8 research outputs found
Predictive energetic tuning of quinoid O-nucleophiles for the electrochemical capture of carbon dioxide
No full text
The need for robust, scalable methods for the capture and storage of carbon dioxide is increasingly pressing. Electric power-based carbon capture methods have drawn attention as a promising strategy due to their potential to couple to renewable energy sources. Materials for the capture of CO2 from air need to overcome the challenges of parasitic reactivity with oxygen, selective removal of CO2 at 415 ppm, and long-term durability in air. Quinones and their reduced forms are a promising family of such sorbents. However, the design of robust quinone sorbents has been limited, and no systematic study exists that unifies the relationship between reduction potential, binding free energy and the effect of CO2 concentration on the average number of CO2 molecules captured. Our work addresses this knowledge gap through a synergistic computational and experimental study of a family of electrochemically generated quinoid molecular sorbents for CO2 capture with tunable redox chemistries. Our findings indicate that while quinones with reduction potentials positive of oxygen reduction exist, the O-nucleophiles generated at these potentials are weak CO2 binders. Using microkinetic analysis to examine binding speciation, we identify sorbent candidates that bind one CO2 molecule within a narrow potential window positive of oxygen reduction. This behavior is calculated to occur at CO2 concentrations relevant to direct air capture. Additionally, while electron-rich quinones are found to generally bind two CO2 units per quinone dianion with little variation across CO2 concentrations relevant to carbon capture, weaker quinones generally exhibit lower stoichiometries and are more sensitive to CO2 concentration. Furthermore, we establish a linear correlation between the second reduction potential of a quinone and the free energy of binding CO2 to the quinone dianion. This correlation has important predictive power, as it allows new molecular materials of the quinoid family to be assessed with simple electrochemical measurements. However, based on our findings, such analyses must be punctuated by careful considerations of reaction stoichiometry and operating concentration ranges.
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Predictive energetic tuning of quinoid O-nucleophiles for the electrochemical capture of carbon dioxide
No full text
The need for robust, scalable methods for the capture and storage of carbon dioxide is increasingly pressing. Electric power-based carbon capture methods have drawn attention as a promising strategy due to their potential to couple to renewable energy sources. Materials for the capture of CO2 from air need to overcome the challenges of parasitic reactivity with oxygen, selective removal of CO2 at 415 ppm, and long-term durability in air. Quinones and their reduced forms are a promising family of such sorbents. However, the design of robust quinone sorbents has been limited, and no systematic study exists that unifies the relationship between reduction potential, binding free energy and the effect of CO2 concentration on the average number of CO2 molecules captured. Our work addresses this knowledge gap through a synergistic computational and experimental study of a family of electrochemically generated quinoid molecular sorbents for CO2 capture with tunable redox chemistries. Our findings indicate that while quinones with reduction potentials positive of oxygen reduction exist, the O-nucleophiles generated at these potentials are weak CO2 binders. Using microkinetic analysis to examine binding speciation, we identify sorbent candidates that bind one CO2 molecule within a narrow potential window positive of oxygen reduction. This behavior is calculated to occur at CO2 concentrations relevant to direct air capture. Additionally, while electron-rich quinones are found to generally bind two CO2 units per quinone dianion with little variation across CO2 concentrations relevant to carbon capture, weaker quinones generally exhibit lower stoichiometries and are more sensitive to CO2 concentration. Furthermore, we establish a linear correlation between the second reduction potential of a quinone and the free energy of binding CO2 to the quinone dianion. This correlation has important predictive power, as it allows new molecular materials of the quinoid family to be assessed with simple electrochemical measurements. However, based on our findings, such analyses must be punctuated by careful considerations of reaction stoichiometry and operating concentration ranges.
