Monitoring of Ionospheric D-Region Behavior Utilizing the Dual VLF Experiment

2021 ◽  
Author(s):  
Michael Danielides ◽  
Vladimir O. Skripachev
Keyword(s):  
Ionospheric Disturbances ◽  
Limited Information ◽  
Monitoring Networks ◽  
Natural Sources ◽  
X Ray ◽  
Investigation Methods ◽  
Single Station ◽  
D Region ◽  
Propagation Paths ◽  
Composition Changes

<p>Studying Earth's ionosphere applying very low radio frequency (VLF) ground-based networks or only single station instrumentation provides spatially and temporal limited information. The majority of the VLF experiments utilize strong naval communication transmitters as their signal sources. In most of those cases, the signal is relatively unknown, except perhaps for its frequency and field strength. Other than ionosondes (vertical ionospheric sounder), VLF radio transmitters are usually located at different locations than their receiver stations. This results in very different radio wave propagation paths and because of different ionospheric regimes (longitudinal, latitudinal, or seasonal variations).<br><br>Because VLF radio transmission can be influenced by regular natural sources, e.g. sunrise or sunset, or irregular natural sources, e.g. solar X-ray flare or earthquake, it is non-trivial to provide accurate ionospheric weather forecasts or detect precursors for possible hazards. For natural hazards, such as earthquakes, ionospheric disturbances are often found only after the occurrence of the hazard. Therefore, it is essential to experiment with modified approaches, other than the common ionospheric investigation methods.<br><br>The aim of this study is a case-based analysis of the two VLF transmissions from Iceland at 37.5 kHz and 57.4 kHz originating from the Naval Radio Transmitter Facility at Grindavik. Utilizing passive broadband VLF ground-based measurements, we compare observed delay times of the signal behaviors at sunrise and sunset, as well as sudden ionospheric disturbances (SID). Other than the zenith angle dependence, which causes changes of the photoionization at the ionospheric D-region, SID is caused by solar X-ray flare radiation. The solar X-ray flare flux data are provided by NOAA's GOES satellite. The temporal difference in the VLF signal level is of the order of minutes for dusk and dawn. The difference between the two VLF signal levels can not be caused by significant differences in their propagation paths. However, it is assumed that this temporal delay reflects vertical ionospheric composition changes.<br><br>Usually, VLF monitoring networks are used for comparing an observed SID event at various VLF frequencies and recorded from various VLF monitoring stations. The D-region enhancement during daytime is stronger during solar flare events. Especially, by comparing the VLF signal levels the spatial effects of solar flares are studied. However, the present study focuses mainly on temporal variation of the signal levels during dusk, dawn, and during SID events, which again could be caused by vertical ionospheric composition changes.</p>

Problems in Thin-Film X-ray Quantification

1990 ◽  
Vol 48 (2) ◽  
pp. 458-459
Author(s):  
J N Chapman ◽  
W A P Nicholson
Keyword(s):  
Thin Film ◽  
Specimen Thickness ◽  
X Rays ◽  
Characteristic Peak ◽  
Local Composition ◽  
X Ray ◽  
Measured Ratio ◽  
Path Lengths ◽  
Composition Changes

Energy dispersive x-ray microanalysis (EDX) is widely used for the quantitative determination of local composition in thin film specimens. Extraction of quantitative data is usually accomplished by relating the ratio of the number of atoms of two species A and B in the volume excited by the electron beam (nA/nB) to the corresponding ratio of detected characteristic photons (NA/NB) through the use of a k-factor. This leads to an expression of the form nA/nB = kAB NA/NB where kAB is a measure of the relative efficiency with which x-rays are generated and detected from the two species.Errors in thin film x-ray quantification can arise from uncertainties in both NA/NB and kAB. In addition to the inevitable statistical errors, particularly severe problems arise in accurately determining the former if (i) mass loss occurs during spectrum acquisition so that the composition changes as irradiation proceeds, (ii) the characteristic peak from one of the minority components of interest is overlapped by the much larger peak from a majority component, (iii) the measured ratio varies significantly with specimen thickness as a result of electron channeling, or (iv) varying absorption corrections are required due to photons generated at different points having to traverse different path lengths through specimens of irregular and unknown topography on their way to the detector.

scholarly journals Case study of the mesospheric and lower thermospheric effects of solar X-ray flares: coupled ion-neutral modelling and comparison with EISCAT and riometer measurements

2008 ◽  
Vol 26 (8) ◽  
pp. 2311-2321 ◽  
Author(s):  
C.-F. Enell ◽  
P. T. Verronen ◽  
M. J. Beharrell ◽  
J. P. Vierinen ◽  
A. Kero ◽  
...  
Keyword(s):  
Solar Proton ◽  
Spectral Irradiance ◽  
Cluster Ions ◽  
Ion Chemistry ◽  
Density Profiles ◽  
X Ray ◽  
Noise Absorption ◽  
D Region ◽  
Electron Density Profiles ◽  
Cosmic Noise

Abstract. Two case studies of upper mesospheric and lower thermospheric (UMLT) high-latitude effects of solar X-ray flares are presented. Sodankylä Ion-neutral Chemistry Model (SIC) electron density profiles agree with D-region EISCAT and riometer observations, provided that the profiles of the most variable ionisable component, nitric oxide, are adjusted to compensate for NOx production during preceding geomagnetically active periods. For the M6-class flare of 27 April 2006, following a quiet period, the agreement with cosmic noise absorption observed by the Sodankylä riometers was within reasonable limits without adjustment of the [NO] profile. For the major (X17-class) event of 28 October 2003, following high auroral activity and solar proton events, the NO concentration had to be increased up to on the order of 108 cm−3 at the D-region minimum. Thus [NO] can in principle be measured by combining SIC with observations, if the solar spectral irradiance and particle precipitation are adequately known. As the two case events were short and modelled for high latitudes, the resulting neutral chemical changes are insignificant. However, changes in the model ion chemistry occur, including enhancements of water cluster ions.

