Experimental and numerical study of a magnetic realization of a Bose-Einstein Condensate in a purely organic spin-1/2 quantum magnet (NIT2Py)

Cette étude porte sur les propriétés magnétiques de cristaux stables à température ambiante composés de molécules organiques à radical libre du nom de NIT2Py. Les mesures de l’aimantation révèlent que chaque molécule a un moment magnétique dû à l’existence d’un électron non apparrié un spin 1/2. Son ordre magnétique est antiferromagnétique. La dépendance du champ issue de la mesure de l’aimantation isothermique à 0.5 K démontre un plateau 1/2 en aimantation. La limite de la phase de la température de champ qui atteint une loi de puissance près d’un point critique quantique, ayant un exposant critique de 1.47 (9), est compatible avec la valeur universelle de 3/2 pour un BEC 3D. La dépendance en température de la chaleur spécifique et l’effet magnétocalorique sont utilisés pour produire un diagramme de phases (H,T). Les phases ordonnées générées par un champ menant à la formation de dômes, ainsi que les niveaux de spins qui se croisent, ont été observées dans le NIT2Py. Ces deux caractéristiques sont des signatures de la réalisation magnétique d’un condensat de Bose-Einstein, et c’est la première fois qu’elles ont été observées dans un aimant quantique purement organique ayant un spin 1/2. Afin de mieux comprendre ce système, nous proposons ici un modèle hamiltonien de spins basé sur les interactions d’échange-Heisenberg. Pour évaluer les constantes du couplage d’échange (Js), nous utilisons des calculs de pointe pour la structure électronique basée sur la théorie de la fonctionnelle de la densité; combinés à l’approche de la symétrie brisée, et nous faisons également usage de l’approche de la cartographie énergétique. Ces méthodes nous fournissent les amplitudes des interactions d’échange du système ainsi que leur signe. Les interactions d’échange dominantes sont reliées à trois Js antiferromagnétiques. Un réseau magnétique, composé de la répétition d’un ensemble minimal de Js dominants, doit être construit. En fait, le réseau magnétique le plus approprié pour ce système, celui qui explique le mieux les propriétés magnétiques de NIT2Py, en est un composé de tétramères possédant chacun quatre spins avec deux interactions antiferromagnétiques entre trétramères. En faisant usage de l’approximation du champ moyen, nous pouvons établir un modèle d’aimantation pour le système de tétramères interagissants qui reproduit les propriétés magnétiques du système, comme celle de la saturation à deux niveaux avec un plateau intermédiaire à la mi-saturation. De plus, la diagonalisation exacte de l’hamiltonien de Heisenberg pour un système incluant quatre tétramères est effectuée afin de reproduire l’aimantation ainsi que d’autres propriétés thermodynamiques du système.The research presented in this thesis focuses on studying the magnetic properties of a purely organic free radical molecule NIT2Py, which can condense into highly stable crystals at room temperature. The magnetization measurements reveal that each molecule carries a magnetic moment due to the existence of a spin-1/2 unpaired electron. The magnetic order is found to be antiferromagnetic (AFM). The field dependence of the magnetization isotherm measurement at 0.5 K shows a 1/2 magnetization plateau. Temperature dependence specific heat and magnetocaloric effect are used to produce the (H,T) phase diagram. In the vicinity of a quantum critical point, the (H,T) phase boundary moves towards a power law with a critical exponent of 1.47(9) that is compatible with the universal value of 1.5 for a 3D BEC. The dome-shaped field-induced ordering phases and the intersecting spin levels observed in NIT2Py are signatures of magnetic realisation of BEC, which is seen for the first time in a purely organic quantum spin-1/2 AFM. We propose a relevant model spin Hamiltonian based on the Heisenberg exchange interactions. We exploit state-of-the art electronic structure calculations through density functional theory combined with the broken-symmetry and the energy mapping approaches to evaluate the exchange coupling constants (Js), which in turn provide us with the sign and strengths of the exchange interactions in the system. The strongest exchange interactions are found to be related to three AFM Js. An appropriate magnetic lattice, which is a repeat pattern of a minimal set of strong Js, is constructed. We found that the magnetic lattice consisting of spin tetramers, each having four spins with two intratetramer AFM interactions, explains the magnetic properties of NIT2Py. By resorting to mean-field approximation, we establish a magnetization model for a system of interacting tetramers, which can reproduce the magnetic properties of the system such as the two-step saturation with an intermediate plateau at half saturated magnetization. Furthermore, an exact diagonalization of the Heisenberg Hamiltonian for a system including four tetramers is carried out, and yields the magnetization and other required thermodynamic properties of the system

