Acceleration Schemes for Ab-Initio Molecular Dynamics and Electronic Structure Calculations

We study the convergence and the stability of fictitious dynamical methods for electrons. First, we show that a particular damped second-order dynamics has a much faster rate of convergence to the ground-state than first-order steepest descent algorithms while retaining their numerical cost per time step. Our damped dynamics has efficiency comparable to that of conjugate gradient methods in typical electronic minimization problems. Then, we analyse the factors that limit the size of the integration time step in approaches based on plane-wave expansions. The maximum allowed time step is dictated by the highest frequency components of the fictitious electronic dynamics. These can result either from the large wavevector components of the kinetic energy or from the small wavevector components of the Coulomb potential giving rise to the so called {\it charge sloshing} problem. We show how to eliminate large wavevector instabilities by adopting a preconditioning scheme that is implemented here for the first-time in the context of Car-Parrinello ab-initio molecular dynamics simulations of the ionic motion. We also show how to solve the charge-sloshing problem when this is present. We substantiate our theoretical analysis with numerical tests on a number of different silicon and carbon systems having both insulating and metallic character.Comment: RevTex, 9 figures available upon request, to appear in Phys. Rev.

Small bowel enteroscopy - A joint clinical guideline from the spanish and portuguese small bowel study groups

The present evidence-based guidelines are focused on the use of device-assisted enteroscopy in the management of small-bowel diseases. A panel of experts selected by the Spanish and Portuguese small bowel study groups reviewed the available evidence focusing on the main indications of this technique, its role in the management algorithm of each indication and on its diagnostic and therapeutic yields. A set of recommendations were issued accordingly.Estas recomendações baseadas na evidência detalham o uso da enteroscopia assistida por dispositivo no manejo clínico das doenças do intestino delgado. Um conjunto de Gastrenterologistas diferenciados em patologia do intestino delgado foi selecionado pelos grupos de estudos Espanhol e Português de intestino delgado para rever a evidência disponível sobre as principais indicações desta técnica, o seu papel nos algoritmos de manejo de cada indicação e sobre o seu rendimento diagnóstico e terapêutico. Foi gerado um conjunto de recomendações pelos autores

The genetic architecture of the human cerebral cortex

INTRODUCTION The cerebral cortex underlies our complex cognitive capabilities. Variations in human cortical surface area and thickness are associated with neurological, psychological, and behavioral traits and can be measured in vivo by magnetic resonance imaging (MRI). Studies in model organisms have identified genes that influence cortical structure, but little is known about common genetic variants that affect human cortical structure. RATIONALE To identify genetic variants associated with human cortical structure at both global and regional levels, we conducted a genome-wide association meta-analysis of brain MRI data from 51,665 individuals across 60 cohorts. We analyzed the surface area and average thickness of the whole cortex and 34 cortical regions with known functional specializations. RESULTS We identified 306 nominally genome-wide significant loci (P < 5 × 10−8) associated with cortical structure in a discovery sample of 33,992 participants of European ancestry. Of the 299 loci for which replication data were available, 241 loci influencing surface area and 14 influencing thickness remained significant after replication, with 199 loci passing multiple testing correction (P < 8.3 × 10−10; 187 influencing surface area and 12 influencing thickness). Common genetic variants explained 34% (SE = 3%) of the variation in total surface area and 26% (SE = 2%) in average thickness; surface area and thickness showed a negative genetic correlation (rG = −0.32, SE = 0.05, P = 6.5 × 10−12), which suggests that genetic influences have opposing effects on surface area and thickness. Bioinformatic analyses showed that total surface area is influenced by genetic variants that alter gene regulatory activity in neural progenitor cells during fetal development. By contrast, average thickness is influenced by active regulatory elements in adult brain samples, which may reflect processes that occur after mid-fetal development, such as myelination, branching, or pruning. When considered together, these results support the radial unit hypothesis that different developmental mechanisms promote surface area expansion and increases in thickness. To identify specific genetic influences on individual cortical regions, we controlled for global measures (total surface area or average thickness) in the regional analyses. After multiple testing correction, we identified 175 loci that influence regional surface area and 10 that influence regional thickness. Loci that affect regional surface area cluster near genes involved in the Wnt signaling pathway, which is known to influence areal identity. We observed significant positive genetic correlations and evidence of bidirectional causation of total surface area with both general cognitive functioning and educational attainment. We found additional positive genetic correlations between total surface area and Parkinson’s disease but did not find evidence of causation. Negative genetic correlations were evident between total surface area and insomnia, attention deficit hyperactivity disorder, depressive symptoms, major depressive disorder, and neuroticism. CONCLUSION This large-scale collaborative work enhances our understanding of the genetic architecture of the human cerebral cortex and its regional patterning. The highly polygenic architecture of the cortex suggests that distinct genes are involved in the development of specific cortical areas. Moreover, we find evidence that brain structure is a key phenotype along the causal pathway that leads from genetic variation to differences in general cognitive function

