Positive feedback control of Rayleigh-Bénard convection

We consider the problem of active feedback control of rbc via shadowgraphic measurement. Our theoretical studies show, that when the feedback control is positive, i.e. is tuned to advance the onset of convection, there is a critical threshold beyond which the system becomes linearly ill-posed so that short-scale disturbances are greatly amplified. Experimental observation suggests that finite size effects become important and we develop a theory to explain these contributions. As an efficient modelling tool for studying the dynamics of such a controlled pattern forming system, we use a Galerkin approximation to derive a dimension reduced model

Influence of the Neutralization Degree on the Ice Nucleation Ability of Ammoniated Sulfate Particles

Previous laboratory measurements suggest that ammonium sulfate crystals (AS, (NH4)2 SO4) are efficient ice-nucleating particles under cirrus conditions. Sulfate particles not completely neutralized by ammonium are less well studied and include two other solids, ammonium bisulfate (AHS, NH4HSO4 ) and letovicite (LET, (NH 4)3H(SO4)2). In this work, we have obtained the first comprehensive data set for the heterogeneous ice nucleation ability of crystallized particles in the AS–LET–AHS system as a function of their degree of neutralization at a temperature of about 220 K. Quantitative data on nucleation onsets, ice-active fractions, and ice nucleation active surface site densities were derived from expansion cooling experiments in a large cloud chamber and measurements with two continuous flow diffusion chambers. We found a strong dependence of the efficiency and the mode of heterogenous ice nucleation on the degree of neutralization. Ice formation for AS, mixed AS/LET, and LET crystals occurred by the deposition nucleation or pore condensation and freezing mode. The lowest nucleation onset was observed for AS, where 0.1% of the particles became ice-active at an ice saturation ratio of 1.25. This threshold gradually increased to 1.35 for LET, and abruptly further to 1.45 for mixed LET/AHS crystals, which partially deliquesced and induced ice formation via immersion freezing. Pure AHS crystals did not form due to the inhibition of efflorescence. Our data allow for a more sophisticated treatment of ice formation in the AS–LET–AHS system in future model simulations, which have so far only considered the available data for AS alone

Takotsubo Syndrome Associated with COVID-19

Objective: The availability of public health information for optimised supportive care is critical during the COVID-19 pandemic. We describe the first case of COVID-19 complicated by Takotsubo cardiomyopathy. Materials and Methods: We report the clinical, laboratory and radiological findings of a patient with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Results: The nasopharyngeal swab was positive for SARS-CoV-2 and x-ray images demonstrated pathognomonic pneumonia. The patient developed tachycardia and the echocardiogram confirmed the diagnosis of Takotsubo cardiomyopathy. Conclusions: Doctors should be aware of the need to thoroughly study this new infection in order to understand its underlying mechanisms and related complications

The seasonal cycle of ice-nucleating particles linked to the abundance of biogenic aerosol in boreal forests

Ice-nucleating particles (INPs) trigger the formation of cloud ice crystals in the atmosphere. Therefore, they strongly influence cloud microphysical and optical properties and precipitation and the life cycle of clouds. Improving weather forecasting and climate projection requires an appropriate formulation of atmospheric INP concentrations. This remains challenging as the global INP distribution and variability depend on a variety of aerosol types and sources, and neither their short-term variability nor their long-term seasonal cycles are well covered by continuous measurements. Here, we provide the first year-long set of observations with a pronounced INP seasonal cycle in a boreal forest environment. Besides the observed seasonal cycle in INP concentrations with a minimum in wintertime and maxima in early and late summer, we also provide indications for a seasonal variation in the prevalent INP type. We show that the seasonal dependency of INP concentrations and prevalent INP types is most likely driven by the abundance of biogenic aerosol. As current parameterizations do not reproduce this variability, we suggest a new mechanistic description for boreal forest environments which considers the seasonal variation in INP concentrations. For this, we use the ambient air temperature measured close to the ground at 4.2 m height as a proxy for the season, which appears to affect the source strength of biogenic emissions and, thus, the INP abundance over the boreal forest. Furthermore, we provide new INP parameterizations based on the Ice Nucleation Active Surface Site (INAS) approach, which specifically describes the ice nucleation activity of boreal aerosols particles prevalent in different seasons. Our results characterize the boreal forest as an important but variable INP source and provide new perspectives to describe these new findings in atmospheric models.Peer reviewe

