Study of the Electronic Interaction between NiO and Short Polythiophene Chains towards Solar Photon Harvesting.

The sustainable production of energy is a field of interest to which a new requirement is now imposed: the need to be respectful of the environment. New materials and techniques are being developed, but environmental concerns impose the necessity of keeping research active towards the development of green energy. For this reason, we present the study of short polythiophene (PTh) chains (three and five monomers) and their interaction with nickel oxide, looking for properties related to solar photon harvesting in order to produce electricity. The models of the molecules were developed, and the calculations were performed with an M11-L meta-GGA functional, specially developed for electronic structure calculations. The theoretical explorations demonstrated that the geometry of the PTh molecules suffer little distortion when interacting with the NiO molecule. The calculated value of Eg lies between 2.500 and 0.412 eV for a three-ring PTh chain and between 1.944 and 0.556 eV for a five-ring PTh chain. The chemical parameters indicated that, depending on the geometry of the system, the chemical potential varies from 81.27 to 102.38 kcal/mol and the highest amount of electronic charge varies from -2.94 to 21.56 a.u. for three-monomer systems. For five-monomer systems, the values lie within similar ranges as those of the three-monomer systems. The Partial Density of States (PDOS) showed that the valence and conduction electronic bands were composed of states in the NiO and PTh rings, except for a system where there was a non-bonding interaction.

A Comparative DFT Study on Process Control Agents in the Mechanochemical Synthesis of PbTe.

A process control agent is an organic additive used to regulate the balance between fracturing and mechanical kneading, which control the size of the as-milled particles. Tributyl phosphate (TBP) is evaluated to act as surface modifier of PbTe, and it is compared with the results obtained using formaldehyde (CH2O). In order to elucidate the nature of the interaction between TBP and the PbTe surface, global and local descriptors were calculated via the density functional theory. First, TBP and CH2O molecules are structurally optimized. Then, vertical ionization energies as well as vertical electron affinities are calculated to elucidate how both molecules behave energetically against removal and electron gain, respectively. The results were compared with those obtained from the electrostatic potential mapped on the van der Waals isosurface. It is inferred that the theoretical insights are useful to propose adsorption modes of TBP and CH2O on the PbTe surface, which are usable to rationalize the facets exposed by PbTe after the surface treatment. The optimized structures of the compound systems showed a close correlation between the surface energy shift (Δγ) and the PbTe facets exhibited. Finally, a Wulff construction was built to compare the usage of TBP and CH2O molecules in PbTe morphology.

Oriented-Attachment- and Defect-Dependent PbTe Quantum Dots Growth: Shape Transformations Supported by Experimental Insights and DFT Calculations.

High-resolution transmission electron microscopy results reveal that oriented-attachment- and defect-dependent mechanisms rule the size and shape evolution of the monodispersed PbTe quantum dots (QDs). The former is characterized by the growth of quasi-cubic PbTe QDs, which depends on both the geometric constraints imposed by the {200} facets and the defect-free lattice, while the latter one is a defect-dependent mechanism which gives way to the formation of decahedral PbTe QDs (∼6 nm). Experimentally, formaldehyde is an important parameter for the mechanochemical synthesis of monodispersed PbTe QDs, which has not been studied until now. In a theoretical context, Fukui functions reveal that Pb surface atoms are the most reactive sites toward nucleophilic attacks, and the Lowdin charge analysis shows that formaldehyde molecules tend to donate their electron pairs to Pb atoms. Besides, formaldehyde-molecule-on-PbTe adsorption energies (-4.46 to -21.16 kcal mol-1) agree with ligand-surface polar electrostatic interactions. Based on dispersion-corrected density functional theory calculations, PbTe QDs exhibited decahedral and faceted shapes. According to modified Wulff constructions, the decahedral shape is a result of (111) facets (Δγ = -2.79 meV Å-2), whereas the faceted and rounded shapes are due to the interaction of (100), (110), and (111) facets.

Optimizing the orbital occupation in the multiple minima problem of magnetic materials from the metaheuristic firefly algorithm.

