Study of the resonant behaviour of bubbles embbeded in gelatin

Many diseases present abnormally high pressures at different points of the circulatory system, such as inside the heart, the portal vein or the pulmonary artery. For this reason, physicians need to know the pressure at these specific points either to help diagnosis or to monitor the evolution of a patient’s condition. Nowadays, these pressure measurements are performed invasively, for instance by navigating a catheter with a pressure sensor at its tip to the point of interest. As any invasive procedure, acquiring these measurements presents a number of shortcomings that medical doctors would like to avoid. Consequently, providing physicians with a non-invasive pressure measurement technique would represent a great advance in the diagnosis and/or treatment of these patients. Ultrasound Contrast Agents (UCAs), microbubbles injected into the blood stream to aid ultrasonic imaging, offer the possibility of obtaining the blood pressure at localized points of the circulatory system in non-invasive ways. Indeed, it can be shown mathematically how these microbubbles oscillate at a characteristic frequency (resonance frequency) when insonated with a pressure pulse with the appropriate features. More interestingly, it can also be shown that this resonant frequency depends on the ambient pressure at the bubble’s location. With these ideas in mind, in this thesis we have conducted an experimental and numerical investigation aimed at measuring how the resonance frequency of bubbles immersed in gelatin depends on the ambient pressure. Since the focus of this work is on the Physics, rather than on implementing a practical technique, we have worked with millimetric bubbles (commercial UCAs are micrometric) in order to overcome a number of experimental problems associated with using very small bubbles. Furthermore, fixing the bubbles in gelatin also allows for a prolonged observation and thus facilitates the experiments. But at the same time, gelatin constitutes a very realistic model of the rheological properties of the soft tissue that would surround bubbles in some real medical applications (think, for instance, of a bubble circulating through a narrow capillary surrounded by soft tissue). In our experiments, bubbles are insonated with chirps: pressure pulses that sweep a range of frequencies that contains the resonance one. Then, the radius vs. time evolution of the bubbles is obtained by applying digital image processing techniques to high-speed movies acquired synchronously with the acoustic insonation. Finally, the time evolutions of the bubble radii are processed using wavelets to extract the main frequency at which they oscillate. Although the experimental procedure designed and implemented in this thesis detects that bubbles oscillate at a well-defined frequency close to the expected resonance ones, our numerical simulations and the analysis of the pressure signals reveal that this frequency is actually arising from an improper behavior of the piezoelectric transducer used to generate the pulses. Finally, we point out future lines in which this work could be improved, most notably replacing the transducer by another one that performs better in the range of frequencies of interest. This solution is being implemented at the time of writing this dissertation.Ingeniería Mecánic

Free-Standing, Thin-Film Sensors for the Trace Detection of Explosives

In a world focused on the development of cybersecurity, many densely populated areas and transportation hubs are still susceptible to terrorist attacks via improvised explosive devices (IEDs). These devices frequently employ a combination of peroxide based explosives as well as nitramines, nitrates, and nitroaromatics. Detection of these explosives can be challenging due to varying chemical composition and the extremely low vapor pressures exhibited by some explosive compounds. No electronic trace detection system currently exists that is capable of continuously monitoring both peroxide based explosives and certain nitrogen based explosives, or their precursors, in the vapor phase. Recently, we developed a thermodynamic sensor that can detect a multitude of explosives in the vapor phase at the parts-per-trillion (ppt) level. The sensors rely on the catalytic decomposition of the explosive and specific oxidation–reduction reactions between the energetic molecule and metal oxide catalyst; i.e. the heat effects associated with catalytic decomposition and redox reactions between the decomposition products and catalyst are measured. Improved sensor response and selectivity were achieved by fabricating free-standing, ultrathin film (1 µm thick) microheater sensors for this purpose. The fabrication method used here relies on the interdiffusion mechanics between a copper (Cu) adhesion layer and the palladium (Pd) microheater sensor. A detailed description of the fabrication process to produce a free-standing 1 µm thick sensor is presented

Label-Free MicroRNA Optical Biosensors

MicroRNAs (miRNAs) play crucial roles in regulating gene expression. Many studies show that miRNAs have been linked to almost all kinds of disease. In addition, miRNAs are well preserved in a variety of specimens, thereby making them ideal biomarkers for biosensing applications when compared to traditional protein biomarkers. Conventional biosensors for miRNA require fluorescent labeling, which is complicated, time-consuming, laborious, costly, and exhibits low sensitivity. The detection of miRNA remains a big challenge due to their intrinsic properties such as small sizes, low abundance, and high sequence similarity. A label-free biosensor can simplify the assay and enable the direct detection of miRNA. The optical approach for a label-free miRNA sensor is very promising and many assays have demonstrated ultra-sensitivity (aM) with a fast response time. Here, we review the most relevant label-free microRNA optical biosensors and the nanomaterials used to enhance the performance of the optical biosensor

Vocal fold vibratory and acoustic features in fatigued Karaoke singers

Session 3aMU - Musical Acoustics and Speech Communication: Singing Voice in Asian CulturesKaraoke is a popular singing entertainment particularly in Asia and is gaining more popularity in the rest of world. In Karaoke, an amateur singer sings with the background music and video (usually guided by the lyric captions on the video screen) played by Karaoke machine, using a microphone and an amplification system. As the Karaoke singers usually have no formal training, they may be more vulnerable to vocal fatigue as they may overuse and/or misuse their voices in the intensive and extensive singing activities. It is unclear whether vocal fatigue is accompanied by any vibration pattern or physiological changes of vocal folds. In this study, 20 participants aged from 18 to 23 years with normal voice were recruited to participate in an prolonged singing task, which induced vocal fatigue. High speed laryngscopic imaging and acoustic signals were recorded before and after the singing task. Images of /i/ phonation were quantitatively analyzed using the High Speed Video Processing (HSVP) program (Yiu, et al. 2010). It was found that the glottis became relatively narrower following fatigue, while the acoustic signals were not sensitive to measure change following fatigue. © 2012 Acoustical Society of Americapublished_or_final_versio