Browsing by Author "Chang, L. C."

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Efficiency Improvement of GaN-Based Light-Emitting Diode Prepared on GaN Nanorod Template
(2010-02-15)
Kuo, C. H.
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Chang, L. C.
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Kuo, C. W.
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Chi, G. C.
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光電工程學系
We demonstrated the formation of GaN-based nanorod (NR) structure by using self-assemble Ni nanoislands as the etching mask. It was found that crystal quality of the GaN epilayer prepared on an NR GaN template was significantly better than that prepared with a conventional low-temperature GaN nucleation layer. With the NR GaN template, it was found that 20-mA light-emitting diode (LED) output power can be enhanced by 39.8%, as compared to the conventional LED.
GaN-Based Light-Emitting-Diode With a p-InGaN Layer
(2014-03-01)
Chen, P. H.
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Kuo, Cheng-Huang
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Lai, W. C.
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Chen, Yu An
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Chang, L. C.
GaN-based LEDs with a p-InGaN layer was proposed and fabricated. By inserting the 50-nm-thick p-In0.01Ga0.99N layer, it was found that we could reduce the 20 mA forward voltage from 3.34 to 2.99 V. It was found the inserted p-InGaN layer could also reduce the efficiency droop from 36.7% to 23.8%.
Identification of net groundwater recharge rate using an expert system model: a case study of Pintung plane
(2012-01-01)
Chang, L. C.
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Tsai, J. P.
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Chen, Y. W.
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Chiang, C. J.
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土木工程學系
Groundwater parameter techniques can be classified into two categories: tried and error methods and auto-calibration methods. Tried and error methods usually are time consuming. Most auto-calibration techniques are optimization techniques which rely on sensitivity analysis or a gradient search, which have increased computational demands with increasing parameter dimension. In addition to run time constraints, the applicability of optimization techniques is restricted by its difficult mathematical set up required in its implementation. This paper develops a rapid parameter calibration model, named RGEIS, using the combination of the expert system model and the groundwater simulation model to reduce the computational time and increase the model applicability. The developed model is applied to identify the net recharge rate, the summation of total recharge and total extraction of the study area, of Pintung plane in southern Taiwan. Pintung plane has an area of 78 km x 30 km with 3 aquifers and complex geological conditions. The study area is divided into 104 parameter zones. Since the planning horizon is 12 months, the total number of the net recharge rate to be calibrated is 1248 (104x12= 1,248). However, only 2,252 seconds are needed for the net recharge identification. The result shows accuracy and efficiency of the proposed model.
Improved measurement of the reactor antineutrino flux and spectrum at Daya Bay
(2017-01)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9 GW(th) nuclear reactors and detected by eight antineutrino detectors deployed in two near (560 m and 600 m flux-weighted baselines) and one far (1640 m flux-weighted baseline) underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay (IBD) candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be 0.946 +/- 0.020 (0.992 +/- 0.021) for the Huber+Mueller (ILL+Vogel) model. A 2.9 sigma deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4-6 MeV was found in the measured spectrum, with a local significance of 4.4 sigma. A reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions.
Improved measurement of the reactor antineutrino flux and spectrum at Daya Bay
(2017-01-01)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9 GW(th) nuclear reactors and detected by eight antineutrino detectors deployed in two near (560 m and 600 m flux-weighted baselines) and one far (1640 m flux-weighted baseline) underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay (IBD) candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be 0.946 +/- 0.020 (0.992 +/- 0.021) for the Huber+Mueller (ILL+Vogel) model. A 2.9 sigma deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4-6 MeV was found in the measured spectrum, with a local significance of 4.4 sigma. A reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions.
Improved Search for a Light Sterile Neutrino with the Full Configuration of the Daya Bay Experiment
(2016-10-07)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
This Letter reports an improved search for light sterile neutrino mixing in the electron antineutrino disappearance channel with the full configuration of the Daya Bay Reactor Neutrino Experiment. With an additional 404 days of data collected in eight antineutrino detectors, this search benefits from 3.6 times the statistics available to the previous publication, as well as from improvements in energy calibration and background reduction. A relative comparison of the rate and energy spectrum of reactor antineutrinos in the three experimental halls yields no evidence of sterile neutrino mixing in the 2 x 10(-4) less than or similar to vertical bar Delta m(41)(2)vertical bar less than or similar to 0.3 eV(2) mass range. The resulting limits on sin(2) 2 theta(14) are improved by approx imately a factor of 2 over previous results and constitute the most stringent constraints to date in the vertical bar Delta m(41)(2)vertical bar less than or similar to 0.2 eV(2) region.
