11,891 research outputs found
Structural modification of TiO2 nanorod films with an influence on the photovoltaic efficiency of a dye-sensitized solar cell (DSSC)
TiO2 nanorod films have been deposited on ITO substrates by dc reactive magnetron sputtering technique. The structures of these nanorod films were modified by the variation of the oxygen pressure during the sputtering process. Although all these TiO2 nanorod films deposited at different oxygen pressures show an anatase structure, the orientation of the nanorod films varies with the oxygen pressure. Only a very weak (101) diffraction peak can be observed for the TiO2 nanorod film prepared at low oxygen pressure. However, as the oxygen pressure is increased, the (220) diffraction peak appears and the intensity of this diffraction peak is increased with the oxygen pressure. The results of the SEM show that these TiO2 nanorods are perpendicular to the ITO substrate. At low oxygen pressure, these sputtered TiO2 nanorods stick together and have a dense structure. As the oxygen pressure is increased, these sputtered TiO2 nanorods get separated gradually and have a porous structure. The optical transmittance of these TiO2 nanorod films has been measured and then fitted by OJL model. The porosities of the TiO2 nanorod films have been calculated. The TiO2 nanorod film prepared at high oxygen pressure shows a high porosity. The dye-sensitized solar cells (DSSCs) have been assembled using these TiO2 nanorod films prepared at different oxygen pressures as photoelectrode. The optimum performance was achieved for the DSSC using the TiO2 nanorod film with the highest (220) diffraction peak and the highest porosity
Discrete R-symmetries and Anomaly Universality in Heterotic Orbifolds
We study discrete R-symmetries, which appear in 4D low energy effective field
theory derived from hetetoric orbifold models. We derive the R-symmetries
directly from geometrical symmetries of orbifolds. In particular, we obtain the
corresponding R-charges by requiring that the couplings be invariant under
these symmetries. This allows for a more general treatment than the explicit
computations of correlation functions made previously by the authors, including
models with discrete Wilson lines, and orbifold symmetries beyond
plane-by-plane rotational invariance. Surprisingly, for the cases covered by
earlier explicit computations, the R-charges differ from the previous result.
We study the anomalies associated with these R-symmetries, and comment on the
results.Comment: 21 pages, 2 figures. Minor changes, typos corrected. Matches JHEP
published versio
Particle-in-cell simulations of rf breakdown
Breakdown voltages of a capacitively coupled radio frequency argon discharge
at 27 MHz are studied. We use a one-dimensional electrostatic PIC code to
investigate the effect of changing the secondary emission properties of the
electrodes on the breakdown voltage, particularly at low pd values. Simulation
results are compared with the available experimental results and a satisfactory
agreement is found.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
A mechanism for extremely weak SpaP-expression in Streptococcus mutans strain Z1
Background: Streptococcus mutans surface-protein antigen (SpaP, PAc, or antigen I/II) has been well known to play an important role in initial attachment to tooth surfaces. However, strains with weak SpaP-expression were recently reported to be found in natural populations of S. mutans. The S. mutans gbpC-negative strain Z1, which we previously isolated from saliva and plaque samples, apparently expresses relatively low levels of SpaP protein compared to S. mutans strains MT8148 or UA159. Objective: To elucidate the mechanism for weak SpaP-expression in this strain, the spaP gene region in strain Z1 was amplified by polymerase chain reaction (PCR) and analyzed. Methods: Allelic exchange mutants between strains Z1 and UA159 involving the spaP gene region were constructed. The SpaP protein expressed in the mutants was detected with Coomasie Brilliant Blue (CBB)-staining and Western blot analysis following SDS-PAGE. Results: The 4689 bp spaP gene coding sequence for Z1 appeared to be intact. In contrast, a 20 bp nucleotide sequence appeared to be deleted from the region immediately upstream from the Z1 spaP gene when compared to the same region in UA159. The 216 bp and 237 bp intergenic fragments upstream from the spaP gene, respectively, from Z1 and UA159 were isolated, modified, and transformed into the other strain by allelic replacement. The resultant UA159-promoter region-mutant exhibited extremely weak SpaP-expression similar to that of strain Z1 and the Z1 complemented mutant expressed Spa protein levels like that of strain UA159. Conclusion: These results suggest that weak SpaP-expression in strain Z1 resulted from a 20 bp-deletion in the spaP gene promoter region
Neutrino Mass, Sneutrino Dark Matter and Signals of Lepton Flavor Violation in the MRSSM
We study the phenomenology of mixed-sneutrino dark matter in the Minimal
R-Symmetric Supersymmetric Standard Model (MRSSM). Mixed sneutrinos fit
naturally within the MRSSM, as the smallness (or absence) of neutrino Yukawa
couplings singles out sneutrino A-terms as the only ones not automatically
forbidden by R-symmetry. We perform a study of randomly generated sneutrino
mass matrices and find that (i) the measured value of is well
within the range of typical values obtained for the relic abundance of the
lightest sneutrino, (ii) with small lepton-number-violating mass terms
for the right-handed sneutrinos, random
matrices satisfying the constraint have a decent probability of
satisfying direct detection constraints, and much of the remaining parameter
space will be probed by upcoming experiments, (iii) the terms radiatively generate appropriately small Majorana neutrino
masses, with neutrino oscillation data favoring a mostly sterile lightest
sneutrino with a dominantly mu/tau-flavored active component, and (iv) a
