Syntheses and characterizations of the in vivo replicative bypass and mutagenic properties of the minor-groove O2-alkylthymidine lesions.

Endogenous metabolism, environmental exposure, and treatment with some chemotherapeutic agents can all give rise to DNA alkylation, which can occur on the phosphate backbone as well as the ring nitrogen or exocyclic nitrogen and oxygen atoms of nucleobases. Previous studies showed that the minor-groove O(2)-alkylated thymidine (O(2)-alkyldT) lesions are poorly repaired and persist in mammalian tissues. In the present study, we synthesized oligodeoxyribonucleotides harboring seven O(2)-alkyldT lesions, with the alkyl group being a Me, Et, nPr, iPr, nBu, iBu or sBu, at a defined site and examined the impact of these lesions on DNA replication in Escherichia coli cells. Our results demonstrated that the replication bypass efficiencies of the O(2)-alkyldT lesions decreased with the chain length of the alkyl group, and these lesions directed promiscuous nucleotide misincorporation in E. coli cells. We also found that deficiency in Pol V, but not Pol II or Pol IV, led to a marked drop in bypass efficiencies for most O(2)-alkyldT lesions. We further showed that both Pol IV and Pol V were essential for the misincorporation of dCMP opposite these minor-groove DNA lesions, whereas only Pol V was indispensable for the T→A transversion introduced by these lesions. Depletion of Pol II, however, did not lead to any detectable alterations in mutation frequencies for any of the O(2)-alkyldT lesions. Thus, our study provided important new knowledge about the cytotoxic and mutagenic properties of the O(2)-alkyldT lesions and revealed the roles of the SOS-induced DNA polymerases in bypassing these lesions in E. coli cells

Integrating non-planar metamaterials with magnetic absorbing materials to yield ultra-broadband microwave hybrid absorbers

Broadening the bandwidth of electromagnetic wave absorbers has greatly challenged material scientists. Here, we propose a two-layer hybrid absorber consisting of a non-planar metamaterial (MM) and a magnetic microwave absorbing material (MAM). The non-planar MM using magnetic MAMs instead of dielectric substrates shows good low frequency absorption and low reflection across a broad spectrum. Benefiting from this and the high frequency strong absorption of the MAM layer, the lightweight hybrid absorber exhibits 90% absorptivity over the whole 2-18 GHz range. Our result reveals a promising and flexible method to greatly extend or control the absorption bandwidth of absorbers. (C) 2014 AIP Publishing LLC

Learnable Blur Kernel for Single-Image Defocus Deblurring in the Wild

Recent research showed that the dual-pixel sensor has made great progress in defocus map estimation and image defocus deblurring. However, extracting real-time dual-pixel views is troublesome and complex in algorithm deployment. Moreover, the deblurred image generated by the defocus deblurring network lacks high-frequency details, which is unsatisfactory in human perception. To overcome this issue, we propose a novel defocus deblurring method that uses the guidance of the defocus map to implement image deblurring. The proposed method consists of a learnable blur kernel to estimate the defocus map, which is an unsupervised method, and a single-image defocus deblurring generative adversarial network (DefocusGAN) for the first time. The proposed network can learn the deblurring of different regions and recover realistic details. We propose a defocus adversarial loss to guide this training process. Competitive experimental results confirm that with a learnable blur kernel, the generated defocus map can achieve results comparable to supervised methods. In the single-image defocus deblurring task, the proposed method achieves state-of-the-art results, especially significant improvements in perceptual quality, where PSNR reaches 25.56 dB and LPIPS reaches 0.111.Comment: 9 pages, 7 figure

A Wireless Covert Channel Based on Constellation Shaping Modulation

Wireless covert channel is an emerging covert communication technique which conceals the very existence of secret information in wireless signal including GSM, CDMA, and LTE. The secret message bits are always modulated into artificial noise superposed with cover signal, which is then demodulated with the shared codebook at the receiver. In this paper, we first extend the traditional KS test and regularity test in covert timing channel detection into wireless covert channel, which can be used to reveal the very existence of secret data in wireless covert channel from the aspect of multiorder statistics. In order to improve the undetectability, a wireless covert channel for OFDM-based communication system based on constellation shaping modulation is proposed, which generates additional constellation points around the standard points in normal constellations. The carrier signal is then modulated with the dirty constellation and the secret message bits are represented by the selection mode of the additional constellation points; shaping modulation is employed to keep the distribution of constellation errors unchanged. Experimental results show that the proposed wireless covert channel scheme can resist various statistical detections. The communication reliability under typical interference is also proved

Structural failure of layered thermoelectric In₄Se_(3-δ) semiconductors is dominated by shear slippage

