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  • 19301.
    Tumwesigye, Alex Behakanira
    et al.
    Mälardalens högskola, Akademin för utbildning, kultur och kommunikation, Utbildningsvetenskap och Matematik.
    Richter, Johan
    Mälardalens högskola, Akademin för utbildning, kultur och kommunikation, Utbildningsvetenskap och Matematik.
    Silvestrov, Sergei
    Mälardalens högskola, Akademin för utbildning, kultur och kommunikation, Utbildningsvetenskap och Matematik.
    Ore extensions of function algebras2018Konferansepaper (Annet (populærvitenskap, debatt, mm))
  • 19302.
    Tumwesigye, Alex
    et al.
    Mälardalens högskola, Akademin för utbildning, kultur och kommunikation, Utbildningsvetenskap och Matematik. Makerere University.
    Richter, Johan
    Mälardalens högskola, Akademin för utbildning, kultur och kommunikation, Utbildningsvetenskap och Matematik.
    Silvestrov, Sergei
    Mälardalens högskola, Akademin för utbildning, kultur och kommunikation, Utbildningsvetenskap och Matematik.
    Commutants in crossed products for algebras of piecewise constant functions on the real lineManuskript (preprint) (Annet (populærvitenskap, debatt, mm))
  • 19303.
    Tumwesigye, Alex
    et al.
    Mälardalens högskola, Akademin för utbildning, kultur och kommunikation, Utbildningsvetenskap och Matematik. Makerere University.
    Silvestrov, Sergei
    Mälardalens högskola, Akademin för utbildning, kultur och kommunikation, Utbildningsvetenskap och Matematik.
    On monomial commutativity of operators satisfying commutation relations and periodic points for one-dimensional dynamical systems2014Inngår i: 10TH INTERNATIONAL CONFERENCE ON MATHEMATICAL PROBLEMS IN ENGINEERING, AEROSPACE AND SCIENCES: ICNPAA 2014 Conference date: 15–18 July 2014 Location: Narvik, Norway ISBN: 978-0-7354-1276-7 Editor: Seenith Sivasundaram Volume number: 1637 Published: 10 december 2014 / [ed] Seenith Sivasundaram, American Institute of Physics (AIP), 2014, s. 1110-1119Konferansepaper (Fagfellevurdert)
    Abstract [en]

    T. Persson and S. D. Sivestrov investigated representations of operators satisfying the relation XX* = F(X*X) in connection with periodic points and orbits of the map F. In particular they derived commutativity conditions for two monomials in operators A and B on a Hilbert space satisfying the relation AB = BF(A). In this article we shall apply their results to special one-dimensional dynamical systems and and give an explicit description of the interplay between periodic orbits of one-dimensional piecewise polynomial maps and commutativity of monomials for special operators A and B. Furthermore we shall apply our results to derive conditions on β for the special case when F β is the β–shift dynamical system.

  • 19304.
    Turaev, Michael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen.
    Numerical Experiments in Billiards2016Student paper other, 10 hpOppgave
  • 19305.
    Turesson, Bengt-Ove
    Linköpings universitet, Matematiska institutionen, Tillämpad matematik. Linköpings universitet, Tekniska högskolan.
    Nonlinear potential theory and weighted Sobolev spaces2000Bok (Fagfellevurdert)
    Abstract [en]

    The book systematically develops nonlinear potential theory and the Sobolev space theory covers results concerning approximation, extension, and interpolation, Sobolev and Poincare inequalities, Maz'ya type embedding theorems, and isoperimetric inequalities

  • 19306.
    Turnqvist, Jonas
    Växjö universitet, Fakulteten för matematik/naturvetenskap/teknik, Matematiska och systemtekniska institutionen.
    Silence in mathematics – A dead end: Knowledge about the importance of communication2007Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Syftet med följande examensarbete är att kartlägga den verbala kommunikationens betydelse för undervisningen i matematik inom de tidigare skolåren. Idag är enskild räkning en vanligt förekommande undervisningsform som möter eleverna i skolan. Undervisningen bedrivs enligt inarbetade rutiner och få ställer sig frågan om detta är rätt väg att gå. En av baksidorna är att eleverna kan isoleras och fastna inom sitt eget tänkande. Matematik är ett språk som bygger på förståelse där ett moment kopplas till nästa. Tillsammans eller i grupper kan man lättare lära sig att sätta ord till sina tankar, ge uttryck för sina egna och lyssna till andras redogörelser. Först när man är väl förtrogen med grunderna är man som elev mogen att ta steget vidare. Dessvärre uteblir denna förståelse för många elever idag och minskat intresse för ämnet är en av följderna. I detta arbete kommer litteratur och personer som beskriver alternativa vägar som bygger på ökad kommunikation att lyftas fram. Vid insamlandet av informationen i det här examensarbetet har verksamma lärare intervjuats, samt observerats. Resultatet från de tillfrågade lärarna pekar på att många fördelar och möjligheter finns med alternativa vägar parallellt med läromedlet. Den ökade kommunikationen medför att ingående parter kan lära sig mera och lättare förstå varandra. Elever som tidigare stannat upp i sin utveckling erbjuds fler möjligheter och kan efterhand utvecklas som individer.

  • 19307.
    TUĞLU, ZÜBEYDE
    Linnéuniversitetet, Fakultetsnämnden för naturvetenskap och teknik, Institutionen för datavetenskap, fysik och matematik, DFM.
    Geometric Transformations of the Euclidean Plane2012Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    Klein defined a geometry as a study of the properties of a set S that remain invariant when its elements are subjected to the transformations of some transformation groups. The focus of this thesis is on the definitions, theorems and properties of transformations with a lot of different examples and figures. Also, this thesis aims to teach geometric transformations to future mathematics teachers at the Faculties of Education. In last sections, we will present frieze patterns which are mostly used in our daily life.

  • 19308.
    Tveiten, Ketil
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    B-splines, polytopes and their characteristic D-modulesInngår i: Communications in Algebra, ISSN 0092-7872, E-ISSN 1532-4125Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Given a polytope σ⊂R m  , its characteristic distribution δ σ   generates a D -module which we call the characteristic D -module of σ  and denote by M σ  . More generally, the characteristic distributions of a cell complex K  with polyhedral cells generate a D -module M K  , which we call the characteristic D -module of the cell complex. We prove various basic properties of M K  , and show that under certain mild topological conditions on K , the D -module theoretic direct image of M K   coincides with the module generated by the B -splines associated to the cells of K  (considered as distributions). We also give techniques for computing D -annihilator ideals of polytopes.

  • 19309.
    Tveiten, Ketil
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Period integrals and mutationManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Let f  be a Laurent polynomial in two variables, whose Newton polygon strictly contains the origin and whose vertices are primitive lattice points, and let L f   be the minimal-order differential operator that annihilates the period integral of f . We prove several results about f  and L f   in terms of the Newton polygon of f  and the combinatorial operation of *mutation*, in particular we give an in principle complete description of the monodromy of L f   around the origin. Special attention is given to the class of *maximally mutable* Laurent polynomials, which has applications to the conjectured classification of Fano manifolds via mirror symmetry.

