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  • 3701.
    Yue, C.
    et al.
    China.
    Gao, H.
    China.
    Liu, X.
    China.
    Wang, Lihui
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Produktionssystem.
    Liang, S. Y.
    China.
    Analytical prediction of part dynamics and process damping for machining stability analysis2018Ingår i: Procedia CIRP, Elsevier, 2018, s. 1463-1468Konferensbidrag (Refereegranskat)
    Abstract [en]

    The milling of titanium alloy thin-walled parts is confronted with the double challenges of hard to machined materials and hard machined structures. Aiming at the problem that the effect of the damping process is significant and difficult to measure in the process of machining titanium thin-walled parts, the mathematical model of the process damping is established. The tangential and radial ploughing force coefficients that characterize the damping of the process are obtained based on the power spectral density matrix and the principle of energy balance. The structural dynamic modification method is used to solve the nonlinear problem of the workpiece characteristics with the material removal and the change of the relative position of the tool and the workpiece. The time delay differential equation which considers the damping effect of the process and the dynamic characteristic of the workpiece is solved by the full-discretization method, and the three-dimensional stability lobe diagram of the milling thin-walled parts is obtained. A series of experiments have been conducted to verify the accuracy of the stability prediction.

  • 3702.
    Yuecheng, Yang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    Optimal Control Using Microscopic Models for a Pollutant Elimination Problem2017Ingår i: Journal of Systems Science and Complexity, ISSN 1009-6124, E-ISSN 1559-7067, Vol. 30, nr 1, s. 86-100Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Optimal control problem with partial derivative equation (PDE) constraint is a numericalwise difficult problem because the optimality conditions lead to PDEs with mixed types of boundary values. The authors provide a new approach to solve this type of problem by space discretization and transform it into a standard optimal control for a multi-agent system. This resulting problem is formulated from a microscopic perspective while the solution only needs limited the macroscopic measurement due to the approach of Hamilton-Jacobi-Bellman (HJB) equation approximation. For solving the problem, only an HJB equation (a PDE with only terminal boundary condition) needs to be solved, although the dimension of that PDE is increased as a drawback. A pollutant elimination problem is considered as an example and solved by this approach. A numerical method for solving the HJB equation is proposed and a simulation is carried out.

  • 3703. Yun, D.
    et al.
    Ahn, S.
    Proutiere, Alexandre
    KTH.
    Shin, J.
    Yi, Y.
    Multi-armed bandit with additional observations2018Ingår i: SIGMETRICS 2018 - Abstracts of the 2018 ACM International Conference on Measurement and Modeling of Computer Systems, Association for Computing Machinery (ACM), 2018, s. 53-55Konferensbidrag (Refereegranskat)
    Abstract [en]

    We study multi-armed bandit (MAB) problems with additional observations, where in each round, the decision maker selects an arm to play and can also observe rewards of additional arms (within a given budget) by paying certain costs. We propose algorithms that are asymptotic-optimal and order-optimal in their regrets under the settings of stochastic and adversarial rewards, respectively.

  • 3704.
    Zackrisson, Ella
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematisk statistik.
    Evaluation of Hedging Strategies of Asian Options on Electricity at Nord Pool2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This thesis empirically evaluates a geometric Brownian motion and a stochastic volatility model for modeling futures prices and hedging Asian call options on the electricity spot price. Estimation of parameters for the models is done based on historical futures prices of futures contracts with a one month delivery period using nonlinear regression and Maximum Likelihood techniques. The models are tested on 2014 data and tracking error for each model is presented. The tracking error is investigated through the median value, the spread between minimum and maximum value along with value at risk at a 95% level.

    In addition, a third model for modeling spot and futures prices is presented theoretically. It is an exponential additive model with the advantage that it models the future price process from the spot price, instead of modeling the future price process immediately. This bypasses the issue of no information about the future price process during the delivery period, when there is no prices of the futures contracts.

    The aim of this thesis is to compare the simpler geometric Brownian motion to the more complex stochastic volatility model. It is found that the stochastic volatility model performs better when tested on out-of-sample data. The geometric Brownian motion tends to underestimate the electricity prices, despite that 2014 had low pricest compared to the other years in the data sample. In addition, the approximation of the distribution of the future price process under the geometric Brownian motion model gave a bad fit and led to difficulties when estimating the parameters. The stochastic volatility model produced more stable results and gave a better fit for the distribution.

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  • 3705.
    Zackrisson, Samuel
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematik (Avd.).
    Coefficients and zeros of mixed characteristicpolynomials2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Blandade karaktäristiska polynom (MCP) introducerades i Marcus, Spielman och Srivastavas artiklar från 2013 om Ramanujan-grafer och Kadison-Singers förmodan. Såväl kända resultat som öppna problem kan formuleras i termer av koefficienter och rötter hos MCP:er. Bevisen av Marcus, Spielman och Srivastava handlar alla i någon mån om att begränsa rötter till vissa MCP:er. Gurvits generalisering av van der Waerdens permanentförmodan begränsar den konstanta termen hos MCP:er med hjälp av kapaciteten hos ett underliggande polynom.Denna uppsats sammanfattar utvalda resultat om blandade karaktäristiska polynom. Wanless motexempel till en förmodan av Holens och Ðoković diskuteras i detta sammanhang. Det leder till motexempel till en förmodad monotonicitet hos en följd av koefficienter till MCP:er samt till att rötterna hos associerade Laguerrepolynom skulle majorisera de hos andra MCP:er. Slutligen bevisar vi en begränsning av rötterna hos MCP:er till produktpolynom av dubbelt stokastiska matriser motsvarande den gräns som uppstår i beviset av Kadison-Singers förmodan. Beviset bygger på klassiska resultat ur grafteorin av Godsil, Mohar, Heilmann och Lieb.

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  • 3706.
    Zackrisson, Samuel
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Numerisk analys, NA.
    Suspensions with small, spherical particles2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Det finns sällan vare sig tillräckligt med beräkningskraft eller analytiska lösningar för stora flerpartikelsystem i fluidsmekanik och elektrostatik. Simuleringar och numeriska approximationer är därför grundläggande metoder för att studera dessa system. Partiklarnas banor beräknas vanligen utan att direkt beräkna fluidens hastighetsfält. I denna rapport studeras en simuleringsmetod som utnyttjar den spektrala noggrannheten hos fouriertransformen för att finna partikelhastigheterna via fluidens hastighetsfält. Metoden tillämpas på en periodisk kub med en suspension av små, sfäriska partiklar påverkade av gravitationen i en fluid i ett försök att efterlikna beteendet hos ett likadant, icke-periodiska system. Resultat för fåpartikelsystem förklarar kvalitativt formen på lösningsströmningar i förhållande till valet av inerpolation mellan partikelpositioner och rutnät, samt kvantitativt kartlägger vissa konvergensegenskaper hos en viss klass av interpolerande funktioner, cardinal B-splines. Egenskaperna hos denna metod på det periodiska systemet studeras och jämförs med en liknande studie av det icke-periodiska systemet för många, ~1000, partiklar.

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  • 3707.
    Zahedi, Sara
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Numerisk analys, NA.
    A Space-Time Cut Finite Element Method with Quadrature in Time2017Ingår i: Geometrically Unfitted Finite Element Methods and Applications: Proceedings of the UCL Workshop 2016, Cham: Springer, 2017, s. 281-306Kapitel i bok, del av antologi (Refereegranskat)
  • 3708.
    Zahedi, Sara
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Numerical Methods for Fluid Interface Problems2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis concerns numerical techniques for two phase flowsimulations; the two phases are immiscible and incompressible fluids. Strategies for accurate simulations are suggested. In particular, accurate approximations of the weakly discontinuousvelocity field, the discontinuous pressure, and the surface tension force and a new model for simulations of contact line dynamics are proposed.

