6,195 research outputs found
Complexity reduction of astrochemical networks
We present a new computational scheme aimed at reducing the complexity of the
chemical networks in astrophysical models, one which is shown to markedly
improve their computational efficiency. It contains a flux-reduction scheme
that permits to deal with both large and small systems. This procedure is shown
to yield a large speed-up of the corresponding numerical codes and provides
good accord with the full network results. We analyse and discuss two examples
involving chemistry networks of the interstellar medium and show that the
results from the present reduction technique reproduce very well the results
from fuller calculations.Comment: 9 pages, 7 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society Main Journa
Improving food environments and tackling obesity: a realist systematic review of the policy success of regulatory interventions targeting population nutrition
Published: August 4, 2017Background: This systematic review (PROSPERO: CRD42015025276) employs a realist approach to investigate the effect of “real-world” policies targeting different aspects of the food environment that shape individual and collective nutrition. Objectives: We were interested in assessing intermediate outcomes along the assumed causal pathway to “policy success”, in addition to the final outcome of changed consumption patterns. Data sources: We performed a search of 16 databases through October 2015, with no initial restriction by language. Study eligibility criteria: We included all publications that reported the effect of statutory provisions aimed at reducing the consumption of energy-dense foods and beverages in the general population. We allowed all methodological approaches that contained some measure of comparison, including studies of implementation progress. Study appraisal and synthesis methods: We reviewed included studies using the appraisal tools for pre-post and observational studies developed by the National Heart, Lung, and Blood Institute. Given the considerable heterogeneity in interventions assessed, study designs employed, and outcome measures reported, we opted for a narrative synthesis of results. Results and implications: Results drawn from 36 peer-reviewed articles and grey literature reports demonstrated that isolated regulatory interventions can improve intermediate outcomes, but fail to affect consumption at clinically significant levels. The included literature covered six different types of interventions, with 19 studies reporting on calorie posting on chain restaurant menus. The large majority of the identified interventions were conducted in the US. Early results from recent taxation measures were published after the review cut-off date but these suggested more favorable effects on consumption levels. Nevertheless, the evidence assessed in this review suggests that current policies are generally falling short of anticipated health impacts.Jana Sisnowski, Jackie M. Street, Tracy Merli
Observation of Surface-Avoiding Waves: A New Class of Extended States in Periodic Media
Coherent time-domain optical experiments on GaAs-AlAs superlattices reveal
the exis-tence of an unusually long-lived acoustic mode at ~ 0.6 THz, which
couples weakly to the environment by evading the sample boundaries. Classical
as well as quantum states that steer clear of surfaces are generally shown to
occur in the spectrum of periodic struc-tures, for most boundary conditions.
These surface-avoiding waves are associated with frequencies outside forbidden
gaps and wavevectors in the vicinity of the center and edge of the Brillouin
zone. Possible consequences for surface science and resonant cavity
ap-plications are discussed.Comment: 16 pages, 3 figure
Generation and remote detection of THz sound using semiconductor superlattices
The authors introduce a novel approach to study the propagation of high
frequency acoustic phonons in which the generation and detection involves two
spatially separated superlattices apart. Propagating modes
of frequencies up to escape from the superlattice where they
are generated and reach the second superlattice where they are detected. The
measured frequency spectrum reveals finite size effects, which can be accounted
for by a continuum elastic model.Comment: Submitted to Applied Physics Letter
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