| 1361. |
- Limani, Adem, et al.
(författare)
-
On model spaces and density of functions smooth on the boundary
- 2023
-
Ingår i: Revista matemática iberoamericana. - : European Mathematical Society - EMS - Publishing House GmbH. - 0213-2230 .- 2235-0616. ; 39:3, s. 1059-1071
-
Tidskriftsartikel (refereegranskat)abstract
- We characterize the model spaces symbolscript in which functions with smooth boundary extensions are dense. It is shown that such approximations are possible if and only if the singular measure associated to the singular inner factor of 0 is con-centrated on a countable union of Beurling-Carleson sets. In fact, we use a duality argument to show that if there exists a restriction of the associated singular meas-ure which does not assign positive measure to any Beurling-Carleson set, then even larger classes of functions, such as Holder classes and large collections of analytic Sobolev spaces, fail to be dense. In contrast to earlier results on density of functions with continuous extensions to the boundary in symbolscript and related spaces, the existence of a smooth approximant is obtained through a constructive method.
|
|
| 1362. |
- Limani, Adem, et al.
(författare)
-
On the problem of smooth approximations in H(b) and connections to subnormal operators
- 2023
-
Ingår i: Journal of Functional Analysis. - : Elsevier BV. - 0022-1236 .- 1096-0783. ; 284:5
-
Tidskriftsartikel (refereegranskat)abstract
- For the class of de Branges-Rovnyak spaces H(b) of the unit disk D defined by extreme points b of the unit ball of H infinity, we study the problem of approximation of a general function in H(b) by a function with an extension to the unit circle T of some degree of smoothness, for instance satisfying Holder estimates or being differentiable. We will exhibit connections between this question and the theory of subnormal operators and, in particular, we will tie the possibility of smooth approximations to properties of invariant subspaces of a certain subnormal operator. This leads us to several computable conditions on b which are necessary for such approximations to be possible. For a large class of extreme points b we use our result to obtain explicit necessary and sufficient conditions on the symbol b which guarantee the density of functions with differentiable boundary values in the space H(b). These conditions include an interplay between the modulus of b on T and the spectrum of its inner factor.
|
|
| 1363. |
- Lin, Hongzhen, et al.
(författare)
-
Fate of Excitations in Conjugated Polymers : Single-Molecule Spectroscopy Reveals Nonemissive "Dark" Regions in MEH-PPV Individual Chains
- 2009
-
Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 9:12, s. 4456-4461
-
Tidskriftsartikel (refereegranskat)abstract
- Single chains of the conjugated polymer MEH-PPV (poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene)) were studied with wide-field fluorescence microscopy (dispersion in inert polymer matrices) and with fluorescence correlation spectroscopy (chloroform solution). The fluorescence yield of individual molecules in matrices was found to be 1-2 orders of magnitude lower than that in solution and it decreased substantially with increasing chain length. It suggests that isolation of MEH-PPV molecules in polymer matrices creates favorable conditions for photogeneration of nonemissive primary excited states.
|
|
| 1364. |
- Lindahl, Lars, et al.
(författare)
-
Intermediaries and intervenients in normative systems
- 2008
-
Ingår i: Journal of Applied Logic. - : Elsevier BV. - 1570-8683 .- 1570-8691. ; 6:2, s. 229-250
-
Tidskriftsartikel (refereegranskat)abstract
- Many concepts in legal texts are “intermediaries”, in the sense that they serve as links between statements of legal grounds, on one hand, and of legal consequences, on the other. In our paper, an algebraic representation of normative systems is used for distinguishing between different kinds of intermediaries and making the idea of a joining between grounds and consequences more precise. In Section 1, the idea of intermediaries is presented and earlier discussions of the subjects are outlined. In Section 2, we introduce the algebraic framework and develop the formal theory. After introducing our approach to the representation of a normative system, we here present a theory of “intervenients”, seen as a tool for analysing intermediaries. In Section 3, dealing with applications, after presenting a model of the formal theory, suited for the analysis of concepts in normative systems, we apply the theory to a number of examples, introduced in the first part. Finally, in Section 4, we make some remarks on the methodology of intermediate concepts.
|
|
| 1365. |
- Lindahl, Lars, et al.
