727 research outputs found
A Novel Representation for Two-dimensional Image Structures
This paper presents a novel approach towards two-dimensional (2D) image structures modeling. To obtain more degrees of freedom, a 2D image signal is embedded into a certain geometric algebra. Coupling methods of differential geometry, tensor algebra, monogenic signal and quadrature filter, we can design a general model for 2D structures as the monogenic extension of a curvature tensor. Based on it, a local representation for the intrinsically two-dimensional (i2D) structure is derived as the monogenic curvature signal. From it, independent features of local amplitude, phase and orientation are simultaneously extracted. Besides, a monogenic curvature scale-space can be built by applying a Poisson kernel to the monogenic curvature signal. Compared with the other related work, the remarkable advantage of our approach lies in the rotationally invariant phase evaluation of 2D structures in a multi-scale framework, which delivers access to phase-based processing in many computer vision tasks
The hidden geometric character of relativistic quantum mechanics
The presentation makes use of geometric algebra, also known as Clifford
algebra, in 5-dimensional spacetime. The choice of this space is given the
character of first principle, justified solely by the consequences that can be
derived from such choice and their consistency with experimental results. Given
a metric space of any dimension, one can define monogenic functions, the
natural extension of analytic functions to higher dimensions; such functions
have null vector derivative and have previously been shown by other authors to
play a decisive role in lower dimensional spaces. All monogenic functions have
null Laplacian by consequence; in an hyperbolic space this fact leads
inevitably to a wave equation with plane-like solutions. This is also true for
5-dimensional spacetime and we will explore those solutions, establishing a
parallel with the solutions of the Dirac equation. For this purpose we will
invoke the isomorphism between the complex algebra of 4x4 matrices, also known
as Dirac's matrices. There is one problem with this isomorphism, because the
solutions to Dirac's equation are usually known as spinors (column matrices)
that don't belong to the 4x4 matrix algebra and as such are excluded from the
isomorphism. We will show that a solution in terms of Dirac spinors is
equivalent to a plane wave solution. Just as one finds in the standard
formulation, monogenic functions can be naturally split into positive/negative
energy together with left/right ones. This split is provided by geometric
projectors and we will show that there is a second set of projectors providing
an alternate 4-fold split. The possible implications of this alternate split
are not yet fully understood and are presently the subject of profound
research.Comment: 29 pages. Small changes in V3 suggested by refere
Signal Modeling for Two-Dimensional Image Structures and Scale-Space Based Image Analysis
Model based image representation plays an important role in many computer vision tasks. Consequently, it is of high significance to model image structures with more powerful representation capabilities. In the literature, there exist bulk of researches for intensity based modeling. However, most of them suffer from the illumination variation. On the other hand, phase information, which carries most essential structural information of the original signal, has the advantage of being invariant to the brightness change. Therefore, phase based image analysis is advantageous when compared to purely intensity based approaches. This thesis aims to propose novel image representations for 2D image structures, from which useful local features can be extracted, which are useful for phase based image analysis. The first approach presents a 2D rotationally invariant quadrature filter. This model is able to handle superimposed intrinsically two-dimensional (i2D) patterns with flexible angles of intersection. Hence, it can be regarded as an extension of the structure multivector. The second approach is the monogenic curvature tensor. Coupling methods of differential geometry, tensor algebra, monogenic signal and quadrature filter, we can design a general model for 2D structures as the monogenic extension of a curvature tensor. Based on it, local representations for the intrinsically one-dimensional (i1D) and i2D structures are derived as the monogenic signal and the generalized monogenic curvature signal, respectively. From them, independent features of local amplitude, phase and orientation are simultaneously extracted. Besides, a generalized monogenic curvature scale-space can be built by applying a Poisson kernel to the monogenic curvature tensor. Compared with other related work, the remarkable advantage of our approach lies in the rotationally invariant phase evaluation of 2D structures in a multi-scale framework, which delivers access to phase-based processing in many computer vision tasks. To demonstrate the efficiency and power of the theoretic framework, some computer vision applications are presented, which include the phase based image reconstruction, detecting i2D image structures using local phase and monogenic curvature tensor for optical flow estimation
Eigenvalues of conformally invariant operators on spheres
Spectrum of a certain class of first order conformally invariant operators on
the sphere is explicitly computed. The class contains the (elliptic verions of)
Rarita-Schwinger operator and its higher spin analogues.Comment: 14 page
Fluids mobilization in Arabia Terra, Mars: depth of pressurized reservoir from mounds self-similar clustering
Arabia Terra is a region of Mars where signs of past-water occurrence are
recorded in several landforms. Broad and local scale geomorphological,
compositional and hydrological analyses point towards pervasive fluid
circulation through time. In this work we focus on mound fields located in the
interior of three casters larger than 40 km (Firsoff, Kotido and unnamed crater
20 km to the east) and showing strong morphological and textural resemblance to
terrestrial mud volcanoes and spring-related features. We infer that these
landforms likely testify the presence of a pressurized fluid reservoir at depth
and past fluid upwelling. We have performed morphometric analyses to
characterize the mound morphologies and consequently retrieve an accurate
automated mapping of the mounds within the craters for spatial distribution and
fractal clustering analysis. The outcome of the fractal clustering yields
information about the possible extent of the percolating fracture network at
depth below the craters. We have been able to constrain the depth of the
pressurized fluid reservoir between ~2.5 and 3.2 km of depth and hence, we
propose that mounds and mounds alignments are most likely associated to the
presence of fissure ridges and fluid outflow. Their process of formation is
genetically linked to the formation of large intra-crater bulges previously
interpreted as large scale spring deposits. The overburden removal caused by
the impact crater formation is the inferred triggering mechanism for fluid
pressurization and upwelling, that through time led to the formation of the
intra-crater bulges and, after compaction and sealing, to the widespread mound
fields in their surroundings
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