1,302 research outputs found
Dynamic model of a railway wheelset for corrugation problem analysis
[EN] In the present work a model of flexible shafts is adapted for modelling the railway wheelset. The dynamic properties of the solid are obtained from a solid finite element model of a real wheelset. The model adopts an Eulerian coordinate set for numerical efficiency. Results of the crossed-receptance and mobility functions are presented, where the excitation is the vertical wheel-rail contact force and the displacement (or velocity) is measured in the wheel-rail contact plane. These results let us know that the gyroscopic effect may contribute to define the wavelength-fixing mechanism in some corrugation problems, even if the train speed is low.This work was sponsored by Projects T79/2006 (Ministerio de Fomento - Metro de Madrid- CDM) and TRA2007-67167 (Ministerio de Educación y Ciencia - FEDER).Vila Tortosa, MP.; Rovira, A.; Fayos Sancho, J.; Baeza González, LM. (2009). Dynamic model of a railway wheelset for corrugation problem analysis. Noise & Vibration Worldwide. 40(11):10-18. https://doi.org/10.1260/095745609790251579S1018401
Time-Energy Tradeoffs for Evacuation by Two Robots in the Wireless Model
Two robots stand at the origin of the infinite line and are tasked with
searching collaboratively for an exit at an unknown location on the line. They
can travel at maximum speed and can change speed or direction at any time.
The two robots can communicate with each other at any distance and at any time.
The task is completed when the last robot arrives at the exit and evacuates. We
study time-energy tradeoffs for the above evacuation problem. The evacuation
time is the time it takes the last robot to reach the exit. The energy it takes
for a robot to travel a distance at speed is measured as . The
total and makespan evacuation energies are respectively the sum and maximum of
the energy consumption of the two robots while executing the evacuation
algorithm.
Assuming that the maximum speed is , and the evacuation time is at most
, where is the distance of the exit from the origin, we study the
problem of minimizing the total energy consumption of the robots. We prove that
the problem is solvable only for . For the case , we give an
optimal algorithm, and give upper bounds on the energy for the case .
We also consider the problem of minimizing the evacuation time when the
available energy is bounded by . Surprisingly, when is a
constant, independent of the distance of the exit from the origin, we prove
that evacuation is possible in time , and this is optimal up
to a logarithmic factor. When is linear in , we give upper bounds
on the evacuation time.Comment: This is the full version of the paper with the same title which will
appear in the proceedings of the 26th International Colloquium on Structural
Information and Communication Complexity (SIROCCO'19) L'Aquila, Italy during
July 1-4, 201
Reproductive Biology and Recruitment of Xiphopenaeus kroyeri in a Marine Protected Area in the Western Atlantic: Implications for Resource Management
The potential of a recently established marine protected area (MPA) in the Western Atlantic, Brazil, as a \u27seed production\u27 and nursery ground for Xiphopenaeus kroyeri, an intensively exploited penaeid shrimp, was investigated in an attempt to reveal any future benefit of this new MPA to adjacent populations experiencing heavy exploitation. Overall, we observed that males and females \u3e12 and 20 mm carapace length, respectively, contributed the most to reproduction in the studied population. Reproductive activity of X. kroyeri was continuous at the MPA; 2 annual reproductive peaks were recorded from March to April and from November to December, which were followed by recruitment events occurring from March to April 2009 and November 2009. Sediment, temperature, and algae and plant biomass floating near the bottom were relevant in driving reproductive activity and recruitment in X. kroyeri. The high reproductive potential of the studied population and the occurrence of abundant juveniles throughout the sampling area, indicating the existence of a nursery ground within the region, suggest that this MPA might provide important benefits in the near future. We argue in favor of future long-term studies on the larval dispersion, reproductive biology and ecology of X. kroyeri in MPAs and non-MPAs to construct a base for future management of this species and to aid stock recovery in fishing areas that are heavily exploited
Pseudosubluxación C2-C3: un hallazgo radiológico frecuente en la infancia
Objetivo: Mostrar un hallazgo radiológico fisiológico de la columna cervical infantil que tiende a ser
malinterpretado como patológico: la pseudosubluxación C2-C3. Se presenta un caso de una niña de 14 meses de edad
remitida a nuestro centro bajo sospecha de subluxación C2-C3. Se aporta una metodología para el diagnóstico diferencial
entre pseudosubluxación C2-C3 y subluxación C2-C3 verdadera. Una anamnesis detallada así como una
exploración clínica y radiográfica minuciosas, permiten establecer el diagnóstico en la mayoría de los casos. La normal
movilidad en flexión de C2 sobre C3 en la columna cervical infantil puede ser tan pronunciada que llegue a confundirse
con una lesión. La interpretación adecuada de las radiografías simples de la columna cervical en los niños
requiere el conocimiento de las peculiaridades de este segmento en la edad pediátrica.Objective: To report on a physiological radiographic finding of the cervical spine in childhood that
trends to be misjudged as pathologic: C2-C3 pseudosubluxation. We presented a girl, aged 14 months, who was remitted
to our Center for clinical suspect of C2-C3 subluxation. A diagnostic methodology is offered to distinguish between
C2-C3 pseudosubluxation and a true C2-C3 subluxation. A detailed anamnesis as well as a meticulous radiological
and clinical exploration, allow to establish the right diagnosis in most cases, without any other complementary
probe. The normal mobility of C2 on C3 in flexion could be so pronounced as to be mistaken for a pathological
finding. The suitable radiographic interpretation of the cervical spine in children requires the knowledge of the peculiarities
of this segment in the pediatric age
Data Portraits and Intermediary Topics: Encouraging Exploration of Politically Diverse Profiles
In micro-blogging platforms, people connect and interact with others.
