Case studies of particle formation events observed in boreal forests: implications for nucleation mechanisms

Aerosol nucleation events observed worldwide may have significant climatic and health implications. However, the specific nucleation mechanisms remain ambiguous. Here, we report case studies of eight nucleation events observed during an intensive field campaign at a boreal forest site (Hyytiälä, Finland) in spring 2005. The present analysis is based on comprehensive kinetic simulations using an ion-mediated nucleation (IMN) model in which the key physical and chemical parameters are constrained by a variety of recent measurements. Out of the 22 days of the campaign on which nucleation events were observed, eight major events were selected for detailed analysis on the basis of indications that the observed air masses were relatively homogeneous. In most of these cases, reasonable agreement is found between IMN predictions and field data for a range of variables, including critical nucleation sizes, size-dependent overcharging ratios, and the concentrations of 1.8–3 nm stable clusters and 3–6 nm particles, and their diurnal variations. The possible reasons leading to substantial differences between observation and theory in some cases are also explored. Statistically, roughly 80% of the nucleation events recorded during the Hyytiälä campaign exhibited mean size-dependent particle overcharging ratios within the range of, or exceeding, those predicted by the IMN model, suggesting that ion nucleation processes were significant during these events. The nucleation rates calculated using the IMN modeling approach are contrasted with those predicted by other theories/models, and key differences between the results are discussed. In particular, it is concluded that the ion nucleation model originally developed by Lovejoy et al. (2004) significantly under-predicts ion nucleation rates, and cannot explain the new observations from Hyytiälä regarding the electrical properties of nanoparticles. We also show that, for the well documented conditions of the Hyytiälä project, the binary and ternary homogeneous nucleation rates calculated using the most current theories would fall well below ~10<sup>−7</sup> cm<sup>−3</sup> s<sup>−1</sup>, and thus would be negligible

Ion-mediated nucleation as an important global source of tropospheric aerosols

International audienceAerosol nucleation events have been observed at a variety of locations worldwide, and may have significant climatic and health implications. While ions have long been suggested as favorable nucleation embryos, their significance as a global source of particles has remained uncertain. Here, an ion-mediated nucleation (IMN) mechanism, which incorporates new thermodynamic data and physical algorithms, has been integrated into a global chemical transport model (GEOS-Chem) to study ion-mediated particle formation in the global troposphere. The simulated annual mean results have been compared to a comprehensive set of data relevant to particle nucleation around the globe. We show that predicted annual spatial patterns of particle formation agree reasonably well with land-, ship-, and aircraft-based observations. Our simulations show that, globally, IMN in the boundary layer is largely confined to two broad latitude belts: one in the northern hemisphere (~20° N?70° N), and one in the southern hemisphere (~30° S?90° S). In the middle latitude boundary layer over continents, the annual mean IMN rates are generally above 104 cm?3day?1, with some hot spots reaching 105 cm?3day?1. The zonally-averaged vertical distribution of IMN rates indicates that IMN is significant in the tropical upper troposphere, the entire middle latitude troposphere, and over Antarctica. Comparing the relative strengths of particle sources due to IMN and due to primary particle emissions demonstrates that IMN is significant on a global scale. Further research is needed to reduce modeling uncertainties and to understand the ultimate contribution of freshly nucleated particles to the abundance of cloud condensation nuclei

An investigation of the ionospheric D region at sunrise

The growth over sunrise of the C and D layers of the ionosphere is investigated. The model which is analyzed includes the negative ion species O(-), O2(-), O3(-), O4(-), NO3(-), CO3(-), and CO4(-). Ionization sources due to galactic cosmic rays, precipitated electrons, ionization of NO by scattered Lyman alpha radiation, and the direct solar radiation ionization are also included. The photodetachment of most of the negative ions is discussed, as well as the time variation of these parameters. The time variations of the electron, negative ion, and positive ion densities are calculated over sunrise. From these data, the mesospheric C and D layer development is plotted. Several model parameters are varied until the best agreement with experimentally determined electron densities is obtained. The results are discussed in light of several atmospheric parameters including the O and NO concentrations and the electron-ion recombination coefficient

Preliminary results of fast neutron treatments in carcinoma of the pancreas

A group of 30 patients with adenocarcinoma of the pancreas including some patients with very advanced disease, were treated with the so-called mixed beam modality employing photon treatments three times per week and neutron treatments twice a week. Two hundred Rads or equivalent Rads (RBE 3.3) were given in daily fractions aiming at a total dose of 6000 Rads in 6 to 8 weeks. The treatments were well tolerated and significant palliation was achieved in 26 to 30 cases. Twelve months survival was 33 percent with a median survival of 7 months or 210 days. Treatment techniques and localization procedures are discussed