  • 19310.
    Tveiten, Ketil
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen.
    Period integrals and mutation2018Inngår i: Transactions of the American Mathematical Society, ISSN 0002-9947, E-ISSN 1088-6850, Vol. 370, nr 12, s. 8377-8401Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We define what it means for a Laurent polynomial in two variables to be mutable. For a mutable Laurent polynomial we prove several results about f and its period pi(f) in terms of the Newton polygon of f. In particular, we give an in principle complete description of the monodromy of pi(f) around the origin. Special attention is given to the class of maximally mutable Laurent polynomials, which has applications to the conjectured classification of Fano manifolds via mirror symmetry.

  • 19311.
    Tveiten, Ketil
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Period integrals and other direct images of D-modules2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis consists of three papers, each touching on a different aspect of the theory of rings of differential operators and D-modules. In particular, an aim is to provide and make explicit good examples of D-module directimages, which are all but absent in the existing literature.The first paper makes explicit the fact that B-splines (a particular class of piecewise polynomial functions) are solutions to D-module theoretic direct images of a class of D-modules constructed from polytopes.These modules, and their direct images, inherit all the relevant combinatorial structure from the defining polytopes, and as such are extremely well-behaved.The second paper studies the ring of differential operator on a reduced monomial ring (aka. Stanley-Reisner ring), in arbitrary characteristic.The two-sided ideal structure of the ring of differential operators is described in terms of the associated abstract simplicial complex, and several quite different proofs are given.The third paper computes the monodromy of the period integrals of Laurent polynomials about the singular point at the origin. The monodromy is describable in terms of the Newton polytope of the Laurent polynomial, in particular the combinatorial-algebraic operation of mutation plays an important role. Special attention is given to the class of maximally mutable Laurent polynomials, as these are one side of the conjectured correspondance that classifies Fano manifolds via mirror symmetry.

  • 19312.
    Tveiten, Ketil
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Two-sided ideals in the ring of differential operators on a Stanley-Reisner ringManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Let R be a Stanley-Reisner ring (that is, a reduced monomial ring) with coefficients in a domain k, and K its associated simplicial complex. Also let D_k(R) be the ring of k-linear differential operators on R. We give two different descriptions of the two-sided ideal structure of D_k(R) as being in bijection with certain well-known subcomplexes of K; one based on explicit computation in the Weyl algebra, valid in any characteristic, and one valid in characteristic p based on the Frobenius splitting of R. A result of Traves [Tra99] on the D_k(R)-module structure of R is also given a new proof and different interpretation using these techniques.

  • 19313.
    Tydesjö, Patrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Algebra och geometri.
    Limit Laws for First Order Logic on Random Images2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 19314.
    Tyrcha, Joanna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Hertz, John
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). Niels Bohr Institute, Copenhagen, Denmark.
    NETWORK INFERENCE WITH HIDDEN UNITS2014Inngår i: Mathematical Biosciences and Engineering, ISSN 1547-1063, E-ISSN 1551-0018, Vol. 11, nr 1, s. 149-165Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We derive learning rules for finding the connections between units in stochastic dynamical networks from the recorded history of a visible subset of the units. We consider two models. In both of them, the visible units are binary and stochastic. In one model the hidden units are continuous-valued, with sigmoidal activation functions, and in the other they are binary and stochastic like the visible ones. We derive exact learning rules for both cases. For the stochastic case, performing the exact calculation requires, in general, repeated summations over an number of configurations that grows exponentially with the size of the system and the data length, which is not feasible for large systems. We derive a mean field theory, based on a factorized ansatz for the distribution of hidden-unit states, which offers an attractive alternative for large systems. We present the results of some numerical calculations that illustrate key features of the two models and, for the stochastic case, the exact and approximate calculations.

  • 19315.
    Tyrcha, Joanna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen. Matematisk statistik.
    Hertz, John
    Spike pattern distributions in model cortical networks2008Inngår i: COSYNE-Computational and Systems Neuroscience 2008, Salt Lake City, 2008Konferansepaper (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    We can learn something about coding in large populations of neurons from models of the spike pattern distributions constructed from data. In our work, we do this for data generated from computational models of local cortical networks. This permits us to explore how features of the neuronal and synaptic properties of the network are related to those of the spike pattern distribution model. We employ the approach of Schneidman et al [1] and model this distribution by a Sherrington-Kirkpatrick (SK) model: P[S] = Z-1exp(½ΣijJijSiSj+ΣihiSi). In the work reported here, we analyze spike records from a simple model of a cortical column in a high-conductance state for two different cases: one with stationary tonic firing and the other with a rapidly time-varying input that produces rapid variations in firing rates. The average cross-correlation coefficient in the former is an order of magnitude smaller than that in the latter.

    To estimate the parameters Jij and hi we use a technique [2] based on inversion of the Thouless-Anderson-Palmer equations from spin glass theory. We have performed these fits for groups of neurons of sizes from 12 to 200 for tonic firing and from 6 to 800 for the case of the rapidly time-varying “stimulus”. The first two figures show that the distributions of Jij’s in the two cases are quite similar, both growing slightly narrower with increasing N. They are also qualitatively similar to those found by Schneidman et al and by Tkačik et al [3] for data from retinal networks. As in their work, it does not appear to be necessary to include higher order couplings. The means, which are much smaller than the standard deviations, also decrease with N, and the one for tonic firing is less than half that for the stimulus-driven network.

    However, the models obtained never appear to be in a spin glass phase for any of the sizes studied, in contrast to the finding of Tkačik et al, who reported spin glass behaviour at N=120. This is shown in the third figure panel. The x axis is 1/J, where J = N1/2std(Jij) and the y axis is H/J, where H is the total “field” N-1Σi(hi+ΣjJij‹Sj›). The green curve marks the Almeida-Thouless line separating the normal and spin glass phases in this parameter plane. All our data, for N ≤800 (the number of excitatory neurons in the originally-simulated network), lie in the normal region, and extrapolation from our results predicts spin glass behaviour only for N>5000.

    [1] E. Schneidman et al., Nature 440 1007-1012 (2006)

    [2] T. Tanaka, Phys Rev E 58 2302-2310 (1998); H. J. Kappen and F. B Rodriguez, Neural Comp 10 1137-1156 (1998)

    [3] G. Tkačik et al., arXiv:q-bio.NC/0611072 v1 (2006)

  • 19316.
    Tyrcha, Joanna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen. Matematisk statistik.
    Hertz, John
    Testing Algorithms for Extracting Functional Connectivity from Spike Data2008Inngår i: 1st INCF Congress of Neuroinformatics: Databasing and Modeling the Brain, 2008Konferansepaper (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    We can learn something about how large neuronal networks function from models of their spike pattern distributions constructed from data. We do this using the approach introduced by Schneidman et al [1], modeling this distribution by an Ising model: P[S] = Z-1exp(ΣJijSiSj + ΣihiSi). In the work reported here, we explore the accuracy of two algorithms for extracting the model parameters Jij and hi by testing them on data generated by networks in which these parameters are known.

