Location update algorithms for position sharing

Mit der immer zunehmenden Anzahl an Smartphones innerhalb der letzten Jahre hat auch deren Einfluss auf unser tägliches Leben immer mehr zugenommen. Unter anderem wurden auch die sogenannten Location Based Services immer beliebter. Diese Location Based Services benötigen die Position eines mobilen Benutzers und finden dann z. B. das nächste Restaurant. Natürlich ist die Sicherheit der Benutzerdaten hierbei ein wichtiges Thema. Die Daten sind meistens auf Location Servern gespeichert, und wenn der Anbieter des Servers kompromittiert oder unsicher ist, können die Daten verschlampt oder gestohlen werden. Aus diesem Grund wurden viele Ansätze zum Verschleiern der tatsächlichen Benutzerposition vorgeschlagen, so auch von Rothermel, Dürr und Skvortsov. Diese Diplomarbeit stellt nun neue Techniken vor, um den eben genannten Basis-Ansatz für das Verschleiern von Benutzerpositionen weiter zu verbessern. Das Hauptziel ist dabei, die Anzahl der Update-Nachrichten zu reduzieren, die vom mobilen Objekt an die Location Server geschickt werden, um die Position des Benutzers aktuell zu halten. Die vorgeschlagenen Techniken werden analysiert, und das entwickelte System wird simuliert, um die Kommunikation zwischen dem mobilen Objekt und den Location Servern, sowie die Kommunikation zwischen den Location Servern und den Location Based Services auszuwerten. Hierbei werden echte Benutzer-Trajektorien aus dem GeoLife-Datensatz verwendet. Die Evaluierung zeigt, dass die Nachrichtenzahl in manchen Fällen um über 90% reduziert werden kann. Hierbei findet jedoch im Hinblick auf den Basis-Ansatz weder ein Verlust der Sicherheit noch der Genauigkeit statt

Economic Impact of Infected Total Knee Arthroplasty

Background. An enormous economic impact can be observed for infected total knee arthroplasties (TKA). The aim of the present study was to evaluate whether a cost covering treatment of infected TKA is feasible in the German DRG System. Patients and Methods. Average total treatment costs were evaluated for infected TKA and compared with a matched pair of primary TKA. Data was generated using the health record and the hospitals' health information system. Results were evaluated and compared regarding the total personnel and material costs with respect to the financial receipts. Results. A total of 28 patients diagnosed with an infected TKA were included. A significant increase in the average length of stay, use of medical supplies and third party medical examinations were found for the infected TKA. An average deficiency of 6,356€ per patient was observed for the infected TKA. An average profit of 927€ per patient was made performing primary TKA. Conclusions. A cost-effective treatment of infected TKA was not feasible with the receipts from the German DRG System. An adaption of the receipts has to be evaluated. Moreover, other measures have to be considered in order to achieve a comprehensive medical yet financial reasonable standard in the treatment of infected TKA and THA

Two-stage revision of implant-associated infections after total hip and knee arthroplasty

Septic loosening of total hip and knee endoprostheses gains an increasing proportion of revision arthroplasties. Operative revisions of infected endoprostheses are mentally and physically wearing for the patient, challenging for the surgeon and a significant economic burden for healthcare systems. In cases of early infection within the first three weeks after implantation a one-stage revision with leaving the implant in place is widely accepted. The recommendations for the management of late infections vary by far. One-stage revisions as well as two-stage or multiple revision schedules have been reported to be successful in over 90% of all cases for certain patient collectives. But implant associated infection still remains a severe complication. Moreover, the management of late endoprosthetic infection requires specific logistics, sufficient and standardized treatment protocol, qualified manpower as well as an efficient quality management. With regard to the literature and experience of specialized orthopaedic surgeons from several university and regional hospitals we modified a commonly used treatment protocol for two-stage revision of infected total hip and knee endoprostheses. In addition to the achievement of maximum survival rate of the revision implants an optimisation of the functional outcome of the affected artificial joint is aimed for

Analysis of the Release Characteristics of Cu-Treated Antimicrobial Implant Surfaces Using Atomic Absorption Spectrometry

