82,478 research outputs found
Fully anharmonic infrared cascade spectra of polycyclic aromatic hydrocarbons
The infrared (IR) emission of polycyclic aromatic hydrocarbons (PAHs)
permeates our universe; astronomers have detected the IR signatures of PAHs
around many interstellar objects. The IR emission of interstellar PAHs differs
from their emission as seen under conditions on Earth, as they emit through a
collisionless cascade down through their excited vibrational states from high
internal energies. The difficulty in reproducing interstellar conditions in the
laboratory results in a reliance on theoretical techniques. However, the size
and complexity of PAHs requires careful consideration when producing the
theoretical spectra. In this work we outline the theoretical methods necessary
to lead to a fully theoretical IR cascade spectra of PAHs including: an
anharmonic second order vibrational perturbation theory (VPT2) treatment; the
inclusion of Fermi resonances through polyads; and the calculation of
anharmonic temperature band shifts and broadenings (including resonances)
through a Wang--Landau approach. We also suggest a simplified scheme to
calculate vibrational emission spectra that retains the essential
characteristics of the full IR cascade treatment and can directly transform low
temperature absorption spectra in IR cascade spectra. Additionally we show that
past astronomical models were in error in assuming a 15 cm correction
was needed to account for anharmonic emission effects
Charge and spin density modulations in semiconductor quantum wires
We investigate static charge and spin density modulation patterns along a
ferromagnet/semiconductor single junction quantum wire in the presence of
spin-orbit coupling. Coherent scattering theory is used to calculate the charge
and spin densities in the ballistic regime. The observed oscillatory behavior
is explained in terms of the symmetry of the charge and spin distributions of
eigenstates in the semiconductor quantum wire. Also, we discuss the condition
that these charge and spin density oscillations can be observed experimentally.Comment: 7 pages, 8 figures (low-resolution
Universal Tomonaga-Luttinger liquid phases in one-dimensional strongly attractive SU(N) fermionic cold atoms
A simple set of algebraic equations is derived for the exact low-temperature
thermodynamics of one-dimensional multi-component strongly attractive fermionic
atoms with enlarged SU(N) spin symmetry and Zeeman splitting. Universal
multi-component Tomonaga-Luttinger liquid (TLL) phases are thus determined. For
linear Zeeman splitting, the physics of the gapless phase at low temperatures
belongs to the universality class of a two-component asymmetric TLL
corresponding to spin-neutral N-atom composites and spin-(N-1)/2 single atoms.
The equation of states is also obtained to open up the study of multi-component
TLL phases in 1D systems of N-component Fermi gases with population imbalance.Comment: 12 pages, 3 figure
Application of Volcano Plots in Analyses of mRNA Differential Expressions with Microarrays
Volcano plot displays unstandardized signal (e.g. log-fold-change) against
noise-adjusted/standardized signal (e.g. t-statistic or -log10(p-value) from
the t test). We review the basic and an interactive use of the volcano plot,
and its crucial role in understanding the regularized t-statistic. The joint
filtering gene selection criterion based on regularized statistics has a curved
discriminant line in the volcano plot, as compared to the two perpendicular
lines for the "double filtering" criterion. This review attempts to provide an
unifying framework for discussions on alternative measures of differential
expression, improved methods for estimating variance, and visual display of a
microarray analysis result. We also discuss the possibility to apply volcano
plots to other fields beyond microarray.Comment: 8 figure
Facile O-atom insertion into C-C and C-H bonds by a trinuclear copper complex designed to harness a singlet oxene
Two trinuclear copper [CuICuICuI(L)]1+ complexes have been prepared with the multidentate ligands (L) 3,3'-(1,4-diazepane-1,4-diyl)bis(1-((2-(dimethylamino)ethyl)(methyl)amino)propan-2-ol) (7-Me) and (3,3'-(1,4-diazepane-1,4-diyl)bis(1-((2-(diethylamino) ethyl)(ethyl) amino)propan-2-ol) (7-Et) as models for the active site of the particulate methane monooxygenase (pMMO). The ligands were designed to form the proper spatial and electronic geometry to harness a "singlet oxene," according to the mechanism previously suggested by our laboratory. Consistent with the design strategy, both [CuICuICuI(L)]1+ reacted with dioxygen to form a putative bis(µ3-oxo)CuIICuIICuIII species, capable of facile O-atom insertion across the central C-C bond of benzil and 2,3-butanedione at ambient temperature and pressure. These complexes also catalyze facile O-atom transfer to the C-H bond of CH3CN to form glycolonitrile. These results, together with our recent biochemical studies on pMMO, provide support for our hypothesis that the hydroxylation site of pMMO contains a trinuclear copper cluster that mediates C-H bond activation by a singlet oxene mechanism
Upregulation of glycolysis and oxidative phosphorylation in benzo[β]pyrene and arsenic-induced rat lung epithelial transformed cells
published_or_final_versio
Optical study on doped polyaniline composite films
Localization driven by disorder has a strong influence on the conducting
property of conducting polymer. A class of authors hold the opinion that
disorder in the material is homogeneous and conducting polymer is disordered
metal close to Anderson-Mott Metal-Insulator transition, while others treat the
disorder as inhomogeneous and have the conclusion that conducting polymer is a
composite of ordered metallic regions and disordered insulating regions. The
morphology of conducting polymers is an important factor that have influence on
the type and extent of disorder. Different protonic acids used as dopants and
moisture have affection on polymer chain arrangement and interchain
interactions. A PANI-CSA film, two PANI-CSA/PANI-DBSA composite films with
different dopants ratio, and one of the composite films with different moisture
content are studied. Absolute reflectivity measurements are performed on the
films. Optical conductivity and the real part of dielectric function are
calculated by Kramers-Kronig(KK) relations. and
derivate from simple Drude model in low frequency range
and tendencies of the three sample are different and non-monotonic. The
Localization Modified Drude model(LMD) in the framework of Anderson-Mott theory
can not give a good fit to the experimental data. By introducing a distribution
of relaxation time into LMD, reasonable fits for all three samples are
obtained. This result supports the inhomogeneous picture.Comment: 6 figures, 7 page
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