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- Persson, Ann-Sofie
(författare)
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Flow and Compression of Granulated Powders : The Accuracy of Discrete Element Simulations and Assessment of Tablet Microstructure
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Simulations are powerful and important tools for gaining insight into powder processes. Ultimately, simulations have the potential to replace experiments. Thus, accurate models and insight into the essential factors for descriptions of powder behaviour are required. In this thesis, discrete element method (DEM) simulations of granule flow and compression were evaluated to deduce parameters and potential models essential for the experimental and numerical correspondence. In addition, the evolution in tablet microstructure during compression was studied using mercury porosimetry.Granule flow was measured using angle of repose, discharge rate, and shear. The granular flow depended primarily on particle shape and surface texture due to the mutual influence of these two parameters on the inter-particle forces. Rolling friction stabilised both the heap formation and promoted shear in the elastic quasi-static flow regime. Thus, rolling friction was established to be an essential simulation parameter for the correspondence to experiments.Current compression models often neglect the elastic compact deformation during particle loading. In this thesis, two fundamentally different models were evaluated with focus of including the elastic deformation. The first model comprised a maximal particle overlap, where elastic deformation commences. The second model accounted for the contact dependence and impingement at high relative densities. This model was based on a truncated-sphere followed by a Voronoi extension. The validity of the models was demonstrated by the elastic qualitative correspondence to experimental compressions for ductile materials.In tablets, the void (inter-granular pore) diameter was dependent on the degree of compression. Thus, the degree of compression provides an indication of the tablet microstructure. The microstructure was subsequently observed to be related to the tablet tensile strength as inferred from a percolation threshold required for formation of coherent tablets.In summary, this thesis has shed light onto the potential of simulating flow and compression of granulated pharmaceutical powders using DEM. Continuous work in the area are required to further improve the models to increase the experimental and numerical correspondence.
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- Persson, Ann-Sofie, et al.
(författare)
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Flowability of surface modified pharmaceutical granules : A comparative experimental and numerical study
- 2011
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Ingår i: European Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0928-0987 .- 1879-0720. ; 42:3, s. 199-209
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Tidskriftsartikel (refereegranskat)abstract
- Flowability - as measured by hopper discharge rate, angle of repose and Carr's index (CI) - of surface modified microcrystalline cellulose granules was investigated experimentally. Three-dimensional simulations of the granule flow were performed, using the discrete element method (DEM), including either sliding and rolling friction or sliding friction and cohesion in the model. Granule surface modification with polymer coating and lubrication was found to have a significant effect on the sliding friction coefficient. This effect was also reflected in the ensuing flow behaviour, as quantified by the experimental discharge rate and angle of repose, whereas the results for the Cl were inconclusive. The numerical results demonstrated that granular flow was qualitatively different for non-cohesive and cohesive granules, occurring in the form of individual particles for the former and in larger clusters for the latter. Rolling friction and cohesion nevertheless affected the simulated discharge rate in a similar manner, producing results comparable to those observed experimentally and calculated with the Beverloo equation. The numerical results for the cohesive granules demonstrated that cohesion alone was sufficient to produce stable heaps. However, the agreement with experimental data was satisfactory only for the non-cohesive granules, demonstrating the importance of rolling friction.
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- Persson, Marta, 1979, et al.
(författare)
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Clinically significant copy number alterations and complex rearrangements of MYB and NFIB in head and neck adenoid cystic carcinoma.
- 2012
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Ingår i: Genes, chromosomes & cancer. - : Wiley. - 1098-2264 .- 1045-2257. ; 51:8, s. 805-17
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Tidskriftsartikel (refereegranskat)abstract
- Adenoid cystic carcinoma (ACC) of the head and neck is a malignant tumor with poor long-term prognosis. Besides the recently identified MYB-NFIB fusion oncogene generated by a t(6;9) translocation, little is known about other genetic alterations in ACC. Using high-resolution, array-based comparative genomic hybridization, and massively paired-end sequencing, we explored genomic alterations in 40 frozen ACCs. Eighty-six percent of the tumors expressed MYB-NFIB fusion transcripts and 97% overexpressed MYB mRNA, indicating that MYB activation is a hallmark of ACC. Thirty-five recurrent copy number alterations (CNAs) were detected, including losses involving 12q, 6q, 9p, 11q, 14q, 1p, and 5q and gains involving 1q, 9p, and 22q. Grade III tumors had on average a significantly higher number of CNAs/tumor compared to Grade I and II tumors (P = 0.007). Losses of 1p, 6q, and 15q were associated with high-grade tumors, whereas losses of 14q were exclusively seen in Grade I tumors. The t(6;9) rearrangements were associated with a complex pattern of breakpoints, deletions, insertions, inversions, and for 9p also gains. Analyses of fusion-negative ACCs using high-resolution arrays and massively paired-end sequencing revealed that MYB may also be deregulated by other mechanisms in addition to gene fusion. Our studies also identified several down-regulated candidate tumor suppressor genes (CTNNBIP1, CASP9, PRDM2, and SFN) in 1p36.33-p35.3 that may be of clinical significance in high-grade tumors. Further, studies of these and other potential target genes may lead to the identification of novel driver genes in ACC.
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- Persson, Peter, et al.
(författare)
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Fluid-Structure Interaction Analysis of Vibration Reduction in Pipe Systems
- 2014
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Ingår i: Dynamics of Civil Structures. ; Volume 4, s. 459-468
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Bokkapitel (refereegranskat)abstract
- Transmitted vibrations from water-pipe systems, involving supports standing on a concrete slab and the underlying ground, are investigated here. The effects of varying parameters of the supports, such as location, their elastic modulus and their cross-section, on the level of vibrations transmitted by the water-pipe system are analysed in order to minimise vibrations transmitted to sensitive parts in a facility. A finite element model involving use of both finite and infinite elements was employed for analyses in the frequency domain where account was taken of both fluid-structure interaction and soil-structure interaction. It was concluded from the analyses performed that the parameters of the supports had an appreciable effect on the vibration level in the facility.
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