8,155 research outputs found
Rapidity gap survival in the black-disk regime
We summarize how the approach to the black-disk regime (BDR) of strong
interactions at TeV energies influences rapidity gap survival in exclusive hard
diffraction pp -> p + H + p (H = dijet, Qbar-Q, Higgs). Employing a recently
developed partonic description of such processes, we discuss (a) the
suppression of diffraction at small impact parameters by soft spectator
interactions in the BDR; (b) further suppression by inelastic interactions of
hard spectator partons in the BDR; (c) correlations between hard and soft
interactions. Hard spectator interactions substantially reduce the rapidity gap
survival probability at LHC energies compared to previously reported estimates.Comment: 4 pages, 3 figures. Proceedings of XV International Workshop on
Deep-Inelastic Scattering and Related Subjects (DIS 2007), Munich, Germany,
Apr. 16-20, 200
Transverse imaging of the proton in exclusive diffractive pp scattering
In a recent paper (hep-ph/0608271) we describe a new approach to rapidity gap
survival (RGS) in the production of high-mass systems (H = dijet, Higgs, etc.)
in exclusive double-gap diffractive pp scattering, pp -> p + H + p. It is based
on the idea that hard and soft interactions are approximately independent (QCD
factorization), and allows us to calculate the RGS probability in a
model-independent way in terms of the gluon generalized parton distributions
(GPDs) in the colliding protons and the pp elastic scattering amplitude. Here
we focus on the transverse momentum dependence of the cross section. By
measuring the "diffraction pattern," one can perform detailed tests of the
interplay of hard and soft interactions, and even extract information about the
gluon GPD in the proton from the data.Comment: 4 pages, 2 figures, uses ws-procs9x6.cls. Proceedings of XIV
International Workshop on Deep Inelastic Scattering (DIS2006), Tsukuba City,
Japan, Apr 20 - 24, 200
Determination of complex absorbing potentials from the electron self-energy
The electronic conductance of a molecule making contact to electrodes is
determined by the coupling of discrete molecular states to the continuum
electrode density of states. Interactions between bound states and continua can
be modeled exactly by using the (energy-dependent) self-energy, or
approximately by using a complex potential. We discuss the relation between the
two approaches and give a prescription for using the self-energy to construct
an energy-independent, non-local, complex potential. We apply our scheme to
studying single-electron transmission in an atomic chain, obtaining excellent
agreement with the exact result. Our approach allows us to treat
electron-reservoir couplings independent of single electron energies, allowing
for the definition of a one-body operator suitable for inclusion into
correlated electron transport calculations.Comment: 11 pages, 8 figures; to be published in the J. Chem. Phy
Advanced technology applications for second and third general coal gasification systems
The historical background of coal conversion is reviewed and the programmatic status (operational, construction, design, proposed) of coal gasification processes is tabulated for both commercial and demonstration projects as well as for large and small pilot plants. Both second and third generation processes typically operate at higher temperatures and pressures than first generation methods. Much of the equipment that has been tested has failed. The most difficult problems are in process control. The mechanics of three-phase flow are not fully understood. Companies participating in coal conversion projects are ordering duplicates of failure prone units. No real solutions to any of the significant problems in technology development have been developed in recent years
Detection of equine atypical myopathy-associated hypoglycin A in plant material: Optimisation and validation of a novel LC-MS based method without derivatisation
Hypoglycin A (HGA) toxicity, following ingestion of material from certain plants, is linked to an acquired multiple acyl-CoA dehydrogenase deficiency known as atypical myopathy, a commonly fatal form of equine rhabdomyolysis seen worldwide. Whilst some plants are known to contain this toxin, little is known about its function or the mechanisms that lead to varied HGA concentrations between plants. Consequently, reliable tools to detect this amino acid in plant samples are needed. Analytical methods for HGA detection have previously been validated for the food industry, however, these techniques rely on chemical derivatisation to obtain accurate results at low HGA concentrations. In this work, we describe and validate a novel method, without need for chemical derivatisation (accuracy = 84â94%; precision = 3â16%; reproducibility = 3â6%; mean linear range R2 = 0.999). The current limit of quantitation for HGA in plant material was halved (from 1ÎŒg/g in previous studies) to 0.5ÎŒg/g. The method was tested in Acer pseudoplatanus material and other tree and plant species. We confirm that A. pseudoplatanus is most likely the only source of HGA in trees found within European pastures
The Inclusive-Exclusive Connection and the Neutron Negative Central Charge Density
We find an interpretation of the recent finding that the central charge
density of the neutron is negative by using models of generalized parton
distributions at zero skewness to relate the behavior of deep inelastic
scattering quark distributions, evaluated at large values of Bjorken x, to the
transverse charge density evaluated at small distances. The key physical input
of these models is the Drell-Yan-West relation We find that the d quarks
dominate the neutron structure function for large values of Bjorken x, where
the large longitudinal momentum of the struck quark has a significant impact on
determining the center-of-momentum of the system, and thus the "center" of the
nucleon in the transverse position plane.Comment: 17 pages, 8 figures. Text of an invited talk presented by G. A.
Miller at the 2008 Division of Nuclear Physics Meeting in Oakland. Prepared
for Int. Journ. Mod. Phys.
Two Systems of Non-Symbolic Numerical Cognition
Studies of human adults, infants, and non-human animals demonstrate that non-symbolic numerical cognition is supported by at least two distinct cognitive systems: a âparallel individuation systemâ that encodes the numerical identity of individual items and an âapproximate number systemâ that encodes the approximate numerical magnitude, or numerosity, of a set. The exact nature and role of these systems, however, have been debated for over a 100-years. Some argue that the non-symbolic representation of small numbers (<4) is carried out solely by the parallel individuation system and the non-symbolic representation of large numbers (>4) is carried out solely by the approximate number system. Others argue that all numbers are represented by the approximate number system. This debate has been fueled largely by some studies showing dissociations between small and large number processing and other studies showing similar processing of small and large numbers. Recent work has addressed this debate by showing that the two systems are present and distinct from early infancy, persist despite the acquisition of a symbolic number system, activate distinct cortical networks, and engage differentially based attentional constraints. Based on the recent discoveries, I provide a hypothesis that may explain the puzzling findings and makes testable predictions as to when each system will be engaged. In particular, when items are presented under conditions that allow selection of individuals, they will be represented as distinct mental items through parallel individuation and not as a numerical magnitude. In contrast, when items are presented outside attentional limits (e.g., too many, too close together, under high attentional load), they will be represented as a single mental numerical magnitude and not as distinct mental items. These predictions provide a basis on which researchers can further investigate the role of each system in the development of uniquely human numerical thought
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