Discrete Hartley transform-based dual-mode index modulation OFDM for visible light communications.

Using discrete Hartley transform (DHT) instead of discrete Fourier transform (DFT) in the optical index modulation (IM) aided orthogonal frequency division multiplexing (OFDM) systems for visible light communications (VLC) results in improvement in terms of the spectral efficiency, energy efficiency, peak-to-average power ratio, and bit error rate (BER) performance with a lower computational complexity, benefiting from the removal of the Hermitian symmetry. In this paper, by employing dual-mode (DM) index modulation in the DHT-based OFDM systems, more spectral efficient schemes for VLC are proposed. A reduced-complexity maximum likelihood (ML) detector and a simple log-likelihood ratio (LLR) detector for the DM-OFDM-IM systems are presented, achieving a better performance with a lower complexity over the traditional detectors. The spectral efficiency and the average BER are analyzed. The minimum distance between different transmitted subblock vectors is calculated for characterizing the performance. The simulation results demonstrate that the DHT-based DM-OFDM-IM systems achieve significant performance gains over the DHT-based OFDM-IM counterparts and perform better than the DFT-based counterparts in terms of the spectral efficiency and BER performance.

Generalized transmit laser selection for vertical underwater wireless optical communications over Gamma-Gamma turbulence channels.

Underwater wireless optical communication (UWOC) is a potential technology for high-speed and reliable underwater data transmission. In underwater environment, ocean turbulence has a strong impact on the performance of UWOC systems. Thus, transmission laser selection (TLS) is proposed as an effective technique for fading mitigation in turbulence channels. In this paper, we present a vertical UWOC system with generalized TLS (GTLS) in multi-layer cascaded Gamma-Gamma ocean turbulence channels. With GTLS, the transmitter is equipped with N laser sources and the nth source is selected for transmission. For the ideal case, the optimal laser source is selected, but in practice, a sub-optimal or worse source may be selected due to channel estimation and/or feedback errors. For the GTLS system, we derive an exact closed-form expression for outage probability. Furthermore, based on the outage probability expression, the diversity order and asymptotical diversity order expression are analyzed. Finally, we give simulation results to validate our analytical results. Numerical results show that the GTLS system performs better than the system without GTLS (i.e. N = 1). The number of cascade channel layers, the number of laser sources and the selection of source index significantly affect the performance of the GTLS system.

Facile Preparation of Polysiloxane-Modified Asphalt Binder Exhibiting Enhanced Performance.

The development of polymer-modified asphalt (asphalt = asphalt binder) is significant because the polymer modifier can improve the performance of asphalt mixture and meet the requirements of the modern asphalt pavement. Herein, we present a novel polysiloxane-modified asphalt with enhanced performance, formed by simply mixing hydroxy-terminated polysiloxane (HO-PDMS) into base asphalt at 140 °C. The interaction mechanism of HO-PDMS in base asphalt was characterized by FT-IR, GPC, and DSC. It reveals that HO-PDMS polymers have been chemically bonded into the asphalt, and, thus, the resultant asphalt exhibits optimal compatibility and storage stability. The results based on fluorescence microscopy and a segregation test prove that HO-PDMS has good compatibility with base asphalt. Moreover, by virtue of the intriguing properties of polysiloxane, the present asphalt possesses improved low- and high-temperature properties, higher thermal stability, and enhanced hydrophobicity compared to conventional asphalt when using an appropriate dosage of HO-PDMS. DSC indicated that the Tg of modified asphalt (-12.8 °C) was obviously lower than that of base asphalt (-7.1 °C). DSR shows that the rutting parameter of modified asphalt was obviously higher than that of base asphalt. BBR shows that modified asphalt exhibited the lowest stiffness modulus and the highest creep rate with an HO-PDMS dosage of 6% and 4%, respectively. These results demonstrate that polysiloxane-modified asphalt can be promisingly utilized in realistic asphalt pavement with specific requirements, particularly high-/low-temperature resistance.

P300/HDAC1 regulates the acetylation/deacetylation and autophagic activities of LC3/Atg8-PE ubiquitin-like system.

Protein acetylation plays potential roles in regulating autophagy occurrence. However, it varies greatly between yeast and mammals, and has not been thoroughly investigated in other organisms. Here, we reported that the components of BmAtg8-PE ubiquitin-like system (BmAtg3, BmAtg4, BmAtg7, and BmAtg8) in Bombyx mori were localized in the nucleus under nutrient-rich conditions, whereas they were exported to the cytoplasm upon autophagy induction. RNAi of BmP300 and inhibition of BmP300 activity resulted in nucleo-cytoplasmic translocation of BmAtg3 and BmAtg8, as well as premature induction of autophagy in the absence of stimulus. Conversely, RNAi of BmHDAC1 and inhibition of class I/II HADCs activities led to the nuclear accumulation of BmAtg3 and BmAtg8. In addition, acetylation sites in Atg proteins of BmAtg8-PE ubiquitin-like system were identified by mass spectrometry, and acetylation-site mutations caused nucleo-cytoplasmic translocation of BmAtg3, BmAtg4, and BmAtg8 along with autophagy promotion. Similarly, the subcellular localization of human ATG4b is determined by acetylation modification. In general, BmP300-mediated acetylation sequesters the components of BmAtg8-PE ubiquitin-like system in the nucleus, thus leading to the autophagy inhibition. Oppositely, BmHDAC1-mediated deacetylation leads to the nucleo-cytoplasmic translocation of the components of BmAtg8-PE ubiquitin-like system and promotes autophagy. This process is evolutionarily conserved between insects and mammals.

