- Portillo, S.K.N., Parejko, J.K., Vergara, J.R., Connolly, A. (2020) Dimensionality reduction of SDSS Spectra with Variational Autoencoders. The Astronomical Journal. 160:45.
We implement a Bayesian method for producing point source catalogues. Rather than obtaining a single catalogue, a probability distribution of catalogues that is consistent with the data is inferred. This probabilistic catalogue better captures the inherent uncertainties in point source identification. We use this method to constrain unresolved point source populations and better de-blend stars in crowded fields.
- Portillo, S.K.N.*, Speagle, J.S.*, Finkbeiner, D.P. (2020) Photometric Biases in Modern Surveys. The Astronomical Journal. 159:165. *equal contributions
Interview: AAS Journal Author Series
- Feder, R.M., Portillo, S.K.N., Daylan, T., and Finkbeiner, D.P. (2020) Multiband Probabilistic Cataloging: A Joint Fitting Approach to Point Source Detection and Deblending. The Astronomical Journal. 159:163.
Research Highlight: AAS Nova
- Portillo, S.K.N., Lee, B. C. G., Daylan, T., Finkbeiner, D.P. (2017) Improved Point Source Detection in Crowded Fields using Probabilistic Cataloging. The Astronomical Journal. 154:4.
- Daylan, T., Portillo, S.K.N., Finkbeiner, D.P. (2017) Inference of unresolved point sources at high galactic latitudes using probabilistic catalogs. The Astronomical Journal. 839:4.
Statistics for the Turbulent ISM
- Saydjari, A.K., Portillo, S.K.N., Slepian, Z., Kahraman, S., Burkhart, B., Finkbeiner, D. (2021) Classification of Magnetohydrodynamic Simulations using Wavelet Scattering Transforms. The Astrophysical Journal. 910:122.
- Portillo, S.K.N., Slepian, Z., Burkhart, B., Kahraman, S., Finkbeiner, D.P. (2018) Developing the 3-point Correlation Function for the Turbulent Interstellar Medium. The Astrophysical Journal. 862:119.
Characterizing the Galactic Centre GeV Excess
As a part of event reconstruction, the Fermi-LAT Collaboration estimates the accuracy of the direction reconstruction of each event, as certain events suffer from inefficiencies and inactive regions in the LAT. By creating new analysis classes of Fermi events by imposing a cut on direction reconstruction quality, the tails of the point spread function can be reduced at the expense of effective area. This method is applied in an analysis of the GeV excess seen in the Galactic Centre and Inner Galaxy to mitigate leakage of masked emission into the region of interest and point source confusion.
- Daylan, T., Finkbeiner, D.P., Hooper, D., Linden, T., Portillo, S.K.N., Rodd, N.L., Slatyer, T.R. (2016) The characterization of the gamma-ray signal from the central Milky Way: A case for annihilating dark matter. Physics of the Dark Universe. 12:1.
News articles: Time, Scientific American, New Scientist, NASA, Quanta Magazine
- Portillo, S.K.N. and Finkbeiner, D.P. (2014) Sharper Fermi LAT Images: instrument response functions for an improved event selection. The Astrophysical Journal. 796:54.
High Resolution Proton Radiography and Computed Tomography
Collaboration with Charles-Antoine Collins-Fekete
I assisted in developing a fast maximum-likelihood method to reconstruct projected images of relative stopping power from proton radiography data and in placing cubic spline charged particle path estimators into a Bayesian framework.
- Collins-Fekete, C.-A., Brousmiche, S., Portillo, S.K.N., Beaulieu, L, Seco, J. (2016) A maximum likelihood method for high resolution proton radiography/proton CT. Physics in Medicine and Biology. 61: 8232.
- Collins-Fekete, C.-A., Volz, L., Portillo, S.K.N, Beaulieu, L., Seco, J. (2016) A theoretical framework to predict the most likely hadron path in particle imaging. Physics in Medicine and Biology. 62: 1777.
News article: medicalphysicsweb
Measuring the Lifetime of Trapped Sleptons using ATLAS
Supervised by James Pinfold, University of Alberta (Summer 2011)
- Portillo, S.K.N., Pinfold, J.L. (2011) Towards searching for trapped slepton decays in ATLAS. CERN Summer Student Sessions. Presentation.
In supergravity with the gravitino as the lightest supersymmetric particle, the next-to-lightest supersymmetric particle has a naturally long lifetime of hours to years. These long-lived particles could be produced at the LHC and then trapped in the detectors, with their decays being observed later (see Pinfold and Sibley, 2010). I started implementing a search for these decays in events not associated with collisions, using timing information to remove the downward-going cosmic ray background.
Nanomechanical Torsional Resonator Torque Magnetometry
Supervised by Mark Freeman and John Davis, University of Alberta (Summer 2010)
- Davis, J.P., Vick, D, Li, P; Portillo, S.K.N., Fraser, A.E., Burgess, J.A.J., Fortin, D.C., Hiebert, W.K., and Freeman, M.R. (2011) Nanomechanical Torsional Resonator Torque Magnetometry. Journal of Applied Physics. 109: 07D309.
The Freeman group fabricated nanoscale torsional resonators to conduct magnetometry on nanoscale magnetic elements. I constructed a vacuum chamber apparatus to conduct optical interferometry measurements on these resonators at low temperature and adjustable magnetic field. This apparatus was used to observe the magnetic hysteresis of a magnetic film and the magnetic supercooling of vortex nucleation in a magnetic disk.
Evaluating Machine-Learned Protein Classifiers
Supervised by Paul Lu, University of Alberta (Summer 2007, Summer 2009)
The Proteome Analyst project was a publicly-available, web-based system for predicting protein properties using machine-learned classifiers constructed from labelled training data provided by the user. I created a web-based system to calculate classifier performance statistics by comparing a classifier’s output to known true classifications.