7,270 research outputs found
Jacob: An Educational Agent in a Virtual Environment
The Jacob Project involves the construction of a virtual environment where an animated human-like agent called Jacob gives instruction to the user. The project focuses on three issues: the software engineering aspects of building a virtual reality system, the integration of natural language interaction and other interaction modalities, and the use of agent technology. Jacob has been given a task model and an instruction model in order to teach a particular task. The results of the project can be generalized so that the agent can be used to instruct other tasks in other virtual environments
Fluctuations of the inverse participation ratio at the Anderson transition
Statistics of the inverse participation ratio (IPR) at the critical point of
the localization transition is studied numerically for the power-law random
banded matrix model. It is shown that the IPR distribution function is
scale-invariant, with a power-law asymptotic ``tail''. This scale invariance
implies that the fractal dimensions are non-fluctuating quantities,
contrary to a recent claim in the literature. A recently proposed relation
between and the spectral compressibility is violated in the regime
of strong multifractality, with in the limit .Comment: 4 pages, 3 eps figure
Towards Informative Path Planning for Acoustic SLAM
Acoustic scene mapping is a challenging task as microphone arrays can often localize sound sources only in terms of their directions. Spatial diversity can be exploited constructively to infer source-sensor range when using microphone arrays installed on moving platforms, such as robots. As the absolute location of a moving robot is often unknown in practice, Acoustic Simultaneous Localization And Mapping (a-SLAM) is required in order to localize the moving robot’s positions and jointly map the sound sources. Using a novel a-SLAM approach, this paper investigates the impact of the choice of robot paths on source mapping accuracy. Simulation results demonstrate that a-SLAM performance can be improved by informatively planning robot paths
Finite Size Effects and Irrelevant Corrections to Scaling near the Integer Quantum Hall Transition
We present a numerical finite size scaling study of the localization length
in long cylinders near the integer quantum Hall transition (IQHT) employing the
Chalker-Coddington network model. Corrections to scaling that decay slowly with
increasing system size make this analysis a very challenging numerical problem.
In this work we develop a novel method of stability analysis that allows for a
better estimate of error bars. Applying the new method we find consistent
results when keeping second (or higher) order terms of the leading irrelevant
scaling field. The knowledge of the associated (negative) irrelevant exponent
is crucial for a precise determination of other critical exponents,
including multifractal spectra of wave functions. We estimate ,
which is considerably larger than most recently reported values. Within this
approach we obtain the localization length exponent confirming
recent results. Our stability analysis has broad applicability to other
observables at IQHT, as well as other critical points where corrections to
scaling are present.Comment: 6 pages and 3 figures, plus supplemental material
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
Loading atom lasers by collectivity-enhanced optical pumping
The effect of collectivity on the loading of an atom laser via optical
pumping is discussed. In our model, atoms in a beam are laser-excited and
subsequently spontaneously decay into a trapping state. We consider the case of
sufficiently high particle density in the beam such that the spontaneous
emission is modified by the particle interaction. We show that the collective
effects lead to a better population of the trapping state over a wide range of
system parameters, and that the second order correlation function of the atoms
can be controlled by the applied laser field.Comment: 5 pages, 7 figure
Quantum Size Effects in the Atomistic Structure of Armchair-Nanoribbons
Quantum size effects in armchair graphene nano-ribbons (AGNR) with hydrogen
termination are investigated via density functional theory (DFT) in Kohn-Sham
formulation. "Selection rules" will be formulated, that allow to extract
(approximately) the electronic structure of the AGNR bands starting from the
four graphene dispersion sheets. In analogy with the case of carbon nanotubes,
a threefold periodicity of the excitation gap with the ribbon width (N, number
of carbon atoms per carbon slice) is predicted that is confirmed by ab initio
results. While traditionally such a periodicity would be observed in electronic
response experiments, the DFT analysis presented here shows that it can also be
seen in the ribbon geometry: the length of a ribbon with L slices approaches
the limiting value for a very large width 1 << N (keeping the aspect ratio
small N << L) with 1/N-oscillations that display the electronic selection
rules. The oscillation amplitude is so strong, that the asymptotic behavior is
non-monotonous, i.e., wider ribbons exhibit a stronger elongation than more
narrow ones.Comment: 5 pages, 6 figure
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