685 research outputs found
Surface Instabilities on Liquid Oxygen in an Inhomogeneous Magnetic Field
Liquid oxygen exhibits surface instabilities when subjected to a sufficiently
strong magnetic field. A vertically oriented magnetic field gradient both
increases the magnetic field value at which the pattern forms and shrinks the
length scale of the surface patterning. We show that these effects of the field
gradient may be described in terms of an ``effective gravity'', which in our
experiments may be varied from 1g to 360g.Comment: 4 pages, 5 embedded figures in eps forma
Attempt to detect diamagnetic anisotropy of dust-sized crystal orientated to investigate the origin of interstellar dust alignment
Sudden drop of fractal dimension of electromagnetic emissions recorded prior to significant earthquake
The variation of fractal dimension and entropy during a damage evolution
process, especially approaching critical failure, has been recently
investigated. A sudden drop of fractal dimension has been proposed as a
quantitative indicator of damage localization or a likely precursor of an
impending catastrophic failure. In this contribution, electromagnetic emissions
recorded prior to significant earthquake are analysed to investigate whether
they also present such sudden fractal dimension and entropy drops as the main
catastrophic event is approaching. The pre-earthquake electromagnetic time
series analysis results reveal a good agreement to the theoretically expected
ones indicating that the critical fracture is approaching
Cortical Factor Feedback Model for Cellular Locomotion and Cytofission
Eukaryotic cells can move spontaneously without being guided by external
cues. For such spontaneous movements, a variety of different modes have been
observed, including the amoeboid-like locomotion with protrusion of multiple
pseudopods, the keratocyte-like locomotion with a widely spread lamellipodium,
cell division with two daughter cells crawling in opposite directions, and
fragmentations of a cell to multiple pieces. Mutagenesis studies have revealed
that cells exhibit these modes depending on which genes are deficient,
suggesting that seemingly different modes are the manifestation of a common
mechanism to regulate cell motion. In this paper, we propose a hypothesis that
the positive feedback mechanism working through the inhomogeneous distribution
of regulatory proteins underlies this variety of cell locomotion and
cytofission. In this hypothesis, a set of regulatory proteins, which we call
cortical factors, suppress actin polymerization. These suppressing factors are
diluted at the extending front and accumulated at the retracting rear of cell,
which establishes a cellular polarity and enhances the cell motility, leading
to the further accumulation of cortical factors at the rear. Stochastic
simulation of cell movement shows that the positive feedback mechanism of
cortical factors stabilizes or destabilizes modes of movement and determines
the cell migration pattern. The model predicts that the pattern is selected by
changing the rate of formation of the actin-filament network or the threshold
to initiate the network formation
Current Applications of Computational Chemistry in JACS
Article discussing molecules, mechanisms, and materials and current applications of computational chemistry in the Journal of the American Chemical Society (JACS)
3D Morphology, Ultrastructure and Development of Ceratomyxa puntazzi Stages: First Insights into the Mechanisms of Motility and Budding in the Myxozoa
Free, amoeboid movement of organisms within media as well as substrate-dependent cellular crawling processes of cells and organisms require an actin cytoskeleton. This system is also involved in the cytokinetic processes of all eukaryotic cells. Myxozoan parasites are known for the disease they cause in economical important fishes. Usually, their pathology is related to rapid proliferation in the host. However, the sequences of their development are still poorly understood, especially with regard to pre-sporogonic proliferation mechanisms. The present work employs light microscopy (LM), electron microscopy (SEM, TEM) and confocal laser scanning microscopy (CLSM) in combination with specific stains (Nile Red, DAPI, Phalloidin), to study the three-dimensional morphology, motility, ultrastructure and cellular composition of Ceratomyxa puntazzi, a myxozoan inhabiting the bile of the sharpsnout seabream
Inter-Cellular Variation in DNA Content of Entamoeba histolytica Originates from Temporal and Spatial Uncoupling of Cytokinesis from the Nuclear Cycle
Accumulation of multiple copies of the genome in a single nucleus and several nuclei in a single cell has previously been noted in Entamoeba histolytica, contributing to the genetic heterogeneity of this unicellular eukaryote. In this study, we demonstrate that this genetic heterogeneity is an inherent feature of the cell cycle of this organism. Chromosome segregation occurs on a variety of novel microtubular assemblies including multi-polar spindles. Cytokinesis in E. histolytica is completed by the mechanical severing of a thin cytoplasmic bridge, either independently or with the help of neighboring cells. Importantly, cytokinesis is uncoupled from the nuclear division cycle, both temporally and spatially, leading to the formation of unequal daughter cells. Sorting of euploid and polyploid cells showed that each of these sub-populations acquired heterogeneous DNA content upon further growth. Our study conclusively demonstrates that genetic heterogeneity originates from the unique mode of cell division events in this protist
Magnetic properties of hemoilmenite single crystals in Haruna dacite pumice revealed by the Bitter technique, with special reference to self-reversal of thermoremanent magnetization
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Computational design of transmembrane pores.
Transmembrane channels and pores have key roles in fundamental biological processes1 and in biotechnological applications such as DNA nanopore sequencing2-4, resulting in considerable interest in the design of pore-containing proteins. Synthetic amphiphilic peptides have been found to form ion channels5,6, and there have been recent advances in de novo membrane protein design7,8 and in redesigning naturally occurring channel-containing proteins9,10. However, the de novo design of stable, well-defined transmembrane protein pores that are capable of conducting ions selectively or are large enough to enable the passage of small-molecule fluorophores remains an outstanding challenge11,12. Here we report the computational design of protein pores formed by two concentric rings of α-helices that are stable and monodisperse in both their water-soluble and their transmembrane forms. Crystal structures of the water-soluble forms of a 12-helical pore and a 16-helical pore closely match the computational design models. Patch-clamp electrophysiology experiments show that, when expressed in insect cells, the transmembrane form of the 12-helix pore enables the passage of ions across the membrane with high selectivity for potassium over sodium; ion passage is blocked by specific chemical modification at the pore entrance. When incorporated into liposomes using in vitro protein synthesis, the transmembrane form of the 16-helix pore-but not the 12-helix pore-enables the passage of biotinylated Alexa Fluor 488. A cryo-electron microscopy structure of the 16-helix transmembrane pore closely matches the design model. The ability to produce structurally and functionally well-defined transmembrane pores opens the door to the creation of designer channels and pores for a wide variety of applications
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