1,863 research outputs found
A Lagrangian sub-grid model for the dispersion of clouds of tracers
No full textTurbulence models are expected to satisfy the conflicting requirements of accuracy and computational efficiency. Here we discuss a new model that was recently developed in order to accurately and efficiently describe the dynamic of a clouds of tracers particles in Large Eddy Simulations of homogeneous and isotropic turbulent flows. The models incorporates the multi-scale nature of time and space turbulent velocity correlations that are essential in order to correctly reproduce the relative dispersion of multi-particle clouds. The model can be seen as an off-grid solver for the Eulerian velocity field at the positions of a given number of Lagrangian tracers that self-consistently move with it. Extensions to non homogeneous and isotropic turbulence as well as to the dynamics of particles will be discussed
I.M. Panagiotopoulos as an autobiographer: the adventure of the hero and the personal myth of the author
No full textThe present doctoral dissertation refers to the complex and prominent image of I.M. Panagiotopoulos as a human being, which emerges through his exuberant and diverse work. This dissertation explains man with work and work with man and highlights a special aspect of I.M. Panagiotopoulos that of the pedagogue, through his pedagogical texts, his presence in the classroom and, in general, his pedagogical action. It refers to his childhood, repulsed mostly to the unconscious and to the deeper layers of his psyche. Also, the object of this study is the novel writing of I.M. Panagiotopoulos which istreated as a consequence of the denaturation of his obstructed erotic energy. Next, the two dominant impulses, Love and Death that meet in art and in life, are explored, with the impulses of Death predominant, a fact that leads to their narcissistic character, as well as to their conflicting nature. The anthropogeographical and metaphysical elements that constitute the concept and ontology of Greece are then highlighted. Then, the pedagogical work of I.M. Panagiotopoulos, his positions,contradictions and his proposals for Education is examined. I.M. Panagiotopoulos fought for a school that will offer Liberal Education, within a democratic regime that defines the equality of opportunity in learning. In addition, our national language is presented during its historical course and its expressive and iconographic boldness is highlighted. Finally, this thesis codifies the evolutionary stages of a single hero and creates a typology of his inner adventure, which is the adventure of the hero's desire. It also traces the author's personal myth on a general level, the correspondences and the dialectical relationship between the author and his work, in such a one-way way, that the work defines and composes the author and not vice versa.Η παρούσα διδακτορική διατριβή αναφέρεται στη σύνθετη κα εξέχουσα εικόνα του Ι.Μ. Παναγιωτόπουλου ως ανθρώπου, η οποία ξεπροβάλλει μέσα από το πληθωρικό και πολύμορφο έργο του. Εξηγεί τον άνθρωπο με το έργο και το έργο με τον άνθρωπο. Αναδεικνύει μια ξεχωριστή πλευρά του Ι.Μ. Παναγιωτόπουλου αυτή του Παιδαγωγού, μέσα από τα παιδαγωγικά του κείμενα, από την παρουσία του στην τάξη και γενικότερα από την παιδαγωγική του δράση. Αναφέρεται στην παιδική του ηλικία απωθημένη ως επί το πλείστον στο ασυνείδητο και στα βαθύτερα στρώματα του ψυχισμού του. Επίσης, αντικείμενο της μελέτης είναι η μυθιστορηματική γραφή του Ι.Μ. Παναγιωτόπουλου που αντιμετωπίζεται ως απόρροια μετουσίωσης της παρεμποδισμένης ερωτικής του ενέργειας. Ακολούθως, διερευνώνται οι δύο κυρίαρχες ενορμήσεις, του Έρωτα και του Θανάτου, που ανταμώνουν στην τέχνη και στη ζωή, με κυρίαρχες μάλιστα τις ενορμήσεις του Θανάτου, γεγονός που οδηγεί στον ναρκισσικό χαρακτήρα τους, καθώς και στη συγκρουσιακή τους φύση. Στη συνέχεια, αναδεικνύονται τα ανθρωπογεωγραφικά και μεταφυσικά στοιχεία που συνιστούν την έννοια και την οντολογία της Ελλάδας. Κατόπιν, εξετάζεται το Παιδαγωγικό του έργο και παρουσιάζονται οι θέσεις, οι αντιθέσεις και οι προτάσεις του Ι.Μ. Παναγιωτόπουλου για την Παιδεία. Ο Ι.Μ. Παναγιωτόπουλος αγωνίστηκε για ένα σχολείο, το οποίο θα προσφέρει Αγωγή φιλελεύθερη, μέσα σ’ ένα δημοκρατικό καθεστώς που ορίζει την ισότητα των ευκαιριών στη μάθηση. Επιπλέον, παρουσιάζεται η εθνική μας γλώσσα κατά την ιστορική της διαδρομή και αναδεικνύεται η εκφραστική και εικονοπλαστική της τόλμη. Τέλος, η παρούσα διατριβή κωδικοποιεί τα εξελικτικά στάδια ενός ενιαίου ήρωα και δημιουργεί μια τυπολογία της εσωτερικής του περιπέτειας, που είναι η περιπέτεια της επιθυμίας του ήρωα. Επίσης, ανιχνεύονται ο προσωπικός μύθος του συγγραφέα σε ένα γενικό επίπεδο, οι αντιστοιχίες και η διαλεκτική σχέση ανάμεσα στον συγγραφέα και στο έργο του, με τέτοιο μονοδρομικό τρόπο, ώστε το έργο να καθορίζει και να συνθέτει τον συγγραφέα και όχι αντίθετα
