Optical Investigations of Non-polar m-plane InGaN/GaN Multiple Quantum Wells Grown on LiAlO2 (100) by Using MOVPE

D. R. Hang,Mitch M. C. Chou,J. L. Lin,M. Heuken 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.1

We investigate the optical properties of m-plane InGaN/GaN multiple quantum wells (MQWs) grown on LiAlO2 substrates by using metal organic vapor phase epitaxy (MOVPE). Polarizationdependent photoluminescence (PL) measurements have been employed to study the optical emission characteristics. We demonstrate that the PL emission has a large polarization anisotropy, which can be attributed to the anisotropic in-plane strain. The degree of polarization is studied as a function of temperature, and the dependence can be explained by using the modified band structure model. The energy splitting of the two uppermost valence bands is obtained from polarized PL spectroscopy and is in good agreement with the activation energy deduced from the Arrhenius relationship. From the excitation-dependent PL measurements, we found the optical emission not to be influenced by the polarization-induced electric field. Our results are important for the design and the fabrication of non-polar InGaN/GaN MQW polarization-sensitive optical devices We investigate the optical properties of m-plane InGaN/GaN multiple quantum wells (MQWs) grown on LiAlO2 substrates by using metal organic vapor phase epitaxy (MOVPE). Polarizationdependent photoluminescence (PL) measurements have been employed to study the optical emission characteristics. We demonstrate that the PL emission has a large polarization anisotropy, which can be attributed to the anisotropic in-plane strain. The degree of polarization is studied as a function of temperature, and the dependence can be explained by using the modified band structure model. The energy splitting of the two uppermost valence bands is obtained from polarized PL spectroscopy and is in good agreement with the activation energy deduced from the Arrhenius relationship. From the excitation-dependent PL measurements, we found the optical emission not to be influenced by the polarization-induced electric field. Our results are important for the design and the fabrication of non-polar InGaN/GaN MQW polarization-sensitive optical devices

Applications of Laser-Fabricated Plasma Structures in Laser-Wakefield Accelerators, X-ray Lasers and Plasma Nonlinear Optics

C.T. Hsieh,M.W. Lin,C.L. Chang,Y.C. Ho,S.Y. Chen,J. Wang,M.C. Chou,J.Y. Lin,C.H. Pai,P.H. Lin,L.C. Tai,S.H. Chen,G.Y. Tsaur,C.C. Kuo,T.Y. Chien 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6

A general method for fabricating transient plasma structures with high-intensity laser pulses is developed to gain fine control over laser-plasma interactions. These structures have been used as programmable photonic devices in the development of laser-wakefield accelerators, soft X-ray lasers and plasma nonlinear optics driven by multi-terawatt laser pulses. Plasma ramps are used to control electron injection in laser-wakefield accelerators, plasma waveguides are used to enhance the efficiency of soft X-ray lasers by orders of magnitude and periodic plasma structures are used to achieve quasi-phase matching in relativistic harmonic generation. By scanning the interaction length with the same plasma-fabrication method, tomographic measurements are carried out to resolve the injection/acceleration process in laser-wakefield accelerators and amplification processes in X-ray lasers and relativistic harmonic generation. A theoretical analysis and a computer simulation are also carried out to provide insightful pictures of these processes. These research works show that by controlling plasma structures with optical fabrication methods, laser-plasma interaction can be engineered to expand and enrich the frontier of high-field physics.

Crack growth life model for fatigue susceptible structural components in aging aircraft

Chou, Karen C.,Cox, Glenn C.,Lockwood, Allison M. Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.17 No.1

A total life model was developed to assess the service life of aging aircraft. The primary focus of this paper is the development of crack growth life projection using the response surface method. Crack growth life projection is a necessary component of the total life model. The study showed that the number of load cycles N needed for a crack to propagate to a specified size can be linearly related to the geometric parameter, material, and stress level of the component considered when all the variables are transformed to logarithmic values. By the Central Limit theorem, the ln N was approximated by Gaussian distribution. This Gaussian model compared well with the histograms of the number of load cycles generated from simulated crack growth curves. The outcome of this study will aid engineers in designing their crack growth experiments to develop the stochastic crack growth models for service life assessments.

