Impedance and initial magnetic permeability of gadolinium

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)In the present work we report on measurements of the complex impedance and the magnetoimpedance of a textured sample of gadolinium metal. The preferential c -axis orientation of the Gd hexagonal structure is perpendicular to the long axis of the sample. From the experimental data, the complex initial magnetic permeability, mu = mu' + i mu '', was obtained as a function of temperature and frequency of the ac exciting current. We have found that the results for mu'(T) below the spin reorientation temperature may be described as a power law of the reduced temperature t = 1-T/T(SR), where T(SR) is the spin reorientation temperature. This behavior suggests that a genuine phase transition occurs at T(SR). Although the impedance displays a weak anomaly at the Curie temperature, T(C), magnetic measurements indicate that the ferromagnetic response of Gd extends up to this critical point. Thus, two different phases characterizes the cooperative magnetic state of this metal. The frequency dependent results for mu' and mu '' were fitted to a modified Debye formula and the obtained parameters allow us to discriminate between the contributions from domain-wall motion and from magnetization rotation. We obtain that the dynamical properties of the domain walls in Gd are governed by a broad distribution of frequencies whose average value diverge at T(SR). The isothermal magnetoimpedance measurements in temperatures smaller than T(SR) show an interesting plateau at low dc applied fields. This plateau is limited by a characteristic field H(K) whose magnitude decreases rapidly to nearly zero at T(SR), giving further support for the phase transition scenario at this temperature. (C) 2010 American Institute of Physics. [doi:10.1063/1.3288696]1075Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq [04.0938.0

The Origins and Historical Assembly of the Brazilian Caatinga Seasonally Dry Tropical Forests

This is the final version. Available on open access from Frontiers Media via the DOI in this recordData Availability Statement: The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found in the article/Supplementary Material.The Brazilian Caatinga is considered the richest nucleus of the Seasonally Dry Tropical Forests (SDTF) in the Neotropics, also exhibiting high levels of endemism, but the timing of origin and the evolutionary causes of its plant diversification are still poorly understood. In this study, we integrate comprehensive sampled dated molecular phylogenies of multiple flowering plant groups and estimations of ancestral areas to elucidate the forces driving diversification and historical assembly in the Caatinga flowering plants. Our results show a pervasive floristic exchange between Caatinga and other neotropical regions, particularly those adjacent. While some Caatinga lineages arose in the Eocene/Oligocene, most dry-adapted endemic plant lineages found in region emerged from the middle to late Miocene until the Pleistocene, indicating that only during this period the Caatinga started to coalesce into a SDTF like we see today. Our findings are temporally congruent with global and regional aridification events and extensive denudation of thick layers of sediments in Northeast (NE) Brazil. We hypothesize that global aridification processes have played important role in the ancient plant assembly and long-term Caatinga SDTF biome stability, whereas climate-induced vegetation shifts, as well as the newly opened habitats have largely contributed as drivers of in situ diversification in the region. Patterns of phylogenetic relatedness of Caatinga endemic clades revealed that much modern species diversity has originated in situ and likely evolved via recent (Pliocene/Pleistocene) ecological specialization triggered by increased environmental heterogeneity and the exhumation of edaphically disparate substrates. The continuous assembly of dry-adapted flora of the Caatinga has been complex, adding to growing evidence that the origins and historical assembly of the distinct SDTF patches are idiosyncratic across the Neotropics, driven not just by continental-scale processes but also by unique features of regional-scale geological history

Observation of coherent hybrid reflection with synchrotron radiation

High resolution synchrotron radiation has been used to investigate the occurrence of coherent hybrid reflections (CHR) in the In0.49Ga0.51P/GaAs(001) structure. Several phi scans at the 002 layer reflection were carried out. The scanned phi intervals are correlated by the axis symmetry and [001] should present the same pattern. A break in the symmetry is observed due to constructive/destructive interference of the hybrid amplitudes with the amplitude from the 002 layer reflection. The effects of substrate miscut and interface distance are taken into account to explain the observed patterns. The application of CHR as a high sensitive tool to analyze epitaxial growth is discussed. (C) 1998 American Institute of Physics. [S0003-6951(98)03841-8].73152194219

Evidence of Be3P2 formation during growth of Be-doped phosphorus-based semiconductor compounds

In this work, we present evidence that Be3P2 microcrystals are formed in Be-doped phosphorus-based semiconductor compounds grown by chemical beam epitaxy. Our results suggest that microcrystal formation occurs when high Be concentrations (> 10(18) cm(-3)) and temperatures higher than 500 degrees C are used for crystal growth. The main consequence of Be3P2 formation is a high phosphorus consumption close to these microcrystals that causes a large density of P vacancies in the semiconductor layer. This results in reduced electrical mobility, lattice parameter reduction, and poor crystalinity of the film in general. (c) 1999 American Institute of Physics. [S0003-6951(99)01624-1].74243669367

DNA Sequence Variation among Conspecific Accessions of the Legume Coursetia caribaea Reveals Geographically Localized Clades Here Ranked as Species