Methods and software for significant indicators determination of the natural language texts author profile
No full textMethods for the formation and optimization of author profiles are presented. The author profile is an image – a vector in a multidimensional space, which components are author’s texts measurements by a number of methods based on 4-grams, stemming, recurrence analysis and formal stochastic grammar. The author’s profile is a model of his language, including vocabulary, sentence syntax features. A comparative analysis of each of the methods effectiveness is carried out. By means of the genetic algorithm, a reduced profile of the author is formed. Insignificant indicators are excluded, which allows to reduce their number by 20%. The reduced author’s profile contains attributes that are significant for this author and is an effective attribution of a particular author.Prombles in programming 2023; 3: 22-2
Information about the Golden Horde in the Saltuk-name of the Ottoman author Ebul-Khayri Rumi
No full textThe purpose of the study is to analyze information on the history of the Golden Horde from the multi-volume work of Ebul-Khayri Rumi “Saltuk-name”, an Ottoman author of the 15th century.
Research materials. Ottoman historical works contain quite original information about the Golden Horde and the Tatar khanates. Their information allows us to reveal previously unknown pages of the history of the Golden Horde period. One of such important and early works is the three-volume work “Saltuk-name” by Ebul-Khayri Rumi, an Ottoman author of the 15th century, describing the legendary history of Sary-Saltuk, who was engaged in the spread of Islam, including in the lands of the Golden Horde, primarily in Crimea. In Russian-language historiography, this author is little known and his information has not been used for scientific research. The relevance of the article is explained by the need to introduce into scientific circulation the information of the “Saltuk-name” about the Golden Horde.
Results and scientific novelty. The study is the first attempt at a systematic analysis of Ebul-Khayri Rumi’s Saltuk-name in Russian. The novelty of the study is the introduction of specific information from the Ottoman historical work and its interpretation into scientific circulation. This study provides an important impetus for the introduction of information from the works of Ottoman authors who wrote about the Golden Horde into active scientific circulation
Measurements of fluid flow in weld pools
No full textUnderstanding the fluid flow in weld pools contributes significantly toward controlling the heat distribution in the base material and the mass distribution of molten base and additive materials. Currently, most investigations focus primarily on numerical models, due to the experimental difficulties associated with the challenging environment in and around the weld pool. Numerical simulations based on computational fluid dynamics are currently addressing the dynamic behaviour of weld pools, such as melting, solidification, temperature and velocity fields; these results provide information about conditions inside the weld pool that is impossible to gain experimentally. However, there is still a shortage of experimental validation to support these models. In this thesis, experimental methods are applied to study the fluid flow of the weld pool in both arc and laser generated weld pools. The general conclusions from the experimental study provides some suggestions for understanding the fluid flow in the weld pool, such as flow asymmetry, rotational flow and interface instabilities. For example, the interface instabilities can affect the energy and mass distribution. Describing these instabilities numerically requires three dimensional flow models. Moreover, the current experimental results question the validity of works where the surfactant concentration is assumed to be constant in the weld pool without consideration of dynamic diffusion and convection. This work has focused on experimental measurement of the fluid dynamics of weld pools, and current results provide a number of validation cases for further numerical simulations.Materials Science & EngineeringMechanical, Maritime and Materials Engineerin
Microstructural Evolution during High-Frequency Post Weld Impact Treatments for High-Strength Steels
No full textMaterial Science and EngineeringMechanical, Maritime and Materials Engineerin
Investigation and control of factors influencing resistance upset butt welding.
