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Lehner L.,Perimeter Institute for Theoretical Physics | Lehner L.,University of Guelph | Lehner L.,Canadian Institute for Advanced Research CIFAR | Pretorius F.,Princeton University
Physical Review Letters | Year: 2010

We describe the behavior of 5-dimensional black strings, subject to the Gregory-Laflamme instability. Beyond the linear level, the evolving strings exhibit a rich dynamics, where at intermediate stages the horizon can be described as a sequence of 3-dimensional spherical black holes joined by black string segments. These segments are themselves subject to a Gregory-Laflamme instability, resulting in a self-similar cascade, where ever-smaller satellite black holes form connected by ever-thinner string segments. This behavior is akin to satellite formation in low-viscosity fluid streams subject to the Rayleigh-Plateau instability. The simulation results imply that the string segments will reach zero radius in finite asymptotic time, whence the classical space-time terminates in a naked singularity. Since no fine-tuning is required to excite the instability, this constitutes a generic violation of cosmic censorship.

Yoneda J.,University of Tokyo | Yoneda J.,RIKEN | Otsuka T.,University of Tokyo | Otsuka T.,RIKEN | And 11 more authors.
Physical Review Letters | Year: 2014

We demonstrate fast universal electrical spin manipulation with inhomogeneous magnetic fields. With fast Rabi frequency up to 127 MHz, we leave the conventional regime of strong nuclear-spin influence and observe a spin-flip fidelity >96%, a distinct chevron Rabi pattern in the spectral-time domain, and a spin resonance linewidth limited by the Rabi frequency, not by the dephasing rate. In addition, we establish fast z rotations up to 54 MHz by directly controlling the spin phase. Our findings will significantly facilitate tomography and error correction with electron spins in quantum dots. © 2014 American Physical Society.

Aknin L.B.,Simon Fraser University | Aknin L.B.,Canadian Institute for Advanced Research CIFAR | Broesch T.,Simon Fraser University | Kiley Hamlin J.,Columbia University | Van De Vondervoort J.M.,Columbia University
Journal of Experimental Psychology: General | Year: 2015

Humans are extraordinarily prosocial, and research conducted primarily in North America indicates that giving to others is emotionally rewarding. To examine whether the hedonic benefits of giving represent a universal feature of human behavior, we extended upon previous cross-cultural examinations by investigating whether inhabitants of a small-scale, rural, and isolated village in Vanuatu, where villagers have little influence from urban, Western culture, survive on subsistence farming without electricity, and have minimal formal education, report or display emotional rewards from engaging in prosocial (vs. personally beneficial) behavior. In Study 1, adults were randomly assigned to purchase candy for either themselves or others and then reported their positive affect. Consistent with previous research, adults purchasing goods for others reported greater positive emotion than adults receiving resources for themselves. In Study 2, 2- to 5-year-old children received candy and were subsequently asked to engage in costly giving (sharing their own candy with a puppet) and non-costly giving (sharing the experimenter's candy with a puppet). Emotional expressions were video-recorded during the experiment and later coded for happiness. Consistent with previous research conducted in Canada, children displayed more happiness when giving treats away than when receiving treats themselves. Moreover, the emotional rewards of giving were largest when children engaged in costly (vs. non-costly) giving. Taken together, these findings indicate that the emotional rewards of giving are detectable in people living in diverse societies and support the possibility that the hedonic benefits of generosity are universal. © 2015 American Psychological Association.

Park Y.,Institute For Angewandte Photophysik | Muller-Meskamp L.,Institute For Angewandte Photophysik | Vandewal K.,Institute For Angewandte Photophysik | Leo K.,Institute For Angewandte Photophysik | Leo K.,Canadian Institute for Advanced Research CIFAR
Applied Physics Letters | Year: 2016

The performance of organic optoelectronic devices can be improved by employing a suitable optical cavity design beyond the standard plane layer approach, e.g., by the inclusion of periodically or randomly textured structures which increase light incoupling or extraction. One of the simplest approaches is to add an additional layer containing light scattering particles into the device stack. Solution processed poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films are promising for replacing the brittle and expensive indium tin oxide transparent electrode. We use a blend of 100 nm TiO2 scattering particles in PEDOT:PSS solution to fabricate transparent electrode films which also functions as a scattering layer. When utilized in an organic photovoltaic device, a power conversion efficiency of 7.92% is achieved, which is an 8.6% relative improvement compared to a device with a neat PEDOT:PSS electrode without the nanoparticles. This improvement is caused by an increase in short-circuit current due to an improved photon harvesting in the 320 nm-700 nm spectral wavelength range. © 2016 Author(s).

Gunther A.A.,TU Dresden | Sawatzki M.,TU Dresden | Formanek P.,Leibniz Institute of Polymer Research | Kasemann D.,Creaphys GmbH | And 2 more authors.
Advanced Functional Materials | Year: 2016

Doping is a powerful tool to overcome contact limitations in short-channel organic field-effect transistors (OFETs) and has been successfully used in the past to improve the charge carrier injection in OFETs. The present study applies this familiar concept to the architecture of vertical organic field-effect transistors (VOFETs), which are often severely limited by injection due to their very short channel lengths. The present study shows that the performance of p-type VOFETs with pentacene as an active material can be significantly enhanced by the addition of the common p-dopant C60F36 as a thin injection layer underneath the VOFET source electrode, resulting in an increase of On-state current and On/Off ratio by one order of magnitude. The present study further investigates mixed injection layers of pentacene and the p-dopant and finds that the improvement is less pronounced than for the pure dopant layers and depends on the concentration of dopant molecules in the injection layer. Through application of the transfer length method to equivalent OFET geometries, the present study is finally able to link the observed improvement to a decrease in transfer length and can thus conclude that this length is a crucial parameter onto which further improvement efforts have to be concentrated to realize true short-channel VOFETs. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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