5,436 research outputs found
An Improved Adaptive Background Mixture Model for Real-time Tracking with Shadow Detection
Real-time segmentation of moving regions in image sequences is a fundamental step in many vision systems including automated visual surveillance, human-machine interface, and very low-bandwidth telecommunications. A typical method is background subtraction. Many background models have been introduced to deal with different problems. One of the successful solutions to these problems is to use a multi-colour background model per pixel proposed by Grimson et al [1, 2,3]. However, the method suffers from slow learning at the beginning, especially in busy environments. In addition, it can not distinguish between moving shadows and moving objects. This paper presents a method which improves this adaptive background mixture model. By reinvestigating the update equations, we utilise different equations at different phases. This allows our system learn faster and more accurately as well as adapts effectively to changing environment. A shadow detection scheme is also introduced in this paper. It is based on a computational colour space that makes use of our background model. A comparison has been made between the two algorithms. The results show the speed of learning and the accuracy of the model using our update algorithm over the Grimson et al’s tracker. When incorporate with the shadow detection, our method results in far better segmentation than The Thirteenth Conference on Uncertainty in Artificial Intelligence that of Grimson et al
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Surface mineral crusts: A priority target in search for life on Mars
Mineral crusts are strong candidates in the search for evidence of life during planetary exploration, and should be an important target for examination in impact craters. Crusts in the Haughton crater readily yield a biological signature
Stiffness of Contacts Between Rough Surfaces
The effect of self-affine roughness on solid contact is examined with
molecular dynamics and continuum calculations. The contact area and normal and
lateral stiffnesses rise linearly with the applied load, and the load rises
exponentially with decreasing separation between surfaces. Results for a wide
range of roughnesses, system sizes and Poisson ratios can be collapsed using
Persson's contact theory for continuous elastic media. The atomic scale
response at the interface between solids has little affect on the area or
normal stiffness, but can greatly reduce the lateral stiffness. The scaling of
this effect with system size and roughness is discussed.Comment: 4 pages, 3 figure
Towards a modeling of the time dependence of contact area between solid bodies
I present a simple model of the time dependence of the contact area between
solid bodies, assuming either a totally uncorrelated surface topography, or a
self affine surface roughness. The existence of relaxation effects (that I
incorporate using a recently proposed model) produces the time increase of the
contact area towards an asymptotic value that can be much smaller than
the nominal contact area. For an uncorrelated surface topography, the time
evolution of is numerically found to be well fitted by expressions of
the form [, where the exponent depends on
the normal load as , with close to 0.5. In
particular, when the contact area is much lower than the nominal area I obtain
, i.e., a logarithmic time increase of the
contact area, in accordance with experimental observations. The logarithmic
increase for low loads is also obtained analytically in this case. For the more
realistic case of self affine surfaces, the results are qualitatively similar.Comment: 18 pages, 9 figure
Contact area of rough spheres: Large scale simulations and simple scaling laws
We use molecular simulations to study the nonadhesive and adhesive
atomic-scale contact of rough spheres with radii ranging from nanometers to
micrometers over more than ten orders of magnitude in applied normal load. At
the lowest loads, the interfacial mechanics is governed by the contact
mechanics of the first asperity that touches. The dependence of contact area on
normal force becomes linear at intermediate loads and crosses over to Hertzian
at the largest loads. By combining theories for the limiting cases of nominally
flat rough surfaces and smooth spheres, we provide parameter-free analytical
expressions for contact area over the whole range of loads. Our results
establish a range of validity for common approximations that neglect curvature
or roughness in modeling objects on scales from atomic force microscope tips to
ball bearings.Comment: 2 figures + Supporting Materia
Breakdown of disordered media by surface loads
We model an interface layer connecting two parts of a solid body by N
parallel elastic springs connecting two rigid blocks. We load the system by a
shear force acting on the top side. The springs have equal stiffness but are
ruptured randomly when the load reaches a critical value. For the considered
system, we calculate the shear modulus, G, as a function of the order
parameter, \phi, describing the state of damage, and also the ``spalled''
material (burst) size distribution. In particular, we evaluate the relation
between the damage parameter and the applied force and explore the behaviour in
the vicinity of material breakdown. Using this simple model for material
breakdown, we show that damage, caused by applied shear forces, is analogous to
a first-order phase transition. The scaling behaviour of G with \phi is
explored analytically and numerically, close to \phi=0 and \phi=1 and in the
vicinity of \phi_c, when the shear load is close but below the threshold force
that causes material breakdown. Our model calculation represents a first
approximation of a system subject to wear induced loads.Comment: 15 pages, 7 figure
Characterisation of Float Rocks at Ireson Hill, Gale Crater
Float rocks discovered by surface missions on Mars have given unique insights into the sedimentary, diagenetic and igneous processes that have operated throughout the planets history. In addition, Gale sedimentary rocks, both float and in situ, record a combination of source compositions and diagenetic overprints. We examine a group of float rocks that were identified by the Mars Science Laboratory missions Curiosity rover at the Ireson Hill site, circa. sol 1600 using ChemCam LIBS, APXS and images from the MastCam, Mars Hand Lens Imager (MAHLI) and ChemCam Remote Micro-Imager (RMI) cameras. Geochemical data provided by the APXS and ChemCam instruments allow us to compare the compositions of these rocks to known rock types from Gale crater, as well as elsewhere on Mars. Ireson Hill is a 15 m long butte in the Murray formation with a dark cap-ping unit with chemical and stratigraphic consistency with the Stimson formation. A total of 6 float rocks have been studied on the butte
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