Genetic Algorithm with Optimal Recombination for the Asymmetric Travelling Salesman Problem

We propose a new genetic algorithm with optimal recombination for the asymmetric instances of travelling salesman problem. The algorithm incorporates several new features that contribute to its effectiveness: (i) Optimal recombination problem is solved within crossover operator. (ii) A new mutation operator performs a random jump within 3-opt or 4-opt neighborhood. (iii) Greedy constructive heuristic of W.Zhang and 3-opt local search heuristic are used to generate the initial population. A computational experiment on TSPLIB instances shows that the proposed algorithm yields competitive results to other well-known memetic algorithms for asymmetric travelling salesman problem.Comment: Proc. of The 11th International Conference on Large-Scale Scientific Computations (LSSC-17), June 5 - 9, 2017, Sozopol, Bulgari

Estimating attraction basin sizes

The performance of local search algorithms is influenced by the properties that the neighborhood imposes on the search space. Among these properties, the number of local optima has been traditionally considered as a complexity measure of the instance, and different methods for its estimation have been developed. The accuracy of these estimators depends on properties such as the relative attraction basin sizes. As calculating the exact attraction basin sizes becomes unaffordable for moderate problem sizes, their estimations are required. The lack of techniques achieving this purpose encourages us to propose two methods that estimate the attraction basin size of a given local optimum. The first method takes uniformly at random solutions from the whole search space, while the second one takes into account the structure defined by the neighborhood. They are tested on different instances of problems in the permutation space, considering the swap and the adjacent swap neighborhoods

Практическая программно-аппаратная реализация обработки сигналов глобальных навигационных спутниковых систем методом временного накопления в целях мониторинга радионавигационных сигналов

Currently, a scope of satellite radio-navigation applications is more and more extending. Accordingly, there are also increasing requirements for the quality of determining coordinates and time. Therefore, radio-navigation signals monitoring, in particular their waveform control, waveform distortion analysis, is a challenge. However, a power of navigation signals is lower than the noise level, therefore, the special methods and equipment, which provide increasing a signal-to-noise ratio, are necessary to analyze their waveform. Usually, complexes based on the large aperture antennas are used for this purpose. But they have a number of disadvantages, namely high complexity, high price, large size, necessity to guide and track each individual satellite.The paper gives a brief description of the temporary accumulation method (TAM). This method can be applied to signals containing repetitive elements (basic elements). Radio-navigation signals are such signals. TAM allows you to increase the signal-to-noise ratio and evaluate the waveform of signal basic elements by superimposing and averaging the appropriate signal samples. Gain increases with increasing accumulation time.The paper proposes a small-scale breadboard of the software-hardware complex to monitor signals of global navigation satellite systems (GNSS) based on an omnidirectional antenna, a software-defined radio system, and a personal computer. This breadboard allows recording of digital samples of the navigation signals observed, and then their processing by the temporary accumulation method.Presents operation estimates of the proposed breadboard for monitoring GNSS signals. Gives estimates of the GLONASS navigation signal waveforms in the time domain (signal basic elements) and in the frequency domain (energy spectrum). Also based on the use of TAM, estimates the signal power and energy gain. Proves that using the hardware-software complex proposed for radio-navigation signals monitoring is possible.The proposed scheme of the small-scale breadboard for monitoring GNSS signals can be used directly for monitoring and also to test various methods and technologies of navigation signal processing based on the use of information about the waveform of the received signal.В настоящее время всё больше расширяются области применения спутниковой радионавигации. В связи с этим возрастают и требования к качеству определения координат и времени. Поэтому актуальна задача мониторинга радионавигационных сигналов, в частности контроль их формы, анализ искажений формы. Однако мощность навигационных сигналов ниже уровня шума, поэтому для анализа их формы необходимы специальные методы и оборудование, позволяющие увеличить отношение сигнал/шум. Как правило, для этого используются комплексы на основе крупноапертурных антенн. Но они обладают рядом недостатков: высокая сложность, большая цена, большие размеры, необходимость наведения и сопровождения каждого отдельного спутника. В статье предложен альтернативный подход.Даётся краткое описание метода временного накопления (МВН). Этот метод может быть применён для сигналов, содержащих повторяющиеся элементы (базовые элементы). Такими сигналами являются радионавигационные сигналы. МВН позволяет увеличить отношение сигнал/шум и оценить форму базовых элементов сигнала за счёт наложения и усреднения соответствующих отсчётов сигнала. Энергетический выигрыш увеличивается с увеличением времени накопления.Предложена схема малогабаритного макета программно-аппаратного комплекса мониторинга сигналов глобальных навигационных спутниковых систем (ГНСС) на базе слабонаправленной антенны, программно-определяемой радиосистемы и персонального компьютера. Данный макет позволяет записать цифровые отсчёты наблюдаемых навигационных сигналов, а затем обработать их с помощью метода временного накопления.Получены результаты апробации работы предложенного макета мониторинга сигналов ГНСС. Приведены оценки формы навигационных сигналов ГЛОНАСС во временной области (базовые элементы сигнала) и в частотной области (энергетический спектр). Также представлены оценки мощности сигналов и энергетического выигрыша от применения МВН. Подтверждена возможность использования предложенного программно-аппаратного комплекса в целях мониторинга радионавигационных сигналов.Предложенная схема малогабаритного макета мониторинга сигналов ГНСС может быть использована как непосредственно для целей мониторинга, так и для отработки различных методов и технологий обработки навигационных сигналов, основанных на использовании информации о форме принимаемого сигнала

