Dynamics of a linear magnetic "microswimmer molecule"

In analogy to nanoscopic molecules that are composed of individual atoms, we consider an active "microswimmer molecule". It is built up from three individual magnetic colloidal microswimmers that are connected by harmonic springs and hydrodynamically interact with each other. In the ground state, they form a linear straight molecule. We analyze the relaxation dynamics for perturbations of this straight configuration. As a central result, with increasing self-propulsion, we observe an oscillatory instability in accord with a subcritical Hopf bifurcation scenario. It is accompanied by a corkscrew-like swimming trajectory of increasing radius. Our results can be tested experimentally, using for instance magnetic self-propelled Janus particles, supposably linked by DNA molecules.Comment: 6 pages, 8 figure

How does a flexible chain of active particles swell?

We study the swelling of a flexible linear chain composed of active particles by analytical theory and computer simulation. Three different situations are considered: a free chain, a chain confined to an external harmonic trap, and a chain dragged at one end. First we consider an ideal chain with harmonic springs and no excluded volume between the monomers. The Rouse model of polymers is generalized to the case of self-propelled monomers and solved analytically. The swelling, as characterized by the spatial extension of the chain, scales with the monomer number defining a Flory exponent $\nu$ which is $\nu =1/2, 0, 1$ in the three different situations. As a result, we find that activity does not change the Flory exponent but affects the prefactor of the scaling law. This can be quantitatively understood by mapping the system onto an equilibrium chain with a higher effective temperature such that the chain swells under an increase of the self-propulsion strength. We then use computer simulations to study the effect of self-avoidance on active polymer swelling. In the three different situations, the Flory exponent is now $\nu = 3/4, 1/4, 1$ and again unchanged under self-propulsion. However, the chain extension behaves non-monotonic in the self-propulsion strength.Comment: (9 pages, 5 figures

Zum Zusammenhang von Geschlechterungleichheiten in Bildung, Beruf und Karriere : ein Ausblick

Ziel der folgenden Ausführungen im abschliessenden Teil dieses Sammelbands zur Entwicklung und Genese von geschlechtsspezifischen Bildungsungleichheiten ist es, den Blick zu öffnen in Richtung Berufsleben. Wie sind die verbesserten Bildungsmöglichkeiten von Frauen zu interpretieren? Ist es in den letzten Jahrzehnten gelungen, eines der grundlegendsten gesellschaftlichen Ungleichheitsverhältnisse zu beseitigen? Oder beginnt sich dieses sogar zu verkehren in eine gesellschaftliche Benachteiligung der Männer? Wir gehen bei unseren Überlegungen von der These aus, dass ein Abbau von Benachteiligungen der Frauen im Bildungssystem für sich genommen noch wenig aussagekräftig ist, wenn wir uns mit der klassischen soziologischen Frage der Persistenz bzw. des Wandels von gesellschaftlichen Ungleichheiten befassen wollen. Erst wenn die ganze Verknüpfung von Bildung und gesellschaftlicher Ungleichheit in den Blick genommen wird und sich dabei zeigt, dass Frauen ihre Bildungsgewinne auch in entsprechende Chancen im Beschäftigungssystem umsetzen können, sind ihre verbesserten Bildungschancen ein Gewinn für die Individuen und ein Fortschritt für die Gesellschaft – und erst dann könnten mögliche Bildungsvorteile von Frauen, wie sie in den vorliegenden Aufsätzen z.T. diagnostiziert werden, gar als neue gesellschaftliche Benachteiligungen von Männern skandalisiert werden

Osteosarcopenia, an asymmetrical overlap of two connected syndromes

Osteoporosis and sarcopenia are two chronic conditions, which widely affect older people and share common risk factors. We investigated the prevalence of low bone mineral density (BMD) and sarcopenia, including the overlap of both conditions (osteosarcopenia) in 572 older hospitalized patients (mean age 75.1 $\pm$ 10.8 years, 78% women) with known or suspected osteoporosis in this prospective observational multicenter study. Sarcopenia was assessed according to the revised definition of the European Working Group on Sarcopenia in Older People (EWGSOP2). Low BMD was defined according to the World Health Organization (WHO) recommendations as a T-score < −1.0. Osteosarcopenia was diagnosed when both low BMD and sarcopenia were present. Low BMD was prevalent in 76% and the prevalence of sarcopenia was 9%, with 90% of the sarcopenic patients showing the overlap of osteosarcopenia (8% of the entire population). Conversely, only few patients with low BMD demonstrated sarcopenia (11%). Osteosarcopenic patients were older and frailer and had lower BMI, fat, and muscle mass, handgrip strength, and T-score compared to nonosteosarcopenic patients. We conclude that osteosarcopenia is extremely common in sarcopenic subjects. Considering the increased risk of falls in patients with sarcopenia, they should always be evaluated for osteoporosis

Effect of plasma exchange on COVID-19 associated excess of von Willebrand factor and inflammation in critically ill patients

Ubiquitous microthromboses in the pulmonary vasculature play a crucial role in the pathogenesis of COVID-19 associated acute respiratory distress syndrome (ARDS). Excess of Willebrand factor (vWf) with intravascular multimer formation was identified as a key driver of this finding. Plasma exchange (PLEX) might be a therapeutic option to restore the disbalance between vWf and ADAMTS13. We report the effects of PLEX on vWf, ADAMTS13, inflammatory cytokines and parameters of ventilation. We investigated 25 patients, who were on mechanical ventilation for COVID-19 pneumonia with ARDS at two German university hospitals. All patients received PLEX as an ultima ratio measure for refractory ARDS. VWf antigen (vWf:Ag), ADAMTS13 activity, a cytokine panel mirroring the inflammatory situation and clinical parameters were assessed before and after three to six PLEX therapies with fresh frozen plasma. Before the PLEX sequence there was an excessive release of vWf:Ag (425.4 $\pm$ 167.5%) and mildly reduced ADAMTS13 activity (49.7 $\pm$ 23.3%). After the PLEX series, there was a significant increase of ADAMTS13 activity to 62.4 $\pm$ 17.7% (p = 0.029) and a significant decrease of vWf:Ag to 336.1 $\pm$ 138.2% (p = 0.041) resulting in a 63% improvement of the ADAMT13/vWf:Ag ratio from 14.5 $\pm$ 10.0 to 23.7 $\pm$ 14.6, p = 0.024. Comparison of parameters before and after individual PLEX sessions (n = 35) revealed a mean reduction of vWf from 387.8 $\pm$ 165.1 to 213.2 $\pm$ 62.3% (p = 0.001) and an increase of ADAMTS13 activity from 60.4 $\pm$ 20.1 to 70.5 $\pm$ 14.0% (p = 0.001). Parallelly, monocyte chemotactic protein-1 and interleukin-18 decreased significantly (p = 0.034 each). Along the PLEX sequence lactate dehydrogenase (p = 0.001), C-reactive protein (p = 0.001), and positive end expiratory pressure (p = 0.01) significantly decreased accompanied by an improvement of Horovitz index (p = 0.001). PLEX restores the disbalance between ADAMTS13 and vWf:Ag, a driver of immunothrombosis. Moreover, it reduces the inflammatory state and is associated with a benefit of ventilation parameters. These findings render a further rationale to regard PLEX as a therapeutic option in severe COVID-19

Effect of Antiplatelet Therapy on Survival and Organ Support–Free Days in Critically Ill Patients With COVID-19

International audienc