Stepper microactuators driven by ultrasonic power transfer

Advances in miniature devices for biomedical applications are creating ever-increasing requirements for their continuous, long lasting, and reliable energy supply, particularly for implanted devices. As an alternative to bulky and cost inefficient batteries that require occasional recharging and replacement, energy harvesting and wireless power delivery are receiving increased attention. While the former is generally only suited for low-power diagnostic microdevices, the latter has greater potential to extend the functionality to include more energy demanding therapeutic actuation such as drug release, implant mechanical adjustment or microsurgery. This thesis presents a novel approach to delivering wireless power to remote medical microdevices with the aim of satisfying higher energy budgets required for therapeutic functions. The method is based on ultrasonic power delivery, the novelty being that actuation is powered by ultrasound directly rather than via piezoelectric conversion. The thesis describes a coupled mechanical system remotely excited by ultrasound and providing conversion of acoustic energy into motion of a MEMS mechanism using a receiving membrane coupled to a discrete oscillator. This motion is then converted into useful stepwise actuation through oblique mechanical impact. The problem of acoustic and mechanical impedance mismatch is addressed. Several analytical and numerical models of ultrasonic power delivery into the human body are developed. Major design challenges that have to be solved in order to obtain acceptable performance under specified operating conditions and with minimum wave reflections are discussed. A novel microfabrication process is described, and the resulting proof-of-concept devices are successfully characterized.Open Acces

Electronic spectroscopy of unsaturated hydrocarbons and sulfur-terminated carbon chains by cavity ringdown

Unsaturated hydrocarbons are highly reactive species that are found in flames and plasma discharges being important intermediates in the formation of polyaromatic hydrocarbons (PAHs) and in the processes of chemical vapor deposition (CVD). Some particular unsaturated hydrocarbons have been identified in the interstellar medium where their role is not yet fully understood. Linear carbon chains are one of the simplest rigid nanostructures that can potentially conduct electron current. Most of the unsaturated hydrocarbons are highly reactive species and for this reason they can only be studied in situ during the short time after their formation. The species are generated in the gas phase through an electrical discharge of a precursor gas and cooled in the supersonic expansion. High-resolution optical absorption spectra are recorded using a tunable dye laser. Because the concentrations of the reactive species studied are generally low, highly sensitive detection technique has to be used. This work presents a study of highly unsaturated hydrocarbons by cavity ringdown spectroscopy (CRDS). High-resolution electronic spectra of ions and radicals allow identifying them in remote environments such as interstellar medium and providing information about the physical conditions of the environment. It is shown how the information about the structure of the unknown absorbing species can be deduced from its rotationally resolved spectrum

Thermal equilibration between two quantum systems

Two identical finite quantum systems prepared initially at different temperatures, isolated from the environment, and subsequently brought into contact are demonstrated to relax towards Gibbs-like quasi-equilibrium states with a common temperature and small fluctuations around the time-averaged expectation values of generic observables. The temporal thermalization process proceeds via a chain of intermediate Gibbs-like states. We specify the conditions under which this scenario occurs and corroborate the quantum equilibration with two different models.Comment: 10 pages, 9 figures, including supplementary materia

Modeling and optimization of non-phased two-dimensional ultrasonic arrays.

Ultrasonic image acquisition with non-phased 2D arrays is a relatively new method in NDE inspection. Historically, ultrasonic array development progressed mostly in the medical imaging where phased arrays found a great application. However, in the field of NDE inspection of metals, heavy plastics and composites, and many other materials the applicability of phased arrays is often restricted due to physical limitations. On the other hand, using versatile systems with mechanical scanning is not always convenient. Therefore, non-phased arrays of independent elements have a strong potential for becoming a valuable tool for rapid ultrasonic image acquisition in the industrial environment as well as in many other areas where conventional methods may not be applicable. The main motivation of this work is to build the necessary mathematical apparatus for estimating the process of signal and image formation in such systems. A model of signal penetration through a complex multilayered structure with non-parallel interfaces is discussed in the plane-wave approximation. This model is then refined to finite-size transducers and finite-size defects inside the sample. A new method of obtaining the beam structure in such multi-layered media is presented. The advantage of this method is that it allows for a very fast calculation while the precision is still comparable to more precise and more computationally expensive methods. A new method of calculating the response of the transducer to defects inside the sample is presented and discussed. The results of numerical calculations using these two methods are discussed and compared with experimental data. Using these models, image formation algorithms together with new image refining techniques are discussed. Source: Dissertation Abstracts International, Volume: 65-07, Section: B, page: 3496. Adviser: Roman Gr. Maev. Thesis (Ph.D.)--University of Windsor (Canada), 2002

