580 research outputs found
Gene Expression Noise Facilitates Adaptation and Drug Resistance Independently of Mutation
We show that the effect of stress on the reproductive fitness of noisy cell
populations can be modelled as first-passage time problem, and demonstrate that
even relatively short-lived fluctuations in gene expression can ensure
long-term survival of a drug-resistant population. We examine how this effect
contributes to the development of drug-resistant cancer cells, and demonstrate
that permanent immunity can arise independently of mutations.Comment: 5 pages, 3 figure
Pseudogap, van Hove Singularity, Maximum in Entropy and Specific Heat for Hole-Doped Mott Insulators
The first indication of a pseudogap in cuprates came from a sudden decrease
of NMR Knight shift at a doping-dependent temperature . Since
then, experiments have found phase transitions at a lower
. Using plaquette cellular dynamical mean-field for
the square-lattice Hubbard model at high temperature, where the results are
reliable, we show that shares many features of
. The remarkable agreement with several experiments,
including quantum critical behavior of the electronic specific heat, supports
the view that the pseudogap is controlled by a finite-doping extension of the
Mott transition. We propose further experimental tests.Comment: LaTeX, 2 figures, 6 page
Technical improvements and performances of SpIOMM: an imaging Fourier transform spectrometer for astronomy
We present the most recent technical improvements on SpIOMM, an Imaging
Fourier Transform Spectrometer (IFTS) attached to the 1.6 telescope of the Mont
M\'egantic Observatory. The recent development of SpIOMM demonstrates that the
concept of IFTS for ground telescopes is a promising astronomical 3D
spectroscopy technique for multi-object spectroscopy and multi-band imaging.
SpIOMM has been developed through a collaboration between Universit\'e Laval
and the industry (ABB Bomem). It is designed for optical observations from the
near UV (350 nm) to the near IR (850 nm) with variable spectral resolution. The
circular FOV of the instrument covers 12 arcmin in diameter. We have recently
improved the servo system algorithm which now controls the mirror displacement
and alignment at a rate of ~7000Hz. Hardware improvements to the servo and the
metrology system will be described along with their impacts on performance in
the laboratory and in observing conditions. The instrument has successfully
been operated at the 1.6 meter telescope this year using the revised control
systems and acquired several datacubes. We will discuss some issues regarding
the sensitivity to environmental conditions implied by the use of such an
instrument. An overview of the datacube reduction procedure will show some
solutions proposed for observational problems encountered that affect the
quality of the data such as sky transmission variations, wind, changing gravity
vector and temperature.Comment: 12 pages, 6 figures, to appear in "Ground-based and Airborne
Instrumentation for Astronomy II", SPIE conference, Marseille, 23-28 June
200
Fermi Arcs From Dynamical Variational Monte Carlo
Variational Monte Carlo is a many-body numerical method that scales well with
system size. It has been extended to study the Green function only recently by
Charlebois and Imada (2020). Here we generalize the approach to systems with
open boundary conditions in the absence of translational invariance. Removing
these constraints permits the application of embedding techniques like Cluster
perturbation theory (CPT). This allows us to solve an enduring problem in the
physics of the pseudogap in cuprate high-temperature superconductors, namely
the existence or absence of Fermi arcs in the one-band Hubbard model. We study
the behavior of the Fermi surface and of the density of states as a function of
hole doping for clusters of up to 64 sites, well beyond the reach of modern
exact diagonalization solvers. We observe that the technique reliably captures
the transition from a Mott insulator at half filling to a pseudogap, evidenced
by the formation of Fermi arcs, and finally to a metallic state at large
doping. The ability to treat large clusters with quantum cluster methods helps
to minimize potential finite size effects and enables the study of systems with
long range orders, which will help extend the reach of these already powerful
methods and provide important insights on the nature of various strongly
correlated many-electron systems, including the high-T cuprate
superconductors.Comment: 13 pages, 8 figure
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