73 research outputs found
Towards the resolution of divergences in the holographic computation of extremal correlators
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 09 February 2016.The main goal of this dissertation is to construct a better understanding of the subtleties that arise in
the holographic computation of extremal correlators. It is well known that these computations, in the
gravitational description, su er from divergences, but the interpretation and origin of these divergences
is unclear. The study starts with detailed computations of two- and three-point functions of a scalar eld
minimally coupled to gravity on Euclidean AdSd space, three-point functions of two giant gravitons and
one light graviton, and three-point functions of the Kaluza-Klein gravitons, using supergravity theory.
Further, we also give the computation of these same correlators in the dual CFT. These involve novel
techniques in the matrix model, including methods that employ Schur polynomials in the dual gauge
theory analysis. By employing the usual AdS=CFT dictionary, we argue that extremal correlators are
naturally related to collinear particles. There are divergences that arise in collinear amplitudes as a
consequence of the fact that the particles momenta are parallel. We therefore reach the suggestive
idea that the divergences in extremal correlator computations are linked to collinear divergences. Much
remains to be done to really establish this connection.LG201
Ătude exploratoire des facteurs clĂ©s de succĂšs de la collaboration : le cas du secteur touristique
MalgrĂ© l'intĂ©rĂȘt grandissant pour l'Ă©tude de la collaboration et du partenariat, encore peu de recherches ont explorĂ© toute la complexitĂ© des relations multiples dans une industrie comme celle du tourisme, qui regroupe des intervenants aux profils variĂ©s (entreprises ou organismes privĂ©s, publics ou Ă but non lucratif). La prĂ©sente recherche a pour principal objectif d'explorer les facteurs pouvant influer sur les choix de stratĂ©gie de collaboration et le succĂšs de cette derniĂšre dans un contexte touristique. Plus spĂ©cifiquement, un examen de la littĂ©rature a Ă©tĂ© effectuĂ©, faisant ressortir pour cette Ă©tude, quatre dimensions relatives aux facteurs : l'environnement, les entitĂ©s Ă la collaboration, les relations et le projet/produit\ud
Une approche qualitative est privilĂ©giĂ©e au moyen d'une Ă©tude de cas multiple, avec la rĂ©alisation de quatorze entrevues semi-dirigĂ©es et d'une recherche documentaire. Les donnĂ©es recueillies auprĂšs des intervenants ont Ă©tĂ© traitĂ©es grĂące Ă une matrice ordonnĂ©e. Les rĂ©sultats ont rĂ©vĂ©lĂ© des Ă©lĂ©ments nouveaux, notamment le recours Ă la consultation, la synergie, la concertation comme facteurs clĂ©s de succĂšs de la collaboration. En outre, la compatibilitĂ© des personnalitĂ©s des partenaires constitue un facteur essentiel pour la rĂ©ussite d'une collaboration. Il en ressort que certains facteurs jugĂ©s importants au niveau de la littĂ©rature, la confiance ou la clartĂ© de la mission, ont Ă©tĂ© peu soulignĂ©s. Cette Ă©tude apporte deux contributions majeures. Elle permet d'enrichir le corpus thĂ©orique sur la collaboration dans une industrie complexe, diversifiĂ©e et fragile telle que l'industrie du tourisme et ce, en conciliant les points de vue de partenaires importants. D'une maniĂšre plus pragmatique, ces rĂ©sultats sont profitables aux gestionnaires de projets oeuvrant dans le public ou le privĂ©. ______________________________________________________________________________ MOTS-CLĂS DE LâAUTEUR : Collaboration, Partenariat, Tourisme, Relations multiples, Facteurs clĂ©s de succĂšs
