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"Curtis, Jennifer"
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Thermo-responsive jamming by particle shape change
Granular materials transition between unjammed (deformable) and jammed (rigid) states when adjusting their packing density. Here, we report on experiments demonstrating that the same kind of phase transition can be alternatively achieved through temperature-controlled particle shape change. Using a confined system of randomly-packed rod-like particles made of shape memory alloy (SMA), we exploit that shape recovery of these bent rods with rising temperature at a constant packing density leads to a jammed state. The responsible physical processes are elucidated with numerical simulations based on the Discrete Element Method. As an exemplary application of the uncovered mechanism, we engineer a smart clamp that can actively grip or release an object through the thermo-induced jamming or unjamming of the granular material, and robustly so under cyclic temperature changes. In the jammed state, its load-bearing capability surpasses the total SMA weight by a tunable margin, up to over 800-fold. The clamping design paves the way towards a new kind of functional devices based on the thermo-responsive jamming of shape memory granular materials.
Granular materials transition between unjammed and jammed states when adjusting their packing density. Here, authors find that the same kind of phase transition can be alternatively achieved through temperature-controlled particle shape change.
Journal Article
Climbing the volcano
\"A boy and his family's hike to the peak of Oregon's South Sister volcano is narrated in a series of haikus\"-- Provided by publisher.
Book
O-Specific Antigen-Dependent Surface Hydrophobicity Mediates Aggregate Assembly Type in Pseudomonas aeruginosa
During chronic infection, several factors contribute to the biogeography of microbial communities. Heterogeneous populations of Pseudomonas aeruginosa form aggregates in cystic fibrosis airways; however, the impact of this population heterogeneity on spatial organization and aggregate assembly is not well understood. Bacteria live in spatially organized aggregates during chronic infections, where they adapt to the host environment, evade immune responses, and resist therapeutic interventions. Although it is known that environmental factors such as polymers influence bacterial aggregation, it is not clear how bacterial adaptation during chronic infection impacts the formation and spatial organization of aggregates in the presence of polymers. Here, we show that in an in vitro model of cystic fibrosis (CF) containing the polymers extracellular DNA (eDNA) and mucin, O-specific antigen is a major factor determining the formation of two distinct aggregate assembly types of Pseudomonas aeruginosa due to alterations in cell surface hydrophobicity. Our findings suggest that during chronic infection, the interplay between cell surface properties and polymers in the environment may influence the formation and structure of bacterial aggregates, which would shed new light on the fitness costs and benefits of O-antigen production in environments such as CF lungs. IMPORTANCE During chronic infection, several factors contribute to the biogeography of microbial communities. Heterogeneous populations of Pseudomonas aeruginosa form aggregates in cystic fibrosis airways; however, the impact of this population heterogeneity on spatial organization and aggregate assembly is not well understood. In this study, we found that changes in O-specific antigen determine the spatial organization of P. aeruginosa cells by altering the relative cell surface hydrophobicity. This finding suggests a role for O-antigen in regulating P. aeruginosa aggregate size and shape in cystic fibrosis airways.
Journal Article
How vinculin regulates force transmission
Focal adhesions mediate force transfer between ECM-integrin complexes and the cytoskeleton. Although vinculin has been implicated in force transmission, few direct measurements have been made, and there is little mechanistic insight. Using vinculin-null cells expressing vinculin mutants, we demonstrate that vinculin is not required for transmission of adhesive and traction forces but is necessary for myosin contractility-dependent adhesion strength and traction force and for the coupling of cell area and traction force. Adhesion strength and traction forces depend differentially on vinculin head (V H) and tail domains. V H enhances adhesion strength by increasing ECM-bound integrin–talin complexes, independently from interactions with vinculin tail ligands and contractility. A full-length, autoinhibition-deficient mutant (T12) increases adhesion strength compared with V H, implying roles for both vinculin activation and the actin-binding tail. In contrast to adhesion strength, vinculin-dependent traction forces absolutely require a full-length and activated molecule; V H has no effect. Physical linkage of the head and tail domains is required for maximal force responses. Residence times of vinculin in focal adhesions, but not T12 or V H, correlate with applied force, supporting a mechanosensitive model for vinculin activation in which forces stabilize vinculin’s active conformation to promote force transfer.
