Modelos y modelaje en la enseñanza de las ciencias : una experiencia de formación con profesores mexicanos en servicio

Después de un proceso de preparación, en talleres y discusión con expertos, un grupo de profesores llevó a cabo secuencias de aprendizaje utilizando modelos y modelaje en el aula, mismas que fueron videograbadas. Posteriormente tuvieron oportunidad de analizar, discutir y reflexionar sobre la manera en la que habían llevado a cabo las actividades y modificaron algunos aspectos de las secuencias propuestas. Estas secuencias, así como la narración de los profesores sobre el proceso de construcción se recopilaron en un libro que actualmente está en edición. Además, algunos fragmentos de los videos han sido colocados en una página web (www.modelosymodelajecientifico.com) para ser consultados de manera libre por todos aquellos interesados. Los profesores indican que el esfuerzo realizado se ve recompensado con el entusiasmo de los estudiantes y el desarrollo obtenido

Modelos y modelaje en la enseñanza de las ciencias : una experiencia de formación con profesores mexicanos en servicio

Después de un proceso de preparación, en talleres y discusión con expertos, un grupo de profesores llevó a cabo secuencias de aprendizaje utilizando modelos y modelaje en el aula, mismas que fueron videograbadas. Posteriormente tuvieron oportunidad de analizar, discutir y reflexionar sobre la manera en la que habían llevado a cabo las actividades y modificaron algunos aspectos de las secuencias propuestas. Estas secuencias, así como la narración de los profesores sobre el proceso de construcción se recopilaron en un libro que actualmente está en edición. Además, algunos fragmentos de los videos han sido colocados en una página web (www. modelosymodelajecientifico. com) para ser consultados de manera libre por todos aquellos interesados. Los profesores indican que el esfuerzo realizado se ve recompensado con el entusiasmo de los estudiantes y el desarrollo obtenido

D-brane Instantons as Gauge Instantons in Orientifolds of Chiral Quiver Theories

Systems of D3-branes at orientifold singularities can receive non-perturbative D-brane instanton corrections, inducing field theory operators in the 4d effective theory. In certain non-chiral examples, these systems have been realized as the infrared endpoint of a Seiberg duality cascade, in which the D-brane instanton effects arise from strong gauge theory dynamics. We present the first UV duality cascade completion of chiral D3-brane theories, in which the D-brane instantons arise from gauge theory dynamics. Chiral examples are interesting because the instanton fermion zero mode sector is topologically protected, and therefore lead to more robust setups. As an application of our results, we provide a UV completion of certain D-brane orientifold systems recently claimed to produce conformal field theories with conformal invariance broken only by D-brane instantons.Comment: 50 pages, 32 figures. v2: version published in JHEP with references adde

Insights into the Carbon chemistry of Mon R2

Aiming to learn about the chemistry of the dense PDR around the ultracompact (UC) HII region in Mon R2, we have observed a series of mm-wavelength transitions of C3H2 and C2H. In addition, we have traced the distribution of other molecules, such as H13CO+, SiO, HCO, and HC3N. These data, together with the reactive ions recently detected, have been considered to determine the physical conditions and to model the PDR chemistry. We then identified two kind of molecules. The first group, formed by the reactive ions (CO+, HOC+) and small hydrocarbons (C2H, C3H2), traces the surface layers of the PDR and is presumably exposed to a high UV field (hence we called it as "high UV", or HUV). HUV species is expected to dominate for visual absorptions 2 < Av < 5 mag. A second group (less exposed to the UV field, and hence called "low UV", or LUV) includes HCO and SiO, and is mainly present at the edges of the PDR (Av > 5 mag). While the abundances of the HUV molecules can be explained by gas phase models, this is not the case for the studied LUV ones. Although some efficient gas-phase reactions might be lacking, grain chemistry sounds like a probable mechanism able to explain the observed enhancement of HCO and SiO. Within this scenario, the interaction of UV photons with grains produces an important effect on the molecular gas chemistry and constitutes the first evidence of an ionization front created by the UC HII region carving its host molecular cloud. The physical conditions and kinematics of the gas layer which surrounds the UC HII region were derived from the HUV molecules. Molecular hydrogen densities > 4 10^6 cm^(-3) are required to reproduce the observations. Such high densities suggest that the HII region could be pressure-confined by the surrounding high density molecular gas.Comment: 32 pages, 8 figures. Accepted by Astrophysical Journa

Anomalies and O-plane charges in orientifolded brane tilings

We investigate orientifold of brane tilings. We clarify how the cancellations of gauge anomaly and Witten's anomaly are guaranteed by the conservation of the D5-brane charge. We also discuss the relation between brane tilings and the dual Calabi-Yau cones realized as the moduli spaces of gauge theories. Two types of flavor D5-branes in brane tilings and corresponding superpotentials of fundamental quark fields are proposed, and it is shown that the massless loci of these quarks in the moduli space correctly reproduce the worldvolume of flavor D7-branes in the Calabi-Yau cone dual to the fivebrane system.Comment: 46 pages, 19 figure

