Ternary and quaternary oxides of Bi, Sr, and Cu

Before the discovery of superconductivity in an oxide of Bi, Sr, and Cu, the system Bi-Sr-Cu-O had not been studied, although several solid phases had been identified in the two-component regions of the ternary system Bi2O3-SrO-CuO. The oxides Sr2CuO3, SrCu2O2, SrCuO2, and Bi2CuO4 were then well known and characterized, and the phase diagram of the binary system Bi2O3 -SrO had been established in the temperature range 620 to 1000 C. Besides nine solutions of compositions Bi(2-2x) Sr(x) O(3-2x) and different symmetries, this diagram includes three definite compounds of stoichiometries Bi(2)SrO4, Bi2Sr2O5, and Bi2Sr3O6 (x = 0.50, 0.67 and 0.75 respectively), only the second of which with known unit-cell of orthorhombic symmetry, dimensions (A) a = 14.293(2), b = 7.651(2), c = 6.172(1), and z = 4. The first superconducting oxide in the system Bi-Sr-Cu-O was initially formulated as Bi2Sr2Cu2O(7+x), with an orthorhombic unit-cell of parameters (A) a = 5.32, b = 26.6, c = 48.8. In a preliminary study the same oxide was formulated with half the copper content, Bi(2)Sr(2)CuO(6+x), and indexed its reflections assuming an orthorhombic unit-cell of dimensions (A) a = 5.390(2), b = 26.973(8), c = 24.69(4). Subsequent studies by diffraction techniques have confirmed the composition 2:2:1. A new family of oxygen-deficient perovskites, was characterized, after identifying by x ray diffraction the phases present in the products of thermal treatments of about 150 mixtures of analytical grade Bi2O3, Sr(OH)2-8H2O and CuO at different molar ratios. X ray diffraction data are presented for some other oxides of Bi and Sr, as well as for various quaternary oxides, among them an oxide of Bi, Sr, and Cu

Dynamical stability criterion for inhomogeneous quasi-stationary states in long-range systems

We derive a necessary and sufficient condition of linear dynamical stability for inhomogeneous Vlasov stationary states of the Hamiltonian Mean Field (HMF) model. The condition is expressed by an explicit disequality that has to be satisfied by the stationary state, and it generalizes the known disequality for homogeneous stationary states. In addition, we derive analogous disequalities that express necessary and sufficient conditions of formal stability for the stationary states. Their usefulness, from the point of view of linear dynamical stability, is that they are simpler, although they provide only sufficient criteria of linear stability. We show that for homogeneous stationary states the relations become equal, and therefore linear dynamical stability and formal stability become equivalent.Comment: Submitted to Journal of Statistical Mechanics: Theory and Experimen

Long-Range Effects in Layered Spin Structures

We study theoretically layered spin systems where long-range dipolar interactions play a relevant role. By choosing a specific sample shape, we are able to reduce the complex Hamiltonian of the system to that of a much simpler coupled rotator model with short-range and mean-field interactions. This latter model has been studied in the past because of its interesting dynamical and statistical properties related to exotic features of long-range interactions. It is suggested that experiments could be conducted such that within a specific temperature range the presence of long-range interactions crucially affect the behavior of the system

Antisense reduction of thylakoidal ascorbate peroxidase in Arabidopsis enhances Paraquat-induced photooxidative stress and Nitric Oxide-induced cell death

The production and characterization of Arabidopsis plants containing a transgene in which the Arabidopsis tAPX is inserted in antisense orientation, is described. tAPX activity in these transgenic tAPX plants is around 50% of control level. The tAPX antisense plants are phenotypically indistinguishable from control plants under normal growth conditions; they show, however, enhanced sensitivity to the O 2- -generating herbicide, Paraquat. Interestingly, the tAPX antisense plants show enhanced symptoms of damage when cell death is triggered through treatment with the nitric oxide-donor, SNP. These results are in accordance with the ones recently obtained with transgenic plants overexpressing tAPX; altogether, they suggest that tAPX, besides the known ROS scavenging role, is also involved in the fine changes of H 2O2 concentration during signaling events

An intrinsic timer specifies distal structures of the vertebrate limb

How the positional values along the proximo-distal axis (stylopod-zeugopod-autopod) of the limb are specified is intensely debated. Early work suggested that cells intrinsically change their proximo-distal positional values by measuring time. Recently, however, it is suggested that instructive extrinsic signals from the trunk and apical ectodermal ridge specify the stylopod and zeugopod/autopod, respectively. Here, we show that the zeugopod and autopod are specified by an intrinsic timing mechanism. By grafting green fluorescent protein-expressing cells from early to late chick wing buds, we demonstrate that distal mesenchyme cells intrinsically time Hoxa13 expression, cell cycle parameters and the duration of the overlying apical ectodermal ridge. In addition, we reveal that cell affinities intrinsically change in the distal mesenchyme, which we suggest results in a gradient of positional values along the proximo-distal axis. We propose a complete model in which a switch from extrinsic signalling to intrinsic timing patterns the vertebrate limb

