Wolverhampton Intellectual Repository and E-Theses
http://wlv.openrepository.com:80/wlv
WIRE captures, stores, indexes, preserves, and distributes digital research material.Thu, 18 Jan 2018 00:01:55 GMT2018-01-18T00:01:55ZENERGY LOSS OF SOLAR p MODES DUE TO THE EXCITATION OF MAGNETIC SAUSAGE TUBE WAVES: IMPORTANCE OF COUPLING THE UPPER ATMOSPHERE
http://hdl.handle.net/2436/621037
Title: ENERGY LOSS OF SOLAR p MODES DUE TO THE EXCITATION OF MAGNETIC SAUSAGE TUBE WAVES: IMPORTANCE OF COUPLING THE UPPER ATMOSPHERE
Authors: Gascoyne, A.; Jain, R.; Hindman, B. W.
Abstract: We consider damping and absorption of solar p modes due to their energy loss to magnetic tube waves that can freely carry energy out of the acoustic cavity. The coupling of p modes and sausage tube waves is studied in a model atmosphere composed of a polytropic interior above which lies an isothermal upper atmosphere. The sausage tube waves, excited by p modes, propagate along a magnetic fibril which is assumed to be a vertically aligned, stratified, thin magnetic flux tube. The deficit of p-mode energy is quantified through the damping rate, Γ, and absorption coefficient, α. The variation of Γ and α as a function of frequency and the tube's plasma properties is studied in detail. Previous similar studies have considered only a subphotospheric layer, modeled as a polytrope that has been truncated at the photosphere. Such studies have found that the resulting energy loss by the p modes is very sensitive to the upper boundary condition, which, due to the lack of an upper atmosphere, have been imposed in a somewhat ad hoc manner. The model presented here avoids such problems by using an isothermal layer to model the overlying atmosphere (chromosphere, and, consequently, allows us to analyze the propagation of p-mode-driven sausage waves above the photosphere. In this paper, we restrict our attention to frequencies below the acoustic cut off frequency. We demonstrate the importance of coupling all waves (acoustic, magnetic) in the subsurface solar atmosphere with the overlying atmosphere in order to accurately model the interaction of solar f and p modes with sausage tube waves. In calculating the absorption and damping of p modes, we find that for low frequencies, below ≈3.5 mHz, the isothermal atmosphere, for the two-region model, behaves like a stress-free boundary condition applied at the interface (z = –z 0).Thu, 19 Jun 2014 00:00:00 GMThttp://hdl.handle.net/2436/6210372014-06-19T00:00:00ZFIVE-MINUTE OSCILLATION POWER WITHIN MAGNETIC ELEMENTS IN THE SOLAR ATMOSPHERE
http://hdl.handle.net/2436/621036
Title: FIVE-MINUTE OSCILLATION POWER WITHIN MAGNETIC ELEMENTS IN THE SOLAR ATMOSPHERE
Authors: Jain, Rekha; Gascoyne, Andrew; Hindman, Bradley W.; Greer, Benjamin
Abstract: It has long been known that magnetic plage and sunspots are regions in which the power of acoustic waves is reduced within the photospheric layers. Recent observations now suggest that this suppression of power extends into the low chromosphere and is also present in small magnetic elements far from active regions. In this paper we investigate the observed power suppression in plage and magnetic elements, by modeling each as a collection of vertically aligned magnetic fibrils and presuming that the velocity within each fibril is the response to buffeting by incident p modes in the surrounding field-free atmosphere. We restrict our attention to modeling observations made near the solar disk center, where the line-of-sight velocity is nearly vertical and hence, only the longitudinal component of the motion within the fibril contributes. Therefore, we only consider the excitation of axisymmetric sausage waves and ignore kink oscillations as their motions are primarily horizontal. We compare the vertical motion within the fibril with the vertical motion of the incident p mode by constructing the ratio of their powers. In agreement with observational measurements we find that the total power is suppressed within strong magnetic elements for frequencies below the acoustic cut-off frequency. However, further physical effects need to be examined for understanding the observed power ratios for stronger magnetic field strengths and higher frequencies. We also find that the magnitude of the power deficit increases with the height above the photosphere at which the measurement is made. Furthermore, we argue that the area of the solar disk over which the power suppression extends increases as a function of height.Thu, 06 Nov 2014 00:00:00 GMThttp://hdl.handle.net/2436/6210362014-11-06T00:00:00ZDynamics of charged particle motion in the vicinity of three dimensional magnetic null points: Energization and chaos
