Fungal interactions and control of aflatoxins in maize, pre-and post-harvest under different climate change scenarios.

Aspergillus flavus is a ubiquitous fungus that contaminates maize, the main risk from infection is the production of the carcinogenic mycotoxin aflatoxin B₁ (AFB₁). One strategy to control A. flavus contamination is the use of biocontrol agents (BCAs). The aim of this project was to examine the fungal diversity of Mexican maize cultivars and isolate potential BCAs which could control AFB₁ contamination of maize under existing and future climate change scenarios. The four Mexican maize cultivars had low moisture content, below that which would cause any mould spoilage. A. flavus and other associated mycobiota were enumerated, isolated and identified. Eight candidate BCAs were screened for potential antagonism and dominance of toxigenic strains of A. flavus including a type strain. This showed that the Index of Dominance of the BCAs vs A. flavus was influenced by strain and water activity (aw). On maize-based media, at 50:50 inoculum ratios four potential BCAs, an atoxigenic Afl- MEX02, T. atroviride MEX03, T. funiculosus MEX05 and C. rosea 016 were effective in reducing AFB₁ production. The atoxigenic Afl- MEX02 A. flavus strain decreased AFB₁ production by >95% by the toxigenic strain. These BCAs were then tested in more detail with different inoculum ratios including the atoxigenic A. flavus strain. The 50:50 ratios were used to analyse the expression of two key genes of the aflatoxin biosynthetic pathway, aflR (regulatory) and aflD (structural). For type strain of A. flavus (NRRL 3357) aflD relative gene expression was stimulated by the BCAs at 0.98 and 0.93 aw. The toxigenic MEX01 strain had aflD expression down-regulated at 0.98 aw in the presence of all the BCAs. The atoxigenic strain isolated from Mexican maize was the most effective at inhibiting AFB₁production under all aw x temperature conditions examined on maize-based media giving >90% control. Additionally, the potential reduction of inoculum potential of A. flavus by the best four BCA candidates on senescent maize leaves was examined under different aw levels. None of the four BCAs were able to reduce the conidial production by the toxigenic strain of A. flavus. The best candidate BCAs, atoxigenic Afl- MEX02 and C. rosea 016 were examined for efficacy in stored maize grain under different antagonist: pathogen ratios of 25:75; 50:50 and 75:25 initial inoculum. The relative gene expression of the treatment 50:50 ratio was analysed. The expression of both genes was down-regulated in the presence of the BCAs. Also the atoxigenic A. flavus trains had a lower expression compared to the control. This resulted in >60% control of AFB1 production by the atoxigenic strain under the aw x temperatures tested. For the C. rosea 016 strain this was only affected with relatively freely available water. The two best BCA candidates were examined for efficacy and control of toxigenic A. flavus strain growth and AFB₁ production on maize cobs of different ripening ages which also represented different aw and nutritional levels. Using 50:50 antagonist:pathogen ratios of inoculum this showed that the BCAs down-regulated the expression of the aflD and aflR genes in the aflatoxin biosynthetic pathway. However, there was no effect on growth or AFB₁ production. The resilience of the candidate BCAs was tested under climate change scenarios (aw x temperature x CO₂). This showed that at the different ripening stages A. flavus was able to grow at similar rates to the control and that AFB₁ production was unaffected by the conditions and indeed by the presence of the BCAs examined. The results obtained are discussed in the context of the different minimisation strategies which can be employed to try and reduce exposure of consumers to this carcinogenic mycotoxin.PhD in Environment and Agrifoo

Fabrication of an efficient metal grating coupler for membrane-based integrated photonics

This paper reports the progress on the fabrication process of highly efficient metal grating couplers for membrane-based integrated circuits, using double side processing technology on bonded samples. This type of gratings comprises a buried SiO2/Ag grating of 125nm thickness with a silver layer as metal mirror, and has several advantages over dielectric gratings as metallic gratings are independent from the buffer thickness. We predict a theoretical chip-to-fiber coupling efficiency of 74% and 89% for uniform and apodized gratings respectively, at a wavelength of 1550 nm. Furthermore, the fabrication process can be used for both, SOI and III-V based platforms

