Electrical properties and deep traps spectra of a-plane GaN films grown on r-plane sapphire

Polyakov, A.Y.,Smirnov, N.B.,Govorkov, A.V.,Markov, A.V.,Sun, Q.,Zhang, Y.,Yerino, C.D.,Ko, T.S.,Lee, I.H.,Han, J. Elsevier 2010 Materials science & engineering. B, Advanced funct Vol.166 No.3

Electrical properties, deep traps spectra and luminescence spectra were studied for two undoped a-plane GaN (a-GaN) films grown on r-plane sapphire using metalorganic chemical vapor deposition and differing by structural perfection. For sample A, the a-GaN film was directly deposited on AlN buffer. A two-step growth scheme was implemented for sample B, including an initial islanding growth stage and a subsequent enhanced lateral growth. Preliminary detailed X-ray analysis showed that the stacking faults density was 8x10<SUP>5</SUP>cm<SUP>-1</SUP> for sample A and 1.7x10<SUP>5</SUP>cm<SUP>-1</SUP> for sample B. Electrical properties of a-GaN films were largely determined by deep traps with a level near E<SUB>c</SUB> -0.6eV, with other prominent traps having the activation energy of 0.25eV. The Fermi level was pinned by the E<SUB>c</SUB> -0.6eV deep traps for sample A, but shifted to the vicinity of the shallower 0.25eV traps for sample B, most likely due to the reduced density of the 0.6eV traps. This decrease of deep traps density is accompanied by a very pronounced improvement in the overall luminescence intensity. A correlation of the observed improvement in deep traps spectra and luminescence efficiency with the improved crystalline quality of the films is discussed.

Reaction pattern differences impact physical properties of starches derivatized to the same extent in a model cross-linking system

Hong, Jung Sun,Gomand, Sara V.,Huber, Kerry C.,Delcour, Jan A. Elsevier 2017 Carbohydrate polymers Vol.174 No.-

<P><B>Abstract</B></P> <P>This study investigated the physical properties of maize (MS) and wheat (WS) starches derivatized with 5-(4,6-dichlorotriazinyl)aminofluorescein (model cross-linking system) to have the same overall fluorescence intensity on starch molecules, but reacted either more uniformly throughout granules (UD) or more at granule surfaces (SD). Both MS and WS derivatives had lower swelling powers (SP) at 90°C than their respective native starches. The UD derivatives had lower SP (90°C) and greater retrogradation enthalpies than did SD derivatives, consistent with their lower peak and higher setback pasting viscosities. Also, SD starches were less soluble and retained a greater degree of granular integrity than UD starches in time-lapse, hot-stage light microscopy studies (50–95°C), likely due to a greater concentration of cross-links at the granule surface. The results confirm that derivatization patterns impact the physical properties of modified starches. Thus, varying derivatization patterns can be a strategy to tailor modified starch properties.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Starch granules were derivatized at the surface (S<SUB>SD</SUB>) or uniformly throughout (S<SUB>UD</SUB>). </LI> <LI> The type of derivatization pattern (S<SUB>SD</SUB> vs. S<SUB>UD</SUB>) impacted the starch physical properties. </LI> <LI> Swelling and pasting were more inhibited for S<SUB>UD</SUB> than for S<SUB>SD</SUB> at 70–90°C. </LI> <LI> S<SUB>SD</SUB> had lower cold paste and retrogradation enthalpy values than S<SUB>UD</SUB>. </LI> <LI> When heated, S<SUB>SD</SUB> retained greater granular integrity than S<SUB>UD</SUB>. </LI> </UL> </P>

OGLE-2017-BLG-1049: ANOTHER GIANT PLANET MICROLENSING EVENT

Kim, Yun Hak,Chung, Sun-Ju,Udalski, A.,Bond, Ian A.,Jung, Youn Kil,Gould, Andrew,Albrow, Michael D.,Han, Cheongho,Hwang, Kyu-Ha,Ryu, Yoon-Hyun,Shin, In-Gu,Shvartzvald, Yossi,Yee, Jennifer C.,Zang, Wei The Korean Astronomical Society 2020 Journal of The Korean Astronomical Society Vol.53 No.6

