11,081 research outputs found
ELECTROCHEMICAL SURFACE-ENHANCED RAMAN SPECTRA AND PLASMON-DRIVEN PHOTOELECTROCHEMICAL REACTION OF P-AMINOTHIOPHENOL ON SILVER ELECTRODE OF NANOSTRUCTURES
Surface plasmon resonance (SPR) of noble metal nanoparticles (NPs) provides a pathway to efficiently absorb and confine light to nanoscale surface electrons, thereby bridging photonics and photoelectrochemistry. This not only produces the giant Raman intensity enhancement in surface-enhanced Raman spectroscopy (SERS), but also results in plasmon-driven chemical reaction on metal nanostructures. We have studied the surface-enhanced Raman spectra of p-aminothiophenol adsorbed on silver electrodes of nanostructures. In this work, we studied SPR-enhanced photoelectrochemical synergistic reactions by SERS to improve chemical reaction activity and examine changes in reaction selectivity. We first demonstrate that hot carriers arising from SPR decay contribute to the surface catalytic coupling reaction of PATP on a silver NP electrode. Then, by using potential step electrochemical SERS, we further inspect the kinetics of the surface catalytic coupling reaction by monitoring the time-dependent SERS intensity of the characteristic band at 1436 cm, which can be attributed to the stretching vibration of the N=N double bond of p,p’-dimercaptoazobenzene (DMAB). When synergistically combined with the modulation of pH at electrochemical interfaces, SPR-enhanced photoelectrochemical reactions can be further gain reaction efficiency and selectivity for the formation of DMAB and other surface species at higher potentials. The electrochemical SPR effect provides a viable approach for studying the photoelectrochemistry through combining SERS at the interface of nanoparticle-modified metal electrodes and electrolytes
THEORETICAL STUDY OF SURFACE-ENHANCED RAMAN SPECTRA OF WATER AND IONIC COMPLEXES IN ELECTROCHEMICAL INTERFACES
Water plays a very important role in surface science of electrochemical interfaces, closely associated with energy source, environment, our living, and life processes. However, it is very difficult to be observed from normal Raman spectra of water in electrochemical interfaces. Although the surface-enhanced Raman scattering effect can have million-fold Raman signal enhancement for molecules on adsorbed silver and gold electrodes of nanostructures, the surface-enhanced Raman spectrum of water is hard to be measured due to its very small Raman scattering cross section, weak adsorption ability, and very few surface molecular number relative to the bulk. Thus only electrochemical SERS spectra of water have been observed in electrode/electrolyte interfaces so far. Our present work focuses on the chemical enhancement from hydrogen bonding interaction, surface adsorption, halide ions, interfacial electric field effects on SERS signals of water adsorbed on silver electrodes, by combining the metallic cluster model and hybrid density functional theory (DFT-B3LYP) methods. The interfacial structures, binding interactions and the anion effect from different halides including chloride, bromide, and iodide ions have been analyzed and compared with experimental measurements in literatures. Then the excited states of halide ions modified active sites on roughened silver electrode have been discussed. Especially, our time-dependent DFT (TD-DFT) calculations predicted that halide ions can form low-lying excited states of surface complexes, like the photon-induced electron transfer states, and finally contribute to the chemical enhancement of SERS signals of water. Furthermore, we proposed that the halide effect on the relative SERS intensities of water is a good example for understanding the chemical enhancement of SERS active sites modified by halide ions in electrochemical systems
Modelling the electronic structure and magnetic properties of LiFeAs and FeSe using hybrid-exchange density functional theory
The electronic structure and magnetic properties of LiFeAs and FeSe have been
studied using hybrid exchange density functional theory. The total energies for
a unit cell in LiFeAs and FeSe with different spin states including
non-magnetic and spin-2 are calculated. The spin-2 configuration has the lower
energy for both LiFeAs and FeSe. The computed anti-ferromagnetic exchange
interactions between spins on the nearest (next nearest) neighbouring Fe atoms
in LiFeAs and FeSe are approximately 14 (17) meV and 6 (13) meV respectively.
