Search

Copyright of SHILAP Revista de Lepidopterologia is the property of Sociedad Hispano-Luso-Americana de Lepidopterologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The monophasic polycrystalline ceramic perovskite-based Eu2Bi2Fe4O12 was synthesized by the solid-state reaction method. X-ray diffraction measurements in the Bragg-Brentano geometry and Rietveld analysis reveal that this material crystallizes in an orthorhombic structure with Pnma (#62) space group. Average grain size of 450 nm is calculated of a log-normal distribution and obtained by means scanning electron microscopy images. Results from magnetization, pyroelectric and complex impedance measurements as a function of temperature (50 K up to 300 K) show the occurrence of dielectric and magnetic relaxation process starting simultaneously at 112.8 K. The tendency of real and imaginary curves of the dielectric permittivity at temperatures close to room temperature has also shown strong ac conductivity contributions attributed to porosity effects. The magnetization hysteresis loop at room temperature confirms that this new perovskite-based material has a ferromagnetic response. Signature of superparamagnetism effects is also observed as a consequence of the nanometric grain size. Thermostimulated current measurements as a function of temperature reveal the occurrence of ferroelectric polarization for the temperature regime below T = 112.8 K. Diffuse reflectance experiments permitted to establish the semiconductor nature of this material at room temperature with an energy gap of 2.65 eV. [ABSTRACT FROM AUTHOR]

Little is known regarding the effect of fragmentation and human agricultural management on the genetic variation and gene flow of Cucurbita pepo L., 1753 in moderate fragmented areas in central Guatemala. We hypothesize that the genetic variation of C. pepo is affected by forest fragmentation and by traditional agricultural management. Therefore, we aim to determine: (1) the genetic diversity and genetic structure of C. pepo in the Cloud Forest Corridor (CFC) (2) the extent of genetic admixture between commercial variety (CV) and traditional landraces (TL) of C. pepo, (3) the effect of habitat fragmentation in the population genetics of C. pepo with a landscape approach, and (4) the potential relationship between traditional management practices and genetic diversity of C. pepo in the CFC. We detected the existence of high level of genetic diversity (AR = 3.43; He = 0.50), inbreeding (Fis = 0.25) and moderate population structure of C. pepo in the CFC (Fst = 0.16). No correlation between landscape and genetics was found. Also, we found high genetic admixture between CV and TL. It seems that human practices, mainly related with seed exchange patterns, could affect genetic diversity of C. pepo in the CFC. C. pepo populations in the CFC are structured, with inbreeding, and show admixture with the CV, an aspect that could affect its genetic diversity. The agricultural management influenced the population genetics of C. pepo in the CFC, but the landscape did not. We suggest that special efforts should be made to preserve the diversity of this important indigenous food source for Guatemalan people as well as their management practices. [ABSTRACT FROM AUTHOR]

Plant populations invading new environments might compromise their fitness contribution to the next generation, because of the lack of native specialist pollinators and/or potential mates. Thus, changes in plant mating system and traits linked to it are expected in populations colonising new environments where selection would favour selfing and floral traits that maximise reproductive output. To test this, we studied native (Mexico) and non-native (Spain) populations of the obligate sexual reproducing annual weed Datura stramonium., Flower size, herkogamy, total number of seeds per plant, number of visits by and type of pollinators, and inbreeding depression were assessed in native and non-native populations. Finally, we measured phenotypic selection on corolla size and herkogamy in each population., Flower size and herkogamy showed wide and similar variation in both ranges. However, the largest average flower size was found in one non-native population whereas the highest average positive herkogamy was detected in one native population. On average, flowers in the native range received more visits by pollinators. Hawkmoths were the main visitors in the native populations while only bees were observed visiting flowers in Spain's populations. Only in the native range was inbreeding depression detected. Selection to reduce herkogamy was found only in one native population., Absence of both inbreeding depression and selection on floral traits suggest a change in mating system of D. stramonium in a new range where generalist pollinators may be promoting high reproductive success. Selection against deleterious alleles might explain the reduction of inbreeding depression, promoting the evolution of selfing. [ABSTRACT FROM AUTHOR]

