Sök uppsatser och vetenskapliga publikationer

(0.006 sekunder)

Luleå tekniska universitet Övrigt
N/A / Link / Nyberg , Sven / 1997

Results on quasi-Banach spaces, their type and cotype together with the convexity and concavity of quasi-Banach lattices are collected. Several proofs are included. Then the Lebesgue $L^p$, the Lorentz $L^{p,q}$ and the Marcinkiewicz $L^{p,\infty}$ spaces are the special examples. We review also several results of Kami\'nska and the author on convexity, concavity, type and cotype of general Lorentz spaces $\Lambda_{p,w}$
4-946552-14-6 / Link / Maligranda , Lech / 2004

Luleå tekniska universitet Övrigt
Thin films of zeolite ZSM-5 on quartz substrates have been prepared in the absence of organic templates by growth of adsorbed seed crystals attached to a polymer-modified substrate surface.
N/A / Link / Mintova , Svetlana / 1997

N/A / Link / Johansson , Jan / 1989

Luleå tekniska universitet Övrigt
Let $w$ be a non-negative measurable function on $(0,\infty)$, non-identically zero, such that $W(t)=\int_0^tw(s)ds<\infty$ for all $t>0$. The authors study conditions on $w$ for the Lorentz spaces $\Lambda^p(w)$ and $\Lambda^{p,\infty}(w)$, defined by the conditions $\int_0^\infty (f^*(t))^pw(t)dt<\infty$ and $\sup_{00,$$ it is shown that, if $\varphi$ satisfies the $\Delta_2$-condition and $w>0$, then $\Lambda_{\varphi,w}$ is a linear space if and only if $W$ satisfies the $\Delta_2$-condition.
N/A / Link / Cwikel , Michael / 2004

0-900488-60-3 / Link / Knutsson , Sven / 1981

The rate of stiffness reduction in damaged laminates with increasing transverse crack density in plies depends on two micromechanical parameters: normalized crack face opening displacement (COD) and crack face sliding displacement (CSD). A FE-based parametric study shows that the only properties that affect the CSD are the thickness ratio and the in-plane shear stiffness ratio of the damaged and neighboring undamaged layers. The dependence is described by a power function with respect to the above mentioned properties. This relationship and the previously obtained power law for COD [Lundmark P, Varna J. Constitutive relationships for damaged laminate in in-plane loading. Int J Dam Mech 2005:14(3):235-59] are used in the damaged laminate constitutive relationships [Lundmark P, Varna J. Constitutive relationships for damaged laminate in in-plane loading. Int J Dam Mech 2005:14(3):235-59], which are closed form exact expressions for general symmetric laminates in in-plane loading. The model is validated analyzing reduction in shear modulus of [Sn,90m]s laminates and comparing with direct FE-calculations. The results are excellent in case of cracks in one layer only. For laminates with two orthogonal systems of cracks, the power law underestimates the CSD. To account for interaction between both systems of cracks, which is of importance for crack face sliding, the power law is modified using the effective shear modulus of the cracked neighboring layer.
N/A / Link / Varna , Janis / 2006

Luleå tekniska universitet Övrigt
N/A / Link / Westman , Gustaf / 1995

Luleå tekniska universitet Övrigt
N/A / Link / Lindqvist , Per-Arne / 2005

Luleå tekniska universitet Övrigt
Thin continuous films of zeolite ZSM-5 were synthesized on quartz substrates. The substrates were first surface modified and covered by a monolayer of colloidal silicalite-1 seed crystals. These crystals were grown into continuous films with thicknesses in the range 230-3500 nm by hydrothermal treatment in a synthesis gel free from organic templates. The preferential orientation of the crystals constituting the film was initially one with thec-axis close to parallel to the substrate surface. During the course of crystallization this orientation changed to one with most of the crystals having the c-axes directed approximately 35° from perpendicular to the substrate surface. A mechanism explaining this behavior is proposed. The final thickness of the film was controlled by the synthesis time but also by the addition of seed crystals to the synthesis gel. Films prepared according to this method may be of great value for the development of zeolite based membranes.
N/A / Link / Mintova , Svetlana / 1998