Independent measurement of the neutrino mixing angle theta(13) via neutron capture on hydrogen at Daya Bay
(2014-10-03)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Beriguete, W.
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Bishai, M.
A new measurement of the theta(13) mixing angle has been obtained at the Daya Bay Reactor Neutrino Experiment via the detection of inverse beta decays tagged by neutron capture on hydrogen. The antineutrino events for hydrogen capture are distinct from those for gadolinium capture with largely different systematic uncertainties, allowing a determination independent of the gadolinium-capture result and an improvement on the precision of the theta(13) measurement. With a 217-day antineutrino data set obtained with six antineutrino detectors and from six 2.9 GWth reactors, the rate deficit observed at the far hall is interpreted as sin(2)2 theta(13) = 0.083 +/- 0.018 in the three-flavor oscillation model. When combined with the gadolinium-capture result from Daya Bay, we obtain sin(2)2 theta(13) = 0.089 +/- 0.008 as the final result for the six-antineutrino-detector configuration of the Daya Bay experiment.
Limits on Active to Sterile Neutrino Oscillations from Disappearance Searches in the MINOS, Daya Bay, and Bugey-3 Experiments
(2016-10-07)
Adamson, P.
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An, F. P.
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Anghel, I.
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Aurisano, A.
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Balantekin, A. B.
Searches for a light sterile neutrino have been performed independently by the MINOS and the Daya Bay experiments using the muon (anti) neutrino and electron antineutrino disappearance channels, respectively. In this Letter, results from both experiments are combined with those from the Bugey-3 reactor neutrino experiment to constrain oscillations into light sterile neutrinos. The three experiments are sensitive to complementary regions of parameter space, enabling the combined analysis to probe regions allowed by the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE experiments in a minimally extended four-neutrino flavor framework. Stringent limits on sin(2) 2 theta(mu e) are set over 6 orders of magnitude in the sterile mass-squared splitting Delta m(41)(2). The sterile-neutrino mixing phase space allowed by the LSND and MiniBooNE experiments is excluded for Delta m(41)(2) < 0.8 eV(2) at 95% CLs.
Low operation voltage of GaN-based LEDs with Al-doped ZnO upper contact directly on p-type GaN without insert layer
(2015-07-01)
Chen, P. H.
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Chen, Yu An
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Chang, L. C.
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Lai, W. C.
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Kuo, Cheng Huang
Al-doped ZnO (AZO) film was evaporated on double-side polished sapphire, p-GaN layers, n(+)-InGaN-GaN short-period superlattice (SPS) structures, and GaN-based light-emitting diodes (LEDs) by e-beam. The AZO film on the p-GaN layer after thermal annealing exhibited an extremely high transparency (98% at 450 nm) and a small specific contact resistance of 2.19 x 10(-2) Omega cm(2), which was almost the same as that of as-deposited AZO on n(+)-SPS structure. With 20 mA injection current, the forward voltages were 3.30 and 3.27 V, whereas the output powers were 4.32 and 4.07 mW for the LED with AZO on insert n(+)-SPS upper contact and the LED with AZO on p-GaN upper contact (without insert layer), respectively. The small specific contact resistance and low operation voltage of LED with AZO on p-GaN upper contact was achieved by rapid thermal annealing (RTA) process. (C) 2015 Elsevier Ltd. All rights reserved.
Measurement of electron antineutrino oscillation based on 1230 days of operation of the Daya Bay experiment
(2017-04-06)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
A measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9-GWth nuclear power reactors of the Daya Bay and Ling Ao nuclear power facilities served as intense sources of nu((e) over bar)'s. Comparison of the (v) over bare rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors (similar to 1500-1950 m) relative to detectors near the reactors (similar to 350-600 m) allowed a precise measurement of (v) over bar (e) disappearance. More than 2.5 million (v) over bar (e) inverse beta-decay interactions were observed, based on the combination of 217 days of operation of six antineutrino detectors (December, 2011-July, 2012) with a subsequent 1013 days using the complete configuration of eight detectors (October, 2012-July, 2015). The (v) over bar (e) rate observed at the far detectors relative to the near detectors showed a significant deficit, R = 0.949 +/- 0.002(stat) +/- 0.002(syst). The energy dependence of (v) over bar (e) disappearance showed the distinct variation predicted by neutrino oscillation. Analysis using an approximation for the three-flavor oscillation probability yielded the flavor-mixing angle sin(2)2 theta(13) = 0.0841 +/- 0.0027(stat) +/- 0.0019(syst) and the effective neutrino mass-squared difference of broken vertical bar Delta m(ee)(2)vertical bar = (2.50 +/- 0.06(stat) +/- 0.06(syst)) x 10(-3) eV(2). Analysis using the exact three-flavor probability found Delta m(32)(2) = (2.45 +/- 0.06(stat) +/- 0.06d(syst)) x 10(-3) eV(2) assuming the normal neutrino mass hierarchy and Delta m(32)(2) = (-2.56 +/- 0.06(stat) +/- 0.06(syst)) x 10(-3) eV(2) for the inverted hierarchy.
