First ice core records of NO3− stable isotopes from Lomonosovfonna, Svalbard

Samples from two ice cores drilled at Lomonosovfonna, Svalbard, covering the period 1957–2009, and 1650–1995, respectively, were analyzed for NO3− concentrations, and NO3− stable isotopes (δ15N and δ18O). Post-1950 δ15N has an average of (−6.9 ± 1.9) ‰, which is lower than the isotopic signal known for Summit, Greenland, but agrees with values observed in recent Svalbard snow and aerosol. Pre-1900 δ15N has an average of (4.2 ± 1.6) ‰ suggesting that natural sources, enriched in the 15 N-isotope, dominated before industrialization. The post-1950 δ18O average of (75.1 ± 4.1) ‰ agrees with data from low and polar latitudes, suggesting similar atmospheric NOy (NOy = NO + NO2 + HNO3) processing pathways. The combination of anthropogenic source δ15N and transport isotope effect was estimated as −29.1 ‰ for the last 60 years. This value is below the usual range of NOx (NOx = NO + NO2) anthropogenic sources which is likely the result of a transport isotope effect of –32 ‰. We suggest that the δ15N recorded at Lomonosovfonna is influenced mainly by fossil fuel combustion, soil emissions and forest fires; the first and second being responsible for the marked decrease in δ15N observed in the post-1950s record with soil emissions being associated to the decreasing trend in δ15N observed up to present time, and the third being responsible for the sharp increase of δ15N around 2000

Evaluation of a coupled dispersion and aerosol process model against measurements near a major road

International audienceA field measurement campaign was conducted near a major road "Itäväylä" in an urban area in Helsinki in 17?20 February 2003. Aerosol measurements were conducted using a mobile laboratory "Sniffer" at various distances from the road, and at an urban background location. Measurements included particle size distribution in the size range of 7 nm?10 ?m (aerodynamic diameter) by the Electrical Low Pressure Impactor (ELPI) and in the size range of 3?50 nm (mobility diameter) by Scanning Mobility Particle Sizer (SMPS), total number concentration of particles larger than 3 nm detected by an ultrafine condensation particle counter (UCPC), temperature, relative humidity, wind speed and direction, driving route of the mobile laboratory, and traffic density on the studied road. In this study, we have compared measured concentration data with the predictions of the road network dispersion model CAR-FMI used in combination with an aerosol process model MONO32. The vehicular exhaust emissions, and atmospheric dispersion and transformation of fine and ultrafine particles was evaluated within the distance scale of 200 m (corresponding to a time scale of a couple of minutes). We computed the temporal evolution of the number concentrations, size distributions and chemical compositions of various particle size classes. The atmospheric dilution rate of particles is obtained from the roadside dispersion model CAR-FMI. Considering the evolution of total number concentration, dilution was shown to be the most important process. The influence of coagulation and condensation on the number concentrations of particle size modes was found to be negligible at this distance scale. Condensation was found to affect the evolution of particle diameter in the two smallest particle modes. The assumed value of the concentration of condensable organic vapour of 1012 molecules cm?3 was shown to be in a disagreement with the measured particle size evolution, while the modelling runs with the concentration of condensable organic vapour of 109?1010 molecules cm?3 resulted in particle sizes that were closest to the measured values

Interference through quantum dots

We discuss the effect of quantum interference on transport through a quantum dot system. We introduce an indirect coherent coupling parameter alpha, which provides constructive/destructive interference in the transport current depending on its phase and the magnetic flux. We estimate the current through the quantum dot system using the non-equilibrium Green's function method as well as the master equation method in the sequential tunneling regime. The visibility of the Aharonov-Bohm oscillation is evaluated. For a large inter-dot Coulomb interaction, the current is strongly suppressed by the quantum interference effect, while the current is restored by applying an oscillating resonance field with the frequency of twice the inter-dot tunneling energy.Comment: 10 pages, 3 figure

Interference in interacting quantum dots with spin

We study spectral and transport properties of interacting quantum dots with spin. Two particular model systems are investigated: Lateral multilevel and two parallel quantum dots. In both cases different paths through the system can give rise to interference. We demonstrate that this strengthens the multilevel Kondo effect for which a simple two-stage mechanism is proposed. In parallel dots we show under which conditions the peak of an interference-induced orbital Kondo effect can be split.Comment: 8 pages, 8 figure

Evaluation and modelling of the size fractionated aerosol particle number concentration measurements nearby a major road in Helsinki ? Part I: Modelling results within the LIPIKA project

