205,119 research outputs found
Numerical Methods for the 3-dimensional 2-body Problem in the Action-at-a-Distance Electrodynamics
We develop two numerical methods to solve the differential equations with
deviating arguments for the motion of two charges in the action-at-a-distance
electrodynamics. Our first method uses St\"urmer's extrapolation formula and
assumes that a step of integration can be taken as a step of light ladder,
which limits its use to shallow energies. The second method is an improvement
of pre-existing iterative schemes, designed for stronger convergence and can be
used at high-energies.Comment: 17 pages, 11 figure
Surface Tension in Unitary Fermi Gases with Population Imbalance
We study the effects of surface tension between normal and superfluid regions
of a trapped Fermi gas at unitarity. We find that surface tension causes
notable distortions in the shape of large aspect ratio clouds. Including these
distortions in our theories resolves many of the apparent discrepancies among
different experiments and between theory and experiments.Comment: 4 pages, 4 figures, Published versio
Recommended from our members
China’s rise in a liberal world order in transition – introduction to the FORUM
In a time of great uncertainty about the future and resilience of the liberal world order this Forum focuses on China’s rise and interplay with the foundations of that liberal order. The key question is the extent to and variegated ways in which China - with its (re)ascendance to power and potential global leadership – is adapting to and perhaps even strengthening liberal institutions and rules of the game, confronting them, or developing alternative paths. In this introduction to the Forum we advance three key points based on the contributions. First, contrasting the orthodox binary scenarios of either inevitable conflict or co-optation offered in the mainstream IR debate, the Forum highlights the possibility of a third scenario of China’s interplay with the liberal world and its key actors, institutions, and rules. A hybrid and variegated scenario that entails both conflict and adaptation, differently entangled in different issue areas. Second, it stresses the need to conceptualize and empirically comprise the essentially interlinked nature of domestic state-society models and the global political economy. Third, we argue for a perspective that incorporates underlying economic and social structures and the power relations embedded therein
Rotational Mixing in Magellanic Clouds B Stars - Theory versus Observation
We have used VLT FLAMES data to constrain the uncertain physics of rotational
mixing in stellar evolution models. We have simulated a population of single
stars and find two groups of observed stars that cannot be explained: (1) a
group of fast rotating stars which do not show evidence for rotational mixing
and (2) a group of slow rotators with strong N enrichment. Binary effects and
fossil magnetic fields may be considered to explain those two groups. We
suggest that the element boron could be used to distinguish between rotational
mixing and the binary scenario. Our single star population simulations quantify
the expected amount of boron in fast and slow rotators and allow a comparison
with measured nitrogen and boron abundances in B-stars.Comment: to appear in Comm. in Astroseismology - Contribution to the
Proceedings of the 38th LIAC, 200
Characterization of non-intentional emissions from distributed energy resources up to 500 kHz: A case study in Spain
Narrow Band Power Line Communications (NB-PLC) systems are currently used for smart metering and power quality monitoring as a part of the Smart Grid (SG) concept. However, non-intentional emissions generated by the devices connected to the grid may sometimes disturb the communications and isolate metering equipment. Though some research works have been recently developed to characterize these emissions, most of them have been limited to frequencies below 150 kHz and they are mainly focused on in-house electronic appliances and lightning devices. As NB-PLC can also be allocated in higher frequencies up to 500 kHz, there is still a lack of analysis in this frequency range, especially for emissions from Distributed Energy Resources (DERs). The identification and characterization of the emissions is essential to develop solutions that avoid a negative impact on the proper performance of NB-PLC.
In this work, the non-intentional emissions of different types of DERs composing a representative microgrid have been measured in the 35–500 kHz frequency range and analyzed both in time and frequency domains. Different working conditions and coupling and commutation procedures to mains are considered in the analysis. Results are then compared to the limits recommended by regulatory bodies for spurious emissions from communication systems in this frequency band, as no specific limits for DERs have been established. Field measurements show clear differences in the characteristics of non-intentional emissions for different devices, working conditions and coupling procedures and for frequencies below and above 150 kHz. Results of this study demonstrate that a further characterization of the potential emissions from the different types of DERs connected to the grid is required in order to guarantee current and future applications based on NB-PLC.This work has been financially supported in part by the Basque
Government (Elkartek program)
Coupled quantum wires
We study a set of crossed 1D systems, which are coupled with each other via
tunnelling at the crossings. We begin with the simplest case with no
electron-electron interactions and find that besides the expected level
splitting, bound states can emerge. Next, we include an external potential and
electron-electron interactions, which are treated within the Hartree
approximation. Then, we write down a formal general solution to the problem,
giving additional details for the case of a symmetric external potential.
Concentrating on the case of a single crossing, we were able to explain recent
experinents on crossed metallic and semiconducting nanotubes [J. W. Janssen, S.
G. Lemay, L. P. Kouwenhoven, and C. Dekker, Phys. Rev. B 65, 115423 (2002)],
which showed the presence of localized states in the region of crossing.Comment: 11 pages, 10 figure
Science with the World Space Observatory - Ultraviolet
The World Space Observatory-Ultraviolet (WSO-UV) will provide access to the
UV range during the next decade. The instrumentation on board will allow to
carry out high resolution imaging, high sensitivity imaging, high resolution
(R~55000) spectroscopy and low resolution (R~2500) long slit spectroscopy. In
this contribution, we briefly outline some of the key science issues that
WSO-UV will address during its lifetime. Among them, of special interest are:
the study of galaxy formation and the intergalactic medium; the astronomical
engines; the Milky Way formation and evol ution, and the formation of the Solar
System and the atmospheres of extrasolar p lanets.Comment: Just one text file (aigomezdecastro.tex). To be published in the
proceeding of the conference: "New Quest in Stellar Astrophysics II: UV
properties of evolved stellar populations" held in Puerto Vallarta - Mexico,
in april 200
Generalization of the Fierz-Pauli Action
We consider the Lagrangian of gravity covariantly amended by the mass and
polynomial interaction terms with arbitrary coefficients, and reinvestigate the
consistency of such a theory in the decoupling limit, up to the fifth order in
the nonlinearities. We calculate explicitly the self-interactions of the
helicity-0 mode, as well as the nonlinear mixing between the helicity-0 and -2
modes. We show that ghost-like pathologies in these interactions disappear for
special choices of the polynomial interactions, and argue that this result
remains true to all orders in the decoupling limit. Moreover, we show that the
linear, and some of the nonlinear mixing terms between the helicity-0 and -2
modes can be absorbed by a local change of variables, which then naturally
generates the cubic, quartic, and quintic Galileon interactions, introduced in
a different context. We also point out that the mixing between the helicity-0
and 2 modes can be at most quartic in the decoupling limit. Finally, we discuss
the implications of our findings for the consistency of the effective field
theory away from the decoupling limit, and for the Boulware-Deser problem.Comment: 18 pages, no figure
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