| 51. |
- Sotres, Javier, et al.
(author)
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Friction Force Spectroscopy of β- and κ-casein monolayers
- 2011
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:3, s. 981-992
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Journal article (peer-reviewed)abstract
- Friction force spectroscopy (FFS) has been applied to study the tribological properties of β- and κ-casein layers on hydrophobic substrates in aqueous solutions. Nanometer-sized imaging tips were employed. This allowed exerting and determining the high pressures needed to remove the layers, and registering the topographic evolution during this process. Both β- and κ-casein layers showed similar and not particularly high initial frictional responses (friction coefficient of ~1 when measure with a silicon nitride tip). The pressures needed to remove the layers were of the same order of magnitude for both proteins, ~1e8 Pa, but slightly higher for those composed of β-casein. The technique has also shown to be useful in studying the two-dimensional lateral diffusion of the proteins and the wear on the layers they form.
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| 52. |
- Souihi, Nabil, et al.
(author)
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A Quality by Design approach to investigate the effect of mannitol and dicalcium phosphate qualities on roll compaction
- 2013
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In: International Journal of Pharmaceutics. - : Elsevier. - 0378-5173 .- 1873-3476. ; 447:1-2, s. 47-61
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Journal article (peer-reviewed)abstract
- Roll compaction is a continuous process for solid dosage form manufacturing increasingly popular within pharmaceutical industry. Although roll compaction has become an established technique for dry granulation, the influence of material properties is still not fully understood. In this study, a quality by design (QbD) approach was utilized, not only to understand the influence of different qualities of mannitol and dicalcium phosphate (DCP), but also to predict critical quality attributes of the drug product based solely on the material properties of that filler. By describing each filler quality in terms of several representative physical properties, orthogonal projections to latent structures (OPLS) was used to understand and predict how those properties affected drug product intermediates as well as critical quality attributes of the final drug product. These models were then validated by predicting product attributes for filler qualities not used in the model construction. The results of this study confirmed that the tensile strength reduction, known to affect plastic materials when roll compacted, is not prominent when using brittle materials. Some qualities of these fillers actually demonstrated improved compactability following roll compaction. While direct compression qualities are frequently used for roll compacted drug products because of their excellent flowability and good compaction properties, this study revealed that granules from these qualities were more poor flowing than the corresponding powder blends, which was not seen for granules from traditional qualities. The QbD approach used in this study could be extended beyond fillers. Thus any new compound/ingredient would first be characterized and then suitable formulation characteristics could be determined in silico, without running any additional experiments.
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| 53. |
- Stollenwerk, Maria M, 1959-, et al.
(author)
-
Adsorption of low-density lipoprotein, its oxidation, and subsequent binding of specific recombinant antibodies-an in situ ellipsometric study.
- 2011
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In: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 0304-4165 .- 1872-8006. ; 1810:2, s. 211-217
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Journal article (peer-reviewed)abstract
- BACKGROUND: Low-density lipoprotein (LDL) particles accumulate in the arterial wall and become oxidized during atherogenesis, leading to the formation of atherosclerotic plaques. The major protein of the LDL particle, apolipoprotein B-100 (apoB-100), becomes fragmented during oxidation and a target for the immune system. METHODS: In this study we used in situ ellipsometry to monitor the adsorption of LDL to solid silica surfaces and the effects of oxidation on the structure of the adsorbed LDL layer. We additionally investigated the binding kinetics of two recombinant human antibodies with different specificities recognizing epitopes of apoB-100 in surface-bound native and CuCl(2)-oxidized LDL (oxLDL). The latter process was studied by adsorbing LDL and then adding the antibody and CuCl(2) while continuously monitoring the amount of LDL adsorbed and the thickness of the film. The molar ratios between the antibodies and surface-bound LDL and oxLDL were calculated from these data. RESULTS: Our results indicate that oxidation of surface-bound LDL induces swelling of the layer, accompanied by a slight desorption. We further found that both antibodies were able to recognize LDL and oxLDL in its adsorbed orientation. Quantitative information was obtained on the number of available binding sites on surface-bound LDL and oxLDL for these two antibodies. GENERAL SIGNIFICANCE: Using ellipsometry for real-time monitoring of adsorption, in situ oxidation of LDL and binding of specific recombinant antibodies to surface-bound LDL, will open up possibilities to map different conformations and orientations of LDL in the adsorbed state.
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| 54. |
- Sulla, Francesco, et al.
(author)
-
Fault Behaviour of Wind Farms with Fixed-Speed and Doubly-Fed Induction Generators
- 2011
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In: PowerTech, 2011 IEEE Trondheim. - 9781424484195 ; , s. 1-7
-
Conference paper (peer-reviewed)abstract
- Abstract in UndeterminedThis paper focuses on the fault current contribution of wind farms with Fixed-Speed (FSIG) and Doubly-Fed Induction Generators (DFIG). The fault current delivered by a single FSIG during both symmetrical and unsymmetrical faults is found analytically and validated through simulations. Simulations of a detailed model of a wind farm with several FSIG or DFIG are then performed to investigate the total fault current contribution at the Point of Common Coupling. The scope is to check the validity of a single-machine approach to predict the fault contribution of the wind farm. It has been found that both in the case of FSIG and DFIG wind farms, the single-machine approach is reasonable. For DFIG wind farms, the initial operating point of each DFIG has an important impact on its fault current and the single-machine should be given an initial slip close to the average slip of all DFIG in the wind farm.
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| 55. |
- Sulla, Francesco, et al.
