2,124 research outputs found
On the mechanism of trailing vortex wandering
The mechanism of trailing vortex wandering has long been debated and is often attributed to either wind-tunnel effects or an instability. Using particle image velocimetry data obtained in the wake of a NACA0012 airfoil, we remove the effect of wandering from the measured velocity field and, through a triple decomposition, recover the coherent wandering motion. Based on this wandering motion, the most energetic structures are computed using the proper orthogonal decomposition (POD) and exhibit a helical mode with an azimuthal wavenumber of |m|=1 whose kinetic energy grows monotonically in the downstream direction. To investigate the nature of the vortex wandering, we perform a spatial stability analysis of a matched Batchelor vortex. The primary stability mode is found to be marginally stable and nearly identical in both size and structure to the leading POD mode. The strikingly similar structure, coupled with the measured energy growth, supports the proposition that the vortex wandering is the result of an instability. We conclude that the cause of the wandering is the non-zero radial velocity of the |m|=1 mode on the vortex centreline, which acts to transversely displace the trailing vortex, as observed in experiments. However, the marginal nature of the stability mode prevents a definitive conclusion regarding the specific type of instability
Non-Abelian Stokes Theorem and Quark Confinement in SU(3) Yang-Mills Gauge Theory
We derive a new version of SU(3) non-Abelian Stokes theorem by making use of
the coherent state representation on the coset space , the flag space. Then we outline a derivation of the area law of the
Wilson loop in SU(3) Yang-Mills theory in the maximal Abelian gauge (The
detailed exposition will be given in a forthcoming article). This derivation is
performed by combining the non-Abelian Stokes theorem with the reformulation of
the Yang-Mills theory as a perturbative deformation of a topological field
theory recently proposed by one of the authors. Within this framework, we show
that the fundamental quark is confined even if is broken by partial
gauge fixing into just as is broken to . An
origin of the area law is related to the geometric phase of the Wilczek-Zee
holonomy for U(2). Abelian dominance is an immediate byproduct of these results
and magnetic monopole plays the dominant role in this derivation.Comment: 14 pages, Latex, no figures, version accepted for publication in Mod.
Phys. Lett. A (some comments are added in the final parts
Role of the peripheral vasculature in changes in venous return caused by isoproterenol, norepinephrine, and methoxamine in anesthetized dogs
Design considerations for a hierarchical semantic compositional framework for medical natural language understanding
Medical natural language processing (NLP) systems are a key enabling
technology for transforming Big Data from clinical report repositories to
information used to support disease models and validate intervention methods.
However, current medical NLP systems fall considerably short when faced with
the task of logically interpreting clinical text. In this paper, we describe a
framework inspired by mechanisms of human cognition in an attempt to jump the
NLP performance curve. The design centers about a hierarchical semantic
compositional model (HSCM) which provides an internal substrate for guiding the
interpretation process. The paper describes insights from four key cognitive
aspects including semantic memory, semantic composition, semantic activation,
and hierarchical predictive coding. We discuss the design of a generative
semantic model and an associated semantic parser used to transform a free-text
sentence into a logical representation of its meaning. The paper discusses
supportive and antagonistic arguments for the key features of the architecture
as a long-term foundational framework
siRNAs generated by recombinant human Dicer induce specific and significant but target site-independent gene silencing in human cells
Spin-Glass-like Transition and Hall Resistivity of Y2-xBixIr2O7
Various physical properties of the pyrochlore oxide Y2-xBixIr2O7 have been
studied. The magnetizations M measured under the conditions of the
zero-field-cooling(ZFC) and the field-cooling(FC) have different values below
the temperature T=TG. The anomalous T-dependence of the electrical
resistivities r and the thermoelectric powers S observed at around TG indicates
that the behavior of the magnetization is due to the transition to the state
with the spin freezing. In this spin-frozen state, the Hall resistivities rH
measured with the ZFC and FC conditions are found to have different values,
too, in the low temperature phase (T<TG). Possible mechanisms which induce such
the hysteretic behavior are discussed.Comment: 9 pages, 7 figures, J. Phys. Soc. Jpn. 72 (2003) No.
Convertible source system of thermal neutron and X-ray at Hokkaido University electron linac facility
The convertible source system for the neutron and the X-ray
imagings was installed in the 45MeV electron linear accelerator facility at Hokkaido University. The source system is very useful for a complementary imaging. The
imaging measurements for a sample were performed with both beams by using a vacuum tube type image intensifier. The enhanced contrast was obtained from the dataset of the radiograms measured with the neutron and X-ray beams
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