175 research outputs found
Line shape of the muH(3p - 1s) hyperfine transitions
The (3p - 1s) X-ray transition to the muonic hydrogen ground state was
measured with a high resolution crystal spectrometer. A Doppler effect
broadening of the X-ray line was established which could be attributed to
different Coulomb de-excitation steps preceding the measured transition. The
assumption of a statistical population of the hyperfine levels of the muonic
hydrogen ground state was directly confirmed by the experiment and measured
values for the hyperfine splitting can be reported. The results allow a
decisive test of advanced cascade model calculations and establish a method to
extract fundamental strong-interaction parameters from pionic hydrogen
experiments.Comment: Submitted to Physical Review Letter
Enhance the Efficiency of Heuristic Algorithm for Maximizing Modularity Q
Modularity Q is an important function for identifying community structure in
complex networks. In this paper, we prove that the modularity maximization
problem is equivalent to a nonconvex quadratic programming problem. This result
provide us a simple way to improve the efficiency of heuristic algorithms for
maximizing modularity Q. Many numerical results demonstrate that it is very
effective.Comment: 9 pages, 3 figure
Pionic Deuterium
The strong interaction shift and broadening in pionic deuterium have been
remeasured with high statistics by means of the (3p-1s) X-ray transition using
the cyclotron trap and a high-resolution crystal spectrometer. Preliminary
results are (-2325+/-31) meV (repulsive) for the shift and (1171+23/-49} meV
for the width, which yields precise values for the pion-deuteron scattering
length and the threshold parameter for pion production.Comment: Conf. Proc. Few Body 19 (FB19), August 31 - September 5, 2009, Bonn,
Germany 9 pages, 13 figure
Precision determination of the dpi -> NN transition strength at threshold
An unusual but effective way to determine at threshold the dpi -> NN
transition strength is to exploit the hadronic ground-state broadening in
pionic deuterium, accessible by x-ray spectroscopy. The broadening is dominated
by the true absorption channel dpi- -> nn, which is related to s-wave pion
production pp -> dpi+ by charge symmetry and detailed balance. Using the exotic
atom circumvents the problem of Coulomb corrections to the cross section as
necessary in the production experiments. Our dedicated measurement finds
(1171+23/-49) meV for the broadening yielding (252+5/-11) \mub.Comment: 4 pages, 2 figures, 1 tabl
Line shape analysis of the K transition in muonic hydrogen
The K transition in muonic hydrogen was measured with a
high-resolution crystal spectrometer. The spectrum is shown to be sensitive to
the ground-state hyperfine splitting, the corresponding triplet-to-singlet
ratio, and the kinetic energy distribution in the state. The hyperfine
splitting and triplet-to-singlet ratio are found to be consistent with the
values expected from theoretical and experimental investigations and,
therefore, were fixed accordingly in order to reduce the uncertainties in the
further reconstruction of the kinetic energy distribution. The presence of
high-energetic components was established and quantified in both a
phenomenological, i.e. cascade-model-free fit, and in a direct deconvolution of
the Doppler broadening based on the Bayesian approach.Comment: 22 pages, 21 figure
Line shape of the μ H(3 p - 1 s ) transition
The line shape of the (3p − 1s) X-ray transition in muonic hydrogen was measured for the first time with a high-resolution crystal spectrometer. The assumption of a statistical population of the hyperfine levels was directly confirmed by experiment, and a measured value for the hyperfine splitting is reported. An X-ray line broadening due to Doppler effect could be clearly identified and attributed to different Coulomb de-excitation transitions which precede the measured radiative transition. The results allow a decisive test of advanced cascade model calculations and establish an alternative and "model free” method to extract the strong-interaction parameters from pionic hydrogen dat
Nanoethics, science communication, and a fourth model for public engagement
This paper develops a fourth model of public engagement with science, grounded in the principle of nurturing scientific agency through online participatory bioethics. It argues that social media is an effective device through which to enable such engagement, as it has the capacity to empower users and transforms audiences into co-producers of knowledge, rather than consumers of content, the value of which is recognised within the citizen science movement. Social media also fosters greater engagement with the political and legal implications of science, thus promoting the value of scientific citizenship through the acquisition of science capital. This argument is explored by considering the case of nanoscience and nanotechnology, as an exemplar for how emerging technologies may be handled by the scientific community and science policy makers, and as a technology that has defined a second era of science communication
The Rewiring of Ubiquitination Targets in a Pathogenic Yeast Promotes Metabolic Flexibility, Host Colonization and Virulence
Funding: This work was funded by the European Research Council [http://erc.europa.eu/], AJPB (STRIFE Advanced Grant; C-2009-AdG-249793). The work was also supported by: the Wellcome Trust [www.wellcome.ac.uk], AJPB (080088, 097377); the UK Biotechnology and Biological Research Council [www.bbsrc.ac.uk], AJPB (BB/F00513X/1, BB/K017365/1); the CNPq-Brazil [http://cnpq.br], GMA (Science without Borders fellowship 202976/2014-9); and the National Centre for the Replacement, Refinement and Reduction of Animals in Research [www.nc3rs.org.uk], DMM (NC/K000306/1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Acknowledgments We thank Dr. Elizabeth Johnson (Mycology Reference Laboratory, Bristol) for providing strains, and the Aberdeen Proteomics facility for the biotyping of S. cerevisiae clinical isolates, and to Euroscarf for providing S. cerevisiae strains and plasmids. We are grateful to our Microscopy Facility in the Institute of Medical Sciences for their expert help with the electron microscopy, and to our friends in the Aberdeen Fungal Group for insightful discussions.Peer reviewedPublisher PD
Physical basis of the inducer-dependent cooperativity of the Central glycolytic genes Repressor/DNA complex
The Central glycolytic genes Repressor (CggR) from Bacillus subtilis belongs to the SorC family of transcription factors that control major carbohydrate metabolic pathways. Recent studies have shown that CggR binds as a tetramer to its tandem operator DNA sequences and that the inducer metabolite, fructose 1,6-bisphosphate (FBP), reduces the binding cooperativity of the CggR/DNA complex. Here, we have determined the effect of FBP on the size, shape and stoichiometry of CggR complexes with full-length and half-site operator sequence by small-angle X-ray scattering, size-exclusion chromatography, fluorescence cross-correlation spectroscopy and noncovalent mass spectrometry (MS). Our results show that CggR forms a compact tetrameric assembly upon binding to either the full-length operator or two half-site DNAs and that FBP triggers a tetramer–dimer transition that leaves a single dimer on the half-site or two physically independent dimers on the full-length target. Although the binding of other phospho-sugars was evidenced by MS, only FBP was found to completely disrupt dimer–dimer contacts. We conclude that inducer-dependent dimer–dimer bridging interactions constitute the physical basis for CggR cooperative binding to DNA and the underlying repression mechanism. This work provides experimental evidences for a cooperativity-based regulation model that should apply to other SorC family members
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