Extreme-ultraviolet- and X-Ray-driven Photochemistry of Gaseous Exoplanets

The interaction of exoplanets with their host stars causes a vast diversity in bulk and atmospheric compositions and physical and chemical conditions. Stellar radiation, especially at the shorter wavelengths, drives the chemistry in the upper atmospheric layers of close orbiting gaseous giants, providing drastic departures from equilibrium. In this study, we aim at unfolding the effects caused by photons in different spectral bands on the atmospheric chemistry. This task is particularly difficult because the characteristics of chemical evolution emerge from many feedbacks on a wide range of timescales, and because of the existing correlations among different portions of the stellar spectrum. In describing the chemistry, we have placed particular emphasis on the molecular synthesis induced by X-rays. The weak X-ray photoabsorption cross sections of the atmospheric constituents boost the gas ionization to pressures inaccessible to vacuum and extreme-ultraviolet photons. Although X-rays interact preferentially with metals, they produce a secondary electron cascade able to ionize efficiently hydrogen- and helium-bearing species, giving rise to a distinctive chemistry.

Approaches to Inactivating Aflatoxins—A Review and Challenges

According to the World Health Organization, the contamination of crops with aflatoxins poses a significant economic burden, estimated to affect 25% of global food crops. In the event that the contaminated food is processed, aflatoxins enter the general food supply and can cause serious diseases. Aflatoxins are distributed unevenly in food or feedstock, making eradicating them both a scientific and a technological challenge. Cooking, freezing, or pressurizing have little effect on aflatoxins. While chemical methods degrade toxins on the surface of contaminated food, the destruction inside entails a slow process. Physical techniques, such as irradiation with ultraviolet photons, pulses of extensive white radiation, and gaseous plasma, are promising; yet, the exact mechanisms concerning how these techniques degrade aflatoxins require further study. Correlations between the efficiency of such degradation and the processing parameters used by various authors are presented in this review. The lack of appropriate guidance while interpreting the observed results is a huge scientific challenge.

Rare-Earth Doped Upconverting Nanophosphors for Light-Mediated Biocidal Surface Development

Since the earliest civilization, diminishing the occurrence and subsequent transmission of pathogenic microorganisms in the indoor environment has been one of the utmost priorities to the human society. In line with intensive research towards the surface disinfection through the use of several photocatalytic processes, rare-earth doped upconverting nanophosphors (UCNPs) have recently drawn a great attention on the basis of their purely optical phenomenon of directly converting visible light into germicidal ultraviolet radiation (namely ultraviolet C) via the unique photoluminescence process namely ‘upconversion’. The efficient upconversion of abundant visible light into ultraviolet photons in the germicidal range and, consequently, effective biocidal action while coated onto surfaces enable UCNPs as a potential candidate to be used for inhibiting germ spreading through the inanimate surface in public places, hospitals and so forth.

The nature of intrinsic recombination emission in SrSO4 irradiated with ultraviolet photons

The synthesized SrSO4 crystalline powders were irradiated at photon energies from 6 ÷ 12 eV, in the temperature range from 15 ÷ 300 K. The investigation was carried out by the methods of atomic absorption, luminescence and vacuum ultraviolet spectroscopy. Intrinsic emissions were found at 3.7-3.8 eV, 4.2-4.6 eV and 4.9-5 eV, and long-wavelength recombination emissions at 2.6-2.7 eV and 2.9-3.0 eV.The synthesized SrSO4 crystalline powders were irradiated at photon energies from 6 ÷ 12 eV, in the temperature range from 15 ÷ 300 K. The investigation was carried out by the methods of atomic absorption, luminescence and vacuum ultraviolet spectroscopy. Intrinsic emissions were found at 3.7-3.8 eV, 4.2-4.6 eV and 4.9-5 eV, and long-wavelength recombination emissions at 2.6-2.7 eV and 2.9-3.0 eV.

Applications of Cold Atmospheric Pressure Plasma in Dentistry

Plasma is an electrically conducting medium that responds to electric and magnetic fields. It consists of large quantities of highly reactive species, such as ions, energetic electrons, exited atoms and molecules, ultraviolet photons, and metastable and active radicals. Non-thermal or cold plasmas are partially ionized gases whose electron temperatures usually exceed several tens of thousand degrees K, while the ions and neutrals have much lower temperatures. Due to the presence of reactive species at low temperature, the biological effects of non-thermal plasmas have been studied for application in the medical area with promising results. This review outlines the application of cold atmospheric pressure plasma (CAPP) in dentistry for the control of several pathogenic microorganisms, induction of anti-inflammatory, tissue repair effects and apoptosis of cancer cells, with low toxicity to healthy cells. Therefore, CAPP has potential to be applied in many areas of dentistry such as cariology, periodontology, endodontics and oral oncology.