An integrated method for ranking of risk in BOT projects

In BOT approach, the private sector is granted a concession to plan, design, construct, operate and maintain a project in a certain period of time and after that it should be transferred to the government. In this paper, at first the risks of the BOT projects are identified, then we rank the risks based on their severity and effect on project objectives (time, cost, quality, safety and environmental) by two methods, namely FTOPSIS and FSAW. In the next stage, obtained results by NGT method are integrated. Afterward, the occurrence and detection values of each risk are determined by experts and ultimately the risks are evaluated according to risk priority number (RPN) of failure mode and effect analysis (FMEA) technique. Finally, an example is shown to highlight the procedure of the proposed method at the end of this paper

A Fuzzy AHP Model in Risk Ranking

The signification risks associated with construction projects need special attention from contractors to analyze and mange the risks. Risk management is the art and science of identifying, analyzing and responding to risk factors throughout the life cycle of the project and in the best interest of its objectives. In proposed model, we firstly identify risks in the construction projects and suitable criteria for evaluate risks and then structure the proposed AHP model. Finally we measure the significant risks in construction projects (SRCP) based on the project’s objectives by using fuzzy analytical hierarchy process (FAHP) technique. Keyword: Construction projects, Project Risk Management, Fuzzy AH

Prolapsed Epiploica of the Sigmoid Colon After Total Laparoscopic Hysterectomy

A laparoscopic approach is recommended for the complication of prolapsed sigmoid colon epiploica after total laparoscopic hysterectomy

Teacher Perfectionism and Iranian English Language Learners’ Motivation and Achievement

Educational psychology has recently reflected a policy shift from focusing on “what goes wrong” in schools, including psychological, physical, and educational disabilities, to recognizing and promoting strengths and positive aspects of students and their environments. Within this scope, some lines of research have examined the extent to which setting personal high standards influences such positive outcomes as educational achievement and high level of motivation. The present study was motivated by the concern that Iranian English language teachers' setting high standards, i.e. perfectionism, may predict English language learners’ motivation and language achievement. Through cluster random sampling, a total of 30 English language teachers with more than one year of experience and 300 elementary English language learners were selected from English Language Institutes in Fars province, Iran. Frost Multidimensional Perfectionism scale and Motivations Underlying English Language Learning questionnaire were used to measure teachers' perfectionism and learners’ language learning motivation, respectively. The learners' final scores in the English courses were collected as a measure of their language learning achievement. The result of simple regression analysis revealed that the teachers' perfectionism did not predict English language learners’ motivation and language achievement. In other words, Iranian English language teachers' perfectionism did not account for any variance in these two variables of interest. Keywords: Perfectionism, Motivation, Language Learning Achievemen

A quality control tool for HDR prostate brachytherapy based on patient-specific geometry and stochastic frontier analysis

