Singlet fission, the generation of two triplet excited states from the absorption of a single photon, may potentially increase solar energy conversion efficiency. A major roadblock in realizing this ...potential is the limited number of molecules available with high singlet fission yields and sufficient chemical stability. Here, we demonstrate a strategy for developing singlet fission materials in which we start with a stable molecular platform and use strain to tune the singlet and triplet energies. Using perylene diimide as a model system, we tune the singlet fission energetics from endoergic to exoergic or iso-energetic by straining the molecular backbone. The result is an increase in the singlet fission rate by 2 orders of magnitude. This demonstration opens a door to greatly expanding the molecular toolbox for singlet fission.
Background: Phthalates, ubiquitous environmental pollutants that may disturb the endocrine system, are used primarily as plasticizers of polyvinyl chloride and as additives in consumer and personal ...care products. Objectives: In this study, we examined the association between urinary concentrations of nine phthalate metabolites and breast cancer (BC) in Mexican women. Methods: We age-matched 233 BC cases to 221 women residing in northern Mexico. Sociodemographic and reproductive characteristics were obtained by direct interviews. Phthalates were determined in urine samples (collected pretreatment from the cases) by isotope dilution/high-performance liquid chromatography coupled to tandem mass spectrometry. Results: Phthalate metabolites were detected in at least 82% of women. The geometric mean concentrations of monoethyl phthalate (MEP) were higher in cases than in controls (169.58 vs. 106.78 μg/g creatinine). Controls showed significantly higher concentrations of mono-n-butyl phthalate, mono(2-ethyl-5-oxohexyl) phthalate, and mono(3-carboxypropyl) phthalate (MCPP) than did the cases. After adjusting for risk factors and other phthalates, MEP urinary concentrations were positively associated with BC odds ratio (OR), highest vs. lowest tertile = 2.20; 95% confidence interval (CI), 1.33–3.63; p for trend < 0.01. This association became stronger when estimated for premenopausal women (OR, highest vs. lowest tertile = 4.13; 95% CI, 1.60–10.70; p for trend < 0.01). In contrast, we observed significant negative associations for monobenzyl phthalate (MBzP) and MCPP. Conclusions: We show for the first time that exposure to diethyl phthalate, the parent compound of MEP, may be associated with increased risk of BC, whereas exposure to the parent phthalates of MBzP and MCPP might be negatively associated. These findings require confirmation.
La región centro del estado de Veracruz se considera una de las más importantes productoras de café bajo sombra y la innovación en la cafeticultura estatal ha aportado numerosas mejoras en ...beneficio de los productores y de los consumidores. La diversificación con árboles maderables es una de ellas. Con el fin de documentar la existencia y las formas de utilización de la madera y los aportes económicos de especies arbóreas introducidas en fincas de café de sombra en el centro del estado de Veracruz, se realizaron entrevistas semiestructuradas en Huatusco y Coatepec, y se identificó a las principales especies maderables. Se reconocieron especies introducidas y nativas o de la región; de las primeras, destacan el cedro rosado de la India (Acrocarpus fraxinifolius), grevilia (Grevillia robusta), tulipán de la India (Spathodea campanulata), bracatinga (Mimosa scabrella), piocho (Azadirachta indica), duela (Schizolobium parahyba) y la primavera (Tabebuia chrysantha). De las del segundo tipo, ixpepelt (Trema micrantha), texmol (Quercus robur), cacaotillo (Virola guatemalensis), cedro rojo (Cedrela odorata), mango (Mangifera indica), vainillo (Inga vera), roble (Quercus laurina) y pambacillo (Alchornea latifolia). Los productores prefieren la madera de cedro rojo y de encino, conocido localmente como tezmol, pero para leña, encino, cedro rosado, pambacillo o vainillo, y este último para sombra de cafetales.
Aplodinotus grunniens represent a crucial artisanal fishery in the Usumacinta River’s middle basin that generates food and a subsistence economy. This study aimed to create a model that best ...describes growth for A. grunniens and provides information on the growth of this poorly known pecies from the Usumacinta River. Data collection was carried out over one year through monthly sampling. A total of 447 specimens were collected from January to December 2017. Von Bertalanffy’s growth constants were calculated by separate sexes using linear fit and the non-linear Levenberg-Marquardt method. Hotelling’s T-squared test showed that growth was significantly faster in females than males. The estimated age at first maturity was two years in males and three in females. Considering the age reported for A. grunniens in other studies, the age determined in this study indicates that the population could be overexploited. Larger fish are more vulnerable to fishing pressure, mainly during their highest reproductive activity when they aggregate for spawning. More research is needed to evaluate the population status, catch per unit effort, distribution, and abundance of adults, juveniles, and larvae.
