Sub-milliKelvin spatial thermometry of a single Doppler cooled ion in a Paul trap

We report on observations of thermal motion of a single, Doppler-cooled ion along the axis of a linear radio-frequency quadrupole trap. We show that for a harmonic potential the thermal occupation of energy levels leads to Gaussian distribution of the ion's axial position. The dependence of the spatial thermal spread on the trap potential is used for precise calibration of our imaging system's point spread function and sub-milliKelvin thermometry. We employ this technique to investigate the laser detuning dependence of the Doppler temperature.Comment: 5 pages, 4 figure

New cloud chamber experiments on the heterogeneous ice nucleation ability of oxalic acid in the immersion mode

The heterogeneous ice nucleation ability of oxalic acid in the immersion mode has been investigated by controlled expansion cooling runs with airborne, ternary solution droplets composed of, (i), sodium chloride, oxalic acid, and water (NaCl/OA/H₂O) and, (ii), sulphuric acid, oxalic acid, and water (H₂SO₄/OA/H₂O). Polydisperse aerosol populations with median diameters ranging from 0.5–0.7 μm and varying solute concentrations were prepared. The expansion experiments were conducted in the AIDA aerosol and cloud chamber of the Karlsruhe Institute of Technology at initial temperatures of 244 and 235 K. In the ternary NaCl/OA/H₂O system, solid inclusions of oxalic acid, presumably nucleated as oxalic acid dihydrate, were formed by temporarily exposing the ternary solution droplets to a relative humidity below the efflorescence point of NaCl. The matrix of the crystallised NaCl particulates triggered the precipitation of the organic crystals which later remained as solid inclusions in the solution droplets when the relative humidity was subsequently raised above the deliquescence point of NaCl. The embedded oxalic acid crystals reduced the critical ice saturation ratio required for the homogeneous freezing of pure NaCl/H₂O solution droplets at a temperature of around 231 K from 1.38 to about 1.32. Aqueous solution droplets with OA inclusions larger than about 0.27 μm in diameter efficiently nucleated ice by condensation freezing when they were activated to micron-sized cloud droplets at 241 K, i.e., they froze well above the homogeneous freezing temperature of pure water droplets of about 237 K. Our results on the immersion freezing potential of oxalic acid corroborate the findings from a recent study with emulsified aqueous solutions containing crystalline oxalic acid. In those experiments, the crystallisation of oxalic acid diyhdrate was triggered by a preceding homogeneous freezing cycle with the emulsion samples. The expansion cooling cycles with ternary H₂SO₄/OA/H₂O solution droplets were aimed to analyse whether those findings can be transferred to ice nucleation experiments with airborne oxalic acid containing aerosol particles. Under our experimental conditions, the efficiency by which the surface of homogeneously nucleated ice crystals triggered the precipitation of oxalic acid dihydrate was very low, i.e., less than one out of a hundred ice crystals that were formed by homogeneous freezing in a first expansion cooling cycle left behind an ice-active organic crystal that acted as immersion freezing nucleus in a second expansion cooling cycle

Probing ice clouds by broadband mid-infrared extinction spectroscopy: case studies from ice nucleation experiments in the AIDA aerosol and cloud chamber

International audienceSeries of infrared extinction spectra of ice crystals were recorded in the 6000?800 cm-1 wavenumber regime during expansion cooling experiments in the large aerosol and cloud chamber AIDA of Forschungszentrum Karlsruhe. Either supercooled sulphuric acid solution droplets or dry mineral dust particles were added as seed aerosols to initiate ice formation after having established ice supersaturated conditions inside the chamber. The various ice nucleation runs were conducted at temperatures between 237 and 195 K, leading to median sizes of the nucleated ice particles of 1?15 µm. The measured infrared spectra were fitted with reference spectra from T-matrix calculations to retrieve the number concentration as well as the number size distribution of the generated ice clouds. The ice particles were modelled as finite circular cylinders with aspect ratios ranging from 0.5 to 3.0. Benefiting from the comprehensive diagnostic tools for the characterisation of ice clouds which are available at the AIDA facility, the infrared retrieval results with regard to the ice particle number concentration could be compared to independent measurements with various optical particle counters. This provided a unique chance to quantitatively assess potential errors or solution ambiguities in the retrieval procedure which mainly originate from the difficulty to find an appropriate shape representation for the aspherical particle habits of the ice crystals. Based on these inter-comparisons, we demonstrate that there is no standard retrieval approach which can be routinely applied to all different experimental scenarios. In particular, the concept to account for the asphericity of the ice crystals, the a priori constraints which might be imposed on the unknown number size distribution of the ice crystals (like employing an analytical distribution function), and the wavenumber range which is included in the fitting algorithm should be carefully adjusted to each single retrieval problem

