Phase transitions in the Shastry-Sutherland lattice

Two recently developed theoretical approaches are applied to the Shastry-Sutherland lattice, varying the ratio $J'/J$ between the couplings on the square lattice and on the oblique bonds. A self-consistent perturbation, starting from either Ising or plaquette bond singlets, supports the existence of an intermediate phase between the dimer phase and the Ising phase. This existence is confirmed by the results of a renormalized excitonic method. This method, which satisfactorily reproduces the singlet triplet gap in the dimer phase, confirms the existence of a gapped phase in the interval $0.66<J'/J<0.86$Comment: Submited for publication in Phys. Rev.

A renormalized excitonic method in terms of block excitations. Application to spin lattices

Dividing the lattice into blocks with singlet ground state and knowing the exact low energy spectrum of the blocks and of dimers (or trimers) of blocks, it is possible to approach the lowest part of the lattice spectrum through an excitonic type effective model. The potentialities of the method are illustrated on the 1-D frustrated chain and the 1/5-depleted square and the plaquette 2-D lattices. The method correctly locates the phase transitions between gapped and non-gapped phases.Comment: Submitted for publication in Phys. Rev.

Theoretical studies of the phase transition in the anisotropic 2-D square spin lattice

The phase transition occurring in a square 2-D spin lattice governed by an anisotropic Heisenberg Hamiltonian has been studied according to two recently proposed methods. The first one, the Dressed Cluster Method, provides excellent evaluations of the cohesive energy, the discontinuity of its derivative around the critical (isotropic) value of the anisotropy parameter confirms the first-order character of the phase transition. Nevertheless the method introduces two distinct reference functions (either N\'eel or XY) which may in principle force the discontinuity. The Real Space Renormalization Group with Effective Interactions does not reach the same numerical accuracy but it does not introduce a reference function and the phase transition appears qualitatively as due to the existence of two domains, with specific fixed points. The method confirms the dependence of the spin gap on the anisotropy parameter occurring in the Heisenberg-Ising domain

A self-consistent perturbative evaluation of ground state energies: application to cohesive energies of spin lattices

The work presents a simple formalism which proposes an estimate of the ground state energy from a single reference function. It is based on a perturbative expansion but leads to non linear coupled equations. It can be viewed as well as a modified coupled cluster formulation. Applied to a series of spin lattices governed by model Hamiltonians the method leads to simple analytic solutions. The so-calculated cohesive energies are surprisingly accurate. Two examples illustrate its applicability to locate phase transition.Comment: Accepted by Phys. Rev.

Adherence to the United States Department of Agriculture Dietary Recommendations Pre- and During the Coronavirus Disease-19 Pandemic Among Pregnant Women in Arab Countries

During pregnancy, woman’s diet is one of the most preeminent factors affecting mother and child’s health. Prior to the coronavirus disease-19 (COVID-19) pandemic, inadequate maternal diet and low adherence to dietary guidelines was reported among pregnant women in the Arab countries. Nowadays, COVID-19 infection during pregnancy is widely discussed among literature. However, there is limited data on the health impacts of the COVID-19 pandemic on non-infected pregnant women. This substantially larger group also suffered significant lifestyle changes during the lockdown period. The aim of the study is to characterize dietary patterns, intake and adherence to the United States Department of Agriculture (USDA) pregnancy guidelines before and during the COVID-19 pandemic in Arab pregnant women. Using a specially designed questionnaire and using the snowball sampling method, the survey was carried out among a convenient sample of 1,939 pregnant women from five Arab countries. Our study found an increment in the consumption of cereals, fruits, vegetables, dairy products, meats, and nuts that occurred during the pandemic compared to the preceding period. Despite this noticeable increase during the pandemic, the Arab pregnant women in this study had significantly lower adherence to the USDA pregnancy guidelines. The daily consumption of almost all food groups was lower than the USDA’s daily recommendations, except for fruits intake, which was higher than the daily standard. Demonstrated poor adherence to prenatal USDA dietary guidelines by Arab pregnant women can lead to numerous deficiencies and health risks among their offspring. In conclusion, our study showed that before and during the COVID-19 pandemic, poor adherence to dietary recommendations occurred in a considerable number of Arab pregnant women. The findings emphasize the need for nutritional education and intervention during prenatal visits

