Attosecond (as) physics has become a wide spreaded and still growing research field over the last decades. It allows for probing and controlling core- and outer shell electron dynamics with never before achieved temporal precision.

High harmonic generation in gases in combination with advanced extreme ultraviolet (XUV ) optical components enable the generation of isolated attosecond pulses as required for absolute time measurements. But until recently, single attosecond pulse generation has been restricted to the energy range below 100 eV due to the availability of sources and attosecond optics.

Multilayer mirrors are the up to date widest tunable optical components in the XUV and key components in attosecond physics from the outset.

In this thesis, the design, fabrication and measurement of periodic and aperiodic XUV multilayer mirrors and their application in the generation and shaping of isolated attosecond pulses is presented. Two- and three material coatings based on a combination of molybdenum, silicon, boron carbide, lanthanum and scandium covering the complete spectral range between 30 and 200 eV are developed and characterized. Excellent agreement between reflectivity simulations and experiments is based on the highly stable ion beam sputter deposition technique. It allows for atomically smooth deposition and the realization of aperiodic multilayer structures with high precision and reproducibility.

XUV reflectivity simulation of lanthanum containing multilayer coatings are based on an improved measured set of optical constants, introduced in this thesis.

This work enabled the generation of the shortest ever measured isolated light pulses so far, the creation of the first isolated attosecond pulses above 100 eV , the first demonstration of absolute control of the “attochirp” by means of multilayer mirrors and the formation of spectrally cleaned attosecond pulses, in a spectral region which lacks appropriate filter materials, for a never before achieved combination of spectral and temporal resolution at 125 eV .

Here presented concepts are in principle not restricted to specific energies or experimental set-ups and may be extended in the near future to enter completely new regimes of ultrashort physics.

Diese Arbeit untersucht mithilfe eines axisymmetrischen numerischen Modells die Prozesse, die zur Intensivierung tropischer Zyklone führen. Das Modell ist hydrostatisch, die Mo-dellgleichungen sind in Sigmakoordinaten auf einer f-Ebene formuliert. Es besteht aus drei Schichten: einer für die Grenzschicht und zwei für die freie Troposphäre.

Insbesondere wird der Einfluss des Coriolisparameters f auf die Intensität und Größe von tropischen Zyklonen untersucht. In der ersten von zwei Experimentreihen zeigt sich, dass sich die stärksten Stürme bei mittleren Werten von f entwickeln. Ebenso gibt es einen optimalen Wert von f im mittleren Bereich, bei dem die größten Stürme entstehen. Diese Ergebnisse scheinen zunächst mit klassischen Laborexperimenten von Turner und Lilly übereinzustimmen. Eine mögliche Analogie dieser Laborexperimente zu tropischen Zyklonen wird eingehend untersucht. Dabei zeigt sich, dass diese Analogie unter anderem aufgrund des in der Grenzschicht stattfindenden Intensivierungsprozesses begrenzt ist. Zum weiteren Verständnis wird eine zweite Experimentreihe durchgeführt. Die modellierten Stürme werden hierbei durch ein vorgeschriebenes Profil der diabatischen Erwärmungsrate angetrieben. Andere Feuchtprozesse werden ausgeschlossen. Es ergibt sich nun kein optimaler Wert von f für die Intensität der Stürme. Die Beziehung zwischen der Stärke des Antriebs und der Stärke der Rotation ist somit ein wichtiger zusätzlicher limitierender Faktor bei tropischen Zyklonen. Dennoch gibt es einen optimalen Breitengrad für die Größe der Zyklone, vergleichbar mit dem in der ersten Experimentreihe.

Außerdem wird die Sensitivität des Modells bezüglich der horizontalen Auflösung, des Eddy-Diffusions- und Reibungskoeffizienten und der Windgeschwindigkeitsabhängigkeit des Bodenflusses von Enthalpie untersucht. Die Intensität nimmt geringfügig mit größerer horizontaler Auflösung zu, die Größe des Sturms bleibt nahezu unverändert. In Übereinstimmung mit anderen Ergebnissen in der Literatur ist die Intensität stark abhängig vom horizontalen Eddy-Diffusionskoeffizienten. Erhöht man den Reibungskoeffizienten und lässt den Wärmeaustauschkoeffizienten konstant, bewirkt dies eine erhöhte Feuchtekonvergenz und damit einen früheren Beginn der schnellen Intensivierung. Die Intensität am Ende der Simulation nimmt, im Unterschied zu neuesten Ergebnissen von Montgomery et al., jedoch ab. Kappt man die Windgeschwindigkeitsabhängigkeit des Bodenflusses von Enthalpie bei kleinen Werten von 10 m/s, so simuliert das Modell dennoch Stürme mit Intensitäten, die Hurrikanstärke übersteigen. Dies zeigt, dass der in weiten Kreisen akzeptierte 'Verdunstungs-Wind-Rückkopplungsmechanismus' nicht wesentlich für die Intensivierung tropischer Zyklone ist.

