859 research outputs found
Online Algorithms for Maximum Cardinality Matching with Edge Arrivals
No full textIn the adversarial edge arrival model for maximum cardinality matching, edges of an unknown graph are revealed one-by-one in arbitrary order, and should be irrevocably accepted or rejected. Here, the goal of an online algorithm is to maximize the number of accepted edges while maintaining a feasible matching at any point in time. For this model, the standard greedy heuristic is 1/2-competitive, and on the other hand, no algorithm that outperforms this ratio is currently known, even for very simple graphs.
We present a clean Min-Index framework for devising a family of randomized algorithms, and provide a number of positive and negative results in this context. Among these results, we present a 5/9-competitive algorithm when the underlying graph is a forest, and prove that this ratio is best possible within the Min-Index framework. In addition, we prove a new general upper bound of 2/(3+1/phi^2) ~ 0.5914 on the competitiveness of any algorithm in the edge arrival model. Interestingly, this bound holds even for an easier model in which vertices (along with their adjacent edges) arrive online, and when the underlying graph is a tree of maximum degree at most 3
Improved Bounds for Online Preemptive Matching
No full textWhen designing a preemptive online algorithm for the maximum matching problem, we wish to maintain a valid matching M while edges of the underlying graph are presented one after the other. When presented with an edge e, the algorithm should decide whether to augment the matching M by adding e (in which case e may be removed later on) or to keep M in its current form without adding e (in which case e is lost for good). The objective is to eventually hold a matching M with maximum weight.
The main contribution of this paper is to establish new lower and upper bounds on the competitive ratio achievable by preemptive online algorithms:
- We provide a lower bound of 1 + ln 2 \approx 1.693 on the competitive ratio of any randomized algorithm for the maximum cardinality matching problem, thus improving on the currently best known bound of e / (e-1) \approx 1.581 due to Karp, Vazirani, and Vazirani [STOC'90].
- We devise a randomized algorithm that achieves an expected competitive ratio of 5.356 for maximum weight matching. This finding demonstrates the power of randomization in this context, showing how to beat the tight bound of 3 + 2\sqrt{2} \approx 5.828 for deterministic algorithms, obtained by combining the 5.828 upper bound of McGregor [APPROX'05] and the recent 5.828 lower bound of Varadaraja [ICALP'11]
Improved approximation guarantees for weighted matching in the semi-streaming model
No full textWe study the maximum weight matching problem in the semi-streaming
model, and improve on the currently best one-pass algorithm due to
Zelke (Proc.\ STACS~'08, pages 669--680) by devising a deterministic
approach whose performance guarantee is 4.91 + \eps. In addition,
we study {\em preemptive} online algorithms, a sub-class of one-pass
algorithms where we are only allowed to maintain a feasible matching
in memory at any point in time. All known results prior to Zelke's
belong to this sub-class. We provide a lower bound of on the
competitive ratio of any such deterministic algorithm, and hence
show that future improvements will have to store in memory a set of
edges which is not necessarily a feasible matching. We conclude by
presenting an empirical study, conducted in order to compare the
practical performance of our approach to that of previously
suggested algorithms
Approaching the diamond surface: first principles modelling the physics and chemistry of approaching radicals
No full textThe diamond surface plays a central role in much of the diamond research, and as such much of its properties are described and studied in great detail. There is a clear picture of the atomic scale structure of the different facets and their reconstructions. Also terminations with H, O, N and other atomic species as well as the incorporation of these elements has been modelled [1,2]. The electronic structure and the negative electron affinity mechanism is elucidated and so on. In contrast, however, the atomic scale models of diamond growth are much less developed, though progress is being made [3]. In these models the reaction barriers between stable and meta-stable intermediates are being calculated, providing insights into the kinetics of the surface. However, quantum mechanical models can provide much more insights than this. In this work, we simulated the approach of radical atoms and molecules towards the H-terminated diamond 001 surface. By allowing the model to equilibrate at every step, the physics and chemistry of the approach can be followed in minute detail. It allows us to indicate at which distance the surface and radical start interacting, and what that interaction entails. The charge evolution of the radical and the surface is followed by means of Hirshfeld-I charges, providing insights into charge transfer mechanisms. [4] Throughout the approach, the interaction can be followed through different physical and chemical concepts. Different types of bonding are identified as well as H-abstraction events and covalent bonding. In this work, our focus goes to C and P based radicals, showing them to behave very differently near the surface, providing insights into the requirements for improved P incorporation.The author name needs to be updated to include the middle names: Danny E.P. Vanpoucke, and linked to the correct personel account which incorrectly is missing the author middle names
Approaching the diamond surface: first principles modelling the physics and chemistry of approaching radicals