The global burden of cancer attributable to risk factors, 2010-19 : a systematic analysis for the Global Burden of Disease Study 2019

Background Understanding the magnitude of cancer burden attributable to potentially modifiable risk factors is crucial for development of effective prevention and mitigation strategies. We analysed results from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 to inform cancer control planning efforts globally. Methods The GBD 2019 comparative risk assessment framework was used to estimate cancer burden attributable to behavioural, environmental and occupational, and metabolic risk factors. A total of 82 risk-outcome pairs were included on the basis of the World Cancer Research Fund criteria. Estimated cancer deaths and disability-adjusted life-years (DALYs) in 2019 and change in these measures between 2010 and 2019 are presented. Findings Globally, in 2019, the risk factors included in this analysis accounted for 4.45 million (95% uncertainty interval 4.01-4.94) deaths and 105 million (95.0-116) DALYs for both sexes combined, representing 44.4% (41.3-48.4) of all cancer deaths and 42.0% (39.1-45.6) of all DALYs. There were 2.88 million (2.60-3.18) risk-attributable cancer deaths in males (50.6% [47.8-54.1] of all male cancer deaths) and 1.58 million (1.36-1.84) risk-attributable cancer deaths in females (36.3% [32.5-41.3] of all female cancer deaths). The leading risk factors at the most detailed level globally for risk-attributable cancer deaths and DALYs in 2019 for both sexes combined were smoking, followed by alcohol use and high BMI. Risk-attributable cancer burden varied by world region and Socio-demographic Index (SDI), with smoking, unsafe sex, and alcohol use being the three leading risk factors for risk-attributable cancer DALYs in low SDI locations in 2019, whereas DALYs in high SDI locations mirrored the top three global risk factor rankings. From 2010 to 2019, global risk-attributable cancer deaths increased by 20.4% (12.6-28.4) and DALYs by 16.8% (8.8-25.0), with the greatest percentage increase in metabolic risks (34.7% [27.9-42.8] and 33.3% [25.8-42.0]). Interpretation The leading risk factors contributing to global cancer burden in 2019 were behavioural, whereas metabolic risk factors saw the largest increases between 2010 and 2019. Reducing exposure to these modifiable risk factors would decrease cancer mortality and DALY rates worldwide, and policies should be tailored appropriately to local cancer risk factor burden. Copyright (C) 2022 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license.Peer reviewe

Etudes théoriques des transitions de phase dans des réseaux bidimensionnels périodiques de spins

This thesis presents developments of methods devoted to the theoretical treatment of periodic spins lattices. One of them (Self-Consistent Perturbation) is inspired by perturbative expansion of the wave function from a very localized reference function. This variant of the Coupled Cluster formalism leads to easily solvable sets of coupled polynomial equations. The other methods are based on scale changes, in the spirit of the Real Space Renormalization Group, the lattice being seen as blocks in interaction. The theory of effective Hamiltonians, using the exact spectrum of the dimers or trimers allows one to define effective interactions. One may work with blocks involving odd number of sites, considered as quasi-spins, which may produce isomorphic lattices in an iterative scheme and keeps the concepts and elegance of the Renormalization Group, or blocks of even number of sites, that drives to a renormalized excitonic description of the excited states. The methods were tested on simple lattices, then applied to the research of phase transitions on a series of two-dimensional lattices (anisotropic square, 1/5-depleted, plaquette, Shastry-Sutherland) and ribbons of graphite. The locations of the phase transitions (and the values of the gaps) are consistently predicted by the various methods used and in good agreement with the best available evaluations. The suggestion of the existence of an intermediate phase in the Shastry-Sutherland lattice is reinforced by our computations.Cette thèse présente des développements de méthodes applicables au traitement théorique de réseaux de spins périodiques. Une méthode (Self-Consistent Perturbation), est inspirée par une expansion perturbative de la fonction d'onde à partir d'une fonction de référence très localisée. Cette variante d'un formalisme Coupled Cluster conduit à des équations polynomiales couplées, aisément résolues. Les autres méthodes sont basées sur des changements d'échelle, dans l'esprit du Groupe de Renormalisation dans l'Espace Réel, le réseau étant vu comme des blocs en interaction. La théorie des Hamiltoniens effectifs, utilisant le spectre exact de dimères ou trimères de blocs, permet de définir des interactions effectives. On a considéré soit des blocs à nombre impair de sites, qu'on peut voir comme des quasi-spins, ce qui est susceptible de produire des réseaux isomorphes et permet, d'itérer le processus et de garder l'élégance et les concepts du formalisme du Groupe de Renormalisation, soit des blocs à nombre pair de sites, qui conduisent à une description excitonique renormalisée des états excités. Les méthodes ont été testées sur des réseaux simples, puis appliquées à la recherche de transitions de phase sur une série de réseaux bidimensionnels (carré anisotrope, 1/5-depleted, plaquette, Shastry-Sutherland) et à des rubans graphitiques. Les localisations des transitions de phase (et les valeurs des gaps) sont prédites de façon très cohérentes par les diverses méthodes utilisées et en bon accord avec les meilleurs évaluations disponibles. L'hypothèse de l'existence d'une phase intermédiaire dans le réseau Shastry-Sutherland est confortée par nos calculs

