95 research outputs found
Modified extended backward differentiation formulae for the numerical solution of stiff initial value problems in ODEs and DAEs
AbstractFor many years the methods of choice for the numerical solution of stiff initial value problems and certain classes of differential algebraic equations have been the well-known backward differentiation formulae (BDF). More recently, however, new classes of formulae which can offer some important advantages over BDF have emerged. In particular, some recent large-scale independent comparisons have indicated that modified extended backward differentiation formulae (MEBDF) are particularly efficient for general stiff initial value problems and for linearly implicit DAEs with index â©˝3. In the present paper we survey some of the more important theory associated with these formulae, discuss some of the practical applications where they are particularly effective, e.g., in the solution of damped highly oscillatory problems, and describe some significant recent extensions to the applicability of MEBDF codes
Almost Block Diagonal Linear Systems: Sequential and Parallel Solution Techniques, and Applications
Almost block diagonal (ABD) linear systems arise in a variety of contexts, specifically in numerical methods for two-point boundary value problems for ordinary differential equations and in related partial differential equation problems. The stable, efficient sequential solution of ABDs has received much attention over the last fifteen years and the parallel solution more recently. We survey the fields of application with emphasis on how ABDs and bordered ABDs (BABDs) arise. We outline most known direct solution techniques, both sequential and parallel, and discuss the comparative efficiency of the parallel methods. Finally, we examine parallel iterative methods for solving BABD systems. Copyright (C) 2000 John Wiley & Sons, Ltd
ADIPLS -- the Aarhus adiabatic oscillation package
Development of the Aarhus adiabatic pulsation code started around 1978.
Although the main features have been stable for more than a decade, development
of the code is continuing, concerning numerical properties and output. The code
has been provided as a generally available package and has seen substantial use
at a number of installations. Further development of the package, including
bringing the documentation closer to being up to date, is planned as part of
the HELAS Coordination Action.Comment: Astrophys. Space Sci., in the pres
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Transonic flutter analysis using a fully coupled density based solver for inviscid flow
This paper focuses on the coupling between the high fidelity aerodynamic model for the flow field and the modal analysis of a typical wing section to carry out flutter analysis. This coupled aeroelastic model is implemented in one of the most widely used open source CFD codes called OpenFOAM. The model is designed to calculate the structural displacement in the time domain based on the free vibration modes of the structure by constructing the numerical model directly from the modal analysis. Essentially a second order ordinary differential equation is solved for each mode as a function of the generalised coordinates. A density based solver using central difference scheme of Kurganov and Tadmor is used to model the flow field. Two main cases of transonic flow over NACA 64A010 are modelled for a forced pitching oscillation airfoil and a self-sustained aerofoil respectively. The self-sustained two degrees of freedom case is modelled for three different possibilities covering damped, neutral and divergent oscillations. Predicted results show very good agreement with the numerical and experimental data available in the literature
GTI-space : the space of generalized topological indices
A new extension of the generalized topological indices (GTI) approach is carried out torepresent 'simple' and 'composite' topological indices (TIs) in an unified way. Thisapproach defines a GTI-space from which both simple and composite TIs represent particular subspaces. Accordingly, simple TIs such as Wiener, Balaban, Zagreb, Harary and Randićconnectivity indices are expressed by means of the same GTI representation introduced for composite TIs such as hyper-Wiener, molecular topological index (MTI), Gutman index andreverse MTI. Using GTI-space approach we easily identify mathematical relations between some composite and simple indices, such as the relationship between hyper-Wiener and Wiener index and the relation between MTI and first Zagreb index. The relation of the GTI space with the sub-structural cluster expansion of property/activity is also analysed and some routes for the applications of this approach to QSPR/QSAR are also given
Electron-multiplying CCDs for future soft X-ray spectrometers
CCDs have been used in several high resolution soft X-ray spectrometers for both space and terrestrial applications such as the Reflection Grating Spectrometer on XMM-Newton and the Super Advanced X-ray Emission Spectrometer at the Paul Scherrer Institut in Switzerland. However, with their ability to use multiplication gain to amplify signal and suppress readout noise, EM-CCDs are being considered instead of CCDs for future soft X-ray spectrometers. When detecting low energy X-rays, EM-CCDs are able to increase the Signal-to-Noise ratio of the device, making the X-rays much easier to detect. If the signal is also significantly split between neighbouring pixels, the increase in the size of the signal will make complete charge collection and techniques such as centroiding easier to accomplish. However, multiplication gain from an EM-CCD does cause a degradation of the energy resolution of the device and there are questions about how the high field region in an EM-CCD will behave over time in high radiation environments. This paper analyses the possible advantages and disadvantages of using EM-CCDs for high resolution soft X-ray spectroscopy and suggests in which situations using them would not only be possible, but also beneficial to the instrument
Effects of a single aerobic exercise session on body image
Background and Objectives
Most research on the effects of exercise on body image has concentrated on the benefits of regular exercise. However, some research has indicated that exercise has an immediate impact on body image. The aims of this study were to investigate the immediate effects of aerobic exercise in a fitness class and the at-home environment on body image, and to examine the impact of nutritional status (i.e., normal weight vs. overweight/obesity) and exercise addiction on these changes.
