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Hierarchical core–shell architectures with multi-walled carbon nanotubes as core and MnO2 sheets shaped in an array mode as shell (MWCNTs@MnO2) were successfully synthesized via a simple wet chemical method. X-ray diffraction patterns and X-ray photoelectron spectroscopy analysis revealed that the composites were successfully prepared. Morphological characterizations were made by scanning electron microscopy and transmission electron microscopy. Vector network analyzer was employed to investigate the electromagnetic parameters of the composites. A possible attenuation mechanism was discussed, and the high-performance microwave absorption properties were attributed to the porous microstructure, polarization effect, dielectric loss and the synergistic action between MWCNTs and δ -MnO2. A minimum reflection loss (RL) of − 50.6 dB was achieved at a thickness of 1.4 mm, and an effective absorption bandwidth (RL < − 1 0 dB) covered 4.2 GHz (from 13.8 GHz to 18 GHz) at a thickness of 1.3 mm. Therefore, these results suggested that the MWCNTs@ δ -MnO2 composites can be an excellent candidate for microwave absorption materials. The cross-linked δ-MnO2 nanoflakes attached on the sidewalls of MWCNTs and the unique open porous 3D conductive structure of the nanocomposites contributed to the multiple reflections and scattering of microwaves in long propagation periods. Moreover, MWCNTs with high electrical conductivity can generate loss current and energy dissipation by electron migration and hop across the interfaces. [ABSTRACT FROM AUTHOR]

The dark current mechanism of extended wavelength InxGa1-xAs photo-detectors is still a debated issue. In this paper, the deep-level transient spectroscopy (DLTS) and dark current characteristics of InxGa1-xAs/InP detectors are investigated. Using trap parameters obtained from DLTS measurement, the device simulations of current-voltage characteristics are carried out by Silvaco Altas. The results reveal that the dark current at the low reverse bias voltage is associated with deep level trap induced trap assisted tunneling and Shockley-Read-Hall generation mechanism. The reduction of the deep level trap concentration in InxGa1-xAs absorption layer could dramatically suppress the dark current near zero bias in extended wavelength InxGa1-xAs/InP detectors. [ABSTRACT FROM AUTHOR]

The Al@MnO2 composites were synthesized by flake aluminum powder and potassium permanganate via a facile one-step method. As a multi-band stealth material, the composites have both enhanced microwave absorbing property and low infrared emissivity. We can use XRD, XPS, SEM, and TEM to detect structure and performance, respectively. The microwave absorbing properties and infrared emissivity were investigated by vector network analyzer and dual-band infrared emissometer. It was found that the MnO2 nanoparticles were anchored on the aluminum sheets densely, and the concentration of MnO2 nanoparticles had a certain effect on absorption performance and infrared emissivity. As an absorber, with its polarization effect, resonance effect, and good impedance matching, the composite with the filler loading is 60 wt% can perform excellent microwave absorption performance (Chen et al. in Optik (Stuttg) 172:840–846, 2018). The minimum reflection loss reached − 42.93 dB at 12.72 GHz with a thickness of 1.0 mm, and the bandwidth that exceed − 10 dB ranged from 12.08 GHz to 13.36 GHz (Li et al. in J Colloid Interface Sci 507:131–138, 2017). As an infrared stealth material, the composite exhibits low infrared emissivity in the band range of 8–14 µm, which was attributed to the existence constituent of flake aluminum powder. The infrared emissivity reached 0.55 at the lowest, as well as enlarged with the increase of MnO2 concentration. Therefore, the Al@MnO2 composites could be a potential superior microwave and infrared compatible stealth material. [ABSTRACT FROM AUTHOR]

The physical mechanism of VT degradations under negative bias temperature stress below room temperature has been studied for SiO2 and plasma nitrided oxide (PNO-based) pMOSFETs. It is found that VT degradations in both devices exhibit strong dependence on the electric field and temperature. The analysis shows that this strong dependence follows multi-phonon field-assisted tunneling theory, which indicates the inelastic hole trapping mechanism in the low temperature negative bias temperature instability (NBTI). On the other hand, by applying a low temperature sweeping technique, the energy distribution of these NBTI-induced hole traps below room temperature is indentified. The energy distribution of hole traps has two obvious peaks, one in the lower and one in the upper half of the silicon band gap. Both peaks gradually develop with increasing the stress time and temperature. We attempt to compare the energy profile for SiO2 and PNO devices to identify the trap precursors in NBTI below room temperature. [ABSTRACT FROM AUTHOR]

