| 92511. |
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| 92512. |
- Larsson, Karl
(författare)
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Analytical Approximation of Contingent Claims
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This PhD thesis consists of three separate papers. The common theme is methods to calculate analytical approximations for prices of different contingent claims under various model assumptions. The first two papers deals with approximations of standard European options in stochastic volatility models. The third paper is focused on approximating prices of commodity swaptions in a general model framework. In the first paper, Dynamic Extensions and Probabilistic Expansions of the SABR model, a closed form approximation to prices of call options and implied volatilities in the so called SABR model of Hagan et al. (2002) is derived. The SABR model is one of the most frequently used stochastic volatility models used for option pricing in practice. The method relies on perturbing the model dynamics and approximations are obtained from a second order Taylor expansion. It is shown how the expansion terms can be calculated in a straightforward fashion using the flows of the perturbed model and results from the Malliavin calculus. This technique is further applied to calculate a closed form approximation of the option price in a useful dynamic extension of the original model. The dynamic model is able to match the prices of several options with different maturities and can therefore be used to price path dependents products in a consistent way. In addition, we propose an alternative model specification for the dynamic SABR model where the dynamics of the underlying asset are given by a displaced diffusion. In its non-dynamic version this model has similar properties as the original SABR model but it is more analytically tractable. A closed form approximation of the dynamic version of this model is also derived. The accuracy of the approximations is evaluated in a Monte Carlo study and the method is found to work well for many parameters of interest. The second paper, General Approximation Schemes for Option Prices in Stochastic Volatility Models, further examines the method of approximation employed in the first paper. The method is developed for a general stochastic volatility specification that can generate many commonly employed models as special cases. As an important application the method is used to calculate a second order expansion for the Heston (1993) model. The Heston model is arguably the most often used stochastic volatility model in practice and academic work. A numerical study of the approximations is performed where they are compared to prices and implied volatilities calculated from numerical Fourier transforms. It is found that for several parameters of interest the approximation is very accurate. Relating the proposed method to the existing literature we find that it generalizes the work by Lewis (2005) in several directions. In the case of the Heston model the first order expansion coincides with the approximation proposed in Alos (2006). However, an important advantage of the proposed method is that it can be used to generate higher order terms and it is verified that extending to second order substantially improves the accuracy of the approximation. The third paper, Approximative Valuation of Commodity Swaptions, is concerned with the numerical calculation of prices of European options on commodity swaps. A general approximation scheme for these claims is derived within the model framework of Heath, Jarrow and Morton (1992) extended to include commodity forwards. In models with deterministic volatilities the approach generates a closed form approximation allowing the swaptions to be conveniently priced using Blacks formula. The approximation is evaluated when applied to a Gaussian 2-factor model frequently employed in the literature. A comparison of the approximative prices to Monte Carlo simulations shows that the incurred errors are small for a large set of relevant parameters.
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| 92513. |
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| 92514. |
- Larsson, Karin, et al.
(författare)
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Annual screening detects celiac disease in children with type 1 diabetes
- 2008
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Ingår i: Pediatric Diabetes. - : Hindawi Limited. - 1399-543X .- 1399-5448. ; 9:4, s. 354-359
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Tidskriftsartikel (refereegranskat)abstract
- Objective: To investigate the prevalence of celiac disease (CD) in a cohort of type 1 diabetes mellitus (T1DM) children and adolescents at the time of clinical diagnosis and to evaluate the screening procedure and possible role of human leukocyte antigen (HLA)-DQ during a 5-yr follow-up. Research design and methods: The study group was a cohort of 300 newly diagnosed T1DM children and youths younger than 20 yr followed for 5 yr at six clinical centers for pediatric diabetes in the region Skane in Sweden. Immunoglobulin A endomysium antibodies were used to screen the patients annually to be considered for an intestinal biopsy. All patients were analyzed for HLA-DQA1-B1 genotypes. Results: While 0.7% (2/300) already had a diagnosed symptomatic CD, an additional 3% (10/300) had silent CD at the diagnosis of T1DM. During follow-up, another 6% (17/300) developed CD as follows: 10 after 1 yr, 5 after 2 yr, 1 after 3 yr, and 1 after 5 yr. Therefore, the cumulative frequency of CD confirmed by intestinal biopsies was 10% (29/300). HLA genotypes among T1DM patients developing CD were not different from those among patients with T1DM alone. Conclusions: Our study confirmed the low prevalence (0.7%) of diagnosed symptomatic CD at the time of clinical diagnosis but document by screening an increasing prevalence of silent CD during a 5-yr follow-up to reach an overall prevalence of 10%. We suggest that children with T1DM should be screened for CD at the onset of T1DM and annually for a minimum of at least 2 yr. HLA genotypes among T1DM patients developing CD were not different from those among patients with T1DM alone.
