Τριδιάστατα μη-γραμμικά υβριδικά προσομοιώματα για την ανάλυση μεγάλη κλίμακας κατασκευών από οπλισμένο σκυρόδεμα

308 σ.Αντικείμενο της παρούσας Διατριβής αποτέλεσε η διερεύνηση της μη-γραμμικής συμπεριφοράς κατασκευών οπλισμένου σκυροδέματος με τριδιάστατα υβριδικά προσομοιώματα πεπερασμένων στοιχείων. Η έρευνα αυτή έχει ως σκοπό την ανάπτυξη νέων ή βελτίωση υπαρχουσών μεθόδων προσομοίωσης κατασκευών από οπλισμένο σκυρόδεμα, με σκοπό τον ορθότερο και ασφαλέστερο σχεδιασμό των κατασκευών αυτών. Στα πλαίσια της παρούσας Διατριβής, αναπτύχθηκε ένας κώδικας βασισμένος στις αρχές του εγγενούς αντικειμενοστραφούς προγραμματισμού (ReConAn: Reinforced Concrete Analysis) ο οποίος περιέχει στις βιβλιοθήκες του όλα τα πεπερασμένα στοιχεία και καταστατικούς νόμους υλικών με τους οποίους πραγματεύεται η ερευνητική αυτή εργασία. Τα αποτελέσματα έδειξαν ότι ο νέος κώδικας είναι αρκετά γρήγορος σε σχέση με τα εμπορικά λογισμικά (Femap with NXNastran, Opensees). Επιπρόσθετα, αναπτύχθηκε ένα λογισμικό μετεπεξεργασίας (ReConAn Eye) το οποίο επιτρέπει την αναπαράσταση της ρηγμάτωσης. Ο κώδικας ReConAn, ενσωματώνει προσομοιώματα τριδιάστατων εξαεδρικών πεπερασμένων στοιχείων για τη λεπτομερή προσομοίωση κατασκευών οπλισμένου σκυροδέματος. Παράλληλα, έχει τη δυνατότητα προσομοίωσης του φαινομένου της ρηγμάτωσης μέσω της θεώρησης της μεθόδου της διανεμημένης ρωγμής (smeared crack approach) η οποία συνδυάζεται με τον αλγοριθμικά βελτιωμένο καταστατικό νόμο υλικού σκυροδέματος των Kotsovos & Pavlovic ο οποίος ενσωματώνεται για πρώτη φορά σε τριδιάστατα εξαεδρικά πεπερασμένα στοιχεία 8 κόμβων, γεγονός το οποίο καθιστούν την προτεινόμενη μεθοδολογία προσομοίωσης ταχύτατη. Οι οπλισμοί προσομοιώνονται ως εγκιβωτισμένα στοιχεία δοκού (στοιχείο δυνάμεων ΝΒCFB) τα οποία λαμβάνουν υπόψη την διατμητική και καμπτική στιβαρότητα των ράβδων οπλισμού. Η ακρίβεια των αποτελεσμάτων και η υπολογιστική συμπεριφορά του προτεινόμενου προσομοιώματος συγκρίθηκαν με άλλες μεθοδολογίες προσομοίωσης οι οποίες ενσωματώνονται σε εμπορικά λογισμικά πακέτα που υπάρχουν διεθνώς (ΑΤΕΝΑ, ABAQUS, LS-DYNA, ANSYS). Αναπτύχθηκε μία νέα μεθοδολογία αναγνώρισης εγκιβωτισμένων ραβδωτών στοιχείων οπλισμού εντός εξαεδρικών στοιχείων. Η μέθοδος αυτή επιτρέπει την ελεύθερη τοποθέτηση των οπλισμών εντός των εξαεδρικών στοιχείων και απαιτεί ελάχιστο υπολογιστικό χρόνο για την αναγνώριση και δημιουργία του δικτύου των εγκιβωτισμένων πεπερασμένων στοιχείων οπλισμού. Αναγνωρίστηκε η αδυναμία των λεπτομερών τριδιάστατων προσομοιωμάτων να μοντελοποιήσουν μεγάλης κλίμακας κατασκευές από οπλισμένο σκυρόδεμα λόγω του μεγάλου υπολογιστικού κόστους και αναπτύχθηκε ένα νέο τριδιάστατο μη-γραμμικό υβριδικό προσομοίωμα πεπερασμένων στοιχείων για την ανάλυση κατασκευών από οπλισμένο σκυρόδεμα. Για τον σκοπό αυτό, έγινε η σύνδεση του φυσικού στοιχείου δυνάμεων ΝΒCFB οπλισμένου σκυροδέματος με το εξαεδρικό στοιχείο σκυροδέματος με εγκιβωτισμένες ράβδους. Η λογική διακριτοποίησης μίας κατασκευής με υβριδικό προσομοίωμα, προβλέπει την προσομοίωση των κατασκευαστικών μελών τα οποία αναμένεται να αναπτύξουν σημαντικές μη-γραμμικότητες μέσω τριδιάστατων λεπτομερών προσομοιωμάτων και τα υπόλοιπα κατασκευαστικά μέλη μέσω στοιχείων δοκού-υποστυλώματος.Modeling of RC structures with beam-column type finite elements was proven to be insufficient and inaccurate, especially when dealing with shear dominated structural members and structures with complex geometries. Nevertheless, this type of finite element is used widely for the analysis and design of RC structures due to its computational efficiency which is attributed to the resulting reduced-size numerical finite element models. Based on these limitations, an extensive literature survey was conducted, with the intention to allocate the most promising beam-column FE formulation for modeling RC structures. It was concluded that one of the most numerically advanced beam FE type was the Natural Beam-Column Flexibility-Based (NBCFB) element, which was