1,468 research outputs found
The biological origin of linguistic diversity
In contrast with animal communication systems, diversity is characteristic of almost every aspect of human language. Languages variously employ tones, clicks, or manual signs to signal differences in meaning; some languages lack the noun-verb distinction (e.g., Straits Salish), whereas others have a proliferation of fine-grained syntactic categories (e.g., Tzeltal); and some languages do without morphology (e.g., Mandarin), while others pack a whole sentence into a single word (e.g., Cayuga). A challenge for evolutionary biology is to reconcile the diversity of languages with the high degree of biological uniformity of their speakers. Here, we model processes of language change and geographical dispersion and find a consistent pressure for flexible learning, irrespective of the language being spoken. This pressure arises because flexible learners can best cope with the observed high rates of linguistic change associated with divergent cultural evolution following human migration. Thus, rather than genetic adaptations for specific aspects of language, such as recursion, the coevolution of genes and fast-changing linguistic structure provides the biological basis for linguistic diversity. Only biological adaptations for flexible learning combined with cultural evolution can explain how each child has the potential to learn any human language
Baryons in the relativistic jets of the stellar-mass black-hole candidate 4U 1630-47
Accreting black holes are known to power relativistic jets, both in stellar-mass binary systems and at the centres of galaxies. The power carried away by the jets, and, hence, the feedback they provide to their surroundings, depends strongly on their composition. Jets containing a baryonic component should carry significantly more energy than electronâpositron jets. Energetic considerations1, 2 and circular-polarization measurements3 have provided conflicting circumstantial evidence for the presence or absence of baryons in jets, and the only system in which they have been unequivocally detected is the peculiar X-ray binary SSâ433 (refs 4, 5). Here we report the detection of Doppler-shifted X-ray emission lines from a more typical black-hole candidate X-ray binary, 4Uâ1630-47, coincident with the reappearance of radio emission from the jets of the source. We argue that these lines arise from baryonic matter in a jet travelling at approximately two-thirds the speed of light, thereby establishing the presence of baryons in the jet. Such baryonic jets are more likely to be powered by the accretion disk6 than by the spin of the black hole7, and if the baryons can be accelerated to relativistic speeds, the jets should be strong sources of Îł-rays and neutrino emission
Fortnightly changes in water transport direction across the mouth of a narrow estuary
This research investigates the dynamics of the axial
tidal flow and residual circulation at the lower Guadiana
Estuary, south Portugal, a narrow mesotidal estuary with low
freshwater inputs. Current data were collected near the deepest
part of the channel for 21 months and across the channel
during two (spring and neap) tidal cycles. Results indicate
that at the deep channel, depth-averaged currents are stronger
and longer during the ebb at spring and during the flood at
neap, resulting in opposite water transport directions at a
fortnightly time scale. The net water transport across the entire
channel is up-estuary at spring and down-estuary at neap, i.e.,
opposite to the one at the deep channel. At spring tide, when
the estuary is considered to be well mixed, the observed
pattern of circulation (outflow in the deep channel, inflow
over the shoals) results from the combination of the Stokes
transport and compensating return flow, which varies laterally
with the bathymetry. At neap tide (in particular for those of
lowest amplitude each month), inflows at the deep channel are
consistently associated with the development of gravitational
circulation. Comparisons with previous studies suggest that
the baroclinic pressure gradient (rather than internal tidal
asymmetries) is the main driver of the residual water transport.
Our observations also indicate that the flushing out of the
water accumulated up-estuary (at spring) may also produce
strong unidirectional barotropic outflow across the entire
channel around neap tide.info:eu-repo/semantics/publishedVersio
Measurement of the running of the QED coupling in small-angle Bhabha scattering at LEP
Using the OPAL detector at LEP, the running of the effective QED coupling
alpha(t) is measured for space-like momentum transfer from the angular
distribution of small-angle Bhabha scattering. In an almost ideal QED
framework, with very favourable experimental conditions, we obtain:
Delta alpha(-6.07GeV^2) - Delta alpha(-1.81GeV^2) = (440 pm 58 pm 43 pm 30) X
10^-5, where the first error is statistical, the second is the experimental
systematic and the third is the theoretical uncertainty. This agrees with
current evaluations of alpha(t).The null hypothesis that alpha remains constant
within the above interval of -t is excluded with a significance above 5sigma.