Light-emission contributed from discrete energy levels of self-assembly InGaN quantum dots is explored to fabricate broadband light-emitting diodes (LEDs). A series of InGaN quantum dots samples are self-assembly grown on sapphire substrate by metal-organic vapor phase epitaxy. Emission from the discrete energy states of the InGaN quantum dots is detected by micro-zone photoluminescence under cryogenic temperature. The peaks assignments are also verified by theoretical simulation. A green LED incorporating InGaN multi-quantum dots as active medium is fabricated, demonstrating a broader emission than the referred multi-quantum wells LED. It suggests quantum dots be of great potential to improve the color-rendering index of white LEDs. • InGaN quantum dots are suggested to fabricate broadband LEDs for improvement of the color-rendering index of white LEDs. • Well-resolved discrete levels are observed in high-density self-assembled InGaN quantum dots. • Broadband emission induced by discrete energy states is successfully demonstrated in InGaN MQD green LED. [ABSTRACT FROM AUTHOR]

Hexagonal flake Co3O4 was prepared by calcining Co-MOF precursors in air. Co3O4@PANI was obtained via hydrothermal and oxidative polymerization processes, and the electromagnetic wave absorption properties of the composites were investigated. Scanning emission microscopy and transmission electron microscopy images show that hexagonal flake Co3O4 possesses a diameter in the range of 2-4 µm and a side length 550-950 nm. With the decrease in Co3O4 content, the absorption performance of Co3O4@PANI increases gradually. When the mass ratio of Co3O4 to PANI is 1:8, the minimum reflection loss value is − 37.39 dB at 7.28 GHz with a layer thickness of 4 mm. Co3O4@PANI also has effective absorption with the entire test thickness, and the maximum absorption bandwidth can reach 3.52 GHz. Therefore, the as prepared hexagonal flake Co3O4@PANI has potential for application in the field of electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]

This article provides preliminary validity evidence for the shorter Mandarin version of the Vocabulary Size Test (VST) under the content aspect, technical quality, substantive and generalizability aspect of Messick's (1995) construct validity framework. The shorter version with 177 Chinese university students in three proficiency levels indicates that the test enjoys a high level of validity both from the perspective of classical test theory and item response theory. A one-way ANOVA and detailed statistics of Rasch analyses demonstrate that the test could effectively distinguish learners from different proficiency levels. The first eight levels of the VST generally display an ascending difficulty continuum except that some loan words in the seventh and the eighth level prove to be problematic in assessing Chinese learners' vocabulary size accurately. The generalizability aspect of construct validity is demonstrated in that there is no item bias for learners of the same proficiency group in terms of gender. Compared with the results of other studies either on monolingual or bilingual version, this research attempts to justify the appropriateness of the Mandarin version and calls for cautious applications of the test instrument on Chinese learners. [ABSTRACT FROM AUTHOR]

Propose: To explore the value of unmeasurable enhancement pattern of residual cavity in predicting survival at early stage after gross-total resection in high-grade glioma (HGG) patients.Methods: This retrospective study enrolled consecutive 51 HGG patients with unmeasurable enhancement who underwent gross-total resection followed by concurrent chemoradiotherapy and adjuvant chemotherapy. We evaluated the enhancement patterns of residual cavity on contrast-T1WI made within 1 month after tumor resection (20 ± 3 days). The survival state of different enhancement was compared.Results: Thin-linear, thick-linear and nodular enhancement were observed in 22 patients (43%), 10 patients (20%), and 19 patients (37%), respectively. The progression-free survival of patients with thin-linear (487, 151-887 days) was longer than those patients with thick-linear (277, 133-573 days), and nodular enhancement (210, 120-765 days) (P = 0.002). The overall survival of patients with thin-linear (774, 457-1343 days) was longer than those with thick-linear (462, 320-678 days), and nodular enhancement (326, 234-1393 days) (P = 0.002). There was no significant difference of orthogonal value between thick-linear and nodular enhancement (0.854), neither between grade III and IV with same enhancement patterns (P = 0.540, P = 0.720).Conclusions: The unmeasurable enhancement patterns in HGG patients within 1 month after gross-total resection, which might be better than the grade of tumor, holds a potential marker in survival state. [ABSTRACT FROM AUTHOR]