Right triangles with algebraic sides and elliptic curves over number fields

Given any positive integer n, we prove the existence of infinitely many right triangles with area n and side lengths in certain number fields. This generalizes the famous congruent number problem. The proof allows the explicit construction of these triangles; for this purpose we find for any positive integer n an explicit cubic number field Q(\lambda) (depending on n) and an explicit point P_\lambda of infinite order in the Mordell-Weil group of the elliptic curve Y^2=X^3-n^2*X over Q(\lambda).Comment: To appear in Math. Slovac

Tile Based Self-Assembly of the Rook\u27s Graph

The properties of DNA make it a useful tool for designing self-assembling nanostructures. Branched junction molecules provide the molecular building blocks for creating target complexes. We model the underlying structure of a DNA complex with a graph and we use tools from linear algebra to optimize the self-assembling process. Some standard classes of graphs have been studied in the context of DNA self-assembly, but there are many open questions about other families of graphs. In this work, we study the rook\u27s graph and its related design strategies

The incidence of graft on developing-country firms

This paper measures the extent to which firms in developing countries are the target of bribes. Using new firm-level survey data from 33 African and Latin American countries, we first show that perceptions adjust slowly tofirms'experience with corrupt officials and hence are an imperfect proxy for the true incidence of graft. We then construct an experience-based index that reflects the probability that a firm will be asked for a bribe in order to complete a specified set of business transactions. On average, African firms are three times as likely to be asked for bribes as are firms in Latin America, although there is substantial variation within each region. Last, we show that graft appears to be more prevalent in countries with excessive regulation and where democracy is weak. In particular, our results suggest that the incidence of graft in Africa would fall by approximately 85 percent if countries in the region had levels of democracy and regulation similar to those that exist in Latin America.Public Sector Corruption&Anticorruption Measures,Corruption&Anitcorruption Law,Crime and Society,E-Business,Access to Finance

Salt Tolerance of Lactococcus lactis R-604 as Influenced by Exposure to Various Stress Conditions

Lactococcus lactis is a dairy culture bacterium widely used in dairy products that contain salt (NaCl) such as cheese and salted butter. Osmotic conditions generally hinder the growth of both pathogen and desirable bacteria. It has been observed that many stress-induced proteins are produced after exposure to an environmental stress protecting the cell against other stresses since the first exposure starts the defense mechanisms of the cells creating an effect of cross-protection. If salt tolerance is enhanced in desirable bacteria they would survive better in salty environments. The objective of this study was to evaluate the salt tolerance of Lactococcus lactis R-604 after exposure of various stress conditions. The culture was subjected to 10% v/v ethanol for 30 minutes, 15 mM of hydrogen peroxide for 30 minutes, mild heat at 52°C for 30 minutes and UV light (245 nm) for 5 minutes. The culture was also subjected to starvation (no lactose in M17 broth) for 24 hours or prior osmotic adaption (3% w/v NaCl in M17 broth) for 24 h aerobically at 30°C. A control was run without any stress under the same conditions of each experiment. An initial concentration of 7 log CFU’s/mL was used for all treatments. Growth was determined under 5 concentrations of NaCl (0, 1, 3, 5 and 7% w/v). Plating was done every 24 h for 5 days in M17 agar with 0.5% w/v of lactose and incubated aerobically at 30°C for 48 hours. Salt tolerance was enhanced after mild heat or ethanol exposure at 5% w/v NaCl on days 3, 4 and 5. Salt tolerance was also enhance after hydrogen peroxide stress at 5% w/v NaCl on days 4 and 5 and after 24 hours of lactose starvation at 3% w/v on day 3. L. lactis R-604 was not negatively affected by any of the stress conditions applied at salt concentrations of 0, 1 and 3% w/v NaCl. The culture was able to grow in 3% NaCl or no lactose after 24 hours and these stress conditions did not affect its salt tolerance. Growth was maintained at 7% w/v NaCl regardless the stress conditions, however combination of ethanol or hydrogen peroxide at 7% w/v NaCl reduced growth of L. lactis R-604

Fears and catastrophic thoughts in medically complicated pregnancies

In our experience "High-risk" diagnosis stigmatizes the patient, compromises her self-esteem, fears come up, and often modifies her expectations of a successful pregnancy in a catastrophizing, unrealistic way. Thinking about the worst possible outcomes would facilitate adaptation to hostile environments, while optimistic thinking increases the risk of not reacting in time, but although this could explains why it could be possible to react with catastrophic thoughts to ambiguous situations, it still remains open the question about why some people have more frequent and harmful catastrophic thoughts leading to psychological distress and making it very difficult to cope with the unexpected pregnancy situationUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The Role of Water Solubility and Diffusion Coefficient in Air of Chlorine Dioxide Gas during Surface Decontamination and Compatibility of Selected Plastics and Elastomers

