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  • American Institute of Physics  (38)
  • American Institute of Physics (AIP)  (9)
  • International Union of Crystallography (IUC)  (7)
  • Nature Publishing Group (NPG)  (4)
  • Royal Society  (4)
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  • 1
    Publication Date: 2014-04-11
    Description: In obesity and type 2 diabetes, Glut4 glucose transporter expression is decreased selectively in adipocytes. Adipose-specific knockout or overexpression of Glut4 alters systemic insulin sensitivity. Here we show, using DNA array analyses, that nicotinamide N-methyltransferase (Nnmt) is the most strongly reciprocally regulated gene when comparing gene expression in white adipose tissue (WAT) from adipose-specific Glut4-knockout or adipose-specific Glut4-overexpressing mice with their respective controls. NNMT methylates nicotinamide (vitamin B3) using S-adenosylmethionine (SAM) as a methyl donor. Nicotinamide is a precursor of NAD(+), an important cofactor linking cellular redox states with energy metabolism. SAM provides propylamine for polyamine biosynthesis and donates a methyl group for histone methylation. Polyamine flux including synthesis, catabolism and excretion, is controlled by the rate-limiting enzymes ornithine decarboxylase (ODC) and spermidine-spermine N(1)-acetyltransferase (SSAT; encoded by Sat1) and by polyamine oxidase (PAO), and has a major role in energy metabolism. We report that NNMT expression is increased in WAT and liver of obese and diabetic mice. Nnmt knockdown in WAT and liver protects against diet-induced obesity by augmenting cellular energy expenditure. NNMT inhibition increases adipose SAM and NAD(+) levels and upregulates ODC and SSAT activity as well as expression, owing to the effects of NNMT on histone H3 lysine 4 methylation in adipose tissue. Direct evidence for increased polyamine flux resulting from NNMT inhibition includes elevated urinary excretion and adipocyte secretion of diacetylspermine, a product of polyamine metabolism. NNMT inhibition in adipocytes increases oxygen consumption in an ODC-, SSAT- and PAO-dependent manner. Thus, NNMT is a novel regulator of histone methylation, polyamine flux and NAD(+)-dependent SIRT1 signalling, and is a unique and attractive target for treating obesity and type 2 diabetes.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4107212/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4107212/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kraus, Daniel -- Yang, Qin -- Kong, Dong -- Banks, Alexander S -- Zhang, Lin -- Rodgers, Joseph T -- Pirinen, Eija -- Pulinilkunnil, Thomas C -- Gong, Fengying -- Wang, Ya-chin -- Cen, Yana -- Sauve, Anthony A -- Asara, John M -- Peroni, Odile D -- Monia, Brett P -- Bhanot, Sanjay -- Alhonen, Leena -- Puigserver, Pere -- Kahn, Barbara B -- K01 DK094943/DK/NIDDK NIH HHS/ -- K08 DK090149/DK/NIDDK NIH HHS/ -- P01 CA120964/CA/NCI NIH HHS/ -- P01CA120964/CA/NCI NIH HHS/ -- P30 DK040561/DK/NIDDK NIH HHS/ -- P30 DK0460200/DK/NIDDK NIH HHS/ -- P30 DK046200/DK/NIDDK NIH HHS/ -- P30 DK057521/DK/NIDDK NIH HHS/ -- P30 DK57521/DK/NIDDK NIH HHS/ -- P30CA006516-46/CA/NCI NIH HHS/ -- R01 DK069966/DK/NIDDK NIH HHS/ -- R01 DK100385/DK/NIDDK NIH HHS/ -- R01 DK69966/DK/NIDDK NIH HHS/ -- R37 DK043051/DK/NIDDK NIH HHS/ -- R37 DK43051/DK/NIDDK NIH HHS/ -- England -- Nature. 2014 Apr 10;508(7495):258-62. doi: 10.1038/nature13198.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Avenue, Boston, Massachusetts 02215, USA [2] [3] Division of Nephrology, Department of Internal Medicine I, Wurzburg University Hospital, Oberdurrbacher Strasse 6, 97080 Wurzburg, Germany (D.K.); Department of Medicine, Physiology and Biophysics, Center for Diabetes Research and Treatment, and Center for Epigenetics and Metabolism, University of California, Irvine, California 92697, USA (Q.Y.); Research Programs Unit, Molecular Neurology, Biomedicum Helsinki, University of Helsinki, 00290, Helsinki, Finland (E.P.); Department of Biochemistry and Molecular Biology, Faculty of Medicine, Dalhousie Medicine New Brunswick, Dalhousie University, Saint John, New Brunswick E2L4L5, USA (T.C.P.); Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100730, China (F.G.); School of Pharmacy, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland (L.A.). ; Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Avenue, Boston, Massachusetts 02215, USA. ; Department of Cancer Biology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA. ; 1] Biotechnology and Molecular Medicine, A.I. Virtanen Institute