A simple circuit realization of the tent map

We present a very simple electronic implementation of the tent map, one of the best-known discrete dynamical systems. This is achieved by using integrated circuits and passive elements only. The experimental behavior of the tent map electronic circuit is compared with its numerical simulation counterpart. We find that the electronic circuit presents fixed points, periodicity, period doubling, chaos and intermittency that match with high accuracy the corresponding theoretical valuesComment: 6 pages, 6 figures, 10 references, published versio

Requirement of initial long-range substrate structure in unusual CO pre-oxidation on Pt(111) electrodes

The activation pathway of CO electro-oxidation at low potentials is frequently favored on a catalyst with surface defects. Here, we report a discovery in which an initial long-range substrate structure is required for the activation of an unusual CO pre-oxidation reaction pathway on Pt(111) surfaces which have been flame annealed and then cooled in a CO atmosphere. Different to current understanding about the oxidation of CO on Pt, the activation of this reaction pathway is inhibited as the (111) planes become defect-rich.M.J.S.F and A.A.T. thanks the CAPES (Brazil) Finance Code 001. J.M.F. thanks the MINECO (Spain) CTQ2013-44083-P project

Kinetic characterization of a novel cysteine peptidase from the protozoan Babesia bovis, a potential target for drug design

C1A cysteine peptidases have been shown to play an important role during apicomplexan invasion and egress of host red blood cells (RBCs) and therefore have been exploited as targets for drug development, in which peptidase specificity is deterministic. Babesia bovis genome is currently available and from the 17 putative cysteine peptidases annotated four belong to the C1A subfamily. In this study, we describe the biochemical characterization of a C1A cysteine peptidase, named here BbCp (B. bovis cysteine peptidase) and evaluate its possible participation in the parasite asexual cycle in host RBCs. The recombinant protein was obtained in bacterial inclusion bodies and after a refolding process, presented typical kinetic features of the cysteine peptidase family, enhanced activity in the presence of a reducing agent, optimum pH between 6.5 and 7.0 and was inhibited by cystatins from R. microplus. Moreover, rBbCp substrate specificity evaluation using a peptide phage display library showed a preference for Val > Leu > Phe. Finally, antibodies anti-rBbCp were able to interfere with B. bovis growth in vitro, which highlights the BbCp as a potential target for drug design.Instituto de PatobiologíaFil: Lu, Stephen. Universidade Federal de São Paulo. Escola Paulista de Medicina. Department of Biochemistry; BrasilFil: Ascencio, Mariano E. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Patobiología; ArgentinaFil: Torquato, Ricardo J.S. Universidade Federal de São Paulo. Escola Paulista de Medicina. Department of Biochemistry; BrasilFil: Florin-Christensen, Monica. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Patobiologia; ArgentinaFil: Florin-Christensen, Monica. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Tanaka, Aparecida S. Universidade Federal de São Paulo. Escola Paulista de Medicina. Department of Biochemistry; BrasilFil: Tanaka, Aparecida S. Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular; Brasi

Magnetoresistance Effect in Spin-Polarized Junctions of Ferromagnetically Contacting Multiple Conductive Paths: Applications to Atomic Wires and Carbon Nanotubes

For spin-polarized junctions of ferromagnetically contacting multiple conductive paths, such as ferromagnet (FM)/atomic wires/FM and FM/carbon nanotubes/FM junctions, we theoretically investigate spin-dependent transport to elucidate the intrinsic relation between the number of paths and conduction, and to enhance the magnetoresistance (MR) ratio. When many paths are randomly located between the two FMs, electronic wave interference between the FMs appears, and then the MR ratio increases with increasing number of paths. Furthermore, at each number of paths, the MR ratio for carbon nanotubes becomes larger than that for atomic wires, reflecting the characteristic shape of points in contact with the FM.Comment: 7 pages, 3 figures, accepted for publication in Phys. Rev.

