10,343 research outputs found
Diffractive parton distributions from perturbative QCD
The asymptotic collinear factorisation theorem, which holds for diffractive
deep-inelastic scattering, has important modifications in the sub-asymptotic
HERA regime. We use perturbative QCD to quantify these modifications. The
diffractive parton distributions are shown to satisfy an inhomogeneous
evolution equation. We emphasise that it is necessary to include both the
gluonic and sea-quark t-channel components of the perturbative Pomeron. The
corresponding Pomeron-to-parton splitting functions are derived in the
Appendix.Comment: 34 pages, 13 figures. Version published in Eur. Phys. J.
The description of F2 at small x incorporating angular ordering
We study the perturbative QCD description of the HERA measurements of using a gluon distribution that is obtained from an evolution
incorporating angular ordering of the gluon emissions, and which embodies both
GLAP and BFKL dynamics. We compare the predictions with recent HERA data for
. We present estimates of the charm component and of .Comment: 8 LaTeX pages + 4 uuencoded figure
Use of Cone Beam Computed Tomography in Endodontics
Cone Beam Computed Tomography (CBCT) is a diagnostic imaging modality that provides high-quality, accurate three-dimensional (3D) representations of the osseous elements of the maxillofacial skeleton. CBCT systems are available that provide small field of view images at low dose with sufficient spatial resolution for applications in endodontic diagnosis, treatment guidance, and posttreatment evaluation. This article provides a literature review and pictorial demonstration of CBCT as an imaging adjunct for endodontics
NLO prescription for unintegrated parton distributions
We show how parton distributions unintegrated over the parton transverse
momentum, k_t, may be generated, at NLO accuracy, from the known integrated
(DGLAP-evolved) parton densities determined from global data analyses. A few
numerical examples are given, which demonstrate that sufficient accuracy is
obtained by keeping only the LO splitting functions together with the NLO
integrated parton densities. However, it is important to keep the precise
kinematics of the process, by taking the scale to be the virtuality rather than
the transverse momentum, in order to be consistent with the calculation of the
NLO splitting functions.Comment: 20 pages, 8 figures. v2: version to appear in Eur. Phys. J.
Q^2 dependence of diffractive vector meson electroproduction
We give a general formula for the cross section for diffractive vector meson
electroproduction, gamma^* p -> Vp. We first calculate diffractive qqbar
production, and then use parton-hadron duality by projecting out the J^P = 1^-
state in the appropriate mass interval. We compare the Q^2 dependence of the
cross section for the diffractive production of rho and J/psi mesons with
recent HERA data. We include the characteristic Q^2 dependence associated with
the use of the skewed gluon distribution. We give predictions for
sigma_L/sigma_T for both rho and J/psi production.Comment: 15 pages, LaTeX, including five PostScript figure
Investigation of beauty production and parton shower effects at LHC
We present hadron-level predictions from the Monte Carlo generator Cascade
and parton level calculations of open b quark, b-flavored hadron and inclusive
b-jet production in the framework of the kt-factorization QCD approach for the
LHC energies. The unintegrated gluon densities in a proton are determined using
the CCFM evolution equation and the Kimber-Martin-Ryskin (KMR) prescription.
Our predictions are compared with the first data taken by the CMS and LHCb
collaborations at 7 TeV. We study the theoretical uncertainties of our
calculations and investigate the effects coming from parton showers in initial
and final states. The special role of initial gluon transverse momenta in
description of the data is pointed out.Comment: 19 pages, 11 figures. arXiv admin note: substantial text overlap with
arXiv:1105.507
Rapid subduction of organic matter by maldanid polychaetes on the North Carolina slope
In situ tracer experiments conducted on the North Carolina continental slope reveal that tube-building worms (Polychaeta: Maldanidae) can, without ingestion, rapidly subduct freshly deposited, algal carbon (13C-labeled diatoms) and inorganic materials (slope sediment and glass beads) to depths of 10 cm or more in the sediment column. Transport over 1.5 days appears to be nonselective but spatially patchy, creating localized, deep hotspots. As a result of this transport, relatively fresh organic matter becomes available soon after deposition to deep-dwelling microbes and other infauna, and both aerobic and anaerobic processes may be enhanced. Comparison of tracer subduction with estimates from a diffusive mixing model using 234Th-based coefficients, suggests that maldanid subduction activities, within 1.5 d of particle deposition, could account for 25–100% of the mixing below 5 cm that occurs on 100-day time scales. Comparisons of community data from the North Carolina slope for different places and times indicate a correlation between the abundance of deep-dwelling maldanids and the abundance and the dwelling depth in the sediment column of other infauna. Pulsed inputs of organic matter occur frequently in margin environments and maldanid polychaetes are a common component of continental slope macrobenthos. Thus, the activities we observe are likely to be widespread and significant for chemical cycling (natural and anthropogenic materials) on the slope. We propose that species like maldanids, that rapidly redistribute labile organic matter within the seabed, probably function as keystone resource modifiers. They may exert a disproportionately strong influence (relative to their abundance) on the structure of infaunal communities and on the timing, location and nature of organic matter diagenesis and burial in continental margin sediments
Field-Induced Magnetization Steps in Intermetallic Compounds and Manganese Oxides: The Martensitic Scenario
Field-induced magnetization jumps with similar characteristics are observed
at low temperature for the intermetallic germanide Gd5Ge4and the mixed-valent
manganite Pr0.6Ca0.4Mn0.96Ga0.04O3. We report that the field location -and even
the existence- of these jumps depends critically on the magnetic field sweep
rate used to record the data. It is proposed that, for both compounds, the
martensitic character of their antiferromagnetic-to-ferromagnetic transitions
is at the origin of the magnetization steps.Comment: 4 pages,4 figure
Benchmarks for the Forward Observables at RHIC, the Tevatron-run II and the LHC
We present predictions on the total cross sections and on the ratio of the
real part to the imaginary part of the elastic amplitude (rho parameter) for
present and future pp and pbar p colliders, and on total cross sections for
gamma p -> hadrons at cosmic-ray energies and for gamma gamma-> hadrons up to
sqrt{s}=1 TeV. These predictions are based on an extensive study of possible
analytic parametrisations invoking the biggest hadronic dataset available at
t=0. The uncertainties on total cross sections, including the systematic errors
due to contradictory data points from FNAL, can reach 1.9% at RHIC, 3.1% at the
Tevatron, and 4.8% at the LHC, whereas those on the rho parameter are
respectively 5.4%, 5.2%, and 5.4%.Comment: 11 pages, 2 figures, 4 tables, RevTeX
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