Beat Tracking by Dynamic Programming

Beat tracking — i.e. deriving from a music audio signal a sequence of beat instants that might correspond to when a human listener would tap his foot — involves satisfying two constraints. On the one hand, the selected instants should generally correspond to moments in the audio where a beat is indicated, for instance by the onset of a note played by one of the instruments. On the other hand, the set of beats should reflect a locally-constant inter-beat-interval, since it is this regular spacing between beat times that defines musical rhythm. These dual constraints map neatly onto the two constraints optimized in dynamic programming, the local match, and the transition cost. We describe a beat tracking system which first estimates a global tempo, uses this tempo to construct a transition cost function, then uses dynamic programming to find the best-scoring set of beat times that reflect the tempo as well as corresponding to moments of high 'onset strength' in a function derived from the audio. This very simple and computationally efficient procedure is shown to perform well on the MIREX-06 beat tracking training data, achieving an average beat accuracy of just under 60% on the development data. We also examine the impact of the assumption of a fixed target tempo, and show that the system is typically able to track tempo changes in a range of ±10% of the target tempo

Dynamics of Inflationary Universes with Positive Spatial Curvature

If the spatial curvature of the universe is positive, then the curvature term will always dominate at early enough times in a slow-rolling inflationary epoch. This enhances inflationary effects and hence puts limits on the possible number of e-foldings that can have occurred, independently of what happened before inflation began and in particular without regard for what may have happened in the Planck era. We use a simple multi-stage model to examine this limit as a function of the present density parameter $\Omega_0$ and the epoch when inflation ends.Comment: 9 Pages RevTex4. Revised and update

On Communicating Computational Research

Prof. Ellis's presentation focuses on the challenges, and the benefits, of sharing the results of computational research through various methods, including: traditional publications, public talks, interactive online demos, APIs and libraries, and code sharing. He particularly emphasizes the potential of code sharing in a world where commodity machines can make reproducibility increasingly affordable and attainable

Irrotational dust with Div H=0

For irrotational dust the shear tensor is consistently diagonalizable with its covariant time derivative: $\sigma_{ab}=0=\dot{\sigma}_{ab},\; a\neq b$, if and only if the divergence of the magnetic part of the Weyl tensor vanishes: $div~H = 0$. We show here that in that case, the consistency of the Ricci constraints requires that the magnetic part of the Weyl tensor itself vanishes: $H_{ab}=0$.Comment: 19 pages. Latex. Also avaliable at http://shiva.mth.uct.ac.za/preprints/text/lesame2.te

Preliminary study of creep thresholds and thermomechanical response in Haynes 188 at temperatures in the range 649 to 871 C

The following conclusions were drawn from this study of creep thresholds and thermomechanical response: (1) creep threshold can be determined using the latest electrohydraulic test equipment, providing that test durations are short and relatively large accumulations of creep strain are used in defining the threshold; (2) significant creep strains were measured under monotonic loading as stress levels as low as 4 ksi at temperatures predicted for solar receiver service; and (3) the material exhibited creep ratchetting during simulated service cycles, a result not predicted by analysis using current constitutive models for Haynes 188

Semantic Audio Analysis

An overview of the current status and applications of semantic audio analysis