160 research outputs found
Alien Registration- Beaulieu, Samuel (Van Buren, Aroostook County)
https://digitalmaine.com/alien_docs/33316/thumbnail.jp
Optimizing the Model of the Viking-400 UAS
This project intends to update and redesign imperfections in the scanned 3D CAD model of the Viking 400 aircraft. This aircraft, similar to the Sierra-B UAS, will carry payloads of scientific instruments for research purposes. The goals of this project are to modify the current scanned model such that it better represents the physical qualities of the aircraft, as well as creating the features that are missing from the model. As the model was imported from a different software, many of the critical surfaces did not accurately reflect the actual aircraft. Those parts of the model were redesigned entirely so that they can be edited for future use, as well as correctly representing the aircraft as it is now. Additionally, parts of the aircraft that did not appear in the scanned model were designed and added to the new model. In order to prioritize ease of use for future missions, the model has been reorganized in a logical fashion that enables modification of specific parts of the aircraft. The organization of this model imitates the drawing tree of the Sierra-B, with the intention of maintaining a functional system of redesign, analysis, and implementation. Ultimately, this project will be a catalyst for making Viking 400 into a functional aircraft and increasing scientific research in airborne vehicles
A machine learning route between band mapping and band structure
The electronic band structure (BS) of solid state materials imprints the
multidimensional and multi-valued functional relations between energy and
momenta of periodically confined electrons. Photoemission spectroscopy is a
powerful tool for its comprehensive characterization. A common task in
photoemission band mapping is to recover the underlying quasiparticle
dispersion, which we call band structure reconstruction. Traditional methods
often focus on specific regions of interests yet require extensive human
oversight. To cope with the growing size and scale of photoemission data, we
develop a generic machine-learning approach leveraging the information within
electronic structure calculations for this task. We demonstrate its capability
by reconstructing all fourteen valence bands of tungsten diselenide and
validate the accuracy on various synthetic data. The reconstruction uncovers
previously inaccessible momentum-space structural information on both global
and local scales in conjunction with theory, while realizing a path towards
integrating band mapping data into materials science databases
Bloch Wavefunction Reconstruction using Multidimensional Photoemission Spectroscopy
Angle-resolved spectroscopy is the most powerful technique to investigate the
electronic band structure of crystalline solids. To completely characterize the
electronic structure of topological materials, one needs to go beyond band
structure mapping and probe the texture of the Bloch wavefunction in
momentum-space, associated with Berry curvature and topological invariants.
Because phase information is lost in the process of measuring photoemission
intensities, retrieving the complex-valued Bloch wavefunction from
photoemission data has yet remained elusive. In this Article, we introduce a
novel measurement methodology and observable in extreme ultraviolet
angle-resolved photoemission spectroscopy, based on continuous modulation of
the ionizing radiation polarization axis. By tracking the energy- and
momentum-resolved amplitude and phase of the photoemission modulation upon
polarization variation, we reconstruct the Bloch wavefunction of prototypical
semiconducting transition metal dichalcogenide 2H-WSe with minimal theory
input. This novel experimental scheme, which is articulated around the
manipulation of the photoionization transition dipole matrix element, in
combination with a simple tight-binding theory, is general and can be extended
to provide insights into the Bloch wavefunction of many relevant crystalline
solids.Comment: 11 pages, 5 figure
Role of Spin-Orbit Coupling in High-order Harmonic Generation Revealed by Super-Cycle Rydberg Trajectories
High-harmonic generation is typically thought of as a sub-laser-cycle
process, with the electron's excursion in the continuum lasting a fraction of
the optical cycle. However, it was recently suggested that long-lived Rydberg
states can play a particularly important role in atoms driven by the
combination of the counter-rotating circularly polarized fundamental light
field and its second harmonic. Here we report direct experimental evidence of
long and stable Rydberg trajectories contributing to high-harmonic generation.
We confirm their effect on the harmonic emission via Time-Dependent
Schr{\"o}dinger Equation simulations and track their dynamics inside the laser
pulse using the spin-orbit evolution in the ionic core, utilizing the
spin-orbit Larmor clock. Our observations contrast sharply with the general
view that long-lived Rydberg orbits should generate negligible contribution to
the macroscopic far-field high harmonic response of the medium. Indeed, we show
how and why radiation from such states can lead to well collimated macroscopic
signal in the far field
Observation of Multi-Directional Energy Transfer in a Hybrid Plasmonic–Excitonic Nanostructure
Hybrid plasmonic devices involve a nanostructured metal supporting localized surface plasmons to amplify light–matter interaction, and a non-plasmonic material to functionalize charge excitations. Application-relevant epitaxial heterostructures, however, give rise to ballistic ultrafast dynamics that challenge the conventional semiclassical understanding of unidirectional nanometal-to-substrate energy transfer. Epitaxial Au nanoislands are studied on WSe2 with time- and angle-resolved photoemission spectroscopy and femtosecond electron diffraction: this combination of techniques resolves material, energy, and momentum of charge-carriers and phonons excited in the heterostructure. A strong non-linear plasmon–exciton interaction that transfers the energy of sub-bandgap photons very efficiently to the semiconductor is observed, leaving the metal cold until non-radiative exciton recombination heats the nanoparticles on hundreds of femtoseconds timescales. The results resolve a multi-directional energy exchange on timescales shorter than the electronic thermalization of the nanometal. Electron–phonon coupling and diffusive charge-transfer determine the subsequent energy flow. This complex dynamics opens perspectives for optoelectronic and photocatalytic applications, while providing a constraining experimental testbed for state-of-the-art modelling
Ultrafast Hidden Spin Polarization Dynamics of Bright and Dark Excitons in 2H-WSe
We performed spin-, time- and angle-resolved extreme ultraviolet
photoemission spectroscopy (STARPES) of excitons prepared by photoexcitation of
inversion-symmetric 2H-WSe with circularly polarized light. The very short
probing depth of XUV photoemission permits selective measurement of
photoelectrons originating from the top-most WSe layer, allowing for direct
measurement of hidden spin polarization of bright and momentum-forbidden dark
excitons. Our results reveal efficient chiroptical control of bright excitons'
hidden spin polarization. Following optical photoexcitation, intervalley
scattering between nonequivalent K-K' valleys leads to a decay of bright
excitons' hidden spin polarization. Conversely, the ultrafast formation of
momentum-forbidden dark excitons acts as a local spin polarization reservoir,
which could be used for spin injection in van der Waals heterostructures
involving multilayer transition metal dichalcogenides
- …