Uranium and Radon in Private Bedrock Well Water in Maine: Geospatial Analysis at Two Scales

In greater Augusta of central Maine, 53 out of 1093 (4.8%) private bedrock well water samples from 1534 km² contained [U] > 30 μg/L, the U.S. Environmental Protection Agency’s (EPA) Maximum Contaminant Level (MCL) for drinking water; and 226 out of 786 (29%) samples from 1135 km² showed [Rn] > 4,000 pCi/L (148 Bq/L), the U.S. EPA’s Alternative MCL. Groundwater pH, calcite dissolution and redox condition are factors controlling the distribution of groundwater U but not Rn due to their divergent chemical and hydrological properties. Groundwater U is associated with incompatible elements (S, As, Mo, F, and Cs) in water samples within granitic intrusions. Elevated [U] and [Rn] are located within 5–10 km distance of granitic intrusions but do not show correlations with metamorphism at intermediate scales (10⁰−10¹ km). This spatial association is confirmed by a high-density sampling (n = 331, 5–40 samples per km²) at local scales (≤10–1 km) and the statewide sampling (n = 5857, 1 sample per 16 km²) at regional scales (10²–103 km). Wells located within 5 km of granitic intrusions are at risk of containing high levels of [U] and [Rn]. Approximately 48 800–63 900 and 324 000 people in Maine are estimated at risk of exposure to U (> 30 μg/L) and Rn (> 4000 pCi/L) in well water, respectively

Fusion pore expansion is a slow, discontinuous, and Ca2+-dependent process regulating secretion from alveolar type II cells

In alveolar type II cells, the release of surfactant is considerably delayed after the formation of exocytotic fusion pores, suggesting that content dispersal may be limited by fusion pore diameter and subject to regulation at a postfusion level. To address this issue, we used confocal FRAP and N-(3-triethylammoniumpropyl)-4-(4-[dibutylamino]styryl) pyridinium dibromide (FM 1-43), a dye yielding intense localized fluorescence of surfactant when entering the vesicle lumen through the fusion pore (Haller, T., J. Ortmayr, F. Friedrich, H. Volkl, and P. Dietl. 1998. Proc. Natl. Acad. Sci. USA. 95:1579–1584). Thus, we have been able to monitor the dynamics of individual fusion pores up to hours in intact cells, and to calculate pore diameters using a diffusion model derived from Fick's law. After formation, fusion pores were arrested in a state impeding the release of vesicle contents, and expanded at irregular times thereafter. The expansion rate of initial pores and the probability of late expansions were increased by elevation of the cytoplasmic Ca2+ concentration. Consistently, content release correlated with the occurrence of Ca2+ oscillations in ATP-treated cells, and expanded fusion pores were detectable by EM. This study supports a new concept in exocytosis, implicating fusion pores in the regulation of content release for extended periods after initial formation

Thermal Stability of Fluorocarbon Films Deposited from Pentafluoroethane/Argon Plasmas

