69 research outputs found
Measuring Electron Diffusion and Constraining the Neutral Current π0 Background for Single-Photon Events in MicroBooNE
Get PDFLiquid Argon Time Projection Chambers (LArTPCs) are a rising technology in the field of experimental neutrino physics. LArTPCs use ionization electrons and scintillation light to reconstruct neutrino interactions with exceptional calorimetric and position resolution capabilities. Here, I present two analyses conducted in the MicroBooNE LArTPC at Fermilab: a measurement of the longitudinal electron diffusion coefficient, DL, in the MicroBooNE detector and a constraint of the systematic uncertainty on MicroBooNE\u27s single-photon analysis due to the dominant neutral current (NC) π0 background. Longitudinal electron diffusion modifies the spatial and timing resolution of the detector, and measuring it will help correct for these effects. Furthermore, current measurements of DL in liquid argon are sparse and in tension with one another, making the MicroBooNE measurement especially valuable. We report a measurement of DL = 3.74+0.28-0.29 cm2/s. MicroBooNE is searching for single-photon events as a potential explanation for the MiniBooNE low-energy excess (LEE) of electron neutrino-like events, which has been interpreted as evidence for low-mass sterile neutrinos. However, this search is overwhelmed by a large NC π0 background. By performing a sideband selection of NC π0 events, we apply a data-driven rate constraint to the single-photon analysis to reduce the systematic uncertainties. At present, this constraint improves the single-photon analysis\u27 median sensitivity to the LEE-like signal from 0.9σ to 1.5σ. This sensitivity is expected to improve significantly as more data become available. Both of these measurements will not only benefit MicroBooNE, but also inform future LArTPC experiments
Multiagent Routing Problem with Dynamic Target Arrivals Solved via Approximate Dynamic Programming
Get PDFThis research formulates and solves the multiagent routing problem with dynamic target arrivals (MRP-DTA), a stochastic system wherein a team of autonomous unmanned aerial vehicles (AUAVs) executes a strike coordination and reconnaissance (SCAR) mission against a notional adversary. Dynamic target arrivals that occur during the mission present the team of AUAVs with a sequential decision-making process which we model via a Markov Decision Process (MDP). To combat the curse of dimensionality, we construct and implement a hybrid approximate dynamic programming (ADP) algorithmic framework that employs a parametric cost function approximation (CFA) which augments a direct lookahead (DLA) model via a parameterization to the objective function. We show a statistically significant improvement over the repeated greedy marginal heuristic benchmark policy for 19 out of 20 problem instances and a statistically significant improvement over the repeated sequential orienteering problem benchmark policy for 8 out of 10 problem instances of the MRP-DTA. Results of excursion analysis show the value trade off of balancing solution quality and computational effort when selecting the base optimization model for our CFA-DLA algorithm
STING/MPYS Mediates Host Defense against <i>Listeria monocytogenes</i> Infection by Regulating Ly6Chi Monocyte Migration
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MPYS (also known as STING, MITA, and TMEM173) is a type I IFN stimulator that is essential for host defense against DNA virus infection and appears important in defense against certain bacteria. The in vivo significance and mechanisms by which MPYS mediates host defense against nonviral pathogens are unknown. Using an MPYS-deficient mouse (Tmem173&lt;tm1Camb&gt;), we determined that, distinct from the IFNAR−/− mice, MPYS deficiency leads to increased bacterial burden in the liver upon Listeria monocytogenes infection. The increase was correlated with the diminished MCP-1 and MCP-3 chemokine production and decreased blood and liver Ly6Chi monocyte frequency. We further demonstrate that MPYS-deficient Ly6Chi monocytes are intrinsically defective in migration to the liver. Lastly, adoptive transfer of wild-type Ly6Chi monocyte into MPYS-deficient mice decreases their liver bacterial burden. Our findings reveal a novel in vivo function of MPYS that is distinct from its role in activating type I IFN production.</jats:p
Measuring Electron Diffusion and Constraining the Neutral Current Background for Single-Photon Events in MicroBooNE
No full text3D Monte-Carlo simulation of Ganymede’s atmosphere
Get PDFWe present new model results for H2O, O2, H2, O, and H in the atmosphere of Ganymede. The results are
obtained from a collision-less 3D Monte-Carlo model that includes sublimation, ion and electron sputtering, and
ion and electron radiolysis. Because Ganymede has its own magnetic field, its immediate plasma environment
is particularly complex. The interaction between Ganymede’s and Jupiter’s magnetospheres makes it highly
variable in both space and time. The recent Juno Ganymede flyby provided us with new data on the
electron local environment. Based on the electron measurements recorded by the Jovian Auroral Distributions
Experiment (JADE), we implement two electron populations, one for the moon’s polar regions and one for the
moon’s auroral regions. Comparing the atmospheric contribution of these newly defined electron populations
to the overall source and loss processes is one of the main goals of this work.
Our analysis shows that for H2O, sublimation remains the most important source process even after
accounting for the new electron populations, delivering more than three orders of magnitude more H2O
molecules to the atmosphere than all other source processes combined. The source fluxes for O2 and H2,
on the other hand, are dominated by radiolysis induced by the auroral electrons, assuming that the electron
fluxes JADE measured during Juno’s transit of Ganymede’s magnetopause current layer are representative of
auroral electrons. Atomic O and H are mainly added to the atmosphere through the dissociation of O2 and
H2, which is primarily induced by auroral electrons.