However, due to cognitive biases, they tend to interact with like-minded people
and read agreeable information only. Many efforts to make people connect with
those who think differently have not worked well. In this paper, we
hypothesize, first, that previous approaches have not worked because they have
been direct -- they have tried to explicitly connect people with those having
opposing views on sensitive issues. Second, that neither recommendation or
presentation of information by themselves are enough to encourage behavioral
change. We propose a platform that mixes a recommender algorithm and a
visualization-based user interface to explore recommendations. It recommends
politically diverse profiles in terms of distance of latent topics, and
displays those recommendations in a visual representation of each user's
personal content. We performed an "in the wild" evaluation of this platform,
and found that people explored more recommendations when using a biased
algorithm instead of ours. In line with our hypothesis, we also found that the
mixture of our recommender algorithm and our user interface, allowed
politically interested users to exhibit an unbiased exploration of the
recommended profiles. Finally, our results contribute insights in two aspects:
first, which individual differences are important when designing platforms
aimed at behavioral change; and second, which algorithms and user interfaces
should be mixed to help users avoid cognitive mechanisms that lead to biased
behavior.Comment: 12 pages, 7 figures. To be presented at ACM Intelligent User
Interfaces 201
Collagenase nanocapsules: An approach to fibrosis treatment
Fibrosis is a common lesion in different pathologic diseases and defined by the excessive accumulation ofcollagen. Different approaches have been used to treat different conditions characterized by fibrosis. TheFDA and EMA approved the use of collagenase to treat palmar fibromatosis (Dupuytren’s contracture).The EMA approved additionally its use in severe Peyronie’s disease, but it has been used off label in otherconditions [1,2]. The approved treatment includes up to three (in palmar fibromatosis) or up to eight (inpenile fibromatosis) injections followed by finger extension or penile modeling procedures, typicallycausing severe pain. Frequent single injections are adequate to treat palmar fibromatosis [3]. The needto repeatedly inject doses of this enzyme can be due to the labile nature of collagenase, which exhibitsa complete activity loss after a short period of time. This study presents a novel strategy to manage thisenzyme based on the synthesis of polymeric nanocapsules that contain collagenase encapsulated withintheir matrix. These nanocapsules have been engineered for achieving a gradual release of the encapsu-lated enzyme for a longer time, which can be up to ten days. The efficacy of these nanocapsules has beentested in a murine model of local dermal fibrosis, and the results demonstrate a reduction in fibrosisgreater than that with the injection of free enzyme; this type of treatment showed a significant improve-ment compared to conventional therapy of free collagenase
Study of the Falling Friction Effect on Rolling Contact Parameters
[EN] The existence of a wheel rail friction coefficient that depends on the slip velocity has been associated in the literature with important railway problems like the curving squeal and certain corrugation problems in rails. Rolling contact models that take into account this effect were carried out through the so-called Exact Theories adopting an exact elastic model of the solids in contact, and Simplified Theories which assume simplified elastic models such as Winkler. The former ones, based on Kalker s Variational Theory, give rise to numerical problems; the latter ones need to adopt hypotheses that significantly deviate from actual conditions, leading to unrealistic solutions of the contact problem. In this paper, a methodology based on Kalker s Variational Theory is presented, in which a local slip velocity-dependent friction law is considered. A formulation to get steady-state conditions of rolling contact by means of regularisation of the Coulomb s law is proposed. The model allows establishing relationships in order to estimate the global properties (creepage velocities vs. total longitudinal forces) through local properties (local slip velocity vs. coefficient of friction) or vice versa. The proposed model shows a good agreement with experimental tests while solving the numerical problems previously mentioned.The authors acknowledge the financial contribution of the Spanish Ministry of Economy and Competitiveness through the Project TRA2013-45596-C2-1-R.Giner Navarro, J.; Baeza González, LM.; Vila Tortosa, MP.; Alonso Pazos, A. (2017). Study of the Falling Friction Effect on Rolling Contact Parameters. Tribology Letters. 