Parameters optimization of laser brazing in crimping butt using Taguchi and BPNN-GA

NASA Astrophysics Data System (ADS)

Rong, Youmin; Zhang, Zhen; Zhang, Guojun; Yue, Chen; Gu, Yafei; Huang, Yu; Wang, Chunming; Shao, Xinyu

2015-04-01

The laser brazing (LB) is widely used in the automotive industry due to the advantages of high speed, small heat affected zone, high quality of welding seam, and low heat input. Welding parameters play a significant role in determining the bead geometry and hence quality of the weld joint. This paper addresses the optimization of the seam shape in LB process with welding crimping butt of 0.8 mm thickness using back propagation neural network (BPNN) and genetic algorithm (GA). A 3-factor, 5-level welding experiment is conducted by Taguchi L25 orthogonal array through the statistical design method. Then, the input parameters are considered here including welding speed, wire speed rate, and gap with 5 levels. The output results are efficient connection length of left side and right side, top width (WT) and bottom width (WB) of the weld bead. The experiment results are embed into the BPNN network to establish relationship between the input and output variables. The predicted results of the BPNN are fed to GA algorithm that optimizes the process parameters subjected to the objectives. Then, the effects of welding speed (WS), wire feed rate (WF), and gap (GAP) on the sum values of bead geometry is discussed. Eventually, the confirmation experiments are carried out to demonstrate the optimal values were effective and reliable. On the whole, the proposed hybrid method, BPNN-GA, can be used to guide the actual work and improve the efficiency and stability of LB process.

Optimized power simulation of AlGaN/GaN HEMT for continuous wave and pulse applications

NASA Astrophysics Data System (ADS)

Tiwat, Pongthavornkamol; Lei, Pang; Xinhua, Wang; Sen, Huang; Guoguo, Liu; Tingting, Yuan; Xinyu, Liu

2015-07-01

An optimized modeling method of 8 × 100 μm AlGaN/GaN-based high electron mobility transistor (HEMT) for accurate continuous wave (CW) and pulsed power simulations is proposed. Since the self-heating effect can occur during the continuous operation, the power gain from the continuous operation significantly decreases when compared to a pulsed power operation. This paper extracts power performances of different device models from different quiescent biases of pulsed current-voltage (I-V) measurements and compared them in order to determine the most suitable device model for CW and pulse RF microwave power amplifier design. The simulated output power and gain results of the models at Vgs = -3.5 V, Vds = 30 V with a frequency of 9.6 GHz are presented. Project supported by the National Natural Science Foundation of China (No. 61204086).

Hybrid intelligent optimization methods for engineering problems

NASA Astrophysics Data System (ADS)

Pehlivanoglu, Yasin Volkan

The purpose of optimization is to obtain the best solution under certain conditions. There are numerous optimization methods because different problems need different solution methodologies; therefore, it is difficult to construct patterns. Also mathematical modeling of a natural phenomenon is almost based on differentials. Differential equations are constructed with relative increments among the factors related to yield. Therefore, the gradients of these increments are essential to search the yield space. However, the landscape of yield is not a simple one and mostly multi-modal. Another issue is differentiability. Engineering design problems are usually nonlinear and they sometimes exhibit discontinuous derivatives for the objective and constraint functions. Due to these difficulties, non-gradient-based algorithms have become more popular in recent decades. Genetic algorithms (GA) and particle swarm optimization (PSO) algorithms are popular, non-gradient based algorithms. Both are population-based search algorithms and have multiple points for initiation. A significant difference from a gradient-based method is the nature of the search methodologies. For example, randomness is essential for the search in GA or PSO. Hence, they are also called stochastic optimization methods. These algorithms are simple, robust, and have high fidelity. However, they suffer from similar defects, such as, premature convergence, less accuracy, or large computational time. The premature convergence is sometimes inevitable due to the lack of diversity. As the generations of particles or individuals in the population evolve, they may lose their diversity and become similar to each other. To overcome this issue, we studied the diversity concept in GA and PSO algorithms. Diversity is essential for a healthy search, and mutations are the basic operators to provide the necessary variety within a population. After having a close scrutiny of the diversity concept based on qualification and

Subpixel displacement measurement method based on the combination of particle swarm optimization and gradient algorithm

NASA Astrophysics Data System (ADS)

Guang, Chen; Qibo, Feng; Keqin, Ding; Zhan, Gao

2017-10-01

A subpixel displacement measurement method based on the combination of particle swarm optimization (PSO) and gradient algorithm (GA) was proposed for accuracy and speed optimization in GA, which is a subpixel displacement measurement method better applied in engineering practice. An initial integer-pixel value was obtained according to the global searching ability of PSO, and then gradient operators were adopted for a subpixel displacement search. A comparison was made between this method and GA by simulated speckle images and rigid-body displacement in metal specimens. The results showed that the computational accuracy of the combination of PSO and GA method reached 0.1 pixel in the simulated speckle images, or even 0.01 pixels in the metal specimen. Also, computational efficiency and the antinoise performance of the improved method were markedly enhanced.

Load forecast method of electric vehicle charging station using SVR based on GA-PSO

NASA Astrophysics Data System (ADS)

Lu, Kuan; Sun, Wenxue; Ma, Changhui; Yang, Shenquan; Zhu, Zijian; Zhao, Pengfei; Zhao, Xin; Xu, Nan

2017-06-01

This paper presents a Support Vector Regression (SVR) method for electric vehicle (EV) charging station load forecast based on genetic algorithm (GA) and particle swarm optimization (PSO). Fuzzy C-Means (FCM) clustering is used to establish similar day samples. GA is used for global parameter searching and PSO is used for a more accurately local searching. Load forecast is then regressed using SVR. The practical load data of an EV charging station were taken to illustrate the proposed method. The result indicates an obvious improvement in the forecasting accuracy compared with SVRs based on PSO and GA exclusively.

Formation mechanism of thermally optimized Ga-doped MgZnO transparent conducting electrodes for GaN-based light-emitting diodes

NASA Astrophysics Data System (ADS)

Jang, Seon-Ho; Jo, Yong-Ryun; Lee, Young-Woong; Kim, Sei-Min; Kim, Bong-Joong; Bae, Jae-Hyun; An, Huei-Chun; Jang, Ja-Soon

2015-05-01

We report a highly transparent conducting electrode (TCE) scheme of MgxZn1-xO:Ga/Au/NiOx which was deposited on p-GaN by e-beam for GaN-based light emitting diodes (LEDs). The optical and electrical properties of the electrode were optimized by thermal annealing at 500°C for 1 minute in N2 + O2 (5:3) ambient. The light transmittance at the optimal condition increased up to 84-97% from the UV-A to yellow region. The specific contact resistance decreased to 4.3(±0.3) × 10-5 Ωcm2. The improved properties of the electrode were attributed to the directionally elongated crystalline nanostructures formed in the MgxZn1-xO:Ga layer which is compositionally uniform. Interestingly, the Au alloy nano-clusters created in the MgxZn1-xO:Ga layer during annealing at 500°C may also enhance the properties of the electrode by acting as a conducting bridge and a nano-sized mirror. Based on studies of the external quantum efficiency of blue LED devices, the proposed electrode scheme combined with an optimized annealing treatment suggests a potential alternative to ITO. [Figure not available: see fulltext.

The optimal thickness of a transmission-mode GaN photocathode

NASA Astrophysics Data System (ADS)

Wang, Xiao-Hui; Shi, Feng; Guo, Hui; Hu, Cang-Lu; Cheng, Hong-Chang; Chang, Ben-Kang; Ren, Ling; Du, Yu-Jie; Zhang, Jun-Ju

2012-08-01

A 150-nm-thick GaN photocathode with a Mg doping concentration of 1.6 × 1017 cm-3 is activated by Cs/O in an ultrahigh vacuum chamber, and a quantum efficiency (QE) curve of the negative electron affinity transmission-mode (t-mode) of the GaN photocathode is obtained. The maximum QE reaches 13.0% at 290 nm. According to the t-mode QE equation solved from the diffusion equation, the QE curve is fitted. From the fitting results, the electron escape probability is 0.32, the back-interface recombination velocity is 5 × 104 cm·s-1, and the electron diffusion length is 116 nm. Based on these parameters, the influence of GaN thickness on t-mode QE is simulated. The simulation shows that the optimal thickness of GaN is 90 nm, which is better than the 150-nm GaN.

On the physical operation and optimization of the p-GaN gate in normally-off GaN HEMT devices

NASA Astrophysics Data System (ADS)

Efthymiou, L.; Longobardi, G.; Camuso, G.; Chien, T.; Chen, M.; Udrea, F.

2017-03-01

In this study, an investigation is undertaken to determine the effect of gate design parameters on the on-state characteristics (threshold voltage and gate turn-on voltage) of pGaN/AlGaN/GaN high electron mobility transistors (HEMTs). Design parameters considered are pGaN doping and gate metal work function. The analysis considers the effects of variations on these parameters using a TCAD model matched with experimental results. A better understanding of the underlying physics governing the operation of these devices is achieved with a view to enable better optimization of such gate designs.

Design and optimization of ARC less InGaP/GaAs single-/multi-junction solar cells with tunnel junction and back surface field layers

NASA Astrophysics Data System (ADS)

Chee, Kuan W. A.; Hu, Yuning

2018-07-01

There has always been an inexorable interest in the solar industry in boosting the photovoltaic conversion efficiency. This paper presents a theoretical and numerical simulation study of the effects of key design parameters on the photoelectric performance of single junction (InGaP- or GaAs-based) and dual junction (InGaP/GaAs) inorganic solar cells. The influence of base layer thickness, base doping concentration, junction temperature, back surface field layer composition and thickness, and tunnel junction material, were correlated with open circuit voltage, short-circuit current, fill factor and power conversion efficiency performance. The InGaP/GaAs dual junction solar cell was optimized with the tunnel junction and back surface field designs, yielding a short-circuit current density of 20.71 mAcm-2 , open-circuit voltage of 2.44 V and fill factor of 88.6%, and guaranteeing an optimal power conversion efficiency of at least 32.4% under 1 sun AM0 illumination even without an anti-reflective coating.

Long-term evaluation of TiO2-based 68Ge/68Ga generators and optimized automation of [68Ga]DOTATOC radiosynthesis.

PubMed

Lin, Mai; Ranganathan, David; Mori, Tetsuya; Hagooly, Aviv; Rossin, Raffaella; Welch, Michael J; Lapi, Suzanne E

2012-10-01

Interest in using (68)Ga is rapidly increasing for clinical PET applications due to its favorable imaging characteristics and increased accessibility. The focus of this study was to provide our long-term evaluations of the two TiO(2)-based (68)Ge/(68)Ga generators and develop an optimized automation strategy to synthesize [(68)Ga]DOTATOC by using HEPES as a buffer system. This data will be useful in standardizing the evaluation of (68)Ge/(68)Ga generators and automation strategies to comply with regulatory issues for clinical use. Copyright © 2012 Elsevier Ltd. All rights reserved.

Optimization of conditions for thermal smoothing GaAs surfaces

NASA Astrophysics Data System (ADS)

Akhundov, I. O.; Kazantsev, D. M.; Kozhuhov, A. S.; Alperovich, V. L.

2018-03-01

GaAs thermal smoothing by annealing in conditions which are close to equilibrium between the surface and vapors of As and Ga was earlier proved to be effective for the step-terraced surface formation on epi-ready substrates with a small root-mean-square roughness (Rq ≤ 0.15 nm). In the present study, this technique is further developed in order to reduce the annealing duration and to smooth GaAs samples with a larger initial roughness. To this end, we proposed a two-stage anneal with the first high-temperature stage aimed at smoothing "coarse" relief features and the second stage focused on "fine" smoothing at a lower temperature. The optimal temperatures and durations of two-stage annealing are found by Monte Carlo simulations and adjusted after experimentation. It is proved that the temperature and duration of the first high-temperature stage are restricted by the surface roughening, which occurs due to deviations from equilibrium conditions.

A method of network topology optimization design considering application process characteristic

NASA Astrophysics Data System (ADS)

Wang, Chunlin; Huang, Ning; Bai, Yanan; Zhang, Shuo

2018-03-01

Communication networks are designed to meet the usage requirements of users for various network applications. The current studies of network topology optimization design mainly considered network traffic, which is the result of network application operation, but not a design element of communication networks. A network application is a procedure of the usage of services by users with some demanded performance requirements, and has obvious process characteristic. In this paper, we first propose a method to optimize the design of communication network topology considering the application process characteristic. Taking the minimum network delay as objective, and the cost of network design and network connective reliability as constraints, an optimization model of network topology design is formulated, and the optimal solution of network topology design is searched by Genetic Algorithm (GA). Furthermore, we investigate the influence of network topology parameter on network delay under the background of multiple process-oriented applications, which can guide the generation of initial population and then improve the efficiency of GA. Numerical simulations show the effectiveness and validity of our proposed method. Network topology optimization design considering applications can improve the reliability of applications, and provide guidance for network builders in the early stage of network design, which is of great significance in engineering practices.

The optimization of Ga (1-x)Al (x)As-GaAs solar cells for air mass zero operation and a study of Ga (1-x)Al (x)As-GaAs solar cells at high temperatures, phase 1

NASA Technical Reports Server (NTRS)

Hovel, H. J.; Woodall, J. M.

1976-01-01

The three types of solar cells investigated were: (1) one consisting of a nGaAs substrate, a Zn doped pGaAs region, and a Zn doped Ga(1-x)Al(x)As layer, (2) one consisting of an nGaAs substrate, a Ge doped pGaAs region, and a pGa(1-x)Al(x)As upper layer, and (3) one consisting of an n+GaAs substrate, an nGa(1-x)Al(X)As region, a pGa(1-x)Bl(X) As region, and a pGa(1-y)Al(y)As upper layer. In all three cases, the upper alloy layer is thin and of high Al composition in order to obtain high spectral response over the widest possible range of photon energies. Spectral response, capacitance-voltage, current-voltage, diffusion length, sunlight (or the equivalent)-efficiency, and efficiency-temperature measurements were made as a function of device parameters in order to analyze and optimize the solar cell behavior.

Optimal design approach for heating irregular-shaped objects in three-dimensional radiant furnaces using a hybrid genetic algorithm-artificial neural network method

NASA Astrophysics Data System (ADS)

Darvishvand, Leila; Kamkari, Babak; Kowsary, Farshad

2018-03-01

In this article, a new hybrid method based on the combination of the genetic algorithm (GA) and artificial neural network (ANN) is developed to optimize the design of three-dimensional (3-D) radiant furnaces. A 3-D irregular shape design body (DB) heated inside a 3-D radiant furnace is considered as a case study. The uniform thermal conditions on the DB surfaces are obtained by minimizing an objective function. An ANN is developed to predict the objective function value which is trained through the data produced by applying the Monte Carlo method. The trained ANN is used in conjunction with the GA to find the optimal design variables. The results show that the computational time using the GA-ANN approach is significantly less than that of the conventional method. It is concluded that the integration of the ANN with GA is an efficient technique for optimization of the radiant furnaces.

Epitaxial GaN layers formed on langasite substrates by the plasma-assisted MBE method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lobanov, D. N., E-mail: dima@ipmras.ru; Novikov, A. V.; Yunin, P. A.

2016-11-15

In this publication, the results of development of the technology of the epitaxial growth of GaN on single-crystal langasite substrates La{sub 3}Ga{sub 5}SiO{sub 14} (0001) by the plasma-assisted molecular-beam epitaxy (PA MBE) method are reported. An investigation of the effect of the growth temperature at the initial stage of deposition on the crystal quality and morphology of the obtained GaN layer is performed. It is demonstrated that the optimal temperature for deposition of the initial GaN layer onto the langasite substrate is about ~520°C. A decrease in the growth temperature to this value allows the suppression of oxygen diffusion frommore » langasite into the growing layer and a decrease in the dislocation density in the main GaN layer upon its subsequent high-temperature deposition (~700°C). Further lowering of the growth temperature of the nucleation layer leads to sharp degradation of the GaN/LGS layer crystal quality. As a result of the performed research, an epitaxial GaN/LGS layer with a dislocation density of ~10{sup 11} cm{sup –2} and low surface roughness (<2 nm) is obtained.« less

A new optimized GA-RBF neural network algorithm.

PubMed

Jia, Weikuan; Zhao, Dean; Shen, Tian; Su, Chunyang; Hu, Chanli; Zhao, Yuyan

2014-01-01

When confronting the complex problems, radial basis function (RBF) neural network has the advantages of adaptive and self-learning ability, but it is difficult to determine the number of hidden layer neurons, and the weights learning ability from hidden layer to the output layer is low; these deficiencies easily lead to decreasing learning ability and recognition precision. Aiming at this problem, we propose a new optimized RBF neural network algorithm based on genetic algorithm (GA-RBF algorithm), which uses genetic algorithm to optimize the weights and structure of RBF neural network; it chooses new ways of hybrid encoding and optimizing simultaneously. Using the binary encoding encodes the number of the hidden layer's neurons and using real encoding encodes the connection weights. Hidden layer neurons number and connection weights are optimized simultaneously in the new algorithm. However, the connection weights optimization is not complete; we need to use least mean square (LMS) algorithm for further leaning, and finally get a new algorithm model. Using two UCI standard data sets to test the new algorithm, the results show that the new algorithm improves the operating efficiency in dealing with complex problems and also improves the recognition precision, which proves that the new algorithm is valid.

Robust Sliding Mode Control Based on GA Optimization and CMAC Compensation for Lower Limb Exoskeleton

PubMed Central

Long, Yi; Du, Zhi-jiang; Wang, Wei-dong; Dong, Wei

2016-01-01

A lower limb assistive exoskeleton is designed to help operators walk or carry payloads. The exoskeleton is required to shadow human motion intent accurately and compliantly to prevent incoordination. If the user's intention is estimated accurately, a precise position control strategy will improve collaboration between the user and the exoskeleton. In this paper, a hybrid position control scheme, combining sliding mode control (SMC) with a cerebellar model articulation controller (CMAC) neural network, is proposed to control the exoskeleton to react appropriately to human motion intent. A genetic algorithm (GA) is utilized to determine the optimal sliding surface and the sliding control law to improve performance of SMC. The proposed control strategy (SMC_GA_CMAC) is compared with three other types of approaches, that is, conventional SMC without optimization, optimal SMC with GA (SMC_GA), and SMC with CMAC compensation (SMC_CMAC), all of which are employed to track the desired joint angular position which is deduced from Clinical Gait Analysis (CGA) data. Position tracking performance is investigated with cosimulation using ADAMS and MATLAB/SIMULINK in two cases, of which the first case is without disturbances while the second case is with a bounded disturbance. The cosimulation results show the effectiveness of the proposed control strategy which can be employed in similar exoskeleton systems. PMID:27069353

Robust Sliding Mode Control Based on GA Optimization and CMAC Compensation for Lower Limb Exoskeleton.

PubMed

Long, Yi; Du, Zhi-Jiang; Wang, Wei-Dong; Dong, Wei

2016-01-01

A lower limb assistive exoskeleton is designed to help operators walk or carry payloads. The exoskeleton is required to shadow human motion intent accurately and compliantly to prevent incoordination. If the user's intention is estimated accurately, a precise position control strategy will improve collaboration between the user and the exoskeleton. In this paper, a hybrid position control scheme, combining sliding mode control (SMC) with a cerebellar model articulation controller (CMAC) neural network, is proposed to control the exoskeleton to react appropriately to human motion intent. A genetic algorithm (GA) is utilized to determine the optimal sliding surface and the sliding control law to improve performance of SMC. The proposed control strategy (SMC_GA_CMAC) is compared with three other types of approaches, that is, conventional SMC without optimization, optimal SMC with GA (SMC_GA), and SMC with CMAC compensation (SMC_CMAC), all of which are employed to track the desired joint angular position which is deduced from Clinical Gait Analysis (CGA) data. Position tracking performance is investigated with cosimulation using ADAMS and MATLAB/SIMULINK in two cases, of which the first case is without disturbances while the second case is with a bounded disturbance. The cosimulation results show the effectiveness of the proposed control strategy which can be employed in similar exoskeleton systems.

A Novel Extraction Approach of Extrinsic and Intrinsic Parameters of InGaAs/GaN pHEMTs

DTIC Science & Technology

2015-07-01

presented, for the first time, artificial bee colony algorithm is applied to the global-optimization based parameter extraction and a novel intrinsic...conservation of the gate charge is well satisfied which further validates this novel extraction method. Index Terms —InGaAs/GaN pHEMTs, artificial bee ...increase the uniqueness of the extraction. Artificial bee colony (ABC) algorithm is adopted as the optimizer due to its excellent ability to escape

Luminescence and efficiency optimization of InGaN/GaN core-shell nanowire LEDs by numerical modelling

NASA Astrophysics Data System (ADS)

Römer, Friedhard; Deppner, Marcus; Andreev, Zhelio; Kölper, Christopher; Sabathil, Matthias; Strassburg, Martin; Ledig, Johannes; Li, Shunfeng; Waag, Andreas; Witzigmann, Bernd

2012-02-01

We present a computational study on the anisotropic luminescence and the efficiency of a core-shell type nanowire LED based on GaN with InGaN active quantum wells. The physical simulator used for analyzing this device integrates a multidimensional drift-diffusion transport solver and a k . p Schrödinger problem solver for quantization effects and luminescence. The solution of both problems is coupled to achieve self-consistency. Using this solver we investigate the effect of dimensions, design of quantum wells, and current injection on the efficiency and luminescence of the core-shell nanowire LED. The anisotropy of the luminescence and re-absorption is analyzed with respect to the external efficiency of the LED. From the results we derive strategies for design optimization.

Optimization of Ammonium Sulfate Concentration for Purification of Colorectal Cancer Vaccine Candidate Recombinant Protein GA733-FcK Isolated from Plants.

PubMed

Park, Se-Ra; Lim, Chae-Yeon; Kim, Deuk-Su; Ko, Kisung

2015-01-01

A protein purification procedure is required to obtain high-value recombinant injectable vaccine proteins produced in plants as a bioreactor. However, existing purification procedures for plant-derived recombinant proteins are often not optimized and are inefficient, with low recovery rates. In our previous study, we used 25-30% ammonium sulfate to precipitate total soluble proteins (TSPs) in purification process for recombinant proteins from plant leaf biomass which has not been optimized. Thus, the objective in this study is to optimize the conditions for plant-derived protein purification procedures. Various ammonium sulfate concentrations (15-80%) were compared to determine their effects on TSPs yield. With 50% ammonium sulfate, the yield of precipitated TSP was the highest, and that of the plant-derived colorectal cancer-specific surface glycoprotein GA733 fused to the Fc fragment of human IgG tagged with endoplasmic reticulum retention signal KDEL (GA733(P)-FcK) protein significantly increased 1.8-fold. SDS-PAGE analysis showed that the purity of GA733(P)-FcK protein band appeared to be similar to that of an equal dose of mammalian-derived GA733-Fc (GA733(M)-Fc). The binding activity of purified GA733(P)-FcK to anti-GA733 mAb was as efficient as the native GA733(M)-Fc. Thus, the purification process was effectively optimized for obtaining a high yield of plant-derived antigenic protein with good quality. In conclusion, the purification recovery rate of large quantities of recombinant protein from plant expression systems can be enhanced via optimization of ammonium sulfate concentration during downstream processes, thereby offering a promising solution for production of recombinant GA733-Fc protein in plants.

Photoluminescence and Band Alignment of Strained GaAsSb/GaAs QW Structures Grown by MBE on GaAs

PubMed Central

Sadofyev, Yuri G.; Samal, Nigamananda

2010-01-01

An in-depth optimization of growth conditions and investigation of optical properties including discussions on band alignment of GaAsSb/GaAs quantum well (QW) on GaAs by molecular beam epitaxy (MBE) are reported. Optimal MBE growth temperature of GaAsSb QW is found to be 470 ± 10 °C. GaAsSb/GaAs QW with Sb content ~0.36 has a weak type-II band alignment with valence band offset ratio QV ~1.06. A full width at half maximum (FWHM) of ~60 meV in room temperature (RT) photoluminescence (PL) indicates fluctuation in electrostatic potential to be less than 20 meV. Samples grown under optimal conditions do not exhibit any blue shift of peak in RT PL spectra under varying excitation.

Optimization of ELISA Conditions to Quantify Colorectal Cancer Antigen-Antibody Complex Protein (GA733-FcK) Expressed in Transgenic Plant

PubMed Central

Ahn, Junsik; Lee, Kyung Jin

2014-01-01

The purpose of this study is to optimize ELISA conditions to quantify the colorectal cancer antigen GA733 linked to the Fc antibody fragment fused to KDEL, an ER retention motif (GA733-FcK) expressed in transgenic plant. Variable conditions of capture antibody, blocking buffer, and detection antibody for ELISA were optimized with application of leaf extracts from transgenic plant expressing GA733-FcK. In detection antibody, anti-EpCAM/CD362 IgG recognizing the GA733 did not detect any GA733-FcK whereas anti-human Fc IgG recognizing the human Fc existed in plant leaf extracts. For blocking buffer conditions, 3% BSA buffer clearly blocked the plate, compared to the 5% skim-milk buffer. For capture antibody, monoclonal antibody (MAb) CO17-1A was applied to coat the plate with different amounts (1, 0.5, and 0.25 μg/well). Among the amounts of the capture antibody, 1 and 0.5 μg/well (capture antibody) showed similar absorbance, whereas 0.25 μg/well of the capture antibody showed significantly less absorbance. Taken together, the optimized conditions to quantify plant-derived GA733-FcK were 0.5 μg/well of MAb CO17-1A per well for the capture antibody, 3% BSA for blocking buffer, and anti-human Fc conjugated HRP. To confirm the optimized ELISA conditions, correlation analysis was conducted between the quantified amount of GA733-FcK in ELISA and its protein density values of different leaf samples in Western blot. The co-efficient value R2 between the ELISA quantified value and protein density was 0.85 (p<0.01), which indicates that the optimized ELISA conditions feasibly provides quantitative information of GA733-FcK expression in transgenic plant. PMID:24555929

Differences in optoelectronic properties between H-saturated and unsaturated GaN nanowires with DFT method

NASA Astrophysics Data System (ADS)

Diao, Yu; Liu, Lei; Xia, Sihao; Kong, Yike

2017-05-01

To investigate the influences of dangling bonds on GaN nanowires surface, the differences in optoelectronic properties between H-saturated and unsaturated GaN nanowires are researched through first-principles study. The GaN nanowires along the [0001] growth direction with diameters of 3.7, 7.5 and 9.5 Å are considered. According to the results, H-saturated GaN nanowires are more stable than the unsaturated ones. With increasing nanowire diameter, unsaturated GaN nanowires become more stable, while the stability of H-saturated GaN nanowires has little change. After geometry optimization, the atomic displacements of unsaturated and H-saturated models are almost reversed. In (0001) crystal plane, Ga atoms tend to move inwards and N atoms tend to move outwards slightly for the unsaturated nanowires, while Ga atoms tend to move outwards and N atoms tend to move inwards slightly for the H-saturated nanowires. Besides, with increasing nanowire diameter, the conduction band minimum of H-saturated nanowire moves to the lower energy side, while that of the unsaturated nanowire changes slightly. The bandgaps of H-saturated nanowires are approaching to bulk GaN as the diameter increases. Absorption curves and reflectivity curves of the unsaturated and H-saturated nanowires exhibit the same trend with the change of energy except the H-saturated models which show larger variations. Through all the calculated results above, we can better understand the effects of dangling bonds on the optoelectronic properties of GaN nanowires and select more proper calculation models and methods for other calculations.

GaAs thin films and methods of making and using the same

DOEpatents

Boettcher, Shannon; Ritenour, Andrew; Boucher, Jason; Greenaway, Ann

2016-06-14

Disclosed herein are embodiments of methods for making GaAs thin films, such as photovoltaic GaAs thin films. The methods disclosed herein utilize sources, precursors, and reagents that do not produce (or require) toxic gas and that are readily available and relatively low in cost. In some embodiments, the methods are readily scalable for industrial applications and can provide GaAs thin films having properties that are at least comparable to or potentially superior to GaAs films obtained from conventional methods.

Growth optimization toward low angle incidence microchannel epitaxy of GaN using ammonia-based metal-organic molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Lin, Chia-Hung; Abe, Ryota; Uchiyama, Shota; Maruyama, Takahiro; Naritsuka, Shigeya

2012-08-01

Growth optimization toward low angle incidence microchannel epitaxy (LAIMCE) of GaN was accomplished using ammonia-based metal-organic molecular beam epitaxy (NH3-based MOMBE). Firstly, the [NH3]/[trimethylgallium (TMG)] ratio (R) dependence of selective GaN growth was studied. The growth temperature was set at 860 °C while R was varied from 5 to 200 with precursors being supplied parallel to the openings cut in the SiO2 mask. The selectivity of the growth was superior for all R, because TMG and NH3 preferably decompose on the GaN film. The formation of {112¯0}GaN or {112¯2}GaN sidewalls and (0001)GaN surface were observed by the change in R. The intersurface diffusion of Ga adatoms was also changed by a change in R. Ga adatoms migrate from the sidewalls to the top at R lower than 50, whereas the migration weakened with R greater than 100. Secondly, LAIMCE was optimized by changing the growth temperature. Consequently, 6 μm wide lateral overgrowth in the direction of precursor incidence was achieved with no pit after etching by H3PO4, which was six times wider than that in the opposite direction.

Mathematical Modeling and Optimizing of in Vitro Hormonal Combination for G × N15 Vegetative Rootstock Proliferation Using Artificial Neural Network-Genetic Algorithm (ANN-GA)

PubMed Central

Arab, Mohammad M.; Yadollahi, Abbas; Ahmadi, Hamed; Eftekhari, Maliheh; Maleki, Masoud

2017-01-01

The efficiency of a hybrid systems method which combined artificial neural networks (ANNs) as a modeling tool and genetic algorithms (GAs) as an optimizing method for input variables used in ANN modeling was assessed. Hence, as a new technique, it was applied for the prediction and optimization of the plant hormones concentrations and combinations for in vitro proliferation of Garnem (G × N15) rootstock as a case study. Optimizing hormones combination was surveyed by modeling the effects of various concentrations of cytokinin–auxin, i.e., BAP, KIN, TDZ, IBA, and NAA combinations (inputs) on four growth parameters (outputs), i.e., micro-shoots number per explant, length of micro-shoots, developed callus weight (CW) and the quality index (QI) of plantlets. Calculation of statistical values such as R2 (coefficient of determination) related to the accuracy of ANN-GA models showed a considerably higher prediction accuracy for ANN models, i.e., micro-shoots number: R2 = 0.81, length of micro-shoots: R2 = 0.87, CW: R2 = 0.88, QI: R2 = 0.87. According to the results, among the input variables, BAP (19.3), KIN (9.64), and IBA (2.63) showed the highest values of variable sensitivity ratio for proliferation rate. The GA showed that media containing 1.02 mg/l BAP in combination with 0.098 mg/l IBA could lead to the optimal proliferation rate (10.53) for G × N15 rootstock. Another objective of the present study was to compare the performance of predicted and optimized cytokinin–auxin combination with the best optimized obtained concentrations of our other experiments. Considering three growth parameters (length of micro-shoots, micro-shoots number, and proliferation rate), the last treatment was found to be superior to the rest of treatments for G × N15 rootstock in vitro multiplication. Very little difference between the ANN predicted and experimental data confirmed high capability of ANN-GA method in predicting new optimized protocols for plant in vitro propagation

Optimization of structural and growth parameters of metamorphic InGaAs photovoltaic converters grown by MOCVD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rybalchenko, D. V.; Mintairov, S. A.; Salii, R. A.

Metamorphic Ga{sub 0.76}In{sub 0.24}As heterostructures for photovoltaic converters are grown by the MOCVD (metal–organic chemical vapor deposition) technique. It is found that, due to the valence-band offset at the p-In{sub 0.24}Al{sub 0.76}As/p-In{sub 0.24}Ga{sub 0.76}As (wide-gap window/emitter) heterointerface, a potential barrier for holes arises as a result of a low carrier concentration in the wide-gap material. The use of an InAlGaAs solid solution with an Al content lower than 40% makes it possible to raise the hole concentration in the widegap window up ~9 × 10{sup 18} cm{sup –3} and completely remove the potential barrier, thereby reducing the series resistance ofmore » the device. The parameters of an GaInAs metamorphic buffer layer with a stepwise In content profile are calculated and its epitaxial growth conditions are optimized, which improves carrier collection from the n-GaInAs base region and provides a quantum efficiency of 83% at a wavelength of 1064 nm. Optimization of the metamorphic heterostructure of the photovoltaic converter results in that its conversion efficiency for laser light with a wavelength of 1064 nm is 38.5%.« less

InGaN/GaN multilayer quantum dots yellow-green light-emitting diode with optimized GaN barriers.

PubMed

Lv, Wenbin; Wang, Lai; Wang, Jiaxing; Hao, Zhibiao; Luo, Yi

2012-11-07

InGaN/GaN multilayer quantum dot (QD) structure is a potential type of active regions for yellow-green light-emitting diodes (LEDs). The surface morphologies and crystalline quality of GaN barriers are critical to the uniformity of InGaN QD layers. While GaN barriers were grown in multi-QD layers, we used improved growth parameters by increasing the growth temperature and switching the carrier gas from N2 to H2 in the metal organic vapor phase epitaxy. As a result, a 10-layer InGaN/GaN QD LED is demonstrated successfully. The transmission electron microscopy image shows the uniform multilayer InGaN QDs clearly. As the injection current increases from 5 to 50 mA, the electroluminescence peak wavelength shifts from 574 to 537 nm.

Study on the optimization of the deposition rate of planetary GaN-MOCVD films based on CFD simulation and the corresponding surface model.

PubMed

Li, Jian; Fei, Ze-Yuan; Xu, Yi-Feng; Wang, Jie; Fan, Bing-Feng; Ma, Xue-Jin; Wang, Gang

2018-02-01

Metal-organic chemical vapour deposition (MOCVD) is a key technique for fabricating GaN thin film structures for light-emitting and semiconductor laser diodes. Film uniformity is an important index to measure equipment performance and chip processes. This paper introduces a method to improve the quality of thin films by optimizing the rotation speed of different substrates of a model consisting of a planetary with seven 6-inch wafers for the planetary GaN-MOCVD. A numerical solution to the transient state at low pressure is obtained using computational fluid dynamics. To evaluate the role of the different zone speeds on the growth uniformity, single factor analysis is introduced. The results show that the growth rate and uniformity are strongly related to the rotational speed. Next, a response surface model was constructed by using the variables and the corresponding simulation results. The optimized combination of the matching of different speeds is also proposed as a useful reference for applications in industry, obtained by a response surface model and genetic algorithm with a balance between the growth rate and the growth uniformity. This method can save time, and the optimization can obtain the most uniform and highest thin film quality.

Study on the optimization of the deposition rate of planetary GaN-MOCVD films based on CFD simulation and the corresponding surface model

NASA Astrophysics Data System (ADS)

Li, Jian; Fei, Ze-yuan; Xu, Yi-feng; Wang, Jie; Fan, Bing-feng; Ma, Xue-jin; Wang, Gang

2018-02-01

Metal-organic chemical vapour deposition (MOCVD) is a key technique for fabricating GaN thin film structures for light-emitting and semiconductor laser diodes. Film uniformity is an important index to measure equipment performance and chip processes. This paper introduces a method to improve the quality of thin films by optimizing the rotation speed of different substrates of a model consisting of a planetary with seven 6-inch wafers for the planetary GaN-MOCVD. A numerical solution to the transient state at low pressure is obtained using computational fluid dynamics. To evaluate the role of the different zone speeds on the growth uniformity, single factor analysis is introduced. The results show that the growth rate and uniformity are strongly related to the rotational speed. Next, a response surface model was constructed by using the variables and the corresponding simulation results. The optimized combination of the matching of different speeds is also proposed as a useful reference for applications in industry, obtained by a response surface model and genetic algorithm with a balance between the growth rate and the growth uniformity. This method can save time, and the optimization can obtain the most uniform and highest thin film quality.

InGaN/GaN multilayer quantum dots yellow-green light-emitting diode with optimized GaN barriers

PubMed Central

2012-01-01

InGaN/GaN multilayer quantum dot (QD) structure is a potential type of active regions for yellow-green light-emitting diodes (LEDs). The surface morphologies and crystalline quality of GaN barriers are critical to the uniformity of InGaN QD layers. While GaN barriers were grown in multi-QD layers, we used improved growth parameters by increasing the growth temperature and switching the carrier gas from N2 to H2 in the metal organic vapor phase epitaxy. As a result, a 10-layer InGaN/GaN QD LED is demonstrated successfully. The transmission electron microscopy image shows the uniform multilayer InGaN QDs clearly. As the injection current increases from 5 to 50 mA, the electroluminescence peak wavelength shifts from 574 to 537 nm. PMID:23134721

Optimal reentry prediction of space objects from LEO using RSM and GA

NASA Astrophysics Data System (ADS)

Mutyalarao, M.; Raj, M. Xavier James

2012-07-01

The accurate estimation of the orbital life time (OLT) of decaying near-Earth objects is of considerable importance for the prediction of risk object re-entry time and hazard assessment as well as for mitigation strategies. Recently, due to the reentries of large number of risk objects, which poses threat to the human life and property, a great concern is developed in the space scientific community all over the World. The evolution of objects in Low Earth Orbit (LEO) is determined by a complex interplay of the perturbing forces, mainly due to atmospheric drag and Earth gravity. These orbits are mostly in low eccentric (eccentricity < 0.2) and have variations in perigee and apogee altitudes due to perturbations during a revolution. The changes in the perigee and apogee altitudes of these orbits are mainly due to the gravitational perturbations of the Earth and the atmospheric density. It has become necessary to use extremely complex force models to match with the present operational requirements and observational techniques. Further the re-entry time of the objects in such orbits is sensitive to the initial conditions. In this paper the problem of predicting re-entry time is attempted as an optimal estimation problem. It is known that the errors are more in eccentricity for the observations based on two line elements (TLEs). Thus two parameters, initial eccentricity and ballistic coefficient, are chosen for optimal estimation. These two parameters are computed with response surface method (RSM) using a genetic algorithm (GA) for the selected time zones, based on rough linear variation of response parameter, the mean semi-major axis during orbit evolution. Error minimization between the observed and predicted mean Semi-major axis is achieved by the application of an optimization algorithm such as Genetic Algorithm (GA). The basic feature of the present approach is that the model and measurement errors are accountable in terms of adjusting the ballistic coefficient

Genetic algorithm with maximum-minimum crossover (GA-MMC) applied in optimization of radiation pattern control of phased-array radars for rocket tracking systems.

PubMed

Silva, Leonardo W T; Barros, Vitor F; Silva, Sandro G

2014-08-18

In launching operations, Rocket Tracking Systems (RTS) process the trajectory data obtained by radar sensors. In order to improve functionality and maintenance, radars can be upgraded by replacing antennas with parabolic reflectors (PRs) with phased arrays (PAs). These arrays enable the electronic control of the radiation pattern by adjusting the signal supplied to each radiating element. However, in projects of phased array radars (PARs), the modeling of the problem is subject to various combinations of excitation signals producing a complex optimization problem. In this case, it is possible to calculate the problem solutions with optimization methods such as genetic algorithms (GAs). For this, the Genetic Algorithm with Maximum-Minimum Crossover (GA-MMC) method was developed to control the radiation pattern of PAs. The GA-MMC uses a reconfigurable algorithm with multiple objectives, differentiated coding and a new crossover genetic operator. This operator has a different approach from the conventional one, because it performs the crossover of the fittest individuals with the least fit individuals in order to enhance the genetic diversity. Thus, GA-MMC was successful in more than 90% of the tests for each application, increased the fitness of the final population by more than 20% and reduced the premature convergence.

Genetic Algorithm with Maximum-Minimum Crossover (GA-MMC) Applied in Optimization of Radiation Pattern Control of Phased-Array Radars for Rocket Tracking Systems

PubMed Central

Silva, Leonardo W. T.; Barros, Vitor F.; Silva, Sandro G.

2014-01-01

In launching operations, Rocket Tracking Systems (RTS) process the trajectory data obtained by radar sensors. In order to improve functionality and maintenance, radars can be upgraded by replacing antennas with parabolic reflectors (PRs) with phased arrays (PAs). These arrays enable the electronic control of the radiation pattern by adjusting the signal supplied to each radiating element. However, in projects of phased array radars (PARs), the modeling of the problem is subject to various combinations of excitation signals producing a complex optimization problem. In this case, it is possible to calculate the problem solutions with optimization methods such as genetic algorithms (GAs). For this, the Genetic Algorithm with Maximum-Minimum Crossover (GA-MMC) method was developed to control the radiation pattern of PAs. The GA-MMC uses a reconfigurable algorithm with multiple objectives, differentiated coding and a new crossover genetic operator. This operator has a different approach from the conventional one, because it performs the crossover of the fittest individuals with the least fit individuals in order to enhance the genetic diversity. Thus, GA-MMC was successful in more than 90% of the tests for each application, increased the fitness of the final population by more than 20% and reduced the premature convergence. PMID:25196013

Investigating and Optimizing Carrier Transport, Carrier Distribution, and Efficiency Droop in GaN-based Light-emitting Diodes

NASA Astrophysics Data System (ADS)

Zhu, Di

2011-12-01

-current efficiency and reduced efficiency droop. Compared with 4-QB-doped LEDs, 1-QB-doped LEDs show a 37.5% increase in light-output power at high currents. Consistent with the measurements, simulation shows a shift of radiative recombination among the MQWs and a reduced electron leakage current into the p-type GaN when fewer QBs are doped. The results can be attributed to a more symmetric carrier transport and uniform carrier distribution which help to reduce electron leakage and thus reduce the efficiency droop. In this dissertation, artificial evolution is introduced to the LED optimization process which combines a genetic algorithm (GA) and device-simulation software. We show that this approach is capable of generating novel concepts in designing and optimizing LED devices. Application of the GA to the QB-doping in the MQWs yields optimized structures which is consistent with the tailored QB doping experiments. Application of the GA to the EBL region suggests a novel structure with an inverted sheet charge at the spacer-EBL interface. The resulting repulsion of electrons can significantly reduce electron leakage and enhance the efficiency. Finally, dual-wavelength LEDs, which have two types of quantum wells (QWs) emitting at two different wavelengths, are experimentally characterized and compared with numerical simulations. These dual-wavelength LEDs allow us to determine which QW emits most of the light. An experimental observation and a quantitative analysis of the radiative recombination shift within the MQW active region are obtained. In addition, an injection-current dependence of the radiative recombination shift is predicted by numerical simulations and indeed observed in dual-wavelength LEDs. This injection-current dependence of the radiative recombination distribution can be explained very well by incorporating quantum-mechanical tunneling of carriers into and through the QBs into to the classical drift-diffusion model. In summary, using the LEDs with tailored QB

Analysis of light extraction efficiency enhancement for thin-film-flip-chip InGaN quantum wells light-emitting diodes with GaN micro-domes.

PubMed

Zhao, Peng; Zhao, Hongping

2012-09-10

The enhancement of light extraction efficiency for thin-film flip-chip (TFFC) InGaN quantum wells (QWs) light-emitting diodes (LEDs) with GaN micro-domes on n-GaN layer was studied. The light extraction efficiency of TFFC InGaN QWs LEDs with GaN micro-domes were calculated and compared to that of the conventional TFFC InGaN QWs LEDs with flat surface. The three dimensional finite difference time domain (3D-FDTD) method was used to calculate the light extraction efficiency for the InGaN QWs LEDs emitting at 460nm and 550 nm, respectively. The effects of the GaN micro-dome feature size and the p-GaN layer thickness on the light extraction efficiency were studied systematically. Studies indicate that the p-GaN layer thickness is critical for optimizing the TFFC LED light extraction efficiency. Significant enhancement of the light extraction efficiency (2.5-2.7 times for λ(peak) = 460nm and 2.7-2.8 times for λ(peak) = 550nm) is achievable from TFFC InGaN QWs LEDs with optimized GaN micro-dome diameter and height.

Determination of gallium at trace levels using a spectrofluorimetric method in synthetic U-Ga and Ga-As solutions.

PubMed

Kara, Derya; Fisher, Andrew; Foulkes, Mike; Hill, Steve J

2010-01-01

A simple, easy to use and selective spectrofluorimetric method for the determination of trace levels of gallium has been developed. A new Schiff base, N-o-vanillidine-2-amino-p-cresol (OVAC) was synthesized and its fluorescence activity with gallium investigated. Based on this chelation reaction, a spectrofluorimetric method has been developed for the determination of gallium in synthetically prepared Ga-U and Ga-As samples buffered at pH 4.0 using acetic acid-sodium acetate. The chelation reaction between Ga(III) and N-o-vanillidine-2-amino-p-cresol was very fast, requiring only 30min at room temperature to complex completely. The limit of detection (LOD) (3sigma) for Ga(III) was 7.17 nM (0.50 microgL(-1)), determined from the analysis of 11 different solutions of 20 microg L(-1) Ga(III). Copyright 2009 Elsevier B.V. All rights reserved.

Multidisciplinary design optimization using genetic algorithms

NASA Technical Reports Server (NTRS)

Unal, Resit

1994-01-01

Multidisciplinary design optimization (MDO) is an important step in the conceptual design and evaluation of launch vehicles since it can have a significant impact on performance and life cycle cost. The objective is to search the system design space to determine values of design variables that optimize the performance characteristic subject to system constraints. Gradient-based optimization routines have been used extensively for aerospace design optimization. However, one limitation of gradient based optimizers is their need for gradient information. Therefore, design problems which include discrete variables can not be studied. Such problems are common in launch vehicle design. For example, the number of engines and material choices must be integer values or assume only a few discrete values. In this study, genetic algorithms are investigated as an approach to MDO problems involving discrete variables and discontinuous domains. Optimization by genetic algorithms (GA) uses a search procedure which is fundamentally different from those gradient based methods. Genetic algorithms seek to find good solutions in an efficient and timely manner rather than finding the best solution. GA are designed to mimic evolutionary selection. A population of candidate designs is evaluated at each iteration, and each individual's probability of reproduction (existence in the next generation) depends on its fitness value (related to the value of the objective function). Progress toward the optimum is achieved by the crossover and mutation operations. GA is attractive since it uses only objective function values in the search process, so gradient calculations are avoided. Hence, GA are able to deal with discrete variables. Studies report success in the use of GA for aircraft design optimization studies, trajectory analysis, space structure design and control systems design. In these studies reliable convergence was achieved, but the number of function evaluations was large compared

Determining the optimal number of Kanban in multi-products supply chain system

NASA Astrophysics Data System (ADS)

Widyadana, G. A.; Wee, H. M.; Chang, Jer-Yuan

2010-02-01

Kanban, a key element of just-in-time system, is a re-order card or signboard giving instruction or triggering the pull system to manufacture or supply a component based on actual usage of material. There are two types of Kanban: production Kanban and withdrawal Kanban. This study uses optimal and meta-heuristic methods to determine the Kanban quantity and withdrawal lot sizes in a supply chain system. Although the mix integer programming method gives an optimal solution, it is not time efficient. For this reason, the meta-heuristic methods are suggested. In this study, a genetic algorithm (GA) and a hybrid of genetic algorithm and simulated annealing (GASA) are used. The study compares the performance of GA and GASA with that of the optimal method using MIP. The given problems show that both GA and GASA result in a near optimal solution, and they outdo the optimal method in term of run time. In addition, the GASA heuristic method gives a better performance than the GA heuristic method.

Warpage improvement on wheel caster by optimizing the process parameters using genetic algorithm (GA)

NASA Astrophysics Data System (ADS)

Safuan, N. S.; Fathullah, M.; Shayfull, Z.; Nasir, S. M.; Hazwan, M. H. M.

2017-09-01

In injection moulding process, the defects will always encountered and affected the final product shape and functionality. This study is concerning on minimizing warpage and optimizing the process parameter of injection moulding part. Apart from eliminating product wastes, this project also giving out best recommended parameters setting. This research studied on five parameters. The optimization showed that warpage have been improved 42.64% from 0.6524 mm to 0.30879 mm in Autodesk Moldflow Insight (AMI) simulation result and Genetic Algorithm (GA) respectively.

Study on the optimization of the deposition rate of planetary GaN-MOCVD films based on CFD simulation and the corresponding surface model

PubMed Central

Fei, Ze-yuan; Xu, Yi-feng; Wang, Jie; Fan, Bing-feng; Ma, Xue-jin; Wang, Gang

2018-01-01

Metal-organic chemical vapour deposition (MOCVD) is a key technique for fabricating GaN thin film structures for light-emitting and semiconductor laser diodes. Film uniformity is an important index to measure equipment performance and chip processes. This paper introduces a method to improve the quality of thin films by optimizing the rotation speed of different substrates of a model consisting of a planetary with seven 6-inch wafers for the planetary GaN-MOCVD. A numerical solution to the transient state at low pressure is obtained using computational fluid dynamics. To evaluate the role of the different zone speeds on the growth uniformity, single factor analysis is introduced. The results show that the growth rate and uniformity are strongly related to the rotational speed. Next, a response surface model was constructed by using the variables and the corresponding simulation results. The optimized combination of the matching of different speeds is also proposed as a useful reference for applications in industry, obtained by a response surface model and genetic algorithm with a balance between the growth rate and the growth uniformity. This method can save time, and the optimization can obtain the most uniform and highest thin film quality. PMID:29515883

Optimization design on breakdown voltage of AlGaN/GaN high-electron mobility transistor

NASA Astrophysics Data System (ADS)

Yang, Liu; Changchun, Chai; Chunlei, Shi; Qingyang, Fan; Yuqian, Liu

2016-12-01

Simulations are carried out to explore the possibility of achieving high breakdown voltage of GaN HEMT (high-electron mobility transistor). GaN cap layers with gradual increase in the doping concentration from 2 × 1016 to 5 × 1019 cm-3 of N-type and P-type cap are investigated, respectively. Simulation results show that HEMT with P-doped GaN cap layer shows more potential to achieve higher breakdown voltage than N-doped GaN cap layer under the same doping concentration. This is because the ionized net negative space charges in P-GaN cap layer could modulate the surface electric field which makes more contribution to RESURF effect. Furthermore, a novel GaN/AlGaN/GaN HEMT with P-doped GaN buried layer in GaN buffer between gate and drain electrode is proposed. It shows enhanced performance. The breakdown voltage of the proposed structure is 640 V which is increased by 12% in comparison to UID (un-intentionally doped) GaN/AlGaN/GaN HEMT. We calculated and analyzed the distribution of electrons' density. It is found that the depleted region is wider and electric field maximum value is induced at the left edge of buried layer. So the novel structure with P-doped GaN buried layer embedded in GaN buffer has the better improving characteristics of the power devices. Project supported by the National Basic Research Program of China (No. 2014CB339900) and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (No. 2015-0214.XY.K).

Biosurfactant-biopolymer driven microbial enhanced oil recovery (MEOR) and its optimization by an ANN-GA hybrid technique.

PubMed

Dhanarajan, Gunaseelan; Rangarajan, Vivek; Bandi, Chandrakanth; Dixit, Abhivyakti; Das, Susmita; Ale, Kranthikiran; Sen, Ramkrishna

2017-08-20

A lipopeptide biosurfactant produced by marine Bacillus megaterium and a biopolymer produced by thermophilic Bacillus licheniformis were tested for their application potential in the enhanced oil recovery. The crude biosurfactant obtained after acid precipitation effectively reduced the surface tension of deionized water from 70.5 to 28.25mN/m and the interfacial tension between lube oil and water from 18.6 to 1.5mN/m at a concentration of 250mgL -1 . The biosurfactant exhibited a maximum emulsification activity (E 24 ) of 81.66% against lube oil. The lipopeptide micelles were stabilized by addition of Ca 2+ ions to the biosurfactant solution. The oil recovery efficiency of Ca 2+ conditioned lipopeptide solution from a sand-packed column was optimized by using artificial neural network (ANN) modelling coupled with genetic algorithm (GA) optimization. Three important parameters namely lipopeptide concentration, Ca 2+ concentration and solution pH were considered for optimization studies. In order to further improve the recovery efficiency, a water soluble biopolymer produced by Bacillus licheniformis was used as a flooding agent after biosurfactant incubation. Upon ANN-GA optimization, 45% tertiary oil recovery was achieved, when biopolymer at a concentration of 3gL -1 was used as a flooding agent. Oil recovery was only 29% at optimal conditions predicted by ANN-GA, when only water was used as flooding solution. The important characteristics of biopolymers such as its viscosity, pore plugging capabilities and bio-cementing ability have also been tested. Thus, as a result of biosurfactant incubation and biopolymer flooding under the optimal process conditions, a maximum oil recovery of 45% was achieved. Therefore, this study is novel, timely and interesting for it showed the combined influence of biosurfactant and biopolymer on solubilisation and mobilization of oil from the soil. Copyright © 2017 Elsevier B.V. All rights reserved.

