National Repository of Grey Literature 351 records found  1 - 10nextend  jump to record: Search took 0.02 seconds. 
Effect of Cylinder Roughness on Strouhal Number
Yanovych, Vitalii ; Duda, D. ; Uruba, Václav ; Procházka, Pavel P. ; Antoš, Pavel
The main goal of this paper is to establish a better understanding of the relationship between a Strouhal number and surface roughness. Hot-wire anemometry was used to evaluations the characteristics of turbulent flow behind circular cylinders with different relative roughness 0% (smooth surface) 0.83%, 1.67%, 3.33%, and 6.67%. At the experimental investigation, the Reynolds number based on the cylinder diameter was 5 × 103 < Red < 2 × 104. The obtained data showed that the Strouhal number decreased with increasing roughness. While, the dissipation rate decreases, and the value of the Kolmogorov and Taylor microscales increases. Also, spectral analysis of streamwise velocity fluctuations allowed us to estimate the location of the vortex-shedding frequency which at growing roughness tends to reduce.
The Design and Aerodynamic Testing of DPIK Probe
Procházka, Pavel P. ; Barraclough, V. ; Skála, Vladislav ; Uruba, Václav
The isokinetic probe used to detect the liquid phase drift from the cooling tower is presented here. The main motivation is costs reduction that arises during standard drift measurements. The probe was developed in the framework of the grant project between private company 4Jtech and Institute of Thermomechanics. The aerodynamic design and optimization of this probe should fulfill one important criterion – to capture the droplets from the drift with maximal efficiency. Kalorimetric principle is then used to evaluate the amount of trapped water. Standard PIV (Particle Image Velocimetry) measurement technique and modified IPI (Interferometric Particle Imaging) methods were used to measure the flow field topology and the particle size distribution, respectively.
Interspecific nest parasitism in diving ducks - Common Pochard Aythya ferina and Tufted Duck Aythya fuligula and its effect on reproductive performnce
Neužilová, Šárka ; Musil, Petr (advisor) ; Weidinger, Karel (referee) ; Procházka, Petr (referee)
This PhD thesis is connecting three publications and one manuscript and focuses on the study of interspecific nest parasitism among particular duck species of family Anatidae. The first part describes the occurrence of interspecific nest parasitism, in the study area of Trebon between years 1999 and 2008 in three diving duck species (Aythini): the Common pochard (Aythya ferina), the Tufted duck (Aythya fuligula) and the Red-crested Pochard (Netta rufina) and two dabbling duck species the Gadwall (Anas strepera and the mallard (Anas platyrhynchos). The most of parasitic eggs was laid by Red-creasted Pochard and Common Pochard. In this period, inter-specific nest parasitism was recorded in 6.6% of nests. The values were compared with the results of studies in the same species between 1975 and 1980. when inter-specific nest parasitism was in 13.9% of nests. The difference in rate of nest parasitism is caused as a result of a decline in breeding populations of the studied species. In the second analysis, we investigate whether parasitically laid eggs are of different size than non-parasitic eggs in three diving duck species; the Common Pochards, the Tufted Ducks and the Red-Crested Pochards. Parasitic eggs of the Common Pochard were significantly longer than non-parasitic eggs of the same species and...
Final report on the MIT project no. CZ.01.1.02/0.0/0.0ú20_321/0023673
Zolotarev, Igor ; Pešek, Luděk ; Gabriel, Dušan ; Procházka, Pavel P.
The MIT project entitled Development of a switchgear for severe conditions and reduction of risks of critical infrastructure threat was focused on research, development of optimized design and provision of configuration technology for repeated production of different variants of modular system switchgear for use in severe conditions and reduction of risks of seismic threat, to ensure the reliability of critical infrastructure. The output is to be a prototype seismically robust device with a dynamically lightweight design, high reliability of switchgear and electrical equipment assembly function, and a software application for interactive design and documentation.
A new blade cascade for flutter studies
Šnábl, Pavel ; Pešek, Luděk ; Procházka, Pavel P. ; Skála, V.
In this paper, a new blade cascade, developed in the Institute of Thermomechanics, is presented. The geometry of the cascade was modified so now the stall flutter can occur. It has some major construction improvements over the original cascade which now allow more precise and reliable measurements. The stability of the new blade cascade with five NACA 0010 profiles with rotational degree of freedom is assessed by Travelling Wave Mode approach and Aerodynamic Influence Coefficient approach.
Ecological consequences of seasonal bird migration
Brlík, Vojtěch ; Procházka, Petr (advisor) ; Maggini, Ivan (referee) ; Piersma, Theunis (referee)
Environmental seasonality, and associated fluctuation in resource abundance, affects organisms throughout their life cycles. Periods of resource scarcity can be avoided by seasonal migration, strategy common in animals, including birds. However, the long journeys of migratory birds separate the stages of their annual cycles in space and time, and present them with a variety of challenges. Environmental conditions that migrants experience may have local effects, or may carry over across seasons, and have delayed impacts on individuals and populations. To better understand the interactions between migratory animals and their environment, we integrated individual tracking, environmental measures, and population data within a full annual cycle perspective. We contributed to the understanding that environmental conditions can affect migratory populations both en route and during stationary non-breeding periods, and that their effects can be observed on a continental scale. We also showed, across species and migratory flyways, that stages of the annual cycle are tightly linked during migration, but that these links weaken during prolonged non-breeding stationarity, with implications for individual success and future prospects under ongoing environmental change. To enhance the ability to trace animal...
