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Nanoscale ; 12(3): 1356-1365, 2020 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-31854411


High-density growth nanotwins enable high-strength and good ductility in metallic materials. However, twinning propensity is greatly reduced in metals with high stacking fault energy. Here we adopted a hybrid technique coupled with template-directed heteroepitaxial growth method to fabricate single-crystal-like, nanotwinned (nt) Ni. The nt Ni primarily contains hierarchical twin structures that consist of coherent and incoherent twin boundary segments with few conventional grain boundaries. In situ compression studies show the nt Ni has a high flow strength of ∼2 GPa and good deformability. Moreover, the nt Ni has superb corrosion behavior due to the unique twin structure in comparison to coarse grained and nanocrystalline counterparts. The hybrid technique opens the door for the fabrication of a wide variety of single-crystal-like nt metals with unique mechanical and chemical properties.

Artigo em Inglês | MEDLINE | ID: mdl-31794404


Artificial neural network (ANN) and its variants are favored algorithm in designing cardiac arrhythmia classifier (CAC) for its high accuracy. However, the implementation of ultralow power ANN-CAC is challenging due to the intensive computation. Moreover, the imbalanced MIT-BIH database limits the ANN-CAC performance. Several novel techniques are proposed to address the challenges in the low power implementation. Firstly, continuous-in-time discrete-in-amplitude (CTDA) signal flow is adopted to reduce the multiplication operations. Secondly, conditional grouping scheme (CGS) in combination of biased training (BT) is proposed to handle the imbalanced training samples for better training convergency and evaluation accuracy. Thirdly, arithmetic unit sharing with customized high-performance multiplier improves power efficiency. Verified in FPGA and synthesized in 0.18µm CMOS process, the proposed CTDA ANN-CAC can classify an arrhythmia within 252's at 25MHz clock frequency with average power of 13.34µW for 75bpm heart rate. Evaluated on MIT-BIH database, it shows over 98% classification accuracy, 97% sensitivity, and 94% positive predictivity.

Materials (Basel) ; 12(17)2019 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-31450669


Nanocrystalline metals have shown enhanced radiation tolerance as grain boundaries serve as effective defect sinks for removing radiation-induced defects. However, the thermal and radiation stability of nanograins are of concerns since radiation may induce grain boundary migration and grain coarsening in nanocrystalline metals when the grain size falls in the range of several to tens of nanometers. In addition, prior in situ radiation studies on nanocrystalline metals have focused primarily on single heavy ion beam radiations, with little consideration of the helium effect on damage evolution. In this work, we utilized in situ single-beam (1 MeV Kr++) and dual-beam (1 MeV Kr++ and 12 keV He+) irradiations to investigate the influence of helium on the radiation response and grain coarsening in nanocrystalline Cu at 300 °C. The grain size, orientation, and individual grain boundary character were quantitatively examined before and after irradiations. Statistic results suggest that helium bubbles at grain boundaries and grain interiors may retard the grain coarsening. These findings provide new perspective on the radiation response of nanocrystalline metals.

IEEE Trans Biomed Circuits Syst ; 13(5): 918-926, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31247560


High input impedance, low noise, high common mode rejection ratio (CMRR), and ultralow power are the most important performance indicators in the design of analog front end (AFE) for wearable biomedical sensors. This paper presents a fully differential difference amplifier based AFE that employs dc-coupled input stage to increase the input impedance and improve CMRR. A parasitic capacitor reuse technique is proposed to improve the noise/area efficiency and CMRR. An on-body dc bias scheme is introduced to deal with the input dc offset. Implemented in 0.35 µm CMOS process with an area of 0.405 mm2, the proposed AFE consumes 0.9 µW at 1.8 V and shows excellent noise effective factor of 2.55, and CMRR of 76 dB. Experiment shows the proposed AFE not only picks up clean ECG signal with electrodes placed as close as 2 cm under both resting and walking conditions, but also obtain the distinct α-wave after eye blink from EEG recording.

Nat Commun ; 9(1): 5389, 2018 12 19.
Artigo em Inglês | MEDLINE | ID: mdl-30568181


Nanocrystalline (NC) metals are stronger and more radiation-tolerant than their coarse-grained (CG) counterparts, but they often suffer from poor thermal stability as nanograins coarsen significantly when heated to 0.3 to 0.5 of their melting temperature (Tm). Here, we report an NC austenitic stainless steel (NC-SS) containing 1 at% lanthanum with an average grain size of 45 nm and an ultrahigh yield strength of ~2.5 GPa that exhibits exceptional thermal stability up to 1000 °C (0.75 Tm). In-situ irradiation to 40 dpa at 450 °C and ex-situ irradiation to 108 dpa at 600 °C produce neither significant grain growth nor void swelling, in contrast to significant void swelling of CG-SS at similar doses. This thermal stability is due to segregation of elemental lanthanum and (La, O, Si)-rich nanoprecipitates at grain boundaries. Microstructure dependent cluster dynamics show grain boundary sinks effectively reduce steady-state vacancy concentrations to suppress void swelling upon irradiation.

Conf Proc IEEE Eng Med Biol Soc ; 2018: 6002-6005, 2018 07.
Artigo em Inglês | MEDLINE | ID: mdl-30441704


FIR filter is one of the best choices for ECG signal processing because of its linear phase property. With frequency response masking (FRM) technique, the multipliers needed to implement FIR filter can be reduced dramatically. This paper proposes an architecture for asymmetrical bandpass FIR filter based on the FRM technique. The optimum interpolation factor for the filter is derived and the design procedure for all the sub-filters is given. A design example is included to illustrate the effectiveness of the proposed filter for ECG signal processing. It shows that the filter can fulfill the design objectives with 70.3% less multipliers comparing to the conventional FIR synthesizing technique.

Eletrocardiografia , Processamento de Sinais Assistido por Computador , Humanos