Les antécédents et les conséquences de la confiance en ligne : le cas du secteur financier
La confiance en ligne revĂȘt un rĂŽle important dans le secteur financier caractĂ©risĂ© notamment par la complexitĂ© et l'intangibilitĂ© des produits/services, le contact humain limitĂ© et le risque perçu sur Internet. En outre, ses antĂ©cĂ©dents et ses consĂ©quences sont rarement intĂ©grĂ©s dans un mĂȘme modĂšle. Ce travail doctoral vise ainsi Ă Ă©tudier les antĂ©cĂ©dents et les consĂ©quences de la confiance en ligne dans le secteur financier suivant une approche intĂ©gratrice. Plus spĂ©cifiquement, cette recherche rĂ©pond Ă deux questions : - Quels sont les antĂ©cĂ©dents qui ont un impact sur la confiance en ligne, et parmi ceux-ci, lesquels sont les plus importants? - Quelles sont les consĂ©quences de la confiance en ligne, et parmi celles-ci, lesquelles sont les plus importantes? Suite Ă une revue dĂ©taillĂ©e de la littĂ©rature traitant du sujet, le cadre conceptuel a pu ĂȘtre dĂ©gagĂ©. Celui-ci fait ressortir les caractĂ©ristiques de quatre catĂ©gories principales d'antĂ©cĂ©dents de la confiance en ligne se rapportant respectivement au site, au marchand, Ă la nature des relations et Ă l'individu. Ensuite, le cadre montre que la valeur perçue, la fidĂ©litĂ© cognitive, affective et conative, la frĂ©quence des visites, le bouche Ă oreille positif/recommandation, la part du portefeuille et les coĂ»ts de transfert constituent les consĂ©quences de la confiance en ligne. Quant Ă la recherche empirique, dont le secteur financier est le terrain, elle a Ă©tĂ© effectuĂ©e par une grande maison de sondage canadienne au moyen d'un sondage sur le Web sous forme de questionnaire auto-administrĂ© auprĂšs de 476 membres d'un panel, clients en ligne de 18 ans et plus. Les donnĂ©es recueillies ont Ă©tĂ© analysĂ©es au moyen du logiciel EQS 6.1 de modĂ©lisation par Ă©quations structurelles. Les rĂ©sultats indiquent notamment que, par ordre d'importance, ce sont le design, la qualitĂ© du support, la qualitĂ© de l'information et la vie privĂ©e/sĂ©curitĂ© qui influent le plus sur la confiance en ligne dans un modĂšle global. Enfin, la fidĂ©litĂ© affective/conative est la principale consĂ©quence de la confiance en ligne. Les rĂ©sultats associĂ©s aux variables modĂ©ratrices montrent, entre autres, que la vie privĂ©e/sĂ©curitĂ© a un impact plus Ă©levĂ© sur la confiance en ligne chez les personnes ayant une propension faible Ă faire confiance et que la rĂ©putation a un impact significatif sur la confiance en ligne chez les personnes percevant un risque Ă©levĂ©. Ainsi, cette recherche permet d'approfondir les connaissances thĂ©oriques liĂ©es Ă la confiance en ligne dans le secteur financier. Elle permet Ă©galement aux gestionnaires de bĂ©nĂ©ficier de recommandations pertinentes.\ud
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Cardiovasc Diabetol
BACKGROUND: Advanced glycation end-products play a role in diabetic vascular complications. Their optical properties allow to estimate their accumulation in tissues by measuring the skin autofluorescence (SAF). We searched for an association between SAF and major adverse cardiovascular events (MACE) incidence in subjects with Type 1 Diabetes (T1D) during a 7 year follow-up. METHODS: During year 2009, 232 subjects with T1D were included. SAF measurement, clinical [age, sex, body mass index (BMI), comorbidities] and biological data (HbA1C, blood lipids, renal