No full textThe purpose of this work is to investigate the factors influencing the resistance upset butt welding process to obtain an understanding of the metal behaviour and welding process characteristics, so that new automotive steels can be welded with reduced development time and fewer failures in production. In principle the welding process is rather simple, the materials to be joined are clamped between two electrodes and pressed together. Because there is an interface present with a higher resistance than the base material, heat will be generated at the joint position once the welding current and voltage are applied. As soon as the material is warm and soft enough, an extra (upsetting) pressure is applied and a weld is formed. For making wheel rims, after welding, the upset is removed by means of chisels and shear cut- ting the edges of the weld, followed by rolling the remaining material into the rim. After the upset has been removed the wheel rim is cold formed in several steps to its final shape. For the purpose of this research 2.0 mm thick S460MC and 1.65 mm thick HR45 steel were examined at a test welding facility at Fontijne Grotnes BV. Both steels were specially developed for cold forming and deep drawing purposes and have a mainly ferritic microstructure. An initial research into the crack formation in wheel rims during production was performed, proving that there were no hard and crack susceptible microstructures present in the weld area of the researched materials. The idea that the wheel rims crack due to for example to the presence of bainite and martensite was rejected. There were two main types of cracks discovered, large cracks which are formed due to initial misalignment of the sheets, grease and/or oil at the interface during welding and an uneven heat distribution during welding. The other type of cracks were micro-cracks, which originate from notches introduced during the trimming and rolling of the wheel rim edges after welding. A good alignment of the chisels and cutting tools is necessary to minimise the amount of material that is pushed into the wheel rim Because it was not feasible to do welding experiments in a full wheel rim welding machine at a production facility, the Fontijne Holland Welderr was employed, this is a scaled down version of a production welding machine, but without the material feed or post weld handling facilities. During welding it was observed that the weld sample did not heat up evenly, the emitted light at the interface was brighter at some places than at others. Also after welding the oxidation of the joint area showed that there was a non-uniform heating, with warmer and colder areas. This non-uniformity results in non-uniform weld characteristics and weld quality differences over the length of the weld. Tensile tests of samples taken both from the edges and the centre of welded samples showed that the maximum tensile strength can be as high as 95% of the tensile strength of the base material. However, the strain to failure of the welded samples was only a maximum of 60% with a 30% difference between the central test sample and the edge samples. Erichsen testing was also employed to provide an indication of weld quality. Only the centre of samples was tested due to the way the Erichsen tester is constructed. The Erichsen height was upto 85% of the base material height for the welded samples and it was found that if there are no edge defects present, the Erichsen test is a quick and valid weld quality test. Due to observed non-uniform weld quality and heating of the weld area, the focus of the research shifted to understanding why there was a non-uniformity present. Temperature measurements both by thermal camera and thermocouples showed that there is indeed a non-uniform temperature distribution present during welding over the joint interface. The outer edges of the joint line have higher temperatures than the central part of the weld. Local difference can be as high as 300 K over just 20 mm distance. Also there are hot spots present at either end of the joint line approximately 10 mm from the edges. These hot spots can give rise to local melting in steels with low melting temperature segregation bands. The causes of the uneven temperature distribution were sought. Employing local current measurements during welding was not possible, however when the welding process is just started and there has been no signifcant heating of the weld sample, it is possible to link the voltage distribution directly to the current density distribution. Measuring voltage distributions is relatively easy, voltage probes were spot welded to the surface of the weld samples and measurements showed that there was a non- uniform voltage distribution present during welding. This non-uniformity had the same distribution as the temperature distribution, low voltages at the places were the temperatures were low and high voltage signals where the temperatures were high. Because the non-uniform voltage distribution was measured for both 1 and 2-piece samples (samples with and without an interface) it can be concluded that the boundary conditions governed by the welding equipment have a major influence. The