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  • 1
    Electronic Resource
    Electronic Resource
    Simultaneous measurement of electron and hole escape times from biased single quantum wells (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 426-428 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Picosecond pump probe measurements on waveguides containing a single GaAs/GaAlAs quantum well have enabled us to determine for the first time both electron and hole escape times from biased quantum wells. Contributions from excitonic saturation and field screening by photogenerated carriers can be clearly identified in the nonlinear transition signal and are quantitatively modeled. Preliminary analysis suggests that thermally assisted escape is dominant at room temperature, but discrepancies are found with conventional thermionic emission models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107903
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  • 2
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    Structural and relaxor-like dielectric properties of unfilled tungsten bronzes Ba5−5xSm5xTi5xNb10−5xO30 (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-03-29
    Description: New unfilled tetragonal tungsten bronze (TTB) oxides, Ba 5−5x Sm 5x Ti 5x Nb 10−5x O 30 (BSTN-x), where 0.10 ≤ x ≤ 0.35, have been synthesized in this work. Their crystal structure was determined and analyzed based on Rietveld structural refinement. It is found that single TTB phase can be formed in a particular x range (i.e., 0.15 ≤ x ≤ 0.3) due to the competition interaction between tolerance factor and electronegativity difference. Furthermore, dielectric and ferroelectric results indicate that phase transitions and ferroelectric states are sensitive to x. Referring to the local chemistry, we suggest that the raise of vacancies at the A 2 -site compared with that of A 1 -site will intensely depress the normal ferroelectric phase and is in favor of relaxor ferroelectric state. Macroscopically, previous A-site size difference standpoint on fill TTB compounds cannot give a reasonable explanation about the variation of dielectric maximum temperature (T m ) for present BSTN-x compounds. Alternatively, tetragonality (c/a) is adopted which can well describe the variation of T m in whole x range. In addition, one by one correspondence between tetragonality and electrical features can be found, and the compositions involving high c/a are usually stabilized in normal ferroelectric phase. It is believed that c/a is a more appropriate parameter to illustrate the variation of ferroelectric properties for unfilled TTB system.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    X-ray magnetic circular dichroism study of epitaxial magnetite ultrathin film on MgO(100) (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-03-27
    Description: The spin and orbital magnetic moments of the Fe 3 O 4 epitaxial ultrathin film synthesized by plasma assisted simultaneous oxidization on MgO(100) have been studied with X-ray magnetic circular dichroism. The ultrathin film retains a rather large total magnetic moment, i.e., (2.73 ± 0.15)  μ B /f.u., which is ∼70% of that for the bulk-like Fe 3 O 4 . A significant unquenched orbital moment up to 0.54 ± 0.05  μ B /f.u. was observed, which could come from the symmetry breaking at the Fe 3 O 4 /MgO interface. Such sizable orbital moment will add capacities to the Fe 3 O 4 -based spintronics devices in the magnetization reversal by the electric field.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Fourfold symmetric planar Hall effect in epitaxial La1−xSrxCoO3 thin films (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-04-07
    Description: The effect of Sr concentration on the planar Hall effect (PHE) in epitaxial magnetic phase separated La 1− x Sr x CoO 3 (0.07 ≤  x  ≤ 0.60) thin films was studied systematically. It was found that crystalline anisotropy and spin-orbital coupling are the main contributions to the unexpected fourfold symmetric PHE. The uniaxial anisotropy field was given by H uni  = 70 Oe and cubic anisotropic field H cub  = 143 Oe, respectively. The magnetic anisotropy was weakened by Sr doping, which corresponds with the disappearance of the fourfold symmetry in PHE with the increasing Sr concentration. The first principle calculations proved that the contribution of Co- d orbitals to the magnetic anisotropy strongly depends on the Sr concentration. e g − d x 2 − y 2 and e g − d 3 z 2 − r 2 orbitals play a dominant role in the magnetic anisotropy of the samples with x  = 0.125, 0.25, while the t 2 g − d x y ,   d y z ,   d x z orbitals contribute mainly to the magnetic anisotropy of the samples with x  = 0.375, 0.5, 0.625.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    The effect of strain on the domain switching of ferroelectric polycrystals (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-02-18
