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Institution

Technical University of Berlin

EducationBerlin, Germany
About: Technical University of Berlin is a education organization based out in Berlin, Germany. It is known for research contribution in the topics: Quantum dot & Laser. The organization has 27292 authors who have published 59342 publications receiving 1414623 citations. The organization is also known as: Technische Universität Berlin & TU Berlin.


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Journal ArticleDOI
TL;DR: In this article, it was shown that a simple C*-algebra A with unit is stably finite if and only if it contains at least one non-trivial ideal.
Abstract: In order to make available for C*-atgebras the results of Goodearl and Handelman [5] on existence and uniqueness of rank functions on regular rings, we associate in the present note with every C*-algebra A an abelian group K*(A). The construction of this group is analogous to the construction of the Grothendieck group Ko(A ) (which recently has been applied successfully to the classification of AF-algebras by G. Elliott [4]) but the group K~(A) itself is in general quite different from Ko(A ), We are mainly interested in the case where A is a simple C*algebra with unit. If A is such an algebra we call A finite, if x*x =a implies xx* =1 (x~A), and we call A stably finite if M,®A (M,=C*-algebra of n× n complex matrices) is finite for all n~ N. Then K](A) is non-trivial if and only if A is stably finite. We note, incidentally, that it was shown in [3, 2.4] that a simple C*-algebra A with unit is stably finite if and only if ~ ® A (grf= C*-algebra of compact operators on a separable infinite-dimensional Hilbert space) contains at least one non-trivial ideal (which can of course not be closed). It is an open problem which is probably difficult to decide if every finite simple C*-algebra with unit is stably finite. However, if one studies traces on A, one may restrict attention to stably finite algebras. In fact, if there is a trace on A, then A is stably finite.

215 citations

Journal ArticleDOI
TL;DR: A dynamically perfused chip-based bioreactor platform capable of applying variable mechanical shear stress and extending culture periods is described, leading to improvements of culture conditions for integrated in vitro skin models, ex vivo skin organ cultures and biopsies of single hair follicular units.
Abstract: Substantial progress has been achieved over the last few decades in the development of skin equivalents to model the skin as an organ. However, their static culture still limits the emulation of essential physiological properties crucial for toxicity testing and compound screening. Here, we describe a dynamically perfused chip-based bioreactor platform capable of applying variable mechanical shear stress and extending culture periods. This leads to improvements of culture conditions for integrated in vitro skin models, ex vivo skin organ cultures and biopsies of single hair follicular units.

215 citations

Journal ArticleDOI
TL;DR: In this paper, the authors considered the one-dimensional dynamic response of an infinite bar composed of a linear "microelastic material" and examined the effects of long-range forces.
Abstract: The one-dimensional dynamic response of an infinite bar composed of a linear “microelastic material” is examined. The principal physical characteristic of this constitutive model is that it accounts for the effects of long-range forces. The general theory that describes our setting, including the accompanying equation of motion, was developed independently by Kunin (Elastic Media with Microstructure I, 1982), Rogula (Nonlocal Theory of Material Media, 1982) and Silling (J. Mech. Phys. Solids 48 (2000) 175), and is called the peridynamic theory. The general initial-value problem is solved and the motion is found to be dispersive as a consequence of the long-range forces. The result converges, in the limit of short-range forces, to the classical result for a linearly elastic medium. Explicit solutions in elementary form are given in a broad class of special cases. The most striking observations arise in the Riemann-like problem corresponding to a constant initial displacement field and a piecewise constant initial velocity field. Even though, initially, the displacement field is continuous, it involves a jump discontinuity for all later times, the Lagrangian location of which remains stationary. For some materials the magnitude of the discontinuity-jump oscillates about an average value, while for others it grows monotonically, presumably fracturing the material when it exceeds some critical level.

215 citations

Journal ArticleDOI
TL;DR: This work investigates two systems of fully proportional representation suggested by Chamberlin & Courant and Monroe and investigates the parameterized complexity of winner determination of the two classical and two new rules with respect to several parameters.
Abstract: We investigate two systems of fully proportional representation suggested by Chamberlin & Courant and Monroe. Both systems assign a representative to each voter so that the "sum of misrepresentations" is minimized. The winner determination problem for both systems is known to be NP-hard, hence this work aims at investigating whether there are variants of the proposed rules and/or specific electorates for which these problems can be solved efficiently. As a variation of these rules, instead of minimizing the sum of misrepresentations, we considered minimizing the maximal misrepresentation introducing effectively two new rules. In the general case these "minimax" versions of classical rules appeared to be still NP-hard. We investigated the parameterized complexity of winner determination of the two classical and two new rules with respect to several parameters. Here we have a mixture of positive and negative results: e.g., we proved fixed-parameter tractability for the parameter the number of candidates but fixed-parameter intractability for the number of winners. For single-peaked electorates our results are overwhelmingly positive: we provide polynomial-time algorithms for most of the considered problems. The only rule that remains NP-hard for single-peaked electorates is the classical Monroe rule.

215 citations

Journal ArticleDOI
TL;DR: It is shown that introductions on varying spatial scales may strongly foster invasions throughout the whole invasion process, and the term `invasive' should preferably be used in a broader sense to describe the entire invasion process.
Abstract: The human mediation of biological invasions is still an underestimated phenomenon. This paper attempts to show that introductions on varying spatial scales may strongly foster invasions throughout the whole invasion process. As shown by data from central Europe, invasions frequently result from an interplay of biological and anthropogenic mechanisms. The latter, however, cannot be explained nor predicted by ecological rules. This may be an important reason for the limited predictability of invasions. Initial introductions from a donor to a new range are here distinguished from following secondary releases within the new range. The rate of naturalisation is higher in deliberately introduced plants as compared to accidental introductions. Due to higher numbers of accidental introductions, such species contribute significantly to the pool of naturalised species. Secondary releases of alien species are frequently made over long periods subsequent to the initial introduction. They may mimic demographic and dispersal processes that lead to population growth and range expansion. They also offer a pathway to overcome spatial isolation in species whose propagules are not naturally moved long distances. This even holds for most of Germany's noxious alien plant species. Secondary releases may thus promote invasions even beyond the threshold of naturalisation. In consequence, attempts at prevention should focus on secondary releases as well as on initial introductions. In the last section of the paper, the final invasion stage subsequent to naturalisation is shown as a multi-scale phenomenon. In consequence, the classification of a species as 'invasive' depends on the perspective chosen. Using different biologically or anthropocentrically based approaches leads to sub-sets of alien species that overlap only partially. In conclusion, the term `invasive' should preferably be used in a broader sense to describe the entire invasion process.

214 citations


Authors

Showing all 27602 results

NameH-indexPapersCitations
Markus Antonietti1761068127235
Jian Li133286387131
Klaus-Robert Müller12976479391
Michael Wagner12435154251
Shi Xue Dou122202874031
Xinchen Wang12034965072
Michael S. Feld11955251968
Jian Liu117209073156
Ary A. Hoffmann11390755354
Stefan Grimme113680105087
David M. Karl11246148702
Lester Packer11275163116
Andreas Heinz108107845002
Horst Weller10545144273
G. Hughes10395746632
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
2023191
2022650
20213,307
20203,387
20193,105
20182,910