Patterns in the Fermion Mixing Matrix, a bottom-up approach

We first obtain the most general and compact parametrization of the unitary transformation diagonalizing any 3 by 3 hermitian matrix H, as a function of its elements and eigenvalues. We then study a special class of fermion mass matrices, defined by the requirement that all of the diagonalizing unitary matrices (in the up, down, charged lepton and neutrino sectors) contain at least one mixing angle much smaller than the other two. Our new parametrization allows us to quickly extract information on the patterns and predictions emerging from this scheme. In particular we find that the phase difference between two elements of the two mass matrices (of the sector in question) controls the generic size of one of the observable fermion mixing angles: i.e. just fixing that particular phase difference will "predict" the generic value of one of the mixing angles, irrespective of the value of anything else.Comment: 29 pages, 3 figures, references added, to appear in PR

Influence of hydrodynamics on many-particle diffusion in 2D colloidal suspensions

We study many-particle diffusion in 2D colloidal suspensions with full hydrodynamic interactions through a novel mesoscopic simulation technique. We focus on the behaviour of the effective scaled tracer and collective diffusion coefficients $D_T(\rho) / D_0$ and $D_C(\rho) / D_0$, where $D_0$ is the single-particle diffusion coefficient, as a function of the density of the colloids $\rho$. At low Schmidt numbers $Sc={\cal O}(1)$, we find that hydrodynamics has essentially no effect on the behaviour of $D_T(\rho)/D_0$. At larger $Sc$, $D_T(\rho)/D_0$ is enhanced at all densities, although the differences compared to the case without hydrodynamics are minor. The collective diffusion coefficient, on the other hand, is much more strongly coupled to hydrodynamical conservation laws and is distinctly different from the purely dissipative case

Sound-propagation gap in fluid mixtures

We discuss the behavior of the extended sound modes of a dense binary hard-sphere mixture. In a dense simple hard-sphere fluid the Enskog theory predicts a gap in the sound propagation at large wave vectors. In a binary mixture the gap is only present for low concentrations of one of the two species. At intermediate concentrations sound modes are always propagating. This behavior is not affected by the mass difference of the two species, but it only depends on the packing fractions. The gap is absent when the packing fractions are comparable and the mixture structurally resembles a metallic glass.Comment: Published; withdrawn since ordering in archive gives misleading impression of new publicatio

Inspecting the potential physiological and biomedical value of 44 conserved uncharacterised proteins of Streptococcus pneumoniae

BACKGROUND: The major Gram-positive coccoid pathogens cause similar invasive diseases and show high rates of antimicrobial resistance. Uncharacterised proteins shared by these organisms may be involved in virulence or be targets for antimicrobial therapy. RESULTS: Forty four uncharacterised proteins from Streptococcus pneumoniae with homologues in Enterococcus faecalis and/or Staphylococcus aureus were selected for analysis. These proteins showed differences in terms of sequence conservation and number of interacting partners. Twenty eight of these proteins were monodomain proteins and 16 were modular, involving domain combinations and, in many cases, predicted unstructured regions. The genes coding for four of these 44 proteins were essential. Genomic and structural studies showed one of the four essential genes to code for a promising antibacterial target. The strongest impact of gene removal was on monodomain proteins showing high sequence conservation and/or interactions with many other proteins. Eleven out of 40 knockouts (one for each gene) showed growth delay and 10 knockouts presented a chaining phenotype. Five of these chaining mutants showed a lack of putative DNA-binding proteins. This suggest this phenotype results from a loss of overall transcription regulation. Five knockouts showed defective autolysis in response to penicillin and vancomycin, and attenuated virulence in an animal model of sepsis. CONCLUSIONS: Uncharacterised proteins make up a reservoir of polypeptides of different physiological importance and biomedical potential. A promising antibacterial target was identified. Five of the 44 examined proteins seemed to be virulence factors.This work was supported by a Miguel Servet Research contract funded by the Fondo de Investigación Sanitaria (Ministerio de Economía y Competitividad de España) to Antonio J. Martin-Galiano, a Plan Nacional de I + D + I of Ministerio de Ciencia e Innovación grant (BIO2011-25343) to Adela G. de la Campa, and funds from the CIBER Enfermedades Respiratorias group (an initiative of the Instituto de Salud Carlos III).S