Unoccupied Topological States on Bismuth Chalcogenides

The unoccupied part of the band structure of topological insulators Bi$_2$Te$_{x}$Se$_{3-x}$ ($x=0,2,3$) is studied by angle-resolved two-photon photoemission and density functional theory. For all surfaces linearly-dispersing surface states are found at the center of the surface Brillouin zone at energies around 1.3 eV above the Fermi level. Theoretical analysis shows that this feature appears in a spin-orbit-interaction induced and inverted local energy gap. This inversion is insensitive to variation of electronic and structural parameters in Bi$_2$Se$_3$ and Bi$_2$Te$_2$Se. In Bi$_2$Te$_3$ small structural variations can change the character of the local energy gap depending on which an unoccupied Dirac state does or does not exist. Circular dichroism measurements confirm the expected spin texture. From these findings we assign the observed state to an unoccupied topological surface state

On Non-Elitist Evolutionary Algorithms Optimizing Fitness Functions with a Plateau

We consider the expected runtime of non-elitist evolutionary algorithms (EAs), when they are applied to a family of fitness functions with a plateau of second-best fitness in a Hamming ball of radius r around a unique global optimum. On one hand, using the level-based theorems, we obtain polynomial upper bounds on the expected runtime for some modes of non-elitist EA based on unbiased mutation and the bitwise mutation in particular. On the other hand, we show that the EA with fitness proportionate selection is inefficient if the bitwise mutation is used with the standard settings of mutation probability.Comment: 14 pages, accepted for proceedings of Mathematical Optimization Theory and Operations Research (MOTOR 2020). arXiv admin note: text overlap with arXiv:1908.0868

Preservation of the High Quality Factor and Accelerating Gradient of Nb3Sn-coated Cavity During Pair Assembly

Two CEBAF 5-cell accelerator cavities have been coated with Nb3Sn film using the vapor diffusion technique. One cavity was coated in the Jefferson Lab Nb3Sn cavity coating system, and the other in the Fermilab Nb3Sn coating system. Both cavities were measured at 4 K and 2 K in the vertical dewar test in each lab and then assembled into a cavity pair at Jefferson Lab. Previous attempts to assemble Nb3Sn cavities into a cavity pair degraded the superconducting properties of Nb3Sn-coated cavities. This contribution discusses the efforts to identify and mitigate the pair assembly challenges and will present the results of the vertical tests before and after pair assembly. Notably, one of the cavities reached the highest gradient above 80 mT in the vertical test after the pair assembly.Comment: 21st Intl Conf Radio Frequency Superconductivity (SRF 2023

Bulk and surface electron dynamics in a p-type topological insulator SnSb2Te4

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al.Time-resolved two-photon photoemission was used to study the electronic structure and dynamics at the surface of SnSb2Te4, a p-type topological insulator. The Dirac point is found 0.32±0.03 eV above the Fermi level. Electrons from the conduction band minimum are scattered on a time scale of 43±4 fs to the Dirac cone. From there they decay to the partly depleted valence band with a time constant of 78±5 fs. The significant interaction of the Dirac states with bulk bands is attributed to their bulk penetration depth of ∼3 nm as found from density functional theory calculations.We acknowledge partial support from the Basque Country Government, Departamento de Educacion, Universidades e Investigacion (Grant No. IT-366-07), the Spanish Ministerio de Ciencia e Innovacion (Grant No. FIS2010-19609-C02-00), the Ministry of Education and Science of Russian Federation (Grant No. 2.8575.2013), the Russian Foundation for Basic Research (Grant No. 13-02-12110_ofi_m), and Science Development Foundation under the President of the Republic of Azerbaijan [Grant No. EIF-2011-1(3)-82/69/4-M-50].Peer Reviewe

Pareto Local Optima of Multiobjective NK-Landscapes with Correlated Objectives

International audienceIn this paper, we conduct a fitness landscape analysis for multiobjective combinatorial optimization, based on the local optima of multiobjective NK-landscapes with objective correlation. In single-objective optimization, it has become clear that local optima have a strong impact on the performance of metaheuristics. Here, we propose an extension to the multiobjective case, based on the Pareto dominance. We study the co-influence of the problem dimension, the degree of non-linearity, the number of objectives and the correlation degree between objective functions on the number of Pareto local optima

Level-Based Analysis of Genetic Algorithms and Other Search Processes

The fitness-level technique is a simple and old way to derive upper bounds for the expected runtime of simple elitist evolutionary algorithms (EAs). Recently, the technique has been adapted to deduce the runtime of algorithms with non-elitist populations and unary variation operators [2,8]. In this paper, we show that the restriction to unary variation operators can be removed. This gives rise to a much more general analytical tool which is applicable to a wide range of search processes. As introductory examples, we provide simple runtime analyses of many variants of the Genetic Algorithm on well-known benchmark functions, such as OneMax, LeadingOnes, and the sorting problem