1,939 research outputs found
Transverse momentum dependence of the angular distribution of the Drell-Yan process
We calculate the transverse momentum Q_{\perp} dependence of the helicity
structure functions for the hadroproduction of a massive pair of leptons with
pair invariant mass Q. These structure functions determine the angular
distribution of the leptons in the pair rest frame. Unphysical behavior in the
region Q_{\perp} --> 0 is seen in the results of calculations done at
fixed-order in QCD perturbation theory. We use current conservation to
demonstrate that the unphysical inverse-power and \ln(Q/Q_{\perp}) logarithmic
divergences in three of the four independent helicity structure functions share
the same origin as the divergent terms in fixed-order calculations of the
angular-integrated cross section. We show that the resummation of these
divergences to all orders in the strong coupling strength \alpha_s can be
reduced to the solved problem of the resummation of the divergences in the
angular-integrated cross section, resulting in well-behaved predictions in the
small Q_{\perp} region. Among other results, we show the resummed part of the
helicity structure functions preserves the Lam-Tung relation between the
longitudinal and double spin-flip structure functions as a function of
Q_{\perp} to all orders in \alpha_s.Comment: 18 pages, 4 figures; typos corrected, references updated, a few
clarifications recommended by the referee. Paper accepted for publication in
Physical Review
Finite-Element Limit Analysis of the Tucker High School Gymnasium Roof Failure
The Randolph Tucker High School gymnasium roof failure of 1970 has received much scholarly attention. This study will provide a conclusion to a large body of previously published works by means of limit state analysis of the roof failure using state of the art parametric finite-element modeling. Parametric modeling within a general purpose finite-element analysis program allows for extremely rapid changes to the model because key terms are objects or parameters that can be adjusted internally by the program, rather than laboriously entered by the user. The failure of the roof was investigated by means of a limit state analysis, which accurately captured the cracking of the concrete and the yielding of the reinforcing steel. Concrete creep and shrinkage and relaxation of the prestressing steel were also accounted for. Finally, the authors also studied the idea that camber in the roof geometry might have prevented collapse
Sausu - Malonas - Tolai ou les leçons d'une transmigration réussie : étude agro-économique de 3 Centres de Transmigration dans la Province de Sulawesi Tengah
Cette étude concerne 3 centres de transmigration situés à Sulawesi Centre : Sausu,Malonas,Tolai.L'essentiel des données de base a été obtenu auprès des transmigrants.Un échantillon de 160 familles de colons a été suivi par enquête en quatre passages répétés espacés de 2 mois et observation sur le terrain.En Indonésie,les transferts de population commencés sous l'administration coloniale hollandaise avaient pour objectifs de réduire les déséquilibres démographiques entre les différentes iles.En 1980,la densité de population était de 690 habitants au km2 à Java et de 18 km2 à Sulawesi Centre.Dans la première partie de cette étude,les auteurs analysent l'origine,les motivations des transmigrants,ce qui fait l'originalité des 3 Centres qui jouissent d'un environnement favorable du point de vue de la pluviométrie,du relief,de la fertilité du sol.Pour chacun des centres,il est signalé les surfaces cultivées,les cultures adoptées (riz,soja) et les revenus dont bénéficient les transmigrants grace aux activités agricoles et non agricoles.Dans la dernière partie,les auteurs analysent les causes de certains échecs et des succès de l'opération en signalant le nombre trés important des transmigrants spontanés dans cette région et présentent des recommandations pour l'avenir
Fingerprint of dynamical charge/spin correlations in the tunneling spectra of colossal magnetoresistive manganites
We present temperature-dependent scanning tunneling spectroscopy measurements
on () films with different degrees of biaxial
strain. A depletion in normalized conductance around the Fermi level is
observed both above and below the insulator-to-metal transition temperature
, for weakly as well as highly-strained films. This pseudogap-like
depletion globally narrows on cooling. The zero-bias conductance decreases on
cooling in the insulating phase, reaches a minimum close to and
increases on cooling in the metallic phase, following the trend of macroscopic
conductivity. These results support a recently proposed scenario in which
dynamical short-range antiferromagnetic/charge order correlations play a
preeminent role in the transport properties of colossal magnetoresistive
manganites [R. Yu \textit{et al}., Phys. Rev. B \textbf{77}, 214434 (2008)].Comment: 9 pages, 4 figure
A quality monitor and monitoring technique employing optically stimulated electron emission
A light source directs ultraviolet light onto a test surface and a detector detects a current of photoelectrons generated by the light. The detector includes a collector which is positively biased with respect to the test surface. Quality is indicated based on the photoelectron current. The collector is then negatively biased to replace charges removed by the measurement of a nonconducting substrate to permit subsequent measurements. Also, the intensity of the ultraviolet light at a particular wavelength is monitored and the voltage of the light source varied to maintain the light a constant desired intensity. The light source is also cooled via a gas circulation system. If the test surface is an insulator, the surface is bombarded with ultraviolet light in the presence of an electron field to remove the majority of negative charges from the surface. The test surface is then exposed to an ion field until it possesses no net charge. The technique described above is then performed to assess quality
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