208 research outputs found
Konfrontation und Kooperation am Kavango (Nord-Namibia) von 1891 bis 1921
Thema der Arbeit sind Konfrontation und Kooperation infolge kolonialen Machtstrebens am Kavango, der angolanisch-namibischen Grenzregion, im Zeitraum von 1891 bis 1921. Koloniales Machtstreben wird nicht primär verstanden als ein Phänomen oder ein Prozeß, das bzw. der geprägt ist von einfachen Dichotomien, wo je nach Perspektive die einen Täter, die anderen Opfer sind oder umgekehrt, die einen die Handlungsspielräume und Optionen der anderen begrenzen oder umgekehrt etc. Statt dessen wird der Versuch unternommen, alle an der kolonialen Situation Beteiligten als eigenständige Akteure bzw. Interessengruppen zu begreifen und ihnen als solchen adäquates Gewicht zu verleihen. Die Interaktion von traditionellen Machthabern, politischer Elite, Kavango-Bevölkerung, deutschen, portugiesischen und britischen Kolonialbeamten sowie katholischen Missionaren war von sehr unterschiedlichen, teils konkurrierenden, teils kongruenten Erwartungen, Interessen und Vorstellungen geprägt. Diese variierten nicht nur nach Fragestellung, sie veränderten sich auch im Laufe der Zeit, indem sie sich veränderten Rahmenbedingungen anpaßten. Es gilt deshalb nicht nur zu untersuchen, wie die einzelnen Akteure in bestimmten Situationen mit welchen Zielsetzungen agierten, sondern zugleich nach den Bedingungen der Handlungsweisen und den Grenzen zu fragen, denen sie durch die Optionen und das Verhalten der anderen Akteure unterlagen. Das zentrale Erkenntnisinteresse dieser Arbeit ist somit die Untersuchung der Verhaltens- und Handlungsmuster der einzelnen Akteure in der Kavango-Region vor dem Hintergrund ihrer jeweiligen Interessen, Optionen und Strategien in ihrer jeweiligen gegenseitigen Beeinflussung und Bedingung und in Hinblick auf das konkurrierende Streben nach Herrschaft, Macht und Einfluß
Phase-fluctuation induced reduction of the kinetic energy at the superconducting transition
Recent reflectivity measurements provide evidence for a "violation" of the
in-plane optical integral in the underdoped high-T_c compound
Bi_2Sr_2CaCu_2O_{8+\delta} up to frequencies much higher than expected by
standard BCS theory. The sum rule violation may be related to a loss of
in-plane kinetic energy at the superconducting transition. Here, we show that a
model based on phase fluctuations of the superconducting order parameter can
account for this change of in-plane kinetic energy at T_c. The change is due to
a transition from a phase-incoherent Cooper-pair motion in the pseudogap regime
above T_c to a phase-coherent motion at T_c.Comment: 5 pages, 3 eps-figure
In Vitro Aging of Human Skin Fibroblasts: Age-Dependent Changes in 4-Hydroxynonenal Metabolism
Evidence suggests that the increased production of free radicals and reactive oxygen species lead to cellular aging. One of the consequences is lipid peroxidation generating reactive aldehydic products, such as 4-hydroxynonenal (HNE) that modify proteins and form adducts with DNA bases. To prevent damage by HNE, it is metabolized. The primary metabolic products are the glutathione conjugate (GSH-HNE), the corresponding 4-hydroxynonenoic acid (HNA), and the alcohol 1,4-dihydroxynonene (DHN). Since HNE metabolism can potentially change during in vitro aging, cell cultures of primary human dermal fibroblasts from several donors were cultured until senescence. After different time points up to 30 min of incubation with 5 \ub5M HNE, the extracellular medium was analyzed for metabolites via liquid chromatography coupled with electrospray ionization mass spectrometry (LC/ESI-MS). The metabolites appeared in the extracellular medium 5 min after incubation followed by a time-dependent increase. But, the formation of GSH-HNL and GSH-DHN decreased with increasing in vitro age. As a consequence, the HNE levels in the cells increase and there is more protein modification observed. Furthermore, after 3 h of incubation with 5 \ub5M HNE, younger cells showed less proliferative capacity, while in older cells slight increase in the mitotic index was noticed
Exact ground states for the four-electron problem in a two-dimensional finite Hubbard square system
We present exact explicit analytical results describing the exact ground
state of four electrons in a two dimensional square Hubbard cluster containing
16 sites taken with periodic boundary conditions. The presented procedure,
which works for arbitrary even particle number and lattice sites, is based on
explicitly given symmetry adapted base vectors constructed in r-space. The
Hamiltonian acting on these states generates a closed system of 85 linear
equations providing by its minimum eigenvalue the exact ground state of the
system. The presented results, described with the aim to generate further
creative developments, not only show how the ground state can be exactly
obtained and what kind of contributions enter in its construction, but
