352 research outputs found
Noise-Driven Mechanism for Pattern Formation
We extend the mechanism for noise-induced phase transitions proposed by
Ibanes et al. [Phys. Rev. Lett. 87, 020601-1 (2001)] to pattern formation
phenomena. In contrast with known mechanisms for pure noise-induced pattern
formation, this mechanism is not driven by a short-time instability amplified
by collective effects. The phenomenon is analyzed by means of a modulated mean
field approximation and numerical simulations
Spatial Patterns Induced Purely by Dichotomous Disorder
We study conditions under which spatially extended systems with coupling a la
Swift-Hohenberg exhibit spatial patterns induced purely by the presence of
quenched dichotomous disorder. Complementing the theoretical results based on a
generalized mean-field approximation, we also present numerical simulations of
particular dynamical systems that exhibit the proposed phenomenology
Assessment of ferroptosis inducers and Nrf2 inhibitors as radiosensitisers in 2D and 3D breast cancer cell cultures
Ferroptosis is a form of programmed cell death that is modulated in some cancer cells as a pro-survival mechanism. Induction of ferroptosis is a potential anti-cancer strategy, and enhancement of ferroptosis using ferroptosis inducers has the potential to enhance current anti-tumour mechanisms. In this study, we assessed the effect of the ferroptosis inducers Erastin, RSL-3 and FIN-56 on radiosensitivity in 2D cell culture, and in 3D alginate tumour spheroids from breast cancer cell lines. Since some tumours modulate ferroptosis via increased Nrf2 production, and MCF-7 and MDA-MB-231 both produce Nrf2 protein, we also assessed the effects of the Nrf2 inhibitor ML385 on radiosensitivity. MDA-MB-231 was highly sensitive to all ferroptosis inducers, and ferroptosis was reversed by the ferroptosis inhibitors Ferrostatin-1, Liproxstatin-1 and Deferoxamine. MCF-7 was resistant to all ferroptosis inducers. MDA-MB-231 and MCF-7 cells were sensitive to irradiation in 2D cell culture but resistant to irradiation in 3D alginate spheroids. Ferroptosis inducers did not synergistically enhance irradiation-induced cell death in 2D cell cultures. There was also no robust enhancement to irradiation effects with ferroptosis inducers in 2D or 3D cell culture. Ferroptosis inducers did, however, show a heterogeneous response in 3D cell culture, in that isogenic spheroids responded differently within the same spheroid. The Nrf2 inhibitor ML385 showed no synergistic enhancement of ferroptotic cell death when combined with irradiation. These studies suggest targeting ferroptosis does not induce short-term enhancement of ferroptotic cell death
Disorder and relaxation mode in the lattice dynamics of PbMgNbO relaxor ferroelectric
The low-energy part of vibration spectrum in PbMgNbO
relaxor ferroelectric was studied by inelastic neutron scattering. We observed
the coexistence of a resolution-limited central peak with strong quasielastic
scattering. The line-width of the quasielastic component follows a
dependence. We find that is temperature-dependent.
The relaxation time follows the Arrhenius law well. The presence of a
relaxation mode associated with quasi-elastic scattering in PMN indicates that
order-disorder behaviour plays an important r\^ole in the dynamics of diffuse
phase transitions
Heat kernel regularization of the effective action for stochastic reaction-diffusion equations
The presence of fluctuations and non-linear interactions can lead to scale
dependence in the parameters appearing in stochastic differential equations.
Stochastic dynamics can be formulated in terms of functional integrals. In this
paper we apply the heat kernel method to study the short distance
renormalizability of a stochastic (polynomial) reaction-diffusion equation with
real additive noise. We calculate the one-loop {\emph{effective action}} and
its ultraviolet scale dependent divergences. We show that for white noise a
polynomial reaction-diffusion equation is one-loop {\emph{finite}} in and
, and is one-loop renormalizable in and space dimensions. We
obtain the one-loop renormalization group equations and find they run with
scale only in .Comment: 21 pages, uses ReV-TeX 3.
Magnetization plateau in the spin ladder with the four-spin exchange
The magnetization process of the =1/2 antiferromagnetic spin ladder with
the four-spin cyclic exchange interaction at T=0 is studied by the exact
diagonalization of finite clusters and size scaling analyses. It is found that
a magnetization plateau appears at half the saturation value if the ratio of
the four- and two-spin exchange coupling constants is larger than the
critical value 0.04. The phase transition with respect to
at is revealed to be the Kosterlitz-Thouless-type.Comment: 4 pages, Revtex, with 5 eps figure
Dynamic structure selection and instabilities of driven Josephson lattice in high-temperature superconductors
We investigate the dynamics of the Josephson vortex lattice in layered
high-T superconductors at high magnetic fields. Starting from coupled
equations for superconducting phases and magnetic field we derive equations for
the relative displacements [phase shifts] between the planar Josephson arrays
in the layers. These equations reveal two families of steady-state solutions:
lattices with constant phase shifts between neighboring layers, starting from
zero for a rectangular configuration to for a triangular configuration,
and double-periodic lattices. We find that the excess Josephson current is
resonantly enhanced when the Josephson frequency matches the frequency of the
plasma mode at the wave vector selected by the lattice structure. The regular
lattices exhibit several kinds of instabilities. We find stability regions of
the moving lattice in the plane lattice structure - Josephson frequency. A
specific lattice structure at given velocity is selected uniquely by boundary
conditions, which are determined by the reflection properties of
electromagnetic waves generated by the moving lattice. With increase of
velocity the moving configuration experiences several qualitative
transformations. At small velocities the regular lattice is stable and the
phase shift between neighboring layers smoothly decreases with increase of
velocity, starting from for a static lattice. At the critical velocity
the lattice becomes unstable. At even higher velocity a regular lattice is
restored again with the phase shift smaller than . With increase of
velocity, the structure evolves towards a rectangular configuration.Comment: 28 pages, 12 figures, submitted to Phys. Rev.
Cu Nuclear Quadrupole Resonance Study of the Spin-Peierls Compound Cu1-xMgxGeO3: A Possibility of Precursory Dimerization
We report on a zero-field 63Cu nuclear quadrupole resonance (NQR) study of
nonmagnetic Mg impurity substituted Cu1-xMgxGeO3 (single crystals; the
spin-Peierls transition temperature Tsp~14, 13.5, and 11 K for x=0, 0.0043, and
0.020) in a temperature range from 4.2 K to 250 K. We found that below T*~77 K,
Cu NQR spectra are broadened and nonexponential Cu nuclear spin-lattice
relaxation increases for undoped and more remarkably for Mg-doped samples. The
results indicate that random lattice distortion and impurity-induced spins
appear below T*, which we associate with a precursor of the spin-Peierls
transition. Conventional magnetic critical slowing down does not appear down to
4.2 K below Tsp.Comment: 4 pages, 4 figure
Summation of emission from superradiant sources as a way to obtain extreme power density microwaves
A theoretical model that covers both spontaneous and stimulated Cherenkov emission from an extended electron bunch has been developed. The initiation is described of the generation of superradiant pulses [1-3] by emission from the leading edge of the electron bunch. In combination with the proven experimentally picosecond stability of explosive emission from a cold cathode [4], it provides the possibility for strong correlation of phase of the SR pulses with respect to the leading edge of the electron pulse [5]
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