265 research outputs found
Fermionic Collective Modes of an Anisotropic Quark-Gluon Plasma
We determine the fermionic collective modes of a quark-gluon plasma which is
anisotropic in momentum space. We calculate the fermion self-energy in both the
imaginary- and real-time formalisms and find that numerically and analytically
(for two special cases) there are no unstable fermionic modes. In addition we
demonstrate that in the hard-loop limit the Kubo-Martin-Schwinger condition,
which relates the off-diagonal components of the real-time fermion self-energy,
holds even for the anisotropic, and therefore non-equilibrium, quark-gluon
plasma considered here. The results obtained here set the stage for the
calculation of the non-equilibrium photon production rate from an anisotropic
quark-gluon plasma.Comment: 16 pages, 8 figures; v2 typos fixed and one reference adde
3+1D hydrodynamic simulation of relativistic heavy-ion collisions
We present MUSIC, an implementation of the Kurganov-Tadmor algorithm for
relativistic 3+1 dimensional fluid dynamics in heavy-ion collision scenarios.
This Riemann-solver-free, second-order, high-resolution scheme is characterized
by a very small numerical viscosity and its ability to treat shocks and
discontinuities very well. We also incorporate a sophisticated algorithm for
the determination of the freeze-out surface using a three dimensional
triangulation of the hyper-surface. Implementing a recent lattice based
equation of state, we compute p_T-spectra and pseudorapidity distributions for
Au+Au collisions at root s = 200 GeV and present results for the anisotropic
flow coefficients v_2 and v_4 as a function of both p_T and pseudorapidity. We
were able to determine v_4 with high numerical precision, finding that it does
not strongly depend on the choice of initial condition or equation of state.Comment: 16 pages, 11 figures, version accepted for publication in PRC,
references added, minor typos corrected, more detailed discussion of
freeze-out routine adde
H2-powered aviation – Design and economics of green LH2 supply for airports
The economic competitiveness of hydrogen-powered aviation highly depends on the supply costs of green liquid hydrogen to enable true-zero CO2 flying. This study uses non-linear energy system optimization to analyze three main liquid hydrogen (LH2) supply pathways for five locations. Final liquid hydrogen costs at the dispenser supply costs could reach 2.04 USD/kgLH2 in a 2050 base case scenario for locations with strong renewable energy source conditions. This could lead to cost-competitive flying with hydrogen. Reflecting techno-economic uncertainties in two additional scenarios, the liquid hydrogen cost span at all five airport locations ranges between 1.37–3.48 USD/kgLH2, if hydrogen import options from larger hydrogen markets are also available. Import setups are of special importance for airports with a weaker renewable energy source situation, e.g., selected Central European airports. There, on-site supply might not only be too expensive, but space requirements for renewable energy sources could be too large for feasible implementation in densely populated regions. Furthermore, main costs for liquid hydrogen are caused by renewable energy sources, electrolysis systems, and liquefaction plants. Seven detailed design rules are derived for optimized energy systems for these and the storage components. This and the cost results should help infrastructure planners and general industry and policy players prioritize research and development needs
Cardiomyocyte generation from somatic sources — current status and future directions
Transdifferentiation of one cell type to another has garnered significant research efforts in recent years. As cardiomyocyte loss following myocardial infarction becomes debilitating for cardiac patients, the option of an autologous source of cardiomyocytes not derived from multi/pluripotent stem cell sources is an attractive option. Such direct programming has been clearly realized with the use of transcription factors, microRNAs and more recently small molecule delivery to enhance epigenetic modifications, all albeit with low efficiencies in vitro. In this review, we aim to present a brief overview of the current in vitro and in vivo transdifferentiation strategies in the generation of cardiomyocytes from somatic sources. The interdisciplinary fields of tissue, cell, material and regenerative engineering offer many opportunities to synergistically achieve directly programmed cardiac tissue in vitro and enhance transdifferentiation in vivo. This review aims to present a concise outlook on this topic with these fields in mind
Temporal evolution of tubular initial conditions and their influence on two-particle correlations in relativistic nuclear collisions
Relativistic nuclear collisions data on two-particle correlations exhibit
structures as function of relative azimuthal angle and rapidity. A unified
description of these near-side and away-side structures is proposed for low to
moderate transverse momentum. It is based on the combined effect of tubular
initial conditions and hydrodynamical expansion. Contrary to expectations, the
hydrodynamics solution shows that the high energy density tubes (leftover from
the initial particle interactions) give rise to particle emission in two
directions and this is what leads to the various structures. This description
is sensitive to some of the initial tube parameters and may provide a probe of
the strong interaction. This explanation is compared with an alternative one
where some triangularity in the initial conditions is assumed. A possible
experimental test is suggested.Comment: 6 pages, 6 figure
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