1,288 research outputs found
Are we talking about the same structure?: A unified approach to hypertext links, xml, rdf and zigzag
There are many different hypertext systems and paradigms, each with their apparent advantages. However the distinctions are perhaps not as significant as they seem. If we can reduce the core linking functionality to some common structure, which allows us to consider hypertext systems within a common model, we could identify what, if anything, distinguishes hypertext systems from each other. This paper offers such a common structure, showing the conceptual similarities between each of these systems and paradigms
Collisional Transfer of Population and Orientation in NaK
We report current work to study transfer of population and orientation in collisions of NaK molecules with argon and potassium atoms using polarization labeling (PL) and laser- induced fluorescence (LIF) spectroscopy. In the PL experiment, a circularly polarized pump laser excites a specific NaK A1Σ +(v 0=16, J 0 ) ← X1Σ +(v 00=0, J 0 ± 1) transition, creating an orientation (non-uniform MJ0 level distribution) in both levels. The linearly polarized probe laser is scanned over various 31Π(v, J 0±1) ← A1Σ +(v 0=16, J 0 ) transitions. The probe laser passes through a crossed linear polarizer before detection, and signal is recorded if the probe laser polarization has been modified by the vapor (which occurs when it comes into resonance with an oriented level). Using both spectroscopic methods, analysis of weak collisional satellite lines adjacent to these directly populated lines, as a function of argon buffer gas pressure and cell temperature, allows us to discern separately the effects collisions with argon atoms and potassium atoms have on the population and orientation of the molecule. In addition, code has been written which provides a theoretical analysis of the process, through a solution of the density matrix equations of motion for the system
Polarization Spectroscopy and Collisions in NaK
We report current work to study transfer of population and orientation in collisions of NaK molecules with argon and potassium atoms using polarization labeling (PL) and laser-induced fluorescence (LIF) spectroscopy. In the PL experiment, a circularly polarized pump laser excites a specific NaK A1Σ +(v=16, J) ← X1Σ +(v=0, J ± 1) transition, creating an orientation (non-uniform MJ level distribution) in both levels. The linear polarized probe laser is scanned over various 3 1Π(v=8, J 0 ± 1) ← A1Σ +(v=16, J 0 ) transitions. The probe laser passes through a crossed linear polarizer before detection, and signal is recorded if the probe laser polarization has been modified by the vapor (which occurs when it comes into resonance with an oriented level). In addition to strong direct transitions (J 0 = J), we also observe weak collisional satellite lines (J 0 = J ±n with n = 1, 2, 3, ...) indicating that orientation is transferred to adjacent rotational levels during a collision. An LIF experiment (with linear polarized pump and probe beams) gives information on the collisional transfer of population. From these data, cross sections for both processes can be determined. We experimentally distinguish collisions of NaK with argon atoms from collisions with alkali atoms
Nuclear parton distribution functions and their uncertainties
We analyze experimental data of nuclear structure-function ratios
F_2^A/F_2^{A'} and Drell-Yan cross section ratios for obtaining optimum parton
distribution functions (PDFs) in nuclei. Then, uncertainties of the nuclear
PDFs are estimated by the Hessian method. Valence-quark distributions are
determined by the F_2 data at large x; however, the small-x part is not obvious
from the data. On the other hand, the antiquark distributions are determined
well at x~0.01 from the F_2 data and at x~0.1 by the Drell-Yan data; however,
the large-x behavior is not clear. Gluon distributions cannot be fixed by the
present data and they have large uncertainties in the whole x region.
