4,349 research outputs found
Wave function statistics at the symplectic 2D Anderson transition: bulk properties
The wavefunction statistics at the Anderson transition in a 2d disordered
electron gas with spin-orbit coupling is studied numerically. In addition to
highly accurate exponents (), we report three qualitative results: (i) the anomalous dimensions are
invariant under which is in agreement with a recent analytical
prediction and supports the universality hypothesis. (ii) The multifractal
spectrum is not parabolic and therefore differs from behavior suspected, e.g.,
for (integer) quantum Hall transitions in a fundamental way. (iii) The critical
fixed point satisfies conformal invariance.Comment: 4 pages, 3 figure
Bearing-only acoustic tracking of moving speakers for robot audition
This paper focuses on speaker tracking in robot audition for human-robot interaction. Using only acoustic signals, speaker tracking in enclosed spaces is subject to missing detections and spurious clutter measurements due to speech inactivity, reverberation and interference. Furthermore, many acoustic localization approaches estimate speaker direction, hence providing bearing-only measurements without range information. This paper presents a probability hypothesis density (PHD) tracker that augments the bearing-only speaker directions of arrival with a cloud of range hypotheses at speaker initiation and propagates the random variates through time. Furthermore, due to their formulation PHD filters explicitly model, and hence provide robustness against, clutter and missing detections. The approach is verified using experimental results
Revisiting delivery in the basic course
When comparing the ancient and modern pedagogies of speech and speech delivery, discrepancies begin to emerge. The significance of delivery in today’s speech pedagogy, for instance, is minimal, which is perhaps most evident in the foundational public speaking course (basic course) textbook. As my thesis demonstrates, speech composition receives far more consideration than speech performance, which marginalizes the canon of delivery as inferior to both rhetoric and speech communication. Supporting this notion is McClish (2016), who argues that while delivery remains germane to contemporary public speaking pedagogy, its treatment in the twenty-first-century basic course is widely understated. Moreover, McClish (2016) argues that, “contemporary speech pedagogy strives to communicate the importance of delivery to oratorical activity, but not its essential role in establishing extraordinary speech or eloquence” (p. 174). Eloquence, according to Emerson (1904), “…is the power to translate a truth into language perfectly intelligible to the person to whom you speak” (p. 130).
Unlike Aristotle’s other rhetorical canons (invention, arrangement, style, and memory), delivery is presented as a formality to speech, but not a skill worth mastering. By under emphasizing the role of delivery in public oration, textbook authors and editors are doing a disservice to instructors, students, and the discipline. I argue that by reevaluating delivery’s role in course textbooks and the field of rhetoric, the foundational public speaking course will produce more persuasive and captivating public speakers. However, as my research shows, the textbook is not the only example of delivery’s overshadowing. Animosities against delivery emerged thousands of years prior to this thesis. To begin my argument, I first turn to the current structuring of the basic communication course.
Keywords: basic course, rhetoric, delivery, genre, textbooks, persuasion, public speakin
Non-diffracting Optical Beams in a Three-level Raman System
Diffractionless propagation of optical beams through atomic vapors is
investigated. The atoms in the vapor are operated in a three-level Raman
configuration. A suitably chosen control beam couples to one of the
transitions, and thereby creates a spatially varying index of refraction
modulation in the warm atomic vapor for a probe beam which couples to the other
transition in the atoms. We show that a Laguerre-Gaussian control beam allows
to propagate single Gaussian probe field modes as well as multi-Gaussian modes
and non-Gaussian modes over macroscopic distances without diffraction. This
opens perspectives for the propagation of arbitrary images through warm atomic
vapors.Comment: 8 pages, 7 figure
Data compression and regression based on local principal curves.
Frequently the predictor space of a multivariate regression problem of the type y = m(x_1, …, x_p ) + ε is intrinsically one-dimensional, or at least of far lower dimension than p. Usual modeling attempts such as the additive model y = m_1(x_1) + … + m_p (x_p ) + ε, which try to reduce the complexity of the regression problem by making additional structural assumptions, are then inefficient as they ignore the inherent structure of the predictor space and involve complicated model and variable selection stages. In a fundamentally different approach, one may consider first approximating the predictor space by a (usually nonlinear) curve passing through it, and then regressing the response only against the one-dimensional projections onto this curve. This entails the reduction from a p- to a one-dimensional regression problem.
As a tool for the compression of the predictor space we apply local principal curves. Taking things on from the results presented in Einbeck et al. (Classification – The Ubiquitous Challenge. Springer, Heidelberg, 2005, pp. 256–263), we show how local principal curves can be parametrized and how the projections are obtained. The regression step can then be carried out using any nonparametric smoother. We illustrate the technique using data from the physical sciences
Superconductivity in Pseudo-Binary Silicide SrNixSi2-x with AlB2-Type Structure
We demonstrate the emergence of superconductivity in pseudo-binary silicide
SrNixSi2-x. The compound exhibits a structural phase transition from the cubic
SrSi2-type structure (P4132) to the hexagonal AlB2-type structure (P6/mmm) upon
substituting Ni for Si at approximately x = 0.1. The hexagonal structure is
stabilized in the range of 0.1 < x < 0.7. The superconducting phase appears in
the vicinity of the structural phase boundary. Ni acts as a nonmagnetic dopant,
as confirmed by the Pauli paramagnetic behavior.Comment: 12 pages, 5 figure
Integer Quantum Hall Transition and Random SU(N) Rotation
We reduce the problem of integer quantum Hall transition to a random rotation
of an N-dimensional vector by an su(N) algebra, where only N specially selected
generators of the algebra are nonzero. The group-theoretical structure revealed
in this way allows us to obtain a new series of conservation laws for the
equation describing the electron density evolution in the lowest Landau level.
The resulting formalism is particularly well suited to numerical simulations,
allowing us to obtain the critical exponent \nu numerically in a very simple
way. We also suggest that if the number of nonzero generators is much less than
N, the same model, in a certain intermediate time interval, describes
percolating properties of a random incompressible steady two-dimensional flow.
In other words, quantum Hall transition in a very smooth random potential
inherits certain properties of percolation.Comment: 4 pages, 1 figur
Exact relations between multifractal exponents at the Anderson transition
Two exact relations between mutlifractal exponents are shown to hold at the
critical point of the Anderson localization transition. The first relation
implies a symmetry of the multifractal spectrum linking the multifractal
exponents with indices . The second relation
connects the wave function multifractality to that of Wigner delay times in a
system with a lead attached.Comment: 4 pages, 3 figure
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