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Influence of temperature variations on calibrated cameras
Peter Podbreznik, Božidar Potočnik, 2008, izvirni znanstveni članek

Opis: The camera parameters are changed due to temperature variations, which directly influence calibrated cameras accuracy. Robustness of calibration methods were measured and their accuracy was tested. An error ratio due to camera parameters change with respect to total error originated during calibration process was determined. It pointed out that influence of temperature variations decrease by increasing distance of observed objects from cameras.
Ključne besede: camera calibration, perspective projection matrix, epipolar geometry, temperature variation
Objavljeno: 31.05.2012; Ogledov: 997; Prenosov: 29
URL Povezava na celotno besedilo

On the application of a simple computational model for slender transversely cracked beams in buckling problems
Matjaž Skrinar, 2007, izvirni znanstveni članek

Opis: This paper discusses the implementation of a simplified computational model that is widely used for the computation of transverse displacements in transversely cracked slender beams into the Euler's elastic flexural buckling theory. Two alternatives are studied instead of solving the corresponding differential equations to obtain exact analytical expressions for the buckling load ▫$P_{cr}$▫ due to the complexity of this approach. The first approach implements wisely selected polynomials to describe the behavior of the structure, which allows the derivation of approximate expressions for the critical buckling load. Although the relevance of the results strongly depends on the proper prime selection of the polynomial, it is shown that the later upgrading of the polynomials can lead to even more reliable results. The second approach is a purely numerical approach and presents the geometrical stiffness matrix for a beam finite element with a transverse crack. To support the discussed approaches, numerical examples covering several structures with different boundary conditions are briefly presented. The results obtained with the presented approaches are further compared with the values from enormous 2D finite elements models, where a detailed description of the crack was achieved with the discrete approach. It is evident that the drastic difference in the computational effort is not reflected in the significant differences in the results between the models.
Ključne besede: columns, transverse cracks, stability problems, buckling load, computational model, polynomial solutions, finite element method, geometrical stiffness matrix
Objavljeno: 01.06.2012; Ogledov: 1334; Prenosov: 62
URL Povezava na celotno besedilo

The wavelet transform for BEM computational fluid dynamics
Jure Ravnik, Leopold Škerget, Matjaž Hriberšek, 2004, izvirni znanstveni članek

Opis: A wavelet matrix compression technique was used to solve systems of linear equations resulting from BEM applied to fluid dynamics. The governing equations were written in velocity-vorticity formulation and solutions of the resulting systems of equations were obtained with and without wavelet matrix compression. A modification of the Haar wavelet transform, which can transformvectors of any size, is proposed. The threshold, used for making fully populated matrices sparse, was written as a product of a user defined factor and the average value of absolute matrix elements values. Numerical tests were performed to assert, that the error caused by wavelet compression depends linearly on the factor , while the dependence of the error on the share of thresholded elements in the system matrix is highly non-linear. The results also showed that the increasing non-linearity (higher Ra and Re numbervalues) limits the extent of compression. On the other hand, higher meshdensity enables higher compression ratios.
Ključne besede: fluid mechanics, computational fluid dynamics, boundary element method, wavelet transform, linear systems of equations, velocity vorticity formulation, driven cavity, natural convection, system matrix compression
Objavljeno: 01.06.2012; Ogledov: 1279; Prenosov: 58
URL Povezava na celotno besedilo

On semigroups of normal matrices
Bojana Zalar, 2003, izvirni znanstveni članek

Opis: Semigroups of normal complex square matrices having a finite spectrum are studied. It is shown that every mamber ▫$A$▫ of such a semigroup satisfies the condition ▫$A^ast = A^n$▫, where ▫$n$▫ does not depend on the matrix ▫$A$▫. Further, it is shown that such a semigroup is completely reducible, and each irreducible contraction consists of a group of unitary matrices and, aventually, the zero matrix.
Ključne besede: mathematics, matrix theory, normal matrices, spectrum, semigroups, reducability
Objavljeno: 01.06.2012; Ogledov: 959; Prenosov: 57
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Experimental investigation of the stability of particulate dispersoid suspensions in aluminium and magnesium melts
Varužan Kevorkijan, 2000, izvirni znanstveni članek

Opis: The rejection of Si3N4,Mg3N2, AlN and Si particles from different slurries consisting of molten aluminum and magnesium alloy with 10% of silicon or pure molten metals was experimentally investigated by measuring changes in the electrical resistance of the slurries before and after rejection occurred. In stirring experiments, only individual powder fractions which passed through a 45 µm sieve screen and remained on a 30 µm screenwere applied. The experiments showed that the rejection of Si3N4 particles from Al-10%Si and Mg-10%Si melts occurs when more than 17-18 vol.% of the ceramic phase is dispersed into the melt, while in pure Al and Mg molten metals spontaneous rejection occurs at 7-8 vol.% of the introduced ceramic phase. A similar tendency of rejection (at 16-18 vol.% of particulate in slurry) was also observed during the introduction of silicon particles into Al-10%Si and Mg-10%Si melts.
Ključne besede: metal matrix composites, particle reinforcement, interface, chemically activated wetting
Objavljeno: 01.06.2012; Ogledov: 986; Prenosov: 31
.pdf Celotno besedilo (215,84 KB)
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Non-linear commutativity preserving maps on symetric matrices
Ajda Fošner, 2007, izvirni znanstveni članek

Opis: We study bijective maps on the set of all symmetric matrices in ▫$M_n(Cc), n ge 3$▫ that preserve commutativity in both directions.
Ključne besede: mathematics, linear algebra, symmetric matrix, orthogonal matrix, commutativity preserving map, symmetric Jordan canonical form
Objavljeno: 07.06.2012; Ogledov: 933; Prenosov: 15
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