We report the discovery of a giant exoplanet in the microlensing event OGLE-2017-BLG-1049, with a planet-host star mass ratio of q = 9.53 ± 0.39 × 10-3 and a caustic crossing feature in Korea Microlensing Telescope Network (KMTNet) observations. The caustic crossing feature yields an angular Einstein radius of θE = 0.52 ± 0.11 mas. However, the microlens parallax is not measured because the time scale of the event, tE ≃ 29 days, is too short. Thus, we perform a Bayesian analysis to estimate physical quantities of the lens system. We find that the lens system has a star with mass Mh = 0.55+0.36-0.29 M⊙ hosting a giant planet with Mp = 5.53+3.62-2.87 MJup, at a distance of DL = 5.67+1.11-1.52 kpc. The projected star-planet separation is a⊥ = 3.92+1.10-1.32 au. This means that the planet is located beyond the snow line of the host. The relative lens-source proper motion is μrel ~ 7 mas yr-1, thus the lens and source will be separated from each other within 10 years. After this, it will be possible to measure the flux of the host star with 30 meter class telescopes and to determine its mass.

KITENIN increases invasion and migration of mouse squamous cancer cells and promotes pulmonary metastasis in a mouse squamous tumor model

Lee, J.K.,Bae, J.A.,Sun, E.G.,Kim, H.D.,Yoon, T.M.,Kim, K.,Lee, J.H.,Lim, S.C.,Kim, K.K. North-Holland Pub ; Elsevier Science Ltd 2009 FEBS letters Vol.583 No.4

KAI1 C-terminal interacting tetraspanin (KITENIN) is reported to promote metastasis in mouse colon cancer models. We investigated the role of KITENIN on the progression of squamous cell carcinoma (SCC). In a preliminary clinical study using resected tissues from head and neck SCC patients, KITENIN was highly expressed in tumors and metastatic lymph nodes, while KAI1 was more increased in adjacent mucosa than in tumor. KITENIN-transfected mouse squamous cancer (SCC VII/KITENIN) cells showed significantly higher invasion, migration, and proliferation than empty vector-transfected cells. In syngeneic mouse squamous tumor models, more increased tumor volume and enhanced lung metastasis were found in SCC VII/KITENIN cells-injected mice. Thus, KITENIN increases invasion and migration of squamous cancer cells and thereby promotes distant metastasis in mouse squamous tumor models.

In-situ high-energy synchrotron X-ray diffraction study of micromechanical behavior of multiple phases in Ni₄₇Ti₄₄Nb₉ shape memory alloy

Sun, G.A.,Wang, X.L.,Wang, Y.D.,Woo, W.C.,Wang, H.,Liu, X.P.,Chen, B.,Fu, Y.Q.,Sheng, L.S.,Ren, Y. Elsevier Sequoia 2013 Materials science & engineering. properties, micro Vol.560 No.-

High-energy synchrotron X-ray diffraction technique was used to in-situ characterize microstructure, lattice strain, and phase transition behavior of a Ni<SUB>47</SUB>Ti<SUB>44</SUB>Nb<SUB>9</SUB> shape memory alloy. Phase transformation kinetics and deformation mechanisms were studied under a uniaxial tension at three testing temperatures, i.e., -70<SUP>o</SUP>C, 25<SUP>o</SUP>C, and 150<SUP>o</SUP>C. At a testing temperature of -70<SUP>o</SUP>C, a complicated phase transformation with four stages of micromechanical deformation was identified which is associated with changes of martensite substructures. At room temperature of 25<SUP>o</SUP>C, there was no stress-induced selection process of variants of B19' phases observed. Whereas at a testing temperature of 150<SUP>o</SUP>C, there was no any phase transformation observed. It is verified that β-Nb phase, an effective stabilizer for the austenite, delays the process of martensitic transformation and relaxes the strain energy without strengthening the matrix. This new finding is important to understand the relationship between the micromechanical deformation behavior and phase transformations in the Ni<SUB>47</SUB>Ti<SUB>44</SUB>Nb<SUB>9</SUB> SMA.

