1,721,086 research outputs found
Polynomial algebras and smooth functions in Banach spaces
No full textLet An(X) be the algebra of polynomials on a real Banach space X , which is generated by all continuous polynomials of degree not exceeding n . Let m be the minimal integer such that there is a non-compact m -homogeneous polynomial. Then n>m implies that the uniform closure of An(X) does not contain all polynomials of degree n+1, and hence the chain of closures cl(A_n(X)), n>m is strictly increasing. In the rest of the note we give solutions to three problems concerning the behaviour of smooth functions on Banach spaces posed in the literature. In particular, we construct an example of a uniformly differentiable real valued function f on the unit ball of a certain Banach space X , such that there exists no uniformly differentiable function g on λBX, for any λ>1, which coincides with f in some neighbourhood of the origin
Role of endothelial cells in severe malaria pathogenesis: effects of parasites and antimalarial drugs
No full textEndothelium plays a crucial role in the regulation of vascular homeostasis and permeability. Its adhesion proprieties are highly regulated to allow physiologic functions, such as the migration of leucocytes into tissue, and to avoid pathologic degenerations. In particular, the adhesion of red blood cells (RBC) to endothelial cells (ECs) is involved in pathologies such as sickle cell anaemia, diabetes and malaria.
In severe malaria RBC infected with Plasmodium falciparum (Pf) undergo membrane alterations which cause a receptor-mediated adhesion to endothelium. This phenomenon is called cytoadherence and is responsible for the microvascular occlusions and consequent tissue hypoxia, which are associated with severe malaria. The mechanisms and the molecular pathways activated by cytoadherence are extensively studied due to the high necessity of new adjuvant therapies for severe malaria. The apoptosis of ECs by PRBC is one of the processes described in vitro and in vivo. It is considered critical for the development of the disease but its mechanisms and molecular consequences have not been clarified yet.
Among the drugs used to treat malaria, including the severe forms, the derivatives of artemisinin, an active principle extracted from the plant Artemisia annua, are very important due to their high efficacy and tolerability. Besides their antimalarial activity, this class of molecules is studied for the antiangiogenic and antitumor effect. In a previous work from our laboratory we investigated the antiangiogenic effect of artemisone, one of the newest artemisinin derivatives. In particular, the inhibition of ECs growth and the production of pro-angiogenic cytokines have been demonstrated in different in vitro and ex vivo models.
The aim of this work was to study the role of ECs in malaria considering two aspects: the effect of parasitized RBC (PRBC) and the effect of dihydroartemisinin (DHA), the active metabolite of most artemisinins.
The first part of the project was performed at INSERM/UPMC UMR S511 Faculté de Médecine Pierre et Marie Curie, Paris, under the supervision of Dominique Mazier. We characterised two genes of Pf with putative pro-apoptotic function on pulmonary ECs. Using sera from immunised mice, we demonstrated the nuclear localisation of the proteins encoded by these genes. Therefore, it was not possible to proceed with the functional studies, which consisted in using the antibodies to inhibit the pro-apoptotic function. However, the information obtained is important to further investigate the function of these proteins.
The second part of the thesis reports the studies on the effect of DHA on ECs in hypoxia, which is a condition common to the microvessels of severe malaria patients and to the tumour microenvironment. In the first case hypoxia may contribute to inflammation and endothelial damage, whereas in tumours it is a potent stimulus for the production of new vessels, fundamental to bring nutrients to the tumour mass. We demonstrated that the inhibition of ECs growth by DHA is strongly influenced by the oxygen tension: at low doses (similar to those found in the plasma of malaria patients) DHA is more active in hypoxia, whereas at high doses (more similar to the doses proposed as antiangiogenic and antitumor) it is more effective in normoxia. We verified that DHA induces apoptosis only at high doses and affects the cell cycle via induction of oxidative stress. Further studies are needed to understand the mechanisms of growth inhibition in hypoxia, evidenced at the low doses of DHA, and to envisage the possible therapeutic application of this phenomenon
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
POLYNOMIAL ALGEBRAS AND SMOOTH FUNCTIONS IN BANACH SPACES
Full text linkAccording to the fundamental Stone-Weierstrass theorem, if X is a finite dimensional real Banach space, then every continuous function on the unit ball B_X can be uniformly approximated by polynomials. For infinite dimensional Banach spaces the statement of the Stone-Weierstrass Theorem is false, even if we replace continuous functions by the uniformly continuous ones (which is a natural condition that coincides with continuity in the finite dimensional setting): in fact, on every infinite-dimensional Banach space X there exists a uniformly continuous real function not approximable by continuous polynomials.
The natural problem of the proper generalization of the result for infinite dimensional spaces was posed by Shilov (in the case of a Hilbert space). Aron observed that the uniform closure on B_X of the space of all polynomials of the finite type is precisely the space of all functions which are weakly uniformly continuous on B_X. Since there exist infinite dimensional Banach spaces such that all bounded polynomials are weakly uniformly continuous on B_X (e.g. C_0 or more generally all Banach spaces not containing a copy of l_1 and such that all bounded polynomials are weakly sequentially continuous on B_X), this result gives a very satisfactory solution to the problem. Unfortunately, most Banach spaces, including L_p, do not have this special property. In this case, no characterization of the uniform limits of polynomials is known. But the problem has a more subtle formulation as well. Let us consider the algebras consisting of all polynomials which can be generated by finitely many algebraic operations of addition and multiplication, starting from polynomials on X of degree not exceeding n. Of course, such polynomials can have arbitrarily high degree. It is clear that, if n is the lowest degree such that there exists a polynomial P which is not weakly uniformly continuous, then the we have equalities among the algebras up to n-1 and then we have a strict inclusion. The problem of what happens from n on has been studied in several papers. The natural conjecture appears to be that once the chain of eualities has been broken, it is going to be broken at each subsequent step. The proof of this latter statement given by Hajek in 1996, for all classical Banach spaces, based on the theory of algebraic bases, is unfortunately not entirely correct, as was pointed out by our colleague Michal Johanis. It is not clear to us if the theory of algebraic bases developed therein can be salvaged. Fortunately, the main statement of this theory can be proved using another approach. The complete proof can be found in this thesis. Most of the results in this area are therefore safe.
The main result of this thesis implies all previously known results in this area (all confirming the above conjecture) as special cases.
We also give solutions to three other problems posed in the literature, which are concerning smooth functions rather than polynomials, but which belong to the same field of study of smooth mappings on a Banach space.
The first result is a construction of a non-equivalent C^k-smooth norm on every Banach space admitting a C^k-smooth norm, answering a problem posed in several places in the literature.
We solve a another question by proving that a real Banach space admitting a separating real analytic function whose holomorphic extension is Lipschitz in some strip around X admits a separating polynomial.
Eventually, we solve a problem posed by Benyamini and Lindenstrauss, concerning the extensions of uniformly differentiable functions from the unit ball into a larger set, preserving the values in some neighbourhood of the origin. More precisely, we construct an example of a uniformly differentiable real-valued function f on the unit ball of a certain Banach space X, such that there exists no uniformly differentiable function g on cB_X for any c>1 which coincides with f in some neighbourhood of the origin. To do so, we construct suitable renormings of c_0, based on the theory of W-spaces
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Corrigendum to the paper "Polynomial algebras on classical Banach spaces", Israel journal of mathematics 106 (1998), 209–220
No full textWe give a corrected proof of the main Lemma 2 from the paper in the title (our Corollary 7)
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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