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  • 2000-2004  (72)
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  • 1
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    Axonal neuregulin-1 regulates myelin sheath thickness (2004)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2004-03-27
    Description: In the nervous system of vertebrates, myelination is essential for rapid and accurate impulse conduction. Myelin thickness depends on axon fiber size. We use mutant and transgenic mouse lines to show that axonal Neuregulin-1 (Nrg1) signals information about axon size to Schwann cells. Reduced Nrg1 expression causes hypomyelination and reduced nerve conduction velocity. Neuronal overexpression of Nrg1 induces hypermyelination and demonstrates that Nrg1 type III is the responsible isoform. We suggest a model by which myelin-forming Schwann cells integrate axonal Nrg1 signals as a biochemical measure of axon size.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Michailov, Galin V -- Sereda, Michael W -- Brinkmann, Bastian G -- Fischer, Tobias M -- Haug, Bernhard -- Birchmeier, Carmen -- Role, Lorna -- Lai, Cary -- Schwab, Markus H -- Nave, Klaus-Armin -- New York, N.Y. -- Science. 2004 Apr 30;304(5671):700-3. Epub 2004 Mar 25.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Neurogenetics, Max Planck Institute of Experimental Medicine, 37075 Gottingen, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15044753" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Axons/*physiology/*ultrastructure ; Ganglia, Spinal/chemistry ; Gene Targeting ; Genes, erbB ; Genes, erbB-2 ; Heterozygote ; Mice ; Mice, Knockout ; Mice, Transgenic ; Models, Neurological ; Myelin Sheath/*physiology/*ultrastructure ; Neural Conduction ; Neuregulin-1/genetics/*physiology ; Protein Isoforms/physiology ; Receptor, Epidermal Growth Factor/analysis/physiology ; Receptor, ErbB-2/analysis/physiology ; Receptor, ErbB-3/analysis/physiology ; Schwann Cells/physiology ; Sciatic Nerve/chemistry ; Signal Transduction
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
    Electronic Resource
    Electronic Resource
    Scanning electron filling modulation reflectance of charged InGaAs self-assembled quantum dot (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 4399-4402 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present the scanning electron-filling modulation reflectance (SEFR) of charged In0.5Ga0.5As self-assembled quantum dots. The SEFR is performed by applying a small constant modulation voltage and scanning the dc bias through the quantum dot energy levels. The spectral intensity of the SEFR can be related to the electron density confined in each quantum state, which shows a good agreement with the apparent carrier concentration deduced from the capacitance–voltage measurements. In this study, we find that the transition energy of quantum-dot excited state is about 10 meV smaller than the values obtained from the photoluminescence and electron-filling modulation reflectance. This phenomenon is explained by the Coulomb interactions between the optical excited electron–hole pair and the electrons occupied in the quantum dots. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1456942
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  • 3
    Electronic Resource
    Electronic Resource
    High frequency impedance spectra on the chromium dioxide thin film (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7702-7704 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the study of high frequency magnetotransport properties of the chromium dioxide (CrO2) thin films, grown on Si substrate using chemical vapor deposition. The film exhibits a ferromagnetic transition with a Curie temperature near 390 K. The temperature dependent spontaneous magnetization follows Bloch's law. The impedance spectra, being analyzed based on the fundamental electrodynamics, are demonstrated to be in a low-loss dielectric limit along with the occurrence of dielectric relaxation and magnetization response. The specific features of impedance spectra, distinct from the usual metallic ferromagnet, are attributed to the half metallic nature of CrO2. The results explore the possibility for high frequency device applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1358352
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  • 4
    Electronic Resource
    Electronic Resource
    Room temperature study of low temperature grown Al0.3Ga0.7As/GaAs multiple quantum wells by modulation reflectance (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 8589-8593 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We studied the subband energy levels in AlGaAs/GaAs multiple quantum wells grown at different temperatures (200–600 °C) by using the piezoreflectance and photoreflectance in room temperature. Under subsequent 30 s rapid-thermal annealing at different temperatures (600–1000 °C), we observed a large energy blueshift in samples with growth temperature below 400 °C. This blueshift energy may be attributed to the modification of quantum wells caused by gallium vacancy enhanced Al–Ga interdiffusion. The energy blueshifts were analyzed by solving Fick's second law for Al diffusion in quantum wells, obtaining an effective activation energy of 0.75 eV. We discuss our results using the nonequilibrium diffusion equation and comparing them with other experiments. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373583
