000     

Operational Considerations for Teaming Manned and Unmanned Helicopter

“Manned-Unmanned Teaming” among others refers to the use of an unmanned, flying sensor. One use for this is as an integral part of air units’ flying systems. Secondly, it can be used as an independent, recessed robotic component during missions, even from far away and ahead of time. As part of the German R&T project “Manned- Unmanned Teaming” (MUM-T), Elektroniksystem- und Logistik-GmbH (ESG) was assigned the task of investigating these concepts and the options for their realization. The focus of the investigation was initial operation capability within a narrow time frame concentrating on German Army Aviation helicopters. The paper focuses on the results achieved by ESG and begins with a short project overview. In the main part a representative MUM-T mission based on a personnel recovery mission is presented. The mission was demonstrated by ESG in close cooperation with German Army Aviation Combat Development Division (Ger AAV CDD). Beside operational aspects, technical aspects will be discussed. The lecture will close with a short outlook on the next steps, bringing MUM-T missions into service.