influence of the clamping system and the contact surface of the electrodes were researched to determine their its influence on the heating of the weld area. It was shown that the clamping pressure of the samples was not high enough to prevent slip of the samples during welding and that the samples had to be positioned in the centre of the electrodes to minimise non-uniform heating. At the places of the highest local pressure, the contact resistance is the lowest and heating will consequently be slower at those locations. The highest edge temperatures were measured at the far end of the electrodes, where the lowest clamping pressures are expected. To obtain more uniform heating it is necessary to obtain a more uniform current distribution. This can be accomplished by changing the contact interface between the electrode and the sample surface or the interface between the weld samples. Adapting the electrodes has a small influence but will also result in longer welding times due to a decrease in contact surface area (decrease of 10% results in a 5% increase in weld time). The interface change can decrease the welding time by up to 20% due to a local faster initial heating. Unfortunately the change in interface surface resulted in less repeatable welds. Residual stress in the welded samples was also examined. Both samples with the upset present as well as samples where the upset was removed were measured. The samples with the weld present showed tensile stresses at the centre of the joint line, but compressive stresses at the edges of the sample. When the upset was removed the overall stress state of the sheet became more neutral, the compressive and tensile stress peaks become lower. The stress distribution was explained conceptually with the aid of a modified bar model. Modelling with both MS.Marc and ABAQUS was employed in this research to obtain a better understanding of the complex electrical, thermal and mechanical relationships as observed during real experiments. Three different models were developed, a thermal model, a thermo-mechanical model and a local strain model. The local strain model showed that the Erichsen testing method is a valid method for weld quality assessment. The modelled total strain observed during flaring of wheel rims was lower than the modelled and measured strain during Erichsen testing. Both the thermal and thethermo-mechanical models are predictive. The first one is based on input parameters directly coming from measurements during welding experiments. The thermo-mechanical model is based on the temperature dependent material parameters. The initial thermal model was designed to determine if the non-uniform current density distribution, as measured during experiments, could result in a non-uniform heating of the weld area. The model did not include any temperature dependent parameters nor a mechanical coupling. This showed that the non-uniform current input resulted in a non-uniform heating of the sample. By obtaining a more uniform current distribution over the length of the joint area, a more uniform heating can be obtained. It was also indicated that around contaminations at the interface, either conductive or insulating, a locally higher temperature exists. The mechan- ical model is a more realistic model as it includes the upsetting force. The model predicts the formation of the upset when there are misalignments of the sheets during welding. Because this model includes the temperature dependent material parameters, it is possible to predict the residual stresses after welding, which are in qualitative agreement with the measured residual stresses in real welds.Materials Science and Engineering, Joining and Mechanical BehaviourMechanical, Maritime and Materials Engineerin
Liquid Metal Oscillation and Arc Behaviour during Welding
No full textThe purpose of this research is to obtain insight into the oscillation behaviour of the liquid metal and the arc behaviour during GMA welding. Observations of the weld pool and the arc were undertaken by visual means using a high-speed video and by analysis of the voltage. To deal with the complex phenomena that take place, the research is performed in two steps; firstly, with cold-wire GTA welding on stainless steel AISI 316L tubes where a filler wire is introduced into the weld pool without being preheated, and secondly with pulsed-current GMA (P-GMA) welding on mild steel S235JR plate. The results of the cold-wire GTA experiments showed that for the same penetration state the oscillation modes of the cold-wire and the autogenous GTA weld pools are similar. The partially and the fully penetrated welds oscillate in a sloshy mode and frequencies can be predicted from relatively simple analytical expressions based on weld pool length rather than an equivalent weld pool diameter. When cold-wire GTA welding is performed in the uninterrupted bridging transfer mode the metal transfer does not disturb the voltage signals. The oscillation frequency can be determined from the analysis of voltage signals with the same accuracy as in the case of autogenous GTA welding. Penetration sensing based on pool oscillation can be applied successfully with this welding mode. The pendant droplet