8,806 research outputs found
Parton densities and structure functions at next-to-next-to-leading order and beyond
We summarize recent results on the evolution of unpolarized parton densities
and deep-inelastic structure functions in massless perturbative QCD. Due to
last year's extension of the integer-moment calculations of the three-loop
splitting functions, the NNLO evolution of the parton distributions can now be
performed reliably at momentum fractions x >= 10^-4, facilitating a
considerably improved theoretical accuracy of their extraction from data on
deep-inelastic scattering. The NNLO corrections are not dominated, at relevant
values of x, by their leading small-x terms. At large x the splitting-function
series converges very rapidly, hence, employing results on the three-loop
coefficient functions, the structure functions can be analysed at N^3LO for x >
10^-2. The resulting values for alpha_s do not significantly change beyond
NNLO, their renormalization scale dependence reaches about +-1% at N^3LO.Comment: 10 pages, LaTeX, 6 figures. Talk presented at the workshops `New
Trends in HERA Physics 2001', Ringberg Castle (Germany), June 2001 and `DIS
2001', Bologna (Italy), April 2001. To appear, slightly shortened in the
latter case, in the proceeding
NNLO evolution of deep-inelastic structure functions: the singlet case
We study the next-to-next-to-leading order (NNLO) evolution of flavour
singlet parton densities and structure functions in massless perturbative QCD.
Present information on the corresponding three-loop splitting functions is used
to derive parametrizations of these quantities, including Bjorken-x dependent
estimates of their residual uncertainties. Compact expressions are also
provided for the exactly known, but in part rather lengthy two-loop singlet
coefficient functions. The size of the NNLO corrections and their effect on the
stability under variations of the renormalization and mass-factorizations
scales are investigated. Except for rather low values of the scales, the
residual uncertainty of the three-loop splitting functions does not lead to
relevant effects for x > 10^-3. Inclusion of the NNLO contributions
considerably reduces the theoretical uncertainty of determinations of the quark
and gluon densities from deep-inelastic structure functions.Comment: 31 pages, LaTeX, 14 eps-figure
The effect of bedrest on various parameters of physiological function. part viii- the . . . effect on the cardiovascular tolerance to passive tilt
Effect of short and long term bed rest on cardiovascular tolerance to passive til
The effect of bedrest on various parameters of physiological function. part xi- the effect of bedrest on blood volume, urinary volume, and urinary electrolyte excretion
Effect of bed rest on blood volume, urinary volume, and urinary electrolyte excretio
The effect of bedrest on various parameters of physiological function. Part XIII - A review of possible mechanisms of orthostatic intolerance to passive tilt
Possible mechanisms of orthostatic intolerance to passive tilt - bed rest and water immersion effects on various parameters of physiological functio
The effect of bedrest on various parameters of physiological function. Part X - The effect of bedrest on the circulatory response to a valsalva maneuver
Quantitative arterial blood pressure change during Valsalva maneuver after bed res
The effect of bedrest on various parameters of physiological function. part vii- cardiac and ventilatory response to the bicycle ergometer test
Cardiac and ventilatory response to bicycle ergometer tes
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