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  • 1
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    Terahertz electron cyclotron maser interactions with an axis-encircling electron beam (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-04-11
    Description: To generate terahertz radiation via the electron cyclotron maser instability, harmonic interactions are essential in order to reduce the required magnetic field to a practical value. Also, high-order mode operation is required to avoid excessive Ohmic losses. The weaker harmonic interaction and mode competition associated with an over-moded structure present challenging problems to overcome. The axis-encircling electron beam is a well-known recipe for both problems. It strengthens the harmonic interaction, as well as minimizing the competing modes. Here, we examine these advantages through a broad data base obtained for a low-power, step-tunable, gyrotron oscillator. Linear results indicate far more higher-harmonic modes can be excited with an axis-encircling electron beam than with an off-axis electron beam. However, multi-mode, time-dependent simulations reveal an intrinsic tendency for a higher-harmonic mode to switch over to a lower-harmonic mode at a high beam current or upon a rapid current rise. Methods are presented to identify the narrow windows in the parameter space for stable harmonic interactions.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Tuning from failed superconductor to failed insulator with magnetic field (2019)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2019
    Description: 〈p〉Do charge modulations compete with electron pairing in high-temperature copper oxide superconductors? We investigated this question by suppressing superconductivity in a stripe-ordered cuprate compound at low temperature with high magnetic fields. With increasing field, loss of three-dimensional superconducting order is followed by reentrant two-dimensional superconductivity and then an ultraquantum metal phase. Circumstantial evidence suggests that the latter state is bosonic and associated with the charge stripes. These results provide experimental support to the theoretical perspective that local segregation of doped holes and antiferromagnetic spin correlations underlies the electron-pairing mechanism in cuprates.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    Superconductivity in 4 angstrom single-walled carbon nanotubes (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-06-30
    Description: Investigation of the magnetic and transport properties of single-walled small-diameter carbon nanotubes embedded in a zeolite matrix revealed that at temperatures below 20 kelvin, 4 angstrom tubes exhibit superconducting behavior manifest as an anisotropic Meissner effect, with a superconducting gap and fluctuation supercurrent. The measured superconducting characteristics display smooth temperature variations owing to one-dimensional fluctuations, with a mean-field superconducting transition temperature of 15 kelvin. Statistical mechanic calculations based on the Ginzburg-Landau free-energy functional yield predictions that are in excellent agreement with the experiments.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Tang, Z K -- Zhang, L -- Wang, N -- Zhang, X X -- Wen, G H -- Li, G D -- Wang, J N -- Chan, C T -- Sheng, P -- New York, N.Y. -- Science. 2001 Jun 29;292(5526):2462-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics and Institute of Nano Science and Technology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11431560" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Real-time simulation of large-scale floods (2016)
    Institute of Physics (IOP)
    Details
    Publication Date: 2016-09-03
    Description: According to the complex real-time water situation, the real-time simulation of large-scale floods is very important for flood prevention practice. Model robustness and running efficiency are two critical factors in successful real-time flood simulation. This paper proposed a robust, two-dimensional, shallow water model based on the unstructured Godunov- type finite volume method. A robust wet/dry front method is used to enhance the numerical stability. An adaptive method is proposed to improve the running efficiency. The proposed model is used for large-scale flood simulation on real topography. Results compared to those of MIKE21 show the strong performance of the proposed model.
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
    Published by Institute of Physics (IOP)
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  • 5
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    The effect of different particle diameters on waste submersible motor-pump's two-phase flows (2013)
    Institute of Physics (IOP)
    Details
    Publication Date: 2013-12-22
    Description: Dispersed turbulence model in Euler model was employed to analyze liquid-solid two-phase flow for a WQ87-28-15 waste submersible motor-pump. The comparisons between the results indicated that the pressure of outlet, the absolute velocity of fluid and the turbulent intensity of vent are in direct proportion to the diameter when the diameter is smaller than 4mm; otherwise, they will go up. The head declined until the diameter of the particle reached 1mm, and efficiency fell while the particle diameter was increasing, but it was fixed and even rose when the diameter was between 1mm to 20mm; It inferred that it has a right area of the diameter when the waste submersible motor-pump operated, and the maximum diameter of particles can be gained.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 6
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    Analysis on the blade inlet pressure fluctuation of the centrifugal pump based on LES (2013)
    Institute of Physics (IOP)
    Details
    Publication Date: 2013-12-22
