The twin paradox in compact spaces

Twins travelling at constant relative velocity will each see the other's time dilate leading to the apparent paradox that each twin believes the other ages more slowly. In a finite space, the twins can both be on inertial, periodic orbits so that they have the opportunity to compare their ages when their paths cross. As we show, they will agree on their respective ages and avoid the paradox. The resolution relies on the selection of a preferred frame singled out by the topology of the space.Comment: to be published in PRA, 3 page

Note on Varying Speed of Light Cosmologies

The various requirements on a consistent varying speed of light (`VSL') theory are surveyed, giving a short check-list of issues that should be satisfactorily handled by such theories.Comment: 6 pages; to appear in the GRG Journa

Potential energy threshold for nano-hillock formation by impact of slow highly charged ions on a CaF2_2(111) surface

We investigate the formation of nano-sized hillocks on the (111) surface of CaF$_2$ single crystals by impact of slow highly charged ions. Atomic force microscopy reveals a surprisingly sharp and well-defined threshold of potential energy carried into the collision of about 14 keV for hillock formation. Estimates of the energy density deposited suggest that the threshold is linked to a solid-liquid phase transition (``melting'') on the nanoscale. With increasing potential energy, both the basal diameter and the height of the hillocks increase. The present results reveal a remarkable similarity between the present predominantly potential-energy driven process and track formation by the thermal spike of swift ($\sim$ GeV) heavy ions.Comment: 10 pages, 2 figure

The UKIRT infrared deep sky survey early data release

This paper defines the UKIRT Infrared Deep Sky Survey (UKIDSS) Early Data Release (EDR). UKIDSS is a set of five large near-infrared surveys being undertaken with the United Kingdom Infrared Telescope Wide Field Camera (WFCAM). The programme began in 2005 May and has an expected duration of 7 yr. Each survey uses some or all of the broad-band filter complement ZY JHK. The EDR is the first public release of data to the European Southern Observatory (ESO) community. All worldwide releases occur after a delay of 18 months from the ESO release. The EDR provides a small sample data set, ∼50 deg2 (about 1 per cent of the whole of UKIDSS), that is a lower limit to the expected quality of future survey data releases. In addition, an EDR+ data set contains all EDR data plus extra data of similar quality, but for areas not observed in all of the required filters (amounting to ∼220 deg2). The first large data release, DR1, will occur in mid-2006. We provide details of the observational implementation, the data reduction, the astrometric and photometric calibration and the quality control procedures. We summarize the data coverage and quality (seeing, ellipticity, photometricity, depth) for each survey and give a brief guide to accessing the images and catalogues from the WFCAM Science Archive

Star Formation and Dynamics in the Galactic Centre

The centre of our Galaxy is one of the most studied and yet enigmatic places in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre (GC) is the ideal environment to study the extreme processes that take place in the vicinity of a supermassive black hole (SMBH). Despite the hostile environment, several tens of early-type stars populate the central parsec of our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The formation of such early-type stars has been a puzzle for a long time: molecular clouds should be tidally disrupted by the SMBH before they can fragment into stars. We review the main scenarios proposed to explain the formation and the dynamical evolution of the early-type stars in the GC. In particular, we discuss the most popular in situ scenarios (accretion disc fragmentation and molecular cloud disruption) and migration scenarios (star cluster inspiral and Hills mechanism). We focus on the most pressing challenges that must be faced to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A., 'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201

Measurement of D*+/- meson production in jets from pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

This paper reports a measurement of D*+/- meson production in jets from proton-proton collisions at a center-of-mass energy of sqrt(s) = 7 TeV at the CERN Large Hadron Collider. The measurement is based on a data sample recorded with the ATLAS detector with an integrated luminosity of 0.30 pb^-1 for jets with transverse momentum between 25 and 70 GeV in the pseudorapidity range |eta| < 2.5. D*+/- mesons found in jets are fully reconstructed in the decay chain: D*+ -> D0pi+, D0 -> K-pi+, and its charge conjugate. The production rate is found to be N(D*+/-)/N(jet) = 0.025 +/- 0.001(stat.) +/- 0.004(syst.) for D*+/- mesons that carry a fraction z of the jet momentum in the range 0.3 < z < 1. Monte Carlo predictions fail to describe the data at small values of z, and this is most marked at low jet transverse momentum.Comment: 10 pages plus author list (22 pages total), 5 figures, 1 table, matches published version in Physical Review

