48,683 research outputs found
A simple disc wind model for broad absorption line quasars
No full textApproximately 20 per cent of quasi-stellar objects (QSOs) exhibit broad, blue-shifted absorption lines in their ultraviolet spectra. Such features provide clear evidence for significant outflows from these systems, most likely in the form of accretion disc winds. These winds may represent the ‘quasar’ mode of feedback that is often invoked in galaxy formation/evolution models, and they are also key to unification scenarios for active galactic nuclei (AGN) and QSOs. To test these ideas, we construct a simple benchmark model of an equatorial, biconical accretion disc wind in a QSO and use a Monte Carlo ionization/radiative transfer code to calculate the ultraviolet spectra as a function of viewing angle. We find that for plausible outflow parameters, sightlines looking directly into the wind cone do produce broad, blue-shifted absorption features in the transitions typically seen in broad absorption line (BAL) QSOs. However, our benchmark model is intrinsically X-ray weak in order to prevent overionization of the outflow, and the wind does not yet produce collisionally excited line emission at the level observed in non-BAL QSOs. As a first step towards addressing these shortcomings, we discuss the sensitivity of our results to changes in the assumed X-ray luminosity and mass-loss rate, Ṁwind. In the context of our adopted geometry, Ṁwind ∼ Ṁacc is required in order to produce significant BAL features. The kinetic luminosity and momentum carried by such outflows would be sufficient to provide significant feedback
K-theory for group C*-algebras
No full textThese notes are based on a lecture course given by the first author in the Sedano Winter School on K-theory held in Sedano, Spain, on January 22-27th of 2007. They aim at introducing K-theory of C*-algebras, equivariant K-homology and KK-theory in the context of the Baum-Connes conjectur
Evolving Fuzzy Rules for Relaxed-Criteria Negotiation
No full textIn the literature on automated negotiation, very few negotiation agents are designed with the flexibility to slightly relax their negotiation criteria to reach a consensus more rapidly and with more certainty. Furthermore, these relaxed-criteria negotiation agents were not equipped with the ability to enhance their performance by learning and evolving their relaxed-criteria negotiation rules. The impetus of this work is designing market-driven negotiation agents (MDAs) that not only have the flexibility of relaxing bargaining criteria using fuzzy rules, but can also evolve their structures by learning new relaxed-criteria fuzzy rules to improve their negotiation outcomes as they participate in negotiations in more e-markets. To this end, an evolutionary algorithm for adapting and evolving relaxed-criteria fuzzy rules was developed. Implementing the idea in a testbed, two kinds of experiments for evaluating and comparing EvEMDAs (MDAs with relaxed-criteria rules that are evolved using the evolutionary algorithm) and EMDAs (MDAs with relaxed-criteria rules that are manually constructed) were carried out through stochastic simulations. Empirical results show that: 1) EvEMDAs generally outperformed EMDAs in different types of e-markets and 2) the negotiation outcomes of EvEMDAs generally improved as they negotiated in more e-markets
BLGAN: Bayesian Learning and Genetic Algorithm for Supporting Negotiation With Incomplete Information
No full textAutomated negotiation provides a means for resolving
differences among interacting agents. For negotiation with
complete information, this paper provides mathematical proofs
to show that an agent’s optimal strategy can be computed using
its opponent’s reserve price (RP) and deadline. The impetus of
this work is using the synergy of Bayesian learning (BL) and
genetic algorithm (GA) to determine an agent’s optimal strategy
in negotiation (N) with incomplete information. BLGAN adopts:
1) BL and a deadline-estimation process for estimating an opponent’s
RP and deadline and 2) GA for generating a proposal
at each negotiation round. Learning the RP and deadline of an
opponent enables the GA in BLGAN to reduce the size of its search
space (SP) by adaptively focusing its search on a specific region
in the space of all possible proposals. SP is dynamically defined
as a region around an agent’s proposal P at each negotiation
round. P is generated using the agent’s optimal strategy determined
using its estimations of its opponent’s RP and deadline.
Hence, the GA in BLGAN is more likely to generate proposals
that are closer to the proposal generated by the optimal strategy.
