Insights to the European debt crisis using recurrence quantification and network analysis

URL des Documents de travail : http://centredeconomiesorbonne.univ-paris1.fr/documents-de-travail/Documents de travail du Centre d'Economie de la Sorbonne 2015.35 - ISSN : 1955-611XThe turmoil in the sovereign debt markets in Europe has raised concerns on the usefulness of sovereign credit default swaps and government bond yields in periods of distress. In addressing this issue, we introduce a novel nonlinear approach for the analysis of non-stationary multivariate data based on complex networks and recurrence analysis. We show the relevance of the approach in studying joint risk connections, extracting hidden spatial information, time dependence, detection of regime changes and providing early warning indicators. The feasibility and relevance of the approach in studying systemic risk is discussed. Finally, we share more light on possible extensions and applications of the approach to systemic risk.Les turbulences sur les marchés de la dette souveraine en Europe ont suscité les intérêts sur l'utilité des contrats d'échange sur risque de crédits (CDS) et des rendements sur les obligations d'État dans les périodes de crise. En examinant cette question, nous introduisons une nouvelle approche non linéaire pour l'analyse des données à variables multiples non-stationnaires, basée sur les réseaux complexes et l'analyse de récurrence. Nous montrons la pertinence de l'approche en étudiant les risques communs, en extrayant les informations spatiales cachées et la dépendance par rapport au temps, en détectant des changements de régime et en fournissant des indicateurs d'alerte précoce. La faisabilité et la pertinence de l'approche dans l'étude du risque systémique est discutée. Enfin, la lumière est faite sur d'éventuelles extensions et applications de l'approche du risque systémique

Using small-angle X-ray scattering to investigate the compaction behaviour of a granulated clay

The compaction behaviour of a commercial granulated clay (magnesium aluminium smectite, gMgSm) was investigated using macroscopic pressure-density measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray microtomography (XμT) and small-angle X-ray scattering (SAXS). This material was studied as a potential compaction excipient for pharmaceutical tabletting, but also as a model system demonstrating the capabilities of SAXS for investigating compaction in other situations. Bulk compaction measurements showed that the gMgSm was more difficult to compact than polymeric pharmaceutical excipients such as spheronised microcrystalline cellulose (sMCC), corresponding to harder granules. Moreover, in spite of using lubrication (magnesium stearate) on the tooling surfaces, rather high ejection forces were observed, which may cause problems during commercial tabletting, requiring further amelioration. Although the compacted gMgSm specimens were more porous, however, they still exhibited acceptable cohesive strengths, comparable to sMCC. Hence, there may be scope for using granular clay as one component of a tabletting formulation. Following principles established in previous work, SAXS revealed information concerning the intragranular structure of the gMgSm and its response to compaction. The results showed that little compression of the intragranular morphology occurred below a relative density of 0 · 6, suggesting that granule rearrangements or fragmentation were the dominant mechanisms during this stage. By contrast, granule deformation became considerably more important at higher relative density, which also coincided with a significant increase in the cohesive strength of compacted specimens. Spatially-resolved SAXS data was also used to investigate local variations in compaction behaviour within specimens of different shape. The results revealed the expected patterns of density variations within flat-faced cylindrical specimens. Significant variations in density, the magnitude of compressive strain and principal strain direction were also revealed in the vicinity of a debossed feature (a diametral notch) and within bi-convex specimens. The variations in compaction around the debossed notch, with a small region of high density below and low density along the flanks, appeared to be responsible for extensive cracking, which could also cause problems in commercial tabletting

In utero exposure to cigarette smoking, environmental tobacco smoke and reproductive hormones in US girls approaching puberty

BACKGROUND/AIMS: Evidence is unclear whether prenatal smoking affects age at menarche and pubertal development, and its impact upon hormones has not been well studied. We aim to identify potential pathways through which prenatal smoking and environmental tobacco smoke (ETS) affect reproductive hormones in girls approaching puberty. METHODS: We examined the association between prenatal smoking, current ETS and luteinizing hormone (LH) and inhibin B (InB) in 6- to 11-year-old girls in the 3rd National Health and Nutrition Examination Survey, 1988-1994. Parents/guardians completed interviewer-assisted questionnaires on health and demographics at the time of physical examination. Residual blood samples were analyzed for reproductive hormones in 2008. RESULTS: Of 660 girls, 19 and 39% were exposed to prenatal smoke and current ETS, respectively. Accounting for multiple pathways in structural equation models, prenatally exposed girls had significantly lower LH (β = -0.205 log-mIU/ml, p < 0.0001) and InB (β = -0.162, log-pg/ml, p < 0.0001). Prenatal smoking also influenced LH positively and InB negatively indirectly through BMI-for-age. ETS was positively associated with LH, but not with InB. CONCLUSION: Exposure to maternal smoking may disrupt reproductive development manifesting in altered hormone levels near puberty

Food variety, dietary diversity, and type 2 diabetes in a multi-center cross-sectional study among Ghanaian migrants in Europe and their compatriots in Ghana: the RODAM study.

