184 research outputs found
Direct reconstruction of the two-dimensional pair distribution function in systems with angular correlations
An x-ray scattering approach to determine the two-dimensional (2D) pair
distribution function (PDF) in partially ordered 2D systems is proposed. We
derive relations between the structure factor and PDF that enable quantitative
studies of positional and bond-orientational (BO) order in real space. We apply
this approach in the x-ray study of a liquid crystal (LC) film undergoing the
smectic-hexatic phase transition, to analyze the interplay between the
positional and BO order during the temperature evolution of the LC film. We
analyze the positional correlation length in different directions in real
space.Comment: 23 pages, 8 figure
Spatial properties of conjugated network in semicrystalline polymer thin films studied by intensity x-ray cross-correlation functions
We present results of x-ray study of spatial properties of
conjugated networks in polymer thin films. We applied the x-ray
cross-correlation analysis to x-ray scattering data from blends of
poly(3-hexylthiophene) (P3HT) and gold nanoparticles. The Fourier spectra of
the intensity cross-correlation functions for different films contain non-zero
components of orders and measuring the degree of structural order
in the system.Comment: 6 pages, 2 figures, Proceedings ICXOM22 Conference, 2-6 September
2013, Hamburg, German
Hanbury Brown and Twiss interferometry at a free-electron laser
We present measurements of second- and higher-order intensity correlation
functions (so-called Hanbury Brown and Twiss experiment) performed at the
free-electron laser (FEL) FLASH in the non-linear regime of its operation. We
demonstrate the high transverse coherence properties of the FEL beam with a
degree of transverse coherence of about 80% and degeneracy parameter of the
order 10^9 that makes it similar to laser sources. Intensity correlation
measurements in spatial and frequency domain gave an estimate of the FEL
average pulse duration of 50 fs. Our measurements of the higher-order
correlation functions indicate that FEL radiation obeys Gaussian statistics,
which is characteristic to chaotic sources.Comment: 19 pages, 6 figures, 1 table, 40 reference
Statistical properties of a free-electron laser revealed by the Hanbury Brown and Twiss interferometry
We present a comprehensive experimental analysis of statistical properties of
the self-amplified spontaneous emission (SASE) free-electron laser (FEL) FLASH
at DESY in Hamburg by means of Hanbury Brown and Twiss (HBT) interferometry.
The experiments were performed at the FEL wavelengths of 5.5 nm, 13.4 nm, and
20.8 nm. We determined the 2-nd order intensity correlation function for all
wavelengths and different operation conditions of FLASH. In all experiments a
high degree of spatial coherence (above 50%) was obtained. Our analysis
performed in spatial and spectral domains provided us with the independent
measurements of an average pulse duration of the FEL that were below 60 fs. To
explain complicated behaviour of the 2-nd order intensity correlation function
we developed advanced theoretical model that includes the presence of multiple
beams and external positional jitter of the FEL pulses. By this analysis we
determined that in most experiments several beams were present in radiating
field and in one of the experiments external positional jitter was about 25% of
the beam size. We envision that methods developed in our study will be used
widely for analysis and diagnostics of the FEL radiation.Comment: 29 pages, 14 figures, 3 table
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One strategy doesn’t fit all: determinants of urban adaptation in mammals
Urbanization exposes wildlife to new challenging conditions and environmental pressures. Some mammalian species have adapted to these novel environments, but it remains unclear which characteristics allow them to persist. To address this question we identified 190 mammals regularly recorded in urban settlements worldwide, and used phylogenetic path analysis to test hypotheses regarding which behavioural, ecological, and life history traits favour adaptation to urban environments for different mammalian groups. Our results show that all urban mammals produce larger litters; whereas other traits such as body size, behavioural plasticity and diet diversity were important for some but not all taxonomic groups. This variation highlights the idiosyncrasies of the urban adaptation process and likely reflects the diversity of ecological niches and roles mammals can play. Our study contributes towards a better understanding of mammal association to humans, which will ultimately allow the design of wildlife-friendly urban environments and contribute to mitigate human-wildlife conflicts
Characterization of Spatial Coherence of Synchrotron Radiation with Non-Redundant Arrays of Apertures
We present a method to characterize the spatial coherence of soft X-ray
radiation from a single diffraction pattern. The technique is based on
scattering from non-redundant arrays (NRA) of slits and records the degree of
spatial coherence at several relative separations from one to 15 microns,
simultaneously. Using NRAs we measured the transverse coherence of the X-ray
beam at the XUV X-ray beamline P04 of the PETRA III synchrotron storage ring as
a function of different beam parameters. To verify the results obtained with
the NRAs additional Young's double pinhole experiments were conducted and show
good agreement.Comment: 15 pages, 6 figures, 2 tables, 42 reference
Diffraction based Hanbury Brown and Twiss interferometry performed at a hard x-ray free-electron laser
We demonstrate experimentally Hanbury Brown and Twiss (HBT) interferometry at
a hard X-ray Free Electron Laser (XFEL) on a sample diffraction patterns. This
is different from the traditional approach when HBT interferometry requires
direct beam measurements in absence of the sample. HBT analysis was carried out
on the Bragg peaks from the colloidal crystals measured at Linac Coherent Light
Source (LCLS). We observed high degree (80%) spatial coherence of the full beam
and the pulse duration of the monochromatized beam on the order of 11 fs that
is significantly shorter than expected from the electron bunch measurements.Comment: 32 pages, 10 figures, 2 table
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