Guide plates on wind uplift of a solar collector model

K.M. Chung,K.C. Chang,C.K. Chen,C.C. Chou 한국풍공학회 2013 Wind and Structures, An International Journal (WAS Vol.16 No.2

One of the key issues affecting the promotion of solar water heaters in Taiwan is the severe impact of typhoon each year. An experimental study was conducted to investigate the wind uplift characteristic of a solar collector model with and without a guide plate. The guide plate with different lengths and orientations with respect to wind direction was adopted. It is found that the wind uplift of a solar collector is associated with the tilt angle of the flat panel as expected. A cavity formed between the guide plate and the flat panel has a significant effect on the distributions of streamwsie and lateral pressure. Reduction in uplift is essentially coupled with the projected area of a guide plate on the lower surface of the tilt flat panel.

Synchronized Bursting Induced by Network Connectivity in Cortical Neuronal Cultures

L.C. Jia,P.-Y. Lai,C. K. Chan,C.H. Chang,C.R. Han,M.T. Tsai,Y.S. Chou 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.1I

Synchronization of cortical neural cultures is studied as a function of the effective network connectivity in the phenomenon of synchronized firing (SF). The synchronized bursting frequency (during SF) of the network is found to be much slower than the characteristic time scale of a neuron and increases with the network connectivity. Using fluorescence imaging techniques, we found that SF occurs only when the incubation time is longer than some critical age tc and the synchronized bursting frequency f increases with time as f = fc + fo log( t tc ). Furthermore, tc is found to scale with the cell plating density as tc 1 p . Based on the result of photolysis of neurons, the synchronized bursting frequency is shown to be related to the network connectivity, hence, the growth behavior can be inferred from the measured SF frequencies. We further build a network growth model with the characteristics of an early stage active growth followed by a late-stage retarded growth, which can account for the experimental data quantitatively. Electrophysiological measurements using double-patch techniques reveal that even though the bursting frequencies are synchronized, the intra-burst spikes are not. We also present a mean-field model of the neural network that enables the neuron firing to be inhibited and generates inter-spike intervals with long time scales resulting in bursting.

Glucose and Its Role in Generating Reactive Oxygen Species Required for Mouse Sperm Fertilizing Ability

Lin, S.C.,Chen, M.C.,Huang, A.J.,Salem, B.,Li, K.C.,Chou, K. Asian Australasian Association of Animal Productio 2000 Animal Bioscience Vol.13 No.6

Effects of xanthine (X), xanthine oxidase (XO), and catalase (C), $H_2O_2$, and carbohydrates on sperm capacitation, acrosome reaction, and fertilizing ability in vitro were examined. Glucose alone, but not fructose, supported the maximum rate of sperm capacitation and acrosome reaction. However, in the combination of X, XO, and C (XXOC) or $H_2O_2$, fructose alone also supported maximum capacitation, acrosome reaction, and fertilization. Either insufficient or excessive amounts of $H_2O_2$ decreased sperm capacitation and the acrosome reaction. In order to understand how glucose generates $H_2O_2$ or other reactive oxygen species in sperm cells, 6-aminonicotinamide, an inhibitor of the pentose-phosphate pathway (PPP), and apocynin, an inhibitor of NADPH oxidase, were added to sperm suspensions in glucose-containing medium. Results appeared that sperm capacitation, acrosome reaction, and fertilization were consequently inhibited by either one of these compounds. These inhibitory effects were nullified by addition of XXOC. These results support the hypothesis that glucose, in addition to being a substrate for glycolysis, facilitates sperm capacitation and the acrosome reaction by generating reactive oxygen species through G-6-P dehydrogenase and NADPH oxidase.

An Imperfectly Passive Nature: Bright Submillimeter Emission from Dust-obscured Star Formation in the <i>z</i> = 3.717 “Passive” System, ZF 20115

Simpson, J. M.,Smail, Ian,Wang, Wei-Hao,Riechers, D.,Dunlop, J. S.,Ao, Y.,Bourne, N.,Bunker, A.,Chapman, S. C.,Chen, Chian-Chou,Dannerbauer, H.,Geach, J. E.,Goto, T.,Harrison, C. M.,Hwang, H. S.,Iviso American Astronomical Society 2017 ASTROPHYSICAL JOURNAL LETTERS - Vol.844 No.1

Guide plates on wind uplift of a solar collector model

Chung, K.M.,Chang, K.C.,Chen, C.K.,Chou, C.C. Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.16 No.2

One of the key issues affecting the promotion of solar water heaters in Taiwan is the severe impact of typhoon each year. An experimental study was conducted to investigate the wind uplift characteristic of a solar collector model with and without a guide plate. The guide plate with different lengths and orientations with respect to wind direction was adopted. It is found that the wind uplift of a solar collector is associated with the tilt angle of the flat panel as expected. A cavity formed between the guide plate and the flat panel has a significant effect on the distributions of streamwsie and lateral pressure. Reduction in uplift is essentially coupled with the projected area of a guide plate on the lower surface of the tilt flat panel.

