107,670 research outputs found
Mechanistic Aspects on the Electrografting of Carbon Surfaces by Oxidation of Carboxylates Bearing Unsaturated Groups
No full textThe anodic oxidation of tetrabutylammonium carboxylates bearing aromatic or unsaturated terminal groups is a reaction that allows the covalent grafting of organic moieties on carbon electrodes in acetonitrile as solvent. The electron transfer step is followed by a fast decarboxylation reaction, which releases the respective unsaturated free radicals, whose transient formation at the interface explain the surface grafting phenomenon, however; the lack of grafting during the oxidation of saturated aliphatic carboxylates is unexpected. Therefore, this work shows that the covalent grafting by oxidation of unsaturated carboxylates is favored for a parallel orientation of the radicals on the electrode surface, which is originated by the positive polarization of the electrode and the partially negative electronic density on the terminal unsaturated groups in the radical structure. This orientation is furthermore the result of a previous similar orientation of the unsaturated carboxylates, which is transitorily retained because of the very high rate of the decarboxylation step. Cyclic voltammetry experiments performed using different saturated and unsaturated alkyl-carboxylates, their respective carboxylic acids, as well as the use of ferrocene derivatives as redox probes were used to indirectly support the main conclusions given here
Myoxanthus cereus Luer ex Rojas-Alvarado & Karremans 2017
No full text6. Myoxanthus cereus (Ames) Luer ex Rojas-Alvarado & Karremans (2017: 210). (Fig. 12F) Basionym: Pleurothallis cerea Ames (1923a: 19–20). TYPE:— COSTA RICA. Cartago: Agua Caliente, Lankester 358 (holotype: K, photo of type, illustration of type, AMES!). Distribution:— Costa Rica and Panama. Notes:— Pleurothallis cerea has been commonly placed under the synonymy of M. octomeriae or M. congestus. However, Luer noted differences between the two species, and in 1991 annotated a specimen collected by Endrés from Costa Rica as “ M. cereus (Ames) Luer ”, a combination that he never published. When Soto (2008) revised the taxonomy of the Mexican Myoxanthus, he reduced M. octomeriae, with all its synonyms, to the synonymy of the older M. congestus, a name based on material from Mexico. However, he also noted the odd features of P. cerea, especially in leaf size and shape and lip structure. After studying material of Pleurothallis cerea from Costa Rica, Rojas-Alvarado & Karremans (2017) formally recognized it as a species and transferred it to Myoxanthus. This Central American species is easily distinguished from the closely related M. octomerioides (Mexico), M. congestus (Mexico to Colombia-Venezuela) and M. pulvinatus (Peru and Brazil) by its broad, elliptic to ovate petiolate leaves, and oblong, conspicuously adaxially verrucose, frequently apiculate lip vs. narrow elliptic, sessile leaves and lip not apiculate of the other species (Rojas-Alvarado & Karremans 2017). FIGURE 12. Myoxanthus species. A –C. M. affinis. D. M. antennifer. E. M. ceratothallis. F. M. cereus. G. M. chloe. H–I. M. cimex. J–K. M. colothrix. L. M. conceicionensis. Photographs by: L. Grobler (A). L.E. Yupanqui (B). G. Rojas-Alvarado (C, J, K). A. Karremans (F, G). Ecuagenera (D). R. Parsons (E, L). S. Vieira-Uribe (H). H. R. Ellis (I).Published as part of Rojas-Alvarado, Gustavo, Blanco, Mario A. & Karremans, Adam P., 2021, A taxonomic synopsis and morphological characterization of Myoxanthus (Orchidaceae: Pleurothallidinae), pp. 211-258 in Phytotaxa 507 (3) on pages 231-232, DOI: 10.11646/phytotaxa.507.3.1, http://zenodo.org/record/542572
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
On the origin of the mitochondrial genetic code: Towards a unified mathematical framework for the management of genetic information
Get PDFThe origin of the genetic code represents one of the most challenging problems in molecular evolution. The genetic code is an important universal feature of extant organisms and indicates a common ancestry of different forms of life on earth. Known variants of the genetic code can be mainly divided in mitochondrial and nuclear classes. Here we provide a new insight on the origin of the mitochondrial genetic code: we found that its degeneracy distribution can be explained by using a mathematical approach recently developed for the description of the Euplotes nuclear variant of the genetic code. The results point to a primeval mitochondrial genetic code composed of four base codons, which we call tesserae, that, among other features, exhibit outstanding error detection capabilities. The theoretical description suggests also a formulation of a plausible biological theory about the origin of protein coding. Such theory is based on the symmetry properties of hypothetical primeval chemical adaptors between nucleic acids and amino acids (ancient tRNA’s). Our paper provides a unified mathematical framework for different hypotheses on the origin of genetic coding. Also, it contributes to revisit our present view about the evolutionary steps that led to extant genetic codes by giving a new first-principles perspective on the difficult problem of the origin of the genetic code, and consequently, on the origin of life on earth
MeSH term explosion and author rank improve expert recommendations
Get PDFInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Five New Species of <i>Diplazium</i> Sw. (Athyriaceae) from Nicaragua, Costa Rica and Colombia
No full textFive new species are described in the genus Diplazium Sw. from Nicaragua,
Costa Rica and Colombia, as results of studies in the Neotropical ferns. The
new species are Diplazium chirripoense A. Rojas, Diplazium cornutum A.
