Energy oscillations and a possible route to chaos in a modified Riga dynamo

Starting from the present version of the Riga dynamo experiment with its rotating magnetic eigenfield dominated by a single frequency we ask for those modifications of this set-up that would allow for a non-trivial magnetic field behaviour in the saturation regime. Assuming an increased ratio of azimuthal to axial flow velocity, we obtain energy oscillations with a frequency below the eigenfrequency of the magnetic field. These new oscillations are identified as magneto-inertial waves that result from a slight imbalance of Lorentz and inertial forces. Increasing the azimuthal velocity further, or increasing the total magnetic Reynolds number, we find transitions to a chaotic behaviour of the dynamo.Comment: 8 pages, 8 figures, submitted to Astronomische Nachrichte

Marangoni driven turbulence in high energy surface melting processes

Experimental observations of high-energy surface melting processes, such as laser welding, have revealed unsteady, often violent, motion of the free surface of the melt pool. Surprisingly, no similar observations have been reported in numerical simulation studies of such flows. Moreover, the published simulation results fail to predict the post-solidification pool shape without adapting non-physical values for input parameters, suggesting the neglect of significant physics in the models employed. The experimentally observed violent flow surface instabilities, scaling analyses for the occurrence of turbulence in Marangoni driven flows, and the fact that in simulations transport coefficients generally have to be increased by an order of magnitude to match experimentally observed pool shapes, suggest the common assumption of laminar flow in the pool may not hold, and that the flow is actually turbulent. Here, we use direct numerical simulations (DNS) to investigate the role of turbulence in laser melting of a steel alloy with surface active elements. Our results reveal the presence of two competing vortices driven by thermocapillary forces towards a local surface tension maximum. The jet away from this location at the free surface, separating the two vortices, is found to be unstable and highly oscillatory, indeed leading to turbulence-like flow in the pool. The resulting additional heat transport, however, is insufficient to account for the observed differences in pool shapes between experiment and simulations

History and results of the Riga dynamo experiments

On 11 November 1999, a self-exciting magnetic eigenfield was detected for the first time in the Riga liquid sodium dynamo experiment. We report on the long history leading to this event, and on the subsequent experimental campaigns which provided a wealth of data on the kinematic and the saturated regime of this dynamo. The present state of the theoretical understanding of both regimes is delineated, and some comparisons with other laboratory dynamo experiments are made.Comment: 8 pages, 5 figure, accepted for publication in Comptes Rendus Physiqu

Business cycle coherence analysis: the case of Slovenia

Nakon istraživanja pokazalo se da većina znanstvenika koristi pojam usklađenosti kako bi objasnili koherentnost između cikličkih kretanja rasta između zemalja. Varijable poput BDP-a, potrošnje i investicija rastu/padaju/osciliraju kroz vrijeme stoga statistička mjerenja poslovnih ciklusa zahtijevaju vremenske serije. Upravo taj problem riješen je izvlačenjem trenda, odnosno detrendiranjem podataka. Takva procedura u makroekonomiji omogućena je pomoću Hodrick Prescott filtera koji smo koristili u analizi poslovnih ciklusa. Metodologijski okvir ove studije je baziran na dvije analize: prva je evaluacija cikličkih karakteristika osnovnih makroekonomskih varijabli i druga je mjerenje sinkronizacije poslovnih ciklusa Slovenske ekonomije sa prosjekom EU. Rezultati analize koji su prikazani pokazuju da razine usklađenosti i sličnosti fluktuiraju kroz vrijeme, Usklađenost je puno manje volatilna nego sličnost. Korelacija od 0,17% između ove dvije mjere kroz vrijeme ilustrira da su usklađenost i sličnost zapravo dva različita koncepta koja teže promjenama i fluktuiraju unutar vremenske domene. Isto tako, to nam pokazuje da odstupanja u poslovnim ciklusima i utjecaji različitih šokova imaju različite efekte na ponašanje i opseg rasta u Sloveniji što je indikativno za razumnu ekonomsku politiku. Nakon svega, zaključak je da obje koherentnosti rastu unutar analiziranog perioda, odnosno, njihov (međusobni) pozitivni trend je ponešto drugačiji dok većina odabranih varijabli pokazuje procikličke vodeće trendove. Stoga se ne može govoriti o čistoj fazi razdvajanja za Sloveniju, sve dok razvoj trgovine i financijski tokovi utječu na veću sinkronizaciju ekonomskog rasta između Slovenije i EU, osobito nakon prihvaćanja eura, jedino prethodna kriza opstruira ovaj uzorak u nekim ponašanjima. Zapravo, koncept usklađenosti još ima i vremena i prostora kako bi zadobio višu razinu empirijskog uvažavanja, osobito u zemljama srednje i istočne Europe.After the research we can conclude that most scientists use the term synchronization to explain the coherence between the cyclical growths between countries. The variables such as GDP, consumption and investment are rising/falling/changing over time because the statistical measurements of business cycles require time series. This specific problem is resolved by the extraction of trend, or de-trending data. Such a procedure in macroeconomics is enabled by using the Hodrick Prescott filter that we used in the analysis of business cycles. Methodological framework of this study is based on two analyses: the first is evaluation of cyclical characteristics of macroeconomic variables and the second is measuring of synchronization of business cycles of Slovenian economy with the EU average. Results of the analysis, as presented, show that the level of synchronization and similarity fluctuate over time, however, synchronization is much less volatile than similarity. The correlation of 0.17% between the two measures over time illustrates that the synchronicity and similarity are in fact two different concepts which tend to change and fluctuate within the time domain. Also, it shows that variations in the business cycles and the effects of different shocks have different effects on the behaviour and the extent of growth in Slovenia, which is indicative for the rational economic policy. After all, the conclusion is that both coherence measurements increase under the analyzed period, or, their positive trend is somewhat different while most of the selected variables show pro-cyclical leading trends. The conclusion is that we cannot talk about the clear separation phase for Slovenia, as long as the development of trade and financial flows affect the greater synchronization of economic growth between Slovenia and the EU, especially after the adoption of the euro, only the previous crises obstruct this pattern in certain aspects. In fact, the concept of synchronization still has time and space to gain a higher level of empirical respect, especially within the countries of Central and Eastern Europe

