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1.
2.
The aim of this work is to study the dynamic formation and dissociation of trions and excitons in double barrier resonant tunneling diodes. We propose a system of rate equations that takes into account the formation, dissociation and annihilation of these complexes inside the quantum well. From the solutions of the coupled equations, we are able to study the modulation of excitons and trions formation in the device as a function of the applied bias. The results of our model agree qualitatively with the experiments showing the viability of these rate equations system to study the dynamics of complex systems. 相似文献
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G. Garcia-Belmonte J. Bisquert L. M. Navarro J. R. Jurado F. M. B. Marques 《Ionics》1995,1(5-6):377-383
In ionic conductors, long range-migrating charges are a main cause of polarization processes. This has complicated, up to
date, the study of ionic thermocurrents (ITC) in solid electrolytes. However, the method is appealing, as it probes directly
charge-formation phenomena that are important both from a scientific point of view and for applications.
This work reports on the observation of ITC in solid electrolytes. Under appropriate experimental conditions, the ITC response
of a zirconia sample electroded with platinum is a reproducible one, thus opening the way to a new characterization method
that may complement other well established methods, such as Impedance Spectroscopy and a number of electrochemical techniques.
The general trends of the response, which is composed of two well resolved ITC peaks, is discussed. One of them, taking place
at higher temperatures, conforms to the standard shape of a first order kinetics depolarization process.
Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995 相似文献
5.
Maria Marques Zhengtian Yu Marvin D. Rausch James C. W. Chien 《Journal of polymer science. Part A, Polymer chemistry》1995,33(16):2787-2793
4-Vinylcyclohexene (VCH) and cyclooctadiene (COD) were investigated as termonomers in EPDM (ethylene/propylene/diene) synthesis by using rac-ethylenebis (1-η5-indenyl) zir-conium dichloride ( 1 ) as a catalyst precursor. Homopolymerizations of VCH, vinylcycloh-exane and cyclohexene were compared. The parameter Kπκp, which is the apparent rate constant for Ziegler-Natta polymerization, is about the same for VCH and vinylcyclohexanebut is 10 times smaller for cyclohexene. Therefore, the linear olefinic double bond is more active than the cyclic internal double bond. VCH reduces ethylene polymerization rate but not propylene polymerization rate in copolymerizations. In terpolymerizations, VCH tends to suppress ethylene incorporation especially at elevated polymerization temperature and Lowers the polymer MW by about two-fold. COD has very low activity as a termonomer. © 1995 John Wiley & Sons, Inc. 相似文献
6.
P. Mun F. C. Fonseca R. Muccillo R. F. Jardim 《Physica C: Superconductivity and its Applications》2003,390(4):363-373
A systematic study of the magnetic hysteresis in transport properties of polycrystalline YBa2Cu3O7−δ–Ag compounds has been made based on two kinds of measurements at 77 K and under applied magnetic fields up to 30 mT: critical current density Jc(Ba) and magnetoresistance R(Ba). The R(Ba) curves show a minimum in their decreasing branch occurring at B=Bmin which was found to be both the excitation current Iex and the maximum applied magnetic field Bam dependent. In addition, for a certain value of Bam>5 mT, we have observed that Bmin increases with increasing Iex and reaches a saturation value. The Jc(Ba) curves show a maximum in decreasing applied magnetic fields occurring at B=Bmax. We have also found that Bmax increases with increasing Bam and reaches a saturation value. The minimum in the R(Ba) and the maximum in Jc(Ba) curves were found to be related to the trapped flux within the grains. All the experimental results are discussed within the context of the flux dynamics and transport mechanisms in these high-Tc materials. 相似文献
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H.D. Fonseca Filho R. Prioli M.P. Pires A.S. Lopes P.L. Souza F.A. Ponce 《Applied Physics A: Materials Science & Processing》2007,89(4):945-949
Atomic-force nanolithography was used to control the nucleation sites of InAs nanostructures on InP substrates. Indentations
with a wide range of dimensions were produced on InP. InAs nanostructures were selectively grown by metal organic vapor phase
epitaxy. It is shown that the number of active nucleation sites depends on the normal force applied during nanoindentation.
Crystalline defects introduced by nanoindentation are shown to be nucleation sites for these nanostructures. The presence
of screw dislocations within the grown nanostructures further supports this observation.
PACS 81.07.-b; 68.37.Ps; 81.16.Nd 相似文献
10.
Theoretical concerns about the use of cemented and press-fit stems in revision total knee arthroplasty (TKA) include stress
shielding with adverse effects on prosthesis fixation. Radiological studies have showed distal femoral bone resorption after
revision TKA. The revision with use of stems can place abnormal stresses. These stresses can promote the effect of bone stress
shielding and may contribute to bone loss. Experimental quantification of strain shielding in the distal synthetic femur following
TKA is the main purpose of the present study. Three different constructs of TKA were assessed. The first construct included
a stemless femoral component. The other two included a press-fit and a cemented femoral stem. Cortical bone strains were measured
experimentally with tri-axial strain gauges in synthetic femurs before and after in-vitro knee surgery. The difference between
principal strains of implanted and intact femur was calculated for each strain gauge position. This study indicates that the
use of stems in distal femur changes the distribution and magnitude of bone strains. The press-fit stem provoked relevant
bone area (stem length) subjected to strain shielding and also originated the highest reduction of strains in the distal region,
which can potentially induce bone resorption. The stemless implanted femur produced minor bone strain changes relatively to
the intact femur. The use of distal femur stems increases initial stability in the bone, but the observed reduction of strains
in this region, relative to the intact femur, provokes strain shielding that can induce bone resorption and may compromise
the long term implant stability. 相似文献