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  • 5
    Electronic Resource
    Electronic Resource
    Direct measurement of piezoelectric field in In0.23Ga0.77N/GaN multiple quantum wells by electrotransmission spectroscopy (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 531-533 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this communication, we present experimental evidence of the piezoelectric-field-induced quantum-confined Stark effect on In0.23Ga0.77N/GaN multiple quantum wells. The optical transitions in In0.23Ga0.77N/GaN p-i-n multiple quantum wells were studied by using electrotransmission (ET) at room temperature. Quantum-well-related signals are well resolved in our ET spectra. Since the strong internal electric field breaks the symmetry of the quantum wells, both the allowed and the forbidden transitions are observed. Clear energy blueshifts in accordance with increasing reversed bias are observed in ET spectra. The strength of piezoelectric field is found to be 1.7–1.9 MV/cm in the In0.23Ga0.77N strain quantum well layer, which is comparable with the measurement reported in the literature. We have shown experimentally how the piezoelectric field affects the energy shift for the strained multiple quantum wells. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1426237
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  • 6
    Electronic Resource
    Electronic Resource
    High-dielectric-constant Ta2O5/n-GaN metal-oxide-semiconductor structure (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 3788-3790 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-dielectric-constant Ta2O5 has been grown on the n-GaN epifilm by rf magnetron sputtering. Photoluminescence measurement has been performed to compare the luminescence intensity with and without the dielectrics. Threefold increase in intensity is obtained, and a surface recombination velocity is estimated to be 3×104 cm/s as an upper limit using a modified dead-layer model. A metal-oxide-semiconductor structure has been fabricated with Al on n-GaN as the ohmic contact and on Ta2O5 as the gate metal. Capacitance-versus-voltage characteristics have been measured. The doping concentration obtained from the depletion regime is compared with the result of Hall measurement, which is 7.0×1016 cm−3. The flat-band voltage is obtained from the high-frequency data, and the effective oxide charge number density is calculated as 4.1×1012 cm−2. Indication of strong inversion appears at low reverse bias due to the high dielectric constant of Ta2O5, and matches closely with calculated values. Hysteresis is observed and ascribed to positive mobile charges derived as 2.1×1012 cm−2. The capacitance dependence on the frequency and the leakage current are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1332815
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  • 7
    Electronic Resource
    Electronic Resource
    Modelling assimilation and intercellular CO2 from measured conductance: a synthesis of approaches (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A spectrum of models that estimate assimilation rate A from intercellular carbon dioxide concentration (Ci) and measured stomatal conductance to CO2 (gc) were investigated using leaf-level gas exchange measurements. The gas exchange measurements were performed in a uniform loblolly pine stand (Pinus taeda L.) using the Free Air CO2 Enrichment (FACE) facility under ambient and elevated atmospheric CO2 for 3 years. These measurements were also used to test a newly proposed framework that combines basic properties of the A–Ci curve with a Fickian diffusion transport model to predict the relationship between Ci/Ca and gc, where Ca is atmospheric carbon dioxide concentration. The widely used Ball–Berry model and five other models as well as the biochemical model proposed by Farquhar et al. (1980) were also reformulated to express variations in Ci/Ca as a function of their corresponding driving mechanisms. To assess the predictive capabilities of these approaches, their respective parameters were estimated from independent measurements of long-term stable carbon isotope determinations (δ13C), meteorological variables, and ensemble A–Ci curves. All eight approaches reproduced the measured A reasonably well, in an ensemble sense, from measured water vapour conductance and modeled Ci/Ca. However, the scatter in the instantaneous A estimates was sufficiently large for both ambient and elevated Ca to suggest that other transient processes were not explicitly resolved by all eight parameterizations. An important finding from our analysis is that added physiological complexity in modeling Ci/Ca (when gc is known) need not always translate to increased accuracy in predicting A. Finally, the broader utility of these approaches to estimate assimilation and net ecosystem exchange is discussed in relation to elevated atmospheric CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00641.x
