| 1. |
- Alexandersson, Erik, et al.
(författare)
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Transcriptional regulation of aquaporins in accessions of Arabidopsis in response to drought stress.
- 2010
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Ingår i: Plant Journal. - 1365-313X. ; 61, s. 650-660
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Tidskriftsartikel (refereegranskat)abstract
- Summary Aquaporins facilitate water transport over cellular membranes and are therefore believed to play an important role in water homeostasis. In higher plants aquaporin-like proteins, also called major intrinsic proteins (MIPs), are divided into 5 subfamilies. We have previously shown that MIP transcription in Arabidopsis thaliana generally is down-regulated in leaves upon drought stress, apart from two members of the Plasma membrane Intrinsic Protein (PIP) subfamily, AtPIP1;4 and AtPIP2;5, which are up-regulated. In order to assess if this regulation is general or accession-specific we monitored gene expression of all PIPs in five Arabidopsis accessions. Overall drought regulation of PIPs was well conserved for all five accessions tested suggesting a general and fundamental physiological role of this drought response. In addition, significant differences among accessions were identified for transcripts of three PIP genes. Principal component analysis showed that most of the PIP transcriptional variation during drought stress could be explained by one variable linked to leaf water content. Promoter-GUS constructs of AtPIP1;4, AtPIP2;5 and also AtPIP2;6, which is unresponsive to drought stress, had distinct expression patterns concentrated to the base of the leaf petioles and parts of the flowers. The presence of drought stress response elements within the 1.6 kb promoter regions of AtPIP1;4 and AtPIP2;5, was demonstrated by comparing transcription of the promoter reporter construct and the endogenous gene upon drought stress. Analysis by ATTED-II and other web-based bioinformatical tools showed that several of the MIPs down-regulated upon drought are strongly co-expressed, whereas AtPIP1;4, AtPIP2;5 and AtPIP2;6 are not co-expressed.
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| 2. |
- Alexandersson, Henrik, 1975, et al.
(författare)
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Fisken i forskningen
- 2019
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Bok (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Alexandersson, Karin, et al.
(författare)
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Let´s Come Together : A Macro-Oriented Model for Organizing the Support o EBP
- 2012
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Ingår i: Implementing Evicence-Informed Practice. International Perspectives. - : Canadian Scholars' Press. - 9781551304014 ; , s. 156-169
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Bokkapitel (refereegranskat)abstract
- In this chapter a macro oriented model for understanding what is needed to develope EBP in socialt welfare work is developed and illustrated.
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| 4. |
- Alexandersson, Per, et al.
(författare)
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A Major-Index Preserving Map on Fillings
- 2017
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Ingår i: The Electronic Journal of Combinatorics. - : The Electronic Journal of Combinatorics. - 1097-1440 .- 1077-8926. ; 24:4
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Tidskriftsartikel (refereegranskat)abstract
- We generalize a map by S. Mason regarding two combinatorial models for key polynomials, in a way that accounts for the major index. Furthermore we define a similar variant of this map, that regards alternative models for the modified Macdonald polynomials at t = 0, and thus partially answers a question by J. Haglund. These maps together imply a certain uniqueness property regarding inversion- and coinversion-free fillings. These uniqueness properties allow us to generalize the notion of charge to a non-symmetric setting, thus answering a question by A. Lascoux and the analogous question in the symmetric setting proves a conjecture by K. Nelson.
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| 5. |
- Alexandersson, Per, et al.
(författare)
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Around multivariate Schmidt-Spitzer theorem
- 2014
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Ingår i: Linear Algebra and its Applications. - : Elsevier BV. - 0024-3795 .- 1873-1856. ; 446, s. 356-368
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Tidskriftsartikel (refereegranskat)abstract
- Given an arbitrary complex-valued infinite matrix $\infmatA=(a_{ij}),$$i=1,\dotsc,\infty;$ $j=1,\dotsc,\infty$ and a positive integer $n$ we introduce anaturally associated polynomial basis $\polybasis_\infmatA$ of$\C[x_0,\dotsc,x_n]$.We discuss some properties of the locus of common zeros of all polynomials in $\polybasis_A$ having a given degree $m$; the latter locus can beinterpreted as the spectrum of the $m\times (m+n)$-submatrix of $\infmatA$ formed by its $m$ first rows and$(m+n)$ first columns. We initiate the study of the asymptotics of these spectra when $m\to \infty$ inthe case when $\infmatA$ is a banded Toeplitz matrix.In particular, we present and partially prove a conjectural multivariate analogof the well-known Schmidt-Spitzer theorem which describes the spectral asymptotics for the sequence of principal minors of an arbitrarybanded Toeplitz matrix.Finally, we discuss relations between polynomial bases $\polybasis_\infmatA$ andmultivariate orthogonal polynomials.