We present the use and implementation of the firefly algorithm to help in scanning the multiple metastable minima of orbital occupations in density functional theory (DFT) plus Hubbard U correction and to identify the ground state occupations in strongly correlated materials. We show the application of this implementation with the Abinit code on KCoF3 and UO2 crystals, which are typical d and f electron systems with numerous occupation minima. We demonstrate the validity and performance of the method by comparing with previous methodologies. The method is general and can be applied to any code using constrained occupation matrices.

Machine-Learning Prediction of CO Adsorption in Thiolated, Ag-Alloyed Au Nanoclusters.

We propose a machine-learning model, based on the random-forest method, to predict CO adsorption in thiolate protected nanoclusters. Two phases of feature selection and training, based initially on the Au25 nanocluster, are utilized in our model. One advantage to a machine-learning approach is that correlations in defined features disentangle relationships among the various structural parameters. For example, in Au25, we find that features based on the distribution of Ag atoms relative to the CO adsorption site are the most important in predicting adsorption energies. Our machine-learning model is easily extended to other Au-based nanoclusters, and we demonstrate predictions about CO adsorption on Ag-alloyed Au36 and Au133 nanoclusters.

Structural search for stable Mg-Ca alloys accelerated with a neural network interatomic model.

We have combined a neural network formalism with metaheuristic structural global search algorithms to systematically screen the Mg-Ca binary system for new (meta)stable alloys. The combination of these methods allows for an efficient exploration of the potential energy surface beyond the possibility of the traditional searches based on ab initio energy evaluations. The identified pool of low-enthalpy structures was complemented with special quasirandom structures (SQS) at different stoichiometries. In addition to the only Mg-Ca phase known to form under standard synthesis conditions, C14-Mg2Ca, the search has uncovered several candidate materials that could be synthesized under elevated temperatures or pressures. We show that the vibrational entropy lowers the relative free energy of several phases with magnesium kagome layers: C15 and C36 Laves structures at the 2 : 1 composition and an orthorhombic oS36 structure at the 7 : 2 composition. The estimated phase transition temperatures close to the melting point leave open the possibility of synthesizing the predicted materials at high temperatures. At high pressures up to 10 GPa, two new phases at the 1 : 1 and 3 : 1 Mg : Ca stoichiometries become thermodynamically stable and should form in multi-anvil experiments.

Firefly Algorithm Applied to Noncollinear Magnetic Phase Materials Prediction.

In most noncollinear crystal magnets, the number of metastable states is quite large and any calculation that tries to predict the ground state can fall into one of the possible metastable phases. In this work, we generalize the population based meta-heuristic firefly algorithm to the problem of the noncollinear magnetic phase ground state prediction within density functional theory (DFT). We extend the different steps in the firefly algorithm to this specific problem by using polarized constrained DFT calculations, whereby using Lagrange multipliers the directions of the atom magnetic moments remain fixed. By locking the directions of the magnetic moments at each search iteration, the method allows one to explore the entire Born-Oppenheimer energy surface of existing and physically plausible noncollinear configurations present in a crystal. We demonstrate that the number of minima can be large, which restrains the use of exhaustive searches.

A Machine-Driven Hunt for Global Reaction Coordinates of Azobenzene Photoisomerization.

Azobenzene is a very important system that is often studied for better understanding light-activated mechanical transformations via photoisomerization. The central C-N═N-C dihedral angle is widely recognized as the primary reaction coordinate for changing cis- to trans-azobenzene and vice versa. We report on a global reaction coordinate (containing all internal coordinates) to thoroughly describe the reaction mechanism for azobenzene photoisomerization. Our global reaction coordinate includes all of the internal coordinates of azobenzene contributing to the photoisomerization reaction coordinate. We quantify the contribution of each internal coordinate of azobenzene to the overall reaction mechanism. Finally, we provide a detailed mapping on how each significantly contributing internal coordinate changes throughout the energy profile (from trans to transition state and subsequently to cis). In our results, the central C-N═N-C dihedral remains the primary internal coordinate responsible for the reaction coordinate; however, we also conclude that the disputed inversion-assisted rotation is half as important to the overall reaction mechanism and the inversion-assisted rotation is driven by four adjacent dihedral angles C-C-N═N with very little change to the adjacent C-C-N angles.

