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Search Results: 1 - 10 of 170520 matches for " Christina E. Sarris "
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Sleep Insufficiency, Sleep Health Problems and Performance in High School Students
Xue Ming, Rebecca Koransky, Victor Kang, Sarah Buchman, Christina E. Sarris, and George C. Wagner
Clinical Medicine Insights: Circulatory, Respiratory and Pulmonary Medicine , 2012, DOI: 10.4137/CCRPM.S7955
Abstract: A survey on sleep schedule, sleep health, school performance and school start times was conducted in 1,941 adolescents. A high level of early and circadian-disadvantaged sleep/wake schedules during weekdays was observed. Shorter sleep duration on weekdays was reported, especially in upper classmen. Complaints of inadequate sleep and sleepiness during weekdays, alarm clock use, and napping were prevalent. Night awakening and prolonged sleep onset were common and associated with poor school performance. Students with a sleep length of less than 7 hours on both weekdays and weekends exhibited poorer performance, while those who made up this sleep loss on weekends did not. The total number of poor sleep factors in an individual also correlated with poor school performance. Earlier school start times were associated with a perception of poor sleep quality, shorter sleep duration and more sleep health problems. We conclude that sleep inadequacies and sleep health problems were prevalent in this population, especially in those who started school earlier in the morning, and that these poor sleep factors were associated with school performance.
Location Privacy on DVB-RCS using a “Spatial-Timing” Approach
A. Aggelis,E. T. Sarris
Radioengineering , 2011,
Abstract: DVB-RCS synchronization scheme on the Return Channel requires the RCSTs to be programmed with their location coordinates with an accuracy of no more than a few kilometers. RCSTs use this location information in their ranging calculation to the servicing satellite. For certain users this location information disclosure to the network operator can be seen as a serious security event. Recent work of the authors overcame this requirement by cloaking the location of an RCST in such a way (based on "spatial/geometric" symmetries of the network) that the respective ranging calculations are not affected. In this work we argue that timing tolerances in the Return Channel synchronization scheme, accepted by the DVB-RCS standard, can be used in combination to the "spatial" method, further enhancing the location privacy of an RCST. Theoretical findings of the proposed "spatial-timing" approach were used to develop a practical method that can be used by workers in the field. Finally this practical method was successfully tested on a real DVB-RCS system.
A Location Privacy Extension for DVB-RCS
A. Aggelis,E. T. Sarris,V. Katos
Radioengineering , 2011,
Abstract: In this paper we studied the DVB-RCS (Return Channel through Satellite) standard from a privacy perspective and proposed an approach to incorporate a location privacy enhancing mechanism into the standard. Offering location based privacy in DVB-RCS communication is a challenge as the location of a satellite terminal must be revealed to the network operator of the DVB-RCS network for technical and administrative reasons. We proposed an approach of cloaking the location by intentionally compromising its accuracy whilst maintaining the operability and integrity of the communications system. In addition we implemented a proof of concept technique utilizing the theoretical findings of this work on a real DVB-RCS system, presenting the methodology along with the tools used and the experimental results.
“Playing With Words”: Effects of an Anagram Solving Game-Like Application for Primary Education Students
Chris T. Panagiotakopoulos,Menelaos E. Sarris
International Education Studies , 2013, DOI: 10.5539/ies.v6n2p110
Abstract: The present study reports the basic characteristics of a game-like application entitled “Playing with Words – PwW”. PwW is a single-user application where a word must be guessed given an anagram of that word. Anagrams are presented from a predefined word list and users can repeatedly try to guess the word, from which the anagram is derived, by placing (drag & drop) successively the given letters into the correct orthotactic order. Each effort is assessed as either correct or incorrect, while reaction and total time consumed are also recorded. The purpose of this game is both to entertain the user and to provide teachers with a simple computerized assessment tool. Summative evaluation results, based on 76 primary schoolchildren sample, indicate that the performance of anagram solving tasks explain a significant proportion of variance in reading fluency.