Quantum machine using cold atoms

For a machine to be useful in practice, it preferably has to meet two requirements: namely, (i) to be able to perform work under a load and (ii) its operational regime should ideally not depend on the time at which the machine is switched-on. We devise a minimal setup, consisting of two atoms only, for an ac-driven quantum motor which fulfills both these conditions. Explicitly, the motor consists of two different interacting atoms placed into a ring-shaped periodic optical potential -- an optical "bracelet" --, resulting from the interference of two counter-propagating Laguerre-Gauss laser beams. This bracelet is additionally threaded by a pulsating magnetic flux. While the first atom plays a role of a quantum "carrier", the second serves as a quantum "starter", which sets off the "carrier" into a steady rotational motion. For fixed zero-momentum initial conditions the asymptotic carrier velocity saturates to a unique, nonzero value which becomes increasingly independent on the starting time with increasing "bracelet"-size. We identify the quantum mechanisms of rectification and demonstrate that our quantum motor is able to perform useful work.Comment: simplified notations, extended figure captions; 16 pages, 6 figure

Propagating large open quantum systems towards their steady states: cluster implementation of the time-evolving block decimation scheme

Many-body quantum systems are subjected to the Curse of Dimensionality: The dimension of the Hilbert space $\mathcal{H}$, where these systems live in, grows exponentially with systems' 'size' (number of their components, "bodies"). It means that, in order to specify a state of a quantum system, we need a description whose length grows exponentially with the system size. However, with some systems it is possible to escape the curse by using low-rank tensor approximations known as `matrix-product state/operator (MPS/O) representation' in the quantum community and `tensor-train decomposition' among applied mathematicians. Motivated by recent advances in computational quantum physics, we consider chains of $N$ spins coupled by nearest-neighbor interactions. The spins are subjected to an action coming from the environment. Spatially disordered interaction and environment-induced decoherence drive systems into non-trivial asymptotic states. The dissipative evolution is modeled with a Markovian master equation in the Lindblad form. By implementing the MPO technique and propagating system states with the time-evolving block decimation (TEBD) scheme (which allows to keep the length of the state descriptions fixed), it is in principle possible to reach the corresponding steady states. We propose and realize a cluster implementation of this idea. The implementation on four nodes allowed us to resolve steady states of the model systems with $N = 128$ spins

Astrocyte dystrophy in ageing brain parallels impaired synaptic plasticity

Little is known about age-dependent changes in structure and function of astrocytes and of the impact of these on the cognitive decline in the senescent brain. The prevalent view on the age-dependent increase in reactive astrogliosis and astrocytic hypertrophy requires scrutiny and detailed analysis. Using two-photon microscopy in conjunction with 3D reconstruction, Sholl and volume fraction analysis, we demonstrate a significant reduction in the number and the length of astrocytic processes, in astrocytic territorial domains andin astrocyte-to-astrocyte coupling in the aged brain. Probing physiology of astrocytes with patch clamp, and Ca2+ imaging revealed deficits in K+ and glutamate clearance and spatiotemporal reorganisation of Ca2+ events in old astrocytes. These changes paralleled impaired synaptic long-term potentiation (LTP) in hippocampal CA1 in old mice. Our findings may explain the astroglial mechanisms of age-dependent decline in learning and memory.The research was supported by the Russian Science Foundation grant 20‐14‐00241

Tuning the mobility of a driven Bose-Einstein condensate via diabatic Floquet bands

We study the response of ultracold atoms to a weak force in the presence of a temporally strongly modulated optical lattice potential. It is experimentally demonstrated that the strong ac-driving allows for a tailoring of the mobility of a dilute atomic Bose-Einstein condensate with the atoms moving ballistically either along or against the direction of the applied force. Our results are in agreement with a theoretical analysis of the Floquet spectrum of a model system, thus revealing the existence of diabatic Floquet bands in the atom's band spectra and highlighting their role in the non-equilibrium transport of the atoms