| 51. |
- Jirström, Magnus, et al.
(författare)
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The State and Green Revolutions in East Asia
- 2005
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Ingår i: The African Food Crisis: Lessons from the Asian Green Revolution. - UK : CABI Publishing. - 0851999980 ; , s. 25-42
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Bokkapitel (refereegranskat)
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| 52. |
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| 53. |
- Karlsson, Peter
(författare)
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On the Asymptotics of Increasing Dimension Models : Methods for Complete or Incomplete Data
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In some multivariate contexts there is a close relation between the number of parameters (p) and the number of observations (n). In a situation where p grows with n it frequently happens that the statistic does not converge to its true parameter. An additional issue is if the data set also contain missing observations and , for example, as p grows with n so does the number of missing observations. This situation arises in the context of empirical applications of the Arbitrage Pricing Theory model, where the data is incomplete due to the nature of stocks leaving or entering the stock exchange. In this thesis two situations of increasing dimension are considered: firstly, the case of complete data sets where the statistic of interest is the inverse covariance matrix where three types of shrinkage estimators of the inverse covariance matrix are investigated, particularly as an ingredient of a composite estimator, specifically Zellners seemingly unrelated regression models and the Mahalanobis distance. Secondly, the case arising in empirical application of the APT model where the data set is incomplete and the interest is to model the underlying covariance structure among the variables by a few factors. Two possible solutions to the problem are considered and a case study using the Swedish OMX data is conducted for demonstration.
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| 54. |
- Klinth, J. E., et al.
(författare)
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A novel application of multi-wavelength TIRF spectroscopy for real time monitoring of antithrombin interactions with immobilized heparin
- 2006
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Ingår i: Biosensors & bioelectronics. - : Elsevier BV. - 0956-5663 .- 1873-4235. ; 21:10, s. 1973-80
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Tidskriftsartikel (refereegranskat)abstract
- Real time interactions of antithrombin (AT) with Corline Heparin Surfaces (CHS) with one and two layers of heparin conjugate have been examined using a multi-wavelength TIRF spectroscopy technique with continuous flow. Fluorescently labeled AT, adsorbed from citrated human blood plasma, showed significantly higher signals on CHS compared to the cationic surface used to attach the heparin conjugate. The AT binding to CHS was very stable, also after exposure to soluble heparin at a concentration of 1.5 IU/mL. Only a few percent of the bound AT were displaced from the surfaces by AT present in plasma after long-term exposure to plasma. In contrast, larger amounts of the freshly added AT had adsorbed to the surfaces, especially to the surface with two layers of heparin conjugate, indicating the presence of unsaturated AT binding sites. The amount of AT bound to the different surfaces was quantified after elution using an enzyme immunoassay (EIA). Characteristic emission spectra of proteins and fluorophores of labeled proteins, obtained at the surfaces after a long-term exposure to plasma, confirmed their presence at the surfaces. The multi-wavelength TIRF technique proved to be a useful tool when combined with other techniques to study the time course of interactions of fluorescently labeled proteins with biomaterials, even in a complex environment such as plasma.
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| 55. |
- Korsell, Nicklas, 1974-
(författare)
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Statistical Properties of Preliminary Test Estimators
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates the statistical properties of preliminary test estimators of linear models with normally distributed errors. Specifically, we derive exact expressions for the mean, variance and quadratic risk (i.e. the Mean Square Error) of estimators whose form are determined by the outcome of a statistical test. In the process, some new results on the moments of truncated linear or quadratic forms in normal vectors are established.In the first paper (Paper I), we consider the estimation of the vector of regression coefficients under a model selection procedure where it is assumed that the analyst chooses between two nested linear models by some of the standard model selection criteria. This is shown to be equivalent to estimation under a preliminary test of some linear restrictions on the vector of regression coefficients. The main contribution of Paper I compared to earlier research is the generality of the form of the test statistic; we only assume it to be a quadratic form in the (translated) observation vector. Paper II paper deals with the estimation of the regression coefficients under a preliminary test for homoscedasticity of the error variances. In Paper III, we investigate the statistical properties of estimators, truncated at zero, of variance components in linear models with random effects. Paper IV establishes some new results on the moments of truncated linear and/or quadratic forms in normally distributed vectors. These results are used in Papers I-III. In Paper V we study some algebraic properties of matrices that occur in the comparison of two nested models. Specifically we derive an expression for the inertia (the number of positive, negative and zero eigenvalues) of this type of matrices.
