National Repository of Grey Literature 42 records found  previous11 - 20nextend  jump to record: Search took 0.00 seconds. 
Friction of compliant contacts
Vala, Martin ; Galas, Radovan (referee) ; Nečas, David (advisor)
This bachelor’s thesis deals with the study of the friction of compliant contacts and parameters affecting it. First section of this thesis provides analysis of current problematics with friction and compliant materials. In the next section basic definition of friction, compliant material and compliant contacts is provided with an actual study of up-to-date articles. Last section of this thesis is discussion dealing with all the articles and pointing out the influencing parameters. Followed by potential research pathways.
Bearings for space
Vavřík, Petr ; Nečas, David (referee) ; Košťál, David (advisor)
Currently, space satellites in orbit are required to operate reliably for more than 10 years. This places high demands on the satellite's tribological systems, which must function properly in the hostile space environment for this period. This bachelor thesis deals with the description of suitable bearings and their lubrication for space applications. Lubrication regimes are described at the outset. Then, space factors affecting the proper operation of tribological systems are summarized. The largest part is devoted to the description of the most used bearings and lubricants. The thesis concludes with the design of suitable bearings and their lubrication for the satellite reaction wheel.
Reactions of Alkenes Iniciated by Transition Metals Alkyls and Hydrides
Nečas, David
Reactions of Alkenes Iniciated by Transition Metals Alkyls and Hydrides David Nečas Department of Organic and Nuclear Chemistry, Faculty of Science, Charles University, Hlavova 8, 128 40 Prague 2, Czech Republic. Keywords: C-C bond cleavage, C-C bond formation, Nickel, catalysis The C-C bond activation (cleavage) as well as the C-C bond formation under mild and simple reaction conditions are intensively sought after processes. In the course of this thesis new nickel based catalytic system was found suitable for formation of C-C bonds (cyclization of α,ω-dienes) and for cleavage of unactivated C-C bonds in allyl malonates and related compounds. Mechanistic and structural aspects of these reactions are also discussed as well as a relation of C-C bond formation (cyclization) to the C-C bond cleavage (deallylation). This work was supported by FRVŠ No. 42-202755, MŠMT No. 1M0508 Centre for New Antivirals and Antineoplastics, MŠMT No. LC 06070 Center for Structural and Synthetic Application of Transition Metal Complexes and is a part of the Research Project MSM0021620857.
An investigation of lubrication of knee joint replacement
Sýkora, Tomáš ; Horák, Zdeněk (referee) ; Nečas, David (advisor)
This diploma thesis deals with an experimental analysis of knee joint replacement lubrication. The experiments were realized at a knee joint simulator which can apply conditions according to certain standard and survey the phenomena by using fluorescence microscopy. The aim of thesis is to clarify the influence of particular components of synovial fluid on the lubrication process. The intensity of fluorescence expresses dimensionless parameter of a lubrication film thickness. There was a fundamental study with mineral oils before the experiments with the synovial fluid. The study allows to have a look at contact transformation during walk. Results are shown in graphs as dependency of intensity on time, including pictures showing phenomena in the contact zone. Experiment results show that protein -globulin creates a layer on the surface. There is albumin on the layer and it makes the lubricating film thicker. The protein interaction is supported by hyaluronic acid and fosfolipids which stabilizes the created structure. According to lubrication is behaviour of film related to a complex structure of synovial fluid. Thesis gives more information about behaviour of synovial fluid and can be used for future development of knee replacements.
The effect of surface modification of acetabular cup on friction coefficient of hip implant
Cahová, Aneta ; Valena, Martin (referee) ; Nečas, David (advisor)
This bachelor’s thesis is focused on limited longevity of hip joint replacements. In order to extend the longevity of replacements effect of microtexture application on surface of artificial acetabulum cup on coefficient of friction was investigated. Attention was paid to composition of model synovial fluid and geometry and layout of texture. For joint simulation, a pendulum hip joint simulator was employed. In first part three femoral heads, two acetabulum cups and five fluids were tested, respectively two heads, four acetabulum cups and one fluid in second part. Significant effect of fluid composition and geometry and layout of texture was observed during measurement. Compared smooth and textured cup the highest decline of friction was 78 %. Results can be used for further research of micortextures. Friction reduction and prolonging lifespan of implants may eventually improve life quality of many patients.
