Expression of Staphylococcus aureus translation elongation factor P is regulated by a stress-inducible promotor.

Translation elongation factor P, expressed by the efp gene, is a conserved protein closely related to bacterial virulence and environmental stress regulation responses, however, little is known about the efp gene expression regulations. Here, the strain of Staphylococcus aureus subsp. aureus NCTC 8325 was taken as the research object and cultured under different conditions, including different culture temperatures, pH, and antibiotics, to study the expression of the efp gene in S. aureus by qRT-PCR, the results showed that the expression of the efp gene is upregulated under high temperature (40 °C), acidic (pH 5.4) or alkaline (pH 9.4) culture conditions, but upregulated early and downregulated later under the conditions of 0.5 MIC antibiotics (chloramphenicol at the final concentration of 2 µg/mL and vancomycin at the final concentration of 0.25 µg/mL), indicating that the efp promoter in S. aureus is inducible. The efp promoter sequence and structure in S. aureus were predicted by bioinformatics methods, and the predicted promoter was validated by constructing a promoter-probe vector and a series of promoter mutants, the results showed that the efp promoter sequence in S. aureus, named Pro, located in 1,548,179-1,548,250 of the S. aureus genome (NC_007795.1), and the sequence of - 10 element is CCTTATAGT, - 35 element is TTTACT. The results above could lay a foundation for screening transcription factors involved in the expression of the efp gene and then exploring the transcriptional regulation mechanism of EF-P in S. aureus.

Photoalignment of sub-micrometer periodic liquid crystal polarization grating by using the optical imprinting method.

Photoalignment of liquid crystal polarization grating based on optical imprinting is a promising technique for polarization grating mass production. However, when the period of the optical imprinting grating is in the sub-micrometer level, the zero-order energy from the master grating will become high, and it will strongly affect the photoalignment quality. This paper proposes a double-twisted polarization grating structure to eliminate the zero-order disturbance of master grating and gives the design method. Based on the designed results, a master grating was prepared, and the optically imprinted photoalignment of polarization grating with a period of 0.5µm was fabricated. This method has the advantages of high efficiency and significantly greater environmental tolerance than the traditional polarization holographic photoalignment methods. It has the potential to be used for large-area polarization holographic gratings production.

Liquid-crystal-polymer binary diffractive optical elements with a sub-micrometer feature size realized by a contact polarization holography.

In this Letter, a contact polarization holographic photoalignment method is proposed. In the holographic recording, a phase mask is contacted with a photoalignment film, making light carrying wavefront information interfere with reference light in the near-field region to realize polarization holographic pattern recording with a sub-micrometer feature size. The relevant theoretical derivation is given, and holographic recording of a 0.4 µm feature-size phase mask is realized. The proposed method can conveniently realize liquid-crystal binary diffractive optical elements with a sub-micrometer feature size. Off-axis diffraction can also be realized by superimposing the grating information by changing the angle between the substrate and the interference light.

Dual-task convolutional neural network based on the combination of the U-Net and a diffraction propagation model for phase hologram design with suppressed speckle noise.

In this paper, a dual-task convolutional neural network based on the combination of the U-Net and a diffraction propagation model is proposed for the design of phase holograms to suppress speckle noise of the reconstructed images. By introducing a Fresnel transmission layer, based on angular spectrum diffraction theory, as the diffraction propagation model and incorporating it into U-Net as the output layer, the proposed neural network model can describe the actual physical process of holographic imaging, and the distributions of both the light amplitude and phase can be generated. Afterwards, by respectively using the Pearson correlation coefficient (PCC) as the loss function to modulate the distribution of the amplitude, and a proposed target-weighted standard deviation (TWSD) as the loss function to limit the randomness and arbitrariness of the reconstructed phase distribution, the dual tasks of the amplitude reconstruction and phase smoothing are jointly solved, and thus the phase hologram that can produce high quality image without speckle is obtained. Both simulations and optical experiments are carried out to confirm the feasibility and effectiveness of the proposed method. Furthermore, the depth of field (DOF) of the image using the proposed method is much larger than that of using the traditional Gerchberg-Saxton (GS) algorithm due to the smoothness of the reconstructed phase distribution, which is also verified in the experiments. This study provides a new phase hologram design approach and shows the potential of neural networks in the field of the holographic imaging and more.

