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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The concentration distributions of Y dopings in LiTaO3 across the growth striations in as-grown crystals are obtained by means of x-ray energy dispersive spectrum analysis in a scanning transmission electron microscope at room temperature. The results show that it is the concentration gradient of the dopings which determines the configurations of ferroelectric domains. The mechanism for the formation of the periodic laminar ferroelectric domains (PLFDs) is explained theoretically by considering the influence of the distributions of the dopings on the para-ferroelectric phase transitions in LiTaO3 and LiNbO3 crystals. It is shown that the coupling between the order parameter and the conjugate external field, which results from the ambipolar diffusion or from the strain-induced polarization mechanism associated with the dopings and their compensated point defects, is just the physical reason for the formation of such PLFDs in these two materials.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Applied mathematics and mechanics 11 (1990), S. 33-43 
    ISSN: 1573-2754
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract An elastic-viscoplastic constitutive model is proposed instead of the usual elastoplastic model. It is assumed that when crack-tip is approached the viscosity coefficient lends to zero (η=η0r). Asymptotic analysis of the dynamic field near a propagating crack-tip is given, and the uniparameter solution is obtained. The numerical result is given for various Mach number and viscosity coefficient. Based on the asymptotic solution, a fracture criterion is proposed and the stability of crack propagation is discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-2754
    Keywords: incompressible material ; plane stress condition ; crack-tip field fully nonlinear ; equilibrium theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract The crack-tip field under plane stress condition for an incompressible rubber material[1] is investigated by the use of the fully nonlinear equilibrium theory. It is found that the crack-tip field is composed of two shrink sectors and one expansion sector. At the crack-tip, stress and strain possess the singularity of R−1 and R−1 n, respectively, (R is the distance to the crack-tip before deformation. n is the material constant). When the crack-tip is approached, the thickness of the sheet shrinks to zero with the order of R1 4n. The results obtained in this paper are consistent with that obtained in[8] when s→∞.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Fiber spinning of polyethylene terephthalate (PET) was studied at take-up speeds ranging from 2000 m/min to 7000 m/min under various spinning conditions. Effects of changes in process variables on the molecular orientation, crystallinity, and properties of as-spun PET fibers are reported. Conventional cross-flow quench in high-speed spinning yields fibers with undesirable crimp and asymmetric structure with respect to the fiber axis. Radial-flow quench eliminates these problems. Changes in other spinning conditions, such as extrusion temperature, throughput or take-up denier, and molecular weight, may also affect the development of PET fiber structure in the high-speed threadline.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The flow behavior and the effect of the spinning conditions on the fiber properties and structure of poly(ethylene terephthalate) modified with 60 mol% p-hydroxybenzoic acid (PET/60PHB) were investigated. PET and its copolyesters with 28 and 80 mol% PHB were used as control samples. The melt of PET/60PHB at temperatures above 265°C exhibited extremely low viscosity and low flow activation energy. High birefringence, indicating the presence of a mesophase, was observed between 265 and 300°C on a hot-stage polarizing light microscope. The maximum tensile strength and initial modulus, 438 MPa and 37 GPa, respectively, were obtained at 275°C for a 0.69 IV polymer. The fiber strength and modulus were significantly lowered when extrusion was conducted at temperatures below 265°C. The fiber properties could also be improved when a high extrusion rate and/or a high draw down ratio was used. Scanning electron microscopy revealed that the fibers spun at temperatures above 265°C had a well-developed, highly oriented fibrillar structure. The fibers spun at lower temperatures, however, were poorly oriented and nonfibrillar in character. The high orientation and superior mechanical performance achieved at high temperatures were attributed to the presence of the nematic mesophase in the polymer melt.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    ISSN: 0887-6266
    Keywords: extrusion from hyperbolic dies, characteristics and design procedures in ; strain rate in extrusion procedures, hyperbolic die design and ; filament production with constant extensional strain rate with hyperbolic dies ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nozzle profiles capable of generating constant extensional strain rates are termed hyperbolic dies. When used in polymer extrusion, they exhibit greater potential in inducing and retaining polymer molecular orientation than conventional capillary dies. Most mathematical expressions found in the literature involve several processing variables in describing and designing such nozzle profiles. This report reveals that a hyperbolic die profile, although rather complicated, can be expressed with equations in terms of two ordinary geometrical parameters - the exit diameter and the hyperbolic length. This finding greatly simplifies the design procedure of hyperbolic dies. The extensional strain rate of a hyperbolic die can be related to the length-to-diameter ratio for any given exit diameter. Examples of various types of die profiles are presented and their constant extensional strain-rate characteristics are discussed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2019
    Description: Scientific and reasonable battery thermal management systems contribute to improve the performance of a power battery, prolong its life of service, and improve its safety. Based on TAFEL-LAE895 type 100Ah ternary lithium ion power battery, this paper is conducted on charging and discharging experiments at different rates to study the rise of temperature and the uniformity of the battery. Paraffin can be used to reduce the surface temperature of the battery, while expanded graphite (EG) is added to improve the thermal conductivity and viscosity of the composite phase change material (CPCM), and to reduce the fluidity after melting. With the increase of graphite content, the heat storage capacity of phase change material (PCM) decreases, which affects the thermal management effect directly. Therefore, this paper combines heat pipe and semiconductor refrigeration technology to transform heat from the inner CPCM to the thermoelectric cooling sheet for heat dissipation. The results show that the surface temperature of the battery can be kept within a reasonable range when discharging at high rate. The temperature uniformity of the battery is improved and the energy of the battery is saved.
    Electronic ISSN: 1996-1073
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by MDPI
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  • 8
  • 9
    Publication Date: 2018-09-14
    Description: Materials, Vol. 11, Pages 1713: Investigating Metal–Insulator Transition and Structural Phase Transformation in the (010)-VO2/(001)-YSZ Epitaxial Thin Films Materials doi: 10.3390/ma11091713 Authors: Yuanjun Yang Yingxue Yao Benjian Zhang Hui Lin Zhenlin Luo Chen Gao Cong Zhang Chaoyang Kang The VO2 thin films with sharp metal–insulator transition (MIT) were epitaxially grown on (001)-oriented Yttria-stabilized zirconia substrates (YSZ) using radio-frequency (RF) magnetron sputtering techniques. The MIT and structural phase transition (SPT) were comprehensively investigated under in situ temperature conditions. The amplitude of MIT is in the order of magnitude of 104, and critical temperature is 342 K during the heating cycle. It is interesting that both electron concentration and mobility are changed by two orders of magnitude across the MIT. This research is distinctively different from previous studies, which found that the electron concentration solely contributes to the amplitude of the MIT, although the electron mobility does not. Analysis of the SPT showed that the (010)-VO2/(001)-YSZ epitaxial thin film presents a special multi-domain structure, which is probably due to the symmetry matching and lattice mismatch between the VO2 and YSZ substrate. The VO2 film experiences the SPT from the M1 phase at low temperature to a rutile phase at a high temperature. Moreover, the SPT occurs at the same critical temperature as that of the MIT. This work may shed light on a new MIT behavior and may potentially pave the way for preparing high-quality VO2 thin films on cost-effective YSZ substrates for photoelectronic applications.
    Electronic ISSN: 1996-1944
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by MDPI Publishing
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  • 10
    Publication Date: 2017-12-08
    Description: Analytical Chemistry DOI: 10.1021/acs.analchem.7b03873
    Print ISSN: 0003-2700
    Electronic ISSN: 1520-6882
    Topics: Chemistry and Pharmacology
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