747 research outputs found
The BFKL-Pomeron In Deep Inelastic Diffractive Dissociation near t=0
The small- behaviour of the deep inelastic diffractive dissociation cross
section in the triple Regge region is investigated, using the BFKL
approximation in perturbative QCD. We show that the cross section is finite at
, but the diffusion in leads to a large contribution of small
momenta at the triple Pomeron vertex. We study the dependence upon the total
energy and the invariant mass. At , there is a decoupling of the three
BFKL singularities which is a consequence of the conservation of the conformal
dimension. For large invariant masses, the four gluon state in the upper
t-channel plays an important role and cannot be neglected.Comment: 43 pages, LaTex , 11 ps-figures (uuencoded) appende
The Total Cross Section and the BFKL Pomeron at Collider
We present a numerical estimate of the total cross
section at LEP and at the designed Next Linear Collider (NLC), based
upon the BFKL Pomeron. We find for the linear collider that the event rate is
substantial provided electrons scattered under small angles can be detected,
and a measurement of this cross section provides an excellent test of the BFKL
Pomeron. For LEP, although the number of events is substantially smaller, an
initial study of this process is feasible.Comment: 10 pages, latex, 5 figures included using epsfi
The Victoria west: Earliest prepared core technology in the acheulean at canteen kopje and implications for the cognitive evolution of early hominids
Prepared core technology illustrates in-depth planning and the presence of a mental template during the core reduction process. This technology is, therefore, a significant indicator in studying the evolution of abstract thought and the cognitive abilities of hominids. Here, we report on Victoria West cores excavated from the Canteen Kopje site in central South Africa, with a preliminary age estimate of approximately 1Ma (million years ago) for these cores. Technological analysis shows that the VictoriaWest cores bear similarities to the ‘Volumetric Concept’ as defined for the Levallois, a popular and widely distributed prepared core technology from at least 200 ka (thousand years ago). Although these similarities are present, several notable differences also occur that make the Victoria West a unique and distinctive prepared core technology; these are: elongated and convergent core shapes, consistent blow directions for flake removal, a predominance of large side-struck flakes, and the use of these flakes to make Acheulean large cutting tools. This innovative core reduction strategy at Canteen Kopje extends the roots of prepared core technology to the latter part of the Early Acheulean and clearly demonstrates an increase in the cognitive abilities and complexities of hominids in this time period.EM201
Lake eutrophication and its implications for organic carbon sequestration in Europe
The eutrophication of lowland lakes in Europe by excess nitrogen (N) and phosphorus (P) is severe because of the long history of land-cover change and agricultural intensification. The ecological and socio-economic effects of eutrophication are well understood but its effect on organic carbon (OC) sequestration by lakes and its change overtime has not been determined. Here, we compile data from ~90 culturally impacted European lakes [~60% are eutrophic, Total P (TP) >30 μg P l] and determine the extent to which OC burial rates have increased over the past 100-150 years. The average focussing corrected, OC accumulation rate (C AR) for the period 1950-1990 was ~60 g C m yr, and for lakes with >100 μg TP l the average was ~100 g C m yr. The ratio of post-1950 to 1900-1950 C AR is low (~1.5) indicating that C accumulation rates have been high throughout the 20th century. Compared to background estimates of OC burial (~5-10 g C m yr), contemporary rates have increased by at least four to fivefold. The statistical relationship between C AR and TP derived from this study (r = 0.5) can be used to estimate OC burial at sites lacking estimates of sediment C-burial. The implications of eutrophication, diagenesis, lake morphometry and sediment focussing as controls of OC burial rates are considered. A conservative interpretation of the results of the this study suggests that lowland European meso- to eutrophic lakes with >30 μg TP l had OC burial rates in excess of 50 g C m yr over the past century, indicating that previous estimates of regional lake OC burial have seriously underestimated their contribution to European carbon sequestration. Enhanced OC burial by lakes is one positive side-effect of the otherwise negative impact of the anthropogenic disruption of nutrient cycles. © 2014 John Wiley & Sons Ltd
Inclusive 1-jet Production Cross Section at Small x in QCD: Multiple Interactions
We study corrections due to two Pomeron exchanges to the inclusive 1-jet
production cross section in the Regge limit of perturbative QCD for a finite
number of colors. By considering deep inelastic scattering on a weakly bound
two-nucleon system, we carefully follow the logic of the AGK cutting rules and
show, for the single inclusive cross section, that, due to the reggeization of
the gluon, modifications of the AGK cutting rules appear. As our main result,
we investigate and calculate the jet production vertex in the presence of a
two-Pomeron cut correction. Compared to previous studies, we find a novel
structure of the jet vertex which has not been considered before. We discuss a
few implications of this new piece.Comment: 42 pages, 22 figures, few references and comments added, to appear on
JHE
Proximate content and lipid profile of seeds from rapanea melanophloeos (the Cape beech) tree
Abstract: Rapanea melanophloeos (Cape beech) is a fruit-bearing tree indigenous to Southern Africa which produces edible fruit. Previous studies have focussed on investigating the nutritional potential of the tree’s fruit pulp. The nutritional potential of R. melanophloeos seeds is unknown. Seed samples obtained from ripe fruit of the Cape beech trees had their proximate analysis and lipid profiling done. The dry matter and ash contributed 91.29 ± 0.00 %, 1.50 ± 0.01 % of the mass of the seed. Whilst the other proximate analytes namely crude fibre, crude protein and ether extract made up 5.71 ± 0.43 % , 10.50 ± 0.49 % and 4.75 ± 0.09 % the mass of the seeds respectively. The fatty acid profile of the seed oil revealed Linoleic acid (50.43 ± 0.38 %) to be the most dominant. R. melanophloeos seeds are not a viable source of nutrients
Azimuthal Distribution of Quark-Antiquark Jets in DIS Diffractive Dissociation
We investigate the azimuthal distribution of quark-antiquark jets in DIS
diffractive dissociation with large transverse momentum. In this kinematical
region the matrix element is expressed in terms of the gluon structure
function. For the transverse part of the cross section we find a -distribution with the maximum at , i.e.\ the jets
prefer a direction perpendicular to the electron plane. This is in contrast to
boson gluon fusion where the jet cross section for transversely
polarized bosons peaks at and . We discuss the origin of
this striking difference and present numerical results relevant for the
diffractive dissociation at HERA.Comment: 12 pages, latex, 7 figure
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