Luleå tekniska universitet Övrigt
På uppdrag av Skellefteå kommun pågår en studie som avser möjligheten att skapa ett forsknings- och utvecklingscenter i norra Sverige. Ett så kallat "Centre of Excellence". Centret ska vara inriktat på forskning och utveckling av hydrometallurgiska processer, med särskild inriktning på biohydrometallurgi. Studien genomförs i samarbete med Umeå Universitet, Luleå tekniska Universitet och Boliden Mineral. Centret planeras bli en självständig juridisk enhet med egna anläggningar för forskning och utveckling. Samtidigt är tanken att centret ska samarbeta intimt med institut och universitet. Målsättningen är också att knyta högre utbildning till centret. I studien ingår byggandet av en hydrometallurgisk demonstrationsanläggning placerad i Boliden. Anläggningen planeras bli i en sådan skala och omfattning att den tillåter utveckling och demonstration av olika processer för en mängd olika produkter. Idén är att olika företag och organisationer ska kunna använda centret med dess resurser, för att utveckla och demonstrera processer tekniskt, miljömässigt och ekonomiskt.
N/A / Link / Sandström , Åke / 2002

Luleå tekniska universitet Övrigt
91-86992-20-1 / Link / Söderholm , Kristina / 2002

Compressive behavior of phenol-formaldehyde impregnated paper composites is studied in creep and strain recovery tests observing large nonlinear viscoelastic strains and irreversible strains, describing the latter as viscoplasticity. Stiffness reduction was not observed in experiments and therefore is not included in the material model. Schapery's nonlinear viscoelastic and nonlinear viscoplastic constitutive law is used as a material model and the stress dependent non-linearity functions are determined. First, the time and stress dependence of viscoplastic strains is described by Zapas et al. model and identified measuring the irreversible strains after creep tests of different length at the same stress and doing the same for creep tests of a fixed length but at different stress. Then, the determination of nonlinear viscoelastic stress dependent parameters is performed.
N/A / Link / Nordin , Lars-Olof / 2006

Luleå tekniska universitet Övrigt
N/A / Link / Friberg , Ingemar / 1997

Luleå tekniska universitet Övrigt
The author, whose untimely passing in April 2006 was a great loss to the logic community, used this short paper primarily to dispel a few popular and not so popular misinterpretations of Gödel's incompleteness theorems. The most obvious misconceptions arise in areas having no direct connection with mathematics. But even within scientific circles, it is useful for the author to have pointed out that no unsolved problem in "traditional mathematics" has been shown to be undecidable via Gödel's first incompleteness theorem. (The Paris-Harrington undecidable problem does have to do with standard mathematical concepts, but it was not obtained from Gödel's result.) The author also makes illuminating remarks about Gödel's second incompleteness theorem concerning unprovability of the consistency of sufficiently strong mathematical theories. For example, the role of consistency proofs in justifying mathematical reasoning has been overemphasized. Moreover, there are informal `proofs' on the same level as ordinary mathematical argumentation that may convince most mathematicians of the consistency of, say, Peano arithmetic. For a more extensive treatment of all of these matters, the author refers the reader to his recent book Gödel's theorem, A K Peters, Wellesley, MA, 2005
N/A / Link / Franzén , Torkel / 2006

N/A / Link / Alatalo , Johanna / 2006

Light weight structures with high structural performance are one of the most important goals for automotive and transportation applications. One manufacturing technology, aiming to enable low weight design, is the combined forming and quenching of tubular thin-walled profiles of high strength steel. For optimal utilisation of this technology it is necessary to simulate and analyse the processes involved in a fast and efficient way. In this work, experiments of high temperature bending of thin walled profiles are performed and the forming response force is compared with results from finite element simulations. The analysed forming is modelled as a constant temperature forming and the material data for the specified temperature is evaluated from experiments and literature. The simulations and experiments are conducted to study the ability of the finite element model to predict high temperature forming characteristics and simulate the influence of profile and tool geometry. The need for further improvements and developments in the simulation technology is however identified. This work is part of a research project LOWHIPS (Low Weight High Performance Steel structures) aiming to obtain new knowledge concerning the involved forming and quenching processes and how they will affect the performance of the product.
N/A / Link / Eriksson , Magnus / 2001

Luleå tekniska universitet Övrigt
N/A / Link / Cervantes , Michel / 1998

Luleå tekniska universitet Övrigt
N/A / Link / Yanmin , Wang / 2004

N/A / Link / Lindqvist , Per-Arne / 2005

Luleå tekniska universitet Övrigt
Ultrathin oriented films of zeolite LTA are prepared on single-crystal alumina supports by a method including adsorption of LTA seeds on the support followed by hydrothermal film crystallization.
N/A / Link / Hedlund , Jonas / 1997