Correction: Wu, W., et al. Tip60 Phosphorylation at Ser 99 Is Essential for Autophagy Induction in Bombyx mori. Int. J. Mol. Sci. 2020, 21, 6893.

The author wishes to make the following correction to this paper [...].

Tip60 Phosphorylation at Ser 99 Is Essential for Autophagy Induction in Bombyx mori.

Tip60, a key histone acetyltransferase of the MYST family and member of the nuclear multimeric protein complex (NuA4), regulates the activity and stability of proteins involved in the cell cycle, DNA damage responses, autophagy, etc. However, the function and regulatory mechanism of Tip60 homolog in Bombyx mori are not elucidated. In the present study, Bombyx Tip60 (BmTip60) was functionally identified. Developmental profiles showed that the protein levels and nuclear localization of BmTip60 peaked in fat body during the larval-pupal metamorphosis when autophagy was intensive; simultaneously, the BmTip60 protein migrated to form an upper band as detected by Western blot. Interestingly, the upper band of BmTip60 was reduced by λ-phosphatase treatment, indicating that it was a phosphorylated form of BmTip60. Results showed that BmTip60 was promoted by starvation but not 20-hydroxyecdysone treatment. Transcription factor AMP-activated protein kinase (AMPK) affected by starvation was pivotal for BmTip60 protein migration. In addition, one mammalian phosphorylation site was identified in BmTip60 at Ser99, the constitutive-activation mutation of Ser99 to Asp99 but not its inactive mutation to Ala99 significantly upregulated autophagy, showing the critical role of phosphorylation at Ser99 for BmTip60-mediated autophagy. In conclusion, the starvation-AMPK axis promotes BmTip60 in B. mori, which was requisite for autophagy induction. These results reveal a regulatory mechanism of histone acetyltransferase Tip60 homologs by phosphorylation in insects, and sheds light on further related studies of acetylation regulation.

Functional identification of Bombyx mori Atg13 in autophagy.

The autophagy process involves a series of autophagy-related (Atg) proteins, which are conserved in eukaryotes. ULK1/Atg1-ATG13/Atg13 is the core protein complex for autophagy initiation in response to nutrient and hormone signaling. However, how Atg13 is regulated to participate in autophagy is unclear in insects. Here in Bombyx mori, the variation of BmAtg13 was correlated with autophagy induced by steroid hormone 20-hydroxyecdysone (20E) or starvation. Developmental profiles from feeding to prepupal stage revealed that there were two bands of BmAtg13 protein detected by western blot analysis, therein the upper band was intensively decreased, while the lower band was significantly increased which was in accordance with its mRNA variation; and immunofluorescent staining indicated that BmAtg13 was nucleocytoplasmic translocated during larval-pupal metamorphosis when autophagy was dramatically induced. BmAtg13 knockdown and overexpression both inhibits autophagy. Besides, 20E treatment-induced BmAtg13 gene expression, while blocking 20E signaling transduction by knockdown of BmUsp reduced both gene expression and protein level of BmAtg13. These results reveal that BmAtg13 is required for 20E- and starvation-induced autophagy in B. mori, which provides the foundation for further related studies.

Clathrin-dependent endocytosis predominantly mediates protein absorption by fat body from the hemolymph in Bombyx mori.

During insect larval-pupal metamorphosis, proteins in the hemolymph are absorbed by the fat body for the maintenance of intracellular homeostasis; however, the type of proteins and how these proteins are internalized into the fat body are unclear. In Bombyx mori, the developmental profiles of total proteins in the hemolymph and fat body showed that hemolymph-decreased protein bands (55-100 kDa) were in accordance with those protein bands that increased in the fat body. Inhibition of clathrin-dependent endocytosis predominantly blocked the transportation of 55-100 kDa proteins from the hemolymph into the fat body, which was further verified by RNA interference treatment of Bmclathrin. Six hexamerins were shown to comprise ∼90% of the total identified proteins in both the hemolymph and fat body by mass spectrum (MS) analysis. In addition, hemolymph-specific proteins were mainly involved in material transportation, while fat body-specific proteins particularly participated in metabolism. In this paper, four hexamerins were found for the first time, and potential proteins absorbed by the fat body from the hemolymph through clathrin-dependent endocytosis were identified. This study sheds light on the protein absorption mechanism during insect metamorphosis.