Enterprise development through networks:a case study of PETRECOZIM and the beverages sector networks in Zimbabwe

Inter-organisational networks contribute towards attainment of a Circular Economy (CE). Through effective collaboration, enterprise development can be achieved. In Zimbabwe, plastic waste, mainly PET is a major challenge in the quest for attaining sustainable development of the country. This research focuses on the role of collaboration between bottlers, manufacturers and brand owners in facilitating enterprise development in the context of waste recycling. A case study research design was undertaken of a PET Recycling Company commonly known as PETRECOZIM, which is located on the southern part of Harare, the capital city of Zimbabwe. Interviews were undertaken with key informants and experts in the field of waste management. Document review was carried out on key documentation from the recycling centre in order to assess activities, business models, barriers, challenges, opportunities and core aspects of the operations of PETRECOZIM. The research concludes that organisations can collaborate as private sector players in a particular economic sector such as beverages, manufacturing and brand owners; to form enterprises that can thrive and undertake recycling activities. The research concludes that networks can facilitate enterprise development and self-regulation. It can also be concluded that in certain contexts, networks can operate without external interference and yield significant benefits in circular economy thematic areas such as waste management. The research also concludes that the business model of recycling networks requires blended financing models beyond network partners of one sector, to ensure sustainability. Key barriers identified include lack of participation in the network by organisations which operate in the bottling sector, but are not part of the PETRECOZIM initiative. These firms also lack technical capacity for advanced PET recycling as well as lack of financing to complete recycling stages beyond bales and flakes. The research also concludes that in order to attain circularity and “close the loop”, PETRECOZIM should recycle the waste further into usable products. The Case study also concludes that, without the support of the network members who finance the enterprise PETRECOZIM, its survival is not guaranteed beyond the network. It is recommended that, networks develop models which are sustainable beyond network support, in order to ensure long-term viability

Development and characterization of bioactive alginate microcapsules with cedarwood essential oil

In this work, sodium alginate microcapsules containing cedarwood essential oil (CWO) for uses in anti-acne tonic were prepared by ionic gelification of alginate with calcium chloride (CaCl2) and subsequent addition of glutaraldehyde to improve the crosslinking degree. Alginate microcapsules with cedarwood essential oil were obtained in an encapsulator with a 600 &#956;m nozzle using different alginate concentrations (1, 3 and 4% w/v) , and different compositions of the coagulation solution with CaCl2 concentrations of 0.1, 0.25 and 0.5 M, and addition of glutaraldehyde at two concentrations: 12.5% and 50% (0.1 g L&#8722;1 and 10 g L&#8722;1, respectively). The effect of alginate concentration was followed by viscosimetry and the influence of the CaCl2 concentration and presence of glutaraldehyde on the microcapsules' shape as well as the total content on encapsulated cedarwood essential oil were evaluated by means of stereoscopic magnifying glass, scanning electron microscopy (SEM) and UV vis spectrophotometry. Results show that proper shape formation is obtained for an alginate concentration of 3% w/v. With regard to the total encapsulated cedarwood oil, as the CaCl2 concentration in the gelifying-coagulating solution increases the efficiency of the encapsulated oil. Best results in terms of micro-bead shape and total amount of encapsulated oil were obtained for a CaCl2 concentration of 0.5 M without glutaraldehyde with a maximum encapsulation of 177.2 mg per gram of microcapsule.Ferrandiz, M.; Lopez, A.; Franco, E.; Garcia-Garcia, D.; Fenollar, D.; Balart, R. (2017). Development and characterization of bioactive alginate microcapsules with cedarwood essential oil. Flavour and Fragrance Journal. 32(3):184-190. doi:10.1002/ffj.3373S18419032

Financing and Business Models for Scaling Up Sustainable Business Networks—Building a Circular Economy

Transition towards a circular economy (CE) requires collaboration amongst stakeholders. Sustainable Business Networks bring together different organisations to learn and disseminate CE innovations. However, without proper financing models, networks struggle to survive and attain financial independence. In this paper, we explore the different models which are used by African networks to finance their activities. The methodological approach involved nine case studies from three African countries (Zimbabwe, Kenya and South Africa) and selected regional networks. Semi-structured interviews were undertaken with key informants of the networks, and a questionnaire was sent to each network. Content analysis of networks was undertaken, and documents were assessed for each network in order to evaluate network activities under different funding regimes. The main funding models that were observed include membership subscriptions, donor funding, conference fees for network events, consultancy services, crowdfunding and selling knowledge products. The challenge of low payments of subscriptions is common in all countries, and networks devised innovative ways of generating funds such as consultancy fees for services rendered by the network. We conclude that there is still a high level of involvement of donor agencies in financing Sustainable Business Networks. However, this donor-funded approach is failing to steer networks to sustainability beyond projects and programmes which involve networking. Based on the existing literature and the information collected during the interviews, it was possible to recommend a hybrid financing model that is based in two crucial elements, (i) on country specific actors and (ii) on ownership of the network at national level