10,120 research outputs found
Lensing of 21cm Absorption "Halos" of 20-30 First Galaxies
Extended 21cm absorption regions (dubbed ``21cm absorption halos'') around
first galaxies at are likely the first distinctive structures
accessible to radio observations. Though the radio array capable of detecting
and resolving them must have km total collecting area, given the
great impact of such detections to the understanding of the reionization
process and cosmology, such radio survey would be extremely profitable. As an
example, we point out a potentially useful byproduct of such survey. The
resolved 21cm absorption ``halos'', likely close to spherical, can serve as
(almost) ideal sources for measuring the {\it cosmic shear} and mapping the
matter distribution to . We investigate the expected lensing signal
and consider a variety of noise contributions on the shear measurement. We find
that S/N can be achieved for individual ``halos''. Given millions of
21cm absorption ``halos'' across the sky, the total S/N will be comparable to
traditional shear measurement of galaxies at .Comment: Minor revisions and expanded discussions. Accepted to MNRA
Observation of anisotropic diffusion of light in compacted granular porous materials
It is known that compaction of granular matter can lead to anisotropic
mechanical properties. Recent work has confirmed the link to pore space
anisotropy, but the relation between compression, mechanical properties and
material microstructure remains poorly understood and new diagnostic tools are
needed. By studying the temporal and spatial characteristics of short optical
pulses diffusively transmitted through compacted granular materials, we show
that powder compaction can also give rise to strongly anisotropic diffusion of
light. Investigating technologically important materials such as
microcrystalline cellulose, lactose and calcium phosphate, we report increasing
optical anisotropy with compaction force and radial diffusion constants being
up to 1.7 times the longitudinal. This open new and attractive routes to
material characterization and investigation of compression-induced structural
anisotropy. In addition, by revealing inadequacy of isotropic diffusion models,
our observations also have important implications for quantitative spectroscopy
of powder compacts (e.g., pharmaceutical tablets).Comment: New version with significantly improved presentation. Data and
argumentation identical to previous versio
Photon Parameterisation for Robust Relaxation Constraints
This paper presents a novel approach to detecting and preserving fine illumination structure within photon maps. Data derived from each photon's primal trajectory is encoded and used to build a high-dimensional kd-tree. Incorporation of these new parameters allows for precise differentiation between intersecting ray envelopes, thus minimizing detail degradation when combined with photon relaxation. We demonstrate how parameter-aware querying is beneficial in both detecting and removing noise. We also propose a more robust structure descriptor based on principal components analysis that better identifies anisotropic detail at the sub-kernel level. We illustrate the effectiveness of our approach in several example scenes and show significant improvements when rendering complex caustics compared to previous methods
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