Diffuser screen with flat-top angular distribution of scattered light realized by a dual-beam holographic speckle.

Holographic speckle screens with the Gaussian type distribution of scattered light, which are used to increase the viewing angle of the image in projection display systems, result in nonuniform image brightness in different observing positions. In this study, based on Helmholtz-Kirchhoff theory, a dual-beam scattering theory of rough surface is derived. By analyzing the spatial frequency spectrum of the scattered light, it is found that when two laser beams irradiated the ground glass at a certain angle, the resulting speckles recorded on the photoresist can generate a flat-top angular distribution of the scattered light. Speckle screens are fabricated by two light beams at different angles, and the angular intensity distribution of scattered light is measured. The results are in good agreement with the theory. Compared with the Gaussian type diffuser, the energy efficiency of the speckle screen proposed has a 46% increase when the angular luminance uniformity is set to be 80%, which effectively improves the brightness when used in a head up display system.

U-Net convolutional neural network-based modification method for precise fabrication of three-dimensional microstructures using laser direct writing lithography.

In this paper, a modification method based on a U-Net convolutional neural network is proposed for the precise fabrication of three-dimensional microstructures using laser direct writing lithography (LDWL). In order to build the correspondence between the exposure intensity distribution data imported to the laser direct writing system and the surface profile data of the actual fabricated microstructure, these two kinds of data are used as training tensors of the U-Net convolutional neural network, which is proved to be capable of generating their accurate mapping relations. By employing such mapping relations to modify the initial designed exposure intensity data of the parabolic and saddle concave micro-lens with an aperture of 24µm×24µm, it is demonstrated that their fabrication precision, characterized by the mean squared error (MSE) and the peak signal-to-noise ratio (PSNR) between the fabricated and the designed microstructure, can be improved significantly. Specifically, the MSE of the parabolic and saddle concave micro-lens decreased from 100 to 17 and 151 to 50, respectively, and the PSNR increased from 22dB to 29dB and 20dB to 25dB, respectively. Furthermore, the effect of laser beam shaping using these two kinds of micro-lens has also been improved considerably. This study provides a new solution for the fabrication of high-precision three-dimensional microstructures by LDWL.

Crystalline Control of {111} Bounded Pt3Cu Nanocrystals: Multiply-Twinned Pt3Cu Icosahedra with Enhanced Electrocatalytic Properties.

Despite that different facets have distinct catalytic behavior, the important role of twin defects on enhancing the catalytic performance of metallic nanocrystals is largely unrevealed. The key challenge in demonstrating the importance of twin defects for catalysis is the extreme difficulties in creating nanostructures with the same exposed facets but tunable twin defects that are suitable for catalytic investigations. Herein, we show an efficient synthetic strategy to selectively synthesize {111}-terminated Pt3Cu nanocrystals with controllable crystalline features. Two distinct {111}-bounded shapes, namely, multiply-twinned Pt3Cu icosahedra and single-crystalline Pt3Cu octahedra, are successfully prepared by simply changing the types of Cu precursors with the other growth parameters unchanged. Electrocatalytic studies show that the {111}-terminated Pt3Cu nanocrystals exhibit the very interesting crystalline nature-dependent electrocatalytic activities toward both the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) with multiply-twinned Pt3Cu icosahedra demonstrating enhanced electrocatalytic activities compared to the single-crystalline Pt3Cu octahedra due to their additional yet important effect of twin defect. As a result, under the multiple tuning conditions (alloy, shape, and twin effects), the multiply-twinned Pt3Cu icosahedra exhibit much enhanced electrocatalytic activities in both ORR and MOR with respect to the Pt black. The present work highlights the importance of twin defects in enhancing electrocatalytic activities of metallic nanocrystals.

Controlling and self assembling of monodisperse platinum nanocubes as efficient methanol oxidation electrocatalysts.

An efficient synthetic approach that enables not only the control of Pt nanocubes but also the one-pot fabrication of novel Pt nanocube assemblies was developed for the first time. The integration of well-defined building blocks and unique superstructures endows Pt nanocube assemblies with enhanced performance in the methanol electrooxidation, showing a new concept for further enhancing the performance of these catalysts.