Similarly, our results are inconsistent at the level of 3sigma with the
hypothesis that only leptonic loops contribute to the running. This is
currently the most significant direct measurment where the running alpha(t) is
probed differentially within the measured t range.Comment: 43 pages, 12 figures, Submitted to Euro. Phys. J.
A Measurement of Rb using a Double Tagging Method
The fraction of Z to bbbar events in hadronic Z decays has been measured by
the OPAL experiment using the data collected at LEP between 1992 and 1995. The
Z to bbbar decays were tagged using displaced secondary vertices, and high
momentum electrons and muons. Systematic uncertainties were reduced by
measuring the b-tagging efficiency using a double tagging technique. Efficiency
correlations between opposite hemispheres of an event are small, and are well
understood through comparisons between real and simulated data samples. A value
of Rb = 0.2178 +- 0.0011 +- 0.0013 was obtained, where the first error is
statistical and the second systematic. The uncertainty on Rc, the fraction of Z
to ccbar events in hadronic Z decays, is not included in the errors. The
dependence on Rc is Delta(Rb)/Rb = -0.056*Delta(Rc)/Rc where Delta(Rc) is the
deviation of Rc from the value 0.172 predicted by the Standard Model. The
result for Rb agrees with the value of 0.2155 +- 0.0003 predicted by the
Standard Model.Comment: 42 pages, LaTeX, 14 eps figures included, submitted to European
Physical Journal
Measurement of the B+ and B-0 lifetimes and search for CP(T) violation using reconstructed secondary vertices
The lifetimes of the B+ and B-0 mesons, and their ratio, have been measured in the OPAL experiment using 2.4 million hadronic Z(0) decays recorded at LEP. Z(0) --> b (b) over bar decays were tagged using displaced secondary vertices and high momentum electrons and muons. The lifetimes were then measured using well-reconstructed charged and neutral secondary vertices selected in this tagged data sample. The results aretau(B+) = 1.643 +/- 0.037 +/- 0.025 pstau(Bo) = 1.523 +/- 0.057 +/- 0.053 pstau(B+)/tau(Bo) = 1.079 +/- 0.064 +/- 0.041,where in each case the first error is statistical and the second systematic.A larger data sample of 3.1 million hadronic Z(o) decays has been used to search for CP and CPT violating effects by comparison of inclusive b and (b) over bar hadron decays, No evidence fur such effects is seen. The CP violation parameter Re(epsilon(B)) is measured to be Re(epsilon(B)) = 0.001 +/- 0.014 +/- 0.003and the fractional difference between b and (b) over bar hadron lifetimes is measured to(Delta tau/tau)(b) = tau(b hadron) - tau((b) over bar hadron)/tau(average) = -0.001 +/- 0.012 +/- 0.008
Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector
The inclusive and dijet production cross-sections have been measured for jets
containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass
energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The
measurements use data corresponding to an integrated luminosity of 34 pb^-1.
The b-jets are identified using either a lifetime-based method, where secondary
decay vertices of b-hadrons in jets are reconstructed using information from
the tracking detectors, or a muon-based method where the presence of a muon is
used to identify semileptonic decays of b-hadrons inside jets. The inclusive
b-jet cross-section is measured as a function of transverse momentum in the
range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet
cross-section is measured as a function of the dijet invariant mass in the
range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets
and the angular variable chi in two dijet mass regions. The results are
compared with next-to-leading-order QCD predictions. Good agreement is observed
between the measured cross-sections and the predictions obtained using POWHEG +
Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet
cross-section. However, it does not reproduce the measured inclusive
cross-section well, particularly for central b-jets with large transverse
momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final
version published in European Physical Journal
Observation of associated near-side and away-side long-range correlations in âsNN=5.02ââTeV proton-lead collisions with the ATLAS detector
Two-particle correlations in relative azimuthal angle (ÎÏ) and pseudorapidity (Îη) are measured in âsNN=5.02ââTeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1ââÎŒb-1 of data as a function of transverse momentum (pT) and the transverse energy (ÎŁETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Îη|<5) ânear-sideâ (ÎÏâŒ0) correlation that grows rapidly with increasing ÎŁETPb. A long-range âaway-sideâ (ÎÏâŒÏ) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ÎŁETPb, is found to match the near-side correlation in magnitude, shape (in Îη and ÎÏ) and ÎŁETPb dependence. The resultant ÎÏ correlation is approximately symmetric about Ï/2, and is consistent with a dominant cosâĄ2ÎÏ modulation for all ÎŁETPb ranges and particle pT
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