parameters) were recorded. MACE (myocardial infarction, stroke, lower extremity amputation or a revascularization procedure) were registered at visits in the center or by phone call to general practitioners until 2016. RESULTS: The participants were mainly men (59.5%), 51.5 +/- 16.7 years old, with BMI 25.0 +/- 4.1 kg/m(2), diabetes duration 21.5 +/- 13.6 years, HbA1C 7.6 +/- 1.1%. LDL cholesterol was 1.04 +/- 0.29 g/L, estimated Glomerular Filtration Rates (CKD-EPI): 86.3 +/- 26.6 ml/min/1.73 m(2). Among these subjects, 25.1% were smokers, 45.3% had arterial hypertension, 15.9% had elevated AER (>/= 30 mg/24 h), and 9.9% subjects had a history of previous MACE. From 2009 to 2016, 22 patients had at least one new MACE: 6 myocardial infarctions, 1 lower limb amputation, 15 revascularization procedures. Their SAF was 2.63 +/- 0.73 arbitrary units (AU) vs 2.08 +/- 0.54 for other patients (p = 0.002). Using Cox-model, after adjustment for age (as the scale time), sex, diabetes duration, BMI, hypertension, smoking status, albumin excretion rates, statin treatment and a previous history of MACE, higher baseline levels of SAF were significantly associated with an increased risk of MACE during follow-up (HR = 4.13 [1.30-13.07]; p = 0.02 for 1 AU of SAF) and Kaplan-Meier curve follow-up showed significantly more frequent MACE in group with SAF upper the median (p = 0.001). CONCLUSION: A high SAF predicts MACE in patients with T1D
Fatty Acid Biomarkers of Dairy Fat Consumption and Incidence of Type 2 Diabetes: A Pooled Analysis of Prospective Cohort Studies
Background
We aimed to investigate prospective associations of circulating or adipose tissue odd-chain fatty acids 15:0 and 17:0 and trans-palmitoleic acid, t16:1n-7, as potential biomarkers of dairy fat intake, with incident type 2 diabetes (T2D).
Methods and findings
Sixteen prospective cohorts from 12 countries (7 from the United States, 7 from Europe, 1 from Australia, 1 from Taiwan) performed new harmonised individual-level analysis for the prospective associations according to a standardised plan. In total, 63,682 participants with a broad range of baseline ages and BMIs and 15,180 incident cases of T2D over the average of 9 years of follow-up were evaluated. Study-specific results were pooled using inverse-variance±weighted meta-analysis. Prespecified interactions by age, sex, BMI, and race/ethnicity were explored in each cohort and were meta-analysed. Potential heterogeneity by cohort-specific characteristics (regions, lipid compartments used for fatty acid assays) was assessed with metaregression. After adjustment for potential confounders, including measures of adiposity (BMI, waist circumference) and lipogenesis (levels of palmitate, triglycerides), higher levels of 15:0, 17:0, and t16:1n-7 were associated with lower incidence of T2D. In the most adjusted model, the hazard ratio (95% CI) for incident T2D per cohortspecific 10th to 90th percentile range of 15:0 was 0.80 (0.73±0.87); of 17:0, 0.65 (0.59± 0.72); of t16:1n7, 0.82 (0.70±0.96); and of their sum, 0.71 (0.63±0.79). In exploratory analyses, similar associations for 15:0, 17:0, and the sum of all three fatty acids were present in both genders but stronger in women than in men (pinteraction \u3c 0.001). Whereas studying associations with biomarkers has several advantages, as limitations, the biomarkers do not distinguish between different food sources of dairy fat (e.g., cheese, yogurt, milk), and residual confounding by unmeasured or imprecisely measured confounders may exist.
