1,721,184 research outputs found
Sunscreen tests: Correspondence between in vitro data and values reported by the manufacturers
Get PDFBackground: In vitro sunscreen tests are diffusively used to test both the sun
protection factor (SPF) and the photo-stability of filters. Spectrophotometric measurements
of the absorbance of ultraviolet radiations through a sunscreen applied on
a suitable substrate allow a rapid evaluation of its protection factor both at short and
long wavelength ultraviolet radiation (UVB and UVA).
Objectives: The objective of this study has been to demonstrate if Teflon can be
adopted as substrate both for SPF evaluation and photo-stability tests. Moreover, we
have investigated if there is a correspondence between in vitro SPF measurements
and values reported by manufacturers on sunscreens.
Material and methods: Teflon has been used to perform several photo-stability tests
by irradiating the filters with different wavebands and analyzing the combined effect
of UVand infrared (IR) light. Similar analyses have been carried out using PMMA Plates,
which is the standard substrate for UVA in vitro test.
Results: We have demonstrated that it is possible to establish a good correspondence
between in vitro SPF and values reported by manufacturers on sunscreens. We have
also verified that the in vitro/label SPF correlation curve depends on the quantity of
product applied while this does not seem to be true for other parameters like Critical
Wavelength and UVA ratio. With regard to photo-stability studies, our results indicate
for the first time that IR irradiation may have a role on photo-degradation.
Conclusions: The results show that there is a good correlation between the in vitro
SPF determined by the present method and the SPF reported by the manufacturer
Osmium atomic-oxygen protection by an iridium overcoat for increased extreme-ultraviolet grating efficiency
No full textThe deposition of a 30-Å-thick layer of iridium upon a 250-Å-thick osmium reflective layer for use as a diffraction grating in the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) satellite observatory has provided sufficient protection from an expected maximum orbital atomic-oxygen fluence of 1 × 1016 atoms/cm−2. The grating parameters of groove constant and depth, efficiencies of zeroth-order, first and second inside orders, and first inside-order efficiency positional uniformity as well as stray light near the first inside order of the Ir–Os-coated grating were measured within a CHIPS spectral bandpass of 90–260 Å. Stray-light measurements were also made near the first inside spectral order at 304, 584, and 1216 Å. The results make the Ir–Os coat an acceptable grating reflectivity layer for CHIPS and other spaceborne extreme-ultraviolet spectrometers that employ grazing-incidence reflection optics. © 2003 Optical Society of America
Extreme ultraviolet multilayers for solar physics applications: A brief review
No full textA review of extreme ultraviolet (EUV) multilayers for solar physics applications is presented. Several promising material couples, as well as different optimization strategies, have been explored to optimize the peak reflectance at different wavelengths. For example, ad-hoc capping layers can be employed both to protect the structure underneath and to enhance the reflectance performance at a specific wavelength or to achieve other features such as spectral width and purity. Wide-band and multiband EUV coatings can be achieved by using a-periodic designs, which are still largely unexplored. Aperiodic structures provide novel solutions to be considered in view of future space missions. All the proposed designs are discussed considering their stability in time and along space missions
Extreme-ultraviolet calibration of thin-film zr filters for the cosmic hot interstellar plasma spectrometer
No full textThe design and calibration of thin-film Zr transmission filters for the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) spaceborne astronomical telescope is presented. The transmission of a 1000-Åthick Zr filter is measured for wavelengths from 45 to 1304 Å as well as its variability with respect to expected space-flight environmental extremes of temperature, vibration, and atomic O bombardment. For the CHIPS spectral band of 90–260 Å, the transmission of the Zr filter is deemed useful between 90 and 200 Å and is stable with respect to expected temperature and vibrational changes. The maximum atomic O bombardment decreases the filter transmission between 90 and 130 Å by 20% and does not appreciably affect the rest of the CHIPS bandpass. These results make Zr an acceptable filter candidate for CHIPS. © 2002 Optical Society of America
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mirrors for space telescopes: Degradation issues
No full textMirrors are a subset of optical components essential for the success of current and future space missions. Most of the telescopes for space programs ranging from Earth Observation to Astrophysics and covering all the electromagnetic spectrum from X-rays to Far-Infrared are based on reflective optics. Mirrors operate in diverse and harsh environments that range from Low-Earth Orbit, to interplanetary orbits and the deep space. The operational life of space observatories spans from minutes (sounding rockets) to decades (large observatories), and the performance of the mirrors within the optical system is susceptible to degrade, which results in a transient optical efficiency of the instrument. The degradation that occurs in space environments depends on the operational life on the orbital properties of the space mission, and it reduces the total system throughput and hence compromises the science return. Therefore, the knowledge of potential degradation physical mechanisms, how they affect mirror performance, and how to prevent it, is of paramount importance to ensure the long-term success of space telescopes. In this brief review paper we report an overview on current mirror technology for space missions with a particular focus on the importance of degradation and radiation resistance of the coating materials
Delay systems and phase retarders based on multilayers coated mirrors for FEL beam manipulation
No full textThe intensity of the radiation produced by a Free Electron Laser (FEL) is more intense, coherent, and with much higher photon density with respect to the radiation generated by storage rings undulators. FERMI@Elettra will use a seeding technique which provides near Gaussian temporal structure of the pulse with a bandwidth close to the transform limit. In order to preserve the properties of such pulse, the beam manipulation towards the ending station is performed by the use of multilayer coatings (MLs). The primary application is in the delay line systems, useful in pump and probe experiment: the beam is split and one of the arm is equipped with multilayer mirrors which are able to reject the fundamental harmonic, selecting the third; the two beams are then recombined and the relative delay can be controlled by changing the mirrors distance. Specific designs and working principle of such MLs are presented elsewhere. In this work the time delay of pulse travelling in the nanostructures is investigated and photoemission experiment applied to its evaluation conceived. MLs are also studied for verifying their possible application in a phase shifter set-up, useful to have control of the source polarization or to produce elliptical and circularly polarized light. In this way, the FELs circular polarized radiation, which is emitted out of the electron plane and therefore it is very difficult to be manipulated, can be generated from a plane pulse linearly polarized. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE)
Nanowire Grid Reflecting Polarizers for Ultraviolet Applications
Get PDFPolarimetry in the far ultraviolet (FUV) is a powerful tool in many applications such as UV/EUV ellipsometry, characterization and control of the beam polarization status in large scale facilities and solar physics. FUV polarizers are among the most difficult components to manufacture, mainly due to the lack of dichroic and transparent materials in this spectral range. Although many different solutions for their fabrication have been investigated in the last decades, surprisingly, the use of Wire Grid Polarizers (WGPs) is still poorly investigated in this spectral region. In this work, two different concepts of WGPs have been designed and optimized for the FUV range: one is based on absorptive nano-wires on top of an highly reflective substrate, and the second one is based on highly reflective nano-wires on top of an absorptive substrate. Different wires' shapes have been considered and relative structures optimized at a target wavelength of 121.6 nm. Two very promising solutions have been selected, which exhibit a polarization degree over 99.9% and a TE-reflectance over 0.2. Their sensitivity to the wires' dimension parameters have been investigated to assess their feasibility
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