Study on the Electronic Transport Properties of Zigzag GaN Nanotubes

NASA Astrophysics Data System (ADS)

Li, Enling; Wang, Xiqiang; Hou, Liping; Zhao, Danna; Dai, Yuanbin; Wang, Xuewen

2011-02-01

The electronic transport properties of zigzag GaN nanotubes (n, 0) (4 <= n <= 9) have been calculated using the density functional theory and non-equilibrium Green's functions method. Firstly, the density functional theory (DFT) is used to optimize and calculate the electronic structure of GaNNTs (n, 0) (4<=n<=9). Secondly, DFT and non-equilibrium Green function (NEGF) method are also used to predict the electronic transport properties of GaNNTs two-probe system. The results showed: there is a corresponding relation between the electronic transport properties and the valley of state density of each GaNNT. In addition, the volt-ampere curve of GaNNT is approximately linear.

A prediction model of drug-induced ototoxicity developed by an optimal support vector machine (SVM) method.

PubMed

Zhou, Shu; Li, Guo-Bo; Huang, Lu-Yi; Xie, Huan-Zhang; Zhao, Ying-Lan; Chen, Yu-Zong; Li, Lin-Li; Yang, Sheng-Yong

2014-08-01

Drug-induced ototoxicity, as a toxic side effect, is an important issue needed to be considered in drug discovery. Nevertheless, current experimental methods used to evaluate drug-induced ototoxicity are often time-consuming and expensive, indicating that they are not suitable for a large-scale evaluation of drug-induced ototoxicity in the early stage of drug discovery. We thus, in this investigation, established an effective computational prediction model of drug-induced ototoxicity using an optimal support vector machine (SVM) method, GA-CG-SVM. Three GA-CG-SVM models were developed based on three training sets containing agents bearing different risk levels of drug-induced ototoxicity. For comparison, models based on naïve Bayesian (NB) and recursive partitioning (RP) methods were also used on the same training sets. Among all the prediction models, the GA-CG-SVM model II showed the best performance, which offered prediction accuracies of 85.33% and 83.05% for two independent test sets, respectively. Overall, the good performance of the GA-CG-SVM model II indicates that it could be used for the prediction of drug-induced ototoxicity in the early stage of drug discovery. Copyright © 2014 Elsevier Ltd. All rights reserved.

LROC assessment of non-linear filtering methods in Ga-67 SPECT imaging

NASA Astrophysics Data System (ADS)

De Clercq, Stijn; Staelens, Steven; De Beenhouwer, Jan; D'Asseler, Yves; Lemahieu, Ignace

2006-03-01

In emission tomography, iterative reconstruction is usually followed by a linear smoothing filter to make such images more appropriate for visual inspection and diagnosis by a physician. This will result in a global blurring of the images, smoothing across edges and possibly discarding valuable image information for detection tasks. The purpose of this study is to investigate which possible advantages a non-linear, edge-preserving postfilter could have on lesion detection in Ga-67 SPECT imaging. Image quality can be defined based on the task that has to be performed on the image. This study used LROC observer studies based on a dataset created by CPU-intensive Gate Monte Carlo simulations of a voxelized digital phantom. The filters considered in this study were a linear Gaussian filter, a bilateral filter, the Perona-Malik anisotropic diffusion filter and the Catte filtering scheme. The 3D MCAT software phantom was used to simulate the distribution of Ga-67 citrate in the abdomen. Tumor-present cases had a 1-cm diameter tumor randomly placed near the edges of the anatomical boundaries of the kidneys, bone, liver and spleen. Our data set was generated out of a single noisy background simulation using the bootstrap method, to significantly reduce the simulation time and to allow for a larger observer data set. Lesions were simulated separately and added to the background afterwards. These were then reconstructed with an iterative approach, using a sufficiently large number of MLEM iterations to establish convergence. The output of a numerical observer was used in a simplex optimization method to estimate an optimal set of parameters for each postfilter. No significant improvement was found for using edge-preserving filtering techniques over standard linear Gaussian filtering.

Optimization of ion-atomic beam source for deposition of GaN ultrathin films.

PubMed

Mach, Jindřich; Šamořil, Tomáš; Kolíbal, Miroslav; Zlámal, Jakub; Voborny, Stanislav; Bartošík, Miroslav; Šikola, Tomáš

2014-08-01

We describe the optimization and application of an ion-atomic beam source for ion-beam-assisted deposition of ultrathin films in ultrahigh vacuum. The device combines an effusion cell and electron-impact ion beam source to produce ultra-low energy (20-200 eV) ion beams and thermal atomic beams simultaneously. The source was equipped with a focusing system of electrostatic electrodes increasing the maximum nitrogen ion current density in the beam of a diameter of ≈15 mm by one order of magnitude (j ≈ 1000 nA/cm(2)). Hence, a successful growth of GaN ultrathin films on Si(111) 7 × 7 substrate surfaces at reasonable times and temperatures significantly lower (RT, 300 °C) than in conventional metalorganic chemical vapor deposition technologies (≈1000 °C) was achieved. The chemical composition of these films was characterized in situ by X-ray Photoelectron Spectroscopy and morphology ex situ using Scanning Electron Microscopy. It has been shown that the morphology of GaN layers strongly depends on the relative Ga-N bond concentration in the layers.

Spiral bacterial foraging optimization method: Algorithm, evaluation and convergence analysis

NASA Astrophysics Data System (ADS)

Kasaiezadeh, Alireza; Khajepour, Amir; Waslander, Steven L.

2014-04-01

A biologically-inspired algorithm called Spiral Bacterial Foraging Optimization (SBFO) is investigated in this article. SBFO, previously proposed by the same authors, is a multi-agent, gradient-based algorithm that minimizes both the main objective function (local cost) and the distance between each agent and a temporary central point (global cost). A random jump is included normal to the connecting line of each agent to the central point, which produces a vortex around the temporary central point. This random jump is also suitable to cope with premature convergence, which is a feature of swarm-based optimization methods. The most important advantages of this algorithm are as follows: First, this algorithm involves a stochastic type of search with a deterministic convergence. Second, as gradient-based methods are employed, faster convergence is demonstrated over GA, DE, BFO, etc. Third, the algorithm can be implemented in a parallel fashion in order to decentralize large-scale computation. Fourth, the algorithm has a limited number of tunable parameters, and finally SBFO has a strong certainty of convergence which is rare in existing global optimization algorithms. A detailed convergence analysis of SBFO for continuously differentiable objective functions has also been investigated in this article.

Genetic programming assisted stochastic optimization strategies for optimization of glucose to gluconic acid fermentation.

PubMed

Cheema, Jitender Jit Singh; Sankpal, Narendra V; Tambe, Sanjeev S; Kulkarni, Bhaskar D

2002-01-01

This article presents two hybrid strategies for the modeling and optimization of the glucose to gluconic acid batch bioprocess. In the hybrid approaches, first a novel artificial intelligence formalism, namely, genetic programming (GP), is used to develop a process model solely from the historic process input-output data. In the next step, the input space of the GP-based model, representing process operating conditions, is optimized using two stochastic optimization (SO) formalisms, viz., genetic algorithms (GAs) and simultaneous perturbation stochastic approximation (SPSA). These SO formalisms possess certain unique advantages over the commonly used gradient-based optimization techniques. The principal advantage of the GP-GA and GP-SPSA hybrid techniques is that process modeling and optimization can be performed exclusively from the process input-output data without invoking the detailed knowledge of the process phenomenology. The GP-GA and GP-SPSA techniques have been employed for modeling and optimization of the glucose to gluconic acid bioprocess, and the optimized process operating conditions obtained thereby have been compared with those obtained using two other hybrid modeling-optimization paradigms integrating artificial neural networks (ANNs) and GA/SPSA formalisms. Finally, the overall optimized operating conditions given by the GP-GA method, when verified experimentally resulted in a significant improvement in the gluconic acid yield. The hybrid strategies presented here are generic in nature and can be employed for modeling and optimization of a wide variety of batch and continuous bioprocesses.

A study of optical design and optimization of laser optics

NASA Astrophysics Data System (ADS)

Tsai, C.-M.; Fang, Yi-Chin

2013-09-01

This paper propose a study of optical design of laser beam shaping optics with aspheric surface and application of genetic algorithm (GA) to find the optimal results. Nd: YAG 355 waveband laser flat-top optical system, this study employed the Light tools LDS (least damped square) and the GA of artificial intelligence optimization method to determine the optimal aspheric coefficient and obtain the optimal solution. This study applied the aspheric lens with GA for the flattening of laser beams using collimated laser beam light, aspheric lenses in order to achieve best results.

Truss Optimization for a Manned Nuclear Electric Space Vehicle using Genetic Algorithms

NASA Technical Reports Server (NTRS)

Benford, Andrew; Tinker, Michael L.

2004-01-01

The purpose of this paper is to utilize the genetic algorithm (GA) optimization method for structural design of a nuclear propulsion vehicle. Genetic algorithms provide a guided, random search technique that mirrors biological adaptation. To verify the GA capabilities, other traditional optimization methods were used to generate results for comparison to the GA results, first for simple two-dimensional structures, and then for full-scale three-dimensional truss designs.

Twin InSb/GaAs quantum nano-stripes: Growth optimization and related properties

NASA Astrophysics Data System (ADS)

Narabadeesuphakorn, Phisut; Thainoi, Supachok; Tandaechanurat, Aniwat; Kiravittaya, Suwit; Nuntawong, Noppadon; Sopitopan, Suwat; Yordsri, Visittapong; Thanachayanont, Chanchana; Kanjanachuchai, Songphol; Ratanathammaphan, Somchai; Panyakeow, Somsak

2018-04-01

Growth of InSb/GaAs quantum nanostructures on GaAs substrate by using molecular beam epitaxy with low growth temperature and slow growth rate typically results in a mixture of isolated and paired nano-stripe structures, which are termed as single and twin nano-stripes, respectively. In this work, we investigate the growth conditions to maximize the number ratio between twin and single nano-stripes. The highest percentage of the twin nano-stripes of up to 59% was achieved by optimizing the substrate temperature and the nano-stripe growth rate. Transmission electron microscopy reveals the substantial size and height reduction of the buried nano-stripes. We also observed the Raman shift and photon emission from our twin nano-stripes. These twin nano-stripes are promising for spintronics and quantum computing devices.

Comparison of Structural Optimization Techniques for a Nuclear Electric Space Vehicle

NASA Technical Reports Server (NTRS)

Benford, Andrew

2003-01-01

The purpose of this paper is to utilize the optimization method of genetic algorithms (GA) for truss design on a nuclear propulsion vehicle. Genetic Algorithms are a guided, random search that mirrors Darwin s theory of natural selection and survival of the fittest. To verify the GA s capabilities, other traditional optimization methods were used to compare the results obtained by the GA's, first on simple 2-D structures, and eventually on full-scale 3-D truss designs.

Radiation dosimetry of (68)Ga-PSMA-11 (HBED-CC) and preliminary evaluation of optimal imaging timing.

PubMed

Afshar-Oromieh, Ali; Hetzheim, Henrik; Kübler, Wolfgang; Kratochwil, Clemens; Giesel, Frederik L; Hope, Thomas A; Eder, Matthias; Eisenhut, Michael; Kopka, Klaus; Haberkorn, Uwe

2016-08-01

The clinical introduction of (68)Ga-PSMA-11 ("HBED-CC") ligand targeting the prostate-specific membrane antigen (PSMA) has been regarded as a significant step forward in the diagnosis of prostate cancer (PCa). In this study, we provide human dosimetry and data on optimal timing of PET imaging after injection. Four patients with recurrent PCa were referred for (68)Ga-PSMA-11 PET/CT. Whole-body PET/CTlow-dose scans were conducted at 5 min, and 1, 2, 3, 4 and 5 h after injection of 152-198 MBq (68)Ga-PSMA-11. Organs of moderate to high uptake were used as source organs; their total activity was determined at all measured time points. Time-activity curves were created for each source organ as well as for the remainder. The radiation exposure of a (68)Ga-PSMA-11 PET was identified using the OLINDA-EXM software. In addition, tracer uptake was measured in 16 sites of metastases. The highest tracer uptake was observed in the kidneys, liver, upper large intestine, and the urinary bladder. Mean organ doses were: kidneys 0.262 ± 0.098 mGy/MBq, liver 0.031 ± 0.004 mGy/MBq, upper large intestine 0.054 ± 0.041 mGy/MBq, urinary bladder 0.13 ± 0.059 mGy/MBq. The calculated mean effective dose was 0.023 ± 0.004 mSv/MBq (=0.085 ± 0.015 rem/mCi). Most tumor lesions (n = 16) were visible at 3 h p.i., while at all other time points many were not qualitatively present (10/16 visible at 1 h p.i.). The mean effective dose of a (68)Ga-PSMA-11 PET is 0.023 mSv/MBq. A 3-h delay after injection was optimal timing for (68)Ga-PSMA-11 PET/CT in this patient cohort.

Optimal power flow with optimal placement TCSC device on 500 kV Java-Bali electrical power system using genetic Algorithm-Taguchi method

NASA Astrophysics Data System (ADS)

Apribowo, Chico Hermanu Brillianto; Ibrahim, Muhammad Hamka; Wicaksono, F. X. Rian

2018-02-01

The growing burden of the load and the complexity of the power system has had an impact on the need for optimization of power system operation. Optimal power flow (OPF) with optimal location placement and rating of thyristor controlled series capacitor (TCSC) is an effective solution used to determine the economic cost of operating the plant and regulate the power flow in the power system. The purpose of this study is to minimize the total cost of generation by placing the location and the optimal rating of TCSC using genetic algorithm-design of experiment techniques (GA-DOE). Simulation on Java-Bali system 500 kV with the amount of TCSC used by 5 compensator, the proposed method can reduce the generation cost by 0.89% compared to OPF without using TCSC.

Self-consistent optimization of [111]-AlGaInAs/InP MQWs structures lasing at 1.55 μm by a genetic algorithm

NASA Astrophysics Data System (ADS)

Saidi, Hosni; Msahli, Melek; Ben Dhafer, Rania; Ridene, Said

2017-12-01

Band structure and optical gain properties of [111]-oriented AlGaInAs/AlGaInAs-delta-InGaAs multi-quantum wells, subjected to piezoelectric field, for the near-infrared lasers diodes applications was proposed and investigated in this paper. By using genetic algorithm based on optimization technique we demonstrate that the structural parameters can be conveniently optimized to achieve high-efficiency laser diode performance at room temperature. In this work, significant optical gain for the wished emission wavelength at 1.55 μm and low threshold injection current are the optimization target. The end result of this optimization is a laser diode based on InP substrate using quaternary compound material of AlGaInAs in both quantum wells and barriers with different composition. It has been shown that the transverse electric polarized optical gain which reaches 3500 cm-1 may be acquired for λ = 1.55 μm with a threshold carrier density Nth≈1.31018cm-3, which is very promising to serve as an alternative active region for high-efficiency near-infrared lasers. Finally, from the design presented here, we show that it is possible to apply this technique to a different III-V compound semiconductors and wavelength ranging from deep-ultra-violet to far infrared.

New Passivation Methods of GaAs.

DTIC Science & Technology

1980-01-01

Fabrication of Thin Nitride Layers on GaAs 33 - 35 CHAPTER 7 Passivation of InGaAsP 36 - 37 CHAPTER 8 Emulsions on GaAs Surfaces 38 - 42 APPENDIX...not yet given any useful results. The deposition of SiO2 by using emulsions is pursued and first results on the possibility of GaAs doping are...glycol-tartaric acid based aqueous solution was used in order to anodically oxidise the gate notch after the source and drain ohmic contacts were formed

[Model and analysis of spectropolarimetric BRDF of painted target based on GA-LM method].

PubMed

Chen, Chao; Zhao, Yong-Qiang; Luo, Li; Pan, Quan; Cheng, Yong-Mei; Wang, Kai

2010-03-01

Models based on microfacet were used to describe spectropolarimetric BRDF (short for bidirectional reflectance distribution function) with experimental data. And the spectropolarimetric BRDF values of targets were measured with the comparison to the standard whiteboard, which was considered as Lambert and had a uniform reflectance rate up to 98% at arbitrary angle of view. And then the relationships between measured spectropolarimetric BRDF values and the angles of view, as well as wavelengths which were in a range of 400-720 nm were analyzed in details. The initial value needed to be input to the LM optimization method was difficult to get and greatly impacted the results. Therefore, optimization approach which combines genetic algorithm and Levenberg-Marquardt (LM) was utilized aiming to retrieve parameters of nonlinear models, and the initial values were obtained using GA approach. Simulated experiments were used to test the efficiency of the adopted optimization method. And the simulated experiment ensures the optimization method to have a good performance and be able to retrieve the parameters of nonlinear model efficiently. The correctness of the models was validated by real outdoor sampled data. The parameters of DoP model retrieved are the refraction index of measured targets. The refraction index of the same color painted target but with different materials was also obtained. Conclusion has been drawn that the refraction index from these two targets are very near and this slight difference could be understood by the difference in the conditions of paint targets' surface, not the material of the targets.

A Novel Growth Method To Improve the Quality of GaAs Nanowires Grown by Ga-Assisted Chemical Beam Epitaxy.

PubMed

García Núñez, Carlos; Braña, Alejandro F; López, Nair; García, Basilio J

2018-06-13

The successful synthesis of high crystalline quality and high aspect ratio GaAs nanowires (NWs) with a uniform diameter is needed to develop advanced applications beyond the limits established by thin film and bulk material properties. Vertically aligned GaAs NWs have been extensively grown by Ga-assisted vapor-liquid-solid (VLS) mechanism on Si(111) substrates, and they have been used as building blocks in photovoltaics, optoelectronics, electronics, and so forth. However, the nucleation of parasitic species such as traces and nanocrystals on the Si substrate surface during the NW growth could affect significantly the controlled nucleation of those NWs, and therefore the resulting performance of NW-based devices. Preventing the nucleation of parasitic species on the Si substrate is a matter of interest, because they could act as traps for gaseous precursors and/or chemical elements during VLS growth, drastically reducing the maximum length of grown NWs, affecting their morphology and structure, and reducing the NW density along the Si substrate surface. This work presents a novel and easy to develop growth method (i.e., without using advanced nanolithography techniques) to prevent the nucleation of parasitic species, while preserving the quality of GaAs NWs even for long duration growths. GaAs NWs are grown by Ga-assisted chemical beam epitaxy on oxidized Si(111) substrates using triethylgallium and tertiarybutylarsine precursors by a two-step-based growth method presented here; this method includes a growth interruption for an oxidation on air between both steps of growth, reducing the nucleation of parasitic crystals on the thicker SiO x capping layer during the second and longer growth step. VLS conditions are preserved overtime, resulting in a stable NW growth rate of around 6 μm/h for growth times up to 1 h. Resulting GaAs NWs have a high aspect ratio of 85 and average radius of 35 nm. We also report on the existence of characteristic reflection high

Lamb Wave Damage Quantification Using GA-Based LS-SVM.

PubMed

Sun, Fuqiang; Wang, Ning; He, Jingjing; Guan, Xuefei; Yang, Jinsong

2017-06-12

Lamb waves have been reported to be an efficient tool for non-destructive evaluations (NDE) for various application scenarios. However, accurate and reliable damage quantification using the Lamb wave method is still a practical challenge, due to the complex underlying mechanism of Lamb wave propagation and damage detection. This paper presents a Lamb wave damage quantification method using a least square support vector machine (LS-SVM) and a genetic algorithm (GA). Three damage sensitive features, namely, normalized amplitude, phase change, and correlation coefficient, were proposed to describe changes of Lamb wave characteristics caused by damage. In view of commonly used data-driven methods, the GA-based LS-SVM model using the proposed three damage sensitive features was implemented to evaluate the crack size. The GA method was adopted to optimize the model parameters. The results of GA-based LS-SVM were validated using coupon test data and lap joint component test data with naturally developed fatigue cracks. Cases of different loading and manufacturer were also included to further verify the robustness of the proposed method for crack quantification.

Lamb Wave Damage Quantification Using GA-Based LS-SVM

PubMed Central

Sun, Fuqiang; Wang, Ning; He, Jingjing; Guan, Xuefei; Yang, Jinsong

2017-01-01

Lamb waves have been reported to be an efficient tool for non-destructive evaluations (NDE) for various application scenarios. However, accurate and reliable damage quantification using the Lamb wave method is still a practical challenge, due to the complex underlying mechanism of Lamb wave propagation and damage detection. This paper presents a Lamb wave damage quantification method using a least square support vector machine (LS-SVM) and a genetic algorithm (GA). Three damage sensitive features, namely, normalized amplitude, phase change, and correlation coefficient, were proposed to describe changes of Lamb wave characteristics caused by damage. In view of commonly used data-driven methods, the GA-based LS-SVM model using the proposed three damage sensitive features was implemented to evaluate the crack size. The GA method was adopted to optimize the model parameters. The results of GA-based LS-SVM were validated using coupon test data and lap joint component test data with naturally developed fatigue cracks. Cases of different loading and manufacturer were also included to further verify the robustness of the proposed method for crack quantification. PMID:28773003

Design Optimization of Ge/GaAs-Based Heterojunction Gate-All-Around (GAA) Arch-Shaped Tunneling Field-Effect Transistor (A-TFET).

PubMed

Seo, Jae Hwa; Yoon, Young Jun; Kang, In Man

2018-09-01

The Ge/GaAs-based heterojunction gate-all-around (GAA) arch-shaped tunneling field-effect transistor (A-TFET) have been designed and optimized using technology computer-aided design (TCAD) simulations. In our previous work, the silicon-based A-TFET was designed and demonstrated. However, to progress the electrical characteristics of A-TFET, the III-V compound heterojunction structures which has enhanced electrical properties must be adopted. Thus, the germanium with gallium arsenide (Ge/GaAs) is considered as key materials of A-TFET. The proposed device has a Ge-based p-doped source, GaAs-based i-doped channel and GaAs-based n-doped drain. Due to the critical issues of device performances, the doping concentration of source and channel region (Dsource, Dchannel), height of source region (Hsource) and epitaxially grown thickness of channel (tepi) was selected as design optimization variables of Ge/GaAs-based GAA A-TFET. The DC characteristics such as on-state current (ion), off-state current (ioff), subthreshold-swing (S) were of extracted and analyzed. Finally, the proposed device has a gate length (LG) of 90 nm, Dsource 5 × 1019 cm-3, Dchannel of 1018 cm-3, tepi of 4 nm, Hsource of 90 nm, R of 10 nm and demonstrate an ion of 2 mA/μm, S of 12.9 mV/dec.

Promoting Charge Separation and Injection by Optimizing the Interfaces of GaN:ZnO Photoanode for Efficient Solar Water Oxidation.

PubMed

Wang, Zhiliang; Zong, Xu; Gao, Yuying; Han, Jingfeng; Xu, Zhiqiang; Li, Zheng; Ding, Chunmei; Wang, Shengyang; Li, Can

2017-09-13

Photoelectrochemical water splitting provides an attractive way to store solar energy in molecular hydrogen as a kind of sustainable fuel. To achieve high solar conversion efficiency, the most stringent criteria are effective charge separation and injection in electrodes. Herein, efficient photoelectrochemical water oxidation is realized by optimizing charge separation and surface charge transfer of GaN:ZnO photoanode. The charge separation can be greatly improved through modified moisture-assisted nitridation and HCl acid treatment, by which the interfaces in GaN:ZnO solid solution particles are optimized and recombination centers existing at the interfaces are depressed in GaN:ZnO photoanode. Moreover, a multimetal phosphide of NiCoFeP was employed as water oxidation cocatalyst to improve the charge injection at the photoanode/electrolyte interface. Consequently, it significantly decreases the overpotential and brings the photocurrent to a benchmark of 3.9 mA cm -2 at 1.23 V vs RHE and a solar conversion efficiency over 1% was obtained.

Short-wavelength light beam in situ monitoring growth of InGaN/GaN green LEDs by MOCVD

PubMed Central

2012-01-01

In this paper, five-period InGaN/GaN multiple quantum well green light-emitting diodes (LEDs) were grown by metal organic chemical vapor deposition with 405-nm light beam in situ monitoring system. Based on the signal of 405-nm in situ monitoring system, the related information of growth rate, indium composition and interfacial quality of each InGaN/GaN QW were obtained, and thus, the growth conditions and structural parameters were optimized to grow high-quality InGaN/GaN green LED structure. Finally, a green LED with a wavelength of 509 nm was fabricated under the optimal parameters, which was also proved by ex situ characterization such as high-resolution X-ray diffraction, photoluminescence, and electroluminescence. The results demonstrated that short-wavelength in situ monitoring system was a quick and non-destroyed tool to provide the growth information on InGaN/GaN, which would accelerate the research and development of GaN-based green LEDs. PMID:22650991

Ultralow-voltage-drop GaN/InGaN/GaN tunnel junctions with 12% indium content

NASA Astrophysics Data System (ADS)

Akyol, Fatih; Zhang, Yuewei; Krishnamoorthy, Sriram; Rajan, Siddharth

2017-12-01

We report a combination of highly doped layers and polarization engineering that achieves highly efficient blue-transparent GaN/InGaN/GaN tunnel junctions (In content = 12%). NPN diode structures with a low voltage drop of 4.04 V at 5 kA/cm2 and a differential resistance of 6.51 × 10-5 Ω·cm2 at 3 kA/cm2 were obtained. The tunnel junction design with n++-GaN (Si: 5 × 1020 cm-3)/3 nm p++-In0.12Ga0.88N (Mg: 1.5 × 1020 cm-3)/p++-GaN (Mg: 5 × 1020 cm-3) showed the best device performance. Device simulations agree well with the experimentally determined optimal design. The combination of low In composition and high doping can facilitate lower tunneling resistance for blue-transparent light-emitting diodes.

Optimal activation condition of nonpolar a-plane p-type GaN layers grown on r-plane sapphire substrates by MOCVD

NASA Astrophysics Data System (ADS)

Son, Ji-Su; Hyeon Baik, Kwang; Gon Seo, Yong; Song, Hooyoung; Hoon Kim, Ji; Hwang, Sung-Min; Kim, Tae-Geun

2011-07-01

The optimal conditions of p-type activation for nonpolar a-plane (1 1 -2 0) p-type GaN films on r-plane (1 -1 0 2) sapphire substrates with various off-axis orientations have been investigated. Secondary ion mass spectrometry (SIMS) measurements show that Mg doping concentrations of 6.58×10 19 cm -3 were maintained in GaN during epitaxial growth. The samples were activated at various temperatures and periods of time in air, oxygen (O 2) and nitrogen (N 2) gas ambient by conventional furnace annealing (CFA) and rapid thermal annealing (RTA). The activation of nonpolar a-plane p-type GaN was successful in similar annealing times and temperatures when compared with polar c-plane p-type GaN. However, activation ambient of nonpolar a-plane p-type GaN was clearly different, where a-plane p-type GaN was effectively activated in air ambient. Photoluminescence shows that the optical properties of Mg-doped a-plane GaN samples are enhanced when activated in air ambient.

Good manufacturing practice production of [68Ga]Ga-ABY-025 for HER2 specific breast cancer imaging

PubMed Central

Velikyan, Irina; Wennborg, Anders; Feldwisch, Joachim; Lindman, Henrik; Carlsson, Jörgen; Sörensen, Jens

2016-01-01

Therapies targeting human epidermal growth factor receptor type 2 (HER2) have revolutionized breast cancer treatment, but require invasive biopsies and rigorous histopathology for optimal patient stratification. A non-invasive and quantitative diagnostic method such as positron emission tomography (PET) for the pre-therapeutic determination of the presence and density of the HER2 would significantly improve patient management efficacy and treatment cost. The essential part of the PET methodology is the production of the radiopharmaceutical in compliance with good manufacturing practice (GMP). The use of generator produced positron emitting 68Ga radionuclide would provide worldwide accessibility of the agent. GMP compliant, reliable and highly reproducible production of [68Ga]Ga-ABY-025 with control over the product peptide concentration and amount of radioactivity was accomplished within one hour. Two radiopharmaceuticals were developed differing in the total peptide content and were validated independently. The specific radioactivity could be kept similar throughout the study, and it was 6-fold higher for the low peptide content radiopharmaceutical. Intrapatient comparison of the two peptide doses allowed imaging optimization. The high peptide content decreased the uptake in healthy tissue, in particular liver, improving image contrast. The later imaging time points enhanced the contrast. The combination of high peptide content radiopharmaceutical and whole-body imaging at 2 hours post injection appeared to be optimal for routine clinical use. PMID:27186441

Method of plasma etching Ga-based compound semiconductors

DOEpatents

Qiu, Weibin; Goddard, Lynford L.

2012-12-25

A method of plasma etching Ga-based compound semiconductors includes providing a process chamber and a source electrode adjacent to the process chamber. The process chamber contains a sample comprising a Ga-based compound semiconductor. The sample is in contact with a platen which is electrically connected to a first power supply, and the source electrode is electrically connected to a second power supply. The method includes flowing SiCl.sub.4 gas into the chamber, flowing Ar gas into the chamber, and flowing H.sub.2 gas into the chamber. RF power is supplied independently to the source electrode and the platen. A plasma is generated based on the gases in the process chamber, and regions of a surface of the sample adjacent to one or more masked portions of the surface are etched to create a substantially smooth etched surface including features having substantially vertical walls beneath the masked portions.

Optimization of Post-selenization Process of Co-sputtered CuIn and CuGa Precursor for 11.19% Efficiency Cu(In, Ga)Se2 Solar Cells

NASA Astrophysics Data System (ADS)

Cheng, Ke; Han, Kaikai; Kuang, Zhongcheng; Jin, Ranran; Hu, Junxia; Guo, Longfei; Liu, Ya; Lu, Zhangbo; Du, Zuliang

2017-04-01

In this work, CuInGa alloy precursor films are fabricated by co-sputtering of CuIn and CuGa targets simultaneously. After selenization in a tube-type rapid thermal annealing system under a Se atmosphere, the Cu(In, Ga)Se2 (CIGS) absorber layers are obtained. Standard soda lime glass (SLG)/Mo/CIGS/CdS/i-ZnO/ITO/Ag grid structural solar cells are fabricated based on the selenized CIGS absorbers. The influences of selenization temperatures on the composition, crystallinity, and device performances are systematically investigated by x-ray energy dispersive spectroscopy, x-ray diffraction, Raman spectroscopy, and the current density-voltage ( J- V) measurement. It is found that the elemental ratio of Cu/(In + Ga) strongly depends on the selenization temperatures. Because of the appropriate elemental ratio, a 9.92% conversion efficiency is reached for the CIGS absorber selenized at 560°C. After the additional optimization by pre-annealing treatment at 280°C before the selenization, a highest conversion efficiency of 11.19% with a open-circuit ( V oc) of 456 mV, a short-circuit ( J sc) of 40.357 mA/cm2 and a fill factor of 60.82% without antireflection coating has been achieved. Above 13% efficiency improvement was achievable. Our experimental findings presented in this work demonstrate that the post-selenization of co-sputtered CuIn and CuGa precursor is a promising way to fabricate high quality CIGS absorbers.

AlGaAs-GaAs cascade solar cell

NASA Technical Reports Server (NTRS)

Lamorte, M. F.; Abbott, D. H.

1980-01-01

Computer modeling studies are reported for a monolithic, two junction, cascade solar cell using the AlGaAs GaAs materials combination. An optimum design was obtained through a serial optimization procedure by which conversion efficiency is maximized for operation at 300 K, AM 0, and unity solar concentration. Under these conditions the upper limit on efficiency was shown to be in excess of 29 percent, provided surface recombination velocity did not exceed 10,000 cm/sec.

Modeling and Optimization of Sub-Wavelength Grating Nanostructures on Cu(In,Ga)Se2 Solar Cell

NASA Astrophysics Data System (ADS)

Kuo, Shou-Yi; Hsieh, Ming-Yang; Lai, Fang-I.; Liao, Yu-Kuang; Kao, Ming-Hsuan; Kuo, Hao-Chung

2012-10-01

In this study, an optical simulation of Cu(In,Ga)Se2 (CIGS) solar cells by the rigorous coupled-wave analysis (RCWA) method is carried out to investigate the effects of surface morphology on the light absorption and power conversion efficiencies. Various sub-wavelength grating (SWG) nanostructures of periodic ZnO:Al (AZO) on CIGS solar cells were discussed in detail. SWG nanostructures were used as efficient antireflection layers. From the simulation results, AZO structures with nipple arrays effectively suppress the Fresnel reflection compared with nanorod- and cone-shaped AZO structures. The optimized reflectance decreased from 8.44 to 3.02% and the efficiency increased from 14.92 to 16.11% accordingly. The remarkable enhancement in light harvesting is attributed to the gradient refractive index profile between the AZO nanostructures and air.

Processing of AlGaAs/GaAs quantum-cascade structures for terahertz laser

NASA Astrophysics Data System (ADS)

Szerling, Anna; Kosiel, Kamil; Szymański, Michał; Wasilewski, Zbig; Gołaszewska, Krystyna; Łaszcz, Adam; Płuska, Mariusz; Trajnerowicz, Artur; Sakowicz, Maciej; Walczakowski, Michał; Pałka, Norbert; Jakieła, Rafał; Piotrowska, Anna

2015-01-01

We report research results with regard to AlGaAs/GaAs structure processing for THz quantum-cascade lasers (QCLs). We focus on the processes of Ti/Au cladding fabrication for metal-metal waveguides and wafer bonding with indium solder. Particular emphasis is placed on optimization of technological parameters for the said processes that result in working devices. A wide range of technological parameters was studied using test structures and the analysis of their electrical, optical, chemical, and mechanical properties performed by electron microscopic techniques, energy dispersive x-ray spectrometry, secondary ion mass spectroscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, and circular transmission line method. On that basis, a set of technological parameters was selected for the fabrication of devices lasing at a maximum temperature of 130 K from AlGaAs/GaAs structures grown by means of molecular beam epitaxy. Their resulting threshold-current densities were on a level of 1.5 kA/cm2. Furthermore, initial stage research regarding fabrication of Cu-based claddings is reported as these are theoretically more promising than the Au-based ones with regard to low-loss waveguide fabrication for THz QCLs.

Implementation of atomic layer deposition-based AlON gate dielectrics in AlGaN/GaN MOS structure and its physical and electrical properties

NASA Astrophysics Data System (ADS)

Nozaki, Mikito; Watanabe, Kenta; Yamada, Takahiro; Shih, Hong-An; Nakazawa, Satoshi; Anda, Yoshiharu; Ueda, Tetsuzo; Yoshigoe, Akitaka; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

2018-06-01

Alumina incorporating nitrogen (aluminum oxynitride; AlON) for immunity against charge injection was grown on a AlGaN/GaN substrate through the repeated atomic layer deposition (ALD) of AlN layers and in situ oxidation in ozone (O3) ambient under optimized conditions. The nitrogen distribution was uniform in the depth direction, the composition was controllable over a wide range (0.5–32%), and the thickness could be precisely controlled. Physical analysis based on synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) revealed that harmful intermixing at the insulator/AlGaN interface causing Ga out-diffusion in the gate stack was effectively suppressed by this method. AlON/AlGaN/GaN MOS capacitors were fabricated, and they had excellent electrical properties and immunity against electrical stressing as a result of the improved interface stability.

Significantly improved surface morphology of N-polar GaN film grown on SiC substrate by the optimization of V/III ratio

NASA Astrophysics Data System (ADS)

Deng, Gaoqiang; Zhang, Yuantao; Yu, Ye; Yan, Long; Li, Pengchong; Han, Xu; Chen, Liang; Zhao, Degang; Du, Guotong

2018-04-01

In this paper, N-polar GaN films with different V/III ratios were grown on vicinal C-face SiC substrates by metalorganic chemical vapor deposition. During the growth of N-polar GaN film, the V/III ratio was controlled by adjusting the molar flow rate of ammonia while keeping the trimethylgallium flow rate unchanged. The influence of the V/III ratio on the surface morphology of N-polar GaN film has been studied. We find that the surface root mean square roughness of N-polar GaN film over an area of 20 × 20 μm2 can be reduced from 8.13 to 2.78 nm by optimization of the V/III ratio. Then, using the same growth conditions, N-polar InGaN/GaN multiple quantum wells (MQWs) light-emitting diodes (LEDs) were grown on the rough and the smooth N-polar GaN templates, respectively. Compared with the LED grown on the rough N-polar GaN template, dramatically improved interface sharpness and luminescence uniformity of the InGaN/GaN MQWs are achieved for the LED grown on the smooth N-polar GaN template.

Multicycle rapid thermal annealing optimization of Mg-implanted GaN: Evolution of surface, optical, and structural properties

NASA Astrophysics Data System (ADS)

Greenlee, Jordan D.; Feigelson, Boris N.; Anderson, Travis J.; Tadjer, Marko J.; Hite, Jennifer K.; Mastro, Michael A.; Eddy, Charles R.; Hobart, Karl D.; Kub, Francis J.

2014-08-01

The first step of a multi-cycle rapid thermal annealing process was systematically studied. The surface, structure, and optical properties of Mg implanted GaN thin films annealed at temperatures ranging from 900 to 1200 °C were investigated by Raman spectroscopy, photoluminescence, UV-visible spectroscopy, atomic force microscopy, and Nomarski microscopy. The GaN thin films are capped with two layers of in-situ metal organic chemical vapor deposition -grown AlN and annealed in 24 bar of N2 overpressure to avoid GaN decomposition. The crystal quality of the GaN improves with increasing annealing temperature as confirmed by UV-visible spectroscopy and the full widths at half maximums of the E2 and A1 (LO) Raman modes. The crystal quality of films annealed above 1100 °C exceeds the quality of the as-grown films. At 1200 °C, Mg is optically activated, which is determined by photoluminescence measurements. However, at 1200 °C, the GaN begins to decompose as evidenced by pit formation on the surface of the samples. Therefore, it was determined that the optimal temperature for the first step in a multi-cycle rapid thermal anneal process should be conducted at 1150 °C due to crystal quality and surface morphology considerations.

Simulation of thermal management in AlGaN/GaN HEMTs with integrated diamond heat spreaders

NASA Astrophysics Data System (ADS)

Wang, A.; Tadjer, M. J.; Calle, F.

2013-05-01

We investigated the impact of diamond heat spreading layers on the performance of AlGaN/GaN high-electron-mobility-transistors (HEMTs). A finite element method was used to simulate the thermal and electrical characteristics of the devices under dc and pulsed operation conditions. The results show that the device performance can be improved significantly by optimized heat spreading, an effect strongly dependent on the lateral thermal conductivity of the initial several micrometers of diamond deposition. Of crucial importance is the proximity of the diamond layer to the heat source, which makes this method advantageous over other thermal management procedures, especially for the device in pulsed operation. In this case, the self-heating effect can be suppressed, and it is not affected by either the substrate or its thermal boundary resistance at the GaN/substrate at wider pulses. The device with a 5 µm diamond layer can present 10.5% improvement of drain current, and the self-heating effect can be neglected for a 100 ns pulse width at 1 V gate and 20 V drain voltage.

Efficient Ga(As)Sb quantum dot emission in AlGaAs by GaAs intermediate layer

NASA Astrophysics Data System (ADS)

Loeber, Thomas Henning; Richter, Johannes; Strassner, Johannes; Heisel, Carina; Kimmle, Christina; Fouckhardt, Henning

2013-03-01

Ga(As)Sb quantum dots (QDs) are epitaxially grown in AlGaAs/GaAs in the Stranski-Krastanov mode. In the recent past we achieved Ga(As)Sb QDs in GaAs with an extremely high dot density of 9.8•1010 cm-2 by optimization of growth temperature, Sb/Ga flux pressure ratio, and coverage. Additionally, the QD emission wavelength could be chosen precisely with these growth parameters in the range between 876 and 1035 nm. Here we report a photoluminescence (PL) intensity improvement for the case with AlGaAs barriers. Again growth parameters and layer composition are varied. The aluminium content is varied between 0 and 90%. Reflectance anisotropy spectroscopy (RAS) is used as insitu growth control to determine growth rate, layer thickness, and AlGaAs composition. Ga(As)Sb QDs, directly grown in AlxGa1-xAs emit no PL signal, even with a very low x ≈ 0.1. With additional around 10 nm thin GaAs intermediate layers between the Ga(As)Sb QDs and the AlGaAs barriers PL signals are detected. Samples with 4 QD layers and AlxGa1-xAs/GaAs barriers in between are grown. The thickness and composition of the barriers are changed. Depending on these values PL intensity is more than 4 times as high as in the case with simple GaAs barriers. With these results efficient Ga(As)Sb QD lasers are realized, so far only with pure GaAs barriers. Our index-guided broad area lasers operate continuous-wave (cw) @ 90 K, emit optical powers of more than 2•50 mW and show a differential quantum efficiency of 54% with a threshold current density of 528 A/cm2.

A new method of making ohmic contacts to p-GaN

NASA Astrophysics Data System (ADS)

Hernández-Gutierrez, C. A.; Kudriavtsev, Yu.; Mota, Esteban; Hernández, A. G.; Escobosa-Echavarría, A.; Sánchez-Resendiz, V.; Casallas-Moreno, Y. L.; López-López, M.

2016-12-01

The structural, chemical, and electrical characteristics of In+ ion-implanted Au/Ni, Au/Nb and Au/W ohmic contacts to p-GaN were investigated. After the preparation of Ni, Nb and W electrode on the surface of p-GaN, the metal/p-GaN contact interface was implanted by 30 keV In+ ions with an implantation dose of 5 × 1015 ions/cm2 at room temperature to form a thin layer of InxGa1-xN located at the metal-semiconductor interface, achieved to reduce the specific contact resistance due to the improving quantum tunneling transport trough to the structure. The characterization was carried out by high-resolution X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and secondary ion mass spectrometry to investigate the formation of ternary alloy, re-crystallization by rapid thermal annealing process after In+ implantation, and the redistribution of elements. The specific contact resistance was extracted by current-voltage (I-V) curves using transmission line method; the lowest specific contact resistance of 2.5 × 10-4 Ωcm2 was achieved for Au/Ni/p-InxGa1-xN/p-GaN ohmic contacts.

GaAsP on GaP top solar cells

NASA Technical Reports Server (NTRS)

Mcneely, J. B.; Negley, G. H.; Barnett, A. M.

1985-01-01

GaAsP on GaP top solar cells as an attachment to silicon bottom solar cells are being developed. The GaAsP on GaP system offers several advantages for this top solar cell. The most important is that the gallium phosphide substrate provides a rugged, transparent mechanical substrate which does not have to be removed or thinned during processing. Additional advantages are that: (1) gallium phosphide is more oxidation resistant than the III-V aluminum compounds, (2) a range of energy band gaps higher than 1.75 eV is readily available for system efficiency optimization, (3) reliable ohmic contact technology is available from the light-emitting diode industry, and (4) the system readily lends itself to graded band gap structures for additional increases in efficiency.

Electron-nuclear spin dynamics of Ga centers in GaAsN dilute nitride semiconductors probed by pump-probe spectroscopy

NASA Astrophysics Data System (ADS)

Sandoval-Santana, J. C.; Ibarra-Sierra, V. G.; Azaizia, S.; Carrère, H.; Bakaleinikov, L. A.; Kalevich, V. K.; Ivchenko, E. L.; Marie, X.; Amand, T.; Balocchi, A.; Kunold, A.

2018-03-01

We propose an experimental procedure to track the evolution of electronic and nuclear spins in Ga2+ centers in GaAsN dilute semiconductors. The method is based on a pump-probe scheme that enables to monitor the time evolution of the three components of the electronic and nuclear spin variables. In contrast to other characterization methods, as nuclear magnetic resonance, this one only needs moderate magnetic fields (B≈ 10 mT), and does not require microwave irradiation. Specifically, we carry out a series of tests for different experimental conditions in order to optimize the procedure for maximum sensitivity in the measurement of the circular degree of polarization. Based on previous experimental results and the theoretical calculations presented here, we estimate that the method could yield a time resolution of about 10ps.

High In-content InGaN nano-pyramids: Tuning crystal homogeneity by optimized nucleation of GaN seeds

NASA Astrophysics Data System (ADS)

Bi, Zhaoxia; Gustafsson, Anders; Lenrick, Filip; Lindgren, David; Hultin, Olof; Wallenberg, L. Reine; Ohlsson, B. Jonas; Monemar, Bo; Samuelson, Lars

2018-01-01

Uniform arrays of submicron hexagonal InGaN pyramids with high morphological and material homogeneity, reaching an indium composition of 20%, are presented in this work. The pyramids were grown by selective area metal-organic vapor phase epitaxy and nucleated from small openings in a SiN mask. The growth selectivity was accurately controlled with diffusion lengths of the gallium and indium species, more than 1 μm on the SiN surface. High material homogeneity of the pyramids was achieved by inserting a precisely formed GaN pyramidal seed prior to InGaN growth, leading to the growth of well-shaped InGaN pyramids delimited by six equivalent {" separators="| 10 1 ¯ 1 } facets. Further analysis reveals a variation in the indium composition to be mediated by competing InGaN growth on two types of crystal planes, {" separators="| 10 1 ¯ 1 } and (0001). Typically, the InGaN growth on {" separators="| 10 1 ¯ 1 } planes is much slower than on the (0001) plane. The formation of the (0001) plane and the growth of InGaN on it were found to be dependent on the morphology of the GaN seeds. We propose growth of InGaN pyramids seeded by {" separators="| 10 1 ¯ 1 }-faceted GaN pyramids as a mean to avoid InGaN material grown on the otherwise formed (0001) plane, leading to a significant reduction of variations in the indium composition in the InGaN pyramids. The InGaN pyramids in this work can be used as a high-quality template for optoelectronic devices having indium-rich active layers, with a potential of reaching green, yellow, and red emissions for LEDs.

Optimization of the interfacial misfit array growth mode of GaSb epilayers on GaAs substrate

NASA Astrophysics Data System (ADS)

Benyahia, D.; Kubiszyn, Ł.; Michalczewski, K.; Kębłowski, A.; Martyniuk, P.; Piotrowski, J.; Rogalski, A.

2018-02-01

The growth of undoped GaSb epilayers on GaAs (0 0 1) substrates with 2° offcut towards 〈1 1 0〉, by molecular beam epitaxy system (MBE) at low growth temperature is reported. The strain due to the lattice mismatch of 7.78% is relieved spontaneously at the interface by using interfacial misfit array (IMF) growth mode. Three approaches of this technique are investigated. The difference consists in the steps after the growth of GaAs buffer layer. These steps are the desorption of arsenic from the GaAs surface, and the cooling down to the growth temperature, under or without antimony flux. The X-ray analysis and the transmission electron microscopy point out that desorption of arsenic followed by the substrate temperature decreasing under no group V flux leads to the best structural and crystallographic properties in the GaSb layer. It is found that the 2 μm-thick GaSb is 99.8% relaxed, and that the strain is relieved by the formation of a periodic array of 90° pure-edge dislocations along the [1 1 0] direction with a periodicity of 5.6 nm.

Multicycle rapid thermal annealing optimization of Mg-implanted GaN: Evolution of surface, optical, and structural properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greenlee, Jordan D., E-mail: jordan.greenlee.ctr@nrl.navy.mil; Feigelson, Boris N.; Anderson, Travis J.

2014-08-14

The first step of a multi-cycle rapid thermal annealing process was systematically studied. The surface, structure, and optical properties of Mg implanted GaN thin films annealed at temperatures ranging from 900 to 1200 °C were investigated by Raman spectroscopy, photoluminescence, UV-visible spectroscopy, atomic force microscopy, and Nomarski microscopy. The GaN thin films are capped with two layers of in-situ metal organic chemical vapor deposition -grown AlN and annealed in 24 bar of N{sub 2} overpressure to avoid GaN decomposition. The crystal quality of the GaN improves with increasing annealing temperature as confirmed by UV-visible spectroscopy and the full widths at halfmore » maximums of the E{sub 2} and A{sub 1} (LO) Raman modes. The crystal quality of films annealed above 1100 °C exceeds the quality of the as-grown films. At 1200 °C, Mg is optically activated, which is determined by photoluminescence measurements. However, at 1200 °C, the GaN begins to decompose as evidenced by pit formation on the surface of the samples. Therefore, it was determined that the optimal temperature for the first step in a multi-cycle rapid thermal anneal process should be conducted at 1150 °C due to crystal quality and surface morphology considerations.« less

Radiation hardness of Ga0.5In0.5 P/GaAs tandem solar cells

NASA Technical Reports Server (NTRS)

Kurtz, Sarah R.; Olson, J. M.; Bertness, K. A.; Friedman, D. J.; Kibbler, A.; Cavicchi, B. T.; Krut, D. D.

1991-01-01

The radiation hardness of a two-junction monolithic Ga sub 0.5 In sub 0.5 P/GaAs cell with tunnel junction interconnect was investigated. Related single junction cells were also studied to identify the origins of the radiation losses. The optimal design of the cell is discussed. The air mass efficiency of an optimized tandem cell after irradiation with 10(exp 15) cm (-2) 1 MeV electrons is estimated to be 20 percent using currently available technology.

A comparison of GaAs and Si hybrid solar power systems

NASA Technical Reports Server (NTRS)

Heinbockel, J. H.; Roberts, A. S., Jr.

1977-01-01

Five different hybrid solar power systems using silicon solar cells to produce thermal and electric power are modeled and compared with a hybrid system using a GaAs cell. Among the indices determined are capital cost per unit electric power plus mechanical power, annual cost per unit electric energy, and annual cost per unit electric plus mechanical work. Current costs are taken to be $35,000/sq m for GaAs cells with an efficiency of 15% and $1000/sq m for Si cells with an efficiency of 10%. It is shown that hybrid systems can be competitive with existing methods of practical energy conversion. Limiting values for annual costs of Si and GaAs cells are calculated to be 10.3 cents/kWh and 6.8 cents/kWh, respectively. Results for both systems indicate that for a given flow rate there is an optimal operating condition for minimum cost photovoltaic output. For Si cell costs of $50/sq m optimal performance can be achieved at concentrations of about 10; for GaAs cells costing 1000/sq m, optimal performance can be obtained at concentrations of around 100. High concentration hybrid systems offer a distinct cost advantage over flat systems.

Fuel Optimal, Finite Thrust Guidance Methods to Circumnavigate with Lighting Constraints

NASA Astrophysics Data System (ADS)

Prince, E. R.; Carr, R. W.; Cobb, R. G.

This paper details improvements made to the authors' most recent work to find fuel optimal, finite-thrust guidance to inject an inspector satellite into a prescribed natural motion circumnavigation (NMC) orbit about a resident space object (RSO) in geosynchronous orbit (GEO). Better initial guess methodologies are developed for the low-fidelity model nonlinear programming problem (NLP) solver to include using Clohessy- Wiltshire (CW) targeting, a modified particle swarm optimization (PSO), and MATLAB's genetic algorithm (GA). These initial guess solutions may then be fed into the NLP solver as an initial guess, where a different NLP solver, IPOPT, is used. Celestial lighting constraints are taken into account in addition to the sunlight constraint, ensuring that the resulting NMC also adheres to Moon and Earth lighting constraints. The guidance is initially calculated given a fixed final time, and then solutions are also calculated for fixed final times before and after the original fixed final time, allowing mission planners to choose the lowest-cost solution in the resulting range which satisfies all constraints. The developed algorithms provide computationally fast and highly reliable methods for determining fuel optimal guidance for NMC injections while also adhering to multiple lighting constraints.

Theoretical research on bandgap of H-saturated Ga1-xAlxN nanowires

NASA Astrophysics Data System (ADS)

Xia, Sihao; Liu, Lei; Kong, Yike; Wang, Honggang; Wang, Meishan

2017-01-01

Based on first-principles plane-wave ultra-soft pseudopotential method, bandgaps of Ga1-xAlxN nanowires with different diameters and different Al constituents are calculated. After the optimization of the model, the bandgaps are achieved. According to the results, the bandgap of Ga1-xAlxN decreases with increasing diameter and finally, closed to that of the bulk. In addition, with increasing Al constituent, the bandgaps of Ga1-xAlxN nanowires increase. However, the amount of the increase is lower than that of the bulk Ga1-xAlxN with the increase of Al constituent.

