59,730 research outputs found
Heavy metal pollution and blackheaded gull (larus ridibundus L.) breeding ecology
No full textHeavy metals in air, soil and water are a global problem and present a growing threat to the environment. These metals may have profound consequences for birds and can cause a number of sub-lethal effects, such as decreased reproductive success. The concentrations of selected heavy metals (As, Cd. Co, Cu, Fe, Pb, Mn, Ni, V, Zn) and Se in eggs and feathers from populations of black-headed gulls (Larus ridibundus L.) located on different colonies in the UK, which have different characteristics and are subject to different sources, types and degrees of pollution, were examined. Concentrations of As, Cu, Pb, Ni, Se and V measured in black-headed gull eggs were consistently high relative to those reported in previous field studies with other gull species. However, no significant effect was observed on the egg characteristics in terms of egg size and dimensions, shell thickness and index as a result of concentrations of metals measured in this study. Concentrations of Co, Fe and Ni were significantly negatively correlated with yolk:albumen ratio in the egg. The usefulness of sampling eggs to provide a reflection of local contamination has been demonstrated, with concentrations related to local sources of metal pollution and site differences reflected in sediment concentrations from previous studies. The importance of taking into account diffuse and historical pollution in addition to point source discharges has also been highlighted. As, Fe, Mn, Pb, Se, V and Zn were found at significantly higher concentrations in egg contents than egg shell, and Cd, Co and Ni concentrations were higher in shell than contents. Cu was distributed approximately equally. Within the egg contents, concentrations of As, Cu, Se and V were higher in the albumen than in the yolk, and Co, Fe, Mn, Ni, Pb and Zn concentrations were higher in the yolk than the albumen. Cd was found mainly in the shell and concentrations in egg contents were largely undetectable. Comparisons were made between a colony subject to high-level commercial egg harvesting and an un-harvested site, and between pre- and post-harvesting eggs on the harvested site. Postcollection eggs were found to be of significantly lower quality than the pre-collection eggs and the eggs from the uncollected site, as indicated by yolk:albumen ratio. Concentration of metals in eggs as a result of relaying forced by commercial harvesting has been demonstrated, with concentrations of Co, Fe and Ni significantly higher in post-collection eggs compared to precollection eggs. Average nesting density was significantly lower on the collected colony than the uncollected colony. No effect on egg size was found as a result of changes in nesting density. Concentrations of metals in black-headed gull chick down were measured and compared to egg data in order to assess the usefulness of feathers as a tool for non-destructive monitoring of metal pollution. The results suggest that feathers may be good indicators for As and Zn, and possibly also for Mn and Ni. However, the sample masses were very small and for a number of metals concentrations were largely undetectable using the analytical equipment available in this study. Future work with larger samples of down would be prudent to further examine the use of chick down to provide an indication of the level of pollution to which birds are exposed. The importance of using appropriate washing procedures to remove exogenous contamination of feathers to assess internal concentrations has been demonstrate
Branching fraction and CP asymmetry of the decays B+→K0Sπ+ and B+→K0SK+
No full textAn analysis of B+ → K0
Sπ+ and B+ → K0
S K+ decays is performed with the LHCb experiment. The pp
collision data used correspond to integrated luminosities of 1 fb−1 and 2 fb−1 collected at centre-ofmass
energies of
√
s = 7 TeV and
√
s = 8 TeV, respectively. The ratio of branching fractions and the
direct CP asymmetries are measured to be B(B+ → K0
S K+
)/B(B+ → K0
Sπ+
) = 0.064 ± 0.009 (stat.) ±
0.004 (syst.), ACP(B+ → K0
Sπ+
) = −0.022 ± 0.025 (stat.) ± 0.010 (syst.) and ACP(B+ → K0
S K+
) =
−0.21 ± 0.14 (stat.) ± 0.01 (syst.). The data sample taken at
√
s = 7 TeV is used to search for
