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This master's thesis deals with security of wireless network standard 802.11. There are described security mechanisms as hide SSID, MAC address filtering, WEP, WPA, WPA2 protocols. There are described also the most often kinds of attacks (Denial of Service, disclosure WEP key, Man-in-the-Middle). The work contains investigation of used security mechanisms in wireless networks in parts of Brno. There were used NetStumbler and inSSIDer applications for this measurement. The last part of work contains measurement of security mechanisms (WEP, WPA, WPA2) effect to transfer rate from the point of view of the end user. The measurement was realized with Iperf application.

This study presents the numerical analysis of steady laminar flow heat transfer in a horizontal rectangular duct with differential heating on the vertical walls. Three heating configurations: one uniform wall temperature (CS1) and two linearly varying wall temperature cases (CS2 and CS3) are analysed. The study considers the combined effects of natural convection, forced convection and radiation heat transfer on the overall heat transfer characteristics. Air, which is assumed to be a non-participating medium, is chosen as the working fluid. A computational fluid dynamics solver is used to solve a set of governing equations for a range of parameters.For chosen duct aspect ratios, the numerical model simulates the flow and heat transfer for two main effects: buoyancy and radiation heat transfer. Buoyancy effect is represented by Grashof number, which is varied from 2,000 to 1,000,000. The effect of radiation heat transfer is examined by choosing different wall surface emissivity values. The weak and strong radiation effect is represented by the emissivity values of 0.05 and 0.85 respectively. Three duct aspect ratios are considered - 0.5, 1 and 2. The heat transfer characteristics of all the above heating configurations - CS1, CS2, and CS3 are analysed and compared. The numerical results show that, for all heating configurations and duct aspect ratios, the overall heat transfer rate is enhanced when the buoyancy effect increases. Since buoyancy effect induces natural circulation, this circulation is therefore the main mechanism that enhances heat transfer. Radiation heat transfer is found to significantly influence convection heat transfer in high Grashof numbers.

In this investigation, two separate methods for determining oxygen transfer rates were applied to the oxidation ditches of an activated sludge plant. Steady state oxygen uptake rate testing and an oxygen mass balance technique were used to propose an in-process procedure for monitoring aeration efficiency using available resources. Although some overall averages offered promise, the testing results revealed that the mass balance analysis yielded results that do not accurately represent the oxygen transfer capabilities within the individual reactors due to shared variables that control the oxygen transfer rate. The steady state method provided more favorable results. Overall averages of daily oxygen transfer rates determined using the steady state method displayed a ratio of oxygen transfer rate between the reactors that corresponds to the expected ratio of 5/6 derived from the linear feet of aerator rotor present in each reactor.

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Although the static measure of accommodation is well documented, the dynamic aspect of the resting state (dark focus) of accommodation is still unknown. Previous studies suggest that refractive error is minimal at the intermediate resting point of accommodation — i.e., at the dark focus distances. Additionally, aging is closely linked to increased refractive error. In order to assess the effects of age on dark focus distance and its utility in enhancing the visual information transfer rate, two experiments were conducted under nighttime condition (scotopic vision) in a laboratory setting. A total of forty participants with normal vision or corrected to normal vision were recruited from four different age groups (younger: 26.9±5.0 years; middle-aged: 50.7±4.8 years; young-old: 64.6±2.8 years; and old-old: 79.8±6.1 years). Each age group included ten participants. In Experiment I, the accommodative status of dark focus at the fovea was assessed objectively using the modified autorefractor, a newly developed method to continuously monitor the accommodation process. The mean dark focus distances for younger, middle-aged, young-old, and old-old adults were 64.5±6.6, 73.4±20.6, 84.4±29, and 92.1±33.4 cm, respectively. There was a significant difference between the dark focus distances among different age groups. Post-hoc analysis indicated that there were statistically significant differences among young and old-old, young and young-old, and middle-aged and old-old age groups. In Experiment II, the information transfer rate was determined while viewing a target at three different distances: 52 cm, 73 cm (current recommended reading distances) and the individual's dark focus. A set of randomized alphabet characters were presented on a visual display with a luminance level of 20 cd/m2 and ambient illumination level of 4 lux. To assess the information transfer rate, participants were asked to read a set of characters aloud with their fastest rate for three seconds. Three measurements of information transfer rate at each viewing distance at random were made. Results obtained from each viewing distance were collected and averaged. The results showed that the mean visual information transfer rate for younger, middle-aged, young-old, and old-old adults were 14.27±1.43, 10.58±2.25, 9.35±2.13, and 7.73±2.36 bits/sec, respectively. There were statistically significant differences at α < 0.05 in means and standard deviations of visual information transfer rate in young and old-old, young and young-old, young and middle-aged, and middle-aged and old-old age groups. The mean visual information transfer rate at 52 cm, 73 cm and individual dark focus were 11.08±3.10, 10.14±2.97, and 10.22±3.42 bits/sec, respectively. There were statistically significant differences at α < 0.05 in means and standard deviations of visual information transfer rate at different viewing distances at 52 cm and 73 cm, and 52 cm and individual's dark focus. However, there were no statistically significant differences in the interaction between age and viewing distance (F = 1.6818, P = 0.1378) on the amount of visual information transfer rate. In summary, the visual information transfer rate was not greater when presenting visual stimulus at the individual's dark focus as compared with two fixed recommended viewing distances (52 cm and 73 cm). The greatest amount of visual information gained was at 52 cm. Actual and potential applications of this study including specifications for designs were also discussed. / Ph. D.