Growth condition optimization and mobility enhancement through prolonging the GaN nuclei coalescence process of AlGaN/AlN/GaN structure

NASA Astrophysics Data System (ADS)

He, Xiao-Guang; Zhao, De-Gang; Jiang, De-Sheng; Zhu, Jian-Jun; Chen, Ping; Liu, Zong-Shun; Le, Ling-Cong; Yang, Jing; Li, Xiao-Jing; Zhang, Shu-Ming; Yang, Hui

2015-09-01

AlGaN/AlN/GaN structures are grown by metalorganic vapor phase epitaxy on sapphire substrates. Influences of AlN interlayer thickness, AlGaN barrier thickness, and Al composition on the two-dimensional electron gas (2DEG) performance are investigated. Lowering the V/III ratio and enhancing the reactor pressure at the initial stage of the high-temperature GaN layer growth will prolong the GaN nuclei coalescence process and effectively improve the crystalline quality and the interface morphology, diminishing the interface roughness scattering and improving 2DEG mobility. AlGaN/AlN/GaN structure with 2DEG sheet density of 1.19 × 1013 cm-2, electron mobility of 2101 cm2·V-1·s-1, and square resistance of 249 Ω is obtained. Project support by the National Natural Science Foundation of China (Grant Nos. 61474110, 61377020, 61376089, 61223005, and 61176126), the National Science Fund for Distinguished Young Scholars, China (Grant No. 60925017), the One Hundred Person Project of the Chinese Academy of Sciences, and the Basic Research Project of Jiangsu Province, China (Grant No. BK20130362).

Investigation on high-efficiency Ga0.51In0.49P/In0.01Ga0.99As/Ge triple-junction solar cells for space applications

NASA Astrophysics Data System (ADS)

Zhang, Lei; Niu, Pingjuan; Li, Yuqiang; Song, Minghui; Zhang, Jianxin; Ning, Pingfan; Chen, Peizhuan

2017-12-01

Ga0.51In0.49P/In0.01Ga0.99As/Ge triple-junction solar cells for space applications were grown on 4 inch Ge substrates by metal organic chemical vapor deposition methods. The triple-junction solar cells were obtained by optimizing the subcell structure, showing a high open-circuit voltage of 2.77 V and a high conversion efficiency of 31% with 30.15 cm2 area under the AM0 spectrum at 25 °C. In addition, the In0.01Ga0.99As middle subcell structure was focused by optimizing in order to improve the anti radiation ability of triple-junction solar cells, and the remaining factor of conversion efficiency for middle subcell structure was enhanced from 84% to 92%. Finally, the remaining factor of external quantum efficiency for triple-junction solar cells was increased from 80% to 85.5%.

Genetic algorithm optimized triply compensated pulses in NMR spectroscopy

NASA Astrophysics Data System (ADS)

Manu, V. S.; Veglia, Gianluigi

2015-11-01

Sensitivity and resolution in NMR experiments are affected by magnetic field inhomogeneities (of both external and RF), errors in pulse calibration, and offset effects due to finite length of RF pulses. To remedy these problems, built-in compensation mechanisms for these experimental imperfections are often necessary. Here, we propose a new family of phase-modulated constant-amplitude broadband pulses with high compensation for RF inhomogeneity and heteronuclear coupling evolution. These pulses were optimized using a genetic algorithm (GA), which consists in a global optimization method inspired by Nature's evolutionary processes. The newly designed π and π / 2 pulses belong to the 'type A' (or general rotors) symmetric composite pulses. These GA-optimized pulses are relatively short compared to other general rotors and can be used for excitation and inversion, as well as refocusing pulses in spin-echo experiments. The performance of the GA-optimized pulses was assessed in Magic Angle Spinning (MAS) solid-state NMR experiments using a crystalline U-13C, 15N NAVL peptide as well as U-13C, 15N microcrystalline ubiquitin. GA optimization of NMR pulse sequences opens a window for improving current experiments and designing new robust pulse sequences.

Further improvements in conducting and transparent properties of ZnO:Ga films with perpetual c-axis orientation: Materials optimization and application in silicon solar cells

NASA Astrophysics Data System (ADS)

Mondal, Praloy; Das, Debajyoti

2017-07-01

Technologically appropriate device friendly ZnO:Ga films have been prepared at a low growth temperature (100 °C) by changing the RF power (P) applied to the magnetron plasma. Structurally preferred c-axis orientation of the ZnO:Ga network has been attained with I〈002〉/I〈103〉 > 5. The c-axis oriented grains of wurtzite ZnO:Ga grows geometrically and settles in tangentially, providing favorable conduction path for stacked layer devices. Nano-sheet like structures produced at the surface are interconnected and provide conducting path across the surface; however, those accommodate a lot of pores in between that help better light trapping and reduce the reflection loss. The optimized ZnO:Ga thin film prepared at RF power of 200 W has 〈002〉 oriented grains of average size ∼10 nm and exhibits a very high conductivity ∼200 S cm-1 and elevated transmission (∼93% at 500 nm) in the visible range. The optimized ZnO:Ga film has been used as the transparent conducting oxide (TCO) window layer of RF-PECVD grown silicon thin film solar cells in glass/TCO/p-i-n-Si/Al configuration. The characteristics of identically prepared p-i-n-Si solar cells are compared by replacing presently developed ZnO:Ga TCO with the best quality U-type SnO2 coated Asahi glass substrates. The ZnO:Ga coated glass substrate offers a higher open circuit voltage (VOC) and the higher fill factor (FF). The ZnO:Ga film being more stable in hydrogen plasma than its SnO2 counterpart, maintains a high transparency to the solar radiation and improves the VOC, while reduced diffusion of Zn across the p-layer creates less defects at the p-i interface in Si:H cells and thereby, increases the FF. Nearly identical conversion efficiency is preserved for both TCO substrates. Excellent c-axis orientation even at low growth temperature promises improved device performance by extended parametric optimization.

New Method of Calibrating IRT Models.

ERIC Educational Resources Information Center

Jiang, Hai; Tang, K. Linda

This discussion of new methods for calibrating item response theory (IRT) models looks into new optimization procedures, such as the Genetic Algorithm (GA) to improve on the use of the Newton-Raphson procedure. The advantages of using a global optimization procedure like GA is that this kind of procedure is not easily affected by local optima and…

Design of high-efficiency, radiation-hard, GaInP/GaAs solar cells

NASA Technical Reports Server (NTRS)

Kurtz, Sarah R.; Bertness, K. A.; Kibbler, A. E.; Kramer, C.; Olson, J. M.

1994-01-01

In recently years, Ga(0.5)In((0.5)P/GaAs cells have drawn increased attention both because of their high efficiencies and because they are well suited for space applications. They can be grown and processed as two-junction devices with roughly twice the voltage and half the current of GaAs cells. They have low temperature coefficients, and have good potential for radiation hardness. We have previously reported the effects of electron irradiation on test cells which were not optimally designed for space. From those results we estimated that an optimally designed cell could achieve 20 percent after irradiation with 10(exp 15) cm(exp -2) 1 MeV electrons. Modeling studies predicted that slightly higher efficiencies may be achievable. Record efficiencies for EOL performance of other types of cells are significantly lower. Even the best Si and InP cells have BOL efficiencies lower than the EOL efficiency we report here. Good GaAs cells have an EOL efficiency of 16 percent. The InP/Ga(0.5)In(0.5)As two-junction, two-terminal device has a BOL efficiency as high as 22.2 percent, but radiation results for these cells were limited. In this study we use the previous modeling and irradiation results to design a set of Ga(0.5)In(0.5)P/GaAs cells that will demonstrate the importance of the design parameters and result in high-efficiency devices. We report record AMO efficiencies: a BOL efficiency of 25.7 percent for a device optimized for BOL performance and two of different designs with EOL efficiencies of 19.6 percent (at 10(exp 15) cm(exp -2) 1MeV electrons). We vary the bottom-cell base doping and the top-cell thickness to show the effects of these two important design parameters. We get an unexpected result indicating that the dopant added to the bottom-cell base also increases the degradation of the top cell.

Prediction and Optimization of Key Performance Indicators in the Production of Stator Core Using a GA-NN Approach

NASA Astrophysics Data System (ADS)

Rajora, M.; Zou, P.; Xu, W.; Jin, L.; Chen, W.; Liang, S. Y.

2017-12-01

With the rapidly changing demands of the manufacturing market, intelligent techniques are being used to solve engineering problems due to their ability to handle nonlinear complex problems. For example, in the conventional production of stator cores, it is relied upon experienced engineers to make an initial plan on the number of compensation sheets to be added to achieve uniform pressure distribution throughout the laminations. Additionally, these engineers must use their experience to revise the initial plans based upon the measurements made during the production of stator core. However, this method yields inconsistent results as humans are incapable of storing and analysing large amounts of data. In this article, first, a Neural Network (NN), trained using a hybrid Levenberg-Marquardt (LM) - Genetic Algorithm (GA), is developed to assist the engineers with the decision-making process. Next, the trained NN is used as a fitness function in an optimization algorithm to find the optimal values of the initial compensation sheet plan with the aim of minimizing the required revisions during the production of the stator core.

Optimum Design of ARC-less InGaP/GaAs DJ Solar Cell with Hetero Tunnel Junction

NASA Astrophysics Data System (ADS)

Abbasian, Sobhan; Sabbaghi-Nadooshan, Reza

2018-07-01

The operation of hetero In0.49Ga0.51P-Al0.7Ga0.3As tunnel diodes has been evaluated, and an approach for optimizing the back surface field (BSF) layer of a InGaP/GaAs dual-junction (DJ) solar cell developed. The results show that the hetero In0.49Ga0.51P-Al0.7Ga0.3As tunnel diode transferred more electrons and holes and showed less recombination between the top and bottom cells with increased efficiency ( η) in the InGaP/GaAs DJ solar cell. To achieve higher open-circuit voltage ( V oc), GaAs semiconductor was investigated to match with Al0.52In0.48P with bandgap of 2.4 eV, and replacement of the bottom cell in the InGaP/GaAs DJ solar cell with such an Al0.52In0.48P-GaAs heterojunction increased the photogeneration in this region. In the next step, addition of a BSF layer to the top cell required two BSF layers in the bottom cell to optimize the short-circuit current ( J sc) and η. The thickness and doping of the BSF layers were increased to obtain the highest η for the cell. The proposed structure was then compared with previous works. The proposed structure yielded V oc = 2.46 V, J sc = 30 mA/cm2, fill factor (FF) = 88.61%, and η = 65.51% under AM1.5 (1 sun) illumination.

Self-consistent vertical transport calculations in AlxGa1-xN/GaN based resonant tunneling diode

NASA Astrophysics Data System (ADS)

Rached, A.; Bhouri, A.; Sakr, S.; Lazzari, J.-L.; Belmabrouk, H.

2016-03-01

The formation of two-dimensional electron gases (2DEGs) at AlxGa1-xN/GaN hexagonal double-barriers (DB) resonant tunneling diodes (RTD) is investigated by numerical self-consistent (SC) solutions of the coupled Schrödinger and Poisson equations. Spontaneous and piezoelectric effects across the material interfaces are rigorously taken into account. Conduction band profiles, band edges and corresponding envelope functions are calculated in the AlxGa1-xN/GaN structures and likened to those where no polarization effects are included. The combined effect of the polarization-induced bound charge and conduction band offsets between the hexagonal AlGaN and GaN results in the formation of 2DEGs on one side of the DB and a depletion region on the other side. Using the transfer matrix formalism, the vertical transport (J-V characteristics) in AlGaN/GaN RTDs is calculated with a fully SC calculation in the ballistic regime. Compared to standard calculations where the voltage drop along the structure is supposed to be linear, the SC method leads to strong quantitative changes in the J-V characteristics showing that the applied electric field varies significantly in the active region of the structure. The influences of the aluminum composition and the GaN(AlGaN) thickness layers on the evolution of the current characteristics are also self-consistently investigated and discussed. We show that the electrical characteristics are very sensitive to the potential barrier due to the interplay between the potential symmetry and the barrier height and width. More interestingly, we demonstrate that the figures of merit namely the peak-to-valley ratio (PVR) of GaN/AlGaN RTDs can be optimized by increasing the quantum well width.

Parallel computation of GA search for the artery shape determinants with CFD

NASA Astrophysics Data System (ADS)

Himeno, M.; Noda, S.; Fukasaku, K.; Himeno, R.

2010-06-01

We studied which factors play important role to determine the shape of arteries at the carotid artery bifurcation by performing multi-objective optimization with computation fluid dynamics (CFD) and the genetic algorithm (GA). To perform it, the most difficult problem is how to reduce turn-around time of the GA optimization with 3D unsteady computation of blood flow. We devised two levels of parallel computation method with the following features: level 1: parallel CFD computation with appropriate number of cores; level 2: parallel jobs generated by "master", which finds quickly available job cue and dispatches jobs, to reduce turn-around time. As a result, the turn-around time of one GA trial, which would have taken 462 days with one core, was reduced to less than two days on RIKEN supercomputer system, RICC, with 8192 cores. We performed a multi-objective optimization to minimize the maximum mean WSS and to minimize the sum of circumference for four different shapes and obtained a set of trade-off solutions for each shape. In addition, we found that the carotid bulb has the feature of the minimum local mean WSS and minimum local radius. We confirmed that our method is effective for examining determinants of artery shapes.

Sequential Optimization Methods for Augmentation of Marine Enzymes Production in Solid-State Fermentation: l-Glutaminase Production a Case Study.

PubMed

Sathish, T; Uppuluri, K B; Veera Bramha Chari, P; Kezia, D

There is an increased l-glutaminase market worldwide due to its relevant industrial applications. Salt tolerance l-glutaminases play a vital role in the increase of flavor of different types of foods like soya sauce and tofu. This chapter is presenting the economically viable l-glutaminases production in solid-state fermentation (SSF) by Aspergillus flavus MTCC 9972 as a case study. The enzyme production was improved following a three step optimization process. Initially mixture design (MD) (augmented simplex lattice design) was employed to optimize the solid substrate mixture. Such solid substrate mixture consisted of 59:41 of wheat bran and Bengal gram husk has given higher amounts of l-glutaminase. Glucose and l-glutamine were screened as a finest additional carbon and nitrogen sources for l-glutaminase production with help of Plackett-Burman Design (PBD). l-Glutamine also acting as a nitrogen source as well as inducer for secretion of l-glutaminase from A. flavus MTCC 9972. In the final step of optimization various environmental and nutritive parameters such as pH, temperature, moisture content, inoculum concentration, glucose, and l-glutamine levels were optimized through the use of hybrid feed forward neural networks (FFNNs) and genetic algorithm (GA). Through sequential optimization methods MD-PBD-FFNN-GA, the l-glutaminase production in SSF could be improved by 2.7-fold (453-1690U/g). © 2016 Elsevier Inc. All rights reserved.

Ultrafast carrier dynamics in GaN/InGaN multiple quantum wells nanorods

NASA Astrophysics Data System (ADS)

Chen, Weijian; Wen, Xiaoming; Latzel, Michael; Yang, Jianfeng; Huang, Shujuan; Shrestha, Santosh; Patterson, Robert; Christiansen, Silke; Conibeer, Gavin

2018-01-01

GaN/InGaN multiple quantum wells (MQW) is a promising material for high-efficiency solid-state lighting. Ultrafast optical pump-probe spectroscopy is an important characterization technique for examining fundamental phenomena in semiconductor nanostructure with sub-picosecond resolution. In this study, ultrafast exciton and charge carrier dynamics in GaN/InGaN MQW planar layer and nanorod are investigated using femtosecond transient absorption (TA) techniques at room temperature. Here nanorods are fabricated by etching the GaN/InGaN MQW planar layers using nanosphere lithography and reactive ion etching. Photoluminescence efficiency of the nanorods have been proved to be much higher than that of the planar layers, but the mechanism of the nanorod structure improvement of PL efficiency is not adequately studied. By comparing the TA profile of the GaN/InGaN MQW planar layers and nanorods, the impact of surface states and nanorods lateral confinement in the ultrafast carrier dynamics of GaN/InGaN MQW is revealed. The nanorod sidewall surface states have a strong influence on the InGaN quantum well carrier dynamics. The ultrafast relaxation processes studied in this GaN/InGaN MQW nanostructure is essential for further optimization of device application.

Multiple sequence alignment using multi-objective based bacterial foraging optimization algorithm.

PubMed

Rani, R Ranjani; Ramyachitra, D

2016-12-01

Multiple sequence alignment (MSA) is a widespread approach in computational biology and bioinformatics. MSA deals with how the sequences of nucleotides and amino acids are sequenced with possible alignment and minimum number of gaps between them, which directs to the functional, evolutionary and structural relationships among the sequences. Still the computation of MSA is a challenging task to provide an efficient accuracy and statistically significant results of alignments. In this work, the Bacterial Foraging Optimization Algorithm was employed to align the biological sequences which resulted in a non-dominated optimal solution. It employs Multi-objective, such as: Maximization of Similarity, Non-gap percentage, Conserved blocks and Minimization of gap penalty. BAliBASE 3.0 benchmark database was utilized to examine the proposed algorithm against other methods In this paper, two algorithms have been proposed: Hybrid Genetic Algorithm with Artificial Bee Colony (GA-ABC) and Bacterial Foraging Optimization Algorithm. It was found that Hybrid Genetic Algorithm with Artificial Bee Colony performed better than the existing optimization algorithms. But still the conserved blocks were not obtained using GA-ABC. Then BFO was used for the alignment and the conserved blocks were obtained. The proposed Multi-Objective Bacterial Foraging Optimization Algorithm (MO-BFO) was compared with widely used MSA methods Clustal Omega, Kalign, MUSCLE, MAFFT, Genetic Algorithm (GA), Ant Colony Optimization (ACO), Artificial Bee Colony (ABC), Particle Swarm Optimization (PSO) and Hybrid Genetic Algorithm with Artificial Bee Colony (GA-ABC). The final results show that the proposed MO-BFO algorithm yields better alignment than most widely used methods. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Evolution of Query Optimization Methods

NASA Astrophysics Data System (ADS)

Hameurlain, Abdelkader; Morvan, Franck

Query optimization is the most critical phase in query processing. In this paper, we try to describe synthetically the evolution of query optimization methods from uniprocessor relational database systems to data Grid systems through parallel, distributed and data integration systems. We point out a set of parameters to characterize and compare query optimization methods, mainly: (i) size of the search space, (ii) type of method (static or dynamic), (iii) modification types of execution plans (re-optimization or re-scheduling), (iv) level of modification (intra-operator and/or inter-operator), (v) type of event (estimation errors, delay, user preferences), and (vi) nature of decision-making (centralized or decentralized control).

Design and simulation of GaN based Schottky betavoltaic nuclear micro-battery.

PubMed

San, Haisheng; Yao, Shulin; Wang, Xiang; Cheng, Zaijun; Chen, Xuyuan

2013-10-01

The current paper presents a theoretical analysis of Ni-63 nuclear micro-battery based on a wide-band gap semiconductor GaN thin-film covered with thin Ni/Au films to form Schottky barrier for carrier separation. The total energy deposition in GaN was calculated using Monte Carlo methods by taking into account the full beta spectral energy, which provided an optimal design on Schottky barrier width. The calculated results show that an 8 μm thick Schottky barrier can collect about 95% of the incident beta particle energy. Considering the actual limitations of current GaN growth technique, a Fe-doped compensation technique by MOCVD method can be used to realize the n-type GaN with a carrier concentration of 1×10(15) cm(-3), by which a GaN based Schottky betavoltaic micro-battery can achieve an energy conversion efficiency of 2.25% based on the theoretical calculations of semiconductor device physics. Copyright © 2013 Elsevier Ltd. All rights reserved.

Temporal behavior of RHEED intensity oscillations during molecular beam epitaxial growth of GaAs and AlGaAs on (111)B GaAs substrates

NASA Astrophysics Data System (ADS)

Yen, Ming Y.; Haas, T. W.

1990-10-01

We present the temporal behavior of intensity oscillations in reflection high-energy electron diffraction (RHEED) during molecular beam epitaxial (MBE) growth of GaAs and A1GaAs on (1 1 1)B GaAs substrates. The RHEED intensity oscillations were examined as a function of growth parameters in order to provide the insight into the dynamic characteristics and to identify the optimal condition for the two-dimensional layer-by-layer growth. The most intense RHEED oscillation was found to occur within a very narrow temperature range which seems to optimize the surface migration kinetics of the arriving group III elements and the molecular dissodiative reaction of the group V elements. The appearance of an initial transient of the intensity upon commencement of the growth and its implications are described.

Strategies for global optimization in photonics design.

PubMed

Vukovic, Ana; Sewell, Phillip; Benson, Trevor M

2010-10-01

This paper reports on two important issues that arise in the context of the global optimization of photonic components where large problem spaces must be investigated. The first is the implementation of a fast simulation method and associated matrix solver for assessing particular designs and the second, the strategies that a designer can adopt to control the size of the problem design space to reduce runtimes without compromising the convergence of the global optimization tool. For this study an analytical simulation method based on Mie scattering and a fast matrix solver exploiting the fast multipole method are combined with genetic algorithms (GAs). The impact of the approximations of the simulation method on the accuracy and runtime of individual design assessments and the consequent effects on the GA are also examined. An investigation of optimization strategies for controlling the design space size is conducted on two illustrative examples, namely, 60° and 90° waveguide bends based on photonic microstructures, and their effectiveness is analyzed in terms of a GA's ability to converge to the best solution within an acceptable timeframe. Finally, the paper describes some particular optimized solutions found in the course of this work.

Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Jr-Tai, E-mail: jrche@ifm.liu.se; Hsu, Chih-Wei; Forsberg, Urban

2015-02-28

Severe surface decomposition of semi-insulating (SI) GaN templates occurred in high-temperature H{sub 2} atmosphere prior to epitaxial growth in a metalorganic chemical vapor deposition system. A two-step heating process with a surface stabilization technique was developed to preserve the GaN template surface. Utilizing the optimized heating process, a high two-dimensional electron gas mobility ∼2000 cm{sup 2}/V·s was obtained in a thin AlGaN/AlN/GaN heterostructure with an only 100-nm-thick GaN spacer layer homoepitaxially grown on the GaN template. This technique was also demonstrated viable for native GaN substrates to stabilize the surface facilitating two-dimensional growth of GaN layers. Very high residual silicon andmore » oxygen concentrations were found up to ∼1 × 10{sup 20 }cm{sup −3} at the interface between the GaN epilayer and the native GaN substrate. Capacitance-voltage measurements confirmed that the residual carbon doping controlled by growth conditions of the GaN epilayer can be used to successfully compensate the donor-like impurities. State-of-the-art structural properties of a high-mobility AlGaN/AlN/GaN heterostructure was then realized on a 1 × 1 cm{sup 2} SI native GaN substrate; the full width at half maximum of the X-ray rocking curves of the GaN (002) and (102) peaks are only 21 and 14 arc sec, respectively. The surface morphology of the heterostructure shows uniform parallel bilayer steps, and no morphological defects were noticeable over the entire epi-wafer.« less

Optimization of sputter deposition parameters for magnetostrictive Fe62Co19Ga19/Si(100) films

NASA Astrophysics Data System (ADS)

Jen, S. U.; Tsai, T. L.

2012-04-01

A good magnetostrictive material should have large saturation magnetostriction (λS) and low saturation (or anisotropy) field (HS), such that its magnetostriction susceptibility (SH) can be as large as possible. In this study, we have made Fe62Co19Ga19/Si(100) nano-crystalline films by using the dc magnetron sputtering technique under various deposition conditions: Ar working gas pressure (pAr) was varied from 1 to 15 mTorr; sputtering power (Pw) was from 10 to 120 W; deposition temperature (TS) was from room temperature (RT) to 300 °C, The film thickness (tf) was fixed at 175 nm. Each magnetic domain looked like a long leaf, with a long-axis of about 12-15 μm and a short-axis of about 1.5 μm. The optimal magnetic and electrical properties were found from the Fe62Co19Ga19 film made with the sputter deposition parameters of pAr = 5 mTorr, Pw = 80 W, and TS = RT. Those optimal properties include λS = 80 ppm, HS = 19.8 Oe, SH = 6.1 ppm/Oe, and electrical resistivity ρ = 57.0 μΩ cm. Note that SH for the conventional magnetostrictive Terfenol-D film is, in general, equal to 1.5 ppm/Oe only.

Combinatorial Multiobjective Optimization Using Genetic Algorithms

NASA Technical Reports Server (NTRS)

Crossley, William A.; Martin. Eric T.

2002-01-01

The research proposed in this document investigated multiobjective optimization approaches based upon the Genetic Algorithm (GA). Several versions of the GA have been adopted for multiobjective design, but, prior to this research, there had not been significant comparisons of the most popular strategies. The research effort first generalized the two-branch tournament genetic algorithm in to an N-branch genetic algorithm, then the N-branch GA was compared with a version of the popular Multi-Objective Genetic Algorithm (MOGA). Because the genetic algorithm is well suited to combinatorial (mixed discrete / continuous) optimization problems, the GA can be used in the conceptual phase of design to combine selection (discrete variable) and sizing (continuous variable) tasks. Using a multiobjective formulation for the design of a 50-passenger aircraft to meet the competing objectives of minimizing takeoff gross weight and minimizing trip time, the GA generated a range of tradeoff designs that illustrate which aircraft features change from a low-weight, slow trip-time aircraft design to a heavy-weight, short trip-time aircraft design. Given the objective formulation and analysis methods used, the results of this study identify where turboprop-powered aircraft and turbofan-powered aircraft become more desirable for the 50 seat passenger application. This aircraft design application also begins to suggest how a combinatorial multiobjective optimization technique could be used to assist in the design of morphing aircraft.

Electron and proton degradation in /AlGa/As-GaAs solar cells

NASA Technical Reports Server (NTRS)

Loo, R.; Knechtli, R. C.; Kamath, G. S.; Goldhammer, L.; Anspaugh, B.

1978-01-01

Results on radiation damage in (AlGa)As-GaAs solar cells by 1 MeV electron fluences up to 10 to the 16th electrons/sq cm and by 15, 20, 30 and 40 MeV proton fluences up to 5 times 10 to the 11th protons/sq cm are presented. The damage is compared with data on state-of-the-art silicon cells which were irradiated along with the gallium arsenide cells. The theoretical expectation that the junction depth has to be kept relatively shallow, to minimize radiation damage has been verified experimentally. The damage to the GaAs cells as a function of irradiation, is correlated with the change in their spectral response and dark I-V characteristics. The effect of thermal annealing on the (AlGa)As-GaAs solar cells was also investigated. This data is used to predict further avenues of optimization of the GaAs cells.

Process dependency on threshold voltage of GaN MOSFET on AlGaN/GaN heterostructure

NASA Astrophysics Data System (ADS)

Wang, Qingpeng; Jiang, Ying; Miyashita, Takahiro; Motoyama, Shin-ichi; Li, Liuan; Wang, Dejun; Ohno, Yasuo; Ao, Jin-Ping

2014-09-01

GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) with recessed gate on AlGaN/GaN heterostructure are reported in which the drain and source ohmic contacts were fabricated on the AlGaN/GaN heterostructure and the electron channel was formed on the GaN buffer layer by removing the AlGaN barrier layer. Negative threshold voltages were commonly observed in all devices. To investigate the reasons of the negative threshold voltages, different oxide thickness, etching gas and bias power of inductively-coupled plasma (ICP) system were utilized in the fabrication process of the GaN MOSFETs. It is found that positive charges of around 1 × 1012 q/cm2 exist near the interface at the just threshold condition in both silane- and tetraethylorthosilicate (TEOS)-based devices. It is also found that the threshold voltages do not obviously change with the different etching gas (SiCl4, BCl3 and two-step etching of SiCl4/Cl2) at the same ICP bias power level (20-25 W) and will become deeper when higher bias power is used in the dry recess process which may be related to the much serious ion bombardment damage. Furthermore, X-ray photoelectron spectroscopy (XPS) experiments were done to investigate the surface conditions. It is found that N 1s peaks become lower with higher bias power of the dry etching process. Also, silicon contamination was found and could be removed by HNO3/HF solution. It indicates that the nitrogen vacancies are mainly responsible for the negative threshold voltages rather than the silicon contamination. It demonstrates that optimization of the ICP recess conditions and improvement of the surface condition are still necessary to realize enhancement-mode GaN MOSFETs on AlGaN/GaN heterostructure.

High-Temperature Growth of GaN and Al x Ga1- x N via Ammonia-Based Metalorganic Molecular-Beam Epitaxy

NASA Astrophysics Data System (ADS)

Billingsley, Daniel; Henderson, Walter; Doolittle, W. Alan

2010-05-01

The effect of high-temperature growth on the crystalline quality and surface morphology of GaN and Al x Ga1- x N grown by ammonia-based metalorganic molecular-beam epitaxy (NH3-MOMBE) has been investigated as a means of producing atomically smooth films suitable for device structures. The effects of V/III ratio on the growth rate and surface morphology are described herein. The crystalline quality of both GaN and AlGaN was found to mimic that of the GaN templates, with (002) x-ray diffraction (XRD) full-widths at half- maximum (FWHMs) of ~350 arcsec. Nitrogen-rich growth conditions have been found to provide optimal surface morphologies with a root-mean-square (RMS) roughness of ~0.8 nm, yet excessive N-rich environments have been found to reduce the growth rate and result in the formation of faceted surface pitting. AlGaN exhibits a decreased growth rate, as compared with GaN, due to increased N recombination as a result of the increased pyrolysis of NH3 in the presence of Al. AlGaN films grown directly on GaN templates exhibited Pendellösung x-ray fringes, indicating an abrupt interface and a planar AlGaN film. AlGaN films grown for this study resulted in an optimal RMS roughness of ~0.85 nm with visible atomic steps.

Four-junction AlGaAs/GaAs laser power converter

NASA Astrophysics Data System (ADS)

Huang, Jie; Sun, Yurun; Zhao, Yongming; Yu, Shuzhen; Dong, Jianrong; Xue, Jiping; Xue, Chi; Wang, Jin; Lu, Yunqing; Ding, Yanwen

2018-04-01

Four-junction AlGaAs/GaAs laser power converters (LPCs) with n+-GaAs/p+-Al0.37Ga0.63As heterostructure tunnel junctions (TJs) have been designed and grown by metal-organic chemical vapor deposition (MOCVD) for converting the power of 808 nm lasers. A maximum conversion efficiency η c of 56.9% ± 4% is obtained for cells with an aperture of 3.14 mm2 at an input laser power of 0.2 W, while dropping to 43.3% at 1.5 W. Measured current–voltage (I–V) characteristics indicate that the performance of the LPC can be further improved by increasing the tunneling current density of TJs and optimizing the thicknesses of sub-cells to achieve current matching in LPC. Project financially supported by the National Natural Science Foundation of China (No. 61376065) and Zhongtian Technology Group Co. Ltd.

Built-in-polarization field effect on lattice thermal conductivity of AlxGa1-xN/GaN heterostructure

NASA Astrophysics Data System (ADS)

Pansari, Anju; Gedam, Vikas; Kumar Sahoo, Bijaya

2015-12-01

The built-in-polarization field at the interface of AlxGa1-xN/GaN heterostructure enhances elastic constant, phonon velocity, Debye temperature and their bowing constants of barrier material AlxGa1-xN. The combined phonon relaxation time of acoustics phonons has been computed for with and without built-in-polarization field at room temperature for different aluminum (Al) content (x). Our result shows that the built-in-polarization field suppresses the scattering mechanisms and enhances the combined relaxation time. The thermal conductivity of AlxGa1-xN has been estimated as a function of temperature for x=0, 0.1, 0.5 and 1 for with and without polarization field. Minimum thermal conductivity has been observed for x=0.1 and 0.5. Analysis shows that up to a certain temperature (different for different x) the polarization field acts as negative effect and reduces the thermal conductivity and after this temperature thermal conductivity is significantly contributed by polarization field. This signifies pyroelectric character of AlxGa1-xN. The pyroelectric transition temperature of AlxGa1-xN alloy has been predicted for different x. Our study reports that room temperature thermal conductivity of AlxGa1-xN/GaN heterostructure is enhanced by built-in-polarization field. The temperature dependence of thermal conductivity for x=0.1 and 0.5 are in line with prior experimental studies. The method we have developed can be used for the simulation of heat transport in nitride devices to minimize the self heating processes and in polarization engineering strategies to optimize the thermoelectric performance of AlxGa1-xN/GaN heterostructures.

Isotype InGaN/GaN heterobarrier diodes by ammonia molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fireman, Micha N.; Browne, David A.; Speck, James S.

The design of isotype InGaN/GaN heterobarrier diode structures grown by ammonia molecular beam epitaxy is presented. On the (0001) Ga-polar plane, a structure consisting of a surface n{sup +} GaN contact layer, followed by a thin InGaN layer, followed by a thick unintentionally doped (UID) GaN layer, and atop a buried n{sup +} GaN contact layer induces a large conduction band barrier via a depleted UID GaN layer. Suppression of reverse and subthreshold current in such isotype barrier devices under applied bias depends on the quality of this composite layer polarization. Sample series were grown under fixed InGaN growth conditionsmore » that varied either the UID GaN NH{sub 3} flow rate or the UID GaN thickness, and under fixed UID GaN growth conditions that varied InGaN growth conditions. Decreases in subthreshold current and reverse bias current were measured for thicker UID GaN layers and increasing InGaN growth rates. Temperature-dependent analysis indicated that although extracted barrier heights were lower than those predicted by 1D Schrödinger Poisson simulations (0.9 eV–1.4 eV for In compositions from 10% to 15%), optimized growth conditions increased the extracted barrier height from ∼11% to nearly 85% of the simulated values. Potential subthreshold mechanisms are discussed, along with those growth factors which might affect their prevalence.« less

Structural and optical studies of nitrogen incorporation into GaSb-based GaInSb quantum wells

NASA Astrophysics Data System (ADS)

Nair, Hari P.; Crook, Adam M.; Yu, Kin M.; Bank, Seth R.

2012-01-01

We investigate the incorporation of nitrogen into (Ga,In)Sb grown on GaSb and report room temperature photoluminescence from GaInSb(N) quantum wells. X-ray diffraction and channeling nuclear reaction analysis, together with Rutherford backscattering, were employed to identify the optimal molecular beam epitaxial growth conditions that minimized the incorporation of non-substitutional nitrogen into GaNSb. Consistent with this hypothesis, GaInSb(N) quantum wells grown under the conditions that minimized non-substitutional nitrogen exhibited room temperature photoluminescence, indicative of significantly improved radiative efficiency. Further development of this material system could enable type-I laser diodes emitting throughout the (3-5 μm) wavelength range.

Near-infrared cathodoluminescence imaging of defect distributions in In(0.2)Ga(0.8)As/GaAs multiple quantum wells grown on prepatterned GaAs

NASA Technical Reports Server (NTRS)

Rich, D. H.; Fajkumar, K. C.; Chen, LI; Madhukar, A.; Grunthaner, F. J.

1992-01-01

The defect distribution in a highly strained In(0.2)Ga(0.8)As/GaAs multiple-quantum-well (MQW) structure grown on a patterned GaAs substrate is examined with cathodoluminescence imaging and spectroscopy in the near IR. By spatially correlating the luminescence arising from the MQW exciton recombination (950 nm) with the longer wavelength (1000-1200 nm) luminescence arising from the defect-induced recombination, it is demonstrated that it is possible to determine the regions of highest film quality in both the mesa and valley regions. The present approach enables a judicious determination of the optimal regions to be used for active pixels in InGaAs/GaAs spatial light modulators.

Method of plasma etching GA-based compound semiconductors

DOEpatents

Qiu, Weibin; Goddard, Lynford L.

2013-01-01

A method of plasma etching Ga-based compound semiconductors includes providing a process chamber and a source electrode adjacent thereto. The chamber contains a Ga-based compound semiconductor sample in contact with a platen which is electrically connected to a first power supply, and the source electrode is electrically connected to a second power supply. SiCl.sub.4 and Ar gases are flowed into the chamber. RF power is supplied to the platen at a first power level, and RF power is supplied to the source electrode. A plasma is generated. Then, RF power is supplied to the platen at a second power level lower than the first power level and no greater than about 30 W. Regions of a surface of the sample adjacent to one or more masked portions of the surface are etched at a rate of no more than about 25 nm/min to create a substantially smooth etched surface.

AlGaN/GaN high electron mobility transistors with selective area grown p-GaN gates

NASA Astrophysics Data System (ADS)

Yuliang, Huang; Lian, Zhang; Zhe, Cheng; Yun, Zhang; Yujie, Ai; Yongbing, Zhao; Hongxi, Lu; Junxi, Wang; Jinmin, Li

2016-11-01

We report a selective area growth (SAG) method to define the p-GaN gate of AlGaN/GaN high electron mobility transistors (HEMTs) by metal-organic chemical vapor deposition. Compared with Schottky gate HEMTs, the SAG p-GaN gate HEMTs show more positive threshold voltage (V th) and better gate control ability. The influence of Cp2Mg flux of SAG p-GaN gate on the AlGaN/GaN HEMTs has also been studied. With the increasing Cp2Mg from 0.16 μmol/min to 0.20 μmol/min, the V th raises from -0.67 V to -0.37 V. The maximum transconductance of the SAG HEMT at a drain voltage of 10 V is 113.9 mS/mm while that value of the Schottky HEMT is 51.6 mS/mm. The SAG method paves a promising way for achieving p-GaN gate normally-off AlGaN/GaN HEMTs without dry etching damage. Project supported by the National Natural Sciences Foundation of China (Nos. 61376090, 61306008) and the National High Technology Program of China (No. 2014AA032606).

Experimental validation of structural optimization methods

NASA Technical Reports Server (NTRS)

Adelman, Howard M.

1992-01-01

The topic of validating structural optimization methods by use of experimental results is addressed. The need for validating the methods as a way of effecting a greater and an accelerated acceptance of formal optimization methods by practicing engineering designers is described. The range of validation strategies is defined which includes comparison of optimization results with more traditional design approaches, establishing the accuracy of analyses used, and finally experimental validation of the optimization results. Examples of the use of experimental results to validate optimization techniques are described. The examples include experimental validation of the following: optimum design of a trussed beam; combined control-structure design of a cable-supported beam simulating an actively controlled space structure; minimum weight design of a beam with frequency constraints; minimization of the vibration response of helicopter rotor blade; minimum weight design of a turbine blade disk; aeroelastic optimization of an aircraft vertical fin; airfoil shape optimization for drag minimization; optimization of the shape of a hole in a plate for stress minimization; optimization to minimize beam dynamic response; and structural optimization of a low vibration helicopter rotor.

Structural optimization of large structural systems by optimality criteria methods

NASA Technical Reports Server (NTRS)

Berke, Laszlo

1992-01-01

The fundamental concepts of the optimality criteria method of structural optimization are presented. The effect of the separability properties of the objective and constraint functions on the optimality criteria expressions is emphasized. The single constraint case is treated first, followed by the multiple constraint case with a more complex evaluation of the Lagrange multipliers. Examples illustrate the efficiency of the method.

apGA: An adaptive parallel genetic algorithm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liepins, G.E.; Baluja, S.

1991-01-01

We develop apGA, a parallel variant of the standard generational GA, that combines aggressive search with perpetual novelty, yet is able to preserve enough genetic structure to optimally solve variably scaled, non-uniform block deceptive and hierarchical deceptive problems. apGA combines elitism, adaptive mutation, adaptive exponential scaling, and temporal memory. We present empirical results for six classes of problems, including the DeJong test suite. Although we have not investigated hybrids, we note that apGA could be incorporated into other recent GA variants such as GENITOR, CHC, and the recombination stage of mGA. 12 refs., 2 figs., 2 tabs.

Design Optimization of a Hybrid Electric Vehicle Powertrain

NASA Astrophysics Data System (ADS)

Mangun, Firdause; Idres, Moumen; Abdullah, Kassim

2017-03-01

This paper presents an optimization work on hybrid electric vehicle (HEV) powertrain using Genetic Algorithm (GA) method. It focused on optimization of the parameters of powertrain components including supercapacitors to obtain maximum fuel economy. Vehicle modelling is based on Quasi-Static-Simulation (QSS) backward-facing approach. A combined city (FTP-75)-highway (HWFET) drive cycle is utilized for the design process. Seeking global optimum solution, GA was executed with different initial settings to obtain sets of optimal parameters. Starting from a benchmark HEV, optimization results in a smaller engine (2 l instead of 3 l) and a larger battery (15.66 kWh instead of 2.01 kWh). This leads to a reduction of 38.3% in fuel consumption and 30.5% in equivalent fuel consumption. Optimized parameters are also compared with actual values for HEV in the market.

Modeling and simulation of InGaN/GaN quantum dots solar cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aissat, A., E-mail: sakre23@yahoo.fr; LASICOMLaboratory, Faculty of Sciences, University of Blida 1; Benyettou, F.

2016-07-25

Currently, quantum dots have attracted attention in the field of optoelectronics, and are used to overcome the limits of a conventional solar cell. Here, an In{sub 0.25}Ga{sub 0.75}N/GaN Quantum Dots Solar Cell has been modeled and simulated using Silvaco Atlas. Our results show that the short circuit current increases with the insertion of the InGaN quantum dots inside the intrinsic region of a GaN pin solar cell. In contrary, the open circuit voltage decreases. A relative optimization of the conversion efficiency of 54.77% was achieved comparing a 5-layers In{sub 0.25}Ga{sub 0.75}N/GaN quantum dots with pin solar cell. The conversion efficiencymore » begins to decline beyond 5-layers quantum dots introduced. Indium composition of 10 % improves relatively the efficiency about 42.58% and a temperature of 285 K gives better conversion efficiency of 13.14%.« less

Thermodynamic assessment and binary nucleation modeling of Sn-seeded InGaAs nanowires

NASA Astrophysics Data System (ADS)

Ghasemi, Masoomeh; Selleby, Malin; Johansson, Jonas

2017-11-01

We have performed a thermodynamic assessment of the As-Ga-In-Sn system based on the CALculation of PHAse Diagram (CALPHAD) method. This system is part of a comprehensive thermodynamic database that we are developing for nanowire materials. Specifically, the As-Ga-In-Sn can be used in modeling the growth of GaAs, InAs, and InxGa1-xAs nanowires assisted by Sn liquid seeds. In this work, the As-Sn binary, the As-Ga-Sn, As-In-Sn, and Ga-In-Sn ternary systems have been thermodynamically assessed using the CALPHAD method. We show the relevant phase diagrams and property diagrams. They all show good agreement with experimental data. Using our optimized description we have modeled the nucleation of InxGa1-xAs in the zinc blende phase from a Sn-based quaternary liquid alloy using binary nucleation modeling. We have linked the composition of the solid nucleus to the composition of the liquid phase. Eventually, we have predicted the critical size of the nucleus that forms from InAs and GaAs pairs under various conditions. We believe that our modeling can guide future experimental realization of Sn-seeded InxGa1-xAs nanowires.

High-efficiency thin-film GaAs solar cells, phase2

NASA Technical Reports Server (NTRS)

Yeh, Y. C. M.

1981-01-01

Thin GaAs epi-layers with good crystallographic quality were grown using a (100) Si-substrate on which a thin Ge epi-interlayer was grown by CVD from germane. Both antireflection-coated metal oxide semiconductor (AMOS) and n(+)/p homojunction structures were studied. The AMOS cells were fabricated on undoped-GaAs epi-layers deposited on bulk poly-Ge substrates using organo-metallic CVD film-growth, with the best achieved AM1 conversion efficiency being 9.1%. Both p-type and n(+)-type GaAs growth were optimized using 50 ppm dimethyl zinc and 1% hydrogen sulfide, respectively. A direct GaAs deposition method in fabricating ultra-thin top layer, epitaxial n(+)/p shallow homojunction solar cells on (100) GaAs substrates (without anodic thinning) was developed to produce large area (1 sq/cm) cells, with 19.4% AM1 conversion efficiency achieved. Additionally, an AM1 conversion efficiency of 18.4% (17.5% with 5% grid coverage) was achieved for a single crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer.

Optical gain spectra of 1.55 μm GaAs/GaN.58yAs1-1.58yBiy/GaAs single quantum well

NASA Astrophysics Data System (ADS)

Guizani, I.; Bilel, C.; Habchi, M. M.; Rebey, A.

2017-02-01

The optical gain spectra of doped lattice-matched GaNAsBi-based single quantum well (SQW) was theoretically investigated using a (16 × 16) band anti-crossing (BAC) model combined with self-consistent calculation. For the sake of comparison, we computed the optical gain of both (i-n-i) and (i-p-i) doped well types in GaAs/GaNAsBi/GaAs quantum structure. The highest obtained material gain Gmax was 1.2 ×104 cm-1 for (i-n-i) type doped with N2Dd = 2.5 ×1012 cm-2 . We proposed investigating the p-i-n type structure to enhance the optical performance of GaAs/GaNAsBi/GaAs SQW. The Bi composition was optimized in order to obtain Te 1 - h 1 = 1.55 μ m . The effect of well width on optical gain spectra was also discussed.

Fully automated GMP production of [68Ga]Ga-DO3A-VS-Cys40-Exendin-4 for clinical use

PubMed Central

Velikyan, Irina; Rosenstrom, Ulrika; Eriksson, Olof

2017-01-01

[68Ga]Ga-DO3A-VS-Cys40-Exendin-4/PET-CT targeting glucagon like peptide-1 receptor (GLP-1R) has previously demonstrated its potential clinical value for the detection of insulinomas. The production and accessibility of this radiopharmaceutical is one of the critical factors in realization of clinical trials and routine clinical examinations. Previously, the radiopharmaceutical was prepared manually, however larger scale of clinical trials and healthcare requires automation of the production process in order to limit the operator radiation dose as well as improve tracer manufacturing robustness and on-line documentation for enhanced good manufacturing practice (GMP) compliance. A method for 68Ga-labelling of DO3A-VS-Cys40-Exendin-4 on a commercially available synthesis platform was developed. Equipment such as 68Ge/68Ga generator, synthesis platform, and disposable cassettes for 68Ga-labelling used in the study was purchased from Eckert & Ziegler. DO3A-VS-Cys40-Exendin-4 was synthesized in-house. The parameters such as time, temperature, precursor concentration, radical scavenger, buffer concentration, pH, product purification step were investigated and optimised. Reproducible and GMP compliant automated production of [68Ga]Ga-DO3A-VS-Cys40-Exendin-4 was developed. Exendin-4 comprising methionine amino acid residue was prone to oxidation which was strongly influenced by the elevated temperature, radioactivity amount, and precursor concentration. The suppression of the oxidative radiolysis was achieved by addition of ethanol, dihydroxybenzoic acid and ascorbic acid to the reaction buffer as well as by optimizing heating temperature. The non-decay corrected radiochemical yield was 43±2% with radiochemical purity of over 90% wherein the individual impurity signals in HPLC chromatogram did not exceed 5%. Automated production and quality control methods were established for paving the pathway for broader clinical use of [68Ga]Ga-DO3A-VS-Cys40-Exendin-4. PMID:28721305

a Comparison of Simulated Annealing, Genetic Algorithm and Particle Swarm Optimization in Optimal First-Order Design of Indoor Tls Networks

NASA Astrophysics Data System (ADS)

Jia, F.; Lichti, D.

2017-09-01

The optimal network design problem has been well addressed in geodesy and photogrammetry but has not received the same attention for terrestrial laser scanner (TLS) networks. The goal of this research is to develop a complete design system that can automatically provide an optimal plan for high-accuracy, large-volume scanning networks. The aim in this paper is to use three heuristic optimization methods, simulated annealing (SA), genetic algorithm (GA) and particle swarm optimization (PSO), to solve the first-order design (FOD) problem for a small-volume indoor network and make a comparison of their performances. The room is simplified as discretized wall segments and possible viewpoints. Each possible viewpoint is evaluated with a score table representing the wall segments visible from each viewpoint based on scanning geometry constraints. The goal is to find a minimum number of viewpoints that can obtain complete coverage of all wall segments with a minimal sum of incidence angles. The different methods have been implemented and compared in terms of the quality of the solutions, runtime and repeatability. The experiment environment was simulated from a room located on University of Calgary campus where multiple scans are required due to occlusions from interior walls. The results obtained in this research show that PSO and GA provide similar solutions while SA doesn't guarantee an optimal solution within limited iterations. Overall, GA is considered as the best choice for this problem based on its capability of providing an optimal solution and fewer parameters to tune.

A study of optical design and optimization applied to lens module of laser beam shaping of advanced modern optical device

NASA Astrophysics Data System (ADS)

Tsai, Cheng-Mu; Fang, Yi-Chin; Chen, Zhen Hsiang

2011-10-01

This study used the aspheric lens to realize the laser flat-top optimization, and applied the genetic algorithm (GA) to find the optimal results. Using the characteristics of aspheric lens to obtain the optimized high quality Nd: YAG 355 waveband laser flat-top optical system, this study employed the Light tools LDS (least damped square) and the GA of artificial intelligence optimization method to determine the optimal aspheric coefficient and obtain the optimal solution. This study applied the aspheric lens with GA for the flattening of laser beams using two aspheric lenses in the aspheric surface optical system to complete 80% spot narrowing under standard deviation of 0.6142.

AlGaN-Cladding-Free m-Plane InGaN/GaN Laser Diodes with p-Type AlGaN Etch Stop Layers

NASA Astrophysics Data System (ADS)

Farrell, Robert M.; Haeger, Daniel A.; Hsu, Po Shan; Hardy, Matthew T.; Kelchner, Kathryn M.; Fujito, Kenji; Feezell, Daniel F.; Mishra, Umesh K.; DenBaars, Steven P.; Speck, James S.; Nakamura, Shuji

2011-09-01

We present a new method of improving the accuracy and reproducibility of dry etching processes for ridge waveguide InGaN/GaN laser diodes (LDs). A GaN:Al0.09Ga0.91N etch rate selectivity of 11:1 was demonstrated for an m-plane LD with a 40 nm p-Al0.09Ga0.91N etch stop layer (ESL) surrounded by Al-free cladding layers, establishing the effectiveness of AlGaN-based ESLs for controlling etch depth in ridge waveguide InGaN/GaN LDs. These results demonstrate the potential for integrating AlGaN ESLs into commercial device designs where accurate control of the etch depth of the ridge waveguide is necessary for stable, kink-free operation at high output powers.

Formation of Ohmic contact to semipolar (11-22) p-GaN by electrical breakdown method

NASA Astrophysics Data System (ADS)

Jeong, Seonghoon; Lee, Sung-Nam; Kim, Hyunsoo

2018-01-01

The electrical breakdown (EBD) method was used to obtain Ohmic contact to semipolar (11-20) p-GaN surfaces using the Ti/SiO2/ p-GaN structure. The EBD method by which the electrical stress voltage was increased up to 70 V with a compliance current of 30 mA resulted in an Ohmic contact with a specific contact resistance of 3.1×10-3 Ωcm2. The transmission electron microscope (TEM) analysis revealed that the oxygen was slightly out-diffused from SiO2 layer toward Ti surface and the oxidation occurred at the Ti surface, while the GaN remained unchanged.

Evolutionary optimization methods for accelerator design

NASA Astrophysics Data System (ADS)

Poklonskiy, Alexey A.

