365 research outputs found
Life and death at precolumbian Lavoutte, Saint Lucia, Lesser Antilles
The Caribbean archaeological record requires immediate attention and protection. Development and natural forces have impacted archaeological sites, destroying or severely damaging them. The precolumbian site of Lavoutte, located in northern Saint Lucia, has been known as a major Late Ceramic Age (A.D. 1000–1500) settlement since the 1960s, but it has been damaged over the past decades by both natural and human processes. Multidisciplinary field and laboratory methodologies were implemented during a rescue project at the site from 2009 to 2010. This paper presents the results of collaborative efforts between local and international organizations. The first goal was to demonstrate the importance of protection and rescue of endangered archaeological sites. Secondly, we aimed to show that by adopting a
multidisciplinary approach including artifact analysis, bioarchaeology, paleoenvironmental reconstruction, and geochemistry, severely damaged sites can be of significant informational value. Archaeology of indigenous Americ
B Production Asymmetries in Perturbative QCD
This paper explores a new mechanism for B production in which a b quark
combines with a light parton from the hard-scattering process before
hadronizing into the B hadron. This recombination mechanism can be calculated
within perturbative QCD up to a few nonperturbative constants. Though
suppressed at large transverse momentum by a factor Lambda_QCD m_b/p_t^2
relative to b quark fragmentation production, it can be important at large
rapidities. A signature for this heavy-quark recombination mechanism in
proton-antiproton colliders is the presence of rapidity asymmetries in B cross
sections. Given reasonable assumptions about the size of nonperturbative
parameters entering the calculation, we find that the asymmetries are only
significant for rapidities larger than those currently probed by collider
experiments.Comment: 17 pages, LaTeX, 4 ps figures, tightenlines, sections added, final
version accepted for publication in Phys. Rev.
Active Galactic Nuclei at the Crossroads of Astrophysics
Over the last five decades, AGN studies have produced a number of spectacular
examples of synergies and multifaceted approaches in astrophysics. The field of
AGN research now spans the entire spectral range and covers more than twelve
orders of magnitude in the spatial and temporal domains. The next generation of
astrophysical facilities will open up new possibilities for AGN studies,
especially in the areas of high-resolution and high-fidelity imaging and
spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These
studies will address in detail a number of critical issues in AGN research such
as processes in the immediate vicinity of supermassive black holes, physical
conditions of broad-line and narrow-line regions, formation and evolution of
accretion disks and relativistic outflows, and the connection between nuclear
activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic
Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical
Symposia Serie
The asymmetry of the proton in a Pion Cloud Model approach
We study the asymmetry of the proton in a model approach
in which hadronic fluctuations of the nucleon are generated through gluon
splitting and recombination mechanisms. Within this framework, it is shown that
the
asymmetry of the proton is consistently described by including only
nucleon fluctuations to and bound states. Predictions
of the model closely agree with the recent experimental data of the E866/NuSea
Collaboration.Comment: Final version. To appear in Phys. Rev.
