Design, fabrication and characterization of composite piezoelectric ultrafine fibers for cochlear stimulation

Sensorineural hearing loss, primed by dysfunction or death of hair cells in the cochlea, is the main cause of severe or profound deafness. Piezoelectric materials work similarly to hair cells, namely, as mechano-electrical transducers. Polyvinylidene fluoride (PVDF) films have demonstrated potential to replace the hair cell function, but the obtained piezoresponse was insufficient to stimulate effectively the auditory neurons. In this study, we reported on piezoelectric nanocomposites based on ultrafine PVDF fibers and barium titanate nanoparticles (BTNPs), as a strategy to improve the PVDF performance for this application. BTNP/PVDF fiber meshes were produced via rotating-disk electrospinning, up to 20/80 weight composition. The BTNP/PVDF fibers showed diameters ranging in 0.160-1.325 μm. Increasing collector velocity to 3000 rpm improved fiber alignment. The piezoelectric β phase of PVDF was well expressed following fabrication and the piezoelectric coefficients increased according to the BTNP weight ratio. The BTNP/PVDF fibers were not cytotoxic towards cochlear epithelial cells. Neural-like cells adhered to the composite fibers and, upon mechanical stimulation, showed enhanced viability. Using BTNP filler for PVDF matrices, in the form of aligned ultrafine fibers, increased the piezoresponse of PVDF transducers and favored neural cell contact. Piezoelectric nanostructured composites might find application in next generation cochlear implants

Self-Contained Hybrid Electro-Hydraulic Actuators using Magnetostrictive and Electrostrictive Materials

Hybrid electro-hydraulic actuators using smart materials along with flow rectification have been widely reported in recent years. The basic operation of these actuators involves high frequency bidirectional operation of an active material that is converted into unidirectional fluid motion by a set of valves. While theoretically attractive, practical constraints limit the efficacy of the solid-fluid hybrid actuation approach. In particular, inertial loads, fluid viscosity and compressibility combine with loss mechanisms inherent in the active material to limit the effective bandwidth of the driving actuator and the total output power. A hybrid actuator was developed by using magnetostrictive TerFeNOL-D as the active driving element and hydraulic oil as the working fluid. Tests, both with and without an external load, were carried out to measure the unidirectional performance of the actuator at different pumping frequencies and operating conditions. The maximum no-load output velocity was 84 mm/s with a 51 mm long rod and 88 mm/s with a 102 mm long rod, both noted around 325 Hz pumping frequency, while the blocked force was close to 89 N. Dynamic tests were performed to analyze the axial vibration characteristics of the Terfenol-D rods and frequency responses of the magnetic circuits. A second prototype actuator employing the same actuation principle was then designed by using the electrostrictive material PMN-32%PT as the driving element. Tests were conducted to measure the actuator performance for varying electrical input conditions and fluid bias pressures. The peak output velocity obtained was 330 mm/s while the blocked force was 63 N. The maximum volume flow rate obtained with the PMN-based actuator was more than double that obtained from the Terfenol-D-based actuator. Theoretical modeling of the dynamics of the coupled structural-hydraulic system is extremely complex and several models have been proposed earlier. At high pumping frequencies, the fluid inertia dominates the viscous effects and the problem becomes unsteady in nature. Due to high pressures inside the actuator and the presence of entrained air, compressibility of the hydraulic fluid is important. A new mathematical model of the hydraulic hybrid actuator was formulated in time-domain to show the basic operational principle under varying operating conditions and to capture the phenomena affecting system performance. Linear induced strain behavior was assumed to model the active material. Governing equations for the moving parts were obtained from force equilibrium considerations, while the coupled inertia-compliance of the fluid passages was represented by a lumped parameter approach to the transmission line model, giving rise to strongly coupled ordinary differential equations. Compressibility of the working fluid was incorporated by using the bulk modulus. The model was then validated using the measured performance of both the magnetostrictive and electrostrictive-based hybrid actuators

The Fluid Dynamics of Heart Development: The effect of morphology on flow at several stages

