A conservative, optimization-based semi-lagrangian spectral element method for passive tracer transport

We present a new optimization-based, conservative, and quasi-monotone method for passive tracer transport. The scheme combines high-order spectral element discretization in space with semi-Lagrangian time stepping. Solution of a singly linearly constrained quadratic program with simple bounds enforces conservation and physically motivated solution bounds. The scheme can handle efficiently a large number of passive tracers because the semi-Lagrangian time stepping only needs to evolve the grid points where the primitive variables are stored and allows for larger time steps than a conventional explicit spectral element method. Numerical examples show that the use of optimization to enforce physical properties does not affect significantly the spectral accuracy for smooth solutions. Performance studies reveal the benefits of high-order approximations, including for discontinuous solutions

An Estimator for the Sensitivity to Perturbations of Deep Neural Networks

For Deep Neural Networks (DNNs) to become useful in safety-critical applications, such as self-driving cars and disease diagnosis, they must be stable to perturbations in input and model parameters. Characterizing the sensitivity of a DNN to perturbations is necessary to determine minimal bit-width precision that may be used to safely represent the network. However, no general result exists that is capable of predicting the sensitivity of a given DNN to round-off error, noise, or other perturbations in input. This paper derives an estimator that can predict such quantities. The estimator is derived via inequalities and matrix norms, and the resulting quantity is roughly analogous to a condition number for the entire neural network. An approximation of the estimator is tested on two Convolutional Neural Networks, AlexNet and VGG-19, using the ImageNet dataset. For each of these networks, the tightness of the estimator is explored via random perturbations and adversarial attacks.Comment: Actual work and paper concluded in January 201

Miscellaneous Problems

Contains reports on three research projects

Miscellaneous Problems

Contains reports on two research projects

The Quasar Outflow Contribution to AGN Feedback: VLT Measurements of SDSS J0318-0600

We present high spectral resolution VLT observations of the BAL quasar SDSS J0318-0600. This high quality data set allows us to extract accurate ionic column densities and determine an electron number density of n_e=10^3.3 +/- 0.2 cm^-3 for the main outflow absorption component. The heavily reddened spectrum of SDSS J0318-0600 requires purely silicate dust with a reddening curve characteristic of predominately large grains, from which we estimate the bolometric luminosity. We carry out photoionization modeling to determine the total column density, ionization parameter and distance of the gas and find that the photionization models suggest abundances greater than solar. Due to the uncertainty in the location of the dust extinction, we arrive at two viable distances for the main ouflow component from the central source, 6 and 18 kpc, where we consider the 6 kpc location as somewhat more physically plausable. Assuming the canonical global covering of 20% for the outflow and a distance of 6 kpc, our analysis yields a mass flux of 120 M_sun yr^-1 and a kinetic luminosity that is ~0.1% of the bolometric luminosity of the object. Should the dust be part of the outflow, then these values are ~4x larger. The large mass flux and kinetic luminosity make this outflow a significant contributor to AGN feedback processes.Comment: Accepted for publication in ApJ, 57 pages, 14 figure

Prospectus, March 31, 1982

BOARD MOVES TO UP TUITION BY \u2783; Monroe to speak to grads; Office Careers contest set; Reserve fall courses; Opinions and Views: StuGo leader speaks on budget plans, TV purchase; Music Association learns from clinics; 2 from Parkland featured in art exhibit; Maya Angelou speaks on black literature, writers; Class strains nerves, but teaches discipline well; P.C. Happenings...: Series on parent-child interaction scheduled, Program on childhood illness set, Doctor to discuss stomach disorders, Choral Union to perform concert, Two EMT workshops scheduled. Opportunity to explore careers, How to be a smart consumer; Broadcast option model for colleges; Award offered to students in education; Radio show premieres April 4; Counselor sees solution to teen pregnancies; Brown baggers enjoy convenience, variety, savings; Check your change...: Coin collecting big-booming hobby; First P.C. variety show goes off without a hitch; Classifieds; Community Calendar; \u27Quest for Fire\u27: unique in more ways than one; Chicago school provides world with several comic success; \u27Angel Street\u27 coming your way; B-52\u27s explore ancient country; Joni relives struggle in inspirational movie; Women off to good start with first sotfball game; Madden leads men to win over Lincoln; Parkland Sports Watch; Score Card; Coach predicts teams will be formidablehttps://spark.parkland.edu/prospectus_1982/1024/thumbnail.jp