Food safety is a concern for all individuals involved in the food supply chain. Besides controlling the food product itself to improve safety, washing and sanitizing surfaces and equipment are critical. Chlorine dioxide (ClO2) is a green-yellow gas, known as a strong antimicrobial agent against multiple pathogenic microorganisms and effective on biofilms. Plastics such as polypropylene (PP), polyester (PET), cast nylon, ultra-high-molecular-weight polyethylene (UHMWPE), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) and white Acetal; and elastomers like nitrile rubber (Buna-N), ethylene propylene diene monomer (EPDM), and fluoroelastomer (FKM) are widely used in food processing surfaces and equipment. However, few studies have been conducted to address the depletion of gas by materials that might be present during the decontamination procedure nor the change in mechanical properties of plastics and elastomers. The objective of this study was to develop a model to simulate ClO2 transport into stainless steel crevices during surface decontamination. Also, to determine the resistance to ClO2 gas for selected materials. The gas was circulated inside a closed chamber with three different volumes of deionized water (20, 40, and 60 mL), and 0 mL (control). The gas decay was monitored and recorded until the concentration dropped below the detection limit. A physics-based simulation model was developed using COMSOL and validated by previously reported results in the literature, and the data obtained at the first stage of this experiment. A mathematical model was proposed for analyzing the time needed for ClO2 gas to reach the bottom at any possible crevice during equipment surface decontamination, which is depth-dependent. Additionally, selected material were exposed to 3000 ppm [parts per million] for 7 days inside a chamber following ASTM International Standards. This investigation showed an increase in the reaction rate due to water presence at different water volume and exposure surface area. After 7 days’ exposure at 3000 ppm of ClO2 gas, none of the plastics nor elastomers selected showed a significance difference (p\u3c0.05) in the hardness value. This can help the food processing industry in constructing an effective system and establishing optimum sanitizing treatment conditions

Human Frataxin Folds Via an Intermediate State. Role of the C-Terminal Region

The aim of this study is to investigate the folding reaction of human frataxin, whose deficiency causes the neurodegenerative disease Friedreich’s Ataxia (FRDA). The characterization of different conformational states would provide knowledge about how frataxin can be stabilized without altering its functionality. Wild-type human frataxin and a set of mutants, including two highly destabilized FRDA-associated variants were studied by urea-induced folding/unfolding in a rapid mixing device and followed by circular dichroism. The analysis clearly indicates the existence of an intermediate state (I) in the folding route with significant secondary structure content but relatively low compactness, compared with the native ensemble. However, at high NaCl concentrations I-state gains substantial compaction, and the unfolding barrier is strongly affected, revealing the importance of electrostatics in the folding mechanism. The role of the C-terminal region (CTR), the key determinant of frataxin stability, was also studied. Simulations consistently with experiments revealed that this stretch is essentially unstructured, in the most compact transition state ensemble (TSE2). The complete truncation of the CTR drastically destabilizes the native state without altering TSE2. Results presented here shed light on the folding mechanism of frataxin, opening the possibility of mutating it to generate hyperstable variants without altering their folding kinetics.Fil: Faraj, Santiago Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; ArgentinaFil: Gonzalez-Lebrero, Rodolfo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; ArgentinaFil: Roman, Ernesto Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; ArgentinaFil: Santos, Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; Argentin

The Discovery of New Export Products in Ecuador

This paper examines export diversification in Ecuador in the cases of fresh cut flowers, canned tuna, palm heart, broccoli and mangoes, using the theoretical framework on “pioneers” and “discoveries” developed by Hausmann and Rodrik(2003), as well as work by Sánchez and Butler (2006) on export costs and related uncertainties. It is found that the discoveries were mainly of traditional competitive advantage, with various degrees of technology adoption. The following policy implications are derived: i) innovative mechanisms to share the costs of new discoveries must be found and intellectual property rights strengthened; ii) cooperation among industry experts needs to improve; iii) deeper collective action to promote public-private partnerships should be undertaken; iv) relevant information and knowledge should be made available to all interested parties; and v) a national-level agenda should be undertaken to increase private investment in promising sectors while promoting the creation of public goods and minimizing rent-seeking behavior.Export diversification, Ecuador

Effect of sulfur and nitrogen dioxides on the performance of a proton exchange membrane fuel cell

There is presently much interest in the clean and efficient generation of energy by proton exchange membrane fuel cells (PEMFC), using hydrogen as fuel. The generation of hydrogen by the reforming of other fuels, anaerobic fermentation of residual waters and other methods, often produce contaminants that affect the performance of the cell. In this work, the effect of gaseous SO2 and NO2 on the performance of a H2/O2 single PEMFC is studied. The results show that SO2 decreases irreversibly the performance of the cell under operating conditions, while NO2 has a milder effect that allows the recovery of the system.FAPESPCNP