3-D numerische Modellierung polarer mesosphärischer Eisschichten: Simulation und Analyse von PMC/NLC Strukturen im Vergleich mit Lidar/Satellitendaten

Polare mesosphärische Wolken (PMC) reagieren empfindlich auf atmosphärische Hintergrundfelder. Das Verständnis über Prozesse der mesosphärischen Eisbildung und der Variabilität der Eiswolken ist essentiell, um auf die Dynamik, langfristige Veränderungen und Zusammensetzung der Atmosphäre zu schließen. In dieser Dissertation wurde das Eistransportmodell MIMAS verwendet, um Wechselwirkungen zwischen PMC und atmosphärischen Hintergrundbedingungen in der Nordhemisphäre im Zeitraum 1979 – 2013 zu untersuchen.Polar mesospheric clouds (PMC) are sensitive to atmospheric background fields. Understanding the processes of mesospheric ice formation and variability of these ice clouds are essential to derive conclusions about the dynamics, long-term changes and atmospheric composition. In this work, the ice transport model MIMAS was used to examines the relationships between PMC and atmospheric background conditions in the northern hemisphere in the period 1979 – 2013

Local time dependence of polar mesospheric clouds: A model study

The Mesospheric Ice Microphysics And tranSport model (MIMAS) is used to study local time (LT) variations of polar mesospheric clouds (PMCs) in the Northern Hemisphere during the period from 1979 to 2013. We investigate the tidal behavior of brightness, altitude, and occurrence frequency and find a good agreement between model and lidar observations. At the peak of the PMC layer the mean ice radius varies from 35 to 45nm and the mean number density varies from 80 to 150cm−3 throughout the day. We also analyze PMCs in terms of ice water content (IWC) and show that only amplitudes of local time variations in IWC are sensitive to threshold conditions, whereas phases are conserved. In particular, relative local time variations decrease with larger thresholds. Local time variations also depend on latitude. In particular, absolute local time variations increase towards the pole. Furthermore, a phase shift exists towards the pole which is independent of the threshold value. In particular, the IWC maximum moves backward in time from 08:00LT at midlatitudes to 02:00LT at high latitudes. The persistent features of strong local time modulations in ice parameters are caused by local time structures in background temperature and water vapor. For a single year local time variations of temperature at 69°N are in a range of ±3K near 83km altitude. At sublimation altitudes the water vapor variation is about ±3.5ppmv, leading to a change in the saturation ratio by a factor of about 2 throughout the day

National Landscape of Human Immunodeficiency Virus-Positive Deceased Organ Donors in the United States.

BackgroundOrgan transplantation from donors with human immunodeficiency virus (HIV) to recipients with HIV (HIV D+/R+) presents risks of donor-derived infections. Understanding clinical, immunologic, and virologic characteristics of HIV-positive donors is critical for safety.MethodsWe performed a prospective study of donors with HIV-positive and HIV false-positive (FP) test results within the HIV Organ Policy Equity (HOPE) Act in Action studies of HIV D+/R+ transplantation (ClinicalTrials.gov NCT02602262, NCT03500315, and NCT03734393). We compared clinical characteristics in HIV-positive versus FP donors. We measured CD4 T cells, HIV viral load (VL), drug resistance mutations (DRMs), coreceptor tropism, and serum antiretroviral therapy (ART) detection, using mass spectrometry in HIV-positive donors.ResultsBetween March 2016 and March 2020, 92 donors (58 HIV positive, 34 FP), representing 98.9% of all US HOPE donors during this period, donated 177 organs (131 kidneys and 46 livers). Each year the number of donors increased. The prevalence of hepatitis B (16% vs 0%), syphilis (16% vs 0%), and cytomegalovirus (CMV; 91% vs 58%) was higher in HIV-positive versus FP donors; the prevalences of hepatitis C viremia were similar (2% vs 6%). Most HIV-positive donors (71%) had a known HIV diagnosis, of whom 90% were prescribed ART and 68% had a VL <400 copies/mL. The median CD4 T-cell count (interquartile range) was 194/µL (77-331/µL), and the median CD4 T-cell percentage was 27.0% (16.8%-36.1%). Major HIV DRMs were detected in 42%, including nonnucleoside reverse-transcriptase inhibitors (33%), integrase strand transfer inhibitors (4%), and multiclass (13%). Serum ART was detected in 46% and matched ART by history.ConclusionThe use of HIV-positive donor organs is increasing. HIV DRMs are common, yet resistance that would compromise integrase strand transfer inhibitor-based regimens is rare, which is reassuring regarding safety