9,067 research outputs found
Simple Model of the Transduction of Cell-Penetrating Peptides
Cell-penetrating peptides (CPPs) such as HIV's trans-activating
transcriptional activator (TAT) and polyarginine rapidly pass through the
plasma membranes of mammalian cells by an unknown mechanism called
transduction. They may be medically useful when fused to well-chosen chains of
fewer than about 35 amino acids. I offer a simple model of transduction in
which phosphatidylserines and CPPs effectively form two plates of a capacitor
with a voltage sufficient to cause the formation of transient pores
(electroporation). The model is consistent with experimental data on the
transduction of oligoarginine into mouse C2-C12 myoblasts and makes three
testable predictions.Comment: Seven pages. For a more complete version including the effects of
counterions, see arXiv:0810.2358v3 [q-bio.BM
Free Motion of a Dirac Particle with a Minimum Uncertainty in Position
In this paper, we present a covariant, relativistic noncommutative algebra
which includes two small deformation parameters. Using this algebra, we obtain
a generalized uncertainty principle which predicts a minimal observable length
in measure of space-time distances. Then, we introduce a new representation for
coordinate and momentum operators which leads to a generalized Dirac equation.
The solutions of the generalized Dirac equation for a free particle will be
explicitly obtained. We also obtain the modified fermionic propagator for a
free Dirac particle.Comment: 14 pages . . . accepted for publication in Reports on Mathematical
Physics. arXiv admin note: text overlap with arXiv:1103.1015,arXiv:1103.3805
by different author
N=2 Superparticles, RR Fields and Noncommutative Structures of (super)-Spacetime
The recent developments in superstring theory prompted the study of
non-commutative structures in superspace. Considering bosonic and fermionic
strings in a constant antisymmetric tensor background yields a non-vanishing
commutator between the bosonic coordinates of the spacetime. Likewise, the
presence of constant Ramond-Ramond (RR) background leads to a non-vanishing
anti-commutator for the Grassmann coordinates of the superspace. The
non-vanishing commutation relation between bosonic coordinates can also be
derived using a particle moving in a magnetic background, we use N=2 pure
spinor superparticles and D0-branes to show how the non-commutative structures
emerge in superspace. It is argued how a D0-brane in a background of RR fields
reproduces the results obtained in string theory.Comment: Based on a lectures given at 43rd International School of Subnuclear
Physics, Erice, Sicily, Italy, Aug. 200
Purine nucleoside phosphorylase: A new marker for free oxygen radical injury to the endothelial cell
The effect of ischemia and reperfusion on purine nucleoside phosphorylase was studied in an isolated perfused rat liver model. This enzyme is localized primarily in the cytoplasm of the endothelial and Kupffer cells; some activity is associated with the parenchymal cells. Levels of this enzyme accurately predicted the extent of ischemia and reperfusion damage to the microvascular endothelial cell of the liver. Livers from Lewis rats were subjected to 30, 45 and 60 min of warm (37° C) no flow ischemia that was followed by a standard reperfusion period lasting 45 min. Purine nucleoside phosphorylase was measured at the end of the no flow ischemia and reperfusion periods as was superoxide generation (O2‐). Bile production was monitored throughout the no flow ischemia and reperfusion periods. Control perfusions were carried out for 120 min. A significant rise in purine nucleoside phosphorylase levels as compared with controls was observed at the end of ischemia in all the three groups. The highest level, 203.5 ± 29.2 mU/ml, was observed after 60 min of ischemia. After the reperfusion period, levels of purine nucleoside phosphorylase decreased in the 30‐ and 45‐min groups 58.17 ± 9.66 mU/ml and 67.5 ± 17.1 mU/ml, respectively. These levels were equal to control perfusions. In contrast, after 60 min of ischemia, levels of purine nucleoside phosphorylase decreased early in the reperfusion period and then rose to 127.8 ± 14.8 mU/ml by the end of reperfusion (p < 0.0001). Superoxide generation at the beginning of reperfusion was higher than in controls with similar values observed at the end of 30, 45 and 60 min of ischemia. During reperfusion, production of superoxide continued. Bile production was significantly lower at the end of 30 min (0.044 ± 0.026 μl/min/gm), 45 min (0.029 ± 0.0022 μ/min/gm) and 60 min of ischemia (0.022 ± 0.008 μ/min/gm) when compared with bile production by control livers during the corresponding time (0.680 ± 0.195, 0.562 ± 0.133 and 0.480 ± 0.100 μ/min/gm respectively; p < 0.001). During reperfusion, rates of bile production were normal after 30 and 45 min of ischemia. In contrast, significantly lower rates of bile production, 0.046 ± 0.36 μ/min/gm (p < 0.001) occurred during reperfusion after 60 min of ischemia. Control livers during the same period produced 0.330 ± 0.056 μl/min/gm of bile. The results indicate that purine nucleoside phosphorylase levels may be a good index of oxidative injury to the liver in ischemia reperfusion and reliably predict the functional state of the organ after reperfusion. Copyright © 1990 American Association for the Study of Liver Disease