(author)
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Short-circuit analysis of a doubly fed induction generator wind turbine with direct current chopper?protection
- 2013
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In: Wind Energy. - : Wiley. - 1099-1824 .- 1095-4244. ; 16:1, s. 37-49
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Journal article (peer-reviewed)abstract
- Modern doubly fed induction generator (DFIG) wind turbines can ride through a symmetrical fault in the network by using a chopper protection on the direct current (DC) link without triggering a crowbar protection. A novel method to model the DC link system of such wind turbines as an equivalent resistance during symmetrical faults is presented in this paper. The method allows looking at the DFIG with chopper protection as to one with an equivalent crowbar protection and, hence, to apply to the former type of DFIG short-circuit calculation methods developed for a DFIG with crowbar protection. This may be a valid help in short-circuit calculations, for example, for protection settings. It also allows simulating for short-circuit studies a DFIG with chopper protection, often not available in a standard power system simulation software, by using an equivalent DFIG with crowbar protection, which is a standard model in power system simulation software. The results for the short-circuit current obtained through the proposed method are compared with simulations of a detailed model of a DFIG with chopper protection under different conditions, which showed good agreement. It is also shown that the DFIG with chopper protection delivers lower short-circuit current than a DFIG with standard crowbar protection, especially for low initial loading. Copyright (C) 2011 John Wiley & Sons, Ltd.
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| 56. |
- Sulla, Francesco, et al.
(author)
-
Symmetrical and unsymmetrical short-circuit current of squirrel-cage and doubly-fed induction generators
- 2011
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In: Electric Power Systems Research. - : Elsevier BV. - 1873-2046 .- 0378-7796. ; 81:7, s. 1610-1618
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Journal article (peer-reviewed)abstract
- A general method for calculating the short-circuit currents of a squirrel-cage (SCIG) and a doubly fed induction generator (DFIG) using crowbar protection is presented. The method results in an approximate analytic expression that allows calculating the SCIG and DFIG short-circuit currents as a function of time for symmetrical and unsymmetrical faults in the power system. The presented theoretical analysis highlights some important differences between the short-circuit behavior of the SCIG and the DFIG with high crowbar resistance. A comparison with time simulations of the same model shows that the proposed approach leads to results whose accuracy is comparable to those obtained through dynamic simulations and may be sufficient to replace the use of simulations in many contexts, e.g. calculation of maximum current, calculation of its DC and AC components and short-circuit calculations for protection relay settings. (C) 2011 Elsevier B.V. All rights reserved.
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| 57. |
- Sulla, Francesco, et al.
(author)
-
Wind turbines voltage support in weak grids
- 2013
-
In: Power and Energy Society General Meeting (PES), 2013 IEEE. - 1944-9925.
-
Conference paper (peer-reviewed)abstract
- This paper investigates how Full-Scale Converter (FSC) wind turbines can contribute to voltage support in weak grids. A novel voltage support strategy is proposed, which optimizes the voltage support during the fault. This strategy is compared to the voltage support required by two grid codes, the Danish and the German E.ON ones. The influence of a number of parameters, as the network X/R ratio, the voltage support controller gain and the post-fault power ramp is investigated. A sensitivity analysis with regard to uncertainties in the knowledge of the X/R ratio is performed. Finally, the voltage support provided by a wind power plant (WPP) is compared to that provided by a conventional power plant with synchronous generation. Simulation results indicate that a FSC WPP if properly controlled is able to provide a post-fault voltage support comparable to the one provided by a synchronous generator.
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| 58. |
- Svensson, Anna Maria
(author)
-
Rektors ledarskap : styrningssammanhang och stil
- 2010
-
Licentiate thesis (other academic/artistic)abstract
- The role of the principal in Sweden has undergone significant changes over the past two decades. Task and responsibility has been decentralized from the national level to o the local school board affecting principals´ everyday life. At the same time a new inspection system for all schools has been introduced. These changes puts focus on how principals implement and report political decisions within established guidelines. For many principals it is a balancing act to achieve the national goals within a local context. All the above include for the principal important work with evaluations of quality in different processes in the school, especially those related to teacher performance and children’s grades and results. In the mid 1990’s a debate about the lack of evaluations and school improvement in Swedish schools started, and as a result the Government decided in 1997 that every school should write a quality assessments and that the school board should write a summery for the whole school district. Many schools had problems in the beginning with the working processes around quality assessments, and many schools view this national law only as a top-down control decision from the Government and were not able to see the school improvement part of the law. The aim of this study is to describe how principals take responsibility for the quality assessment regulation and to analyze how they act and lead their schools in relation to quality assessments. In this study, results are presented from survey data, done with 131 principals who attended the National Principal Training Program at Umeå University. A theoretical model which discusses four leadership styles is used as a theoretical background. This model has an organizational frame. After making an argument for the importance of each of these styles for understanding principals work with quality assessments, two strands are examined. First, leadership styles are described from a principal perspective and factor analysis is used to investigate if these styles can illustrate principals´ work with quality assessments. Second, important factors explaining different ways in which principals tackle the work with quality assessments is highlighted. These factors are affected by different laws and regulations and even some time local political decisions and policies which here is understood as structure and culture, and personal background, for example the principals´ age, sex, education and experience. Based on the empirical results, my theoretical conclusion is that the four leadership styles used are relevant for understanding how principals work with quality assessments. The study also shows that structure and culture are important factors when it comes to explaining how principals´ work with quality assessments. Personal background, however, are not shown as important in this study.
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| 59. |
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| 60. |
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