Three-dimensional Inkjet Printed Solid Oxide Electrochemical Reactors. I. Yttria-stabilized zirconia Electrolyte

Solid oxide fuel cell (SOFC) and electrolyser (SOE) performances can be enhanced significantly by increasing the densities of (electrode | electrolyte | pore) triple phase boundaries and improving geometric reproducibility and control over composite electrode | electrolyte microstructures, thereby also aiding predictive performance modelling. We developed stable aqueous colloidal dispersions of yttria-stabilized zirconia (YSZ), a common SOFC electrolyte material, and used them to fabricate 2D planar and highly-customisable 3D microstructures by inkjet printing. The effects of solids fraction, particle size, and binder concentration on structures were investigated, and crack-free, non-porous electrolyte planes were obtained by tailoring particle size and minimising binder concentration. Micro-pillar arrays and square lattices were printed with the optimised ink composition, and a minimum feature size of 35 μm was achieved in sintered structures, the smallest published to-date. YSZ particles were printed and sintered to a 23 μm thick planar electrolyte in a Ni-YSZ|YSZ|YSZ-LSM|LSM electrolyser for CO2 splitting; a feed of 9:1 CO2:CO mixture at 1.5 V and 809 °C produced a current density of −0.78 A cm−2 even without more complex 3D electrode | electrolyte geometries

Quantum Oscillations in an Impurity-Band Anderson Insulator

We show that for a system of localized electrons in an impurity band, which form an Anderson insulating state at zero temperature, there can appear quantum oscillations of the magnetization, i.e. the Anderson insulator can exhibit the de Haas-van Alphen effect. This is possible when the electronic band from which the localized states are formed has an extremum that traces out a nonzero area in reciprocal space. Our work extends existing theories for clean band insulators of this form to the situation where they host an impurity band. We show that the energies of these impurity levels oscillate with magnetic field, and compute the conditions under which these oscillations can dominate the de Haas-van Alphen effect. We discuss our results in connection with experimental measurements of quantum oscillations in Kondo insulators, and propose other experimental systems where the impurity band contribution can be dominant.Comment: Submission to SciPost, updated following referee comment

Description of rotating N=ZN=Z nuclei in terms of isovector pairing

A systematic investigation of the rotating $N=Z$ even-even nuclei in the mass $A=58-80$ region has been performed within the frameworks of the Cranked Relativistic Mean field, Cranked Relativistic Hartree Bogoliubov theories and cranked Nilsson-Strutinsky approach. Most of the experimental data is well accounted for in the calculations. The present study suggests that there is strong isovector $np$-pair field at low spin, the strength of which is defined by the isospin symmetry. At high spin, the isovector pair field is destroyed and the data are well described by the calculations assuming zero pairing. No clear evidence for the existence of the isoscalar $t=0$ $np$-pairing has been obtained in the present investigation.Comment: 20 pages + 19 figures, submitted to Phys. Rev.

Self-consistent scattering theory of transport and output characteristics of quantum cascade lasers

Electron transport in GaAs/AlGaAs quantum cascade lasers operating in midinfrared is calculated self-consistently using an intersubband scattering model. Subband populations and carrier transition rates are calculated and all relevant electron-LO phonon and electron-electron scatterings between injector/collector, active region, and continuum resonance levels are included. The calculated carrier lifetimes and subband populations are then used to evaluate scattering current densities, injection efficiencies, and carrier backflow into the active region for a range of operating temperatures. From the calculated modal gain versus total current density dependencies the output characteristics, in particular the gain coefficient and threshold current, are extracted. For the original GaAs/Al0.33Ga0.67As quantum cascade structure [C. Sirtori , Appl. Phys. Lett. 73, 3486 (1998)] these are found to be g=11.3 cm/kA and J(th)=6+/-1 kA/cm(2) (at T=77 K), and g=7.9 cm/kA and J(th)=10+/-1 kA/cm(2) (at T=200 K), in good agreement with the experiment. Calculations shows that threshold cannot be achieved in this structure at T=300 K, due to the small gain coefficient and the gain saturation effect, also in agreement with experimental findings. The model thus promises to be a powerful tool for the prediction and optimization of new, improved quantum cascade structures. © 2002 American Institute of Physics

On the coherence/incoherence of electron transport in semiconductor heterostructure optoelectronic devices

