Elementary Components of the Quadratic Assignment Problem

The Quadratic Assignment Problem (QAP) is a well-known NP-hard combinatorial optimization problem that is at the core of many real-world optimization problems. We prove that QAP can be written as the sum of three elementary landscapes when the swap neighborhood is used. We present a closed formula for each of the three elementary components and we compute bounds for the autocorrelation coefficient.Comment: 10 pages, 1 figure. An extended version of this paper was published in GECCO 201

Multiphysics Computational Analysis of a Solid-Core Nuclear Thermal Engine Thrust Chamber

The objective of this effort is to develop an efficient and accurate computational heat transfer methodology to predict thermal, fluid, and hydrogen environments for a hypothetical solid-core, nuclear thermal engine - the Small Engine. In addition, the effects of power profile and hydrogen conversion on heat transfer efficiency and thrust performance were also investigated. The computational methodology is based on an unstructured-grid, pressure-based, all speeds, chemically reacting, computational fluid dynamics platform, while formulations of conjugate heat transfer were implemented to describe the heat transfer from solid to hydrogen inside the solid-core reactor. The computational domain covers the entire thrust chamber so that the afore-mentioned heat transfer effects impact the thrust performance directly. The result shows that the computed core-exit gas temperature, specific impulse, and core pressure drop agree well with those of design data for the Small Engine. Finite-rate chemistry is very important in predicting the proper energy balance as naturally occurring hydrogen decomposition is endothermic. Locally strong hydrogen conversion associated with centralized power profile gives poor heat transfer efficiency and lower thrust performance. On the other hand, uniform hydrogen conversion associated with a more uniform radial power profile achieves higher heat transfer efficiency, and higher thrust performance

Thermal Hydraulics Design and Analysis Methodology for a Solid-Core Nuclear Thermal Rocket Engine Thrust Chamber

Nuclear thermal propulsion is a leading candidate for in-space propulsion for human Mars missions. This chapter describes a thermal hydraulics design and analysis methodology developed at the NASA Marshall Space Flight Center, in support of the nuclear thermal propulsion development effort. The objective of this campaign is to bridge the design methods in the Rover/NERVA era, with a modern computational fluid dynamics and heat transfer methodology, to predict thermal, fluid, and hydrogen environments of a hypothetical solid-core, nuclear thermal engine the Small Engine, designed in the 1960s. The computational methodology is based on an unstructured-grid, pressure-based, all speeds, chemically reacting, computational fluid dynamics and heat transfer platform, while formulations of flow and heat transfer through porous and solid media were implemented to describe those of hydrogen flow channels inside the solid24 core. Design analyses of a single flow element and the entire solid-core thrust chamber of the Small Engine were performed and the results are presented herei

Energy harvesting circuit with high RF-to-DC conversion efficiency

This paper presents an energy harvesting circuit for high efficiency performance. The proposed circuit consists of an RLC shunt resonance circuit integrated to an RF antenna. The resonance circuit is used to (i) selectively pick the desired signal whose output is fed to a Cockcroft–Walton voltage multiplier circuit; and (ii) match the impedance of the antenna with the Cockcroft–Walton voltage multiplier circuit for optimum power (DC) transfer. The proposed circuit exhibits an efficiency of 68% for an input power of 200 microwatts

Mutual-Coupling Reduction in Metamaterial Substrate Integrated Waveguide Slotted Antenna Arrays Using Metal Fence Isolators for SAR and MIMO Applications

A new type of mutual coupling reduction technique is applied to metamaterial substrate integrated waveguide (SIW) slotted antennas array. The circular shaped reference SIW antenna is constructed from Alumina substrate with dimensions of 40×5×1.5 mm3. Embedded in the reference antenna is an array of 38 slots with dimensions of 2×1×1.5 mm3. The reference SIW antenna covers six frequency bands from X- to Ku-bands with maximum and average isolation between the radiation slots of approximately -20 dB and -10 dB, respectively. Isolation was increased by inserting metal fences between the radiation slots, which also improves the antenna’s impedance matching properties. Maximum, minimum, and average suppression on mutual coupling between radiation slots after application of the metal fences are 20 dB, 8 dB, and 13 dB, respectively. The proposed metal fence isolators (MFI) improve the radiation patterns without degrading the antenna’s performance. With MFI the maximum gain achieved improves by ~10%. The technique is simple to implement and proposed for synthetic aperture radar (SAR) and multiple input multiple output (MIMO) applications

Array antenna for synthetic aperture radar operating in X and Ku-Bands: a study to enhance isolation between radiation elements

Modern synthetic aperture radars (SAR) require a system bandwidth of greater than 1 GHz. Waveguide slot antennas are popular for use in SAR applications because of their inherent advantages, namely high efficiency and power handling capability, but such antennas have a limited bandwidth. Although the bandwidth of slot antennas can be broadened by using ridge waveguides however this approach introduces manufacturing complexity and is costly. A novel solution is presented in this paper to realize a large bandwidth by using 2×3 array antenna where the mutual coupling between the radiating elements is suppressed by inserting an isolation wall between the radiating elements. The isolation wall comprises three intercoupled U-shaped microstrip transmission-lines. With this technique the antenna’s bandwidth for VSWR<1.5 is greater than 2 GHz inside the X- and Ku-bands

A new waveguide slot array antenna with high isolation and high antenna bandwidth operation on Ku- and K- bands for radar and MIMO systems

In this paper a novel technique is proposed to reduce the mutual coupling between the radiating elements of a waveguide slot array antenna. This is achieved by inserting slots between the waveguide oval shaped slots. The reference waveguide array antenna used in the study was implemented with an arrangement of 3×5 oval shaped slots. By incorporating linear slots between the radiating oval shaped slots in both horizontal and vertical directions significant reduction in mutual coupling is achieved of 24 dB, 20 dB, and 32 dB in the frequency bands of 12.95-13.75 GHz (Ku-band), 15.45-16.85 GHz (Ku-band), and 18.85-23.0 GHz (K-band), respectively. Edge-to-edge distance between the slot radiators is 0.2λ, which is at least two-fold smaller than conventional array antennas. With the slot isolators the antenna’s minimum and maximum gains improve by 53.5% and 25.5%, respectively. In addition, the radiation patterns are unaffected. The proposed method is simple to implement, low cost solution mass production

Experimental Impact Laboratory

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