    Description: The effect of external strain on the non-linear electromechanical behavior of a ferroelectric poly-crystal is investigated under different applied electric fields by using a phase field model. Simulation results show that the domain switching induced by electric field under a tensile strain is much easier than that under a compressive strain, which is attributed to that a multi-domain structure can be more easily formed under the tensile strain than in the case of compressive strain when the electric field is absent. It is also found that a compressive misfit strain increases the macroscopic coercive field and remnant polarization while a tensile misfit strain decreases both of them. In addition, a compressive strain decreases the non-linear dielectric constant while a tensile strain increases it.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 6
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    The realization of ferro-ferrimagnetic transition and half-metallicity in half-Heusler CoMnGa alloy (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-11-25
    Description: We theoretically predicted that half-Heusler CoMnGa alloy to be half-metallic ferrimagnet at the equilibrium lattice parameter. With the lattice expansion, a local energy minimum occurs at a larger lattice parameter where CoMnGa alloy is in a metastable ferromagnetic state. However, a ferro-ferrimagnetic transition (Fo-Fi-T) is not observed in experiment. We found the Co-Mn antisites can induce the Fo-Fi-T by adjusting the driving force of magnetic transition and the energy barrier. The antisites are sensitive to the preparation methods and annealing temperatures. The highly ordered CoMnGa is achieved by annealing at 1073 K. The Fo-Fi-T occurs in a sample annealed at 1083 K.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 7
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    Giant planar Hall effect in reactive sputtered epitaxial CrxFe3–xO4 films (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-09-09
    Description: The epitaxial Cr x Fe 3- x O 4 films were fabricated by dc reactive sputtering on MgO (001) substrates. The longitudinal resistivity ρ x x was enhanced 3 orders of magnitude with the increase of Cr content x from 0 to 0.87. The tunneling magnetoresistance like planar Hall effect in the Cr x Fe 3- x O 4 films was observed while the angle between ⟨100⟩ in (001) oriented films and the direction of magnetic field is 45° and 135°, respectively. Both the phase relation of angular dependent planar Hall resistivity ρ x y and the numeral relation of ρ x y with longitudinal resistivity difference ρ / / − ρ ⊥ cannot be understood by the planar Hall effect expression in isotropic magnetic medium. The largest planar Hall resistivity was ∼10 5   μ Ω cm for x  = 0.71, which is one, two, and six orders of magnitude larger than that in Fe 3 O 4 , GaMnAs, and ferromagnetic metals, respectively. The giant planar Hall resistivity ρ x y is weak saturated at high fields and increases with the magnetic field. This giant planar Hall effect in the highly resistive Cr x Fe 3- x O 4 films is closely correlated to the longitudinal resistivity and antiphase boundaries.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 8
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    Spray-cooling concept for wind-based compressed air energy storage (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-08-16
    Description: Wind turbine output energy varies over time with local wind speed and is typically inconsistent with grid power demand. Without energy storage, the resulting difference between rated (peak) power and average power output leads to over-sizing of electrical generator and transmission lines. This conventional arrangement can be avoided if wind turbines can be coupled with energy storage to eliminate the output variations and instead produce their average power on a continuous basis. This would allow a smaller, lower-cost, constant-speed generator and a reduced capacity transmission system sized only for average power output. To accomplish this goal, this study discusses a concept for a storage system for a 5 MW off-shore wind turbine, which integrates a spray-based compressed air energy storage with a 35 MPa accumulator. The compressor employs a liquid piston for air sealing and employs water spray to augment heat transfer for high-efficiency. The overall compression is proposed in three stages with pressure ratios of 10:1, 7:1, and 5:1, all operated at 1 Hz to maintain moderate liquid surface acceleration. Based on a simple and fundamental description of the system, compression efficiency was found to be strongly dependent on droplet surface area, which can be achieved through either high mass loading or small drop sizes. The simulations also show that direct injection spray can increase overall three-stage compression efficiency to as high as 89%, substantially better than the 27% associated with a conventional adiabatic compression at the same pressure ratio. In addition, this study introduces a key performance parameter, termed the Levelization Factor, which can be used to quantify the impact of storage on wind energy systems. However, experiments and simulations based on 3-D geometries with design details are needed to determine the potential of this concept.