Conclusions
In a large meta-analysis that pooled the findings from 16 prospective cohort studies, higher levels of 15:0, 17:0, and t16:1n-7 were associated with a lower risk of T2D
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Fatty acids in the de novo lipogenesis pathway and incidence of type 2 diabetes: A pooled analysis of prospective cohort studies
Funder: Dutch Scientific OrganizationFunder: Foundation Plan AlzheimerFunder: Icelandic Heart AssociationFunder: Academy of FinlandFunder: VicHealth and Cancer Council VictoriaFunder: Juselius FoundationFunder: Uppsala University Hospital and the Swedish Research Council for Health, Working Life and WelfareFunder: the Institut National de la Sante et de la Recherche MedicaleFunder: , the University Bordeaux 2 Victor SegalenFunder: Sanofi; funder-id: http://dx.doi.org/10.13039/100004339Funder: Fondation pour la Recherche Medicale, the Caisse Nationale Maladie des Travailleurs Salaries, Direction Generale de la Sante, MGEN, Institut de la Longevite, Conseils Regionaux dâAquitaine et Bourgogne, Fondation de France, Ministry of ResearchâInstitut National de la Sante and de la Recherche Medicale Programme CohortesFunder: Caisse Nationale pour la Solidarite et lâAutonomieFunder: Swedish Research Council for Health, Working Life and Welfare, Uppsala City Council, Swedish Research Council, and Swedish Diabetes FoundationBackground: De novo lipogenesis (DNL) is the primary metabolic pathway synthesizing fatty acids from carbohydrates, protein, or alcohol. Our aim was to examine associations of in vivo levels of selected fatty acids (16:0, 16:1n7, 18:0, 18:1n9) in DNL with incidence of type 2 diabetes (T2D). Methods and findings: Seventeen cohorts from 12 countries (7 from Europe, 7 from the United States, 1 from Australia, 1 from Taiwan; baseline years = 1970â1973 to 2006â2010) conducted harmonized individual-level analyses of associations of DNL-related fatty acids with incident T2D. In total, we evaluated 65,225 participants (mean ages = 52.3â75.5 years; % women = 20.4%â62.3% in 12 cohorts recruiting both sexes) and 15,383 incident cases of T2D over the 9-year follow-up on average. Cohort-specific association of each of 16:0, 16:1n7, 18:0, and 18:1n9 with incident T2D was estimated, adjusted for demographic factors, socioeconomic characteristics, alcohol, smoking, physical activity, dyslipidemia, hypertension, menopausal status, and adiposity. Cohort-specific associations were meta-analyzed with an inverse-variance-weighted approach. Each of the 4 fatty acids positively related to incident T2D. Relative risks (RRs) per cohort-specific range between midpoints of the top and bottom quintiles of fatty acid concentrations were 1.53 (1.41â1.66; p < 0.001) for 16:0, 1.40 (1.33â1.48; p < 0.001) for 16:1n-7, 1.14 (1.05â1.22; p = 0.001) for 18:0, and 1.16 (1.07â1.25; p < 0.001) for 18:1n9. Heterogeneity was seen across cohorts (I2 = 51.1%â73.1% for each fatty acid) but not explained by lipid fractions and global geographical regions. Further adjusted for triglycerides (and 16:0 when appropriate) to evaluate associations independent of overall DNL, the associations remained significant for 16:0, 16:1n7, and 18:0 but were attenuated for 18:1n9 (RR = 1.03, 95% confidence interval (CI) = 0.94â1.13). These findings had limitations in potential reverse causation and residual confounding by imprecisely measured or unmeasured factors. Conclusions: Concentrations of fatty acids in the DNL were positively associated with T2D incidence. Our findings support further work to investigate a possible role of DNL and individual fatty acids in the development of T2D
Omega-6 Fatty Acid Biomarkers and Incident Type 2 Diabetes: Pooled Analysis of Individual-Level Data for 39â740 Adults from 20 Prospective Cohort Studies
