scispace - formally typeset
Search or ask a question
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.


Papers
More filters
Journal ArticleDOI
01 Jun 2000-Ecology
TL;DR: Based on conceptual ideas about the balance between interference and facilitation, it is predicted that positive effects of the shrubs on the understory should dominate in dry years, while in favorable years...
Abstract: Recently, numerous studies have pointed to the importance of positive interactions in natural communities. There is now a broad consensus that the balance between negative and positive interactions should shift along environmental gradients, with competition prevailing under environmentally benign conditions and positive interactions dominating under harsh conditions. A commonly cited example of the importance of facilitation in harsh environments is the preference of desert annual plants for the areas under the canopy of shrubs. The recognition of apparently positive effects of desert shrubs on annuals, however, has been mostly based on density measurements, while fitness parameters of the understory plants have been ignored. Also, the temporal consistency of such effects has not been previously tested. Based on conceptual ideas about the balance between interference and facilitation, we predicted that positive effects of the shrubs on the understory should dominate in dry years, while in favorable years, negative effects would be stronger. We tested our hypothesis by measuring the direction and magnitude of the shrub effect on demographic responses of four desert annual plant species during four consecutive seasons of differing rainfall. The results contradicted our initial hypothesis. Depending on the species, the effect of the shrubs shifted from either negative to neutral or from neutral to positive with increasing annual rainfall. However, this trend was stronger for the effect of shrubs on plant reproductive success than on their densities. Our data highlight the importance of measuring fitness parameters in studies of plant-plant interactions. We suggest that the negative effects of shrubs on plant fitness were due to rainfall interception, while positive effects were related to increased nutrient availability beneath shrubs. However, the mechanisms by which the shrubs and annuals interact can only be resolved using an experimental approach. Our results contradict previous hypotheses about the relative importance of positive and negative interactions along environmental gradients. A simple conceptual model summarizing the proposed role of rainfall in determining the direction of shrub effects on their understory annuals is presented.

454 citations

BookDOI
01 Jan 2005
TL;DR: The aim of this book is to survey some of the most successful model reduction methods in tutorial style articles and to present benchmark problems from several application areas for testing and comparing existing and new algorithms.
Abstract: In the past decades, model reduction has become an ubiquitous tool in analysis and simulation of dynamical systems, control design, circuit simulation, structural dynamics, CFD, and many other disciplines dealing with complex physical models. The aim of this book is to survey some of the most successful model reduction methods in tutorial style articles and to present benchmark problems from several application areas for testing and comparing existing and new algorithms. As the discussed methods have often been developed in parallel in disconnected application areas, the intention of the mini-workshop in Oberwolfach and its proceedings is to make these ideas available to researchers and practitioners from all these different disciplines.

453 citations

Journal ArticleDOI
TL;DR: In this paper, a laterally ordered array of nanoscale structures inserted in a GaAs matrix, where each structure is composed of several vertically merging InAs parts, was found to decrease the radiative lifetime and to result in low energy shifts of the corresponding peaks in luminescence and absorption spectra.
Abstract: Alternate short-period GaAs-InAs deposition following InAs pyramid formation on a GaAs (100) surface leads to the creation of vertically split pyramids. This splitting is driven by the energetics of the Stranski-Krastanow growth mode. The strain energy is reduced due to the successive transfer of InAs from the buried part of the pyramid to the uncovered part. The resulting arrangement represents a laterally ordered array of nanoscale structures inserted in a GaAs matrix, where each structure is composed of several vertically merging InAs parts. Results of optical studies demonstrate the expected electronic coupling in vertical direction. Coupling is found to decrease the radiative lifetime and to result in low-energy shifts of the corresponding peaks in luminescence and absorption spectra. Vertically coupled quantum dots exhibit injection lasing at very low current densities. \textcopyright{} 1996 The American Physical Society.

452 citations

Journal ArticleDOI
TL;DR: This work shows that high-speed, high-density spintronics devices based on current-driven spin textures can be realized using materials in which TA and TM are close together using compensated ferrimagnets.
Abstract: Spintronics is a research field that aims to understand and control spins on the nanoscale and should enable next-generation data storage and manipulation. One technological and scientific key challenge is to stabilize small spin textures and to move them efficiently with high velocities. For a long time, research focused on ferromagnetic materials, but ferromagnets show fundamental limits for speed and size. Here, we circumvent these limits using compensated ferrimagnets. Using ferrimagnetic Pt/Gd44Co56/TaOx films with a sizeable Dzyaloshinskii–Moriya interaction, we realize a current-driven domain wall motion with a speed of 1.3 km s–1 near the angular momentum compensation temperature (TA) and room-temperature-stable skyrmions with minimum diameters close to 10 nm near the magnetic compensation temperature (TM). Both the size and dynamics of the ferrimagnet are in excellent agreement with a simplified effective ferromagnet theory. Our work shows that high-speed, high-density spintronics devices based on current-driven spin textures can be realized using materials in which TA and TM are close together. Ferrimagnetic Gd44Co56 near the compensation temperature enables domain wall motion with a speed of 1.3 km s–1 and room temperature skyrmions with diameters close to 10 nm.

451 citations

Journal ArticleDOI
01 Apr 2007-Energy
TL;DR: In this paper, the definitions of some terms used in exergy analysis and exergy costing, and options for the symbols to be used for exergy and some exergoeconomic variables, and the nomenclature for the remaining terms.

450 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
Network Information
Related Institutions (5)
ETH Zurich
122.4K papers, 5.1M citations

93% related

École Polytechnique Fédérale de Lausanne
98.2K papers, 4.3M citations

93% related

RWTH Aachen University
96.2K papers, 2.5M citations

93% related

Technische Universität München
123.4K papers, 4M citations

92% related

École Normale Supérieure
99.4K papers, 3M citations

92% related

Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
2023191
2022650
20213,307
20203,387
20193,105
20182,910