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1.
I.?Courtillot A.?Quessada-Vial A.?Brusch D.?Kolker G. D.?Rovera P.?LemondeEmail author 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,33(2):161-171
We report the frequency measurement with an accuracy in the
100 kHz range of several optical transitions of atomic Sr:
1S0-3P1 at 689 nm, 3P1-3S1 at 688 nm and
3P0-3S1 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
transition of 87Sr at 698 nm and
in a second step its direct observation. Frequency measurements
are performed for 88Sr and 87Sr, allowing the
determination of 3P0, 3P1 and 3S1 isotope shifts, as
well as the 3S1 hyperfine constants. 相似文献
2.
Jensen BB Ming H Westergaard PG Gunnarsson K Madsen MH Brusch A Hald J Thomsen JW 《Physical review letters》2011,107(11):113001
We present the first experimental determination of the electric-dipole forbidden (3s3p)3P?→(3s2)1S? (M2) transition rate in 2?Mg and compare to state-of-the-art theoretical predictions. Our measurement exploits a magnetic trap isolating the sample from perturbations and a magneto-optical trap as an amplifier converting each 3P?→1S? decay event into millions of photons readily detected. The transition rate is determined to be (4.87 ± 0.3)×10?? s?1 corresponding to a 3P? lifetime of 2050(-110)(+140) sec. This value is in agreement with recent theoretical predictions, and to our knowledge the longest lifetime ever determined in a laboratory environment. 相似文献
3.
L. Lorini N. Ashby A. Brusch S. Diddams R. Drullinger E. Eason T. Fortier P. Hastings T. Heavner D. Hume W. Itano S. Jefferts N. Newbury T. Parker T. Rosenband J. Stalnaker W. Swann D. Wineland J. Bergquist 《The European physical journal. Special topics》2008,163(1):19-35
The record of atomic clock frequency comparisons at NIST over the past half-decade provides one of the tightest constraints
of any present-day temporal variations of the fundamental constants. Notably, the 6-year record of increasingly precise measurements
of the absolute frequency of the Hg+ single-ion optical clock (using the cesium primary frequency standard NIST-F1) constrains the temporal variation of the fine
structure constant α to less than 2 · 10−6yr−1 and offers a Local Position Invariance test in the framework of General Relativity. The most recent measurement of the frequency
ratio of the Al+ and Hg+ optical clocks is reported with a fractional frequency uncertainty of ±5.2 · 10−17. The record of such measurements over the last year sensitively tests for a temporal variation of α and constrains , consistent with zero. 相似文献
4.
The mechanism for transitions from phase to defect chaos in the one-dimensional complex Ginzburg-Landau equation (CGLE) is presented. We describe periodic coherent structures of the CGLE, called modulated amplitude waves (MAWs). MAWs of various periods P occur in phase chaotic states. A bifurcation study of the MAWs reveals that for sufficiently large period, pairs of MAWs cease to exist via a saddle-node bifurcation. For periods beyond this bifurcation, incoherent near-MAW structures evolve towards defects. This leads to our main result: the transition from phase to defect chaos takes place when the periods of MAWs in phase chaos are driven beyond their saddle-node bifurcation. 相似文献
5.
Thomas L. Vincent Richard G. Brusch 《Journal of Optimization Theory and Applications》1970,6(4):299-319
A complete set of necessary and sufficient conditions for selecting optimal endpoints for extremals obtained from the variational Bolza problem in control notation has been developed. The method used to obtain these conditions is based on a seldom used concept of performing a dichotomy on the general optimization problem. With this concept, the problem of Bolza is decomposed into two problems, the first of which involves the selection of optimal paths with the endpoints considered fixed. The second problem involves the selection of optimal endpoints with the paths between the endpoints taken to be stationary curves. The convenience of the dichotomy in deriving the necessary and sufficient conditions for endpoints lies in its simplicity and elementary character; well-known necessary and sufficient conditions from the theory of ordinary maxima and minima are used.An endpoint necessary condition is first obtained which is simply the well-known transversality condition. An additional condition is then developed which, together with the transversality condition, leads to a set of necessary and sufficient conditions for a given extremal to be locally optimal with respect to endpoint variations. While the second condition presented is akin to the classical focal-point condition, the result is new in form and is directly applicable to the optimal control problem. In addition, it is relatively simple to apply and is easy to implement numerically when an analytical solution is not possible. It should be useful in situations where the transversality conditions yield more than one choice for an optimal endpoint.An analytic solution for a simple geodetics problem is presented to illustrate the theory. A discussion of numerical implementation of the sufficiency conditions and its application to an orbit transfer example is also included.This work was supported in part by the National Aeronautics and Space Administration, Grant No. NGR-03-002-001. 相似文献
6.
We report the observation of a higher-order frequency shift due to the trapping field in a (87)Sr optical lattice clock. We show that, at the magic wavelength of the lattice, where the first-order term cancels, the higher-order shift will not constitute a limitation to the fractional accuracy of the clock at a level of 10(-18). This result is achieved by operating the clock at very high trapping intensity up to 400 kW/cm(2) and by a specific study of the effect of the two two-photon transitions near the magic wavelength. 相似文献
7.
Blatt S Ludlow AD Campbell GK Thomsen JW Zelevinsky T Boyd MM Ye J Baillard X Fouché M Le Targat R Brusch A Lemonde P Takamoto M Hong FL Katori H Flambaum VV 《Physical review letters》2008,100(14):140801
The 1S0-3P0 clock transition frequency nuSr in neutral 87Sr has been measured relative to the Cs standard by three independent laboratories in Boulder, Paris, and Tokyo over the last three years. The agreement on the 1 x 10(-15) level makes nuSr the best agreed-upon optical atomic frequency. We combine periodic variations in the 87Sr clock frequency with 199Hg+ and H-maser data to test local position invariance by obtaining the strongest limits to date on gravitational-coupling coefficients for the fine-structure constant alpha, electron-proton mass ratio mu, and light quark mass. Furthermore, after 199Hg+, 171Yb+, and H, we add 87Sr as the fourth optical atomic clock species to enhance constraints on yearly drifts of alpha and mu. 相似文献
8.
Journal of Optimization Theory and Applications - Space shuttle trajectory design requires the optimization of highly-constrained, branched, atmospheric trajectories. This paper presents a general... 相似文献
9.
D Wang J Wang GM Bonamy S Meeusen RG Brusch C Turk P Yang PG Schultz 《Angewandte Chemie (International ed. in English)》2012,51(37):9302-9305
Mitochondrial dynamics: An image-based screen identified a small molecule, M1, that specifically promotes the fusion of fragmented mitochondria and protects cells from mitochondrial-fragmentation-associated cell death. Mechanistic studies revealed that M1 shifts the mitochondrial dynamic balance towards fusion. 相似文献
10.