Browsing by Author "Wang, Y."

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A detailed ellipsometric porosimetry and positron annihilation spectroscopy study of porous organosilicate-glass films with various ratios of methyl terminal and ethylene bridging groups
(2020-10-15)
Rasadujjaman, M.
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Wang, Y.
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Zhang, L.
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Naumov, S.
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Attallah, A. G.
Organosilicate-glass films with a varying ratio of terminal methyl and bridging ethylene groups are synthesized using 1,2-bis(trimethoxysilyl)ethane/methyltrimethoxysilane mixtures and sol-gel technology. The films are characterized by Fourier Transform Infrared spectroscopy, Ellipsometric Porosimetry and Positron Annihilation Spectroscopy. The hard bake at 400 degrees C generates the final pore structure, which depends on the curing environment. It is shown that ethylene bridge is destructed during the hard bake in the air via formation of peroxide radicals that form equivalent to SiOH during the transformation. Continuous hard bake leads to condensation of silanol groups and form a structure similar to the ordinary silica. The pore size of highly porous materials (>30%) is larger in air cured films. Destruction of the ethylene bridge makes the films matrix soft and micropores collapse due to the capillary forces during the template evaporation. It leads to the film shrinkage, increases the size of internal voids. The air cured samples showed better mechanical properties than N2 cured ones although in the last case ethylene bridging groups were preserved. The reason is that the collapse of micropores increase the internal density and creates more favorable condition for condensation of silanol groups.
A high precision calibration of the nonlinear energy response at Daya Bay
(2019-10-01)
Adey, D.
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An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
A high precision calibration of the nonlinearity in the energy response of the Daya Bay Reactor Neutrino Experiment's antineutrino detectors is presented in detail. The energy nonlinearity originates from the particle-dependent light yield of the scintillator and charge-dependent electronics response. The nonlinearity model is constrained by.. calibration points from deployed and naturally occurring radioactive sources, the.. spectrum from B-12 decays, and a direct measurement of the electronics nonlinearity with a new flash analog-to-digital converter readout system. Less than 0.5% uncertainty in the energy nonlinearity calibration is achieved for positrons of kinetic energies greater than 1 MeV.
Brain-Display Interactive System by Using Steady-State Visual Evoke Potential(SSVEP) Stimulation
(2014-01-01)
Huang, Y. P.
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Chien, Y. Y.
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Lin, F. C.
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Zao, J. K.
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Wang, Y.
Steady-state visual evoked potential (SSVEP) is one of the most effective modalities for brain-computer interaction. However, its flickering visual stimuli may cause discomfort, even induce migraine and seizure attacks among its viewers. This paper presents a novel approach to induce SSVEP with high signal-to-noise ratios (SNRs) using composite color lights flickering near or above its critical flicker fusion (CFF) thresholds. Different combinations of frequencies, relative phases and pulse widths of the stimuli waveforms were tested for their effectiveness to produce high SNR values among their SSVEP responses. Results of our experiments were analyzed and studied. The rationale behind the special design of high-frequency polychromatic stimuli and the implications towards the development of an effective brain-display interaction (BDI) system were also discussed.
Effect of the C-bridge on UV properties of organosilicate films
(2019-09-01)
Seregin, D. S.
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Naumov, S.
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Chang, W-Y
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Wu, Y-H
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Wang, Y.
Carbon-bridged organosilicate films deposited by using different precursors are studied by both experimentally and theoretically. It is shown that carbon-bridged OSG films have higher Young Modulus (E) than methyl-terminated films and E(phenylene) > E(ethylene) > E(methylene). However, the k-values of these films show the same tendency and this is one of the drawbacks of carbon terminated materials when they are considered as low-k candidates. It is shown that the films having a phenylene bridge can be destructed by UV light with wavelength > 200 nm while ethylene or an ethylene bridged samples are stable. Mechanism of UV initiated destruction of phenylene bridged materials is analyzed by using quantum chemical calculations. The presented results allow to conclude that the presence of long aliphatic and aromatic bridges makes OSG materials more sensitive to UV light
Extraction of the U-235 and Pu-239 Antineutrino Spectra at Daya Bay
(2019-09-13)
Adey, D.
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An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
This Letter reports the first extraction of individual antineutrino spectra from U-235 and Pu-239 fission and an improved measurement of the prompt energy spectrum of reactor antineutrinos at Daya Bay. The analysis uses 3.5 x 10(6) inverse beta-decay candidates in four near antineutrino detectors in 1958 days. The individual antineutrino spectra of the two dominant isotopes, U-235 and Pu-239, are extracted using the evolution of the prompt spectrum as a function of the isotope fission fractions. In the energy window of 4-6 MeV, a 7% (9%) excess of events is observed for the U-235 (Pu-239) spectrum compared with the normalized Huber-Mueller model prediction. The significance of discrepancy is 4.0 sigma for U-235 spectral shape compared with the Huber-Mueller model prediction. The shape of the measured inverse beta-decay prompt energy spectrum disagrees with the prediction of the Huber-Mueller model at 5.3 sigma. In the energy range of 4-6 MeV, a maximal local discrepancy of 6.3 sigma is observed.
Improved Constraints on Sterile Neutrino Mixing from Disappearance Searches in the MINOS, MINOS+, Daya Bay, and Bugey-3 Experiments
(2020-08-10)
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 electron antineutrino, muon neutrino, and muon antineutrino disappearance driven by sterile neutrino mixing have been carried out by the Daya Bay and MINOS+ collaborations. This Letter presents the combined results of these searches, along with exclusion results from the Bugey-3 reactor experiment, framed in a minimally extended four-neutrino scenario. Significantly improved constraints on the theta(mu e) mixing angle are derived that constitute the most constraining limits to date over five orders of magnitude in the mass-squared splitting Delta m(41)(2), excluding the 90% C.L. sterile-neutrino parameter space allowed by the LSND and MiniBooNE observations at 90% CLs for Delta m(41)(2) < 13 eV(2). Furthermore, the LSND and MiniBooNE 99% C.L. allowed regions are excluded at 99% CLs for Delta m(41)(2) < 1.6 eV(2).
Magnetoresistance study of patterned permalloy nanostructures
(2008-05-01)
Chen, D. C.
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Mei, J. K.
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Wang, Y.
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Yao, Y. D.
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Wu, J. K.
We demonstrated the domain wall motion along the direction of the perimeter of a permalloy ring in the onion state. From the magnetoresistance (MR) measurement with a rotating ring at different constant fields, the critical field to form the onion state is near 200 Gauss and the lowest field that can still drag the domain wall is between 20 and 10 Gauss. The results also revealed a tendency for angle shifting and indicated that the lowest field component in the perimeter direction (the tangential component) was near 10 Gauss at an applied field of 20 Gauss.
Thermal fluctuations and vortex melting in the Nb3Sn superconductor from high resolution specific heat measurements
(2006-09-01)
Lortz, R.
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Lin, F.
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Musolino, N.
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Wang, Y.
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Junod, A.
The range of critical thermal fluctuations in "classical" bulk superconductors is extremely small and especially in low fields hardly experimentally accessible. With a new type of calorimeter we have been able to resolve a small lambda anomaly within a narrow temperature range around the H-c2 line. We show that the evolution of the anomaly as a function of magnetic field follows scaling laws expected in the presence of critical fluctuations. The lower onset of the fluctuation regime shows many characteristics of a continuous solid-to-liquid transition in the vortex matter. It can be driven into a first-order vortex melting transition by a small ac field which helps the vortex matter to reach equilibrium.