523 research outputs found
Magnetohydrodynamic instabilities in liquid mercury
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Physics, 1961.Includes bibliographical references (leaf [106]).by David S. Wiley.M.S
P2X7 is an archaic scavenger receptor recognizing apoptotic neuroblasts in early human neurogenesis
The expression and function of P2X7 receptors in adult CNS have been widely studied, however, the roles of these purinergic receptors in human neural development has largely focused on the effects of receptor activation. Previous studies of embryonic and adult rodent neural precursors suggest adenosine triphosphate (ATP), the physiological agonist for P2X receptors, can act as a potent modifier of proliferation, migration and differentiation, mediated via intracellular calcium ([Ca2+]i) signaling. The P2X7 receptor has a ubiquitous distribution in the body but is most abundant on macrophages and microglia where its activation by ATP leads to secretion of proinflammatory cytokines. However, extracellular ATP concentrations in the CNS are usually at sub-micromolar levels suggesting that ATP-induced activation of the P2X7 receptor will not occur under physiological circumstances in the CNS. Another possible role for P2X7 receptors has been suggested by recent work on macrophages and neural precursor cells. In these studies the P2X7 receptor was shown to act as a scavenger receptor i.e. a receptor present on a phagocytotic cell which detects molecules present on the surface of apoptotic cells and facilitates phagocytosis of the apoptotic cell. In a recent study of human neural precursor cells (hNPCs) and neuroblasts isolated from human fetal telencephalons at 16-19 WG, our group showed that both P2X7Rhigh/DCXlow hNPCs and P2X7Rhigh/DCXhigh neuroblasts were capable of phagocytic engulfment of a range of targets including latex beads, apoptotic ReN cells and apoptotic neuroblasts. We found that these neuroblasts and their precursor cells expressed functional P2X7 receptors on their cell surface. Although expression of P2X7 is widespread in the cells of the neuroblast, it is those DCX+ neuroblasts with the highest expression of P2X7 which are actively phagocytic towards an autologous apoptotic neighbour or other phagocytic targets, including latex beads and apoptotic ReNcells. Pre-incubation of P2X7high neuroblasts with ATP or oxidized ATP inhibited phagocytosis of targets by these cells. Moreover siRNA knockdown of P2X7R also inhibited phagocytosis of the apoptotic targets. This review considers this major new role for the P2X7 receptor in early human neurogenesis
(R)-β-lysine Modified Elongation Factor P Functions in Translation Elongation
Post-translational modification of bacterial elongation factor P (EF-P) with (R)-β-lysine at a conserved lysine residue activates the protein in vivo and increases puromycin reactivity of the ribosome in vitro. The additional hydroxylation of EF-P at the same lysine residue by the YfcM protein has also recently been described. The roles of modified and unmodified EF-P during different steps in translation, and how this correlates to its physiological role in the cell, have recently been linked to the synthesis of polyproline stretches in proteins. Polysome analysis indicated that EF-P functions in translation elongation, rather than initiation as proposed previously. This was further supported by the inability of EF-P to enhance the rate of formation of fMet-Lys or fMet-Phe, indicating that the role of EF-P is not to specifically stimulate formation of the first peptide bond. Investigation of hydroxyl-(β)-lysyl-EF-P showed 30% increased puromycin reactivity but no differences in dipeptide synthesis rates when compared with the β-lysylated form. Unlike disruption of the other genes required for EF-P modification, deletion of yfcM had no phenotypic consequences in Salmonella. Taken together, our findings indicate that EF-P functions in translation elongation, a role critically dependent on post-translational β-lysylation but not hydroxylation
Scaling of swimming performance in baleen whales
The scale dependence of locomotor factors has long been studied in comparative biomechanics, but remains poorly understood for animals at the upper extremes of body size. Rorqual baleen whales include the largest animals, but we lack basic kinematic data about their movements and behavior below the ocean surface. Here, we combined morphometrics from aerial drone photogrammetry, whale-borne inertial sensing tag data and hydrodynamic modeling to study the locomotion of five rorqual species. We quantified changes in tail oscillatory frequency and cruising speed for individual whales spanning a threefold variation in body length, corresponding to an order of magnitude variation in estimated body mass. Our results showed that oscillatory frequency decreases with body length (proportional to length(-0.5)(3)) while cruising speed remains roughly invariant (proportional to length(0.08)) at 2 m s(-1). We compared these measured results for oscillatory frequency against simplified models of an oscillating cantilever beam (proportional to length(-1)) and an optimized oscillating Strouhal vortex generator (proportional to length(-1)). The difference between our length-scaling exponent and the simplified models suggests that animals are often swimming non-optimally in order to feed or perform other routine behaviors. Cruising speed aligned more closely with an estimate of the optimal speed required to minimize the energetic cost of swimming (proportional to length(-1)). Our results are among the first to elucidate the relationships between both oscillatory frequency and cruising speed and body size for free-swimming animals at the largest scale
