100 research outputs found
Large-scale convex optimization: parallelization and variance reduction
No full textIn this work, we investigate two aspects of large-scale optimization for convex functions defined on an infinite-dimensional separable Hilbert space: parallelized methods and incremental methods. These methods are used to efficiently solve problems that arise in data science, especially in machine learning and inverse problems.
In parallelized optimization methods, the computational load of running the algorithm is distributed among several workers. For example, if the algorithm comprises a gradient computation, one can give each worker a coordinate of the gradient to compute, and then put everything back together. A parallelized algorithm is called synchronous if there is a synchronization phase where local information of all workers are updated. It is called asynchronous if there is no such phase. In practice, asynchronous implementations are preferred to synchronous ones. However, their analysis has to account for delayed information, which is modeled by a delay vector. In this document, we study an asynchronous version of random block coordinate descent, where only one randomly selected coordinate is used at each iteration. We consider a version in which the selection probability of the coordinates is arbitrary, in contrast to what is done in the literature for asynchronous algorithms. We also allow coordinate-wise stepsize rule. Under convexity assumption, we prove weak convergence of the iterates and sublinear convergence rate. Assuming an additional error bound condition, we prove a linear convergence rate and strong convergence of the iterates. In both cases, the dependence on the delay vector is linear.
Incremental optimization methods are iterative algorithms used to minimize a function defined as a finite sum of functions. The function is then minimized by using one summand at each iteration instead of the whole function. We are interested in the case where the choice of the summand is random. This leads to stochastic algorithms such as stochastic gradient descent (SGD) or stochastic proximal point algorithm (SPPA). While they are cheaper to implement in terms of computation and memory than their deterministic counterparts that use the entire function, stochastic methods suffer from a drop in convergence rates. This drop is mainly due to the variance introduced by the stochasticity. Therefore, variance reduction techniques have been used in the literature to successfully recover the rates of deterministic algorithms. These techniques were first applied to stochastic gradient methods. In our work, we are, instead, concerned with the stochastic proximal point algorithm (SPPA). This method has recently been studied and has been shown to be more stable compared to stochastic gradient descent (SGD). Our work focuses on the application of variance reduction methods to SPPA. In particular, we introduce a general variance reduction scheme for SPPA. Many variance-reduced SPPA-based algorithms can be recovered from this scheme, mimicking those that already exist for SGD (SVRG, SAGA, etc.). We recover standard sublinear (respectively linear) convergence rates of the proximal point algorithm (PPA) when the stepsize is constant and the function is convex (respectively convex plus satisfying the Polyak-Łojasiewicz condition)
Variance Reduction Techniques for Stochastic Proximal Point Algorithms
No full textIn the context of finite sums minimization, variance reduction techniques are widely used to improve the performance of state-of-the-art stochastic gradient methods. Their practical impact is clear, as well as their theoretical properties. Stochastic proximal point algorithms have been studied as an alternative to stochastic gradient algorithms since they are more stable with respect to the choice of the step size. However, their variance-reduced versions are not as well studied as the gradient ones. In this work, we propose the first unified study of variance reduction techniques for stochastic proximal point algorithms. We introduce a generic stochastic proximal-based algorithm that can be specified to give the proximal version of SVRG, SAGA, and some of their variants. For this algorithm, in the smooth setting, we provide several convergence rates for the iterates and the objective function values, which are faster than those of the vanilla stochastic proximal point algorithm. More specifically, for convex functions, we prove a sublinear convergence rate of O(1/k). In addition, under the Polyak-& lstrok;ojasiewicz condition, we obtain linear convergence rates. Finally, our numerical experiments demonstrate the advantages of the proximal variance reduction methods over their gradient counterparts in terms of the stability with respect to the choice of the step size in most cases, especially for difficult problems
Broken needle during spinal anesthesia: an avoidable complication
No full textRawéléguinbasba Armel Flavien Kabore,1 Ibrahim Alain Traore,2 Salah Idriss Séif Traore,3 Cheik Tidiane Hafi Wind-Pouiré Bougouma,1 Pascal Augustin,4 Aboudoul-Fataou Ouro-Bang’na Maman5 1Department of Anesthesia, University Hospital Blaise Comparoé, Ouagadougou, Burkina Faso; 2Department of Anesthesia, Uiversity Hospital Sourou Sanou, Bobo Dioulasso, Burkina Faso; 3Department of Anesthesia, District Hospital of Bogodogo, Ouagadougou, Burkina Faso; 4Department of Anesthesia, Intercommunity Hospital of Meulan, Les Mureaux, Meulan en Yvelines, France; 5Department of Anesthesia, Ales-en-Cévennes Hospital, Alès-en-Cévennes, France Abstract: The occurrence of a needle breaking is a very rare complication of spinal anesthesia (SA). We report a case of a broken spinal needle occurring in a morbid obese pregnant woman during SA indicated for an emergent cesarean section. Multiple puncture attempts due to difficult identification of lumbar spine, associated with an inadequate use of the introducer, contributed to this complication. The recognition of predictive factors for difficult neuraxial anesthesia, the use of ultrasound in obese patients, and a properly executed technique may have allowed avoiding this complication. Keywords: spinal anesthesia, needle breaking, cesarean section, obesit
Biodégradation anaérobie des tourteaux de karité: Biodegradation of shea-nut residues
No full textFrançais
Le karité est une essence très répandue dans les pays de la zone soudano-guinéenne. L'amande de karité est riche en lipides (environ 50 % p/p). C'est une source de matières grasses pour beaucoup d'activités artisanale et industrielle. (cuisine, fabrication du savon, cosmétique, etc.).