Quiet-time Pc 5 pulsations in the Earth's magnetotail: IMP-8, ISEE-1 and ISEE-3 simultaneous observations
D. V. Sarafopoulos,E. T. Sarris
Annales Geophysicae (ANGEO) , 2003,
Abstract: Quasi-periodic Pc 5 pulsations have been reported inside and just outside the Earth's magnetotail during intervals of low geomagnetic activity. In order to further define their characteristics and spatial extent, we present three case studies of simultaneous magnetic field and plasma observations by IMP-8, ISEE-1 (and ISEE-2 in one case) in the Earth's magnetotail and ISEE-3 far upstream of the bow shock, during intervals in which the spacecraft were widely separated. In the first case study, similar pulsations are observed by IMP-8 at the dawn flank of the plasma sheet and by ISEE-1 near the plasma sheet boundary layer (PSBL) near midnight local time. In the second case study, simultaneous pulsations are observed by IMP-8 in the dusk magnetosheath and by ISEE-1 and 2 in the dawn plasma sheet. In the third case study, simultaneous pulsations are observed in the north plasma sheet boundary layer and the south plasma sheet. We conclude that the pulsations occur simultaneously throughout much of the nightside magnetosphere and the surrounding magnetosheath, i.e. that they have a global character. Some additional findings are the following: (a) the observed pulsations are mixed mode compressional and transverse, where the compressional character is more apparent in the close vicinity of the plane ZGSM=0; (b) the compressional pulsations of the magnetic field in the dusk magnetosheath show peaks that coincide (almost one-to-one) with similar peaks observed inside the dawn plasma sheet; (c) in the second case study the polarization sense of the magnetic field and the recurrent left-hand plasma vortices observed in the dawn plasma sheet are consistent with anti-sunward moving waves on the magneto-pause; (d) pulsation amplitudes are weaker in the PSBL(or lobe) as compared with those in the magneto-tail's flanks, suggesting a decay with distance from the magnetopause; (e) the thickness of the plasma sheet (under extremely quiet conditions) is estimated to be ~22 RE at an average location of (X, Y)GSM=(16, 17) RE, whereas at midnight local time the thickness is ~14 RE. The detected pulsations are probably due to the pressure variations (recorded by ISEE-3) in the solar wind, and/or the Kelvin Helmholtz instability in the low-latitude boundary layer or the magnetopause due to a strongly northward IMF.
Probing the magnetic topology of coronal mass ejections by means of Ulysses/HI-SCALE energetic particle observations
O. Malandraki,E. T. Sarris,P. Trochoutsos
Annales Geophysicae (ANGEO) , 2003,
Abstract: In this work, solar flare energetic particle fluxes (Ee ≥ 42 keV) observed by the HI-SCALE instrument onboard Ulysses, a spacecraft that is probing the heliosphere in 3-D, are utilized as diagnostics of the large-scale structure and topology of the interplanetary magnetic field (IMF) embedded within two well-identified interplanetary coronal mass ejection (ICME) structures. On the basis of the energetic solar flare particle observations firm conclusions are drawn on whether the detected ICMEs have been detached from the solar corona or are still magnetically anchored to it when they arrive at 2.5 AU. From the development of the angular distributions of the particle intensities, we have inferred that portions of the ICMEs studied consisted of both open and closed magnetic field lines. Both ICMEs present a filamentary structure comprising magnetic filaments with distinct electron anisotropy characteristics. Subsequently, we studied the evolution of the anisotropies of the energetic electrons along the magnetic field loop-like structure of one ICME and computed the characteristic decay time of the anisotropy which is a measure of the amount of scattering that the trapped electron population underwent after injection at the Sun. Key words: Interplanetary physics (energetic particles; interplanetary magnetic fields)
Study of high-beta supra-thermal plasma events in the vicinity of magneto-hydrodynamic shock-waves
P. K. Marhavilas,E. T. Sarris
Journal of Engineering Science and Technology Review , 2010,