Energetic and physical limitations on the breaching performance of large whales
The considerable power needed for large whales to leap out of the water may represent the single most expensive burst maneuver found in nature. However, the mechanics and energetic costs associated with the breaching behaviors of large whales remain poorly understood. In this study we deployed whale-borne tags to measure the kinematics of breaching to test the hypothesis that these spectacular aerial displays are metabolically expensive. We found that breaching whales use variable underwater trajectories, and that high-emergence breaches are faster and require more energy than predatory lunges. The most expensive breaches approach the upper limits of vertebrate muscle performance, and the energetic cost of breaching is high enough that repeated breaching events may serve as honest signaling of body condition. Furthermore, the confluence of muscle contractile properties, hydrodynamics, and the high speeds required likely impose an upper limit to the body size and effectiveness of breaching whales
Words Volume 2 2009-2011
https://openspace.dmacc.edu/words/1001/thumbnail.jp
21st Annual Midwest/Midsouth Estate Planning Institute
Materials from UK/CLE\u27s 21st Annual Midwest/Midsouth Estate Planning Institute held in July 1994
Panoramic SETI: Program Update and High-Energy Astrophysics Applications
Optical SETI (Search for Extraterrestrial Intelligence) instruments that can
explore the very fast time domain, especially with large sky coverage, offer an
opportunity for new discoveries that can complement multimessenger and time
domain astrophysics. The Panoramic SETI experiment (PANOSETI) aims to observe
optical transients with nanosecond to second duration over a wide field-of-view
(2,500 sq.deg.) by using two assemblies of tens of telescopes to
reject spurious signals by coincidence detection. Three PANOSETI telescopes,
connected to a White Rabbit timing network used to synchronize clocks at the
nanosecond level, have been deployed at Lick Observatory on two sites separated
by a distance of 677 meters to distinguish nearby light sources (such as
Cherenkov light from particle showers in the Earth's atmosphere) from
astrophysical sources at large distances. In parallel to this deployment, we
present results obtained during four nights of simultaneous observations with
the four 12-meter VERITAS gamma-ray telescopes and two PANOSETI telescopes at
the Fred Lawrence Whipple Observatory. We report PANOSETI's first detection of
astrophysical gamma rays, comprising three events with energies in the range
between 15 TeV and 50 TeV. These were emitted by the Crab
Nebula, and identified as gamma rays using joint VERITAS observations.Comment: 9 pages, 5 figures, SPIE Astronomical Telescopes + Instrumentation
conference, 2022, Montr\'eal, Qu\'ebec, Canad
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Evidence for acoustic communication among bottom foraging humpback whales
Humpback whales (Megaptera novaeangliae), a mysticete with a cosmopolitan distribution, demonstrate
marked behavioural plasticity. Recent studies show evidence of social learning in the transmission of specific
population level traits ranging from complex singing to stereotyped prey capturing behaviour. Humpback
whales have been observed to employ group foraging techniques, however details on how individuals
coordinate behaviour in these groups is challenging to obtain. This study investigates the role of a novel
broadband patterned pulsed sound produced by humpback whales engaged in bottom-feeding behaviours,
referred to here as a ‘paired burst’ sound. Data collected from 56 archival acoustic tag deployments were
investigated to determine the functional significance of these signals. Paired burst sound production was
associated exclusively with bottom feeding under low-light conditions, predominantly with evidence of
associated conspecifics nearby suggesting that the sound likely serves either as a communicative signal to
conspecifics, a signal to affect prey behaviour, or possibly both. This study provides additional evidence for
individual variation and phenotypic plasticity of foraging behaviours in humpback whales and provides
important evidence for the use of acoustic signals among foraging individuals in this species
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