454 research outputs found
Scour features at wood bundles
Structures like blunt-nosed chevrons, log deflectors and double-winged log frames help in modifying the flow regime in the channel by concentrating the flow and increasing navigability. Moreover, they create scour pools in the downstream stilling basin, which can be used either as fish refuge or as an in-stream storage site for previously dredged material. In this respect, the use of wood debris in the channel in the form of wood bundles has gained attention for the ability of these structures to integrate into the surrounding fluvial habitat and to divert the flow partially towards the central part of the channel when placed in curves. Considering the absence of studies dealing with wood bundles as a restoration structure, the aim of this paper is to analyse the scour mechanism and equilibrium scour morphology of wood bundles in straight and curved channels. In doing so, a wide range of hydraulic conditions, structure positions and configurations were tested. Thereafter, dimensional analysis was carried out to derive useful empirical relationships to predict the maximum scour depth and length as well as the maximum dune height based on a novel, equivalent Froude number, which accounts for the effects of channel curvature and structure position. Moreover, the various resulting scour morphology types were classified, and conditions of their existence were determined depending on the abovementioned Froude number and other key hydraulic parameters
A Critical Analysis of Jet-Induced Scour Formulas
Many studies investigate erosive processes occurring in non-cohesive granular materials downstream of grade-control structures, dam spillways, headcuts, and other hydraulic structures. Because of the complexity of the scour mechanism, the analysis of the scour phenomenon caused by plunging jets is generally conducted by using physical models and particularly for specific structure geometries. In this regard, many researchers proposed empirical approaches to estimate the main scour lengths, but their contributions are limited to tested conditions and cannot be generalized. This lack of generality has been (partially) overcome by other, more recent, approaches, that are either semitheoretical or fully theoretical. Previous works assessed the predictive capability of the most well-known empirical relationships but did not present a comparative analysis between empirical and (semi- )theoretical relationships. The aim of this paper is to contribute to fill this gap of knowledge. Namely, we present an experimental validation of the most popular relationships using a large database. In addition, we compare the predictive capability of some (semi-)theoretical relationships with that of the best known empirical formulas. In doing so, we provide interesting insights into the different approaches, highlighting their limits in assessing the main scour features. Overall, this paper provides a critical and updated analysis of different approaches for scour problems caused by plunging jets
Strange quark matter in explosive astrophysical systems
Explosive astrophysical systems, such as supernovae or compact star binary
mergers, provide conditions where strange quark matter can appear. The high
degree of isospin asymmetry and temperatures of several MeV in such systems may
cause a transition to the quark phase already around saturation density.
Observable signals from the appearance of quark matter can be predicted and
studied in astrophysical simulations. As input in such simulations, an equation
of state with an integrated quark matter phase transition for a large
temperature, density and proton fraction range is required. Additionally,
restrictions from heavy ion data and pulsar observation must be considered. In
this work we present such an approach. We implement a quark matter phase
transition in a hadronic equation of state widely used for astrophysical
simulations and discuss its compatibility with heavy ion collisions and pulsar
data. Furthermore, we review the recently studied implications of the QCD phase
transition during the early post-bounce evolution of core-collapse supernovae
and introduce the effects from strong interactions to increase the maximum mass
of hybrid stars. In the MIT bag model, together with the strange quark mass and
the bag constant, the strong coupling constant provides a parameter
to set the beginning and extension of the quark phase and with this the mass
and radius of hybrid stars.Comment: 6 pages, 5 figures, talk given at the International Conference on
Strangeness in Quark Matter (SQM2009), Buzios, Brasil, September 28 - October
2, 2009, to be published in Journal Phys.
