Topological confinement in an antisymmetric potential in bilayer graphene in the presence of a magnetic field

We investigate the effect of an external magnetic field on the carrier states that are localized at a potential kink and a kink-antikink in bilayer graphene. These chiral states are localized at the interface between two potential regions with opposite signs.PACS numbers: 71.10.Pm, 73.21.-b, 81.05.Uw.     

Modification of a Nafion membrane by n-dodecyltrimethylammonium cation inclusion for potential application in DMFC

Changes in a protonated Nafion-112 membrane as a result of the incorporation of the cation n-dodecyltrimethylammonium (DTA⁺) by proton exchange mechanism are studied. Membrane surface modifications were analysed by AFM, XPS and contact angle measurements in order to obtain information about changes in the membrane surface roughness, chemical nature and hydrophobic character, while electrochemical impedance spectroscopy (EIS) and methanol permeation measurements were carried out to establish changes in the bulk membrane. The reduction obtained for the surface roughness and the hydrophobic character of Nafion-112/DTA⁺ equilibrated membrane as well as for the fluorine atomic concentration percentage and the increase in nitrogen percentage indicates modification of Nafion-112 membrane surface, while the increase of electrical resistance and the decrease of methanol permeability give information on bulk membrane changes. The higher thermal stability and lower water loss of the Nafion-112/DTA⁺ membrane are points of interest for applications such as PEMFC or DMFCs, respectively.     

The Cdc14 Phosphatase Controls Resolution of Recombination Intermediates and Crossover Formation during Meiosis

Meiotic defects derived from incorrect DNA repair during gametogenesis can lead to mutations, aneuploidies and infertility. The coordinated resolution of meiotic recombination intermediates is required for crossover formation, ultimately necessary for the accurate completion of both rounds of chromosome segregation. Numerous master kinases orchestrate the correct assembly and activity of the repair machinery. Although much less is known, the reversal of phosphorylation events in meiosis must also be key to coordinate the timing and functionality of repair enzymes. Cdc14 is a crucial phosphatase required for the dephosphorylation of multiple CDK1 targets in many eukaryotes. Mutations that inactivate this phosphatase lead to meiotic failure, but until now it was unknown if Cdc14 plays a direct role in meiotic recombination. Here, we show that the elimination of Cdc14 leads to severe defects in the processing and resolution of recombination intermediates, causing a drastic depletion in crossovers when other repair pathways are compromised. We also show that Cdc14 is required for the correct activity and localization of the Holliday Junction resolvase Yen1/GEN1. We reveal that Cdc14 regulates Yen1 activity from meiosis I onwards, and this function is essential for crossover resolution in the absence of other repair pathways. We also demonstrate that Cdc14 and Yen1 are required to safeguard sister chromatid segregation during the second meiotic division, a late action that is independent of the earlier role in crossover formation. Thus, this work uncovers previously undescribed functions of the evolutionary conserved Cdc14 phosphatase in the regulation of meiotic recombination.     

Nontoxic glasses: Preparation,structural, electrical and biological properties

Bacterial infections affect about 1 in 5 patients who receive a dental implant within 5 years of surgery. To avoid the implant rejection it is necessary for the development of innovative biomaterials, with addition or substitution of the ions, for implant coatings that promote a strong bond with the new host bone and antibacterial action. The objective of this work was to synthesize a bioactive glass with different silver concentrations to evaluate their antibacterial performance. The glasses were synthesized with up to 2% silver content by melt-quenching. Structural, morphological, biological, and electrical properties of all samples were studied. The biological behavior was evaluated through cytotoxicity tests and antibacterial activity. The structural analysis shows that the introduction of silver do not promote significant changes, not altering the advantageous properties of the bioglass of the bioglass. It was verified that the glasses with a silver content from 0.5% to 2%, completely prevented the growth of both Staphylococcus aureus and Escherichia coli while being nontoxic toward mammalian cells. Therefore, these bioglasses are promising materials to be used in the production of dental implants with antimicrobial activity.     

Prevalence of lameness and leg lesions of lactating dairy cows housed in southern Brazil: Effects of housing systems