Recent interest in potassium-doped p-terphenyl has been fueled by reports of superconductivity at T c values surprisingly high for organic compounds. Despite these interesting properties, studies of ...the structure–function relationships within these materials have been scarce. Here, we isolate a phase-pure crystal of potassium-doped p-terphenyl: K(222)2p-terphenyl3. Emerging antiferromagnetism in the anisotropic structure is studied in depth by magnetometry and electron spin resonance. Combining these experimental results with density functional theory calculations, we describe the antiferromagnetic coupling in this system that occurs in all 3 crystallographic directions. The strongest coupling was found along the ends of the terphenyls, where the additional electron on neighboring p-terphenyls antiferromagnetically couple. This delocalized bonding interaction is reminiscent of the doubly degenerate resonance structure depiction of polyacetylene. These findings hint toward magnetic fluctuation-induced superconductivity in potassium-doped p-terphenyl, which has a close analogy with high T c cuprate superconductors. The new approach described here is very versatile as shown by the preparation of two additional salts through systematic changing of the building blocks.
Pathological detonations in mono-disperse spray media Hernández-Sánchez, Raúl; Huete, César; Martínez-Ruiz, Daniel
Proceedings of the Combustion Institute,
2024, 2024-00-00, Letnik:
40, Številka:
1-4
Journal Article
Recenzirano
Odprti dostop
Detonation waves differ from deflagration fronts in several distinct properties, with perhaps the most significant distinction being the supersonic propagation and pressure variations of the former. ...In the absence of additional supporting mechanisms and non-ideal effects, the supersonic speed can be accurately predicted by considering the global properties associated with the state of the fresh mixture. Specifically, at the Chapman–Jouguet (CJ) speed, the velocity is determined by the maximum expansion that the hot products can undergo associated with the attainment of the sonic condition at the end of the reaction zone. However, there is a specific mode of propagation known as pathological (or eigenvalue) detonation when the sonic condition is not achieved at the end of the reaction zone but occurs at an intermediate finite distance from the shock. This type of detonation can occur when endothermic effects are present in the system, resulting in the formation of an internal frozen sonic point, where the local thermicity becomes negligible. This condition is typically associated with the presence of two or more irreversible steps describing the overall chemical reaction that ends with a final endothermic process. The propagation speed of the detonation is then determined by the placement of the sonic locus at the neutrally thermal zone, which depends on the internal profiles. Then, this kind of detonation resembles a deflagration as it is influenced by its inner structure to determine its speed. In turn, the subsequent supersonic region uncouples part of the endothermic effects from the detonation driving mechanism, resulting in greater propagation speeds. In this study, we find that pathological detonations can also occur when the fuel exists in multi-phase state, so endothermic fuel vaporization dominates at the end of the non-equilibrium region. The range of occurrence of pathological detonations increases with the Stokes number and the fuel equivalence ratio of the fuel liquid phase.
Electron Cartography in Clusters Hernández Sánchez, Raúl; Champsaur, Anouck M.; Choi, Bonnie ...
Angewandte Chemie,
October 15, 2018, Letnik:
130, Številka:
42
Journal Article
Recenzirano
Odprti dostop
Deconvoluting the atom‐specific electron density within polynuclear systems remains a challenge. A multiple‐wavelength anomalous diffraction study on four clusters that share the same Co6Se8 core was ...performed. Two cluster types were designed, one having a symmetric ligand sphere and the other having an asymmetric ligand sphere. It was found that in the neutral, asymmetric, CO‐bound cluster, the Co−CO site is more highly oxidized than the other five Co atoms; when an electron is removed, the hole is distributed among the Se atoms. In the neutral, symmetric cluster, the Co atoms divide by electron population into two sets of three, each set being meridional; upon removal of an electron, the hole is distributed among all the Co atoms. This ligand‐dependent tuning of the electron/hole distribution relates directly to the performance of clusters in biological and synthetic systems.
Das Aufschlüsseln der Atom‐individuellen Valenzinformation in delokalisierten gemischtvalenten mehrkernigen Systemen bleibt anspruchsvoll. Die Elektronendichte über Co6Se8‐Cluster hinweg wurde kartiert, und ihre Rekonfiguration in einer Ein‐Elektronen‐Oxidation wurde aufgeklärt.