Effect of NF-κB/Rel inhibition on spontaneous vs chemotherapy-induced apoptosis in AML and normal cord blood CD34+ cells

n/

Economic Downturns, Urban Growth and Suburban Fertility in a Mediterranean Context

Despite the wealth of micro–macro data on short-term demographic dynamics, the impact of metropolitan growth and economic downturns on local fertility is still under-investigated in advanced economies. Recent studies in low-fertility contexts have assumed suburban birth rates as being systematically higher than urban and rural rates. This assumption (hereafter, known as the ‘suburban fertility hypothesis’) was grounded on stylized facts and spatial regularities that imply a significant role of both macro (contextual) and micro (behavioral) factors positively influencing fertility in suburban locations. To verify such a hypothesis from a macro (contextual) perspective, the present study compares the general fertility rate of urban, suburban, and rural settlements of the Athens’ metropolitan region (Greece) at various observation years between 1860 and 2020. Long-term Athens’ growth represented a sort of ‘quasi-experiment’ for Mediterranean Europe, linking sequential urban stages and distinctive waves of economic expansion and recession. Using multivariate exploratory analysis and global/local econometric models, a dominant ‘rural’ fertility regime was recorded for 1860 and 1884. A characteristic ‘urban’ fertility regime was, instead, found over a relatively long, intermediate period between 1956 and 1990. Higher fertility in suburban settlements (10 km away from downtown Athens, on average) was, finally, observed since 2000. Considering a sufficiently long-time interval, the existence of multiple fertility regimes along the distance gradient has demonstrated how fertility dynamics are intrinsically bonded with metropolitan growth, economic downturns, and social transformations in Mediterranean Europe

A nonlinear Lagrangian particle model for grains assemblies including grain relative rotations

International audienceWe formulate a discrete Lagrangian model for a set of interacting grains, which is purely elastic. The considered degrees of freedom for each grain include placement of barycenter and rotation. Further, we limit the study to the case of planar systems. A representative grain radius is introduced to express the deformation energy to be associated to relative displacements and rotations of interacting grains. We distinguish inter‐grains elongation/compression energy from inter‐grains shear and rotations energies, and we consider an exact finite kinematics in which grain rotations are independent of grain displacements. The equilibrium configurations of the grain assembly are calculated by minimization of deformation energy for selected imposed displacements and rotations at the boundaries. Behaviours of grain assemblies arranged in regular patterns, without and with defects, and similar mechanical properties are simulated. The values of shear, rotation, and compression elastic moduli are varied to investigate the shapes and thicknesses of the layers where deformation energy, relative displacement, and rotations are concentrated. It is found that these concentration bands are close to the boundaries and in correspondence of grain voids. The obtained results question the possibility of introducing a first gradient continuum models for granular media and justify the development of both numerical and theoretical methods for including frictional, plasticity, and damage phenomena in the proposed model

Prolonged epileptic discharges predict seizure recurrence in JME: Insights from prolonged ambulatory EEG

Objective: Markers of seizure recurrence are needed to personalize antiseizure medication (ASM) therapy. In the clinical practice, EEG features are considered to be related to the risk of seizure recurrence for genetic generalized epilepsies (GGE). However, to our knowledge, there are no studies analyzing systematically specific EEG features as indices of ASM efficacy in GGE. In this study, we aimed at identifying EEG indicators of ASM responsiveness in Juvenile Myoclonic Epilepsy (JME), which, among GGE, is characterized by specific electroclinical features. Methods: We compared the features of prolonged ambulatory EEG (paEEG, 22 h of recording) of JME patients experiencing seizure recurrence within a year (“cases”) after EEG recording, with those of patients with sustained seizure freedom for at least 1 year after EEG (“controls”). We included only EEG recordings of patients who had maintained the same ASM regimen (dosage and type) throughout the whole time period from the EEG recording up to the outcome events (which was seizure recurrence for the “cases”, or 1-year seizure freedom for “controls”). As predictors, we evaluated the total number, frequency, mean and maximum duration of epileptiform discharges (EDs) and spike density (i.e. total EDs duration/artifact-free EEG duration) recorded during the paEEG. The same indexes were assessed also in standard EEG (stEEG), including activation methods. Results: Both the maximum length and the mean duration of EDs recorded during paEEG significantly differed between cases and controls; when combined in a binary logistic regression model, the maximum length of EDs emerged as the only valid predictor. A cut-off of EDs duration of 2.68 seconds discriminated between cases and controls with a 100% specificity and a 93% sensitivity. The same indexes collected during stEEG lacked both specificity and sensitivity. Significance: The occurrence of prolonged EDs in EEG recording might represent an indicator of antiepileptic drug failure in JME patients