Many problems from the fields of accelerator physics and beam theory can be formulated as optimization problems and, as such, solved using optimization methods. Despite growing efficiency of the optimization methods, the adoption of modern optimization techniques in these fields is rather limited. Evolutionary Algorithms (EAs) form a relatively new and actively developed optimization methods family. They possess many attractive features such as: ease of the implementation, modest requirements on the objective function, a good tolerance to noise, robustness, and the ability to perform a global search efficiently. In this work we study the application of EAs to problems from accelerator physics and beam theory. We review the most commonly used methods of unconstrained optimization and describe the GATool, evolutionary algorithm and the software package, used in this work, in detail. Then we use a set of test problems to assess its performance in terms of computational resources, quality of the obtained result, and the tradeoff between them. We justify the choice of GATool as a heuristic method to generate cutoff values for the COSY-GO rigorous global optimization package for the COSY Infinity scientific computing package. We design the model of their mutual interaction and demonstrate that the quality of the result obtained by GATool increases as the information about the search domain is refined, which supports the usefulness of this model. We Giscuss GATool's performance on the problems suffering from static and dynamic noise and study useful strategies of GATool parameter tuning for these and other difficult problems. We review the challenges of constrained optimization with EAs and methods commonly used to overcome them. We describe REPA, a new constrained optimization method based on repairing, in exquisite detail, including the properties of its two repairing techniques: REFIND and REPROPT. We assess REPROPT's performance on the standard constrained

Application of GA, PSO, and ACO algorithms to path planning of autonomous underwater vehicles

NASA Astrophysics Data System (ADS)

Aghababa, Mohammad Pourmahmood; Amrollahi, Mohammad Hossein; Borjkhani, Mehdi

2012-09-01

In this paper, an underwater vehicle was modeled with six dimensional nonlinear equations of motion, controlled by DC motors in all degrees of freedom. Near-optimal trajectories in an energetic environment for underwater vehicles were computed using a numerical solution of a nonlinear optimal control problem (NOCP). An energy performance index as a cost function, which should be minimized, was defined. The resulting problem was a two-point boundary value problem (TPBVP). A genetic algorithm (GA), particle swarm optimization (PSO), and ant colony optimization (ACO) algorithms were applied to solve the resulting TPBVP. Applying an Euler-Lagrange equation to the NOCP, a conjugate gradient penalty method was also adopted to solve the TPBVP. The problem of energetic environments, involving some energy sources, was discussed. Some near-optimal paths were found using a GA, PSO, and ACO algorithms. Finally, the problem of collision avoidance in an energetic environment was also taken into account.

Effects of two-step Mg doping in p-GaN on efficiency characteristics of InGaN blue light-emitting diodes without AlGaN electron-blocking layers

NASA Astrophysics Data System (ADS)

Ryu, Han-Youl; Lee, Jong-Moo

2013-05-01

A light-emitting diode (LED) structure containing p-type GaN layers with two-step Mg doping profiles is proposed to achieve high-efficiency performance in InGaN-based blue LEDs without any AlGaN electron-blocking-layer structures. Photoluminescence and electroluminescence (EL) measurement results show that, as the hole concentration in the p-GaN interlayer between active region and the p-GaN layer increases, defect-related nonradiative recombination increases, while the electron current leakage decreases. Under a certain hole-concentration condition in the p-GaN interlayer, the electron leakage and active region degradation are optimized so that high EL efficiency can be achieved. The measured efficiency characteristics are analyzed and interpreted using numerical simulations.

GaAs/AlOx high-contrast grating mirrors for mid-infrared VCSELs

NASA Astrophysics Data System (ADS)

Almuneau, G.; Laaroussi, Y.; Chevallier, C.; Genty, F.; Fressengeas, N. s.; Cerutti, L.; Gauthier-Lafaye, Olivier

2015-02-01

Mid-infrared Vertical cavity surface emitting lasers (MIR-VCSEL) are very attractive compact sources for spectroscopic measurements above 2μm, relevant for molecules sensing in various application domains. A long-standing issue for long wavelength VCSEL is the large structure thickness affecting the laser properties, added for the MIR to the tricky technological implementation of the antimonide alloys system. In this paper, we propose a new geometry for MIR-VCSEL including both a lateral confinement by an oxide aperture, and a high-contrast sub-wavelength grating mirror (HCG mirror) formed by the high contrast combination AIOx/GaAs in place of GaSb/A|AsSb top Bragg reflector. In addition to drastically simplifying the vertical stack, HCG mirror allows to control through its design the beam properties. The robust design of the HCG has been ensured by an original method of optimization based on particle swarm optimization algorithm combined with an anti-optimization one, thus allowing large error tolerance for the nano-fabrication. Oxide-based electro-optical confinement has been adapted to mid-infrared lasers, byusing a metamorphic approach with (Al) GaAs layer directly epitaxially grown on the GaSb-based VCSEL bottom structure. This approach combines the advantages of the will-controlled oxidation of AlAs layer and the efficient gain media of Sb-based for mid-infrared emission. We finally present the results obtained on electrically pumped mid-IR-VCSELs structures, for which we included oxide aperturing for lateral confinement and HCG as high reflectivity output mirrors, both based on AlxOy/GaAs heterostructures.

Optimal groundwater remediation design of pump and treat systems via a simulation-optimization approach and firefly algorithm

NASA Astrophysics Data System (ADS)

Javad Kazemzadeh-Parsi, Mohammad; Daneshmand, Farhang; Ahmadfard, Mohammad Amin; Adamowski, Jan; Martel, Richard

2015-01-01

In the present study, an optimization approach based on the firefly algorithm (FA) is combined with a finite element simulation method (FEM) to determine the optimum design of pump and treat remediation systems. Three multi-objective functions in which pumping rate and clean-up time are design variables are considered and the proposed FA-FEM model is used to minimize operating costs, total pumping volumes and total pumping rates in three scenarios while meeting water quality requirements. The groundwater lift and contaminant concentration are also minimized through the optimization process. The obtained results show the applicability of the FA in conjunction with the FEM for the optimal design of groundwater remediation systems. The performance of the FA is also compared with the genetic algorithm (GA) and the FA is found to have a better convergence rate than the GA.

In situ passivation of GaAsP nanowires.

PubMed

Himwas, C; Collin, S; Rale, P; Chauvin, N; Patriarche, G; Oehler, F; Julien, F H; Travers, L; Harmand, J-C; Tchernycheva, M

2017-12-08

We report on the structural and optical properties of GaAsP nanowires (NWs) grown by molecular-beam epitaxy. By adjusting the alloy composition in the NWs, the transition energy was tuned to the optimal value required for tandem III-V/silicon solar cells. We discovered that an unintentional shell was also formed during the GaAsP NW growth. The NW surface was passivated by an in situ deposition of a radial Ga(As)P shell. Different shell compositions and thicknesses were investigated. We demonstrate that the optimal passivation conditions for GaAsP NWs (with a gap of 1.78 eV) are obtained with a 5 nm thick GaP shell. This passivation enhances the luminescence intensity of the NWs by 2 orders of magnitude and yields a longer luminescence decay. The luminescence dynamics changes from single exponential decay with a 4 ps characteristic time in non-passivated NWs to a bi-exponential decay with characteristic times of 85 and 540 ps in NWs with GaP shell passivation.

Guided particle swarm optimization method to solve general nonlinear optimization problems

NASA Astrophysics Data System (ADS)

Abdelhalim, Alyaa; Nakata, Kazuhide; El-Alem, Mahmoud; Eltawil, Amr

2018-04-01

The development of hybrid algorithms is becoming an important topic in the global optimization research area. This article proposes a new technique in hybridizing the particle swarm optimization (PSO) algorithm and the Nelder-Mead (NM) simplex search algorithm to solve general nonlinear unconstrained optimization problems. Unlike traditional hybrid methods, the proposed method hybridizes the NM algorithm inside the PSO to improve the velocities and positions of the particles iteratively. The new hybridization considers the PSO algorithm and NM algorithm as one heuristic, not in a sequential or hierarchical manner. The NM algorithm is applied to improve the initial random solution of the PSO algorithm and iteratively in every step to improve the overall performance of the method. The performance of the proposed method was tested over 20 optimization test functions with varying dimensions. Comprehensive comparisons with other methods in the literature indicate that the proposed solution method is promising and competitive.

Improved Fractal Space Filling Curves Hybrid Optimization Algorithm for Vehicle Routing Problem.

PubMed

Yue, Yi-xiang; Zhang, Tong; Yue, Qun-xing

2015-01-01

Vehicle Routing Problem (VRP) is one of the key issues in optimization of modern logistics system. In this paper, a modified VRP model with hard time window is established and a Hybrid Optimization Algorithm (HOA) based on Fractal Space Filling Curves (SFC) method and Genetic Algorithm (GA) is introduced. By incorporating the proposed algorithm, SFC method can find an initial and feasible solution very fast; GA is used to improve the initial solution. Thereafter, experimental software was developed and a large number of experimental computations from Solomon's benchmark have been studied. The experimental results demonstrate the feasibility and effectiveness of the HOA.

AlGaN/GaN HEMTs regrown by MBE on epi-ready semi-insulating GaN-on-sapphire with inhibited interface contamination

NASA Astrophysics Data System (ADS)

Cordier, Y.; Azize, M.; Baron, N.; Chenot, S.; Tottereau, O.; Massies, J.

2007-11-01

In this work, we show that, by carefully designing the subsurface Fe doping profile in SI-GaN templates grown by MOVPE and by optimizing the MBE regrowth conditions, a highly resistive GaN buffer can be achieved on these epi-ready GaN-on-sapphire templates without any addition of acceptors during the regrowth. As a result, high-quality high electron mobility transistors can be fabricated. Furthermore, we report on the excellent properties of two-dimensional electron gas and device performances with electron mobility greater than 2000 cm 2/V s at room temperature and off-state buffer leakage currents as low as 5 μA/mm at 100 V.

Long-wavelength room-temperature luminescence from InAs/GaAs quantum dots with an optimized GaAsSbN capping layer

PubMed Central

2014-01-01

An extensive study on molecular beam epitaxy growth conditions of quaternary GaAsSbN as a capping layer (CL) for InAs/GaAs quantum dots (QD) was carried out. In particular, CL thickness, growth temperature, and growth rate were optimized. Problems related to the simultaneous presence of Sb and N, responsible for a significant degradation of photoluminescence (PL), are thereby solved allowing the achievement of room-temperature (RT) emission. A particularly strong improvement on the PL is obtained when the growth rate of the CL is increased. This is likely due to an improvement in the structural quality of the quaternary alloy that resulted from reduced strain and composition inhomogeneities. Nevertheless, a significant reduction of Sb and N incorporation was found when the growth rate was increased. Indeed, the incorporation of N is intrinsically limited to a maximum value of approximately 1.6% when the growth rate is at 2.0 ML s−1. Therefore, achieving RT emission and extending it somewhat beyond 1.3 μm were possible by means of a compromise among the growth conditions. This opens the possibility of exploiting the versatility on band structure engineering offered by this QD-CL structure in devices working at RT. PACS 81.15.Hi (molecular beam epitaxy); 78.55.Cr (III-V semiconductors); 73.21.La (quantum dots) PMID:24438542

An Analytic Approach for Optimal Geometrical Design of GaAs Nanowires for Maximal Light Harvesting in Photovoltaic Cells

PubMed Central

Wu, Dan; Tang, Xiaohong; Wang, Kai; Li, Xianqiang

2017-01-01

Semiconductor nanowires(NWs) with subwavelength scale diameters have demonstrated superior light trapping features, which unravel a new pathway for low cost and high efficiency future generation solar cells. Unlike other published work, a fully analytic design is for the first time proposed for optimal geometrical parameters of vertically-aligned GaAs NW arrays for maximal energy harvesting. Using photocurrent density as the light absorbing evaluation standard, 2 μm length NW arrays whose multiple diameters and periodicity are quantitatively identified achieving the maximal value of 29.88 mA/cm2 under solar illumination. It also turns out that our method has wide suitability for single, double and four different diameters of NW arrays for highest photon energy harvesting. To validate this analytical method, intensive numerical three-dimensional finite-difference time-domain simulations of the NWs’ light harvesting are also carried out. Compared with the simulation results, the predicted maximal photocurrent densities lie within 1.5% tolerance for all cases. Along with the high accuracy, through directly disclosing the exact geometrical dimensions of NW arrays, this method provides an effective and efficient route for high performance photovoltaic design. PMID:28425488

Homogeneous transparent conductive ZnO:Ga by ALD for large LED wafers

NASA Astrophysics Data System (ADS)

Szabó, Zoltán; Baji, Zsófia; Basa, Péter; Czigány, Zsolt; Bársony, István; Wang, Hsin-Ying; Volk, János

2016-08-01

Highly conductive and uniform Ga doped ZnO (GZO) films were prepared by atomic layer deposition (ALD) as transparent conductive layers for InGaN/GaN LEDs. The optimal Ga doping concentration was found to be 3 at%. Even for 4" wafers, the TCO layer shows excellent homogeneity of film resistivity (0.8 %) according to Eddy current and spectroscopic ellipsometry mapping. This makes ALD a favourable technique over concurrent methods like MBE and PLD where the up-scaling is problematic. In agreement with previous studies, it was found that by an annealing treatment the quality of the GZO/p-GaN interface can be improved, although it causes the degradation of TCO conductivity. Therefore, a two-step ALD deposition technique was proposed and demonstrated: a "buffer layer" deposited and annealed first was followed by a second deposition step to maintain the high conductivity of the top layer.

Rayleigh wave dispersion curve inversion by using particle swarm optimization and genetic algorithm

NASA Astrophysics Data System (ADS)

Buyuk, Ersin; Zor, Ekrem; Karaman, Abdullah

2017-04-01

Inversion of surface wave dispersion curves with its highly nonlinear nature has some difficulties using traditional linear inverse methods due to the need and strong dependence to the initial model, possibility of trapping in local minima and evaluation of partial derivatives. There are some modern global optimization methods to overcome of these difficulties in surface wave analysis such as Genetic algorithm (GA) and Particle Swarm Optimization (PSO). GA is based on biologic evolution consisting reproduction, crossover and mutation operations, while PSO algorithm developed after GA is inspired from the social behaviour of birds or fish of swarms. Utility of these methods require plausible convergence rate, acceptable relative error and optimum computation cost that are important for modelling studies. Even though PSO and GA processes are similar in appearence, the cross-over operation in GA is not used in PSO and the mutation operation is a stochastic process for changing the genes within chromosomes in GA. Unlike GA, the particles in PSO algorithm changes their position with logical velocities according to particle's own experience and swarm's experience. In this study, we applied PSO algorithm to estimate S wave velocities and thicknesses of the layered earth model by using Rayleigh wave dispersion curve and also compared these results with GA and we emphasize on the advantage of using PSO algorithm for geophysical modelling studies considering its rapid convergence, low misfit error and computation cost.

GaSb thermophotovoltaic cells grown on GaAs by molecular beam epitaxy using interfacial misfit arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Juang, Bor-Chau, E-mail: bcjuang@ucla.edu; Laghumavarapu, Ramesh B.; Foggo, Brandon J.

There exists a long-term need for foreign substrates on which to grow GaSb-based optoelectronic devices. We address this need by using interfacial misfit arrays to grow GaSb-based thermophotovoltaic cells directly on GaAs (001) substrates and demonstrate promising performance. We compare these cells to control devices grown on GaSb substrates to assess device properties and material quality. The room temperature dark current densities show similar characteristics for both cells on GaAs and on GaSb. Under solar simulation the cells on GaAs exhibit an open-circuit voltage of 0.121 V and a short-circuit current density of 15.5 mA/cm{sup 2}. In addition, the cells on GaAsmore » substrates maintain 10% difference in spectral response to those of the control cells over a large range of wavelengths. While the cells on GaSb substrates in general offer better performance than the cells on GaAs substrates, the cost-savings and scalability offered by GaAs substrates could potentially outweigh the reduction in performance. By further optimizing GaSb buffer growth on GaAs substrates, Sb-based compound semiconductors grown on GaAs substrates with similar performance to devices grown directly on GaSb substrates could be realized.« less

Sensitivity Analysis of Genetic Algorithm Parameters for Optimal Groundwater Monitoring Network Design

NASA Astrophysics Data System (ADS)

Abdeh-Kolahchi, A.; Satish, M.; Datta, B.

2004-05-01

A state art groundwater monitoring network design is introduced. The method combines groundwater flow and transport results with optimization Genetic Algorithm (GA) to identify optimal monitoring well locations. Optimization theory uses different techniques to find a set of parameter values that minimize or maximize objective functions. The suggested groundwater optimal monitoring network design is based on the objective of maximizing the probability of tracking a transient contamination plume by determining sequential monitoring locations. The MODFLOW and MT3DMS models included as separate modules within the Groundwater Modeling System (GMS) are used to develop three dimensional groundwater flow and contamination transport simulation. The groundwater flow and contamination simulation results are introduced as input to the optimization model, using Genetic Algorithm (GA) to identify the groundwater optimal monitoring network design, based on several candidate monitoring locations. The groundwater monitoring network design model is used Genetic Algorithms with binary variables representing potential monitoring location. As the number of decision variables and constraints increase, the non-linearity of the objective function also increases which make difficulty to obtain optimal solutions. The genetic algorithm is an evolutionary global optimization technique, which is capable of finding the optimal solution for many complex problems. In this study, the GA approach capable of finding the global optimal solution to a groundwater monitoring network design problem involving 18.4X 1018 feasible solutions will be discussed. However, to ensure the efficiency of the solution process and global optimality of the solution obtained using GA, it is necessary that appropriate GA parameter values be specified. The sensitivity analysis of genetic algorithms parameters such as random number, crossover probability, mutation probability, and elitism are discussed for solution of

Influence of cost functions and optimization methods on solving the inverse problem in spatially resolved diffuse reflectance spectroscopy

NASA Astrophysics Data System (ADS)

Rakotomanga, Prisca; Soussen, Charles; Blondel, Walter C. P. M.

2017-03-01

Diffuse reflectance spectroscopy (DRS) has been acknowledged as a valuable optical biopsy tool for in vivo characterizing pathological modifications in epithelial tissues such as cancer. In spatially resolved DRS, accurate and robust estimation of the optical parameters (OP) of biological tissues is a major challenge due to the complexity of the physical models. Solving this inverse problem requires to consider 3 components: the forward model, the cost function, and the optimization algorithm. This paper presents a comparative numerical study of the performances in estimating OP depending on the choice made for each of the latter components. Mono- and bi-layer tissue models are considered. Monowavelength (scalar) absorption and scattering coefficients are estimated. As a forward model, diffusion approximation analytical solutions with and without noise are implemented. Several cost functions are evaluated possibly including normalized data terms. Two local optimization methods, Levenberg-Marquardt and TrustRegion-Reflective, are considered. Because they may be sensitive to the initial setting, a global optimization approach is proposed to improve the estimation accuracy. This algorithm is based on repeated calls to the above-mentioned local methods, with initial parameters randomly sampled. Two global optimization methods, Genetic Algorithm (GA) and Particle Swarm Optimization (PSO), are also implemented. Estimation performances are evaluated in terms of relative errors between the ground truth and the estimated values for each set of unknown OP. The combination between the number of variables to be estimated, the nature of the forward model, the cost function to be minimized and the optimization method are discussed.

Isolating GaSb membranes grown metamorphically on GaAs substrates using highly selective substrate removal etch processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lavrova, Olga; Balakrishnan, Ganesh

2017-02-24

The etch rates of NH 4OH:H 2O 2 and C 6H 8O 7:H 2O 2 for GaAs and GaSb have been investigated to develop a selective etch for GaAs substrates and to isolate GaSb epilayers grown on GaAs. The NH 4OH:H 2O 2 solution has a greater etch rate differential for the GaSb/GaAs material system than C 6H 8O 7:H 2O 2 solution. The selectivity of NH 4OH:H 2O 2 for GaAs/GaSb under optimized etch conditions has been observed to be as high as 11471 ± 1691 whereas that of C 6H 8O 7:H 2O 2 has been measured upmore » to 143 ± 2. The etch contrast has been verified by isolating 2 μm thick GaSb epi-layers that were grown on GaAs substrates. GaSb membranes were tested and characterized with high-resolution X-Ray diffraction (HR-XRD) and atomic force microscopy (AFM).« less

Optimal design of loudspeaker arrays for robust cross-talk cancellation using the Taguchi method and the genetic algorithm.

PubMed

Bai, Mingsian R; Tung, Chih-Wei; Lee, Chih-Chung

2005-05-01

An optimal design technique of loudspeaker arrays for cross-talk cancellation with application in three-dimensional audio is presented. An array focusing scheme is presented on the basis of the inverse propagation that relates the transducers to a set of chosen control points. Tikhonov regularization is employed in designing the inverse cancellation filters. An extensive analysis is conducted to explore the cancellation performance and robustness issues. To best compromise the performance and robustness of the cross-talk cancellation system, optimal configurations are obtained with the aid of the Taguchi method and the genetic algorithm (GA). The proposed systems are further justified by physical as well as subjective experiments. The results reveal that large number of loudspeakers, closely spaced configuration, and optimal control point design all contribute to the robustness of cross-talk cancellation systems (CCS) against head misalignment.

Research on energy-saving optimal control of trains in a following operation under a fixed four-aspect autoblock system based on multi-dimension parallel GA

NASA Astrophysics Data System (ADS)

Lu, Qiheng; Feng, Xiaoyun

2013-03-01

After analyzing the working principle of the four-aspect fixed autoblock system, an energy-saving control model was created based on the dynamics equations of the trains in order to study the energy-saving optimal control strategy of trains in a following operation. Besides the safety and punctuality, the main aims of the model were the energy consumption and the time error. Based on this model, the static and dynamic speed restraints under a four-aspect fixed autoblock system were put forward. The multi-dimension parallel genetic algorithm (GA) and the external punishment function were adopted to solve this problem. By using the real number coding and the strategy of ramps divided into three parts, the convergence of GA was speeded up and the length of chromosomes was shortened. A vector of Gaussian random disturbance with zero mean was superposed to the mutation operator. The simulation result showed that the method could reduce the energy consumption effectively based on safety and punctuality.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1979-01-01

The optimization of space processing of GaAs is described. The detailed compositional, structural, and electronic characterization of GaAs on a macro- and microscale and the relationships between growth parameters and the properties of GaAs are among the factors discussed. The key parameters limiting device performance are assessed.

Improved 68 Ga-labeling method using ethanol addition: Application to the α-helical peptide DOTA-FAMP.

PubMed

Hasegawa, Koki; Kawachi, Emi; Uehara, Yoshinari; Yoshida, Tsuyoshi; Imaizumi, Satoshi; Ogawa, Masahiro; Miura, Shin-Ichiro; Saku, Keijiro

2017-01-01

We examined the 68 Ga labeling of the α-helical peptide, DOTA-FAMP, and evaluated conformational changes during radiolabeling. 68 Ga-DOTA-FAMP is a positron emission tomography probe candidate for atherosclerotic plaques. The labeling yield achieved by Zhernosekov's method (using acetone for 68 Ga purification) was compared with that achieved by the original and 2 modified Mueller's methods (using NaCl solution). Modified method I involves desalting the 68 Ga prior to labeling, and modified method II involves the inclusion of ethanol in the labeling solution. The labeling yield using Zhernosekov's method was 62% ± 5.4%. In comparison, Mueller's original method gave 8.9% ± 1.7%. Modified method I gave a slight improvement of 32% ± 2.1%. Modified method II further increased the yield to 66% ± 3.4%. Conformational changes were determined by circular dichroism spectroscopy, revealing that these differences could be attributed to conformational changes. Heat treatment affects peptide conformation, which leads to aggregation and decreases the labeling yield. Mueller's method is simpler, but harsh conditions preclude its application to biomolecules. To suppress aggregation, we included a desalting process and added ethanol in the labeling solution. These changes significantly improved the labeling yield. Before use for imaging, conformational changes of biomolecules during radiolabeling should be evaluated by circular dichroism spectroscopy to ensure the homogeneity of the labeled product. Copyright © 2016 John Wiley & Sons, Ltd.

Performance index and meta-optimization of a direct search optimization method

NASA Astrophysics Data System (ADS)

Krus, P.; Ölvander, J.

2013-10-01

Design optimization is becoming an increasingly important tool for design, often using simulation as part of the evaluation of the objective function. A measure of the efficiency of an optimization algorithm is of great importance when comparing methods. The main contribution of this article is the introduction of a singular performance criterion, the entropy rate index based on Shannon's information theory, taking both reliability and rate of convergence into account. It can also be used to characterize the difficulty of different optimization problems. Such a performance criterion can also be used for optimization of the optimization algorithms itself. In this article the Complex-RF optimization method is described and its performance evaluated and optimized using the established performance criterion. Finally, in order to be able to predict the resources needed for optimization an objective function temperament factor is defined that indicates the degree of difficulty of the objective function.

An Integrated Method for Airfoil Optimization

NASA Astrophysics Data System (ADS)

Okrent, Joshua B.

Design exploration and optimization is a large part of the initial engineering and design process. To evaluate the aerodynamic performance of a design, viscous Navier-Stokes solvers can be used. However this method can prove to be overwhelmingly time consuming when performing an initial design sweep. Therefore, another evaluation method is needed to provide accurate results at a faster pace. To accomplish this goal, a coupled viscous-inviscid method is used. This thesis proposes an integrated method for analyzing, evaluating, and optimizing an airfoil using a coupled viscous-inviscid solver along with a genetic algorithm to find the optimal candidate. The method proposed is different from prior optimization efforts in that it greatly broadens the design space, while allowing the optimization to search for the best candidate that will meet multiple objectives over a characteristic mission profile rather than over a single condition and single optimization parameter. The increased design space is due to the use of multiple parametric airfoil families, namely the NACA 4 series, CST family, and the PARSEC family. Almost all possible airfoil shapes can be created with these three families allowing for all possible configurations to be included. This inclusion of multiple airfoil families addresses a possible criticism of prior optimization attempts since by only focusing on one airfoil family, they were inherently limiting the number of possible airfoil configurations. By using multiple parametric airfoils, it can be assumed that all reasonable airfoil configurations are included in the analysis and optimization and that a global and not local maximum is found. Additionally, the method used is amenable to customization to suit any specific needs as well as including the effects of other physical phenomena or design criteria and/or constraints. This thesis found that an airfoil configuration that met multiple objectives could be found for a given set of nominal

Thermal Analysis of AlGaN/GaN High-Electron-Mobility Transistor and Its RF Power Efficiency Optimization with Source-Bridged Field-Plate Structure.

PubMed

Kwak, Hyeon-Tak; Chang, Seung-Bo; Jung, Hyun-Gu; Kim, Hyun-Seok

2018-09-01

In this study, we consider the relationship between the temperature in a two-dimensional electron gas (2-DEG) channel layer and the RF characteristics of an AlGaN/GaN high-electron-mobility transistor by changing the geometrical structure of the field-plate. The final goal is to achieve a high power efficiency by decreasing the channel layer temperature. First, simulations were performed to compare and contrast the experimental data of a conventional T-gate head structure. Then, a source-bridged field-plate (SBFP) structure was used to obtain the lower junction temperature in the 2-DEG channel layer. The peak electric field intensity was reduced, and a decrease in channel temperature resulted in an increase in electron mobility. Furthermore, the gate-to-source capacitance was increased by the SBFP structure. However, under the large current flow condition, the SBFP structure had a lower maximum temperature than the basic T-gate head structure, which improved the device electron mobility. Eventually, an optimum position of the SBFP was used, which led to higher frequency responses and improved the breakdown voltages. Hence, the optimized SBFP structure can be a promising candidate for high-power RF devices.

Nonlinear absorption in AlGaAs/GaAs multiple quantum well structures grown by metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Lee, H. C.; Hariz, A.; Dapkus, P. D.; Kost, A.; Kawase, M.

1987-01-01

This paper reports the study of growth conditions for achieving the sharp exciton resonances and low-intensity saturation of these resonances in AlGaAs-GaAs multiple quantum well structures grown by metalorganic chemical vapor deposition. Low growth temperature is necessary to observe this sharp resonance feature at room temperature. The optimal growth conditions are a tradeoff between the high temperatures required for high quality AlGaAs and low temperatures required for high-purity GaAs. A strong optical saturation of the excitonic absorption has been observed. A saturation density as low as 250 W/sq cm is reported.

A novel hybrid genetic algorithm for optimal design of IPM machines for electric vehicle

NASA Astrophysics Data System (ADS)

Wang, Aimeng; Guo, Jiayu

2017-12-01

A novel hybrid genetic algorithm (HGA) is proposed to optimize the rotor structure of an IPM machine which is used in EV application. The finite element (FE) simulation results of the HGA design is compared with the genetic algorithm (GA) design and those before optimized. It is shown that the performance of the IPMSM is effectively improved by employing the GA and HGA, especially by HGA. Moreover, higher flux-weakening capability and less magnet usage are also obtained. Therefore, the validity of HGA method in IPMSM optimization design is verified.

Basic ammonothermal GaN growth in molybdenum capsules

NASA Astrophysics Data System (ADS)

Pimputkar, S.; Speck, J. S.; Nakamura, S.

2016-12-01

Single crystal, bulk gallium nitride (GaN) crystals were grown using the basic ammonothermal method in a high purity growth environment created using a non-hermetically sealed molybdenum (Mo) capsule and compared to growths performed in a similarly designed silver (Ag) capsule and capsule-free René 41 autoclave. Secondary ion mass spectrometry (SIMS) analysis revealed transition metal free (<1×1017 cm-3) GaN crystals. Anomalously low oxygen concentrations ((2-6)×1018 cm-3) were measured in a {0001} seeded crystal boule grown using a Mo capsule, despite higher source material oxygen concentrations ((1-5)×1019 cm-3) suggesting that molybdenum (or molybdenum nitrides) may act to getter oxygen under certain conditions. Total system pressure profiles from growth runs in a Mo capsule system were comparable to those without a capsule, with pressures peaking within 2 days and slowly decaying due to hydrogen diffusional losses. Measured Mo capsule GaN growth rates were comparable to un-optimized growth rates in capsule-free systems and appreciably slower than in Ag-capsule systems. Crystal quality replicated that of the GaN seed crystals for all capsule conditions, with high quality growth occurring on the (0001) Ga-face. Optical absorption and impurity concentration characterization suggests reduced concentrations of hydrogenated gallium vacancies (VGa-Hx).

Study of gain and photoresponse characteristics for back-illuminated separate absorption and multiplication GaN avalanche photodiodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xiaodong; Pan, Ming; Hou, Liwei

2014-01-07

The gain and photoresponse characteristics have been numerically studied for back-illuminated separate absorption and multiplication (SAM) GaN avalanche photodiodes (APDs). The parameters of fundamental models are calibrated by simultaneously comparing the simulated dark and light current characteristics with the experimental results. Effects of environmental temperatures and device dimensions on gain characteristics have been investigated, and a method to achieve the optimum thickness of charge layer is obtained. The dependence of gain characteristics and breakdown voltage on the doping concentration of the charge layer is also studied in detail to get the optimal charge layer. The bias-dependent spectral responsivity and quantummore » efficiency are then presented to study the photoresponse mechanisms inside SAM GaN APDs. It is found the responsivity peak red-shifts at first due to the Franz-Keldysh effect and then blue-shifts due to the reach-through effect of the absorption layer. Finally, a new SAM GaN/AlGaN heterojunction APD structure is proposed for optimizing SAM GaN APDs.« less

Genetic Algorithm Optimization of Phononic Bandgap Structures

DTIC Science & Technology

2006-09-01

a GA with a computational finite element method for solving the acoustic wave equation, and find optimal designs for both metal-matrix composite...systems consisting of Ti/SiC, and H2O-filled porous ceramic media, by maximizing the relative acoustic bandgap for these media. The term acoustic here...stress minimization, global optimization, phonon bandgap, genetic algorithm, periodic elastic media, inhomogeneity, inclusion, porous media, acoustic

Particle Swarm Optimization Toolbox

NASA Technical Reports Server (NTRS)

Grant, Michael J.

2010-01-01

The Particle Swarm Optimization Toolbox is a library of evolutionary optimization tools developed in the MATLAB environment. The algorithms contained in the library include a genetic algorithm (GA), a single-objective particle swarm optimizer (SOPSO), and a multi-objective particle swarm optimizer (MOPSO). Development focused on both the SOPSO and MOPSO. A GA was included mainly for comparison purposes, and the particle swarm optimizers appeared to perform better for a wide variety of optimization problems. All algorithms are capable of performing unconstrained and constrained optimization. The particle swarm optimizers are capable of performing single and multi-objective optimization. The SOPSO and MOPSO algorithms are based on swarming theory and bird-flocking patterns to search the trade space for the optimal solution or optimal trade in competing objectives. The MOPSO generates Pareto fronts for objectives that are in competition. A GA, based on Darwin evolutionary theory, is also included in the library. The GA consists of individuals that form a population in the design space. The population mates to form offspring at new locations in the design space. These offspring contain traits from both of the parents. The algorithm is based on this combination of traits from parents to hopefully provide an improved solution than either of the original parents. As the algorithm progresses, individuals that hold these optimal traits will emerge as the optimal solutions. Due to the generic design of all optimization algorithms, each algorithm interfaces with a user-supplied objective function. This function serves as a "black-box" to the optimizers in which the only purpose of this function is to evaluate solutions provided by the optimizers. Hence, the user-supplied function can be numerical simulations, analytical functions, etc., since the specific detail of this function is of no concern to the optimizer. These algorithms were originally developed to support entry

Improved Fractal Space Filling Curves Hybrid Optimization Algorithm for Vehicle Routing Problem

PubMed Central

Yue, Yi-xiang; Zhang, Tong; Yue, Qun-xing

2015-01-01

Vehicle Routing Problem (VRP) is one of the key issues in optimization of modern logistics system. In this paper, a modified VRP model with hard time window is established and a Hybrid Optimization Algorithm (HOA) based on Fractal Space Filling Curves (SFC) method and Genetic Algorithm (GA) is introduced. By incorporating the proposed algorithm, SFC method can find an initial and feasible solution very fast; GA is used to improve the initial solution. Thereafter, experimental software was developed and a large number of experimental computations from Solomon's benchmark have been studied. The experimental results demonstrate the feasibility and effectiveness of the HOA. PMID:26167171

Optimization of a Tube Hydroforming Process

NASA Astrophysics Data System (ADS)

Abedrabbo, Nader; Zafar, Naeem; Averill, Ron; Pourboghrat, Farhang; Sidhu, Ranny

2004-06-01

An approach is presented to optimize a tube hydroforming process using a Genetic Algorithm (GA) search method. The goal of the study is to maximize formability by identifying the optimal internal hydraulic pressure and feed rate while satisfying the forming limit diagram (FLD). The optimization software HEEDS is used in combination with the nonlinear structural finite element code LS-DYNA to carry out the investigation. In particular, a sub-region of a circular tube blank is formed into a square die. Compared to the best results of a manual optimization procedure, a 55% increase in expansion was achieved when using the pressure and feed profiles identified by the automated optimization procedure.

Rapid thermal anneal in InP, GaAs and GaAs/GaAlAs

NASA Astrophysics Data System (ADS)

Descouts, B.; Duhamel, N.; Godefroy, S.; Krauz, P.

Ion implantation in semiconductors provides a doping technique with several advantages over more conventional doping methods and is now extensively used for device applications, e.g. field effect transistors (MESFET GaAs, MIS (InP), GaAs/GaAlAs heterojunction bipolar transistors (HBT). Because of the lattice disorder produced by the implantation, the dopant must be made electrically active by a postimplant anneal. As the device performances are very dependent on its electrical characteristics, the anneal is a very important stage of the process. Rapid anneal is known to provide less exodiffusion and less induffusion of impurities compared to conventional furnace anneal, so this technique has been used in this work to activate an n-type dopant (Si) in InP and a p-type dopant (Mg) in GaAs and GaAs/GaAIAs. These two ions have been chosen to realize implanted MIS InP and the base contacts for GaAs/GaAlAs HBTs. The experimental conditions to obtain the maximum electrical activity in these two cases will be detailed. For example, although we have not been able to obtain a flat profile in Mg + implanted GaAs/GaAlAs heterostructure by conventional thermal anneal, rapid thermal anneal gives a flat hole profile over a depth of 0.5 μm with a concentration of 1 x 10 19 cm -3.

Gallium-68-labelled NOTA-oligonucleotides: an optimized method for their preparation.

PubMed

Gijs, Marlies; Dammicco, Sylvestre; Warnier, Corentin; Aerts, An; Impens, Nathalie R E N; D'Huyvetter, Matthias; Léonard, Marc; Baatout, Sarah; Luxen, André

2016-02-01

One of the most essential aspects to the success of radiopharmaceuticals is an easy and reliable radiolabelling protocol to obtain pure and stable products. In this study, we optimized the bioconjugation and gallium-68 ((68) Ga) radiolabelling conditions for a single-stranded 40-mer DNA oligonucleotide, in order to obtain highly pure and stable radiolabelled oligonucleotides. Quantitative bioconjugation was obtained for a disulfide-functionalized oligonucleotide conjugated to the macrocylic bifunctional chelator MMA-NOTA (maleimido-mono-amide (1,4,7-triazanonane-1,4,7-triyl)triacetic acid). Next, this NOTA-oligonucleotide bioconjugate was radiolabelled at room temperature with purified and pre-concentrated (68) Ga with quantitative levels of radioactive incorporation and high radiochemical and chemical purity. In addition, high chelate stability was observed in physiological-like conditions (37 °C, PBS and serum), in the presence of a transchelator (EDTA) and transferrin. A specific activity of 51.1 MBq/nmol was reached using a 1470-fold molar excess bioconjugate over (68) Ga. This study presents a fast, straightforward and reliable protocol for the preparation of (68) Ga-radiolabelled DNA oligonucleotides under mild reaction conditions and without the use of organic solvents. The methodology herein developed will be applied to the preparation of oligonucleotidic sequences (aptamers) targeting the human epidermal growth factor receptor 2 (HER2) for cancer imaging. Copyright © 2015 John Wiley & Sons, Ltd.

Novel model of a AlGaN/GaN high electron mobility transistor based on an artificial neural network

NASA Astrophysics Data System (ADS)

Cheng, Zhi-Qun; Hu, Sha; Liu, Jun; Zhang, Qi-Jun

2011-03-01

In this paper we present a novel approach to modeling AlGaN/GaN high electron mobility transistor (HEMT) with an artificial neural network (ANN). The AlGaN/GaN HEMT device structure and its fabrication process are described. The circuit-based Neuro-space mapping (neuro-SM) technique is studied in detail. The EEHEMT model is implemented according to the measurement results of the designed device, which serves as a coarse model. An ANN is proposed to model AlGaN/GaN HEMT based on the coarse model. Its optimization is performed. The simulation results from the model are compared with the measurement results. It is shown that the simulation results obtained from the ANN model of AlGaN/GaN HEMT are more accurate than those obtained from the EEHEMT model. Project supported by the National Natural Science Foundation of China (Grant No. 60776052).

Optimization of Boiling Water Reactor Loading Pattern Using Two-Stage Genetic Algorithm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kobayashi, Yoko; Aiyoshi, Eitaro

2002-10-15

A new two-stage optimization method based on genetic algorithms (GAs) using an if-then heuristic rule was developed to generate optimized boiling water reactor (BWR) loading patterns (LPs). In the first stage, the LP is optimized using an improved GA operator. In the second stage, an exposure-dependent control rod pattern (CRP) is sought using GA with an if-then heuristic rule. The procedure of the improved GA is based on deterministic operators that consist of crossover, mutation, and selection. The handling of the encoding technique and constraint conditions by that GA reflects the peculiar characteristics of the BWR. In addition, strategies suchmore » as elitism and self-reproduction are effectively used in order to improve the search speed. The LP evaluations were performed with a three-dimensional diffusion code that coupled neutronic and thermal-hydraulic models. Strong axial heterogeneities and constraints dependent on three dimensions have always necessitated the use of three-dimensional core simulators for BWRs, so that optimization of computational efficiency is required. The proposed algorithm is demonstrated by successfully generating LPs for an actual BWR plant in two phases. One phase is only LP optimization applying the Haling technique. The other phase is an LP optimization that considers the CRP during reactor operation. In test calculations, candidates that shuffled fresh and burned fuel assemblies within a reasonable computation time were obtained.« less

Thermodynamic properties of gadolinium in Ga-Sn and Ga-Zn eutectic based alloys

NASA Astrophysics Data System (ADS)

Maltsev, Dmitry S.; Volkovich, Vladimir A.; Yamshchikov, Leonid F.; Chukin, Andrey V.

2016-09-01

Thermodynamic properties of gadolinium in Ga-Sn and Ga-Zn eutectic based alloys were studied. Temperature dependences of gadolinium activity in the studied alloys were determined at 573-1073 K employing the EMF method. Solubility of gadolinium in the Ga-Sn and Ga-Zn alloys was measured at 462-1073 K using IMCs sedimentation method. Activity coefficients as well as partial and excess thermodynamic functions of gadolinium in the studied alloys were calculated on the basis of the obtained experimental data.

Fine structure of Fe-Co-Ga and Fe-Cr-Ga alloys with low Ga content

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kleinerman, Nadezhda M., E-mail: kleinerman@imp.uran.ru; Serikov, Vadim V., E-mail: kleinerman@imp.uran.ru; Vershinin, Aleksandr V., E-mail: kleinerman@imp.uran.ru

2014-10-27

Investigation of Ga influence on the structure of Fe-Cr and Fe-Co alloys was performed with the use of {sup 57}Fe Mössbauer spectroscopy and X-ray diffraction methods. In the alloys of the Fe-Cr system, doping with Ga handicaps the decomposition of solid solutions, observed in the binary alloys, and increases its stability. In the alloys with Co, Ga also favors the uniformity of solid solutions. The analysis of Mössbauer experiments gives some grounds to conclude that if, owing to liquation, clusterization, or initial stages of phase separation, there exist regions enriched in iron, some amount of Ga atoms prefer to entermore » the nearest surroundings of iron atoms, thus forming binary Fe-Ga regions (or phases)« less

Particle swarm optimization - Genetic algorithm (PSOGA) on linear transportation problem

NASA Astrophysics Data System (ADS)

Rahmalia, Dinita

2017-08-01

Linear Transportation Problem (LTP) is the case of constrained optimization where we want to minimize cost subject to the balance of the number of supply and the number of demand. The exact method such as northwest corner, vogel, russel, minimal cost have been applied at approaching optimal solution. In this paper, we use heurisitic like Particle Swarm Optimization (PSO) for solving linear transportation problem at any size of decision variable. In addition, we combine mutation operator of Genetic Algorithm (GA) at PSO to improve optimal solution. This method is called Particle Swarm Optimization - Genetic Algorithm (PSOGA). The simulations show that PSOGA can improve optimal solution resulted by PSO.

A graph decomposition-based approach for water distribution network optimization

NASA Astrophysics Data System (ADS)

Zheng, Feifei; Simpson, Angus R.; Zecchin, Aaron C.; Deuerlein, Jochen W.

2013-04-01

A novel optimization approach for water distribution network design is proposed in this paper. Using graph theory algorithms, a full water network is first decomposed into different subnetworks based on the connectivity of the network's components. The original whole network is simplified to a directed augmented tree, in which the subnetworks are substituted by augmented nodes and directed links are created to connect them. Differential evolution (DE) is then employed to optimize each subnetwork based on the sequence specified by the assigned directed links in the augmented tree. Rather than optimizing the original network as a whole, the subnetworks are sequentially optimized by the DE algorithm. A solution choice table is established for each subnetwork (except for the subnetwork that includes a supply node) and the optimal solution of the original whole network is finally obtained by use of the solution choice tables. Furthermore, a preconditioning algorithm is applied to the subnetworks to produce an approximately optimal solution for the original whole network. This solution specifies promising regions for the final optimization algorithm to further optimize the subnetworks. Five water network case studies are used to demonstrate the effectiveness of the proposed optimization method. A standard DE algorithm (SDE) and a genetic algorithm (GA) are applied to each case study without network decomposition to enable a comparison with the proposed method. The results show that the proposed method consistently outperforms the SDE and GA (both with tuned parameters) in terms of both the solution quality and efficiency.

Profile Optimization Method for Robust Airfoil Shape Optimization in Viscous Flow

NASA Technical Reports Server (NTRS)

Li, Wu

2003-01-01

Simulation results obtained by using FUN2D for robust airfoil shape optimization in transonic viscous flow are included to show the potential of the profile optimization method for generating fairly smooth optimal airfoils with no off-design performance degradation.

On the Convergence Analysis of the Optimized Gradient Method.

PubMed

Kim, Donghwan; Fessler, Jeffrey A

2017-01-01

This paper considers the problem of unconstrained minimization of smooth convex functions having Lipschitz continuous gradients with known Lipschitz constant. We recently proposed the optimized gradient method for this problem and showed that it has a worst-case convergence bound for the cost function decrease that is twice as small as that of Nesterov's fast gradient method, yet has a similarly efficient practical implementation. Drori showed recently that the optimized gradient method has optimal complexity for the cost function decrease over the general class of first-order methods. This optimality makes it important to study fully the convergence properties of the optimized gradient method. The previous worst-case convergence bound for the optimized gradient method was derived for only the last iterate of a secondary sequence. This paper provides an analytic convergence bound for the primary sequence generated by the optimized gradient method. We then discuss additional convergence properties of the optimized gradient method, including the interesting fact that the optimized gradient method has two types of worstcase functions: a piecewise affine-quadratic function and a quadratic function. These results help complete the theory of an optimal first-order method for smooth convex minimization.

On the Convergence Analysis of the Optimized Gradient Method

PubMed Central

Kim, Donghwan; Fessler, Jeffrey A.

2016-01-01

This paper considers the problem of unconstrained minimization of smooth convex functions having Lipschitz continuous gradients with known Lipschitz constant. We recently proposed the optimized gradient method for this problem and showed that it has a worst-case convergence bound for the cost function decrease that is twice as small as that of Nesterov’s fast gradient method, yet has a similarly efficient practical implementation. Drori showed recently that the optimized gradient method has optimal complexity for the cost function decrease over the general class of first-order methods. This optimality makes it important to study fully the convergence properties of the optimized gradient method. The previous worst-case convergence bound for the optimized gradient method was derived for only the last iterate of a secondary sequence. This paper provides an analytic convergence bound for the primary sequence generated by the optimized gradient method. We then discuss additional convergence properties of the optimized gradient method, including the interesting fact that the optimized gradient method has two types of worstcase functions: a piecewise affine-quadratic function and a quadratic function. These results help complete the theory of an optimal first-order method for smooth convex minimization. PMID:28461707

Fuzzy Mixed Assembly Line Sequencing and Scheduling Optimization Model Using Multiobjective Dynamic Fuzzy GA

PubMed Central

Tahriri, Farzad; Dawal, Siti Zawiah Md; Taha, Zahari

2014-01-01

A new multiobjective dynamic fuzzy genetic algorithm is applied to solve a fuzzy mixed-model assembly line sequencing problem in which the primary goals are to minimize the total make-span and minimize the setup number simultaneously. Trapezoidal fuzzy numbers are implemented for variables such as operation and travelling time in order to generate results with higher accuracy and representative of real-case data. An improved genetic algorithm called fuzzy adaptive genetic algorithm (FAGA) is proposed in order to solve this optimization model. In establishing the FAGA, five dynamic fuzzy parameter controllers are devised in which fuzzy expert experience controller (FEEC) is integrated with automatic learning dynamic fuzzy controller (ALDFC) technique. The enhanced algorithm dynamically adjusts the population size, number of generations, tournament candidate, crossover rate, and mutation rate compared with using fixed control parameters. The main idea is to improve the performance and effectiveness of existing GAs by dynamic adjustment and control of the five parameters. Verification and validation of the dynamic fuzzy GA are carried out by developing test-beds and testing using a multiobjective fuzzy mixed production assembly line sequencing optimization problem. The simulation results highlight that the performance and efficacy of the proposed novel optimization algorithm are more efficient than the performance of the standard genetic algorithm in mixed assembly line sequencing model. PMID:24982962

Curie temperatures of cubic (Ga, Mn)N diluted magnetic semiconductors from the RKKY spin model.

PubMed

Zhu, Li-Fang; Liu, Bang-Gui

2009-11-04

We explore how much the RKKY spin interaction can contribute to the high-temperature ferromagnetism in cubic (Ga, Mn)N diluted magnetic semiconductors. The usual coupling constant is used and effective carriers are considered independent of doped magnetic atoms, as is shown experimentally. Our Monte Carlo simulated results show that maximal Curie temperature is reached at the optimal carrier concentration for a given Mn concentration, equaling 373 K for 5% Mn and 703 K for 8% Mn. Because such a Monte Carlo method does not overestimate transition temperatures, these calculations indicate that the RKKY spin interaction alone can yield high-enough Curie temperatures in cubic (Ga, Mn)N under optimized conditions.

Fabrication of p(+)-n junction GaAs solar cells by a novel method

NASA Technical Reports Server (NTRS)

Ghandhi, S. K.; Mathur, G.; Rode, H.; Borrego, J. M.

1984-01-01

A novel method for making p(+)-n diffused junction GaAs solar cells, with the formation of a diffusion source, an anti-reflective coating, and a protective cover glass in a single chemical-vapor deposition operation is discussed. Consideration is given to device fabrication and to solar-cell characteristics. The advantages of the technique are that the number of process steps is kept to an absolute minimum, the fabrication procedure is low-cost, and the GaAs surface is protected during the entire operation.

Review of design optimization methods for turbomachinery aerodynamics

NASA Astrophysics Data System (ADS)

Li, Zhihui; Zheng, Xinqian

2017-08-01

In today's competitive environment, new turbomachinery designs need to be not only more efficient, quieter, and ;greener; but also need to be developed at on much shorter time scales and at lower costs. A number of advanced optimization strategies have been developed to achieve these requirements. This paper reviews recent progress in turbomachinery design optimization to solve real-world aerodynamic problems, especially for compressors and turbines. This review covers the following topics that are important for optimizing turbomachinery designs. (1) optimization methods, (2) stochastic optimization combined with blade parameterization methods and the design of experiment methods, (3) gradient-based optimization methods for compressors and turbines and (4) data mining techniques for Pareto Fronts. We also present our own insights regarding the current research trends and the future optimization of turbomachinery designs.

Elimination of Bimodal Size in InAs/GaAs Quantum Dots for Preparation of 1.3-μm Quantum Dot Lasers

NASA Astrophysics Data System (ADS)

Su, Xiang-Bin; Ding, Ying; Ma, Ben; Zhang, Ke-Lu; Chen, Ze-Sheng; Li, Jing-Lun; Cui, Xiao-Ran; Xu, Ying-Qiang; Ni, Hai-Qiao; Niu, Zhi-Chuan

2018-02-01

The device characteristics of semiconductor quantum dot lasers have been improved with progress in active layer structures. Self-assembly formed InAs quantum dots grown on GaAs had been intensively promoted in order to achieve quantum dot lasers with superior device performances. In the process of growing high-density InAs/GaAs quantum dots, bimodal size occurs due to large mismatch and other factors. The bimodal size in the InAs/GaAs quantum dot system is eliminated by the method of high-temperature annealing and optimized the in situ annealing temperature. The annealing temperature is taken as the key optimization parameters, and the optimal annealing temperature of 680 °C was obtained. In this process, quantum dot growth temperature, InAs deposition, and arsenic (As) pressure are optimized to improve quantum dot quality and emission wavelength. A 1.3-μm high-performance F-P quantum dot laser with a threshold current density of 110 A/cm2 was demonstrated.

Elimination of Bimodal Size in InAs/GaAs Quantum Dots for Preparation of 1.3-μm Quantum Dot Lasers.

PubMed

Su, Xiang-Bin; Ding, Ying; Ma, Ben; Zhang, Ke-Lu; Chen, Ze-Sheng; Li, Jing-Lun; Cui, Xiao-Ran; Xu, Ying-Qiang; Ni, Hai-Qiao; Niu, Zhi-Chuan

2018-02-21

The device characteristics of semiconductor quantum dot lasers have been improved with progress in active layer structures. Self-assembly formed InAs quantum dots grown on GaAs had been intensively promoted in order to achieve quantum dot lasers with superior device performances. In the process of growing high-density InAs/GaAs quantum dots, bimodal size occurs due to large mismatch and other factors. The bimodal size in the InAs/GaAs quantum dot system is eliminated by the method of high-temperature annealing and optimized the in situ annealing temperature. The annealing temperature is taken as the key optimization parameters, and the optimal annealing temperature of 680 °C was obtained. In this process, quantum dot growth temperature, InAs deposition, and arsenic (As) pressure are optimized to improve quantum dot quality and emission wavelength. A 1.3-μm high-performance F-P quantum dot laser with a threshold current density of 110 A/cm 2 was demonstrated.

Simultaneous optimization method for absorption spectroscopy postprocessing.

PubMed

Simms, Jean M; An, Xinliang; Brittelle, Mack S; Ramesh, Varun; Ghandhi, Jaal B; Sanders, Scott T

2015-05-10

A simultaneous optimization method is proposed for absorption spectroscopy postprocessing. This method is particularly useful for thermometry measurements based on congested spectra, as commonly encountered in combustion applications of H2O absorption spectroscopy. A comparison test demonstrated that the simultaneous optimization method had greater accuracy, greater precision, and was more user-independent than the common step-wise postprocessing method previously used by the authors. The simultaneous optimization method was also used to process experimental data from an environmental chamber and a constant volume combustion chamber, producing results with errors on the order of only 1%.

