DISCOVERY OF AN X-RAY-EMITTING CONTACT BINARY SYSTEM 2MASS J11201034−2201340

Hu, Chin-Ping,Yang, Ting-Chang,Chou, Yi,Liu, L.,Qian, S.-B.,Hui, C. Y.,Kong, Albert K. H.,Lin, L. C. C.,Tam, P. H. T.,Li, K. L.,Ngeow, Chow-Choong,Chen, W. P.,Ip, Wing-Huen American Astronomical Society 2016 The Astronomical journal Vol.151 No.6

<P>We report the detection of orbital modulation, a model solution, and the X-ray properties of a newly discovered contact binary, Two Micron All Sky Survey (2MASS) J11201034-2201340. We serendipitously found this X-ray point source outside the error ellipse when searching for possible X-ray counterparts of 7-ray millisecond pulsars among the unidentified objects detected by the Fermi Gamma-ray Space Telescope. The optical counterpart of the X-ray source (unrelated to the 7-ray source) was then identified using archival databases. The long-term Catalina Real-Time Transient Survey detected a precise signal with a period of P = 0.28876208 (56) days. A follow-up observation made by the Super Light Telescope of Lulin Observatory revealed the binary nature of the object. Utilizing archived photometric data of multi-band surveys, we construct the spectral energy distribution (SED), which is well fit by a K2V spectral template. The fitting result of the orbital profile using the Wilson Devinney code suggests that 2MASS J11201034-2201340 is a short-period A-type contact binary and the more massive component has a cool spot. The X-ray emission was first noted in observations made by Swift, and then further confirmed and characterized by an XMM-Newton observation. The X-ray spectrum can be described by a power law or thermal Bremsstrahlung. Unfortunately, we could not observe significant X-ray orbital modulation. Finally, according to the SED, this system is estimated to be 690 pc from Earth with a calculated X-ray intensity of (0.7 - 1.5) x 10(30) erg s(-1), which is in the expected range of an X-ray emitting contact binary.</P>

High‐Mobility Air‐Stable Naphthalene Diimide‐Based Copolymer Containing Extended π‐Conjugation for n‐Channel Organic Field Effect Transistors

Kim, Ran,Amegadze, Paul S. K.,Kang, Il,Yun, Hui‐,Jun,Noh, Yong‐,Young,Kwon, Soon‐,Ki,Kim, Yun‐,Hi WILEY‐VCH Verlag 2013 Advanced Functional Materials Vol.23 No.46

<P><B>Abstract</B></P><P>A high‐performance naphthalene diimide (NDI)‐based conjugated polymer for use as the active layer of n‐channel organic field‐effect transistors (OFETs) is reported. The solution‐processable n‐channel polymer is systematically designed and synthesized with an alternating structure of long alkyl substituted‐NDI and thienylene–vinylene–thienylene units (PNDI‐TVT). The material has a well‐controlled molecular structure with an extended π‐conjugated backbone, with no increase in the LUMO level, achieving a high mobility and highly ambient stable n‐type OFET. The top‐gate, bottom‐contact device shows remarkably high electron charge‐carrier mobility of up to 1.8 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> (<I>I</I><SUB>on</SUB>/<I>I</I><SUB>off</SUB> = 10<SUP>6</SUP>) with the commonly used polymer dielectric, poly(methyl methacrylate) (PMMA). Moreover, PNDI‐TVT OFETs exhibit excellent air and operation stability. Such high device performance is attributed to improved π–π intermolecular interactions owing to the extended π‐conjugation, apart from the improved crystallinity and highly interdigitated lamellar structure caused by the extended π–π backbone and long alkyl groups.</P>

Biomolecule-entrapped SiO₂ nanoparticles for ultrafast green synthesis of silver nanoparticle–decorated hybrid nanostructures as effective catalysts

Otari, Sachin V.,Shinde, Vijay V.,Hui, Gao,Patel, Sanjay K.S.,Kalia, Vipin C.,Kim, In-Won,Lee, Jung-Kul Elsevier 2019 CERAMICS INTERNATIONAL Vol.45 No.5

<P><B>Abstract</B></P> <P>Noble-metal hybrid nanostructures have gained tremendous attention due to their potential roles in biomedical and catalytic applications. In this study, for the synthesis of silver nanoparticles (Ag NPs)–silica (SiO<SUB>2</SUB>) NPs, a novel green chemistry approach was employed, in which green tea biomolecule–encapsulated SiO<SUB>2</SUB> nanostructures were used for the reduction of silver ions to produce hybrid nanostructures within 300 s. The high-resolution transmission electron microscopy (HrTEM) revealed the formation of uniform ultrafine spherical Ag NPs that were evenly distributed in the nanostructures. The formed nanohybrid structures showed efficient catalytic activity for the formation of derivatives of dihydroquinoline, and retained 91% of their reusability capacity, even after 5 repeated cycles. Hence, this work provides a novel synthesis method not only for the synthesis of biomolecule-entrapped SiO<SUB>2</SUB> nanostructures, but also for the rapid formation of catalytically active hybrid nanostructures.</P>

