1,807 research outputs found
Exact density-functional potentials for time-dependent quasiparticles
We calculate the exact Kohn-Sham potential that describes, within
time-dependent density-functional theory, the propagation of an electron
quasiparticle wavepacket of non-zero crystal momentum added to a ground-state
model semiconductor. The potential is observed to have a highly nonlocal
functional dependence on the charge density, in both space and time, giving
rise to features entirely lacking in local or adiabatic approximations. The
dependence of the non-equilibrium part of the Kohn-Sham electric field on the
local current and charge density is identified as a key element of the correct
Kohn-Sham functional.Comment: 4 pages, 3 figure
Electron localisation in static and time-dependent one-dimensional model systems
Electron localization is the tendency of an electron in a many-body system to
exclude other electrons from its vicinity. Using a new natural measure of
localization based on the exact manyelectron wavefunction, we find that
localization can vary considerably between different ground-state systems, and
can also be strongly disrupted, as a function of time, when a system is driven
by an applied electric field. We use our new measure to assess the well-known
electron localization function (ELF), both in its approximate single-particle
form (often applied within density-functional theory) and its full
many-particle form. The full ELF always gives an excellent description of
localization, but the approximate ELF fails in time-dependent situations, even
when the exact Kohn-Sham orbitals are employed.Comment: 7 pages, 4 figure
Myelin basic protein peptide 45–89 induces the release of nitric oxide from microglial cells.
Continuous (24 h) exposure of mixed oligodendrocyte/microglial cells to peptides
45–89 derived from citrullinated C8 isoforms of myelin basic protein (MBP) induces
cell death. In contrast, MBP-C8 at the same molecular concentration is not
toxic to oligodendrocyte/microglial cells as detected by the MTT test and trypan
blue exclusion method. The loss of oligodendrocyte/microglial cells resulted in the
release of cytochrome c from mitochondria, suggesting MBP 45–89-induced
apoptosis. On the other hand, peptides 45–89 stimulated the secretion of nitric
oxide from microglial cells only via induction of iNOS. The addition of peptide
45–89 to the microglial cells led to a decrease of the level of the inhibitory protein
IkB, indicating that activation of the transcription factor NF-kB is involved in these
processes. We propose that the immunodominant peptide 45–89 induces damage of
oligodendrocytes by activation of microglial cells and subsequent generation of
nitric oxide, and that this may be the first step in the initiation of autoimmunity
Diffusional Relaxation in Random Sequential Deposition
The effect of diffusional relaxation on the random sequential deposition
process is studied in the limit of fast deposition. Expression for the coverage
as a function of time are analytically derived for both the short-time and
long-time regimes. These results are tested and compared with numerical
simulations.Comment: 9 pages + 2 figure
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