    Both algorithms use, as input, the firing rates and mutual correlations of the neurons in the network. The first algorithm is straightforward Boltzmann learning. It will yield the parameters correctly if the input statistics are known exactly,but it may be very slow to converge. The second, very fast, algorithm [2] is based on inversion of the Thouless-Anderson-Palmer equations from spin glass theory. It is derived from a small-Jij expansion, but it is in principle correct for all Jij when the network is infinitely large and densely connected.

    In practice, however, the rates and correlations used as inputs to the algorithms are estimates based on a finite number of measurements. Therefore, there will be errors in the extracted model parameters. Errors will also occur if the data are incomplete, i.e., if the rates and correlations are not measured for all neurons or all pairs. This case is highly relevant to the experimental situation, since in practice it is only possible to record from a small fraction of the neurons in a network.

    Two particular kinds of error statistics are of special interest: variances of the differences between true and extracted parameters, and variances of the differences between parameters extracted for two independent sets of training data. We study the relation between the two, since the first is what we are interested in but only the second can be computed in the realistic situation, where we do not know the parameters a priori. We also examine the variance of the difference between the true and extracted correlations.

    Finally, we apply the algorithms to the data of Schneidman et al from salamander retinal ganglion neurons.

    References

    --------------------------------------------------------------------------------

    1. E Schneidman et al, Nature 440 1007-1012 (2006); G Tkacik et al, arXiv:q-bio.NC/0611072 (2006)

    2. T Tanaka, Phys Rev E 58 2302-2310 (1998); H J Kappen and F B Rodriguez, Neural Comp 10 1137-1156 (1998)

  • 19317.
    Tyrcha, Joanna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Roudi, Yasser
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). Kavli Institute for Systems Neuroscience, NTNU, Norway.
    Marsili, Matteo
    Hertz, John
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). Niels Bohr Institute, Denmark.
    The effect of nonstationarity on models inferred from neural data2013Inngår i: Journal of Statistical Mechanics: Theory and Experiment, ISSN 1742-5468, E-ISSN 1742-5468, artikkel-id P03005Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Neurons subject to a common nonstationary input may exhibit a correlated firing behavior. Correlations in the statistics of neural spike trains also arise as the effect of interaction between neurons. Here we show that these two situations can be distinguished with machine learning techniques, provided that the data are rich enough. In order to do this, we study the problem of inferring a kinetic Ising model, stationary or nonstationary, from the available data. We apply the inference procedure to two data sets: one from salamander retinal ganglion cells and the other from a realistic computational cortical network model. We show that many aspects of the concerted activity of the salamander retinal neurons can be traced simply to the external input. A model of non-interacting neurons subject to a nonstationary external field outperforms a model with stationary input with couplings between neurons, even accounting for the differences in the number of model parameters. When couplings are added to the nonstationary model, for the retinal data, little is gained: the inferred couplings are generally not significant. Likewise, the distribution of the sizes of sets of neurons that spike simultaneously and the frequency of spike patterns as a function of their rank (Zipf plots) are well explained by an independent-neuron model with time-dependent external input, and adding connections to such a model does not offer significant improvement. For the cortical model data, robust couplings, well correlated with the real connections, can be inferred using the nonstationary model. Adding connections to this model slightly improves the agreement with the data for the probability of synchronous spikes but hardly affects the Zipf plot.

  • 19318. Tysell, Lars
    et al.
    Nordström, Jan
    Uppsala universitet, Avdelningen för teknisk databehandling.
    Accuracy evaluation of the unstructured node-centered finite volume method in aerodynamic computations2007Inngår i: Proc. 10th ISGG Conference on Numerical Grid Generation, Red Hook, NY: Curran Associates , 2007, s. 146-158Konferansepaper (Fagfellevurdert)
  • 19319. Tysell, Lars
    et al.
    Nordström, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Accuracy evaluation of the unstructured node-centered finite volume method in aerodynamic computations2007Inngår i: Proc. 10th ISGG Conference on Numerical Grid Generation, Red Hook, NY: Curran Associates , 2007, s. 146-158Konferansepaper (Fagfellevurdert)
  • 19320.
    Tysk, Johan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Matematik I-5.
    Ekström, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen, Matematik I-5.
    Options written on stocks with known dividends2004Inngår i: Int. J. Theor. Appl. Finance, Vol. 7, s. 901-907Artikkel i tidsskrift (Fagfellevurdert)
  • 19321.
    Tångdahl, Sara
    Örebro universitet, Handelshögskolan vid Örebro universitet.
    Nonresponse bias for some common estimators and its change over time in the data collection process2004Rapport (Annet vitenskapelig)
    Abstract [en]

    In most surveys, the risk of nonresponse is a factor taken into account at the planning stage. Commonly, resources are set aside for a follow-up procedure which aims at reducing the nonresponse rate. However, we should pay attention to the effect of nonresponse, rather than the nonresponse rate itself.

    When considering nonresponse error, i.e. bias and variance, it is not obvious that the resources spent on nonresponse rate reduction efforts are time and money well spent. In this paper we address this issue, focusing on the effect of follow-ups on nonresponse bias. The nonresponse biases for some common estimators are derived, and the change in bias for these estimators is studied under a setup that allows us to take into account the data collection process, and follow-up efforts in particular.

  • 19322.
    Tångdahl, Sara
    Örebro universitet, Handelshögskolan vid Örebro universitet.
    On the evaluation of the cost efficiency of nonresponse rate reduction efforts: some general considerations2006Rapport (Annet vitenskapelig)
    Abstract [en]

    Virtually every survey today suffers from nonresponse to some extent. To counter this, survey administrators and researchers have a host of methods at their disposal, many of which are both expensive and time consuming. Reduction efforts, aiming at reducing the nonresponse rate, are an important part of the data collection process, but commonly also a substantial part of the available survey budget.

    We propose that the effciency of the reduction efforts be evaluated in relation to the costs. In this paper we point in the direction of an evaluation procedure, using a measure of cost effciency, that can be used in an "ideal" situation, where all relevant quantities are known. It can not be applied directly in practice, but will serve as a point of reference when practically feasible approaches are developed.

  • 19323.
    Tångdahl, Sara
    Örebro universitet, Handelshögskolan vid Örebro universitet.
    The variance of some common estimators and its components under nonresponse2005Rapport (Annet vitenskapelig)
    Abstract [en]

    In most surveys, the risk of nonresponse is a factor taken into account at the planning stage. Commonly, resources are set aside for a follow-up procedure which aims at reducing the nonresponse rate. However, we should pay attention to the effect of nonresponse, rather than the nonresponse rate itself. When considering nonresponse error, i.e. bias and variance, it is not obvious that the resources spent on nonresponse rate reduction efforts are time and money well spent.

    In this paper we address this issue, continuing the work begun in Tångdahl (2004), now focusing on the effect of follow-ups on estimator variance. The components of the variance for some common estimators are derived under a setup that allows us to take into account the data collection process, and follow-up efforts in particular.

