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  • 1
    Publication Date: 2016-01-12
    Description: Eu-doped GaN is a promising material with potential application not only in optoelectronics but also in magneto-optical and quantum optical devices “beyond the light emitting diode.” Its interesting spectroscopy is unfortunately complicated by spectral overlaps due to “site multiplicity,” the existence in a given sample of multiple composite centers in which Eu ions associate with intrinsic or extrinsic defects. We show here that elementary crystalfield analysis of the 5 D 0 to 7 F 1 transition can critically distinguish such sites. Hence, we find that the center involved in the hysteretic photochromic switching observed in GaN(Mg):Eu, proposed as the basis of a solid state qubit material, is not in fact Eu1, as previously reported, but a related defect, Eu1(Mg). Furthermore, the decomposition of the crystalfield distortions of Eu0, Eu1(Mg), and Eu1 into axial and non-axial components strongly suggests reasonable microscopic models for the defects themselves.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 2
    Publication Date: 2016-02-09
    Description: Gd-doped ZnO thin films were prepared using pulsed laser deposition at different oxygen pressures and varied Gd concentrations. The effects of oxygen deficiency-related defects on the Gd incorporation, optical and structural properties, were explored by studying the impact of oxygen pressure during deposition and post-growth thermal annealing in vacuum. Rutherford Backscattering Spectrometry revealed that the Gd concentration increases with increasing oxygen pressure for samples grown with the same Gd-doped ZnO target. Unexpectedly, the c -lattice parameter of the samples tends to decrease with increasing Gd concentration, suggesting that Gd-defect complexes play an important role in the structural properties. Using low-temperature photoluminescence (PL), Raman measurements and density functional theory calculations, we identified oxygen vacancies as the dominant intrinsic point defects. PL spectra show a defect band related to oxygen vacancies for samples grown at oxygen deficiency.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 3
    Publication Date: 2016-09-01
    Description: Al x Ga 1-x N samples, with different AlN molar fractions, x = 0, 0.15, 0.77, and 1, grown by halide vapor phase epitaxy were implanted with Tm ions. Photoluminescence (PL) measurements revealed that after thermal annealing all the samples exhibit intraionic Tm 3+ luminescence. In samples with x 〉 0, the low temperature emission is dominated by the lines that appear in the near infrared (NIR) spectral region, corresponding to the overlapped 1 G 4 → 3 H 5 and 3 H 4 → 3 H 6 multiplet transitions. A detailed spectroscopic analysis of NIR emission of the thulium implanted and annealed Al x Ga 1-x N layers is presented by using temperature dependent steady-state PL, room temperature PL excitation, and time resolved PL. The results indicate that the excitonic features sensitive to the alloy disorder are involved in the excitation population processes of the Tm 3+ luminescence and the highest thermal stability for the NIR emission occurs for the AlN:Tm sample.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 4
    Publication Date: 2014-12-18
    Description: We report the interplay between In incorporation and strain relaxation kinetics in high-In-content In x Ga 1-x N ( x  = 0.3) layers grown by plasma-assisted molecular-beam epitaxy. For In mole fractions x  = 0.13–0.48, best structural and morphological qualities are obtained under In excess conditions, at In accumulation limit, and at a growth temperature where InGaN decomposition is active. Under such conditions, in situ and ex situ analyses of the evolution of the crystalline structure with the layer thickness point to an onset of misfit relaxation after the growth of 40 nm, and a gradual relaxation during more than 200 nm, which results in an inhomogeneous strain distribution along the growth axis. This process is associated with a compositional pulling effect, i.e., indium incorporation is partially inhibited in presence of compressive strain, resulting in a compositional gradient with increasing In mole fraction towards the surface.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 5
    Publication Date: 2009-01-24
