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Control Techniques of Grid Connected PWM Rectifiers under Unbalanced Input Voltage Conditions
Bejvl, Martin ; Šimek, Petr ; Škramlík, Jiří ; Valouch, Viktor
Current-controlled voltage source converters are widely used in grid-connected applications,for example at ac drives with indirect frequency converters.The structure and parameters of the PLL are developed and proposed in order to cope with the grid containing both the positive and the negative sequence component, and minimize the wrong frequency transients during phase angle steps and also in the start-up stage. The DSC technique was realised. There is also necessary to compensate the negative sequence component in the grid voltage. The negative sequence component of the grid voltage causes ripple of the dc voltage in the intermediate circuit. Several sophisticated topologies of converter current controller were developed, simulated and tested for this purpose. Results of simulation and experimental tests are provided to evaluate different current control schemes and phase locked loop techniques.
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Differences in CO2 Extraction of Vegetable Oils, Essential Oils, and Minor Components from Plants
Sovová, Helena
Significant progress in understanding the phenomena that control supercritical fluid extraction from plants was made in the last years and is reflected in the literature. Combination of chemical engineering approach and botanical knowledge has appeared to be fruitful for the choice of extraction model and even for the prediction of extraction kinetics. This contribution refers to the papers utilizing knowledge of plant microstructure and location of extracted substances together with extraction equilibrium and attempts to specify the differences among extraction kinetics of vegetable oils, essential oils, and other substances. The most abundant substances like vegetable oils in seeds can be regarded in first approximation as non-interacting with plant matrix, in contrast to the minor components whose equilibrium concentration in CO2 is affected by their adsorption on matrix and often also by co-extracted substances.
Fulltext: content.csg -  PDF
Plný tet: SKMBT_C22012102414100 - PDF
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Ethics of auditors in practice
SVOJŠOVÁ, Pavlína
In my thesis I evaluated and assessed the activities of auditors in relation to the ethics of behavior in terms of legislation of the Czech Republic. I focused on the published cases of misconduct of auditors and the subsequent punitive sanctions. Ethical behavior is the basis for the auditor's professionalism. In connection with the accounting scandals and falsification of accounting and audit reports, the public began to discuss - among other things - auditors' liability for fraud detection leading to distorted accounts of the entities and the principles of ethical behavior started to get into the spotlight of auditors?, which was later enshrined in legal and professional standards including Code of Ethics of the International Federation of Accountants (IFAC). Expectations of many users of financial statements from the auditor's report are too high and usually go up beyond what the auditor can actually verify and confirm. However, it must be acknowledged that not all auditors are sufficiently aware of their responsibilities in relation to the distortion of financial statements due to fraud or misconduct, and adequately adapt their audit procedures due to them. Certainly worth mentioning is the most visible impact of accounting scandals in the accounting and auditing profession - the fall of Arthur Andersen, one of the former "Big Five" auditing firms. Accounting profession has responded by developing and tightening ethical standards with an emphasis on the conduct of professional accountants in the public interest, not only in the interests of individual clients or employers. The role of audit in society is irreplaceable. Quality of the audits undertaken, however, ultimately depends on the auditor's discipline and education, the control of the Council Chamber and also public oversight of auditing, as well as pressure of the users of financial statements and of the representatives on the appropriateness and quality of outputs. Ethics in the auditor's work and its compliance in life are the things that determine auditor?s reputation.
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Microalgal Growth Problem for the Photosynthetitc Factory and its Optimization: An Overview and Further Analysis
Čelikovský, Sergej
The overview of the micro-algal growth problem for the photosynthetic factory and its optimal control solution is presented here. First, the model description and its properties like Haldan steady state dynamics, light integration property and the forward invariance of the set of biologically well-de ned states are described. This shows that the model meets basic experimentally based requirements. Further, its optimal control problem is formulated and solved analytically for the one dimensional singular perturbation based reduction. Properties of the optimal control for the reduced model are discussed and compared with some experimental observations. Among them, the general biotechnological paradigm that on large time intervals the optimal solution is, in certain sense, almost constant, is substantiated. As a new original result of this paper, the explicit solvable di erentiable equation for the unsaturated part of the optimal control is derived.