3D hierarchical transition-metal sulfides deposited on MXene as binder-free electrode for high-performance supercapacitors

Hui Li,Xin Chen,Erfan Zalnezhad,K.N. Hui,K.S. Hui,Min Jae Ko 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.82 No.-

MXene has been considered as a promising two-dimensional material for supercapacitors owing to itslarge surface area, high conductivity, and excellent cycling stability. However, its low specific capacitancerestricts its extensive applications. Therefore, to address the issue, we homogeneously deposited NiCo2S4nanoflakes on the surface of MXene on conductive nickel foam (denoted as MXene-NiCo2S4@NF), whichwas used as a composite binder-free electrode for supercapacitor applications. The NiCo2S4 nanoflakesincreased the surface area of the composite electrode, thereby increasing its specific capacity from106.34 C g 1 to 596.69 C g 1 at 1 A g 1. Compared to the pristine MXene, MXene-NiCo2S4@NF maintainedthe high retention rate of pristine MXene and exhibited excellent cycling stability with 80.4% of its initialspecific capacity after 3000 cycles. The composite electrode exhibited improved electrochemicalperformance for supercapacitors, owing to the combined merits of NiCo2S4 (high specific capacity) andMXene (high retention rate and good cycling stability. The fabricated asymmetric solid-statesupercapacitor using MXene-NiCo2S4 as a positive electrode and active carbon as a negative electrode,exhibited an energy density of 27.24 Wh kg 1 at 0.48 kW kg 1 of power density.

EXPLORING THE X-RAY AND gamma-RAY PROPERTIES OF THE REDBACK MILLISECOND PULSAR PSR J1723-2837

Hui, C. Y.,Tam, P. H. T.,Takata, J.,Kong, A. K. H.,Cheng, K. S.,Wu, J. H. K.,Lin, L. C. C.,Wu, E. M. H. University of Chicago Press for the American Astro 2014 ASTROPHYSICAL JOURNAL LETTERS - Vol.781 No.1

We have investigated the X-ray and gamma-ray properties of the redback millisecond pulsar PSR J1723-2837 with XMM-Newton, Chandra, and Fermi. We have discovered the X-ray orbital modulation of this binary system with a minimum that coincides with the phases of radio eclipse. The X-ray emission is clearly non-thermal in nature, which can be described well by a simple power law with a photon index of similar to 1.2. The phase-averaged luminosity is similar to 9 x 10(31) erg s(-1) in 0.3-10 keV, which consumes similar to 0.2% of the spin-down power. We have detected the gamma-ray emission in 0.1-300 GeV from this system at a significance of similar to 6 sigma for the first time. The gamma-rays in this energy range consume similar to 2% of the spin-down power and can be modeled by a power law with a photon index of similar to 2.6. We discuss the high energy properties of the new redback in the context of an intrabinary shock model.

SEARCHES FOR MILLISECOND PULSAR CANDIDATES AMONG THE UNIDENTIFIED<i>FERMI</i>OBJECTS

Hui, C. Y.,Park, S. M.,Hu, C. P.,Lin, L. C. C.,Li, K. L.,Kong, A. K. H.,Tam, P. H. T.,Takata, J.,Cheng, K. S.,Jin, Ruolan,Yen, T.-C.,Kim, Chunglee IOP Publishing 2015 The Astrophysical journal Vol.809 No.1

<P>Here we report the results of searching millisecond pulsar (MSP) candidates from the Fermi LAT second source catalog (2FGL). Seven unassociated gamma-ray sources in this catalog are identified as promising MSP candidates based on their gamma-ray properties. Through the X-ray analysis, we have detected possible X-ray counterparts, localized to an arcsecond accuracy. We have systematically estimated their X-ray fluxes and compared them with the corresponding gamma-ray fluxes. The X-ray to gamma-ray flux ratios for 2FGL J1653.6-0159 and 2FGL J1946.4-5402 are comparable with the typical value for pulsars. For 2FGL J1625.2-0020, 2FGL J1653.6-0159, and 2FGL J1946.4-5402, their candidate X-ray counterparts are bright enough to perform a detailed spectral and temporal analysis to discriminate their thermal/non-thermal nature and search for the periodic signal. We have also searched for possible optical/IR counterparts at the X-ray positions. For the optical/IR source coincident with the brightest X-ray object associated with 2FGL J1120.0-2204, its spectral energy distribution is comparable with a late-type star. Evidence for the variability has also been found by examining its optical light curve. All the aforementioned 2FGL sources resemble a pulsar in one or more aspects, making them promising targets for follow-up investigations.</P>

