Focus presuppositions

This paper reviews notions related to focus and presupposition and addresses the hypothesis that focus triggers an existential presupposition. Presupposition projection behavior in certain examples appears to favor a presuppositional analysis of focus. It is argued that these examples are open to a different analysis using givenness theory. Overall, the analysis favors a weak semantics for focus not including an existential presupposition

Early onset of ground-state deformation in the neutron-deficient polonium isotopes

In-source resonant ionization laser spectroscopy of the even-$A$ polonium isotopes $^{192-210,216,218}$Po has been performed using the $6p^37s$ $^5S_2$ to $6p^37p$ $^5P_2$ ($\lambda=843.38$ nm) transition in the polonium atom (Po-I) at the CERN ISOLDE facility. The comparison of the measured isotope shifts in $^{200-210}$Po with a previous data set allows to test for the first time recent large-scale atomic calculations that are essential to extract the changes in the mean-square charge radius of the atomic nucleus. When going to lighter masses, a surprisingly large and early departure from sphericity is observed, which is only partly reproduced by Beyond Mean Field calculations.Comment: As submitted to PR

Accumulation of polonium-210 in different species of fish in Lake Mead

Discovered by Pierre Curie and Marie Skłodowska-Curie in 1898, polonium is a chemical element with an atomic number of 84. This rare naturally occurring radioactive element is chemically similar to bismuth and tellurium, and forms in uranium ores. Polonium-210 is an naturally occurring radioactive element with a half-life of 138.376 days(1). This element is found in trace amounts in most organisms. Our research is focused on the accumulation of polonium-210 in fish that occupy in Lake Mead. The sample species is chosen based on varying lake stratification (layers of the lake). This gives us a good idea of the difference in polonium-210 amounts, based on diet since it tends to change with lake stratification. This research will be based on a previous research that concluded that the polonium 210 is found generally in the internal organs especially the Gastro-intestinal tract of the fish and 97% of polonium acquired by fish is from food intake. The results from our research will help identify the causes for accumulation and compare the level of polonium 210 accumulation in different species based on the strata they are found in

The “polonium in vivo” study. Polonium-210 in bronchial lavages of patients with suspected lung cancer

Few studies have reported on polonium-210, a decay breakdown product of radon-222 and lead-210, in human lungs and there has been no study in patients with suspected lung cancer. The main aim of this "Polonium in vivo" study was to evaluate polonium-210 radioactivity in bronchopulmonary systems of smoker, ex-smoker and never smoker patients with suspected lung cancer. Alpha-spectrometric analyses were performed on bronchial lavage (BL) fluids from two Italian hospitals in 2013-2016. Socio-demographic, smoking, occupational and spirometric characteristics, lung cancer confirmation and histologic type and radon-222 concentration in patients' homes were collected. Seventy BL samples from never (n = 13), former (n = 35) and current smokers (n = 22) were analyzed; polonium-210 was detected in all samples from current and former smokers and in 54% of samples from never smokers (p < 0.001; median values: 1.20, 1.43 and 0.40 mBq, respectively). Polonium-210 levels were significantly higher in COPD versus no COPD patients (median value: 3.60 vs. 0.97 mBq; p = 0.007); former and current smokers, without and with COPD, had significantly increased polonium-210 levels (p = 0.012); 96% of confirmed versus 69% of non-confirmed lung cancer patients recorded detectable polonium-210 levels (p = 0.018). A polonium-210 detectable activity was measured in BL samples from all current and former smokers. Polonium-210 in the lungs could be the result of lead-210 entrapment, which, with its half-life of 22 years, could provide a continuous emission of alpha radioactivity, even many years after quitting, thus proposing a possible explanation for the onset of lung cancer, particularly in former smokers

Polonium-210 dynamics in the northern Gulf of Mexico

Polonium-210 (t1/2=138 d) is the most common among the 33 known radioisotopes of Polonium found in the natural environment. It is produced by the radioactive decay of its long-lived grandparent Lead-210(t1/2=22.3 d) via Bismuth-210 (t1/2=5.012 d) and forms as part of the natural Uranium-238 decay series. The primary hazard associated with Polonium-210 is its radioactivity, as an alpha particle emitter. Marine organisms receive their maximum radioactive dose in the natural environment from Polonium-210. Polonium has been known to bioaccumulate in the marine food web and can be potentially harmful to humans via the intake of certain marine organisms. Thus it is important to understand the source and sink of Polonium-210 in the marine environment. A number of studies in the past have observed Polonium-210 remobilization from sediments in anoxic lake environments but the release mechanism has never been studied in low oxygen marine systems. On the other hand, the biological affinity of Polonium-210 allows it to be used as an effective tracer of POC export from the upper ocean, although no such study using Polonium-210 as a tracer of POC flux has been carried out in the northern Gulf of Mexico. The present work is aimed at understanding both remobilization of Polonium-210 from sediments in the hypoxia zone of the northern Gulf of Mexico and utilizing Polonium-210 as a tracer of POC export in the northern Gulf of Mexico. Results from our study indicate Polonium-210 was enriched in bottom waters by as much as 50% compared to surface waters from sample stations in the hypoxia zone in 2011 and 2012. No strong correlation between oxygen concentration and unsupported Polonium-210 activity was apparent. However, there was a good correlation between Polonium-210 enrichment and the release of redox sensitive trace metals like Fe and Mn. Due to the affinity of Polonium-210 to Fe and Mn, the cycling of redox sensitive elements such as Fe and Mn and the degradation of organic matter in the water column are likely the driving mechanisms of Polonium-210 remobilization from sediments to the water column under hypoxic conditions. The second study utilized Polonium-210 as a tracer for POC export and was carried out along a north south transect in the Gulf of Mexico beginning near the mouth of the Atchafalaya River and ending on the slope of the continental shelf. POC fluxes were estimated using the Lead-210 – Polonium-210 disequilibria in the water column and varied between 10.4 mg C m-2 d-1 and 85.6 mg C m-2 d-1 and showed a general decreasing trend further offshore similar to the decrease in net primary productivity further from shore. The efficiency of the biological pump was found to decrease from 21% at stations close to shore to 4% at stations further offshore, suggesting a transition in POC export efficiency from nutrient rich eutrophic water to nutrient poor oligotrophic water

Modeling of electron emission processes accompanying Radon-α\alpha-decays within electrostatic spectrometers

Electrostatic spectrometers utilized in high-resolution beta-spectroscopy studies such as in the Karlsruhe Tritium Neutrino (KATRIN) experiment have to operate with a background level of less than 10^(-2) counts per second. This limit can be exceeded by even a small number of Rn-219 or Rn-220 atoms being emanated into the volume and undergoing alpha-decay there. In this paper we present a detailed model of the underlying background-generating processes via electron emission by internal conversion, shake-off and relaxation processes in the atomic shells of the Po-215 and Po-216 daughters. The model yields electron energy spectra up to 400 keV and electron multiplicities of up to 20 which are compared to experimental data.Comment: 7 figure