Efficient approaches for ℓ2-ℓ0 regularization and applications to feature selection in SVM

For solving a class of ?₂- ?₀- regularized problems we convexify the nonconvex ?₂- ?₀ term with the help of its biconjugate function. The resulting convex program is explicitly given which possesses a very simple structure and can be handled by convex optimization tools and standard softwares. Furthermore, to exploit simultaneously the advantage of convex and nonconvex approximation approaches, we propose a two phases algorithm in which the convex relaxation is used for the first phase and in the second phase an efficient DCA (Difference of Convex functions Algorithm) based algorithm is performed from the solution given by Phase 1. Applications in the context of feature selection in support vector machine learning are presented with experiments on several synthetic and real-world datasets. Comparative numerical results with standard algorithms show the efficiency the potential of the proposed approaches.     

Branched polymeric media: boron-chelating resins from hyperbranched polyethylenimine

Extraction of boron from aqueous solutions using selective resins is important in a variety of applications including desalination, ultrapure water production, and nuclear power generation. Today's commercial boron-selective resins are exclusively prepared by functionalization of styrene-divinylbenzene (STY-DVB) beads with N-methylglucamine to produce resins with boron-chelating groups. However, such boron-selective resins have a limited binding capacity with a maximum free base content of 0.7 eq/L, which corresponds to a sorption capacity of 1.16 ± 0.03 mMol/g in aqueous solutions with equilibrium boron concentration of ～70 mM. In this article, we describe the synthesis and characterization of a new resin that can selectively extract boron from aqueous solutions. We show that branched polyethylenimine (PEI) beads obtained from an inverse suspension process can be reacted with glucono-1,5-d-lactone to afford a resin consisting of spherical beads with high density of boron-chelating groups. This resin has a sorption capacity of 1.93 ± 0.04 mMol/g in aqueous solution with equilibrium boron concentration of ～70 mM, which is 66% percent larger than that of standard commercial STY-DVB resins. Our new boron-selective resin also shows excellent regeneration efficiency using a standard acid wash with a 1.0 M HCl solution followed by neutralization with a 0.1 M NaOH solution.     

Preliminary design and simulation of a microstructured reactor for production of synthesis gas by steam methane reforming

The present study considers the potentials of the well-known production of syngas by steam methane reforming (SMR), by operation within microstructured reactors. The model of a microchannel reactor is developed, including very fast kinetic reaction rates on the coated catalytic walls of the reactor module. By varying the characteristic dimensions of the channels, and considering technical constraints on the design and operating conditions, the results demonstrate that the SMR reactor can be drastically miniaturized while maintaining its productivity without any additional pressure drop. Furthermore, by reducing the channel characteristic dimensions, it is possible to suppress heat and mass-transfer limitations enabling SMR reactor operation at thermodynamic equilibrium. A fast method for preliminary design of microstructured heat-exchanger reactors is developed, that enables to identify the optimal channels number and heat power needed to reach process specifications.     

Investigation on the Effect of Condensing Moisture before Heating Air on the Performance of a Batch Tray Dryer: Application to the Drying of Vanilla

This article presents the results of an investigation of the effect of pre-dehumidifying the drying air before it is heated and supplied into a batch tray dryer. Dehumidification is achieved through moisture condensation as the air flowing through a coil is cooled by chilled water from a cold source. As an example, this process is applied to the drying of vanilla and is based on a numerical method already validated by former results. Then, it is established through comparisons with a conventional batch tray dryer model that pre-dehumidification significantly reduces drying time. Furthermore, preheating air by an intermediate heating source reduces total energy consumption of the primary heating system to a level depending on the preset drying temperature. As regards batch tray dryer design and optimization purposes, these results open up particularly interesting heating and cooling sources utilization prospects.     

Thermodynamic Properties of Asphaltenes Through Computer Assisted Structure Elucidation and Atomistic Simulations. 1. Bulk Arabian Light Asphaltenes

This article describes a new method for estimating the thermodynamic properties of asphaltenes. To illustrate this methodology, we used a computer assisted structure elucidation software (SIGNATURE) to generate an ensemble of 10 isomers for Arabian Light (AL) asphaltenes compatible with (i) analytical data from elemental analysis, FT-IR spectroscopy, 1-D ¹H/¹³C solution NMR and vapor pressure osmometry and (ii) literature data on the molecular composition of asphaltenes. The 10 model isomers were packed into a 3-D periodic cell to form the condensed phase model for the fraction of bulk AL asphaltenes with a number average molar mass (M_n) approximately equal to 1280 Dalton. This cell was subsequently used in molecular dynamics (MD) simulations to estimate the molar volume, density, enthalpy, specific heat at constant pressure, solubility parameter, and isothermal compressibility of the AL asphaltene fraction. The results of the MD simulations compare favorably with the available experimental data.     