The Value of Coastal Wetlands for Flood Damage Reduction in the Northeastern USA.

As exposure to coastal hazards increases there is growing interest in nature-based solutions for risk reduction. This study uses high-resolution flood and loss models to quantify the impacts of coastal wetlands in the northeastern USA on (i) regional flood damages by Hurricane Sandy and (ii) local annual flood losses in Barnegat Bay in Ocean County, New Jersey. Using an extensive database of property exposure, the regional study shows that wetlands avoided $625 Million in direct flood damages during Hurricane Sandy. The local study combines these models with a database of synthetic storms in Ocean County and estimates a 16% average reduction in annual flood losses by salt marshes with higher reductions at lower elevations. Together, the studies quantify the risk reduction ecosystem services of marsh wetlands. Measuring these benefits in collaboration with the risk modelling industry is crucial for assessing risk accurately and, where appropriate, aligning conservation and risk reduction goals.

Investigation of novel crystal structures of Bi-Sb binaries predicted using the minima hopping method.

Semi-conducting alloys BixSb1-x have emerged as a potential candidate for topological insulators and are well known for their novel thermoelectric properties. In this work, we present a systematic study of the low-energy phases of 35 different compositions of BixSb1-x (0 < x < 1) at zero temperature and zero pressure. We explore the potential energy surface of BixSb1-x as a function of Sb concentration by using the ab initio minima hopping structural search method. Even though Bi and Sb crystallize in the same R3[combining macron]m space group, our calculations indicate that BixSb1-x alloys can have several other thermodynamically stable crystal structures. In addition to the configurations on the convex hull, we find a large number of metastable structures which are dynamically stable. The electronic band structure calculations of several stable phases reveal the presence of strong spin-orbit interaction leading to the Rashba-Dresselhaus spin-splitting of bands which is of great interest for spintronics applications. We also find an orthorhombic structure of BiSb in the Imm2 space group which exhibits signatures of type-II Weyl semimetal. Additionally, we have studied the thermoelectric properties of the selected structures. Regarding thermoelectric properties, we find that the compositions which crystallize in the rhombohedral structure exhibit values of the Seebeck coefficient and the power factor similar to that of Bi2Te3 at room temperature, while the theoretical maximum figure of merit (ZeT) is smaller than that of Bi2Te3. We observe enhancement in the thermopower with the increase in the strength of the Rashba-Dresselhaus spin-splitting effect.

A Review of Flood Loss Models as Basis for Harmonization and Benchmarking.

Risk-based approaches have been increasingly accepted and operationalized in flood risk management during recent decades. For instance, commercial flood risk models are used by the insurance industry to assess potential losses, establish the pricing of policies and determine reinsurance needs. Despite considerable progress in the development of loss estimation tools since the 1980s, loss estimates still reflect high uncertainties and disparities that often lead to questioning their quality. This requires an assessment of the validity and robustness of loss models as it affects prioritization and investment decision in flood risk management as well as regulatory requirements and business decisions in the insurance industry. Hence, more effort is needed to quantify uncertainties and undertake validations. Due to a lack of detailed and reliable flood loss data, first order validations are difficult to accomplish, so that model comparisons in terms of benchmarking are essential. It is checked if the models are informed by existing data and knowledge and if the assumptions made in the models are aligned with the existing knowledge. When this alignment is confirmed through validation or benchmarking exercises, the user gains confidence in the models. Before these benchmarking exercises are feasible, however, a cohesive survey of existing knowledge needs to be undertaken. With that aim, this work presents a review of flood loss-or flood vulnerability-relationships collected from the public domain and some professional sources. Our survey analyses 61 sources consisting of publications or software packages, of which 47 are reviewed in detail. This exercise results in probably the most complete review of flood loss models to date containing nearly a thousand vulnerability functions. These functions are highly heterogeneous and only about half of the loss models are found to be accompanied by explicit validation at the time of their proposal. This paper exemplarily presents an approach for a quantitative comparison of disparate models via the reduction to the joint input variables of all models. Harmonization of models for benchmarking and comparison requires profound insight into the model structures, mechanisms and underlying assumptions. Possibilities and challenges are discussed that exist in model harmonization and the application of the inventory in a benchmarking framework.

