Effect of glow discharge treatment of poly(acrylic acid) preadsorbed onto poly(ethylene)

In order to introduce carboxylic acid groups at the surface of poly(ethylene) (PE) films, an attempt was made to covalently link a preadsorbed layer of poly(acrylic acid) (PAAc) on a PE film by an argon or tetrafluoromethane (CF4) plasma treatment. Surface analysis was performed by XPS (X-ray photoelectron spectroscopy) and water contact angle measurements. It was shown that by treatment of a PAAc layer preadsorbed on PE with an argon or a CF4 plasma, a small amount of carboxylic acid groups was introduced at the surface. A similar amount of these groups was obtained by plasma treatment of PE films without a preadsorbed PAAc layer. A comparison of the etching rates of PAAc and PE by either an argon or a CF4 plasma, showed that PAAc is etched much faster by both types of plasmas than PE. The preadsorbed PAAc layer on PE is etched off before it could be immobilized by either an argon or a CF4 plasma treatment. Additionally the effect of treating PE films for very short times with an argon or a CF4 plasma was studied. After an induction period of approximately 0.1 s, the oxidation during the argon plasma treatment and the fluorination during the CF4 plasma treatment were proportional to the logarithm of the treatment time for time periods up to 50 s

Introduction of functional groups on polyethylene surfaces by a carbon dioxide plasma treatment

Poly(ethylene) (PE) films were treated with a carbon dioxide (CO2) plasma to study the formation of oxygen-containing functional groups at the surface. Modified and nonmodified films were characterized by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. During the CO2 plasma treatment, the PE surface is etched and oxidized, yielding films with a very hydrophilic surface. The oxygen incorporation at the surface is fast and can be described by a combination of a zero-order incoraporation and a first-order etching process. Several oxygen functionalities such as carboxylic acid (approximately 14% of the oxygen persent), ketone/aldehyde (25%), and hydroxyl/epoxide (5-9%) groups were introduced at the surface by the plasma treatment. This was shown by using derivatization reactions for specific functional groups followed by XPS analysis. The wettability of the plasma-treated surface decreased when the films were stroed for prolonged periods of time in air. This aging process could not be completely reversed by immersion of the films in water

On the effect of treating poly(acrylic acid) with argon and tetrafluoromethane plasmas:kinetics and degradation mechanism

Poly(acrylic acid) (PAAc) films were treated with either an argon or a tetrafluoromethane (CF4) plasma and subsequently analyzed with X-ray photoelectron spectroscopy (XPS). PAAc films were decarboxylated during both types of plasma treatments. In addition, during the CF4 plasma treatment, the PAAc films became fluorinated. The plasma phase during the argon plasma treatment of PAAc films was investigated with optical emission spectroscopy. It was shown that during this plasma treatment carbon dioxide, water, and possibly hydrogen were liberated from the PAAc surface. By covering the surface of PAAc films with different materials (lithium fluoride, UV fused silica, and glass) during the plasma treatment, it was possible to differentiate between photochemically induced and particle-induced changes of the surface. This method was used to show that decarboxylation during the argon plasma treatment was caused by vacuum UV radiation (wavelength < 150 nm) and the decarboxylation/fluorination during the CF4 plasma treatment was induced by reactive fluorine-containing species from the plasma phase. Furthermore, during both processes, etching of the PAAc surface occurred. Based on these mechanisms, kinetic models were derived that could be used to describe the measured kinetic data adequately

Direct neutron capture cross sections of 62Ni in the s-process energy range

Direct neutron capture on 62Ni is calculated in the DWBA and the cross sections in the energy range relevant for s-process nucleosynthesis are given. It is confirmed that the thermal value of the capture cross section contains a subthreshold resonance contribution. Contrary to previous investigations it is found that the capture at higher energies is dominated by p-waves, thus leading to a considerably increased cross section at s-process energies and a modified energy dependence.Comment: 10 pages, 1 figure, corrected typos in Eq. 6 and subsequent paragrap

ON THE INTRINSIC CHARM COMPONENT OF THE NUCLEON

Using a $\overline D$ meson cloud model we calculate the squared charm radius of the nucleon . The ratio between this squared radius and the ordinary baryon squared radius is identified with the probability of ``seeing'' the intrinsic charm component of the nucleon. Our estimate is compatible with those used to successfully describe the charm production phenomenology.Comment: 9 pages, 2 figures not included, avaiable from the author

Assessment of patient-derived tumour xenografts (PDXs) as a discovery tool for cancer epigenomics

Background: The use of tumour xenografts is a well-established research tool in cancer genomics but has not yet been comprehensively evaluated for cancer epigenomics. Methods: In this study, we assessed the suitability of patient-derived tumour xenografts (PDXs) for methylome analysis using Infinium 450 K Beadchips and MeDIP-seq. Results: Controlled for confounding host (mouse) sequences, comparison of primary PDXs and matching patient tumours in a rare (osteosarcoma) and common (colon) cancer revealed that an average 2.7% of the assayed CpG sites undergo major (Δβ ≥ 0.51) methylation changes in a cancer-specific manner as a result of the xenografting procedure. No significant subsequent methylation changes were observed after a second round of xenografting between primary and secondary PDXs. Based on computational simulation using publically available methylation data, we additionally show that future studies comparing two groups of PDXs should use 15 or more samples in each group to minimise the impact of xenografting-associated changes in methylation on comparison results. Conclusions: Our results from rare and common cancers indicate that PDXs are a suitable discovery tool for cancer epigenomics and we provide guidance on how to overcome the observed limitations

Dark matter halos and the anisotropy of ultra-high energy cosmic rays

Several explanations for the existence of Ultra High Energy Cosmic Rays invoke the idea that they originate from the decay of massive particles created in the reheating following inflation. It has been suggested that the decay products can explain the observed isotropic flux of cosmic rays. We have calculated the anisotropy expected for various models of the dark matter distribution and find that at present data are too sparse above $4 \times 10^{19}$ eV to discriminate between different models. However we show that with data from three years of operation of the southern section of the Pierre Auger Observatory significant progress in testing the proposals will be made.Comment: 21 pages, 6 figures (ps), Astroparticle Physics (accepted for publication

The clustering of ultra-high energy cosmic rays and their sources

The sky distribution of cosmic rays with energies above the 'GZK cutoff' holds important clues to their origin. The AGASA data, although consistent with isotropy, shows evidence for small-angle clustering, and it has been argued that such clusters are aligned with BL Lacertae objects, implicating these as sources. It has also been suggested that clusters can arise if the cosmic rays come from the decays of very massive relic particles in the Galactic halo, due to the expected clumping of cold dark matter. We examine these claims and show that both are in fact not justified.Comment: 13 pages, 8 figures, version in press at Phys. Rev.

A Measurement of Time-Averaged Aerosol Optical Depth using Air-Showers Observed in Stereo by HiRes

Air fluorescence measurements of cosmic ray energy must be corrected for attenuation of the atmosphere. In this paper we show that the air-showers themselves can yield a measurement of the aerosol attenuation in terms of optical depth, time-averaged over extended periods. Although the technique lacks statistical power to make the critical hourly measurements that only specialized active instruments can achieve, we note the technique does not depend on absolute calibration of the detector hardware, and requires no additional equipment beyond the fluorescence detectors that observe the air showers. This paper describes the technique, and presents results based on analysis of 1258 air-showers observed in stereo by the High Resolution Fly's Eye over a four year span.Comment: 7 pages, 3 figures, accepted for publication by Astroparticle Physics Journa