V-invariant methods for the generalised least squares problem extend the techniques based on orthogonal factorization for ordinary least squares to problems with multiscaled, even singular covariances. These methods are summarised briefly here, and the ability to handle multiple scales indicated. An application to a class of Kalman filter problems derived from generalised smoothing splines is considered. Evidence of severe illconditioning of the covariance matrices is demonstrated in several examples. This suggests that this is an appropriate application for the V-invariant techniques.
N/A / Link / Osborne , M. R. / 2004

Luleå tekniska universitet Övrigt
1-60021-124-0 / Link / Berglund , Christer / 2006

A model accounting for linear viscoelasticity and microdamage evolution in short fibre composites is described. An incremental 2D formulation suitable for FE-simulation is derived and implemented in FE-solver ABAQUS. The implemented subroutine allows for simulation close to the final failure of the material. The formulation and subroutine is validated with analytical results and experimental data in a tensile test with constant strain rate using sheet moulding compound composites. FE-simulation of a four-point bending test is performed using shell elements. The result is compared with linear elastic solution and test data using a plot of maximum surface strain in compression and tension versus applied force. The model accounts for damage evolution due to tensile loading and neglects any damage evolution in compression, where the material has higher strength. Simulation and test results are in very good agreement regarding the slope of the load-strain curve and the slope change.
N/A / Link / Varna , Janis / 2005

Numerical investigation of methane combustion in a pipe with turbulent flow is studied. The space discretization error is investigated quantitatively and qualitatively, using the Richardson extrapolation and profiles comparisons. Comparison of the profiles indicates that the solution converges to a grid-independent solution. The Richardson method gives unsatisfactory results to determine the grid error, because of the rigidity of the method. A second-order polynomial is used as an alternative to the Richardson method. The results are more stable and have a better goodness of fit. The results of the simulations are compared with those of a similar experiment and the corresponding analytical solution.
N/A / Link / Lindberg , Jenny / 2005

Luleå tekniska universitet Övrigt
N/A / Link / Lindqvist , Per-Arne / 2005

The direct synthesis of thin films of crystalline silicalite-1 upon single crystal silicon wafers at a crystallization temperature of 100°C has been investigated by varying the composition of the clear tetrapropylammonium (TPA) silicate synthesis solutions. Synthesis mixture compositions known to yield monodisperse colloidal crystals of TPA-silicalite-1 upon hydrothermal treatment as well as those reported to yield silicalite-1 films at higher temperatures have been found not suitable for the preparation of silicalite-1 films at 100°C. Lower crystal growth rates and smaller thicknesses of the gel film that forms on the wafer at this temperature decrease the tolerance to alkalinity, resulting in etching via the consumption of the gel layer before the growing crystals succeed in forming a closed film followed by the removal of the protective silicon oxide film on the wafer. Thin oriented silicalite-1 films with thicknesses in the range of 180 nm to 1 μm have been obtained by varying the alkalinity and water, the TPA, and the silica contents of the reaction mixture. Lower alkalinities and higher silica concentrations favor the formation of a thicker amorphous gel layer. Although increased TPA+ concentrations at constant alkalinity increase the number of nuclei that form on this layer, higher TPA+ concentrations have been observed to be required at higher alkalinities to achieve similar rates of nucleation. Rinsing the wafer surfaces initially with a 0.025 M TPAOH solution before rinsing with water and acetone produces cleaner surfaces free of post-treatment artifacts
N/A / Link / Schoeman , Brian / 1997

Thin films of silicalite-1 grown on silicon substrates were studied by spectroscopic ellipsometry. Analysis of spectra using an optical model consisting of a single porous layer on silicon yielded average film thicknesses of 84 and 223 nm for films synthesized for 10 and 30 h. Void fraction for the films was 0.32-0.33. Vapor adsorption from a nitrogen carrier gas at room temperature was monitored by ellipsometry. Isotherms for different adsorbates were obtained by analysis of spectra taken at different vapor concentrations using an optical model where the void volume was filled with both nitrogen and condensed vapors. Quantification of the condensed vapor amount was based on the changes in refractive index when adsorbates replaced nitrogen in the pores. Adsorbate volumes for water, toluene, 1-propanol, and hexane were 0.12, 0.12, 0.15, and 0.17 cm3 liquid g-1 film, respectively.
N/A / Link / Bjorklund , Robert B. / 1998