Role of blood cells dynamism on hemostatic complications in low-risk patients with essential thrombocythemia

Patients with essential thrombocythemia (ET) aged less than 60 years, who have not suffered a previous vascular event (low-risk patients), may develop thrombotic or hemorrhagic events. So far, it has not been possible to identify useful markers capable of predicting which of these patients are more likely to develop an event and therefore who needs to be treated. In the present study, we analysed the relationship between vascular complications and longitudinal blood counts of 136 low-risk ET patients taken over a sustained period of time (blood cells dynamism). After a median follow-up of 60 months, 45 out of 136 patients (33%) suffered 40 major thrombotic and 5 severe hemorrhagic complications. A total number of 5,781 blood counts were collected longitudinally. Thrombotic and hemorrhagic events were studied together (primary endpoint) but also separately (thrombotic alone = secondary endpoint; hemorrhagic alone = tertiary endpoint). The primary endpoint showed no significant association between platelet and WBC count at diagnosis and risk of any event (platelet, p = 0.797; WBC, p = 0.178), while Hb at baseline did show an association (p = 0.024). In the dynamic analysis with Cox regression model, where the blood count values were studied by time of follow-up, we observed that the risk for Hb was 1.49 (95% CI 1.13-1.97) for every increase of 1 g/dL, and that this risk then marginally decreased during follow-up. WBC was associated with an increased risk at baseline for every increase of 1 7 10(9)/L (hazard ratio (HR) 1.07, 95% CI 1.01-1.13, p = 0.034), the risk was stable during follow-up (HR 0.95, p = 0.187 at 60 months). Also, for each increment at baseline of 100 7 10(9) platelets/L, HR was increased by 1.08 (95% CI 0.97-1.22, p = 0.159) and decreases during follow-up. In conclusion, this study is the first to evaluate in ET low-risk patients, the risk of developing a thrombotic/hemorrhagic event considering blood counts over time. Overall our study shows that the risk changes over time. For example, the risk associated with WCC is not linear as previously reported. An interesting new finding is that PLT and even Hb contribute to the risk of developing vascular events. Future treatments should take into consideration these findings and aim to control all parameters over time. We believe this early study may help develop a dynamic analysis model to predict thrombosis in the single patient. Further studies are now warranted to further validate our findings

Measurement report : Introduction to the HyICE-2018 campaign for measurements of ice-nucleating particles and instrument inter-comparison in the Hyytiala boreal forest

The formation of ice particles in Earth's atmosphere strongly influences the dynamics and optical properties of clouds and their impacts on the climate system. Ice formation in clouds is often triggered heterogeneously by ice-nucleating particles (INPs) that represent a very low number of particles in the atmosphere. To date, many sources of INPs, such as mineral and soil dust, have been investigated and identified in the low and mid latitudes. Although less is known about the sources of ice nucleation at high latitudes, efforts have been made to identify the sources of INPs in the Arctic and boreal environments. In this study, we investigate the INP emission potential from high-latitude boreal forests in the mixed-phase cloud regime. We introduce the HyICE-2018 measurement campaign conducted in the boreal forest of Hyytiala, Finland, between February and June 2018. The campaign utilized the infrastructure of the Station for Measuring Ecosystem-Atmosphere Relations (SMEAR) II, with additional INP instruments, including the Portable Ice Nucleation Chamber I and II (PINC and PINCii), the SPectrometer for Ice Nuclei (SPIN), the Portable Ice Nucleation Experiment (PINE), the Ice Nucleation SpEctrometer of the Karlsruhe Institute of Technology (INSEKT) and the Microlitre Nucleation by Immersed Particle Instrument (mu L-NIPI), used to quantify the INP concentrations and sources in the boreal environment. In this contribution, we describe the measurement infrastructure and operating procedures during HyICE-2018, and we report results from specific time periods where INP instruments were run in parallel for inter-comparison purposes. Our results show that the suite of instruments deployed during HyICE-2018 reports consistent results and therefore lays the foundation for forthcoming results to be considered holistically. In addition, we compare measured INP concentrations to INP parameterizations, and we observe good agreement with the Tobo et al. (2013) parameterization developed from measurements conducted in a ponderosa pine forest ecosystem in Colorado, USA.Peer reviewe

