| 1. |
- Allard, Christina, et al.
(författare)
-
Rasbiologiskt språkbruk i statens rättsprocess mot sameby : DN Debatt 2015-06-11
- 2015
-
Annan publikation (populärvet., debatt m.m.)abstract
- Statens hantering av forskningsresultat i rättsprocessen med Girjas sameby utgör ett hot mot Sverige som rättsstat och kunskapsnation. Åratal av svensk och internationell forskning underkänns och man använder ett språkbruk som skulle kunna vara hämtat från rasbiologins tid. Nu måste staten ta sitt ansvar och börja agera som en demokratisk rättsstat, skriver 59 forskare.
|
|
| 2. |
- Ekman, Petter, 1988-, et al.
(författare)
-
Accuracy and Speed for Scale-Resolving Simulations of the DrivAer Reference Model
- 2019
-
Ingår i: WCX SAE World Congress Experience. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
-
Konferensbidrag (refereegranskat)abstract
- In aerodynamic development of ground vehicles, the use of Computational Fluid Dynamics (CFD) is crucial for improving the aerodynamic performance, stability and comfort of the vehicle. Simulation time and accuracy are two key factors of a well working CFD procedure. Using scale-resolving simulations, accurate predictions of the flow field and aerodynamic forces are possible, but often leads to long simulation time. For a given solver, one of the most significant aspects of the simulation time/cost is the temporal resolution. In this study, this aspect is investigated using the realistic vehicle model DrivAer with the notchback geometry as the test case. To ensure a direct and accurate comparison with wind tunnel measurements, performed at TU Berlin, a large section of the wind tunnel is included in the simulation domain. All simulations are performed at a Reynolds number of 3.12 million, based on the vehicle length. Three spatial resolutions were compared, where it could be seen that a hybrid element mesh consisting of 102 million cells only revealed small differences to the finest mesh investigated, well as showing excellent agreement with wind tunnel measurements. An investigation of the temporal resolution is performed, in order to see its effect on the simulation time/cost and accuracy of the results. The finest temporal resolution resulted in a Courant-Friedrichs-Lewy number less than unity, while the coarsest reached a CFL number of around 100. From these results, it is seen that it is possible to reduce the simulation time with more than 90 % (CFL 20) and still keep sufficient accuracy of the forces and important features of the flow field.
|
|
| 3. |
- Rollborn, Niclas, et al.
(författare)
-
Good Agreement Between Hba1c Analyzed Using Capillary Electrophoresis, HPLC, Immunological and Enzymatic Methods
- 2019
-
Ingår i: Journal of Diabetes, Metabolism and its Complications. ; 1:1, s. 1-7
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: Hemoglobin A1c (HbA1c) is an essential marker for assessment of glycemic control in diabetes patients. The aim of this study was to evaluate the agreement between different HbA1c methods.Methodology: We used blood samples to compare HbA1c results analyzed with Capillarys 3 Tera, Roche Tina-Quant HbA1c Gen 3, BioRad Variant II Turbo (3 sites), Mono S® and Abbott Architect enzymatic method. The comparisons were made as paired instrument comparisons with Capillarys 3 Tera.Results: The linear correlations between the HbA1c methods were as follows:Cobas 6000 = 0.982 x Capillarys 3 Tera + 0.975, R² = 0.994;Architect c8000 = 0.982 x Capillarys 3 Tera + 1.064, R² = 0.994; Mono S® = 0.916 x Capillarys 3 Tera + 3.397, R² = 0.965;BioRad Variant II Turbo = 0.923 x Capillarys 3 Tera + 4.062, R² = 0.990; Tosoh G8 = 0.963 x Capillarys 3 Tera + 3.895, R² = 0.996.Conclusions: The different instrument platforms showed the best agreement in the 50-70 mmol/mol interval. Above and below this range the methods separated into 2 groups, one consisting of Capillarys 3 Tera, Roche Tina-Quant and Abbott enzymatic method and the other group consisting of BioRad Variant II Turbo, Tosoh G8 and Mono S®.
|
|
| 4. |
- Abujrais, Sandy, et al.
(författare)
-
A sensitive method detecting trace levels of levonorgestrel using LC-HRMS
- 2019
-
Ingår i: Contraception. - : Elsevier BV. - 0010-7824 .- 1879-0518. ; 100:3, s. 247-249
-
Tidskriftsartikel (refereegranskat)abstract
- Objective: To develop a high resolution mass spectrometry (HRMS) method to quantify levonorgestrel (LNG) in serum. Study design: Levonorgestrel was extracted using solid phase extraction and measured using liquid chromatography (LC) HRMS. Results: Low limit of quantification (LLOQ) was 25 pg/mL and low limit of detection (LLOD) was 12.5 pg/mL. Precision and accuracy bias were <10%. LNG in serum samples from Mirena® users ranged between 37 to 219 pg/mL (n=12). In eight out of 22 patients with suspected intrauterine device (IUD) expulsion LNG was detected (26–1272 pg/mL). Conclusion: A sensitive, fast and simple LC-HRMS method was developed to detect trace levels of LNG. © 2019 Elsevier Inc.
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Erlandsson, Johan, et al.
(författare)
-
On the mechanism behind freezing-induced chemical crosslinking in ice-templated cellulose nanofibril aerogels
- 2018
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 6:40, s. 19371-19380
-
Tidskriftsartikel (refereegranskat)abstract
- The underlying mechanism related to freezing-induced crosslinking of aldehyde-containing cellulose nanofibrils (CNFs) has been investigated, and the critical parameters behind this process have been identified. The aldehydes introduced by periodate oxidation allows for formation of hemiacetal bonds between the CNFs provided the fibrils are in sufficiently close contact before the water is removed. This is achieved during the freezing process where the cellulose components are initially separated, and the growth of ice crystals forces the CNFs to come into contact in the thin lamellae between the ice crystals. The crosslinked 3-D structure of the CNFs can subsequently be dried under ambient conditions after solvent exchange and still maintain a remarkably low density of 35 kg m-3, i.e. a porosity greater than 98%. A lower critical amount of aldehydes, 0.6 mmol g-1, was found necessary in order to generate a crosslinked 3-D CNF structure of sufficient strength not to collapse during the ambient drying. The chemical stability of the 3-D structure can be further enhanced by converting the hemiacetals to acetals by treatment with an alcohol under acidic conditions.
|
|
| 9. |
- Finnsgård, Christian, 1974, et al.
(författare)
-
High Performance Sailing in Olympic Classes - a Research Outlook and Proposed Directions
- 2015
-
Ingår i: Proceedings, 5th High Performance Yacht Design Conference, Auckland, 8-11 March 2015. - : Royal Institution of Naval Architects. - 9781909024373 ; , s. 141-149
-
Konferensbidrag (refereegranskat)abstract
- The purpose of this paper is to explore research opportunities in Olympic sailing classes. Olympic classes provide high-performance sailing using a diversity of equipment, with the understanding that the equipment, individual athletes, and the knowledge relating to those two factors impacts performance. Thus, the Olympic motto, “Citius, Altius, Fortius” (Latin for “Faster, Higher, Stronger”), governs everyday life for many engineers. During the last few years, Chalmers has supported a project that focuses on the possibilities and challenges for research combined with engineering knowledge in the area of sports. The initiative has generated external funding and gained great acclaim within Chalmers, among staff and students, in the Swedish sports movement, and in large companies, as well as within small and medium sized enterprises. The project focuses on five sports: swimming, equestrian events, floorball, athletics, and sailing. The contribution from this paper describes an outlook identifying eight areas containing research opportunities: sailing dynamics, how to sail in Olympic classes, fluid structure interaction, surface structures, turbulence induction on the rig, equipment in Olympic classes, and applying game theory to sailing.
|
|
| 10. |
- Flentie, Kelly, et al.
