SLICING THE EARTH: A layer-stripping method employing a causality-based imaging condition

During the last decades many different seismic inversion algorithms have been developed. Since the problem to be solved is non-linear and does not have a unique solution, every method makes use of its own approximations and assumptions. As a step towards a new approach to the inversion of seismic data we have designed and partly implemented a...

Nanoelectromechanics of suspended carbon nanotubes

Nanomechanical properties of few-layer graphene membranes

We have measured the mechanical properties of few-layer graphene and graphite flakes that are suspended over circular holes. The spatial profile of the flake’s spring constant is measured with an atomic force microscope. The bending rigidity of and the tension in the membranes are extracted by fitting a continuum model to the data. For flakes...

Self-detecting gate-tunable nanotube paddle resonators

We have fabricated suspended metal paddle resonators with carbon nanotubes functioning as self-detecting torsional springs. We observe gate-tunable resonances that either tune to higher or to lower frequencies when increasing the dc voltage on the back gate. We attribute the former modes to flexural vibrations of the paddle resonator, while the...

Mechanical systems at the nanoscale

This thesis describes experiments that were done with a wide range of nano(electro)mechanical systems (NEMS). These devices are promising candidates to study mechanics in the quantum regime. The experiments range from AFM measurements on few-layer graphene nanodrums, electrical detection of flexural modes of suspended carbon nanotubes both at...

Estimation of Diffusion Properties in Crossing Fiber Bundles

There is an ongoing debate on how to model diffusivity in fiber crossings. We propose an optimization framework for the selection of a dual tensor model and the set of diffusion weighting parameters b, such that both the diffusion shape and orientation parameters can be precisely as well as accurately estimated. For that, we have adopted the...

Nonlinear Modal Interactions in Clamped-Clamped Mechanical Resonators

A theoretical and experimental investigation is presented on the intermodal coupling between the flexural vibration modes of a single clamped-clamped beam. Nonlinear coupling allows an arbitrary flexural mode to be used as a self-detector for the amplitude of another mode, presenting a method to measure the energy stored in a specific resonance...

Tunable Backaction of a DC SQUID on an Integrated Micromechanical Resonator

We have measured the backaction of a dc superconducting quantum interference device (SQUID) position detector on an integrated 1 MHz flexural resonator. The frequency and quality factor of the micromechanical resonator can be tuned with bias current and applied magnetic flux. The backaction is caused by the Lorentz force due to the change in...

Discrete-time quadrature feedback cooling of a radio-frequency mechanical resonator

We have employed a feedback cooling scheme, which combines high-frequency mixing with digital signal processing. The frequency and damping rate of a 2 MHz micromechanical resonator embedded in a dc SQUID are adjusted with the feedback, and active cooling to a temperature of 14.3 mK is demonstrated. This technique can be applied to GHz resonators...

Mechanical properties of freely suspended semiconducting graphene-like layers based on MoS2

We fabricate freely suspended nanosheets of molybdenum disulphide (MoS2) which are characterized by quantitative optical microscopy and high-resolution friction force microscopy. We study the elastic deformation of freely suspended nanosheets of MoS2 using an atomic force microscope. The Young’s modulus and the initial pretension of the...

Interactive local super-resolution reconstruction of whole-body MRI mouse data: A pilot study with applications to bone and kidney metastases

In small animal imaging studies, when the locations of the micro-structures of interest are unknown a priori, there is a simultaneous need for full-body coverage and high resolution. In MRI, additional requirements to image contrast and acquisition time will often make it impossible to acquire such images directly. Recently, a resolution...