192 research outputs found
Modelling of surfactant-driven front instabilities in spreading bacterial colonies
The spreading of bacterial colonies at solid-air interfaces is determined by
the physico-chemical properties of the involved interfaces. The production of
surfactant molecules by bacteria is a widespread strategy that allows the
colony to efficiently expand over the substrate. On the one hand, surfactant
molecules lower the surface tension of the colony, effectively increasing the
wettability of the substrate, which facilitates spreading. On the other hand,
gradients in the surface concentration of surfactant molecules result in
Marangoni flows that drive spreading. These flows may cause an instability of
the circular colony shape and the subsequent formation of fingers. In this
work, we study the effect of bacterial surfactant production and substrate
wettability on colony growth and shape within the framework of a hydrodynamic
thin film model. We show that variations in the wettability and surfactant
production are sufficient to reproduce four different types of colony growth,
which have been described in the literature, namely, arrested and continuous
spreading of circular colonies, slightly modulated front lines and the
formation of pronounced fingers
From a thin film model for passive suspensions towards the description of osmotic biofilm spreading
Biofilms are ubiquitous macro-colonies of bacteria that develop at various
interfaces (solid-liquid, solid-gas or liquid-gas). The formation of biofilms
starts with the attachment of individual bacteria to an interface, where they
proliferate and produce a slimy polymeric matrix - two processes that result in
colony growth and spreading. Recent experiments on the growth of biofilms on
agar substrates under air have shown that for certain bacterial strains, the
production of the extracellular matrix and the resulting osmotic influx of
nutrient-rich water from the agar into the biofilm are more crucial for the
spreading behaviour of a biofilm than the motility of individual bacteria. We
present a model which describes the biofilm evolution and the advancing biofilm
edge for this spreading mechanism. The model is based on a gradient dynamics
formulation for thin films of biologically passive liquid mixtures and
suspensions, supplemented by bioactive processes which play a decisive role in
the osmotic spreading of biofilms. It explicitly includes the wetting
properties of the biofilm on the agar substrate via a disjoining pressure and
can therefore give insight into the interplay between passive surface forces
and bioactive growth processes
Thin-Film Modelling of Resting and Moving Active Droplets
We propose a generic model for thin films and shallow drops of a polar active
liquid that have a free surface and are in contact with a solid substrate. The
model couples evolution equations for the film height and the local
polarization profile in the form of a gradient dynamics supplemented with
active stresses and fluxes. A wetting energy for a partially wetting liquid is
incorporated allowing for motion of the liquid-solid-gas contact line. This
gives a consistent basis for the description of drops of dense bacterial
suspensions or compact aggregates of living cells on solid substrates. As
example, we analyze the dynamics of two-dimensional active drops (i.e., ridges)
and demonstrate how active forces compete with passive surface forces to shape
droplets and drive contact line motion. The model reproduces moving and resting
states of polarized droplets: Drops containing domains of opposite polarization
are stationary and evolve after long transients into drops with a uniform
polarization moving actively over the substrate. In our simple two-dimensional
scenario droplet motion sets in at infinitely small self-propulsion force,
i.e., it does not need to overcome a critical threshold.Comment: 17 pages, 16 figure
A new method to distinguish gravitational-wave signals from detector noise transients with Gravity Spy
The Advanced LIGO and Advanced Virgo detectors have enabled the confident
detection of dozens of mergers of black holes and neutron stars. However, the
presence of detector noise transients (glitches) hinders the search for these
gravitational wave (GW) signals. We prototyped a restructuring of Gravity Spy's
classification model to distinguish between glitches and astrophysical signals.