    Description: In order to study the characteristics of the blade inlet pressure fluctuation under unsteady flow in centrifugal pump, a three-dimensional model of a pump n s =50 was built. Based on large eddy simulation (LES), the inner flow field of the pump was simulated by the flow field simulation software Fluent in design condition and off-design conditions. The pressure fluctuation of the monitored points was obtained at the blade suction surface and pressure surface at impeller inlet, which was analyzed by time and frequency domain with Fast Fourier Transformation (FFT). The results show that the pressure fluctuation of inlet and outlet in large flow rate is more obvious than low flow rate. It is easily found that the static pressure of outlet in 1.2 Q d condition has five peaks and five valleys, but this phenomenon does not exist in 0.6 Q d condition. In the time domain spectrums, the static pressure curve has five peaks and five valleys...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 7
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    Numerical simulation and performance prediction in multi-stage submersible centrifugal pump (2013)
    Institute of Physics (IOP)
    Details
    Publication Date: 2013-12-22
    Description: In order to study the inner flow field of multi-stage submersible centrifugal pump, the model named QD3-60/4-1.1 was selected. Steady turbulence characteristics of impellers, diffusers and return channel were calculated by Fluent software, the SIMPLEC algorithm and RNG κ-ε turbulence model with sliding mesh technology. Then, the distributions of pressure, velocity and Turbulence kinetic energy was obtained and the distributions of velocity field of a channel were analysed. The results show that the static pressure in impeller is increasing with the increasing of radius. The circumferential component of relative velocity is in the opposite direction of impeller rotating. At the same radius, the component value of pressure surface is larger than suction surface. With the increasing of flow rate, absolute velocity and relative velocity flow angle are becoming small, in opposite of the relative velocity and absolute velocity flow angle. The high turbulent zone of impeller is ...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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  • 8
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    A broadband gyrotron backward-wave oscillator with tapered interaction structure and magnetic field (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-11-12
    Description: The gyro-monotron and gyrotron backward-wave oscillator (gyro-BWO) are the two oscillator versions of gyrotrons. While serving different functions, they are also radically different in the RF field formation mechanisms. The gyro-monotron RF field profile is essentially fixed by the resonant interaction structure, while the gyro-BWO possesses an extra degree of freedom in that the axial RF field profile is self-determined by the beam-wave interaction in a waveguide structure. The present study examines ways to utilize the latter feature for bandwidth broadening with a tapered magnetic field, while also employing a tapered waveguide to enhance the interaction efficiency. We begin with a mode competition analysis, which suggests the theoretical feasibility of broadband frequency tuning in single-mode operation. It is then shown in theory that, by controlling the RF field profile with an up- or down-tapered magnetic field, the gyro-BWO is capable of efficient operation with a much improved tunable bandwidth.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 9
    Electronic Resource
    Electronic Resource
    Materials science Single-walled 4 Å carbon nanotube arrays (2000)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 408 (2000), S. 50-51 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Here we describe the smallest carbon nanotubes possible, prepared by the pyrolysis of tripropylamine molecules in the channels of porous zeolite AlPO4-5 (AFI) single crystals. These uniformly sized carbon nanotubes have a diameter of 0.4 nm and are the best example of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35040702
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  • 10
    Electronic Resource
    Electronic Resource
    Regrowth, morphology and persistence of Grasslands Puna chicory (Cichorium intybus L.) in response to grazing frequency and intensity (1997)
    Oxford, UK : Blackwell Science Ltd
    Grass and forage science 52 (1997), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Effects of different grazing frequencies and intensities on herbage production (on both a unit pasture and individual plant basis) and on persistence of chicory (Cichorium intybus L. cv. Grasslands Puna) were studied at Palmerston North, New Zealand (latitude 40°23′S) from November 1994 to November 1995. Three experiments were conducted on the same chicory stand, sown on 12 May 1994. The main grazing experiment had two grazing intensities, hard-lax grazing (50- to 100-mm stem stubble to mid-January, and thereafter 100- to 150-mm stem stubble) and lax grazing (100- to 150-mm stem stubble), and three grazing frequencies (1-, 2- or 4-week intervals). A subsidiary plant survival experiment compared the survival of 120 marked plants in ungrazed and grazed treatments. A late autumn grazing experiment examined the effects on plant persistence in the following spring. The greatest herbage mass (leaf + stem) resulted from the 4-week grazing frequency [9640 ± 874 kg dry matter (DM) ha−1], in which stem mass was reasonably low (1270 ± 410 kg DM ha−1), but was significantly higher in the 4-week grazing frequency than 1- and 2-week grazing frequencies (P 〈 0·01). Grazing intensity had no significant effect except on the average stem mass of individual plants when the hard-lax intensity gave a lower stem mass (P 〈 0·01). There were no interactions between grazing frequency and intensity in herbage mass. Plant density declined by 35% over the growing season with the decline unaffected by grazing intensity or frequency during the season. Grazing in late autumn resulted in approximately 27% less plants the following spring. It was concluded that grazing management through the growing season cannot be used to improve persistence without compromising leaf growth rate, but that avoidance of grazing late autumn will improve the persistence of chicory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2494.1997.00051.x
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