emphasize further characteristics of the spectrum. On this line i) possible
explications are found regarding why weak coupling expansions often provide a
good approximation for the Hubbard model at intermediate couplings, or ii)
explicitly given low lying energy states of the kinetic energy, avoiding double
occupancy, suggest new roots for pairing mechanism attracting decrease in the
kinetic energy, as emphasized by kinetic energy driven superconductivity
theories.Comment: 37 pages, 18 figure
Pair Phase Fluctuations and the Pseudogap
The single-particle density of states and the tunneling conductance are
studied for a two-dimensional BCS-like Hamiltonian with a d_{x^2-y^2}-gap and
phase fluctuations. The latter are treated by a classical Monte Carlo
simulation of an XY model. Comparison of our results with recent scanning
tunneling spectra of Bi-based high-T_c cuprates supports the idea that the
pseudogap behavior observed in these experiments can be understood as arising
from phase fluctuations of a d_{x^2-y^2} pairing gap whose amplitude forms on
an energy scale set by T_c^{MF} well above the actual superconducting
transition.Comment: 5 pages, 6 eps-figure
Electromotive forces and the Meissner effect puzzle
In a voltaic cell, positive (negative) ions flow from the low (high)
potential electrode to the high (low) potential electrode, driven by an
`electromotive force' which points in opposite direction and overcomes the
electric force. Similarly in a superconductor charge flows in direction
opposite to that dictated by the Faraday electric field as the magnetic field
is expelled in the Meissner effect. The puzzle is the same in both cases: what
drives electric charges against electromagnetic forces? I propose that the
answer is also the same in both cases: kinetic energy lowering, or `quantum
pressure'
Optical Sum Rule anomalies in the High-Tc Cuprates
We provide a brief summary of the observed sum rule anomalies in the
high-T cuprate materials. A recent issue has been the impact of a
non-infinite frequency cutoff in the experiment. In the normal state, the
observed anomalously high temperature dependence can be explained as a `cutoff
effect'. The anomalous rise in the optical spectral weight below the
superconducting transition, however, remains as a solid experimental
observation, even with the use of a cutoff frequency.Comment: 4 pages, 2 figures, very brief review of optical sum rule anomal
Critical and direct involvement of the CD23 stalk region in IgE binding
BackgroundThe low-affinity receptor for IgE, FcεRII (CD23), contributes to allergic inflammation through allergen presentation to T cells, regulation of IgE responses, and enhancement of transepithelial allergen migration.ObjectiveWe sought to investigate the interaction between CD23, chimeric monoclonal human IgE, and the corresponding birch pollen allergen Bet v 1 at a molecular level.MethodsWe expressed 4 CD23 variants. One variant comprised the full extracellular portion of CD23, including the stalk and head domain; 1 variant was identical with the first, except for an amino acid exchange in the stalk region abolishing the N-linked glycosylation site; and 2 variants represented the head domain, 1 complete and 1 truncated. The 4 CD23 variants were purified as monomeric and structurally folded proteins, as demonstrated by gel filtration and circular dichroism. By using a human IgE mAb, the corresponding allergen Bet v 1, and a panel of antibodies specific for peptides spanning the CD23 surface, both binding and inhibition assays and negative stain electron microscopy were performed.ResultsA hitherto unknown IgE-binding site was mapped on the stalk region of CD23, and the non–N-glycosylated monomeric version of CD23 was superior in IgE binding compared with glycosylated CD23. Furthermore, we demonstrated that a therapeutic anti-IgE antibody, omalizumab, which inhibits IgE binding to FcεRI, also inhibited IgE binding to CD23.ConclusionOur results provide a new model for the CD23-IgE interaction. We show that the stalk region of CD23 is crucially involved in IgE binding and that the interaction can be blocked by the therapeutic anti-IgE antibody omalizumab
Optical Sum Rule in Finite Bands
In a single finite electronic band the total optical spectral weight or
optical sum carries information on the interactions involved between the charge
carriers as well as on their band structure. It varies with temperature as well
as with impurity scattering. The single band optical sum also bears some
relationship to the charge carrier kinetic energy and, thus, can potentially
provide useful information, particularly on its change as the charge carriers
go from normal to superconducting state. Here we review the considerable
advances that have recently been made in the context of high oxides, both
theoretical and experimental.Comment: Review article accepted for publication in J. Low Temp. Phys. 29
pages, 33 figure
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