DC arc extinguishing in low voltage switching devices for critical currents

Bakalářská práce se zabývá problematikou zhášení oblouku v oblasti kritických proudů při stejnosměrném napájení. První část teorie popisuje obecně oblouk a poté navazuje popis stejnosměrného oblouku a způsoby jeho zhášení. Druhá teoretická část se věnuje spektrální analýze, obzvlášť emisní metodě. Taktéž jsou představeny metody pro výzkum kritických proudů při zhášení. Praktická část se skládá ze dvou měření. První měření spočívalo v měření spekter v závislosti na čase společně s průběhy napětí a proudu. V druhém měření šlo o závislost doby hoření oblouku na velikosti napětí a proudu. Závěr poté shrnuje výsledky jednotlivých měření, která jsou poté dány do souvislosti.This bachelor’s thesis deals with DC arc extinguishing for critical currents. The first, theoretical part describes and defines an arc, a DC arc and methods of its extinguishing. The second, theoretical part concerns spectral analysis – specifically, the emission method. Methods of research of extinguishing critical currents are also presented. The practical part consists of two measurements. The first measurement consists of spectrum measuring in time, in conjunction with voltage and current measurements. In the second measurement, the goal was to measure the dependence of arc burning time on voltage and current. The thesis concludes with summary of the results of each individual measurement and their presentation in the wider context.

Evaluation of error components in rainfall retrieval from collocated commercial microwave links

Opportunistic rainfall sensing using commercial microwave links (CMLs) operating in telecommunication networks has the potential to complement conventional rainfall monitoring, however, the diversity of sensors and their errors are difficult to handle. This analysis empirically evaluates errors of CML observations that manifest discrepancies between collocated sensors without reference rainfall measurements. Collocated CMLs are evaluated as independent rainfall sensors, which enable us to assess the effect of hardware homogeneity and measurement consistency using CML observations at twelve sites within a real telecommunication network in Prague. The evaluation considers 33 rainfall events distinguishing between stratiform and convective rainfall type in the period 2014 and 2016, monitored in 1-min temporal resolution. Collocated CMLs of identical and different frequencies are evaluated, and different rainfall types are discussed. The collocated commercial microwave links are in excellent agreement. The inherent error of rain-induced attenuation for paired independent commercial microwave links is 0.4 dB. The high correlation of the rainfall intensity measurements between the collocated sensors was obtained in a range between 0.96 and 0.99, and the root mean square error ranges between 0.4 mm h&minus;1 and 1.7 mm h&minus;1. This confirms homogeneous behaviour of the hardware in a real network. Therefore, the data of CMLs of the same characteristics can be processed with identi-cal parameters for rainfall retrieval models.</p

Transboundary Rainfall Estimation Using Commercial Microwave Links

Unlike actual rainfall, the spatial extent of rainfall maps is often determined by administrative and political boundaries. Similarly, data from commercial microwave links (CMLs) is usually acquired on a national basis and exchange among countries is limited. Up to now, this has prohibited the generation of transboundary CML-based rainfall maps despite the great extension of networks across the world. We present CML based transboundary rainfall maps for the first time, using independent CML data sets from Germany and the Czech Republic. We show that straightforward algorithms used for quality control strongly reduce anomalies in the results. We find that, after quality control, CML-based rainfall maps can be generated via joint and consistent processing, and that these maps allow to seamlessly visualize rainfall events traversing the German-Czech border. This demonstrates that quality control represents a crucial step for large-scale (e.g., continental) CML-based rainfall estimation

FLT-PET in previously untreated patients with low-grade glioma can predict their overall survival

BACKGROUND: Low-grade gliomas (LGG) of the brain have an uncertain prognosis, as many of them show continuous growth or upgrade over the course of time. We retrospectively investigated the role of positron emission tomography with 3’-deoxy-3’-[18F]fluorothymidine (FLT-PET) in the prediction of overall survival and event free survival in patients with untreated LGG. No such information is yet available in the literature. MATERIAL AND METHODS: Forty-one patients with previously untreated LGG underwent 55 FLT-PET investigations during their follow-up because of subjective complaints, objective worsening of clinical conditions, equivocal findings or progression on magnetic resonance imaging. The time interval before referral for neurosurgical or radiation treatment was considered to be event free survival, the interval until death as overall survival, respectively. Standardized uptake values (SUV) were measured, and a 3-point scale of subjective assessment was also applied. ROC analysis was used to define cut-off values. The log rank test was used for comparison of Kaplan-Meier survival curves. RESULTS: Eight patients (a total of 9 FLT-PET studies performed) died during follow-up. Progression leading to referral to therapy was recorded in 24 patients (a total of 33 FLT-PET studies). With a cut-off value of SUVmean = 0.236, a median overall survival of 1.007 days was observed in the test positive subgroup while median overall survival for the test negative subgroup was not achieved (p = 0.0002), hazard ratio = 17.6. Subjective assessment resulted in hazard ratio 11.5 (p = 0.0001). Only marginal significance (p=0.0562) was achieved in prediction of event free survival. CONCLUSIONS: Increased FLT uptake in previously untreated patients with LGG is a strong predictor of overall survival. On the other hand, prediction of event free survival was not successful in our cohort, probably because of high prevalence of patients who needed treatment due to symptoms caused by a space-occupying lesion without respect to the proliferative activity of the tumour