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Honey as a topical treatment for wounds (Review)
No full textBackgroundHoney is a viscous, supersaturated sugar solution derived from nectar gathered and modified by the honeybee, Apis mellifera. Honey has been used since ancient times as a remedy in wound care. Evidence from animal studies and some trials has suggested that honey may accelerate wound healing.ObjectivesThe objective of this review was to assess the effects of honey compared with alternative wound dressings and topical treatments on the of healing of acute (e.g. burns, lacerations) and/or chronic (e.g. venous ulcers) wounds.Search methodsFor this update of the review we searched the Cochrane Wounds Group Specialised Register (searched 15 October 2014); The Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2014, Issue 9); Ovid MEDLINE (1946 to October Week 1 2014); Ovid MEDLINE (In-Process & Other Non-Indexed Citations 13 October 2014); Ovid EMBASE (1974 to 13 October 2014); and EBSCO CINAHL (1982 to 15 October 2014).Selection criteriaRandomised and quasi-randomised trials that evaluated honey as a treatment for any sort of acute or chronic wound were sought. There was no restriction in terms of source, date of publication or language. Wound healing was the primary endpoint.Data collection and analysisData from eligible trials were extracted and summarised by one review author, using a data extraction sheet, and independently verified by a second review author. All data have been subsequently checked by two more authors.Main resultsWe identified 26 eligible trials (total of 3011 participants). Three trials evaluated the effects of honey in minor acute wounds, 11 trials evaluated honey in burns, 10 trials recruited people with different chronic wounds including two in people with venous leg ulcers, two trials in people with diabetic foot ulcers and single trials in infected post-operative wounds, pressure injuries, cutaneous Leishmaniasis and Fournier's gangrene. Two trials recruited a mixed population of people with acute and chronic wounds. The quality of the evidence varied between different comparisons and outcomes. We mainly downgraded the quality of evidence for risk of bias, imprecision and, in a few cases, inconsistency.There is high quality evidence (2 trials, n= 992) that honey dressings heal partial thickness burns more quickly than conventional dressings (WMD -4.68 days, 95% CI -5.09 to -4.28) but it is unclear if there is a difference in rates of adverse events (very low quality evidence) or infection (low quality evidence).There is very low quality evidence (4 trials, n= 332) that burns treated with honey heal more quickly than those treated with silver sulfadiazine (SSD) (WMD-5.12 days, 95% CI -9.51 to -0.73) and high quality evidence from 6 trials (n= 462) that there is no difference in overall risk of healing within 6 weeks for honey compared with SSD (RR 1.00, 95% CI 0.98 to 1.02) but a reduction in the overall risk of adverse events with honey relative to SSD.There is low quality evidence (1 trial, n= 50) that early excision and grafting heals partial and full thickness burns more quickly than honey followed by grafting as necessary (WMD 13.6 days, 95% CI 9.82 to 17.38). There is low quality evidence (2 trials, different comparators, n= 140) that honey heals amixed population of acute and chronic wounds more quickly than SSD or sugar dressings.Honey healed infected post-operative wounds more quickly than antiseptic washes followed by gauze and was associated with fewer adverse events (1 trial, n= 50, moderate quality evidence, RR of healing 1.69, 95% CI 1.10 to 2.61); healed pressure ulcers more quickly than saline soaks (1 trial, n= 40, very low quality evidence, RR 1.41, 95% CI 1.05 to 1.90), and healed Fournier's gangrene more quickly than Eusol soaks (1 trial, n= 30, very low quality evidence, WMD -8.00 days, 95% CI -6.08 to -9.92 days).The effects of honey relative to comparators are unclear for: venous leg ulcers (2 trials, n= 476, low quality evidence); minor acute wounds (3 trials, n= 213, very low quality evidence); diabetic foot ulcers (2 trials, n= 93, low quality evidence); Leishmaniasis (1 trial, n= 100, low quality evidence); mixed chronic wounds (2 trials, n= 150, low quality evidence).Authors' conclusionsIt is difficult to draw overall conclusions regarding the effects of honey as a topical treatment for wounds due to the heterogeneous nature of the patient populations and comparators studied and the mostly low quality of the evidence. The quality of the evidence was mainly downgraded for risk of bias and imprecision. Honey appears to heal partial thickness burns more quickly than conventional treatment (which included polyurethane film, paraffin gauze, soframycin-impregnated gauze, sterile linen and leaving the burns exposed) and infected post-operative wounds more quickly than antiseptics and gauze. Beyond these comparisons any evidence for differences in the effects of honey and comparators is of low or very low quality and does not form a robust basis for decision making