Measurement of the Reactor Antineutrino Flux and Spectrum at Daya Bay
(2016-02-12)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
This Letter reports a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9 GW(th) nuclear reactors with six detectors deployed in two near (effective baselines 512 and 561 m) and one far (1579 m) underground experimental halls in the Daya Bay experiment. Using 217 days of data, 296 721 and 41 589 inverse beta decay (IBD) candidates were detected in the near and far halls, respectively. The measured IBD yield is (1.55 +/- 0.04) x 10(-18) cm(2) GW(-1) day(-1) or (5.92 +/- 0.14) x 10(-43) cm(2) fission(-1). This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is 0.946 +/- 0.022 (0.991 +/- 0.023) relative to the flux predicted with the Huber-Mueller (ILL-Vogel) fissile antineutrino model. The measured IBD positron energy spectrum deviates from both spectral predictions by more than 2 sigma over the full energy range with a local significance of up to similar to 4 sigma between 4-6 MeV. A reactor antineutrino spectrum of IBD reactions is extracted from the measured positron energy spectrum for model-independent predictions.
New Measurement of Antineutrino Oscillation with the Full Detector Configuration at Daya Bay
(2015-09-11)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
We report a new measurement of electron antineutrino disappearance using the fully constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9 x 10(5) GW(th) ton days, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six Am-241-C-13 radioactive calibration sources reduced the background by a factor of 2 for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of sin(2)2 theta(13) and vertical bar Delta m(ee)(2)vertical bar were halved as a result of these improvements. An analysis of the relative antineutrino rates and energy spectra between detectors gave sin(2)2 theta(13) = 0.084 +/- 0.005 and vertical bar Delta m(ee)(2)vertical bar = (2.42 +/- 0.11) x 10(-3) eV(2) in the three-neutrino framework.
New measurement of theta(13) via neutron capture on hydrogen at Daya Bay
(2016-04-21)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
This article reports an improved independent measurement of neutrino mixing angle theta(13) at the Daya Bay Reactor Neutrino Experiment. Electron antineutrinos were identified by inverse beta-decays with the emitted neutron captured by hydrogen, yielding a data set with principally distinct uncertainties from that with neutrons captured by gadolinium. With the final two of eight antineutrino detectors installed, this study used 621 days of data including the previously reported 217-day data set with six detectors. The dominant statistical uncertainty was reduced by 49%. Intensive studies of the cosmogenic muon-induced Li-9 and fast neutron backgrounds and the neutron-capture energy selection efficiency, resulted in a reduction of the systematic uncertainty by 26%. The deficit in the detected number of antineutrinos at the far detectors relative to the expected number based on the near detectors yielded sin(2)2 theta(13) = 0.071 +/- 0.011 in the three-neutrino-oscillation framework. The combination of this result with the gadolinium-capture result is also reported.
Nitride-Based Blue Light-Emitting Diodes Grown With InN/GaN Matrix Quantum Wells
(2014-04-01)
Kuo, Cheng-Huang
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Fu, Yi Keng
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Chang, L. C.
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Chen, Yu An
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照明與能源光電研究所
Nitride-based light-emitting diodes (LEDs) grown with a structure of InN/GaN matrix quantum-wells (QWs) using metal-organic chemical vapor deposition are fabricated and characterized. The InN/GaN matrix QWs can significantly enhance the formation of phase-separated In-rich regions. Under an injection current of 500 A/cm(2), the LED output power can be enhanced by 26%, and the efficiency droop can be improved as compared with a conventional LED. These improvements could be attributed to the strong localization effect to remove carriers from the confining potential and capture these carriers at nonradiative centers in the active layer.
Search for a Light Sterile Neutrino at Daya Bay
(2014-10-01)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Beriguete, W.
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Bishai, M.