    Description: Our understanding of the genetic basis of phenotypic diversity is limited by the paucity of examples in which multiple, interacting loci have been identified. We show that natural variation in the efficiency of sporulation, the program in yeast that initiates the sexual phase of the life cycle, between oak tree and vineyard strains is due to allelic variation between four nucleotide changes in three transcription factors: IME1, RME1, and RSF1. Furthermore, we identified that selection has shaped quantitative variation in yeast sporulation between strains. These results illustrate how genetic interactions between transcription factors are a major source of phenotypic diversity within species.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gerke, Justin -- Lorenz, Kim -- Cohen, Barak -- NHGRI-T32HG000045/PHS HHS/ -- R01 GM092910/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 2009 Jan 23;323(5913):498-501. doi: 10.1126/science.1166426.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Genetics, Washington University School of Medicine, St. Louis, MO 63108, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19164747" target="_blank"〉PubMed〈/a〉
    Keywords: Alleles ; Crosses, Genetic ; Epistasis, Genetic ; *Genetic Variation ; Models, Genetic ; Molecular Sequence Data ; Nuclear Proteins/*genetics/metabolism ; Phenotype ; Polymorphism, Genetic ; *Quantitative Trait Loci ; Repressor Proteins/*genetics/metabolism ; Saccharomyces cerevisiae/*genetics/physiology ; Saccharomyces cerevisiae Proteins/*genetics/metabolism ; Selection, Genetic ; Spores, Bacterial/physiology ; Transcription Factors/*genetics/metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
    Publication Date: 2016-08-31
    Description: Cardiopulmonary complications are the leading cause of mortality in sickle cell anemia (SCA). Elevated tricuspid regurgitant jet velocity, pulmonary hypertension, diastolic, and autonomic dysfunction have all been described, but a unifying pathophysiology and mechanism explaining the poor prognosis and propensity to sudden death has been elusive. Herein, SCA mice underwent...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 7
    Publication Date: 2016-10-28
    Description: Al x Ga 1-x N (x = 0.15 and 0.77) films, grown by halide vapor phase epitaxy, were implanted with 300 keV Tm ions. Implantation damage accumulation is investigated with Rutherford backscattering spectrometry/channeling (RBS/C), transmission electron microscopy (TEM), and high resolution X-ray diffraction (XRD). Distinct damage behavior for samples with different AlN contents was found. Surface nanocrystallization occurs for samples with x = 0.15, similar to implantation effects observed in GaN. Samples with x = 0.77 approach the behavior of AlN. In particular, surface nanocrystallization is suppressed and the depth range of the stacking fault network, typical for implanted III-nitrides, is decreased. The crystalline quality of the sample with x = 0.15 was investigated to compare random and channeled implantation, showing less concentration of damage but with a higher range for channeled implantation. Surprisingly, the strain field caused by the implantation reaches much deeper into the sample than the defect profiles measured by RBS/C and TEM. This is attributed to the fact that XRD is much more sensitive to low defect densities caused by ions which are channeled to deep regions of the sample.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 8
    Publication Date: 2017-09-30
    Description: The New Siberian Islands are affected by a number of Mesozoic tectonic events. The oldest event (D1a) is characterized by NW-directed thrusting within the South Anyui Suture Zone combined with north–south-trending sinistral strike-slip in the foreland during the Early Cretaceous. This compressional deformation was followed by dextral transpression along north–south-trending faults, which resulted in NE–SW shortening in the Kotelny Fold Zone (D1b). The dextral deformation can be related to a north–south-trending boundary fault zone west of the New Siberian Islands, which probably represented the Laptev Sea segment of the Amerasia Basin Transform Fault in pre-Aptian–Albian times. The presence of a transform fault west of the islands may be an explanation for the long and narrow sliver of continental lithosphere of the Lomonosov Ridge and the sudden termination of the South Anyui Suture Zone against the present Laptev Sea Rift System. The intrusion of magmatic rocks 114 myr ago was followed by NW–SE-trending sinistral strike-slip faults of unknown origin (D2). In the Late Cretaceous–Paleocene, east–west extension (D3) west of the New Siberian Islands initiated the development of the Laptev Sea Rift System, which continues until today and is largely related to the development of the Eurasian Basin.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 9
    Publication Date: 2016-03-24