(författare)
-
Chemical disarming of isoniazid resistance in Mycobacterium tuberculosis
- 2019
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : The National Academy of Scionces of the United States of America. - 0027-8424 .- 1091-6490. ; 116:21, s. 10510-10517
-
Tidskriftsartikel (refereegranskat)abstract
- Mycobacterium tuberculosis (Mtb) killed more people in 2017 than any other single infectious agent. This dangerous pathogen is able to withstand stresses imposed by the immune system and tolerate exposure to antibiotics, resulting in persistent infection. The global tuberculosis (TB) epidemic has been exacerbated by the emergence of mutant strains of Mtb that are resistant to frontline antibiotics. Thus, both phenotypic drug tolerance and genetic drug resistance are major obstacles to successful TB therapy. Using a chemical approach to identify compounds that block stress and drug tolerance, as opposed to traditional screens for compounds that kill Mtb, we identified a small molecule, C10, that blocks tolerance to oxidative stress, acid stress, and the frontline antibiotic isoniazid (INH). In addition, we found that C10 prevents the selection for INH-resistant mutants and restores INH sensitivity in otherwise INH-resistant Mtb strains harboring mutations in the katG gene, which encodes the enzyme that converts the prodrug INH to its active form. Through mechanistic studies, we discovered that C10 inhibits Mtb respiration, revealing a link between respiration homeostasis and INH sensitivity. Therefore, by using C10 to dissect Mtb persistence, we discovered that INH resistance is not absolute and can be reversed.
|
|
| 11. |
|
|
| 12. |
- Gårdebjer, Sofie, 1985, et al.
(författare)
-
The impact of interfaces in laminated packaging on transport of carboxylic acids
- 2016
-
Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 518, s. 305-312
-
Tidskriftsartikel (refereegranskat)abstract
- The permeability of oleic and acetic acid through low density polyethylene (LDPE) and ethylene acrylic acid (EAA) have been measured using diffusion cells. In addition, the permeability through combinations of LDPE and EAA in the form of laminates with different numbers of layers has been determined. Oleic acid shows an almost 30 times higher permeability compared to acetic acid, which was partly explained by the adsorption of oleic acid to the film surface during the permeability experiment. In addition, the permeability is lower for both oleic and acetic acid in the laminates compared to the pure films. The decreased permeability can be explained by the presence of crystalline domains close to the interface. This is supported by SAXS data which suggests an ordering of polymer chains in the EAA film close to the interface. In summary, the results show that it is possible to create barrier materials with decreased permeability, which is interesting for example in the packaging industry.
|
|
| 13. |
- Herman, Stephanie, et al.
(författare)
-
Integration of magnetic resonance imaging and protein and metabolite CSF measurements to enable early diagnosis of secondary progressive multiple sclerosis
- 2018
-
Ingår i: Theranostics. - : Ivyspring International Publisher. - 1838-7640. ; 8:16, s. 4477-4490
-
Tidskriftsartikel (refereegranskat)abstract
- Molecular networks in neurological diseases are complex. Despite this fact, contemporary biomarkers are in most cases interpreted in isolation, leading to a significant loss of information and power. We present an analytical approach to scrutinize and combine information from biomarkers originating from multiple sources with the aim of discovering a condensed set of biomarkers that in combination could distinguish the progressive degenerative phenotype of multiple sclerosis (SPMS) from the relapsing-remitting phenotype (RRMS). Methods: Clinical and magnetic resonance imaging (MRI) data were integrated with data from protein and metabolite measurements of cerebrospinal fluid, and a method was developed to sift through all the variables to establish a small set of highly informative measurements. This prospective study included 16 SPMS patients, 30 RRMS patients and 10 controls. Protein concentrations were quantitated with multiplexed fluorescent bead-based immunoassays and ELISA. The metabolome was recorded using liquid chromatography-mass spectrometry. Clinical follow-up data of the SPMS patients were used to assess disease progression and development of disability. Results: Eleven variables were in combination able to distinguish SPMS from RRMS patients with high confidence superior to any single measurement. The identified variables consisted of three MRI variables: the size of the spinal cord and the third ventricle and the total number of T1 hypointense lesions; six proteins: galectin-9, monocyte chemoattractant protein-1 (MCP-1), transforming growth factor alpha (TGF-alpha), tumor necrosis factor alpha (TNF-alpha), soluble CD40L (sCD40L) and platelet-derived growth factor AA (PDGF-AA); and two metabolites: 20 beta-dihydrocortisol (20 beta-DHF) and indolepyruvate. The proteins myelin basic protein (MBP) and macrophage-derived chemokine (MDC), as well as the metabolites 20 beta-DHF and 5,6-dihydroxyprostaglandin F1a (5,6-DH-PGF1), were identified as potential biomarkers of disability progression. Conclusion: Our study demonstrates, in a limited but well-defined and data-rich cohort, the importance and value of combining multiple biomarkers to aid diagnostics and track disease progression.
|
|
| 14. |
- Holm, Åsa, et al.
(författare)
-
Heuristics for Integrated Optimization of Catheter Positioning and Dwell Time Distribution in Prostate HDR Brachytherapy
- 2016
-
Ingår i: Annals of Operations Research. - : Springer. - 0254-5330 .- 1572-9338. ; 236:2, s. 319-339
-
Tidskriftsartikel (refereegranskat)abstract
- High dose-rate (HDR) brachytherapy is a kind of radiotherapy used to treat, among others, prostate cancer. When applied to prostate cancer a radioactive source is moved through catheters implanted into the prostate. For each patient a treatment plan is constructed that decide for example catheter placement and dwell time distribution, that is where to stop the radioactive source and for how long.Mathematical optimization methods has been used to find quality plans with respect to dwell time distribution, however few optimization approaches regarding catheter placement have been studied. In this article we present an integrated optimization model that optimize catheter placement and dwell time distribution simultaneously. Our results show that integrating the two decisions yields greatly improved plans, from 15% to 94% improvement.Since the presented model is computationally demanding to solve we also present three heuristics: tabu search, variable neighbourhood search and genetic algorithm. Of these variable neighbourhood search is clearly the best, outperforming a state-of-the-art optimization software (CPLEX) and the two other heuristics.
|
|
| 15. |
- Holmlund, Thorbjörn, 1968-, et al.
(författare)
-
Tonsillectomy in adults with obstructive sleep apnea
- 2016
-
Ingår i: The Laryngoscope. - : Wiley. - 0023-852X .- 1531-4995. ; 126:12, s. 2859-2862
-
Tidskriftsartikel (refereegranskat)abstract
- Objectives/Hypothesis To study whether tonsillectomy is effective on obstructive sleep apnea (OSA) in adults with large tonsils. Study Design A multicenter prospective interventional study. Methods The study comprised 28 patients with OSA, an apnea-hypopnea index of > 10, large tonsils (Friedman tonsil size 3 and 4), and age 18 to 59 years. They were derived from 41 consecutive males and females with large tonsils referred for a suspicion of sleep apnea to the ear, nose, and throat departments in Umea, Skelleftea, and Sunderbyn in northern Sweden. The primary outcome was the apnea-hypopnea index, measured with polygraphic sleep apnea recordings 6 months after surgery. Secondary outcomes included daytime sleepiness, as measured with the Epworth Sleepiness Scale, and swallowing function, using video-fluoroscopy. Results The apnea-hypopnea index was reduced from a mean of 40 units per hour (95% confidence interval [CI] 28-51) to seven units per hour (95% CI 3-11), P < 0.001, at the 6-month follow-up after surgery. The apnea-hypopnea index was reduced in all patients and 18 (64%) were cured. The Epworth Sleepiness Scale was reduced from a mean of 11 (95% CI 8-13) to 6.0 (95% CI 4-7), P < 0.001. A swallowing dysfunction was found in seven of eight investigated patients before surgery. Of those, swallowing function improved in five patients after surgery, whereas no one deteriorated. Conclusion Tonsillectomy may be effective treatment for adult patients with OSA and large tonsils. Tonsillectomy may be suggested for adults with OSA and large tonsils. Level of Evidence 4.
