23,028 research outputs found
Mechanics of the turbulent/non-turbulent interface of a jet
We report the results of an experimental investigation of the mechanics and transport processes at the bounding interface between the turbulent and nonturbulent regions of flow in a turbulent jet, which shows the existence of a finite jump in the tangential velocity at the interface. This is associated with small-scale eddying motion at the outward propagating interface (nibbling) by which irrotational fluid becomes turbulent, and this implies that large-scale engulfment is not the dominant entrainment process. Interpretation of the jump as a singular structure yields an essential and significant contribution to the mean shear in the jet mixing region. Finally, our observations provide a justification for Prandtl’s original hypothesis of a constant eddy viscosity in the nonturbulent outer jet region
Adiabatic Elimination in a Lambda System
This paper deals with different ways to extract the effective two-dimensional
lower level dynamics of a lambda system excited by off-resonant laser beams. We
present a commonly used procedure for elimination of the upper level, and we
show that it may lead to ambiguous results. To overcome this problem and better
understand the applicability conditions of this scheme, we review two rigorous
methods which allow us both to derive an unambiguous effective two-level
Hamiltonian of the system and to quantify the accuracy of the approximation
achieved: the first one relies on the exact solution of the Schrodinger
equation, while the second one resorts to the Green's function formalism and
the Feshbach projection operator technique.Comment: 14 pages, 3 figure
Improving survey response rates in online panels: effects of low-cost incentives and cost-free text appeal interventions
Identifying ways to efficiently maximize the response rate to surveys is important in survey-based research. However, evidence on the response rate effect of donation incentives and especially altruistic and egotistic text appeal interventions is sparse and ambiguous. Via a randomized survey experiment among 6,162 members of an online survey panel, this article shows how low-cost incentives and cost-free text appeal interventions may affect the survey response rate in online panels. The experimental treatments comprise (a) a cash prize lottery incentive, (b) two donation incentives that promise a monetary donation to a good cause in return for survey response, (c) an egotistic text appeal, and (d) an altruistic text appeal. Relative to a control group, we find higher response rates among recipients of the egotistic text appeal and the lottery incentive. Donation incentives yield lower response rates
A repulsive reference potential reproducing the dynamics of a liquid with attractions
A well-known result of liquid state theory is that the structure of dense
fluids is mainly determined by repulsive forces. The WCA potential, which cuts
intermolecular potentials at their minima, is therefore often used as a
reference. However, this reference gives quite wrong results for the viscous
dynamics of the Kob-Andersen binary Lennard-Jones liquid [Berthier and Tarjus,
Phys. Rev. Lett. 103, 170601 (2009)]. We show that repulsive inverse-power law
potentials provide a useful reference for this liquid by reproducing its
structure, dynamics, and isochoric heat capacity
Phylogeny of the moss family Bryaceae inferred from chloroplast DNA sequences and morphology
AbstractPhylogenetic relationships within the moss family Bryaceae were studied using chloroplast DNA sequences (atpB-rbcL, rpl16 intron, rps4, and trnL-trnF region) and anatomical and morphological data. Phylogenetic analyses using maximum parsimony, maximum likelihood, and Bayesian methods indicate that the genera Brachymenium, Bryum, and Rhodobryum are not monophyletic
Skew Category Algebras Associated with Partially Defined Dynamical Systems
We introduce partially defined dynamical systems defined on a topological
space. To each such system we associate a functor from a category to
\Top^{\op} and show that it defines what we call a skew category algebra . We study the connection between topological freeness of
and, on the one hand, ideal properties of and, on
the other hand, maximal commutativity of in . In
particular, we show that if is a groupoid and for each e \in \ob(G) the
group of all morphisms is countable and the topological space
is Tychonoff and Baire, then the following assertions are equivalent:
(i) is topologically free; (ii) has the ideal intersection property,
that is if is a nonzero ideal of , then ; (iii) the ring is a maximal abelian complex subalgebra of . Thereby, we generalize a result by Svensson, Silvestrov
and de Jeu from the additive group of integers to a large class of groupoids.Comment: 16 pages. This article is an improvement of, and hereby a replacement
for, version 1 (arXiv:1006.4776v1) entitled "Category Dynamical Systems and
Skew Category Algebras
Clar Sextet Analysis of Triangular, Rectangular and Honeycomb Graphene Antidot Lattices
Pristine graphene is a semimetal and thus does not have a band gap. By making
a nanometer scale periodic array of holes in the graphene sheet a band gap may
form; the size of the gap is controllable by adjusting the parameters of the
lattice. The hole diameter, hole geometry, lattice geometry and the separation
of the holes are parameters that all play an important role in determining the
size of the band gap, which, for technological applications, should be at least
of the order of tenths of an eV. We investigate four different hole
configurations: the rectangular, the triangular, the rotated triangular and the
honeycomb lattice. It is found that the lattice geometry plays a crucial role
for size of the band gap: the triangular arrangement displays always a sizable
gap, while for the other types only particular hole separations lead to a large
gap. This observation is explained using Clar sextet theory, and we find that a
sufficient condition for a large gap is that the number of sextets exceeds one
third of the total number of hexagons in the unit cell. Furthermore, we
investigate non-isosceles triangular structures to probe the sensitivity of the
gap in triangular lattices to small changes in geometry
Reporting radiographers in Europe survey: An overview of the role within the European Federation of Radiographer Society (EFRS) member countries
Introduction
Reporting radiographers undertake an important role in healthcare and for the radiographer profession in general. First introduced in the United Kingdom, reporting radiographers are now practicing in several other European countries. Our objective was to investigate the workforce of reporting radiographers across the European Federation of Radiographer Societies (EFRS) community.
Method and material
A voluntary anonymous 34 item electronic survey was distributed online using social media accounts such as Twitter, Facebook and LinkedIn covering a wide range of topics relating to professional role, advanced practice, education, and seniority. The questionnaire was distributed during a 12-week period in 2022.
Result
A total of 345 individual responses were received from 15 countries with majorities of respondent from United Kingdom (n = 245, 71%) and Denmark (n = 66, 19%). Mean age was 41.9 (S.D 9.8), similar for females, 42.5 (S.D 9.0) and men 40.9 years (S.D 9.7). Most reporting radiographers worked in public hospitals (90%). The vast majority of the respondents (n = 270, n = 94%) authored and signed their own clinical reports while a minority (n = 18, 6%) stated that their reports were checked by radiologists.
Conclusion
The survey highlights the scope of practice of reporting radiographers working in Europe. Reporting is becoming a career path for an increasing number of radiographers across Europe and there is assess to academic education and clinical support.
Implication for practice
Reporting radiographers fulfil an important role within the current demands of healthcare. This demand is likely to increase in the future, and therefore it is vital that there is some form of standardisation in the level of education that this group of healthcare professionals receive
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