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Search Results: 1 - 10 of 325271 matches for " S; Wirths "
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On Some Problems of James Miller
Bhowmik,B; Ponnusamy,S; Wirths,K.-J;
Cubo (Temuco) , 2010, DOI: 10.4067/S0719-06462010000100003
Abstract: we consider the class of meromorphic univalent functions having a simple pole at and that map the unit disc onto the exterior of a domain which is starlike with respect to a point . we denote this class of functions by . in this paper, we find the exact region of variability for the second taylor coefficient for functions in . in view of this result we rectify some results of james miller.
On Some Problems of James Miller
B Bhowmik,S Ponnusamy,K.-J Wirths
Cubo : A Mathematical Journal , 2010,
Abstract: We consider the class of meromorphic univalent functions having a simple pole at and that map the unit disc onto the exterior of a domain which is starlike with respect to a point . We denote this class of functions by . In this paper, we find the exact region of variability for the second Taylor coefficient for functions in . In view of this result we rectify some results of James Miller. Consideramos la clase de funciones univalentes meromoforficos teniendo un polo simple en y la aplicación del disco unitario sobre el exterior de un dominio el cual es estrellado con respecto al punto . Denotamos esta clase de funciones por . En este artículo encontramos la región exacta de variabilidad del segundo coeficiente de Taylor para funciones in . En vista de estos resultados nosotros rectificamos algunos resultados de James Miller.
On the Fekete-Szeg? problem for concave univalent functions
B. Bhowmik,S. Ponnusamy,K-J. Wirths
Mathematics , 2010,
Abstract: We consider the Fekete-Szeg\"o problem with real parameter $\lambda$ for the class $Co(\alpha)$ of concave univalent functions.
Domains of variability of Laurent coefficients and the convex hull for the family of concave univalent functions
B. Bhowmik,S. Ponnusamy,K-J. Wirths
Mathematics , 2010,
Abstract: Let $\ID$ denote the open unit disc and let $p\in (0,1)$. We consider the family $Co(p)$ of functions $f:\ID\to \overline{\IC}$ that satisfy the following conditions: \bee \item[(i)] $f$ is meromorphic in $\ID$ and has a simple pole at the point $p$. \item[(ii)] $f(0)=f'(0)-1=0$. \item[(iii)] $f$ maps $\ID$ conformally onto a set whose complement with respect to $\overline{\IC}$ is convex. \eee We determine the exact domains of variability of some coefficients $a_n(f)$ of the Laurent expansion $$f(z)=\sum_{n=-1}^{\infty} a_n(f)(z-p)^n,\quad |z-p|<1-p, $$ for $f\in Co(p)$ and certain values of $p$. Knowledge on these Laurent coefficients is used to disprove a conjecture of the third author on the closed convex hull of $Co(p)$ for certain values of $p$.
Characterization and the pre-Schwarzian norm estimate for concave univalent functions
B. Bhowmik,S. Ponnusamy,K-J. Wirths
Mathematics , 2010,
Abstract: Let $Co(\alpha)$ denote the class of concave univalent functions in the unit disk $\ID$. Each function $f\in Co(\alpha)$ maps the unit disk $\ID$ onto the complement of an unbounded convex set. In this paper we find the exact disk of variability for the functional $(1-|z|^2)\left ( f''(z)/f'(z)\right)$, $f\in Co(\alpha)$. In particular, this gives sharp upper and lower estimates for the pre-Schwarzian norm of concave univalent functions. Next we obtain the set of variability of the functional $(1-|z|^2)\left(f''(z)/f'(z)\right)$, $f\in Co(\alpha)$ whenever $f''(0)$ is fixed. We also give a characterization for concave functions in terms of Hadamard convolution. In addition to sharp coefficient inequalities, we prove that functions in $Co(\alpha)$ belong to the $H^p$ space for $p<1/\alpha$.
On some problems of James Miller
B. Bhowmik,S. Ponnusamy,K-J. Wirths
Mathematics , 2010,
Abstract: We consider the class of meromorphic univalent functions having a simple pole at $p\in(0,1)$ and that map the unit disc onto the exterior of a domain which is starlike with respect to a point $w_0 \neq 0,\, \infty$. We denote this class of functions by $\Sigma^*(p,w_0)$. In this paper, we find the exact region of variability for the second Taylor coefficient for functions in $\Sigma^*(p,w_0)$. In view of this result we rectify some results of James Miller.
Improving the residual resistivity of pure gold
Manfred Poniatowski,Axel Wirths
Gold Bulletin , 1977, DOI: 10.1007/BF03215441
Abstract: The achievement of exceptionally high purity in gold necessitates extreme care not only in refining but also in subsequent rolling and drawing. This paper describes the precautions adopted to produce extremely high purity gold, as measured by its residual resistivity ratio.
