A pulse prototype of a W-band TE01 mode gyrotron traveling-wave tube (gyro-TWT) amplifier is designed, and it features high gain and broadband capabilities. The TE01 mode input coupler is constructed by mounting a sapphire pill-box window onto a Y-type mode converter. The high power output window will employ a triple-sapphire-disc configuration to achieve return loss lower than -30 dB over a bandwidth of 8 GHz. To suppress the spurious oscillations and realize high-average power potential, a new lossy ceramic material with weak electric conductivity is loaded in the TE01 mode cylindrical interaction waveguide. The loss-free output taper is carefully optimized to suppress oscillations and maintain broadband amplification. Employing a magnetic injection gun of beam voltage 70 kV, beam current 3 A, pitch factor 1.5, and axial-velocity spread 5%, theoretical investigation predicts that the gyro-TWT amplifier is of excellent performance, which includes being driven to saturation with input power Pin <; 0.4 W, highest efficiency of 32.4%, and the bandwidth of 4.2 GHz with output power exceeding 50 kW.
Trifluoroacetic acid (TFA) were determined in air samples by a sampling device composed of annular denuders coupled with a quartz filter, which was efficient for the collection and separation of gaseous and particulate TFA. Gaseous TFA was performed by means of annular denuders coated with alkaline solution, while particulate TFA was absorbed by quartz filters. TFA can be determined by gas chromatography-mass spectrometer after derivatizated with 2,4-difluoroaniline. Calibration curves were linear with correlation coefficients of 0.9991. Detection limit of TFA was 66 ng L−1, which was 31 pg m−3 when sampling volume was 48 m3. Recoveries of the TFA sampling device ranged from 98% to 105% with relative standard deviation (RSD) ≤ 3%. The developed method was applied to the determination of TFA in atmosphere samples collected in Peking University in Beijing in 2012. Total TFA concentrations ranged from 501 to 7447 pg m−3. Concentrations of gaseous TFA were significantly higher than those of particulate, and the gas-particle partition coefficient of TFA decreased as air temperature rose.
An asymmetric T-shape nanoslit in a metal film is proposed to act as an efficient dichroic surface-plasmon-polariton (SPP) splitter, which is composed of a single nanoslit in immediate contacting with two nanogrooves with different widths. Simulations show that, due to the interferences of SPPs in the upper part of the asymmetric T-shape nanoslit, the generated SPPs propagating to the left and right directions on the front metal surface can be manipulated nearly independently by altering the right and left groove widths, respectively. Based on such effects, a dichroic SPP splitter is demonstrated and the splitting wavelengths can easily be adjusted. High splitting ratios of 31: 1 and 1: 12 at splitting wavelengths of 680 nm and 884 nm are numerically presented with a device's lateral dimension of only 1200 nm. Further experimental results match the simulations well. (C)2013 Optical Society of America
Mobilization of Arctic permafrost carbon is expected to increase with warming-induced thawing. However, this effect is challenging to assess due to the diverse processes controlling the release of various organic carbon (OC) pools from heterogeneous Arctic landscapes. Here, by radiocarbon dating various terrestrial OC components in fluvially and coastally integrated estuarine sediments, we present a unique framework for deconvoluting the contrasting mobilization mechanisms of surface vs. deep (permafrost) carbon pools across the climosequence of the Eurasian Arctic. Vascular plant-derived lignin phenol 14C contents reveal significant inputs of young carbon from surface sources whose delivery is dominantly controlled by river runoff. In contrast, plant wax lipids predominantly trace ancient (permafrost) OC that is preferentially mobilized from discontinuous permafrost regions, where hydrological conduits penetrate deeper into soils and thermokarst erosion occurs more frequently. Because river runoff has significantly increased across the Eurasian Arctic in recent decades, we estimate from an isotopic mixing model that, in tandem with an increased transfer of young surface carbon, the proportion of mobilized terrestrial OC accounted for by ancient carbon has increased by 3–6% between 1985 and 2004. These findings suggest that although partly masked by surface carbon export, climate change-induced mobilization of old permafrost carbon is well underway in the Arctic.