In₄Se_(3-δ) semiconductors exhibit high zT as an n-type TE material, making them promising materials for thermoelectric (TE) applications. However, their commercial applications have been limited by the degradation of their mechanical properties upon cyclic thermal loading, making it important to understand their stress response under external loadings. Thus we applied molecular dynamics (MD) simulations using a density functional theory (DFT) derived force field to investigate the stress response and failure mechanism of In₄Se_(3-δ) under shear loading as a function of strain rates and temperatures. We considered the most plausible slip system (001)/ based on the calculations. We find that shear slippage among In/Se layered structures dominates the shear failure of In₄Se_(3-δ). Particularly, Se vacancies promote disorder of the In atoms in the shear band, which accelerates the shear failure. With increasing temperature, the critical failure strength of In4Se3 and the fracture strain of In₄Se₃ decrease gradually. In contrast, the fracture strain of In₄Se_(2.75) is improved although the ultimate strength decreases as temperature increases, suggesting that the Se vacancies enhance the ductility at high temperature. In addition, the ultimate strength and the fracture strain for In₄Se_(2.75) increase slightly with the strain rate. This strain rate effect is more significant at low temperature for In₄Se_(2.75) because of the Se vacancies. These findings provide new perspectives of intrinsic failure of In₄Se_(3-δ) and theory basis for developing robust In₄Se_(3-δ) TE devices

Synergetic Evolution of Sacrificial Bonds and Strain-Induced Defects Facilitating Large Deformation of Bi₂Te₃ Semiconductor

Bismuth telluride (Bi₂Te₃)-based semiconductors are one of the typical inorganic thermoelectric (TE) materials with excellent energy conversion efficiency, but the intrinsic brittleness severely limits their mechanical performance for further application with long-term reliability and in wearable devices. To understand the recent mechanical improvement of ductile and flexible inorganic TE materials at the atomic scale, here, we use molecular dynamics simulations to intuitively illuminate the enhanced shear deformability and performance stability of the brittle Bi2Te3 crystal through the tailored effects of surfaces. We reveal that the peculiar microbehavior originates from the layered hierarchical bonding structure with weak but reversible van der Waals force, namely, a sacrificial bond (SB), between Te1–Te1 adjacent layers. The synergetic evolution of local structures including SBs and strain-induced defects tends to partly compensate for the mechanical degradation caused by structure softening during shearing, achieving a relatively large strain before cleavage. The inspired engineering strategy of synergistically optimizing bonds and defects opens a pathway for designing multiscale hierarchical inorganic TE materials with excellent overall performance

Structure and Failure Mechanism of the Thermoelectric CoSb_3/TiCoSb Interface

The brittle behavior and low strength of CoSb_3/TiCoSb interface are serious issues concerning the engineering applications of CoSb_3 based or CoSb_3/TiCoSb segmented thermoelectric devices. To illustrate the failure mechanism of the CoSb_3/TiCoSb interface, we apply density functional theory to investigate the interfacial behavior and examine the response during tensile deformations. We find that both CoSb_3(100)/TiCoSb(111) and CoSb_3(100)/TiCoSb(110) are energetically favorable interfacial structures. Failure of the CoSb_3/TiCoSb interface occurs in CoSb_3 since the structural stiffness of CoSb_3 is much weaker than that of TiCoSb. This failure within CoSb_3 can be explained through the softening of the Sb–Sb bond along with the cleavage of the Co–Sb bond in the interface. The failure mechanism the CoSb_3/TiCoSb interface is similar to that of bulk CoSb_3, but the ideal tensile strength and failure strain of the CoSb_3/TiCoSb interface are much lower than those of bulk CoSb_3. This can be attributed to the weakened stiffness of the Co–Sb framework due to structural rearrangement near the interfacial region

Intrinsic mechanical behavior of MgAgSb thermoelectric material: An ab initio study

α-MgAgSb based thermoelectric (TE) device attracts much attention for its commercial application because it shows an extremely high conversion efficiency of ∼8.5% under a temperature difference of 225 K. However, the mechanical behavior of α-MgAgSb is another serious consideration for its engineering applications. Here, we apply density functional theory (DFT) simulations to examine the intrinsic mechanical properties of all three MgAgSb phases, including elastic properties, shear-stress – shear-strain relationships, deformation and failure mechanism under ideal shear and biaxial shear conditions. We find that the ideal shear strength of α-MgAgSb is 3.25 GPa along the most plausible (100) slip system. This strength is higher than that of β-MgAgSb (0.80 GPa) and lower than that of γ-MgAgSb (3.43 GPa). The failure of α-MgAgSb arises from the stretching and breakage of Mg-Sb bond α-MgAgSb under pure shear load, while it arises from the softening of Mg-Ag bond and the breakage of Ag-Sb bond under biaxial shear load. This suggests that the deformation mechanism changes significantly under different loading conditions