Research

Existing nanofluidic systems can perform parallel manipulation of single biopolymers via geometric confinement in nanoscale structures such as nanoslits, nanochannels and nanocavities. Such technology is powerful but the need to introduce molecules intact from bulk solution into nanoconfined environments introduces certain challenges and limitations (such as fragmentation of large molecules). Here we present a device that can perform molecular confinement electrically and allows direct loading of dsDNA from bulk solution. In our approach, we locally sculpt an electric field applied between two parallel electrodes via coating the lower electrode with a dielectric layer that contains arrays of etched holes. The field lines are concentrated at the position of the etched holes, leading to a locally enhanced field at the holes that acts electrokinetically to capture dsDNA; the holes thus act as attractive potential wells for the DNA. We find periodic driving of the device using signals with frequencies in the 1kHz to 1MHz range leads to long-range capture and reversible confinement of the molecules in the field wells while avoiding electrochemical degradation of the device and analytes. We find that the degree of confinement is frequency-dependent, allowing fine sub nanometer control of the molecules; different tunable confinement regimes can be described by the dynamics of resetting. Trapping of larger dsDNA leads to multi-well states where a molecule spans multiple wells with a resulting frequency dependent well occupancy.

The epoch when the first stars in the Universe were born is an unsolved mystery in cosmology. Observations of this time are possible only through measurements of the redshifted 21-cm neutral hydrogen line, which are fundamental to our understanding of the Universe. The epoch known as the Cosmic Dawn can be probed by making 21-cm brightness temperature measurements averaged spatially across the sky, and the glow of the first stars is expected to cause a spectral absorption feature in this global signal. The EDGES experiment in 2018 reported an absorption feature centered at 78~MHz, with 0.5 K in depth; this absorption feature can be interpreted as being a detection of the global signal. RFI contamination, strong foreground emissions from the Milky Way (1000 K), ionospheric effects, and instrumental systematics are the biggest challenges to overcome experimentally, representing the primary limitations in obtaining a high-fidelity detection, and therefore new independent measurements are necessary. This thesis focuses on the development of MIST and Mini-MIST, new experimental efforts for detecting the global signal. These instruments will be installed in northern Chile and at the McGill Arctic Research Station (MARS), two of the most radio quiet sites on Earth. Because the measurement is limited by systematics, rather than statistical error, the primary challenge is precise design and characterization of MIST subsystems. The ultimate goal involves distinguishing the signal from Galactic foreground emission, which requires rigorously calibrating the instrument to approximately 1 part in 10,000. This thesis presents the development of a variety of MIST subsystems, including antenna design, readout electronics characterization, data acquisition, software development, and environmental monitoring of soil conductivity and permittivity.  With our efforts, MIST and Mini-MIST will provide invaluable, independent measurements of the Cosmic Dawn signal.  More details on the MIST website.

In this work, we develop solutions for a generalized acoustic scattering by a fluidic sphere and the resulting acoustic force exerted on the scatterer. Simulations for the scattered field generated by standing waves are obtained to validate the boundary conditions. Experimentally, methods for the visualization of the field were built such as a Schlieren imaging technique and an apparatus for the  angular resolved acoustic scattering intensity but both provided no conclusive results. The resulting acoustic trap was able to trap air microbubbles ranging from 40µm to 60µm. The corresponding radiation acoustic force was obtained considering the forces to which the bubbles were submitted: Stokes' drag, buoyancy, and the acoustic force. Results show forces ranging from F ~25µN to F~120 µN. Theoretically, the radiation force upon the bubbles canceled in the direction transverse to the standing wave for the theoretical model and thus the modeling of a focused beam should be considered for a complete plausible description of the phenomenon.

The mechanisms of production and acceleration of Ultra-High Energy Cosmic Rays (UCAEs) are one of the main open problems in Astroparticle Physics. Studies on the anisotropy of events at the Pierre Auger Observatory revealed an important correlation between the arrival directions of the highest energy events and the positions of Active Galaxy Nuclei (NAGs). This result motivated a series of studies on small and large scale anisotropies using the larger number of events that was obtained in recent years and that will be increased in the future. There is also motivation to search for correlations with other types of astrophysical sources, such as gamma radiation bursts. In this scientific initiation project, research activities are proposed in a theme related to the analysis of the anisotropy of the arrival directions of RCUAE events.