11 research outputs found
Neutron scattering and molecular correlations in a supercooled liquid
We show that the intermediate scattering function for neutron
scattering (ns) can be expanded naturely with respect to a set of molecular
correlation functions that give a complete description of the translational and
orientational two-point correlations in the liquid. The general properties of
this expansion are discussed with special focus on the -dependence and hints
for a (partial) determination of the molecular correlation functions from
neutron scattering results are given. The resulting representation of the
static structure factor is studied in detail for a model system using
data from a molecular dynamics simulation of a supercooled liquid of rigid
diatomic molecules. The comparison between the exact result for and
different approximations that result from a truncation of the series
representation demonstrates its good convergence for the given model system. On
the other hand it shows explicitly that the coupling between translational
(TDOF) and orientational degrees of freedom (ODOF) of each molecule and
rotational motion of different molecules can not be neglected in the
supercooled regime.Further we report the existence of a prepeak in the
ns-static structure factor of the examined fragile glassformer, demonstrating
that prepeaks can occur even in the most simple molecular liquids. Besides
examining the dependence of the prepeak on the scattering length and the
temperature we use the expansion of into molecular correlation
functions to point out intermediate range orientational order as its principle
origin.Comment: 13 pages, 7 figure
Leading Chiral Logarithms to the Hyperfine Splitting of the Hydrogen and Muonic Hydrogen
We study the hydrogen and muonic hydrogen within an effective field theory
framework. We perform the matching between heavy baryon effective theory
coupled to photons and leptons and the relevant effective field theory at
atomic scales. This matching can be performed in a perturbative expansion in
alpha, 1/m_p and the chiral counting. We then compute the O(m_{l_i}^3
alpha^5/m_p^2 x logarithms) contribution (including the leading chiral
logarithms) to the Hyperfine splitting and compare with experiment. They can
explain about 2/3 of the difference between experiment and the pure QED
prediction when setting the renormalization scale at the rho mass. We give an
estimate of the matching coefficient of the spin-dependent proton-lepton
operator in heavy baryon effective theory.Comment: 17 pages, LaTeX, minor changes, one reference adde
Proton radius, Darwin-Foldy term and radiative corrections
We discuss the role of the so-called Darwin-Foldy term in the evaluation of
the proton and deuteron charge radii from atomic hydrogen spectroscopy and
nuclear scattering data. The question of whether this term should be included
or excluded from the nuclear radius has been controversially discussed in the
literature. We attempt to clarify which literature values correspond to which
conventions. A detailed discussion of the conventions appears useful because a
recent experiment [R. Pohl et al., Nature vol. 466, p. 213 (2010)] has
indicated that there is a discrepancy between the proton charge radii inferred
from ordinary ("electronic") atomic hydrogen and muonic hydrogen. We also
investigate the role of quantum electrodynamic radiative corrections in the
determination of nuclear radii from scattering data, and propose a definition
of the nuclear self energy which is compatible with the subtraction of the
radiative corrections in scattering experiments.Comment: 8 pages, LaTeX, EPJD styl
What's new with the neutron and proton
The existence and importance of the proton radius puzzle, observed via a Lamb shift measurement in muonic atoms, is discussed. Possible resolutions of the puzzle are discussed. Then the broader question of the meaning of the proton radius is addressed and examples of correctly defined charge densities are presented.Gerald A. Miller, Anthony W. Thomas, Jonathan D. Carroll, Johann Rafelsk
Novel and emerging biotechnological crop protection approaches
Traditional breeding or genetically modified organisms (GMOs) have for a long time been the sole approaches to effectively cope with biotic and abiotic stresses and implement the quality traits of crops. However, emerging diseases as well as unpredictable climate changes affecting agriculture over the entire globe force scientists to find alternative solutions required to quickly overcome seasonal crises. In this review, we first focus on cisgenesis and genome editing as challenging biotechnological approaches for breeding crops more tolerant to biotic and abiotic stresses. In addition, we take into consideration a toolbox of new techniques based on applications of RNA interference and epigenome modifications, which can be adopted for improving plant resilience. Recent advances in these biotechnological applications are mainly reported for non‐model plants and woody crops in particular. Indeed, the characterization of RNAi machinery in plants is fundamental to transform available information into biologically or biotechnologically applicable knowledge. Finally, here we discuss how these innovative and environmentally friendly techniques combined with traditional breeding can sustain a modern agriculture and be of potential contribution to climate change mitigation