6,981 research outputs found
A Field-Induced Re-Entrant Novel Phase and A Ferroelectric-Magnetic Order Coupling in HoMnO3
A re-entrant novel phase has been observed in the hexagonal ferroelectric
HoMnO3 in the presence of magnetic fields, in the temperature ranges defined by
the plateau of the dielectric constant anomaly. The dielectric plateau evolves
with fields from a narrow sharp dielectric peak at the Mn-spin rotation
transition at 32.8 K in zero magnetic field. Such a field-induced dielectric
plateau anomaly appears both in the temperature sweep at a constant field and
in the field sweep at a constant temperature without detectable hysteresis.
This is attributed to the indirect coupling between the ferroelectric and
antiferromagnetic orders, arising from an antiferromagnetic domain wall effect,
where the magnetic order parameter of the Mn subsystem has to change sign
across the ferroelectric domain wall in the compound, that influences the
ferroelectric domains via a local magnetostrictive effect
Massive galaxies in cosmological simulations: UV-selected sample at redshift z=2
We study the properties of galaxies at z=2 in a Lambda CDM universe, using
two different types of hydrodynamic simulation methods (Eulerian TVD and SPH)
and a spectrophotometric analysis in the Un, G, R filter set. The simulated
galaxies at z=2 satisfy the color-selection criteria proposed by Adelberger et
al. (2004) when we assume Calzetti extinction with E(B-V)=0.15. We find that
the number density of simulated galaxies brighter than R<25.5 at z=2 is about
2e-2 h^3/Mpc^3, roughly one order of magnitude larger than that of Lyman break
galaxies at z=3. The most massive galaxies at z=2 have stellar masses >~1e11
Msun, and their observed-frame G-R colors lie in the range 0.0<G-R<1.0. They
typically have been continuously forming stars with a rate exceeding 30 Msun/yr
over a few Gyrs from z=10 to z=2, although the TVD simulation indicates a more
sporadic star formation history than the SPH simulations. Of order half of
their stellar mass was already assembled by z~4. The reddest massive galaxies
at z=2 with G-R >= 1.0 and Mstar>1e10 Msun/h finished the build-up of their
stellar mass by z~3. Interestingly, our study suggests that the majority of the
most massive galaxies at z=2 should be detectable at rest-frame UV wavelengths,
contrary to some recent claims made on the basis of near-IR studies of galaxies
at the same epoch, provided the median extinction is less than E(B-V)<0.3.
However, our results also suggest that the fraction of stellar mass contained
in galaxies that pass the color-selection criteria could be as low as 50% of
the total stellar mass in the Universe at z=2. Our simulations suggest that the
missing stellar mass is contained in fainter (R>25.5) and intrinsically redder
galaxies. Our results do not suggest that hierarchical galaxy formation fails
to account for the massive galaxies at z>=1. (abridged)Comment: 35 pages, 11 figures. Submitted to ApJ. Error in AB magnitude
calculation corrected. Higher resolution version available at
http://cfa-www.harvard.edu/~knagamine/redgal.ps.g
K-Ras and β-catenin mutations cooperate with Fgfr3 mutations in mice to promote tumorigenesis in the skin and lung, but not in the bladder
The human fibroblast growth factor receptor 3 (FGFR3) gene is frequently mutated in superficial urothelial cell carcinoma (UCC). To test the functional significance of FGFR3 activating mutations as a ‘driver’ of UCC, we targeted the expression of mutated Fgfr3 to the murine urothelium using Cre-loxP recombination driven by the uroplakin II promoter. The introduction of the Fgfr3 mutations resulted in no obvious effect on tumorigenesis up to 18 months of age. Furthermore, even when the Fgfr3 mutations were introduced together with K-Ras or β-catenin (Ctnnb1) activating mutations, no urothelial dysplasia or UCC was observed. Interestingly, however, owing to a sporadic ectopic Cre recombinase expression in the skin and lung of these mice, Fgfr3 mutation caused papilloma and promoted lung tumorigenesis in cooperation with K-Ras and β-catenin activation, respectively. These results indicate that activation of FGFR3 can cooperate with other mutations to drive tumorigenesis in a context-dependent manner, and support the hypothesis that activation of FGFR3 signaling contributes to human cancer
Theoretical analysis for critical fluctuations of relaxation trajectory near a saddle-node bifurcation
A Langevin equation whose deterministic part undergoes a saddle-node
bifurcation is investigated theoretically. It is found that statistical
properties of relaxation trajectories in this system exhibit divergent
behaviors near a saddle-node bifurcation point in the weak-noise limit, while
the final value of the deterministic solution changes discontinuously at the
point. A systematic formulation for analyzing a path probability measure is
constructed on the basis of a singular perturbation method. In this
formulation, the critical nature turns out to originate from the neutrality of
exiting time from a saddle-point. The theoretical calculation explains results
of numerical simulations.Comment: 18pages, 17figures.The version 2, in which minor errors have been
fixed, will be published in Phys. Rev.
Dynamics of k-core percolation in a random graph
We study the edge deletion process of random graphs near a k-core percolation
point. We find that the time-dependent number of edges in the process exhibits
critically divergent fluctuations. We first show theoretically that the k-core
percolation point is exactly given as the saddle-node bifurcation point in a
dynamical system. We then determine all the exponents for the divergence based
on a universal description of fluctuations near the saddle-node bifurcation.Comment: 16 pages, 4 figure
Demonstration of unconditional one-way quantum computations for continuous variables
Quantum computing promises to exploit the laws of quantum mechanics for
processing information in ways fundamentally different from today's classical
computers, leading to unprecedented efficiency. One-way quantum computation,
sometimes referred to as the cluster model of quantum computation, is a very
promising approach to fulfil the capabilities of quantum information
processing. The cluster model is realizable through measurements on a highly
entangled cluster state with no need for controlled unitary evolutions. Here we
demonstrate unconditional one-way quantum computation experiments for
continuous variables using a linear cluster state of four entangled optical
modes. We implement an important set of quantum operations, linear
transformations, in the optical phase space through one-way computation. Though
not sufficient, these are necessary for universal quantum computation over
continuous variables, and in our scheme, in principle, any such linear
transformation can be unconditionally and deterministically applied to
arbitrary single-mode quantum states.Comment: 9 pages, 3 figure
Systematic perturbation approach for a dynamical scaling law in a kinetically constrained spin model
The dynamical behaviours of a kinetically constrained spin model
(Fredrickson-Andersen model) on a Bethe lattice are investigated by a
perturbation analysis that provides exact final states above the nonergodic
transition point. It is observed that the time-dependent solutions of the
derived dynamical systems obtained by the perturbation analysis become
systematically closer to the results obtained by Monte Carlo simulations as the
order of a perturbation series is increased. This systematic perturbation
analysis also clarifies the existence of a dynamical scaling law, which
provides a implication for a universal relation between a size scale and a time
scale near the nonergodic transition.Comment: 17 pages, 7 figures, v2; results have been refined, v3; A figure has
been modified, v4; results have been more refine
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