The timing of the formation and usage of replicase clusters in S-phase nuclei of human diploid fibroblasts

The sites of nascent DNA synthesis were compared with the distribution of the proliferating cell nuclear antigen (PCNA) in S-phase nuclei of human diploid fibroblasts (HDF) by two in vitro techniques. Firstly, proliferating fibroblasts growing in culture that had been synchronised at S-phase were microinjected with the thymidine analogue biotin-11-dUTP. The sites of incorporation of biotin into injected cells were compared with the distribution of PCNA by indirect immunofluorescence microscopy and laser scanning confocal microscopy (LSCM). In common with other studies, a progression of patterns for both biotin incorporation and PCNA localisation was observed. However, we did not always observe coincidence in these patterns, the pattern of biotin incorporation often resembling the expected, preceding distribution of PCNA. In nuclei in which the pattern of biotin incorporation appeared to be identical to the distribution of PCNA, LSCM revealed that not all of the sites of PCNA immunofluorescence were incorporating biotin at the same time. Secondly, nuclei which had been isolated from quiescent cultures of HDF were innoculated into cell-free extracts of Xenopus eggs which support DNA replication in vitro. Following innoculation into these extracts DNA replication was initiated in each nucleus. The sites of DNA synthesis were detected by biotin-11-dUTP incorporation and compared with the distribution of PCNA by indirect immunofluorescence. Only a single pattern of biotin incorporation and PCNA distribution was observed. PCNA accumulated at multiple discrete spots some 15min before any biotin incorporation was observed. When biotin incorporation did occur, LSCM revealed almost complete coincidence between the sites of DNA synthesis and the sites at which PCNA was localised.Brunel Open Access Publishing Fun

Nucleation- and Emergence-Limited Growth of Ice from Pores

Nucleation of ice from vapor on atmospheric aerosols has been attributed to the condensation and freezing of supercooled water in small pores. Here we use wedge pores on mica to directly observe the growth of ice in confinement prior to the growth of bulk crystals. We report a transition in behavior with a decreasing temperature: At low temperatures, the limiting step is not nucleation but a free energy barrier associated with the growth of ice through a narrow pore mouth to become a bulk phase

Parton Distributions for Event Generators

In this paper, conventional Global QCD analysis is generalized to produce parton distributions optimized for use with event generators at the LHC. This optimization is accomplished by combining the constraints due to existing hard-scattering experimental data with those from anticipated cross sections for key representative SM processes at LHC (by the best available theory) as joint input to the global analyses. The PDFs obtained in these new type of global analyses using matrix elements calculated in any given order will be best suited to work with event generators of that order, for predictions at the LHC. This is most useful for LO event generators at present. Results obtained from a few candidate PDF sets (labeled as CT09MCS, CT09MC1 and CT09MC2) for LO event generators produced in this way are compared with those from other approaches.Comment: 35 pages, 19 figures, and 4 table

Design of Marine Protected Areas on high seas and territorial waters of rockall bank

Fisheries closures are rapidly being developed to protect vulnerable marine ecosystems worldwide. Satellite monitoring of fishing vessel activity indicates that these closures can work effectively with good compliance by international fleets even in remote areas. Here we summarise how remote fisheries closures were designed to protect Lophelia pertusa habitat in a region of the NE Atlantic that straddles the EU fishing zone and the high seas. We show how scientific records, fishers' knowledge and surveillance data on fishing activity can be combined to provide a powerful tool for the design of Marine Protected Areas. © Inter-Research 2009

t \bar{t} W production and decay at NLO

We present results for the production of a top pair in association with a W-boson at next-to-leading order. We have implemented this process into the parton-level integrator MCFM including the decays of both the top quarks and the W-bosons with full spin correlations. Although the cross section for this process is small, it is a Standard Model source of same-sign lepton events that must be accounted for in many new physics searches. For a particular analysis of same-sign lepton events in which b-quarks are also present, we investigate the effect of the NLO corrections as a function of the signal region cuts.Comment: 10 pages, 7 figure