Modelling fine scale route choice of upstream migrating fish as they approach an instream structure

This study used pattern-oriented modelling (POM) to investigate the space use and behavioural response of upstream migrating European river lamprey (Lampetra fluviatilis) to the two-dimensional hydrodynamic conditions created by an instream structure (triangular profile gauging weir). Passive Integrated Transponder (PIT) and acoustic telemetry were used to map the spatial-temporal distribution patterns of lamprey as they migrated upstream. Acoustic Doppler velocimetry and computer modelling were used to quantify the hydrodynamic environment. In adherence with the POM methodology, multiple movement models, incorporating increasingly complex environmental feedback mechanisms and behavioural rules were created and systematically assessed to identify which factors might reproduce the observed patterns. The best model was a spatially explicit Eulerian-Lagrangian Individual Based Model (IBM) that included two simple behaviours: 1) tortuous non-directed swimming when in low flow velocity (< 0.1 m s−1) and 2) persistent directed (against the flow) swimming in moderate to high flow velocity (≥ 0.1 m s−1). The POM indicated that flow heterogeneity was an important influence of lamprey space use and that simple behavioural rules (i.e. two separate movement behaviours in response to flow velocity) were sufficient to reproduce the main movement pattern observed: avoidance of flow recirculating regions near the banks. The combination of field telemetry, hydrodynamic modelling and POM provided a useful framework for systematically identifying the key factors (hydrodynamic and behavioural) that governed the space use of the target species and would likely work well for investigating similar relationships in other aquatic species

Search for supersymmetry in final states with jets, missing transverse momentum and one isolated lepton in sqrt{s} = 7 TeV pp collisions using 1 fb-1 of ATLAS data

We present an update of a search for supersymmetry in final states containing jets, missing transverse momentum, and one isolated electron or muon, using 1.04 fb^-1 of proton-proton collision data at sqrt{s} = 7 TeV recorded by the ATLAS experiment at the LHC in the first half of 2011. The analysis is carried out in four distinct signal regions with either three or four jets and variations on the (missing) transverse momentum cuts, resulting in optimized limits for various supersymmetry models. No excess above the standard model background expectation is observed. Limits are set on the visible cross-section of new physics within the kinematic requirements of the search. The results are interpreted as limits on the parameters of the minimal supergravity framework, limits on cross-sections of simplified models with specific squark and gluino decay modes, and limits on parameters of a model with bilinear R-parity violation.Comment: 18 pages plus author list (30 pages total), 9 figures, 4 tables, final version to appear in Physical Review

Influence of Pre-Turbine Small-Sized Oxidation Catalyst on Engine Performance and Emissions under Driving Conditions