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| 92515. |
- Larsson, Kristin, et al.
(författare)
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Brominated Flame Retardants and Organophosphate Esters in Preschool Dust and Children's Hand Wipes
- 2018
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 52:8, s. 4878-4888
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Tidskriftsartikel (refereegranskat)abstract
- Children spend a considerable part of their day in preschool, where they may be exposed to hazardous chemicals in indoor dust. In this study, brominated flame retardants (BFRs) and organophosphate esters (OPEs) were analyzed in preschool dust ( n = 100) and children's hand wipe samples ( n = 100), and diphenyl phosphate (DPHP) was analyzed in urine ( n = 113). Here we assessed children's exposure via dust, identified predictors for chemicals in dust, and studied correlations between different exposure measures. The most abundant BFRs in dust were decabromodiphenyl ether (BDE-209) and decabromodiphenyl ethane (DBDPE) found at median levels of 270 and 110 ng/g dust, respectively. Tris(2-butoxyethyl) phosphate (TBOEP) was the most abundant OPE, found at a median level of 79 000 ng/g dust. For all OPEs and some BFRs, there were significant correlations between the levels in dust and hand wipes. In addition, triphenyl phosphate (TPHP) in preschool dust was significantly correlated with the corresponding metabolite DPHP in children's urine. The levels of pentaBDEs in dust were higher in older preschools compared with newer, whereas levels of DBDPE were higher in newer preschools. Children's estimated intakes of individual BFRs and OPEs via preschool dust were below available health-based reference values. However, there are uncertainties about the potential health effects of some emerging BFRs and OPEs.
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| 92516. |
- Larsson, Kristina, et al.
(författare)
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CD4+ T-cells have a key instructive role in educating dendritic cells in allergy
- 2009
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Ingår i: International Archives of Allergy and Immunology. - : S. Karger AG. - 1423-0097 .- 1018-2438. ; 149:1, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- Background: Dendritic cells (DCs) are central in allergy as regulators of the Th1/Th2 balance. We have recently demonstrated a unique transcriptional profile of DCs in patients with ongoing allergy compared with healthy subjects and shown that crosstalk between DCs and memory T cells affects the transcriptional profile of T cells. However, the transcriptional profile of DCs educated by T cells in allergy is unknown. Methods: In the present study, we have examined the transcriptional profiles of DCs after stimulation with grass pollen allergens, Phleum pratense and coculture with autologous CD4+ memory T cells using high-density microarray. Protein analysis was performed using flow cytometry and recombinant antibody protein microarrays. Patients with allergic rhinitis and healthy subjects were compared. Results: The results reveal a distinct T-cell-induced DC profile in atopic individuals. Accordingly, about 170 genes were upregulated and 40 genes downregulated. For example, the chemokine receptor CXCR4 and the tumor necrosis factor receptor CD30 were upregulated in DCs derived from atopic donors, and this could also be verified at the protein level. Conclusion: We conclude that crosstalk between CD4+ memory T cells and autologous DCs induces transcriptional reprogramming in DCs. This finding suggests that T cells have a key instructive role in educating DCs in Th2-type responses.
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| 92517. |
- Larsson, Karolina, et al.
(författare)
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Children's use of English as lingua franca in Swedish preschools
- 2023
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Ingår i: Multilingua-Journal of Cross-Cultural and Interlanguage Communication. - : Walter de Gruyter GmbH. - 0167-8507 .- 1613-3684. ; 42:4, s. 527-557
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Forskningsöversikt (refereegranskat)abstract
- This paper highlights a current phenomenon reported from preschools placed in multilingual areas in Sweden, namely that some preschoolers with mutually different language backgrounds sometimes use English as lingua franca instead of Swedish during play. The data stems from a study of language environments in Swedish preschools situated in both monolingual and multilingual areas. The analyses reveal that many children are influenced by the English language in both areas, but to a much greater extent in multilingual areas. An interesting situation arises when the majority language of society, which is also the language of education and lingua franca of the preschool, acquires a less prevailing role in children's accomplishment of everyday practices. Data show that the participating children are exposed to and speak English to a varying extent. They learn and teach each other English, and speak English in an array of pragmatic purposes; to position themselves in the social hierarchies of the preschool group, to create meaning within their shared peer culture and for the purpose of exclusion of intruders. English is also used as a secret language of friendship.