International audienceA field measurement campaign was conducted near a major road "Itäväylä" in an urban area in Helsinki in 17?20 February 2003. Aerosol measurements were conducted using a mobile laboratory "Sniffer" at various distances from the road, and at an urban background location. Measurements included particle size distribution in the size range of 7 nm?10 ?m (aerodynamic diameter) by the Electrical Low Pressure Impactor (ELPI) and in the size range of 3?50 nm (mobility diameter) by Scanning Mobility Particle Sizer (SMPS), total number concentration of particles larger than 3 nm detected by an ultrafine condensation particle counter (UCPC), temperature, relative humidity, wind speed and direction, driving route of the mobile laboratory, and traffic density on the studied road. In this study, we have compared measured concentration data with the predictions of the road network dispersion model CAR-FMI used in combination with an aerosol process model MONO32. For model comparison purposes, one of the cases was additionally computed using the aerosol process model UHMA, combined with the CAR-FMI model. The vehicular exhaust emissions, and atmospheric dispersion and transformation of fine and ultrafine particles was evaluated within the distance scale of 200 m (corresponding to a time scale of a couple of minutes). We computed the temporal evolution of the number concentrations, size distributions and chemical compositions of various particle size classes. The atmospheric dilution rate of particles is obtained from the roadside dispersion model CAR-FMI. Considering the evolution of total number concentration, dilution was shown to be the most important process. The influence of coagulation and condensation on the number concentrations of particle size modes was found to be negligible on this distance scale. Condensation was found to affect the evolution of particle diameter in the two smallest particle modes. The assumed value of the concentration of condensable organic vapour of 1012 molecules cm?3 was shown to be in a disagreement with the measured particle size evolution, while the modelling runs with the concentration of condensable organic vapour of 109?1010 molecules cm?3 resulted in particle sizes that were closest to the measured values

Longitudinal interrelationships between dental fear and dental attendance among adult Finns in 2000-2011

Objectives: The aim of this longitudinal study was to investigate causal pathways among as well as interrelationships between changes in dental fear and dental attendance in a nationally representative sample of adult Finns aged 19 years or older in 2000, with 11 years of follow‐up.Methods: Data from the Health 2000 and 2011 Surveys (BRIF8901) in Finland were used. The Health 2000 survey used a stratified two‐stage cluster sampling design (N=9742). Of the participants in 2000, 7964 were eligible and invited to participate in 2011. Of the participants in 2011 (n=5806), 3,631 (63%) responded to both dental fear and attendance questions in both years. Both fear and attendance were assessed using single questions and dichotomized. The background variables included were age, gender and education. Path analysis and logistic regression models were used.Results: Dental fear led to nonhabitual use of dental services rather than vice versa (−0.07 to 0.04 vs. 0.00). When confounders were considered, in both age groups (29‐39 years and 40+ years) an increase in fear predicted nonhabitual dental attendance. This association was stronger among the younger age group (OR = 4.91) than among those aged 40 years and older (OR = 2.88). Among the younger age group, improved dental fear decreased the risk of nonhabitual dental attendance (OR = 0.16), while among older age group, stable fear increased the risk of nonhabitual dental attendance (OR = 2.33).Conclusions: Dental fear causes nonhabitual dental attendance, and decreasing dental fear increases habitual attendance. Oral health personnel should adapt measures to prevent and treat dental fear.</p

Spin dynamics of Mn12-acetate in the thermally-activated tunneling regime: ac-susceptibility and magnetization relaxation

In this work, we study the spin dynamics of Mn12-acetate molecules in the regime of thermally assisted tunneling. In particular, we describe the system in the presence of a strong transverse magnetic field. Similar to recent experiments, the relaxation time/rate is found to display a series of resonances; their Lorentzian shape is found to stem from the tunneling. The dynamic susceptibility $\chi(w)$ is calculated starting from the microscopic Hamiltonian and the resonant structure manifests itself also in $\chi(w)$. Similar to recent results reported on another molecular magnet, Fe8, we find oscillations of the relaxation rate as a function of the transverse magnetic field when the field is directed along a hard axis of the molecules. This phenomenon is attributed to the interference of the geometrical or Berry phase. We propose susceptibility experiments to be carried out for strong transverse magnetic fields to study of these oscillations and for a better resolution of the sharp satellite peaks in the relaxation rates.Comment: 22 pages, 23 figures; submitted to Phys. Rev. B; citations/references adde

Studies of transverse and longitudinal relaxations of 55^{55}Mn in molecular cluster magnet Mn12_{12}Ac

The transverse and longitudinal relaxation rates 1/$T_2$ and 1/$T_1$ of $^{55}$Mn in molecular cluster magnet Mn$_{12}$Ac have been measured al low temperatures down to 200mK and in the fields upto 9T. Both of 1/$T_2$ and 1/$T_1$ exhibit remarkable decreases with decreasing temperature and with increasing field, with the relative relation $T_1/T_2 \approx 200$. In the analysis, we adopt a simple model that the thermal fluctuation of the cluster spin $S$=10 associated with the spin-phonon interactionis, is only due to the excitation to the first excited state from the ground state with the average life-times $\tau_ 1$ and $\tau_0$ ($\tau_ 0$$\gg$$\tau_1$). We show that 1/$T_2$ is interpreted in terms of the strong collision regime as given by 1/$\tau_ 0$, and that 1/$T_1$ is understood by the high-frequency limit based on standard perturbation treatment for the step-wise fluctuating field, thus being proportional to 1/$\tau_0\omega_N^2$.Comment: 12 pages, 11 fugures, revtex