662 research outputs found
Interacting Dirac Materials
We investigate the extent to which the class of Dirac materials in
two-dimensions provides general statements about the behavior of both fermionic
and bosonic Dirac quasiparticles in the interacting regime. For both
quasiparticle types, we find common features for the interaction induced
renormalization of the conical Dirac spectrum. We perform the perturbative
renormalization analysis and compute the self-energy for both quasiparticle
types with different interactions and collate previous results from the
literature whenever necessary. Guided by the systematic presentation of our
results in Table~\ref{Summary}, we conclude that long-range interactions
generically lead to an increase of the slope of the single-particle Dirac cone,
whereas short-range interactions lead to a decrease. The quasiparticle
statistics does not qualitatively impact the self-energy correction for
long-range repulsion but does affect the behavior of short-range coupled
systems, giving rise to different thermal power-law contributions. The
possibility of a universal description of the Dirac materials based on these
features is also mentioned.Comment: 19 pages and 12 Figures; Contains 6 Appendice
Fluorescence-based measurements of membrane-bound angiotensin converting enzyme 2 activity using Xenopus Laevis Oocytes
Functional investigations of enzymes involving cellular expression systems are important for pharmacological studies. The precise control of expression is challenging in transiently transfected mammalian cell lines. Here, we explored the ability of Xenopus laevis oocytes to express a membrane-bound enzyme for functional characterization using standard 96-well plates and a fluorescence-based plate reader assay. We microinjected oocytes with cRNA encoding the angiotensin converting enzyme 2 (ACE2) and measured the enzymatic activity in single oocytes using a commercial fluorescence-based assay. The injected oocytes showed up to a 50-fold increase in fluorescence compared to uninjected oocytes. This fluorescence intensity was dose-dependent on the amount of ACE2 cRNA. These results suggest that Xenopus oocytes can be used for the functional evaluation of membrane-bound enzymes, decreasing the experimental workload
The electronic structure of poly(pyridine-2,5-diyl) investigated by soft x-ray absorption and emission spectroscopies
The electronic structure of the poly-pyridine conjugated polymer has been
investigated by resonant and nonresonant inelastic X-ray scattering and X-ray
absorption spectroscopies using synchrotron radiation. The measurements were
made for both the carbon and nitrogen contents of the polymer. The analysis of
the spectra has been carried out in comparison with molecular orbital
calculations taking the repeat-unit cell as a model molecule of the polymer
chain. The simulations indicate no significant differences in the absorption
and in the non-resonant X-ray scattering spectra for the different isomeric
geometries, while some isomeric dependence of the resonant spectra is
predicted. The resonant emission spectra show depletion of the {\pi} electron
bands in line with symmetry selection and momentum conservation rules. The
effect is most vizual for the carbon spectra; the nitrogen spectra are
dominated by lone pair n orbital emission of {\sigma} symmetry and are less
frequency dependent.Comment: 11 pages, 7 figures, 1 table,
http://www.sciencedirect.com/science/article/pii/S030101049800262
Competition between decay and dissociation of core-excited OCS studied by X-ray scattering
We show the first evidence of dissociation during resonant inelastic soft
X-ray scattering. Carbon and oxygen K-shell and sulfur L-shell resonant and
non-resonant X-ray emission spectra were measured using monochromatic
synchrotron radiation for excitation and ionization. After sulfur, L2,3 ->
{\pi}*, {\sigma}* excitation, atomic lines are observed in the emission spectra
as a consequence of competition between de-excitation and dissociation. In
contrast the carbon and oxygen spectra show weaker line shape variations and no
atomic lines. The spectra are compared to results from ab initio calculations
and the discussion of the dissociation paths is based on calculated potential
energy surfaces and atomic transition energies.Comment: 12 pages, 6 pictures, 2 tables,
http://link.aps.org/doi/10.1103/PhysRevA.59.428
Resonant inelastic soft-x-ray scattering spectra at the N1s and C1s edges of poly(pyridine-2,5-diyl)
Resonant inelastic scattering measurements of poly(pyridine-2,5-diyl) have
been performed at the N1s and C1s edges using synchrotron radiation. For
comparison, molecular orbital calculations of the spectra have been carried out
with the repeat unit as a model molecule of the polymer chain. The resonant
emission spectra show depletion of the p electron bands which is consistent
with symmetry selection and momentum conservation rules. The depletion is most
obvious in the resonant inelastic scattering spectra of carbon while the
nitrogen spectra are dominated by lone pair n orbital emission of s symmetry
and are less excitation energy dependent. By comparing the measurements to
calculations an isomeric dependence of the resonant spectra is found giving
preference to two of the four possible isomers in the polymer.Comment: 6 pages, 3 figures,
http://www.sciencedirect.com/science/article/pii/S036820489800354
X-ray Raman scattering study of aligned polyfluorene
We present a non-resonant inelastic x-ray scattering study at the carbon
K-edge on aligned poly[9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl] and show that
the x-ray Raman scattering technique can be used as a practical alternative to
x-ray absorption measurements. We demonstrate that this novel method can be
applied to studies on aligned -conjugated polymers complementing
diffraction and optical studies. Combining the experimental data and a very
recently proposed theoretical scheme we demonstrate a unique property of x-ray
Raman scattering by performing the symmetry decomposition on the density of
unoccupied electronic states into - and -type symmetry contributions.Comment: 19 pages, 8 figure
Nitrogen to phosphorus ratio of plant biomass versus soil solution in a tropical pioneer tree, Ficus insipida
It is commonly assumed that the nitrogen to phosphorus (N:P) ratio of a terrestrial plant reflects the relative availability of N and P in the soil in which the plant grows. Here, this was assessed for a tropical pioneer tree, Ficus insipida. Seedlings were grown in sand and irrigated with nutrient solutions containing N:P ratios ranging from <1 to >100. The experimental design further allowed investigation of physiological responses to N and P availability. Homeostatic control over N:P ratios was stronger in leaves than in stems or roots, suggesting that N:P ratios of stems and roots are more sensitive indicators of the relative availability of N and P at a site than N:P ratios of leaves. The leaf N:P ratio at which the largest plant dry mass and highest photosynthetic rates were achieved was ∼11, whereas the corresponding whole-plant N:P ratio was ∼6. Plant P concentration varied as a function of transpiration rate at constant nutrient solution P concentration, possibly due to transpiration-induced variation in the mass flow of P to root surfaces. The transpiration rate varied in response to nutrient solution N concentration, but not to nutrient solution P concentration, demonstrating nutritional control over transpiration by N but not P. Water-use efficiency varied as a function of N availability, but not as a function of P availability
Coevolution of Genome Architecture and Social Behavior.
Although social behavior can have a strong genetic component, it can also result in selection on genome structure and function, thereby influencing the evolution of the genome itself. Here we explore the bidirectional links between social behavior and genome architecture by considering variation in social and/or mating behavior among populations (social polymorphisms) and across closely related species. We propose that social behavior can influence genome architecture via associated demographic changes due to social living. We establish guidelines to exploit emerging whole-genome sequences using analytical approaches that examine genome structure and function at different levels (regulatory vs structural variation) from the perspective of both molecular biology and population genetics in an ecological context
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