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| 56. |
- Kristensen, Emma, 1976-
(författare)
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Characterization of Surfaces Designed for Biomedical Applications
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In order to develop blood biocompatible materials a heparin surface and a phosphorylcholine (PC) functionalized polymer surface were characterized using photoelectron spectroscopy (PES). The formation of the heparin surface was studied by quartz crystal microbalance with dissipation monitoring (QCM-D). This heparin surface consists of heparin conjugates deposited on a conditioning layer, applied once or twice. The PC functionalized polymer, poly(trimethylene carbonate), was linked to a silicon substrate through 3-amino- propyltrimethoxysilane (APTMS), also studied using PES. Synchrotron radiation based PES showed that the thicker heparin film resulted in complete coverage of the substrate, while the thinner did not. This could explain the difference in blood biocompatibility between the two films, as observed by others. It was also found that the heparin chains bend down towards the substrate (under vacuum). For the thinner heparin film the modifications, resulting from extensive irradiation of the sample, were studied with synchrotron radiation based PES. This was done at a pressure of about 10-7 mbar and in 0.5 mbar water vapor. It was found that the modification is slower under water vapor than at low pressures and that the damaged film incorporates water upon exposure.The heparin coating was found to be stable and wear resistant enough to still be present on artificial heart valves after three weeks testing in circulating plasma. It then had about the same antithrombin uptake as a non-tested surface. The film was, however, partly destroyed by the durability test and plasma proteins were deposited. The PC functionalized, APTMS linked polymer was found to be much shorter than could be expected from random reactions. One plausible explanation is an interaction between the PC group and the silane surface, favoring aminolysis close to the PC group. This is consistent with our finding that the PC group bends down towards the surface.
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| 57. |
- Kristensen, Emma, et al.
(författare)
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Heparin coating durability on artificial heart valves studied by XPS and antithrombin binding capacity
- 2006
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Ingår i: Colloids and Surfaces B. - : Elsevier BV. - 0927-7765 .- 1873-4367. ; 49:1, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- The durability and functionality of a heparin coating on artificial heart valve leaflets were evaluated with X-ray photoelectron spectroscopy (XPS) and by the coatings’ capacity to bind antithrombin. Current methods for accelerated life-time testing are based on exposing leaflets to water solutions. In this paper a method is explored, in which heart valve leaflets were exposed to a continuous high shear rate (4 L/min) of human citrated plasma. It was found that the heparin coating was stable and wear resistant enough to still be present after 3 weeks and to have about the same antithrombin uptake as coatings not exposed to circulating plasma. It was, however, partly destroyed by the test as found using XPS. We suggest that heparin chains from the upper layer of heparin have been torn off from the carrier chain, in combination with loss of heparin conjugate and plasma deposition in patches. This study showed that XPS provides additional information to biological measurements such as antithrombin uptake. XPS is therefore a valuable technique not only to characterize biomaterials but also to evaluate the effect of a performance test.
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| 58. |
- Larsson, Andreas, et al.
(författare)
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Orientation of individual C60 molecules adsorbed on Cu(111) : Low-temperature scanning tunneling microscopy and density functional calculations
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 77:11
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory (DFT) and low-temperature scanning tunneling microscopy (STM) have been combined to examine the bonding of individual C60 molecules on Cu(111). Energy-resolved differential-conductance maps have been measured for individual C60 molecules adsorbed on a Cu(111) surface by means of low-temperature STM, which are compared to and complemented by theoretically computed spectral images. It has been found that C60 chemisorbs with a six-membered ring parallel to the surface at two different Cu(111) binding sites that constitute two exclusive hexagonal sublattices. On each sublattice, C60 is bonded in one particular rotational conformer, i.e., C60 molecules bind to the Cu(111) surface in two different azimuthal orientations differing by 60°depending on which sublattice the binding site belongs to. The binding conformation of C60 and its orientation with regard to the copper surface can be deduced by this joint experimental-theoretical approach. Six possible pairs of C60 configurations on three different Cu surface binding sites have been identified that fulfil the requirements of the two sublattices and are consistent with all experimental and theoretical data. Theory proposes that two of these configuration pairs are most likely. We have found that DFT does not get the binding energy between rotational conformers in the correct order. We also report two different C60 monolayers on Cu(111): one with alternating orientations of neighboring molecules at low temperature and the other with (4×4) structure after annealing above room temperature.
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| 59. |
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| 60. |
- Larsson, Per-Ola, et al.
(författare)
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Construction and Control of an Educational Lab Process - The Gantry Crane
- 2008
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Konferensbidrag (refereegranskat)abstract
- In this paper, we describe the construction and control of a gantry crane that is used in courses at the Department of Automatic Control, Lund university. Two different models of the crane are developed. A thorough example of path following, including on-line time-varying input/state-transformations and LQG control, used in a laboratory exercise is shown together with experimental results. Time-optimal trajectories for position control, with constraints on positions, load angles, and control signals are computed using Modelica and Optimica.
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