Après extraction du beurre, il reste une importante quantité de tourteau qui constitue un produit polluant pour l'environnement. Sa composition est d'environ 14 % de protéines, 25 % de sucres, 22,5 % de lipides et 20 % de polyphénols, les tannins en particulier. Les tannins sont des composés biologiquement actifs, toxiques pour les animaux à sang froid et possédant des propriétés antimicrobiennes. Les lipides empêchent la diffusion de l'air et de !'eau dans le sol au niveau des sites de dépôts. Ces rejets constituent donc un produit polluant pour l’environnement.
Les essais de biodégradation anaérobie effectués par des fermentations en batch indiquent que la production de méthane à partir des tourteaux s'accompagne d'une importante accumulation d'acides organiques, de tannins, d'ammoniaque et de sulfures dans les milieux à taux de charge élevé. Un degré d'épuration de 90 % environ a été obtenu à partir de 2 % (p/v) de substrat. Un consortium microbien spécifique a été utilisé après une année d'acclimatation.
Anglais
Shea-nut has fruits high in oil content (approximately 50 %, wt/wt). These trees are found i n soudano-guinean area. They provide shea-nut butter that populations use for many purposes ( cooking oil, soap manufacture. cosmetics, etc.)
After extraction of this butter, big quantities of residues remain. Their proximate composition are: proteins (14%), sugars (25%), fats (22.5%), and polyphenols (20.03 %), mainly tannins compounds. Tannins compound are not easily biodegradable and are toxic for cold blood animals. Furtherrnore, when deposited on ground these residues stop water and air diffusion in soil, provoking threat for microt1ora and micro-organisms in this area.
In order to eliminate the harmful effects of tannins compounds on the environment, it has been undertaken in our laboratory the study focusing on the biodegradation of these compounds in anaerobiosis. As result it has been obtained a rate of depollution of approximately 90% with a 2% of substrate loading and quantities of biomethane. Specific microbial consortium has been used after they become acclimatized for one year
Continuous Authentication using Stylometry
No full textStatic authentication, where user identity is checked once at login time, can be circumvented no matter how strong the authentication mechanism is. Through attacks such as man-in-the-middle and its variants, an authenticated session can be hijacked later after the initial login process has been completed. In the last decade, continuous authentication (CA) using biometrics has emerged as a possible remedy against session hijacking. CA consists of testing the authenticity of the user repeatedly throughout the authenticated session as data becomes available. CA is expected to be carried out unobtrusively, due to its repetitive nature, which means that the authentication information must be collectible without any active involvement of the user and without using any special purpose hardware devices (e.g. biometric readers). Stylometry analysis, which consists of checking whether a target document was written or not by a specific individual, could potentially be used for CA. Although stylometric techniques can achieve high accuracy rates for long documents, it is still challenging to identify an author for short documents, in particular when dealing with large author populations.
