Yes, Topology Matters in Decentralized Optimization: Refined Convergence and Topology Learning under Heterogeneous Data

One of the key challenges in federated and decentralized learning is to design algorithms that efficiently deal with highly heterogeneous data distributions across agents. In this paper, we revisit the analysis of Decentralized Stochastic Gradient Descent algorithm (D-SGD), a popular decentralized learning algorithm, under data heterogeneity. We exhibit the key role played by a new quantity, that we call neighborhood heterogeneity, on the convergence rate of D-SGD. Unlike prior work, neighborhood heterogeneity is measured at the level of the neighborhood of an agent in the graph topology. By coupling the topology and the heterogeneity of the agents' distributions, our analysis sheds light on the poorly understood interplay between these two concepts in decentralized learning. We then argue that neighborhood heterogeneity provides a natural criterion to learn sparse data-dependent topologies that reduce (and can even eliminate) the otherwise detrimental effect of data heterogeneity on the convergence time of D-SGD. For the important case of classification with label skew, we formulate the problem of learning such a good topology as a tractable optimization problem that we solve with a Frank-Wolfe algorithm. Our approach provides a principled way to design a sparse topology that balances the number of iterations and the per-iteration communication costs of D-SGD under data heterogeneity

Impact of slowdown of Atlantic overturning circulation on heat and freshwater transports

Recent measurements of the strength of the Atlantic overturning circulation at 26°N show a 1 year drop and partial recovery amid a gradual weakening. To examine the extent and impact of the slowdown on basin wide heat and freshwater transports for 2004–2012, a box model that assimilates hydrographic and satellite observations is used to estimate heat transport and freshwater convergence as residuals of the heat and freshwater budgets. Using an independent transport estimate, convergences are converted to transports, which show a high level of spatial coherence. The similarity between Atlantic heat transport and the Agulhas Leakage suggests that it is the source of the surface heat transport anomalies. The freshwater budget in the North Atlantic is dominated by a decrease in freshwater flux. The increasing salinity during the slowdown supports modeling studies that show that heat, not freshwater, drives trends in the overturning circulation in a warming climate

Influence de deux douvicides à base de tétrachlorure de carbone sur l’évolution de l’ornithine-carbamyl-transférase et de la phosphatase alcaline sériques chez le mouton infesté avec Fasciola hepatica

Influence of two flukicides based on carbon tetrachloride on serum O. C. T. and phosphatase alcaline changes in Fasciola hepatica infested sheep. Phamalogical effects of carbon tetrachloride in artificially Fasciola hepatica infested sheep are compared with those observed with C. 1372, a preparation containing CCI, plus an antioxydant, NN' Diphenyl-p-phenylene Diamine (DppD). The inclusion of DppD in the preparation avoids hepatic dysfunction observed with carbon tetrachloride alone and enables a prompt return to normal hepatic function previously disturbed by the flukes. Anthelmintic activity of the two preparations are equivalent.Les effets pharmacologiques du tétrachlorure de carbone chez le mouton artificiellement infesté avec Fasciola hepatica sont comparés à ceux d’une préparation, le C. 1372 contenant le CCI, et un antioxydant, la NN' Diphényl-p-phénylène Diamine (DppD). L’addition de DppD permet d’éviter l’atteinte hépatique constatée avec le CCI, seul et permet une récupération rapide de la fonction hépatique perturbée par les douves. L’activité fasciolicide est la même pour les deux préparations.Le Bars Henri, Laistre Banting Alan de. Influence de deux douvicides à base de tétrachlorure de carbone sur l’évolution de l’omithine-carbamyl-transférase et de la phosphatase alcaline sériques chez le mouton infesté avec Fasciola hepatica. In: Bulletin de l'Académie Vétérinaire de France tome 128 n°4-5, 1975. pp. 221-227

Systematic review of the behavioural assessment of pain in cats

Objectives The objectives were to review systematically the range of assessment tools used in cats to detect the behavioural expression of pain and the evidence of their quality; and to examine behavioural metrics (considering both the sensory and affective domains) used to assess pain. Methods A search of PubMed and ScienceDirect, alongside articles known to the authors, from 2000 onwards, for papers in English was performed. This was followed by a manual search of the references within the primary data sources. Only peer-reviewed publications that provided information on the assessment tool used to evaluate the behavioural expression of pain in cats, in conscious animals (not anaesthetised cats), were included. Results No previous systematic reviews were identified. One hundred papers were included in the final assessment. Studies were primarily related to the assessment of pain in relation to surgical procedures, and no clear distinction was made concerning the onset of acute and chronic pain. Ten broad types of instrument to assess pain were identified, and generally the quality of evidence to support the use of the various instruments was poor. Only one specific instrument (UNESP-Botucatu scale) had published evidence of validity, reliability and sensitivity at the level of a randomised control trial, but with a positive rather than placebo control, and limited to its use in the ovariohysterectomy situation. The metrics used within the tools appeared to focus primarily on the sensory aspect of pain, with no study clearly discriminating between the sensory and affective components of pain. Conclusions and relevance Further studies are required to provide a higher quality of evidence for methods used to assess pain in cats. Furthermore, a consistent definition for acute and chronic pain is needed. Tools need to be validated that can detect pain in a range of conditions and by different evaluators (veterinary surgeons and owners), which consider both the sensory and emotional aspects of pain

