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Park, Dae-Sung,Vasheghani Farahani, Sepehr K.,Walker, Marc,Mudd, James J.,Wang, Haiyuan,Krupski, Aleksander,Thorsteinsson, Einar B.,Seghier, Djelloul,Choi, Chel-Jong,Youn, Chang-Ju,McConville, Chris F American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.21
<P>We investigate the effect of thermally induced phase transformations on a metastable oxide alloy film, a multiphase Be<SUB><I>x</I></SUB>Zn<SUB>1–<I>x</I></SUB>O (BZO), grown on Al<SUB>2</SUB>O<SUB>3</SUB>(0001) substrate for annealing temperatures in the range of 600–950 °C. A pronounced structural transition is shown together with strain relaxation and atomic redistribution in the annealed films. Increasing annealing temperature initiates out-diffusion and segregation of Be and subsequent nucleation of nanoparticles at the surface, corresponding to a monotonic decrease in the lattice phonon energies and band gap energy of the films. Infrared reflectance simulations identify a highly conductive ZnO interface layer (thicknesses in the range of ≈10–29 nm for annealing temperatures ≥800 °C). The highly degenerate interface layers with temperature-independent carrier concentration and mobility significantly influence the electronic and optical properties of the BZO films. A parallel conduction model is employed to determine the carrier concentration and conductivity of the bulk and interface regions. The density-of-states-averaged effective mass of the conduction electrons for the interfaces is calculated to be in the range of 0.31<I>m</I><SUB>0</SUB> and 0.67<I>m</I><SUB>0</SUB>. A conductivity as high as 1.4 × 10<SUP>3</SUP> S·cm<SUP>–1</SUP> is attained, corresponding to the carrier concentration <I>n</I><SUB>Int</SUB> = 2.16 × 10<SUP>20</SUP> cm<SUP>–3</SUP> at the interface layers, and comparable to the highest conductivities achieved in highly doped ZnO. The origin of such a nanoscale degenerate interface layer is attributed to the counter-diffusion of Be and Zn, rendering a high accumulation of Zn interstitials and a giant reduction of charge-compensating defects. These observations provide a broad understanding of the thermodynamics and phase transformations in Be<SUB><I>x</I></SUB>Zn<SUB>1–<I>x</I></SUB>O alloys for the application of highly conductive and transparent oxide-based devices and fabrication of their alloy nanostructures.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-21/am5043388/production/images/medium/am-2014-043388_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5043388'>ACS Electronic Supporting Info</A></P>
Karimi, Mohammad Hadi,Zamani, Hassan,Kanzi, Khalil,Farahani, Qasem Vasheghani The Korean Institute of Power Electronics 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.5
This paper discussed a transformer-less shunt static synchronous compensator (STATCOM) with consideration of the following aspects: fast compensation of the reactive power, harmonic cancelation and reducing the unbalancing of the 3-phase source side currents. The STATCOM control algorithm is based on the theory of instantaneous reactive power (P-Q theory). A self charging technique is proposed to regulate the dc capacitor voltage at a desired level with the use of a PI controller. In order to regulate the DC link voltage, an off-line Genetic Algorithm (GA) is used to tune the coefficients of the PI controller. This algorithm arranged these coefficients while considering the importance of three factors in the DC link voltage response: overshoot, settling time and rising time. For this investigation, the entire system including the STATCOM, network, harmonics and unbalancing load are simulated in MATLAB/SIMULINK. After that, a 35KVA STATCOM laboratory setup test including two parallel converter modules is designed and the control algorithm is executed on a TMS320F2812 controller platform.
Mohammad Hadi Karimi,Hassan Zamani,Khalil Kanzi,Qasem Vasheghani Farahani 전력전자학회 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.5
This paper discussed a transformer-less shunt static synchronous compensator (STATCOM) with consideration of the following aspects: fast compensation of the reactive power, harmonic cancelation and reducing the unbalancing of the 3-phase source side currents. The STATCOM control algorithm is based on the theory of instantaneous reactive power (P-Q theory). A self charging technique is proposed to regulate the dc capacitor voltage at a desired level with the use of a PI controller. In order to regulate the DC link voltage, an off-line Genetic Algorithm (GA) is used to tune the coefficients of the PI controller. This algorithm arranged these coefficients while considering the importance of three factors in the DC link voltage response: overshoot, settling time and rising time. For this investigation, the entire system including the STATCOM, network, harmonics and unbalancing load are simulated in MATLAB/SIMULINK. After that, a 35KVA STATCOM laboratory setup test including two parallel converter modules is designed and the control algorithm is executed on a TMS320F2812 controller platform.
Amir Maghsoudi,Safoura Hosseini,Seyed Abbas Shojaosadati,Ebrahim Vasheghani-Farahani,Mohsen Nosrati,Ali Bahrami 한국생물공학회 2012 Biotechnology and Bioprocess Engineering Vol.17 No.1
Developing novel methanol-feeding strategies for the improved production of heterologous proteins in high cell-density fed-batch cultures of Pichia pastoris has been of great interest during recent years. In this study, a recombinant P. pastoris strain (GS115/His+ Mut+) producing β-galactosidase (β-Gal) was used to investigate conventional feeding strategies and to develop a new strategy to increase the recombinant protein production during fedbatch cultures on methanol. Three types of conventional methanol-feeding strategies, including μ-stat, dissolved oxygen-stat (DO-stat) and constant methanol concentration were investigated and compared with respect to alcohol oxidase (AOX), formate dehydrogenase (FDH) and β-gal activities, and cell dry weight (CDW), methanol, and formaldehyde concentration variations during the production phase. Methanol feeding with μ-stat 0.025/h exhibited the highest β-gal activity. Supplementing ammonium and magnesium in μ-stat 0.025/h did not affect the cell growth or methanol or formaldehyde concentrations throughout the fermentation but did improved the maximum β-gal activity from 148.2 to 158.1 kU/mL. A new three-step methanol-feeding strategy was developed based on the results obtained from conventional feeding strategies, which started with μ-stat 0.025/ h for 5 h, then μ-stat 0.030/h, and finally, was switched to DO-stat when maintaining the DO above 20% air saturation became difficult. Implementation of this new feeding strategy resulted in a CDW of 107.2 ±0.7 g/L, AOX specific activity of 0.1890 ± 0.0030 U/mg CDW, and β-gal activity of 173.5 ± 2.1 kU/mL after 29 h of fermentation, which shows a 5.6, 29.1, and 15.7%increase in CDW, AOX, and β-gal activity, respectively,compared to that of μ-stat at 0.025/h.
Porosity changes during packed bed solid-state fermentation
A. Karimi,S.A. Shojaosadati,P. Hejazi,E. Vasheghani-Farahani,M. Hashemi 한국공업화학회 2014 Journal of Industrial and Engineering Chemistry Vol.20 No.6
Porosity is one of the key parameters in a typical solid-state fermentationmodel that represents the intraand inter-particle void spaces in bioreactor bed. In this research, the particle density and moisturecontent of the bed were used to determine the porosity changes of the solid substrate bed during thefermentation of Aspergillus niger in a laboratory scale packed-bed bioreactor. Biomass growth was alsomonitored by means of measuring CO2 and O2 in the bioreactors outlet gas online. As such, anexperimental relationship between humidity and porosity has been developed and can be used in solidstatefermentation modeling.