for Molecular Sciences, Biocenter Kuopio, University of Eastern Finland, Kuopio Campus, PO Box 1627, FI-70211 Kuopio, Finland [2] Division of Nephrology, Department of Internal Medicine I, Wurzburg University Hospital, Oberdurrbacher Strasse 6, 97080 Wurzburg, Germany (D.K.); Department of Medicine, Physiology and Biophysics, Center for Diabetes Research and Treatment, and Center for Epigenetics and Metabolism, University of California, Irvine, California 92697, USA (Q.Y.); Research Programs Unit, Molecular Neurology, Biomedicum Helsinki, University of Helsinki, 00290, Helsinki, Finland (E.P.); Department of Biochemistry and Molecular Biology, Faculty of Medicine, Dalhousie Medicine New Brunswick, Dalhousie University, Saint John, New Brunswick E2L4L5, USA (T.C.P.); Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100730, China (F.G.); School of Pharmacy, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland (L.A.). ; 1] Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Avenue, Boston, Massachusetts 02215, USA [2] Division of Nephrology, Department of Internal Medicine I, Wurzburg University Hospital, Oberdurrbacher Strasse 6, 97080 Wurzburg, Germany (D.K.); Department of Medicine, Physiology and Biophysics, Center for Diabetes Research and Treatment, and Center for Epigenetics and Metabolism, University of California, Irvine, California 92697, USA (Q.Y.); Research Programs Unit, Molecular Neurology, Biomedicum Helsinki, University of Helsinki, 00290, Helsinki, Finland (E.P.); Department of Biochemistry and Molecular Biology, Faculty of Medicine, Dalhousie Medicine New Brunswick, Dalhousie University, Saint John, New Brunswick E2L4L5, USA (T.C.P.); Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100730, China (F.G.); School of Pharmacy, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland (L.A.). ; Department of Pharmacology, Weill Medical College of Cornell University, 1300 York Avenue, New York, New York 10065, USA. ; Division of Signal Transduction, Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Ave, Boston, Massachusetts 02215, USA. ; Isis Pharmaceuticals, 1896 Rutherford Road, Carlsbad, California 92008-7326, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24717514" target="_blank"〉PubMed〈/a〉
    Keywords: Acetyltransferases/metabolism ; Adipocytes/metabolism/secretion ; Adipose Tissue/enzymology/metabolism ; Adipose Tissue, White/enzymology/metabolism ; Animals ; Diabetes Mellitus, Type 2/enzymology/metabolism ; *Diet ; Energy Metabolism ; Fatty Liver ; Gene Knockdown Techniques ; Glucose Intolerance ; Glucose Transporter Type 4/deficiency/genetics/metabolism ; Insulin Resistance ; Liver/enzymology ; Male ; Mice ; Mice, Inbred C57BL ; NAD/metabolism ; Niacinamide/metabolism ; Nicotinamide N-Methyltransferase/*deficiency/genetics/*metabolism ; Obesity/*enzymology/etiology/genetics/*prevention & control ; Ornithine Decarboxylase/metabolism ; Oxidoreductases Acting on CH-NH Group Donors/metabolism ; S-Adenosylmethionine/metabolism ; Sirtuin 1/metabolism ; Spermine/analogs & derivatives/metabolism ; Thinness/enzymology/metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2012-03-30
    Description: During tissue morphogenesis, simple epithelial sheets undergo folding to form complex structures. The prevailing model underlying epithelial folding involves cell shape changes driven by myosin-dependent apical constriction. Here we describe an alternative mechanism that requires differential positioning of adherens junctions controlled by modulation of epithelial apical-basal polarity. Using live embryo imaging, we show that before the initiation of dorsal transverse folds during Drosophila gastrulation, adherens junctions shift basally in the initiating cells, but maintain their original subapical positioning in the neighbouring cells. Junctional positioning in the dorsal epithelium depends on the polarity proteins Bazooka and Par-1. In particular, the basal shift that occurs in the initiating cells is associated with a progressive decrease in Par-1 levels. We show that uniform reduction of the activity of Bazooka or Par-1 results in uniform apical or lateral positioning of junctions and in each case dorsal fold initiation is abolished. In addition, an increase in the Bazooka/Par-1 ratio causes formation of ectopic dorsal folds. The basal shift of junctions not only alters the apical shape of the initiating cells, but also forces the lateral membrane of the adjacent cells to bend towards the initiating cells, thereby facilitating tissue deformation. Our data thus establish a direct link between modification of epithelial polarity and initiation of epithelial folding.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3597240/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3597240/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wang, Yu-Chiun -- Khan, Zia -- Kaschube, Matthias -- Wieschaus, Eric F -- 5R37HD15587/HD/NICHD NIH HHS/ -- P50 GM071508/GM/NIGMS NIH HHS/ -- R37 HD015587/HD/NICHD NIH HHS/ -- Howard Hughes Medical Institute/ -- England -- Nature. 2012 Mar 28;484(7394):390-3. doi: 10.1038/nature10938.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22456706" target="_blank"〉PubMed〈/a〉
