High temperature oxidation of nickel

Using a sensitive volumetric technique, a study was made of the kinetics of oxidation of nickel at 1200° C. and 1300° C. Three purities of nickel were used for the investigation which was limited to the initial three hours of reaction. The rate of oxidation of nickel followed the parabolic rate law after an initial period of deviation which lasted up to 40 minutes. No direct correlation was found between the oxide thickness and the end of the period of deviation from the parabolic rate law. The purity of the nickel was found to have a marked effect on the rate of oxidation of nickel which increased as the purity decreased. The color of the oxide on nickel was found to be related to the thickness of the oxide layer. The oxide on high-purity nickel was gray initially but rapidly changed to green and then gradually to black with thickening --Abstract, page 2

High Density Mesoscopic Atom Clouds in a Holographic Atom Trap

We demonstrate the production of micron-sized high density atom clouds of interest for meso- scopic quantum information processing. We evaporate atoms from 60 microK, 3x10^14 atoms/cm^3 samples contained in a highly anisotropic optical lattice formed by interfering di racted beams from a holographic phase plate. After evaporating to 1 microK by lowering the con ning potential, in less than a second the atom density reduces to 8x10^13 cm^- 3 at a phase space density approaching unity. Adiabatic recompression of the atoms then increases the density to levels in excess of 1x10^15 cm^-3. The resulting clouds are typically 8 microns in the longest dimension. Such samples are small enough to enable mesoscopic quantum manipulation using Rydberg blockade and have the high densities required to investigate new collision phenomena.Comment: 4 pages, 4 figures, submitted to PR

National trends in emergency readmission rates: A longitudinal analysis of administrative data for England between 2006 and 2016

Objective To assess trends in 30-day emergency readmission rates across England over one decade. Design Retrospective study design. Setting 150 non-specialist hospital trusts in England. Participants 23 069 134 patients above 18 years of age who were readmitted following an initial admission (n=62 584 297) between April 2006 and February 2016. Primary and secondary outcomes We examined emergency admissions that occurred within 30 days of discharge from hospital (‘emergency readmissions’) as a measure of healthcare quality. Presented are overall readmission rates, and disaggregated by the nature of the indexed admission, including whether it was elective or emergency, and by clinical health condition recorded. All rates were risk-adjusted for patient age, gender, ethnicity, socioeconomic status, comorbidities and length of stay. Results The average risk-adjusted, 30-day readmission rate increased from 6.56% in 2006/2007 to 6.76% (P<0.01) in 2012/2013, followed by a small decrease to 6.64% (P<0.01) in 2015/2016. Emergency readmissions for patients discharged following elective procedures decreased by 0.13% (P<0.05), whereas those following emergency admission increased by 1.27% (P<0.001). Readmission rates for hip or knee replacements decreased (−1.29%; P<0.001); for acute myocardial infarction (−0.04%; P<0.49), stroke (+0.62%; P<0.05), chronic obstructive pulmonary disease (+0.41%; P<0.05) and heart failure (+0.15%; P<0.05) remained stable; and for pneumonia (+2.72%; P<0.001), diabetes (+7.09%; P<0.001), cholecystectomy (+1.86%; P<0.001) and hysterectomy (+2.54%; P<0.001) increased. Conclusions Overall, emergency readmission rates in England remained relatively stable across the observation period, with trends of slight increases contained post 2012/2013. However, there were large variations in trends across clinical areas, with some experiencing marked increases in readmission rates. This highlights the need to better understand variations in outcomes across clinical subgroups to allow for targeted interventions that will ensure highest standards of care provided for all patients

Anharmonic parametric excitation in optical lattices

We study both experimentally and theoretically the losses induced by parametric excitation in far-off-resonance optical lattices. The atoms confined in a 1D sinusoidal lattice present an excitation spectrum and dynamics substantially different from those expected for a harmonic potential. We develop a model based on the actual atomic Hamiltonian in the lattice and we introduce semiempirically a broadening of the width of lattice energy bands which can physically arise from inhomogeneities and fluctuations of the lattice, and also from atomic collisions. The position and strength of the parametric resonances and the evolution of the number of trapped atoms are satisfactorily described by our model.Comment: 7 pages, 5 figure

Nonperturbative and perturbative treatments of parametric heating in atom traps

We study the quantum description of parametric heating in harmonic potentials both nonperturbatively and perturbatively, having in mind atom traps. The first approach establishes an explicit connection between classical and quantum descriptions; it also gives analytic expressions for properties such as the width of fractional frequency parametric resonances. The second approach gives an alternative insight into the problem and can be directly extended to take into account nonlinear effects. This is specially important for shallow traps.Comment: 12 pages, 2 figure

Cooling atoms in an optical trap by selective parametric excitation

We demonstrate the possibility of energy-selective removal of cold atoms from a tight optical trap by means of parametric excitation of the trap vibrational modes. Taking advantage of the anharmonicity of the trap potential, we selectively remove the most energetic trapped atoms or excite those at the bottom of the trap by tuning the parametric modulation frequency. This process, which had been previously identified as a possible source of heating, also appears to be a robust way for forcing evaporative cooling in anharmonic traps.Comment: 5 pages, 5 figure

Evanescent-wave trapping and evaporative cooling of an atomic gas near two-dimensionality

A dense gas of cesium atoms at the crossover to two-dimensionality is prepared in a highly anisotropic surface trap that is realized with two evanescent light waves. Temperatures as low as 100nK are reached with 20.000 atoms at a phase-space density close to 0.1. The lowest quantum state in the tightly confined direction is populated by more than 60%. The system offers intriguing prospects for future experiments on degenerate quantum gases in two dimensions

Multiple micro-optical atom traps with a spherically aberrated laser beam

We report on the loading of atoms contained in a magneto-optic trap into multiple optical traps formed within the focused beam of a CO_{2} laser. We show that under certain circumstances it is possible to create a linear array of dipole traps with well separated maxima. This is achieved by focusing the laser beam through lenses uncorrected for spherical aberration. We demonstrate that the separation between the micro-traps can be varied, a property which may be useful in experiments which require the creation of entanglement between atoms in different micro-traps. We suggest other experiments where an array of these traps could be useful.Comment: 10 pages, 3 figure

Very long storage times and evaporative cooling of cesium atoms in a quasi-electrostatic dipole trap

We have trapped cesium atoms over many minutes in the focus of a CO$_2$-laser beam employing an extremely simple laser system. Collisional properties of the unpolarized atoms in their electronic ground state are investigated. Inelastic binary collisions changing the hyperfine state lead to trap loss which is quantitatively analyzed. Elastic collisions result in evaporative cooling of the trapped gas from 25 $\mu$K to 10 $\mu$K over a time scale of about 150 s.Comment: 5 pages, 3 figure