1,720 research outputs found
Original Sin in Arminian Theology and its Antitheses
The study or this doctrine of original sin in Arminian theology and its antitheses shall be our theme, since it is beneficial for understanding the religious thinking of modern man
Order-disorder transition in nanoscopic semiconductor quantum rings
Using the path integral Monte Carlo technique we show that semiconductor
quantum rings with up to six electrons exhibit a temperature, ring diameter,
and particle number dependent transition between spin ordered and disordered
Wigner crystals. Due to the small number of particles the transition extends
over a broad temperature range and is clearly identifiable from the electron
pair correlation functions.Comment: 4 pages, 5 figures, For recent information on physics of small
systems see http://www.smallsystems.d
Optical Response of Grating-Coupler-Induced Intersubband Resonances: The Role of Wood's Anomalies
Grating-coupler-induced collective intersubband transitions in a
quasi-two-dimensional electron system are investigated both experimentally and
theoretically. Far-infrared transmission experiments are performed on samples
containing a quasi-two-dimensional electron gas quantum-confined in a parabolic
quantum well. For rectangular shaped grating couplers of different periods we
observe a strong dependence of the transmission line shape and peak height on
the period of the grating, i.e. on the wave vector transfer from the diffracted
beams to the collective intersubband resonance. It is shown that the line shape
transforms with increasing grating period from a Lorentzian into a strongly
asymmetric line shape. Theoretically, we treat the problem by using the
transfer-matrix method of local optics and apply the modal-expansion method to
calculate the influence of the grating. The optically uniaxial
quasi-two-dimensional electron gas is described in the long-wavelength limit of
the random-phase approximation by a local dielectric tensor, which includes
size quantization effects. Our theory reproduces excellently the experimental
line shapes. The deformation of the transmission line shapes we explain by the
occurrence of both types of Wood's anomalies.Comment: 28 pages, 7 figures. Physical Review B , in pres
Inelastic light scattering and the excited states of many-electron quantum dots
A consistent calculation of resonant inelastic (Raman) scattering amplitudes
for relatively large quantum dots, which takes account of valence-band mixing,
discrete character of the spectrum in intermediate and final states, and
interference effects, is presented. Raman peaks in charge and spin channels are
compared with multipole strengths and with the density of energy levels in
final states. A qualitative comparison with the available experimental results
is given.Comment: 5 pages, accepted in J. Phys.: Condens. Matte
Localized magnetoplasmon modes arising from broken translational symmetry in semiconductor superlattices
The electromagnetic propagator associated with the localized collective
magnetoplasmon excitations in a semiconductor superlattice with broken
translational symmetry, is calculated analytically within linear response
theory. We discuss the properties of these collective excitations in both
radiative and non-radiative regimes of the electromagnetic spectra. We find
that low frequency retarded modes arise when the surface density of carriers at
the symmetry breaking layer is lower than the density at the remaining layers.
Otherwise a doublet of localized, high-frequency magnetoplasmon-like modes
occurs.Comment: Revtex file + separate pdf figure
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Extracellular vesicles swarm the cancer microenvironment: from tumor–stroma communication to drug intervention
Intercellular communication sets the pace for transformed cells to survive and to thrive. Extracellular vesicles (EVs), such as exosomes, microvesicles and large oncosomes, are involved in this process shuttling reciprocal signals and other molecules between transformed and stromal cells, including fibroblasts, endothelial and immune cells. As a result, these cells are adapted or recruited to a constantly evolving cancer microenvironment. Moreover, EVs take part in the response to anticancer therapeutics not least by promoting drug resistance throughout the targeted tumor. Finally, circulating EVs can also transport important molecules to remote destinations in order to prime metastatic niches in an otherwise healthy tissue. Although the understanding of EV biology remains a major challenge in the field, their characteristics create new opportunities for advances in cancer diagnostics and therapeutics
The Sphingosine-1-phospate receptor 1 mediates S1P action during cardiac development
<p>Abstract</p> <p>Background</p> <p>Sphingosine-1-phosophate (S1P) is a biologically active sphingolipid metabolite that influences cellular events including differentiation, proliferation, and migration. S1P acts through five distinct cell surface receptors designated S1P<sub>1-5</sub>R, with S1P<sub>1</sub>R having the highest expression level in the developing heart. S1P<sub>1</sub>R is critical for vascular maturation, with its loss leading to embryonic death by E14.5; however, its function during early cardiac development is not well known. Our previous studies demonstrated that altered S1P levels adversely affects atrioventricular (AV) canal development <it>in vitro</it>, with reduced levels leading to cell death and elevated levels inhibiting cell migration and endothelial to mesenchymal cell transformation (EMT).</p> <p>Results</p> <p>We determined, by real-time PCR analysis, that S1P<sub>1</sub>R was expressed at least 10-fold higher than other S1P receptors in the developing heart. Immunohistochemical analysis revealed S1P<sub>1</sub>R protein expression in both endothelial and myocardial cells in the developing atrium and ventricle. Using AV canal cultures, we observed that treatment with either FTY720 (an S1P<sub>1,3,4,5</sub>R agonist) or KRP203 (an S1P<sub>1</sub>R-specific agonist) caused similar effects on AV canal cultures as S1P treatment, including induction of cell rounding, inhibition of cell migration, and inhibition of EMT. <it>In vivo</it>, morphological analysis of embryonic hearts at E10.5 revealed that S1P<sub>1</sub>R-/- hearts were malformed with reduced myocardial tissue. In addition to reduced myocardial tissue, E12.5 S1P<sub>1</sub>R-/- hearts had disrupted morphology of the heart wall and trabeculae, with thickened and disorganized outer compact layer and reduced fibronectin (FN) deposition compared to S1P<sub>1</sub>R+/+ littermates. The reduced myocardium was accompanied by a decrease in cell proliferation but not an increase in apoptosis.</p> <p>Conclusions</p> <p>These data indicate that S1P<sub>1</sub>R is the primary mediator of S1P action in AV canal cultures and that loss of S1P<sub>1</sub>R expression <it>in vivo </it>leads to malformed embryonic hearts, in part due to reduced fibronectin expression and reduced cell proliferation.</p
Jahn-Teller stabilization of a "polar" metal oxide surface: Fe3O4(001)
Using ab initio thermodynamics we compile a phase diagram for the surface of
Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto
ignored polar termination with octahedral iron and oxygen forming a wave-like
structure along the [110]-direction is identified as the lowest energy
configuration over a broad range of oxygen gas-phase conditions. This novel
geometry is confirmed in a x-ray diffraction analysis. The stabilization of the
Fe3O4(001)-surface goes together with dramatic changes in the electronic and
magnetic properties, e.g., a halfmetal-to-metal transition.Comment: 4 pages, 4 figure
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