Instability Heating of Sympathetically-Cooled Ions in a Linear Paul Trap

Sympathetic laser cooling of ions stored within a linear-geometry, radio frequency, electric-quadrupole trap has been investigated using computational and theoretical techniques. The simulation, which allows 5 sample ions to interact with 35 laser-cooled atomic ions, revealed an instability heating mechanism, which can prevent ions below a certain critical mass from being sympathetically cooled. This critical mass can however be varied by changing the trapping field parameters thus allowing ions with a very large range of masses to be sympathetically cooled using a single ion species. A theoretical explanation of this instability heating mechanism is presented which predicts that the cooling-heating boundary in trapping parameter space is a line of constant $q_u$ (ion trap stability coefficient), a result supported by the computational results. The threshold value of $q_u$ depends on the masses of the interacting ions. A functional form of this dependence is given

Opportunities for financing sustainable development using complementary local currencies

Financing building retrofit projects that contribute to climate change mitigation has always represented a significant barrier. With 28% of global emissions coming from existing buildings, it is of paramount importance to carry out retrofit measures that lead to significant reduction of these emissions. Whilst this is perfectly possible to achieve with current methods and current technology, there is no sufficient conventional finance to carry out zero carbon retrofit at scale required for climate change mitigation. The article introduces an alternative and sustainable business model that creates new opportunities for financing zero carbon retrofit of buildings. It demonstrates that the value of solar energy falling on roofs of buildings can become a driver for new local economic systems, and discusses the requirements for practical application.Peer reviewedFinal Published versio

Spatial Structure of Ion Beams in an Expanding Plasma

We report spatially resolved perpendicular and parallel, to the magnetic field, ion velocity distribution function (IVDF) measurements in an expanding argon helicon plasma. The parallel IVDFs, obtained through laser induced fluorescence (LIF), show an ion beam with v ≈ 8000 m/s flowing downstream and confined to the center of the discharge. The ion beam is measurable for tens of centimeters along the expansion axis before the LIF signal fades, likely a result of metastable quenching of the beam ions. The parallel ion beam velocity slows in agreement with expectations for the measured parallel electric field. The perpendicular IVDFs show an ion population with a radially outward flow that increases with distance from the plasma axis. Structures aligned to the expanding magnetic field appear in the DC electric field, the electron temperature, and the plasma density in the plasma plume. These measurements demonstrate that at least two-dimensional and perhaps fully three-dimensional models are needed to accurately describe the spontaneous acceleration of ion beams in expanding plasmas

Platinum instability in PEM fuel cells MEA’s subjected to chloride contamination

In this work a low power fuel cell, intended for passive management of water, was operated integrating a range of relative humidity (RH) from ~30 to 80% and temperatures from 5 to 55 ºC. The stack was fed with pure hydrogen. An open air cathode was designed for easy water removal and stack cooling. The stack uses own design flow field drawn on graphite plates from Schunk and a commercial MEA with carbon supported catalyst containing 0.3 mgcm-2 Pt. Polarization curves were registered for a full stack characterization using a purpose-built test station and a climatic chamber with temperature and RH control. Results indicated that 60% RH is associated to maximum fuel cell performance over the studied temperature range. While water management is done in a passive fashion, heat management is done on the basis of the injection of air at the cathode with the fuel cell showing good performances at relatively low currents where back diffusion towards the anode is favored. The loss of performance with temperature increase was related to an increase in the membrane resistance which may correspond to loss of water on the anode side. Performances at temperatures lower that room temperature showed only slight decrease in power. An examination of the fuel cell components after 100 h of operation revealed that chloride contamination has produced cathode failure associated to catalyst migration anomalies favored by operation conditions that allowed platinum particles to break free from their carbon backing and migrate toward the polymer electrolyte. Migration resulted in precipitation with larger mean particle size distribution within the solid electrolyte when compared to the original catalyst layer, rendering a very significant loss of thickness in the cathode material. Coarsening of platinum particles occurs at nano and micro-scale. The mechanism for the lost of catalyst by dissolution and growth is discussed on the basis of a joint electrochemical and SEM/TEM study

Materials degradation mechanisms in an open cathode low power PEM Fuel Cell

In this work, a low power PEM fuel cell intended for passive management of water was operated integrating a range of relative humidity (RH) from 30 to 80% and temperatures from 5 to 55ºC. An open air cathode, provided with an excess air stoichiometry condition, was designed for easy water removal and stack cooling. The 4 cell stack was fed with pure hydrogen and uses own design flow field drawn on graphite plates from Schunk and a commercial MEA with carbon supported catalyst containing 0.3 mgcm-2 Pt. Full stack characterization was made using a purpose-built test station and a climatic chamber with temperature and RH control. Results indicated that 60% RH is associated to maximum performance on the fuel cell under study over the studied temperature range. While water management is done in a passive fashion, heat management is accomplished on the basis of the injection of air at the cathode with the fuel cell showing good performances at relatively low currents where back diffusion towards the anode is favored

Exclusion of the Locus for Autosomal Recessive Pseudohypoaldosteronism Type 1 from the Mineralocorticoid Receptor Gene Region on Human Chromosome 4q by Linkage Analysis.

