Free Rota-Baxter algebras and rooted trees

A Rota-Baxter algebra, also known as a Baxter algebra, is an algebra with a linear operator satisfying a relation, called the Rota-Baxter relation, that generalizes the integration by parts formula. Most of the studies on Rota-Baxter algebras have been for commutative algebras. Two constructions of free commutative Rota-Baxter algebras were obtained by Rota and Cartier in the 1970s and a third one by Keigher and one of the authors in the 1990s in terms of mixable shuffles. Recently, noncommutative Rota-Baxter algebras have appeared both in physics in connection with the work of Connes and Kreimer on renormalization in perturbative quantum field theory, and in mathematics related to the work of Loday and Ronco on dendriform dialgebras and trialgebras. This paper uses rooted trees and forests to give explicit constructions of free noncommutative Rota--Baxter algebras on modules and sets. This highlights the combinatorial nature of Rota--Baxter algebras and facilitates their further study. As an application, we obtain the unitarization of Rota-Baxter algebras.Comment: 23 page

Red mud-based geopolymers with tailored alkali diffusion properties and pH buffering ability

This study develop novel porous red mud (RM) based geopolymers and evaluates their potential to ensure prolonged pH control. Several properties of the novel geopolymers were examined including buffering ability, alkalis leaching behaviour, mineralogical composition, microstructure and physical properties. Two experimental plans were defined to evaluate the influence of porosity and RM content on those properties. The pH values of the eluted water and geopolymers OH ions leaching have been determined over time showing that total OH ions and the leaching rate can be tailored by controlling the geopolymers porous structure and the availability of free alkaline species. The lower pH gradient over 28th d (1.64 pH units) was achieved by combining a 0.025 wt% pore forming agent (aluminium powder) with 45 wt% MK replacement by red mud. A high and prolonged buffer capacity was accomplished, proving that red mud-based geopolymers have potential to be applied as pH buffering material.This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement.info:eu-repo/semantics/publishedVersio

Emissão de CO2 em culturas de soja e arroz irrigado - Safra 2013/2014 - RS.

Made available in DSpace on 2018-02-27T00:40:59Z (GMT). No. of bitstreams: 1 WalkyriaBuenoRevistaBrasileiradeGeografiaFisica.pdf: 1411172 bytes, checksum: f06657b43682994138269dc613913642 (MD5) Previous issue date: 2018-02-26bitstream/item/173132/1/Walkyria-Bueno-Revista-Brasileira-de-Geografia-Fisica.pd

Imaginary Phases in Two-Level Model with Spontaneous Decay

We study a two-level model coupled to the electromagnetic vacuum and to an external classic electric field with fixed frequency. The amplitude of the external electric field is supposed to vary very slow in time. Garrison and Wright [{\it Phys. Lett.} {\bf A128} (1988) 177] used the non-hermitian Hamiltonian approach to study the adiabatic limit of this model and obtained that the probability of this two-level system to be in its upper level has an imaginary geometric phase. Using the master equation for describing the time evolution of the two-level system we obtain that the imaginary phase due to dissipative effects is time dependent, in opposition to Garrison and Wright result. The present results show that the non-hermitian hamiltonian method should not be used to discuss the nature of the imaginary phases in open systems.Comment: 11 pages, new version, to appear in J. Phys.

One-part geopolymers versus Ordinary Portland Cement (OPC) mortars : durability assessment

Investigations on the field of geopolymeric binders, state that this new material is likely to have high potential to become an alternative to Ordinary Portland cement (OPC). Recent results on the Life Cycle Analysis (LCA) of geopolymers they have a lower impact on global warming than OPC but on the other side they have a higher environmental impact regarding other impact categories. Lower CO2 emissions geopolymers are therefore needed. Classical two part geopolymers could be made more eco-efficient with a lower carbon dioxide footprint if the use of sodium silicate is avoided. Besides current geopolymeric mixes can suffer from efflorescence originated by the fact that alkaline and/or soluble silicates that are added during processing cannot be totally consumed during geopolymerisation. Therefore new and improved geopolymer mixes are needed. One-part geopolymers (sodium silicate free) were described by the first time in 2008 still a lot of issues remain unexplained about them. This paper compares the durability performance of one-part geopolymers with OPC mortars. The obtained results revealed that replacing 70% Portland cement by 58.3% Fly ash, 4% calcined stuff and 7.7% calcium hydroxide results in satisfactory and promising results in durability tests

