The folding of centromeric DNA strands into intercalated structures: a physicochemical and computational study

We have carried out a physicochemical and computational analysis on the stability of the intercalated structures formed by cytosine-rich DNA strands. In the computational study, the electrostatic energy components have been calculated using a Poisson-Boltzmann model, and the non-polar energy components have been computed with a van der Waals function and/or a term dependent on the solvent-accessible surface area of the molecules. The results have been compared with those obtained for Watson-Crick duplexes and with thermodynamic data derived from UV experiments. We have found that intercalated DNA is mainly stabilized by very favorable electrostatic interactions between hydrogen-bonded protonated and neutral cytosines, and by non-polar forces including the hydrophobic effect and enhanced van der Waals contacts. Cytosine protonation electrostatically promotes the association of DNA strands into a tetrameric structure. The electrostatic interactions between stacked C.C+ pairs are strongly attenuated by the reaction field of the solvent, and are modulated by a complex interplay of geometric and protonation factors. The forces stabilizing intercalated DNA must offset an entropic penalty due to the uptake of protons for cytosine protonation, at neutral pH, and also the electrostatic contribution to the solvation free energy. The latter energy component is less favorable for protonated DNA due to the partial neutralization of the negative charge of the molecule, and probably affects other protonated DNA and RNA structures such as C+-containing triplexes.     

Optimal capacitor placement in radial distribution networks

The capacitor placement (replacement) problem for radial distribution networks determines capacitor types, sizes, locations and control schemes. Optimal capacitor placement is a hard combinatorial problem that can be formulated as a mixed integer nonlinear program. Since this is a NP complete problem (nonpolynomial time) the solution approach uses a combinatorial search algorithm. The paper proposes a hybrid method drawn upon the Tabu Search approach, extended with features taken from other combinatorial approaches such as genetic algorithms and simulated annealing, and from practical heuristic approaches. The proposed method has been tested in a range of networks available in the literature with superior results regarding both quality and cost of solutions     

Electrical conductivity of vapor‐grown carbon nanofiber/polyester textile‐based composites

Polyamide 6/ethylene–propylene–diene metallocene terpolymer/(ethylene–propylene–diene copolymer)‐graft‐(maleic anhydride) blends with clay (3 and 5 wt % depending on the formulation), different clays (montmorillonite and sepiolite) and different surface functionalization (ammonium salts and silanes) were studied to analyze the effect of the shape of clay and type of modifier on their properties. The results have shown that sepiolite has higher influence on the morphology and on the mechanical properties than montmorillonite. In that sense, blends with 3 wt % of sepiolite have reached the best balanced properties, i.e., tensile modulus and impact strength, than their homologous with montmorillonite. Furthermore, the blends with 3 wt % of sepiolite have reached the highest mechanical properties compared with blends with higher montmorillonite content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Erratum: A wavelet‐based approach for large wind power ramp characterization

The large and rapid variations (ramp events) of wind power output experienced in wind farms and portfolios represent one of the main challenges facing short‐term wind power forecasting. In countries with high wind power penetration, a ramp event forecasting tool is required by transmission system operators and energy traders to schedule ancillary services properly and minimize economic penalties in liberalized electricity markets, respectively. From the forecaster/modeller's point of view, locating ramp events within a wind power time series is important, because it allows them to regard meteorological processes and operational states of the wind farm in the proper time periods to analyse the ramp causes. This work introduces the ramp function as a means of characterizing the ramp performance of a wind power time series. The underlying idea is that a ramp event is characterized by high‐power output gradients evaluated under different time scales. The ramp function is based on the wavelet transform and provides a continuous index related to the ramp intensity at each time step, which permits to take into account the fuzzy limits of the ramp notion, as well as the development of new approaches to wind power ramp analysis that are not feasible from a binary classification standpoint. Several advantages of the ramp function for end‐users are outlined, and applications concerning different aspects of ramp forecasting are described for several wind farms located in Spain. Copyright © 2013 John Wiley & Sons, Ltd.     

Estimation of effective solar irradiation using an unscented Kalman filter in a parabolic-trough field

Measurement of direct solar radiation has been shown to be very useful to improve control performance and disturbance rejection in solar fields by anticipating the effect of sudden changes in solar radiation due to clouds. Since direct solar radiation is measured locally by pyrheliometers, important errors in the estimation of the overall effective solar radiation can be produced when the pyrheliometer is covered by clouds while the rest of the solar field is not or viceversa. Furthermore, estimation of the overall efficiency affected by the reflectivity and absortance of metal tubes is very difficult because only local measurements can be obtained. This work proposes an algorithm for estimating overall solar radiation and efficiency at the field. The algorithm uses an unscented Kalman filter and it is validated by data obtained at the Plataforma Solar of Almer?´a (Spain).     