[EN] The earlier activation of the catalytic converters in internal combustion engines is becoming highly challenging due to the reduction in exhaust gas temperature caused by the application of CO2 reduction technologies. In this context, the use of pre-turbine catalysts arises as a potential way to increase the conversion efficiency of the exhaust aftertreatment system. In this work, a small-sized oxidation catalyst consisting of a honeycomb thin-wall metallic substrate was placed upstream of the turbine to benefit from the higher temperature and pressure prior to the turbine expansion. The change in engine performance and emissions in comparison to the baseline configuration are analyzed under driving conditions. As an individual element, the pre-turbine catalyst contributed positively with a relevant increase in the overall CO and HC conversion efficiency. However, its placement produced secondary effects on the engine and baseline aftertreatment response. Although small-sized monoliths are advantageous to minimize the thermal inertia impact on the turbocharger lag, the catalyst cross-section is in trade-off with the additional pressure drop that the monolith causes. As a result, the higher exhaust manifold pressure in pre-turbine pre-catalyst configuration caused a fuel consumption increase higher than 3% while the engine-out CO and HC emissions did around 50%. These increments were not completely offset despite the high pre-turbine pre-catalyst conversion efficiency (>40%) because the partial abatement of the emissions in this device conditioned the performance of the close-coupled oxidation catalyst.This research has been partially supported by FEDER and the Government of Spain through project TRA2016-79185-R and by Universitat Politecnica de Valencia under a grant with reference number FPI-2018-S2-10 to the Ph.D. student Maria Jose Ruiz.Serrano, J.; Piqueras, P.; De La Morena, J.; Ruiz-Lucas, MJ. (2020). Influence of Pre-Turbine Small-Sized Oxidation Catalyst on Engine Performance and Emissions under Driving Conditions. Applied Sciences. 10(21):1-17. https://doi.org/10.3390/app10217714S1171021Serrano, J. R., Novella, R., & Piqueras, P. (2019). Why the Development of Internal Combustion Engines Is Still Necessary to Fight against Global Climate Change from the Perspective of Transportation. Applied Sciences, 9(21), 4597. doi:10.3390/app9214597Road Transport: Reducing CO2 Emissions from Vehicles. European Commissionhttps://ec.europa.eu/clima/policies/transport/vehicles/carsJoshi, A. (2020). Review of Vehicle Engine Efficiency and Emissions. SAE Technical Paper Series. doi:10.4271/2020-01-0352Gohil, D. B., Pesyridis, A., & Serrano, J. R. (2020). Overview of Clean Automotive Thermal Propulsion Options for India to 2030. Applied Sciences, 10(10), 3604. doi:10.3390/app10103604Jain, A., Krishnasamy, A., & V, P. (2020). Computational optimization of reactivity controlled compression ignition combustion to achieve high efficiency and clean combustion. International Journal of Engine Research, 22(7), 2213-2232. doi:10.1177/1468087420931730Claßen, J., Pischinger, S., Krysmon, S., Sterlepper, S., Dorscheidt, F., Doucet, M., … Thewes, S. C. (2020). Statistically supported real driving emission calibration: Using cycle generation to provide vehicle-specific and statistically representative test scenarios for Euro 7. International Journal of Engine Research, 21(10), 1783-1799. doi:10.1177/1468087420935221Di Maio, D., Beatrice, C., Fraioli, V., Napolitano, P., Golini, S., & Rutigliano, F. G. (2019). Modeling of Three-Way Catalyst Dynamics for a Compressed Natural Gas Engine during Lean–Rich Transitions. Applied Sciences, 9(21), 4610. doi:10.3390/app9214610Reitz, R. D., Ogawa, H., Payri, R., Fansler, T., Kokjohn, S., Moriyoshi, Y., … Zhao, H. (2019). IJER editorial: The future of the internal combustion engine. International Journal of Engine Research, 21(1), 3-10. doi:10.1177/1468087419877990Kawaguchi, A., Wakisaka, Y., Nishikawa, N., Kosaka, H., Yamashita, H., Yamashita, C., … Tomoda, T. (2019). Thermo-swing