Electronic Structure and X-Ray Magnetic Circular Dichroism in (Zn, T)O (T = V, Fe, Co) Diluted Magnetic Semiconductors

The electronic structure of the (Zn, T)O (T = V, Fe, Co) diluted magnetic semiconductors is investigated theoretically from first principles, using the fully relativistic Dirac linear muffin-tin orbital band structure method. The X-ray absorption spectra, X-ray magnetic circular dichroism spectra at the Co, Fe, and V L2,3 edges are investigated theoretically. The origin of the dichroism spectra in such compounds is examined. Using the magnetic force theorem, as it is implemented within the multiple scattering theory, the exchange interaction parameters for the transition metal atoms are calculated.За допомогою зонної повністю релятивістської лінійної методи МТ-орбіталей теоретично досліджено з перших принципів електронні структури розбавлених магнетних напівпровідників (Zn, T)O (T = V, Fe, Co). Теоретично досліджено спектри поглинання Рентґенового випромінення і спектри Рентґенового магнетного циркулярного дихроїзму на L2,3-краях поглинання атомів Co, Fe та V. Вивчено природу спектрів дихроїзму в цих сполуках. За допомогою теореми про магнетні сили на основі теорії багатократного розсіяння було обчислено параметри обмінної взаємодії між атомами перехідних металів.Электронная структура разбавленных магнитных полупроводников (Zn, T)O (T = V, Fe, Co) исследована теоретически, исходя из первых принципов, полностью релятивистским линейным методом МТ-орбиталей. Теоретически исследованы рентгеновские спектры поглощения и спектры рентгеновского циркулярного дихроизма на L2,3-краях поглощения атомов Co, Fe и V. Изучена природа спектров дихроизма. С помощью теоремы о магнитных силах на основе теории многократного рассеяния вычислены параметры обменного взаимодействия между атомами переходных металлов

Elastic behavior of model membranes with antimicrobial peptides depends on lipid specificity and d-enantiomers

In an effort to provide new treatments for the global crisis of bacterial resistance to current antibiotics, we have used a rational approach to design several new antimicrobial peptides (AMPs). The present study focuses on 24-mer WLBU2 and its derivative, D8, with the amino acid sequence, RRWVRRVRRWVRRVVRVVRRWVRR. In D8, all of the valines are the Denantiomer. We use X-ray low- and wide-angle diffuse scattering data to measure elasticity and lipid chain order. We show a good correlation between in vitro bacterial killing efficiency and both bending and chain order behavior in bacterial lipid membrane mimics; our results suggest that AMP-triggered domain formation could be the mechanism of bacterial killing in both Grampositive and Gram-negative bacteria. In red blood cell lipid mimics, D8 stiffens and orders the membrane, while WLBU2 softens and disorders it, which correlate with D8’s harmless vs. WLBU2’s toxic behavior in hemolysis tests. These results suggest that elasticity and chain order behavior can be used to predict mechanisms of bactericidal action and toxicity of new AMPs.Fil: Kumagai, Akari. University of Carnegie Mellon; Estados UnidosFil: Dupuy, Fernando Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto Superior de Investigaciones Biológicas. Grupo de Investigación y Desarrollo del Noroeste Argentino | Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas. Grupo de Investigación y Desarrollo del Noroeste Argentino; ArgentinaFil: Arsov, Zoran. Jožef Stefan Institute; EsloveniaFil: Elhady, Yasmene. University of Carnegie Mellon; Estados UnidosFil: Moody, Diamond. University of Carnegie Mellon; Estados UnidosFil: Erns, Robert. University of Maryland; Estados UnidosFil: Deslouches, Berthony. University of Pittsburgh; Estados UnidosFil: Montelaro, Ronald. University of Pittsburgh; Estados UnidosFil: Di, Yuanpu Peter. University of Pittsburgh; Estados UnidosFil: Tristram-Nagle, Stephanie. University of Carnegie Mellon; Estados Unido

Integrated analysis of topography and gravity anomalies in analogue modelling: a model of relief evolution in the Iberian Peninsula