Measurement report : Introduction to the HyICE-2018 campaign for measurements of ice-nucleating particles and instrument inter-comparison in the Hyytiala boreal forest

The formation of ice particles in Earth's atmosphere strongly influences the dynamics and optical properties of clouds and their impacts on the climate system. Ice formation in clouds is often triggered heterogeneously by ice-nucleating particles (INPs) that represent a very low number of particles in the atmosphere. To date, many sources of INPs, such as mineral and soil dust, have been investigated and identified in the low and mid latitudes. Although less is known about the sources of ice nucleation at high latitudes, efforts have been made to identify the sources of INPs in the Arctic and boreal environments. In this study, we investigate the INP emission potential from high-latitude boreal forests in the mixed-phase cloud regime. We introduce the HyICE-2018 measurement campaign conducted in the boreal forest of Hyytiala, Finland, between February and June 2018. The campaign utilized the infrastructure of the Station for Measuring Ecosystem-Atmosphere Relations (SMEAR) II, with additional INP instruments, including the Portable Ice Nucleation Chamber I and II (PINC and PINCii), the SPectrometer for Ice Nuclei (SPIN), the Portable Ice Nucleation Experiment (PINE), the Ice Nucleation SpEctrometer of the Karlsruhe Institute of Technology (INSEKT) and the Microlitre Nucleation by Immersed Particle Instrument (mu L-NIPI), used to quantify the INP concentrations and sources in the boreal environment. In this contribution, we describe the measurement infrastructure and operating procedures during HyICE-2018, and we report results from specific time periods where INP instruments were run in parallel for inter-comparison purposes. Our results show that the suite of instruments deployed during HyICE-2018 reports consistent results and therefore lays the foundation for forthcoming results to be considered holistically. In addition, we compare measured INP concentrations to INP parameterizations, and we observe good agreement with the Tobo et al. (2013) parameterization developed from measurements conducted in a ponderosa pine forest ecosystem in Colorado, USA.Peer reviewe

Survival of newly formed particles in haze conditions

Intense new particle formation events are regularly observed under highly polluted conditions, despite the high loss rates of nucleated clusters. Higher than expected cluster survival probability implies either ineffective scavenging by pre-existing particles or missing growth mechanisms. Here we present experiments performed in the CLOUD chamber at CERN showing particle formation from a mixture of anthropogenic vapours, under condensation sinks typical of haze conditions, up to 0.1 s(-1). We find that new particle formation rates substantially decrease at higher concentrations of pre-existing particles, demonstrating experimentally for the first time that molecular clusters are efficiently scavenged by larger sized particles. Additionally, we demonstrate that in the presence of supersaturated gas-phase nitric acid (HNO3) and ammonia (NH3), freshly nucleated particles can grow extremely rapidly, maintaining a high particle number concentration, even in the presence of a high condensation sink. Such high growth rates may explain the high survival probability of freshly formed particles under haze conditions. We identify under what typical urban conditions HNO3 and NH3 can be expected to contribute to particle survival during haze.Peer reviewe