insulation to reduce heat loss from the combustion chamber wall of a diesel engine. International Journal of Engine Research, 20(7), 805-816. doi:10.1177/1468087419852013Luján, J. M., Serrano, J. R., Piqueras, P., & Diesel, B. (2019). Turbine and exhaust ports thermal insulation impact on the engine efficiency and aftertreatment inlet temperature. Applied Energy, 240, 409-423. doi:10.1016/j.apenergy.2019.02.043Arnau, F. J., Martín, J., Pla, B., & Auñón, Á. (2020). Diesel engine optimization and exhaust thermal management by means of variable valve train strategies. International Journal of Engine Research, 22(4), 1196-1213. doi:10.1177/1468087419894804Maniatis, P., Wagner, U., & Koch, T. (2018). A model-based and experimental approach for the determination of suitable variable valve timings for cold start in partial load operation of a passenger car single-cylinder diesel engine. International Journal of Engine Research, 20(1), 141-154. doi:10.1177/1468087418817119Luján, J. M., Bermúdez, V., Piqueras, P., & García-Afonso, Ó. (2015). Experimental assessment of pre-turbo aftertreatment configurations in a single stage turbocharged diesel engine. Part 1: Steady-state operation. Energy, 80, 599-613. doi:10.1016/j.energy.2014.05.048Luján, J. M., Serrano, J. R., Piqueras, P., & García-Afonso, Ó. (2015). Experimental assessment of a pre-turbo aftertreatment configuration in a single stage turbocharged diesel engine. Part 2: Transient operation. Energy, 80, 614-627. doi:10.1016/j.energy.2014.12.017Serrano, J. R., Climent, H., Piqueras, P., & Angiolini, E. (2014). Analysis of fluid-dynamic guidelines in diesel particulate filter sizing for fuel consumption reduction in post-turbo and pre-turbo placement. Applied Energy, 132, 507-523. doi:10.1016/j.apenergy.2014.07.043Joergl, V., Keller, P., Weber, O., Mueller-Haas, K., & Konieczny, R. (2008). Influence of Pre Turbo Catalyst Design on Diesel Engine Performance, Emissions and Fuel Economy. SAE International Journal of Fuels and Lubricants, 1(1), 82-95. doi:10.4271/2008-01-0071Serrano, J. R., Bermúdez, V., Piqueras, P., & Angiolini, E. (2017). On the impact of DPF downsizing and cellular geometry on filtration efficiency in pre- and post-turbine placement. Journal of Aerosol Science, 113, 20-35. doi:10.1016/j.jaerosci.2017.07.014Kröcher, O., Elsener, M., Bothien, M.-R., & Dölling, W. (2014). Pre-Turbo Scr - Influence of Pressure on NOx Reduction. MTZ worldwide, 75(4), 46-51. doi:10.1007/s38313-014-0140-xBermúdez, V., Serrano, J. R., Piqueras, P., & García-Afonso, O. (2011). Assessment by means of gas dynamic modelling of a pre-turbo diesel particulate filter configuration in a turbocharged HSDI diesel engine under full-load transient operation. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 225(9), 1134-1155. doi:10.1177/0954407011402278Payri, F., Serrano, J. R., Piqueras, P., & García-Afonso, O. (2011). Performance Analysis of a Turbocharged Heavy Duty Diesel Engine with a Pre-turbo Diesel Particulate Filter Configuration. SAE International Journal of Engines, 4(2), 2559-2575. doi:10.4271/2011-37-0004Serrano, J. R., Guardiola, C., Piqueras, P., & Angiolini, E. (2014). Analysis of the Aftertreatment Sizing for Pre-Turbo DPF and DOC Exhaust Line Configurations. SAE Technical Paper Series. doi:10.4271/2014-01-1498Klaewkla, R., Arend, M., & F., W. (2011). A Review of Mass Transfer Controlling the Reaction Rate in Heterogeneous Catalytic Systems. Mass Transfer - Advanced Aspects. doi:10.5772/22962Piqueras, P., García, A., Monsalve-Serrano, J., & Ruiz, M. J. (2019). Performance of a diesel oxidation catalyst under diesel-gasoline reactivity controlled compression ignition combustion conditions. Energy Conversion and Management, 196, 18-31. doi:10.1016/j.enconman.2019.05.111Sampara, C. S., Bissett, E. J., & Chmielewski, M. (2007). Global Kinetics for a Commercial Diesel Oxidation Catalyst with Two Exhaust Hydrocarbons. Industrial & Engineering Chemistry Research, 47(2), 311-322. doi:10.1021/ie070813