Abstract: The ratio value – known as plasma parameter “beta” (β) - of the interplanetary-plasma pressure (thermal pressure) to themagnetic field’s (magnetic pressure) or of their energy densities, is critical for the space plasmas and has important consequencesto their properties. Although in the scientific literature the contribution of the supra-thermal particles to the plasmapressure is generally assumed negligible, we deduced, by analyzing energetic particles and magnetic field measurementsrecorded by the Ulysses spacecraft, that in a series of events, the energy density contained in the supra-thermal tail of theparticle distribution is comparable to or even higher than the energy density of the magnetic field, creating conditions ofhigh-beta plasma. In particular, in this paper we analyze Ulysses measurements of the energy density ratio (parameter βep) ofthe supra-thermal (20 keV to ~5 MeV) ions’ (by the HI-SCALE instrument) to the magnetic field’s (by the VHM/FGM instrument)in order to find occurrences of high-beta (βep >1) supra-thermal plasma conditions in the vicinity of interplanetaryshock-waves. These high-beta ion events are associated with energetic particle intensity enhancements which have beenproduced by reacceleration at the shock fronts.
Magnetic topology of coronal mass ejection events out of the ecliptic: Ulysses/HI-SCALE energetic particle observations
O. E. Malandraki,E. T. Sarris,G. Tsiropoula
Annales Geophysicae (ANGEO) , 2003,
Abstract: Solar energetic particle fluxes (Ee > 38 keV) observed by the ULYSSES/HI-SCALE experiment are utilized as diagnostic tracers of the large-scale structure and topology of the Interplanetary Magnetic Field (IMF) embedded within two well-identified Interplanetary Coronal Mass Ejections (ICMEs) detected at 56° and 62° south heliolatitudes by ULYSSES during the solar maximum southern high-latitude pass. On the basis of the energetic solar particle observations it is concluded that: (A) the high-latitude ICME magnetic structure observed in May 2000 causes a depression in the solar energetic electron intensities which can be accounted for by either a detached or an attached magnetic field topology for the ICME; (B) during the traversal of the out-of-ecliptic ICME event observed in July 2000 energetic electrons injected at the Sun are channeled by the ICME and propagate freely along the ICME magnetic field lines to 62° S heliolatitude. Key words. Interplanetary physics (energetic particles; interplanetary magnetic fields)
Broadband radial discone antenna: Design, application and measurements
N. I. Yannopoulou,P. E. Zimourtopoulos,E. T. Sarris
Physics , 2006,
Abstract: The wide band of frequencies that includes all those allocated to 2G/3G applications was defined as 2G/3G band and the discone antenna with a structure of radial wires was defined as radial discone. This antenna was theoretically analysed and software simulated with the purpose of computationally design a broadband model of it. As an application, a radial discone for operation from 800 to 3000 MHz, which include the 2G/3G band, was designed and an experimental model was built and tested. Mathematically expressed measurement error bounds were computed in order to evaluate the agreement between theory and practice.
Computational Modeling of an MRI Guided Drug Delivery System Based on Magnetic Nanoparticle Aggregations for the Navigation of Paramagnetic Nanocapsules
N. K. Lampropoulos,E. G. Karvelas,I. E. Sarris
Computer Science , 2015,
Abstract: A computational method for magnetically guided drug delivery is presented and the results are compared for the aggregation process of magnetic particles within a fluid environment. The model is developed for the simulation of the aggregation patterns of magnetic nanoparticles under the influence of MRI magnetic coils. A novel approach for the calculation of the drag coefficient of aggregates is presented. The comparison against experimental and numerical results from the literature is showed that the proposed method predicts well the aggregations in respect to their size and pattern dependance, on the concentration and the strength of the magnetic field, as well as their velocity when particles are driven through the fluid by magnetic gradients.
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