A single-field-period quasi-isodynamic stellarator

A single-field-period quasi-isodynamic stellarator configuration is presented. This configuration, which resembles a twisted strip, is obtained by the method of direct construction, that is, it is found via an expansion in the distance from the magnetic axis. Its discovery, however, relied on an additional step involving numerical optimization, performed within the space of near-axis configurations defined by a set of adjustable magnetic-field parameters. This optimization, completed in 30 seconds on a single cpu core using the SIMSOPT code, yields a solution with excellent confinement, as measured by the conventional figure of merit for neoclassical transport, effective ripple, at a modest aspect ratio of eight. The optimization parameters that led to this configuration are described, its confinement properties are assessed, and a set of magnetic-field coils is found. The resulting transport at low collisionality is much smaller than that of W7-X, and the device needs significantly fewer coils thanks to the reduced number of field periods.Comment: 13 pages, 9 figure

Perfil do consumidor e do consumo de produtos orgânicos no Rio Grande do Norte.

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Programa computacional de simulação da produtividade para suporte a decisão no plantio de milho.

O objetivo deste trabalho foi desenvolver um programa computacional que simule a produção do milho, sendo utilizado como um suporte a decisão para o produtor. O algoritmo utilizado consta de modelos de regressão obtidos a partir de resultados de uma pesquisa de campo realizada na Embrapa Milho e Sorgo, sob condições de plantio direto e com modelos de estimativas de produção obtidos em tabelas e resultados de outros trabalhos constantes na literatura. O pacote computacional resultante é completo o suficiente para a simulação da produtividade em um determinado solo e implantação e uso por produtores (usuários) como uma ferramenta de Agricultura de Precisão, capaz de auxiliar à tomada de decisão. O programa é de fácil manuseio, onde o usuário pode optar em digitar os valores que representam as condições do solo de plantio, ou resgatar valores de um banco de dados histórico que pode ser implementado pelo próprio usuário, ou obtido através da Embrapa que disponibilizará, através da rede mundial de computadores, condições de solo de todo o país. A saída do programa é de simples interpretação e fornece, entre outros resultados, a produtividade máxima de um solo sob as condições de simulação, auxiliando o produtor na tomada de decisão quanto a aplicação de insumos

Dynamical confirmation of a stellar-mass black hole in the transient X-ray dipping binary MAXI J1305-704

MAXI J1305-704 has been proposed as a high-inclination candidate black hole X-ray binary in view of its X-ray properties and dipping behaviour during outburst. We present photometric and spectroscopic observations of the source in quiescence that allow us to reveal the ellipsoidal modulation of the companion star and absorption features consistent with those of an early K-type star (Teff = 4610 +130 -160 K). The central wavelengths of the absorption lines vary periodically at Porb = 0.394 +- 0.004 d with an amplitude of K2 = 554 +- 8 km/s . They imply a mass function for the compact object of f(M1) = 6.9 +- 0.3 Msun, confirming its black hole nature. The simultaneous absence of X-ray eclipses and the presence of dips set a conservative range of allowed inclinations 60 deg < i < 82 deg, while modelling of optical light curves further constrain it to i = 72 +5 -8 deg. The above parameters together set a black hole mass of M1 = 8.9 +1.6 -1.0 Msun and a companion mass of M2=0.43 +- 0.16 Msun, much lower than that of a dwarf star of the observed spectral type, implying it is evolved. Estimates of the distance to the system (d = 7.5 +1.8 -1.4 kpc) and space velocity (vspace = 270 +- 60 km/s ) place it in the Galactic thick disc and favour a significant natal kick during the formation of the BH if the supernova occurred in the Galactic Plane.Comment: 14 pages, 6 figures. Submitted to MNRA

Recent Overview of Solar Photocatalysis and Solar Photo-Fenton Processes for Wastewater Treatment

This literature research, although not exhaustive, gives perspective to solar-driven photocatalysis, such as solar photo-Fenton and TiO2 solar photocatalysis, reported in the literature for the degradation of aqueous organic pollutants. Parameters that influence the degradation and mineralization of organics like catalyst preparation, type and load of catalyst, catalyst phase, pH, applied potential, and type of organic pollutant are addressed. Such parameters may also affect the photoactivity of the catalysts used in the studied solar processes. Solar irradiation is a renewable, abundant, and pollution-free energy source for low-cost commercial applications. Therefore, these solar processes represent an environmentally friendly alternative mainly because the use of electricity can be decreased/avoided

Polarity in GaN and ZnO: Theory, measurement, growth, and devices

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Rev. 3, 041303 (2016) and may be found at https://doi.org/10.1063/1.4963919.The polar nature of the wurtzite crystalline structure of GaN and ZnO results in the existence of a spontaneous electric polarization within these materials and their associated alloys (Ga,Al,In)N and (Zn,Mg,Cd)O. The polarity has also important consequences on the stability of the different crystallographic surfaces, and this becomes especially important when considering epitaxial growth. Furthermore, the internal polarization fields may adversely affect the properties of optoelectronic devices but is also used as a potential advantage for advanced electronic devices. In this article, polarity-related issues in GaN and ZnO are reviewed, going from theoretical considerations to electronic and optoelectronic devices, through thin film, and nanostructure growth. The necessary theoretical background is first introduced and the stability of the cation and anion polarity surfaces is discussed. For assessing the polarity, one has to make use of specific characterization methods, which are described in detail. Subsequently, the nucleation and growth mechanisms of thin films and nanostructures, including nanowires, are presented, reviewing the specific growth conditions that allow controlling the polarity of such objects. Eventually, the demonstrated and/or expected effects of polarity on the properties and performances of optoelectronic and electronic devices are reported. The present review is intended to yield an in-depth view of some of the hot topics related to polarity in GaN and ZnO, a fast growing subject over the last decade

The 1989 and 2015 outbursts of V404 Cygni: a global study of wind-related optical features

The black hole transient V404 Cygni exhibited a bright outburst in June 2015 that was intensively followed over a wide range of wavelengths. Our team obtained high time resolution optical spectroscopy (~90 s), which included a detailed coverage of the most active phase of the event. We present a database consisting of 651 optical spectra obtained during this event, that we combine with 58 spectra gathered during the fainter December 2015 sequel outburst, as well as with 57 spectra from the 1989 event. We previously reported the discovery of wind-related features (P-Cygni and broad-wing line profiles) during both 2015 outbursts. Here, we build diagnostic diagrams that enable us to study the evolution of typical emission line parameters, such as line fluxes and equivalent widths, and develop a technique to systematically detect outflow signatures. We find that these are present throughout the outburst, even at very low optical fluxes, and that both types of outflow features are observed simultaneously in some spectra, confirming the idea of a common origin. We also show that the nebular phases depict loop patterns in many diagnostic diagrams, while P-Cygni profiles are highly variable on time-scales of minutes. The comparison between the three outbursts reveals that the spectra obtained during June and December 2015 share many similarities, while those from 1989 exhibit narrower emission lines and lower wind terminal velocities. The diagnostic diagrams presented in this work have been produced using standard measurement techniques and thus may be applied to other active low-mass X-ray binaries.Comment: Accepted for publication in MNRAS. 23 pages paper, plus a 9 pages appendix with extra tables and figures. 18 figures are included in the paper and 8 in the appendi