Our understanding of Ganymede’s atmosphere today is mainly based on spectroscopic observations. The
interpretation of spectroscopic data strongly depends on assumptions taken, though. Our analysis shows that
for a holistic understanding of Ganymede’s atmosphere, simultaneous observations of the moon’s surface,
atmosphere, and full plasma environment (thermal and energetic ions and electrons) at different times and
locations (both with respect to Ganymede and with respect to Jupiter) are particularly important. Such
measurements are planned by ESA’s Jupiter ICy moons Explorer (JUICE), in particular by the Particle
Environment Package (PEP), which will greatly advance our understanding of Ganymede and its atmosphere
and plasma environment
Constraining the radiolytic production of Callisto&#8217;s O2 atmosphere
No full text&lt;p&gt;Herein we constrain the radiolytic production rate of O&lt;sub&gt;2&lt;/sub&gt; from Callisto&#039;s exposed ice patches as well as the corresponding steady-state abundance of O&lt;sub&gt;2&lt;/sub&gt; in Callisto&#039;s atmosphere. That is, by simulating the fluxes of thermal plasma and energetic particles irradiating Callisto&#039;s surface, taking into account energy deposition within the atmosphere, we determine the initial source flux of O&lt;sub&gt;2&lt;/sub&gt; to estimate the corresponding column density for Callisto&#039;s O&lt;sub&gt;2 &lt;/sub&gt;component, which we compare to those suggested in the literature. This study provides constraints for Callisto&#039;s O&lt;sub&gt;2&lt;/sub&gt; atmosphere in preparation for future observations, particularly those that will be made by the JUpiter ICy moons Explorer (JUICE) and Europa Clipper spacecraft, as well as the Hubble Space Telescope (HST). Further, based on this analysis at Callisto, we can better our understanding on how the atmospheres of other icy satellites in the Solar System can evolve to their observed state.&lt;/p&gt;</jats:p
3D Monte Carlo simulation of Ganymede's atmosphere - lessons learned from Juno's Ganymede flyby
No full text&lt;p&gt;Among Jupiter&#039;s satellites, Ganymede undoubtedly has one of the most complex atmospheres. This is primarily due to the fact that Ganymede has its own magnetic field, which forms a small magnetosphere within the much larger magnetosphere of Jupiter. This interaction not only results in atmospheric auroral emissions in the UV range but also strongly influences Ganymede&amp;#8217;s space environment.&lt;/p&gt;
&lt;p&gt;With the recent Ganymede flyby by the Juno spacecraft, new information on Ganymede&amp;#8217;s environment has become available. We have included these measurements into our 3D Monte Carlo model, determining Ganymede&amp;#8217;s resulting H&lt;sub&gt;2&lt;/sub&gt;O, O&lt;sub&gt;2&lt;/sub&gt;, H&lt;sub&gt;2&lt;/sub&gt;, O, and H atmosphere. Our simulations show that accounting for all major source and loss processes, sublimation is still the dominating source process for the water in Ganymede&amp;#8217;s atmosphere, delivering more than three orders of magnitude more molecules to the atmosphere than all other source processes combined. For the non-condensing atmospheric species (O&lt;sub&gt;2&lt;/sub&gt; and H&lt;sub&gt;2&lt;/sub&gt;), on the other hand, it is the auroral electrons that mainly govern the atmospheric structure and density. The auroral electrons also govern the structure and density of the atomic species O and H, which are mainly added to the atmosphere by electron-impact dissociation of O&lt;sub&gt;2&lt;/sub&gt; and H&lt;sub&gt;2&lt;/sub&gt; in the auroral belts. Comparison with available spectroscopic observations of Ganymede&amp;#8217;s atmospheric constituents shows that our results agree well with the results inferred from these observations, with the exception of H, where our derived line-of-sight column density is about one order of magnitude lower than the column density inferred from Lyman-&amp;#945; measurements.&lt;/p&gt;
&lt;p&gt;Our analysis shows that for a complete understanding of Ganymede&#039;s atmosphere, simultaneous observations of Ganymede&#039;s surface, atmosphere, and plasma environment at different times and locations are particularly important. Such measurements are planned with the Jupiter ICy moons Explorer, in particular with the Particle Environment Package (PEP). In this presentation we will show how PEP will help us learn more about Ganymede&amp;#8217;s complex atmosphere, providing simultaneous in-situ electron, ion, and neutral gas measurements.&lt;/p&gt;</jats:p
Callisto&#8217;s atmosphere: First evidence for H2, and the implications this has for Europa&#8217;s and Ganymede&#8217;s atmosphere
No full text&lt;p&gt;We explore the parameter space for the contribution to Callisto&#039;s H corona observed by the Hubble Space Telescope from sublimated H&lt;sub&gt;2&lt;/sub&gt;O and radiolytically produced H&lt;sub&gt;2&lt;/sub&gt; using the Direct Simulation Monte Carlo (DSMC) method. The spatial morphology of this corona produced via photo- and magnetospheric electron impact-induced dissociation is described by tracking the motion of and simulating collisions between the hot H atoms and thermal molecules including a near-surface O&lt;sub&gt;2&lt;/sub&gt; component. Our results presented indicate that sublimated H&lt;sub&gt;2&lt;/sub&gt;O produced from the surface ice, whether assumed to be intimately mixed with or distinctly segregated from the dark non-ice or ice-poor regolith, cannot explain the observed structure of the H corona. On the other hand, a global H&lt;sub&gt;2&lt;/sub&gt; component can reproduce the observation, and is also capable of producing the enhanced electron densities observed at high altitudes by &lt;em&gt;Galileo&lt;/em&gt;&#039;s plasma-wave instrument, providing the first evidence of H&lt;sub&gt;2&lt;/sub&gt; in Callisto&#039;s atmosphere. Finally, we discuss the implications of these results, in particular how they compare to Europa and Ganymede.&lt;/p&gt;</jats:p
2017 Caltech Space Challenge - Lunarport: Lunar Extraction for Extraterrestrial Prospecting (LEEP)
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