Impact of slowdown of Atlantic overturning circulation on heat and freshwater transports

Recent measurements of the strength of the Atlantic overturning circulation at 26°N show a 1 year drop and partial recovery amid a gradual weakening. To examine the extent and impact of the slowdown on basin wide heat and freshwater transports for 2004–2012, a box model that assimilates hydrographic and satellite observations is used to estimate heat transport and freshwater convergence as residuals of the heat and freshwater budgets. Using an independent transport estimate, convergences are converted to transports, which show a high level of spatial coherence. The similarity between Atlantic heat transport and the Agulhas Leakage suggests that it is the source of the surface heat transport anomalies. The freshwater budget in the North Atlantic is dominated by a decrease in freshwater flux. The increasing salinity during the slowdown supports modeling studies that show that heat, not freshwater, drives trends in the overturning circulation in a warming climate

An observed 20-year time series of Agulhas leakage

We provide a time series of Agulhas leakage anomalies over the last 20-years from satellite altimetry. Until now, measuring the interannual variability of Indo-Atlantic exchange has been the major barrier in the investigation of the dynamics and large scale impact of Agulhas leakage. We compute the difference of transport between the Agulhas Current and Agulhas Return Current, which allows us to deduce Agulhas leakage. The main difficulty is to separate the Agulhas Return Current from the southern limb of the subtropical "supergyre" south of Africa. For this purpose, an algorithm that uses absolute dynamic topography data is developed. The algorithm is applied to a state-of-the-art ocean model. The comparison with a Lagrangian method to measure the leakage allows us to validate the new method. An important result is that it is possible to measure Agulhas leakage in this model using the velocity field along a section that crosses both the Agulhas Current and the Agulhas Return Current. In the model a good correlation is found between measuring leakage using the full depth velocities and using only the surface geostrophic velocities. This allows us to extend the method to along-track absolute dynamic topography from satellites. It is shown that the accuracy of the mean dynamic topography does not allow us to determine the mean leakage but that leakage anomalies can be accurately computed

La perfusion des organes digestifs. Méthode d'étude de l'absorption

Le Bars Henri, Mollé J., Rérat Alain, Simonnet Henri. La perfusion des organes digestifs. Méthode d'étude de l'absorption. In: Bulletin de l'Académie Vétérinaire de France tome 111 n°6, 1958. pp. 305-310

Prefrontal cortex markers of suicidal vulnerability in mood disorders: a model-based structural neuroimaging study with a translational perspective

Open access article. Available from the publisher via doi: 10.1038/tp.2015.1The vulnerability to suicidal behavior has been modeled in deficits in both valuation and cognitive control processes, mediated by ventral and dorsal prefrontal cortices. To uncover potential markers of suicidality based on this model, we measured several brain morphometric parameters using 1.5T magnetic resonance imaging in a large sample and in a specifically designed study. We then tested their classificatory properties. Three groups were compared: euthymic suicide attempters with a past history of mood disorders and suicidal behavior (N=67); patient controls with a past history of mood disorders but not suicidal behavior (N=82); healthy controls without any history of mental disorder (N=82). A hypothesis-driven region-of-interest approach was applied targeting the orbitofrontal cortex (OFC), ventrolateral (VLPFC), dorsal (DPFC) and medial (including anterior cingulate cortex; MPFC) prefrontal cortices. Both voxel-based (SPM8) and surface-based morphometry (Freesurfer) analyses were used to comprehensively evaluate cortical gray matter measure, volume, surface area and thickness. Reduced left VLPFC volume in attempters vs both patient groups was found (P=0.001, surviving multiple comparison correction, Cohen's d=0.65 95% (0.33-0.99) between attempters and healthy controls). In addition, reduced measures in OFC and DPFC, but not MPFC, were found with moderate effect sizes in suicide attempters vs healthy controls (Cohen's d between 0.34 and 0.52). Several of these measures were correlated with suicidal variables. When added to mood disorder history, left VLPFC volume increased within-sample specificity in identifying attempters in a significant but limited way. Our study, therefore, confirms structural prefrontal alterations in individuals with histories of suicide attempts. A future clinical application of these markers will, however, necessitate further research.American Foundation for Suicide PreventionFondation pour la Recherche MédicaleRoyal SocietyProjet Hospitalier de Recherche CliniqueAcadémie Nationale de MédecineInstitut Servie

Absorption des acides aminés au niveau du rumen de l’intestin grêle et du caecum chez le mouton

Demaux G., Le Bars Henri, Mollé J., Rérat Alain, Simonnet Henri. Absorption des acides aminés, au niveau du rumen, de l’intestin grêle et du cæcum chez le Mouton. In: Bulletin de l'Académie Vétérinaire de France tome 114 n°2, 1961. pp. 85-88