A search for light sterile neutrino mixing was performed with the first 217 days of data from the Daya Bay Reactor Antineutrino Experiment. The experiment's unique configuration of multiple baselines from six 2.9 GW(th) nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512 m and 561 m) and one far (1579 m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the 10(-3) eV(2) < vertical bar Delta m(41)(2)vertical bar < 0.3 eV(2) range. The relative spectral distortion due to the disappearance of electron antineutrinos was found to be consistent with that of the three-flavor oscillation model. The derived limits on sin(2) 2 theta(14) cover the 10(-3) eV(2) less than or similar to vertical bar Delta m(41)(2)vertical bar less than or similar to 0.1 eV(2) region, which was largely unexplored.
Strengthening teachers' abilities to implement a vision health program in Taiwanese schools
(2017-10-01)
Chang, L. C.
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Liao, L. L.
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Chen, M. I.
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Niu, Y. Z.
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Hsieh, P. L.
We designed a school-based, nationwide program called the 'New Era in Eye Health' to strengthen teacher training and to examine whether the existence of a government vision care policy influenced teachers' vision care knowledge and students' behavior. Baseline data and 3-month follow-up data were compared. A random sample of teachers (n = 660) from school vision health clusters in 22 cities/counties in Taiwan were invited to participate in our study and 436 agreed to participate (response rate = 66.1%). The mean age of participant teachers was 41.2 years, while the length of service mean was 14.6 years. For monitoring teacher outcomes, five cities/counties were selected as the intensely monitored group based on certain criteria. Sunlight diaries (n = 5434) were distributed and 3342 (61.5%) were returned. Teachers showed significant improvements in knowledge and behavior on the school vision health questionnaire. At the 3-month follow-up, the number of recesses as recorded by students' 'sunlight diary' increased. When teachers had better knowledge and behavior, recesses also increased. This study provided valuable insights to guide dissemination efforts for school vision health interventions and to help teachers implement research into their school vision health activities.
Study of the wave packet treatment of neutrino oscillation at Daya Bay
(2017-09-14)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
The disappearance of reactor (v) over bar (e) observed by the Daya Bay experiment is examined in the framework of a model in which the neutrino is described by a wave packet with a relative intrinsic momentum dispersion sigma(rel). Three pairs of nuclear reactors and eight antineutrino detectors, each with good energy resolution, distributed among three experimental halls, supply a high-statistics sample of (v) over bar (e) acquired at nine different baselines. This provides a unique platform to test the effects which arise from the wave packet treatment of neutrino oscillation. The modified survival probability formula was used to fit Daya Bay data, providing the first experimental limits: 2.38 x 10(-1)7 < sigma(rel) < 0.23. Treating the dimensions of the reactor cores and detectors as constraints, the limits are improved: 10-(14) less than or similar to sigma(rel) < 0.23, and an upper limit of sigma(rel) < 0.20 (which corresponds to sigma(x) greater than or similar to 10(-11) cm) is obtained. All limits correspond to a 95% C. L. Furthermore, the effect due to the wave packet nature of neutrino oscillation is found to be insignificant for reactor antineutrinos detected by the Daya Bay experiment thus ensuring an unbiased measurement of the oscillation parameters sin(2) 2 theta(13) and Delta m(32)(2) within the plane wave model.
The detector system of the Daya Bay reactor neutrino experiment
(2016-03-01)
An, F. P.
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Bai, J. Z.
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Balantekin, A. B.
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Band, H. R.
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Beavis, D.
The Daya Bay experiment was the first to report simultaneous measurements of reactor antineutrinos at multiple baselines leading to the discovery of (nu) over bar (e) oscillations over km-baselines. Subsequent data has provided the world\'s most precise measurement of sin 2 2013 and the effective mass splitting Delta m(ee)(2). The experiment is located in Daya Bay, China where the cluster of six nuclear reactors is among the world\'s most prolific sources of electron antineutrinos. Multiple antineutrino detectors are deployed in three underground water pools at different distances from the reactor cores to search for deviations in the antineutrino rate and energy spectrum due to neutrino mixing. Instrumented with photomultiplier tubes, the water pools serve as shielding against natural radioactivity from the surrounding rock and provide efficient muon tagging. Arrays of resistive plate chambers over the top of each pool provide additional muon detection. The antineutrino detectors were specifically designed for measurements of the antineutrino flux with minimal systematic uncertainty. Relative detector efficiencies between the near and far detectors are known to better than 0.2%. With the unblinding of the final two detectors\' baselines and target masses, a complete description and comparison of the eight antineutrino detectors can now be presented. This paper describes the Daya Bay detector systems, consisting of eight antineutrino detectors in three instrumented water pools in three underground halls, and their operation through the first year of eight detector data-taking. (C) 2015 Elsevier B.V. All rights reserved.