Pathogenicity of <i>Yersinia pestis</i> Synthesis of 1-Dephosphorylated Lipid A

Sun, Wei,Six, David A.,Reynolds, C. Michael,Chung, Hak Suk,Raetz, Christian R. H.,Curtiss 3rd, Roy American Society for Microbiology 2013 Infection and immunity Vol.81 No.4

<P>Synthesis of <I>Escherichia coli</I> LpxL, which transfers a secondary laurate chain to the 2′ position of lipid A, in <I>Yersinia pestis</I> produced bisphosphoryl hexa-acylated lipid A at 37°C, leading to significant attenuation of virulence. Our previous observations also indicated that strain χ10015(pCD1Ap) (Δ<I>lpxP32</I>::P<SUB>lpxL</SUB> <I>lpxL</I>) stimulated a strong inflammatory reaction but sickened mice before recovery and retained virulence via intranasal (i.n.) infection. The development of live, attenuated <I>Y. pestis</I> vaccines may be facilitated by detoxification of its lipopolysaccharide (LPS). Heterologous expression of the lipid A 1-phosphatase, LpxE, from <I>Francisella tularensis</I> in <I>Y. pestis</I> yields predominantly 1-dephosphorylated lipid A, as confirmed by mass spectrometry. Results indicated that expression of LpxE on top of LpxL provided no significant reduction in virulence of <I>Y. pestis</I> in mice when it was administered i.n. but actually reduced the 50% lethal dose (LD<SUB>50</SUB>) by 3 orders of magnitude when the strain was administered subcutaneously (s.c.). Additionally, LpxE synthesis in wild-type <I>Y. pestis</I> KIM6+(pCD1Ap) led to slight attenuation by s.c. inoculation but no virulence change by i.n. inoculation in mice. In contrast to <I>Salmonella enterica</I>, expression of LpxE does not attenuate the virulence of <I>Y. pestis</I>.</P>

Facile fabrication of activated charcoal decorated functionalized multi-walled carbon nanotube electro-catalyst for high performance quasi-solid state dye-sensitized solar cells

Memon, A.A.,Arbab, A.A.,Sahito, I.A.,Mengal, N.,Sun, K.C.,Qadir, M.B.,Choi, Y.S.,Jeong, S.H. Pergamon Press 2017 ELECTROCHIMICA ACTA Vol.234 No.-

<P>The proposed research presents significant progress in the photovoltaic performance of quasi-solid state dye-sensitized solar cells (DSSCs) by synthesizing a highly electro-catalytic active activated charcoal decorated functionalized multi-walled carbon nanotube (MWCNT) composite electro-catalyst as a counter electrode (CE). The proposed carbon composite structure was synthesize by facile acid functionalization of MWCNTs followed by the addition of mesoporous activated charcoal, decorating the tubular graphitic structure of the CNTs. The carbon composite paste deposited on FTO glass by a sequential process of doctor blade coating under an air-drying technique. The porous functionalized mesoporous carbon (f-MC) with a dominant oxygen rich surface displays greatly enhanced electrocatalytic activity, low charge transfer resistance (RCT), and exceptional cyclic stability as compared with pristine CNTs. The DSSC fabricated with f-MC CE demonstrated efficient electrochemical characteristics and photovoltaic performance when fabricated with a high-viscosity quasi-solid electrolyte. The highly conductive and porous carbon structure locates manifold sites for tri-iodide reduction reaction. High mobility of the quasi-solid electrolyte within defect rich (f-MC) surface confirmed a low RCT of (0.60 Omega. cm(2)), and exhibited superior electrocatalytic activity compared to a conventional platinum (Pt) reference CE. The f-MC CE based DSSCs showed high power conversion efficiency (PCE) of 8.42%, exceeding the Pt reference CE of 8.11%. Based on the facile synthesis of f-MC composites and fabrication of CE, the proposed DSSCs stand out as efficient next generation solar cells. (C) 2017 Elsevier Ltd. All rights reserved.</P>

Fabrication of a flexible and conductive lyocell fabric decorated with graphene nanosheets as a stable electrode material

Mengal, N.,Sahito, I.A.,Arbab, A.A.,Sun, K.C.,Qadir, M.B.,Memon, A.A.,Jeong, S.H. Applied Science Publishers ; Elsevier Science Ltd 2016 Carbohydrate polymers Vol.152 No.-

