5,903 research outputs found
On new alkaline‐earth hexafluorogermanates as host structures for UV phosphors
Two new hexafluorogermanate dihydrates, viz. SrGeF6 ⋅ 2H2O and CaGeF6 ⋅ 2H2O, were synthesised from aqueous solutions; their crystal structures were refined in space group P21/n (SrGeF6 ⋅ 2H2O: a=5.9605(2) Å, b=9.6428(3) Å, a=10.9866(3) Å and β=99.1590(10), Z=4, 5122 refl., 104 param., R1=0.0195, wR2=0.0470; CaGeF6 ⋅ 2H2O: a=5.8472(5) Å, b=10.5099(9) Å, c=9.6267(9) Å and β=103.521(3), Z=4, 4756 refl., 101 param., R1=0.0224, wR2=0.0616). Upon doping with Eu2+ luminescence in the NUV regime was observed. The crystal structures of CaGeF6 and MgGeF6 could be solved and refined via Rietveld refinement from powder samples gained by thermal decomposition of the respective hydrates; both compounds adopt the LiSbF6 structure type (CaGeF6: a=5.4099(5) Å, c=13.9835(13) Å, Z=3, Rwp=0.0291, RBragg=0.0142; MgGeF6: a=5.1219(2) Å, c=13.0851(7), Z=3, Rwp=0.034, RBragg=0.01). Further, the luminescence of MgGeF6 ⋅ 6H2O:Eu2+, which emits light in the violet to blue regime, is reported
Deeply virtual Compton scattering in next-to-leading order
We study the amplitude of deeply virtual Compton scattering in
next-to-leading order of perturbation theory including the two-loop evolution
effects for different sets of skewed parton distributions (SPDs). It turns out
that in the minimal subtraction scheme the relative radiative corrections are
of order 20-50%. We analyze the dependence of our predictions on the choice of
SPD, that will allow to discriminate between possible models of SPDs from
future high precision experimental data, and discuss shortly theoretical
uncertainties induced by the radiative corrections.Comment: 10 pages, LaTeX, 3 figure
Quantifying differences between primary cortical areas in humans based on laminar profiles in in vivo MRI data
This paper presents an approach for mapping the human cortical architecture in vivo based on quantitative MRI indices of myelin. We automatically construct laminar profiles in several primary cortical areas and investigate different sampling strategies. The results demonstrate that our method is able to distinguish these areas at specific cortical depths
Transverse Double-Spin Asymmetries for Muon Pair Production in pp-Collisions
We calculate the rapidity dependence of the transverse double-spin asymmetry
for the Drell-Yan process to next-to-leading order in the strong coupling.
Input transversity distributions are obtained by saturating the Soffer
inequality at a low hadronic mass scale. Results for the polarized BNL-RHIC
proton-proton collider and the proposed HERA-N fixed-target experiment are
presented, and the influence of the limited muon acceptance of the detectors on
measurements of the asymmetry is studied in detail.Comment: 7 pages including 5 figures; significantly shortened, to be published
in Phys. Rev.
Influence of selective serotonin reuptake inhibitors on bleeding risk in patients with severe thrombocytopenia after chemotherapy: a retrospective study
Radiative corrections to deeply virtual Compton scattering
We discuss possibilities of measurement of deeply virtual Compton scattering
amplitudes via different asymmetries in order to access the underlying skewed
parton distributions. Perturbative one-loop coefficient functions and two-loop
evolution kernels, calculated recently by a tentative use of residual conformal
symmetry of QCD, are used for a model dependent numerical estimation of
scattering amplitudes.Comment: 9 pages LaTeX, 3 figures, czjphyse.cls required Talk given by D.
M\"uller at Inter. Workshop ``PRAHA-Spin99'', Prague, Sept. 6-11, 199
QCD factorization for the pion diffractive dissociation to two jets
We calculate the cross section of a pion diffraction dissociation in two jets
with large transverse momenta originating from a hard gluon exchange between
the pion constituents. To the leading logarithmic accuracy (in energy), the
contribution coming from small transverse separations between the quark and the
antiquark in the pion acquires the expected factorized form, the longitudinal
momentum distribution of the jets being proportional to the pion distribution
amplitude. The hard gluon exchange can in this case be considered as a part of
the unintegrated gluon distribution. Beyond the leading logarithms (in energy)
this proportionality does not hold. Moreover, the collinear factorization
appears to be broken by the end-point singularities. Remarkably enough, the
longitudinal momentum distribution of the jets for the non-factorizable
contribution is calculable, and turns out to be the same as for the
factorizable contribution with the asymptotic pion distribution amplitude.Comment: Original version from 9 April restore
Intraspecific mating system evolution and its effect on complex male secondary sexual traits: Does male–male competition increase selection on size or shape?
Sexual selection is generally held responsible for the exceptional diversity in secondary sexual traits in animals. Mating system evolution is therefore expected to profoundly affect the covariation between secondary sexual traits and mating success. Whereas there is such evidence at the interspecific level, data within species remain scarce. We here investigate sexual selection acting on the exaggerated male fore femur and the male wing in the common and widespread dung flies Sepsis punctum and S. neocynipsea (Diptera: Sepsidae). Both species exhibit intraspecific differences in mating systems and variation in sexual size dimorphism (SSD) across continents that correlates with the extent of male–male competition. We predicted that populations subject to increased male–male competition will experience stronger directional selection on the sexually dimorphic male foreleg. Our results suggest that fore femur size, width and shape were indeed positively associated with mating success in populations with male‐biased SSD in both species, which was not evident in conspecific populations with female‐biased SSD. However, this was also the case for wing size and shape, a trait often assumed to be primarily under natural selection. After correcting for selection on overall body size by accounting for allometric scaling, we found little evidence for independent selection on any of these size or shape traits in legs or wings, irrespective of the mating system. Sexual dimorphism and (foreleg) trait exaggeration is therefore unlikely to be driven by direct precopulatory sexual selection, but more so by selection on overall size or possibly selection on allometric scaling
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