Technical University of Berlin

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

Nanoplasma Dynamics of Single Large Xenon Clusters Irradiated with Superintense X-Ray Pulses from the Linac Coherent Light Source Free-Electron Laser

Abstract: The plasma dynamics of single mesoscopic Xe particles irradiated with intense femtosecond x-ray pulses exceeding ${10}^{16}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$ from the Linac Coherent Light Source free-electron laser are investigated. Simultaneous recording of diffraction patterns and ion spectra allows eliminating the influence of the laser focal volume intensity and particle size distribution. The data show that for clusters illuminated with intense x-ray pulses, highly charged ionization fragments in a narrow distribution are created and that the nanoplasma recombination is efficiently suppressed.

Spectral proper orthogonal decomposition

Abstract: The identification of coherent structures from experimental or numerical data is an essential task when conducting research in fluid dynamics. This typically involves the construction of an empirical mode base that appropriately captures the dominant flow structures. The most prominent candidates are the energy-ranked proper orthogonal decomposition (POD) and the frequency-ranked Fourier decomposition and dynamic mode decomposition (DMD). However, these methods are not suitable when the relevant coherent structures occur at low energies or at multiple frequencies, which is often the case. To overcome the deficit of these ‘rigid’ approaches, we propose a new method termed spectral proper orthogonal decomposition (SPOD). It is based on classical POD and it can be applied to spatially and temporally resolved data. The new method involves an additional temporal constraint that enables a clear separation of phenomena that occur at multiple frequencies and energies. SPOD allows for a continuous shifting from the energetically optimal POD to the spectrally pure Fourier decomposition by changing a single parameter. In this article, SPOD is motivated from phenomenological considerations of the POD autocorrelation matrix and justified from dynamical systems theory. The new method is further applied to three sets of PIV measurements of flows from very different engineering problems. We consider the flow of a swirl-stabilized combustor, the wake of an airfoil with a Gurney flap and the flow field of the sweeping jet behind a fluidic oscillator. For these examples, the commonly used methods fail to assign the relevant coherent structures to single modes. The SPOD, however, achieves a proper separation of spatially and temporally coherent structures, which are either hidden in stochastic turbulent fluctuations or spread over a wide frequency range. The SPOD requires only one additional parameter, which can be estimated from the basic time scales of the flow. In spite of all these benefits, the algorithmic complexity and computational cost of the SPOD are only marginally greater than those of the snapshot POD.

Struggling for the right to the (creative) city in Berlin and Hamburg: new urban social movements, new 'spaces of hope'?

Abstract: In cities across the globe there is mounting evidence of growing mobilization by members of the so-called ‘creative class’ in urban social movements, defending particular urban spaces and influencing urban development. This essay discusses the meaning of such developments with reference to the hypothesis made by David Harvey in Spaces of Capital about the increasing mobilization of cultural producers in oppositional movements in an era of wholesale instrumentalization of culture and ‘creativity’ in contemporary processes of capitalist urbanization. After briefly reviewing recent scholarly contributions on the transformations of urban social movements, as well as Harvey's hypothesis about the potential role of cultural producers in mobilizations for the construction of ‘spaces of hope’, the essay describes two specific urban protests that have occurred in Berlin and Hamburg in recent years: the fight for Berlin's waterfront in the Media Spree area, and the conflict centred on the Gangeviertel in Hamburg. In both protests artists, cultural producers and creative milieux have played a prominent role. The essay analyses the composition, agenda, contribution and contradictions of the coalitions behind the protests, discussing whether such movements represent the seeds of new types of coalitions with a wide-ranging agenda for urban change. The essay finally proposes a future research agenda on the role of artists, cultural producers and the ‘creative class’ in urban social movements across the globe.

Statistical Mechanics of Disordered Systems: A Mathematical Perspective

Abstract: Preface Part I. Statistical Mechanics: 1. Introduction 2. Principles of statistical mechanics 3. Lattice gases and spin systems 4. Gibbsian formalism 5. Cluster expansions Part II. Disordered Systems: Lattice Models: 6. Gibbsian formalism and metastates 7. The random field Ising model Part III: Disordered Systems: Mean Field Models: 8. Disordered mean field models 9. The random energy model 10. Derrida's generalised random energy models 11. The SK models and the Parisi solution 12. Hopfield models 13. The number partitioning problem Bibliography Index of notation Index.

Ultrasensitive Chemical Analysis by Raman Spectroscopy

Abstract: In the Raman effect, incident light is inelastically scattered from a sample and shifted in frequency by the energy of its characteristic molecular vibrations. Since its discovery in 1927, the effect has attracted attention from a basic research point of view as well as a powerful spectroscopic technique with many practical applications. The advent of laser light sources with monochromatic photons at high flux densities was a milestone in the history of Raman spectroscopy and resulted in dramatically improved scattering signals (for a general overview of modern Raman spectroscopy, see refs 1-5). In addition to this so-called spontaneous or incoherent Raman scattering, the development of lasers also opened the field of stimulated or coherent Raman spectroscopies, in which molecular vibrations are coherently excited. Whereas the intensity of spontaneous Raman scattering depends linearly on the number of probed molecules, the coherent Raman signal is proportional to the square of this number (for an overview, see refs 6 and 7). Coherent Raman techniques can provide interesting new opportunities such as vibrational imaging of biological samples,8 but they have not yet advanced the field of ultrasensitive trace detection. Therefore, in the following article, we shall focus on the spontaneous Raman effect, in the following simply called Raman scattering. Today, laser photons over a wide range of frequencies from the near-ultraviolet to the near-infrared region are used in Raman scattering studies, allowing selection of optimum excitation conditions for each sample. By choosing wavelengths which excite appropriate electronic transitions, resonance Raman studies of selected components of a sample or parts of a molecule can be performed.9 In the past few years, the range of excitation wavelengths has been extended to the near-infrared (NIR) region, in which background fluorescence is reduced and photoinduced degradation from the sample is diminished. High-intensity NIR diode lasers are easily available, making this region attractive for compact, low cost Raman instrumentation. Further, the development of low noise, high quantum efficiency multichannel detectors (chargecoupled device (CCD) arrays), combined with highthroughput single-stage spectrographs used in combination with holographic laser rejection filters, has led to high-sensitivity Raman spectrometers (for an overview on state-of-the-art NIR Raman systems, see ref 10). As we shall show in section 2, the nearinfrared region also has special importance for ultrasensitive Raman spectroscopy at the singlemolecule level. As with optical spectroscopy, the Raman effect can be applied noninvasively under ambient conditions in almost every environment. Measuring a Raman spectrum does not require special sample preparation techniques, in contrast with infrared absorption spectroscopy. Optical fiber probes for bringing excitation laser light to the sample and transporting scattered light to the spectrograph enable remote detection of Raman signals. Furthermore, the spatial and temporal resolution of Raman scattering are determined by the spot size and pulse length, respectively, of the excitation laser. By using a confocal microscope, Raman signals from femtoliter volumes (∼1 μm3) can by observed, enabling spatially resolved measurements in chromosomes and cells.11 Techniques such as multichannel Hadamard transform Raman microscopy12,13 or confocal scanning Fourier transform Raman microscopy14 allow generation of high-resolution Raman images of a sample. Recently, Raman spectroscopy was performed using near-field optical microscopy.15-17 Such techniques overcome the diffraction limit and allow volumes significantly smaller than the cube of the wavelength to be investigated. In the time domain, Raman spectra can be measured on the picosecond time scale, providing information on short-lived species such as excited 2957 Chem. Rev. 1999, 99, 2957−2975