Graphite to diamond transition induced by photoelectric absorption of ultraviolet photons

The phase transition from graphite to diamond is an appealing object of study because of many fundamental and also, practical reasons. The out-of-plane distortions required for the transition are a good tool to understand the collective behaviour of layered materials (graphene, graphite) and the van der Waals forces. As today, two basic processes have been successfully tested to drive this transition: strong shocks and high energy femtolaser excitation. They induce it by increasing either pressure or temperature on graphite. In this work, we report a third method consisting in the irradiation of graphite with ultraviolet photons of energies above 4.4 eV. We show high resolution electron microscopy images of pyrolytic carbon evidencing the dislocation of the superficial graphitic layers after irradiation and the formation of crystallite islands within them. Electron energy loss spectroscopy of the islands show that the sp2 to sp3 hybridation transition is a surface effect. High sensitivity X-ray diffraction experiments and Raman spectroscopy confirm the formation of diamond within the islands.

Optimizing spectral quality with quantum dots to enhance crop yield in controlled environments

Bioregenerative life-support systems (BLSS) involving plants will be required to realize self-sustaining human settlements beyond Earth. To improve plant productivity in BLSS, the quality of the solar spectrum can be modified by lightweight, luminescent films. CuInS2/ZnS quantum dot (QD) films were used to down-convert ultraviolet/blue photons to red emissions centered at 600 and 660 nm, resulting in increased biomass accumulation in red romaine lettuce. All plant growth parameters, except for spectral quality, were uniform across three production environments. Lettuce grown under the 600 and 660 nm-emitting QD films respectively increased edible dry mass (13 and 9%), edible fresh mass (11% each), and total leaf area (8 and 13%) compared with under a control film containing no QDs. Spectral modifications by the luminescent QD films improved photosynthetic efficiency in lettuce and could enhance productivity in greenhouses on Earth, or in space where, further conversion is expected from greater availability of ultraviolet photons.

Mechanism of Electronegativity Heterojunction of Nanometer Amorphous-Boron on Crystalline Silicon: An Overview

The discovery of the extremely shallow amorphous boron-crystalline silicon heterojunction occurred during the development of highly sensitive, hard and robust detectors for low-penetration-depth ionizing radiation, such as ultraviolet photons and low-energy electrons (below 1 keV). For many years it was believed that the junction created by the chemical vapor deposition of amorphous boron on n-type crystalline silicon was a shallow p-n junction, although experimental results could not provide evidence for such a conclusion. Only recently, quantum-mechanics based modelling revealed the unique nature and the formation mechanism of this new junction. Here, we review the initiation and the history of understanding the a-B/c-Si interface (henceforth called the “boron-silicon junction”), as well as its importance for the microelectronics industry, followed by the scientific perception of the new junctions. Future developments and possible research directions are also discussed.

Revealing the photo-degradation mechanism of PM6:Y6 based high-efficiency organic solar cells

The photo-degradation mechanism of OSCs based on PM6:Y6 or its derivatives is studied. Ultraviolet photons cause more severe photo-degradation in OSCs than others, and the photo-degradation of PM6 can dominate the photo-degradation in devices.

What lies immediately outside of the heliosphere in the very local interstellar medium (VLISM): What will ISP detect?

<p>The Interstellar Probe (ISP) will provide the first direct<br />measurements of interstellar gas and dust when it travels far beyond the<br />heliopause where the solar wind no longer influences the ambient medium.<br />We summarize in this presentation what we have been learning about the VLISM<br />from 20 years of remote observations with the high-resolution spectrographs<br />on the Hubble Space Telescope. Radial velocity measurements of interstellar<br />absorption lines seen in the lines of sight to nearby stars allow us to<br />measure the kinematics of gas flows in the VLISM. We find that the heliosphere<br />is passing through a cluster of warm partially ionized interstellar clouds.<br />The heliosphere is now at the edge of the Local Interstellar Cloud (LIC) and<br />heading in the direction of the slighly cooler G cloud. Two other warm clouds<br />(Blue and Aql) are very close to the heliosphere. We find that there is a<br />large region of the sky with very low neutral hydrogen column density, which<br />we call the hydrogen hole. In the direction of the hydrogen hole is the<br />brightest photoionizing source, the star Epsilon Canis Majoris (CMa). Extreme<br />ultraviolet photons from this star produce a Stromgren sphere region of<br />ionized gas as large as the Local Cavity (extending to 100-200 parsecs)<br />and produce Stromgren shells at the outer regions of the local warm clouds<br />including the LIC.</p> <p>When the ISP passes beyond the hydrogen wall at a distance of about 500 AU,<br />it will likely enter the outer edge of the LIC where photoionization from<br />Epsilon CMa plays an important role. Analysis of Hubble observations of<br />interstellar absorption proves estimates of the densities, temperature,<br />pressure, and flow properties of the main portion of the LIC, but we have<br />little informtion on these properties at the LIC's edge. Comparison with the<br />inflow vector of neutral helium measured by IBEX and Ulysses indicates a<br />slightly different flow speed and direction than the mean flow of the LIC gas.<br />ISP will provide direct measurements of the flow and gas properties of this<br />poorly understood region. In particular, ISP will provide information on<br />how photoionization from Epsilon CMa influences warm clouds through ionization,<br />heating, and perhaps pressure balance. This information may resolve questions<br />concerning the magnetic field surrounding the heliosphere.</p>