639 research outputs found
On an asymptotic estimate of the -loop correction in perturbative QCD
A recently proposed method of estimating the asymptotic behaviour of QCD
perturbation theory coefficients is critically reviewed and shown to contain
numerous invalid mathematical operations and unsubstantiated assumptions. We
discuss in detail why this procedure, based solely on renormalization group
(RG) considerations and analyticity constraints, cannot lead to such estimates.
We stress the importance of correct renormalization scheme (RS) dependence of
any meaningful asymptotic estimate and argue that the unambiguous summation of
QCD perturbation expansions for physical quantities requires information from
outside of perturbation theory itself.Comment: PRA-HEP-92/17, Latex, 20 pages of text plus 5 figures contained in 5
separate PS files. Four of them (corresponding to Figs.1,2,3,5) are appended
at the end of this file, the (somewhat larger one) corresponding to Fig.4 can
be obtained from any of the mentioned E-mail addresses upon request. E-mail
connections: J. Chyla - [email protected]) or h1kchy@dhhdesy3 P. Kolar -
[email protected]
Exile Vol. XI No. 1
FICTION
By the Fire of the Chief by Peggy Schmidt 9-17
From the Diary of a Vanishing Man by Ed Brunner 19-29
Dialogue by Ken Booth 35-37
POETRY
Johnny Joe by Bill West 6-7
Caterpillar by Barb Bergantz 17
Poem by Bonnie McCarthy 29
The Queen by Hugh Wilder 31
The Clown by Barb Bergantz 32
Poem by Gretchen Schenck 33
Treatise on Cosmology by P. M. Grout 37
Stimulus by Susan Sherwood 37
Depot by Susan Sherwood 39
GRAPHICS
Pen and Ink by Dave Goodwin 7
Pen and Ink by Ramona Gibbs 8
Pen and Ink by Tod Riddell 18
Charcoal by Dave Goodwin 30
Woodcut by Parker Waite III 34
Woodcut by Lela Giles 3
High-resolution maps show that rubber causes substantial deforestation
Understanding the effects of cash crop expansion on natural forest is of fundamental importance. However, for most crops there are no remotely sensed global maps1, and global deforestation impacts are estimated using models and extrapolations. Natural rubber is an example of a principal commodity for which deforestation impacts have been highly uncertain, with estimates differing more than fivefold1,2,3,4. Here we harnessed Earth observation satellite data and cloud computing5 to produce high-resolution maps of rubber (10 m pixel size) and associated deforestation (30 m pixel size) for Southeast Asia. Our maps indicate that rubber-related forest loss has been substantially underestimated in policy, by the public and in recent reports6,7,8. Our direct remotely sensed observations show that deforestation for rubber is at least twofold to threefold higher than suggested by figures now widely used for setting policy4. With more than 4 million hectares of forest loss for rubber since 1993 (at least 2 million hectares since 2000) and more than 1 million hectares of rubber plantations established in Key Biodiversity Areas, the effects of rubber on biodiversity and ecosystem services in Southeast Asia could be extensive. Thus, rubber deserves more attention in domestic policy, within trade agreements and in incoming due-diligence legislation
Holographic analysis of diffraction structure factors
We combine the theory of inside-source/inside-detector x-ray fluorescence
holography and Kossel lines/x ray standing waves in kinematic approximation to
directly obtain the phases of the diffraction structure factors. The influence
of Kossel lines and standing waves on holography is also discussed. We obtain
partial phase determination from experimental data obtaining the sign of the
real part of the structure factor for several reciprocal lattice vectors of a
vanadium crystal.Comment: 4 pages, 3 figures, submitte
Inclusive electron scattering in a relativistic Green function approach
A relativistic Green function approach to the inclusive quasielastic (e,e')
scattering is presented. The single particle Green function is expanded in
terms of the eigenfunctions of the nonhermitian optical potential. This allows
one to treat final state interactions consistently in the inclusive and in the
exclusive reactions. Numerical results for the response functions and the cross
sections for different target nuclei and in a wide range of kinematics are
presented and discussed in comparison with experimental data.Comment: 12 pages, 7 figures, REVTeX
Search for the Proton Decay Mode proton to neutrino K+ in Soudan 2
We have searched for the proton decay mode proton to neutrino K+ using the
one-kiloton Soudan 2 high resolution calorimeter. Contained events obtained
from a 3.56 kiloton-year fiducial exposure through June 1997 are examined for
occurrence of a visible K+ track which decays at rest into mu+ nu or pi+ pi0.
