1,669 research outputs found
Évaluation de la capacité de rétention des métaux dissous d'un marais artificiel en utilisant le périphyton et le gastéropode Helisoma trivolvis
Le but de cette étude est de déterminer si le périphyton et le gastéropode pulmoné Helisoma trivolvis peuvent être utilisés pour évaluer la capacité de rétention des métaux dissous d'un marais construit. Cette étude a été menée dans un marais de la région d'Ottawa-Carleton (Ontario, Canada), qui a été construit en 1995 afin d'améliorer la qualité des eaux de ruissellement provenant d'un bassin versant à usage résidentiel et agricole. Au cours du mois de septembre 1999, des échantillons d'eau ont été prélevés, des escargots (H. trivolvis) ont été recoltés et un substrat artificiel a été utilisé pour faire croître du périphyton, à l'entrée et à la sortie d'eau du marais. En moyenne, les calculs de balance de masse indiquaient une rétention des formes dissoutes du Cu, Mn, Ni et Zn dans le marais. Cependant, les tendances observées pour les concentrations de métaux dissous et pour les concentrations dans les organismes différaient pour certains métaux. Les concentrations de Cd et Ni dans les tissus de H. trivolvis et le périphyton étaient significativement plus élevées à l'entrée qu'à la sortie. Cependant, les concentrations de Cr et Al dans les organismes n'étaient pas significativement différentes entre l'entrée et la sortie alors que celle de Mn était significativement plus élevée à la sortie du marais. Pour tous les métaux sauf le Cd et le Zn, les concentrations dans le périphyton étaient en moyenne plus elevées que celles dans les escargots. Le périphyton peut donc fournir une mesure plus conservatrice de la contamination du milieu pas les métaux. Cette étude montre l'importance de considérer, non-seulement les mesures chimiques, mais aussi les mesures biologiques, dans l'évaluation de l'efficacité d'un ouvrage de contrôle de pollution.Urban and agricultural development has had a significant impact on the water quality of rivers and lakes around the world. In the last few decades, constructed wetlands have been designed as wastewater treatment systems to prevent water quality deterioration in natural receiving waters. Constructed wetlands are built because they are considered sinks for many pollutants thereby protecting the water quality of downstream ecosystems. The treatment performance of these wetlands is generally assessed using mass balance calculations. However, the retention of metals by constructed wetlands is highly variable and the factors involved are still poorly understood. If wetlands are sinks for metals, the metal content of organisms should be lower downstream than upstream. In this context, organisms can be useful to assess the retention or transformation of metals by wetlands.The objective of this study was to determine whether periphyton and the gastropod Helisoma trivolvis could be used to evaluate the retention of dissolved metals in a constructed wetland. H. trivolvis is a freshwater pulmonate snail widespread in ponds across North America. It feeds mostly on periphyton and is more or less sedentary. Snails have been used as biomonitors because several species are metal tolerant. However, compared to snails, periphytic microorganisms may track more closely dissolved metal concentrations as they take up metals principally from the water column.This study was conducted at the Monahan Pond in Kanata, Ontario (Canada). This wetland was built in 1995 to treat run-off from an agricultural and residential watershed. Water chemistry samples, snails and periphyton grown on artificial substrata were collected at both the inlet and the outlet of the wetland in the fall of 1999. Tissue samples were digested with concentrated nitric acid and metal analyses were done by ICP-MS (Inductively Coupled Plasma Mass Spectrometry). During the experiment several chemical parameters differed between the inlet and the outlet. Alkalinity was significantly higher at the inflow and all major cation concentrations were higher at the inflow. The temperature was on average 3 ºC higher at the outlet. Mass balance calculations showed that the wetland was a sink for most dissolved metals. Snails and periphyton tissue metal concentrations were higher at the inflow than at the outlet for Cd and Ni. However, no significant differences were observed between inflow and outlet tissue concentrations for Cr and Al, whereas Mn was actually significantly higher at the outlet. As a result, the metal content of the organisms did not consistently reflect the dissolved metal concentrations in water. For all metals except Cd and Zn, periphyton concentrations were on average higher than snail metal concentrations. Periphyton analyses can provide a more conservative measure of metal contamination and, when artificial substrates are used, correspond to defined and known periods of exposure.This study demonstrates that constructed wetlands may lead to increased metal content of downstream organisms even if these wetlands appear to be overall sinks for dissolved metals based on mass balance calculations. It also shows the need to consider not only metal concentrations, but also biological data when assessing the performance of pollution control facilities
Normal tau polarisation as a sensitive probe of CP violation in chargino decay
CP violation in the spin-spin correlations in chargino production and
subsequent two-body decay into a tau and a tau-sneutrino is studied at the ILC.
