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Vibrio parahaemolyticus is a moderately halophilic foodborne pathogen that is mainly distributed in marine and freshwater environments. The transition of V. parahaemolyticus between aquatic ecosystems and hosts is essential for infection. Both freshwater and host environments have low salinity. In this study, we sought to further investigate the effects of low salinity (0.5% NaCl) on the fitness and virulence of V. parahaemolyticus. We found that V. parahaemolyticus could survive in Luria–Bertani (LB) and M9 mediums with different NaCl concentrations, except for the M9 medium containing 9% NaCl. Our results further showed that V. parahaemolyticus cultured in M9 medium with 0.5% NaCl had a higher cell density than that cultured at other NaCl concentrations when it entered the stationary phase. Therefore, we compared the transcriptomes of V. parahaemolyticus wild type (WT) cultured in an M9 medium with 0.5% and 3% NaCl at the stationary phase using RNA-seq. A total of 658 genes were significantly differentially expressed in the M9 medium with 0.5% NaCl, including regulators, osmotic adaptive responses (compatible solute synthesis systems, transporters, and outer membrane proteins), and virulence factors (T3SS1 and T6SS1). Furthermore, a low salinity concentration in the M9 medium induced the expression of T3SS1 to mediate the cytotoxicity of V. parahaemolyticus to HeLa cells. Similarly, low salinity could also induce the secretion of the T3SS2 translocon protein VPA1361. These factors may result in the high pathogenicity of V. parahaemolyticus in low-salinity environments. Taken together, these results suggest that low salinity (0.5% NaCl) could affect gene expression to mediate fitness and virulence, which may contribute to the transition of V. parahaemolyticus between aquatic ecosystems and the host. [ABSTRACT FROM AUTHOR]

A novel mid-infrared Ge20Sb15Se65 chalcogenide-based single-polarization single-mode (SPSM) photonic crystal fiber (PCF) with rectangular latticed circular air holes is proposed. The properties of SPSM bandwidth, confinement loss, and nonlinearity are analyzed in the 3 μm~8 μm mid-infrared region using the finite -difference time-domain (FDTD) method. The influences of different geometrical parameters on the properties of SPSM-PCF are analyzed. All numerical computational results reveal that for the optimized geometrical parameters, the proposed PCF can deliver a SPSM region of more than 2.3814 μm with high nonlinearity of 3,705 w−1 km−1. Therefore, such a SPSM-PCF will become an excellent candidate for mid-infrared photonic. [ABSTRACT FROM AUTHOR]

We propose a mid-infrared dual-rhombic air hole hexagonal lattice photonic crystal fiber with high birefringence and large nonlinearity based on Ge 20 Sb 15 Se 65 chalcogenide glass. The properties of birefringence, dispersion, nonlinearity, and confinement loss were investigated in the 3 µm~5 µm mid-infrared range by using the Finite Difference Time Domain (FDTD) method with perfectly matched layer (PML) absorption boundary conditions. The results indicate that for the optimized structural parameters of Λ = 2.0 µm, D = 1.932 µm, d = 0.8 µm, and H = 0.8 µm, an ultrahigh birefringence of 0.041, a very low confinement loss of 0.0013 dB/km (for x -polarization modes) and 0.0342 dB/km (for y -polarization modes), and the maximum nonlinearity coefficient of 4375 w −1 km −1 (for x -polarization modes) and 3960 w −1 km −1 (for y -polarization modes) were achieved, respectively. The proposed PCF has a lower confinement loss and higher birefringence than an elliptical-hole PCF with the same air-filling fraction. Thus, it will be an excellent candidate for mid-infrared optical fiber sensing, precision optical instruments and nonlinear optics. [ABSTRACT FROM AUTHOR]

A novel high birefringence As2Se3-based hexagonal lattice photonic crystal fiber (PCF) is proposed. In the structure, a central defect core and three kinds of elliptical air holes with different major axes length and ellipticity are introduced in the cladding. The finite difference time domain (FDTD) method with perfectly matched layer (PML) absorption boundary conditions are used to simulate the guided modes of the designed PCF. The properties of this PCF are investigated in detail including the birefringence, beat length, dispersion, nonlinearity and polarization mode dispersion in the 2-5 mid-infrared range. The results show that for the optimized structure parameters of , , , , , , , the high birefringence of 0.1192 and beat length of 41.93 are obtained. The maximum nonlinearity coefficient of 10,050 wkm and 15,200 wkm for x- and y-polarization modes are achieved. The distinctive dispersion is analyzed, which is all-normal in x-polarization direction while it has two zero dispersion points at 3.18 and 3.65 in y-polarization direction. The designed PCF with high birefringence, large nonlinearity and distinctive dispersion will be beneficial for mid-infrared fiber sensing, mid-infrared spectroscopy and nonlinear optics applications. [ABSTRACT FROM AUTHOR]