Via pulchritudinis-the power of the image in Christian religious education

Sadržaj je rada motiviran željom za dubljim prepoznavanjem važnosti i uloge umjetnosti unutar ljudske stvarnosti, osobito u životu Crkve. Rad će biti strukturiran u tri međusobno povezana dijela. U prvom dijelu kanimo prikazati povijesni pregled i ambijent unutar kojega se kretala misao i stvarnost umjetnosti razlažući različite povijesno kulturološke epohe s naglaskom na kršćansku misao. U nastavku će biti predstavljen teološki put ljepote – via pulchritudinis - s ciljem rasvjetljavanja ispravnog pogleda na umjetnost i njezin temeljni Izvor – Stvoritelja kojega nam je predstavio sveti papa Ivan Pavao II. U trećem, ujedno i završnom dijelu, usmjerit ćemo se na moć slike promatrajući je s različitih teološko kulturoloških upotreba s naglaskom na njezinu aktualnost u današnjem životu Crkve. Prijeđenim putem, dakle, doprinos rada ići će u smjeru prikazivanja i približavanja navještaja, stvaranja i svjedočenja koje bi slika, kao umjetnički izraz lijepoga, mogla i trebala imati unutar odgoja sadašnjih, ali i budućih naraštaja.The content of this master’s thesis is motivated by the desire for deeper recognition of the importance and role of art within human reality, especially in the life of the Church. The thesis will be structured in three interconnected parts. In the first part we intend to show the historical overview and ambience within which the thought and the reality of art existed, following the paths of various historical culturological epochs that are as well marked by Christian ideas. Below, the theological way of beauty - via pulchritudinis - will be presented with the aim of illuminating the correct view of art and its fundamental Source - the Creator whom St. Pope John Paul II introduced to us. In the manner of concluded so far, in the third, and also the final part, we will focus on the power of the image, observing it in the light of various theological and cultural uses, with an emphasis on its existence in the present life of the Church. Through passed way, therefore, focus of the work will shift in the direction of presenting and bringing forward the proclamation, creation and testimony which the image, as an artistic expression of the good, could have had in the education of the present but also the future generation

