573 research outputs found
Analytic Approaches to the Evolution of Polarised Parton Distributions at Small
The evolution of polarised parton distributions at small is
studied. Various analytic approximations are critically discussed. We compare
the full evolution with that obtained from the leading-pole approximation to
the splitting functions, and show that the validity of this approximation
depends critically on the behaviour of the starting distributions. A
new analytic solution which is valid at small is obtained, and its domain
of applicability is discussed.Comment: 14 pages, LATeX, 4 figures availabe as .uu-fil
Air Mass Frequency During Precipitation Events in the Northern Plains of the United States
Since 1980, numerous billion-dollar disasters have affected the Northern Plains of the United States, including nine droughts and four floods. The atmospheric environment present during precipitation events can largely be described by the presiding air mass conditions since air masses characterize a multitude of meteorological variables at one time over a large region. The goal of this research is to add knowledge to current understandings of the factors responsible for precipitation in the Northern Plains through an assessment of synoptic air mass conditions. The Spatial Synoptic Classification is used to categorize 30 years of daily surface air mass types across the region alongside precipitation from the United States Historical Climatological Network. Annual and seasonal air mass frequencies are examined for all precipitation events. Precipitation days are also examined by intensity. Results indicate that the Transitional air mass, associated with changing air mass conditions commonly related to passing fronts, is not the leading producer of rainfall in the region. All moist air mass varieties are generally more dominant during precipitation events and the Moist Moderate (MM) and Moist Polar (MP) air masses are frequently responsible for half of all rainfall in the region. MM and MP tend to be particularly prominent during the winter season. The MM and Moist Tropical air masses dominate around 65% of summer precipitation events. Interestingly, there is a tendency for precipitation while dry air masses are present to the north and west within the study region
OPE analysis for polarized deep inelastic scattering
We present an explicit OPE analysis for the first moment of up to order
. This result allows to calculate power corrections to the Bjorken and
Ellis--Jaffe sum rules.Comment: 10 pages, minor modifications, revised version for the journa
Clinical Presentation and Conservative Management of Tympanic Membrane Perforation during Intrapartum Valsalva Maneuver
Background. Tympanic membrane perforation may occur when ear pressures are excessive, including valsalva maneuver associated with active labor and vaginal delivery. A pressure differential across the eardrum of about 5âpsi can cause rupture; the increased intraabdominal pressure spikes repeatedly manifested by âpushingâ during second-stage labor easily approach (and may exceed) this level. Material and Method. We describe a healthy 21-year old nulliparous patient admitted in active labor at 39-weeks' gestational age. Results. Blood appeared asymptomatically in the left ear canal at delivery during active, closed-glottis pushing. Otoscopic examination confirmed perforation of the left tympanic membrane. Complete resolution of the eardrum rupture was noted at postpartum check-up six weeks later. Conclusion. While the precise incidence of intrapartum tympanic membrane rupture is not known, it may be unrecognized without gross blood in the ear canal or subjective hearing loss following delivery. Only one prior published report on tympanic membrane perforation during delivery currently appears in the medical literature; this is the first English language description of the event. Since a vigorous and repetitive valsalva effort is common in normal vaginal delivery, clinicians should be aware of the potential for otic complications associated with the increased intraabdominal pressure characteristic of this technique
On the Q^2 Dependence of Measured Polarized Structure Funtions
We analyse the available data on the polarized asymmetries for proton,
neutron and deuteron targets. We use a homogeneous and updated set of
unpolarized structure functions to derive from , and we accurately
correct for the scaling violations in order to obtain with the
same for all values. The contribution to the evolution of a
possible large gluon polarized density is also considered. The implications for
the Ellis-Jaffe and for the Bjorken sum rules are discussed.Comment: 11 pages (LaTex) + 4 figures (topdrawer, included at the end) CERN-TH
7023/9
Production of -pairs at HERA-
The production of -pairs as a possible measure of the polarized gluon
distribution is studied for proton--nucleon collisions at
\sqrt{s} =40\;\mbox{GeV}^2 (HERA-). Possibilities of
reconstructing the helicity state of at least one of the 's are
critically reviewed. The observation of production asymmetries in the single
polarized mode of HERA- is found to be not feasible.Comment: 8 pages, LATeX, 3 figures availabe as .uu-fil
Jet Production in Polarized Lepton-Hadron Scattering
We calculate exact analytical expressions for \oas 3-jet and \oasz \\ 4-jet
cross sections in polarized deep inelastic lepton nucleon scattering.
Introducing an invariant jet definition scheme, we present differential
distributions of 3- and 4-jet cross sections in the basic kinematical variables
and as well as total jet cross sections and show their dependence on
the chosen spin-dependent (polarized) parton distributions. Noticebly
differences in the predictions are found for the two extreme choices, i.e. a
large negative sea-quark density or a large positive gluon density. Therefore,
it may be possible to discriminate between different parametrizations of
polarized parton densities, and hence between the different physical pictures
of the proton spin underlying these parametrizations.Comment: 35 pages, LaTeX, 9 ps figures available upon request, MAD/PH/827, KA
TTP94-
Partons and QCD in high-energy polarized pp collisions
We present and use a technique for implementing in a fast way, and without
any approximations, higher-order calculations of partonic cross sections into
global analyses of parton distribution functions. The approach, which is set up
in Mellin-moment space, is particularly suited for analyses of future data from
polarized proton-proton collisions at RHIC, but not limited to this case. We
also briefly discuss the effects of soft-gluon resummations on spin
asymmetries.Comment: 6 pages, LaTeX, 5 eps figures, Invited talk presented by W. Vogelsang
at the ``International Workshop on the Spin Structure of the Proton and
Polarized Collider Physics'', ECT*, Trento, Italy, July 23-28, 200
QCD corrections to the longitudinally polarized Drell-Yan process
In this paper we calculate the O() corrections to the - and
-distributions of lepton pairs produced in collisions of longitudinally
polarized hadrons. The numerical importance of these corrections is studied and
consequences for the extraction of the polarized sea quark distributions from a
measurement of the longitudinally polarized Drell-Yan cross section are
discussed.Comment: 21 pages, LaTeX, 8 figures include
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