The Dilaton and Modified Gravity

We consider the dilaton in the strong string coupling limit and elaborate on the original idea of Damour and Polyakov whereby the dilaton coupling to matter has a minimum with a vanishing value at finite field-value. Combining this type of coupling with an exponential potential, the effective potential of the dilaton becomes matter density dependent. We study the background cosmology, showing that the dilaton can play the role of dark energy. We also analyse the constraints imposed by the absence of violation of the equivalence principle. Imposing these constraints and assuming that the dilaton plays the role of dark energy, we consider the consequences of the dilaton on large scale structures and in particular the behaviour of the slip functions and the growth index at low redshift.Comment: 14 pages, 4 figure

Physics of Interpulse Emission in Radio Pulsars

The magnetized induced Compton scattering off the particles of the ultrarelativistic electron-positron plasma of pulsar is considered. The main attention is paid to the transverse regime of the scattering, which holds in a moderately strong magnetic field. We specifically examine the problem on induced transverse scattering of the radio beam into the background, which takes place in the open field line tube of a pulsar. In this case, the radiation is predominantly scattered backwards and the scattered component may grow considerably. Based on this effect, we for the first time suggest a physical explanation of the interpulse emission observed in the profiles of some pulsars. Our model can naturally account for the peculiar spectral and polarization properties of the interpulses. Furthermore, it implies a specific connection of the interpulse to the main pulse, which may reveal itself in the consistent intensity fluctuations of the components at different timescales. Diverse observational manifestations of this connection, including the moding behavior of PSR B1822-09, the peculiar temporal and frequency structure of the giant interpulses in the Crab pulsar, and the intrinsic phase correspondence of the subpulse patterns in the main pulse and the interpulse of PSR B1702-19, are discussed in detail. It is also argued that the pulse-to-pulse fluctuations of the scattering efficiency may lead to strong variability of the interpulse, which is yet to be studied observationally. In particular, some pulsars may exhibit transient interpulses, i.e. the scattered component may be detectable only occasionally.Comment: 28 pages, 2 figures. Accepted for publication in Ap

Lorentz-Abraham-Dirac vs Landau-Lifshitz radiation friction force in the ultrarelativistic electron interaction with electromagnetic wave (exact solutions)

When the parameters of electron - extreme power laser interaction enter the regime of dominated radiation reaction, the electron dynamics changes qualitatively. The adequate theoretical description of this regime becomes crutially important with the use of the radiation friction force either in the Lorentz-Abraham-Dirac form, which possess unphysical runaway solutions, or in the Landau-Lifshitz form, which is a perturbation valid for relatively low electromagnetic wave amplitude. The goal of the present paper is to find the limits of the Landau-Lifshitz radiation force applicability in terms of the electromagnetic wave amplitude and frequency. For this a class of the exact solutions to the nonlinear problems of charged particle motion in the time-varying electromagnetic field is used.Comment: 14 pages, 5 figure

The Initial Mass Function of the Stellar Association NGC 602 in the Small Magellanic Cloud with Hubble Space Telescope ACS Observations

We present our photometric study of the stellar association NGC 602 in the wing of the Small Magellanic Cloud (SMC). The data were taken in the filters F555W and F814W using the Advanced Camera for Surveys (ACS) on-board the Hubble Space Telescope (HST). Photometry was performed using the ACS module of the stellar photometry package DOLPHOT. We detected more than 5,500 stars with a magnitude range of 14 \lsim m_{555} \lsim 28 mag. Three prominent stellar concentrations are identified with star counts in the observed field, the association NGC 602 itself, and two clusters, one of them not being currently in any known catalog. The Color-Magnitude Diagrams (CMDs) of both clusters show features typical for young open clusters, while that of the association reveals bright main sequence (MS) and faint pre-main sequence (PMS) stars as the members of the system. We construct the initial mass spectrum (IMS) of the association by applying an age-independent method of counting the PMS stars within evolutionary tracks, while for the bright MS stars we transform their magnitudes to masses with the use of mass-luminosity relations. The IMS of NGC 602 is found to be well represented by a single-power law, corresponding to an Initial Mass Function (IMF) of slope \Gamma\approx -1.2 for 1 \lsim M/M{\solar} \lsim 45. This indicates that the shape of the IMF of a star forming system in the SMC for stars with masses higher than 1 M{\solar} seems to be quite similar to the field IMF in the solar neighborhood.Comment: Accepted for publication in ApJ, 13 pages, 14 figures, emulateapj.cls LaTeX style, full resolution version available on http://www.astro.uni-bonn.de/~dgoulier/Science/NGC602/ms.pd

