1,178 research outputs found
Reducing or enhancing chaos using periodic orbits
A method to reduce or enhance chaos in Hamiltonian flows with two degrees of
freedom is discussed. This method is based on finding a suitable perturbation
of the system such that the stability of a set of periodic orbits changes
(local bifurcations). Depending on the values of the residues, reflecting their
linear stability properties, a set of invariant tori is destroyed or created in
the neighborhood of the chosen periodic orbits. An application on a
paradigmatic system, a forced pendulum, illustrates the method
The sound of violets: the ethnographic potency of poetry?
This paper takes the form of a dialogue between the two authors, and is in two halves, the first half discursive and propositional, and the second half exemplifying the rhetorical, epistemological and metaphysical affordances of poetry in critically scrutinising the rhetoric, epistemology and metaphysics of educational management discourse.
Phipps and Saunders explore, through ideas and poems, how poetry can interrupt and/or illuminate dominant values in education and in educational research methods, such as:
• alternatives to the military metaphors – targets, strategies and the like – that dominate the soundscape of education;
• the kinds and qualities of the cognitive and feeling spaces that might be opened up by the shifting of methodological boundaries;
• the considerable work done in ethnography on the use of the poetic: anthropologists have long used poetry as a medium for expressing their sense of empathic connection to their field and their subjects, particularly in considering the creativity and meaning-making that characterise all human societies in different ways;
• the particular rhetorical affordances of poetry, as a discipline, as a practice, as an art, as patterned breath; its capacity to shift phonemic, and therewith methodological, authority; its offering of redress to linear and reductive attempts at scripting social life, as always already given and without alternative
Mode-locked Bloch oscillations in a ring cavity
We present a new technique for stabilizing and monitoring Bloch oscillations
of ultracold atoms in an optical lattice under the action of a constant
external force. In the proposed scheme, the atoms also interact with a
unidirectionally pumped optical ring cavity whose one arm is collinear with the
optical lattice. For weak collective coupling, Bloch oscillations dominate over
the collective atomic recoil lasing instability and develop a synchronized
regime in which the atoms periodically exchange momentum with the cavity field.Comment: 7 pages, 5 figure
The Function of Bachelardian Epistemology in the Post-colonial Project of Mohammed ‘Abed al-Jabri
This paper explores the function of historical epistemology in the thought of Gaston Bachelard (1884–1962) and Mohammed ‘Abed al-Jabri (1935–2010). Attributing thought with a particular function challenges our tendency to explain the development of thought in other socio-historical contexts in terms of mere conceptual influence. Available English-language literature on al-Jabri commonly references Bachelard’s concept of epistemological rupture as a source of inspiration. Though the reference is astute, this term remains poorly understood and has long been overshadowed by Thomas Kuhn’s notion of ‘paradigm shift’. The broader function of Bachelard’s thought as a renegotiation of time, place, subject, and reason in the natural sciences has been largely neglected in historiographies of the philosophy of science outside of France. This paper emphasizes the level of insight and ingenuity with which al-Jabri employs the function of Bachelard’s epistemology by re-interpreting it within the framework of his own socio-historical context. Far from reducing al-Jabri’s thought to a mere programmatic reproduction of French thought, I suggest that al-Jabri was among the most astute interpreters of this long-misunderstood theorist
Targeted mixing in an array of alternating vortices
Transport and mixing properties of passive particles advected by an array of
vortices are investigated. Starting from the integrable case, it is shown that
a special class of perturbations allows one to preserve separatrices which act
as effective transport barriers, while triggering chaotic advection. In this
setting, mixing within the two dynamical barriers is enhanced while long range
transport is prevented. A numerical analysis of mixing properties depending on
parameter values is performed; regions for which optimal mixing is achieved are
proposed. Robustness of the targeted mixing properties regarding errors in the
applied perturbation are considered, as well as slip/no-slip boundary
conditions for the flow
Experimental perspectives for systems based on long-range interactions
The possibility of observing phenomena peculiar to long-range interactions,
and more specifically in the so-called Quasi-Stationary State (QSS) regime is
investigated within the framework of two devices, namely the Free-Electron
Laser (FEL) and the Collective Atomic Recoil Laser (CARL). The QSS dynamics has
been mostly studied using the Hamiltonian Mean-Field (HMF) toy model,
demonstrating in particular the presence of first versus second order phase
transitions from magnetized to unmagnetized regimes in the case of HMF. Here,
we give evidence of the strong connections between the HMF model and the
dynamics of the two mentioned devices, and we discuss the perspectives to
observe some specific QSS features experimentally. In particular, a dynamical
analog of the phase transition is present in the FEL and in the CARL in its
conservative regime. Regarding the dissipative CARL, a formal link is
established with the HMF model. For both FEL and CARL, calculations are
performed with reference to existing experimental devices, namely the
FERMI@Elettra FEL under construction at Sincrotrone Trieste (Italy) and the
CARL system at LENS in Florence (Italy)
Chaos in free electron laser oscillators
The chaotic nature of a storage-ring Free Electron Laser (FEL) is
investigated. The derivation of a low embedding dimension for the dynamics
allows the low-dimensionality of this complex system to be observed, whereas
its unpredictability is demonstrated, in some ranges of parameters, by a
positive Lyapounov exponent. The route to chaos is then explored by tuning a
single control parameter, and a period-doubling cascade is evidenced, as well
as intermittence.Comment: Accepted in EPJ
Phase transitions of quasistationary states in the Hamiltonian Mean Field model
The out-of-equilibrium dynamics of the Hamiltonian Mean Field (HMF) model is
studied in presence of an externally imposed magnetic field h. Lynden-Bell's
theory of violent relaxation is revisited and shown to adequately capture the
system dynamics, as revealed by direct Vlasov based numerical simulations in
the limit of vanishing field. This includes the existence of an
out-of-equilibrium phase transition separating magnetized and non magnetized
phases. We also monitor the fluctuations in time of the magnetization, which
allows us to elaborate on the choice of the correct order parameter when
challenging the performance of Lynden-Bell's theory. The presence of the field
h removes the phase transition, as it happens at equilibrium. Moreover, regions
with negative susceptibility are numerically found to occur, in agreement with
the predictions of the theory.Comment: 6 pages, 7 figure
Bodily relations and reciprocity in the art of Sonia Khurana
This article explores the significance of the ‘somatic’ and ‘ontological turn’ in locating the radical politics articulated in the contemporary performance, installation, video and digital art practices of New Delhi-based artist, Sonia Khurana (b. 1968). Since the late 1990s Khurana has fashioned a range of artworks that require new sorts of reciprocal and embodied relations with their viewers. While this line of art practice suggests the need for a primarily philosophical mode of inquiry into an art of the body, such affective relations need to be historicised also in relation to a discursive field of ‘difference’ and public expectations about the artist’s ethnic, gendered and national identity. Thus, this intimate, visceral and emotional field of inter- and intra-action is a novel contribution to recent transdisciplinary perspectives on the gendered, social and sentient body, that in turn prompts a wider debate on the ethics of cultural commentary and art historiography
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