Optimization of a Boiling Water Reactor Loading Pattern Using an Improved Genetic Algorithm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kobayashi, Yoko; Aiyoshi, Eitaro

2003-08-15

A search method based on genetic algorithms (GA) using deterministic operators has been developed to generate optimized boiling water reactor (BWR) loading patterns (LPs). The search method uses an Improved GA operator, that is, crossover, mutation, and selection. The handling of the encoding technique and constraint conditions is designed so that the GA reflects the peculiar characteristics of the BWR. In addition, some strategies such as elitism and self-reproduction are effectively used to improve the search speed. LP evaluations were performed with a three-dimensional diffusion code that coupled neutronic and thermal-hydraulic models. Strong axial heterogeneities and three-dimensional-dependent constraints have alwaysmore » necessitated the use of three-dimensional core simulators for BWRs, so that an optimization method is required for computational efficiency. The proposed algorithm is demonstrated by successfully generating LPs for an actual BWR plant applying the Haling technique. In test calculations, candidates that shuffled fresh and burned fuel assemblies within a reasonable computation time were obtained.« less

Simulation and analysis of the absorption enhancement in p-i-n InGaN/GaN solar cell using photonic crystal light trapping structures

NASA Astrophysics Data System (ADS)

Gupta, Nikhil Deep; Janyani, Vijay

2016-10-01

The structure of p-i-n InGaN/GaN based solar cell having a photonic crystal (PhC)-based light trapping structure (LTS) at the top assisted by the planar metallic (aluminum) back reflector (BR) is proposed. We propose two different designs for efficiency enhancement: in one we keep the PhC structure etching depth extending from the top antireflective coating (ARC) of indium tin oxide (ITO) up to the p-GaN layer (which is beneath the ITO and above the active layer), whereas in the other design, the PhC LTS etching depth has been extended up to the InxGa1-xN absorbing layer, starting from the top ITO layer. The theoretical optical simulation studies and optimization of the required parameters of the structure, which help to investigate and demonstrate the effectiveness of the LTS in the efficiency enhancement of the structure, are presented. The work also demonstrates the Lambertian light trapping limits for the practical indium concentrations in a InxGa1-xN active layer cell. The paper also presents the comparison between the proposed designs and compares their results with that of a planar reference cell. The studies are carried out for various indium concentrations. The results indicate considerable enhancement in the efficiency due to the PhC LTS, mainly because of better coupling, low reflectance, and diffraction capability of the proposed LTS, although it is still under the Lambertian limits. The performance evaluation of the proposed structure with respect to the angle of incident light has also been done, indicating improved performance. The parameters have been optimized and calculated by means of rigorous coupled wave analysis (RCWA) method.

Method of making V.sub.3 Ga superconductors

DOEpatents

Dew-Hughes, David

1980-01-01

An improved method for producing a vanadium-gallium superconductor wire having aluminum as a component thereof is disclosed, said wire being encased in a gallium bearing copper sheath. The superconductors disclosed herein may be fabricated under normal atmospheres and room temperatures by forming a tubular shaped billet having a core composed of an alloy of vanadium and aluminum and an outer sheath composed of an alloy of copper, gallium and aluminum. Thereafter the entire billet is swage reduced to form a wire therefrom and heat treated to form a layer of V.sub.3 Ga in the interior of the wire.

Mg doping of GaN by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Lieten, R. R.; Motsnyi, V.; Zhang, L.; Cheng, K.; Leys, M.; Degroote, S.; Buchowicz, G.; Dubon, O.; Borghs, G.

2011-04-01

We present a systematic study on the influence of growth conditions on the incorporation and activation of Mg in GaN layers grown by plasma-assisted molecular beam epitaxy. We show that high quality p-type GaN layers can be obtained on GaN-on-silicon templates. The Mg incorporation and the electrical properties have been investigated as a function of growth temperature, Ga : N flux ratio and Mg : Ga flux ratio. It was found that the incorporation of Mg and the electrical properties are highly sensitive to the Ga : N flux ratio. The highest hole mobility and lowest resistivity were achieved for slightly Ga-rich conditions. In addition to an optimal Ga : N ratio, an optimum Mg : Ga flux ratio was also observed at around 1%. We observed a clear Mg flux window for p-type doping of GaN : 0.31% < Mg : Ga < 5.0%. A lowest resistivity of 0.98 Ω cm was obtained for optimized growth conditions. The p-type GaN layer then showed a hole concentration of 4.3 × 1017 cm-3 and a mobility of 15 cm2 V-1 s-1. Temperature-dependent Hall effect measurements indicate an acceptor depth in these samples of 100 meV for a hole concentration of 5.5 × 1017 cm-3. The corresponding Mg concentration is 5 × 1019 cm-3, indicating approximately 1% activation at room temperature. In addition to continuous growth of Mg-doped GaN layers we also investigated different modulated growth procedures. We show that a modulated growth procedure has only limited influence on Mg doping at a growth temperature of 800 °C or higher. This result is thus in contrast to previously reported GaN : Mg doping at much lower growth temperatures of 500 °C.

An improved genetic algorithm for designing optimal temporal patterns of neural stimulation

NASA Astrophysics Data System (ADS)

Cassar, Isaac R.; Titus, Nathan D.; Grill, Warren M.

2017-12-01

Objective. Electrical neuromodulation therapies typically apply constant frequency stimulation, but non-regular temporal patterns of stimulation may be more effective and more efficient. However, the design space for temporal patterns is exceedingly large, and model-based optimization is required for pattern design. We designed and implemented a modified genetic algorithm (GA) intended for design optimal temporal patterns of electrical neuromodulation. Approach. We tested and modified standard GA methods for application to designing temporal patterns of neural stimulation. We evaluated each modification individually and all modifications collectively by comparing performance to the standard GA across three test functions and two biophysically-based models of neural stimulation. Main results. The proposed modifications of the GA significantly improved performance across the test functions and performed best when all were used collectively. The standard GA found patterns that outperformed fixed-frequency, clinically-standard patterns in biophysically-based models of neural stimulation, but the modified GA, in many fewer iterations, consistently converged to higher-scoring, non-regular patterns of stimulation. Significance. The proposed improvements to standard GA methodology reduced the number of iterations required for convergence and identified superior solutions.

Highly efficient X-range AlGaN/GaN power amplifier

NASA Astrophysics Data System (ADS)

Tural'chuk, P. A.; Kirillov, V. V.; Osipov, P. E.; Vendik, I. B.; Vendik, O. G.; Parnes, M. D.

2017-09-01

The development of microwave power amplifiers (PAs) based on transistors with an AlGaN/GaN heterojunction are discussed in terms of the possible enhancement of their efficiency. The main focus is on the synthesis of the transforming circuits, which ensure the reactive load at the second- and third-harmonic frequencies and complex impedance at the fundamental frequency. This makes it possible to optimize the complex operation mode of a PA; i.e., to reduce the scattering power and enhance the efficiency. A microwave PA based on the Schottky-barrier-gate field-effect transistor with 80 electrodes based on the GaN pHEMT transistor with a gate length of 0.25 nm and a gate width of 125 nm is experimentally investigated. The amplifier has a pulse output power of 35 W and a power-added efficiency of at least 50% at a working frequency of 9 GHz.

Study of GaN nanorods converted from β-Ga2O3

NASA Astrophysics Data System (ADS)

Li, Yuewen; Xiong, Zening; Zhang, Dongdong; Xiu, Xiangqian; Liu, Duo; Wang, Shuang; Hua, Xuemei; Xie, Zili; Tao, Tao; Liu, Bin; Chen, Peng; Zhang, Rong; Zheng, Youdou

2018-05-01

We report here high-quality β-Ga2O3 nanorods (NRs) grown on sapphire substrates by hydrothermal method. Ammoniating the β-Ga2O3 NRs results in strain-free wurtzite gallium nitride (GaN) NRs. It was shown by XRD and Raman spectroscopy that β-Ga2O3 was partially converted to GaN/β-Ga2O3 at 1000 °C and then completely converted to GaN NRs at 1050 °C, as confirmed by high-resolution transmission electron microscopy (HRTEM). There is no band-edge emission of β-Ga2O3 in the cathodoluminescence spectrum, and only a deep-level broad emission observed at 3.68-3.73 eV. The band edge emission (3.39 eV) of GaN NRs converted from β-Ga2O3 can also be observed.

Optimel: Software for selecting the optimal method

NASA Astrophysics Data System (ADS)

Popova, Olga; Popov, Boris; Romanov, Dmitry; Evseeva, Marina

Optimel: software for selecting the optimal method automates the process of selecting a solution method from the optimization methods domain. Optimel features practical novelty. It saves time and money when conducting exploratory studies if its objective is to select the most appropriate method for solving an optimization problem. Optimel features theoretical novelty because for obtaining the domain a new method of knowledge structuring was used. In the Optimel domain, extended quantity of methods and their properties are used, which allows identifying the level of scientific studies, enhancing the user's expertise level, expand the prospects the user faces and opening up new research objectives. Optimel can be used both in scientific research institutes and in educational institutions.

RBT-GA: a novel metaheuristic for solving the Multiple Sequence Alignment problem.

PubMed

Taheri, Javid; Zomaya, Albert Y

2009-07-07

Multiple Sequence Alignment (MSA) has always been an active area of research in Bioinformatics. MSA is mainly focused on discovering biologically meaningful relationships among different sequences or proteins in order to investigate the underlying main characteristics/functions. This information is also used to generate phylogenetic trees. This paper presents a novel approach, namely RBT-GA, to solve the MSA problem using a hybrid solution methodology combining the Rubber Band Technique (RBT) and the Genetic Algorithm (GA) metaheuristic. RBT is inspired by the behavior of an elastic Rubber Band (RB) on a plate with several poles, which is analogues to locations in the input sequences that could potentially be biologically related. A GA attempts to mimic the evolutionary processes of life in order to locate optimal solutions in an often very complex landscape. RBT-GA is a population based optimization algorithm designed to find the optimal alignment for a set of input protein sequences. In this novel technique, each alignment answer is modeled as a chromosome consisting of several poles in the RBT framework. These poles resemble locations in the input sequences that are most likely to be correlated and/or biologically related. A GA-based optimization process improves these chromosomes gradually yielding a set of mostly optimal answers for the MSA problem. RBT-GA is tested with one of the well-known benchmarks suites (BALiBASE 2.0) in this area. The obtained results show that the superiority of the proposed technique even in the case of formidable sequences.

RBT-GA: a novel metaheuristic for solving the multiple sequence alignment problem

PubMed Central

Taheri, Javid; Zomaya, Albert Y

2009-01-01

Background Multiple Sequence Alignment (MSA) has always been an active area of research in Bioinformatics. MSA is mainly focused on discovering biologically meaningful relationships among different sequences or proteins in order to investigate the underlying main characteristics/functions. This information is also used to generate phylogenetic trees. Results This paper presents a novel approach, namely RBT-GA, to solve the MSA problem using a hybrid solution methodology combining the Rubber Band Technique (RBT) and the Genetic Algorithm (GA) metaheuristic. RBT is inspired by the behavior of an elastic Rubber Band (RB) on a plate with several poles, which is analogues to locations in the input sequences that could potentially be biologically related. A GA attempts to mimic the evolutionary processes of life in order to locate optimal solutions in an often very complex landscape. RBT-GA is a population based optimization algorithm designed to find the optimal alignment for a set of input protein sequences. In this novel technique, each alignment answer is modeled as a chromosome consisting of several poles in the RBT framework. These poles resemble locations in the input sequences that are most likely to be correlated and/or biologically related. A GA-based optimization process improves these chromosomes gradually yielding a set of mostly optimal answers for the MSA problem. Conclusion RBT-GA is tested with one of the well-known benchmarks suites (BALiBASE 2.0) in this area. The obtained results show that the superiority of the proposed technique even in the case of formidable sequences. PMID:19594869

Influence of the AlN nucleation layer on the properties of AlGaN/GaN heterostructure on Si (1 1 1) substrates

NASA Astrophysics Data System (ADS)

Pan, Lei; Dong, Xun; Li, Zhonghui; Luo, Weike; Ni, Jinyu

2018-07-01

AlGaN/GaN heterostructures were grown on Si (1 1 1) substrates with different AlN nucleation layers (NL) by metal-organic chemical vapor deposition (MOCVD). The results indicate that the growth temperature of AlN NL has a noticeable influence on the structural, electronic and optical properties of the AlGaN/GaN heterostructures. Optimizing the growth temperature to 1040 °C led to quasi-2D smooth surface of the AlN NL with providing sufficient compressive stress to suppress cracking of the subsequent GaN layer during the cooling process, resulting in improved crystalline quality of GaN layer and superior two-dimensional electron gas (2DEG) performance of the AlGaN/GaN heterostructure.

Ohmic contact formation between metal and AlGaN/GaN heterostructure via graphene insertion

NASA Astrophysics Data System (ADS)

Sung Park, Pil; Reddy, Kongara M.; Nath, Digbijoy N.; Yang, Zhichao; Padture, Nitin P.; Rajan, Siddharth

2013-04-01

A simple method for the creation of Ohmic contact to 2D electron gas in AlGaN/GaN high electron-mobility transistors using Cr/graphene layer is demonstrated. A weak temperature dependence of this Ohmic contact observed in the range 77 to 300 K precludes thermionic emission or trap-assisted hopping as possible carrier-transport mechanisms. It is suggested that the Cr/graphene combination acts akin to a doped n-type semiconductor in contact with AlGaN/GaN heterostructure, and promotes carrier transport along percolating Al-lean paths through the AlGaN layer. This use of graphene offers a simple method for making Ohmic contacts to AlGaN/GaN heterostructures, circumventing complex additional processing steps involving high temperatures. These results could have important implications for the fabrication and manufacturing of AlGaN/GaN-based microelectronic and optoelectronic devices/sensors of the future.

SiO2/AlON stacked gate dielectrics for AlGaN/GaN MOS heterojunction field-effect transistors

NASA Astrophysics Data System (ADS)

Watanabe, Kenta; Terashima, Daiki; Nozaki, Mikito; Yamada, Takahiro; Nakazawa, Satoshi; Ishida, Masahiro; Anda, Yoshiharu; Ueda, Tetsuzo; Yoshigoe, Akitaka; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

2018-06-01

Stacked gate dielectrics consisting of wide bandgap SiO2 insulators and thin aluminum oxynitride (AlON) interlayers were systematically investigated in order to improve the performance and reliability of AlGaN/GaN metal–oxide–semiconductor (MOS) devices. A significantly reduced gate leakage current compared with that in a single AlON layer was achieved with these structures, while maintaining the superior thermal stability and electrical properties of the oxynitride/AlGaN interface. Consequently, distinct advantages in terms of the reliability of the gate dielectrics, such as an improved immunity against electron injection and an increased dielectric breakdown field, were demonstrated for AlGaN/GaN MOS capacitors with optimized stacked structures having a 3.3-nm-thick AlON interlayer.

Two-level optimization of composite wing structures based on panel genetic optimization

NASA Astrophysics Data System (ADS)

Liu, Boyang

The design of complex composite structures used in aerospace or automotive vehicles presents a major challenge in terms of computational cost. Discrete choices for ply thicknesses and ply angles leads to a combinatorial optimization problem that is too expensive to solve with presently available computational resources. We developed the following methodology for handling this problem for wing structural design: we used a two-level optimization approach with response-surface approximations to optimize panel failure loads for the upper-level wing optimization. We tailored efficient permutation genetic algorithms to the panel stacking sequence design on the lower level. We also developed approach for improving continuity of ply stacking sequences among adjacent panels. The decomposition approach led to a lower-level optimization of stacking sequence with a given number of plies in each orientation. An efficient permutation genetic algorithm (GA) was developed for handling this problem. We demonstrated through examples that the permutation GAs are more efficient for stacking sequence optimization than a standard GA. Repair strategies for standard GA and the permutation GAs for dealing with constraints were also developed. The repair strategies can significantly reduce computation costs for both standard GA and permutation GA. A two-level optimization procedure for composite wing design subject to strength and buckling constraints is presented. At wing-level design, continuous optimization of ply thicknesses with orientations of 0°, 90°, and +/-45° is performed to minimize weight. At the panel level, the number of plies of each orientation (rounded to integers) and inplane loads are specified, and a permutation genetic algorithm is used to optimize the stacking sequence. The process begins with many panel genetic optimizations for a range of loads and numbers of plies of each orientation. Next, a cubic polynomial response surface is fitted to the optimum buckling

Proton-Induced Conductivity Enhancement in AlGaN/GaN HEMT Devices

NASA Astrophysics Data System (ADS)

Lee, In Hak; Lee, Chul; Choi, Byoung Ki; Yun, Yeseul; Chang, Young Jun; Jang, Seung Yup

2018-04-01

We investigated the influence of proton irradiation on the AlGaN/GaN high-electron-mobility transistor (HEMT) devices. Unlike previous studies on the degradation behavior upon proton irradiation, we observed improvements in their electrical conductivity and carrier concentration of up to 25% for the optimal condition. As we increased the proton dose, the carrier concentration and the mobility showed a gradual increase and decrease, respectively. From the photoluminescence measurements, we observed a reduction in the near-band-edge peak of GaN ( 366 nm), which correlate on the observed electrical properties. However, neither the Raman nor the X-ray diffraction analysis showed any changes, implying a negligible influence of protons on the crystal structures. We demonstrated that high-energy proton irradiation could be utilized to modify the transport properties of HEMT devices without damaging their crystal structures.

Genetic algorithm for the optimization of features and neural networks in ECG signals classification

NASA Astrophysics Data System (ADS)

Li, Hongqiang; Yuan, Danyang; Ma, Xiangdong; Cui, Dianyin; Cao, Lu

2017-01-01

Feature extraction and classification of electrocardiogram (ECG) signals are necessary for the automatic diagnosis of cardiac diseases. In this study, a novel method based on genetic algorithm-back propagation neural network (GA-BPNN) for classifying ECG signals with feature extraction using wavelet packet decomposition (WPD) is proposed. WPD combined with the statistical method is utilized to extract the effective features of ECG signals. The statistical features of the wavelet packet coefficients are calculated as the feature sets. GA is employed to decrease the dimensions of the feature sets and to optimize the weights and biases of the back propagation neural network (BPNN). Thereafter, the optimized BPNN classifier is applied to classify six types of ECG signals. In addition, an experimental platform is constructed for ECG signal acquisition to supply the ECG data for verifying the effectiveness of the proposed method. The GA-BPNN method with the MIT-BIH arrhythmia database achieved a dimension reduction of nearly 50% and produced good classification results with an accuracy of 97.78%. The experimental results based on the established acquisition platform indicated that the GA-BPNN method achieved a high classification accuracy of 99.33% and could be efficiently applied in the automatic identification of cardiac arrhythmias.

Promoted nitrogen dissolution due to the addition of Li or Ca to Ga-Na melt; some effects of additives on the growth of GaN single crystals using the sodium flux method

NASA Astrophysics Data System (ADS)

Morishita, Masanori; Kawamura, Fumio; Kawahara, Minoru; Yoshimura, Masashi; Mori, Yusuke; Sasaki, Takatomo

2005-10-01

The effect of the addition of Li or Ca to Ga-Na melt on the promotion of nitrogen dissolution was examined quantitatively in the growth of GaN single crystals using the sodium flux method. The addition of Li or Ca to Ga-Na melt increased both the solubility of solid GaN and that of gaseous nitrogen against the solution. The increase in the solubility of gaseous nitrogen seems to be caused by additives having a high binding energy with nitrogen. We measured the solubility of GaN and that of gaseous nitrogen against Ga-Na, Ga-Na-Li and Ga-Na-Ca melt in this study. On the basis of these data, we clarified the relationship between the N/Ga ratio in the solution and the coloration of GaN crystals grown in each system, and between changes in the yield of GaN and the absolute value of supersaturation.

Optimizing Robinson Operator with Ant Colony Optimization As a Digital Image Edge Detection Method

NASA Astrophysics Data System (ADS)

Yanti Nasution, Tarida; Zarlis, Muhammad; K. M Nasution, Mahyuddin

2017-12-01

Edge detection serves to identify the boundaries of an object against a background of mutual overlap. One of the classic method for edge detection is operator Robinson. Operator Robinson produces a thin, not assertive and grey line edge. To overcome these deficiencies, the proposed improvements to edge detection method with the approach graph with Ant Colony Optimization algorithm. The repairs may be performed are thicken the edge and connect the edges cut off. Edge detection research aims to do optimization of operator Robinson with Ant Colony Optimization then compare the output and generated the inferred extent of Ant Colony Optimization can improve result of edge detection that has not been optimized and improve the accuracy of the results of Robinson edge detection. The parameters used in performance measurement of edge detection are morphology of the resulting edge line, MSE and PSNR. The result showed that Robinson and Ant Colony Optimization method produces images with a more assertive and thick edge. Ant Colony Optimization method is able to be used as a method for optimizing operator Robinson by improving the image result of Robinson detection average 16.77 % than classic Robinson result.

Photovoltaic Properties of Selenized CuGa/In Films with Varied Compositions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muzzillo, Christopher P.; Mansfield, Lorelle M.; Ramanathan, Kannan

2016-11-21

Thin CuGa/In films with varied compositions were deposited by co-evaporation and then selenized in situ with evaporated selenium. The selenized Cu(In, Ga)Se2 absorbers were used to fabricate 390 solar cells. Cu/(Ga+In) and Ga/(Ga+In) (Cu/III and Ga/III) were independently varied, and photovoltaic performance was optimal at Cu/III of 77-92% for all Ga/III compositions studied (Ga/III ~ 30, 50, and 70%). The best absorbers at each Ga/III composition were characterized with time-resolved photoluminescence, scanning electron microscopy, and secondary ion mass spectrometry, and devices were studied with temperature-dependent current density-voltage, light and electrical biased quantum efficiency, and capacitance-voltage. The best cells with Ga/IIImore » ~ 30, 50, and 70% had efficiencies of 14.5, 14.4, and 12.2% and maximum power temperature coefficients of -0.496, -0.452, and -0.413%/degrees C, respectively. This resulted in the Ga/III ~ 50% champion having the highest efficiency at temperatures greater than 40 degrees C, making it the optimal composition for practical purposes. This optimum is understood as a result of the absorber's band gap grading- where minimum band gap dominates short-circuit current density, maximum space charge region band gap dominates open-circuit voltage, and average absorber band gap dominates maximum power temperature coefficient.« less

A Study of Penalty Function Methods for Constraint Handling with Genetic Algorithm

NASA Technical Reports Server (NTRS)

Ortiz, Francisco

2004-01-01

COMETBOARDS (Comparative Evaluation Testbed of Optimization and Analysis Routines for Design of Structures) is a design optimization test bed that can evaluate the performance of several different optimization algorithms. A few of these optimization algorithms are the sequence of unconstrained minimization techniques (SUMT), sequential linear programming (SLP) and the sequential quadratic programming techniques (SQP). A genetic algorithm (GA) is a search technique that is based on the principles of natural selection or "survival of the fittest". Instead of using gradient information, the GA uses the objective function directly in the search. The GA searches the solution space by maintaining a population of potential solutions. Then, using evolving operations such as recombination, mutation and selection, the GA creates successive generations of solutions that will evolve and take on the positive characteristics of their parents and thus gradually approach optimal or near-optimal solutions. By using the objective function directly in the search, genetic algorithms can be effectively applied in non-convex, highly nonlinear, complex problems. The genetic algorithm is not guaranteed to find the global optimum, but it is less likely to get trapped at a local optimum than traditional gradient-based search methods when the objective function is not smooth and generally well behaved. The purpose of this research is to assist in the integration of genetic algorithm (GA) into COMETBOARDS. COMETBOARDS cast the design of structures as a constrained nonlinear optimization problem. One method used to solve constrained optimization problem with a GA to convert the constrained optimization problem into an unconstrained optimization problem by developing a penalty function that penalizes infeasible solutions. There have been several suggested penalty function in the literature each with there own strengths and weaknesses. A statistical analysis of some suggested penalty functions

Growth temperature optimization of GaAs-based In0.83Ga0.17As on InxAl1-xAs buffers

NASA Astrophysics Data System (ADS)

Chen, X. Y.; Gu, Y.; Zhang, Y. G.; Ma, Y. J.; Du, B.; Zhang, J.; Ji, W. Y.; Shi, Y. H.; Zhu, Y.

2018-04-01

Improved quality of gas source molecular beam epitaxy grown In0.83Ga0.17As layer on GaAs substrate was achieved by adopting a two-step InxAl1-xAs metamorphic buffer at different temperatures. With a high-temperature In0.83Al0.17As template following a low-temperature composition continuously graded InxAl1-xAs (x = 0.05-0.86) buffer, better structural, optical and electrical properties of succeeding In0.83Ga0.17As were confirmed by atomic force microscopy, photoluminescence and Hall-effect measurements. Cross-sectional transmission electron microscopy revealed significant effect of the two-step temperature grown InAlAs buffer layers on the inhibition of threading dislocations due to the deposition of high density nuclei on GaAs substrate at the low growth temperature. The limited reduction for the dark current of GaAs-based In0.83Ga0.17As photodetectors on the two-step temperature grown InxAl1-xAs buffer layers was ascribed to the contribution of impurities caused by the low growth temperature of InAlAs buffers.

Selective formation of GaN-based nanorod heterostructures on soda-lime glass substrates by a local heating method.

PubMed

Hong, Young Joon; Kim, Yong-Jin; Jeon, Jong-Myeong; Kim, Miyoung; Choi, Jun Hee; Baik, Chan Wook; Kim, Sun Il; Park, Sung Soo; Kim, Jong Min; Yi, Gyu-Chul

2011-05-20

We report on the fabrication of high-quality GaN on soda-lime glass substrates, heretofore precluded by both the intolerance of soda-lime glass to the high temperatures required for III-nitride growth and the lack of an epitaxial relationship with amorphous glass. The difficulties were circumvented by heteroepitaxial coating of GaN on ZnO nanorods via a local microheating method. Metal-organic chemical vapor deposition of ZnO nanorods and GaN layers using the microheater arrays produced high-quality GaN/ZnO coaxial nanorod heterostructures at only the desired regions on the soda-lime glass substrates. High-resolution transmission electron microscopy examination of the coaxial nanorod heterostructures indicated the formation of an abrupt, semicoherent interface. Photoluminescence and cathodoluminescence spectroscopy was also applied to confirm the high optical quality of the coaxial nanorod heterostructures. Mg-doped GaN/ZnO coaxial nanorod heterostructure arrays, whose GaN shell layers were grown with various different magnesocene flow rates, were further investigated by using photoluminescence spectroscopy for the p-type doping characteristics. The suggested method for fabrication of III-nitrides on glass substrates signifies potentials for low-cost and large-size optoelectronic device applications.

Combined Approach for Government E-Tendering Using GA and TOPSIS with Intuitionistic Fuzzy Information.

PubMed

Wang, Yan; Xi, Chengyu; Zhang, Shuai; Zhang, Wenyu; Yu, Dejian

2015-01-01

As E-government continues to develop with ever-increasing speed, the requirement to enhance traditional government systems and affairs with electronic methods that are more effective and efficient is becoming critical. As a new product of information technology, E-tendering is becoming an inevitable reality owing to its efficiency, fairness, transparency, and accountability. Thus, developing and promoting government E-tendering (GeT) is imperative. This paper presents a hybrid approach combining genetic algorithm (GA) and Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) to enable GeT to search for the optimal tenderer efficiently and fairly under circumstances where the attributes of the tenderers are expressed as fuzzy number intuitionistic fuzzy sets (FNIFSs). GA is applied to obtain the optimal weights of evaluation criteria of tenderers automatically. TOPSIS is employed to search for the optimal tenderer. A prototype system is built and validated with an illustrative example from GeT to verify the feasibility and availability of the proposed approach.

Combined Approach for Government E-Tendering Using GA and TOPSIS with Intuitionistic Fuzzy Information

PubMed Central

Zhang, Wenyu; Yu, Dejian

2015-01-01

As E-government continues to develop with ever-increasing speed, the requirement to enhance traditional government systems and affairs with electronic methods that are more effective and efficient is becoming critical. As a new product of information technology, E-tendering is becoming an inevitable reality owing to its efficiency, fairness, transparency, and accountability. Thus, developing and promoting government E-tendering (GeT) is imperative. This paper presents a hybrid approach combining genetic algorithm (GA) and Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) to enable GeT to search for the optimal tenderer efficiently and fairly under circumstances where the attributes of the tenderers are expressed as fuzzy number intuitionistic fuzzy sets (FNIFSs). GA is applied to obtain the optimal weights of evaluation criteria of tenderers automatically. TOPSIS is employed to search for the optimal tenderer. A prototype system is built and validated with an illustrative example from GeT to verify the feasibility and availability of the proposed approach. PMID:26147468

MOVPE growth of violet GaN LEDs on β-Ga2O3 substrates

NASA Astrophysics Data System (ADS)

Li, Ding; Hoffmann, Veit; Richter, Eberhard; Tessaro, Thomas; Galazka, Zbigniew; Weyers, Markus; Tränkle, Günther

2017-11-01

We report that a H2-free atmosphere is essential for the initial stage of metalorganic vapour phase epitaxy (MOVPE) growth of GaN on β-Ga2O3 to prevent the surface from damage. A simple growth method is proposed that can easily transfer established GaN growth recipes from sapphire to β-Ga2O3 with both (-2 0 1) and (1 0 0) orientations. This method features a thin AlN nucleation layer grown below 900 °C in N2 atmosphere to protect the surface of β-Ga2O3 from deterioration during further growth under the H2 atmosphere. Based on this, we demonstrate working violet vertical light emitting diodes (VLEDs) on n-conductive β-Ga2O3 substrates.

Electrochemical removal of hydrogen atoms in Mg-doped GaN epitaxial layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, June Key, E-mail: junekey@jnu.ac.kr, E-mail: hskim7@jbnu.ac.kr; Hyeon, Gil Yong; Tawfik, Wael Z.

2015-05-14

Hydrogen atoms inside of an Mg-doped GaN epitaxial layer were effectively removed by the electrochemical potentiostatic activation (EPA) method. The role of hydrogen was investigated in terms of the device performance of light-emitting diodes (LEDs). The effect of the main process parameters for EPA such as solution type, voltage, and time was studied and optimized for application to LED fabrication. In optimized conditions, the light output of 385-nm LEDs was improved by about 26% at 30 mA, which was caused by the reduction of the hydrogen concentration by ∼35%. Further removal of hydrogen seems to be involved in the breaking ofmore » Ga-H bonds that passivate the nitrogen vacancies. An EPA process with high voltage breaks not only Mg-H bonds that generate hole carriers but also Ga-H bonds that generate electron carriers, thus causing compensation that impedes the practical increase of hole concentration, regardless of the drastic removal of hydrogen atoms. A decrease in hydrogen concentration affects the current-voltage characteristics, reducing the reverse current by about one order and altering the forward current behavior in the low voltage region.« less

Electrochemical removal of hydrogen atoms in Mg-doped GaN epitaxial layers

NASA Astrophysics Data System (ADS)

Lee, June Key; Hyeon, Gil Yong; Tawfik, Wael Z.; Choi, Hee Seok; Ryu, Sang-Wan; Jeong, Tak; Jung, Eunjin; Kim, Hyunsoo

2015-05-01

Hydrogen atoms inside of an Mg-doped GaN epitaxial layer were effectively removed by the electrochemical potentiostatic activation (EPA) method. The role of hydrogen was investigated in terms of the device performance of light-emitting diodes (LEDs). The effect of the main process parameters for EPA such as solution type, voltage, and time was studied and optimized for application to LED fabrication. In optimized conditions, the light output of 385-nm LEDs was improved by about 26% at 30 mA, which was caused by the reduction of the hydrogen concentration by ˜35%. Further removal of hydrogen seems to be involved in the breaking of Ga-H bonds that passivate the nitrogen vacancies. An EPA process with high voltage breaks not only Mg-H bonds that generate hole carriers but also Ga-H bonds that generate electron carriers, thus causing compensation that impedes the practical increase of hole concentration, regardless of the drastic removal of hydrogen atoms. A decrease in hydrogen concentration affects the current-voltage characteristics, reducing the reverse current by about one order and altering the forward current behavior in the low voltage region.

Optimal sensor placement for leak location in water distribution networks using genetic algorithms.

PubMed

Casillas, Myrna V; Puig, Vicenç; Garza-Castañón, Luis E; Rosich, Albert

2013-11-04

This paper proposes a new sensor placement approach for leak location in water distribution networks (WDNs). The sensor placement problem is formulated as an integer optimization problem. The optimization criterion consists in minimizing the number of non-isolable leaks according to the isolability criteria introduced. Because of the large size and non-linear integer nature of the resulting optimization problem, genetic algorithms (GAs) are used as the solution approach. The obtained results are compared with a semi-exhaustive search method with higher computational effort, proving that GA allows one to find near-optimal solutions with less computational load. Moreover, three ways of increasing the robustness of the GA-based sensor placement method have been proposed using a time horizon analysis, a distance-based scoring and considering different leaks sizes. A great advantage of the proposed methodology is that it does not depend on the isolation method chosen by the user, as long as it is based on leak sensitivity analysis. Experiments in two networks allow us to evaluate the performance of the proposed approach.

Optimal Sensor Placement for Leak Location in Water Distribution Networks Using Genetic Algorithms

PubMed Central

Casillas, Myrna V.; Puig, Vicenç; Garza-Castañón, Luis E.; Rosich, Albert

2013-01-01

This paper proposes a new sensor placement approach for leak location in water distribution networks (WDNs). The sensor placement problem is formulated as an integer optimization problem. The optimization criterion consists in minimizing the number of non-isolable leaks according to the isolability criteria introduced. Because of the large size and non-linear integer nature of the resulting optimization problem, genetic algorithms (GAs) are used as the solution approach. The obtained results are compared with a semi-exhaustive search method with higher computational effort, proving that GA allows one to find near-optimal solutions with less computational load. Moreover, three ways of increasing the robustness of the GA-based sensor placement method have been proposed using a time horizon analysis, a distance-based scoring and considering different leaks sizes. A great advantage of the proposed methodology is that it does not depend on the isolation method chosen by the user, as long as it is based on leak sensitivity analysis. Experiments in two networks allow us to evaluate the performance of the proposed approach. PMID:24193099

Efficient carrier relaxation and fast carrier recombination of N-polar InGaN/GaN light emitting diodes

NASA Astrophysics Data System (ADS)

Feng, Shih-Wei; Liao, Po-Hsun; Leung, Benjamin; Han, Jung; Yang, Fann-Wei; Wang, Hsiang-Chen

2015-07-01

Based on quantum efficiency and time-resolved electroluminescence measurements, the effects of carrier localization and quantum-confined Stark effect (QCSE) on carrier transport and recombination dynamics of Ga- and N-polar InGaN/GaN light-emitting diodes (LEDs) are reported. The N-polar LED exhibits shorter ns-scale response, rising, delay, and recombination times than the Ga-polar one does. Stronger carrier localization and the combined effects of suppressed QCSE and electric field and lower potential barrier acting upon the forward bias in an N-polar LED provide the advantages of more efficient carrier relaxation and faster carrier recombination. By optimizing growth conditions to enhance the radiative recombination, the advantages of more efficient carrier relaxation and faster carrier recombination in a competitive performance N-polar LED can be realized for applications of high-speed flash LEDs. The research results provide important information for carrier transport and recombination dynamics of an N-polar InGaN/GaN LED.

Efficient carrier relaxation and fast carrier recombination of N-polar InGaN/GaN light emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Shih-Wei, E-mail: swfeng@nuk.edu.tw; Liao, Po-Hsun; Leung, Benjamin

2015-07-28

Based on quantum efficiency and time-resolved electroluminescence measurements, the effects of carrier localization and quantum-confined Stark effect (QCSE) on carrier transport and recombination dynamics of Ga- and N-polar InGaN/GaN light-emitting diodes (LEDs) are reported. The N-polar LED exhibits shorter ns-scale response, rising, delay, and recombination times than the Ga-polar one does. Stronger carrier localization and the combined effects of suppressed QCSE and electric field and lower potential barrier acting upon the forward bias in an N-polar LED provide the advantages of more efficient carrier relaxation and faster carrier recombination. By optimizing growth conditions to enhance the radiative recombination, the advantagesmore » of more efficient carrier relaxation and faster carrier recombination in a competitive performance N-polar LED can be realized for applications of high-speed flash LEDs. The research results provide important information for carrier transport and recombination dynamics of an N-polar InGaN/GaN LED.« less

The Properties of p-GaN with Different Cp2Mg/Ga Ratios and Their Influence on Conductivity

NASA Astrophysics Data System (ADS)

Shang, Lin; Ma, Shufang; Liang, Jian; Li, Tianbao; Yu, Chunyan; Liu, Xuguang; Xu, Bingshe

2016-06-01

The effect of Cp2Mg/Ga ratio on the properties of p-GaN was explored by scanning Hall probe, photoluminescence (PL), and atomic force microscopy measurement. It was found that p-GaN has an optimal doping concentration under 2% Cp2Mg/Ga ratio, and higher or lower doping concentration is not beneficial to the conductivity. Hole concentration under the optimum condition is 4.2 × 1017 cm-3 at room temperature. If the Cp2Mg/Ga ratio exceeds the optimum value of 2%, surface morphology and electrical conduction properties become poor, and blue emission at 440 nm, considered deep donor-to-acceptor pair transitions in the PL spectra, are dominant. The decrease in electrical properties indicates the existence of compensating donors because the hole concentration decreases at such high Cp2Mg/Ga ratio. The obtained results indicate that Mg is not incorporated in the exact acceptor site under a heavy doping condition, but acts as a deep donor, instead.

A Theoretical Study of Self Assembled InAs/GaAs and InAs/GaP/GaAs Quantum Dots: Effects of Strain Balancing

NASA Astrophysics Data System (ADS)

Lin, Yih-Yin; Singh, Jasprit

2002-03-01

The past few years have been considerable efforts in growth and device application of self-assembled quantum dots. Quantum dots based on the InAs/GaAs system have been widely studied for lasers and detectors. In these structures InAs is under a large compressive strain making it difficult to have a large number stacked InAs/GaAs dots. In this paper we examine self assembled dots based on using GaAs as a substrate but using a GaAsP region to counterbalance the compressive strain in the InAs region allowing for a lower overall strain energy. We will present a comparison of the InAs/GaAs and InAs/GaAsP/GaAs self assembled dots by examining the strain energy per unit volume and the electronic spectra. The strain energy is calculated using the valence force field method and the electronic spectra is calculated using the 8 band k -- p method. The effective energy bandgap of the same size InAs dot in GaAs matrice is found 0.952 eV and is 0.928 eV in GaAs_0.8P_0.2 matrice.

Development and applications of various optimization algorithms for diesel engine combustion and emissions optimization

NASA Astrophysics Data System (ADS)

Ogren, Ryan M.

For this work, Hybrid PSO-GA and Artificial Bee Colony Optimization (ABC) algorithms are applied to the optimization of experimental diesel engine performance, to meet Environmental Protection Agency, off-road, diesel engine standards. This work is the first to apply ABC optimization to experimental engine testing. All trials were conducted at partial load on a four-cylinder, turbocharged, John Deere engine using neat-Biodiesel for PSO-GA and regular pump diesel for ABC. Key variables were altered throughout the experiments, including, fuel pressure, intake gas temperature, exhaust gas recirculation flow, fuel injection quantity for two injections, pilot injection timing and main injection timing. Both forms of optimization proved effective for optimizing engine operation. The PSO-GA hybrid was able to find a superior solution to that of ABC within fewer engine runs. Both solutions call for high exhaust gas recirculation to reduce oxide of nitrogen (NOx) emissions while also moving pilot and main fuel injections to near top dead center for improved tradeoffs between NOx and particulate matter.

Study of LPE methods for growth of InGaAsP/InP CW lasers

NASA Technical Reports Server (NTRS)

Ladany, I.; Hawrylo, F. Z.; Smith, R. T.; Levin, E. R.

1980-01-01

Two methods for liquid phase growth of InGaAsP/InP lasers were studied. Single phase growth, based on saturated melts and 5 C supercooling, was compared to two phase growth excess InP and 20 C nominal supercooling. Substrates cut on the (100) plane were used, and morphology in both cases was excellent and comparable to that obtainable in AlGaAs materials. A high degree of reproducibility was obtained in the materials grown by the two phased method, which is therefore presently preferred for the preparation of laser material. A refractive index step of 0.28 and an index n = 3.46 were obtained for In.81Ga.19As,5P5 lasing at 1.3 microns. Oxide-stripe lasers with typical room temperature cw threshold currents of 180 mA were obtained and some of them showed single mode behavior without lateral cavity modifications. COntinuous operation of 800 h at room temperature was obtained without noticeable degradation.

Heuristic rules embedded genetic algorithm for in-core fuel management optimization

NASA Astrophysics Data System (ADS)

Alim, Fatih

The objective of this study was to develop a unique methodology and a practical tool for designing loading pattern (LP) and burnable poison (BP) pattern for a given Pressurized Water Reactor (PWR) core. Because of the large number of possible combinations for the fuel assembly (FA) loading in the core, the design of the core configuration is a complex optimization problem. It requires finding an optimal FA arrangement and BP placement in order to achieve maximum cycle length while satisfying the safety constraints. Genetic Algorithms (GA) have been already used to solve this problem for LP optimization for both PWR and Boiling Water Reactor (BWR). The GA, which is a stochastic method works with a group of solutions and uses random variables to make decisions. Based on the theories of evaluation, the GA involves natural selection and reproduction of the individuals in the population for the next generation. The GA works by creating an initial population, evaluating it, and then improving the population by using the evaluation operators. To solve this optimization problem, a LP optimization package, GARCO (Genetic Algorithm Reactor Code Optimization) code is developed in the framework of this thesis. This code is applicable for all types of PWR cores having different geometries and structures with an unlimited number of FA types in the inventory. To reach this goal, an innovative GA is developed by modifying the classical representation of the genotype. To obtain the best result in a shorter time, not only the representation is changed but also the algorithm is changed to use in-core fuel management heuristics rules. The improved GA code was tested to demonstrate and verify the advantages of the new enhancements. The developed methodology is explained in this thesis and preliminary results are shown for the VVER-1000 reactor hexagonal geometry core and the TMI-1 PWR. The improved GA code was tested to verify the advantages of new enhancements. The core physics code

GaAs MOEMS Technology

DOE Office of Scientific and Technical Information (OSTI.GOV)

SPAHN, OLGA B.; GROSSETETE, GRANT D.; CICH, MICHAEL J.

2003-03-01

Many MEMS-based components require optical monitoring techniques using optoelectronic devices for converting mechanical position information into useful electronic signals. While the constituent piece-parts of such hybrid opto-MEMS components can be separately optimized, the resulting component performance, size, ruggedness and cost are substantially compromised due to assembly and packaging limitations. GaAs MOEMS offers the possibility of monolithically integrating high-performance optoelectronics with simple mechanical structures built in very low-stress epitaxial layers with a resulting component performance determined only by GaAs microfabrication technology limitations. GaAs MOEMS implicitly integrates the capability for radiation-hardened optical communications into the MEMS sensor or actuator component, a vitalmore » step towards rugged integrated autonomous microsystems that sense, act, and communicate. This project establishes a new foundational technology that monolithically combines GaAs optoelectronics with simple mechanics. Critical process issues addressed include selectivity, electrochemical characteristics, and anisotropy of the release chemistry, and post-release drying and coating processes. Several types of devices incorporating this novel technology are demonstrated.« less

Lyophilized Kit for the Preparation of the PET Perfusion Agent [(68)Ga]-MAA.

PubMed

Amor-Coarasa, Alejandro; Milera, Andrew; Carvajal, Denny; Gulec, Seza; McGoron, Anthony J

2014-01-01

Rapid developments in the field of medical imaging have opened new avenues for the use of positron emitting labeled microparticles. The radioisotope used in our research was (68)Ga, which is easy to obtain from a generator and has good nuclear properties for PET imaging. Methods. Commercially available macroaggregated albumin (MAA) microparticles were suspended in sterile saline, centrifuged to remove the free albumin and stannous chloride, relyophilized, and stored for later labeling with (68)Ga. Labeling was performed at different temperatures and times. (68)Ga purification settings were also tested and optimized. Labeling yield and purity of relyophilized MAA microparticles were compared with those that were not relyophilized. Results. MAA particles kept their original size distribution after relyophilization. Labeling yield was 98% at 75°C when a (68)Ga purification system was used, compared to 80% with unpurified (68)Ga. Radiochemical purity was over 97% up to 4 hours after the labeling. The relyophilized MAA and labeling method eliminate the need for centrifugation purification of the final product and simplify the labeling process. Animal experiments demonstrated the high in vivo stability of the obtained PET agent with more than 95% of the activity remaining in the lungs after 4 hours.

Lyophilized Kit for the Preparation of the PET Perfusion Agent [68Ga]-MAA

PubMed Central

Amor-Coarasa, Alejandro; Milera, Andrew; Gulec, Seza; McGoron, Anthony J.

2014-01-01

Rapid developments in the field of medical imaging have opened new avenues for the use of positron emitting labeled microparticles. The radioisotope used in our research was 68Ga, which is easy to obtain from a generator and has good nuclear properties for PET imaging. Methods. Commercially available macroaggregated albumin (MAA) microparticles were suspended in sterile saline, centrifuged to remove the free albumin and stannous chloride, relyophilized, and stored for later labeling with 68Ga. Labeling was performed at different temperatures and times. 68Ga purification settings were also tested and optimized. Labeling yield and purity of relyophilized MAA microparticles were compared with those that were not relyophilized. Results. MAA particles kept their original size distribution after relyophilization. Labeling yield was 98% at 75°C when a 68Ga purification system was used, compared to 80% with unpurified 68Ga. Radiochemical purity was over 97% up to 4 hours after the labeling. The relyophilized MAA and labeling method eliminate the need for centrifugation purification of the final product and simplify the labeling process. Animal experiments demonstrated the high in vivo stability of the obtained PET agent with more than 95% of the activity remaining in the lungs after 4 hours. PMID:24800071

Influence of the gate position on source-to-drain resistance in AlGaN/AlN/GaN heterostructure field-effect transistors

NASA Astrophysics Data System (ADS)

Liu, Yan; Lin, Zhaojun; Cui, Peng; Zhao, Jingtao; Fu, Chen; Yang, Ming; Lv, Yuanjie

2017-08-01

Using a suitable dual-gate structure, the source-to-drain resistance (RSD) of AlGaN/AlN/GaN heterostructure field-effect transistor (HFET) with varying gate position has been studied at room temperature. The theoretical and experimental results have revealed a dependence of RSD on the gate position. The variation of RSD with the gate position is found to stem from the polarization Coulomb field (PCF) scattering. This finding is of great benefit to the optimization of the performance of AlGaN/AlN/GaN HFET. Especially, when the AlGaN/AlN/GaN HFET works as a microwave device, it is beneficial to achieve the impedance matching by designing the appropriate gate position based on PCF scattering.

Normally-off p-GaN/AlGaN/GaN high electron mobility transistors using hydrogen plasma treatment

NASA Astrophysics Data System (ADS)

Hao, Ronghui; Fu, Kai; Yu, Guohao; Li, Weiyi; Yuan, Jie; Song, Liang; Zhang, Zhili; Sun, Shichuang; Li, Xiajun; Cai, Yong; Zhang, Xinping; Zhang, Baoshun

2016-10-01

In this letter, we report a method by introducing hydrogen plasma treatment to realize normally-off p-GaN/AlGaN/GaN HEMT devices. Instead of using etching technology, hydrogen plasma was adopted to compensate holes in the p-GaN above the two dimensional electron gas (2DEG) channel to release electrons in the 2DEG channel and form high-resistivity area to reduce leakage current and increase gate control capability. The fabricated p-GaN/AlGaN/GaN HEMT exhibits normally-off operation with a threshold voltage of 1.75 V, a subthreshold swing of 90 mV/dec, a maximum transconductance of 73.1 mS/mm, an ON/OFF ratio of 1 × 107, a breakdown voltage of 393 V, and a maximum drain current density of 188 mA/mm at a gate bias of 6 V. The comparison of the two processes of hydrogen plasma treatment and p-GaN etching has also been made in this work.

Improved InGaN/GaN light-emitting diodes with a p-GaN/n-GaN/p-GaN/n-GaN/p-GaN current-spreading layer.

PubMed

Zhang, Zi-Hui; Tan, Swee Tiam; Liu, Wei; Ju, Zhengang; Zheng, Ke; Kyaw, Zabu; Ji, Yun; Hasanov, Namig; Sun, Xiao Wei; Demir, Hilmi Volkan

2013-02-25

This work reports both experimental and theoretical studies on the InGaN/GaN light-emitting diodes (LEDs) with optical output power and external quantum efficiency (EQE) levels substantially enhanced by incorporating p-GaN/n-GaN/p-GaN/n-GaN/p-GaN (PNPNP-GaN) current spreading layers in p-GaN. Each thin n-GaN layer sandwiched in the PNPNP-GaN structure is completely depleted due to the built-in electric field in the PNPNP-GaN junctions, and the ionized donors in these n-GaN layers serve as the hole spreaders. As a result, the electrical performance of the proposed device is improved and the optical output power and EQE are enhanced.

Extremal Optimization: Methods Derived from Co-Evolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boettcher, S.; Percus, A.G.

1999-07-13

We describe a general-purpose method for finding high-quality solutions to hard optimization problems, inspired by self-organized critical models of co-evolution such as the Bak-Sneppen model. The method, called Extremal Optimization, successively eliminates extremely undesirable components of sub-optimal solutions, rather than ''breeding'' better components. In contrast to Genetic Algorithms which operate on an entire ''gene-pool'' of possible solutions, Extremal Optimization improves on a single candidate solution by treating each of its components as species co-evolving according to Darwinian principles. Unlike Simulated Annealing, its non-equilibrium approach effects an algorithm requiring few parameters to tune. With only one adjustable parameter, its performance provesmore » competitive with, and often superior to, more elaborate stochastic optimization procedures. We demonstrate it here on two classic hard optimization problems: graph partitioning and the traveling salesman problem.« less

Design of high breakdown voltage GaN vertical HFETs with p-GaN buried buffer layers for power switching applications

NASA Astrophysics Data System (ADS)

Du, Jiangfeng; Liu, Dong; Zhao, Ziqi; Bai, Zhiyuan; Li, Liang; Mo, Jianghui; Yu, Qi

2015-07-01

To achieve a high breakdown voltage, a GaN vertical heterostructure field effect transistor with p-GaN buried layers (PBL-VHFET) is proposed in this paper. The breakdown voltage of this GaN-based PBL-VHFET could be improved significantly by the optimizing thickness of p-GaN buried layers and doping concentration in PBL. When the GaN buffer layer thickness is 15 μm, the thickness, length and p-doping concentration of PBL are 0.3 μm, 2.7 μm, and 3 × 1017 cm-3, respectively. Simulation results show that the breakdown voltage and on-resistance of the device with two p-GaN buried layers are 3022 V and 3.13 mΩ cm2, respectively. The average breakdown electric field would reach as high as 201.5 V/μm. Compared with the typical GaN vertical heterostructure FETs without PBL, both of breakdown voltage and average breakdown electric field of device are increased more than 50%.

Multidisciplinary Optimization Methods for Aircraft Preliminary Design

NASA Technical Reports Server (NTRS)

Kroo, Ilan; Altus, Steve; Braun, Robert; Gage, Peter; Sobieski, Ian

1994-01-01

This paper describes a research program aimed at improved methods for multidisciplinary design and optimization of large-scale aeronautical systems. The research involves new approaches to system decomposition, interdisciplinary communication, and methods of exploiting coarse-grained parallelism for analysis and optimization. A new architecture, that involves a tight coupling between optimization and analysis, is intended to improve efficiency while simplifying the structure of multidisciplinary, computation-intensive design problems involving many analysis disciplines and perhaps hundreds of design variables. Work in two areas is described here: system decomposition using compatibility constraints to simplify the analysis structure and take advantage of coarse-grained parallelism; and collaborative optimization, a decomposition of the optimization process to permit parallel design and to simplify interdisciplinary communication requirements.