Efficacy of fungal and bacterial antagonists for controlling growth, FUM1 gene expression and fumonisin B 1 production by Fusarium verticillioides on maize cobs of different ripening stages

This study was carried out to examine the efficacy of two biocontrol agents (Clonostachys rosea 016, BCA1; Gram-negative bacterium, BCA5) for control of FUM1 gene expression and fumonisin B1 (FB1) production by F. verticillioides FV1 on maize cobs of different ripening stages: R3, Milk (0.985 aw); R4, Dough (0.976 aw); R5, Dent (0.958 aw). Initially, temporal studies on FUM1 gene expression and FB1 production were performed on maize kernels for up to 14 days. This revealed that day 10 was optimum for both parameters, and was used in the biocontrol studies. Maize cobs were inoculated with 50:50 mixtures of the pathogen:antagonist inoculum and incubated in environmental chambers to maintain the natural aw conditions for ten days at 25 and 30 °C. The growth rates of F. verticillioides FV1, the relative expression of the FUM1 gene and FB1 production were quantified. It was found that, aw × temp had significant impacts on growth, FUM1 gene expression and FB1 production by F. verticillioides FV1 on maize cobs of different maturities. The fungal antagonist (BCA1) significantly reduced FB1 contamination on maize cobs by > 70% at 25 °C, and almost 60% at 30 °C regardless of maize ripening stage. For the bacterial antagonist (BCA5) however, FB1 levels on maize cobs were significantly decreased only in some treatments. These results suggest that efficacy of antagonists to control mycotoxin production in ripening maize cobs needs to take account of the ecophysiology of the pathogen and the antagonists, as well as the physiological status of the maize during silking to ensure effective control

Low-optical-loss, low-resistance Ag/Ge based ohmic contacts to n-type InP for membrane based waveguide devices

We present the development of Ag/Ge based ohmic contacts to n-type InP with both low contact resistances and relatively low optical losses. A specific contact resistance as low as 1.5×10-6 O cm2 is achieved by optimizing the Ge layer thickness and annealing conditions. The use of Ge instead of metal as the first deposited layer results in a low optical absorption loss in the telecommunication wavelength range. Compared to Au based contacts, the Ag based metallization also shows considerably reduced spiking effects after annealing. Contacts with different lengths are deposited on top of InP membrane waveguides to characterize the optical loss before and after annealing. A factor of 5 reduction of the propagation loss compared to the conventional Au/Ge/Ni contact is demonstrated. This allows for much more optimized designs for membrane photonic devices

Omisiones en la expedición de licencias urbanísticas: un análisis de la responsabilidad del Estado