Cette étude porte sur le développement d’un outil de contrôle qualité basé sur l’expérience, dérivé du concept de frontière stochastique en économie et s’appuyant sur des connaissances géométriques spécifiques au patient pour améliorer la qualité des traitements de curiethérapie à haut débit de dose pour le cancer de la prostate. Cent plans cliniques de curiethérapie à haut débit de dose de la prostate ont été utilisés dans cette étude, dans laquelle l’échographie transrectale était la seule modalité d’imagerie. Une fraction unique de 15 Gy a était prescrite à tous ces patients. Un algorithme de recuit simulé de planification inverse a été appliqué pour réaliser tous les plans et Oncentra Prostate a été employé comme système d’imagerie et de planification du traitement en temps réel. Les recommandations relatives aux paramètres de dose de la société américaine de curiethérapie pour la cible et les organes à risque ont été suivies. Les relations entre les paramètres géométriques et les paramètres dosimétriques d’intérêt sont examinées. Les paramètres géométriques sont liés aux dimensions anatomiques des patients et ceux associés aux cathéters. Pour déterminer les paramètres géométriques dominants dans un modèle de frontière stochastique donné, les relations monotones entre les paramètres géométriqueset les paramètres dosimétriques d’intérêt sont mesurées avec une approche non paramétrique, à savoir le coefficient de corrélation de Spearman. Ensuite, une recherche de force brute est effectuée pour un modèle donné dans lequel différents modèles, incluant toutes les combinaisons possibles des paramètres géométriques dominantes, sont optimisés. L’optimisation est accomplie en utilisant une méthode de vraisemblance maximale implémentée dans le progiciel de calcul statistique R, avec son algorithme de recuit simulée généralisée. Le test du rapport de vraisemblance et sa valeur-p correspondante sont utilisés pour comparer la signification statistique de l’ajout de nouveaux paramètres géométriques aux modèles. Un modèle de production pour la cible et un modèle de coût pour chacun des organes à risque sont développés pour le traitement par curiethérapie à haut débit de dose guidé par l’échographie transrectale. De plus, pour valider si chacun des modèles développés est universel, nous l’appliquons à une autre catégorie de traitement de la curiethérapie à haut débit de dose, dans laquelle la tomodensitométrie était utilisée comme modalité d’imagerie plutôt que de l’échographie transrectale. Ainsi, une nouvelle cohorte de cent plans cliniques curiethérapie à haut débit de dose guidés par la tomodensitométrie est prise en compte. Un modèle de frontière stochastique de production pour la cible et trois modèles de coût pour les organes à risque basés sur la tomodensitométrie sont développés. Enfin, les modèles intégrés de la tomodensitométrie et de l’échographie transrectale sont comparés.This thesis focuses on developing an experience-based quality control (QC) tool, derived from the concept of stochastic frontier (SF) analysis in economics and based on patient-specific geometric knowledge to improve the quality of the high-dose-rate brachytherapy (HDR-BT) treatment for prostate cancer. One hundred clinical HDR prostate BT plans, using the transrectal ultrasound (TRUS) asthe only imaging modality, all treated with a single fraction of 15 Gy, and made using Inverse PlanningSimulated Annealing (IPSA) algorithm, are studied. Also, Oncentra Prostate system is employed as the real-time 3D prostate imaging and treatment planning system. American Brachytherapy Society dose parameter recommendations for target and organs at risk (OARs) were followed. Relationships between all the different geometric parameters (GPs) and the four dosimetric parameters (DPs) V100 of the prostate, V75 of the bladder and rectum, and D10 of the urethra were examined. Geometricinformation of the patients and catheters are considered as different GPs. To find the dominant GPs in a given SF model, monotonic relationships between the GPs and DPs of interest are measured using a nonparametric approach: the Spearman correlation coefficient. Then, to determine the optimal SF model for each of the target production SF, and the OARs cost SF models, brute-force searches are performed. Different SF models including all the possible combinations of the dominant GPs in the SF model under study are optimized. Optimization is done using a maximum likelihood method implemented in the statistical computing package R, along with its Generalized Simulated Annealing algorithm. The likelihood ratio test and its corresponding p-value are used to compare the statistical significance of adding new GPs to SF models. A production SF (PSF) model for the target, and a costSF (CSF) model for each of the bladder, rectum, and urethra are developed for TRUS-guided HDR-BTtreatment. The difference between the dose value of a plan obtained by IPSA and the one predicted by an SF model is explored. Additionally, to verify if each of the models developed for the TRUS-guided category of the HDR-BT treatment for prostate is universal, we apply it on another category of HDR-BT treatment, in which computed tomography (CT) was used as the imaging modality. So, a different cohort of one hundred clinical CT-guided HDR-BT plans is taken into consideration. A target production SF and three OARs cost SF models are developed for the CT-based plans. Subsequently, the built-in SF models for the TRUS-based and CT-based plans are compared

An integrated method for ranking of risk in BOT projects

In BOT approach, the private sector is granted a concession to plan, design, construct, operate and maintain a project in a certain period of time and after that it should be transferred to the government. In this paper, at first the risks of the BOT projects are identified, then we rank the risks based on their severity and effect on project objectives (time, cost, quality, safety and environmental) by two methods, namely FTOPSIS and FSAW. In the next stage, obtained results by NGT method are integrated. Afterward, the occurrence and detection values of each risk are determined by experts and ultimately the risks are evaluated according to risk priority number (RPN) of failure mode and effect analysis (FMEA) technique. Finally, an example is shown to highlight the procedure of the proposed method at the end of this paper

Hydrogen embrittlement behavior in FeCCrNiBSi TRIP steel

The effect of plastic deformations on the hydrogen embrittlement (HE) of transformation-induced plasticity (TRIP) steel was studied. In situ tensile tests showed that with increasing hydrogen current density, total elongation loss was raised to 36.8% as compared to an uncharged specimen. The electron backscatter diffraction (EBSD) observation indicated that hydrogen charging decreased stacking fault energy (SFE), resulting in the formation of more α′- martensite by both indirect and direct transformation. The α′- martensite volume fraction at the same degree of deformation in uncharged and charged samples was 31% and 39%, respectively. With plastic deformation, reversible trap sites were raised because of the increased dislocation density and the formation of α′- martensite, which was obtained from EBSD characterization and had a good correlation with the results of the thermal desorption spectroscopy (TDS) analysis