Thin metal coating of polymer materials
Zatloukal, Filip ; Furmann, Denis (referee) ; Nečas, David (advisor)
The study of compliant contacts from a tribological standpoint is very complicated due to low reflectivity and electrical conductivity of materials such as polymers or rubber. These properties significantly limit the possibilities of using conventional methods which are being used to study the film formation and lubricant flow. To enable the use of the conventional methods it is necessary to apply a thin reflective layer on the non-reflective surface. This work evaluates the current literature dealing with the coating of polymeric materials. A method was chosen based on the analysis of the currently available technologies, which is used to apply a thin reflective layer on the polydimethylsiloxane sample. This part is followed by a feasibility study to clarify the effects of the coating on friction processes. This work can significantly contribute to the field of compliant contacts, especially in terms of clarifying the mechanisms of lubrication.
The effect of proteins on friction of artificial articular cartilage
Plachý, Tomáš ; Nečas, David (referee) ; Rebenda, David (advisor)
This bachelor thesis deals with the influence of the composition of synovial fluid on the coefficient of friction of artificial cartilage. The effect of protein concentration and their combination with other components of synovial fluid on the coefficient of friction of CD hydrogels simulating artificial cartilage is observed. All experiments were performed at a constant load of 10 N, speed 10 mm / s, temperature 37 ° C. In experiments investigating the effect of a combination of hyaluronic acid and phospholipids together with proteins, concentrations corresponding to a healthy individual were used. In experiments where the effect of the proteins themselves and their own combinations was investigated, concentrations corresponding to both a healthy individual and patients with advanced osteoarthritis or patients with aseptic release of the prosthesis were used. The work shows that when using the proteins alone, or their combination, there is a decrease in concentration of friction coefficient with increasing concentration. However, if hyaluronic acid alone or phospholipids alone is added to the protein, the coefficient of friction increases. The reduction occurs only after the addition of the combination of acid and phospholipid.
The design of eye-lens simulator
Špaček, Matěj ; Rebenda, David (referee) ; Nečas, David (advisor)
The aim of this bachelor thesis is a design of an eye-lens simulator. Tribometer module in pin-on-ring configuration was designed to allow direct observation of a contact zone. The survey of existing tribometers was conducted as a part of the thesis, based on which, three concept solutions were suggested. Final solution of the module was chosen and designed based on the concepts. The apparatus enables to simulate conditions of real human eye so it could contribute to a contact lens research and eye lubrication solution development.
The effect of surface condition of artificial joint cup on the friction coefficient
Černohlávek, Mikuláš ; Dočkal, Kryštof (referee) ; Nečas, David (advisor)
This bachelor’s thesis deals with the effect of microtextured surface of an artificial joint cup on a friction coefficient. The primary aim of this thesis was to compare friction coefficients of original and microtextured joint cups. Experimental measurements were made on pendulum hip joint simulator and results were evaluated in Matlab. Four types of femoral heads (CoCrMo, BIOLOX Delta, BIOLOX Forte and oxinium) and three types of lubricants (PBS, model synovial fluid and hyaluronic acid solution) were used during the measurements. The results show, that using PBS and synovial fluid leads to decrease of the coefficient of friction while using modified joint cup. We can assume that microtextured surface of artificial joint cup (separately or in combination with microtextured femoral head) could be a significant benefit for prolonging lifespan of implants.
The effect of synovial fluid composition on friction of joint cartilage
Furmann, Denis ; Daniel, Matej (referee) ; Nečas, David (advisor)
This thesis deals with the study of the effect of the constituents of the model synovial fluid on the frictional properties of articular cartilage. The influence of constituents, concentration, speed and load is observed. Experiments were performed on a commercial tribometer at configuration pin-on-plate. Several types of lubricants containing synovial fluid constituents have been selected for the experiments. Lubricants were prepared at two concentrations, the concentration of healthy individuals and at a concentration typical of for osteoarthritic patients. Speeds 5 and 10 mm/s and 5 and 10 N loads were used for all experiments. It is shown that when using only lubricant containing proteins, no difference in the coefficient of friction is observed and the effect of concentration is also not observed. The addition of hyaluronic acid has a synergistic effect with -globulin, however in the case of lubricants containing albumin, the effect is opposite. After the addition of phospholipids, no significant effect on friction is observed in -globulin containing lubricants. No significant effect of the composition and concentration of the lubricants is observed with the load change.

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2 Nečas, Dalibor
1 Nečas, Daniel
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