62 research outputs found
Assessment of the release of atomic Na from a burning black liquor droplet using quantitative PLIF
The quantitative measurement of atomic sodium (Na) release, at high concentration, from a burning
black liquor droplet has been demonstrated using a planar laser-induced fluorescence (PLIF) technique,
corrected for fluorescence trapping. The local temperature of the particle was measured to be approximately
1700 C, at a height of 10 mm above a flat flame burner. The PLIF technique was used to assess
the temporal release of atomic Na from the combustion of black liquor and compare it with the Na concentration
in the remaining smelt. A first-order model was made to provide insight using a simple Plug
Flow Reactor model based on the independently measured concentration of residual Na in the smelt as a
function of time. This model also required the dilution ratio of the combustion products in the flat flame
entrained into the plume gas from the black liquor particle to be estimated. The key findings of these
studies are: (i) the peak concentration of atomic Na from the combustion of the black liquor droplets
is around 1.4 ppm; (ii) very little atomic Na is present during the drying, devolatilisation or char combustion
stages; and (iii) the presence of atomic Na during smelt phase dominates over that from the other
combustion stages
Probing transverse quark polarization via azimuthal asymmetries in leptoproduction
We consider the leading order result for polarized leptoproduction, putting
emphasis on transverse momentum dependent effects appearing in azimuthal
asymmetries. Measurements of weighted cross sections enable extraction of the
distribution of transversely polarized quarks. We focus on the distribution in
a longitudinally polarized hadron and estimate the expected asymmetries in
leptoproduction.Comment: 7 pages RevTex using epsfig.sty, including 2 figures; revised
version, accepted for publication in Phys. Lett.
Evolution of the spin of the nucleon
We compare momentum sum rules from unpolarized electroproduction and the spin
sum rule for in polarized electroproduction, and their evolution in
the framework of the operator product expansion. Second order effects in
are included. We show that in comparing the evolution of the spin
sum rule with the momentum sum rule one is not overly sensitive to using first
or second order, even when going to the extreme low limit in which gluons
carry no momentum. Our results show that in that limit there is no need to
include any contribution of strange quarks.Comment: 17 pages RevTeX, 4 uuencoded figure
O(\alpha_s^2) contributions to the fragmentation function g_1(x,Q^2) in polarized e^+e^- annihilation
Misprints in the C_F^2 part of the splitting function \Delta P_{gq}^(1) Eq.
(3.29) are corrected. Due to a minus sign error between the C_F^2- 1/2 C_A C_F
piece and the remaining part of Eq. (A.4), Eq. (3.46) is changed. Finally
z_{qq}^{PS,(2)} is know so that we can give the full expression for \Delta \bar
{\cal C}_{1,q}^{PS} in Eq. (A.1).Comment: 29 pages Late
The role of orbital angular momentum in the proton spin
The orbital angular momenta and of up and down quarks in the
proton are estimated as functions of the energy scale as model-independently as
possible, on the basis of Ji's angular momentum sum rule. This analysis
indicates that is large and negative even at low energy scale of
nonperturbative QCD, in contrast to Thomas' similar analysis based on the
refined cloudy bag model. We pursuit the origin of this apparent discrepancy
and suggest that it may have a connection with the fundamental question of how
to define quark orbital angular momenta in QCD.Comment: 14 pages, 3 figures, 1 table A slightly extended version to appear in
Eur. Phys. J.
Meson Cloud of the Nucleon in Polarized Semi-Inclusive Deep-Inelastic Scattering
We investigate the possibility of identifying an explicit pionic component of
the nucleon through measurements of polarized baryon fragments
produced in deep-inelastic leptoproduction off polarized protons, which may
help to identify the physical mechanism responsible for the breaking of the
Gottfried sum rule. The pion-exchange model predicts highly correlated
polarizations of the and target proton, in marked contrast with
the competing diquark fragmentation process. Measurement of asymmetries in
polarized production may also reveal the presence of a kaon cloud in
the nucleon.Comment: 23 pages REVTeX, 7 uuencoded figures, accepted for publication in
Zeit. Phys.
The Tutoring Role of Mentors Working with Adults and Elderly People with Learning Disabilities Using Virtual Environments
Azimuthal asymmetries of charged hadrons produced by high-energy muons scattered off longitudinally polarised deuterons
Azimuthal asymmetries in semi-inclusive production of positive (h^+) and
negative hadrons (h^-) have been measured by scattering 160 GeV muons off
longitudinally polarised deuterons at CERN. The asymmetries were decomposed in
several terms according to their expected modulation in the azimuthal angle phi
of the outgoing hadron. Each term receives contributions from one or several
spin and transverse-momentum-dependent parton distribution and fragmentation
functions. The amplitudes of all phi-modulation terms of the hadron asymmetries
integrated over the kinematic variables are found to be consistent with zero
within statistical errors, while the constant terms are nonzero and equal for
h^+ and h^- within the statistical errors. The dependencies of the
phi-modulated terms versus the Bjorken momentum fraction x, the hadron
fractional momentum z, and the hadron transverse momentum p_h^T were studied.
The x dependence of the constant terms for both positive and negative hadrons
is in agreement with the longitudinal double-spin hadron asymmetries, measured
in semi-inclusive deep-inelastic scattering. The x dependence of the sin
phi-modulation term is less pronounced than that in the corresponding HERMES
data. All other dependencies of the phi-modulation amplitudes are consistent
with zero within the statistical errors.Comment: 12 pages, 11 Figures; revision 1 signs in Eq 5 corrected, polishe
Strangeness in the Nucleon on the Light-Cone
Strange matrix elements of the nucleon are calculated within the light-cone
formulation of the meson cloud model. The dependence of the strange
vector and axial vector form factors is computed, and the strangeness radius
and magnetic moment extracted, both of which are found to be very small and
slightly negative. Within the same framework one finds a small but non-zero
excess of the antistrange distribution over the strange at large . Kaon
loops are unlikely, however, to be the source of a large polarized strange
quark distribution.Comment: 22 pages revtex, 7 postscript figures, accepted for publication in
Phys. Rev.
TRY plant trait database â enhanced coverage and open access
Plant traitsâthe morphological, anatomical, physiological, biochemical and phenological characteristics of plantsâdetermine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of traitâbased plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traitsâalmost complete coverage for âplant growth formâ. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and traitâenvironmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives
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