Characteristics of laser-induced steel plasmas generated with different focusing conditions.

Laser focusing is an important parameter that affects the characteristics of laser-induced plasma. Focusing lenses with different F-numbers form different energy density distributions near the surface of a sample, thus affecting the characteristics of plasma. In this study, the plasma generated by a nanosecond laser ablation of a micro-alloy steel certified sample at 1 atm of air was investigated. We compare the spectrally integrated plasma images obtained at different defocusing distances for short- and long-focus lenses and investigate the optical emission spectra of laser-induced plasma on steel alloy by using focusing lenses with different F-numbers. With an increase in the defocusing distance, the plasma plume changes from flat to hemispherical and then splitting occurs. The spectral line intensity increases first and then decreases, then increases slightly, and finally decreases gradually. For the long-focus lens, when the focal point is above the sample surface, the laser beam strongly interacts with air over a longer distance, leading to longer air plasma and weaker sample plasma compared with the short-focus lens. Thus, the relative intensity of the second peak in the spectral line intensity, according to the defocusing distance, gradually decreases with increasing F-number. We also obtain two-dimensional spatial distributions of the spectral line intensity according to the F-number and defocusing distance. The optimal defocusing distances for all focusing lenses occur when the focal point is below the sample surface. The relation between the optimal defocusing distance and F-number follows a single- exponential decay function.

The effectiveness of travel restriction measures in alleviating the COVID-19 epidemic: evidence from Shenzhen, China.

With the expansion of the global novel coronavirus disease (COVID-19) pandemic, unprecedented interventions have been widely implemented in many countries, including China. In view of this scenario, this research aims to explore the effectiveness of population mobility restriction in alleviating epidemic transmission during different stages of the outbreak. Taking Shenzhen, a city with a large immigrant population in China, as a case study, the real-time reproduction number of COVID-19 is estimated by statistical methods to represent the dynamic spatiotemporal transmission pattern of COVID-19. Furthermore, migration data between Shenzhen and other provinces are collected to investigate the impact of nationwide population flow on near-real-time dynamic reproductive numbers. The results show that traffic flow control between populated cities has an inhibitory effect on urban transmission, but this effect is not significant in the late stage of the epidemic spread in China. This finding implies that the government should limit international and domestic population movement starting from the very early stage of the outbreak. This work confirms the effectiveness of travel restriction measures in the face of COVID-19 in China and provides new insight for densely populated cities in imposing intervention measures at various stages of the transmission cycle.

Spin-orbit Hall effect in the tight focusing of a radially polarized vortex beam.

When the first-order radially polarized vortex beam propagates in an uniaxial crystal, the spin and the orbital angular momentum parts can be separated. It is called the optical spin-orbit Hall effect. In this study, we investigate the tight focusing of the radially polarized vortex beam theoretically and find the spatial separation of the spin and the orbital angular momentum parts occurs in the focal plane when the polarization order equals 1 and the vortex charge equals 1 (or -1). Moreover, when the initial phase of the polarization state takes π/2, the spatial separation of intensity in the focal plane corresponds to the spatial separation of the spin and the orbital angular momentum parts. This phenomenon can be considered as a manifestation of the optical spin-orbit Hall effect in the tight focusing of radially polarized vortex beam. Also, we show that, when the polarization order is greater than 1, the initial phase change of polarization state just leads to the rotation of the focal field and the spin and the orbital angular momentum density in the focal plane. Our results provide the potential application in the field of optical micro-manipulation.

Efficient long fragment editing technique enables large-scale and scarless bacterial genome engineering.

Bacteria are versatile living systems that enhance our understanding of nature and enable biosynthesis of valuable chemicals. Long fragment editing techniques are of great importance for accelerating bacterial genome engineering to obtain desirable and genetically stable strains. However, the existing genome editing methods cannot meet the needs of engineers. We herein report an efficient long fragment editing method for large-scale and scarless genome engineering in Escherichia coli. The method enabled us to insert DNA fragments up to 12 kb into the genome and to delete DNA fragments up to 186.7 kb from the genome, with positive rates over 95%. We applied this method for E. coli genome simplification, resulting in 12 individual deletion mutants and four cumulative deletion mutants. The simplest genome lost a total of 370.6 kb of DNA sequence containing 364 open reading frames. Additionally, we applied this technique to metabolic engineering and obtained a genetically stable plasmid-independent isobutanol production strain that produced 1.3 g/L isobutanol via shake-flask fermentation. These results suggest that the method is a powerful genome engineering tool, highlighting its potential to be applied in synthetic biology and metabolic engineering. KEY POINTS: • This article reports an efficient genome engineering tool for E. coli. • The tool is advantageous for the manipulations of long DNA fragments. • The tool has been successfully applied for genome simplification. • The tool has been successfully applied for metabolic engineering.