Signals of the QCD phase transition in core-collapse supernovae
We explore the implications of the QCD phase transition during the postbounce
evolution of core-collapse supernovae. Using the MIT bag model for the
description of quark matter and assuming small bag constants, we find that the
phase transition occurs during the early postbounce accretion phase. This stage
of the evolution can be simulated with general relativistic three-flavor
Boltzmann neutrino transport. The phase transition produces a second shock wave
that triggers a delayed supernova explosion. If such a phase transition happens
in a future galactic supernova, its existence and properties should become
observable as a second peak in the neutrino signal that is accompanied by
significant changes in the energy of the emitted neutrinos. In contrast to the
first neutronization burst, this second neutrino burst is dominated by the
emission of anti-neutrinos because the electron-degeneracy is lifted when the
second shock passes through the previously neutronized matter.Comment: 5 pages, 3 figures, 1 table, submitted to PR
Late Summer Phytoplankton Blooms in the Changing Polar Environment of the Kongsfjorden (Svalbard, Arctic)
Kongsfjorden (Spitsbergen, Svalbard) is an inlet treated as a model site for studies on the impact of climate change in the Arctic due to its hydrological features. In this research, seven-days monitoring was carried out to evaluate the effects of hydrological variability on phytoplankton biomass and diversity in the late summer period. Temperature, salinity, nutrients, total suspended matter, phytoplankton abundance and biomass were determined for each sample. The thermo-haline properties of the column water seemed to affect phytoplankton communities. Their abundances and biomass were correlated with the amount of the total suspended matter. Moreover, species composition and biomass dramatically changed throughout the study period. Cold-water and Atlantic species were replaced by temperatewarm water dinoflagellates, including harmful species. An increase in phytoplankton biomass as well as the presence of dinoflagellate aggregations, mainly composed of Prorocentrum cf. gracile, were detected. This kind of algal accumulation is a new phenomenon in the Arctic and was probably related to the mobilization of sediment-rich glacial meltwaters. These findings, even if preliminary, suggest the need to study how additional biomass pulses and the increase of harmful species may alter the food web structure and the biogeochemical cycles, leading to major ecosystem changes
Deep-Learning-Driven Techniques for Real-Time Multimodal Health and Physical Data Synthesis
With the advent of Artificial Intelligence for healthcare, data synthesis methods present crucial benefits in facilitating the fast development of AI models while protecting data subjects and bypassing the need to engage with the complexity of data sharing and processing agreements. Existing technologies focus on synthesising real-time physiological and physical records based on regular time intervals. Real health data are, however, characterised by irregularities and multimodal variables that are still hard to reproduce, preserving the correlation across time and different dimensions. This paper presents two novel techniques for synthetic data generation of real-time multimodal electronic health and physical records, (a) the Temporally Correlated Multimodal Generative Adversarial Network and (b) the Document Sequence Generator. The paper illustrates the need and use of these techniques through a real use case, the H2020 GATEKEEPER project of AI for healthcare. Furthermore, the paper presents the evaluation for both individual cases and a discussion about the comparability between techniques and their potential applications of synthetic data at the different stages of the software development life-cycle
Quantification of fluoroquinolone uptake through the outer membrane channel OmpF of Escherichia coli
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Decreased drug accumulation is a common cause of antibiotic resistance in microorganisms. However, there are few reliable general techniques capable of quantifying drug uptake through bacterial membranes. We present a semiquantitative optofluidic assay for studying the uptake of autofluorescent drug molecules in single liposomes. We studied the effect of the Escherichia coli outer membrane channel OmpF on the accumulation of the fluoroquinolone antibiotic, norfloxacin, in proteoliposomes. Measurements were performed at pH 5 and pH 7, corresponding to two different charge states of norfloxacin that bacteria are likely to encounter in the human gastrointestinal tract. At both pH values, the porins significantly enhance drug permeation across the proteoliposome membranes. At pH 5, where norfloxacin permeability across pure phospholipid membranes is low, the porins increase drug permeability by 50-fold on average. We estimate a flux of about 10 norfloxacin molecules per second per OmpF trimer in the presence of a 1 mM concentration gradient of norfloxacin. We also performed single channel electrophysiology measurements and found that the application of transmembrane voltages causes an electric field driven uptake in addition to concentration driven diffusion. We use our results to propose a physical mechanism for the pH mediated change in bacterial susceptibility to fluoroquinolone antibiotics.This work was supported by a European Research Council (ERC) Grant (261101
Passmembrane) to UFK. JC acknowledges support from an Internal Graduate Studentship, Trinity
College, Cambridge, and a Research Studentship from the Cambridge Philosophical Society. SP
was supported by the Leverhulme Trust through an Early Career Fellowship. TM acknowledges
support from the Konrad-Adenauer Foundation and the German National Merit Foundation. HB,
YB and MW are part of the TRANSLOCATION consortium and have received support from the
Innovative Medicines Joint Undertaking under grant agreement 115525, the European Union’s
seventh framework program (FP7/2007-2013), and European Federation of Pharmaceutical
Industries and Associates companies in-kind contribution
Strange Exotic States and Compact Stars
We discuss the possible appearance of strange exotic multi-quark states in
the interior of neutron stars and signals for the existence of strange quark
matter in the core of compact stars. We show how the in-medium properties of
possible pentaquark states are constrained by pulsar mass measurements. The
possibility of generating the observed large pulsar kick velocities by
asymmetric emission of neutrinos from strange quark matter in magnetic fields
is outlined.Comment: 10 pages, invited talk given at the International Conference on
Strangeness in Quark Matter 2006 (SQM2006), UCLA, USA, March 26-31, 2006,
Journal of Physics G in press, refs. adde
Ultrafast dynamics in unaligned MWCNTs decorated with metal nanoparticles
The relaxation dynamics of unaligned multi-walled carbon nanotubes decorated with metallic nanoparticles have been studied by using transient optical measurements. The fast dynamics due to the short-lived free-charge carriers excited by the pump are not affected by the presence of nanoparticles. Conversely, a second long dynamics, absent in bare carbon nanotubes, appears only in the decorated samples. A combination of experiment and theory allows us to ascribe this long dynamics to relaxation channels involving electronic states localized at the tube-nanoparticle interface
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