3,318 research outputs found
Magnetic excitations in two-leg spin 1/2 ladders: experiment and theory
Magnetic excitations in two-leg S=1/2 ladders are studied both experimentally
and theoretically. Experimentally, we report on the reflectivity, the
transmission and the optical conductivity sigma(omega) of undoped La_x Ca_14-x
Cu_24 O_41 for x=4, 5, and 5.2. Using two different theoretical approaches
(Jordan-Wigner fermions and perturbation theory), we calculate the dispersion
of the elementary triplets, the optical conductivity and the momentum-resolved
spectral density of two-triplet excitations for 0.2 <=
J_parallel/J_perpendicular <= 1.2. We discuss phonon-assisted two-triplet
absorption, the existence of two-triplet bound states, the two-triplet
continuum, and the size of the exchange parameters.Comment: 6 pages, 7 eps figures, submitted to SNS 200
DC generation from peripheral blood mononuclear cells in patients with chronic myeloid leukemia: Influence of interferons on DC yield and functional properties
In Chronic Myeloid Leukemia (CML), standard treatment consists of modern tyrosine-kinase inhibitors (TKI). Nevertheless, there is evidence that immune responses against leukemia-associated antigens (LAA) may play an important role in disease control. Dendritic cell (DC)- based immunotherapy is able to induce T cell responses against LAA and might therefore pose an interesting therapeutic option in CML, especially in the setting of minimal residual disease (MRD). GMP production of DC for clinical vaccination remains a time- and cost- intensive procedure and standardized DC generation is warranted. We asked whether maturation-induction with IFN-{gamma} and IFN-{alpha} has an influence on functional properties of DC derived from peripheral blood mononuclear cells (PBMC) in CML patients. Monocyte-derived DC from healthy donors and from patients with CML were analyzed after maturation-induction with our TNF-{alpha}-containing standard cytokine cocktail with or without addition of IFN-{alpha} and/or IFN-{gamma}. Our results confirm that the addition of IFN-{gamma} leads to enhanced IL-12 secretion in healthy donors. In contrast, in CML patients, IFN-{gamma} was not able to increase IL-12 secretion, possibly due to a higher degree of cell adherence and lower cell yield during the cell culture. Our data suggest, that- in contrast to healthy donors-, additional interferons are not beneficial for maturation induction during large-scale DC production in patients with CML
Optical spectroscopy of (La,Ca)14Cu24O41 spin ladders: comparison of experiment and theory
Transmission and reflectivity of La_x Ca_14-x Cu_24 O_41 two-leg spin-1/2
ladders were measured in the mid-infrared regime between 500 and 12000 1/cm.
This allows us to determine the optical conductivity sigma_1 directly and with
high sensitivity. Here we show data for x=4 and 5 with the electrical field
polarized parallel to the rungs (E||a) and to the legs (E||c). Three
characteristic peaks are identified as magnetic excitations by comparison with
two different theoretical calculations.Comment: 4 pages, 2 figures, submitted to SCES 200
Coherent Matter Wave Transport in Speckle Potentials
This article studies multiple scattering of matter waves by a disordered
optical potential in two and in three dimensions. We calculate fundamental
transport quantities such as the scattering mean free path , the
Boltzmann transport mean free path \elltrb, and the Boltzmann diffusion
constant , using a diagrammatic Green functions approach. Coherent
multiple scattering induces interference corrections known as weak localization
which entail a reduced diffusion constant. We derive the corresponding
expressions for matter wave transport in an correlated speckle potential and
provide the relevant parameter values for a possible experimental study of this
coherent transport regime, including the critical crossover to the regime of
strong or Anderson localization.Comment: 33 pages, minor corrections, published versio
Does permanent extensional deformation in lower forearc slopes indicate shallow plate-boundary rupture?
Highlights
• We document marine forearc deformation in the Northern Chile seismic gap.
• Upper-plate normal faulting off Northern Chile locally extends close to the trench.
• Normal faults indicate that past earthquakes may reached the shallow plate-boundary.