sneutrino LSP with a significant mu component can lead to striking signals of
e-mu flavor violation in dilepton invariant-mass distributions at the LHC.Comment: Revised collider analysis in Sec. 5 after fixing error in particle
spectrum, References adde
Selective patterning of ZnO nanorods on silicon substrates using nanoimprint lithography
In this research, nanoimprint lithography (NIL) was used for patterning crystalline zinc oxide (ZnO) nanorods on the silicon substrate. To fabricate nano-patterned ZnO nanorods, patterning of an n-octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) on SiO2 substrate was prepared by the polymer mask using NI. The ZnO seed layer was selectively coated only on the hydrophilic SiO2 surface, not on the hydrophobic OTS SAMs surface. The substrate patterned with the ZnO seed layer was treated with the oxygen plasma to oxidize the silicon surface. It was found that the nucleation and initial growth of the crystalline ZnO were proceeded only on the ZnO seed layer, not on the silicon oxide surface. ZnO photoluminescence spectra showed that ZnO nanorods grown from the seed layer treated with plasma showed lower intensity than those untreated with plasma at 378 nm, but higher intensity at 605 nm. It is indicated that the seed layer treated with plasma produced ZnO nanorods that had a more oxygen vacancy than those grown from seed layer untreated with plasma. Since the oxygen vacancies on ZnO nanorods serve as strong binding sites for absorption of various organic and inorganic molecules. Consequently, a nano-patterning of the crystalline ZnO nanorods grown from the seed layer treated with plasma may give the versatile applications for the electronics devices
Nuclear receptors in vascular biology
Nuclear receptors sense a wide range of steroids and hormones (estrogens, progesterone, androgens, glucocorticoid, and mineralocorticoid), vitamins (A and D), lipid metabolites, carbohydrates, and xenobiotics. In response to these diverse but critically important mediators, nuclear receptors regulate the homeostatic control of lipids, carbohydrate, cholesterol, and xenobiotic drug metabolism, inflammation, cell differentiation and development, including vascular development. The nuclear receptor family is one of the most important groups of signaling molecules in the body and as such represent some of the most important established and emerging clinical and therapeutic targets. This review will highlight some of the recent trends in nuclear receptor biology related to vascular biology
Benchmark performance of low-cost Sb2Se3 photocathodes for unassisted solar overall water splitting
Determining cost-effective semiconductors exhibiting desirable properties for commercial photoelectrochemical water splitting remains a challenge. Herein, we report a Sb2Se3 semiconductor that satisfies most requirements for an ideal high-performance photoelectrode, including a small band gap and favourable cost, optoelectronic properties, processability, and photocorrosion stability. Strong anisotropy, a major issue for Sb2Se3, is resolved by suppressing growth kinetics via close space sublimation to obtain high-quality compact thin films with favourable crystallographic orientation. The Sb2Se3 photocathode exhibits a high photocurrent density of almost 30mAcm(-2) at 0V against the reversible hydrogen electrode, the highest value so far. We demonstrate unassisted solar overall water splitting by combining the optimised Sb2Se3 photocathode with a BiVO4 photoanode, achieving a solar-to-hydrogen efficiency of 1.5% with stability over 10h under simulated 1 sun conditions employing a broad range of solar fluxes. Low-cost Sb2Se3 can thus be an attractive breakthrough material for commercial solar fuel production. While photoelectrochemical water splitting offers an integrated means to convert sunlight to a renewable fuel, cost-effective light-absorbers are rare. Here, authors report Sb2Se3 photocathodes for high-performance photoelectrochemical water splitting devices
A critical evaluation of network and pathway based classifiers for outcome prediction in breast cancer
Recently, several classifiers that combine primary tumor data, like gene
expression data, and secondary data sources, such as protein-protein
interaction networks, have been proposed for predicting outcome in breast
cancer. In these approaches, new composite features are typically constructed
by aggregating the expression levels of several genes. The secondary data
sources are employed to guide this aggregation. Although many studies claim
that these approaches improve classification performance over single gene
classifiers, the gain in performance is difficult to assess. This stems mainly
from the fact that different breast cancer data sets and validation procedures
are employed to assess the performance. Here we address these issues by
employing a large cohort of six breast cancer data sets as benchmark set and by
performing an unbiased evaluation of the classification accuracies of the
different approaches. Contrary to previous claims, we find that composite
feature classifiers do not outperform simple single gene classifiers. We
investigate the effect of (1) the number of selected features; (2) the specific
gene set from which features are selected; (3) the size of the training set and
(4) the heterogeneity of the data set on the performance of composite feature
and single gene classifiers. Strikingly, we find that randomization of
secondary data sources, which destroys all biological information in these
sources, does not result in a deterioration in performance of composite feature
classifiers. Finally, we show that when a proper correction for gene set size
is performed, the stability of single gene sets is similar to the stability of
composite feature sets. Based on these results there is currently no reason to
prefer prognostic classifiers based on composite features over single gene
classifiers for predicting outcome in breast cancer
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