    In two phase flow problems discontinuities arise in the pressure and the gradient of the velocity field due to surface tension forces and differences in the fluids' viscosity. In this thesis, a new finite element method which allows for discontinuities along an interface that can be arbitrarily located with respect to the mesh is presented. Using standard linear finite elements, the method is for an elliptic PDE proven to have optimal convergence order and a system matrix with condition number bounded independently of the position of the interface.The new finite element method is extended to the incompressible Stokes equations for two fluid systemsand enables accurate approximations of the weakly discontinuous velocity field and the discontinuous pressure.

    An alternative way to handle discontinuities is regularization. In this thesis, consistent regularizations of Dirac delta functions with support on interfaces are proposed. These regularized delta functions make it easy to approximate surface tension forces in level set methods.

    A new model for simulating contact line dynamics is also proposed. Capillary dominated flows are considered and it is assumed that contact line movement is driven by the deviation of the contact angle from its static value. This idea is used together with the conservative level set method. The need for fluid slip at the boundary is eliminated by providing a diffusive mechanism for contact line movement. Numerical experiments in two space dimensions show that the method is able to qualitatively correctly capture contact line dynamics.

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  • 3709.
    Zahedi, Sara
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA (stängd 2012-06-30).
    Knonbichler, Martin
    Uppsala Univ, Uppsala, Sweden .
    Kreiss, Gunilla
    Uppsala University.
    Spurious currents in finite element based level set methods for two-phase flow2012Ingår i: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 69, nr 9, s. 1433-1456Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A study of spurious currents in continuous finite element based simulations of the incompressible Navier-Stokes equations for two-phase flows is presented on the basis of computations on a circular drop in equilibrium. The conservative and the standard level set methods are used. It is shown that a sharp surface tension force, expressed as a line integral along the interface, can give rise to large spurious currents and oscillations in the pressure that do not decrease with mesh refinement. If instead a regularized surface tension representation is used, exact force balance at the interface is possible, both for a fully coupled discretization approach and for a fractional step projection method. However, the numerical curvature calculation introduces errors that cause spurious currents. Different ways to extend the curvature from the interface to the whole domain are discussed and investigated. The impact of using different finite element spaces and stabilization methods is also considered.

  • 3710.
    Zahedi, Sara
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Kreiss, Gunilla
    An unfitted Nitsche method for the incompressible two fluid Stokes systemManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    An easy-to-use finite element method for two fluid Stokes flow, with accurate treatment of jumps in pressure and in velocity gradients at the fluid-fluid interface, is presented. The method allows for an interface not aligned with the grid, and is based on continuous linear finite elements. The jumps at the interface are enforced by a variant of Nitsche's method. Numerical experiments demonstrate optimal convergence order.

  • 3711.
    Zahedi, Sara
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Kreiss, Gunilla
    Gustavsson, Katarina
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    An Interface Capturing Method for Two-Phase Flow with Moving Contact Lines2008Ingår i: Proccedings of the 1st European Conference on Microfluidics 2008, SOCIETE HYDROTECHNIQUE DE FRANCE , 2008Konferensbidrag (Refereegranskat)
  • 3712.
    Zahedi, Sara
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk analys, NA.
    Wadbro, Eddie
    Kreiss, Gunilla
    Berggren, Martin
    A uniformly well-conditioned, unfitted Nitsche method for interface problems: PartIIngår i: SIAM Journal on Numerical Analysis, ISSN 0036-1429, E-ISSN 1095-7170Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    A finite element method for elliptic partial differential equations that allows for discontinuities along an interface not aligned with the mesh is presented.The solution on each side of the interface is separately expanded in standard continuous, piecewise-linear functions, and a variant of Nitsche's method enforces the jump conditions at the interface.In this method, the solutions on each side of the interface are extended to the entire domain, which results in a fixed number of unknowns independent of the location of the interface. A stabilization procedure is included to ensure well-defined extensions. Numerical experiments are presented showing optimal convergence order in the energy and $L^2$ norms, and also for pointwise errors. The presented results also show that the condition number of the system matrix is independent of the position of the interface relative to the grid.

  • 3713.
    Zanello, Fabrizio
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    Improving the bounds of the multiplicity conjecture: The codimension 3 level case2007Ingår i: Journal of Pure and Applied Algebra, ISSN 0022-4049, E-ISSN 1873-1376, Vol. 209, nr 1, s. 79-89Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Multiplicity Conjecture (MC) of Huneke and Srinivasan provides upper and lower bounds for the multiplicity of a Cohen-Macaulay algebra A in terms of the shifts appearing in the modules of the minimal free resolution (MFR) of A. All the examples studied so far have lead to conjecture (see [J. Herzog, X. Zheng, Notes on the multiplicity conjecture. Collect. Math. 57 (2006) 211-226] and [J. Mighore, U. Nagel, T. Romer, Extensions of the multiplicity conjecture, Trans. Amer. Math. Soc. (preprint: math. AC/0505229) (in press)]) that, moreover, the bounds of the MC are sharp if and only if A has a pure MFR. Therefore, it seems a reasonable - and useful - idea to seek better, if possibly ad hoc, bounds for particular classes of Cohen-Macaulay algebras. In this work we will only consider the codimension 3 case. In the first part we will stick to the bounds of the MC, and show that they hold for those algebras whose h-vector is that of a compressed algebra. In the second part, we will (mainly) focus on the level case: we will construct new conjectural upper and lower bounds for the multiplicity of a codimension 3 level algebra A, which can be expressed exclusively in terms of the h-vector of A, and which are better than (or equal to) those provided by the MC. Also, our bounds can be sharp even when the MFR of A is not pure. Even though proving our bounds still appears too difficult a task in general, we are already able to show them for some interesting classes of codimension 3 level algebras A: namely, when A is compressed, or when its h-vector h(A) ends with (.., 3, 2). Also, we will prove our lower bound when h(A) begins with (1, 3, h,), where h(2) : 4, and our upper bound when h (A) ends with (.... h(c-1), h(c)), where h(c-1) < h(c) + 1.

  • 3714.
    Zanello, Fabrizio
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    The h-vector of a relatively compressed level algebra2007Ingår i: Communications in Algebra, ISSN 0092-7872, E-ISSN 1532-4125, Vol. 35, nr 4, s. 1087-1091Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The purpose of this note is to supply an upper and a lower bound (which are in general sharp) for the h-vector of a level algebra which is relatively compressed with respect to any arbitrary level algebra A. The useful concept of relatively compressed algebra was recently introduced in Migliore et al. (2005) (whose investigations mainly focused on the particular case of A a complete intersection). The key idea of this note is the simple observation that the level algebras which are relatively compressed with respect to A coincide (after an obvious isomorphism) with the generic level quotients of suitable truncations of A. Therefore, we are able to apply to relatively compressed algebras the main result of our recent work, Zanello (2007).