Prognostički čimbenici raka vulve

The aim of this retrospective study was to show the effect of clinical, pathologic, cytologic and therapeutic prognostic factors on treatment outcome and survival of patients suffering from vulvar cancer and to determine prognostic significance of each of the individual factors, their mutual significance and impact on survival. The study included patients treated for vulvar cancer at Department of Gynecology and Obstetrics, Osijek University Hospital Centre during the 2000-2011 period. Retrospective analysis included data from patient medical files, along with their pathologic and cytologic findings, and oncologist findings. The study included 59 patients aged 45 to 88 years. Diagnosis was based on pathologic and cytologic status and staging. Univariate analysis showed the lymph node status, adjuvant radiotherapy, chemotherapy and clinical staging of the disease to be statistically significant prognostic factors for overall survival and prognosis of vulvar cancer patients. Multivariate analysis of independent prognostic factors for survival of vulvar cancer patients yielded lymph node status, adjuvant radiotherapy and chemotherapy as positive prognostic factors.Cilj ove retrospektivne studije bio je istražiti utjecaj kliničkih, patoloških, citoloških i terapijskih prognostičkih čimbenika na ishod liječenja i preživljavanje bolesnica s karcinomom vulve te utvrditi prognostičko značenje svakog od pojedinačnih čimbenika kao i njihovo uzajamno značenje i utjecaj na sveukupno preživljavanje. Istraživanje je obuhvatilo bolesnice liječene od karcinoma vulve u razdoblju od 2000. do 2011. godine na Klinici za ginekologiju i porodništvo KBC-a Osijek. Retrospektivna analiza je obuhvaćala njihove povijesti bolesti zajedno s patološkim i citološkim nalazima te nalazima onkologa. Studija je obuhvatila 59 bolesnica u dobi od 45 do 88 godina. Dijagnoza se temeljila na patološkom i citološkom statusu i stadiju. Kao statistički značajni prognostički čimbenici preživljavanja bolesnica s karcinomom vulve u univarijatnoj analizi pokazali su se status limfnih čvorova, adjuvantna radioterapija, kemoterapija i klinički stadij bolesti. U multivarijatnoj analizi neovisnih prognostičkih čimbenika za preživljavanje bolesnica s karcinomom vulve, status limfnih čvorova, pomoćna terapija zračenjem i kemoterapija smatrani su pozitivnim prognostičkim čimbenicima

4D Flow Patterns and Relative Pressure Distribution in a Left Ventricle Model by Shake-the-Box and Proper Orthogonal Decomposition Analysis

Purpose: Intraventricular blood flow dynamics are associated with cardiac function. Accurate, noninvasive, and easy assessments of hemodynamic quantities (such as velocity, vortex, and pressure) could be an important addition to the clinical diagnosis and treatment of heart diseases. However, the complex time-varying flow brings many challenges to the existing noninvasive image-based hemodynamic assessments. The development of reliable techniques and analysis tools is essential for the application of hemodynamic biomarkers in clinical practice. Methods: In this study, a time-resolved particle tracking method, Shake-the-Box, was applied to reconstruct the flow in a realistic left ventricle (LV) silicone model with biological valves. Based on the obtained velocity, 4D pressure field was calculated using a Poisson equation-based pressure solver. Furthermore, flow analysis by proper orthogonal decomposition (POD) of the 4D velocity field has been performed. Results: As a result of the Shake-the-Box algorithm, we have extracted: (i) particle positions, (ii) particle tracks, and finally, (iii) 4D velocity fields. From the latter, the temporal evolution of the 3D pressure field during the full cardiac cycle was obtained. The obtained maximal pressure difference extracted along the base-to-apex was about 2.7 mmHg, which is in good agreement with those reported in vivo. The POD analysis results showed a clear picture of different scale of vortices in the pulsatile LV flow, together with their time-varying information and corresponding kinetic energy content. To reconstruct 95% of the kinetic energy of the LV flow, only the first six POD modes would be required, leading to significant data reduction. Conclusions: This work demonstrated Shake-the-Box is a promising technique to accurately reconstruct the left ventricle flow field in vitro. The good spatial and temporal resolutions of the velocity measurements enabled a 4D reconstruction of the pressure field in the left ventricle. The application of POD analysis showed its potential in reducing the complexity of the high-resolution left ventricle flow measurements. For future work, image analysis, multi-modality flow assessments, and the development of new flow-derived biomarkers can benefit from fast and data-reducing POD analysis.</p

The integral equation approach to kinematic dynamo theory and its application to dynamo experiments in cylindrical geometry

The conventional magnetic induction equation that governs hydromagnetic dynamo action is transformed into an equivalent integral equation system. An advantage of this approach is that the computational domain is restricted to the region occupied by the electrically conducting fluid and to its boundary. This integral equation approach is first employed to simulate kinematic dynamos excited by Beltrami-like flows in a finite cylinder. The impact of externally added layers around the cylinder on the onset of dynamo actions is investigated. Then it is applied to simulate dynamo experiments within cylindrical geometry including the von Karman sodium (VKS) experiment and the Riga dynamo experiment. A modified version of this approach is utilized to investigate magnetic induction effects under the influence of externally applied magnetic fields which is also important to measure the proximity of a given dynamo facility to the self-excitation threshold.Comment: 22 pages, 14 figure