Proper cardiogenesis requires a delicate balance between genetic and environmental (epigenetic) signals, and mechanical forces. While many cellular biologists and geneticists have extensively studied heart morphogenesis using various experimental techniques, only a few scientists have begun using mathematical modeling as a tool for studying cardiogenic events. Hemodynamic processes, such as vortex formation, are important in the generation of shear at the endothelial surface layer and strains at the epithelial layer, which aid in proper morphology and functionality. The purpose of this thesis is to study the underlying fluid dynamics in various stages on heart development, in particular, the morphogenic stages when the heart is a linear heart tube as well as during the onset of ventricular trabeculation. Previous mathematical models of the linear heart tube stage have focused on mechanisms of valveless pumping, whether dynamic suction pumping (impedance pumping) or peristalsis; however, they all have neglected hematocrit. The impact of blood cells was examined by fluid-structure interaction simulations, via the immersed boundary method. Moreover, electrophysiology models were incorporated into an immersed boundary framework, and bifurcations within the morphospace were studied that give rise to a spectrum of pumping regimes, with peristaltic-like waves of contraction and impedance pumping at the extremes. Lastly, effects of resonant pumping, damping, and boundary inertial effects (added mass) were studied for dynamic suction pumping. The other stage of heart development considered here is during the onset of ventricular trabeculation. This occurs after the heart has undergone the cardiac looping stage and now is a multi-chambered pumping system with primitive endocardial cushions, which act as precursors to valve leaflets. Trabeculation introduces complex morphology onto the inner lining of the endocardium in the ventricle. This transition of a smooth endocardium to one with complex geometry, may have significant effect on the intracardial fluid dynamics and stress distribution within emrbyonic hearts. Previous studies have not included these geometric perturbations along the ventricular endocardium. The role of trabeculae on intracardial (and intertrabecular) flows was studied using two different mathematical models implemented within an immersed boundary framework. It is shown that the trabecular geometry and number density have a significant effect on such flows. Furthermore this thesis also focused attention to the creation of software for scientists and engineers to perform fluid-structure interaction simulations at an accelerated rate, in user-friendly environments for beginner programmers, e.g., MATLAB or Python 3.5. The software, IB2d, performs fully coupled fluid-structure interaction problems using Charles Peskin's immersed boundary method. IB2d is capable of running a vast range of biomechanics models and contains multiple options for constructing material properties of the fiber structure, advection-diffusion of a chemical gradient, muscle mechanics models, Boussinesq approximations, and artificial forcing to drive boundaries with a preferred motion. The software currently contains over 50 examples, ranging from rubber-bands oscillating to flow past a cylinder to a simple aneurysm model to falling spheres in a chemical gradient to jellyfish locomotion to a heart tube pumping coupled with electrophysiology, muscle, and calcium dynamics modelsDoctor of Philosoph

Belle II Technical Design Report

The Belle detector at the KEKB electron-positron collider has collected almost 1 billion Y(4S) events in its decade of operation. Super-KEKB, an upgrade of KEKB is under construction, to increase the luminosity by two orders of magnitude during a three-year shutdown, with an ultimate goal of 8E35 /cm^2 /s luminosity. To exploit the increased luminosity, an upgrade of the Belle detector has been proposed. A new international collaboration Belle-II, is being formed. The Technical Design Report presents physics motivation, basic methods of the accelerator upgrade, as well as key improvements of the detector.Comment: Edited by: Z. Dole\v{z}al and S. Un

Text Similarity Between Concepts Extracted from Source Code and Documentation

Context: Constant evolution in software systems often results in its documentation losing sync with the content of the source code. The traceability research field has often helped in the past with the aim to recover links between code and documentation, when the two fell out of sync. Objective: The aim of this paper is to compare the concepts contained within the source code of a system with those extracted from its documentation, in order to detect how similar these two sets are. If vastly different, the difference between the two sets might indicate a considerable ageing of the documentation, and a need to update it. Methods: In this paper we reduce the source code of 50 software systems to a set of key terms, each containing the concepts of one of the systems sampled. At the same time, we reduce the documentation of each system to another set of key terms. We then use four different approaches for set comparison to detect how the sets are similar. Results: Using the well known Jaccard index as the benchmark for the comparisons, we have discovered that the cosine distance has excellent comparative powers, and depending on the pre-training of the machine learning model. In particular, the SpaCy and the FastText embeddings offer up to 80% and 90% similarity scores. Conclusion: For most of the sampled systems, the source code and the documentation tend to contain very similar concepts. Given the accuracy for one pre-trained model (e.g., FastText), it becomes also evident that a few systems show a measurable drift between the concepts contained in the documentation and in the source code.</p