New order parameters in the Potts model on a Cayley tree

For the $q-$state Potts model new order parameters projecting on a group of spins instead of a single spin are introduced. On a Cayley tree this allows the physical interpretation of the Potts model at noninteger values q of the number of states. The model can be solved recursively. This recursion exhibits chaotic behaviour changing qualitatively at critical values of $q_0$ . Using an additional order parameter belonging to a group of zero extrapolated size the additional ordering is related to a percolation problem. This percolation distinguishes different phases and explains the critical indices of percolation class occuring at the Peierls temperature.Comment: 16 pages TeX, 5 figures PostScrip

Ocorrência de insetos predadores de pulgões em cultivo orgânico de couve em sistema solteiro e consorciado com adubos verdes.

bitstream/CNPAB-2010/34509/1/cot101.pdfParceria: UFRR

Evaluación de la disponibilidad de N en suelo en pastos biodiversos ricos en leguminosas mediante el cultivo de plantas nitrófilas dentro de la dehesa

Biodiverse legume-rich pastures (BLRP) have been recommended for extensive animal production since they can improve productivity and pasture quality. However, the consequences for the N balance within the agro-system, due to the increase in biological N 2 fixation, must be monitored. A field trial was carried out to evaluate the soil N availability in a BLRP in comparison with an adjacent unsown pasture. The field experiment consisted of growing tufts of nitrophilic species (turnip, Brassica campestris and rye, Secale cereale) in the pastures rounded by PVC rings. Soil inorganic-N levels were monitored during a period of one year. The potentially available soil N was determined by growing ryegrass (Lolium multiflorum) in a pot experiment and carrying out several chemical extraction methods. The mean values of N recovered by field-grown turnip and rye were, respectively, 30.6 and 31.1 kg ha–1 in BLRP, not statistically higher than that recovered in the unsown pasture. This is consistent with the very low levels of soil inorganic-N observed both in BLRP and the unsown pasture. Nitrogen recovered by ryegrass grown in pots was significantly higher in the soil collected from the BLRP than in soil from the unsown pasture. In this study, plant-available inorganic-N appeared as a strong limiting factor for the growth of the non-legume component. The BLRP seems to be currently environmentally sound, since the risk of N loss is practically non-existent. However, the potentially mineralisable organic N is increasing, which requires a further monitoring of the soil N dynamic as the pasture ages.Los pastos biodiversos ricos en leguminosas (PBRL) están siendo recomendados para la ganadería extensiva, ya que pueden mejorar la calidad de los pastos. Sin embargo, las implicaciones en el balance de nitrógeno (N) en suelo, debido a la fijación biológica de N, deben ser monitorizadas. Este estudio se estableció para evaluar la disponibilidad de N en suelo en PBRL en comparación con pastizales naturales. El ensayo consistió en el establecimiento de especies nitrófilas (nabo y centeno) en matas rodeadas por anillos de PVC. Durante un año se monitorizaron también los niveles de N mineral en suelo. El N potencialmente disponible se determinó mediante el cultivo de raigrás en macetas y mediante varios análisis químicos de laboratorio. En los PBRL los valores medios de N recuperado por el nabo y el centeno fueron 30,6 y 31,1 kg ha –1, respectivamente, no existiendo diferencias significativas con los valores registrados en los pastos naturales. Durante todo el año se registraron niveles bajos de N inorgánico en suelo. El N recuperado por el raigrás fue significativamente más elevado en los PBRL que en el pasto natural. Los resultados mostraron que el N fue un factor ecológico muy limitante para el crecimiento de las especies no leguminosas. Por otro lado, en los PBRL el riesgo de pérdida de N para el medio ambiente fue prácticamente nulo. Sin embargo, el N orgánico potencialmente mineralizable aumenta en el suelo, lo cual justificaría la necesidad de realizar nuevos análisis de dinámica del N en el suelo en un futuro