Paradigmenwechsel bei der Alzheimer-Krankheit: Intrazellul re Aggregation von Amyloid-beta verursacht den Zellverlust unabh ngig von extrazellul ren Plaques
Bayer TA,Wirths O
Journal für Neurologie, Neurochirurgie und Psychiatrie , 2008,
Abstract: Vermehrte Hinweise deuten auf eine wichtige Rolle von intraneuronalem Aβ als Ausl ser der pathologischen Kaskade hin, welche zu Neurodegeneration und schlie lich zur Alzheimer-Demenz mit ihren typischen klinischen Symptomen wie Ged chtnisverlust und Ver nderung der Pers nlichkeit führt. Die Amyloid-Aβ-Plaques haben keine toxische Funktion und ihre Anzahl und Lokalisation korreliert nicht mit Zellverlust und kognitiver Beeintr chtigung. Die vorliegende übersicht fokussiert auf das APP/PS1KI-Mausmodell, da es als einziges Modell einen massiven Nervenzellverlust im Hippokampus zeigt. Der hohe Nervenzellverlust, die Hippokampusatrophie und der synaptische Funktionsverlust entwickeln sich aufgrund der intraneuronalen Amyloid-Pathologie und nicht als Folge der extrazellul ren Plaque-Ablagerungen. Dieser Befund stellt das g ngige therapeutische Konzept der Reduzierung von extrazellul ren Plaques in Frage.
Neuron Loss in Transgenic Mouse Models of Alzheimer's Disease
Oliver Wirths,Thomas A. Bayer
International Journal of Alzheimer's Disease , 2010, DOI: 10.4061/2010/723782
Abstract: Since their initial generation in the mid 1990s, transgenic mouse models of Alzheimers's disease (AD) have been proven to be valuable model systems which are indispensable for modern AD research. Whereas most of these models are characterized by extensive amyloid plaque pathology, inflammatory changes and often behavioral deficits, modeling of neuron loss was much less successful. The present paper discusses the current achievements of modeling neuron loss in transgenic mouse models based on APP/A and Tau overexpression and provides an overview of currently available AD mouse models showing these pathological alterations. 1. Introduction Alzheimer’s disease (AD) represents the most frequent form of dementia and is characterized by two major neuropathological hallmarks: (i) extracellular plaques composed of the 40–42 residues Aβ peptide [1] and (ii) neurofibrillary tangles (NFTs), consisting of abnormal phosphorylated Tau protein [2]. There is increasing evidence that, in addition to the well-known extracellular amyloid deposition in the parenchyma, Aβ peptides accumulate within neurons [3]. It has been hypothesized that this initial accumulation is one of the earliest pathological events, which is able to trigger the cascade leading to neurodegeneration [4]. Whereas the vast majority of AD cases occur sporadically, a small percentage ( 2%) of all cases represents familial forms of AD with an autosomal dominant mode of inheritance. Identification of the underlying mutations opened manifold opportunities for the generation of transgenic mouse models. Since their initial generation in the mid 1990s, transgenic mice have been proven to represent valuable model systems reflecting various pathological aspects of AD including plaque deposition, inflammatory changes or behavioral abnormalities (reviewed in [5, 6]). In the present short paper, we summarize the current achievements of modeling neuron loss in transgenic mice based on APP/A overexpression. 2. APP-/A -Based Mouse Models with Neuron Loss A variety of different transgenic AD mouse models have been developed during the last 15 years which can be categorized as either APP single transgenic mice (e.g., PD-APP [7], Tg2576 [8], APP/Ld [9], TgCRND8 [10], APP23 [11], tg APP_ArcSwe [12], APP-Au [13], or [14]), bigenic mice expressing both APP and PS1/PS2 or Tau (e.g., APPswe/PS1dE9 [15], APP/PS1 [16], PS2APP [17], APP/PS1KI [18], or APP/tau [19]), and triple transgenic mice expressing APP, PS1, and Tau (e.g., 3xTg [20] or TauPS2APP [21]). Whereas most of these models present abundant extracellular amyloid
Geometric studies on the class ${\mathcal U}(λ)$
Milutin Obradovi?,Saminathan Ponnusamy,Karl-Joachim Wirths
Mathematics , 2015,
Abstract: The article deals with the family ${\mathcal U}(\lambda)$ of all functions $f$ normalized and analytic in the unit disk such that $\big |\big (z/f(z)\big )^{2}f'(z)-1\big |<\lambda $ for some $0<\lambda \leq 1$. The family ${\mathcal U}(\lambda)$ has been studied extensively in the recent past and functions in this family are known to be univalent in $\ID$. However, the problem of determining sharp bounds for the second coefficients of functions in this family was solved recently in \cite{VY2013} by Vasudevarao and Yanagihara but the proof was complicated. In this article, we first present a simpler proof. We obtain a number of new subordination results for this family and their consequences. In addition, we show that the family ${\mathcal U}(\lambda )$ is preserved under a number of elementary transformations such as rotation, conjugation, dilation and omitted value transformations, but surprisingly this family is not preserved under the $n$-th root transformation for any $n\geq 2$. This is a basic here which helps to generate a number of new theorems and in particular provides a way for constructions of functions from the family ${\mathcal U}(\lambda)$. Finally, we deal with a radius problem.
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