140,668 research outputs found
Continuous Diffraction of Molecules and Disordered Molecular Crystals
The diffraction pattern of a single non-periodic compact object, such as a
molecule, is continuous and is proportional to the square modulus of the
Fourier transform of that object. When arrayed in a crystal, the coherent sum
of the continuous diffracted wave-fields from all objects gives rise to strong
Bragg peaks that modulate the single-object transform. Wilson statistics
describe the distribution of continuous diffraction intensities to the same
extent that they apply to Bragg diffraction. The continuous diffraction
obtained from translationally-disordered molecular crystals consists of the
incoherent sum of the wave-fields from the individual rigid units (such as
molecules) in the crystal, which is proportional to the incoherent sum of the
diffraction from the rigid units in each of their crystallographic
orientations. This sum over orientations modifies the statistics in a similar
way that crystal twinning modifies the distribution of Bragg intensities. These
statistics are applied to determine parameters of continuous diffraction such
as its scaling, the beam coherence, and the number of independent wave-fields
or object orientations contributing. Continuous diffraction is generally much
weaker than Bragg diffraction and may be accompanied by a background that far
exceeds the strength of the signal. Instead of just relying upon the smallest
measured intensities to guide the subtraction of the background it is shown how
all measured values can be utilised to estimate the background, noise, and
signal, by employing a modified "noisy Wilson" distribution that explicitly
includes the background. Parameters relating to the background and signal
quantities can be estimated from the moments of the measured intensities. The
analysis method is demonstrated on previously-published continuous diffraction
data measured from imperfect crystals of photosystem II.Comment: 34 pages, 11 figures, 2 appendice
The rise of policy coherence for development: a multi-causal approach
In recent years policy coherence for development (PCD) has become a key principle in international development debates, and it is likely to become even more relevant in the discussions on the post-2015 sustainable development goals. This article addresses the rise of PCD on the Western donors’ aid agenda. While the concept already appeared in the work of Organisation for Economic Co-operation and Development (OECD) in the early 1990s, it took until 2007 before PCD became one of the Organisation’s key priorities. We adopt a complexity-sensitive perspective, involving a process-tracing analysis and a multi-causal explanatory framework. We argue that the rise of PCD is not as contingent as it looks. While actors such as the EU, the DAC and OECD Secretariat were the ‘active causes’ of the rise of PCD, it is equally important to look at the underlying ‘constitutive causes’ which enabled policy coherence to thrive well
QCD and studies at FCC-ee
The Future Circular Collider (FCC) is a post-LHC project aiming at searches
for physics beyond the SM in a new 80--100~km tunnel at CERN. Running in its
first phase as a very-high-luminosity electron-positron collider (FCC-ee), it
will provide unique possibilities for indirect searches of new phenomena
through high-precision tests of the SM. In addition, by collecting tens of
ab integrated luminosity in the range of center-of-mass energies
~=90--350~GeV, the FCC-ee also offers unique physics opportunities
for precise measurements of QCD phenomena and of photon-photon collisions
through, literally, billions of hadronic final states as well as unprecedented
large fluxes of quasireal 's radiated from the beams. We
succinctly summarize the FCC-ee perspectives for high-precision extractions of
the QCD coupling, for detailed analyses of parton radiation and fragmentation,
and for SM and BSM studies through collisions.Comment: 6 pages, Proceedings ICHEP'16 (Chicago
Flux tubes at finite temperature
The chromoelectric field generated by a static quark-antiquark pair, with its
peculiar tube-like shape, can be nicely described, at zero temperature, within
the dual superconductor scenario for the QCD confining vacuum. In this work we
investigate, by lattice Monte Carlo simulations of the SU(3) pure gauge theory,
the fate of chromoelectric flux tubes across the deconfinement transition. We
find that, as the temperature is increased towards and above the deconfinement
temperature , the amplitude of the field inside the flux tube gets
smaller, while the shape of the flux tube does not vary appreciably across
deconfinement. This scenario with flux-tube "evaporation" above has no
correspondence in ordinary (type-II) superconductivity, where instead the
transition to the phase with normal conductivity is characterized by a
divergent fattening of flux tubes as the transition temperature is approached
from below. We present also some evidence about the existence of flux-tube
structures in the magnetic sector of the theory in the deconfined phase.Comment: arXiv admin note: text overlap with arXiv:1404.117
Magnetic Resonance Lithography with Nanometer Resolution
We propose an approach for super-resolution optical lithography which is
based on the inverse of magnetic resonance imaging (MRI). The technique uses
atomic coherence in an ensemble of spin systems whose final state population
can be optically detected. In principle, our method is capable of producing
arbitrary one and two dimensional high-resolution patterns with high contrast
Post-selected weak measurement beyond the weak value
Closed expressions are derived for the quantum measurement statistics of
pre-and postselected gaussian particle beams. The weakness of the pre-selection
step is shown to compete with the non-orthogonality of post-selection in a
transparent way. The approach is shown to be useful in analyzing
post-selection-based signal amplification, allowing measurements to be extended
far beyond the range of validity of the well-known Aharonov-Albert-Vaidman
limit.Comment: The published version; with respect to previous one, note changes in
Eqs. (16),(17),(19)
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