Firefly Algorithm for Structural Search.

The problem of computational structure prediction of materials is approached using the firefly (FF) algorithm. Starting from the chemical composition and optionally using prior knowledge of similar structures, the FF method is able to predict not only known stable structures but also a variety of novel competitive metastable structures. This article focuses on the strengths and limitations of the algorithm as a multimodal global searcher. The algorithm has been implemented in software package PyChemia ( https://github.com/MaterialsDiscovery/PyChemia ), an open source python library for materials analysis. We present applications of the method to van der Waals clusters and crystal structures. The FF method is shown to be competitive when compared to other population-based global searchers.

Factores asociados a mayores niveles de carga familiar en cuidadores principales de pacientes con esquizofrenia en actual atención ambulatoria del Hospital Victor Larco Herrera. Marzo - Julio 2012 / Factors associated with higher levels of family burden in primary caregivers of patients with schizophrenia in current ambulatory attention of the Hospital Victor Larco Herrera. March - July 2012

El desarrollo de los tratamientos comunitarios de las enfermedades mentales crónicas y graves tras la sobrepoblación de los hospitales psiquiátricos ha supuesto una carga para los familiares, cuidadores de los pacientes. Objetivo: determinar cuáles son los factores asociados a mayores niveles de carga familiar en cuidadores principales de pacientes con esquizofrenia. Material y Método: se estudió 50 cuidadores de pacientes con diagnóstico de esquizofrenia según CIE-10, en actual atención ambulatoria. Se aplicó, a los cuidadores, una ficha sociodemográfica y la entrevista de carga familiar objetiva y subjetiva (ECFOS-II) validada. Los pacientes fueron evaluados con la Positive and Negative Syndrome Scale (PANSS), la WHO/Disability Assessment Schedule (OMS/DAS) y la Global Assessment Functioning (GAF). Se analizó la asociación entre las dimensiones de la carga familiar del cuidador y las características del paciente, los síntomas de la enfermedad y la discapacidad asociada a la misma. Resultados: la carga familiar del cuidador se asocia con mayor gasto económico en el cuidado del paciente, reingresos en el último año, la intensidad de síntomas propios de la enfermedad y el grado de discapacidad derivada de la misma. Conclusiones: el ECFOS-II es de utilidad clínica y de investigación para la evaluación de carga familiar. Los resultados de este estudio así como los de otros similares de la literatura internacional muestran especial relevancia, tanto para el desarrollo de los programas específicos de tratamiento psiquiátrico como en el desarrollo de las políticas sociales específicas, a nivel de Atención Primaria, para este tipo de patología.

Two-year clinical performance of Clearfil SE and Clearfil S3 in restoration of unabraded non-carious class V lesions.

This study was undertaken to evaluate the two-year clinical performance of a self-etching primer and a self-etching adhesive, both of which employ the same acidic monomer. Forty pairs of restorations of AP-X hybrid resin composite (Kuraray Co, Ltd, Osaka, Japan) were placed in caries-free cervical erosion/abfraction lesions. Based on insensitivity to air, the dentin in 62% of these lesions was considered to be sclerotic. The restorations were placed with no abrasion of tooth surfaces, except for cleaning with plain pumice and no use of phosphoric acid etching, which is counter to the manufacturer's instructions that call for etching of unprepared enamel. One restoration from each pair was placed using Clearfil SE Bond, an adhesive employing a self-etching primer, and the other was placed using Clearfil S3 Bond, a self-etching adhesive. To emulate the results likely to occur in a private practice, the restorations were placed by well-educated, experienced clinicians who had no particular expertise in adhesive dentistry research and who placed the restorations according only to their interpretation of the manufacturer's instructions. The restorations were clinically evaluated at baseline and at 6, 12 and 24 months, using modified Ryge/USPHS criteria. For both products, retention of 81%-84% of the restorations was observed over two years, which is lower than has been previously observed with these products and is likely due to limitations in the manufacturer's instructions compounded by inexperience of the operators in adhesive dentistry research. One restoration placed with each adhesive demonstrated secondary caries, which was probably attributable to the study being conducted in a non-fluoridated area and which reduced the percentages of clinically successful restorations to 78%-81%. No statistically significant difference (p = 0.50) between the two adhesives was observed in overall performance.

