Contact zone analysis based on multidexel workpiece model and detailed tool geometry representation

A new method for analyzing the tool-workpiece-contact area in cutting processes is presented. To gain enhanced knowledge about tool-workpiece interaction, determination of chip thickness, contact length and resulting cross-section area of the undeformed chip is of major interest. Compared to common simulation approaches, where rotation-symmetrically constructed tool geometry is used, the new method uses a detailed three dimensional tool shape model for an extended and more accurate contact zone analysis. As a corresponding representation of the workpiece and its time dependent shape-changes a multidexel model is used. To prepare the geometric tool model, the contained BREP topology is built up within the simulation system using data from a STEP-file. First of all functional parts of the tool like rake and flank faces and cutting edges are labeled for further processing. In a second step the identified NURBS-faces are discretized for the application in material-removal calculation. This way a mesh is built-up based on triangle elements which maps the geometry of each cutting edge into a 2D parametric representation. In relation to rake face, each node is described by its position on the cutting edge and its perpendicular distance to this edge. To perform contact zone analysis each cutting geometry and a multidexel model are intersected in discrete time steps corresponding to a tool rotation of about three degrees. The intersection point of each dexel and the cutting geometry is calculated. Parametric cutting geometry allows for a direct computation of local cutting depth and contact length for each involved point. Based on the local values of contact length and cross section area of the undeformed chip the characteristic values for the entire contact zone are calculated and used to predict mechanical as well as thermal loads caused by the cutting process. To demonstrate the application of the novel approach, prediction of forces in slot milling of 1.1191 steel is presented.DFG/PP/148

Late Mesolithic burials at Casa Corona (Villena, Spain): direct radiocarbon and palaeodietary evidence of the last forager populations in Eastern Iberia

Current knowledge about the Mesolithic-Neolithic transition in the Central and Western Mediterranean European regions is deeply limited by the paucity of Late Mesolithic human osteological data and the presence of chronological gaps covering several centuries between the last foragers and the first archaeological evidence of farming peoples. In this work, we present new data to fill these gaps. We provide direct AMS radiocarbon dating and carbon (d13C) and nitrogen (d15N) stable isotope analysis were carried out on bone collagen samples of two single burials from the recently discovered open-air Late Mesolithic site of Casa Corona (Villena, Spain). The results shed new light on the chronology and subsistence patterns of the last Mesolithic communities in the Central Mediterranean region of the Iberian Peninsula. Radiocarbon results date the human remains and funerary activity of the site to 6059e5849 cal BC, statistically different from other Late Mesolithic sites and the earliest Neolithic contexts, and bridging the 500 yrs chronological gap of the Mesolithic-Neolithic transition from the area. Isotopic evidence shows that diet was based on terrestrial resources despite the proximity to the site of lagoon and marine ecosystems. This and previous isotope studies from the region suggest a lower reliance upon marine resources than for Atlantic and Cantabrian sites, although intra-regional patterns of neighbouring Mesolithic populations exhibit both fully terrestrial diets and diets with significant amounts of aquatic resources in them. We hypothesize that in the Central Mediterranean region of Spain the Late Mesolithic dietary adaptations imposed structural limits on demographic growth of the last foragers and favoured rapid assimilation by the earliest Neolithic populations

Genome amplification and gene expression in the ciliate macronucleus

The focus of this review is on the micronucleus and macronucleus in the ciliated protozoa and the organization and function of the DNA molecules within them. We present (1) some of the structural and functional differences which are known, (2) the genetic evidence for macronuclear units, (3) two hypotheses for the organization of the DNA molecules in the macronucleus to explain these units, and (4) experiments designed to discriminate between these hypotheses. We conclude that the size of the genome is not reduced in the macronucleus and that there are 45 copies of the haploid genome present in the macronucleus of normal strains of Tetrahymena pyriformis and 800 copies in the macronucleus of Paramecium aurelia . The ciliate genome is relatively simple in terms of repeated sequences. However, not all copies of the genes present in the macronucleus may be identical since fractions of differing thermal stability appear after renaturation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44178/1/10528_2004_Article_BF00486122.pd

Corneal Cross-Linking in Microbial Keratitis to Prevent a chaud Keratoplasty: A Retrospective Case Series

Background: Corneal cross-linking (CXL) with riboflavin is being used more frequently for the treatment of therapy-resistant microbial keratitis, since increasing drug resistance and specific pathogens, e. g. contact lens-associated Acanthamoeba, make this therapy appear as an attractive option to avoid a keratoplasty chaud. Patients and Methods: This retrospective case series of 11 consecutive patients (4 women, 7 men, aged 24-82 years) who received standardised antimicrobial CXL for therapy-resistant keratitis to avoid a keratoplasty chaud, included 4 cases with detection of bacterial pathogens, one case with proven fungal infection and 6 cases without pathogen detection. Analysed data comprised ophthalmic medical history, general risk factors for microbial keratitis, treatment before and after CXL. The characterisation of the corneal ulcer included photometric measurements of the infiltrates with a median of 16.2 mm(2) and four unmeasurable cases due to extended, not circumscribed lesions. Results: Within the follow-up period (mean 134 +/- standard deviation 82 days), a penetrating keratoplasty was successfully avoided in 6 patients (55%). After CXL 9 patients (82%) received additionally amniotic membrane transplantation. After CXL treatment, topical antibiotic therapy was continued for a mean 27 +/- 13 days postoperatively. Steroids were applied in 91% of the patients. The cornea cleared at least to some extent in 9 patients (82%). Patients with neurotrophic keratopathy or potentially compromised immune system showed no increased failure rate. Conclusion: These results suggest that antimicrobial CXL might be a useful option in patients with therapy-resistant corneal ulcer in order to avoid a perforating keratoplasty chaud. For a comprehensive scientific assessment of this therapy, however, further, ideally prospective randomised interventional studies with large sample sizes are needed