D4.3 - Report on infrastructure requirements for developing sustainably PEDs,summarizing the outcome of the techno-economic modelling activities

Implementation of PEDs requires immense infrastructure investments in energy efficiency measures, energy generation, transformation and storage as well as in new mobility solutions. On the other hand, it is crucial to create affordable living arrangements despite the high costs of the aforementioned measures. Thus, this work aims to answer the overarching question of which infrastructure will be required to turn an existing neighbourhood into a PED. As existing districts in Europe are highly heterogeneous and, thus, difficult to analyse, this study uses a case study with a specific district archetype. To address this issue, this study utilises the district comparability tool, a framework created as part of the SMARTBEEjS project to enable technical comparability across districts in Europe. In addition, the cost of the necessary infrastructure is estimated, which leads to the discussion of inclusion and affordability issues as potential barriers of PEDs. An integrated techno-economic modelling consisting of different modelling approaches for the power, heating and cooling and mobility sectors as well as demand-side measures are applied. Those include tailor-made mixed integer linear programming, synPro simulations, agent based modelling and statistical correlations. Using these modelling methods, several plausible transition scenarios are analysed based on the building, climate and socio-demographic data of an archetype district of Griesheim-Mitte in Frankfurt am Main (Germany). The results show that envelope retrofitting is crucial to fulfil the PED requirement of energy positivity and to reduce the capacities of the energy generation and storage technology. Furthermore, the PED concept can be more economical than the business-as-usual scenario of importing the required energy. However, high upfront costs can be a barrier for less wealthy societies. This barrier needs to be reduced by public schemes or smart business models to avoid creating a neighbourhood concept that does not uphold the principles of energy justice and inclusion. This study has its limitations in terms of the scope of the study. Only one district archetype (based on Griesheim-Mitte in Frankfurt am Main and relevant for districts in Nottingham and Amsterdam) is analysed. Further work could look into different archetypes and the transition scenarios for those. Moreover, not all scenarios, i.e. transition measures could be modelled quantitatively within the frame of this work. In particular, the waste heat from data centers in the selected district was not considered. Hence, applying industrial waste heat for powering district heat networks should be investigated more thoroughly in the future

D4.4 - Report on developed methodologies and models for techno-economic modelling of PEDs and the transition towards their realisation

Executive Summary: In the light of urgent need for decarbonisation of the building sector, techno-economic modelling of energy systems is an essential part of the planning process of urban development. Positive Energy Districts (PEDs) should contribute to this transformation towards less carbon-intensive and more energy independent urban areas. Therefore, this report presents the techno-economic models that have been developed throughout the Smart-BEEjS project to determine the energy infrastructure required to transform current districts into PEDs. This report reviews the existing models that focus on the district and neighborhood energy modelling (Section 2). The literature emphasises that existing models are not sufficient for PED planning, as PED analysis requires a large diversity of data inputs and have very specific modelling requirements. Moreover, it is important to further advance an integrated systems approach that brings together technoeconomic and social aspects with sufficient detail. Four modelling approaches address four different sectors of the PED's energy infrastructure that needsto be included in the planning of the transition from exiting districts to PEDs. The electricity based system, including local renewable energy generation and electricity-based heating and cooling is covered by a mixed integer linear programming approach to guarantee an optimal technology portfolio while ensuring a positive energy balance (Section 3.1). The heating and cooling system is focusing on district solutions such as the 4th generation district heating/cooling with a mathematical approach (Section 3.2). The energy efficiency uptake of the building stock is addressed by agent based modeling (Section 3.3). Finally, the electric vehicle related charging infrastructure is modelled using statistics on real data (Section 3.4). Furthermore, as sector coupling is highly important these days, the interconnections of the presented models are drawn (Section 3.5). The models include important social factors such as affordability, inclusiveness and energy justice that is often not the focus of mainstream techno-economic models. As affordability, inclusiveness and energy justice are cornerstones of the PED concept, the models aim to address those values. The combined model can holistically evaluate what energy infrastructure is needed to transition from current districts to high-performance PEDs