Estudio sobre la capacidad de absorción de nutrientes de cuatro genotipos de arroz (Oryza sativa L.) en función de concentraciones variables de mercurio total (HgT)
No full textEl arroz (Oryza sativa L.) es considerado uno de los principales cultivos de gran importancia en el mundo por ser el alimento básico en muchas culturas culinarias. En los últimos años ha presentado problemas de contaminación con Hg, al estar este metal en constante flujo: suelo-aire-agua, sobre todo en la región de La Mojana donde los suelos son contaminados por efecto de lavado y arrastre de las aguas provenientes de la ciénaga de Ayapel y la cuenca del rio San Jorge. El objetivo de esta investigación fue cuantificar las cantidades de HgT y nutrientes absorbidos por la planta en función de seis [Hg] en el suelo (86, 500, 1000, 2500, 5000, y 10000 μg Hg kg-1 de suelo) de cuatro variedades de arroz sembradas en dos texturas diferentes: ArL (F-2000 y F-473) y FArL (F-67 y F-68). El estudio fue hecho en materas con 18 kg con suelos de la región de La Mojana bajo condiciones controladas, se investigaron seis tratamientos con cuatro repeticiones las variedades F-2000 y F-473 y tres repeticiones las variedades F-67 y F-68. Los tratamientos se distribuyeron en un diseño de bloques completos al azar (1x2x6). Al final del ciclo se evaluó: HgT/planta, Hg en raíces y granos pilados y cantidad de nutriente absorbido por planta, en cada una de las variedades. Para la evaluación de medias se utilizó la prueba de Tukey al 5% de probabilidades, comparando el factor de interacción [Hg] en el suelo e interacción entre variedades. El ANAVA de HgT/planta presento diferencias estadísticas (p<0,01) en cada una de las variedades, sobre todo en los tratamientos (2500, 5000, y 10000 μg Hg kg-1 de suelo). La variedad F-473 con acumulación de 1190,4 μg de Hg kg-1 de biomasa seca tuvo mayor absorción de Hg que la variedad F-2000. Mientras que la variedad F-67 con 1332,8 μg de Hg kg-1 de biomasa seca logro acumular mayor Hg que F- 68. El ANAVA de Hg en raíces y granos pilados en la evaluación de F-2000 y F-473 presento diferencia (p<0,01) en raíz y grano con mayor acumulación en la raíz la variedad F-473 (1069,6 μg de Hg kg-1 de biomasa seca) y mayor acumulación en el grano la variedad F-2000 (29,5 μg de Hg kg-1 de biomasa seca); mientras que en la evaluación de F-67 y F-68 se presentaron diferencias estadísticas (p<0,01) en raíz y grano con mayor acumulación en la raíz la variedad F-67 (1133,0 μg de Hg kg-1 de biomasa seca) y mayor acumulación en el grano la variedad F-68 (41,1 μg de Hg kg-1 de biomasa seca), demostrándose así que las raíces actúan como barreras retenedoras de Hg hacia la parte aérea de la planta. Las variedades emplazadas en las dos texturas no presentaron diferencias en la toma de nutrientes, el K, Ca, B, Mn y Fe fueron los únicos absorbidos en cantidades suficientes. Los resultados determinaron que el Hg incide en la absorción de nutrientes afectando la nutrición de la planta negativamente.Rice (Oryza sativa L.) is considered one of the main crops of great importance in the world for being the staple food in many culinary cultures. In recent years, it has presented Hg contamination problems, as this metal is in constant flux: soil-air-water, especially in the La Mojana region where soils are contaminated by the effect of washing and entrainment of the water coming from the Ayapel swamp and the San Jorge river basin. The objective of this research was to quantify the amounts of HgT and nutrients absorbed by the plant as a function of six [Hg] in the soil (86, 500, 1000, 2500, 5000, and 10000 μg Hg kg-1 of soil) of four rice varieties planted in two different textures: ArL (F-2000 and F-473) and FArL (F-67 and F-68). The study was carried out in 18 kg pots with soils from the La Mojana region under controlled conditions, six treatments with four replications of varieties F-2000 and F-473 and three replications of varieties F-67 and F-68 were investigated. Treatments were distributed in a randomized complete block design (1x2x6). At the end of the cycle, we evaluated: HgT/plant, Hg in roots and stacked grains and amount of nutrient absorbed per plant, in each of the varieties. For the evaluation of means, the Tukey test was used at 5% probability, comparing the interaction factor [Hg] in the soil and interaction between varieties. The ANAVA of HgT/plant presented statistical differences (p<0.01) in each of the varieties, especially in the treatments (2500, 5000, and 10000 μg Hg kg-1 of soil). The F-473 variety with accumulation of 1190,4 µg of Hg kg-1 of dry biomass had higher absorption of Hg than the F-2000 variety. While the F-67 variety with 1332,8 µg of Hg kg-1 of dry biomass managed to accumulate greater Hg than F-68. The ANAVA of Hg in roots and stacks grains in the evaluation of F-2000 and F-473 showed difference (p<0.01) in root and grain with