[Low-magnitude vibration promotes osteogenesis of osteoblasts in ovariectomized osteoporotic rats via the estrogen receptor α].

The purpose of this study was to investigate the effect of low-magnitude vibration on osteogenesis of osteoblasts in ovariectomized rats with osteoporosis via estrogen receptor α(ERα). The mRNA expression of osteogenic markers were examined with qRT-PCR, based on which the optimal vibration parameter for promoting osteogenesis was determined (45 Hz × 0.9 g, g = 9.8 m/s2). Then we loaded the optimal vibration parameter on the osteoblasts of ovariectomized rats with osteoporosis. The protein expression of osteogenic markers and ERα were detected with Western blot; the distribution of ERα was examined with immunofluorescence technique. Finally, through inhibiting the expression of ERα with estrogen receptor inhibitor ICI182780, the protein and mRNA expression of osteogenic markers were examined. First, the results showed that low-magnitude vibration could promote the expression of osteogenic markers and ERα in osteoblasts of ovariectomized rats with osteoporosis (P < 0.05), and make ERα transfer to the nucleus. On the other hand, the results also showed that after inhibiting the expression of ERα in osteoblasts of ovariectomized rats with osteoporosis, the protein and mRNA expression of osteogenic marker were decreased (P < 0.05). In our study, low-magnitude vibration played an important role in the osteogenesis of osteoblasts in ovariectomized rats with osteoporosis through increasing the expression and causing translocation of ERα. Furthermore, it provides a theoretical basis for the application of low-magnitude vibration in the prevention and treatment of postmenopausal osteoporosis.

Optical vortex shaping via a phase jump factor.

Topological charge (TC) of an optical vortex (OV) is a crucial parameter. We propose two factors, namely, the phase jump factor and the phase gradient factor, to replace the parameter of TC through unwrapping the TC definition integral. Based on these two factors, we report on a novel OV, referred to as the remainder-phase optical vortex (ROV). The properties of the ROV are studied in depth by adjusting these two factors. Results show that the phase gradient factor determines the total orbital angular momentum (OAM), whereas the phase jump factor decides the number of split unit vortices and reshapes the structure of the OAM distribution. This work provides a novel OV with controllable OAM distribution, which will open up new applications such as particle manipulation, beam shaping, and micro-fabrication.

CRISPR-Cas9-assisted native end-joining editing offers a simple strategy for efficient genetic engineering in Escherichia coli.

Unlike eukaryotes, prokaryotes are less proficient in homologous recombination (HR) and non-homologous end-joining (NHEJ). All existing genomic editing methods for Escherichia coli (E. coli) rely on exogenous HR or NHEJ systems to repair DNA double-strand breaks (DSBs). Although an E. coli native end-joining (ENEJ) system has been reported, its potential in genetic engineering has not yet been explored. Here, we present a CRISPR-Cas9-assisted native end-joining editing and show that ENEJ-dependent DNA repair can be used to conduct rapid and efficient deletion of chromosome fragments up to 83 kb or gene inactivation. Moreover, the positive rate and editing efficiency are independent of high-efficiency competent cells. The method requires neither exogenous DNA repair systems nor introduced editing template. The Cas9-sgRNA complex is the only foreign element in this method. This study is the first successful engineering effort to utilize ENEJ mechanism in genomic editing and provides an effective strategy for genetic engineering in bacteria that are inefficient in HR and NHEJ.

[Screening of the Optimum Medium for Rat Mesenchymal Stem Cells].

OBJECTIVE: To investigate the effect of three different cell culture mediums, DMEM-LG, α-MEM and DMEM/F12, on the growth of rat bone marrow mesenchymal stem cells (BMSCs) in vitro, and so that to screen out the most suitable medium for in vitro culturing the rat BMSCs. METHODS: BMSCS were isolated from the femur and tibia of SD rats by whole bone marrow differential adherence method. The isolated cells were then cultured with three culture mediums, DMEM-LG, α-MEM and DMEM/F12. The rat BMSCs morphology, adhesion, proliferation, the time of passage and the number the colony at day 14 in three mediums respectively were observed with inverted phase contrast microscopy and compared. Flow cytometry was used to identify and observe the effects of different mediums on the surface antigen expression of rats BMSCs. RESULTS: Compared with the other two groups of media, BMSCs cultured in DMEM-LG had shorter colony formation time, shorter first passage time, more clone formation (14±2) and showed uniform morphology and the highest attachment efficiency (47.0±2.8)%. Meanwhile, BMSCs cultured with DMEM-LG entered logarithmic growth phase after only 4 days of culturing and showed the highest average specific growth rate and the largest average number of propagations per unit time. The total number of cells reached about (2.2-2.7)×105 mL-1 within three days. The cells cultured with 3 mediums were all identified as rat BMSCs, and the expression of surface antigen in BMSCs was not significantly affected by different media. CONCLUSION: DMEM-LG is more suitable for proliferation of rat BMSCs in vitro.