Parametrization results are shown in comparison with the data. We provide a
useful code for calculating nuclear PDFs at given x and Q^2.Comment: 9 pages, REVTeX, 23 eps files, Phys. Rev. C in press. Nuclear PDF
library is available at http://hs.phys.saga-u.ac.jp/nuclp.htm
QCD Sum Rule Calculation of Twist-4 Corrections to Bjorken and Ellis-Jaffe Sum Rules
We calculate the twist-4 corrections to the integral of in the
framework of QCD sum rules using an interpolating nucleon field which contains
explicitly a gluonic degree of freedom. This information can be used together
with previous calculations of the twist-3 contribution to the second moment of
to estimate the higher-twist corrections to the Ellis-Jaffe and
Bjorken sum rules. We get and
. Numerically our results roughly agree
with those obtained by Balitsky, Braun and Kolesnichenko based on a sum rule
for a simpler current. Our calculations are far more stable as tested within
the sum rule approach but are more sensitive to less well known condensates.Comment: 18pp., 1 figure (uuencoded eps-file), Late
QCD Sum Rule Calculation of Twist-3 Contributions to Polarized Nucleon Structure Functions
Using the framework of QCD sum rules we predict the twist-3 contribution to
the second moment of the polarized nucleon structure function . As the
relevant local operator depends explicitely on the gluon field, we employ a
recently studied interpolating nucleon current which contains three quark field
and one gluon field operator. Despite the fact that our calculation is based on
the analysis of a completely different correlation function, our estimates are
consitent with those of Balitsky, Braun and Kolesnichenko who used a
three-quark current.Comment: 16pp. , 2 figures (uuencoded eps-files), LateX. Some misprints
corrected, results unchange
Leading Chiral Contributions to the Spin Structure of the Proton
The leading chiral contributions to the quark and gluon components of the
proton spin are calculated using heavy-baryon chiral perturbation theory.
Similar calculations are done for the moments of the generalized parton
distributions relevant to the quark and gluon angular momentum densities. These
results provide useful insight about the role of pions in the spin structure of
the nucleon, and can serve as a guidance for extrapolating lattice QCD
calculations at large quark masses to the chiral limit.Comment: 8 pages, 2 figures; a typo in Ref. 7 correcte
Extracting the Proton ubar content from pp->Direct Photon plus Jet Cross Sections
An analysis procedure is proposed to measure the antiquark distributions in
the proton over the region 0.01 < x < 0.1. The procedure involves the
measurement of high p_t asymmetric direct photon and jet final states in pp
interactions. This measurement can be made at the RHIC collider running in pp
mode at an energy of sqrt(s)=500 GeV/c. This analysis identifies a region of
phase space where the contribution from quark-antiquark annihilation
uncharacteristically approaches the magnitude of the contribution from the
leading process, quark-gluon Compton scattering. The forward-backward angular
asymmetry in the parton center of mass is sensitive to the antiquark content of
the proton and the ubar parton density function can be extracted.Comment: 21 pages, 7 figure
Nuclear Attenuation of high energy two-hadron system in the string model
Nuclear attenuation of the two-hadron system is considered in the string
model. The two-scale model and its improved version with two different choices
of constituent formation time and sets of parameters obtained earlier for the
single hadron attenuation, are used to describe available experimental data for
the -dependence of subleading hadron, whereas satisfactory agreement with
the experimental data has been observed. A model prediction for
-dependence of the nuclear attenuation of the two-hadron system is also
presented.Comment: 8 page
Spectra of globular clusters in the Sombrero galaxy: evidence for spectroscopic metallicity bimodality
We present a large sample of over 200 integrated-light spectra of confirmed
globular clusters (GCs) associated with the Sombrero (M104) galaxy taken with
the DEIMOS instrument on the Keck telescope. A significant fraction of the
spectra have signal-to-noise levels high enough to allow measurements of GC
metallicities using the method of Brodie & Huchra (1990). We find a
distribution of spectroscopic metallicities ranging from -2.2 < [Fe/H] < +0.1
that is bimodal, with peaks at [Fe/H] ~ -1.4 and -0.6. Thus the GC system of
the Sombrero galaxy, like a few other galaxies now studied in detail, reveals a
bimodal spectroscopic metallicity distribution supporting the long-held belief
that colour bimodality reflects two metallicity subpopulations. This further
suggests that the transformation from optical colour to metallicity for old
stellar populations, such as GCs, is not strongly non-linear. We also explore
the radial and magnitude distribution with metallicity for GC subpopulations
but small number statistics prevent any clear trends in these distributions.Comment: 18 pages, 10 figures, 3 tables, MNRAS accepte
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