Rojas, Diplazium crassirhizoma A. Rojas, Diplazium lustrosum A. Rojas and
Diplazium rodriguezii A. Rojas. The first species is related to D. skutchii Lellinger, but differs from it by having glabrous stipe, glabrous blade abaxially,
hyaline and entire indusia, and distributed and higher elevations. The second
species is different to D. diplazioides (Klotzsch et H. Karst.) Alston by having
densely scaly stipe, rachis and costa, relative bigger pinnae and entire to erose
indusia. After that, the third species differs from D. werckleanum Christ by
thicker rhizome, bigger rhizome scales and blade with 1 - 2 [1] buds at apex.
Consecutively, the fourth species differs from D. lindbergii (Mett.) H. Christ
by thinner rhizome, shorter fronds, longer stipe, smaller blade, less pinnae
pairs, shiny laminar tissue and veins 3 - 5 pairs per segment. Finally, the fifth
species is related to D. tungurahuae (Sodiro) C. Chr., but with abaxially
glabrous rachis and costae, pinnules 4 - 5 times longer than wide and entire,
costules adaxially without wings, veins abaxially glabrous and reticulate along
costae and between pinnate veins.Se describen cinco nuevas especies en el género Diplazium Sw. de Nicaragua,
Costa Rica y Colombia, como resultados de estudios en los helechos Neotropicales. El
nuevas especies son Diplazium chirripoense A. Rojas, Diplazium cornutum A.
Rojas, Diplazium crassirhizoma A. Rojas, Diplazium lustrosum A. Rojas y
Diplazium rodriguezii A. Rojas. La primera especie está relacionada con D. skutchii Lellinger, pero se diferencia de ella por tener un estípite glabro, una lámina glabra en la parte inferior,
indusia hialina y entera, y elevaciones distribuidas y más altas. El segundo
especie es diferente a D. diplazioides (Klotzsch et H. Karst.) Alston por tener
estípite densamente escamoso, raquis y costa, pinnas relativamente más grandes y enteras para erosionar
industria Después de eso, la tercera especie se diferencia de D. werckleanum Cristo por
rizoma más grueso, escamas de rizoma más grandes y hoja con 1 - 2 [1] yemas en el ápice.
Consecutivamente, la cuarta especie difiere de D. lindbergii (Mett.) H. Christ
por rizoma más delgado, frondas más cortas, estípite más largo, lámina más pequeña, menos pinnas
pares, tejido laminar brillante y venas 3 - 5 pares por segmento. Finalmente, el quinto
especie está relacionada con D. tungurahuae (Sodiro) C. Chr., pero con abaxialmente
raquis y costas glabros, pínnulas 4 - 5 veces más largas que anchas y enteras,
Costules adaxialmente sin alas, venas baxialmente glabras y reticuladas a lo largo
costae y entre las venas pinnadas.Universidad Nacional, Costa RicaEscuela de Ciencias Biológica
FIGURE 4 in Stingless bees of the genus Nannotrigona Cockerell (Hymenoptera: Apidae Meliponini) in Colombia
No full textFIGURE 4. Male paratype of Nannotrigona gaboi Jaramillo, Ospina & Gonzalez, n. sp. a = Facial view. b = Lateral habitus. c = Dorsal habitus. d = Fifth sternum. e = Sixth sternum. f = Seventh sternum. g = Eighth sternum. h = genital capsule (a–c: LABUN12529; d–h: LABUN12584).Published as part of Jaramillo, Joanna, Ospina, Rodulfo & Gonzalez, Victor H., 2019, Stingless bees of the genus Nannotrigona Cockerell (Hymenoptera: Apidae Meliponini) in Colombia, pp. 349-365 in Zootaxa 4706 (2) on page 356, DOI: 10.11646/zootaxa.4706.2.8, http://zenodo.org/record/356745
H/D Isotope Effects Reveal Factors Controlling Catalytic Activity in Co-Based Oxides for Water Oxidation