The effect of montmorillonite and compatibilizer quantities on stiffness and toughness of polyamide nanoblends

Although polymer blend nanocomposites are widely studied, the balance between stiffness and toughness has not yet been investigated in detail. Some materials producers as well as some sectors in the automotive industry try to improve the toughness of materials without an important loss in stiffness. With this in mind, the aim of the study reported here was to obtain a good balance between toughness and stiffness of polymer blends with different amounts of clay and compatibilizer. In this context, the microstructure of polyamide 6/ethylene–propylene–diene metallocene terpolymer/(ethylene–propylene–diene copolymer)‐graft‐(maleic anhydride) blends with various amounts of clay (2, 3, 4 and 5 wt%) and compatibilizer (10 and 20 wt%) was studied to analyse the achieved morphology to understand the macroscopic properties. The morphology of the rubber phase and the dispersion of the montmorillonite (MMT) are the main factors that influence the mechanical properties. In this sense, the highest Young's modulus is achieved for nanoblends with 5 wt% of MMT, although this nanoblend has the lowest value of notched Izod impact strength. The results obtained suggest that there is a clear trade‐off between stiffness, toughness and temperature behaviour when the ratio of (ethylene–propylene–diene copolymer)‐graft‐(maleic anhydride) to MMT is 5:1. Copyright © 2009 Society of Chemical Industry     

Production of hydrogen and MWCNTs by methane decomposition over catalysts originated from LaNiO3 perovskite

LaNiO₃ type perovskite was prepared by the “self-combustion” method and was used as catalyst precursor for the methane decomposition reaction at 600 and 700 °C. CH₄ conversion reaches 80% at 700 °C and 65% at 600 °C using pure CH₄. The yield of CNT and H₂ were 2.2 g_CNT g^?1 h^?1 and 8.2 L g^?1 h^?1 at 700 °C respectively after 4 h of reaction. When the reaction is prolonged to 22 h the catalytic activity decreases but the catalyst is still active, the production of hydrogen reaches 63.5 L (STP) per gram of catalyst and the production of MWCNT was equal to 17 g per gram of catalyst.Multi-wall carbon nanotubes were characterized by X-ray diffraction (XRD), surface area (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Raman spectroscopy. TEM micrographs showed that MWCNT longer than 20 μm were formed with inner diameters ranging from 5 to 16 nm and outer diameters up to about 40 nm.The results obtained here clearly show that the use of the perovskite LaNiO₃ as catalytic precursor is very effective for the simultaneous production of carbon nanotubes and hydrogen.     

Thoracoabdominal pattern of breathing in neuromuscular disorders

STUDY OBJECTIVE: To assess abnormalities in thoracoabdominal pattern of breathing (TAPB) in neuromuscular disorders during spontaneous breathing, intermittent positive pressure ventilation (IPPV) with and without abdominal (AB) binder, and immediately after IPPV. DESIGN: Repeated measures design: Pre-IPPV spontaneous breathing, IPPV, IPPV with AB binder, and post-IPPV spontaneous breathing. In protocol 1, ventilator pressure was held constant at the individual value habitually adopted in sessions of IPPV. In protocol 2, it was increased stepwise from 5 to 30 cm H2O. SETTING: University hospital, Department of Pediatrics, Intensive Care, and Neuro-Ventilatory Rehabilitation. PATIENTS: Thirty-one patients with spinal muscular atrophy (SMA) and 19 patients with myopathy, mean age (+/- SD) 9.7 +/- 3 years. MEASUREMENTS: Tidal volume (VT), percent thoracic contribution to VT (%RC), the phase angle between the thoracic and the AB volume changes and the labored breathing index, which is an index of asynchrony taking into account both the phase relationships and relative volumes of rib cage and AB compartments. RESULTS: We observed marked abnormalities in TAPB during spontaneous breathing, especially in the SMA group. %RC, labored breathing index, and phase angle displayed nearly normal values during IPPV. IPPV pressures of 25 to 30 cm H2O were necessary to increase %RC above 80%. AB binding decreased VT, but led to larger thoracic volumes, especially in patients with SMA. Thoracic contribution to VT and thoracic volume after IPPV were higher than baseline levels. CONCLUSIONS: The quantitative assessment of TAPB enhances the ability to estimate pulmonary function in neuromuscular disorders, and the efficiency of mechanical ventilation.