  • 3715.
    Zarabi, Patrick
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Denes, August
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Solving the Facility Location Problem using Graph Theory and Shortest Path Algorithms2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Detta examensarbete inom systemteknik och optimeringslära syftar till att lösa ett lagerplaceringsproblem. Lagret ska ställas inom en liten yta med hänsyn till ruttbegränsningar och närhet till andra byggnader. Denna uppsats är begärd av LKAB Kiruna for att underlätta i deras beslut om var ett nytt lager skulle kunna byggas inom deras industriområde. Lagerplaceringsproblemet delades upp i två problem, huvudproblemet var att lokalisera den basta platsen för lagret att byggas. Subproblemet var hur distanser och tillåtna placeringar ska modelleras i denna specifika kontext med rutt- och narhetsbegränsningar. Distans- och platsmodelleringen gjordes genom att skapa en grafrepresentation av industriområdet. Sedan användes Dijkstras kortaste vägen algoritm för att erhålla alla distanser mellan möjliga byggområden och de produktionsanläggningar som behöver tillgång till lagret. Huvudproblemet kunde sedan lösas med hjälp av dessa distanser och en linjär heltalsoptimeringsmodell. Modellen utökades sedan för att tillåta placeringen av två separata lagerbyggnader. Den utökade modellen löstes med hjälp av tre olika implementeringar, en heuristisk algoritm, en ickelinjär heltalsoptimeringsmodell samt en linjär heltalsoptimeringsmodell. 

    Resultaten visade att implementeringen av det ursprungliga lagerplaceringsproblemet konsekvent kunde beräkna optimala lösningar. Den utökade modellen löstes bäst av den linjära heltalsoptimeringsimplementeringen, då denna implementering konsekvent resulterade i bäst (lägst) värde i målfunktion samt löste problemet med låg beräkningstid. Slutligen identifierades flertalet potentiella modellförbättringar som skulle kunna implementeras för att ge modellen mer generaliserbarhet. Detta skulle även innebära att modellen själv kan utvärdera hur många lager som bör byggas givet en satt budget. Således kan modellen även erbjuda mer strategiska beslut om dessa förbättringar implementeras. Ytterligare forskning skulle även kunna göras inom metaheuristik och maskininlärning för att ytterligare förbättra distansmodelleringen.

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  • 3716.
    Zarembo, Konstantin L.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Stockholm, Sweden; Uppsala University, Uppsala, Sweden; Institute for Theoretical and Experimental Physics, Moscow, Russian Federation .
    STRONG-COUPLING PHASES OF PLANAR N=2* SUPER-YANG-MILLS THEORY2014Ingår i: Theoretical and mathematical physics, ISSN 0040-5779, E-ISSN 1573-9333, Vol. 181, nr 3, s. 1522-1530Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The N=2* theory (mass deformation of the N=4 super-Yang-Mills theory) undergoes an infinite number of quantum phase transitions in the large-N limit. The phase structure and critical behavior can be analyzed using supersymmetric localization, which reduces the problem to an effective matrix model. We study this model in the strong-coupling phase.

  • 3717.
    Zetoun, Mirella
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematisk statistik.
    Pricing With Uncertainty: The impact of uncertainty in the valuation models ofDupire and Black&Scholes2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Syftet med dettaexamensarbete är att studera inverkan av osäkerhet, i prissättningen av struktureradeprodukter, som uppkommer på grund av förändringar i volatilitetsytan. I dennastudie värderas olika slags autocall- och kapitalskyddade struktureradeprodukter. Strukturerade produkter har typiskt långa löptider vilket medförosäkerhet i värderingen då mängden data är begränsad och man behöver ta tillextrapolations metoder för att komplettera. En annan faktor som avgörstorleksordningen på osäkerheten är illikviditeten, vilken mäts som spreadenmellan listade Bid och Ask priset. Dessa orsaker ligger bakom intresset attstudera osäkerheten för långa löptider över alla lösenpriser och dess inverkanpå två olika värderingsmodeller.Värderingsmodellerna som används i denna studie är Dupires lokala volatilitetsmodell samt Black&Scholes implicita volatilitets modell. Dessa ställs motvarandra i en jämförelse gällande stabilitet och förmåga att fånga uppvolatilitets ändringar. Man utgår från Mid volatilitetsytan som referens ochuppmäter prisändringar i intervallet från Bid upp till Ask volatilitetsytornagenom att skala Mid ytan. Resultaten indikerar på större prisskillnader inom Dupires modell i jämförelsemot Black&Scholes. Detta kan tolkas som att Dupires modell är mer känslig isammanhanget och har en starkare förmåga att fånga upp förändringar isvansarna. Vidare notering är att priserna beräknade i Dupire är relativtbilligare än motsvarande från Black&Scholes modellen. En ytterligareobservation är att osäkerheten mellan värderingsmodellerna är av högre ordningän inom var modell för sig. Ett annat resultat visar att CPN priset beräknat iBlack&Scholes modell ligger närmast marknadspriset medans marknadsprisetför Autocallen ligger närmare Dupires. Detta kan vara en indikation påosäkerheten i kalibreringsmetoden eventuellt det valda osäkerhetsintervalletoch konstanta extrapolations antagandet.

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  • 3718.
    Zhang, Anda
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematisk statistik.
    Analys av bostadsrättspriset i Stockholms innerstad: En multipel linjär regression2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    I denna studie används en multipel linjär regression för att analysera ett antal variablers inverkan på bostadsrättspriset i Stockholms innerstad. Resultatet kan användas till att prediktera och betrakta procentuella förändringar för slutpriset av en bostadsrätt i Stockholms innerstad. Fem olika modeller konstruerades varefter de analyserades och jämfördes. Modellerna konstrueras med hjälp av data för alla sålda bostadsrätter i Stockholms innerstad mellan åren 2010 - 2014 från fastighetsförmedlingen Erik Olsson. Resultatet av studien visar bland annat att boarean har störst positiv påverkan på slutpriset. Bland stadsdelarna i innerstaden är Östermalm stadsdelen som bidrar mest till ett dyrare bostadsrättspris. Samtliga modeller hade förklaringsgrader på 89%-94%.

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  • 3719.
    Zhang, Anda
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Optimal Path Smoothing using Clothoids for Autonomous Vehicles in the Quarry Environment2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Autonoma fordon är ett område som har fått mycket uppmärksamhet inom forskningen och kommer ha en viktig roll i samhället i framtiden. Introduktionen av självkörande fordon i öppna gruvmiljöer ökar säkerheten för personer som jobbar i dessa kritiska områden och reducerar olyckor från mänskliga misstag. Genom att låta maskinerna vara elektriskt drivna kommer också effektivisera bränsle användningen och minska koldioxidutsläppen.

    Resultaten som har tagits fram i denna uppsats är i samarbete med Volvo Construction Equipment i Eskilstuna, Sverige inom projektet Electric Site. Målet är att transformera den öppna gruvindustrin som använder dieselfordon till att använda självkörande och elektriska fordon vilket ska kunna reducera koldioxidutsläppen med upp till 95 %. I uppsatsen tar vi upp problemet med banplanering av brusig kurvatur från banor som är inspelade från en GPS på en manuell körande bil. Syfte med denna uppsats är att utveckla ett system som kan beskriva banor och släta upp dessa sådan att kurvaturen blir mjuka och autonomt körbara för en lastare.

    För att släta ut banorna använder vi klotoider, som är kurvor med linj ärt varierande kurvatur längs kurvan. Klotoider är ett välanvänt koncept inom vägdesign på grund av mjuka kurvaturegenskaper. Vi löser utslätningsproblemet genom att formulera det som ett optimeringsproblem där vi minimerar antalet klotoidsegment för att undvika onödiga kurvaturvariationer i form av brus.

    Resultaten är framgångsrika och vi lyckas skapa körbara banor för två testbanor som Volvo Construction Equipment använder. Vi skapar också ett grafiskt användergränssnitt i MATLAB för att underlätta användare att skapa klotoidbaserade banor från GPS-koordinater som spelats in.