The total energies of the checkerboard and stripe-type anti-ferromagnetic
ordering for LiFeAs and FeSe are compared, yielding that for LiFeAs the
checkerboard is lower whereas for FeSe the stripe-type is lower. However, owing
to the fact that the exchange interaction of the next nearest neighbour is
larger than that of the nearest one, which means that the collinear ordering
might be the ground state. These results are in agreement with previous
theoretical calculations and experiments. Especially the calculations for
LiFeAs indicate a co-existence of conducting d-bands at the Fermi surface and
d-orbital magnetism far below the Fermi surface. The theoretical results
presented here might be useful for the experimentalists working on the
electronic structure and magnetism of iron-based superconductors.Comment: 7 pages, 4 figures, 1 table, accepted by Solid State Communication
The color gradients of spiral disks in the Sloan Digital Sky Survey
We investigate the radial color gradients of galactic disks using a sample of
about 20,000 face-on spiral galaxies selected from the fourth data release of
the Sloan Digital Sky Survey (SDSS-DR4). We combine galaxies with similar
concentration, size and luminosity to construct composite galaxies, and then
measure their color profiles by stacking the azimuthally averaged radial color
profiles of all the member galaxies. Except for the smallest galaxies (R_{50}<3
kpc), almost all galaxies show negative disk color gradients with mean g-r
gradient G_{gr}=-0.006 mag kpc^{-1} and r-z gradient G_{rz}=-0.018 mag
kpc^{-1}. The disk color gradients are independent of the morphological types
of galaxies and strongly dependent on the disk surface brightness \mu_{d}, with
lower surface brightness galactic disks having steeper color gradients. We
quantify the intrinsic correlation between color gradients and surface
brightness as G_{gr}=-0.011\mu_{d}+0.233 and G_{rz}=-0.015\mu_{d}+0.324. These
quantified correlations provide tight observational constraints on the
formation and evolution models of spiral galaxies.Comment: 20 pages, 5 figures, Accepted for publication in RAA (Research in
Astronomy and Astrophysics
Association of Intrarenal B-Cell Infiltrates with Clinical Outcome in Lupus Nephritis: A Study of 192 Cases
Background. Lupus nephritis (LN) remains a major cause of morbidity and end-stage renal disease. Dysfunction of B lymphocytes is thought to be important in the pathogenesis of SLE/LN. Intrarenal B cells have been found in several forms of inflammatory kidney diseases although their role in LN renal is not well defined. Methods. Intrarenal B cells were analyzed in 192 renal biopsies from patients diagnosed with lupus nephritis. Immunohistochemical staining of serial sections was performed for each LN patient using CD20, CD3, and CD21 antibodies. Results. Intrarenal B cells were more likely to be associated with class IV LN and were mainly distributed in the renal interstitium, with very few in the glomerulus. The systemic lupus erythematosus disease activity index (SLEDAI), blood urea nitrogen, and serum creatinine levels were all significantly greater in the LN-B cell groups (all P<0.05). LN renal activity and chronicity indices correlated with B-cells infiltrates (all P<0.0001). Renal biopsies were classified into four distinct categories according to the organizational grade of inflammatory cell infiltrates. Germinal center- (GC-) like structures were not identified in any LN biopsies. Conclusion. It is hypothesized that intrarenal B cells enhance immunological responses and exaggerate the local immune response to persisting autoimmune damage in the tubulointerstitium
Radio Continuum and HI study of Blue Compact Dwarf Galaxies
The multifrequency radio continuum and 21cm HI observations of five blue
compact dwarf (BCD) galaxies, Mrk 104, Mrk 108, Mrk 1039, Mrk 1069 and I Zw 97
using the Giant Meterwave Radio Telescope (GMRT) are presented here. Radio
continuum emission at 610 MHz and 325 MHz is detected from all the observed
galaxies whereas only a few are detected at 240 MHz. In our sample, three
galaxies are members of groups and two galaxies (Mrk 1069 and I Zw 97) are
isolated galaxies. The radio emission from Mrk 104 and Mrk 108 is seen to
encompass the entire optical galaxy whereas the radio emission from Mrk 1039,
Mrk 1069, I Zw 97 is confined to massive HII regions. This, we suggest,
indicates that the star formation in the latter group of galaxies has recently
been triggered and that the environment in which the galaxy is evolving plays a
role. Star formation rates (SFR) calculated from 610 MHz emission is in the
range 0.01-0.1 M_sun/yr; this is similar to the SFR obtained for individual
star forming regions in BCDs. The integrated radio spectra of four galaxies are
modelled over the frequency range where data is available. We find that two of
the galaxies Mrk 1069 and Mrk 1039, show a turnover at low frequencies which is
well fitted by free-free absorption whereas the other two galaxies, Mrk 104 and
Mrk 108, show a power law at the lowest GMRT frequencies. The flatter spectrum,
localized star formation and radio continuum in isolated galaxies lend support
to stochastic self-propagating star formation (SSPSF). The HI observations of
four galaxies Mrk 104, Mrk 108, Mrk 1039 and Mrk 1069 show extended disks as
large as ~1.1-6 times the optical size. All the observed BCDs (except Mrk 104)
show rotating disk with a half power width of ~50-124 km/s. Solid body rotation
is common in our sample. We note that the tidal dwarf (TD) origin is possible
for two of the BCDs in our sample.Comment: 39 pages, 8 figures, 38 sub-figures. Accepted for publication in Ap
Loss of survivin in intestinal epithelial progenitor cells leads to mitotic catastrophe and breakdown of gut immune homeostasis
A tightly regulated balance of proliferation and cell death of intestinal epithelial cells (IECs) is essential for maintenance of gut homeostasis. Survivin is highly expressed during embryogenesis and in several cancer types, but little is known about its role in adult gut tissue. Here, we show that Survivin is specifically expressed in transit-amplifying cells and Lgr5(+) stem cells. Genetic loss of Survivin in IECs resulted in destruction of intestinal integrity, mucosal inflammation, and death of the animals. Survivin deletion was associated with decreased epithelial proliferation due to defective chromosomal segregation. Moreover, Survivin-deficient animals showed induced phosphorylation of p53 and H2AX and increased levels of cell-intrinsic apoptosis in IECs. Consequently, induced deletion of Survivin in Lgr5(+) stem cells led to cell death. In summary, Survivin is a key regulator of gut tissue integrity by regulating epithelial homeostasis in the stem cell niche
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