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"Meier, Joachim"
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الدولار واليورو : هل يحتم العجز الكبير في ميزان الحساب الجاري الأمريكي ارتفاعا في قيمة اليورو ؟
يهدف الكتاب إلى البحث في هذه الآراء والتصورات وانطلق المؤلفون في القسم الأول من أن سبب العجز يعود بالأساس إلى تطور الأوضاع في الولايات المتحدة نفسها أما القسم الثاني فيقدم ملخصا عن دراسة أوستفيلد وروجوف كونها مثالا جيدا لسيناريو ينطلق ضمنيا من انخفاض شديد في قيمة الدولار، ويستعرض القسم الثالث مشكلة العجز في الحساب الجاري الأمريكي والأسباب المحتملة لنشأة هذا العجز من منظور عالمي الأبعاد ويناقش القسم الرابع ملامح العملية التي يمكن أن تقود إلى تخفيض هذا العجز.
BOOK
Megahertz‐rate ultrafast X‐ray scattering and holographic imaging at the European XFEL
The advent of X‐ray free‐electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X‐rays with unprecedented brightness, coherence and pulse duration. All XFEL facilities built until recently provided X‐ray pulses at a relatively low repetition rate, with limited data statistics. Here, results from the first megahertz‐repetition‐rate X‐ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL are presented. The experimental capabilities that the SCS instrument offers, resulting from the operation at megahertz repetition rates and the availability of the novel DSSC 2D imaging detector, are illustrated. Time‐resolved magnetic X‐ray scattering and holographic imaging experiments in solid state samples were chosen as representative, providing an ideal test‐bed for operation at megahertz rates. Our results are relevant and applicable to any other non‐destructive XFEL experiments in the soft X‐ray range. Results from the first megahertz‐repetition‐rate X‐ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL are presented.
Journal Article
Laser system design for table-top X-ray light source
We present possible conceptual designs of a laser system for driving table-top free-electron lasers based on terahertz acceleration. After discussing the achievable performances of laser amplifiers with Yb:YAG at cryogenic and room temperature and Yb:YLF at cryogenic temperature, we present amplification modules with available results and concepts of amplifier chains based on these laser media. Their performances are discussed in light of the specifications for the tasks within the table-top light source. Technical and engineering challenges, such as cooling, control, synchronization and diagnostics, are outlined. Three concepts for the laser layout feeding the accelerator are eventually derived and presented.
Journal Article
Discrete nonlinear wave propagation in Kerr nonlinear media
Discrete optical systems are a subgroup of periodic structures in which the evolution of a continuous electromagnetic field can be described by a discrete model. In this model, the total field is the sum of localized, discrete modes. Weakly coupled arrays of single mode channel waveguides have been known to fall into this class of systems since the late 1960's. Nonlinear discrete optics has received a considerable amount of interest in the last few years, triggered by the experimental realization of discrete solitons in a Kerr nonlinear AlGaAs waveguide array by H. Eisenberg and coworkers in 1998. In this work a detailed experimental investigation of discrete nonlinear wave propagation and the interactions between beams, including discrete solitons, in discrete systems is reported for the case of a strong Kerr nonlinearity. The possibility to completely overcome “discrete” diffraction and create highly localized solitons, in a scalar or vector geometry, as well as the limiting factors in the formation of such nonlinear waves is discussed. The reversal of the sign of diffraction over a range of propagation angles leads to the stability of plane waves in a material with positive nonlinearity. This behavior can not be found in continuous self-focusing materials where plane waves are unstable against perturbations. The stability of plane waves in the anomalous diffraction region, even at highest powers, has been experimentally verified. The interaction of high power beams and discrete solitons in arrays has been studied in detail. Of particular interest is the experimental verification of a theoretically predicted unique, all optical switching scheme, based on the interaction of a so called “blocker” soliton with a second beam. This switching method has been experimentally realized for both the coherent and incoherent case. Limitations of such schemes due to nonlinear losses at the required high powers are shown.
Dissertation
Megahertz-rate Ultrafast X-ray Scattering and Holographic Imaging at the European XFEL
The advent of X-ray free-electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X-rays with unprecedented brightness, coherence, and pulse duration. All XFEL facilities built until recently provided X-ray pulses at a relatively low repetition rate, with limited data statistics. Here, we present the results from the first megahertz repetition rate X-ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL. We illustrate the experimental capabilities that the SCS instrument offers, resulting from the operation at MHz repetition rates and the availability of the novel DSSC 2D imaging detector. Time-resolved magnetic X-ray scattering and holographic imaging experiments in solid state samples were chosen as representative, providing an ideal test-bed for operation at megahertz rates. Our results are relevant and applicable to any other non-destructive XFEL experiments in the soft X-ray range.
Paper