Microstructural effects of Sn addition to Fe2O3 thin films.

The influence of Sn in Fe2O3 thin films is addressed. The presence of the tin ions decreases the Fe2O3 particle sizes and surface roughness decreasing of the films' surface is observed as a consequence. X-ray diffraction and atomic force microscopy measurements together with literature results support this phenomenon to be related to the segregation of the additive onto the surface and consequently surface energy decrease, which constitutes the driving force for the microstructure modification, similarly to results previously obtained for powders with same compositions. The effect of the anions introduced in the system as counter-ions of the precursors is also discussed.

Activation of nucleoplasmin, an oligomeric histone chaperone, challenges its stability.

Nucleoplasmin (NP) is a pentameric, ring-shaped histone chaperone involved in chromatin remodeling processes such as sperm decondensation at fertilization. Monomers are formed by a core domain, responsible for oligomerization, that confers the protein a high stability and compactness and a flexible tail domain, that harbors a polyglutamic tract and the nuclear localization signal. Fully activated NP presents multiple phosphorylated residues in the tail and in flexible regions of the core domain. In this work, we analyze the effect of activation on the structure and stability of the full-length protein and the isolated core domain through phosphorylation mimicking mutations. We have solved the crystal structure of an activated NP core domain that, however, is not significantly different from that of the wild-type,inactive, NP core. Nevertheless, we find that NP activation results in a strong destabilization of the pentamer probably due to electrostatic repulsion. Moreover, characterization of the hydrodynamic properties of both full-length and core domain proteins indicates that activating mutations lead to an expansion of the NP pentamer in solution. These findings suggest that NP needs a compact and stable structure to afford the accumulation of negative charges that weakens its quaternary interactions but is required for its biological function.

Thermodynamic characterization of nucleoplasmin unfolding: interplay between function and stability.

The unfolding equilibrium of recombinant (rNP) and natural variants of nucleoplasmin (NP) from Xenopus laevis has been analyzed using biochemical and spectroscopic techniques. In the presence of denaturing concentrations of guanidinium salts (GuHCl and GuSCN), both domains, core and tail, of the rNP pentamer unfold as proven using single-carrying tryptophan mutants, whereas urea is remarkably unable to fully unfold rNP. Chemical unfolding is reversible and can be described well as a two-state transition in which the folded pentamer is directly converted to unfolded monomers, with no evidence of (partially) folded monomers. Therefore, rNP dissociates and fully unfolds simultaneously (N 5 <--> 5U). Activation of the protein by hyperphosphorylation is accompanied by a destabilization of the protein oligomer. A comparison of natural NP forms isolated from eggs and oocytes of X. laevis and recombinant NP reveals that natural variants can be fully unfolded by urea and exhibit D 50 (denaturant concentration at the transition midpoint) values lower than that of the nonphosphorylated protein. Progressive phosphorylation of NP correlates with a gradual loss of stability of 6 kcal/mol (oNP) and 10 kcal/mol (eNP), as compared with the nonphosphorylated protein pentamer. These results suggest that the remarkable stability of the recombinant protein is required to cope with the destabilization brought about by its phosphorylation-induced activation.

Attributable cost and length of stay for patients with central venous catheter-associated bloodstream infection in Mexico City intensive care units: a prospective, matched analysis.