Transboundary rainfall estimation using commercial microwave links

Unlike actual rainfall, the spatial extent of rainfall maps is often determined by administrative and political boundaries. Similarly, data from commercial microwave links (CMLs) is usually acquired on a national basis and exchange among countries is limited. Up to now, this has prohibited the generation of transboundary CML-based rainfall maps despite the great extension of networks across the world. We present CML based transboundary rainfall maps for the first time, using independent CML data sets from Germany and the Czech Republic. We show that straightforward algorithms used for quality control strongly reduce anomalies in the results. We find that, after quality control, CML-based rainfall maps can be generated via joint and consistent processing, and that these maps allow to seamlessly visualize rainfall events traversing the German-Czech border. This demonstrates that quality control represents a crucial step for large-scale (e.g., continental) CML-based rainfall estimation

A mathematical model of tumour & blood pHe regulation: The HCO-3/CO2 buffering system

Malignant tumours are characterised by a low, acidic extracellular pH (pHe) which facilitates invasion and metastasis. Previous research has proposed the potential benefits of manipulating systemic pHe, and recent experiments have highlighted the potential for buffer therapy to raise tumour pHe, prevent metastases, and prolong survival in laboratory mice. To examine the physiological regulation of tumour buffering and investigate how perturbations of the buffering system (via metabolic/respiratory disorders or changes in parameters) can alter tumour and blood pHe, we develop a simple compartmentalised ordinary differential equation model of pHe regulation by the View the MathML source buffering system. An approximate analytical solution is constructed and used to carry out a sensitivity analysis, where we identify key parameters that regulate tumour pHe in both humans and mice. From this analysis, we suggest promising alternative and combination therapies, and identify specific patient groups which may show an enhanced response to buffer therapy. In addition, numerical simulations are performed, validating the model against well-known metabolic/respiratory disorders and predicting how these disorders could change tumour pHe

Acute mountain sickness.

Acute mountain sickness (AMS) is a clinical syndrome occurring in otherwise healthy normal individuals who ascend rapidly to high altitude. Symptoms develop over a period ofa few hours or days. The usual symptoms include headache, anorexia, nausea, vomiting, lethargy, unsteadiness of gait, undue dyspnoea on moderate exertion and interrupted sleep. AMS is unrelated to physical fitness, sex or age except that young children over two years of age are unduly susceptible. One of the striking features ofAMS is the wide variation in individual susceptibility which is to some extent consistent. Some subjects never experience symptoms at any altitude while others have repeated attacks on ascending to quite modest altitudes. Rapid ascent to altitudes of 2500 to 3000m will produce symptoms in some subjects while after ascent over 23 days to 5000m most subjects will be affected, some to a marked degree. In general, the more rapid the ascent, the higher the altitude reached and the greater the physical exertion involved, the more severe AMS will be. Ifthe subjects stay at the altitude reached there is a tendency for acclimatization to occur and symptoms to remit over 1-7 days

Bifurcations in reaction-diffusion problems

Náplní této práce je studium bifurkací v superlineárních neurčitých problémech a systémech reakce--difuze, které vykazují Turingovu difuzí řízenou nestabilitu. Při zkoumání těchto problémů využíváme metod matematické a numerické analýzy. Tato disertace je rozdělena na dvě části. V první se věnujeme již zmíněným superlineárním problémům. Jednak jde o studium globální struktury pozitivních řešení pomocí numerické kontinuace a objasnění domněnky o počtu těchto řešení. Dále se pak zabýváme superlineárním problémem s váhovou funkcí. Zde jsme se věnovali nečekaným spektrálním vlastnostem tohoto problému a jejich důsledkům na chování bifurkačních větví. V druhé části této práce shrneme naše výsledky týkající se vlivu jednostranných členů a jednostranných členů obsahujících integrální průměr v rovnici pro aktivátor u systému reakce--difuze na vznik prostorových vzorků. Ukážeme, že množina difuzních parametrů, pro které je bifurkace z konstantního řešení možná, je v takovém případě menší, než u problému bez jednostranných členů. Zároveň prozkoumáme tvorbu vzorků u problému se Schnakenbergovou kinetikou pomocí numerických experimentů pro různé jednostranné členy a okrajové podmínky. Závěrem přikládáme ve čtyřech apendixech články s výsledky, které prezentujeme v textu této disertační práce.ObhájenoThis dissertation thesis presents our recent results concerning bifurcations in superlinear indefinite problems and in reaction-diffusion systems exhibiting Turing's diffusion-driven instability. All problems in the thesis are studied both by analytical and numerical methods. We divided the thesis into two main parts. The first one is focused on superlinear indefinite problems. We study the global structure of positive solutions using numerical continuation and solve the conjecture about number of positive solutions under some additional conditions. Subsequently, we explore a weighted superlinear indefinite problem with unexpected spectral properties, which lead to complex behaviour of branches of nodal solutions. The second part contains results concerning a system of two reaction-diffusion equations exhibiting Turing's instability. We show that adding unilateral terms or unilateral terms involving integral average to the activator equation of the system results in a smaller set of positive diffusion parameters, for which the bifurcation from the trivial solution can occur. All analytical results in the part are accompanied by numerical experiments with Schnakenberg reaction kinetics. The main aim of these experiments is to observe changes in pattern formation provoked by various unilateral terms and boundary conditions. The last part of the thesis is composed of four appendices containing our original publications with all details and technicalities for any interested readers