Method
322 Hungarian women participated in the study with two different environmental conditions, fitness class condition (N = 155) and at-home video condition (N = 167). They completed the Body Appreciation Scale and Exercise Addiction Inventory before and after a one-hour aerobic exercise session. Self-report data on weight, height and exercise frequency were also collected.
Results
There were no significant differences between the fitness class and video groups in terms of age, educational level, BMI, body appreciation, exercise frequency and exercise addiction. We found that 7.5% (N = 24) of the participants were at risk for exercise addiction. Aerobic exercise had a significant positive effect on body appreciation (t(321) = 7.564, p < .001) independently from environment and nutritional status. Exercise addiction moderated the relationship between exercise and body image, the at risk for exercise addiction group showed the greatest improvement (F(1) = 3.252, p = .040).
Conclusion
The results indicate that even a one-hour aerobic exercise session has a positive effect on body image; this has important practical implications for intervention strategies and weight-loss treatments.
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Elméleti háttér és célkitűzés
Bár a legtöbb kutatás a rendszeres testedzĂ©s testkĂ©pre gyakorolt pozitĂv hatására fĂłkuszál, nĂ©hány vizsgálat eredmĂ©nye a testedzĂ©s testkĂ©pre tett azonnali hatására hĂvja fel a figyelmet. Jelen tanulmány cĂ©lja az aerobik edzĂ©s testkĂ©pre gyakorolt azonnali hatásának vizsgálata fitnesztermi Ă©s otthoni edzĂ©si körĂĽlmĂ©nyek között, továbbá a tápláltsági állapot (normális testsĂşly vs. tĂşlsĂşly/elhĂzás) Ă©s a testedzĂ©sfĂĽggĹ‘sĂ©g potenciális moderátor szerepĂ©nek vizsgálata az edzĂ©s Ă©s a testkĂ©p alakulása közötti kapcsolatban.
MĂłdszer
A vizsgálatba aerobikedzĂ©st folytatĂł nĹ‘ket vontunk be (n = 322). A rĂ©sztvevĹ‘k egyik rĂ©sze edzĹ‘teremben folytatta a testgyakorlást (n = 155), másik rĂ©sze otthon vĂ©gzett aerobik testedzĂ©st, video vagy DVD segĂtsĂ©gĂ©vel (n = 167).
Mérőeszközök
önbeszámolĂłval nyert testtömeg Ă©s testmagasság, a testedzĂ©s gyakoriságára vonatkozĂł kĂ©rdĂ©s, TestĂ©rtĂ©kelĂ©si Skála, TestedzĂ©s AddikciĂł KĂ©rdĹ‘Ăv. Az adatfelvĂ©tel az egyĂłrás testgyakorlást megelĹ‘zĹ‘en Ă©s azt követĹ‘en törtĂ©nt.
Eredmények
Nem találtunk szignifikáns kĂĽlönbsĂ©get az edzĹ‘teremben Ă©s az otthonukban aerobik edzĂ©st folytatĂł nĹ‘k között az Ă©letkor, az iskolai vĂ©gzettsĂ©g, a BMI, a testĂ©rtĂ©kelĂ©s, a testedzĂ©s gyakorisága Ă©s a testedzĂ©sfĂĽggĹ‘sĂ©g tekintetĂ©ben. A válaszadĂłk 7,5%-a (n = 24) esetĂ©ben jelenik meg a testedzĂ©sfĂĽggĹ‘sĂ©g kockázata. Az egyĂłrás testedzĂ©s szignifikáns, kedvezĹ‘ hatást gyakorolt a testkĂ©pre (t(321) = 7,564; p < 0,001), amely hatás a testgyakorlás helyszĂnĂ©tĹ‘l (edzĹ‘terem vs. otthon) Ă©s a tápláltsági állapottĂłl fĂĽggetlennek bizonyult. A testedzĂ©sfĂĽggĹ‘sĂ©g azonban moderálta a testgyakorlás Ă©s a testkĂ©p változásának kapcsolatát: a testedzĂ©st követĹ‘en a testedzĂ©sfĂĽggĹ‘sĂ©g szempontjábĂłl veszĂ©lyeztetett csoportban mutatkozott meg a legnagyobb mĂ©rtĂ©kű, pozitĂv irányĂş változás a testkĂ©p tekintetĂ©ben (F(1) = 3,252; p = 0,040).
Következtetés
EredmĂ©nyeink arra utalnak, hogy akár egy egyĂłrás testgyakorlásnak is pozitĂv hatása lehet a testkĂ©pre, amelynek jelentĹ‘s gyakorlati implikáciĂłi vannak a testsĂşlycsökkentĹ‘ kezelĂ©sek szempontjábĂłl
Active Galactic Nuclei at the Crossroads of Astrophysics
Over the last five decades, AGN studies have produced a number of spectacular
examples of synergies and multifaceted approaches in astrophysics. The field of
AGN research now spans the entire spectral range and covers more than twelve
orders of magnitude in the spatial and temporal domains. The next generation of
astrophysical facilities will open up new possibilities for AGN studies,
especially in the areas of high-resolution and high-fidelity imaging and
spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These
studies will address in detail a number of critical issues in AGN research such
as processes in the immediate vicinity of supermassive black holes, physical
conditions of broad-line and narrow-line regions, formation and evolution of
accretion disks and relativistic outflows, and the connection between nuclear
activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic
Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical
Symposia Serie
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