This paper compares and contrasts different theoretical approaches based on incoherent electron scattering transport with experimental measurements of optoelectronic devices formed from semiconductor heterostructures. The Monte Carlo method which makes no a priori assumptions about the carrier distribution in momentum or phase space is compared with less computationally demanding energy-balance rate equation models which assume thermalised carrier distributions. It is shown that the two approaches produce qualitatively similar results for hole transport in p-type Si1-xGex/Si superlattices designed for terahertz emission. The good agreement of the predictions of rate equation calculations with experimental measurements of mid- and far-infrared quantum cascade lasers, quantum well infrared photodetectors and quantum dot infrared photodetectors substantiate the assumption of incoherent scattering dominating the transport in these quantum well based devices. However, the paper goes on to consider the possibility of coherent transport through the density matrix method and suggests an experiment that could allow coherent and incoherent transport to be distinguished from each other

Population inversion in optically pumped asymmetric quantum well terahertz lasers

Intersubband carrier lifetimes and population ratios are calculated for three- and four-level optically pumped terahertz laser structures. Laser operation is based on intersubband transitions between the conduction band states of asymmetric GaAs-Ga(1 – x)Al(x)As quantum wells. It is shown that the carrier lifetimes in three-level systems fulfill the necessary conditions for stimulated emission only at temperatures below 200 K. The addition of a fourth level, however, enables fast depopulation of the lower laser level by resonant longitudinal optical phonon emission and thus offers potential for room temperature laser operation. © 1997 American Institute of Physics

Interwell relaxation times in p-Si/SiGe asymmetric quantum well structures: the role of interface roughness

We report the direct determination of nonradiative lifetimes in Si∕SiGe asymmetric quantum well structures designed to access spatially indirect (diagonal) interwell transitions between heavy-hole ground states, at photon energies below the optical phonon energy. We show both experimentally and theoretically, using a six-band k∙p model and a time-domain rate equation scheme, that, for the interface quality currently achievable experimentally (with an average step height ⩾1 Å), interface roughness will dominate all other scattering processes up to about 200 K. By comparing our results obtained for two different structures we deduce that in this regime both barrier and well widths play an important role in the determination of the carrier lifetime. Comparison with recently published experimental and theoretical data obtained for mid-infrared GaAs∕AlxGa1−xAs multiple quantum well systems leads us to the conclusion that the dominant role of interface roughness scattering at low temperature is a general feature of a wide range of semiconductor heterostructures not limited to IV-IV material

The influence of the patient's health-state compared with time to surgery on the outcomes following hip fracture surgery: a longitudinal study of 4,791 patients.

INTRODUCTION: This study investigated whether the health-state of hip fracture patients or the time to surgery had a greater effect on outcomes. METHODS: Of the 5,120 patients admitted with a fragility hip fracture, 4,791 (93.6%) were included in the analysis. Patients operated after 36 hours were initially group by length of delay (36-48 hours and >48 hours) and then regrouped by delay cause (medical and administrative). Patients operated within 36 hours were the comparative group. Data were collected at admission, discharge, 120 days and 365 days post discharge. RESULTS: Multivariate logistic regression analysis revealed that the patients who were delayed over 36 hours, owing to medical causes, had a higher mortality at all studied time points, but the patients who were delayed owing to administrative causes had no increase in mortality. Analysis by time to surgery revealed that patients operated after 36 and 48 hours had a higher mortality at discharge only. Medically delayed patients were less likely to return to their premorbid level of residence at discharge. Older, male patients had a higher risk of inferior outcomes. Postoperative length of stay was significantly greater in the >48-hour delay group and the medical delay group. All delay groups had a significantly higher rate of reoperation within 30 days compared with the no-delay group. CONCLUSIONS: The health-state of the hip fracture patient had a greater impact on the outcome in contrast to time to surgery. This study concurs that hip fracture patients should receive surgery within the timeframe of current guidelines, but medically unwell patients have relatively worse outcomes and should receive enhanced clinical attention

Survey of the ISM in Early-Type Galaxies. IV. The Hot Dust Component

We present mid-IR photometric properties for a sample of 28 early-type galaxies observed at 6.75, 9.63 and 15 um with the ISOCAM instrument on board the ISO satellite. We find total mid-IR luminosities in the range 3-48x10^8 L_sun. The spectral energy distribution (SED) of the galaxies were derived using the mid-IR data together with previously published UV, optical and near-IR data. These SEDs clearly show a mid-IR emission coming from dust heated at T ~ 260 K. Dust grains properties are inferred from the mid-IR colors. The masses of the hot dust component are in the range 10-400 M_sun. The relationship between the masses derived from mid-IR observations and those derived from visual extinction are discussed. The possible common heating source for the gas and dust is investigated through the correlations between Ha and mid-IR luminosities.Comment: 10 pages, LaTeX (aa.cls), 11 figures (f. 2-4 are colour plates). Accepted for publication in Astronomy & Astrophysic