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
- John Mwakisisile, Andongwisye, et al.
(författare)
-
Asset liability management for Tanzania pension funds by stochastic programming
- 2018
-
Ingår i: Afrika Statistika. - : The Statistics and Probability African Society Discipline(s). - 2316-090X. ; 13:3, s. 1733-1758
-
Tidskriftsartikel (refereegranskat)abstract
- We present a long-term model of asset liability management for Tanzania pension funds. The pension system is pay-as-you-go where contributions are used to pay current benefits. The pension plan is a final salary defined benefit. Two kinds of pension benefits, a commuted (at retirement) and a monthly (old age) pension are considered. A decisive factor for a long-term asset liability management is that, Tanzania pension funds face an increase of their members’ life expectancy, which will cause the retirees to contributors dependence ratio to increase. We present a stochastic programming approach which allocates assets with the best return to raise the asset value closer to the level of liabilities. The model is based on work by Kouwenberg in 2001, with features from Tanzania pension system. In contrast to most asset liability management models for pension funds by stochastic programming, liabilities are modeled by using number of years of life expectancy for monthly benefit. Scenario trees are generated by using Monte Carlo simulation. Numerical results suggest that, in order to improve the long-term sustainability of the Tanzania pension fund system, it is necessary to make reforms concerning the contribution rate, investment guidelines and formulate target funding ratios to characterize the pension funds’ solvency situation.
|
|
| 19. |
- John Mwakisisile, Andongwisye, et al.
(författare)
-
Projecting Tanzania Pension Fund System
- 2017
-
Ingår i: African Journal of Applied Statistics. - : Afrika Statistika - SPAS. - 2316-0861. ; 4:1, s. 193-218
-
Tidskriftsartikel (refereegranskat)abstract
- A mandatory Tanzania pension fund with a final salary defined benefit is analyzed. This fund is a contributory pay-as-you-go defined benefit pension system which is much affected by the change in demography. Two kinds of pension benefit, a commuted (at retirement) and a monthly (old age) pension are considered. A decisive factor in the analysis is the increased life expectancy of members of the fund. The projection of the fund’s future members and retirees is done using expected mortality rates of working population and expected longevity. The future contributions, benefits, asset values and liabilities are analyzed. The projection shows that the fund will not be fully sustainable on a long term due to the increase in life expectancy of its members. The contributions will not cover the benefit payouts and the asset value will not fully cover liabilities. Evaluation of some possible reforms of the fund shows that they cannot guarantee a long-term sustainability. Higher returns on asset value will improve the funding ratio, but contributions are still insufficient to cover benefit payouts.
|
|
| 20. |
- Jonsson, Torbjörn, 1970, et al.
(författare)
-
High-Temperature Oxidation of FeCr(Ni) Alloys : The Behaviour After Breakaway
- 2017
-
Ingår i: Oxidation of Metals. - : Springer Nature. - 0030-770X .- 1573-4889. ; 87:3-4, s. 333-341
-
Tidskriftsartikel (refereegranskat)abstract
- The oxidation of an austenitic FeCr(Ni) steel at 600 C in H2O ?KCl ? O2/H2 ? H2O ? Ar environments is studied up to 168 h. The oxidationbehaviour after ‘‘breakaway’’ is investigated by microstructural investigations, andthermodynamic calculations (Thermo-Calc) on the FeCr(Ni)–O system are used tointerpret the results. The characteristic ‘‘breakaway’’ scale morphology exhibits anoutward-growing iron oxide and a bottom layer consisting of inward-growing spineloxide and reaction zones containing Cr-rich oxide precipitates and Cr-depletedmetal. The equilibrium calculations show that a miscibility gap appears in the FeCrspinel oxide below 665 C influencing the microstructure of the inward-growingscale. Equilibrium calculations on the FeCrNi–O system show that Ni is notexpected to enter the spinel oxide in low oxygen activity conditions, in accordancewith observations
|
|
| 21. |
- Jordan, Stanley C, et al.
(författare)
-
IgG Endopeptidase in Highly Sensitized Patients Undergoing Transplantation.
- 2017
-
Ingår i: New England Journal of Medicine. - : Massachusetts Medical Society. - 0028-4793 .- 1533-4406. ; 377:5, s. 442-453
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Donor-specific antibodies create an immunologic barrier to transplantation. Current therapies to modify donor-specific antibodies are limited and ineffective in the most highly HLA-sensitized patients. The IgG-degrading enzyme derived from Streptococcus pyogenes (IdeS), an endopeptidase, cleaves human IgG into F(ab')2 and Fc fragments inhibiting complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity, which suggests that IdeS might be useful for desensitization. We report on the combined experience of two independently performed open-label, phase 1-2 trials (conducted in Sweden and the United States) that assessed the efficacy of IdeS with regard to desensitization and transplantation of a kidney from an HLA-incompatible donor.METHODS: We administered IdeS to 25 highly HLA-sensitized patients (11 patients in Uppsala or Stockholm, Sweden, and 14 in Los Angeles) before the transplantation of a kidney from an HLA-incompatible donor. Frequent monitoring for adverse events, outcomes, donor-specific antibodies, and renal function was performed, as were renal biopsies. Immunosuppression after transplantation consisted of tacrolimus, mycophenolate mofetil, and glucocorticoids. Patients in the U.S. study also received intravenous immune globulin and rituximab after transplantation to prevent antibody rebound.RESULTS: Recipients in the U.S. study had a significantly longer cold ischemia time (the time elapsed between procurement of the organ and transplantation), a significantly higher rate of delayed graft function, and significantly higher levels of class I donor-specific antibodies than those in the Swedish study. A total of 38 serious adverse events occurred in 15 patients (5 events were adjudicated as being possibly related to IdeS). At transplantation, total IgG and HLA antibodies were eliminated. A total of 24 of 25 patients had perfusion of allografts after transplantation. Antibody-mediated rejection occurred in 10 patients (7 patients in the U.S. study and 3 in the Swedish study) at 2 weeks to 5 months after transplantation; all these patients had a response to treatment. One graft loss, mediated by non-HLA IgM and IgA antibodies, occurred.CONCLUSIONS: IdeS reduced or eliminated donor-specific antibodies and permitted HLA-incompatible transplantation in 24 of 25 patients. (Funded by Hansa Medical; ClinicalTrials.gov numbers, NCT02224820 , NCT02426684 , and NCT02475551 .).
|
|
| 22. |
- Karlsson, Rose-Marie Pernilla, et al.
(författare)
-
Carbohydrate gel beads as model probes for quantifying non-ionic and ionic contributions behind the swelling of delignified plant fibers
- 2018
-
Ingår i: Journal of Colloid and Interface Science. - : Academic Press. - 0021-9797 .- 1095-7103. ; 519, s. 119-129
-
Tidskriftsartikel (refereegranskat)abstract
- Macroscopic beads of water-based gels consisting of uncharged and partially charged beta-(1,4)-D-glucan polymers were developed to be used as a novel model material for studying the water induced swelling of the delignified plant fiber walls. The gel beads were prepared by drop-wise precipitation of solutions of dissolving grade fibers carboxymethylated to different degrees. The internal structure was analyzed using Solid State Cross-Polarization Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance and Small Angle X-ray Scattering showing that the internal structure could be considered a homogeneous, non-crystalline and molecularly dispersed polymer network. When beads with different charge densities were equilibrated with aqueous solutions of different ionic strengths and/or pH, the change in water uptake followed the trends expected for weak polyelectrolyte gels and the trends found for cellulose-rich fibers. When dried and subsequently immersed in water the beads also showed an irreversible loss of swelling depending on the charge and type of counter-ion which is commonly also found for cellulose-rich fibers. Taken all these results together it is clear that the model cellulose-based beads constitute an excellent tool for studying the fundamentals of swelling of cellulose rich plant fibers, aiding in the elucidation of the different molecular and supramolecular contributions to the swelling.
|
|
| 23. |
- Karlsson, Sofia, 1982, et al.