Background: The metabolic effects of omega-6 polyunsaturated fatty acids (PUFAs) remain contentious, and little evidence is available regarding their potential role in primary prevention of type 2 diabetes. We aimed to assess the associations of linoleic acid and arachidonic acid biomarkers with incident type 2 diabetes. Methods: We did a pooled analysis of new, harmonised, individual-level analyses for the biomarkers linoleic acid and its metabolite arachidonic acid and incident type 2 diabetes. We analysed data from 20 prospective cohort studies from ten countries (Iceland, the Netherlands, the USA, Taiwan, the UK, Germany, Finland, Australia, Sweden, and France), with biomarkers sampled between 1970 and 2010. Participants included in the analyses were aged 18 years or older and had data available for linoleic acid and arachidonic acid biomarkers at baseline. We excluded participants with type 2 diabetes at baseline. The main outcome was the association between omega-6 PUFA biomarkers and incident type 2 diabetes. We assessed the relative risk of type 2 diabetes prospectively for each cohort and lipid compartment separately using a prespecified analytic plan for exposures, covariates, effect modifiers, and analysis, and the findings were then pooled using inverse-variance weighted meta-analysis. Findings: Participants were 39 740 adults, aged (range of cohort means) 49-76 years with a BMI (range of cohort means) of 23·3-28·4 kg/m(2), who did not have type 2 diabetes at baseline. During a follow-up of 366 073 person-years, we identified 4347 cases of incident type 2 diabetes. In multivariable-adjusted pooled analyses, higher proportions of linoleic acid biomarkers as percentages of total fatty acid were associated with a lower risk of type 2 diabetes overall (risk ratio [RR] per interquintile range 0·65, 95% CI 0·60-0·72,
Autofluorescence cutanée des produits de glycation avancée (AGE), mémoire métabolique et complications du diabÚte
In the context of the ageing of the population and the increase of age related diseases such as diabetes, new biomarquers of the long-term health status should be considered. Advanced glycation end products (AGE) are molecules indicators of the metabolic burden over time, called âmetabolic memoryâ. AGE play an important role in long term diabetes injuries and in the global decline of the metabolism related to ageing. Skin accumulation of AGE can be measured by autofluorescence instantly and non-invasivly with a tool called AGE-READER. The objectives of my dissertation were to evaluate the value of the skin autofluorescence (sAF) of AGE as marker of metabolic memory in elderly people from the 3-City cohort and in parallel, in patients with type 1 diabetes, evaluate the prognostic value of sAF for diabetes complications. In the elderly population, we showed that sAF reflected glycemic and renal status of 10 years before. In patients with type 1 diabetes, sAF was associated to the presence of neuropathy 4 years later. Moreover, in this same population, we described the evolution of sAF in 4 years of follow-up and we showed that the principal determinants of the evolution of sAF were kidney function and insulin pump therapy. Finally, we also found that increase of sAF in 4 years was associated with the occurrence of kidney disease. This work rises new research opportunities about the interest of sAF at differents key ages as biomarker of pathologies which evolve in several decades.Dans un contexte de vieillissement de la population et dâaccroissement des maladies chroniques liĂ©es Ă lâĂąge comme le diabĂšte, de nouveaux biomarqueurs de lâĂ©tat de santĂ© Ă long terme doivent ĂȘtre Ă©tudiĂ©s. Les produits de glycation avancĂ©e (AGE) sont des molĂ©cules tĂ©moins de la charge mĂ©tabolique accumulĂ©e au cours du temps, dĂ©nommĂ©e "mĂ©moire mĂ©tabolique". Les AGE jouent un rĂŽle important dans les lĂ©sions Ă long terme dans le diabĂšte et dans le dĂ©clin du mĂ©tabolisme global liĂ© au vieillissement. Lâaccumulation cutanĂ©e des AGE peut ĂȘtre mesurĂ©e par autofluorescence (AF) de maniĂšre instantanĂ©e et non invasive grĂące Ă lâAGE-READER. Les objectifs de cette thĂšse Ă©taient dâĂ©valuer la valeur de lâAF cutanĂ©e des AGE en tant que marqueur de mĂ©moire mĂ©tabolique chez des personnes ĂągĂ©es de la cohorte des 3-CitĂ©s et parallĂšlement dâĂ©valuer la valeur pronostique de lâAF pour les complications du diabĂšte chez des patients porteurs de diabĂšte de type 1. Chez les personnes ĂągĂ©es, nous avons montrĂ© que lâAF reflĂ©tait les statuts glycĂ©mique et rĂ©nal 10 