Parallélisme et équilibrage de charges dans le traitement de la jointure sur des architectures distribuées.

The appeal of parallel processing becomes very strong in applications which require ever higher performance and particularly in applications such as: data-warehousing, decision support, On-Line Analytical Processing (OLAP) and more generally DBMS. A linear speed-up is the main objective of parallel algorithms. However, in real applications, it's not obvious to reach this objective due to the high communication cost in parallel and distributed systems and to the possible skew in the charge of different processors. In addition, on heterogeneous multi-user architectures, the load of each processor may highly vary in a dynamic and unpredictable way. In this thesis, we are interested in treating the join and multi-join queries on distributed multi-user heteregeneous systems, grid systems and distributed file systems. We have proposed several algorithms based on using distributed histograms. These algorithms are based on a dynamic data distribution and task allocation which makes them insensitive to data skew and ensure perfect balancing properties during all stages of join computation even on heteregeneous multi-user environment. The complexity analysis of our algorithms and the experimental results show that they have a near-linear speedup.L'émergence des applications de bases de données dans les domaines tels que le data warehousing, le data mining et l'aide à la décision qui font généralement appel à de très grands volumes de données rend la parallélisation des algorithmes des jointures nécessaire pour avoir un temps de réponse acceptable. Une accélération linéaire est l'objectif principal des algorithmes parallèles, cependant dans les applications réelles, elle est difficilement atteignable : ceci est dû généralement d'une part aux coûts de communications inhérents aux systèmes multi-processeur et d'autre part au déséquilibre des charges des différents processeurs. En plus, dans un environnement hétérogène multi-utilisateur, la charge des différents processeurs peut varier de manière dynamique et imprévisible. Dans le cadre de cette thèse, nous nous intéressons au traitement de la jointure et de la multi-jointure sur les architectures distribuées hétérogènes, les grilles de calcul et les systèmes de fichiers distribués. Nous avons proposé une variété d'algorithmes, basés sur l'utilisation des histogrammes distribués, pour traiter de manière efficace le déséquilibre des données, tout en garantissant un équilibrage presque parfait de la charge des différents processeurs même dans un environnement hétérogène et multi-utilisateur. Ces algorithmes sont basés sur une approche dynamique de redistribution des données permettant de réduire les coûts de communication à un minimum tout en traitant de manière très efficace le problème de déséquilibre des valeurs de l'attribut de jointure. L'analyse de complexité de nos algorithmes et les résultats expérimentaux obtenus montrent que ces algorithmes possèdent une accélération presque linéaire

Parallelism and load balancing in the treatment of the join on distributed architectures

