Machine-learning identification of galaxies in the WISExSuperCOSMOS all-sky catalogue

The two currently largest all-sky photometric datasets, WISE and SuperCOSMOS, were cross-matched by Bilicki et al. (2016) (B16) to construct a novel photometric redshift catalogue on 70% of the sky. Galaxies were therein separated from stars and quasars through colour cuts, which may leave imperfections because of mixing different source types which overlap in colour space. The aim of the present work is to identify galaxies in the WISExSuperCOSMOS catalogue through an alternative approach of machine learning. This allows us to define more complex separations in the multi-colour space than possible with simple colour cuts, and should provide more reliable source classification. For the automatised classification we use the support vector machines learning algorithm, employing SDSS spectroscopic sources cross-matched with WISExSuperCOSMOS as the training and verification set. We perform a number of tests to examine the behaviour of the classifier (completeness, purity and accuracy) as a function of source apparent magnitude and Galactic latitude. We then apply the classifier to the full-sky data and analyse the resulting catalogue of candidate galaxies. We also compare thus produced dataset with the one presented in B16. The tests indicate very high accuracy, completeness and purity (>95%) of the classifier at the bright end, deteriorating for the faintest sources, but still retaining acceptable levels of 85%. No significant variation of classification quality with Galactic latitude is observed. Application of the classifier to all-sky WISExSuperCOSMOS data gives 15 million galaxies after masking problematic areas. The resulting sample is purer than the one in B16, at a price of lower completeness over the sky. The automatic classification gives a successful alternative approach to defining a reliable galaxy sample as compared to colour cuts.Comment: 12 pages, 15 figures, accepted for publication in A&A. Obtained catalogue will be included in the public release of the WISExSuperCOSMOS galaxy catalogue available from http://ssa.roe.ac.uk/WISExSCO

The optimization problem of the shaped knife profiling

Проаналізовано переваги та недоліки процесу гарячого поділу безперервнолитої квадратної заготовки на ножицях з фасонними ножами. Відзначається доцільність проведення теоретичних досліджень розділових операцій на ножицях з використанням методу скінченних елементів (МСЕ). Метою даної роботи було визначення оптимальної форми профілювання фасонного ножа для поділу квадратної заготовки в гарячому стані шляхом математичного моделювання на базі МСЕ. Представлено методику проведення досліджень, що включали два етапи. На першому етапі використовували математичне моделювання відповідно до плану повного факторного експерименту 24 згідно виробничих умов реалізації процесу з ножами що мали значення кута розкриття ножів 90…98° та ухилу контактних поверхонь 3…11°. При обробці даних моделювання були отримані три відносних параметра, два з яких характеризують зминання (затяжка) і загин кінців розкату, і ще один – ромбічність торцевої поверхні. Для кожного з параметрів, отримані лінійні рівняння регресії як функція температури різання та розмірів заготовок, величини кута розкриття ножів та ухилу контактних поверхонь. На другому етапі дослідження вирішували оптимізаційну задачу пошуку мінімуму цільової функції – ромбічності. За результатами відзначено, що оптимальні значення профілювання ножів залежать від вимог, що висуваються до якості зрізу. Введено фактор граничного відхилення зминання і загину кінців, встановлений діапазон його значень та проаналізовано вплив на оптимальні параметри. Запропоновано величини кута розкриття ножів та ухилу контактних поверхонь, за умови мінімізації граничного відхилення зминання і загину кінців у досліджуваних діапазонах температур та розмірів заготовок. Отримано залежності параметрів профілювання ножів від граничного відхилення зминання і загину кінців заготовок після поділу. Результати роботи можуть бути рекомендовані для використання при прийнятті проектно-конструкторських і технологічних рішень в питаннях гарячого розділення безперервнолитої квадратної заготовки фасонними ножами на кут.The advantages and disadvantages of the process of separation in hot condition of billet with square shape by special profiled knives were analyzed. There is expediency of carrying out theoretical researches the separating operations by shears based on finite elements method (FEM) is noted. The purpose of the work was to determine the optimal shape for make form a profiled knife for separating a square billet in a hot state by simulating based on the FEM. A methodology of study realization consisting of two stages is presented. At the first stage, simulating was used in accordance with the plan of the full factorial experiment 24 according to the technological environment for the process implementation with knives having a knife opening angle of 90...98° and a contact surface inclination of 3...11°. At the processing the simulation results, three relative parameters were obtained. Two parameters characterize the crumpling (tightening) and bending of the billet ends, and one more – the rhomboidity of the end surface. For each of the parameters, the linear regression equations obtained as a function of cutting temperature and billet sizes, the knife opening angle and contact surface inclination. At the second stage of the study, the optimization problem of determining the minimum of the objective function – rhomboidity – was solved. According to the results, it was noted that the optimal values of the profiling of knives depend on the requirements for the quality of the cut. The factor of the maximum deviation of crumpling and bending of the ends is introduced. The range of its values is established and the influence on the optimal parameters is analyzed. The values of the knife opening angle and contact surface inclination are proposed, provided that the maximum deviation of the crumpling and bending of the ends, at the studied temperature ranges and sizes of the billets, is minimized. The dependences of the optimal parameters of the profiling of knives on the maximum deviation of the crumpling and bending of the ends of the billets after separation are obtained. Results of work can be recommended for use to get solutions in design and technology questions of hot separation square billet by profiled knife on the angle