    Electronic ISSN: 1941-7012
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by American Institute of Physics (AIP)
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  • 9
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    A genome-wide RNAi screen reveals determinants of human embryonic stem cell identity (2010)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2010-10-19
    Description: The derivation of human ES cells (hESCs) from human blastocysts represents one of the milestones in stem cell biology. The full potential of hESCs in research and clinical applications requires a detailed understanding of the genetic network that governs the unique properties of hESCs. Here, we report a genome-wide RNA interference screen to identify genes which regulate self-renewal and pluripotency properties in hESCs. Interestingly, functionally distinct complexes involved in transcriptional regulation and chromatin remodelling are among the factors identified in the screen. To understand the roles of these potential regulators of hESCs, we studied transcription factor PRDM14 to gain new insights into its functional roles in the regulation of pluripotency. We showed that PRDM14 regulates directly the expression of key pluripotency gene POU5F1 through its proximal enhancer. Genome-wide location profiling experiments revealed that PRDM14 colocalized extensively with other key transcription factors such as OCT4, NANOG and SOX2, indicating that PRDM14 is integrated into the core transcriptional regulatory network. More importantly, in a gain-of-function assay, we showed that PRDM14 is able to enhance the efficiency of reprogramming of human fibroblasts in conjunction with OCT4, SOX2 and KLF4. Altogether, our study uncovers a wealth of novel hESC regulators wherein PRDM14 exemplifies a key transcription factor required for the maintenance of hESC identity and the reacquisition of pluripotency in human somatic cells.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Chia, Na-Yu -- Chan, Yun-Shen -- Feng, Bo -- Lu, Xinyi -- Orlov, Yuriy L -- Moreau, Dimitri -- Kumar, Pankaj -- Yang, Lin -- Jiang, Jianming -- Lau, Mei-Sheng -- Huss, Mikael -- Soh, Boon-Seng -- Kraus, Petra -- Li, Pin -- Lufkin, Thomas -- Lim, Bing -- Clarke, Neil D -- Bard, Frederic -- Ng, Huck-Hui -- England -- Nature. 2010 Nov 11;468(7321):316-20. doi: 10.1038/nature09531. Epub 2010 Oct 17.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Gene Regulation Laboratory, Genome Institute of Singapore, 60 Biopolis Street, Singapore 138672.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20953172" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Base Sequence ; Cell Line ; Cellular Reprogramming/genetics ; DNA-Binding Proteins/genetics/metabolism ; Embryonic Stem Cells/*cytology/*metabolism ; Enhancer Elements, Genetic/genetics ; Fibroblasts/cytology/metabolism ; Gene Expression Regulation/genetics ; Genome, Human/*genetics ; Humans ; Induced Pluripotent Stem Cells/cytology/metabolism ; Mice ; Octamer Transcription Factor-3/genetics/metabolism ; *RNA Interference ; Repressor Proteins/genetics/*metabolism ; SOXB1 Transcription Factors/metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 10
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    Production of p53 gene knockout rats by homologous recombination in embryonic stem cells (2010)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2010-08-13
    Description: The use of homologous recombination to modify genes in embryonic stem (ES) cells provides a powerful means to elucidate gene function and create disease models. Application of this technology to engineer genes in rats has not previously been possible because of the absence of germline-competent ES cells in this species. We have recently established authentic rat ES cells. Here we report the generation of gene knockout rats using the ES-cell-based gene targeting technology. We designed a targeting vector to disrupt the tumour suppressor gene p53 (also known as Tp53) in rat ES cells by means of homologous recombination. p53 gene-targeted rat ES cells can be routinely generated. Furthermore, the p53 gene-targeted mutation in the rat ES-cell genome can transmit through the germ line via ES-cell rat chimaeras to create p53 gene knockout rats. The rat is the most widely used animal model in biological research. The establishment of gene targeting technology in rat ES cells, in combination with advances in genomics and the vast amount of research data on physiology and pharmacology in this species, now provide a powerful new platform for the study of human disease.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2937076/" 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/PMC2937076/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Tong, Chang -- Li, Ping -- Wu, Nancy L -- Yan, Youzhen -- Ying, Qi-Long -- 1R01 RR025881/RR/NCRR NIH HHS/ -- R01 OD010926/OD/NIH HHS/ -- R01 RR025881/RR/NCRR NIH HHS/ -- R01 RR025881-01A2/RR/NCRR NIH HHS/ -- England -- Nature. 2010 Sep 9;467(7312):211-3. doi: 10.1038/nature09368. Epub 2010 Aug 11.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research at USC, Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20703227" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Base Sequence ; Cell Culture Techniques ; Embryo, Mammalian/cytology ; Embryonic Stem Cells/*cytology ; Female ; Gene Knockout Techniques/*methods ; *Genes, p53 ; Germ-Line Mutation ; Male ; Mice ; Molecular Sequence Data ; Rats/*genetics ; Rats, Inbred F344 ; Rats, Sprague-Dawley ; Recombination, Genetic
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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