(författare)
-
Normative positions within an algebraic approach to normative systems
- 2004
-
Ingår i: Journal of Applied Logic. - : Elsevier BV. - 1570-8683 .- 1570-8691. ; 2:1, s. 63-91
-
Tidskriftsartikel (refereegranskat)abstract
- The formal analysis of normative systems as initiated by Alchourrón and Bulygin can be complemented by the analysis of normative positions as pursued by Kanger, Lindahl, Sergot and Jones. The paper is a step towards integrating the two approaches within an algebraic theory of so-called Boolean quasi-orderings (Bqo's). In the general Bqo theory presented, a number of theoretical tools are introduced and elucidated by theorems, in particular those of fragment, connection, coupling and pair coupling. Condition implication structures (cis's) are models of the Bqo theory used for the representation of normative systems. A system of normative positions is introduced as a special kind of cis. The final section is devoted to an example exhibiting a legal mini-system where a cis of normative positions (np-cis) is joined to a descriptive cis.
|
|
| 1366. |
- Lindahl, Lars, et al.
(författare)
-
Normative systems and their revision: an algebraic approach
- 2003
-
Ingår i: Artificial Intelligence and Law. ; 11:2-3, s. 81-104
-
Tidskriftsartikel (refereegranskat)abstract
- The paper discusses normative systems and their revision within an algebraic framework. If a system is logically well-formed, certain norms, called connecting norms, determine the system as a whole. It is maintained that, if the system is well-formed, a relation at least as low as determines a lattice or quasi-lattice of its connecting norms. The ideas are presented mainly in the form of comments on a legal example concerning acquisition of movable property by extinction of another person's previous rights.
|
|
| 1367. |
- Lindahl, Lars, et al.
(författare)
-
Strata of intervenient concepts in normative systems
- 2008
-
Ingår i: Lecture Notes in Artificial Intelligence, LNAI. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 0302-9743 .- 1611-3349. - 3540705244 - 9783540705246 ; LNAI 5076, s. 203-217
-
Konferensbidrag (refereegranskat)abstract
- In a legal system, there are different strata of concepts exhibiting the pattern of a network. Our paper presents an algebraic representation of legal concepts as intermediate between factual events and circumstances on one hand, and deontic positions, on the other. In this representation, we use the notion of "intervenient" as a theoretical tool, defining intervenients in terms of weakest grounds and strongest consequences. Important features of intervenients are different kinds of "minimality", since minimality is relevant for the effective formulation of a normative system, as well as for changes in such a system. By distinguishing different kinds of minimality, a rudimentary typology of intervenients is obtained. The results are illustrated by a legal example concerning "ownership" as an intermediate concept.
|
|
| 1368. |
- Lindahl, Martin
(författare)
-
tmRNA to the rescue : Structural motives for the salvage of stalled ribosomes
- 2010
-
Ingår i: RNA Biology. - : Informa UK Limited. - 1547-6286 .- 1555-8584. ; 7:5, s. 577-581
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- During translation, mRNA molecules are incidentally damaged, leaving the ribosome unable to reach or recognize the stop codon and thus stalled with mRNA and a potentially harmful polypeptide product attached to tRNA in the ribosomal P-site. In bacteria, a process called trans-translation has evolved, where a protein-RNA complex (smpB-tmRNA) mimicks the role of aminoacyl charged tRNA in the ribosomal A-site. The ribosome then resumes protein synthesis guided by an mRNA-like portion of the tmRNA which ends with a stop codon and codes for a peptide sequence susceptible to proteolysis, thus allowing the bacteria to salvage stalled ribosomes and degrade ill-defined and potentially harmful protein products. In this article, we will recollect how structural studies have yielded a model for how the pre-translocation stages of trans-translation employing structural mimicry. We will also discuss possible models for
|
|
| 1369. |
- Lindahl, Viveca, et al.
(författare)
-
Permeability and ammonia selectivity in aquaporin TIP2;1 : linking structure to function
- 2018
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Aquaporin TIP2;1 is a protein channel that is permeable to both water and ammonia. Thestructural origin of ammonia selectivity remains obscure, but experiments have revealed that adouble mutation renders it impermeable to ammonia without affecting water permeability. Here,we aim to reproduce and explain these observations by performing an extensive mutationalstudy using microsecond long molecular dynamics simulations, applying two popular force fields.We calculate permeabilities and free energy profiles along the channel axis, for ammonia andwater. For one force field, the permeability of the double mutant decreases by a factor of 2.5 forwater and a factor of 4 for ammonia, thus increasing the selectivity for water. We attribute thiseffect to decreased entropy of water in the pore, due to the observed increase in pore–waterinteractions and narrower pore. Additionally, we observe spontaneous opening and closing ofthe pore on the cytosolic side, which suggests a gating mechanism for the pore. Our resultsshow that sampling methods and simulation times are sufficient to delineate even subtle effectsof mutations on structure and function and to capture important long-timescale events, butalso underline the importance of improving models further.
|
|
| 1370. |
|
|
