6,971 research outputs found
High-performance functional renormalization group calculations for interacting fermions
We derive a novel computational scheme for functional Renormalization Group
(fRG) calculations for interacting fermions on 2D lattices. The scheme is based
on the exchange parametrization fRG for the two-fermion interaction, with
additional insertions of truncated partitions of unity. These insertions
decouple the fermionic propagators from the exchange propagators and lead to a
separation of the underlying equations. We demonstrate that this separation is
numerically advantageous and may pave the way for refined, large-scale
computational investigations even in the case of complex multiband systems.
Furthermore, on the basis of speedup data gained from our implementation, it is
shown that this new variant facilitates efficient calculations on a large
number of multi-core CPUs. We apply the scheme to the , Hubbard model on
a square lattice to analyze the convergence of the results with the bond length
of the truncation of the partition of unity. In most parameter areas, a fast
convergence can be observed. Finally, we compare to previous results in order
to relate our approach to other fRG studies.Comment: 26 pages, 9 figure
Chirp mitigation of plasma-accelerated beams using a modulated plasma density
Plasma-based accelerators offer the possibility to drive future compact light
sources and high-energy physics applications. Achieving good beam quality,
especially a small beam energy spread, is still one of the major challenges.
For stable transport, the beam is located in the focusing region of the
wakefield which covers only the slope of the accelerating field. This, however,
imprints a longitudinal energy correlation (chirp) along the bunch. Here, we
propose an alternating focusing scheme in the plasma to mitigate the
development of this chirp and thus maintain a small energy spread
The Presence of Weak Active Galactic Nuclei in High Redshift Star Forming Galaxies
We present [OIII 5007A] observations of the star forming galaxy HDF-BMZ1299
(z=1.598) using Keck Observatory's Adaptive Optics system with the
near-infrared integral field spectrograph OSIRIS. Using previous Halpha and
[NII] measurements of the same source, we are able for the first time to use
spatially resolved observations to place a high-redshift galaxy's substructure
on a traditional HII diagnostic diagram. We find that HDF-BMZ1299's spatially
concentrated nebular ratios in the central ~1.5 kiloparsec (0."2) are best
explained by the presence of an AGN: log([NII]/Halpha)=-0.22+/-0.05 and 2sigma
limit of log([OIII]/Hbeta)>0.26. The dominant energy source of this galaxy is
star formation, and integrating a single aperture across the galaxy yields
nebular ratios that are composite spectra from both AGN and HII regions. The
presence of an embedded AGN in HDF-BMZ1299 may suggest a potential
contamination in a fraction of other high-redshift star forming galaxies, and
we suggest that this may be a source of the "elevated" nebular ratios
previously seen in seeing-limited metallicity studies. HDF-BMZ1299's estimated
AGN luminosity is L_Halpha = 3.7e41 erg/s and L_[OIII] = 5.8e41 erg/s, making
it one of the lowest luminosity AGN discovered at this early epoch.Comment: 15 pages, 4 figures, ApJ Accepted, new version to be published
(updated text, figures, and table
Coulomb Parameter U and Correlation Strength in LaFeAsO
First principles constrained density functional theory scheme in Wannier
functions formalism has been used to calculate Coulomb repulsion U and Hund's
exchange J parameters for iron 3d electrons in LaFeAsO. Results strongly depend
on the basis set used in calculations: when O-2p, As-4p, and Fe-3d orbitals and
corresponding bands are included, computation results in U=3-4 eV, however,
with the basis set restricted to Fe-3d orbitals and bands only, computation
gives parameters corresponding to F^0=0.8 eV, J=0.5 eV. LDA+DMFT (the Local
Density Approximation combined with the Dynamical Mean-Field Theory)
calculation with this parameters results in weakly correlated electronic
structure that is in agreement with X-ray experimental spectra
Eliza Haywoods geschichte des fräuleins Elisabeth Thoughtless (1756): frühe selbsterkenntnis und ehekritik in der englischen ubersetzungsliteratur
Die Tradition, Frauenerleben aus weiblicher Perspektive zum Mittelpunkt eines Romans zu machen, beginnt in Deutschland nicht mit Sophie La Roches Geschichte des Fräuleins von Sternheim (1771), sondern mit den Werken englischer Schriftstellerinnen, die bereits bedeutend früher in deutschen Übersetzungen erschienen und bisher von der Germanistik nicht beachtet worden sind. An Eliza Haywoods Geschichte des Fräuleins Elisabeth Thoughtless (1756) soll hier exemplarisch gezeigt werden, wie in Deutschland Mitte des 18. Jahrhunderts bereits eine Form der Literatur von Frauen erscheint, die die Entwicklung eines weiblichen Charakters zum Mittelpunkt hat. Obwohl der Übersetzer die in diesem Roman enthaltene Kritik an der patriarchalisch geführten Ehe und der Idealisierung der Frau durch eine bewusst gewählte Übersetzungsstrategie abschwächt, um der Leserschaft den für deutsche Verhältnisse zu radikalen Text angenehmer zu machen, ist dieser, von Lessing als das Werk eines Genies bewertete Roman ein Meilenstein in der Literatur von Frauen
The boson-fermion model with on-site Coulomb repulsion between fermions
The boson-fermion model, describing a mixture of itinerant electrons
hybridizing with tightly bound electron pairs represented as hard-core bosons,
is here generalized with the inclusion of a term describing on-site Coulomb
repulsion between fermions with opposite spins. Within the general framework of
the Dynamical Mean-Field Theory, it is shown that around the symmetric limit of
the model this interaction strongly competes with the local boson-fermion
exchange mechanism, smoothly driving the system from a pseudogap phase with
poor conducting properties to a metallic regime characterized by a substantial
reduction of the fermionic density. On the other hand, if one starts from
correlated fermions described in terms of the one-band Hubbard model, the
introduction in the half-filled insulating phase of a coupling with hard-core
bosons leads to the disappearance of the correlation gap, with a consequent
smooth crossover to a metallic state.Comment: 7 pages, 6 included figures, to appear in Phys. Rev.
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