The efficacy of resistance training in hypoxia to enhance strength and muscle growth: A systematic review and meta-analysis

Recent studies have reported that resistance training in hypoxia (RTH) may augment muscle size and strength development. However, consensus on the effects of RTH via systematic review and meta-analysis is not yet available. This work aimed to systematically review studies which have investigated using RTH versus normoxic resistance training (NRT) to improve muscular size and strength, and to perform a meta-analysis to determine the effect of RTH on these adaptive parameters. Searches were conducted in PubMed, Web of Science and the Cochrane Library from database inception until 17 June 2017 for original articles assessing the effects of RTH on muscle size and strength versus NRT. The effects on outcomes were expressed as standardized mean differences (SMD). Nine studies (158 participants) reported on the effects of RTH versus NRT for muscle cross-sectional area (CSA) (n=4) or strength (n=6). RTH significantly increased CSA (SMD=0.70, 95% confidence intervals (CI) 0.05, 1.35; p=.04) and strength (SMD=1.88; 95% CI=1.20, 2.56; p<.00001). However, RTH did not produce significant change in CSA (SMD=0.24, 95% CI -0.19, 0.68, p=.27) or strength (SMD=0.20; 95% CI=-0.27, 0.78; p=.23) when compared to NRT. Although RTH improved muscle size and strength, this protocol did not provide significant benefit over resistance training in normoxia. Nevertheless, this paper identified marked differences in methodologies for implementing RTH, and future research using standardized protocols is therefore warranted

CARACTERIZACIÓN CARIOTÍPICA DEL YAMÚ (Brycon siebenthalae)

RESUMEN: El yamú (Brycon siebenthalae) es un pez de escama, nativo de la Orinoquia Colombiana, con alto potencial para acuicultura. Sin embargo, el conocimiento sobre su biología es aún muy limitado. En consecuencia, para determinar el número de cromosomas de esta especie, linfocitos de individuos juveniles y adultos fueron cultivados, empleando protocolos y técnicas utilizadas con éxito en otras especies de peces nativos. El número cromosómico revelado fue 2n=50(24m(metacéntricos), 26sm/st(sububmetacéntricos/subtelocéntricos) el cual es similar al de otros bryconidos de la cuenca amazónica.Palabras Claves: Brycon siebenthalae, yamú, número cromosómico.ABSTRACT: The yamú (Brycon siebenthalae) it is a flake fish, native of the Colombian Orinoquia, with high potential for continental aquaculture. However, the knowledge on its biology is even very limited. In consequence, to determine the number of chromosomes of the this species, lymphocytes from juvenile and adults individuals were cultivated, using protocols and techniques used with success in other species of native fish. The chromosomal number was 2n=50(24m (metacentric) and 26sm/st (sububmetacéntricos/subtelocéntricos), which is similar to that of other bryconidos of the Amazon basin.Key Words: Yamú, Brycon siebenthalae, chromosomal number.RESUMEN: El yamú (Brycon siebenthalae) es un pez de escama, nativo de la Orinoquia Colombiana, con alto potencial para acuicultura. Sin embargo, el conocimiento sobre su biología es aún muy limitado. En consecuencia, para determinar el número de cromosomas de esta especie, linfocitos de individuos juveniles y adultos fueron cultivados, empleando protocolos y técnicas utilizadas con éxito en otras especies de peces nativos. El número cromosómico revelado fue 2n=50(24m(metacéntricos), 26sm/st(sububmetacéntricos/subtelocéntricos) el cual es similar al de otros bryconidos de la cuenca amazónica.Palabras Claves: Brycon siebenthalae, yamú, número cromosómico.ABSTRACT: The yamú (Brycon siebenthalae) it is a flake fish, native of the Colombian Orinoquia, with high potential for continental aquaculture. However, the knowledge on its biology is even very limited. In consequence, to determine the number of chromosomes of the this species, lymphocytes from juvenile and adults individuals were cultivated, using protocols and techniques used with success in other species of native fish. The chromosomal number was 2n=50(24m (metacentric) and 26sm/st (sububmetacéntricos/subtelocéntricos), which is similar to that of other bryconidos of the Amazon basin.Key Words: Yamú, Brycon siebenthalae, chromosomal number