80,887 research outputs found
Operadores seudodiferenciales con símbolos : Distribuciones
No full textFil: Alvarez Alonso, Josefina D.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Operadores seudodiferenciales con símbolos : Distribuciones
No full textFil: Alvarez Alonso, Josefina D.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Extracting Boer-Mulders functions from p+D Drell-Yan processes
No full textWe extract the Boer- Mulders functions of valence and sea quarks in the proton from unpolarized p + D Drell- Yan data measured by the FNAL E866 Collaboration. Using these Boer- Mulders functions, we calculate the cos2 phi asymmetries in unpolarized pp Drell- Yan processes, both for the FNAL E866/ NuSea and the BNL Relativistic Heavy Ion Collider experiments. We also estimate the cos2 phi asymmetries in the unpolarized p (P) over bar Drell- Yan processes at GSI.Astronomy & AstrophysicsPhysics, Particles & FieldsSCI(E)37ARTICLE5null7
Detailed Diagnostics of an X-Ray Flare in the Single Giant HR 9024
No full textWe analyze a 96 ks Chandra HETGS observation of the single G-type giant HR 9024. The high flux allows us to examine spectral line and continuum diagnostics at high temporal resolution, to derive plasma parameters. A time-dependent one-dimensional hydrodynamic model of a loop with half-length L=5×1011 cm (~R*/2) and cross-sectional radius r=4.3×1010 cm, with a heat pulse of 15 ks and 2×1011 ergs cm-2 s-1 deposited at the loop footpoints, satisfactorily reproduces the observed evolution of temperature and emission measure, derived from the analysis of the strong continuum emission. For the first time we can compare predictions from the hydrodynamic model with single spectral features, other than with global spectral properties. We find that the model closely matches the observed line emission, especially for the hot (~108 K) plasma emission of the Fe XXV complex at ~1.85 Å. The model loop has L/R*~1/2 and aspect ratio r/L~0.1, as typically derived for flares observed in active stellar coronae, suggesting that the underlying physics is the same for these very dynamic and extreme phenomena in stellar coronae independently of stellar parameters and evolutionary stage
CliSAT: A new exact algorithm for hard maximum clique problems
No full textGiven a graph, the maximum clique problem (MCP) asks for determining a complete subgraph with the
largest possible number of vertices. We propose a new exact algorithm, called CliSAT , to solve the
MCP to proven optimality. This problem is of fundamental importance in graph theory and combinatorial
optimization due to its practical relevance for a wide range of applications. The newly developed exact approach is a combinatorial branch-and-bound algorithm that exploits the state-of-the-art branching
scheme enhanced by two new bounding techniques with the goal of reducing the branching tree. The
first one is based on graph colouring procedures and partial maximum satisfiability problems arising in
the branching scheme. The second one is a filtering phase based on constraint programming and domain
propagation techniques. CliSAT is designed for structured MCP instances which are computationally
difficult to solve since they are dense and contain many interconnected large cliques. Extensive experiments on hard benchmark instances, as well as new hard instances arising from different applications,
show that CliSAT outperforms the state-of-the-art MCP algorithms, in some cases by several orders of
magnitude
Prompt charm production in pp collisions at √<span style="text-decoration:overline">s</span>=7 TeV
No full textCharm production at the LHC in pp collisions at s√=7 TeV is studied with the LHCb detector. The decays D0→K−π+, D+→K−π+π+, D⁎+→D0(K−π+)π+, D+s→ϕ(K−K+)π+, Λ+c→pK−π+, and their charge conjugates are analysed in a data set corresponding to an integrated luminosity of 15 nb−1. Differential cross-sections dσ/dpT are measured for prompt production of the five charmed hadron species in bins of transverse momentum and rapidity in the region 0<pT<8 GeV/c and 2.0<y<4.5. Theoretical predictions are compared to the measured differential cross-sections. The integrated cross-sections of the charm hadrons are computed in the above pT-y range, and their ratios are reported. A combination of the five integrated cross-section measurements gives
σ(cc¯)pT<8 GeV/c,2.0<y<4.5=1419±12(stat)±116(syst)±65(frag) μb,
where the uncertainties are statistical, systematic, and due to the fragmentation functions
Mobile genetic elements, cloning vectors and genetic manipulation of bifidobacteria
No full textGrowth difficulties, because of their fastidious nutritive nature and oxygen sensitivity, and a lack of efficient genetic tools have impeded until recently proper development of molecular studies in Bifidobacterium. These studies, however, are critical to uncover the cross-talk between bifidobacteria and their hosts' cells, and also to prove unequivocally the supposed beneficial activities supplied through the gastrointestinal tract of mammals either endogenously or after ingestion as probiotics. Analysis of gene sequences provided by whole genome sequencing projects has opened new avenues to decipher the genetic basis of bacteria-cell interactions and probiotic effects. However, the purposeful development of stable cloning and expression vectors based on robust replicons -either from temperate phages or resident plasmids- is additionally needed. This chapter addresses the current knowledge on the mobile genetic elements of bifidobacteria (phages, plasmids, and transposons) and reviews the different types of vectors already available for the Bifidobacterium species, together with the transformation procedures for introducing DNA into bifidobacterial cells. It also covers recent molecular studies performed with such vectors and incipient results on the genetic modification of these organisms, establishing the basis that would allow the use of bifidobacteria for many biotechnological applications. Pitfalls, drawbacks, and future needs in the field are also discussed
Search for the decay Bs0→D*∓π±
No full textA search for the decay Bs0→D*∓π± is presented using a data sample corresponding to an integrated luminosity of 1.0 fb-1 of pp collisions collected by LHCb. This decay is expected to be mediated by a W-exchange diagram, with little contribution from rescattering processes, and therefore a measurement of the branching fraction will help us to understand the mechanism behind related decays such as Bs0→π+π- and Bs0→DD̅ . Systematic uncertainties are minimized by using B0→D*∓π± as a normalization channel. We find no evidence for a signal, and set an upper limit on the branching fraction of B(Bs0→D*∓π±)<6.1(7.8)×10-6 at 90% (95%) confidence level
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