Star formation and environmental quenching of GEEC2 group galaxies at z ∼ 1

We present new analysis from the Group Environment Evolution Collaboration 2 (GEEC2) spectroscopic survey of galaxy groups at 0.8 < z < 1. Our previous work revealed an intermediate population between the star-forming and quiescent sequences and a strong environmental dependence in the fraction of quiescent galaxies. Only ∼5 per cent of star-forming galaxies in both the group and field sample show a significant enhancement in star formation, which suggests that quenching is the primary process in the transition from the star-forming to the quiescent state. To model the environmental quenching scenario, we have tested the use of different exponential quenching time-scales and delays between satellite accretion and the onset of quenching. We find that with no delay, the quenching time-scale needs to be long in order to match the observed quiescent fraction, but then this model produces too many intermediate galaxies. Fixing a delay time of 3 Gyr, as suggested from the local Universe, produces too few quiescent galaxies. The observed fractions are best matched with a model that includes a delay that is proportional to the dynamical time and a rapid quenching time-scale (∼0.25 Gyr), but this model also predicts intermediate galaxies Hδ strength higher than that observed. Using stellar synthesis models, we have tested other scenarios, such as the rejuvenation of star formation in early-type galaxies and a portion of quenched galaxies possessing residual star formation. If environment quenching plays a role in the GEEC2 sample, then our work suggests that only a fraction of intermediate galaxies may be undergoing this transition and that quenching occurs quite rapidly in satellite galaxies (≲0.25 Gyr)

A novel type 1 cystatin involved in the regulation of Rhipicephalus microplus midgut cysteine proteases

Rhipicephalus microplus is a cattle ectoparasite found in tropical and subtropical regions around the world with great impact on livestock production. R. microplus can also harbor pathogens, such as Babesia sp. and Anaplasma sp. which further compromise cattle production. Blood meal acquisition and digestion are key steps for tick development. In ticks, digestion takes place inside midgut cells and is mediated by aspartic and cysteine peptidases and, therefore, regulated by their inhibitors. Cystatins are a family of cysteine peptidases inhibitors found in several organisms and have been associated in ticks with blood acquisition, blood digestion, modulation of host immune response and tick immunity. In this work, we characterized a novel R. microplus type 1 cystatin, named Rmcystatin-1b. The inhibitor transcripts were found to be highly expressed in the midgut of partially and fully engorged females and they appear to be modulated at different days post-detachment. Purified recombinant Rmcystatin-1b displayed inhibitory activity towards typical cysteine peptidases with high affinity. Moreover, rRmcystatin-1b was able to inhibit native R. microplus cysteine peptidases and RNAi-mediated knockdown of the cystatin transcripts resulted in increased proteolytic activity. Moreover, rRmcystatin-1b was able to interfere with B. bovis growth in vitro. Taken together our data strongly suggest that Rmcystatin-1b is a regulator of blood digestion in R. microplus midgut.Fil: Lu, Stephen. Universidade Federal de Sao Paulo; BrasilFil: da Rocha, Leticia A.. Universidade Federal de Sao Paulo; BrasilFil: Torquato, Ricardo J.S.. Universidade Federal de Sao Paulo; BrasilFil: da Silva Vaz Junior, Itabajara. Universidade Federal do Rio Grande do Sul; BrasilFil: Jacobsen, Monica Ofelia. Instituto Nacional de Tecnologia Agropecuaria. Centro de Investigacion En Ciencias Veterinarias y Agronomicas. Instituto de Patobiologia Veterinaria. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Pque. Centenario. Instituto de Patobiologia Veterinaria.; ArgentinaFil: Tanaka, Aparecida S.. Universidade Federal de Sao Paulo; Brasi

Nonuniform Synergistic Effect of Sn and Ru in Site-Specific Catalytic Activity of Pt at Bimetallic Surfaces toward CO Electro-oxidation