greater accumulation in the root variety F-473 (1069,6 µg of Hg kg-1 of dry biomass) and greater accumulation in the grain of the F-2000 variety (29,5 µg of Hg kg-1 of dry biomass); while in the evaluation of F-67 and F-68 there were statistical differences (p<0.01) in root and grain with greater accumulation in the root of the variety F-67 (1133,0 µg of Hg kg-1 of dry biomass) and greater accumulation in the grain of the variety F-68 (41,1 µg of Hg kg-1 of dry biomass), thus demonstrating that the roots act as retaining barriers of Hg towards the aerial part of the plant. The varieties located in the two textures did not show differences in the intake of nutrients, the K, Ca, B, Mn and Fe were the only ones absorbed in sufficient quantities. The results determined that Hg affects the absorption of nutrients, negatively affecting the nutrition of the plant1. INTRODUCCIÓN ................................................................................................... 202. MARCO TEÓRICO.................................................................................................. 232.1 LA PLANTA DE ARROZ ....................................................................................... 232.1.1 Origen .............................................................................................................. 232.1.2 Taxonomía ....................................................................................................... 242.1.3 Morfología de la planta ................................................................................. 242.1.4 Crecimiento y desarrollo ............................................................................... 252.1.5 Las fases de crecimiento de la planta de arroz ......................................... 262.1.6 Nutrición de la planta de arroz ..................................................................... 292.1.7 Requerimientos Edafo-climáticos ............................................................... 302.1.8 El cultivo de arroz .......................................................................................... 302.1.9. Importancia del cultivo de arroz ................................................................ 312.1.10 Suelos arroceros .......................................................................................... 312.1.11 Irrigación del cultivo del arroz ................................................................... 312.2 EL MERCURIO .................................................................................................... 322.2.1 Uso del mercurio en Colombia .................................................................... 332.2.2 Implicaciones del mercurio a la salud humana ........................................ 342.2.3 Mitigación del peligro del mercurio en el mundo ..................................... 342.2.4 Efectos del mercurio en las plantas ........................................................... 352.2.5 El mercurio en la planta de arroz ............................................................... 352.2.6 El mercurio en el suelo ................................................................................. 362.2.7 Dinámica del mercurio en el suelo ............................................................. 372.2.8 Transferencia suelo-planta del mercurio ................................................... 373. MATERIALES Y MÉTODOS .................................................................................. 393.1 LOCALIZACIÓN GEOGRÁFICA DEL PROYECTO ............................................. 393.2 MATERIAL GENÉTICO ........................................................................................ 393.3 CONDICIONES EDÁFICAS .................................................................................. 403.4 VARIABLES INDEPENDIENTES .......................................................................... 413.5 VARIABLES DEPENDIENTES .............................................................................. 423.6 DISEÑO EXPERIMENTAL ................................................................................... 423.7 PROCEDIMIENTO .............................................................................................. 433.7.1. Selección de suelo ....................................................................................... 433.7.2. Preparación del suelo .................................................................................. 443.7.3. Dosificación de mercurio en el suelo ........................................................ 443.7.4. Selección de semillas ................................................................................... 453.7.5. Siembra de las semillas ............................................................................... 453.7.6. Manejo agronómico del cultivo .................................................................. 453.7.7. Procesamiento de las muestras de cada órgano de la planta (raíces,
