7,469 research outputs found

    A study of the applicability of nucleation theory to quasi-thermodynamic transformations of second and higher Ehrenfest-order

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    Transient and steady-state phenomena in temperature, stress, and electric, field intensity in ferroelectric polymers were investigated. The application and extension of the theory in the primary stage to the polarization domain nucleation and growth in ferroelectric polymers were developed. The kinetics of this growth were investigated. Expressions describing nucleation under the influence of an electric field were found through the expansion of the Gibbs' free energy in a Maclaurin series. The series was expanded in the electric field strength rather than the degree of undercooling. The resulting expressions were manipulated and applied to the case of nucleation of polarized domains in ferroelectric polymers. The kinetics of the nucleation and growth of polarized domains are also investigated. This was accomplished through the modification of the Johnson-Mehl-Avrami treatment of crystallization kinetics to be applicable to the growth of polarization domains in ferroelectric materials

    A study of the applicability of nucleation theory to quasi-thermodynamic transitions of second and higher Ehrenfest-order, supplement 3

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    The work includes an investigation of the applicability of the nucleation theory to second and higher order thermodynamic transitions in the Ehrenfest sense, and a number of significant conclusions relevant to first order transitions, as well. The underlying theoretical method consisted of expanding the Gibbs' free energy in a Maclarin or Taylor series and then using fundamental thermodynamic determinable quantities, and interpreting the results. Work was performed on the existence and interpretation of an interfacial energy between phases in a second order transition in addition to an investigation of the solid-liquid interfacial energy for various polymers. Extensive considerations were devoted to various aspects of a particular polymer, polyvinylidene fluoride (PVDF or PVF2), including an experimetal investigation of the effects of an applied electric field on the morphology of melt crystallization and on the nucleation and growth of polarized domains

    A study of the applicability of nucleation theory to quasi-thermodynamic transitions of second and higher Ehrenfest-order

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    The applicability of classical nucleation theory to second (and higher) order thermodynamic transitions in the Ehrenfest sense has been investigated and expressions have been derived upon which the qualitative and quantitative success of the basic approach must ultimately depend. The expressions describe the effect of temperature undercooling, hydrostatic pressure, and tensile stress upon the critical parameters, the critical nucleus size, and critical free energy barrier, for nucleation in a thermodynamic transition of any general order. These expressions are then specialized for the case of first and second order transitions. The expressions for the case of undercooling are then used in conjunction with literature data to estimate values for the critical quantities in a system undergoing a pseudo-second order transition (the glass transition in polystyrene). Methods of estimating the interfacial energy gamma in systems undergoing a first and second order transition are also discussed

    Electrolytic Recovery of Copper and Zinc from Brasses

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    Reclaimed metals, or secondary metals, are becoming of great im­portance in the metal industries of the world. Secondary metals are an important factor in production. The increase in the secondary production of copper is due to many factors. One of these may be its permenance, that is, the metal does not corrode very readily. Another reason for increase in production is the high price paid for it

    Direct Observation of Sub-picosecond Hole Injection from Lead Halide Perovskite by Differential Transient Transmission Spectroscopy

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    Efficient charge separation at the interfaces between the perovskite and with the carrier transport layers is crucial for perovskite solar cells to achieve high power conversion efficiency. We systematically investigate the hole injection dynamics from MAPbI3_3 perovskite to three typical hole transport materials (HTMs) PEDOT:PSS, PTAA and NiOx_x by means of pump-probe transmission measurements. We photoexcite only near the MAPbI3_3/HTM interface or near the back surface, and measure the differential transient transmission between the two excitation configurations to extract the carrier dynamics directly related to the hole injection. The differential transmission signals directly monitor the hole injections to PTAA and PEDOT:PSS being complete within 1 and 2 ps, respectively, and that to NiOx_x exhibiting an additional slow process of 40 ps time scale. The obtained injection dynamics are discussed in comparison with the device performance of the solar cells containing the same MAPbI3_3/HTM interfaces.Comment: 5 pages, 5 figure

    Development and application of a local linearization algorithm for the integration of quaternion rate equations in real-time flight simulation problems

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    High angular rates encountered in real-time flight simulation problems may require a more stable and accurate integration method than the classical methods normally used. A study was made to develop a general local linearization procedure of integrating dynamic system equations when using a digital computer in real-time. The procedure is specifically applied to the integration of the quaternion rate equations. For this application, results are compared to a classical second-order method. The local linearization approach is shown to have desirable stability characteristics and gives significant improvement in accuracy over the classical second-order integration methods

