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Now showing items 65 - 70 of 70

  • InGaN micro-pixellated light-emitting diodes with nano-textured surfaces and modified emission profiles RID C-2303-2012

    Gong, Z.   Zhang, Y. F.   Kelm, P.   Watson, I. M.   Gu, E.   Dawson, M. D.  

    We present the fabrication details and performance characteristics of InGaN light-emitting diodes (LEDs) consisting of arrays of interconnected micro-pixels where each micro-pixel is nano-textured via nano-imprinting. We have taken the further step of embodying the pixels in a rhomboidal geometry. It is found that the power output of these nano-textured micro-LEDs with rhomboidal geometries is 57% higher than that of conventional square-shaped broad-area reference LEDs. The series resistance of the textured LEDs is reduced, owing to the multi-finger electrodes introduced. Furthermore, these LEDs can sustain higher operation current of up to 500 mA without encapsulation, suggesting improved thermal dissipation capability. Finally, the combined effects of surface texturing, micro-LED configuration, and geometric shaping on the light extraction are analyzed. It is found that the power enhancement by surface texturing, micro-pixellating and the rhomboidal geometry are 32%, 16%, and 9%, respectively, implying that surface texturing is the most effective contribution to increasing the light extraction efficiency in our design. The angular dependent far-field beam profile is also remarkably changed, compared with the standard Lambertian emission pattern of the conventional square-shaped LEDs. Substantial increase in the EL intensity is evident from both the top surface and the sidewall.
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  • Mask-less ultraviolet photolithography based on CMOS-driven micro-pixel light emitting diodes

    Elfstroumlm, D.   Guilhabert, B.   McKendry, J.   Poland, S.   Gong, Z.   Massoubre, D.   Richardson, E.   Rae, B.R.   Valentine, G.   Blanco-Gomez, G.   Gu, E.   Cooper, J.M.   Henderson, R.K.   Dawson, M.D.  

    We report on an approach to ultraviolet (UV) photolithography and direct writing where both the exposure pattern and dose are determined by a complementary metal oxide semiconductor (CMOS) controlled micro-pixellated light emitting diode array. The 370nm UV light from a demonstrator 8 times 8 gallium nitride micro-pixel LED is projected onto photoresist covered substrates using two back-to-back microscope objectives, allowing controlled demagnification. In the present setup, the system is capable of delivering up to 8.8W/cm 2 per imaged pixel in circular spots of diameter ~8mum. We show example structures written in positive as well as in negative photoresist.
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  • Signatures of the topological s(+-) superconducting order parameter in the type-II Weyl semimetal T-d-MoTe2

    Guguchia, Z.   von Rohr, F.   Shermadini, Z.   Lee, A. T.   Banerjee, S.   Wieteska, A. R.   Marianetti, C. A.   Frandsen, B. A.   Luetkens, H.   Gong, Z.   Cheung, S. C.   Baines, C.   Shengelaya, A.   Taniashvili, G.   Pasupathy, A. N.   Morenzoni, E.   Billinge, S. J. L.   Amato, A.   Cava, R. J.   Khasanov, R.   Uemura, Y. J.  

    In its orthorhombic T-d polymorph, MoTe2 is a type-II Weyl semimetal, where the Weyl fermions emerge at the boundary between electron and hole pockets. Non-saturating magnetoresistance and superconductivity were also observed in T-d-MoTe2. Understanding the superconductivity in T-d-MoTe2, which was proposed to be topologically non-trivial, is of eminent interest. Here, we report high-pressure muon-spin rotation experiments probing the temperature-dependent magnetic penetration depth in T-d-MoTe2. A substantial increase of the superfluid density and a linear scaling with the superconducting critical temperature T-c is observed under pressure. Moreover, the superconducting order parameter in T-d-MoTe2 is determined to have 2-gap s-wave symmetry. We also exclude time-reversal symmetry breaking in the superconducting state with zero-field mu SR experiments. Considering the strong suppression of T-c in MoTe2 by disorder, we suggest that topologically non-trivial s(+-) state is more likely to be realized in MoTe2 than the topologically trivial s(++) state.
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  • The rotation of Iberia during the Aptian and the opening of the Bay of Biscay

    Gong, Z.   Langereis, C. G.   Mullender, T. A. T.  