Pseudohypoaldosteronism type 1 (PHA1) is an uncommon inherited disorder characterized by salt-wasting in infancy arising from target organ unresponsiveness to mineralocorticoids. Clinical expression of the disease varies from severely affected infants who may die to apparently asymptomatic individuals. Inheritance is Mendelian and may be either autosomal dominant or autosomal recessive. A defect in the mineralocorticoid receptor has been implicated as a likely cause of PHA1. The gene for human mineralocorticoid receptor (MLR) has been cloned and physically mapped to human chromosome 4q31.1-31.2. The etiological role of MLR in autosomal recessive PHA1 was investigated by performing linkage analysis between PHA1 and three simple sequence length polymorphisms (D4S192, D4S1548, and D4S413) on chromosome 4q in 10 consanguineous families. Linkage analysis was carried out assuming autosomal recessive inheritance with full penetrance and zero phenocopy rate using the MLINK program for two-point analysis and the HOMOZ program for multipoint analysis. Lod scores of less than -2 were obtained over the whole region from D4S192 to D4S413 encompassing MLR. This provdes evidence against MLR as the site of mutations causing PHA1 in the majority of autosomal recessive families

The Clusters AgeS Experiment (CASE). I. V209 omega Cen - An Eclipsing Post-Common Envelope Binary in the Globular Cluster omega Cen

We use photometric and spectroscopic observations of the detached eclipsing binary V209 omega Cen to derive the masses, radii, and luminosities of the component stars. The system exhibits total eclipses and, based on the measured systemic velocity and the derived distance, is a member of the globular cluster omega Cen. We obtain 0.945 +/- 0.043 Msun, 0.983 +/- 0.015 Rsun and 6.68 +/- 0.88 Lsun for the cooler, but larger and more luminous primary component. The secondary component has 0.144 +/- 0.008 Msun, 0.425 +/- 0.008 Rsun and 2.26 +/- 0.28 Lsun. The effective temperatures are estimated at 9370 K for the primary and at 10866 K for the secondary. On the color-magnitude diagram of the cluster, the primary component occupies a position between the tip of the blue straggler region and the extended horizontal branch while the secondary component is located close to the red border of the area occupied by hot subdwarfs. However, its radius is too large and its effective temperature is too low for it to be an sdB star. We propose a scenario leading to the formation of a system with such unusual properties with the primary component ``re-born'' from a former white dwarf which accreted a new envelope through mass transfer from its companion. The secondary star has lost most of its envelope while starting its ascent onto the sub-giant branch. It failed to ignite helium in its core and is currently powered by a hydrogen burning shell.Comment: 24 pages, 9 figures, AJ, in pres

Role of dynamic Jahn-Teller distortions in Na2C60 and Na2CsC60 studied by NMR

Through 13C NMR spin lattice relaxation (T1) measurements in cubic Na2C60, we detect a gap in its electronic excitations, similar to that observed in tetragonal A4C60. This establishes that Jahn-Teller distortions (JTD) and strong electronic correlations must be considered to understand the behaviour of even electron systems, regardless of the structure. Furthermore, in metallic Na2CsC60, a similar contribution to T1 is also detected for 13C and 133Cs NMR, implying the occurence of excitations typical of JT distorted C60^{2-} (or equivalently C60^{4-}). This supports the idea that dynamic JTD can induce attractive electronic interactions in odd electron systems.Comment: 3 figure

The effect of chloride as catalyst layer contaminant on the degradation of PEMFCs

In this work, the effect of chloride as a catalyst contaminant was studied on the performance and durability of a low power open-cathode fuel cell, intended for passive management of water. In an ex-situ study, cyclic voltammetry was used to assess the redox behaviour of platinum in chloride contaminated solutions at room temperature.The cell was operated integrating a range of relative humidity (RH) from ~30 to 80% and temperatures from 5 to 55 ºC. Results indicated that 60% RH is associated to maximum fuel cell performance over the studied temperature range. An examination of the fuel cell components after 100 h of operation revealed that chloride contamination has produced cathode failure associated to catalyst migration favored by operation conditions that allowed platinum particles to break free from their carbon backing and migrate toward the polymer electrolyte. Migration resulted in precipitation with larger mean particle size distribution within the solid electrolyte when compared to the original catalyst layer, rendering a very significant loss of thickness in the cathode material