  • 19324. Törmä, Hans
    et al.
    Lindberg, Magnus
    Örebro universitet, Hälsoakademin.
    Berne, Berit
    Skin barrier disruption by sodium lauryl sulfate-exposure alters the expressions of involucrin, transglutaminase 1, profilaggrin, and kallikreins during the repair phase in human skin in vivo2008Inngår i: Journal of Investigative Dermatology, ISSN 0022-202X, E-ISSN 1523-1747, Vol. 128, nr 5, s. 1212-1219Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Detergents are skin irritants affecting keratinocytes. In this study, healthy volunteers were exposed to water (vehicle) and 1% sodium lauryl sulfate (SLS) under occlusive patch tests for 24 hours. The messenger RNA (mRNA) expression of keratinocyte differentiation markers and of enzymes involved in corneodesmosome degradation was examined in skin biopsies (n=8) during the repair phase (6 hours to 7 days postexposure) using real-time reverse-transcription PCR. It was found that the expression of involucrin was increased at 6 hours, but then rapidly normalized. The expression of transglutaminase 1 exhibited a twofold increase after 24 hours in the SLS-exposed skin. Profilaggrin was decreased after 6 hours. Later (4–7 days), the expression in SLS-exposed areas was >50% above than in control areas. An increased and altered immunofluorescence pattern of involucrin, transglutaminase 1, and filaggrin was also found (n=4). At 6 hours post-SLS exposure, the mRNA expression of kallikrein-7 (KLK-7) and kallikrein-5 (KLK-5) was decreased by 50 and 75%, respectively, as compared with control and water-exposed areas. Thereafter, the expression pattern of KLK-7 and KLK-5 was normalized. Changes in protein expression of KLK-5 were also found. In conclusion, SLS-induced skin barrier defects induce altered mRNA expression of keratinocyte differentiation markers and enzymes degrading corneodesmosomes.

  • 19325. Törner, Anna
    et al.
    Dickman, Paul
    Duberg, Ann-Sofi
    Kristinsson, Sigurdur
    Landgren, Ola
    Björkholm, Magnus
    Svensson, Åke
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    A method to visualize and adjust for selection bias in prevalent cohort studies2011Inngår i: American Journal of Epidemiology, ISSN 0002-9262, E-ISSN 1476-6256, Vol. 174, nr 8, s. 969-76Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Selection bias and confounding are concerns in cohort studies where the reason for inclusion of subjects in the cohort may be related to the outcome of interest. Selection bias in prevalent cohorts is often corrected by excluding observation time and events during the first time period after inclusion in the cohort. This time period must be chosen carefully-long enough to minimize selection bias but not too long so as to unnecessarily discard observation time and events. A novel method visualizing and estimating selection bias is described and exemplified by using 2 real cohort study examples: a study of hepatitis C virus infection and a study of monoclonal gammopathy of undetermined significance. The method is based on modeling the hazard for the outcome of interest as a function of time since inclusion in the cohort. The events studied were "hospitalizations for kidney-related disease" in the hepatitis C virus cohort and "death" in the monoclonal gammopathy of undetermined significance cohort. Both cohorts show signs of considerable selection bias as evidenced by increased hazard in the time period after inclusion in the cohort. The method was very useful in visualizing selection bias and in determining the initial time period to be excluded from the analyses.

  • 19326.
    Törnfeldt, Tobias
    Linköpings universitet, Matematiska institutionen.
    Graph Similarity, Parallel Texts, and Automatic Bilingual Lexicon Acquisition2008Independent thesis Basic level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    In this masters’ thesis report we present a graph theoretical method used for automatic bilingual lexicon acquisition with parallel texts. We analyze the concept of graph similarity and give an interpretation, of the parallel texts, connected to the vector space model. We represent the parallel texts by a directed, tripartite graph and from here use the corresponding adjacency matrix, A, to compute the similarity of the graph. By solving the eigenvalue problem ρS = ASAT + ATSA we obtain the self-similarity matrix S and the Perron root ρ. A rank k approximation of the self-similarity matrix is computed by implementations of the singular value decomposition and the non-negative matrix factorization algorithm GD-CLS. We construct an algorithm in order to extract the bilingual lexicon from the self-similarity matrix and apply a statistical model to estimate the precision, the correctness, of the translations in the bilingual lexicon. The best result is achieved with an application of the vector space model with a precision of about 80 %. This is a good result and can be compared with the precision of about 60 % found in the literature.

  • 19327.
    Törnkvist, Robin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Tychonoff's theorem and its equivalence with the axiom of choice2015Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    In this essay we give an elementary introduction to topology so that we can prove Tychonoff’s theorem, and also its equivalence with the axiom of choice.

  • 19328. Törnquist, Johanna
    Dynamic railway traffic management during disturbances: focus on the complexity imposed by deregulation2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    While the railway traffic volumes in Europe continuously are increasing, the networks are facing difficulties to meet the demand and suffer from congestion and disturbances that cause insufficient reliability. The need to forecast the effects of the disturbances and efficiently re-schedule the traffic becomes evident, and especially in a deregulated network, where several private operators with competing objectives share the same tracks. This paper presents results from an experimental study where five re-scheduling policies were evaluated by simulation using real data: Three optimisation-based policies that minimise the total final delay, the accumulated delay and the delay costs respectively, one First- Come-First-Served policy, and one policy prioritising trains on time. The optimisationbased policies performed overall best, but required more computation time.

  • 19329. Törnquist, Johanna
    Railway traffic disturbance management2006Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    With the increasing traffic volumes in many railway networks and reports on capacity deficiencies that result in insufficient punctuality and reliability, the need for efficient disturbance management solutions becomes evident. This thesis focuses on solutions that aim to minimise the consequences of disturbances for the various stakeholders and specifically on methods for re-scheduling the traffic. Railway traffic re-scheduling is a complex task with many influencing factors to consider and multiple stakeholders with sometimes conflicting interests. This problem is typically handled manually by traffic dispatchers that have a very limited access to support systems to facilitate their decision-making. This limitation hampers the possibilities to achieve sustainable and system-optimal decision-making and to provide the stakeholders with reliable traffic prognoses. We first study how railway traffic system users experience and are affected by the way the disturbances are communicated and handled by the traffic dispatchers. The results indicate that the disturbance-related information provided by the dispatchers is currently insufficient. The stakeholders need to acquire improved prognoses of their traffic and immediate part of the network to internally be able to minimise the negative effects of the disturbances. Furthermore, an analysis of the disturbance management problem structure and how the problem can be modelled is provided. The analysis shows that there exist fundamental restrictions in the traffic system that bounds the traffic flow but also a large number of context-dependent considerations such as sustaining certain connections or prioritising specific trains. The prevalence and feasibility of such considerations are difficult to identify and model. Moreover, the objectives of the disturbance management are vague and partly unclear, and therefore it is also difficult to measure and evaluate the outcome of the corresponding decision-making. Finally, a number of optimisation-based solution approaches with the purpose to facilitate for the dispatchers and their decision-making has been developed. The performance and applicability of the approaches have been evaluated for various disturbance settings using data for parts of the Swedish railway network that currently experience capacity deficiencies. The evaluation has identified certain disturbances characteristics that have a significant influence on the disturbance propagation, and which in some cases complicate the re-scheduling procedure. Furthermore, the significance of applying certain re-scheduling objectives and their correlation with performance measures has been analysed. The analysis shows e.g. that a minimisation of accumulated delays has a tendency to delay more trains than a minimisation of total final delay or total delay costs. An experimental study of the long-term effects when applying a limited planning perspective has also been conducted. The results indicate that solutions which are good on longer-term can be achieved despite the use of a limited planning horizon. In parallel to the optimisation-based approaches, an agent-based conceptual model with emphasis on the interplay between the different components in the railway traffic system has been proposed.

