334 research outputs found
Trust-Building through Social Media Communications in Disaster Management
open4Social media provides a digital space – a meeting place, for different people, often representing one or more groups in a
society. The use of this space during a disaster, especially where information needs are high and the availability of factually accurate and ethically sourced data is scarce, has increased substantially over the last 5-10 years. This paper attempts to address communication in social media and trust between the public and figures of authority during a natural disaster in order to suggest communication strategies that can enhance or reinforce trust between these bodies before, during and after a natural disaster.openM. G. Busà; M. T. Musacchio; S. Finan; C. FennelBusa', MARIA GRAZIA; Musacchio, MARIA TERESA; S., Finan; C., Fenne
A knowledge-based approach to configuration layout, justification, and documentation
The design, development, and implementation is described of a prototype expert system which could aid designers and system engineers in the placement of racks aboard modules on Space Station Freedom. This type of problem is relevant to any program with multiple constraints and requirements demanding solutions which minimize usage of limited resources. This process is generally performed by a single, highly experienced engineer who integrates all the diverse mission requirements and limitations, and develops an overall technical solution which meets program and system requirements with minimal cost, weight, volume, power, etc. This system architect performs an intellectual integration process in which the underlying design rationale is often not fully documented. This is a situation which lends itself to an expert system solution for enhanced consistency, thoroughness, documentation, and change assessment capabilities
A Knowledge-Based Approach to Configuration Layout, Justification, and Documentation
The design, development, and implementation of a prototype expert system which could aid designers and system engineers in the placement of racks aboard modules on the Space Station Freedom are described. This type of problem is relevant to any program with multiple constraints and requirements demanding solutions which minimize usage of limited resources. This process is generally performed by a single, highly experienced engineer who integrates all the diverse mission requirements and limitations, and develops an overall technical solution which meets program and system requirements with minimal cost, weight, volume, power, etc. This system architect performs an intellectual integration process in which the underlying design rationale is often not fully documented. This is a situation which lends itself to an expert system solution for enhanced consistency, thoroughness, documentation, and change assessment capabilities
Single-particle spectral function for the classical one-component plasma
The spectral function for an electron one-component plasma is calculated
self-consistently using the GW0 approximation for the single-particle
self-energy. In this way, correlation effects which go beyond the mean-field
description of the plasma are contained, i.e. the collisional damping of
single-particle states, the dynamical screening of the interaction and the
appearance of collective plasma modes. Secondly, a novel non-perturbative
analytic solution for the on-shell GW0 self-energy as a function of momentum is
presented. It reproduces the numerical data for the spectral function with a
relative error of less than 10% in the regime where the Debye screening
parameter is smaller than the inverse Bohr radius, kappa<1/a_B. In the limit of
low density, the non-perturbative self-energy behaves as n^(1/4), whereas a
perturbation expansion leads to the unphysical result of a density independent
self-energy [W. Fennel and H. P. Wilfer, Ann. Phys. Lpz._32_, 265 (1974)]. The
derived expression will greatly facilitate the calculation of observables in
correlated plasmas (transport properties, equation of state) that need the
spectral function as an input quantity. This is demonstrated for the shift of
the chemical potential, which is computed from the analytical formulae and
compared to the GW0-result. At a plasma temperature of 100 eV and densities
below 10^21 cm^-3, both approaches deviate less than 10% from each other.Comment: 14 pages, 9 figures accepted for publication in Phys. Rev. E v2:
added section V (application of presented formalism to chemical potential of
the OCP
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Phase- and intensity-resolved measurements of above threshold ionization by few-cycle pulses