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  • 8
    Electronic Resource
    Electronic Resource
    Modelling the limits on the response of net carbon exchange to fertilization in a south-eastern pine forest (2002)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 25 (2002), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Using a combination of model simulations and detailed measurements at a hierarchy of scales conducted at a sandhills forest site, the effect of fertilization on net ecosystem exchange (NEE) and its components in 6-year-old Pinus taeda stands was quantified. The detailed measurements, collected over a 20-d period in September and October, included gas exchange and eddy covariance fluxes, sampled for a 10-d period each at the fertilized stand and at the control stand. Respiration from the forest floor and above-ground biomass was measured using chambers during the experiment. Fertilization doubled leaf area index (LAI) and increased leaf carboxylation capacity by 20%. However, this increase in total LAI translated into an increase of only 25% in modelled sunlit LAI and in canopy photosynthesis. It is shown that the same climatic and environmental conditions that enhance photosynthesis in the September and October periods also cause an increase in respiration The increases in respiration counterbalanced photosynthesis and resulted in negligible NEE differences between fertilized and control stands. The fact that total biomass of the fertilized stand exceeded 2·5 times that of the control, suggests that the counteracting effects cannot persist throughout the year. In fact, modelled annual carbon balance showed that gross primary productivity (GPP) increased by about 50% and that the largest enhancement in NEE occurred in the spring and autumn, during which cooler temperatures reduced respiration more than photosynthesis. The modelled difference in annual NEE between fertilized  and  control  stands  (approximately  200 1;g 2;C 3;m−2 y−1)  suggest that the effect of fertilization was sufficiently large to transform the stand from a net terrestrial carbon source to a net sink.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2002.00896.x
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  • 9
    Electronic Resource
    Electronic Resource
    An identification and classification of enterprise portal functions and features (2003)
    Bingley : Emerald
    Industrial management & data systems 103 (2003), S. 693-702 
    Details
    ISSN: 0263-5577
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Computer Science , Economics
    Notes: Enterprise portal is a type of new information system that can help companies and their employees to manage, share, and use previously disparate information. The primary objective of this research is to identify and evaluate the functions and features in enterprise portal products. In particular, this study develops a simplified model that can be used for identifying and classifying the functions and features in corporate portal software. The results of this study may be useful to information technology managers, educators, and students involved in knowledge management, business intelligence, information systems resources management, and data management. System developers, software engineers, project managers, financial managers, and data architects can use the functions and features identified in this study as benchmarking tools for evaluating portals capabilities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1108/02635570310506115
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  • 10
    Electronic Resource
    Electronic Resource
    An identification and classification of enterprise portal functions and features (2002)
    Bingley : Emerald
    Industrial management & data systems 102 (2002), S. 390-399 
    Details
    ISSN: 0263-5577
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Computer Science , Economics
    Notes: Enterprise portal is a type of new information system that can help companies and their employees to manage, share, and use previously disparate information. There are more than 60 vendors that are offering corporate portal solutions. With so many vendors, selecting the right one can be a difficult task. The primary objective of this research is to identify and evaluate the functions and features in enterprise portal products. In particular, this study develops a simplified model that can be used for identifying and classifying the functions and features in corporate portal software. The results of this study may be useful to information technology managers, educators, and students involved in knowledge management, business intelligence, information systems resources management, and data management. System developers, software engineers, project managers, financial managers, and data architects can use the functions and features identified in this study as benchmarking tools for evaluating portals capabilities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1108/02635570210439481
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