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  • 3720. Zhang, C.
    et al.
    Kjellström, Hedvig
    KTH, Skolan för datavetenskap och kommunikation (CSC), Robotik, perception och lärande, RPL.
    Mandt, S.
    Determinantal point processes for mini-batch diversification2017Ingår i: Uncertainty in Artificial Intelligence - Proceedings of the 33rd Conference, UAI 2017, AUAI Press Corvallis , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    We study a mini-batch diversification scheme for stochastic gradient descent (SGD). While classical SGD relies on uniformly sampling data points to form a mini-batch, we propose a non-uniform sampling scheme based on the Determinantal Point Process (DPP). The DPP relies on a similarity measure between data points and gives low probabilities to mini-batches which contain redundant data, and higher probabilities to mini-batches with more diverse data. This simultaneously balances the data and leads to stochastic gradients with lower variance. We term this approach Diversified Mini-Batch SGD (DM-SGD). We show that regular SGD and a biased version of stratified sampling emerge as special cases. Furthermore, DM-SGD generalizes stratified sampling to cases where no discrete features exist to bin the data into groups. We show experimentally that our method results more interpretable and diverse features in unsupervised setups, and in better classification accuracies in supervised setups.

  • 3721.
    Zhang, Cheng
    et al.
    Microsoft Res, Cambridge CB1 2FB, England..
    Butepage, Judith
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Robotik, perception och lärande, RPL.
    Kjellström, Hedvig
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Robotik, perception och lärande, RPL.
    Mandt, Stephan
    Advances in Variational Inference2019Ingår i: IEEE Transaction on Pattern Analysis and Machine Intelligence, ISSN 0162-8828, E-ISSN 1939-3539, Vol. 41, nr 8, s. 2008-2026Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many modern unsupervised or semi-supervised machine learning algorithms rely on Bayesian probabilistic models. These models are usually intractable and thus require approximate inference. Variational inference (VI) lets us approximate a high-dimensional Bayesian posterior with a simpler variational distribution by solving an optimization problem. This approach has been successfully applied to various models and large-scale applications. In this review, we give an overview of recent trends in variational inference. We first introduce standard mean field variational inference, then review recent advances focusing on the following aspects: (a) scalable VI, which includes stochastic approximations, (b) generic VI, which extends the applicability of VI to a large class of otherwise intractable models, such as non-conjugate models, mean field approximation or with atypical divergences, and (d) amortized VI, which implements the inference over local latent variables with inference networks. Finally, we provide a summary of promising future research directions.

  • 3722.
    Zhang, Erik
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Integration of IMU and Velodyne LiDAR sensor in an ICP-SLAM framework2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Lokalisering och kartläggning (SLAM) i en okänd miljö är ett viktigt steg för många autonoma system. Den föreslagna lösningen är inte beroende på att hitta nyckelpunkter eller nyckelobjekt. Till skillnad från många andra SLAM baserade metoder så arbetar denna metod med glesa punktmoln där 'generalized ICP' (GICP)algoritmen används för punktmolns registrering. I denna uppsats så föreslås en variant av GICP och undersöker, ifall en tröghetssensor (IMU) kan hjälpa till med SLAM-processen. LiDAR-data som har använts i denna uppsats har varit uppmätta från en Velodyne LiDAR monterat på en ryggsäck, en bil och på en UAV. Resultatet tyder på att IMU-data kan göra algoritmen robustare och från mätningar i stadsmiljö så visar det sig att IMU kan hjälpa till att minska vinkeldrift, vilket är det största felkällan för noggrannhet i det globala koordinat systemet.

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  • 3723.
    Zhang, Haibo
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Österlind, F.
    Soldati, Pablo
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Voigt, T.
    Johansson, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Rapid convergecast on commodity hardware: Performance limits and optimal policies2010Ingår i: SECON 2010 - 2010 7th Annual IEEE Communications Society Conference on Sensor, 2010, Vol. Mesh and Ad Hoc Communications and NetworksKonferensbidrag (Refereegranskat)
    Abstract [en]

    The increased industrial interest in wireless sensor networks demands a shift from optimizing protocols for reporting sporadic events, to solutions for high-rate data collection and dissemination. We study time-optimal convergecast under the communication constraints of commodity sensor network platforms. We propose a novel convergecast model in which packet copying between the microcontroller and the radio transceiver is separated from packet transmission, thereby improving channel utilization and system throughput. Based on this model, we establish the tight lower bound on the number of time slots for convergecast in networks with tree routing topology, and present both centralized and distributed algorithms for computing time-optimal convergecast schedules. Our scheme is memory-efficient as each node buffers at most one packet at any time. We evaluate our scheme in simulation and on real hardware, and show that our scheme can achieve a throughput of 203 kbit/s (86.4% of the theoretical upper bound): up to 86.24 % improvement compared with traditional TDMA-based convergecast. With an optimal routing tree and the maximum MAC layer payload, convergecast in a network with 20 sensor nodes can be completed in only 100ms.

  • 3724.
    Zhang, Han
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Optimizing Networked Systems and Inverse Optimal Control2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis is concerned with the problems of optimizing networked systems, including designing a distributed energy optimal consensus controller for homogeneous networked linear systems, maximizing the algebraic connectivity of a network by projected saddle point dynamics. In addition, the inverse optimal control problems for discrete-time finite time-horizon Linear Quadratic Regulators (LQRs) are considered. The goal is to infer the Q matrix in the quadratic cost function using the observations (possibly noisy) either on the optimal state trajectories, optimal control input or the system output.

    In Paper A, an optimal energy cost controller design for identical networked linear systems asymptotic consensus is considered. It is assumed that the topology of the network is given and the controller can only depend on relative information of the agents. Since finding the control gain for such a controller is hard, we focus on finding an optimal controller among a classical family of controllers which is based on the Algebraic Riccati Equation (ARE) and guarantees asymptotic consensus. We find that the energy cost is bounded by an interval and hence we minimize the upper bound. Further, the minimization for the upper bound boils down to optimizing the control gain and the edge weights of the graph separately. A suboptimal control gain is obtained by choosing Q=0 in the ARE. Negative edge weights are allowed, meaning that "competitions" between the agents are allowed. The edge weight optimization problem is formulated as a Semi-Definite Programming (SDP) problem. We show that the lowest control energy cost is reached when the graph is complete and with equal edge weights. Furthermore, two sufficient conditions for the existence of negative optimal edge weights realization are given. In addition, we provide a distributed way of solving the SDP problem when the graph topology is regular.

    In Paper B, a projected primal-dual gradient flow of augmented Lagrangian is presented to solve convex optimization problems that are not necessarily strictly convex. The optimization variables are restricted by a convex set with computable projection operation on its tangent cone as well as equality constraints. We show that the projected dynamical system converges to one of the saddle points and hence finding an optimal solution. Moreover, the problem of distributedly maximizing the algebraic connectivity of an undirected network by optimizing the "port gains" of each nodes is considered. The original SDP problem is relaxed into a nonlinear programming (NP) problem that will be solved by the aforementioned projected dynamical system. Numerical examples show the convergence of the aforementioned algorithm to one of the optimal solutions. The effect of the relaxation is illustrated empirically with numerical examples. A methodology is presented so that the number of iterations needed to converge is reduced. Complexity per iteration of the algorithm is illustrated with numerical examples.

    In Paper C and D, the inverse optimal control problems over finite-time horizon for discrete-time LQRs are considered. The well-posedness of the inverse optimal control problem is first justified. In the noiseless case, when these observations of the optimal state trajectories or the optimal control input are exact, we analyze the identifiability of the problem and provide sufficient conditions for uniqueness of the solution. In the noisy case, when the observations are corrupted by additive zero-mean noise, we formulate the problem as an optimization problem and prove that the solution to this problem is statistically consistent. The following two scenarios are further considered: 1) the distributions of the initial state and the observation noise are unknown, yet the exact observations on the initial states and the noisy observations on the system output are available; 2) the exact observations on the initial states are not available, yet the observation noises are known to be white Gaussian and the distribution of the initial state is also Gaussian (with unknown mean and covariance). For the first scenario, we show statistical consistency for the estimation. For the second scenario, we fit the problem into the framework of maximum-likelihood and Expectation Maximization (EM) algorithm is used to solve this problem. The performance of the proposed method is illustrated through numerical examples.

