7,743 research outputs found
Tip-Enhanced Fluorescence Microscopy at 10 Nanometer Resolution
We demonstrate unambiguously that the field enhancement near the apex of a laser-illuminated silicon tip decays according to a power law that is moderated by a single parameter characterizing the tip sharpness. Oscillating the probe in intermittent contact with a semiconductor nanocrystal strongly modulates the fluorescence excitation rate, providing robust optical contrast and enabling excellent background rejection. Laterally encoded demodulation yields images with <10 nm spatial resolution, consistent with independent measurements of tip sharpness
Single-stage sealing of ceramic tiles by means of high power diode laser radiation
An investigation has been carried out using a 60 W high power diode laser (HPDL) to determine the feasibility of sealing the void between adjoining ceramic tiles with a specially developed grout material. A single-stage process has subsequently been devised using a new grout material which consists of two distinct components: a crushed ceramic tile mix substrate and a glazed enamel surface; the crushed ceramic tile mix provides a tough, inexpensive bulk substrate, whilst the enamel provides an impervious surface glaze. HPDL processing has resulted in crack and porosity free seals produced in normal atmospheric conditions. The single-stage grout is simple to formulate and easy to apply. Tiles were successfully sealed with power densities as low as 750 W/cm2 and at rates of up to 420 mm/min. Bonding of the enamel to the crushed ceramic tile mix was identified as being primarily due to van der Waals forces and, on a very small scale, some of the crushed ceramic tile mix material dissolving into the glaze
Probabilistic movement modeling for intention inference in human-robot interaction.
Intention inference can be an essential step toward efficient humanrobot interaction. For this purpose, we propose the Intention-Driven Dynamics Model (IDDM) to probabilistically model the generative process of movements that are directed by the intention. The IDDM allows to infer the intention from observed movements using Bayes â theorem. The IDDM simultaneously finds a latent state representation of noisy and highdimensional observations, and models the intention-driven dynamics in the latent states. As most robotics applications are subject to real-time constraints, we develop an efficient online algorithm that allows for real-time intention inference. Two human-robot interaction scenarios, i.e., target prediction for robot table tennis and action recognition for interactive humanoid robots, are used to evaluate the performance of our inference algorithm. In both intention inference tasks, the proposed algorithm achieves substantial improvements over support vector machines and Gaussian processes.
Continuum theory of vacancy-mediated diffusion
We present and solve a continuum theory of vacancy-mediated diffusion (as
evidenced, for example, in the vacancy driven motion of tracers in crystals).
Results are obtained for all spatial dimensions, and reveal the strongly
non-gaussian nature of the tracer fluctuations. In integer dimensions, our
results are in complete agreement with those from previous exact lattice
calculations. We also extend our model to describe the vacancy-driven
fluctuations of a slaved flux line.Comment: 25 Latex pages, subm. to Physical Review
Observed Effect of Magnetic Fields on the Propagation of Magnetoacoustic Waves in the Lower Solar Atmosphere
We study Hinode/SOT-FG observations of intensity fluctuations in Ca II H-line
and G-band image sequences and their relation to simultaneous and co-spatial
magnetic field measurements. We explore the G-band and H-line intensity
oscillation spectra both separately and comparatively via their relative phase
differences, time delays and cross-coherences. In the non-magnetic situations,
both sets of fluctuations show strong oscillatory power in the 3 - 7 mHz band
centered at 4.5 mHz, but this is suppressed as magnetic field increases. A
relative phase analysis gives a time delay of H-line after G-band of 20\pm1 s
in non-magnetic situations implying a mean effective height difference of 140
km. The maximum coherence is at 4 - 7 mHz. Under strong magnetic influence the
measured delay time shrinks to 11 s with the peak coherence near 4 mHz. A
second coherence maximum appears between 7.5 - 10 mHz. Investigation of the
locations of this doubled-frequency coherence locates it in diffuse rings
outside photospheric magnetic structures. Some possible interpretations of
these results are offered.Comment: 19 pages, 6 figure
On the algorithmic construction of classifying spaces and the isomorphism problem for biautomatic groups
We show that the isomorphism problem is solvable in the class of central
extensions of word-hyperbolic groups, and that the isomorphism problem for
biautomatic groups reduces to that for biautomatic groups with finite centre.