PURPOSE: The importance of dietary diversification for type 2 diabetes (T2D) risk remains controversial. We investigated associations of between- and within-food group variety with T2D, and the role of dietary diversification for the relationships between previously identified dietary patterns (DPs) and T2D among Ghanaian adults. METHODS: In the multi-center cross-sectional Research on Obesity and Diabetes among African Migrants (RODAM) Study (n = 3810; Ghanaian residence, 56%; mean age, 46.2 years; women, 63%), we constructed the Food Variety Score (FVS; 0-20 points), the Dietary Diversity Score (DDS; 0-7 points), and the Diet Quality Index-International (DQI-I) variety component (0-20 points). The associations of these scores, of a "rice, pasta, meat and fish" DP, of a "mixed" DP, and of a "roots, tubers and plantain" DP with T2D were calculated by logistic regression. RESULTS: The FVS was inversely associated with T2D, adjusted for socio-demographic, lifestyle, and anthropometric factors [odds ratio (OR) for T2D per 1 standard deviation (SD) increase: 0.81; 95% confidence interval (CI) 0.71-0.93]. The DDS and the DQI-I variety component were not associated with T2D. There was no association of the "mixed" DP and the "roots, tubers and plantain" DP with T2D. Yet, the "rice, pasta, meat and fish" DP is inversely associated with T2D (OR for T2D per 1 SD increase: 0.82; 95% CI 0.71-0.95); this effect was slightly attenuated by the FVS. CONCLUSIONS: In this Ghanaian population, between-food group variety may exert beneficial effects on glucose metabolism and partially explains the inverse association of the "rice, pasta, meat and fish" DP with T2D

Obesity and type 2 diabetes in sub-Saharan Africans - Is the burden in today's Africa similar to African migrants in Europe? The RODAM study.

BACKGROUND: Rising rates of obesity and type 2 diabetes (T2D) are impending major threats to the health of African populations, but the extent to which they differ between rural and urban settings in Africa and upon migration to Europe is unknown. We assessed the burden of obesity and T2D among Ghanaians living in rural and urban Ghana and Ghanaian migrants living in different European countries. METHODS: A multi-centre cross-sectional study was conducted among Ghanaian adults (n = 5659) aged 25-70 years residing in rural and urban Ghana and three European cities (Amsterdam, London and Berlin). Comparisons between groups were made using prevalence ratios (PRs) with adjustments for age and education. RESULTS: In rural Ghana, the prevalence of obesity was 1.3 % in men and 8.3 % in women. The prevalence was considerably higher in urban Ghana (men, 6.9 %; PR: 5.26, 95 % CI, 2.04-13.57; women, 33.9 %; PR: 4.11, 3.13-5.40) and even more so in Europe, especially in London (men, 21.4 %; PR: 15.04, 5.98-37.84; women, 54.2 %; PR: 6.63, 5.04-8.72). The prevalence of T2D was low at 3.6 % and 5.5 % in rural Ghanaian men and women, and increased in urban Ghanaians (men, 10.3 %; PR: 3.06; 1.73-5.40; women, 9.2 %; PR: 1.81, 1.25-2.64) and highest in Berlin (men, 15.3 %; PR: 4.47; 2.50-7.98; women, 10.2 %; PR: 2.21, 1.30-3.75). Impaired fasting glycaemia prevalence was comparatively higher only in Amsterdam, and in London, men compared with rural Ghana. CONCLUSION: Our study shows high risks of obesity and T2D among sub-Saharan African populations living in Europe. In Ghana, similarly high prevalence rates were seen in an urban environment, whereas in rural areas, the prevalence of obesity among women is already remarkable. Similar processes underlying the high burden of obesity and T2D following migration may also be at play in sub-Saharan Africa as a consequence of urbanisation

Peripheral insulin resistance rather than beta cell dysfunction accounts for geographical differences in impaired fasting blood glucose among sub-Saharan African individuals: findings from the RODAM study.