  • 19330.
    Törnqvist, Gustav
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Modelling insurance claims with spatial point processes: An applied case-control study to improve the use of geographical information in insurance pricing2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    An important prerequisite for running a successful insurance business is to predict

    risk. By forecasting the future in as much detail as possible, competitive advantages are

    created in terms of price differentiation. This work aims at using spatial point processes

    to provide a proposal for how the geographical position of the customer can be used

    in developing risk differentiation tools. For spatial variation in claim frequency an approach

    is presented which is common in spatial epidemiology by considering a group of

    policyholders, with and without claims, as a realisation of a multivariate Poisson point

    process in two dimensions. Claim costs are then included by considering the claims as a

    realisation of a point process with continuous marks. To describe the spatial variation in

    relative risk, demographic and socio-economic information from Swedish agencies have

    been used. The insurance data that have been used come from the insurance company If

    Skadeförsäkring AB, where also the work has been carried out. The result demonstrates

    problems with parametric modelling of the intensity of policyholders, which makes it

    difficult to validate the spatial varying intensity of claim frequency. Therefore different

    proposals of non-parametric estimation are discussed. Further, there are no tendencies

    that the selected information is able to explain the variation in claim costs.

  • 19331.
    Törring, Ove
    et al.
    Uppsala universitet, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Samhällsvetenskapliga fakulteten, Institutionen för informationsvetenskap.
    Tallstedt, Leif
    Wallin, Göran
    Lundell, Göran
    Ljunggren, Jan-Gustaf
    Taube, Adam
    Sääf, Maria, Hamberger, Bertil
    The, Thyroid Study Group
    Graves´ Hyperthyroidism: Treatment with Antithyroid Drugs, Surgery or Radioiodine - A prospective, Randomized Study1996Inngår i: Journal of Clinical Endicronology and Metabolism, Vol. 81, nr 8, s. 2986-2993Artikkel i tidsskrift (Fagfellevurdert)
  • 19332.
    Türkkan, Nazife
    et al.
    Högskolan i Jönköping, Högskolan för lärande och kommunikation, HLK, Skolnära forskning, Matematikdidaktik.
    Fransson, Nicklas
    Högskolan i Jönköping, Högskolan för lärande och kommunikation, HLK, Skolnära forskning, Matematikdidaktik.
    IKT och elevers lärande: Hur påverkar IKT elevers intresse och förståelseför matematik?2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Vi är två högskolestudenter som studerar med inriktning mot grundskolans årskurs 4-6. Vi är intresserade av ny teknik och dess påverkan på elever och lärare inom ämnet matematik.Syftet med detta arbete är att undersöka om användning av IKT har effekt på matematikundervisningen och hur det påverkar elevernas lärande i ämnet. I denna uppsats genomförs en studie av relevant litteratur. Den-na studie inriktar sig mot årskurs 4-9 i ämnet matematik och IKT-användning i detta ämne.Resultatet visar att eleverna blir mer aktiva i sin inlärning med hjälp av IKT-verktyg. Eleverna visar på bete-endeförändringar i form av att de blir bättre förberedda för inlärning och att de blir mer engagerade i sin utbildningsprocess. IKT-verktyg i matematikklassrummet ger eleverna möjligheter att samarbeta med var-andra. Ett flertal studier visar att elever med datorbaserad undervisning uppvisar högre kunskapsnivå på tes-ter, än elever med traditionell undervisning. IKT-undervisning ger unika fördelar och bättre provresultat för elever med läs- och skrivsvårigheter. IKT-verktyg kan med fördel inkluderas i prov. Med olika medieverktyg, som exempelvis GeoGebra, kan eleverna se och experimentera med olika matematiska koncept och de kan nå en djupare förståelse än vid användning av exempelvis läroböcker. Inspelning av filmer ger möjlighet till att aktivt utveckla matematikundervisningen och introducera nya begrepp då ljud och bild ger eleverna möj-lighet att förklara hur de tänker

  • 19333.
    Türkkan, Nazife
    et al.
    Högskolan i Jönköping, Högskolan för lärande och kommunikation, HLK, Skolnära forskning, Matematikdidaktik.
    Fransson, Nicklas
    Högskolan i Jönköping, Högskolan för lärande och kommunikation, HLK, Skolnära forskning, Matematikdidaktik.
    När boken inte alltid räcker till: En kvalitativ studie om lärares upplevelser om användning av surfplattor i matematikundervisningen2015Independent thesis Advanced level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Inom ämnet matematik inkluderas surfplattor allt oftare i undervisningen. Syftet med denna studie var att bidra med kunskap om hur grundlärare i årskurs ett till sex upplevt användning av surfplat-tor i matematikundervisningen. I studien riktades intresse mot hur grundlärare använde surfplattor och vilka fördelar respektive nackdelar de såg med denna användning. Studien hade en kvalitativ fe-nomenologisk forskningsansats och materialet samlades in genom intervjuer. Materialet analyse-rades med fokus på att se mönster i lärarnas utsa-gor. Resultatet visade att lärarna utnyttjar surfplat-tor främst för färdighetsträning och för att doku-mentera undervisningen. Lärarna är överlag posi-tiva till användandet av surfplattor i matematikun-dervisningen och fördelar som nämndes var att eleverna erhöll direkt respons, ökad motivation samt att individanpassning underlättades. Eleverna blev självgående och lärarna kunde ägna mer tid åt elever som behövde stöttning. Resultatet visade också att lärarna upplever nackdelar med surfplat-tor i matematikundervisningen, framförallt då tek-niken inte alltid fungerar. Andra nackdelar som nämndes var problem med lagring, att olika appar inte sparar material samt svårigheter med att kon-trollera elevernas aktivitetsnivå.

  • 19334.
    Udawalpola, Rajitha
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Shape Optimization for Acoustic Wave Propagation Problems2010Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Boundary shape optimization is a technique to search for an optimal shape by modifying the boundary of a device with a pre-specified topology. We consider boundary shape optimization of acoustic horns in loudspeakers and brass wind instruments. A horn is an interfacial device, situated between a source, such as a waveguide or a transducer, and surrounding space. Horns are used to control both the transmission properties from the source and the spatial power distribution in the far-field (directivity patterns).