La propiedad privada como derecho constitucional implica obligaciones, identificándose una de ellas con la necesidad de acreditar una licencia que autorice la construcción y/o intervención urbana sobre determinado predio de uso privado debidamente emitida por un curador urbano, el cual, siendo un particular, actúa como agente del Estado y por ello, sus actos u omisiones le vinculan a la administración, lo que se conjuga con la cláusula general de responsabilidad del Estado prevista en el artículo 90 de la Constitución Política de 1991 y a partir del cual, se pretende con el presente estudio, determinar la procedencia de la declaratoria de responsabilidad estatal, como consecuencia de las omisiones en los deberes impuestos a las curadurías urbanas en la verificación del cumplimiento de los requisitos y condiciones exigidos para la intervención de predios o edificaciones urbanas de orden privado. Para lo anterior, se acude a los fundamentos normativos existentes en la legislación nacional para la expedición de licencias de construcción, así como el análisis de la forma en como se desarrolla esta función del Estado. Así mismo, se realiza una revisión de la jurisprudencia del Consejo de Estado sobre los elementos que determinan la responsabilidad del Estado y de su configuración respecto de las omisiones en la expedición de licencias urbanísticas.Private property as a constitutional right implies obligations, identifying one of them with the need to accredit a license that authorizes the construction and / or urban intervention on a certain private use property duly issued by an urban curator, which, being a private individual, acts as an agent of the State and therefore, his acts or omissions bind him to the administration, which is combined with the general clause of responsibility of the State provided for in article 90 of the 1991 Political Constitution and from which, it is intended with the In this study, determine the origin of the declaration of state responsibility, as a result of the omissions in the duties imposed on urban curatorships in the verification of compliance with the requirements and conditions required for the intervention of private land or urban buildings. For the above, the existing normative foundations in national legislation for issuing construction licenses are used, as well as the analysis of how this State function is carried out. Likewise, a review of the jurisprudence of the State Council is carried out on the elements that determine the responsibility of the State and its configuration regarding omissions in the issuance of urban planning licenses.Monroy Ramos (2016). La responsabilidad del estado por las omisiones administrativas en la expedición de licencias urbanísticas. (Tesis de pregrado).Villavicencio: Universidad Santo Tomas de Aquino. Obtenido de: https://repository.usta.edu.co/bitstream/handle/11634/12624/2016andr%C3%A9smonroy.pdf?sequence=1&isAllowed=

Comparison of hierarchical temporal memories and artificial neural networks under noisy data

The ability of two different machine learning approaches to map non-linear problems from experimental data is evaluated under controlled experiments. A well-known machine learning algorithm (Artificial Neural Network) is compared against a new computing paradigm (Hierarchical Temporal Memory) under a controlled scenario. The chosen scenario is the detection of impacts in a cantilever beam under vibration instrumented with fiber Bragg gratings. The main characteristics of both of the machine learning approaches are analyzed while varying environmental parameters such as the number of sensing points and their location. From the achieved results some clues can be extracted regarding dealing with noisy or partial data using different machine learning approaches

Sampled Fiber Bragg Grating spectral synthesis

In this paper, a technique to estimate the deformation profile of a Sampled Fiber Bragg Grating (SFBG) is proposed and experimentally verified. From the SFBG intensity reflection spectrum, any arbitrary longitudinal axis deformation profile applied to a SFBG is estimated. The synthesis algorithm combines a custom defined error metric to compare the measured and the synthetic spectra and the Particle Swarm Optimization technique to get the deformation profile. Using controlled deformation profiles, the proposed method has been successfully checked by means of simulated and experimental tests. The results obtained under different controlled cases show a remarkable repetitiveness (< 50 με) and good spatial accuracy (< 1 mm).This work has been supported by the project TEC2010-20224-C02-02 and grant AP2009-1403

Wavelength converter using a highly erbium doped optical fiber ring laser

RESUMEN: En este trabajo se presenta un conversor de longitud de onda ultra-estrecho, de alta eficiencia y todo-fibra basado en el efecto de la competición de modos en un láser de fibra dopada con erbio. Se han llevado a cabo estudios experimentales con frecuencias que van desde varios kilohercios hasta las decenas de gigahercios y para más de una longitud de onda de emisión, demostrando así que este efecto puede ser utilizado para la conversión en longitud de onda de múltiples longitudes de emisión simultáneamente.ABSTRACT: This work presents an all-fiber wavelength converter based on a highly Erdoped fiber laser which has been experimentally demonstrated. Frequencies from several kilohertz up to tens of gigahertz have been investigated. Making use of the gain competition in the amplifying medium, the wavelength conversion can be carried out over not only one lasing wavelength but over several ones. These analyses have been also carried out for more than one all-fiber ring structure, demonstrating the viability of this wavelength converter.Este trabajo ha sido financiado por la Comisión Interministerial de Ciencia y Tecnología dentro de los proyectos TEC2013-47264-C2 y TEC2016-76021-C2