BACKGROUND: No information is available about the financial impact of central venous catheter (CVC)-associated bloodstream infection (BSI) in Mexico. OBJECTIVE: To calculate the costs associated with BSI in intensive care units (ICUs) in Mexico City. DESIGN: An 18-month (June 2002 through November 2003), prospective, nested case-control study of patients with and patients without BSI. SETTING: Adult ICUs in 3 hospitals in Mexico City. PATIENTS AND METHODS: A total of 55 patients with BSI (case patients) and 55 patients without BSI (control patients) were compared with respect to hospital, type of ICU, year of hospital admission, length of ICU stay, sex, age, and mean severity of illness score. Information about the length of ICU stay was obtained prospectively during daily rounds. The daily cost of ICU stay was provided by the finance department of each hospital. The cost of antibiotics prescribed for BSI was provided by the hospitals' pharmacy departments. RESULTS: For case patients, the mean extra length of stay was 6.1 days, the mean extra cost of antibiotics was US dollars 598, the mean extra hospital cost was US dollars 11,591, and the attributable extra mortality was 20%. CONCLUSIONS: In this study, the duration of ICU stay for patients with central venous catheter-associated BSI was significantly longer than that for control patients, resulting in increased healthcare costs and a higher attributable mortality. These conclusions support the need to implement preventive measures for hospitalized patients with central venous catheters in Mexico.

The effect of process control on the incidence of central venous catheter-associated bloodstream infections and mortality in intensive care units in Mexico.

PURPOSE: To ascertain the effect of an infection control program including process control on intensive care unit (ICU) rates of intravascular device (IVD)-associated bloodstream infection (BSI). SETTING: Two level III adult ICUs in one public university hospital in Mexico: one medical surgical ICU and one neurosurgical ICU. POPULATION STUDY: All adult patients admitted to study units who had a central venous catheter (CVC) in place for at least 24 hrs. METHODS: A prospective before/after trial in which rates of IVD-associated BSI are determined during a period of active surveillance without process control (phase 1) were compared with rates of IVD-associated BSI after implementing an infection control program applying process control (phase 2). RESULTS: Six hundred five IVD-days were accumulated in phase 1, and 2824 IVD-days were accumulated during phase 2. Compliance with CVC site care and hand hygiene improved significantly from baseline during the study period: placing a gauze dressing over the catheter insertion site (99.24% vs. 86.69%, respectively; relative risk [RR] = 1.14; 95% confidence interval [CI] = 1.07-1.22; p = .0000), proper use of gauze for vascular catheter insertion site (97.87% vs. 84.21%, respectively; RR = 1.16; 95% CI = 1.09-1.24; p = .0000), documentation of the duration of the administration set of the vascular catheter (93.85% vs. 40.69%, respectively; RR = 2.34; 95% CI = 2.14-2.56; p = .0000), and hand hygiene before contact with the patient (84.9% vs. 62%, respectively; RR = 1.37; 95% CI = 1.21-1.51; p = .0000). Overall rates of IVD-associated BSI were lowered significantly from baseline rates after implementation of process control (19.5 vs. 46.3 BSIs per 1000 IVD-days, respectively; RR = 0.42; 95% CI = 0.27-0.66; p = .0001). Overall rates of crude unadjusted mortality were lowered significantly from baseline rates (48.5% vs. 32.8% per 100 discharges, respectively; RR = 0.68; 95% CI = 0.50-0.31; p = .01). CONCLUSION: Implementation of an infection control program utilizing education, process control, and performance feedback was associated with significant reductions in rates of IVD-associated BSI and mortality.

Eighteen-month clinical performance of a self-etching primer in unprepared class V resin restorations.

This study evaluated the clinical performance of unprepared Class V resin composites, placed using a self-etching primer and a single-bottle adhesive, over a period of 18 months. Thirty-eight pairs of restorations of Renew hybrid resin composite (BISCO, Inc) were placed using adhesives from the same manufacturer in caries-free cervical erosion/abfraction lesions. Based on insensitivity to air, the dentin in 76% of these lesions was considered to be sclerotic. The restorations were placed without abrasion of tooth surfaces, except for cleaning with plain pumice. One of each pair was placed using Tyrian, a self-etching primer and the other was placed using One-Step, a single-bottle adhesive placed after acid etching. Both the etchant and self-etching primer were applied for 20 seconds. The restorations were clinically evaluated at baseline, 6, 12 and 18 months, using modified Ryge/USPHS criteria. For both adhesives, very low retention of 50% to 56% of the restorations was observed over 18 months, leading to the conclusion that tooth surfaces must receive some additional treatment prior to restoration with these adhesives. No statistically significant difference (p=0.75) between the two adhesives was observed in overall performance, and dentinal sclerosis and axial depth did not appear to be important factors in the study.