Probable Performance of Steiner Tree Algorithms

In this paper we consider the probable performance of three polynomial time approximation algorithms for the Steiner tree problem with respect to a specific random graph model. The Steiner problem asks us to find a minimum cost spanning subgraph (tree) for a subset D of modes in a graph

New Approximation Algorithms for the Steiner Tree Problem

In this paper we consider several approximation algorithms for the Steiner tree problem in an attempt to find one whose worst case performance is better than two times optimal. We first examine Rayward-Smith\u27s algorithm to gain insight into why it has worst case performance no better than two. Based on these ideas we propose several new algorithms (approximation schemes). We eliminate from further consideration those which we have bene able to showed have worst case performance that is still no better than two. Then we conjecture that one of these schemes not only has improved worst case performance, but is also the basis for a polynomial scheme. That is, given an e greater than 0 we conjecture that this scheme specifies a polynomial time approximation algorithm with worst case performance within 1 + e times optimal

Thesis Proposal: Routing of Multipoint Connections

This proposal addresses the problem of routing connections in a large scale packet switched communications system supporting multipoint communication. In this proposal a number of topics are considered including: the requirements imposed by routing in a large system, the Steiner tree problem of distributed algorithms which have access to limited information. In addition, this proposal outlines the work done to date and work that remains to be done

Dynamic Steiner Tree Problem

This paper proposes a new problem, which we call the Dynamic Steiner Tree Problem. This is related to multipoint connection routing in communications networks, where the set of nodes to be connected changes over time. This problem can be divided into two cases, one in which rearrangement of existing routes is not allowed and a second in which rearrangement is allowed. In the first case, we show that there is no algorithm whose worst error ratio is less than 1/2 log n where n is the number of nodes to be connected. In the second case, we present an algorithm whose error rate is bounded by a constant and rearrangement is relatively small

Nivolumab versus Everolimus in Advanced Renal-Cell Carcinoma

This randomised phase III trial compared standard of care Everolimus with the anti-PD1 monoclonal antibody Nivolumab in previously treated patients with locally advanced inoperable or metastatic clear cell renal cancer. 810 patients were randomised to receive either Everolimus 10 mg orally daily or 3 mg/kg of Nivolumab intravenously every two weeks. Patients were treated until unacceptable toxicity or disease progression. Patients could be treated beyond progression if the investigator believed that the patient was gaining clinical benefit. The primary endpoint was overall survival. The median survival was 25 months for Nivolumab and 19.8 months for Everolimus (p=0.002). The objective response rate was higher for Nivolumab (25 versus 5%; p=<0.001).The median progression free survivals were 4.6 & 4.4 months (p=0.11). Grade 3 & 4 treatment related toxicities were observed in 19 & 37% of patients on Nivolumab or Everolimus respectively. In patients with previously treated renal cell carcinoma Nivolumab produced superior survival and more tolerable treatment than Everolimus

Genome Sequence of Erythromelalgia-Related Poxvirus Identifies it as an Ectromelia Virus Strain

Erythromelagia is a condition characterized by attacks of burning pain and inflammation in the extremeties. An epidemic form of this syndrome occurs in secondary students in rural China and a virus referred to as erythromelalgia-associated poxvirus (ERPV) was reported to have been recovered from throat swabs in 1987. Studies performed at the time suggested that ERPV belongs to the orthopoxvirus genus and has similarities with ectromelia virus, the causative agent of mousepox. We have determined the complete genome sequence of ERPV and demonstrated that it has 99.8% identity to the Naval strain of ectromelia virus and a slighly lower identity to the Moscow strain. Small DNA deletions in the Naval genome that are absent from ERPV may suggest that the sequenced strain of Naval was not the immediate progenitor of ERPV

Worst Case Performance of Rayward-Smith\u27s Steiner Tree Heuristic

In this paper, we prove that the worst case performance of the Steiner tree approximation algorithm by Rayward-Smith is within two times optimal and that two is the best bound in the sense that there are instances for which RS will do worse than any value less than two

Secondary organic aerosol formation from semi- and intermediate-volatility organic compounds and glyoxal: Relevance of O/C as a tracer for aqueous multiphase chemistry

International audienceThe role of aqueous multiphase chemistry in the formation of secondary organic aerosol (SOA) remains difficult to quantify. We investigate it here by testing the rapid formation of moderate oxygen-to-carbon (O/C) SOA during a case study in Mexico City. A novel laboratory-based glyoxal-SOA mechanism is applied to the field data, and explains why less gas-phase glyoxal mass is observed than predicted. Furthermore, we compare an explicit gas-phase chemical mechanism for SOA formation from semi- and intermediate-volatility organic compounds (S/IVOCs) with empirical parameterizations of S/IVOC aging. The mechanism representing our current understanding of chemical kinetics of S/IVOC oxidation combined with traditional SOA sources and mixing of background SOA underestimates the observed O/C by a factor of two at noon. Inclusion of glyoxal-SOA with O/C of 1.5 brings O/C predictions within measurement uncertainty, suggesting that field observations can be reconciled on reasonable time scales using laboratory-based empirical relationships for aqueous chemistry

Secondary organic aerosol formation from semi- and intermediate-volatility organic compounds and glyoxal

The role of aqueous multiphase chemistry in the formation of secondary organic aerosol (SOA) remains difficult to quantify. We investigate it here by testing the rapid formation of moderate oxygen-to-carbon (O/C) SOA during a case study in Mexico City. A novel laboratory-based glyoxal-SOA mechanism is applied to the field data, and explains why less gas-phase glyoxal mass is observed than predicted. Furthermore, we compare an explicit gas-phase chemical mechanism for SOA formation from semi- and intermediate-volatility organic compounds (S/IVOCs) with empirical parameterizations of S/IVOC aging. The mechanism representing our current understanding of chemical kinetics of S/IVOC oxidation combined with traditional SOA sources and mixing of background SOA underestimates the observed O/C by a factor of two at noon. Inclusion of glyoxal-SOA with O/C of 1.5 brings O/C predictions within measurement uncertainty, suggesting that field observations can be reconciled on reasonable time scales using laboratory-based empirical relationships for aqueous chemistry