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  • 1
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    Attenuation compensation in anisotropic least-squares reverse time migration (2017)
    Society of Exploration Geophysicists (SEG)
    Details
    Publication Date: 2017-09-19
    Description: Anisotropic and attenuating properties of subsurface media cause amplitude loss and waveform distortion in seismic wave propagation, resulting in negative influence on seismic imaging. To correct the anisotropy effect and compensate amplitude attenuation, a compensated-amplitude vertical transverse isotropic (VTI) least-squares reverse time migration (LSRTM) method is adopted. In this method, the attenuation term of an attenuated acoustic wave equation is extended to a VTI quasi-differential wave equation, which takes care of effects from anisotropy and attenuation. The finite-difference method is used to solve the equation, in which attenuation terms are solved in the wavenumber domain, and other terms are solved in the space or wavenumber domain. Stable regularization operators are derived and introduced to the equations to eliminate severe numerical noise in high-frequency components during backward propagation. Meanwhile, a demigration operator, migration operator, and gradient formula for attenuated VTI media are derived to implement the amplitude-compensated VTI LSRTM. Test of a homogeneous model proves the accuracy of the attenuated VTI quasi-differential equations and the effectiveness of the regularization operators. A numerical example for a modified Marmousi model verifies the accuracy and superiority to the amplitude-compensated VTI LSRTM. Our results show that the sensitivity to anisotropic parameters is much higher than that to the Q parameters.
    Print ISSN: 0016-8033
    Electronic ISSN: 1942-2156
    Topics: Geosciences , Physics
    Published by Society of Exploration Geophysicists (SEG)
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  • 2
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    Biochemistry and application of a TET-like protein [Biochemistry] (2015)
    National Academy of Sciences
    Details
    Publication Date: 2015-04-08
    Description: Modified DNA bases in mammalian genomes, such as 5-methylcytosine (5mC) and its oxidized forms, are implicated in important epigenetic regulation processes. In human or mouse, successive enzymatic conversion of 5mC to its oxidized forms is carried out by the ten-eleven translocation (TET) proteins. Previously we reported the structure of a...
    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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  • 3
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    Chain walking: A new strategy to control polymer topology (1999)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1999-03-26
    Description: Ethylene pressure has been used to control the competition between isomerization (chain walking) and monomer insertion processes for ethylene coordination polymerization catalyzed by a palladium-alpha-diimine catalyst. The topology of the polyethylene varies from linear with moderate branching to "hyperbranched" structures. Although the overall branching number and the distribution of short-chain branching change very slightly, the architecture or topology of the polyethylene changes from linear polyethylene with moderate branches at high ethylene pressures to a hyperbranched polyethylene at low pressures.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Guan -- Cotts -- McCord -- McLain -- New York, N.Y. -- Science. 1999 Mar 26;283(5410):2059-62.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉DuPont Central Research, Experimental Station, Wilmington, DE 19880, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10092223" target="_blank"〉PubMed〈/a〉
    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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  • 4
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    Synthesis of fluoropolymers in supercritical carbon dioxide (1992)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1992-08-14
    Description: Fluoropolymers are used in many technologically demanding applications because of their balance of high-performance properties. A significant impediment to the synthesis of variants of commercially available amorphous fluoropolymers is their general insolubility in most solvents except chlorofluorocarbons (CFCs). The environmental concerns about CFCs can be circumvented by preparing these technologically important materials in supercritical fluids. The homogeneous solution polymerization of highly fluorinated acrylic monomers can be achieved in supercritical carbon dioxide by using free radical methods. In addition, detailed decomposition rates and efficiency factors were measured for azobisisobutyronitrile in supercritical carbon dioxide and were compared to those obtained with conventional liquid solvents.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Desimone, J M -- Guan, Z -- Elsbernd, C S -- New York, N.Y. -- Science. 1992 Aug 14;257(5072):945-7.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17789638" target="_blank"〉PubMed〈/a〉
    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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  • 5
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    General strategies for nanoparticle dispersion (2006)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2006-03-25
    Description: Traditionally the dispersion of particles in polymeric materials has proven difficult and frequently results in phase separation and agglomeration. We show that thermodynamically stable dispersion of nanoparticles into a polymeric liquid is enhanced for systems where the radius of gyration of the linear polymer is greater than the radius of the nanoparticle. Dispersed nanoparticles swell the linear polymer chains, resulting in a polymer radius of gyration that grows with the nanoparticle volume fraction. It is proposed that this entropically unfavorable process is offset by an enthalpy gain due to an increase in molecular contacts at dispersed nanoparticle surfaces as compared with the surfaces of phase-separated nanoparticles. Even when the dispersed state is thermodynamically stable, it may be inaccessible unless the correct processing strategy is adopted, which is particularly important for the case of fullerene dispersion into linear polymers.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mackay, Michael E -- Tuteja, Anish -- Duxbury, Phillip M -- Hawker, Craig J -- Van Horn, Brooke -- Guan, Zhibin -- Chen, Guanghui -- Krishnan, R S -- New York, N.Y. -- Science. 2006 Mar 24;311(5768):1740-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824, USA. mackay@msu.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16556836" target="_blank"〉PubMed〈/a〉
    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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  • 6
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    Crystal structure of MraY, an essential membrane enzyme for bacterial cell wall synthesis (2013)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2013-08-31