In this dissertation, we propose a new framework for continuous authentication using authorship verification based on the writing style. Authorship verification can be checked using stylometric techniques through the analysis of linguistic styles and writing characteristics of the authors. Different from traditional authorship verification that focuses on long texts, we tackle the use of short messages. Shorter authentication delay (i.e. smaller data sample) is essential to reduce the window size of the re-authentication period in CA. We validate our method using different block sizes, including 140, 280, and 500 characters, and investigate shallow and deep learning architectures for machine learning classification. Experimental evaluation of the proposed authorship verification approach based on the Enron emails dataset with 76 authors yields an Equal Error Rate (EER) of 8.21% and Twitter dataset with 100 authors yields an EER of 10.08%. The evaluation of the approach using relatively smaller forgery samples with 10 authors yields an EER of 5.48%.Graduat
Etude d'identification des prototypes d'ecofermes au Mali rapport diagnostic et plan d'action pour 2005
No full textThe role of Plasmodium falciparum var genes in malaria in pregnancy
No full textSequestration of Plasmodium falciparum-infected erythrocytes in the placenta is responsible for many of the harmful effects of malaria during pregnancy. Sequestration occurs as a result of parasite adhesion molecules expressed on the surface of infected erythrocytes binding to host receptors in the placenta such as chondroitin sulphate A (CSA). Identification of the parasite ligand(s) responsible for placental adhesion could lead to the development of a vaccine to induce antibodies to prevent placental sequestration. Such a vaccine would reduce the maternal anaemia and infant deaths that are associated with malaria in pregnancy. Current research indicates that the parasite ligands mediating placental adhesion may be members of the P. falciparum variant surface antigen family PfEMP1, encoded by var genes. Two relatively well-conserved subfamilies of var genes have been implicated in placental adhesion, however, their role remains controversial. This review examines the evidence for and against the involvement of var genes in placental adhesion, and considers whether the most appropriate vaccine candidates have yet been identified
From the Theory of the African Origin of Humankind to Modern Social, Legal and Technological Innovations: a Brief Analytical Excursion into Anthroposociogenesis
No full textObjective: to trace the evolution of humanity and to identify the role of various social institutions in order to understand the existential role of laws aimed at ensuring the coexistence of society in the context of technological innovations.Methods: the author used general scientific and special methods of cognition, which allowed tracing the dialectical development of humanity, social transformations and technological innovations.Results: looking back at the history of humanity, which originated on the African continent (the theory of African descent), the author notes the most important changes in the human way of life and environment, which led to the need to build organized societies and regulate social behavior with the help of legislative norms. Law is seen as part of the evolutionary process that was to emerge in the course of human evolution. The critical importance of law in overcoming the global challenges and existential questions of humanity’s continued coexistence arising in the course of evolution is emphasized. In this regard, the historical significance of the Kurukan Fuga Charter of the Malian Empire is emphasized as one of the oldest constitutions in the world, recognized internationally as an important source of legal and political norms for modern societies, regulating the structure of state power and social behaviour, although preserved largely in oral form. It is argued that social and technological change often served as the impetus for the development of new laws. Humanity has many times intervened in its own biological evolution with the help of technology; now it is an important moment from the viewpoint of law and ethics when technology may interfere in further human evolution. The greatest concern in this regard is the era of rapid development of artificial intelligence, which makes new demands on a human being.Scientific novelty: the article shows the role of the African continent in the origin and development of humanity and socio-legal institutions in the light of modern transformations and the construction of a new social reality.Practical significance: the conducted research creates prerequisites for further development of the theory of anthroposociogenesis and in-depth conceptual historical and legal study of the role of the African continent in the development of humanity and its social institutions
A well-conserved Plasmodium falciparum var gene shows an unusual stage-specific transcript pattern
No full textThe var multicopy gene family encodes Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) variant antigens, which, through their ability to adhere to a variety of host receptors, are thought to be important virulence factors. The predominant expression of a single cytoadherent PfEMP1 type on an infected red blood cell, and the switching between different PfEMP1 types to evade host protective antibody responses, are processes thought to be controlled at the transcriptional level. Contradictory data have been published on the timing of var gene transcription. Reverse transcription-polymerase chain reaction (RT-PCR) data suggested that transcription of the predominant var gene occurs in the later (pigmented trophozoite) stages, whereas Northern blot data indicated such transcripts only in early (ring) stages. We investigated this discrepancy by Northern blot, with probes covering a diverse var gene repertoire. We confirm that almost all var transcript types were detected only in ring stages. However, one type, the well-conserved varCSA transcript, was present constitutively in different laboratory parasites and does not appear to undergo antigenic variation. Although varCSA has been shown to encode a chondroitin sulphate A (CSA)-binding PfEMP1, we find that the presence of full-length varCSA transcripts does not correlate with the CSA-binding phenotype
Heme Adventures: Roles In Catalysis and Structural Insights
No full textThe full text of this item is not available at this time because the author has placed this item under an embargo until May 15, 2030.Heme enzymes represent a vast class of biological catalysts that enable diverse oxidative transformations essential to life. This dissertation explores the roles of heme in catalysis through detailed biochemical, structural, and mechanistic studies of four distinct enzymes. Beginning with a comprehensive analysis of charge maintenance in non-heme iron oxygenases, the work highlights how ligand scaffolds and substrate interactions govern reaction outcomes. This is followed by subsequent investigations into tyrosine hydroxylase which reveal a novel free radical pathway, providing new insight into substrate oxidation. Structural and functional characterization of Mycobacterium tuberculosis catalase-peroxidase (KatG) identifies a unique indole-N-linked hydroperoxyl adduct that modulates enzymatic activity. The study of RufO, a heme enzyme implicated in rufomycin biosynthesis, suggests that tyrosine is not the native substrate, supported by spectroscopic, crystallographic, docking analyses. Finally, structural and spectroscopic studies of the streptococcal heme-binding protein HupZ demonstrate an unusual mode of heme coordination influenced by C-terminal tagging. Together, these studies underscore the diverse catalytic strategies enabled by heme and iron cofactors and offer broader implications for the design of biomimetic catalysts and therapeutic targets.Chemistr
- …