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| 6. |
- Alexandersson, Per, 1987-
(författare)
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Combinatorial Methods in Complex Analysis
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The theme of this thesis is combinatorics, complex analysis and algebraic geometry. The thesis consists of six articles divided into four parts.Part A: Spectral properties of the Schrödinger equationThis part consists of Papers I-II, where we study a univariate Schrödinger equation with a complex polynomial potential. We prove that the set of polynomial potentials that admit solutions to the Schrödingerequation is connected, under certain boundary conditions. We also study a similar result for even polynomial potentials, where a similar result is obtained.Part B: Graph monomials and sums of squaresIn this part, consisting of Paper III, we study natural bases for the space of homogeneous, symmetric and translation-invariant polynomials in terms of multigraphs. We find all multigraphs with at most six edges that give rise to non-negative polynomials, and which of these that can be expressed as a sum of squares. Such polynomials appear naturally in connection to expressing certain non-negative polynomials as sums of squares.Part C: Eigenvalue asymptotics of banded Toeplitz matricesThis part consists of Papers IV-V. We give a new and generalized proof of a theorem by P. Schmidt and F. Spitzer concerning asymptotics of eigenvalues of Toeplitz matrices. We also generalize the notion of eigenvalues to rectangular matrices, and partially prove the a multivariate analogue of the above.Part D: Stretched Schur polynomials This part consists of Paper VI, where we give a combinatorial proof that certain sequences of skew Schur polynomials satisfy linear recurrences with polynomial coefficients.
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| 7. |
- Alexandersson, Per, 1987-, et al.
(författare)
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Discriminants, Symmetrized Graph monomials and Sums of Squares
- 2012
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Ingår i: Experimental Mathematics. - : Informa UK Limited. - 1058-6458 .- 1944-950X. ; 21:4, s. 353-361
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Tidskriftsartikel (refereegranskat)abstract
- In 1878, motivated by the requirements of the invariant the-ory of binary forms, J. J. Sylvester constructed, for every graphwith possible multiple edges but without loops, its symmetrizedgraph monomial, which is a polynomial in the vertex labels ofthe original graph. We pose the question for which graphs thispolynomial is nonnegative or a sum of squares. This problem ismotivated by a recent conjecture of F. Sottile and E. Mukhin onthe discriminant of the derivative of a univariate polynomial andby an interesting example of P. and A. Lax of a graph with fouredges whose symmetrized graph monomial is nonnegative butnot a sum of squares. We present detailed information about sym-metrized graph monomials for graphs with four and six edges,obtained by computer calculations.
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| 8. |
- Alexandersson, Per, et al.
(författare)
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Enumeration of Border-Strip Decompositions and Weil-Petersson Volumes
- 2019
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Ingår i: Journal of Integer Sequences. - : UNIV WATERLOO. - 1530-7638. ; 22:4
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Tidskriftsartikel (refereegranskat)abstract
- We describe an injection from border-strip decompositions of certain diagrams to permutations. This allows us to provide enumeration results as well as q-analogues of enumeration formulas. Finally, we use this injection to prove a connection between the number of border-strip decompositions of the n x 2n rectangle and the Weil-Petersson volume of the moduli space of an n-punctured Riemann sphere.
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| 9. |
- Alexandersson, Per, et al.
(författare)
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LLT polynomials, chromatic quasisymmetric functions and graphs with cycles
- 2018
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Ingår i: Discrete Mathematics. - : ELSEVIER SCIENCE BV. - 0012-365X .- 1872-681X. ; 341:12, s. 3453-3482
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Tidskriftsartikel (refereegranskat)abstract
- We use a Dyck path model for unit-interval graphs to study the chromatic quasisymmetric functions introduced by Shareshian and Wachs, as well as unicellular LLT polynomials, revealing some parallel structure and phenomena regarding their e-positivity. The Dyck path model is also extended to circular arc digraphs to obtain larger families of polynomials, giving a new extension of LLT polynomials. Carrying over a lot of the noncircular combinatorics, we prove several statements regarding the e-coefficients of chromatic quasisymmetric functions and LLT polynomials, including a natural combinatorial interpretation for the e-coefficients for the line graph and the cycle graph for both families. We believe that certain e-positivity conjectures hold in all these families above. Furthermore, beyond the chromatic analogy, we study vertical-strip LLT polynomials, which are modified Hall-Littlewood polynomials.
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| 10. |
- Alexandersson, Per
(författare)
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On Eigenvalues of the Schrodinger Operator with an Even Complex-Valued Polynomial Potential
- 2012
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Ingår i: Computational methods in Function Theory. - : Springer Science and Business Media LLC. - 1617-9447 .- 2195-3724. ; 12:2, s. 465-481
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we generalize several results in the article Analytic continuation of eigenvalues of a quartic oscillator of A. Eremenko and A. Gabrielov [4]. We consider a family of eigenvalue problems for a Schrodinger equation with even polynomial potentials of arbitrary degree d with complex coefficients, and k < (d + 2)/2 boundary conditions. We show that the spectral determinant in this case consists of two components, containing even and odd eigenvalues respectively. In the case with k = (d + 2)/2 boundary conditions, we show that the corresponding parameter space consists of infinitely many connected components.
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