Rolling-sliding laboratory tests of friction modifiers in dry and wet wheel-rail contacts

Friction management has been carried out extensively in the majority of railway networks in the last few years. A popular practice is the application of friction modifiers to increase the adhesion level in contaminated wheel-rail contacts. Two friction modifiers have particularly been used or tested on several railway networks as adhesion enhancers to facilitate the traction and braking operation under poor adhesion conditions. However, for assessment of the performance the railway operators and infrastructure managers mostly rely on practical observations that do not elucidate completely the effectiveness and side effects of these adhesion enhancers. In this paper, the constituents of the two friction modifiers are identified and the solid components are analyzed. A twin-disk roller rig has been used to study their performance in dry and wet contacts under closely controlled laboratory conditions. The adhesion characteristics of both friction modifiers are examined for different slip ratios. Furthermore, the wheel and rail disks are examined after a series of dry tests to analyze the mass loss, the surface damage, the change in surface hardness and roughness, and the subsurface deformation caused by the friction modifiers compared to dry clean contacts. (C) 2009 Elsevier B.V. All rights reserved

Energy conversion theorems for some linear steady-states

One of the main issues that real energy converters present, when they produce effective work, is the inevitable entropy production. Within the context of Non-equilibrium Thermodynamics, entropy production tends to energetically degrade man-made or living systems. On the other hand, it is also not useful to think about designing an energy converter that works in the so-called minimum entropy production regime since the effective power output and efficiency are zero. In this manuscript, we establish some \textit{Energy Conversion Theorems} similar to Prigogine's one with constrained forces, their purpose is to reveal trade-offs between design and the so-called operation modes for $\left(2\times2\right)$--linear isothermal energy converters. The objective functions that give rise to those thermodynamic constraints show stability. A two--meshes electric circuit was built as an example to demonstrate the Theorems' validity. Likewise, we reveal a type of energetic hierarchy for power output, efficiency and dissipation function when the circuit is tuned to any of the operating regimes studied here: maximum power output ($MPO$), maximum efficient power ($MP\eta$), maximum omega function ($M\Omega$), maximum ecological function ($MEF$), maximum efficiency ($M\eta$) and minimum dissipation function ($mdf$).Comment: 33 pages, 15 figures, 2 table

A first--order irreversible thermodynamic approach to a simple energy converter

Several authors have shown that dissipative thermal cycle models based on Finite-Time Thermodynamics exhibit loop-shaped curves of power output versus efficiency, such as it occurs with actual dissipative thermal engines. Within the context of First-Order Irreversible Thermodynamics (FOIT), in this work we show that for an energy converter consisting of two coupled fluxes it is also possible to find loop-shaped curves of both power output and the so-called ecological function against efficiency. In a previous work Stucki [J.W. Stucki, Eur. J. Biochem. vol. 109, 269 (1980)] used a FOIT-approach to describe the modes of thermodynamic performance of oxidative phosphorylation involved in ATP-synthesis within mithochondrias. In that work the author did not use the mentioned loop-shaped curves and he proposed that oxidative phosphorylation operates in a steady state simultaneously at minimum entropy production and maximum efficiency, by means of a conductance matching condition between extreme states of zero and infinite conductances respectively. In the present work we show that all Stucki's results about the oxidative phosphorylation energetics can be obtained without the so-called conductance matching condition. On the other hand, we also show that the minimum entropy production state implies both null power output and efficiency and therefore this state is not fulfilled by the oxidative phosphorylation performance. Our results suggest that actual efficiency values of oxidative phosphorylation performance are better described by a mode of operation consisting in the simultaneous maximization of the so-called ecological function and the efficiency.Comment: 20 pages, 7 figures, submitted to Phys. Rev.

