1,761 research outputs found
Post-copulatory opportunities for sperm competition and cryptic female choice provide no offspring fitness benefits in externally fertilizing salmon
There is increasing evidence that females can somehow improve their offspring fitness by mating with multiple males, but we understand little about the exact stage(s) at which such benefits are gained. Here, we measure whether offspring fitness is influenced by mechanisms operating solely between sperm and egg. Using externally-fertilising and polyandrous Atlantic salmon (Salmo salar), we employed split-clutch and split-ejaculate in vitro fertilisation experiments to generate offspring using designs that either denied or applied opportunities for sperm competition and cryptic female choice. Following fertilisations, we measured 140 days of offspring fitness after hatch, through growth and survival in hatchery and near-natural conditions. Despite an average composite mortality of 61%, offspring fitness at every life stage was near-identical between groups fertilised under the absence versus presence of opportunities for sperm competition and cryptic female choice. Of the 21,551 and 21,771 eggs from 24 females fertilised under monandrous versus polyandrous conditions, 68% versus 67.8% survived to the 100-day juvenile stage; sub-samples showed similar hatching success (73.1% versus 74.3%), had similar survival over 40 days in near-natural streams (57.3% versus 56.2%), and grew at similar rates throughout. We therefore found no evidence that gamete-specific interactions allow offspring fitness benefits when polyandrous fertilisation conditions provide opportunities for sperm competition and cryptic female choice
Can electronic assessment tools improve the process of shared decision-making? A systematic review
Background:
Patient involvement in decision-making plays a prominent role in improving the quality of healthcare. Despite this, shared decision-making is not routinely implemented. However, electronic assessment tools that capture patients’ history, symptoms, opinions and values prior to their medical appointment are used by healthcare professionals during patient consultations to facilitate shared decision-making.
Objective:
To assess the effectiveness of electronic assessment tools to improve the shared decision-making process.
Method:
A systematic review was conducted following PRISMA guidelines. Published literature was searched on MEDLINE, EMBASE and PsycINFO to identify potentially relevant studies. Data were extracted and analysed narratively.
Results:
Seventeen articles, representing 4004 participants, were included in this review. The main findings were significant improvement in patient–provider communication and provider management of patient condition in the intervention group compared to the control group. In contrast, patient–provider satisfaction and time efficiency were assessed by relatively few included studies, and the effects of these outcomes were inconclusive.
Conclusion:
This review found that communication and healthcare professional’s management of a patient’s condition improves because of the use of electronic questionnaires. This is encouraging because the process of shared decision-making is reliant on high-quality communication between healthcare professionals and patients.
Implications:
We found that this intervention is especially important for people with chronic diseases, as they need to establish a long-term relationship with their healthcare provider and agree to a treatment plan that aligns with their values. More rigorous research with validated instruments is required
The Polymer Stress Tensor in Turbulent Shear Flows
The interaction of polymers with turbulent shear flows is examined. We focus
on the structure of the elastic stress tensor, which is proportional to the
polymer conformation tensor. We examine this object in turbulent flows of
increasing complexity. First is isotropic turbulence, then anisotropic (but
homogenous) shear turbulence and finally wall bounded turbulence. The main
result of this paper is that for all these flows the polymer stress tensor
attains a universal structure in the limit of large Deborah number \De\gg 1.