B+
c
→ K0
S K+ decays and results in the upper limit ( fc · B(B+
c
→ K0
S K+
))/( fu · B(B+ → K0
Sπ+
)) <
5.8 × 10−2 at 90% confidence level, where fc and fu denote the hadronisation fractions of a ¯b
quark
into a B+
c or a B+ meson, respectively
All-electron magnetic response with pseudopotentials: NMR chemical shifts
No full textA theory for the ab initio calculation of all-electron NMR chemical shifts in insulators using pseudopotentials is presented. It is formulated for both finite and infinitely periodic systems and is based on an extension to the projector augmented-wave approach of Blochl [P. E. Blochl, Phys. Rev. B 50, 17 953 (1994)] and the method of Mauri et al. [F. Mauri, B. G. Pfrommer, and S. G. Louie, Phys. Rev. Lett. 77, 5300 (1996)]. The theory is successfully validated for molecules by comparison with a selection of quantum chemical results, and in periodic systems by comparison with plane-wave all-electron results for diamond
Observations of Bºs→ψ(2S)η and Bº(s)→ψ(2S)π+π- decays
No full textFirst observations of the B0s
→ψ(2S)η, B0 →ψ(2S)π
+
π
− and B0s
→ψ(2S)π
+
π
− decays are made
using a dataset corresponding to an integrated luminosity of 1.0 fb−1 collected by the LHCb experiment in
proton–proton collisions at a centre-of-mass energy of
√
s = 7 TeV. The ratios of the branching fractions
of each of the ψ(2S) modes with respect to the corresponding J/ψ decays are
B(B0s
→ψ(2S)η)
÷
B(B0s
→J/ψη)
= 0.83± 0.14 (stat)±0.12 (syst) ±0.02 (B),
;
B(B0→ψ(2S)π
+
π
−
)
÷
B(B0→J/ψπ
+
π
−
)
= 0.56± 0.07 (stat)±0.05 (syst)± 0.01 (B),
;
B(B0s
→ψ(2S)π
+
π
−
)
÷
B(B0s
→J/ψπ
+
π
−
)
= 0.34± 0.04 (stat)±0.03 (syst)± 0.01 (B),
where the third uncertainty corresponds to the uncertainties of the dilepton branching fractions of the J/ψ
and ψ(2S) meson decays
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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
Evidence for the decay B0→J/ψω and measurement of the relative branching fractions of meson decays to J/ψη and J/ψη′
No full textFirst evidence of the B 0 → J / ψ ω decay is found and the B s 0 → J / ψ η and B s 0 → J / ψ η ′ decays are studied using a dataset corresponding to an integrated luminosity of 1.0 fb -1 collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV. The branching fractions of these decays are measured relative to that of the B 0 → J / ψ ρ 0 decay:frac(B (B 0 → J / ψ ω), B (B 0 → J / ψ ρ 0)) = 0.89 ± 0.19 (stat) - 0.13 + 0.07 (syst),frac(B (B s 0 → J / ψ η), B (B 0 → J / ψ ρ 0)) = 14.0 ± 1.2 (stat) - 1.5 + 1.1 (syst) - 1.0 + 1.1 (frac(f d, f s)),frac(B (B s 0 → J / ψ η ′), B (B 0 → J / ψ ρ 0)) = 12.7 ± 1.1 (stat) - 1.3 + 0.5 (syst) - 0.9 + 1.0 (frac(f d, f s)), where the last uncertainty is due to the knowledge of f d / f s, the ratio of b-quark hadronization factors that accounts for the different production rate of B 0 and B s 0 mesons. The ratio of the branching fractions of B s 0 → J / ψ η ′ and B s 0 → J / ψ η decays is measured to befrac(B (B s 0 → J / ψ η ′), B (B s 0 → J / ψ η)) = 0.90 ± 0.09 (stat) - 0.02 + 0.06 (syst)
Measurement of the branching fraction
No full textThe B
0
s
→ J/ψK
0
S
branching fraction is measured in a data sample corresponding to 0.41 fb−1
of integrated luminosity collected with the LHCb detector at the LHC. This channel is sensitive to
the penguin contributions affecting the sin 2β measurement from B
0
→ J/ψK
0
S
. The time-integrated
branching fraction is measured to be B(B
0
s
→ J/ψK
0
S
) = (1.83±0.28)×10−5
. This is the most precise
measurement to date
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Measurement of the differential inclusive B+ hadron cross sections in pp collisions at root s=13TeV
No full textThe differential cross sections for inclusive production of B+ hadrons are measured as a function of the B+ transverse momentum p(T)(B) and rapidity y(B) in pp collisions at a centre-of-mass energy of 13 TeV, using data collected by the CMS experiment that correspond to an integrated luminosity of 48.1 pb(-1). The measurement uses the exclusive decay channel B+ -> J/psi K+, with J/psi mesons that decay to a pair of muons. The results show a reasonable agreement with theoretical calculations within the uncertainties. (C) 2017 The Author(s). Published by Elsevier B.V
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