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  • 1
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    Resonant few-photon excitation of a single-ion oscillator (2013)
    American Physical Society (APS)
    Details
    Publication Date: 2013-02-01
    Description: Author(s): Y.-W. Lin, S. Williams, and B. C. Odom We study the motion of an undamped single-ion harmonic oscillator, resonantly driven with a pulsed radiation pressure force. We demonstrate that a barium ion, initially cooled to the Doppler limit, quickly phase locks to the drive and builds up coherent oscillations above the thermal distribution af... [Phys. Rev. A 87, 011402] Published Thu Jan 31, 2013
    Keywords: Atomic and molecular processes in external fields, including interactions with strong fields and short pulses
    Print ISSN: 1050-2947
    Electronic ISSN: 1094-1622
    Topics: Physics
    Published by American Physical Society (APS)
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  • 2
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    Rational design of a structural and functional nitric oxide reductase (2009)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2009-11-27
    Description: Protein design provides a rigorous test of our knowledge about proteins and allows the creation of novel enzymes for biotechnological applications. Whereas progress has been made in designing proteins that mimic native proteins structurally, it is more difficult to design functional proteins. In comparison to recent successes in designing non-metalloproteins, it is even more challenging to rationally design metalloproteins that reproduce both the structure and function of native metalloenzymes. This is because protein metal-binding sites are much more varied than non-metal-containing sites, in terms of different metal ion oxidation states, preferred geometry and metal ion ligand donor sets. Because of their variability, it has been difficult to predict metal-binding site properties in silico, as many of the parameters, such as force fields, are ill-defined. Therefore, the successful design of a structural and functional metalloprotein would greatly advance the field of protein design and our understanding of enzymes. Here we report a successful, rational design of a structural and functional model of a metalloprotein, nitric oxide reductase (NOR), by introducing three histidines and one glutamate, predicted as ligands in the active site of NOR, into the distal pocket of myoglobin. A crystal structure of the designed protein confirms that the minimized computer model contains a haem/non-haem Fe(B) centre that is remarkably similar to that in the crystal structure. This designed protein also exhibits NO reduction activity, and so models both the structure and function of NOR, offering insight that the active site glutamate is required for both iron binding and activity. These results show that structural and functional metalloproteins can be rationally designed in silico.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4297211/" 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/PMC4297211/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Yeung, Natasha -- Lin, Ying-Wu -- Gao, Yi-Gui -- Zhao, Xuan -- Russell, Brandy S -- Lei, Lanyu -- Miner, Kyle D -- Robinson, Howard -- Lu, Yi -- GM062211/GM/NIGMS NIH HHS/ -- R01 GM062211/GM/NIGMS NIH HHS/ -- England -- Nature. 2009 Dec 24;462(7276):1079-82. doi: 10.1038/nature08620. Epub 2009 Nov 25.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19940850" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Crystallization ; Iron/metabolism ; Models, Molecular ; Myoglobin/chemistry ; Nitric Oxide/metabolism ; Oxidoreductases/*chemical synthesis/*chemistry/metabolism ; Protein Binding ; Protein Structure, Tertiary
    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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  • 3
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    TERRA stimulates telomere recombination [Biochemistry] (2014)
    National Academy of Sciences
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    Publication Date: 2014-03-05
    Description: In human somatic cells or yeast cells lacking telomerase, telomeres are shortened upon each cell division. This gradual shortening of telomeres eventually leads to senescence. However, a small population of telomerase-deficient cells can survive by bypassing senescence through the activation of alternative recombination pathways to maintain their telomeres. Although genes...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 4
    Electronic Resource
    Electronic Resource
    Application of "critical compositional difference'' concept to the growth of low dislocation density (〈104/cm2) InxGa1−xAs (x≤0.5) on GaAs (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1752-1757 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Multilayer epitaxial structures consisting of InxGa1−xAs layers of various compositions were grown on GaAs substrates by the molecular beam epitaxy technique. Dislocation evolution and residual strain in these heterostructures were studied using cross-sectional transmission electron microscopy (XTEM) and high-resolution x-ray diffraction analyses, respectively. The multilayer heterostructures were designed such that the compositional difference between two adjacent InxGa1−xAs layers in the stack was less than a critical compositional difference of Δx=0.18, taking partial lattice-relaxation into account. XTEM studies of the stacked structures indicated dislocation evolution to be confined to the GaAs substrate and the InxGa1−xAs layers underlying the top InxGa1−xAs layer in the stack, the top InxGa1−xAs layer being essentially dislocation-free. This phenomenon is attributed to a monotonic increase in the yield strength of InxGa1−xAs at the appropriate growth temperatures with increasing values of x. Such behavior appears to persist up to an InxGa1−xAs composition of approximately x=0.5, whereupon a further increase in composition results in dislocation evolution in the top layer of the stack. It is postulated that the yield strength of InxGa1−xAs decreases with increasing values of x beyond x=0.5. Extremely low dislocation density InxGa1−xAs material was grown on GaAs using the stacked structure approach as evidenced by etch pit analysis. For example, dislocation densities of 1–2×103/cm2 and 5–6×103/cm2 were recorded from In0.35Ga0.65As and In0.48Ga0.52As top layers, respectively. Such InxGa1−xAs alloys would be potentially suitable for the fabrication of photonic devices operating at 1.3 μm (x=0.35) and 1.55 μm (x=0.48).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351699
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  • 5
    Electronic Resource
    Electronic Resource