Abstract
Seismic rupture of the shallow plate-boundary can result in large tsunamis with tragic socio-economic consequences, as exemplified by the 2011 Tohoku-Oki earthquake. To better understand the processes involved in shallow earthquake rupture in seismic gaps (where megathrust earthquakes are expected), and investigate the tsunami hazard, it is important to assess whether the region experienced shallow earthquake rupture in the past. However, there are currently no established methods to elucidate whether a margin segment has repeatedly experienced shallow earthquake rupture, with the exception of mechanical studies on subducted fault-rocks. Here we combine new swath bathymetric data, unpublished seismic reflection images, and inter-seismic seismicity to evaluate if the pattern of permanent deformation in the marine forearc of the Northern Chile seismic gap allows inferences on past earthquake behavior. While the tectonic configuration of the middle and upper slope remains similar over hundreds of kilometers along the North Chilean margin, we document permanent extensional deformation of the lower slope localized to the region 20.8°S–22°S. Critical taper analyses, the comparison of permanent deformation to inter-seismic seismicity and plate-coupling models, as well as recent observations from other subduction-zones, including the area that ruptured during the 2011 Tohoku-Oki earthquake, suggest that the normal faults at the lower slope may have resulted from shallow, possibly near-trench breaking earthquake ruptures in the past. In the adjacent margin segments, the 1995 Antofagasta, 2007 Tocopilla, and 2014 Iquique earthquakes were limited to the middle and upper-slope and the terrestrial forearc, and so are upper-plate normal faults. Our findings suggest a seismo-tectonic segmentation of the North Chilean margin that seems to be stable over multiple earthquake cycles. If our interpretations are correct, they indicate a high tsunami hazard posed by the yet un-ruptured southern segment of the seismic gap
New Constraints from PAMELA anti-proton data on Annihilating and Decaying Dark Matter
Recently the PAMELA experiment has released its updated anti-proton flux and
anti-proton to proton flux ratio data up to energies of ~200GeV. With no clear
excess of cosmic ray anti-protons at high energies, one can extend constraints
on the production of anti-protons from dark matter. In this letter, we consider
both the cases of dark matter annihilating and decaying into standard model
particles that produce significant numbers of anti-protons. We provide two sets
of constraints on the annihilation cross-sections/decay lifetimes. In the one
set of constraints we ignore any source of anti-protons other than dark matter,
which give the highest allowed cross-sections/inverse lifetimes. In the other
set we include also anti-protons produced in collisions of cosmic rays with
interstellar medium nuclei, getting tighter but more realistic constraints on
the annihilation cross-sections/decay lifetimes.Comment: 7 pages, 3 figures, 3 table
Magnetic ordering in trigonal chain compounds
We present electronic structure calculations for the one-dimensional magnetic
chain compounds Ca_3CoRhO_6 and Ca_3FeRhO_6. The calculations are based on
density functional theory and the local density approximation. We use the
augmented spherical wave (ASW) method. The observed alternation of low- and
high-spin states along the Co-Rh and Fe-Rh chains is related to differences in
the oxygen coordination of the transition metal sites. Due to strong
hybridization the O 2p states are polarized, giving rise to extended localized
magnetic moments centered at the high-spin sites. Strong metal-metal overlap
along the chains leads to a substantial contribution of the low-spin Rh
4d_{3z^2-r^2} orbitals to the exchange coupling of the extended moments.
Interestingly, this mechanism holds for both compounds, even though the
coupling is ferromagnetic for the cobalt and antiferromagnetic for the iron
compound. However, our results allow to understand the different types of
coupling from the filling dependence of the electronic properties.Comment: 8 pages, 3 figures, more information at
http://www.physik.uni-augsburg.de/~eyert
Invisible Higgs and Scalar Dark Matter
In this proceeding, we show that when we combined WMAP and the most recent
results of XENON100, the invisible width of the Higgs to scalar dark matter is
negligible(<10%), except in a small region with very light dark matter (< 10
GeV) not yet excluded by XENON100 or around 60 GeV where the ratio can reach
50% to 60%. The new results released by the Higgs searches of ATLAS and CMS set
very strong limits on the elastic scattering cross section.Comment: 4 pages, 2 figures, proceeding TAUP2011 References adde
Observation of two-magnon bound states in the two-leg ladders of (Ca,La)14Cu24O41
Phonon-assisted 2-magnon absorption is studied at T=4 K in the spin-1/2
two-leg ladders of Ca_14-x La_x Cu_24 O_41 (x=5 and 4) for polarization of the
electrical field parallel to the legs and the rungs, respectively. Two peaks at
about 2140 and 2800 1/cm reflect van-Hove singularities in the density of
states of the strongly dispersing 2-magnon singlet bound state, and a broad
peak at about 4000 1/cm is identified with the 2-magnon continuum. Two
different theoretical approaches (Jordan-Wigner fermions and perturbation
theory) describe the data very well for J_parallel = 1050 - 1100 1/cm and
J_parallel / J_perp = 1 - 1.1. A striking similarity of the high-energy
continuum absorption of the ladders and of the undoped high T_c cuprates is
observed.Comment: 4 pages, 3 figures, Revte
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