incorporated in ReConAn software code following an extensive parametric investigation regarding its nonlinear numerical behavior. The second objective of this Dissertation was the literature investigation of 2D and 3D nonlinear modeling methods for RC structures with the purpose of acquiring a general idea about the trends on more sophisticated FE models. Furthermore, the selection of the numerically most promising 3D modeling method was a primary objective, in order to develop a sophisticated software tool capable of predicting the nonlinear response of full-scale RC structures in an acceptable computational time. After this literature review, it was concluded that the existing three-dimensional modeling techniques exhibit a number of limitations for capturing the nonlinear behavior of RC structures and that the corresponding software with sophisticated models for the simulation of nonlinear phenomena, such as cracking and detailed rebar modeling, are very sparse. This is attributed to the numerical restrictions and difficulties described above, whereas the required CPU resources become excessive when dealing with such numerical models even for the case of small-scale FE models. It is well known that the analysis of multistory RC buildings is performed through the use of beam-column elements which allow fast simulation times without serious numerical instabilities. In order to be able to analyze this type of structures with three-dimensional constitutive material models incorporated into 3D finite elements and the use of standard CPU systems, the availability of a powerful software tool is not enough. This constraint derives from the fact that CPU processors are bounded from an upper limit which is determined from the hardware itself. Processing power was not and will never be enough since the demand for the solution of larger numerical models constantly increases. In general, this is attributed to the necessity of large-scale simulations with detailed models for the purpose of capturing, as realistically as possible, the nonlinear behavior of structural systems. Therefore, the third objective of this Dissertation was to determine numerical techniques which will overcome these limitations when dealing with full-scale RC structures. A well-known approach that is used widely in computational mechanics is the use of parallel solvers which in this case will become a subject of future work. A second approach for overcoming this numerical restriction is to use models which combine different types of FE models and which will be called “hybrid models”. This type of modeling assumes that shear dominated structural members with an expected highly nonlinear behavior are modeled with 3D detailed finite elements and the rest of the structure is modeled with simpler beam-column finite elements. This technique leads to a reduction in the complexity of the model and of the required computational demand for the solution of the discretized model, retaining at the same time an acceptable accuracy during the analysis procedure. Finally, the last objective of this research work, was the development of an object-oriented FEA code, capable of easily incorporating advanced numerical techniques and modeling methods for the analysis of RC structures. In addition, it will have the ability to incorporate easily future work and simulation enhancements, which will result into a more general FEA code that will provide the ability of realistic and reliable predictions of the nonlinear response of any type of structure. For the purpose of developing an extendable and sustainable program code, modern programming techniques are used and new numerical methods are developed to create the necessary program structure which will incorporate these state of-the-art features. It is the author’s personal opinion that this task is of great importance, especially when dealing with the solution of computationally complex numerical problems.Γεώργιος Α. Μάρκο