In this paper, the synthesis and study of the structural, morphological, electrical, magnetic and electronic properties of the $$\hbox {LaBiFe}_{2}\hbox {O}_{6}$$ novel material are reported. The material was produced using the standard ceramic method. The Rietveld analysis of experimental data of X-ray diffraction showed that it synthesizes in an orthorhombic perovskite structure ( Pnma space group, # 62). Two types of grain, micro and sub-micrometric, with the $$\hbox {LaBiFe}_{2}\hbox {O}_{6}$$ stoichiometry were identified by scanning electron microscopy and X-ray dispersive spectroscopy. Results of electrical polarization and dielectric constant reveal the occurrence of hysteretic loops of polarization with evidences of dielectric loss. At room temperature, the material is ferromagnetic and exhibits an anomaly at T = 258 K, which is attributed to anisotropy effects. Results of diffuse reflectance suggest a semiconductor feature with energy gap $$E_{g}=2.17$$ eV, which is in agreement with calculations of band structure and density of states for one spin orientation, while for the other spin configuration from the calculations a conductor behavior is expected. [ABSTRACT FROM AUTHOR]

The synthesis process of the polycrystalline ceramic compound Nd2SrMn2TiO9 by means of the solid-state reaction procedure is reported. The crystalline structure was analyzed through X-ray diffraction experiments in the Bragg-Brentano recipe. The Rietveld refinement of the diffraction pattern by using the GSAS code shows that this material crystallizes in an orthorhombic structure, space group Pnma (#62), with lattice parameters a = 5.4764(6) Ǻ, b = 7.7468(6) Ǻ, and 5.4810(6) Ǻ. The surface morphology was studied by scanning electron microscopy images, which evidence the formation and compacting of grain with mean size 352.63 nm. Semiquantitative compositional analysis performed by means of Energy Dispersive X-ray Spectroscopy shows the stoichiometric composition of the samples. Measurements of magnetization as a function of temperature reveal that this compound has a ferromagnetic behavior. The analysis with the Curie equation permitted to establish an effective magnetic moment μeff = 4.33 μB, which is 95.7% in agreement with the theoretical value expected from the Hund's rules. Measurements of DC resistivity as a function of temperature show a conductor behavior below the Curie temperature and insulator above. Evidences of a nonlinear response as a function of frequency with high values of relative dielectric constant reveal the occurrence of giant dielectric constant with ϵr = 6480 for ν = 100 Hz. [ABSTRACT FROM AUTHOR]

Habitat fragmentation can change the ecological context of populations, rupturing genetic connectivity among them, changing genetic structure, and increasing the loss of genetic diversity. We analyzed mating system and pollen structure in two population fragments and two continuous forest populations of Dieffenbachia seguine (Araceae), an insect-pollinated understory herb in the tropical rain forest of Los Tuxtlas, México, using nine allozyme loci. Mating system analysis indicated almost complete outcrossing but some inbreeding among the adults. Pollen structure analysis indicated highly restricted pollen flow, both within and among populations. We showed that the effective pollination neighborhood was small in all populations, and slightly (though not significantly) smaller in fragments, partially as a consequence of an increase in density of reproductive individuals in those fragments. Using assignment analysis, we showed that all populations were strongly structured, suggesting that pollen and seed flow across the Los Tuxtlas landscape has been spatially restricted, though sufficient to maintain connectedness. Forest fragmentation at Los Tuxtlas has (so far) had limited impact on pollen dynamics, despite the changing ecological context, with reduced pollinator abundance being partially offset by increased flowering density in fragments. Continued outcrossing and limited pollen immigration, coupled with more extensive seed migration, should maintain genetic connectedness in D. seguine, if fragmentation is not further exacerbated by additional deforestation. [ABSTRACT FROM AUTHOR]

We report the production of type perovskite ceramics Sr2FeMnO6, Ba2NdSbO6, Sr2YSbO6 y Ho- Ba2Cu3O7 by means the standard solid state reaction recipe. X-ray diffraction analysis shows that these materials crystallize in complex perovskite with the A2BB'O6 form. [ABSTRACT FROM AUTHOR]

This research paper shows the electrical characterization of tablets type complex perovskite (Sr2FeMnO6, Ba2NdSbO6 and Sr2YSbO6 -semiconductors to room temperature) and HoBa2Cu3O7 (conductor to room temperature but superconductor to 92 K) by means of the Impedance Spectroscopy (IS) technique in solid materials. The measures were carried out in a rank of frequency of 1 mHz to 100 KHz, the experimental assembling was shown, the analysis of the impedance change based on the frequency was also shown, the elements of constant phase that appear in the transmission lines were presented, and the equivalent circuits that can be used to simulate the behavior of the electrical conductivity of these perovskites were also shown. [ABSTRACT FROM AUTHOR]