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Simulation of flow and dissipation of turbulent kinetic energy in an agitated vessel
Kysela, Bohuš ; Skočilas, J. ; Konfršt, Jiří ; Chára, Zdeněk
Velocity field and distribution of dissipation rate are key parameters for design of mixing apparatuses. In this contribution we compared the CFD (Computational Fluid Dynamics) calculations with results of mean ensemble-averaged velocities measured by LDA (Laser Doppler Anemometry) and with results of derived dissipation rates where the total dissipation rate was used as control value. The comparison showed that the neither k-ε model (based on isotropic turbulence) nor RSM (Reynolds Stress Model) did not calculate the velocities in regions where the trailing vortices are developed (near impeller blade edges etc.) and in a region of main stream of the impeller where the flow is strongly anisotropic quite accurately. Similar discrepancies were observed for the dissipation rate; moreover the lower values of dissipation rate are also calculated in bulk volume of mixing vessel. Generally, the total dissipation rate results from the CFD calculations are lower then the real values. This is in an agreement with other published results.
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Centralized multirobot system
Staněk, Ondřej ; Obdržálek, David (advisor) ; Mráz, František (referee)
Title: Centralized multirobot system Author: Ondřej Staněk Department: The Department of Software Engineering Supervisor: RNDr. David Obdržálek Supervisor's e-mail address: David.Obdrzalek@mff.cuni.cz This thesis focuses on design and implementation of a centralized multi-robot system. A host computer (or cellphone) controls several tiny PocketBot2 mobile robots. These robots feature various sensors. They can perform line-following and they are equipped with a system for detecting obstacles and other robots. Although the PocketBot2 robots were designed and built within the frame of this thesis, the core of the thesis itself lies in the software. For the PocketBot2 hardware, an embedded control system was designed and implemented. It interfaces robot's sensors and carries out basic movement commands. Bluetooth technology is used for wireless data transfer between robots and the host. In the host, a multi-platform control library was implemented. It provides access to sensors of individual robots and controls their movement. The library ensures convenient interface for implementing centralized multi-robot algorithms. Keywords: robot, library, PocketBot, Bluetooth, Java
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Economic research bulletin (2011, No.2). Macro-financial linkages: theory and applications
Česká národní banka
The first article presents a model that incorporates credit frictions and serves to describe the dynamics of credit spreads in moderate as well as crisis times. The model is then used to evaluate the effects of quantitative easing and credit easing. The second article proposes a model that shows how the conditions of a parent bank might affect the interest rate setting of its subsidiary or branch in a foreign country, and is followed by an empirical assessment of the ten largest banks in the Czech Republic under foreign control. The remaining papers are of an empirical nature. The third article investigates the household credit market in the Czech Republic, proposing a new indicator of default risk and examining its determinants. The fourth article evaluates the extent to which financial variables help predict key Czech macroeconomic indicators. The last article presents evidence on the degree and evolution of financial integration of the Czech Republic and four other EU countries outside the euro area.
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PCR based assay for detection garden pea lec gene
Vráblík, Aleš ; Hodek, Jan ; Ovesná, Jaroslava
The method was developed and verified by staff of National reference laboratory for GMO identification and DNA fingerprinting suited for governmental control laboratories and private laboratories that analyze food and feed derived from various plant matrices. Method can be applied for quantification of GM pea in a sample, when reference gene is used as a standard. The method describe internal garden pea specific gene, lektin in this case, detection using PCR and real-time PCR. The general principle of the assay relies on lektin specific sequence presence that represents a species specific gene of garden pea. In many matrices DNA is damaged so amplification of short stretches of DNA is used. After amplification of target exploiting newly developer species specific gene primers PCR products are separated by electrophoresis in agarose gel. Resulting band is visualized by UV light and its position is compare with size standard. Alternatively, real-time PCR and ABI platform in combination with SYBR® Green can be used. Reaction parameters are described and specificity of reaction was verified. LOD as well as LOQ was defined.
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