    Transmission and directivity properties of a horn are sensitive to the shape of the horn flare. By changing the horn flare we design transmission efficient horns. However, it is difficult to achieve both controllability of directivity patterns and high transmission efficiency by using only changes in the horn flare. Therefore we use simultaneous shape and so-called topology optimization to design a horn/acoustic-lens combination to achieve high transmission efficiency and even directivity. We also design transmission efficient interfacial devices without imposing an upper constraint on the mouth diameter. The results demonstrate that there appears to be a natural limit on the optimal mouth diameter.

    We optimize brasswind instruments with respect to its intonation properties. The instrument is modeled using a hybrid method between a one-dimensional transmission line analogy for the slowly flaring part of the instrument, and a finite element model for the rapidly flaring part.

    An experimental study is carried out to verify the transmission properties of optimized horn. We produce a prototype of an optimized horn and then measure the input impedance of the horn. The measured values agree reasonably well with the predicted optimal values.

    The finite element method and the boundary element method are used as discretization methods in the thesis. Gradient-based optimization methods are used for optimization, in which the gradients are supplied by the adjoint methods.

  • 19335.
    Udawalpola, Rajitha
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Berggren, Martin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Optimization of an acoustic horn with respect to efficiency and directivity2008Inngår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 73, s. 1571-1606Artikkel i tidsskrift (Fagfellevurdert)
  • 19336.
    Udawalpola, Rajitha
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Wadbro, Eddie
    Berggren, Martin
    Optimization of a variable mouth acoustic horn2011Inngår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 85, s. 591-606Artikkel i tidsskrift (Fagfellevurdert)
  • 19337.
    Udd, Mattias
    et al.
    Linköpings universitet, Institutionen för datavetenskap.
    Pettersson, Niklas
    Linköpings universitet, Institutionen för datavetenskap.
    Analys av bortfall i en uppföljningsundersökning av hälsa2008Independent thesis Basic level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    The LSH-study started in 2003 at the department of Health and Society at the University of Linköping. The purpose of the study was to examine the relationship between life condition, stress and health. A total of 1007 people from ten different health centres in Östergötlands län participated. At the follow up, a couple of years later, 795 of the 1007 participated. 127 of the 212 in the attrition turned down the follow up, twelve people were not invited (for example in case of death) and the rest did not respond at all. The purpose of this paper is to find out in what degree the attrition in the follow up can be predicted using the information from the first survey and which variables are important. The differences between different types of attrition have also been examined. Simple and multiple bi- and multinomial logistic regression have been used in the analysis.

    In total 34 variables were examined and in the final model six variables remained with a significant relation to the attrition. High BMI, regular smoking, high pulse and lack of daily exercise at the first survey were connected to a higher risk for an individual to not participate at the follow up. It is interesting that these factors are considered as risk factors for unhealthy living. Other factors related to a higher attrition were unemployment in the last year before the first survey and if the individual had parents born in another country than Sweden. The risk for attrition increased gradually when more risk factors were shown by the individual. The factors contributing an individual to turn down the follow up instead of not responding at all was if he or she were in the older age segments in the survey or if they were not active in any type of association.

  • 19338.
    Uddbom, Anna
    et al.
    Linnéuniversitetet, Fakultetsnämnden för naturvetenskap och teknik, Institutionen för datavetenskap, fysik och matematik, DFM.
    Conradsson, Ulrika
    Linnéuniversitetet, Fakultetsnämnden för naturvetenskap och teknik, Institutionen för datavetenskap, fysik och matematik, DFM.
    Pedagogisk kartläggning i matematik: en kvalitativ studie av specialpedagogers tillvägagångssätt2011Independent thesis Advanced level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Abstrakt

    En avgörande faktor för att kunna förebygga, avhjälpa eller lindra matematiksvårigheter är ifall pedagoger har kompetens att genomföra en kartläggning, som ger vägledning för fortsatta pedagogiska insatser (Lundberg & Sterner, 2009). Med detta som utgångspunkt var syftet med studien att undersöka yrkesverksamma specialpedagogers syn på kartläggning och yngre elevers räknesvårigheter samt hur de går till väga vid en pedagogisk kartläggning i matematik. Studien har en kvalitativ ansats med semistrukturerad intervju som metod. Deltagarna i undersökningen är två specialpedagoger med gedigen utbildning och erfarenhet inom området. Resultatet av undersökningen visar att informanterna har en formativ syn på kartläggning. De fokuserade på att via individuellt anpassade kartläggningar försöka finna pedagogiska lösningar till svårigheterna. De uppgav flera orsaksförklaringar till att yngre elever hamnade i räknesvårigheter och de använde olika verktyg för att analysera dessa. Det fanns inga rutiner, utan det var specialpedagogens erfarenhet och kompetens som avgjorde, från fall till fall, hur de gick till väga.

  • 19339.
    Uddin, Sheikh Fakhar
    et al.
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Khattak, Ismail Khan
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Spectrum Selection Technique to Satisfy the QoS Requirements in Cognitive Radio Network2012Independent thesis Advanced level (degree of Master (Two Years))Oppgave
    Abstract [en]

    The demand of wireless spectrum is increasing very fast as the field of telecommunication is advancing rapidly. The spectrum was underutilized because of fixed spectrum assignment policy and this valuable spectrum can be utilized efficiently by cognitive radio technology. In this thesis we have studied spectrum selection problems in cognitive radio network. Channel sharing and channel contention problems arise when multiple secondary users tend to select same channel. The thesis work is focused on spectrum selection issue with the aim to minimize the overall system time and to solve the problem of channel contention and channel sharing. The overall system time of secondary connection is an important performance measure to provide quality of service for secondary users in cognitive radio network. We studied two spectrum selection schemes that considerably reduce the overall system time and resolve the problems of channel sharing and channel contention. An analytical model associated with Preemptive Resume Priority (PRP) M/G/1 queuing model has been provided to evaluate the studied spectrum selection scheme. This model also analyzes the effect of multiple handoffs due to arrival of primary users. According to this scheme, the traffic load is distributed among multiple channels to balance the traffic load. Secondary users select the operating channels based on the spectrum selection algorithm. They can intelligently adopt better channel selection scheme by considering traffic statistics and overall transmission time. All simulation scenarios are developed in MATLAB. Based on our result we can conclude that both channel selection schemes considerably reduce the overall transmission time of secondary users in cognitive radio network. The overall transmission time increase with the rise of arrival rate of secondary user. The probability based channel selection scheme perform better with lower arrival rate and sensing based channel selection scheme perform better with higher arrival rate of secondary users. These channel selection schemes help distribute the traffic load of secondary users evenly among multiple channels. Hence, increase the channel utilization and resolve the channel contention problem.

  • 19340.
    Ueckert, Sebastian
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaceutisk biovetenskap.
    Andrew, Marilee A.
    Amgen Inc.
    Karlsson, Mats
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaceutisk biovetenskap.
    Ito, Kaori
    Pfizer Inc.
    Corrigan, Brian
    Pfizer Inc.
    Hooker, Andrew C.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaceutisk biovetenskap.
    Challenges and potential of optimal design in late phase clinical trials through application in Alzheimer’s diseaseManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Optimal design is a methodology that can be a valuable tool for the planning of clinical studies. Current applications however, are largely limited to early phases of the drug development process. The increasing complexity in late phase trials is a major reason why optimal design is not applied at these stages. This work uses the example of Alzheimer's disease to investigate challenges and potential of applying optimal design in late phase clinical trials.