b-Initiated processes at the LHC: a reappraisal

Several key processes at the LHC in the standard model and beyond that involve $b$ quarks, such as single-top, Higgs, and weak vector boson associated production, can be described in QCD either in a 4-flavor or 5-flavor scheme. In the former, $b$ quarks appear only in the final state and are typically considered massive. In 5-flavor schemes, calculations include $b$ quarks in the initial state, are simpler and allow the resummation of possibly large initial state logarithms of the type $\log \frac{{\cal Q}^2}{m_b^2}$ into the $b$ parton distribution function (PDF), ${\cal Q}$ being the typical scale of the hard process. In this work we critically reconsider the rationale for using 5-flavor improved schemes at the LHC. Our motivation stems from the observation that the effects of initial state logs are rarely very large in hadron collisions: 4-flavor computations are pertubatively well behaved and a substantial agreement between predictions in the two schemes is found. We identify two distinct reasons that explain this behaviour, i.e., the resummation of the initial state logarithms into the $b$-PDF is relevant only at large Bjorken $x$ and the possibly large ratios ${\cal Q}^2/m_b^2$'s are always accompanied by universal phase space suppression factors. Our study paves the way to using both schemes for the same process so to exploit their complementary advantages for different observables, such as employing a 5-flavor scheme to accurately predict the total cross section at NNLO and the corresponding 4-flavor computation at NLO for fully exclusive studies.Comment: Fixed typo in Eq. (A.10) and few typos in Eq. (C.2) and (C.3

Giant QCD K-factors beyond NLO

Hadronic observables in Z+jet events can be subject to large NLO corrections at TeV scales, with K-factors that even reach values of order 50 in some cases. We develop a method, LoopSim, by which approximate NNLO predictions can be obtained for such observables, supplementing NLO Z+jet and NLO Z+2-jet results with a unitarity-based approximation for missing higher loop terms. We first test the method against known NNLO results for Drell-Yan lepton pt spectra. We then show our approximate NNLO results for the Z+jet observables. Finally we examine whether the LoopSim method can provide useful information even in cases without giant K-factors, with results for observables in dijet events that can be compared to early LHC data.Comment: 38 pages, 13 figures; v2 includes additional reference

Four-lepton production at hadron colliders: aMC@NLO predictions with theoretical uncertainties

We use aMC@NLO to study the production of four charged leptons at the LHC, performing parton showers with both HERWIG and Pythia6. Our underlying matrix element calculation features the full next-to-leading order $O(\alpha_S)$ result and the $O(\alpha_S^2)$ contribution of the $gg$ channel, and it includes all off-shell, spin-correlation, virtual-photon-exchange, and interference effects. We present several key distributions together with the corresponding theoretical uncertainties. These are obtained through a process-independent technique that allows aMC@NLO to compute scale and PDF uncertainties in a fully automated way and at no extra CPU-time costComment: 24 pages, 6 figure

Automation of one-loop QCD corrections

We present the complete automation of the computation of one-loop QCD corrections, including UV renormalization, to an arbitrary scattering process in the Standard Model. This is achieved by embedding the OPP integrand reduction technique, as implemented in CutTools, into the MadGraph framework. By interfacing the tool so constructed, which we dub MadLoop, with MadFKS, the fully automatic computation of any infrared-safe observable at the next-to-leading order in QCD is attained. We demonstrate the flexibility and the reach of our method by calculating the production rates for a variety of processes at the 7 TeV LHC.Comment: 64 pages, 12 figures. Corrected the value of m_Z in table 1. In table 2, corrected the values of cross sections in a.4 and a.5 (previously computed with mu=mtop/2 rather than mu=mtop/4). In table 2, corrected the values of NLO cross sections in b.3, b.6, c.3, and e.7 (the symmetry factor for a few virtual channels was incorrect). In sect. A.4.3, the labeling of the four-momenta was incorrec