4,017 research outputs found
EXPLAINING INTERNATIONAL DIFFERENCES IN GENETICALLY MODIFIED FOOD LABELING REGULATIONS
Replaced with revised version of paper 07/13/04.Food Consumption/Nutrition/Food Safety,
Large N Scaling Behavior of the Lipkin-Meshkov-Glick Model
We introduce a novel semiclassical approach to the Lipkin model. In this way
the well-known phase transition arising at the critical value of the coupling
is intuitively understood. New results -- showing for strong couplings the
existence of a threshold energy which separates deformed from undeformed states
as well as the divergence of the density of states at the threshold energy --
are explained straightforwardly and in quantitative terms by the appearance of
a double well structure in a classical system corresponding to the Lipkin
model. Previously unnoticed features of the eigenstates near the threshold
energy are also predicted and found to hold.Comment: 4 pages, 2 figures, to appear in PR
Functional and computational identification of a rescue mutation near the active site of an mRNA methyltransferase
RNA-based drugs are an emerging class of therapeutics combining the immense potential of DNA
gene-therapy with the absence of genome integration-associated risks. While the synthesis of such
molecules is feasible, large scale in vitro production of humanised mRNA remains a biochemical and
economical challenge. Human mRNAs possess two post-transcriptional modifcations at their 5′ end:
an inverted methylated guanosine and a unique 2′O-methylation on the ribose of the penultimate
nucleotide. One strategy to precisely methylate the 2′ oxygen is to use viral mRNA methyltransferases
that have evolved to escape the host’s cell immunity response following virus infection. However,
these enzymes are ill-adapted to industrial processes and sufer from low turnovers. We have
investigated the efects of homologous and orthologous active-site mutations on both stability and
transferase activity, and identifed new functional motifs in the interaction network surrounding the
catalytic lysine. Our fndings suggest that despite their low catalytic efciency, the active-sites of viral
mRNA methyltransferases have low mutational plasticity, while mutations in a defned third shell
around the active site have strong efects on folding, stability and activity in the variant enzymes,
mostly via network-mediated efects
Quantum breaking time near classical equilibrium points
By using numerical and semiclassical methods, we evaluate the quantum
breaking, or Ehrenfest time for a wave packet localized around classical
equilibrium points of autonomous one-dimensional systems with polynomial
potentials. We find that the Ehrenfest time diverges logarithmically with the
inverse of the Planck constant whenever the equilibrium point is exponentially
unstable. For stable equilibrium points, we have a power law divergence with
exponent determined by the degree of the potential near the equilibrium point.Comment: 4 pages, 5 figure
Eigenfunction statistics for a point scatterer on a three-dimensional torus
In this paper we study eigenfunction statistics for a point scatterer (the
Laplacian perturbed by a delta-potential) on a three-dimensional flat torus.
The eigenfunctions of this operator are the eigenfunctions of the Laplacian
which vanish at the scatterer, together with a set of new eigenfunctions
(perturbed eigenfunctions). We first show that for a point scatterer on the
standard torus all of the perturbed eigenfunctions are uniformly distributed in
configuration space. Then we investigate the same problem for a point scatterer
on a flat torus with some irrationality conditions, and show uniform
distribution in configuration space for almost all of the perturbed
eigenfunctions.Comment: Revised according to referee's comments. Accepted for publication in
Annales Henri Poincar
AMP-activated protein kinase (AMPK) as a potential therapeutic target independent of PI3K/Akt signaling in prostate cancer
Depletion of cellular energy activates the AMP-activated protein kinase (AMPK) to favor energy-producing catabolic processes during tumorigenesis. Using a panel of in vitro cell lines and resected tumors, we investigated the therapeutic value of manipulating AMPK in prostate cancer (PC). Phospho-AMPK expression was significantly elevated in human PC cells and clinical PC samples. In clinical PC, we observed a trend for increasing phospho-AMPK with increasing Gleason sum score; Phospho-AMPK expression was associated with phospho-ACC (p=0.0023). Using the paired PC3 and PC3M cells to model progressive androgen-independent
PC, treatment with either 5-aminoimidazole-4-carboxamide riboside (AICAR) or A-769662 suppressed proliferation, migration and invasion in both cell lines, and down-regulated mTOR and P70S6Ki levels regardless of the Akt status. Involvement of AMPK was confirmed by Compound C (AMPK inhibitor) and siRNA-mediated AMPK silencing. Despite similar functional responses in PC3 and PC3M cells, AMPK activation resulted in sustained phospho-Akt activation in PC3M cells, but not in PC3 cells. This prompted the addition of the PI3K inhibitor LY-294002 to AICAR treatment of PC3M cells in a proliferation assay. Interestingly, we found no synergistic effects upon combined treatment. Collectively, these findings support AMPK as a potential therapeutic target independent of PI3K/Akt signalling
Topological properties of quantum periodic Hamiltonians
We consider periodic quantum Hamiltonians on the torus phase space
(Harper-like Hamiltonians). We calculate the topological Chern index which
characterizes each spectral band in the generic case. This calculation is made
by a semi-classical approach with use of quasi-modes. As a result, the Chern
index is equal to the homotopy of the path of these quasi-modes on phase space
as the Floquet parameter (\theta) of the band is varied. It is quite
interesting that the Chern indices, defined as topological quantum numbers, can
be expressed from simple properties of the classical trajectories.Comment: 27 pages, 14 figure
CDM, Feedback and the Hubble Sequence
We have performed TreeSPH simulations of galaxy formation in a standard LCDM
cosmology, including effects of star formation, energetic stellar feedback
processes and a meta-galactic UV field, and obtain a mix of disk, lenticular
and elliptical galaxies. The disk galaxies are deficient in angular momentum by
only about a factor of two compared to observed disk galaxies. The stellar
disks have approximately exponential surface density profiles, and those of the
bulges range from exponential to r^{1/4}, as observed. The bulge-to-disk ratios
of the disk galaxies are consistent with observations and likewise are their
integrated B-V colours, which have been calculated using stellar population
synthesis techniques. Furthermore, we can match the observed I-band
Tully-Fisher (TF) relation, provided that the mass-to-light ratio of disk
galaxies, (M/L_I), is about 0.8. The ellipticals and lenticulars have
approximately r^{1/4} stellar surface density profiles, are dominated by
non-disklike kinematics and flattened due to non-isotropic stellar velocity
distributions, again consistent with observations.Comment: 6 pages, incl. 4 figs. To appear in the proceedings of the
EuroConference "The Evolution of Galaxies: II - Basic Building Blocks", Ile
de La Reunion (France), 16-21 October 2001 (Slightly updated version). A much
more comprehensive paper about this work with links to pictures of some of
the galaxies can be found at http://babbage.sissa.it/abs/astro-ph/020436
Eigenvalues of Laplacian with constant magnetic field on non-compact hyperbolic surfaces with finite area
We consider a magnetic Laplacian on a
noncompact hyperbolic surface \mM with finite area. is a real one-form
and the magnetic field is constant in each cusp. When the harmonic
component of satifies some quantified condition, the spectrum of
is discrete. In this case we prove that the counting function of
the eigenvalues of satisfies the classical Weyl formula, even
when $dA=0.
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