2,780 research outputs found
Lyman Break Galaxies at z = 4 - 6 in cosmological SPH Simulations
We perform a spectrophotometric analysis of galaxies at redshifts z = 4 - 6
in cosmological SPH simulations of a Lambda CDM universe. Our models include
radiative cooling and heating by a uniform UV background, star formation,
supernova feedback, and a phenomenological model for galactic winds. Analysing
a series of simulations of varying boxsize and particle number allows us to
isolate the impact of numerical resolution on our results. Specifically, we
determine the luminosity functions in B, V, R, i', and z' filters, and compare
the results with observed galaxy surveys done with the Subaru telescope and the
Hubble Space Telescope. We find that the simulated galaxies have UV colours
consistent with observations and fall in the expected region of the
colour-colour diagrams used by the Subaru group. Assuming a uniform extinction
of E(B-V) = 0.15, we also find reasonable agreement between simulations and
observations in the space density of UV bright galaxies at z = 3 - 6, down to
the magnitude limit of each survey. For the same moderate extinction level of
E(B-V) ~ 0.15, the simulated luminosity functions match observational data, but
have a steep faint-end slope with alpha ~ -2.0. We discuss the implications of
the steep faint-end slope found in the simulations.Comment: 13 pages, 16 figures, MNRAS in pres
Lattice QCD based on OpenCL
We present an OpenCL-based Lattice QCD application using a heatbath algorithm
for the pure gauge case and Wilson fermions in the twisted mass formulation.
The implementation is platform independent and can be used on AMD or NVIDIA
GPUs, as well as on classical CPUs. On the AMD Radeon HD 5870 our double
precision dslash implementation performs at 60 GFLOPS over a wide range of
lattice sizes. The hybrid Monte-Carlo presented reaches a speedup of four over
the reference code running on a server CPU.Comment: 19 pages, 11 figure
Symmetry and structure of carbon-nitrogen complexes in gallium arsenide from infrared spectroscopy and first-principles calculations
Molecular-like carbon-nitrogen complexes in GaAs are investigated both
experimentally and theoretically. Two characteristic high-frequency stretching
modes at \num{1973} and \SI{2060}{cm^{-1}}, detected by Fourier transform
infrared absorption (FTIR) spectroscopy, appear in carbon- and
nitrogen-implanted and annealed layers. From isotopic substitution it is
deduced that the chemical composition of the underlying complexes is CN and
CN, respectively. Piezospectroscopic FTIR measurements reveal that both
centers have tetragonal symmetry. For density functional theory (DFT)
calculations linear entities are substituted for the As anion, with the axis
oriented along the \hkl direction, in accordance with the experimentally
ascertained symmetry. The DFT calculations support the stability of linear
N-C-N and C-C-N complexes in the GaAs host crystal in the charge states ranging
from to . The valence bonds of the complexes are analyzed using
molecular-like orbitals from DFT. It turns out that internal bonds and bonds to
the lattice are essentially independent of the charge state. The calculated
vibrational mode frequencies are close to the experimental values and reproduce
precisely the isotopic mass splitting from FTIR experiments. Finally, the
formation energies show that under thermodynamic equilibrium CN is more
stable than CN
Port-Hamiltonian realizations of linear time invariant systems
The question when a general linear time invariant control system is equivalent to a port-Hamiltonian systems is answered. Several equivalent characterizations are derived which extend the characterizations of [38] to the general non-minimal case. An explicit
construction of the transformation matrices is presented. The methods are applied in the stability analysis of disc brake squeal.DFG, SFB 1029, Substantial efficiency increase in gas turbines through direct use of coupled unsteady combustion and flow dynamic
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