heavy-ion collisions at present RHIC top energies or future LHC energies. However, at RHIC bottom energies, at SPS energies and, in particular, at FAIR energies, baryon density effects become significant and require different approaches.

Quasiparticle models (QPM), describing the quark-gluon plasma as assembly of essentially non-interacting excitations emerging from the strong interaction, have proven to represent useful phenomenological parametrizations of QCD thermodynamics above $T_{c}$ [@Pes94; @LH98; @Pes02; @LR03; @TSW04]. At zero chemical potential, lattice results are described with surprising accuracy allowing the adjustment of model parameters. Thermodynamic self-consistency, supplemented by the stationarity of the thermodynamic potential, can then be used to extrapolate thermodynamic properties of systems to nonzero net baryon density.

Our quasiparticle model [@KBS06; @BKS06; @BKS07a; @BKS07b] is based on the HTL approximation [@BP90a] to the 1-loop self-energies. This gives rise to four quasiparticle families. While quasiquarks and transversal gluons within the model represent excitations with quantum numbers of actual quarks and gluons with modified masses, quark holes (plasminos) and longitudinal gluons (plasmons) are quanta of collective excitations. The residues of the poles in the spectral density of the collective modes vanish exponentially for momenta $k\sim T$, from which the main contributions to thermodynamic phase space integrals originate. Therefore, 