501 research outputs found
Epitaxy and Device Properties of InGaAs Photodetectors with Relatively High Lattice Mismatch
In this chapter, our works on the developments of wavelength-extended InGaAs photodetectors with cutoff wavelength >1.7 μm are reviewed. Various InGaAs/InAlAs p-i-n heterojunction structures have been grown on InP and GaAs substrates by gas source molecular beam epitaxy, some details on the InGaAs photodetector structures and the techniques of metamorphic buffer layer such as linearly, step, and one-step continuously InAlAs graded buffer, and dislocation restraint methods of compositional overshoot and digital alloy are introduced. The material characteristics and device properties were evaluated by atomic force microscopy, high-resolution X-ray diffraction and reciprocal space mapping, cross-sectional transmission electron microscopy, and current-voltage measurements, etc. The results provide clues to the development of metamorphic device structures on lattice-mismatched material systems
Wireless sEMG System with a Microneedle-Based High-Density Electrode Array on a Flexible Substrate
Surface electromyography (sEMG) signals reflect muscle contraction and hence, can provide information regarding a user's movement intention. High-density sEMG systems have been proposed to measure muscle activity in small areas and to estimate complex motion using spatial patterns. However, conventional systems based on wet electrodes have several limitations. For example, the electrolyte enclosed in wet electrodes restricts spatial resolution, and these conventional bulky systems limit natural movements. In this paper, a microneedle-based high-density electrode array on a circuit integrated flexible substrate for sEMG is proposed. Microneedles allow for high spatial resolution without requiring conductive substances, and flexible substrates guarantee stable skin-electrode contact. Moreover, a compact signal processing system is integrated with the electrode array. Therefore, sEMG measurements are comfortable to the user and do not interfere with the movement. The system performance was demonstrated by testing its operation and estimating motion using a Gaussian mixture model-based, simplified 2D spatial pattern.111Ysciescopu
A Comparative Study of within QCD Sum Rules with Two Typical Correlators up to Next-to-Leading Order
The B-decay constant is an important component for studying -meson
decays, which can be studied through QCD sum rules. We make a detailed
discussion on from two sum rules, i.e. sum rules I and II, which are
derived from the conventional correlator and the correlator with chiral
currents respectively. It is found that these two sum rules are consistent with
each other. However, the sum rules II has less uncertainty sources than that of
sum rules I, and then it can be more accurate if we know the dimension-four
gluon condensate well. It is found that decreases with the increment of
, and to compare with the Belle experimental data on , both sum rules
prefer smaller pole -quark mass, GeV. By varying all the
input parameters in their reasonable region and adding all the uncertainties
together in quadrature, we obtain MeV for sum rules I and
MeV for sum rules II.Comment: 11 pages, 4 figures, 2 tables. To match the printed version. To be
published in Communications in Theoretical Physic
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Phase Control on Surface for the Stabilization of High Energy Cathode Materials of Lithium Ion Batteries.
The development of high energy electrode materials for lithium ion batteries is challenged by their inherent instabilities, which become more aggravated as the energy densities continue to climb, accordingly causing increasing concerns on battery safety and reliability. Here, taking the high voltage cathode of LiNi0.5Mn1.5O4 as an example, we demonstrate a protocol to stabilize this cathode through a systematic phase modulating on its particle surface. We are able to transfer the spinel surface into a 30 nm shell composed of two functional phases including a rock-salt one and a layered one. The former is electrochemically inert for surface stabilization while the latter is designated to provide necessary electrochemical activity. The precise synthesis control enables us to tune the ratio of these two phases, and achieve an optimized balance between improved stability against structural degradation without sacrificing its capacity. This study highlights the critical importance of well-tailored surface phase property for the cathode stabilization of high energy lithium ion batteries
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