Continuous flow reaction using micro-reactors is a valued technology due to its excellent mass and heat transfer performance, reduced reactor volume, handling capacity of hazardous reactions, and many other process intensifications. These intensifications opportunities interest the fine chemicals, pharmaceuticals producers and other multiphase reaction users who currently use batch processes or already use continuous flow. In this thesis, elements of passive and active mixing are investigated for the application of immiscible liquid-liquid systems. In the first study, the effects of geometrical arrangements of a residence time between mixing units on the interphase mass transfer rates are evaluated with four different immiscible liquid-liquid systems. A presentation of an algorithm for the optimal selection of a reactor and its operating conditions is given in order to enable easy and improved use of one’s micro-reactor. In the second study, the impact of a secondary pulse flow on interphase mass transfer is investigated. A coil without internal baffles is used as the oscillatory-flow coil reactor with a continuous active mixing source. The best application for the reactor is determined using a comparison to other complementary continuous flow platforms in the toolbox approach. The novel advancements presented here will help lead new molecular discoveries and connect the laboratory science scale to the process engineering production scale.

L'intégration de molécules électroactives dans des composants électroniques suscite un intérêt croissant en raison de la miniaturisation constante des dispositifs de microélectronique. Dans ce contexte les propriétés redox des polyoxométallates (POMs) en font des candidats potentiellement attractifs. Ce mémoire présente les différents travaux effectués lors de cette thèse dans le but d'immobiliser des POMs de manière covalente sur des surfaces conductrices. Des composés hybrides organique/inorganique à base de tungstène et de molybdène ont été synthétisés et immobilisés sur des surfaces de carbone, d'or et de silicium, puis la vitesse de transfert électronique entre la surface et le POM a été mesurée par électrochimie. Des études complémentaires ont montré que la densité de greffage a peu d'influence sur la constante de transfert électronique, à l'inverse de paramètres comme la nature du lien covalent ou la présence d'acide en solution. Enfin, la dispersion contrôlée de POMs sur des surfaces d'or a été effectuée. / Introduction of redox active molecules in electronic devices is currently attracting a lot of attention due to the unceasing downscaling of microelectronics components. In this context, the redox properties of polyoxometalates (POMs) make them interesting candidates. This thesis presents the results of this PhD work aiming at covalently grafting POMs on conductive surfaces. Organic/inorganic hybrids based on tungsten and molybdenum cores have been synthesised and grafted onto carbon, gold and silicon surfaces. The electron transfer rate between the electrode surface and the POM has been measured by electrochemistry. Whereas parameters such as the covalent link or the presence of acid have an important effect on the transfer rate, the grafting density does not impact it noticeably. In a last study, POMs were spread on gold surfaces in a controlled manner.

This work concerns the efficient treatment of wastewaters from pulp and paper mills by means of aerobic biological processes. For treatment processes there are many aspects of efficiency and the present study investigates both energy efficiency and purification efficiency during disturbances. Special focus is put on wood extractives, such as resin acids and fatty acids, since they can cause negative effects in fish and other organisms in the receiving waters. They can furthermore be toxic to microorganisms in a biological treatment plant. They also affect oxygen transfer, which is important for energy efficient aeration of aerobic biological treatment processes. This thesis includes five papers/studies and presents a strategy for efficient treatment of forest industrial wastewaters. The results should help creating resilient wastewater treatment strategies with efficient use of energy. One new strategy proposed here includes separation of extractives before the wastewater is treated biologically, and the use of the extra amount of sludge as an energy source, shifting the energy balance from negative to positive.

No description available.