95,764 research outputs found
Natural and laser-induced cavitation in corn stems: On the mechanisms of acoustic emissions
Water in plant xylem is often superheated, and therefore in a meta-stable
state. Under certain conditions, it may suddenly turn from the liquid to the
vapor state. This cavitation process produces acoustic emissions. We report the
measurement of ultrasonic acoustic emissions (UAE) produced by natural and
induced cavitation in corn stems. We induced cavitation and UAE in vivo, in
well controlled and reproducible experiments, by irradiating the bare stem of
the plants with a continuous-wave laser beam. By tracing the source of UAE, we
were able to detect absorption and frequency filtering of the UAE propagating
through the stem. This technique allows the unique possibility of studying
localized embolism of plant conduits, and thus to test hypotheses on the
hydraulic architecture of plants. Based on our results, we postulate that the
source of UAE is a transient "cavity oscillation" triggered by the disruptive
effect of cavitation inception.Comment: 8 pages, 5 figure
Study of passenger-bus-traffic interactions on bus stop operations
Buses are the unsung heroes of public transport in modern cities around the world in high,medium and low income countries. However, the bus system is usually cobbled by poordesign which has resulted from poor understanding of how a busThis paper examines theimpacts of the interactions between buses, passengers and traffic on bus operations, especiallyin relation to delays and capacity at bus stops. First, the principles of bus stop operations arepresented. Issues like the stages of bus stop operations, the classification of times spent at busstops, causes of delays, and the interaction between bus flow and stop delays are analysed.This leads to the necessity of microscopic simulation to study stops operations. Then, anillustration of the sort of understanding that can be achieved with a simulation modem isshown. Simulation experiments regarding arrival patterns of buses and passengers, boardingtimes, difficulties for buses to leave the stop, and vehicle capacity are presented. Resultsindicate that it is important not to underestimate the real situation found at bus stops, asdesigning for ideal conditions will be insufficient if the reality is different
Linking microsimulators of bus stops and traffic operations: the case of PASSION and BusSIGSIM
The aim of this article is to explore the linkage of two microsimulators developed at theUniversity College London. At present, these models deal independently with buses ateither bus stops or traffic networks. First, both microsimulators are described in somedetail. The generic way in which both models can be connected is then proposed. As aresult of this analysis, the main issues for a comprehensive introduction of public transportvehicles (buses) into microscopic traffic simulators are highlighted. One practical outcomeof this study is that the improvement in the representation of buses in microscopic trafficsimulators will allow the engineers to take into account traffic management measures thatotherwise will not be assessed
Measurement errors with low-cost citizen science radiometers
The KdUINO is a Do-It-Yourself buoy with low-cost radiometers that
measure a parameter related to water transparency, the diffuse attenuation coefficient
integrated into all the photosynthetically active radiation. In this contribution,
we analyze the measurement errors of a novel low-cost multispectral radiometer
that is used with the KdUINO.Peer Reviewe
Ediacaran Obduction of a Fore-Arc Ophiolite in SW Iberia: A Turning Point in the Evolving Geodynamic Setting of Peri- Gondwana
The Calzadilla Ophiolite is an ensemble of mafic and ultramafic rocks that represents the
transition between lower crust and upper mantle of a Cadomian (peri-Gondwanan) fore arc. Mapping and
structural analysis of the ophiolite demonstrates that it was obducted in latest Ediacaran times, because the
Ediacaran-Early Cambrian sedimentary series (Malcocinado Formation) discordantly covers it. The ophiolite
and emplacement-related structures are affected by Variscan deformation (Devonian-Carboniferous),
which includes SW verging overturned folds (D1) and thrusts (D2), upright folds (D3), extensional faults (D4),
and later faults (D5). These phases of deformation are explained in the context of Variscan tectonics as the
result of the progressive collision between Gondwana and Laurussia. Qualitative unstraining of Variscan
deformation reveals the primary geometry of Ediacaran-Cambrian structures and uncovers the generation of
east verging thrusts as responsible for the primary obduction of the Calzadilla Ophiolite. Restoration of