Exploring New Ultrafast Operation Regimes in Quantum Dot Lasers and Amplifiers

We will present our recent results, harnessing the flexibility of quantum dot materials towards the development of increasingly versatile regimes of ultrashort pulse generation and amplification in edge-emitting devices

Wave and plasma measurements and GPS diagnostics of the main ionospheric trough as a hybrid method used for Space Weather purposes

The region of the main ionospheric trough is a unique region of the ionosphere, where different types of waves and instabilities can be generated. This region of the ionosphere acts like a lens, focusing a variety of indicators from the equator of plasmapause and local ionospheric plasma. This paper reports the results of monitoring the mid-latitude trough structure, dynamics and wave activity. For these purposes, the data gathered by the currently-operating DEMETER satellite and past diagnostics located on IK-19, Apex, and MAGION-3 spacecraft, as well as TEC measurements were used. A global-time varying picture of the ionospheric trough was reconstructed using the sequence of wave spectra registered and plasma measurements in the top-side ionosphere. The authors present the wave activity from ULF frequency band to the HF frequency detected inside the trough region and discuss its properties during geomagnetic disturbances. It is thought that broadband emissions are correlated with low frequency radiation, which is excited by the wave-particle interaction in the equatorial plasmapause and moves to the ionosphere along the geomagnetic field line. In the ionosphere, the suprathermal electrons can interact with these electrostatic waves and excite electron acoustic waves or HF longitudinal plasma waves. <br><br> Furthermore, the electron density trough can provide useful data on the magnetosphere ionosphere dynamics and morphology and, in consequence, can be used for Space Weather purposes

Two-dimensional carrier density distribution inside a high power tapered laser diode

The spontaneous emission of a GaAs-based tapered laser diode emitting at lambda = 1060 nm was measured through a window in the transparent substrate in order to study the carrier density distribution inside the device. It is shown that the tapered geometry is responsible for nonuniform amplification of the spontaneous/stimulated emission which in turn influences the spatial distribution of the carriers starting from below threshold. The carrier density does not clamp at the lasing threshold and above it the device shows lateral spatial hole-burning caused by high stimulated emission along the cavity center. (C) 2011 American Institute of Physics. (doi: 10.1063/1.3596445

Simulation of high brightness tapered lasers

Tapered semiconductor lasers have demonstrated both high power and good beam quality, and are of primary interest for those applications demanding high brightness optical sources. The complex non-linear interaction between the optical field and the active material requires accurate numerical simulations to improve the device design and to understand the underlying physics. In this work we present results on the design and simulation of tapered lasers by means of a Quasi- 3D steady-state single-frequency model. The results are compared with experiments on Al-free active region devices emitting at 1060 nm. The performance of devices based on symmetric and asymmetric epitaxial designs is compared and the influence of the design on the beam properties is analyzed. The role of thermal effects on the beam properties is experimentally characterized and analyzed by means of the numerical simulations. Tapered lasers with separate electrical contacts in the straight and tapered sections, based on symmetrical and asymmetrical epitaxial designs are also presented and analyze

High-brightness all semiconductor laser at 1.57 µm for space-borne lidar measurements of atmospheric carbon dioxide: device design and analysis of requirements

The availability of suitable laser sources is one of the main challenges in future space missions for accurate measurement of atmospheric CO2. The main objective of the European project BRITESPACE is to demonstrate the feasibility of an all-semiconductor laser source to be used as a space-borne laser transmitter in an Integrated Path Differential Absorption (IPDA) lidar system. We present here the proposed transmitter and system architectures, the initial device design and the results of the simulations performed in order to estimate the source requirements in terms of power, beam quality, and spectral properties to achieve the required measurement accuracy. The laser transmitter is based on two InGaAsP/InP monolithic Master Oscillator Power Amplifiers (MOPAs), providing the ON and OFF wavelengths close to the selected absorption line around 1.57 µm. Each MOPA consists of a frequency stabilized Distributed Feedback (DFB) master oscillator, a modulator section, and a tapered semiconductor amplifier optimized to maximize the optical output power. The design of the space-compliant laser module includes the beam forming optics and the thermoelectric coolers.The proposed system replaces the conventional pulsed source with a modulated continuous wave source using the Random Modulation-Continuous Wave (RM-CW) approach, allowing the designed semiconductor MOPA to be applicable in such applications. The system requirements for obtaining a CO2 retrieval accuracy of 1 ppmv and a spatial resolution of less than 10 meters have been defined. Envelope estimated of the returns indicate that the average power needed is of a few watts and that the main noise source is the ambient noise