The distribution of Dishevelled in convergently extending mesoderm
Convergent extension (CE) is a conserved morphogenetic movement that drives axial lengthening of the primary body axis and depends on the planar cell polarity (PCP) pathway. In Drosophila epithelia, a polarised subcellular accumulation of PCP core components, such as Dishevelled (Dvl) protein, is associated with PCP function. Dvl has long been thought to accumulate in the mediolateral protrusions in Xenopus chordamesoderm cells undergoing CE. Here we present a quantitative analysis of Dvl intracellular localisation in Xenopus chordamesoderm cells. We find that, surprisingly, accumulations previously observed at mediolateral protrusions of chordamesodermal cells are not protrusion-specific but reflect yolk-free cytoplasm and are quantitatively matched by the distribution of the cytoplasm-filling lineage marker dextran. However, separating cell cortex-associated from bulk Dvl signal reveals a statistical enrichment of Dvl in notochord–somite boundary-(NSB)-directed protrusions, which is dependent upon NSB proximity. Dvl puncta were also observed, but only upon elevated overexpression. These puncta showed no statistically significant spatial bias, in contrast to the strongly posteriorly-enriched GFP-Dvl puncta previously reported in zebrafish. We propose that Dvl distribution is more subtle and dynamic than previously appreciated and that in vertebrate mesoderm it reflects processes other than protrusion as such
Sparse-grid Discontinuous Galerkin Methods for the Vlasov-Poisson-Lenard-Bernstein Model
Sparse-grid methods have recently gained interest in reducing the
computational cost of solving high-dimensional kinetic equations. In this
paper, we construct adaptive and hybrid sparse-grid methods for the
Vlasov-Poisson-Lenard-Bernstein (VPLB) model. This model has applications to
plasma physics and is simulated in two reduced geometries: a 0x3v space
homogeneous geometry and a 1x3v slab geometry. We use the discontinuous
Galerkin (DG) method as a base discretization due to its high-order accuracy
and ability to preserve important structural properties of partial differential
equations. We utilize a multiwavelet basis expansion to determine the
sparse-grid basis and the adaptive mesh criteria. We analyze the proposed
sparse-grid methods on a suite of three test problems by computing the savings
afforded by sparse-grids in comparison to standard solutions of the DG method.
The results are obtained using the adaptive sparse-grid discretization library
ASGarD
Review of Tidal Lagoon Technology and Opportunities for Integration within the UK Energy System
The number of distributed resources for renewable energy installed worldwide has been increasing rapidly in the last decade, and the great majority of these installations consist of solar panels and wind turbines. Other renewable sources of energy are not exploited to the same level: for instance, tidal energy is still a minute portion of the global energy capacity, in spite of the large amount of potential energy stored in tidal waves, and of the successful experience of the few existing plants. The world’s second largest tidal range occurs in the UK but at the moment tidal installations in this country are limited to a few prototypes. More recently, there has been a renewed interest in harnessing tidal energy in the UK, and a few tidal lagoon projects have been evaluated by the UK government. This paper provides an overview of the historical and current developments of tidal plants, a description of operation of tidal lagoons, challenges and opportunities for their integration within the UK energy systems and solutions to improve the dispatchability of tidal energy. The concepts described in the paper are applied to a tidal project proposed for South Wales
The Lantern Vol. 7, No. 3, June 1939
• Commencement Sonnet • Largo Appassionato • More Sonnets to Earth • Vladimir • Abe Lincoln in Illinois • Dark Lives • Enter Mr. Smithingham II • A Character is Sketched • Sonnet • Out of the Dawn • Wistaria • Poem Without a Name • You Have Loved the Nighthttps://digitalcommons.ursinus.edu/lantern/1018/thumbnail.jp
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