planar and linear structures associated with this event indicates an Ediacaran, east directed obduction of the
ophiolite, that is, emplacement of the Cadomian fore arc onto inner sections of the northern margin of
Gondwana. According to regional data, the obduction separates two extension-dominated stages in the
tectonic evolution of the African margin of northern Gondwana preserved in southern Europe. Preobduction
extension brought about the onset and widening of fore-arc and back-arc basins in the external part
of the continent, while postobduction extension facilitated the formation of extensional migmatitic domes,
an oceanward migration of back-arc spreading centers across peri-Gondwana, and the eventual opening
of a major basin such as the Rheic Ocean
A cluster expansion approach to renormalization group transformations
The renormalization group (RG) approach is largely responsible for the
considerable success which has been achieved in developing a quantitative
theory of phase transitions. This work treats the rigorous definition of the RG
map for classical Ising-type lattice systems in the infinite volume limit at
high temperature. A cluster expansion is used to justify the existence of the
partial derivatives of the renormalized interaction with respect to the
original interaction. This expansion is derived from the formal expressions,
but it is itself well-defined and convergent. Suppose in addition that the
original interaction is finite-range and translation-invariant. We will show
that the matrix of partial derivatives in this case displays an approximate
band property. This in turn gives an upper bound for the RG linearization.Comment: 13 page
90Sr uptake in the freshwater liverwort Riccia fluitans L.
90Sr is a radioactive isotope of strontium produced by nuclear fission, with a half-life of 28.8 years. This artificial radioisotope is present in natural ecosystems as the results of radioactive fallout from nuclear weapons or releases during nuclear power plants accidents; because of its similarity with Ca*2 is quickly incorporated into the biota. The high mobility of Sr+2 in aquatic compared with terrestrial ecosystems makes the uptake and accumulation of 90Sr+2 higher in aquatic than in terrestrial plants. Here we analyse the uptake rate, kinetics and retention, concentration factor (CF) of 90Sr in the freshwater liverwort Riccia fluiants. 90Sr uptake by R. fluitnas shows a bi-phasic kinetics that fits the Michaelis & Menten model in both micro and milimolar concentration ranges. Apparent semi-saturation constants (KM) were 15 µM and 2 mM for the high and low affinity ranges, respectively. The presence of the K+ channels blocker tetraethyamonium (10 mM TEA) inhibits 90Sr uptake by a 25%. However, the presence of 1 mM La+3 completely inhibits 90Sr uptake in this plant. Maximum incorporation rate occurs at alkaline external pH (8.3), either in plants grown in the presence of K+ or in the absence. Finally, gradual increases of the Ca2+ concentration in the medium progressively inhibits 90Sr uptake. CF values are higher in K+ -deficient plants, CF maximum of 1500, than in K+ -sufficient, (maximum CF of 600) and show similar responses to inhibitors, pH or Ca2+. CF values progressively decrease at increasing external Ca2+ concentrations, higher CF values are found at pH 8.3 but lower values are observed in the presence of TEA, being close to zero in the presence of La+3. The different 90Sr uptake rates in K+-sufficient and K+-deficient plants and TEA sensitivity indicate that one part of 90Sr would be transported through non-selective cation channels. Furthermore, Ca2+ and La3+ sensitivities suggest that 90Sr could be incorporated through Ca2+ channels.Universidad de Málaga. Campus de Excelencia Internacional AndalucĂa Tech.
Spanish MINECO: BFU2017-85117-R and BIO2016-81957-RED
Non-homogeneous polygonal Markov fields in the plane: graphical representations and geometry of higher order correlations
We consider polygonal Markov fields originally introduced by Arak and
Surgailis (1989). Our attention is focused on fields with nodes of order two,
which can be regarded as continuum ensembles of non-intersecting contours in
the plane, sharing a number of features with the two-dimensional Ising model.
We introduce non-homogeneous version of polygonal fields in anisotropic
enviroment. For these fields we provide a class of new graphical constructions
and random dynamics. These include a generalised dynamic representation,
generalised and defective disagreement loop dynamics as well as a generalised
contour birth and death dynamics. Next, we use these constructions as tools to
obtain new exact results on the geometry of higher order correlations of
polygonal Markov fields in their consistent regime.Comment: 54 page
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