Obstruction theory on 8-manifolds

This note gives a uniform, self-contained, and fairly direct approach to a variety of obstruction-theoretic problems on 8-manifolds. We give necessary and sufficient cohomological critera for the existence of almost complex and almost quaternionic structures on the tangent bundle and for the reduction of the structure group to U(3) by the homomorphism U(3) --> O(8) given by the Lie algebra representation of PU(3).Comment: 19 page

Understanding the role of promoters in catalysis: operando XAFS/DRIFTS study of CeO_x/Pt/Al₂O₃ during CO oxidation

A combined operando XAFS/DRIFTS study on CeOx/Pt/Al2O3 catalysts has been performed during CO oxidation and provides insights into the changes in nanoparticle structure and adsorbed species during the reaction profile. The onset of CO2 formation is shown to be concurrent with a rapid re-oxidation of the Pt nanoparticles, evidenced by XAFS spectroscopy, and the loss of bridge bonded CO adsorbed on Pt, as shown by simultaneous DRIFTS acquisition. The continued appearance of linear bound CO on the catalyst surface is shown to remain long after catalytic light off. The interaction of Pt and CeOx is evidenced by the improved performance towards CO oxidation, compared to the non-CeOx modified Pt/Al2O3, and changes in the CO adsorption properties on Pt previously linked to Pt-CeO2 interfaces

Generalized parton distributions, the hunt for quark orbital momenta

The Generalized Parton Distributions (GPDs) are the appropriate framework for a universal description of the partonic structure of the nucleon. They characterize the dynamics of quarks and gluons inside the nucleon and consequently contain information about the spin of the nucleon. The current experimental knowledge about GPDs is reviewed with the emphasis on the determination of E^q(Q^2,x,xi,t), the least known and constrained GPD, of particular importance in the nucleon spin puzzle. The perspectives of this experimental program are also addressed.Comment: 6 pages, 2 figures Proceedings of the XVIIIth Symposium on Spin Physics, Charlottesville (Virginia, USA), October 6-11,200

Sum rules for spin asymmetries

Starting from rotational invariance we derive sum rules for the single-spin asymmetries in inclusive production and binary processes. We also get sum rules for spin correlation parameters in elastic pp-scattering.Comment: 4 page

High precision determination of the Q2Q^2-evolution of the Bjorken Sum

We present a significantly improved determination of the Bjorken Sum for 0.6$\leq Q^{2}\leq$4.8 GeV$^{2}$ using precise new $g_{1}^{p}$ and $g_{1}^{d}$ data taken with the CLAS detector at Jefferson Lab. A higher-twist analysis of the $Q^{2}$-dependence of the Bjorken Sum yields the twist-4 coefficient $f_{2}^{p-n}=-0.064 \pm0.009\pm_{0.036}^{0.032}$. This leads to the color polarizabilities $\chi_{E}^{p-n}=-0.032\pm0.024$ and $\chi_{B}^{p-n}=0.032\pm0.013$. The strong force coupling is determined to be \alpha_{s}^{\overline{\mbox{ MS}}}(M_{Z}^{2})=0.1124\pm0.0061, which has an uncertainty a factor of 1.5 smaller than earlier estimates using polarized DIS data. This improvement makes the comparison between $\alpha_{s}$ extracted from polarized DIS and other techniques a valuable test of QCD.Comment: Published in Phys. Rev. D. V1: 8 pages, 3 figures. V2: Updated references; Included threshold matching in \alpha_s evolution. Corrected a typo on the uncertainty for \Lambda_QCD. V3: Published versio

Status of Longitudinal Polarized Parton Densities and Higher Twist

The present status of the longitudinal polarized parton densities (PDFs) and the contribution of their first moments to the nucleon spin is discussed. Special attention is paid to the role of higher twist effects in determining the PDFs and to the polarized strange quark and gluon densities, which are still not well determined from the present data.Comment: 6 pages, 5 figures; to appear in the proceedings of the 18th International Symposium on Spin Physics (SPIN20008), October 6 - 11, 2008, Charlottesville, Virginia, US

