Results 1 - 10 of 4302
Results 1 - 10 of 4302. Search took: 0.032 seconds
|Sort by: date | relevance|
[en] Gliomas are the most common type of primary brain tumor and have a dismal prognosis. Understanding the genetic alterations that drive glioma formation and progression may help improve patient prognosis by identification of novel treatment targets. Recently, two major studies have performed in-depth mutation analysis of glioblastomas (the most common and aggressive subtype of glioma). This systematic approach revealed three major pathways that are affected in glioblastomas: The receptor tyrosine kinase signaling pathway, the TP53 pathway and the pRB pathway. Apart from frequent mutations in the IDH1/2 gene, much less is known about the causal genetic changes of grade II and III (anaplastic) gliomas. Exceptions include TP53 mutations and fusion genes involving the BRAF gene in astrocytic and pilocytic glioma subtypes, respectively. In this review, we provide an update on all common events involved in the initiation and/or progression across the different subtypes of glioma and provide future directions for research into the genetic changes
[en] Solving geometric and sample alignment issues is a major part of multi-axial Rutherford backscattering channeling (RBS-C) analysis of materials, especially involving complicated samples. However, a geometric standard does not exist for RBS-C, which complicates experimental procedures and makes experimental methods and data presentation inconsistent among different experiments. Our approach to solving RBS-C geometric issues, discussed here, is to introduce a geometric adjustment and sample manipulation procedure which defines the orientation and rotation of the sample with respect to a fixed coordinate system. This method makes rotational, alignment and sample manipulation operations involved in RBS-C more flexible and simpler. As a test case, we present multi-axial RBS-C maps of Si obtained via this methodology. Distortions arising in such RBS-C maps due to geometric effects, how they can affect alignment procedure and data extraction, and how our approach treats these issues are discussed.
[en] In this paper, we demonstrate the ability of the Le-PIXE (Low Energy PIXE) technique, using proton energies < 1 MeV, for the monitoring of the thickness and the thickness uniformity of ultra thin (0.5 nm < t < 20 nm) chromium layers deposited onto quartz substrates. Chromium is a good candidate for obtaining conductive ultra thin layers on insulator substrates such as quartz (SiO2). The resistivity of such layers is highly related to the quality of the deposited chromium film. In order to optimize the deposition process, there is a need for rapid and accurate monitoring of such films (film thickness, thickness uniformity over a big surface...). The acquisition time needed to obtain results with less than 3-4 % precision was 5 minutes for the thinnest layers. The validation for the use of the Le-PIXE technique was checked by means of conventional RB S technique.
[en] The visigothic treasure of Torredonjimeno (Jaen, Spain) was found by chance in the year 1926 buried in an olive grove. The finding consisted of some hundreds fragments of gold objects and gems coming from several votive crowns and crosses, some of them belonging to an unidentified visigothic king. The treasure may belong chronologically to the same period as the Guarrazar treasure or, possibly, to a somewhat later time, but the pieces are fragmented and of less technological workmanship than the latter. This is the reason why the Torredonjimeno treasure has not attracted as much attention from archeologists and art historians as that from Guarrazar. On the occasion of an exhibition showing together all the objects of the treasure, it is normally kept in three different museums in Barcelona, Cordoba and Madrid, a number of pieces were analyzed, using PIXE, PIGE and RBS, at the external microbeam facility installed at the Center for Micro-Analysis of Materials
[en] Evaluation of lattice displacement in Mg-ion implanted GaN is studied by combining elastic recoil detection analysis (ERDA), Rutherford backscattering spectroscopy (RBS) and Photoluminescence (PL) measurements. Mg-ion implantation into GaN single crystal wafer is performed with energies of 30 keV (ion fluence; 3.5 × 1014 cm−2) and 60 keV (6.5 × 1014 cm−2) at room temperature. The ERDA measurements using the 1.5 MeV helium beam can evaluate hydrogen from the surface to ∼300 nm. The hydrogen concentration for un-implanted and as-implanted GaN is 3.1 × 1014 cm−2 and 6.1 × 1014 cm−2 at around 265 nm in depth. χmin (the ratio of aligned and random yields) near the surface of the 〈0 0 0 1〉 direction for Ga is 1.61% for un-implanted and 2.51% for Mg-ion implanted samples. On the other hand, the value of χmin for N is 10.08% for un-implanted and 11.20% for Mg-ion implanted samples. The displacement concentration of Ga and N estimated from these χmin values is 4.01 × 1020 cm−3 and 5.46 × 1020 cm−3, respectively. This suggests that Ga vacancy (VGa), N vacancy (VN), Ga interstitial (Gai), and N interstitial (Ni) is introduced in Mg-ion implanted GaN. A strong emission at around 400 nm in as-implanted GaN is related to a VN donor and some acceptor pairs. It is suggested that the origin of the very high resistivity after the Mg-ion implantation is attributed to the carrier compensation effect due to the deep level of Ni as a non-radiative center.
[en] The erosion of Be and W marker layers was investigated using long-term samples during the first ITER-like wall discharge campaign 2011–2012. The markers were mounted in Be coated Inconel tiles between the inner wall guard limiters (IWGL). They were analyzed using Rutherford backscattering (RBS) before and after exposure. All samples showed strong erosion. The results were compared to the data for Be and W erosion rates for the 2005–2009 and the 2001–2004 campaigns, respectively, when JET was operated with a carbon wall. In 2005–2009 Be and C samples were used, and W samples were used in 2001–2004. The mean W erosion rates and the toroidal and poloidal distributions of the W erosion were the same for the 2001–2004 and the 2011–2012 campaigns. The mean erosion rate of Be during the 2011–2012 campaign was smaller by a factor of about two compared to the 2005–2009 campaign and showed a different poloidal distribution. The mean erosion rate of the inner JET ITER-like wall was about 4–5 times smaller than the mean erosion rate of the carbon wall
[en] An analytical model for Rayleigh–Brillouin scattering (RBS) spectra of gases is developed and discussed in this paper. The well-recognized S6 and S7 models only have a numerical form and are complex to process in real applications; simple Gaussian models are imprecise and suffer from greater error. A new model (V3) based on the spectral line broadening theory and the Voigt profile is established. This model is easy to process as it has an analytical form, and it is proved to have good accordance with the S7 model. In addition, this model can separate the Rayleigh and Brillouin lines, and the measured Brillouin shift is proved to match theoretical values. (paper)
[en] Microbeam PIXE was used to analyse platinum in single ovarian cancer cells. Carboplatin sensitive and resistant cells were grown as a monolayer on polypropylene and treated with either carboplatin or cisplatin. Pt from the carboplatin could not be detected. The Pt from cisplatin in the cells could be detected, and significantly more Zn was found in the resistant cells compared to the sensitive cells. The sensitive cells probably accumulated more cisplatin than the resistant ones.
[en] Ion beam channelling, with Rutherford backscattering spectrometry (RBS) is well established as a technique for providing information about the sub-microscopic structure of materials. Inspired by this method, and the need to characterise high aspect ratio periodic structures on a scale too small for nuclear microprobe analysis, we have developed a macroscopic ion beam channelling technique for the characterisation of micro and nanaoscale high aspect ratio periodic structures. The technique exploits the fact that samples exhibiting porosity or surface roughness have RBS spectra of characteristic shape and this shape may be calculated for simple periodic sample geometries. Macrochannelling is the term we use to apply RBS to sub-microscopic high-aspect ratio periodic structures. We have adapted the macrochannelling technique which we previously applied to simple gratings to the experimental study of more complex samples, which include a number of different materials. 5 refs., 6 figs