We describe an algorithm that, given an arbitrary finite presentation of an
automatic group , will construct explicit finite models for the skeleta
of and hence compute the integral homology and cohomology of
.Comment: 21 pages, 4 figure
GeneraciĂłn @
Si la adolescencia fue descubierta a
finales del siglo XIX, y se democratizĂł
en la primera mitad del XX, la segunda
mitad del siglo ha presenciado la irrupciĂłn
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pasivo sino como actor protagonista en
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Optical and Near-Infrared Imaging of the IRAS 1-Jy Sample of Ultraluminous Infrared Galaxies: II. The Analysis
The present paper discusses the results from an analysis of the images
presented in Paper I (astro-ph/0207373) supplemented with new spectroscopic
data obtained at Keck. All but one object in the 1-Jy sample show signs of a
strong tidal interaction/merger. Multiple mergers involving more than two
galaxies are seen in no more than 5 of the 118 (< 5%) systems. None of the 1-Jy
sources is in the first-approach stage of the interaction, and most (56%) of
them harbor a single disturbed nucleus and are therefore in the later stages of
a merger. Seyfert galaxies (especially those of type 1), warm ULIGs
(f_{25}/f_{60} > 0.2) and the more luminous systems (> 10^{12.5} L_sun) all
show a strong tendency to be advanced mergers with a single nucleus. An
analysis of the surface brightness profiles of the host galaxies in
single-nucleus sources reveals that about 73% of the R and K' surface
brightness profiles are fit adequately by an elliptical-like R^{1/4}-law. These
elliptical-like 1-Jy systems have luminosities, half-light radii, and R-band
axial ratio distribution that are similar to those of normal (inactive)
intermediate-luminosity ellipticals and follow with some scatter the same mu_e
- r_e relation. These elliptical-like hosts are most common among merger
remnants with Seyfert 1 nuclei (83%), Seyfert 2 optical characteristics (69%)
or mid-infrared (ISO) AGN signatures (80%). In general, the results from the
present study are consistent with the merger-driven evolutionary sequence
``cool ULIGs --> warm ULIGs --> quasars,'' although there are many exceptions.
(abridged)Comment: Correction to D.-C. Kim's affiliations. 42 pages + 3 tables + 3
multi-page jpeg figures; see
http://www.astro.umd.edu/~veilleux/pubs/paper2.tar.gz for original figure
Anomaly Free Non-Supersymmetric Large Gauge Theories from Orientifolds
We construct anomaly free non-supersymmetric large N gauge theories from
orientifolds of Type IIB on C^3/G orbifolds. In particular, massless as well as
tachyonic one-loop tadpoles are cancelled in these models. This is achieved by
starting with supersymmetric orientifolds with well defined
world-sheet description and including discrete torsion (which breaks
supersymmetry) in the orbifold action. In this way we obtain non-trivial
non-chiral as well as anomaly free chiral large N gauge theories. We point out
certain subtleties arising in the chiral cases. Subject to certain assumptions,
these theories are shown to have the property that computation of any M-point
correlation function in these theories reduces to the corresponding computation
in the parent oriented theory. This generalizes the analogous
results recently obtained in supersymmetric large N gauge theories from
orientifolds, as well as in (non)supersymmetric large N gauge theories without
orientifold planes.Comment: 18 pages, revtex, minor misprints corrected, a clarifying footnote
added (to appear in Phys. Rev. D
Tilt Modulus and Angle-Dependent Flux Lattice Melting in the Lowest Landau Level Approximation
For a clean high-T superconductor, we analyze the Lawrence-Doniach free
energy in a tilted magnetic field within the lowest Landau level (LLL)
approximation. The free energy maps onto that of a strictly -axis field, but
with a reduced interlayer coupling. We use this result to calculate the tilt
modulus of a vortex lattice and vortex liquid. The vortex contribution
to can be expressed in terms of the squared -axis Josephson plasmon
frequency . The transverse component of the field has very
little effect on the position of the melting curve.Comment: 8 pages, 2 figures, accepted for publication in Physical Review B
(Rapid Communications
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