Within the last few decades, the North American and European dairy industries have been collecting information about lameness and leg injury prevalence on dairy farms and have tried to develop solutions to mitigate these ailments. Few published articles report the prevalence of lameness and leg lesions in areas outside of those 2 regions, or how alternative housing systems, such as compost-bedded packs, affect the prevalence of these maladies. The objectives of this study were to compare the prevalence of lameness and leg lesions on confined dairies that used freestall, compost-bedded packs, or a combination of these 2 systems in Brazil. Data were collected in the autumn and winter of 2016 from 50 dairy farms located in Paraná state, including 12 compost-bedded pack dairies (CB), 23 freestall dairies (FS), and 15 freestall dairies that used compost-bedded packs for vulnerable cows (FS+C). A visit to the farm consisted of a management questionnaire, an inspection of the housing areas as well as the milking parlor, and an evaluation of all lactating cows as they exited the parlor for lameness (score 1–5), hygiene (score 0–2), body condition score (score 1–5), and hock and knee lesions (score 0–1). Median 1-way chi-squared test was used to compare production systems. We found no difference between farm types in management practices related to hoof health management or average daily milk production per cow [31 (29–33.9) kg/d; median (quartile 1–3)], percentage of Holstein cattle in the herd [100% (90–100%)], conception rate [35.8% (30.2–38%)], or pregnancy rate [15% (13.7–18%)]. The CB farms were smaller [85 (49.5–146.5) milking cows] than both the FS [270 (178–327.5) milking cows] and FS+C farms [360 (150–541.5) milking cows). The overall prevalence of severe lameness (score 4 and 5) across all farms was 21.2% (15.2–28.5%) but was lower on the CB farms [14.2% (8.45–15.5%)] in comparison to the FS [22.2% (16.8–26.7%)] and the FS+C farms [22.2% (17.4–32.8%)]. Less than 1% of all cows scored on CB farms were observed with swollen or wounded knees (or both), which was lower than either the FS or FS+C farms [7.4% (3.6–11.9%) and 6.4% (2.6–11.8%) of all cows scored, respectively]. The same pattern was found for hock lesions, where the farm-level prevalence within the 3 different housing types was 0.5% (0–0.9%), 9.9% (0.8–15.3%), and 5.7% (2.6–10.9%) for CB, FS, and FS+C farms, respectively. No differences between farm systems were observed for hygiene or body condition score. On average, 2.7% (0.8–10.9%) of lactating cows had a soiled side, 15.4% (2.1–37.4%) had dirty legs and 1.7% (0–9.3%) had dirty udders. The average herd-level body condition score across farms was 2.9 (2.9–3), with 0.86% of the all cows scored having a body condition score <2.5. These results indicate that lameness prevalence on confined dairies in Brazil is high and highlight the need for remedial changes in environmental design and management practices. We found that CB farms in this region had reduced lameness and lesions in relation to FS or FS+C dairies.     

Preparation and Characterization of Hydroxyapatite Coatings on Ti6Al4V Alloy by a Sol-Gel Method

Hydroxyapatite coatings on Ti6Al4V substrates were prepared by a sol–gel method, and characterized by X-ray diffraction, scanning electron microscopy, and infrared reflection spectroscopy. The coatings obtained at 500°C in air had a hydroxyapatite phase, some of which was carbonated hydroxyapatite, and had a dense and smooth morphology. When the coatings were treated in a simulated body fluid, the coatings had an increase in large hydroxyapatite grains, and a rough and porous morphology. The adhesive strength of the coatings was more than 14 MPa.     

Impedance spectroscopy studies of dual membrane fuel cell

This paper reports impedance studies of a dual membrane fuel cell - an innovative design based on the idea for a junction between an oxygen ion conducting cathode/electrolyte part and proton conducting anode/electrolyte part through a mixed oxygen ion and proton conducting porous membrane. Thus oxygen, hydrogen and water are located in three independent chambers. This concept allows avoiding all the severe pitfalls connected to the presence of water at electrodes in both SOFC and PCFC. The performed measurements of the 3 compartments and the data analysis are improved by introducing some specialized approaches and techniques, which are discussed. The impedance contribution in the proof of the new concept is also presented.     

A microstructural insight into the hygro-mechanical behaviour of a stabilised hypercompacted earth

The use of raw earth as construction material can save embodied and operational energy because of low processing costs and passive regulation of indoor ambient conditions. Raw earth must however be mechanically and/or chemically stabilised to enhance stiffness, strength and water durability. In this work, stiffness and strength are enhanced by compacting raw earth to very high pressures up to 100 MPa while water durability is improved by using alkaline solutions and silicon based admixtures. The effect of these stabilisation methods on hygro-mechanical behaviour is explored and interpreted in terms of the microstructural features of the material. Stiffness and strength are defined at different humidity levels by unconfined compression tests while the moisture buffering capacity is measured by humidification/desiccation cycles as prescribed by the norm ISO 24353 (Hygrothermal performance of building materials and products determination of moisture adsorption/desorption properties in response to humidity variation. International Organization for Standardization, Geneva, 2008). As for the microstructural characterisation, different tests (i.e. X-ray diffractometry, Infrared Spectroscopy, Mercury Intrusion Porosimetry, Nitrogen Adsorption) are performed to analyse the effect of stabilisation on material fabric and mineralogy. Results indicate that the use of alkaline activators and silicon based admixtures significantly improves water durability while preserving good mechanical and moisture buffering properties. Similarly, the compaction to very high pressures results in high levels of stiffness and strength, which are comparable to those of standard masonry bricks. This macroscopic behaviour is then linked to the microscopic observations to clarify the mechanisms through which stabilisation affects the properties of raw earth at different scales.