This work investigates the mechanisms by which Sn and Ru can improve or inhibit the site-specific catalytic activity of Pt (neighboring or distant from foreign atoms) at bimetallic surfaces. For this purpose, we decorated Pt stepped surfaces (nonequivalent sites) by site-selective electrodeposition of different coverages of either Sn or Ru on (110) Pt steps, forming Snsteps/Pt(hkl) and Rusteps/Pt(hkl) bimetallic surfaces, and we used CO adlayer electro-oxidation as a surface probe reaction, monitored by in situ FTIR and cyclic voltammetry techniques. The results showed that both Sn and Ru selectively accelerated the reaction pathway of CO electro-oxidation only at the (111) Pt terrace sites but importantly played different underlying roles in favoring activity at these active sites. In the case of Snsteps/Pt(hkl) catalysts, the CO adlayer oxidation started at potentials lower than those on Rusteps/Pt(hkl), but Sn only improved the activity at sites on atoms of the first rows of (111) Pt terraces, while the catalytic benefit of Ru seemed to extend further along the (111) Pt terraces. In comparison to unmodified Pt surfaces, Ru did not influence the activity at the line of the (110) Pt steps, while Sn slightly inhibited the activity there, which characterized a slight contrasting effect in catalytic activity at the (111) terraces in comparison to the (110) step sites. In this regard, the chemical modification by irreversible deposition of either Sn or Ru at lines of Pt steps on a stepped Pt surface interestingly resulted in a nonuniform synergistic effect or balancing of energies involving different site-specific catalytic activities at nonequivalent Pt surface sites. Since the electro-oxidation of CO takes place at the (111) Pt terrace sites away from Sn or Ru, and because COads behaves as an immobile species during its oxidation, it is reasonable to assume that the classical bifunctional mechanism completely fails as a model to interpret the enhancement of catalytic activity toward CO electro-oxidation at Snsteps/Pt(hkl) or Rusteps/Pt(hkl) catalysts. The selective alteration in site-specific catalytic activity of Pt was related to (i) the type and coverage of foreign atoms (Sn or Ru) at the lines of Pt steps, (ii) the crystallographic orientation of Pt sites, whether (111) terraces or steps, and (iii) the width of the (111) Pt terraces.M.J.S.F. acknowledges financial support from PNPD/CAPES (Brazil). A.A.T. acknowledges support from CAPES (PROCAD 2013) and CNPq (grant #309066/2013-1). J.M.F. thanks MINECO (Project CTQ2016-76221-P) and GV (Project PROMETEOII/2014/013) for financial support. W.C. is grateful for the award of an F.P.I. grant associated with project CTQ2009-13142

Unraveling the Nature of Active Sites in Ethanol Electro-oxidation by Site-Specific Marking of a Pt Catalyst with Isotope-Labeled 13CO

This works deals with the identification of preferential site-specific activation at a model Pt surface during a multiproduct reaction. The (110)-type steps of a Pt(332) surface were selectively marked by attaching isotope-labeled 13CO molecules to them, and ethanol oxidation was probed by in situ Foureir transfrom infrared spectroscopy in order to precisely determine the specific sites at which CO2, acetic acid, and acetaldehyde were preferentially formed. The (110) steps were active for splitting the C–C bond, but unexpectedly, we provide evidence that the pathway of CO2 formation was preferentially activated at (111) terraces, rather than at (110) steps. Acetaldehyde was formed at (111) terraces at potentials comparable to those for CO2 formation also at (111) terraces, while the acetic acid formation pathway became active only when the (110) steps were released by the oxidation of adsorbed 13CO, at potentials higher than for the formation of CO2 at (111) terraces of the stepped surface.M.J.S.F. is grateful to PNPD/CAPES (Brazil). A.A.T. acknowledges CAPES (PROCAD-2013) and CNPq (309066/2013-1). J.M.F. thanks the MINECO (Spain) project-CTQ2013-44083-P