    Comparison of bungee-aided and free-bouncing accelerations on trampoline

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    Trampolines remain the single best apparatus for the training of aerial acrobatics skills. Trampoline use has led to catastrophic injuries from poor landings. Passive injury prevention countermeasures such as specialized matting have been largely ineffective. Active injury countermeasures such as hand spotting, ‚Äúthrow-in‚ÄĚ mats, and overhead spotting rigs provide the most effective methods. The recent addition of several bungee cords between the ropes and the gymnast‚Äôs spotting harness has resulted in altered teaching and coaching of trampoline-related acrobatics. Bungee cords have eliminated the need for a coach/spotter to manage the ropes during skill learning. The purpose of this study was to assess the influence of the addition of bungee cords with a traditional rope-based overhead spotting rig. There is a paucity of any research involving trampoline injury countermeasures. Ten experienced trampoline acrobatic athletes (5 males, 5 females) from the U.S. Ski and Snowboard Association Aerials National Team performed 10 bounces as high as they could control. A triaxial accelerometer (200 Hz) characterized 10 bungee cord aided bounces and 10 freebounces on a trampoline from each athlete. Bed contact times, peak accelerations, and average accelerations were obtained. The results supported our hypotheses that the bungeeaided bounces achieved only 40% (average) to 70% (peak) of the free-bouncing accelerations (all ŌĀ 0.092). The bed contact time was approximately 65% longer during the bungee-aided bounces (ŌĀ < 0.001). Bungee cords may reduce the harshness of landings on trampoline

    Muscle function and size in the lumbar spine before and after a four week exercise intervention

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    ArticleThis is the author accepted manuscript. The final version is available from IOS Press via the DOI in this record.BACKGROUND: Exercise of the spinal muscles is recommended for a variety of rehabilitative reasons but it is not always clear whether interventions are effective in improving the performance of the muscles or whether their benefit is elicited via other mechanisms. OBJECTIVE: To explore the effects of an exercise intervention on the size and exercise performance of the lumbar spine extensor muscles. METHODS: Eleven healthy participants undertook a four week programme of exercise. Magnetic resonance imaging and phosphorus spectroscopy were performed before and after the intervention to determine the time to fatigue and phosphocreatine (PCr) depletion during a muscle endurance test (modified Biering-S√łrensen) together with muscle crosssectional area (CSA). RESULTS: The post intervention measures were significantly different to the preintervention results for the time to fatigue (post-pre: 20.5 ¬Ī 22.7 s (P=0.014)) and PCr depletion both at the point of fatigue (post-pre: 9.5 ¬Ī 11.9 % (P= 0.024)) and at a matched time-point (post-pre: 12.2 ¬Ī 11.9 % (P=0.007)). CSA was not significantly different in any muscle. CONCLUSIONS: Exercise improved the performance of the trunk muscles despite no impact on CSA. This demonstrated the importance of obtaining a wide range of measures when assessing the effectiveness of exercise intervention programmes.We thank the participants who volunteered to take part in our study and also thank the NIHR Clinical Research Facility, University of Exeter for funding J Fulford‚Äôs salary

    Empirical potentials for rovibrational energy transfer of hydrogen fluoride in collisions with argon

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    Rovibrational energy transfer of hydrogen fluoride in collisions with argon was investigated by using the coupled-states approximation to the quantum scattering problem. Empirically determined 3-D ab initio potential energy surfaces (PES) for the interaction between hydrogen fluoride and argon are presented. Second-order M√łller-Plesset perturbation theory (MP2) was used to provide an initial approximate PES for the complex. The MP2 PES was subsequently modified to compensate for the underestimated dispersion interaction and adjusted until the desired agreement between calculated and observed spectroscopic quantities was achieved. Calculated rotational cross sections are in good agreement with experimental results as well as those obtained with a highly accurate vibrationally averaged empirical PES [J. M. Hutson, J. Chem. Phys. 96, 6752 (1992)]. The rate constants for the collision induced relaxation of the first vibrational state of hydrogen fluoride are presented as functions of temperature. The rate constants show structure at low temperature corresponding to cross-section resonances. The calculated rate constants are in good agreement with available high temperature experimental results. The calculations provide lower temperature rate constants and a wealth of detailed state-to-state information that are not available from experiment. ¬© 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71344/2/JCPSA6-115-10-4573-1.pd
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