(författare)
-
A Laboratory Study of the in Situ Sulfation of Alkali Chloride Rich Deposits: Corrosion Perspective
- 2016
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:9, s. 7256-7267
-
Tidskriftsartikel (refereegranskat)abstract
- The initial corrosive effect of small (1.35 mu mol/cm(2)) and large (13.5 mu mol/cm(2)) amounts of KCl on 304L has been investigated. The investigations were performed in both the absence and presence of 300 ppm of SO2 at 600 degrees C. The results showed that in the absence of SO2 KCl accelerates the rate of corrosion by means of two types of corrosion attack: a general attack and a steel grain boundary attack. The general attack has been proved to be initiated by K2CrO4 formation. Meanwhile, the steel grain boundary attack is suggested to be accelerated by HCl released due to the chromate formation which increased with higher amounts of KCl. The presence of KCl and SO2 resulted in the simultaneous formation of K2SO4 and K2CrO4. The chromate formation resulted in a general corrosion attack. However, the oxide growth was significantly reduced due to the very fast sulfation reaction. In contrast, the steel grain boundary attack increased in the presence of SO2. It is suggested that the attack is accelerated by HCl released from the sulfation reaction and by sulfidation of the steel grain boundaries.
|
|
| 24. |
- Larsson, Erik, 1983, et al.
(författare)
-
A Comparative Study of the Initial Corrosion of KCl and PbCl2 on a Low-Alloyed Steel
- 2017
-
Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 87:5-6, s. 779-787
-
Tidskriftsartikel (refereegranskat)abstract
- Heat exchange surfaces in biomass- and waste-fired boilers are exposed to corrosive species due to the considerable amounts of alkali chlorides and PbCl2 which are released during combustion. The corrosivity of alkali chlorides toward superheater alloys exposed at high temperature has been studied extensively. However, at lower material temperatures, i.e., at waterwall conditions, considerably less research has been performed. In order to investigate the effect of small amounts of KCl and PbCl2 during the initial stages of the corrosion attack, a Fe–2.25Cr–1Mo steel was exposed for 24 h in an atmospheres consisting of O2 + H2O + N2 at 400 °C. Both KCl and PbCl2 resulted in an increased corrosion rate compared to the reference. The aim of the present paper is to investigate the influence of KCl and PbCl2 on the initial oxidation of a Fe–2.25Cr–1Mo steel. The work involves a detailed microstructural investigation as well as thermodynamic equilibrium calculations.
|
|
| 25. |
- Larsson, Henrik, et al.
(författare)
-
Oxidation of iron at 600 degrees C - experiments and simulations
- 2016
-
Ingår i: Materials and corrosion - Werkstoffe und Korrosion. - : Wiley-Blackwell. - 0947-5117 .- 1521-4176.
-
Tidskriftsartikel (refereegranskat)abstract
- Pure iron has been oxidized at 600°C and 1bar in dry O2 (oxygen partial pressure 0.05, bal. N2) and the mass gain as well as the thicknesses of the individual oxide phases have been measured. The oxidation process has been simulated using a modified version of the homogenization model as implemented in Dictra; this has helped to rationalize the kinetics of oxide scale formation and in particular the evolution of the hematite (Fe2O3), magnetite (Fe3O4), and wustite (FeO) which form. Independently assessed thermodynamic and kinetic Calphad databases are needed for the calculations; details of these are given. Reasonable agreement between simulation results and experimental data is obtained, though it is concluded that the large influence of grain boundary diffusion on the oxidation rate needs further consideration.
|
|
| 26. |
- Larsson, Lars, et al.
(författare)
-
Interdisciplinary archaeological prospection, excavation and 3D documentation exemplified through the investigation of a burial at the Iron Age settlement site of Uppåkra in Sweden
- 2015
-
Ingår i: Archaeological Prospection. - : Wiley. - 1099-0763 .- 1075-2196. ; 22:3, s. 143-156
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the archaeological prospection, excavation and digital three-dimensional documentation of a previously unknown neolithic grave, presumably late neolithic, at the outstanding Iron Age site of Uppåkra in southern Sweden, and exemplifies a multidisciplinary approach to modern archaeological fieldwork. In the framework of a large-scale archaeological prospection pilot study conducted at the archaeological site of Uppåkra using remote sensing and large-scale near-surface geophysical prospection methods a peculiar circular structure was discovered and mapped using both manual and motorized high-resolution ground-penetrating radar (GPR) measurements. The structure, consisting of a ring ditch of ca. 10m diameter, encloses an east–west oriented strongly reflecting rectangular body in the centre, which therefore was interpreted as being caused by the buried remains of a prehistoric barrow. Subsequent archaeological excavation was conducted across this structure in order to determine the exact cause of the GPR anomaly. This excavation resulted in detailed confirmation of the archaeological prospection results as well as in the discovery of dateable finds. The excavation was documented using the latest image-based three-dimensional modelling techniques. Copyright © 2015 John Wiley & Sons, Ltd.
|
|
| 27. |
- Larsson, Sylvia, et al.
(författare)
-
Assessment on bulk solids best practice techniques for flow characterization and storage/handling equipment design for biomass materials of different classes
- 2015
-
Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 138, s. 540-554
-
Tidskriftsartikel (refereegranskat)abstract
- This paper shows the results of a collaborative project in which four different laboratories have carried out complementary characterization tests on samples of the same set of lignocellulosic biomass materials with the objectives of better understanding their properties and identifying any critical features of the different characterization procedures. Three different types of material were used as model biomasses: 1) Scots pine wood chips, as an example of a coarse and flaky particulate biomass with some elastic properties; 2) chopped straw of reed canary grass as a nesting biomass having long and flaky fibers; and 3) Scots pine wood powder as a fine particulate with elastic and cohesive properties. Particle size and shape analyses were carried out with; calipers, 2D image analysis, 3D image analysis (ScanChip) and through mechanical sieving. Applications and validity limits of each of these techniques are evaluated and discussed. The flowfunction and internal friction were determined with a Schulze ring shear tester, a Brookfield powder flow tester and a large ring shear tester. No significant differences in the results generated by these shear testing techniques were found. Wall friction measurements were carried out with a Schulze ring shear tester; a Brookfield powder flow tester; a large Jenike shear tester and a Casagrande shear box. Results, in this case, showed significant differences with a higher wall friction coefficient obtained with the larger shear cell. Additionally, tensile strengths of biomass materials were measured by the use of a novel measurement technique. Arching tests were carried out in a pilot scale plane silo with variable hopper geometry and results were compared with those predicted by applying the Jenike procedure and a modified procedure which assumed that tensile strength was the controllingmaterial property (rather than unconfined yield strength). Finally, safety of handling and storage was assessed by carrying out explosion tests on dusts from Scots pine and reed canary grass.
|
|
| 28. |
|
|
| 29. |
- Larsson, Torbjörn, et al.