No full textThe diamond surface plays a central role in much of the diamond research, and as such much of its properties are described and studied in great detail. There is a clear picture of the atomic scale structure of the different facets and their reconstructions. Also terminations with H, O, N and other atomic species as well as the incorporation of these elements has been modelled [1,2]. The electronic structure and the negative electron affinity mechanism is elucidated and so on. In contrast, however, the atomic scale models of diamond growth are much less developed, though progress is being made [3]. In these models the reaction barriers between stable and meta-stable intermediates are being calculated, providing insights into the kinetics of the surface. However, quantum mechanical models can provide much more insights than this. In this work, we simulated the approach of radical atoms and molecules towards the H-terminated diamond 001 surface. By allowing the model to equilibrate at every step, the physics and chemistry of the approach can be followed in minute detail. It allows us to indicate at which distance the surface and radical start interacting, and what that interaction entails. The charge evolution of the radical and the surface is followed by means of Hirshfeld-I charges, providing insights into charge transfer mechanisms. [4] Throughout the approach, the interaction can be followed through different physical and chemical concepts. Different types of bonding are identified as well as H-abstraction events and covalent bonding. In this work, our focus goes to C and P based radicals, showing them to behave very differently near the surface, providing insights into the requirements for improved P incorporation.The author name needs to be updated to include the middle names: Danny E.P. Vanpoucke, and linked to the correct personel account which incorrectly is missing the author middle names
Jere Nash Interview with Danny Cupit (Part 1 of 2)
No full textInterview conducted by author Jere Nash with lawyer and former chair of the Mississippi Democratic Executive Committee Danny Cupit in the process of writing Mississippi Politics: The Struggle for Power, 1976-2006 (Part 1 of 2). Topics covered include the formation of the Young Democrats; Hodding Carter; attending the Democratic National Convention of 1968; Lawrence Guyot Jr.; precinct caucuses and the state Democratic conference; assistance from labor unions and Millie Jeffrey; Charles Evers; Billy Car and Pat Derian running for committeewoman; Robert F. Kennedy campaign in Mississippi; death of Kennedy; Hubert Humphrey; Curtis Wilkie; Legal services work for a sanitation worker\u27s union in Holly Springs, Mississippi; labor lawyer Dixon Pyles; William Winter; 1972 congressional race between Ellis Bodron, Thad Cochran, and Walter Brown; Ed Ellington campaign for the state senate; Bankers Trust law suit; Jimmy Carter campaign and unified precinct meetings; attending the Democratic National Convention in 1976; running the Carter campaign in Mississippi; George Wallace; Griffin Bell getting senators Jim Eastland and John Stennis to endorse Carter; Gerald Blessey versus Trent Lott campaign; working with Eastland on the Carter campaign; restructuring of the state Democratic Executive Committee; Eastland\u27s decision not to run for reelection; Bill Waller; senate campaign of Maurice Dantin; Tom Ridell; and the asbestos law suit
Jere Nash Interview with Danny Cupit (Part 2 of 2)
No full textInterview conducted by author Jere Nash with lawyer and former chair of the Mississippi Democratic Executive Committee Danny Cupit in the process of writing Mississippi Politics: The Struggle for Power, 1976-2006 (Part 2 of 2). Topics covered included acting as contact person for the Jimmy Carter administration for Mississippi issues and appointments; Senator James O. Eastland on judicial appointments; Farmers Home Administration appointments of Jeffrey Barbour and Mark Hazzard; planning Carter\u27s visit to Yazoo City, Mississippi in 1977; Eastland\u27s decision not to run for reelection in 1978; Bill Waller; Cliff Finch; Maurice Dantin, Charles Evers, and Thad Cochran race for Senate seat; Democratic Party in Mississippi; Wayne Dowdy versus Trent Lott campaign; John Hampton Stennis versus Jon Hinson campaign for U.S. House of Representatives; William Winter; Haley Barbour; Evelyn Gandy; Bill Allain; dispute over Democratic Party Executive Committee leadership in Mississippi; 1980 presidential race; Jon Hinson homosexuality scandal and Wayne Dowdy campaign for the U.S. House; congressional district reapportionment, litigation, and creation of the Delta district; Bill Allain homosexuality scandal; Dick Molpus; Ray Mabus; education reform during Winter\u27s administration; Winter\u27s post-gubernatorial career options; and Walter Mondale presidential campaign race
First person – Danny Legge
No full textFirst Person is a series of interviews with the first authors of a selection of papers published in Disease Models & Mechanisms (DMM), helping early-career researchers promote themselves alongside their papers. Danny Legge is first author on ‘BCL-3 promotes a cancer stem cell phenotype by enhancing β-catenin signalling in colorectal tumour cells’, published in DMM. Danny conducted the research described in this article while a PhD student in Professor Ann Williams's lab at Colorectal Tumour Biology Group, School of Cellular and Molecular Medicine, University of Bristol, UK. He is now a postdoc in the lab of Dr Keith Brown at Cancer Epigenetics Laboratory, School of Cellular and Molecular Medicine, University of Bristol, UK, investigating the role of cancer stem cells in colorectal cancer
Eleven Months After Pittsburgh: What Did We Learn?
No full text2019-2020 Judaic Studies Scholar in Residence… Rabbi Danny Schiff, PhD, Author, Foundation Scholar, Jewish Federation of Greater Pittsburgh.https://digitalcommons.fairfield.edu/bennettcenter-posters/1358/thumbnail.jp
- …
