Use of optical superbeams in atmospheric turbulence applications

The use of nonconventional beam classes in turbulence applications is investigated. Through the study on pseudo-Bessel correlated beam propagation in the atmosphere, it is shown that scintillation reduction by a partially coherent beam can be obtained by a corresponding incoherent beam array with finite number of beamlets. General guidelines for scintillation reduction by incoherent beam arrays are developed; these guidelines include reducing correlation of beamlet atmospheric propagation, maximizing the total intensity arriving at the detector, and selecting beamlets with small scintillation. With these goals in mind, Airy beams, a novel beam class, are applied to generate an incoherent beam array whose scintillations are significantly reduced. By the analogy with two-mode partially coherent beams, nonuniformly polarized beams are demonstrated to be of small scintillation. This suggests a relatively easy and inexpensive method to reduce the scintillation of a coherent optical beam. Finally a method to measure atmospheric turbulence strength by using vortex beams is proposed and its feasibility is theoretically demonstrated

Anomalous enhancement of mechanical properties in the ammonia adsorbed defective graphene

Pure graphene is known as the strongest material ever discovered. However, the unavoidable defect formation in the fabrication process renders the strength of defective graphene much lower (~14%) than that of its perfect counterpart. By means of density functional theory computations, we systematically explored the effect of gas molecules (H2, N2, NH3, CO, CO2 and O2) adsorption on the mechanical strength of perfect/defective graphene. The NH3 molecule is found to play a dominant role in enhancing the strength of defective graphene by up to ~15.6%, while other gas molecules decrease the strength of graphene with varying degrees. The remarkable strength enhancement can be interpreted by the decomposition of NH3, which saturates the dangling bond and leads to charge redistribution at the defect site. The present work provides basic information for the mechanical failure of gas-adsorbed graphene and guidance for manufacturing graphene-based electromechanical devices

The Stimulative Effect of Yangjing Capsule on Testosterone Synthesis through Nur77 Pathway in Leydig Cells

Yangjing Capsule (YC), an innovative Chinese medicine based on traditional prescription, promotes testosterone synthesis by upregulating the expression of steroidogenic enzymes. Nur77 as a nuclear receptor is known to regulate the expression of many steroid synthetases. This study aimed to explore the potential mechanisms by which YC regulates testosterone synthesis in Leydig cells. Real-time PCR and Western blot analysis were employed to assess the expressions of steroidogenic enzymes and Nur77 after treating MLTC-1 cells with YC. The luciferase reporter gene assay was performed to detect the activity of Nur77 gene promoter. Also, the expressions of steroid synthases were detected after Nur77 gene was knocked down. YC significantly stimulated Nur77 production and upregulated StAR and HSD3B expression, and this agrees with the activity of Nur77 gene promoter that was significantly enhanced by YC. Interestingly, knockdown of Nur77 blocked the above YC’s effects and consequently inhibited testosterone synthesis in MLTC-1 cells. YC promotes StAR and HSD3B expression and upregulates testosterone synthesis in Leydig cells, which is mediated by Nur77 pathway

Scintillation of nonuniformly correlated beams in atmospheric turbulence

We investigated the scintillation properties of nonuniformly correlated (NUC) beams in atmospheric turbulence and have shown that NUC beams can not only have lower scintillation but also higher intensity than Gaussian-Schell model beams and even higher intensity than coherent Gaussian beams over certain propagation distances

Scintillation of Nonuniformly Polarized Beams in Atmospheric Turbulence

We demonstrate, through numerical simulations, that an appropriately chosen nonuniformly polarized coherent optical field can have appreciably smaller scintillation than comparable beams of uniform polarization. This results from the fact that a nonuniformly polarized field acts as an effective two-mode partially coherent field. The results described here are of direct relevance to the development of free-space optical communication systems.</p

Single layer bismuth iodide: Computational exploration of structural, electrical, mechanical and optical properties

Layered graphitic materials exhibit new intriguing electronic structure and the search for new types of two-dimensional (2D) monolayer is of importance for the fabrication of next generation miniature electronic and optoelectronic devices. By means of density functional theory (DFT) computations, we investigated in detail the structural, electronic, mechanical and optical properties of the single-layer bismuth iodide (BiI3) nanosheet. Monolayer BiI3 is dynamically stable as confirmed by the computed phonon spectrum. The cleavage energy (Ecl) and interlayer coupling strength of bulk BiI3 are comparable to the experimental values of graphite, which indicates that the exfoliation of BiI3 is highly feasible. The obtained stress-strain curve shows that the BiI3 nanosheet is a brittle material with a breaking strain of 13%. The BiI3 monolayer has an indirect band gap of 1.57 eV with spin orbit coupling (SOC), indicating its potential application for solar cells. Furthermore, the band gap of BiI3 monolayer can be modulated by biaxial strain. Most interestingly, interfacing electrically active graphene with monolayer BiI3 nanosheet leads to enhanced light absorption compared to that in pure monolayer BiI3 nanosheet, highlighting its great potential applications in photonics and photovoltaic solar cells

Polymorphism of low dimensional boron nanomaterials driven by electrostatic gating: A computational discovery

The successful synthesis of two-dimensional (2D) boron sheets typically relies on the utilization of a silver surface, which acts as a gated substrate compensating for the electron-deficiency of boron. However, how the structures of one-dimensional (1D) boron are affected by the gating effect remains unclear. By means of an unbiased global minimum structure search and density functional theory (DFT) computations, we discovered the coexistence of 2D boron sheets and 1D ribbons triggered by electrostatic gating. Specifically, at a low excess charge density level (0.3 e per atom), more 1D boron ribbons emerge, while the number of 2D layers is reduced. Additionally, a number of low-lying 1D boron ribbons were discovered, among which a flat borophene-like ribbon (FBR) was predicted to be stable and possess high mechanical strength. Moreover, the electride Ca2N was identified as an ideal substrate for the fabrication of the FBR because of its ability to supply a strong electrostatic field. This work bridges the gap between 2D and 1D boron structures, reveals the polymorphism of 1D boron ribbons under the electrostatic gating effect, and in general provides broad implications for future synthesis and applications of low-dimensional boron materials.</p

Elimination of Artificial Bright Pixels in VIIRS DNB Nighttime IMage over the South Atlantic Anomaly Region

The Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB) is a panchromatic visible and near-infrared band capable of quantitative measurement of light radiances from 3×10-9 W∙cm-2∙sr-1 to 2×10-2 W∙cm-2∙sr-1. Its extreme sensitivity of the HGS to low lights, together with the nearly constant spatial resolution over the whole swath, enables numerous applications of environmental remote sensing and global monitoring of anthropogenic activities in nighttime. However, the DNB is susceptible to high energy particles (HEPs) hitting over the South Atlantic Anomaly (SAA) region. Although a special algorithm was designed to filter out high radiance pixels induced by HEPs, large amount of artificial bright pixels are still observed in the generated DNB nighttime images, leaving obstacles for several image based applications, such as automatic fishing boat detection over the SAA region. In this study, we investigated DNB nighttime images over the SAA region. It has been shown that the DNB gain selection logic is the possible root cause for the isolated bright pixels in DNB nighttime images over the SAA region. This result was confirmed by a recent DNB special data acquisition over the SAA region. With the knowledge acquired from the analysis of root cause, we explored method to eliminate artificial bright pixels induced by the HEPs over the SAA region. Our method could improve the DNB nighttime image quality over the SAA region and potentially benefits monitoring of anthropogenic activities in nighttime over that region