Ab initio phonon thermal transport in monolayer InSe, GaSe, GaS, and alloys

NASA Astrophysics Data System (ADS)

Pandey, Tribhuwan; Parker, David S.; Lindsay, Lucas

2017-11-01

We compare vibrational properties and phonon thermal conductivities (κ) of monolayer InSe, GaSe, and GaS systems using density functional theory and Peierls-Boltzmann transport methods. In going from InSe to GaSe to GaS, system mass decreases giving both increasing acoustic phonon velocities and decreasing scattering of these heat-carrying modes with optic phonons, ultimately giving {κ }{InSe}< {κ }{GaSe}< {κ }{GaS}. This behavior is demonstrated by correlating the scattering phase space limited by fundamental conservation conditions with mode scattering rates and phonon dispersions for each material. We also show that, unlike flat monolayer systems such as graphene, in InSe, GaSe and GaS thermal transport is governed by in-plane vibrations. Alloying of InSe, GaSe, and GaS systems provides an effective method for modulating their κ through intrinsic vibrational modifications and phonon scattering from mass disorder giving reductions ˜2-3.5 times. This disorder also suppresses phonon mean free paths in the alloy systems compared to those in their crystalline counterparts. This work provides fundamental insights of lattice thermal transport from basic vibrational properties for an interesting set of two-dimensional materials.

First Principles Electronic Structure of Mn doped GaAs, GaP, and GaN Semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schulthess, Thomas C; Temmerman, Walter M; Szotek, Zdzislawa

We present first-principles electronic structure calculations of Mn doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extractingmore » binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn-d levels in GaAs. We find good agreement between computed values and estimates from photoemisison experiments.« less

Design of CGMP Production of 18F- and 68Ga-Radiopharmaceuticals

PubMed Central

Chu, Pei-Chun; Chao, Hao-Yu; Shieh, Wei-Chen; Chen, Chuck C.

2014-01-01

Objective. Radiopharmaceutical production process must adhere to current good manufacturing process (CGMP) compliance to ensure the quality of precursor, prodrug (active pharmaceutical ingredient, API), and the final drug product that meet acceptance criteria. We aimed to develop an automated system for production of CGMP grade of PET radiopharmaceuticals. Methods. The hardware and software of the automated synthesizer that fit in the hot cell under cGMP requirement were developed. Examples of production yield and purity for 68Ga-DOTATATE and 18F-FDG at CGMP facility were optimized. Analytical assays and acceptance criteria for cGMP grade of 68Ga-DOTATATE and 18F-FDG were established. Results. CGMP facility for the production of PET radiopharmaceuticals has been established. Radio-TLC and HPLC analyses of 68Ga-DOTATATE and 18F-FDG showed that the radiochemical purity was 92% and 96%, respectively. The products were sterile and pyrogenic-free. Conclusion. CGMP compliance of radiopharmaceuticals has been reviewed. 68Ga-DOTATATE and 18F-FDG were synthesized with high radiochemical yield under CGMP process. PMID:25276810

Thin film electroluminescent cells on the basis of Ce-doped CaGa2S4 and SrGa2S4 prepared by flash evaporation method

NASA Astrophysics Data System (ADS)

Gambarov, E.; Bayramov, A.; Kato, A.; Iida, S.

2006-09-01

Ce-doped CaGa2S4 and SrGa2S4 thin film electroluminescent (TFEL) devices were prepared for the first time on the basis of films deposited by flash evaporation method. Significant crystallization, stoichiometry improvement of the films and increase of photoluminescence intensity were found after annealing in H2S and O2 gas stream. EL spectra of the cells exhibited the characteristic double-band emission similar to that seen for Ce3+ activated CaGa2S4 and SrGa2S4 films under photon excitation. Applied voltage and frequency dependences of the electroluminescence were studied. Low voltage operation as low as 20 V was observed for these cells. Luminance of about 4 cd/m2 at 100 V operating voltage with 2.5 kHz frequency was achieved for the TFEL cell with films annealed in O2 gas stream.

A Swarm Optimization Genetic Algorithm Based on Quantum-Behaved Particle Swarm Optimization.

PubMed

Sun, Tao; Xu, Ming-Hai

2017-01-01

Quantum-behaved particle swarm optimization (QPSO) algorithm is a variant of the traditional particle swarm optimization (PSO). The QPSO that was originally developed for continuous search spaces outperforms the traditional PSO in search ability. This paper analyzes the main factors that impact the search ability of QPSO and converts the particle movement formula to the mutation condition by introducing the rejection region, thus proposing a new binary algorithm, named swarm optimization genetic algorithm (SOGA), because it is more like genetic algorithm (GA) than PSO in form. SOGA has crossover and mutation operator as GA but does not need to set the crossover and mutation probability, so it has fewer parameters to control. The proposed algorithm was tested with several nonlinear high-dimension functions in the binary search space, and the results were compared with those from BPSO, BQPSO, and GA. The experimental results show that SOGA is distinctly superior to the other three algorithms in terms of solution accuracy and convergence.

Optimal placement of FACTS devices using optimization techniques: A review

NASA Astrophysics Data System (ADS)

Gaur, Dipesh; Mathew, Lini

2018-03-01

Modern power system is dealt with overloading problem especially transmission network which works on their maximum limit. Today’s power system network tends to become unstable and prone to collapse due to disturbances. Flexible AC Transmission system (FACTS) provides solution to problems like line overloading, voltage stability, losses, power flow etc. FACTS can play important role in improving static and dynamic performance of power system. FACTS devices need high initial investment. Therefore, FACTS location, type and their rating are vital and should be optimized to place in the network for maximum benefit. In this paper, different optimization methods like Particle Swarm Optimization (PSO), Genetic Algorithm (GA) etc. are discussed and compared for optimal location, type and rating of devices. FACTS devices such as Thyristor Controlled Series Compensator (TCSC), Static Var Compensator (SVC) and Static Synchronous Compensator (STATCOM) are considered here. Mentioned FACTS controllers effects on different IEEE bus network parameters like generation cost, active power loss, voltage stability etc. have been analyzed and compared among the devices.

Finding optimal vaccination strategies for pandemic influenza using genetic algorithms.

PubMed

Patel, Rajan; Longini, Ira M; Halloran, M Elizabeth

2005-05-21

In the event of pandemic influenza, only limited supplies of vaccine may be available. We use stochastic epidemic simulations, genetic algorithms (GA), and random mutation hill climbing (RMHC) to find optimal vaccine distributions to minimize the number of illnesses or deaths in the population, given limited quantities of vaccine. Due to the non-linearity, complexity and stochasticity of the epidemic process, it is not possible to solve for optimal vaccine distributions mathematically. However, we use GA and RMHC to find near optimal vaccine distributions. We model an influenza pandemic that has age-specific illness attack rates similar to the Asian pandemic in 1957-1958 caused by influenza A(H2N2), as well as a distribution similar to the Hong Kong pandemic in 1968-1969 caused by influenza A(H3N2). We find the optimal vaccine distributions given that the number of doses is limited over the range of 10-90% of the population. While GA and RMHC work well in finding optimal vaccine distributions, GA is significantly more efficient than RMHC. We show that the optimal vaccine distribution found by GA and RMHC is up to 84% more effective than random mass vaccination in the mid range of vaccine availability. GA is generalizable to the optimization of stochastic model parameters for other infectious diseases and population structures.

Enhanced mobility in vertically scaled N-polar high-electron-mobility transistors using GaN/InGaN composite channels

NASA Astrophysics Data System (ADS)

Li, Haoran; Wienecke, Steven; Romanczyk, Brian; Ahmadi, Elaheh; Guidry, Matthew; Zheng, Xun; Keller, Stacia; Mishra, Umesh K.

2018-02-01

A GaN/InGaN composite channel design for vertically scaled N-polar high-electron-mobility transistor (HEMT) structures is proposed and demonstrated by metal-organic chemical vapor deposition. In a conventional N-polar HEMT structure, as the channel thickness (tch) decreases, the sheet charge density (ns) decreases, the electric field in the channel increases, and the centroid of the two-dimensional electron gas (2DEG) moves towards the back-barrier/channel interface, resulting in stronger scattering and lower electron mobility (μ). In this study, a thin InGaN layer was introduced in-between the channel and the AlGaN cap to increase the 2DEG density and reduce the electric field in the channel and therefore increase the electron mobility. The dependence of μ on the InGaN thickness (tInGaN) and the indium composition (xIn) was investigated for different channel thicknesses. With optimized tInGaN and xIn, significant improvements in electron mobility were observed. For a 6 nm channel HEMT structure, the electron mobility increased from 606 to 1141 cm2/(V.s) when the 6 nm thick pure GaN channel was replaced by the 4 nm GaN/2 nm In0.1Ga0.9N composite channel.

Band-Bending of Ga-Polar GaN Interfaced with Al2O3 through Ultraviolet/Ozone Treatment.

PubMed

Kim, Kwangeun; Ryu, Jae Ha; Kim, Jisoo; Cho, Sang June; Liu, Dong; Park, Jeongpil; Lee, In-Kyu; Moody, Baxter; Zhou, Weidong; Albrecht, John; Ma, Zhenqiang

2017-05-24

Understanding the band bending at the interface of GaN/dielectric under different surface treatment conditions is critically important for device design, device performance, and device reliability. The effects of ultraviolet/ozone (UV/O 3 ) treatment of the GaN surface on the energy band bending of atomic-layer-deposition (ALD) Al 2 O 3 coated Ga-polar GaN were studied. The UV/O 3 treatment and post-ALD anneal can be used to effectively vary the band bending, the valence band offset, conduction band offset, and the interface dipole at the Al 2 O 3 /GaN interfaces. The UV/O 3 treatment increases the surface energy of the Ga-polar GaN, improves the uniformity of Al 2 O 3 deposition, and changes the amount of trapped charges in the ALD layer. The positively charged surface states formed by the UV/O 3 treatment-induced surface factors externally screen the effect of polarization charges in the GaN, in effect, determining the eventual energy band bending at the Al 2 O 3 /GaN interfaces. An optimal UV/O 3 treatment condition also exists for realizing the "best" interface conditions. The study of UV/O 3 treatment effect on the band alignments at the dielectric/III-nitride interfaces will be valuable for applications of transistors, light-emitting diodes, and photovoltaics.

Dependence of Ag/Ga composition ratio in AgGaSe2 thin film

NASA Astrophysics Data System (ADS)

Matsuo, H.; Yoshino, K.; Ikari, T.

2006-09-01

AgGaSe2 thin film was deposited on glass substrates by vacuum evaporation method. The starting material was mixed Ag2Se and Ga2Se3 powders. Ag/Ga ratios of the samples were 1.5, 1.2, 1.0, 0.8, 0.7 and 0.4. The samples were annealed from 100 to 600 °C for 10 min. After these processes, single phase AgGaSe2 thin films could be obtained except Ag/Ga ratio of 0.4 at annealing temperature of 600 °C. Ag-rich samples had large grain. On the other hand, Ga-rich samples had small grain. Furthermore, Ga-rich and Ag-rich samples indicated p- and n-types because of Ag- and/or Ga-vacancy and Se-vacancy, respectively.

Optical and scintillation properties of ce-doped (Gd2Y1)Ga2.7Al2.3O12 single crystal grown by Czochralski method

NASA Astrophysics Data System (ADS)

Wang, Chao; Wu, Yuntao; Ding, Dongzhou; Li, Huanying; Chen, Xiaofeng; Shi, Jian; Ren, Guohao

2016-06-01

Multicomponent garnets, due to their excellent light yield and energy resolution, become one of the most promising scintillators used for homeland security and nuclear non-proliferation applications. This work focuses on the optimization of Ce-doped (Gd,Y)3(Ga,Al)5O12 scintillators using a combination strategy of pre-screening and scale-up. Ce-doped GdxY1-xGayAl5-yO12 (x=1, 2 and y=2, 2.2, 2.5, 2.7, 3) polycrystalline powders were prepared by high-temperature solid state reaction method. The desired garnet phase in all the samples was confirmed using X-ray diffraction measurement. By comparing the radioluminescence intensity, the highest scintillation efficiency was achieved at a component of Gd2Y1Ga2.7Al2.3O12:Ce powders. A (Gd2Y1)Ga2.7Al2.3O12 doped with 1% Ce single crystal with dimensions of Ø35×40 mm was grown by Czochralski method using a <111> oriented seed. Luminescence and scintillation properties were measured. An optical transmittance of 84% was achieved in the concerned wavelength from 500 to 800 nm. Its 5d-4f emission of Ce3+ is at 530 nm. The light yield of a Ce1%: Gd2Y1Ga2.7Al2.3O12 single crystal slab at a size of 5×5×1 mm3 can reach about 65,000±3000 Ph/MeV along with two decay components of 94 and 615 ns under 137Cs source irradiation.

Comparative investigation of InGaP/GaAs/GaAsBi and InGaP/GaAs heterojunction bipolar transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Yi-Chen; Tsai, Jung-Hui, E-mail: jhtsai@nknucc.nknu.edu.tw; Chiang, Te-Kuang

2015-10-15

In this article the characteristics of In{sub 0.49}Ga{sub 0.51}P/GaAs/GaAs{sub 0.975}Bi{sub 0.025} and In{sub 0.49}Ga{sub 0.51}P/GaAs heterojunction bipolar transistor (HBTs) are demonstrated and compared by two-dimensional simulated analysis. As compared to the traditional InGaP/GaAs HBT, the studied InGaP/GaAs/GaAsBi HBT exhibits a higher collector current, a lower base-emitter (B–E) turn-on voltage, and a relatively lower collector-emitter offset voltage of only 7 mV. Because the more electrons stored in the base is further increased in the InGaP/GaAs/GaAsBi HBT, it introduces the collector current to increase and the B–E turn-on voltage to decrease for low input power applications. However, the current gain is slightlymore » smaller than the traditional InGaP/GaAs HBT attributed to the increase of base current for the minority carriers stored in the GaAsBi base.« less

Identification of the limiting factors for high-temperature GaAs, GaInP, and AlGaInP solar cells from device and carrier lifetime analysis

NASA Astrophysics Data System (ADS)

Perl, E. E.; Kuciauskas, D.; Simon, J.; Friedman, D. J.; Steiner, M. A.

2017-12-01

We analyze the temperature-dependent dark saturation current density and open-circuit voltage (VOC) for GaAs, GaInP, and AlGaInP solar cells from 25 to 400 °C. As expected, the intrinsic carrier concentration, ni, dominates the temperature dependence of the dark currents. However, at 400 °C, we measure VOC that is ˜50 mV higher for the GaAs solar cell and ˜60-110 mV lower for the GaInP and AlGaInP solar cells compared to what would be expected from commonly used solar cell models that consider only the ni2 temperature dependence. To better understand these deviations, we measure the carrier lifetimes of p-type GaAs, GaInP, and AlGaInP double heterostructures (DHs) from 25 to 400 °C using time-resolved photoluminescence. Temperature-dependent minority carrier lifetimes are analyzed to determine the relative contributions of the radiative recombination, interface recombination, Shockley-Read-Hall recombination, and thermionic emission processes. We find that radiative recombination dominates for the GaAs DHs with the effective lifetime approximately doubling as the temperature is increased from 25 °C to 400 °C. In contrast, we find that thermionic emission dominates for the GaInP and AlGaInP DHs at elevated temperatures, leading to a 3-4× reduction in the effective lifetime and ˜40× increase in the surface recombination velocity as the temperature is increased from 25 °C to 400 °C. These observations suggest that optimization of the minority carrier confinement layers for the GaInP and AlGaInP solar cells could help to improve VOC and solar cell efficiency at elevated temperatures. We demonstrate VOC improvement at 200-400 °C in GaInP solar cells fabricated with modified AlGaInP window and back surface field layers.

Identification of the limiting factors for high-temperature GaAs, GaInP, and AlGaInP solar cells from device and carrier lifetime analysis

DOE PAGES

Perl, E. E.; Kuciauskas, D.; Simon, J.; ...

2017-12-21

We analyze the temperature-dependent dark saturation current density and open-circuit voltage (VOC) for GaAs, GaInP, and AlGaInP solar cells from 25 to 400 degrees C. As expected, the intrinsic carrier concentration, ni, dominates the temperature dependence of the dark currents. However, at 400 degrees C, we measure VOC that is ~50 mV higher for the GaAs solar cell and ~60-110 mV lower for the GaInP and AlGaInP solar cells compared to what would be expected from commonly used solar cell models that consider only the ni2 temperature dependence. To better understand these deviations, we measure the carrier lifetimes of p-typemore » GaAs, GaInP, and AlGaInP double heterostructures (DHs) from 25 to 400 degrees C using time-resolved photoluminescence. Temperature-dependent minority carrier lifetimes are analyzed to determine the relative contributions of the radiative recombination, interface recombination, Shockley-Read-Hall recombination, and thermionic emission processes. We find that radiative recombination dominates for the GaAs DHs with the effective lifetime approximately doubling as the temperature is increased from 25 degrees C to 400 degrees C. In contrast, we find that thermionic emission dominates for the GaInP and AlGaInP DHs at elevated temperatures, leading to a 3-4x reduction in the effective lifetime and ~40x increase in the surface recombination velocity as the temperature is increased from 25 degrees C to 400 degrees C. These observations suggest that optimization of the minority carrier confinement layers for the GaInP and AlGaInP solar cells could help to improve VOC and solar cell efficiency at elevated temperatures. We demonstrate VOC improvement at 200-400 degrees C in GaInP solar cells fabricated with modified AlGaInP window and back surface field layers.« less

Identification of the limiting factors for high-temperature GaAs, GaInP, and AlGaInP solar cells from device and carrier lifetime analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perl, E. E.; Kuciauskas, D.; Simon, J.

We analyze the temperature-dependent dark saturation current density and open-circuit voltage (VOC) for GaAs, GaInP, and AlGaInP solar cells from 25 to 400 degrees C. As expected, the intrinsic carrier concentration, ni, dominates the temperature dependence of the dark currents. However, at 400 degrees C, we measure VOC that is ~50 mV higher for the GaAs solar cell and ~60-110 mV lower for the GaInP and AlGaInP solar cells compared to what would be expected from commonly used solar cell models that consider only the ni2 temperature dependence. To better understand these deviations, we measure the carrier lifetimes of p-typemore » GaAs, GaInP, and AlGaInP double heterostructures (DHs) from 25 to 400 degrees C using time-resolved photoluminescence. Temperature-dependent minority carrier lifetimes are analyzed to determine the relative contributions of the radiative recombination, interface recombination, Shockley-Read-Hall recombination, and thermionic emission processes. We find that radiative recombination dominates for the GaAs DHs with the effective lifetime approximately doubling as the temperature is increased from 25 degrees C to 400 degrees C. In contrast, we find that thermionic emission dominates for the GaInP and AlGaInP DHs at elevated temperatures, leading to a 3-4x reduction in the effective lifetime and ~40x increase in the surface recombination velocity as the temperature is increased from 25 degrees C to 400 degrees C. These observations suggest that optimization of the minority carrier confinement layers for the GaInP and AlGaInP solar cells could help to improve VOC and solar cell efficiency at elevated temperatures. We demonstrate VOC improvement at 200-400 degrees C in GaInP solar cells fabricated with modified AlGaInP window and back surface field layers.« less

Control of Ga-oxide interlayer growth and Ga diffusion in SiO2/GaN stacks for high-quality GaN-based metal-oxide-semiconductor devices with improved gate dielectric reliability

NASA Astrophysics Data System (ADS)

Yamada, Takahiro; Watanabe, Kenta; Nozaki, Mikito; Yamada, Hisashi; Takahashi, Tokio; Shimizu, Mitsuaki; Yoshigoe, Akitaka; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

2018-01-01

A simple and feasible method for fabricating high-quality and highly reliable GaN-based metal-oxide-semiconductor (MOS) devices was developed. The direct chemical vapor deposition of SiO2 films on GaN substrates forming Ga-oxide interlayers was carried out to fabricate SiO2/GaO x /GaN stacked structures. Although well-behaved hysteresis-free GaN-MOS capacitors with extremely low interface state densities below 1010 cm-2 eV-1 were obtained by postdeposition annealing, Ga diffusion into overlying SiO2 layers severely degraded the dielectric breakdown characteristics. However, this problem was found to be solved by rapid thermal processing, leading to the superior performance of the GaN-MOS devices in terms of interface quality, insulating property, and gate dielectric reliability.

A new optimal seam method for seamless image stitching

NASA Astrophysics Data System (ADS)

Xue, Jiale; Chen, Shengyong; Cheng, Xu; Han, Ying; Zhao, Meng

2017-07-01

A novel optimal seam method which aims to stitch those images with overlapping area more seamlessly has been propos ed. Considering the traditional gradient domain optimal seam method and fusion algorithm result in bad color difference measurement and taking a long time respectively, the input images would be converted to HSV space and a new energy function is designed to seek optimal stitching path. To smooth the optimal stitching path, a simplified pixel correction and weighted average method are utilized individually. The proposed methods exhibit performance in eliminating the stitching seam compared with the traditional gradient optimal seam and high efficiency with multi-band blending algorithm.

Impacts of oxidants in atomic layer deposition method on Al2O3/GaN interface properties

NASA Astrophysics Data System (ADS)

Taoka, Noriyuki; Kubo, Toshiharu; Yamada, Toshikazu; Egawa, Takashi; Shimizu, Mitsuaki

2018-01-01

The electrical interface properties of GaN metal-oxide-semiconductor (MOS) capacitors with an Al2O3 gate insulator formed by atomic layer deposition method using three kinds of oxidants were investigated by the capacitance-voltage technique, Terman method, and conductance method. We found that O3 and the alternate supply of H2O and O3 (AS-HO) are effective for reducing the interface trap density (D it) at the energy range of 0.15 to 0.30 eV taking from the conduction band minimum. On the other hand, we found that surface potential fluctuation (σs) induced by interface charges for the AS-HO oxidant is much larger than that for a Si MOS capacitor with a SiO2 layer formed by chemical vapor deposition despite the small D it values for the AS-HO oxidant compared with the Si MOS capacitor. This means that the total charged center density including the fixed charge density, charged slow trap density, and charged interface trap density for the GaN MOS capacitor is higher than that for the Si MOS capacitor. Therefore, σs has to be reduced to improve the performances and reliability of GaN devices with the Al2O3/GaN interfaces.

Growth of GaN@InGaN Core-Shell and Au-GaN Hybrid Nanostructures for Energy Applications

DOE PAGES

Kuykendall, Tevye; Aloni, Shaul; Jen-La Plante, Ilan; ...

2009-01-01

We demonstrated a method to control the bandgap energy of GaN nanowires by forming GaN@InGaN core-shell hybrid structures using metal organic chemical vapor deposition (MOCVD). Furthermore, we show the growth of Au nanoparticles on the surface of GaN nanowires in solution at room temperature. The work shown here is a first step toward engineering properties that are crucial for the rational design and synthesis of a new class of photocatalytic materials. The hybrid structures were characterized by various techniques, including photoluminescence (PL), energy dispersive x-ray spectroscopy (EDS), transmission and scanning electron microscopy (TEM and SEM), and x-ray diffraction (XRD).

Meningiomas: A Comparative Study of 68Ga-DOTATOC, 68Ga-DOTANOC and 68Ga-DOTATATE for Molecular Imaging in Mice

PubMed Central

Soto-Montenegro, María Luisa; Peña-Zalbidea, Santiago; Mateos-Pérez, Jose María; Oteo, Marta; Romero, Eduardo; Morcillo, Miguel Ángel; Desco, Manuel

2014-01-01

Purpose The goal of this study was to compare the tumor uptake kinetics and diagnostic value of three 68Ga-DOTA-labeled somatostatin analogues (68Ga-DOTATOC, 68Ga-DOTANOC, and 68Ga-DOTATATE) using PET/CT in a murine model with subcutaneous meningioma xenografts. Methods The experiment was performed with 16 male NUDE NU/NU mice bearing xenografts of a human meningioma cell line (CH-157MN). 68Ga-DOTATOC, 68Ga-DOTANOC, and 68Ga-DOTATATE were produced in a FASTLab automated platform. Imaging was performed on an Argus small-animal PET/CT scanner. The SUVmax of the liver and muscle, and the tumor-to-liver (T/L) and tumor-to-muscle (T/M) SUV ratios were computed. Kinetic analysis was performed using Logan graphical analysis for a two-tissue reversible compartmental model, and the volume of distribution (Vt) was determined. Results Hepatic SUVmax and Vt were significantly higher with 68Ga-DOTANOC than with 68Ga-DOTATOC and 68Ga-DOTATATE. No significant differences between tracers were found for SUVmax in tumor or muscle. No differences were found in the T/L SUV ratio between 68Ga-DOTATATE and 68Ga-DOTATOC, both of which had a higher fraction than 68Ga-DOTANOC. The T/M SUV ratio was significantly higher with 68Ga-DOTATATE than with 68Ga-DOTATOC and 68Ga-DOTANOC. The Vt for tumor was higher with 68Ga-DOTATATE than with 68Ga-DOTANOC and relatively similar to that of 68Ga-DOTATOC. Conclusions This study demonstrates, for the first time, the ability of the three radiolabeled somatostatin analogues tested to image a human meningioma cell line. Although Vt was relatively similar with 68Ga-DOTATATE and 68Ga-DOTATOC, uptake was higher with 68Ga-DOTATATE in the tumor than with 68Ga-DOTANOC and 68Ga-DOTATOC, suggesting a higher diagnostic value of 68Ga-DOTATATE for detecting meningiomas. PMID:25369268

Growth of InP, InGaAs, and InGaAsP on InP by gas-source molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Asonen, H.; Rakennus, K.; Tappura, K.; Hovinen, M.; Pessa, M.

1990-10-01

Gas-source molecular beam epitaxy (GSMBE), designating the method where the group III beams are derived from the evaporation of solid materials while the group V beams are derived from the high-temperature cracking of AsH 3 and PH 3, is a very promising method. We show in this work that using indium of high purity and optimizing the growth conditions, unintentional impurities in these films prepared by GSMBE can be reduced to a level comparable to that obtained by all-vapor-source chemical beam epitaxy (CBE). The films grown by GSMBE are of very high quality, as deduced from the measurements of electrical, optical, and structural properties. Furthermore, we have found that the alloy composition in InGaAsP for the wavelength λ of 1.1 μm changes significantly in a range of growth temperature from 525 to 530°C, likely due to an abrupt change in the sticking probability of phosphorus. We have also found that the phosphorus-to-gallium flux ratio strongly affects surface morphology of InGaAsP for λ = 1.3 μm.

Optical properties in GaAs/AlGaAs semiparabolic quantum wells by the finite difference method: Combined effects of electric field and magnetic field

NASA Astrophysics Data System (ADS)

Yan, Ru-Yu; Tang, Jian; Zhang, Zhi-Hai; Yuan, Jian-Hui

2018-05-01

In the present work, the optical properties of GaAs/AlGaAs semiparabolic quantum wells (QWs) are studied under the effect of applied electric field and magnetic field by using the compact-density-matrix method. The energy eigenvalues and their corresponding eigenfunctions of the system are calculated by using the differential method. Simultaneously, the nonlinear optical rectification (OR) and optical absorption coefficients (OACs) are investigated, which are modulated by the applied electric field and magnetic field. It is found that the position and the magnitude of the resonant peaks of the nonlinear OR and OACs can depend strongly on the applied electric field, magnetic field and confined potential frequencies. This gives a new way to control the device applications based on the intersubband transitions of electrons in this system.

Ab initio phonon thermal transport in monolayer InSe, GaSe, GaS, and alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pandey, Tribhuwan; Parker, David S.; Lindsay, Lucas

We compare vibrational properties and phonon thermal conductivities (κ) of monolayer InSe, GaSe and GaS systems using density functional theory and Peierls-Boltzmann transport methods. In going from InSe to GaSe to GaS, system mass decreases giving both increasing acoustic phonon velocities and decreasing scattering of these heat-carrying modes with optic phonons, ultimately giving κInSe< κGaSe< κGaS. This behavior is demonstrated by correlating the scattering phase space limited by fundamental conservation conditions with mode scattering rates and phonon dispersions for each material. We also show that, unlike flat monolayer systems such as graphene, thermal transport is governed by in-plane vibrations inmore » InSe, GaSe and GaS, similar to buckled monolayer materials such as silicene. Alloying of InSe, GaSe and GaS systems provides an effective method for modulating their κ through intrinsic vibrational modifications and phonon scattering from mass disorder giving reductions ~2-3.5 times. This disorder also suppresses phonon mean free paths in the alloy systems compared to those in their crystalline counterparts. This work provides fundamental insights of lattice thermal transport from basic vibrational properties for an interesting set of two-dimensional materials.« less

Optimal design of solidification processes

NASA Technical Reports Server (NTRS)

Dantzig, Jonathan A.; Tortorelli, Daniel A.

1991-01-01

An optimal design algorithm is presented for the analysis of general solidification processes, and is demonstrated for the growth of GaAs crystals in a Bridgman furnace. The system is optimal in the sense that the prespecified temperature distribution in the solidifying materials is obtained to maximize product quality. The optimization uses traditional numerical programming techniques which require the evaluation of cost and constraint functions and their sensitivities. The finite element method is incorporated to analyze the crystal solidification problem, evaluate the cost and constraint functions, and compute the sensitivities. These techniques are demonstrated in the crystal growth application by determining an optimal furnace wall temperature distribution to obtain the desired temperature profile in the crystal, and hence to maximize the crystal's quality. Several numerical optimization algorithms are studied to determine the proper convergence criteria, effective 1-D search strategies, appropriate forms of the cost and constraint functions, etc. In particular, we incorporate the conjugate gradient and quasi-Newton methods for unconstrained problems. The efficiency and effectiveness of each algorithm is presented in the example problem.

Identification of handwriting by using the genetic algorithm (GA) and support vector machine (SVM)

NASA Astrophysics Data System (ADS)

Zhang, Qigui; Deng, Kai

2016-12-01

As portable digital camera and a camera phone comes more and more popular, and equally pressing is meeting the requirements of people to shoot at any time, to identify and storage handwritten character. In this paper, genetic algorithm(GA) and support vector machine(SVM)are used for identification of handwriting. Compare with parameters-optimized method, this technique overcomes two defects: first, it's easy to trap in the local optimum; second, finding the best parameters in the larger range will affects the efficiency of classification and prediction. As the experimental results suggest, GA-SVM has a higher recognition rate.

Robust Dynamic Multi-objective Vehicle Routing Optimization Method.

PubMed

Guo, Yi-Nan; Cheng, Jian; Luo, Sha; Gong, Dun-Wei

2017-03-21

For dynamic multi-objective vehicle routing problems, the waiting time of vehicle, the number of serving vehicles, the total distance of routes were normally considered as the optimization objectives. Except for above objectives, fuel consumption that leads to the environmental pollution and energy consumption was focused on in this paper. Considering the vehicles' load and the driving distance, corresponding carbon emission model was built and set as an optimization objective. Dynamic multi-objective vehicle routing problems with hard time windows and randomly appeared dynamic customers, subsequently, were modeled. In existing planning methods, when the new service demand came up, global vehicle routing optimization method was triggered to find the optimal routes for non-served customers, which was time-consuming. Therefore, robust dynamic multi-objective vehicle routing method with two-phase is proposed. Three highlights of the novel method are: (i) After finding optimal robust virtual routes for all customers by adopting multi-objective particle swarm optimization in the first phase, static vehicle routes for static customers are formed by removing all dynamic customers from robust virtual routes in next phase. (ii)The dynamically appeared customers append to be served according to their service time and the vehicles' statues. Global vehicle routing optimization is triggered only when no suitable locations can be found for dynamic customers. (iii)A metric measuring the algorithms' robustness is given. The statistical results indicated that the routes obtained by the proposed method have better stability and robustness, but may be sub-optimum. Moreover, time-consuming global vehicle routing optimization is avoided as dynamic customers appear.

A new method to determine the 2DEG density distribution for passivated AlGaN/AlN/GaN heterostructure field-effect transistors

NASA Astrophysics Data System (ADS)

Fu, Chen; Lin, Zhaojun; Cui, Peng; Lv, Yuanjie; Zhou, Yang; Dai, Gang; Luan, Chongbiao; Liu, Huan; Cheng, Aijie

2018-01-01

A new method to determine the two-dimensional electron gas (2DEG) density distribution of the AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) after the Si3N4 passivation process has been presented. Detailed device characteristics were investigated and better transport properties have been observed for the passivated devices. The strain variation and the influence of the surface trapping states were analyzed. By using the polarization Coulomb field (PCF) scattering theory, the 2DEG density after passivation was both quantitively and qualitatively determined, which has been increased by 45% under the access regions and decreased by 2% under the gate region.

Oxygen-induced high diffusion rate of magnesium dopants in GaN/AlGaN based UV LED heterostructures.

PubMed

Michałowski, Paweł Piotr; Złotnik, Sebastian; Sitek, Jakub; Rosiński, Krzysztof; Rudziński, Mariusz

2018-05-23

Further development of GaN/AlGaN based optoelectronic devices requires optimization of the p-type material growth process. In particular, uncontrolled diffusion of Mg dopants may decrease the performance of a device. Thus it is meaningful to study the behavior of Mg and the origins of its diffusion in detail. In this work we have employed secondary ion mass spectrometry to study the diffusion of magnesium in GaN/AlGaN structures. We show that magnesium has a strong tendency to form Mg-H complexes which immobilize Mg atoms and restrain their diffusion. However, these complexes are not present in samples post-growth annealed in an oxygen atmosphere or Al-rich AlGaN structures which naturally have a high oxygen concentration. In these samples, more Mg atoms are free to diffuse and thus the average diffusion length is considerably larger than for a sample annealed in an inert atmosphere.

On the effect of N-GaN/P-GaN/N-GaN/P-GaN/N-GaN built-in junctions in the n-GaN layer for InGaN/GaN light-emitting diodes.

PubMed

Kyaw, Zabu; Zhang, Zi-Hui; Liu, Wei; Tan, Swee Tiam; Ju, Zhen Gang; Zhang, Xue Liang; Ji, Yun; Hasanov, Namig; Zhu, Binbin; Lu, Shunpeng; Zhang, Yiping; Sun, Xiao Wei; Demir, Hilmi Volkan

2014-01-13

N-GaN/P-GaN/N-GaN/P-GaN/N-GaN (NPNPN-GaN) junctions embedded between the n-GaN region and multiple quantum wells (MQWs) are systematically studied both experimentally and theoretically to increase the performance of InGaN/GaN light emitting diodes (LEDs) in this work. In the proposed architecture, each thin P-GaN layer sandwiched in the NPNPN-GaN structure is completely depleted due to the built-in electric field in the NPNPN-GaN junctions, and the ionized acceptors in these P-GaN layers serve as the energy barriers for electrons from the n-GaN region, resulting in a reduced electron over flow and enhanced the current spreading horizontally in the n- GaN region. These lead to increased optical output power and external quantum efficiency (EQE) from the proposed device.

Optimization of the Al2O3/GaSb Interface and a High-Mobility GaSb pMOSFET

DTIC Science & Technology

2011-10-01

explored the use of in situ deposition of Al2O3 on GaSb grown on InP using molecular beam epitaxy and reported Dit values in the low 1012/cm2eV range near...M. Heyns, M. Caymax, and J. Dekoster, “GaSb mole- cular beam epitaxial growth on p-InP(001) and passivation with in situ deposited Al2O3 gate oxide...transmission electron microscopy. Capacitors were made on these films using platinum (Pt) electrode deposited in an e- beam evaporator through a shadow

Honey Bees Inspired Optimization Method: The Bees Algorithm.

PubMed

Yuce, Baris; Packianather, Michael S; Mastrocinque, Ernesto; Pham, Duc Truong; Lambiase, Alfredo

2013-11-06

Optimization algorithms are search methods where the goal is to find an optimal solution to a problem, in order to satisfy one or more objective functions, possibly subject to a set of constraints. Studies of social animals and social insects have resulted in a number of computational models of swarm intelligence. Within these swarms their collective behavior is usually very complex. The collective behavior of a swarm of social organisms emerges from the behaviors of the individuals of that swarm. Researchers have developed computational optimization methods based on biology such as Genetic Algorithms, Particle Swarm Optimization, and Ant Colony. The aim of this paper is to describe an optimization algorithm called the Bees Algorithm, inspired from the natural foraging behavior of honey bees, to find the optimal solution. The algorithm performs both an exploitative neighborhood search combined with random explorative search. In this paper, after an explanation of the natural foraging behavior of honey bees, the basic Bees Algorithm and its improved versions are described and are implemented in order to optimize several benchmark functions, and the results are compared with those obtained with different optimization algorithms. The results show that the Bees Algorithm offering some advantage over other optimization methods according to the nature of the problem.

Data mining-based coefficient of influence factors optimization of test paper reliability

NASA Astrophysics Data System (ADS)

Xu, Peiyao; Jiang, Huiping; Wei, Jieyao

2018-05-01

Test is a significant part of the teaching process. It demonstrates the final outcome of school teaching through teachers' teaching level and students' scores. The analysis of test paper is a complex operation that has the characteristics of non-linear relation in the length of the paper, time duration and the degree of difficulty. It is therefore difficult to optimize the coefficient of influence factors under different conditions in order to get text papers with clearly higher reliability with general methods [1]. With data mining techniques like Support Vector Regression (SVR) and Genetic Algorithm (GA), we can model the test paper analysis and optimize the coefficient of impact factors for higher reliability. It's easy to find that the combination of SVR and GA can get an effective advance in reliability from the test results. The optimal coefficient of influence factors optimization has a practicability in actual application, and the whole optimizing operation can offer model basis for test paper analysis.

Thermodynamic assessments and inter-relationships between systems involving Al, Am, Ga, Pu, and U

DOE PAGES

Perron, A.; Turchi, P. E. A.; Landa, A.; ...

2016-12-01

We present a newly developed self-consistent CALPHAD thermodynamic database involving Al, Am, Ga, Pu, and U. A first optimization of the slightly characterized Am-Al and completely unknown Am-Ga phase diagrams is proposed. To this end, phase diagram features as crystal structures, stoichiometric compounds, solubility limits, and melting temperatures have been studied along the U-Al → Pu-Al → Am-Al, and U-Ga → Pu-Ga → Am-Ga series, and the thermodynamic assessments involving Al and Ga alloying are compared. In addition, two distinct optimizations of the Pu-Al phase diagram are proposed to account for the low temperature and Pu-rich region controversy. We includedmore » the previously assessed thermodynamics of the other binary systems (Am-Pu, Am-U, Pu-U, and Al-Ga) in the database and is briefly described in the present work. In conclusion, predictions on phase stability of ternary and quaternary systems of interest are reported to check the consistency of the database.« less

Thermodynamic assessments and inter-relationships between systems involving Al, Am, Ga, Pu, and U

NASA Astrophysics Data System (ADS)

Perron, A.; Turchi, P. E. A.; Landa, A.; Oudot, B.; Ravat, B.; Delaunay, F.

2016-12-01

A newly developed self-consistent CALPHAD thermodynamic database involving Al, Am, Ga, Pu, and U is presented. A first optimization of the slightly characterized Am-Al and completely unknown Am-Ga phase diagrams is proposed. To this end, phase diagram features as crystal structures, stoichiometric compounds, solubility limits, and melting temperatures have been studied along the U-Al → Pu-Al → Am-Al, and U-Ga → Pu-Ga → Am-Ga series, and the thermodynamic assessments involving Al and Ga alloying are compared. In addition, two distinct optimizations of the Pu-Al phase diagram are proposed to account for the low temperature and Pu-rich region controversy. The previously assessed thermodynamics of the other binary systems (Am-Pu, Am-U, Pu-U, and Al-Ga) is also included in the database and is briefly described in the present work. Finally, predictions on phase stability of ternary and quaternary systems of interest are reported to check the consistency of the database.

Numerical optimization methods for controlled systems with parameters

NASA Astrophysics Data System (ADS)

Tyatyushkin, A. I.

2017-10-01

First- and second-order numerical methods for optimizing controlled dynamical systems with parameters are discussed. In unconstrained-parameter problems, the control parameters are optimized by applying the conjugate gradient method. A more accurate numerical solution in these problems is produced by Newton's method based on a second-order functional increment formula. Next, a general optimal control problem with state constraints and parameters involved on the righthand sides of the controlled system and in the initial conditions is considered. This complicated problem is reduced to a mathematical programming one, followed by the search for optimal parameter values and control functions by applying a multimethod algorithm. The performance of the proposed technique is demonstrated by solving application problems.

The effect of synthetic method and annealing temperature on metal site preference in Al(1-x)Ga(x)FeO3.

PubMed

Walker, James D S; Grosvenor, Andrew P

2013-08-05

Magnetoelectric materials couple both magnetic and electronic properties, making them attractive for use in multifunctional devices. The magnetoelectric AFeO3 compounds (Pna2(1); A = Al, Ga) have received attention as the properties of the system depend on composition as well as the synthetic method used. Al(1-x)Ga(x)FeO3. (0 ≤ x ≤ 1) was synthesized by the sol-gel and coprecipitation methods and studied by X-ray absorption near-edge spectroscopy (XANES). Al L(2,3-), Ga K-, and Fe K-edge XANES spectra were collected to examine how the average metal coordination number (CN) changes with the synthetic method. Al and Fe were found to prefer octahedral sites, while Ga prefers the tetrahedral site. It was found that composition played a larger role in determining site occupancies than synthetic method. Samples made by the sol-gel or ceramic methods (reported previously; Walker, J. D. S.; Grosvenor, A. P. J. Solid State Chem. 2013, 197, 147-153) showed smaller spectral changes than samples made via the coprecipitation method. This is attributed to greater ion mobility in samples synthesized via coprecipitation as the reactants do not have a long-range polymeric or oxide network during synthesis like samples synthesized via the sol-gel or ceramic method. Increasing annealing temperature increases the average coordination number of Al, and to a lesser extent Ga, while the average coordination number of Fe decreases. This study indicates that greater disorder is observed when the Al(1-x)Ga(x)FeO3. compounds have high Al content, and when annealed at higher temperatures.

Evaluation of the Possible Utilization of 68Ga-DOTATOC in Diagnosis of Adenocarcinoma Breast Cancer

PubMed Central

Zolghadri, Samaneh; Naderi, Mojdeh; Yousefnia, Hassan; Alirezapour, Behrouz; Beiki, Davood

2018-01-01

Objective(s): Studies have indicated advantageous properties of [DOTA-DPhe1, Tyr3] octreotide (DOTATOC) in tumor models and labeling with gallium. Breast cancer is the second leading cause of cancer mortality in women, and most of these cancers are often an adenocarcinoma. Due to the importance of target to non-target ratios in the efficacy of diagnosis, the pharmacokinetic of 68Ga-DOTATOC in an adenocarcinoma breast cancer animal model was studied in this research, and the optimized time for imaging was determined. Methods: 68Ga was obtained from 68Ge/68Ga generator. The complex was prepared at optimized conditions. Radiochemical purity of the complex was checked using both HPLC and ITLC methods. Biodistribution of the complex was studied in BALB/c mice bearing adenocarcinoma breast cancer. Also, PET/CT imaging was performed up to 120 min post injection. Results: The complex was produced with radiochemical purity of greater than 98% and specific activity of about 40 GBq/mM at optimized conditions. Biodistribution of the complex was studied in BALB/c mice bearing adenocarcinoma breast cancer indicated fast blood clearance and significant uptake in the tumor. Significant tumor: blood and tumor:muscle uptake ratios were observed even at early times post-injection. PET/CT images were also confirmed the considerable accumulation of the tracer in the tumor. Conclusion: Generally, the results proved the possible application of the radiolabelled complex for the detection of the adenocarcinoma breast cancer and according to the pharmacokenitic data, the suitable time for imaging was determined as at least 30 min after injection. PMID:29333466

Welded joints integrity analysis and optimization for fiber laser welding of dissimilar materials

NASA Astrophysics Data System (ADS)

Ai, Yuewei; Shao, Xinyu; Jiang, Ping; Li, Peigen; Liu, Yang; Liu, Wei

2016-11-01

Dissimilar materials welded joints provide many advantages in power, automotive, chemical, and spacecraft industries. The weld bead integrity which is determined by process parameters plays a significant role in the welding quality during the fiber laser welding (FLW) of dissimilar materials. In this paper, an optimization method by taking the integrity of the weld bead and weld area into consideration is proposed for FLW of dissimilar materials, the low carbon steel and stainless steel. The relationships between the weld bead integrity and process parameters are developed by the genetic algorithm optimized back propagation neural network (GA-BPNN). The particle swarm optimization (PSO) algorithm is taken for optimizing the predicted outputs from GA-BPNN for the objective. Through the optimization process, the desired weld bead with good integrity and minimum weld area are obtained and the corresponding microstructure and microhardness are excellent. The mechanical properties of the optimized joints are greatly improved compared with that of the un-optimized welded joints. Moreover, the effects of significant factors are analyzed based on the statistical approach and the laser power (LP) is identified as the most significant factor on the weld bead integrity and weld area. The results indicate that the proposed method is effective for improving the reliability and stability of welded joints in the practical production.

A combined kick-out and dissociative diffusion mechanism of grown-in Be in InGaAs and InGaAsP. A new finite difference-Bairstow method for solution of the diffusion equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koumetz, Serge D., E-mail: Serge.Koumetz@univ-rouen.fr; Martin, Patrick; Murray, Hugues

Experimental results on the diffusion of grown-in beryllium (Be) in indium gallium arsenide (In{sub 0.53}Ga{sub 0.47}As) and indium gallium arsenide phosphide (In{sub 0.73}Ga{sub 0.27}As{sub 0.58}P{sub 0.42}) gas source molecular beam epitaxy alloys lattice-matched to indium phosphide (InP) can be successfully explained in terms of a combined kick-out and dissociative diffusion mechanism, involving neutral Be interstitials (Be{sub i}{sup 0}), singly positively charged gallium (Ga), indium (In) self-interstitials (I{sub III}{sup +}) and singly positively charged Ga, In vacancies (V{sub III}{sup +}). A new numerical method of solution to the system of diffusion equations, based on the finite difference approximations and Bairstow's method,more » is proposed.« less

Merits and limitations of optimality criteria method for structural optimization

NASA Technical Reports Server (NTRS)

Patnaik, Surya N.; Guptill, James D.; Berke, Laszlo

1993-01-01

The merits and limitations of the optimality criteria (OC) method for the minimum weight design of structures subjected to multiple load conditions under stress, displacement, and frequency constraints were investigated by examining several numerical examples. The examples were solved utilizing the Optimality Criteria Design Code that was developed for this purpose at NASA Lewis Research Center. This OC code incorporates OC methods available in the literature with generalizations for stress constraints, fully utilized design concepts, and hybrid methods that combine both techniques. Salient features of the code include multiple choices for Lagrange multiplier and design variable update methods, design strategies for several constraint types, variable linking, displacement and integrated force method analyzers, and analytical and numerical sensitivities. The performance of the OC method, on the basis of the examples solved, was found to be satisfactory for problems with few active constraints or with small numbers of design variables. For problems with large numbers of behavior constraints and design variables, the OC method appears to follow a subset of active constraints that can result in a heavier design. The computational efficiency of OC methods appears to be similar to some mathematical programming techniques.

Optimization Methods in Sherpa

NASA Astrophysics Data System (ADS)

Siemiginowska, Aneta; Nguyen, Dan T.; Doe, Stephen M.; Refsdal, Brian L.

2009-09-01

Forward fitting is a standard technique used to model X-ray data. A statistic, usually assumed weighted chi^2 or Poisson likelihood (e.g. Cash), is minimized in the fitting process to obtain a set of the best model parameters. Astronomical models often have complex forms with many parameters that can be correlated (e.g. an absorbed power law). Minimization is not trivial in such setting, as the statistical parameter space becomes multimodal and finding the global minimum is hard. Standard minimization algorithms can be found in many libraries of scientific functions, but they are usually focused on specific functions. However, Sherpa designed as general fitting and modeling application requires very robust optimization methods that can be applied to variety of astronomical data (X-ray spectra, images, timing, optical data etc.). We developed several optimization algorithms in Sherpa targeting a wide range of minimization problems. Two local minimization methods were built: Levenberg-Marquardt algorithm was obtained from MINPACK subroutine LMDIF and modified to achieve the required robustness; and Nelder-Mead simplex method has been implemented in-house based on variations of the algorithm described in the literature. A global search Monte-Carlo method has been implemented following a differential evolution algorithm presented by Storn and Price (1997). We will present the methods in Sherpa and discuss their usage cases. We will focus on the application to Chandra data showing both 1D and 2D examples. This work is supported by NASA contract NAS8-03060 (CXC).

Optimal preconditioning of lattice Boltzmann methods

NASA Astrophysics Data System (ADS)

Izquierdo, Salvador; Fueyo, Norberto

2009-09-01

A preconditioning technique to accelerate the simulation of steady-state problems using the single-relaxation-time (SRT) lattice Boltzmann (LB) method was first proposed by Guo et al. [Z. Guo, T. Zhao, Y. Shi, Preconditioned lattice-Boltzmann method for steady flows, Phys. Rev. E 70 (2004) 066706-1]. The key idea in this preconditioner is to modify the equilibrium distribution function in such a way that, by means of a Chapman-Enskog expansion, a time-derivative preconditioner of the Navier-Stokes (NS) equations is obtained. In the present contribution, the optimal values for the free parameter γ of this preconditioner are searched both numerically and theoretically; the later with the aid of linear-stability analysis and with the condition number of the system of NS equations. The influence of the collision operator, single- versus multiple-relaxation-times (MRT), is also studied. Three steady-state laminar test cases are used for validation, namely: the two-dimensional lid-driven cavity, a two-dimensional microchannel and the three-dimensional backward-facing step. Finally, guidelines are suggested for an a priori definition of optimal preconditioning parameters as a function of the Reynolds and Mach numbers. The new optimally preconditioned MRT method derived is shown to improve, simultaneously, the rate of convergence, the stability and the accuracy of the lattice Boltzmann simulations, when compared to the non-preconditioned methods and to the optimally preconditioned SRT one. Additionally, direct time-derivative preconditioning of the LB equation is also studied.

Quality-enhanced In{sub 0.3}Ga{sub 0.7}As film grown on GaAs substrate with an ultrathin amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Fangliang; Li, Guoqiang, E-mail: msgli@scut.edu.cn

2014-01-27

Using low-temperature molecular beam epitaxy, amorphous In{sub 0.6}Ga{sub 0.4}As layers have been grown on GaAs substrates to act as buffer layers for the subsequent epitaxial growth of In{sub 0.3}Ga{sub 0.7}As films. It is revealed that the crystallinity of as-grown In{sub 0.3}Ga{sub 0.7}As films is strongly affected by the thickness of the large-mismatched amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer. Given an optimized thickness of 2 nm, this amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer can efficiently release the misfit strain between the In{sub 0.3}Ga{sub 0.7}As epi-layer and the GaAs substrate, trap the threading and misfit dislocations from propagating to the following In{sub 0.3}Ga{submore » 0.7}As epi-layer, and reduce the surface fluctuation of the as-grown In{sub 0.3}Ga{sub 0.7}As, leading to a high-quality In{sub 0.3}Ga{sub 0.7}As film with competitive crystallinity to that grown on GaAs substrate using compositionally graded In{sub x}Ga{sub 1-x}As metamorphic buffer layers. Considering the complexity of the application of the conventional In{sub x}Ga{sub 1-x}As graded buffer layers, this work demonstrates a much simpler approach to achieve high-quality In{sub 0.3}Ga{sub 0.7}As film on GaAs substrate and, therefore, is of huge potential for the InGaAs-based high-efficiency photovoltaic industry.« less

Local Approximation and Hierarchical Methods for Stochastic Optimization

NASA Astrophysics Data System (ADS)

Cheng, Bolong

In this thesis, we present local and hierarchical approximation methods for two classes of stochastic optimization problems: optimal learning and Markov decision processes. For the optimal learning problem class, we introduce a locally linear model with radial basis function for estimating the posterior mean of the unknown objective function. The method uses a compact representation of the function which avoids storing the entire history, as is typically required by nonparametric methods. We derive a knowledge gradient policy with the locally parametric model, which maximizes the expected value of information. We show the policy is asymptotically optimal in theory, and experimental works suggests that the method can reliably find the optimal solution on a range of test functions. For the Markov decision processes problem class, we are motivated by an application where we want to co-optimize a battery for multiple revenue, in particular energy arbitrage and frequency regulation. The nature of this problem requires the battery to make charging and discharging decisions at different time scales while accounting for the stochastic information such as load demand, electricity prices, and regulation signals. Computing the exact optimal policy becomes intractable due to the large state space and the number of time steps. We propose two methods to circumvent the computation bottleneck. First, we propose a nested MDP model that structure the co-optimization problem into smaller sub-problems with reduced state space. This new model allows us to understand how the battery behaves down to the two-second dynamics (that of the frequency regulation market). Second, we introduce a low-rank value function approximation for backward dynamic programming. This new method only requires computing the exact value function for a small subset of the state space and approximate the entire value function via low-rank matrix completion. We test these methods on historical price data from the

Path optimization method for the sign problem

NASA Astrophysics Data System (ADS)

Ohnishi, Akira; Mori, Yuto; Kashiwa, Kouji

2018-03-01

We propose a path optimization method (POM) to evade the sign problem in the Monte-Carlo calculations for complex actions. Among many approaches to the sign problem, the Lefschetz-thimble path-integral method and the complex Langevin method are promising and extensively discussed. In these methods, real field variables are complexified and the integration manifold is determined by the flow equations or stochastically sampled. When we have singular points of the action or multiple critical points near the original integral surface, however, we have a risk to encounter the residual and global sign problems or the singular drift term problem. One of the ways to avoid the singular points is to optimize the integration path which is designed not to hit the singular points of the Boltzmann weight. By specifying the one-dimensional integration-path as z = t +if(t)(f ɛ R) and by optimizing f(t) to enhance the average phase factor, we demonstrate that we can avoid the sign problem in a one-variable toy model for which the complex Langevin method is found to fail. In this proceedings, we propose POM and discuss how we can avoid the sign problem in a toy model. We also discuss the possibility to utilize the neural network to optimize the path.

