Explicit time-reversible orbit integration in Particle In Cell codes with static homogeneous magnetic field

A new explicit time-reversible orbit integrator for the equations of motion in a static homogeneous magnetic field – called Cyclotronic integrator – is presented. Like Spreiter and Walter’s Taylor expansion algorithm, for sufficiently weak electric field gradients this second order method does not require a fine resolution of the Larmor motion; it has however the essential advantage of being symplectic, hence time-reversible. The Cyclotronic integrator is only subject to a linear stability constraint (ΩΔt < π, Ω being the Larmor angular frequency), and is therefore particularly suitable to electrostatic Particle In Cell codes with uniform magnetic field where Ω is larger than any other characteristic frequency, yet a resolution of the particles’ gyromotion is required. Application examples and a detailed comparison with the well-known (time-reversible) Boris algorithm are presented; it is in particular shown that implementation of the Cyclotronic integrator in the kinetic codes SCEPTIC and Democritus can reduce the cost of orbit integration by up to a factor of ten.     

Magnetic normalization of particle size effects in a heavy metal pollution study of intertidal sediments from the Yangzte Estuary

Magnetic, granulometric and geochemical analyses were conducted on an intertidal sediment core from the Yangtze Estuary to evaluate the possibility of normalizing samples for particle size effects in a heavy metal pollution study by means of magnetic proxies. It has been found that the magnetic parameter_ϰARM, indicating fine grained ferrimagnetic minerals, correlates well with the clay content and organic matter concentration of the sediments._ϰARM also shows significant relationship with heavy metals. Therefore_ϰARM is proposed as a proxy for clay content in the sediments, and can be used to compensate for the particle size effect in sedimentary heavy metal records, where magnetic minerals are not subject to significant post-depositional alteration.

     

Atomgewichte

Ohne Zusammenfassung     

Ein Verfahren zur Bestimmung des Kalkbedarfs des Bodens

Ohne Zusammenfassung     

Die Trennung des Kupfers vom Cadmium

Ohne Zusammenfassung     

Convergence of phase interfaces in the van der Waals-Cahn-Hilliard theory

We study the general asymptotic behavior of critical points, including those of non-minimal energy type, of the functional for the van der Waals-Cahn-Hilliard theory of phase transitions. We prove that the interface is close to a hypersurface with mean curvature zero when no Lagrange multiplier is present, and with locally constant mean curvature in general. The energy density of the limiting measure has integer multiplicity almost everywhere modulo division by a surface energy constant. Received March 16, 1999 / Accepted June 11, 1999     

Uptake and biological responses to nano-Fe versus soluble FeCl3 in excised mussel gills

Nano-Fe particle uptake was experimentally examined in vitro using excised gills and blood cells of the edible blue mussel Mytilus sp. Whole gills were exposed to both Fe₂O₃ nanoparticles and a solution of the hydrated FeCl₃ salt, for up to 12 h, and blood cells for 30 min. Equimolar Fe⁺³ in the nano- and the soluble form was estimated under the assumption of dense spherical particles accommodating the same number of Fe⁺³ as in the dissolved salt solution, namely: 1,000 μg L⁻¹ Fe₂O₃ equivalent to 100 μg L⁻¹ FeCl₃·6H₂O. Putative toxic impact of nano-Fe in gill epithelia and blood cells was assessed by an array of techniques including light- and electron microscopy, biomarkers for oxidative stress (lipid peroxidation levels), neurotoxic effects (acetylcholinesterase activity) and cytotoxicity (neutral red retention). Total and filtered fractions (20 and 200 nm, respectively) of Fe were analysed by ICP-OES. Our results provide evidence for the following: (1) much of both the soluble (95%) and the nano-Fe (90%) were removed from the water column within 12 h; (2) dissolved- and nano-Fe seemed to follow different routes of uptake within the gill epithelium; (3) both nano-Fe and soluble FeCl₃ caused similar impairment of lysosomal stability in circulating blood cells; (4) lipid peroxidation in gills exposed to the two distinct forms of Fe was increased, while acetylcholinesterase activity was unaffected. In these short-term in vitro studies, there appears to be little difference in toxic response between exposure to the Fe salt and the nano-Fe indicating that, in this case, the nanoparticles do not invoke special properties affecting biological function in gills. However, with the use of nano-Fe as a food additive, clearly longer-term in vivo studies are warranted.     

Effects on feeding rate and biomarker responses of marine mussels experimentally exposed to propranolol and acetaminophen

Environmental risk assessments of human pharmaceuticals and other ‘emerging contaminants’ should integrate both population-relevant endpoints and biomarkers of potential modes of action in a range of species. Adult Mytilus galloprovincialis were exposed to the beta-adrenergic receptor blocker propranolol or to the anti-inflammatory drug acetaminophen (paracetamol), both commonly used therapeutic drugs present in aquatic ecosystems. Mussels were exposed under semi-static conditions for 10 days to either acetaminophen (CAS number 103-90-2; mean measured concentrations 23 and 403 μg/L) or propranolol hydrochloride (CAS number 318-98-9; mean measured propranolol concentrations 11 and 147 μg/L) at 15 ± 1 °C sea water. Feeding rate was assessed as an indicator of general toxicity. For propranolol, the 10-day no-observed effect concentration (^{feeding rate}NOEC) and lowest observed effect concentration (^{feeding rate}LOEC) were 11 and 147 μg/L, respectively. For acetaminophen, feeding rate was increased at both 23 and 403 μg/L, suggesting a 10-day ^{feeding rate}NOEC of 403 μg/L. Primarily, phase I carboxylesterase (CbE), phase II glutathione S-transferase (GST) and the anti-oxidant catalase activities were evaluated in digestive gland. Gill GST and acetylcholinesterase (AChE) activities were also measured. Lipid peroxidation (LPO) levels were measured in both tissues to assess oxidative stress. Some enzymatic activities in liver were also reduced after propranolol exposure whilst acetaminophen enhanced them (CbE p < 0.05). Acetaminophen exposure significantly increased hepatic LPO levels and inhibited AChE activity in gill (10-day NOEC and LOEC of 23 and 403 μg/L, respectively), whereas propranolol (11 μg/L) enhanced gill GST.     

Forces on a small grain in the nonlinear plasma wake of another

The transverse force on a spherical charged grain lying in the plasma wake of another grain is analyzed to assess the importance of ion-drag perturbation, in addition to the wake-potential-gradient. The ion-drag perturbation is intrinsically one order smaller than the wake-potential force in the ratio of grain size (r(p)) to Debye length (λ(De)). So ion-drag perturbation is important only in nonlinear wakes. Rigorous particle-in-cell calculations of the force are performed in the nonlinear regime with two interacting grains. It is found that even for quite large grains, r(p)/λ(De)=0.1, the force is dominated by the wake-potential gradient. The wake-potential structure can then help explain the preferred alignment of floating dust grains.