    Information from several sources was used to construct a disease progression model for Alzheimer's disease. The resulting model was used to optimize the study design of an Alzheimer's trial for three distinct metrics: maximal information, minimal number of samples and maximal power to detect a drug effect. Challenges encountered and addressed during the implementation included covariates, dropout and clinical constraints.

    Depending on the optimization criterion used, the optimal designs had 35% a higher efficiency, needed 33% fewer samples to obtain the same amount of information or required 70% fewer individuals to achieve 80% power compared to the reference design.

    Optimal design can improve the design and therefore reduce the costs of late phase trials. Several tools and techniques have been identified to address the main challenges connected to this application.

  • 19341.
    Ueckert, Sebastian
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaceutisk biovetenskap.
    Karlsson, Mats O.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaceutisk biovetenskap.
    Hooker, Andrew C
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaceutisk biovetenskap.
    Accelerating Monte Carlo power studies through parametric power estimation2016Inngår i: Journal of Pharmacokinetics and Pharmacodynamics, ISSN 1567-567X, E-ISSN 1573-8744, Vol. 43, nr 2, s. 223-234Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Estimating the power for a non-linear mixed-effects model-based analysis is challenging due to the lack of a closed form analytic expression. Often, computationally intensive Monte Carlo studies need to be employed to evaluate the power of a planned experiment. This is especially time consuming if full power versus sample size curves are to be obtained. A novel parametric power estimation (PPE) algorithm utilizing the theoretical distribution of the alternative hypothesis is presented in this work. The PPE algorithm estimates the unknown non-centrality parameter in the theoretical distribution from a limited number of Monte Carlo simulation and estimations. The estimated parameter linearly scales with study size allowing a quick generation of the full power versus study size curve. A comparison of the PPE with the classical, purely Monte Carlo-based power estimation (MCPE) algorithm for five diverse pharmacometric models showed an excellent agreement between both algorithms, with a low bias of less than 1.2 % and higher precision for the PPE. The power extrapolated from a specific study size was in a very good agreement with power curves obtained with the MCPE algorithm. PPE represents a promising approach to accelerate the power calculation for non-linear mixed effect models.

  • 19342.
    Uhliarik, Marek
    Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE). Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Tillämpad matematik och fysik (MPE-lab).
    Operator Splitting Methods and Artificial Boundary Conditions for a nonlinear       Black-Scholes equation2010Independent thesis Advanced level (degree of Master (One Year)), 15 poäng / 22,5 hpOppgave
    Abstract [en]

    There are some nonlinear models for pricing financial derivatives which can improve the linear Black-Scholes model introduced by Black, Scholes and Merton. In these models volatility is not constant anymore, but depends on some extra variables. It can be, for example, transaction costs, a risk from a portfolio, preferences of a large trader, etc. In this thesis we focus on these models.

    In the first chapter we introduce some important theory of financial derivatives. The second chapter is devoted to the volatility models. We derive three models concerning transaction costs (RAPM, Leland's  and Barles-Soner's model) and Frey's model which assumes a large (dominant) trader on the market. In the third and in the forth chapter we derive portfolio and make numerical experiments with a free boundary. We use the first order additive and the second order Strang splitting methods. We also use approximations of Barles-Soner's model using the identity function and introduce an approximation with the logarithm function of Barles-Soner's model. These models we finally compare with models where the volatility includes constant transaction costs.

  • 19343.
    Ul Hassan, Mahmood
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Stockhammar, Pär
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Fitting probability distributions to economic growth: a maximum likelihood approach2016Inngår i: Journal of Applied Statistics, ISSN 0266-4763, E-ISSN 1360-0532, Vol. 43, nr 9, s. 1583-1603Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The growth rate of the gross domestic product (GDP) usually carries heteroscedasticity, asymmetry and fat-tails. In this study three important and significantly heteroscedastic GDP series are examined. A Normal, normal-mixture, normal-asymmetric Laplace distribution and a Student's t-Asymmetric Laplace (TAL) distribution mixture are considered for distributional fit comparison of GDP growth series after removing heteroscedasticity. The parameters of the distributions have been estimated using maximum likelihood method. Based on the results of different accuracy measures, goodness-of-fit tests and plots, we find out that in the case of asymmetric, heteroscedastic and highly leptokurtic data the TAL-distribution fits better than the alternatives. In the case of asymmetric, heteroscedastic but less leptokurtic data the NM fit is superior. Furthermore, a simulation study has been carried out to obtain standard errors for the estimated parameters. The results of this study might be used in e.g. density forecasting of GDP growth series or to compare different economies.

  • 19344.
    Ulfat, I.
    et al.
    Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden; Energy and Environment Research Group, Department of Physics, University of Karachi, Karachi, Pakistan.
    Javed, Farrukh
    Energy and Environment Research Group, Department of Physics, University of Karachi, Karachi, Pakistan; Department of Statistics, School of Economics and Management, Lund University, Lund, Sweden.
    Abbasi, F. A.
    Energy & Environment Research Group, Department of Physics, University of Karachi, Karachi, Pakistan; Department of Physics, Government National College, Karachi, Pakistan.
    Kanwal, F.
    Energy & Environment Research Group, Department of Physics, University of Karachi, Karachi, Pakistan .
    Usman, A.
    Pakistan Meteorological Department, Karachi, Pakistan.
    Jahangir, M.
    Energy & Environment Research Group, Department of Physics, University of Karachi, Karachi, Pakistan; Department of Physics, Government National College, Karachi, Pakistan.
    Ahmed, F.
    Energy & Environment Research Group, Department of Physics, University of Karachi, Karachi, Pakistan .
    Estimation of solar energy potential for Islamabad, Pakistan2012Inngår i: / [ed] Chafic Salame, Michel Aillerie, Gaby Khoury, Elsevier, 2012, Vol. 18, s. 1496-1500Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In order to design a solar energy system with optimized performance a thorough knowledge of solar radiation data for a considerably long period (20-25 years) is a pre-requisite. For developing countries like Pakistan, the need of empirical models to assess the feasibility of solar energy utilization seems inevitable due to the absence and scarcity of trustworthy solar radiation data. We present such models for the capital city of Pakistan, Islamabad to estimate global and diffuse solar radiation. It is found that with the exception of monsoon month, solar energy can be utilized very efficiently throughout the year. The models suggested could be used for most of the north-eastern areas of Pakistan, which are similar to Islamabad with respect to the climate and the availability of solar radiation but lack in the record of solar radiation data.