    The Cretaceous rotation of the Iberian plate in a geodynamical active setting between Africa and Europe is contemporaneous with the opening of the northern Atlantic Ocean, and provides fundamental, temporal and kinematical constraints on the evolution of the Bay of Biscay and the Pyrenees. Here, we report new paleomagnetic data from 50 sites (1109 drilled cores) from marine sediments of the Cretaceous Organya Basin in the southern Pyrenees, to constrain the timing and magnitude of the rotation of Iberia. Berriasian to Barremian directions in exclusively limestone lithology are remagnetised, in agreement with previous Organya Basin studies. The Aptian to Cenomanian marls and limestones in the Orgainy Basin, however, provide primary magnetisations asserted by rock magnetic experiments and positive fold tests. Our results constrain the rotation of Iberia to be finished just before the Albian. Paleomagnetic data cannot well constrain the onset of the rotation, but sea-floor anomaly studies restrict the onset of the rotation to anomaly MO, or the Barremian-Aptian boundary. This implies that the entire rotation of Iberia happened in one single phase, and is confined to the Aptian. This is in contrast to earlier studies that suggested a two-phase rotation of Iberia, but we argue that the large errors in published ages are not in disagreement with our results. In summary, we constrain the similar to 35 degrees rotation of Iberia to the Aptian period which implies a rotation rate of 2.7-5.1 degrees/Myr, depending on the (controversial) duration of the Aptian. (C) 2008 Elsevier B.V. All rights reserved.
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  • Management of paediatric mandibular condylar fractures with screw-based semi-rigid intermaxillary fixation

    Wu, Y.   Long, X.   Fang, W.   Li, B.   Cheng, Y.   Deng, M.   Cai, H.   Gong, Z.  

    This study was designed to evaluate the feasibility and safety of screw-based semi-rigid intermaxillary fixation (IMF) combined with a specially designed occlusal splint in the conservative treatment of paediatric mandibular condylar fractures. Thirteen paediatric patients with 20 sides of condylar fractures treated with semi-rigid IMF were analyzed retrospectively. Semi-rigid IMF was achieved by inserting self-drilling IMF screws into the anterior alveolar bone of the maxilla and mandible suspended with elastic bands. An occlusal splint with a molar fulcrum was used for functional repositioning of the condylar fragment. After 4 weeks, the screws and occlusal splint were removed. During a mean period of 28.6 months' follow-up, the patients' maximal mouth opening increased to a mean of 37.69 mm. Clinical and radiological examinations revealed satisfactory results in facial symmetry and condylar remodelling. No clinical symptoms or radiographic evidence showed dental injuries associated with screw insertion. This study suggests that this method might be a safe, easy, and effective management of paediatric condylar fractures.
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  • Alcohol consumption and body weight change in postmenopausal women: results from the Women's Health Initiative

    Wertheim, B. C.   Hingle, M.   Wang, L.   Neuhouser, M. L.   Gong, Z.   Garcia, L.   Stefanick, M. L.   Manson, J. E.  

    OBJECTIVE: To determine whether alcohol consumption is associated with incident overweight or obesity in normal-weight, postmenopausal women.DESIGN: Prospective cohort study considering baseline alcohol consumption and subsequent weight change over 7 years.SUBJECTS: 15 920 normal-weight (body mass index (BMI): 18.5 to <25 kgm(-2)), postmenopausal women enrolled in the Women's Health Initiative Clinical Trial.MEASUREMENTS: Body weight change, and incident overweight and obesity (BMI, 25.0 to <30 and >= 30 kgm(-2)) over 7 years.RESULTS: One-third of the 13822 women included in the analytical cohort reported no alcohol consumption. BMI differed little between abstainers (22.8 +/- 1.58 kgm(-2)) and alcohol consumers in the upper quintile (22.7 +/- 1.53 kgm(-2)). Among normal-weight women, the risk of becoming overweight or obese over a 7-year follow-up period was 35% or 88% lower, respectively, for women in the upper quintile of alcohol intake relative to abstainers (hazard ratio (HR), 0.65; 95% confidence interval (CI), 0.58-0.73; or HR, 0.12; 95% CI, 0.05-0.25, respectively). Risk for overweight and obesity was not significantly modified by age. Wine consumption showed the greatest protective association for risk of overweight (HR, 0.75; 95% CI, 0.68-0.84), followed by liquor (HR, 0.85; 95% CI, 0.78-0.93) and beer (HR, 0.90; 95% CI, 0.82-1.00).CONCLUSION: Postmenopausal women of normal weight who report moderate alcohol intake have a reduced risk of becoming overweight or obese over time. Perhaps, weight control measures in this population should target behaviors other than reduction in alcohol for those of normal BMI consuming moderate amounts.
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