16 research outputs found
Recovering a variable exponent
We consider an inverse problem of recovering the non-linearity in the one
dimensional variable exponent -Laplace equation from the
Dirichlet-to-Neumann map. The variable exponent can be recovered up to the
natural obstruction of rearrangements. The main technique is using a
M\"untz-Sz\'asz theorem after reducing the problem to determining a function
from its -norms.Comment: 20 pages, no figure
Variable exponent Calder\'on's problem in one dimension
We consider one-dimensional Calder\'on's problem for the variable exponent
-Laplace equation and find out that more can be seen than in the
constant exponent case. The problem is to recover an unknown weight
(conductivity) in the weighted -Laplace equation from Dirichlet and
Neumann data of solutions. We give a constructive and local uniqueness proof
for conductivities in restricted to the coarsest sigma-algebra that
makes the exponent measurable.Comment: 28 page
Monotonicity and enclosure methods for the p-Laplace equation
We show that the convex hull of a monotone perturbation of a homogeneous
background conductivity in the -conductivity equation is determined by
knowledge of the nonlinear Dirichlet-Neumann operator. We give two independent
proofs, one of which is based on the monotonicity method and the other on the
enclosure method. Our results are constructive and require no jump or
smoothness properties on the conductivity perturbation or its support.Comment: 18 page
Inverse problems for a model of biofilm growth
A bacterial biofilm is an aggregate of micro-organisms growing fixed onto a
solid surface, rather than floating freely in a liquid. Biofilms play a major
role in various practical situations such as surgical infections and water
treatment. We consider a non-linear PDE model of biofilm growth subject to
initial and Dirichlet boundary conditions, and the inverse coefficient problem
of recovering the unknown parameters in the model from extra measurements of
quantities related to the biofilm and substrate. By addressing and analysing
this inverse problem we provide reliable and robust reconstructions of the
primary physical quantities of interest represented by the diffusion
coefficients of substrate and biofilm, the biomass spreading parameters, the
maximum specific consumption and growth rates, the biofilm decay rate and the
half saturation constant. We give particular attention to the constant
coefficients involved in the leading-part non-linearity, and present a
uniqueness proof and some numerical results. In the course of the numerical
investigation, we have identified extra data information that enables improving
the reconstruction of the eight-parameter set of physical quantities associated
to the model of biofilm growth.Comment: 25 pages, 5 figure
CalderoÌn's problem for p-laplace type equations
We investigate a generalization of CalderĂłnâs problem of recovering the conductivity coeïŹcient in a conductivity equation from boundary measurements. As a model
equation we consider the p-conductivity equation
div Ï |âu|pâ2 âu = 0
with 1 < p < â, which reduces to the standard conductivity equation when p = 2.
The thesis consists of results on the direct problem, boundary determination and
detecting inclusions. We formulate the equation as a variational problem also when
the conductivity Ï may be zero or inïŹnity in large sets. As a boundary determination
result we recover the ïŹrst order derivative of a smooth conductivity on the boundary.
We use the enclosure method of Ikehata to recover the convex hull of an inclusion of
ïŹnite conductivity and ïŹnd an upper bound for the convex hull if the conductivity
within an inclusion is zero or inïŹnite
Expected characteristic in Tunnels & Trolls character creation, with generalizations
