Conductance through atomic point contacts between fcc(100) electrodes of gold

Electrical conductance through various nanocontacts between gold electrodes is studied by using the density functional theory, scalar-relativistic pseudopotentials, generalized gradient approximation for the exchange-correlation energy and the recursion-transfer-matrix method along with channel decomposition. The nanocontact is modeled with pyramidal fcc(100) tips and 1 to 5 gold atoms between the tips. Upon elongation of the contact by adding gold atoms between the tips, the conductance at Fermi energy E_F evolves from G ~ 3 G_0 to G ~ 1 G_0 (G_0 = 2e/h^2). Formation of a true one-atom point contact, with G ~ 1 G_0 and only one open channel, requires at least one atom with coordination number 2 in the wire. Tips that share a common vertex atom or tips with touching vertex atoms have three partially open conductance channels at E_F, and the symmetries of the channels are governed by the wave functions of the tips. The long 5-atom contact develops conductance oscillations and conductance gaps in the studied energy range -3 < E-E_F < 5 eV, which reflects oscillations in the local density of electron states in the 5-atom linear "gold molecule" between the electrodes, and a weak coupling of this "molecule" to the tips

Hydrophobically modified polyelectrolytes as potential drugs reservoirs of n-alkyl-nitroimidazoles

Indexación: ScieloThe solubilization of three commercial drugs (ornindazole, metronidazole and tinidazole) and model compounds (N-alkyl-2-methyl-4-nitroimidazoles) on aggregates formed by anionic polyelectrolytes, carrying alkyl side chains of different length, have been investigated in aqueous solution at pH 3.0, 7.0 and 11.0. Potassium salts of poly(maleic acid-co-1-olefins), PA-nK2 with n ranging from 8 to 18, were used as micelle-forming polymers. The partition of these drugs between water and the hydrophobic microdomains provided by PA-nK2 was studied by the pseudo-phase model to determinate the distribution coefficient KS, and the standard free energy of transfer Δμºt. The results indicate that solubility of alkyl-nitroimidazoles on these polymer micelles depends moderately on the length of the alkyl chain, and therefore is mainly determined by the heterocyclic group. On the other hand, the solubilization of 1-hexyl-2-methyl-4-nitroimidazole increase with decreasing length of the side alkyl chain; i.e. KS follows the order PA-8K2 > PA-10K2 > PA-12K2 > PA-14K2 > PA-16K2 >PA-18K2.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072007000100014&nrm=is

Studies on the clinical significance of nonesterified and total cholesterol in urine

Gas-liquid chromatographic determinations of nonesterified and total urinary cholesterol were performed in 137 normals, 264 patients with various internal diseases without evidence of neoplasias or diseases of the kidney or urinary tract, 497 patients with malignancies and 236 patients with diseases of the kidney, urinary tract infections or prostatic adenoma with residual urine. A normal range (mean±2 SD) of 0.2–2.2 mg/24 hours nonesterified cholesterol (NEC) and of 0.3–3.0 mg/24 hours total cholesterol (TC) was calculated. Values of urinary cholesterol excretion were independent of age and sex and did not correlate with cholesterol levels in plasma. Patients with various internal diseases, without evidence of neoplasias nor diseases of the kidney or obstruction of the urinary tract, showed normal urinary cholesterol excretions, as did patients with infections of the urinary tract. However, elevated urinary cholesterol was found in patients with diseases of the kidney or urinary tract obstruction (prostatic adenoma with residual urine), malignant diseases of the urogenital tract and metastasing carcinoma of the breast. In patients with other malignant diseases urinary cholesterol was usually normal. Lesions of the urothelial cell membranes are considered to be the most likely cause of urinary cholesterol hyperexcretion. The clinical value of urinary cholesterol determinations as a possible screening test for urogenital carcinomas in unselected populations is limited by lacking specificity, expensive methodology and low prevalence of the mentioned carcinomas, although elevated urinary cholesterol excretions have been observed in early clinical stages of urogenital cancers

Aerobic fitness impacts sympathoadrenal axis responses to concurrent challenges

The combination of mental and physical challenges can elicit exacerbated cardiorespiratory (CR) and catecholamine responses above that of a single challenge alone. Purpose This study examined the effects of a combination of acute mental challenges and physical stress on cardiorespiratory and catecholamine responses. Method Eight below-average fitness (LF VO2max = 36.58 +/- 3.36 ml(-1) kg(-1) min(-1)) and eight above-average fitness (HF VO2max = 51.18 +/- 2.09 ml(-1) kg(-1) min(-1)) participants completed an exercise-alone condition (EAC) session consisting of moderate-intensity cycling at 60% VO2max for 37 min, and a dual-challenge condition (DCC) that included concurrent participation in mental challenges while cycling. Result The DCC resulted in increases in perceived workload, CR, epinephrine, and norepinephrine responses overall. HF participants had greater absolute CR and catecholamine responses compared to LF participants and quicker HR recovery after the dual challenge. Conclusion These findings demonstrate that cardiorespiratory fitness does impact the effect of concurrent stressors on CR and catecholamine responses

Pericentromeric heterochromatin is hierarchically organized and spatially contacts H3K9me2 islands in euchromatin.

