Browsing by Subject "Adjustable parameters"

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Open Access
Energy relaxation probed by weak antilocalization measurements in GaN heterostructures
(2009) Cheng H.; Bıyıklı, Necmi; Xie J.; Kurdak Ç.; Morko̧ H.
Energy relaxation and electron-phonon (e-p) interaction are investigated in wurtzite Al0.15Ga0.85 N/AlN/GaN and Al0.83 In0.17 N/AlN/GaN heterostructures with polarization induced two-dimensional electron gases in the Bloch-Grüneisen regime. Weak antilocalization (WAL) and Shubnikov-de Haas measurements were performed on gated Hall bar structures at temperatures down to 0.3 K. We used WAL as a thermometer to measure the electron temperature Te as a function of the dc bias current. We found that the power dissipated per electron, P e, was proportional to Te4 due to piezoelectric acoustic phonon emission by hot electrons. We calculated Pe as a function of Te without any adjustable parameters for both the static and the dynamic screening cases of piezoelectric e-p coupling. In the temperature range of this experiment, the static screening case was expected to be applicable; however, our data was in better agreement with the dynamic screening case. © 2009 American Institute of Physics.
Open Access
Zero-free-parameter modeling approach to predict the voltage of batteries of different chemistries and supercapacitors under arbitrary load
(Electrochemical Society, Inc., 2017) Özdemir, E.; Uzundal, C. B.; Ulgut, B.
Performance modeling of electrochemical energy storage systems is gathering increasingly higher attention in recent years. With the ever increasing power demand of mobile applications, predicting voltage behavior under different load profiles is of utmost importance for communications, automotive and consumer electronics. The ideal modelling approach needs not only to accurately predict the response of the battery, but also be robust, easy to implement and have low computational complexity. We will present a new algorithm that is algebraically straightforward, that has no adjustable parameters and that can accurately predict the voltage response of batteries and supercapacitors. The approach works well in a variety of discharge profiles ranging from simple long DC discharge/charge profiles to pulse schemes based on drive schedules published by regulatory bodies. Our approach is based on Electrochemical Impedance Spectroscopy measurements done on the system to be predicted. The spectrum is used in the frequency domain without any further processing to predict the fast moving portion of the voltage in the frequency domain. DC response is added in through a straightforward lookup table. This widely applicable approach can predict the voltage of with less than 1% error, without any adjustable parameters to a large variety of discharge profiles.