Using GA to search around a proposal generated by its current
strategy, an agent in BLGAN compensates for possible errors in
estimating its opponent’s RP and deadline. Empirical results show
that agents adopting BLGAN reached agreements successfully,
and achieved: 1) higher utilities and better combined negotiation
outcomes (CNOs) than agents that only adopt GA to generate their
proposals, 2) higher utilities than agents that adopt BL to learn
only RP, and 3) higher utilities and better CNOs than agents that
do not learn their opponents’ RPs and deadlines
Grid Commerce, Market-Driven G-Negotiation, and Grid Resource Management
No full textAlthough the management of resources is essential
for realizing a computational grid, providing an efficient resource
allocation mechanism is a complex undertaking. Since Grid
providers and consumers may be independent bodies, negotiation
among them is necessary. The contribution of this paper
is showing that market-driven agents (MDAs) are appropriate
tools for Grid resource negotiation.MDAs are e-negotiation agents
designed with the flexibility of: 1) making adjustable amounts of
concession taking into account market rivalry, outside options,
and time preferences and 2) relaxing bargaining terms in the
face of intense pressure. A heterogeneous testbed consisting of
several types of e-negotiation agents to simulate a Grid computing
environment was developed. It compares the performance
of MDAs against other e-negotiation agents (e.g., Kasbah) in a
Grid-commerce environment. Empirical results show that MDAs
generally achieve: 1) higher budget efficiencies in many market
situations than other e-negotiation agents in the testbed and
2) higher success rates in acquiring Grid resources under high
Grid loadings
The sim gene of Escherichia coli phage P1: nucleotide sequence and purification of the processed protein
No full textMaillou J, Dreiseikelmann B. The sim gene of Escherichia coli phage P1: nucleotide sequence and purification of the processed protein. Virology. 1990;175(2):500-507.The sim gene of bacteriophage P1 causes exclusion of a superinfecting P1 phage. We determined the nucleotide sequence of a 1.9-kb DNA fragment that, in plasmids, causes Sim phenotype. There are two open reading frames within this region for proteins of 82 and 259 amino acids. A 1.3-kb fragment containing the larger open reading frame was inserted into an expression vector. Induced cells carrying the hybrid plasmid, termed pBD5, were not infected by phage P1 and produced a 24-kDa protein and, to a smaller extent, a 25-kDa protein. The 24-kDa protein was purified. Comparison of its amino-terminal amino acid sequence with the nucleotide sequence indicated that it is processed from a precursor protein by removal of a hydrophobic leader peptide of 20 amino acids. In vivo processing depends on secA gene function and is necessary for Sim interference with P1 infection. The data are discussed with respect to the function of the sim gene in superinfection exclusion
Grid Resource Negotiation: Survey and New Directions
No full textSince Grid computing systems involve large-scale resource sharing, resource management is central to their operations. Whereas there are more Grid resource management systems adopting auction, commodity market, and contract-net (tendering) models, this survey supplements and complements existing surveys by reviewing, comparing, and highlighting existing research initiatives on applying bargaining (negotiation) as a mechanism to Grid resource management. The contributions of this paper are: 1) discussing the motivations for considering bargaining models for Grid resource allocation; 2) discussing essential design considerations such as modeling devaluation of Grid resources, considering market dynamics, relaxing bargaining terms, and co-allocation of resources when building Grid negotiation mechanisms; 3) reviewing the strategies and protocols of state-of-the-art Grid negotiation mechanisms; 4) providing detailed comparisons and analyses on how state-of-the-art Grid negotiation mechanisms address the design considerations mentioned in 3); and 5) suggesting possible new directions
Search for eta(c) decays into pi pi and K(K)over-bar
No full textUsing 58 million J/psi) events taken with the BESII detector, a search for eta(c) CP violating decays into pi pi and K (K) over bar has been performed. No clear 77, signal is observed, and upper limits for B(eta(c) -> pi pi) and B(eta(c) -> K (K) over bar) are given at the 90% confidence level, B(J/psi -> gamma eta(c)) center dot B(eta(c) -> pi(+)pi(-)) < 1.1 x 10(-5), B(J/psi -> gamma eta(c)) center dot B(eta(c) -> pi(0)pi(0)) < 0.71 x 10(-5), B(J/psi -> gamma(eta c)) center dot B(eta(c) -> K+K-) < 0.96 x 10(-5), and B(J/psi -> gamma eta(c)) center dot B(eta(c) (KSKS0)-K-0) < 0.53 x 10(-5).Physics, Particles & FieldsSCI(E)1ARTICLE2337-3414
Measurement of the ratio of branching fractions B(B0→K∗0γ )/B(B0s→φγ ) and the directCP asymmetry inB 0→K∗0γ
No full textThe ratio of branching fractions of the radiative B decays B0→K⁎0γ and B0s→ϕγ has been measured using an integrated luminosity of 1.0 fb−1 of pp collision data collected by the LHCb experiment at a centre-of-mass energy of s√=7TeV. The value obtained is
B(B0→K⁎0γ)B(B0s→ϕγ)=1.23±0.06(stat.)±0.04(syst.)±0.10(fs/fd),
where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is associated with the ratio of fragmentation fractions fs/fd. Using the world average value for B(B0→K⁎0γ), the branching fraction B(B0s→ϕγ) is measured to be (3.5±0.4)×10−5.
The direct CP asymmetry in B0→K⁎0γ decays has also been measured with the same data and found to be
ACP(B0→K⁎0γ)=(0.8±1.7(stat.)±0.9(syst.))%.
Both measurements are the most precise to date and are in agreement with the previous experimental results and theoretical expectations
An Overview of Service-Oriented Architecture
No full textThis report is a literature review of Service-Oriented Architectures (SOA). An SOA is a loosely couple network of communicating services. The key elements and characteristics of SOAs are outlined to guide the CORE project in creating a Virtual Research Environment (VRE). The benefits of using SOA concepts in implementing the VRE are presented and justifications of their use in the CORE project are also discussed
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