We present analytic results for the suppression of the coil-stretch transition
at large Deborah numbers. Above the transition the turbulent velocity
fluctuations are strongly correlated with the polymer's elongation: there
appear high-quality "hydro-elastic" waves in which turbulent kinetic energy
turns into polymer potential energy and vice versa. These waves determine the
trace of the elastic stress tensor but practically do not modify its universal
structure. We demonstrate that the influence of the polymers on the balance of
energy and momentum can be accurately described by an effective polymer
viscosity that is proportional to to the cross-stream component of the elastic
stress tensor. This component is smaller than the stream-wise component by a
factor proportional to \De ^2 . Finally we tie our results to wall bounded
turbulence and clarify some puzzling facts observed in the problem of drag
reduction by polymers.Comment: 11 p., 1 Fig., included, Phys. Rev. E., submitte
Stretching of polymers in a random three-dimensional flow
Behavior of a dilute polymer solution in a random three-dimensional flow with
an average shear is studied experimentally. Polymer contribution to the shear
stress is found to be more than two orders of magnitude higher than in a
laminar shear flow. The results indicate that the polymer molecules get
strongly stretched by the random motion of the fluid.Comment: 4 pages, 3 figure
Shell Model for Drag Reduction with Polymer Additive in Homogeneous Turbulence
Recent direct numerical simulations of the FENE-P model of non-Newtonian
hydrodynamics revealed that the phenomenon of drag reduction by polymer
additives exists (albeit in reduced form) also in homogeneous turbulence. We
introduce here a simple shell model for homogeneous viscoelastic flows that
recaptures the essential observations of the full simulations. The simplicity
of the shell model allows us to offer a transparent explanation of the main
observations. It is shown that the mechanism for drag reduction operates mainly
on the large scales. Understanding the mechanism allows us to predict how the
amount of drag reduction depends of the various parameters in the model. The
main conclusion is that drag reduction is not a universal phenomenon, it peaks
in a window of parameters like Reynolds number and the relaxation rate of the
polymer
Multi-Zone Shell Model for Turbulent Wall Bounded Flows
We suggested a \emph{Multi-Zone Shell} (MZS) model for wall-bounded flows
accounting for the space inhomogeneity in a "piecewise approximation", in which
cross-section area of the flow, , is subdivided into "-zones". The area
of the first zone, responsible for the core of the flow, , and
areas of the next -zones, , decrease towards the wall like . In each -zone the statistics of turbulence is assumed to be space
homogeneous and is described by the set of "shell velocities" for
turbulent fluctuations of the scale . The MZS-model includes a
new set of complex variables, , , describing the
amplitudes of the near wall coherent structures of the scale
and responsible for the mean velocity profile. Suggested MZS-equations of
motion for and preserve the actual conservations laws
(energy, mechanical and angular momenta), respect the existing symmetries
(including Galilean and scale invariance) and account for the type of the
non-linearity in the Navier-Stokes equation, dimensional reasoning, etc. The
MZS-model qualitatively describes important characteristics of the wall bounded
turbulence, e.g., evolution of the mean velocity profile with increasing
Reynolds number, \RE, from the laminar profile towards the universal
logarithmic profile near the flat-plane boundary layer as \RE\to \infty.Comment: 27 pages, 17 figs, included, PRE, submitte
Drag Reduction by Polymers in Turbulent Channel Flows: Energy Redistribution Between Invariant Empirical Modes
We address the phenomenon of drag reduction by dilute polymeric additive to
turbulent flows, using Direct Numerical Simulations (DNS) of the FENE-P model
of viscoelastic flows. It had been amply demonstrated that these model
equations reproduce the phenomenon, but the results of DNS were not analyzed so
far with the goal of interpreting the phenomenon. In order to construct a
useful framework for the understanding of drag reduction we initiate in this
paper an investigation of the most important modes that are sustained in the
viscoelastic and Newtonian turbulent flows respectively. The modes are obtained
empirically using the Karhunen-Loeve decomposition, allowing us to compare the
most energetic modes in the viscoelastic and Newtonian flows. The main finding
of the present study is that the spatial profile of the most energetic modes is
hardly changed between the two flows. What changes is the energy associated
with these modes, and their relative ordering in the decreasing order from the
most energetic to the least. Modes that are highly excited in one flow can be
strongly suppressed in the other, and vice versa. This dramatic energy
redistribution is an important clue to the mechanism of drag reduction as is
proposed in this paper. In particular there is an enhancement of the energy
containing modes in the viscoelastic flow compared to the Newtonian one; drag
reduction is seen in the energy containing modes rather than the dissipative
modes as proposed in some previous theories.Comment: 11 pages, 13 figures, included, PRE, submitted, REVTeX
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