No full textUnderstanding the mechanism for electrochemical water oxidation is important for the development of more efficient catalysts for artificial photosynthesis. A basic step is the proton-coupled electron transfer, which enables accumulation of oxidizing equivalents without buildup of a charge. We find that substituting deuterium for hydrogen resulted in an 87% decrease in the catalytic activity for water oxidation on Co-based amorphous-oxide catalysts at neutral pH, while 160-to-180 substitution lead to a 10% decrease. In situ visible and quasi-in situ X-ray absorption spectroscopy reveal that the hydrogen-to-deuterium isotopic substitution induces an equilibrium isotope effect that shifts the oxidation potentials positively by approximately 60 mV for the proton coupled Co-II/III and Co-II/III electron transfer processes. Time resolved spectroelectrochemical measurements indicate the absence of a kinetic isotope effect, implying that the precatalytic proton-coupled electron transfer happens through a stepwise mechanism in which electron transfer is rate-determining. An observed correlation between Co oxidation states and catalytic current for both isotopic conditions indicates that the applied potential has no direct effect on the catalytic rate, which instead depends exponentially on the average Co oxidation state. These combined results provide evidence that neither proton nor electron transfer is involved in the catalytic rate-determining step. We propose a mechanism with an active species composed by two adjacent Cow atoms and a rate-determining step that involves oxygen oxygen bond formation and compare it with models proposed in the literature
First record of the orchid bee genus Eufriesea Cockerell (Hymenoptera: Apidae: Euglossini) in the United States
No full textGriswold, Terry, Herndon, James D., Gonzalez, Victor H. (2015): First record of the orchid bee genus Eufriesea Cockerell (Hymenoptera: Apidae: Euglossini) in the United States. Zootaxa 3957 (3): 342-346, DOI: 10.11646/zootaxa.3957.3.
Myoxanthus pennellius Rojas-Alv. & Karremans, comb. nov.
No full text38. Myoxanthus pennellius (Luer) Rojas-Alv. & Karremans, comb. nov. (Fig. 17E) Basionym: Pleurothallis pennellia Luer (1976b: 160–161). TYPE:— ECUADOR. Pastaza: epiphytic in felled trees about 20 km east of Puyo, ca. 600 m, 28 Jul 1975, Luer et al. 687 (holotype: SELspirit; illustration in Luer 1976b as f. 183!). FIGURE 17. Myoxanthus species. A. M. panamense. B – C. M. parahybuensis. D. M. parvilabius. E. M. pennellius. F. M. priapus. G. M. pulvinatus. H – J. M. punctatus. K – L. M. reymondii. Photographs by: L. Nauheimer (A). G. Rojas-Alvarado (B, C). S. Moreno (D). A. Hirtz (E). Y. Dewèvre (F). M. Rosim (G). J. Gastin (H). R. Stalder (I). L. F. Varella (J). R. Parsons (K). J. Riksen (L). Distribution: — Ecuador and perhaps Peru (see below). Notes:— Pleurothallis pennellia was described from Ecuador on the basis of a specimen that flowered in cultivation at the Marie Selby Botanical Gardens (Luer 1976b). Luer compared it with M. scandens, but described it as having a much less prolific plant. The plant that served as type of P. pennellia eventually became prolific in cultivation, just like specimens of M. scandens, prompting Luer (1992) to place it under the synonymy of that species (Luer 1992). However, based on the original description and illustration of the type, even with the prolific habit, M. pennellius is still easily distinguished from M. scandens. It differs from M. scandens in its sepals with an obtuse to rounded apex vs. acute, narrowly ovate petals slightly contracted above the middle, vs. wider basally then conspicuously contracted into a thickened apex and a lip with two longitudinal lamellae above the middle vs. with two longitudinal lamellae from the base to near the apex, a short clinandrium vs. long-hooded. None of the specimens of M. scandens studied here shares any of these features. We agree with Pupulin et al. (2010) that the photo of a Peruvian plant labelled M. scandens in Zelenko & Bermúdez (2008) fits the description of M. pennellius.Published as part of Rojas-Alvarado, Gustavo, Blanco, Mario A. & Karremans, Adam P., 2021, A taxonomic synopsis and morphological characterization of Myoxanthus (Orchidaceae: Pleurothallidinae), pp. 211-258 in Phytotaxa 507 (3) on pages 244-247, DOI: 10.11646/phytotaxa.507.3.1, http://zenodo.org/record/542572
- …