(författare)
-
A generic column generation principle: derivation and convergence analysis
- 2015
-
Ingår i: Operational Research. - : Springer Science and Business Media LLC. - 1109-2858 .- 1866-1505. ; 15:2, s. 163-198
-
Tidskriftsartikel (refereegranskat)abstract
- Given a non-empty, compact and convex set, and an a priori definedcondition which each element either satisfies or not, we want to find an elementbelonging to the former category. This is a fundamental problem of mathematicalprogramming which encompasses nonlinear programs, variational inequalities,saddle-point problems. We present a conceptual column generation scheme, whichalternates between solving a restriction of the original problem and a columngeneration phase which is used to augment the restricted problems. We establishgeneral applicability of the conceptual method, as well as to the three problemclasses mentioned. We also establish a version of the conceptual method in whichthe restricted and column generation problems are allowed to be solvedproximately, and of a version allowing for the dropping of columns. We showsome solution methods (e.g., Dantzig–Wolfe decomposition and simplicialcomposition) are special instances, and present new convergent column generationmethods in nonlinear programming, such as a sequential linear programming typemethod. Along the way, we also relate our quite general scheme in nonlinearprogramming presented in this paper with several other classic, and more recent,iterative methods in nonlinear optimization.
|
|
| 30. |
|
|
| 31. |
- Larsson, Torbjörn, et al.
(författare)
-
Subbens checklist
- 2016
-
Ingår i: Computers & Operations Research. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0305-0548 .- 1873-765X. ; 71, s. 163-164
-
Tidskriftsartikel (refereegranskat)abstract
- Excellent guides on academic writing and presentation in science in general, and in mathematics and computer science in particular, do abound (see, for example, Refs. [1-8], while guides on the assessment of the results of academic writing are rather more scarce. This short article presents two itemized lists that may be helping hands during the assessment of a scientific article in the field of mathematical optimization and operations research-be it your own, a work by a Master or PhD student of yours, or even a manuscript that you are refereeing for a scientific journal or conference proceedings volume. The first list-"Subbens checklist"-describes necessary ingredients of a complete article. The second list provides criteria for assessing the quality and scientific value of an article. (C) 2016 Elsevier Ltd. All rights reserved.
|
|
| 32. |
- Lundqvist, Anette, 1963-
(författare)
-
Nutritional aspects of behaviour and biology during pregnancy and postpartum
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- BackgroundA well-balanced nutritious diet is important for the pregnant woman and the growing fetus, as well as for their future health. Poor nutrition results from both over-consumption of energy-rich foods which can lead to a higher weight gain than is healthy and under-nutrition of essential nutrients. Food intake is regulated in complex biological systems by many factors, where steroid hormone is one factor involved.The overall aim of this thesis is to describe dietary intake, vitamin D levels, dietary information and dietary changes, and to study the relation between allopregnanolone and weight gain during pregnancy and postpartum.Methods Study I was a qualitative study with focus group interviews with 23 pregnant women. The text was analysed with content analysis. Study II was a quantitative cross-sectional study conducted in early pregnancy (n=209) with a reference group (n=206). Self-reported dietary data from a questionnaire was analysed using descriptive comparative statistics and a cluster analysis model (Partial Least Squares modelling). Study III had a quantitative longitudinal design. Vitamin D concentrations were analysed in 184 women, collected on five occasions during pregnancy and postpartum. Descriptive comparative statistics and a linear mixed model were used. Study IV was a quantitative longitudinal study with 60 women. Concentrations of allopregnanolone were analysed in gestational week 12 and 35. Descriptive and comparative statistics as well as Spearman’s correlation (rho) were used to describe the relationship between weight gain and allopregnanolone concentrations. Results The focus group interviews showed that women wanted to know more about different foods to reduce any risk for their child but the information about foods was partly up to themselves to find out. They expressedfeelingsof insecurityand guiltif they accidentallyate something“forbidden”. The recommendationswere followedas best as possiblealong withcommon sense todeal with dietchanges. The main themes were “Finding out by oneself”, “Getting professional advice when health problems occur”, “Being uncertain” and “Being responsible with a pinch of salt”. Some differences in the dietary patterns were found among the pregnant women compared to references, with less, vegetables (47 g/day), potatoes/rice/pasta (31 g/day), meat/fish (24 g/day) and intake of alcohol and tobacco/snuff but a higher intake of supplements. Bothpregnant women and referenceshad intakes offolatethrough diet45% (pregnant) and 22% (references) lower than current recommendations(500vs400g/day). Vitamin Dintake was34% lower than the recommendationsof 10mg/day. At least a third of the participants had insufficient plasma levels below 50 nmol/L of vitamin D. Season was a strong factor influencing the longitudinal pattern. Gestational week, season, total energy intake, dietary intake of vitamin D, and multivitamin supplementation over the previous 14 days were factors related to vitamin D levels. A correlation betweenallopregnanoloneconcentrations ingestationalweek 35and weight gainin weeks12–35was seen (p = 0.016). Therewas alsoa correlation betweenthe increase inallopregnanolone(weeks12–35) andweight gain(see above) (p = 0.028). ConclusionsDietary recommendations were described as contradictory and confusing and the dietary advice felt inadequate. The women faced their diet changes and sought information on their own but would have wished for more extensive advice from the midwife. The intake of vitamins essential for pregnancy was lower than recommended, which is also confirmed by low plasma levels of vitamin D in at least one third of the pregnant women. Vitamin D levels peaked in late pregnancy. Aside from gestational week and season which were related to plasma levels, intake from foods and supplements also affected the levels. Reasons for weight gain are complex and depend on many factors. Allopregnanolone is a factor that was seen to relate to the weight gain of the studied pregnant women.
|
|
| 33. |
- Marchesi, Silvia, MD, 1985-
(författare)
-
The effect of mechanical ventilation on abdominal organs : Analysing the role of PEEP and perfusion.
- 2019
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: The effect of mechanical ventilation on abdominal organs is not well understood and investigated yet. Previous studies, using an animal sepsis-like model, found an association between mechanical ventilation (MV) and abdominal edema and inflammation.The presented thesis was aimed to investigate the role of perfusion in edema formation and inflammation, and to study the abdomen during mechanical ventilation in an ARDS model to reduce the confounding effect of inflammation related to sepsis.Methods: In the first paper presented, inflammation and edema in the abdomen were investigated in an endotoxin model. The study subjects were divided into two groups with different mean arterial pressures (MAP), another small group of healthy controls were studied as well. MRI analyses were used to measure perfusion in the different abdominal organs. In the second paper presented, differences in abdominal edema and inflammation were assessed in two groups of subjects, one group underwent MV and one group had spontaneously breathing.Results: In the first study, MRI analyses confirm that the group with higher MAP had better perfusion than the low MAP group. In the liver, perfusion was lower in LowMAP group compared to HighMAP group, but the HighMAP group had lower perfusion than the healthy controls. However, in the other studied organs HighMAP group and healthy controls had similar perfusion.Edema did not differ between the groups. Inflammation was globally higher in LowMAP group and correlated with hemodynamics. TNFα in liver tissue and portal vein serum correlated with intra-abdominal pressure (IAP).In the second study, the cytokine concentration was higher in serum in the MV group. MV did not increase abdominal edema or inflammation, compared to spontaneous breathing. Discussion and conclusion: Abdominal edema and inflammation are multifactorial phenomena, and many elements have to be included in the analysis. Perfusion plays an important role in determining inflammation and IAP. MV per se was not found to be related to increased edema and inflammation. In a previous study, the role of different levels of PEEP and different respiratory rate between mechanically ventilated and spontaneously breathing animals were not analyzed, but could have contributed to the results. The efforts made in this study to maintain similar respiratory rate and PEEP in both groups, could have contributed to the presented results.It is important to underline that, even if MV was not related to inflammation in abdomen, it was related to an increase in systemic inflammation, most probably because of an enhanced lung production of inflammatory mediators.Further studies, focusing on the role of respiratory rate and PEEP on abdomen, as well as the analysis of the inter-relations among inflammation, perfusion and edema, are needed to increase the pathophysiological understanding of these phenomena.
|
|
| 34. |
- Mayambala, Fred, 1985-, et al.
