Search results for "Trefoil"

2016

We determine knotting probabilities and typical sizes of knots in double-stranded DNA for chains of up to half a million base pairs with computer simulations of a coarse-grained bead-stick model: Single trefoil knots and composite knots which include at least one trefoil as a prime factor are shown to be common in DNA chains exceeding 250,000 base pairs, assuming physiologically relevant salt conditions. The analysis is motivated by the emergence of DNA nanopore sequencing technology, as knots are a potential cause of erroneous nucleotide reads in nanopore sequencing devices and may severely limit read lengths in the foreseeable future. Even though our coarse-grained model is only based on …

Entropic Interactions between Two Knots on a Semiflexible Polymer.

2017

Two knots on a string can either be separated or intertwined, and may even pass through each other. At the microscopic scale, such transitions may occur spontaneously, driven by thermal fluctuations, and can be associated with a topological free energy barrier. In this manuscript, we study the respective location of a trefoil ( 3 1 ) and a figure-eight ( 4 1 ) knot on a semiflexible polymer, which is parameterized to model dsDNA in physiological conditions. Two cases are considered: first, end monomers are grafted to two confining walls of varying distance. Free energy profiles and transition barriers are then compared to a subset of free chains, which contain exactly one 3 1 and one 4 1 kn…

Effect of 3rd-order aberrations on human vision

2007

To investigate the effect of 3rd-order aberrations on human vision.Grupo de Ciencias de la Visión, University of Murcia, Murcia, Spain.The 3rd-order aberrations coma and trefoil were induced with purpose-designed soft contact lenses, 3 inducing coma (low [0.05 microm], medium [0.13 microm], high [1.03 microm]) and 3 inducing trefoil (low [0.07 microm], medium [0.17 microm], high [0.96 microm]). Monocular high-contrast (HCVA) and low-contrast (LCVA) visual acuities and contrast sensitivity were measured in 11 subjects wearing contact lenses with a 5.0 mm artificial pupil.The reduction in HCVA and LCVA was statistically significant only for the highest coma and trefoil values (P.0001). For co…

A knot without tritangent planes

1991

We show, with computations aided by a computer, that the (3,2)-curve on some standard torus (which topologically is the trefoil knot) has no tritangent planes, thus answering in the negative a conjecture of M. H. Freedman.

A knot without triple bitangency

1997

It is proved that certain trefoil knot has not triple bitangency, answering thus in the negative a conjecture of S. Izumiya and W. L. Marar.

Quantum computing thanks to Bianchi groups

2018

It has been shown that the concept of a magic state (in universal quantum computing: uqc) and that of a minimal informationally complete positive operator valued measure: MIC-POVMs (in quantum measurements) are in good agreement when such a magic state is selected in the set of non-stabilizer eigenstates of permutation gates with the Pauli group acting on it [1]. Further work observed that most found low-dimensional MICs may be built from subgroups of the modular group PS L(2, Z) [2] and that this can be understood from the picture of the trefoil knot and related 3-manifolds [3]. Here one concentrates on Bianchi groups PS L(2, O10) (with O10 the integer ring over the imaginary quadratic fie…

INVOLUTIONS ON KNOT GROUPS AND VARIETIES OF REPRESENTATIONS IN A LIE GROUP

2002

We prove the existence of a rationalisation [Formula: see text] of a classical or high-dimensional knot group Π which admits an involution if the Alexander polynomials of the knot are reciprocal. Using the group [Formula: see text] and its involution, we study the local structure, in the neighbourhood of an abelian representation, of the space of representation of the knot group Π in a a Lie group. We apply these results to the groups of classical prime knots up to 10 crossings.

Trefoil factor TFF1-induced protection of conjunctival cells from apoptosis at premitochondrial and postmitochondrial levels.

2008

PURPOSE. Goblet cells of the conjunctival epithelium synthesize and secrete TFF1 (Trefoil factor 1), a small protease-resistant peptide that, together with mucins, is responsible for the rheologic properties of the tear film. This study aimed to determine whether TFF1, whose synthesis increases in inflammatory conditions such as pterygium, could protect conjunctival cells from apoptosis. METHODS. Chang conjunctival cells, either wild-type or expressing TFF1 through stable transfection, were exposed to benzalkonium chloride (BAK) and ultraviolet (UV) irradiation to trigger apoptosis. The authors used cell fractionation to detect lipid raft‐associated proteins, coimmunoprecipitation to explor…

iNOS-derived nitric oxide mediates the increase in TFF2 expression associated with gastric damage: role of HIF-1.

2009

Trefoil (TFF) peptides are involved in gastrointestinal mucosal restitution. An hypoxia inducible factor 1 (HIF-1)-dependent induction of TFF genes has been reported in gastric epithelial cells. Nitric oxide (NO) is associated with mucosal damage and modulates HIF-1 activity. The aim of the present study was to analyze the role of iNOS-derived NO in HIF-1alpha stabilization and TFF gene expression in damaged gastric mucosa. Aspirin caused gastric injury that peaked 6 h after dosing and returned to normality at 24 h. iNOS mRNA expression occurs in the corpus in parallel with damage. Blockade of iNOS activity did not modify gastric lesions induced by aspirin but delayed mucosal healing. Aspir…

Induction of trefoil factor (TFF)1, TFF2 and TFF3 by hypoxia is mediated by hypoxia inducible factor-1: implications for gastric mucosal healing

2008

Background and purpose:  Mucosal microcirculation is compromised during gastric damage induced by non-steroidal anti-inflammatory drugs, such as aspirin. Consequently, oxygen supply to epithelial cells is decreased. The trefoil factor (TFF) peptides are involved in mechanisms of defence and repair in the gastrointestinal tract but their regulation at sites of gastric injury is unknown. Experimental approach:  Hypoxia and expression of TFF genes and peptides were measured in the damaged stomach of aspirin-treated rats. In a human gastric cell line (AGS cells), the effects of hypoxia and of hypoxia inducible factor (HIF)-1 (through transient transfection of HIF-1α siRNA or over-expression of …