59,264 research outputs found
Free Cooling Phase-Diagram of Hard-Spheres with Short- and Long-Range Interactions
We study the stability, the clustering and the phase-diagram of free cooling
granular gases. The systems consist of mono-disperse particles with additional
non-contact (long-range) interactions, and are simulated here by the
event-driven molecular dynamics algorithm with discrete (short-range shoulders
or wells) potentials (in both 2D and 3D). Astonishingly good agreement is found
with a mean field theory, where only the energy dissipation term is modified to
account for both repulsive or attractive non-contact interactions. Attractive
potentials enhance cooling and structure formation (clustering), whereas
repulsive potentials reduce it, as intuition suggests. The system evolution is
controlled by a single parameter: the non-contact potential strength scaled by
the fluctuation kinetic energy (granular temperature). When this is small, as
expected, the classical homogeneous cooling state is found. However, if the
effective dissipation is strong enough, structure formation proceeds, before
(in the repulsive case) non-contact forces get strong enough to undo the
clustering (due to the ongoing dissipation of granular temperature). For both
repulsive and attractive potentials, in the homogeneous regime, the cooling
shows a universal behaviour when the (inverse) control parameter is used as
evolution variable instead of time. The transition to a non-homogeneous regime,
as predicted by stability analysis, is affected by both dissipation and
potential strength. This can be cast into a phase diagram where the system
changes with time, which leaves open many challenges for future research.Comment: 22 pages, 15 figure
Lagoon water-level oscillations driven by rainfall and wave climate
Barrier breaching and subsequent inlet formation represent critical processes that ensure the temporary or permanent connection and transference of water, nutrients, or living organisms between a lagoon and the open sea. Here, we investigate the conditions inducing natural barrier breaching through a 34 months monitoring program of water-level oscillations within a shallow lagoon and the adjacent nearshore, at the Northern coast of the Iberian Peninsula, Louro lagoon. Seven natural openings were identified to have occurred during the three monitored wet seasons, from the 2009 to 2012, (Wet1, Wet2 and Wet3); four in the Wetl, two in the Wet2 and one in. the Wet3. The openings were grouped in three types depending on the observed relation between the lagoon water-level (L-wl), the estimated berm height (B-h) and the water-level at the beach (B-wl): (i) openings by lagoon outflow, which include those characterized by L-wl higher than B-h and lower B-wl; (ii) openings by wave inundation, including those induced by B-wl higher than B-h, and (iii) mixed openings, which result from a combination of the two previous conditions. We observed that L-wl is modulated by the rainfall regime (R-f) and can be explained by the accumulated precipitation. We estimated applying runup equations to obtain B-h and B-wl which depend on the wave climate and tidal level. The inlet lifespan was found to be regulated by the wave climate and rainfall regime; in particular barrier sealing was associated with a sudden increase in wave period and a reduction in precipitation. This work proves that the natural openings could be predicted successfully with support to medium term water-level monitoring programs, which in turn may significantly contribute to strategic decision making for management and conservation purposes.Xunta de Galicia [08MDS036000PR, PlanI2C-ED481B 2014/132-0]MICINN [CTM2012-39599-C03-01]Portuguese Science Foundation [IF/01047/2014]info:eu-repo/semantics/publishedVersio
The impact of a wave farm on large scale sediment transport
This study investigates the interactions of waves and tides at a wave farm in the southwest of England, in particular their effects on radiation stress, bottom stress, and consequently on the sediment transport and the coast adjacent to the wave-farm (the Wave Hub). In this study, an integrated complex numerical modelling system is setup at the Wave Hub site and is used to compute the wave and current fields by taking into account the wave-current interaction, as well as the sediment transport. Results show that tidal elevation and tidal currents have a significant effect on the wave height and direction predictions; tidal forcing and wind waves have a significant effect on the bed shear-stress, relevant to sediment transport; waves via radiation stresses have an important effect on the longshore and cross-shore velocity components, particularly during the spring tides. Waves can impact on bottom boundary layer and mixing in the water column. The results highlight the importance of the interactions between waves and tides when modelling coastal morphology with presence of wave energy devices
Reporting ethics committee approval and patient consent by study design in five general medical journals.