Benign thyroid nodules respond to a single administration of 0.3mg recombinant human thyrotropin with highly variable volume increase

IntroductionThe nature of thyroid nodules is heterogenous. Most of them are benign and, in the absence of pressure symptoms of adjunct structures, no treatment is needed. Our objective was to investigate the acute effects of a low dose of recombinant human TSH (rhTSH) on the volume of benign thyroid nodules.Methodswe studied 27 nodules (14 isoechoic and 13 hypoechoic) in 15 (11 women and 4 men; mean age: 51.0 ± 15.9 years) consecutive patients with one to three well-separated asymptomatic benign thyroid nodules. All subjects were euthyroid, with negative thyroid antibodies, and none received levothyroxine. The total thyroid volume and thyroid nodule volume were sonographically determined by two independent examiners (P.B. and M.M.) before, 48 hours and 6 months post intramuscular (IM) administration of 0.3mg rhTSH, and the mean values of the two examiners’ measurements were used; thyroid function tests were obtained at the same time points.ResultsThe mean volume of isoechoic nodules increased by 57.3%, of hypoechoic nodules by 46.6% and of the surrounding thyroid parenchyma by 70.4% 48 hours post-rhTSH; mean volumes had returned to baseline levels 6 months later. A large variance in the volume change responses was observed. The relative change in nodule volume (defined as the percent change in nodule volume divided by the percent change in the surrounding parenchyma) from baseline to 48 hours was significantly higher in isoechoic versus hypoechoic nodules (p<0.05).ConclusionsA single dose of 0.3 mg rhTSH transiently increased the volume of benign thyroid nodules. The increase was more pronounced in isoechoic nodules and had a great variability. Our findings could be useful in the management of benign thyroid nodules, by helping in understanding which nodules would be more responsive to TSH suppression therapy

Energy Resolution Performance of the CMS Electromagnetic Calorimeter

The energy resolution performance of the CMS lead tungstate crystal electromagnetic calorimeter is presented. Measurements were made with an electron beam using a fully equipped supermodule of the calorimeter barrel. Results are given both for electrons incident on the centre of crystals and for electrons distributed uniformly over the calorimeter surface. The electron energy is reconstructed in matrices of 3 times 3 or 5 times 5 crystals centred on the crystal containing the maximum energy. Corrections for variations in the shower containment are applied in the case of uniform incidence. The resolution measured is consistent with the design goals

Penilaian Kinerja Keuangan Koperasi di Kabupaten Pelalawan

This paper describe development and financial performance of cooperative in District Pelalawan among 2007 - 2008. Studies on primary and secondary cooperative in 12 sub-districts. Method in this stady use performance measuring of productivity, efficiency, growth, liquidity, and solvability of cooperative. Productivity of cooperative in Pelalawan was highly but efficiency still low. Profit and income were highly, even liquidity of cooperative very high, and solvability was good

Severe early onset preeclampsia: short and long term clinical, psychosocial and biochemical aspects

Preeclampsia is a pregnancy specific disorder commonly defined as de novo hypertension and proteinuria after 20 weeks gestational age. It occurs in approximately 3-5% of pregnancies and it is still a major cause of both foetal and maternal morbidity and mortality worldwide1. As extensive research has not yet elucidated the aetiology of preeclampsia, there are no rational preventive or therapeutic interventions available. The only rational treatment is delivery, which benefits the mother but is not in the interest of the foetus, if remote from term. Early onset preeclampsia (<32 weeks’ gestational age) occurs in less than 1% of pregnancies. It is, however often associated with maternal morbidity as the risk of progression to severe maternal disease is inversely related with gestational age at onset2. Resulting prematurity is therefore the main cause of neonatal mortality and morbidity in patients with severe preeclampsia3. Although the discussion is ongoing, perinatal survival is suggested to be increased in patients with preterm preeclampsia by expectant, non-interventional management. This temporising treatment option to lengthen pregnancy includes the use of antihypertensive medication to control hypertension, magnesium sulphate to prevent eclampsia and corticosteroids to enhance foetal lung maturity4. With optimal maternal haemodynamic status and reassuring foetal condition this results on average in an extension of 2 weeks. Prolongation of these pregnancies is a great challenge for clinicians to balance between potential maternal risks on one the eve hand and possible foetal benefits on the other. Clinical controversies regarding prolongation of preterm preeclamptic pregnancies still exist – also taking into account that preeclampsia is the leading cause of maternal mortality in the Netherlands5 - a debate which is even more pronounced in very preterm pregnancies with questionable foetal viability6-9. Do maternal risks of prolongation of these very early pregnancies outweigh the chances of neonatal survival? Counselling of women with very early onset preeclampsia not only comprises of knowledge of the outcome of those particular pregnancies, but also knowledge of outcomes of future pregnancies of these women is of major clinical importance. This thesis opens with a review of the literature on identifiable risk factors of preeclampsia