Textile electrodes are highly desirable for wearable electronics as they offer light-weight, flexibility, cost effectiveness and ease of fabrication. Here, we propose the use of lyocell fabric as a flexible textile electrode because of its inherently super hydrophilic characteristics and increased moisture uptake. A highly concentrated colloidal solution of graphene oxide nanosheets (GONs) was coated on to lyocell fabric and was then reduced in to graphene nanosheets (GNs) using facile chemical reduction method. The proposed textile electrode has a very high surface conductivity with a very low value of surface resistance of only 40Ωsq<SUP>-1</SUP>, importantly without use of any binding or adhesive material in the processing step. Atomic force spectroscopy (AFM) and Transmission electron microscopy (TEM) were conducted to study the topographical properties and sheet exfoliation of prepared GONs. The surface morphology, structural characterization and thermal stability of the fabricated textile electrode were studied by field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), X ray photon spectroscopy (XPS), Raman spectroscopy, Wide angle X ray diffraction spectroscopy (WAXD) and Thermogravimetric analysis (TGA) respectively. These results suggest that the GONs is effectively adhered on to the lyocell fabric and the conversion of GONs in to GNs by chemical reduction has no adverse effect on the crystalline structure of textile substrate. The prepared graphene coated conductive lyocell fabric was found stable in water and electrolyte solution and it maintained nearly same surface electrical conductivity at various bending angles. The electrical resistance results suggest that this lyocell based textile electrode (L-GNs) is a promising candidate for flexible and wearable electronics and energy harvesting devices.

Family of smart tuned mass dampers with variable frequency under harmonic excitations and ground motions: closed-form evaluation

Sun, C.,Nagarajaiah, S.,Dick, A.J. Techno-Press 2014 Smart Structures and Systems, An International Jou Vol.13 No.2

A family of smart tuned mass dampers (STMDs) with variable frequency and damping properties is analyzed under harmonic excitations and ground motions. Two types of STMDs are studied: one is realized by a semi-active independently variable stiffness (SAIVS) device and the other is realized by a pendulum with an adjustable length. Based on the feedback signal, the angle of the SAIVS device or the length of the pendulum is adjusted by using a servomotor such that the frequency of the STMD matches the dominant excitation frequency in real-time. Closed-form solutions are derived for the two types of STMDs under harmonic excitations and ground motions. Results indicate that a small damping ratio (zero damping is the best theoretically) and an appropriate mass ratio can produce significant reduction when compared to the case with no tuned mass damper. Experiments are conducted to verify the theoretical result of the smart pendulum TMD (SPTMD). Frequency tuning of the SPTMD is implemented through tracking and analyzing the signal of the excitation using a short time Fourier transformation (STFT) based control algorithm. It is found that the theoretical model can predict the structural responses well. Both the SAIVS STMD and the SPTMD can significantly attenuate the structural responses and outperform the conventional passive TMDs.

Family of smart tuned mass dampers with variable frequency under harmonic excitations and ground motions: closed-form evaluation

C. Sun,S. Nagarajaiah,A.J. Dick 국제구조공학회 2014 Smart Structures and Systems, An International Jou Vol.13 No.2

A family of smart tuned mass dampers (STMDs) with variable frequency and damping properties is analyzed under harmonic excitations and ground motions. Two types of STMDs are studied: one is realized by a semi-active independently variable stiffness (SAIVS) device and the other is realized by a pendulum with an adjustable length. Based on the feedback signal, the angle of the SAIVS device or the length of the pendulum is adjusted by using a servomotor such that the frequency of the STMD matches the dominant excitation frequency in real-time. Closed-form solutions are derived for the two types of STMDs under harmonic excitations and ground motions. Results indicate that a small damping ratio (zero damping is the best theoretically) and an appropriate mass ratio can produce significant reduction when compared to the case with no tuned mass damper. Experiments are conducted to verify the theoretical result of the smart pendulum TMD (SPTMD). Frequency tuning of the SPTMD is implemented through tracking and analyzing the signal of the excitation using a short time Fourier transformation (STFT) based control algorithm. It is found that the theoretical model can predict the structural responses well. Both the SAIVS STMD and the SPTMD can significantly attenuate the structural responses and outperform the conventional passive TMDs.