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  • 1
    Publication Date: 2015-05-05
    Description: The temperature dependence of carrier dynamics in GaN x As 1−y P y alloys has been investigated by time resolved photoluminescence. This investigation has shown that the decay time constant does not change significantly up to 100 K, and then starts to decrease rapidly above this temperature. Additionally, the decay times at the high-energy side of the spectrum decrease faster than those at the low-energy side. The effects have been explained by the interplay between carrier capture by radiative and nonradiative recombination centers. Detailed simulations show that the effect of carrier localization in the investigated materials is better described by double-scale potential fluctuations that are related to (i) distribution of localized states energy and (ii) bandgap fluctuations. In addition, it was observed that the increase in nitrogen concentration leads to a shorter decay time at room temperature, which is attributed to a larger concentration of non-radiative recombination centers. Furthermore, a post-growth annealing step leads to a longer decay time at room temperature, which is attributed to a reduction in non-radiative recombination centers. At low temperatures, the role of non-radiative centers is suppressed, and therefore the decay time does not differ significantly for samples with either different nitrogen concentrations or in both the as-grown and annealed samples.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 2
    Publication Date: 2014-11-11
    Description: Raman spectroscopy is employed to characterize structural and phonon properties of GaP/GaNP core/shell nanowires (NWs) grown by molecular beam epitaxy on Si substrates. According to polarization-dependent measurements performed on single NWs, the dominant Raman modes associated with zone-center optical phonons obey selection rules in a zinc-blende lattice, confirming high crystalline quality of the NWs. Two additional modes at 360 and 397 cm −1 that are specific to the NW architecture are also detected in resonant Raman spectra and are attributed to defect-activated scattering involving zone-edge transverse optical phonons and surface optical phonons, respectively. It is concluded that the formation of the involved defect states are mainly promoted during the NW growth with a high V/III ratio.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 3
    Publication Date: 2015-02-18
    Description: The Krüppel-associated box (KRAB) domain is a transcription repression module from the largest family of transcriptional regulators encoded by higher vertebrates. We developed a drug-controllable regulation system based on an artificial KRAB-containing repressor (tTS) that targets the endogenous Hprt gene to explore the regulatory mechanism and molecular basis of KRAB-containing regulators within the context of an endogenous gene in vivo . We show that KRAB can mediate irreversible and reversible regulation of endogenous genes in mouse that is dependent on embryonic developmental stage. KRAB-induced stable DNA methylation within the KRAB binding region during the early embryonic stage, resulting in irreversible gene repression. In later stages, KRAB mainly induced de-acetylation and methylation of histone, resulting in reversible gene repression. Thus, we have characterized the KRAB-mediated regulation system within the context of an endogenous gene and multiple spatiotemporal ranges, thereby providing a basis for identifying the function of KRAB-containing regulators and aiding development of novel KRAB-based gene regulation tools in vivo .
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 4
    Publication Date: 2014-10-31
    Description: Self-assembled dilute nitride InNP quantum dots (QDs) in GaP matrix grown under the Stranski-Krastanov mode by gas-source molecular beam epitaxy are studied. The N-related localized states inside the InNP QDs provide a spatially direct recombination channel, in contrast to the spatially indirect channel through the strained In(N)P QDs/GaP interface states. The N incorporation into InP QDs therefore causes a blueshift and double-peak features in photoluminescence, which are not observed in other dilute nitride materials.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 5
    Publication Date: 2014-08-21
    Description: We have demonstrated self-catalyzed GaN x P 1−x and GaN x P 1−x /GaN y P 1−y core/shell nanowire growth by gas-source molecular beam epitaxy. The growth window for GaN x P 1−x nanowires was observed to be comparable to that of GaP nanowires (∼585 °C to ∼615 °C). Transmission electron microscopy showed a mixture of cubic zincblende phase and hexagonal wurtzite phase along the [111] growth direction in GaN x P 1−x nanowires. A temperature-dependent photoluminescence (PL) study performed on GaN x P 1−x /GaN y P 1−y core/shell nanowires exhibited an S-shape dependence of the PL peaks. This suggests that at low temperature, the emission stems from N-related localized states below the conduction band edge in the shell, while at high temperature, the emission stems from band-to-band transition in the shell as well as recombination in the GaN x P 1−x core.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 6
    Publication Date: 1998-01-07
