Seminars archive

With the trend of cloud computing, data and computing are moved away from desktop and are instead provided as a service from the cloud. Data-as-a-service enables access to a wealth of data across distributed and heterogeneous data sources in the cloud. It remains a challenge, however, to ensure the privacy, interoperability, and scalability for such services.\\ \\ We designed and developed DObjects, a general-purpose P2P-based query and data operations infrastructure that can be deployed in the cloud and provides access to heterogeneous data sources. The system builds on top of a distributed mediator-wrapper architecture where individual system nodes serve as mediators and/or wrappers and interact with each other in a P2P fashion what guarantees good scalability. As an analogy, the system nodes can be considered as droplets, small elements that provide similar functionality in the cloud. Just as thousands or millions of droplets form a single drop in nature, in cloud computing, groups of droplets that provide similar functionality can form a micro-cloud. Micro-clouds are an integral part of the whole cloud computing system and can provide specific services to users.\\ \\ The dissertation also discusses the novel dynamic query execution engine within the data query infrastructure that dynamically adapts to network and node (or droplet) conditions. The query processing is capable of fully benefiting from all the distributed resources to minimize the query response time and maximize system throughput. In addition to leveraging the traditional distributed query optimization techniques, the (sub)queries are deployed and executed on droplets in a dynamic and iterative manner in order to guarantee the best reaction to network and resource dynamics.\\ \\ Finally, the dissertation presents an extension to the basic DObjects model that enables access to private data that is distributed and needs anonymization. The extension enables droplets to form virtual groups in order to addresses two important privacy issues for the sensitive data: privacy of data subjects and confidentiality of data providers. The dissertation discusses decentralized protocols that enable data sharing for horizontally partitioned databases given these constraints. These protocols can be run by the groups of droplets. Concretely, given a query spanning multiple databases, the query results do not contain individually identifiable information. In addition, institutions do not reveal their databases to each other apart from the query results.

TBA

Motivated by a question of Hajnal on independent finite sum-sets in triangle-free graphs with vertex sets being the set of positive integers we consider the following problem: Given are fixed integers k,l > 0 and a finite field F. Given is any graph G = (V, E) with vertex set being the set of all affine or linear points of an n-dimensional affine or linear vector space over F, where G does not contain a complete graph on l vertices. Is it possible to find a k-dimensional subspace, such that the set of all its affine or linear points forms an independent set in G? Having answered this questions, we give some applications to the corresponding problem for the set of solutions of partition regular systems of linear equations over Abelian groups. This is some joint work with D. Gunderson.

The recent proof of Serre's conjecture allows one to prove the finiteness of certain types of Galois representations (2-dimensional mod $p$, odd, semisimple respresentations of the absolute Galois group of the rationals with bounded prime to $p$ Artin conductor). One may ask for quantitative refinements of this. It seems hard to get a grip on this, although one can formulate a natural expectation. This is in the spirit of the theorem of Hermite-Minskowski which asserts that there are only finitely many extensions of the rationals of bounded discriminant. One can ask for quantitative versions of this: a precise count is again unknown.

We will discuss the following reflector problem. Given a parallel light beam emitted from a bounded domain in a hyperplane of n+1 dimensional Euclidean space and a receiver surface as well as prescribed in advance intensities for the source domain and the receiver, can we design a reflector surface that redistributes the emitted light accordingly?

High-throughput data production technologies are revolutionizing modern biology. Translating this experimental data into discoveries of relevance to human health relies on sophisticated computational tools that can handle large-scale data. However, sophisticated methods for the analysis of biological data are of little value if they are not accessible. Powerful analysis tools, data warehouses, and browsers exist, but for the average experimental biologists with limited computer expertise, making effective use of these resources is still out of reach. We have developed "Galaxy", which solves this problem by providing an integrated web-based workspace that bridges the gap between different tools and data sources. For computational tool developers, Galaxy eliminates the repetitive effort involved in creating high-quality user interfaces, while giving them the benefit of being able to provide their tools in an integrated environment. For experimental biologists, Galaxy allows running complex analyses on huge datasets with nothing more than a web browser, and without needing to worry about details like resource allocation, and format conversions. Galaxy makes high-end computational biology more accessible, efficient, and reproducible.

Recently, David Harbater and Julia Hartmann have developed a technique called ``field patching," which provides a new set of tools to study and construct algebraic objects of various types over function fields of curves defined over complete discretely valued fields. In this talk, I will describe these techniques, and give a survey of applications to central simple algebras and quadratic forms, including results on the period-index problem, the $u$-invariant, and admissibility of finite groups over these fields.

50 years ago Aleksandrov proved that the only embedded compact surfaces of constant mean curvature are round spheres. In this talk, we will continue the presentation of Aleksandrov's proof and some interesting geometric techniques.

Almost \$4 billion in federal dollars, provided by the 2002 Help America Vote Act (HAVA), resulted in the initial widespread purchase of paperless computerized voting systems (Direct Recording Electronic or DREs) by many states, including Georgia. Election officials were told that DREs would be cheaper than alternative voting systems, a claim that ignored the costs of testing and secure storage, as well as very expensive annual maintenance contracts. They were told that DREs had been extensively tested and that the certification process guaranteed that the machines were reliable and secure. They were also told that DREs would allow people with disabilities to vote independently. In some cases officials were threatened with lawsuits or actually sued by certain disability rights groups if they expressed hesitation at purchasing DREs. However, early independent security studies, followed by recent results from California’s “Top-to-Bottom Review” have revealed that the DREs that were tested by California – all of which had been federally qualified and state certified – are poorly designed, badly programmed, insecure, unreliable, and at times very difficult for people with disabilities to use. As a result the California Secretary of State Debra Bowen decertified all of the tested systems. While she recertified them, her conditional recertification orders, which contain long lists of detected problems, have still longer lists of conditions, some quite arduous, that must be met. HAVA also required each state to create a statewide computerized database of all registered voters. Congressional Democrats and Republicans supported the computerized databases, because they felt the databases would prevent widespread voter disenfranchisement or voting by illegal aliens, respectively. However, if the databases are not secure and properly monitored, it will be possible to strip large numbers of voters’ names from the databases or to pad the databases with the names of non-citizens. We shall discuss some of the voting technologies that will be used in November, as well as national efforts to make our elections more secure and accurate through the use of voter verified paper ballots. We shall also review the situation in Georgia. Because Georgia still uses paperless Diebold DREs, there will be no way to conduct an audit or recount of the November 2008 election in Georgia. Information on this speaker can be found here: http://usacm.acm.org/usacm/Committee/Simons.htm

The Brauer group, comprising classes of central simple algebras over a field, plays an important role in the study of a field's arithmetic. We will give an overview of the Brauer group, and discuss how it has been used to produce some important examples in field arithmetic and algebraic geometry.

50 years ago Aleksandrov proved that the only embedded compact surfaces of constant mean curvature are round spheres. In this talk, Aleksandrov's proof and some interesting geometric techniques will be presented.