New developments of antimicrobial implant surfaces doped with copper (Cu) ions may minimize the risk of implant-associated infections. However, experimental evaluation of the Cu release is influenced by various test parameters. The aim of our study was to evaluate the Cu release characteristics in vitro according to the storage fluid and surface roughness. Plasma immersion ion implantation of Cu (Cu-PIII) and pulsed magnetron sputtering process of a titanium copper film (Ti-Cu) were applied to titanium alloy (Ti6Al4V) samples with different surface finishing of the implant material (polished, hydroxyapatite and corundum blasted). The samples were submersed into either double-distilled water, human serum, or cell culture medium. Subsequently, the Cu concentration in the supernatant was measured using atomic absorption spectrometry. The test fluid as well as the surface roughness can alter the Cu release significantly, whereby the highest Cu release was determined for samples with corundum-blasted surfaces stored in cell medium

Simulation and fabrication of active laser mirrors

Common laser mirrors made of copper for high power applications in metal working have to be cooled in order to minimize thermal deformations. This paper presents a new approach: The principal idea is to use metal-coated mirrors made of silicon carbide (SiC) and to preheat them. The mirror surface shall be manufactured so that the induced heat deforms it to the ideal form. Simulations concerning the thermal behavior prove the feasibility of the idea. The simulations are verified by interferometric measurement during heating

Evaluation of osseointegration of titanium alloyed implants modified by plasma polymerization

By means of plasma polymerization, positively charged, nanometre-thin coatings can be applied to implant surfaces. The aim of the present study was to quantify the adhesion of human bone cells in vitro and to evaluate the bone ongrowth in vivo, on titanium surfaces modified by plasma polymer coatings. Different implant surface configurations were examined: titanium alloy (Ti6Al4V) coated with plasma-polymerized allylamine (PPAAm) and plasma-polymerized ethylenediamine (PPEDA) versus uncoated. Shear stress on human osteoblast-like MG-63 cells was investigated in vitro using a spinning disc device. Furthermore, bone-to-implant contact (BIC) was evaluated in vivo. Custom-made conical titanium implants were inserted at the medial tibia of female Sprague-Dawley rats. After a follow-up of six weeks, the BIC was determined by means of histomorphometry. The quantification of cell adhesion showed a significantly higher shear stress for MG-63 cells on PPAAm and PPEDA compared to uncoated Ti6Al4V. Uncoated titanium alloyed implants showed the lowest BIC (40.4%). Implants with PPAAm coating revealed a clear but not significant increase of the BIC (58.5%) and implants with PPEDA a significantly increased BIC (63.7%). In conclusion, plasma polymer coatings demonstrate enhanced cell adhesion and bone ongrowth compared to uncoated titanium surfaces

A model of implant-associated infection in the tibial metaphysis of rats

Objective. Implant-associated infections remain serious complications in orthopaedic and trauma surgery. A main scientific focus has thus been drawn to the development of anti-infective implant coatings. Animal models of implant-associated infections are considered helpful in the in vivo testing of new anti-infective implant coatings. The aim of the present study was to evaluate a novel animal model for generation of implant-associated infections in the tibial metaphysis of rats. Materials and Methods. A custom-made conical implant made of Ti6Al4V was inserted bilaterally at the medial proximal tibia of 26 female Sprague-Dawley rats. Staphylococcus aureus in amounts spanning four orders of magnitude and each suspended in 15 l phosphate buffered saline (PBS) was inoculated into the inner cavity of the implant after the implantation into the defined position. Controls were treated accordingly with PBS alone. Animals were then followed for six weeks until sacrifice. Implant-associated infection was evaluated by microbiological investigation using swabs and determination of viable bacteria in the bone around the implant and the biofilm on the implants after sonification. Results. Irrespective of the initial inoculum, all animals in the various groups harbored viable bacteria in the intraoperative swabs as well as the sonication fluid of the implant and the bone samples. No correlation could be established between initially inoculated CFU and population sizes on implant surfaces at sacrifice. However, a significantly higher viable count was observed from peri-implant bone samples for animals inoculated with 10 6 CFU. Macroscopic signs of animal infection (pus and abscess formation) were only observed for implants inoculated with at least 10 5 CFU S. aureus. Discussion/Conclusion. The results demonstrate the feasibility of this novel animal model to induce an implant-associated infection in the metaphysis of rats, even with comparatively low bacterial inocula. The specific design of the implant allows an application of bacteria in reproducible numbers at well-defined contact sites to the animal bone