PREDICTING THE SUMMER TEMPERATURE OF SMALL STREAMS IN SOUTHWESTERN WISCONSIN 1
One of the biggest challenges in managing cold water streams in the Midwest is understanding how stream temperature is controlled by the complex interactions among meteorologic processes, channel geometry, and ground water inflow. Inflow of cold ground water, shade provided by riparian vegetation, and channel width are the most important factors controlling summer stream temperatures. A simple screening model was used to quantitatively evaluate the importance of these factors and guide management decisions. The model uses an analytical solution to the heat transport equation to predict steady-state temperature throughout a stream reach. The model matches field data from four streams in southwestern Wisconsin quite well (typically within 1°C) and helps explain the observed warming and cooling trends along each stream reach. The distribution of ground water inflow throughout a stream reach has an important influence on stream temperature, and springs are especially effective at providing thermal refuge for fish. Although simple, this model provides insight into the importance of ground water and the impact different management strategies, such as planting trees to increase shade, may have on summer stream temperature.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74032/1/j.1752-1688.2005.tb03714.x.pd
Neutral-Current Four-Fermion Production in e+e- Interactions at LEP
Neutral-current four-fermion production, e+e- -> ffff is studied in 0.7/fb of
data collected with the L3 detector at LEP at centre-of-mass energies
root(s)=183-209GeV. Four final states are considered: qqvv, qqll, llll and
llvv, where l denotes either an electron or a muon. Their cross sections are
measured and found to agree with the Standard Model predictions. In addition,
the e+e- -> Zgamma* -> ffff process is studied and its total cross section at
the average centre-of-mass energy 196.6GeV is found to be 0.29 +/- 0.05 +/-
0.03 pb, where the first uncertainty is statistical and the second systematic,
in agreement with the Standard Model prediction of 0.22 pb. Finally, the mass
spectra of the qqll final states are analysed to search for the possible
production of a new neutral heavy particle, for which no evidence is found
Measurement of the Cross Section of W-boson pair production at LEP
The cross section of W-boson pair-production is measured with the L3 detector
at LEP. In a data sample corresponding to a total luminosity of 629.4/pb,
collected at centre-of-mass energies ranging from 189 to 209 GeV, 9834
four-fermion events with W bosons decaying into hadrons or leptons are
selected. The total cross section is measured with a precision of 1.4 % and
agrees with the Standard Model expectation. Assuming charged-lepton
universality, the branching fraction for hadronic W-boson decays is measured to
be: Br(W-->hadrons) = 67.50 +- 0.42 (stat.) +- 0.30(syst.) %, in agreement with
the Standard Model. Differential cross sections as a function of the W-
production angle are also measured for the semi-leptonic channels qqev and
qqmv
Determination of alphaS from Hadronic Event Shapes in e+e- Annihilation at 192 < sqrt(s) < 208 GeV
Results are presented from a study of the structure of high energy hadronic
events recorded by the L3 detector at sqrt(s)>192 GeV. The distributions of
several event shape variables are compared to resummed O(alphaS^2) QCD
calculations. We determine the strong coupling constant at three average
centre-of-mass energies: 194.4, 200.2 and 206.2 GeV. These measurements,
combined with previous L3 measurements at lower energies, demonstrate the
running of alphaS as expected in QCD and yield alphaS(mZ) = 0.1227 +- 0.0012 +-
0.0058, where the first uncertainty is experimental and the second is
theoretical
Measurement of the Topological Branching Fractions of the tau lepton at LEP
Using data collected with the L3 detector at LEP from 1992 to 1995 on the Z
peak, we determine the branching fractions of the tau lepton into one, three
and five charged particles to be:
B(tau->(1-prong)) = 85.274 +- 0.105 +- 0.073 %,
B(tau->(3-prong)) = 14.556 +- 0.105 +- 0.076 %,
B(tau->(5-prong)) = 0.170 +- 0.022 +- 0.026 %.
The first uncertainties are statistical and the second systematic. The
accuracy of these measurements alone is similar to that of the current world
average
Study of Inclusive Strange-Baryon Production and Search for Pentaquarks in Two-Photon Collisions at LEP
Measurements of inclusive production of the Lambda, Xi- and Xi*(1530) baryons
in two-photon collisions with the L3 detector at LEP are presented. The
inclusive differential cross sections for Lambda and Xi- are measured as a
function of the baryon transverse momentum, pt, and pseudo-rapidity, eta. The
mean number of Lambda, Xi- and Xi*(1530) baryons per hadronic two-photon event
is determined in the kinematic range 0.4 GeV < pt< 2.5 GeV, |eta| < 1.2.
Overall agreement with the theoretical models and Monte Carlo predictions is
observed. A search for inclusive production of the pentaquark theta+(1540) in
two-photon collisions through the decay theta+ -> proton K0s is also presented.
No evidence for production of this state is found
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