10,680 research outputs found
Grasses and clovers : effect of ripeness on yield and composition
Caption title.Includes bibliographical references
The patchy Method for the Infinite Horizon Hamilton-Jacobi-Bellman Equation and its Accuracy
We introduce a modification to the patchy method of Navasca and Krener for
solving the stationary Hamilton Jacobi Bellman equation. The numerical solution
that we generate is a set of polynomials that approximate the optimal cost and
optimal control on a partition of the state space. We derive an error bound for
our numerical method under the assumption that the optimal cost is a smooth
strict Lyupanov function. The error bound is valid when the number of subsets
in the partition is not too large.Comment: 50 pages, 5 figure
Simplicial Nonlinear Principal Component Analysis
We present a new manifold learning algorithm that takes a set of data points
lying on or near a lower dimensional manifold as input, possibly with noise,
and outputs a simplicial complex that fits the data and the manifold. We have
implemented the algorithm in the case where the input data can be triangulated.
We provide triangulations of data sets that fall on the surface of a torus,
sphere, swiss roll, and creased sheet embedded in a fifty dimensional space. We
also discuss the theoretical justification of our algorithm.Comment: 21 pages, 6 figure
Math anxiety, intrusive thoughts and performance: Exploring the relationship between mathematics anxiety and performance: The role of intrusive thoughts
The current study examined the relationship between math anxiety and arithmetic performance by focusing on intrusive thoughts experienced during problem solving. Participants (N = 122) performed two-digit addition problems on a verification task. Math anxiety significantly predicted response time and error rate. Further, the extent to which intrusive thoughts impeded calculation mediated the relationship between math anxiety and per cent of errors on problems involving a carry operation. Moreover, results indicated that participants experienced a range of intrusive thoughts and these were related to significantly higher levels of math anxiety. The findings lend support to a deficient inhibition account of the math anxiety-to-performance relationship and highlight the importance of considering intrusive thoughts in future work
Observations of the Vertical Structure of Tidal Currents in Two Inlets
Observations of the vertical structure of broad band tidal currents were obtained at two energetic inlets. Each experiment took place over a 4 week period, the first at Hampton Inlet in southeastern New Hampshire, USA, in the Fall of 2011, and the second at New River Inlet in southern North Carolina, USA, in the spring of 2012. The temporal variation and vertical structure of the currents were observed at each site with 600 kHz and 1200 kHz RDI Acoustic Doppler Current Profilers (ADCP) deployed on low-profile bottom tripods in 7.5 and 12.5 m water depths near the entrance to Hampton Inlet, and in 8 and 9 m water depth within and outside New River Inlet, respectively. In addition, a Nortek Aquapro ADCP was mounted on a jetted pipe in about 2.5 m water depth on the flank of the each inlet channel. Flows within the Hampton/Seabrook Inlet were dominated by semi-diurnal tides ranging 2.5 - 4 m in elevation, with velocities exceeding 2.5 m/s. Flows within New River inlet were also semi-diurnal with tides ranging about 1 – 1.5 m in elevation and with velocities exceeding 1.5 m/s. Vertical variation in the flow structure at the dominant tidal frequency are examined as a function of location within and near the inlet. Outside the inlet, velocities vary strongly over the vertical, with a nearly linear decay from the surface to near the bottom. The coherence between the upper most velocity bin and the successively vertically separated bins drops off quickly with depth, with as much as 50% coherence decay over the water column. The phase relative to the uppermost velocity bin shifts over depth, with as much as 40 deg phase lag over the vertical, with bottom velocities leading the surface. Offshore, rotary coefficients indicate a stable ellipse orientation with rotational directions consistent over the vertical. At Hampton, the shallower ADCP, but still outside the inlet, shows a rotational structure that changes sign in the vertical indicating a sense of rotation at the bottom that is opposite to that at the surface. Within the inlet, the flow is more aligned with the channel, the decay in amplitude over the vertical is diminished, the coherence and phase structure is nearly uniform, and the rotary coefficients indicate no sense of rotation in the flow. The observations are qualitatively consistent with behavior described by Prandle (1982) for shallow water tidal flows
Comment on "Long Time Evolution of Phase Oscillator Systems" [Chaos 19,023117 (2009), arXiv:0902.2773]
A previous paper (arXiv:0902.2773, henceforth referred to as I) considered a
general class of problems involving the evolution of large systems of globally
coupled phase oscillators. It was shown there that, in an appropriate sense,
the solutions to these problems are time asymptotically attracted toward a
reduced manifold of system states (denoted M). This result has considerable
utility in the analysis of these systems, as has been amply demonstrated in
recent papers. In this note, we show that the analysis of I can be modified in
a simple way that establishes significant extensions of the range of validity
of our previous result. In particular, we generalize I in the following ways:
(1) attraction to M is now shown for a very general class of oscillator
frequency distribution functions g(\omega), and (2) a previous restriction on
the allowed class of initial conditions is now substantially relaxed
Saturation-Dependence of Dispersion in Porous Media
In this study, we develop a saturation-dependent treatment of dispersion in
porous media using concepts from critical path analysis, cluster statistics of
percolation, and fractal scaling of percolation clusters. We calculate spatial
solute distributions as a function of time and calculate arrival time
distributions as a function of system size. Our previous results correctly
predict the range of observed dispersivity values over ten orders of magnitude
in experimental length scale, but that theory contains no explicit dependence
on porosity or relative saturation. This omission complicates comparisons with
experimental results for dispersion, which are often conducted at saturation
less than 1. We now make specific comparisons of our predictions for the
arrival time distribution with experiments on a single column over a range of
saturations. This comparison suggests that the most important predictor of such
distributions as a function of saturation is not the value of the saturation
per se, but the applicability of either random or invasion percolation models,
depending on experimental conditions
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