Journal Article
The lucky litter : wolf pups rescued from wildfire
\"As a huge wildfire roared along the Funny River in the Kenai National Wildlife Refuge in Alaska, firefighters rushed to the rescue. When they found five three-week-old wolf pups in need, they raced into action to save the whole litter. With no wolf parents to help, zookeepers and vets at the Alaska Zoo made sure the babies grew into a healthy, happy pack. Follow this true story as the pups travel from their charred forest to the Alaska Zoo, where they grow big and strong before finally moving to their forever home at the Minnesota Zoo\"-- Provided by publisher.
Book
2022 McKinney rain-on-wildfire event, dissolved oxygen sags, and a fish kill on the Klamath River, California
The longitudinal propagation of water-quality and ecological impairments in rivers during and after wildfires remain poorly understood. In Northern California, the 2022 McKinney Fire burned 243 km
2
of the Klamath National Forest, with 83% of the burned area classified as moderate to high severity. During the active wildfire, a high-intensity monsoonal rain event triggered sediment-laden flooding and runoff-initiated debris flows, causing extreme water-quality impairments and a 95 km fish kill zone along the main-stem Klamath River. This rain-on-wildfire event produced a flood wave that outpaced a sediment pulse, diminishing the dilution effect of the floodwaters. A network of high-frequency water-quality sensors recorded water-quality impairments that propagated 296 km downstream. Impairments at the nearest monitoring station, situated 71 km downstream from the fire perimeter, included dissolved oxygen sags to zero (anoxia) for 5.25 h, turbidity spikes exceeding 1000 FNU, a doubling of specific conductance from 175 to 415 µS/cm (at 25 °C), and pH anomalies of 0.5 units from 7.8 to 7.3. This novel rain-on-wildfire event triggered the first flush of fire-scar material during an active wildfire, resulting in water-quality impairments unprecedented in the historical monitoring data for the river spanning 2012 to 2022. This study provides new insights into the potential role of rain-on-wildfire events in generating extreme downstream water-quality and ecological impairments in a more fire-prone future.
Journal Article
Moonlight crab count
\"Even kids can get involved in science! Ecologist Dr. Neeti Bathala and Jennifer Keats Curtis collaborate to bring us the story of these adventurous citizen scientists. Leena and her mom volunteer each summer to count the horseshoe crabs that visit their beach. With their dog Bobie at their sides, the duo spends a night on the shore surveying horseshoe crabs who have come to mate and lay eggs. Readers will learn valuable facts about these ancient animals and how they can get involved in the effort to conserve horseshoe crabs\"-- Provided by publisher.
Book
Discrete element method–computational fluid dynamics analyses of flexible fibre fluidization
Gas-fluidized beds of flexible fibres, which have been rarely studied before, are investigated in this work using the coupled approach of the discrete element method and computational fluid dynamics. In the present numerical method, gas–fibre interaction is modelled by calculating the interaction force for each constituent element in the fibre, and the composition of the interaction forces on the constituent elements generates a resultant hydrodynamic force and a resultant hydrodynamic torque on the fibre. Pressure drops and fibre orientation results from the present simulations with various fibre aspect ratios are in good agreement with previous experimental and simulation results. Some novel results are obtained for the effects of fibre flexibility. Larger hydrodynamic forces on fibres (before the bed is fluidized) and smaller minimum fluidization velocities (MFVs) are observed for more flexible fibre beds due to the smaller porosities, while smaller hydrodynamic forces are obtained for the more flexible fibres when the beds are fluidized with significant fibre motion. By scaling the superficial gas velocity using the MFVs, the data of pressure drop can collapse onto the Ergun correlation for stiff fibres of various aspect ratios; however, the pressure drop curves deviate from the Ergun correlation for very flexible fibres, due to the significant fibre bed expansion before the MFV is reached. The fibre aspect ratio and flexibility both have an impact on the solids mixing rate, and it is found that the solids mixing rates are essentially determined by the ratio of the superficial gas velocity to MFV.
Journal Article