El análisis integrado de la topografía y las anomalías gravimétricas en la Península Ibérica invoca a la presencia de grandes pliegues que afectan a toda la litosfera como precursores de los relieves E-O a NE-SO que se distribuyen por el Macizo Varisco, así como a un mecanismo de engrosamiento cortical nucleado a partir de fallas Tardi-Variscas, como origen del relieve del este peninsular (Cadena Ibérica-Costero Catalana), con patrones dominantes E-O, NE-SO y NO-SE. El modo de deformación, así como el estilo, dependen tanto de las propiedades reológicas iniciales de una litosfera a otra (litosfera resistente Varisca hacia el oeste peninsular/litosfera débil y caliente resultado de la extensión Mesozoica hacia el este) como a los accidentes tectónicos pre-existentes. Presentamos una nueva metodología aplicada a la modelación análoga, basada en el estudio del espectro de las anomalías gravimétricas y la topografía que nos han permitido inferir los procesos responsables de la asimetría en el patrón del relieve intra-placa de la Península Ibérica. A su vez, nuestros resultados arrojan luz sobre los mecanismos generadores del relieve en zonas de intra-placa donde la escasez o falta de resolución de los perfiles sísmicos y geomagnéticos impide la interpretación de la parte más profunda de la litosfera como Asia Central o los Atlas del norte de África.The integrated analysis of topography and gravity anomalies carried out in the Iberian Peninsula invokes to the presence of large-scale folds affecting the entire lithosphere. Such folds are the precursors of E-W to NE-SO reliefs distributed along the Variscan Massif, meanwhile a mechanism of crustal thickening nucleated along Late-Variscan faults can influence the topographic pattern in the eastern part of Iberia (Iberian Range-Costero Catalan Ranges) characterised by E-W, NE-SW and NW-SE trends. The mechanism of deformation as well as the style depends on the initial rheological properties from one lithosphere to another (strong and cold Variscan lithosphere to the west and a relative weak and hot lithosphere affected by the Mesozoic extension to the east) and influenced by pre-existent faults. We present a new approach based on the spectral analyses of topography and gravity over the analogue modelling results that can help to infer the responsible mechanisms for the observed intra-plate relief asymmetry in Iberia. Our results enhance the study of other areas within plate interiors like Central Asia or the Atlas in northern Africa, where the lack of data or resolution from deep seismic profiles or geomagnetics may hamper the interpretation of the lithosphere in depth.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu

Pyrolysis of Eucalyptus grandis

Thesis (MScEng)--Stellenbosch University, 2013.ENGLISH ABSTRACT: In recent times, governments around the world have placed increasing focus on cleaner technologies and sustainable methods of power generation in an attempt to move away from fossil fuel derived power, which is deemed unsustainable and unfriendly to the environment. This trend has also been supported by the South African government, with clear intentions to diversify the country’s power generation by including, among others, biomass as a renewable resource for electricity generation. Woody biomass and associated forestry residues in particular, could potentially be used as such a renewable resource when considering the large amount of fast growing hardwood species cultivated in South Africa. Approximately 6.3 million ton of Eucalyptus grandis is sold annually for pulp production while a further 7 million ton of Eucalyptus species are sold as round wood. With these tree species reaching commercial maturity within 7 – 9 years in the South African climate, there is real potential in harnessing woody biomass as a renewable energy source. In this study, pyrolysis was investigated as a method to condense and upgrade E.grandis into energy and chemical rich products. The pyrolysis of E.grandis is the study of the thermal degradation of the biomass, in the absence of oxygen, to produce char and bio-oil. The thermal degradation behaviour of E.grandis was studied using thermo-gravimetric analysis (TGA) at the Karlsruhe Institute of Technology (KIT) in Germany and subsequently used to determine the isoconversional kinetic constants for E.grandis and its main lignocellulosic components. Slow, Vacuum and Fast Pyrolysis were investigated and optimised to maximise product yields and to identify the key process variables affecting product quality. The Fast Pyrolysis of E.grandis was investigated and compared on bench (KIT0.1 kg/h), laboratory (SU1 kg/h) and pilot plant scale (KIT10 kg/h), using Fast Pyrolysis reactors at Stellenbosch University (SU) in South Africa and at KIT in Germany. The Slow and Vacuum Pyrolysis of E.grandis was investigated and compared using a packed bed reactor at Stellenbosch University. The TGA revealed that biomass particle size had a negligible effect on the thermal degradation behaviour of E.grandis at a heating rate set point of 50 °C/min. It was also shown that increasing the furnace heating rates shifted the thermo-gravimetric (TG) and differential thermo-gravimetric (DTG) curves towards higher temperatures while also increasing the maximum rate of volatilisation. Lignin resulted in the largest specific char yield and also reacted across the widest temperature range of all the samples investigated. The average activation energies found for the samples investigated were 177.8, 141.0, 106.2 and 170.4 kJ/mol for holocellulose, alpha-cellulose, Klason lignin and raw E.grandis, respectively. Bio-oil yield was optimised at 76 wt. % (daf) for the SU1 kg/h Fast Pyrolysis plant using an average biomass particle size of 570 μm and a reactor temperature of 470 °C. Differences in the respective condensation chains of the various Fast Pyrolysis reactor configurations investigated resulted in higher gas and char yields for the KIT reactor configurations compared to the SU1 kg/h Fast Pyrolysis plant. Differences in the vapour residence time between Slow (>400 s) and Vacuum Pyrolysis (< 2 s) resulted in a higher liquid and lower char yield for Vacuum Pyrolysis. Local liquid yield maxima of 41.1 and 64.4 wt. % daf were found for Slow and Vacuum Pyrolysis, respectively (achieved at a reactor temperature of 450 °C and a heating rate of 17 °C/min). Even though char yields were favoured at low reactor temperatures (269 – 300 °C), the higher heating values of the char were favoured at high reactor temperatures (29 – 34 MJ/kg for 375 – 481 °C). Reactor temperature had the most significant effects on product yield and quality for the respective Slow and Vacuum Pyrolysis experimental runs. The bio-oils yielded for SP and VP were found to be rich in furfural and acetic acid.AFRIKAANSE OPSOMMING: Regerings regoor die wêreld het in die afgelope tyd toenemende fokus geplaas op skoner tegnologie en volhoubare metodes van kragopwekking in 'n poging om weg te beweeg van fossielbrandstof gebasseerde energie, wat geag word as nie volhoubaar nie en skadelik vir die omgewing. Hierdie tendens is ook ondersteun deur die Suid-Afrikaanse regering, met 'n duidelike bedoeling om die land se kragopwekking te diversifiseer deur, onder andere, biomassa as 'n hernubare bron vir die opwekking van elektrisiteit te gebruik. Houtagtige biomassa en verwante bosbou afval in die besonder, kan potensieel gebruik word as so 'n hernubare hulpbron, veral aangesien ‘n groot aantal vinnig groeiende hardehout spesies tans in Suid-Afrika verbou word. Ongeveer 6,3 miljoen ton Eucalyptus grandis word jaarliks verkoop vir pulp produksie, terwyl 'n verdere 7 miljoen ton van Eucalyptus spesies verkoop word as paal hout. Met hierdie boom spesies wat kommersiële volwassenheid bereik binne 7 - 9 jaar in die Suid-Afrikaanse klimaat, is daar werklike potensiaal vir die benutting van houtagtige biomassa as 'n hernubare energiebron. In hierdie studie is pirolise ondersoek as 'n metode om E.grandis te kondenseer en op te gradeer na energie en chemikalie ryke produkte. Die pirolise van E.grandis is die proses van termiese afbreking van die biomassa, in die afwesigheid van suurstof, om houtskool en bio-olie te produseer. Die termiese afbrekingsgedrag van E.grandis is bestudeer deur gebruik te maak van termo-gravimetriese analise (TGA) by die Karlsruhe Instituut van Tegnologie in Duitsland en daarna gebruik om die kinetiese konstantes vir die iso-omskakeling van E.grandis en sy hoof komponente te bepaal. Stadige, Vakuum en Snel pirolise is ondersoek en geoptimiseer om produk opbrengste te maksimeer en die sleutel proses veranderlikes wat die kwaliteit van die produk beïnvloed te identifiseer. Die Snel Pirolise van E.grandis is ondersoek en vergelyk op bank- (KIT0.1 kg / h), laboratorium- (SU1 kg / h) en proefaanlegskaal (KIT10 kg / h) deur gebruik te maak van Snel pirolise reaktore by die Universiteit van Stellenbosch (US) in Suid-Afrika en die Karlsruhe Instituut van Tegnologie (KIT) in Duitsland. Die Stadige en Vakuum Pirolise van E.grandis is ondersoek en vergelyk met behulp van 'n gepakte bed reaktor aan die Universiteit van Stellenbosch. Die TGA studie het openbaar dat biomassa deeltjiegrootte 'n onbeduidende uitwerking op die termiese afbrekingsgedrag van E.grandis het by 'n verhittings tempo van 50 ° C / min. Dit is ook bewys dat die verhoging van die oond verwarming tempo die termo-gravimetriese (TG) en differensiële termo-gravimetriese (DTG) kurwes na hoër temperature verskuif, terwyl dit ook die maksimum tempo van vervlugtiging laat toeneem het. Lignien het gelei tot die grootste spesifieke houtskool opbrengs en het ook oor die wydste temperatuur interval gereageer van al die monsters wat ondersoek is. Die gemiddelde aktiveringsenergieë vir die monsters wat ondersoek is, was 177,8, 141,0, 106,2 en 170,4 kJ / mol, onderskeidelik vir holosellulose, alpha-sellulose, Klason lignien en rou E.grandis. Bio-olie opbrengs is geoptimeer teen 76 wt. % (DAF) vir die SU1 kg / h Snel Pirolise aanleg met behulp van 'n gemiddelde biomassa deeltjiegrootte van 570 μm en 'n reaktor temperatuur van 470 ° C. Verskille in die onderskeie kondensasie kettings van die verskillende Snel Pirolise aanlegte wat ondersoek is, het gelei tot hoër gas- en houtskool opbrengste vir die KIT reaktor konfigurasies in vergelyking met die SU1kg/h FP plant. Verskille in die damp retensie tyd tussen Stadige (> 400 s) en Vakuum pirolise (<2 s) het gelei tot 'n hoër vloeistof en laer houtskool opbrengs vir Vakuum Pirolise. Plaaslike vloeistof opbrengs maksima van 41,1 en 64,4 wt. % (daf) is gevind vir Stadig en Vakuum pirolise onderskeidelik, bereik by 'n reaktor temperatuur van 450 ° C en 'n verhittingstempo van 17 ° C / min. Selfs al is houtskool opbrengste bevoordeel by lae reaktor temperature (269 - 300 ° C), is die hoër warmte waardes van die houtskool bevoordeel deur hoë reaktor temperature (29 - 34 MJ / kg vir 375 - 481 ° C). Reaktor temperatuur het die mees beduidende effek op die produk opbrengs en kwaliteit vir die onderskeie Stadige Pirolise en Vakuum Pirolise eksperimentele lopies gehad. Die bio-olies geproduseer tydens Stadige en Vakuum Pirolise was ryk aan furfuraal en asynsuur