Precision spectroscopy of the 3s-3p fine structure doublet in Mg+

We apply a recently demonstrated method for precision spectroscopy on strong transitions in trapped ions to measure both fine structure components of the 3s-3p transition in 24-Mg+ and 26-Mg+. We deduce absolute frequency reference data for transition frequencies, isotope shifts and fine structure splittings that are in particular useful for comparison with quasar absorption spectra, which test possible space-time variations of the fine structure constant. The measurement accuracy improves previous literature values, when existing, by more than two orders of magnitude

Housing situation and healthcare for patients in a psychiatric centre in Berlin, Germany: a cross-sectional patient survey

OBJECTIVE: To determine the housing situation among people seeking psychiatric treatment in relation to morbidity and service utilisation. DESIGN: Cross-sectional patient survey. SETTING: Psychiatric centre with a defined catchment area in Berlin, Germany, March-September 2016. PARTICIPANTS: 540 psychiatric inpatients including day clinics (43.2% of all admitted patients in the study period (n=1251)). MAIN OUTCOME MEASURES: Housing status 30 days prior the interview as well as influencing variables including service use, psychiatric morbidity and sociodemographic variables. RESULTS: In our survey, 327 participants (68.7%) currently rented or owned an own apartment; 62 (13.0%) reported to be homeless (living on the street or in shelters for homeless or refugees); 87 (18.3%) were accommodated in sociotherapeutic facilities. Participants without an own apartment were more likely to be male and younger and to have a lower level of education. Homeless participants were diagnosed with a substance use disorder significantly more often (74.2%). Psychotic disorders were the highest among homeless participants (29.0%). Concerning service use, we did neither find a lower utilisation of ambulatory services nor a higher utilisation of hospital-based care among homeless participants. CONCLUSIONS: Our findings underline the need for effective housing for people with mental illness. Despite many sociotherapeutic facilities, a concerning number of people with mental illness is living in homelessness. Especially early interventions addressing substance use might prevent future homelessness

Enhanced dielectronic recombination of lithium-like Ti19+ ions in external ExB fields

Dielectronic recombination(DR) of lithium-like Ti19+(1s2 2s) ions via 2s->2p core excitations has been measured at the Heidelberg heavy ion storage ring TSR. We find that not only external electric fields (0 <= Ey <= 280 V/cm) but also crossed magnetic fields (30 mT <= Bz <= 80 mT) influence the DR via high-n (2p_j nl)-Rydberg resonances. This result confirms our previous finding for isoelectronic Cl14+ ions [Bartsch T et al, PRL 82, 3779 (1999)] that experimentally established the sensitivity of DR to ExB fields. In the present investigation the larger 2p_{1/2}-2p_{3/2} fine structure splitting of Ti19+ allowed us to study separately the influence of external fields via the two series of Rydberg DR resonances attached to the 2s -> 2p_{1/2} and 2s -> 2p_{3/2} excitations of the Li-like core, extracting initial slopes and saturation fields of the enhancement. We find that for Ey > 80 V/cm the field induced enhancement is about 1.8 times stronger for the 2p_{3/2} series than for the 2p_{1/2} series.Comment: 10 pages, 3 figures, to be published in Journal of Physics B, see also http://www.strz.uni-giessen.de/~k