Plasma deposited fluorocarbon films have received considerable attention recently as potential interlevel dielectrics for future generation integrated circuits (ICs). 1,2 Apart from their low dielectric constant (<2.6), they also possess other favorable characteristics such as low moisture absorption, high chemical inertness, and plasma-assisted conformal step coverage. In this study, the effect of applied power and substrate temperature on the chemical structure, chemical composition, and thermal stability of the plasma-deposited fluorocarbon films was investigated by means of X-ray photoelectron spectroscopy (XPS), IR spectroscopy, and thermogravimetric analysis (TGA). The monomer studied, pentafluoroethane (CF 3 CHF 2 ), was selected because of its shorter atmospheric lifetime relative to that of pure fluorocarbon gases. Experimental A parallel-plate radio frequency (rf) plasma reactor was used for the deposition of fluorocarbon films from pentafluoroethane/argon mixtures. Details of the reactor setup and operation are given elsewhere, 7 so only a brief description is presented here. The distance between the 4 cm diam, parallel-plate, stainless steel disk electrodes was fixed at 2.9 cm for all experiments. RF power at 13.56 MHz from an ENI power systems HF-300 rf generator was coupled to the top electrode using a Heathkit SA-2060A antenna tuner. Substrates were placed on the grounded electrode whose temperature was regulated with a Syskon RKC temperature controller. Depositions were carried out at substrate temperatures of 120, 180, and 210ЊC, and a constant operating pressure of 1 Torr. The flow rates of pentafluoroethane and argon were set at 20 and 75 sccm, respectively, for all depositions. In some cases, films deposited at a specific substrate or deposition temperature were heated to 200ЊC in the reactor immediately after deposition and held there for 2 h in vacuum. In the following discussions, this heat-treatment of the deposited films in vacuum is referred to as postdeposition annealing. In this study, films deposited onto both the temperature-controlled, grounded electrode and the powered electrode without temperature control, were characterized by various analytical techniques including TGA, IR, XPS, and mass spectrometry. IR spectra of the deposited films were collected in reflection mode at a grazing angle of 70Њ using a Nicolet Magna-IR 560 Fourier transform infrared (FTIR) spectrometer. All spectra were recorded at a resolution of 4 cm Ϫ1 and averaged over 512 scans. In order to improve the signal-to-noise ratio, fluorocarbon films were deposited onto silicon substrates that had been sputter coated with a 300 nm layer of aluminum. Films deposited on the powered electrode were analyzed directly on the stainless steel powered electrode. XPS was used to obtain the chemical composition and bonding structure of polymer films. Spectra were collected using a PHI model 1600 XPS system equipped with a monochromator. The sample was exposed to monochromatized Al K␣ X-rays, and the ejected photoelectrons were detected by a multichannel hemispherical detector that provided high-energy sensitivity and resolution. Chamber pressure was typically below 5 ϫ 10 Ϫ9 Torr during analysis. High-resolution spectra were collected for C 1s, O 1s, N 1s, and F 1s Fluorocarbon films were deposited from pentafluoroethane/argon mixtures in a parallel-plate reactor at a pressure of 1 Torr and substrate temperatures between 120 and 210ЊC. Films deposited on substrates placed on the heated, grounded electrode as well as films formed on the powered electrode were analyzed using infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). Polymer deposition rates decreased with an increase in substrate temperature indicating that reactant adsorption is the rate-limiting step. Films deposited on the powered electrode had an O/C ratio of 0.14, which was significantly higher than that of films deposited on the grounded electrode at elevated temperatures. Likewise, IR spectra of films on the powered electrode also showed significant contributions from CϭO related groups. TGA data indicated that the powered electrode films had ϳ3% weight loss at 250ЊC, while films deposited on the grounded electrode had ϳ1% weight loss at 250ЊC. The thermal stability of films deposited on the grounded electrode was significantly enhanced when deposited at higher substrate temperatures. XPS analyses indicated a decrease in the F/C ratio of the deposited films with an increase in substrate temperature. TGA analyses indicated that weight loss below 250ЊC was due primarily to the outgassing of low-molecular weight species from the fluorocarbon films. The higher weight loss region between 320 and 425ЊC was ascribed to polymer degradation due to scission of main chain C-C bonds and to evolution of HF and CO 2

Molecular Dynamics Simulations

A tutorial introduction to the technique of Molecular Dynamics (MD) is given, and some characteristic examples of applications are described. The purpose and scope of these simulations and the relation to other simulation methods is discussed, and the basic MD algorithms are described. The sampling of intensive variables (temperature T, pressure p) in runs carried out in the microcanonical (NVE) ensemble (N= particle number, V = volume, E = energy) is discussed, as well as the realization of other ensembles (e.g. the NVT ensemble). For a typical application example, molten SiO2, the estimation of various transport coefficients (self-diffusion constants, viscosity, thermal conductivity) is discussed. As an example of Non-Equilibrium Molecular Dynamics (NEMD), a study of a glass-forming polymer melt under shear is mentioned.Comment: 38 pages, 11 figures, to appear in J. Phys.: Condens. Matte

Observational constraints on the chemistry of isoprene nitrates over the eastern United States

