778 research outputs found
Filament Nucleation Tunes Mechanical Memory in Active Polymer Networks
Incorporating growth into contemporary material functionality presents a grand challenge in materials design. The Fâactin cytoskeleton is an active polymer network that serves as the mechanical scaffolding for eukaryotic cells, growing and remodeling in order to determine changes in cell shape. Nucleated from the membrane, filaments polymerize and grow into a dense network whose dynamics of assembly and disassembly, or âturnover,â coordinates both fluidity and rigidity. Here, the extent of Fâactin nucleation is varied from a membrane surface in a biomimetic model of the cytoskeleton constructed from purified protein. It is found that nucleation of Fâactin mediates the accumulation and dissipation of polymerizationâinduced Fâactin bending energy. At high and low nucleation, bending energies are low and easily relaxed yielding an isotropic material. However, at an intermediate critical nucleation, stresses are not relaxed by turnover and the internal energy accumulates 100âfold. In this case, high filament curvatures template further assembly of Fâactin, driving the formation and stabilization of vortexâlike topological defects. Thus, nucleation coordinates mechanical and chemical timescales to encode shape memory into active materials
Enabled Negatively Regulates Diaphanous-Driven Actin Dynamics In Vitro and In Vivo
Actin regulators facilitate cell migration by controlling cell protrusion architecture and dynamics. As the behavior of individual actin regulators becomes clear, we must address why cells require multiple regulators with similar functions and how they cooperate to create diverse protrusions. We characterized Diaphanous (Dia) and Enabled (Ena) as a model, using complementary approaches: cell culture, biophysical analysis, and Drosophila morphogenesis. We found that Dia and Ena have distinct biochemical properties that contribute to the different protrusion morphologies each induces. Dia is a more processive, faster elongator, paralleling the long, stable filopodia it induces in vivo, while Ena promotes filopodia with more dynamic changes in number, length, and lifetime. Acting together, Ena and Dia induce protrusions distinct from those induced by either alone, with Ena reducing Dia-driven protrusion length and number. Consistent with this, EnaEVH1 binds Dia directly and inhibits DiaFH1FH2-mediated nucleation in vitro. Finally, Ena rescues hemocyte migration defects caused by activated Dia
Household serial interval of COVID-19 and the effect of Variant B.1.1.7: analyses from prospective community cohort study (Virus Watch) [version 2; peer review: 2 approved]
Introduction: Increased transmissibility of B.1.1.7 variant of concern
(VOC) in the UK may explain its rapid emergence and global spread.
We analysed data from putative household infector - infectee pairs in
the Virus Watch Community cohort study to assess the serial interval
of COVID-19 and whether this was affected by emergence of the
B.1.1.7 variant. /
Methods: The Virus Watch study is an online, prospective, community
cohort study following up entire households in England and Wales
during the COVID-19 pandemic. Putative household infector-infectee
pairs were identified where more than one person in the household
had a positive swab matched to an illness episode. Data on whether or
not individual infections were caused by the B.1.1.7 variant were not
available. We therefore developed a classification system based on the
percentage of cases estimated to be due to B.1.1.7 in national
surveillance data for different English regions and study weeks. /
Results: Out of 24,887 illnesses reported, 915 tested positive for SARSCoV-2 and 186 likely âinfector-infecteeâ pairs in 186 households
amongst 372 individuals were identified. The mean COVID-19 serial
interval was 3.18 (95%CI: 2.55 - 3.81) days. There was no significant
difference (p=0.267) between the mean serial interval for VOC
hotspots (mean = 3.64 days, (95%CI: 2.55 â 4.73)) days and non-VOC
hotspots, (mean = 2.72 days, (95%CI: 1.48 â 3.96))
Kinetics of concurrent desorption and diffusion into the solid: D/Zr(0001)
Rapid adsorbate diffusion into the solid is known to suppress the desorption yield measured in a thermal desorption experiment. We show that this suppression can be controlled (at least partly) by pulsed-laser heating at rates in excess of 10(10) K/s. As an example, we analyze the D/Zr system. In this case, deuterium adsorbed on a surface rapidly diffuses into the bulk of Zr with increasing temperature, and the deuterium desorption probability measured with conventional heating rates (beta less than or equal to 100 K/s) is as low as approximate to 10(-4) for polycrystalline Zr foils (deuterium desorption is not observed at all from single-crystal Zr from which dissolved H/D has been removed). Heating the Zr(0001) surface by pulsed-laser thermal excitation with beta similar or equal to 10(11) K/s is demonstrated to result in the increase of the deuterium desorption probability up to approximately 0.01. To interpret this observation, general equations for describing associative desorption accompanied by adsorbate diffusion into the solid are simplified by employing the specifics of the temperature-programmed kinetic regimes with a linear increase of temperature. The desorption yield calculated without any adjustable parameters is in good agreement with the experimental results
Elastic scattering and breakup of 17^F at 10 MeV/nucleon
Angular distributions of fluorine and oxygen produced from 170 MeV 17^F
incident on 208^Pb were measured. The elastic scattering data are in good
agreement with optical model calculations using a double-folding potential and
parameters similar to those obtained from 16^O+208^Pb. A large yield of oxygen
was observed near \theta_lab=36 deg. It is reproduced fairly well by a
calculation of the (17^F,16^O) breakup, which is dominated by one-proton
stripping reactions. The discrepancy between our previous coincidence
measurement and theoretical predictions was resolved by including core
absorption in the present calculation.Comment: 9 pages, 5 figure
Dual-Wavelength Imaging of Tumor Progression by Activatable and Targeting Near-Infrared Fluorescent Probes in a Bioluminescent Breast Cancer Model
Bioluminescence imaging (BLI) has shown its appeal as a sensitive technique for in vivo whole body optical imaging. However, the development of injectable tumor-specific near-infrared fluorescent (NIRF) probes makes fluorescence imaging (FLI) a promising alternative to BLI in situations where BLI cannot be used or is unwanted (e.g., spontaneous transgenic tumor models, or syngeneic mice to study immune effects)
Tests of a large airâcore superconducting solenoid as a nuclearâreactionâproduct spectrometer
An airâcore superconducting solenoid, with a diameter of 0.2 m and a length of 0.4 m, has been configured for use as a heavyâion reactionâproduct spectrometer (E/Aâ€5 MeV/u) near Ξ=0° (10 to 35 msr). The performance of the spectrometer was established using αâparticle sources and nuclearâreaction products from (18O,â18Ne), (18O,â20Ne) and (18O, 14O) and masses determined for 30Mg, 108Ru and 109Rh. A system suitable for production of radioactive beams has been constructed, and inâbeam tests are in progress at the University of Notre Dame. Large airâcore solenoids with dΩâ€20 msr and capable of focusing ions with E/Aâ„30 MeV/u appear feasible.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87304/2/845_1.pd
Reported exposure to SARS-CoV-2 and relative perceived importance of different settings for SARS-CoV-2 acquisition in England and Wales: Analysis of the Virus Watch Community Cohort [version 1; peer review: awaiting peer review]
We aimed to assess the relative importance of different settings for
SARS-CoV-2 transmission in a large community cohort based on
perceived location of infection for self-reported confirmed SARS-COV-2
cases. We demonstrate the importance of home, work and education
as perceived venues for transmission. In children, education was most
important and in older adults essential shopping was of high
importance. Our findings support public health messaging about
infection control at home, advice on working from home and
restrictions in different venues
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