Close-packed optical vortex lattices with controllable structures.

As a spatial structured light field, the optical vortex (OV) has attracted extensive attention in recent years. In practice, the OV lattice (OVL) is an optimal candidate for applications of orbital angular momentum (OAM)-based optical communications, microparticle manipulation, and micro/nanofabrication. However, traditional methods for producing OVLs meet a significant challenge: the OVL structures cannot be adjusted freely and form a close-packed arrangement, simultaneously. To overcome these difficulties, we propose an alternative scheme to produce close-packed OVLs (CPOVLs) with controllable structures. By borrowing the concept of the close-packed lattice from solid-state physics, CPOVLs with versatile structures are produced by using logical operations of expanding OV primitive cells combined with the technique of phase mask generation. Then, the existence of OAM states in the CPOVLs is verified. Furthermore, the energy flow and OAM distribution of the CPOVLs are visualized and analyzed. From a light field physics viewpoint, this work increases the adjustment dimensions and extends the fundamental understanding of the OVL, which will introduce novel applications.

Controllable mode transformation in perfect optical vortices.

We report a novel method to freely transform the modes of a perfect optical vortex (POV). By adjusting the scaling factor of the Bessel-Gauss beam at the object plane, the POV mode transformation can be easily controlled from circle to ellipse with a high mode purity. Combined with the modulation of the cone angle of an axicon, the ellipse mode can be freely adjusted along the two orthogonal directions. The properties of the "perfect vortex" are experimentally verified. Moreover, fractional elliptic POVs with versatile modes are presented, where the number and position of the gaps are controllable. These findings are significant for applications that require the complex structured optical field of the POV.

Influence of the vaccinating density of A549 cells on tumorigenesis and distant organ metastasis in a lung cancer mice model.

Lung metastasis of malignant tumors, such as lung carcinoma, is a major cause of cancer-related deaths worldwide. The commonly used lung tumor models were established by subcutaneous or intravenous injection of the non-small cell lung cancer cell line A549 in mice. However, the influence of cell densities on tumorigenesis and distant organ metastasis remains poorly investigated. In this study, A549 cells were subcutaneously injected into mice at 1 × 107 cells/mL, 5 × 106 cells/mL, and 1 × 106 cells/mL or intravenously at 1 × 106 cells/mL, 5 × 106 cells/mL, and 1 × 106 cells/mL. Then, histology analysis, immunohistochemistry staining, and in-situ TUNEL assay were performed to evaluate tumor growth and metastasis. Results showed that subcutaneously injecting the A549 cells could develop tumors and that fewer apoptotic cells were found in the 5 × 106 cells/mL group than in the other two groups. In groups intravenously injected with A549 cells, there were tumor nodules in all groups, and the 1 × 105 cells/mL group showed longer survival time than the other two groups without any distant organ metastasis. There were tumor nodules formed in the liver in the 1 × 106 cells/mL group at 14 d. Together, our results demonstrated that 5 × 106 cells/mL and 1 × 105 cells/mL are the optimal cell concentrations for the subcutaneous and experimental metastatic models, respectively.

In situ measurement of the topological charge of a perfect vortex using the phase shift method.

We propose a method to determine the topological charge (TC) of a perfect vortex. With the phase shift technique, the perfect vortex and its conjugate beam exactly overlap and interfere. Consequently, the TC of a perfect vortex is determined by counting the number of interference fringes. This proposed method enables in situ determination of the TC of the perfect vortex without the need for additional optical elements, and it is immune to environmental vibration and parasitic interference.

Polarization-dependent effects of an Airy beam due to the spin-orbit coupling.

We investigate the polarization-dependent effects when a circularly polarized Airy beam propagates in an inhomogeneous medium. It shows that there are some interesting polarization-dependent phenomena induced by the spin-orbit coupling: the circularly polarized Airy beam will follow a polarization-dependent trajectory in an inhomogeneous medium, and there are the polarization-dependent self-acceleration of the Airy beam in the linear-index inhomogeneous medium and the polarization-dependent rotation of the Airy beam in the quadratic-index inhomogeneous medium. These polarization-dependent phenomena are different from the manifestation of the "traditional" spin Hall effect of a light beam, which just displays the polarization-dependent transverse deflection of the beam.