    Strain relaxation of GaNxAs1−x on GaAs (001) grown by molecular-beam epitaxy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5302-5304 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of samples consisting of a strained layer of GaNxAs1−x of different thickness, covered by a GaAs cap layer of 100 nm were grown by molecular-beam epitaxy. The samples have been characterized by high-resolution x-ray diffraction and simulations based on the dynamical theory in order to determine the strain relaxation in GaNxAs1−x layers. It is found that there is a huge difference between the critical thickness determined by x-ray diffraction and the theoretical calculations according to the Matthews and Blakeslee model. The critical thickness of GaNxAs1−x on GaAs is ten times smaller than the theoretical value. The strain relaxation is a crucial point that affects the quality of GaNAs. Photoluminescence measurements are in good agreement with the x-ray diffraction results. The optical properties degraded rapidly when the GaNxAs1−x thickness exceeded the critical thickness determined above. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371516
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  • 6
    Electronic Resource
    Electronic Resource
    Low dark current, planar In0.4Ga0.6As p-i-n photodiode prepared by molecular beam epitaxy growth on GaAs (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2396-2398 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report here the successful fabrication of a planar, low dark current, and high sensitivity In0.4Ga0.6As p-i-n photodiode fabricated on a semi-insulating GaAs substrate with the aid of a multistage strain-relief buffer system. Without using surface passivation and anti-reflection coatings, the detector has a quantum efficiency of 42% and a peak responsivity of 0.45 A/W at 1.3 μm wavelength. The reverse leakage current for the mesa-etched photodiode with an active area of 2×10−4 cm2 is 5×10−9 A at −5 V, and the breakdown voltage exceeds 25 V.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104882
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of rapid thermal annealing on the optical properties of GaNxAs1−x/GaAs single quantum well structure grown by molecular beam epitaxy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 245-248 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of rapid thermal annealing (RTA) on the optical properties of GaNxAs1−x/GaAs strained single quantum well (SQW) was studied by low-temperature photoluminescence (PL). The GaNxAs1−x/GaAs SQW structures were prepared by dc active nitrogen plasma assisted molecular beam epitaxy. PL measurements on a series of samples with different well widths and nitrogen compositions were used to evaluate the effects of RTA. The annealing temperature and time were varied from 650 to 850 °C and 30 s to 15 min, respectively. Remarkable improvements of the optical properties of the samples were observed after RTA under optimum conditions. The interdiffusion constants have been calculated by taking into account error function diffusion and solving the Schrodinger equation. The estimated interdiffusion constants D are 10−17–10−16 cm2/s for the earlier annealing conditions. Activation energies of 6–7 eV are obtained by fitting the temperature dependence of the interdiffusion constants. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371852
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  • 8
    Electronic Resource
    Electronic Resource
    Residual strain analysis of InxGa1−xAs/GaAs heteroepitaxial layers (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 2680-2682 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: InxGa1−xAs/GaAs heteroepitaxial layers, having various compositions and thicknesses, have been analyzed using the high resolution x-ray diffraction technique which has revealed that the residual strain in the epilayers is strongly dependent on both the epilayer composition as well as thickness. However, published theoretical models concerning residual strain in InxGa1−xAs/GaAs epilayers suggest that the extent of relaxation is independent of epilayer composition. In this letter, we present an empirical model based on our findings which can be used to accurately predict the extent of lattice relaxation in InxGa1−xAs/GaAs epilayers which includes the influence of epilayer composition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108107
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  • 9
    Electronic Resource
    Electronic Resource
    Uniform, high-gain AlGaAs/InGaAs/GaAs heteroemitter bipolar transistors using chemical passivation and nonalloyed ohmic contacts (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 383-385 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An Al0.25Ga0.75As/In0.08Ga0.92As/GaAs heteroemitter bipolar transistor (HEBIT) with a uniformly high common-emitter current gain (β) of 500 was demonstrated for the first time. Using a simple chemical treatment [P2S5/(NH4)2S], we have greatly reduced the surface recombination in the emitter-base junction perimeters, resulting in a tenfold increase in the maximum current gain of the device at low collector currents. InGaAs nonalloyed ohmic contacts were also employed to form both emitter and base electrodes in a one-step process. To evaluate the performance of the HEBIT, we conducted current-voltage measurements and compared the Gummel plots at 300 and 77 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106664
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  • 10
    Electronic Resource
    Electronic Resource
    Investigation of periodicity fluctuations in strained (GaNAs)1(GaAs)m superlattices by the kinematical simulation of x-ray diffraction (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 223-225 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Periodicity fluctuations of layer thickness and composition in a superlattice not only decrease the intensity, they also broaden the width of the satellite peaks in the x-ray diffraction pattern. In this letter, we develop a method that is dependent on the width of satellite peaks to assess periodicity fluctuations of a superlattice quickly. A linear relation of the magnitude of fluctuations, peak width and peak order has been derived from x-ray diffraction kinematical theory. By means of this method, periodicity fluctuations in strained (GaNAs)1(GaAs)m superlattices grown on GaAs substrates by molecular beam epitaxy have been studied. Distinct satellite peaks indicate that the superlattices are of high quality. The N composition of 0.25 and its fluctuation of 20% in a strained GaNxAs1−x monolayer are obtained from simulations of the measured diffraction pattern. The x-ray simulations and in situ observation results of reflection high-energy electron diffraction are in good agreement. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124329
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