    Description: (beta-)Arrestins are important regulators of G-protein-coupled receptors (GPCRs). They bind to active, phosphorylated GPCRs and thereby shut off 'classical' signalling to G proteins, trigger internalization of GPCRs via interaction with the clathrin machinery and mediate signalling via 'non-classical' pathways. In addition to two visual arrestins that bind to rod and cone photoreceptors (termed arrestin1 and arrestin4), there are only two (non-visual) beta-arrestin proteins (beta-arrestin1 and beta-arrestin2, also termed arrestin2 and arrestin3), which regulate hundreds of different (non-visual) GPCRs. Binding of these proteins to GPCRs usually requires the active form of the receptors plus their phosphorylation by G-protein-coupled receptor kinases (GRKs). The binding of receptors or their carboxy terminus as well as certain truncations induce active conformations of (beta-)arrestins that have recently been solved by X-ray crystallography. Here we investigate both the interaction of beta-arrestin with GPCRs, and the beta-arrestin conformational changes in real time and in living human cells, using a series of fluorescence resonance energy transfer (FRET)-based beta-arrestin2 biosensors. We observe receptor-specific patterns of conformational changes in beta-arrestin2 that occur rapidly after the receptor-beta-arrestin2 interaction. After agonist removal, these changes persist for longer than the direct receptor interaction. Our data indicate a rapid, receptor-type-specific, two-step binding and activation process between GPCRs and beta-arrestins. They further indicate that beta-arrestins remain active after dissociation from receptors, allowing them to remain at the cell surface and presumably signal independently. Thus, GPCRs trigger a rapid, receptor-specific activation/deactivation cycle of beta-arrestins, which permits their active signalling.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Nuber, Susanne -- Zabel, Ulrike -- Lorenz, Kristina -- Nuber, Andreas -- Milligan, Graeme -- Tobin, Andrew B -- Lohse, Martin J -- Hoffmann, Carsten -- 1 R01 DA038882/DA/NIDA NIH HHS/ -- BB/K019864/1/Biotechnology and Biological Sciences Research Council/United Kingdom -- England -- Nature. 2016 Mar 31;531(7596):661-4. doi: 10.1038/nature17198. Epub 2016 Mar 23.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute of Pharmacology and Toxicology, University of Wurzburg, Versbacher Str. 9, 97078 Wurzburg, Germany. ; Rudolf Virchow Center, University of Wurzburg, Versbacher Str. 9, 97078 Wurzburg, Germany. ; Comprehensive Heart Failure Center, University of Wurzburg, Versbacher Str. 9, 97078 Wurzburg, Germany. ; Molecular Pharmacology Group, Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK. ; MRC Toxicology Unit, University of Leicester, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/27007855" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Arrestins/chemistry/*metabolism ; Biosensing Techniques ; Cattle ; Cell Line ; Cell Membrane/metabolism ; Cell Survival ; Crystallography, X-Ray ; Fluorescence Resonance Energy Transfer ; Humans ; Kinetics ; Models, Molecular ; Protein Binding ; Protein Conformation ; Receptors, G-Protein-Coupled/chemistry/*metabolism ; Signal Transduction ; Substrate Specificity ; Time Factors
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 10
    Publication Date: 2014-08-01
    Description: Producing highly efficient GaN-based optoelectronic devices has been a challenge for a long time due to the large lattice mismatch between III-nitride materials and the most common substrates, which causes a high density of threading dislocations. Therefore, it is essential to obtain alternative substrates with small lattice mismatches, appropriate structural, thermal and electrical properties, and a competitive price. Our results show that ( 2 ¯ 01 ) oriented β-Ga 2 O 3 has the potential to be used as a transparent and conductive substrate for GaN-growth. Photoluminescence spectra of thick GaN layers grown on ( 2 ¯ 01 ) oriented β-Ga 2 O 3 are found to be dominated by intense bandedge emission. Atomic force microscopy studies show a modest threading dislocation density of ∼10 8  cm −2 . X-ray diffraction studies show the high quality of the single-phase wurtzite GaN thin film on ( 2 ¯ 01 ) β-Ga 2 O 3 with in-plane epitaxial orientation relationships between the β-Ga 2 O 3 and the GaN thin film defined by (010) β-Ga 2 O 3 || ( 11 2 ¯ 0 ) GaN and ( 2 ¯ 01 ) β-Ga 2 O 3 || (0001) GaN leading to a lattice mismatch of ∼4.7%. Complementary Raman spectroscopy indicates that the quality of the GaN epilayer is high.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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