We investigate the carrier-envelope phase (CEP) and intensity dependence of the longitudinal momentum distribution of photoelectrons resulting from above threshold ionization of argon by few-cycle laser pulses. The intensity of the pulses with a center wavelength of 750 nm is varied in a range between 0.7 × 1014 and . Our measurements reveal a prominent maximum in the CEP-dependent asymmetry at photoelectron energies of 2 U P (U P being the ponderomotive potential), that is persistent over the entire intensity range. Further local maxima are observed around 0.3 and 0.8 U P. The experimental results are in good agreement with theoretical results obtained by solving the three-dimensional time-dependent Schrödinger equation. We show that for few-cycle pulses, the amplitude of the CEP-dependent asymmetry provides a reliable measure for the peak intensity on target. Moreover, the measured asymmetry amplitude exhibits an intensity-dependent interference structure at low photoelectron energy, which could be used to benchmark model potentials for complex atoms
Evolution of dopant-induced helium nanoplasmas
Two-component nanoplasmas generated by strong-field ionization of doped
helium nanodroplets are studied in a pump-probe experiment using few-cycle
laser pulses in combination with molecular dynamics simulations. High yields of
helium ions and a pronounced, droplet size-dependent resonance structure in the
pump-probe transients reveal the evolution of the dopant-induced helium
nanoplasma. The pump-probe dynamics is interpreted in terms of strong inner
ionization by the pump pulse and resonant heating by the probe pulse which
controls the final charge states detected via the frustration of electron-ion
recombination
Phase- and intensity-resolved measurements of above threshold ionization by few-cycle pulses
We investigate the carrier-envelope phase and intensity dependence of the
longitudinal momentum distribution of photoelectrons resulting from
above-threshold ionization of argon by few-cycle laser pulses. The intensity of
the pulses with a center wavelength of 750\,nm is varied in a range between
and \unit[5.5 \times 10^{14}]{W/cm^2}. Our measurements
reveal a prominent maximum in the carrier-envelope phase-dependent asymmetry at
photoelectron energies of 2\, ( being the
ponderomotive potential), that is persistent over the entire intensity range.
Further local maxima are observed at 0.3 and 0.8\,. The
experimental results are in good agreement with theoretical results obtained by
solving the three-dimensional time-dependent Schr\"{o}dinger equation (3D
TDSE). We show that for few-cycle pulses, the carrier-envelope phase-dependent
asymmetry amplitude provides a reliable measure for the peak intensity on
target. Moreover, the measured asymmetry amplitude exhibits an
intensity-dependent interference structure at low photoelectron energy, which
could be used to benchmark model potentials for complex atoms
Three-Dimensional Shapes of Spinning Helium Nanodroplets
A significant fraction of superfluid helium nanodroplets produced in a
free-jet expansion have been observed to gain high angular momentum resulting
in large centrifugal deformation. We measured single-shot diffraction patterns
of individual rotating helium nanodroplets up to large scattering angles using
intense extreme ultraviolet light pulses from the FERMI free-electron laser.
Distinct asymmetric features in the wide-angle diffraction patterns enable the
unique and systematic identification of the three-dimensional droplet shapes.
The analysis of a large dataset allows us to follow the evolution from
axisymmetric oblate to triaxial prolate and two-lobed droplets. We find that
the shapes of spinning superfluid helium droplets exhibit the same stages as
classical rotating droplets while the previously reported metastable, oblate
shapes of quantum droplets are not observed. Our three-dimensional analysis
represents a valuable landmark for clarifying the interrelation between
morphology and superfluidity on the nanometer scale
Efficient Indirect Interatomic Coulombic Decay Induced by Photoelectron Impact Excitation in Large He Nanodroplets
Ionization of matter by energetic radiation generally causes complex
secondary reactions which are hard to decipher. Using large helium nanodroplets
irradiated by XUV photons, we show that the full chain of processes ensuing
primary photoionization can be tracked in detail by means of high-resolution
electron spectroscopy. We find that elastic and inelastic scattering of
photoelectrons efficiently induces interatomic Coulombic decay (ICD) in the
droplets. This type of indirect ICD even becomes the dominant process of
electron emission in nearly the entire XUV range in large droplets with radius
nm. Indirect ICD processes induced by electron scattering likely
play an important role in other condensed phase systems exposed to ionizing
radiation as well, including biological matter
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