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Our objective was to compare 2 friction couples: ceramic/ceramic and metal/polyethylene in total hip prosthesis. Between 2005-2007, 64 patients with primary osteoarthritis of the hip were enrolled in a prospective study: 32 cases underwent arthroplasty with uncemented total hip prosthesis with a friction couple ceramic/ceramic (Group1), while the other 32 cases underwent arthroplasty with uncemented total hip prostheses with a friction couple of metal on Ultra-High Molecular Weight Polyethylene (UHMWPE) (Group 2). Group 1 was considered the test group and group 2 was designed so that the two groups to be similar in terms of gender and age distribution. We followed: the emergence of osteolysis areas, component loosening to a degree requiring revision, clinical outcome quantified by Harris score. The radiological aspect was determined by several radiological check-ups: immediately after operation, at 6 weeks, at 3 months postoperatively and then annually. Mean follow-up time was 5.2 years (ranging from 3 years and 2 months to 7 years and 8 months). The presence of osteolysis areas was observed in a single case in the ceramic/ceramic group (3.12%) and in 4 cases in the metal/polyethylene group (12.5%), the difference not being statistically significant (p > 0.05). In Group 1 we performed one revision which required replacement of both components (3.12%), while in Group 2 there were 2 such kind of interventions (6.24%) - the difference being not statistically significant (p > 0.05). Harris Score evolved in Group 1 from 52.34 ±6.36 preoperatively to 94.32 ±8.82 at the end of the follow-up period (p < 0.01), and in Group 2 from 51.52 ±7.21 to 92.44 ±9.24, respectively (p < 0.01). Keywords: ceramic, friction couple, hip prosthesis

A non invasive method as numerical simulation was employed to evaluate the periodontium comportment under the occlusal force appliances. Three types of periodontal support for a three elements metal polymeric fixed partial prosthesis were considered. The retractions trends of the periodontium were correlated with the occlusal conditions. Keywords: metal - polymeric fixed partial prosthesis, numerical simulation, periodontium

The compression properties of a novel family of hydrogels prepared from diepoxy-terminated poly(ethylene glycol)s of approximate molecular weights 600, 1000, 2000 and 4000 Daltons and various aliphatic polyamines of different chain length and functionality (ethylenediamine, 1,4-diaminobutane, hexamethylenediamine, 1,8-octanediamine, diethylenetriamine, triethylenetetramine, tris(2-aminoethyl)amine) were determined by uniaxial compression. It was shown that both elastic and compression moduli, and compression strength of the fully swelled hydrogels depended on the molecular weight of the PEG oligomer, structure and functionality of the aliphatic amine employed as crosslinker, and mole ratio between the reacting groups, as a consequence of the different crosslinking degree of the resulting networks. Keywords: hydrogels; poly(ethylene glycol), epoxy groups, aliphatic polyamines, uniaxial compression

A molecular rheological model for amorphous homopolymers filled with nanoparticles is presented. The fillers are non-agglomerated and interact energetically with the polymers. The model applies to situations in which the polymer-filler affinity is relatively weak. The essential physics represented in the model includes chain reptation, the slowing down of diffusion due to energetic interactions of polymers and fillers, chain stretch, and contour length fluctuations. The model is based on insight obtained from extensive simulations of the structure and dynamics of these systems. The chain population is composed of free, dangling and bridging chains, i.e. those that at given time do not contact fillers, contact one filler or multiple fillers, respectively. As the system evolves, a representative chain switches randomly between these categories. The representative chain reptates only when free, while contour length fluctuations are performed at all times. Relaxation is controlled by both tube renewal and the process of chain attachment/detachment to/from the filler surface. The second process modulates the first, leading to a relaxation with two characteristic times, in agreement with experimental observations. The parameters entering the model can be calibrated based on the rheology of the neat polymer and based on results from simulations of the respective filled system. Keywords: rheology of polymer nano-composites; reptation; contour length fluctuation; tube renewal

We started this study considering the fact that, in our surgical clinic, the association of umbilical and inguinal hernias in cirrhotic patients was found in 47,6% of cases. Although this joined pathology is quite frequent, the data comparing surgical complications and long-term recurrence when using the two mesh procedures are limited. Keywords: mesh, polipropylen, umbilical, hernia, polyvinylidene, inguinal, cirrhosis

In this paper, some aspects of electrospun nanofiber diameter measurement has been presented. The method was tested by a simulated image with known characteristics and a real web. The results show that this approach is successful in making fast, accurate automated measurements of electrospun fiber diameters. Keywords: transport properties, automated measurement, electrospinning, nanofiber diameter, image analysis

In this article we present our work on the combination of two thermostats, motivated by our research on multiscaling molecular dynamics simulations. Molecular dynamics are used for studying the properties of polymers. Two schemes - global Berendsen and stochastic dynamics - are combined. A leap-frog algorithm was used for the calculation of kthermal. Simulation results on temperature, thermal rate, and diffusion for coarse-grained (MARTINI) water are discussed. Using these thermostats we observe no deviation from the reference temperature and show that the measured thermal relaxation rates agree well with theoretical predictions. Keywords: molecular dynamics, polymers, thermostats

Manufacturing process of rubber parts have to take into consideration a set of parameters of production to accomplish the requirements of the quality standards, especially in the automotive industry. Starting from input data obtained from different rubber parts production process, this paper presents results and conclusion obtained with simulation software and specific application based on numerical methods, compared with measurements obtained in industrial process. Benefits of 3D simulations lead to important product development cycle time reduction, radical manufacturing cost reduction and possibility to optimize cycle times and product quality. Keywords: rubber injection process; Finite Element Analysis; numerical methods

The rubber is widely used at railway infrastructure and rolling stock. Rubber plates are used at rail – sleeper fastening systems, rubber elements are used for primary suspension at electrical locomotives (in Romania and abroad) and metro (subway trains) as elastic elements in buffers, or as insertion plates at streetcar wheels etc. From those examples we can see that rubber elements are used as elements which are directly involved in circulation safety. Keywords: rubber plate, rail pad, K fastening, test, railway polyethylene

The paper presents an experimental validation, through modal analysis, of some models of plates with discontinuities, made of plastic materials. The numerical study was undertaken using the Finite Element Method. The geometrical model was obtained with nondestructive evaluations using computer tomography, allowing thus to find the shape, position and dimensions of defects. The good agreement between the experimental and numerical results led to the validation of the investigated models. Key-words: defect, modal analysis, computer tomography, numerical analysis