GTD analysis of airborne antennas radiating in the presence of lossy dielectric layers

The patterns of monopole or aperture antennas mounted on a perfectly conducting convex surface radiating in the presence of a dielectric or metal plate are computed. The geometrical theory of diffraction is used to analyze the radiating system and extended here to include diffraction by flat dielectric slabs. Modified edge diffraction coefficients valid for wedges whose walls are lossy or lossless thin dielectric or perfectly conducting plates are developed. The width of the dielectric plates cannot exceed a quarter of a wavelength in free space, and the interior angle of the wedge is assumed to be close to 0 deg or 180 deg. Systematic methods for computing the individual components of the total high frequency field are discussed. The accuracy of the solutions is demonstrated by comparisons with measured results, where a 2 lambda by 4 lambda prolate spheroid is used as the convex surface. A jump or kink appears in the calculated pattern when higher order terms that are important are not included in the final solution. The most immediate application of the results presented here is in the modelling of structures such as aircraft which are composed of nonmetallic parts that play a significant role in the pattern

Quantum Hall states under conditions of vanishing Zeeman energy

We report on magneto-transport measurements of a two-dimensional electron gas confined in a Cd$_{0.997}$Mn$_{0.003}$Te quantum well structure under conditions of vanishing Zeeman energy. The electron Zeeman energy has been tuned via the $s-d$ exchange interaction in order to probe different quantum Hall states associated with metallic and insulating phases. We have observed that reducing Zeeman energy to zero does not necessary imply the disappearing of quantum Hall states, i.e. a closing of the spin gap. The spin gap value under vanishing Zeeman energy conditions is shown to be dependent on the filling factor. Numerical simulations support a qualitative description of the experimental data presented in terms of a crossing or an avoided-crossing of spin split Landau levels with same orbital quantum number $N$

Coping Strategies of Diabetic Yam Farming Households in Benue State, Nigeria

This study engaged the Multinomial Logistic Model (MLN) to determine factors influencing te choice of coping strategies of diabetic yam farming households in Benue State, Nigeria. A multi-stage random sampling technique was used to select 340 yam farming households with emphasis on 2015 farming season. Primary data were obtained using a well structured and pretested questionnaire. The results of analysis shows that the most frequently used coping strategies were special diets such as millet, cocoyam, locust bean, groundnut, fruits and vegetables accounting for 39%, constant intake of drugs like metformin, biguarnide, sulphorylureas and insulin 25%, hired labour, 23.2%, routine exercise, 12.6%, while hawking was 0.3%. The choice of constant drug was -0.012, while the choice of hawking was significantly (p < 0.05) and negatively affected by education as a coping strategy. The marginal effect of education on constant drug was -0.012, while the choice of hawking was significantly (p < 0.05) and positively affected by the age as a coping strategy. The marginal effect of age on hawking was 0.04. It is recommended that government at Federal, State and Local levels with partners in progress should consider critical ways of managing diabetes by emphasizing healthy lifestyles such as ceasation of smoking, moderate alcohol intake, regular medical check-up and improvement of the socio-economic status of the diabetic farm households through good road network, steady supply of electricity which will better the quality of life of the farm households

Collective character of spin excitations in a system of Mn2+^{2+} spins coupled to a two-dimensional electron gas

We have studied the low energy spin excitations in n-type CdMnTe based dilute magnetic semiconductor quantum wells. For magnetic fields for which the energies for the excitation of free carriers and Mn spins are almost identical an anomalously large Knight shift is observed. Our findings suggests the existence of a magnetic field induced ferromagnetic order in these structures, which is in agreement with recent theoretical predictions [J. K{\"o}nig and A. H. MacDonald, submitted Phys. Rev. Lett. (2002)]Comment: 4 figure

Enhancement of the spin-gap in fully occupied two-dimensional Landau levels

Polarization-resolved magneto-luminescence, together with simultaneous magneto-transport measurements, have been performed on a two-dimensional electron gas (2DEG) confined in CdTe quantum well in order to determine the spin-splitting of fully occupied electronic Landau levels, as a function of the magnetic field (arbitrary Landau level filling factors) and temperature. The spin splitting, extracted from the energy separation of the \sigma+ and \sigma- transitions, is composed of the ordinary Zeeman term and a many-body contribution which is shown to be driven by the spin-polarization of the 2DEG. It is argued that both these contributions result in a simple, rigid shift of Landau level ladders with opposite spins.Comment: 4 pages, 3 figure