[Research on Temporal and Spatial Evolution of Reheating Double-Pulse Laser-Induced Plasma].

In order to investigate the emission enhancement mechanisms of reheating Double Pulse Laser-Induced Breakdown Spectroscopy (DP-LIBS), single pulse LIBS (SP-LIBS) and reheating DP-LIBS were carried out on an alloy steel sample respectively. The plasma emission was collected by an Echelle spectrometer with high resolution, while the plasma structure was monitored via fast-photography. The temporal and spatial evolutio ns of the plasma generated by SP-LIBS and reheating DP-LIBS were being studied. It is found that the plasma temperature in reheating DP-LIBS was higher than that of SP-LIBS, and there was a turning point for the decay rate of plasma temperature in reheating DP-LIBS when the delay time was equal to the interpulse time of DP-LIBS. Moreover, the inte nsity of the plasma image was increased by reheating DP-LIBS, and the height and width of the central region of the plasma were increased about 23.5% and 15.1% respectively. The results of spatial distribution showed that the intensity of Fe II and N I lines in the plasma were obviously enhanced by reheating DP-LIBS when the distance from the sample surface was larger than 0.6 mm. While the intensity enhancement for Fe I lines were little, even in some positio ns the intensity of Fe I lines decreased. The plasma temperature of double-pulse configuration was about 2 000 K higher than that of SP-LIBS, and a larger hot region in the plasma was generated. It is evidenced that the emission enhancement mechanisms in reheating DP-LIBS is that the second laser pulse re-excited the plasma induced by the first laser pulse, and the higher plasma temperature resulted from the re-exciting process.

[Research on algorithm for self-absorption correction based on multi-particles LIBS spectra].

In order to overcome the influence of self-absorption on quantitative analysis, the optimizing process of very fast simulated annealing algorithm was studied. According to basic theory of plasma emission spectrum, a new algorithm for self-absorpton correction based on multi-particles spectra was proposed, and the algorithm flowchart was given. With the self-absorption correction algorithm mentioned above, the spectra of refining slag and blast furnace slag were corrected. The effect of self-ab sorption correction on the quantitative analysis results was analyzed based on calibration free method. Comparison of Boltzmann plots before and after self-absorption correction indicated that the plasma temperatures calculated with spectra after self-absorption correction tended to be uniform, and remained stable around 11,600 K. The Boltzmann plots constructed with plasma spectra of the same particle after self-absorption correction indicated that the intercepts were almost the same except for one group data. With calibration free method and spectra after self-absorption correction, the contents of components in slag were analyzed. For refining slag, quantitative analysis precision of MgO was low. If ignoring the existence of MgO, the relative errors of quantitative analysis results of CaO, Al2 O3 and SiOs were much smaller. For blast furnace slag in which the content of MgO was 8.49%, the relative error of quantitative analysis result of Al2 O3 was 2.38%, which was the smallest. And the relative error of quantitative analysis result of MgO was 28.27%, which was still the biggest.

[A multivariate nonlinear model for quantitative analysis in laser-induced breakdown spectroscopy].

Most quantitative models used in laser-induced breakdown spectroscopy (LIBS) are based on the hypothesis that laser-induced plasma approaches the state of local thermal equilibrium (LTE). However, the local equilibrium is possible only at a specific time segment during the evolution. As the populations of each energy level does not follow Boltzmann distribution in non-LTE condition, those quantitative models using single spectral line would be inaccurate. A multivariate nonlinear model, in which the LTE is not required, was proposed in this article to reduce the signal fluctuation and improve the accuracy of quantitative analysis. This multivariate nonlinear model was compared with the internal calibration model which is based on the LTE condition. The content of Mn in steel samples was determined by using the two models, respectively. A minor error and a minor relative standard deviation (RSD) were observed in multivariate nonlinear model. This result demonstrates that multivariate nonlinear model can improve measurement accuracy and repeatability.

Mecp2 Deficiency in Peripheral Sensory Neuron Improves Cognitive Function by Enhancing Hippocampal Dendritic Spine Densities in Mice.