in the case of interrupted metal transfer can oscillate due to the action of the plasma jet. This oscillation may disturb the voltage signals associated with weld pool oscillations. The interaction between the transferred droplets and the weld pool triggers the pool into oscillation. Accordingly the results of voltage analysis to determine the weld pool oscillation frequency can be less accurate than those obtained in the case of autogenous GTA welding or the uninterrupted cold-wire GTA welding. The results of the P-GMA welding experiments showed that the current pulses cannot be used to trigger weld pool oscillation effectively, but the impact of the transferred metal droplets can generate travelling liquid waves on the pool. It is also found that the pendant droplet oscillates in an up-and-down motion. In P-GMA welding the dynamics of the weld pool are not reflected clearly on the voltage. In contrast, the oscillation of the pendant droplet is indicated on the voltage signals. The experiments showed that the arc can be divided into different regions based on its intensities. The extent of the different arc regions changes due to the growth and the oscillation of the droplet, which influences the voltage and leads to a nonlinear relationship between the arc voltage and the arc length. There is strong evidence that the modification of the arc structure is caused by the alteration of metal vapour concentration in the plasma. A proposed conceptual model describes the relationship between the arc voltage and the extent of the different arc regions. The model indicates that the average electric field strength of the bright arc region close to the electrode is higher than that of the normal arc. This result can be of importance for improving welding process control and through the arc sensing, for example for optimising droplet detachment to minimise spatter and reduce fume generation The physical phenomena taking place within the different regions of the arc however require further research. This should include experimental measurements of arc composition and temperature, and the development of a mathematical model of the plasma, including energy exchange due to radiative transport and multi-component diffusion.Materials Science & EngineeringMechanical, Maritime and Materials Engineerin
Modelling of welding distortion; the influence of clamping and sequencing
No full textIn past decades, mitigation methods have been developed to reduce welding distortion using different approaches such as low-stress no distortion welding with additional cooling, pre-deformation, thermal tensioning, or by using optimized welding sequences. One parameter that affects the distortion, wich is not explicitly considered in most studies, is the influence of the clamping system. This is an important aspect since clamps are almost always present during the welding process in order to hold the workpiece components in place. Unline most of the mitigation techniques, making use of the clamps for in-line distortion control has the potential advantage that no further energy consuming technique has to be introduced into the process. This thesis deals with techniques to model welding distortion as well as the influence of clamping and sequencing on rlhe esidual welding distortion.Materials Science and EngineeringMechanical, Maritime and Materials Engineerin
Pharmacokinetics of parenteral and oral sustained-release morphine sulphate in dogs
No full textThe pharmacokinetics of single-dose morphine sulphate (MS) administered intravenously (i.v.) and intramuscularly (i.m.) and of oral sustained-release morphine sulphate (OSRMS) were studied in dogs. Beagles (n = 6) were randomly assigned to six treatment groups using a Latin square design. Treatments included MS 0.5 and 0.8 mg/kg i.v. and i.m. and OSRMS 15 and 30 mg orally (p.o). Serum samples were drawn at intervals up to 420 min following parenteral MS and 720 min following OSRMS. Serum was analysed for morphine concentration using a radioimmunoassay. Pharmacokinetic analysis of the results revealed that MS was eliminated by a first-order process best described by a two-compartment model. For i.v. and i.m. data there were no statistically significant differences (P < 0.05) between steady-state volume of distribution, half-life of elimination and plasma clearance. As expected, area under the concentration vs. time curve (AUC) was significantly greater for the 0.8 mg/kg dosage for i.v. and i.m. routes, and time to maximum serum concentration was significantly longer following i.m. administration. For OSRMS there were no significant differences between dosage for any parameter (AUC, Cmax, tmax, t1/2, F) and prolonged absorption of the drug occurred over approximately 6 h. Bioavailability (F) for both oral dosages was approximately 20%. The i.m. route is an effective method for rapid and complete delivery of MS to dogs. OSRMS may be useful in the provision of long-term analgesic therapy in dogs, but further work is required to verify the safety and effectiveness of this preparation.LR: 20061115; PUBM: Print; JID: 7910920; 57-27-2 (Morphine); ppublishSource type: Electronic(1
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