L’émergence des applications de bases de données dans les domaines tels que le data warehousing,le data mining et l’aide à la décision qui font généralement appel à de très grands volumes de donnéesrend la parallélisation des algorithmes des jointures nécessaire pour avoir un temps de réponse acceptable.Une accélération linéaire est l’objectif principal des algorithmes parallèles, cependant dans les applicationsréelles, elle est difficilement atteignable : ceci est dû généralement d’une part aux coûts de communicationsinhérents aux systèmes multi-processeurs et d’autre part au déséquilibre des charges des différents processeurs.En plus, dans un environnement hétérogène multi-utilisateur, la charge des différents processeurspeut varier de manière dynamique et imprévisible.Dans le cadre de cette thèse, nous nous intéressons au traitement de la jointure et de la multi-jointure surles architectures distribuées hétérogènes, les grilles de calcul et les systèmes de fichiers distribués. Nousavons proposé une variété d’algorithmes, basés sur l’utilisation des histogrammes distribués, pour traiterde manière efficace le déséquilibre des données, tout en garantissant un équilibrage presque parfait dela charge des différents processeurs même dans un environnement hétérogène et multi-utilisateur. Cesalgorithmes sont basés sur une approche dynamique de redistribution des données permettant de réduire lescoûts de communication à un minimum tout en traitant de manière très efficace le problème de déséquilibredes valeurs de l’attribut de jointure.L’analyse de complexité de nos algorithmes et les résultats expérimentaux obtenus montrent que cesalgorithmes possèdent une accélération presque linéaire.The appeal of parallel processing becomes very strong in applications which require ever higher performanceand particularly in applications such as : data-warehousing, decision support, On-Line Analytical Processing(OLAP) and more generally DBMS. A linear speed-up is the main objective of parallel algorithms. However,in real applications, it’s not obvious to reach this objective due to the high communication cost in parallel anddistributed systems and to the possible skew in the charge of different processors. In addition, on heterogeneousmulti-user architectures, the load of each processor may highly vary in a dynamic and unpredictableway.In this thesis, we are interested in treating the join and multi-join queries on distributed multi-user heteregeneoussystems, grid systems and distributed file systems. We have proposed several algorithms based onusing distributed histograms. These algorithms are based on a dynamic data distribution and task allocationwhich makes them insensitive to data skew and ensure perfect balancing properties during all stages of joincomputation even on heteregeneous multi-user environment. The complexity analysis of our algorithms andthe experimental results show that they have a near-linear speedup

Parallélisme et équilibrage de charges dans le traitement de la jointure sur des architectures distribuées

L émergence des applications de bases de données dans les domaines tels que le data warehousing,le data mining et l aide à la décision qui font généralement appel à de très grands volumes de donnéesrend la parallélisation des algorithmes des jointures nécessaire pour avoir un temps de réponse acceptable.Une accélération linéaire est l objectif principal des algorithmes parallèles, cependant dans les applicationsréelles, elle est difficilement atteignable : ceci est dû généralement d une part aux coûts de communicationsinhérents aux systèmes multi-processeurs et d autre part au déséquilibre des charges des différents processeurs.En plus, dans un environnement hétérogène multi-utilisateur, la charge des différents processeurspeut varier de manière dynamique et imprévisible.Dans le cadre de cette thèse, nous nous intéressons au traitement de la jointure et de la multi-jointure surles architectures distribuées hétérogènes, les grilles de calcul et les systèmes de fichiers distribués. Nousavons proposé une variété d algorithmes, basés sur l utilisation des histogrammes distribués, pour traiterde manière efficace le déséquilibre des données, tout en garantissant un équilibrage presque parfait dela charge des différents processeurs même dans un environnement hétérogène et multi-utilisateur. Cesalgorithmes sont basés sur une approche dynamique de redistribution des données permettant de réduire lescoûts de communication à un minimum tout en traitant de manière très efficace le problème de déséquilibredes valeurs de l attribut de jointure.L analyse de complexité de nos algorithmes et les résultats expérimentaux obtenus montrent que cesalgorithmes possèdent une accélération presque linéaire.The appeal of parallel processing becomes very strong in applications which require ever higher performanceand particularly in applications such as : data-warehousing, decision support, On-Line Analytical Processing(OLAP) and more generally DBMS. A linear speed-up is the main objective of parallel algorithms. However,in real applications, it s not obvious to reach this objective due to the high communication cost in parallel anddistributed systems and to the possible skew in the charge of different processors. In addition, on heterogeneousmulti-user architectures, the load of each processor may highly vary in a dynamic and unpredictableway.In this thesis, we are interested in treating the join and multi-join queries on distributed multi-user heteregeneoussystems, grid systems and distributed file systems. We have proposed several algorithms based onusing distributed histograms. These algorithms are based on a dynamic data distribution and task allocationwhich makes them insensitive to data skew and ensure perfect balancing properties during all stages of joincomputation even on heteregeneous multi-user environment. The complexity analysis of our algorithms andthe experimental results show that they have a near-linear speedup.ORLEANS-SCD-Bib. electronique (452349901) / SudocSudocFranceF