Temperature Dependence of the Stokes Shift in Tensile InGaN/GaN MQWs with Advanced Buer Layers

D. R. Hang,M. M. C. Chou,M. H. Hsieh,M. Heuken 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.3

The influence of buer layers on the optical absorption and the emission properties of tensile InGaN/GaN multiple quantum wells (MQWs) has been studied. Here, sets of buffer structures consisting of low-temperature AlN and high-temperature AlN/AlGaN/GaN stacks have been employed to compensate for the detrimental eects brought about by the large lattice mismatch and by the difference in thermal expansion coefficients when silicon substrates are used. We found the biaxial tensile strain could be reduced and that the internal quantum efficiency could be considerably improved. Moreover, the Stokes shift could be reduced and its temperature variation became stabilized. The underlying mechanism is mainly due to the quantum confined Stark effect while the contribution from the localization effect is relatively small in our tensile InGaN/GaN MQWs.

Overdensity of submillimeter galaxies around the <i>z</i> ≃ 2.3 MAMMOTH-1 nebula : The environment and powering of an enormous Lyman-<i>α</i> nebula

Arrigoni Battaia, F.,Chen, Chian-Chou,Fumagalli, M.,Cai, Zheng,Calistro Rivera, G.,Xu, Jiachuan,Smail, I.,Prochaska, J. X.,Yang, Yujin,De Breuck, C. Springer-Verlag 2018 Astronomy and astrophysics Vol.620 No.-

<P>In the hierarchical model of structure formation, giant elliptical galaxies form through merging processes within the highest density peaks known as protoclusters. While high-redshift radio galaxies usually pinpoint the location of these environments, we have recently discovered at <I>z</I> ∼ 2−3 three enormous (> 200 kpc) Lyman-<I>α</I> nebulae (ELANe) that host multiple active galactic nuclei (AGN) and that are surrounded by overdensities of Lyman-<I>α</I> emitters (LAE). These regions are prime candidates for massive protoclusters in the early stages of assembly. To characterize the star-forming activity within these rare structures - both on ELAN and protocluster scales - we have initiated an observational campaign with the <I>James Clerk Maxwell</I> Telescope (JCMT) and the Atacama Pathfinder EXperiment (APEX) telescopes. In this paper we report on sensitive SCUBA-2/JCMT 850 and 450 <I>μ</I>m observations of a ∼128 arcmin<SUP>2</SUP> field comprising the ELAN MAMMOTH-1, together with the peak of the hosting BOSS1441 LAE overdensity at <I>z</I> = 2.32. These observations unveil 4.0 ± 1.3 times higher source counts at 850 <I>μ</I>m with respect to blank fields, likely confirming the presence of an overdensity also in obscured tracers. We find a strong detection at 850 <I>μ</I>m associated with the continuum source embedded within the ELAN MAMMOTH-1, which - together with the available data from the literature - allow us to constrain the spectral energy distribution of this source to be of an ultra-luminous infrared galaxy (ULIRG) with a far-infrared luminosity of LFIR<SUP>SF</SUP> = 2.4−2.1<SUP>+7.4</SUP>×10<SUP>12</SUP><I>L</I>⊙, and hosting an obscured AGN. Such a source is thus able to power a hard photoionization plus outflow scenario to explain the extended Lyman-<I>α</I>, He II<I>λ</I>1640, and C IV<I>λ</I>1549 emission, and their kinematics. In addition, the two brightest detections at 850 <I>μ</I>m (<I>f</I>850 > 18 mJy) sit at the density peak of the LAEs’ overdensity, likely pinpointing the core of the protocluster. Future multiwavelength and spectroscopic datasets targeting the full extent of the BOSS1441 overdensity have the potential to firmly characterize a cosmic nursery of giant elliptical galaxies, and ultimately of a massive cluster.</P>