We found one candidate event consistent with background, yielding a limit,
tau/B > 4.3 10^{31} years at 90% CL with no background subtraction.Comment: 13 pages, Latex, 3 tables and 3 figures, Accepted by Physics Letters
The Origins of Bagan: The archaeological landscape of Upper Burma to AD 1300.
The archaeological landscape of Upper Burma from the middle of the first millennium BC to the Bagan period in the 13th-14th century AD is a landscape of continuity. Finds of polished stone and bronze artifacts suggest the existence of early metal-using cultures in the Chindwin and Samon River Valleys, and along parts of the Ayeyarwady plain. Increasing technological and settlement complexity in the Samon Valley suggests that a distinctive culture whose agricultural and trade success can be read in the archaeological record of the Late Prehistoric period developed there. The appearance of the early urban "Pyu" system of walled central places during the early first millennium AD seems to have involved a spread of agricultural and management skills and population from the Samon. The leaders of the urban centres adopted Indic symbols and Sanskrit modes of kingship to enhance and extend their authority. The early urban system was subject over time to a range of stresses including siltation of water systems, external disruption and social changes as Buddhist notions of leadership eclipsed Brahmanical ones. The archaeological evidence indicates that a settlement was forming at Bagan during the last centuries of the first millennium AD. By the mid 11th century Bagan began to dominate Upper Burma, and the region began a transition from a system of largely autonomous city states to a centralised kingdom. Inscriptions of the 11th to 13th centuries indicate that as the Bagan Empire expanded it subsumed the agricultural lands that had been developed by the Pyu
Finite Theories and the SUSY Flavor Problem
We study a finite SU(5) grand unified model based on the non-Abelian discrete
symmetry A_4. This model leads to the democratic structure of the mass matrices
for the quarks and leptons. In the soft supersymmetry breaking sector, the
scalar trilinear couplings are aligned and the soft scalar masses are
degenerate, thus solving the SUSY flavor problem.Comment: 17 pages, LaTeX, 1 figur
A Study of Ultraviolet Renormalon Ambiguities in the Determination of \as from Decay
The divergent large-order behaviour of the perturbative series relevant for
the determination of \as from decay is controlled by the leading
ultraviolet (UV) renormalon. Even in the absence of the first infrared (IR)
renormalon, an ambiguity of order is introduced. We make a
quantitative study of the practical implications of this ambiguity. We discuss
the magnitude of UV renormalon corrections obtained in the large- limit,
which, although unrealistic, is nevertheless interesting to some extent. We
then study a number of improved approximants for the perturbative series, based
on a change of variable in the Borel representation, such as to displace the
leading UV renormalon singularity at a larger distance from the origin than the
first IR renormalon. The spread of the resulting values of \as(m^2_\tau)
obtained by different approximants, at different renormalization scales, is
exhibited as a measure of the underlying ambiguities. Finally, on the basis of
mathematical models, we discuss the prospects of an actual improvement, given
the signs and magnitudes of the computed coefficients, the size of
\as(m^2_\tau) and what is known of the asymptotic properties of the series.
Our conclusion is that a realistic estimate of the theoretical error cannot go
below \delta\as(m^2_\tau) \sim \pm 0.060, or \delta\as(m^2_{\sss Z}) \sim
\pm 0.006.Comment: 32 pages, epsfig.sty
Renormalization Scheme Dependence and the Problem of Theoretical Uncertainties in Next-Next-to-Leading Order QCD Predictions
Renormalization scheme uncertainties in the next-next-to-leading order QCD
predictions are discussed. To obtain an estimate of these uncertainties it is
proposed to compare predictions in all schemes that do not have unnaturally
large expansion coefficients. A concrete prescription for eliminating the
unnatural schemes is given, based on the requirement that large cancellations
in the expression for the characteristic renormalization scheme invariant
should be avoided. As an example the QCD corrections to the Bjorken sum rule
are considered. The importance of the next-next-to-leading order corrections
for a proper evaluation of perturbative QCD predictions is emphasized.Comment: 15 pages, 3 figures,Late
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