Fabrication and improved photoelectrochemical properties of a transferred GaN-based thin film with InGaN/GaN layers.

PubMed

Cao, Dezhong; Xiao, Hongdi; Gao, Qingxue; Yang, Xiaokun; Luan, Caina; Mao, Hongzhi; Liu, Jianqiang; Liu, Xiangdong

2017-08-17

Herein, a lift-off mesoporous GaN-based thin film, which consisted of a strong phase-separated InGaN/GaN layer and an n-GaN layer, was fabricated via an electrochemical etching method in a hydrofluoric acid (HF) solution for the first time and then transferred onto quartz or n-Si substrates, acting as photoanodes during photoelectrochemical (PEC) water splitting in a 1 M NaCl aqueous solution. Compared to the as-grown GaN-based film, the transferred GaN-based thin films possess higher and blue-shifted light emission, presumably resulting from an increase in the surface area and stress relaxation in the InGaN/GaN layer embedded on the mesoporous n-GaN. The properties such as (i) high photoconversion efficiency, (ii) low turn-on voltage (-0.79 V versus Ag/AgCl), and (iii) outstanding stability enable the transferred films to have excellent PEC water splitting ability. Furthermore, as compared to the film transferred onto the quartz substrate, the film transferred onto the n-Si substrate exhibits higher photoconversion efficiency (2.99% at -0.10 V) due to holes (h + ) in the mesoporous n-GaN layer that originate from the n-Si substrate.

Low-thrust trajectory optimization in a full ephemeris model

NASA Astrophysics Data System (ADS)

Cai, Xing-Shan; Chen, Yang; Li, Jun-Feng

2014-10-01

The low-thrust trajectory optimization with complicated constraints must be considered in practical engineering. In most literature, this problem is simplified into a two-body model in which the spacecraft is subject to the gravitational force at the center of mass and the spacecraft's own electric propulsion only, and the gravity assist (GA) is modeled as an instantaneous velocity increment. This paper presents a method to solve the fuel-optimal problem of low-thrust trajectory with complicated constraints in a full ephemeris model, which is closer to practical engineering conditions. First, it introduces various perturbations, including a third body's gravity, the nonspherical perturbation and the solar radiation pressure in a dynamic equation. Second, it builds two types of equivalent inner constraints to describe the GA. At the same time, the present paper applies a series of techniques, such as a homotopic approach, to enhance the possibility of convergence of the global optimal solution.

Review: Optimization methods for groundwater modeling and management

NASA Astrophysics Data System (ADS)

Yeh, William W.-G.

2015-09-01

Optimization methods have been used in groundwater modeling as well as for the planning and management of groundwater systems. This paper reviews and evaluates the various optimization methods that have been used for solving the inverse problem of parameter identification (estimation), experimental design, and groundwater planning and management. Various model selection criteria are discussed, as well as criteria used for model discrimination. The inverse problem of parameter identification concerns the optimal determination of model parameters using water-level observations. In general, the optimal experimental design seeks to find sampling strategies for the purpose of estimating the unknown model parameters. A typical objective of optimal conjunctive-use planning of surface water and groundwater is to minimize the operational costs of meeting water demand. The optimization methods include mathematical programming techniques such as linear programming, quadratic programming, dynamic programming, stochastic programming, nonlinear programming, and the global search algorithms such as genetic algorithms, simulated annealing, and tabu search. Emphasis is placed on groundwater flow problems as opposed to contaminant transport problems. A typical two-dimensional groundwater flow problem is used to explain the basic formulations and algorithms that have been used to solve the formulated optimization problems.

Demonstration of GaAsSb/InAs nanowire backward diodes grown using position-controlled vapor-liquid-solid method

NASA Astrophysics Data System (ADS)

Kawaguchi, Kenichi; Takahashi, Tsuyoshi; Okamoto, Naoya; Sato, Masaru

2018-02-01

p-GaAsSb/n-InAs type-II nanowire (NW) diodes were fabricated using the position-controlled vapor-liquid-solid growth method. InAs and GaAsSb NW segments were grown vertically on GaAs(111)B substrates with the assistance of Au catalysts. Transmission electron microscopy-energy-dispersive X-ray spectroscopy analysis revealed that the GaAsSb segments have an Sb content of 40%, which is sufficient to form a tunnel heterostructure. Scanning capacitance microscope images clearly indicated the formation of a p-n junction in the NWs. Backward diode characteristics, that is, current flow toward negative bias originating from a tunnel current and current suppression toward positive bias by a heterobarrier, were demonstrated.

Designing a multistage supply chain in cross-stage reverse logistics environments: application of particle swarm optimization algorithms.

PubMed

Chiang, Tzu-An; Che, Z H; Cui, Zhihua

2014-01-01

This study designed a cross-stage reverse logistics course for defective products so that damaged products generated in downstream partners can be directly returned to upstream partners throughout the stages of a supply chain for rework and maintenance. To solve this reverse supply chain design problem, an optimal cross-stage reverse logistics mathematical model was developed. In addition, we developed a genetic algorithm (GA) and three particle swarm optimization (PSO) algorithms: the inertia weight method (PSOA_IWM), V(Max) method (PSOA_VMM), and constriction factor method (PSOA_CFM), which we employed to find solutions to support this mathematical model. Finally, a real case and five simulative cases with different scopes were used to compare the execution times, convergence times, and objective function values of the four algorithms used to validate the model proposed in this study. Regarding system execution time, the GA consumed more time than the other three PSOs did. Regarding objective function value, the GA, PSOA_IWM, and PSOA_CFM could obtain a lower convergence value than PSOA_VMM could. Finally, PSOA_IWM demonstrated a faster convergence speed than PSOA_VMM, PSOA_CFM, and the GA did.

Designing a Multistage Supply Chain in Cross-Stage Reverse Logistics Environments: Application of Particle Swarm Optimization Algorithms

PubMed Central

Chiang, Tzu-An; Che, Z. H.

2014-01-01

This study designed a cross-stage reverse logistics course for defective products so that damaged products generated in downstream partners can be directly returned to upstream partners throughout the stages of a supply chain for rework and maintenance. To solve this reverse supply chain design problem, an optimal cross-stage reverse logistics mathematical model was developed. In addition, we developed a genetic algorithm (GA) and three particle swarm optimization (PSO) algorithms: the inertia weight method (PSOA_IWM), V Max method (PSOA_VMM), and constriction factor method (PSOA_CFM), which we employed to find solutions to support this mathematical model. Finally, a real case and five simulative cases with different scopes were used to compare the execution times, convergence times, and objective function values of the four algorithms used to validate the model proposed in this study. Regarding system execution time, the GA consumed more time than the other three PSOs did. Regarding objective function value, the GA, PSOA_IWM, and PSOA_CFM could obtain a lower convergence value than PSOA_VMM could. Finally, PSOA_IWM demonstrated a faster convergence speed than PSOA_VMM, PSOA_CFM, and the GA did. PMID:24772026

Comprehensive growth and characterization study on highly n-doped InGaAs as a contact layer for quantum cascade laser applications

NASA Astrophysics Data System (ADS)

Demir, Ilkay; Altuntas, Ismail; Bulut, Baris; Ezzedini, Maher; Ergun, Yuksel; Elagoz, Sezai

2018-05-01

We present growth and characterization studies of highly n-doped InGaAs epilayers on InP substrate by metal organic vapor phase epitaxy to use as an n-contact layer in quantum cascade laser applications. We have introduced quasi two-dimensional electrons between 10 s pulsed growth n-doped InGaAs epilayers to improve both carrier concentration and mobility of structure by applying pulsed growth and doping methods towards increasing the Si dopant concentration in InGaAs. Additionally, the V/III ratio optimization under fixed group III source flow has been investigated with this new method to understand the effects on both crystalline quality and electrical properties of n-InGaAs epilayers. Finally, we have obtained high crystalline quality of n-InGaAs epilayers grown by 10 s pulsed as a contact layer with 2.8 × 1019 cm‑3 carrier concentration and 1530 cm2 V‑1 s‑1 mobility.

Optimisation of warpage on plastic injection moulding part using response surface methodology (RSM) and genetic algorithm method (GA)

NASA Astrophysics Data System (ADS)

Miza, A. T. N. A.; Shayfull, Z.; Nasir, S. M.; Fathullah, M.; Hazwan, M. H. M.

2017-09-01

In this study, Computer Aided Engineering was used for injection moulding simulation. The method of Design of experiment (DOE) was utilize according to the Latin Square orthogonal array. The relationship between the injection moulding parameters and warpage were identify based on the experimental data that used. Response Surface Methodology (RSM) was used as to validate the model accuracy. Then, the RSM and GA method were combine as to examine the optimum injection moulding process parameter. Therefore the optimisation of injection moulding is largely improve and the result shown an increasing accuracy and also reliability. The propose method by combining RSM and GA method also contribute in minimising the warpage from occur.

Structural and optical characterization of Eu3+ doped beta-Ga2O3 nanoparticles using a liquid-phase precursor method.

PubMed

Kim, Moung-O; Kang, Bongkyun; Yoon, Daeho

2013-08-01

Eu3+ doped beta-Ga2O3 and non-doped beta-Ga2O3 nanoparticles were synthesized at 800 degrees C using a liquid-phase precursor (LPP) method, with different annealing times and Eu3+ ion concentrations. Eu3+ doped beta-Ga2O3 nanoparticles showed broad XRD peaks, revealing a second phase compared with the non-doped beta-Ga2O3 nanoparticles. The cathode luminescence (CL) spectra of beta-Ga2O3 and Eu3+ doped beta-Ga2O3 nanoparticles showed a broad band emission (300-500 nm) of imperfection and two component emissions. The luminescence quenching properties of Eu3+ dopant ion concentration appeared gradually beyond 5 mol% in our investigation.

A convenient route to [68Ga]Ga-MAA for use as a particulate PET perfusion tracer.

PubMed

Mathias, Carla J; Green, Mark A

2008-12-01

A convenient method is described for compounding [(68)Ga]Ga-MAA (MAA=macroaggregated human serum albumin) with the eluate of a commercially available TiO(2)-based (68)Ge/(68)Ga generator. The final [(68)Ga]Ga-MAA product was obtained with an 81.6+/-5.3% decay-corrected radiochemical yield and a radiochemical purity of 99.8+/-0.1% (n=5). Microscopic examination showed the [(68)Ga]Ga-MAA product to remain within the original particle size range. The entire procedure, from generator elution to delivery of the final [(68)Ga]Ga-MAA suspension, could be completed in 25 min. Only 4.4+/-0.9% of the total (68)Ge breakthrough remaining associated with the final [(68)Ga]Ga-MAA product. The procedure allows reasonably convenient preparation of [(68)Ga]Ga-MAA in a fashion that can be readily adapted to sterile product compounding for human use.

Constrained Optimization Methods in Health Services Research-An Introduction: Report 1 of the ISPOR Optimization Methods Emerging Good Practices Task Force.

PubMed

Crown, William; Buyukkaramikli, Nasuh; Thokala, Praveen; Morton, Alec; Sir, Mustafa Y; Marshall, Deborah A; Tosh, Jon; Padula, William V; Ijzerman, Maarten J; Wong, Peter K; Pasupathy, Kalyan S

2017-03-01

Providing health services with the greatest possible value to patients and society given the constraints imposed by patient characteristics, health care system characteristics, budgets, and so forth relies heavily on the design of structures and processes. Such problems are complex and require a rigorous and systematic approach to identify the best solution. Constrained optimization is a set of methods designed to identify efficiently and systematically the best solution (the optimal solution) to a problem characterized by a number of potential solutions in the presence of identified constraints. This report identifies 1) key concepts and the main steps in building an optimization model; 2) the types of problems for which optimal solutions can be determined in real-world health applications; and 3) the appropriate optimization methods for these problems. We first present a simple graphical model based on the treatment of "regular" and "severe" patients, which maximizes the overall health benefit subject to time and budget constraints. We then relate it back to how optimization is relevant in health services research for addressing present day challenges. We also explain how these mathematical optimization methods relate to simulation methods, to standard health economic analysis techniques, and to the emergent fields of analytics and machine learning. Copyright © 2017 International Society for Pharmacoeconomics and Outcomes Research (ISPOR). Published by Elsevier Inc. All rights reserved.

Optimization of the ANFIS using a genetic algorithm for physical work rate classification.

PubMed

Habibi, Ehsanollah; Salehi, Mina; Yadegarfar, Ghasem; Taheri, Ali

2018-03-13

Recently, a new method was proposed for physical work rate classification based on an adaptive neuro-fuzzy inference system (ANFIS). This study aims to present a genetic algorithm (GA)-optimized ANFIS model for a highly accurate classification of physical work rate. Thirty healthy men participated in this study. Directly measured heart rate and oxygen consumption of the participants in the laboratory were used for training the ANFIS classifier model in MATLAB version 8.0.0 using a hybrid algorithm. A similar process was done using the GA as an optimization technique. The accuracy, sensitivity and specificity of the ANFIS classifier model were increased successfully. The mean accuracy of the model was increased from 92.95 to 97.92%. Also, the calculated root mean square error of the model was reduced from 5.4186 to 3.1882. The maximum estimation error of the optimized ANFIS during the network testing process was ± 5%. The GA can be effectively used for ANFIS optimization and leads to an accurate classification of physical work rate. In addition to high accuracy, simple implementation and inter-individual variability consideration are two other advantages of the presented model.

Optical and structural characteristics of high indium content InGaN/GaN multi-quantum wells with varying GaN cap layer thickness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, J.; Zhao, D. G., E-mail: dgzhao@red.semi.ac.cn; Jiang, D. S.

2015-02-07

The optical and structural properties of InGaN/GaN multi-quantum wells (MQWs) with different thicknesses of low temperature grown GaN cap layers are investigated. It is found that the MQW emission energy red-shifts and the peak intensity decreases with increasing GaN cap layer thickness, which may be partly caused by increased floating indium atoms accumulated at quantum well (QW) surface. They will result in the increased interface roughness, higher defect density, and even lead to a thermal degradation of QW layers. An extra growth interruption introduced before the growth of GaN cap layer can help with evaporating the floating indium atoms, andmore » therefore is an effective method to improve the optical properties of high indium content InGaN/GaN MQWs.« less

Laser diode bars based on strain-compensated AlGaPAs/GaAs heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marmalyuk, Aleksandr A; Ladugin, M A; Yarotskaya, I V

2012-01-31

Traditional (in the AlGaAs/GaAs system) and phosphorus-compensated (in the AlGaAs/AlGaPAs/GaAs system) laser heterostructures emitting at a wavelength of 850 nm are grown by MOVPE and studied. Laser diode bars are fabricated and their output characteristics are studied. The method used to grow heterolayers allowed us to control (minimise) mechanical stresses in the AlGaPAs/GaAs laser heterostructure, which made it possible to keep its curvature at the level of the initial curvature of the substrate. It is shown that the use of a compensated AlGaPAs/GaAs heterostructure improves the linear distribution of emitting elements in the near field of laser diode arrays andmore » allows the power - current characteristic to retain its slope at high pump currents owing to a uniform contact of all emitting elements with the heat sink. The radius of curvature of the grown compensated heterostructures turns out to be smaller than that of traditional heterostructures.« less

The Secondary Development of ABAQUS by using Python and the Application of the Advanced GA

NASA Astrophysics Data System (ADS)

Luo, Lilong; Zhao, Meiying

Realizing the secondary development of the ABAQUS based on the manual of ABAQUS. In order to overcome the prematurity and the worse convergence of the Simple Genetic Algorithm (SGA), a new strategy how to improve the efficiency of the SGA has been put forward. In the new GA, the selection probability and the mutation probability are self-adaptive. Taking the stability of the composite laminates as the target, the optimized laminates sequences and radius of the hatch are analyzed with the help of ABAQUS. Compared with the SGA, the new GA method shows a good consistency, fast convergence and practical feasibility.

Characteristic optimization of 1.55-μm InGaAsP/InP high-power diode laser

NASA Astrophysics Data System (ADS)

Ke, Qing; Tan, Shaoyang; Zhai, Teng; Zhang, Ruikang; Lu, Dan; Ji, Chen

2014-11-01

A comprehensive design optimization of 1.55-μm high power InGaAsP/InP board area lasers is performed aiming at increasing the internal quantum efficiency (IQE) while maintaing a low internal loss of the device as well. The P-doping profile and separate confinement heterostructure (SCH) layer band gap are optimized respectively with commercial software Crosslight. Analysis of lasers with different p-doping profiles shows that, although heavy doping in P-cladding layer increases the internal loss of the device, it ensures a high IQE because higher energy barrier at the SCH/P-cladding interface as a result of heavy doping helps reduce the carrier leakage from the waveguide to the InP-cladding layer. The band gap of the SCH layer are also optimized for high slope efficiency. Smaller band gap helps reduce the vertical carrier leakage from the waveguide to the P-cladding layer, but the corresponding higher carrier concentration in SCH layer will cause some radiative recombination, thus influencing the IQE. And as the injection current increases, the carrier concentration increases faster with smaller band gap, therefore, the output power saturates sooner. An optimized band gap in SCH layer of approximately 1.127eV and heavy doping up to 1e18/cm3 at the SCH/P-cladding interface are identified for our high power laser design, and we achieved a high IQE of 94% and internal loss of 2.99/cm for our design.

A Metallurgical Study of Nāga Bhasma.

PubMed

Singh Gautam, Dev Nath

2017-01-01

The metal Nāga (Lead) is being used by Indians since ancient times. Its external and internal uses have been described in Caraka, Suśruta and other Ayurvedic Saṃhitā . According to most of the Rasa texts, Nāga Bhasma and its formulations are used in many diseases such as Prameha , Jvara , Gulma , Śukrameha etc. In the present study, Nāga Bhasma was prepared by the traditional Puṭa method (TPM) and by the electric muffle furnace Puṭa method (EMFPM) and standardized using Metallographic studies. Doing so helps in the study of the microstructure of Nāga Bhasma and also helps in the identification of the metal particles along with the nature of compound formed during the Māraṇa (Bhasmīkaraṇa) process. Different samples from initial raw material to final product of Nāga Bhasma were collected during the pharmaceutical process (1 st , 30 th and 60 th Puṭa ) from both methods i.e. TPM and EMFPM. Samples from both methods were studied using metallographic examination. The processing of the Nāga Bhasma ( ṣaṣṭipuṭa ) was done according to Ānanda Kanda [9] Samples from the raw material i.e. Aśodhita Nāga (raw Lead) and that processed after 1 st , 30 th and 60 th Puṭa from both methods i.e. traditional Puṭa method (using heat from burning of cow dung cakes) and electric muffle furnace Puṭa method were taken. They were mounted on self hardening acrylic base. After careful polishing to obtain scratch free surface of product, they were used for metallurgical study. This study shows that traditional Puṭa method may be better than electric muffle furnace Puṭa method because of more homogeneous distribution of Lead sulphide in the Nāga Bhasma which is prepared by traditional method.

Ga/1-x/Al/x/As LED structures grown on GaP substrates.

NASA Technical Reports Server (NTRS)

Woodall, J. M.; Potemski, R. M.; Blum, S. E.; Lynch, R.

1972-01-01

Ga(1-x)Al(x)As light-emitting diode structures have been grown on GaP substrates by the liquid-phase-epitaxial method. In spite of the large differences in lattice constants and thermal-expansion coefficients, room-temperature efficiencies up to 5.5% in air have been observed for a peak emission of 8500 A. Using undoped GaP substrates, which are transparent to the infrared and red portions of the spectrum, thin structures of Ga(1-x)Al(x)As with large external efficiencies can now be made.

Optimized molecular design of ADAPT-based HER2-imaging probes labelled with 111In and 68Ga.

PubMed

Lindbo, Sarah; Garousi, Javad; Mitran, Bogdan; Vorobyeva, Anzhelika; Oroujeni, Maryam; Orlova, Anna; Hober, Sophia; Tolmachev, Vladimir

2018-06-04

Radionuclide molecular imaging is a promising tool for visualization of cancer associated molecular abnormalities in vivo and stratification of patients for specific therapies. ADAPT is a new type of small engineered proteins based on the scaffold of an albumin binding domain of protein G. ADAPTs have been utilized to select and develop high affinity binders to different proteinaceous targets. ADAPT6 binds to human epidermal growth factor 2 (HER2) with low nanomolar affinity and can be used for its in vivo visualization. Molecular design of 111 In-labeled anti-HER2 ADAPT has been optimized in several earlier studies. In this study, we made a direct comparison of two of the most promising variants, having either a DEAVDANS or a (HE) 3 DANS sequence at the N-terminus, conjugated with a maleimido derivative of DOTA to a GSSC amino acids sequence at the C-terminus. The variants (designated DOTA-C 59 - DEAVDANS-ADAPT6-GSSC and DOTA-C 61 -(HE) 3 DANS-ADAPT6-GSSC) were stably labeled with 111 In for SPECT and 68 Ga for PET. Biodistribution of labeled ADAPT variants was evaluated in nude mice bearing human tumor xenografts with different levels of HER2 expression. Both variants enabled clear discrimination between tumors with high and low levels of HER2 expression. 111 In-labeled ADAPT6 derivatives provided higher tumor-to-organ ratios compared to 68 Ga-labeled counterparts. The best performing variant was DOTA-C 61 -(HE) 3 DANS-ADAPT6-GSSC, providing tumor-to-blood ratios of 208±36 and 109±17 at 3 h for 111 In and 68 Ga labels, respectively.

A Convenient Route to [68Ga]Ga-MAA for Use as a Particulate PET Perfusion Tracer

PubMed Central

Mathias, Carla J.; Green, Mark A.

2008-01-01

A convenient method is described for compounding [68Ga]Ga-MAA (MAA = macroaggregated human serum albumin) with the eluate of a commercially available TiO2-based 68Ge/68Ga generator. The final [68Ga]Ga-MAA product was obtained with an 81.6 ± 5.3% decay-corrected radiochemical yield and a radiochemical purity of 99.8 ± 0.1% (n = 5). Microscopic examination showed the [68Ga]Ga-MAA product to remain within the original particle size range. The entire procedure, from generator elution to delivery of the final [68Ga]Ga-MAA suspension, could be completed in 25 minutes. Only 4.4 ± 0.9% of the total 68Ge breakthrough remaining associated with the final [68Ga]Ga-MAA product. The procedure allows reasonably convenient preparation of [68Ga]Ga-MAA in a fashion that can be readily adapted to sterile product compounding for human use. PMID:18640845

Growth and Optimization of 2 Micrometers InGaSb/AlGaSb Quantum-Well-Based VECSELs on GaAs/AlGaAs DBRs

DTIC Science & Technology

2013-08-01

overwhelming nonradiative recombination losses in the antimonide active region. Furthermore, if the growth of the antimonide active region is done on a GaAs...This is important as threading dislocations would introduce a strong nonradiative recombination process in the QWs and relaxation that is not 100...These defects can act as nonradiative recombination centers. Thus, the source of the threading dislocations and their density in the active region

An historical survey of computational methods in optimal control.

NASA Technical Reports Server (NTRS)

Polak, E.

1973-01-01

Review of some of the salient theoretical developments in the specific area of optimal control algorithms. The first algorithms for optimal control were aimed at unconstrained problems and were derived by using first- and second-variation methods of the calculus of variations. These methods have subsequently been recognized as gradient, Newton-Raphson, or Gauss-Newton methods in function space. A much more recent addition to the arsenal of unconstrained optimal control algorithms are several variations of conjugate-gradient methods. At first, constrained optimal control problems could only be solved by exterior penalty function methods. Later algorithms specifically designed for constrained problems have appeared. Among these are methods for solving the unconstrained linear quadratic regulator problem, as well as certain constrained minimum-time and minimum-energy problems. Differential-dynamic programming was developed from dynamic programming considerations. The conditional-gradient method, the gradient-projection method, and a couple of feasible directions methods were obtained as extensions or adaptations of related algorithms for finite-dimensional problems. Finally, the so-called epsilon-methods combine the Ritz method with penalty function techniques.

Lattice Gas Model Based Optimization of Plasma-Surface Processes for GaN-Based Compound Growth

NASA Astrophysics Data System (ADS)

Nonokawa, Kiyohide; Suzuki, Takuma; Kitamori, Kazutaka; Sawada, Takayuki

2001-10-01

Progress of the epitaxial growth technique for GaN-based compounds makes these materials attractive for applications in high temperature/high-power electronic devices as well as in short-wavelength optoelectronic devices. For MBE growth of GaN epilayer, atomic nitrogen is usually supplied from ECR-plasma while atomic Ga is supplied from conventional K-cell. To grow high-quality epilayer, fundamental knowledge of the detailed atomic process, such as adsorption, surface migration, incorporation, desorption and so forth, is required. We have studied the influence of growth conditions on the flatness of the growth front surface and the growth rate using Monte Carlo simulation based on the lattice gas model. Under the fixed Ga flux condition, the lower the nitrogen flux and/or the higher the growth temperature, the better the flatness of the front surface at the sacrifice of the growth rate of the epilayer. When the nitrogen flux is increased, the growth rate reaches saturation value determined from the Ga flux. At a fixed growth temperature, increasing of nitrogen to Ga flux ratio results in rough surface owing to 3-dimensional island formation. Other characteristics of MBE-GaN growth using ECR-plasma can be well reproduced.

CIP (cleaning-in-place) stability of AlGaN/GaN pH sensors.

PubMed

Linkohr, St; Pletschen, W; Schwarz, S U; Anzt, J; Cimalla, V; Ambacher, O

2013-02-20

The CIP stability of pH sensitive ion-sensitive field-effect transistors based on AlGaN/GaN heterostructures was investigated. For epitaxial AlGaN/GaN films with high structural quality, CIP tests did not degrade the sensor surface and pH sensitivities of 55-58 mV/pH were achieved. Several different passivation schemes based on SiO(x), SiN(x), AlN, and nanocrystalline diamond were compared with special attention given to compatibility to standard microelectronic device technologies as well as biocompatibility of the passivation films. The CIP stability was evaluated with a main focus on the morphological stability. All stacks containing a SiO₂ or an AlN layer were etched by the NaOH solution in the CIP process. Reliable passivations withstanding the NaOH solution were provided by stacks of ICP-CVD grown and sputtered SiN(x) as well as diamond reinforced passivations. Drift levels about 0.001 pH/h and stable sensitivity over several CIP cycles were achieved for optimized sensor structures. Copyright © 2012 Elsevier B.V. All rights reserved.

Enhanced current collection in 1.7 eV GaInAsP solar cells grown on GaAs by metalorganic vapor phase epitaxy

DOE PAGES

Jain, Nikhil; Geisz, John F.; France, Ryan M.; ...

2017-02-08

Quaternary GaInAsP solar cells with a bandgap of ~1.7 eV offer an attractive Al-free alternative to AlGaAs solar cells for integration in next generation of III-V multijunction solar cells with five or more junctions. Development of a high quality 1.7 eV solar cell is also highly sought for III-V/Si tandem solar cells. In this work, we systematically investigate the impact of varying base thicknesses and doping concentrations on the carrier collection and performance of 1.7 eV GaInAsP solar cells. The photoresponse of these cells is found to be very sensitive to p-type zinc doping concentration in the base layer. Prototypemore » 1.7 eV GaInAsP n-i-p solar cell designs are demonstrated that leverage enhanced depletion width as an effective method to achieve peak quantum efficiency exceeding 90%. We also show the importance of optimal i-layer thickness as a critical parameter to reduce the drop in fill-factor (FF) due to field-aided collection. Furthermore, we demonstrate substantial improvement in the cell performance when the GaInAsP base layer is grown at 650 degrees C instead of 600 degrees C. The best GaInAsP solar cell (Eg ~ 1.65 eV) in this study achieved JSC of 21.1 mA/cm 2, VOC of 1.18 V, FF of 83.8%, and an efficiency of 20.8 +/- 1% under AM1.5D spectrum (21.5 +/- 1% under AM1.5G spectrum). Finally, these results highlight the potential of Al-free GaInAsP solar cells for integration in the next generation of III-V multijunction solar cells.« less

Enhanced current collection in 1.7 eV GaInAsP solar cells grown on GaAs by metalorganic vapor phase epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jain, Nikhil; Geisz, John F.; France, Ryan M.

Quaternary GaInAsP solar cells with a bandgap of ~1.7 eV offer an attractive Al-free alternative to AlGaAs solar cells for integration in next generation of III-V multijunction solar cells with five or more junctions. Development of a high quality 1.7 eV solar cell is also highly sought for III-V/Si tandem solar cells. In this work, we systematically investigate the impact of varying base thicknesses and doping concentrations on the carrier collection and performance of 1.7 eV GaInAsP solar cells. The photoresponse of these cells is found to be very sensitive to p-type zinc doping concentration in the base layer. Prototypemore » 1.7 eV GaInAsP n-i-p solar cell designs are demonstrated that leverage enhanced depletion width as an effective method to achieve peak quantum efficiency exceeding 90%. We also show the importance of optimal i-layer thickness as a critical parameter to reduce the drop in fill-factor (FF) due to field-aided collection. Furthermore, we demonstrate substantial improvement in the cell performance when the GaInAsP base layer is grown at 650 degrees C instead of 600 degrees C. The best GaInAsP solar cell (Eg ~ 1.65 eV) in this study achieved JSC of 21.1 mA/cm 2, VOC of 1.18 V, FF of 83.8%, and an efficiency of 20.8 +/- 1% under AM1.5D spectrum (21.5 +/- 1% under AM1.5G spectrum). Finally, these results highlight the potential of Al-free GaInAsP solar cells for integration in the next generation of III-V multijunction solar cells.« less

Application of the gravity search algorithm to multi-reservoir operation optimization

NASA Astrophysics Data System (ADS)

Bozorg-Haddad, Omid; Janbaz, Mahdieh; Loáiciga, Hugo A.

2016-12-01

Complexities in river discharge, variable rainfall regime, and drought severity merit the use of advanced optimization tools in multi-reservoir operation. The gravity search algorithm (GSA) is an evolutionary optimization algorithm based on the law of gravity and mass interactions. This paper explores the GSA's efficacy for solving benchmark functions, single reservoir, and four-reservoir operation optimization problems. The GSA's solutions are compared with those of the well-known genetic algorithm (GA) in three optimization problems. The results show that the GSA's results are closer to the optimal solutions than the GA's results in minimizing the benchmark functions. The average values of the objective function equal 1.218 and 1.746 with the GSA and GA, respectively, in solving the single-reservoir hydropower operation problem. The global solution equals 1.213 for this same problem. The GSA converged to 99.97% of the global solution in its average-performing history, while the GA converged to 97% of the global solution of the four-reservoir problem. Requiring fewer parameters for algorithmic implementation and reaching the optimal solution in fewer number of functional evaluations are additional advantages of the GSA over the GA. The results of the three optimization problems demonstrate a superior performance of the GSA for optimizing general mathematical problems and the operation of reservoir systems.

Optimization of wave-guided luminescence for higher efficiency of bifacial thin-film microscale GaAs solar cells

NASA Astrophysics Data System (ADS)

Shen, Ling; Shen, Yifeng; Li, Feng

2018-01-01

In pursuit of capturing more wave-guided luminescence for surface-printed bifacial GaAs μ-cells, the pyramid structure has been incorporated with specular back side reflector (BSR) to change the direction of photon propagation. Based on ray tracing model, the calculated photon capturing efficiency of GaAs μ-cells from back side via pyramid, dependent on the parameters of pyramid structure, achieve the largest 1.7× increase for dye absorption peak of 480 nm compared to the case without pyramid. More significantly, the short circuit current in experiment has been improved from original 16.5 mA/cm2 to 23.75 mA/cm2 for the AM 1.5G solar spectrum. Further experiment demonstrates that the optimized pyramid structure enables the integrated luminescent intensity to reach ∼3× increase in a smaller distance of optical transport, which means the advantages in photon capturing efficiency for cells with higher aspect ratio. The calculation further confirms that the cells with higher aspect ratio, among all cells with the same area, realize the higher concentration ratio for the same geometric gain. This provides a guideline for design of cell geometries to guarantee a higher power output in terms of cell modules.

Effects of surface passivation dielectrics on carrier transport in AlGaN/GaN heterostructure field-effect transistors

NASA Astrophysics Data System (ADS)

Oh, Sejoon; Jang, Han-Soo; Choi, Chel-Jong; Cho, Jaehee

2018-04-01

Dielectric layers prepared by different deposition methods were used for the surface passivation of AlGaN/GaN heterostructure field-effect transistors (HFETs) and the corresponding electrical characteristics were examined. Increases in the sheet charge density and the maximum drain current by approximately 45% and 28%, respectively, were observed after the deposition of a 100 nm-thick SiO2 layer by plasma-enhanced chemical vapor deposition (PECVD) on the top of the AlGaN/GaN HFETs. However, SiO2 deposited by a radio frequency (rf) sputter system had the opposite effect. As the strain applied to AlGaN was influenced by the deposition methods used for the dielectric layers, the carrier transport in the two-dimensional electron gas formed at the interface between AlGaN and GaN was affected accordingly.

MOVPE growth of (GaIn)As/Ga(AsSb)/(GaIn)As type-II heterostructures on GaAs substrate for near infrared laser applications

NASA Astrophysics Data System (ADS)

Fuchs, C.; Beyer, A.; Volz, K.; Stolz, W.

2017-04-01

The growth of high quality (GaIn)As/Ga(AsSb)/(GaIn)As "W"-quantum well heterostructures is discussed with respect to their application in 1300 nm laser devices. The structures are grown using metal organic vapor phase epitaxy and characterized using high-resolution X-ray diffraction, scanning transmission electron microscopy and photoluminescence measurements. The agreement between experimental high-resolution X-ray diffraction patterns and full dynamical simulations is verified for these structurally challenging heterostructures. Scanning transmission electron microscopy is used to demonstrate that the structure consists of well-defined quantum wells and forms the basis for future improvements of the optoelectronic quality of this materials system. By altering the group-V gas phase ratio, it is possible to cover a large spectral range between 1200 nm and 1470 nm using a growth temperature of 550 °C and a V/III ratio of 7.5. A comparison of a sample with a photoluminescence emission wavelength at 1360 nm with single quantum well material reference samples proves the type-II character of the emission. A further optimization of these structures for application in 1300 nm lasers by applying different V/III ratios yields a stable behavior of the photoluminescence intensity using a growth temperature of 550 °C.

Distributed optimization system and method

DOEpatents

Hurtado, John E.; Dohrmann, Clark R.; Robinett, III, Rush D.

2003-06-10

A search system and method for controlling multiple agents to optimize an objective using distributed sensing and cooperative control. The search agent can be one or more physical agents, such as a robot, and can be software agents for searching cyberspace. The objective can be: chemical sources, temperature sources, radiation sources, light sources, evaders, trespassers, explosive sources, time dependent sources, time independent sources, function surfaces, maximization points, minimization points, and optimal control of a system such as a communication system, an economy, a crane, and a multi-processor computer.

Optimal GENCO bidding strategy

NASA Astrophysics Data System (ADS)

Gao, Feng

Electricity industries worldwide are undergoing a period of profound upheaval. The conventional vertically integrated mechanism is being replaced by a competitive market environment. Generation companies have incentives to apply novel technologies to lower production costs, for example: Combined Cycle units. Economic dispatch with Combined Cycle units becomes a non-convex optimization problem, which is difficult if not impossible to solve by conventional methods. Several techniques are proposed here: Mixed Integer Linear Programming, a hybrid method, as well as Evolutionary Algorithms. Evolutionary Algorithms share a common mechanism, stochastic searching per generation. The stochastic property makes evolutionary algorithms robust and adaptive enough to solve a non-convex optimization problem. This research implements GA, EP, and PS algorithms for economic dispatch with Combined Cycle units, and makes a comparison with classical Mixed Integer Linear Programming. The electricity market equilibrium model not only helps Independent System Operator/Regulator analyze market performance and market power, but also provides Market Participants the ability to build optimal bidding strategies based on Microeconomics analysis. Supply Function Equilibrium (SFE) is attractive compared to traditional models. This research identifies a proper SFE model, which can be applied to a multiple period situation. The equilibrium condition using discrete time optimal control is then developed for fuel resource constraints. Finally, the research discusses the issues of multiple equilibria and mixed strategies, which are caused by the transmission network. Additionally, an advantage of the proposed model for merchant transmission planning is discussed. A market simulator is a valuable training and evaluation tool to assist sellers, buyers, and regulators to understand market performance and make better decisions. A traditional optimization model may not be enough to consider the distributed

Interleaved segment correction achieves higher improvement factors in using genetic algorithm to optimize light focusing through scattering media

NASA Astrophysics Data System (ADS)

Li, Runze; Peng, Tong; Liang, Yansheng; Yang, Yanlong; Yao, Baoli; Yu, Xianghua; Min, Junwei; Lei, Ming; Yan, Shaohui; Zhang, Chunmin; Ye, Tong

2017-10-01

Focusing and imaging through scattering media has been proved possible with high resolution wavefront shaping. A completely scrambled scattering field can be corrected by applying a correction phase mask on a phase only spatial light modulator (SLM) and thereby the focusing quality can be improved. The correction phase is often found by global searching algorithms, among which Genetic Algorithm (GA) stands out for its parallel optimization process and high performance in noisy environment. However, the convergence of GA slows down gradually with the progression of optimization, causing the improvement factor of optimization to reach a plateau eventually. In this report, we propose an interleaved segment correction (ISC) method that can significantly boost the improvement factor with the same number of iterations comparing with the conventional all segment correction method. In the ISC method, all the phase segments are divided into a number of interleaved groups; GA optimization procedures are performed individually and sequentially among each group of segments. The final correction phase mask is formed by applying correction phases of all interleaved groups together on the SLM. The ISC method has been proved significantly useful in practice because of its ability to achieve better improvement factors when noise is present in the system. We have also demonstrated that the imaging quality is improved as better correction phases are found and applied on the SLM. Additionally, the ISC method lowers the demand of dynamic ranges of detection devices. The proposed method holds potential in applications, such as high-resolution imaging in deep tissue.

Optimal correction and design parameter search by modern methods of rigorous global optimization

NASA Astrophysics Data System (ADS)

Makino, K.; Berz, M.

2011-07-01

Frequently the design of schemes for correction of aberrations or the determination of possible operating ranges for beamlines and cells in synchrotrons exhibit multitudes of possibilities for their correction, usually appearing in disconnected regions of parameter space which cannot be directly qualified by analytical means. In such cases, frequently an abundance of optimization runs are carried out, each of which determines a local minimum depending on the specific chosen initial conditions. Practical solutions are then obtained through an often extended interplay of experienced manual adjustment of certain suitable parameters and local searches by varying other parameters. However, in a formal sense this problem can be viewed as a global optimization problem, i.e. the determination of all solutions within a certain range of parameters that lead to a specific optimum. For example, it may be of interest to find all possible settings of multiple quadrupoles that can achieve imaging; or to find ahead of time all possible settings that achieve a particular tune; or to find all possible manners to adjust nonlinear parameters to achieve correction of high order aberrations. These tasks can easily be phrased in terms of such an optimization problem; but while mathematically this formulation is often straightforward, it has been common belief that it is of limited practical value since the resulting optimization problem cannot usually be solved. However, recent significant advances in modern methods of rigorous global optimization make these methods feasible for optics design for the first time. The key ideas of the method lie in an interplay of rigorous local underestimators of the objective functions, and by using the underestimators to rigorously iteratively eliminate regions that lie above already known upper bounds of the minima, in what is commonly known as a branch-and-bound approach. Recent enhancements of the Differential Algebraic methods used in particle

Radiolabeling optimization and characterization of (68)Ga labeled DOTA-polyamido-amine dendrimer conjugate - Animal biodistribution and PET imaging results.

PubMed

Ghai, Aanchal; Singh, Baljinder; Panwar Hazari, Puja; Schultz, Michael K; Parmar, Ambika; Kumar, Pardeep; Sharma, Sarika; Dhawan, Devinder; Kumar Mishra, Anil

2015-11-01

The present study describes the optimization of (68)Ga radiolabeling with PAMAM dendrimer-DOTA conjugate. A conjugate (PAMAM-DOTA) concentration of 11.69µM, provided best radiolabeling efficiency of more than 93.0% at pH 4.0, incubation time of 30.0min and reaction temperature ranging between 90 and 100°C. The decay corrected radiochemical yield was found to be 79.4±0.01%. The radiolabeled preparation ([(68)Ga]-DOTA-PAMAM-D) remained stable (radiolabeling efficiency of 96.0%) at room temperature and in serum for up to 4-h. The plasma protein binding was observed to be 21.0%. After intravenous administration, 50.0% of the tracer cleared from the blood circulation by 30-min and less than 1.0% of the injected activity remained in blood by 1.0h. The animal biodistribution studies demonstrated that the tracer excretes through the kidneys and about 0.33% of the %ID/g accumulated in the tumor at 1h post injection. The animal organ's biodistribution data was supported by animal PET imaging showing good 'non-specific' tracer uptake in tumor and excretion is primarily through kidneys. Additionally, DOTA-PAMAM-D conjugation with αVβ3 receptors targeting peptides and drug loading on the dendrimers may improve the specificity of the (68)Ga labeled product for imaging and treating angiogenesis respectively. Copyright © 2015 Elsevier Ltd. All rights reserved.

High Performance 50 nm InAlAs/In0.75GaAs Metamorphic High Electron Mobility Transistors with Si3N4 Passivation on Thin InGaAs Layer

NASA Astrophysics Data System (ADS)

Yeon, Seongjin; Seo, Kwangseok

2008-04-01

We fabricated 50 nm InAlAs/InGaAs metamorphic high electron mobility transistors (HEMTs) with a very thin barrier. Through the reduction of the gate-channel distance (dGC) in the epitaxial structure, a channel aspect ratio (ARC) of over three was achieved when Lg was 50 nm. We inserted a thin InGaAs layer as a protective layer, and tested various gate structures to reduce surface problems induced by barrier shrinkage and to optimize the device characteristics. Through the optimization of the gate structure with the thin InGaAs layer, the fabricated 50 nm metamorphic HEMT exhibited high DC and RF characteristics, Gm of 1.5 S/mm, and fT of 490 GHz.

Color tunable monolithic InGaN/GaN LED having a multi-junction structure.

PubMed

Kong, Duk-Jo; Kang, Chang-Mo; Lee, Jun-Yeob; Kim, James; Lee, Dong-Seon

2016-03-21

In this study, we have fabricated a blue-green color-tunable monolithic InGaN/GaN LED having a multi-junction structure with three terminals. The device has an n-p-n structure consisting of a green and a blue active region, i.e., an n-GaN / blue-MQW / p-GaN / green-MQW / n-GaN / Al₂O₃ structure with three terminals for independently controlling the two active regions. To realize this LED structure, a typical LED consisting of layers of n-GaN, blue MQW, and p-GaN is regrown on a conventional green LED by using a metal organic chemical vapor deposition (MOCVD) method. We explain detailed mechanisms of three operation modes which are the green, blue, and cyan mode. Moreover, we discuss optical properties of the device.

Proposal of Evolutionary Simplex Method for Global Optimization Problem

NASA Astrophysics Data System (ADS)

Shimizu, Yoshiaki

To make an agile decision in a rational manner, role of optimization engineering has been notified increasingly under diversified customer demand. With this point of view, in this paper, we have proposed a new evolutionary method serving as an optimization technique in the paradigm of optimization engineering. The developed method has prospects to solve globally various complicated problem appearing in real world applications. It is evolved from the conventional method known as Nelder and Mead’s Simplex method by virtue of idea borrowed from recent meta-heuristic method such as PSO. Mentioning an algorithm to handle linear inequality constraints effectively, we have validated effectiveness of the proposed method through comparison with other methods using several benchmark problems.

A Metallurgical Study of Nāga Bhasma

PubMed Central

Singh Gautam, Dev Nath

2017-01-01

Background: The metal Nāga (Lead) is being used by Indians since ancient times. Its external and internal uses have been described in Caraka, Suśruta and other Ayurvedic Saṃhitā. According to most of the Rasa texts, Nāga Bhasma and its formulations are used in many diseases such as Prameha, Jvara, Gulma, Śukrameha etc. Objectives: In the present study, Nāga Bhasma was prepared by the traditional Puṭa method (TPM) and by the electric muffle furnace Puṭa method (EMFPM) and standardized using Metallographic studies. Doing so helps in the study of the microstructure of Nāga Bhasma and also helps in the identification of the metal particles along with the nature of compound formed during the Māraṇa (Bhasmīkaraṇa) process. Setting and Design: Different samples from initial raw material to final product of Nāga Bhasma were collected during the pharmaceutical process (1st, 30th and 60th Puṭa) from both methods i.e. TPM and EMFPM. Samples from both methods were studied using metallographic examination. Materials and Methods: The processing of the Nāga Bhasma (ṣaṣṭipuṭa) was done according to Ānanda Kanda[9] Samples from the raw material i.e. Aśodhita Nāga (raw Lead) and that processed after 1st, 30th and 60th Puṭa from both methods i.e. traditional Puṭa method (using heat from burning of cow dung cakes) and electric muffle furnace Puṭa method were taken. They were mounted on self hardening acrylic base. After careful polishing to obtain scratch free surface of product, they were used for metallurgical study. Conclusion: This study shows that traditional Puṭa method may be better than electric muffle furnace Puṭa method because of more homogeneous distribution of Lead sulphide in the Nāga Bhasma which is prepared by traditional method. PMID:29269968

Preclinical evaluation of potential infection-imaging probe [68 Ga]Ga-DOTA-K-A9 in sterile and infectious inflammation.

PubMed

Nielsen, Karin M; Jørgensen, Nis P; Kyneb, Majbritt H; Borghammer, Per; Meyer, Rikke L; Thomsen, Trine R; Bender, Dirk; Jensen, Svend B; Nielsen, Ole L; Alstrup, Aage K O

2018-05-23

The development of bacteria-specific infection radiotracers is of considerable interest to improve diagnostic accuracy and enabling therapy monitoring. The aim of this study was to determine if the previously reported radiolabelled 1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid (DOTA) conjugated peptide [ 68 Ga]Ga-DOTA-K-A9 could detect a staphylococcal infection in vivo and distinguish it from aseptic inflammation. An optimized [ 68 Ga]Ga-DOTA-K-A9 synthesis omitting the use of acetone was developed, yielding 93 ± 0.9% radiochemical purity. The in vivo infection binding specificity of [ 68 Ga]Ga-DOTA-K-A9 was evaluated by micro positron emission tomography/magnetic resonance imaging of 15 mice with either subcutaneous Staphylococcus aureus infection or turpentine-induced inflammation and compared with 2-deoxy-2-[ 18 F]fluoro-D-glucose ([ 18 F]FDG). The scans showed that [ 68 Ga]Ga-DOTA-K-A9 accumulated in all the infected mice at injected doses ≥3.6 MBq. However, the tracer was not found to be selective towards infection, since the [ 68 Ga]Ga-DOTA-K-A9 also accumulated in mice with inflammation. In a concurrent in vitro binding evaluation performed with a 5-carboxytetramethylrhodamine (TAMRA) fluorescence analogue of the peptide, TAMRA-K-A9, the microscopy results suggested that TAMRA-K-A9 bound to an intracellular epitope and therefore preferentially targeted dead bacteria. Thus, the [ 68 Ga]Ga-DOTA-K-A9 uptake observed in vivo is presumably a combination of local hyperemia, vascular leakiness and/or binding to an epitope present in dead bacteria. Copyright © 2018 John Wiley & Sons, Ltd.

Semi-automated lab-on-a-chip for dispensing GA-68 radiotracers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weinberg, Irving

We solved a technical problem that is hindering American progress in molecular medicine, and restricting US citizens from receiving optimal diagnostic care. Specifically, the project deals with a mother/daughter generator of positron-emitting radiotracers (Ge-68/Ga-68). These generator systems are approved in Europe but cannot be used in the USA, because of safety issues related to possible breakthrough of long-lived Ge-68 (mother) atoms. Europeans have demonstrated abilities of Ga-68-labeled radiotracers to image cancer foci with high sensitivity and specificity, and to use such methods to effectively plan therapy.The USA Food and Drug Administration (FDA) and Nuclear Regulatory Commission (NRC) have taken themore » position that every patient administration of Ga-68 should be preceded by an assay demonstrated that Ge-68 breakthrough is within acceptable limits. Breakthrough of parent elements is a sensitive subject at the FDA, as evidenced by the recent recall of Rb-82 generators due to inadvertent administrations of Sr-82. Commercially, there is no acceptable rapid method for assaying breakthrough of Ge-68 prior to each human administration. The gamma emissions of daughter Ga-68 have higher energies than the parent Ge-68, so that the shielding assays typically employed for Mo-99/Tc-99m generators cannot be applied to Ga-68 generators. The half-life of Ga-68 is 68 minutes, so that the standard 10-half-life delay (used to assess breakthrough in Sr-82/Rb-82 generators) cannot be applied to Ga-68 generators. As a result of the aforementioned regulatory requirements, Ga-68 generators are sold in the USA for animal use only.The American clinical community’s inability to utilize Ga-68 generators impairs abilities to treat patients domestically, and puts the USA at a disadvantage in developing exportable products. The proposed DOE project aimed to take advantage of recent technological advances developed for lab-on-a-chip (LOC) applications. Based on our experiences

Thermal characterization of GaN-based laser diodes by forward-voltage method

NASA Astrophysics Data System (ADS)

Feng, M. X.; Zhang, S. M.; Jiang, D. S.; Liu, J. P.; Wang, H.; Zeng, C.; Li, Z. C.; Wang, H. B.; Wang, F.; Yang, H.

2012-05-01

An expression of the relation between junction temperature and forward voltage common for both GaN-based laser diodes (LDs) and light emitting diodes is derived. By the expression, the junction temperature of GaN-based LDs emitting at 405 nm was measured at different injection current and compared with the result of micro-Raman spectroscopy, showing that the expression is reasonable. In addition, the activation energy of Mg in AlGaN/GaN superlattice layers is obtained based on the temperature dependence of forward voltage.

Ultra-fast scintillation properties of β-Ga2O3 single crystals grown by Floating Zone method

NASA Astrophysics Data System (ADS)

He, Nuotian; Tang, Huili; Liu, Bo; Zhu, Zhichao; Li, Qiu; Guo, Chao; Gu, Mu; Xu, Jun; Liu, Jinliang; Xu, Mengxuan; Chen, Liang; Ouyang, Xiaoping

2018-04-01

In this investigation, β-Ga2O3 single crystals were grown by the Floating Zone method. At room temperature, the X-ray excited emission spectrum includes ultraviolet and blue emission bands. The scintillation light output is comparable to the commercial BGO scintillator. The scintillation decay times are composed of the dominant ultra-fast component of 0.368 ns and a small amount of slightly slow components of 8.2 and 182 ns. Such fast component is superior to most commercial inorganic scintillators. In contrast to most semiconductor crystals prepared by solution method such as ZnO, β-Ga2O3 single crystals can be grown by traditional melt-growth method. Thus we can easily obtain large bulk crystals and mass production.