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  • 3725.
    Zhang, Han
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Inverse Optimal Control for Finite-Horizon Discrete-time Linear Quadratic Regulator Under Noisy OutputManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    In this paper, the problem of inverse optimal control for finite-horizon discrete-time Linear Quadratic Regulators (LQRs) is considered. The goal of the inverse optimal control problem is to recover the corresponding objective function by the noisy observations. We consider the problem of inverse optimal control in two scenarios: 1) the distributions of the initial state and the observation noise are unknown, yet the exact observations on the initial states and the noisy observations on system output are available; 2) the exact observations on the initial states are not available, yet the observation noises are known white Gaussian and the distribution of the initial state is also Gaussian (with unknown mean and covariance). For the first scenario, we formulate the problem as a risk minimization problem and show that its solution is statistically consistent. For the second scenario, we fit the problem into the framework of maximum-likelihood and Expectation Maximization (EM) algorithm is used to solve this problem. The performance for the estimations are shown by numerical examples.

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  • 3726.
    Zhang, Han
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Inverse Optimal Control for Finite-Horizon Discrete-time Linear Quadratic Regulator Under Noisy OutputManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    In this paper, the problem of inverse optimal control for finite-horizon discrete-time Linear Quadratic Regulators (LQRs) is considered. The goal of the inverse optimal control problem is to recover the corresponding objective function by the noisy observations. We consider the problem of inverse optimal control in two scenarios: 1) the distributions of the initial state and the observation noise are unknown, yet the exact observations on the initial states and the noisy observations on system output are available; 2) the exact observations on the initial states are not available, yet the observation noises are known white Gaussian and the distribution of the initial state is also Gaussian (with unknown mean and covariance). For the first scenario, we formulate the problem as a risk minimization problem and show that its solution is statistically consistent. For the second scenario, we fit the problem into the framework of maximum-likelihood and Expectation Maximization (EM) algorithm is used to solve this problem. The performance for the estimations are shown by numerical examples.

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  • 3727.
    Zhang, Han
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Umenberger, Jack
    Department of Information Technology, Uppsala University, Uppsala, Sweden.
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Inverse optimal control for discrete-time finite-horizon Linear Quadratic Regulators2019Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 110, artikel-id 108593Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we consider the inverse optimal control problem for discrete-time Linear Quadratic Regulators (LQR), over finite-time horizons. Given observations of the optimal trajectories, or optimal control inputs, to a linear time-invariant system, the goal is to infer the parameters that define the quadratic cost function. The well-posedness of the inverse optimal control problem is first justified. In the noiseless case, when these observations are exact, we analyze the identifiability of the problem and provide sufficient conditions for uniqueness of the solution. In the noisy case, when the observations are corrupted by additive zero-mean noise, we formulate the problem as an optimization problem and prove that the solution to this problem is statistically consistent. The performance of the proposed method is illustrated through numerical examples.

  • 3728.
    Zhang, Han
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Umenberger, Jack
    Department of Information Technology, Division of Systems and Control, Uppsala University.
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Inverse Quadratic Optimal Control for Discrete-Time Linear SystemsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    In this paper, we consider the inverse optimal control problem for discrete-time Linear Quadratic Regulators (LQRs), over finite-time horizons. Given observations of the optimal trajectories, or optimal control inputs, to a linear time-invariant system, the goal is to infer the parameters that define the quadratic cost function. The well-posedness of the inverse optimal control problem is first justied. In the noiseless case, when these observations are exact, we analyze the identiability of the problem and provide sufficient conditions for uniqueness of the solution. In the noisy case, when the observations are corrupted by additive zero-mean noise, we formulate the problem as an optimization problem and prove that the solution to this problem is statistically consistent. The performance of the proposed method is illustrated through numerical examples.

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  • 3729.
    Zhang, Han
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Umenberger, Jack
    Department of Information Technology, Division of Systems and Control, Uppsala University.
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Inverse Quadratic Optimal Control for Discrete-Time Linear SystemsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    In this paper, we consider the inverse optimal control problem for discrete-time Linear Quadratic Regulators (LQRs), over finite-time horizons. Given observations of the optimal trajectories, or optimal control inputs, to a linear time-invariant system, the goal is to infer the parameters that define the quadratic cost function. The well-posedness of the inverse optimal control problem is first justied. In the noiseless case, when these observations are exact, we analyze the identiability of the problem and provide sufficient conditions for uniqueness of the solution. In the noisy case, when the observations are corrupted by additive zero-mean noise, we formulate the problem as an optimization problem and prove that the solution to this problem is statistically consistent. The performance of the proposed method is illustrated through numerical examples.

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  • 3730.
    Zhang, Han
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    Wei, Jieqiang
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Yi, Peng
    Washington Univ, Dept Elect & Syst Engn, St Louis, MO USA..
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    Projected primal-dual gradient flow of augmented Lagrangian with application to distributed maximization of the algebraic connectivity of a network2018Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 98, s. 34-41Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, a projected primal-dual gradient flow of augmented Lagrangian is presented to solve convex optimization problems that are not necessarily strictly convex. The optimization variables are restricted by a convex set with computable projection operation on its tangent cone as well as equality constraints. As a supplement of the analysis in Niederlander and Cortes (2016), we show that the projected dynamical system converges to one of the saddle points and hence finding an optimal solution. Moreover, the problem of distributedly maximizing the algebraic connectivity of an undirected network by optimizing the port gains of each nodes (base stations) is considered. The original semi-definite programming (SDP) problem is relaxed into a nonlinear programming (NP) problem that will be solved by the aforementioned projected dynamical system. Numerical examples show the convergence of the aforementioned algorithm to one of the optimal solutions. The effect of the relaxation is illustrated empirically with numerical examples. A methodology is presented so that the number of iterations needed to reach the equilibrium is suppressed. Complexity per iteration of the algorithm is illustrated with numerical examples.

  • 3731. Zhang, Jiangbo
    et al.
    Hong, Yiguang
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    MULTIAGENT OPINION DYNAMICS OF BOUNDED CONFIDENCE WITH NONLOCAL AGGREGATIVE INTERACTION2017Ingår i: SIAM Journal of Control and Optimization, ISSN 0363-0129, E-ISSN 1095-7138, Vol. 2017, nr 55, s. -2573, artikel-id 4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we propose nonlocal aggregative opinion interactions for a bounded-confidence opinion model to demonstrate the fluctuation mechanism, and then study this opinion fluctuation mechanism by both theoretical analyses and numerical simulations. In this proposed agent-based opinion model, there are stubborn agents and regular agents: while each stubborn agent never changes its opinion, a regular agent updates his/her opinion based on selected agents' opinion values and his/her confidence bound. At first, we show that the global fluctuation for opinions of regular agents occurs almost surely if and only if the confidence bound of regular agents is larger than a critical value. Next, we give an estimated probability bound of the local fluctuation for regular agent opinions when the confidence bound is sufficiently small. Finally, we provide upper and lower bounds on the fluctuation strength and the regular agent opinion mean in the case when the global fluctuation occurs almost surely.

