Detecting the nir fingerprint of colors: The characteristic response of modern blue pigments

Reflectance spectroscopy in the ultraviolet (UV), visible (Vis), and near infrared (NIR) range is widely applied to art studies for the characterization of paints and pigments, with the advantages of non-invasive techniques. Isolating and detecting the fingerprint of pigments, especially in the NIR range, is quite challenging, since the presence of vibrational transitions of the most common organic functional groups prevents to relate the optical spectrum of a composite sample, as an artwork is, to each one of its elements (i.e., support, binder, and specific pigment). In this work, a method is presented to obtain the UV-Vis-NIR optical response of the single components of a model composite sample reproducing an artwork, i.e., the support, the binder, and the pigment or dye, by using diffuse reflectance spectroscopy. This allowed us to obtain the NIR spectral fingerprint of blue pigments and to identify specific features possibly applicable for detecting cobalt and phthalocyanine blue colors in artwork analysis

Chemical separation of acrylic color components enabling the identification of the pigment spectroscopic response

Acrylic colors are mixtures of several components that can be identified as pigments, binders, and fillers, so that, when analyzed, the characteristic response of the different components may not be recognizable. This limits the accuracy of spectroscopic techniques, nonetheless particularly useful as they are noninvasive and can be applied in situ on real artworks. Here, a method is proposed to chemically separate and identify the different components of acrylic colors, in order to be able to study their spectroscopic response separately, in particular by ultraviolet visible near infrared diffuse reflectance. The results clearly show that the chemical and analytical method developed here is fully reliable, with the advantage of clearly separating the response of the different components without any change of their chromatic chemical properties. As a case study, the new method is applied here to original acrylic colors used by the Italian artist Ico Parisi, in view of building a spectra databas

First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole

When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42 ± 3 μas, which is circular and encompasses a central depression in brightness with a flux ratio 10:1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M = (6.5 ± 0.7) × 109 Me. Our radiowave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible

First M87 Event Horizon Telescope Results. II. Array and Instrumentation

The Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array that comprises millimeter- and submillimeter-wavelength telescopes separated by distances comparable to the diameter of the Earth. At a nominal operating wavelength of ~1.3 mm, EHT angular resolution (λ/D) is ~25 μas, which is sufficient to resolve nearby supermassive black hole candidates on spatial and temporal scales that correspond to their event horizons. With this capability, the EHT scientific goals are to probe general relativistic effects in the strong-field regime and to study accretion and relativistic jet formation near the black hole boundary. In this Letter we describe the system design of the EHT, detail the technology and instrumentation that enable observations, and provide measures of its performance. Meeting the EHT science objectives has required several key developments that have facilitated the robust extension of the VLBI technique to EHT observing wavelengths and the production of instrumentation that can be deployed on a heterogeneous array of existing telescopes and facilities. To meet sensitivity requirements, high-bandwidth digital systems were developed that process data at rates of 64 gigabit s−1, exceeding those of currently operating cm-wavelength VLBI arrays by more than an order of magnitude. Associated improvements include the development of phasing systems at array facilities, new receiver installation at several sites, and the deployment of hydrogen maser frequency standards to ensure coherent data capture across the array. These efforts led to the coordination and execution of the first Global EHT observations in 2017 April, and to event-horizon-scale imaging of the supermassive black hole candidate in M87

Characterization of organic semiconductors by a large-signal capacitance-voltage method at high and low frequencies.

ITO/semiconductor/metal structures, with metal-free tetraphenylporphyrin (H2-TPP) as organic semiconductor, are investigated by means of a capacitance–voltage (C–V) method employing a large-signal triangular voltage waveform, which allows C–V measurements to be performed from 100 kHz to 100 mHz. The semiconductor layer, 60 nm in thickness, was deposited by molecular beam epitaxy on an ITO substrate and covered by aluminum back contacts. By performing the C–V measurements at low frequencies, transport and trapping of carriers are studied. On the contrary, when the signal frequencies are high in comparison with the carrier transit time in the device, metal–semiconductor interactions at the contacts are investigated

Electrical characterization of organic semiconductors by transient current methods

This paper presents a method for characterizing the transport properties of organic semiconductors by means of large-signal electrical transients. For validating the method, poly(phenylene-vinylene) (PPV) was chosen as a test material, thanks to its widely investigated properties. Large voltage steps are applied to Au/PPV/Au test structures and, from the resulting current transient, the carrier mobility is measured. Transient phenomena are shown to give insight on the physical properties of the material and on the technological characteristics of the device, while requiring a simpler test system in comparison to other methods, like impedance spectroscopy and time-of-flight measurements

Molecular beam deposition of thin films of organic semiconductors.

The ultra-high vacuum technique of organic molecular beam deposition (OMBD) has been recently proved to provide a very good method for growing highly controlled thin films of organic semiconductors. The approximate ordering of a crystalline layer to a substrate, also called quasi-epitaxy, can be achieved with a proper choice of substrate and deposition conditions. Poly- and oligo-thiophenes are among the most interesting and widely studied organic semiconductors for applications in electronic and photonic devices, thanks to their high carrier mobility and large nonlinear optical response, combined with an exceptionally high flexibility of molecular engineering. Here, the deposition and the main properties of films of substituted sexithiophene molecules (6T) obtained by OMBD are discussed on the basis of X-ray diffraction and optical absorption measurements