Membraneless pericentromeric heterochromatin (PCH) domains play vital roles in chromosome dynamics and genome stability. However, our current understanding of 3D genome organization does not include PCH domains because of technical challenges associated with repetitive sequences enriched in PCH genomic regions. We investigated the 3D architecture of Drosophila melanogaster PCH domains and their spatial associations with the euchromatic genome by developing a novel analysis method that incorporates genome-wide Hi-C reads originating from PCH DNA. Combined with cytogenetic analysis, we reveal a hierarchical organization of the PCH domains into distinct territories. Strikingly, H3K9me2-enriched regions embedded in the euchromatic genome show prevalent 3D interactions with the PCH domain. These spatial contacts require H3K9me2 enrichment, are likely mediated by liquid-liquid phase separation, and may influence organismal fitness. Our findings have important implications for how PCH architecture influences the function and evolution of both repetitive heterochromatin and the gene-rich euchromatin

Comportamiento clínico, epidemiológico y uso de suero antiofídico BIOL, en el manejo de accidentes ofídico en hospitales de Chontales, Rio San Juan, Matagalpa y Jinotega, en el período de Enero a Agosto de 2013

Las mordeduras por serpientes constituyen algunas de las urgencias más importantes que se atienden en las unidades de salud de Nicaragua, el tratamiento clave para este tipo de lesiones es el suero antiofídico. Existen dos familias venenosas de serpientes, elapidaes o corales manejadas con suero anticoral, y familia Viperidaes tratadas con suero polivalente. El suero utilizado para Viperidaes tradicionalmente ha sido el suero del Instituto de Clodomiro Picado, pero recientemente se ha incluido un nuevo suero polivalente (BIOL) para el manejo de los mismos. Con el objetivo de determinar el comportamiento clínico, epidemiológico y uso del suero BIOL en mejorar el cuadro clínico, se realizó un estudio descriptivo de corte transversal, donde se analizaron datos recolectados de los expedientes clínicos de 70 pacientes, con antecedentes de accidentes ofídicos en los departamentos de Matagalpa, Jinotega, Chontales y Río San Juan, entre enero y agosto de 2013. La tasa de incidencia fue de 5.5 casos por 100,000 habitantes, con predominio en el sexo masculino (73%), en edades comprendidas entre 10 y 49 años(62%), realizaban en su mayoría labores agrícolas (32.8%). El género Bothrops asper fue el responsable del 71.4% de los casos. Del total de pacientes lesionados, el 71.4 % acudió por atención a los puestos y centros de salud de su comunidad o municipio, y a un 86 % de estos les fue suministrado suero antiveneno. Los cuadros clínicos más frecuentes al momento del ingreso al hospital fueron edema y dolor en la extremidad. A 38 pacientes se les suministró suero BIOL-CLB, 22 se clasificaron como envenenamiento leve (57.8 %), 12 pacientes en la categoría de envenenamiento moderado (31.6%) y 4 pacientes (10.5 %) en cuadro de envenenamiento severo. Una vez aplicado el suero hubo mejoría en los síntomas y en las determinaciones de laboratorio, además solamente 3 de 38 pacientes sufrieron algún tipo de reacción al suero, prurito generalizado y aumento de calo

Techno-economic analysis of on-grid biomass renewable energy power station: A case study in Caribbean region of Colombia

In this article a techno-economic study of an Electric-Biomass on-grid power plant is presented, in order to compare the performance and the operating annual cost under some types of biogas produced from poultry, bovine and porcine manure, and solid urban organic waste, using the Homer® software to develop many solutions. Certainly, the best set up had the maximum combined renewable energy with a minimum electric consumption from the grid. The scheme was integrated by two 500kW biogas-powered electric generator on grid to supply an average energy of 1401.6kW, with an annual operating cost of $2.09 million when the energy supply is electric. Results presented a significant operational cost reduction when the biogas generator is operating on grid, finding an 8.61% of cost decrease using biogas generated from poultry, bovine and porcine manure, and a 10.53% of cost decrease using biogas from solid urban organic waste from centers and grocery market places at Caribbean Region of Colombia

PEST analysis of wind energy in the world: From the worldwide boom to the emergent in Colombia

This article presents the analysis of the political, economic, social and technological aspects of the countries with the greatest development and generation of wind energy in the world, with the aim of studying the successes and disadvantages over the years and serve as a reference to a country like Colombia, which is in full technological development and is very interested in investing in new alternatives to the imminent ecological disaster resulting from polluting emissions. Colombia signs the Paris Agreement and immediately creates a large number of opportunities supported by state policies and economic investment, specifically in the construction of wind farms that guarantee a real alternative to the country's energy demand. Wind energy supplies 5% of the world's electricity, a contribution in which countries such as the United States, China, and Germany are the main producers. For this reason, it is necessary to study and analyze the factors that prevent the technological development of wind energy in Colombia, if it is considered a country with abundant resources in renewable energy sources and zero cost, a country that aspires to be a protagonist in the next 5 years according to the Ministry of Mines and Energy