From the normal polarisation of the tau, an asymmetry is defined to test the
CP-violating phase of the higgsino mass parameter \mu. Asymmetries of more than
\pm70% are obtained, also in scenarios with heavy first and second generation
sfermions. Bounds on the statistical significances of the CP asymmetries are
estimated. As a result, the normal tau polarisation in the chargino decay is
one of the most sensitive probes to constrain or measure the phase \phi_\mu at
the ILC, motivating further detailed experimental studies.Comment: 20 pages, 10 figures, gzipped tar fil
Neutralino Pair Production and 3-Body Decays at Linear Colliders as Probes of CP Violation in the Neutralino System
In the CP-invariant supersymmetric theories, the steep S-wave (slow P-wave)
rise of the cross section for any non-diagonal neutralino pair production in
annihilation, (), near threshold is accompanied by the slow P-wave (steep S-wave) decrease
of the fermion invariant mass distribution of the 3-body neutralino decay,
( or ), near the end
point. These selection rules, unique to the neutralino system due to its
Majorana nature, guarantee that the observation of simultaneous sharp S-wave
excitations of the production cross section near threshold and the lepton and
quark invariant mass distribution near the end point is a qualitative,
unambiguous evidence for CP violation in the neutralino system.Comment: 11 pages, 1 eps figure, a reference adde
Regular vs. classical M\"obius transformations of the quaternionic unit ball
The regular fractional transformations of the extended quaternionic space
have been recently introduced as variants of the classical linear fractional
transformations. These variants have the advantage of being included in the
class of slice regular functions, introduced by Gentili and Struppa in 2006, so
that they can be studied with the useful tools available in this theory. We
first consider their general properties, then focus on the regular M\"obius
transformations of the quaternionic unit ball B, comparing the latter with
their classical analogs. In particular we study the relation between the
regular M\"obius transformations and the Poincar\'e metric of B, which is
preserved by the classical M\"obius transformations. Furthermore, we announce a
result that is a quaternionic analog of the Schwarz-Pick lemma.Comment: 14 page
A concise synthesis of a methyl ester 2-resorcinarene: A chair-conformation macrocycle
Anions are important hydrogen bond acceptors in a range of biological, chemical, environ-mental and medical molecular recognition processes. These interactions have been exploited for the design and synthesis of ditopic resorcinarenes as the hydrogen bond strength can be tuned through the modification of the substituent at the 2-position. However, many potentially useful compounds, especially those incorporating electron-withdrawing functionalities, have not been prepared due to the challenge of their synthesis: their incorporation slows resorcinarene formation that is accessed by electrophilic aromatic substitution. As part of our broader campaign to employ resorcinarenes as selective recognition elements, we need access to these specialized materials. In this article, we report a straightforward synthetic pathway for obtaining a 2-(carboxymethyl)-resorcinarene, and resorcinarene esters in general. We discuss the unusual conformation it adopts and propose that this arises from the electron-withdrawing nature of the ester substituents that renders them better hydrogen bond acceptors than the phenols, ensuring that each of them acts as a donor only. Density Functional Theory (DFT) calculations show that this conformation arises as a consequence of the unusual configurational isomerism of this compound and interruption of the archetypal hydrogen bonding by the ester functionality
Dynamical-charge neutrality at a crystal surface
For both molecules and periodic solids, the ionic dynamical charge tensors
which govern the infrared activity are known to obey a dynamical neutrality
condition. This condition enforces their sum to vanish (over the whole finite
system, or over the crystal cell, respectively). We extend this sum rule to the
non trivial case of the surface of a semiinfinite solid and show that, in the
case of a polar surface of an insulator, the surface ions cannot have the same
dynamical charges as in the bulk. The sum rule is demonstrated through
calculations for the Si-terminated SiC(001) surface.Comment: 4 pages, latex file, 1 postscript figure automatically include
Ice: a strongly correlated proton system
We discuss the problem of proton motion in Hydrogen bond materials with
special focus on ice. We show that phenomenological models proposed in the past
for the study of ice can be recast in terms of microscopic models in close
relationship to the ones used to study the physics of Mott-Hubbard insulators.
