Nuclear quadrupole resonance as a non-destructive testing tool

Nuclear pure quadrupole resonance (NQR) is a resonance technique that provides distinctly different information from that provided by nuclear magnetic resonance (NMR). In NMR the splitting of the energy levels, and therefore the frequency observed, occurs because of the interaction of the nuclear magnetic moment with an external magnetic field. Information about the system under study comes from perturbations on this magnetic interaction. These perturbations lead to a broadening of the line, or to relaxation effects on the interchange of energy between the spins and the lattice, and among the spins. In NQR the primary interaction is between the electric quadrupole moment of a nucleus and the electric field gradient at that nucleus. The field gradient is provided by internal interactions in the sample itself, arising from the chemical bonds, rather than by an external field. Anything that changes the bonding environment, such as tensile stress, will cause shifts in the quadrupole resonance frequency. All nuclei with spin greater than 1/2 have a nuclear quadrupole moment, in addition to their magnetic moment. The nucleus used as an example in this paper is 75As, which has spin 3/2

Scalable, ultra-resistant structural colors based on network metamaterials

Structural colors have drawn wide attention for their potential as a future printing technology for various applications, ranging from biomimetic tissues to adaptive camouflage materials. However, an efficient approach to realize robust colors with a scalable fabrication technique is still lacking, hampering the realization of practical applications with this platform. Here, we develop a new approach based on large-scale network metamaterials that combine dealloyed subwavelength structures at the nanoscale with lossless, ultra-thin dielectric coatings. By using theory and experiments, we show how subwavelength dielectric coatings control a mechanism of resonant light coupling with epsilon-near-zero regions generated in the metallic network, generating the formation of saturated structural colors that cover a wide portion of the spectrum. Ellipsometry measurements support the efficient observation of these colors, even at angles of 70°. The network-like architecture of these nanomaterials allows for high mechanical resistance, which is quantified in a series of nano-scratch tests. With such remarkable properties, these metastructures represent a robust design technology for real-world, large-scale commercial applications

The infrared properties of active extragalactic nuclei

In this paper we review the observed infrared properties of the general classes of active extragalactic nuclei with the purpose of relating the observations to the mechanisms responsible for the emission processes. We will first give a summary of those observations which define the energy distributions and emission line ratios of broad groups of objects. We will intersperse measurements of specific features throughout the discussion that illustrate definite emission mechanisms

The X-ray cataclysmic variable 1E0643.0 −1648

Original article can be found at: http://www.nature.com/nature/index.html Copyright Nature Publishing Group. DOI: 10.1038/293204a0 [Full text of this article is not available in the UHRA]We have used a new simultaneous IR/optical high-speed photometer on the UK IR telescope to study the recently discovered X-ray cataclysmic variable 1E0643.0−1648 (refs 1, 2). The light curve of this object obtained by the American Association of Variable Star Observers (AAVSO) (T. Chlebowski, personal communication) has shown it to be a dwarf nova with a recurrence time scale of 15 days. We report here that our photometry, obtained during the decline from an outburst, shows slow flickering, with the optical and IR light curves correlated with no delay. We have also obtained moderate resolution spectra of the star using the Anglo−Australian telescope.Peer reviewe

Simultaneous IR and optical light curves of 2A0311−227

Original article can be found at: http://www.nature.com/nature/index.html Copyright Nature Publishing Group. DOI: 10.1038/301223a0 [Full text of this article is not available in the UHRA]The complex wavelength dependence shown by the light curves of the AM Herculis type binaries such as 2A0311−227 (EFERI) and AM Her itself has led to suggestions that accretion occurs onto both magnetic poles of the white dwarf. The field strengths of the two poles being sufficiently different that one pole dominates at optical wavelengths, while the other produces most of the emission in the IR. Other authors have argued for a single pole model explaining the wavelength dependence of the light curves in terms of the rapidly changing cyclotron opacity with wavelength. An observational method of distinguishing between these two models is provided by the rapid flickering, which is a characteristic property of the light curves at both optical and IR wavelengths. We report here that the optical and IR flickering of 2A0311−227 are highly correlated indicating that in this object the dominant source of cyclotron radiation at both wavelengths is the same accretion column.Peer reviewe