Hopf Bifurcations in a Watt Governor With a Spring

This paper pursues the study carried out by the authors in "Stability and Hopf bifurcation in a hexagonal governor system", focusing on the codimension one Hopf bifurcations in the hexagonal Watt governor differential system. Here are studied the codimension two, three and four Hopf bifurcations and the pertinent Lyapunov stability coefficients and bifurcation diagrams, ilustrating the number, types and positions of bifurcating small amplitude periodic orbits, are determined. As a consequence it is found an open region in the parameter space where two attracting periodic orbits coexist with an attracting equilibrium point.Comment: 30 pages and 7 figure

Proposal of Flowable Fill Designs for improvement of excavation and filling works of trenches in sanitation systems

Population grow in recent years requires an extension of the current pipeline sanitary system. For this purpose, granular excavation and landfill works are associated with pedestrian traffic congestion. Therefore, it is necessary to develop an innovative and sustainable alternative to reduce the problems generated during the execution of the conventional process. This research proposes the use of flowable fill due to the multiple advantages offered by this material. On the one hand, it is economical for medium to large trench fill volumes, considering savings in labor (it is done with a small number of workers), in equipment (does not require the rental or purchase of compaction equipment) and in time (the pouring is done by directly pumping the mixture, from the mixing machines to the excavation). On the other hand, being self-compacting and self-leveling decreases the width of the trenches, reducing excavation and filling volumes; which, in turn, incur money savings. Also, this material guarantees work safety, since people are not required inside the excavation and fill in poorly accessible areas without any problem. Dosages were established for ten flowable fill mixtures with cement contents of 50, 60, 70, 80 and 90 kg of cement and a range of admixture from 1.75 to 2.00%; The results indicated that decreasing the fine aggregate - coarse aggregate ratio, the compressive strength of the mixtures increases and the slumps of the mixtures decreases, and the compressive strength increases directly proportional to the cement content

Equatorial outflows driven by jets in Population III microquasars

Binary systems of Population III can evolve to microquasars when one of the stars collapses into a black hole. When the compact object accretes matter at a rate greater than the Eddington rate, powerful jets and winds driven by strong radiation pressure should form. We investigate the structure of the jet-wind system for a model of Population III microquasar on scales beyond the jet-wind formation region. Using relativistic hydrodynamic simulations we find that the ratio of kinetic power between the jet and the disk wind determines the configuration of the system. When the power is dominated by the wind, the jet fills a narrow channel, collimated by the dense outflow. When the jet dominates the power of the system, part of its energy is diverted turning the wind into a quasi-equatorial flow, while the jet widens. From the results of our simulations, we implement semi-analytical calculations of the impact of the quasi-equatorial wind on scales of the order of the size of the binary system. Our results indicate that Population III microquasars might inject gamma rays and relativistic particles into the early intergalactic medium, contributing to its reionization at large distances from the binary system

Polyphenols and Novel Insights Into Post-kidney Transplant Complications and Cardiovascular Disease:A Narrative Review

Kidney transplantation is the preferred treatment for end-stage kidney disease. It is, however, not devoid of complications. Delayed graft function related to ischemia-reperfusion injury (IRI), calcineurin inhibitor (CNI) nephrotoxicity, diabetes, and a particularly high-rate cardiovascular disease (CVD) risk, represent important complications following kidney transplantation. Oxidative stress and chronic low-grade inflammation are mechanisms of disease incompletely abrogated in stable kidney transplant recipient (KTR), contributing to the occurrence of these complications. Polyphenols, bioactive compounds with recognized antioxidant and anti-inflammatory properties have been strongly associated with prevention of CVD in the general population and have been shown to decrease IRI and antagonize CNI nephrotoxicity in animal experimental models, therefore they may have a role in prevention of complications in KTR. This narrative review aims to summarize and discuss current evidence on different polyphenols for prevention of complications, particularly prevention of CVD in KTR, pointing toward the need of further studies with potential clinical impact

Els residus són recursos amb Rafael Luque

El Departament de Química de la UAB ha organitzat recentment la tercera edició de les "Jornades Doctorals", en què es pretén interrelacionar la recerca doctoral que es porta a terme en aquest departament amb les iniciatives empresarials en el món de la química. En aquest marc, el Doctor Rafael Luque va impartir una conferència sobre la valorització dels residus. L'any 2012, Luque va ser considerat un dels 10 innovadors menors de 35 anys pel Massachusets Institute of Technology pel descobriment d'una nova família de materials anomenats Starbon. Actualment, és professor a la universitat de Còrdova i gestiona dues empreses relacionades amb aquests materials. En aquesta entrevista, Luque ens explica com les tecnologies que ha descobert permeten transformar els residus orgànics en materials amb valor econòmic i sobre la seva experiència com a emprenedor en el món de la ciència.El Departamento de Química de la UAB ha organizado recientemente la tercera edición de las "Jornadas Doctorales", en las que se pretende interrelacionar la investigación doctoral que se lleva a cabo en este departamento con las iniciativas empresariales en el mundo de la química. En este marco, el Doctor Rafael Luque impartió una conferencia sobre la valorización de los residuos. En 2012, Luque fue considerado uno de los 10 innovadores menores de 35 años por el Massachusets Institute of Technology por el descubrimiento de una nueva familia de materiales llamados Starbon. Actualmente, es profesor en la universidad de Córdoba y gestiona dos empresas relacionadas con estos materiales. En esta entrevista, Luque nos explica cómo las tecnologías que ha descubierto permiten transformar los residuos orgánicos en materiales con valor económico y sobre su experiencia como emprendedor en el mundo de la ciencia

High-capacity Li4Ti5O12-C thick ceramic electrodes manufactured by powder injection moulding