tallos, hojas, raquis y granos) ............................................................................... 473.7.8. Determinación de la biomasa ..................................................................... 483.7.9. Contenido de mercurio en cada órgano de la planta (raíces, tallos, hojas, raquis y granos) ........................................................................................................ 493.7.10. Contenido de mercurio en el suelo ........................................................... 503.7.11. Contenido de nutrientes en la planta ....................................................... 513.8 ANÁLISIS ESTADÍSTICO Y PROCESAMIENTO DE DATOS ............................... 514. RESULTADOS Y DISCUSIONES ............................................................................ 524.1 MERCURIO TOTAL EN LA PLANTA DE ARROZ ................................................ 524.1.1. Concentraciones de Hg acumulado en toda la planta de arroz de las variedades F-2000 y F-473 (textura Arcillo Limosa) en μg de Hg kg-1 de biomasa seca .................................................................................................................................... 544.1.2. Concentraciones de Hg acumulado en toda la planta de arroz de las variedades F-67 y F-68 (textura Franco Arcillo Limosa) en μg de Hg kg-1 de biomasa seca ............................................................................................................................ 574.2. CONCENTRACIÓN DE MERCURIO EN RAÍCES Y GRANOS PILADOS DE ACUERDO CON LAS VARIEDADES DE ARROZ Y TEXTURAS DE SUELO EN FUNCIÓN DE LAS SEIS CONCENTRACIONES DE Hg EN EL SUELO ........................................ 604.2.1. Concentraciones de Hg acumulado en las raíces y granos pilados de las variedades F-2000 y F-473 (textura Arcillo Limosa) en μg de Hg kg-1 de biomasa seca ............................................................................................................................ 654.2.2. Concentraciones de Hg acumulado en las raíces y granos pilados de las variedades F-67 y F-68 (textura Franco Arcillo Limosa) en μg de Hg kg-1 de biomasa seca ........................................................................................................................... 724.2.3. Concentraciones de Hg acumulado en las raíces y granos pilados de las plantas en μg de Hg kg-1 de biomasa seca en función a las texturas de suelo (Arcillo Limosa y Franco Arcillo Limosa) y seis concentraciones de Hg en el suelo ..................................................................................................................................... 774.3 CURVAS DE ABSORCIÓN DE NUTRIENTES ...................................................... 804.3.1 Absorción foliar de macronutrientes primarios (Nitrógeno, fosforo y potasio) de las variedades F-2000 y F-473 en función de las concentraciones de Hg variables en el suelo. ............................................................................................... 824.3.2 Absorción foliar de macronutrientes secundarios (Calcio, magnesio, Sodio y azufre) de las variedades F-2000 y F-473 en función de las concentraciones de Hg variables en el suelo ......................................................................................... 834.3.3 Absorción foliar de micronutrientes (Boro, zinc, cobre, hierro y manganeso) de las variedades F-2000 y F-473 en función de las concentraciones de Hg variables en el suelo ........................................................................................................ 854.3.4 Absorción foliar de macronutrientes primarios (Nitrógeno, fosforo y potasio) de las variedades F-67 y F-68 en función de las concentraciones de Hg variables en el suelo ........................................................................................................ 864.3.5 Absorción foliar de macronutrientes secundarios (Calcio, magnesio, Sodio y azufre) de las variedades F-67 y F-68 en función de las concentraciones de Hg variables en el suelo .................................................................................................. 884.3.6 Absorción foliar de micronutrientes (Boro, zinc, cobre, hierro y manganeso) de las variedades F-67 y F-68 en función de las concentraciones de Hg variables en el suelo ................................................................................................................ 894.3.7 Absorción foliar de macronutrientes primarios (Nitrógeno, fosforo y potasio) en función de las texturas de suelo y las concentraciones de Hg variables en el suelo ..................................................................................................................... 934.3.8 Absorción foliar de macronutrientes secundarios (Calcio, magnesio, Sodio y azufre) en función de las texturas de suelo y las concentraciones de Hg variables en el suelo ............................................................................................................... 944.3.9 Absorción foliar de micronutrientes (Boro, zinc, cobre, hierro y manganeso) en función de las texturas de suelo y las concentraciones de Hg variables en el suelo ......................................................................................................................... 965. CONCLUSIONES .................................................................................................. 986. RECOMENDACIONES .......................................................................................... 997. REFERENCIAS BIBLIOGRÁFICAS ....................................................................... 100PregradoIngeniero(a) Agronómico(a