    Description: MraY (phospho-MurNAc-pentapeptide translocase) is an integral membrane enzyme that catalyzes an essential step of bacterial cell wall biosynthesis: the transfer of the peptidoglycan precursor phospho-MurNAc-pentapeptide to the lipid carrier undecaprenyl phosphate. MraY has long been considered a promising target for the development of antibiotics, but the lack of a structure has hindered mechanistic understanding of this critical enzyme and the enzyme superfamily in general. The superfamily includes enzymes involved in bacterial lipopolysaccharide/teichoic acid formation and eukaryotic N-linked glycosylation, modifications that are central in many biological processes. We present the crystal structure of MraY from Aquifex aeolicus (MraYAA) at 3.3 A resolution, which allows us to visualize the overall architecture, locate Mg(2+) within the active site, and provide a structural basis of catalysis for this class of enzyme.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3906829/" 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/PMC3906829/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Chung, Ben C -- Zhao, Jinshi -- Gillespie, Robert A -- Kwon, Do-Yeon -- Guan, Ziqiang -- Hong, Jiyong -- Zhou, Pei -- Lee, Seok-Yong -- AI-55588/AI/NIAID NIH HHS/ -- GM-069338/GM/NIGMS NIH HHS/ -- GM-51310/GM/NIGMS NIH HHS/ -- R01 AI055588/AI/NIAID NIH HHS/ -- R01 GM051310/GM/NIGMS NIH HHS/ -- R01 GM100984/GM/NIGMS NIH HHS/ -- U54 GM069338/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 2013 Aug 30;341(6149):1012-6. doi: 10.1126/science.1236501.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23990562" target="_blank"〉PubMed〈/a〉
    Keywords: Bacteria/*enzymology ; Bacterial Proteins/*chemistry/genetics ; Catalytic Domain ; Cell Wall/*chemistry/enzymology ; Crystallography, X-Ray ; Cytoplasm/enzymology ; Membrane Proteins/*chemistry/genetics ; Periplasm/enzymology ; Protein Conformation ; Protein Structure, Secondary ; Transferases/*chemistry/genetics
    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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  • 7
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    Research on simulation based material delivery system for an automobile company with multi logistics center (2017)
    Institute of Physics (IOP)
    Details
    Publication Date: 2017-07-28
    Description: Distribution of different parts to the assembly lines is significant for companies to improve production. Current research investigates the problem of distribution method optimization of a logistics system in a third party logistic company that provide professional services to an automobile manufacturing case company in China. Current research investigates the logistics leveling the material distribution and unloading platform of the automobile logistics enterprise and proposed logistics distribution strategy, material classification method, as well as logistics scheduling. Moreover, the simulation technology Simio is employed on assembly line logistics system which helps to find and validate an optimization distribution scheme through simulation experiments. Experimental results indicate that the proposed scheme can solve the logistic balance and levels the material problem and congestion of the unloading pattern in an efficient way as compared to the original method employed b...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 8
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    Research on remanufacturing scheduling problem based on critical chain management (2017)
    Institute of Physics (IOP)
    Details
    Publication Date: 2017-07-28
    Description: Remanufacturing is the recycling process of waste products as “as good as new products”, compared with materials recycling, remanufacturing represents a higher form of recycling. The typical structure of remanufacturing system consists of three parts: disassembly workshop, remanufacturing workshop and assembly workshop. However, the management of production planning and control activities can differ greatly from management activities in traditional manufacturing. Scheduling in a remanufacturing environment is more complex and the scheduler must deal with more uncertainty than in a traditional manufacturing environment. In order to properly schedule in a remanufacturing environment the schedule must be able to cope with several complicating factors which increase variability. This paper introduced and discussed seven complicating characteristics that require significant changes in production planning and control activities, in order to provide a new method for remanufacturing pro...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 9
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    Slotting optimization of automated storage and retrieval system (AS/RS) for efficient delivery of parts in an assembly shop using genetic algorithm: A case Study (2017)
    Institute of Physics (IOP)
    Details
    Publication Date: 2017-07-28
    Description: In recent years, the competitive pressure on manufacturing companies shifted them from mass production to mass customization to produce large variety of products. It is a great challenge for companies nowadays to produce customized mixed flow mode of production to meet customized demand on time. Due to large variety of products, the storage system to deliver variety of products to production lines influences on the timely production of variety of products, as investigated from by simulation study of an inefficient storage system of a real Company, in the current research. Therefore, current research proposed a slotting optimization model with mixed model sequence to assemble in consideration of the final flow lines to optimize whole automated storage and retrieval system (AS/RS) and distribution system in the case company. Current research is aimed to minimize vertical height of centre of gravity of AS/RS and total time spent for taking the materials out from the AS/RS simultane...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 10
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    Comparison and Research on Seismic Design Practice for Elec-tric Substation Equipment in China, Japan, USA and Europe (2018)
    Institute of Physics (IOP)
    Details
    Publication Date: 2018-06-03
    Description: This paper compares the key aspects, i.e. the objectives, methods of seismic qualification, site classification and required response spectra (RRS) of GB 50260, JEAG 5003, IEEE Std 693 and IEC 62271-300. This study provides an understanding of the similarities and differences among Chinese, Japanese, U.S. and European seismic design practice. In terms of the performance objectives, site assignments and RRS, IEEE Std 693 and IEC 62271-300 present numerous similar standards, although there are many minor differences in the detailed provisions, while GB 50260 and JEAG 5003 are different in definition of ground types and determination of design response spectra. Among the four codes, the IEEE standard is generally the most restrictive, particularly at higher qualification levels. The four have strengths as well as shortcomings, and may benefit from learning each other's experience. This study may provide linkages among these standards for seismic qualification, as well as potential ...
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
    Published by Institute of Physics (IOP)
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