  • 3732.
    Zhang, Kuize
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Centra, ACCESS Linnaeus Centre.
    Zhang, L.
    School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an, China.
    Xie, L.
    School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.
    Generalized reversibility of cellular automata2020Ingår i: Communications and Control Engineering, Springer International Publishing , 2020, s. 213-220Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    Reversibility is a fundamental property of microscopic physical systems, implied by the laws of quantum mechanics, which seems to be at odds with the Second Law of Thermodynamics (Schiff 2008; Toffoli and Margolus 1990). Nonreversibility always implies energy dissipation, in practice, in the form of heat. Using reversible cellular automata (CAs) to simulate such systems has caused wide attention since the early days of the investigation of CAs (Toffoli and Margolus 1990; Kari 2005). On the other hand, if a CA is not reversible but reversible over an invariant closed subset, e.g., the limit set (Taaki 2007), it can also be used to describe physical systems locally. In this chapter, (Theorems 11.1, 11.2, and 11.4 were reproduced from Zhang and Zhang (2015) with permission @ 2015 Old City Publishing Inc. Theorems 11.3 and 11.5 were reproduced from Taaki (2007) with permission @ 2007 Old City Publishing Inc.) we present a formal definition to represent this class of generalized reversible CAs, and investigate some of their topological properties. We refer the reader to Zhang and Zhang (2015), Taaki (2007) for further reading. Other variants of generalized reversibility can be found in Castillo-Ramirez and Gadouleau (2017).

  • 3733.
    Zhang, Li
    Filosofi och historia, KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Filosofi och teknikhistoria, Filosofi.
    On Non-Prioritized Multiple Belief Revision2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis investigates a sort of non-prioritized multiple revision, the operation of making up one's mind, and its generalization, the operation of choice revision. Making up one's mind about a sentence is a belief change that takes the agent to a belief state in which either the sentence or its negation is believed. In choice revision, the input information is represented by a set of sentences, and the agent should make a choice on which sentences to be accepted. Apart from being practically important, these operations are technically interesting since the standard approach of intersecting a set of optimal outcomes is not workable.

    Paper I provides a construction based on descriptor revision in which the operation of making up one's mind can be modelled in a ``select-direct'' way, which is different from the traditional ``select-and-intersect'' methodology employed in the AGM model. The article shows that this construction is axiomatically characterized with a set of plausible postulates, and investigates the additional postulates that correlate with properties of the construction.

    Paper II investigates a new modelling for sentential belief revision operations, which is based on a set of relations on sentences named believability relations. It demonstrates that two special kinds of such relations, i.e. H-believability relations and basic believability relations, are faithful alternative models of two typical sentential revision generated from descriptor revision. It also shows that traditional AGM revision operations can be reconstructed from a strengthened variant of the basic believability relation and there exists a close connection between this strengthened believability relation and the standard epistemic entrenchment relation.

    Paper III studies the constructions of choice revision based on descriptor revision and multiple believability relations, which extends the domain of believability relations from sentences to sets of sentences. It is shown that each of two variants of choice revision based on descriptor revision is axiomatically characterized with a set of plausible postulates, assuming that the object language is finite. Furthermore, without assuming a finite language, it is shown that choice revision constructed from multiple believability relations is axiomatically characterized with the same sets of postulates proposed for choice revision derived from descriptor revision, whenever these relations satisfy certain rationality conditions.

    Paper IV explores choice revision on belief bases. A generalized version of expansion operation called partial expansion is introduced for developing models of this kind of choice revision. Based on the partial expansion as well as two multiple contraction operations from the literature, two kinds of choice revision operators on belief bases are constructed. This paper proposes several postulates for such two operators and shows that they can be axiomatically characterized by such postulates. Furthermore, it investigates two kinds of making up one's mind operators generated from these two choice revision operators and presents the axiomatic characterizations of them.

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  • 3734.
    Zhang, Li
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Filosofi och teknikhistoria, Filosofi.
    Hansson, Sven Ove
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Filosofi och teknikhistoria, Filosofi.
    How to make up one's mind2015Ingår i: Logic journal of the IGPL (Print), ISSN 1367-0751, E-ISSN 1368-9894, Vol. 23, nr 4, s. 705-717Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The operation of making up one's mind about a sentence phi is a belief change operation that takes the agent to a belief state in which either phi or phi is believed. Apart from being practically important, this operation is technically interesting since the standard approach of intersecting a set of optimal outcomes is not workable. A construction based on descriptor revision is provided in which the operation can be modelled. This construction is axiomatically characterized with a set of plausible postulates, and additional postulates that correlate with properties of the construction are investigated.

  • 3735. Zhang, Mengmeng
    et al.
    Rizzi, Arthur William
    Assessment of Inverse and Direct Methods for Airfoil and Wing Design2016Ingår i: SIMULATION-DRIVEN MODELING AND OPTIMIZATION, 2016, s. 75-109Konferensbidrag (Refereegranskat)
    Abstract [en]

    The goal of aerodynamic design for airfoils and wings is to improve the performance of the lifting surfaces, e.g., by minimizing the drag. We consider here two approaches, the classical inverse design approach that finds the surface which produces desired pressure distributions, and the direct mathematical optimization based on local parameter searches, that is usually enabled by fast gradient computation, for example, by the adjoint method. The hybrid approach is to combine both of them. Each approach has its own pros and cons. In this chapter the approaches are assessed by application to the design of transonic RAE2822 airfoil and ONERA M6 wing.

  • 3736.
    Zhang, Silun
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Intrinsic Formation and Macroscopic Intervention in Multi-agent Systems2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In this dissertation, we study two problems within the field of the multi-agent systems theory. One is the formation control for multiple reducedattitudes, which are extensively utilized in many pointing applications and under-actuated scenarios for attitude maneuvers. In contrast to most existing methodologies on the formation control, the proposed method does notneed to contain any formation errors in the protocol. Instead, the constructedformation is attributed to geometric properties of the configuration space andthe designed connection topology. We refer to this type of formation controlas intrinsic formation control. Besides, the control protocols proposed in thiswork are designed directly in space S^2 , avoiding to use any attitude parameterizations. Moreover, along the studies, some elementary tools for reducedattitudes control are developed.

    Another problem is a moment-based methodology to modeling and ana-lyzing collective behavior of a group of agents. The theory is applicable fora wide range of applications, such as multi-agent systems with interactionsas well as with leaders and/or control input, and the use of this frameworkcan considerably reduce the computational burden for controlling and ana-lyzing such systems. We therefore propose to develop and use this theory forthe multi-agent applications such as crowd dynamics, opinion dynamics andother macroscopic problems.

    Particularly, in paper A a continuous control law is provided for a reduced attitude system, by which a regular tetrahedron formation can achieveasymptotic stability under a quite large family of gain functions in the con-trol. Then, with a further restriction on the control gain, almost global stability of the tetrahedron formation is also obtained. In this work, we introducea novel coordinates transformation that represents the relative reduced atti-tudes between the agents. The proposed method is an intrinsic formationcontrol that does not need to involve any information of the desired formation beforehand. Another virtue of the method proposed is that only relativeattitude measurement is required.

    Paper B further concerns the formation control of all regular polyhedralconfigurations (also called Platonic solids) for reduced attitudes. Accord-ing to the symmetries possessed by regular polyhedra, a unified frameworkis proposed for their formations. Via using the coordinates transformationpreviously proposed, it is shown that stability of the desired formations canbe provided by stabilizing a constrained nonlinear system. Then, a method-ology to investigate the stability of this type of constrained systems is alsopresented.

