174,754 research outputs found
Theoretical optimal modulation frequencies for scattering parameter estimation and ballistic photon filtering in diffusive media
The efficiency of using intensity modulated light for estimation of
scattering properties of a turbid medium and for ballistic photon
discrimination is theoretically quantified in this article. Using the diffusion
model for modulated photon transport and considering a noisy quadrature
demodulation scheme, the minimum-variance bounds on estimation of parameters of
interest are analytically derived and analyzed. The existence of a
variance-minimizing optimal modulation frequency is shown and its evolution
with the properties of the intervening medium is derived and studied.
Furthermore, a metric is defined to quantify the efficiency of ballistic photon
filtering which may be sought when imaging through turbid media. The analytical
derivation of this metric shows that the minimum modulation frequency required
to attain significant ballistic discrimination depends only on the reduced
scattering coefficient of the medium in a linear fashion for a highly
scattering medium
Centrality and connectivity in public transport networks and their significance for transport sustainability in cities
The promotion of public transport as a backbone of mobility in urban agglomerations, or at least as an alternative to the dominance of the automobile, has become a prominent policy focus in most large cities around the world. However, while some cities have been successful in shifting car journeys onto rail and buses, others are struggling despite considerable effort to make public transport more attractive. This paper provides a brief overview of success factors for public transport and then takes the configuration of public transport networks as a vantage point for policy evaluation. The development of centrality and connectivity indicators for the public transport network of Melbourne's north-eastern suburbs delivers an instrument for assessing the congruence of the systems with the geographical structure of central areas and urban activities in these cities. It is hypothesised that a higher number of convenient transfer points and a choice of routes to users (network connectivity), as well as a high degree of spatial overlap and integration between public transport infrastructure and urban activity centres and corridors (centrality of facilities) will lead to a greater role for public transport in the mobility patterns of the city as a whole
Reconstruction of hidden 3D shapes using diffuse reflections
We analyze multi-bounce propagation of light in an unknown hidden volume and
demonstrate that the reflected light contains sufficient information to recover
the 3D structure of the hidden scene. We formulate the forward and inverse
theory of secondary and tertiary scattering reflection using ideas from energy
front propagation and tomography. We show that using careful choice of
approximations, such as Fresnel approximation, greatly simplifies this problem
and the inversion can be achieved via a backpropagation process. We provide a
theoretical analysis of the invertibility, uniqueness and choices of
space-time-angle dimensions using synthetic examples. We show that a 2D streak
camera can be used to discover and reconstruct hidden geometry. Using a 1D high
speed time of flight camera, we show that our method can be used recover 3D
shapes of objects "around the corner"
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