T2-weighted spin-echo MR imaging of the liver: breath-hold fast spin-echo versus non-breath-hold fast spin-echo images with and without fat suppression

OBJECTIVE: The goal of our study was to compare a T2-weighted breath-hold fast spin-echo (BHSE) technique with T2-weighted non-breath-hold fast spin-echo techniques for imaging the liver. SUBJECTS AND METHODS: Thirty-three patients with hepatic lesions had T2-weighted BHSE images obtained in 22 sec and conventional T2-weighted non-breath-hold fast spin-echo images obtained in 3 min 12 sec with and without fat suppression. Images were analyzed quantitatively by measuring the lesion-liver contrast, spleen-liver contrast, and signal-to-noise ratios of lesions and qualitatively by evaluating the sharpness of hepatic contours, visibility of intrahepatic vessels and other segmental landmarks, and presence of artifacts. RESULTS: Quantitatively, lesion-liver contrast, spleen-liver contrast, and signal-to-noise ratios obtained with the BHSE technique were inferior to those obtained with fast spin-echo techniques with and without fat suppression (11.2 +/- 7.1 versus 15.4 +/- 10.6 and 14.5 +/- 9.8, p < .001; 5.3 +/- 3.7 versus 8.7 +/- 3.5 and 7.0 +/- 3.8, p < .001; 16.2 +/- 8.2 versus 20.1 +/- 10.9 and 19.7 +/- 9.5, p < .01, respectively; Student's t test). Qualitatively, image artifacts and intrahepatic vessel depiction on BHSE images were similar to those obtained with the fast spin-echo techniques. The BHSE technique was superior to fat-suppressed fast spin-echo technique for showing hepatic contours (p < .01; Wilcoxon signed-rank test). CONCLUSION: The BHSE technique is quantitatively inferior to non-breath-hold fast spin-echo techniques. However, further studies with a surgical standard of reference are needed to compare the three techniques in terms of sensitivity.     

The burden of erectile dysfunction in dialysis patients in Senegal

Erectile dysfunction (ED) is very common in dialysis patients because of organic and psychological risk factors. It has a negative impact on patients' quality of life. In Senegal, ED is assumed to be frequent in the general adult population but its prevalence in dialysis patients is unknown. This cross-sectional study aimed to assess the prevalence and risk factors associated with ED in Senegalese dialysis patients. Seventy dialyzed men >18 years old were included. Erectile dysfunction was assessed using the abridged version of International Index of Erectile Function already validated in dialysis patients. Multivariate analysis was performed to identify the factors associated with ED in patients. The mean age of the patients was 52 ± 11.3 years (21-70 years) and the median dialysis vintage was 39.4 months (interquartile range 9-51 months). The prevalence of ED was 81.5% for all patients (80% in hemodialysis and 81.75% in peritoneal dialysis). Severe ED was found in 11.5% of patients. The prevalence of ED was 74.5% in patients younger than 50 years and 86.6% in those 50 years or older. Marital status, comorbidity, hemoglobin level, and use of antihypertensive drugs were not different between patients with and without ED. Libido was conserved in 77% of patients and 44.7% were not satisfied during sexual intercourse. Multivariate analysis identified age and dialysis vintage as risk factors of ED in our patients. Only 7 patients received treatment for ED and 22% sought a consultation with a specialist (urologist and psychologist).     

Identification algorithm for fracture parameters by combining DIC and FEM approaches

This research program focuses on a hybrid experimental and numerical approach to identifying the mechanical state in the vicinity of a crack. The digital image correlation, as corrected by interpolating a theoretical displacement field, enables determining the crack opening intensity factors representative of the kinematic state of crack lips. A finite element model is introduced for calculating stress intensity factors. The parallelism derived from the DIC method and FEM approach is presented by means of a specific identification algorithm that allows computing the energy release rate within a common finite element mesh. This algorithm is then illustrated by testing the opening-mode configuration for a PVC sample.     

Impact of Tetracationic Calix[4]arene Conformation—from Conic Structure to Expanded Bolaform—on Their Antibacterial and Antimycobacterial Activities

The four possible conformers of a new tetrakisguanidino calix[4]arene thought to interact deleteriously with bacterial membranes have been synthesized, characterized, and evaluated for their in vitro cytotoxicity and antibacterial activity against various reference Gram-negative and Gram-positive bacteria, as well as Mycobacterium tuberculosis. It appears that reversal of at least one phenolic unit results in clear increases in their activities. This can be attributed to the evolution towards bolaform structures, which are able to interact more deeply with the bacterial membrane. Indeed, the 1,3-alternate conformer 16 exhibits the best antibacterial activity (MIC<1.0 μg mL⁻¹ on Staphylococcus aureus). Moreover, 16 displays very good antibacterial activities against an isoniazid-resistant strain of M. tuberculosis (MIC=1.2 μg mL⁻¹), associated with the lowest cytotoxicity, thus making it the most potent compound of the series; this could open new ways of research in the field of anti-infective drug development to meet the huge current demand.     

Statistical modeling of global geogenic fluoride contamination in groundwaters

The use of groundwater with high fluoride concentrations poses a health threat to millions of people around the world. This study aims at providing a global overview of potentially fluoride-rich groundwaters by modeling fluoride concentration. A large database of worldwide fluoride concentrations as well as available information on related environmental factors such as soil properties, geological settings, and climatic and topographical information on a global scale have all been used in the model. The modeling approach combines geochemical knowledge with statistical methods to devise a rule-based statistical procedure, which divides the world into 8 different "process regions". For each region a separate predictive model was constructed. The end result is a global probability map of fluoride concentration in the groundwater. Comparisons of the modeled and measured data indicate that 60-70% of the fluoride variation could be explained by the models in six process regions, while in two process regions only 30% of the variation in the measured data was explained. Furthermore, the global probability map corresponded well with fluorotic areas described in the international literature. Although the probability map should not replace fluoride testing, it can give a first indication of possible contamination and thus may support the planning process of new drinking water projects.