Metal-insulator transition in YHx: scaling of the sub-THz conductivity

The established scaling laws of the conductivity with temperature and doping are strong indications for the quantum nature of the metal-insulator transition in YH$_x$. Here we report the first results on the frequency scaling of the conductivity. Samples were brought from the insulating to the metallic phase by carrier doping via illumination. In the metallic phase, the sub-terahertz conductivity coincides with the dc data. These results do not agree with the simplest picture of a quantum-phase transition.Comment: 4 pages, accepted to PR

Magnetic dipolar ordering and relaxation in the high-spin molecular cluster compound Mn6

Few examples of magnetic systems displaying a transition to pure dipolar magnetic order are known to date, and single-molecule magnets can provide an interesting example. The molecular cluster spins and thus their dipolar interaction energy can be quite high, leading to reasonably accessible ordering temperatures, provided the crystal field anisotropy is sufficiently small. This condition can be met for molecular clusters of sufficiently high symmetry, as for the Mn6 compound studied here. Magnetic specific heat and susceptibility experiments show a transition to ferromagnetic dipolar order at T_{c} = 0.16 K. Classical Monte-Carlo calculations indeed predict ferromagnetic ordering and account for the correct value of T_{c}. In high magnetic fields we detected the contribution of the ^{55}Mn nuclei to the specific heat, and the characteristic timescale of nuclear relaxation. This was compared with results obtained directly from pulse-NMR experiments. The data are in good mutual agreement and can be well described by the theory for magnetic relaxation in highly polarized paramagnetic crystals and for dynamic nuclear polarization, which we extensively review. The experiments provide an interesting comparison with the recently investigated nuclear spin dynamics in the anisotropic single molecule magnet Mn12-ac.Comment: 19 pages, 11 eps figures. Contains extensive discussions on dipolar ordering, specific heat and nuclear relaxation in molecular magnet

A quantitative evaluation of metallic conduction in conjugated polymers

As the periodicity in crystalline materials creates the optimal condition for electronic delocalization, one might expect that in partially crystalline conjugated polymers delocalization is impeded by intergrain transport. However, for the best conducting polymers this presumption fails. Delocalization is obstructed by interchain rather than intergrain charge transfer and we propose a model of weakly coupled disordered chains to describe the physics near the metal-insulator transition. Our quantitative calculations match the outcome of recent broad-band optical experiments and provide a consistent explanation of metallic conduction in polymers.Comment: 4 pages incl. 3 figure

Density of states and magnetoconductance of disordered Au point contacts

We report the first low temperature magnetotransport measurements on electrochemically fabricated atomic scale gold nanojunctions. As $T \to 0$, the junctions exhibit nonperturbatively large zero bias anomalies (ZBAs) in their differential conductance. We consider several explanations and find that the ZBAs are consistent with a reduced local density of states (LDOS) in the disordered metal. We suggest that this is a result of Coulomb interactions in a granular metal with moderate intergrain coupling. Magnetoconductance of atomic scale junctions also differs significantly from that of less geometrically constrained devices, and supports this explanation.Comment: 5 pages, 5 figures. Accepted to PRB as Brief Repor

Hydrogen Recovery by Methane Pyrolysis to Elemental Carbon

Use of a Sabatier reactor to recover the oxygen from the carbon dioxide exhaled by the crew on the International Space Station has been limited by the loss of the hydrogen contained in the methane it generates. Maximizing the oxygen recovered requires the hydrogen to be recovered from the methane product and recycled back to the Sabatier reactor. We describe the use of a tailored methane pyrolysis reactor to completely recover this hydrogen. The carbon-containing byproduct is elemental carbon, which is generated in the form of easily handled, non-sooty material that may have various uses. The process of creating this tailored carbon vapor deposition process involved exploration of the effects of temperature, pressure, substrate design and other variables to develop a high yield process that cleanly generates the desired products. Reaction kinetics and kinetics modelling were used to specify the temperature, pressure and reactor volume required to achieve the target conversion and to assure that the final average density was as high as possible. Reactor design included the selection of materials that will survive the high temperatures and environment in the pyrolysis reactor, and thermal modeling to achieve the required temperatures with minimum power consumption. The successful construction and demonstration of a brassboard prototype will allow the results of the chemical, thermal and mechanical models to be validated and should provide a useful alternative for a completely closed loop ECLS system. Integration of this technology with state-of-the-art (SOA) Sabatier hardware on ISS requires a complete understanding of the effects of impurities in the product hydrogen on the Sabatier catalyst. SOA Sabatier catalyst was evaluated over short and long-term exposure to anticipated contaminants to identify effects

Experiences and needs of patients with incurable cancer regarding advance care planning:results from a national cross-sectional survey

Introduction: Patients faced with incurable cancer may experience a lack of support from their physician throughout and after treatment. Studies on the needs and experiences of these patients are scarce. In this study, we explored the needs and experiences of patients diagnosed with incurable cancer regarding the conversation, in which they were told that their cancer was incurable, the care received after this conversation, and their preferences regarding end-of-life conversations. Methods: Data were cross-sectionally collected through a national online survey in the Netherlands (September 2018). Descriptive statistics and correlation coefficients were reported and subgroups were compared. Results: Six hundred fifty-four patients (mean age 60 years; 58% women) completed the survey. Patients were primarily diagnosed with breast cancer (22%) or a hematological malignancy (21%). Patients reported a strong need for emotional support during the conversation, in which they were told their cancer was incurable (mean score 8.3; scale 1–10). Their experienced satisfaction with received emotional support was mediocre (mean score 6.4; scale 1–10). Of those patients who felt like they did not receive any additional care (37%) after the diagnosis, the majority expressed a clear need for this kind of care (59%). Mostly, support pertained to psychosocial issues. Regarding conversations about the end of life, most patients (62%) expressed a need to discuss this topic, and preferred their healthcare provider to initiate this conversation. Conclusion: Care for patients with incurable cancer can be further improved by tailoring conversations to specific needs and timely providing appropriate supportive care services

Mesoscopic phase separation in La2CuO4.02 - a 139La NQR study

In crystals of La2CuO4.02 oxygen diffusion can be limited to such small length scales, that the resulting phase separation is invisible for neutrons. Decomposition of the 139La NQR spectra shows the existence of three different regions, of which one orders antiferromagnetically below 17K concomitantly with the onset of a weak superconductivity in the crystal. These regions are compared to the macroscopic phases seen previously in the title compound and the cluster-glass and striped phases reported for the underdoped Sr-doped cuprates.Comment: 4 pages, RevTeX, 5 figures, to be published in PR