    In paper C, we introduce an approach for modeling collective behaviorof a group of agents using moments. We represent the swarming via their dis-tribution and derive a method to estimate the dynamics of the moments. We use this to predict the evolution of the distribution of agents by first computing the moment trajectories and then use this to reconstruct the distributionof the agents. In the latter an inverse problem is solved in order to reconstructa nominal distribution and to recover the macro-scale properties of the groupof agents. The proposed method is applicable for several types of multi-agent systems, including leader-follower systems.

    Paper D considers the problem of tracking and encircling a moving target by agents in the 3-dimensional space. In this work, we show that similardesign techniques proposed for reduced attitudes formations can also be applied to the formation control for point mass systems. Therein, a group ofagents are driven to some desired formation on a spherical surface and simultaneously the center of this spherical formation is kept coinciding withthe target to be tracked. By properly designing communication topology, theagents constitute a cyclic formation along the equator of an encircling sphere.

    In Paper E, a methodology based on differential geometry techniquesis proposed to investigate exponential stability of a formation for reducedattitudes. By such a method, there is no need in finding any relative coordinates, which is typically needed but shown to be difficult when the formationproblem is evolving in a non-Euclidean space. In the paper, the desired formation is treated as an embedding submanifold in (S^2)^N and by using therotation symmetries owned by the attitude dynamics its stability is directlyexamined. Moreover, such a method turns out to be coordinates free, namely,exponential stability of a formation can be completely determined by just investigating any one equilibrium which can result in the formation under anylocal chart of (S^2 )^N . This greatly simplifies the stability analysis for theformation problems.

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  • 3737.
    Zhang, Silun
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori. Harbin Inst Technol, Control & Simulat Ctr, Harbin 150001, Heilongjiang, Peoples R China.
    He, Fenghua
    Hong, Yiguang
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Intrinsic Formation Control of Regular Polyhedra for Reduced Attitudes2017Ingår i: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017, IEEE , 2017, s. 1002-1007Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper addresses formation control of reduced attitudes in which a continuous protocol is proposed for achieving and stabilizing all regular polyhedra (also known as Platonic solids) under a unified framework. The protocol contains only relative reduced attitude measurements and does not depend on any particular parametrization as is usually used in the literature. A key feature of the control proposed is that it is intrinsic in the sense that it does not need to incorporate any information of the desired formation. Instead, the achieved formation pattern is totally attributed to the geometric properties of the space and the designed inter-agent connection topology. Using a novel coordinates transformation, asymptotic stability of the desired formations is proven by studying stability of a constrained nonlinear system. In addition, a methodology to investigate stability of such constrained systems is also presented.

  • 3738.
    Zhang, Silun
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Song, Wenjun
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    He, Fenghua
    Control and Simulation Center, Harbin Institute of Technology, 150001, China.
    Yao, Yu
    Control and Simulation Center, Harbin Institute of Technology, 150001, China.
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Spherical cyclic formation control2016Ingår i: Proceedings of the 35th Chinese Control Conference 2016, IEEE Computer Society, 2016, Vol. 2016, s. 8207-8212, artikel-id 7554663Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we study the problem of tracking and encircling a moving target by agents in 3D. Specifically, a group of agents are driven to some desired formation on a spherical surface and simultaneously keep the center of this spherical formation coinciding with the target to be tracked. In our control design, the desired formation is not used as a reference signal for tracking. Rather by designing communication topology for the agents we can achieve the desired formation using relative positions only. We can also place the desired cyclic formation on the equator if the north pole is specified.

  • 3739.
    Zhang, Tianfang
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematisk statistik.
    Machine learning multicriteria optimization in radiation therapy treatment planning2019Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Inom strålterapiplanering har den senaste forskningen använt maskininlärning baserat på historiskt levererade planer för att automatisera den process i vilken kliniskt acceptabla planer produceras. Jämfört med traditionella angreppssätt, såsom upprepad optimering av en viktad målfunktion eller flermålsoptimering (MCO), har automatiska planeringsmetoder generellt sett fördelarna av lägre beräkningstider och minimal användarinteraktion, men saknar däremot flexibiliteten hos allmänna ramverk som exempelvis MCO. Maskininlärningsmetoder kan vara speciellt känsliga för avvikelser i dosprediktionssteget på grund av särskilda egenskaper hos de optimeringsfunktioner som vanligtvis används för att återskapa dosfördelningar, och lider dessutom av problemet att det inte finns något allmängiltigt orsakssamband mellan prediktionsnoggrannhet och kvalitet hos optimerad plan. I detta arbete presenterar vi ett sätt att förena idéer från maskininlärningsbaserade planeringsmetoder med det väletablerade MCO-ramverket. Mer precist kan vi, givet förkunskaper i form av antingen en tidigare optimerad plan eller en uppsättning av historiskt levererade kliniska planer, automatiskt generera Paretooptimala planer som täcker en dosregion motsvarande uppnåeliga såväl som kliniskt acceptabla planer. I det förra fallet görs detta genom att introducera dos--volym-bivillkor; i det senare fallet görs detta genom att anpassa en gaussisk blandningsmodell med viktade data med förväntning--maximering-algoritmen, modifiera den med exponentiell lutning och sedan använda speciellt utvecklade optimeringsfunktioner för att ta hänsyn till prediktionsosäkerheter.Numeriska resultat för konceptuell demonstration erhålls för ett fall av prostatacancer varvid behandlingen levererades med volymetriskt modulerad bågterapi, där det visas att metoderna utvecklade i detta arbete är framgångsrika i att automatiskt generera Paretooptimala planer med tillfredsställande kvalitet och variation medan kliniskt irrelevanta dosregioner utesluts. I fallet då historiska planer används som förkunskap är beräkningstiderna markant kortare än för konventionell MCO.

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  • 3740.
    Zhang, Zhiyuan
    KTH.
    On topological genericity of the mode-locking phenomenon2020Ingår i: Mathematische Annalen, ISSN 0025-5831, E-ISSN 1432-1807, Vol. 376, nr 1-2, s. 707-728Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study circle homeomorphisms extensions over a strictly ergodic homeomorphism. Under a very mild restriction, we show that the fibered rotation number is locally constant on an open and dense subset of all circle homeomorphisms extensions homotopic to the trivial extension. In the complement of this set, we find a dense subset in which every map is conjugate to a direct product. Our result provides a generalisation of Avila–Bochi–Damanik’s result on SL (2 , R) -cocycles, and Jäger–Wang–Zhou’s result on quasi-periodically forced maps, to a broader setting.

  • 3741.
    Zheltukhin, Oleksandr
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Kharkov Institute of Physics and Technology.
    Inflation versus collapse in brane matter2017Ingår i: Modern Physics Letters A, ISSN 0217-7323, E-ISSN 1793-6632, Vol. 32, nr 36, artikel-id 1750199Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mapping of fundamental branes to their worldsheet (ws) multiplets originating from spontaneous breaking of the Poincaré symmetry is studied. The interaction Lagrangian for fields of the Nambu-Goldstone multiplet is shown to encode R2 gravity on the ws. The power law kp ∼ Tp 3-p 2(p+1) for the SO(D - p - 1) gauge coupling kp as the function of the p-brane tension Tp is assumed. It points to the presence of asymptotic freedom and confinement phases in brane matter. Their connection with collapse and inflation of the branes is discussed.

  • 3742. Zhong, J.
    et al.
    Karasalo, M.
    Cheng, D.
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori. KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Centrum för Autonoma System, CAS.
    New results on non-regular linearization of non-linear systems2007Ingår i: International Journal of Control, ISSN 0020-7179, E-ISSN 1366-5820, Vol. 80, nr 10, s. 1651-1664Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents some new results on non-regular linearization of non-linear systems. Based on a normal form and a non-regular linearization technique developed recently, the paper first provides a set of calculating formulas for the linearization procedure. As an application, the linearization of bilinear systems is investigated. Then, it presents easily veri. able sufficient conditions for the global (semi-global) (approximate) linearization. Finally, an estimate of the region of attraction for the kth degree approximately linearized systems with state feedback control is given, which illustrates one of the advantages of the approximate linearization.