    Keywords: Adherens Junctions/*physiology/ultrastructure ; Animals ; *Cell Polarity ; Cell Shape ; Choristoma ; Drosophila Proteins/deficiency/genetics/metabolism ; Drosophila melanogaster/*cytology/*embryology/genetics/metabolism ; Epithelial Cells/*cytology/metabolism/ultrastructure ; Epithelium/*embryology/metabolism/ultrastructure ; Gastrula/cytology/embryology/metabolism/ultrastructure ; Gastrulation/*physiology ; Glycogen Synthase Kinase 3 ; Intracellular Signaling Peptides and Proteins/deficiency/genetics/metabolism ; Protein-Serine-Threonine Kinases/metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 2016-03-17
    Description: The integrated stress response (ISR) is a homeostatic mechanism by which eukaryotic cells sense and respond to stress-inducing signals, such as amino acid starvation. General controlled non-repressed (GCN2) kinase is a key orchestrator of the ISR, and modulates protein synthesis in response to amino acid starvation. Here we demonstrate in mice that GCN2 controls intestinal inflammation by suppressing inflammasome activation. Enhanced activation of ISR was observed in intestinal antigen presenting cells (APCs) and epithelial cells during amino acid starvation, or intestinal inflammation. Genetic deletion of Gcn2 (also known as Eif2ka4) in CD11c(+) APCs or intestinal epithelial cells resulted in enhanced intestinal inflammation and T helper 17 cell (TH17) responses, owing to enhanced inflammasome activation and interleukin (IL)-1beta production. This was caused by reduced autophagy in Gcn2(-/-) intestinal APCs and epithelial cells, leading to increased reactive oxygen species (ROS), a potent activator of inflammasomes. Thus, conditional ablation of Atg5 or Atg7 in intestinal APCs resulted in enhanced ROS and TH17 responses. Furthermore, in vivo blockade of ROS and IL-1beta resulted in inhibition of TH17 responses and reduced inflammation in Gcn2(-/-) mice. Importantly, acute amino acid starvation suppressed intestinal inflammation via a mechanism dependent on GCN2. These results reveal a mechanism that couples amino acid sensing with control of intestinal inflammation via GCN2.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4854628/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4854628/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ravindran, Rajesh -- Loebbermann, Jens -- Nakaya, Helder I -- Khan, Nooruddin -- Ma, Hualing -- Gama, Leonardo -- Machiah, Deepa K -- Lawson, Benton -- Hakimpour, Paul -- Wang, Yi-chong -- Li, Shuzhao -- Sharma, Prachi -- Kaufman, Randal J -- Martinez, Jennifer -- Pulendran, Bali -- R01 DK088227/DK/NIDDK NIH HHS/ -- R01 DK103185/DK/NIDDK NIH HHS/ -- R37 AI048638/AI/NIAID NIH HHS/ -- R37 DK042394/DK/NIDDK NIH HHS/ -- R37 DK057665/DK/NIDDK NIH HHS/ -- U19 AI057266/AI/NIAID NIH HHS/ -- U19 AI090023/AI/NIAID NIH HHS/ -- ZIA ES103286-01/Intramural NIH HHS/ -- England -- Nature. 2016 Mar 24;531(7595):523-7. doi: 10.1038/nature17186. Epub 2016 Mar 16.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Emory Vaccine Center, Yerkes National Primate Research Center, 954 Gatewood Road, Atlanta, Georgia 30329, USA. ; School of Pharmaceutical Sciences, University of Sao Paulo, Sao Paulo 05508, Brazil. ; Department of Biotechnology and Bioinformatics, School of Life Sciences, University of Hyderabad, Hyderabad 500 046, India. ; Division of Pathology, Yerkes National Primate Research Center, 954 Gatewood Road, Atlanta, Georgia 30329, USA. ; Virology Core, Emory Vaccine Center and Yerkes National Primate Research Center, 954 Gatewood Road, Atlanta, Georgia 30329, USA. ; Degenerative Disease Program, Sanford Burnham Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, California 92037 USA. ; National Institute of Environmental Health Sciences, Mail Drop D2-01 Research Triangle Park, North Carolina 27709, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26982722" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acids/administration & dosage/deficiency/*metabolism/pharmacology ; Animals ; Antigen-Presenting Cells/immunology/metabolism ; Autophagy ; Colitis/etiology/*metabolism/pathology/prevention & control ; Disease Models, Animal ; Epithelial Cells/metabolism ; Female ; Humans ; Inflammasomes/*antagonists & inhibitors/metabolism ; Inflammation/etiology/*metabolism/pathology/prevention & control ; Interleukin-1beta/immunology ; Intestines/*metabolism/*pathology ; Male ; Mice ; Microtubule-Associated Proteins/deficiency/metabolism ; Protein-Serine-Threonine Kinases/deficiency/genetics/*metabolism ; Reactive Oxygen Species/metabolism ; Stress, Physiological ; Th17 Cells/immunology ; Ubiquitin-Activating Enzymes/deficiency/metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 4
    Publication Date: 2016-02-11
    Description: Sexual reproduction requires recognition between the male and female gametes. In flowering plants, the immobile sperms are delivered to the ovule-enclosed female gametophyte by guided pollen tube growth. Although the female gametophyte-secreted peptides have been identified to be the chemotactic attractant to the pollen tube, the male receptor(s) is still unknown. Here we identify a cell-surface receptor heteromer, MDIS1-MIK, on the pollen tube that perceives female attractant LURE1 in Arabidopsis thaliana. MDIS1, MIK1 and MIK2 are plasma-membrane-localized receptor-like kinases with extracellular leucine-rich repeats and an intracellular kinase domain. LURE1 specifically binds the extracellular domains of MDIS1, MIK1 and MIK2, whereas mdis1 and mik1 mik2 mutant pollen tubes respond less sensitively to LURE1. Furthermore, LURE1 triggers dimerization of the receptors and activates the kinase activity of MIK1. Importantly, transformation of AtMDIS1 to the sister species Capsella rubella can partially break down the reproductive isolation barrier. Our findings reveal a new mechanism of the male perception of the female attracting signals.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wang, Tong -- Liang, Liang -- Xue, Yong -- Jia, Peng-Fei -- Chen, Wei -- Zhang, Meng-Xia -- Wang, Ying-Chun -- Li, Hong-Ju -- Yang, Wei-Cai -- England -- Nature. 2016 Mar 10;531(7593):241-4. doi: 10.1038/nature16975. Epub 2016 Feb 10.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉State Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China. ; University of Chinese Academy of Sciences, Beijing 100049, China.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26863186" target="_blank"〉PubMed〈/a〉
    Keywords: Arabidopsis/genetics/*metabolism/physiology ; Arabidopsis Proteins/chemistry/genetics/*metabolism ; Capsella/genetics/metabolism/physiology ; Cell Membrane/metabolism ; Mutation ; Ovule/metabolism ; Phenotype ; Phosphotransferases/chemistry/genetics/*metabolism ; Pollen Tube/genetics/growth & development/metabolism ; Protein Kinases/genetics/metabolism ; Protein Multimerization ; Protein Structure, Quaternary ; Protein Structure, Tertiary ; Receptors, Cell Surface/chemistry/genetics/*metabolism ; Reproduction ; *Signal Transduction
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    Electronic ISSN: 1476-4687
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  • 5
    Publication Date: 2017-04-13
    Description: Locating sources of diffusion and spreading from minimum data is a significant problem in network science with great applied values to the society. However, a general theoretical framework dealing with optimal source localization is lacking. Combining the controllability theory for complex networks and compressive sensing, we develop a framework with high efficiency and robustness for optimal source localization in arbitrary weighted networks with arbitrary distribution of sources. We offer a minimum output analysis to quantify the source locatability through a minimal number of messenger nodes that produce sufficient measurement for fully locating the sources. When the minimum messenger nodes are discerned, the problem of optimal source localization becomes one of sparse signal reconstruction, which can be solved using compressive sensing. Application of our framework to model and empirical networks demonstrates that sources in homogeneous and denser networks are more readily to be located. A surprising finding is that, for a connected undirected network with random link weights and weak noise, a single messenger node is sufficient for locating any number of sources. The framework deepens our understanding of the network source localization problem and offers efficient tools with broad applications.
