RESUMEN
Acoustic recordings of artillery shots feature the signatures of the shot's muzzle, projectile, and impact waves modulated by the environment. This study aims at improving the sensing of such shots using a set of synchronous acoustic sensors distributed over a 1 km2 area. It uses the time matching approach, which is based on finding the best match between the observed and pre-calculated times of arrivals of the various waves at each sensor. The pre-calculations introduced here account for the complex acoustic source with a 6-degrees-of-freedom ballistic trajectory model, and for the propagation channel with a wavefront-tracking acoustic model including meteorological and terrain effects. The approach is demonstrated using three recordings of artillery shots measured by sensors which are more than 10 km from the point of fire and distributed at several hundred meters away from and around the target points. Using only the impact wave, it locates the impact point with an error of a few meters. Processing the muzzle and impact and projectile waves enables the estimation of the weapon's position with a 1 km error. Sensitivities of the localization method to various factors such as the number of sensors, atmospheric data, and the number of processed waves are discussed.
RESUMEN
Propagating impulse sounds are sensitive to the varying near-surface atmosphere. This study reports on an experimental assessment of this sensitivity under well-controlled outdoor conditions. The experiment, conducted over a flat terrain, features 14 synchronous acoustic sensors at ranges up to 450 m from reproducible, transient sources. It scanned over the upwind, crosswind, and downwind propagations, and also documents the temporal and spatial coherences of the acoustic field. Concurrent atmospheric measurements documented the near-surface, essentially wind-driven atmosphere, and included turbulence monitoring. The analysis reveals how the environmental propagation processes combine to form the large variety of recorded signatures. The deterministic versus stochastic variations of the signatures are distinguished, and both are shown to affect the time of arrival (wander) and the shape (spread) of the pulses. The study also discusses the potential impacts of these variations on acoustic sensing of transient signals like gun shots and explosions.
RESUMEN
Nanoscale bubbles generated around laser-excited metallic nanoparticles are promising candidates for targeted drug and gene delivery in living cells. The development of new nanomaterials for efficient nanobubble-based therapy is however limited by the lack of reliable computational approaches for the prediction of their size and dynamics, due to the wide range of time and space scales involved. In this work, we present a multiscale modeling framework that segregates the various channels of plasmon de-excitation and energy transfer to describe the generation and dynamics of plasmonic nanobubbles. Detailed comparison with time-resolved shadowgraph imaging and spectroscopy data demonstrates that the bubble size, dynamics, and formation threshold can be quantitatively predicted for various types of nanostructures and irradiation parameters, with an error smaller than the experimental uncertainty. Our model in addition provides crucial physical insights into non-linear interactions in the near-field that should guide the experimental design of nanoplasmonic materials for nanobubble-based applications in nanomedicine.
RESUMEN
Precise spatial and temporal control of pressure stimulation at the nanometer scale is essential for the fabrication and manipulation of nano-objects, and for exploring single-molecule behaviour of matter under extreme conditions. However, state-of-the-art nano-mechanical transducers require sophisticated driving hardware and are currently limited to moderate pressure regimes. Here we report a gold plasmonic bowtie (AuBT) nano-antennas array that can generate extreme pressure stimulus of â¼100 GPa in the ps (10-12 s) time scale with sub-wavelength resolution upon irradiation with ultra-short laser pulses. Our method leverages the non-linear interaction of photons with water molecules to excite a nano-plasma in the plasmon-enhanced near-field and induce extreme thermodynamic states. The proposed method utilizes laser pulses, which in contrast to micro- and nano-mechanical actuators offers simplicity and versatility. We present time-resolved shadowgraphic imaging, electron microscopy and simulation data that suggest that our platform can efficiently create cavitation nano-bubbles and generate intense pressure in specific patterns, which can be controlled by the selective excitation of plasmon modes of distinct polarizations. This novel platform should enable probing non-invasively the mechanical response of cells and single-molecules at time and pressure regimes that are currently difficult to reach with other methods.