Rival's absorptive capacity and innovation performance: Mediating effect of the strategic orientation

Introduction. In the literature there are contradictory results on the effects of the evaluation of rival's absorptive capacity (RAC) on innovation performance (IP). Moreover, the incidence of strategic aspects in this relationship has not been explored. Objective. Analyze the mediating effects of the strategic orientation towards competition (SOC) and the strategic orientation towards innovation (SOI) on the RAC-IP relationship. Materials and methods. The hypothesis model was contrasted in a sample of medium and low-technology manufacturing firms and a sample of service firms. To achieve this, structural equations were used by the consistent partial least squares method. Results. It was found that only the SOC has a mediating effect, which is a total effect. Conclusions. The main contribution of this paper is the empirical evidence it provides which demonstrates that the evaluation of RAC has a positive effect on IP, although this effect is mediated by SOC. This helps to discern the controversy triggered by contradictory results yielded in previous studies. Therefore, this finding is in agreement with the theoretical stance which highlights the benefits derived from understanding RAC's strengths and weaknesses, and from the pressures exerted by rivals on their counterpart, which force the latter to be more innovativeIntroducción. En la literatura hay resultados contradictorios sobre los efectos de la evaluación de la capacidad de absorción del rival (CAR) sobre el desempeño innovador (DI). Tampoco, se ha explorado la incidencia de aspectos estratégicos sobre esa relación. Objetivo. Analizar los efectos mediadores de la orientación estratégica a la competencia (OEC) y a la innovación (OEI) en la relación entre CAR y DI. Materiales y métodos. El modelo de hipótesis se contrastó en una muestra de empresas manufactureras, de media y baja tecnología, y de servicios. Para ello, se utilizaron ecuaciones estructurales por el método de mínimos cuadrados. Resultados. Se encontró que únicamente la OEC tiene un efecto mediador el cual es total. Conclusiones. La principal contribución del artículo gira en torno al aporte de evidencia empírica que demuestra que la evaluación de la CAR tiene un efecto positivo sobre el DI, si bien está mediado por la OEC. Esto es importante porque ayuda a dilucidar la controversia suscitada por los resultados contradictorios que arrojaron estudios previos. Por lo tanto, este hallazgo concuerda con la postura teórica que resalta los beneficios que se derivan del entendimiento de las fortalezas y debilidades de la CAR, y de las presiones que ejercen los rivales sobre su contraparte, que la obligan a ser más innovadora

Biochemical characterization of recombinant Candida albicans mannosyltransferases Mnt1, Mnt2 and Mnt5 reveals new functions in O- and N-mannan biosynthesis

Peer reviewedPublisher PD

Recurring adaptive introgression of a supergene variant that determines social organization

Introgression has been proposed as an essential source of adaptive genetic variation. However, a key barrier to adaptive introgression is that recombination can break down combinations of alleles that underpin many traits. This barrier might be overcome in supergene regions, where suppressed recombination leads to joint inheritance across many loci. Here, we study the evolution of a large supergene region that determines a major social and ecological trait in Solenopsis fire ants: whether colonies have one queen or multiple queens. Using coalescent-based phylogenies built from the genomes of 365 haploid fire ant males, we show that the supergene variant responsible for multiple-queen colonies evolved in one species and repeatedly spread to other species through introgressive hybridization. This finding highlights how supergene architecture can enable a complex adaptive phenotype to recurrently permeate species boundaries

The 2HWC HAWC Observatory Gamma Ray Catalog

We present the first catalog of TeV gamma-ray sources realized with the recently completed High Altitude Water Cherenkov Observatory (HAWC). It is the most sensitive wide field-of-view TeV telescope currently in operation, with a 1-year survey sensitivity of ~5-10% of the flux of the Crab Nebula. With an instantaneous field of view >1.5 sr and >90% duty cycle, it continuously surveys and monitors the sky for gamma ray energies between hundreds GeV and tens of TeV. HAWC is located in Mexico at a latitude of 19 degree North and was completed in March 2015. Here, we present the 2HWC catalog, which is the result of the first source search realized with the complete HAWC detector. Realized with 507 days of data and represents the most sensitive TeV survey to date for such a large fraction of the sky. A total of 39 sources were detected, with an expected contamination of 0.5 due to background fluctuation. Out of these sources, 16 are more than one degree away from any previously reported TeV source. The source list, including the position measurement, spectrum measurement, and uncertainties, is reported. Seven of the detected sources may be associated with pulsar wind nebulae, two with supernova remnants, two with blazars, and the remaining 23 have no firm identification yet.Comment: Submitted 2017/02/09 to the Astrophysical Journa