(författare)
-
Eigendecomposition of the mean-variance portfolio optimization model
- 2015
-
Ingår i: Optimization, control, and applications in the information age. - Cham : Springer. - 9783319185668 - 9783319185675 ; , s. 209-232
-
Bokkapitel (refereegranskat)abstract
- We provide new insights into the mean-variance portfolio optimization problem, based on performing eigendecomposition of the covariance matrix. The result of this decomposition can be given an interpretation in terms of uncorrelated eigenportfolios. When only some of the eigenvalues and eigenvectors are used, the resulting mean-variance problem is an approximation of the original one. A solution to the approximation yields lower and upper bounds on the original mean-variance problem; these bounds are tight if sufficiently many eigenvalues and eigenvectors are used in the approximation. Even tighter bounds are obtained through the use of a linearized error term of the unused eigenvalues and eigenvectors.We provide theoretical results for the upper bounding quality of the approximate problem and the cardinality of the portfolio obtained, and also numerical illustrations of these results. Finally, we propose an ad hoc linear transformation of the mean-variance problem, which in practice significantly strengthens the bounds obtained from the approximate mean-variance problem.
|
|
| 35. |
- Mayambala, Fred, 1985-
(författare)
-
Mean-Variance Portfolio Optimization : Eigendecomposition-Based Methods
- 2015
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern portfolio theory is about determining how to distribute capital among available securities such that, for a given level of risk, the expected return is maximized, or for a given level of return, the associated risk is minimized. In the pioneering work of Markowitz in 1952, variance was used as a measure of risk, which gave rise to the wellknown mean-variance portfolio optimization model. Although other mean-risk models have been proposed in the literature, the mean-variance model continues to be the backbone of modern portfolio theory and it is still commonly applied. The scope of this thesis is a solution technique for the mean-variance model in which eigendecomposition of the covariance matrix is performed.The first part of the thesis is a review of the mean-risk models that have been suggested in the literature. For each of them, the properties of the model are discussed and the solution methods are presented, as well as some insight into possible areas of future research.The second part of the thesis is two research papers. In the first of these, a solution technique for solving the mean-variance problem is proposed. This technique involves making an eigendecomposition of the covariance matrix and solving an approximate problem that includes only relatively few eigenvalues and corresponding eigenvectors. The method gives strong bounds on the exact solution in a reasonable amount of computing time, and can thus be used to solve large-scale mean-variance problems.The second paper studies the mean-variance model with cardinality constraints, that is, with a restricted number of securities included in the portfolio, and the solution technique from the first paper is extended to solve such problems. Near-optimal solutions to large-scale cardinality constrained mean-variance portfolio optimization problems are obtained within a reasonable amount of computing time, compared to the time required by a commercial general-purpose solver.
|
|
| 36. |
- Mayambala, Fred, et al.
(författare)
-
Tight Upper Bounds on the Cardinality Constrained Mean-Variance Portfolio Optimization Problem Using Truncated Eigendecomposition
- 2016
-
Ingår i: Operations Research Proceedings 2014. - Cham : Springer. - 9783319286952 - 9783319286976 ; , s. 385-392
-
Konferensbidrag (refereegranskat)abstract
- The mean-variance problem introduced by Markowitz in 1952 is a fundamental model in portfolio optimization up to date. When cardinality and bound constraints are included, the problem becomes NP-hard and the existing optimizing solution methods for this problem take a large amount of time.We introduce a core problem based method for obtaining upper bounds to the meanvariance portfolio optimization problem with cardinality and bound constraints. The method involves performing eigendecomposition on the covariance matrix and then using only few of the eigenvalues and eigenvectors to obtain an approximation of the original problem. A solution of this approximate problem has a relatively low cardinality and is used to construct a core problem. When solved, the core problem provides an upper bound. We test the method on large scale problems of up to 1000 assets. The obtained upper bounds are of high quality and the time required to obtain them is much less than what state-of-the-art mixed integer softwares use, which makes it practically useful.
|
|
| 37. |
- Morén, Björn, 1987-, et al.
(författare)
-
A mathematical optimization model for spatial adjustments of dose distributions in high dose-rate brachytherapy
- 2019
-
Ingår i: Physics in Medicine and Biology. - : IOP PUBLISHING LTD. - 0031-9155 .- 1361-6560. ; 64:22
-
Tidskriftsartikel (refereegranskat)abstract
- High dose-rate brachytherapy is a modality of radiation therapy used for cancer treatment, in which the radiation source is placed within the body. The treatment goal is to give a high enough dose to the tumour while sparing nearby healthy tissue and organs (organs-at-risk). The most common criteria for evaluating dose distributions are dosimetric indices. For the tumour, such an index is the portion of the volume that receives at least a specified dose level (e.g. the prescription dose), while for organs-at-risk it is instead the portion of the volume that receives at most a specified dose level. Dosimetric indices are aggregate criteria and do not consider spatial properties of the dose distribution. Further, there are neither any established evaluation criteria for characterizing spatial properties, nor have such properties been studied in the context of mathematical optimization of brachytherapy. Spatial properties are however of clinical relevance and therefore dose plans are sometimes adjusted manually to improve them. We propose an optimization model for reducing the prevalence of contiguous volumes with a too high dose (hot spots) or a too low dose (cold spots) in a tentative dose plan. This model is independent of the process of constructing the tentative plan. We conduct computational experiments with tentative plans obtained both from optimization models and from clinical practice. The objective function considers pairs of dose points and each pair is given a distance-based penalty if the dose is either too high or too low at both dose points. Constraints are included to retain dosimetric indices at acceptable levels. Our model is designed to automate the manual adjustment step in the planning process. In the automatic adjustment step large-scale optimization models are solved. We show reductions of the volumes of the largest hot and cold spots, and the computing times are feasible in clinical practice.
|
|
| 38. |
- Morén, Björn, 1987-, et al.
(författare)
-
An extended dose-volume model in high dose-rate brachytherapy : Using mean-tail-dose to reduce tumor underdosage
- 2019
-
Ingår i: Medical physics (Lancaster). - : Wiley-Blackwell Publishing Inc.. - 0094-2405 .- 2473-4209. ; 46:6, s. 2556-2566
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose High dose-rate brachytherapy is a method of radiotherapy for cancer treatment in which the radiation source is placed within the body. In addition to give a high enough dose to a tumor, it is also important to spare nearby healthy organs [organs at risk (OAR)]. Dose plans are commonly evaluated using the so-called dosimetric indices; for the tumor, the portion of the structure that receives a sufficiently high dose is calculated, while for OAR it is instead the portion of the structure that receives a sufficiently low dose that is of interest. Models that include dosimetric indices are referred to as dose-volume models (DVMs) and have received much interest recently. Such models do not take the dose to the coldest (least irradiated) volume of the tumor into account, which is a distinct weakness since research indicates that the treatment effect can be largely impaired by tumor underdosage even to small volumes. Therefore, our aim is to extend a DVM to also consider the dose to the coldest volume. Methods An improved DVM for dose planning is proposed. In addition to optimizing with respect to dosimetric indices, this model also takes mean dose to the coldest volume of the tumor into account. Results Our extended model has been evaluated against a standard DVM in ten prostate geometries. Our results show that the dose to the coldest volume could be increased, while also computing times for the dose planning were improved. Conclusion While the proposed model yields dose plans similar to other models in most aspects, it fulfils its purpose of increasing the dose to cold tumor volumes. An additional benefit is shorter solution times, and especially for clinically relevant times (of minutes) we show major improvements in tumour dosimetric indices.