    Description: Pin1 is an essential and conserved mitotic peptidyl-prolyl isomerase (PPIase) that is distinct from members of two other families of conventional PPIases, cyclophilins and FKBPs (FK-506 binding proteins). In response to their phosphorylation during mitosis, Pin1 binds and regulates members of a highly conserved set of proteins that overlaps with antigens recognized by the mitosis-specific monoclonal antibody MPM-2. Pin1 is here shown to be a phosphorylation-dependent PPIase that specifically recognizes the phosphoserine-proline or phosphothreonine-proline bonds present in mitotic phosphoproteins. Both Pin1 and MPM-2 selected similar phosphorylated serine-proline-containing peptides, providing the basis for the specific interaction between Pin1 and MPM-2 antigens. Pin1 preferentially isomerized proline residues preceded by phosphorylated serine or threonine with up to 1300-fold selectivity compared with unphosphorylated peptides. Pin1 may thus regulate mitotic progression by catalyzing sequence-specific and phosphorylation-dependent proline isomerization.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Yaffe, M B -- Schutkowski, M -- Shen, M -- Zhou, X Z -- Stukenberg, P T -- Rahfeld, J U -- Xu, J -- Kuang, J -- Kirschner, M W -- Fischer, G -- Cantley, L C -- Lu, K P -- GM56203/GM/NIGMS NIH HHS/ -- GM56230/GM/NIGMS NIH HHS/ -- R01 GM056203/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 1997 Dec 12;278(5345):1957-60.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Medicine Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9395400" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Isomerases/metabolism ; Antibodies, Monoclonal ; Binding Sites ; Carrier Proteins/metabolism ; Cell Cycle Proteins/chemistry/*metabolism ; DNA-Binding Proteins/metabolism ; Epitopes ; HeLa Cells ; Heat-Shock Proteins/metabolism ; Humans ; Isomerism ; *Mitosis ; Models, Molecular ; Oligopeptides/chemistry/*metabolism ; Peptide Library ; Peptidylprolyl Isomerase/chemistry/*metabolism ; Phosphoproteins/chemistry/immunology/*metabolism ; Phosphorylation ; Phosphoserine/metabolism ; Phosphothreonine/metabolism ; Proline/*metabolism ; Protein Conformation ; Recombinant Fusion Proteins/chemistry/metabolism ; Substrate Specificity ; Tacrolimus Binding Proteins
    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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  • 7
    Publication Date: 1989-12-08
    Description: Vascular endothelial growth factor (VEGF) was purified from media conditioned by bovine pituitary folliculostellate cells (FC). VEGF is a heparin-binding growth factor specific for vascular endothelial cells that is able to induce angiogenesis in vivo. Complementary DNA clones for bovine and human VEGF were isolated from cDNA libraries prepared from FC and HL60 leukemia cells, respectively. These cDNAs encode hydrophilic proteins with sequences related to those of the A and B chains of platelet-derived growth factor. DNA sequencing suggests the existence of several molecular species of VEGF. VEGFs are secreted proteins, in contrast to other endothelial cell mitogens such as acidic or basic fibroblast growth factors and platelet-derived endothelial cell growth factor. Human 293 cells transfected with an expression vector containing a bovine or human VEGF cDNA insert secrete an endothelial cell mitogen that behaves like native VEGF.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Leung, D W -- Cachianes, G -- Kuang, W J -- Goeddel, D V -- Ferrara, N -- New York, N.Y. -- Science. 1989 Dec 8;246(4935):1306-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Molecular Biology, Genetech, South San Francisco, CA 94080.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2479986" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Animals ; Base Sequence ; Blotting, Northern ; Cattle ; Cell Division ; Cloning, Molecular ; Endothelium, Vascular/*cytology ; Gene Library ; Humans ; Lymphokines/genetics/*physiology/secretion ; Molecular Sequence Data ; Neovascularization, Pathologic/*physiopathology ; Sequence Homology, Nucleic Acid ; Vascular Endothelial Growth Factor A ; Vascular Endothelial Growth Factors
    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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  • 8
    Publication Date: 2008-11-14
    Description: Competition and predation are the most heavily investigated species interactions in ecology, dominating studies of species diversity maintenance. However, these two interactions are most commonly viewed highly asymmetrically. Competition for resources is seen as the primary interaction limiting diversity, with predation modifying what competition does, although theoretical models have long supported diverse views. Here we show, using a comprehensive three-trophic-level model, that competition and predation should be viewed symmetrically: these two interactions are equally able to either limit or promote diversity. Diversity maintenance requires within-species density feedback loops to be stronger than between-species feedback loops. We quantify the contributions of predation and competition to these loops in a simple, interpretable form, showing their equivalent potential to strengthen or weaken diversity maintenance. Moreover, we show that competition and predation can undermine each other, with the tendency of the stronger interaction to promote or limit diversity prevailing. The past failure to appreciate the symmetrical effects and interactions of competition and predation has unduly restricted diversity maintenance studies. A multitrophic perspective should be adopted to examine a greater variety of possible effects of predation than generally considered in the past. Conservation and management strategies need to be much more concerned with the implications of changes in the strengths of trophic interactions.