The formation of organic nitrates during the oxidation of the biogenic hydrocarbon isoprene can strongly affect boundary layer concentrations of ozone and nitrogen oxides (NOx = NO + NO2). We constrain uncertainties in the chemistry of these isoprene nitrates using chemical transport model simulations in conjunction with observations over the eastern United States from the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) field campaign during summer 2004. The model best captures the observed boundary layer concentrations of organic nitrates and their correlation with ozone using a 4% yield of isoprene nitrate production from the reaction of isoprene hydroxyperoxy radicals with NO, a recycling of 40% NOx when isoprene nitrates react with OH and ozone, and a fast dry deposition rate of isoprene nitrates. Simulated boundary layer concentrations are only weakly sensitive to the rate of photochemical loss of the isoprene nitrates. An 8% yield of isoprene nitrates degrades agreement with the observations somewhat, but concentrations are still within 50% of observations and thus cannot be ruled out by this study. Our results indicate that complete recycling of NOx from the reactions of isoprene nitrates and slow rates of isoprene nitrate deposition are incompatible with the observations. We find that ∼50% of the isoprene nitrate production in the model occurs via reactions of isoprene (or its oxidation products) with the NO3 radical, but note that the isoprene nitrate yield from this pathway is highly uncertain. Using recent estimates of rapid reaction rates with ozone, 20–24% of isoprene nitrates are lost via this pathway, implying that ozonolysis is an important loss process for isoprene nitrates. Isoprene nitrates are shown to have a major impact on the nitrogen oxide (NOx = NO + NO2) budget in the summertime U.S. continental boundary layer, consuming 15–19% of the emitted NOx, of which 4–6% is recycled back to NOx and the remainder is exported as isoprene nitrates (2–3%) or deposited (8–10%). Our constraints on reaction rates, branching ratios, and deposition rates need to be confirmed through further laboratory and field measurements. The model systematically underestimates free tropospheric concentrations of organic nitrates, indicating a need for future investigation of the processes controlling the observed distribution

Islet lymphocyte subsets in male and female NOD mice are qualitatively similar but quantitatively distinct

Islet-infiltrating lymphocytes of individual male and female non-obese diabetic (NOD) mice were examined with the purpose of determining the differences that lead to a predominance of diabetes in female versus males NOD mice. When normalized for the amount of islet lymphocytes recovered, the infiltrating lymphocytes of female NOD mice were indistinguishable from those of male NOD mice. The only observed difference was that islet inflammation progressed at an increased rate in female compared to male NOD mice. There was no difference in the composition of islet infiltrates in male and female NOD mice. Unexpectedly, the ratio of CD4+:CD8+ T cells was tightly controlled in the islets throughout diabetogenesis. The frequency of IL-4+ CD4+ T cells started high but quickly fell to 3% of the population which was maintained with increasing inflammation. A significant portion of the CD8+ T cells were islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) specific in both male and female NOD mice and this population was antigen experienced and increased at high levels of islet inflammation. Surprisingly, a large pool of antigen inexperienced naïve T cells was detected in the islets. We conclude the underlying immunological processes in both male and female NOD mice are similar while the rates differ and the presence of naïve T cell in the islets may contribute to epitope spreading

Observation of a prethermal discrete time crystal

The conventional framework for defining and understanding phases of matter requires thermodynamic equilibrium. Extensions to non-equilibrium systems have led to surprising insights into the nature of many-body thermalization and the discovery of novel phases of matter, often catalyzed by driving the system periodically. The inherent heating from such Floquet drives can be tempered by including strong disorder in the system, but this can also mask the generality of non-equilibrium phases. In this work, we utilize a trapped-ion quantum simulator to observe signatures of a non-equilibrium driven phase without disorder: the prethermal discrete time crystal (PDTC). Here, many-body heating is suppressed not by disorder-induced many-body localization, but instead via high-frequency driving, leading to an expansive time window where non-equilibrium phases can emerge. We observe a number of key features that distinguish the PDTC from its many-body-localized disordered counterpart, such as the drive-frequency control of its lifetime and the dependence of time-crystalline order on the energy density of the initial state. Floquet prethermalization is thus presented as a general strategy for creating, stabilizing and studying intrinsically out-of-equilibrium phases of matter.Comment: 9 + 10 pages, 3 + 6 figure

Conformational and Structural Relaxations of Poly(ethylene oxide) and Poly(propylene oxide) Melts: Molecular Dynamics Study of Spatial Heterogeneity, Cooperativity, and Correlated Forward-Backward Motion

Performing molecular dynamics simulations for all-atom models, we characterize the conformational and structural relaxations of poly(ethylene oxide) and poly(propylene oxide) melts. The temperature dependence of these relaxation processes deviates from an Arrhenius law for both polymers. We demonstrate that mode-coupling theory captures some aspects of the glassy slowdown, but it does not enable a complete explanation of the dynamical behavior. When the temperature is decreased, spatially heterogeneous and cooperative translational dynamics are found to become more important for the structural relaxation. Moreover, the transitions between the conformational states cease to obey Poisson statistics. In particular, we show that, at sufficiently low temperatures, correlated forward-backward motion is an important aspect of the conformational relaxation, leading to strongly nonexponential distributions for the waiting times of the dihedrals in the various conformational statesComment: 13 pages, 13 figure