60,612 research outputs found
The NASA integrated test facility and its impact on flight research
The Integrated Test Facility (ITF), being built at NASA Ames-Dryden Flight Research Facility, will provide new test capabilities for emerging research aircraft. An overview of the ITF and the challenges being addressed by this unique facility are outlined. The current ITF capabilities, being developed with the X-29 Forward Swept Wing Program, are discussed along with future ITF activities
Bayesian learning of joint distributions of objects
There is increasing interest in broad application areas in defining flexible
joint models for data having a variety of measurement scales, while also
allowing data of complex types, such as functions, images and documents. We
consider a general framework for nonparametric Bayes joint modeling through
mixture models that incorporate dependence across data types through a joint
mixing measure. The mixing measure is assigned a novel infinite tensor
factorization (ITF) prior that allows flexible dependence in cluster allocation
across data types. The ITF prior is formulated as a tensor product of
stick-breaking processes. Focusing on a convenient special case corresponding
to a Parafac factorization, we provide basic theory justifying the flexibility
of the proposed prior and resulting asymptotic properties. Focusing on ITF
mixtures of product kernels, we develop a new Gibbs sampling algorithm for
routine implementation relying on slice sampling. The methods are compared with
alternative joint mixture models based on Dirichlet processes and related
approaches through simulations and real data applications.Comment: Appearing in Proceedings of the 16th International Conference on
Artificial Intelligence and Statistics (AISTATS) 2013, Scottsdale, AZ, US
Spatial and Temporal Variation of Indonesian Throughflow in the Makassar Strait
Using outputs of INDESO model, this study investigated vertical structure, spatial and temporal variation of the Indonesian Throughflow in Makassar Strait (M-ITF). It was shown that the main axis of persistent southward jet of M-ITF formed a unique path following the western shelf slope along the strait, which was associated with a high kinetic energy (KE) region from near-surface down to the thermocline layer. Furthermore, a drastic jump of KE appeared in the narrow and deep Libani Chan-nel (near 3°S) where the strait's width shrinks significantly, thus an elevated flow velocity was needed to maintain transport volume balance. Here, maximum southward velocity at thermocline exceeded 1.2 m/s. Spatial pattern of M-ITF can be described by the first EOF mode which accounts for 79 % of the total variances. It exhibited that contours of the flow amplitudes were similar to M-ITF path, and the largest amplitude was located near the Libani Channel. Out-of-phase relationship of the flow was found between M-ITF and eddies circulation that developed in the edges of the strait. Corresponding temporal fluctuation of the first EOF mode indicated that M-ITF variabilities varied from intra-seasonal to inter-annual scales. Annual fluctuation of M-ITF was seen from EOF mode-2 (at thermocline layer) and mode-3 at lower-thermocline. Cross-spectra analysis revealed that variability of M- ITF (e.g. on annual scale) at northern entrance was highly coherent to the fluctuations of North Equatorial Current (NEC) and Mindanao Current (MC), suggesting that variability of M-ITF was remotely influenced by the Pacific low-latitude western boundary currents
Fokker-Planck approach to quantum lattice Hamiltonians
Fokker-Planck equations have been applied in the past to field theory topics
such as the stochastic quantization and the stabilization of bottomless action
theories. In this paper we give another application of the FP-techniques in a
way appropriate to the study of the ground state, the excited states and the
critical behaviour of quantum lattice Hamiltonians. With this purpose, we start
by considering a discrete or lattice version of the standard FP-Hamiltonian.
The well known exponential ansatz for the ground state wave functional becomes
in our case an exponential ``cluster" expansion. With a convenient choice for
this latter, we are able to construct FP-Hamiltonians which to a large extent
reproduce critical properties of ``realistic" quantum lattice Hamiltonians, as
the one of the Ising model in a transverse field (ITF). In one dimension, this
statement is made manifest by proving that the FP-Hamiltonian we built up
belongs to the same universality class as the standard ITF model or,
equivalently, the 2D-classical Ising model. To this respect, some
considerations concerning higher dimensional ITF models are outlined.Comment: 42 pages, LaTeX, 3 figures available upon reques
Many-body Lattice Wavefunctions From Conformal Blocks
We introduce a general framework to construct many-body lattice wavefunctions
starting from the conformal blocks (CBs) of rational conformal field theories
(RCFTs). We discuss the different ways of encoding the physical degrees of
freedom of the lattice system using both the internal symmetries of the theory
and the fusion channels of the CBs. We illustrate this construction both by
revisiting the known Haldane-Shastry model and by providing a novel
implementation for the Ising RCFT. In the latter case, we find a connection to
the Ising transverse field (ITF) spin chain via the Kramers-Wannier duality and
the Temperley-Lieb-Jones algebra. We also find evidence that the ground state
of the finite-size critical ITF Hamiltonian corresponds exactly to the
wavefunction obtained from CBs of spin fields
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