Modeling and control with friction compensation of a pendubot system

[EN] The pendubot is a two degree of freedom mechanical underactuated system that is used as an educational and research platform in the areas of robotics and control. It is considered as an  underactuated system because it has only one control input. Although several control laws have been applied to stabilize the pendubot, most of them neglect the effects of friction. In this article, the analysis is different, since it is considered a pendubot system in which the actuated joint has a significant amount of friction that cannot be neglected. First, we review some of the existing friction models in the literature, including one that was recently proposed by the authors. Then we describe the implementation of some stabilization controllers that compensate for the effects of friction. Finally, an exhaustive comparison of the presented friction compensators is made to improve the performance of a real pendubot system.[ES] El pendubot es un sistema mecánico subactuado de dos grados de libertad que comúnmente se utiliza como plataforma educacional y de investigación en las áreas de robótica y control. Se le considera como un sistema subactuado debido a que sólo cuenta con una entrada de control. Aunque se han aplicado distintas leyes de control para estabilizar el pendubot, la mayoría de ellas desprecian los efectos de fricción. En este artículo el análisis es diferente, ya que se considera un sistema pendubot en el que la articulación actuada tiene una cantidad de fricción significativa, que no se puede despreciar. En primer lugar, se revisan algunos modelos de fricción existentes en la literatura, incluyendo uno que fue propuesto por los autores recientemente. Después, se describe la implementación de algunos controladores de estabilización que compensan los efectos de la fricción. Por ultimo, se hace una comparación exhaustiva de los compensadores de fricción presentados para mejorar el desempeno de un sistema pendubot real.Este trabajo fue apoyado parcialmente por el Tecnológico Nacional de México y la Universidad Autónoma de Ciudad Juárez.Soto, I.; Campa, R.; Sánchez-Mazuca, S. (2020). Modelado y control con compensación de fricción de un sistema pendubot. Revista Iberoamericana de Automática e Informática industrial. 18(1):39-47. https://doi.org/10.4995/riai.2020.13083OJS3947181Armstrong-Helouvry, B., 1991. Control of Machines with Friction. Kluwer Academic Publishers. https://doi.org/10.1007/978-1-4615-3972-8Canudas de Wit, C., Olson, H., Astrom, K., Lischinsky, P., 1995. 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Wear 24, 381-385. https://doi.org/10.1016/0043-1648(73)90166-XMa, X. Q., Su, C. Y., 2002. A new fuzzy approach for swing up control of pendubot. In: Proceedings of the American Control Conference. Anchorage, AK, USA.Morin, A., 1833. New friction experiments carried out at Metz in 1831-1833. Proceedings of the French Royal Academy of Sciences 4, 1-128.O'Flaherty, R. W., Sanfelice, R. G., Teel, A. R., 2008. Hybrid control strategy for robust global swing-up of the pendubot. In: Proceedings of the American Control Conference. Seattle, WA, USA. https://doi.org/10.1109/ACC.2008.4586692Rabinowics, E., 1956. Stick and slip. Scientific American 194, 109-118. https://doi.org/10.1038/scientificamerican0256-109Sanchez-Mazuca, S., Campa, R., 2013. An improvement proposal to the static friction model. Mathematical Problems in Engineering 2013. https://doi.org/10.1155/2013/946526Sanchez-Mazuca, S., Soto, I., Campa, R., 2015. Modeling and control of a pendubot with static friction. In: Cecarelli, M., Hernandez Martínez, E. E. (Eds.), Multibody Mechatronic Systems: Proceedings of the MUSME Conference held in Huatulco, Mexico, October 21-24, 2014. Springer, pp. 229- 240. https://doi.org/10.1007/978-3-319-09858-6_22Spong, M. W., Block, D. J., 1995. The pendubot: a mechatronic system for control research and education. In: Proceedings of the IEEE Conference on Decision and Control. New Orleans, LA, USA.Stribeck, R., 1902. The key qualities of sliding and rolling bearings. (in German) Zeitschrift Des Vereins Deutscher Ingenieure 46, 1342-1348.Wang, W., Yi, J., Zhao, D., Liu, X., 2004. Adaptive sliding mode controller for an underactuated manipulator. In: Proceedings of the International Conference on Machine Learning and Cybernetics. Shangai, China.Xin, X., Kaneda, M., Oki, T., 2002. The swing-up control for the pendubot based on energy control approach. In: Proceeding of the IFAC World Congress. Barcelona, Spain. https://doi.org/10.3182/20020721-6-ES-1901.00889Zhang, M. J., Tarn, T. J., 2002. Hybrid control of the pendubot. IEEE Transactions on Mechatronics 7, 79-86. https://doi.org/10.1109/3516.99089