161 research outputs found
Convective and absolute Eckhaus instability leading to modulated waves in a finite box
We report experimental study of the secondary modulational instability of a
one-dimensional non-linear traveling wave in a long bounded channel. Two
qualitatively different instability regimes involving fronts of spatio-temporal
defects are linked to the convective and absolute nature of the instability.
Both transitions appear to be subcritical. The spatio-temporal defects control
the global mode structure.Comment: 5 pages, 7 figures (ReVTeX 4 and amsmath.sty), final versio
Isotope shifts of the (3s3p)P - (3s4s)S Mg I transitions
We report measurements of the isotope shifts of the (3s3p)P -
(3s4s)S Mg I transitions for the stable isotopes Mg (I=0),
Mg (I=5/2) and Mg (I=0). Furthermore the Mg S
hyperfine coefficient A(S) = (-321.6 1.5) MHz is extracted and
found to be in excellent agreement with state-of-the-art theoretical
predictions giving A(S) = -325 MHz and B(S)
MHz. Compared to previous measurements, the data presented in this work is
improved up to a factor of ten.Comment: 4 pages, 4 figures submitted to PR
Frequency evaluation of the doubly forbidden transition in bosonic Yb
We report an uncertainty evaluation of an optical lattice clock based on the
transition in the bosonic isotope Yb by use
of magnetically induced spectroscopy. The absolute frequency of the
transition has been determined through comparisons
with optical and microwave standards at NIST. The weighted mean of the
evaluations is (Yb)=518 294 025 309 217.8(0.9) Hz. The uncertainty
due to systematic effects has been reduced to less than 0.8 Hz, which
represents in fractional frequency.Comment: 4 pages, 3 figure -Submitted to PRA Rapid Communication
SPIRAL INSTABILITIES IN PERIODICALLY FORCED EXTENDED OSCILLATORY MEDIA
We investigate two instabilities of spiral waves in oscillatory media subject to different types of forcing using the complex Ginzburg-Landau equation. First, the transition of spiral waves via so-called superspirals to spatio-temporal chaos is related to a coexistence of the Eckhaus instability of the wave field and the intrinsic oscillatory meandering instability of the spiral core. Second, resonantly forced oscillatory media are shown to possess a novel scenario of spiral breakup. Bifurcation analysis and linear stability analysis yield explanations for the phenomenology observed by direct simulations
Accurate spectroscopy of Sr atoms
We report the frequency measurement with an accuracy in the 100 kHz range of
several optical transitions of atomic Sr : at 689 nm, at 688 nm and at 679 nm. Measurements are performed with
a frequency chain based on a femtosecond laser referenced to primary frequency
standards. They allowed the indirect determination with a 70 kHz uncertainty of
the frequency of the doubly forbidden 5s^2^1S_0- 5s5p^3P_0 transition of
Sr at 698 nm and in a second step its direct observation. Frequency
measurements are performed for Sr and Sr, allowing the
determination of , and isotope shifts, as well as the
hyperfine constants.Comment: 12 pages, 16 figure
Forecasting the SST space-time variability of the Alboran Sea with genetic algorithms
We propose a nonlinear ocean forecasting technique based on a combination of
genetic algorithms and empirical orthogonal function (EOF) analysis. The method
is used to forecast the space-time variability of the sea surface temperature
(SST) in the Alboran Sea. The genetic algorithm finds the equations that best
describe the behaviour of the different temporal amplitude functions in the EOF
decomposition and, therefore, enables global forecasting of the future
time-variability.Comment: 15 pages, 3 figures; latex compiled with agums.st
Dewetting of thin films on heterogeneous substrates: Pinning vs. coarsening
We study a model for a thin liquid film dewetting from a periodic
heterogeneous substrate (template). The amplitude and periodicity of a striped
template heterogeneity necessary to obtain a stable periodic stripe pattern,
i.e. pinning, are computed. This requires a stabilization of the longitudinal
and transversal modes driving the typical coarsening dynamics during dewetting
of a thin film on a homogeneous substrate. If the heterogeneity has a larger
spatial period than the critical dewetting mode, weak heterogeneities are
sufficient for pinning. A large region of coexistence between coarsening
dynamics and pinning is found.Comment: 4 pages, 4 figure
An Optical Lattice Clock with Spin-polarized 87Sr Atoms
We present a new evaluation of an 87Sr optical lattice clock using spin
polarized atoms. The frequency of the 1S0-3P0 clock transition is found to be
429 228 004 229 873.6 Hz with a fractional accuracy of 2.6 10^{-15}, a value
that is comparable to the frequency difference between the various primary
standards throughout the world. This measurement is in excellent agreement with
a previous one of similar accuracy
On elliptic solutions of the cubic complex one-dimensional Ginzburg-Landau equation
The cubic complex one-dimensional Ginzburg-Landau equation is considered.
Using the Hone's method, based on the use of the Laurent-series solutions and
the residue theorem, we have proved that this equation has neither elliptic
standing wave nor elliptic travelling wave solutions. This result amplifies the
Hone's result, that this equation has no elliptic travelling wave solutions.Comment: LaTeX, 12 page
Ligand-Specific c-Fos Expression Emerges from the Spatiotemporal Control of ErbB Network Dynamics
SummaryActivation of ErbB receptors by epidermal growth factor (EGF) or heregulin (HRG) determines distinct cell-fate decisions, although signals propagate through shared pathways. Using mathematical modeling and experimental approaches, we unravel how HRG and EGF generate distinct, all-or-none responses of the phosphorylated transcription factor c-Fos. In the cytosol, EGF induces transient and HRG induces sustained ERK activation. In the nucleus, however, ERK activity and c-fos mRNA expression are transient for both ligands. Knockdown of dual-specificity phosphatases extends HRG-stimulated nuclear ERK activation, but not c-fos mRNA expression, implying the existence of a HRG-induced repressor of c-fos transcription. Further experiments confirmed that this repressor is mainly induced by HRG, but not EGF, and requires new protein synthesis. We show how a spatially distributed, signaling-transcription cascade robustly discriminates between transient and sustained ERK activities at the c-Fos system level. The proposed control mechanisms are general and operate in different cell types, stimulated by various ligands
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