Periodical radiation spectrum with a frequency difference of ~160 MHz is observed in hot-test experiments of Ku-band gyrotron traveling-wave tubes (gyro-TWTs). By the means of eigenmode analyses and ...particle-in-cell (PIC) simulation considering the whole output transition section from the interaction circuit end to the output window, we found that the circuit oscillation is pronounced because of frequency self-modulation (FSM). As a comparison, the cutoff taper contributing to the FSM is removed and a new amplifier has been developed; hot-test results indicate that the periodical property has been greatly alleviated as expected and the stability of the amplifier is well improved.
Aiming at the fault traveling wave on the LCC-MMC HVDC transmission line, this paper analyzed its reflection and refraction characteristics at the DC buses and the fault point, plotted its ...propagation grid diagrams, obtained the relationship between the polarity of fault traveling wave and the boundary elements, and drew the conclusion that when the impedance of DC filter is far less than the wave impedance of transmission line, the existing fault location methods that need to distinguish these two waves according to their polarities are not applicable to the LCC-MMC HVDC system. On these bases, this paper proposed a modal traveling wave arrival time difference-based location principle for pole-to-ground fault, and a fault traveling wave propagation path ratio-based location principle for pole-to-pole fault, these principles neither need to identify the wave polarity, nor need the wave velocity value. In order to better extract the wave heads and their arrival time, this paper pre-treated the sampling data to make sure all the wave heads are extracted from the same frequency band, then the wave heads and their arrival time can be extracted with the empirical mode decomposition. The simulation results verified the effectiveness of the proposed fault location principle.
The traveling salesman problem Applegate, David L; Applegate, David L; Bixby, Robert E ...
2006., 20110919, 2011, 2007, 2007-01-01, Letnik:
17
eBook
This book presents the latest findings on one of the most intensely investigated subjects in computational mathematics--the traveling salesman problem. It sounds simple enough: given a set of cities ...and the cost of travel between each pair of them, the problem challenges you to find the cheapest route by which to visit all the cities and return home to where you began. Though seemingly modest, this exercise has inspired studies by mathematicians, chemists, and physicists. Teachers use it in the classroom. It has practical applications in genetics, telecommunications, and neuroscience.
In the above article <xref ref-type="bibr" rid="ref1">1 , comparing (14) and (15) with (1), for all units of the NP ML-SWS to satisfy the BWS condition, the simplest way is to define the relationship ...between <inline-formula> <tex-math notation="LaTeX">L_{n} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">d_{n} </tex-math></inline-formula> as (16). Such that (16) should read as
The fast and cost-efficient home delivery of goods ordered online is logistically challenging. Many companies are looking for new ways to cross the last mile to their customers. One ...technology-enabled opportunity that recently has received much attention is the use of drones to support deliveries. An innovative last-mile delivery concept in which a truck collaborates with a drone to make deliveries gives rise to a new variant of the traveling salesman problem (TSP) that we call the TSP with drone. In this paper, we model this problem as an integer program and develop several fast route-first, cluster-second heuristics based on local search and dynamic programming. We prove worst-case approximation ratios for the heuristics and test their performance by comparing the solutions to the optimal solutions for small instances. In addition, we apply our heuristics to several artificial instances with different characteristics and sizes. Our experiments show that substantial savings are possible with this concept compared to truck-only delivery.
The online appendix is available at
https://doi.org/10.1287/trsc.2017.0791
.
The Traveling Salesman Problem with a Drone (TSP-D) is a hybrid truck and drone model of delivery, in which the drone rides on the truck and launches from the truck to deliver packages. Our approach ...to the TSP-D uses branch and bound, whereby each node of the branch-and-bound tree corresponds with a potential order to deliver a subset of packages. An approximate lower bound at each node is given by solving a dynamic program. We provide additional variants of our heuristic approach and compare solution quality and computation times. Consideration is given to various input parameters and distance metrics.
The online supplement is available at
https://doi.org/10.1287/ijoc.2018.0826
.
Space-time-modulated electromagnetic structures have become a topic of significant research interest due to their frequency-converting, amplifying, and nonreciprocal properties. In particular, ...traveling-wave modulation (TWM) is of interest due to its simplicity. Often, TWM is realized by applying staggered time-modulation signals to a discrete array of unit cells. This modulation is referred to as spatially discrete TWM (SDTWM), and the constituent unit cells are called stixels: space-time pixels. Recently, a boundary condition referred to as the interpath relation was derived that relates the field in neighboring stixels. In this article, the interpath relation is applied to SDTWM electrical networks to obtain a generalized eigenvalue problem that can be used to efficiently simulate a cascade of SDTWM stixels. The proposed eigenmode analysis technique is used to simulate three representative SDTWM structures designed to support frequency conversion, parametric amplification, and nonreciprocal propagation. While currently available techniques would require an entire spatial period (or even the whole cascade) to be simulated simultaneously, the presented technique relies only on a single stixel.
In this article, a folded waveguide with two coupling grooves is proposed for high-power and high-frequency traveling wave tubes (TWTs). The structure allows a modified TE<inline-formula> <tex-math ...notation="LaTeX">_{\text{20}}</tex-math> </inline-formula> high-order mode interact with two sheet electron beams. The transmission characteristics of this novel structure were simulated and measured. A good <inline-formula> <tex-math notation="LaTeX">\textit{S}_{\text{21}}</tex-math> </inline-formula> of <inline-formula> <tex-math notation="LaTeX">-</tex-math> </inline-formula>10 dB and <inline-formula> <tex-math notation="LaTeX">\textit{S}_{\text{11}}</tex-math> </inline-formula> of less than <inline-formula> <tex-math notation="LaTeX">-</tex-math> </inline-formula>15 dB were achieved in the 218-230-GHz range. Moreover, simulations of the beam-wave interaction in this structure predicted an output power of 930 W at 220 GHz, with a small signal gain of 58 dB and a 3-dB bandwidth of 1.3 GHz.
In this letter, we present a novel non-quasi-2D slow-wave structure (NQSWS) for THz sheet beam traveling-wave tubes (THz SB TWTs), which have been conceived, fabricated and tested. Our proposed ...structure differs from the conventional quasi-2D structure, in which featured cosine fluctuation in the horizontal direction on the metallic roof in the proximity of the SB tunnel. This modification results in lower cutoff frequency, flatter dispersion property, and higher average interaction impedance. Comparing with its quasi-2D counterpart with the same tunnel area, the two-section NQSWS-TWT reaches a maximum power of 285 W (32% increase) at 220 GHz, while achieving 3-dB bandwidth of 17 GHz (13% increase), according to particle-in-cell simulations. Additionally, the NQSWS can significantly reduce the magnetic field (10% reduction) while guaranteeing full beam transmission. Finally, the cold test demonstrates good consistency with the theoretical simulations, which confirms its feasibility as novel SWS in the THz TWTs applications.
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