A high birefringence Ge20Sb15Se65based photonic crystal fiber (PCF) is proposed. It consists of a central defect core surrounded by two kinds of elliptical air holes with different size. The Finite Difference Time Domain method (FDTD) is used to simulate the guided modes of the designed PCF. The properties of this PCF are investigated including the birefringence, nonlinearity, and polarization mode dispersion in the mid-infrared range. The results show that for the optimized structure parameters, the highest birefringence of 0.1176 is obtained. The maximum nonlinearity coefficients of 38390 w−1km−1and 49760 w−1km−1forx- andy-polarization modes are achieved. [ABSTRACT FROM AUTHOR]

Land resources not only provide support for urban development, but play a feedback and restricting role in unregulated urban growth. Taking Beijing City as an example, this paper analyzes supply and demand relationships and upper limits for the growth of land resources during the process of urban development. By analyzing dominant factors and trends in the demand for land resources, this paper gives preliminary estimates on the minimum size of the land demand in Beijing in view of constructing a World City. According to the basic characteristics of supply and demand relationships for land, current land use in Beijing is confronting a grim situation of conflict between supply and demand. We also point out maximum growth and three types of constraints on land resources. Last, we propose solutions to resource and environmental bottlenecks, and urban disease amid urban development. [ABSTRACT FROM AUTHOR]

This paper proposes a mid-infrared (mid-IR) Ge 20 Sb 15 Se 65 -based photonic crystal fiber (PCF) with hexagonally latticed dual-rhombic air holes to deliver single-polarization single-mode (SPSM) over a broad waveband. The properties of SPSM bandwidth, confinement loss, birefringence, effective mode area and nonlinear coefficient are investigated in 2 μm–7 μm region by utilizing the finite difference time domain method (FDTD) together with anisotropic perfectly matched layer (PML). The results reveal that for the optimized geometric parameters of Λ = 2.6 μm, D = 2.4 μm, d = 1.2 μm, D 1 = 2.2 μm, and d 1 = 0.4 μm, the proposed PCF is a low-loss SPSM-PCF within the wavelengths ranging from 4.0338 μm to 7 μm, where only the x -polarization mode exists with the highest nonlinearity coefficient of 1468 w−1 km-1 (at 4.0338 μm). It will become an outstanding candidate for mid-IR optical fiber sensing/detection/ imaging/monitoring and nonlinear fiber optics. [ABSTRACT FROM AUTHOR]

Vibrio parahaemolyticus is an increasingly important foodborne pathogen that cause acute gastroenteritis in humans. However, the prevalence and transmission of this pathogen in freshwater food remains unclear. This study aimed to determine the molecular characteristics and genetic relatedness of V. parahaemolyticus isolates obtained from freshwater food, seafood, environmental, and clinical samples. A total of 138 (46.6%) isolates were detected from 296 food and environmental samples, and 68 clinical isolates from patients. Notably, V. parahaemolyticus was more prevalent in freshwater food (56.7%, 85/150) than in seafood (38.8%, 49/137). Virulence phenotype analyses revealed that the high motility of isolates from freshwater food (40.0%) and clinical isolates (42.0%) was higher than that of isolates from seafood (12.2%), whereas the biofilm-forming capacity of freshwater food isolates (9.4%) was lower than that of seafood (22.4%) and clinical isolates (15.9%). Virulence genes analysis showed that 46.4% of the clinical isolates contained the tdh gene encoding thermostable direct hemolysin (TDH) and only two freshwater food isolates contained the trh gene encoding TDH-related hemolysin (TRH). Multilocus sequence typing (MLST) analysis divided the 206 isolates into 105 sequence types (STs), including 56 (53.3%) novel STs. ST2583, ST469, and ST453 have been isolated from freshwater food and clinical samples. Whole-genome sequence (WGS) analyses revealed that the 206 isolates were divided into five clusters. Cluster II contained isolates from freshwater food and clinical samples, whereas the other clusters contained isolates from seafood, freshwater food, and clinical samples. In addition, we observed that ST2516 had the same virulence pattern, with a close phylogenetic relationship to ST3. The increased prevalence and adaption of V. parahaemolyticus in freshwater food is a potential cause of clinical cases closely related to the consumption of V. parahaemolyticus contaminated freshwater food. • The high prevalence of Vibrio parahaemolyticus in the freshwater food. • A specific clonal populations of V. parahaemolyticus strains isolated from freshwater food. • The potential transmission of V. parahaemolyticus from freshwater food to humans. [ABSTRACT FROM AUTHOR]