Methyl-CpG-binding protein 2 (Mecp2) is an epigenetic modulator and numerous studies have explored its impact on the central nervous system manifestations. However, little attention has been given to its potential contributions to the peripheral nervous system (PNS). To investigate the regulation of Mecp2 in the PNS on specific central regions, we generated Mecp2fl/flAdvillincre mice with the sensory-neuron-specific deletion of the Mecp2 gene and found the mutant mice had a heightened sensitivity to temperature, which, however, did not affect the sense of motion, social behaviors, and anxiety-like behavior. Notably, in comparison to Mecp2fl/fl mice, Mecp2fl/flAdvillincre mice exhibited improved learning and memory abilities. The levels of hippocampal synaptophysin and PSD95 proteins were higher in Mecp2fl/flAdvillincre mice than in Mecp2fl/fl mice. Golgi staining revealed a significant increase in total spine density, and dendritic arborization in the hippocampal pyramidal neurons of Mecp2fl/flAdvillincre mice compared to Mecp2fl/fl mice. In addition, the activation of the BDNF-TrkB-CREB1 pathway was observed in the hippocampus and spinal cord of Mecp2fl/flAdvillincre mice. Intriguingly, the hippocampal BDNF/CREB1 signaling pathway in mutant mice was initiated within 5 days after birth. Our findings suggest a potential therapeutic strategy targeting the BDNF-TrkB-CREB1 signaling pathway and peripheral somasensory neurons to treat learning and cognitive deficits associated with Mecp2 disorders.

Optogenetic Activation of Peripheral Somatosensory Neurons in Transgenic Mice as a Neuropathic Pain Model for Assessing the Therapeutic Efficacy of Analgesics.

Optogenetics is a novel biotechnology widely used to precisely manipulate a specific peripheral sensory neuron or neural circuit. However, the use of optogenetics to assess the therapeutic efficacy of analgesics is elusive. In this study, we generated a transgenic mouse stain in which all primary somatosensory neurons can be optogenetically activated to mimic neuronal hyperactivation in the neuropathic pain state for the assessment of analgesic effects of drugs. A transgenic mouse was generated using the advillin-Cre line mated with the Ai32 strain, in which channelrhodopsin-2 fused to enhanced yellow fluorescence protein (ChR2-EYFP) was conditionally expressed in all types of primary somatosensory neurons (advillincre/ChR2+/+). Immunofluorescence and transdermal photostimulation on the hindpaws were used to verify the transgenic mice. Optical stimulation to evoke pain-like paw withdrawal latency was used to assess the analgesic effects of a series of drugs. Injury- and pain-related molecular biomarkers were investigated with immunohistofluorescence. We found that the expression of ChR2-EYFP was observed in many primary afferents of paw skin and sciatic nerves and in primary sensory neurons and laminae I and II of the spinal dorsal horns in advillincre/ChR2+/+ mice. Transdermal blue light stimulation of the transgenic mouse hindpaw evoked nocifensive paw withdrawal behavior. Treatment with gabapentin, some channel blockers, and local anesthetics, but not opioids or COX-1/2 inhibitors, prolonged the paw withdrawal latency in the transgenic mice. The analgesic effect of gabapentin was also verified by the decreased expression of injury- and pain-related molecular biomarkers. These optogenetic mice provide a promising model for assessing the therapeutic efficacy of analgesics in neuropathic pain.

Weak Metal-Support Interaction over CuO/TiO2 Catalyst Governed Low-Temperature Toluene Oxidation.

Regulating the metal-support interaction is essential for obtaining highly efficient catalysts for the catalytic oxidation of volatile organic compounds (VOCs). In this work, CuO-TiO2(coll) and CuO/TiO2(imp) with different metal-support interactions were prepared via colloidal and impregnation methods, respectively. The results demonstrated that CuO/TiO2(imp) has higher low-temperature catalytic activity, with a 50% removal of toluene at 170 °C compared to CuO-TiO2(coll). Additionally, the normalized reaction rate (6.4 × 10-6 mol·g-1·s-1) at 160 °C over CuO/TiO2(imp) was almost four-fold higher than that over CuO-TiO2(coll) (1.5 × 10-6 mol·g-1·s-1), and the apparent activation energy value (27.9 ± 2.9 kJ·mol-1) was lower. Systematic structure and surface analysis results disclosed that abundant Cu2+ active species and numerous small CuO particles were presented over CuO/TiO2(imp). Owing to the weak interaction of CuO and TiO2 in this optimized catalyst, the concentration of reducible oxygen species associated with the superior redox property could be enhanced, thus significantly contributing to its low-temperature catalytic activity for toluene oxidation. This work is helpful in exploring the influence of metal-support interaction on the catalytic oxidation of VOCs and developing low-temperature catalysts for VOCs catalytic oxidation.

Corrigendum: Antimicrobial resistance and genomic characterization of Escherichia coli from pigs and chickens in Zhejiang, China.

[This corrects the article DOI: 10.3389/fmicb.2022.1018682.].