4,825 research outputs found
Reflectionless measures and the Mattila-Melnikov-Verdera uniform rectifiability theorem
A new proof is given of the Mattila-Melnikov-Verdera theorem on the uniform
rectifiability of an Ahlfors-David regular measure whose associated Cauchy
transform operator is bounded.Comment: 31 pages, 5 figure
An Iterative Abstraction Algorithm for Reactive Correct-by-Construction Controller Synthesis
In this paper, we consider the problem of synthesizing
correct-by-construction controllers for discrete-time dynamical systems. A
commonly adopted approach in the literature is to abstract the dynamical system
into a Finite Transition System (FTS) and thus convert the problem into a two
player game between the environment and the system on the FTS. The controller
design problem can then be solved using synthesis tools for general linear
temporal logic or generalized reactivity(1) specifications. In this article, we
propose a new abstraction algorithm. Instead of generating a single FTS to
represent the system, we generate two FTSs, which are under- and
over-approximations of the original dynamical system. We further develop an
iterative abstraction scheme by exploiting the concept of winning sets, i.e.,
the sets of states for which there exists a winning strategy for the system.
Finally, the efficiency of the new abstraction algorithm is illustrated by
numerical examples.Comment: A shorter version has been accepted for publication in the 54th IEEE
Conference on Decision and Control (held Tuesday through Friday, December
15-18, 2015 at the Osaka International Convention Center, Osaka, Japan
Using chemical ionization mass spectrometry to probe indoor and outdoor atmospheric chemistry
2021 Spring.Includes bibliographical references.People spend the majority of their time in indoor environments. Knowledge of the sources, sinks, and chemistry of indoor pollutants is therefore imperative to indoor air quality and human health. We studied the indoor chemistry of cooking and cleaning at the House Observations of Microbial and Environmental Chemistry (HOMEChem) field campaign during summer 2018 at the University of Texas test house (UTest house) in Austin, TX. We performed measurements of several gas-phase cooking- and cleaning-related analytes using a fast (1 Hz), online chemical ionization mass spectrometry (CIMS) measurement technique utilizing iodide reagent ions. Combining these and other measurements of gas-phase analytes and particulate matter present in indoor air during HOMEChem enables us to piece together a holistic story of the indoor chemistry of cooking and cleaning. We observed enhanced levels of several chlorinated and nitrogenated compounds when cleaning indoors with a commercial bleach solution during HOMEChem. We observed production of several inorganic chlorinated and nitrogenated pollutants from bleaching, including hypochlorous acid, chlorine gas, and chloramines. Levels of hypochlorous acid and nitrogen trichloride observed during cleaning are likely detrimental to human health. Bleach cleaning indoors also lead to the production of secondary organic aerosol—a common outdoor atmospheric pollutant associated with respiratory and cardiovascular issues—as well as potentially harmful organic isocyanates, cyanogen chloride, and chlorocarbons. These results collectively demonstrate bleach cleaning as a source of indoor pollution which impacts indoor air quality and occupant health. We characterized indoor reactive organic carbon (ROC) emissions from cooking and cleaning during HOMEChem, and directly compared resultant chemical complexity of indoor air to outdoors. Cooking indoors greatly impacts ROC concentrations and physiochemical properties, and thus carbon reactivities and lifetimes. Cleaning indoors yielded relatively insubstantial changes. Consistently higher indoor ROC concentrations compared to outdoors demonstrated that indoor emissions were a net source of reactive carbon to the outdoor atmosphere, following their removal by ventilation. ROC dominated indoor and outdoor oxidant reactivity compared to other atmospheric carbon species, thereby greatly influencing secondary pollutant formation, including carbon dioxide, ozone, and secondary particulate matter. Most oxidation chemistry to produce these secondary pollutants likely took place outdoors following the ventilation of ROC species, given the low oxidant levels typical of indoor environments. Moving outdoors, we demonstrated the efficacy of a CIMS instrument utilizing acetate ionization toward quantifying various gas-phase acids in the troposphere. Here, we performed measurements during the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) field campaign in summer 2014. Diurnal increases in mixing ratios were consistent with photochemical sources of nitric, isocyanic, formic, propionic, butyric, valeric, and pyruvic acid. Vertical profiles taken on the 300 m Boulder Atmospheric Observatory tower demonstrated net surface-level emissions of alkanoic acids, but net surface deposition of nitric and pyruvic acid. Nearby traffic emissions and agricultural activity were a primary source of propionic, butyric, and valeric acids, and likely contributed photochemical precursors to nitric and isocyanic acids. The combined diel and vertical profiles of the alkanoic acids and isocyanic acid were inconsistent with dry deposition and photochemical losses being the only sinks, suggesting additional loss mechanisms
Super star clusters and Supernovae in interacting LIRGs unmasked by NIR adaptive optics
We report on an on-going near-IR adaptive optics survey targeting interacting
luminous IR galaxies. High-spatial resolution NIR data are crucial to enable
interpretation of kinematic, dynamical and star formation (SF) properties of
these very dusty objects. Whole progenitor nuclei in the interactions can be
missed if only optical HST imaging is used. Here we specifically present the
latest results regarding core-collapse supernovae found within the highly
extincted nuclear regions of these galaxies. Direct detection and study of such
highly obscured CCSNe is crucial for revising the optically-derived SN rates
used for providing an independent measurement of the SF history of the
Universe. We also present thus-far the first NIR luminosity functions of super
star cluster (SSC) candidates. The LFs can then be used to constrain the
formation and evolution of SSCs via constraints based on initial mass functions
and cluster disruption models.Comment: 6 pages. To appear in proceedings of 'Galaxies and their Masks'
(Namibia, April 2010), published by Springer, New York, eds. D.L. Block, K.C.
Freeman, I. Puerar
Progenitor's signatures in Type Ia supernova remnants
The remnants of Type Ia supernovae can provide important clues about their
progenitor-histories. We discuss two well-observed supernova remnants (SNRs)
that are believed to result from a Type Ia SN and use various tools to shed
light on the possible progenitor history. We find that Kepler's SNR is
consistent with a symbiotic binary progenitor consisted of a white dwarf and an
AGB star. Our hydrosimulations can reproduce the observed kinematic and
morphological properties. For Tycho's remnant we use the characteristics of the
X-ray spectrum and the kinematics to show that the ejecta has likely interacted
with dense circumstellar gas.Comment: 4 pages, 9 figures, proceedings for IAU Symposium 281, Padova, July
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