Synthesis of Co₃O₄ nanowires on nickel foam by a novel microwave-assisted template-free method

Hui, K.S.,Hui, K.N.,Yin, C.L.,Hong, X. North-Holland 2013 Materials letters Vol.97 No.-

Spinel cobalt oxide (Co<SUB>3</SUB>O<SUB>4</SUB>) nanowires grown on Ni foam are successfully synthesized using a novel microwave-assisted template-free method. The effect of reaction temperature, concentration of reactants, and reaction time on the morphology and crystalline structures of the prepared nanowires is studied. The present work has demonstrated that uniform Co<SUB>3</SUB>O<SUB>4</SUB> nanowires with diameters of 500-580nm and lengths of 6-8μm can be synthesized under proper reaction condition. Moreover, the proposed microwave-assisted template-free method can significantly reduce reaction time, increase reaction efficiency, and provide better control over the geometry of the nanostructures.

Synthesis of Co3O4 nanowire arrays supported on Ni foam for removal of volatile organic compounds.

Hui, K N,Yin, Cui-Lei,Hui, K S,Lee, J Y,Li, M,Lee, S K,Tsui, K L,Chao, C Y H,Kwong, C W American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.4

<P>Crystalline Co3O4 nanowire arrays freely supported on Ni foam are successfully synthesized using a template-free method. The effects of reaction time, concentration of reactants, and temperature on the morphology of the nanowires are studied. The results indicate that uniform Co3O4 nanowires could be synthesized at 90 degrees C, and a transformation of the samples' morphology from nanoparticles to nanowires to microrods is observed by controlling the concentration of the reactants. The well-ordered nanowires synthesized under the selected reaction conditions are composed of spinel Co3O4 with diameters of 500-580 nm and lengths of 6-8 microm. These nanowires show good catalytic activity for the ozone catalytic oxidation of toluene.</P>

Electroreduction of H2O2 by Co3O4 and NiCo2O4 nanowires and beta-Ni(OH)2 nanoplates grown on Ni foam.

Hui, K N,Yin, Cui-Lei,Hui, K S,Lee, J Y,Cao, Dianxue,Wang, Guiling American Scientific Publishers 2012 Journal of nanoscience and nanotechnology Vol.12 No.4

<P>Nanowires (Co3O4 and NiCo2O4) and nanoplates (beta-Ni(OH)2) grown on Ni foam are successfully prepared by a template-free method and used as cathode electrodes for the electroreduction of H2O2, in an alkaline medium. Catalytic performance is investigated via cyclic voltammetry and chronoamperometry. The Co3O4 and NiCo2O4 nanowire electrodes exhibit much better catalytic activity, stability, and mass transfer properties for H2O2 electroreduction than pressed Co3O4 and NiCo2O4 nanoparticle/carbon/PTFE electrodes. A current density of 101.8 mA cm(-2) and 122.7 mA cm(-2) are respectively achieved on Co3O4 and NiCo2O4 nanowire electrodes at -0.4 V in 0.4 mol/L H2O2, and 3.0 mol/L NaOH solution at room temperature.</P>

The Growth Characteristics of a GaN Layer on a Cone-Shaped Patterned Sapphire Substrate by TEM Observation

Hui-Youn Shin,K. H. Park,K. T. Lee,M. J. Cho,S. K. Kwon,Y. I. Chang 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.4

The growth characteristics of a GaN layer deposited on a cone-shaped patterned sapphire substrate (PSS) by using metalorganic chemical vapor deposition (MOVCD) were observed by transmission electron microscope (TEM) to investigate the influence of cone-shaped PSS on the GaN layer. The GaN/sapphire interfaces were analyzed by using high-resolution TEM (HRTEM) and convergent beam electron diffraction (CBED), and the residual strain was evaluated by measuring the variation of the lattice parameters quantitatively. From the TEM images, a large number of threading dislocations were found above the flat region of the GaN/sapphire interface. In contrast, only a few threading dislocations were identified above the cone-shaped region. The HOLZ pattern analysis revealed that the lattice parameter of the GaN layer was lower above the flat region of the GaN/sapphire interface compared with the cone-shaped region, and the difference was estimated to be about 0.1 %. This may be attributed to the formation of a GaN layer by the lateral overgrowth above the cone-shaped region, resulting in less lattice mismatch and incoherency between the GaN layer and the sapphire substrate.