    Keywords: complexity, graph theory
    Electronic ISSN: 2054-5703
    Topics: Natural Sciences in General
    Published by Royal Society
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4757-4760 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Formation of Schottky barrier contacts to n-type 6H-SiC for a number of metals chosen to include a variety of physical and chemical properties has been investigated. The metals (Pd, Au, Ag, Tb, Er, Mn, Al, and Mg) were deposited onto room temperature surfaces terminated with a submonolayer coverage of oxygen. The metal/6H-SiC interface chemistry and Schottky barrier height φB during contact formation were obtained with x-ray photoemission spectroscopy; the electrical properties of subsequently formed thick contacts were characterized by current-voltage and capacitance-voltage techniques. The øB values for these metals extend over a wide 1.3 eV range. To a varying degree φB depends on the 6H-SiC crystal face (Si vs C). Mg and Al (Si face of latter) have φB=0.3 eV, a value which is suitable for nonalloyed ohmic contacts.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1765-1767 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Room temperature photoreflectance (PR) was used to investigate the surface state densities of GaAs and In0.52Al0.48As surface intrinsic-n+ structures. The built-in electric field and thus the surface barrier height are evaluated using the observed Franz–Keldysh oscillations in the PR spectra. Based on the thermionic emission theory and current-transport theory, the surface state density as well as the pinning position of the Fermi level can be determined from the dependence of the surface barrier height on the pump beam intensity. Even though this method is significantly simpler, easier to perform, and time efficient compared with other approaches, the results obtained agree with the literature. © 1999 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6458-6465 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Particulate composites with negative stiffness inclusions in a viscoelastic matrix are shown to have higher thermal expansion than that of either constituent and exceeding conventional bounds. It is also shown theoretically that other extreme linear coupled field properties including piezoelectricity and pyroelectricity occur in layer- and fiber-type piezoelectric composites, due to negative inclusion stiffness effects. The causal mechanism is a greater deformation in and near the inclusions than the composite as a whole. A block of negative stiffness material is unstable, but negative stiffness inclusions in a composite can be stabilized by the surrounding matrix and can give rise to extreme viscoelastic effects in lumped and distributed composites. In contrast to prior proposed composites with unbounded thermal expansion, neither the assumptions of void spaces nor slip interfaces are required in the present analysis. © 2001 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 2857-2859 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Built-in electric fields and interfacial state densities (Dit) in a series of oxide–GaAs heterostructures fabricated by in situ molecular beam epitaxy were studied using room temperature photoreflectance. The samples investigated were air-, Al2O3–Ga2Ox–, and Ga2O3(Gd2O3)–GaAs. We found that the built-in electric fields are 48, 44, and 38 kV/cm for air-, Al2O3-, and Ga2Ox–GaAs samples, respectively. For the Ga2O3(Gd2O3)–GaAs sample, the built-in electric field is negligibly small, indicating a very low interfacial state density. Estimated by the low field limit criterion, Dit is less than 1×1011 cm−2 eV−1. Our results on the Ga2O3(Gd2O3)–GaAs sample are consistent with the data obtained previously using capacitance–voltage measurements in quasistatic/high frequency modes and photoluminescence measurements. © 1998 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3452-3454 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoreflectance measurements have been performed on a δ-doped GaAs homojunction. Two Franz–Keldysh oscillation features originating from two different regions (a buffer layer and a top layer) of the structure superimpose with each other in the photoreflectance spectrum. By properly selecting the reference phase, one of the features can be suppressed, thus enabling us to determine the electric fields from the two regions unambiguously. The electric field in the top layer is 3.5±0.2×105 V/cm, which is in good agreement with theoretical calculation. The electric field in the buffer layer is 1.2±0.1×104 V/cm. © 1996 American Institute of Physics.
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