Daily monitoring of TeV gamma-ray emission from Mrk 421, Mrk 501, and the Crab Nebula with HAWC

We present results from daily monitoring of gamma rays in the energy range $\sim0.5$ to $\sim100$ TeV with the first 17 months of data from the High Altitude Water Cherenkov (HAWC) Observatory. Its wide field of view of 2 steradians and duty cycle of $>95$% are unique features compared to other TeV observatories that allow us to observe every source that transits over HAWC for up to $\sim6$ hours each sidereal day. This regular sampling yields unprecedented light curves from unbiased measurements that are independent of seasons or weather conditions. For the Crab Nebula as a reference source we find no variability in the TeV band. Our main focus is the study of the TeV blazars Markarian (Mrk) 421 and Mrk 501. A spectral fit for Mrk 421 yields a power law index $\Gamma=2.21 \pm0.14_{\mathrm{stat}}\pm0.20_{\mathrm{sys}}$ and an exponential cut-off $E_0=5.4 \pm 1.1_{\mathrm{stat}}\pm 1.0_{\mathrm{sys}}$ TeV. For Mrk 501, we find an index $\Gamma=1.60\pm 0.30_{\mathrm{stat}} \pm 0.20_{\mathrm{sys}}$ and exponential cut-off $E_0=5.7\pm 1.6_{\mathrm{stat}} \pm 1.0_{\mathrm{sys}}$ TeV. The light curves for both sources show clear variability and a Bayesian analysis is applied to identify changes between flux states. The highest per-transit fluxes observed from Mrk 421 exceed the Crab Nebula flux by a factor of approximately five. For Mrk 501, several transits show fluxes in excess of three times the Crab Nebula flux. In a comparison to lower energy gamma-ray and X-ray monitoring data with comparable sampling we cannot identify clear counterparts for the most significant flaring features observed by HAWC.Comment: 18 pages, 10 figures, accepted for publication in The Astrophysical Journa

Search for very-high-energy emission from Gamma-ray Bursts using the first 18 months of data from the HAWC Gamma-ray Observatory

The High Altitude Water Cherenkov (HAWC) Gamma-ray Observatory is an extensive air shower detector operating in central Mexico, which has recently completed its first two years of full operations. If for a burst like GRB 130427A at a redshift of 0.34 and a high-energy component following a power law with index -1.66, the high-energy component is extended to higher energies with no cut-off other than from extragalactic background light attenuation, HAWC would observe gamma rays with a peak energy of $\sim$300 GeV. This paper reports the results of HAWC observations of 64 gamma-ray bursts (GRBs) detected by $\mathit{Swift}$ and $\mathit{Fermi}$, including three GRBs that were also detected by the Large Area Telescope ($\mathit{Fermi}$-LAT). An ON/OFF analysis method is employed, searching on the time scale given by the observed light curve at keV-MeV energies and also on extended time scales. For all GRBs and time scales, no statistically significant excess of counts is found and upper limits on the number of gamma rays and the gamma-ray flux are calculated. GRB 170206A, the third brightest short GRB detected by the Gamma-ray Burst Monitor on board the $\mathit{Fermi}$ satellite ($\mathit{Fermi}$-GBM) and also detected by the LAT, occurred very close to zenith. The LAT measurements can neither exclude the presence of a synchrotron self-Compton (SSC) component nor constrain its spectrum. Instead, the HAWC upper limits constrain the expected cut-off in an additional high-energy component to be less than $100~\rm{GeV}$ for reasonable assumptions about the energetics and redshift of the burst.Comment: 19 pages, 6 figures, published in Ap