 This is the author accepted manuscript. The final version is available from ASPT via the DOI in this recordCoursetia caribaea is geographically and morphologically the most variable species in the genus Coursetia and in the tribe Robinieae (Leguminosae, Papilionoideae). Because of potentially undetected species, we assessed the phylogenetic relationships among the eight taxonomic varieties of C. caribaea. Sampling included nuclear ribosomal internal transcribed spacer sequences from 489 Robinieae accessions representing all varieties of C. caribaea and 38 of the 40 species of Coursetia, in addition to chloroplast trnD-trnT sequences from 186 accessions. Separate and combined phylogenetic analyses resolved a clade of conspecific accessions of the Bolivian C. caribaea var. astragalina as sister to the central Andean Coursetia grandiflora clade. Also distantly related to Coursetia caribaea var. caribaea accessions were those of the coastal Oaxacan C. caribaea var. pacifica, which formed the sister clade to accessions of the central Andean C. caribaea var. ochroleuca. The estimated mean ages of the stem clades for these three lineages, 11, 7.7, and 7.7 Ma, respectively, contrasted to the estimated mean ages of the corresponding crown clades of 0, 0, and 1.5 Ma. The contrasting stem and crown ages suggest that these taxa, appropriately ranked as species, Coursetia astragalina , Coursetia diversifolia , and Coursetia ochroleuca , each have persisted over evolutionary time frames as distinct geographically localized populations in seasonally dry tropical forests and woodlands.USDA National Institute of Food and Agricultur

Piezoelectric coefficients of mNA organic nonlinear optical material using synchrotron X-ray multiple diffraction

Distortions produced in the unit cell of a nonlinear organic crystal under the influence of an applied electric field E are investigated by using synchrotron x-ray multiple diffraction (MD). A typical MD pattern shows numerous (hkl) secondary peaks and the position of each one is basically a function of the unit cell lattice parameters. Thus small changes in any parameter due to a strain produced by E give rise to a corresponding variation in the (hkl) peak position. The method was applied to the meta-nitroaniline (mNA) crystal and we were able to determine three piezoelectric coefficients. [S0031-9007(98)07912-5].81245426542

Piezoelectric coefficients d(14), d(16), d(34) and d(36) of an L-arginine hydrochloride monohydrate crystal by X-ray three-beam diffraction

Previous work employed X-ray three-beam diffraction techniques to obtain part of the L-arginine hydrochloride monohydrate (L-AHCL. H2O) piezoelectric coefficients, namely d(21), d(22), d(23) and d(25). Those coefficients were obtained by measuring the shift in the angular position of a number of secondary reflections as a function of the electric field applied in the [ 010] piezoelectric direction. In this paper a similar procedure has been used to measure the remaining four piezoelectric coefficients in L-AHCL. H2O: with the electric field applied in the [100] direction, d(14) and d(16) were measured; with the electric field applied in the [001] direction, d(34) and d(36) were obtained. Therefore the entire piezoelectric matrix of the L-AHCL. H2O crystal has been successfully measured.13643543

Spatial ordering in InP/InGaP nanostructures

We report the observation of a spatially-ordered bidimensional array of self-assembled InP quantum dots grown on slightly In-rich InGaP layers. The alignment of InP dots is observed along [100] and [010] directions. This effect is enhanced when 2degrees off vicinal substrates are used; it is also strongly dependent on growth temperature. Our results suggest that the density and size of CuPt-type atomically ordered regions as well as compositional modulation of InGaP layers play an important role on the spatial alignment of InP/InGaP quantum dots. (C) 2003 American Institute of Physics.82203523352

Synchrotron-radiation x-ray multiple diffraction applied to the study of electric-field-induced strain in an organic nonlinear optical material

In this work, distortions produced in the unit cell of a MBANP [(-)-2-(alpha-methylbenzylamino)-5-nitropyridine] nonlinear organic crystal under the influence of an applied electric field, (E) over bar, are investigated by using synchrotron-radiation x-ray multiple diffraction (XRMD). The method is based in the inherent sensitivity of this technique to determine small changes in the crystal lattice, which provide peak position changes in the XRMD pattern (Renninger scan). A typical Renninger scan shows numerous secondary peaks, each one carrying information on one particular direction within the crystal. The (hkl) peak position in the pattern, for a fixed wavelength, is basically a function of the unit cell lattice parameters. Thus small changes in any parameter due to a strain produced by (E) over right arrow give rise to a corresponding variation in the (hkl) peak position and the observed strain is related to the piezoelectric coefficients. The advantage of this method is the possibility of determining more than one piezoelectric coefficient from a single Renninger scan measurement [L. H. Avanci, L. P. Cardoso, S. E. Girdwood, D. Pugh, J. N. Sherwood, and K. J. Roberts, Phys. Rev. Lett. 81, 5426 (1998)]. The method has been applied to the MBANP (monoclinic, point group 2) crystal and we were able to determine four piezoelectric coefficients: \d(21)\ = 0.2(1) X 10(-11) CN-1, \d(22)\ = 24.8(3) X 10(-11) CN-1, \d(23)\ = 1.3(1) x 10(-11) CN-1, and \d(25)\ = 5.9(1) X 10(-11) CN-1. The measurements were carried out using the SRS stations 16.3, Daresbury Laboratory, Warrington, UK.61106507651