Two dimensional hybrid simulations of small scale obstacles in the solar wind

The structure and dynamics of the solar wind interaction with two small scale obstacles (of the order of a pickup ion gyroradius) is examined. These are a comet, comparable to Grigg-Skjellerup, and a weakly ionospheric planet. We also perform a pilot study of an intrinsically magnetized planet in such flow, in preparation for a future three-dimensional simulation. Here, we use two-dimensional hybrid simulations (particle ions, fluid electrons) and consider different solar wind Alfven Mach number flow (MA) and interplanetary magnetic field orientation relative to this plane. This allows control of the available wave types. The cometary simulations display magnetosonic "turbulence" as MA is increased, when the field is perpendicular to the simulation plane. If we allow parallel propagating modes by setting the field parallel to the plane, we find the "turbulence" significantly changes in scale and extent, suggesting resonant growth of Alfven ion cyclotron waves in the presence of magnetosonic "turbulence" occurs. Free energy is available from picked up cometary ions. The process depends on the cometary ion density, which strongly varies, and we conclude this explains the broadband nature of the disturbances. In the perpendicular field orientation, the planetary source produces a novel two tail structure which continuously strips the planetary ionosphere. We find these tails have very distinct characteristics, resulting in the wake being filled relatively quickly downstream, by complex structure. At higher MAl magnetosonic "turbulence" again appears. Switching the field parallel to the plane causes massive field line draping and pile-up, and causes instability. A long lasting wake appears, and we conclude that a three-dimensional simulation is required. The magnetized ionospheric planet pilot study proved difficult to scale accurately in two dimensions. The planetary field failed to penetrate the solar wind, however it appears the simulation would be stable and achieve equilibrium in three dimensions

Experimental observations and numerical modeling of lipid-shell microbubbles with calcium-adhering moieties for minimally-invasive treatment of urinary stones

A novel treatment modality incorporating calcium-adhering microbubbles has recently entered human clinical trials as a new minimally-invasive approach to treat urinary stones. In this treatment method, lipid-shell gas-core microbubbles can be introduced into the urinary tract through a catheter. Lipid moities with calcium-adherance properties incorporated into the lipid shell facilitate binding to stones. The microbubbles can be excited by an extracorporeal source of quasi-collimated ultrasound. Alternatively, the microbubbles can be excited by an intraluminal source, such as a fiber-optic laser. With either excitation technique, calcium-adhering microbubbles can significantly increase rates of erosion, pitting, and fragmentation of stones. We report here on new experiments using high-speed photography to characterize microbubble expansion and collapse. The bubble geometry observed in the experiments was used as one of the initial shapes for the numerical modeling. The modeling showed that the bubble dynamics strongly depends on bubble shape and stand-off distance. For the experimentally observed shape of microbubbles, the numerical modeling showed that the collapse of the microbubbles was associated with pressure increases of some two-to-three orders of magnitude compared to the excitation source pressures. This in-vitro study provides key insights into the use of microbubbles with calcium-adhering moieties in treatment of urinary stones

Capital Breeding in a Diapausing Copepod: A Transcriptomics Analysis

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No Consistent Simulated Trends in the Atlantic Meridional Overturning Circulation for the Past 6,000 Years

The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the North Atlantic with global ocean impacts. The AMOC's response to past changes in forcings during the Holocene provides important context for the coming centuries. Here, we investigate AMOC trends using an emerging set of transient simulations using multiple global climate models for the past 6,000 years. Although some models show changes, no consistent trend in overall AMOC strength during the mid-to-late Holocene emerges from the ensemble. We interpret this result to suggest no overall change in AMOC, which fits with our assessment of available proxy reconstructions. The decadal variability of the AMOC does not change in ensemble during the mid- and late-Holocene. There are interesting AMOC changes seen in the early Holocene, but their nature depends a lot on which inputs are used to drive the experiment

When simple sequence comparison fails: the cryptic case of the shared domains of the bacterial replication initiation proteins DnaB and DnaD

DnaD and DnaB are essential DNA-replication-initiation proteins in low-G+C content Gram-positive bacteria. Here we use sensitive Hidden Markov Model-based techniques to show that the DnaB and DnaD proteins share a common structure that is evident across all their structural domains, termed DDBH1 and DDBH2 (DnaD DnaB Homology 1 and 2). Despite strong sequence divergence, many of the DNA-binding and oligomerization properties of these domains have been conserved. Although eluding simple sequence comparisons, the DDBH2 domains share the only strong sequence motif; an extremely highly conserved YxxxIxxxW sequence that contributes to DNA binding. Sequence alignments of DnaD alone fail to identify another key part of the DNA-binding module, since it includes a poorly conserved sequence, a solvent-exposed and somewhat unstable helix and a mobile segment. We show by NMR, in vitro mutagenesis and in vivo complementation experiments that the DNA-binding module of Bacillus subtilis DnaD comprises the YxxxIxxxW motif, the unstable helix and a portion of the mobile region, the latter two being essential for viability. These structural insights lead us to a re-evaluation of the oligomerization and DNA-binding properties of the DnaD and DnaB proteins