The intention of the ChiralTEM project (2004-2007) was the detection of electron (energy loss) magnetic chiral dichroism in a transmission electron microscope (TEM), in analogy to X-ray magnetic circular dichroism (XMCD). For the experiments, single-crystal electron transparent specimen's with magnetic induction perpendicular to the specimen's plane are required. In this thesis, different preparation techniques are evaluated regarding their usability to produce ideal specimen's for a verification of EMCD. After the demonstration of a dichroic measurement, an obvious way to prove the chiral effect is to invert the specimen's magnetization from parallel to antiparallel to the electron beam trajectory, leaving all other parameters of the experimental setup unchanged. For this case, one would - according to theory - expect a change in the dichroic signal measured. In the magnetic field of the objective lens of a 300kV TEM, typical ferromagnetic specimens will be close to saturation perpendicular to the specimen's plane. Reversing the current through the coils of the objective lens will then simply invert the magnetization of the specimen. In consequence, any magnetic chiral effect is expected to change sign. A switching unit for Tecnai microscopes has been constructed for save commutation of the lens currents. The direct sensitivity of the dichroic signal to the direction of the magnetization gives evidence to the magnetic origin of the effect.
The intention of the ChiralTEM project (2004-2007) was the detection of electron (energy loss) magnetic chiral dichroism in a transmission electron microscope (TEM), in analogy to X-ray magnetic circular dichroism (XMCD). For the experiments, single-crystal electron transparent specimen's with magnetic induction perpendicular to the specimen's plane are required. In this thesis, different preparation techniques are evaluated regarding their usability to produce ideal specimen's for a verification of EMCD. After the demonstration of a dichroic measurement, an obvious way to prove the chiral effect is to invert the specimen's magnetization from parallel to antiparallel to the electron beam trajectory, leaving all other parameters of the experimental setup unchanged. For this case, one would - according to theory - expect a change in the dichroic signal measured. In the magnetic field of the objective lens of a 300kV TEM, typical ferromagnetic specimens will be close to saturation perpendicular to the specimen's plane. Reversing the current through the coils of the objective lens will then simply invert the magnetization of the specimen. In consequence, any magnetic chiral effect is expected to change sign. A switching unit for Tecnai microscopes has been constructed for save commutation of the lens currents. The direct sensitivity of the dichroic signal to the direction of the magnetization gives evidence to the magnetic origin of the effect.
This book presents the electrical models for the different elements of a photonic microwave link like lasers, external modulators, optical fibers, photodiodes and phototransistors. The future trends of these components are also introduced: lasers to VCSEL, external modulators to electro-absorption modulators, glass optical fibers to plastic optical fibers, photodiodes to UTC photodiodes or phototransistors. It also describes an original methodology to evaluate the performance of a microwave photonic link, based on the developed elcetrical models, that can be easily incorporated in commercial electrical circuits simulation software to simulate this complete link.
Can San Francisco survive a marauding gang of Vespa-riding vampires? Before it's sucked dry, the city's only hope may be Valentino, who's only a trainee for the supernatural law enforcement agency, Le Counseil Carmin. Swept up in the whole blood-sucking business when his mentor goes missing, Valentino is called upon to deal with the menace of these "Bloody Marys." But Valentino soon realizes that, in order to dispose of the gang, he must go into areas he never dreamed of, deal with some very strange characters and learn the truth about the dark side of town. The Very Bloody Marys is a comic horror novel about vampires, ghouls, faeries, and the undead that move around after dark. Part chase, part gallows humor, and all shivery excitement, this new story from the wildly imaginative M. Christian is funny, frightening, and very entertaining.
Modern complementary metal oxide semiconductor (CMOS) digital-to-analog converters (DACs) are limited in their bandwidth due to technological constraints. These limitations can be overcome by parallel DAC architectures, which are called interleaving concepts. Christian Schmidt analyzes the limitations and the potential of two innovative DAC interleaving concepts to provide the basis for a practical implementation: the analog multiplexing DAC (AMUX-DAC) and the frequency interleaving DAC (FI-DAC). He presents analytical and discrete-time models as a theoretical foundation and develops digital signal processing (DSP) algorithms to compensate the analog impairments. Further, he quantifies the impact of various limiting parameters with numerical simulations and verifies both concepts in laboratory experiments. About the Author: Christian Schmidt works at the Fraunhofer Heinrich-Hertz-Institute, Berlin, Germany, on innovative solutions for broadband signal generation in the field of optical communications. The studies for his dissertation were carried out at the Technische Universität Berlin and at the Fraunhofer Heinrich-Hertz-Institute, both Berlin, Germany.
The serial optical data format has attracted attention for decades now, because of its promise to reduce the number of active components in a communication system. Indeed, historically increasing the serial bit rate by a factor of 4, reduced the cost per bit by 40%. Going beyond the available electronic bandwidth (roughly 100GHz today) can be obtained using optical time division multiplexing (OTDM), and symbol rates up to 1.28Tbaud per polarization have been demonstrated. As most optical signal processing devices operate on a per channel basis, it is advantageous to aggregate the data in a serial format, since this allows for optical signal processing of many bits in a single device. This chapter gives an overview of the state-of-the-art of OTDM systems to reach multi-Tbit/s serial data and means to handle these ultra-high bit rate signals using for instance nonlinear silicon waveguides for e.g. serial-to-parallel conversion.
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