BACKGROUND: Authors are required to describe in their manuscripts ethical approval from an appropriate committee and how consent was obtained from participants when research involves human participants. OBJECTIVE: To assess the reporting of these protections for several study designs in general medical journals. DESIGN: A consecutive series of research papers published in the Annals of Internal Medicine, BMJ, JAMA, Lancet and The New England Journal of Medicine between February and May 2003 were reviewed for the reporting of ethical approval and patient consent. Ethical approval, name of approving committee, type of consent, data source and whether the study used data collected as part of a study reported elsewhere were recorded. Differences in failure to report approval and consent by study design, journal and vulnerable study population were evaluated using multivariable logistic regression. RESULTS: Ethical approval and consent were not mentioned in 31% and 47% of manuscripts, respectively. 88 (27%) papers failed to report both approval and consent. Failure to mention ethical approval or consent was significantly more likely in all study designs (except case-control and qualitative studies) than in randomised controlled trials (RCTs). Failure to mention approval was most common in the BMJ and was significantly more likely than in The New England Journal of Medicine. Failure to mention consent was most common in the BMJ and was significantly more likely than in all other journals. No significant differences in approval or consent were found when comparing studies of vulnerable and non-vulnerable participants. CONCLUSION: The reporting of ethical approval and consent in RCTs has improved, but journals are less good at reporting this information for other study designs. Journals should publish this information for all research on human participants
Flexible Parametrization of Generalized Parton Distributions: The Chiral-Odd Sector
We present a physically motivated parameterization of the chiral-odd
generalized parton distributions. The parametrization is an extension of our
previous one in the chiral-even sector which was based on the reggeized diquark
model. While for chiral even generalized distributions a quantitative fit with
uncertainty estimation can be performed using deep inelastic scattering data,
nucleon electromagnetic, axial and pseudoscalar form factors measurements, and
all available deeply virtual Compton scattering data, the chiral-odd sector is
far less constrained. While awaiting the analysis of measurements on
pseudoscalar mesons exclusive electroproduction which are key for the
extraction of chiral odd GPDs, we worked out a connection between the
chiral-even and chiral-odd reduced helicity amplitudes using Parity
transformations. The connection works for a class of models including
two-components models. This relation allows us to estimate the size of the
various chiral odd contributions and it opens the way for future quantitative
fits.Comment: 35 pages, 18 figures, text changes, corrected typos, added fig.
High resolution spectroscopy of HgMn stars: a time of surprises
We present the results of a high spectral resolution study of a few
spectroscopic binaries with HgMn primary stars. We detect for the first time in
the spectra of HgMn stars that for many elements the line profiles are variable
over the rotation period. The strongest profile variations are found for the
elements Pt, Hg, Sr, Y, Zr, Mn, Ga, He and Nd. The slight variability of He and
Y is also confirmed from the study of high resolution spectra of another HgMn
star, alpha And.Comment: 2 pages, 2 figures, to appear in "Precision Spectroscopy in
Astrophysics
Malmquist Bias and the Distance to the Virgo Cluster
This paper investigates the impact of Malmquist bias on the distance to the
Virgo cluster determined by the H_0 Key Project using M100, and consequently on
the derived value of H_0. Malmquist bias is a volume-induced statistical effect
which causes the most probable distance to be different from the raw distance
measured. Consideration of the bias in the distance to the Virgo cluster raises
this distance and lowers the calculated value of H_0. Monte Carlo simulations
of the cluster have been run for several possible distributions of spirals
within the cluster and of clusters in the local universe. Simulations
consistent with known information regarding the cluster and the errors of
measurement result in a bias of about 6.5%-8.5%. This corresponds to an
unbiased distance of 17.2-17.4 Mpc and a value of H_0 in the range 80-82
km/s/Mpc.
The problem of determining the bias to Virgo illustrates several key points
regarding Malmquist bias. Essentially all conventional astronomical distance
measurements are subject to this bias. In addition, the bias accumulates when
an attempt is made to construct "distance ladders" from measurements which are
individually biased. As will be shown in the case of Virgo, the magnitude and
direction of the bias are sensitive to the spatial distribution of the parent
poputation from which the observed object is drawn - a distribution which is
often poorly known. This leads to uncertainty in the magnitude of the bias, and
adds to the importance of minimizing the number of steps in "distance ladders".Comment: 19 pages, 3 figures, Latex, To appear in Ap
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