University of Delaware

About: University of Delaware is a education organization based out in Newark, Delaware, United States. It is known for research contribution in the topics: Population & Catalysis. The organization has 22223 authors who have published 54810 publications receiving 2049136 citations. The organization is also known as: University of Delaware Emergency Care Unit & UD.

Boundary Element Methods: Foundation and Error Analysis

Abstract: This chapter gives an expository introduction to the Galerkin-BEM for the elliptic boundary value problems from the mathematical point of view. Emphasis will be placed on the variational formulations of the boundary integral equations and the general error estimates for the approximate solution in appropriate Sobolev spaces. A classification of boundary integral equations will be given on the basis of the Sobolev index. The simple relations between the variational formulations of the boundary integral equations and the corresponding partial differential equations under consideration will be indicated. Basic concepts such as stability, consistency, and convergence, as well as the condition numbers and ill-posedness, will be discussed by using elementary examples. Keywords: boundary integral equations; fundamental solutions; variational formulations; Garding's inequality; Galerkin's method; boundary elements; stability; ill-posedness; asymptotic error estimates

Camouflage: automated anonymization of field data

Abstract: Privacy and security concerns have adversely affected the usefulness of many types of techniques that leverage information gathered from deployed applications. To address this issue, we present an approach for automatically anonymizing failure-inducing inputs that builds on a previously developed technique. Given an input I that causes a failure f, our approach generates an anonymized input I′ that is different from I but still causes f. I′ can thus be sent to developers to enable them to debug f without having to know I. We implemented our approach in a prototype tool, camouflage, and performed an extensive empirical evaluation where we applied camouflage to a large set of failure-inducing inputs for several real applications. The results of the evaluation are promising, as they show that camouflage is both practical and effective at generating anonymized inputs; for the inputs that we considered, I and I′ shared no sensitive information. The results also show that our approach can outperform the general technique it extends.

Microbial acceleration of aerobic pyrite oxidation at circumneutral pH

Abstract: Pyrite (FeS2) is the most abundant sulfide mineral on Earth and represents a significant reservoir of reduced iron and sulfur both today and in the geologic past. In modern environments, oxidative transformations of pyrite and other metal sulfides play a key role in terrestrial element partitioning with broad impacts to contaminant mobility and the formation of acid mine drainage systems. Although the role of aerobic micro-organisms in pyrite oxidation under acidic-pH conditions is well known, to date there is very little known about the capacity for aerobic micro-organisms to oxidize pyrite at circumneutral pH. Here, we describe two enrichment cultures, obtained from pyrite-bearing subsurface sediments, that were capable of sustained cell growth linked to pyrite oxidation and sulfate generation at neutral pH. The cultures were dominated by two Rhizobiales species (Bradyrhizobium sp. and Mesorhizobium sp.) and a Ralstonia species. Shotgun metagenomic sequencing and genome reconstruction indicated the presence of Fe and S oxidation pathways in these organisms, and the presence of a complete Calvin–Benson–Bassham CO2 fixation system in the Bradyrhizobium sp. Oxidation of pyrite resulted in thin (30–50 nm) coatings of amorphous Fe(III) oxide on the pyrite surface, with no other secondary Fe or S phases detected by electron microscopy or X-ray absorption spectroscopy. Rates of microbial pyrite oxidation were approximately one order of magnitude higher than abiotic rates. These results demonstrate the ability of aerobic microbial activity to accelerate pyrite oxidation and expand the potential contribution of micro-organisms to continental sulfide mineral weathering around the time of the Great Oxidation Event to include neutral-pH environments. In addition, our findings have direct implications for the geochemistry of modern sedimentary environments, including stimulation of the early stages of acid mine drainage formation and mobilization of pyrite-associated metals.