Juxtaposing BTE and ATE – on the role of the European insurance industry in funding civil litigation

One of the ways in which legal services are financed, and indeed shaped, is through private insurance arrangement. Two contrasting types of legal expenses insurance contracts (LEI) seem to dominate in Europe: before the event (BTE) and after the event (ATE) legal expenses insurance. Notwithstanding institutional differences between different legal systems, BTE and ATE insurance arrangements may be instrumental if government policy is geared towards strengthening a market-oriented system of financing access to justice for individuals and business. At the same time, emphasizing the role of a private industry as a keeper of the gates to justice raises issues of accountability and transparency, not readily reconcilable with demands of competition. Moreover, multiple actors (clients, lawyers, courts, insurers) are involved, causing behavioural dynamics which are not easily predicted or influenced. Against this background, this paper looks into BTE and ATE arrangements by analysing the particularities of BTE and ATE arrangements currently available in some European jurisdictions and by painting a picture of their respective markets and legal contexts. This allows for some reflection on the performance of BTE and ATE providers as both financiers and keepers. Two issues emerge from the analysis that are worthy of some further reflection. Firstly, there is the problematic long-term sustainability of some ATE products. Secondly, the challenges faced by policymakers that would like to nudge consumers into voluntarily taking out BTE LEI

Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at √s = 7 TeV

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb[superscript −1]. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

Impacts of the Tropical Pacific/Indian Oceans on the Seasonal Cycle of the West African Monsoon

The current consensus is that drought has developed in the Sahel during the second half of the twentieth century as a result of remote effects of oceanic anomalies amplified by local land–atmosphere interactions. This paper focuses on the impacts of oceanic anomalies upon West African climate and specifically aims to identify those from SST anomalies in the Pacific/Indian Oceans during spring and summer seasons, when they were significant. Idealized sensitivity experiments are performed with four atmospheric general circulation models (AGCMs). The prescribed SST patterns used in the AGCMs are based on the leading mode of covariability between SST anomalies over the Pacific/Indian Oceans and summer rainfall over West Africa. The results show that such oceanic anomalies in the Pacific/Indian Ocean lead to a northward shift of an anomalous dry belt from the Gulf of Guinea to the Sahel as the season advances. In the Sahel, the magnitude of rainfall anomalies is comparable to that obtained by other authors using SST anomalies confined to the proximity of the Atlantic Ocean. The mechanism connecting the Pacific/Indian SST anomalies with West African rainfall has a strong seasonal cycle. In spring (May and June), anomalous subsidence develops over both the Maritime Continent and the equatorial Atlantic in response to the enhanced equatorial heating. Precipitation increases over continental West Africa in association with stronger zonal convergence of moisture. In addition, precipitation decreases over the Gulf of Guinea. During the monsoon peak (July and August), the SST anomalies move westward over the equatorial Pacific and the two regions where subsidence occurred earlier in the seasons merge over West Africa. The monsoon weakens and rainfall decreases over the Sahel, especially in August.Peer reviewe

Search for stop and higgsino production using diphoton Higgs boson decays

Results are presented of a search for a "natural" supersymmetry scenario with gauge mediated symmetry breaking. It is assumed that only the supersymmetric partners of the top-quark (stop) and the Higgs boson (higgsino) are accessible. Events are examined in which there are two photons forming a Higgs boson candidate, and at least two b-quark jets. In 19.7 inverse femtobarns of proton-proton collision data at sqrt(s) = 8 TeV, recorded in the CMS experiment, no evidence of a signal is found and lower limits at the 95% confidence level are set, excluding the stop mass below 360 to 410 GeV, depending on the higgsino mass

Measurement of associated W plus charm production in pp collisions at √s=7 TeV

Peer reviewe