Lithium-ion batteries are the most efficient electrochemical energy storage devices. However, there is still room for improvement in terms of safety and energy density, presently limited by conventional tape-casting electrode processing. In this study, a blend of the anodic material Li$_{4}$Ti$_{5}$O$_{12}$ with 2 wt% carbon black has been processed through powder injection moulding (PIM) yielding, after subsequent debinding and sintering processes, to ultra-thick (>500 µm) ceramic binder-free electrodes. The mixture of Li$_{4}$Ti$_{5}$O$_{12}$ with the thermoplastic binder composed of polypropylene, paraffin wax, and stearic acid is investigated to identify a rheologically suitable feedstock for the PIM process. The resulting disk-type green parts contain 50 vol% of ceramic powder. After removing the binder with solvents and subsequent thermal treatment, the parts are sintered at 900 °C, aiming for a relatively high porosity, i.e., 25.7%. The resulting electrodes show very high areal and volumetric capacities up to 26.0 mA·h·cm−2 and 403 mA·h·cm−3 at C/24, respectively, in a half-cell against lithium metal

High-performance Ni-YSZ thin-walled microtubes for anode-supported solid oxide fuel cells obtained by powder extrusion moulding

Aiming at the fabrication of microtubular anode-supports for Solid Oxide Fuel Cell (SOFC) applications, this contribution deals with the production of Ni-YSZ thin-walled tubes (<1 mm thickness) via Powder Extrusion Moulding (PEM). The overall method has been optimized with an emphasis on the effect of NiO particle size using two commercial NiO powders with mean sizes of 0.7 and 8 μm. A thermoplastic binder system based on polypropylene (PP), paraffin wax (PW) and stearic acid (SA) in volume ratios of 50, 46 and 4, respectively, was used along with corn starch as a pore forming agent. Different feedstocks with solid loadings varying from 45 to 65 vol% were processed and characterized to determine the optimal formulation. Typically, the mixtures exhibited a pseudoplastic behaviour from 100 to 1000 s. Feedstocks with finer NiO particles had the most balanced properties for PEM purposes and an optimal powder volume content of 65 vol% was established. After extrusion and debinding steps, defect-free and constant cross-section tubes with 15 mm of length and 4 mm of nominal diameter were obtained. The final microstructure and DC conductivity were found to be closely linked to the NiO particle size, yielding a higher degree of open porosity and a better performance when using finer NiO powder. Based on this study, the packing mechanism was found to be likely limited by the contribution of steric hindrances when dissimilar and coarse powders are mixed, which may play a decisive role in order to set tailored formulations.Authors would like to thank financial support received from MICINN and Feder program of the European Community (MAT2013-46452-C4-3R and MAT2012-30763 projects), and Madrid regional government (MATERYENER3CM S2013/MIT-2753 Program).Peer Reviewe

Comparison of Zn_{1-x}Mn_xTe/ZnTe multiple-quantum wells and quantum dots by below-bandgap photomodulated reflectivity

Large-area high density patterns of quantum dots with a diameter of 200 nm have been prepared from a series of four Zn_{0.93}Mn_{0.07}Te/ZnTe multiple quantum well structures of different well width (4 nm, 6 nm, 8 nm and 10 nm) by electron beam lithography followed by Ar+ ion beam etching. Below-bandgap photomodulated reflectivity spectra of the quantum dot samples and the parent heterostructures were then recorded at 10 K and the spectra were fitted to extract the linewidths and the energy positions of the excitonic transitions in each sample. The fitted results are compared to calculations of the transition energies in which the different strain states in the samples are taken into account. We show that the main effect of the nanofabrication process is a change in the strain state of the quantum dot samples compared to the parent heterostructures. The quantum dot pillars turn out to be freestanding, whereas the heterostructures are in a good approximation strained to the ZnTe lattice constant. The lateral size of the dots is such that extra confinement effects are not expected or observed.Comment: 23 pages, LaTeX2e (amsmath, epsfig), 7 EPS figure

Piecewise smooth systems near a co-dimension 2 discontinuity manifold: can one say what should happen?

We consider a piecewise smooth system in the neighborhood of a co-dimension 2 discontinuity manifold $\Sigma$. Within the class of Filippov solutions, if $\Sigma$ is attractive, one should expect solution trajectories to slide on $\Sigma$. It is well known, however, that the classical Filippov convexification methodology is ambiguous on $\Sigma$. The situation is further complicated by the possibility that, regardless of how sliding on $\Sigma$ is taking place, during sliding motion a trajectory encounters so-called generic first order exit points, where $\Sigma$ ceases to be attractive. In this work, we attempt to understand what behavior one should expect of a solution trajectory near $\Sigma$ when $\Sigma$ is attractive, what to expect when $\Sigma$ ceases to be attractive (at least, at generic exit points), and finally we also contrast and compare the behavior of some regularizations proposed in the literature. Through analysis and experiments we will confirm some known facts, and provide some important insight: (i) when $\Sigma$ is attractive, a solution trajectory indeed does remain near $\Sigma$, viz. sliding on $\Sigma$ is an appropriate idealization (of course, in general, one cannot predict which sliding vector field should be selected); (ii) when $\Sigma$ loses attractivity (at first order exit conditions), a typical solution trajectory leaves a neighborhood of $\Sigma$; (iii) there is no obvious way to regularize the system so that the regularized trajectory will remain near $\Sigma$ as long as $\Sigma$ is attractive, and so that it will be leaving (a neighborhood of) $\Sigma$ when $\Sigma$ looses attractivity. We reach the above conclusions by considering exclusively the given piecewise smooth system, without superimposing any assumption on what kind of dynamics near $\Sigma$ (or sliding motion on $\Sigma$) should have been taking place.Comment: 19 figure