Cirugía mínimamente invasiva de estrabismo modificada Teresita de Jesús Méndez Sánchez; Juan Raúl Hernández Silva; Haymy Caridad Casanueva Cabeza ...
Revista cubana de medicina militar,
12/2023, Letnik:
53, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Introducción: La cirugía mínimamente invasiva de estrabismo ha revolucionado el concepto de la cirugía tradicional de estrabismo. Este procedimiento se realiza con mínima disrupción anatómica entre ...el músculo y el tejido perimuscular. Objetivo: Describir una propuesta de modificación a la técnica de cirugía mínimamente invasiva de estrabismo. Métodos: Se revisó la literatura en español e inglés, sin restricciones de fecha, para investigar modificaciones reportadas a la técnica de cirugía mínimamente invasiva de estrabismo. En las modificaciones revisadas, coexiste la posibilidad de que ocurra la complicación de músculo deslizado o músculo perdido. Para realizar una técnica quirúrgica segura se identificaron los aspectos que pueden influir en esta, que son el agarre muscular y su fijación escleral, sin ampliar las microincisiones. Resultados: En la técnica modificada se emplearon pinzas curvas de Moody-Castroviejo, para ampliar el campo operatorio. Se utilizó una sola sutura no reabsorbible de ácido poliglicólico para el agarre muscular; se pasa primero por el espesor muscular y después por los extremos superior e inferior de la inserción muscular, lo cual ofrece seguridad al procedimiento. Se propone el uso del Dardenne, instrumento oftalmológico utilizado en la realización de pupiloplastias, para traer el extremo opuesto de la sutura y realizar un nudo de Siepser; al cortar la sutura, quedan los cabos por debajo del túnel conjuntival, sin ampliar las microincisiones. Conclusiones: Las modificaciones a la técnica de cirugía mínimamente invasiva de estrabismo, que propone este trabajo, permiten mejor agarre y fijación del músculo.
Gastric cancer (GC) is among the leading causes of cancer mortality worldwide. The objective of this study was to investigate the association between dietary fiber intake and GC.
We pooled data from ...11 population or hospital-based case-control studies included in the Stomach Cancer Pooling (StoP) Project, for a total of 4865 histologically confirmed cases and 10,626 controls. Intake of dietary fibers and other dietary factors was collected using food frequency questionnaires. We calculated the odds ratios (OR) and 95% confidence intervals (CI) of the association between dietary fiber intake and GC by using a multivariable logistic regression model adjusted for study site, sex, age, caloric intake, smoking, fruit and vegetable intake, and socioeconomic status. We conducted stratified analyses by these factors, as well as GC anatomical site and histological type.
The OR of GC for an increase of one quartile of fiber intake was 0.91 (95% CI: 0.85, 0.97), that for the highest compared to the lowest quartile of dietary fiber intake was 0.72 (95% CI: 0.59, 0.88). Results were similar irrespective of anatomical site and histological type.
Our analysis supports the hypothesis that dietary fiber intake may exert a protective effect on GC.
Phenolic compounds may exert a favorable effect on the risk of several cancer types, including gastric cancer (GC). However, selected polyphenol classes have not been adequately investigated in ...relation to GC. The aim of this study is to evaluate the association between the intake of polyphenols in relation to GC risk. We used data from the Stomach cancer Pooling (StoP) Project, including 10 studies from six countries (3471 GC cases and 8344 controls). We carried out an individual participant data pooled analysis using a two-stage approach. The summary odds ratios (ORs) of GC for each compound, and the corresponding 95% confidence intervals (95% CI), were computed by pooling study specific ORs obtained through multivariate logistic regression, using random effect models. Inverse associations with GC emerged for total polyphenols (OR = 0.67, 95% CI = 0.54–0.81, for the highest versus lowest quartile of intake), total flavonoids (OR = 0.73, 95% CI = 0.55–0.90), anthocyanidins (OR = 0.74, 95% CI = 0.56–0.92), flavanols (OR = 0.77, 95% CI = 0.66–0.88), flavanones (OR = 0.57, 95%CI = 0.44–0.69), total phenolic acids (OR = 0.75, 95%CI = 0.55–0.94), and hydroxybenzoic acids (OR = 0.73, 95%CI = 0.57–0.89). Results were consistent across strata of age, sex, social class, and smoking habit. Suggestive inverse associations were also found for flavonols (OR = 0.76, 95%CI = 0.51–1.01) and hydroxycinnamic acids (OR = 0.82, 95%CI = 0.58–1.06). Further investigations from longitudinal data are needed to confirm this association.
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