6,917 research outputs found
Detection Techniques for Trapped Ions
Various techniques are used to detect the presence of charged particles
stored in electromagnetic traps, their energy, their mass, or their internal
states. Detection methods can rely on the variation of the number of trapped
particles (destructive methods) or the use of the ion's interaction with
electromagnetic radiation as a non-destructive tool to probe the trapped
particles. This review gives an introduction into various methods, discussing
the basic mode of operation completed by the description of recent
realizations
How to Upscale The Kinetics of Complex Microsystems
The rate constants of chemical reactions are typically inferred from slopes
and intersection points of observed concentration curves. In small systems that
operate far below the thermodynamic limit, these concentration profiles become
stochastic and such an inference is less straightforward. By using elements of
queuing theory, we introduce a procedure for inferring (time dependent) kinetic
parameters from microscopic observations that are given by molecular
simulations of many simultaneously reacting species. We demonstrate that with
this procedure it is possible to assimilate the results of molecular
simulations in such a way that the latter become descriptive on the macroscopic
scale. As an example, we upscale the kinetics of a molecular dynamics system
that forms a complex molecular network. Incidentally, we report that the
kinetic parameters of this system feature a peculiar time and temperature
dependences, whereas the probability of a network strand to close a cycle
follows a universal distribution
Scattering lengths of calcium and barium isotopes
We have calculated the s-wave scattering length of all the even isotopes of
calcium (Ca) and barium (Ba), in order to investigate the prospect of
Bose-Einstein condensation (BEC). For Ca we have used an accurate molecular
potential based on detailed spectroscopic data. Our calculations show that Ca
does not provide other isotopes alternative to the recently Bose condensed 40Ca
that suffers strong losses because of a very large scattering length. For Ba we
show by using a model potential that the even isotopes cover a broad range of
scattering lengths, opening the possibility of BEC for at least one of the
isotopes.Comment: 4 page
The Mediaeval Mason: An Economic History of English Stone Building in the Later Middle Ages and Early Modern Times
Quantum-State Controlled Penning Ionization Reactions between Ultracold Alkali and Metastable Helium Atoms
In an ultracold, optically trapped mixture of Rb and metastable
triplet He atoms we have studied trap loss for different spin-state
combinations, for which interspecies Penning ionization is the main two-body
loss process. We observe long trapping lifetimes for the purely quartet
spin-state combination, indicating strong suppression of Penning ionization
loss by at least two orders of magnitude. For the other spin-mixtures we
observe short lifetimes that depend linearly on the doublet character of the
entrance channel. We compare the extracted loss rate coefficient with recent
predictions of multichannel quantum-defect theory for reactive collisions
involving a strong exothermic loss channel and find near-universal loss for
doublet scattering. Our work demonstrates control of reactive collisions by
internal atomic state preparation.Comment: 5 pages, 5 figures + Supplemental Material
Global nitrogen and phosphate in urban wastewater for the period 1970 to 2050
This paper presents estimates for global N and P emissions from sewage for the period 1970-2050 for the four Millennium Ecosystem Assessment scenarios. Using country-specific projections for population and economic growth, urbanization, development of sewage systems, and wastewater treatment installations, a rapid increase in global sewage emissions is predicted, from 6.4 Tg of N and 1.3 Tg of P per year in 2000 to 12.0-15.5 Tg of N and 2.4-3.1 Tg of P per year in 2050. While North America (strong increase), Oceania (moderate increase), Europe (decrease), and North Asia (decrease) show contrasting developments, in the developing countries, sewage N and P discharge will likely increase by a factor of 2.5 to 3.5 between 2000 and 2050. This is a combined effect of increasing population, urbanization, and development of sewage systems. Even in optimistic scenarios for the development of wastewater treatment systems, global N and P flows are not likely to declin
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