863 research outputs found
Velocity profiles in shear-banding wormlike micelles
Using Dynamic Light Scattering in heterodyne mode, we measure velocity
profiles in a much studied system of wormlike micelles (CPCl/NaSal) known to
exhibit both shear-banding and stress plateau behavior. Our data provide
evidence for the simplest shear-banding scenario, according to which the
effective viscosity drop in the system is due to the nucleation and growth of a
highly sheared band in the gap, whose thickness linearly increases with the
imposed shear rate. We discuss various details of the velocity profiles in all
the regions of the flow curve and emphasize on the complex, non-Newtonian
nature of the flow in the highly sheared band.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
The reuse of sediments dredged from artificial reservoirs for beach nourishment: Technical and economic feasibility
Sedimentation has significant impacts on the useful capacity of an artificial reservoir, a resource to preserve. Interventions of dredging are therefore often unavoidable, even because decommissioning of dams is often impossible in many contexts and entails high costs. Dredging generates an undesired accumulation of materials that represent an environmental cost, but that could be used as intermediate products in other processes, such as beach nourishment. The study develops a method for the evaluation of the feasibility of an investment aimed at coastal nourishment with sediments dredged from artificial reservoirs. The method considers the set of technical conditions that make such use possible. The presence of economies of scope, with environmental diseconomies utilized as joint product, modifies the evaluation approach. The results of the approach show a possible environmental and economic sustainability of the proposed investment even in the presence of highly unfavorable scenarios. The study applies the feasibility appraisal to the case of the Guardialfiera reservoir in Molise, Italy
Semiempirical model for assessing dewatering process by flocculation of dredged sludge in an artificial reservoir
Understanding sedimentation behaviour of clay material is crucial in planning project for sediment removal from bottom of a reservoir. The sedimentation of samples taken from Occhito reservoir ( Italy) is investigated. Samples containing and not containing polyacrylamide have been monitored. Results reveal that polymer induces bridging flocculation and the particle-size distribution tends to become uniform. The sedimentation profiles follow a mater curve. Such experimental observation is used to develop a semi-empirical model for assessment of dewatering process by flocculation of dredged sludge in artificial reservoir. A two-step stage model for assessing the volume of solids in a geotextile tube is suggested. Such model is based on the idea that for very long dewatering times solids reach the configuration of free sedimentation
Cohomological tautness for Riemannian foliations
In this paper we present some new results on the tautness of Riemannian
foliations in their historical context. The first part of the paper gives a
short history of the problem. For a closed manifold, the tautness of a
Riemannian foliation can be characterized cohomologically. We extend this
cohomological characterization to a class of foliations which includes the
foliated strata of any singular Riemannian foliation of a closed manifold
A performance prediction model for pumps as turbines (PATs)
In recent years, the interest towards the use of pumps operating as turbines (PATs) for the generation of electrical energy has increased, due to the low cost of implementation and maintenance. The main issue that inhibits a wider use of PATs is the lack of corresponding characteristic curves, because manufacturers usually provide only the pump-mode performance characteristics. In the PAT selection phase, the lack of turbine-mode characteristic curves forces users to expend expensive and time-consuming efforts in laboratory testing. In the technical literature, numerous methods are available for the prediction of PAT turbine-mode performance based on the pump-mode characteristics, but these models are usually calibrated making use of few devices. To overcome this limit, a performance database called Redawn is presented and the data collected are used to calibrate novel PAT performance models
Photometric type Ia supernova surveys in narrow band filters
We study the characteristics of a narrow band type Ia supernova survey
through simulations based on the upcoming Javalambre Physics of the
accelerating universe Astrophysical Survey (J-PAS). This unique survey has the
capabilities of obtaining distances, redshifts, and the SN type from a single
experiment thereby circumventing the challenges faced by the resource-intensive
spectroscopic follow-up observations. We analyse the flux measurements
signal-to-noise ratio and bias, the supernova typing performance, the ability
to recover light curve parameters given by the SALT2 model, the photometric
redshift precision from type Ia supernova light curves and the effects of
systematic errors on the data. We show that such a survey is not only feasible
but may yield large type Ia supernova samples (up to 250 supernovae at
per month of search) with low core collapse contamination ( per
cent), good precision on the SALT2 parameters (average ,
and ) and on the distance modulus (average
, assuming an intrinsic scatter
), with identified systematic uncertainties
. Moreover, the
filters are narrow enough to detect most spectral features and obtain excellent
photometric redshift precision of , apart from 2 per
cent of outliers. We also present a few strategies for optimising the survey's
outcome. Together with the detailed host galaxy information, narrow band
surveys can be very valuable for the study of supernova rates, spectral feature
relations, intrinsic colour variations and correlations between supernova and
host galaxy properties, all of which are important information for supernova
cosmological applications.Comment: 20 pages, 12 tables and 26 figures. Version accepted by MNRAS, with
results slightly different from previous on
Sporangia and Spores in the Fern Genera Spicantopsis and Struthiopteris (Blechnaceae, Polypodiopsida)
Struthiopteris (Blechnaceae) has recently been classified on the basis of molecular and morphological evidence, and some of its species are now included in the sister genus Spicantopsis. However, the lack of studies on several important morphological features impedes a sound assessment of their congruence with this new systematic arrangement, as well as of their range of variation and taxonomic value in this group of ferns. Here we present a study on the spores and sporangia using both light and scanning electron microscopy in Struthiopteris and Spicantopsis, using samples of all their species, and almost all their varieties. We provide full morphological descriptions of the spores and sporangia of all these taxa. We point out that the perispore structure and ornamentation and the number and the thickness of stomium cells in the sporangium clearly distinguish both generaThe Universidad Complutense de Madrid partially supported this research through the funding of a project PR26/16-20295, and a field trip to Iceland (International Mobility Program 2016
Entropic phase separation of linked beads
We study theoretically a model system of a transient network of microemulsion
droplets connected by telechelic polymers and explain recent experimental
findings. Despite the absence of any specific interactions between either the
droplets or polymer chains, we predict that as the number of polymers per drop
is increased, the system undergoes a first order phase separation into a dense,
highly connected phase, in equilibrium with dilute droplets, decorated by
polymer loops. The phase transition is purely entropic and is driven by the
interplay between the translational entropy of the drops and the
configurational entropy of the polymer connections between them. Because it is
dominated by entropic effects, the phase separation mechanism of the system is
extremely robust and does not depend on the particlular physical realization of
the network. The discussed model applies as well to other polymer linked
particle aggregates, such as nano-particles connected with short DNA linkers
Valorization of local almond genotypes regarding their biochemical and mineral composition: abstract
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