http://hdl.handle.net/2436/621034
Title: Dynamics of charged particle motion in the vicinity of three dimensional magnetic null points: Energization and chaos
Authors: Gascoyne, Andrew
Abstract: Using a full orbit test particle approach, we analyse the motion of a single proton in the vicinity of magnetic null point configurations which are solutions to the kinematic, steady state, resistive magnetohydrodynamics equations. We consider two magnetic configurations, namely, the sheared and torsional spine reconnection regimes [E. R. Priest and D. I. Pontin, Phys. Plasmas 16, 122101 (2009); P. Wyper and R. Jain, Phys. Plasmas 17, 092902 (2010)]; each produce an associated electric field and thus the possibility of accelerating charged particles to high energy levels, i.e., > MeV, as observed in solar flares [R. P. Lin, Space Sci. Rev. 124, 233 (2006)]. The particle's energy gain is strongly dependent on the location of injection and is characterised by the angle of approach β, with optimum angle of approach βopt as the value of β which produces the maximum energy gain. We examine the topological features of each regime and analyse the effect on the energy gain of the proton. We also calculate the complete Lyapunov spectrum for the considered dynamical systems in order to correctly quantify the chaotic nature of the particle orbits. We find that the sheared model is a good candidate for the acceleration of particles, and for increased shear, we expect a larger population to be accelerated to higher energy levels. In the strong electric field regime (E0=1500E0=1500 V/m), the torsional model produces chaotic particle orbits quantified by the calculation of multiple positive Lyapunov exponents in the spectrum, whereas the sheared model produces chaotic orbits only in the neighbourhood of the null point.Sun, 01 Mar 2015 00:00:00 GMThttp://hdl.handle.net/2436/6210342015-03-01T00:00:00ZTreating anti-social behaviour in adolescents: A comparison of Multimodal and psychodynamic oriented group interventions
http://hdl.handle.net/2436/621035
Title: Treating anti-social behaviour in adolescents: A comparison of Multimodal and psychodynamic oriented group interventions
Authors: Taiwo, Abigail Olubola; Osinowo, Helen Ohiokhafe
Abstract: This study compared the efficacy of a multimodal intervention (MMI) and a psychodynamic oriented group Intervention (POGI) on antisocial behavior among Nigerian adolescents. A pretest-posttest design was used. Forty-one adolescents drawn from the streets of a Nigerian city (N =20), and a state child correction facility (N=21) participated in the study. The children were randomly assigned to a MMI, POGI and waiting list control (WLC) groups. Ages ranged from 10 to 18 years (mean =14.5; SD=2.1). Data collected were analyzed using multiple group comparison procedures. Results showed that MMI significantly reduced self-reported antisocial behavior of the adolescents as compared to WLC and POGI, respectively. A multimodal intervention approach appears to be more effective in treating antisocial behavior in adolescents than a psychodynamic oriented group Intervention.
Treating Anti-sociai Behavior in Adoiescents: A Comparison of i\/lulti-modal and Psychodynamic Oriented Group Interventions (PDF Download Available). Available from: https://www.researchgate.net/publication/275344274_Treating_Anti-sociai_Behavior_in_Adoiescents_A_Comparison_of_ilulti-modal_and_Psychodynamic_Oriented_Group_Interventions [accessed Jan 15 2018].Sun, 01 May 2011 00:00:00 GMThttp://hdl.handle.net/2436/6210352011-05-01T00:00:00Z