In this thesis we study microscopic aspects of Calabi-Yau black holes in string theory.

We compute the absorption cross-section of the space-time massless scalars by the world-volume

of D2-branes, wrapped on the S2 of an AdS_2 x S^2 x CY_3 geometry of a four-dimensional

D4-D0 Calabi-Yau black hole. The D2-brane can also have a generic D0

probe-brane charge. However, we restrict ourselves to D2-branes with small D0-charge

so that the perturbation theory is applicable. According to the proposed AdS_2/QM correspondence

the candidate for the dual theory is the quantum mechanics of a set of probe

D0-branes in the AdS2 geometry. For small but non-zero probe D0-charge we find the quantum

mechanical absorption cross-section seen by an asymptotic anti-de Sitter observer. We

repeat the calculations for vanishing probe D0-charge as well and discuss our result by

comparing with the classical absorption cross-section. In other project, for a given four-dimensional

Calabi-Yau black hole with generic D6-D4-D2-D0 charges we identify a set of

supersymmetric branes, which are static or stationary in the global coordinates, of the corresponding

eleven-dimensional near horizon geometry. The set of these BPS states, which

include the branes partially or fully wrap the horizon, should play a role in understanding

the partition function of black holes with D6-charge.

We are experiencing a unique epoch in the history of galaxy cluster studies.

We have now open windows across the whole electromagnetic spectrum which offer

us complementary approaches for cluster detection and analyses.

Almost forty years after its theoretical prediction, first large

radio telescopes started to scan the sky looking for massive clusters as "shadows"

in the cosmic microwave background imprinted there by their hot gas content

via the Sunyaev-Zel'dovich effect (SZE). In X-rays this hot

plasma can be observed also directly. Optical and infrared telescopes give us

a view on the galaxy population of clusters and through gravitational lensing

also on its dominant, invisible component - the dark matter.

The advent of multi-wavelength cluster surveys brings also the necessity to

compare and cross-calibrate each cluster detection approach. This is the

main aim of this work carried out in the framework of the XMM-\emph{Newton}-Blanco

Cosmology Survey project (XMM-BCS). This project is a coordinated

multi-wavelength survey in a 14~deg$^2$ test region covered in the optical band

by the Blanco Cosmology Survey, in the mid-infrared by the \emph{Spitzer} Space

Telescope and in X-rays by XMM-\emph{Newton}. This area is also part of the sky scanned

by both SZE survey instruments: the South Pole Telescope (SPT) and the Atacama

Cosmology Telescope (ACT).

In the first part of the thesis I describe the analysis of the initial 6~deg$^2$

core of the X-ray survey field. From the detected extended sources a cluster

catalog comprising 46 objects is constructed. These cluster candidates are

confirmed as significant galaxy overdensities in the optical data, their

photometric redshifts are measured and for a subsample confirmed with

spectroscopic measurements.

I provide physical parameters of the

clusters derived from X-ray luminosity and carry out a first comparison with

optical studies. The cluster catalog will be useful for direct cross-comparison

with optical/mid-infrared catalogs, for the investigation of the survey selection

functions, stacking analysis of the SZE signal and for cosmological analyses after combing

with clusters detected in the extension of the survey.

The extension of the survey to 14~deg$^2$ is a first scientific utilization of

the novel XMM-\emph{Newton} mosaic mode observations. I have developed a data analysis

pipeline for this operation mode and report on the discovery of two galaxy

clusters, SPT-CL~J2332-5358 and SPT-CL~J2342-5411, in X-rays. The clusters were

also independently detected through their SZE signal by the SPT and in the

optical band in the BCS data. They are thus the first clusters detected under

survey conditions by all major cluster search approaches. This work also

demonstrates the potential of the mosaic mode observations to effectively cover

large sky areas and detect massive clusters out to redshifts $\sim1$ even with

shallow exposures.

The last part of the thesis provides an example of a multi-wavelength

analysis of two high-redshift ($z>1$) systems in the framework of the XMM-\emph{Newton}

Distant Cluster Project. With the detection and studies of these

high redshift systems we are for the first time able to see the

assembly phase of the galaxy population of the clusters, which in

nearby systems is totally passive, but at these high redshifts

still show signatures of star formation.