We discuss the physics of the paramagnetic phase of ice at 1/4 filling (neutral
ice) and its mapping to a transverse field Ising model and also to a gauge
theory in two and three dimensions. We show that H3O+ and HO- ions can be
either in a confined or deconfined phase. We obtain the phase diagram of the
problem as a function of temperature T and proton hopping energy t and find
that there are two phases: an ordered insulating phase which results from an
order-by-disorder mechanism induced by quantum fluctuations, and a disordered
incoherent metallic phase (or plasma). We also discuss the problem of
decoherence in the proton motion introduced by the lattice vibrations (phonons)
and its effect on the phase diagram. Finally, we suggest that the transition
from ice-Ih to ice-XI observed experimentally in doped ice is the
confining-deconfining transition of our phase diagram.Comment: 12 pages, 9 figure
Quantum geometry from 2+1 AdS quantum gravity on the torus
Wilson observables for 2+1 quantum gravity with negative cosmological
constant, when the spatial manifold is a torus, exhibit several novel features:
signed area phases relate the observables assigned to homotopic loops, and
their commutators describe loop intersections, with properties that are not yet
fully understood. We describe progress in our study of this bracket, which can
be interpreted as a q-deformed Goldman bracket, and provide a geometrical
interpretation in terms of a quantum version of Pick's formula for the area of
a polygon with integer vertices.Comment: 19 pages, 11 figures, revised with more explanations, improved
figures and extra figures. To appear GER
Theory of structural response to macroscopic electric fields in ferroelectric systems
We have developed and implemented a formalism for computing the structural
response of a periodic insulating system to a homogeneous static electric field
within density-functional perturbation theory (DFPT). We consider the
thermodynamic potentials E(R,eta,e) and F(R,eta,e) whose minimization with
respect to the internal structural parameters R and unit cell strain eta yields
the equilibrium structure at fixed electric field e and polarization P,
respectively. First-order expansion of E(R,eta,e) in e leads to a useful
approximation in which R(P) and eta(P) can be obtained by simply minimizing the
zero-field internal energy with respect to structural coordinates subject to
the constraint of a fixed spontaneous polarization P. To facilitate this
minimization, we formulate a modified DFPT scheme such that the computed
derivatives of the polarization are consistent with the discretized form of the
Berry-phase expression. We then describe the application of this approach to
several problems associated with bulk and short-period superlattice structures
of ferroelectric materials such as BaTiO3 and PbTiO3. These include the effects
of compositionally broken inversion symmetry, the equilibrium structure for
high values of polarization, field-induced structural phase transitions, and
the lattice contributions to the linear and the non-linear dielectric
constants.Comment: 19 pages, with 15 postscript figures embedded. Uses REVTEX4 and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/sai_pol/index.htm
Momentum asymmetries as CP violating observables
Three body decays can exhibit CP violation that arises from interfering
diagrams with different orderings of the final state particles. We construct
several momentum asymmetry observables that are accessible in a hadron collider
environment where some of the final state particles are not reconstructed and
not all the kinematic information can be extracted. We discuss the
complications that arise from the different possible production mechanisms of
the decaying particle. Examples involving heavy neutralino decays in
supersymmetric theories and heavy Majorana neutrino decays in Type-I seesaw
models are examined.Comment: 20 pages, 9 figures. Clarifying comments and one reference added,
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