In the roleplaying game Tunnels & Trolls the characteristics of player characters are determined by rolling dice in the following manner: First, one rolls three dice and calculates their sum. If the three dice all give the same result, another three dice are rolled and added to the total. This is continued until the three dice no longer match. We calculate the average result of the stochastic sum: 10 + 4 / 5. We also consider a generalized dice rolling scheme where we roll an arbitrary number of dice with an arbitrary number of sides. This generalization is motivated by various exotic dice that are used in many roleplaying games. We calculate the expectation, and how much it differs from the situation where we only roll the set of dice once, with no rerolling and adding. As the number of dice increases, or the number of sides the dice have increases, this difference approaches zero, unless there are two dice (with the number of sides increasing), in which case the difference approaches one
A posteriori-virhearvio Uzawan algoritmille Stokesin yhtÀlön ratkaisemiseksi
TÀssÀ tutkielmassa esitÀn ensin lyhyesti Sobolevin avaruudet, totean joitakin epÀyhtÀlöitÀ ja Stokesin yhtÀlön ajasta riippumattoman, englanniksi stationary, version. Jatkan todistamalla ratkaisun löytymisen Stokesin ongelmaan etsimÀllÀ Lagrangen funktion satulapisteen -- tÀmÀn todistuksen yksityiskohdat olen tarkastanut itse, vaikka todistus seuraakin hyvin tarkasti S. Repinin kirjasta \cite{repin2008} löytyvÀÀ tekstiÀ. Kappaleessa \ref{aposterioriarvio} kerron lyhyesti a~posteriori-tyylisen virhearvion luonteesta sekÀ totean erÀÀn Stokesin yhtÀlöÀ koskevan arvion. Seuraavassa kappaleessa esitÀn Uzawan algoritmin suoraan Stokesin yhtÀlöÀ varten. ViimeisessÀ kappaleessa esitÀn vihdoin kaksi a posteriori-tyypin virhearviota Uzawan algoritmin avulla saaduille nopeuskentille. Viimeisen kappaleen laskut ovat suureksi osaksi omiani. Ideat antoi S. Repin. KirjallisuusviitettÀ nimenomaan tÀlle arviolle ei kÀsittÀÀkseni löydy
CalderĂłn problem for the p-Laplace equation : First order derivative of conductivity on the boundary
We recover the gradient of a scalar conductivity defined on a smooth bounded open set in Rd from the Dirichlet to Neumann map arising from the p-Laplace equation. For any boundary point we recover the gradient using Dirichlet data supported on an arbitrarily small neighbourhood of the boundary point. We use a Rellich-type identity in the proof. Our results are new when p 6 = 2. In the p = 2 case boundary determination plays a role in several methods for recovering the conductivity in the interior.peerReviewe
Hamilton-Jacobi equations
TÀmÀ Pro gradu-tutkielma kÀsittelee Hamiltonin ja Jacobin yhtÀlöitÀ, jotka kuvaavat mekaanisen jÀrjestelmÀn kehitystÀ klassisen mekaniikan puitteissa. Hamiltonin ja Jacobin yhtÀlöitÀ kÀytetÀÀn myös sÀÀtöteoriassa sekÀ kvanttimekaniikassa. Hamiltonin mekaaniikan kehitti Sir William Rowan Hamilton valon kÀytöksen mallintamiseen ja Carl Gustav Jacob Jacobi kehitti sitÀ edelleen.
Tutkielmassa annamme ehdot, joiden nojalla Hopfin ja Laxin kaava antaa ratkaisun Hamiltonin ja Jacobin yhtÀlöihin liittyvÀÀn alkuarvo-ongelmaan. Sen jÀlkeen mÀÀritÀmme sopivan heikon ratkaisun kÀsitteen ja nÀytÀmme heikkojen ratkaisujen olevan yksikÀsitteisiÀ tietyillÀ ehdoilla. LÀhestymme Hamiltonin ja Jacobin alkuarvo-ongelmaa asettamalla variaatio-ongelman, jonka Hopfin ja Laxin kaava ratkaisee. Osoitamme, ettÀ Hopfin ja Laxin kaavan antama ratkaisuehdokas on Lipschitz-jatkuva ja toteuttaa dynaamisen ohjelmoinnin periaatteen, joka kytkee sen optimaalisen sÀÀdön teoriaan. Sen jÀlkeen nÀytÀmme, ettÀ Hopfin ja Laxin kaavan antama funktio todella ratkaisee Hamiltonin ja Jacobin yhtÀlön alkuarvo-ongelman.
TÀrkeÀ työkalu Hopfin ja Laxin kaavan kÀsittelyssÀ on Legendren muunnos, joka muuntaa funktion sen konveksiksi duaaliksi. NÀytÀmme, ettÀ konvekseille ja tarpeeksi nopeasti kasvaville funktioille Legendren muunnos sovellettuna kahteen kertaan antaa alkuperÀisen funktion takaisin. Tutkielmassa tutkitaan Hamiltonin ja Lagrangen funktioita, jotka tÀyttÀvÀt nÀmÀ ehdot.
Lopuksi mÀÀrittelemme, mitÀ tarkoitamme heikolla ratkaisulla Hamiltonin ja Jacobin yhtÀlön alkuarvo-ongelmaan. MÀÀritelmÀssÀ kÀytÀmme semikonkaaveja funktioita. Osoitamme, ettÀ alkuehtojen semikonkaavius tai Hamiltonin funktion vahva konveksisuus takaavat heikkojen ratkaisuiden semikonkaaviuden, ja ettÀ semikonkaaveja ratkaisuja voi olla vain yksi, kunhan alkuarvo-ongelma tÀyttÀÀ sopivat sÀÀnnöllisyysehdot