Stability of trions in strongly spin-polarized two-dimensional electron gases

Low-temperature magneto-photoluminescence studies of negatively charged excitons (X- trions) are reported for n-type modulation-doped ZnSe/Zn(Cd,Mn)Se quantum wells over a wide range of Fermi energy and spin-splitting. The magnetic composition is chosen such that these magnetic two-dimensional electron gases (2DEGs) are highly spin-polarized even at low magnetic fields, throughout the entire range of electron densities studied (5e10 to 6.5e11 cm^-2). This spin polarization has a pronounced effect on the formation and energy of X-, with the striking result that the trion ionization energy (the energy separating X- from the neutral exciton) follows the temperature- and magnetic field-tunable Fermi energy. The large Zeeman energy destabilizes X- at the nu=1 quantum limit, beyond which a new PL peak appears and persists to 60 Tesla, suggesting the formation of spin-triplet charged excitons.Comment: 5 pages (RevTex), 4 embedded EPS figs. Submitted to PRB-R

Spontaneous polarisation of the neutral interface for valence asymmetric coulombic systems

In this paper, we discuss the phenomenon of a spontaneous polarisation of a neutral hard planar interface for valence asymmetric coulombic systems. Within a field theoretical description, we account for the existence of non trivial charge density and electric potential profiles. The analysis of the phenomenon shows that the effect is related to combinatorics in relation with the existence of the two independent species cations and anions. This simple and basic feature is related to the quantum mechanical properties of the system. The theoretical results are compared with numerical simulations data and are shown to be in very good agreement, which a fortiori justifies our physical interpretation.Comment: 12 pages, 11 figure

Medical students learning styles in Latin American and Spanish universities: relation with geographical and curricular contexts

Objetivo. Determinar si los estilos de aprendizaje (EA) de los estudiantes de medicina se correlacionan con el contexto geográfico, con el contexto curricular o con el nivel de la carrera. Sujetos y métodos. El estudio se realizó en 490 estudiantes de las Escuelas de Medicina de las Universidades de Chile (Santiago, Chile), Nacional de Cuyo (Mendoza, Argentina), San Francisco Xavier (Sucre, Bolivia), Zaragoza y País Vasco (España). Se aplicó el cuestionario Honey-Alonso, que valora la preferencia por cada uno de cuatro EA: activo, reflexivo, teórico y pragmático. También se evaluó el EA de acuerdo al modelo de Kolb. Resultados. Al relacionar el EA con el contexto geográfico se observó que mientras los estudiantes de universidades españolas muestran un estilo preferentemente asimilador, siguiendo la denominación de Kolb, para Chile fue el acomodador y para Bolivia los estudiantes se distribuyen entre los estilos asimilador y divergente. Al comparar la distribución de los EA durante el tercer curso de medicina en dos facultades que poseen diferente currículo, no se observaron diferencias significativas. Los EA en una Facultad de Medicina con un currículo basado en asignaturas (Chile) no mostraron diferencias en los tres cursos del estudio (1.o, 3.o y 5.o), siendo preferentes los estilos reflexivo y teórico. Conclusiones. El estudio permitió establecer diferencias significativas entre los estilos de aprendizaje de los estudiantes de Medicina en relación con el contexto geográfico, más que con los diferentes currículos, o a lo largo de los distintos cursos de la carrera.Aim. To establish a correlation between medical student learning styles (LS) and the geographical context, the curricular context and different academic levels. Subjects and methods. The study was performed in 490 undergraduate students from Medical Schools of the Universities of Chile (Santiago, Chile), Nacional de Cuyo (Mendoza, Argentina), San Francisco Xavier (Sucre, Bolivia), Zaragoza and País Vasco (Spain). The instrument used was the Honey-Alonso learning style questionnaire that assesses the student preference for one of four LS: active, reflexive, theoretic and pragmatic. In addition, LS according to the Kolb inventory were also assessed. Results. Using the Kolb inventory, significant differences were found when the LS were correlated with the geographical context. While Spanish students showed a high preference for the assimilator style of learning, Chilean students resulted to be mainly accommodators, and Bolivian students were both assimilators and divergent. Comparing the LS distribution during the third course in two universities with different curricula (problem and lecture based learning), there were no significant differences. LS of medical students from a Medical School with a lecture based curriculum (University of Chile) were not significantly different during the first, the third and the fifth level of their undergraduate students. They showed a significant preference for reflexive and theoretic styles of learning. Conclusions. The present study allowed demonstrating that significant differences among the styles of learning of medical students correlated with the geographical context more than with the different curricula, or along the different courses of the career.Fil: Diaz Veliz, G.. Universidad de Chile; ChileFil: Mora, S.. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas; ArgentinaFil: Lafuente Sanchez, J. V.. Universidad del País Vasco; EspañaFil: Gargiulo, Pascual Angel. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; ArgentinaFil: Bianchi, R.. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas; ArgentinaFil: Teran, C.. Universidad Andina Simón Bolívar; BoliviaFil: Gorena, D.. Universidad Andina Simón Bolívar; BoliviaFil: Arce, J.. Universidad San Francisco Xavier; BoliviaFil: Escanero Marcen, J. F.. Universidad de Zaragoza; Españ