  • 19345.
    Ulrika, Bonnedahl
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för matematik (MA).
    Simonsson, Malin
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för matematik (MA).
    Matematiklyftet, ett lyft för SUM-elever?: En studie om hur den undervisning som förespråkas i Matematiklyftet möter SUM-elevernas särskilda utbildningsbehov i matematik.2016Independent thesis Advanced level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Syftet med den här studien är att utveckla en förståelse för om eller hur den undervisning som förespråkas i Matematiklyftet skapar möjligheter till en ökad måluppfyllelse för SUM-elever (SUM-särskilda utbildningsbehov i matematik)? I studien har en kvalitativ textanalys av innehållet i Matematiklyftets modul ”Taluppfattning och tals användning årskurs 1-3” genomförts för att studera undervisningen och hur den möter SUM-elevernas särskilda utbildningsbehov i matematik.

    Studien visar att Matematiklyftet förordar en undervisning som i hög grad överensstämmer med forskning om lämplig undervisning för SUM-elever men genom studien har några svagheter identifierats. Bland annat har SUM-elever i regel behov av en mer strukturerad, explicit och lärarledd undervisning än vad som huvudsakligen rekommenderas i Matematiklyftet. SUM-elever är även i stort behov av en cyklisk undervisning med repetition och regelbundna återkopplingar till tidigare undervisningsområden något som inte framhävs tydligt i materialet. Trots dessa anmärkningar så menar vi att den undervisning som rekommenderas i Matematiklyftet både stärker och lyfter undervisningens kvalité för alla elever vilket borde skapa möjligheter till en ökad måluppfyllelse.

  • 19346.
    Ulriksson, Marcus
    et al.
    Uppsala universitet, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Armaki, Shahin
    Uppsala universitet, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Analys av prestations- och prediktionsvariabler inom fotboll2017Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Uppsatsen ämnar att försöka förklara hur olika variabler angående matchbilden i en fotbollsmatch påverkar slutresultatet. Dessa variabler är uppdelade i prestationsvariabler och kvalitétsvariabler. Prestationsvariablerna är baserade på prestationsindikatorer inspirerat av Hughes och Bartlett (2002). Kvalitétsvariablerna förklarar hur bra de olika lagen är. Som verktyg för att uppnå syftet används olika klassificeringsmodeller utifrån både prestationsvariablerna och kvalitétsvariablerna. Först undersöktes vilka prestationsindikatorer som var viktigast. Den bästa modellen klassificerade cirka 60 % rätt och rensningar och skott på mål var de viktigaste prestationsvariablerna. Sedan undersöktes vilka prediktionsvariabler som var bäst. Den bästa modellen klassificerade rätt slutresultat cirka 88 % av matcherna. Utifrån vad författarna ansågs vara de viktigaste prediktionsvariablerna skapades en prediktionsmodell med färre variabler. Denna lyckades klassificera rätt cirka 86 % av matcherna. Prediktionsmodellen var konstruerad med spelarbetyg, odds på oavgjort och domare.

  • 19347.
    Umavathi, Jawali C
    et al.
    Department of Mathematics, Gulbarga University, Gulbarga, Karnataka, India, and Department of Engineering, University of Sannio, Benevento, Italy.
    Vajravelu, Kuppalapalle
    Department of Mathematics, University of Central Florida, Orlando, FL 32816, USA,.
    Metri, Prashant G
    Mälardalens högskola, Akademin för utbildning, kultur och kommunikation, Utbildningsvetenskap och Matematik.
    Silvestrov, Sergei
    Mälardalens högskola, Akademin för utbildning, kultur och kommunikation, Utbildningsvetenskap och Matematik.
    Effect of Time-Periodic Boundary TemperatureModulations on the Onset of Convection in aMaxwell Fluid-Nanofluid Saturated Porous Layer2016Inngår i: Engineering Mathematics I: Electromagnetics, Fluid Mechanics, Material Physics and Financial Engineering / [ed] Sergei Silvestrov, Milica Rančić, Springer, 2016, s. 221-245Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    The linear stability of Maxwell fluid-nanofluid flow in a saturated porous layer is examined theoretically when the walls of the porous layers are subjected to time-periodic temperature modulations. A modified Darcy-Maxwell model is used to describe the fluid motion, and the nanofluid model used includes the effects of the Brownian motion. The thermal conductivity and viscosity are considered to be dependent on the nanoparticle volume fraction. A perturbation method based on a small amplitude of an applied temperature field is used to compute the critical value of the Rayleigh number and the wave number. The stability of the system characterized by a critical Rayleigh number is calculated as a function of the relaxation parameter, the concentration Rayleigh number, the porosity parameter, the Lewis number, the heat capacity ratio, the Vad´asz number, the viscosity parameter, the conductivity variation parameter, and the frequency of modulation. Three types of temperature modulations are considered, and the effects of all three types of modulations are found to destabilize the system as compared to the unmodulated system.

  • 19348.
    Umegård, Torbjörn
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen.
    MindReader – An Intelligent Virtual SalesmanA Recommendation System for the Tacton Configurator2001Independent thesis Advanced level (degree of Master (One Year)), 20 poäng / 30 hpOppgave
  • 19349.
    Unnikrishnan, Vishnu
    et al.
    Linköpings universitet, Institutionen för systemteknik, Elektroniska Kretsar och System. Linköpings universitet, Tekniska fakulteten.
    Vesterbacka, Mark
    Linköpings universitet, Institutionen för systemteknik, Elektroniska Kretsar och System. Linköpings universitet, Tekniska fakulteten.
    Linearization of VCO-based ADCs using asynchronous sigma-delta modulation2016Inngår i: 2016 IEEE 59TH INTERNATIONAL MIDWEST SYMPOSIUM ON CIRCUITS AND SYSTEMS (MWSCAS), New York: Institute of Electrical and Electronics Engineers , 2016, s. 842-845Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Asynchronous sigma-delta modulation is investigated as an alternative linearization scheme for all-digital voltage controlled oscillator based analog-to-digital converters, which commonly require digital post processing to achieve good linearity. The modulator output, when used to drive a VCO-based converter, causes the oscillator to operate at two fixed frequencies thereby removing the VCO nonlinearity from the transfer function. A circuit is proposed consisting of a digital block and a passive RC circuit operating as an integrator. Spectre simulation of the design synthesized using a 65 nm standard cell library indicate that a harmonic suppression up to -60 dB is feasible.

  • 19350.
    Unosson, Måns
    Uppsala universitet, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    A Mixed Frequency Steady-State Bayesian Vector Autoregression: Forecasting the Macroeconomy2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis suggests a Bayesian vector autoregressive (VAR) model which allows for explicit parametrization of the unconditional mean for data measured at different frequencies, without the need to aggregate data to the lowest common frequency. Using a normal prior for the steady-state and a normal-inverse Wishart prior for the dynamics and error covariance, a Gibbs sampler is proposed to sample the posterior distribution. A forecast study is performed using monthly and quarterly data for the US macroeconomy between 1964 and 2008. The proposed model is compared to a steady-state Bayesian VAR model estimated on data aggregated to quarterly frequency and a quarterly least squares VAR with standard parametrization. Forecasts are evaluated using root mean squared errors and the log-determinant of the forecast error covariance matrix. The results indicate that the inclusion of monthly data improves the accuracy of quarterly forecasts of monthly variables for horizons up to a year. For quarterly variables the one and two quarter forecasts are improved when using monthly data.

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