1,225 research outputs found
Caracterização fĂsico-quĂmica de amostras de mĂ©is produzidas por Apis mellifera L. em fragmento de cerrado no municĂpio de Itirapina, SĂŁo Paulo.
A fisionomia vegetal mais representativa do paĂs, depois da floresta amazĂ´nica, Ă© o cerrado, que ocupa atualmente dois milhões de km2 do territĂłrio brasileiro. Este trabalho teve como objetivo determinar as caracterĂsticas fĂsicoquĂmicas de amostras de mel produzidas por Apis mellifera em um fragmento de cerrado, localizado em Itirapina, SP (22Âş14?S e 47Âş49?W). As amostras foram coletadas mensalmente, em cinco colmĂ©ias, entre fevereiro e outubro de 2005 e as caracterĂsticas avaliadas foram: açúcares redutores, redutores totais, sacarose, umidade, hidroximetilfurfural (HMF), cor, condutividade elĂ©trica, pH, acidez, Ăndice de formol, teor de cinzas, proteĂnas e viscosidade, alĂ©m da análise polĂnica. Os resultados obtidos indicam que os limites estabelecidos pela legislação brasileira para parâmetros fĂsico-quĂmicos analisados sĂŁo atendidos pela maioria das amostras de mel. Com relação Ă análise polĂnica, foi verificada a presença de Eucalyptus sp. como pĂłlen dominante nos meses de fevereiro a julho e o de Citrus sp. no mĂŞs de outubro, em virtude da maior atratividade destes dois cultivos sobre as abelhas
Characterization of nanometer-sized, mechanically exfoliated graphene on the H-passivated Si(100) surface using scanning tunnelling microscopy
We have developed a method for depositing graphene monolayers and bilayers
with minimum lateral dimensions of 2-10 nm by the mechanical exfoliation of
graphite onto the Si(100)-2x1:H surface. Room temperature, ultra-high vacuum
(UHV) tunnelling spectroscopy measurements of nanometer-sized single-layer
graphene reveal a size dependent energy gap ranging from 0.1-1 eV. Furthermore,
the number of graphene layers can be directly determined from scanning
tunnelling microscopy (STM) topographic contours. This atomistic study provides
an experimental basis for probing the electronic structure of nanometer-sized
graphene which can assist the development of graphene-based nanoelectronics.Comment: Accepted for publication in Nanotechnolog
Reconstructing Bioinvasion Dynamics Through Micropaleontologic Analysis Highlights the Role of Temperature Change as a Driver of Alien Foraminifera Invasion
Invasive alien species threaten biodiversity and ecosystem structure and functioning, but incomplete assessments of their origins and temporal trends impair our ability to understand the relative importance of different factors driving invasion success. Continuous time-series are needed to assess invasion dynamics, but such data are usually difficult to obtain, especially in the case of small-sized taxa that may remain undetected for several decades. In this study, we show how micropaleontologic analysis of sedimentary cores coupled with radiometric dating can be used to date the first arrival and to reconstruct temporal trends of foraminiferal species, focusing on the alien Amphistegina lobifera and its cryptogenic congener A. lessonii in the Maltese Islands. Our results show that the two species had reached the Central Mediterranean Sea several decades earlier than reported in the literature, with considerable implications for all previous hypotheses of their spreading patterns and rates. By relating the population dynamics of the two foraminifera with trends in sea surface temperature, we document a strong relationship between sea warming and population outbreaks of both species. We conclude that the micropaleontologic approach is a reliable procedure for reconstructing the bioinvasion dynamics of taxa having mineralized remains, and can be added to the toolkit for studying invasions
Novel Cu(I)-5-nitropyridine-2-thiol Cluster with NIR Emission: Structural and Photophysical Characterization
A novel Cu(I) cluster compound has been synthesized by reacting CuI with the 2,2′-dithiobis(5-nitropyridine) ligand under solvothermal conditions. During the reaction, the original ligand breaks into the 5-nitropyridine-2-thiolate moiety, which acts as the coordinating ligand with both N- and S-sites, leading to a distorted octahedral Cu6S6 cluster. The structure has been determined by single-crystal X-ray diffraction and FT-IR analysis, and the photophysical properties have been determined in the solid state by means of steady-state and time-resolved optical techniques. The cluster presents a near-infrared emission showing an unusual temperature dependence: when passing from 77 to 298 K, a blue-shift of the emission band is observed, associated with a decrease in its intensity. Time-dependent-density functional theory calculations suggest that the observed behavior can be ascribed to a complex interplay of excited states, basically in the triplet manifold
Cyclic RGD peptidomimetics containing bifunctional diketopiperazine scaffolds as new potent integrin ligands
The synthesis of eight bifunctional diketopiperazine (DKP) scaffolds is described; these were formally derived from 2,3-diaminopropionic acid and aspartic acid (DKP-1-DKP-7) or glutamic acid (DKP-8) and feature an amine and a carboxylic acid functional group. The scaffolds differ in the configuration at the two stereocenters and the substitution at the diketopiperazinic nitrogen atoms. The bifunctional diketopiperazines were introduced into eight cyclic peptidomimetics containing the Arg-Gly-Asp (RGD) sequence. The resulting RGD peptidomimetics were screened for their ability to inhibit biotinylated vitronectin binding to the purified integrins \u3b1 v\u3b2 3 and \u3b1 v\u3b2 5, which are involved in tumor angiogenesis. Nanomolar IC 50 values were obtained for the RGD peptidomimetics derived from trans DKP scaffolds (DKP-2-DKP-8). Conformational studies of the cyclic RGD peptidomimetics by 1H NMR spectroscopy experiments (VT-NMR and NOESY spectroscopy) in aqueous solution and Monte Carlo/Stochastic Dynamics (MC/SD) simulations revealed that the highest affinity ligands display well-defined preferred conformations featuring intramolecular hydrogen-bonded turn motifs and an extended arrangement of the RGD sequence [C\u3b2(Arg)-C\u3b2(Asp) average distance 658.8 \uc5]. Docking studies were performed, starting from the representative conformations obtained from the MC/SD simulations and taking as a reference model the crystal structure of the extracellular segment of integrin \u3b1 v\u3b2 3 complexed with the cyclic pentapeptide, Cilengitide. The highest affinity ligands produced top-ranked poses conserving all the important interactions of the X-ray complex. Copyright \ua9 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Multivariate analysis based on the physicochemical characteristics of samples of honey produced by Apis mellifera L. (Hymenoptera: Apidae) from the northern coast of Bahia state, Brazil