Marine invertebrates and sound

Peer ReviewedPostprint (published version

Studies of mechanical and optical properties of thin film coatings for future gravitational wave detectors

Gravitational radiation in the form of gravitational waves was the last prediction to be verified from Einstein's general theory of relativity. Einstein suggested that when a body or bodies with an asymmetric distribution of mass accelerated, energy from the motion would create distortions in space-time which would propagate in all directions at the speed of light. Until the first confirmed observation of gravitational waves from the coalescence of two black holes, this theory had not been experimentally proven. The first gravitational wave (GW) event, `GW150914' confirmed Einstein's predictions, with the event releasing 3 solar masses worth of energy as gravitational radiation during the collision. Since this event, more than 50 confident GW events have been detected, including the first observation of an extremely rare kilonova event after the collision of two neutron stars. Gravitational waves exert fluctuating strains on space as they propagate, resulting in changes in the length of objects that they pass through. Current gravitational wave detectors use laser interferometry to measure this effect using a single laser source and beamsplitter. Two perpendicular laser beams are created and used to monitor the positions of suspended mirrors at the ends of km-scale perpendicular arms. The laser beams reflected from the mirrors are recombined at the beam splitter, creating an interference pattern. Any changes in these mirrors' position then result in a differential change in the arm length inside the detector, altering the generated interference pattern. As the expected change in differential arm length produced by a gravitational wave event is 1x10^-18m all other sources of motion, or noise, must be reduced to exceedingly low levels to maximise the sensitivity to such events. Throughout the range of frequencies to which a gravitational wave detector is sensitive too, its highest sensitivity occurs between approx 50 Hz and 150 Hz. In this frequency band, thermal noise stemming from thermal vibrations in the materials used to create highly reflecting mirror coatings for each test mass limits the sensitivity of the detector. Each material's contributions to the level of thermal noise are proportional to its level of mechanical loss, its temperature and dimensions of the laser beam on its surface. This thesis will focus on the development of coating materials with low mechanical loss and low optical absorption, which can be used to decrease levels of thermal noise inside and increase the stability of a gravitational wave detector. As the amount of laser light absorbed into the coating layer also dictates the test mass's thermal state, a large part of this research will also focus on this aspect of coating measurement. A large part of the work in this thesis involves the first experimental verification of the so-called `multimaterial coating' principle, through testing the optical absorption and room-temperature and cryogenic mechanical loss, of an example of this type of novel coating design. Chapter 1 describes the nature of gravitational radiation and its possible sources. An introduction to the experimental interferometry techniques used in a gravitational wave detector is considered, and notable sources of noise are summarised. Chapter 2 provides a detailed summary of coating thermal noise in gravitational wave detectors. This chapter also introduces some of the recent advancements and current avenues of research in HR gravitational wave detector coatings. Chapter 3 is an account of work carried out by the author at the LIGO Livingston Observatory to develop a technique for monitoring the absorption of the detector mirrors in situ. By studying the resonant frequencies of coated test masses in a gravitational wave detector, a relationship between frequency and the change in test mass temperature by laser heating can be produced. If the total laser power and the level of optical absorption of the coated optic are known, predictions of how its resonant frequencies will change can be modelled using finite element analysis (FEA). If the optical absorption of the coating material at the time of deposition was known, the shift in resonant frequencies of the test mass in response to laser heating could be used to predict any changes in the absorption of the optic. Chapter 4 discusses the experimental Photothermal Common-path Interferometry (PCI) technique used by the author to measure the optical absorption of thin-film coatings. This technique is used to study the peculiar changes in optical absorption of tantalum pentoxide Ta2O5 coatings after heat treatment in a laboratory atmosphere and under a low vacuum. Implementation of a polarisation stabilisation and power correction system into the PCI techniques has allowed for 2-dimensional absorption maps to produce these samples. In this chapter, measurements of a novel multimaterial coating designed to decrease coating thermal noise and optical absorption are studied. The material is subjected to two different heat treatment studies, and its optical absorption is characterised using 1064 nm, 1550 nm and 2000 nm laser light. In Chapter 5, the methods and techniques used to measure the mechanical loss (internal friction) of coating materials are introduced. Throughout this chapter, the development of an automated measurement technique used to characterise the mechanical loss diameter = 3" (76.2 mm), t = 2. 6 mm is discussed and compared to existing measurement techniques. Chapter 6 describes the use of the technique developed in Chapter 5 to study the mechanical loss of the same novel multimaterial coating as a function of heat-treatment temperature. These measurements allow the level of coating thermal noise produced by each multimaterial coating to be calculated using the methods described in Chapter 2. The development of the gentle nodal support described in Chapter 5 is continued in Chapter 7, upgrading the apparatus to function at cryogenic temperatures (80 K<T<293 K). By creating an automated gentle nodal support that operates at cryogenic temperatures, the mechanical loss of coating materials can be characterised for third-generation gravitational wave detector applications. This chapter describes the development of the CryoGeNS system and the characterisation of uncoated diameter = 2" (50.8 mm), t=360um crystalline silicon disks. Chapter 8 details cryogenic mechanical loss measurements of the prototype multimaterial coating, carried out using the CryoGeNS nodal support. Coating loss calculated from each disk is compared to measurements of the same samples carried out in a second commercial cryostat and cryogenic measurements of cSi cantilevers coated in the same materials. This allows the level of thermal noise improvement of these coatings to be calculated as a function of temperature

