34 research outputs found
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EISCAT/CRRES observations: Nightside ionospheric ion outflow and oxygen-rich substorm injections
No full textWe present combined observations made near midnight by the EISCAT radar, all-sky cameras and the combined released and radiation efects satellite (CRRES) shortly before and during a substorm. In particular, we study a discrete, equatorward-drifting auroral arc, seen several degrees poleward of the onset region. The arc passes through the field-aligned beam of the EISCAT radar and is seen to be associated with a considerable upflow of ionospheric plasma. During the substorm, the CRRES satellite observed two major injections, 17 min apart, the second of which was dominated by O+ ions. We show that the observed are was in a suitable location in both latitude and MLT to have fed O+ ions into the second injection and that the upward flux of ions associated with it was sufficient to explain the observed injection. We interpret these data as showing that arcs in the nightside plasma-sheet boundary layer could be the source of O+ ions energised by a dipolarisation of the mid- and near-Earth tail, as opposed to ions ejected from the dayside ionosphere in the cleft ion fountain
A Review of Wireless Sensor Networks: Early Accident Detection Models for South African Mine Industries
No full textA Survey of Biometric Recognition Systems in E-Business Transactions
No full textThe global expansion of e-business applications has introduced novel challenges, with an escalating number of security issues linked to online transactions, such as phishing attacks and identity theft. E-business involves conducting buying and selling activities online, facilitated by the Internet. The application of biometrics has been proposed as a solution to mitigate security concerns in e- business transactions. Biometric recognition involves the use of automated techniques to validate an individual's identity based on both physiological and behavioural characteristics. This research focuses specifically on implementing a multimodal biometric recognition system that incorporates face and fingerprint data to enhance the security of e-business transactions. In contrast to unimodal systems relying on a single biometric modality, this approach addresses limitations such as noise, universality, and variations in both interclass and intraclass scenarios. The study emphasizes the advantages of multimodal biometric systems while shedding light on vulnerabilities in biometrics within the e- business context. This in-depth analysis serves as a valuable resource for those exploring the intersection of e-business and biometrics, providing insights into the strengths, challenges, and best practices for stakeholders in this domain. Finally, the paper concludes with a summary and outlines potential avenues for future research
Reconstruction of nonmonotonic electron density profiles of the Martian topside ionosphere
No full textOne of the problems in reconstructing the real ionosphere from an ionogram is the occurrence of a 'valley,' where electron density decreases with altitude and make a non-monotonic profile. For the case of the Earth ionosphere, the ordinary and extraordinary ray data, accompanied with an empirical model, based on the observations, are necessary to obtain a mathematical solution for a 'valley,' such as the region between the E and F layers. MARSIS/MEX is a topside sounder designed to observe the ionosphere of Mars. Some 'valley' structures were found in the ionograms measured by MARSIS. The echoes of the extraordinary ray are not available owing to the absence of the strong magnetic field on Mars. Therefore, it is difficult to have a mathematical solution for the valleys in the Martian ionosphere. In this paper, a least square method with a simple model is presented to solve the 'valley' problem in the topside ionosphere of Mars. The electron density profiles with 'valleys' observed by the Radio Occultation experiment onboard MGS are used to rebuild the virtual depths at MARSIS frequencies. The reconstructed electron density profile by the least square method with a simple model from the rebuilt virtual depth curve is compared with the original electron density profile. It is proved that this method can reproduce small valleys in the profile of the Martian ionosphere well. (C) 2010 Elsevier Ltd. All rights reserved.Astronomy & AstrophysicsSCI(E)EI3ARTICLE101391-13995
Dynamic Bandwidth Allocation Algorithm to improve Quality of Service in Intelligent Home Networks
No full textAnalysis of a topside ionospheric model using GPS and ionosonde observables
No full textGround-based vertical incidence soundings are well suited to model the bottom-side ionosphere but are not so good for dependably modelling the topside ionosphere. This study aims to combine vertical incidence sounding and dual-frequency GPS measurements to reconstruct the topside profile. The reconstruction technique relays on the use of the so-called vary-Chap approach that use an α-Chapman function with a continuously varying scale height. We tested our technique with ionograms and GPS observations recorded at Ebro observatory, Spain (geomagnetic coordinates 43.6°N and 80.9°E). The contribution of the topside ionosphere to the vertical TEC was calculated as the difference between the vertical TEC estimated from GPS measurements and the contribution of the bottom-side ionosphere estimated by integration of the electron density obtained from ionograms. The obtained topside vertical TEC were used to estimate the parameters of the vary-Chap function that represents the topside profile, namely the transition height where the dominant ion species change from O + to H + , the scale height at the transition height, and the shape factor that controls the steepness of the O + to H + transition. The results are analyzed for solstices and equinoxes for a high solar activity year. The values obtained for the transition height are in agreement with those derived by other author. The topside profile seems to merge swiftly with an empirical plasmasphere model based on Radio Plasma Image measurements.Fil: Meza, Amalia Margarita. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Brunini, Claudio Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Gularte Scarone, Angela Erika. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Mosert, Marta Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; Argentin