ans avant la mesure. Chez les patients atteints de diabĂšte de type 1, lâAF Ă©tait associĂ©e Ă la prĂ©sence dâune neuropathie 4 ans plus tard. De plus, dans cette mĂȘme population, nous avons dĂ©crit lâĂ©volution de lâAF sur 4 ans de suivi. Nous avons montrĂ© que les principaux dĂ©terminants de son Ă©volution Ă©taient la fonction rĂ©nale et le traitement par pompe Ă insuline. Enfin nous avons trouvĂ© que lâaugmentation de lâAF sur 4 ans de suivi Ă©tait associĂ©e Ă la survenue de la maladie rĂ©nale. Ces travaux soulĂšvent de nouvelles perspectives de recherche quant Ă lâintĂ©rĂȘt de lâAF Ă diffĂ©rents Ăąges clĂ©s de la vie en tant que biomarqueur de pathologies qui Ă©voluent sur des dizaines dâannĂ©es
Autofluorescence cutanée des produits de glycation avancée (AGE), mémoire métabolique et complications du diabÚte
In the context of the ageing of the population and the increase of age related diseases such as diabetes, new biomarquers of the long-term health status should be considered. Advanced glycation end products (AGE) are molecules indicators of the metabolic burden over time, called âmetabolic memoryâ. AGE play an important role in long term diabetes injuries and in the global decline of the metabolism related to ageing. Skin accumulation of AGE can be measured by autofluorescence instantly and non-invasivly with a tool called AGE-READER. The objectives of my dissertation were to evaluate the value of the skin autofluorescence (sAF) of AGE as marker of metabolic memory in elderly people from the 3-City cohort and in parallel, in patients with type 1 diabetes, evaluate the prognostic value of sAF for diabetes complications. In the elderly population, we showed that sAF reflected glycemic and renal status of 10 years before. In patients with type 1 diabetes, sAF was associated to the presence of neuropathy 4 years later. Moreover, in this same population, we described the evolution of sAF in 4 years of follow-up and we showed that the principal determinants of the evolution of sAF were kidney function and insulin pump therapy. Finally, we also found that increase of sAF in 4 years was associated with the occurrence of kidney disease. This work rises new research opportunities about the interest of sAF at differents key ages as biomarker of pathologies which evolve in several decades.Dans un contexte de vieillissement de la population et dâaccroissement des maladies chroniques liĂ©es Ă lâĂąge comme le diabĂšte, de nouveaux biomarqueurs de lâĂ©tat de santĂ© Ă long terme doivent ĂȘtre Ă©tudiĂ©s. Les produits de glycation avancĂ©e (AGE) sont des molĂ©cules tĂ©moins de la charge mĂ©tabolique accumulĂ©e au cours du temps, dĂ©nommĂ©e "mĂ©moire mĂ©tabolique". Les AGE jouent un rĂŽle important dans les lĂ©sions Ă long terme dans le diabĂšte et dans le dĂ©clin du mĂ©tabolisme global liĂ© au vieillissement. Lâaccumulation cutanĂ©e des AGE peut ĂȘtre mesurĂ©e par autofluorescence (AF) de maniĂšre instantanĂ©e et non invasive grĂące Ă lâAGE-READER. Les objectifs de cette thĂšse Ă©taient dâĂ©valuer la valeur de lâAF cutanĂ©e des AGE en tant que marqueur de mĂ©moire mĂ©tabolique chez des personnes ĂągĂ©es de la cohorte des 3-CitĂ©s et parallĂšlement dâĂ©valuer la valeur pronostique de lâAF pour les complications du diabĂšte chez des patients porteurs de diabĂšte de type 1. Chez les personnes ĂągĂ©es, nous avons montrĂ© que lâAF reflĂ©tait les statuts glycĂ©mique et rĂ©nal 10 ans avant la mesure. Chez les patients atteints de diabĂšte de type 1, lâAF Ă©tait associĂ©e Ă la prĂ©sence dâune neuropathie 4 ans plus tard. De plus, dans cette mĂȘme population, nous avons dĂ©crit lâĂ©volution de lâAF sur 4 ans de suivi. Nous avons montrĂ© que les principaux dĂ©terminants de son Ă©volution Ă©taient la fonction rĂ©nale et le traitement par pompe Ă insuline. Enfin nous avons trouvĂ© que lâaugmentation de lâAF sur 4 ans de suivi Ă©tait associĂ©e Ă la survenue de la maladie rĂ©nale. Ces travaux soulĂšvent de nouvelles perspectives de recherche quant Ă lâintĂ©rĂȘt de lâAF Ă diffĂ©rents Ăąges clĂ©s de la vie en tant que biomarqueur de pathologies qui Ă©voluent sur des dizaines dâannĂ©es
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