23,437 research outputs found
Estimating tropical forest biomass with a combination of SAR image texture and Landsat TM data:an assessment of predictions between regions
Bubble Growth in Superfluid 3-He: The Dynamics of the Curved A-B Interface
We study the hydrodynamics of the A-B interface with finite curvature. The
interface tension is shown to enhance both the transition velocity and the
amplitudes of second sound. In addition, the magnetic signals emitted by the
growing bubble are calculated, and the interaction between many growing bubbles
is considered.Comment: 20 pages, 3 figures, LaTeX, ITP-UH 11/9
Just in time: defining historical chronographics
The paper is historical in two respects, both concerned with visual representations of past time. Its first purpose is to enquire how visual representations of historical time can be used to bring out patterns in a museum collection. A case study is presented of the visualisation of data with sufficient subtlety to be useful to historians and curators. Such a visual analytics approach raises questions about the proper representation of time and of objects and events within it. It is argued that such chronographics can support both an externalised, objectivising point of view from ‘outside’ time and one which is immersive and gives a sense of the historic moment. These modes are set in their own historical context through original historical research, highlighting the shift to an Enlightenment view of time as a uniform container for events. This in turn prompts new ways of thinking about chronological visualisation, in particular the separation of the ‘ideal’ image of time from contingent, temporary rendered views
Evidence of slow-light effects from rotary drag of structured beams
Self-pumped slow light, typically observed within laser gain media, is created by an intense pump field. By observing the rotation of a structured laser beam upon transmission through a spinning ruby window, we show that the slowing effect applies equally to both the dark and bright regions of the incident beam. This result is incompatible with slow-light models based on simple pulse-reshaping arising from optical bleaching. Instead, the slow-light effect arises from the long upper-state lifetime of the ruby and a saturation of the absorption, from which the Kramers–Kronig relation gives a highly dispersive phase index and a correspondingly high group index
Ultraslow light propagation in an inhomogeneously broadened rare-earth ion-doped crystal
We show that Coherent Population Oscillations effect allows to burn a narrow
spectral hole (26Hz) within the homogeneous absorption line of the optical
transition of an Erbium ion-doped crystal. The large dispersion of the index of
refraction associated with this hole permits to achieve a group velocity as low
as 2.7m/s with a ransmission of 40%. We especially benefit from the
inhomogeneous absorption broadening of the ions to tune both the transmission
coefficient, from 40% to 90%, and the light group velocity from 2.7m/s to
100m/s
A typical reconstruction limit of compressed sensing based on Lp-norm minimization
We consider the problem of reconstructing an -dimensional continuous
vector \bx from constraints which are generated by its linear
transformation under the assumption that the number of non-zero elements of
\bx is typically limited to (). Problems of this
type can be solved by minimizing a cost function with respect to the -norm
||\bx||_p=\lim_{\epsilon \to +0}\sum_{i=1}^N |x_i|^{p+\epsilon}, subject to
the constraints under an appropriate condition. For several , we assess a
typical case limit , which represents a critical relation
between and for successfully reconstructing the original
vector by minimization for typical situations in the limit
with keeping finite, utilizing the replica method. For ,
is considerably smaller than its worst case counterpart, which
has been rigorously derived by existing literature of information theory.Comment: 12 pages, 2 figure
Narrow structure in the coherent population trapping resonances in rubidium and Rayleigh scattering
The measurement of the coherent-population-trapping (CPT) resonances in
uncoated Rb vacuum cells has shown that the shape of the resonances is
different in different cells. In some cells the resonance has a complex shape -
a narrow Lorentzian structure, which is not power broadened, superimposed on
the power broadened CPT resonance. The results of the performed investigations
on the fluorescence angular distribution are in agreement with the assumption
that the narrow structure is a result of atom interaction with Rayleigh
scattering light. The results are interesting for indication of the vacuum
cleanness of the cells and building of magnetooptical sensors
Strong nonlinear optical response of graphene flakes measured by four-wave mixing
We present the first experimental investigation of nonlinear optical
properties of graphene flakes. We find that at near infrared frequencies a
graphene monolayer exhibits a remarkably high third-order optical nonlinearity
which is practically independent of the wavelengths of incident light. The
nonlinear optical response can be utilized for imaging purposes, with image
contrasts of graphene which are orders of magnitude higher than those obtained
using linear microscopy.Comment: 4 pages, 5 figure
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