Exact anisotropic brane cosmologies

We present exact solutions of the gravitational field equations in the generalized Randall-Sundrum model for an anisotropic brane with Bianchi type I and V geometry, with perfect fluid and scalar fields as matter sources. Under the assumption of a conformally flat bulk (with vanishing Weyl tensor) for a cosmological fluid obeying a linear barotropic equation of state the general solution of the field equations can be expressed in an exact parametric form for both Bianchi type I and V space-times. In the limiting case of a stiff cosmological fluid with pressure equal to the energy density, for a Bianchi type I Universe the solution of the field equations are obtained in an exact analytic form. Several classes of scalar field models evolution on the brane are also considered, corresponding to different choices of the scalar field potential. For all models the behavior of the observationally important parameters like shear, anisotropy and deceleration parameter is considered in detail.Comment: revised version to appear in PR

Accelerated Sizing of a Power Split Electrified Powertrain

Component sizing generally represents a demanding and time-consuming task in the development process of electrified powertrains. A couple of processes are available in literature for sizing the hybrid electric vehicle (HEV) components. These processes employ either time-consuming global optimization techniques like dynamic programming (DP) or near-optimal techniques that require iterative and uncertain tuning of evaluation parameters like the Pontryagin's minimum principle (PMP). Recently, a novel near-optimal technique has been devised for rapidly predicting the optimal fuel economy benchmark of design options for electrified powertrains. This method, named slope-weighted energy-based rapid control analysis (SERCA), has been demonstrated producing results comparable to DP, while limiting the associated computational time by near two orders of magnitude. In this paper, sizing parameters for a power split electrified powertrain are considered that include the internal combustion engine size, the two electric motor/generator sizes, the transmission ratios, and the final drive ratio. The SERCA approach is adopted to rapidly evaluate the fuel economy capabilities of each sizing option in various driving missions considering both type-approval drive cycles and real-world driving profiles. While screening out for optimal sizing options, the implemented methodology includes drivability criteria along with fuel economy potential. Obtained results will demonstrate the agility of the developed sizing tool in identifying optimal sizing options compared to state-of-the-art sizing tools for electrified powertrains

Brane-world inflation without inflaton on the brane

Inspired by the Randall-Sundrum brane-world scenario, we investigate the possibility of brane-world inflation driven not by an inflaton field on the brane, but by a bulk, dilaton-like gravitational field. As a toy model for the dilaton-like gravitational field, we consider a minimally coupled massive scalar field in the bulk 5-dimensional spacetime, and look for a perturbative solution in the anti-de Sitter (AdS) background. For an adequate range of the scalar field mass, we find a unique solution that has non-trivial dependence on the 5th dimensional coordinate and that induces slow-roll inflation on the brane.Comment: 10 pages, 2 figures, final version, to be published in Phys. Rev.

Dynamical Instabilities of the Randall-Sundrum Model

We derive dynamical equations to describe a single 3-brane containing fluid matter and a scalar field coupling to the dilaton and the gravitational field in a five dimensional bulk. First, we show that a scalar field or an arbitrary fluid on the brane cannot evolve to cancel the cosmological constant in the bulk. Then we show that the Randall-Sundrum model is unstable under small deviations from the fine-tuning between the brane tension and the bulk cosmological constant and even under homogeneous gravitational perturbations. Implications for brane world cosmologies are discussed.Comment: 12 pages, 2 figure