Experimental probing of exchange interactions between localized spins in the dilute magnetic insulator (Ga,Mn)N

The sign, magnitude, and range of the exchange couplings between pairs of Mn ions is determined for (Ga,Mn)N and (Ga,Mn)N:Si with x < 3%. The samples have been grown by metalorganic vapor phase epitaxy and characterized by secondary-ion mass spectroscopy; high-resolution transmission electron microscopy with capabilities allowing for chemical analysis, including the annular dark-field mode and electron energy loss spectroscopy; high-resolution and synchrotron x-ray diffraction; synchrotron extended x-ray absorption fine-structure; synchrotron x-ray absorption near-edge structure; infra-red optics and electron spin resonance. The results of high resolution magnetic measurements and their quantitative interpretation have allowed to verify a series of ab initio predictions on the possibility of ferromagnetism in dilute magnetic insulators and to demonstrate that the interaction changes from ferromagnetic to antiferromagnetic when the charge state of the Mn ions is reduced from 3+ to 2+.Comment: 12 pages, 14 figures; This version contains the detailed characterization of the crystal structure as well as of the Mn distribution and charge stat

The Fe-Mg interplay and the effect of deposition mode in (Ga,Fe)N doped with Mg

The effect of Mg codoping and its deposition mode on the Fe distribution in (Ga,Fe)N layers grown by metalorganic vapor phase epitaxy is investigated. Both homogeneously- and digitally-Mg codoped samples are considered and contrasted to the case of (Ga,Fe)N layers obtained without any codoping by shallow impurities. The structural analysis of the layers by high-resolution transmission electron microscopy and by high-resolution- and synchrotron x-ray diffraction gives evidence of the fact that in the case of homogenous-Mg doping, Mg and Fe competitively occupy the Ga-substitutional cation sites, reducing the efficiency of Fe incorporation. Accordingly, the character of the magnetization is modified from ferromagnetic-like in the non-codoped films to paramagnetic in the case of homogeneous Mg codoping. The findings are discussed vis-`a-vis theoretical results obtained by ab initio computations, showing only a weak effect of codoping on the pairing energy of two Fe cations in bulk GaN. However, according to these computations, codoping reverses the sign of the paring energy of Fe cations at the Ga-rich surface, substantiating the view that the Fe aggregation occurs at the growth surface. In contrast to the homogenous deposition mode, the digital one is found to remarkably promote the aggregation of the magnetic ions. The Fe-rich nanocrystals formed in this way are distributed non-uniformly, giving reason for the observed deviation from a standard superparamagnetic behavior.Comment: 13 pages, 14 figure

B-RAF Mutant Alleles Associated with Langerhans Cell Histiocytosis, a Granulomatous Pediatric Disease

Langerhans cell histiocytosis (LCH) features inflammatory granuloma characterised by the presence of CD1a+ dendritic cells or 'LCH cells'. Badalian-Very et al. recently reported the presence of a canonical (V600E)B-RAF mutation in 57% of paraffin-embedded biopsies from LCH granuloma. Here we confirm their findings and report the identification of two novel B-RAF mutations detected in LCH patients.Mutations of B-RAF were observed in granuloma samples from 11 out of 16 patients using 'next generation' pyrosequencing. In 9 cases the mutation identified was (V600E)B-RAF. In 2 cases novel polymorphisms were identified. A somatic (600DLAT)B-RAF insertion mimicked the structural and functional consequences of the (V600E)B-RAF mutant. It destabilized the inactive conformation of the B-RAF kinase and resulted in increased ERK activation in 293 T cells. The (600DLAT)B-RAF and (V600E)B-RAF mutations were found enriched in DNA and mRNA from the CD1a+ fraction of granuloma. They were absent from the blood and monocytes of 58 LCH patients, with a lower threshold of sequencing sensitivity of 1%-2% relative mutation abundance. A novel germ line (T599A)B-RAF mutant allele was detected in one patient, at a relative mutation abundance close to 50% in the LCH granuloma, blood monocytes and lymphocytes. However, (T599A)B-RAF did not destabilize the inactive conformation of the B-RAF kinase, and did not induce increased ERK phosphorylation or C-RAF transactivation.Our data confirmed presence of the (V600E)B-RAF mutation in LCH granuloma of some patients, and identify two novel B-RAF mutations. They indicate that (V600E)B-RAF and (600DLAT)B-RAF mutations are somatic mutants enriched in LCH CD1a(+) cells and absent from the patient blood. Further studies are needed to assess the functional consequences of the germ-line (T599A)B-RAF allele

Rare suprasellar glioblastoma: report of two cases and review of the literature

BACKGROUND AND IMPORTANCE: The suprasellar and hypothalamic/chiasmatic regions can harbor a broad range of pathologic conditions, both neoplastic and nonneoplastic; however, malignant gliomas are extremely rare in those regions. CLINICAL PRESENTATIONS: Patient 1 was a 70 year-old man with weight loss and rapidly progressive visual impairment. A mass centered in the hypothalamus was detected on magnetic resonance (MR) imaging. The second patient, a 45 year-old woman, complained of visual symptoms and headaches. MR imaging revealed a combined intra- and suprasellar mass. In both instances, the preoperative differential diagnosis favored craniopharyngioma. Histological examination confirmed the diagnosis of glioblastoma. CONCLUSION: We report two rare adult cases of hypothalamic/chiasmatic glioblastoma. The authors review the literature, highlighting the importance of considering this rare entity in the differential diagnosis of suprasellar and hypothalamic lesions

Langerhans cell histiocytosis (histiocytosis X)

There has been a renewed interest in Langerhans cell histiocytosis in recent years due both to advances in basic research and to improvements in diagnostic and treatment approaches. In this article, we review the various aspects of the disease and the potential implications of these recent scientific researches for our understanding and management of the disorder.published_or_final_versio

Performance comparison of H.265/MPEG-HEVC, VP9, and H.264/MPEG-AVC encoders

This work presents a performance comparison of the two latest video coding standards H.264/MPEG-AVC and H.265/MPEG-HEVC (High-Efficiency Video Coding) as well as the recently published proprietary video coding scheme VP9. According to the experimental results, which were obtained for a whole test set of video sequences by using similar encoding configurations for all three examined representative encoders, H.265/MPEG-HEVC provides significant average bit-rate savings of 43.3% and 39.3% relative to VP9 and H.264/MPEG-AVC, respectively. As a particular aspect of the conducted experiments, it turned out that the VP9 encoder produces an average bit-rate overhead of 8.4% at the same objective quality, when compared to an open H.264/MPEG-AVC encoder implementation - the x264 encoder. On the other hand, the typical encoding times of the VP9 encoder are more than 100 times higher than those measured for the x264 encoder. When compared to the full-fledged H.265/MPEG-HEVC referen ce software encoder implementation, the VP9 encoding times are lower by a factor of 7.35, on average