  • 3743. Zhong, Jianghua
    et al.
    Cheng, Daizhan
    Hu, Xiaoming
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    CONSTRUCTIVE STABILIZATION OF QUADRATIC-INPUT NONLINEAR SYSTEMS WITH BOUNDED CONTROLS2008Ingår i: Journal of dynamical and control systems, ISSN 1079-2724, E-ISSN 1573-8698, Vol. 14, nr 4, s. 571-593Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the stabilization of quadratic-input nonlinear systems with bounded controls is considered. According to the type of quadratic-input forms, two cases, namely, positive definite and positive semi-definite, are considered. For the case of positive definiteness, a universal formula for bounded stabilizers is given via a known Lyapunov control function. For the case of positive semidefiniteness, a constructive parametrization of bounded stabilizers is proposed under the assumption that there exists a known Lyapunov control function with respect to a smaller control set than the admissible control set.

  • 3744.
    zhong, Liang
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematik (Avd.).
    Betting on Volatility: A Delta Hedging Approach2011Självständigt arbete på avancerad nivå (magisterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
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  • 3745. Zhong, Yimin
    et al.
    Ren, Kui
    Tsai, Yen-Hsi Richard
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Numerisk analys, NA. University of Texas, United States.
    An implicit boundary integral method for computing electric potential of macromolecules in solvent2018Ingår i: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 359, s. 199-215Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A numerical method using implicit surface representations is proposed to solve the linearized Poisson-Boltzmann equation that arises in mathematical models for the electrostatics of molecules in solvent. The proposed method uses an implicit boundary integral formulation to derive a linear system defined on Cartesian nodes in a narrowband surrounding the closed surface that separates the molecule and the solvent. The needed implicit surface is constructed from the given atomic description of the molecules, by a sequence of standard level set algorithms. A fast multipole method is applied to accelerate the solution of the linear system. A few numerical studies involving some standard test cases are presented and compared to other existing results.

  • 3746.
    Zhou, Tianzhi
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Damping Profile Research for Corpower Ocean's Wave Energy Converter2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    With increasing energy demanding and greenhouse gases from fossil fuel, the need to develop new ways to convert energy in sustainable methods is becoming more and more urgent. Corpower Ocean AB designed a point absorber type wave energy converter to harvest energy from surface wave. To maximize the energy output, phase and amplitude control of the converter are needed. Falnes and Budal proposed latching around 1980s which could deliver almost perfect phase and thusly boost power output, however, the peaky machinery force and power output result from it’s discontinuity remained a problem. A continuous phase control method using a negative spring called WaveSpring which further increased power absorption was recently proposed by Jørgen Hals Todalshaug. Meanwhile, there are more and more promising results indicate it is possible to predict the wave in coming seconds.

    Corpower Ocean’s wave energy converter implements the WaveSpring approach, further more, flywheels are used in the system to increase damping capacity and in the mean time work as a temporary energy storage. In this thesis project, an optimized damping profile making use of wave estimation applying wave to wave control was researched. Optimal damping during regular waves with certain wave height and wave period were first calculated by approximating the wave energy converter using linear oscillation theories. They were then used in wave to wave control by predicting and discretizing irregular ocean waves. The damping was first implemented using only generator and then with a combination of generator and flywheel making use of flywheel equivalent damping and inertia calculated from Fourier decomposition.

    Damping profiles were tested in Corpower Ocean’s simulation model, simulation results showed that the specific wave to wave control significantly increased energy output, and using the combination of flywheel and generator was confirmed effectively decrease the maximum torque requirement of the generator while maintain high energy output.

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  • 3747.
    Zhou, Yang
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematisk statistik.
    Modelling Swedish Inflation Using Market Data2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

     

    Denna studie är ett försök att modellera svensk inflation genom att använda ARIMA-modell och variationer av distributed lag modell med marknadsdata som förklarande variabler. Modellen är konstrukterad på underkomponents nivå av KPI och sedan aggregerad till KPI. Tre metoder prövas i denna studie. I första metoden modelleras underkomponenterna direkt med ARIMA-modeller. I andra metoden används distributed lag modell (DLM) på underkomponenter med signifikant korrelation till marknadsdata, residualen från DLM modelleras i sin tur med ARIMA-modeller. I den tredje metoden ersätter vi DLM med restricted finite distributed lag modell (RFDLM). Resultaten från studien visar att RFDLM är den bästa metoden att modellera inflationen och hade ett RMSE på 20 %. Detta jämfört med den naiva prognosen som hade en RMSE på 32 %. Däremot har RFDLM inte särskilt mycket praktiskt nytta i prognostisering av inflationen då man behöver marknadsdata för prognosperiod i förhand på grund att modellen använder sig av väldigt korta lagg. Däremot skulle modellen kunna ha nytta i scenario byggande med prognoser and antagande på marknadsdata som input.

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  • 3748.
    Zhu, Yunyi
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Numerisk analys, NA.
    Epitope Mapping using Local Alignment Features2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Our immune system uses antibodies to neutralize pathogens such as bacteria and viruses. Antibodies bind to parts of foreign proteins with high efficiency and specificity. We call such parts epitopes. The identification of epitopes, namely epitope mapping, may contribute to various immunological applications such as vaccine design, antibody production and immunological diagnosis.

    Therefore, a fast and reliable method that can predict epitopes from the whole proteome is highly desirable.

     

    In this work we have developed a computational method that predicts epitopes based on sequence information. We focus on using local alignment to extract features from peptides and classifying them using Support Vector Machine. We also propose two approaches to optimize the features. Results show that our method can reliably predict epitopes and significantly outperforms some most commonly used tools.

     

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  • 3749.
    Zickert, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematik (Avd.).
    Furstenberg's conjecture and measure rigidity for some classes of non-abelian affine actions on tori2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    1967 bevisade Furstenberg att mängden {2n3mα(mod 1) | n, m ∈N} är tät i cirkeln för alla irrationella tal α. Furstenberg ligger även bakom följande berömda förmodan: de enda ergodiska måtten påcirkeln som är invarianta under både x 􏰀—> 2x och x 􏰀—> 3x är Lebesguemåttet och mått med ändligt stöd. I det här examensarbetet behandlar vi Furstenbergs sats, Furstenbergs förmodan och Rudolphs sats. Vi följer Matheus presentation av Avilas idéer för ett bevis av en svag variant av Rudolphs sats och vi bevisar att en måttbevarande semigruppverkan under vissa antaganden kan utökas till en semigruppverkan av en större semigrupp. Med hjälp av detta resultat erhåller vi begränsningar av mängden av mått invarianta under vissa klasser av icke-abelska affina verkningar påtorusen. Vi studerar även allmänna egenskaper hos affina abelska och icke-abelska verkningar och vi visar att satser analoga med Furstenbergs sats håller för affina verkningar påcirkeln.

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  • 3750.
    Ziegenhagen, Stephanie
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematik (Avd.).
    En-cohomology with coefficients as functor cohomology2016Ingår i: Algebraic and Geometric Topology, ISSN 1472-2747, E-ISSN 1472-2739, Vol. 16, nr 5, s. 2981-3004Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Building on work of Livernet and Richter, we prove that En -homology and En - cohomology of a commutative algebra with coefficients in a symmetric bimodule can be interpreted as functor homology and cohomology. Furthermore, we show that the associated Yoneda algebra is trivial.

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