Ipsdienol Dehydrogenase (IDOLDH), a Novel Oxidoreductase Important in the Last Steps of Pheromone Biosynthesis in Ips Spp. (Coleoptera: Scolytinae: Curculionidae)

Ips spp. beetles biosynthesize ipsdienol and ipsenol in different enantiomeric blends and ratios as pheromones. In order to understand how these beetles evolved the ability to use the same components to synthesize different pheromone blends, the last steps of ipsdienol and ipsenol biosynthesis, which are probably catalyzed by oxidoreductases, must be characterized. Here I report the isolation of ipsdienol dehydrogenase (IDOLDH) from the three bark beetles (Coleoptera): western Ips pini (wIDOLDH), I. confusus (IcIDOLDH) and eastern I. pini (eIpIDOLDH). IDOLDH is the first characterized non-dipteran insect monoterpene short-chain dehydrogenase/reductase (SDR). Quantitative real-time PCR experiments showed that wIDOLDH transcript was induced by feeding in male midguts, the hallmark of pheromone biosynthetic genes. Surprisingly, protein levels were unaffected by feeding, suggesting other factor(s) control pheromone biosynthesis. IDOLDH was present only in male midguts, not in females or other tissues. Functional characterization of wIDOLDH and IcIDOLDH provide the first direct evidence for ipsenol biosynthesis through ketone intermediates and interconversion of (-)-ipsdienol to ipsdienone. WIpIDOLDH oxidized racemic and (-)-ipsdienol to ipsdienone and reduced ipsdienone to (-)-ipsdienol and ipsenone to (-)-ipsenol, but discriminated against (+)- ipsdienol as a substrate. IcIDOLDH similarly oxidized (-)-ipsdienol to ipsdienone, discriminated against (+)-ipsdienol, reduced ipsdienone to ipsdienol (stereochemistry not determined), and used ipsenone as a substrate. Ongoing studies showed eIpIDOLDH had similar activities. Kinetic analysis of IDOLDH oxidation of (-)-ipsdienol with NADP⁺ followed the Michaelis-Menton model, indicating this type of analysis is adequate to characterize IDOLDH catalyzed reactions. The expression profiles and conservation of activities across three species strongly supports that IDOLDH has evolved specifically for pheromone biosynthesis in Ips beetles. The functional data indicates that IDOLDH contributes to, but does not solely control the enantiomeric blend of ipsdienol in Ips spp. Additionally, ipsenone was not a reduction product of ipsdienone, suggesting an ipsenone reductase (IDONER) is required for ipsenone biosynthesis. IDOLDH’s primary structure contains all the critical motifs of an alcohol dehydrogenase in the SDR superfamily. Primary sequence identity of IDOLDH isozymes was not as high as expected for sibling species (82%), however the substrate binding loop was highly identical (99%) and the fact that they retain similar substrate profiles suggest that the differences are not important in determining function. Primary sequence comparisons with the human L-3-hydroxyacyl-CoA dehydrogenase type II/ amyloid-β binding alcohol dehydrogenase (hHADH II/ ABAD) showed a much lower identity (36%) but was still surprisingly high for such diverse organisms with different substrate preferences. Although the overall architecture of these enzymes is similar the substrate binding loop regions are completely different, except for the anchor portions, suggesting that much of the substrate specificity differences are probably found in this region. This work adds to our overall understanding of monoterpene and insect SDRs. The data in this dissertation allow the prediction that Ips beetles probably attain their final pheromone blends by the interplay between pheromone biosynthetic enzymes including IDOLDH, myrcene hydroxylase, (+)-ipsdienol oxidoreductase (unidentified), and ipsdienone reductase (unidentified), whose activities are probably controlled by the redox state of the cell. Additionally, this work provides a solid foundation for future studies on insect SDRs and their involvement in pheromone biosynthesis. Future work to identify, model, and kinetically characterize, other pheromone biosynthetic genes will provide a map for understanding how insects have evolved the ability to tune pheromone blends, and aid in identification of targets for pest management