Selective cancer cell toxicity and radiosensitization using different high atomic number nanoparticles

Radiotherapy is currently used in around 50% of cancer treatments. Although it is generally effective, it is damaging to surrounding healthy tissues. This damage can be reduced by by better targeting to cancer cells. Improved radiotherapy outcomes can be achieved by targeting heavy elements to cancer cells, since these produce energetic electrons and free radicals upon irradiation that further increase the effectiveness of radiotherapy. Because of their biocompatibility and amenability to surface modification, gold nanoparticles (AuNPs) show significant promise in this area.We observe that acute 3hr exposure of cells to 2nm gold nanoparticles, bearing a 50:50 ratio of alpha-galactose and PEGamine ligands, results in selective chemotoxicity toward cancer cells at nanomolar concentrations, without affecting normal cells (Figure 1). Chemotoxicity is prevented by antioxidant co-administration and is partially prevented by a pan-caspase inhibitor (ZVAD- fmk). Our initial results suggest that AuNP toxicity is additive with using X-ray radiotherapy. Cerium oxide NPs are one of the most studied metal oxides NPs due to their high redox and oxygen transport properties [1]. They are interesting for radiotherapy applications because they adsorb oxygen and may therefore favour the radiolytic production of oxygen-containing free radicals, especially under low-oxygen conditions, such as the environment of most solid tumours. The surface oxygen vacancy of ceria NPs therefore makes them an interesting tool for prooxidant properties [2,3]. Nevertheless, the potential of ceria as a radiosensitiser has not been investigated extensively as it has a relatively low atomic number. It will therefore produce a low flux of secondary electrons upon irradiation which could potentially displace the adsorbed oxygen. We have been working on the fabrication of mixed ceria NPs, incorporating gold or bismuth, to increase the flux of secondary electrons (Figure 2). It is hoped these effects combined will further facilate the localized generation of ROS and increase effectiveness of targetted radiotherapy We predict that these new mixed-oxide ceria NPs will have better radiosensitisation potential than pure ceria NPs, and could be used to effectively target hypoxic cancer cells

Age-Related Changes in the Retinal Pigment Epithelium (RPE)

<div><h3>Background</h3><p>Age-related changes in the retina are often accompanied by visual impairment but their mechanistic details remain poorly understood.</p> <h3>Methodology</h3><p>Proteomic studies were pursued toward a better molecular understanding of retinal pigment epithelium (RPE) aging mechanisms. RPE cells were isolated from young adults (3–4 month-old) and old (24–25 month-old) F344BN rats, and separated into subcellular fractions containing apical microvilli (MV) and RPE cell bodies (CB) lacking their apical microvilli. Proteins were extracted in detergent, separated by SDS-PAGE, digested in situ with trypsin and analyzed by LC MS/MS. Select proteins detected in young and old rat RPE were further studied using immunofluorescence and Western blot analysis.</p> <h3>Principal Findings</h3><p>A total of 356 proteins were identified in RPE MV from young and 378 in RPE MV from old rats, 48% of which were common to each age group. A total of 897 proteins were identified in RPE CB from young rats and 675 in old CB, 56% of which were common to each age group. Several of the identified proteins, including proteins involved in response to oxidative stress, displayed both quantitative and qualitative changes in overall abundance during RPE aging. Numerous proteins were identified for the first time in the RPE. One such protein, collectrin, was localized to the apical membrane of apical brush border of proximal tubules where it likely regulates several amino acid transporters. Elsewhere, collectrin is involved in pancreatic β cell proliferation and insulin secretion. In the RPE, collectrin expression was significantly modulated during RPE aging. Another age-regulated, newly described protein was DJ-1, a protein extensively studied in brain where oxidative stress-related functions have been described.</p> <h3>Conclusions/Significance</h3><p>The data presented here reveals specific changes in the RPE during aging, providing the first protein database of RPE aging, which will facilitate future studies of age-related retinal diseases.</p> </div