Year-round specialists? Habitat niches of migratory birds on breeding and non-breeding grounds
Zálišová, Jaromíra ; Procházka, Petr (advisor) ; Reif, Jiří (referee)
Migratory birds undertake challenging journeys over vast distances each year to cope with seasonality in their environment and to exploit peaks in seasonal resources. The environments in which they are found in these geographically distinct regions over the course of the annual cycle vary considerably, forcing them to cope with a wide range of conditions. By examining whether migratory birds are year-round specialists that follow their niche or generalists that inhabit a broader range of habitats, we can better understand their ecology and the conservation implications associated with global change. However, our knowledge of habitat selection across seasons is still limited. This thesis aimed to explore and evaluate, through a literature review, existing knowledge on habitat selection by migratory bird species on breeding and wintering grounds. Emphasis was placed on the mechanisms influencing habitat selection, including geographical and anthropogenic influences, as well as to clarify the ecological requirements and potential specialization of migratory birds during their annual cycle. The current literature shows that migratory birds are most likely less opportunistic than previously thought, but a comprehensive analysis of data on habitat use by individual species is still missing and I would...
Spectral Indices as a Tool for Hop Growth Evaluation
Seidlová, Jana ; Procházka, Pavel ; Kumhálová, Jitka
The use of unmanned aerial vehicles (UAV) to monitor crop growth is nowadays a common non-invasive way how to obtain information on the current state of crops. Spectral indices derived from multispectral images obtained in the right growth stage can then serve as a good data source for agro-technical interventions and yield estimation. Hop belongs among the crops where it is possible to scan the individual growth parameters very exactly. In the year 2021, significant precipitation amounts were recorded during the growing season, when it turned out that UAVs are a very powerful tool for determining the quality of production or quantification of vegetation damage compared to the previous year (2020). It was found that the common spectral indices were possible to use for calculation leaf area, structure, vigor and chlorophyll content of hop gardens.
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2D Physical Modelling of Semiconductor Equations for Verification of 1D Lumped-Charge Model of Bipolar Power Devices
Mikláš, Jan ; Procházka, Petr
The paper demonstrates a finite-element method(FEM) simulation model of semiconductor devices operation.Classical semiconductor equations employing drift, diffusionand generation-recombination transport of charge carriers areestablished and variational forms for FEM assembly are derivedin detail, including a basic voltage and current boundary conditions.Mathematically, a system of mutually coupled nonlinearequations need to be solved, which requires extensive use ofnonlinear iteration solver. The derived model was coded inPython by strict use of open source tools, mainly grouped aroundFEniCSx project. Graphic output figures and characteristics forbasic semiconductor structures are presented to demonstrate thefunctionality of model.An ultimate goal of presented effort is derivation and verificationof simplified semi-analytical model of Insulated-gate bipolartransistor (IGBT), including precise transient behavior.This kind of model should be calibrated by use ofmeasurement-obtained data, so the qualitative behavior of devicephysics at reasonable computational cost is of primary interestof presented FEM model as opposed to commercial devicedevelopment tools aiming at precise quantitative outputs; whichneed to be experimentally calibrated even so.As an additional step to simplified one-dimensional modelusability verification, results of unusual way of experimentalestimation of minority-carrier excess charge within power bipolartransistor collector and base during on-state is presented andcompared to simulation result.
Growth of organic heterostructures on metal surfaces
Kugler, David ; Novák,, Jiří (referee) ; Procházka, Pavel (advisor)
Během depozice organických molekul na kovové substráty často dochází k spontánnímu uspořádání molekul vlivem mezimolekulárních a molekulárně-substrátových interakcí. Tento jev se nazývá samouspořádání a může být využit k vytváření atomárně přesných funkčních struktur. Vzrůstající zájem vzbuzují zejména tenké vrstvy organických polovodičů pro jejich potenciální využití v polovodičovém průmyslu. Efektivita takovýchto zařízení je však nevyhnutelně spojena s přechodovým odporem na rozhraní polovodiče a kovové elektrody. Studium typu růstu organických polovodičů na kovových substrátech je tak zcela zásadní pro jejich budoucí využití. Tato diplomová práce se nejprve zabývá vytvořením krycí monovrstvy substrátu Ag(111) z dobře uspořádaných molekul kyseliny 1,3,5-benzen-trikarboxylové (BTB). Hlavním cílem práce je pak použití této vrstvy jako substrátu pro růst dalších vrstvev tvořených molekulami pentacenu, což je jeden z intenzivně zkoumaných organických polovodičů. Bylo dosaženo pokrytí povrchu uspořádanou vrstvou pentacenu o rozloze vhodné pro praktické využití. Pro studium růstu molekulárních vrstev a jejich vlastností byla použita nízkoenergiová elektronová mikroskopie, skenovací tunelovací mikroskopie, rentgenová fotoelektronová spektroskopie a ultrafialová fotoelektronová spektroskopie.

National Repository of Grey Literature : 351 records found   1 - 10nextend  jump to record:
See also: similar author names
42 PROCHÁZKA, Petr
42 Prochazka, Petr
49 Procházka, Pavel
19 Procházka, Pavel P.
42 Procházka, Petr
2 Procházka, Přemysl
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