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Fiber combiner is an effective device to enhance the power level or broaden the spectral wavelengths through a single monolithic output aperture, by fusing multiple fibers together. This is particularly important in mid‐infrared (MIR) 2–5 µm range, in which the output power of a single laser is limited. Due to the high MIR transmission, chalcogenide glass is an ideal host for constructing MIR fiber combiner. In this study, we report the design, fabrication, and characterization of a homemade 3 × 1 chalcogenide glass fiber combiner. The fiber combiner includes a 3 × 1 As–S input fiber bundle and an output fiber. The input fiber bundle was made by tapering three As–S multimode fibers with a core diameter of 200 µm and a cladding diameter of 250 µm. The taper reduction ratio R was 2, and the length of the taper transition region was ∼2 cm. The output fiber with core diameter of 360 µm and cladding diameter of 570 µm was then spliced with the tapered end of the fiber bundle. The total length of the combiner was ∼53 cm. The measurement of power combination at 4.56 µm indicated that the transmission efficiency of three ports reached 80%, whereas the power combining efficiency of the combiner was measured to be ∼48%. In addition, efficient wavelength combining over one octave has been demonstrated, by launching three different lasers at 2.1, 3.39, and 4.56 µm through the 3 × 1 combiner. It proves that chalcogenide fiber combiner is promising for the applications of high‐level power combination and broadband wavelength combining in MIR 2–5 µm range. [ABSTRACT FROM AUTHOR]

As one of the most sensitive regions to global climate change, alpine tundra in many places around the world has been undergoing dramatic changes in vegetation communities over the past few decades. Herbaceous plant species in the Changbai Mountains area have significantly expanded into tundra shrub communities over the past 30 yr. Soil microbial communities, enzyme activities, and soil nutrients are intertwined with this expansion process. In order to understand the responses of the soil microbial communities to such an expansion, we analyzed soil microbial community structures and enzyme activities in shrub tundra as well as areas with three different levels of herbaceous plant expansion. Our investigation was based on phospholipid fatty acid (PLFA) analysis and 96-well microtiter plates. The results showed that herbs have expanded greatly in the tundra, and they have become the dominant species in herbaceous plant expansion areas. There were differences for community composition and appearance among the shrub tundra and the mild expansion, moderate expansion, and severe expansion areas. Except for soil organic matter, soil nutrients were increased in herbaceous plant expansion areas, and the total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), and available phosphorus (AP) were greatest in moderate expansion areas (MOE), while soil organic matter levels were highest in the non-expanded areas (CK). The total soil PLFAs in the three levels of herbaceous plant expansion areas were significantly higher than those in the non-expanded areas, and total soil PLFAs were highest in the moderately expanded area and lowest in the severely expanded area (SEE). Bacteria increased significantly more than fungi and actinomycetes with herbaceous plant expansion. Soil hydrolase activities (β-1,4-glucosidase (βG) activity, β-1, 4-N-acetylglucosaminidase (NAG) activity, and acid phosphatase (aP) activity) were highest in MOE and lowest in the CK treatment. Soil oxidase activities (polyphenol oxidase (PPO) activities and peroxidase (PER) activities) were also highest in MOE, but they were lowest in the SEE treatment. The variations in total soil PLFAs with herbaceous plant expansion were mostly correlated with soil organic matter and available phosphorus concentrations, while soil enzyme activities were mostly correlated with the total soil nitrogen concentration. Our results suggest that herbaceous plant expansion increase the total soil PLFAs and soil enzyme activities and improved soil nutrients. However, soil microorganisms, enzyme activity, and nutrients responded differently to levels of herbaceous plant expansion. The soil conditions in mild and moderate expansion areas are more favorable than those in severe expansion areas. [ABSTRACT FROM AUTHOR]

Neurotransmitters are essential for interneuronal signalling, and the specification of appropriate transmitters in differentiating neurons has been related to intrinsic neuronal identity and to extrinsic signalling proteins. Here we show that altering the distinct patterns of Ca2+ spike activity spontaneously generated by different classes of embryonic spinal neurons in vivo changes the transmitter that neurons express without affecting the expression of markers of cell identity. Regulation seems to be homeostatic: suppression of activity leads to an increased number of neurons expressing excitatory transmitters and a decreased number of neurons expressing inhibitory transmitters; the reverse occurs when activity is enhanced. The imposition of specific spike frequencies in vitro does not affect labels of cell identity but again specifies the expression of transmitters that are inappropriate for the markers they express, during an early critical period. The results identify a new role of patterned activity in development of the central nervous system. [ABSTRACT FROM AUTHOR]