3,249 research outputs found
Mammalian cells in culture actively export specific microRNAs
The discovery of microRNAs (miRNAs) as a new class of regulators of gene expression has triggered an explosion of research, but has left many unanswered questions about how this regulation works and how it is integrated with other regulatory mechanisms. A number of miRNAs have been found to be present in blood plasma and other body fluids of humans and mice in surprisingly high concentrations. This observation was unexpected in two respects: first, the fact that these molecules are present at all outside the cell at significant concentrations; and second, that these molecules appear to be stable outside of the cell. In light of this it has been suggested that the biological function of miRNAs may also extend outside of the cell and mediate cell-cell communication^[1-5]^. Such a system would be expected to export specific miRNAs from cells in response to specific biological stimuli. We report here that after serum deprivation several human cell lines tested do export a spectrum of miRNAs into the culture medium. The export response is substantial and prompt. The exported miRNAs are found both within and outside of microvesicles and exosomes. We have identified some candidate protein components of this system outside the cell, and found one exported protein that plays a role in protecting miRNA from degradation. Our results point to a hitherto unrecognized and uncharacterized miRNA trafficking system in mammalian cells that may involve cell-cell communication
Entropy of Folding of the Triangular Lattice
The problem of counting the different ways of folding the planar triangular
lattice is shown to be equivalent to that of counting the possible 3-colorings
of its bonds, a dual version of the 3-coloring problem of the hexagonal lattice
solved by Baxter. The folding entropy Log q per triangle is thus given by
Baxter's formula q=sqrt(3)(Gamma[1/3])^(3/2)/2pi =1.2087...Comment: 9 pages, harvmac, epsf, uuencoded, 5 figures included, Saclay
preprint T/9401
Critical and Tricritical Hard Objects on Bicolorable Random Lattices: Exact Solutions
We address the general problem of hard objects on random lattices, and
emphasize the crucial role played by the colorability of the lattices to ensure
the existence of a crystallization transition. We first solve explicitly the
naive (colorless) random-lattice version of the hard-square model and find that
the only matter critical point is the non-unitary Lee-Yang edge singularity. We
then show how to restore the crystallization transition of the hard-square
model by considering the same model on bicolored random lattices. Solving this
model exactly, we show moreover that the crystallization transition point lies
in the universality class of the Ising model coupled to 2D quantum gravity. We
finally extend our analysis to a new two-particle exclusion model, whose
regular lattice version involves hard squares of two different sizes. The exact
solution of this model on bicolorable random lattices displays a phase diagram
with two (continuous and discontinuous) crystallization transition lines
meeting at a higher order critical point, in the universality class of the
tricritical Ising model coupled to 2D quantum gravity.Comment: 48 pages, 13 figures, tex, harvmac, eps
Phosphatidylinositol 3 kinase activation and AMPA receptor subunit trafficking underlie the potentiation of miniature EPSC amplitudes triggered by the activation of L-type calcium channels
The packing of two species of polygons on the square lattice
We decorate the square lattice with two species of polygons under the
constraint that every lattice edge is covered by only one polygon and every
vertex is visited by both types of polygons. We end up with a 24 vertex model
which is known in the literature as the fully packed double loop model. In the
particular case in which the fugacities of the polygons are the same, the model
admits an exact solution. The solution is obtained using coordinate Bethe
ansatz and provides a closed expression for the free energy. In particular we
find the free energy of the four colorings model and the double Hamiltonian
walk and recover the known entropy of the Ice model. When both fugacities are
set equal to two the model undergoes an infinite order phase transition.Comment: 21 pages, 4 figure
Glassy behaviour in an exactly solved spin system with a ferromagnetic transition
We show that applying simple dynamical rules to Baxter's eight-vertex model
leads to a system which resembles a glass-forming liquid. There are analogies
with liquid, supercooled liquid, glassy and crystalline states. The disordered
phases exhibit strong dynamical heterogeneity at low temperatures, which may be
described in terms of an emergent mobility field. Their dynamics are
well-described by a simple model with trivial thermodynamics, but an emergent
kinetic constraint. We show that the (second order) thermodynamic transition to
the ordered phase may be interpreted in terms of confinement of the excitations
in the mobility field. We also describe the aging of disordered states towards
the ordered phase, in terms of simple rate equations.Comment: 11 page
Using Experience and Case History Data to Enhance the Design of Piled Foundations and Predict Behaviour Characteristics
This paper explores the process of piled foundation design and how it can benefit from the inclusion of previous test data and case histories from nearby or geologically similar sites. The interaction between the soil and the structure is critical to the behaviour of a pile and is a function of both the ground conditions and the method of pile construction. An accurate model of the ground conditions is required for the design, as is a detailed knowledge of the method of pile installation and its subsequent interaction with the soil. Where case histories are available they can be utilised to refine the design or to reduce the risk associated with a solution. This is currently often done in a subjective manner by the application of engineering judgement and personal experience. This paper discusses a quantitative method which can be used to employ data from case histories and provide an objective approach to the inclusion of existing knowledge and experience. Bayesian updating is utilised to improve the model of the ground conditions and subsequently the degree of uncertainty is reduced. The probability of failure has been seen to be reduced by this process, as demonstrated through the application an example situation
Glassy states in fermionic systems with strong disorder and interactions
We study the competition between interactions and disorder in two dimensions.
Whereas a noninteracting system is always Anderson localized by disorder in two
dimensions, a pure system can develop a Mott gap for sufficiently strong
interactions. Within a simple model, with short-ranged repulsive interactions,
we show that, even in the limit of strong interaction, the Mott gap is
completely washed out by disorder for an infinite system for dimensions . The probability of a nonzero gap falls onto a universal curve, leading to a
glassy state for which we provide a scaling function for the frequency
dependent susceptibility.Comment: 8 pages, 5 figures, expanded to contain some analytical results for
one dimensio
Theoretical Studies of Electron Transfer in Metal Dimers: XY+âX+Y, Where X, Y=Be, Mg, Ca, Zn, Cd
The electronic matrix element responsible for electron exchange in a series of metal dimers was calculated using ab initio wave functions. The distance dependence is approximately exponential for a large range of internuclear separations. A localized description, where the two nonorthogonal structures characterizing the electron localized at the left and right sites are each obtained selfâconsistently, is found to provide the best description of the electron exchange process. We find that Gaussian basis sets are capable of predicting the expected exponential decay of the electronic interactions even at quite large internuclear distances
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