Our method is able to correctly classify three-quarters of retracted candidate
events in O3b as non-astrophysical and 100\% of the confirmed astrophysical
events as true signals. This approach will inform candidate event validation
efforts in the latest observing run.Comment: 11 pages, 7 figures, submitted to PHYSICAL REVIEW
Cardioprotective Effects of Palmitoleic Acid (C16:1n7) in a Mouse Model of Catecholamine-Induced Cardiac Damage Are Mediated by PPAR Activation
Palmitoleic acid (C16:1n7) has been identified as a regulator of physiological cardiac hypertrophy. In the present study, we aimed to investigate the molecular pathways involved in C16:1n7 responses in primary murine cardiomyocytes (PCM) and a mouse model of isoproterenol (ISO)-induced cardiac damage. PCMs were stimulated with C16:1n7 or a vehicle. Afterwards, RNA sequencing was performed using an Illumina HiSeq sequencer. Confirmatory analysis was performed in PCMs and HL-1 cardiomyocytes. For an in vivo study, 129 sv mice were orally treated with a vehicle or C16:1n7 for 22 days. After 5 days of pre-treatment, the mice were injected with ISO (25 mg/kg/d s. c.) for 4 consecutive days. Cardiac phenotyping was performed using echocardiography. In total, 129 genes were differentially expressed in PCMs stimulated with C16:1n7, including Angiopoietin-like factor 4 (Angptl4) and Pyruvate Dehydrogenase Kinase 4 (Pdk4). Both Angptl4 and Pdk4 are proxisome proliferator-activated receptor α/δ (PPARα/δ) target genes. Our in vivo results indicated cardioprotective and anti-fibrotic effects of C16:1n7 application in mice. This was associated with the C16:1n7-dependent regulation of the cardiac PPAR-specific signaling pathways. In conclusion, our experiments demonstrated that C16:1n7 might have protective effects on cardiac fibrosis and inflammation. Our study may help to develop future lipid-based therapies for catecholamine-induced cardiac damage
Refocusing marketing effort to support net-positive social impact
Purpose.
Social impact research remains in its infancy. The purpose of the paper is to build on Keeling and Marshall’s (2022) “Call for impact” paper and develop a comprehensive social impact pathway (SIP) framework. The aim is to encourage marketing researchers, non-profits and corporations to pursue impactful work that is valued, planned, monitored and evaluated.
Design/methodology/approach.
The conceptual paper explores the complexities of estimating social impact drawing from a range of illustrative cases.
Findings.
The paper identifies a lack of clarity in the understanding and application of impact and presents a pathway aimed at increasing focus on social impact across future work to deliver the net-positive changes that are needed to reverse biodiversity decline, climate change and social and health inequalities that continue to be persist and be experienced by so many planet wide.
Research limitations/implications.
This paper contributes a pathway forward to encourage and support increased utilisation of the framework in future marketing research.
Practical implications.
Mapping and measuring SIPs are concerted efforts directing understanding towards identifying the activities that are contributing to the delivery of outputs that can achieve intended outcomes. The measurement of impact directs investment towards activities that ensure net-positive gains are achieved.
Social implications.
Ever growing social inequities, health disparities, loss of biodiversity and environmental degradation occur when practices are left unchecked. A focus on impact avoids greenwashing practices, ensuring that an understanding of what has changed because of the work is transparently reported.
Originality/value.
This paper aims to encourage marketing researchers to engage in social change projects, rather than solely disseminating academic findings. Emphasising the importance of an outside-in approach, this paper highlights the necessity of showcasing accumulated outcomes to demonstrate impact
Intermediate-mass Stars Become Magnetic White Dwarfs
When a star exhausts its nuclear fuel, it either explodes as a supernova or more quiescently becomes a white dwarf, an object about half the mass of our Sun with a radius of about that of the Earth. About one-fifth of white dwarfs exhibit the presence of magnetic fields, whose origin has long been debated as either the product of previous stages of evolution or of binary interactions. We here report the discovery of two massive and magnetic white-dwarf members of young star clusters in the Gaia second data release (DR2) database, while a third massive and magnetic cluster white dwarf was already reported in a previous paper. These stars are most likely the product of single-star evolution and therefore challenge the merger scenario as the only way to produce magnetic white dwarfs. The progenitor masses of these stars are all above 5 solar masses, and there are only two other cluster white dwarfs whose distances have been unambiguously measured with Gaia and whose progenitors' masses fall in this range. This high incidence of magnetic white dwarfs indicates that intermediate-mass progenitors are more likely to produce magnetic remnants and that a fraction of magnetic white dwarfs forms from intermediate-mass stars
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