COMPARISON OF NONLINEAR DYNAMICS OPTIMIZATION METHODS FOR APS-U

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Y.; Borland, Michael

Many different objectives and genetic algorithms have been proposed for storage ring nonlinear dynamics performance optimization. These optimization objectives include nonlinear chromaticities and driving/detuning terms, on-momentum and off-momentum dynamic acceptance, chromatic detuning, local momentum acceptance, variation of transverse invariant, Touschek lifetime, etc. In this paper, the effectiveness of several different optimization methods and objectives are compared for the nonlinear beam dynamics optimization of the Advanced Photon Source upgrade (APS-U) lattice. The optimized solutions from these different methods are preliminarily compared in terms of the dynamic acceptance, local momentum acceptance, chromatic detuning, and other performance measures.

Gate frequency sweep: An effective method to evaluate the dynamic performance of AlGaN/GaN power heterojunction field effect transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Santi, C. de; Meneghini, M., E-mail: matteo.meneghini@dei.unipd.it; Meneghesso, G.

2014-08-18

With this paper we propose a test method for evaluating the dynamic performance of GaN-based transistors, namely, gate-frequency sweep measurements: the effectiveness of the method is verified by characterizing the dynamic performance of Gate Injection Transistors. We demonstrate that this method can provide an effective description of the impact of traps on the transient performance of Heterojunction Field Effect Transistors, and information on the properties (activation energy and cross section) of the related defects. Moreover, we discuss the relation between the results obtained by gate-frequency sweep measurements and those collected by conventional drain current transients and double pulse characterization.

Interfacial relaxation analysis of InGaAs/GaAsP strain-compensated multiple quantum wells and its optical property

NASA Astrophysics Data System (ADS)

Dong, Hailiang; Sun, Jing; Ma, Shufang; Liang, Jian; Jia, Zhigang; Liu, Xuguang; Xu, Bingshe

2018-02-01

InGaAs/GaAsP strain-compensated multiple quantum wells were prepared by metal organic chemical vapor deposition on GaAs (100) substrates with misorientation of 15° toward [111]. In order to obtain better strain-compensated abrupt heterojunction interfaces, the compressive strain and relaxation of different quantum well and the total accumulated strain were investigated by adjusting In composition and the thickness of InxGa1-xAs well and GaAs1-yPy barrier keep constant. High resolution X-ray diffraction results indicate the crystal and interfacial structures of In0.18Ga0.82As (7 nm)/GaAs1-yPy with the least relaxation and total strain mismatch are better than others. From in-situ surface reflectivity curves, we observed the slope of reflectivity curve of multiple quantum wells increases with increasing lattice relaxation. Atomic force microscopic results show surface morphologies of three samples are Volmer-Weber mode. Indium segregation at heterointerface between well and barrier were investigated by secondary ion mass spectrometry which indicate indium diffusion width increase with the increasing total strain mismatch. Finally, a shoulder peak was observed from Gaussian fitting of photoluminescence, stemming from the lattice relaxation. These results demonstrate that the relaxation process is introduced and indium segregation length widens as the relaxation increases. The experimental results will be favorable for optimizing the epitaxial growth of InGaAs/GaAsP strain-compensated quantum wells in order to obtain high quality smooth heterointerface.

Investigation of directionally solidified InGaSb ternary alloys from Ga and Sb faces of GaSb(111) under prolonged microgravity at the International Space Station

PubMed Central

Nirmal Kumar, Velu; Arivanandhan, Mukannan; Rajesh, Govindasamy; Koyama, Tadanobu; Momose, Yoshimi; Sakata, Kaoruho; Ozawa, Tetsuo; Okano, Yasunori; Inatomi, Yuko; Hayakawa, Yasuhiro

2016-01-01

InGaSb ternary alloys were grown from GaSb (111)A and B faces (Ga and Sb faces) under microgravity conditions on board the International Space Station by a vertical gradient freezing method. The dissolution process of the Ga and Sb faces of GaSb and orientation-dependent growth properties of InGaSb were analysed. The dissolution of GaSb(111)B was greater than that of (111)A, which was found from the remaining undissolved seed and feed crystals. The higher dissolution of the Sb face was explained based on the number of atoms at that face, and its bonding with the next atomic layer. The growth interface shape was almost flat in both cases. The indium composition in both InGaSb samples was uniform in the radial direction and it gradually decreased along the growth direction because of segregation. The growth rate of InGaSb from GaSb (111)B was found to be higher than that of GaSb (111)A because of the higher dissolution of GaSb (111)B. PMID:28725736

Investigation of directionally solidified InGaSb ternary alloys from Ga and Sb faces of GaSb(111) under prolonged microgravity at the International Space Station.

PubMed

Nirmal Kumar, Velu; Arivanandhan, Mukannan; Rajesh, Govindasamy; Koyama, Tadanobu; Momose, Yoshimi; Sakata, Kaoruho; Ozawa, Tetsuo; Okano, Yasunori; Inatomi, Yuko; Hayakawa, Yasuhiro

2016-01-01

InGaSb ternary alloys were grown from GaSb (111)A and B faces (Ga and Sb faces) under microgravity conditions on board the International Space Station by a vertical gradient freezing method. The dissolution process of the Ga and Sb faces of GaSb and orientation-dependent growth properties of InGaSb were analysed. The dissolution of GaSb(111)B was greater than that of (111)A, which was found from the remaining undissolved seed and feed crystals. The higher dissolution of the Sb face was explained based on the number of atoms at that face, and its bonding with the next atomic layer. The growth interface shape was almost flat in both cases. The indium composition in both InGaSb samples was uniform in the radial direction and it gradually decreased along the growth direction because of segregation. The growth rate of InGaSb from GaSb (111)B was found to be higher than that of GaSb (111)A because of the higher dissolution of GaSb (111)B.

X-ray probe of GaN thin films grown on InGaN compliant substrates

NASA Astrophysics Data System (ADS)

Xu, Xiaoqing; Li, Yang; Liu, Jianming; Wei, Hongyuan; Liu, Xianglin; Yang, Shaoyan; Wang, Zhanguo; Wang, Huanhua

2013-04-01

GaN thin films grown on InGaN compliant substrates were characterized by several X-ray technologies: X-ray reciprocal space mapping (RSM), grazing incidence X-ray diffraction (GIXRD), and X-ray photoemission spectrum (XPS). Narrow Lorentz broadening and stress free state were observed for GaN grown on InGaN compliant substrate, while mosaic structure and large tensile stress were observed at the presence of residual indium atoms. RSM disclosed the mosaicity, and the GIXRD was conducted to investigate the depth dependences of crystal quality and strain states. XPS depth profile of indium contents indicated that residual indium atoms deteriorated the crystal quality of GaN not only by producing lattice mismatch at the interface of InGaN and GaN but also by diffusing into GaN overlayers. Accordingly, two solutions were proposed to improve the efficiency of self-patterned lateral epitaxial overgrowth method. This research goes a further step in resolving the urgent substrate problem in GaN fabrication.

Molecular dynamics studies of defect formation during heteroepitaxial growth of InGaN alloys on (0001) GaN surfaces

NASA Astrophysics Data System (ADS)

Gruber, J.; Zhou, X. W.; Jones, R. E.; Lee, S. R.; Tucker, G. J.

2017-05-01

We investigate the formation of extended defects during molecular-dynamics (MD) simulations of GaN and InGaN growth on (0001) and ( 11 2 ¯ 0 ) wurtzite-GaN surfaces. The simulated growths are conducted on an atypically large scale by sequentially injecting nearly a million individual vapor-phase atoms towards a fixed GaN surface; we apply time-and-position-dependent boundary constraints that vary the ensemble treatments of the vapor-phase, the near-surface solid-phase, and the bulk-like regions of the growing layer. The simulations employ newly optimized Stillinger-Weber In-Ga-N-system potentials, wherein multiple binary and ternary structures are included in the underlying density-functional-theory training sets, allowing improved treatment of In-Ga-related atomic interactions. To examine the effect of growth conditions, we study a matrix of >30 different MD-growth simulations for a range of InxGa1-xN-alloy compositions (0 ≤ x ≤ 0.4) and homologous growth temperatures [0.50 ≤ T/T*m(x) ≤ 0.90], where T*m(x) is the simulated melting point. Growths conducted on polar (0001) GaN substrates exhibit the formation of various extended defects including stacking faults/polymorphism, associated domain boundaries, surface roughness, dislocations, and voids. In contrast, selected growths conducted on semi-polar ( 11 2 ¯ 0 ) GaN, where the wurtzite-phase stacking sequence is revealed at the surface, exhibit the formation of far fewer stacking faults. We discuss variations in the defect formation with the MD growth conditions, and we compare the resulting simulated films to existing experimental observations in InGaN/GaN. While the palette of defects observed by MD closely resembles those observed in the past experiments, further work is needed to achieve truly predictive large-scale simulations of InGaN/GaN crystal growth using MD methodologies.

A rapid application of GA-MODFLOW combined approach to optimization of well placement and operation for drought-ready groundwater reservoir design

NASA Astrophysics Data System (ADS)

Park, C.; Kim, Y.; Jang, H.

2016-12-01

Poor temporal distribution of precipitation increases winter drought risks in mountain valley areas in Korea. Since perennial streams or reservoirs for water use are rare in the areas, groundwater is usually a major water resource. Significant amount of the precipitation contributing groundwater recharge mostly occurs during the summer season. However, a volume of groundwater recharge is limited by rapid runoff because of the topographic characteristics such as steep hill and slope. A groundwater reservoir using artificial recharge method with rain water reuse can be a suitable solution to secure water resource for the mountain valley areas. Successful groundwater reservoir design depends on optimization of well placement and operation. This study introduces a combined approach using GA (Genetic Algorithm) and MODFLOW and its rapid application. The methodology is based on RAD (Rapid Application Development) concept in order to minimize the cost of implementation. DEAP (Distributed Evolutionary Algorithms in Python), a framework for prototyping and testing evolutionary algorithms, is applied for quick code development and CUDA (Compute Unified Device Architecture), a parallel computing platform using GPU (Graphics Processing Unit), is introduced to reduce runtime. The application was successfully applied to Samdeok-ri, Gosung, Korea. The site is located in a mountain valley area and unconfined aquifers are major source of water use. The results of the application produced the best location and optimized operation schedule of wells including pumping and injecting.

Record-level quantum efficiency from a high polarization strained GaAs/GaAsP superlattice photocathode with distributed Bragg reflector

DOE PAGES

Liu, Wei; Chen, Yiqiao; Lu, Wentao; ...

2016-12-19

Photocathodes that provide high polarization and high quantum efficiency (QE) can significantly enhance the physics capabilities of electron accelerators. We report record-level QE from a high-polarization strained GaAs/GaAsP superlattice photocathode fabricated with a Distributed Bragg Reflector (DBR). The DBR photocathode technique enhances the absorption of incident laser light thereby enhancing QE, but as literature suggests, it is very challenging to optimize all of the parameters associated with the fabrication of complicated photocathode structures composed of many distinct layers. Past reports of DBR photocathodes describe high polarization but typically QE of only ~ 1%, which is comparable to QE of highmore » polarization photocathodes grown without a DBR structure. As a result, this work describes a new strained GaAs/GaAsP superlattice DBR photocathode exhibiting polarization of 84% and QE of 6.4%.« less

Record-level quantum efficiency from a high polarization strained GaAs/GaAsP superlattice photocathode with distributed Bragg reflector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Wei; Chen, Yiqiao; Lu, Wentao

Photocathodes that provide high polarization and high quantum efficiency (QE) can significantly enhance the physics capabilities of electron accelerators. We report record-level QE from a high-polarization strained GaAs/GaAsP superlattice photocathode fabricated with a Distributed Bragg Reflector (DBR). The DBR photocathode technique enhances the absorption of incident laser light thereby enhancing QE, but as literature suggests, it is very challenging to optimize all of the parameters associated with the fabrication of complicated photocathode structures composed of many distinct layers. Past reports of DBR photocathodes describe high polarization but typically QE of only ~ 1%, which is comparable to QE of highmore » polarization photocathodes grown without a DBR structure. As a result, this work describes a new strained GaAs/GaAsP superlattice DBR photocathode exhibiting polarization of 84% and QE of 6.4%.« less

Deterministic methods for multi-control fuel loading optimization

NASA Astrophysics Data System (ADS)

Rahman, Fariz B. Abdul

We have developed a multi-control fuel loading optimization code for pressurized water reactors based on deterministic methods. The objective is to flatten the fuel burnup profile, which maximizes overall energy production. The optimal control problem is formulated using the method of Lagrange multipliers and the direct adjoining approach for treatment of the inequality power peaking constraint. The optimality conditions are derived for a multi-dimensional multi-group optimal control problem via calculus of variations. Due to the Hamiltonian having a linear control, our optimal control problem is solved using the gradient method to minimize the Hamiltonian and a Newton step formulation to obtain the optimal control. We are able to satisfy the power peaking constraint during depletion with the control at beginning of cycle (BOC) by building the proper burnup path forward in time and utilizing the adjoint burnup to propagate the information back to the BOC. Our test results show that we are able to achieve our objective and satisfy the power peaking constraint during depletion using either the fissile enrichment or burnable poison as the control. Our fuel loading designs show an increase of 7.8 equivalent full power days (EFPDs) in cycle length compared with 517.4 EFPDs for the AP600 first cycle.

Optimal boarding method for airline passengers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steffen, Jason H.; /Fermilab

2008-02-01

Using a Markov Chain Monte Carlo optimization algorithm and a computer simulation, I find the passenger ordering which minimizes the time required to board the passengers onto an airplane. The model that I employ assumes that the time that a passenger requires to load his or her luggage is the dominant contribution to the time needed to completely fill the aircraft. The optimal boarding strategy may reduce the time required to board and airplane by over a factor of four and possibly more depending upon the dimensions of the aircraft. I explore some features of the optimal boarding method andmore » discuss practical modifications to the optimal. Finally, I mention some of the benefits that could come from implementing an improved passenger boarding scheme.« less

Using and comparing metaheuristic algorithms for optimizing bidding strategy viewpoint of profit maximization of generators

NASA Astrophysics Data System (ADS)

Mousavi, Seyed Hosein; Nazemi, Ali; Hafezalkotob, Ashkan

2015-03-01

With the formation of the competitive electricity markets in the world, optimization of bidding strategies has become one of the main discussions in studies related to market designing. Market design is challenged by multiple objectives that need to be satisfied. The solution of those multi-objective problems is searched often over the combined strategy space, and thus requires the simultaneous optimization of multiple parameters. The problem is formulated analytically using the Nash equilibrium concept for games composed of large numbers of players having discrete and large strategy spaces. The solution methodology is based on a characterization of Nash equilibrium in terms of minima of a function and relies on a metaheuristic optimization approach to find these minima. This paper presents some metaheuristic algorithms to simulate how generators bid in the spot electricity market viewpoint of their profit maximization according to the other generators' strategies, such as genetic algorithm (GA), simulated annealing (SA) and hybrid simulated annealing genetic algorithm (HSAGA) and compares their results. As both GA and SA are generic search methods, HSAGA is also a generic search method. The model based on the actual data is implemented in a peak hour of Tehran's wholesale spot market in 2012. The results of the simulations show that GA outperforms SA and HSAGA on computing time, number of function evaluation and computing stability, as well as the results of calculated Nash equilibriums by GA are less various and different from each other than the other algorithms.

An efficient multilevel optimization method for engineering design

NASA Technical Reports Server (NTRS)

Vanderplaats, G. N.; Yang, Y. J.; Kim, D. S.

1988-01-01

An efficient multilevel deisgn optimization technique is presented. The proposed method is based on the concept of providing linearized information between the system level and subsystem level optimization tasks. The advantages of the method are that it does not require optimum sensitivities, nonlinear equality constraints are not needed, and the method is relatively easy to use. The disadvantage is that the coupling between subsystems is not dealt with in a precise mathematical manner.

A constraint optimization based virtual network mapping method

NASA Astrophysics Data System (ADS)

Li, Xiaoling; Guo, Changguo; Wang, Huaimin; Li, Zhendong; Yang, Zhiwen

2013-03-01

Virtual network mapping problem, maps different virtual networks onto the substrate network is an extremely challenging work. This paper proposes a constraint optimization based mapping method for solving virtual network mapping problem. This method divides the problem into two phases, node mapping phase and link mapping phase, which are all NP-hard problems. Node mapping algorithm and link mapping algorithm are proposed for solving node mapping phase and link mapping phase, respectively. Node mapping algorithm adopts the thinking of greedy algorithm, mainly considers two factors, available resources which are supplied by the nodes and distance between the nodes. Link mapping algorithm is based on the result of node mapping phase, adopts the thinking of distributed constraint optimization method, which can guarantee to obtain the optimal mapping with the minimum network cost. Finally, simulation experiments are used to validate the method, and results show that the method performs very well.

[Optimized application of nested PCR method for detection of malaria].

PubMed

Yao-Guang, Z; Li, J; Zhen-Yu, W; Li, C

2017-04-28

Objective To optimize the application of the nested PCR method for the detection of malaria according to the working practice, so as to improve the efficiency of malaria detection. Methods Premixing solution of PCR, internal primers for further amplification and new designed primers that aimed at two Plasmodium ovale subspecies were employed to optimize the reaction system, reaction condition and specific primers of P . ovale on basis of routine nested PCR. Then the specificity and the sensitivity of the optimized method were analyzed. The positive blood samples and examination samples of malaria were detected by the routine nested PCR and the optimized method simultaneously, and the detection results were compared and analyzed. Results The optimized method showed good specificity, and its sensitivity could reach the pg to fg level. The two methods were used to detect the same positive malarial blood samples simultaneously, the results indicated that the PCR products of the two methods had no significant difference, but the non-specific amplification reduced obviously and the detection rates of P . ovale subspecies improved, as well as the total specificity also increased through the use of the optimized method. The actual detection results of 111 cases of malarial blood samples showed that the sensitivity and specificity of the routine nested PCR were 94.57% and 86.96%, respectively, and those of the optimized method were both 93.48%, and there was no statistically significant difference between the two methods in the sensitivity ( P > 0.05), but there was a statistically significant difference between the two methods in the specificity ( P < 0.05). Conclusion The optimized PCR can improve the specificity without reducing the sensitivity on the basis of the routine nested PCR, it also can save the cost and increase the efficiency of malaria detection as less experiment links.

Comparison of trap characteristics between AlGaN/GaN and AlGaN/InGaN/GaN heterostructure by frequency dependent conductance measurement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chakraborty, Apurba, E-mail: apurba.chakraborty86@gmail.com; Biswas, Dhrubes; Advanced Technology Development Centre, IIT Kharagpur, Kharagpur 721302

2015-02-23

Frequency dependent conductance measurement is carried out to observe the trapping effect in AlGaN/InGaN/GaN double heterostructure and compared that with conventional AlGaN/GaN single heterostructure. It is found that the AlGaN/InGaN/GaN diode structure does not show any trapping effect, whereas single heterostructure AlGaN/GaN diode suffers from two kinds of trap energy states in near depletion to higher negative voltage bias region. This conductance behaviour of AlGaN/InGaN/GaN heterostructure is owing to more Fermi energy level shift from trap energy states at AlGaN/InGaN junction compare to single AlGaN/GaN heterostructure and eliminates the trapping effects. Analysis yielded interface trap energy state in AlGaN/GaN ismore » to be with time constant of (33.8–76.5) μs and trap density of (2.38–0.656) × 10{sup 12 }eV{sup −1} cm{sup −2} in −3.2 to −4.8 V bias region, whereas for AlGaN/InGaN/GaN structure no interface energy states are found and the extracted surface trap energy concentrations and time constants are (5.87–4.39) ×10{sup 10} eV{sup −1} cm{sup −2} and (17.8–11.3) μs, respectively, in bias range of −0.8–0.0 V.« less

High energy proton radiation damage to (AlGa)As-G aAs solar cells

NASA Technical Reports Server (NTRS)

Loo, R.; Goldhammer, L.; Kamath, S.; Knechtli, R. C.

1979-01-01

Twelve 2 + 2 sq cm (AlGa)As-GaAs solar cells were fabricated and were subjected to 15.4 and 40 MeV of proton irradiation. The results showed that the GaAs cells degrade considerably less than do conventional and developmental K7 silicon cells. The detailed characteristics of the GaAs and silicon cells, both before and after irradiation, are described. Further optimization of the GaAs cells seems feasible, and areas for future work are suggested.

Optimization methods applied to hybrid vehicle design

NASA Technical Reports Server (NTRS)

Donoghue, J. F.; Burghart, J. H.

1983-01-01

The use of optimization methods as an effective design tool in the design of hybrid vehicle propulsion systems is demonstrated. Optimization techniques were used to select values for three design parameters (battery weight, heat engine power rating and power split between the two on-board energy sources) such that various measures of vehicle performance (acquisition cost, life cycle cost and petroleum consumption) were optimized. The apporach produced designs which were often significant improvements over hybrid designs already reported on in the literature. The principal conclusions are as follows. First, it was found that the strategy used to split the required power between the two on-board energy sources can have a significant effect on life cycle cost and petroleum consumption. Second, the optimization program should be constructed so that performance measures and design variables can be easily changed. Third, the vehicle simulation program has a significant effect on the computer run time of the overall optimization program; run time can be significantly reduced by proper design of the types of trips the vehicle takes in a one year period. Fourth, care must be taken in designing the cost and constraint expressions which are used in the optimization so that they are relatively smooth functions of the design variables. Fifth, proper handling of constraints on battery weight and heat engine rating, variables which must be large enough to meet power demands, is particularly important for the success of an optimization study. Finally, the principal conclusion is that optimization methods provide a practical tool for carrying out the design of a hybrid vehicle propulsion system.

Controllable Growth of Ga Film Electrodeposited from Aqueous Solution and Cu(In,Ga)Se2 Solar Cells.

PubMed

Bi, Jinlian; Ao, Jianping; Gao, Qing; Zhang, Zhaojing; Sun, Guozhong; He, Qing; Zhou, Zhiqiang; Sun, Yun; Zhang, Yi

2017-06-07

Electrodepositon of Ga film is very challenging due to the high standard reduction potential (-0.53 V vs SHE for Ga 3+ ). In this study, Ga film with compact structure was successfully deposited on the Mo/Cu/In substrate by the pulse current electrodeposition (PCE) method using GaCl 3 aqueous solution. A high deposition rate of Ga 3+ and H + can be achieved by applying a large overpotential induced by high pulse current. In the meanwhile, the concentration polarization induced by cation depletion can be minimized by changing the pulse frequency and duty cycle. Uniform and smooth Ga film was fabricated at high deposition rate with pulse current density 125 mA/cm 2 , pulse frequency 5 Hz, and duty cycle 0.25. Ga film was then selenized together with electrodeposited Cu and In films to make a CIGSe absorber film for solar cells. The solar cell based on the Ga film presents conversion efficiency of 11.04%, fill factor of 63.40%, and V oc of 505 mV, which is much better than those based on the inhomogeneous and rough Ga film prepared by the DCE method, indicating the pulse current electrodeposition process is promising for the fabrication of CIGSe solar cell.

An investigation of GaN thin films on AlN on sapphire substrate by sol-gel spin coating method

NASA Astrophysics Data System (ADS)

Amin, Nur Fahana Mohd; Ng, Sha Shiong

2017-12-01

In this research, the gallium nitride (GaN) thin films were deposited on aluminium nitride on sapphire (AlN/Al2O3) substrate by sol-gel spin coating method. Simple ethanol-based precursor with the addition of diethanolamine solution was used. The structural and morphology properties of synthesized GaN thin films were characterized by using X-ray Diffraction, Field-Emission Scanning Electron Microscopy and Atomic Force Microscopy. While the elemental compositions and the lattice vibrational properties of the films were investigated by means of the Energy Dispersive X-ray spectroscopy and Raman spectroscopy. All the results revealed that the wurtzite structure GaN thin films with GaN(002) preferred orientation and smooth surface morphology were successfully grown on AlN/Al2O3 substrate by using inexpensive and simplified sol-gel spin coating technique. The sol-gel spin coated GaN thin film with lowest oxygen content was also achieved.FESEM images show that GaN thin films with uniform and packed grains were formed. Based on the obtained results, it can be concluded that wurtzite structure GaN thin films were successfully deposited on AlN/Al2O3 substrate.

Preclinical Study of 68Ga-DOTATOC: Biodistribution Assessment in Syrian Rats and Evaluation of Absorbed Dose in Human Organs

PubMed Central

Naderi, Mojdeh; Zolghadri, Samaneh; Yousefnia, Hassan; Ramazani, Ali; Jalilian, Amir Reza

2016-01-01

Objective(s): Gallium-68 DOTA-DPhe1-Tyr3-Octreotide (68Ga-DOTATOC) has been applied by several European centers for the treatment of a variety of human malignancies. Nevertheless, definitive dosimetric data are yet unavailable. According to the Society of Nuclear Medicine and Molecular Imaging, researchers are investigating the safety and efficacy of this radiotracer to meet Food and Drug Administration requirements. The aim of this study was to introduce the optimized procedure for 68Ga-DOTATOC preparation, using a novel germanium-68 (68Ge)/68Ga generator in Iran and evaluate the absorbed doses in numerous organs with high accuracy. Methods: The optimized conditions for preparing the radiolabeled complex were determined via several experiments by changing the ligand concentration, pH, temperature and incubation time. Radiochemical purity of the complex was assessed, using high-performance liquid chromatography and instant thin-layer chromatography. The absorbed dose of human organs was evaluated, based on biodistribution studies on Syrian rats via Radiation Absorbed Dose Assessment Resource Method. Results: 68Ga-DOTATOC was prepared with radiochemical purity of >98% and specific activity of 39.6 MBq/nmol. The complex demonstrated great stability at room temperature and in human serum at 37°C at least two hours after preparation. Significant uptake was observed in somatostatin receptor-positive tissues such as pancreatic and adrenal tissues (12.83 %ID/g and 0.91 %ID/g, respectively). Dose estimations in human organs showed that the pancreas, kidneys and adrenal glands received the maximum absorbed doses (0.105, 0.074 and 0.010 mGy/MBq, respectively). Also, the effective absorbed dose was estimated at 0.026 mSv/MBq for 68Ga-DOTATOC. Conclusion: The obtained results showed that 68Ga-DOTATOC can be considered as an effective agent for clinical PET imaging in Iran. PMID:27904870

Decision-Aiding and Optimization for Vertical Navigation of Long-Haul Aircraft

NASA Technical Reports Server (NTRS)

Patrick, Nicholas J. M.; Sheridan, Thomas B.

1996-01-01

Most decisions made in the cockpit are related to safety, and have therefore been proceduralized in order to reduce risk. There are very few which are made on the basis of a value metric such as economic cost. One which can be shown to be value based, however, is the selection of a flight profile. Fuel consumption and flight time both have a substantial effect on aircraft operating cost, but they cannot be minimized simultaneously. In addition, winds, turbulence, and performance vary widely with altitude and time. These factors make it important and difficult for pilots to (a) evaluate the outcomes associated with a particular trajectory before it is flown and (b) decide among possible trajectories. The two elements of this problem considered here are: (1) determining what constitutes optimality, and (2) finding optimal trajectories. Pilots and dispatchers from major u.s. airlines were surveyed to determine which attributes of the outcome of a flight they considered the most important. Avoiding turbulence-for passenger comfort-topped the list of items which were not safety related. Pilots' decision making about the selection of flight profile on the basis of flight time, fuel burn, and exposure to turbulence was then observed. Of the several behavioral and prescriptive decision models invoked to explain the pilots' choices, utility maximization is shown to best reproduce the pilots' decisions. After considering more traditional methods for optimizing trajectories, a novel method is developed using a genetic algorithm (GA) operating on a discrete representation of the trajectory search space. The representation is a sequence of command altitudes, and was chosen to be compatible with the constraints imposed by Air Traffic Control, and with the training given to pilots. Since trajectory evaluation for the GA is performed holistically, a wide class of objective functions can be optimized easily. Also, using the GA it is possible to compare the costs associated with

Assessment of gene order computing methods for Alzheimer's disease

PubMed Central

2013-01-01

Background Computational genomics of Alzheimer disease (AD), the most common form of senile dementia, is a nascent field in AD research. The field includes AD gene clustering by computing gene order which generates higher quality gene clustering patterns than most other clustering methods. However, there are few available gene order computing methods such as Genetic Algorithm (GA) and Ant Colony Optimization (ACO). Further, their performance in gene order computation using AD microarray data is not known. We thus set forth to evaluate the performances of current gene order computing methods with different distance formulas, and to identify additional features associated with gene order computation. Methods Using different distance formulas- Pearson distance and Euclidean distance, the squared Euclidean distance, and other conditions, gene orders were calculated by ACO and GA (including standard GA and improved GA) methods, respectively. The qualities of the gene orders were compared, and new features from the calculated gene orders were identified. Results Compared to the GA methods tested in this study, ACO fits the AD microarray data the best when calculating gene order. In addition, the following features were revealed: different distance formulas generated a different quality of gene order, and the commonly used Pearson distance was not the best distance formula when used with both GA and ACO methods for AD microarray data. Conclusion Compared with Pearson distance and Euclidean distance, the squared Euclidean distance generated the best quality gene order computed by GA and ACO methods. PMID:23369541

An improved reaction path optimization method using a chain of conformations

NASA Astrophysics Data System (ADS)

Asada, Toshio; Sawada, Nozomi; Nishikawa, Takuya; Koseki, Shiro

2018-05-01

The efficient fast path optimization (FPO) method is proposed to optimize the reaction paths on energy surfaces by using chains of conformations. No artificial spring force is used in the FPO method to ensure the equal spacing of adjacent conformations. The FPO method is applied to optimize the reaction path on two model potential surfaces. The use of this method enabled the optimization of the reaction paths with a drastically reduced number of optimization cycles for both potentials. It was also successfully utilized to define the MEP of the isomerization of the glycine molecule in water by FPO method.

Band gap bowing and crossing of BxGa1-xN alloy investigated by hybrid functional method

NASA Astrophysics Data System (ADS)

Jiaping, Jiang; Yanqin, Gai; Gang, Tang

2016-02-01

The electronic properties of zinc-blende BxGa1-xN alloys are comparatively investigated by employing both the Perdewe-Burkee-Ernzerhof generalized-gradient approximation (PBE-GGA) and the Heyd-Scuseria-Ernzerhof screened hybrid functional methods (HSE06). HSE06 reproduced much closer ground-state properties to experiments. Large and composition-dependent bowing parameters bγ for the direct band gaps were obtained from both PBE and HSE06. The crossover composition where alloy switches from direct to indirect was predicted to occur at very similar x from PBE and HSE06. We can obtain direct gap BxGa1-xN with a gap value much larger than that of GaN by alloying x < 0.557 boron into GaN. Project supported by the Fundamental Research Funds for the Central Universities (No. 2010LKWL03), the Special Fund for Theoretical Physics (No. 11047130), and the National Natural Science Foundation of China (No. 11104345).

Structure and Photoluminescence Properties of β-Ga2O3 Nanofibres Synthesized via Electrospinning Method

NASA Astrophysics Data System (ADS)

Sun, Chao; Deng, Jinxiang; Kong, Le; Chen, Liang; Shen, Zhen; Cao, Yisen; Zhang, Hao; Wang, Xiaoran

2017-12-01

This paper reported the β-Ga2O3 nanofibres which fabricated by electrospinning, and then calcining in oxygen at 750, 850, 950 and 1050°C. The structure and properties of β-Ga2O3 nanofibers have been studied though kinds of methods such as XRD, Photoluminescence (PL) spectrum, Raman spectrum, Scanning electron microscope (SEM) and FT-IR. The diameters of these nanofibres are from 60 to 130nm and the lengths of these nanofibres are about couple millimetres. The spectrum of PL which excitation at 365nm gave us the information that the emission peak of these β-Ga2O3 nanofibres is about 470nm, it may be coursed by the various defects including the vacancies of gallium and oxygen and the gallium-oxygen vacancy pairs as well, and observed that with the increasing of the annealing temperature, the emission peaks have a small bule swifting, and the crystallinity become better at the same time.

Optimal least-squares finite element method for elliptic problems

NASA Technical Reports Server (NTRS)

Jiang, Bo-Nan; Povinelli, Louis A.

1991-01-01

An optimal least squares finite element method is proposed for two dimensional and three dimensional elliptic problems and its advantages are discussed over the mixed Galerkin method and the usual least squares finite element method. In the usual least squares finite element method, the second order equation (-Delta x (Delta u) + u = f) is recast as a first order system (-Delta x p + u = f, Delta u - p = 0). The error analysis and numerical experiment show that, in this usual least squares finite element method, the rate of convergence for flux p is one order lower than optimal. In order to get an optimal least squares method, the irrotationality Delta x p = 0 should be included in the first order system.

Defect phase diagram for doping of Ga2O3

NASA Astrophysics Data System (ADS)

Lany, Stephan

2018-04-01

For the case of n-type doping of β-Ga2O3 by group 14 dopants (C, Si, Ge, Sn), a defect phase diagram is constructed from defect equilibria calculated over a range of temperatures (T), O partial pressures (pO2), and dopant concentrations. The underlying defect levels and formation energies are determined from first-principles supercell calculations with GW bandgap corrections. Only Si is found to be a truly shallow donor, C is a deep DX-like (lattice relaxed donor) center, and Ge and Sn have defect levels close to the conduction band minimum. The thermodynamic modeling includes the effect of association of dopant-defect pairs and complexes, which causes the net doping to decline when exceeding a certain optimal dopant concentration. The optimal doping levels are surprisingly low, between about 0.01% and 1% of cation substitution, depending on the (T, pO2) conditions. Considering further the stability constraints due to sublimation of molecular Ga2O, specific predictions of optimized pO2 and Si dopant concentrations are given. The incomplete passivation of dopant-defect complexes in β-Ga2O3 suggests a design rule for metastable doping above the solubility limit.

One-step rapid synthesis of ultrafine γ-Ga2O3 nanocrystals by microwave hydrothermal method in ammonium hydroxide medium

NASA Astrophysics Data System (ADS)

Cui, Lu; Wang, Hong; Xin, Baifu; Mao, Guijie

2017-10-01

Ultrafine nanocrystals of γ-gallium oxide (γ-Ga2O3) were rapidly synthesized via microwave hydrothermal method at 140 °C, in which Ga(NO3)3 was used as the gallium source and urea was the precipitant. The samples were characterized by X-ray diffraction (XRD), ultraviolet-visible absorption spectroscopy (UV-Vis), transmission electron microscopy (TEM), nitrogen physisorption and photoluminescence spectroscopy (PL). The crystallite size of ultrafine spinel γ-Ga2O3 was in the range from 4 to 5 nm and the optical bandgap was 4.61 eV. To improve the crystallinity, the ultrafine γ-Ga2O3 nanocrystals were calcined at 300-700 °C further. The ultrafine γ-Ga2O3 calcined at 500 °C (calcined-γ-Ga2O3) still remained the metastable γ-phase with relatively high crystallinity and the crystallite size around 5-7 nm. Photocatalytic performances of the synthesized samples were also evaluated by the degradation of rhodamine B (RhB). Results revealed that the ultrafine γ-Ga2O3 and the calcined-γ-Ga2O3 samples exhibited high photocatalytic efficiencies of 68.2 and 90.7%, respectively.

Application of the GA-BP Neural Network in Earthwork Calculation

NASA Astrophysics Data System (ADS)

Fang, Peng; Cai, Zhixiong; Zhang, Ping

2018-01-01

The calculation of earthwork quantity is the key factor to determine the project cost estimate and the optimization of the scheme. It is of great significance and function in the excavation of earth and rock works. We use optimization principle of GA-BP intelligent algorithm running process, and on the basis of earthwork quantity and cost information database, the design of the GA-BP neural network intelligent computing model, through the network training and learning, the accuracy of the results meet the actual engineering construction of gauge fan requirements, it provides a new approach for other projects the calculation, and has good popularization value.

Anodic etching of GaN based film with a strong phase-separated InGaN/GaN layer: Mechanism and properties

NASA Astrophysics Data System (ADS)

Gao, Qingxue; Liu, Rong; Xiao, Hongdi; Cao, Dezhong; Liu, Jianqiang; Ma, Jin

2016-11-01

A strong phase-separated InGaN/GaN layer, which consists of multiple quantum wells (MQW) and superlattices (SL) layers and can produce a blue wavelength spectrum, has been grown on n-GaN thin film, and then fabricated into nanoporous structures by electrochemical etching method in oxalic acid. Scanning electron microscopy (SEM) technique reveals that the etching voltage of 8 V leads to a vertically aligned nanoporous structure, whereas the films etched at 15 V show branching pores within the n-GaN layer. Due to the low doping concentration of barriers (GaN layers) in the InGaN/GaN layer, we observed a record-low rate of etching (<100 nm/min) and nanopores which are mainly originated from the V-pits in the phase-separated layer. In addition, there exists a horizontal nanoporous structure at the interface between the phase-separated layer and the n-GaN layer, presumably resulting from the high transition of electrons between the barrier and the well (InGaN layer) at the interface. As compared to the as-grown MQW structure, the etched MQW structure exhibits a photoluminescence (PL) enhancement with a partial relaxation of compressive stress due to the increased light-extracting surface area and light-guiding effect. Such a compressive stress relaxation can be further confirmed by Raman spectra.

Genetic Algorithm for Optimization: Preprocessor and Algorithm

NASA Technical Reports Server (NTRS)

Sen, S. K.; Shaykhian, Gholam A.

2006-01-01

Genetic algorithm (GA) inspired by Darwin's theory of evolution and employed to solve optimization problems - unconstrained or constrained - uses an evolutionary process. A GA has several parameters such the population size, search space, crossover and mutation probabilities, and fitness criterion. These parameters are not universally known/determined a priori for all problems. Depending on the problem at hand, these parameters need to be decided such that the resulting GA performs the best. We present here a preprocessor that achieves just that, i.e., it determines, for a specified problem, the foregoing parameters so that the consequent GA is a best for the problem. We stress also the need for such a preprocessor both for quality (error) and for cost (complexity) to produce the solution. The preprocessor includes, as its first step, making use of all the information such as that of nature/character of the function/system, search space, physical/laboratory experimentation (if already done/available), and the physical environment. It also includes the information that can be generated through any means - deterministic/nondeterministic/graphics. Instead of attempting a solution of the problem straightway through a GA without having/using the information/knowledge of the character of the system, we would do consciously a much better job of producing a solution by using the information generated/created in the very first step of the preprocessor. We, therefore, unstintingly advocate the use of a preprocessor to solve a real-world optimization problem including NP-complete ones before using the statistically most appropriate GA. We also include such a GA for unconstrained function optimization problems.

Prepositioning emergency supplies under uncertainty: a parametric optimization method

NASA Astrophysics Data System (ADS)

Bai, Xuejie; Gao, Jinwu; Liu, Yankui

2018-07-01

Prepositioning of emergency supplies is an effective method for increasing preparedness for disasters and has received much attention in recent years. In this article, the prepositioning problem is studied by a robust parametric optimization method. The transportation cost, supply, demand and capacity are unknown prior to the extraordinary event, which are represented as fuzzy parameters with variable possibility distributions. The variable possibility distributions are obtained through the credibility critical value reduction method for type-2 fuzzy variables. The prepositioning problem is formulated as a fuzzy value-at-risk model to achieve a minimum total cost incurred in the whole process. The key difficulty in solving the proposed optimization model is to evaluate the quantile of the fuzzy function in the objective and the credibility in the constraints. The objective function and constraints can be turned into their equivalent parametric forms through chance constrained programming under the different confidence levels. Taking advantage of the structural characteristics of the equivalent optimization model, a parameter-based domain decomposition method is developed to divide the original optimization problem into six mixed-integer parametric submodels, which can be solved by standard optimization solvers. Finally, to explore the viability of the developed model and the solution approach, some computational experiments are performed on realistic scale case problems. The computational results reported in the numerical example show the credibility and superiority of the proposed parametric optimization method.

INNOVATIVE METHODS FOR THE OPTIMIZATION OF GRAVITY STORM SEWER DESIGN

EPA Science Inventory

The purpose of this paper is to describe a new method for optimizing the design of urban storm sewer systems. Previous efforts to optimize gravity sewers have met with limited success because classical optimization methods require that the problem be well behaved, e.g. describ...

Growth of GaN single crystals by a Ca- and Ba-added Na flux method

NASA Astrophysics Data System (ADS)

Ukegawa, H.; Konishi, Y.; Fujimori, T.; Miyoshi, N.; Imade, M.; Yoshimura, M.; Kitaoka, Y.; Sasaki, T.; Mori, Y.

2011-02-01

GaN substrates are desirable for fabricating ultra-violet LEDs and LDs, and high-power and high-frequency transistors. High-quality GaN single crystals can be obtained by using Na flux method, but the growth habit of bulk crystals must be controlled. In this study, we investigated the effects of additives (Ca, Ba) on the growth habit and impurity concentration in the crystals. The aspect ratio (c/a) of the crystals was increased by increasing the amount of additives, showing that the growth habit could be changed from the pyramidal shape to the prism shape. Ba concentration was below the detection limit (1x1015 atoms/cm3).

Optimizing How We Teach Research Methods

ERIC Educational Resources Information Center

Cvancara, Kristen E.

2017-01-01

Courses: Research Methods (undergraduate or graduate level). Objective: The aim of this exercise is to optimize the ability for students to integrate an understanding of various methodologies across research paradigms within a 15-week semester, including a review of procedural steps and experiential learning activities to practice each method, a…

Conversion between hexagonal GaN and beta-Ga(2)O(3) nanowires and their electrical transport properties.

PubMed

Li, Jianye; An, Lei; Lu, Chenguang; Liu, Jie

2006-02-01

We have observed that the hexagonal GaN nanowires grown from a simple chemical vapor deposition method using gallium metal and ammonia gas are usually gallium-doped. By annealing in air, the gallium-doped hexagonal GaN nanowires could be completely converted to beta-Ga(2)O(3) nanowires. Annealing the beta-Ga(2)O(3) nanowires in ammonia could convert them back to undoped hexagonal GaN nanowires. Field effect transistors based on these three kinds of nanowires were fabricated, and their performances were studied. Because of gallium doping, the as-grown GaN nanowires show a weak gating effect. Through the conversion process of GaN nanowires (gallium-doped) --> Ga(2)O(3) nanowires --> GaN nanowires (undoped) via annealing, the final undoped GaN nanowires display different electrical properties than the initial gallium-doped GaN nanowires, show a pronounced n-type gating effect, and can be completely turned off.

Surrogate Based Uni/Multi-Objective Optimization and Distribution Estimation Methods

NASA Astrophysics Data System (ADS)

Gong, W.; Duan, Q.; Huo, X.

2017-12-01

Parameter calibration has been demonstrated as an effective way to improve the performance of dynamic models, such as hydrological models, land surface models, weather and climate models etc. Traditional optimization algorithms usually cost a huge number of model evaluations, making dynamic model calibration very difficult, or even computationally prohibitive. With the help of a serious of recently developed adaptive surrogate-modelling based optimization methods: uni-objective optimization method ASMO, multi-objective optimization method MO-ASMO, and probability distribution estimation method ASMO-PODE, the number of model evaluations can be significantly reduced to several hundreds, making it possible to calibrate very expensive dynamic models, such as regional high resolution land surface models, weather forecast models such as WRF, and intermediate complexity earth system models such as LOVECLIM. This presentation provides a brief introduction to the common framework of adaptive surrogate-based optimization algorithms of ASMO, MO-ASMO and ASMO-PODE, a case study of Common Land Model (CoLM) calibration in Heihe river basin in Northwest China, and an outlook of the potential applications of the surrogate-based optimization methods.

A Novel Algorithm Combining Finite State Method and Genetic Algorithm for Solving Crude Oil Scheduling Problem

PubMed Central

Duan, Qian-Qian; Yang, Gen-Ke; Pan, Chang-Chun

2014-01-01

A hybrid optimization algorithm combining finite state method (FSM) and genetic algorithm (GA) is proposed to solve the crude oil scheduling problem. The FSM and GA are combined to take the advantage of each method and compensate deficiencies of individual methods. In the proposed algorithm, the finite state method makes up for the weakness of GA which is poor at local searching ability. The heuristic returned by the FSM can guide the GA algorithm towards good solutions. The idea behind this is that we can generate promising substructure or partial solution by using FSM. Furthermore, the FSM can guarantee that the entire solution space is uniformly covered. Therefore, the combination of the two algorithms has better global performance than the existing GA or FSM which is operated individually. Finally, a real-life crude oil scheduling problem from the literature is used for conducting simulation. The experimental results validate that the proposed method outperforms the state-of-art GA method. PMID:24772031

Optimization methods and silicon solar cell numerical models

NASA Technical Reports Server (NTRS)

Girardini, K.; Jacobsen, S. E.

1986-01-01

An optimization algorithm for use with numerical silicon solar cell models was developed. By coupling an optimization algorithm with a solar cell model, it is possible to simultaneously vary design variables such as impurity concentrations, front junction depth, back junction depth, and cell thickness to maximize the predicted cell efficiency. An optimization algorithm was developed and interfaced with the Solar Cell Analysis Program in 1 Dimension (SCAP1D). SCAP1D uses finite difference methods to solve the differential equations which, along with several relations from the physics of semiconductors, describe mathematically the performance of a solar cell. A major obstacle is that the numerical methods used in SCAP1D require a significant amount of computer time, and during an optimization the model is called iteratively until the design variables converge to the values associated with the maximum efficiency. This problem was alleviated by designing an optimization code specifically for use with numerically intensive simulations, to reduce the number of times the efficiency has to be calculated to achieve convergence to the optimal solution.

Optimized method for manufacturing large aspheric surfaces

NASA Astrophysics Data System (ADS)

Zhou, Xusheng; Li, Shengyi; Dai, Yifan; Xie, Xuhui

2007-12-01

Aspheric optics are being used more and more widely in modern optical systems, due to their ability of correcting aberrations, enhancing image quality, enlarging the field of view and extending the range of effect, while reducing the weight and volume of the system. With optical technology development, we have more pressing requirement to large-aperture and high-precision aspheric surfaces. The original computer controlled optical surfacing (CCOS) technique cannot meet the challenge of precision and machining efficiency. This problem has been thought highly of by researchers. Aiming at the problem of original polishing process, an optimized method for manufacturing large aspheric surfaces is put forward. Subsurface damage (SSD), full aperture errors and full band of frequency errors are all in control of this method. Lesser SSD depth can be gained by using little hardness tool and small abrasive grains in grinding process. For full aperture errors control, edge effects can be controlled by using smaller tools and amendment model with material removal function. For full band of frequency errors control, low frequency errors can be corrected with the optimized material removal function, while medium-high frequency errors by using uniform removing principle. With this optimized method, the accuracy of a K9 glass paraboloid mirror can reach rms 0.055 waves (where a wave is 0.6328μm) in a short time. The results show that the optimized method can guide large aspheric surface manufacturing effectively.

Engineering applications of heuristic multilevel optimization methods

NASA Technical Reports Server (NTRS)

Barthelemy, Jean-Francois M.

1988-01-01

Some engineering applications of heuristic multilevel optimization methods are presented and the discussion focuses on the dependency matrix that indicates the relationship between problem functions and variables. Coordination of the subproblem optimizations is shown to be typically achieved through the use of exact or approximate sensitivity analysis. Areas for further development are identified.

Engineering applications of heuristic multilevel optimization methods

NASA Technical Reports Server (NTRS)

Barthelemy, Jean-Francois M.

1989-01-01

Some engineering applications of heuristic multilevel optimization methods are presented and the discussion focuses on the dependency matrix that indicates the relationship between problem functions and variables. Coordination of the subproblem optimizations is shown to be typically achieved through the use of exact or approximate sensitivity analysis. Areas for further development are identified.

Optimal laser wavelength for efficient laser power converter operation over temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Höhn, O., E-mail: oliver.hoehn@ise.fraunhofer.de; Walker, A. W.; Bett, A. W.

2016-06-13

A temperature dependent modeling study is conducted on a GaAs laser power converter to identify the optimal incident laser wavelength for optical power transmission. Furthermore, the respective temperature dependent maximal conversion efficiencies in the radiative limit as well as in a practically achievable limit are presented. The model is based on the transfer matrix method coupled to a two-diode model, and is calibrated to experimental data of a GaAs photovoltaic device over laser irradiance and temperature. Since the laser wavelength does not strongly influence the open circuit voltage of the laser power converter, the optimal laser wavelength is determined tomore » be in the range where the external quantum efficiency is maximal, but weighted by the photon flux of the laser.« less

Characterization and Optimization Design of the Polymer-Based Capacitive Micro-Arrayed Ultrasonic Transducer

NASA Astrophysics Data System (ADS)

Chiou, De-Yi; Chen, Mu-Yueh; Chang, Ming-Wei; Deng, Hsu-Cheng

2007-11-01

This study constructs an electromechanical finite element model of the polymer-based capacitive micro-arrayed ultrasonic transducer (P-CMUT). The electrostatic-structural coupled-field simulations are performed to investigate the operational characteristics, such as collapse voltage and resonant frequency. The numerical results are found to be in good agreement with experimental observations. The study of influence of each defined parameter on the collapse voltage and resonant frequency are also presented. To solve some conflict problems in diversely physical fields, an integrated design method is developed to optimize the geometric parameters of the P-CMUT. The optimization search routine conducted using the genetic algorithm (GA) is connected with the commercial FEM software ANSYS to obtain the best design variable using multi-objective functions. The results show that the optimal parameter values satisfy the conflicting objectives, namely to minimize the collapse voltage while simultaneously maintaining a customized frequency. Overall, the present result indicates that the combined FEM/GA optimization scheme provides an efficient and versatile approach of optimization design of the P-CMUT.

Enhanced light extraction from a GaN-based green light-emitting diode with hemicylindrical linear grating structure.

PubMed

Jin, Yuanhao; Yang, Fenglei; Li, Qunqing; Zhu, Zhendong; Zhu, Jun; Fan, Shoushan

2012-07-02

Significant enhancement in the light output from GaN-based green light-emitting diodes (LEDs) was achieved with a hemicylindrical grating structure on the top layer of the diodes. The grating structure was first optimized by the finite-difference time-domain (FDTD) method, which showed that the profile of the grating structure was critical for light extraction efficiency. It was found that the transmission efficiency of the 530 nm light emitted from the inside of the GaN LED increased for incidence angles between 23.58° and 60°. Such a structure was fabricated by electron-beam lithography and an etching method. The light output power from the LED was increased approximately 4.7 times compared with that from a conventional LED. The structure optimization is the key to the great increase in transmission efficiency. Furthermore, the light emitted from the edge of the LED units could be collected and extracted by the grating structures in adjacent LED units, thus enhancing the performance of the whole LED chip.

Optimal projection method determination by Logdet Divergence and perturbed von-Neumann Divergence.

PubMed

Jiang, Hao; Ching, Wai-Ki; Qiu, Yushan; Cheng, Xiao-Qing

2017-12-14

Positive semi-definiteness is a critical property in kernel methods for Support Vector Machine (SVM) by which efficient solutions can be guaranteed through convex quadratic programming. However, a lot of similarity functions in applications do not produce positive semi-definite kernels. We propose projection method by constructing projection matrix on indefinite kernels. As a generalization of the spectrum method (denoising method and flipping method), the projection method shows better or comparable performance comparing to the corresponding indefinite kernel methods on a number of real world data sets. Under the Bregman matrix divergence theory, we can find suggested optimal λ in projection method using unconstrained optimization in kernel learning. In this paper we focus on optimal λ determination, in the pursuit of precise optimal λ determination method in unconstrained optimization framework. We developed a perturbed von-Neumann divergence to measure kernel relationships. We compared optimal λ determination with Logdet Divergence and perturbed von-Neumann Divergence, aiming at finding better λ in projection method. Results on a number of real world data sets show that projection method with optimal λ by Logdet divergence demonstrate near optimal performance. And the perturbed von-Neumann Divergence can help determine a relatively better optimal projection method. Projection method ia easy to use for dealing with indefinite kernels. And the parameter embedded in the method can be determined through unconstrained optimization under Bregman matrix divergence theory. This may provide a new way in kernel SVMs for varied objectives.

A guided search genetic algorithm using mined rules for optimal affective product design