This research was carried out to determine how honey samples are grouped based on physicochemical characteristics. A total of 36 honey samples, collected from January of 1999 to June of 2000, on the northern coast of Bahia State, were evaluated. with regard to humidity, color, protein, pH, acidity, formol index, electrical conductivity, ash, diastase number, hydroxymethylfurfural (HMF), total sugar, reducing sugars, sucrose, and types of pollen. The results indicate that HMF, reducing sugar and total sugars are the characteristics that most influenced the grouping. Two plant genera, Eucalyptus and Mimosa, were observed as predominant bee plants in the region
Mmf1p, a novel yeast mitochondrial protein conserved throughout evolution and involved in maintenance of the mitochondrial genome
A novel protein family (p14.5, or YERO57c/YJGFc) highly conserved throughout evolution has recently been identified. The biological role of these proteins is not yet well characterized. Two members of the p14.5 family are present in the yeast Saccharomyces cerevisiae. In this study, we have characterized some of the biological functions of the two yeast proteins. Mmf1p is a mitochondrial matrix factor, and homologous Mmf1p factor (Hmf1p) copurifies with the soluble cytoplasmic fraction. Δmmf1 cells lose mitochondrial DNA (mtDNA) and have a decreased growth rate, while Δhmf1 cells do not display any visible phenotype. Furthermore, we demonstrate by genetic analysis that Mmf1p does not play a direct role in replication and segregation of the mtDNA. rho(+) Δmmf1 haploid cells can be obtained when tetrads are directly dissected on medium containing a nonfermentable carbon source. Our data also indicate that Mmf1p and Hmf1p have similar biological functions in different subcellular compartments. Hmf1p, when fused with the Mmf1p leader peptide, is transported into mitochondria and is able to functionally replace Mmf1p. Moreover, we show that homologous mammalian proteins are functionally related to Mmf1p. Human p14.5 localizes in yeast mitochondria and rescues the Δmmf1-associated phenotypes. In addition, fractionation of rat liver mitochondria showed that rat p14.5, like Mmf1p, is a soluble protein of the matrix. Our study identifies a biological function for Mmf1p and furthermore indicates that this function is conserved between members of the p14.5 family
Decreasing pH impairs sexual reproduction in a Mediterranean coral transplanted at a CO2 vent
Ocean acidification, due to the increase of carbon dioxide (CO2) concentration in the atmosphere and its absorption by the oceans, affects many aspects of marine calcifying organisms' biology, including reproduction. Most of the available studies on low pH effects on coral reproduction have been conducted on tropical species under controlled conditions, while little information is reported for either tropical or temperate species in the field. This study describes the influence of decreasing pH on sexual reproduction of the temperate non-zooxanthellate colonial scleractinian Astroides calycularis, transplanted in four sites along a natural pH gradient at the underwater volcanic crater of Panarea Island (Tyrrhenian Sea, Italy). The average pH values of each site (range: pHTS 8.07–7.40) match different scenarios of the Intergovernmental Panel on Climate Change (IPCC) for the end of the century. After 3 months under experimental conditions, the reproductive parameters of both oocytes and spermaries (abundance, gonadal index, and diameters) seem to be unaffected by low pH. However, a delay in spermary development in the pre-fertilization period and a persistence of mature oocytes in the fertilization period were observed in the most acidic site. Furthermore, no embryos were found in colonies from the two most acidic sites, suggesting a delay or an interruption of the fertilization process due to acidified conditions. These findings suggest a negative effect of low pH on A. calycularis sexual reproduction. However, long-term experiments, including the synergistic impact of pH and temperature, are needed to predict if this species will be able to adapt to climate change over the next century
Emergence of Superlattice Dirac Points in Graphene on Hexagonal Boron Nitride
The Schr\"odinger equation dictates that the propagation of nearly free
electrons through a weak periodic potential results in the opening of band gaps
near points of the reciprocal lattice known as Brillouin zone boundaries.
However, in the case of massless Dirac fermions, it has been predicted that the
chirality of the charge carriers prevents the opening of a band gap and instead
new Dirac points appear in the electronic structure of the material. Graphene
on hexagonal boron nitride (hBN) exhibits a rotation dependent Moir\'e pattern.
In this letter, we show experimentally and theoretically that this Moir\'e
pattern acts as a weak periodic potential and thereby leads to the emergence of
a new set of Dirac points at an energy determined by its wavelength. The new
massless Dirac fermions generated at these superlattice Dirac points are
characterized by a significantly reduced Fermi velocity. The local density of
states near these Dirac cones exhibits hexagonal modulations indicating an
anisotropic Fermi velocity.Comment: 16 pages, 6 figure
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