scholarly journals The Effect of Silica Sand Proportion in Laser Scabbling Process on Cement Mortar

Metals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1914
Author(s):  
Tam-Van Huynh ◽  
Youngjin Seo ◽  
Dongkyoung Lee
Keyword(s):  
Cement Mortar ◽  
Silica Sand ◽  
Construction Sites ◽  
Power Laser ◽  
Concrete Repair ◽  
X Ray ◽  
Micro Cracks ◽  
Wide Range ◽  
Cement Based Materials ◽  
Composition Changes

Cement mortar composite has a wide range of applications on construction sites, including masonry, plastering and concrete repair. In construction sites, scabbling process is a method to remove from a few millimeters to several centimeters of defect concrete surfaces. As a result, it is essential to investigate the scabbling characteristics for cement mortar with different silica sand proportion in laser scabbling process. In this study, 5 types of cement mortar with different silica sand proportions in mixing were fabricated and scabbled by using a high-density power laser beam. The effects of silica sand proportion in color changing and penetration depth of the samples after laser scabbling process were studied. Furthermore, the generation of micro-cracks and pores were observed by using scanning electron microscopy (SEM). In addition, chemical composition changes between processed zone and non-processed zone were also evaluated by Energy Dispersive X-ray (EDX) analysis. The results of this study are expected to provide valuable knowledge in understanding of the laser scabbling process for cement-based materials.

The Seven Last Infra-Uranium Elements to Be Discovered

2019 ◽  
Author(s):  
Eric Scerri
Keyword(s):  
Periodic Table ◽  
Atomic Weight ◽  
Weak Acid ◽  
Ray Method ◽  
Natural Sources ◽  
Transuranium Elements ◽  
X Ray ◽  
Naturally Occurring ◽  
Missing Element

The term “infra-uranium,” meaning before uranium, is one that I have proposed by contrast to the better-known term transuranium elements that are discussed in the following chapter. The present chapter concerns the last seven elements that formed the missing gaps in the old periodic table that ended with the element uranium. After Moseley developed his X-ray method, it became clear that there were just seven elements yet to be isolated among the 92 naturally occurring elements or hydrogen (#1) to uranium (#92). This apparent simplicity is somewhat spoiled by the fact that, as it turned out, some of these seven elements were first isolated from natural sources following their being artificially created, but this raises more issues that are best left to the next chapter of this book. The fact remains that five of these seven elements are radioactive, the two exceptions being hafnium and rhenium, the second and third of them to be isolated. The first of the seven final infra-uranium elements to be discovered was protactinium, and it was one of the lesser-known predictions made by Mendeleev. In his famous 1896 paper, Mendeleev indicated incorrect values for both thorium (118) and uranium (116). (See figure 1.6.) A couple of years later, he corrected both of these values and showed a missing element between thorium and uranium (figure 4.4). In doing so, Mendeleev added the following paragraph, in which he made some specific predictions. . . . Between thorium and uranium in this series we can further expect an element with an atomic weight of about 235. This element should form a highest oxide R2O5, like Nb and Ta to which it should be analogous. Perhaps in the minerals which contain these elements a certain amount of weak acid formed from this metal will also be found.. . . The modern atomic weight for eka-tantalum or protactinium is 229.2. The apparent inaccuracy in Mendeleev’s prediction is not too surprising, however, since he never knew that protactinium is a member of only four “pair reversals” in the entire periodic table.

Biocompatible Hydroxyapatite Derive from Selayang Fish Bone via Mechanochemical Treatment

2020 ◽  
Vol 307 ◽  
pp. 339-344
Author(s):  
Ishak Qayyum Afiqah ◽  
Nik Aziz Nik Ali ◽  
Abd Majid Siti Nurhaziqah ◽  
Hasiah Salleh
Keyword(s):  
Room Temperature ◽  
Fish Bone ◽  
X Ray Diffraction ◽  
Synthetic Process ◽  
Calcination Process ◽  
Natural Sources ◽  
X Ray ◽  
Fish Bones ◽  
Phosphate Mineral

Age of monstrous amount of underutilized marine processing byproducts has been perceived as waste and many effort were given to utilize these materials in various application. With an incredible number of study on these byproducts, some compound were identified and apply for human utilization. Hydroxyapatite (HAp) is the main inorganic calcium phosphate mineral with excellent osteoconductivity, good bioactivity and biocompatibility. The production of HAp powder from synthetic process involves many chemicals with complicated procedures. Due to this matter, the raw HAp powder was extracted from natural sources selayang fish bones. Extortion process started with boiling fish bones to eliminate adherent fish meats. After calcination process fish bone were dried in room temperature before crushed by using grinder to obtain the powder. Next, the powder undergo calcination process at 900°C for 5 hours. The characterization of raw HAp was done via X-ray Diffraction, Fourier Transform Infrared Spectometer, Scanning Electron Microscopy, and Thermogravimetric analysis.

scholarly journals GNSS and SAR Signal Delay in Perturbed Ionospheric D-Region During Solar X-Ray Flares

2020 ◽  
Vol 17 (7) ◽  
pp. 1198-1202 ◽  
Author(s):  
Aleksandra Nina ◽  
Giovanni Nico ◽  
Oleg Odalovic ◽  
Vladimir M. Cadez ◽  
Miljana Todorovic Drakul ◽  
...  
Keyword(s):  
Signal Delay ◽  
X Ray ◽  
D Region
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