Nonlinear Alfvén wave dynamics at a 2D magnetic null point: ponderomotive force

Context: In the linear, β = 0 MHD regime, the transient properties of magnetohydrodynamic (MHD) waves in the vicinity of 2D null points are well known. The waves are decoupled and accumulate at predictable parts of the magnetic topology: fast waves accumulate at the null point; whereas Alfvén waves cannot cross the separatricies. However, in nonlinear MHD mode conversion can occur at regions of inhomogeneous Alfvén speed, suggesting that the decoupled nature of waves may not extend to the nonlinear regime. Aims: We investigate the behaviour of low-amplitude Alfvén waves about a 2D magnetic null point in nonlinear, β = 0 MHD. Methods: We numerically simulate the introduction of low-amplitude Alfvén waves into the vicinity of a magnetic null point using the nonlinear LARE2D code. Results: Unlike in the linear regime, we find that the Alfvén wave sustains cospatial daughter disturbances, manifest in the transverse and longitudinal fluid velocity, owing to the action of nonlinear magnetic pressure gradients (viz. the ponderomotive force). These disturbances are dependent on the Alfvén wave and do not interact with the medium to excite magnetoacoustic waves, although the transverse daughter becomes focused at the null point. Additionally, an independently propagating fast magnetoacoustic wave is generated during the early stages, which transports some of the initial Alfvén wave energy towards the null point. Subsequently, despite undergoing dispersion and phase-mixing due to gradients in the Alfvén-speed profile (∇c_A ≠ 0) there is no further nonlinear generation of fast waves. Conclusions: We find that Alfvén waves at 2D cold null points behave largely as in the linear regime, however they sustain transverse and longitudinal disturbances - effects absent in the linear regime - due to nonlinear magnetic pressure gradients

Product Assurance Targeted to Meet Mission Objectives

Topics concerning the Common Lunar Lander for the Space Exploration Initiative are covered and include the following: product assurance tools and supports; project goals; and product assurance structured for optimal payback

Dialogical encounter argument as a source of rigour in the practice based PhD

This paper distinguishes between three views of argument: “argument as structure,” “argument as confrontation” and “argument as dialogical encounter.” Empirical studies of the criteria that examiners bring to the assessment of PhDs are cited. The studies provide evidence that qualities that align one or other of the three modes of argument figure significantly in the criteria that examiners bring to the assessment process. Embedded in the studies are respondents’ comments that suggest that the range of conceptions of argument held by PhD examiners is broad. Explicit use of the term “argument” is often made in reference to a minimal concept of argument ¬– “argument as structure.” However, the reported comments indicate a significant bias towards qualities associated with concepts of argument that lie somewhere along the spectrum between “argument as confrontation” and “argument as dialogical encounter” as a marker of quality in PhD research. Drawing on the work of Hans Georg Gadamer the paper will explore the possibilities opened up by adopting the view of “argument as dialogical encounter” in the context of the PhD. In particular I consider the issue of how PhD projects be structured so as to support the construction of arguments appropriate to practice based research in design? Keywords: Argument; Gadamer; Hermeneutics; Rigour; Practice Based Research; Phd Examination</p

Book Review: \u3cem\u3eModern Hindu Personalism: The History, Life and Thought of Bhaktisiddhānta Sarasvatī\u3c/em\u3e

Book Review of Modern Hindu Personalism: The History, Life and Thought of Bhaktisiddhānta Sarasvatī. Ferdinando Sardella. Oxford University Press, 2013, xv + 342 pp

Book Review: \u3cem\u3eDalit Theology in the Twenty-first Century: Discordant Voices, Discerning Pathways\u3c/em\u3e

A review of Dalit Theology in the Twenty-first Century: Discordant Voices, Discerning Pathways edited by Sathianathan Clarke, Deenabandhu Manchala, and Philip Vinod Peacock

Elmer\u27s Evolution

Spring is here! Can\u27t you hear the rumble of skates as the children zip by the house in their youthful glee? Can\u27t you hear the mingled chatter of the spring birds? Can\u27t you smell the sweetness of the pure, clean air - such a relief from that choking smog of the long winter? Can\u27t you see the first buds as they peep through the small gray tips of the dismal twigs? And can\u27t you see Elmer - his beautiful red hair and his bright eyes gleaming as they catch the ray of the warm, mellow sun? Can\u27t you see him? He\u27s standing right out there in the yard like a victorious king in the center of his domain