AIMS/HYPOTHESIS: The aim of this study was to assess the extent to which insulin resistance and beta cell dysfunction account for differences in impaired fasting blood glucose (IFBG) levels in sub-Saharan African individuals living in different locations in Europe and Africa. We also aimed to identify determinants associated with insulin resistance and beta cell dysfunction among this population. METHODS: Data from the cross-sectional multicentre Research on Obesity and Diabetes among African Migrants (RODAM) study were analysed. Participants included Ghanaian individuals without diabetes, aged 18-96 years old, who were residing in Amsterdam (n = 1337), Berlin (n = 502), London (n = 961), urban Ghana (n = 1309) and rural Ghana (n = 970). Glucose and insulin were measured in fasting venous blood samples. Anthropometrics were assessed during a physical examination. Questionnaires were used to assess demographics, physical activity, smoking status, alcohol consumption and energy intake. Insulin resistance and beta cell function were determined using homeostatic modelling (HOMA-IR and HOMA-B, respectively). Logistic regression analysis was used to study the contribution of HOMA-IR and inverse HOMA-B (beta cell dysfunction) to geographical differences in IFBG (fasting glucose 5.6-6.9 mmol/l). Multivariate linear regression analysis was used to identify determinants associated with HOMA-IR and inverse HOMA-B. RESULTS: IFBG was more common in individuals residing in urban Ghana (OR 1.41 [95% CI 1.08, 1.84]), Amsterdam (OR 3.44 [95% CI 2.69, 4.39]) and London (OR 1.58 [95% CI 1.20 2.08), but similar in individuals living in Berlin (OR 1.00 [95% CI 0.70, 1.45]), compared with those in rural Ghana (reference population). The attributable risk of IFBG per 1 SD increase in HOMA-IR was 69.3% and in inverse HOMA-B was 11.1%. After adjustment for HOMA-IR, the odds for IFBG reduced to 0.96 (95% CI 0.72, 1.27), 2.52 (95%CI 1.94, 3.26) and 1.02 (95% CI 0.78, 1.38) for individuals in Urban Ghana, Amsterdam and London compared with rural Ghana, respectively. In contrast, adjustment for inverse HOMA-B had very minor impact on the ORs of IFBG. In multivariate analyses, BMI (β = 0.17 [95% CI 0.11, 0.24]) and waist circumference (β = 0.29 [95%CI 0.22, 0.36]) were most strongly associated with higher HOMA-IR, whereas inverse HOMA-B was most strongly associated with age (β = 0.20 [95% CI 0.16, 0.23]) and excess alcohol consumption (β = 0.25 [95% CI 0.07, 0.43]). CONCLUSIONS/INTERPRETATION: Our findings suggest that insulin resistance, rather than beta cell dysfunction, is more important in accounting for the geographical differences in IFBG among sub-Saharan African individuals. We also show that BMI and waist circumference are important factors in insulin resistance in this population

An epigenome-wide association study in whole blood of measures of adiposity among Ghanaians: the RODAM study

Background: Epigenome-wide association studies (EWAS) have identified DNA methylation loci involved in adiposity. However, EWAS on adiposity in sub- Saharan Africans are lacking despite the high burden of adiposity among African populations. We undertook an EWAS for anthropometric indices of adiposity among Ghanaians aiming to identify DNA methylation loci that are significantly associated. Methods: The Illumina 450k DNA methylation array was used to profile DNA methylation in whole blood samples of 547 Ghanaians from the Research on Obesity and Diabetes among African Migrants (RODAM) study. Differentially methylated positions (DMPs) and differentially methylation regions (DMRs) were identified for BMI and obesity (BMI ≥ 30 kg/m2), as well as for waist circumference (WC) and abdominal obesity (WC ≥ 102 cm in men, ≥88 cm in women). All analyses were adjusted for age, sex, blood cell distribution estimates, technical covariates, recruitment site and population stratification. We also did a replication study of previously reported EWAS loci for anthropometric indices in other populations. Results: We identified 18 DMPs for BMI and 23 for WC. For obesity and abdominal obesity, we identified three and one DMP, respectively. Fourteen DMPs overlapped between BMI and WC. DMP cg00574958 annotated to gene CPT1A was the only DMP associated with all outcomes analysed, attributing to 6.1 and 5.6% of variance in obesity and abdominal obesity, respectively. DMP cg07839457 (NLRC5) and cg20399616 (BCAT1) were significantly associated with BMI, obesity and with WC and had not been reported by previous EWAS on adiposity. Conclusions: This first EWAS for adiposity in Africans identified three epigenome-wide significant loci (CPT1A, NLRC5 and BCAT1) for both general adiposity and abdominal adiposity. The findings are a first step in understanding the role of DNA methylation in adiposity among sub-Saharan Africans. Studies on other sub-Saharan African populations as well as translational studies are needed to determine the role of these DNA methylation variants in the high burden of adiposity among sub- Saharan Africans