|
|
| 39. |
- Morén, Björn, 1987-
(författare)
-
Mathematical Modelling of Dose Planning in High Dose-Rate Brachytherapy
- 2019
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cancer is a widespread type of diseases that each year affects millions of people. It is mainly treated by chemotherapy, surgery or radiation therapy, or a combination of them. One modality of radiation therapy is high dose-rate brachytherapy, used in treatment of for example prostate cancer and gynecologic cancer. Brachytherapy is an invasive treatment in which catheters (hollow needles) or applicators are used to place the highly active radiation source close to or within a tumour.The treatment planning problem, which can be modelled as a mathematical optimization problem, is the topic of this thesis. The treatment planning includes decisions on how many catheters to use and where to place them as well as the dwell times for the radiation source. There are multiple aims with the treatment and these are primarily to give the tumour a radiation dose that is sufficiently high and to give the surrounding healthy tissue and organs (organs at risk) a dose that is sufficiently low. Because these aims are in conflict, modelling the treatment planning gives optimization problems which essentially are multiobjective.To evaluate treatment plans, a concept called dosimetric indices is commonly used and they constitute an essential part of the clinical treatment guidelines. For the tumour, the portion of the volume that receives at least a specified dose is of interest while for an organ at risk it is rather the portion of the volume that receives at most a specified dose. The dosimetric indices are derived from the dose-volume histogram, which for each dose level shows the corresponding dosimetric index. Dose-volume histograms are commonly used to visualise the three-dimensional dose distribution.The research focus of this thesis is mathematical modelling of the treatment planning and properties of optimization models explicitly including dosimetric indices, which the clinical treatment guidelines are based on. Modelling dosimetric indices explicitly yields mixedinteger programs which are computationally demanding to solve. The computing time of the treatment planning is of clinical relevance as the planning is typically conducted while the patient is under anaesthesia. Research topics in this thesis include both studying properties of models, extending and improving models, and developing new optimization models to be able to take more aspects into account in the treatment planning.There are several advantages of using mathematical optimization for treatment planning in comparison to manual planning. First, the treatment planning phase can be shortened compared to the time consuming manual planning. Secondly, also the quality of treatment plans can be improved by using optimization models and algorithms, for example by considering more of the clinically relevant aspects. Finally, with the use of optimization algorithms the requirements of experience and skill level for the planners are lower.This thesis summary contains a literature review over optimization models for treatment planning, including the catheter placement problem. How optimization models consider the multiobjective nature of the treatment planning problem is also discussed.
|
|
| 40. |
- Morén, Björn, 1987-, et al.
(författare)
-
Mathematical optimization of high dose-rate brachytherapy-derivation of a linear penalty model from a dose-volume model
- 2018
-
Ingår i: Physics in Medicine and Biology. - : IOP PUBLISHING LTD. - 0031-9155 .- 1361-6560. ; 63:6
-
Tidskriftsartikel (refereegranskat)abstract
- High dose-rate brachytherapy is a method for cancer treatment where the radiation source is placed within the body, inside or close to a tumour. For dose planning, mathematical optimization techniques are being used in practice and the most common approach is to use a linear model which penalizes deviations from specified dose limits for the tumour and for nearby organs. This linear penalty model is easy to solve, but its weakness lies in the poor correlation of its objective value and the dose-volume objectives that are used clinically to evaluate dose distributions. Furthermore, the model contains parameters that have no clear clinical interpretation. Another approach for dose planning is to solve mixed-integer optimization models with explicit dose-volume constraints which include parameters that directly correspond to dose-volume objectives, and which are therefore tangible. The two mentioned models take the overall goals for dose planning into account in fundamentally different ways. We show that there is, however, a mathematical relationship between them by deriving a linear penalty model from a dose-volume model. This relationship has not been established before and improves the understanding of the linear penalty model. In particular, the parameters of the linear penalty model can be interpreted as dual variables in the dose-volume model.
|
|
| 41. |
- Morén, Björn, 1987-, et al.
(författare)
-
Preventing Hot Spots in High Dose-Rate Brachytherapy
- 2018
-
Ingår i: Operations Research Proceedings 2017. - Cham : Springer International Publishing. - 9783319899190 - 9783319899206 ; , s. 369-375
-
Konferensbidrag (refereegranskat)abstract
- High dose-rate brachytherapy is a method of radiation cancer treatment, where the radiation source is placed inside the body. The recommended way to evaluate dose plans is based on dosimetric indices which are aggregate measures of the received dose. Insufficient spatial distribution of the dose may however result in hot spots, which are contiguous volumes in the tumour that receive a dose that is much too high. We use mathematical optimization to adjust a dose plan that is acceptable with respect to dosimetric indices to also take spatial distribution of the dose into account. This results in large-scale nonlinear mixed-binary models that are solved using nonlinear approximations. We show that there are substantial degrees of freedom in the dose planning even though the levels of dosimetric indices are maintained, and that it is possible to improve a dose plan with respect to its spatial properties.
|
|
| 42. |
- Mwakisisile, Andongwisye John, 1972-
(författare)
-
Asset Liability Management for Tanzania Pension Funds
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a long-term asset liability management for Tanzania pension funds. As an application, the largest pension fund in Tanzania is considered. This is a pay-as-you-go pension fund where the contributions are used to pay current benefits. The Pension plan analyzed is a final salary defined benefit. Two kinds of pension benefit are considered, a commuted (at retirement) and a monthly (old age) pension. A decision factor in the analysis is the increased life expectancy of the members of the pension fund.The presentation is divided into two parts. First is a long-term projection of the fund using a fixed and relatively low return on asset value. Basing on the number of members in 2015, a 50 years projection of members and retirees is done. The corresponding amount of contributions, asset values, benefit payouts, and liabilities are also projected. The evaluation of some possible reforms of the fund is done. Then, the growth of asset values using different asset returns is studied. The projection shows that the fund will not be fully sustainable in a long future due to the increase in life expectancy of its members. The contributions will not cover the benefit payouts and the asset value will not fully cover liabilities. Evaluation of some reforms of the fund shows that they cannot guarantee a long-term sustainability. Higher returns on asset value will improve the asset to liability ratio, but contributions are still insufficient to cover benefit payouts.Second is a management based on stochastic programming. This approach allocates investment in assets with the best return to raise the asset value closer to the level of liabilities. The model is based on work by Kouwenberg in 2001 includes some features from Tanzania pension system. In contrast with most asset liability management models for pension funds by stochastic programming, liabilities are modeled by number of years of life expectancy. Scenario trees are generated by using Monte Carlo simulation. Two models according to different investment guidelines are built. First is using the existing investment guidelines and second is using modified guidelines which are practical and suitable for modeling. Numerical results suggest that, in order to improve a long-term sustainability of the Tanzania pension fund system, it is necessary to make reforms concerning the contribution rate, investment guidelines and formulate target levels (funding ratios) to characterize the pension funds’ solvency situation. These reforms will improve the sustainability of the system.
|
|
| 43. |
- Palmér, Robert, et al.