Etude des processus de transport et conversion d'énergie dans la magnétosphère terrestre à partir des observations THEMIS

Les magnétosphères sont des objets universels qui résultent de l'interaction entre un écoulement plasma et un obstacle magnétisé. Leurs structures reposent sur un système de courant qui assurent la transition entre différents régimes plasma et à travers lesquels l'énergie électromagnétique peut être convertie en énergie cinétique et thermique et inversement. Dans le cas de la Terre, c'est la couche de courant s'écoulant dans le plan médian de la queue magnétosphérique qui est la clef de voûte du système et c'est là que se développe une instabilité majeure autour de laquelle s'organise le cycle énergétique du système. A la suite d'une instabilité globale, l'énergie transmise par le vent solaire et accumulée dans la queue magnétosphérique est dissipée de façon explosive lors de périodes perturbées appelées sous-orages magnétosphériques. Les missions multi-points telles Cluster, Double Star ou THEMIS permettent une analyse multi-échelle de la queue magnétosphérique. Une étude de cas de trois sous-orages successifs montre que, les changements observés dans la queue (dipolarisation se propageant vers la queue et injections de particules vers la Terre) correspondent à une disruption de courant se propageant en direction anti-solaire. La comparaison des données avec des simulations cinétiques (PIC, Particle In Cell) suggère que les signatures observées peuvent être celle du processus de reconnexion magnétique initié dans la queue proche se propageant en direction antisolaire. Les dipolarisations sont des signatures caractéristiques des sous-orages magnétosphériques. L'analyse d'une série de huit dipolarisations montre qu'elles ne sont pas toujours associées aux sous-orages mais à de petites perturbations très localisées en région aurorale. Une analyse statistique de ce type de dipolarisations a permis de caractériser les changements de l'état de la couche de plasma qu'elles provoquent (épaississement, réduction de la densité de courant, augmentation de la densité d'énergie).Magnetospheres are universal objects which result from the interaction between plasma flows and a magnetized obstacle. Their structures are based on a system of currents which insure the transition between various plasma regimes and through which the electromagnetic energy can be converted in kinetic and thermal energy. In the case of the Earth, the current sheet flowing in the median plan of the magnetotail is the keystone of the system and the place where a major instability occur. The energy cycle of the system is organized around it. Following the global instability, the energy transmitted by the solar wind and accumulated in the magnetotail is dissipated in an explosive way during perturbed periods called magnetospheric substorms. Multi-points missions such as Cluster, Double Star or THEMIS, permit a multi-scale analysis of the magnetotail. A case study of three successive substorms show that, the changes observed in the tail (dipolarisations propagating towards the tail and injections of particles towards the Earth) correspond to a current disruption propagating in anti-solar direction. Comparing data with kinetics simulation (PIC, Particle In Cell) suggests that the signatures observed can also be interpreted as magnetic reconnexion initiated in the near tail and propagating in antisolar direction. Dipolarisations are characteristic signatures of substorms. The analysis of eight successive dipolarisations shows that they are not always associated with substorms but with very localized disturbances in the auroral region. A statistical analysis of this type of dipolarisations allows characterizing the changes they make in the plasma sheet (thickening, current density reduction, increase of the energy density)