A test for a new modelling : The Univariate MT-STAR Model

In ESTAR models it is usually quite difficult to obtain parameter estimates, as it is discussed in the literature. The problem of properly distinguishing the transition function in relation to extreme parameter combinations often leads to getting strongly biased estimators. This paper proposes a new procedure to test for the unit root in a nonlinear framework, and contributes to the existing literature in three separate directions. First, we propose a new alternative model - the MT-STAR model - which has similar properties as the ESTAR model but reduces the effects of the identification problem and can also account for cases where the adjustment mechanism towards equilibrium is not symmetric. Second, we develop a testing procedure to detect the presence of a nonlinear stationary process by establishing the limiting non-standard asymptotic distributions of the proposed test-statistics. Finally, we perform Monte Carlo simulations to assess the small sample performance of the test and then to highlight its power gain over existing tests for a unit root. We proposed two applications.Nonlinearity, smooth transition, unit root testing, Monte Carlo simulations.

Cardiovascular disease risk prediction in sub-Saharan African populations - Comparative analysis of risk algorithms in the RODAM study.

BACKGROUND: Validated absolute risk equations are currently recommended as the basis of cardiovascular disease (CVD) risk stratification in prevention and control strategies. However, there is no consensus on appropriate equations for sub-Saharan African populations. We assessed agreement between different cardiovascular risk equations among Ghanaian migrant and home populations with no overt CVD. METHODS: The 10-year CVD risks were calculated for 3586 participants aged 40-70years in the multi-centre RODAM study among Ghanaians residing in Ghana and Europe using the Framingham laboratory and non-laboratory and Pooled Cohort Equations (PCE) algorithms. Participants were classified as low, moderate or high risk, corresponding to 20% respectively. Agreement between the risk algorithms was assessed using kappa and correlation coefficients. RESULTS: 19.4%, 12.3% and 5.8% were ranked as high 10-year CVD risk by Framingham non-laboratory, Framingham laboratory and PCE, respectively. The median (25th-75th percentiles) estimated 10-year CVD risk was 9.5% (5.4-15.7), 7.3% (3.9-13.2) and 5.0% (2.3-9.7) for Framingham non-laboratory, Framingham laboratory and PCE, respectively. The concordance between PCE and Framingham non-laboratory was better in the home Ghanaian population (kappa=0.42, r=0.738) than the migrant population (kappa=0.24, r=0.732) whereas concordance between PCE and Framingham laboratory was better in migrant Ghanaians (kappa=0.54, r=0.769) than the home population (kappa=0.51, r=0.758). CONCLUSION: CVD prediction with the same algorithm differs for the migrant and home populations and the interchangeability of Framingham laboratory and non-laboratory algorithms is limited. Validation against CVD outcomes is needed to inform appropriate selection of risk algorithms for use in African ancestry populations

PROSECUTABILITY OF THE CRIME OF AGGRESSION: ANOTHER DECLARATION IN A TREATY OR AN ACHIEVABLE NORM?

This review critically examines the prosecutability of the crime of aggression under international criminal law, questioning whether it functions as a tangible legal norm or remains a declaratory provision lacking enforceability. Tracing its historical roots from the Nuremberg Trials through the Rome Statute and the Kampala Amendments, the paper explores the legal definition, jurisdictional framework, and implementation challenges that distinguish aggression from other core international crimes. It analyzes the interplay between state sovereignty, political will, and institutional limitations that have obstructed efforts to hold individuals accountable for illegal uses of force. The study also contrasts the crime of aggression with genocide and war crimes, highlighting its underdeveloped jurisprudence and procedural hurdles. While the Kampala Amendments signify a normative commitment to criminalizing aggressive war-making, their limited ratification and reliance on state consent undermine universality and enforcement. The paper concludes that without legal reform, broader ratification, and stronger political consensus, the crime of aggression risks remaining aspirational. However, its codification represents a critical step toward promoting accountability, peace enforcement, and the evolving architecture of global justice. Keywords: Prosecutability, Crime, Aggression, Declaration, Treaty, Achievable, Norm