65(1). https://doi.org/10.1007/s11249-016-0810-8S651Grassie, S.L., Elkins, J.A.: Rail corrugation on North American transit systems. Veh. Syst. Dyn. 28, 5–17 (1998)Hsu, S.S., Huang, Z., Iwnicki, S.D., Thompson, D.J., Jones, C.J.C., Xie, G., Allen, P.D.: Experimental and theoretical investigation of railway wheel squeal. Proc. Inst. Mech. Eng. F J. Rail Rapid Transit 221, 59–73 (2007)Kalker, J.J.: Three-Dimensional Elastic Bodies in Rolling Contact. Kluwer, Dordrecht (1990)Polach, O.: Influence of locomotive tractive effort on the forces between wheel and rail. Veh. Syst. Dyn. 35, 7–22 (2001)Giménez, J.G., Alonso, A., Gómez, E.: Introduction of a friction coefficient dependent on the slip in the FastSim algorithm. Veh. Syst. Dyn. 43, 233–244 (2005)Baeza, L., Vila, P., Roda, A., Fayos, J.: Prediction of corrugation in rails using a non-stationary wheel–rail contact model. Wear 265, 1156–1162 (2008)Vollebregt, E.A.H., Schuttelaars, H.M.: Quasi-static analysis of two-dimensional rolling contact with slip-velocity dependent friction. J. Sound Vib. 331, 2141–2155 (2012)Avlonitis, M., Kalaitzidou, K., Streator, J.: Investigation of friction statics and real contact area by means a modified OFC model. Tribol. Int. 69, 168–175 (2014)Berger, E.J., Mackin, T.J.: On the walking stick–slip problem. Tribol. Int. 75, 51–60 (2014)Alonso, A., Guiral, A., Baeza, B., Iwnicki, S.D.: Wheel–rail contact: experimental study of the creep forces–creepage relationships. Veh. Syst. Dyn. 52(S1), 469–487 (2014)Spiryagin, M., Polach, O., Cole, C.: Creep force modelling for rail traction vehicles based on the Fastsim algorithm. Veh. Syst. Dyn. 51, 1765–1783 (2013)Vollebregt, E.A.H.: Numerical modeling of measured railway creep versus creep-force curves with CONTACT. Wear 314, 87–95 (2014)Kalker, J.J.: On the Rolling Contact of Two Elastic Bodies in the Presence of Dry Friction. PhD Thesis, Technical University of Delft (Holland) (1967)Baeza, L., Fuenmayor, F.J., Carballeira, J., Roda, A.: Influence of the wheel–rail contact instationary process on contact parameters. J. Strain Anal. Eng. 42, 377–387 (2007)Le Rouzic, J., Le Bot, A., Perret-Liaudet, J., Guibert, M., Rusanov, A., Douminge, L., Bretagnol, F., Mazuyer, D.: Friction-induced vibration by Stribeck’s law: application to wiper blade squeal noise. Tribol. Lett. 49, 563–572 (2013)Rabinowicz, E.: The nature of the static and kinetic coefficients of friction. J. Appl. Phys. 22, 1373–1379 (1951)Carter, F.W.: On the action of locomotive driving wheel. Proc. R. Soc. Lon. Ser. A 112, 151–157 (1926)Kalker, J.J.: A fast algorithm for the simplified theory of rolling contact. Veh. Syst. Dyn. 11, 1–13 (1982
Exploration of the treatment of fish-canning industry effluents by aqueous-phase reforming using Pt/C catalysts
In the current work, an exploratory study on the application of catalytic aqueous phase reforming (APR) to the treatment of fish-canning wastewater was performed for the first time. Pt/C (3%, w) catalysts were supported on different commercial carbon supports (two activated carbons and a carbon black) and tested in the APR of tuna-cooking wastewater. The effect of the supports and the reaction systems (batch vs. semi-continuous) on the performance of the catalysts was tested. The stability of the catalysts upon 3 successive reuse cycles was checked. TOC and COD removal ranged within 45-60%, which was ascribed to adsorption on the supports, hydrothermal carbonization and APR. The percentage of valuable gases (H2 and alkanes) reached up to 18% of the gas production showing the potential of APR for the valorization and treatment of wastewater. The production of gases is affected by the high chloride, acetate and phosphate concentrations, which may provoke catalyst deactivation. The use of a catalyst with a basic support significantly increased the production of gases and the H2 percentage in the gas fraction. Gas production was higher in semi-continuous compared to batch operation, maybe because the withdrawn gas displaces the reaction towards the products. The percentage of alkanes in the gas phase decreased upon successive catalyst reuse cycles at the expense of H2, which is probably due to sintering of Pt nanoparticles with the corresponding decrease of the number of low-coordinated Pt sites promoting methanation reactionsThe authors greatly appreciate financial support from Spanish MINECO (CTQ2015-65491-R). A. S. Oliveira thanks the Spanish MINECO for a research grant (BES-2016-077244
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