(författare)
-
Dipeptidyl Peptidase 1 Inhibitor AZD7986 Induces a Sustained, Exposure-Dependent Reduction in Neutrophil Elastase Activity in Healthy Subjects
- 2018
-
Ingår i: Clinical Pharmacology and Therapeutics. - : Wiley-Blackwell. - 0009-9236 .- 1532-6535. ; 104:6, s. 1155-1164
-
Tidskriftsartikel (refereegranskat)abstract
- Neutrophil serine proteases (NSPs), such as neutrophil elastase (NE), are activated by dipeptidyl peptidase 1 (DPP1) during neutrophil maturation. High NSP levels can be detrimental, particularly in lung tissue, and inhibition of NSPs is therefore an interesting therapeutic opportunity in multiple lung diseases, including chronic obstructive pulmonary disease (COPD) and bronchiectasis. We conducted a randomized, placebo-controlled, first-in-human study to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of single and multiple oral doses of the DPP1 inhibitor AZD7986 in healthy subjects. Pharmacokinetic and pharmacodynamic data were analyzed using nonlinear mixed effects modeling and showed that AZD7986 inhibits whole blood NE activity in an exposure-dependent, indirect manner-consistent with in vitro and preclinical predictions. Several dose-dependent, possibly DPP1-related, nonserious skin findings were observed, but these were not considered to prevent further clinical development. Overall, the study results provided confidence to progress AZD7986 to phase II and supported selection of a clinically relevant dose.
|
|
| 44. |
|
|
| 45. |
- Patriksson, Michael, 1964, et al.
(författare)
-
Time out of mind: “Subben’s checklist” revisited – A partial description of the development of quantitative OR papers over a period of 25 years
- 2017
-
Ingår i: ORbit. ; :29, s. 27-29
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This short paper aims to investigate some of the historical developments of a classic, well-cited and highly esteemed scientific journal in the domain of quantitative operations research – namely the INFORMS journal Operations Research, over a period of 25 years. As such this paper, and the journal in question, represents an opportunity to analyze – also in more generality – how research production has evolved, and evolves, over time. Among the developments over time that we think we can trace are that (a) the historical overviews (or, literature surveys) in the articles, as well as the list of references, somewhat counter-intuitively shrink over time, while (b) the motivating and modelling parts grow. We have also analysed the articles’ utilization of “buzz words” representing the constitutive parts of a journal paper, based on “Subben’s checklist” (Larsson & Patriksson, 2014; 2016), and conclude through a citation study using a collection of either highly or little cited papers that there is a quite strong positive correlation between a journal paper being highly cited and it utilizing this checklist.
|
|
| 46. |
|
|
| 47. |
- Quttineh, Nils-Hassan, et al.
(författare)
-
A Time-Indexed Generalized Vehicle Routing Model and Stabilized Column Generation for Military Aircraft Mission Planning
- 2015
-
Ingår i: OPTIMIZATION, CONTROL, AND APPLICATIONS IN THE INFORMATION AGE: IN HONOR OF PANOS M. PARDALOSS 60TH BIRTHDAY. - Cham : SPRINGER. - 9783319185675 - 9783319185668 ; , s. 299-314
-
Konferensbidrag (refereegranskat)abstract
- We introduce a time-indexed mixed-integer linear programming model for a military aircraft mission planning problem, where a fleet of cooperating aircraft should attack a number of ground targets so that the total expected effect is maximized. The model is a rich vehicle routing problem and the direct application of a general solver is practical only for scenarios of very moderate sizes. We propose a Dantzig-Wolfe reformulation and column generation approach. A column here represents a specific sequence of tasks at certain times for an aircraft, and to generate columns a longest path problem with side constraints is solved. We compare the column generation approach with the time-indexed model with respect to upper bounding quality of their linear programming relaxations and conclude that the former provides a much stronger formulation of the problem.
|
|
| 48. |
- Quttineh, Nils-Hassan, 1979-, et al.
(författare)
-
Military Aircraft Mission Planning : Efficient model-based metaheuristics approaches
- 2015
-
Ingår i: Optimization Letters. - Berlin Heidelberg : Springer Berlin/Heidelberg. - 1862-4472 .- 1862-4480. ; 9:8, s. 1625-1639
-
Tidskriftsartikel (refereegranskat)abstract
- We consider a military mission planning problem where a given fleet of aircraft should attack a number of ground targets. At each attack, two aircraft need to be synchronized in both space and time. Further, there are multiple attack options against each targets, with different target effects. The objective is to maximize the outcome of the entire attack, while also minimizing the mission timespan. Real-life mission planning instances involve only a few targets and a few aircraft, but are still computationally challenging. We present metaheuristic solution methods for this problem, based on an earlier presented model. The problem includes three types of decisions: attack directions, task assignments and scheduling, and the solution methods exploit this structure in a two-stage approach. In an outer stage, a heuristic search is performed with respect to attack directions, while in an inner stage the other two decisions are optimized, given the outer stage decisions. The proposed metaheuristics are capable of producing high-quality solutions and are fast enough to be incorporated in a decision support tool.
|
|
| 49. |
- Ridefelt, Peter, et al.
(författare)
-
Age- and sex-specific reference values for non-HDL cholesterol and remnant cholesterol derived from the Nordic Reference Interval Project (NORIP)
- 2019
-
Ingår i: Scandinavian Journal of Clinical and Laboratory Investigation. - : Taylor & Francis Group. - 0036-5513 .- 1502-7686. ; 79:1-2, s. 39-42
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: Non-HDL-cholesterol (non-HDL-C) has been reported to be a better marker of cardiovascular risk than LDL-cholesterol (LDL-C) especially in individuals with high triglyceride values. Further, levels of remnant cholesterol have been suggested to in part explain residual risk not captured with LDL-C. The aim of the present study was to define reference values for non-HDL-C and remnant cholesterol based on data from the Nordic Reference Interval Project (NORIP).METHODS: We analyzed the test results for total cholesterol, HDL-cholesterol and triglycerides from 1392 healthy females and 1236 healthy males. Non-HDL-C was calculated as measured total cholesterol minus measured HDL-cholesterol. Remnant cholesterol was calculated using the Friedewald equation for LDL-C: measured total cholesterol minus measured HDL-cholesterol and minus calculated LDL-cholesterol. The 2.5th and 97.5th percentiles for these markers were calculated according to the International Federation of Clinical Chemistry guidelines on the statistical treatment of reference values.RESULTS: Age (18-<30, 30-49 and ≥50 years) and sex-specific reference intervals were calculated for non-HDL-cholesterol and remnant-cholesterol. Levels of non-HDL-C and remnant cholesterol differed between sex and age strata.CONCLUSIONS: Age- and sex-specific reference intervals should be used for the triglyceride rich lipid variables non-HDL-C and remnant cholesterol. Since these markers may add information on risk burden beyond LDL-C, our hope is that these reference intervals will aid the introduction of automatic reporting of non-HDL-C by hospital laboratories.
|
|
| 50. |
- Rollborn, Niclas, et al.
(författare)
-
Analysis of HbA1c on an automated multicapillary zone electrophoresis system.
- 2017
-
Ingår i: Scandinavian Journal of Clinical and Laboratory Investigation. - : Informa UK Limited. - 0036-5513 .- 1502-7686. ; 77:1, s. 15-18
-
Tidskriftsartikel (refereegranskat)abstract
- Hemoglobin A1c (HbA1c) is a frequently requested laboratory test and there is thus a need for high throughput instruments for this assay. We evaluated a new automated multicapillary zone electrophoresis instrument (Capillarys 3 Tera, Sebia, Lisses, France) for analysis of HbA1c in venous samples. Routine requested HbA1c samples were analyzed immunologically on a Roche c6000 instrument (n = 142) and then with the Capillarys 3 Tera instrument. The Capillarys 3 Tera instrument performed approximately 70 HbA1c tests/hour. There was a strong linear correlation between Capillarys 3 Tera and Roche Tina-Quant HbA1c Gen 3 assay (y = 1.003x - 0.3246 R(2 )= .996). The total CV for the 12 capillaries varied between 0.8 and 2.2% and there was a good agreement between duplicate samples (R(2 )= .997). In conclusion, the Capillarys 3 Tera instrument has a high assay capacity for HbA1c. It has a good precision and agreement with the Roche Tina-Quant HbA1c method and is well suited for high volume testing of HbA1c.
|
|