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Chesson, Peter -- Kuang, Jessica J -- England -- Nature. 2008 Nov 13;456(7219):235-8. doi: 10.1038/nature07248.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, USA. pchesson@u.arizona.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19005554" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biodiversity ; Competitive Behavior/*physiology ; Conservation of Natural Resources ; *Food Chain ; *Models, Biological ; Population Density ; Predatory Behavior/*physiology
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 9
    Publication Date: 1991-09-13
    Description: Interleukin-8 (IL-8) is a member of a family of pro-inflammatory cytokines. Although the best characterized activities of IL-8 include the chemoattraction and activation of neutrophils, other members of this family have a wide range of specific actions including the chemotaxis and activation of monocytes, the selective chemotaxis of memory T cells, the inhibition of hematopoietic stem cell proliferation, and the induction of neutrophil infiltration in vivo. A complementary DNA encoding the IL-8 receptor from human neutrophils has now been isolated. The amino acid sequence shows that the receptor is a member of the superfamily of receptors that couple to guanine nucleotide binding proteins (G proteins). The sequence is 29% identical to that of receptors for the other neutrophil chemoattractants, fMet-Leu-Phe and C5a. Mammalian cells transfected with the IL-8 receptor cDNA clone bind IL-8 with high affinity and respond specifically to IL-8 by transiently mobilizing calcium. The IL-8 receptor may be part of a subfamily of related G protein-coupled receptors that transduce signals for the IL-8 family of pro-inflammatory cytokines.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Holmes, W E -- Lee, J -- Kuang, W J -- Rice, G C -- Wood, W I -- New York, N.Y. -- Science. 1991 Sep 13;253(5025):1278-80.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Molecular Biology, Genentech, Inc., South San Francisco, CA 94080.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/1840701" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Animals ; Cell Line ; Cloning, Molecular ; DNA Probes ; Humans ; Interleukin-8/*metabolism ; Kinetics ; Molecular Sequence Data ; Nucleic Acid Hybridization ; Plasmids ; RNA, Messenger/genetics ; Receptors, Immunologic/*genetics/metabolism ; Receptors, Interleukin-8A ; Recombinant Proteins/metabolism ; Sequence Homology, Nucleic Acid ; Transfection
    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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  • 10
    Publication Date: 2012-11-10
    Description: Phosphine is a small redox-active gas that is used to protect global grain reserves, which are threatened by the emergence of phosphine resistance in pest insects. We find that polymorphisms responsible for genetic resistance cluster around the redox-active catalytic disulfide or the dimerization interface of dihydrolipoamide dehydrogenase (DLD) in insects (Rhyzopertha dominica and Tribolium castaneum) and nematodes (Caenorhabditis elegans). DLD is a core metabolic enzyme representing a new class of resistance factor for a redox-active metabolic toxin. It participates in four key steps of core metabolism, and metabolite profiles indicate that phosphine exposure in mutant and wild-type animals affects these steps differently. Mutation of DLD in C. elegans increases arsenite sensitivity. This specific vulnerability may be exploited to control phosphine-resistant insects and safeguard food security.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schlipalius, David I -- Valmas, Nicholas -- Tuck, Andrew G -- Jagadeesan, Rajeswaran -- Ma, Li -- Kaur, Ramandeep -- Goldinger, Anita -- Anderson, Cameron -- Kuang, Jujiao -- Zuryn, Steven -- Mau, Yosep S -- Cheng, Qiang -- Collins, Patrick J -- Nayak, Manoj K -- Schirra, Horst Joachim -- Hilliard, Massimo A -- Ebert, Paul R -- R01NS060129/NS/NINDS NIH HHS/ -- New York, N.Y. -- Science. 2012 Nov 9;338(6108):807-10. doi: 10.1126/science.1224951.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Agri-Science Queensland, Department of Agriculture, Fisheries and Forestry, Ecosciences Precinct, Brisbane, QLD 4001, Australia.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23139334" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Arsenicals/pharmacology ; Arsenites/pharmacology ; Beetles/drug effects/*enzymology/genetics/metabolism ; Caenorhabditis elegans/drug effects/*enzymology/genetics/metabolism ; Caenorhabditis elegans Proteins/chemistry/genetics/metabolism ; Catalytic Domain ; Dihydrolipoamide Dehydrogenase/chemistry/*genetics/metabolism ; Insect Proteins/chemistry/genetics/metabolism ; Insecticide Resistance/*genetics ; *Insecticides/pharmacology ; Metabolic Networks and Pathways ; Molecular Sequence Data ; Mutation ; Oxidation-Reduction ; Pesticides ; *Phosphines/pharmacology ; Polymorphism, Genetic ; Protein Multimerization ; Tribolium/drug effects/*enzymology/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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