Never be silent : publishing & imperialism in Kenya, 1884-1963
No full textSocial communications are central to any social struggle. There is a sizable body of literature from other countries on the use of oral medium, newspapers, books and other forms of communications being used as tools for organising against a powerful enemy, as a training ground for cadres and for clarifying and developing revolutionary theory, ideology, organisation and practice. All this ensures a greater unity among those resisting oppression and exploitation. Thus revolutionary and liberation forces of Bolsheviks in the Soviet Union, the Communist Party of China, and in Vietnam had developed theories and practices of revolutionary publishing as part of their revolutionary work. This has also been the case during anti-colonial and anti-imperialist struggles in Africa, but very little of this has been systematically documented as an aspect of revolutionary communications policy and practice. While the
colonial communications systems have been reasonably well documented, the resistance communication systems remain largely undocumented and ignored. This book is an initial attempt to document this dynamic communications process in Kenya with its external struggles against colonialism and its complex internal struggles with overlaying divisions of race and class, Kenyan and foreign peoples. The main theme emerging from this experience is that people struggling to change their society always find ways of establishing their own system of communicating with the people they lead
and by whom they are led. Their mission of revolution, of change, of peace, of social and economic justice requires that they should never be silent. This was well understood and practised by the liberation forces in Kenya. They
were never silent
A preliminary bibliography on focus
No full text[I]n its present form, the bibliography contains approximately 1100 entries. Bibliographical work is never complete, and the present one is still modest in a number of respects. It is not annotated, and it still contains a lot of mistakes and inconsistencies. It has nevertheless reached a stage which justifies considering the possibility of making it available to the public. The first step towards this is its pre-publication in the form of this working paper. […]
The bibliography is less complete for earlier years. For works before 1970, the bibliographies of Firbas and Golkova 1975 and Tyl 1970 may be consulted, which have not been included here
Coronal Heating as Determined by the Solar Flare Frequency Distribution Obtained by Aggregating Case Studies
No full textFlare frequency distributions represent a key approach to addressing one of
the largest problems in solar and stellar physics: determining the mechanism
that counter-intuitively heats coronae to temperatures that are orders of
magnitude hotter than the corresponding photospheres. It is widely accepted
that the magnetic field is responsible for the heating, but there are two
competing mechanisms that could explain it: nanoflares or Alfv\'en waves. To
date, neither can be directly observed. Nanoflares are, by definition,
extremely small, but their aggregate energy release could represent a
substantial heating mechanism, presuming they are sufficiently abundant. One
way to test this presumption is via the flare frequency distribution, which
describes how often flares of various energies occur. If the slope of the power
law fitting the flare frequency distribution is above a critical threshold,
as established in prior literature, then there should be a
sufficient abundance of nanoflares to explain coronal heating. We performed
600 case studies of solar flares, made possible by an unprecedented number
of data analysts via three semesters of an undergraduate physics laboratory
course. This allowed us to include two crucial, but nontrivial, analysis
methods: pre-flare baseline subtraction and computation of the flare energy,
which requires determining flare start and stop times. We aggregated the
results of these analyses into a statistical study to determine that . This is below the critical threshold, suggesting that Alfv\'en
waves are an important driver of coronal heating.Comment: 1,002 authors, 14 pages, 4 figures, 3 tables, published by The
Astrophysical Journal on 2023-05-09, volume 948, page 7
