Analysis of Flexural Vibrations of a Piezoelectric Semiconductor Nanoplate Driven by a Time-Harmonic Force.

The performance of devices fabricated from piezoelectric semiconductors, such as sensors and actuators in microelectromechanical systems, is superior; furthermore, plate structures are the core components of these smart devices. It is thus important to analyze the electromechanical coupling properties of piezoelectric semiconductor nanoplates. We established a nanoplate model for the piezoelectric semiconductor plate structure by extending the first-order shear deformation theory. The flexural vibrations of nanoplates subjected to a transversely time-harmonic force were investigated. The vibrational modes and natural frequencies were obtained by using the matrix eigenvalue solver in COMSOL Multiphysics 5.3a, and the convergence analysis was carried out to guarantee accurate results. In numerical cases, the tuning effect of the initial electron concentration on mechanics and electric properties is deeply discussed. The numerical results show that the initial electron concentration greatly affects the natural frequency and electromechanical fields of piezoelectric semiconductors, and a high initial electron concentration can reduce the electromechanical fields and the stiffness of piezoelectric semiconductors due to the electron screening effect. We analyzed the flexural vibration of typical piezoelectric semiconductor plate structures, which provide theoretical guidance for the development of new piezotronic devices.

Banana Leaflike C-Doped MoS2 Aerogels toward Excellent Microwave Absorption Performance.

We describe the design and manufacturing method of a lightweight C-doped MoS2 aerogel with a special regular banana leaflike microstructure used for high-performance microwave absorbers. The aerogel precursor was first fabricated by a self-assembly process between alginate (Alg) and ammonium thiomolybdate (ATM), where Alg as a template was assembled with ATM into regular banana leaflike architectures along the ice growth direction during oriented freezing. After pyrolysis at 900 °C, the C-doped MoS2 aerogels maintained low densities and porous hierarchal banana leaflike structures, where the banana leaves ranged in diameter from about 2 to 5 µm with the growth of small branches. Benefitting from these features, the C-doped MoS2 aerogel possessed excellent microwave absorption performance in the frequency range of 2-18 GHz. The minimum reflection loss (RL) reached -43 dB at 5.4 GHz with a matching thickness of 4 mm, and the effective microwave absorption band (RL < -10 dB) reached 4 GHz (14-18 GHz) at a thickness of 1.5 mm. Our findings also provide strategies for designing MoS2 aerogel nanostructures for electronic devices, catalysis, and other potential applications.

Hierarchically porous SiO2/polyurethane foam composites towards excellent thermal insulating, flame-retardant and smoke-suppressant performances.

Polyurethane foam (PUF) is widely used in building insulation field but highly flammable. In an effort to develop an efficient way to reduce flammability and smoke release of PUF without sacrificing its inherent merits, a novel strategy has been proposed to decorate silica aerogels onto the surface of PUF to fabricate hierarchically porous SiO2/PUF composites. Due to the unique hierarchically porous structure, the resultant composites showed superior thermal insulation with a lower thermal conductivity of 0.0282 W/(m K). The introduction of silica aerogels also effectively improved the compressive strength, almost 220% of that of neat PUF. Notably, the SiO2/PUF composites were rendered self-extinguishing in vertical burning tests and had a high limiting oxygen index (LOI) value of 32.5%. Cone calorimetry (CC) tests revealed that the peak heat release rate (PHRR) and peak smoke production release (PSPR) of the SiO2/PUF composites were reduced by 40.4% and 45.6%, respectively. Particularly, the specific optical density (Ds) of the composites displayed as 55.7% reduction in the smoke density chamber tests, showing excellent smoke-suppression. The mechanism analysis suggested that a compact silica-rich hybrid barrier formed, preventing thermal degradation products and energy transfer during combustion. These results indicate SiO2/PUF composites have enormous potential as building insulation materials.

p38δ MAPK regulates aggresome biogenesis by phosphorylating SQSTM1 in response to proteasomal stress.

Aggresome formation is a major strategy to enable cells to cope with proteasomal stress. Misfolded proteins are assembled into micro-aggregates and transported to the microtubule organizing center (MTOC) to form perinuclear aggresomes before their degradation through autophagy. So far, multiple factors have been identified as the activators of micro-aggregate formation, but much less is known about the regulatory mechanisms of their transport. Here, we report that proteasomal stress leads to the activation of p38 MAPK family members. Two of them, p38γ (MAPK12) and p38δ (MAPK13), are dispensable for micro-aggregate formation but are required for their targeting to the MTOC. Interestingly, p38δ promotes micro-aggregate transport by phosphorylating SQSTM1, a major scaffold protein that assembles soluble ubiquitylated proteins into micro-aggregates. Expression of the phospho-mimetic mutant of SQSTM1 in p38δ-knockout cells completely rescued their aggresome formation defects and enhanced their resistance to proteasomal stress to wild-type levels. This study reveals p38δ-mediated SQSTM1 phosphorylation as a critical signal for the targeting of micro-aggregates to the MTOC and provides direct evidence for the survival advantages associated with aggresome formation in cells under proteasomal stress.

Cytosolic PINK1 promotes the targeting of ubiquitinated proteins to the aggresome-autophagy pathway during proteasomal stress.

During proteasomal stress, cells can alleviate the accumulation of polyubiquitinated proteins by targeting them to perinuclear aggresomes for autophagic degradation, but the mechanism underlying the activation of this compensatory pathway remains unclear. Here we report that PINK1-s, a short form of Parkinson disease (PD)-related protein kinase PINK1 (PTEN induced putative kinase 1), is a major regulator of aggresome formation. PINK1-s is extremely unstable due to its recognition by the N-end rule pathway, and tends to accumulate in the cytosol during proteasomal stress. Overexpression of PINK1-s induces aggresome formation in cells with normal proteasomal activities, while loss of PINK1-s function leads to a significant decrease in the efficiency of aggresome formation induced by proteasomal inhibition. PINK1-s exerts its effect through phosphorylation of the ubiquitin-binding protein SQSTM1 (sequestosome 1) and increasing its ability to sequester polyubiquitinated proteins into aggresomes. These findings pinpoint PINK1-s as a sensor of proteasomal activities that transduces the proteasomal impairment signal to the aggresome formation machinery.

Anti-tumor activity and immunological modification of ribosome-inactivating protein (RIP) from Momordica charantia by covalent attachment of polyethylene glycol.

Ribosome-inactivating proteins (RIPs) are a family of enzymes that depurinate rRNA and inhibit protein biosynthesis. Here we report the purification, apoptosis-inducing activity, and polyethylene glycol (PEG) modification of RIP from the bitter melon seeds. The protein has a homogenous N-terminal sequence of NAsp- Val-Ser-Phe-Arg. Moreover, the RIP displayed strong apoptosis-inducing activity and suppressed cancer cell growth. This might be attributed to the activation of caspases-3. To make it available for in vivo application, the immunogenicity of RIP was reduced by chemical modification with 20 kDa (mPEG)(2)-Lys-NHS. The inhibition activity of both PEGylated and non-PEGylated RIP against cancer cells was much stronger than against normal cells, and the antigenicity of PEGylated RIP was reduced significantly. Our results suggested that the PEGylated RIP might be potentially developed as anti-cancer drug.