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| 92518. |
- Larsson, Krister, 1973, et al.
(författare)
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Cobalt 2,2 '-biimidazole complexes co-crystallised with di-acids - synthesis, structure and quantum chemical calculations
- 2004
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Ingår i: Crystengcomm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 6, s. 354-359
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and crystal structure of [Co(Hbiim)(2)(H(2)biim)](2)(p-OOCC6H4COOH)(2).H2O (2) is presented. The cobalt(III) complexes are bridged by terephthalates and water molecules, giving a rare, five-fold interpenetrated, net built from 3-connected nodes. The vertex symbol (topology) of this net is determined to 4 122 122, 4 126, 12(4) 12(6) 12(6), or 4 12(2), 4 12(2), 12(3), using the Wellsian point symbol system. However, depending on the interpretation of the hydrogen bond pattern, this structure may also be interpreted as a single self-interpenetrating net via a water bridge. Quantum chemical calculations (DFT and semi-empirical methods) were used to investigate which is the more appropriate description by estimation of the directional forces in the structure. This approach favours five interpenetrating nets.
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| 92519. |
- Larsson, Kristina
(författare)
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Dendritic cells in allergy In vitro models for studies of the human immune response
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis, which is based on four original papers, deals with human dendritic cells (DCs) in immunity and allergy. DCs play a key role in the regulation of immune responses by acting as the sentinels of the immune system, specialized in the uptake of a diverse range of antigens. These cells migrate to local lymph nodes and become highly efficient in inducing T cell proliferation, thus inducing adaptive immune responses. Therefore, DCs function as the link between innate and adaptive immune responses. Besides pathogenic microorganisms, the immune system encounters numerous proteins, many of which are harmless. A proper response against these harmless antigens is tolerance. The balance between induction of immunity or tolerance is in part determined by DCs. A dysfunction in the regulation of this balance may result in diseases such as allergy and autoimmunity. The incidence of allergy has reached up to 40% of the children in industrialized countries and is increasing in developing countries. The reduced quality of life in these conditions increases the need to strive for commercial products of low allergenicity. Tests to verify these products are needed, and directives from the European Union aim for a reduction of animal tests and development of alternative in vitro models. A model based on human DCs would be suitable since they have a central role in the immune system and in allergy. To address this question we studied transcriptional profiles of monocyte-derived DCs (MoDCs) and the differentiated monocytic cell line MUTZ-3 induced by pro-inflammatory signals. We could demonstrate that the cell lines expressed a wide range of molecules that are important for DC function. Thus, MUTZ-3 closely resembles DCs and is suggested to serve as an in vitro model to predict allergenicty of novel compounds. Yet, the functionality of the cell line needs to be further evaluated.The effect of an allergen (timothy) on DCs was demonstrated by transcriptional profiling of grass pollen stimulated DCs from allergic and non-allergic individuals. Furthermore, memory effector T cells were demonstrated to have an instructive role in the cross-talk between DCs and T cells in both allergic and non-allergic conditions. This education of DCs was in part specific in allergy and supports the concept of DC-mediated sustained allergic inflammation in the periphery. In addition, the reported panel of genes reveal novel molecules involved in the enhanced inflammation. The genes reported specific for allergen stimulated DCs and in the subsequent DC/T cell crosstalk in allergy may be interesting targets in the search of novel drugs.New methods for administration of vaccines are desirable to increase the speed and ease for delivery of vaccines in addition to improved safety. DCs are suitable targets for vaccine delivery since they are efficient inducers of adaptive immune responses. As they are located in mucosa and skin they can be reach by vaccine delivery to any of these tissues, e.g. via nasal administration. Nanospheres induce adaptive immune responses and function as both antigen carrier and adjuvants. Transcriptional profiling of MoDCs upon stimulation with nanospheres revealed activated pathways during uptake and processing of the antigen. Next, the efficiency of biodegradable nanospheres to induce DCs to mount adaptive immune responses needs to be identified.
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| 92520. |
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